Journal of Clinical & Experimental Nephrology

Keywords

Type 1 diabetes, Type 2 diabetes, Diabetic nephropathy, Dipeptidyl peptidase-4 inhibitors, Sodium glucose transporter 2 inhibitors, Hyperfiltration

Abbreviations

DN: Diabetic Nephropathy; T1DM: Type 1 Diabetes Mellitus; T2DM: Type 2 Diabetes Mellitus; GFR: Glomerular Filtration Rate; UAE: Urine Albumin Excretion; ACR: Albumin:Creatinine Ratio; BP: Blood Pressure; RAS: Renin-Angiotensin System; ROS: Reactive Oxygen Species; NADPH: Nicotinamide Adenine Dinucleotide Phosphate; SGLT2: Sodium Glucose Transporter 2; PCT: Proximal Convoluted Tubules; ATP: Adenosine Triphosphate; EMT: Epithelial- Mesenchyme Transition; NF-κB: Nuclear Factor-κB; TGF- β: Transforming Growth Factor- β; CCL2: Chemokine Ligand 2; MCP-1: Chemoattractant Protein-1; ICAM1: Intercellular Adhesion Molecule 1; PKC: Protein Kinase C; MAP: Mitogen- Activated Protein; MCs: Mesangial Cells; mTOR: mammalian target of Rapamycin; PI3K: Phosphatidylinosiol-3 Kinase; AKT: Protein Kinase B; CTGF: Connective Tissue Growth Factor; AII: Angiotensin II; ICN1: Notch1 Intracellular Domain; AT1R: Angiotensin Receptors1; AMP: adenosine monophosphate; CDK: Cyclin- Dependent Kinase; DPP-4: Dipeptidyl Peptidase-4; CD26: Cluster Of Differentiation 26; miR29: MicroRNA-29; VEGFR1: vascular endothelial growth factor receptor type 1; EndMT: Endothelial-Mesenchymal Transition; FGF23: Fibroblast Growth Factor 23; VDRs: Vitamin D Receptors; CKD: Chronic Kidney Disease; ET-1: Endothelin-1; nrf2: Nuclear Factor Erythroid 2-Related Factor 2; IL-1: Interleukin-1; TNF α: Tumor Necrosis Factor-α; Keap1: Kelch-Like ECH-Associated Protein 1; JAK/STAT: Janus Kinase/Signal Transducers And Activators Of Transcription; ACE: Angiotensin-Converting Enzyme; ESRD: End-Stage Renal Disease; ARB: Angiotensin II Type 1 Receptor Blocker; UKPDS: United Kingdom Prospective Diabetes Study; GLP-1: Glucagon Like Peptide-1; AMPK: Adenosine Monophosphate Kinase; MET: Mesenchymal to Epithelial Transition; PPARγ: Peroxisomal Proliferator-Activated Receptor γ; PKA: Protein Kinase A; BMI: Body Mass Index; SIRT1: Silent Information Regulator T1; SOCS1: Suppressor Of Cytokine Signaling-1

Introduction

In its earliest stage, diabetic nephropathy (DN) manifests by renal hyper-perfusion and hypertrophy [1]. This stage starts with the onset of diabetes in T1DM before insulin treatment. This is called stage 1 and is followed few years later by stage 2 characterized by clinical silence and morphologic changes characteristic of diabetic glomerulosclerosis. Glomerular filtration rate (GFR) is still higher than normal during this stage. Some diabetic patients continue in this stage throughout their lives. Increased urine albumin excretion (UAE) was first described by Keen and Chlouverakis [2] in 1963. However, microalbuminuria became popular twenty years later after the results of fourteen years longitudinal study that disclosed the predictive value of increased UAE were published [3]. Microalbuminuria is the salient feature of stage 3 DN, also called the stage of incipient nephropathy, and is defined as UAE >30 mg/d, >20 μg/min, or albumin:creatinine ratio (ACR) >30 mg/g creatinine. This stage is initially associated with increased GFR. However, GFR starts a consistent decline that becomes more evident with the continuous increase of UAE above 300 mg/d, 200 μg/min, or when ACR exceeds 300 mg/g. This is the stage of overt nephropathy, also called stage 4 DN (Figure 1) [1,4]. Progressive increase in blood pressure (BP) is usually associated with these renal changes. After the introduction of the different renin-angiotensin system (RAS) blockers in the management of DN, little was added to improve the management of this disease. Moreover, RAS blockers were ineffective in the primary prevention of DN in T1DM and T2DM [5-8]. Additional studies failed to demonstrate a renal protective effect of RAS blockers when used in diabetic patients without overt nephropathy [9]. These results have criticized the use of RAS blockers in incipient nephropathy. RAS blockers were then limited to patients with overt nephropathy [10,11].

Figure 1: Stages of Diabetic nephropathy. Stage 2 is characterised by the progressive increase in mesangial deposits on light microscopy without corresponding clinical or laboratory findings; ESRD= end stage renal disease when eGFR≤15 mL/ min/1.73 m².

The risk of DN is strongly linked to poor glycemic control in both T1DM and T2DM [12,13]. In addition, there is strong evidence that tight blood sugar control has a significant impact on primary prevention of DN [14,15]. However, tight glycemic control is not always an easy task.

After a long time of inertia, many novel agents were introduced as potential additions to the standard of care treatment of DN. These agents have also improved our understanding of the pathogenesis of DN. Moreover, the introduction of some of these agents will change the strategy of management from being postponed to stage 4 DN to a much earlier stage, namely, stage 1DN. This hypothesis needs verification and assessment of cost effectiveness.

In this review, we will concentrate on the different novel therapeutic tools highlighting their impact on the prevention and withhold of the progression of DN.

Pathogenesis

The overproduction of reactive oxygen species (ROS) is one of the hallmarks of diabetic kidney. ROS overproduction is the main cause of DN [16]. Hyperglycemia induces nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme activity and is responsible for ROS overproduction [17]. Up-regulation of sodium glucose transporter 2 (SGLT2) in the brush border of proximal convoluted tubules (PCT) is another pathway of ROS overproduction. SGLT2 up-regulation causes uric acid (UA) overproduction with consequent NADPH oxidase-ROS induction [18]. Excess ROS mediates podocyte apoptosis and alteration in the slit diaphragm podocin protein (Figure 2) [19], increases intracellular oxidative stress, mitochondrial injury, adenosine triphosphate (ATP) depletion [20,21], endothelial injury, RAS activation and increased epithelial-mesenchyme transition (EMT) with consequent fibrosis [22]. ROS overproduction activates the nuclear factor-κB (NF-κB) within the kidney [23]. NF-κB translocates to the nucleus to trigger several genes like those encoding transforming growth factor-β (TGF-β), chemokine ligand 2 (CCL2) also known as monocyte chemoattractant protein-1 (MCP-1) and intercellular Adhesion Molecule 1 (ICAM1) [24-27]. This leads to macrophage recruitment and excess collagen deposition within the diabetic kidney (Figure 3). Beside activation of NF-κB, ROS activates protein kinase C (PKC) and mitogen-activated protein (MAP) kinase within mesangial cells (MCs). All these factors stimulate overproduction of extracellular matrix proteins (Figure 4) [27].

Figure 2: Reactive oxygen species mediated podocyte injury and podocin protein alteration. NADP= Nicotinamide adenine dinucleotide phosphate; ROS= Reactive oxygen species.

Figure 3: Different pathogenic mechanisms of kidney injury possibly induced by uric acid. UA= uric acid; ROS= reactive oxygen species; NF-ᴋB= Nuclear Factor kappa B; MCP1= Macrophage Chemoattractant protein-1; RAS= Renin angiotensin system; EMT= Epithelium mesenchyme transition; VSMC= Vascular smooth muscle cells.

Figure 4: Hyperglycemia induced mesangial expansion. NADP= Nicotinamide adenine dinucleotide phosphate; ROS= Reactive oxygen species; NF-ᴋB= Nuclear Factor kappa B; PKC= Protein kinase C; MAPK= Mitogenactivated protein kinase; ECM= Extracellular matrix.

Activation of mammalian target of Rapamycin (mTOR) is another feature of DN. Hyperglycemia stimulates phosphatidylinosiol-3 kinase (PI3K) and protein kinase B (AKT) pathways, with subsequent activation of mTOR. Activated mTOR is responsible for basement membrane thickening, mesangial matrix expansion [28], and renal fibrosis. The mTOR induced renal fibrosis is a consequence of fibroblast proliferation, EMT and the expression of TGF-β and connective tissue growth factor (CTGF, CCN2) [29,30]. Stimulation of MCP1 by mTOR leads to increased macrophage recruitment within the interstitium of the kidney [30]. In addition, increased mTOR activity can aggravate tubular epithelial damage and apoptosis (Figure 5) [31].

Figure 5: Consequences of mTOR activation induced by hyperglycemia. mTOR= mammalian target of rapamycin; BM= basement membrane; EMT= Epithelium mesenchyme transition; CCN2= Connective tissue growth factor; TGFβ= Transforming Growth Factor β; MCP1= Macrophage chemoattractant protein.

CCN2 is the newer alternative name of CTGF. It has an eminent role in DN [32]. Within the diabetic kidney, CCN2 is detected in almost all cell types [33]. When exposed to high glucose, the glomeruli of diabetic rats and human MCs express a high activity of CCN2 [34]. In the diabetic kidney, CCN2 expression is stimulated by TGF-β1, AGE, and angiotensin II (AII). The CCN2 stimulates EMT, fibroblast proliferation, and extracellular matrix accumulation (Figure 6) [32].

Figure 6: CCN2 mediated glomerular and interstitial fibrosis. mTOR= Mammalian target of rapamycin; AGE= Advanced glycation endproducts; A II= Angiutensin II; TGFβ= Transforming Growth Factor β; CCN2= Connective tissue growth factor; EMT= Epithelium mesenchyme transition.

Nephrin and podocin are slit diaphragm proteins synthesized by podocytes. They are essential for the maintenance of the sieving properties of the glomerular basement membrane [35]. The addition of AII to cultured podocytes causes in vitro loss of nephrin [36]. Moreover, infusion of AII in the renal artery of rat kidney results in effacement of foot processes of podocytes with an increase in proteinuria [37]. In diabetic rats, AII synthesis blockers preserve the nephrin within the slit diaphragm and decrease UAE [38]. AII down-regulates nephrin through a transmembrane receptor called Notch1. Notch1 plays a role in cell differentiation and renal development. When Notch1 receptor is activated, it leads to the release of the active Notch1 intracellular domain (ICN1). ICN1 translocates to the nucleus. Additionally, notch 1 triggers another transcription factor called the snail that exists within the cytoplasm of podocytes. Upon signaling of notch1 by AII, both ICN1 and snail translocate to the nucleus and share in repression of nephrin expression, stimulation of apoptosis, podocyte loss and consequent increase of UAE (Figure 7) [38,39]. Inhibition of Notch1 signaling pathway in human and animal podocytes was associated with restored nephrin protein, decreased podocyte apoptosis, and attenuated UAE [40]. As mentioned before, ROS induced by hyperglycemia mediates alteration of podocin (Figure 2) [19].

Figure 7: Mechanism of podocyte injury and proteinuria induced by angiotensin II.

The expression of RAS genes is induced in diabetes [41]. Angiotensin receptors1 (AT1R) are up-regulated in diabetic rat kidneys, while AT2R are down-regulated [42]. In streptozotocin-induced diabetes rats, increased intraglomerular capillary pressure is the initiating early event. Increased mechanical strain increases AII production and up-regulates AT1R. This increase in AII maintains and aggravates glomerular hypertension [43,44].

Glomerular hyperperfusion and hyperfiltration are the earliest manifestations of diabetic kidney. These glomerular hemodynamic changes are due to afferent and to less extent efferent arteriolar vasodilatation as a consequence of changes in various biochemical factors, including nitrous oxide, atrial natriuretic factor, adenosine, glucagon, and insulin [45]. Increased glucose in the glomerular ultra-filtrate stimulates SGLT2 gene with consequent increased proximal tubular absorption of filtered sodium and glucose. Distal sodium delivery will consequently diminish. Sodium reabsorption by the macula densa would accordingly diminish. Hence, ATP consumption and adenosine monophosphate (AMP) production diminish. Adenosine, the byproduct of AMP, is a potent vasoconstrictor. Decreased availability of adenosine results in afferent arteriolar vasodilatation (Figure 8) [46,47]. This tubuloglomerular feedback would start glomerular hyperperfusion and hyperfiltration. These hemodynamic changes trigger AII that maintains these changes. In addition, SGLT2 contributes to hyperglycemia-induced PCT cell senescence. Knocking down of SGLT2 can abort in vitro induction of P21 in PCT when exposed to hyperglycemia. P21 inhibits cyclindependent kinase (CDK). CDK is an inhibitor of cell senescence (Figure 9) [48,49].

Figure 8: Tubuloglomerular feedback: impact of low salt intake and SGLT2 inhibitors. UF= glomerular ultrafiltrate; SGLT= Sodium glucose transporter; PCT=proximal convoluted tubules; DCT= distal convoluted tubule; MD=Macula densa; AMP= adenosine monophosphate; VD= Vasodilation; AA= Afferent arteriole.

Figure 9: SGLT2 mediated PCT cell senescence. SGLT= Sodium glucose transporter; PCT= Proximal convoluted tubules.

Dipeptidyl peptidase-4 (DPP-4) is a cell surface enzyme that was originally characterized as a T cell cluster of differentiation 26 (CD26). DPP-4 degrades incretins secreted by the gut. It is also found in the endothelial cells in multiple organs including the kidney [50]. The soluble circulating form of DPP-4 is responsible for DPP-4 activity in human serum and is originally shed from cell membranes [51]. MicroRNA-29 (miR29) suppresses DPP-4 gene in normoglycemic status. This suppression is lost in hyperglycemic state with consequent increase of cell surface DPP-4 activity [52]. DN is characterized by increased expression of surface DPP-4 on endothelial and tubular epithelial cells. Activated DPP-4 induces phosphorylation of integrin β1. Activated DPP-4 phosphorylated integrin β1 complex up-regulates TGF β receptor dimerization and activates the vascular endothelial growth factor receptor type 1(VEGFR1). Up-regulated TGF β receptor and VEGFR1 stimulate endothelial-mesenchymal transition (EndMT). These changes enhance fibrogenesis (Figure 10) [53].

Figure 10: DPP-4 mediated renal fibrosis. DPP4= Dipeptyl peptidase-4; TGFβ= Transforming Growth Factor β; EndMT= Endothelial-mesenchymal transition.

The serum level of fibroblast growth factor 23 (FGF23), the phosphatonin responsible for renal phosphate elimination, is higher in T2DM [54]. Although the kidneys of normal rats do not express FGF23 mRNA, it appears in the kidneys of diabetic rats 4 mo after onset of diabetes and increases thereafter [55]. FGF23 suppresses 1-α hydroxylase gene. This leads to decreased calcitriol synthesis. An inverse relation between serum calcitriol and serum renin activity was encountered in a large cohort study [56], a finding that discloses the cross talk between FGF23 and the RAS (Figure 11). Vitamin D receptors (VDRs) suppress activation of NF-κB and MCP1 induced by hyperglycemia [57]. Stimulation of VDRs by 1-α,25-dihydroxyvitamin D3 suppresses activation of RAS and TGF-β induced by hyperglycemia in MCs [58]. After adjustment for GFR, and parathyroid hormone, FGF23 was found as an independent predictor of DN progression [59]. Klotho acts as a co-receptor to enhance FGF23 binding to its ubiquitous FGF receptors. Deficient Klotho is one of the causes of increasing level of FGF23 in chronic kidney disease (CKD) [60]. Plasma α-klotho level negatively correlates with UAE in T2DM patients [61]. In patients with T2DM, systemic hypertension, and albuminuria, the RAS blockers stimulate α-klotho production [62,63].

Figure 11: FGF23 mediated increased renin activity in diabetic patients. FGF23= Fibroblast growth factor 23.

Another feature of diabetic patients is the persistent elevation of endothelin level. Endothelin-1 (ET-1) is a powerful vasoconstrictor agent with additional pro-inflammatory and pro-fibrogenic activities. ET-1 is incriminated in DN progression [64]. ET1 has 2 receptor named ETA and ETB. Stimulation of ETA causes vasoconstriction, cell proliferation, and extracellular matrix accumulation while ETB mediates vasodilatation [65]. Increased ET-1 in the kidney of T2DM db/db mice positively correlated with collagen deposition within their kidneys [66].

In the last 2 decades, inflammation has evolved as an important pathogenic mechanism of DN. The identification of transcription factors, cytokines, chemokines, adhesion molecules, and nuclear receptors would lead to the development of new therapeutic strategies [23]. NF-kB is the pivotal transcription factor involved in DN. NF-κB activators includes hyperglycemia, free oxygen radicals, and proteinuria [67]. Beside its role in macrophage recruitment and excess collagen deposition, activated NF-κB triggers PKC [68], RAS [69], advanced glycation end product proteins (AGEs) accumulation [70], and oxidative stress [71]. NF-κB activation can be offset by thiazolidinediones [72], 1,25-dihydroxyvitamin D3 [73], and Nuclear factor erythroid 2-related factor 2 (nrf2) agonists [74]. Interleukin-1 (IL-1), IL-6, IL-18, and tumor necrosis factor-α (TNF α) have distinguished role in the pathogenesis of DN [75]. Nrf2 regulates the synthesis of antioxidants and cytoprotective factors that can muffle the oxidative stress and the pro-inflammatory signals [76]. It does not exist free in the cytoplasm, but rather as an inactive complex bound to Kelch-like ECH-associated protein 1 (Keap1) [77]. Keap1 has many sensors of the intracellular redox state. On modifying these sensors, ROS can dissociate Nrf2 from Keap1/Nrf2 complex [78]. The dissociated Nrf2 translocates to the nucleus where it triggers the genes encoding the antioxidant and detoxifying molecules, thus activating their transcription. In addition, Nrf2 inhibits transcription of NF-kB [79]. Nrf2 is adaptively activated in diabetic status but is not activated enough to resist the oxidative stress provoked by hyperglycemia [80]. The association between oxidative stress and inflammation stimulated planning of studies looking for efficiency of Nrf2/Keap1 activators as potential renoprotective agents [81].

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway evidently mediate the contribution of hyperglycemia to proliferation, inflammation, and fibrosis encountered in DN [82]. Exposure of cultured glomerular MCs to both high levels of glucose and A2 activates JAK/STAT signaling [83]. A significant increase of JAK2 protein in glomerular and tubulointerstitial compartments is encountered in patients with DN, with a negative correlation between JAK2 mRNA levels and GFR [82].

Diagnosis of DN

The pathologic changes of DN include mesangial expansion, diffuse glomerular basement membrane thickening, diffuse glomerulosclerosis, nodular glomerulosclerosis, afferent and efferent arteriolar hyalinosis, interstitial mononuclear cell infiltrate, tubular atrophy, and interstitial fibrosis [84]. Moreover, diabetic patients can develop non-diabetic renal disease with a prevalence that varies from 10% to 85% in different studies [85-88]. Frequently, diabetic patients do not require kidney biopsy when they develop proteinuria unless non-diabetic kidney disease is suspected [89]. This suspicion is raised when duration of diabetes is less than 5 years, BP is normal, microscopic or frank hematuria is detected, or when diabetic retinopathy is absent in T1DM [89]. However, the presence of microscopic hematuria does not preclude DN. T2DM patients can develop DN without antecedent diabetic retinopathy in contrast to T1DM [90].

Management of DN

Therapeutic interventions that are clinically approved are going to be discussed under the heading “approved interventions”. Other modalities that are not yet clinically approved will be discussed under “potential therapeutic modalities”.

Approved interventions (Table 1)

These interventions include control of BP, control of blood sugar, use of hypolipidemic agents, quitting smoking, diet control, managing hyperuricemia, hyperphosphatemia and metabolic acidosis, use of pentoxifylline, sarpogrelate and use of vitamin D receptor agonists.

Table 1: Approved interventions that can prevent development and progression of DN.

Control of BP: Control of BP significantly muffles GFR decline in pre-dialysis DN patients [91]. Target BP in DN patients is 130/80 mmHg [92]. In DN patients with proteinuria, RAS blockers are the 1st anti-hypertensive agents of choice thanks to their significant impact on GFR decline [93,94]. They achieve their favorable effect through many mechanisms including the reduction of glomerular tuft pressure [95], the inhibition of cytokine overproduction [96-98], the increase of serum and tissue angiotensin1-7 [99] and the stimulation of Klotho gene expression. Klotho gene suppression might mediate RAS-induced renal damage, a mechanism that clarifies the renal protective effects of these agents [61-63]. However, RAS blockers are not able to fully attenuate hyperfiltration in T1DM patients. This failure was still observed even with dual RAS inhibition using angiotensin-converting enzyme (ACE) and direct renin inhibitors [7,8]. Moreover, RAS blockers failed to fully prevent the progression of renal injury in T1DM [100]. In addition, the efficacy of ACE inhibitors in reducing the incidence of overt nephropathy was not encountered in 2 studies in T2DM with incipient nephropathy [101,102]. Moreover, the incidence of end-stage renal disease (ESRD) was not significantly decreased using either ACE inhibitors [103] or an angiotensin II type 1 receptor blocker (ARB) [104]. RAS blockers prescription became limited to diabetic patients with overt nephropathy [10,11].

Control of blood sugar: In order to appreciate the impact of optimized blood sugar control on the course of DN, Fioretto et al. [105], looked at kidney pathologic changes in DN of T1DM patients after undergoing Pancreas transplantation. Repeated kidney biopsies demonstrated that by 10 years post-transplant, normoglycemia was associated with the reversal of glomerulopathy, interstitial fibrosis and tubular atrophy initially encountered [105]. In the United Kingdom Prospective Diabetes Study (UKPDS), blood sugar control for 12 years was associated with 33% reduction in the relative risk of progression from normoalbuminuria to microalbuminuria or from micro to overt proteinuria [106]. In the tight glycemic control group, the chance of doubling of serum creatinine was also significantly reduced. Control of blood glucose might also delay CKD progression and postpones the need for dialysis [107,108]. In a recent study of 891 670 US diabetic veterans with estimated GFR >60 mL/min per 1.73 m2, HbA1c >7.0% was associated with worse risk of all-cause mortality and incident CKD in all systolic BP categories [109]. On the other hand, a meta-analysis of 5 mega-trials that randomly assigned 27159 T2DM patients showed that intensive glycemic control (mean HbA1c=6.6%) compared to those on convention care (mean HbA1c=7.4%) did not improve overall or cardiovascular mortality or ESRD [110].

Metformin, thiazolidinediones, glucagon like peptide-1 (GLP-1) agonists, DPP-4 inhibitors, and SGLT2 inhibitors have additional favorable effects in DN patients beyond their hypoglycemic effects.

Metformin activates adenosine monophosphate kinase (AMPK) pathway [111,112]. AMPK activation leads to inhibition of mTOR [113]. Metformin is also able to inhibit mTOR independent of AMPK [114]. Metformin inhibits hyperglycemia-induced podocyte apoptosis, an effect mediated by AMPK activation and mTOR signaling inhibition [115] and through the restoration of expression of nephrin [116]. In addition, metformin can promote mesenchymal to epithelial transition (MET), a consequence of up-regulation of the epithelial marker cadherin [117]. In T2DM rats, metformin suppresses inflammatory, oxidative and profibrotic renal damage markers and thus improves renal damage [118]. The kidney excretes metformin, thus it can accumulate with the continuous decrease of kidney function. In order to avoid adverse effects, the dose of metformin should be reduced by 50% if GFR goes below 45 mL/min and should be stopped if GFR becomes below 30 mL/min [119].

Peroxisomal proliferator-activated receptor γ (PPARγ) is expressed in different renal cells that include MCs, tubular cells, and renal medullary interstitial cells [120]. The thiazolidinedione, pioglitazone hydrochloride, is one of PPARγ agonists that have anti proteinuric effect in animal models of T1DM and T2DM through amelioration of glucose-induced oxidative stress, and downregulation of MCP1, ICAM1, NF-κB, and TGF β [23]. In order to explore the possible renoprotective mechanisms of pioglitazone hydrochloride, its effect on urinary podocalyxin and MCP-1 excretion were studied in T2DM. After 12 weeks of pioglitazone treatment, there was a significant decline in systolic and diastolic BP, UAE, and urinary podocalyxin excretion. The podocyteprotective capacity of pioglitazone was partly attributed to its effective suppression of local renal inflammation induced by diabetes [121]. The antiproteinuric effect of pioglitazone was still evident after its administration to T2DM patients already treated with RAS blockers [122]. In T2DM patients at stages 3 and 4 of CKD treated with losartan and pioglitazone, the declines in GFR below baseline measurements were significantly slower compared with those treated with losartan alone [123]. After 12 wk of pioglitazone treatment, urinary TGF- β 1 excretion decreases significantly [124]. Pioglitazone use is associated with increased body weight together with salt and water retention. Precaution is therefore needed to avoid these undesirable adverse effects.

GLP-1 receptors deficient Rats develop up-regulation of renal NADPH oxidase, increased glomerular ROS, reduced renal cAMP and protein kinase A (PKA) activity, increased UAE, and advanced mesangial expansion [125]. These changes could be explained by the antioxidative properties of GLP-1. The GLP-1 agonist exendin inhibited expression of TGF- β 1 and CCN2 by human mesangial cells cultured in high glucose medium [126]. Liraglutide suppressed the progression of DN as demonstrated by decreased levels of renal NADPH oxidase, decreased levels of glomerular ROS, elevated renal cAMP, elevated renal PKA activity, reduced UAE and mesangial expansion in diabetic mice [121]. We still lack clinical studies of GLP-1 agonists in patients with T2DM and moderate-to-severe CKD [127].

DPP-4 inhibitors were reported as beneficial renoprotective agents against DN in both experimental and clinical studies. In clinical practice, two types of DPP-4 inhibitors are used: Vildagliptin, sitagliptin, and saxagliptin are dipeptide mimetics while linagliptin and alogliptin are nonpeptidomimetics. In addition to their hypoglycemic effect, DPP-4 inhibitors are protective against kidney fibrosis [52]. Vildagliptin treatment significantly decreased UAE, improved GFR, and dose-dependently inhibited interstitial expansion, glomerulosclerosis, and the thickening of the glomerular basement membrane and significantly decreased renal tissue expression of T GF- β1 in T1DM rats with DN [128]. When T2DM patients were treated by vildagliptin for 8 weeks in a single-arm clinical study, UAE significantly decreased by 44.6% [129]. On the other hand, treatment of T2DM rats with sitagliptin did not significantly affect kidney size, mesangial expansion, glomerular atrophy, glomerular basement membrane thickening, tubular degeneration, tubular atrophy, or interstitial fibrosis while significantly reduced global glomerulosclerosis and vascular glomerular pole hyalinosis [130]. Sitagliptin was able to significantly decrease UAE in normoalbuminuric, microalbuminuric, and overt proteinuric patients in a smalluncontrolled clinical trial on thirty-six T2DM patients [131]. In comparison to other oral hypoglycemic agents that achieved a comparable decrease in HbA1c, sitagliptin significantly reduced UAE in an open-labeled, prospective, randomized study in T2DM [132]. However, a more recent and larger uncontrolled trial of sitagliptin in T2DM patients failed to show a consistent favorable effect on UAE. While two-thirds showed a reduction, one-third of the patients experienced an exacerbation of UAE. Reduction of UAE was likely related to reduction of BP and eGFR [133]. Because of its non-renal route of excretion, linagliptin, in contrast to other DPP-4 inhibitors, does not need dose adjustment with GFR decline. A pooled analysis of four clinical studies of 217 T2DM patients with increased UAE that are receiving stable doses of RAS inhibitors, patients were randomized to either linagliptin 5 mg/d (n=162) or placebo (n=55). After 24 wk of treatment, UAE decreased significantly in the linagliptin group (-32% vs -6% in placebo group) [134]. Linagliptin directly inhibits DPP-4- integrin - β1 interaction, and thus blunts pathological TGF- β signaling and restores the physiological balance of VEGF receptors. Consequently, EndMT and subsequent renal fibrosis are inhibited [53]. Over five thousands of inadequately controlled T2DM patients were recruited to 13 phase 2 or phase 3 randomized, double-blind, placebo-controlled, clinical trials of linagliptin, out of them 3505 received linagliptin, and the remaining cases received placebo. The primary composite outcome included the switch to a higher grade of albuminuria, the increase of serum creatinine above 250 μmol/L, the reduction of eGFR by 50%, the development of acute kidney injury, or death from any cause. The primary composite outcome was significantly lower in the linagliptin group (12.8% in linagliptin versus 15.6% in the placebo group) [135]. The renoprotective effect of linagliptin possibly extends beyond DN. In comparison to telmisartan, linagliptin significantly decreased interstitial fibrosis in 5/6 nephrectomized rats. UAE reduction was comparable to telmisartan in these animals [136]. Saxagliptin add-on treatment in a rat model of T1DM has limited renal hypertrophy, TGF-β upregulation, NF-κB-mediated macrophage infiltration, and histological markers of tubulointerstitial fibrosis in spite of the lack of change in UAE [137]. In the Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus-Thrombolysis in Myocardial Infarction 53 (SAVOR-TIMI 53) trial, the renal outcomes of 16492 T2DM patients, randomized to saxagliptin versus placebo and followed for a median of 25 months were evaluated. Saxagliptin decreased UAE but had no effect on eGFR, an effect that was independent of baseline renal function [138] and the glycemic effect of saxagliptin [139]. In order to assess if alogliptin has a renoprotective effect, a crossover study with sitagliptin and alogliptin in 12 incipient nephropathy T2DM patients taking ARBs was performed. The study design consisted of three treatment periods: the first period of 4 wk using sitagliptin 50 mg/d followed by the second period using alogliptin 25 mg/d for 4 wk instead, and lastly the third period of 4 wk reusing sitagliptin 50 mg/d. The three treatment periods showed no significant changes in body mass index (BMI), BP, serum lipids, serum creatinine, eGFR, and HbA1c. After the switch from sitagliptin to alogliptin, the studied candidates experienced reduced UAE and 8-hydroxy-2’- deoxyguanosine (an oxidative stress marker). These observations have led to the conclusion that the use of alogliptin on top of ARB would offer additional protection against the early-stage of DN beyond that attributed to glycemic control via reduction of renal oxidative stress [140].

SGLT2 inhibitors, the members of a new class of hypoglycemic agents, succeeded to slow progression of DN. SGLT2 inhibition increases distal sodium delivery, increased distal tubular sodium absorption and hence increases adenosine production, causing afferent arteriolar vasoconstriction with fall in renal blood flow, decreased hyperfiltration and reduced renal injury. In RENAAL trial, losartan treatment of T2DM patients having DN was associated with the delay in the onset of ESRD by 28% during a mean follow-up of 3.4 years [141]. On the other hand, empagliflozin in EMPA-REG trial in T2DM patients with DN achieved 55% reduction of the chance of ESRD over a median observation time of 3.1 years [142]. Empagliflozin was also associated with a significant reduction in incident or worsening nephropathy by 39%, progression to overt albuminuria by 38% and doubling of serum creatinine by 44% [142]. The significant favorable outcome of SGLT2 inhibitors is attributed to their effect on hyperfiltration, BP, body weight and serum UA in both T1DM and T2DM [143-145]. We would like to emphasize that the effect of SGLT2 inhibitors on renal blood flow is not related to RAS blockade as empagliflozin and dapagliflozin do increase plasma aldosterone and A2 [146,147], as well as urinary ACE and ACE2 [148].

One thousand four hundred and fifty T2DM patients receiving metformin were randomly assigned to either once-daily canagliflozin 100 mg, canagliflozin 300 mg, or glimepiride titrated to 6-8 mg for 2 years. In glimepiride, canagliflozin 100 mg, and canagliflozine 300 mg groups, eGFR declined by 3.3, 0.5, and 0.9 mL/min per 1.73 m2 per year respectively (P<0.01 for each canagliflozin group versus glimepiride) in spite of comparable reductions in HbA1c. UAE declined more with canagliflozin 100 mg or canagliflozin 300 mg than with glimepiride. These results support the renoprotective effect of canagliflozin compared with glimepiride independent of the glycemic effect [149]. SGLT2 inhibitors muffle hyperglycemia-induced expression of toll-like receptor-4, increased nuclear DNA binding for NF-kB and activator protein 1, increased collagen IV expression as well as IL-6 secretion within renal parenchyma [150]. They can also inhibit high glucose- induced oxidative stress and interstitial macrophage infiltration. SGLT2 antagonists also suppress fibrotic and inflammatory genes [151,152]. Tofogliflozin, ipragliflozin and luseogliflozin are other members that showed similar renoprotective effects in animal studies [153-155], but lack clinical trials. The body weight and BP lowering effects of SGLT2 inhibitors are still observed in T2DM patients in stage 3a and stage 3b CKD [156]. However, the ability of these agents to decrease renal glucose reabsorption fades with declining GFR. Compared with normal or mildly impaired kidney function patients, urinary glucose excretion becomes 50% lower in T2DM patients with CKD stage 3 when treated with dapagliflozin [157]. This poses a negative impact on the hypoglycemic efficacy of these agents beyond stage 3 CKD.

Hypolipidemic treatment: All DN patients should be treated with statins [158,159]. In spite of the significant impact of statin treatment on the risk of atherosclerotic cardiovascular disease in CKD patients, they have a minimal effect, if any, on CKD progression [160]. Statins did not significantly affect either all-cause mortality or stroke in diabetic adults with CKD when compared to placebo [158,159]. Fenofibrate treatment increased the switch of microalbuminuria to normoalbuminuria in DN patients compared to placebo [110].

Quitting smoking: A three years prospective observation study of three hundred T1DM patients that have overt proteinuria (178 were smokers) concluded that smokers did not have a worse decline of GFR [161]. On the other hand, a more recent and larger study of 3613 T1DM patients has reported that the 12-year cumulative risks of microalbuminuria, overt proteinuria and ESRD were significantly higher in current and ex-smokers compared to non-smokers. This risk increased in heavy smokers [162]. Quitting smoking is mandatory in T1DM and T2DM. Smoking is an important factor for DN progression in T2DM [163].

Diet control: Dietary salt restriction to less than 100 mmol (5-6 g)/d significantly reduces BP in T1DM and T2DM [164]. Salt restriction should be advised very early in the course of diabetes mellitus. The reduction of salt intake leads to fall in BP and UAE in individuals with diet-controlled T2DM or with impaired glucose tolerance [165]. In stage 4 CKD T2DM patients, salt intake is an independent factor that affects the annual rate of decline of GFR [166]. On the other hand, the effect of sodium intake on the clinical outcome is more complicated in T1DM. As an index of dietary sodium intake, urinary sodium excretion was associated non-linearly with overall mortality in T1DM. Patients at high and low extremes of urinary sodium excretion had reduced survival. Moreover, the lowest urinary sodium excretion had the highest risk of ESRD [167]. Decreased salt intake can exaggerate glomerular hyper filtration in the hyperglycemic state (Figure 8) [168]. This salt paradox was characterized in T1DM. However, clinical observations suggest its existence in T2DM as well [169].

The impact of protein restriction on CKD progression in DN is debatable. In 1996, a meta-analysis showed that dietary protein restriction effectively slows the progression of DN [170]. In 2000, a new meta-analysis showed similar results in T1DM patients with DN [171]. However, a more recent meta-analysis appeared in 2007 announcing the lack of a significant impact of protein restriction on DN progression in either T1DM or T2DM [172]. The last meta-analysis was performed in 2015 to report a significant impact of protein restriction on the rate of CKD progression only in T1DM [173]. The 2013 KDOQI clinical practice guidelines update on diabetes and CKD endorsed its KDOQI 2007 guidelines regarding the role of protein nutrition in diabetic kidney disease (DKD). For CKD stages 1 and 2, a daily protein intake of 0.8 g/kg is recommended, while in stages 3 and 4 the allowance should decline to 0.6-0.8 g/kg [158]. The source of dietary protein should also be considered. Switching to a predominantly vegetarian diet is associated with significant decrease of UAE in T1DM patients with DN [174]. Similar results were observed in DN complicating T2DM [175]. Essential amino acids content of the vegetarian diet is usually sufficient for optimal nutrition [176].

The potential protective value of polyunsaturated fatty acids in diabetic patients is limited to the cardiovascular system, otherwise, no appreciable benefits could be traced in relation to DKD [177].

Treatment of hyperuricemia: In T1DM patients with normal UAE, serum UA is a strong predictor for the increased UAE. Every 1 mg/dL increase in serum UA increases the risk of development of albuminuria by 80% [178]. In T1DM patients with serum UA >6.6 mg/dL, the unadjusted risk of eGFR loss increases 2.4 folds in comparison to those with lower level [179]. In addition, serum UA was a significant independent predictor of overt proteinuria after 18 years follow-up of 263 newly diagnosed T1DM patients [180]. In a cross-sectional study of 3212 T2DM patients, 68% of the hyperuricemic T2DM patients had DN versus 41.5% of T2DM that have normal serum UA [181]. In a longitudinal study of more than twenty thousand T2DM patients having eGFR > 60 mL/min and normal UAE, the incidence of eGFR <60 mL/min., increased UAE or both over 4 years of follow-up was 7.9%, 14.1%, and 2% respectively. The highest relative risk of eGFR decline was encountered in the highest serum UA quintile. There was a significant association of serum UA and UAE in the cases that developed eGFR decline [182]. A more recent Japanese study has reinforced these findings [183]. In a prospective study of 422 T2DM patients with a disease duration for more than fifteen years that were followed for up to 77 mo, serum UA >7 mg/ dL in males and >6 mg/dL in females had a significantly higher rate of DN progression, and overall mortality [184]. Compared to diabetic control mice, T2DM hyperuricemic mice treated with allopurinol experienced smaller increases in UAE. In addition, allopurinol attenuated the activation of TGF-β 1-induced Smad pathway in tubular epithelial cells [185]. When T2DM patients suffering DN were treated with allopurinol for three years, they experienced a significant decrease of UAE and serum creatinine and a significant increase of GFR [186]. Furthermore, 6 months’ treatment of asymptomatic hyperuricemic stage 3-4 CKD patients (44% of them had T2DM) with febuxostat significantly slowed the decline of GFR compared to placebo [187]. In a recent meta-analysis of 19 randomized controlled trials that enrolled 992 participants proved a significant favorable effect of urate-lowering medications on the rate of GFR decline [188].

Phosphate handling: Hyperphosphatemia, a consequence of impaired excretion by the failing kidney, is a potential risk factor for the perpetuation of the rapid decline in renal function [189]. Renal phosphate excretion is FGF23 dependent. Serum level of FGF23 is higher in T2DM [54] and is an independent predictor of DN progression [59]. FGF23 was able to induce TNF α and TGF β genes within the mouse kidney [190]. Moreover, FGF23 stimulates hepatic secretion of IL6 and CRP [191]. According to these findings, control of FGF23 as soon as its level starts to raise in the very early days of stage 2 CKD is a mandate [192,193]. Intestinal phosphate absorption is the most modifiable target for FGF23 control. Non calcium-based phosphate binders can suppress FGF23, a finding that can explain their anti-inflammatory action and their role in overall mortality [194-197]. Sevelamer carbonate administered to patients with T2DM and early kidney disease, significantly reduced FGF 23, lipids, and markers of inflammation and oxidative stress, and markedly increased antioxidant markers [198]. It also reduced cellular and circulating AGEs [193]. Combining dietary phosphate restriction and sevelamer in predialysis CKD patients (24% of them were diabetic) resulted in a significant decrease in overall mortality and progression to dialysis [199].

Control of chronic metabolic acidosis: Metabolic acidosis is an independent risk factor for CKD progression [200]. Sodium bicarbonate supplementation significantly slowed the rate of decline of GFR and improved nutritional status in stage 4 CKD patients (27.5% of them were diabetic) [201]. Comparable to sodium bicarbonate, base-producing fruits and vegetables can correct metabolic acidosis without appreciable increase in serum potassium [202]. Long-term prospective placebo-controlled studies are still needed to highlight the potential benefits of alkali therapy, the ideal type of alkali supplements, and the optimal serum bicarbonate level.

Pentoxifylline: Low-dose pentoxifylline (400 mg/d) was tried in T2DM patients already maintained on losartan plus enalapril to control proteinuria. A significant decrease of UAE from a baseline of 616 mg/d to 192 mg/d was noticed after 6 mo of pentoxifylline [203]. A higher dose of pentoxifylline (1200 mg/d) added to maximum RAS blockade was associated with a slower rate of GFR loss and a significant reduction in UAE in stage 4 DN T2DM patients [204].

Sarpogrelate: Sarpogrelate, a 5-hydroxy tryptamine receptor antagonist, is used as an anti-platelet agent. It inhibits thromboxane A2 production [205]. A significant decrease of UAE and MCP1 in serum and urine follow Sarpogrelate treatment of DN patients [206]. We still lack long-term studies.

Vitamin D receptor agonists: In T2DM patients with overt nephropathy, paricalcitol in a dose of 2 μg/d showed a significant reduction of UAE [207].

Potential therapeutic modalities (Table 2)

Nuclear factor erythroid 2-related factor 2 activation: Nrf2 is adaptively activated in diabetic patients. However, this degree of activation is not sufficient to combat the oxidative stress aggravated by hyperglycemia [81]. Excess ROS generation is considered the main cause of the development of DN. Nrf2 is emerging as a potential therapeutic target for DN [208]. Non-toxic natural compounds can activate Nrf2. Sulforaphane (present in cruciferous vegetables), resveratrol (found in grapes), rutin (found in buckwheat, black tea, citrus fruits, and apple peels), cinnamic aldehyde (present in cinnamon essential oil), curcumin (found in turmeric), berberine (found in Berberis Mahonia plant), actinidia callosa (found in kiwi fruits), Sinomenine (found in the root of the climbing plant Sinomenium acutum), garlic, and Bitter Melon are natural Nrf2 activators [209-212]. Nrf2 activation suppressed the expression of TGF β, extracellular matrix proteins accumulation, and p21 activation in streptozotocin-induced DN [213]. In streptozotocin-induced T1DM rats, sulforaphane was able to prevent renal inflammation and fibrosis [214]. In T2DM patients with DN, curcumin at the dose of 500 mg/d orally for 15- 30 d caused a significant decrease of UAE, and malondialdehyde (a measure of lipid oxidation index), beside suppression of inflammatory markers [215]. Hyperglycemia-induced glomerular hyperpermeability and a decrease in the junction protein occludin are significantly in vitro corrected by the Nrf2 agonist Rutin when added to the human renal glomerular endothelial cells [216]. Sodium butyrate is another member that activates Nrf2 transcription probably through inhibition of histone deacetylase activity at the nucleus. Consequently, sodium butyrate was able to ameliorate DN pathological changes and UAE in streptozotocin-induced diabetic mice. These effects were completely abolished after deletion of the Nrf2 gene [217]. Resveratrol exerts its cytoprotective effect through two mechanisms, antioxidant activity and Sirtuin 1 gene (silent information regulator T1, SIRT1) activation [218,219]. The antioxidant activity of resveratrol is mediated by either activation of Nrf2 or directly by scavenging different ROS [220]. The SIRT1 cytoprotective action occurs through its anti-oxidative, anti-inflammatory, and anti-apoptotic mechanisms and the regulation of mitochondrial metabolism and autophagy in response to the cell energy and redox status. Among many other diseases, resveratrol can prevent kidney diseases, and cardiovascular disease through SIRT1 activation [218,221,222]. In vitro high glucose-induced mesangial cell proliferation and NF-κB activation are attenuated by resveratrol [222]. Resveratrol increases AMPK phosphorylation and eliminates the suppressive effect of hyperglycemia on AMPK phosphorylation with consequent activation of NADPH oxidase [220]. The inhibitory effect of resveratrol on excess ROS production in the hyperglycemic environment would explain the significant attenuation of renal fibrosis in db/db mice when treated with resveratrol [223]. Similarly, resveratrol alleviates EMT [224] and glomerulosclerosis through suppression of TGF-β/ smad activation [225]. Additionally, Reservatrol increases serum adiponectin and its receptors AdipoR1 and AdipoR2 within the kidney. Through activation of AMPK–SIRT1–PPARγ axis and PPARγ, adiponectin prevented human glomerular endothelial cells oxidative stress and apoptosis [226]. Two-week treatment of streptozotocin-diabetic rats with resveratrol improved UAE and GFR [219]. Resveratrol treatment may also weaken diabetes induced increased expression of VEGF [227]. There’s ongoing clinical trial looking for the effect of resveratrol on UAE and serum creatinine in T2DM. Bardoxolone is Nrf2 activator that was first tried as a radiation protection agent [228]. BEAM study is a phase 2 double-blind randomized placebo-controlled trial of bardoxolone in adult patients with T2DM and CKD (eGFR of 20 to 45 mL/min per 1.73 m²). Two hundred and twenty-seven adults were assigned to receive placebo or bardoxolone methyl at a target dose of 25, 75, or 150 mg once daily for 1 year. At 6 mo onwards of treatment, Bardoxolone methyl significantly increased eGFR [229]. A significant increase of UAE, a trend of higher systolic BP, nausea, weight loss, and muscle spasm represent the most important adverse effects of bardoxolone in this study. Twenty-five percent of patients experienced nausea. While normal BMI patients lost a mean of 3 kg over the year of study, this loss reached 10 kg in high BMI patients. 63% of patients on 75 mg of bardoxolone experienced a muscle spasm. Hypomagnesemia was also encountered among bardoxolone group. This study was followed by a larger study, the BEACON study, of 2185 T2DM DN patients in stage 4CKD (eGFR of 15-30 mL/kg per 1.73 m²). The study was designed to continue for 24 mo using 20 mg of bardoxolone methyl as a single daily dose in the treatment group [230]. At an average follow-up of 9 mo, the study was prematurely terminated thanks to the frequent cases of heart failure and mortality in the active treatment group in comparison to the placebo group. The increased incidence of cardiovascular events is probably unrelated to bardoxolone methyl. Increased excretion of RAS blockers in the bardoxolone methyl group might have deprived these patients the cardioprotective, nephroprotective, and antihypertensive effects of RAS blockers [231]. Endothelial dysfunction as a possible consequence of hypomagnesemia may be another explanation for increased proteinuria, heart failure, increased mortality and muscle spasm [232]. Chromium picolinate, chromium histidinate [233], polydatin (a glucoside of resveratrol) [234], and the tetracycline antibiotic minocycline [235] are other Nrf2 activators that have favorable results in experimental studies. However, long-term prospective randomized placebo-controlled trials that would prove the long-term safety and efficacy of these agents are still needed.

Table 2: The Potential therapeutic modalities.

Inhibitors of renal leukocyte recruitment: Membrane receptors on the surface of leukocytes have evolved as a therapeutic target to interrupt their renal recruitment [236]. A mirror-image (Spiegelmer) of MCP-1(CCL2), the pro-inflammatory chemokine capable for renal leukocytes recruitment in DN [237], was in vitro built-up using non-natural nucleotides. This spiegelmer is called Emapticap Pegol. It is an oligonucleotide that binds and neutralizes MCP-1[238]. In the study of safety and efficacy of Emapticap Pegol in stage 4 DN, statistically significant reduction in UAE showed up after 12 wk of Emapticap Pegol use as 3 times weekly subcutaneous injections[239]. Oral CCX140-B is another CCR2 antagonist that was tried in T2DM DN patients. In a dose of 5 mg/d on top of the standard of care treatment, CCX140-B caused a significant reduction of UAE and the rate of GFR decline. The significant impact on GFR was not supported in phase 3 study of CCX140-B [240].

Exogenous klotho: This anti-senescence protein favors epithelial regeneration and inhibits fibroblast phenotype transformation during EMT [242]. Exogenous klotho was capable of attenuation of TGF-β bioactivity, type II TGF-β receptor protein expression, TGF- β Smad 2/3 signaling, and fibronectin expression in high glucose cultured renal interstitial fibroblasts [243]. Intravenous klotho gene administration was able to prevent the progression of renal hypertrophy and fibrosis in diabetic rats [244].

IL-17: Plasma and urine IL-17A levels are reduced in patients with advanced DN. T1DM mice genetically deficient in IL-17A developed more severe nephropathy. Treatment of T1DM and T2DM mice with low doses of IL-17A reversed the pathologic stigmata of DN in these mice. Low doses of IL-17A significantly decreased kidney size, mesangial matrix expansion, interstitial fibrosis, UAE, urine MCP1, IP10, TNF α, IL-6, and serum urea level in comparison to control animals [245].

Aldose reductase inhibitors: The potential role of aldose reductase inhibitors in the treatment and management of the major complications of diabetes like cataract, retinopathy, neuropathy, and cardiovascular disease has achieved appreciable advances. However, their use in DN is still unsatisfactory [246].

Protein kinase C inhibitors: One-year treatment of T2DM patients using ruboxistaurin mesylate significantly reduced UAE and maintained eGFR [247]. On the other hand, a more recent trial failed to disclose a significant value of ruboxistaurin on urine TGF-β or UAE [248]. This discrepancy will postpone the use of this agent till further trials can settle this controversy.

Sulodexide: Sulodexide, a purified mixture of sulfated glycosaminoglycan polysaccharides, was assessed in 2 clinical studies looking for its potential antiproteinuric effect. In early DN patients with T1DM and T2DM, sulodexide was associated with significant reduction of UAE [249]. In the second trial, reduction of UAE was not statistically significant in T2DM patients [250]. A more recent multicenter double-blind placebo-controlled study failed to demonstrate a significant decrease of UAE in T2DM with incipient nephropathy after use of sulodexide [251].

Endothelin receptor antagonists: The use of endothelin receptor antagonists is associated with serious adverse events in spite of their favorable effect on UAE in DN patients. A meta-analysis of five randomized controlled trials has confirmed this impression [252]. The SONAR is an ongoing hard outcome trial in T2DM patients with DN to evaluate atrasentan. Results of this trial will hopefully settle the possible role of this agent [253].

Intensified Multifactorial Intervention

STENO-2 is an open parallel trial that randomly allocated T2DM patients with incipient nephropathy to either standard treatment (n=80) or intensive treatment (n=80). Patient recruitment occurred during 1992-1993. The intensive treatment group had optimized diet regimen, 30 min exercise program 3-5 times/wk, avoided smoking, got vitamin C, vitamin E, and oral hypoglycemic treatment if diet alone failed to keep HbA1c <6.5%, had statin treatment for hypercholesterolemic and fibrate treatment for hypertriglyceridemic patients. For overweight, oral hypoglycemic agents were metformin and for lean patients, gliclazide was used. If HbA1c did not reach the target with a single agent, a combination of both agents was prescribed. If oral treatment failed to achieve the target, insulin was added. Seventy-one patients in the intensive treatment group received antihypertensive treatment versus only 48 in the standard group thanks to lower BP target in the intensive treatment group. Out of these sixty-nine had ACE inhibitor in the intensive treatment versus thirty-eight in the standard treatment. After 7.8 years, all the patients were subsequently offered intensified multifactorial treatment according to the original protocol due to the marked risk reductions encountered with intensive treatment. In spite of the significant impact on survival and cardiovascular outcome, there was no significant difference in the incidence of ESRD between the 2 groups after a median observation time of 21.2 years [103,254].

Perspectives

In spite of the disappointing finding of the STENO-2 study, the recent developments in the field of management of DN give a big hope of better prevention and management of this progressive distressing disease. These new discoveries mandate the change of management plan. Control of blood sugar to the target often fails. The use of RAS blockers offers, at the best, partial protection. These agents were advised when diabetic patients proceed to stage 4 DN. RAS blockers failed to completely reverse the hemodynamic change encountered since the very early days of diabetes mellitus even with dual blockade of the RAS system. The early introduction of SGLT2 inhibitors to T1DM and T2DM offers a new addition to hyperfiltration control. The co-administration of RAS blocker and SGLT2 inhibitor deserves a long-term prospective trial in both types of diabetic patients with the use of both agents starting in the very early days of stage 1 of DN. This co-administration would avoid RAS system activation triggered by SGLT2 inhibitors. The anti-fibrotic effect of the DPP-4 inhibitors linagliptin and saxagliptin deserves their use as the favorable hypoglycemic agents in patients with DN. Diabetic patients in early stages of DN expectedly would get a maximal benefit after the triple treatment with RAS blocker, SGLT2 inhibitor, and either saxagliptin or linagliptin. In spite of the favorable impact of pioglitazone, its salt and water retaining effect limits its use in DN. With CKD progression to stage 4, Metformin and GLP-1 agonists should be avoided. However, their use in the earlier stages adds to the favorable effect of other agents. Once the DN patient has overt proteinuria, pentoxifylline should be added to the prescribed treatment. Although the chance of hyperuricemia is expectedly lower in patients already kept on SGLT2 inhibitor, serum uric acid should be monitored and hypouricemic treatment must be added if serum UA is above 6.5 mg/dL. A strong evidence of safety and efficacy of the long-term use of Nrf2 agonists, leucocyte recruitment inhibitors, IL17 and klotho is still needed before allowing them to the approved list. Control of hyperphosphatemia and correction of metabolic acidosis are necessary once the patient proceeds to stage 4 CKD. Finally, we should emphasize that metformin, pioglitazone, DPP- 4 inhibitors, and SGLT2 inhibitors can be used in T1DM. Their use might decrease the chance of development and progression of DN.

References

1. Mogensen CE, Christensen CK, Vittinghus E (1983) The stages in diabetic renal disease. With emphasis on the stage of incipient diabetic nephropathy. Diabetes 1983; 32 Suppl 2: 64-78.
2. Keen H, Chlouverakis C (1963) An immunoassay method for urinary albumin at low concentrations. Lancet 2: 913-914.
3. Viberti GC, Hill RD, Jarrett RJ, Argyropoulos A, Mahmud U, et al. (1982) Microalbuminuria as a predictor of clinical nephropathy in insulin-dependent diabetes mellitus. Lancet 1: 1430-1432.
4. Dounousi E, Duni A, Leivaditis K, Vaios V, Eleftheriadis T, et al. (2015) Improvements in the Management of Diabetic Nephropathy. Rev Diabet Stud 12: 119-133.
5. Mauer M, Zinman B, Gardiner R, Suissa S, Sinaiko A, et al. (2009) Renal and retinal effects of enalapril and losartan in type 1 diabetes. N Engl J Med 361: 40-51.
6. Bilous R, Chaturvedi N, Sjølie AK, Fuller J, Klein R, et al. (2009) Effect of candesartan on microalbuminuria and albumin excretion rate in diabetes: three randomized trials. Ann Intern Med 151: 11-20.
7. de Azevedo MJ, Ramos OL, Gross JL (1997) Lack of effect of captopril on glomerular hyperfiltration in normoalbuminuric normotensive insulin-dependent diabetic patients. Horm Metab Res 29: 516-519.
8. Cherney DZ, Scholey JW, Jiang S, Har R, Lai V, et al. (2012) The effect of direct renin inhibition alone and in combination with ACE inhibition on endothelial function, arterial stiffness, and renal function in type 1 diabetes. Diabetes Care 35: 2324-2330.
9. Mann JF, Schmieder RE, Dyal L, McQueen MJ, Schumacher H, et al. (2009) Effect of telmisartan on renal outcomes: a randomized trial. Ann Intern Med 151: 1-10.
10. Weir MR, Bakris GL (2010) Editorial perspective. Should microalbuminuria ever be considered as a renal endpoint in any clinical trial? Am J Nephrol 31: 469-470.
11. Bakris GL, Molitch M (2014) Microalbuminuria as a risk predictor in diabetes: the continuing saga. Diabetes Care 37: 867-875.
12. Mazze RS, Bergenstal R, Ginsberg B (1995) Intensified diabetes management: lessons from the diabetes control and complications trial. Int J Clin Pharmacol Ther 33: 43-51.
13. Stratton IM, Adler AI, Neil HA, Matthews DR, Manley SE, et al. (2000) Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 35): prospective observational study. BMJ 321: 405-412.
14. Diabetes Control and Complications Trial Research Group (1993) The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. The Diabetes Control and Complications Trial Research Group. N Engl J Med 329: 977-986.
15. UK Prospective Diabetes Study Group (1998) Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). UK Prospective Diabetes Study (UKPDS) Group. Lancet 352: 837-853.
16. Giacco F, Brownlee M (2010) Oxidative stress and diabetic complications. Circ Res 107: 1058-1070.
17. Gill PS, Wilcox CS (2006) NADPH oxidases in the kidney. Antioxid Redox Signal 8: 1597-1607.
18. Bjornstad P, Lanaspa MA, Ishimoto T, Kosugi T, Kume S, et al. (2015) Fructose and uric acid in diabetic nephropathy. Diabetologia 58: 1993-2002.
19. Eid S, Boutary S, Braych K, Sabra R, Massaad C, et al. (2016) mTORC2 Signaling Regulates Nox4-Induced Podocyte Depletion in Diabetes. Antioxid Redox Signal 2016; 25: 703-719.
20. Sánchez-Lozada LG, Lanaspa MA, Cristóbal-García M, García-Arroyo F, Soto V, et al. (2012) Uric acid-induced endothelial dysfunction is associated with mitochondrial alterations and decreased intracellular ATP concentrations. Nephron Exp Nephrol 121: e71-e78.
21. Cristóbal-García M, García-Arroyo FE, Tapia E, Osorio H, Arellano-Buendía AS, et al. (2015) Renal oxidative stress induced by long-term hyperuricemia alters mitochondrial function and maintains systemic hypertension. Oxid Med Cell Longev 2015: 535686.
22. Ryu ES, Kim MJ, Shin HS, Jang YH, Choi HS, et al. (2013) Uric acid-induced phenotypic transition of renal tubular cells as a novel mechanism of chronic kidney disease. Am J Physiol Renal Physiol 304: F471-F480.
23. Wada J, Makino H (2013) Inflammation and the pathogenesis of diabetic nephropathy. Clin Sci (Lond) 124: 139-152.
24. Yang B, Hodgkinson A, Oates PJ, Millward BA, Demaine AG (2008) High glucose induction of DNA-binding activity of the transcription factor NFkappaB in patients with diabetic nephropathy. Biochim Biophys Acta 1782: 295-302.
25. Ha H, Yu MR, Choi YJ, Kitamura M, Lee HB (2002) Role of high glucose-induced nuclear factor-kappaB activation in monocyte chemoattractant protein-1 expression by mesangial cells. J Am Soc Nephrol 13: 894-902.
26. Park CW, Kim JH, Lee JH, Kim YS, Ahn HJ, et al. (2000) High glucose-induced intercellular adhesion molecule-1 (ICAM-1) expression through an osmotic effect in rat mesangial cells is PKC-NF-kappa B-dependent. Diabetologia 43: 1544-1553.
27. Kashihara N, Haruna Y, Kondeti VK, Kanwar YS (2010) Oxidative stress in diabetic nephropathy. Curr Med Chem 17: 4256-4269.
28. Estacio RO, Schrier RW (2001) Diabetic nephropathy: pathogenesis, diagnosis, and prevention of progression. Adv Intern Med 46: 359-408.
29. Lieberthal W, Levine JS (2009) The role of the mammalian target of rapamycin (mTOR) in renal disease. J Am Soc Nephrol 20: 2493-2502.
30. Kume S, Koya D, Uzu T, Maegawa H (2014) Role of nutrient-sensing signals in the pathogenesis of diabetic nephropathy. Biomed Res Int 2014: 315494.
31. Velagapudi C, Bhandari BS, Abboud-Werner S, Simone S, Abboud HE, et al. (2011) The tuberin/mTOR pathway promotes apoptosis of tubular epithelial cells in diabetes. J Am Soc Nephrol 22: 262-273.
32. Wang S, Li B, Li C, Cui W, Miao L (2015) Potential Renoprotective Agents through Inhibiting CTGF/CCN2 in Diabetic Nephropathy. J Diabetes Res 2015: 962383.
33. Ito Y, Aten J, Bende RJ, Oemar BS, Rabelink TJ, et al. (1998) Expression of connective tissue growth factor in human renal fibrosis. Kidney Int 53: 853-861.
34. Murphy M, Godson C, Cannon S, Kato S, Mackenzie HS, et al. (1999) Suppression subtractive hybridization identifies high glucose levels as a stimulus for expression of connective tissue growth factor and other genes in human mesangial cells. J Biol Chem 274: 5830-5834.
35. Huber TB, Simons M, Hartleben B, Sernetz L, Schmidts M, et al. (2003) Molecular basis of the functional podocin-nephrin complex: mutations in the NPHS2 gene disrupt nephrin targeting to lipid raft microdomains. Hum Mol Genet 12: 3397-3405.
36. Doublier S, Salvidio G, Lupia E, Ruotsalainen V, Verzola D, et al. (2003) Nephrin expression is reduced in human diabetic nephropathy: evidence for a distinct role for glycated albumin and angiotensin II. Diabetes 52: 1023-1030.
37. Gagliardini E, Perico N, Rizzo P, Buelli S, Longaretti L, et al. (2013) Angiotensin II contributes to diabetic renal dysfunction in rodents and humans via Notch1/Snail pathway. Am J Pathol 2013; 183: 119-130.
38. Gagliardini E, Corna D, Zoja C, Sangalli F, Carrara F, et al. (2009) Unlike each drug alone, lisinopril if combined with avosentan promotes regression of renal lesions in experimental diabetes. Am J Physiol Renal Physiol 297: F1448-F1456.
39. Niranjan T, Bielesz B, Gruenwald A, Ponda MP, Kopp JB, et al. (2008) The Notch pathway in podocytes plays a role in the development of glomerular disease. Nat Med 14: 290-298.
40. Lin CL, Wang FS, Hsu YC, Chen CN, Tseng MJ, et al. (2010) Modulation of notch-1 signaling alleviates vascular endothelial growth factor-mediated diabetic nephropathy. Diabetes 59: 1915-1925.
41. Wang TT, Wu XH, Zhang SL, Chan JS (1998) Effect of glucose on the expression of the angiotensinogen gene in opossum kidney cells. Kidney Int 53: 312-319.
42. Wehbi GJ, Zimpelmann J, Carey RM, Levine DZ, Burns KD (2001) Early streptozotocin-diabetes mellitus downregulates rat kidney AT2 receptors. Am J Physiol Renal Physiol 280: F254-F265.
43. Zatz R, Dunn BR, Meyer TW, Anderson S, Rennke HG, et al. (1986) Prevention of diabetic glomerulopathy by pharmacological amelioration of glomerular capillary hypertension. J Clin Invest 77: 1925-1930.
44. Durvasula RV, Petermann AT, Hiromura K, Blonski M, Pippin J, et al. (2004) Activation of a local tissue angiotensin system in podocytes by mechanical strain. Kidney Int 65: 30-39.
45. Hostetter TH (2003) Hyperfiltration and glomerulosclerosis. Semin Nephrol 23: 194-199.
46. Freitas HS, Anhê GF, Melo KF, Okamoto MM, Oliveira-Souza M, et al. (2008) Na(+) -glucose transporter-2 messenger ribonucleic acid expression in kidney of diabetic rats correlates with glycemic levels: involvement of hepatocyte nuclear factor-1alpha expression and activity. Endocrinology 149: 717-724.
47. Vallon V, Richter K, Blantz RC, Thomson S, Osswald H (1999) Glomerular hyperfiltration in experimental diabetes mellitus: potential role of tubular reabsorption. J Am Soc Nephrol 10: 2569-2576.
48. Hayflick L (2003) Living forever and dying in the attempt. Exp Gerontol 38: 1231-1241.
49. Kitada K, Nakano D, Ohsaki H, Hitomi H, Minamino T, et al. (2014) Hyperglycemia causes cellular senescence via a SGLT2- and p21-dependent pathway in proximal tubules in the early stage of diabetic nephropathy. J Diabetes Complications 28: 604-611.
50. Deacon CF (2005) What do we know about the secretion and degradation of incretin hormones? Regul Pept 128: 117-124.
51. Cordero OJ, Salgado FJ, Nogueira M (2009) On the origin of serum CD26 and its altered concentration in cancer patients. Cancer Immunol Immunother 58: 1723-1747.
52. Kanasaki K, Shi S, Kanasaki M, He J, Nagai T, et al. (2014) Linagliptin-mediated DPP-4 inhibition ameliorates kidney fibrosis in streptozotocin-induced diabetic mice by inhibiting endothelial-to-mesenchymal transition in a therapeutic regimen. Diabetes 63: 2120-2131.
53. Shi S, Srivastava SP, Kanasaki M, He J, Kitada M, et al. (2015) Interactions of DPP-4 and integrin β1 influences endothelial-to-mesenchymal transition. Kidney Int 88: 479-489.
54. Inci A, Sari F, Coban M, Olmaz R, Dolu S, et al. (2016) Soluble Klotho and fibroblast growth factor 23 levels in diabetic nephropathy with different stages of albuminuria. J Investig Med 64: 1128-1133.
55. Zanchi C, Locatelli M, Benigni A, Corna D, Tomasoni S, et al. (2013) Renal expression of FGF23 in progressive renal disease of diabetes and the effect of ACE inhibitor. PLoS One 8: e70775.
56. Tomaschitz A, Pilz S, Ritz E, Grammer T, Drechsler C, et al. (2010) Independent association between 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D and the renin-angiotensin system: The Ludwigshafen Risk and Cardiovascular Health (LURIC) study. Clin Chim Acta 411: 1354-1360.
57. Deb DK, Chen Y, Zhang Z, Zhang Y, Szeto FL, et al. (2009) 1,25-Dihydroxyvitamin D3 suppresses high glucose-induced angiotensinogen expression in kidney cells by blocking the NF-{kappa}B pathway. Am J Physiol Renal Physiol 296: F1212-F1218.
58. Zhang Z, Sun L, Wang Y, Ning G, Minto AW, et al. (2008) Renoprotective role of the vitamin D receptor in diabetic nephropathy. Kidney Int 73: 163-171.
59. Titan SM, Zatz R, Graciolli FG, dos Reis LM, Barros RT, et al. (2011) FGF-23 as a predictor of renal outcome in diabetic nephropathy. Clin J Am Soc Nephrol 6: 241-247.
60. Razzaque MS (2009) The FGF23-Klotho axis: endocrine regulation of phosphate homeostasis. Nat Rev Endocrinol 5: 611-619.
61. Lee EY, Kim SS, Lee JS, Kim IJ, Song SH, et al. (2014) Soluble α-klotho as a novel biomarker in the early stage of nephropathy in patients with type 2 diabetes. PLoS One 9: e102984.
62. Karalliedde J, Maltese G, Hill B, Viberti G, Gnudi L (2013) Effect of renin-angiotensin system blockade on soluble Klotho in patients with type 2 diabetes, systolic hypertension, and albuminuria. Clin J Am Soc Nephrol 8: 1899-1905.
63. Lim SC, Liu JJ, Subramaniam T, Sum CF (2014) Elevated circulating alpha-klotho by angiotensin II receptor blocker losartan is associated with reduction of albuminuria in type 2 diabetic patients. J Renin Angiotensin Aldosterone Syst 15: 487-490
64. Žeravica R, Čabarkapa V, Ilinčić B, Sakač V, Mijović R, et al. (2015) Plasma endothelin-1 level, measured glomerular filtration rate and effective renal plasma flow in diabetic nephropathy. Ren Fail 37: 681-686.
65. Kohan DE, Barton M (2014) Endothelin and endothelin antagonists in chronic kidney disease. Kidney Int 86: 896-904.
66. Mishra R, Emancipator SN, Kern TS, Simonson MS (2006) Association between endothelin-1 and collagen deposition in db/db diabetic mouse kidneys. Biochem Biophys Res Commun 339: 65-70.
67. Mezzano S, Aros C, Droguett A, Burgos ME, Ardiles L, et al. (2004) NF-kappaB activation and overexpression of regulated genes in human diabetic nephropathy. Nephrol Dial Transplant 19: 2505-2512.
68. Kumar A, Hawkins KS, Hannan MA, Ganz MB (2001) Activation of PKC-beta(I) in glomerular mesangial cells is associated with specific NF-kappaB subunit translocation. Am J Physiol Renal Physiol 281: F613-F619.
69. Lee FT, Cao Z, Long DM, Panagiotopoulos S, Jerums G, Cooper ME, et al. (2004) Interactions between angiotensin II and NF-kappaB-dependent pathways in modulating macrophage infiltration in experimental diabetic nephropathy. J Am Soc Nephrol 15: 2139-2151.
70. Liang YJ, Jian JH, Liu YC, Juang SJ, Shyu KG, et al. (2010) Advanced glycation end products-induced apoptosis attenuated by PPARdelta activation and epigallocatechin gallate through NF-kappaB pathway in human embryonic kidney cells and human mesangial cells. Diabetes Metab Res Rev 26: 406-416.
71. Pillarisetti S, Saxena U (2004) Role of oxidative stress and inflammation in the origin of Type 2 diabetes--a paradigm shift. Expert Opin Ther Targets 8: 401-408.
72. Ohga S, Shikata K, Yozai K, Okada S, Ogawa D, et al. (2007) Thiazolidinedione ameliorates renal injury in experimental diabetic rats through anti-inflammatory effects mediated by inhibition of NF-kappaB activation. Am J Physiol Renal Physiol 292: F1141-F1150.
73. Zhang Z, Yuan W, Sun L, Szeto FL, Wong KE, et al. (2007) 1,25-Dihydroxyvitamin D3 targeting of NF-kappaB suppresses high glucose-induced MCP-1 expression in mesangial cells. Kidney Int 72: 193-201.
74. Soetikno V, Sari FR, Veeraveedu PT, Thandavarayan RA, Harima M, et al. (2011) Curcumin ameliorates macrophage infiltration by inhibiting NF-κB activation and proinflammatory cytokines in streptozotocin induced-diabetic nephropathy. Nutr Metab (Lond) 8: 35-65.
75. Navarro-González JF, Mora-Fernández C, Muros de Fuentes M, García-Pérez J (2011) Inflammatory molecules and pathways in the pathogenesis of diabetic nephropathy. Nat Rev Nephrol 7: 327-340.
76. Kobayashi M, Yamamoto M (2006) Nrf2-Keap1 regulation of cellular defense mechanisms against electrophiles and reactive oxygen species. Adv Enzyme Regul 46: 113-140.
77. Kim HJ, Vaziri ND. (2010) Contribution of impaired Nrf2-Keap1 pathway to oxidative stress and inflammation in chronic renal failure. Am J Physiol Renal Physiol 298: F662-F671.
78. Chartoumpekis DV, Kensler TW (2013) New player on an old field; the keap1/Nrf2 pathway as a target for treatment of type 2 diabetes and metabolic syndrome. Curr Diabetes Rev 9: 137-145.
79. Wakabayashi N, Slocum SL, Skoko JJ, Shin S, Kensler TW (2010) When NRF2 talks, who's listening? Antioxid Redox Signal 13: 1649-1663.
80. Chen Z, Xie X, Huang J, Gong W, Zhu X, et al. (2017) Connexin43 regulates high glucose-induced expression of fibronectin, ICAM-1 and TGF- β1 via Nrf2/ARE pathway in glomerular mesangial cells. Free Radic Biol Med 102: 77-86.
81. Zoja C, Benigni A, Remuzzi G (2014) The Nrf2 pathway in the progression of renal disease. Nephrol Dial Transplant 29: i19-i24.
82. Berthier CC, Zhang H, Schin M, Henger A, Nelson RG, et al. (2009) Enhanced expression of Janus kinase-signal transducer and activator of transcription pathway members in human diabetic nephropathy. Diabetes 58: 469-477.
83. Brosius FC (2008) New insights into the mechanisms of fibrosis and sclerosis in diabetic nephropathy. Rev Endocr Metab Disord 9: 245-254.
84. Alsaad KO, Herzenberg AM (2007) Distinguishing diabetic nephropathy from other causes of glomerulosclerosis: an update. J Clin Pathol 60: 18-26.
85. Olsen S, Mogensen CE (1996) How often is NIDDM complicated with non-diabetic renal disease? An analysis of renal biopsies and the literature. Diabetologia 39: 1638-1645.
86. Lee EY, Chung CH, Choi SO (1999) Non-diabetic renal disease in patients with non-insulin dependent diabetes mellitus. Yonsei Med J 40: 321-326.
87. Nzerue CM, Hewan-Lowe K, Harvey P, Mohammed D, Furlong B, et al. (2000) Prevalence of non-diabetic renal disease among African-American patients with type II diabetes mellitus. Scand J Urol Nephrol 34: 331-335.
88. Prakash J, Sen D, Usha NS (2001) Non-diabetic renal disease in patients with type 2 diabetes mellitus. J Assoc Physicians India 49: 415-420.
89. Zhou J, Chen X, Xie Y, Li J, Yamanaka N, et al. (2008) A differential diagnostic model of diabetic nephropathy and non-diabetic renal diseases. Nephrol Dial Transplant 23: 1940-1945.
90. Parving HH, Gall MA, Skøtt P, Jørgensen HE, Løkkegaard H, et al. (1992) Prevalence and causes of albuminuria in non-insulin-dependent diabetic patients. Kidney Int 41: 758-762.
91. Bakris GL, Williams M, Dworkin L, Elliott WJ, Epstein M, et al. (2000) Preserving renal function in adults with hypertension and diabetes: a consensus approach. National Kidney Foundation Hypertension and Diabetes Executive Committees Working Group. Am J Kidney Dis 36: 646-661.
92. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl 2013; 3: 136-150.
93. Bakris GL (2008) Slowing nephropathy progression: focus on proteinuria reduction. Clin J Am Soc Nephrol 3: S3-S10.
94. KDOQI Clinical Practice Guidelines and Clinical Practice Recommendations for Diabetes and Chronic Kidney Disease. Am J Kidney Dis 49: S12-S154.
95. Sochett EB, Cherney DZ, Curtis JR, Dekker MG, Scholey JW, et al. (2006) Impact of renin angiotensin system modulation on the hyperfiltration state in type 1 diabetes. J Am Soc Nephrol 17: 1703-1709.
96. Erman A, Veksler S, Gafter U, Boner G, Wittenberg C, et al. (2004) Renin-angiotensin system blockade prevents the increase in plasma transforming growth factor beta 1, and reduces proteinuria and kidney hypertrophy in the streptozotocin-diabetic rat. J Renin Angiotensin Aldosterone Syst 5: 146-151.
97. Vieitez P, Gómez O, Uceda ER, Vera ME, Molina-Holgado E (2008) Systemic and local effects of angiotensin II blockade in experimental diabetic nephropathy. J Renin Angiotensin Aldosterone Syst 9: 96-102.
98. Ren X, Guan G, Liu G, Liu G (2009) Irbesartan ameliorates diabetic nephropathy by reducing the expression of connective tissue growth factor and alpha-smooth-muscle actin in the tubulointerstitium of diabetic rats. Pharmacology 83: 80-87.
99. Zimmerman D, Burns KD (2012) Angiotensin-(1-7) in kidney disease: a review of the controversies. Clin Sci (Lond) 123: 333-346.
100. Ficociello LH, Perkins BA, Silva KH, Finkelstein DM, Ignatowska-Switalska H, et al. (2007) Determinants of progression from microalbuminuria to proteinuria in patients who have type 1 diabetes and are treated with angiotensin-converting enzyme inhibitors. Clin J Am Soc Nephrol 2: 461-469.
101. Estacio RO, Jeffers BW, Gifford N, Schrier RW (2000) Effect of blood pressure control on diabetic microvascular complications in patients with hypertension and type 2 diabetes. Diabetes Care  B54-B64.
102. Baba S (2001) Nifedipine and enalapril equally reduce the progression of nephropathy in hypertensive type 2 diabetics. Diabetes Res Clin Pract 54: 191-201.
103. Gæde P, Oellgaard J, Carstensen B, Rossing P, Lund-Andersen H, et al. (2016) Years of life gained by multifactorial intervention in patients with type 2 diabetes mellitus and microalbuminuria: 21 years follow-up on the Steno-2 randomised trial. Diabetologia 59: 2298-2307.
104. Lewis EJ, Hunsicker LG, Clarke WR, Berl T, Pohl MA, et al. (2001 ) Renoprotective effect of the angiotensin-receptor antagonist irbesartan in patients with nephropathy due to type 2 diabetes. N Engl J Med 345: 851-860.
105. Fioretto P, Sutherland DE, Najafian B, Mauer M (2006) Remodeling of renal interstitial and tubular lesions in pancreas transplant recipients. Kidney Int 69: 907-912.
106. Bilous R (2008) Microvascular disease: what does the UKPDS tell us about diabetic nephropathy? Diabet Med 25: 25-29.
107. Shurraw S, Hemmelgarn B, Lin M, Majumdar SR, Klarenbach S, et al. (2011) Association between glycemic control and adverse outcomes in people with diabetes mellitus and chronic kidney disease: a population-based cohort study. Arch Intern Med 171: 1920-1927.
108. Lee CL, Li TC, Lin SY, Wang JS, Lee IT, et al. (2013) Dynamic and dual effects of glycated hemoglobin on estimated glomerular filtration rate in type 2 diabetic outpatients. Am J Nephrol 38: 19-26.
109. Gosmanov AR, Lu JL, Sumida K, Potukuchi PK, Rhee CM, et al. (2016) Synergistic association of combined glycemic and blood pressure level with risk of complications in US veterans with diabetes. J Hypertens 34: 907-913.
110. Slinin Y, Ishani A, Rector T, Fitzgerald P, MacDonald R, et al. (2012) Management of hyperglycemia, dyslipidemia, and albuminuria in patients with diabetes and CKD: a systematic review for a KDOQI clinical practice guideline. Am J Kidney Dis 60: 747-769.
111. Stephenne X, Foretz M, Taleux N, van der Zon GC, Sokal E, et al. (2011) Metformin activates AMP-activated protein kinase in primary human hepatocytes by decreasing cellular energy status. Diabetologia 54: 3101-3110.
112. Zhou G, Myers R, Li Y, Chen Y, Shen X, et al. (2001) Role of AMP-activated protein kinase in mechanism of metformin action. J Clin Invest 108: 1167-1174.
113. Dowling RJ, Zakikhani M, Fantus IG, Pollak M, Sonenberg N (2007) Metformin inhibits mammalian target of rapamycin-dependent translation initiation in breast cancer cells. Cancer Res 67: 10804-10812.
114. Ben Sahra I, Regazzetti C, Robert G, Laurent K, Le Marchand-Brustel Y, et al. (2011) Metformin, independent of AMPK, induces mTOR inhibition and cell-cycle arrest through REDD1. Cancer Res 71: 4366-4372.
115. Langer S, Kreutz R, Eisenreich A (2016)  Metformin modulates apoptosis and cell signaling of human podocytes under high glucose conditions. J Nephrol 29: 765-773.
116. Zhai L, Gu J, Yang D, Hu W, Wang W, et al. (2016) Metformin ameliorates podocyte damage by restoring renal tissue nephrin expression in type 2 diabetic rats. J Diabetes.
117. Banerjee P, Surendran H, Chowdhury DR, Prabhakar K, Pal R, et al. (2016) Metformin mediated reversal of epithelial to mesenchymal transition is triggered by epigenetic changes in E-cadherin promoter. J Mol Med 94: 1397-1409.
118. Louro TM, Matafome PN, Nunes EC, da Cunha FX, Seiça RM, et al. (2011) Insulin and metformin may prevent renal injury in young type 2 diabetic Goto-Kakizaki rats. Eur J Pharmacol 653: 89-94.
119. NICE (2009) Type 2 Diabetes: The Management of Type 2 Diabetes: NICE Clinical Guideline 87. National Institute for Health and Clinical Excellence.
120. Yang T, Michele DE, Park J, Smart AM, Lin Z, et al. (1999) Expression of peroxisomal proliferator-activated receptors and retinoid X receptors in the kidney. Am J Physiol 277: F966-F973.
121. Xing Y, Ye S, Hu Y, Chen Y (2012) Podocyte as a potential target of inflammation: role of pioglitazone hydrochloride in patients with type 2 diabetes. Endocr Pract 18: 493-498.
122. Morikawa A, Ishizeki K, Iwashima Y, Yokoyama H, Muto E, et al. (2011) Pioglitazone reduces urinary albumin excretion in renin-angiotensin system inhibitor-treated type 2 diabetic patients with hypertension and microalbuminuria: the APRIME study. Clin Exp Nephrol 15: 848-853.
123. Jin HM, Pan Y (2007) Renoprotection provided by losartan in combination with pioglitazone is superior to renoprotection provided by losartan alone in patients with type 2 diabetic nephropathy. Kidney Blood Press Res 30: 203-211.
124. Hu YY, Ye SD, Zhao LL, Zheng M, Wu FZ, et al. (2010) Hydrochloride pioglitazone decreases urinary cytokines excretion in type 2 diabetes. Clin Endocrinol (Oxf) 73: 739-743.
125. Fujita H, Morii T, Fujishima H, Sato T, Shimizu T, et al. (2014) The protective roles of GLP-1R signaling in diabetic nephropathy: possible mechanism and therapeutic potential. Kidney Int 85: 579-589.
126. Li W, Cui M, Wei Y, Kong X, Tang L, et al. (2012) Inhibition of the expression of TGF- β 1 and CTGF in human mesangial cells by exendin-4, a glucagon-like peptide-1 receptor agonist. Cell Physiol Biochem 30: 749-757.
127. Schernthaner G, Mogensen CE, Schernthaner GH (2014) The effects of GLP-1 analogues, DPP-4 inhibitors and SGLT2 inhibitors on the renal system. Diab Vasc Dis Res 11: 306-323.
128. Liu WJ, Xie SH, Liu YN, Kim W, Jin HY, et al. (2012) Dipeptidyl peptidase IV inhibitor attenuates kidney injury in streptozotocin-induced diabetic rats. J Pharmacol Exp Ther 340: 248-255.
129. Tani S, Nagao K, Hirayama A (2013) Association between urinary albumin excretion and low-density lipoprotein heterogeneity following treatment of type 2 diabetes patients with the dipeptidyl peptidase-4 inhibitor, vildagliptin: a pilot study. Am J Cardiovasc Drugs 13: 443-450.
130. Mega C, de Lemos ET, Vala H, Fernandes R, Oliveira J, et al. (2011) Diabetic nephropathy amelioration by a low-dose sitagliptin in an animal model of type 2 diabetes (Zucker diabetic fatty rat). Exp Diabetes Res.
131. Hattori S (2011) Sitagliptin reduces albuminuria in patients with type 2 diabetes. Endocr J 58: 69-73.
132. Mori H, Okada Y, Arao T, Tanaka Y (2014) Sitagliptin improves albuminuria in patients with type 2 diabetes mellitus. J Diabetes Investig 5: 313-319.
133. Kawasaki I, Hiura Y, Tamai A, Yoshida Y, Yakusiji Y, et al. (2015) Sitagliptin reduces the urine albumin-to-creatinine ratio in type 2 diabetes through decreasing both blood pressure and estimated glomerular filtration rate. J Diabetes 7: 41-46.
134. Groop PH, Cooper ME, Perkovic V, Emser A, Woerle HJ, et al. (2013) Linagliptin lowers albuminuria on top of recommended standard treatment in patients with type 2 diabetes and renal dysfunction. Diabetes Care 36: 3460-3468.
135. Cooper ME, Perkovic V, McGill JB, Groop PH, Wanner C, et al. (2015) Kidney Disease End Points in a Pooled Analysis of Individual Patient-Level Data From a Large Clinical Trials Program of the Dipeptidyl Peptidase 4 Inhibitor Linagliptin in Type 2 Diabetes. Am J Kidney Dis 66: 441-449.
136. Tsuprykov O, Ando R, Reichetzeder C, von Websky K, Antonenko V, et al. (2016) The dipeptidyl peptidase inhibitor linagliptin and the angiotensin II receptor blocker telmisartan show renal benefit by different pathways in rats with 5/6 nephrectomy. Kidney Int 89: 1049-1061.
137. Gangadharan Komala M, Gross S, Zaky A, Pollock C, Panchapakesan U, et al. (2016) Saxagliptin reduces renal tubulointerstitial inflammation, hypertrophy and fibrosis in diabetes. Nephrology (Carlton) 21: 423-431.
138. Udell JA, Bhatt DL, Braunwald E, Cavender MA, Mosenzon O, et al. (2015) Saxagliptin and cardiovascular outcomes in patients with type 2 diabetes and moderate or severe renal impairment: observations from the SAVOR-TIMI 53 Trial. Diabetes Care; 38: 696-705.
139. Mosenzon O, Leibowitz G, Bhatt DL, Cahn A, Hirshberg B, et al. (2017) Effect of Saxagliptin on Renal Outcomes in the SAVOR-TIMI 53 Trial. Diabetes Care 40: 69-76.
140. Fujita H, Taniai H, Murayama H, Ohshiro H, Hayashi H, et al. (2014) DPP-4 inhibition with alogliptin on top of angiotensin II type 1 receptor blockade ameliorates albuminuria via up-regulation of SDF-1α in type 2 diabetic patients with incipient nephropathy. Endocr J 61: 159-166.
141. Brenner BM, Cooper ME, de Zeeuw D, Keane WF, Mitch WE, et al. (2001) Effects of losartan on renal and cardiovascular outcomes in patients with type 2 diabetes and nephropathy. N Engl J Med 345: 861-869.
142. Wanner C, Inzucchi SE, Lachin JM, Fitchett D, von Eynatten M, et al. (2016) Empagliflozin and Progression of Kidney Disease in Type 2 Diabetes. N Engl J Med; 375: 323-334.
143. Yamout H, Bakris GL (2016) Diabetic nephropathy: SGLT2 inhibitors might halt progression of diabetic nephropathy. Nat Rev Nephrol 12: 583-584.
144. Grempler R, Thomas L, Eckhardt M, Himmelsbach F, Sauer A, et al. (2012) Empagliflozin, a novel selective sodium glucose cotransporter-2 (SGLT-2) inhibitor: characterisation and comparison with other SGLT-2 inhibitors. Diabetes Obes Metab 14: 83-90.
145. Cherney DZ, Perkins BA, Soleymanlou N, Maione M, Lai V, et al. (2014) Renal hemodynamic effect of sodium-glucose cotransporter 2 inhibition in patients with type 1 diabetes mellitus. Circulation 129: 587-597.
146. Skrtić M, Yang GK, Perkins BA, Soleymanlou N, Lytvyn Y, et al. (2014) Characterisation of glomerular haemodynamic responses to SGLT2 inhibition in patients with type 1 diabetes and renal hyperfiltration. Diabetologia 57: 2599-2602.
147. Lambers Heerspink HJ, de Zeeuw D, Wie L, Leslie B, List J, et al. (2013) Dapagliflozin a glucose-regulating drug with diuretic properties in subjects with type 2 diabetes. Diabetes Obes Metab 15: 853-862.
148. Cherney DZ, Perkins BA, Soleymanlou N, Xiao F, Zimpelmann J, et al. (2014) Sodium glucose cotransport-2 inhibition and intrarenal RAS activity in people with type 1 diabetes. Kidney Int 86: 1057-1058.
149. Heerspink HJ, Desai M, Jardine M, Balis D, Meininger G, et al. (2017) Canagliflozin Slows Progression of Renal Function Decline Independently of Glycemic Effects. J Am Soc Nephrol 28: 368-375.
150. Panchapakesan U, Pegg K, Gross S, Komala MG, Mudaliar H, et al. (2013) Effects of SGLT2 inhibition in human kidney proximal tubular cells--renoprotection in diabetic nephropathy? PLoS One 8: e54442.
151. Ojima A, Matsui T, Nishino Y, Nakamura N, Yamagishi S, et al. (2015) Empagliflozin, an Inhibitor of Sodium-Glucose Cotransporter 2 Exerts Anti-Inflammatory and Antifibrotic Effects on Experimental Diabetic Nephropathy Partly by Suppressing AGEs-Receptor Axis. Horm Metab Res 47: 686-692.
152. Terami N, Ogawa D, Tachibana H, Hatanaka T, Wada J, et al. (2014) Long-term treatment with the sodium glucose cotransporter 2 inhibitor, dapagliflozin, ameliorates glucose homeostasis and diabetic nephropathy in db/db mice. PLoS One 9: e100777.
153. Kojima N, Williams JM, Takahashi T, Miyata N, Roman RJ, et al. (2013) Effects of a new SGLT2 inhibitor, luseogliflozin, on diabetic nephropathy in T2DN rats. J Pharmacol Exp Ther 345: 464-472.
154. Ishibashi Y, Matsui T, Yamagishi SI. Tofogliflozin (2016) A selective inhibitor of sodium-glucose cotransporter 2, suppresses renal damage in KKAy/Ta mice, obese and type 2 diabetic animals. Diab Vasc Dis Res 13: 438-441.
155. Takakura S, Toyoshi T, Hayashizaki Y, Takasu T (2016) Effect of ipragliflozin, an SGLT2 inhibitor, on progression of diabetic microvascular complications in spontaneously diabetic Torii fatty rats. Life Sci 147: 125-131.
156. Kohan DE, Fioretto P, Tang W, List JF (2014) Long-term study of patients with type 2 diabetes and moderate renal impairment shows that dapagliflozin reduces weight and blood pressure but does not improve glycemic control. Kidney Int 85: 962-971.
157. List JF, Woo V, Morales E, Tang W, Fiedorek FT, et al. (2009) Sodium-glucose cotransport inhibition with dapagliflozin in type 2 diabetes. Diabetes Care 32: 650-657.
158. National Kidney Foundation. KDOQI Clinical Practice Guideline for Diabetes and CKD: 2012 Update. Am J Kidney Dis 60: 850-886.
159. Wanner C, Tonelli M (2014) KDIGO Clinical Practice Guideline for Lipid Management in CKD: summary of recommendation statements and clinical approach to the patient. Kidney Int 85: 1303-1309.
160. Haynes R, Wanner C (2015) Chronic kidney disease: Statins in chronic kidney disease: time to move on? Nat Rev Nephrol 11: 262-263.
161. Hovind P, Rossing P, Tarnow L, Parving HH (2003) Smoking and progression of diabetic nephropathy in type 1 diabetes. Diabetes Care 26: 911-916.
162. Feodoroff M, Harjutsalo V, Forsblom C, Thorn L, Wadén J, et al. (2016) Smoking and progression of diabetic nephropathy in patients with type 1 diabetes. Acta Diabetol 53: 525-533.
163. Gambaro G, Bax G, Fusaro M, Normanno M, Manani SM, et al. (2001) Cigarette smoking is a risk factor for nephropathy and its progression in type 2 diabetes mellitus. Diabetes Nutr Metab 14: 337-342.
164. Suckling RJ, He FJ, Macgregor GA (2010) Altered dietary salt intake for preventing and treating diabetic kidney disease. Cochrane Database Syst Rev 12: CD006763.
165. Suckling RJ, He FJ, Markandu ND, MacGregor GA (2016) Modest Salt Reduction Lowers Blood Pressure and Albumin Excretion in Impaired Glucose Tolerance and Type 2 Diabetes Mellitus: A Randomized Double-Blind Trial. Hypertension 67: 1189-1195.
166. Kanauchi N, Ookawara S, Ito K, Mogi S, Yoshida I, et al. (2015) Factors affecting the progression of renal dysfunction and the importance of salt restriction in patients with type 2 diabetic kidney disease. Clin Exp Nephrol 19: 1120-1126.
167. Thomas MC, Moran J, Forsblom C, Harjutsalo V, Thorn L, et al. (2011) The association between dietary sodium intake, ESRD, and all-cause mortality in patients with type 1 diabetes. Diabetes Care 34: 861-866.
168. Vallon V, Huang DY, Deng A, Richter K, Blantz RC, et al. (2002) Salt-sensitivity of proximal reabsorption alters macula densa salt and explains the paradoxical effect of dietary salt on glomerular filtration rate in diabetes mellitus. J Am Soc Nephrol 13: 1865-1871.
169. Takenaka T, Inoue T, Watanabe Y (2015) How the kidney hyperfiltrates in diabetes: From molecules to hemodynamics. World J Diabetes 6: 576-582.
170. Pedrini MT, Levey AS, Lau J, Chalmers TC, Wang PH (1996) The effect of dietary protein restriction on the progression of diabetic and nondiabetic renal diseases: a meta-analysis. Ann Intern Med 124: 627-632.
171. Waugh NR, Robertson AM (2000) Protein restriction for diabetic renal disease. Cochrane Database Syst Rev (2): CD002181.
172. Robertson L, Waugh N, Robertson A. (2007) Protein restriction for diabetic renal disease. Cochrane Database Syst Rev (4): CD002181.
173. Rughooputh MS, Zeng R, Yao Y (2015) Protein Diet Restriction Slows Chronic Kidney Disease Progression in Non-Diabetic and in Type 1 Diabetic Patients, but Not in Type 2 Diabetic Patients: A Meta-Analysis of Randomized Controlled Trials Using Glomerular Filtration Rate as a Surrogate. PLoS One 10: e0145505.
174. Jibani MM, Bloodworth LL, Foden E, Griffiths KD, Galpin OP (1991) Predominantly vegetarian diet in patients with incipient and early clinical diabetic nephropathy: effects on albumin excretion rate and nutritional status. Diabet Med 8: 949-953.
175. de Mello VD, Zelmanovitz T, Perassolo MS, Azevedo MJ, Gross JL (2006) Withdrawal of red meat from the usual diet reduces albuminuria and improves serum fatty acid profile in type 2 diabetes patients with macroalbuminuria. Am J Clin Nutr  83: 1032-1038.
176. Segasothy M, Phillips PA (1999) Vegetarian diet: panacea for modern lifestyle diseases? QJM  92: 531-544.
177. Shapiro H, Theilla M, Attal-Singer J, Singer P (2011) Effects of polyunsaturated fatty acid consumption in diabetic nephropathy. Nat Rev Nephrol 7: 110-121.
178. Jalal DI, Rivard CJ, Johnson RJ, Maahs DM, McFann K, et al. (2010) Serum uric acid levels predict the development of albuminuria over 6 years in patients with type 1 diabetes: findings from the Coronary Artery Calcification in Type 1 Diabetes study. Nephrol Dial Transplant 25: 1865-1869.
179. Ficociello LH, Rosolowsky ET, Niewczas MA, Maselli NJ, Weinberg JM, et al. (2010) High-normal serum uric acid increases risk of early progressive renal function loss in type 1 diabetes: results of a 6-year follow-up. Diabetes Care 33: 1337-1343.
180. Hovind P, Rossing P, Tarnow L, Johnson RJ, Parving HH (2009) Serum uric acid as a predictor for development of diabetic nephropathy in type 1 diabetes: an inception cohort study. Diabetes 58: 1668-1671.
181. Yan D, Tu Y, Jiang F, Wang J, Zhang R, et al. (2015) Uric Acid is independently associated with diabetic kidney disease: a cross-sectional study in a Chinese population. PLoS One  10: e0129797.
182. De Cosmo S, Viazzi F, Pacilli A, Giorda C, Ceriello A, et al. (2015) Serum Uric Acid and Risk of CKD in Type 2 Diabetes. Clin J Am Soc Nephrol 10: 1921-1929.
183. Takae K, Nagata M, Hata J, Mukai N, Hirakawa Y, et al. (2016) Serum Uric Acid as a Risk Factor for Chronic Kidney Disease in a Japanese Community- The Hisayama Study. Circ J 80: 1857-1862.
184. Bartáková V, Kuricová K, Pácal L, Nová Z, Dvořáková V, et al. (2016) Hyperuricemia contributes to the faster progression of diabetic kidney disease in type 2 diabetes mellitus. J Diabetes Complications 30: 1300-1307.
185. Kim SM, Choi YW, Seok HY, Jeong KH, Lee SH, Lee TW, et al. (2012) Reducing serum uric acid attenuates TGF- β -induced profibrogenic progression in type 2 diabetic nephropathy. Nephron Exp Nephrol 121: e109-e121.
186. Liu P, Chen Y, Wang B, Zhang F, Wang D, et al. (2015) Allopurinol treatment improves renal function in patients with type 2 diabetes and asymptomatic hyperuricemia: 3-year randomized parallel-controlled study. Clin Endocrinol 83: 475-482.
187. Sircar D, Chatterjee S, Waikhom R, Golay V, Raychaudhury A, et al. (2015) Efficacy of Febuxostat for Slowing the GFR Decline in Patients With CKD and Asymptomatic Hyperuricemia: A 6-Month, Double-Blind, Randomized, Placebo-Controlled Trial. Am J Kidney Dis 66: 945-950.
188. Kanji T, Gandhi M, Clase CM, Yang R (2015) Urate lowering therapy to improve renal outcomes in patients with chronic kidney disease: systematic review and meta-analysis. BMC Nephrol 16: 58.
189. Barsotti G, Giannoni A, Morelli E, Lazzeri M, Vlamis I, et al. (1984) The decline of renal function slowed by very low phosphorus intake in chronic renal patients following a low nitrogen diet. Clin Nephrol  21: 54-59.
190. Dai B, David V, Martin A, Huang J, Li H, et al. (2012) A comparative transcriptome analysis identifying FGF23 regulated genes in the kidney of a mouse CKD model. PLoS One 7: e44161
191. Singh S, Grabner A, Yanucil C, Schramm K, Czaya B et al. (2016) Fibroblast growth factor 23 directly targets hepatocytes to promote inflammation in chronic kidney disease. Kidney Int 90: 985-996.
192. Sharaf El Din UA, Salem MM, Abdulazim DO (2017) FGF23 and inflammation. World J Nephrol 6: 57-58.
193. Isakova T, Wolf MS (2010) FGF23 or PTH: which comes first in CKD . Kidney Int 78: 947-949.
194. Zayed BM, Fishawy H, Al-Shihaby AR, Salem MA, Sharaf El Din UA (2015) Salem MM efficacy of sevelamer hydrochloride and calcium carbonate as phosphate binders on FGF23 and coronary calcification in hemodialysis patients. World Congress of Nephrology.
195. Rao M, Steffes M, Bostom A, Ix JH (2014) Effect of niacin on FGF23 concentration in chronic kidney disease. Am J Nephrol 39: 484-490.
196. Navarro-González JF, Mora-Fernández C, Muros de Fuentes M, Donate-Correa J, Cazaña-Pérez V, et al. (2011) Effect of phosphate binders on serum inflammatory profile, soluble CD14, and endotoxin levels in hemodialysis patients. Clin J Am Soc Nephrol 6: 2272-2279.
197. Di Iorio B, Bellasi A, Russo D (2012) Mortality in kidney disease patients treated with phosphate binders: a randomized study. Clin J Am Soc Nephrol 7: 487-493.
198. Vlassara H, Uribarri J, Cai W, Goodman S, Pyzik R, et al. (2012) Effects of sevelamer on HbA1c, inflammation, and advanced glycation end products in diabetic kidney disease. Clin J Am Soc Nephrol  7: 934-942.
199. Russo D, Bellasi A, Pota A, Russo L, Di Iorio B (2015) Effects of phosphorus-restricted diet and phosphate-binding therapy on outcomes in patients with chronic kidney disease. J Nephrol 28: 73-80.
200. Dobre M, Yang W, Chen J, Drawz P, Hamm LL, et al. (2013) Association of serum bicarbonate with risk of renal and cardiovascular outcomes in CKD: a report from the Chronic Renal Insufficiency Cohort (CRIC) study. Am J Kidney Dis 62: 670-678.
201. Jeong J, Kwon SK, Kim HY (2014) Effect of bicarbonate supplementation on renal function and nutritional indices in predialysis advanced chronic kidney disease. Electrolyte Blood Press 12: 80-87.
202. Goraya N, Simoni J, Jo CH, Wesson DE (2013) A comparison of treating metabolic acidosis in CKD stage 4 hypertensive kidney disease with fruits and vegetables or sodium bicarbonate. Clin J Am Soc Nephrol 8: 371-381.
203. Ghorbani A, Omidvar B, Beladi-Mousavi SS, Lak E, Vaziri S (2012) The effect of pentoxifylline on reduction of proteinuria among patients with type 2 diabetes under blockade of angiotensin system: a double blind and randomized clinical trial. Nefrologia 32: 790-796.
204. Navarro-González JF, Mora-Fernández C, Muros de Fuentes M, Chahin J, Méndez ML, et al. (2015) Effect of pentoxifylline on renal function and urinary albumin excretion in patients with diabetic kidney disease: the PREDIAN trial. J Am Soc Nephrol 26: 220-229.
205. Park SY, Rhee SY, Oh S, Kwon HS, Cha BY, et al. (2012) Evaluation of the effectiveness of sarpogrelate on the surrogate markers for macrovascular complications in patients with type 2 diabetes. Endocr J 59: 709-716.
206. Ogawa S, Mori T, Nako K, Ishizuka T, Ito S (2008) Reduced albuminuria with sarpogrelate is accompanied by a decrease in monocyte chemoattractant protein-1 levels in type 2 diabetes. Clin J Am Soc Nephrol 3: 362-368.
207. de Zeeuw D, Agarwal R, Amdahl M, Audhya P, Coyne D, et al. (2010) Selective vitamin D receptor activation with paricalcitol for reduction of albuminuria in patients with type 2 diabetes (VITAL study): a randomised controlled trial. Lancet 376: 1543-1551.
208. Jiang T, Huang Z, Lin Y, Zhang Z, Fang D, et al. (2010) The protective role of Nrf2 in streptozotocin-induced diabetic nephropathy. Diabetes 2010; 59: 850-860.
209. Jiménez-Osorio AS, González-Reyes S, Pedraza-Chaverri J (2015) Natural Nrf2 activators in diabetes. Clin Chim Acta 448: 182-192.
210. Zhang X, He H, Liang D, Jiang Y, Liang W, et al. (2016) Protective Effects of Berberine on Renal Injury in Streptozotocin (STZ)-Induced Diabetic Mice. Int J Mol Sci 17: 1327.
211. Raish M, Ahmad A, Jan BL, Alkharfy KM, Ansari MA, et al. (2016) Momordica charantia polysaccharides mitigate the progression of STZ induced diabetic nephropathy in rats. Int J Biol Macromol 91: 394-399.
212. Yin Q, Xia Y, Wang G (2016) Sinomenine alleviates high glucose-induced renal glomerular endothelial hyperpermeability by inhibiting the activation of RhoA/ROCK signaling pathway. Biochem Biophys Res Commun 477: 881-886.
213. Zheng H, Whitman SA, Wu W, Wondrak GT, Wong PK, et al. (2011) Therapeutic potential of Nrf2 activators in streptozotocin-induced diabetic nephropathy. Diabetes 60: 3055-3066.
214. Cui W, Bai Y, Miao X, Luo P, Chen Q, et al. (2012) Prevention of diabetic nephropathy by sulforaphane: possible role of Nrf2 upregulation and activation. Oxid Med Cell Longev 2012: 821-936.
215. Yang H, Xu W, Zhou Z, Liu J, Li X, et al. (2015) Curcumin attenuates urinary excretion of albumin in type II diabetic patients with enhancing nuclear factor erythroid-derived 2-like 2 (Nrf2) system and repressing inflammatory signaling efficacies. Exp Clin Endocrinol Diabetes 123: 360-367.
216. Wang X, Zhao X, Feng T, Jin G, Li Z (2016) Rutin Prevents High Glucose-Induced Renal Glomerular Endothelial Hyperpermeability by Inhibiting the ROS/Rhoa/ROCK Signaling Pathway. Planta Med 82: 1252-1257.
217. Dong W, Jia Y, Liu X, Zhang H, Li T, et al. (2017) Sodium butyrate activates NRF2 to ameliorate diabetic nephropathy possibly via inhibition of HDAC. J Endocrinol 232: 71-83.
218. Kitada M, Kume S, Takeda-Watanabe A, Kanasaki K, Koya D (2013) Sirtuins and renal diseases: relationship with aging and diabetic nephropathy. Clin Sci (Lond) 124: 153-164.
219. Sharma S, Anjaneyulu M, Kulkarni SK, Chopra K (2006) Resveratrol, a polyphenolic phytoalexin, attenuates diabetic nephropathy in rats. Pharmacology 2006; 76: 69-75.
220. Kitada M, Koya D (2013) Renal protective effects of resveratrol. Oxid Med Cell Longev 2013: 568093.
221. Wang XL, Wu LY, Zhao L, Sun LN, Liu HY, et al. (2016) SIRT1 activator ameliorates the renal tubular injury induced by hyperglycemia in vivo and in vitro via inhibiting apoptosis. Biomed Pharmacother 83: 41-50.
222. Xu F, Wang Y, Cui W, Yuan H, Sun J, et al. (2014) Resveratrol Prevention of Diabetic Nephropathy Is Associated with the Suppression of Renal Inflammation and Mesangial Cell Proliferation: Possible Roles of Akt/NF-κB Pathway. Int J Endocrinol 2014: 289-327.
223. He T, Xiong J, Nie L, Yu Y, Guan X, et al. (2016) Resveratrol inhibits renal interstitial fibrosis in diabetic nephropathy by regulating AMPK/NOX4/ROS pathway. J Mol Med (Berl) 94: 1359-1371.
224. He T, Guan X, Wang S, Xiao T, Yang K, et al. (2015) Resveratrol prevents high glucose-induced epithelial-mesenchymal transition in renal tubular epithelial cells by inhibiting NADPH oxidase/ROS/ERK pathway. Mol Cell Endocrinol 402: 13-20.
225. Chen KH, Hung CC, Hsu HH, Jing YH, Yang CW, et al. (2011) Resveratrol ameliorates early diabetic nephropathy associated with suppression of augmented TGF- β /smad and ERK1/2 signaling in streptozotocin-induced diabetic rats. Chem Biol Interact 190: 45-53.
226. Park HS, Lim JH, Kim MY, Kim Y, Hong YA, et al. (2016) Resveratrol increases AdipoR1 and AdipoR2 expression in type 2 diabetic nephropathy. J Transl Med 14: 176.
227. Wen D, Huang X, Zhang M, Zhang L, Chen J, et al. (2013) Resveratrol attenuates diabetic nephropathy via modulating angiogenesis. PLoS One 8: e82336.
228. Kim SB, Pandita RK, Eskiocak U, Ly P, Kaisani A, et al. (2012) Targeting of Nrf2 induces DNA damage signaling and protects colonic epithelial cells from ionizing radiation. Proc Natl Acad Sci USA 109: E2949-E2955.
229. Pergola PE, Raskin P, Toto RD, Meyer CJ, Huff JW, et al. (2011) Bardoxolone methyl and kidney function in CKD with type 2 diabetes. N Engl J Med 365: 327-336.
230. de Zeeuw D, Akizawa T, Audhya P, Bakris GL, Chin M, et al. (2013) Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease. N Engl J Med 369: 2492-2503.
231. Chartoumpekis DV, Sykiotis GP (2014) Bardoxolone methyl in type 2 diabetes and advanced chronic kidney disease. N Engl J Med 370: 1767.
232. Van Laecke S, Van Biesen W, Vanholder R (2015) The paradox of bardoxolone methyl: a call for every witness on the stand? Diabetes Obes Metab 17: 9-14.
233. Selcuk MY, Aygen B, Dogukan A, Tuzcu Z, Akdemir F, et al. (2012) Chromium picolinate and chromium histidinate protects against renal dysfunction by modulation of NF-κB pathway in high-fat diet fed and Streptozotocin-induced diabetic rats. Nutr Metab (Lond) 9: 30.
234. Huang K, Chen C, Hao J, Huang J, Wang S, et al. (2015) Polydatin promotes Nrf2-ARE anti-oxidative pathway through activating Sirt1 to resist AGEs-induced upregulation of fibronetin and transforming growth factor-β1 in rat glomerular messangial cells. Mol Cell Endocrinol 399: 178-189.
235. Shahzad K, Bock F, Al-Dabet MM, Gadi I, Nazir S, et al. (2016) Stabilization of endogenous Nrf2 by minocycline protects against Nlrp3-inflammasome induced diabetic nephropathy. Sci Rep 6: 34228.
236. Anders HJ, Ninichuk V, Schlöndorff D (2006) Progression of kidney disease: blocking leukocyte recruitment with chemokine receptor CCR1 antagonists. Kidney Int 69: 29-32.
237. Ninichuk V, Khandoga AG, Segerer S, Loetscher P, Schlapbach A, et al. (2007) The role of interstitial macrophages in nephropathy of type 2 diabetic db/db mice. Am J Pathol 170: 1267-1276.
238. Oberthür D, Achenbach J, Gabdulkhakov A, Buchner K, Maasch C, et al. (2015) Crystal structure of a mirror-image L-RNA aptamer (Spiegelmer) in complex with the natural L-protein target CCL2. Nat Commun 6: 6923.
239. Menne J, Eulberg D, Beyer D, Baumann M, Saudek F, et al. (2016) C-C motif-ligand 2 inhibition with emapticap pegol (NOX-E36) in type 2 diabetic patients with albuminuria. Nephrol Dial Transplant 27: 190.
240. de Zeeuw D, Bekker P, Henkel E, Hasslacher C, Gouni-Berthold I, et al. (2015) The effect of CCR2 inhibitor CCX140-B on residual albuminuria in patients with type 2 diabetes and nephropathy: a randomised trial. Lancet Diabetes Endocrinol 3: 687-696.
241. Recio C, Lazaro I, Oguiza A, Lopez-Sanz L, Bernal S, et al. (2017) Suppressor of Cytokine Signaling-1 Peptidomimetic Limits Progression of Diabetic Nephropathy. J Am Soc Nephrol 28: 575-585.
242. Hu MC, Shi M, Zhang J, Quiñones H, Kuro-o M, et al. (2010) Klotho deficiency is an early biomarker of renal ischemia-reperfusion injury and its replacement is protective. Kidney Int 78: 1240-1251.
243. Huang JS, Chuang CT, Liu MH, Lin SH, Guh JY, et al. (2014) Klotho attenuates high glucose-induced fibronectin and cell hypertrophy via the ERK1/2-p38 kinase signaling pathway in renal interstitial fibroblasts. Mol Cell Endocrinol 390: 45-53.
244. Deng M, Luo Y, Li Y, Yang Q, Deng X, et al. (2015) Klotho gene delivery ameliorates renal hypertrophy and fibrosis in streptozotocin-induced diabetic rats by suppressing the Rho-associated coiled-coil kinase signaling pathway. Mol Med Rep 12: 45-54.
245. Mohamed R, Jayakumar C, Chen F, Fulton D, Stepp D, et al. (2016) Low-Dose IL-17 Therapy Prevents and Reverses Diabetic Nephropathy, Metabolic Syndrome, and Associated Organ Fibrosis. J Am Soc Nephrol 27: 745-765.
246. Grewal AS, Bhardwaj S, Pandita D, Lather V, Sekhon BS (2016) Updates on Aldose Reductase Inhibitors for Management of Diabetic Complications and Non-diabetic Diseases. Mini Rev Med Chem 16: 120-162.
247. Tuttle KR, Bakris GL, Toto RD, McGill JB, Hu K, et al. (2005) The effect of ruboxistaurin on nephropathy in type 2 diabetes. Diabetes Care 28: 2686-2690.
248. Gilbert RE, Kim SA, Tuttle KR, Bakris GL, Toto RD, et al. (2007) Effect of ruboxistaurin on urinary transforming growth factor-beta in patients with diabetic nephropathy and type 2 diabetes. Diabetes Care 30: 995-996.
249. Gambaro G, Kinalska I, Oksa A, Pont'uch P, Hertlová M, et al. (2002) Oral sulodexide reduces albuminuria in microalbuminuric and macroalbuminuric type 1 and type 2 diabetic patients: the Di.N.A.S. randomized trial. J Am Soc Nephrol 13: 1615-1625.
250. Heerspink HL, Greene T, Lewis JB, Raz I, Rohde RD, et al. (2008) Effects of sulodexide in patients with type 2 diabetes and persistent albuminuria. Nephrol Dial Transplant 23: 1946-1954.
251. Lewis EJ, Lewis JB, Greene T, Hunsicker LG, Berl T, et al. (2011) Sulodexide for kidney protection in type 2 diabetes patients with microalbuminuria: a randomized controlled trial. Am J Kidney Dis 58: 729-736.
252. Yuan W, Li Y, Wang J, Li J, Gou S, et al. (2015) Endothelin-receptor antagonists for diabetic nephropathy: A meta-analysis. Nephrology (Carlton) 20: 459-466.
253. Schievink B, de Zeeuw D, Smink PA, Andress D, Brennan JJ, et al. (2016) Prediction of the effect of atrasentan on renal and heart failure outcomes based on short-term changes in multiple risk markers. Eur J Prev Cardiol 23: 758-768.
254. Gaede P, Vedel P, Parving HH, Pedersen O (1999) Intensified multifactorial intervention in patients with type 2 diabetes mellitus and microalbuminuria: the Steno type 2 randomised study. Lancet 353: 617-622.