Involvement of angiotensin II in progression of renal injury in rats with genetic non-insulin-dependent diabetes mellitus (Wistar fatty rats)

The roles of sodium-glucose cotransporter 2 inhibitors in preventing kidney injury in diabetes

Diabetic nephropathy (DN) is the leading cause of end stage renal disease (ESRD) worldwide. The early effective treatment of high plasma glucose could delay or prevent the onset of DN. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are new target treatments for ameliorating high plasma glucose and help to maintain glucose homeostasis in diabetic patients. Reduced renal glucose reabsorption by SGLT2 inhibition seems to have high potential to improve glycemic control in diabetes mellitus (DM) not only through glucose lowering but also through glucose-independent effects such as blood pressure-lowering and direct renal effects in diabetes. Of note, the important events in the pathogenesis of glucose-induced renal injury and DN including oxidative stress, inflammation, fibrosis and apoptosis conditions have shown to be ameliorate after the treatment with SGLT2 inhibitors. Interestingly, SGLT2 inhibitors have been reported to reduce albuminuria in DM via an activation of renal tubuloglomerular feedback by increased macula densa sodium and chloride delivery, leading to afferent vasoconstriction and attenuated diabetes-induced renal hyperfiltration. These effects also help to conserve glomerular integrity. Thus, the treatment of diabetes mellitus using SGLT2 inhibitors could be one of the effective approach for the management of diabetic-associated kidney disease like DN. This review summarizes the up to date information and discusses the bidirectional relationship between the SGLT2 inhibitor treatments and the renal functions that are available from both basic research and clinical reports. The details of renal outcomes of SGLT2 inhibitors in DN are also provide in this review.

Caloric restriction or telmisartan control dyslipidemia and nephropathy in obese diabetic Zücker rats

BACKGROUND

The obese Zücker diabetic fatty male rat (ZDF:Gmi™-fa) is an animal model of type II diabetes associated with obesity and related metabolic disturbances like dyslipidaemia and diabetic nephropathy. In addition, diabetic dyslipidaemia has been linked to vascular and glomerular damage too. Dietary fat restriction is a current strategy to tackle obesity and, telmisartan, as a renoprotective agent, may mediate cholesterol efflux by activating PPARγ. To test the hypothesis that both therapeutical alternatives may influence dyslipidaemia and nephropathy in the ZDF rat, we studied their effect on development of diabetes.

METHODS

Male Zücker Diabetic Fatty (ZDF) rats received a low-calorie diet, vehicle or telmisartan for 9 weeks. Blood samples were obtained for analyses of lipids and lipoproteins, LDL-oxidisability, HDL structural and functional properties. Urinalysis was carried out to estimate albumin loss. At the end of the experimental period, rats were sacrificed, liver extracted and APOA1 mRNA quantified.

RESULTS

Results indicated that low-calorie diet and telmisartan can slower the onset of overt hyperglycaemia and renal damage assessed as albuminuria. Both interventions decreased the oxidative susceptibility of LDL and hepatic APOA1 mRNA expression but only dietary restriction lowered hyperlipidaemia.

CONCLUSION

Either a dietary or pharmacologic interventions with telmisartan have important beneficial effects in terms of LDL oxidative susceptibility and progression of albuminuria in obesity related type II diabetes.

Renoprotective effects of telmisartan on renal injury in obese Zucker rats

The purpose of the present study was to investigate the renoprotective effect of telmisartan, an angiotensin II receptor antagonist, on the early stages of diabetic nephropathy in obese Zucker rats, which is a type 2-related diabetes mellitus model. Telmisartan 1, 3 or 10 mg/kg/day was orally administered to 7-week-old rats that demonstrated glucose tolerance without albuminuria or proteinuria, for 24 consecutive weeks (Experiment A). In another experiment (Experiment B), oral administration of telmisartan 10 mg/kg/day was initiated at the age of 16 weeks after the rats demonstrated marked proteinuria, and continued for 24 weeks. Telmisartan inhibited the increase in proteinuria and albuminuria in a dose-dependent manner, and the inhibition for all telmisartan groups was statistically significant by the completion of administration (Experiment A). Telmisartan also displayed similar inhibitory effects on proteinuria and albuminuria in Experiment B. Histologically, telmisartan [3 and 10 mg/kg/day] was associated with a significant decrease in the progression of glomerulosclerosis, and significantly improved interstitial cell infiltration, interstitial fibrosis and dilation and atrophy of renal tubules. Furthermore, telmisartan treatment was associated with a tendency towards normalized plasma lipids (total cholesterol and triglyceride). Our results suggest that telmisartan has a definite renoprotective effect against renal injury in type II diabetic nephropathy.

Jak2-Independent Activation of Stat3 by Intracellular Angiotensin II in Human Mesangial Cells

Ang II is shown to mediate the stimulatory effect of high glucose on TGF-b1 and extracellular matrix proteins in glomerular mesangial cells. Also inhibition of Ang II formation in cell media (extracellular) and lysates (intracellular) blocks high-glucose effects on TGF-b1 and matrix more effectively compared to inhibition of extracellular Ang II alone. To investigate whether intracellular Ang II can stimulate TGF-b1 and matrix independent of extracellular Ang II, cultured human mesangial cells were transfected with Ang II to increase intracellular Ang II levels and its effects on TGF-b1 and matrix proteins were determined. Prior to transfection, cells were treated with candesartan to block extracellular Ang II-induced responses via cell membrane AT1 receptors. Transfection of cells with Ang II resulted in increased levels of intracellular Ang II which was accompanied by increased production of TGF-b1, collagen IV, fibronectin, and cell proliferation as well. On further examination, intracellular Ang II was found to activate Stat3 transcription factor including increased Stat3 protein expression, tyrosine 705 phosphorylation, and DNA-binding activity. Treatment with AG-490, an inhibitor of Jak2, did not block intracellular Ang II-induced Stat3 phosphorylation at tyrosine 705 residue indicating a Jak2-independent mechanism used by intracellular Ang II for Stat3 phosphorylation. In contrast, extracellular Ang II-induced tyrosine 705 phosphorylation of Stat3 was inhibited by AG-490 confirming the presence of a Jak2-dependent pathway. These findings suggest that intracellular Ang II increases TGF-b1 and matrix in human mesangial cells and also activates Stat3 transcription factor without involvement of the extracellular Ang II signaling pathway.

The effect of chronic candesartan therapy on the metabolic profile and renal tissue cytokine levels in the obese Zucker rat

The effect of candesartan, an angiotensin-II type-1 receptor antagonist, on the metabolic profile and renal inflammation is unclear. We evaluated this relationship by feeding male lean (LZ) and obese (OZ) Zucker rats chow or chow with candesartan (23.5 mg/kg · diet) for 14 weeks (n = 6–8/treatment/body type). Candesartan reduced serum triglycerides, plasma creatinine, urine albumin, and renal cortical collagen and glycogen deposition in the OZ. An ELISA-based cytokine array revealed that candesartan normalized elevated renal interleukin (IL) 1-β and monocyte chemoattractant protein-1 (MCP-1) levels in OZ. Nonetheless, candesartan impaired glucose tolerance, and did not lower blood insulin or glucose levels. Moreover, renal IL-1α, -2, -4, -6 and -10 tumor necrosis factor-α, interferon-γ, were significantly reduced in OZ relative to LZ, and increased by candesartan. Furthermore, candesartan increased growth-regulated oncogene, transforming growth factor-β1 and IL-18 in OZ kidneys to a level higher than LZ or untreated OZ. Candesartan did not affect renal cytokine levels in LZ. Overall, candesartan attenuated renal disease and improved renal function in OZ, despite mixed effects on metabolic factors and cytokines. Reduced plasma triglycerides and/or renal MCP-1 and IL-1β may have had a role in this protection. However, these effects were clearly independent of any improvement in glucose tolerance.

Impact of obesity on renal structure and function in the presence and absence of hypertension: evidence from melanocortin-4 receptor-deficient mice

The purpose of this study was to determine the long-term impact of obesity and related metabolic abnormalities in the absence and presence of hypertension on renal injury and salt-sensitivity of blood pressure. Markers of renal injury and blood pressure salt sensitivity were assessed in 52- to 55-wk-old normotensive melanocortin-4 receptor-deficient (MC4R-/-) mice and lean C57BL/6J wild-type (WT) mice and in 22-wk-old MC4R-/- and WT mice made hypertensive by N(G)-nitro-L-arginine methyl ester (L-NAME) in the drinking water for 8 wk. Old MC4R-/- mice were 60% heavier, hyperinsulinemic, and hyperleptinemic but had similar mean arterial pressure (MAP) as WT mice (115 +/- 2 and 117 +/- 2 mmHg) on normal salt diet (0.4% NaCl). A high-salt diet (4.0% NaCl) for 12 days did not raise MAP in obese or lean mice [DeltaMAP: MC4R (-/-) 4 +/- 2 mmHg; WT, 2 +/- 1 mmHg]. Obese MC4R-/- mice had 23% greater glomerular tuft area and moderately increased GFR compared with WT mice. Bowman's space, total glomerular area, mesangial matrix, urinary albumin excretion (UAE), renal TGF-beta and collagen expression were not significantly different between old MC4R-/- and WT mice. Renal lipid content was greater but renal macrophage count was markedly lower in MC4R-/- than WT mice. Mild increases in MAP during L-NAME treatment (approximately 16 mmHg) caused small, but greater, elevations in UAE, renal TGF-beta content, and macrophage infiltration in MC4R-/- compared with WT mice without significant changes in glomerular structure. Thus despite long-term obesity and multiple metabolic abnormalities, MC4R-/- mice have no evidence of renal injury or salt-sensitivity of blood pressure. These observations suggest that elevations in blood pressure may be necessary for obesity and related metabolic abnormalities to cause major renal injury or that MC4R-/- mice are protected from renal injury by mechanisms that are still unclear.

Candesartan Differentially Regulates Epithelial Sodium Channel in Cortex Versus Medulla of Streptozotocin-Induced Diabetic Rats

Diabetes is associated with an activated renal renin-angiotensin-aldosterone system (RAAS) and it was shown that streptozotocin (STZ)-induced diabetic rats had increased whole kidney protein levels of the epithelial sodium channel subunits (α-, β- and γ-ENaC). However, the role of the RAAS on the regional, i.e., cortical versus medullary, regulation of ENaC is unclear. Male Sprague-Dawley rats were injected with STZ (intravenous, 65 mg/kg·bw, n=12/group). After 14 days, half of them received drinking water with candesartan (2 mg/kg·bw/day), an angiotensin-II type-1 receptor (AT1R) antagonist, for one week. In the medulla, i.e., inner stripe of the outer medulla (ISOM), base and/or tip of the inner medulla, immunoblotting revealed increased protein abundances of α1 Na-K-ATPase and ENaC subunits with diabetes (200-600% of controls), which were not reversed by candesartan. In fact, candesartan increased all ENaC subunits and α1 Na-K-ATPase in the ISOM and/or base in control rats. In contrast, in the cortex, diabetes did not increase these proteins. However, candesartan reduced cortical β- and γ-ENaC regardless of diabetic state. In summary, diabetes-induced increases in ENaC were seen preferentially in the medulla. These changes appeared to be due to a mechanism clearly distinct from AT1R activation, because they were not abolished by candesartan. In fact, candesartan treatment tended to increase some of these medullary proteins, perhaps in compensation for increased NaCl load. In contrast, cortical β- and γ-ENaC were reduced by candesartan regardless of diabetic state suggesting their regulation by AT1R at this site; however this did not appear to be a site of diabetes-induced ENaC up-regulation.

Regulation of angiotensin II type I receptor (AT1R) protein levels in the obese Zucker rat kidney and urine

Increased renal expression of the angiotensin II, type-1 receptor (AT1R) has been associated with increased blood pressure (BP) and progression of renal disease. We tested whether common medications used to treat hypertension and the metabolic syndrome alter renal AT1R; and whether urine AT1R can be used as a reasonable noninvasive marker of renal levels in the obese Zucker rat, a model for human metabolic syndrome. Immunoblotting revealed that renal and urinary levels of AT1R were significantly higher in obese versus lean rats and correlated (R = 0.62, p < 0.05). Chronic treatment with BP lowering, candesartan, an AT1R antagonist, increased renal levels of AT1R in both lean (282% of lean controls) and obese (178% of obese controls) rats, but decreased urine AT1R levels in obese rats (72% of obese controls). Similarly, chronic treatment with rosiglitazone (RGZ), a peroxisome proliferator activated receptor (subtype gamma) agonist, significantly decreased urine (43% of obese controls) but not renal AT1R (105%) in obese rats. Blood pressure, measured by radiotelemetry, was significantly correlated in untreated and RGZ-treated rats to renal AT1R (R = 0.57, p = 0.0035). Finally, high- (4%) and medium- (0.4%) NaCl diets increased excretion of AT1R in obese rats to approximately 400% of low- (0.04%) NaCl diet. This effect was markedly blunted in lean rats. Overall, we demonstrate increased renal AT1R levels in obese rats. Urine AT1R correlated with renal levels only in the untreated state. Relative salt-sensitivity of AT1R excretion in obese, relative to lean rats, may have implications for both BP and renal disease in the metabolic syndrome.

Diabetes-associated complications in Spontaneously Diabetic Torii fatty rats

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. The SDT-fa/fa (SDT fatty) rat shows overt obesity, and hyperglycemia and hyperlipidemia are observed at a young age as compared with the SDT-+/+ (SDT normal) rat. However, the features of the diabetic complications in the SDT fatty rat have not been reported. In the present study, the incidence and the progression of diabetic complications in the SDT fatty rat were examined, and compared with those of the SDT normal rat. Renal function parameters, such as blood urea nitrogen, urine volume and urinary protein, increased from 4 weeks of age in the SDT fatty rat, and pathological findings in the renal tubule were observed from 8 weeks. Furthermore, cataract was observed in the SDT fatty rat from 8 weeks of age, and prolongation of peak latencies on electroretinograms was observed at 16 and 24 weeks of age. On the other hand, in the SDT normal rat, renal or ocular changes were observed from 24 weeks of age. With early incidence of diabetes mellitus, diabetes-associated complications in the SDT fatty rat were seen at younger ages than those in the SDT normal rat. In conclusion, the SDT fatty rat is expected to be a useful model for the analysis of diabetic complications and the evaluation of drugs related to metabolic diseases.

Chronic candesartan alters expression and activity of NKCC2, NCC, and ENaC in the obese Zucker rat

The obese Zucker rat reportedly has increased activity of the intrarenal renin-angiotensin-aldosterone system, which conceptually could contribute to elevated salt sensitivity and blood pressure (BP). Our aim was to determine whether there was increased angiotensin II type 1 receptor (AT(1)R)-mediated upregulation of expression or activity of the bumetanide-sensitive Na-K-2Cl cotransporter, the thiazide-sensitive Na-Cl cotransporter (NCC), and/or the epithelial sodium channel (ENaC) in obese vs. lean Zucker rats. Male obese and lean Zucker rats (10-wk old) were fed either 1) control chow (1% NaCl) or 2) chow with candesartan (CAN), an AT(1)R antagonist (25 mg/kg.diet) for 14 wk (n = 8/treatment/body type). BP measured by radiotelemetry, was markedly reduced by CAN ( approximately 20-25 mmHg) in both lean and obese rats with no body-type differences. Obese rats had significantly greater net natriuretic response to single injections of hydrochlorothiazide and benzamil, suggesting increased activity of NCC and ENaC, respectively; however, only the response to benzamil was reduced by CAN. CAN led to a significant reduction in whole kidney levels of NCC and gamma-ENaC (70-kDa band) in both lean and obese rats. However, it significantly increased alpha-ENaC and Na-K-2Cl cotransporter levels, and these increases were greater in obese rats. These studies suggest that relatively increased ENaC, but not NCC activity, in obese rats is due to enhanced AT(1)R activity. CAN attenuated the reduction of several renal transporters in the obese rat kidney. Finally, differences in intrarenal AT(1)R activity do not seem directly responsible for BP differences between lean and obese rats.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Losartan ameliorates progression of glomerular structural changes in diabetic KKAy mice

Pathological changes in glomerular structure are typically associated with the progression of diabetic nephropathy. The involvement of angiotensin II (AII) in pathogenesis of diabetic nephropathy has been extensively studied and the therapeutic advantages associated with blockade of renin-angiotensin system (RAS), primarily with angiotensin converting enzyme (ACE) inhibitors, has been well-documented. We studied the effect of RAS blockade with an AII receptor antagonist (losartan) vs. an ACE inhibitor (enalapril) on glomerular lesions in KKAy mice, a model of type 2 diabetes mellitus. Losartan was administered at 3 and 10 mg/kg/day and enalapril at 3 mg/kg/day for 14 weeks in the drinking water. The doses of losartan at 10 mg/kg/day was expected to be equivalent to 3 mg/kg/day of enalapril when considering clinical doses for lowering blood pressure. The dose of 3 mg/kg/day of losartan was selected to compare the efficacy at equivalent dose of enalapril. Histologic observation demonstrated suppression of glomerular mesangial expansion and glomerulosclerosis with exudative lesion in the 10 mg/kg/day losartan group when compared to the untreated diabetic controls. A lesser degree of glomerulosclerosis was also observed with losartan and enalapril treatment at 3 mg/kg/day. Ultrastructural examination of renal glomeruli from the high dose losartan group revealed a decreased degree of effacement and/or irregular arrangement of glomerular podocytic foot process. The beneficial effect of RAS inhibition with the AII receptor antagonist losartan on diabetic glomerular lesions was clearly demonstrated in this study. These findings, therefore, provide mechanistic explanation for the clinical utility of losartan for use in the treatment of diabetic nephropathy in man.

Antiproteinuric effect of candesartan cilexetil in patients with chronic glomerulonephritis

A prospective, randomised, double-blind, parallel-group, dose-response trial was conducted to investigate the antiproteinuric effect of candesartan cilexetil, the angiotensin II type 1 receptor blocker, in patients with chronic glomerulonephritis. Patients (n=280) were treated for 12 weeks with candesartan cilexetil 2, 4, or 8 mg given orally once-daily (o.d.). The improvement in urinary protein excretion observed at the end of the treatment period was 15.9% in the 2 mg group, 25.6% in the 4 mg group, and 34.6% in the 8 mg group, respectively, showing a clear dose-response (2 mg <4 mg <8 mg; p=0.003). The mean reduction in urinary protein excretion was 11.3% in the 2 mg group, 26.3% in the 4 mg group, and 26.0% in the 8 mg group, showing a dose-response pattern, in that the effect of 4 mg and 8 mg was greater than that of 2 mg (2 mg <4 mg asymptotically equal to 8 mg; p=0.010). As the observed reduction in urinary protein excretion failed to correlate with changes in mean blood pressure, it could not be attributed to the antihypertensive effect of the study drug alone. This suggests that candesartan cilexetil, 4 8 mg o.d., has antiproteinuric effects in patients with chronic glomerulonephritis.

Obesity and renal disease

Obesity, which has reached epidemic proportions in the United States and other western countries, may be complicated by hypertension, an increased incidence of renal cancer or proteinuria. Patients with obesity-associated proteinuria show focal glomerulosclerosis and glomerulomegaly on biopsy, usually have minimal clinical edema and relatively normal levels of serum albumin, cholesterol and blood pressure, and can progress to end-stage renal disease. Severe obesity may also be an additive risk factor in patients with preexisting nephropathy or reduced renal mass. The pathophysiology of obesity-associated proteinuria is unclear but may include hyperfiltration, increased renal venous pressure, glomerular hypertrophy, hyperlipidemia and increased synthesis of vasoactive and fibrogenic substances, including angiotensin II, insulin, leptin and transforming growth factor-beta1. These substances may individually or interactively affect glomerular hyperfiltration, mesangial cell hypertrophy and matrix production, and the production of collagen, fibronectin, transforming growth factor-beta and other fibrogenic mediators of change. Although angiotensin-converting enzyme inhibition has proven to have an impact, perhaps temporarily, on obesity-associated proteinuria in humans, weight reduction early in the course of the disease would appear the most important therapeutic approach.

Renal protective effect of candesartan cilexetil in spontaneously hypercholesterolemic rats

Spontaneously hypercholesterolemic (SHC) rats exhibit hypercholesterolemia, proteinuria and focal glomerulosclerosis with age, and they finally die as a result of renal failure. In this study, the renoprotective effects of candesartan cilexetil, an angiotensin II type 1 receptor antagonist, and enalapril, an angiotensin I converting enzyme inhibitor, were examined in SHC rats. Candesartan cilexetil (0.1 and 1 mg /kg) and enalapril (10 mg/kg) were administered orally to 10-week-old SHC rats for a 6-week period. Candesartan cilexetil (1 mg/kg) and enalapril (10 mg/kg) significantly inhibited proteinuria and hypercholesterolemia to a similar extent. In untreated 16-week-old SHC rats, glomerulosclerosis, basophilic change, cast formation and interstitial mononuclear cell infiltration were observed. Candesartan cilexetil (1 mg/kg) inhibited all of these histological changes. Enalapril inhibited glomerulosclerosis and cast formation. These results show that candesartan cilexetil and enalapril have renal protective effects in SHC rats. Thus, angiotensin II might play an important role in renal pathogenesis in a model of focal glomerulosclerosis with hypercholesterolemia.