Spironolactone prevents early renal injury in streptozotocin-induced diabetic rats

Total glucosides of paeony attenuate renal tubulointerstitial injury in STZ-induced diabetic rats: role of Toll-like receptor 2

Accumulating evidence suggested that macrophages induce tubulointerstitial injury. Total glucosides of paeony (TGP), extracted from Paeonia lactiflora, has presented anti-inflammatory activities in diabetic kidney disease. This research will investigate the protective effect of TGP on renal tubulointerstitium and its mechanism in streptozotocin-induced diabetic rats. TGP was administered orally at a dose of 50, 100, and 200 mg·kg(-1)·d(-1) for 8 weeks. Tubulointerstitial injury was quantified, followed by immunohistochemistry analysis of renal α-smooth muscle actin (α-SMA), E-cadherin (E-cad) expression, nuclear factor kappa B (NF-κB)-p-p-65(+), Toll-like receptor (TLR)2(+), and ED-1(+) cell infiltration in renal tubulointerstitium. Renal TLR2(+) macrophages were detected by double immunohistochemical staining. Western blotting was used to detect the TLR2 expression. Histologically, there was marked accumulation of TLR2(+), NF-κB-p-p-65(+), ED-1(+) cells, and ED-1(+)TLR2(+) cells (macrophages) in the diabetic kidney and TGP treatment could alleviate it. Accompanying with that, the tubulointerstitial injury was ameliorated, α-SMA expression was lower, and E-cad expression was higher compared with the diabetic rats. Western blot analysis showed that the expression of TLR2 protein was significantly increased in the kidney of the diabetic rats, whereas TGP treatment reduced it. Our study showed that TGP could prevent renal tubulointerstitium injury in diabetic rats through a mechanism that may be at least partly correlated with suppression of increased macrophage infiltration and the expression of TLR2.

Mineralocorticoid receptor blockade in addition to angiotensin converting enzyme inhibitor or angiotensin II receptor blocker treatment: an emerging paradigm in diabetic nephropathy: a systematic review

Blockade of the renin-angiotensin-aldosterone system (RAAS) is a standard therapeutic intervention in diabetic patients with chronic kidney disease (CKD). Concomitant mineralocorticoid receptor blockade has been studied as a novel approach to further slow down CKD progression. We used PubMed and EMBASE databases to search for relevant literature. We included in our review eight studies in patients of at least 18 years of age, with a diagnosis of type 1 or type 2 diabetes mellitus and diabetic nephropathy, under an angiotensin converting enzyme inhibitor (ACEI) and/or an angiotensin II receptor blocker (ARB) as standard treatment. A subset of patients in each study also received a mineralocorticoid receptor blocker (MRB) (either spironolactone or eplerenone) in addition to standard treatment. Combined treatment with a mineralocorticoid receptor blocker further reduced albuminuria by 23 to 61% compared with standard treatment. Estimated glomerular filtration rate values upon study completion slightly decreased under combined treatment. Blood pressure levels upon study completion were significantly lower with combined treatment in three studies. Hyperkalemia prevalence increased in patients under combined treatment raising dropout rate up to 17%. Therefore, combined treatment by an ACEI/ARB and a MRB may further decrease albuminuria in diabetic nephropathy. This effect may be due to the specific properties of the MRB treatment. Clinicians should regularly check potassium levels because of the increased risk of hyperkalemia. Available evidence should be confirmed by an adequately powered comparative trial of the standard treatment (ACEI or ARB) versus combined treatment by an ACEI/ARB and a MRB.

Effect of spironolactone on diabetic nephropathy compared to the combination of spironolactone and losartan

Background:

Diabetic nephropathy is the most important cause of end stage renal disease (ESRD). Aldosterone is involved in renal damage through induction of fibrosis, inflammation and necrosis in the kidney tissue. Previous studies have demonstrated that the combination of angiotensin receptor blocker (ARB) and spironolactone (an anti-aldosterone drug) are efficient for albuminuria reduction.

Objectives:

This study was designed to evaluate the effect of spironolactone alone on diabetic nephropathy.

Patients and Methods:

In this double blind randomized clinical trial, 60 type II diabetic patients with microalbuminuria were enrolled. They were divided into two groups: case group (spironolactone 25 mg and placebo, 30 cases) and control (spironolactone 25 mg plus losartan 25 mg, 30 cases). The treatment success rate (more than 50% reduction in microalbuminuria) was compared between the two groups.

Results:

After three months, successful treatment was seen in 70% (95% CI: 52 - 83) and 83.3% (CI 95%: 66 - 93) of case and control groups, respectively (P = 0.4). Mean ± SD of serum potassium levels after three months in case and control groups were 4.56 ± 0.38 and 4.39 ± 0.34 mEq/L, respectively (P = 0.08). Mean ± SD of systolic blood pressures in case and control groups were 129.67 ± 9.4 and 130.97 ± 9.4 mmHg, respectively (P = 0.6). Mean ± SD of serum creatinine levels at the end of the study were 0.95 ± 0.15 in case and 0.90 ± 0.22 mg/dL in control group (P = 0.4).

Conclusions:

Spironolactone alone is as effective as the combination of spironolactone and losartan on albuminuria reduction in type 2 diabetic patients and can be used alone as an effective drug for diabetic nephropathy.

Linking the beneficial effects of current therapeutic approaches in diabetes to the vascular endothelin system

The rising epidemic of diabetes worldwide is of significant concern. Although the ultimate objective is to prevent the development and find a cure for the disease, prevention and treatment of diabetic complications is very important. Vascular complications in diabetes, or diabetic vasculopathy, include macro- and microvascular dysfunction and represent the principal cause of morbidity and mortality in diabetic patients. Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vasculopathy. Endothelin-1 (ET-1), an endothelial cell-derived peptide, is a potent vasoconstrictor with mitogenic, pro-oxidative and pro-inflammatory properties that are particularly relevant to the pathophysiology of diabetic vasculopathy. Overproduction of ET-1 is reported in patients and animal models of diabetes and the functional effects of ET-1 and its receptors are also greatly altered in diabetic conditions. The current therapeutic approaches in diabetes include glucose lowering, sensitization to insulin, reduction of fatty acids and vasculoprotective therapies. However, whether and how these therapeutic approaches affect the ET-1 system remain poorly understood. Accordingly, in the present review, we will focus on experimental and clinical evidence that indicates a role for ET-1 in diabetic vasculopathy and on the effects of current therapeutic approaches in diabetes on the vascular ET-1 system.

Kmup-1 Protects Kidney from Streptozotocin-Induced Pro-Inflammation in Early Diabetic Nephropathy by Restoring Enos/Pparγ and Inhibiting MMP-9

KMUP-1 increases nitric oxide (NO) via endothelium nitric-oxide synthase (eNOS). Deficiency of eNOS and peroxisome proliferator-activated receptor-γ (PPARγ) is the pathogenesis of diabetic nephropathy (DN). This study aims to investigate whether KMUP-1 inhibits streptozotocin (STZ)-induced proinflammation in early DN. In experiments, STZ was used to induce diabetes in Wistar rats. Twenty-four male rats were randomly divided into four groups, including control, STZ (65 mg/kg, i.p.), STZ+KMUP-1(1 mg/kg) and STZ+KMUP-1 (2.5 mg/kg). KMUP-1 HCl was dissolved in distilled water for oral administration. The morphology of renal tissues was evaluated by periodic acid-schiff (PAS) staining and immunohistochemistry of eNOS. The expressions of matrix metalloproteinase-2/-9 (MMP-2/-9), eNOS, B-cell lymphoma 2 (Bcl-2), Bcl-2– associated X protein (Bax) and PPARγ of renal tissues were examined by Western blotting technique. NO production was evaluated by Griess reagent. Oxidative stress was evaluated by measuring reactive oxygen species (ROS). Results indicated that STZ-induced diabetic mellitus (DM) and subsequent DN, including excessive deposition of extracellular matrix (ECM) accompanied by enhanced MMP-2/-9, raised ROS production, increased Bcl-2/Bax ratio and decreased eNOS/PPARy over a period of 4 weeks. KMUP-1 inhibited STZ-induced hyperglycemia, BUN, MMP-2/MMP-9, and restored eNOS-PPARγ expression in renal tissues. Immunohistochemistry (IHC) of eNOS in glomeruli of renal cortical tissue sections indicated that KMUP-1 restored the eNOS caused by STZ. PAS staining of glomeruli indicated that KMUP-1 could not significantly reduce STZ-induced ECM expansion. Moreover, KMUP-1 increased Bcl-2/Bax and decreased ROS. In summary, KMUP-1 inhibits STZ-induced proinflammation in early DN by restoring PPARγ/eNOS and inhibiting MMP-9.

Aldosterone stimulates fibronectin synthesis in renal fibroblasts through mineralocorticoid receptor-dependent and independent mechanisms

In addition to its role in regulation of salt transport in the kidney, the mineralocorticoid hormone aldosterone plays an independent role as a mediator of kidney injury and progression of chronic kidney disease. Studies in both animal models and patients have shown that aldosterone enhances the accumulation of extracellular matrix and progression of fibrosis in the kidney. However, the cellular mechanisms that lead to aldosterone-dependent fibrogenesis are poorly understood. In this study we find that aldosterone stimulates fibronectin synthesis through mineralocorticoid receptor (MCR) dependent activation of the c-Jun NH2-terminal protein kinase (JNK) and subsequent phosphorylation of the AP1 transcription factor c-jun, which forms a nuclear complex with the mineralocorticoid receptor in a kidney fibroblast cell line (NRK 49f). Furthermore, MCR-independent phosphorylation of Src family kinase induces IgF1 receptor phosphorylation, which leads to stimulation of the extracellular signal-regulated kinase (ERK1/2) to enhanced fibronectin synthesis. We further find that the IgF1-R-dependent signaling pathway activates fibronectin expression faster than the MCR-dependent pathway. We propose that the mechanisms described in this study are important to aldosterone-dependent progression of interstitial fibrosis in the kidney. Due to the duality of aldosterone-dependent activation of fibronectin synthesis in kidney fibroblasts, MCR-specific inhibitors may not entirely prevent the progression of fibrosis by aldosterone in the kidney.

Renal metabolic profiling of early renal injury and renoprotective effects of Poria cocos epidermis using UPLC Q-TOF/HSMS/MSE

Poria cocos epidermis is one of ancient traditional Chinese medicines (TCMs), which is usually used for the treatment of chronic kidney disease (CKD) for thousands of years in China. A metabonomic approach based on ultra performance liquid chromatography coupled with quadrupole time-of-flight high-sensitivity mass spectrometry (UPLC Q-TOF/HSMS) and a mass spectrometry(Elevated Energy) (MS(E)) data collection technique was developed to obtained a systematic view of the development and progression of CKD and biochemistry mechanism of therapeutic effects of P. cocos epidermis (Fu-Ling-Pi, FLP). By partial least squares-discriminate analysis, 19 metabolites were identified as potential biomarkers of CKD. Among the 19 biomarkers, 10 biomarkers including eicosapentaenoic acid, docosahexaenoic acid, lysoPC(20:4), lysoPC(18:2), lysoPC(15:0), lysoPE(20:0/0:0), indoxyl sulfate, hippuric acid, p-cresol sulfate and allantoin were reversed to the control level in FLP-treated groups. The study indicates that FLP treatment can ameliorate CKD by intervening in some dominating metabolic pathways, such as fatty acid metabolism, phospholipid metabolism, purine metabolism and tryptophan metabolism. This work was for the first time to investigate the FLP therapeutic effect based on metabonomics technology, which is a potentially powerful tool to study the TCMs.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

Effectiveness of eplerenone or spironolactone treatment in preserving renal function in primary aldosteronism

OBJECTIVE

Primary aldosteronism (PA) has deleterious effects on kidney function independent of blood pressure levels. Up to now, data on effectiveness of different PA therapies regarding renal function are scarce.

DESIGN AND METHODS

This prospective multi-center study included 29 patients with newly diagnosed PA evaluated before and 1 year after treatment initiation, and a second cohort including 119 patients who were evaluated 5.3 and 6.8 years after treatment initiation. Glomerular filtration rate (GFR), spot urine albumin excretion/urinary creatinine (UAE/Ucrea) ratio, biochemical parameters, and 24-h blood pressure were measured. In a larger cross-sectional cohort, renal function was evaluated depending on the type of treatment (adrenalectomy (ADX; n=86); spironolactone (n=65); and eplerenone (n=18)).

RESULTS

GFR and UAE/Ucrea ratio significantly decreased in newly diagnosed PA patients after treatment initiation. In the second cohort, GFR and UAE/Ucrea ratio did not change during study period, and blood pressure was well controlled. In the larger cross-sectional cohort, no differences were seen in GFR and UAE/Ucrea ratio between PA patients on different treatment regimens. However, eplerenone treatment showed lower potassium levels and higher number of required antihypertensive medications.

CONCLUSIONS

Renal dysfunction with elevated albuminuria was seen in PA patients and was reversible after treatment initiation. Medical therapies with spironolactone or eplerenone seem to be as effective as ADX regarding renal function and blood pressure; however, sufficient daily doses need to be given.

Renoprotective effects of mineralocorticoid receptor blockers in patients with proteinuric kidney diseases

BACKGROUND

Several studies have demonstrated a short-term antiproteinuric effect of mineralocorticoid receptor blockers (MRB) on proteinuric kidney diseases, but no information is available about the long-term persistence (>1 year) of such reduction in proteinuria and the long-term effects of MRB on renal function.

METHODS

We prospectively studied the effects of adding spironolactone (25 mg/day) to 87 patients who maintained proteinuria higher than 1 g/day in spite of renin-angiotensin system blockade. The mean follow-up was 25 ± 15 (1-84) months.

RESULTS

Estimated glomerular filtration rate (eGFR) showed an acute fall in the first month of treatment (5.1 ± 9.4 mL/min/1.73 m(2)), but it remained stable thereafter (+0.04 ± 0.7 mL/min/1.73 m(2)/month), with a significant difference with respect to the eGFR slope during the 12-month pre-treatment period. The initial eGFR fall predicted a more stable course of renal function, the higher the eGFR initial fall, the better the long-term evolution of eGFR. Proteinuria showed an important and sustained reduction since the first month of treatment. At the end of follow-up, it had decreased by 61% (43-77%) with respect to baseline values. The antiproteinuric and renoprotective influence of spironolactone was also observed in diabetic patients and in patients with renal function impairment, although tolerance was poorer among the latter.

CONCLUSIONS

Spironolactone induces an initial acute fall in eGFR that predicts a later favourable influence on the course of renal function and a remarkable and sustained reduction in proteinuria.

Spironolactone rescues Dot1a-Af9-mediated repression of endothelin-1 and improves kidney injury in streptozotocin-induced diabetic rats

The molecular mechanism linking aldosterone and endothelin-1 in the development of diabetic nephropathy has not been completely elucidated. Here, we provide evidence showing that streptozotocin-induced diabetic rats have significantly increased aldosterone and endothelin-1 in the kidney tissue and markedly decreased expression of Dot1a and Af9. Blocking aldosterone with spironolactone significantly reduced proteinuria, glomerulosclerosis, tubulointerstitial injury and endothelin-1 expression, and significantly increased Dot1a and Af9 expression. Increasing Dot1a and Af9 expression by spironolactone or by stable transfection led to impaired endothelin-1 expression in NRK-52 cells. In contrast, downregulation of Dot1a and Af9 by aldosterone in NRK-52E cells caused upregulation of endothelin-1. Genetic inactivation of Dot1l, which encodes Dot1a, in Aqp2-expressing principal cells of mouse kidney impaired association of Dot1a and H3 dimethyl K79 with the specific subregions of endothelin-1 promoter, and upregulates endothelin-1 mRNA and protein expression. Our data suggest that Dot1a and Af9 repress endothelin-1 in vitro and in vivo. Excessive aldosterone induces kidney injury, in part possibly by downregulating Dot1a and Af9, and thus relieving Dot1a-Af9-mediated repression to increase endothelin-1 transcription. Spironolactone ameliorates kidney injury in Streptozotocin-induced diabetic rats, possibly by restoring Dot1a-Af9-mediated repression to reduce endothelin-1 expression. Therefore, Dot1a and Af9 as aldosterone-downregulated targets are negative regulators of endothelin-1 transcription in vitro and in vivo, and may be considered as new potential therapeutic targets of kidney injury in diabetes.

Effect of eplerenone, a selective aldosterone blocker, on the development of diabetic nephropathy in type 2 diabetic rats

BACKGROUND

Aldosterone antagonists are reported to have beneficial effects on diabetic nephropathy by effective blocking of the renin-angiotensin-aldosterone system. We investigated the renoprotective effect of the selective aldosterone receptor blocker eplerenone, the angiotensin converting enzyme inhibitor lisinopril, and combined eplerenone and lisinopril treatment in type 2 diabetic rats.

METHODS

ANIMALS WERE DIVIDED INTO SIX GROUPS AS FOLLOWS: Otsuka Long-Evans Tokushima Fatty (OLETF) rat control, OLETF rats treated with a low dose of eplerenone (50 mg/kg/day), OLETF rats treated with a high dose of eplerenone (200 mg/kg/day), OLETF rats treated with lisinopril (10 mg/kg/day), OLETF rats treated with a combination of both drugs (eplerenone 200 mg/kg/day and lisinopril 10 mg/kg/day), and obese non-diabetic Long-Evans Tokushima Otsuka rats for 26 weeks.

RESULTS

Urinary albumin excretion was significantly lower in the lisinopril group, but not in the eplerenone group. Urinary albumin excretion was decreased in the combination group than in the lisinopril group. Glomerulosclerosis and renal expression of type I and type IV collagen, plasminogen activator inhibitor-1, transforming growth factor-β1, connective tissue growth factor, and fibronectin mRNA were markedly decreased in the lisinopril, eplerenone, and combination groups.

CONCLUSION

Eplerenone and lisinopril combination showed additional benefits on type 2 diabetic nephropathy compared to monotherapy of each drug.

Spironolactone lowers portal hypertension by inhibiting liver fibrosis, ROCK-2 activity and activating NO/PKG pathway in the bile-duct-ligated rat

OBJECTIVE

Aldosterone, one of the main peptides in renin angiotensin aldosterone system (RAAS), has been suggested to mediate liver fibrosis and portal hypertension. Spironolactone, an aldosterone antagonist, has beneficial effect on hyperdynamic circulation in clinical practice. However, the mechanisms remain unclear. The present study aimed to investigate the role of spionolactone on liver cirrhosis and portal hypertension.

METHODS

Liver cirrhosis was induced by bile duct ligation (BDL). Spironolactone was administered orally (20 mg/kg/d) after bile duct ligation was performed. Liver fibrosis was assessed by histology, Masson's trichrome staining, and the measurement of hydroxyproline and type I collagen content. The activation of HSC was determined by analysis of alpha smooth muscle actin (α-SMA) expression. Protein expressions and protein phosphorylation were determined by immunohistochemical staining and Western blot analysis, Messenger RNA levels by quantitative real time polymerase chain reaction (Q-PCR). Portal pressure and intrahepatic resistance were examined in vivo.

RESULTS

Treatment with spironolactone significantly lowered portal pressure. This was associated with attenuation of liver fibrosis, intrahepatic resistance and inhibition of HSC activation. In BDL rat liver, spironolactone suppressed up-regulation of proinflammatory cytokines (TNFα and IL-6). Additionally, spironolactone significantly decreased ROCK-2 activity without affecting expression of RhoA and Ras. Moreover, spironolactone markedly increased the levels of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS and the activity of NO effector-protein kinase G (PKG) in the liver.

CONCLUSION

Spironolactone lowers portal hypertension by improvement of liver fibrosis and inhibition of intrahepatic vasoconstriction via down-regulating ROCK-2 activity and activating NO/PKG pathway. Thus, early spironolactone therapy might be the optional therapy in cirrhosis and portal hypertension.

Matrix metalloproteinase 2 induces epithelial-mesenchymal transition in proximal tubules from the luminal side and progresses fibrosis in mineralocorticoid/salt-induced hypertensive rats

OBJECTIVES

Excess mineralocorticoids such as deoxycorticosterone acetate (DOCA) together with salt are known to cause tubulointerstitial fibrosis, but the mechanisms underlying fibrosis progression are unclear. Therefore, we investigated the role of matrix metalloproteinase 2 (MMP2) in the epithelial-mesenchymal transition and fibrosis progression.

METHODS

Uninephrectomized rats drank 0.9% NaCl and 0.3% KCl solution and were treated with DOCA alone, DOCA + spironolactone, or vehicle for 1, 4, or 8 weeks. SBP, kidney function and morphology, and kidney and urine MMP2 activity were compared among the groups.

RESULTS

At week 4, the DOCA-treated group exhibited hypertension, tubulointerstitial fibrosis, increased MMP2 activity in the kidney and urine, and overexpression of MMP2 in proximal tubule cells and MMP14 in apical membranes; these results were more pronounced at week 8. At week 8, the proximal tubule cell apicolateral surface proteins villin, claudin 2, and E-cadherin were downregulated, and the mesenchymal marker α-smooth muscle actin was upregulated in the tubulointerstitium of DOCA-treated rats. These DOCA/salt-induced changes (except for hypertension) and fibrosis progression observed at week 8 were reversed by TISAM (a selective MMP2 inhibitor), which was administered from week 4 to week 8. All of the effects of DOCA/salt at week 8 were attenuated by spironolactone.

CONCLUSION

Eight weeks of treatment with DOCA/salt activated MMP2, primarily on the apical surface of proximal tubule cells, which induced epithelial-mesenchymal transition from the luminal side and promoted tubulointerstitial fibrosis progression. These MMP2-induced changes occurred via downstream processes regulated by mineralocorticoid receptors.

Heart angiotensin II-induced cardiomyocyte hypertrophy suppresses coronary angiogenesis and progresses diabetic cardiomyopathy

To examine whether and how heart ANG II influences the coordination between cardiomyocyte hypertrophy and coronary angiogenesis and contributes to the pathogenesis of diabetic cardiomyopathy, we used Spontaneously Diabetic Torii (SDT) rats treated without and with olmesartan medoxomil (an ANG II receptor blocker). In SDT rats, left ventricular (LV) ANG II, but not circulating ANG II, increased at 8 and 16 wk after diabetes onset. SDT rats developed LV hypertrophy and diastolic dysfunction at 8 wk, followed by LV systolic dysfunction at 16 wk, without hypertension. The SDT rat LV exhibited cardiomyocyte hypertrophy and increased hypoxia-inducible factor-1α expression at 8 wk and to a greater degree at 16 wk and interstitial fibrosis at 16 wk only. In SDT rats, coronary angiogenesis increased with enhanced capillary proliferation and upregulation of the angiogenic factor VEGF at 8 wk but decreased VEGF with enhanced capillary apoptosis and suppressed capillary proliferation despite the upregulation of VEGF at 16 wk. In SDT rats, the phosphorylation of VEGF receptor-2 increased at 8 wk alone, whereas the expression of the antiangiogenic factor thrombospondin-1 increased at 16 wk alone. All these events, except for hyperglycemia or blood pressure, were reversed by olmesartan medoxomil. These results suggest that LV ANG II in SDT rats at 8 and 16 wk induces cardiomyocyte hypertrophy without affecting hyperglycemia or blood pressure, which promotes and suppresses coronary angiogenesis, respectively, via VEGF and thrombospondin-1 produced from hypertrophied cardiomyocytes under chronic hypoxia. Thrombospondin-1 may play an important role in the progression of diabetic cardiomyopathy in this model.

Mineralocorticoid Receptor Blocker Protects against Podocyte-Dependent Glomerulosclerosis

Background

We previously showed that angiotensin type 1 receptor (AT1) blocker (ARB) attenuates glomerular injury in Nphs1-hCD25 (NEP25) transgenic mice, a model of selective podocyte injury. However, subsequent studies in NEP25 mice with podocyte-specific deficiency of AT1 revealed that the protective effects of ARB are not through the podocyte AT1, thereby raising the possibility that the protective effects of ARB involve mineralocorticoids.

Methods

NEP25 mice were treated with the mineralocorticoid receptor blocker (MRB) spironolactone (25 mg/kg/day, n = 10), the ARB losartan (250 mg/kg/day, n = 11), both (ARB+MRB, n = 8) or vehicle (Vehicle, n = 9) from day −7 to day 9 of induction of podocyte injury.

Results

Although MRB did not reduce systolic blood pressure or proteinuria, addition of MRB to ARB significantly attenuated glomerulosclerosis (glomerulosclerosis index: ARB+MRB 1.67 ± 0.19 vs. MRB 2.01 ± 0.29, ARB 2.35 ± 0.19, and Vehicle 2.25 ± 0.26, p < 0.05) and preserved the number of WT1-positive podocytes (ARB+MRB 152.5 ± 9.7 vs. MRB 117.2 ± 9.0 or ARB 113.6 ± 7.4, and ARB+MRB vs. Vehicle 97.5 ± 4.0 per glomerulus; p < 0.05).

Conclusion

These data suggest that, while MRB does not attenuate proteinuria caused by podocyte-specific injury, it provides protective effects against glomerulosclerosis that is independent of systemic blood pressure.

Spironolactone improves nephropathy by enhancing glucose-6-phosphate dehydrogenase activity and reducing oxidative stress in diabetic hypertensive rat

Spironolactone (SPR), a mineralocorticoid receptor blocker, diminishes hyperglycemia-induced reduction in glucose-6-phosphate dehydrogenase (G6PD) activity, improving oxidative stress damage. This study investigated whether SPR ameliorates nephropathy by increasing G6PD activity and reducing oxidative stress in spontaneously hypertensive diabetic rats (SHRs). The streptozotocin-induced diabetic rats received or not SPR 50 mg/kg per day, for eight weeks. A human mesangial cell line was cultured in normal or high glucose conditions, with or without SPR, for 24 h. Plasma glucose levels and systolic blood pressure were unaltered by diabetes or by SPR treatment. Albuminuria, fibronectin expression, 8-OHdG urinary levels, lipid peroxidation and p47phox expression were higher in the diabetic rats compared with the control and were reduced by SPR. The antioxidant GSH/GSSG ratio was reduced in the diabetic rats and the treatment reestablished it. Diabetes-induced SGK1 up-regulation was inhibited by SPR. Reactive oxygen species (ROS) and superoxide production induced by NADPH oxidase were increased by hyperglycemia and high glucose, in vivo and in vitro, respectively, and were reduced with SPR. Hyperglycemia and high glucose decreased G6PD activity, which was restored with SPR. These results suggest that SPR ameliorates nephropathy in diabetic SHRs by restoring G6PD activity and diminishes oxidative stress without affecting glycaemia and blood pressure.

Long-term mineralocorticoid receptor blockade ameliorates progression of experimental diabetic renal disease

The final end point of diabetic renal disease is the accumulation of excess collagen. A number of studies have shown that aldosterone antagonism ameliorates progression of renal fibrosis. This study was designed to examine the effect of the mineralocorticoid receptor blocker eplerenone (EPL) on progression in streptozotocin (STZ)-treated spontaneously hypertensive rats (SHR), an accelerated model of Type I diabetes. STZ-treated SHRs with a blood glucose >18 mmol/L were randomly divided into treatment (100 mg/kg/day EPL) and non-treatment groups. Sham-injected SHR animals were used as a control. Functional parameters were monitored for 16 weeks, with structural parameters assessed at completion. Both hyperglycaemic groups developed progressive albuminuria, but the increase was ameliorated by EPL from Week 12. STZ-SHRs had elevated kidney weight/body weight ratio, glomerular size, glomerular macrophages (ED-1-positive cells), tissue transforming growth factor beta 1 (TGFβ1) concentrations and glomerular collagen IV staining (all P < 0.05 versus control animals). EPL reduced glomerular volume, TGFβ1 expression and glomerular collagen IV without changing glomerular macrophage infiltration. The ability of EPL to ameliorate these functional and structural changes in hyperglycaemic SHRs suggest that EPL has a renoprotective role in diabetic renal disease.

The contribution of hypertension to diabetic nephropathy and retinopathy: the role of inflammation and oxidative stress

Diabetes and hypertension frequently coexist and constitute the most notorious combination for the pathogenesis of diabetic nephropathy and retinopathy. Large clinical trials have clearly demonstrated that tight control of glycemia and/or blood pressure significantly reduces the incidence and progression of diabetic retinopathy (DR) and nephropathy. However, the mechanism by which hypertension interacts with diabetes to induce and/or exacerbate nephropathy and retinopathy is very unclear. Substantial evidence implicates the involvement of chronic inflammation and oxidative stress in the pathogenesis of DR and nephropathy. In addition, hypertension causes oxidative stress and inflammation in the kidney and retina. In the present review, we summarized data obtained from our research along with those from other groups to better understand the role of hypertension in the pathogenesis of diabetic nephropathy and retinopathy. It is suggested that oxidative stress and inflammation may be common denominators of kidney and retinal damage in the concomitant presence of diabetes and hypertension.

[Aldosterone and kidney diseases: an emergent paradigm with important clinical implications]

Slowing the progression of chronic kidney diseases needs new efficient treatments. Aldosterone classically acts on the distal nephron: it allows sodium reabsorption, potassium secretion and participates to blood volume control. Recently, new targets of aldosterone have been described including the heart and the vasculature but also non-epithelial kidney cells such as mesangial cells, podocytes and renal fibroblasts. The pathophysiological implication of aldosterone and its receptor, the mineralocorticoid receptor has been demonstrated ex vivo in cell culture and in vivo in experimental animal models with kidney damages such as diabetic and hypertensive kidney nephropathies, chronic kidney disease and glomerulopathies. The beneficial effects of the pharmacological antagonists of the mineralocorticoid receptor are independent of the hypertensive effect of aldosterone, indicating that blocking the activation of the mineralocorticoid receptor in these non-classical renal targets may be of clinical importance. Several clinical studies now report benefit and safety when using spironolactone or eplerenone, the currently available mineralocorticoid receptor antagonists, in patients with kidney diseases. In this review, we discuss the recent results reported in experimental and clinical research in this domain.

Spironolactone ameliorates podocytic adhesive capacity via restoring integrin alpha 3 expression in streptozotocin-induced diabetic rats

Podocyte responses to various injuries include detachment from the glomerular basement membrane (GBM) with impaired adhesion ability. Growing evidence suggests inappropriately enhanced aldosterone levels in glomeruli may contribute to podocytic injury and subsequently glomerulosclerosis in diabetic nephropathy (DN). In the present study, we aimed to investigate podocytic integrin alpha 3 expression and urinary podocyte excretion in streptozotocin (STZ)-induced diabetic rats, and to evaluate their responses to spironolactone (SPL). STZ-induced male diabetic Wistar rats were treated with vehicle (the STZ group, n=7), or spironolactone (the STZ+SPL group, n=6) for 12 weeks, six additional rats of similar body weight serving as control. Urine specimens were obtained for measurement of urine albumin concentration and urinary podocyte quantitation upon completion of the 12 weeks. Urinary podocyte excretion was quantified by immunofluorescence and expression of integrin alpha 3 was detected by immunohistochemistry and Western blotting. At 12 weeks, rats given STZ alone revealed an increase in blood glucose and were unaffected by spironolactone, whereas the STZ+SPL group showed considerable improvement in urine albumin and podocyte excretion, as well as up-regulation of integrin alpha 3. Our results suggest that spironolactone ameliorates impaired podocytic adhesion capacity and prevents STZ-induced DN progression.

Spironolactone improves glucose and lipid metabolism by ameliorating hepatic steatosis and inflammation and suppressing enhanced gluconeogenesis induced by high-fat and high-fructose diet

Recent evidence suggests that treatment with mineralocorticoid receptor antagonist suppressed local inflammation in vascular tissues or cardiomyocytes; therefore, we examined the effect of spironolactone on glucose and lipid metabolism in a mouse model with diet-induced diabetes and nonalcoholic fatty liver disease. C57BL/6 mice were fed either the control diet, 60% fat diet with 30% fructose water (HFFD), or HFFD with spironolactone for 8 wk. HFFD mice demonstrated apparent phenotypes of metabolic syndrome, including insulin resistance, hypertension, dyslipidemia, and fatty liver. Although treatment with spironolactone did not affect the increased calorie intake and body weight by HFFD, the increments of epididymal fat weight, blood pressure, serum triglyceride, free fatty acids, leptin, and total cholesterol levels were significantly suppressed. Elevation of blood glucose during glucose and insulin tolerance tests in HFFD mice was significantly lowered by spironolactone. Notably, increased glucose levels during pyruvate tolerance test in HFFD mice were almost completely ameliorated to control levels by the treatment. Staining with hematoxylin-eosin (HE) and Oil-red-O demonstrated marked accumulation of triglycerides in the centrilobular part of the hepatic lobule in HFFD mice, and these accumulations were effectively improved by spironolactone. Concomitantly HFFD feeding markedly up-regulated hepatic mRNA expression of proinflammatory cytokines (TNFalpha, IL-6, and monocyte chemoattractant protein-1), gluconeogenic gene phosphoenolpyruvate carboxykinase, transcription factor carbohydrate response element binding protein, and its downstream lipogenic enzymes, all of which were significantly suppressed by spironolactone. These results indicate that inhibition of mineralocorticoid receptor might be a beneficial therapeutic approach for diet-induced phenotypes of metabolic syndrome and fatty liver.

Aldosterone: effects on the kidney and cardiovascular system

Aldosterone, a steroid hormone with mineralocorticoid activity, is mainly recognized for its action on sodium reabsorption in the distal nephron of the kidney, which is mediated by the epithelial sodium channel (ENaC). Beyond this well-known action, however, aldosterone exerts other effects on the kidney, blood vessels and the heart, which can have pathophysiological consequences, particularly in the presence of a high salt intake. Aldosterone is implicated in renal inflammatory and fibrotic processes, as well as in podocyte injury and mesangial cell proliferation. In the cardiovascular system, aldosterone has specific hypertrophic and fibrotic effects and can alter endothelial function. Several lines of evidence support the existence of crosstalk between aldosterone and angiotensin II in vascular smooth muscle cells. The deleterious effects of aldosterone on the cardiovascular system require concomitant pathophysiological conditions such as a high salt diet, increased oxidative stress, or inflammation. Large interventional trials have confirmed the benefits of adding mineralocorticoid-receptor antagonists to standard therapy, in particular to angiotensin-converting-enzyme inhibitor and angiotensin II receptor blocker therapy, in patients with heart failure. Small interventional studies in patients with chronic kidney disease have shown promising results, with a significant reduction of proteinuria associated with aldosterone antagonism, but large interventional trials that test the efficacy and safety of mineralocorticoid-receptor antagonists in chronic kidney disease are needed.

Aldosterone and diabetic kidney disease

Aldosterone plays an important role in salt and water homeostasis and blood pressure control through the classical mineralocorticoid receptor. However, recent findings of the mineralocorticoid receptor in nonepithelial tissues suggest that aldosterone may have additional functions. Significant evidence now exists suggesting that aldosterone directly induces tissue injury. Systemic or local aldosterone has emerged as a multifunctional hormone exhibiting profibrotic and proinflammatory actions that extend beyond the classical hemodynamic effect. The incomplete blockade of the renin-angiotensin-aldosterone system by angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers has led to experimental and clinical efforts using aldosterone inhibition. Recently, these efforts have provided us with an expanded understanding of a new pathogenic role for aldosterone in diabetic vascular complications. This article focuses on the role of aldosterone in the pathogenesis of diabetic kidney disease and recent important clinical data supporting the inhibition of aldosterone in treating diabetic kidney disease.

Effect of RAS inhibition on TGF-β, renal function and structure in experimentally induced diabetic hypertensive nephropathy rats

OBJECTIVE

Transforming growth factor-β (TGF-β) implicated in the pathogenesis of diabetic nephropathy. Hence, developing agents that antagonize fibrogenic signals is a critical issue facing researchers.

MATERIAL AND METHODS

Fifty rats were allocated to five groups: 1=control rats, 2=diabetic hypertensive rats 3=diabetic hypertensive rats treated with spironolactone, 4=diabetic hypertensive rats treated with moexpril, 5=diabetic hypertensive rats treated with both spironolactone and moexpril. Measurement of TGF-β, aldosterone, creatinine and ACE. Degree of fibrosis was calculated.

RESULTS

Serum creatinine, mean arterial blood pressure (MAP), aldosterone, ACE, TGF-β and renal fibrosis increased significantly in untreated diabetic hypertensive rats compared with control rats. Administration of spironolactone, moexpril, or both decreased these changes.

CONCLUSIONS

Addition of the spironolactone to moexpril was more effective in reducing fibrosis and improvement of renal function than monotherapy with either drug, possibly due to a dual inhibitory effect on the RAS, and thus suppression of TGF-β.

Activation of local aldosterone system within podocytes is involved in apoptosis under diabetic conditions

Previous studies have shown that mineralocorticoid receptor (MCR) blocker reduces proteinuria in diabetic nephropathy (DN), but the role of aldosterone in podocyte injury has never been explored in DN. This study was undertaken to elucidate whether a local aldosterone system existed in podocytes and to examine its role in podocyte apoptosis under diabetic conditions. In vitro, immortalized podocytes were exposed to 5.6 mM glucose (NG), NG + 24.4 mM mannitol, and 30 mM glucose (HG) with or without 10(-7) M spironolactone (SPR). In vivo, 32 Sprague-Dawley rats were injected with diluent (C, n = 16) or streptozotocin intraperitoneally [diabetes mellitus (DM), n = 16], and 8 rats from each group were treated with SPR for 3 mo. Aldosterone synthase (CYP11B2) and MCR mRNA and protein expression were determined by real-time PCR and Western blot, respectively, and aldosterone levels by radioimmunoassay. Western blot for apoptosis-related molecules, Hoechst 33342 staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to determine apoptosis. CYP11B2 and MCR expression were significantly higher in HG-stimulated podocytes and DM glomeruli compared with NG cells and C glomeruli, respectively, along with increased aldosterone levels. Western blot analysis revealed that cleaved caspase-3 and Bax expression was significantly increased, whereas Bcl-2 expression was significantly decreased in HG-stimulated podocytes and in DM glomeruli. Apoptosis determined by Hoechst 33342 staining and TUNEL assay were also significantly increased in podocytes under diabetic conditions. These changes in the expression of apoptosis-related proteins and the increase in apoptotic cells were inhibited by SPR treatment. These findings suggest that a local aldosterone system is activated and is involved in podocyte apoptosis under diabetic conditions.

Aldosterone antagonism or synthase inhibition reduces end-organ damage induced by treatment with angiotensin and high salt

In the setting of high salt intake, aldosterone stimulates fibrosis in the heart, great vessels, and kidney of rats. We used uninephrectomized rats treated with angiotensin II and placed on a high salt diet to exaggerate renal fibrosis. We then tested whether mineralocorticoid receptor blockade by spironolactone or aldosterone synthase inhibition by FAD286 have similar effects on end-organ damage and gene expression. Individually, both drugs prevented the hypertensive response to uninephrectomy and high salt intake but not when angiotensin II was administered. Following 4 weeks of treatment with FAD286, plasma aldosterone was reduced, whereas spironolactone increased aldosterone at 8 weeks of treatment. Angiotensin II and high salt treatment caused albuminuria, azotemia, renovascular hypertrophy, glomerular injury, increased plasminogen activator inhibitor-1 (PAI-1), and osteopontin mRNA expression, as well as tubulointerstitial fibrosis in the kidney. Both drugs prevented these renal effects and attenuated cardiac and aortic medial hypertrophy while reducing osteopontin and transforming growth factor-beta mRNA expression in the aorta. The two drugs also reduced cardiac interstitial fibrosis but had no effect on that of the perivascular region. Although spironolactone enhanced angiotensin II and salt-stimulated PAI-1 mRNA expression in aorta and heart, spironolactone and FAD286 prevented renal PAI-1 mRNA protein expression. Our study shows that mineralocorticoid receptor antagonism and aldosterone synthase inhibition similarly decrease hypertrophy and interstitial fibrosis of the kidney and heart caused by angiotensin II and high salt.

Mineralocorticoid receptor antagonism attenuates glomerular filtration barrier remodeling in the transgenic Ren2 rat

Recent evidence suggests that mineralocorticoid receptor (MR) antagonism has beneficial effects on tissue oxidative stress and insulin metabolic signaling as well as reducing proteinuria. However, the mechanisms by which MR antagonism corrects both renin-angiotensin-aldosterone system (RAAS) impairments in renal insulin metabolic signaling and filtration barrier/podocyte injury remain unknown. To explore this potential beneficial interactive effect of MR antagonism we used young transgenic (mRen2)27 (Ren2) rats with increased tissue RAAS activity and elevated serum aldosterone levels. Ren2 and age-matched Sprague-Dawley (SD) control rats (age 6-7 wk) were implanted with a low dose of the MR antagonist spironolactone (0.24 mg/day) or vehicle, both delivered over 21 days. Albuminuria, podocyte-specific proteins (synaptopodin, nephrin, and podocin), and ultrastructural analysis of the glomerular filtration barrier were measured in relation to RAAS activation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, reactive oxygen species (ROS), and the redox-sensitive Rho kinase (ROK). Insulin metabolic signaling was determined via measurement of insulin receptor substrate-1 (IRS-1) phosphorylation, IRS-1 ubiquitin/proteasomal degradation, and phosphorylation of Akt. Ren2 rats exhibited albuminuria, loss of podocyte-specific proteins, and podocyte foot process effacement contemporaneous with reduced renal IRS-1 and protein kinase B/Akt phosphorylation compared with SD control rats (each P < 0.05). Ren2 kidneys also manifested increased NADPH oxidase/ROS/ROK in conjunction with enhanced renal tissue levels of angiotensin II (ANG II), ANG-(1-12), and angiotensin type 1 receptor. Low-dose spironolactone treatment reduced albuminuria and tissue RAAS activity and improved podocyte structural and protein integrity with improvements in IRS-1/Akt phosphorylation. Thus, in this model of RAAS activation, MR antagonism attenuates glomerular/podocyte remodeling and albuminuria, in part through reductions in redox-mediated impairment of insulin metabolic signaling.

Spironolactone ameliorates transplant vasculopathy in renal chronic transplant dysfunction in rats

Chronic transplant dysfunction (CTD) is the leading cause of long-term renal allograft loss and is characterized by specific histological lesions including transplant vasculopathy, interstitial fibrosis, and focal glomerulosclerosis. Increasing evidence indicates that aldosterone is a direct mediator of renal damage via the mineralocorticoid receptor (MR). The MR antagonist spironolactone is renoprotective in native chronic kidney disease, but its effects on CTD are unknown. We studied the effects of spironolactone treatment on CTD development in the Dark Agouti-to-Wistar-Furth renal allograft transplant model, by treatment with 20 mg/kg spironolactone or vehicle daily by oral gavage from 2 days before transplantation (donors and recipients) throughout the experiment (12 wk, recipients). Dark Agouti-to-Dark Agouti isografts served as negative controls. Spironolactone significantly ameliorated the development of transplant vasculopathy in allografts by reducing the number of affected intrarenal arteries. In addition, spironolactone treatment showed a trend toward reduced proteinuria and focal glomerulosclerosis, and significantly reduced glomerular macrophage influx. However, spironolactone treatment did not affect interstitial fibrosis, interstitial macrophage influx, creatinine clearance, and systolic blood pressure. We conclude that spironolactone selectively ameliorates transplant vasculopathy and glomerular lesions in renal CTD in rats. These results suggest that spironolactone may have renoprotective potential as an adjunct treatment in renal transplantation to ameliorate CTD.

PAI-1 and kidney fibrosis

Substantial evidence demonstrates a link of increased plasminogen activator inhibitor-1 (PAI-1) and glomerulosclerosis and kidney fibrosis, providing a novel therapeutic option for prevention and treatment of chronic kidney diseases. Several mechanisms contributing to increased PAI-1 will be addressed, including classic key profibrotic factors such as the renin-angiotensin-system (RAS) and transforming growth factor-beta (TGF-b???and novel molecules identified by proteomic analysis, such as thymosin- b4. The fibrotic sequelae caused by increased PAI-1 in kidney depend not only on its classic inhibition of tissue-type and urokinase-type plasminogen activators (tPA and uPA), but also its influence on cell migration.

Aldosterone-induced TGF-beta1 expression is regulated by mitogen-activated protein kinases and activator protein-1 in mesangial cells

Aldosterone has been shown to stimulate renal TGF-beta(1) expression. However, the mechanisms for aldosterone-induced TGF-beta(1) expression have not been clearly determined in mesangial cells. We examined the role of extracellular-signal regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK) and activator protein-1 (AP-1) in the aldosterone-induced TGF-beta(1) expression in rat mesangial cells. TGF-beta(1) protein in the conditioned medium released from rat mesangial cells was measured by sandwich ELISA, TGF-beta(1) mRNA expression was analyzed by Northern blotting, AP-1 DNA binding activity was measured by EMSA and the ERK1/2, JNK activity was analyzed by western blotting. Aldosterone significantly stimulated TGF-beta(1) protein production and TGF-beta(1) mRNA expression in mesangial cells in a dose-dependent manner. Aldosterone significantly increased AP-1 DNA binding activity in mesangial cells. Pre-treatment of cells with AP-1 inhibitor, curcumin, blocked aldosterone-induced AP-1 DNA binding activity as well as aldosterone-induced TGF-beta(1) production. Aldosterone increased phosphorylation of ERK1/2 and JNK in mesangial cells. Pre-treatment of cells with ERK1/2 inhibitor, PD98059, or JNK inhibitor, SP600125 significantly inhibited aldosterone-induced ERK1/2 and JNK activity and subsequently TGF-beta(1) production, respectively. We conclude that aldosterone-induced TGF-beta(1) expression in mesangial cells is regulated by the ERK1/2, JNK and AP-1 intracellular signaling pathways.

Aldosterone activates NF-kappaB in the collecting duct

Besides its classical effects on salt homeostasis in renal epithelial cells, aldosterone promotes inflammation and fibrosis and modulates cell proliferation. The proinflammatory transcription factor NF-kappaB has been implicated in cell proliferation, apoptosis, and regulation of transepithelial sodium transport. The effect of aldosterone on the NF-kappaB pathway in principal cells of the cortical collecting duct, a major physiologic target of aldosterone, is unknown. Here, in both cultured cells and freshly isolated rat cortical collecting duct, aldosterone activated the canonical NF-kappaB signaling pathway, leading to increased expression of several NF-kappaB-targeted genes (IkappaBalpha, plasminogen activator inhibitor 1, monocyte chemoattractant protein 1, IL-1beta, and IL-6). Small interfering RNA-mediated knockdown of the serum and glucocorticoid-inducible kinase SGK1, a gene induced early in the response to aldosterone, but not pharmacologic inhibition of extracellular signal-regulated kinase and p38 kinase, attenuated aldosterone-induced NF-kappaB activation. Pharmacologic antagonism or knockdown of the mineralocorticoid receptor prevented aldosterone-induced NF-kappaB activity. In addition, activation of the glucocorticoid receptor inhibited the transactivation of NF-kappaB by aldosterone. In agreement with these in vitro findings, spironolactone prevented NF-kappaB-induced transcriptional activation observed in cortical collecting ducts of salt-restricted rats. In summary, aldosterone activates the canonical NF-kappaB pathway in principal cells of the cortical collecting duct by activating the mineralocorticoid receptor and by inducing SGK1.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Effect of eplerenone, enalapril and their combination treatment on diabetic nephropathy in type II diabetic rats

BACKGROUND

Recent data suggest that aldosterone antagonists have beneficial effects on diabetic nephropathy. In this study, we investigated the dose-dependent effect of eplerenone and a combined treatment with eplerenone and enalapril compared with each drug alone on renal function in type II diabetic rats. To further explore the molecular mechanism of action of combination therapy, we also performed in vitro study.

METHODS

The animals were divided into six groups as follows: normal control Long-Evans Tokushima Otsuka (LETO) rats, Otsuka Long-Evans Tokushima Fatty (OLETF) rats, OLETF rats treated with low dose of eplerenone (50 mg/kg/day), OLETF rats treated with high dose of eplerenone (200 mg/kg/day), OLETF rats treated with enalapril (10 mg/kg/day) and OLETF rats treated with a combination of both drugs (eplerenone 200 mg/kg/day and enalapril 10 mg/kg/day) for 6 months.

RESULTS

Treatment of OLETF rats had no significant effect on body weight, kidney weight and blood glucose levels. However, urinary albumin excretion, glomerular filtration rate and glomerulosclerosis were significantly improved in the enalapril group and improvement was observed in a dose-dependent manner in the eplerenone groups; the most dramatic decreases were observed in the combination group. In accordance with these findings, renal expressions of TGF-beta1, type IV collagen and PAI-1 were also markedly decreased in the treatment groups, with the combined treatment providing the most significant level of improvement. In cultured mesangial cells, combined treatment resulted in an additive decrease in TGF-beta1, PAI-1 and collagen gene expressions and protein production induced by high glucose and aldosterone stimulation.

CONCLUSIONS

Aldosterone receptor antagonism provided additional benefits beyond blockade of the renin-angiotensin system in type II diabetic nephropathy.

Local renal aldosterone production induces inflammation and matrix formation in kidneys of diabetic rats

Recently, we reported the presence of a local renal aldosterone production. In the present study, we tested the hypothesis that local aldosterone production in the kidney contributes to renal inflammation, matrix formation and albuminuria associated with diabetes. We evaluated changes in renal aldosterone content (RAC), aldosterone synthase expression, nuclear factor kappaB (NFkappaB), tumour necrosis factor alpha (TNFalpha), interleukin-6 (IL-6), transforming growth factor beta (TGFbeta), glomerular fibronectin, collagen type IV and urinary albumin extraction (UAE) in response to the aldosterone synthase inhibitor FAD286. Studies were conducted in adrenalectomized, normoglycaemic (control) or diabetic rats for 14 weeks. The FAD286 was administered during the last 10 weeks of the study. Plasma aldosterone levels were not detectable in any of the study groups. Compared with control rats, diabetic rats had higher levels of RAC by 488% (P < 0.01), NFkappaB by 293% (P < 0.01), TNFalpha by 356% (P < 0.01), IL-6 by 378% (P < 0.01), TGFbeta by 337% (P < 0.01) and UAE by 1122% (P < 0.01), and increased glomerular fibronectin and collagen type IV immunostaining. In diabetic rats, FAD286 reduced RAC (P < 0.01), UAE (P < 0.05), NFkappaB mRNA, TNFalpha mRNA, IL-6 mRNA and TGFbeta mRNA by 51, 41, 41 and 52% and also their proteins and decreased glomerular fibronectin and collagen type IV immunostaining. In conclusion, diabetes increases local aldosterone production in the kidney, which contributes to development of renal inflammation, matrix formation and albuminuria. Inhibition of aldosterone production in the kidney could be helpful in management of diabetic nephropathy.

Spironolactone exhibits direct renoprotective effects and inhibits renal renin-angiotensin-aldosterone system in diabetic rats

Aldosterone itself has been reported to participate in mediating renal injury, and it was confirmed that the aldosterone synthase CYP11B2 gene, protein, and aldosterone production are locally present in the kidney. To test the hypothesis that a mineralocorticoid receptor antagonist might ameliorate diabetic nephropathy and the inhibition of renal CYP11B2 expression might be associated with these renoprotective effects, spironolactone (50 mg/kg/day) was administered by gavage to uninephrectomized diabetic rats for 3 weeks. Streptozotocin (55 mg/kg, i.v.) significantly increased urinary protein excretion and collagen deposition in glomerular and tubulointerstitial areas in the kidney, which were attenuated by spironolactone treatment. RT-PCR and Western blot analysis revealed that the expression of mRNA for collagen I/IV, transforming growth factor-beta, NADPH oxidase and mineralocorticoid receptor and the mineralocorticoid receptor protein in the kidney was enhanced in the uninephrectomized diabetic rat kidney and that the overexpression of these molecules was suppressed by spironolactone. Renal angiotensin converting enzyme was activated and overexpressed in diabetic rats, and spironolactone inhibited these changes. We demonstrated that spironolactone prevented the streptozotocin-induced increase in the renal CYP11B2 mRNA content. Controlling blood glucose level with insulin also attenuated the renal expression of mRNA for CYP11B2. On the other hand, the treatment of spironolactone in the present study did not affect blood glucose level or blood pressure in uninephrectomized streptozotocin-induced diabetic rats. These results suggest that spironolactone exerted renoprotective effects in uninephrectomized streptozotocin-induced diabetic rats and inhibited local renin-angiotensin-aldosterone system, such as the ACE expression and the hyperglycemia-induced overexpression of CYP11B2, in the kidney.

Mineralocorticoid receptor blockade ameliorates peritoneal fibrosis in new rat peritonitis model

Peritoneal fibrosis (PF) is an important complication of long-term peritoneal dialysis. Although mineralocorticoid and mineralocorticoid receptor (MR) have attracted increasing attention in the field of vascular injury, including the heart, kidney, and vessels, little is known about the role of mineralocorticoid in PF. This work was designed to explore the effects of MR blockade on PF. We developed a new model of PF in rats based on mechanical scraping of the peritoneum. This model is characterized by acute-phase inflammation (neutrophil and macrophage infiltration on days 0–3) and late-phase PF (α-smooth muscle actin-positive fibroblast infiltration, type III collagen accumulation, and neoangiogenesis on days 7–14). Peritoneal thickening peaked on day 14. MR was expressed in rat peritoneum and a rat fibroblast cell line. Expression of its effector kinase [serum- and glucocorticoid-induced kinase-1 (Sgk1)], transforming growth factor-β (TGF-β), plasminogen activator inhibitor-1 (PAI-1), and CD31-positive vessels increased during the course of PF. Rats were treated with spironolactone, angiotensin receptor blockade (ARB), or angiotensin-converting enzyme inhibitor (ACEI)-ARB-spironolactone starting at 6 h after peritoneal scraping. All parameters, including peritoneal thickening, number of macrophages and CD31-positive vessels, and expression of monocyte chemoattractant protein-1, TGF-β, PAI-1, and Sgk1, were significantly suppressed by spironolactone (10 mg·kg−1·day−1). The effects of spironolactone (10 and 20 mg·kg−1·day−1) were very similar to those of triple blockade. ARB, but not ACEI, significantly reduced peritoneal thickening. Furthermore, peritoneal function assessed by peritoneal equilibration test was significantly improved by spironolactone. Our results suggest that MR is a potential target to prevent inflammation-induced PF in patients on peritoneal dialysis.

Aldosterone and TGF-beta1 synergistically increase PAI-1 and decrease matrix degradation in rat renal mesangial and fibroblast cells

Aldosterone is thought to modulate renal fibrosis, in part, through increasing plasminogen activator inhibitor type 1 (PAI-1), a major inhibitor of ECM degradation. The present study investigated aldosterone effects on PAI-1 and transforming growth factor (TGF)-beta(1) and asked whether PAI-1 effects were TGF-beta mediated and whether aldosterone and TGF-beta(1) acted synergistically to increase PAI-1 and decrease ECM degradation. Rat mesangial cells (MCs) and fibroblast cells [normal rat kidney (NRK)-49F] were used. (3)H-labeled ECM was produced by MCs. The effect of aldosterone and TGF-beta on ECM degradation by newly plated MCs or NRK-49F was measured by the release of (3)H into medium. Aldosterone markedly increased PAI-1 mRNA and protein in both cell types, increases completely blocked by spironolactone and partially blocked by TGF-beta neutralizing antibody. Adding both aldosterone and TGF-beta(1) produced PAI-1 mRNA and protein increases higher than the sum of increases seen with either compound alone. Aldosterone or TGF-beta(1) alone inhibited matrix degradation by 39 and 49% in MCs and 21 and 23% in NRK-49F, respectively. When both compounds were added, matrix degradation was further decreased by 93% in MCs and 61% in NRK-49F. The results indicate that aldosterone-induced PAI-1 increases are partially mediated by TGF-beta(1) and lead to decreased ECM degradation. While aldosterone alone induced TGF-beta(1) weakly, aldosterone and TGF-beta(1) added together produced dramatic synergistic effects on PAI-1 production and subsequent ECM accumulation. Thus the elevated aldosterone induced by renin-angiotensin-aldosterone system activation may amplify renin-angiotensin-aldosterone system profibrotic actions.