Enhanced aldosterone signaling in the early nephropathy of rats with metabolic syndrome: possible contribution of fat-derived factors

Metabolic syndrome is an important risk factor for proteinuria and chronic kidney disease independent of diabetes and hypertension; however, the underlying mechanisms have not been elucidated. Aldosterone is implicated in target organ injury of obesity-related disorders. This study investigated the role of aldosterone in the early nephropathy of 17-wk-old SHR/NDmcr-cp, a rat model of metabolic syndrome. Proteinuria was prominent in SHR/NDmcr-cp compared with nonobese SHR, which was accompanied by podocyte injury as evidenced by foot process effacement, induction of desmin and attenuation of nephrin. Serum aldosterone level, renal and glomerular expressions of aldosterone effector kinase Sgk1, and oxidative stress markers all were elevated in SHR/NDmcr-cp. Mineralocorticoid receptors were expressed in glomerular podocytes. Eplerenone, a selective aldosterone blocker, effectively improved podocyte damage, proteinuria, Sgk1, and oxidant stress. An antioxidant tempol also alleviated podocyte impairment and proteinuria, along with inhibition of Sgk1. As for the mechanisms of aldosterone excess, visceral adipocytes that were isolated from SHR/NDmcr-cp secreted substances that stimulate aldosterone production in adrenocortical cells. The aldosterone-releasing activity of adipocytes was not inhibited by candesartan. Adipocytes from nonobese SHR did not show such activity. In conclusion, SHR/NDmcr-cp exhibit enhanced aldosterone signaling, podocyte injury, and proteinuria, which are ameliorated by eplerenone or tempol. The data also suggest that adipocyte-derived factors other than angiotensin II might contribute to the aldosterone excess of this model.     

Activation of the aldosterone/mineralocorticoid receptor system in chronic kidney disease and metabolic syndrome

Recent clinical and experimental studies have shown that aldosterone is a potent inducer of proteinuria and that mineralocorticoid receptor (MR) antagonists confer efficient antiproteinuric effects. We identified glomerular epithelial cells (podocytes) as novel targets of aldosterone; activation of MR injures podocytes possibly via oxidative stress, resulting in disruption of glomerular filtration barrier, proteinuria, and progression of chronic kidney disease. We also demonstrated that SHR/cp, a rat model of metabolic syndrome, was susceptible to podocyte injury and proteinuria. Aldosterone excess caused by adipocyte-derived aldosterone-releasing factors was suggested to underlie the nephropathy. High salt intake augmented MR activation in the kidney and exacerbated the nephropathy. Furthermore, we identified an alternative pathway of MR activation by small GTPase Rac1. RhoGDIα knockout mice, a model with Rac1 activation in the kidney, showed albuminuria, podocyte injury, and glomerulosclerosis. Renal injury in the knockout mice was accompanied by enhanced MR signaling in the kidney despite normoaldosteronemia, and was ameliorated by an MR antagonist, eplerenone. Moreover, Rac-specific inhibitor significantly reduced the nephropathy, concomitantly with repression of MR activation. In vitro transfection studies provided direct evidence of Rac1-mediated MR activation. In conclusion, our findings suggest that MR activation plays a pivotal role in the pathogenesis of chronic kidney disease in metabolic syndrome, and that MR may be activated both aldosterone dependently (via aldosterone-releasing factors) and independently (via Rac1). MR antagonists are promising antiproteinuric drugs in metabolic syndrome, although long-term effects on renal outcomes, mortality, and safety need to be established.     

依普利酮对醛固酮灌注大鼠肾小球细胞凋亡的影响

目的观察醛固酮（ALD）灌注对大鼠肾小球细胞凋亡的影响和ALD特异性拮抗剂依普利酮（Eplerenone）的干预作用。方法18只雄性SD大鼠随机分为空白对照组（A组），ALD灌注组（B组）和Eplerenone治疗组（C组），分别皮下埋置渗透性微泵（osmotic minipumps），B、C组均以1．5μg h的浓度持续灌注ALD，同时C组用Eplerenone（100mg·kg^-1·d^-1）灌胃，A、B组用生理盐水代替。隔周测量大鼠尾动脉收缩压，收集24h尿液测定尿蛋白排泄率（UAER），于第28天心脏取血检测血肌酐（SCr），取肾脏，光镜观察其病理改变，TUNEL法检测细胞凋亡。结果B组大鼠血压和UAER从第14天起均较同期A组显著增高（P〈0．05），C组血压和UAER较同期B组显著降低（P〈0.05）。PAS染色发现B组大鼠肾小球系膜外基质增多，轻度系膜细胞增殖；TUNEL法检测发现B组大鼠肾小球细胞凋亡明显增加，C组凋亡率较B组显著减少[（16．36±1．84）％vs（49．55±5．67）％，P〈0.05]。结论ALD灌注大鼠可导致肾小球病理损伤和细胞凋亡，Eplerenone可减轻ALD诱导的肾小球损伤。     

Angiotensin II- and salt-induced kidney injury through Rac1-mediated mineralocorticoid receptor activation

Experiments with hyperaldosteronemic animals suggest that, despite lowering plasma aldosterone, salt worsens renal injury by paradoxical activation of the mineralocorticoid receptor (MR). Salt and aldosterone synergistically contribute to renal impairment through Rac1-mediated activation of the MR, but whether angiotensin II also promotes renal injury through this mechanism is unknown. Here, we placed angiotensin II-overproducing double transgenic Tsukuba hypertensive mice on a low- or high-salt intake for 6 weeks and treated some animals with adrenalectomy, the MR antagonist eplerenone, the Rac inhibitor EHT1864, or hydralazine. High-salt intake, but not low-salt intake, led to hypertension and prominent kidney injury. Adrenalectomy prevented angiotensin II/salt-induced nephropathy in mice receiving high-salt intake, which was recapitulated by aldosterone supplementation, suggesting the involvement of aldosterone/MR signaling. Plasma aldosterone levels, however, were lower in high- than low-salt conditions. Instead, angiotensin II/salt-evoked MR activation associated with Rac1 activation and was not dependent on plasma aldosterone level. Both EHT1864 and eplerenone repressed the augmented MR signaling and mitigated kidney injury with partial but significant reduction in BP with high-salt intake. Hydralazine similarly reduced BP, but it neither suppressed the Rac1-MR pathway nor ameliorated the nephropathy. Taken together, these results show that angiotensin II and salt accelerate kidney injury through Rac1-mediated MR activation. Rac inhibition may be a promising strategy for the treatment of CKD.     

The Mineralocorticoid Receptor in Salt-Sensitive Hypertension and Renal Injury

Hypertension and its comorbidities pose a major public health problem associated with disease-associated factors related to a modern lifestyle, such high salt intake or obesity. Accumulating evidence has demonstrated that aldosterone and its receptor, the mineralocorticoid receptor (MR), have crucial roles in the development of salt-sensitive hypertension and coexisting cardiovascular and renal injuries. Accordingly, clinical trials have repetitively shown the promising effects of MR blockers in these diseases. We and other researchers have identified novel mechanisms of MR activation involved in salt-sensitive hypertension and renal injury, including the obesity-derived overproduction of aldosterone and ligand-independent signaling. Moreover, recent advances in the analysis of cell-specific and context-dependent mechanisms of MR activation in various tissues—including a classic target of aldosterone, aldosterone-sensitive distal nephrons—are now providing new insights. In this review, we summarize recent updates to our understanding of aldosterone-MR signaling, focusing on its role in salt-sensitive hypertension and renal injury.     

In a type 2 diabetic nephropathy rat model, the improvement of obesity by a low calorie diet reduces oxidative/carbonyl stress and prevents diabetic nephropathy

Background. The present study has been undertaken to unravelthe critical factors involved in the progression of diabeticnephropathy (DN). Methods. A unique type 2 diabetic rat model with a wide rangeof metabolic derangements and hypertension has been utilized,the spontaneously hypertensive/NIH-corpulent rat SHR/NDmcr-cp(cp/cp).It develops histologically evident glomerular injury and tubulointerstitialdamage, including mesangial activation, podocyte injury, andinflammatory cell infiltration in the tubulointerstitium. Results. A low calorie diet for 22 weeks significantly improvesobesity, proteinuria and renal morphological alterations. Thecorrection of renal injury is independent of blood pressurecontrol. Obesity correction, although partial, normalizes therenal content of pentosidine taken as a marker of oxidativestress and advanced glycation end products (AGEs). This occursdespite the fact that, in this model, improvement of glucosecontrol and hyperlipidaemia is limited. Proteinuria and bodyweight are highly correlated with renal pentosidine content,while proteinuria and body weight are also correlated with eachother. Diabetic renal injury is thus inhibited by a low caloriediet with an attendant reduction of oxidative stress and AGEformation, despite sustained hypertension. Conclusion. The present findings suggest a direct role of obesityin the generation of a localized oxidative stress and AGE formation,directly responsible for DN.     

Aldosterone antagonism ameliorates proteinuria and nephrosclerosis independent of glomerular dynamics in L-NAME/SHR model

BACKGROUND: The renin-angiotensin-aldosterone system participates importantly in the progression of hypertensive renal disease. Angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists have been demonstrated to afford renoprotection in L-NAME-exacerbated nephrosclerosis in SHR rats. This study was designed to examine the effects of the aldosterone antagonist eplerenone on systemic and renal hemodynamics, glomerular dynamics, renal function and histopathology in L-NAME/SHR, and determine whether aldosterone antagonism would enhance the effectiveness of ACE inhibition. METHODS: Six groups of 20-week-old SHR were studied using renal micropuncture and histopathological techniques after 3 weeks of treatment: SHR control (tapwater, n = 10); SHR + eplerenone (101 +/- 8.3 mg/kg/day, n = 10); SHR + L-NAME (5.0 +/- 0.12 mg/kg/day, n = 9); SHR + L-NAME + eplerenone (n = 8); SHR + L-NAME + lisinopril (3 mg/kg/day, n = 9), and SHR + L-NAME + eplerenone + lisinopril (n = 9). RESULTS:L-NAME-treated SHR developed massive proteinuria, severe hypertensive nephrosclerosis, and tubulointerstitial damage. Eplerenone significantly reduced proteinuria (127.4 +/- 26.5 vs. 51.9 +/- 16.7 mg/24 h, p < 0.01), improved glomerular and arteriolar injuries (65 +/- 9 vs. 29 +/- 9 score/100 glomeruli, p < 0.01; 116 +/- 18 vs. 41 +/- 13 score/100 arterioles, p < 0.01, respectively), and decreased tubulointerstitial damage index (1.43 +/- 0.07 vs. 0.39 +/- 0.07, p < 0.01) without altering mean arterial pressure or glomerular dynamics. Combined therapy of eplerenone with lisinopril produced no further benefits than lisinopril alone. CONCLUSION: The aldosterone antagonist eplerenone significantly ameliorated proteinuria and nephrosclerosis in the L-NAME/SHR model, independent of hemodynamic effects.     

细胞外信号调节蛋白激酶介导醛固酮诱导的肾小球系膜细胞增殖

Objective To determine the role of extracellular signal-regulated kinases (ERK1/2) in aldosterone-induced rat mesangial cells (RMCs) proliferation. Methods RMCs were obtained from intact glomeruli of 4- to 6-week-old Sprague-Dawley rats and characterized according to published methods. RMCs between passages 5 and passages 10 were used. Protein levels of mineralocorticoid receptor(MR) in RMCs were analyzed by Western blotting. The cells were divided into the following groups: control group, PD98059(10 ?滋mol/L) group, eplerenone (1 ?滋mol/L) group, aldosterone (100 nmol/L) group, aldosterone (100 nmol/L) ＋PD98059 (10 ?滋mol/L) group, aldosterone(100 nmol/L)＋eplerenone (1 ?滋mol/L) group. ERK1/2 activity was measured by Western blotting. Cell proliferation of RMCs was evaluated by [3H]-thymidine uptake measurements. Results MR protein expression in RMCs was confirmed by Western blotting. Aldosterone activated ERK1/2, and the maximal ERK1/2 activation induced by aldosterone was at a concentration of 100 nmol/L. Aldosterone (100 nmol/L)-induced activation of ERK1/2 peaked at 10 minutes (P<0.05). Pretreatment with a selective MR antagonist eplerenone (1 ?滋mol/L) significantly attenuated aldosterone-induced ERK1/2 phosphorylation. Aldosterone (100 nmol/L) treatment for 30 hours increased [3H]-thymidine incorporation of RMCs (135%±8% of controls, P<0.05). Cellular proliferation induced by aldosterone could be prevented by pretreatment with eplerenone or an ERK (MEK) inhibitor PD988059. Conclusion Aldosterone induces RMCs proliferation through MR and ERK1/2 activation, which may contribute to the pathogenesis of glomerular mesangial injury.     

Aldosterone in the development and progression of renal injury

BACKGROUND: The renin-angiotensin-aldosterone system (RAAS) contributes to hypertension and nephropathy. Until recently, aldosterone either has not been considered or has been considered a relatively minor component of the process-a contribution that could be negated with angiotensin-converting enzyme (ACE) inhibition or angiotensin receptor blockade. METHODS: A Medline search was performed to identify relevant literature describing the role of aldosterone in the pathogenesis of renal dysfunction. RESULTS: Growing evidence from experimental and clinical studies indicates that increased aldosterone is an independent contributor to small- and medium-sized arterial injury and nephropathy. Excess mineralocorticoid receptor stimulation of local and systemic origin promotes target organ dysfunction, vascular injury, and fibrosis, independent of the effects of other elements of the RAAS. Blockade of the RAAS with ACE inhibition or angiotensin receptor blockade often does not confer optimal protection from the effects of mineralocorticoids on small- and medium-sized blood vessels. Recent preliminary data from clinical studies indicate that aldosterone blockade protects the kidneys, sharply decreases proteinuria, beyond the activities of ACE inhibition or angiotensin receptor blockade and independent of beneficial blood pressure effects, and can protect patients from vascular injury associated with diabetes mellitus and hypertension. CONCLUSION: Aldosterone blockade with the selective aldosterone blocker eplerenone, in combination with other RAAS inhibitors, is probably renoprotective and should be considered as a component of the treatment regimens of diabetic and hypertensive patients at risk for renal or cardiovascular disease expression. A high priority should be placed on developing the randomized, controlled trials required to establish that role.     

Mineralocorticoid receptor activation and blockade: an emerging paradigm in chronic kidney disease

Slowing the progression of chronic kidney diseases (CKDs) requires new and effective treatment approaches. Aldosterone classically acts on the distal nephron: it facilitates sodium reabsorption, potassium secretion, and participates in blood pressure control. Recently, new targets of aldosterone have been described including the heart and the vasculature, and other kidney cells such as mesangial cells, podocytes, and renal fibroblasts. The pathophysiological implications of increased mineralocorticoid receptor (MR) expression and activation (either dependent on aldosterone or direct ligand-independent activation) and its blockade have been illustrated with ex vivo in cell cultures and in vivo in experimental animal models of CKD, including diabetic and hypertensive nephropathies, and glomerulopathies. The beneficial effects of the MR antagonists are independent of the hypertensive effect of aldosterone, indicating that blocking the activation of the MR may have unique clinical importance. Several studies have reported efficacy and safety studies with spironolactone or eplerenone in patients with kidney diseases. In this review, we discuss the recent results reported in experimental and clinical research in this field, and emphasize the direct activation of the MR that can occur in pathological states associated with CKD, even in the absence of increased circulating levels of aldosterone.     

Aldosterone stimulates reactive oxygen species production through activation of NADPH oxidase in rat mesangial cells

It has recently been shown that glomerular mesangial injury is associated with increases in renal cortical reactive oxygen species (ROS) levels in rats treated chronically with aldosterone and salt. This study was conducted to determine the mechanisms responsible for aldosterone-induced ROS production in cultured rat mesangial cells (RMC). Oxidative fluorescent dihydroethidium was used to evaluate intracellular production of superoxide anion (O(2)(-)) in intact cells. The lucigenin-derived chemiluminescence assay was used to determine NADPH oxidase activity. The staining of dihydroethidium was increased in a dose-dependent manner by aldosterone (1 to 100 nmol/L) with a peak at 3 h in RMC. Aldosterone (100 nmol/L for 3 h) also significantly increased NADPH oxidase activity from 232 +/- 18 to 346 +/- 30 cpm/5 x 10(4) cells. Immunoblotting data showed that aldosterone (100 nmol/L for 3 h) increased p47phox and p67phox protein levels in the membrane fraction by approximately 2.1- and 2.3-fold, respectively. On the other hand, mRNA expression of NADPH oxidase membrane components, p22phox, Nox-1, and Nox-4, were not altered by aldosterone (for 3 to 12 h) in RMC. Pre-incubation with the selective mineralocorticoid receptor (MR) antagonist, eplerenone (10 micromol/L), significantly attenuated aldosterone-induced O(2)(-) production, NADPH oxidase activation and membranous translocation of p47phox and p67phox. These results suggest that aldosterone-induced ROS generation is associated with NAPDH oxidase activation through MR-mediated membranous translocation of p47phox and p67phox in RMC. These cellular actions of aldosterone may play a role in the pathogenesis of glomerular mesangial injury.     

Proteinuria is preceded by decreased nitric oxide synthesis and prevented by a NO donor in cholesterol-fed rats

BACKGROUND: Hypercholesterolemia decreases nitric oxide (NO) availability in the circulation and induces podocyte activation and renal injury in rats. It is unknown whether hypercholesterolemia decreases renal NO availability. To dissociate the injury-independent effect of hypercholesterolemia on renal NO availability from secondary effects of proteinuria, increasing concentrations of cholesterol were administered. To determine whether podocyte activation and renal injury were associated with NO deficiency, molsidomine, an exogenous NO donor, was administered to hypercholesterolemic rats. METHODS: Female rats were fed 0, 0.5, 1, or 2% cholesterol for 24 weeks. Rats fed 2% cholesterol were also studied for two weeks. In addition rats fed 0 or 1% cholesterol received 120 mg molsidomine/L drinking water. Renal NO availability was determined by measuring renal NO synthesis and superoxide activity. Podocyte activation was monitored by desmin staining. RESULTS: Hypercholesterolemia dose-dependently increased proteinuria. In the absence of proteinuria, hypercholesterolemia decreased renal NO synthesis (4.2 +/- 0.5 in 0.5% cholesterol vs. 6.8 +/- 0.6 pmol/min/mg protein in controls; P < 0.05). With the exception of neuronal nitric oxide synthase (nNOS), renal NOS protein mass remained unaffected. Renal superoxide activity was dose-dependently increased, thus further lowering renal NO availability. Podocyte injury was dose-dependently increased even in the absence of proteinuria (score, 40 +/- 4 in 0.5% cholesterol vs. 9 +/- 4 in controls; P < 0.05). After two weeks, hypercholesterolemia caused no proteinuria, but did cause some podocyte injury. Renal NOS activity was decreased, but glomerular endothelial NOS (eNOS) staining was unchanged. Molsidomine prevented proteinuria, podocyte activation, and all further renal injury. CONCLUSIONS: Hypercholesterolemia decreases renal NO synthesis, and induces podocyte activation before proteinuria appears. Renal superoxide activity is increased once rats are proteinuric, further lowering renal NO availability. All of these changes can be prevented by a NO donor.     

Early mechanisms of renal injury in hypercholesterolemic or hypertriglyceridemic rats

Hyperlipidemia in conjunction with uninephrectomy leads to renal injury in rats. It is unknown whether this is due to mesangial cell or podocyte injury and whether the injuries induced by hypercholesterolemia and hypertriglyceridemia share a similar pathogenesis. Therefore, renal effects of hypercholesterolemia were studied in male rats with dietary hypercholesterolemia compared with rats on a regular diet. Renal effects of hypertriglyceridemia were studied in female Nagase analbuminemic rats (NAR). Hypertriglyceridemia was reduced in NAR by ovariectomy. Both models were studied after uninephrectomy or sham operation. Dietary hypercholesterolemia had little effect on plasma triglycerides, whereas ovariectomy in the NAR had no effect on plasma cholesterol. However, an increase in intermediate density lipoprotein cholesterol was common to both models. Dietary hypercholesterolemia and uninephrectomy separately induced a similar increase in proteinuria after 13 wk, which was additive when these interventions were combined. At this stage, only a minimal increase was present in glomerular alpha-smooth muscle actin staining, a marker of mesangial cell activation, or in mesangial matrix expansion. Moreover, platelet-derived growth factor-B chain, a marker of mesangial cell proliferation, was not increased. However, podocyte injury was prominent as evidenced by podocytic de novo expression of desmin and ultrastructural changes. Glomerular macrophage counts were increased by hypercholesterolemia but not by uninephrectomy, and were not related to the level of proteinuria. Hypertriglyceridemia and uninephrectomy in female NAR induced an increase in proteinuria after 24 wk, which was also associated with an increase in podocyte desmin expression without any mesangial activation and proliferation or matrix accumulation. Hypertriglyceridemia, proteinuria, and the increase in desmin staining were largely prevented by ovariectomy. Interstitial myofibroblast activation and tubulointerstitial injury accompanied proteinuria in both models. These findings indicate that both hypercholesterolemia and hypertriglyceridemia aggravate renal injury primarily via podocyte rather than via mesangial cell damage. Such podocyte injury is accompanied by tubulointerstitial cell activation and injury.     

Renoprotective properties of angiotensin receptor blockers beyond blood pressure lowering

Clinical studies have demonstrated that some antihypertensive agents provide renoprotection independent of BP lowering. Recent in vitro and in vivo studies evaluated the mechanisms involved in this protection. First, the in vitro effects of several angiotensin II type 1 receptor blockers (ARB), calcium channel blockers (CCB), and beta blockers (BB) on various mediators were compared: Formation of pentosidine (an advanced glycation end product), hydroxyl radical-induced formation of o-tyrosine, and transition metals-induced oxidation of ascorbic acid (the Fenton reaction). All of the six tested ARB but neither the six CCB nor the nine BB inhibited pentosidine formation. ARB, as well as BB but not CCB, inhibited hydroxyl radicals-mediated o-tyrosine formation. ARB but neither BB nor CCB inhibited efficiently transition metals-catalyzed oxidation of ascorbic acid. Second, the in vivo consequences for the kidney of these various in vitro effects were evaluated. Hypertensive, type 2 diabetic rats with nephropathy, SHR/NDmcr-cp, were given for 20 wk either olmesartan (ARB) or nifedipine (CCB), or atenolol (BB). Despite similar BP reduction, only ARB significantly reduced proteinuria and prevented glomerular and tubulointerstitial damage (mesangial activation, podocyte injury, tubulointerstitial injury, and inflammatory cell infiltration). It is interesting that only ARB prevented abnormal iron deposition in the interstitium, corrected chronic hypoxia, reduced expressions of heme oxygenase and p47phox (a subunit of NADPHoxidase), and inhibited pentosidine formation (which correlates well with proteinuria). These observations confirm unique renoprotective properties of ARB, independent of BP lowering but related to decreased oxidative stress (hydroxyl radicals scavenging and inhibition of the Fenton reaction), correction of chronic hypoxia, and inhibition of advanced glycation end product formation and of abnormal iron deposition. These benefits of ARB may contribute to the renoprotection observed beyond BP lowering.     

Aldosterone induces CTGF in mesangial cells by activation of the glucocorticoid receptor.

BACKGROUND: Aldosterone contributes substantially to cardiac and renal injury by acting on target cells not involved in the regulation of salt and water balance. The profibrotic protein connective tissue growth factor (CTGF) has been identified as one of the target proteins of aldosterone. However, the molecular mechanisms of aldosterone-mediated CTGF induction have not been characterized. METHODS: Mesangial cells were treated with aldosterone or dexamethasone. CTGF expression was characterized at the mRNA and protein level. Translocation of the glucocorticoid receptor (GR) was detected by immunocytochemistry and by Western blotting. RESULTS: Aldosterone and dexamethasone induced CTGF at the mRNA and protein level in a time- and concentration-dependent manner. Specific antagonists of the mineralocorticoid receptor, spironolactone, canrenoate or eplerenone, did not inhibit CTGF induction. However, inhibition of the GR by RU486 prevented dexamethasone-as well as aldosterone-induced CTGF expression, indicating the importance of the GR in aldosterone-mediated regulation of CTGF. This notion was confirmed by translocation of the GR to the nucleus upon stimulation with aldosterone. CONCLUSIONS: CTGF is a functional target of aldosterone in mesangial cells, but aldosterone-induced CTGF gene expression is not directly mediated by the mineralocorticoid receptor.     

Effects of mineralocorticoid and angiotensin II receptor blockers on proteinuria and glomerular podocyte protein expression in a model of minimal change nephrotic syndrome

Aim: Several proteins constituting the slit diaphragm are considered important for maintaining capillary wall permselectivity. Early intervention with blockers of angiotensin II receptors (AR) and mineralocorticoid receptors (MR) is effective against proteinuria in models of chronic hypertensive and protein‐induced renal damage. However, the effects of AR and/or MR blockers in a model of acute nephrotic syndrome remain unknown. The effects of AR and MR blockers were examined in puromycin aminonucleoside (PAN)‐treated rats. Methods: Six week old male Sprague–Dawley (SD) rats were injected with PAN or vehicle and assigned to groups as follows: vehicle (group C); PAN (group P); PAN followed 3 days later by administration of the MR blocker, eplerenone (group MR), and by the AR blocker, losartan (group AR). Blood pressure and urinary protein excretion were measured and all rats were killed for immunohistochemical investigation on day 14 after PAN administration. Results: Blood pressure did not change throughout the study period. Proteinuria was decreased in groups MR and AR compared with group P (on day 14 after PAN administration, respectively; group P vs AR, P < 0.01; group P vs MR, P < 0.05). Nephrin, podocin and podocalyxin staining was preserved in the glomeruli of groups MR and AR compared with group P. Conclusion: The MR and AR blockers decreased proteinuria in the acute model of nephrotic syndrome with preserved expression of glomerular podocyte protein independently of blood pressure.     

Mineralocorticoid receptor activation as an etiological factor in kidney diseases

The mineralocorticoid receptor (MR) is a member of the steroid-responsive nuclear receptor family. Currently, in addition to its classical role in fluid homeostasis, attention has been focused on the pro-proteinuric and pro-inflammatory effects of MR in renal and cardiovascular diseases. Since proteinuria has been shown to be an important factor in the prognosis of patients with chronic kidney disease (CKD) [according to the newest Japanese Society of Nephrology and Kidney Disease: Improving Global Outcomes (KDIGO) guidelines for the treatment of CKD], it is worth discussing the role of MR in the progression of proteinuric CKD and the possible association with podocyte injury. Rac1, a Rho-GTPase family protein, is known for its role in the regulation of the cytoskeleton. We discovered the role of active Rac1 in amplifying MR activation in one of our studies and then continued to study how the Rac1?MR pathway contributes to the progression of kidney diseases. We then discovered the harmful effects of the activation of the Rac1?MR pathway in response to salt loading in the kidney for proteinuric kidney diseases of various animal models with salt-sensitive hypertension, such as Dahl salt-sensitive rats, RhoGDIα-knockout mice, angiotensin II-overproducing mice, and aldosterone-infused rats. In this review, we have introduced recent findings that suggest the contribution of MR activation to kidney diseases and the role of the Rac1?MR pathway in kidney injury associated with salt-sensitive hypertension and proteinuria. Thus, the Rac1?MR pathway is a potential therapeutic target in patients with proteinuric CKD.     

Mineralocorticoid Receptor Antagonism and Aldosterone Synthesis Inhibition Do Not Improve Glomerulosclerosis and Renal Interstitial Fibrosis in a Model of Chronic Kidney Allograft Injury

Chronic allograft injury (CAI) is a major cause of late graft failure with a multifactorial pathogenesis; however, in different experiments an inhibition of the renin-angiotensin system by angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers ameliorated the progression of chronic renal disease. Different concepts supposed that aldosterone is involved in development and/or progression of renal diseases via interaction with a non-epithelial mineralocorticoid receptor (MR), e.g. reducing neointima formation. Our examinations therefore targeted on the effects of the aldosterone synthase inhibitor fadrozole and the MR antagonist spironolactone compared to vehicle in an established rat model of CAI. In our model of CAI, neither the aldosterone biosynthesis inhibitor nor a direct MR blockade had a positive effect on renal CAI in rats. Fadrozole- and spironolactone-treated animals demonstrated a higher proteinuria value, pathologically elevated potassium values, higher tubulointerstitial damage and markedly increased heart weight/body weight as compared to vehicle. Our observations also suggest that inhibition of the MR or the biosynthesis itself had a bad influence on the amount of sclerotic glomeruli and tubulointerstitial damage. The positive effects of inhibition of aldosterone as described in cardiac models could not yet be detected in kidney recipients.