Aldosterone Stimulates Proliferation of Mesangial Cells by Activating Mitogen-Activated Protein Kinase 1/2, Cyclin D1, and Cyclin A

Mineralocorticoid receptor antagonist use in chronic kidney disease with type 2 diabetes: a clinical practice document by the European Renal Best Practice (ERBP) board of the European Renal Association (ERA)

Chronic kidney disease (CKD) in individuals with type 2 diabetes (T2D) represents a major public health issue; it develops in about 30%-40% of patients with diabetes mellitus and is the most common cause of CKD worldwide. Patients with CKD and T2D are at high risk of both developing kidney failure and of cardiovascular events. Renin-angiotensin system (RAS) blockers were considered the cornerstone of treatment of albuminuric CKD in T2D for more than 20 years. However, the residual risk of progression to more advanced CKD stages under RAS blockade remains high, while in major studies with these agents in patients with CKD and T2D no significant reductions in cardiovascular events and mortality were evident. Steroidal mineralocorticoid receptor antagonists (MRAs) are known to reduce albuminuria in individuals on RAS monotherapy, but their wide clinical use has been curtailed by the significant risk of hyperkalemia and absence of trials with hard renal outcomes. In recent years, non-steroidal MRAs have received increasing interest due to their better pharmacologic profile. Finerenone, the first compound of this class, was shown to effectively reduce the progression of kidney disease and of cardiovascular outcomes in participants with T2D in phase 3 trials. This clinical practice document prepared from a task force of the European Renal Best Practice board summarizes current knowledge on the role of MRAs in the treatment of CKD in T2D aiming to support clinicians in decision-making and everyday management of patients with this condition.

Decaying kidney function during cirrhosis correlates with remodeling of distal colon aldosterone target gene expression

Liver cirrhosis is associated to circulatory abnormalities leading to hypovolemia and stimulation of the renin-angiotensin-aldosterone system (RAAS). Advanced stages of the disease cause renal failure, impairing K+ and Na+ homeostasis. It has been proposed that the distal colon undergoes functional remodeling during renal failure, in particular by aldosterone-driven increased K+ excretion. In this study, we compared the transcriptional response of aldosterone target genes in the rat distal colon under two models of increased circulating aldosterone (one with concomitant RAAS activation) and in a model of secondary hyperaldosteronism induced by cirrhosis. The expression of a subset of these genes was also tested in distal colon biopsies from control subjects or patients with cirrhosis with varying levels of disease progression and treated or not with mineralocorticoid receptor inhibitor spironolactone. We examined known aldosterone-regulated transcripts involved in corticosteroid signaling and transepithelial ion transport. In addition, we included aldosterone-regulated genes related to cell proliferation. Our comparison revealed multiple aldosterone target genes upregulated in the rat distal colon during decompensated cirrhosis. Epithelial Na+ channel β and γ subunit expression correlated positively with plasma aldosterone concentration and negatively with glomerular filtration rate. Patients with cirrhosis showed increased expression of 11-β-hydroxysteroid-dehydrogenase 2 (11βHSD2), which was reverted by spironolactone treatment, suggesting a sensitization of the distal colon to aldosterone action. In summary, our data show that decaying kidney function during cirrhosis progression toward a decompensated state with hypovolemia correlates with remodeling of distal colon ion transporter expression, supporting a role for aldosterone in the process.NEW & NOTEWORTHY Liver cirrhosis progression significantly alters ion transporter subunit expression in the rat distal colon, a change that correlated well with declining kidney function and the severity of the disease. Our data suggest that the steroid hormone aldosterone participates in this homeostatic response to maintain electrolyte balance.

Dual deletion of guanylyl cyclase-A and p38 mitogen-activated protein kinase in podocytes with aldosterone administration causes glomerular intra-capillary thrombi

Natriuretic peptides exert not only blood-lowering but also kidney-protective effects through guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. Signaling through GC-A has been shown to protect podocytes from aldosterone-induced glomerular injury, and a p38 mitogen-activated protein kinase (MAPK) inhibitor reduced glomerular injury in aldosterone-infused podocyte-specific GC-A knockout mice. To explore the role of p38 MAPK in podocytes, we constructed podocyte-specific p38 MAPK and GC-A double knockout mice (pod-double knockout mice). Unexpectedly, aldosterone-infused and high salt-fed (B-ALDO)-treated pod-double knockout mice resulted in elevated serum creatinine, massive albuminuria, macrophage infiltration, foot process effacement, nephrin and podocin reduction, and additionally, intra-capillary fibrin thrombi, indicating endothelial injury. Microarray analysis showed increased plasminogen activator inhibitor-1 (PAI-1) in glomeruli of B-ALDO-treated pod-double knockout mice. In B-ALDO-treated pod-double knockout mice, PAI-1 increased in podocytes, and treatment with PAI-1 neutralizing antibody ameliorated intra-capillary thrombus formation. In vitro, deletion of p38 MAPK by the CRISPR/Cas9 system and knockdown of GC-A in human cultured podocytes upregulated PAI-1 and transforming growth factor- β1 (TGF-β1). When p38 MAPK knockout podocytes, transfected with a small interfering RNA to suppress GC-A, were co-cultured with glomerular endothelial cells in a transwell system, the expression of TGF-β1 was increased in glomerular endothelial cells. PAI-1 inhibition ameliorated both podocyte and endothelial injury in the transwell system signifying elevated PAI-1 in podocytes is a factor disrupting normal podocyte-endothelial crosstalk. Thus, our results indicate that genetic dual deletion of p38 MAPK and GC-A in podocytes accelerates both podocyte and endothelial injuries, suggesting these two molecules play indispensable roles in podocyte function.

Mineralocorticoid Receptor Antagonists for Preventing Chronic Kidney Disease Progression: Current Evidence and Future Challenges

Regulation and action of the mineralocorticoid receptor (MR) have been the focus of intensive research over the past 80 years. Genetic and physiological/biochemical analysis revealed how MR and the steroid hormone aldosterone integrate the responses of distinct tubular cells in the face of environmental perturbations and how their dysregulation compromises fluid homeostasis. In addition to these roles, the accumulation of data also provided unequivocal evidence that MR is involved in the pathophysiology of kidney diseases. Experimental studies delineated the diverse pathological consequences of MR overactivity and uncovered the multiple mechanisms that result in enhanced MR signaling. In parallel, clinical studies consistently demonstrated that MR blockade reduces albuminuria in patients with chronic kidney disease. Moreover, recent large-scale clinical studies using finerenone have provided evidence that the non-steroidal MR antagonist can retard the kidney disease progression in diabetic patients. In this article, we review experimental data demonstrating the critical importance of MR in mediating renal injury as well as clinical studies providing evidence on the renoprotective effects of MR blockade. We also discuss areas of future investigation, which include the benefit of non-steroidal MR antagonists in non-diabetic kidney disease patients, the identification of surrogate markers for MR signaling in the kidney, and the search for key downstream mediators whereby MR blockade confers renoprotection. Insights into these questions would help maximize the benefit of MR blockade in subjects with kidney diseases.

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Mineralocorticoid receptor antagonists for cardioprotection in chronic kidney disease: a step into the future

Chronic kidney disease (CKD) and cardiovascular disease (CVD) share major risk factors and mechanistic pathways for progression. Furthermore, either decreased glomerular filtration rate or increased albuminuria are major risk factors for cardiovascular events. Evidence from previous renal outcome trials in patients with proteinuric CKD showed that angiotensin-converting-enzyme inhibitors (ACEIs) and angiotensin-II receptor blockers (ARBs) effectively slow CKD progression, establishing these agents as fundamental CKD pharmacologic treatments. However, in all these trials and subsequent meta-analyses, ACEIs and ARBs did not significantly reduce cardiovascular events or mortality, indicating a high residual risk for CVD progression in individuals with CKD. In contrast to the above, several outcome trials with old and novel mineralocorticoid receptor-antagonists (MRAs) clearly suggest that these agents, apart from nephroprotection, offer important cardioprotection in this population. This article is an overview of previous and recent evidence on the effects of MRAs on cardiovascular outcomes in patients with CKD attempting to highlight a pathway able to improve both cardiovascular and renal prognosis in this population.

Increased glucocorticoid metabolism in diabetic kidney disease

Aims

Glomerular damage indicated by proteinuria is a main symptom in diabetic nephropathy. Mineralocorticoid receptor (MR) antagonists (MRAs) are beneficial irrespective of aldosterone availability. Thus, we hypothesized an alternatively activated MR to promote glomerular damage in proteinuric diabetic nephropathy. Specifically, we aimed first to demonstrate the presence of steroid hormones serving as alternative MR targets in type II diabetic patients with proteinuric kidney disease, second whether MR selectivity was modified, third to characterize MR and glucocorticoid receptor (GR) expression and activity in glomerular cell types exposed to eu- and hyperglycemic conditions, fourth to characterize the pro-fibrotic potential of primary human renal mesangial cells (HRMC) upon stimulation with aldosterone and cortisol, and fifth to specify the involvement of the MR and/or GR in pro-fibrotic signaling.

Materials and methods

Urinary steroid hormone profiles of patients with diabetic kidney disease were analyzed by gas chromatography–mass spectrometry and compared to an age and gender matched healthy control group taken out of a population study. In both cohorts, the activity of the MR pre-receptor enzyme 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2), which inactivates cortisol to prevent it from binding to the MR, was assessed to define a change in MR selectivity. Expression of HSD11B2, MR and GR was quantified in HRMC and primary human renal glomerular endothelial cells (HRGEC). Activity of MR and GR was explored in HRMC by measuring the MR/GR down-stream signal SGK1 and the pro-fibrotic genes TGFB1, FN1 and COL1A1 in normal and high glucose conditions with the MR/GR agonists aldosterone/cortisol and the MR/GR antagonists spironolactone/RU486.

Results

Patients with diabetic kidney disease excreted more tetrahydroaldosterone than the control group reaching significance in men. The excretion of MR-agonistic steroid hormones was only increased for 18-hydroxytetrahydrocorticosterone in diabetic women. The excretion of most glucocorticoids was higher in the diabetic cohort. Higher apparent systemic HSD11B2 activity suggested less activation of the MR by cortisol in diabetic patients. Both cell types, HRMC and HRGEC, lacked expression of HSD11B2. Hyperglycemic conditions did not change MR and GR expression and activity. Stimulation with both aldosterone and cortisol promoted upregulation of pro-fibrotic genes in HRMC. This effect of MR and/or GR activation was more pronounced in high glucose conditions and partially inhibited by MRAs and GR antagonists.

Conclusions

In patients with diabetic kidney disease alternative MR activation is conceivable as cortisol and cortisone metabolites are increased. Systemic availability of active metabolites is counteracted via an increased HSD11B2 activity. As this cortisol deactivation is absent in HRMC and HRGEC, cortisol binding to the MR is enabled. Both, cortisol and aldosterone stimulation led to an increased expression of pro-fibrotic genes in HRMC. This mechanism was related to the MR as well as the GR and more marked in high glucose conditions linking the benefit of MRAs in diabetic kidney disease to these findings.

Renal Effects of Fetal Reprogramming With Pentaerythritol Tetranitrate in Spontaneously Hypertensive Rats

Aims

Current antihypertensive therapies cannot cure hypertension and a life-long medication is necessary. Maternal treatment may represent a promising strategy for hypertension treatment. We have previously shown that maternal treatment of spontaneously hypertensive rats (SHR) with pentaerythritol tetranitrate (PETN) leads to a persistent blood pressure reduction in the female offspring. The underlying mechanisms include improved endothelial function resulting from long-lasting epigenetic changes. In the present study, we address the renal effects of maternal PETN treatment.

Methods and Results

F0 parental SHR were fed with either normal chow or PETN-containing (1 g/kg) chow ad libitum from the time point of mating to the end of lactation period. The F1 offspring received normal chow without PETN from the time point of weaning (at the age of 3 weeks). At the age of 16 weeks, female PETN offspring showed lower blood pressure than the control. No difference was observed in male offspring. All following experiments were performed with kidneys from 16-week-old female offspring. Maternal PETN treatment reduced the mRNA and protein expression of angiotensin-converting enzyme (ACE) and basic fibroblast growth factor (FGF2), resulting from epigenetic modifications found at the proximal promoter regions. The expression levels of mineralocorticoid receptor (MR) and factors in the MR signalling pathway (Rac1 and Sgk1) were also reduced by PETN. Major profibrotic cytokines, including Wnt4, TNF-alpha, TGF-beta, and MMP9, were downregulated by PETN, which was associated with reduced collagen deposition and glomerulus sclerosis in the kidney of PETN offspring. In addition, PETN treatment also decreased the markers of inflammation and immune cell infiltration in the kidneys.

Conclusions

PETN maternal treatment leads to epigenetic changes in the kidney of female SHR offspring. The reduced renal inflammation, alleviated kidney fibrosis, and decreased MR signalling are potential mechanisms contributing to the observed blood pressure-lowering effect.

Mineralocorticoid receptor antagonists and kidney diseases: pathophysiological basis

Chronic kidney disease (CKD) represents a global health concern, and its prevalence is increasing. The ultimate therapeutic option for CKD is kidney transplantation. However, the use of drugs that target specific pathways to delay or halt CKD progression, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and sodium-glucose co-transporter-2 (SGLT-2) inhibitors is limited in clinical practice. Mineralocorticoid receptor activation in nonclassical tissues, such as the endothelium, smooth muscle cells, inflammatory cells, podocytes, and fibroblasts may have deleterious effects on kidney structure and function. Several preclinical studies have shown that mineralocorticoid receptor antagonists (MRAs) ameliorate or cure kidney injury and dysfunction in different models of kidney disease. In this review, we present the preclinical evidence showing a benefit of MRAs in acute kidney injury, the transition from acute kidney injury to CKD, hypertensive and diabetic nephropathy, glomerulonephritis, and kidney toxicity induced by calcineurin inhibitors. We also discuss the molecular mechanisms responsible for renoprotection related to MRAs that lead to reduced oxidative stress, inflammation, fibrosis, and hemodynamic alterations. The available clinical data support a benefit of MRA in reducing proteinuria in diabetic kidney disease and improving cardiovascular outcomes in CKD patients. Moreover, a benefit of MRAs in kidney transplantation has also been observed. The past and present clinical trials describing the effect of MRAs on kidney injury are presented, and the risk of hyperkalemia and use of other options, such as potassium binding agents or nonsteroidal MRAs, are also addressed. Altogether, the available preclinical and clinical data support a benefit of using MRAs in CKD, an approach that should be further explored in future clinical trials.

Effects of the novel nonsteroidal mineralocorticoid receptor blocker, esaxerenone (CS-3150), on blood pressure and urinary angiotensinogen in low-renin Dahl salt-sensitive hypertensive rats

Herein, we studied the effects of the novel nonsteroidal selective mineralocorticoid receptor (MR) blocker, esaxerenone, on blood pressure and renal injury in Dahl salt-sensitive (DSS) rats. We also monitored intact urinary and total angiotensinogen (AGT). DSS rats were given a normal salt diet (NS: 0.4% NaCl, n = 10), a high-salt diet (HS: 8% NaCl, n = 10), HS + esaxerenone (1 mg/kg/day, p.o., n = 10), or HS + losartan (angiotensin II receptor blocker, 10 mg/kg/day, p.o., n = 10) for 6 weeks. Glomerular and tubulointerstitial tissues were obtained via a laser capture method. HS-treated DSS rats developed hypertension, albuminuria, and glomerular injury, which were associated with increased glomerular desmin staining and reduced mRNA levels of glomerular podocin and nephrin. HS-treated DSS rats also showed tubulointerstitial fibrosis with an increase in renal oxidative stress (4-hydroxynonenal staining). The urinary ((total AGT-intact AGT)/intact AGT) ratio, an indicator of intrarenal renin activity, was significantly suppressed in HS-treated DSS rats. Treatment with esaxerenone significantly decreased blood pressure, while losartan did not. Furthermore, esaxerenone attenuated the development of albuminuria, glomerular injury, and tubulointerstitial fibrosis more than losartan did, and this effect was associated with reduced renal oxidative stress. These data indicate that esaxerenone has antihypertensive and renal protective effects in salt-dependent hypertensive mice with suppressed intrarenal renin activity, as indicated by low levels of the urinary (total AGT-intact AGT)/intact AGT ratio.

Modeling the Influence of Seasonal Differences in the HPA Axis on Synchronization of the Circadian Clock and Cell Cycle

Synchronization of biological functions to environmental signals enables organisms to anticipate and appropriately respond to daily external fluctuations and is critical to the maintenance of homeostasis. Misalignment of circadian rhythms with environmental cues is associated with adverse health outcomes. Cortisol, the downstream effector of hypothalamic-pituitary-adrenal (HPA) activity, facilitates synchronization of peripheral biological processes to the environment. Cortisol levels exhibit substantial seasonal rhythmicity, with peak levels occurring during the short-photoperiod winter months and reduced levels occurring in the long-photoperiod summer season. Seasonal changes in cortisol secretion could therefore alter its entraining capabilities, resulting in a season-dependent modification in the alignment of biological activities with the environment. We develop a mathematical model to investigate the influence of photoperiod-induced seasonal differences in the circadian rhythmicity of the HPA axis on the synchronization of the peripheral circadian clock and cell cycle in a heterogeneous cell population. Model simulations predict that the high-amplitude cortisol rhythms in winter result in the greatest entrainment of peripheral oscillators. Furthermore, simulations predict a circadian gating of the cell cycle with respect to the expression of peripheral clock genes. Seasonal differences in cortisol rhythmicity are also predicted to influence mitotic synchrony, with a high-amplitude winter rhythm resulting in the greatest synchrony and a shift in timing of the cell cycle phases, relative to summer. Our results highlight the primary interactions among the HPA axis, the peripheral circadian clock, and the cell cycle and thereby provide an improved understanding of the implications of circadian misalignment on the synchronization of peripheral regulatory processes.

Alterations in the long non‑coding RNA transcriptome in mesangial cells treated with aldosterone in vitro

Clinical and experimental reports indicate that aldosterone (ALD) contributes to the progression of renal failure independent of its hemodynamic effects. However, the mechanisms remain to be completely elucidated. The aim of the present study was to investigate the alterations of long non-coding RNA (lncRNA) in mesangial cells (MCs) treated with ALD. The present study used MCs treated with 10⁻⁶ M ALD as experimental cells. Microarray techniques performed by Agilent Technologies were used to identify the profiles of differentially expressed lncRNAs between the ALD group and the control group. Pathway and gene ontology analysis were applied to determine the roles of the differentially expressed lncRNAs. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to quantify the differentially expressed lncRNAs. A total of 8,459 lncRNA and 13,214 mRNAs with differential expression between MCs treated with and without ALD were identified. The expression of lncRNAs was confirmed by RT-qPCR and the results were consistent with the lncRNA array. The biological functions of lncRNAs are associated with responding to external stimuli, positive regulation of biological and apoptotic processes, cell division, mitosis and nuclear division. The pathways include cell cycle and peroxisome proliferator-activated receptor signaling pathways. The present study revealed distinct sets of lncRNA expressed in MCs treated with ALD, suggesting that this class of transcripts may be involved in the pathogenesis of chronic kidney diseases.

Natriuretic peptide receptor guanylyl cyclase-A pathway counteracts glomerular injury evoked by aldosterone through p38 mitogen-activated protein kinase inhibition

Guanylyl cyclase-A (GC-A) signaling, a natriuretic peptide receptor, exerts renoprotective effects by stimulating natriuresis and reducing blood pressure. Previously we demonstrated massive albuminuria with hypertension in uninephrectomized, aldosterone-infused, and high salt-fed (ALDO) systemic GC-A KO mice with enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in podocytes. In the present study, we examined the interaction between p38 MAPK and GC-A signaling. The administration of FR167653, p38 MAPK inhibitor, reduced systolic blood pressure (SBP), urinary albumin excretion, segmental sclerosis, podocyte injury, and apoptosis. To further investigate the local action of natriuretic peptide and p38 MAPK in podocytes, we generated podocyte-specific (pod) GC-A conditional KO (cKO) mice. ALDO pod GC-A cKO mice demonstrated increased urinary albumin excretion with marked mesangial expansion, podocyte injury and apoptosis, but without blood pressure elevation. FR167653 also suppressed urinary albumin excretion without reducing SBP. Finally, we revealed that atrial natriuretic peptide increased phosphorylation of MAPK phosphatase-1 (MKP-1) concomitant with inhibited phosphorylation of p38 MAPK in response to MAPK kinase 3 activation, thereby resulting in decreased mRNA expression of the apoptosis-related gene, Bax, and Bax/Bcl2 ratio in cultured podocytes. These results indicate that natriuretic peptide exerts a renoprotective effect via inhibiting phosphorylation of p38 MAPK in podocytes.

Epidermal growth factor receptor signaling mediates aldosterone-induced profibrotic responses in kidney

Aldosterone has been recognized as a risk factor for the development of chronic kidney disease (CKD). Studies have indicated that enhanced activation of epidermal growth factor receptor (EGFR) is associated with the development and progression of renal fibrosis. But if EGFR is involved in aldosterone-induced renal fibrosis is less investigated. In the present study, we examined the effect of erlotinib, an inhibitor of EGFR tyrosine kinase activity, on the progression of aldosterone-induced renal profibrotic responses in a murine model underwent uninephrectomy. Erlotinib-treated rats exhibited relieved structural lesion comparing with rats treated with aldosterone alone, as characterized by glomerular hypertrophy, mesangial cell proliferation and expansion. Also, erlotinib inhibited the expression of TGF-β, α-SMA and mesangial matrix proteins such as collagen Ⅳ and fibronectin. In cultured mesangial cells, inhibition of EGFR also abrogated aldosterone-induced expression of extracellular matrix proteins, cell proliferation and migration. We also demonstrated that aldosterone induced the phosphorylation of EGFR through generation of ROS. And the activation of EGFR resulted in the phosphorylation of ERK1/2, leading to the activation of profibrotic pathways. Taken together, we concluded that aldosterone-mediated tissue fibrosis relies on ROS induced EGFR/ERK activation, highlighting EGFR as a potential therapeutic target for modulating renal fibrosis.

Hypothalamic-pituitary-adrenal axis activity is associated with the prevalence of chronic kidney disease in diabetic patients

Progression of chronic kidney disease (CKD) in diabetic patients can occur through enhanced hypothalamic-pituitary-adrenal (HPA) axis activity. The purpose of our study was to determine whether HPA axis activity influences the prevalence of CKD in patients with type 2 diabetes mellitus. Seventy-seven diabetic patients (mean age, 60 years) were enrolled. CKD was defined by K/DOQI criteria, and serum cortisol level was measured after the 1 mg overnight dexamethasone suppression test (F-DST). F-DST values were significantly negatively correlated with estimated glomerular filtration rate (eGFR), and significantly positively correlated with cystatin C level and spot urine albumin to creatinine ratio in simple and multiple regression analyses. The subjects were divided into 3 groups (low, middle, and high) according to the F-DST, and the odds for CKD were 8.7-fold (95% confidence interval 2.56 to 29.6, P=0.01) and 12.5-fold (95% confidence interval 3.3 to 47.9, P<0.001) higher in subjects in the middle and high groups than those in the low group, respectively. In multivariate regression analysis, subjects in the middle group and high group (compared to those in the low group) had 13.0-fold (95% confidence interval, 2.9 to 58.8 and P=0.001) and 14.7-fold (95% confidence interval, 2.8 to 78.5 and P=0.002), respectively, higher risk for CKD. In conclusion, F-DST values have a relationship with decreased eGFR and increased cystatin C or albumin excretion involved in CKD, and enhanced HPA axis activity may be an independent risk factor for CKD in patients with type 2 diabetes mellitus.

CS-3150, a novel non-steroidal mineralocorticoid receptor antagonist, prevents hypertension and cardiorenal injury in Dahl salt-sensitive hypertensive rats

The present study was designed to evaluate the antihypertensive and cardiorenal protective effects of CS-3150, a novel non-steroidal mineralocorticoid receptor antagonist, in Dahl salt-sensitive hypertensive rats (DS rats), and to compare the effects with spironolactone and eplerenone. DS rats were fed a control diet (0.3% NaCl) or high salt diet (8% NaCl) from 7 weeks of age. CS-3150 (0.25-2mg/kg), spironolactone (10-100mg/kg) or eplerenone (10-100mg/kg) were orally administered once a day to DS rats fed a high salt diet for 7 weeks. The high salt diet significantly increased systolic blood pressure, which was prevented by treatment with CS-3150 in a dose-dependent manner with no hyperkalemia (>5.5mEq/L). The antihypertensive effect of CS-3150 (0.5mg/kg) was equivalent to that of spironolactone (100mg/kg) and eplerenone (100mg/kg). CS-3150 also suppressed proteinuria and renal hypertrophy induced by the high salt diet. Histopathological examination of kidneys showed that CS-3150 markedly ameliorated glomerulosclerosis, tubular injury and tubulointerstitial fibrosis. In addition, CS-3150 inhibited left ventricular hypertrophy and elevation of plasma brain natriuretic peptide level. In contrast, the cardiorenal protective effects of spironolactone or eplerenone were partial, and the dose-dependency was not clear, especially in eplerenone-treated rats. These results indicate that chronic treatment with CS-3150 exerts antihypertensive and cardiorenal protective effects in a DS hypertensive rat model, and its potency is much superior to that of spironolactone or eplerenone. Thus, CS-3150 could be a promising agent for the treatment of hypertension and cardiorenal disorders.

Therapeutic targeting of aldosterone: a novel approach to the treatment of glomerular disease

Numerous studies have established a role for mineralocorticoids in the development of renal fibrosis. Originally, the research focus for mineralocorticoid-induced fibrosis was on the collecting duct, where 'classical' mineralocorticoid receptors (MRs) involved with electrolyte transport are present. Epithelial cells in this segment can, under selected circumstances, also respond to MR activation by initiating pro-fibrotic pathways. More recently, 'non-classical' MRs have been described in kidney cells not associated with electrolyte transport, including mesangial cells and podocytes within the glomerulus. Activation of MRs in these cells appears to lead to glomerular sclerosis. Mechanistically, aldosterone induces excess production of reactive oxygen species (ROS) and oxidative stress in glomerular cells through activation of NADPH oxidase. In mesangial cells, aldosterone also has pro-apoptotic, mitogenic and pro-fibrogenic effects, all of which potentially promote active remodelling and expansion of the mesangium. Although mitochondrial dysfunction seems to mediate the aldosterone-induced mesangial apoptosis, the ROS dependent epithelial growth factor receptor (EGFR) transactivation is probably responsible for aldosterone-induced mesangial mitosis and proliferation. In podocytes, mitochondrial dysfunction elicited by oxidative stress is an early event associated with aldosterone-induced podocyte injury. Both the p38 MAPK (p38 mitogen-activated protein kinase) signalling and the redox-sensitive glycogen synthase kinase (GSK)3β pathways are centrally implicated in aldosterone-induced podocyte death. Aldosterone-induced GSK3β over-activity could potentially cause hyperphosphorylation and over-activation of putative GSK3β substrates, including structural components of the mitochondrial permeability transition (MPT) pore, all of which lead to cell injury and death. Clinically, proteinuria significantly decreases when aldosterone inhibitors are included in the treatment of many glomerular diseases further supporting the view that mineralocorticoids are important players in glomerular pathology.

Mineralocorticoid receptor signaling: crosstalk with membrane receptors and other modulators

The mineralocorticoid receptor (MR) belongs to the steroid receptor superfamily. Classically, it acts as a ligand-bound transcription factor in epithelial tissues, where it regulates water and electrolyte homeostasis and controls blood pressure. Additionally, the MR has been shown to elicit pathophysiological effects including inflammation, fibrosis and remodeling processes in the cardiovascular system and the kidneys and MR antagonists have proven beneficial for patients with certain cardiovascular and renal disease. The underlying molecular mechanisms that mediate MR effects have not been fully elucidated but very likely rely on interactions with other signaling pathways in addition to genomic actions at hormone response elements. In this review we will focus on interactions of MR signaling with different membrane receptors, namely receptor tyrosine kinases and the angiotensin II receptor because of their potential relevance for disease. In addition, GPR30 is discussed as a new aldosterone receptor. To gain insights into the problem why the MR only seems to mediate pathophysiological effects in the presence of additional permissive factors we will also briefly discuss factors that lead to modulation of MR activity as well. Overall, MR signaling is part of an intricate network that still needs to be investigated further.

The aldosterone receptor antagonist spironolactone prevents peritoneal inflammation and fibrosis

Peritoneal fibrosis is a complication of patients with long-term continuous ambulatory peritoneal dialysis (CAPD). Reports have indicated that angiotensin (Ang) II may correlate with the development of peritoneal fibrosis. However, it is unknown whether aldosterone also has a role in the development of peritoneal inflammation and fibrosis. The aim of the present study was to clarify the role of aldosterone in peritoneal inflammation and fibrosis. A rat model of peritoneal inflammation and fibrosis was established by daily intraperitoneal injection of dialysates and lipopolysaccharide in a 4-day interval over a period of 7 days. The animals were randomly assigned to five groups as follows: control (C); peritoneal dialysis (PD); peritoneal dialysis-spironolactone (PD-S); peritoneal dialysis-cilazapril (PD-C); and peritoneal dialysis-spironolactone-cilazapril (PD-SC). After 30 days, the TGF-β1 concentration in dialysates from all treatment groups was determined by ELISA. The histopathology of the parietal peritoneum was examined, and the expression of MCP-1, c-Jun, fibronectin (FN) and TGF-β1 in the abdominal membrane was determined by immunohistochemistry. Mineralocorticoid receptor (MR), 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) and CYP11B2 (aldosterone synthase) were analyzed by real time-PCR. Collagen deposition was significantly higher in PD compared with the other groups. The expression of MR, 11β-HSD2 and CYP11B2 was significantly higher in PD compared with the other groups. Spironolactone and/or cilazapril treatment partially ablated the increase in monocyte chemoattractant protein (MCP)-1, p-c-Jun, transforming growth factor (TGF)-β1, FN, MR, 11β-HSD2 and CYP11B2. Furthermore, treatment with spironolactone and/or cilazapril also reduced the infiltration of CD-4- and ED-1-positive cells in rat peritoneal tissues after peritoneal fibrosis. Exogenous aldosterone may have a key role in the development of peritoneal inflammation and fibrosis. Spironolactone decreased peritoneal inflammation and fibrosis, which was associated with reduced secretion from peritoneal macrophages, inactivation of the c-Jun N-terminal kinase (JNK) pathway and subsequent downregulation of the expression of TGF-β1.

Contribution of aldosterone to cardiovascular and renal inflammation and fibrosis

The steroid hormone aldosterone regulates sodium and potassium homeostasis. Aldosterone and activation of the mineralocorticoid receptor also causes inflammation and fibrosis of the heart, fibrosis and remodelling of blood vessels and tubulointerstitial fibrosis and glomerular injury in the kidney. Aldosterone and mineralocorticoid-receptor activation initiate an inflammatory response by increasing the generation of reactive oxygen species by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondria. High salt intake potentiates these effects, in part by activating the Rho family member Rac1, a regulatory subunit of reduced NADPH oxidase that activates the mineralocorticoid receptor. Studies in mice in which the mineralocorticoid receptor has been deleted from specific cell types suggest a key role for macrophages in promoting inflammation and fibrosis. Aldosterone can exert mineralocorticoid-receptor-independent effects via the angiotensin II receptor and via G-protein-coupled receptor 30. Mineralocorticoid-receptor antagonists are associated with decreased mortality in patients with heart disease and show promise in patients with kidney injury, but can elevate serum potassium concentration. Studies in rodents genetically deficient in aldosterone synthase or treated with a pharmacological aldosterone-synthase inhibitor are providing insight into the relative contribution of aldosterone compared with the contribution of mineralocorticoid-receptor activation in inflammation, fibrosis, and injury. Aldosterone-synthase inhibitors are under development in humans.

Natriuretic peptide receptor guanylyl cyclase-A protects podocytes from aldosterone-induced glomerular injury

Natriuretic peptides produced by the heart in response to cardiac overload exert cardioprotective and renoprotective effects by eliciting natriuresis, reducing BP, and inhibiting cell proliferation and fibrosis. These peptides also antagonize the renin-angiotensin-aldosterone system, but whether this mechanism contributes to their renoprotective effect is unknown. Here, we examined the kidneys of mice lacking the guanylyl cyclase-A (GC-A) receptor for natriuretic peptides under conditions of high aldosterone and high dietary salt. After 4 weeks of administering aldosterone and a high-salt diet, GC-A knockout mice, but not wild-type mice, exhibited accelerated hypertension with massive proteinuria. Aldosterone-infused GC-A knockout mice had marked mesangial expansion, segmental sclerosis, severe podocyte injury, and increased oxidative stress. Reducing the BP with hydralazine failed to lessen such changes; in contrast, blockade of the renin-angiotensin-aldosterone system markedly reduced albuminuria, ameliorated podocyte injury, and reduced oxidative stress. Furthermore, treatment with the antioxidant tempol significantly reduced albuminuria and abrogated the histologic changes. In cultured podocytes, natriuretic peptides inhibited aldosterone-induced mitogen-activated protein kinase phosphorylation. Taken together, these results suggest that renoprotective properties of the endogenous natriuretic peptide/GC-A system may result from the local inhibition of the renin-angiotensin-aldosterone system and oxidative stress in podocytes.

Aldosterone deficiency and mineralocorticoid receptor antagonism prevent angiotensin II-induced cardiac, renal, and vascular injury

Angiotensin II causes cardiovascular injury in part by aldosterone-induced mineralocorticoid receptor activation, and it can also activate the mineralocorticoid receptor in the absence of aldosterone in vitro. Here we tested whether endogenous aldosterone contributes to angiotensin II/salt-induced cardiac, vascular, and renal injury by the mineralocorticoid receptor. Aldosterone synthase knockout mice and wild type littermates were treated with angiotensin II or vehicle plus the mineralocorticoid receptor antagonist spironolactone or regular diet while drinking 0.9- saline. Angiotensin II/salt caused hypertension in both the knockout and wild type mice; an effect significantly blunted in the knockout mice. Either genetic aldosterone deficiency or mineralocorticoid receptor antagonism reduced cardiac hypertrophy, aortic remodeling, and albuminuria, as well as cardiac, aortic, and renal plasminogen activator inhibitor-1 mRNA expression during angiotensin II treatment. Mineralocorticoid receptor antagonism reduced angiotensin II/salt-induced glomerular hypertrophy, but aldosterone deficiency did not. Combined mineralocorticoid receptor antagonism and aldosterone deficiency reduced blood urea nitrogen and restored nephrin immunoreactivity. Angiotensin II/salt also promoted glomerular injury through the mineralocorticoid receptor in the absence of aldosterone. Thus, mineralocorticoid antagonism may have protective effects in the kidney beyond aldosterone synthase inhibition.

Mineralocorticoid receptors in the pathophysiology of chronic kidney diseases and the metabolic syndrome

Recent studies indicate that aldosterone/mineralocorticoid receptor (MR) is a major contributor of chronic kidney disease (CKD) progression. Aldosterone/MR induces glomerular podocyte injury, causing the disruption of the glomerular filtration barrier and proteinuria. Conversely, MR antagonists substantially reduce proteinuria, which can be partly attributable to the protective effects on podocytes. Aldosterone excess, caused by adipocyte-derived aldosterone-releasing factors and other mechanisms, can be pathologically important in the renal complication of metabolic syndrome. A rat model of metabolic syndrome exhibits podocyte injury and proteinuria with serum aldosterone elevation, and the renal damage is prevented by MR blockade. Accumulating data also indicate that MR inhibition can confer renoprotection in a subgroup with low or normal aldosterone levels. We have recently identified the cross-talk between MR and small GTPase Rac1, providing one theoretical basis for the renoprotective effects of MR antagonists in non-high-aldosterone subjects. MR blockade can be a promising strategy for preventing CKD progression, and future clinical trials will conclusively determine the efficacy and tolerability of selective MR inhibition in CKD and metabolic syndrome.

Interaction between mineralocorticoid receptor and epidermal growth factor receptor signaling

The mineralocorticoid receptor (MR) is a steroid receptor that physiologically regulates water and electrolyte homeostasis but that can also induce pathophysiological effects in the renocardiovascular system. Classically, the MR acts as a transcription factor at glucocorticoid response elements but additional protein-protein interactions with other signaling cascades have been described. Of these, the crosstalk with EGFR signaling is especially interesting because various vasoactive substances like angiotensin II and endothelin-1 also mediate their pathophysiological effects via the EGFR. Recently, the MR has been shown to interact nongenomically (via transactivation) and genomically with the epidermal growth factor receptor (via altered expression). These interactions seem to contribute to physiological (e.g. salt homeostasis) as well as pathophysiological (e.g. vascular function) MR effects. The current knowledge on the mechanisms of interaction and on the possible cellular and systemic physiological as well as pathophysiological relevance is reviewed in this article.

Tissue-specific modulation of mineralocorticoid receptor function by 11β-hydroxysteroid dehydrogenases: an overview

In the last decade significant progress has been made in the understanding of mineralocorticoid receptor (MR) function and its implications for physiology and disease. The knowledge on the essential role of MR in the regulation of electrolyte concentrations and blood pressure has been significantly extended, and the relevance of excessive MR activation in promoting inflammation, fibrosis and heart disease as well as its role in modulating neuronal cell viability and brain function is now widely recognized. Despite considerable progress, the mechanisms of MR function in various cell-types are still poorly understood. Key modulators of MR function include the glucocorticoid receptor (GR), which may affect MR function by formation of heterodimers and by differential genomic and non-genomic responses on gene expression, and 11β-hydroxysteroid dehydrogenases (11β-HSDs), which determine the availability of intracellular concentrations of active glucocorticoids. In this review we attempted to provide an overview of the knowledge on MR expression with regard to the presence or absence of GR, 11β-HSD2 and 11β-HSD1/hexose-6-phosphate dehydrogenase (H6PDH) in various tissues and cell types. The consequences of cell-specific differences in the coexpression of MR with these proteins need to be further investigated in order to understand the role of this receptor in a given tissue as well as its systemic impact.

Consumption of oxygen: a mitochondrial-generated progression signal of advanced cancer

Changes in mitochondrial genome such as mutation, deletion and depletion are common in cancer and can determine advanced phenotype of cancer; however, detailed mechanisms have not been elucidated. We observed that loss of mitochondrial genome reversibly induced overexpression and activation of proto-oncogenic Ras, especially K-Ras 4A, responsible for the activation of AKT and ERK leading to advanced phenotype of prostate and breast cancer. Ras activation was induced by the overexpression of 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), the rate-limiting enzyme of the mevalonate pathway. Hypoxia is known to induce proteasomal degradation of HMGR. Well differentiated prostate and breast cancer cells with high mitochondrial DNA content consumed a large amount of oxygen and induced hypoxia. Loss of mitochondrial genome reduced oxygen consumption and increased in oxygen concentration in the cells. The hypoxic-to-normoxic shift led to the overexpression of HMGR through inhibiting proteasomal degradation. Therefore, reduction of mitochondrial genome content induced overexpression of HMGR through hypoxic to normoxic shift and subsequently the endogenous induction of the mevalonate pathway activated Ras that mediates advanced phenotype. Reduction of mitochondrial genome content was associated with the aggressive phenotype of prostate cancer in vitro cell line model and tissue specimens in vivo. Our results elucidate a coherent mechanism that directly links the mitochondrial genome with the advanced progression of the disease.

Rac1 GTPase in rodent kidneys is essential for salt-sensitive hypertension via a mineralocorticoid receptor-dependent pathway

Hypertension is a leading contributor to cardiovascular mortality worldwide. Despite this, its underlying mechanism(s) and the role of excess salt in cardiorenal dysfunction are unclear. Previously, we have identified cross-talk between mineralocorticoid receptor (MR), a nuclear transcription factor regulated by the steroid aldosterone, and the small GTPase Rac1, which is implicated in proteinuric kidney disease. We here show that high-salt loading activates Rac1 in the kidneys in rodent models of salt-sensitive hypertension, leading to blood pressure elevation and renal injury via an MR-dependent pathway. We found that a high-salt diet caused renal Rac1 upregulation in salt-sensitive Dahl (Dahl-S) rats and downregulation in salt-insensitive Dahl (Dahl-R) rats. Despite a reduction of serum aldosterone levels, salt-loaded Dahl-S rats showed increased MR signaling in the kidneys, and Rac1 inhibition prevented hypertension and renal damage with MR repression. We further demonstrated in aldosterone-infused rats as well as adrenalectomized Dahl-S rats with aldosterone supplementation that salt-induced Rac1 and aldosterone acted interdependently to cause MR overactivity and hypertension. Finally, we confirmed the key role of Rac1 in modulating salt susceptibility in mice lacking Rho GDP-dissociation inhibitor α. Therefore, our data identify Rac1 as a determinant of salt sensitivity and provide insights into the mechanism of salt-induced hypertension and kidney injury.

Effects of mineralocorticoid receptor blockade on glucocorticoid-induced renal injury in adrenalectomized rats

OBJECTIVES

Aldosterone is well recognized as the selective physiological ligand for mineralocorticoid receptor in epithelia. However, in-vitro studies have demonstrated that the affinity of aldosterone and glucocorticoids for mineralocorticoid receptor is similar. We hypothesized that glucocorticoids are involved in the development of renal injury through an mineralocorticoid receptor-dependent mechanism.

METHODS AND RESULTS

Uninephrectomized (UNX) rats were treated with 1% NaCl and divided into three groups: vehicle, bilateral adrenalectomy (ADX) + hydrocortisone (HYDRO; 5 mg/kg/day, s.c.), ADX + HYDRO + eplerenone (0.125% in chow). HYDRO-treated UNX-ADX rats showed increased blood pressure and urinary albumin-to-creatinine ratio with an increase in the expression of the mineralocorticoid receptor target genes, serum and glucocorticoid-regulated kinases-1 and Na+/H+ exchanger isoform-1, in renal tissues. HYDRO treatment induced morphological changes in the kidney, including glomerulosclerosis and podocyte injury. Treatment with eplerenone markedly decreased the gene expression and reduced the albuminuria and renal morphological changes. In contrast, dexamethasone (0.2 mg/kg per day, s.c.) + UNX + ADX induced hypertension and albuminuria in different groups of rats. Eplerenone failed to ameliorate these changes.

CONCLUSIONS

Our findings indicate that chronic glucocorticoid excess could activate mineralocorticoid receptor and, in turn, induce the development of renal injury.

A PPARγ agonist inhibits aldosterone-induced mesangial cell proliferation by blocking ROS-dependent EGFR intracellular signaling

Mesangial cell (MC) proliferation is a key feature in the pathogenesis of a number of renal diseases. Peroxisome proliferator-activated receptor-γ (PPARγ) has attracted considerable attention for its effects on stimulating cell differentiation and on inducing cell cycle arrest. We previously showed that aldosterone (Aldo) stimulates MC proliferation via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, which was dependent on reactive oxygen species (ROS)-mediated epithelial growth factor receptor (EGFR) transactivation (Huang S, Zhang A, Ding G, and Chen R. Am J Physiol Renal Physiol 296: F1323–F1333, 2009). In this study, we examined whether the PPARγ agonist rosiglitazone inhibited Aldo-induced MC proliferation by modulating ROS-dependent EGFR intracellular signaling. Rosiglitazone at 1–10 μM dose dependently inhibited Aldo-induced MC proliferation of cultured mouse MCs. The inhibitory effect was blocked by the PPARγ antagonist PD-68235, indicating that the rosiglitazone effect acted through PPARγ activation. Rosiglitazone also arrested Aldo-induced cell cycle progression and suppressed expression of cyclins D1 and A. Moreover, rosiglitazone dose dependently blocked Aldo-induced ROS production, EGFR phosphorylation, and PI3K/Akt activation. These results suggest that the PPARγ agonist rosiglitazone may inhibit Aldo-induced MC proliferation directly, by affecting ROS/EGFR/PI3K/Akt signaling pathways and cell cycle-regulatory proteins. PPARγ might be a novel therapeutic target against glomerular diseases.

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. RhoGDIalpha 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.

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.

New insights into the renoprotective actions of the renin inhibitor aliskiren in experimental renal disease

The renin-angiotensin-aldosterone system (RAAS) has a central function in the regulation of blood pressure. Aliskiren, the first direct renin inhibitor to be approved for the treatment of hypertension, blocks the RAAS at its point of activation. As renin inhibition acts at the top of the RAAS cascade, this mechanism has been proposed to offer advantages over existing modes of RAAS blockade. The RAAS is also considered to be a major factor in the pathogenesis of many renal diseases, especially diabetic nephropathy (DN), the main cause of end-stage renal disease. Existing therapies to block the RAAS slow the progression of DN, but they do not halt the disease. Therefore, more effective modes of interventions are needed. Studies to determine the efficacy of aliskiren in human renal disease are in progress. This review summarizes in vivo studies in which the efficacy of aliskiren was tested in experimental models of renal disease, and presents in vitro studies that provide insights into the possible mechanisms by which aliskiren confers renoprotection in animals. These works are discussed in the framework of the intrarenal RAAS and suggest that aliskiren may act by unique renoprotective mechanisms.

Aldosterone abrogates nuclear factor kappaB-mediated tumor necrosis factor alpha production in human neutrophils via the mineralocorticoid receptor

Mineralocorticoid receptor (MR) activation by aldosterone controls salt homeostasis and inflammation in several tissues and cell types. Whether or not a functional MR exists in polymorphonuclear neutrophils is unknown. We investigated the hypothesis that aldosterone modulates inflammatory neutrophil responses via the MR. By flow cytometry, Western blot analysis, and microscopy, we found that neutrophils possess MR. Preincubation with aldosterone (10(-11) to 10(-6) M) dose-dependently inhibited nuclear factor kappaB activation in interleukin (IL)-8- and granulocyte/macrophage colony-stimulating factor-treated neutrophils on fibronectin by IkappaBalpha Western blotting, electrophoretic mobility shift assay, and RT-PCR for IkappaBalpha mRNA. Aldosterone had no effect on tumor necrosis factor alpha- and lipopolysaccharide-mediated nuclear factor kappaB activation or on IL-8- and granulocyte/macrophage colony-stimulating factor-induced extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, or phosphatidylinositol 3-kinase/Akt activation. Spironolactone prevented nuclear factor kappaB inhibition, indicating an MR-specific aldosterone effect. By RT-PCR, we found that neutrophils have 11beta-hydroxysteroid dehydrogenase. Tumor necrosis factor alpha, which is controlled by nuclear factor kappaB, increased in the cell supernatant with IL-8 treatment. Aldosterone completely prevented this effect. RT-PCR showed a strong tumor necrosis factor alpha mRNA increase with IL-8 that was blocked by aldosterone, excluding the possibility that the tumor necrosis factor alpha increase was merely a consequence of secretion. Finally, conditioned medium from IL-8-treated neutrophils increased intercellular adhesion molecule-1 expression on endothelial cells and subsequently the adhesion of IL-8-treated neutrophils to endothelial cells. These effects were reduced when conditioned medium from aldosterone-pretreated neutrophils was used, and spironolactone blocked the aldosterone effect. Our data indicate that a functional MR exists in neutrophils mediating antiinflammatory effects that are at work when neutrophils interact with endothelial cells. These data could be relevant to MR-blockade treatment protocols.

Protein kinase D stabilizes aldosterone-induced ERK1/2 MAP kinase activation in M1 renal cortical collecting duct cells to promote cell proliferation

Aldosterone elicits transcriptional responses in target tissues and also rapidly stimulates the activation of protein kinase signalling cascades independently of de novo protein synthesis. Here we investigated aldosterone-induced cell proliferation and extra-cellular regulated kinase 1 and 2 (ERK1/2) mitogen activated protein (MAP) kinase signalling in the M1 cortical collecting duct cell line (M1-CCD). Aldosterone promoted the proliferative growth of M1-CCD cells, an effect that was protein kinase D1 (PKD1), PKCdelta and ERK1/2-dependent. Aldosterone induced the rapid activation of ERK1/2 with peaks of activation at 2 and 10 to 30 min after hormone treatment followed by sustained activation lasting beyond 120 min. M1-CCD cells suppressed in PKD1 expression exhibited only the early, transient peaks in ERK1/2 activation without the sustained phase. Aldosterone stimulated the physical association of PKD1 with ERK1/2 within 2 min of treatment. The mineralocorticoid receptor (MR) antagonist RU28318 inhibited the early and late phases of aldosterone-induced ERK1/2 activation, and also aldosterone-induced proliferative cell growth. Aldosterone induced the sub-cellular redistribution of ERK1/2 to the nuclei at 2 min and to cytoplasmic sites, proximal to the nuclei after 30 min. This sub-cellular distribution of ERK1/2 was inhibited in cells suppressed in the expression of PKD1.

New aspects of rapid aldosterone signaling

Aldosterone, the endogenous ligand of the mineralocorticoid receptor (MR) in humans, is a steroid hormone that regulates salt and water homeostasis. Recently, additional pathophysiological effects in the renocardiovascular system have been identified. Besides genomic effects mediated by activated MR, rapid aldosterone actions that are independent of translation and transcription have been documented. While these nongenomic actions influence electrolyte homeostasis, pH and cell volume in classical MR target organs, they also participate in pathophysiological effects in the renocardiovascular system causing endothelial dysfunction, inflammation and remodeling. The mechanisms conveying these rapid effects consist of a multitude of signaling molecules and include a cross-talk with genomic aldosterone effects as well as with angiotensin II and epidermal growth factor receptor signaling. Rapid corticosteroid signaling via the MR has also been demonstrated in the brain. Altogether, the function of nongenomic aldosterone effects seems to be to modulate other signaling cascades, depending on the surrounding milieu.

Mineralocorticoid receptor blockade and calcium channel blockade have different renoprotective effects on glomerular and interstitial injury in rats

We hypothesized that combination treatment with the mineralocorticoid receptor antagonist eplerenone and the calcium channel blocker amlodipine elicits better renoprotective effects than monotherapy with either drug, via different mechanisms in Dahl salt-sensitive (DS) hypertensive rats. DS rats were fed a high-salt diet (4% NaCl) for 10 wk and were treated with vehicle ( n = 12), eplerenone (50 mg·kg−1·day−1, po, n = 12), amlodipine (3 mg·kg−1·day−1, po, n = 12), or eplerenone plus amlodipine ( n = 12) after 2 wk of salt feeding. Vehicle-treated DS rats developed proteinuria, which was attenuated by eplerenone or amlodipine. Interestingly, eplerenone attenuated the glomerulosclerosis and podocyte injury, but amlodipine did not. Conversely, treatment with amlodipine markedly improved interstitial fibrosis, while the effect of eplerenone was minimal. Combination treatment markedly improved proteinuria, glomerulosclerosis, podocyte injury, and interstitial fibrosis in DS rats. Renal hypoxia estimated by pimonidazole, vascular endothelial growth factor expression, and density of peritubular endothelial cells was exacerbated by salt feeding. Amlodipine, either as monotherapy or in combination, ameliorated the renal hypoxia, whereas eplerenone treatment had no effect. In conclusion, both eplerenone and amlodipine attenuated renal injuries in high salt-fed DS rats, but the targets for renoprotection differed between these two drugs, with eplerenone predominantly acting on glomeruli and amlodipine acting on interstitium. The combination of eplerenone and amlodipine improved renal injury more effectively than either monotherapy in high salt-fed DS rats, presumably by achieving their own renoprotective effects.

Aldosterone-induced mesangial cell proliferation is mediated by EGF receptor transactivation

Aldosterone (Aldo) stimulates glomerular mesangial cell (MC) proliferation, in part, through an ERK1/2-dependent pathway. In this study, we examined whether Aldo activation of ERK1/2 in MC is mediated through redox-dependent EGF receptor (EGFR) transactivation, as well as the involvement of other signaling mechanisms in Aldo-induced MC proliferation. Aldo increased human MC proliferation, as determined by [3H]thymidine incorporation and cell counts. This increase in proliferation was blocked by inhibition of the mineralocorticoid receptor (MR). Continuing our observations downstream in the signaling pathway, we examined the ability of Aldo to activate both the Ras/MAPK and the PI3K signaling pathways. Aldo increased Ki-RasA and Ki-RasA:GTP levels, and sequentially phosphorylated c-Raf, MAPK kinase (MEK1/2), and ERK1/2. Ki-RasA small interfering RNA (siRNA), the c-Raf inhibitor GW5074, and the MEK1/2 inhibitor PD98059 reduced Aldo-induced cell proliferation by ∼65%. Aldo also increased phosphorylation of PI3K, Akt, the mammalian target of rapamycin (mTOR), and the 70-kDa ribosomal S6 kinase (p70S6K1). Inhibition of the PI3K pathways by the selective PI3K inhibitor LY 294002, an Akt inhibitor, or the mTOR inhibitor rapamycin reduced cell proliferation by 51%. Combining LY 294002 and PD98059 completely blocked Aldo-induced MC proliferation. Next, we confirmed that Aldo exerts its effect on MAPK and PI3K activation, as well as on cell proliferation, by activating the EGFR. Pretreatment with the EGFR antagonist AG1478 inhibited MC proliferation, as well as the activation of Ras/MAPK and PI3K/Akt, suggesting that Ras/MAPK and PI3K/Akt activation occur downstream of EGFR activation. Finally, we examined the role of reactive oxygen species (ROS) in Aldo-induced transactivation of the EGFR. Aldo-induced ROS were predominantly generated by mitochondria. Pretreatment with the antioxidant N-acetyl-l-cysteine, catalase, SOD, mitochondrial respiratory chain complex I inhibitor rotenone (Rot), NADPH oxidase inhibitor apocynin, and DPI significantly inhibited Aldo-stimulated MC proliferation as well as EGFR transactivation. However, Rot reduced MC proliferation more potently than apocynin and DPI. In conclusion, Aldo stimulated cell proliferation through MR-mediated, redox-sensitive EGFR transactivation, which was dependent on the Ki-RasA/c-Raf/MEK/ERK and PI3K/Akt/mTOR/p70S6K1 signaling pathways in human MCs.

Aldosterone and progression of kidney disease

Experimental evidence indicates that aldosterone, besides its mineralcorticoid properties, directly contributes to accelerate renal damage through promotion of cell growth, fibrosis and inflammation. As a consequence, attenuation of growth-promoting and fibroproliferative effects of aldosterone might contribute to slow progression of chronic renal injury. Preliminary clinical observations have documented that aldosterone blockers added to angiotensin-converting enzyme inhibitor- and/or angiotensin receptor blocker-based regimens exerted significant antiproteinuric effects in patients with diabetic and nondiabetic nephropathies. Further studies in larger cohorts are now required to definitively address the safety and efficacy of aldosterone antagonism in patients with chronic kidney diseases.

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.

Aldosterone induces mesangial cell apoptosis both in vivo and in vitro

Both clinical and experimental reports indicate that aldosterone contributes to the progression of renal failure independent of its hemodynamic effects. In the present study, we evaluated effect of aldosterone on human mesangial cell (MC) growth. Aldosterone induced apoptotic and mitogenic effects on MCs. Aldosterone promoted MC apoptosis in a dose- and time-dependent manner. Spironolactone, a mineralocorticoid receptor antagonist, inhibited aldosterone-induced MC apoptosis. Similarly, antioxidants and free radical scavengers partially attenuated proapoaptotic effects of aldosterone. Aldosterone also enhanced dephosphorylation of phospho-Bad and accumulation of cytosolic cytochrome c in MCs. In in vivo studies, rats were randomly assigned to receive normal saline, aldosterone, or eplerenone + aldosterone for 28 days. Systolic blood pressure, urinary albumin excretion rate, serum creatinine, and aldosterone were measured. Aldosterone-infused rats developed elevated systolic blood pressure and albuminuria when compared with control rats. Aldosterone-treated rats also showed greater numbers of apoptosed MCs. This proapoptotic effect of aldosterone was inhibited by eplerenone, a selective aldosterone antagonist. These findings suggest that aldosterone, besides its hemodynamic effects, may also directly contribute to the occurrence of MC apoptosis.