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

Renoprotective Effects of Mineralocorticoid Receptor Antagonists Against Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a growing epidemic worldwide and a leading cause of end-stage kidney disease. Mineralocorticoid receptor (MR) blockade using Finerenone is a recently approved therapeutic approach to slow down the progression of DKD in patients with type 2 diabetes in addition to other therapies such as angiotensin-II converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), sodium-glucose co-transporter 2 (SGLT2) inhibitors, and glucagon-like peptide 1 (GLP-1) analogs. This review elaborates on the pathophysiologic pathways activated by aldosterone (the human mineralocorticoid) in DKD, the pharmacology of three different generations of mineralocorticoid receptor antagonists (MRAs), specifically, spironolactone, eplerenone, and finerenone, and the mechanisms by which these MRAs elicit their protective effects on the kidney under diabetic settings.

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.

Role of high-salt diet in non-alcoholic fatty liver disease: a mini-review of the evidence

With the rising incidence of both obesity and diabetes, non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. However, lifestyle intervention remains to be an effective approach for NAFLD due to lack of therapeutic medication. Recently, salt, an essential micronutrient free of calories, has raised a global concern owing to its wide-range healthy relevance. Accumulated evidence has suggested that a long-term high-salt diet (HSD) independently increases the risk of NAFLD. In the past decades, a number of studies have been reported regarding the mechanism of much investigation concerning HSD-induced NAFLD. Here, we review the updates in epidemiology and molecular mechanism of HSD-induced NAFLD and provide a novel insight into the role of HSD in the regulation of lipid metabolism.

Evaluation of symmetric dimethylarginine and creatinine in dogs with primary hypoadrenocorticism receiving long-term mineralocorticoid replacement therapy

OBJECTIVES

To investigate kidney function by determining serum symmetric dimethylarginine (sSDMA) and serum creatinine (sCr) concentrations in dogs with primary hypoadrenocorticism (PH) receiving long-term mineralocorticoid replacement therapy.

METHODS

Dogs with PH receiving a minimum of 12 months of either desoxycorticosterone pivalate or fludrocortisone acetate were included in the study provided that banked frozen serum samples were available for sSDMA analysis. sCr concentrations were retrieved from the medical records. In dogs still alive and presented for regular re-evaluations and in newly diagnosed patients, blood was prospectively collected for sSDMA and sCr determination.

RESULTS

Thirty-two dogs met the inclusion criteria. The treatment time ranged from 12 to 146 months after initial diagnosis (median, 55.5 months). The majority of dogs had normal sSDMA and sCr concentrations throughout the hormone replacement treatment. Both sSDMA and sCr concentrations were persistently elevated in three of 32 dogs. Further workup confirmed chronic kidney disease (CKD) in all three dogs.

CONCLUSIONS

Based on these data, the prevalence of CKD could be higher in dogs with PH receiving long-term mineralocorticoid replacement treatment than in the general dog population. However, additional studies with a larger number of dogs are needed to confirm it.

Increased SGK1 activity potentiates mineralocorticoid/NaCl-induced kidney injury

Serum and glucocorticoid-regulated kinase 1 (SGK1) stimulates aldosterone-dependent renal Na⁺ reabsorption and modulates blood pressure. In addition, genetic ablation or pharmacological inhibition of SGK1 limits the development of kidney inflammation and fibrosis in response to excess mineralocorticoid signaling. In this work, we tested the hypothesis that a systemic increase in SGK1 activity would potentiate mineralocorticoid/salt-induced hypertension and kidney injury. To that end, we used a transgenic mouse model with increased SGK1 activity. Mineralocorticoid/salt-induced hypertension and kidney damage was induced by unilateral nephrectomy and treatment with deoxycorticosterone acetate and NaCl in the drinking water for 6 wk. Our results show that although SGK1 activation did not induce significantly higher blood pressure, it produced a mild increase in glomerular filtration rate, increased albuminuria, and exacerbated glomerular hypertrophy and fibrosis. Transcriptomic analysis showed that extracellular matrix- and immune response-related terms were enriched in the downregulated and upregulated genes, respectively, in transgenic mice. In conclusion, we propose that systemically increased SGK1 activity is a risk factor for the development of mineralocorticoid-dependent kidney injury in the context of low renal mass and independently of blood pressure.NEW & NOTEWORTHY Increased activity of the protein kinase serum and glucocorticoid-regulated kinase 1 may be a risk factor for accelerated renal damage. Serum and glucocorticoid-regulated kinase 1 expression could be a marker for the rapid progression toward chronic kidney disease and a potential therapeutic target to slow down the process.

Decrease of nitric oxide and increase in diastolic blood pressure are two events that affect renal function in dogs with pituitary dependent hyperadrenocorticism

Hyperadrenocorticism is a frequent disease in dogs. The excess of circulating cortisol affects different organs and metabolic pathways, producing severe adverse effects that endanger the animal’s life. Among these effects, hypertension and renal damage can be mentioned. A group of 20 dogs with pituitary dependent hyperadrenocorticism (PDH) and 12 control dogs were used to study the following parameters: cortisol and nitric oxide (NO nit/nit) concentrations, diastolic and systolic blood pressure, renal artery resistance index by Doppler ultrasound, the rate of glomerular filtration by radio-renogram excretion and the presence of proteins in urine. Dogs with PDH showed a significantly lower NO nit/nit (P<0.0001) than the controls and this correlated with high values of diastolic and systolic pressure (r = -0.87; P<0.0001 and r = -0.81; P<0.0001 respectively). Most dogs (80%) are hypertensive mainly due to an increase in diastolic pressure, which correlated positively with the UPC (r = 0.8; P<0.001) and negatively with the glomerular rate of filtration (r = -0.58; P=0.007). Systolic pressure only increased in 60% of the cases and did not correlate with the mentioned variables. In PDH the decrease of NO affects blood pressure. The diastolic pressure would seem to have the greatest impact on the kidneys, therefore its evaluation and control are important to avoid and/or control renal damage.

Sex-Specific Mechanisms of Resistance Vessel Endothelial Dysfunction Induced by Cardiometabolic Risk Factors

Background

The incidence of obesity is rising, particularly among women. Microvascular dysfunction is more common with female sex, obesity, and hyperlipidemia and predicts adverse cardiovascular outcomes, but the molecular mechanisms are unclear. Because obesity is associated with mineralocorticoid receptor (MR) activation, we tested the hypothesis that MR in endothelial cells contribute to sex differences in resistance vessel dysfunction in response to cardiometabolic risk factors.

Methods and Results

Male and female endothelial cell–specific MR knockout mice and MR‐intact littermates were randomized to high‐fat‐diet–induced obesity or obesity with hyperlipidemia induced by adeno‐associated virus–based vector targeting transfer of the mutant stable form (DY mutation) of the human PCSK9 (proprotein convertase subtilisin/kexin type 9) gene and compared with control diet. Female but not male mice were sensitive to obesity‐induced endothelial dysfunction, whereas endothelial function was impaired in obese hyperlipidemic males and females. In males, obesity or hyperlipidemia decreased the nitric oxide component of vasodilation without altering superoxide production or endothelial nitric oxide synthase expression or phosphorylation. Decreased nitric oxide content in obese males was overcome by enhanced endothelium‐derived hyperpolarization–mediated relaxation along with increased SK3 expression. Conversely, in females, endothelium‐derived hyperpolarization was significantly impaired by obesity with lower IK1 expression and by hyperlipidemia with lower IK1 and SK3 expression, loss of H₂O₂‐mediated vasodilation, and increased superoxide production. Endothelial cell–MR deletion prevented endothelial dysfunction induced by risk factors only in females. Rather than restoring endothelium‐derived hyperpolarization in females, endothelial cell–MR deletion enhanced nitric oxide and prevented hyperlipidemia‐induced oxidative stress.

Conclusions

These data reveal distinct mechanisms driving resistance vessel dysfunction in males versus females and suggest that personalized treatments are needed to prevent the progression of vascular disease in the setting of obesity, depending on both the sex and the metabolic profile of each patient.

Aldosterone is involved in the pathogenesis of obesity-related glomerulopathy through activation of Wnt/β-catenin signaling in podocytes

Obesity-related glomerulopathy (ORG) is morphologically characterized by glomerulomegaly with or without observable focal segmental glomerulosclerosis under light microscope, with decreased podocyte density and number, and with increased foot‑process width observed under electron microscope. The severity of podocyte injury is correlated with the degree of proteinuria and renal dysfunction. However, the pathogenesis of ORG is not well understood. The aim of the present study was to explore the possible pathogenic role of aldosterone (ALDO) in ORG. In the in vivo animal experiments, body weight, Lee's obesity index, abdominal fat index, urinary protein excretion, average glomerular diameter were significantly increased, the mRNA and protein expression of podocyte‑associated molecules including nephrin, podocin, podoplanin and podocalyxin were significantly reduced, and the Wnt/β‑catenin signaling pathway was activated in ORG model mice compared with the Control mice, whereas the administration of spironolactone significantly ameliorated these effects. In the in vitro experiments on cultured podocytes, the mRNA and protein expression levels of the aforementioned podocyte‑associated molecules were significantly downregulated and the Wnt/β‑catenin signaling pathway was activated following ALDO stimulation, whereas eplerenone significantly attenuated all the above effects. Dickkopf‑related protein 1 (DKK1), an inhibitor of Wnt/β‑catenin signaling pathway, also reduced the effects of ALDO exposure on the expression of podocyte‑associated molecules. The present study hypothesized that ALDO may be involved in the pathogenesis of ORG through the activation of Wnt/β‑catenin signaling pathway in podocytes.

Synergistic Interaction of Hypertension and Diabetes in Promoting Kidney Injury and the Role of Endoplasmic Reticulum Stress

Diabetes mellitus and hypertension are major risk factors for chronic kidney injury, together accounting for >70% of end-stage renal disease. In this study, we assessed interactions of hypertension and diabetes mellitus in causing kidney dysfunction and injury and the role of endoplasmic reticulum (ER) stress. Hypertension was induced by aorta constriction (AC) between the renal arteries in 6-month-old male Goto-Kakizaki (GK) type 2 diabetic and control Wistar rats. Fasting plasma glucose averaged 162±11 and 87±2 mg/dL in GK and Wistar rats, respectively. AC produced hypertension in the right kidney (above AC) and near normal blood pressure in the left kidney (below AC), with both kidneys exposed to the same levels of glucose, circulating hormones, and neural influences. After 8 weeks of AC, blood pressure above the AC (and in the right kidney) increased from 109±1 to 152±5 mm Hg in GK rats and from 106±4 to 141±5 mm Hg in Wistar rats. The diabetic-hypertensive right kidneys in GK-AC rats had much greater increases in albumin excretion and histological injury compared with left kidneys (diabetes mellitus only) of GK rats or right kidneys (hypertension only) of Wistar-AC rats. Marked increases in ER stress and oxidative stress indicators were observed in diabetic-hypertensive kidneys of GK-AC rats. Inhibition of ER stress with tauroursodeoxycholic acid for 6 weeks reduced blood pressure (135±4 versus 151±4 mm Hg), albumin excretion, ER and oxidative stress, and glomerular injury, while increasing glomerular filtration rate in hypertensive-diabetic kidneys. These results suggest that diabetes mellitus and hypertension interact synergistically to promote kidney dysfunction and injury via ER stress.

Association of Urinary Sodium Excretion With Insulin Resistance in Korean Adolescents: Results From the Korea National Health and Nutrition Examination Survey 2009-2010

High sodium intake is a well-known risk factor for elevated blood pressure and is responsible for a higher incidence of cardiovascular events. Reports have suggested an association of sodium intake with insulin resistance (IR) and type 2 diabetes mellitus in adults. However, evidence on an association between sodium intake assessed on the basis of urinary sodium excretion and IR in adolescents is scarce. The present study aimed at investigating the association between urinary sodium excretion and IR among South Korean adolescents.This population-based, cross-sectional study analyzed the data obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) 2009 to 2010. The data of a total of 1353 adolescents (779 boys and 574 girls) were included in the final analysis. Spot urine samples were collected, and urinary sodium excretion was estimated by using the urinary sodium concentration (U[Na]), U[Na] to urinary creatinine ratio (U[Na]/Cr), and U[Na] to specific gravity unit (SGU) ratio (U[Na]/SGU). IR was assessed by using the homeostasis model assessment of IR (HOMA-IR). Hierarchical multivariable logistic regression analysis was performed to assess the risk for a high HOMA-IR according to urinary sodium excretion.The mean levels of U[Na], U[Na]/Cr, and U[Na]/SGU were significantly higher in subjects in the highest HOMA-IR quartile (Q4) than in subjects in the lowest, second, or third quartiles (Q1-3) of HOMA-IR. The mean values of HOMA-IR and several cardiometabolic parameters tended to progressively increase with the U[Na], U[Na]/Cr, and U[Na]/SGU quartiles. Q3 of U[Na] was at a significantly higher risk than Q1 of U[Na] of an association with Q4 of HOMA-IR, after adjustment for confounding variables. Q3 and Q4 of U[Na]/Cr and U[Na]/SGU, respectively, had significantly higher risks, than the respective Q1s, of an association with Q4 of HOMA-IR. The risk of an association with Q4 of HOMA-IR demonstrated significantly increasing trends with increasing quartiles of U[Na], U[Na]/Cr, and U[Na]/SGU irrespective of confounding factors.Urinary sodium excretion was positively associated with IR in South Korean adolescents. The monitoring and control of urinary sodium excretion may be recommended as an important intervention for the prevention of IR and related diseases in adolescents.

Context-dependent mechanisms modulating aldosterone signaling in the kidney

The aldosterone-mineralocorticoid receptor (MR) system serves as the major regulator of fluid homeostasis, and is an important drug target for the treatment of hypertension, heart failure, and chronic kidney disease. While the ligand aldosterone plays a central role in facilitating MR activity, recent studies have revealed that MR signaling is modulated through distinct mechanisms at the levels of the receptor and the downstream targets. Notably, phosphorylation of the ligand-binding domain in MR regulates the ability of the receptor to bind to ligand in renal intercalated cells, providing an additional layer of regulation that allows the cell-selective control of MR signaling. These mechanisms are involved in the context-dependent effects of aldosterone in the distal nephron. In this article, the recent progress in the understanding of mechanisms regulating the action of aldosterone is discussed, focusing on the connecting tubules and collecting duct in the kidney.

The multifaceted mineralocorticoid receptor

The primary adrenal cortical steroid hormones, aldosterone, and the glucocorticoids cortisol and corticosterone, act through the structurally similar mineralocorticoid (MR) and glucocorticoid receptors (GRs). Aldosterone is crucial for fluid, electrolyte, and hemodynamic homeostasis and tissue repair; the significantly more abundant glucocorticoids are indispensable for energy homeostasis, appropriate responses to stress, and limiting inflammation. Steroid receptors initiate gene transcription for proteins that effect their actions as well as rapid non-genomic effects through classical cell signaling pathways. GR and MR are expressed in many tissues types, often in the same cells, where they interact at molecular and functional levels, at times in synergy, others in opposition. Thus the appropriate balance of MR and GR activation is crucial for homeostasis. MR has the same binding affinity for aldosterone, cortisol, and corticosterone. Glucocorticoids activate MR in most tissues at basal levels and GR at stress levels. Inactivation of cortisol and corticosterone by 11β-HSD2 allows aldosterone to activate MR within aldosterone target cells and limits activation of the GR. Under most conditions, 11β-HSD1 acts as a reductase and activates cortisol/corticosterone, amplifying circulating levels. 11β-HSD1 and MR antagonists mitigate inappropriate activation of MR under conditions of oxidative stress that contributes to the pathophysiology of the cardiometabolic syndrome; however, MR antagonists decrease normal MR/GR functional interactions, a particular concern for neurons mediating cognition, memory, and affect.

High sodium intake is associated with increased glucocorticoid production, insulin resistance and metabolic syndrome

OBJECTIVE

High sodium (HS) diet is associated with hypertension (HT) and insulin resistance (IR). We evaluated whether HS diet was associated with a dysregulation of cortisol production and metabolic syndrome (MetS).

PATIENTS AND MEASUREMENTS

We recruited 370 adults (18-85 years, BMI 29·3 ± 4·4 kg/m(2) , 70% women, 72% HT, 61% MetS). HS diet (urinary sodium >150 mEq/day) was observed in 70% of subjects. We measured plasma hormones, lipid profile, urinary free cortisol (UFC) and cortisol tetrahydrometabolites (THM).

RESULTS

Urinary sodium was correlated with UFC (r = +0·45, P < 0·001), cortisol THM (r = +0·41, P < 0·001) and inversely with adiponectin, HDL and aldosterone, after adjusting by age, gender and BMI. Subjects with high, compared with adequate sodium intake (50-149 mEq/day) had higher UFC (P < 0·001), THM (P < 0·001), HOMA-IR (P = 0·04), HT (81% vs 50%, P < 0·001), MetS (69% vs 41%, P < 0·001) and lower adiponectin (P = 0·003). A multivariate predictive model adjusted by confounders showed a high discriminative capacity for MetS (ROC curve 0·878) using four clinical variables: HS intake [OR = 5·6 (CI 2·3-15·3)], HOMA-IR [OR 1·7 (1·3-2·2)] cortisol THM [OR 1·2 (1·1-1·4)] and adiponectin [OR = 0·9 (0·8-0·9)], the latter had a protective effect.

CONCLUSIONS

High sodium diet was associated with increased urinary cortisol and its metabolites. Also, HS diet was associated with HT, insulin resistance, dyslipidaemia and hypoadiponectinaemia, even when adjusting by confounding variables. Further, we observed that high salt intake, IR and higher cortisol metabolites, alone or combined in a clinical simple model, accurately predicted MetS status, suggesting an additive mechanism in obesity-related metabolic disorders.

Mineralocorticoid receptor blockade-a novel approach to fight hyperkalaemia in chronic kidney disease

Hyperkalaemia continues to be a major hazard of mineralocorticoid receptor blockade in an effort to retard the progression of chronic kidney disease (CKD). In cardiac patients on mineralocorticoid receptor blockade, RLY-5016 which captures K⁺ in the colon has been effective in reducing the risk of hyperkalaemia. This compound might be useful in CKD as well.

Podocyte energy metabolism and glomerular diseases

Mitochondria are crucial organelles that produce and deliver adenosine triphosphate (ATP), by which all cellular processes are driven. Although the mechanisms that control mitochondrial biogenesis, function and dynamics are complex process and vary among different cell types, recent studies provided many new discoveries in this field. Podocyte injury is a crucial step in the development of a large number of glomerular diseases. Glomerular podocytes are unique cells with complex foot processes that cover the outer layer of the glomerular basement membrane, and are the principle cells composing filtration barriers of glomerular capillaries. Little is known on the modalities and the regulation of podocyte's energetics as well as the type of energy substrate primarily used for their activity, recent studies revealed that dysfunction of energy transduction in podocytes may underlie the podocyte injury associated with numerous glomerular diseases. We herein review and discuss the importance of a fine regulation of energy metabolism in podocytes for maintaining their cellular structure and related kidney function. In the future, understanding these mechanisms will open up new areas of treatment for glomerular diseases.

Human red blood cells alterations in primary aldosteronism

CONTEXT

Aldosterone (Aldo) effects include NADPH oxidase activation involved in Aldo-related oxidative stress. Red blood cells (RBCs) are particularly sensitive to oxidative assault, and both the formation of high molecular weight aggregates (HMWAs) and the diamide-induced Tyr phosphorylation (Tyr-P) level of membrane band 3 can be used to monitor their redox status.

OBJECTIVE

The Aldo-related alterations in erythrocytes were evaluated by comparing in vitro evidence.

DESIGN

This was a multicenter comparative study.

STUDY PARTICIPANTS

The study included 12 patients affected by primary aldosteronism (PA) and 6 healthy control subjects (HCs), whose RBCs were compared with those of patients with PA. For in vitro experiments, RBCs from HCs were incubated with increasing Aldo concentrations.

MAIN OUTCOME MEASURES

The Tyr-P level, band 3 HMWA formation, and autologous IgG binding were evaluated.

RESULTS

In patients with PA, both Tyr-P levels and band 3 HMWAs were higher than those in HCs. RBCs from HCs were treated with increasing Aldo concentrations in both platelet-poor plasma (PPP) and charcoal-stripped (CS)-PPP. Results showed that Aldo had dose- and time-dependent effects on band 3 Tyr-P and HMWA formation in CS-PPP more than in PPP. These effects were almost completely prevented by canrenone or cortisol. Aldo-related membrane alterations led to increased autologous IgG binding.

CONCLUSIONS

Erythrocytes from patients with PA show oxidative-like stress evidenced by increased HMWA content and diamide-induced band 3 Tyr-P level. Aldo effects are mediated by the mineralocorticoid receptor, as suggested by the inhibitory effects of canrenone, an antagonist of Aldo. In CS-PPP, in which Aldo induces remarkable membrane alterations leading to IgG binding, Aldo may be responsible for premature RBC removal from circulation.

The ubiquitous mineralocorticoid receptor: clinical implications

Mineralocorticoid receptors (MR) exist in many tissues, in which they mediate diverse functions crucial to normal physiology, including tissue repair and electrolyte and fluid homeostasis. However, inappropriate activation of MR within these tissues, and especially in the brain, causes hypertension and pathological vascular, cardiac, and renal remodeling. MR binds aldosterone, cortisol and corticosterone with equal affinity. In aldosterone-target cells, co-expression with the 11β-hydroxysteroid dehydrogenase 2 (HSD2) allows aldosterone specifically to activate MR. Aldosterone levels are excessive in primary aldosteronism, but in conditions with increased oxidative stress, like CHF, obesity and diabetes, MR may also be inappropriately activated by glucocorticoids. Unlike thiazide diuretics, MR antagonists are diuretics that do not cause insulin resistance. Addition of MR antagonists to standard treatment for hypertension and cardiac or renal disease decreases end-organ pathology and sympathetic nerve activation (SNA), and increases quality of life indices.

Mechanisms regulating the ductus arteriosus

A patent ductus arteriosus (PDA) results in increased pulmonary blood flow and redistribution of flow to other organs. Several co-morbidities (i.e., necrotizing enterocolitis, intracranial hemorrhage, pulmonary edema/hemorrhage, bronchopulmonary dysplasia, and retinopathy) are associated with the presence of a PDA, but whether or not a PDA is responsible for their development is still unclear. In this review, comparative physiology between the full term and preterm newborn and the barriers preventing the necessary cascade of events leading to permanent constriction of the PDA are reviewed.