Cardiac Specific Increase in Aldosterone Production Induces Coronary Dysfunction in Aldosterone Synthase–Transgenic Mice

Effects of sacubitril-valsartan on remodelling, fibrosis and mitochondria in a murine model of isoproterenol-induced left ventricular dysfunction

BACKGROUND

Sacubitril/valsartan has been demonstrated to promote left ventricular (LV) reverse remodelling and improve outcomes in patients with heart failure (HF) with reduced ejection fraction (EF). Its molecular and tissue effects have not been fully elucidated yet, due to the paucity of preclinical studies, mostly based on ischaemic models. We aimed to evaluate the effects of sacubitril/valsartan on LV remodelling, myocardial fibrosis and mitochondrial biology in a murine model of non-ischaemic LV dysfunction.

METHODS

Adult transgenic male mice with cardiac-specific hyperaldosteronism (AS mice) received subcutaneous isoproterenol injections to induce LV systolic dysfunction. After 7 days, mice were randomized to a 2-week treatment with saline (ISO-AS n = 15), valsartan (ISO + V n = 12) or sacubitril/valsartan (ISO + S/V n = 12). Echocardiography was performed at baseline, at day 7, and after each of the 2 weeks of treatment. After sacrifice at day 21, histological and immunochemical assays were performed. A control group of AS mice was also obtained (Ctrl-AS n = 8).

RESULTS

Treatment with sacubitril/valsartan, but not with valsartan, induced a significant improvement in LVEF (p = 0.009 vs ISO-AS) and fractional shortening (p = 0.032 vs ISO-AS) after 2- week treatment. In both ISO + V and ISO + S/V groups, a trend toward reduction of the cardiac collagen 1/3 expression ratio was detected. ISO + V and ISO + S/V groups showed a significant recovery of mitochondrial morphology and inner membrane function meant for oxidative phosphorylation.

CONCLUSION

In a murine model of non-ischaemic HF, sacubitril/valsartan proved to have beneficial effects on LV systolic function, and on cardiac energetics, by improving mitochondrial activity.

Molecular and Epigenetic Control of Aldosterone Synthase, CYP11B2 and 11-Hydroxylase, CYP11B1

Aldosterone and cortisol serve important roles in the pathogenesis of cardiovascular diseases and metabolic disorders. Epigenetics is a mechanism to control enzyme expression by genes without changing the gene sequence. Steroid hormone synthase gene expression is regulated by transcription factors specific to each gene, and methylation has been reported to be involved in steroid hormone production and disease. Angiotensin II or potassium regulates the aldosterone synthase gene, CYP11B2. The adrenocorticotropic hormone controls the 11b-hydroxylase, CYP11B1. DNA methylation negatively controls the CYP11B2 and CYP11B1 expression and dynamically changes the expression responsive to continuous stimulation of the promoter gene. Hypomethylation status of the CYP11B2 promoter region is seen in aldosterone-producing adenomas. Methylation of recognition sites of transcription factors, including cyclic AMP responsive element binding protein 1 or nerve growth factor-induced clone B, diminish their DNA-binding activity. A methyl-CpG-binding protein 2 cooperates directly with the methylated CpG dinucleotides of CYP11B2. A low-salt diet, treatment with angiotensin II, and potassium increase the CYP11B2 mRNA levels and induce DNA hypomethylation in the adrenal gland. A close association between a low DNA methylation ratio and an increased CYP11B1 expression is seen in Cushing's adenoma and aldosterone-producing adenoma with autonomous cortisol secretion. Epigenetic control of CYP11B2 or CYP11B1 plays an important role in autonomic aldosterone or cortisol synthesis.

DNA Methylation of the Angiotensinogen Gene, AGT, and the Aldosterone Synthase Gene, CYP11B2 in Cardiovascular Diseases

Angiotensinogen (AGT) and aldosterone play key roles in the regulation of blood pressure and are implicated in the pathogenesis of cardiovascular diseases. DNA methylation typically acts to repress gene transcription. The aldosterone synthase gene CYP11B2 is regulated by angiotensin II and potassium. DNA methylation negatively regulates AGT and CYP11B2 expression and dynamically changes in response to continuous promoter stimulation of each gene. High salt intake and excess circulating aldosterone cause DNA demethylation around the CCAAT-enhancer-binding-protein (CEBP) sites of the ATG promoter region, thereby converting the phenotype of AGT expression from an inactive to an active state in visceral adipose tissue and heart. A close association exists between low DNA methylation at CEBP-binding sites and increased AGT expression in salt-sensitive hypertensive rats. Salt-dependent hypertension may be partially affected by increased cardiac AGT expression. CpG dinucleotides in the CYP11B2 promoter are hypomethylated in aldosterone-producing adenomas. Methylation of recognition sequences of transcription factors, including CREB1, NGFIB (NR4A1), and NURR1 (NR4A2) diminish their DNA-binding activity. The methylated CpG-binding protein MECP2 interacts directly with the methylated CYP11B2 promoter. Low salt intake and angiotensin II infusion lead to upregulation of CYP11B2 expression and DNA hypomethylation in the adrenal gland. Treatment with the angiotensin II type 1 receptor antagonist decreases CYP11B2 expression and leads to DNA hypermethylation. A close association between low DNA methylation and increased CYP11B2 expression are seen in the hearts of patients with hypertrophic cardiomyopathy. These results indicate that epigenetic regulation of both AGT and CYP11B2 contribute to the pathogenesis of cardiovascular diseases.

Serum Aldosterone as Predictor of Progression of Coronary Heart Disease in Patients Without Signs of Heart Failure After Acute Myocardial Infarction

Introduction:

In patients with acute myocardial infarction (AMI) early risk assessment of development of complications is of great importance. It is proven that aldosterone level has a major role in progression of cardiovascular pathology.

Aim:

Determination of influence of aldosterone plasma level in the progression of heart disease in patients without signs of heart failure after AMI.

Material and Methods:

Research included 207 patients, hospitalized in the acute phase of myocardial infarction, and who were divided into two groups: 127 patients with no clinical signs of heart failure and 60 patients with heart failure.

Results:

The serum aldosterone concentration was 73.4% higher in the group of decompensated patients, 128 pg/mL (75.4-236 pg/mL) in decompensated and 73.7 pg/mL (42.7 -115.25 pg/mL) in compensated. In the group of compensated patients, changes in aldosterone levels showed a statistically significant effect on the incidence of post-infarction angina (p=0.0001) as well as reinfarction (p=0.009). There is a connection between changes in aldosterone plasma level and positive stress test (p=0.012).

Conclusion:

In patients with AMI, elevated serum aldosterone level can be prognostic factor of the progression of coronary heart disease, development of heart failure, as well of development of post-infarction angina, myocardial reinfarction and pathological finding on the stress test.

Effects of hypoestrogenism and/or hyperaldosteronism on myocardial remodeling in female mice

We investigated the potential adverse effects of hyperaldosteronism and/or hypoestrogenism on cardiac phenotype, and examined their combined effects in female mice overexpressing cardiac aldosterone synthase (AS). We focused on some signaling cascades challenging defensive responses to adapt and/or to survive in the face of double deleterious stresses, such as Ca2+ -homeostasis, pro/anti-hypertrophic, endoplasmic reticulum stress (ER stress), pro- or anti-apoptotic effectors, and MAP kinase activation, and redox signaling. These protein expressions were assessed by immunoblotting at 9 weeks after surgery. Female wild type (FWT) and FAS mice were fed with phytoestrogen-free diet; underwent ovariectomy (Ovx) or sham-operation (Sham). Ovx increased gain weight and hypertrophy index. Transthoracic echocardiograghy was performed. Both Ovx-induced heart rate decrease and fractional shortening increase were associated with collagen type III shift. Cardiac estrogen receptor (ERα, ERβ) protein expression levels were downregulated in Ovx mice. Hypoestrogenism increased plasma aldosterone and MR protein expression in FAS mice. Both aldosterone and Ovx played as mirror effects on up and downstream signaling effectors of calcium/redox homeostasis, apoptosis, such as concomitant CaMKII activation and calcineurin down-regulation, MAP kinase inhibition (ERK1/2, p38 MAPK) and Akt activation. The ratio Bcl2/Bax is in favor to promote cell survivor. Finally, myocardium had dynamically orchestrated multiple signaling cascades to restore tolerance to hostile environment thereby contributing to a better maintenance of Ca2+ /redox homeostasis. Ovx-induced collagen type III isoform shift and its upregulation may be important for the biomechanical transduction of the heart and the recovery of cardiac function in FAS mice. OVX antagonized aldosterone signaling pathways.

Mineralocorticoid Receptor and Cardiovascular Disease

Activation of the mineralocorticoid receptor (MR) in the distal nephron by its ligand, aldosterone, plays an important role in sodium reabsorption and blood pressure regulation. However, expression of the MR goes beyond the kidney. It is expressed in a variety of other tissues in which its activation could lead to tissue injury. Indeed, MR activation in the cardiovascular (CV) system has been shown to promote hypertension, fibrosis, and inflammation. Pharmacological blockade of the MR has protective effects in several animal models of CV disease. Furthermore, the use of MR antagonists is beneficial for heart failure patients, preventing mortality and morbidity. A better understanding of the implications of the MR in the setting of CV diseases is critical for refining treatments and improving patient care. The mechanisms involved in the deleterious effects of MR activation are complex and include oxidative stress, inflammation, and fibrosis. This review will discuss the pathological role of the MR in the CV system and the major mechanisms underlying it.

Does Aldosterone Play a Significant Role for Regulation of Vascular Tone?

Besides the well-known renal effects of aldosterone, the hormone is now known to have direct vascular effects. Clinical observations underline substantial adverse effects of aldosterone on cardiovascular function. The source of systemic circulating aldosterone is the adrenal gland zona glomerulosa cells through stimulus-secretion coupling involving depolarization, opening of L- and T-type calcium channels and aldosterone synthase activation. Local formation and release in peripheral tissues such as perivascular fat is recognized. Where does aldosterone affect the vasculature? Mineralocorticoid receptors (MRs) are present in endothelial and vascular smooth muscle cells, and MR-independent pathways are also involved. The vascular effects of aldosterone are complex, both concentration and temporal and spatial aspects are relevant. The acute response includes vasodilation through endothelial nitric oxide formation and vasoconstrictor effects through endothelial-contracting cyclooxygenase-derived factors and a changed calcium handling. The response to aldosterone can change within the same blood vessels depending on the exposure time and status of the endothelium. Chronic responses involve changed levels of reactive oxygen radicals, endothelial Na-influx and smooth muscle calcium channel expression. Furthermore, perivascular cells for example mast cells have also been suggested to participate in the chronic response. Moreover, the vascular effect of aldosterone depends on the status of the endothelium which is likely the cause of the very different responses to aldosterone and MR treatment observed in human studies going from increased to decreased flow depending on whether the patient had prior cardiovascular disease with endothelial dysfunction or not. A preponderance of constrictor versus dilator responses to aldosterone could therefore be involved in the detrimental vascular actions of the hormone in the setting of endothelial dysfunction and contribute to explain the beneficial action of MR blockers on blood pressure and target organ injury.

Aldosterone breakthrough does not alter central hemodynamics

Introduction:

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are widely used in congestive heart failure and chronic kidney disease, but up to 40% of patients will experience aldosterone breakthrough, with aldosterone levels rising above pre-treatment levels after 6–12 months of renin-angiotensin-aldosterone system blockade. Aldosterone breakthrough has been associated with worsening congestive heart failure and chronic kidney disease, yet the pathophysiology remains unclear. Breakthrough has not been associated with elevated peripheral blood pressure, but no studies have assessed its effect on central blood pressure.

Methods:

Nineteen subjects with well-controlled peripheral blood pressure on stable doses of angiotensin-converting enzyme inhibitor/angiotensin receptor blocker had aldosterone levels checked and central blood pressure parameters measured using the SphygmoCor system. The central blood pressure parameters of subjects with or without breakthrough, defined as serum aldosterone >15 ng/dl, were compared.

Results:

Of the 19 subjects, six had breakthrough with a mean aldosterone level of 33.8 ng/dl, and 13 were without breakthrough with a mean level of 7.1 ng/dl. There was no significant difference between the two groups in any central blood pressure parameter.

Conclusions:

We found no correlation between aldosterone breakthrough and central blood pressure. The clinical impact of aldosterone breakthrough likely depends on its non-genomic, pro-fibrotic, pro-inflammatory effects rather than its regulation of extracellular volume.

Endothelial dysfunction in human essential hypertension

Although the endothelium has a number of important functions, the term endothelial dysfunction is commonly used to describe impairment in its vasodilatory capacity. It is increasingly recognized that this is related to hypertension, although whether it predates essential hypertension or is a consequence of it is still unknown. In this review, we explore the mechanisms of endothelial dysfunction in essential hypertension, its prognostic significance and methods of pharmacological reversal.

Salt-dependent Blood Pressure in Human Aldosterone Synthase-Transgenic Mice

Hypertension is one of the most important, preventable causes of premature morbidity and mortality in the developed world. Aldosterone is a major mineralocorticoid hormone that plays a key role in the regulation of blood pressure and is implicated in the pathogenesis of hypertension and heart failure. Aldosterone synthase (AS, cytochrome P450 11B2, cyp11B2) is the sole enzyme responsible for the production of aldosterone in humans. To determine the effects of increased expression of human aldosterone synthase (hAS) on blood pressure (BP), we established transgenic mice carrying the hAS gene (cyp11B2). We showed that hAS overexpression increased levels of aldosterone in hAS^+/- mice. On high salt diet (HS), BPs of hAS^+/- mice were significantly increased compared with WT mice. Fadrozole (an inhibitor of aldosterone synthase) treatment significantly reduced BPs of hAS^+/- mice on HS. This is the first time overexpression of AS in a transgenic mouse line has shown an ability to induce HP. Specifically inhibiting AS activity in these mice is a promising therapy for reducing hypertension. This hAS transgenic mouse model is therefore an ideal animal model for hypertension therapy studies.

A novel aldosterone synthase inhibitor ameliorates mortality in pressure-overload mice with heart failure

It has been elucidated that mineralocorticoid receptor antagonists reduce mortality in patients with congestive heart failure and post-acute myocardial infarction. A direct inhibition of aldosterone synthase (CYP11B2) is also expected to have therapeutic benefits equal in quality to mineralocorticoid receptor antagonists in terms of reducing mineralocorticoid receptor signaling. Therefore, we have screened our chemical libraries and identified a novel and potent aldosterone synthase inhibitor, 2,2,2-trifluoro-1-{4-[(4-fluorophenyl)amino]pyrimidin-5-y}-1-[1-(methylsulfonyl)piperidin-4-yl]ethanol (compound 1), by lead optimization. Pharmacological properties of compound 1 were examined in in vitro cell-based assays and an in vivo mouse model of pressure-overload hypertrophy by transverse aortic constriction (TAC). Compound 1 showed potent CYP11B2 inhibition against human and mouse enzymes (IC₅₀; 0.003μM and 0.096μM, respectively) in a cell-based assay. The oral administration of 0.06% compound 1 in the food mixture of a mouse TAC model significantly reduced the plasma aldosterone level and ameliorated mortality rate. This study is the first to demonstrate that a CYP11B2 inhibitor improved survival rates of heart failure induced by pressure-overload in mice. The treatment of 0.06% compound 1 did not elevate plasma potassium level in this model, although further evaluation of hyperkalemia is needed. These results suggest that compound 1 can be developed as a promising oral CYP11B2 inhibitor for pharmaceutical applications. Compound 1 could also be a useful compound for clarifying the role of aldosterone in cardiac hypertrophy.

Emerging Roles of the Mineralocorticoid Receptor in Pathology: Toward New Paradigms in Clinical Pharmacology

The mineralocorticoid receptor (MR) and its ligand aldosterone are the principal modulators of hormone-regulated renal sodium reabsorption. In addition to the kidney, there are several other cells and organs expressing MR, in which its activation mediates pathologic changes, indicating potential therapeutic applications of pharmacological MR antagonism. Steroidal MR antagonists have been used for decades to fight hypertension and more recently heart failure. New therapeutic indications are now arising, and nonsteroidal MR antagonists are currently under development. This review is focused on nonclassic MR targets in cardiac, vascular, renal, metabolic, ocular, and cutaneous diseases. The MR, associated with other risk factors, is involved in organ fibrosis, inflammation, oxidative stress, and aging; for example, in the kidney and heart MR mediates hormonal tissue-specific ion channel regulation. Genetic and epigenetic modifications of MR expression/activity that have been documented in hypertension may also present significant risk factors in other diseases and be susceptible to MR antagonism. Excess mineralocorticoid signaling, mediated by aldosterone or glucocorticoids binding, now appears deleterious in the progression of pathologies that may lead to end-stage organ failure and could therefore benefit from the repositioning of pharmacological MR antagonists.

Differences Between Cardiac and Arterial Fibrosis and Stiffness in Aldosterone-Salt Rats: Effect of Eplerenone

Background. Previous experiments have studied separately the development of either cardiac or aortic fibrosis and stiffness in aldosterone (Aldo)-salt hypertensive rats. Our aim was to determine in vivo the effects of Aldo and the Aldo receptor antagonist eplerenone (Epl) on simultaneous changes in cardiac and arterial structure and function and their interactions.

Methods and Results. Aldo was administered in uninephrectomised Sprague-Dawley rats receiving a high-salt diet from 8 to 12 weeks of age. Three groups of Aldo-salt rats were treated with 1 to 100 mg/kg-1. d-1 Epl by gavage. Arterial elasticity was measured by elastic modulus (Einc)-wall stress curves using medial cross-sectional area (MCSA). The cardiac and arterial walls were analysed by histomorphometry (elastin and collagen), immunohistochemistry (EIIIA fibronectin, Fn), and Northern blot (collagens I and III). Aldo caused increased systolic blood pressure (SBP), carotid Einc, MCSA, and EIIIA Fn with no change in wall stress or elastin and collagen densities. No difference in collagen mRNA levels was detected between groups. During the same period, cardiac mass and collagen mRNA and protein levels increased markedly in the myocardial tissue. Epl normalised collagen in the myocardium, Eincwall stress curves, MCSA, and EIIIA Fn in Aldo rats. These dose-dependent effects were not accompanied by a consistent reduction in SBP and cardiac mass.

Conclusions. In exogenous hyperaldosteronism in the rat, Aldo causes independently myocardial collagen and arterial Fn accumulation, the latter being responsible for increased intrinsic carotid stiffness. Epl prevents both cardiac and arterial effects but does not reduce consistently SBP.

Aldosterone-Induced Vascular Remodeling and Endothelial Dysfunction Require Functional Angiotensin Type 1a Receptors

We investigated the role of angiotensin type 1a receptors (AGTR1a) in vascular injury induced by aldosterone activation of mineralocorticoid receptors in Agtr1a(-/-) and wild-type (WT) mice infused with aldosterone for 14 days while receiving 1% NaCl in drinking water. Aldosterone increased systolic blood pressure (BP) by ≈30 mm Hg in WT mice and ≈50 mm Hg in Agtr1a(-/-) mice. Aldosterone induced aortic and small artery remodeling, impaired endothelium-dependent relaxation in WT mice, and enhanced fibronectin and collagen deposition and vascular inflammation. None of these vascular effects were observed in Agtr1a(-/-) mice. Aldosterone effects were prevented by the AGTR1 antagonist losartan in WT mice. In contrast to aldosterone, norepinephrine caused similar BP increase and mesenteric artery remodeling in WT and Agtr1a(-/-) mice. Agtr1a(-/-) mice infused with aldosterone did not increase sodium excretion in response to a sodium chloride challenge, suggesting that sodium retention could contribute to the exaggerated BP rise induced by aldosterone. Agtr1a(-/-) mice had decreased mesenteric artery expression of the calcium-activated potassium channel Kcnmb1, which may enhance myogenic tone and together with sodium retention, exacerbate BP responses to aldosterone/salt in Agtr1a(-/-) mice. We conclude that although aldosterone activation of mineralocorticoid receptors raises BP more in Agtr1a(-/-) mice, AGTR1a is required for mineralocorticoid receptor stimulation to induce vascular remodeling and inflammation and endothelial dysfunction.

Plasma Aldosterone and Left Ventricular Diastolic Function in Treatment-Naïve Patients With Hypertension

Aldosterone has hypertrophic and profibrotic effects on the heart. The relationship between plasma aldosterone levels and left ventricular diastolic function in hypertension, however, is unclear. The aim of this study was to examine this relationship in treatment-naïve hypertensive patients free of comorbidities that could affect left ventricular diastolic filling properties. In 115 patients with primary hypertension who were eating a standard diet and 100 matched normotensive controls, we measured plasma aldosterone and active renin levels and performed both conventional echocardiography and tissue-Doppler imaging for assessment of left ventricular diastolic function. Left ventricular hypertrophy was found in 21% of hypertensive patients, and diastolic dysfunction was detected in 20% by conventional echocardiography and in 58% by tissue-Doppler imaging. Patients with left ventricular diastolic dysfunction at tissue-Doppler imaging were older and more frequently men, had greater body mass index, blood pressure, alcohol intake, left ventricular mass index, relative wall thickness, and lower plasma aldosterone levels than patients with preserved diastolic function. Plasma aldosterone correlated directly with left ventricular mass index in addition to age, body mass index, and systolic blood pressure. Plasma aldosterone was also directly related to e ′ velocity at tissue-Doppler imaging, but this relationship was lost after multivariate adjustment. In conclusion, plasma aldosterone levels are associated with left ventricular hypertrophy but have no independent relationship with left ventricular diastolic properties in hypertensive patients.

Biomarkers of activation of renin-angiotensin-aldosterone system in heart failure: how useful, how feasible?

Renin-angiotensin-aldosterone system (RAAS), participated by kidney, liver, vascular endothelium, and adrenal cortex, and counter-regulated by cardiac endocrine function, is a complex endocrine system regulating systemic functions, such as body salt and water homeostasis and vasomotion, in order to allow the accomplishment of physiological tasks, such as orthostasis, physical and emotional stimuli, and to react towards the hemorrhagic insult, in tight conjunction with other neurohormonal axes, namely the sympathetic nervous system, the endothelin and vasopressin systems. The systemic as well as the tissue RAAS are also dedicated to promote tissue remodeling, particularly relevant after damage, when chronic activation may configure as a maladaptive response, leading to fibrosis, hypertrophy and apoptosis, and organ dysfunction. RAAS activation is a fingerprint of systemic arterial hypertension, kidney dysfunction, vascular atherosclerotic disease, and is definitely an hallmark of heart failure, which rapidly shifts from organ disease to a disorder of neurohormonal regulatory systems. Chronic RAAS activation is an indirect or direct target of most effective pharmacological treatments in heart failure, such as beta-blockers, inhibitors of angiotensin converting enzyme, angiotensin receptor blockers, direct renin inhibitors, and mineralocorticoid receptor blockers. Biomarkers of RAAS activation are available, with different feasibility and accuracy, such as plasma renin activity, renin, angiotensin II, and aldosterone, which all accompany the increasing clinical severity of heart failure disease, and are well recognized prognostic factors, even in patients with optimal therapy. Polymorphisms influencing the expression and activity of RAAS pathways have been recognized as clinically relevant biomarkers, likely influencing either the individual clinical phenotype, or the response to drugs. This solid, growing evidence strongly suggests the rationale for the use of biomarkers of the RAAS activation, as a guide to tailor individual therapy in the current practice, and their implementation as a rule-in marker for future trials on novel drugs in the heart failure setting.

Effects of biological sex on the pathophysiology of the heart

Cardiovascular diseases are the leading causes of death in men and women in industrialized countries. While the effects of biological sex on cardiovascular pathophysiology have long been known, the sex-specific mechanisms mediating these processes have been further elucidated over recent years. This review aims at analysing the sex-based differences in cardiac structure and function in adult mammals, and the sex-based differences in the main molecular mechanisms involved in the response of the heart to pathological situations. It emerged from this review that the sex-based difference is a variable that should be dealt with, not only in basic science or clinical research, but also with regards to therapeutic approaches.

Role of the renin-angiotensin-aldosterone system and the glutathione S-transferase Mu, Pi and Theta gene polymorphisms in cardiotoxicity after anthracycline chemotherapy for breast carcinoma

BACKGROUND

Anthracyclines are among the most active drugs against breast cancer, but can exert cardiotoxic effects eventually resulting in congestive heart failure (CHF). Identifying breast cancer patients at high risk of developing cardiotoxicity after anthracycline therapy would be of value in guiding the use of these agents.

AIMS

We determined whether polymorphisms in the renin-angiotensin-aldosterone system (RAAS) and in the glutathione S-transferase (GST) family of phase II detoxification enzymes might be useful predictors of left ventricular ejection fraction (LVEF) kinetics and risk of developing CHF. We sought correlations between the development of cardiotoxicity and gene polymorphisms in 48 patients with early breast cancer treated with adjuvant anthracycline chemotherapy.

METHODS

We analyzed the following polymorphisms: p.Met235Thr and p.Thr174Met in angiotensinogen (AGT), Ins/Del in angiotensin-converting enzyme (ACE), A1166C in angiotensin II type-1 receptor (AGTR1A), c.-344T>C in aldosterone synthase (CYP11B2), p.Ile105Val in GSTP1. Additionally, we analyzed the presence or absence of the GSTT1 and GSTP1 genes. A LVEF <50% was detected at least once during the 3 years of follow-up period in 13 out of 48 patients (27.1%).

CONCLUSION

RAAS gene polymorphisms were not significantly associated with the development of cardiotoxicity. GSTM1may be useful as a biomarker of higher risk of cardiotoxicity, as demonstrated in our cohort of patients (p=0.147).

Endothelial mineralocorticoid receptor activation mediates endothelial dysfunction in diet-induced obesity

Aims

Aldosterone plays a crucial role in cardiovascular disease. ‘Systemic’ inhibition of its mineralocorticoid receptor (MR) decreases atherosclerosis by reducing inflammation and oxidative stress. Obesity, an important cardiovascular risk factor, is an inflammatory disease associated with increased plasma aldosterone levels. We have investigated the role of the ‘endothelial’ MR in obesity-induced endothelial dysfunction, the earliest stage in atherogenesis.

Methods and results

C57BL/6 mice were exposed to a normal chow diet (ND) or a high-fat diet (HFD) alone or in combination with the MR antagonist eplerenone (200 mg/kg/day) for 14 weeks. Diet-induced obesity impaired endothelium-dependent relaxation in response to acetylcholine, whereas eplerenone treatment of obese mice prevented this. Expression analyses in aortic endothelial cells isolated from these mice revealed that eplerenone attenuated expression of pro-oxidative NADPH oxidase (subunits p22phox, p40phox) and increased expression of antioxidative genes (glutathione peroxidase-1, superoxide dismutase-1 and -3) in obesity. Eplerenone did not affect obesity-induced upregulation of cyclooxygenase (COX)-1 or prostacyclin synthase. Endothelial-specific MR deletion prevented endothelial dysfunction in obese (exhibiting high ‘endogenous’ aldosterone) and in ‘exogenous’ aldosterone-infused lean mice. Pre-incubation of aortic rings from aldosterone-treated animals with the COX-inhibitor indomethacin restored endothelial function. Exogenous aldosterone administration induced endothelial expression of p22phox in the presence, but not in the absence of the endothelial MR.

Conclusion

Obesity-induced endothelial dysfunction depends on the ‘endothelial’ MR and is mediated by an imbalance of oxidative stress-modulating mechanisms. Therefore, MR antagonists may represent an attractive therapeutic strategy in the increasing population of obese patients to decrease vascular dysfunction and subsequent atherosclerotic complications.

Role of Rac1-mineralocorticoid-receptor signalling in renal and cardiac disease

The Rho-family small GTPase, Ras-related C3 botulinum toxin substrate 1 (Rac1), has been implicated in renal and cardiac disease. Rac1 activation in podocytes has been shown in several models of proteinuric kidney disease and a concept involving motile podocytes has been proposed. Evidence also exists for a critical role of Rac1-mediated oxidative stress in cardiac hypertrophy, cardiomyopathy and arrhythmia, and of the aldosterone-mineralocorticoid-receptor system in proteinuria and cardiac disorders. However, plasma aldosterone concentrations are not always increased in these conditions and the mechanisms of mineralocorticoid-receptor overactivation are difficult to determine. Using knockout mice, we identified a novel mechanism of Rac1-mediated podocyte impairment; Rac1 potentiates the activity of the mineralocorticoid receptor, thereby accelerating podocyte injury. We subsequently demonstrated that the Rac1-mineralocorticoid-receptor pathway contributes to ligand-independent mineralocorticoid-receptor activation in several animal models of kidney and cardiac injury. Hyperkalaemia is a major concern associated with the use of mineralocorticoid-receptor antagonists; however, agents that modulate the activity of the Rac1-mineralocorticoid-receptor pathway in target cells, such as cell-type-specific Rac inhibitors and selective mineralocorticoid-receptor modulators, could potentially be novel therapeutic candidates with high efficacy and a low risk of adverse effects in patients with renal and cardiac diseases.

Aldosterone and cortisol affect the risk of sudden cardiac death in haemodialysis patients

BACKGROUND

Sudden cardiac death is common and accounts largely for the excess mortality of patients on maintenance dialysis. It is unknown whether aldosterone and cortisol increase the incidence of sudden cardiac death in dialysis patients.

METHODS AND RESULTS

We analysed data from 1255 diabetic haemodialysis patients participating in the German Diabetes and Dialysis Study (4D Study). Categories of aldosterone and cortisol were determined at baseline and patients were followed for a median of 4 years. By Cox regression analyses, hazard ratios (HRs) were determined for the effect of aldosterone, cortisol, and their combination on sudden death and other adjudicated cardiovascular outcomes. The mean age of the patients was 66 ± 8 years (54% male). Median aldosterone was <15 pg/mL (detection limit) and cortisol 16.8 µg/dL. Patients with aldosterone levels >200 pg/mL had a significantly higher risk of sudden death (HR: 1.69; 95% CI: 1.06-2.69) compared with those with an aldosterone <15 pg/mL. The combined presence of high aldosterone (>200 pg/mL) and high cortisol (>21.1 µg/dL) levels increased the risk of sudden death in striking contrast to patients with low aldosterone (<15 pg/mL) and low cortisol (<13.2 µg/dL) levels (HR: 2.86, 95% CI: 1.32-6.21). Furthermore, all-cause mortality was significantly increased in the patients with high levels of both hormones (HR: 1.62, 95% CI: 1.01-2.62).

CONCLUSIONS

The joint presence of high aldosterone and high cortisol levels is strongly associated with sudden cardiac death as well as all-cause mortality in haemodialysed type 2 diabetic patients. Whether a blockade of the mineralocorticoid receptor decreases the risk of sudden death in these patients must be examined in future trials.

Vascular actions of aldosterone

Aldosterone exerts direct effects on the vascular system by inducing oxidative stress, inflammation, hypertrophic remodeling, fibrosis, and endothelial dysfunction. Aldosterone exerts its effects through genomic and nongenomic pathways in a mineralocorticoid receptor (MR)-dependent or independent manner. Other aldosterone receptors such as GPR30 have been identified. A tight relation exists between the aldosterone and angiotensin II pathways, as well as with the endothelin-1 system. There is a correlation between plasma levels of aldosterone and cardiovascular risk. Recently, an increasing body of evidence has underlined the importance of aldosterone in cardiovascular complications associated with the metabolic syndrome, such as arterial remodeling and endothelial dysfunction. Blockade of MR is an increasingly used evidence-based therapy for many forms of cardiovascular disease, including hypertension, heart failure, chronic kidney disease, and diabetes mellitus.

Aldosterone, atherosclerosis and vascular events in patients with stable coronary artery disease

BACKGROUND AND AIMS

Plasma aldosterone has been associated with all-cause and cardiovascular mortality in high-risk cardiovascular populations, including patients with heart failure, myocardial infarction and high-risk coronary artery disease (CAD) patients. In the present study, we evaluated the association of plasma aldosterone levels with vascular events in a large prospective cohort of stable CAD patients recruited in an outpatient setting. Moreover, we investigated the relationship between aldosterone and atherosclerotic burden.

METHODS AND RESULTS

Baseline plasma aldosterone levels were measured in 2699 subjects with CAD (mean age 60 ± 10 years, 82% male). During a median follow-up of 4.7 years, 308 (11%) patients died, of which 203 were from a vascular cause. Vascular endpoints of myocardial infarction, ischemic stroke or vascular death occurred in 355 (13%) patients. Multivariable Cox regression analysis was performed, adjusting for multiple confounders. Aldosterone (median 96 pg/mL, interquartile range 70-138 pg/mL, normal range 58-362 pg/mL) was independently associated with major vascular events (hazard ratio (HR) 1.56, 95% confidence interval (CI) 1.13-2.15) and vascular mortality (HR 1.95, 95% CI 1.27-3.00). By multivariable regression analysis, aldosterone was also associated with the presence of atherosclerosis in additional vascular territories (cerebrovascular disease and/or peripheral artery disease) (p=0.026).

CONCLUSIONS

In patients with stable coronary artery disease, plasma aldosterone is independently associated with the risk of major vascular events and vascular mortality and with atherosclerotic burden.

Aldosterone inhibits the fetal program and increases hypertrophy in the heart of hypertensive mice

BACKGROUND

Arterial hypertension (AH) induces cardiac hypertrophy and reactivation of "fetal" gene expression. In rodent heart, alpha-Myosin Heavy Chain (MyHC) and its micro-RNA miR-208a regulate the expression of beta-MyHC and of its intronic miR-208b. However, the role of aldosterone in these processes remains unclear.

METHODOLOGY/PRINCIPAL FINDINGS

RT-PCR and western-blot were used to investigate the genes modulated by arterial hypertension and cardiac hyperaldosteronism. We developed a model of double-transgenic mice (AS-Ren) with cardiac hyperaldosteronism (AS mice) and systemic hypertension (Ren). AS-Ren mice had increased (x2) angiotensin II in plasma and increased (x2) aldosterone in heart. Ren and AS-Ren mice had a robust and similar hypertension (+70%) versus their controls. Anatomical data and echocardiography showed a worsening of cardiac hypertrophy (+41%) in AS-Ren mice (P<0.05 vs Ren). The increase of ANP (x 2.5; P<0.01) mRNA observed in Ren mice was blunted in AS-Ren mice. This non-induction of antitrophic natriuretic peptides may be involved in the higher trophic cardiac response in AS-Ren mice, as indicated by the markedly reduced cardiac hypertrophy in ANP-infused AS-Ren mice for one month. Besides, the AH-induced increase of ßMyHC and its intronic miRNA-208b was prevented in AS-Ren. The inhibition of miR 208a (-75%, p<0.001) in AS-Ren mice compared to AS was associated with increased Sox 6 mRNA (x 1.34; p<0.05), an inhibitor of ßMyHC transcription. Eplerenone prevented all aldosterone-dependent effects.

CONCLUSIONS/SIGNIFICANCE

Our results indicate that increased aldosterone in heart inhibits the induction of atrial natriuretic peptide expression, via the mineralocorticoid receptor. This worsens cardiac hypertrophy without changing blood pressure. Moreover, this work reveals an original aldosterone-dependent inhibition of miR-208a in hypertension, resulting in the inhibition of β-myosin heavy chain expression through the induction of its transcriptional repressor Sox6. Thus, aldosterone inhibits the fetal program and increases cardiac hypertrophy in hypertensive mice.

[Hypertension-induced fibrosis: a balance story]

Cardiac remodeling is a deleterious consequence of arterial hypertension. This remodeling results in cardiac transcriptomic changes induced by mechanical and hormonal factors (angiotensin II and aldosterone are the most important). The major features of cardiac remodeling are the hypertrophy of cardiomyocytes, interstitial and perivascular fibrosis, and microvascular rarefaction. Inappropriate stimulation of the renin-angiotensin-aldosterone system (RAAS) participates to the development of heart failure. The respective roles of angiotensin II and aldosterone in cardiac remodeling are poorly understood. The development of fibrosis in the heart depends of a balance between profibrotic (TGFβ, CTGF, inflammation) and antifibrotic (BNP, ANP, BMP4 and BMP7) factors. The profibrotic and proinflammatory effects of angiotensin II and aldosterone are very well demonstrated; however, their actions on antifibrotic factors expression are unknown. In order to explore this, we used RenTgKC mice overexpressing renin into the liver, leading to an increased plasma angiotensin II and thus induction of severe hypertension, and AS mice overexpressing aldosterone synthase (AS) in cardiomyocytes which have a doubled intracardiac aldosterone concentration. Male AS mice have a dysfunction of the coronary arteries relaxation without structural and functional changes of the myocardium. Mice derived from a crossing between the RenTgKC and AS strains were used in this work. It is shown that angiotensin II induces the expression of BNP and BMPs which ultimately slows the progression of myocardial fibrosis, and that aldosterone inhibits the expression of these factors and thus worsens the fibrosis.

Impact of salt on cardiac differential gene expression and coronary lesion in normotensive mineralocorticoid-treated mice

We previously reported that excess of deoxycorticosterone-acetate (DOCA)/salt-induced cardiac hypertrophy in the absence of hypertension in one-renin gene mice. This model allows us to study molecular mechanisms of high-salt intake in the development of cardiovascular remodeling, independently of blood pressure in a high mineralocorticoid state. In this study, we compared the effect of 5-wk low- and high-salt intake on cardiovascular remodeling and cardiac differential gene expression in mice receiving the same amount of DOCA. Differential gene and protein expression was measured by high-density cDNA microarray assays, real-time PCR and Western blot analysis in DOCA-high salt (HS) vs. DOCA-low salt (LS) mice. DOCA-HS mice developed cardiac hypertrophy, coronary perivascular fibrosis, and left ventricular dysfunction. Differential gene and protein expression demonstrated that high-salt intake upregulated a subset of genes encoding for proteins involved in inflammation and extracellular matrix remodeling (e.g., Col3a1, Col1a2, Hmox1, and Lcn2). A major subset of downregulated genes encoded for transcription factors, including myeloid differentiation primary response (MyD) genes. Our data provide some evidence that vascular remodeling, fibrosis, and inflammation are important consequences of a high-salt intake in DOCA mice. Our study suggests that among the different pathogenic factors of cardiac and vascular remodeling, such as hypertension and mineralocorticoid excess and sodium intake, the latter is critical for the development of the profibrotic and proinflammatory phenotype observed in the heart of normotensive DOCA-treated mice.

Aldosterone inhibits antifibrotic factors in mouse hypertensive heart

The renin-angiotensin-aldosterone system is involved in the arterial hypertension-associated cardiovascular remodeling. In this context, the development of cardiac fibrosis results from an imbalance between profibrotic and antifibrotic pathways, in which the role of aldosterone is yet not established. To determine the role of intracardiac aldosterone in the development of myocardial fibrosis during hypertension, we used a double transgenic model (AS-Ren) of cardiac hyperaldosteronism (AS) and systemic hypertension (Ren). The 9-month-old hypertensive mice had cardiac fibrosis, and hyperaldosteronism enhanced the fibrotic level. The mRNA levels of connective tissue growth factor and transforming growth factor-β1 were similarly increased in Ren and AS-Ren mice compared with wild-type and AS mice, respectively. Hyperaldosteronism combined with hypertension favored the macrophage infiltration (CD68(+) cells) in heart, and enhanced the mRNA level of monocyte chemoattractant protein 1, osteopontin, and galectin 3. Interestingly, in AS-Ren mice the hypertension-induced increase in bone morphogenetic protein 4 mRNA and protein levels was significantly inhibited, and B-type natriuretic peptide expression was blunted. The mineralocorticoid receptor antagonist eplerenone restored B-type natriuretic peptide and bone morphogenetic protein 4 levels and decreased CD68 and galectin 3 levels in AS-Ren mice. Finally, when hypertension was induced by angiotensin II infusion in wild-type and AS mice, the mRNA profiles did not differ from those observed in Ren and AS-Ren mice, respectively. The aldosterone-induced inhibition of B-type natriuretic peptide and bone morphogenetic protein 4 expression was confirmed in vitro in neonatal mouse cardiomyocytes. Altogether, we demonstrate that, at the cardiac level, hyperaldosteronism worsens hypertension-induced fibrosis through 2 mineralocorticoid receptor-dependent mechanisms, activation of inflammation/galectin 3-induced fibrosis and inhibition of antifibrotic factors (B-type natriuretic peptide and bone morphogenetic protein 4).

Aldosterone, mineralocorticoid receptor, and heart failure

Several large clinical studies have demonstrated the important benefit of mineralocorticoid receptor (MR) antagonists in patients with heart failure, left ventricular dysfunction after myocardial infarction, hypertension or diabetic nephropathy. Aldosterone adjusts the hydro-mineral balance in the body, and thus participates decisively to the control of blood pressure. This traditional view of the action of aldosterone restricted to sodium reabsorption in epithelial tissues must be revisited. Clinical and experimental studies indicated that chronic activation of the MR in target tissues induces structural and functional changes in the heart, kidneys and blood vessels. These deleterious effects include cardiac and renal fibrosis, inflammation and vascular remodeling. It is important to underscore that these effects are due to elevated MR activation that is inadequate for the body salt requirements. Aldosterone is generally considered as the main ligand of MR. However, this is a matter of debate especially in heart. Complexity arises from the glucocorticoids with circulating concentrations much higher than those of aldosterone, and the fact that the MR has a high affinity for 11β-hydroxyglucocorticoids. Nevertheless, the beneficial effects of MR inhibition in patients with heart failure emphasize the importance of this receptor in cardiovascular tissue. Diverse experimental models and strains of transgenic mice have allowed to dissect the effects of aldosterone and the MR in the heart. Taken together experimental and clinical data clearly highlight the deleterious cardiovascular effects of MR stimulation.

Aldosterone, mortality, and acute ischaemic events in coronary artery disease patients outside the setting of acute myocardial infarction or heart failure

BACKGROUND

Recent studies have demonstrated that aldosterone levels measured in patients with heart failure or acute myocardial infarction (MI) are associated with long-term mortality, but the association with aldosterone levels in patients with coronary artery disease (CAD) outside these specific settings remains unknown. In addition, no clear mechanism has been elucidated to explain these observations. The present study was designed to evaluate the relationship between the level of aldosterone and the risk of death and acute ischaemic events in CAD patients with a preserved left ventricular (LV) function and no acute MI.

METHODS AND RESULTS

In 799 consecutive CAD patients referred for elective coronary angioplasty measurements were obtained before the procedure for: aldosterone (median = 25 pg/mL), brain natriuretic peptide (BNP) (median = 35 pg/mL), hsC-reactive protein (median = 4.17 mg/L), and left ventricular ejection fraction (mean = 58%). Patients with acute MI or coronary syndrome (ACS) who required urgent revascularization were not included in the study. The primary endpoint, cardiovascular death, occurred in 41 patients during a median follow-up period of 14.9 months. Secondary endpoints-total mortality, acute ischaemic events (acute MI or ischaemic stroke), and the composite of death and acute ischaemic events-were observed in 52, 54, and 94 patients, respectively. Plasma aldosterone was found to be related to BMI, hypertension and NYHA class, and inversely related to age, creatinine clearance, and use of beta-blockers. Multivariate Cox model analysis demonstrated that aldosterone was independently associated with cardiovascular mortality (P = 0.001), total mortality (P = 0.001), acute ischaemic events (P = 0.01), and the composite of death and acute ischaemic events (P = 0.004). Reclassification analysis, using integrated discrimination improvement (IDI) and net reclassification improvement (NRI), demonstrated incremental predictive value of aldosterone (P < 0.0001).

CONCLUSION

Our results demonstrate that, in patients with CAD but without heart failure or acute MI, the level of aldosterone is strongly and independently associated with mortality and the occurrence of acute ischaemic events.

Cellular and molecular pathways to myocardial necrosis and replacement fibrosis

Fibrosis is a fundamental component of the adverse structural remodeling of myocardium present in the failing heart. Replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium, but not without adverse functional consequences. The extensive nature of this microscopic scarring suggests cardiomyocyte necrosis is widespread and the loss of these contractile elements, combined with fibrous tissue deposition in the form of a stiff in-series and in-parallel elastic elements, contributes to the progressive failure of this normally efficient muscular pump. Cellular and molecular studies into the signal-transducer-effector pathway involved in cardiomyocyte necrosis have identified the crucial pathogenic role of intracellular Ca2+ overloading and subsequent induction of oxidative stress, predominantly confined within its mitochondria, to be followed by the opening of the mitochondrial permeability transition pore that leads to the destruction of these organelles and cells. It is now further recognized that Ca2+ overloading of cardiac myocytes and mitochondria serves as a prooxidant and which is counterbalanced by an intrinsically coupled Zn2+ entry serving as antioxidant. The prospect of raising antioxidant defenses by increasing intracellular Zn2+ with adjuvant nutriceuticals can, therefore, be preferentially exploited to uncouple this intrinsically coupled Ca2+ - Zn2+ dyshomeostasis. Hence, novel yet simple cardioprotective strategies may be at hand that deserve to be further explored.

Coronary endothelial dysfunction after cardiomyocyte-specific mineralocorticoid receptor overexpression

The deleterious effects of aldosterone excess demonstrated in cardiovascular diseases might be linked in part to coronary vascular dysfunction. However, whether such vascular dysfunction is a cause or a consequence of the changes occurring in the cardiomyocytes is unclear. Moreover, the possible link between mineralocorticoid receptor (MR)-mediated effects on the cardiomyocyte and the coronary arteries is unknown. Thus we used a mouse model with conditional, cardiomyocyte-specific overexpression of human MR (hMR) and observed the effects on endothelial function in isolated coronary segments. hMR overexpression decreased the nitric oxide (NO)-mediated relaxing responses to acetylcholine in coronary arteries (but not in peripheral arteries), and this was prevented by a 1-mo treatment either with an MR antagonist, vitamin E/vitamin C, or a NADPH oxidase inhibitor. hMR overexpression did not affect coronary endothelial NO synthase content nor its level of phosphorylation on serine 1177, but increased cardiac levels of reactive oxygen species, cardiac NADPH oxidase (NOX) activity, and expression of the NOX subunit gp91phox, which was limited to endothelial cells. Thus an increase in hMR activation, restricted to cardiomyocytes, is sufficient to induce a severe coronary endothelial dysfunction. We suggest a new paracrine mechanism by which cardiomyocytes trigger a NOX-dependent, reactive oxygen species-mediated coronary endothelial dysfunction.

Fibrosis in hypertensive heart disease: molecular pathways and cardioprotective strategies

Fibrosis is a fundamental component of the adverse structural remodelling of myocardium found in hypertensive heart disease (HHD). A replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium. Such scarring has adverse functional consequences. The extensive distribution of fibrosis involving the right and left heart suggests cardiomyocyte necrosis is widespread. Together, the loss of these contractile elements and fibrous tissue deposition in the form of stiff in-series and in-parallel elastic elements contribute to the progressive failure of this normally efficient muscular pump. Pathogenic mechanisms modulating fibrous tissue formation at sites of repair include auto/paracrine properties of locally generated angiotensin II and endothelin-1. This study focuses on the signal-transducer-effector pathway involved in cardiomyocyte necrosis and the crucial pathogenic role of intracellular calcium overloading, and the subsequent induction of oxidative stress originating within its mitochondria that dictates the opening of the mitochondrial permeability transition pore. The ensuing osmotic destruction of these organelles is followed by necrotic cell death. It is now further recognized that calcium overloading of cardiac myocytes and mitochondria functioning as pro-oxidant is pathophysiologically counterbalanced by an intrinsically coupled zinc entry, which serves as an antioxidant. The prospect of raising intracellular zinc by adjuvant nutriceutical supplementation can, therefore, be preferentially exploited to uncouple this intrinsically coupled calcium-zinc dyshomeostasis in favour of endogenous antioxidant defences. Novel cardioprotective strategies may thus be at hand and deserve to be explored further in the overall management of patients with HHD.

Cardiovascular and renal damage in primary aldosteronism: outcomes after treatment

Primary aldosteronism (PA) is one of the common forms of curable hypertension. Recent views have suggested that PA is far from being relatively benign, as it was previously thought, but it is associated with a variety of cardiovascular and renal sequelae that reflect the capability of inappropriately elevated aldosterone to induce tissue damage over that induced by hypertension itself. The evidence supporting these views has been obtained from experiments conducted in hypertensive animal models and studies involving patients with PA. Preclinical studies have also indicated that aldosterone causes cardiovascular and renal tissue damage only in the context of inappropriate salt status. It has been suggested that untoward effects of high-salt intake are dependent on activation of mineralocorticoid receptors (MRs) that might result from increased oxidative stress and changes in the intracellular redox potential. Unilateral adrenalectomy or treatment with MR antagonists are the current options for treating an aldosterone-producing adenoma (APA) or idiopathic adrenal hyperplasia (IHA). Treatments are effective in correcting hypertension and hypokalemia, and currently available information on their capability to prevent cardiovascular events and deterioration of renal function indicates that surgery and medical treatment are equally beneficial in the long term.

Impairment of endothelial progenitor cell function and vascularization capacity by aldosterone in mice and humans

Aims

Hyperaldosteronism is associated with vascular injury and increased cardiovascular events. Bone marrow-derived endothelial progenitor cells (EPCs) play an important role in endothelial repair and vascular homeostasis. We hypothesized that hyperaldosteronism impairs EPC function and vascularization capacity in mice and humans.

Methods and results

We characterized the effects of aldosterone and mineralocorticoid receptor (MR) blockade on EPC number and function as well as vascularization capacity and endothelial function. Treatment of human EPC with aldosterone induced translocation of the MR and impaired multiple cellular functions of EPC, such as differentiation, migration, and proliferation in vitro. Impaired EPC function was rescued by pharmacological blockade or genetic ablation of the MR. Aldosterone protein kinase A (PKA) dependently increased reactive oxygen species formation in EPC. Aldosterone infusion in mice impaired EPC function, EPC homing to vascular structures and vascularization capacity in a MR-dependent but blood pressure-independent manner. Endothelial progenitor cells from patients with primary hyperaldosteronism compared with controls of similar age displayed reduced migratory potential. Impaired EPC function was associated with endothelial dysfunction. MR blockade in patients with hyperaldosteronism improved EPC function and arterial stiffness.

Conclusion

Endothelial progenitor cells express a MR that mediates functional impairment by PKA-dependent increase of reactive oxygen species. Normalization of EPC function may represent a novel mechanism contributing to the beneficial effects of MR blockade in cardiovascular disease prevention and treatment.

The mineralocorticoid receptor is a constitutive nuclear factor in cardiomyocytes due to hyperactive nuclear localization signals

The mineralocorticoid receptor (MR), a member of the nuclear receptor family, mediates the action of aldosterone in target epithelia, enhancing sodium reabsorption. In addition, MR may have other physiological functions in nonepithelial tissues. Altered expression or inappropriate activation of cardiac MR is directly linked to the development of cardiac fibrosis, and MR blockade is beneficial for the treatment of heart failure. However, the physiological role, activation status, and target genes of MR in the heart are poorly known. Because ligand-free steroid receptors are typically cytoplasmic and translocate to the nucleus upon ligand binding, we examined the subcellular localization of MR under different corticosteroid levels using subcellular fractionation and immunostaining. Our results demonstrate that MR is a chromatin-bound factor in mouse left ventricle and in a cultured model of cardiomyocytes, HL-1 cells, regardless of circulating corticosteroid levels. Immunohistochemical localization of MR in human heart confirms the subcellular localization pattern. Mutation of nuclear localization signals (NLSs) demonstrates that MR constitutive nuclear localization mainly depends on the synergistic contribution of NLS0 and NLS1. Constitutive nuclear localization in HL-1 cells can be reverted by cotransfection of heat shock protein 90. Heat shock protein 90 expression levels in the mouse heart and HL-1 cells are lower than those found in other tissues, suggesting that low levels of cochaperones render MR NLSs hyperactive in cardiomyocytes. Even though MR is constitutively nuclear, corticosteroids still control the transactivation properties of the receptor in a model promoter, although other MR ligand-independent activities cannot be excluded.

Pharmacodynamic and pharmacokinetic characterization of the aldosterone synthase inhibitor FAD286 in two rodent models of hyperaldosteronism: comparison with the 11beta-hydroxylase inhibitor metyrapone

Aldosterone synthase (CYP11B2) inhibitors (ASIs) represent an attractive therapeutic approach for mitigating the untoward effects of aldosterone. We characterized the pharmacokinetic/pharmacodynamic relationships of a prototypical ASI, (+)-(5R)-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-5-yl]benzonitrile hydrochloride (CGS020286A, FAD286, FAD) and compared these profiles to those of the 11beta-hydroxylase inhibitor metyrapone (MET) in two rodent models of secondary hyperaldosteronism and corticosteronism. In chronically cannulated Sprague-Dawley rats, angiotensin II (ANG II) (300 ng/kg bolus + 100 ng/kg/min infusion) or adrenocorticotropin (100 ng/kg + 30 ng/kg/min) acutely elevated plasma aldosterone concentration (PAC) from approximately 0.26 nM to a sustained level of approximately 2.5 nM for 9 h. Adrenocorticotropin but not ANG II elicited a sustained increase in plasma corticosterone concentration (PCC) from approximately 300 to approximately 1340 nM. After 1 h of Ang II or adrenocorticotropin infusion, FAD (0.01-100 mg/kg p.o.) or MET (0.1-300 mg/kg p.o.) dose- and drug plasma concentration-dependently reduced the elevated PACs over the ensuing 8 h. FAD was approximately 12 times more dose-potent than MET in reducing PAC but of similar or slightly greater potency on a plasma drug concentration basis. Both agents also decreased PCC in the adrenocorticotropin model at relatively higher doses and with similar dose potencies, whereas FAD was 6-fold weaker based on drug exposures. FAD was approximately 50-fold selective for reducing PAC versus PCC, whereas MET was only approximately 3-fold selective. We conclude that FAD is a potent, orally active, and relatively selective ASI in two rat models of hyperaldosteronism. MET is an order of magnitude less selective than FAD but is, nevertheless, more potent as an ASI than as an 11beta-hydroxylase inhibitor.

Myocardial remodeling in low-renin hypertension: molecular pathways to cellular injury in relative aldosteronism

The pathologic hypertrophy of hypertensive heart disease is related to the quality, not the quantity, of myocardium; the presence of fibrosis is inevitably linked to structural and functional insufficiencies with increased cardiovascular risk. Elevations in plasma aldosterone that are inappropriate relative to dietary sodium, or relative aldosteronism, are accompanied by suppressed plasma renin activity, elevation in arterial pressure, and dyshomeostasis of divalent cations. The accompanying hypocalcemia, hypomagnesemia, and hypozincemia of aldosteronism contribute to the appearance of secondary hyperparathyroidism. Parathyroid hormone-mediated intracellular calcium overloading of cardiac myocytes and mitochondria leads to the induction of oxidative stress and molecular pathways associated with cardiomyocyte necrosis and scarring of myocardium, whereas the dyshomeostasis of zinc compromises antioxidant defenses. This dys-homeostasis of calcium and zinc, intrinsically coupling prooxidant calcium and antioxidant zinc, raises the prospect for therapeutic strategies designed to mitigate intracellular calcium overloading while enhancing zinc-mediated antioxidant defenses, thus preventing adverse myocardial remodeling with fibrosis, associated diastolic dysfunction, and cardiac arrhythmias.

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.