Mineralocorticoids, hypertension, and cardiac fibrosis

Association between aldosterone synthase (CYP11B2) polymorphism and left ventricular mass in human essential hypertension

OBJECTIVES

The aim of our study was to evaluate the relationship between aldosterone synthase gene polymorphism and cardiac dimensions in essential hypertension.

BACKGROUND

Higher aldosterone synthase messenger ribonucleic acid levels in the human heart are accompanied by increased intracardiac aldosterone production, a phenomenon that is associated with cardiac fibrosis and hypertrophy. Recent evidence suggests that a polymorphism (-344C/T) in the promoter region of the aldosterone synthase gene is associated with increased constitutive aldosterone production.

METHOD

Relationships between M-mode echocardiographic cardiac dimensions and aldosterone synthase -344C/T polymorphism were studied in 210 never-treated, middle-aged patients (age 41.6 +/- 1.4 years) affected by mild to moderate essential hypertension. Among these patients, 48 had the genotype -C344C, 97 had -C344T, and 65 had -T344T. Patients in the three groups were similar in terms of age, gender, body mass index, and blood pressure.

RESULTS

Left ventricular (LV) mass and thickness were positively correlated with the number of T alleles: LV mass (CC, CT, and TT, respectively: 168 +/- 6.9, 179 +/- 5.2, and 193 +/- 6.9 g; p = 0.03), LV septal thickness (0.99 +/- 0.02, 1.03 +/- 0.02, and 11.08 +/- 0.03 cm, p = 0.04), PWT (0.93 +/- 0.03, 0.95 +/- 0.01, and 1.03 +/- 0.02 cm; p = 0.002), and relative wall thickness (38.3 +/- 1.2%, 38.8 +/- 0.8%, and 42.8 +/- 1.1%; p = 0.004). This trend was confirmed by linear regression, suggesting a "major gene" behavior for the T allele. Multiple regression analysis showed that this effect was independent of anthropometric and clinical factors, including adrenal aldosterone.

CONCLUSIONS

Our data suggest that -344C/T polymorphism affects LV mass and thickness in essential hypertension, independent of adrenal aldosterone. A role for intracardiac aldosterone synthesis is hypothesized.

Fibrosis in hypertensive heart disease: role of the renin-angiotensin-aldosterone system

Structural homogeneity of cardiac tissue is governed by mechanical and humoral factors that regulate cell growth, apoptosis, phenotype, and extracellular matrix turnover. ANGII has endocrine, autocrine, and paracrine properties that influence the behavior of cardiac cells and matrix by AT1 receptor binding. Various paradigms have been suggested, including ANGII-mediated up-regulation of collagen types I and III formation and deposition in cardiac conditions, such as HHD. A growing body of evidence, however, deals with the potential role of aldosterone, either local or systemic, in inducing cardiac fibrosis. Aldosterone might also mediate the profibrotic actions of ANGII. To reduce the risk of heart failure that accompanies HHD, its adverse structural remodeling (eg, myocardial hypertrophy and fibrosis) must be targeted for pharmacologic intervention. Cardioprotective agents must reverse not only the exaggerated growth of cardiac cells, but also regress existing abnormalities in fibrillar collagen. Available experimental and clinical data suggest that agents interfering with ACE, the AT1 receptor, or the mineralocorticoid receptor may provide such a cardioprotective effect.

Increased reactivity of murine mesenteric veins to adrenergic agonists: functional evidence supporting increased alpha1-adrenoceptor reserve in veins compared with arteries

These studies examined adrenergic reactivity of mesenteric arteries and veins from deoxycorticosterone acetate-salt (DOCA-salt) hypertensive and sham control mice. We measured constrictions in unpressurized arteries and veins by monitoring vessel diameter using computer-assisted video micros-copy in vitro. Veins were more sensitive than arteries to the constricting effects of norepinephrine (NE) and phenylephrine (PE), but the alpha2-agonists clonidine and UK 14,304 [5-bromo-6-(2-imidazolin-2-yl-amino)-quinoxaline] did not constrict arteries or veins. Reactivity was not altered in arteries or veins from DOCA-salt mice. We next investigated the mechanism of increased venous reactivity to NE and PE by studying desensitization to maximum concentrations of NE and PE. Sham arteries desensitized to NE and PE more than DOCA-salt arteries, whereas DOCA-salt and sham veins maintained 80% of the initial NE and PE constriction. To determine whether the increased reactivity and resistance to desensitization in veins was due to a greater alpha-adrenoceptor reserve, vessels were incubated with the alkylating agent phenoxybenzamine (PBZ; 0.3, 3, 10, and 30 nM). The NE-elicited initial constriction was reduced by PBZ (3, 10, and 30 nM) in sham but only by PBZ (30 nM) in DOCA-salt veins. All doses of PBZ blocked NE responses in sham and DOCA-salt arteries. These data suggest that mesenteric veins express more alpha1-adrenoceptors than arteries, accounting for greater reactivity and resistance to desensitization compared with arteries.

Aldosterone-Induced Organ Damage: Plasma Aldosterone Level and Inappropriate Salt Status

In recent years, it has been clarified that aldosterone can directly damage various organs, such as the heart, blood vessel, and kidneys, via non-epithelial mineralocorticoid receptors, independent of changes in blood pressure. Anti-aldosterone drugs have been clinically reported to be useful for their organ-protecting effects. The fact that these effects have been considered important for almost 10 years seems to indicate that aldosterone-induced organ damage can develop as a consequence of plasma aldosterone levels being in disproportion to salt status. In a previous study, cardiac fibrosis could not be induced in an experimental model of hyperaldosteronism with a low-salt diet. It is, therefore, extremely important to understand the relationship between plasma aldosterone level and inappropriate salt balance when considering diseases or states for which an anti-aldosterone drug is called for. In this paper we review the fundamental and clinical studies reported to date, mainly to investigate the pathology of organ damage induced by aldosterone and excess salt. Aldosterone-induced direct organ damage mediated through vasculitis essentially requires salt, which is inappropriate for plasma aldosterone level, and studies performed from this standpoint may provide a clue to the clarification of the involvement of salt in the actions of aldosterone via non-epithelial mineralocorticoid receptors. In humans, it is also strongly suggested that organ damage may occur, even at a plasma aldosterone level within a normal range, if salt intake is imbalanced to the aldosterone level. This means that the new aldosterone blocker eplerenone may also have significance as a drug inhibiting inflammation, possibly serving as a trigger of organ damage.

Aldosteronism and peripheral blood mononuclear cell activation: a neuroendocrine-immune interface

Aldosteronism eventuates in a proinflammatory/fibrogenic vascular phenotype of the heart and systemic organs. It remains uncertain whether peripheral blood mononuclear cells (PBMCs) are activated before tissue invasion by monocytes/macrophages and lymphocytes, as is the case for responsible pathogenic mechanisms. Uninephrectomized rats treated for 4 weeks with dietary 1% NaCl and aldosterone (ALDOST, 0.75 microg/h) with or without spironolactone (Spi, 100 mg/kg per daily gavage) were compared with unoperated/untreated and uninephrectomized/salt-treated controls. Before intramural coronary vascular lesions appeared at week 4 of ALDOST, we found (1) a reduction of PBMC cytosolic free [Mg2+]i, together with intracellular Mg2+ and Ca2+ loading, whereas plasma and cardiac tissue Mg2+ were no different from controls; (2) increased H2O2 production by monocytes and lymphocytes together with upregulated PBMC gene expression of oxidative stress-inducible tyrosine phosphatase and Mn2+-superoxide dismutase and the presence of 3-nitrotyrosine in CD4+ and ED-1-positive inflammatory cells that had invaded intramural coronary arteries; (3) B-cell activation, including transcription of immunoglobulins, intracellular adhesion molecule-1, and CC and CXC chemokines and their receptors; (4) expansion of B lymphocyte subset and myosin heavy chain class II-expressing lymphocytes; and (5) autoreactivity with gene expression for antibodies to acetylcholine receptors and a downregulation of RT-6.2, which is in keeping with cell activation and associated with autoimmunity. Spi cotreatment attenuated the rise in intracellular Ca2+, the appearance of oxidative/nitrosative stress in PBMCs and invading inflammatory cells, and alterations in PBMC transcriptome. Thus, aldosteronism is associated with an activation of circulating immune cells induced by iterations in PBMC divalent cations and transduced by oxidative/nitrosative stress. ALDO receptor antagonism modulates this neuroendocrine-immune interface. The full text of this article is available online at http://www.circresaha.org.

Different remodelling against left ventricular overload between diabetic and non-diabetic haemodialysis patients

1. Diabetes mellitus is significantly associated with the occurrence of congestive heart failure in end-stage renal disease patients undergoing maintenance haemodialysis. In the present study, we asked whether the left ventricular remodelling against sustained pressure and/or volume overload to the left ventricle may be different between diabetic and non-diabetic haemodialysis patients. 2. Left ventricular parameters, including left ventricular mass index (LVMI), interventricular septal wall thickness (IVST) and relative left ventricular wall thickness (rLVWT), were assessed in 486 patients receiving maintenance haemodialysis (145 diabetic and 341 non-diabetic patients) using transthoracic echocardiography. Plasma concentrations of B-type natriuretic peptide (BNP), measured with an immunoradiometric assay, were used as a humoral parameter indicating left ventricular wall stress. 3. In non-diabetic patients, the plasma BNP concentration correlated with LVMI (r = 0.245; P = 0.0001), IVST (r = 0.250; P = 0.0001) and rLVWT (r = 0.149; P = 0.006). Furthermore, LVMI was correlated with mean blood pressure and pulse pressure and IVST and rLVWT were correlated with pulse pressure. 4. In contrast, none of the measured factors was correlated with LVMI and IVST in diabetic patients. Plasma BNP concentrations were positively correlated with end-systolic and end-diastolic left intraventricular dimensions and were inversely correlated with rLVWT and left ventricular fractional shortening in diabetic patients, but not in non-diabetic patients. 5. In conclusion, a sustained increase in left ventricular wall stress is likely to elicit eccentric left ventricular remodelling in diabetic haemodialysis patients, whereas it causes concentric left ventricular remodelling in non-diabetic haemodialysis patients. This difference in left ventricular remodelling against left ventricular overload may be associated with the high incidence of congestive heart failure in diabetic haemodialysis patients.

Corticosteroid receptors, 11 beta-hydroxysteroid dehydrogenase, and the heart

Mineralocorticoid and glucocorticoid hormones are known as corticosteroid hormones and are synthesized mainly in the adrenal cortex; however, more recently the enzymes involved in their synthesis have been found in a variety of cells and tissues, including the heart. The effects of these hormones are mediated via both cytoplasmic mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs), which act as ligand-inducible transcription factors. In addition, rapid, nongenomically mediated effects of these steroids can occur that may be via novel corticosteroid receptors. The lipophilic nature of these hormones allows them to pass freely through the cell membrane, although the intracellular concentration of mineralocorticoids and glucocorticoids is dependent on several cellular factors. The main regulators of intracellular glucocorticoid levels are 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) isoforms. 11 beta HSD1 acts predominantly as a reductase in vivo, facilitating glucocorticoid action by converting circulating receptor-inactive 11-ketoglucocorticoids to active glucocorticoids. In contrast, 11 beta HSD 2 acts exclusively as an 11 beta-dehydrogenase and decreases intracellular glucocorticoids by converting them to their receptor-inactive 11-ketometabolites. Furthermore, P-glycoproteins, by actively pumping steroids out of cells, can selectively decrease steroids and local steroid synthesis can increase steroid concentrations. Receptor concentration, receptor modification, and receptor-protein interactions can also significantly impact on the corticosteroid response. This review details the receptors and possible mechanisms involved in both mediating and modulating corticosteroid responses. In addition, direct effects of corticosteroids on the heart are described including a discussion of the corticosteroid receptors and the mechanisms involved in mediating their effects.

Aldosterone receptor antagonists: biology and novel therapeutical applications

Recent studies suggest that a dysregulation of the aldosterone system is involved in the pathophysiology of different cardiovascular diseases, including myocardial failure and several cases of essential hypertension. In both rat models and in humans, aldosterone action has been shown to induce heart remodeling and interstitial and perivascular fibrosis of the myocardium. For these reasons, a rationale for the use of aldosterone antagonists (ARAs) of the spirolactone family, which have been available for decades in the treatment of aldosterone excess syndromes, has now emerged. Moreover, the recent validation of their use, in combination with the current therapy, for the treatment of these cardiovascular diseases by trials like the RALES Study has further strenghtened this approach. The development of compounds, like eplerenone, with a greater selectivity for mineralocorticoid receptors, seems promising also in terms of reduction of endocrine side effects. The addition of aldosterone antagonists to the conventional therapy of myocardial failure and of selected cases of hypertension thus appears beneficial, resulting in an improved survival rate and a reduced incidence of cardiac complications. This review article, after a brief recall of the physiology of the aldosterone system, addresses the emerging role of aldosterone in cardiovascular diseases, considers the pharmacology of ARAs and the novel therapeutical applications of these compounds in hypertension and heart failure.

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure

Aldosterone classically promotes unidirectional transepithelial sodium transport, thereby regulating blood volume and blood pressure. Recently, both clinical and experimental studies have suggested additional, direct roles for aldosterone in the cardiovascular system. To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, transgenic mice overexpressing 11beta-hydroxysteroid dehydrogenase type 2 in cardiomyocytes were generated using the mouse alpha-myosin heavy chain promoter. This enzyme converts glucocorticoids to receptor-inactive metabolites, allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. These studies confirm the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and reveal a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiological conditions. In addition, these data support the hypothesis that aldosterone blockade may provide additional therapeutic benefit in the treatment of heart failure.

Pathophysiological roles of vascular 11beta-hydroxysteroid dehydrogenase and aldosterone

Mineralocorticoid receptor (MR) binding is tightly regulated by the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSDII) which selectively metabolizes glucocorticoids to inactive metabolites, thus allowing for MR activation by aldosterone. To examine whether this enzyme is involved in the pathophysiology of salt-sensitive hypertension, 11beta-HSDII activity and messenger RNA (mRNA) levels were determined in blood vessels of Dahl Iwai salt-sensitive (DS) and salt-resistant (DR) rats. Decreased 11beta-HSDII activity and mRNA levels in mesenteric arteries were observed in 8-week-old DS rats on a high-salt diet, indicating that 11beta-HSDII may play a significant role in salt sensitivity and hypertension. It has been suggested that mineralocorticoids act on blood vessels, leading to increased vasoreactivity and peripheral resistance. We present direct evidence that blood vessels are aldosteronogenic. The production of aldosterone in blood vessels was compared between stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. Vascular aldosterone and CYP11B2 mRNA levels were significantly increased in 2-week-old SHRSP versus WKY rats. However, the vascular aldosterone levels in 4- and 9-week-old SHRSP and WKY rats were similar. High sodium intake further increased both blood pressure and vascular aldosterone synthesis in the SHRSPs. Both the local renin-angiotensin-aldosterone system (RAAS) and the vascular 11beta-HSDII level are critically important in the pathophysiology of cardiovascular disorders.

The possible roles of mineralocorticoid receptor and 11beta-hydroxysteroid dehydrogenase type 2 in cardiac fibrosis in the spontaneously hypertensive rat

In hypertension, aldosterone has been demonstrated to play a crucial role in cardiac fibrosis, which generally increases cardiac morbidity and death. However, few studies have reported the expression of the mineralocorticoid receptor (MR) and 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) in the heart under hypertensive conditions. Therefore, in this study, spontaneously hypertensive rats (SHR) were examined to elucidate the possible actions of mineralocorticoids via binding to MR. Wister Kyoto Rat (WKY), SHR, stroke-prone SHR (SHRSP), and malignant SHRSP (M-SHRSP) were used. Total RNA was extracted from the left ventricle of these rats, and examined for the expression levels of MR, 11beta-HSD2 and Collagen types 1 and 3 using reverse transcription real-time quantitative polymerase chain reaction employing the Light Cycler Instrument. Blood pressure was significantly different among each group. The mean mRNA levels for MR, 11beta-HSD2 and Collagen types 1 and 3 in M-SHRSP were found to be significantly increased compared to those of WKY, whereas no significant differences in mRNA levels were detected among SHR and SHRSP. Findings from the present study appear to demonstrate that MR and 11beta-HSD2 mRNA significantly rise in the left ventricle of M-SHRSP and increase of these mRNA is one of the cause of cardiac fibrosis.

Aldosterone in renal disease

PURPOSE OF REVIEW

Interruption of the renin-angiotensin-aldosterone system, chiefly with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, has yielded beneficial results in retarding injury and progression in numerous intrinsic renal diseases. The renoprotection offered by these agents is incomplete and far from optimal. Studying mediators of progression other than angiotensin II is therefore extremely important. The emerging role of aldosterone in progression of renal disease and the utility of its antagonism is discussed here.

RECENT FINDINGS

The experimental evidence linking aldosterone to renal disease is discussed. The exciting results from clinical studies employing mineralocorticoid receptor blockers are also described.

SUMMARY

Aldosterone antagonism offers additional antiproteinuric benefits to those achieved with angiotensin-converting enzyme inhibition. Long-term trials addressing effectiveness and safety, especially in regards to hyperkalemia, are greatly needed.

Early inflammatory responses in experimental cardiac hypertrophy and fibrosis: effects of 11 beta-hydroxysteroid dehydrogenase inactivation

In epithelial tissues such as kidney, mineralocorticoid receptors (MR) are protected against glucocorticoid occupancy by the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) type 2. If the enzyme is congenitally inactive, or blocked by carbenoxolone, physiologic glucocorticoids act as MR agonists in such tissues. In most nonepithelial tissues, including cardiomyocytes, 11 beta HSD2 is expressed at minimal levels; in these tissues physiologic glucocorticoids act as MR antagonists, with the basis for this tissue selectivity currently unknown. Vascular smooth muscle cells (VSMC) express MR and 11 beta HSD1/2, with 11 beta HSD1 reported to show uncharacteristic oxidase activity, so that VSMC thus constitute a potential physiologic aldosterone target tissue. Because mineralocorticoid/salt administration triggers marked inflammatory responses in coronary vasculature, we reasoned that VSMC (like epithelial) MR may be activated by glucocorticoids if the protective enzyme is blocked. We thus gave uninephrectomized rats 0.9% NaCl solution to drink, and deoxycorticosterone (DOC, as a single 20 mg sc dose) or carbenoxolone (CBX, 2.5 mg/d in the drinking solution). Both DOC and CBX increased systolic blood pressure, heart, and kidney weight, and expression of cyclooxygenase 2, ED-1-positive macrophages, and osteopontin, with effects of both DOC and CBX blocked by the selective MR antagonist eplerenone. These findings suggest that local glucocorticoid excess, reflecting lower VSMC 11 beta HSD1/2 activity may mimic systemic mineralocorticoid excess, and play a direct etiologic role in coronary vascular inflammatory responses under circumstances of a high salt intake.

Na/H exchange isoform 1 is involved in mineralocorticoid/salt-induced cardiac injury

Long-term exposure of uninephrectomized rats to desoxycorticosterone acetate (DOCA)/salt induces cardiac fibrosis and hypertrophy through mineralocorticoid receptors (MRs). However, the underlying cellular mechanisms remain unclear. To determine whether Na/H exchange isoform 1 (NHE1) is involved in the cellular mechanisms, we examined the effects of a specific NHE1 inhibitor, cariporide, and an MR antagonist, spironolactone, on DOCA/salt-induced cardiac fibrosis and hypertrophy. Uninephrectomized rats were given 20 mg of DOCA (single subcutaneous injection) plus 0.9% NaCl/0.3% KCl to drink and were killed at 8 days. Two groups of rats given DOCA/salt were treated with either spironolactone (50 mg/kg per day SC) or cariporide (30 mg/kg per day PO) for 8 days. Control rats were treated with only high salt after the operation. The DOCA/salt-induced perivascular collagen deposition was completely abolished by cariporide and spironolactone. DOCA/salt-induced interstitial collagen deposition was partially and completely suppressed by spironolactone and cariporide, respectively. The rats exposed to DOCA/salt had cardiocyte hypertrophy in the subendocardial and subepicardial regions, a finding that was completely inhibited by cariporide but not by spironolactone. In rats given DOCA/salt, NHE1 protein expression was markedly increased. This was partially and completely reversed by spironolactone and cariporide, respectively. We concluded that cardiac NHE1 contributes to DOCA/salt-induced cardiac fibrosis and hypertrophy and that the NHE1 inhibitor cariporide completely prevents the detrimental effects of DOCA/salt on the heart. We also demonstrated that DOCA/salt-induced cardiac injury through the MRs partly occurs through NHE1 activation.

Inhibitory effect of natriuretic peptides on aldosterone synthase gene expression in cultured neonatal rat cardiocytes

BACKGROUND

Although previously thought to be synthesized solely in adrenal cortex, we have recently showed that aldosterone is also produced in and the expression of CYP11B2 mRNA was induced in the failing or hypertensive human ventricle. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones with wide biological effects, including inhibition of renin and aldosterone production. We hypothesized that natriuretic peptides reduce the expression of CYP11B2 mRNA in the heart.

METHODS AND RESULTS

To test this hypothesis, we examined whether endogenous or exogenous natriuretic peptides reduce the expression of CYP11B2 mRNA using real-time reverse transcription-polymerase chain reaction. By using HS 142-1, a functional guanylyl cyclase-A type receptor antagonist, we showed that angiotensin II (AngII) pretreated with HS 142-1 increased CYP11B2 mRNA expression (1.62+/-0.12-fold, HS 142-1+AngII 10(-7) mol/L versus AngII 10(-7) mol/L alone, P<0.0001). The treatment with exogenous (10(-6) mol/L) ANP and BNP reduced CYP11B2 mRNA expression (ANP, P=0.0042; BNP, P=0.0012).

CONCLUSIONS

We showed that endogenous and exogenous natriuretic peptides reduced CYP11B2 mRNA expression in cultured neonatal rat cardiocytes. This may inhibit the cardiac renin-angiotensin-aldosterone system by suppressing the gene expression of CYP11B2 and restraining cardiac hypertrophy and fibrosis.

Aldosterone-induced inflammation in the rat heart : role of oxidative stress

Heart failure and hypertension have each been linked to an induction of oxidative stress transduced by neurohormones, such as angiotensin II and catecholamines. Herein, we hypothesized that aldosterone (ALDO) likewise induces oxidative stress and accounts for a proinflammatory/fibrogenic phenotype that appears at vascular and nonvascular sites of injury found in both right and left ventricles in response to ALDO/salt treatment and that would be sustained with chronic treatment. Uninephrectomized rats received ALDO (0.75 micro g/hour) together with 1% dietary NaCl, for 3, 4, or 5 weeks. Other groups received this regimen in combination with an ALDO receptor antagonist, spironolactone (200 mg/kg p.o. daily), or an antioxidant, either pyrrolidine dithiocarbamate (PDTC) (200 mg/kg s.c. daily) or N-acetylcysteine (NAC) (200 mg/kg i.p. daily). Unoperated and untreated age- and gender-matched rats served as controls. We monitored spatial and temporal responses in molecular and cellular events using serial, coronal sections of right and left ventricles. Our studies included: assessment of systolic blood pressure; immunohistochemical detection of NADPH oxidase expression and activity; analysis of redox-sensitive nuclear factor-kappaB activation; in situ localization of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha mRNA expression; monitoring cell growth and infiltration of macrophages and T cells; and analysis of the appearance and quantity of fibrous tissue accumulation. At week 3 of ALDO/salt treatment and comparable to controls, there was no evidence of oxidative stress or pathological findings in the heart. However, at weeks 4 and 5 of treatment, increased gp91(phox) and 3-nitrotyrosine expression and persistent activation of RelA were found in endothelial cells and inflammatory cells that appeared in the perivascular space of intramural coronary arteries and at sites of lost cardiomyocytes in both ventricles. Coincident in time and space with these events was increased mRNA expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha. Macrophages, lymphocytes, and proliferating endothelial and vascular smooth muscle cells and fibroblast-like cells were seen at each of these sites, together with an accumulation of fibrillar collagen, or fibrosis, as evidenced by a significant increase in ventricular collagen volume fraction. Co-treatment with spironolactone, PDTC, or NAC attenuated these molecular and cellular responses as well as the appearance of fibrosis at vascular and nonvascular sites of injury. Furthermore, elevated systolic blood pressure in ALDO-treated rats was partially suppressed by spironolactone or either antioxidant. Thus, chronic ALDO/salt treatment is accompanied by a time-dependent sustained activation of NADPH oxidase with 3-nitrotyrosine generation and nuclear factor-kappaB activation expressed by endothelial cells and inflammatory cells. This leads to a proinflammatory/fibrogenic phenotype involving vascular and nonvascular sites of injury found, respectively, in both normotensive and hypertensive right and left ventricles. Spionolactone, PDTC, and NAC each attenuated these responses suggesting ALDO/salt induction of oxidative/nitrosative stress is responsible for the appearance of this proinflammatory phenotype.

Aldosterone antagonist improves diastolic function in essential hypertension

Experimental studies demonstrated that mineralocorticoid antagonists prevent or reverse myocardial fibrosis. Therefore, we tested the hypothesis that the aldosterone antagonist canrenone can improve left ventricular diastolic function in essential hypertension. Using digitized M-mode echocardiography and 24-hour blood pressure monitoring (ABPM), we realized a prospective, randomized, controlled study on 34 never-treated essential hypertensives with left ventricular diastolic dysfunction. Echocardiogram and ABPM were repeated after 6 months of effective antihypertensive treatment with ACE inhibitors and calcium antagonists (second evaluation) and then after a 6-month period with 17 patients randomly assigned to add canrenone 50 mg/d to the previous treatment (third evaluation). At the basal evaluation 32 patients had left ventricular concentric hypertrophy, and 2 patients had left ventricular concentric remodeling. All the patients had normal left ventricular systolic function. At the second evaluation blood pressure was reduced (P<0.0001), left ventricular mass index decreased (P<0.0001), and diastolic function improved (P<0.0001). After randomization, the canrenone and control groups had similar 24-hour blood pressure and left ventricular morpho-functional characteristics. At the third evaluation, despite unchanged blood pressure and similar decrease of left ventricular mass index, the canrenone group, compared with control group, showed a significantly greater increase in left ventricular diastolic indices. In essential hypertension, a low dose of aldosterone antagonist added to antihypertensive treatment significantly improved left ventricular diastolic function. This improvement, not accounted for by changes in blood pressure and left ventricular mass, can be therefore ascribed to a direct action of the drug on the myocardium.

Lower risk of postinfarct rupture in mouse heart overexpressing beta 2-adrenergic receptors: importance of collagen content

This paper addresses whether the enhanced left ventricular (LV) contractility and heart rate, seen in transgenic mice overexpressing beta -adrenergic receptor in the heart, might raise the incidence of LV rupture after myocardial infarct. Transgenic and wild-type mice underwent left coronary artery occlusion. Postinfarct deaths that occurred 1-7 days after surgery were analyzed. Hemodynamics, morphologic parameters, and collagen content in the LV were determined. A significantly lower incidence of LV rupture was observed in transgenic than in wild-type mice 3-5 days after myocardial infarct (2.5 versus 19.7%, p < 0.05), despite a similar infarct size between the two groups and better hemodynamic function in transgenic mouse hearts. Morphologic analysis showed a more severe infarct expansion in wild-type versus transgenic mice or in mice dying of rupture versus those that died of acute heart failure. Collagen content was higher in the LV of sham-operated transgenic than wild-type mice (p < 0.01) with both type I and type III collagen elevated. Such difference in collagen content between transgenic and wild-type mice was maintained in noninfarcted and infarcted LV. In conclusion, transgenic mice overexpressing beta -adrenergic receptor had a lower risk of cardiac rupture during the acute phase after infarction despite the markedly enhanced LV contractility and heart rate. As a hyperdynamic function due to beta-adrenergic activation would likely increase the risk of cardiac rupture and infarct expansion, the lack of rupture in this transgenic mouse model suggests that the interstitial collagen level is a more important factor than functional status in the pathogenesis of rupture and infarct expansion.

Spironolactone increases integrin beta3 gene expression in kidney and heart muscle cells

In clinical trials of heart failure, spironolactone, an antagonist of the mineralocorticoid receptor (MR), reduced mortality rates by unknown mechanisms. We hypothesized that spironolactone functions by upregulating expression of certain cardiovascular genes. An RNA differential display technique was used to identify genes whose expression was increased by spironolactone in an Xenopus kidney epithelial cell line (A6), a known target of aldosterone. We found that integrin beta3 gene expression was increased by spironolactone, and reversed by aldosterone or dexamethasone in a dose dependent manner. Competition binding studies and RT-PCR indicate the presence of MR in A6 cells, suggesting that regulation of expression occurred primarily through MR. Spironolactone also increased integrin beta3 expression in rat neonatal cardiomyocytes. In summary, spironolactone increases integrin beta3 gene expression in kidney epithelial cells and cardiomyocytes. The findings suggest new mechanisms for spironolactone actions with possible relevance to treatment of heart disease.

Idiopathic intracranial hypertension with primary aldosteronism: report of 2 cases

Although unconfirmed, the syndrome idiopathic intracranial hypertension (IIH), commonly seen in overweight 20- to 50-year-old women, has been proposed to have its origins in an endocrine-based disturbance of electrolytes. Herein we report on 2 women with IIH and primary aldosteronism (PAL). Aged 57 and 55 (patients 1 and 2), each had a longstanding history of mild-to-moderate arterial hypertension, recurrent hypokalemia, and headaches. They were found to have IIH at ages 51 and 45. PAL was diagnosed at ages 57 and 35, respectively, due to proven left adrenal adenoma in patient 1; and presumptive adrenal nodular hyperplasia in patient 2. This is the first report to appear in the English medical literature that describes an association between IIH and PAL. It raises the prospect that in some cases of IIH associated with arterial hypertension, an autonomous production of aldosterone should be considered.

Structural changes in small resistance arteries and left ventricular geometry in patients with primary and secondary hypertension

OBJECTIVE

To prospectively evaluate the interrelationships between left ventricular (LV) geometry and structural characteristics of the vessel wall in small resistance arteries in patients with consecutive primary and secondary hypertension.

METHODS

In 14 patients with phaeochromocytoma, 12 with primary aldosteronism, 25 with renovascular, 25 with essential hypertension and 12 normotensive controls, an echocardiographic study for the measurement of LV mass index and relative wall thickness (RWT) was performed. Morphological characteristics of small resistance arteries (relaxed diameter < 300 microm) were directly evaluated by a micromyographic technique.

RESULTS

A total of 25 patients had normal LV mass and geometry, 28 patients had normal RWT (< 0.45) and 23 patients had a RWT >or= 0.45; all normotensive subjects had normal LV mass and geometry. Media to lumen ratio (M/L) in subcutaneous small arteries was greater in hypertensive patients with concentric LV hypertrophy in respect to normotensives (ANOVA P = 0.01) and hypertensives with normal LV geometry (ANOVA P = 0.05). In the whole group of hypertensive patients the correlation coefficient between M/L and LV mass index was 0.33 (P < 0.05); the correlation coefficient between M/L and RWT was 0.46 (P < 0.01) and it was higher in primary aldosteronism (r = 0.67) and renovascular hypertension patients (r = 0.46).

CONCLUSIONS

A close relation between morphology of subcutaneous small resistance arteries and LV geometric patterns may be observed in hypertensive patients; this relationship is more evident when the renin-angiotensin-aldosterone system is activated.

Aldosterone modulates the effect of angiotensin II on the electrical properties of rat heart

Influence of aldosterone on the effect of angiotensin II on action potential duration and cardiac refractoriness was investigated in isolated ventricle of adult rats treated with aldosterone (2 microM/kg/d, intraperitoneally) for 48 h. Results indicated that angiotensin II (10-8 M) increases action potential duration at 50 and 90% of repolarization by 33 +/- 8.3% and 76 +/- 6.5% (p < 0.05), respectively (p < 0.05). Cardiac refractoriness and rheobase were increased by the peptide. These results contrast with those found in controls in which angiotensin II (10-8 M) reduces action potential duration at 50 and 90% of repolarization by 31.8 +/- 3.7% and 23 +/- 4.1% (p < 0.05), respectively, and decreases refractoriness. The increase in cardiac refractoriness elicited by angiotensin II on rats treated with aldosterone was reversed by verapamil (10-6 M) added to the bath. Moreover, verapamil significantly reduced the increment in action potential duration, at 90% repolarization, elicited by the peptide in presence of aldosterone, which suggests than an increase in inward calcium current is involved in the effect of angiotensin II. Aldosterone, however, did not influence effect of isoproterenol on action potential duration and refractoriness. Aldosterone modulates effect of angiotensin II on electrical properties of the heart. These findings indicate that effect of angiotensin II on electrical and probably other properties of the heart must be evaluated considering the presence or absence of aldosterone.

Aldosterone breakthrough during angiotensin II receptor antagonist therapy in stroke-prone spontaneously hypertensive rats

Aldosterone breakthrough during ACE inhibitor therapy has been reported. This study investigates changes in plasma aldosterone concentration (PAC) and its mechanism and effects on target organ damage during long-term angiotensin II type 1 (AT1) receptor antagonist (AT1A) therapy in hypertensive rats. An AT1A (candesartan, 1 mg/kg per day PO) was administered in stroke-prone spontaneously hypertensive rats from 4 weeks of age for 34 weeks. PAC was significantly decreased during the first 4 weeks but showed aldosterone breakthrough after 8 weeks of AT1A administration. Plasma angiotensin II concentration was significantly elevated, whereas no change was seen in plasma ACTH or serum potassium. The mechanism(s) of aldosterone breakthrough were investigated by giving high doses of candesartan (3 mg/kg per day PO), dexamethasone (200 microg/kg per day IP), or the AT2 antagonist (PD123319, 10 mg/kg per day SC) during the last week of the 24-week AT1A treatment period. Dexamethasone and AT2 antagonist but not high-dose AT1A produced a significant decrease in PAC, with a larger decrease produced by the AT2 antagonist. To clarify the effects of the residual aldosterone, effects of coadministration of low-dose spironolactone (10 mg/kg per day SC), an aldosterone antagonist, on left ventricular hypertrophy and expression of brain natriuretic peptide mRNA were determined. Low-dose spironolactone further improved left ventricular hypertrophy and brain natriuretic peptide mRNA expression despite no additional depressor effect. These results suggest that aldosterone breakthrough occurs during long-term AT1A therapy, mainly by an AT2-dependent mechanism. Residual aldosterone may attenuate the cardioprotective effects of AT1A.

Blood pressure, cardiac, and renal responses to salt and deoxycorticosterone acetate in mice: role of Renin genes

Several studies have demonstrated that mice are polymorphic for the number of renin genes, with some inbred strains harboring one gene (Ren-1(c)) and other strains containing two genes (Ren-1(d) and Ren-2). In this study, the effects of 1% salt and deoxycorticosterone acetate (DOCA)/salt were investigated in one- and two-renin gene mice, for elucidation of the role of renin in the modulation of BP, cardiac, and renal responses to salt and DOCA. The results demonstrated that, under baseline conditions, mice with two renin genes exhibited 10-fold higher plasma renin activity, 100-fold higher plasma renin concentrations, elevated BP (which was angiotensin II-dependent), and an increased cardiac weight index, compared with one-renin gene mice (all P < 0.01). The presence of two renin genes markedly increased the BP, cardiac, and renal responses to salt. The number of renin genes also modulated the responses to DOCA/salt. In one-renin gene mice, DOCA/salt induced significant renal and cardiac hypertrophy (P < 0.01) even in the absence of any increase in BP. Treatment with losartan, an angiotensin II AT(1) receptor antagonist, decreased BP in two-renin gene mice but not in one-renin gene mice. However, losartan prevented the development of cardiac hypertrophy in both groups of mice. In conclusion, these data demonstrate that renin genes are important determinants of BP and of the responses to salt and DOCA in mice. The results confirm that the Ren-2 gene, which controls renin production mainly in the submaxillary gland, is physiologically active in mice and is not subject to the usual negative feedback control. Finally, these data provide further evidence that mineralocorticoids promote cardiac hypertrophy even in the absence of BP changes. This hypertrophic process is mediated in part by the activation of angiotensin II AT(1) receptors.

Cardiovascular effects of canrenone in patients with preascitic cirrhosis

In patients with cirrhosis and portal hypertension, standing induces a reduction in cardiac index (CI) and an increase in systemic vascular resistance index. Our previous studies indicate that this abnormal hemodynamic response to standing is due to an altered myocardial function, because cirrhotic patients are unable to compensate for the reduced preload with an increase in left ventricular (LV) ejection fraction (EF) and stroke volume. To evaluate whether the cardiac dysfunction in cirrhosis is influenced by canrenone, an aldosterone antagonist, 8 patients with preascitic, nonalcoholic cirrhosis, and portal hypertension underwent echocardiographic assessment of LV function and systemic hemodynamics and determinations of plasma volume, urinary sodium excretion, and plasma renin activity (PRA), aldosterone (PAC), and norepinephrine (PNE) when on a 150-mmol/d-sodium diet (baseline), after 1 month on canrenone (100 mg/d) plus a 40-mmol/d-sodium diet and after 1 month on canrenone plus a 150-mmol/d-sodium diet. Echocardiographic evaluation was performed with the patient in the supine position and during active standing. At baseline, patients had high plasma volume and normal renal function, PRA, PAC, and PNE. CI, LVEF, and stroke volume index were also normal. Standing caused a significant reduction in CI and LVEF. After canrenone and either sodium diet, CI significantly decreased, and PRA and PNE increased in the supine position. On standing, LVEF and CI did not decrease further. Plasma volume significantly decreased only after low-sodium diet plus canrenone. In conclusion, canrenone normalizes the cardiac response to the postural challenge in patients with preascitic cirrhosis.

An aldosterone synthase gene variant is associated with improvement in left ventricular ejection fraction in dilated cardiomyopathy

OBJECTIVE

To assess whether renin-angiotensin-aldosterone (RAA) system gene polymorphisms shown to be associated with alterations in the activity of the system, may predict cardiac function changes subsequent to initiating medical therapy in heart failure.

METHODS

The impact of RAA system genotypes on left ventricular ejection fraction (LVEF) following therapy to patients with idiopathic dilated cardiomyopathy (IDC) and class II-III heart failure was assessed. In 107 patients LVEF and LV dimensions were determined using radionuclide ventriculography and echocardiography prior to and subsequent to receiving furosemide, digoxin and angiotensin-converting enzyme (ACE) inhibitor therapy. Patients and controls were genotyped for variants of the ACE (insertion-deletion polymorphism), angiotensinogen (AGT; M235T polymorphism) and the aldosterone synthase (CYP11B2, C-344T polymorphism) genes.

RESULTS

RAA system genotypes were not significantly associated with LVEF prior to initiating medical therapy. However, the CYP11B2 gene variant (P=0.0064 on covariate analysis [adjusted for multiple genotyping] with a 1-2% chance of false positive data), but neither the ACE, nor the AGT variants, predicted improvement in LV ejection fraction in patients on medical therapy.

CONCLUSION

A CYP11B2 gene variant predicts the variable improvement in LV ejection fraction that occurs subsequent to initiating medical therapy in IDC. These data suggest a role for the aldosterone synthase locus in regulating the progression of heart failure.

Reversible cardiac fibrosis and heart failure induced by conditional expression of an antisense mRNA of the mineralocorticoid receptor in cardiomyocytes

Cardiac failure is a common feature in the evolution of cardiac disease. Among the determinants of cardiac failure, the renin-angiotensin-aldosterone system has a central role, and antagonism of the mineralocorticoid receptor (MR) has been proposed as a therapeutic strategy. In this study, we questioned the role of the MR, not of aldosterone, on heart function, using an inducible and cardiac-specific transgenic mouse model. We have generated a conditional knock-down model by expressing solely in the heart an antisense mRNA directed against the murine MR, a transcription factor with unknown targets in cardiomyocytes. Within 2-3 mo, mice developed severe heart failure and cardiac fibrosis in the absence of hypertension or chronic hyperaldosteronism. Moreover, cardiac failure and fibrosis were fully reversible when MR antisense mRNA expression was subsequently suppressed.

Aldosterone is produced from ventricles in patients with essential hypertension

This study was designed to examine whether aldosterone is produced from the hearts of patients with essential hypertension without left ventricular systolic dysfunction (LVSD). The study population consisted of 20 patients with essential hypertension without LVSD and 22 control subjects. Plasma levels of aldosterone, serum ACE activity, and B-type natriuretic peptide levels were measured in the anterior interventricular vein (AIV), coronary sinus, and aortic root during cardiac catheterization. The plasma aldosterone levels were significantly higher in AIV and coronary sinus than in aortic root (99+/-11 versus 88+/-10 pg/mL, P<0.01, and 100+/-12 versus 88+/-10 pg/mL, P<0.01, respectively) in the hypertension group. On the other hand, there were no significant differences in aldosterone levels for these sites in the control group. There were no significant differences in ACE activity levels between aortic root, AIV, and coronary sinus in either the hypertension or control group. The levels of B-type natriuretic peptide were significantly higher in AIV than in aortic root in both groups. The difference in aldosterone levels between AIV and aortic root (Delta Aldo[AIV-Ao]) had a significant positive correlation with the difference in ACE activity between AIV and aortic root (DeltaACE[AIV-Ao]) (r=0.501, P<0.05) in the hypertension group. Both Delta Aldo[AIV-Ao] and DeltaACE[AIV-Ao] had a significant positive correlation with diastolic blood pressure (r=0.498, P<0.05; r=0.577, P<0.01, respectively) in the hypertension group. We conclude that production of aldosterone is activated in the left ventricles in patients with essential hypertension without LVSD in proportion to the severity of hypertension.

Aldosterone synthase (CYP11B2) -344 C/T polymorphism is related to antihypertensive response: result from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation versus Atenolol (SILVHIA) trial

BACKGROUND

Our aim was to determine whether the aldosterone synthase (CYP11B2) -344 C/T polymorphism was associated with the blood pressure (BP)-lowering response to antihypertensive treatment.

METHODS

Patients with mild-to-moderate primary hypertension and left ventricular hypertrophy were randomized in a double-blind study to receive treatment with either the angiotensin II type 1 (AT1) receptor antagonist irbesartan (n = 43), or the beta1-adrenergic receptor blocker atenolol (n = 43). The aldosterone synthase (CYP11B2) -344 C/T polymorphism was analyzed using solid-phase minisequencing and related to BP reduction after 3 months treatment. Serum aldosterone levels were measured.

RESULTS

After 3 months treatment the mean reductions in BP were similar for both treatment groups. When assessing the systolic BP reduction in the irbesartan group, patients with the TT variant had a more pronounced reduction (-21 +/- 19 SD mm Hg, n = 17) than both the TC (-14 +/- 18 mm Hg, n= 18) and CC (0 +/- 17 mm Hg, n = 8) genotypes (P = .04). There was no association between this polymorphism and the diastolic BP response. The -344 C/T polymorphism was not associated with the BP response to atenolol. Nor was it related to the baseline serum aldosterone level.

CONCLUSIONS

The aldosterone synthase -344 C/T polymorphism was related to the BP-lowering response in hypertensive patients treated with the AT1-receptor antagonist irbesartan.

Cardiac and vascular fibrosis and hypertrophy in aldosterone-infused rats: role of endothelin-1

Increased endothelin-1 (ET-1) or aldosterone may be associated with promotion of cardiovascular hypertrophy and fibrosis. We evaluated whether the selective ETA receptor-antagonist BMS 182874 (BMS) prevents cardiac and vascular collagen deposition and hypertrophy in aldosterone-infused rats. Rats received subcutaneous aldosterone (0.75 microg/h) and 1% sodium chloride in drinking water +/- BMS (40 mg/kg per day in food) for 6 weeks. Heart and aorta were cross-sectioned and stained with Sirius red. Heart weight did not change with either aldosterone infusion or BMS treatment. Cardiac and aortic interstitial and perivascular collagen were quantified with videomorphometry. Aortic collagen and media cross-sectional area were significantly increased 3.5-fold (P < .01) and 1.13-fold (P < .05), respectively, with aldosterone infusion and decreased in BMS-treated rats (P < .05, P < .001, respectively). Aldosterone infusion increased interstitial and perivascular collagen in the left (1.6- and 2.7-fold, P < .05 and P < .01, respectively) and right ventricle (1.5- and 1.7-fold, P > .05 and P < .05, respectively). BMS prevented collagen deposition except for interstitial collagen in the right ventricle. Cardiac and aortic fibrosis were significantly increased in aldosterone-infused hypertensive rats. The ETA receptor antagonist prevented cardiac and aortic collagen deposition and aortic hypertrophy. This suggests a role for ET-1 in fibrosis of heart and large vessels in conditions associated with mineralocorticoid excess.

Fibrosis, matrix metalloproteinases, and inflammation in the heart of DOCA-salt hypertensive rats: role of ET(A) receptors

In deoxycorticosterone acetate (DOCA)-salt hypertension, the endothelin-1 system is activated and plays a role in cardiac fibrosis. Remodeling of extracellular matrix (ECM) may lead to interstitial fibrosis, which may contribute to heart failure. Imbalance in synthesis and degradation of the ECM by matrix metalloproteinases (MMPs) as well as inflammation may play a role in matrix protein deposition and cardiac remodeling in hypertension. We measured expression of the extracellular matrix protein fibronectin, the activity of the gelatinases MMP-2 and MMP-9, the proinflammatory transcription factor NFkappaB, and the adhesion molecules, vascular cell adhesion molecule (VCAM)-1 and platelet-endothelial cell adhesion molecule (PECAM)-1 in hearts of DOCA-salt hypertensive (DS) rats treated or not with the endothelin ET(A) antagonist BMS 182874 (BMS). Unilaterally nephrectomized rats (UniNx) were compared with DS rats treated or not with BMS 40 mg/kg/d. Fibronectin deposition was detectable at the first week, and remained elevated thereafter. This increase was abrogated by administration of the ET(A) antagonist. Enzymatic activity of gelatinases was increased (P<0.01) in DS compared with control during the first and second week. BMS blocked the increase of MMP-2 and MMP-9 activity at week 1 (P<0.05); MMP activity remained lower than in DS at week 2. NF-kappaB binding activity in DS was higher (P<0.05) than it was in controls during the second week, and was reduced by BMS. The adhesion molecules VCAM-1 and PECAM-1, and the antiapoptotic molecule xIAP were upregulated in the left ventricle of the heart of DS rats and downregulated in the rats treated with the ET(A) antagonist. In conclusion, cardiac extracellular remodeling in rats with endothelin-dependent hypertension was associated with increased fibronectin, MMP activity, and upregulation of inflammatory mediators, all of which were reduced by ET(A) antagonism.

Influence of plasma aldosterone on left ventricular geometry and diastolic function in treated essential hypertension

Since aldosterone is known to promote interstitial fibrosis in cardiac tissues, it is possible that aldosterone may influence cardiac structure and function. In the present study, we investigated whether plasma aldosterone concentration (PAC) is related to the distinct patterns of left ventricular (LV) geometry and LV diastolic function in treated essential hypertension. In 92 patients with chronically treated essential hypertension, two-dimensional and Doppler echocardiographic examinations were performed and LV inflow velocities were measured for evaluation of LV diastolic function. When patients were divided into four groups by the different LV geometric patterns, PAC in patients with eccentric hypertrophy was significantly higher than in those with concentric hypertrophy (15.2+/-2.1 vs. 10.0+/-0.7 ng/dl, p<0.01). However, the ratio of the peak velocity of early diastolic filling to that of atrial filling (EIA), an index of LV diastolic function, was significantly decreased in patients with concentric hypertrophy compared with those showing normal geometry. In the relationship between PAC and LV diastolic function, PAC was negatively correlated with EIA (r=-0.35, p<0.05) only in the subgroup with normal relative wall thickness (i.e., without the concentric change in LV geometry). A multiple linear regression analysis showed that PAC was one of the independent determinants of E/A in the overall subject group. These observations indicate that PAC is associated with the eccentric change in LV geometry in patients with treated essential hypertension and also suggest that the increase in PAC participates in the impairment of LV diastolic function apart from the concentric change in LV geometry, although concentric hypertrophy clearly impairs LV diastolic function.

The renin-angiotensin-aldosterone system and vascular remodeling

Cardiac fibrosis can be accompanied initially by diastolic and ultimately by systolic ventricular dysfunction. Clinical and experimental evidence suggests a clear association between such adverse structural remodeling and activation of the circulating renin-angiotensin-aldosterone system (RAAS). Infusion of either of two RAAS effector hormones, angiotensin II and aldosterone, in rats evokes perivascular fibrosis of arteries and arterioles of the heart and kidneys. Additionally, increasing evidence indicates locally produced angiotensin II and aldosterone have important paracrine and autocrine actions that play a role in vascular remodeling. Both angiotensin II and aldosterone receptor antagonists have been shown to attenuate the appearance of cardiac and renal fibrosis.

Mineralocorticoids and cardiac fibrosis: the decade in review

1. Over the past decade, aldosterone has been shown to have direct extra-epithelial actions and substantial (patho)physiological roles in the cardiovascular system in the context of inappropriate salt status. In experimental studies on uninephrectomized rats given 0.9% NaCl solution to drink, these include blood pressure elevation via activation of circumventricular mineralocorticoid receptors in the central nervous system and production of pressure-independent cardiac hypertrophy and fibrosis by a direct effect on the heart. 2. In the Randomized Aldactone Evaluation Study (RALES) trial, patients with severe congestive heart failure (CHF) were continued on their current therapy (angiotensin-converting enzyme inhibitor, diuretic etc.) and given either placebo or spironolactone at an average dose of 26 mg/day. Mineralocorticoid receptor inhibition was accompanied by a 30% improvement in mortality and 35% less hospitalization, striking confirmation of a pathophysiological role for aldosterone in CHF. 3. Although the current basic and clinical studies are conflicting, there is evidence both for aldosterone synthesis by the failing human heart and for substantial cardiac metabolism of aldosterone. The extent to which this potential paracrine source for aldosterone may be involved in cardiac hypertrophy and cardiac fibrosis remains to be established. 4. Belatedly, aldosterone-induced proteins (e.g. serum and glucocorticoid-regulated kinase (SGK)) have been identified in epithelial mineralocorticoid target tissue. Studies are currently in progress on the cellular and molecular mechanisms involved in the coronary vasculitis provoked early in the mineralocorticoid/salt model, which, in turn, appears to trigger the subsequent perivascular and interstitial fibrotic response.

Alteration of cardiac and renal functions in transgenic mice overexpressing human mineralocorticoid receptor

The mineralocorticoid receptor (MR), a ligand-dependent transcription factor, mediates aldosterone actions in a large variety of tissues. To explore the functional implication of MR in pathophysiology, transgenic mouse models were generated using the proximal human MR (hMR) promoter to drive expression of hMR in aldosterone target tissues. Tissue-specific analysis of transgene expression in two independent transgenic animal (TG) lines by ribonuclease protection assays revealed that hMR is expressed in all mineralocorticoid-sensitive tissues, most notably in the kidney and the heart. TG exhibit both renal and cardiac abnormalities. Enlarged kidneys were histologically associated with renal tubular dilation and cellular vacuolization whose prevalence increased with aging. Renal clearance studies also disclosed a significant decrease in urinary potassium excretion rate in TG. hMR-expressing animals had normal blood pressure but developed mild dilated cardiomyopathy (increased left ventricle diameters and decreased shortening fraction), which was accompanied by a significant increase in heart rate. Differential gene expression analysis revealed a 2- to 5-fold increase in cardiac expression of atrial natriuretic peptide, serum- and glucocorticoid-induced kinase, and early growth response gene 1 as detected by microarrays; renal serum- and glucocorticoid-induced kinase was also induced significantly. Altogether, TG exhibited specific alteration of renal and cardiac functions, thus providing useful pathophysiological models to gain new insights into the tissue-specific mineralocorticoid signaling pathways.

New perspectives on the role of aldosterone excess in cardiovascular disease

1. Evidence from recent experimental and clinical studies suggests that excessive circulating levels of aldosterone can bring about adverse cardiovascular sequelae independent of the effects on blood pressure. Examples of these sequelae are the development of myocardial and vascular fibrosis in uninephrectomized, salt-loaded rats infused with mineralocorticoids and, in humans, an association of aldosterone with left ventricular hypertrophy, impaired diastolic and systolic function, salt and water retention causing aggravation of congestion in patients with established congestive cardiac failure (CCF), reduced vascular compliance and an increased risk of arrhythmias (resulting from intracardiac fibrosis, hypokalaemia, hypomagnesaemia, reduced baroreceptor sensitivity and potentiation of catecholamine effects). 2. These sequelae of aldosterone excess may contribute to the pathogenesis and worsen the prognosis of CCF and hypertension. 3. The heart and blood vessels may be capable of extra-adrenal aldosterone biosynthesis, raising the possibility that aldosterone may have paracrine or autocrine (and not just endocrine) effects on cardiovascular tissues. 4. The high prevalence of CCF, which is associated with secondary aldosteronism, and primary aldosteronism (PAL; recently recognized to be a much more common cause of hypertension than was previously thought) argue for an important role for aldosterone excess as a cause of cardiovascular injury. 5. The recognition of non-blood pressure-dependent adverse sequelae of aldosterone excess raises the question as to whether normotensive individuals with PAL, who have been detected as a result of genetic or biochemical screening among families with inherited forms of PAL, are at excess risk of cardiovascular events. 6. Provided that patients are carefully investigated in order to permit the appropriate selection of specific surgical (laparoscopic adrenalectomy for PAL that lateralizes on adrenal venous sampling) or medical (treatment with aldosterone antagonist medications) management and safety considerations for the use of aldosterone antagonists are kept in mind, the appreciation of a widening role for aldosterone in cardiovascular disease should provide a substantially better outlook for many patients with CCF and hypertension.

Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts

1. Previous in vivo studies in men and experimental animal models have shown that hyperaldosteronemia is correlated with cardiac fibrosis due to increased total collagen synthesis. As yet, it is unclear whether aldosterone has direct pro-fibrogenic effect on cardiac fibroblasts, the fibrogenic effector cell in the myocardium, and if so which procollagens specifically are synthesized at higher rates. 2. The present study aims at establishing whether de novo collagen synthesis by cardiac fibroblasts is enhanced following exposure for 2x24 h to pharmacological (10(-7) - 10(-8) M), near-physiological (10(-9) M) or physiological (10(-10) - 10(-11) M) aldosterone concentrations. During the last 24 h, cells were metabolically labelled with [35S]-methionine/[35S]-cysteine. Labelled procollagens were immunoprecipitated quantitatively using antibodies against specific procollagens. Contrary to expectations, 10(-7) M aldosterone inhibited significantly de novo synthesis of procollagens type I and IV (-35% and -42%, respectively). For procollagen type III, only a tendency towards inhibition was observed. At lower concentrations of aldosterone (10(-8) - 10(-10) M), synthesis of procollagens type I, III or IV was unaffected. 3. Cellular DNA synthesis under influence of aldosterone was evaluated by measuring BrdU incorporation. Cells were treated with aldosterone, while BrdU was added during the last 16 h of treatment. Aldosterone had no demonstrable effect on cellular proliferation. 4. Reverse transcription-polymerase chain reaction (RT - PCR) clearly demonstrated the presence of mineralocorticoid receptor mRNA in cardiac fibroblasts. 5. In spite of the expression of the mineralocorticoid receptor by cultured cardiac fibroblasts, the pro-fibrogenic effect of aldosterone as observed in vivo, is not likely to be due to a direct effect of this hormone in cardiac fibroblasts.

A new human MR splice variant is a ligand-independent transactivator modulating corticosteroid action

Aldosterone effects are mediated by the MR, which possesses the same affinity for mineralocorticoids and glucocorticoids. In addition to the existence of mechanisms regulating intracellular hormone availability, we searched for human MR splice variants involved in tissue-specific corticosteroid function. We have identified a new human MR isoform, hMRDelta5,6, resulting from an alternative splicing event skipping exons 5 and 6 of the human MR gene. hMRDelta5,6 mRNAs are expressed in several human tissues at different levels compared with wild-type human MR, as shown by real time PCR. Introduction of a premature stop codon results in a 75-kDa protein lacking the entire hinge region and ligand binding domain. Interestingly, hMRDelta5,6 is still capable of binding to DNA and acts as a ligand-independent transactivator, with maximal transcriptional induction corresponding to approximately 30-40% of aldosterone-activated wild-type human MR. Coexpression of hMRDelta5,6 with human MR or human GR increases their transactivation potential at high doses of hormone. Finally, hMRDelta5,6 is able to recruit the coactivators, steroid receptor coactivator 1, receptor interacting protein 140, and transcription intermediary factor 1alpha, which enhance its transcriptional activity. Ligand-independent transactivation and enhancement of both wild-type MR and GR activities by hMRDelta5,6 suggests that this new variant might play a role in modulating corticosteroid effects in target tissues.

Experimental cardiac fibrosis: differential time course of responses to mineralocorticoid-salt administration

The rapid (1-4 h) responses of epithelial target tissues to mineralocorticoids contrast with the days/weeks apparently required for responses in the cardiovascular system. The present study explores the time course and pattern of early events leading to cardiac fibrosis in the mineralocorticoid-salt rat model. Uninephrectomized rats were given deoxycorticosterone (20 mg, sc, weekly) plus 0.9% NaCl/0.3% KCl to drink and were killed at 2, 4, 8, 16, and 32 d. Type III collagen increased progressively from d 2, and blood pressure from d 4, with 4 and 8 d rats showing marked perivascular inflammatory cell infiltration. Apoptosis was also noted in perivascular areas at 4 and 8 d and in scar areas at 8, 16, and 32 d. Elevation of mineralocorticoid hormone levels inappropriate for salt status thus provokes a series of changes in cardiac vessels and myocytes leading to increased collagen deposition. When mineralocorticoid levels are elevated acutely by bolus injection, changes are discernible after 2 d, in contrast with previous infusion studies in which 3-4 wk were required for measurable changes.

Eplerenone suppresses constrictive remodeling and collagen accumulation after angioplasty in porcine coronary arteries

BACKGROUND

Coronary artery angioplasty triggers healing that causes constrictive remodeling. Because collagen accumulation correlates with constrictive remodeling and aldosterone has been implicated in collagen accumulation, we examined how aldosterone and the mineralocorticoid receptor antagonists spironolactone and eplerenone affect remodeling and collagen in porcine coronary and iliac arteries after angioplasty.

METHODS AND RESULTS

Twenty-four pigs were allocated into 4 treatment groups: oral eplerenone (100 mg/d), oral spironolactone (200 mg/d), subcutaneous aldosterone (400 microgram/d), or no treatment. Twenty-eight days after angioplasty of the coronary arteries, eplerenone increased total vessel area by 30% (P<0.05) and luminal area by nearly 60% (P<0.05) compared with the no-treatment group, without affecting neointima size. These effects were accompanied by a 65% reduction in neointimal and medial collagen density (both P<0.05). Spironolactone was less effective, and aldosterone tended to exert opposite effects on coronary artery structure after angioplasty. These effects were not observed in angioplastied iliac arteries.

CONCLUSIONS

Eplerenone attenuates constrictive remodeling after coronary artery angioplasty by mechanisms involving reduction in collagen accumulation, which thus appears to be an important contributor to constrictive remodeling of angioplastied coronary arteries.

Aldosterone induces angiotensin-converting-enzyme gene expression in cultured neonatal rat cardiocytes

BACKGROUND

The cardiac renin-angiotensin-aldosterone system is activated in failing hearts in proportion to the severity of the disease. We hypothesized that a positive feedback mechanism might exist within this system and contribute to the progression of the heart failure. Methods and Results-- To test this hypothesis, we examined whether angiotensin II or aldosterone induces the expression of angiotensin-converting-enzyme (ACE) mRNA in cultured neonatal rat ventricular cardiocytes. Expression of ACE mRNA was detected and quantified using real-time reverse transcription-polymerase chain reaction. Exposure to angiotensin II (10(-5) mol/L) for 24 hours had no significant effect on the expression of ACE mRNA (0.7+/-0.5-fold versus control, P=NS), but similar treatment with aldosterone (10(-5) mol/L) induced a 23.3+/-7.9-fold increase (P<0.01) in ACE mRNA expression. The effect of aldosterone was both time- (maximal effect, 24 hours) and dose-dependent (EC(50), 4x10(-7) mol/L), and it was significantly (P<0.01) inhibited by spironolactone, a specific mineralocorticoid receptor antagonist.

CONCLUSIONS

Aldosterone upregulates ACE mRNA expression, which is blocked by spironolactone in neonatal rat cardiocytes. Thus, spironolactone may suppress the progression of heart failure by blocking the effects of aldosterone and angiotensin II.

The Intracellular Localization of the Mineralocorticoid Receptor Is Regulated by 11β-Hydroxysteroid Dehydrogenase Type 2

11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2 has been considered to protect the mineralocorticoid receptor (MR) by converting 11beta-hydroxyglucocorticoids into their inactive 11-keto forms, thereby providing specificity to the MR for aldosterone. To investigate the functional protection of the MR by 11beta-HSD2, we coexpressed epitope-tagged MR and 11beta-HSD2 in HEK-293 cells lacking 11beta-HSD2 activity and analyzed their subcellular localization by fluorescence microscopy. When expressed alone in the absence of hormones, the MR was both cytoplasmic and nuclear. However, when coexpressed with 11beta-HSD2, the MR displayed a reticular distribution pattern, suggesting association with 11beta-HSD2 at the endoplasmic reticulum membrane. The endoplasmic reticulum membrane localization of the MR was observed upon coexpression only with 11beta-HSD2, but not with 11beta-HSD1 or other steroid-metabolizing enzymes. Aldosterone induced rapid nuclear translocation of the MR, whereas moderate cortisol concentrations (10-200 nm) did not activate the receptor, due to 11beta-HSD2-dependent oxidation to cortisone. Compromised 11beta-HSD2 activity (due to genetic mutations, the presence of inhibitors, or saturating cortisol concentrations) led to cortisol-induced nuclear accumulation of the MR. Surprisingly, the 11beta-HSD2 product cortisone blocked the aldosterone-induced MR activation by a strictly 11beta-HSD2-dependent mechanism. Our results provide evidence that 11beta-HSD2, besides inactivating 11beta-hydroxyglucocorticoids, functionally interacts with the MR and directly regulates the magnitude of aldosterone-induced MR activation.

Aldosterone and the hypertensive kidney: its emerging role as a mediator of progressive renal dysfunction: a paradigm shift

End-stage renal disease (ESRD) comprises an enormous public health burden, with an increasing incidence and prevalence. Hypertension is a major risk factor for progressive renal disease. This escalating prevalence suggests that newer therapeutic interventions and strategies are needed to complement current antihypertensive approaches. Although much evidence demonstrates that angiotensin II mediates progressive renal disease, recent evidence also implicates aldosterone as an important pathogenetic factor in progressive renal disease. Several lines of experimental evidence demonstrate that selective blockade of aldosterone, independent of renin-angiotensin blockade, reduces proteinuria and nephrosclerosis in the spontaneously hypertensive stroke-prone rat model and reduces proteinuria and glomerulosclerosis in the subtotally nephrectomized rat model (i.e. remnant kidney). Whereas pharmacological blockade with angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors reduces proteinuria and nephrosclerosis/ glomerulosclerosis, selective reinfusion of aldosterone restores these abnormalities despite continued renin-angiotensin blockade. Aldosterone may promote fibrosis by several mechanisms, including plasminogen activator inhibitor-1 expression and consequent alterations of vascular fibrinolysis, by stimulation of transforming growth factor-beta 1, and by stimulation of reactive oxygen species. Based on this theoretical construct, randomized clinical studies will be initiated to delineate the potential renal-protective effects of antihypertensive therapy utilizing aldosterone receptor blockade.

Effect of spironolactone on plasma brain natriuretic peptide and left ventricular remodeling in patients with congestive heart failure

OBJECTIVES

We sought to evaluate the effects of spironolactone on neurohumoral factors and left ventricular remodeling in patients with congestive heart failure (CHF).

BACKGROUND

Aldosterone (ALD) promotes collagen synthesis and structural remodeling of the heart. Spironolactone, an ALD receptor antagonist, is reported to reduce mortality in patients with CHF, but its influence on left ventricular remodeling has not been clarified.

METHODS

Thirty-seven patients with mild-to-moderate nonischemic CHF were randomly divided into two groups that received treatment with spironolactone (n = 20) or placebo (n = 17). We measured left ventricular volume and mass before treatment and after four months of treatment. We also measured the plasma levels of neurohumoral factors, such as atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), as well as plasma procollagen type III aminoterminal peptide (PIIINP), a marker of myocardial fibrosis.

RESULTS

Left ventricular volume and mass were significantly decreased and ejection fraction was significantly increased in the spironolactone group, while there were no changes in the placebo group. Plasma levels of ANP, BNP and PIIINP were significantly decreased after spironolactone treatment, but were unchanged in the placebo group. There was a significant positive correlation between the changes of PIIINP and changes of the left ventricular volume index (r = 0.45, p = 0.045) as well as the left ventricular mass index (r = 0.65, p = 0.0019) with spironolactone treatment.

CONCLUSIONS

These findings indicate that four months of treatment with spironolactone improved the left ventricular volume and mass, as well as decreased plasma level of BNP, a biochemical marker of prognosis and/or ventricular hypertrophy, suggesting that endogenous aldosterone has an important role in the process of left ventricular remodeling in nonischemic patients with CHF.