Biological determinants of aldosterone-induced cardiac fibrosis in rats

Aldosterone blockade over and above ACE-inhibitors in patients with coronary artery disease but without heart failure

Recent evidence points to a role for the renin-angiotensin-aldosterone system (RAAS) in the pathogenesis of atherosclerosis and its complications, including acute angina pectoris. Two large trials in heart failure have clearly demonstrated that blocking aldosterone improves mortality and that this benefit occurs over and above standard therapy with angiotensin-converting enzyme (ACE) inhibitors. The question that naturally arises from these landmark studies is whether aldosterone blockade would produce the same benefits in patients with coronary artery disease (CAD) but no heart failure. There are three reasons to believe this might be the case. Firstly, angiotensin II (Ang II) and aldosterone produce similar biological effects and Ang II withdrawal has been shown to benefit patients with angina; aldosterone blockade may therefore follow in the footsteps of ACE inhibitors, as it did in heart failure, and produce benefits in vascular patients without heart failure. Secondly, one of the main mechanisms which is thought to be responsible for the benefit of aldosterone blockade in the Randomised ALdactone Evaluation Study (RALES) and Eplerenone Post-AMI Heart Failure Survival Study (EPHESUS), is that it improves endothelial/vascular function and endothelial/vascular dysfunction is the fundamental abnormality in angina pectoris. Finally, aldosterone blockade has been shown to reduce atherosclerosis in animal studies of atherosclerosis without heart failure, which are analogous to CAD patients.

Aldosterone inhibition reduces the risk of sudden cardiac death in patients with heart failure

Sudden cardiac death (SCD) accounts for over 450,000 deaths annually in the USA. Sudden death is estimated to account for approximately 50% of all deaths from cardiovascular causes. Total cardiac mortality has decreased from 728,115 in 1989 to 719,456 in 1999 but the percentage of deaths that are sudden has actually increased from 38% to 47%. Prevention of SCD in patients with risk factors is a high priority for public health professionals. Aldosterone has been shown to be associated with myocardial inflammation, endothelial dysfunction and fibrosis. There is evidence from clinical trials suggesting the role of aldosterone inhibition in prevention of SCD. We reviewed the potential mechanisms and discuss the clinical implications of Randomised ALdactone Evaluation Study (RALES) and Eplerenone Neurohormonal Efficacy and Survival Study (EPHESUS). The use of aldosterone receptor blockers had an overall effect of 21% risk reduction in SCD. Appropriate monitoring and counselling is essential while using either of the aldosterone inhibitors.

Effect of acute aldosterone administration on gene expression profile in the heart

Aldosterone is known to have a number of direct adverse effects on the heart, including fibrosis and myocardial inflammation. However, genetic mechanisms of aldosterone action on the heart remain unclear. This paper describes an investigation of temporal changes in gene expression profile of the whole heart induced by acute administration of a physiologic dose of aldosterone in the mouse. mRNA levels of 34,000 known mouse genes were measured at eight time points after aldosterone administration using oligonucleotide microarrays and compared with those of the control animals who underwent a sham injection. A novel software tool (CAGED) designed for analysis of temporal microarray experiments using a Bayesian approach was used to identify genes differentially expressed between the aldosterone-injected and control group. CAGED analysis identified 12 genes as having significant differences in their temporal profiles between aldosterone-injected and control groups. All of these genes exhibited a decrease in expression level 1-3 h after aldosterone injection followed by a brief rebound and a return to baseline. These findings were validated by quantitative RT-PCR. The differentially expressed genes included phosphatases, regulators of steroid biosynthesis, inactivators of reactive oxygen species, and structural proteins. Several of these genes are known to functionally mediate biochemical phenomena previously observed to be triggered by aldosterone administration, such as phosphorylation of ERK1/2. These results provide the first description of cardiac genetic response to aldosterone and identify several potential mediators of known biochemical sequelae of aldosterone administration in the heart.

Can the dextroenantiomer of the aromatase inhibitor fadrozole be useful for clinical investigation of aldosterone-synthase inhibition?

The beneficial effects of spironolactone, eplerenone, amiloride and potassium in preventing cardiovascular damage in various experimental models of salt-induced hypertension can be dissociated from blood pressure effects, and have drawn attention to the direct genomic and non-genomic actions of aldosterone at the level of the vessels, the heart and the kidneys. Exposure to endogenous aldosterone could be decreased by direct and specific aldosterone-synthase inhibition. FAD 286A, the dextroenantiomer of the aromatase inhibitor fadrozole, might be a first candidate to investigate in humans, the physiological impact and therapeutic properties of aldosterone-synthase inhibition, especially in various forms of primary aldosteronism.

The Antagonism of Aldosterone Receptor Prevents the Development of Hypertensive Heart Failure Induced by Chronic Inhibition of Nitric Oxide Synthesis in Rats

Aldosterone promotes cardiovascular inflammation and remodeling, both of which are characteristic changes in hypertensive and failing hearts. Since chronic inhibition of nitric oxide (NO) synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME) induces systemic hypertension associated with cardiovascular inflammation and remodeling, we examined the potential role of aldosterone in this process using eplerenone, a selective aldosterone receptor antagonist. Ten-week-old male Wistar-Kyoto rats were randomly divided into 3 groups: the control group (no treatment), the L-NAME group (received L-NAME 1 g/L in drinking water), and the L-NAME+Eplerenone group (L-NAME plus eplerenone at 100 mg/kg/day). After 8 weeks of the treatment, the L-NAME group showed significantly higher systolic blood pressure than the control group (198 +/- 7 vs. 141 +/- 3 mmHg, P < 0.05). Eplerenone did not affect the increase in blood pressure caused by L-NAME (189 +/- 12 mmHg). Chronic inhibition of NO synthesis increased the plasma aldosterone concentration and CYP11B2 mRNA in adrenal glands. Cardiac inflammation and fibrosis were detected in the L-NAME group, while both changes were completely prevented by eplerenone. Cardiac hypertrophy was induced in L-NAME group, but was partially prevented by eplerenone. In the L-NAME group, left ventricular fractional shortening (LVFS: 27 +/- 2 vs. 38 +/- 1%) and E/A ratio (1.7 +/- 0.1 vs. 2.1 +/- 0.1) were significantly lower and LV end-diastolic pressure (LVEDP) was higher (4.9 +/- 0.6 vs. 13.9 +/- 0.5 mmHg) without LV enlargement, compared with those in the control group (P < 0.05). Eplerenone completely normalized LVFS (36 +/- 2%), E/A ratio (2.2 +/- 0.1), and LVEDP (6.2 +/- 0.7 mmHg). These results suggest that chronic inhibition of NO synthesis induces cardiac inflammation and dysfunction via an aldosterone receptor-dependent mechanism.

Aldosterone antagonists in the treatment of heart failure

PURPOSE

The clinical benefits, adverse effects, pharmacokinetics, and recommendations for the appropriate use of the aldosterone antagonists spironolactone and eplerenone in patients with heart failure are reviewed.

SUMMARY

Heart failure is a clinical syndrome characterized by the functional inability of the ventricle to meet the metabolic demands of the body. Renal hypoperfusion occurs as a result of reduced cardiac output, resulting in the activation of the renin-angiotensin-aldosterone system, which compensates for the hypoperfusion. However, this contributes to the pathology of the disease by, among other actions, increasing the release of aldosterone. Aldosterone has been shown to cause coronary inflammation, cardiac hypertrophy, myocardial fibrosis, ventricular arrhythmias, and ischemic and necrotic lesions. There are currently two aldosterone antagonists commercially available in the United States, spironolactone and eplerenone. Spironolactone is a nonselective aldosterone antagonist, and eplerenone is selective to the aldosterone receptor. Although numerous clinical trials have evaluated the efficacy of each drug, no studies have directly compared spironolactone and eplerenone. Both have been shown to improve morbidity and mortality in patients with advanced heart failure. Adverse effects of both spironolactone and eplerenone include potentially life-threatening hyperkalemia, which can be induced by renal insufficiency, diabetes mellitus, advanced heart failure, advanced age, and concurrent drug therapy.

CONCLUSION

Spironolactone and eplerenone are life-saving agents in patients with advanced heart failure and may benefit patients with mild heart failure. Potassium and renal function must be routinely assessed to minimize the risk of life-threatening hyperkalemia.

Plasminogen activator inhibitor-1 deficiency protects against aldosterone-induced glomerular injury

This study tests the hypothesis that plasminogen activator inhibitor-1 (PAI-1) contributes to aldosterone-induced renal and cardiac injury. The effects of 12-week aldosterone (2.8 microg/day)/salt (1% drinking water) versus vehicle/salt on renal and cardiac histology and mRNA expression were determined in wild-type (WT) and PAI-1 deficient (PAI-1(-/-)) mice. Systolic blood pressure was similar in aldosterone-infused WT and PAI-1(-/-) mice until 12 weeks, when it was significantly higher in the WT mice. At 12 weeks, urine volume, sodium excretion, and sodium/potassium ratio were similarly increased in the two aldosterone-infused groups. In contrast, urine albumin excretion was greater in aldosterone-infused WT mice (mean+/-s.d.: 699.0+/-873.0 microg/24 h) compared to vehicle-infused WT (23.6+/-9.0 microg/24 h, P=0.003) or aldosterone-infused PAI-1(-/-) mice (131.6+/-110.6 microg/24 h, P=0.007). Aldosterone increased glomerular area to a greater extent in WT (4651+/-577 versus 3278+/-488 microm2/glomerulus in vehicle-infused WT, P<0.001) than in PAI-1(-/-) mice (3713+/-705 microm2/glomerulus, P=0.001 versus aldosterone-infused WT), with corresponding mesangial expansion. Renal collagen content was also increased in aldosterone-infused WT versus PAI-1(-/-) mice. In WT mice, aldosterone increased renal mRNA expression of PAI-1, collagen I, collagen III, osteopontin, fibronectin, monocyte chemoattractant protein-1 (MCP-1), and F4/80 (all P<0.05), but not transforming growth factor beta (TGF-beta). In PAI-1(-/-) mice, aldosterone increased renal expression of collagen I, osteopontin, fibronectin, and MCP-1, and tended to increase collagen III. Renal osteopontin expression was diminished in aldosterone-treated PAI-1(-/-) compared to aldosterone-treated WT mice (P=0.05). Aldosterone induced cardiac hypertrophy but not fibrosis in WT and PAI-1(-/-) mice. PAI-1 contributes to aldosterone-induced glomerular injury.

Eplerenone suppresses neointimal formation after coronary stent implantation in swine

BACKGROUND

Enhanced extracellular matrix accumulation rather than cell proliferation contributes to later stages of in-stent restenosis. Aldosterone itself has been shown to increase cardiovascular fibrosis, therefore, we studied the suppressive effects of eplerenone, a new aldosterone receptor antagonist, on neointimal hyperplasia after coronary stent implantation in swine.

METHODS

Palmatz-Shatz stents were implanted in the left anterior descending artery of 36 pigs. One hundred milligrams of Eplerenone was orally administered from 1 week before, to 4 weeks after stent implantation in Group E (n=18), and vehicle was given to Group C (n=18). Pigs were sacrificed 1 or 4 weeks after stent implantation. The number of infiltrating macrophages was calculated at 1 week. Morphometrical analysis was performed to measure the area of each layer, and %area of fibrosis and mRNA for collagen I, III and TGF-beta was analyzed by RT-PCR at 4 weeks.

RESULTS

The number of infiltrating macrophages was less in Group E than in Group C (p<0.01). The overall size of coronary arteries at 4 weeks was similar in both groups. However, the luminal area was larger in Group E than in Group C (p<0.05), and the intimal area was smaller in Group E than in Group C (p<0.05). The %area of fibrosis was significantly less in Group E than in Group C at 4 weeks (p<0.01). In Group E, the expression of mRNA for collagen I, III and TGF-beta was significantly reduced.

CONCLUSION

Orally administered eplerenone attenuated collagen accumulation within the neointima, thereby inhibiting neointimal hyperplasia after stent implantation.

The extracellular matrix and the cytoskeleton in heart hypertrophy and failure

Cell characteristics and phenotype depend on the nature of the extracellular matrix, the type and organization of integrins and cytoskeleton. The interactions between these components are poorly known at the myocyte level and during cardiac remodeling associated with cardiac hypertrophy and heart failure. We analyze here the nature and organization of extracellular matrix (ECM) proteins, cytoskeleton and integrins and their regulation by growth factors, such as angiotensin II, in normal myocyte growth and in pathological growth (hypertrophy) of the myocardium and heart failure.

Extracellular matrix and growth factors during heart growth

The effects of growth factors on tissue remodeling and cell differentiation depend on the nature of the extracellular matrix, the type and organization of integrins, the activation of metalloproteinases and the presence of secreted proteins associated to the matrix. These interactions are actually poorly known in the cardiovascular system. We describe here: 1) the main components of extracellular matrix within the cardiovascular system; 2) the role of integrins in the transmission of growth signals; 3) the shift in the expression of the components of the extracellular matrix (fibronectin and collagens) and the stimulation of the synthesis of metalloproteinases during normal and hypertrophic growth of the myocardium; 4) the effects of growth factors, such as Angiotensin II, Fibroblast Growth Factors (FGF), Transforming Growth Factor-beta (TGF-beta), on the synthesis of proteins of the extracellular matrix in the heart.

The Role of Aldosterone Blockers in the Management of Chronic Heart Failure

The neurohormonal model of congestive heart failure (CHF) has replaced the previously accepted hemodynamic model. A shift in this paradigm has allowed alterations in therapy of CHF such that agents that target the neurohormonal axis and specifically the renin-angiotensin-aldosterone system, with drugs such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and beta-blockers, are utilized. Employment of these drugs markedly improves survival in patients with CHF. Recent animal and human data demonstrate that aldosterone is directly pathogenic in this disease process and is insufficiently suppressed by these agents. Furthermore, when aldosterone is directly antagonized, vascular and myocardial damage is greatly ameliorated in both experimental animals and humans. Significant mortality benefits of aldosterone antagonists in patients with CHF from systolic dysfunction have been subsequently witnessed. Herein, the pathophysiology of CHF, the beneficial role of aldosterone antagonists in this disease process, and potential adverse consequences of these agents are reviewed.

Conditional mineralocorticoid receptor expression in the heart leads to life-threatening arrhythmias

BACKGROUND

Life-threatening cardiac arrhythmia is a major source of mortality worldwide. Besides rare inherited monogenic diseases such as long-QT or Brugada syndromes, which reflect abnormalities in ion fluxes across cardiac ion channels as a final common pathway, arrhythmias are most frequently acquired and associated with heart disease. The mineralocorticoid hormone aldosterone is an important contributor to morbidity and mortality in heart failure, but its mechanisms of action are incompletely understood.

METHODS AND RESULTS

To specifically assess the role of the mineralocorticoid receptor (MR) in the heart, in the absence of changes in aldosteronemia, we generated a transgenic mouse model with conditional cardiac-specific overexpression of the human MR. Mice exhibit a high rate of death prevented by spironolactone, an MR antagonist used in human therapy. Cardiac MR overexpression led to ion channel remodeling, resulting in prolonged ventricular repolarization at both the cellular and integrated levels and in severe ventricular arrhythmias.

CONCLUSIONS

Our results indicate that cardiac MR triggers cardiac arrhythmias, suggesting novel opportunities for prevention of arrhythmia-related sudden death.

Adverse cardiorenal effects of aldosterone: is aldosterone antagonism beneficial?

Aldosterone has recently been recognized as an important factor in the development and progression of cardiorenal disease. Animal and human data suggest that aldosterone contributes importantly to several disease states. These include congestive heart failure, coronary heart disease and progression of kidney disease. Recently, the discovery that aldosterone antagonists decrease pathologic injury in the kidneys and nonepithelial tissues, such as the myocardium and endothelium, has generated great controversy regarding the actual mechanisms of benefit of these agents. The available data is reviewed and conclusions drawn regarding the relative benefits of modulating aldosterone effects in the cardiovascular system and the kidney. In particular, the authors review their effects on reductions in cardiovascular events and progression of chronic kidney disease, as well as the safety and tolerability of these agents.

The role of mineralocorticoid receptor antagonists in the treatment of cardiac failure

In most countries the last two decades have seen a very substantial rise in the prevalence of heart failure, and in a majority of patients hypertension is both an antecedent condition and a contributing cause. Heart failure is also a major cause of hospital admissions; its amelioration and, as far as possible, prevention is therefore important in terms not only of morbidity and premature mortality for the individual patient, but also containment of healthcare costs. Over the past 5 years, mineralocorticoid receptor (MR) antagonists have been used in two major outcome trials (the Randomized Aldactone Evaluation Study [RALES] with spironolactone, and the Eplerenone Post-AMI Heart Failure Efficacy and Survival Study [EPHESUS]), in severe (New York Heart Association class III) and post-myocardial infarct heart failure, respectively. Experimental studies have largely focused, however, on various animal models of hypertension; on the basis of a portfolio of clinical studies on the efficacy of eplerenone, administered either alone and in combination as an antihypertensive agent, the novel MR antagonist was approved by the FDA for the treatment of hypertension, though it has yet to be launched. In this review, the two major outcome studies (RALES, EPHESUS) are discussed in the context of the new biology of aldosterone action. The relevance to heart failure of current experimental studies, largely on vascular protection, will also be discussed.

Effects of Eplerenone, a Selective Aldosterone Blocker, on the Progression of Left Ventricular Dysfunction and Remodeling in Rats with Dilated Cardiomyopathy

Aldosterone blockade reduces morbidity and mortality in patients with heart failure. We studied the effects of eplerenone, a novel aldosterone blocker, on the progression of left ventricular dysfunction and remodeling in rats with dilated cardiomyopathy after autoimmune myocarditis. Twenty-eight days after immunization, the surviving Lewis rats were randomized to 1 month's oral treatment with low-dose eplerenone (group L), high-dose eplerenone (group H) or vehicle (group V). Five of 15 (33%) rats in group V and 3 of 15 (20%) rats in group L died during the course of treatment. High-dose eplerenone significantly reduced cardiomyocyte hypertrophy, heart weight and heart weight to body weight ratio. Eplerenone improved left ventricular function in a dose-dependent manner. Central venous pressure and left ventricular end-diastolic pressure were lower, and +/-dP/dt and fractional shortening were higher in group H than group V. Eplerenone also attenuated myocardial fibrosis and reduced left ventricular mRNA expressions of TGF-beta(1) and collagen-III. Our results indicate that treatment with eplerenone improved left ventricular dysfunction and attenuated left ventricular remodeling in rats with heart failure.

Aldosterone directly stimulates cardiac myocyte hypertrophy

BACKGROUND

Clinical and experimental studies suggest that aldosterone modulates myocardial hypertrophy. From in vivo studies, it is not possible to distinguish between direct actions on myocyte growth and effects of mechanical load. In this study we tested the hypothesis that aldosterone induces myocyte hypertrophy in low-density, serum-free cultures of neonatal rat ventricular myocytes.

METHODS AND RESULTS

Hypertrophy was quantified by [(14)C]-phenylalanine incorporation and confocal microscopic assessment of myocyte surface area. Aldosterone caused a 27% increase in protein incorporation (EC(50) = 40 nmol/L) and a 29% increase in myocyte surface area compared with the vehicle control. This response was associated with increased mRNA levels of atrial natriuretic factor, alpha- and beta-myosin heavy chain measured by RNase protection assay, and it was suppressed by the mineralocorticoid receptor blocker spironolactone. Analysis of early signaling events showed that aldosterone stimulation acutely translocated protein kinase C (PKC)-alpha to the membrane fraction and increased the levels of phosphorylated ERK1/2 and JNK. PD 98059, an inhibitor of the ERK activator MEK (mitogen-activated protein kinase kinase) and bisindolylmaleimide I, an inhibitor of PKC activation, each blocked aldosterone-stimulated hypertrophy.

CONCLUSION

Aldosterone directly stimulates hypertrophy in neonatal rat ventricular myocytes. The growth response is dependent on the mineralocorticoid receptor and is associated with activation of ERK, JNK, and PKC-alpha.

Aldosterone upregulates connective tissue growth factor gene expression via p38 MAPK pathway and mineralocorticoid receptor in ventricular myocytes

The effect of aldosterone on connective tissue growth factor (CTGF) was examined in rat embryonic ventricular myocytes. Upon aldosterone treatment, CTGF expression was significantly increased in a dose and time-dependent manner. To explore the molecular mechanism for this upregulation, we examined the role of mineralocorticoid receptor. Pre-treatment of an antagonist (spironolactone) at 5-fold excess of aldosterone blocked the CTGF induction by aldosterone, suggesting that the upregulation was mediated by mineralocorticoid receptor. Aldosterone treatment resulted in activation of ERK1/2, p38 MAPK, and JNK pathways with a more transient pattern in p38 MAPK. Blocking studies using pretreatment of the inhibitor of each pathway revealed that p38 MAPK cascade may be important for aldosterone-mediated CTGF upregulation as evidenced by the blocking of CTGF induction by SB203580 (p38 MAPK inhibitor), but not by PD098059 (ERK1/2 inhibitor) and JNK inhibitor I. Interestingly, JNK inhibitor I and PD098059 decreased the basal level of CTGF expression. On the other hand, pretreatment of spironolactone abrogated the p38 MAPK activation, indicating that mineralocorticoid receptor mechanism is linked to p38 MAPK pathway. Taken together, our findings suggest that aldosterone induces CTGF expression via both p38 MAPK cascade and mineralocorticoid receptor and that cross-talk exists between the two pathways.

Eplerenone in the treatment of chronic heart failure

There has been a recent revival of interest in aldosterone receptor antagonists for the treatment of chronic heart failure. This was largely triggered by fresh insights into the role of aldosterone in a number of key pathophysiological processes, including fibrosis and remodeling, inflammation, and the potentiation of catecholamine effects. The therapeutic efficacy of spironolactone (Aldactone), Pfizer) in severe chronic heart failure was established by the Randomized Aldactone Evaluation Study, but hormonal side effects (gynecomastia) associated with the drug posed a problem. More recently, the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study has provided firm support for the use of eplerenone (Inspra, Pfizer) in heart failure following acute myocardial infarction in addition to neurohormonal blockade with angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers and beta-blockers. This strategy can be expected to benefit both mortality and morbidity. Due to the fact that eplerenone is a selective aldosterone receptor antagonist, it does not cause troublesome hormonal side effects. This is an important feature of the drug that is likely to help maintain compliance.

Cardioprotective Action of Perindopril versus Candesartan in Renovascular Hypertensive Rats

We investigated the effects of an angiotensin-converting enzyme inhibitor and an angiotensin II type 1 receptor blocker on cardiac hypertrophy in rats with renovascular hypertension. Renovascular hypertensive (Goldblatt) rats were surgically prepared from Wistar rats. Four weeks later, the rats showed a significant increase in blood pressure. At high doses, both the perindopril (1 mg/kg/day) and the candesartan (2 mg/kg/day) decreased the systolic pressure in these rats to the level of control Wistar rats. At low doses (perindopril 0.1 mg/kg/day and candesartan 0.1 mg/kg/day), these drugs lowered blood pressure to 85% of that in hypertensive rats. Echocardiographic and morphological studies revealed severe cardiac hypertrophy and fibrosis in untreated Goldblatt rats. High-dose treatment with both drugs suppressed the progression of hypertrophy and fibrosis. Also, low-dose perindopril prevented cardiac hypertrophy and fibrosis. In contrast, at the same levels of blood-pressure reduction, low-dose candesartan did not prevent cardiac fibrosis nor the upregulation of cardiac collagen types I and III mRNA observed in untreated Goldblatt rats. Atrial natriuretic peptide mRNA was up-regulated in untreated Goldblatt rats. These changes were significantly decreased by both doses of perindopril or the high dose of candesartan. Serum levels of angiotensin II and aldosterone were significantly higher in untreated Goldblatt rats. Both doses of perindopril inhibited activation of the renin-angiotensin system, whereas candesartan had weaker effects. In particular, serum aldosterone was 347 +/- 20 pg/ml in low-dose perindopril versus 1796 +/- 324 pg/ml in low-dose candesartan. These results suggest that there were no differences between the cardioprotective actions of perindopril and candesartan at high dosages. On the other hand, low-dose treatment with perindopril was more effective in preventing cardiac fibrosis than was low-dose treatment with candesartan, despite similar changes in blood pressure. It is possible that changes in aldosterone secretion are related to this difference.

Direct and indirect effects of aldosterone on cyclooxygenase-2 and interleukin-6 expression in rat cardiac cells in culture and after myocardial infarction

Aldosterone contributes to cardiac failure, which is associated with induction of inflammatory mediators. Moreover, aldosterone was shown to induce a vascular inflammatory phenotype in the rat heart. Using Western blotting and/or real-time RT-PCR, we examined the effect of aldosterone on the expression of the proinflammatory molecules, cyclooxygenase-2 (COX-2), and IL-6 in neonatal rat ventricular cardiac myocytes and fibroblasts as well as in adult cardiomyocytes after myocardial infarction. In cardiomyocytes, aldosterone induced COX-2 but not IL-6 expression. After 4-18 h of stimulation with 1 microm aldosterone, a significant increase in COX-2 protein expression was observed, preceded by an increase of COX-2 mRNA levels. After 18 h treatment, 100 nm and 1 microm aldosterone increased COX-2 protein amount by 2- and 4-fold, respectively. Consistently, aldosterone increased by 2.5-fold prostaglandin E(2) secretion in cardiomyocytes. In cardiac fibroblasts, aldosterone increased neither COX-2 nor IL-6 mRNA expression. Interestingly, prostaglandin E(2) (100 nm) strongly induced both proinflammatory molecules in fibroblasts and cardiomyocytes. Our results indicate that aldosterone directly induces COX-2 expression in cardiomyocytes and suggest that the subsequent increase in prostaglandin secretion may act in an autocrine and/or paracrine manner inducing in turn COX-2 and IL-6 expression. In vivo, myocardial infarction strongly increased both COX-2 and IL-6 expression in ventricular cardiomyocytes. Administration of the aldosterone antagonist RU28318 completely prevented COX-2 induction by infarction and partially inhibited the increase in IL-6 mRNA. These data suggest that after myocardial infarction, mineralocorticoid receptor activity is responsible for COX-2 induction and indirectly participates in IL-6 expression in cardiomyocytes.

Eplerenone, but not steroid withdrawal, reverses cardiac fibrosis in deoxycorticosterone/salt-treated rats

Aldosterone has been thought to act primarily on epithelia to regulate fluid and electrolyte homeostasis. Mineralocorticoid receptors (MR), however, are also expressed in nonepithelial tissues, such as the heart and vascular smooth muscle. Recently, pathophysiological effects of nonepithelial MR activation by aldosterone have been demonstrated in the context of inappropriate mineralocorticoid levels for salt status, including coronary vascular inflammation and cardiac fibrosis. These effects are mostly prevented by the concomitant administration of MR antagonists, but to date, no equivalent studies have determined whether MR blockade can reverse established inflammation and fibrosis. Uninephrectomized rats maintained on 0.9% NaCl solution to drink were treated as follows: group 1 served as controls; group 2 received deoxycorticosterone (DOC; 20 mg/wk) for 4 wk until death, and group 3 received DOC for 8 wk. Group 4 received DOC for 4 wk and no steroid from wk 5-8; group 5 received DOC for 8 wk and eplerenone in their chow during wk 5-8. DOC progressively raised cardiac collagen accumulation at 4 and 8 wk. Rats given DOC for 4 wk and killed at 8 wk showed levels of fibrosis identical to those in animals killed at 4 wk, i.e. persistently elevated above control values. Rats given DOC for 8 wk and eplerenone for the second half of the period showed cardiac collagen levels indistinguishable from control values. Values for inflammatory marker and NAD(P)H oxidase subunit expression in coronary vessels showed a similar pattern of response, with minor variation. Thus, MR antagonists do not only prevent cardiac fibrosis, but also reverse cardiac fibrosis once it is established. In addition, the continuing vascular inflammatory response and fibrosis after DOC withdrawal (group 4) support a role for activation of vascular MR by endogenous glucocorticoids in the context of tissue damage and generation of reactive oxygen species.

Chronic hyperaldosteronism in a transgenic mouse model fails to induce cardiac remodeling and fibrosis under a normal-salt diet

Primary aldosteronism causes severe hypertension in humans (Conn's syndrome) with cardiac hypertrophy, characterized by a fibrosis more severe than the one observed in patients with essential hypertension. This suggests that aldosterone by itself may have specific and direct effects on cardiac remodeling through the activation of the cardiac mineralocorticoid receptor. Experimental evidence obtained in studying uninephrectomized rats treated with aldosterone or deoxycorticosterone (DOC) together with salt loading has led to similar conclusions. To examine the direct consequences of chronically elevated aldosterone levels on cardiac pathophysiology, we analyzed a mouse model (α-epithelial Na channel −/−Tg) that is normotensive under normal-salt diet but exhibits chronic hyperaldosteronism. Sixteen-month-old transgenic rescue mice that were kept under a regular salt diet that contains a small amount of sodium (0.3% Na+) displayed a compensated PHA-1 phenotype with normal body weight, normal kidney index, normal blood pressure, but 6.3-fold elevated plasma aldosterone levels compared with the age-matched control group. Peripheral resistance of distal colon to aldosterone was shown by a significant decrease of the amiloride-sensitive rectal potential difference, and its diurnal cyclicity was blunted. Despite chronically high plasma aldosterone levels, these animals do not show any evidence of cardiac hypertrophy, remodeling, or fibrosis, using collagen staining and anti-α-skeletal and α-smooth actin immunochemical labeling of heart sections. Cardiac fibrosis as seen in DOC- or aldosterone/salt-treated animal models is therefore likely to be due to the synergistic effect of salt, aldosterone, and other confounding factors rather than to the elevated circulating aldosterone levels alone.

Expression and function of the human mineralocorticoid receptor: lessons from transgenic mouse models

The human mineralocorticoid receptor (hMR), a ligand-dependent transcription factor (NR3C2) which belongs to the nuclear receptor superfamily, mediates most of the known effects of aldosterone. Beside its involvement in the regulation of sodium balance and the control of blood pressure, aldosterone-hMR tandem also exerts important regulatory functions on the cardiovascular and central nervous systems. To study the molecular mechanisms involved in the tissue-specific expression of hMR and explore its functional implication in pathophysiology, transgenic mouse models have been generated using both targeted oncogenesis and MR overexpression. We have previously demonstrated that the transcription of hMR is directed by two alternative promoters, P1 and P2, which correspond to the 5'-flanking regions of the untranslated exons 1alpha and 1beta of the hMR gene, respectively. Utilization of P1 and P2 to drive expression of the SV40 large T antigen (TAg) in transgenic mice led us (i) to determine distinct tissue-specific patterns of promoter usage; (ii) to identify novel sites of MR expression including brown adipose tissue, thus providing a new functional link between aldosterone and energy homeostasis; (iii) to generate original immortalized cell lines derived from numerous aldosterone-sensitive tissues most notably distal nephron, brown fat, skin, liver, lung, brain, heart, blood vessels and inner ear. These differentiated cell lines represent suitable models to further explore cell-specific mineralocorticoid responses and cross-talk with other signaling pathways. Generation of transgenic mice in which hMR expression was directed by P1 promoter demonstrated the importance of MR in the cardiac and renal function. Morphological and functional alterations of the renal tubule were observed with basal decreased sodium/potassium ratio exacerbated under sodium depletion. Hypokinetic dilated cardiomyopathies were associated with tachycardia, arrhythmia but normal arterial blood pressure emphasizing the direct role of MR on cardiomyocyte function. Taken together, transgenic animal models constitute valuable experimental systems to gain new insights into the widespread and pleiotropic in vivo functions of MR.

Aldosterone-synthase overexpression in heart: a tool to explore aldosterone's effects

Clinical observations indicate that elevated aldosterone impairs cardiovascular function. The mechanisms, however, are not totally understood although total and cardiovascular mortality are decreased by aldosterone antagonists. Experimentally, increased plasma aldosterone induces pericoronary inflammation and cardiac fibrosis. Our laboratory has discovered that aldosterone is synthesized in the rat heart, and has demonstrated that this cardiac aldosterone is involved in post-infarction cardiac remodeling. In man, activated cardiac aldosterone production has been described in patients with heart failure. In transgenic mice that overexpress aldosterone-synthase in the heart, we observe a normal cardiac function but a major coronary dysfunction, more pronounced in males. These observations converge to a potential physiological and pathological relevance of this system. Beneficial effects of anti-aldosterone treatment in heart failure may thus be secondary in part to blockade of cardiac aldosterone action.

Aldosterone receptor antagonists for hypertension: what do they offer?

Aldosterone is an important and independent target for therapeutic intervention in hypertension and hypertension-related diseases. Its actions, once thought to be limited to the distal convoluted tubule of the kidney, are now recognised to be wide-ranging, including interactions with mineralocorticoid receptors in diverse cardiovascular sites to mediate vascular and myocardial remodelling and dysfunction. The latter are referred as non-epithelial actions. Spironolactone, an aldosterone receptor antagonist, is indicated for the treatment of mineralocorticoid hypertension, but its use is limited by an adverse effect profile that includes not only by hyperkalaemia, but also antiandrogenic and progestational effects resulting from its poor specificity for the aldosterone receptor. Eplerenone is the first selective aldosterone receptor antagonist to be developed and recently gained approval from the US FDA for treatment of systemic hypertension. This was based on studies which demonstrated that eplerenone had a blood pressure-lowering profile that was equivalent to existing antihypertensive agents, was useful for treatment of low-renin and systolic hypertension, maintained utility even as add-on therapy to other antihypertensive agents, and exerted beneficial effects on hypertension-related left ventricular hypertrophy and renal impairment. Perhaps most notably, eplerenone was generally well tolerated, and did not cause the antiandrogenic and progestational adverse effects commonly observed with spironolactone.

The cardiovascular effects of eplerenone, a selective aldosterone-receptor antagonist

BACKGROUND

The role of the renin-angiotensin-aldosterone system in the pathophysiology and treatment of hypertension and heart failure has been extensively studied. Angiotensin-converting enzyme inhibitors and angiotensin II-receptor blockers have been shown to effectively reduce blood pressure, protect the kidney, and reduce morbidity and mortality in patients with heart failure. Therefore, there is increased interest in the effects of aldosterone and the use of aldosterone-receptor antagonists in the treatment of cardiovascular disease. Eplerenone is the first selective aldosterone-receptor antagonist approved for the treatment of hypertension and left ventricular (LV) dysfunction after acute myocardial infarction (AMI).

OBJECTIVE

The goal of this article was to review the pharmacologic properties, clinical efficacy, and tolerability of eplerenone in the treatment of hypertension, LV dysfunction, and proteinuria.

METHODS

Relevant English-language articles were identified through searches of MEDLINE (1966-May 2003), Current Contents, and International Pharmaceutical Abstracts (1970-May 2003) using the terms hypertension, heart failure, eplerenone, aldosterone, and aldosterone antagonist. Other pertinent publications were identified from the reference lists of the identified articles. Information was also obtained from abstracts presented at national meetings and data on file with the manufacturer.

RESULTS

In clinical trials, eplerenone alone and in combination with renin-angiotensin blockade significantly reduced both systolic and diastolic blood pressure compared with placebo (P < 0.05 to P < 0.001). In EPHESUS (Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study), the addition eplerenone to optimal medical therapy reduced morbidity and mortality in patients with AMI and LV dysfunction, although the incidence of serious hyperkalemia was also significantly greater. In comparisons with spironolactone, eplerenone was associated with a lower incidence of gynecomastia and other sex hormone-related adverse effects.

CONCLUSIONS

Either alone or in combination with other antihypertensive agents, eplerenone appears to be effective for the treatment of hypertension. Morbidity and mortality were reduced when eplerenone was added to standard therapy for LV dysfunction complicating AMI. The use of eplerenone for hypertension or heart failure may be limited in patients at risk for hyperkalemia.

Transforming growth factor-beta-dependent and -independent pathways of induction of tubulointerstitial fibrosis in beta6(-/-) mice

Transforming growth factor-beta1 (TGF-beta1) and the renin-angiotensin-aldosterone system are key mediators in kidney fibrosis. Integrin alphavbeta6, a heterodimeric matrix receptor expressed in epithelia, binds and activates latent TGF-beta1. We used beta6 integrin-null mice (beta6(-/-)) to determine the role of local TGF-beta1 activation in renal fibrosis in the unilateral ureteral obstruction (UUO) model. Obstructed kidneys from beta6(-/-) mice showed less injury than obstructed kidneys from wild-type (WT) mice, associated with lower collagen I, collagen III, plasminogen activator inhibitor (PAI-1), and TGF-beta1 mRNA levels and lower collagen content. Infusion with either angiotensin II (Ang II) or aldosterone (Aldo) or combination in beta6(-/-) UUO mice significantly increased collagen contents to levels comparable to those in identically treated WT. Active TGF-beta protein expression in beta6(-/-) mice was less in UUO kidneys with or without Ang II infusion compared to matched WT mice. Activated Smad 2 levels in beta6(-/-) obstructed kidneys were lower than in WT UUO mice, and did not increase when fibrosis was induced in beta6(-/-) UUO mice by Ang II infusion. Anti-TGF-beta antibody only partially decreased this Ang II-stimulated fibrosis in beta6(-/-) UUO kidneys. In situ hybridization and immunostaining showed low expression of PAI-1 mRNA and protein in tubular epithelium in beta6(-/-) UUO kidneys, with increased PAI-1 expression in response to Ang II, Aldo, or both. Our results indicate that interruption of alphavbeta6-mediated activation of TGF-beta1 can protect against tubulointerstitial fibrosis. Further, the robust induction of tubulointerstitial fibrosis without increase in activated Smad 2 levels in obstructed beta6(-/-) mice by Ang II suggests the existence of a TGF-beta1-independent pathway of induction of fibrosis through angiotensin.

Mineralocorticoid action and sodium-hydrogen exchange: studies in experimental cardiac fibrosis

There is increasing evidence that the trigger for cardiac fibrosis in response to mineralocorticoid/salt administration is coronary vasculitis and that effects can be seen within days of deoxycorticosterone acetate (DOCA) administration. Furthermore, rapid, nongenomic mineralocorticoid effects on the sodium-hydrogen exchanger (NHE-1) in vascular smooth muscle cells have recently been described. That this mechanism may act as an inflammatory or profibrotic signal was tested by comparing the specific NHE-1 antagonist cariporide and the mineralocorticoid receptor antagonist K canrenoate in the rat model of mineralocorticoid/salt perivascular fibrosis over 8 d of DOCA/salt administration. Interstitial collagen, inflammatory cell infiltration, and inflammatory markers were determined. DOCA elevated blood pressure above control, cariporide +DOCA, or K canrenoate +DOCA rats, without cardiac hypertrophy. At 8 d interstitial collagen was significantly elevated in the DOCA-alone group, with levels in cariporide- and K canrenoate-treated rats not different from control. Expression of osteopontin, cyclooxygenase-2, and ED-1 were elevated by DOCA treatment, blocked by potassium canrenoate, and (for ED-1 and osteopontin) partially reduced by cariporide. These results suggest mineralocorticoid/salt-induced cardiac fibrosis may involve coronary vascular smooth muscle cell NHE-1 activity as a possible contributor to the cascade of transcriptional events that produce the characteristic coronary vasculitis seen with excess mineralocorticoid and salt.

Revisiting salt and water retention: new diuretics, aquaretics, and natriuretics

Diuretics continue to be a mainstay in patients with CHF. Conventional diuretic therapy is associated, however, with potentially deleterious neurohumoral activation and renal impairment. It is not known to what extent these neurohumoral effects are offset by concurrent therapy with ACE-I, beta-blockers, and other agents. In the past, there was no alternative to conventional diuretic therapy, so their potential for adverse outcome in the long term could not be assessed. Enhancement of the natriuretic peptide system could provide us with a better strategy to treat sodium and water retention. In a unique way, the natriuretic peptides combine several of the beneficial actions of the other diuretics, but without the associated cost. Natriuretic peptides, like conventional diuretics, are natriuretic and diuretic. There are important differences, however. First, unlike conventional diuretics, NPs do not activate RAAS. Activation of this system is associated with progression of CHF. Second, NPs inhibit the sympathetic nervous system, the activation of which is associated with heart failure progression, myocyte necrosis and apoptosis, and arrhythmias. Third, unlike conventional diuretics that lead to a decrease in GFR by reflex mechanisms. NPs maintain or even improve GFR. We now appreciate that some "old" drugs may be beneficial to CHF patients in a new way, as is the case with spironolactone. The survival benefit of this aldosterone antagonist is clear: its usefulness, however, may be more a result of both its antifibrotic actions in addition to its tradional role as a potassium-sparing and natriuretic agent. It is hoped that the SARAs will provide the same survival benefit, but with fewer of the sex-steroid side effects. In addition, AVP-receptor antagonists may become useful tools in the treatment of patients with hyponatremia. Likewise, the A1 AR antagonists may find a role in the CHF armamentarium by providing good diuresis and natriuresis while at the same time maintaining GFR through inhibition of TGF. Many questions remain unanswered, and studies are needed to demonstrate that the positive results seen in basic research translate into improved morbidity and mortality.

The effects of spironolactone monotherapy on blood pressure and myocardial remodeling in spontaneously hypertensive rats: a stereological study

The aim of this study was to evaluate the cardiac structure of spontaneously hypertensive rats (SHRs) treated with different doses of spironolactone. Twenty SHRs were separated into four groups and treated for 13 weeks, as follows: one control group and three spironolactone treatment groups receiving doses of 5, 10 or 30 mg/kg/day. The spironolactone treatment either attenuated or prevented the tendency for increased blood pressure. However, the myocardial structure was not significantly affected by the spironolactone monotherapy treatment (all doses); it showed hypertrophied cardiac myocytes, focal areas of reactive fibrosis, inflammatory infiltrate and a decrease in the density of intramyocardial microvessels. None of the cardiac myocyte stereological parameters in the left ventricular myocardium showed significant differences among the SHR groups. The cardiac myocyte volume density was around 80%, the cardiac myocyte surface density varied from 3.6 to 4.1 x 10(4) mm2/mm3 and the cardiac myocyte mean cross-sectional area varied from 351 to 415 micro m2. The connective tissue volume density of the SHRs treated with the highest dose of spironolactone was 75% lower than in the control SHRs, and this was the only significant difference found for this parameter among SHR groups. The intramyocardial vessels showed some differences when the control SHRs and the other SHRs were compared. The lowest intramyocardial vessel volume density was found in the control group (more than 20% lower than that in the treated SHRs), but no significant difference was detected among the treated SHRs (all doses). The intramyocardial vessel length density (Lv[v]) and surface density (Sv[v]) showed a similar tendency, being significantly greater in the treated SHRs than in the control rats. The Lv[v] was 45% greater in the high-dose spironolactone group than in the control group, and it was 28% greater in the high-dose spironolactone SHRs than in the other treated SHRs. The Sv[v] was 50% greater in the high-dose spironolactone SHRs than in both control and low-dose spironolactone SHRs. Long-term spironolactone monotherapy showed a partial effect in the preservation of intramyocardial vessels and also in the attenuation of interstitial fibrosis.

Aldosterone induces a vascular inflammatory phenotype in the rat heart

Vascular inflammation was examined as a potential mechanism of aldosterone-mediated myocardial injury in uninephrectomized rats receiving 1% NaCl-0.3% KCl to drink for 1, 2, or 4 wk and 1) vehicle, 2) aldosterone infusion (0.75 microg/h), or 3) aldosterone infusion (0.75 microg/h) plus the selective aldosterone blocker eplerenone (100 mg. kg(-1). day(-1)). Aldosterone induced severe hypertension at 4 wk [systolic blood pressure (SBP), 210 +/- 3 mmHg vs. vehicle, 131 +/- 2 mmHg, P < 0.001], which was partially attenuated by eplerenone (SBP, 180 +/- 7 mmHg; P < 0.001 vs. aldosterone alone and vehicle). No significant increases in myocardial interstitial collagen fraction or hydroxyproline concentration were detected throughout the study. However, histopathological analysis of the heart revealed severe coronary inflammatory lesions, which were characterized by monocyte/macrophage infiltration and resulted in focal ischemic and necrotic changes. The histological evidence of coronary lesions was preceded by and associated with the elevation of cyclooxygenase-2 (up to approximately 4-fold), macrophage chemoattractant protein-1 (up to approximately 4-fold), and osteopontin (up to approximately 13-fold) mRNA expression. Eplerenone attenuated proinflammatory molecule expression in the rat heart and subsequent vascular and myocardial damage. Thus aldosterone and salt treatment in uninephrectomized rats led to severe hypertension and the development of a vascular inflammatory phenotype in the heart, which may represent one mechanism by which aldosterone contributes to myocardial disease.

Mineralocorticoid receptors and pathophysiological roles for aldosterone in the cardiovascular system

For almost 40 years since its discovery in 1953, the mineralocorticoid hormone, aldosterone, was considered to affect blood volume, and thus blood pressure, by its action to retain sodium at epithelial tissues. Over the past decade, direct effects of aldosterone on the heart and blood vessels, and on the cerebral control of blood pressure, have been established in experimental animals. Simultaneously, the incidence of primary aldosteronism in essential hypertension is now acknowledged to be 10-20%, rather than <or= 1%, underscoring a previously unrecognized role for aldosterone in hypertension. The 30% improvement in mortality (and 35% in morbidity) seen in the RALES trial with the addition of low-dose spironolactone to best practice therapy in moderate to severe heart failure, similarly points to an unrecognized role for aldosterone in the pathophysiology of heart failure. Currently, both experimental and clinical studies are directed towards establishing the mechanisms involved in these pathophysiological effects of aldosterone in the cardiovascular system, and of the role of mineralocorticoid receptor antagonists in offsetting or blocking such effects. A brief account of the current state of these mechanisms in at a cellular and tissue level forms the basis of this review.

Isoproterenol and angiotensin I-converting enzyme in lung, left ventricle, and plasma during myocardial hypertrophy and fibrosis

This study investigated whether long-term administration of isoproterenol (ISO) induces differential expression of angiotensin-converting enzyme (ACE) in lung, plasma, and left ventricle (LV) during development of left ventricular hypertrophy (LVH) and myocardial fibrosis. Male Sprague-Dawley rats (n = 7-9 per group) were treated with isoproterenol (ISO) 5 mg/kg per day for 10 days or saline and examined at 1, 15, and 33 days after the last injection. ISO stimulated the development of left ventricular hypertrophy (LVH); relative LV weight (mg LV 100/body weight), LV protein content, and LV beta-myosin heavy chain levels increased at day 1. LVH regressed at days 15 and 33. ISO also increased myocardial fibrosis (assessed by hydroxyproline content and morphometry) at days 15 and 33. There no were changes in arterial blood pressure. Long-term beta-adrenergic stimulation with ISO increased ACE expression in lung, LV, and plasma during development of LVH and myocardial fibrosis. However, time courses were markedly different. ISO stimulated a sustained increase in lung and plasma ACE activities, whereas ISO induced a high LV ACE. Plasma ACE activity paralleled lung ACE activity. LV ACE activity correlated with ACE mRNA levels and paralleled development of LVH. Our data suggest long-term beta-adrenergic stimulation induced a differential temporal expression of LV, lung, and plasma ACE in rat during development of LVH and myocardial fibrosis.

Rationale for the use of aldosterone antagonists in congestive heart failure

Traditionally, the role of aldosterone in heart failure was thought to be a result of its effects on epithelial cells where it induces sodium reabsorption and potassium excretion with subsequent haemodynamic effects from intravascular volume expansion. On this basis, spironolactone, a non-selective aldosterone antagonist, has been used for the treatment of congestive heart failure to block aldosterone-mediated effects in epithelial cells. The Randomized Aldactone Evaluation Study (RALES), in which spironolactone was added to existing therapy in patients with heart failure, showed a significant reduction in morbidity and mortality. These results suggest that the role of aldosterone in the pathophysiology of cardiovascular disease may be more complex than previously recognised. There now is extensive experimental and growing clinical evidence for an important physiological role for aldosterone in the pathology of cardiac and renal disease. Classical effects of aldosterone are mediated via its nuclear receptor. Novel non-epithelial effects of aldosterone are mediated via a second messenger system, which involves activation of the sodium/hydrogen antiporter. These effects of aldosterone have been demonstrated in the kidney, vascular smooth muscle cell and leukocytes, and in the regulation of rapid corticotropin suppression. It has been hypothesised that cardiac damage induced by aldosterone is independent of the presence of hypertension. In support of this, experimental evidence demonstrates that cardiovascular damage induced by aldosterone can be prevented by administration of a selective mineralocorticoid receptor antagonist. These findings suggest the dissociation between cardiovascular lesions and high blood pressure, and highlight the importance of aldosterone in the pathological changes.

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 as a mediator in cardiovascular injury

The renin-angiotensin-aldosterone system plays a central role in the development of hypertension and the progression of end-organ damage. Although angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists can initially suppress plasma aldosterone, it is now well established that aldosterone escape may occur, whereby aldosterone levels return to or exceed baseline levels. The classic effects of aldosterone relate mainly to its action on epithelial cells to regulate water and electrolyte balance. However, blood pressure reduction or fluid loss could not account for the results of the Randomized Aldactone Evaluation Study, which showed that a low dose of spironolactone in addition to conventional therapy could decrease the overall risk of mortality by 30% among patients with severe congestive heart failure. The action of aldosterone at nonepithelial sites in the brain, heart, and vasculature is consistent with the presence of mineralocorticoid receptors in these tissues. Aldosterone has a number of deleterious effects on the cardiovascular system, including myocardial necrosis and fibrosis, vascular stiffening and injury, reduced fibrinolysis, endothelial dysfunction, catecholamine release, and production of cardiac arrhythmias. Several studies have now shown vascular and target-organ protective effects of aldosterone receptor antagonism in the absence of significant blood pressure lowering, consistent with a major role for endogenous mineralocorticoids as mediators of cardiovascular injury. The advent of selective aldosterone receptor antagonists such as eplerenone should prove of great therapeutic value in the prevention of cardiovascular disease and associated end-organ damage.

Mutations in aldosterone synthase gene of Milan hypertensive rats: phenotypic consequences

Using in vitro and in vivo methods, we have demonstrated increased sensitivity of adrenocortical steroidogenesis to ACTH in Milan hypertensive (MHS) compared with normotensive (MNS) rats and have investigated whether this is caused by mutations of steroidogenic enzymes. Genes encoding aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) in MHS and MNS have been cloned and sequenced. Nucleotide 752 (G) in exon 4 of MHS CYP11B2 differs from that of MNS (A); CYP11B1 sequences were identical. The nucleotide 752 mutation caused a Q251R substitution in the amino acid sequence of MHS CYP11B2. The phenotype of MHS CYP11B2 alleles, when expressed in COS-1 cells, differed from that of MNS alleles. The relative activities of the three reactions catalyzed by CYP11B2 (11beta-hydroxylation of deoxycorticosterone, 18-hydroxylation of corticosterone, and dehydrogenation of 18-hydroxycorticosterone) were estimated after incubation of transfected cells with [(14)C]deoxycorticosterone and analysis of radioactivity associated with deoxycorticosterone, corticosterone, 18 hydroxycorticosterone, and aldosterone. Both 11- and 18-hydroxylase activities were lower (19 and 12%, respectively; P < 0.01 and P < 0.05) in cells transfected with MHS compared with MNS alleles, whereas 18-oxidase activity was 42% higher (P < 0.01). To assess the significance of the CYP11B2 mutation in vivo, DNA from F2 hybrid MHS x MNS rats was genotyped. MHS alleles were associated with lower urine volumes in both sexes, lower ventricle weights in male rats, but no difference in systolic or diastolic blood pressures between the sexes. We conclude that a mutation in CYP11B2 may affect aldosterone secretion in MHS; however, under normal environmental circumstances, we were unable to demonstrate any influence of this mutation on blood pressure.

Myocardial changes after spironolactone in spontaneous hypertensive rats. A laser scanning confocal microscopy study

The present study aims to objectivate by laser scanning confocal microscopy, the cardiac structure of the spontaneously hypertensive rats (SHR) treated with different doses of spironolactone, either alone or in combination with an angiotensin converting enzyme inhibitor or with a calcium channel blocker. Thirty SHRs were divided into six groups and treated during 13 weeks as follows: control, spironolactone (5, 10 and 30 mg/kg/day), spironolactone + enalapril and spironolactone + verapamil. Spironolactone action on the SHR blood pressure (BP) was dose-dependent. The cardiac hypertrophy was affected by the treatment with spironolactone (high dose) or a combination of spironolactone and Enalapril. The myocardial structure was less affected by the spironolactone monotherapy (at all doses) showing hypertrophied cardiac myocytes, focal areas of the reactive fibrosis, inflammatory infiltrate. The treatment with spironolactone in combination with enalapril or verapamil prevented these alterations. In conclusion, the monotherapy with spironolactone had only a limited effect in the preservation of the myocardial structure and in the attenuation of the interstitial fibrosis in SHRs, even after high dose. This action on the myocardium is more efficient when the spironolactone (even in medium dose) was associated with enalapril or verapamil.

Nontraditional aspects of aldosterone physiology

Aldosterone is the most important circulating mineralocorticoid. It is secreted by the zona glomerulosa of the adrenal gland and plays a major role in sodium and potassium metabolism by binding to epithelial mineralocorticoid receptors (MR) in the renal collecting duct, promoting sodium resorption and potassium excretion. The action of aldosterone on its classic target epithelia has been extensively studied, and many of the signaling events that mediate its effects have been described. Recently, there has been increased interest in aldosterone actions on the cardiovascular system, which are mediated through nonclassical actions. These include local tissue production, nongenomic actions, and effects on nonepithelial targets. In this review article, we focus on the effects of aldosterone in nonepithelial tissues that are mediated through MR, especially cardiovascular effects.

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.

Pathophysiological effects of aldosterone in cardiovascular tissues

The advent of antihypertensive therapy has resulted in a significant decrease in cardiovascular morbidity and mortality. Nevertheless, the incidence of heart failure, stroke and end-stage renal failure continues to increase. This trend suggests that a mechanism, independent of hypertension, is responsible for end-organ damage. Genetic and experimental models of hypertension have demonstrated that excess aldosterone induces severe injury in the heart, brain and kidneys, and that pharmacological antagonism of aldosterone or adrenalectomy markedly reduces myocardial injury, cerebral hemorrhage and renal vascular disease. In clinical studies, plasma aldosterone levels have been shown to correlate with left ventricular hypertrophy, stroke and renal dysfunction. Moreover, aldosterone antagonism has been shown to reduce morbidity and mortality in patients with heart failure. Thus, an increasing body of evidence now indicates that aldosterone is an independent risk factor for cardiovascular disease.

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.

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.

Mineralocorticoid and glucocorticoid receptors inhibit UCP expression and function in brown adipocytes

Uncoupling proteins (UCP), specific mitochondrial proton transporters that function by uncoupling oxidative metabolism from ATP synthesis, are involved in thermoregulation and control of energy expenditure. The hibernoma-derived T37i cells, which possess functional endogenous mineralocorticoid receptors (MR), can undergo differentiation into brown adipocytes. In differentiated T37i cells, UCP1 mRNA levels increased 10- to 20-fold after retinoic acid or beta-adrenergic treatment. Interestingly, UCP2 and UCP3 mRNA was also detected. Aldosterone treatment induced a drastic decrease in isoproterenol- and retinoic acid-stimulated UCP1 mRNA levels in a time- and dose-dependent manner (IC(50) approximately 1 nM aldosterone). This inhibition was unaffected by cycloheximide and did not modify UCP1 mRNA stability (half-life time = 5 h), indicating that it occurs at the transcriptional level. It involves both the MR and/or the glucocorticoid receptor (GR), depending on the retinoic or catecholamine induction pathway. Basal UCP3 expression was also significantly reduced by aldosterone, whereas UCP2 mRNA levels were not modified. Finally, as demonstrated by JC1 aggregate formation in living cells, aldosterone restored mitochondrial membrane potential abolished by isoproterenol or retinoic acid. Our results demonstrate that MR and GR inhibit expression of UCP1 and UCP3, thus participating in the control of energy expenditure.

Disorders of mineralocorticoid synthesis

Abnormalities of mineralocorticoid synthesis and/or metabolism profoundly affect the regulation of electrolyte and water balance and of blood pressure. Characteristic changes in extracellular potassium, sodium and hydrogen ion concentrations are usually diagnostic. Serious deficiency may be acquired, for example in Addison's disease, or inherited. In most of the inherited syndromes, the precise molecular changes in specific steroidogenic enzymes have been identified. Mineralocorticoid excess may be caused by aldosterone or 11-deoxycorticosterone by inadequate conversion of cortisol to cortisone by 11beta-hydroxysteroid dehydrogenase type 2 in target tissues (see Chapter 4), by glucocorticoid receptor deficiency or by constitutive activation of renal sodium channels. Changes in electrolyte balance and renin as well as the abnormal pattern of corticosteroid metabolism are usually diagnostic. Where these abnormalities are inherited (e.g. 11beta- or l7alpha-hydroxylase deficiencies, glucocorticoid remediable hyperaldosteronism (GRA), receptor defects, Liddle's syndrome), the molecular basis is again usually known and, in some cases, may provide the simplest diagnostic tests. Primary aldosteronism, although readily identifiable, presents problems of differential diagnosis, important because optimal treatment is different for each variant. Moreover, the mechanisms by which the variants develop are poorly understood. Finally, a significant proportion of patients with essential hypertension show characteristics of mild mineralocorticoid excess, for example low renin levels. Is this relevant to pathophysiology and, if so, is the effect induced via classic mechanisms of action or through newly discovered direct actions on the brain, heart and blood vessels? These questions are the subject of current research.

The combination ace-inhibitors plus canreonate in patients with anterior myocardial infarction: safety and tolerability study

BACKGROUND

There is recent evidence that aldosterone (ALDO) exerts pro-fibrotic effects, acting via the mineral-corticoid receptors in cardiovascular tissues and partial aldosterone escape during ACE-inhibition treatment occurs.

METHODS

A double blind randomised study was performed to evaluate the feasibility, and tolerability of the administration of the 25 mg/day of canreonate plus captopril versus captopril alone in patients with anterior AMI unsuitable for thrombolysis and/or not receiving thrombolytic treatment, and unreperfused after thrombolysis. Fifty five patients hospitalised for anterior AMI,with a serum creatinine concentration <2.0 mg/dl and a serum K concentration <5.0 mmol per liter were randomised in 2 groups: Group A included 27 patients who received captopril and 25 mg i.v. of canreonate (1 mg/h for the 1st 72 h and then orally 25 mg/day. Group B (28 patients) received captopril and placebo. Ten days after admission they underwent echocardiography to determine end systolic volume (ESV), ejection fraction (EF), End diastolic diameter EDD, E/A ratio, E deceleration time (dec. time) and isovolumetric relaxation time (IVRT), E and A peak velocities.

RESULTS

All patients did not show patency of the infarct related artery (7-10 days after AMI) and the 2 groups were similar in regard to age, sex, diabetes, smoking habits, hypertension, CK enzymatic peak, adjuvant therapy, EF, ESV, and incidence of CABG/PTCA. One patient only showed increase of serum K>5.5 mmol/dl and creatinine >2.0 mg per liter after 10 days of treatment (group A). The mitral E/A ratio was higher in group A than group B (0.85+/-0.18 and 0.75+/-0.14) respectively, P=0.024. Creatinine, blood urea and serum K did not show significant differences between groups. No side effects were observed during the study period. The incidence of vessel diseases was similar in both groups.

CONCLUSIONS

Our data suggest that the combination of captopril plus canreonate in feasible in early treatment of AMI patients.

Spironolactone inhibits the transcardiac extraction of aldosterone in patients with congestive heart failure

OBJECTIVES

The study evaluated the transcardiac extraction or spillover of aldosterone (ALDO) in normal subjects and in patients with congestive heart failure (CHF).

BACKGROUND

Aldosterone promotes collagen synthesis and structural remodeling of target organs such as the heart. Spironolactone, an ALDO receptor antagonist, has recently been reported to reduce the mortality of patients with CHF; however, the effects of spironolactone on the transcardiac gradient of ALDO have not been clarified.

METHODS

We measured plasma ALDO in the aortic root (AO) and coronary sinus (CS) in normal subjects and 113 consecutive CHF patients and also measured plasma procollagen type III aminoterminal peptide (PIIINP) in CS, a biochemical marker of myocardial fibrosis.

RESULTS

Plasma ALDO was significantly lower in the CS than in the AO in normal subjects (n = 15; 61.2 +/- 9.3 vs. 83.1 +/- 11.8 pg/ml, p < 0.0001). In 96 CHF patients who did not receive spironolactone, plasma ALDO was significantly lower in the CS than in the AO (59.3 +/- 3.9 vs. 73.8 +/- 4.9 pg/ml, p < 0.0001). In contrast to the difference in these 96 patients, there was no significant difference in ALDO between the AO and CS in 17 patients who received spironolactone (127.4 +/- 20 vs. 124.0 +/- 19 pg/ml, p = 0.50). Stepwise multivariate analyses showed that spironolactone therapy had an independent and significant negative relationship with the transcardiac gradient of plasma ALDO in patients with CHF. In addition, significant positive correlations were seen between the transcardiac gradient of plasma ALDO and PIIINP (r = 0.565, p < 0.0001) and the left ventricular end-diastolic volume index (r = 0.484, p < 0.0001).

CONCLUSIONS

These results indicate that plasma ALDO is extracted through the heart in normal subjects and in CHF patients who do not receive spironolactone and that spironolactone inhibits the transcardiac extraction of ALDO in CHF patients, suggesting that spironolactone blocks the effects of ALDO on the failing heart in patients with CHF.