Toward a broader understanding of aldosterone in congestive heart failure

The multifaceted mineralocorticoid receptor

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

Effect of furosemide and high-dosage pimobendan administration on the renin-angiotensin-aldosterone system in dogs

OBJECTIVE

To determine whether a high dosage of pimobendan, when administered concurrently with moderate-dosage furosemide to healthy dogs, would activate the renin-angiotensin-aldosterone system (RAAS) more than furosemide alone.

ANIMALS

12 healthy dogs.

PROCEDURES

6 dogs received furosemide (2.0 mg/kg, PO, q 12 h) only, as an RAAS activator, for 10 days. The other 6 dogs received furosemide (2.0 mg/kg, PO, q 12 h) and pimobendan (0.6 mg/kg, PO, q 12 h) for 10 days. The effect of these drugs on the RAAS was determined by measurement of the aldosterone-to-creatinine ratio (A:C) in urine collected in the morning and evening of study days -2, -1, 1, 5, and 10.

RESULTS

Although there was an increase in the urine A:C during the study period in both groups, it was significant only for dogs that received both drugs. The urine A:C only differed significantly between groups on day 1, at which time A:C was greater in the group that received both drugs.

CONCLUSIONS AND CLINICAL RELEVANCE

High-dosage pimobendan administration neither substantially suppressed nor potentiated the RAAS when administered with furosemide in healthy dogs.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

Effects of mineralocorticoid receptor antagonists on the risk of sudden cardiac death in patients with left ventricular systolic dysfunction: a meta-analysis of randomized controlled trials

BACKGROUND

Sudden cardiac death (SCD) is an important cause of death in patients with left ventricular systolic dysfunction. Mineralocorticoid receptor antagonists (MRAs) may attenuate this risk. The objective of this meta-analysis was to assess the impact of MRAs on SCD in patients with left ventricular systolic dysfunction.

METHODS AND RESULTS

We systematically searched PubMed, EMBASE, Cochrane, and other databases through March 30, 2012, without language restrictions. We included trials that enrolled patients with left ventricular ejection fraction of ≤45%, randomized subjects to MRAs versus control and reported outcomes on SCD, total and cardiovascular mortality. Eight published trials that enrolled 11 875 patients met inclusion criteria. Of these, 6 reported data on SCD and cardiovascular mortality, and 7 reported data on total mortality. No heterogeneity was observed among the trials. Patients treated with MRAs had 23% lower odds of experiencing SCD compared with controls (odds ratio, 0.77; 95% confidence interval, 0.66-0.89; P=0.001). Similar reductions were observed in cardiovascular (0.75; 95% confidence interval, 0.68-0.84; P<0.001) and total mortality (odds ratio, 0.74; 95% confidence interval, 0.63-0.86; P<0.001). Although publication bias was observed, the results did not change after a trim and fill test, suggesting that the impact of this bias was likely insignificant.

CONCLUSIONS

MRAs reduce the risk of SCD in patients with left ventricular systolic dysfunction. Comparative effectiveness studies of MRAs on SCD in usual care as well as studies evaluating the efficacy of other therapies to prevent SCD in patients receiving optimal MRA therapy are needed to guide clinical decision-making.

Aldosterone predicts major adverse cardiovascular events in patients with acute myocardial infarction

OBJECTIVE

Aldosterone is associated with increased mortality in chronic heart failure patients and correlates with adverse outcomes after an acute myocardial infarction (AMI) in smaller cohorts. We evaluated the prognostic significance of plasma aldosterone in a large cohort of post-AMI patients in relation to major adverse cardiovascular events (MACE).

DESIGN

A prospective cohort study.

SETTING

University Hospitals of Leicester, UK.

PATIENTS

Consecutive 955 patients admitted with AMI. Plasma aldosterone levels were measured in these patients.

MAIN OUTCOME MEASURES

During the 2 years follow-up, MACE which was a composite of all-cause mortality, myocardial reinfarction, and hospitalisation for heart failure as well as secondary endpoints (all-cause mortality and a combination of all-cause mortality and hospitalisation for heart failure), were ascertained.

RESULTS

MACE occured in N=261, 27.3%, all-cause mortality (N=114, 11.9%) and a combination of all-cause mortality and hospitalisation for heart failure (N=176, 18.4%). Patients with MACE had significantly higher median levels of aldosterone than those without (1150.1 vs 950.4 pmol/l, p=0.0118). The multivariate adjusted HR (95% CI) for log aldosterone on MACE was 1.26 (1.01 to 1.56), p=0.041; all-cause mortality 1.60 (1.13 to 2.27), p=0.008; and combination of all-cause mortality and heart failure 1.50 (1.14 to 1.97), p=0.003.

CONCLUSIONS

The prognostic significance of aldosterone for a variety of endpoints in this large cohort of post-AMI patients is not new and adds to the findings by others. The magnitude of the increase in aldosterone secretion post infarction is higher than previously believed.

Mineralocorticoid accelerates transition to heart failure with preserved ejection fraction via "nongenomic effects"

BACKGROUND

Mechanisms promoting the transition from hypertensive heart disease to heart failure with preserved ejection fraction are poorly understood. When inappropriate for salt status, mineralocorticoid (deoxycorticosterone acetate) excess causes hypertrophy, fibrosis, and diastolic dysfunction. Because cardiac mineralocorticoid receptors are protected from mineralocorticoid binding by the absence of 11-beta hydroxysteroid dehydrogenase, salt-mineralocorticoid-induced inflammation is postulated to cause oxidative stress and to mediate cardiac effects. Although previous studies have focused on salt/nephrectomy in accelerating mineralocorticoid-induced cardiac effects, we hypothesized that hypertensive heart disease is associated with oxidative stress and sensitizes the heart to mineralocorticoid, accelerating hypertrophy, fibrosis, and diastolic dysfunction.

METHODS AND RESULTS

Cardiac structure and function, oxidative stress, and mineralocorticoid receptor-dependent gene transcription were measured in sham-operated and transverse aortic constriction (studied 2 weeks later) mice without and with deoxycorticosterone acetate administration, all in the setting of normal-salt diet. Compared with sham mice, sham plus deoxycorticosterone acetate mice had mild hypertrophy without fibrosis or diastolic dysfunction. Transverse aortic constriction mice displayed compensated hypertensive heart disease with hypertrophy, increased oxidative stress (osteopontin and NOX4 gene expression), and normal systolic function, filling pressures, and diastolic stiffness. Compared with transverse aortic constriction mice, transverse aortic constriction plus deoxycorticosterone acetate mice had similar left ventricular systolic pressure and fractional shortening but more hypertrophy, fibrosis, and diastolic dysfunction with increased lung weights, consistent with heart failure with preserved ejection fraction. There was progressive activation of markers of oxidative stress across the groups but no evidence of classic mineralocorticoid receptor-dependent gene transcription.

CONCLUSIONS

Pressure-overload hypertrophy sensitizes the heart to mineralocorticoid excess, which promotes the transition to heart failure with preserved ejection fraction independently of classic mineralocorticoid receptor-dependent gene transcription.

Aldosterone and long-term outcome after myocardial infarction: A substudy of the french nationwide Observatoire sur la Prise en charge hospitalière, l'Evolution à un an et les caRactéristiques de patients présentant un infArctus du myocarde avec ou sans onde Q (OPERA) study

BACKGROUND

High plasma aldosterone levels at presentation are correlated to poor outcome after ST elevation acute myocardial infarction (AMI). Whether there is a relationship between aldosterone levels and outcome in a broader spectrum of patients admitted for AMI defined by the new definition based on troponin levels remains unknown.

METHODS

Plasma aldosterone, C-reactive protein, and brain natriuretic peptide (BNP) were measured in 471 patients, 24 and 72 hours after admission for AMI defined by the new definition. The primary outcome was the composite of death, resuscitated cardiac arrest, recurrent/extended myocardial infarction, recurrent ischemia, heart failure, and stroke.

RESULTS

The highest aldosterone levels quartile at 24 hours was significantly associated with the occurrence of the primary outcome (P < .0001), death (P < .05), heart failure (P < .05), ventricular (P < .0001) and supraventricular arrhythmias (P < .05), and acute renal failure (P < .01) during the in-hospital period, and higher rates of mortality (P < .05) at 1-year follow-up. Independent correlates of the primary outcome at 1 year were age > or =73 (odds ratio [OR] 2.22 [1.38-3.57]), heart failure (OR 6.46 [1.99-20.98]), 24-hour aldosterone > or =103.6 pg.mL(-1) (OR 1.72 [1.07-2.77]), and BNP > or =389 pg.mL(-1) (OR 2.35 [1.44-3.84]) concentrations. The model applied to the 72-hour variables, identified the same correlates.

CONCLUSIONS

Using the new definition of AMI, based on troponin levels, regardless of ST-segment elevation and management strategies, high aldosterone concentration is associated with major adverse in-hospital events and is an independent correlate of clinical outcome at 1 year. These findings warrant trials assessing the benefit of early aldosterone blockade in such patients.

Chronic treatment with the mineralocorticoid hormone aldosterone results in increased anxiety-like behavior

Aldosterone is the last component of the renin-angiotensin-aldosterone system inducing its peripheral effects via mineralocorticoid receptors (MR). Brain MR bind preferentially glucocorticoids. So far, the role of MR in behavioral functions has been investigated almost exclusively in relation to glucocorticoids. Recently, aldosterone itself has been linked to affective disorders. The aim of this study was to test the hypothesis that chronic elevation of circulating levels of aldosterone leads to increased anxiety. We have investigated the effects of chronic aldosterone treatment on (1) anxiety-like behavior, and (2) basal and stress-induced levels of selected hormones. Forty male Wistar rats were subcutaneously implanted with osmotic minipumps and treated with aldosterone (2 microg/100 g/day) or vehicle for two weeks. Aldosterone concentrations in plasma showed a mild (approximately four-fold) increase at the end of two-week aldosterone treatment. This mild hyperaldosteronism resulted in a significant enhancement of anxiety as demonstrated by alterations in all indicators of anxiety-like behavior measured in the open field and elevated plus-maze tests, without significant changes in measures of general locomotor activity. Aldosterone treatment affected not only the spatiotemporal measures of anxiety, but also the ethological parameters related to exploration and risk assessment. Chronic treatment with aldosterone was associated with increased water intake and decreased plasma renin activity, but failed to modify basal or stress-induced activity of the hypothalamic-pituitary-adrenocortical axis. The results provide evidence on anxiogenic action of prolonged increase in circulating aldosterone concentrations. Thus, aldosterone may represent an important target for future antidepressant and anxiolytic drug development.

Paraventricular nucleus, stress response, and cardiovascular disease

The paraventricular nucleus of the hypothalamus (PVN) is a complex effector structure that initiates endocrine and autonomic responses to stress. It receives inputs from visceral receptors, circulating hormones such as angiotensin II, and limbic circuits and contains neurons that release vasopressin, activate the adrenocortical axis, and activate preganglionic sympathetic or parasympathetic outflows. The neurochemical control of the different subgroups of PVN neurons is complex. The PVN has been implicated in the pathophysiology of congestive heart failure and the metabolic syndrome.

Eplerenone blocks nongenomic effects of aldosterone on the Na+/H+ exchanger, intracellular Ca2+ levels, and vasoconstriction in mesenteric resistance vessels

There is increasing evidence for rapid nongenomic effects of aldosterone. Aldosterone has been demonstrated to alter intracellular pH and calcium in isolated cells. However, few studies have correlated these effects with aldosterone-mediated physiological responses. Therefore, we studied rapid effects of aldosterone on vascular reactivity, intracellular Ca2+, and pH in resistance vessels. Furthermore, we explored whether the new antimineralocorticoid drug eplerenone could effectively block nongenomic aldosterone-mediated effects. The vasoconstrictor action of aldosterone was examined directly by determining the diameter of small resistance mesenteric vessels (160-200 microm resting diameter), simultaneously with intracellular pH or Ca2+. Aldosterone (10 nm) caused a rapid constriction of resistance vessels (8.1% +/- 1.0% reduction in the diameter below control conditions, P < 0.05). Aldosterone potentiated phenylephrine-mediated constriction in small and large mesenteric vessels. Aldosterone induced a rapid increase of intracellular Ca2+ and cellular alkalinization. Vasoconstrictor action of aldosterone and nongenomic effects on the sodium-proton exchanger (NHE1) activity or intracellular Ca2+ responses was abolished by eplerenone. The vasoconstrictor response of aldosterone was related to phosphatidylinositol 3-kinase (PI3-K): the hormone decreased protein kinase B phosphorylation; pharmacological inhibition of PI3-K (10 microm LY294002 or 1 microm wortmannin) increased arterial contractility. Inhibitors of ERK 1/2 phosphorylation (15 microm PD98059) had no effect on aldosterone-mediated vasoconstriction. Inhibition of protein kinase C with 1 microm bi-sindolylmaleimide I and/or inhibition of NHE1 with 100 microm amiloride abolished aldosterone vasoconstrictor action of resistance mesenteric arteries. We conclude that aldosterone-mediated increase in vascular tone is related to a nongenomic mechanism that involves protein kinase C, PI3-K, and NHE1 activity. Eplerenone is an effective blocker of nongenomic effects of aldosterone in vascular tissue.