Aldosterone is produced from ventricles in patients with essential hypertension

Extra-adrenal aldosterone: a mini review focusing on the physiology and pathophysiology of intrarenal aldosterone

PURPOSE

Accumulating evidence has demonstrated the existence of extra-adrenal aldosterone in various tissues, including the brain, heart, vascular, adipocyte, and kidney, mainly based on the detection of the CYP11B2 (aldosterone synthase, cytochrome P450, family 11, subfamily B, polypeptide 2) expression using semi-quantitative methods including reverse transcription-polymerase chain reaction and antibody-based western blotting, as well as local tissue aldosterone levels by antibody-based immunosorbent assays. This mini-review highlights the current evidence and challenges in extra-adrenal aldosterone, focusing on intrarenal aldosterone.

METHODS

A narrative review.

RESULTS

Locally synthesized aldosterone may play a vital role in various physio-pathological processes, especially cardiovascular events. The site of local aldosterone synthesis in the kidney may include the mesangial cells, podocytes, proximal tubules, and collecting ducts. The synthesis of renal aldosterone may be regulated by (pro)renin receptor/(pro)renin, angiotensin II/Angiotensin II type 1 receptor, wnt/β-catenin, cyclooxygenase-2/prostaglandin E2, and klotho. Enhanced renal aldosterone release promotes Na+ reabsorption and K+ excretion in the distal nephron and may contribute to the progress of diabetic nephropathy and salt-related hypertension.

CONCLUSIONS

Inhibition of intrarenal aldosterone signaling by aldosterone synthase inhibitors or mineralocorticoid receptor antagonists may be a hopeful pharmacological technique for the therapy of diabetic nephropathy and saltrelated hypertension. Yet, current reports are often conflicting or ambiguous, leading many to question whether extra-adrenal aldosterone exists, or whether it is of any physiological and pathophysiological significance.

Evolution of Mineralocorticoid Receptor Antagonists in the Treatment of Chronic Kidney Disease Associated with Type 2 Diabetes Mellitus

Chronic kidney disease (CKD) is one of the most frequent complications associated with type 2 diabetes mellitus (T2DM) and is also an independent risk factor for cardiovascular disease. The mineralocorticoid receptor (MR) is a nuclear receptor expressed in many tissue types, including kidney and heart. Aberrant and long-term activation of MR by aldosterone in patients with T2DM triggers detrimental effects (eg, inflammation and fibrosis) in these tissues. The suppression of aldosterone at the early stage of T2DM has been a therapeutic strategy for patients with T2DM-associated CKD. Although patients have been treated with renin-angiotensin system (RAS) blockers for decades, RAS blockers alone are not sufficient to prevent CKD progression. Steroidal MR antagonists (MRAs) have been used in combination with RAS blockers; however, undesired adverse effects have restricted their usage, prompting the development of nonsteroidal MRAs with better target specificity and safety profiles. Recently conducted studies, Finerenone in Reducing Kidney Failure and Disease Progression in Diabetic Kidney Disease (FIDELIO-DKD) and Finerenone in Reducing Cardiovascular Mortality and Morbidity in Diabetic Kidney Disease (FIGARO-DKD), have reported that finerenone, a nonsteroidal MRA, improves both renal and cardiovascular outcomes compared with placebo. In this article, we review the history of MRA development and discuss the possibility of its combination with other treatment options, such as sodium-glucose cotransporter 2 inhibitors, glucagon-like peptide-1 receptor agonists, and potassium binders for patients with T2DM-associated CKD.

Safety and Efficacy of Spironolactone in Dialysis-Dependent Patients: Meta-Analysis of Randomized Controlled Trials

Background

Patients with end-stage renal disease (ESRD) are characterized with high risk of heart failure. Although mineralocorticoid receptor antagonists have beneficial effect on relieving cardiac fibrosis and, thus, reduce the incidence of cardiovascular disease and cardiac death, the therapeutic benefits and adverse effects are still controversial. We conducted a meta-analysis to measure the safety and efficacy of spironolactone in patients undergoing dialysis.

Methods

A systematic search for randomized controlled trials (RCTs) was performed in PubMed, Embase, and Cochrane databases. Primary outcomes included changes in all-cause mortality (ACM), serum potassium concentration, incidence of hyperkalemia and gynecomastia (GYN). Secondary outcomes included changes in blood pressure (BP), left ventricular mass index (LVMI) and left ventricular ejection fraction (LVEF). Subgroup analysis and sensitivity analysis were further conducted. This research was registered with PROSPERO (International Prospective Register of Systematic Reviews; No. CRD42021287493).

Results

Fifteen RCTs with 1,258 patients were enrolled in this pooled-analysis. Spironolactone treatment significantly decreased ACM (RR = 0.42, P < 0.0001), CCV (RR = 0.54, P = 0.008) and LVMI (MD = −6.28, P = 0.002), also increased occurrence of GYN (RR = 4.36, P = 0.0005). However, LVEF (MD = 2.63, P = 0.05), systolic BP (MD = −4.61, P = 0.14) and diastolic BP (MD = −0.12, P = 0.94) did not change between two groups after treatment. Although serum potassium concentration was increased (MD = 0.22, P < 0.0001) after spironolactone supplement, the risk of hyperkalemia remained unchanged (RR = 1.21, P = 0.31). Further subgroup analysis found more obvious advantageous as well as disadvantageous effects in Asian subjects than European or American ones. Also, with more than 9 months of treatment duration, patients achieved more favorable influence than shorter duration.

Conclusions

These results highlight the therapeutic effects of spironolactone on cardiovascular indexes, including ACM, CCV, and LVMI. However, the unignorable increase of GYN incidence and serum potassium level indicate that close monitor in dialysis-dependent patients, especially Asian patients, is essential.

Novel molecular mechanisms in the inhibition of adrenal aldosterone synthesis: Action of tolvaptan via vasopressin V2 receptor-independent pathway

BACKGROUND AND PURPOSE

We investigated the inhibitory effect and associated molecular mechanisms of tolvaptan on angiotensin II (AngII)-induced aldosterone production in vitro and in vivo.

EXPERIMENTAL APPROACH

In vitro, H295R human adrenocarcinoma cells were incubated with 1 μmol·L^-1 arginine vasopressin (AVP) or dDAVP, or tolvaptan (0.1, 1, and 3 μmol·L^-1 ) in the presence and absence of 100 nmol·L^-1 of AngII. In vivo, Sprague-Dawley rats were treated with tolvaptan 0.05% in the diet for 6 days in the presence and absence of 200 pmol·min^-1 AngII.

KEY RESULTS

Tolvaptan suppressed AngII-induced aldosterone production in a dose-dependent manner in H295R cells, whereas neither AVP nor dDAVP in the presence or absence of AngII altered aldosterone production, suggesting the vasopressin V₂ receptor was not involved in the inhibitory effect of tolvaptan on aldosterone synthesis. In addition, tolvaptan inhibited the AngII-induced increase in aldosterone synthase (CYP11B2) protein levels without suppressing CYP11B2 mRNA expression. Notably, tolvaptan increased the levels of unfolded protein response (UPR) marker DDIT3 and eIF2α phosphorylation (a UPR-induced event), which could block the translation of CYP11B2 mRNA into protein and thereby inhibit aldosterone production. In vivo, tolvaptan significantly inhibited AngII-induced increases in serum and adrenal aldosterone levels and CYP11B2 protein levels. This anti-aldosterone effect was associated with a reduction in the elevated systolic and diastolic BP.

CONCLUSIONS AND IMPLICATIONS

Tolvaptan inhibited AngII-stimulated aldosterone production via a V₂ receptor-independent pathway, which can counteract or even surpass its potential activating effect of diuresis-induced aldosterone secretion in certain aldosterone-mediated pathological conditions.

Myeloid cells are capable of synthesizing aldosterone to exacerbate damage in muscular dystrophy

FDA-approved mineralocorticoid receptor (MR) antagonists are used to treat heart failure. We have recently demonstrated efficacy of MR antagonists for skeletal muscles in addition to heart in Duchenne muscular dystrophy mouse models and that mineralocorticoid receptors are present and functional in skeletal muscles. The goal of this study was to elucidate the underlying mechanisms of MR antagonist efficacy on dystrophic skeletal muscles. We demonstrate for the first time that infiltrating myeloid cells clustered in damaged areas of dystrophic skeletal muscles have the capacity to produce the natural ligand of MR, aldosterone, which in excess is known to exacerbate tissue damage. Aldosterone synthase protein levels are increased in leukocytes isolated from dystrophic muscles compared with controls and local aldosterone levels in dystrophic skeletal muscles are increased, despite normal circulating levels. All genes encoding enzymes in the pathway for aldosterone synthesis are expressed in muscle-derived leukocytes. 11β-HSD2, the enzyme that inactivates glucocorticoids to increase MR selectivity for aldosterone, is also increased in dystrophic muscle tissues. These results, together with the demonstrated preclinical efficacy of antagonists, suggest MR activation is in excess of physiological need and likely contributes to the pathology of muscular dystrophy. This study provides new mechanistic insight into the known contribution of myeloid cells to muscular dystrophy pathology. This first report of myeloid cells having the capacity to produce aldosterone may have implications for a wide variety of acute injuries and chronic diseases with inflammation where MR antagonists may be therapeutic.

Modulation of Immunity and Inflammation by the Mineralocorticoid Receptor and Aldosterone

The mineralocorticoid receptor (MR) is a ligand dependent transcription factor. MR has been traditionally associated with the control of water and electrolyte homeostasis in order to keep blood pressure through aldosterone activation. However, there is growing evidence indicating that MR expression is not restricted to vascular and renal tissues, as it can be also expressed by cells of the immune system, where it responds to stimulation or antagonism, controlling immune cell function. On the other hand, aldosterone also has been associated with proinflammatory immune effects, such as the release of proinflammatory cytokines, generating oxidative stress and inducing fibrosis. The inflammatory participation of MR and aldosterone in the cardiovascular disease suggests an association with alterations in the immune system. Hypertensive patients show higher levels of proinflammatory mediators that can be modulated by MR antagonism. Although these proinflammatory properties have been observed in other autoimmune and chronic inflammatory diseases, the cellular and molecular mechanisms that mediate these effects remain unknown. Here we review and discuss the scientific work aimed at determining the immunological role of MR and aldosterone in humans, as well as animal models.

Effects of spironolactone on dialysis patients with refractory hypertension: a randomized controlled study

The purpose of this study was to evaluate the effects of spironolactone on dialysis patients with refractory hypertension and possible adverse effects. This was a 12-week prospective, randomized, double-blind trial of 82 patients randomly assigned to 12-week treatment with 25 mg/d spironolactone or placebo as add-on therapy. Visits were scheduled at the start of treatment and after 12 weeks. Measurements of 24-hour ambulatory blood pressure (BP) monitoring and morning BP were performed. After 12 weeks, spironolactone significantly improved refractory hypertension. Average placebo-corrected morning BP was reduced by 16.7/7.6 mm Hg. Mean 24-hour ambulatory BP was reduced by 10.9/5.8 mm Hg. In contrast, serum aldosterone levels in the spironolactone group slightly increased and serum potassium levels insignificantly increased. This study has demonstrated that spironolactone (50 mg) safely and effectively reduces BP in patients with refractory hypertension undergoing dialysis.

Changes in cardiac aldosterone and its synthase in rats with chronic heart failure: an intervention study of long-term treatment with recombinant human brain natriuretic peptide

The physiological mechanisms involved in isoproterenol (ISO)-induced chronic heart failure (CHF) are not fully understood. In this study, we investigated local changes in cardiac aldosterone and its synthase in rats with ISO-induced CHF, and evaluated the effects of treatment with recombinant human brain natriuretic peptide (rhBNP). Sprague-Dawley rats were divided into 4 different groups. Fifty rats received subcutaneous ISO injections to induce CHF and the control group (n=10) received equal volumes of saline. After establishing the rat model, 9 CHF rats received no further treatment, rats in the low-dose group (n=8) received 22.5 μg/kg rhBNP and those in the high-dose group (n=8) received 45 μg/kg rhBNP daily for 1 month. Cardiac function was assessed by echocardiographic and hemodynamic analysis. Collagen volume fraction (CVF) was determined. Plasma and myocardial aldosterone concentrations were determined using radioimmunoassay. Myocardial aldosterone synthase (CYP11B2) was detected by quantitative real-time PCR. Cardiac function was significantly lower in the CHF group than in the control group (P<0.01), whereas CVF, plasma and myocardial aldosterone, and CYP11B2 transcription were significantly higher than in the control group (P<0.05). Low and high doses of rhBNP significantly improved hemodynamics (P<0.01) and cardiac function (P<0.05) and reduced CVF, plasma and myocardial aldosterone, and CYP11B2 transcription (P<0.05). There were no significant differences between the rhBNP dose groups (P>0.05). Elevated cardiac aldosterone and upregulation of aldosterone synthase expression were detected in rats with ISO-induced CHF. Administration of rhBNP improved hemodynamics and ventricular remodeling and reduced myocardial fibrosis, possibly by downregulating CYP11B2 transcription and reducing myocardial aldosterone synthesis.

Effects of spironolactone on long-term mortality and morbidity in patients with heart failure and mild or no symptoms

BACKGROUND

The purpose of this study is to evaluate long-term effects of spironolactone, an affordable and widely used aldosterone receptor blocker, in patients with heart failure (HF) and mild or no symptoms.

METHODS

The study is a single-blind, placebo-controlled, blinded endpoint, randomized study. Patients with New York Heart Association (NYHA) classes I to II HF and left ventricular ejection fraction < 40% were randomized to spironolactone or placebo in addition to optimal therapy. The primary endpoint was the composite of death from any cause or cardiovascular hospitalization.

RESULTS

A total of 130 patients were randomized to spironolactone (n = 65) or placebo (n = 65). Patients on spironolactone had a better event-free survival for cardiovascular death or cardiovascular hospitalizations and for cardiovascular hospitalizations alone. At multivariable analysis, only spironolactone therapy, left ventricular ejection fraction and serum creatinine levels had an independent prognostic value for the combined endpoint, whereas only spironolactone therapy and serum creatinine levels had an independent prognostic value for cardiovascular hospitalizations alone.

CONCLUSIONS

Administration of spironolactone reduced the composite of death and cardiovascular hospitalization in patients with NYHA classes I to II HF. These results suggest that spironolactone could be beneficial when administered on top of optimal therapy among patients with HF and mild or no symptoms.

Extra-adrenal glucocorticoid synthesis: immune regulation and aspects on local organ homeostasis

Systemic glucocorticoids (GCs) mainly originate from de novo synthesis in the adrenal cortex under the control of the hypothalamus-pituitary-adrenal (HPA)-axis. However, research during the last 1-2 decades has revealed that additional organs express the necessary enzymes and have the capacity for de novo synthesis of biologically active GCs. This includes the thymus, intestine, skin and the brain. Recent research has also revealed that locally synthesized GCs most likely act in a paracrine or autocrine manner and have significant physiological roles in local homeostasis, cell development and immune cell activation. In this review, we summarize the nature, regulation and known physiological roles of extra-adrenal GC synthesis. We specifically focus on the thymus in which GC production (by both developing thymocytes and epithelial cells) has a role in the maintenance of proper immunological function.

Rapid induction of aldosterone synthesis in cultured neonatal rat cardiomyocytes under high glucose conditions

In addition to classical adrenal cortical biosynthetic pathway, there is increasing evidence that aldosterone is produced in extra-adrenal tissues. Although we previously reported aldosterone production in the heart, the concept of cardiac aldosterone synthesis remains controversial. This is partly due to lack of established experimental models representing aldosterone synthase (CYP11B2) expression in robustly reproducible fashion. We herein investigated suitable conditions in neonatal rat cardiomyocytes (NRCMs) culture system producing CYP11B2 with considerable efficacy. NRCMs were cultured with various glucose doses for 2-24 hours. CYP11B2 mRNA expression and aldosterone concentrations secreted from NRCMs were determined using real-time PCR and enzyme immunoassay, respectively. We found that suitable conditions for CYP11B2 induction included four-hour incubation with high glucose conditions. Under these particular conditions, CYP11B2 expression, in accordance with aldosterone secretion, was significantly increased compared to those observed in the cells cultured under standard-glucose condition. Angiotensin II receptor blocker partially inhibited this CYP11B2 induction, suggesting that there is local renin-angiotensin-aldosterone system activation under high glucose conditions. The suitable conditions for CYP11B2 induction in NRCMs culture system are now clarified: high-glucose conditions with relatively brief period of culture promote CYP11B2 expression in cardiomyocytes. The current system will help to accelerate further progress in research on cardiac tissue aldosterone synthesis.

Interaction between the heme oxygenase system and aldosterone in hypertension

The chronic intraperitoneal administration of the heme oxygenase inducer, hemin (15 mg/kg daily), for three weeks reduced blood pressure in adult spontaneously hypertensive rats (SHR) from 210.1±1.03 mmHg to 127±0.9 mmHg (n=10, P<0.01) but had no effect on age-matched normotensive Wistar-Kyoto or Sprague-Dawley strains. The antihypertensive effect of hemin was accompanied by reduced expression of aldosterone synthase messenger RNA and depleted levels of plasma aldosterone (675.7±121.6 pg/mL versus 365.7±37 pg/mL; n=4, P<0.05).Because aldosterone is known to stimulate phospholipase C (PLC), the effect of hemin on PLC was examined. Hemin abated PLC activity (29.6±1.5 nmol/min/mL versus 3.1±0.9 nmol/min/mL; n=5, P<0.01) and this was accompanied by depleted levels of intracellular calcium (551±46 nM versus 103.2±6.3 nM; n=4, P<0.01) in the aorta of SHR. In contrast, enhanced heme oxygenase activity and elevated cyclic GMP levels (17.74±0.08 pmol/mg versus 30.4±2.3 pmol/mg protein; n=6, P<0.01) were detected in hemin-treated SHR. Additionally, hemin therapy also suppressed inflammatory and oxidative insults by significantly reducing nuclear factor kappa B messenger RNA expression while enhancing the total antioxidant capacity (0.22±0.02 Trolox equivalent antioxidant capacity (TEA C)/mg protein versus 0.60±0.04 TEA C/mg protein; n=4, P<0.01).The concomitant depletion of aldosterone, PLC activity, intracellular calcium and the corresponding decline of inflammatory and oxidative insults may account for the antihypertensive effects of hemin.

Aldosterone as a modulator of immunity: implications in the organ damage

High plasmatic levels of aldosterone cause hypertension and contribute to progressive organ damage to the heart, vasculature, and kidneys. Recent studies have demonstrated a role for the immune system in these pathological processes. Aldosterone promotes an inflammatory state characterized by vascular infiltration of immune cells, reactive oxidative stress, and proinflammatory cytokine production. Further, cells of the adaptive immune system, such as T cells, seem to participate in the genesis of mineralocorticoid hormone-induced hypertension. In addition, the observation that aldosterone can promote CD4⁺ T-cell activation and Th17 polarization suggests that this hormone could contribute to the onset of autoimmunity. Here we discuss recent evidence supporting a significant involvement of the immune system, especially adaptive immunity, in the genesis of hypertension and organ damage induced by primary aldosteronism. In addition, possible new therapeutic approaches consisting of immunomodulator drugs to control exacerbated immune responses triggered by elevated aldosterone concentrations will be described.

Extra-adrenal glucocorticoids and mineralocorticoids: evidence for local synthesis, regulation, and function

Glucocorticoids and mineralocorticoids are steroid hormones classically thought to be secreted exclusively by the adrenal glands. However, recent evidence has shown that corticosteroids can also be locally synthesized in various other tissues, including primary lymphoid organs, intestine, skin, brain, and possibly heart. Evidence for local synthesis includes detection of steroidogenic enzymes and high local corticosteroid levels, even after adrenalectomy. Local synthesis creates high corticosteroid concentrations in extra-adrenal organs, sometimes much higher than circulating concentrations. Interestingly, local corticosteroid synthesis can be regulated via locally expressed mediators of the hypothalamic-pituitary-adrenal (HPA) axis or renin-angiotensin system (RAS). In some tissues (e.g., skin), these local control pathways might form miniature analogs of the pathways that regulate adrenal corticosteroid production. Locally synthesized glucocorticoids regulate activation of immune cells, while locally synthesized mineralocorticoids regulate blood volume and pressure. The physiological importance of extra-adrenal glucocorticoids and mineralocorticoids has been shown, because inhibition of local synthesis has major effects even in adrenal-intact subjects. In sum, while adrenal secretion of glucocorticoids and mineralocorticoids into the blood coordinates multiple organ systems, local synthesis of corticosteroids results in high spatial specificity of steroid action. Taken together, studies of these five major organ systems challenge the conventional understanding of corticosteroid biosynthesis and function.

Rationale and design of the 'aldosterone receptor blockade in diastolic heart failure' trial: a double-blind, randomized, placebo-controlled, parallel group study to determine the effects of spironolactone on exercise capacity and diastolic function in patients with symptomatic diastolic heart failure (Aldo-DHF)

AIMS

Increasing evidence suggests that enhanced aldosterone signalling plays a key role in the onset and progression of diastolic heart failure (DHF). Aldo-DHF will test the hypothesis that aldosterone receptor blockade by spironolactone will improve exercise capacity and diastolic function in patients with DHF.

METHODS

Aldo-DHF is a randomized, placebo-controlled, double-blinded, two-armed, multicentre, parallel group study. Four hundred and twenty patients with DHF will be randomly assigned to receive spironolactone 25 mg per day or placebo. The main inclusion criteria are: age > or = 50 years, New York Heart Association II/III, preserved left ventricular ejection fraction (> or =50%), and echocardiographic evidence of diastolic dysfunction. The two primary endpoints are changes in exercise capacity (peak VO(2), spiroergometry) and in diastolic function (E/é, echocardiography) after 12 months. Secondary endpoints include effects of spironolactone on additional parameters of exercise performance and diastolic as well as systolic function, neurohumoral activation, and quality of life. Morbidity and mortality as well as safety aspects will also be assessed.

CONCLUSION

Aldo-DHF is the first large-scale clinical trial to evaluate the effects of aldosterone receptor blockade on exercise capacity and diastolic function in patients with DHF. Aldo-DHF will provide important information about the clinical course of this condition and may have significant impact on treatment strategies and future trials in these patients.

Synergistic inhibitory effect of angiotensin II receptor blocker and thiazide diuretic on the tissue renin-angiotensin-aldosterone system

ARBs are conceptually more potent in a high renin state than in a low renin state at blood pressure reduction and cardiovascular protection, whereas the potency of thiazide diuretics in the contrary. However, the additive effect of the agents when used in combination remains unclear. Thus, the goal of the present review was to analyse available data to explain the mechanistic actions of the ARB-thiazide diuretic combination. Although the circulating renin-angiotensin-aldosterone system (RAAS) has been well characterised in the context of cardiovascular disease, recent attention has also focused on the role of the tissue RAAS. For example, both angiotensin II and aldosterone are produced in small amounts within cardiac tissue, and the angiotensin II type 1 receptor is widely distributed and activated within cardiovascular tissues. Recent reports also suggest that the mineralocorticoid receptor is activated through Rac1 GTP-ase in high salt-intake rats. Thus, many components of the RAAS are activated in cardiovascular tissues under high salt-intake conditions, and a low salt diet or use of diuretics likely suppresses the tissue RAAS. Since ARBs can block the effect of both tissue angiotensin II and circulating angiotensin II, it follows that the combination of an ARB and a thiazide diuretic results in synergistic inhibition of the tissue RAAS.

Aldosterone and the cardiovascular system: a dangerous association

Initial studies have focussed on the actions of aldosterone in renal electrolyte handling and, as a consequence, blood pressure control. More recently, attention has primarily been focussed on its actions on the heart and vascular system, where it is locally produced. Aldosterone by binding mineralocorticoid receptors causes oxidative stress, fibrosis and triggers an inflammatory response in the cardiovascular system. All these effects could be underlying the role of aldo-sterone on cardiac and vascular remodelling associated with different pathological situations. At the vascular level, aldo-sterone affects endothelial function because administration of aldosterone to rats impaired endothelium-dependent relaxations. In addition, the administration of mineralocorticoid receptor antagonists ameliorates endothelium-dependent relaxation in models of both hypertension and atherosclerosis, and in patients with heart failure. Several mechanisms can participate in this effect, including production of vasoconstrictor factors and a reduction in nitric oxide levels. This reduction can involve both a decrease in its production as well as an increase in its degradation by reactive oxygen species. Aldosterone can produce oxidative stress by the activation of transcription factors such as the NF-κB system, which can also trigger an inflammatory process through the production of different cytokines. At cardiac level, high levels of aldosterone can also adversely impact heart function by producing cardiac hypertrophy, diastolic dysfunction and electrical remodelling through changes in ionic channels. All these effects can explain the beneficial effect of mineralocorticoid blockade in the cardiovascular system.

Aldosterone, but not angiotensin II, reduces angiotensin converting enzyme 2 gene expression levels in cultured neonatal rat cardiomyocytes

BACKGROUND

A previous report showed that aldosterone upregulates angiotensin converting enzyme (ACE) gene expression levels in cultured neonatal rat cardiocytes. ACE2 is a novel homologue of ACE, which exists in the human heart, and ACE2 converts angiotensin I to angiotensin 1-9 and angiotensin II to angiotensin 1-7, thereby decreasing angiotensin II levels. In the present study, an investigation took place to see whether aldosterone regulates the expression of ACE2 as well as that of ACE in cultured neonatal rat cardiomyocytes.

METHODS AND RESULTS

Primary neonatal rat cardiomyocytes were cultured with aldosterone. Total RNA was extracted from these cardiomyocytes and quantified the mRNA levels of ACE2, ACE and GAPDH by using real-time reverse transcription polymerase chain reaction analysis. Aldosterone significantly decreased ACE2 mRNA levels and increased ACE mRNA levels at 12 h. Angiotensin II, however, had no effect on either ACE2 mRNA levels or ACE mRNA levels. Eplerenone, a mineralocorticoid receptor antagonist, completely blocked the increase in ACE mRNA levels and the reduction in ACE2 mRNA levels due to aldosterone.

CONCLUSION

Aldosterone, but not angiotensin II, reduced ACE2 mRNA levels and increased ACE mRNA levels in rat cardiomyocytes via mineralocorticoid receptor. Aldosterone might play an important role in cardiac remodeling by upregulating ACE and downregulating ACE2 levels.

Clinical factors affecting serum potassium concentration in cardio-renal decompensation syndrome

BACKGROUND

Renin-angiotensin-aldosterone system (RAAS) inhibitors are currently indispensable for the treatment of heart failure. It is well known that hyperkalemia is likely to occur in renal failure; however, it has not yet been clarified how the serum potassium concentration changes as heart failure progresses. Currently, the cardio-renal decompensation syndrome holds that the serum potassium concentration is altered similarly by both heart failure and renal failure; however, there are no definitive reports on this. In order to use RAAS inhibitors more safely and effectively in heart failure, it is necessary to understand the factors affecting serum potassium concentration in the clinical setting.

METHODS AND RESULTS

We examined the clinical factors affecting serum potassium concentration in 1035 consecutive patients with cardiovascular disease who were hospitalized in our institution. Multiple regression analysis showed that the independent factors associated with an elevated serum potassium concentration were renal insufficiency evaluated by estimated glomerular filtration rate (eGFR) (P<0.0001), diabetes mellitus evaluated by HbA(1c) (P=0.0005) and the use of RAAS inhibitors (P=0.0010). The independent factors associated with a decreased serum potassium concentration were mean blood pressure (P<0.0001), heart failure evaluated by log BNP (P=0.0164) and the use of diuretics (P=0.0232).

CONCLUSIONS

The serum potassium concentration decreases with the severity of heart failure if renal function is preserved. From the perspective of potassium homeostasis, we could use the RAAS inhibitors more aggressively in patients with heart failure who do not have renal failure.

Crosstalk between the heme oxygenase system, aldosterone, and phospholipase C in hypertension

BACKGROUND

Aldosterone is a mineral corticoid hormone that is produced in response to angiotensin-II, and like angiotensin-II, stimulates inflammation, oxidative stress, and fibrosis by activating nuclear factor-kappaB and activating protein-1. Recent evidence, however, indicates that aldosterone stimulates phospholipase C and activates nuclear factor-kappaB and activating protein-1. Although the heme oxygenase system is cytoprotective, its effects on aldosterone-phospholipase C signaling in deoxycorticosterone acetate (DOCA-salt) hypertension, a model of aldosteronism, and spontaneously hypertensive rat, a genetic model of human essential hypertension, have not been fully characterized.

METHODS

In the present study, the heme oxygenase inducer, hemin, was given to spontaneously hypertensive and deoxycorticosterone acetate hypertensive rats, and the effects on blood pressure, aldosterone, nuclear factor-kappaB, activating protein-1, phospholipase C, and inositol 1,4,5-triphosphate were examined.

RESULTS

Hemin therapy restored physiological blood pressure to spontaneously hypertensive rats (209.9 +/- 0.9 to 127.3 +/- 0.85 mmHg, n = 10, P < 0.01) and to deoxycorticosterone acetate salt hypertensive rats (195.7 +/- 1.8 vs.132.5 +/- 2.1 mmHg; P < 0.01, n = 10), but had no effect on age-matched normotensive Wistar-Kyoto or Sprague-Dawley strains. The antihypertensive effect was accompanied by enhanced heme oxygenase activity, upregulated cyclic guanosine monophosphate-protein kinase G signaling, increased superoxide dismutase activity, and the potentiation of total antioxidant capacity, whereas aldosterone, activating protein-1, and nuclear factor-kappaB were reduced. Furthermore, hemin suppressed phospholipase C activity, attenuated inositol 1,4,5-triphosphate, and reduced resting intracellular calcium in the aorta.

CONCLUSION

Collectively, our results suggest that the concomitant depletion of aldosterone, phospholipase C-inositol 1,4,5-triphosphate activity, resting intracellular calcium and the corresponding decline of inflammatory, and oxidative insults may account for the antihypertensive effects of hemin in deoxycorticosterone acetate hypertension and spontaneously hypertensive rats.

A lifetime of aldosterone excess: long-term consequences of altered regulation of aldosterone production for cardiovascular function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Left Ventricular Hypertrophy and Geometry in Untreated Essential Hypertension is Associated With Blood Levels of Aldosterone and Procollagen Type III Amino-Terminal Peptide

BACKGROUND

The present study examined the role of aldosterone in left ventricular hypertrophy (LVH) and geometry in patients with untreated essential hypertension (EHT), and investigated the contribution of myocardial fibrosis to the process of LVH.

METHODS AND RESULTS

The relationship of the plasma aldosterone concentration (PAC) to LVH and left ventricular (LV) geometry was investigated in 57 consecutive patients with untreated EHT. PAC correlated with both LV mass index (LVMI: r=0.46, p=0.0004) and relative wall thickness (RWT: r=0.33, p=0.013). In patients with LVH (LVMI > or =125 g/m(2)), the serum concentration of procollagen type III amino-terminal peptide (PIIINP), a marker of myocardial fibrosis, correlated with RWT (r=0.46, p=0.029). These patients were divided into 2 groups: concentric hypertrophy (CH) with RWT > or =0.44, and eccentric hypertrophy (EH) with RWT <0.44. The serum PIIINP concentration was significantly higher in the CH group than in the EH group (0.52+/-0.02 ng/ml vs 0.44+/-0.03 ng/ml, respectively; p<0.05).

CONCLUSIONS

Aldosterone may be involved in LVH and LV geometry, particularly in the development of CH. Myocardial fibrosis seems more strongly involved in the hypertrophic geometry of CH than with EH.

Spironolactone Modulates Expressions of Cardiac Mineralocorticoid Receptor and 11.BETA.-Hydroxysteroid Dehydrogenase 2 and Prevents Ventricular Remodeling in Post-Infarct Rat Hearts

Aldosterone antagonists have been reported to prevent ventricular remodeling after myocardial infarction (MI) via their action to extracellular matrix (ECM). However, it remains largely unknown whether aldosterone antagonists attenuate myocyte loss in the remodeling process. The present study examined whether spironolactone prevents myocyte apoptosis and improves post-infarct ventricular remodeling in rats. MI was achieved by permanent occlusion of the left coronary artery. Administration of spironolactone (100 mg/kg/day) was started immediately after MI. Sprague-Dawley rats were divided into four groups: 1) sham, 2) spironolactone-treated sham, 3) untreated MI, 4) spironolactone-treated MI. Echocardiographic parameters (left ventricular [LV] diastolic dimension [LVDd], fractional shortening [%FS]), hemodynamic parameters (LV systolic pressure [LVSP], LV end-diastolic pressure [LVEDP], dP/dt(max) and dP/dt(min)) and collagen accumulation quantitated by Masson's Trichrome staining were significantly improved in the spironolactone-treated MI group on the 14th day, compared with the untreated MI group. Moreover, the percentage of apoptotic myocytes evaluated by terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay was significantly lower in the spironolactone-treated MI group on the 2nd (3.54% vs. 5.79% in untreated MI group), 7th (0.65% vs. 1.37% in untreated MI group) and 14th days (0.11% vs. 0.16% in untreated MI group). Real time reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the expression of mineralocorticoid receptor (MR) mRNA and that of 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD2) mRNA, which is known to confer aldosterone selectivity on MR, were upregulated in the untreated MI group, and that spironolactone significantly suppressed the expression of these genes. Moreover, spironolactone significantly inhibited aldosterone-induced apoptosis in cultured rat cardiac myocytes in a dose-dependent fashion. Our study demonstrates that, in addition to their effect on ECM, aldosterone antagonists inhibit myocyte apoptosis and prevent post-infarct ventricular remodeling by modulating the expression levels of MR and 11beta-HSD2, which are enhanced in the remodeling heart.

Coronary sinus and ascending aortic levels of aldosterone, angiotensin II, and B-type natriuretic peptide in patients with aortic stenosis and in patients with coronary heart disease

Demonstration that aldosterone synthesis occurs in the myocardium would suggest that the clinical benefits of aldosterone receptor antagonists may extend to patients with normal circulating plasma levels of aldosterone. Previous studies have reported myocardial aldosterone synthesis in patients with heart failure. This study determined whether myocardial aldosterone and angiotensin II release occurs in patients with aortic stenosis (AS) and/or coronary heart disease (CHD) with normal left ventricular ejection fractions and no clinical heart failure. In 19 patients with severe AS and 18 patients with stable CHD, plasma levels of aldosterone, angiotensin II, B-type natriuretic peptide (BNP), and procollagen type III amino terminal peptide (PIIINP) were measured in blood samples taken from the coronary sinus and aortic root before diagnostic coronary angiography. Plasma aldosterone was approximately 20% greater in the coronary sinus than the aorta, respectively, in the 2 patient groups (AS: 120 vs 102 pmol/L, p <0.001; CHD: 94 vs 77 pmol/L, p <0.001). Plasma angiotensin II was also greater in the coronary sinus (AS: 16 vs 11 pmol/L, p <0.001; CHD: 12 vs 9 pmol/L, p <0.001). Plasma levels of BNP in the coronary sinus were approximately double those in the aorta in the 2 groups of patients (p <0.001). In contrast, there was no transmyocardial gradient in the plasma level of PIIINP for either AS or CHD. In conclusion, these results indicate that aldosterone, angiotensin II, and BNP are released into the coronary sinus in severe AS and in stable CHD, even when the left ventricular ejection fraction is normal and there is no clinical heart failure.

Gender-related differences in target organ damage in untreated patients with essential hypertension

We examined the gender-related differences in target organ damage in 220 untreated patients with essential hypertension (106 men and 114 women). As the indices of target organ damage, we examined the left ventricular mass index and the intima-media thickness in the carotid and femoral arteries obtained from echocardiography. In a multiple regression model, there was a significant positive correlation between the intima-media thickness and age in both groups. In men, there was a significant positive correlation between the left ventricular mass index and age, as well as the diastolic blood pressure, and body mass index. In women, there was a significant positive correlation between the left ventricular mass index and age, as well as plasma renin activity and smoking. In conclusion, there are gender-related differences in the contributing factors, which relate to left ventricular hypertrophy in patients with essential hypertension.

The risks and benefits of aldosterone antagonists

Spironolactone and eplerenone are mineralocorticoid- blocking agents used for their ability to block a host of epithelial and nonepithelial actions of aldosterone. These compounds are of proven benefit in reducing blood pressure and urine protein excretion, and in conferring cardiovascular gain in diverse circumstances of heart failure. However, as enthusiasm grows for use of mineralocorticoid-blocking agents, the risks inherent to use of such drugs become more pertinent. Whereas the endocrine side effects of spironolactone are in reality little more than a cosmetic disfigurement, the potassium-sparing properties of spironolactone and eplerenone can prove life-threatening if hyperkalemia develops. However, for most patients the risk of developing hyperkalemia should not dissuade the prudent clinician from use of these compounds. Hyperkalemia should be considered as a possibility in any patient receiving these medications and as such is best addressed preemptively.

Persistent Cardiac Aldosterone Synthesis in Angiotensin II Type 1A Receptor–Knockout Mice After Myocardial Infarction

Background— The renin-angiotensin-aldosterone system is implicated in the pathogenesis of heart failure. Pharmacological blockade of angiotensin II (Ang II)–dependent signaling is clinically effective in reducing cardiovascular events after myocardial infarction (MI) but still fails to completely prevent remodeling. The molecular basis underlying this Ang II–independent remodeling is unclear.

Methods and Results— Acute MI was induced by coronary ligation in wild-type (WT) and angiotensin II type IA receptor–knockout (AT 1A -KO) mice. Left ventricular (LV) geometry, hemodynamics, and cardiac gene expression were evaluated on day 28. Severe LV remodeling and resultant cardiac dysfunction were observed in WT mice, whereas less marked, but still significant, LV remodeling and cardiac dysfunction were induced in AT 1A -KO mice. Gene expression levels of aldosterone synthase and the cardiac aldosterone content were both elevated in the MI hearts, even in AT 1A -KO mice. In AT 1A -KO mice treated with spironolactone (20 mg/kg per day), LV remodeling, cardiac dysfunction, and cardiac gene expression of collagens and natriuretic peptides were almost normalized.

Conclusions— Our results indicate that genetic blockade of AT 1A signaling fails to arrest aldosterone production in cardiac tissues and that cardiac aldosterone plays a critical role in post-MI LV remodeling. The results suggest that spironolactone could be potentially effective in patients with MI, when used in combination with renin-angiotensin system blockade, by blocking the actions of aldosterone produced by Ang II–independent mechanisms.

Current Treatment Options for CHF Management: Focus on the Renin-Angiotensin-Aldosterone System

Heart failure (HF) is highly prevalent in our society and its incidence is increasing in concert with the growing aged population. Experimental and clinical studies have consistently shown that HF is ameliorated by inhibition of the renin-angiotensin-aldosterone system (RAAS). Acknowledging that heightened activation of the RAAS contributes significantly to HF progression has led to the development of pharmacologic antagonists of RAAS components that have greatly improved both symptoms and prognosis of patients suffering from this syndrome. Angiotensin-converting enzyme (ACE) inhibitors represent the first developed agents that block the production of angiotensin II, and have been shown to be effective across a broad spectrum of patients with HF, including those with asymptomatic left ventricular dysfunction to overt HF. Initiation of ACE inhibitors prior to the onset of symptoms in those with left ventricular systolic dysfunction, and as early as feasible following a myocardial infarction, has been shown to reduce mortality and the development of overt HF in several clinical trials. Clinical data also support the use of angiotensin II receptor antagonists as an alternative to ACE inhibitors in patients who are allergic to, or intolerant of, ACE inhibitors. Agents that antagonize aldosterone via blockade of mineralocorticoid receptors improve clinical outcomes in patients with advanced HF or those with reduced ejection fraction and HF following an acute myocardial infarction. Maximally inhibiting the RAAS, in conjunction with other neurohormonal systems (eg, the sympathetic nervous system by b-adrenergic blockade), leads to improved clinical outcomes in HF, a highly prevalent and costly disease in our society.

Adrenocorticotropic hormone is produced in the ventricle of patients with essential hypertension

OBJECTIVE

Aldosterone is produced in the ventricle of patients with hypertension. The present study was designed to examine whether adrenocorticotropic hormone (ACTH) and cortisol are also produced from the heart in patients with essential hypertension.

METHODS

The study population consisted of 57 patients with essential hypertension and 28 control subjects. Plasma levels of ACTH, aldosterone, and cortisol were measured in the aortic root, the anterior interventricular vein and the coronary sinus during cardiac catheterization.

RESULTS

The plasma levels of ACTH were significantly higher at the anterior interventricular vein and coronary sinus than at the aortic root (12.7 +/- 1.0 versus 10.7 +/- 0.9 pmol/l, P < 0.001; and 12.3 +/- 1.0 versus 10.7 +/- 0.9 pmol/l, P < 0.001, respectively) in the hypertension group, whereas there were no significant differences in the levels among these sites in the control group. The plasma levels of aldosterone were significantly higher at the anterior interventricular vein and the coronary sinus than at the aortic root (261.7 +/- 16.4 versus 239.1 +/- 15.1 pmol/l, P < 0.001; and 258.8 +/- 17.0 versus 239.1 +/- 15.1 pmol/l, P < 0.01, respectively) in the hypertension group, whereas there were no significant differences in the levels among these sites in the control group.

CONCLUSIONS

ACTH as well as aldosterone is produced, but cortisol is not produced, from the ventricle of patients with essential hypertension.

The influence of aldosterone on the development of left ventricular geometry and hypertrophy in patients with essential hypertension

The identification of risk factors for the initiation of left ventricle hypertrophy (LVH), which is an independent risk factor for cardiovascular mortality and morbidity in hypertensive patients, is very important. The objective of the present study was to identify the relationship of aldosterone with LVH and different geometrical patterns of left ventricle that develop in patients with essential hypertension. A total of 83 patients with essential hypertension (44 females, mean age, 51 +/- 8 years, 39 males, mean age, 57 +/- 10 years) were included in this study. Thirty-two had LVH. When evaluated according to the geometrical patterns of LVH, 18 patients had concentric LVH, 14 had eccentric LVH, and 17 had concentric remodeling. Thirty-four patients had normal left ventricle geometry. Two weeks after the cessation of antihypertensive medications, sodium, potassium, and proteinuria in 24-hour urine samples and plasma aldosterone levels and plasma renin activity were measured. Plasma aldosterone levels of the patients with LVH were found to be significantly higher (9.92 +/- 6.34 ng/dL versus 5.83 +/- 3.5 ng/dL, P < 0.01). The difference between plasma renin activities was not statistically significant. Linear regression analysis revealed that plasma aldosterone level and age were independent parameters increasing left ventricle mass index. The plasma aldosterone levels of patients with concentric hypertrophy of the left ventricle were significantly higher than those of patients with normal geometry and concentric remodeling. There was no significant difference between plasma renin activities. Twenty-four hour urine protein concentrations of the patients with LVH were found to be significantly higher and sodium to be significantly lower. Plasma aldosterone levels seem to be correlated with LVH especially with concentric hypertrophy of the left ventricle in patients with essential hypertension.

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.

Mechanisms of Disease: local renin–angiotensin–aldosterone systems and the pathogenesis and treatment of cardiovascular disease

Accumulating evidence has made it clear that not only does the renin-angiotensin-aldosterone system (RAAS) exist in the circulation where it is driven by renal renin, but it is also active in many tissues-and likely within cells as well. These systems might not be completely independent of each other, but rather interact. These local RAASs affect tissue and cellular angiotensin II concentrations and appear to be associated with clinically relevant physiologic and pathophysiologic actions in the cardiovascular system and elsewhere. Evidence in support of this possibility is reviewed here. In addition, direct (pro)renin action after binding to its specific receptor, the existence of renin transcripts, which apparently encode an intracellular renin, the discovery of an angiotensin-converting-enzyme homologue (ACE2), which leads to enhanced generation of angiotensin-(1-7) and the newly appreciated role of angiotensin-receptor dimerization in the regulation of angiotensin activity, all point to the conclusion that the RAASs are complexly regulated, multifunctional systems with important roles both within and outside the cardiovascular system.

Prevention and Reversal of LV Remodeling with Neurohormonal Inhibitors

Left ventricular (LV) remodeling refers to alterations in ventricular mass, chamber size, and shape that result from myocardial injury, pressure, or volume overload. Numerous studies have demonstrated that LV remodeling correlates with the incidence of heart failure and death, supporting a causative role for remodeling in heart failure progression. Heart failure trials have shown that neurohormonal antagonists, including angiotensin-converting enzyme (ACE) inhibitors and beta-adrenergic receptor blockers (beta blockers), reduce remodeling in parallel with improved clinical outcomes. Existing data favor using angiotensin II type 1 (AT1) receptor antagonists (or "ARBs"), although their anti-remodeling effects are less well established. Recently, mineralocorticoid receptor antagonists have gained substantial interest based on favorable clinical trial results, although data regarding their effects on remodeling are limited. Thus, an optimal medical regimen to prevent or limit LV remodeling in patients with LV dysfunction should include both an ACE inhibitor and beta-adrenergic receptor antagonist, irrespective of the degree of LV dysfunction and symptom status. For patients intolerant to ACE inhibitors, an AT1 receptor antagonist should be substituted. An aldosterone antagonist should be administered to patients with severe, New York Heart Association class III to IV heart failure who have normal or only mildly impaired renal function, or to those patients with depressed LV function following an acute myocardial infarction. Through the aggressive pharmacologic inhibition of both the renin-angiotensin-aldosterone and sympathetic nervous systems, progressive LV remodeling can be prevented or hindered, thereby favorably altering the natural history of the heart failure syndrome.

Relations of Serum Aldosterone to Cardiac Structure

Aldosterone is associated with myocardial fibrosis in experimental studies and with left ventricular remodeling in heart failure patients. We hypothesized that aldosterone influences ventricular remodeling in people without congestive heart failure in the community. We examined the relations between serum aldosterone and echocardiographic left ventricular measurements in 2820 Framingham Study subjects (mean age 57 years, 58% women, 88% white) free of myocardial infarction and overt heart failure. Serum aldosterone levels were higher in women compared with men. In linear regression models (adjusted for age, systolic blood pressure, weight, height, diabetes, heart rate, hypertension treatment, and ethnicity), left ventricular wall thickness and relative wall thickness were positively related, and left ventricular diastolic dimensions were inversely related to serum aldosterone in women ( P <0.05 for all), but not in men ( P >0.20 for all). There was no effect modification of the relations observed in women by menopausal status. The gender-related differences in relations of serum aldosterone to relative wall thickness were consistent across subgroups defined on the basis of sex-specific median values of systolic blood pressure and body mass index. Fractional shortening, left ventricular mass, and left atrial dimensions were not related to serum aldosterone in either sex. In conclusion, in our community-based sample of individuals free of myocardial infarction and heart failure, serum aldosterone was positively associated with a left ventricular geometric pattern suggestive of concentric remodeling (increased left ventricular wall thickness and relative wall thickness but decreased internal dimensions) in women but not in men. Additional investigations are warranted to confirm these findings.

Aldosterone target organ protection by eplerenone

The classical mineralocorticoid effect of aldosterone on unidirectional transepithelial sodium transport in the kidney was long thought to be the predominant effect of this hormone. However, there is convincing evidence for additional extrarenal actions of aldosterone that are mediated via activation of mineralocorticoid receptors (MRs) in the heart, vasculature and brain. It is now postulated that many of the detrimental effects of aldosterone are mediated through MR activation in these nonclassical target organs. The selective aldosterone blocker, eplerenone (Inspra), is under development for human therapeutic use for treatment of hypertension and heart failure post-myocardial infarction (MI). Clinical and preclinical studies have linked elevated aldosterone to hypertension, left ventricular and vascular remodeling, cardiac, renal, and cerebral vascular inflammation and injury, and increased risk of mortality in heart failure patients. Multiple studies in experimental models of hypertension and heart failure demonstrate that selective blockade of aldosterone by eplerenone effectively preserves cardiac function, attenuates maladaptive left ventricular remodeling and tissue and vascular injury in part by reducing vascular inflammation in aldosterone target organs.

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

OBJECTIVES

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

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

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

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

Cardioprotective Effects of Vasopeptidase Inhibition vs. Angiotensin Type 1-Receptor Blockade in Spontaneously Hypertensive Rats on a High Salt Diet

The aim of our study was to compare the cardioprotective effects of vasopeptidase inhibition with those of angiotensin type 1 (AT1)-receptor blockade, a diuretic and the combination of AT1-receptor blockade and a diuretic in an experimental rat model of essential hypertension on a high salt diet. Spontaneously hypertensive rats (SHR) (n =73) were divided into 6 groups to receive the following diet and drug regimens for 8 weeks: 1) low salt controls (NaCl 0.5%); 2) high salt controls (NaCl 6%); 3) omapatrilat (40 mg/kg/d) on a high salt diet; 4) losartan (30 mg/kg/d) on a high salt diet; 5) hydrochlorothiazide (HCTZ; 10 mg/kg/d) on a high salt diet; and 6) losartan+HCTZ (30+10 mg/kg/d) on a high salt diet. Blood pressure was measured by tail-cuff plethysmography. The histological score of myocardial damage, myocardial collagen volume fraction (CVF), connective tissue growth factor (CTGF) expression and cardiomyocyte apoptosis were determined. As an antihypertensive, omapatrilat showed greater efficacy than monotherapy with losartan or HCTZ, and was equally effective as the combination of losartan+HCTZ. Assessed by myocardial damage score, omapatrilat and losartan protected cardiac morphology better than HCTZ or the drug combination. Omapatrilat decreased CVF to a greater extent than the other therapies, whereas losartan was most effective in decreasing CTGF expression. All drug treatments, except HCTZ, decreased cardiomyocyte apoptosis. Our findings provide evidence that both vasopeptidase inhibition and AT1-receptor blockade exert cardioprotective properties beyond their blood pressure-lowering effects. Cardioprotection was associated with prevention of cardiomyocyte apoptosis and inhibition of extracellular matrix formation.

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

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

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

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure

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