Mineralocorticoid and angiotensin receptor antagonism during hyperaldosteronemia

Effect of high-dose mineralocorticoid receptor antagonist eplerenone on urinary albumin excretion in patients with type 2 diabetes and high cardiovascular risk: Data from the MIRAD trial

AIM

As mineralocorticoid receptor antagonists (MRAs) may possess renoprotective effects in type 2 diabetes (T2D), it was decided to investigate the impact of high-dose MRA on prespecified secondary endpoints-namely, change in urinary albumin-creatinine ratio (UACR) and 24-h ambulatory blood pressure-in the MIRAD trial.

METHODS

This was a double-blind clinical trial in which T2D patients at high risk of or with established cardiovascular disease (CVD) were randomized to either high-dose (100-200 mg) eplerenone or a dose-matched placebo as an add-on to background antihypertensive treatment for 26 weeks. Safety was evaluated by the incidence of hyperkalaemia and kidney-related adverse events.

RESULTS

A total of 140 patients were enrolled (70 in each group). Baseline UACR was 17 mg/g (geometric mean; 95% CI: 13-22); this decreased by 34% in the eplerenone group compared with the placebo group at week 26 (95% CI: -51% to -12%; P =  0.005). There was no significant decrease in 24-h systolic blood pressure (SBP) due to treatment (-3 mmHg; 95% CI: -6 to 1; P = 0.150). However, the observed change in 24-h SBP correlated with the relative change in UACR in the eplerenone group (r = 0.568, P < 0.001). Mean baseline (± SD) estimated glomerular filtration rate (eGFR) was 85 (± 18.6) mL/min/1.73 m², and 12 (± 9%) had an eGFR of 41-59 mL/min/1.73 m². No significant differences in the incidence of mild hyperkalaemia (≥ 5.5 mmol/L; eplerenone vs placebo: 6 vs 2, respectively; P = 0.276) and no severe hyperkalaemia (≥ 6.0 mmol/L) were observed.

CONCLUSION

The addition of high-dose eplerenone to T2D patients at high risk of CVD can markedly reduce UACR with an acceptable safety profile.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Nongenomic effects via the mineralocorticoid receptor

The mineralocorticoid receptor (MR) belongs to the steroid hormone receptor family and classically functions as a ligand-dependent transcription factor. It is involved in water-electrolyte homeostasis and blood pressure regulation but independent from these effects also furthers inflammation, fibrosis, hypertrophy and remodeling in cardiovascular tissues. Next to genomic effects, aldosterone elicits very rapid actions within minutes that do not require transcription or translation and that occur not only in classical MR epithelial target organs like kidney and colon but also in nonepithelial tissues like heart, vasculature and adipose tissue. Most of these effects can be mediated by classical MR and its crosstalk with different signaling cascades. Near the plasma membrane, the MR seems to be associated with caveolin and striatin as well as with receptor tyrosine kinases like EGFR, PDGFR and IGF1R and G protein-coupled receptors like AT1 and GPER1, which then mediate nongenomic aldosterone effects. GPER1 has also been named a putative novel MR. There is a close interaction and functional synergism between the genomic and the nongenomic signaling so that nongenomic signaling can lead to long-term effects and support genomic actions. Therefore, understanding nongenomic aldosterone/MR effects is of potential relevance for modulating genomic aldosterone effects and may provide additional targets for intervention.

Adrenal beta-arrestin 1 inhibition in vivo attenuates post-myocardial infarction progression to heart failure and adverse remodeling via reduction of circulating aldosterone levels

OBJECTIVES

We investigated whether adrenal beta-arrestin 1 (βarr1)-mediated aldosterone production plays any role in post-myocardial infarction (MI) heart failure (HF) progression.

BACKGROUND

Heart failure represents 1 of the most significant health problems worldwide, and new and innovative treatments are needed. Aldosterone contributes significantly to HF progression after MI by accelerating adverse cardiac remodeling and ventricular dysfunction. It is produced by the adrenal cortex after angiotensin II activation of angiotensin II type 1 receptors (AT₁Rs), G protein-coupled receptors that also signal independently of G proteins. The G protein-independent signaling is mediated by βarr1 and βarr2. We recently reported that adrenal βarr1 promotes AT₁R-dependent aldosterone production leading to elevated circulating aldosterone levels in vivo.

METHODS

Adrenal-targeted, adenoviral-mediated gene delivery in vivo in 2-week post-MI rats, a time point around which circulating aldosterone significantly increases to accelerate HF progression, was performed to either increase the expression of adrenal βarr1 or inhibit its function via expression of a βarr1 C-terminal-derived peptide fragment.

RESULTS

We found that adrenal βarr1 overexpression promotes aldosterone elevation after MI, resulting in accelerated cardiac adverse remodeling and deterioration of ventricular function. Importantly, these detrimental effects of aldosterone are prevented when adrenal βarr1 is inhibited in vivo, which markedly decreases circulating aldosterone after MI. Finally, the prototypic AT₁R antagonist losartan seems unable to lower this adrenal βarr1-driven aldosterone elevation.

CONCLUSIONS

Adrenal βarr1 inhibition, either directly or with AT₁R "biased" antagonists that prevent receptor-βarr1 coupling, might be of therapeutic value for curbing HF-exacerbating hyperaldosteronism.

Effects of selective mineralocorticoid receptor antagonism on atrial ion currents and early ionic tachycardia-induced electrical remodelling in rabbits

Over the past years, the importance of the renin-angiotensin-aldosterone system in atrial fibrillation (AF) pathophysiology has been recognised. Lately, the role of aldosterone in AF pathophysiology and mineralocorticoid receptor (MR) antagonism in "upstream" AF treatment is discussed. Hypothesising that selective MR antagonism might also influence atrial ion currents (L-type calcium current [I (Ca,L)], transient outward potassium current [I (to)], sustained outward potassium current [I (sus)]) and their tachycardia-induced remodelling, the effects of an eplerenone treatment were studied in a rabbit model. Six groups each with four animals were built. Animals of the control group received atrial pacing leads, but in contrast to the pacing groups, no atrial tachypacing (600 per minute for 24 and 120 h immediately before heart removal) was applied. Animals of the eplerenone groups were instrumented/paced as the corresponding control/pacing groups, but were additionally treated with eplerenone (7 days before heart removal). Atrial tachypacing was associated with a reduction of I (Ca,L). I (to) was decreased after 24 h of tachypacing, but returned to control values after 120 h. In the absence of rapid atrial pacing, MR antagonism reduced I (Ca,L) to a similar extent as 120 h of tachypacing alone. Based on this lower "take-off level", I (Ca,L) was not further decreased by high-rate pacing. I (to) and its expected tachycardia-induced alterations were not influenced by MR antagonism. In our experiments, selective MR antagonism influenced atrial I (Ca,L) and its tachycardia-induced alterations. As changes of I (Ca,L) are closely linked with atrial calcium signalling, the relevance of these alterations in AF pathophysiology and, accordingly, AF treatment is likely and has to be further evaluated.

New aspects of rapid aldosterone signaling

Aldosterone, the endogenous ligand of the mineralocorticoid receptor (MR) in humans, is a steroid hormone that regulates salt and water homeostasis. Recently, additional pathophysiological effects in the renocardiovascular system have been identified. Besides genomic effects mediated by activated MR, rapid aldosterone actions that are independent of translation and transcription have been documented. While these nongenomic actions influence electrolyte homeostasis, pH and cell volume in classical MR target organs, they also participate in pathophysiological effects in the renocardiovascular system causing endothelial dysfunction, inflammation and remodeling. The mechanisms conveying these rapid effects consist of a multitude of signaling molecules and include a cross-talk with genomic aldosterone effects as well as with angiotensin II and epidermal growth factor receptor signaling. Rapid corticosteroid signaling via the MR has also been demonstrated in the brain. Altogether, the function of nongenomic aldosterone effects seems to be to modulate other signaling cascades, depending on the surrounding milieu.

An adrenal beta-arrestin 1-mediated signaling pathway underlies angiotensin II-induced aldosterone production in vitro and in vivo

Aldosterone produces a multitude of effects in vivo, including promotion of postmyocardial infarction adverse cardiac remodeling and heart failure progression. It is produced and secreted by the adrenocortical zona glomerulosa (AZG) cells after angiotensin II (AngII) activation of AngII type 1 receptors (AT(1)Rs). Until now, the general consensus for AngII signaling to aldosterone production has been that it proceeds via activation of G(q/11)-proteins, to which the AT(1)R normally couples. Here, we describe a novel signaling pathway underlying this AT(1)R-dependent aldosterone production mediated by beta-arrestin-1 (betaarr1), a universal heptahelical receptor adapter/scaffolding protein. This pathway results in sustained ERK activation and subsequent up-regulation of steroidogenic acute regulatory protein, a steroid transport protein regulating aldosterone biosynthesis in AZG cells. Also, this betaarr1-mediated pathway appears capable of promoting aldosterone turnover independently of G protein activation, because treatment of AZG cells with SII, an AngII analog that induces betaarr, but not G protein coupling to the AT(1)R, recapitulates the effects of AngII on aldosterone production and secretion. In vivo, increased adrenal betaarr1 activity, by means of adrenal-targeted adenoviral-mediated gene delivery of a betaarr1 transgene, resulted in a marked elevation of circulating aldosterone levels in otherwise normal animals, suggesting that this adrenocortical betaarr1-mediated signaling pathway is operative, and promotes aldosterone production and secretion in vivo, as well. Thus, inhibition of adrenal betaarr1 activity on AT(1)Rs might be of therapeutic value in pathological conditions characterized and aggravated by hyperaldosteronism.

Aldosterone-and-salt-induced cardiac fibrosis is independent from angiotensin II type 1a receptor signaling in mice

Aldosterone infusion with high salt treatment induces cardiac fibrosis in rats. Aldosterone enhanced angiotensin II (Ang II) has been shown to induce proliferation and increase the expression of Ang II receptor mRNA and Ang II binding in vitro. To investigate the role of Ang II type 1a receptor (AT1aR) in aldosterone-and-salt (Ald-NaCl)-induced cardiac fibrosis, we subcutaneously infused aldosterone (0.15 microg/h) and 1% NaCl (Ald-NaCl) into AT1aR knockout mice (AT1aR-KO) or wild type mice (Wt). To examine the role of NaCl on cardiac fibrosis, we gave some of the aldosterone-treated AT1aR-KO tap water (Ald-H2O). Ald-NaCl treatment increased systolic blood pressure and induced cardiac hypertrophy in both strains, whereas there were no such changes in the mice without aldosterone. Severe cardiac fibrosis was seen in Ald-NaCl-treated AT1aR-KO and not in Ald-NaCl-treated Wt. In contrast, Ald-NaCl-treated Wt with co-administration of an active metabolite of olmesartan, the AT1aR antagonist (10 mg/kg/day) did not show cardiac fibrosis. Na+/H+ exchanger, and Na+-K+ ATPase alpha2 subunit mRNA were decreased in AT1aR-KO. Na+/Ca2) exchanger mRNA was lower in AT1aR-KO than Wt and was decreased by Ald-NaCl in both strains. Phosphorylation of epidermal growth factor receptor and extracellular signal-regulated kinase was increased by Ald-NaCl treatment in AT1aR-KO. Connective tissue growth factor (CTGF) and osteopontin mRNA were increased and accumulation of CTGF proteins was seen in the hearts of Ald-NaCl-treated AT1aR-KO. Ald-H2O-treated AT1aR-KO did not show any cardiac fibrosis. These results suggest that Ald-NaCl-induced cardiac fibrosis required both aldosterone and salt. Because cardiac fibrosis was exaggerated in Ald-NaCl-treated AT1aR-KO but was not seen in Wt treated with Ald-NaCl and olmesartan, AT1aR may not play a primary role in progression of cardiac fibrosis by Ald-NaCl, and gene disruption of AT1aR may have some implications in this model.

Addition of eplerenone to an angiotensin-converting enzyme inhibitor effectively improves nitric oxide bioavailability

Angiotensin II and aldosterone both promote endothelial dysfunction and atherosclerosis. We investigated the effect of a combination of eplerenone, a selective aldosterone antagonist, and enalapril, an angiotensin-converting enzyme inhibitor, on NO bioavailability and spontaneous atherosclerotic changes. Twenty-four myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits were treated with vehicle (control), eplerenone (50 mg/kg per day), enalapril (3 mg/kg per day), or eplerenone plus enalapril for 8 weeks (n=6 in each group). After treatment, acetylcholine-induced NO production was measured as a surrogate for endothelium-protective function, and vascular peroxynitrite (a product of superoxide and NO) was measured to assess dysfunctional endothelial NO synthase activity. Plaque area was quantified by histology. Intra-aortic infusion of acetylcholine produced an increase in plasma NO concentration that was significantly higher with all of the drug treatments compared with the control. Eplerenone and enalapril, in combination, increased acetylcholine-induced NO by 7.9 nM, which was significantly higher than with either eplerenone or enalapril alone. Vascular peroxynitrite was significantly higher in the control group (1.3 pmol/mg of protein) and significantly lower with combination treatment (0.4 pmol/mg of protein) compared with the enalapril or eplerenone group. The highest tetrahydrobiopterin levels were observed after cotreatment with eplerenone and enalapril. Histology of the thoracic aorta showed a significantly decreased plaque area with combination therapy compared with monotherapy. Combined treatment with a selective aldosterone antagonist and an angiotensin-converting enzyme inhibitor has additive protective effects on endothelial function and on atherosclerotic changes via decreased nitrosative stress.

The nongenomic actions of aldosterone

Aldosterone has physiological effects to regulate fluid and electrolyte homeostasis across epithelia and proinflammatory effects on a variety of nonepithelial cells in the context of inappropriate salt status. These effects are mediated by mineralocorticoid receptors, members of a large family of nuclear transcription factors, by DNA-directed, RNA-mediated protein synthesis. Rapid effects of aldosterone, insensitive to actinomycin D or cycloheximide and thus clearly nongenomic, have been convincingly documented in a variety of epithelial and nonepithelial tissues. Despite strenuous attempts, isolation of a nonclassical membrane receptor for aldosterone has proven unsuccessful, and rapid nongenomic effects mediated by classical mineralocorticoid receptors are increasingly recognized in the kidney, heart, and vascular wall. The mechanism of rapid nongenomic actions of aldosterone may vary between tissues in terms of pathways; in addition, what remains to be established is the physiological role of aldosterone action via such rapid nongenomic mechanisms and how they might synergize with the longer time course genomic actions of mineralocorticoids.

Aldosterone antagonism attenuates obesity-induced hypertension and glomerular hyperfiltration

This study examined the importance of aldosterone (ALDO) in mediating changes in renal function and increased mean arterial pressure (MAP) during the development of dietary-induced obesity in chronically instrumented dogs. Mean arterial pressure, heart rate (HR), and cardiac output (CO) were recorded 24 hours per day in lean dogs (n=7) before and after administration of an ALDO antagonist, eplerenone (EP) (10 mg/kg twice daily), for 10 days. After 10 days of EP treatment, the dogs (n=7) were given a supplement of cooked beef fat for 5 weeks while EP was continued. An untreated group (n=6) was fed a high fat diet for 5 weeks and used as control (C). In lean dogs, EP decreased MAP from 89+/-4 to 84+/-4 mm Hg and glomerular filtration rate from 67.4+/-6.8 to 53.2+/-4.9 mL/min while inducing a small negative Na+ balance (-42+/-12 mEq). Plasma renin activity increased from 0.4+/-0.1 to 2.7+/-0.7 ng AI/mL per hour and plasma K+ increased from 4.8+/-0.1 to 6.1+/-0.3 mEq/L. After 5 weeks of a high fat diet, body weight increased 45% to 53% in EP and C obese dogs. In C dogs, MAP increased by 16+/-3 mm Hg, compared with only 7+/-1 mm Hg in EPLE dogs. Compared with untreated dogs, the EP dogs had smaller increases in CO (18+/-4.6% versus 43+/-1.5%), HR (33+/-5% versus 60+/-3%), glomerular filtration rate (19+/-5% versus 38+/-6%), and cumulative Na+ balance (138+/-35 mEq versus 472+/-110 mEq) after 5 weeks of a high fat diet. Thus, EP markedly attenuated glomerular hyperfiltration, sodium retention, and hypertension associated with chronic dietary-induced obesity. These observations indicate that ALDO plays an important role in the pathogenesis of obesity hypertension.

Aldosterone: a risk factor for vascular disease

Blockade of the renin-angiotensin-aldosterone system with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor antagonists has resulted in beneficial effects in essential hypertensive patients. However, occurrence of cardiovascular events has not been appropriately controlled beyond a certain percentage. One reason could be the effects of aldosterone, the final component of the system. The aldosterone escape phenomenon could explain undesirable outcomes observed in hypertensive patients even under treatment with ACE inhibitors or angiotensin antagonists. Aldosterone has direct effects on the vasculature and has been associated with vascular smooth muscle cell hypertrophy, endothelial dysfunction, cardiac fibrosis, proteinuria, and renal vascular injury. Animal models and clinical trials have proven the benefit of aldosterone receptor antagonism. With increased recognition of the prevalence of hyperaldosteronism in patients thought to have "essential" hypertension, the use of drugs that block aldosterone action may become more widespread and protect the vasculature from the deleterious effects of aldosterone.