Aldosterone receptor antagonists: biology and novel therapeutical applications

Aldosterone induces fibrosis, oxidative stress and DNA damage in livers of male rats independent of blood pressure changes

Mineralocorticoid receptor blockers show antifibrotic potential in hepatic fibrosis. The mechanism of this protective effect is not known yet, although reactive oxygen species seem to play an important role. Here, we investigated the effects of elevated levels of aldosterone (Ald), the primary ligand of the mineralocorticoid receptor, on livers of rats in a hyperaldosteronism model: aldosterone-induced hypertension. Male Sprague-Dawley rats were treated for 4 weeks with aldosterone. To distinguish if damage caused in the liver depended on increased blood pressure or on increased Ald levels, the mineralocorticoid receptor antagonist spironolactone was given in a subtherapeutic dose, not normalizing blood pressure. To investigate the impact of oxidative stress, the antioxidant tempol was administered. Aldosterone induced fibrosis, detected histopathologically, and by expression analysis of the fibrosis marker, α-smooth muscle actin. Further, the mRNA amount of the profibrotic cytokine TGF-β was increased significantly. Fibrosis could be reduced by scavenging reactive oxygen species, and also by blocking the mineralocorticoid receptor. Furthermore, aldosterone treatment caused oxidative stress and DNA double strand breaks in livers, as well as the elevation of DNA repair activity. An increase of the transcription factor Nrf2, the main regulator of the antioxidative response could be observed, and of its target genes heme oxygenase-1 and γ-glutamylcysteine synthetase. All these effects of aldosterone were prevented by spironolactone and tempol. Already after 4 weeks of treatment, aldosteroneinfusion induced fibrosis in the liver. This effect was independent of elevated blood pressure. DNA damage caused by aldosterone might contribute to fibrosis progression when aldosterone is chronically increased.

Aldosterone receptor antagonists--how cardiovascular actions may explain their beneficial effects in heart failure

Historically, aldosterone receptor antagonists (ARA) have been classified as 'potassium sparing diuretics'. However, the positive effect of spironolactone, the most extensively studied ARA, on morbidity and mortality observed in humans suffering cardiac insufficiency could not be explained by the renal effect of the drug alone, and a pivotal clinical study has led to extensive research. Many experimental studies have demonstrated that ARA have previously unexpected beneficial effects on the cardiovascular system including reduction in remodelling of the vascular smooth muscle cells and myocytes and improvement of endothelial cell dysfunction in heart failure. These effects improve vascular compliance and slow down the progression of left ventricular dysfunction and end-organ damage. Furthermore, aldosterone receptor blockade also restores the baroreceptor reflex, improving heart rate variability in heart failure in humans. Some of these effects have been demonstrated in dog models of cardiac disease and so justified further investigation of the potential benefit of ARA in dogs with congestive heart failure (CHF). Positive effects of spironolactone on morbidity and mortality appear to have been seen in studies conducted in dogs suffering from naturally occurring CHF. In addition, eplerenone has been shown to have benefits in canine models of heart failure. The precise mechanisms by which ARA produce these beneficial effects in dogs remain to be determined but this group of drugs clearly provide therapeutic actions out-with their diuretic effects.

Left ventricular geometry in patients with obstructive sleep apnea coexisting with treated systemic hypertension

BACKGROUND

Left ventricular (LV) hypertrophy is a common consequence of systemic hypertension (SH) and obstructive sleep apnea (OSA). However, little is known about the degree of LV involvement in patients with OSA coexisting with treated SH.

OBJECTIVES

Our study was designed in order to assess the prevalence of distinct types of LV geometry in treated hypertensive OSA patients.

METHODS

PATIENTS

183 patients with treated SH were enrolled to the study. Group 1 consisted of 38 patients with newly-diagnosed OSA and ineffectively treated SH. The remaining 145 patients with effectively treated SH were divided into three groups: group 2 - 70 patients with newly-diagnosed OSA, group 3 - 31 patients with OSA treated with continuous positive airway pressure (CPAP), and group 4 - 44 patients without OSA. Overnight sleep studies and M-mode echocardiography were performed.

RESULTS

LV mass index did not differ between the study groups. Mean values of LV end-diastolic diameter (LVED) were 55.4 +/- 6.8 mm in group 1 and 53.6 +/- 6.9 mm in group 2 and were significantly increased in comparison to subjects treated with CPAP and controls (49.8 +/- 6.8 mm and 50.1 +/- 64.7 mm, respectively; p = 0.001). LVED correlated positively with the apnea-hypopnea index and desaturation index. LV eccentric hypertrophy was the commonest type of LV geometry in newly-diagnosed OSA patients.

CONCLUSIONS

The major finding of our study is the predominance of LV eccentric hypertrophy in newly-diagnosed OSA patients. We suggest that a relatively moderate degree of LV involvement in hypertensive OSA patients may depend on the cardioprotective effect of concomitant antihypertensive therapy, ameliorating OSA-dependent neurohumoral abnormalities.