Spironolactone increases integrin beta3 gene expression in kidney and heart muscle cells

The cardioprotective effects of mineralocorticoid receptor antagonists

Despite state-of-the-art reperfusion therapy, morbidity and mortality remain significant in patients with an acute myocardial infarction. Therefore, novel strategies to limit myocardial ischemia-reperfusion injury are urgently needed. Mineralocorticoid receptor (MR) antagonists are attractive candidates for this purpose, since several clinical trials in patients with heart failure have reported a survival benefit with MR antagonist treatment. MRs are expressed by several cells of the cardiovascular system, including cardiomyocytes, cardiac fibroblasts, vascular smooth muscle cells, and endothelial cells. Experiments in animal models of myocardial infarction have demonstrated that acute administration of MR antagonists, either before ischemia or immediately at the moment of coronary reperfusion, limits infarct size. This action appears to be independent of the presence of aldosterone and cortisol, which are the endogenous ligands for the MR. The cardioprotective effect is mediated by a nongenomic intracellular signaling pathway, including adenosine receptor stimulation, and activation of several components of the Reperfusion Injury Salvage Kinase (RISK) pathway. In addition to limiting infarct size, MR antagonists can improve scar healing when administered shortly after reperfusion and can reduce cardiac remodeling post myocardial infarction. Clinical trials are currently being performed studying whether early administration of MR antagonists can indeed improve prognosis in patients with an acute myocardial infarction, independent of the presence of heart failure.

Glucocorticoids Activate Cardiac Mineralocorticoid Receptors During Experimental Myocardial Infarction

Myocardial ischemia-reperfusion leads to significant changes in redox state, decreased postischemic functional recovery, and cardiomyocyte apoptosis, with development and progression of heart failure. Ischemia-reperfusion in the isolated perfused rat heart has been used as a model of heart failure. Clinically, mineralocorticoid receptor blockade in heart failure decreases morbidity and mortality versus standard care alone. The effects of corticosteroids on infarct area and apoptosis were determined in rat hearts subjected to 30 minutes of ischemia and 2.5 hours of reperfusion. Both aldosterone and cortisol increased infarct area and apoptotic index, an effect half-maximal between 1 and 10 nM and reversed by spironolactone. Dexamethasone and mifepristone aggravated infarct area and apoptotic index, similarly reversed by spironolactone. Spironolactone alone reduced infarct area and apoptotic index below ischemia-reperfusion alone, in hearts from both intact and adrenalectomized rats. The present study shows that cardiac damage is aggravated by activation of mineralocorticoid receptors by aldosterone or cortisol or of glucocorticoid receptors by dexamethasone. Mifepristone unexpectedly acted as a glucocorticoid receptor agonist, for which there are several precedents. Spironolactone protected cardiomyocytes via inverse agonist activity at mineralocorticoid receptors, an effect near maximal at a relatively low dose (10 nM). Spironolactone acts not merely by excluding corticosteroids from mineralocorticoid receptors but as a protective inverse agonist at low concentration. Mineralocorticoid receptor antagonists may, thus, provide an additional therapeutic advantage in unstable angina and acute myocardial infarction.

Aldosterone increases plasminogen activator inhibitor-1 synthesis in rat cardiomyocytes

Plasminogen activator inhibitor-1 (PAI-1) is an anti-thrombolytic factor that also promotes tissue fibrosis. Under certain conditions, exposure to aldosterone can result in cardiac fibrosis by an unknown mechanism. In the current study, we tested the hypothesis that PAI-1 is a mediator of aldosterone's fibrotic effects. Aldosterone increased levels of PAI-1 mRNA and protein in the H9c2 rat cardiac cell line, responses that could be blocked by the mineralocorticoid receptor (MR) antagonist spironolactone. Confocal microscopy confirmed an effect of aldosterone to increase PAI-1 expression with reversal by spironolactone. Aldosterone also increased PAI-1 expression in neonatal rat cardiomyocytes, which was again blocked by spironolactone. In the neonatal cardiomyocytes (but not the H9c2 cells), anti-transforming growth factor-beta1 antibody inhibited the PAI-1 response to aldosterone. In summary, aldosterone directly increased PAI-1 expression in two different cardiac muscle cell types, an effect that was dependent on MR. In the neonatal cells, there appeared to be a requirement for transforming growth factor-beta1.