Hirotaka Kimata

Mineralocorticoid Receptor Antagonism Attenuates Cardiac Hypertrophy and Failure in Low-Aldosterone Hypertensive Rats

Chronic elevation of plasma aldosterone contributes to heart failure. Mineralocorticoid receptor (MR) antagonism is cardioprotective in such a setting, but whether such protection occurs in the presence of low-aldosterone concentrations remains unclear. We investigated whether MR blockade attenuates cardiac hypertrophy and failure in rats with salt-sensitive hypertension. Dahl salt-sensitive (DS) rats fed a high-salt diet from 7 weeks develop concentric left ventricular (LV) hypertrophy secondary to hypertension at 12 weeks followed by heart failure at 19 weeks (DS-CHF). DS rats on such a diet were treated with a non-antihypertensive dose of the selective MR antagonist eplerenone from 12 to 19 weeks. Renin activity and aldosterone concentration in plasma were decreased in DS-CHF rats compared with controls. LV hypertrophy and fibrosis, as well as macrophage infiltration around coronary vessels, were apparent in DS-CHF rats. The amounts of mRNAs for 11&bgr;-hydroxysteroid dehydrogenase type 1, MR, monocyte chemoattractant protein 1, and osteopontin were increased in these hearts. Treatment of DS-CHF rats with eplerenone inhibited these changes in gene expression, as well as coronary vascular inflammation and heart failure. Eplerenone attenuated both the decrease in the ratio of reduced to oxidized glutathione and the increase in NADPH oxidase activity apparent in DS-CHF rat hearts. MR blockade with eplerenone thus resulted in attenuation of LV hypertrophy and failure, without an antihypertensive effect, in rats with low-aldosterone hypertension. The beneficial cardiac effects of eplerenone are likely attributable, at least in part, to attenuation of myocardial oxidative stress and coronary vascular inflammation induced by glucocorticoid-activated MRs.

Pitavastatin improves cardiac function and survival in association with suppression of the myocardial endothelin system in a rat model of hypertensive heart failure.

Statin therapy may be associated with lower mortality in patients with heart failure, but the underlying mechanism of such an association is unknown. We have evaluated the effects of pitavastatin on cardiac function and survival in a rat model of hypertensive heart failure and investigated the molecular mechanism of the observed effects. Dahl salt-sensitive rats fed with high-salt diet from 7 weeks of age developed compensatory left ventricular hypertrophy at 12 weeks and heart failure at 19 weeks. Dahl salt-sensitive rats were treated with either vehicle or pitavastatin (0.3 mg/kg per day) from 7 or 12 weeks. Both early-onset and late-onset pitavastatin treatment reduced left ventricular fibrosis, improved cardiac function, and increased the survival rate apparent at 19 weeks. The increases in the expression levels of hypertrophic, profibrotic, and metalloproteinase genes as well as in gelatinase activities in the heart induced by the high-salt diet were suppressed by pitavastatin treatment. Furthermore, the level of cardiac endothelin-1 was increased in association with the development of heart failure in a manner sensitive to treatment with pitavastatin. Both early and late pitavastatin treatment thus improved cardiac function and survival, with modulation of extracellular matrix remodeling and endothelin-1 signaling possibly contributing to these beneficial effects.

Attenuation of ventricular hypertrophy and fibrosis in rats by pitavastatin: potential role of the RhoA-extracellular signal-regulated kinase-serum response factor signalling pathway.

1 Inhibitors of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase (statins) manifest pleiotropic effects that may contribute to their therapeutic efficacy. However, the mechanism of the beneficial action of statins on cardiac hypertrophy and fibrosis remains unclear. We have now investigated this action of pitavastatin in Dahl salt‐sensitive (DS) rats. 2 The DS rats progressively develop marked hypertension when fed a diet containing 8% NaCl from 7 weeks of age. These animals exhibited pronounced cardiac hypertrophy and fibrosis, as well as upregulation of fetal‐type cardiac gene expression at 12 weeks of age, compared with DS rats fed a diet containing 0.3% NaCl. The abundance of mRNAs for collagen types I and III, angiotensin‐converting enzyme, transforming growth factor‐β1 and connective tissue growth factor was also increased in the heart of rats on the high‐salt diet. 3 Treatment of rats on the high‐salt diet with a non‐antihypertensive dose of pitavastatin (0.3 or 1 mg/kg per day) from 7 to 12 weeks of age attenuated the development of cardiac hypertrophy and fibrosis, as well as inhibiting the upregulation of cardiac gene expression. Pitavastatin also blocked the translocation of RhoA to the membrane fraction of the left ventricle and RhoA activation, as well as the phosphorylation of the mitogen‐activated protein kinases extracellular signal‐regulated kinase (ERK)‐1 and ERK‐2 and an increase in the DNA binding activity of serum response factor (SRF) in the heart induced by the high‐salt diet. 4 These findings suggest that the effects of pitavastatin on load‐induced cardiac hypertrophy and fibrosis are independent of its cholesterol‐lowering action and may be mediated, at least in part, through inhibition of RhoA–ERK–SRF signalling.

Xanthine oxidase inhibition improves left ventricular dysfunction in dilated cardiomyopathic hamsters.

BACKGROUND Oxidative stress is implicated in cardiac remodeling and failure. We tested whether xanthine oxidase (XO) inhibition could decrease myocardial oxidative stress and attenuate left ventricular (LV) remodeling and dysfunction in the TO-2 hamster model of dilated cardiomyopathy. METHODS AND RESULTS TO-2 hamsters were randomized to treatment with the XO inhibitor, allopurinol, or vehicle from 6 to 12 weeks of age. F1B hamsters served as controls. TO-2 hamsters treated with vehicle progressively developed severe LV systolic dysfunction and dilation between 6 and 12 weeks. Marked cardiac fibrosis was apparent in these hamsters at 12 weeks in comparison with F1B controls. The ratio of reduced to oxidized glutathione (GSH/GSSG) was decreased and malondialdehyde levels were increased in the hearts of vehicle-treated TO-2 hamsters. Treatment with allopurinol from 6 to 12 weeks attenuated LV dysfunction and dilation as well as myocardial fibrosis and the upregulation of a fetal-type cardiac gene. Allopurinol also inhibited both the decrease in GSH/GSSG ratio and the increase in malondialdehyde levels in the heart. CONCLUSIONS These results indicate that chronic XO inhibition with allopurinol attenuates LV remodeling and dysfunction as well as myocardial oxidative stress in this model of heart failure. Allopurinol may prove beneficial for the treatment of heart failure.