Abstract 346: Lipophilic Statins Attenuate Human Atrial Fibroblast Viability In Vitro

Abstract

Cardiovascular diseases (CVD) leading to heart failure are associated with myocardial cell loss and cardiac fibrosis. Hydroxymethylglutaryl-Coenzyme-A Reductase (HMGR) inhibitors ("statins") are widely used to limit cardiovascular events in patients with hypercholesterolemia and CVD by altering their lipid profile. HMGR inhibition reduces cholesterol precursor L-mevalonate production, whose depletion induces autophagy, apoptosis, and endoplasmic reticulum stress in various cell types. However it is unclear if this is a class effect or a phenomenon specific to various compounds. We examined the in vitro effect of HMGR inhibition on human atrial fibroblast (hATF) viability with particular reference to hydrophilic vs lipophilic compounds. Hypothesis- Lipophilic statins induce cell death in primary hATF via mevalonate depletion; whereas hydrophilic statins do not have any effect on hATF viability. IRB approval was obtained for collection of hATF from consenting patients undergoing open heart surgery. Cells were treated with atorvastatin, simvastatin or pravastatin (0.1, 1.0 or 10 λM) for 24, 48, 72 or 96 hours. Expression of proteins involved in the regulation of apoptosis and autophagy was assessed using immunoblotting. Cell viability was assessed using MTT assay. Treatment of hATF with 0.1 - 10 λM atorvastatin or simvastatin (lipophilic statins) resulted in progressively reduced cell viability in time and dose-dependent manner. Viability could be rescued by coincubation with mevalonate. Expression of key apoptotic cascade proteins -Bcl2, Bax and cleaved Caspase3 showed a clear induction of apoptosis. Also, there was an increase in Atg5-12 expression at 24h indicating induction of early autophagic response. Pravastatin (hydrophilic statin) did not affect cell viability or autophagy and apoptosis. We conclude that statin-induced cell death is mediated by mevalonate depletion, which activates intrinsic apoptotic pathways in hATF. Lipophilic statins impair the viability of hATFs in vitro, whereas hydrophilic statins have no effect on cell growth and cell viability of hATFs. This may represent an additional pleiotropic effect of statins, and may represent a novel therapeutic option for the prevention and treatment of cardiac fibrosis.