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The purpose of this study is to examine the molecular mechanism underlying the toxicity of arsenic trioxide (ATO) in cardiac cells. H9c2 rat cardiomyoblastoma cells undergo apoptosis during exposure to the concentrations of ATO > 10 μM for 24 h. The process is accompanied by the activation of caspases and is suppressed by the pan-caspase inhibitor z-VAD. Since ATO-induced H9c2 cell death is suppressed by Rho-kinase (ROCK) inhibitor Y-27632, but not by any antioxidants tested, apoptosis by ATO seems to be initiated through a ROCK-dependent and reactive oxygen species-independent mechanism. During the execution of apoptosis by ATO, the induction of autophagy is also observed. Importantly, autophagy is accelerated in cells treated with ATO plus Y-27632, although Y-27632 alone does not induce autophagy. The cytoprotective effect of Y-27632 against ATO toxicity is abrogated by the co-administration of an autophagy inhibitor, 3-methyladenine, suggesting that autophagy contributes to the cytoprotection by Y-27632. Taken together, the data indicate that the activation of ROCK is required for apoptotic H9c2 cardiomyoblastoma cell death by ATO, and that the ROCK inhibition not only inhibits caspase-dependent apoptotic machinery, but also causes a rise in the cytoprotective autophagy processes during ATO exposure.

The aim of this study was to examine the possible involvement of smooth muscle cell remodeling and the induction of MFG-E8 (milk fat globule protein epidermal growth factor-VIII) in vascular pathophysiology during cocaine administration in cultured cells and rats. Cocaine exerts bifurcate effects on vascular cells; it stimulates vasoconstriction through enhancement of catecholamine release at low doses, while it suppresses cardiovascular functions through inhibition of ion channels at high doses. Short-term exposure to a high concentration of cocaine (3 mM, 24 hr) resulted in cell death of A7r5 rat aorta-derived smooth muscle cells. On the other hand, long-term exposure of the same cells to a low concentration (0.3 mM, ~7 days) resulted in a transient increase in MFG-E8 expression followed by an increased tendency toward cyclin D1, PCNA (proliferating cell nuclear antigen), and CDK4 (cyclin-dependent protein kinase-4) expression. Interestingly, autophagy was not induced, but rather was impaired, in cocaine-treated cells. Increased expressions of MFG-E8, PCNA, and CDK4 were also observed in the aortic vascular cells of rats administered cocaine (50 mg/kg, 2 days, i.v.), confirming that cocaine induced MFG-E8 expression in vivo. Taken together, the results show that MFG-E8 is induced in vascular cells exposed to cocaine, and that this induction is likely to be involved in the vascular toxicity elicited by cocaine abuse.

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