Cardiac overexpression of metallothionein attenuates chronic alcohol intake-induced cardiomyocyte contractile dysfunction

Chronic alcohol ingestion leads to alcoholic cardiomyopathy manifested by ventricular dysfunction and heart failure. Although accumulation of reactive oxygen species may play a role in alcohol-induced heart injury, direct impact of enhanced antioxidant defense on pathogenesis of alcoholic cardiomyopathy has not been elucidated. This study was designed to examine the effect of transgenic overexpression of the free radical scavengermetallothionein on alcohol-induced cardiac contractile dysfunction. Wild-type FVB and metallothionein mice were placed on a 4% alcohol or control diet for 12 wk. Cardiac contractile function was evaluated in cardiomyocytes including peak shortening (PS), time-to-peak shortening, time-to-90% relengthening (TR₉₀), maximal velocity of shortening/relengthening (±dL/dt), intracellular Ca²⁺ rise (change in fura-2 fluorescent intensity [ΔFF1]) and intracellular Ca²⁺ decay rate. Intracellular Ca²⁺ cycling proteins including sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2a), Na⁺−Ca²⁺ exchanger (NCX) and phospholamban were assessed using Western blot analysis. Alcohol intake depressed PS, ±dL/dt, and ΔFF1, increased baseline fura-2 fluorescence intensity (FF1), and prolonged intracellular Ca²⁺ decay and TR₉₀, all of which with the exception of ΔFF1 were abrogated by metallothionein. Enhanced stimulating frequency caused lessened PS decline at 1.0 Hz from FVB ethanol group, which was not affected by metallothionein. Immunoblotting data showed reduced SERCA2a, NCX and phospholamban expression in FVB group consuming alcohol. All of these alcohol-induced changes in cardiac proteins were nullified by the metallothionein transgene. In summary, our findings suggest a beneficial role of antioxidants in alcohol-induced cardiomyocyte dysfunction.