Glutathione depletion and cardiomyocyte apoptosis in viral myocarditis

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Abstract
The course of viral myocarditis is highly variable. Oxidative stress and Bcl-2 family genes may play a role in its pathogenesis by regulating the amount of cardiomyocyte apoptosis. Apoptosis is difficult to detect and quantify in vivo. Therefore, we set to look for indicators of this potentially preventable form of cell death during various phases of experimental murine coxsackievirus B3 myocarditis. BALB/c mice were infected with the cardiotropic coxsackievirus B3 variant. Glutathione (HPLC), cardiomyocyte apoptosis (TUNEL and caspase-3 cleavage), Bax and Bcl-X(L) mRNA expression (real time RT-PCR), histopathology and viral replication (plaque assay and real time RT-PCR) were measured from day 3 to day 20 after infection. Infection caused severe myocarditis and led to progressive decrease of plasma glutathione levels. Myocardial mRNA levels of pro-apoptotic Bax and antiapoptotic Bcl-X(L) were significantly increased from day 3 onwards. Bax mRNA and ratio of Bax to Bcl-X(L) correlated with cardiomyocyte apoptosis (r = 0.77, P = < 0.001 and r 0.51, P < 0.01, respectively). Cardiomyocyte apoptosis was highest on day 5, coinciding with a rapid decline in plasma glutathione (r = -0.52, P = 0.003). Systemic oxidative stress as indicated by decreased plasma glutathione levels coincides with cardiomyocyte apoptosis in experimental coxsackievirus myocarditis. Decreased plasma glutathione levels and changes in cardiac Bax and Bcl-X(L) mRNA expression identify a phase of myocarditis in which the potentially preventable cardiomyocyte apoptosis is mostly observed.