Physiological and metabolic actions of mycophenolate mofetil on cultured newborn rat cardiomyocytes in normoxia and in simulated ischemia.

Abstract

Mycophenolate mofetil (MMF) is a new immunosuppressive drug used to reduce acute rejection after heart transplantation. As with other immunosuppressive drugs, MMF therapy is associated with several adverse effects. However, the direct effects of MMF on myocardial tissue has not been yet evaluated. The aim of the work was thus to evaluate the effects of MMF on isolated cardiomyocytes (CM) in normal conditions and in an in vitro model of simulated ischemia (SI; substrate-free hypoxia) and reperfusion (R; reoxygenation). Myocyte-enriched cultures were prepared from newborn rat heart ventricles. The transmembrane potentials were recorded using conventional microelectrodes and the cell contractions were monitored with a photoelectric device. In basal conditions, MMF (10(-6) and 10(-5) M) exerted no significant effects on the survival and on the electrical and contractile activities of CM in culture, even during long-term exposure (up to 48 h). SI per se led to a gradual decrease and then an abortion of the spontaneous automaticity and electromechanical activity of CM. Pretreating CM with either 10(-6) or 10(-5) M MMF was able to reduce the SI-induced cell dysfunctions. The presence of MMF at these concentrations did not hamper the post-SI functional recovery of CM during reoxygenation. At 10(-5) M, MMF applied during reoxygenation only permitted a better recovery of CM. However, the mitochondrial function after reoxygenation, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl-tetrazolium bromide (MTT) test, was not significantly influenced by the addition of MMF before as well as after ischemia. Conversely, MMF was able to reduce in this model the postischemic rise in xanthine and hypoxanthine. These data from CM-enriched model show that MMF: (i) had no cytotoxic effect, (ii) displayed a cytoprotective effect during SI, and (iii) exerted its beneficial effect at least partly through the decrease in the xanthine oxidase-dependent free radical production.