Expression of bcl-2 protein, an inhibitor of apoptosis, and Bax, an accelerator of apoptosis, in ventricular myocytes of human hearts with myocardial infarction

Background In general, myocyte death in myocardial infarctions (MIs) is attributed to necrosis, but recently the involvement of apoptosis has been suggested. The ratio of bcl-2 protein, an inhibitor of apoptosis, to Bax protein, an inducer of apoptosis, determines survival or death after an apoptotic stimulus. We speculated that bcl-2 or Bax expression is induced by ischemia and that it may be related to myocyte death in human hearts. Methods and Results We studied immunohistochemically 37 autopsied human hearts (acute MI, n=15; old MI, n=12; normal hearts as a control, n=10) with the use of bcl-2 and Bax antibodies. There were no myocytes with positive bcl-2 immunoreactivity in the controls or hearts with old MI. However, myocytes with positive bcl-2 immunoreactivity were seen in 9 of 15 hearts (60%) with acute MI, in that it was localized only in salvaged areas surrounding the infarcted tissues. Myocytes with slightly positive Bax immunoreactivity were observed in the control hearts. In the salvaged myocytes surrounding the infarcted tissues, Bax was overexpressed in 2 of 15 hearts (13%) with acute MI but in 10 of 12 hearts (83%) with old MI. Conclusions bcl-2 protein is induced in salvaged myocytes at the acute stage of infarction, but Bax protein is overexpressed at the old stage. The expression of bcl-2 and the overexpression of Bax may play an important pathophysiological role in the protection or acceleration of the apoptosis of human myocytes after ischemia and/or reperfusion.