L-carnosine and verapamil inhibit hypoxia-induced expression of hypoxia inducible factor (HIF-1α) in H9c2 cardiomyoblasts

Contractile failure of myocardial cells is a common cause of mortality in ischemic heart disease. In response to hypoxic conditions, cells upregulate the activity of hypoxia-inducible factor 1 (HIF-1) and express a number of genes encoding proteins that either enhance O-2 delivery or increase cellular ATP levels. HIF-1 is a heterodimer of bHLH-PAS proteins, HIF-1alpha and HIF-1. Both subunits are constitutively expressed under normoxic conditions, but HIF-1alpha levels are kept low by proteolytic degradation, then stabilized under conditions of low O-2 by a mechanism that is poorly understood. Here we tested the hypothesis that expression of HIF-1alpha in cardiac cells may be affected by two known cardioprotective agents. We tested L-carnosine, a naturally occurring dipeptide which has been shown to improve myocardial contractility during hypoxia, and verapamil, a calcium channel blocker frequently prescribed for the treatment of heart disease. The levels of HIF-1alpha mRNA remained relatively stable during time course hypoxia (1% O-2) in H9c2 cardiomyoblasts, then increased slightly after 24 h. In cells pretreated with 1 muM carnosine, the levels of mRNA were transiently reduced, but then increased after 24 h similar to the controls. The levels of HIF-1alpha protein increased rapidly in H9c2 cells within 30 min of hypoxia, but this induction was significantly reduced in cells treated with either carnosine or verapamil. In addition, treatment of cells with these agents further reduced the low levels of HIF-1 under normoxic conditions. These results suggest that L-carnosine and verapamil may affect the regulated proteolytic degradation of HIF-1alpha in heart cells during hypoxia. (C) 2002 Elsevier Science Ltd.