l-carnosine and verapamil inhibit hypoxia-induced expression of hypoxia inducible factor (HIF-1 alpha) 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-1 alpha and HIF-1 beta. Both subunits are constitutively expressed under normoxic conditions, but HIF-1 alpha 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-1 alpha 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-1 alphamRNA remained relatively stable during time course hypoxia (1% O (2)) in H9c2 cardiomyoblasts, then increased slightly after 24 h. In cells pretreated with 1 microM carnosine, the levels of mRNA were transiently reduced, but then increased after 24 h similar to the controls. The levels of HIF-1 alpha 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-1 alpha in heart cells during hypoxia.

Increased D-Values for Salmonella enteritidis Following Heat Shock.

Early stationary-phase cells of Salmonella enteritidis (ATCC 4931) were heat shocked at 42°C for 60 min. Following heat shock, the cells were transferred to casein soymeal peptone-yeast extract broth medium and experiments were conducted to generate survivor curves and D-values. Survivors were enumerated after heat shock under both aerobic and strict anaerobic conditions. Control cells were not stressed. Heat-shocked cells had significantly (P < 0.05) higher D-values than unstressed cells at 52, 54, and 56°C, but not at 58°C. Anaerobic enumeration further increased D-values, but not always to a significant extent. Heat shock resulted in the overexpression of seven proteins, detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This study suggests that (i) short-term temperature abuse of foods containing S. enteritidis may render these cells more resistant to subsequent heat treatments; (ii) anaerobic microenvironments may enhance survival of heat-stressed S. enteritidis ; and (iii) heat shock results in the overexpression of proteins that may be related to increased thermotolerance.