A rapid ischemia-induced apoptosis in isolated rat hearts and its attenuation by the sodium-hydrogen exchange inhibitor HOE 642 (cariporide)

Abstract

Apoptosis is a potentially important myocardial response to pathology including ischemia and reperfusion. Na-H exchange (NHE) represents an important mechanism for mediating such injury. The present study was done to determine if NHE inhibition can affect early apoptosis in an acute model of ischemia and reperfusion. Isolated rat hearts were subjected to zero-flow ischemia for various durations with or without subsequent 30 min of reperfusion. Nick-end-labelling of biotin-dUTP (TUNEL staining), as well as DNA extraction followed by agarose gel electrophoresis, were used to semiquantify apoptotic cells and identify DNA laddering, respectively. Apoptosis first appeared after 10 min of ischemia and reached a maximum level after 30 min. The number of apoptotic cells after 30 min of ischemia was 31 +/- 3 per 100 high power microscopic fields, whereas in reperfused hearts the number of cells was 34 +/- 3. To determine the effect of NHE inhibition, hearts were pretreated 15 min prior to ischemia with HOE 642, a potent and specific inhibitor of the isoform (NHE-1) found in myocardium. HOE 642 significantly reduced the number of apoptotic cells in the ischemic and reperfused heart to 2 +/- 1 and 6 +/- 1, respectively (P<0.05 from untreated hearts). DNA laddering was not observed with electrophoretic DNA analysis, likely owing to the small number of apoptotic cells involved. Hearts recovered nearly 100% of function in both groups, although there was a significantly higher recovery after 1 and 2 min of reperfusion in those hearts treated with HOE 642. Our study shows that apoptosis, albeit very mild in nature, can be rapidly induced in isolated hearts by a relatively brief period of ischemia without reperfusion, which can be markedly attenuated by the NHE inhibitor HOE 642. The ability of HOE 642 to markedly attenuate apoptosis may be important in terms of understanding the drug's cardioprotective properties as well as the overall role of NHE in heart disease.