Ischemic preconditioning attenuates ischemia/reperfusion-induced activation of caspases and subsequent cleavage of poly(ADP-ribose) polymerase in rat hearts in vivo.

Recently, we have demonstrated that ischemic preconditioning (IP) both limits infarct size and decreases internucleosomal DNA fragmentation in rat hearts in vivo, and that there was a direct correlation between myocardial infarct size and DNA fragmentation even after IP. In this study, we examined the ability of IP to attenuate processing and activation of caspase-1 and caspase-3, and cleavage of poly(ADP-ribose) polymerase (PARP), after prolonged ischemia and reperfusion using the same in vivo animal model. Rats that underwent IP and controls (Ctrl) were subjected to 30 min of left coronary artery occlusion followed by 180 min of reperfusion. IP was accomplished by five 5-min cycles of ischemia, each followed by 5 min of reperfusion. The amount of soluble nucleosomes was measured by enzyme-linked immunosorbent assay. Cleavage of caspases-1 and -3, and of one of their substrates PARP, was analyzed by Western blotting. Nucleosomal DNA fragmentation was significantly reduced in ischemic left ventricular (LV) tissue obtained from IP compared with Ctrl animals. The proforms of caspases-1 and -3, and the active form of PARP were not cleaved in the nonischemic LV region of both IP and Ctrl hearts. In contrast, the proform of caspase-3 and the active form of PARP were cleaved in the ischemic LV region of Ctrl hearts, while processing of caspase-1 was increased. Cleavages of caspases-1 and -3, and inactivation of PARP were prevented by IP. The results of this study indicate that IP attenuates both internucleosomal DNA fragmentation and caspases processing, and suggest that the prevention of caspases activation by IP may be important steps in protecting the heart against ischemia/reperfusion injury in vivo.

Ischemic preconditioning decreases apoptosis in rat hearts in vivo.

BACKGROUND: Previous studies have demonstrated that ischemic preconditioning prevents lethal cell injury and, as a consequence, limits infarct size in rat heart. Although both apoptosis and necrosis have been shown to contribute to myocardial cell death after myocardial ischemia and reperfusion, the ability of ischemic preconditioning to prevent programmed cell death remains unknown. METHODS AND RESULTS: To test the hypothesis that ischemic preconditioning reduces irreversible ischemic injury in part by decreasing apoptosis, rats that underwent ischemic preconditioning and controls were subjected to 30 minutes of left coronary artery occlusion followed by 180 minutes of reperfusion. Ischemic preconditioning was achieved by five 5-minute cycles of ischemia, each followed by 5 minutes of reperfusion. Infarct size, determined by dual staining with triphenyltetrazolium chloride and phthalocyanine blue dye, was significantly reduced in preconditioned compared with nonpreconditioned rats (11.4+/-1.4% versus 58.7+/-1.4%; n=20 in each group; P<.001; infarct size/risk area). Genomic DNA from preconditioned hearts showed little or no oligonucleosome-sized fragments (200-bp multiples), whereas genomic DNA from nonpreconditioned hearts showed a typical nucleosome fragmentation. The TUNEL assay localized fewer and sparsely stained nuclei within the infarct zone of ischemic preconditioned hearts compared with nonpreconditioned hearts. Consistent with these findings, the number of cytosolic histone-associated low-molecular-weight DNA fragments was significantly decreased in preconditioned hearts compared with controls (0.17+/-0.02 versus 1.07+/-0.09 U; n=10 in each group; P<.001; absorbance 405 nm/490 nm). CONCLUSIONS: This study suggests that ischemic preconditioning reduces irreversible ischemic injury in part by decreasing apoptosis after prolonged ischemia and reperfusion.