EXTENDED THERAPEUTIC WINDOW FOR CASPASE INHIBITION AND SYNERGY WITH MK-801 IN THE TREATMENT OF CEREBRAL HISTOTOXIC HYPOXIA

In rats, striatal histotoxic hypoxic lesions produced by the mitochond rial toxin malonate resemble those of focal cerebral ischemia, Intrast riatal injections of malonate induced cleavage of caspase-2 beginning at 6 h, and caspase-3-like activity as identified by DEVD biotin affin ity-labeling within 12 h. DEVD affinity-labeling was prevented and les ion volume reduced in transgenic mice overexpressing BCL-2 in neuronal cells. Intrastriatal injection of the tripeptide, N-benzyloxycarbonyl -Val-Ala-Asp-fluoromethylketone (zVAD-fmk), a caspase inhibitor, at 3 h, 6 h, or 9 h after malonate injections reduced the lesion volume pro duced by malonate, A combination of pretreatment with the NMDA antagon ist, dizocilpine (MK-801), and delayed treatment with zVAD-fmk provide d synergistic protection compared with either treatment alone and exte nded the therapeutic window for caspase inhibition to 12 h, Treatment with cycloheximide and zVAD-fmk, but not with MK-801, blocked the malo nate-induced cleavage of caspase-2. NMDA injections alone resulted in a weak caspase-2 cleavage, These results suggest that malonate toxicit y induces neuronal death by more than one pathway. They strongly impli cate early excitotoxicity and delayed caspase activation in neuronal l oss after focal ischemic lesions and offer a new strategy for the trea tment of stroke.