Prolonged therapeutic window for ischemic brain damage caused by delayed caspase activation.

Apoptotic cell death is prominent in neurodegenerative disorders, such as Alzheimer's disease and Huntington's disease, and is found in cerebral ischemia. Using a murine model of delayed cell death, we determined that cleavage of zDEVD-amino-4-trifluoromethyl coumarin (zDEVD-afc) in brain homogenate, a measure of caspase activation, increased initially 9 hours after brief (30 minutes) middle cerebral artery occlusion along with caspase-3p20 immunoreactive cleavage product as determined by immunoblotting. zDEVD-afc cleavage activity was blocked by pretreatment or posttreatment with the caspase-inhibitor N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl-ketone (zDEVD-fmk), and ischemic damage was reduced when the drug was injected up to 9 hours after reperfusion. The protection was long lasting (21 days). Hence, the period before caspase activation defined the therapeutic opportunity for this neuroprotective agent after mild ischemic brain injury. Prolonged protection after caspase inhibition plus the extended treatment window may be especially relevant to the treatment of neurodegenerative disorders.