Synthetic catalytic scavengers of reactive oxygen species (ROS) may have broad clinical applicability. In previous papers, two salen-manganese complexes, EUK-8 and EUK-134, had superoxide dismutase (SOD) and catalase activities and prevented ROS-associated tissue injury. This study describes two series of salen-manganese complexes, comparing catalytic ROS scavenging properties and cytoprotective activities. The compounds vary widely in ability to scavenge hydrogen peroxide, with this activity most influenced by salen ring alkoxy substitution and aromatic bridge modifications. In contrast, all compounds show comparable SOD activities. The most active alkoxy-substituted catalase mimetics protected cultured cells from hydrogen peroxide, and a subset of these were also neuroprotective in a rodent stroke model. Thus, structural modification of the prototype EUK-8 yields compounds with enhanced catalase activity and, in turn, biological effectiveness. This supports the concept that salen-manganese complexes represent a class of SOD and, in particular, catalase mimetics potentially useful against ROS-associated diseases.

Background and PurposeThis research was performed to determine whether a selective inhibitor of the calcium-dependent protease, calpain, could reduce ischemia-associated brain damage when peripherally administered after a vascular occlusion.Methods A variation of the rat middle cerebral artery occlusion model was used. A range of doses of AK295 (a novel calpain inhibitor synthesized for this purpose) was continuously infused through the internal carotid artery, beginning 1.25 hours from the initiation of the occlusion. Rats were killed at 21 hours, and the infarct volume was quantified.Results Postocdusion (1.25-hour) infusion of the calpain inhibitor AK295 elicited a dose-dependent neuroprotective effect after focal ischemia. The highest dose tested (3 mg/kg

Summary: Experiments were conducted to determine whether a potent, reversible calpain inhibitor could re duce the cortical ischemic brain damage associated with focal ischemia in the rat. AK275 (Z-Leu-Abu-CONH CH 2 CH 3 ), the active isomer of the diastereomeric mix ture, CX275, was employed in conjunction with a novel method of perfusing drug directly onto the infarcted cor tical surface. This protocol reduced or eliminated numer ous, nonspecific pharmacokinetic, hemodynamic, and other potentially confounding variables that might com plicate interpretation of any drug effect. Focal ischemia was induced using a variation of the middle cerebral arIschemic episodes in the brain initiate a time related series of extracellular and intraneuronal events that lead to delayed degeneration of vulner able neurons (Zivin and Choi, 1991). With global ischemia (e. g. , cardiac arrest, drowning), substan tial neuronal death can take several days (Ginsberg and Busto, 1989), whereas with focal ischemia (e. g. , stroke), significant cell death typically occurs within hours (Selman et aI. , 1990; Buchan et aI. , 1992). This delayed cell death in response to isch emia is believed to provide a "therapeutic window 537 tery occlusion method. These studies demonstrated a re liable and robust neuroprotective effect of AK275 over the concentration range of 10 to 200 fLM (perfused supra cortically at 4 fLl/h for 21 h). Moreover, a 75% reduction in infarct volume was observed when initiation of drug treatment was delayed for 3 h postocclusion. Our data further support an important role of calpain in ischemia induced neuropathology and suggest that calpain inhibi tors may provide a unique and potentially powerful means of treating stroke and other ischemic brain inci dents.