A selective cysteine protease inhibitor is non-toxic and cerebroprotectivein rats undergoing transient middle cerebral artery ischemia

Ischemic neuronal injury mediated by cysteine proteases such as calpains an d caspases has been demonstrated in various experimental models. Cathepsins B and L are also cysteine proteases which may contribute to neuronal death after ischemia. The authors measured in vitro and in vivo toxicity and pos t-ischemic cytoprotective effects of a cysteine protease inhibitor which do es not block calpain or caspase but, rather, is relatively selective for ca thepsins B and L. The compound belongs to the peptidyl-diazomethane family (cysteine protease inhibitor 1, termed CP-1). In vitro toxicity was measure d using an assay of cell viability, and in vivo toxicity was measured by hi stological tissue analysis after infusion of CP-1 in rats. Two hours of mid dle cerebral artery (MCA) occlusion in rats was performed by the intravascu lar suture method. Immediately following reperfusion, intravenous infusion of CP-1 or vehicle was performed for 4 h at 0.9 ml/h. After a 7-day surviva l, the infarct volumes were measured. CP-1 was non-toxic to cultured glial cells to a local concentration of 200 muM, and relatively non-toxic to cult ured endothelial cells at concentrations of 100-200 muM. No animal exhibite d toxic effects at any of the doses used. Histologic comparisons revealed n o signs of tissue toxicity. CP-1 significantly reduced hemispheric infarct volume compared to control (37+/-8.2%) at concentrations of 10, 50, and 250 muM [22+/-15%, P = 0.008; 20+/-13%. P = 0.002; 23+/-15%, P = 0.022, respec tively (mean+/-standard deviation: N = 7-10 per group)]. CP-1. at the conce ntration of 50 muM, improved the functional score of the animals, but did n ot significantly alter cerebral blood flow. This study supports the hypothe sis that the lysosomal cathepsins B and/or L contribute to cerebral injury after focal ischemia with reperfusion. Cysteine protease inhibitors which a re relatively selective for cathepsins B and L, but not the calpains or cas pases, are effective at reducing infarct volume after intravenous post-isch emic administration. (C) 2001 Elsevier Science B.V. All rights reserved.