AN ALPHA-MERCAPTOACRYLIC ACID-DERIVATIVE IS A SELECTIVE NONPEPTIDE CELL-PERMEABLE CALPAIN INHIBITOR AND IS NEUROPROTECTIVE

Overactivation of calcium-activated neutral protease (calpain) has bee n implicated in the pathophysiology of several degenerative conditions , including stroke, myocardial ischemia, neuromuscular degeneration, a nd cataract formation, Alpha-mercaptoacrylate derivatives (exemplified by PD150606), with potent and selective inhibitory actions against ca lpain, have been identified, PD150606 exhibits the following character istics: (i) K-i values for mu- and m-calpains of 0.21 mu M and 0.37 mu M, respectively, (ii) high specificity for calpains relative to other proteases, (iii) uncompetitive Inhibition with respect to substrate, and (iv) it does not shield calpain against inactivation by the active -site inhibitor ans-(epoxysuccinyl)-L-leucyl-amido-3-methylbutane, sug gesting a nonactive site action for PD150606. The recombinant calcium- binding domain from each of the large or small subunits of mu-calpain was found to interact with PD150606. In low micromolar range, PD150606 inhibited calpain activity in two intact cell systems, The neuroprote ctive effects of this class of compound were also demonstrated by the ability of PD150606 to attenuate hypoxic/hypoglycemic injury to cerebr ocortical neurons in culture and excitotoxic injury to Purkinje cells in cerebellar slices.