AURINTRICARBOXYLIC ACm IS AN INHIBITOR OF 11- AND m-CALPAIN

Aurintricarboxylic acid (AT A) is an endonuclease inhibitor which has been shown to block apoptotic cell death. We have now demonstrated that ATA is also an inhibitor of the Ca2+activated neutral protease (calpain), a class of cytosolic enzyme that may also be activated during apoptosis. The two major calpain isoforms (~- and m-calpain) were both inhibited by A T A with IC50's of 22 ~M and 10 ~M, respectively. The autolysis of purified ~-calpain was prevented by ATA in a concentration-dependent manner. Using casein zymography, it was found that the inhibition of ~ -calpain by A T A was reversible. Finally, in a fetal rat cerebrocortical culture model of excitotoxicity, pre- and post-treatment of ATA (50 ~M) reduced N-methyl-D-aspartate (NMDA)-induced spectrin breakdown and neuronal death, while application of AT A concurrent to NMDA challenge alone had no effect This pattern of protection could not be explained by simple NMDA receptor antagonism. We thus propose that the neuroprotective effect of AT A could be in part due to its ability to inhibit calpain.