AURINTRICARBOXYLIC ACID IS AN INHIBITOR OF MU-CALPAIN AND M-CALPAIN

Aurintricarboxylic acid (ATA) is an endonuclease inhibitor which has b een shown to block apoptotic cell death. We have now demonstrated that ATA is also an inhibitor of the Ca2+-activated neutral protease (calp ain), a class of cytosolic enzyme that may also be activated during ap optosis. The two major calpain isoforms (mu- and m-calpain) were both inhibited by ATA with IC50's of 22 mu M and 10 mu M, respectively. The autolysis of purified mu-calpain was prevented by ATA in a concentrat ion-dependent manner. Using casein zymography, it was found that the i nhibition of mu-calpain by ATA was reversible. Finally, in a fetal rat cerebrocortical culture model of excitotoxicity, pre- and post-treatm ent of ATA (50 mu M) reduced N-methyl-D-aspartate (NMDA)-induced spect rin breakdown and neuronal death, while application of ATA concurrent to NMDA challenge alone had no effect. This pattern of protection coul d not be explained by simple NMDA receptor antagonism. We thus propose that the neuroprotective effect of ATA could be in part due to its ab ility to inhibit calpain.