Inhibition of proteolysis by a cyclooxygenase inhibitor, indomethacin

The effect of indomethacin, a non-steroidal anti-inflammatory drug upon pur ified calpain has been studied. Also, its effects upon Ca2+-mediated degrad ation of cytoskeletal proteins (neurofilament) in spinal cord homogenate ha s been investigated. A dose-dependent inhibition of purified calpain activi ty was observed. A 50% inhibition of C-14-caseinolytic activity was obtaine d with less than 1.1 mM of indomethacin while the activity was completely i nhibited at 3.3 mM concentration. The inhibitory effect of ketorlac, anothe r non-steroidal anti-inflammatory drug, upon calpain was weaker than that o f indomethacin. The degradation of myelin basic protein (MBP) by cathepsin B, a lysosomal cysteine protease, was significantly inhibited by indomethac in. It also inhibited the Ca2+-mediated degradation of neurofilament protei n (NFP) in spinal cord homogenate. The extent of NFP degradation was analyz ed by SDS-PAGE and the inhibition shown by indomethacin was weaker than tha t observed with leupeptin and the calpain inhibitor E64-d. The inhibitory e ffect of indomethacin on the activity of multicatalytic proteinase complex was negligible. These results suggest that indomethacin, a non-steroidal an ti-inflammatory drug and cyclooxygenase inhibitor also inhibits proteinases , including cathepsin B and calpain.