Calpeptin is a cell - permeable calpain inhibitor. It inhibits calpain I (porcine erythrocytes, ID50 52 nM), calpain II (porcine kidney, ID50 34 nM), papain (ID50 138 nM), and calpain I (human platelets, ID50 40 nM). In vitro, it inhibits 20K phosphorylation in thrombin/ionomycin/collagen - stimulated platelets, promotes neurite elongation in differentiating PC12 cells by inhibiting calpain, and attenuates apoptosis in rat retinal ganglion cells. In vivo, it blocks calpain and caspase - 3 activation in a feline RVPO model and reduces neuronal apoptosis in rat hippocampal CA1 sector via inhibiting caspase - 3 expression.
