Role of antioxidants in the O-hydroxyethyl- d-(Ser) 8-cyclosporine A (SDZ IMM125)-induced apoptosis in rat hepatocytes

Abstract

The mechanisms underlying the apoptotic activity of the immunosuppressive drug cyclosporine A and its O-hydroxyethyl- d-(Ser) 8-derivative SDZ IMM125 in rat hepatocytes are not yet fully understood. It was the purpose of the present study to investigate the role of anti- and pro-oxidants and of caspase-3 and intracellular Ca 2+ in SDZ IMM125-induced apoptosis in rat hepatocytes. SDZ IMM125 induced an increase in chromatin condensation and fragmentation, and the activation of caspase-3. Supplementing the cell cultures with the antioxidants, d,l-α-tocopherol-polyethylene-glycol-1000-succinate, ascorbic acid, and the reducing agent, dithiothreitol, significantly inhibited the SDZ IMM125-mediated increase in chromatin condensation and fragmentation, and caspase-3 activity. d,l-α-tocopherol-polyethylene-glycol-1000-succinate and dithiothreitol caused significant inhibition on SDZ IMM125-mediated cellular Ca 2+ uptake. The glutathione synthetase inhibitor, buthionine sulfoximine, increased SDZ IMM125-mediated caspase-3 action in parallel to chromatin condensation and fragmentation as well as Ca 2+ influx. Supplementation the culture medium with the intracellular Ca 2+ chelator bis-( o-aminophenoxy)-ethane- N, N, N′, N′-tetraacetic acid as well as omission of calcium in the medium reduced SDZ IMM125-induced apoptosis whereas the calcium supplementation of the culture medium elevated SDZ IMM125-induced apoptosis. Calcium antagonists inhibited SDZ IMM125-induced caspase-3 activation. Our data indicate that SDZ IMM125-mediated apoptosis in rat hepatocytes can be inhibited by antioxidants, and that the intracellular redox-state can act as a modulator of cytotoxicity and apoptosis. Further, the results suggest that SDZ IMM125-induced uptake of extracellular calcium is also a redox-sensitive process and that the increased intracellular calcium might directly cause apoptosis by increasing the caspase-3 activity as a central event in the cyclosporine-induced apoptotic mechanism.