BLOCKAGE OF APOPTOTIC SIGNALING OF TRANSFORMING-GROWTH-FACTOR-BETA INHUMAN HEPATOMA-CELLS BY CARBOXYFULLERENE

Transforming growth factor-beta (TGF-beta) has been shown to induce ap optosis in normal hepatocytes and hepatoma cells both in vivo and in v itro. However, the mechanism by which TGF-beta induces apoptosis is no t clear. The antiapoptotic activity of antioxidants including N-acetyl -L-cysteine (Ac-Cys), ascorbic acid and a novel free radical scavenger , carboxyfullerene (C-60) on TGF-beta-treated human hepatoma Hep3B cel ls was examined. Only the water-soluble hexacarboxylic acid derivative of C-60 was found to prevent TGF-beta-induced apoptosis. Antiapoptoti c activity of C-60 correlated its ability to eliminate TGF-beta-genera ted reactive oxygen species (ROSs). However, C-60 did not interfere wi th TGF-beta-activated PAI-1 promoter activity in the Hep3B cells. Thes e results indicate that the signaling pathway of TGF-beta-induced apop tosis may be related to the generation of ROSs and may be uncoupled fr om the TGF-beta-activated gene promoter activity. Furthermore, the reg ioisomer of C-60 with a C-3 symmetry was more potent in protecting cel ls from apoptosis than that with a D-3 symmetry, and the C-3 isomer ha d stronger interactions with lipid bilayers than the D-3 isomer. The s pectroscopic analysis revealed that the C-3 isomer had stranger intera ctions with artificial lipid bilayers than the D-3 isomer. Therefore, our study indicates that C-60 may interact with membrane to eliminate TGF-beta-induced ROSs and to prevent apoptosis occur in human hepatoma cells.