Blockage of apoptotic signaling of transforming growth factor-β in human hepatoma cells by carboxyfullerene

Transforming growth factor-beta (TGF-beta) has been shown to induce apoptosis in normal hepatocytes and hepatoma cells both in vivo and in vitro. However, the mechanism by which TGF-beta induces apoptosis is not 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 cells was examined. Only the water-soluble hexacarboxylic acid derivative of C-60 was found to prevent TGF-beta-induced apoptosis. Antiapoptotic activity of C-60 correlated its ability to eliminate TGF-beta-generated reactive oxygen species (ROSs). However, C-60 did not interfere with TGF-beta-activated PAI-1 promoter activity in the Hep3B cells. These results indicate that the signaling pathway of TGF-beta-induced apoptosis may be related to the generation of ROSs and may be uncoupled from the TGF-beta-activated gene promoter activity. Furthermore, the regioisomer of C-60 with a C-3 symmetry was more potent in protecting cells from apoptosis than that with a D-3 symmetry, and the C-3 isomer had stronger interactions with lipid bilayers than the D-3 isomer. The spectroscopic analysis revealed that the C-3 isomer had stranger interactions 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.