Mechanism of Clostridium difficile toxin A-induced apoptosis in T84 cells.

This study is an investigation into the mechanism of Clostridium difficile toxin A-induced apoptosis in human intestinal epithelial cells. Toxin A induced apoptosis of T84 cells in a dose- and time-dependent fashion. Toxin A-induced apoptosis was completely inhibited by blocking toxin enzymatic activity on Rho GTPases with uridine 5'-diphosphate-2',3'-dialdehyde by a nonspecific caspase inhibitor and was partially inhibited by caspase-1, -3, -6, -8, and -9 inhibitors. Caspases 3, 6, 8, and 9 and Bid activation were detected. Toxin A also induced changes in mitochondrial membrane potential and cytochrome c release at 18-24 h, a time course similar to caspase-9 activation. In conclusion, toxin A induces apoptosis by a mechanism dependent on inactivation of Rho, activation of caspases 3, 6, 8, and 9 and Bid, and mitochondrial damage followed by cytochrome c release. Toxin A proapoptotic activity may contribute to the mucosal disruption seen in toxin A-induced enteritis.