Induction of apoptosis in human T-cells by methyl mercury: Temporal relationship between mitochondrial dysfunction and loss of reductive reserve

The objective of our study was to define the mechanism by which MeHgCl indu ces human T-cell apoptosis. We asked the question: does mercury disrupt the Delta psi(m) and induce a mitochondrial permeability transition state? Usi ng two fluorescent reagents, JC-1 and DiOC(6)(3), we demonstrated that MeHg Cl exposure resulted in a decrease in the Delta psi(m). Since a decline in Delta psi(m) can disturb the pH(i), we employed SNARF-1 to assess pH(i); re sults indicate that mercury treatment reduced the pH(i) from 7.0 to 6.5. Co nsistent with these observations, we noted that uncoupled electron transfer reactions generated ROS, while cardiolipin, a mitochondrial phospholipid, was oxidized. In concert with the biochemical changes, there was a decrease in overall dimension of the mitochondria of mercury-treated cells and a lo ss in cristae architecture. The toxicant also depleted the thiol reserves o f the cell and promoted translocation of cytochrome c from the mitochondria to the cytosol. Furthermore, when T cells were thiol-depleted, there was i ncreased susceptibility to MeHgCl-induced apoptosis. Finally, we establishe d a temporal relationship between the decline in Delta psi(m), generation o f ROS, and depletion of thiol reserves. The earliest detectable event was a t the level of the mitochondrion; in the presence of MeHgCl there was a pro found reduction in mitochondrial Delta psi(m), and a decline in GSH levels within 1 h. Subsequently, a further decrease in thiol reserves was linked t o the generation of ROS. We propose that the target organelle for MeHgCl is the mitochondrion and that induction of oxidative stress leads to activati on of death-signaling pathways. (C) 1999 Academic Press.