Arsenic trioxide induces apoptosis in peripheral blood T lymphocyte subsets by inducing oxidative stress: a role of Bcl-2.

Arsenic trioxide (As(2)O(3)) has been used successfully in the treatment of acute promyelocytic leukemia. However, effects of As(2)O(3) in normal peripheral blood T cells have not been studied in detail. The purpose of this study was to investigate whether As(2)O(3) would induce apoptosis in normal T cells and therefore may have immunosuppressive side effects. Apoptosis was measured by terminal deoxynucleotidyl transferase-mediated nick end labeling assay, caspase activation by flow cytometry and colorimetric assay, mitochondrial transmembrane potential (deltapsi(m)), intracellular reactive oxygen species (ROS), and intracellular reduced glutathione (GSH) by flow cytometry. The release of cytochrome c and apoptosis-inducing factor (AIF) from the mitochondria was measured by confocal microscopy, and the expression of molecules regulating apoptosis was measured by Western blotting. As(2)O(3), at clinically achievable therapeutic concentrations, induces apoptosis in peripheral blood T cells. As(2)O(3)-induced apoptosis was associated with reduced deltapsi(m), enhanced generation of intracellular ROS, decreased levels of intracellular GSH, release of cytochrome c and AIF from the mitochondria, activation of caspases, down-regulation of Bcl-2 and Bcl-x(L), and up-regulation of Bax expression. In addition, exogenous GSH protected lymphocytes from As(2)O(3)-induced apoptosis. Furthermore, overexpression of Bcl-2 inhibited As(2)O(3)-induced apoptosis and blocked depolarization of deltapsi(m), generation of ROS, and release of both cytochrome c and AIF. These data indicate that As(2)O(3) induces apoptosis in T cells by enhancing oxidative stress and that Bcl-2 appears to play a major role in As(2)O(3)-induced apoptosis.