Selective involvement of superoxide anion, but not downstream compounds hydrogen peroxide and peroxynitrite, in tumor necrosis factor-α-induced apoptosis of rat mesangial cells

Tumor necrosis factor-alpha (TNF-alpha) induces reactive oxygen species (ROS) that serve as second messengers for intracellular signaling. Currently, precise roles of individual ROS in the actions of TNF-alpha remain to be elucidated. In this report, we investigated the roles of super-oxide anion (O-2(<(.)over bar>)) hydrogen peroxide (H2O2), and peroxynitrite (ONOO-) in TNF-alpha-triggered apoptosis of mesangial cells. Mesangial cells stimulated by TNF-alpha produced O-2(<(.)over bar>) and underwent apoptosis. The apoptosis was inhibited by transfection with manganese superoxide dismutase or treatment with a pharmacological scavenger of O-2(<(.)over bar>) Tiron. In contrast, although exogenous H2O2 induced apoptosis, TNF-alpha-triggered apoptosis was not affected either by transfection with catalase cDNA or by treatment with catalase protein or glutathione ethyl ester. Similarly, although ONOO- precursor SIN-1 induced apoptosis, treatment with a scavenger of ONOO-, uric acid, or an inhibitor of nitric oxide synthesis, N-G-nitro-L-argininemethyl ester hydrochloride, did not affect the TNF-alpha-triggered apoptosis. Like TNF-alpha-induced apoptosis, treatment with a O-2(<(.)over bar>)-releasing agent, pyrogallol, induced typical apoptosis even in the concurrent presence of scavengers for H2O2 and ONOO-. These results suggested that, in mesangial cells, TNF-alpha induces apoptosis through selective ROS. O-2(<(.)over bar>) but not H2O2 or ONOO-, was identified as the crucial mediator for the TNF-alpha-initiated, apoptotic pathway.