Synergism between tumor necrosis factor-alpha and H2O2 enhances cell damage in rat PC12 cells

Tumor necrosis factor-alpha (TNFalpha) is harmful in the early phase and beneficial in the long-term phase after brain injury. Reactive oxygen species (ROS) are among the most toxic mediators activated by injury. We speculate that part of the TNFalpha toxicity is mediated by its synergism with ROS. Thus, toxicity of TNFalpha and ROS, alone or together, were studied in PC12 cells. PC12 cells were exposed for 18 h to TNFalpha (0-100 ng/ml), to H2O2 (1-300 microM) or to both, each at sub-toxic concentrations. Lactic dehydrogenase release, prostaglandin E2 accumulation and morphology indicated cell death and stress response. TNFalpha toxicity was seen at >50 ng/ml, and that of H2O2 at >150 microM, however, when together, sub-lethal levels (25 ng/ml TNFalpha and 30 microM H2O2) induced toxicity. Dexanabinol, an N-methyl-D-aspartate antagonist with antioxidant and anti-TNFalpha properties, completely rescued the cells. These findings corroborate our hypothesis on the cooperative toxicity exerted by TNFalpha and ROS after brain injury.