Arsenite exposure potentiates apoptosis-inducing effects of tumor necrosis factor-alpha- through reactive oxygen species

Tumor necrosis factor-alpha (TNF-α) is a proinflammatory cytokine released by immune cells during inflammation process. Sodium arsenite (NaAsO2) is an environmental toxic metal. The effects of excess NaAsO2 on TNF-α response and its intracellular signaling are not well understood. We hypothesized that NaAsO2 exposure might affect cellular response to TNF-α. Using HeLa cell model, we found that the combination of NaAsO2 and TNF-α clearly decreased cell viability and mitochondrial membrane potential, but increased percentage of early and late apoptotic cells and cleaved-poly (ADP-ribose) polymerase (PARP). Moreover, the combination prolonged the phosphorylation of mitogen-activated protein kinase (MAPK) members, including c-Jun-N-terminal kinase (JNK), p38, and extracellular signal related kinases (ERK), and increased intracellular reactive oxygen species (ROS), in comparison to treatment of NaAsO2 or TNF-α alone. We further investigated the role of ROS and MAPK signaling on this event by inhibiting ROS production and MAPK. An antioxidant N-acetylcysteine pretreatment diminished the apoptosis-inducing effect of NaAsO2 and TNF-α combination and also inhibited MAPK signaling. Using specific inhibitor of p38 (SB203580) and siRNA-p38 surprisingly increased cell apoptosis and this effect was not observed by JNK and ERK inhibition. This study suggests that p38 may possibly be a survival mediator in response to environmental toxicant-related inflammation. In conclusion, NaAsO2 exposure might amplify inflammation-related tissue injury by potentiating the apoptosis-inducing effect of TNF-α through ROS-dependent mechanism.