The role of oxidative stress in hormesis induced by sodium arsenite in human embryo lung fibroblast (HELF) cellular proliferation model.

Hormetic dose-response relationships induced by environmental agents are often characterized by a low-dose stimulation and a high-dose inhibition. The mechanisms underlying hormesis induced by environmental agents still remain an enigma; however, hormetic consequences may have significant implications for health risk assessments. To investigate the role of oxidative stress in hormetic phenomena associated with cell proliferation induced by sodium arsenite, the levels of reactive oxygen species (ROS), lipid peroxidation (LPO), and heat-shock proteins (HSP) and the activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were measured in human embryo lung fibroblast (HELF) cells after treatment with sodium arsenite at various concentrations for differing times. Results showed that sodium arsenite induced significant cell proliferation at low concentrations (0.5 microM for 12, 24, and 48 h), but inhibited cell growth at high amounts (5 and 10 microM for 24 and 48 h), reflected as a beta concentration-response curve. Data indicated that the relationship between ROS levels and sodium arsenite exposure concentration displayed a positive correlation. It was found out that sodium arsenite at high concentrations induced LPO damage. The activities of SOD were enhanced at low metal concentrations but inhibited with high amounts in a concentration-dependent manner. Similarly, heat-shock protein 27 (HSP27) levels were increased by sodium arsenite of low concentrations with early exposure time (3, 6, and 12 h), but decreased with high metal concentrations with greater exposure time (24 and 48 h). Sodium arsenite decreased HSP70 expression at lower concentrations, but increased HSP70 expression at higher concentration. The results indicated that this cellular hormetic model of cell proliferation induced by sodium arsenite occurred in HELF cells, which may explain contradictory effects seen with this metal. Sodium arsenite at low concentrations induced enhanced ROS generation without cytotoxicity and a cellular protective effect. In contrast, sodium arsenite at high concentrations produced marked ROS formation, marked oxidative stress, and cellular damage, as evidenced by LPO.