Increased susceptibility of human small airway epithelial cells to apoptosis after long term arsenate treatment

Inorganic arsenic (arsenate and arsenite) are well known human carcinogens. Apoptosis is a normal biological process that is involved in regulating cell development and differentiation, and is an important protective response to cell injury. The aim of this study was to determine the long term arsenic effect on human small airway epithelial cells (SAEC) by analyzing two distinct apoptosis-inducing agents, Fas ligand (Fas L), which evokes death receptor-mediated apoptosis, and hydrogen peroxide H₂O₂, which induces apoptosis mediated by reactive oxygen species (ROS). The SAEC were continuously exposed to 0.5 μg/mL arsenic for 28 weeks, and apoptosis was examined after 24 h treatment with either Fas L or H₂O₂. SAEC displayed decreased cell viability and increased apoptosis after treatment with Fas L and H₂O₂, compared to non-arsenic treated control cells. Furthermore, treatment of these arsenic-exposed SAEC with Fas L or H₂O₂ induced cleavage of the DNA damage recognition protein, poly (ADP-ribose) polymerase (PARP), and the 'effector' caspase, Caspase-3, both canonical indicators of apoptosis. We observed increased phosphorylation of p38, a member of the MAP kinase family, following treatment with Fas L or H₂O₂. To confirm the involvement of p38 in the regulation of apoptosis we pretreated cells with the p38 kinase inhibitor, SB 203580 and observed a significant decrease in apoptosis.