Involvement of hydrogen peroxide in the differentiation and apoptosis of preosteoclastic cells exposed to arsenite

Long-term exposure to sodium arsenite (AsO2) promotes the development of various cancers. Paradoxically, arsenic also induces pro-myelomonocytic leukemia cell differentiation, and at higher concentrations, apoptosis. The present study investigated the effects of AsO2 on preosteoclasts. When treated with 2.5–5 μM AsO2, RAW264.7 cells underwent osteoclast differentiation as evidenced by an increase in the number of multinucleate cells expressing tartrate resistant acid phosphatase (TRAP). The appearance of these phenotypic markers was preceded by a low level increase in extracellular production of H2O2 and was prevented by the addition of catalase (4.5 μg/ml), an enzyme that removes H2O2. Only at high concentrations (10–25 μM) of AsO2 was a significant loss of cell viability and a high level increase in H2O2 production (1.5 μM) observed. Apoptosis was blocked by pretreatment with diphenylene iodonium chloride (2 μM), a NAD(P)H-flavoprotein inhibitor, suggesting the involvement of NADPH-oxidase. The data show that AsO2, dose-dependently, stimulates increasing amounts of H2O2 production. Moreover, at concentrations found in tissues of individuals exposed to geochemical AsO2, osteoclasts underwent an H2O2-dependent differentiation. Therefore, chronic exposure to low-level amounts of AsO2 could result in increased bone resorption and contribute to bone related pathologies.