Differential sensitivities of bone marrow, spleen and thymus to genotoxicity induced by environmentally relevant concentrations of arsenite

It is known in humans and mouse models, that drinking water exposures to arsenite (As⁺³) leads to immunotoxicity. Previously, our group showed that certain types of immune cells are extremely sensitive to arsenic induced genotoxicity. In order to see if cells from different immune organs have differential sensitivities to As⁺³, and if the sensitivities correlate with the intracellular concentrations of arsenic species, male C57BL/6J mice were dosed with 0, 100 and 500 ppb As⁺³ via drinking water for 30 d. Oxidation State Specific Hydride Generation- Cryotrapping- Inductively Coupled Plasma- Mass Spectrometry (HG- CT- ICP- MS) was applied to analyze the intracellular arsenic species and concentrations in bone marrow, spleen and thymus cells isolated from the exposed mice. A dose-dependent increase in intracellular monomethylarsonous acid (MMA⁺³) was observed in both bone marrow and thymus cells, but not spleen cells. The total arsenic and MMA⁺³ levels were correlated with an increase in DNA damage in bone marrow and thymus cells. An in vitro treatment of 5, 50 and 500 nM As⁺³ and MMA⁺³ revealed that bone marrow cells are most sensitive to As⁺³ treatment, and MMA⁺³ is more genotoxic than As⁺³. These results suggest that the differential sensitivities of the three immune organs to As⁺³ exposure are due to the different intracellular arsenic species and concentrations, and that MMA⁺³ may play a critical role in immunotoxicity.