Cytotoxicity and gene expression changes induced by inorganic and organic trivalent arsenicals in human cells

Inorganic arsenic (iAs) is a human urinary bladder, skin and lung carcinogen. iAs is metabolized to methylated arsenicals, with trivalent arsenicals more cytotoxic than pentavalent forms in vitro. In this study, cytotoxicity and gene expression changes for arsenite (iAs(III)), monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)) were evaluated in three human cell types, urothelial (1T1), keratinocyte (HEK001) and bronchial epithelial (HBE) cells, corresponding to target organs for iAs-induced cancer. Cells were exposed to arsenicals to determine cytotoxicity and to study gene expression changes. Affymetrix chips were used to determine differentially expressed genes (DEGs) by statistical analysis. Lethal concentrations (LC50) for trivalent arsenicals in all cells ranged from 1.6 to 10μM. MMA(III) and DMA(III) had 4-12-fold greater potency compared to iAs. Increasing concentrations of iAs(III) induced more genes and additional signaling pathways in HBE cells. At equivalent cytotoxic concentrations, greater numbers of DEGs were induced in 1T1 cells compared to the other cells. Each arsenical altered slightly different signaling pathways within and between cell types, but when altered pathways from all three arsenicals were combined, they were similar between cell types. The major signaling pathways altered included NRF2-mediated stress response, interferon, p53, cell cycle regulation and lipid peroxidation. These results show a similar process qualitatively and quantitatively for all three cell types, and support a mode of action involving cytotoxicity and regenerative proliferation.