Monomethylarsonous Acid Induced Cytotoxicity and Endothelial Nitric Oxide Synthase Phosphorylation in Endothelial Cells

Chronic arsenic poisoning is reported to be associated with peripheral and cardiovascular disease, arteriosclerosis, Raynaud’s syndrome, hypertension, and Blackfoot disease. Monomethylarsonous acid (MMA^III) is a reactive metabolite of inorganic arsenic and a potent inhibitor of endothelial nitric oxide synthase (eNOS). Arsenic is also reported to phosphorylate eNOS in cultured keratinocyte and Human T cell leukemia Jurkat cells, respectively. In the present study, we examined the cytotoxicity and eNOS phosphorylation by MMA^III exposure in cultured bovine aortic endothelial cells (BAEC). Results showed that MMA^III is more toxic than arsenite in BAEC cells. The IC₅₀ values for MMA^III and arsenite were determined to be approximately 1.7 and 24.1 μmol/L, respectively. Exposure of BAEC to MMA^III (0.75 μmol/L) caused a significant eNOS phosphorylation 15 min after MMA^III exposure. However, a complex of MMA^III with dithiothreitol (DTT) that lacks the reactivity with vicinal thiols unaffected eNOS phosphorylation. The present study shows that MMA^III generated during biomethylation of arsenic is highly toxic in BAEC. Our study also suggests that MMA^III could induce the eNOS phosphorylation through modification to cellular thiols of the eNOS enzyme. And the initial up-regulation of eNOS phosphorylation by MMA^III seems to be an adaptive response against disruption of eNOS bioactivity during arsenic exposure.