Epidemiological evidence suggests that exposure to the metalloid arsenic constitutes a risk factor for cardiovascular disease. The purpose of this study was to determine whether arsenic could stimulate generation of factors involved in oxidative stress and inflammation, conditions associated with atherosclerosis, or coronary artery disease. We found that production of peroxynitrite, a strong oxidant formed from the coupling of nitric oxide and superoxide anion, was significantly increased in bovine aortic endothelial (BAE) cells exposed to sodium arsenite at concentrations as low as 0.5 microM. Expression of the inflammatory mediator cyclooxygenase-2 (COX-2) was also upregulated in response to arsenite exposure as demonstrated by Western blot analysis. The increase in COX-2 protein was time dependent with highest levels at 30 min and 48 h. This result was supported by an increase in the generation of prostaglandin E(2) following exposure to arsenic. Nitrotyrosine residues in proteins are indicative of peroxynitrite generation, and extensive nitrotyrosine formation has been detected in atherosclerotic plaques. Therefore, COX-2 protein was immunoprecipitated from BAE cells and submitted to Western blot analysis using an antibody to nitrotyrosine. Nitration of COX-2 was detected in arsenic-treated cells, but not in untreated control cells. The findings in this report suggest an increase in reactive species, notably peroxynitrite, in BAE cells exposed to arsenic. Furthermore, induction of important inflammatory mediators such as COX-2 may exacerbate the inflammatory state typical of atherosclerosis.