Abstract
Inorganic arsenic is an immunotoxic environmental contaminant to which millions of humans are chronically exposed. We recently demonstrated that human primary macrophages constituted a critical target for arsenic trioxide (As(2)O(3)), an inorganic trivalent form. To specify the effects of arsenic on macrophage phenotype, we investigated in the present study whether As(2)O(3) could regulate the activity of NADPH oxidase, a major superoxide-generating enzymatic system in human phagocytes. Our results show that superoxide levels were significantly increased in a time-dependent manner in blood monocyte-derived macrophages treated with 1 muM As(2)O(3) for 72 h. Concomitantly, As(2)O(3) induced phosphorylation and membrane translocation of the NADPH oxidase subunit p47(phox) and it also increased translocation of Rac1 and p67(phox). Apocynin, a selective inhibitor of NADPH oxidases, prevented both p47(phox) translocation and superoxide production. NADPH oxidase activation was preceded by phosphorylation of p38-kinase in As(2)O(3)-treated macrophages. The p38-kinase inhibitor SB-203580 prevented phosphorylation and translocation of p47(phox) and subsequent superoxide production. Pretreatment of macrophages with the Rho-kinase inhibitor Y-27632 was found to mimic inhibitory effects of SB-203580 and to prevent As(2)O(3)-induced phosphorylation of p38 kinase. Treatment with As(2)O(3) also resulted in an increased secretion of the proinflammatory chemokine CCL18 that was fully inhibited by both apocynin and SB-203580. Taken together, our results demonstrate that As(2)O(3) induced a marked activation of NADPH oxidase in human macrophages, likely through stimulation of a Rho-kinase/p38-kinase pathway, and which may contribute to some of the deleterious effects of inorganic arsenic on macrophage phenotype.