CELLULAR MECHANISMS FOR THE CARDIOVASCULAR EFFECTS OF ARSENIC
Aaron Barchowsky, Nicole V. Soucy, Linda R. Klei, Chandrashekhar D. Kamat* and Michael A. Ihnat*
Dartmouth Medical School, Hanover, NH 03755 and *The University of Oklahoma Medical School, Oklahoma City, OK 73104

Chronic, low level exposure to arsenite increases the incidence of proliferative vascular diseases, arteriosclerosis, atherosclerosis, and ischemic heart disease. Arsenic-associated changes in blood vessels may also contribute to the vascular components of diabetes and tumor growth. Angiogenesis, the formation of new microvessels, is fundamental to most of these pathological changes and may underlie the vascular actions of arsenic. In support of this hypothesis, arsenite (0.033-1.0 mmol/L) significantly increased blood vessel density in an in vivo chicken chorioallantoic membrane (CAM) model. Above 1.0 mmol/L, arsenite inhibited blood vessel growth. Onset of angiogenesis correlated with increased expression of HIF-1a and plasminogen activator inhibitor-1 (PAI-1) in the CAMs. These increases were reproduced in cultured primary porcine aortic smooth muscle cells (SMC). In addition, arsenite stimulated SMC vascular endothelial cell growth factor (VEGF) expression in both a time- and dose-dependent manner. In contrast to endothelial cells, SMC were highly resistant to the toxic effects of arsenite and demonstrated proliferative responses at concentrations of up to 50 mmol/L. However, lower concentrations of arsenite, which that were compatible with endothelial cell proliferation, increased SMC mRNA levels for HIF-1a, VEGF, and PAI-1 and caused sustained expression of HIF-1a and VEGF protein. In addition, microarray analysis in human airway epithelial cells, demonstrated that exposure to arsenite (5 or 50 microM) for 4 h increased HIF mRNA levels by 1.8-3 fold, suggesting that cells other than SMC can be the source of angiogenic factors. However, PAI-1 expression was not sustained at higher arsenite concentrations; indicating that PAI-1 may be a better predictor of the pro-angiogenic potential of arsenite. These data suggest that arsenite causes specific, dose-dependent effects on cell signaling that promote angiogenic and possibly anti-angiogenic responses that contribute to pathologic vascular changes. Supported by Superfund Basic Research Program Grant ES07373.