| Human epidemiological and animal studies have associated ingestion of arsenic in drinking water with increased cardiovascular disease. The current studies examined the hypothesis that arsenic promotes pro-angiogenic stimuli and angiogenesis in both in vitro and in vivo models. In porcine vascular smooth muscle cells, we demonstrated that arsenic transcriptionally increased gene expression of VEGF as well as increased excreted VEGF protein, a major factor in the induction of angiogenesis. While arsenic also increased HIF-1α message and protein in both vascular smooth muscle cells and in human bronchiol epithelial cells, this increase was not required for arsenic induced VEGF expression. Pre-treatment of vascular smooth muscle cells with PKC inhibitors specific for the novel PKC isoforms inhibited VEGF expression, consistent with an increase in PKCδ activity in response to arsenic. Sub-acute ip exposure to arsenic increased angiogenesis, as measured by the in vivo matrigel assay. In addition, arsenic increased angiogenesis following 5, 10 or 20 weeks of drinking water exposure, as measured by the same assay. The LOAEL (lowest observed adverse effect level) for angiogenesis by this method was 5 ppb, with observable angiogenesis at all dose levels tested between 5 and 500 ppb. Plasma samples collected from mice chronically exposed to arsenic in the drinking water showed increased active PAI-1 in animals from the 500 ppb dose group following 5 weeks of exposure. Differences in active PAI-1 between dose groups were lost by 10 weeks, however, in animals from the 500 ppb dose group total PAI-1 remained significantly higher even at 20 weeks. Levels of mRNA for PAI-1, an inhibitor of urokinase-type plasminogen activator and also a key protein involved in fibrosis as well as angiogenesis, was also increased in cardiac tissue of mice chronically exposed to arsenic at 5, 10 or 20 weeks of exposure. We have also shown increased PAI-1 mRNA expression in vascular smooth muscle cells. These data indicate that arsenic acts to promote angiogenesis in vivo, as well as promoting changes in pro-angiogenic stimuli both in vivo and in vitro. These actions would contribute to the pathobiology of arsenic-induced cardiovascular disease. |
