Modulation of murine peritoneal macrophage function by chronic exposure to arsenate in drinking water.

Exposure of humans to arsenic is associated with various adverse health effects including immunotoxicity and elevated risk of cancer development. Specific mechanisms of these effects are not well understood. In the present study we investigated some functional parameters of peritoneal macrophages isolated from mice exposed for 12 weeks to sodium arsenate in drinking water at 0.5, 5, and 50 mgAs/l. The experimental conditions were matched with the environmental conditions of arsenic exposure in humans. To characterize function of the macrophages, we assessed their ability to release nitric oxide (NO), reactive oxygen species (ROS), and tumor necrosis factor-alpha (TNF-alpha) in response to common stimulants. To this end the isolated cells were stimulated with lipopolysaccharide (1 microg/ml) to assess NO and TNF-alpha production (the WEHI-164 bioassay) or with phorbol myristate acetate (5 microg/ml) to assess superoxide production (NBT reduction test). As a result, in mice exposed to 0.5, 5, and 50 mgAs/l we observed decreased production of NO (9 +/- 2, 8 +/- 2, 11 +/- 5 microM NO2-, respectively, versus 27 +/- 7 microM in control) and superoxide (41.3 +/- 18.2%, 52.8 +/- 15.1% and 55.9 +/- 12.9%, respectively, less than in control). Despite reduced NO production, expression of iNOS mRNA in RT-PCR, showed similar levels in exposed and control animals. We did not see any significant influence of the exposure on TNF-alpha release and mRNA expression. The potential consequences of decreased production of NO and superoxide by peritoneal macrophages as observed in exposed mice may suggest impaired response of the cells against infection or developing tumor cells.