Lymphocyte subpopulations and oxidative stress following sub-acute exposure to natural dust collected from the Nellis Dunes Recreational Area

Abstract

Exposure to particulate matter containing heavy metals has been linked to adverse health effects when exposure occurs in industrial settings; however, little data exist on effects associated with natural exposure settings. In this study, markers of oxidative stress and lymphocyte subpopulations in mice were observed following sub-acute exposure to metals-containing dust collected from a natural setting used heavily for off-road vehicle (ORV) recreation. Adult female B6C3F1 mice were exposed to concentrations of dust collected from seven types of surfaces at the Nellis Dunes Recreation Area. Dust representing each of the seven map units was prepared with a median diameter of < or = 4.5m and suspended in PBS immediately prior to oropharyngeal aspiration at concentrations from 0.01 - 100 mg of dust/kg body weight. Four exposures were given a week apart over 28-days to mimic a month of weekend exposures. Thymi, spleens and blood for evaluation of oxidative stress markers and lymphocyte sub-populations were collected 24 hours after the final exposure. Blood markers of oxidative stress included levels of free radicals, superoxide dismutase, total antioxidant capacity, and total glutathione. CD4, CD8, FoxP3, CD25, IL-17, and B220 cell surface markers were used for T and B cell identification using flow cytometry. Overall, no single surface type was able to consistently induce markers of oxidative stress at a particular dose or in a dose-responsive manner. The two highest concentrations of dust from one surface type increased two markers of oxidative stress, but results of other surface types were inconsistent. No statistically significant changes were observed in the splenic B220+ cells following NDRA dust exposure. Three CBN units (1, 2, and 6) showed decreases in splenic CD4+/CD25+/FoxP3- cells. These observations were relatively consistent with TiO 2, where a significant change at the highest exposure level was observed in only one measure of oxidative stress. Additionally, the TiO 2 dosing groups showed no significant changes in lymphocyte subpopulations. These results indicate that exposure to these natural, mineral dusts, under the exposure scenario of our study, while are unlikely to considerably increase the risk of oxidative damage systemically, may induce a reduction in some cell populations in exposed individuals.