Z. R. Sink3, 5, J. H. Fechner3, R. H. Daley3, J. J. Schauer4, J. D. Mezrich3 3University Of Wisconsin, School Of Medicine And Public Health, Madison, WI, USA 4University Of Wisconsin, Civil And Environmental Engineering, Madison, WI, USA 5Campbell University, School Of Osteopathic Medicine, Lillington, NC, USA
Introduction: Atmospheric pollution has been increasingly implicated as a major contributor to mortality worldwide Military personnel are exposed to sources of particulate matter (PM) that are specific to combat zones, such as burn pits, in addition to common sources of PM, like diesel exhaust. The risks of burn pit exposures are of interest to both the lay public and scientific community; these burn continuously and are utilized to dispose a large variety and quantity of waste at military bases, and concern has been raised that they lead to significant disease in our deployed troops. Exposure to PM has been implicated as an aggravator and predisposing factor for autoimmune diseases, which affect 24.5 million Americans. Three major pathogenic mechanisms have been suggested for PM: genotoxicity, oxidative stress, and activation of the aryl hydrocarbon receptor (AHR). Polycyclic aromatic hydrocarbons, which adhere to PM, are known ligands of the AHR. Upon activation, AHR translocates to the nucleus, where it acts as a transcription factor for a number of genes, including cytochrome P450 genes associated with toxin metabolism and immune inflammatory and immune regulatory pathways. Our lab has previously demonstrated that diesel exhaust particles (DEP), whether intact or following extraction with an organic solvent, contains AHR ligands. Furthermore, inhalation of either the intact or organic fraction of DEP in mice worsens clinical outcome in experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis. The current study sought to assess whether the organic extract of a burn pit surrogate (BPS) PM sample also contains AHR activity and if it impacts EAE.
Methods: To determine AHR ligand activity, a cell-based luciferase assay was utilized. Compared to a 1 to 1000 dilution of DEP (10mg/ml), our standard stock concentration used to treat mice in previous EAE experiments, equivalent AHR activity from BPS was achieved when BPS was diluted 1 to 2.5 x 106. Based on this finding, a preliminary experiment was performed. Female mice (n = 5 per group) were treated via intranasal route 8 times every 3 days with BPS or vehicle control diluted 1 to 2500. On the day of the 5th dose, EAE was induced and mice were scored daily on a 0 – 5 scale for disease symptoms.
Results: 5 of 5 BPS treated mice showed incidence of disease, compared to 3 of 5 mice in the control group. BPS also had significantly greater (p < 0.05) mean +/- std dev cumulative score (12.5 +/- 3.2) compared to control (4.9 +/-4.5) after 18 days followup, and trended towards getting disease earlier.
Conclusion: Our preliminary results suggest that BPS contains high AHR activity. Exposure to BPS appears to exacerbate autoimmune disease with earlier onset and greater severity in vivo.