Inhalation of environmentally persistent free radicals induces endothelial dysfunction via AhR activation in the air-blood interface

Ankit Aryal, Ashlyn C. Harmon, Lavrent Khachatryan, Alexandra Noël, Arthur Penn, Stephania Cormiera and Tammy R. Dugasa

Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana Particulate matter containing environmentally persistent free radicals (EPFRs) is formed by incomplete combustion of organic pollutants, resulting in the chemisorption of these pollutants to the surface of particulate matter containing redox-active transition metals. In initial studies, we exposed mice by inhalation to laboratory-generated EPFRlo: (1.5e16 radicals/g particles) and EPFRhi: (1.0e18 radicals/g) particles at 250 µg/m3 and investigated their effects on the vascular endothelium. We observed EPFR-induced impairment in vascular relaxation that was both dose- and endothelium-dependent. We also observed aryl hydrocarbon receptor (AhR) activation in the alveolar type-II (AT-II) cells that form the air-blood interface. AhR modulates abroad spectrum of biological and toxic effects. We thus hypothesized that AhR activation at the air-blood interface induces the release of systemic mediators that induce endothelium dysfunction in vessels peripheral to the lung. To address our hypothesis, we used a Cre/lox recombinase system to knockout AhR in AT-II cells of male and female mice and exposed these mice to filtered air (FA), EPFRlo, or EPFRhi for 4h/d for one day or five days. Compared to FA-exposed mice, EPFRhi inhalation for 1d caused a significant increase in plasma ET-1. However, EPFR-induced increases in plasma ET-1 were abolished in AT-II cell-specific AhR KO mice. Moreover, impairment in endothelium-dependent vasorelaxation was abolished entirely in AT-II cell-specific AhR KO mice exposed to EPFRhi and EPFRlo. Furthermore, we found that EPFR inhalation decreased the expression of eNOS mRNA levels in both the lungs and vasculature of littermate control but not AT-II cell-specific AhR KO mice. Together, these data suggest that AhR activation in AT-II pneumocytes at the air-blood interface regulates nitric oxide signaling, and this, in turn, induces vascular endothelial dysfunction. (Support: R21 ES030062; P42 ES013648)