Suppression of Lung Oxidative Stress, Inflammation, and Fibrosis following Nitrogen Mustard Exposure by the Selective Farnesoid X Receptor Agonist Obeticholic Acid

Nitrogen mustard (NM) is a cytotoxic vesicant known that causes pulmonary injury that can progress to fibrosis. NM toxicity is associated with an influx of inflammatory macrophages in the lung. Farnesoid X Receptor (FXR) is a nuclear receptor involved in bile acid and lipid homeostasis that has anti-inflammatory activity. In these studies, we analyzed the effects of FXR activation on lung injury, oxidative stress and fibrosis induced by NM. Male Wistar rats were exposed to phosphate buffered saline (CTL) or NM (0.125mg/kg) by i.t. Penn-Century MicroSprayer®{trade mark, serif} aerosolization; this was followed by treatment with the FXR synthetic agonist, obeticholic acid (OCA, 15mg/kg) or vehicle control (0.13-0.18g peanut butter), 2hr later, and then once/day, 5 days/week thereafter for 28d. NM caused histopathological changes in the lung including epithelial thickening, alveolar circularization, and pulmonary edema. Picrosirius Red staining and lung hydroxyproline content were increased indicative of fibrosis; foamy lipid laden macrophages were also identified in the lung. This was associated with aberrations in pulmonary function including increases in resistance and hysteresis. Following NM exposure, lung expression of HO-1 and iNOS, and the ratio of nitrate/nitrites in bronchoalveolar lavage fluid (BAL), markers of oxidative stress increased, along with BAL levels of inflammatory proteins, fibrinogen and sRAGE. Administration of OCA attenuated NM-induced histopathology, oxidative stress, inflammation and altered lung function. These findings demonstrate that FXR plays a role in limiting NM-induced lung injury and chronic disease, suggesting that activating FXR may represent an effective approach to limiting NM-induced toxicity. Significance Statement In these studies, the role of farnesoid-X-receptor (FXR) in mustard vesicant-induced pulmonary toxicity was analyzed using nitrogen mustard (NM) as a model. Our findings that administration of obeticholic acid, an FXR agonist, to rats reduces NM-induced pulmonary injury, oxidative stress, and fibrosis provide novel mechanistic insights into vesicant toxicity which may be useful in the development of efficacious therapeutics.