Role of reactive nitrogen species (RNS) generated via inducible nitric oxide synthase in vesicant-induced lung injury and inflammation

Abstract

Nitrogen mustard (NM) is a toxic vesicant known to damage the respiratory tract by alkylating proteins, lipids and nucleic acids and causing oxidative stress. Acute injury is associated with increased expression of inducible nitric oxide synthase (iNOS) in lung macrophages and epithelial cells. In these studies we analyzed the effects of inhibiting iNOS using aminoguanidine (AG) on NM-induced pulmonary toxicity. Male Wistar rats were treated IT with NM (0.125 mg/kg) or control. Animals were sacrificed 1–28 days later and lungs analyzed for markers of injury, oxidative stress and inflammation. Exposure of rats to NM resulted in progressive histopathological changes including perivascular and peribronchial edema, inflammatory cell infiltration, luminal and alveolar accumulation of debris and fibrin, bronchiolization of the alveolar septal wall, fibroplasia and fibrosis. This was correlated with increased bronchoalveolar lavage protein and inflammatory cell content. NM intoxication also resulted in increased expression of iNOS and COX-2, as well as HO-1 and Mn-SOD at all the post exposure times. Evidence of Type II cell proliferation, as well as YM1 and galectin-3 positive pro-fibrotic macrophages were also noted in the lung 3–28 days post NM exposure. Treatment of rats with AG (50 mg/kg, 2x/day for 3 days) abrogated acute injury, inflammation and oxidative stress induced by NM 1–3 days post exposure; with no effects at 7–28 days. These findings indicate that RNS generated via iNOS contribute to early events in NM-induced lung toxicity, however, transient inhibition of iNOS is not sufficient to protect against pulmonary fibrosis.