Intermittent Hypoxia Increases the Severity of Bleomycin-Induced Lung Injury in Mice

Background. Severe obstructive sleep apnea (OSA) with chronic intermittent hypoxia (IH) is common in idiopathic pulmonary fibrosis (IPF). Here, we evaluated the impact of IH on bleomycin-(BLM-) induced pulmonary fibrosis in mice. Methods. C57BL/6J mice received intratracheal BLM or saline and were exposed to IH (40 cycles/hour; FiO(2) nadir: 6%; 8 hours/day) or intermittent air (IA). In the four experimental groups, we evaluated (i) survival; (ii) alveolar inflammation, pulmonary edema, lung oxidative stress, and antioxidant enzymes; (iii) lung cell apoptosis; and (iv) pulmonary fibrosis. Results. Survival at day 21 was lower in the BLM-IH group (p < 0 05). Pulmonary fibrosis was more severe at day 21 in BLM-IH mice, as assessed by lung collagen content (p = 0 02) and histology. At day 4, BLM-IH mice developed a more severe neutrophilic alveolitis, (p < 0 001). Lung oxidative stress was observed, and superoxide dismutase and glutathione peroxidase expression was decreased in BLM-IH mice (p < 0 05 versus BLM-IA group). At day 8, pulmonary edema was observed and lung cell apoptosis was increased in the BLM-IH group. Conclusion. These results show that exposure to chronic IH increases mortality, lung inflammation, and lung fibrosis in BLM-treated mice. This study raises the question of the worsening impact of severe OSA in IPF patients.