Sex-specific differences in lung mitochondrial function and injury in rats exposed to hyperoxia

Hyperoxia is both an essential therapy and a contributor to lung injury in acute respiratory distress syndrome. We hypothesized that adult female rats are relatively protected from hyperoxia-induced acute lung injury (HALI) compared with males and that this protection is associated with sex-dependent differences in lung mitochondrial bioenergetics and H₂O₂ production. Adult rats were exposed to room air (normoxia) or hyperoxia (>95% O₂) for up to 60 h. Lung injury was assessed by pleural effusion, lung wet weight, pulmonary vascular filtration coefficient (K_f), histologic injury scores, and cleaved caspase-3 (CC3) staining. Expression of mitochondrial complexes I-V was quantified in lung tissue. Mitochondrial oxygen consumption rates (OCRs) and H₂O₂ (mtH₂O₂) production were measured in isolated lung mitochondria, and lung H₂O₂ release rate was quantified in isolated perfused lungs. Hyperoxia caused systemic and pulmonary injury in both sexes. However, compared with females, males showed greater body weight loss and larger increases in lung wet weight, pleural effusion, K_f, and CC3-positive cells. Hyperoxia decreased complex I expression in males but not females and impaired OCRs in both sexes. For both sexes, complex II was the dominant mtH₂O₂ source. Hyperoxia nearly doubled mtH₂O₂ production in female, but not male, mitochondria. Nevertheless, whole lung H₂O₂ release rate in females did not increase, consistent with enhanced tissue-level scavenging. These findings indicate attenuated severity of HALI in adult females, highlight complex II as a major mtH₂O₂ source during hyperoxia, and support consideration of sex as a biological variable in mitochondria-targeted therapies for HALI.NEW & NOTEWORTHY We investigated sex-specific responses to hyperoxia-induced acute lung injury (HALI) in rats. Female rats exhibited attenuated severity, with less pleural effusion, pulmonary edema, and apoptosis than males. Studies in isolated mitochondria, lung tissue homogenates, and isolated lungs indicate that this attenuated severity is associated with mitochondrial adaptations and enhanced tissue H₂O₂ scavenging capacity. These findings underscore the importance of sex as a biological variable and identify mitochondrial complex II as a potential HALI therapeutic target.