Thesis Defense Date: March 2, 2026
Acute Respiratory Distress Syndrome (ARDS) is a life-threatening lung disease that results from direct or indirect insults to the lung, leading to air-blood barrier damage, pulmonary edema, hypoxemia, and multi-organ failure. Hyperoxia, or exposure to high fractions of oxygen, is used as a life-saving therapy to improve blood oxygenation in patients with ARDS. However, it can also worsen lung injury by inducing excessive production of reactive oxygen species (ROS), primarily from mitochondria, and by contributing to the progression of ARDS. Rat exposure to hyperoxia is a well-established animal model of clinical ARDS that replicates key clinical features. Clinical and preclinical studies suggest that males and females have different ARDS severity and mortality rates, with females often showing greater protection. Most preclinical studies have focused on male animal models and have limited understanding of female-specific responses to the exposure of hyperoxia as an animal model of ARDS. This thesis aims to characterize hyperoxia-induced ARDS in adult female rats, particularly regarding mitochondrial bioenergetics and oxidative stress, and assess sex-specific differences. The relative extent of protection of female rats from hyperoxia-induced acute lung injury (HALI) compared with males is hypothesized to be mediated by sex-dependent differences in mitochondrial bioenergetics and ROS handling. Adult male and female Sprague–Dawley (SD) rats were exposed to normoxia or hyperoxia (>95% O₂) for up to 72 hours. Lung injury was assessed using survival, pleural effusion, lung wet and wet-to-dry weight ratios, pulmonary vascular endothelial filtration coefficient, and histological injury scores. Lung expressions of mitochondrial electron transport chain (ETC) complexes, oxidative stress markers, and antioxidant enzymes were quantified. Mitochondrial oxygen consumption rates (OCRs), membrane potential (ΔΨₘ), and H₂O₂ production were measured in isolated perfused lungs (IPLs) and mitochondria isolated from lung tissue. The cationic fluorescent dye rhodamine 6G (R6G), along with a physiologically based pharmacokinetic (PBPK) computational model were used to quantify ΔΨₘ in IPLs under normoxic and hyperoxic conditions. Hyperoxia induced severe lung injury in both sexes, including pulmonary edema, increased permeability, and mitochondrial dysfunction. However, males exhibited greater oxidative protein damage, greater apoptosis induction, and increased lung H₂O₂ release compared to females. Although hyperoxia nearly doubled mitochondrial H₂O₂ production in isolated female mitochondria, whole-lung H₂O₂ release did not increase, consistent with enhanced tissue-level antioxidant scavenging capacity. Model-based ΔΨₘ estimates indicated that females exhibited a slight mitochondrial depolarization, indicating greater bioenergetic resilience following hyperoxic stress. In both sexes, complex II was the dominant source of H₂O₂ production. These findings suggest a potential mechanistic support for epidemiologic evidence of lower ARDS severity and mortality in female patients compared to males and identify complex II as a potential target for mitigating ARDS.
