Mitochondrial reactive oxygen species production in lungs of rats with different susceptibilities to hyperoxia-induced acute lung injury

Adult rats exposed to hyperoxia (>95 % O₂) die within 60-72 h from respiratory failure. However, when preconditioned with either >95 % O₂ for 48 h followed by 24 h in room air (H-T) or 60 % O₂ for 7 days (H-S), they acquire tolerance or susceptibility to hyperoxia, respectively. The aim was to quantify H₂O₂ production rate and identify sources in isolated lung mitochondria and isolated perfused lungs (IPLs) of normoxia, H-T, and H-S rats. Mitochondria were isolated from lungs, and H₂O₂ production rates were quantified in the presence of pyruvate-malate or succinate, with and without inhibitors of mitochondrial complex I (CI), complex II (CII), and/or H₂O₂ scavenging systems. Lung rate of H₂O₂ release was quantified in IPLs with and without CII inhibitor. Results from isolated mitochondria show that CII is the main H₂O₂ source, and that both H₂O₂ production rate and scavenging capacity were ~48 % lower in H-S mitochondria compared to normoxia. Results from IPLs show that CII is also the dominant H₂O₂ source from lung tissue, and that H₂O₂ release rate was lower in H-T lungs compared to normoxia and H-S lungs. These results suggest that for H-S rats, both mitochondrial rate of H₂O₂ production and scavenging capacity were significantly lower than those in normoxia mitochondria and may contribute to their increased hyperoxia susceptibility. The lower H₂O₂ release rate from H-T IPLs, along with no change in mitochondrial H₂O₂ production rate, is consistent with higher antioxidant capacity in the lungs of H-T rats, which may contribute to their hyperoxia tolerance.