Reactive oxygen species contribute to oxygen-related lung injury after acid aspiration

Hyperoxia increases pulmonary damage after acid aspiration. We hypothesize that free radicals play a role in acute lung injury. To examine this hypothesis, we injured rats by intratracheal instillation of acidic isotonic sodium chloride solution (NS) (pH 1.25); NS + gastric particles (particle pH 5.3); or acid + particles (pH 1.25). Animals were exposed to 98% oxygen or air for 5 h. Superoxide (HO₂) generation was measured in either an aliquot of white blood cells (WBCs) recovered from bronchoalveolar lavage (BAL) or from blood. Lungs were analyzed for thiobarbituric acid-reactive substances (TBARS) and carbonylated proteins. The antioxidant capacity was measured using a 2-2'-azo-bis-amidinopropane hydrochloride neutralizing assay. Generation of HO₂ by WBCs in peripheral blood was greater in animals exposed to 98% O₂ (89.8 ± 12.5 U · min-1 · 10⁵ neutrophils) compared with air exposure (37.5 ± 9.2 U · min-1 · 10⁵ neutrophils) after combined injury (P < 0.05). Similarly, HO₂ generation by WBCs retrieved from BAL was higher in oxygen-exposed rats (987.74 ± 128 U · min-1 · 10⁵ WBC) compared with air-exposed animals after an identical injury (348 ± 9.2 U · min-1 · 10⁵ WBC) (P < 0.05). TBARS and carbonylated protein levels in the lungs of oxygen-exposed animals (587.9 ± 58.6 and 55.8 ± 3.1 pmol/mg of protein, respectively) were higher than those in air-exposed rats after combined injury (342.8 ± 15.1 and 28.6 ± 4.6 pmol/mg of protein, respectively) and com pared with air-exposed uninjured rats (340.6 ± 9.8 and 18.3 ± 2.8 pmol/mg of protein, respectively; P < 0.01). Antioxidant capacity decreased in acid and combined injury groups (2.41 ± 0.13 min and 1.94 ± 0.15 min, respectively) compared with the uninjured group after 5 h of exposure to 98% oxygen (4.85 ± 0.19 min; P < 0.01). We demonstrated evidence of increased oxidant activity on lipids and proteins in injured lungs after oxygen exposure. The decrease in antioxidant capacity after low pH aspiration with exposure to hyperoxia may contribute to this increase. Implications: Oxygen ad ministration results in a lung pathology known as oxygen toxicity. This effect is usually not significant if the duration of exposure is limited to <24 h. In the presence of acute inflammatory lung injury, exposure to hyperoxia results in lung damage in a shorter time. We demonstrate that sufficiently decreased lung antioxidant reserve capacity may be accountable for this early toxicity.