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A3858 - Elevated Free Heme Predisposes to Bacterial Lung Infection After Acute Inhalation Injury
Author Block: I. Ahmad1, A. Lam1, M. A. Carlisle2, H. Paiste1, S. Aggarwal1, S. Matalon1; 1Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, United States, 2Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, AL, United States.
RATIONALE: Acute inhalation injury (AII) due to the environmental or occupational exposure of toxic halogen gas, bromine (Br2), can cause acute inhalation injury (AII), respiratory dysfunction, and mortality, which remains as high as 35-40%. Patients who survive inhalation injury are susceptible to bacterial lung infections. However, the molecular mechanisms responsible for the impairment of innate immune response are not well understood. Elevated levels of cell-free heme are well known mediators of oxidative lung injury and has also been shown to promote bacterial infections. We recently showed that treatment with hemopexin (Hx), a plasma protein that scavenges free heme, attenuates inhalation lung injury. Therefore, based upon the published data and our previous studies, we hypothesized that Hx would improve the bactericidal function of immune cells and decrease the susceptibility to lung infection and associated lung morbidity and mortality after inhalation lung injury. METHODS: C57BL/6 mice were exposed to Br2 (600ppm, 30min) or air and returned to room air. One hour post exposure Hx (4µg/g body weight, IP) was administered to the exposed mice. Four days later, animals were received an intratracheal bolus of Pseudomonas aeruginosa (PA) (PAK strain, 105 CFU). One day post infection, we measured indices of lung injury (BALF protein, cell count, lung wet/dry weight ratio) and CFU in the lungs (by culturing lung homogenate on LB agar). In isolated alveolar immune cells and blood neutrophils, we measured the NADPH oxidase activity by assessing the superoxide dismutase-inhibitable reduction of ferricytochrome C; and bacterial killing by co-incubating immune cells with mid-log cultures of PA for 30 minutes and then incubating them on agar plates and counting bacterial colonies. RESULTS: C57BL/6 mice were largely resistant to respiratory infection. However, Br2 exposure increased infection, as indicated by the appearance of numerous bacterial colonies on agar plates. Notably, lungs from Hx treated mice had fewer colonies. Hx also reduced BALF protein, cell count, lung wet/dry weight ratio, and mortality in mice challenged with PA after Br2 exposure. Further, we found that Br2 exposure impaired phagocytosis, NADPH oxidase redox function and bacterial killing by the immune cells. However, these immune functions were not impaired in the immune cells obtained from mice treated with Hx. CONCLUSION: Together, these data suggest that scavenging heme may prove a useful adjuvant therapy to reduce the rate of bacterial infection in patients with ALI.