Mechanisms of Lung Neutrophil Activation After Hemorrhage or Endotoxemia: Roles of Reactive Oxygen Intermediates, NF-κB, and Cyclic AMP Response Element Binding Protein

Abstract

AbstractAcute inflammatory lung injury occurs frequently in the setting of severe infection or blood loss. Accumulation of activated neutrophils in the lungs and increased pulmonary proinflammatory cytokine levels are major characteristics of acute lung injury. In the present experiments, we examined mechanisms leading to neutrophil accumulation and activation in the lungs after endotoxemia or hemorrhage. Levels of IL-1β, TNF-α, and macrophage inflammatory protein-2 mRNA were increased in lung neutrophils from endotoxemic or hemorrhaged mice compared with those present in lung neutrophils from control mice or in peripheral blood neutrophils from endotoxemic, hemorrhaged, or control mice. The transcriptional regulatory factors NF-κB and cAMP response element binding protein were activated in lung but not blood neutrophils after hemorrhage or endotoxemia. Xanthine oxidase inhibition, achieved by feeding allopurinol or tungsten-containing diets, did not affect neutrophil trafficking to the lungs after hemorrhage or endotoxemia. Xanthine oxidase inhibition did prevent hemorrhage- but not endotoxemia- induced increases in proinflammatory cytokine expression among lung neutrophils. Hemorrhage- or endotoxemia-associated activation of NF-κB in lung neutrophils was not affected by inhibition of xanthine oxidase. cAMP response element binding protein activation was increased after hemorrhage, but not endotoxemia, in mice fed xanthine oxidase-inhibiting diets. Our results indicate that xanthine oxidase modulates cAMP response element binding protein activation and proinflammatory cytokine expression in lung neutrophils after hemorrhage, but not endotoxemia. These findings suggest that the mechanisms leading to acute inflammatory lung injury after hemorrhage differ from those associated with endotoxemia.