Altered macrophage function contributes to the development of multiple organ failure in severely injured patients. It has been shown that the phagocytosis of erythrocytes caused by burn injury plays an important role int he alteration of Kupffer cell function after this form of injury. Erythrocytosis depresses macrophage bactericidal function and increases the bacterial lipopolysaccharide-stimulated serum tumor necrosis factor levels. The proposed studies will address the mechanism for the alteration of Kupffer cell function following erythrocyte phagocytosis. The hypothesis to be tested is that the alteration of macrophage function following erythrocyte phagocytosis is due to an oxidative stress generated from the interaction of the products of the respiratory burst (O2-,H2O2) with iron from the degradation of hemoglobin. The role of an oxidative stress in the alteration of Kupffer cell function following burn injury-induced erythrocyte phagocytosis will also be studied. The levels of peroxidation products (conjugated dienes and malondialdehyde) will be used to assess the extent of the oxidative stress. Kupffer cell function will be determined from the capacity to release arachidonate, generate a respiratory burst, phagocytose particulates, kill bacteria and secrete tumor necrosis factor.
The specific aims are 1) To determine the role of an oxidative stress in the alteration of Kupffer cell function following erythrocyte phagocytosis. This will be approached by determining the relationship between altered Kupffer cell function and an oxidative stress following erythrocyte phagocytosis; the ability of an oxidative stress to alter macrophage function; the role of the respiratory burst in generating an oxidative stress; and the ability of antioxidants to prevent the oxidative stress. Preliminary studies have shown that peritoneal macrophages generate peroxidation products following the phagocytosis of erythrocytes. 2) To determine the role of iron in catalyzing the oxidative stress following the phagocytosis of erythrocytes. The effect of changing the availability of iron on the oxidative stress and Kupffer cell function following erythrocyte phagocytosis will be studied. This will be approached by determining the effect of the phagocytosis of erythrocytes loaded with iron salts, the inhibition of heme oxygenase, and the administration of the iron chelator, desferrioxamine. 3) To determine the effect of an oxidative stress on phospholipase activity in Kupffer cells. Phospholipases mediate the release of arachidonate which is required for normal macrophage function. This will be approached by determining the ability of exogenous arachidonate to restor Kupffer cell function, changes in phospholipase activity following erythrocyte phagocytosis, the susceptibility of the isolated enzymes to an oxidative stress, and the effect of antioxidants and altered iron availability on phospholipase activity. The ultimate objective of this project is to elucidate the mechanism for the alteration of macrophage function in severely injured patients and thereby provide a more rational approach for the treatment of multiple organ failure.
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