Our goals are to further characterize the physiologic features, biochemical mechanisms, and therapeutic implications of two observations we have recently made regarding oxidative injury of mammalian cells: (1) that the monokines tumor necrosis factor (TNF) and the lymphokine lymphotoxin (LT), alone of the cytokines tested, trigger a massive respiratory burst from human neutrophils (PMN), but not from monocytes, only after an unprecedentedly prolonged lag period, and only if the PMN are adherent to suitable surfaces, including human unbilical vein endothelial cells (HUVEC), and (2) that the alpha-ketoacid pyruvate is selectively secreted by mammalian cells, acts in the medium as a scavenger of H202 via its rapid, nonenzymatic, oxidative decarboxylation, and acts intracellularly as a target of oxidative injury that may compromise cellular energy supply. For (1), we will further characterize the nature of surfaces that permit the PMN response to TNF and LT, analyze the dependence on adherence with special attention to effects on the number, affinity, clustering, and internalization of TNF receptors, and investigate the basis of the long lag period in response to these agents, in terms of possible induction of a transient suppressive state and the timing of signal transduction reactions, especially those leading to activation, translocation and myristoylation of protein kinase C. For (2), we will analyze the mechanism of pyruvate export, with special attention to HUVEC, quantify the contribution of pyruvate to cell buffering capacity against H202, and analyze the enzymatic basis for the variability in resistance of pyruvate secretory capacity to oxidative inactivation in H202-sensitive versus -resistant cells. Finally, (3) we will test the role of PMN-derived H202, and the antioxidant properties of exogenous pyruvate, in mice with pulmonary inflammation induced by complement activation, in TNF-induced hemorrhagic necrosis, and in TNF-induced lethality.
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