We recently demonstrated activation of 5-lipoxygenase activity in human polymorphonuclear leukocytes (PMN) on preincubation of the cells with glutathione-depleting agents, namely l-chloro-2,4-dinitrobenzene (DnpCl) and azodicarboxylic acid bis [dimethylamide] (diamide). In this paper we show that Dnp-C1, but not diamide, impairs the reduction of added organic peroxides in whole PMN. Also, since co-incubation of fatty acid hydroperoxides with arachidonate caused activation of 5-lipoxygenase, we propose that Dnp-C1 increases the peroxide level in PMN which is required for the onset of lipoxygenase activity. This could be substantiated in PMN homogenates by a glutathione-dependent depression of arachidonate 5-lipoxygenation. At higher arachidonate concentrations and in the presence of Ca2+ the glutathione effect was not observed but additional glutathione peroxidase also blocked this maximally stimulated 5-lipoxygenase. Together with other experiments, it became obvious that the formation of leukotrienes, but also of 15-lipoxygenase products, requires a sharply defined threshold level of fatty acid hydroperoxides which are generated by the lipoxygenases and counteracted by glutathione-dependent peroxidase(s). Dnp-C1 influences this equilibrium by removing glutathione and thereby inhibiting glutathione-dependent peroxidase activity. From our data we conclude that it is the physiological function of the peroxidase activity in PMN to determine an efficiently regulated threshold level of hydroperoxide products, below which no activation of 5-lipoxygenase or 15-lipoxygenase can occur.Activation of human PMN in vivo may be caused by various stimuli, for example bacterial peptides, complement factors or immunoglobulin-coated particles. Activation comprises several events including chemotaxis, phagocytosis, adherence to the endothelium, degranulation, the release of superoxide anions and the generation of lipid mediators like platelet-activating factor and leukotrienes. While these events are regarded as beneficial in the host defence against bacterial infections, they may become harmful under pathophysiological conditions, such as shock, asthma or reperfusion injury Leukotrienes were proposed to be important mediators in inflammatory situations [2] and in the biosynthesis of LTB4 which in view of its enhancer effect as a potent chemoattractant 131, as a stimulator of aggregation 141, degranulation[5] and, to a lesser extent, of NADPH oxidoreductase, [6] seems to be an appropriate target for anti-inflammatory drugs.[31. The regulation of these steps is not yet fully understood. In vitro studies showed that both stimulation of the cells with soluble receptor agonists [12, 131 or with exogenous arachidonic acid [12-151 yielded only small amounts of 5-lipoxygenase-derived metabolites compared to the stimulation with Ca2+ ionophores. The latter seem to fulfill two prerequisites for stimulating 5-lipoxygenase activity: the release of sufficiently high amounts of intracellular arachidonate through activation of the Ca2 +-depen...
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