Modulation of alveolar macrophage-derived 5-lipoxygenase products by the sulfhydryl reactant, N-ethylmaleimide

Abstract

The sulfhydryl reactant N-ethylmaleimide (NEM) stimulates the release and cyclooxygenase metabolism of arachidonic acid in rat alveolar macrophages. Because both 5-lipoxygenation and leukotriene (LT) C4 synthesis represent sulfhydryl-dependent steps in the 5-lipoxygenase pathway, we examined the effect of NEM on 5-lipoxygenase, as well as cyclooxygenase, metabolism in resting and agonist-stimulated cells by reverse-phase high performance liquid chromatography and radioimmunoassay. NEM at 5-10 microM stimulated the synthesis of thromboxane, but not prostaglandin E2 or the 5-lipoxygenase products LTC4, LTB4, or 5-hydroxyeicosatetraenoic acid from endogenously released arachidonate. In the presence of exogenous fatty acid, however, NEM stimulated the synthesis of large quantities of LTB4. The effect of NEM on arachidonate metabolism stimulated by the calcium ionophore A23187 and the particulate zymosan was also investigated. NEM augmented arachidonate release and thromboxane synthesis stimulated by A23187 but inhibited A23187-induced LTC4 synthesis with an IC50 of approximately 4.3 microM. This inhibitory effect closely paralleled the ability of NEM to deplete intracellular glutathione (IC50 approximately 4.3 microM). Preincubation with the intracellular cysteine delivery agent L-2-oxothiazolidine-4-carboxylate augmented intracellular glutathione concentration and A23187-stimulated LTC4 synthesis and attenuated the capacity of NEM to deplete glutathione and inhibit LTC4 synthesis. While LTB4 and 5-hydroxyeicosatetraenoic synthesis were unaffected at these low NEM concentrations, LTB4 synthesis was inhibited at high concentrations (IC50 approximately 210 microM). Zymosan-induced eicosanoid synthesis was modulated by NEM in a similar fashion. Thus, NEM is an agonist of arachidonate metabolism with the capacity to modulate the spectrum of macrophage-derived eicosanoids by virtue of specific biochemical interactions with substrates and enzymes of the 5-lipoxygenase pathway.