The endoperoxides/TxA2 analogue, U46619, inhibits human polymorphonuclear leukocyte function

The effects of the stable analogue of TxA₂, U46619, on polymorphonuclear leukocyte (PMN) function were investigated. U46619, at micromolar concentrations, inhibited fMLP-stimulated aggregation, β-glucuronidase release, and superoxide production. fMLP-induced LTB₄ synthesis was also inhibited. U46619 did not modify intracellular Ca²⁺ increase induced by fMLP in Fura-2-loaded PMN, suggesting that early events of cell activation were not involved. In fact, U46619 also inhibited aggregation, β-glucuronidase release, superoxide anion and LTB₄ production induced by the calcium ionophore A23187. By comparison with the specific 5-lipoxygenase inhibitor, L-663,536, which prevented LTB₄ synthesis without affecting degranulation, we excluded the impairment of PMN function by U46619 as a consequence of the reduction of this endogenous agonist. TLC separation of lipid extracts from [³H]-AA-loaded PMN, stimulated by A23187, showed significant reduction of the radioactivity associated with authentic free AA, suggesting that U46619 could interfere with mechanisms regulating AA release from membrane phospholipids. This suggestion is also supported by the observation that manoalide, a standard inhibitor of phospholipase A₂, similarly to U46619, inhibits β-glucuronidase release from stimulated PMN. Prostaglandin endoperoxides, produced by cells participating in inflammatory reactions, might therefore play a role in modulating PMN activities.