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

Abstract

The effects of the stable analogue of TxA2, U46619, on polymorphonuclear leukocyte (PMN) function were investigated. U46619, at micromolar concentrations, inhibited fMLP-stimulated aggregation, beta-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, beta-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 beta-glucuronidase release from stimulated PMN. Prostaglandin endoperoxides, produced by cells participating in inflammatory reactions, might therefore play a role in modulating PMN activities.

11-Dehydro-thromboxane B2, a Stable Thromboxane Metabolite, Is a Full Agonist of Chemoattractant Receptor-homologous Molecule Expressed on TH2 Cells (CRTH2) in Human Eosinophils and Basophils

“…It has been proposed that TXA 2 modulates leukocyte function, based on observations of TXA 2 analogues enhancing the endothelial expression of adhesion molecules and chemokines (38,39), enhancing neutrophil migration (40), inhibiting neutrophil aggregation, ␤-glucuronidase release and superoxide production (41), and stimulating cytokine release from monocytes (42). In this report, we show that 11-dehydro-TXB 2 , a stable product of thromboxane metabolism, is an effective CRTH2 activator in human eosinophils and basophils, whereas the parent metabolite TXB 2 is inactive.…”

Prostaglandins potentiate U-46619-induced pulmonary microvascular dysfunction

“…One may postulate that in the present study perfusion of the lung with U-46619 [and perhaps PGF 2␣ and PGI 2 (13,17,33,40)] may have acted on sequestered neutrophils, resulting in the generation of a respiratory burst and, ultimately, a neutrophil-mediated microvascular dysfunction (18,26). Other more recent studies have suggested that U-46619, as well as PGE 2 , PGF 2␣ , and PGI 2 , inhibits neutrophil activation, at least as manifested by increases in intracellular free calcium, leukoaggregation, and the release of superoxide radical, ␤-glucuronidase, and leukotriene B 4 (22,32,36). These more recent observations would appear to be inconsistent with the notion that U-46619 or PGE 2 , PGF 2␣ , or PGI 2 increased pulmonary microvascular permeability by activating on neutrophils sequestered within the lung.…”

“…U-46619 (9,11-dideoxy-11␣,9␣-epoxymethanoprostaglandin F 2␣ ) is a thromboxane-endoperoxide receptor agonist that has been commonly used to mimic the physiological effects of TxA 2 (4,22,23,25). The concentration of U-46619 was chosen based on a dose-response curve relating increasing concentrations of U-46619 to increases in K f in this experimental system (data not shown).…”