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The endoperoxides/TxA2 analogue, U46619, inhibits human polymorphonuclear leukocyte function
S Rotondo1, A Celardo, V Evangelista
1Istituto di Ricerche Farmacologiche Mario Negri, G. Bizzozero Laboratory of Platelet and Leukocyte Pharmacology, Santa Maria Imbaro, Italy.
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.
Insights
Thromboxane A2 analogue U46619 inhibits polymorphonuclear leukocyte (PMN) functions like aggregation and enzyme release. This suggests prostaglandin endoperoxides modulate inflammatory cell activities.
Area of Science:
- Immunology
- Inflammation Research
- Cellular Biology
Background:
- Polymorphonuclear leukocytes (PMNs) are key immune cells involved in inflammatory responses.
- Thromboxane A2 (TxA2) is a potent mediator of inflammation and platelet aggregation.
- Understanding how TxA2 analogues affect PMN function is crucial for inflammatory disease research.
Purpose of the Study:
- To investigate the effects of the stable TxA2 analogue, U46619, on various functions of human polymorphonuclear leukocytes (PMNs).
- To elucidate the specific mechanisms by which U46619 modulates PMN activation and mediator release.
Main Methods:
- PMN aggregation, beta-glucuronidase release, and superoxide production were measured following stimulation with formyl-methionyl-leucyl-phenylalanine (fMLP) or calcium ionophore A23187.
- Intracellular calcium ([Ca2+]) levels were monitored using Fura-2.
- Leukotriene B4 (LTB4) synthesis and arachidonic acid (AA) release were analyzed.
- Comparison with a 5-lipoxygenase inhibitor (L-663,536) and a phospholipase A2 inhibitor (manoalide) was performed.
Main Results:
- U46619 inhibited fMLP-stimulated PMN aggregation, beta-glucuronidase release, superoxide production, and LTB4 synthesis.
- U46619 did not affect fMLP-induced intracellular calcium increase.
- U46619 inhibited aggregation, beta-glucuronidase release, superoxide anion, and LTB4 production induced by A23187.
- U46619 reduced the release of free arachidonic acid from membrane phospholipids.
- U46619's effect on beta-glucuronidase release was similar to that of manoalide.
Conclusions:
- U46619 inhibits PMN activation downstream of initial calcium signaling.
- The inhibitory effects of U46619 are likely due to interference with arachidonic acid release from membrane phospholipids, potentially via phospholipase A2.
- Prostaglandin endoperoxides may play a significant role in modulating PMN activities during inflammation.