Stimulation of human neutrophils by 5-oxo-6,8,11,14-eicosatetraenoic acid by a mechanism independent of the leukotriene B4 receptor

Abstract

We recently identified a novel pathway for the metabolism of 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by human neutrophils, resulting in oxidation of the 5-hydroxyl group to give 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) (Powell, W. S., Gravelle, F., and Gravel, S. (1992) J. Biol. Chem. 267, 19233-19241). This pathway is quite specific for 5-HETE and other eicosanoids containing a 5(S)-hydroxyl group followed by a 6-trans double bond. In the present study we have shown that 5-oxo-ETE is very potent in raising cytosolic calcium levels in human neutrophils. This effect was reproducibly observed at concentrations as low as 0.3 nM, and the EC50 was found to be 2 nM. The mechanism of action of 5-oxo-ETE on neutrophils appeared to be distinct from that of leukotriene B4 (LTB4), since it was not blocked by the LTB4 antagonist LY255283 at a concentration which completely prevented the response to LTB4. As would be expected for a receptor-mediated mechanism, the response to 5-oxo-ETE was subject to homologous desensitization and was completely abolished by prior treatment of neutrophils with 5-oxo-ETE (100 nM) but was not affected by pretreatment of these cells with the same concentration of LTB4. 5-Oxo-15(S)-hydroxy-6,8,11,13- eicosatetraenoic acid (5-oxo-15-hydroxy-ETE), formed from 5(S),15(S)-dihydroxy-6,8,11,13- eicosatetraenoic acid (5,15-di-HETE) by the pathway responsible for the formation of 5-oxo-ETE, also raised cytosolic calcium levels in human neutrophils, with an EC50 of about 15 nM. 5-HETE, the precursor of 5-oxo-ETE, also had this effect but was about 100 times less potent than the latter substance. Desensitization experiments indicated that both 5-oxo-15-hydroxy-ETE and 5-HETE act by a mechanism similar to that of 5-oxo-ETE, but different from that of LTB4. In addition to their effects on calcium levels, both 5-oxo-ETE and 5-oxo-15-hydroxy-ETE had chemotactic effects on human neutrophils. Related eicosanoids, including 15-oxo-5,8,11,13-eicosatetraenoic acid, 5,15-diHETE, and 5(S)-hydroxy-15-oxo-6,8,11,13-eicosatetraenoic acid were much less potent, as both chemotactic and calcium-mobilizing agents. These results suggest that neutrophils possess a specific recognition mechanism for 5-oxo-ETE, which may be an important regulator of the activity of neutrophils, especially if they become desensitized to LTB4.