Abstract
We recently demonstrated that the arachidonate metabolite 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) is converted by a highly specific dehydrogenase in human neutrophils to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), which is a potent stimulator of these cells. The objective of this study was to determine whether 5-oxo-ETE is also formed by monocytes and lymphocytes. Human monocytes (74 +/- 2% pure) and lymphocytes (86 +/- 1% pure) were prepared by successive centrifugations of leukocytes over Ficoll-Paque and Percoll. Both cell types converted 5-HETE to a single major product, which was identified as 5-oxo-ETE. The formation of 5-oxo-ETE was stimulated about twofold by phorbol myristate acetate (PMA; 30 nM). Dehydrogenase activity in monocyte fractions did not appear to be due to platelet contamination, since depletion of platelets did not reduce enzyme activity. The dehydrogenase was localized in membrane fractions from monocytes and required NADP+ as a cofactor. It was specific for eicosanoids containing a 5S-hydroxyl group followed by a 6-trans double bond. We also investigated the formation of 5-oxo-ETE from endogenous arachidonic acid by monocytes. 5-Oxo-ETE, 5-HETE, and leukotriene B4 (LTB4) were present in comparable amounts after incubation of these cells with A23187. PMA (EC50 approximately 4 nM) stimulated the formation of 5-oxo-ETE and 5-HETE and, to a lesser extent, LTB4. Although monocytes released considerably less 5-HETE and LTB4 than neutrophils, they released comparable amounts of 5-oxo-ETE. Unlike neutrophils, monocytes did not convert any of these substances to detectable amounts of omega-oxidation products. Although lymphocytes were capable of converting 5-HETE to 5-oxo-ETE, they released little or no 5-lipoxygenase products in response to A23187. We conclude that monocytes have a high capacity to synthesize 5-oxo-ETE and that its formation is stimulated by activation of protein kinase C.
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