CALCIUM CALMODULIN-DEPENDENT CONVERSION OF 5-OXOEICOSANOIDS TO 6,7-DIHYDRO METABOLITES BY A CYTOSOLIC OLEFIN REDUCTASE IN HUMAN NEUTROPHILS/

We previously showed that 6-trans isomers of leukotriene B-4 but not l eukotriene B-4 itself are converted to dihydro metabolites by human ne utrophils. The first step in the formation of these metabolites is oxi dation of the 5-hydroxyl group by 5-hydroxyeicosanoid dehydrogenase, T he objective of the present investigation was to characterize the seco nd step in the formation of the dihydro metabolites, reduction of an o lefinic double bond. We found that the olefin reductase reduces the 6, 7-double bond of 8-oxoeicosanoids, is localized in the cytosolic fract ion of neutrophils, and requires NADPH as a cofactor. Neutrophil cytos ol converts a variety of both 5-oxo- and 15-oxoeicosanoids to dihydro products. However, conversion of 5-oxoeicosanoids to their 6,7-dihydro metabolites is inhibited by EGTA and a calmodulin antagonist and stim ulated by the addition of calcium and calmodulin, whereas the reductio n of 15-oxoeicosanoids to their 13,14-dihydro metabolites is slightly inhibited by calcium. Furthermore, eicosanoid Delta(6)- and Delta(13)- reductases could be separated by chromatography on DEAE-Sepharose. 5-O xo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is converted by the Del ta(6)-reductase to 6,7-dihydro-5-oxo-ETE, which is 1000 times less pot ent than 5-oxo-ETE in mobilizing calcium in neutrophils. We conclude t hat neutrophils contain both 5-oxo-eicosanoid Delta(6)-reductase and p rostaglandin Delta(13)-reductase, Metabolism of 5-oxo-ETE by the Delta (6)-reductase results in loss of its biological activity.