METABOLISM OF 6-TRANS-ISOMERS OF LEUKOTRIENE B-4 IN CULTURED HEPATOMA-CELLS AND IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES - IDENTIFICATION OF A DELTA(6)-REDUCTASE METABOLIC PATHWAY

The intermediate metabolic events which degrade hydroxy polyunsaturated fatty acids is largely unknown. Such molecules are common products of lipid peroxidation and lipoxygenase catalyzed oxidation of arachidonic acid, Metabolism of two 5,12-dihydroxyeicosatetraenoic acids, 6-trans-LTB(4) (leukotriene B-4), and 6-trans-12-epi-LTB(4) was studied in HepG2 cells (a human-derived hepatoma cell line). Extensive metabolism was observed with a major metabolite identified as 4-hydroxy-6-dodecenoic acid for both epimers. Incubation of 6-trans-LTB(4) epimers at shorter times revealed the formation of intermediate metabolites, including 6-hydroxy-4,8-tetradecadienoic acid and 8-hydroxy-4,6,10-hexadecatrienoic acid suggesting beta-oxidation as the major pathway leading to the formation of the common terminal metabolite. Two additional metabolites were structurally elucidated as 5-oxo-6,7-dihydro-LTB(4) and 6,7-dihydro-LTB(4) which have not been previously described. Formation of 5-oxo-6,7-dihydro-LTB(4) and 6,7-dihydro-LTB(4) were also observed during metabolism of 6-trans-12-epi-LTB(4) in human polymorphonuclear leukocytes. Of particular interest is the metabolism of these compounds by beta-oxidation from the carboxyl terminus, a process which is not observed with leukotriene B-4 or leukotriene C-4. Identification of these metabolites suggested the operation of the 5-hydroxyeicosanoid dehydrogenase pathway followed by a Delta(6)-reductase metabolic pathway which has not been previously described, This pathway of beta-oxidation may limit the activity of various 5,12-diHETEs including nonenzymatic hydrolysis products of LTA(4) and also the recently described B-4-isoleukotrienes.