Metabolic transformations of leukotriene B-4 in primary cultures of human hepatocytes

Leukotriene B-4 (LTB4) is a potent lipid mediator of the inflammatory respo nse whose biological half-life is believed to be mediated principally by me tabolism to inactive forms either in the tissue of origin or in the liver. Pathways of metabolic degradation of LTB4 along with structural identificat ion of metabolites have been elucidated previously in isolated rat liver ce lls, human keratinocytes, human polymorphonuclear leukocytes, and cultured HepG2 cells. Research advances in human liver transplantation and preservat ion have made isolated human hepatocytes available for studying the metabol ism of LTB4 in vitro. LTB4 was added to plated human hepatocytes from three different subjects for 24-h periods whereupon the substrate was analyzed b y high-performance liquid chromatography coupled with scintillation countin g, UV spectroscopy, and negative ion electrospray ionization tandem mass sp ectrometry. Each set of hepatocytes yielded a different distribution of met abolites, but several metabolites appeared in all three sets of cells. Thes e central metabolites included the previously identified 20-carboxy-LTB4 an d 18-carboxy-LTB4, implicating the presence in the liver of specific P-450- mediated omega-oxidation as well as the enzymes involved in beta-oxidation from the omega-terminus. Each set of hepatocytes produced the metabolite 10 ,11-dihydro-20-COOH-LTB4, a product of the 12-hydroxyeicosanoid dehydrogena se/Delta(10) reductase pathway. Glucuronides of LTB4 and several metabolite s were found, which represents the first description of glucuronidation as a pathway of LTB4 metabolism. Finally, a series of novel metabolites were o bserved corresponding to beta-oxidation from the carboxyl terminus of LTB4.