Abstract

Leukotriene B₄ (LTB₄) is a potent lipid mediator of the inflammatory response whose biological half-life is believed to be mediated principally by metabolism to inactive forms either in the tissue of origin or in the liver. Pathways of metabolic degradation of LTB₄ along with structural identification of metabolites have been elucidated previously in isolated rat liver cells, human keratinocytes, human polymorphonuclear leukocytes, and cultured HepG2 cells. Research advances in human liver transplantation and preservation have made isolated human hepatocytes available for studying the metabolism of LTB₄ in vitro. LTB₄ was added to plated human hepatocytes from three different subjects for 24-h periods whereupon the substrate was analyzed by high-performance liquid chromatography coupled with scintillation counting, UV spectroscopy, and negative ion electrospray ionization tandem mass spectrometry. Each set of hepatocytes yielded a different distribution of metabolites, but several metabolites appeared in all three sets of cells. These central metabolites included the previously identified 20-carboxy-LTB₄ and 18-carboxy-LTB₄, implicating the presence in the liver of specific P-450-mediated ω-oxidation as well as the enzymes involved in β-oxidation from the ω-terminus. Each set of hepatocytes produced the metabolite 10,11-dihydro-20-COOH-LTB₄, a product of the 12-hydroxyeicosanoid dehydrogenase/Δ¹⁰reductase pathway. Glucuronides of LTB₄ and several metabolites were found, which represents the first description of glucuronidation as a pathway of LTB₄ metabolism. Finally, a series of novel metabolites were observed corresponding to β-oxidation from the carboxyl terminus of LTB₄.