Metabolism and excretion of exogenous [H]-LTC4 in primates

Four novel ω- and β-oxidation (from the ω end) products of peptide leukotrienes, 20-hydroxy and 20-carboxy-LTE₄, 18-carboxy-19,20-dinor-LTE₄ and 16-carboxy-17, 18, 19, 20-tetranor-14, 15-dihydro-LTE₄ were prepared by total synthesis and used as standards for identification of biliary and urinary metabolites in the cynomolgus monkey. After intravenous administration 14, 15,-³H] leukotriene C₄ (10 μCi kg⁻¹ was partially metabolized in and rapidly cleared from the vascular circulation. This resulted, within 24 hours, in significant urinary excretion. (14.8 ± 2.1%, n = 4), consisting largely of material more polar than LET₄ (61% of urinary excretion) as shown by reverse phase HPLC. The polar fraction demonstrated two predominant metabolites which coeluted in several HPLC solvent systems with synthetic 16-carboxytetranordihydro-LTE₄ (major component) and 18-carboxydinor-LTE₄ (minor component). Characterization of the major polar metabolites as 16-carboxytetranordihydro-LTE₄ was substantiated by conversion to its N-acetylated derivative. The absence of the 14, 15 double bond was confirmed by product analysis of oxidative ozonolysis. In a single animal, the bile duct was cannulated, with significant biliary excretion of radioactivity demonstrated over 4 hours (58.6% recovery). The predominant polar biliary metabolites were also identified as the 18-carboxydinor and 16-carboxytetranordihydro derivatives of LTE₄ mentioned above. These data suggest that β-oxidation products generated from the ω-carboxyl end of the 20-carboxyl-LTE₄ are important products of ³H] LTC₄ metabolism in the monkey. Quantitation of these urinary metabolites may be an important index of leukotriene production.