Metabolism of cysteinyl leukotrienes in monkey and man

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Abstract
The proinflammatory cysteinyl leukotrienes are inactivated in primates by (a) intravascular degradation, (b) hepatic and renal uptake from the blood circulation, (c) intracellular metabolism of leukotriene E4 (LTE4), and (d) biliary and renal excretion of LTC4 degradation products. We have analyzed cysteinyl leukotriene metabolites excreted into bile and urine of the monkey Macaca fascicularis and of man. In both species, hepatobiliary leukotriene elimination predominated over renal excretion. In a representative healthy human subject at least 25% of the administered radioactivity were recovered from bile and 20% from urine within 24 h. In monkey and man intravenous administration of 14,15‐3H2‐labeled LTC4 resulted in the biliary and urinary excretion of labeled LTE4, ω‐hydroxy‐LTE4, ω‐carboxy‐LTE4, ω‐carboxy‐tetranor‐ dihydro‐LTE4, and ω‐carboxy‐tetranor‐dihydro‐LTE4. Small amounts of N‐acetyl‐LTE4 were detected in human urine only. Oxidative metabolism of LTE4 proceeded more rapidly in the monkey resulting in the formation of higher relative amounts of ω‐oxidized leukotrienes in this species as compared to man. [3H]H2O amounted to less than 2% of the administered dose in monkey and human bile and urine samples. Incubation of isolated human hepatocytes with [3H2]LTC4, [3H2]LTE4, and [3H2]LTD4 showed that only [3H2]LTE4 underwent intracellular oxidative metabolism resulting in the formation of ω‐ and β‐oxidation products. N‐Acetylated LTE4 derivatives were not detected as products formed by human hepatocytes. By a combination of reversed‐phase high‐performance liquid chromatography and radioimmunoassay, endogenous LTE4 and N‐acetyl‐LTE4 were detected in human urine in concentrations of 220 ± 40 and 24 ± 3 pM, corresponding to 12 ± 1 and 1.5 ± 0.2 nmol/mol creatinine, respectively (mean ± SEM; n= 10). Endogenous LTD4 and LTE4 were detected in human bile (n= 3) in concentrations between 0.2–0.9 nM. Our results demonstrate that LTD4 and LTE4 are major LTC4 metabolites in human bile and/or urine and may serve as index metabolites for the measurement of endogenously generated cysteinyl leukotrienes. Moreover, ω‐oxidation and subsequent β‐oxidation from the ω‐end contribute to the metabolic degradation of LTE4 not only in monkey but also in man.

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