Human bilirubin UDP-glucuronosyltransferase catalyzes the glucuronidation of ethinylestradiol

T. Ebner, R. P. Remmel, B. Burchell

Research output: Contribution to journalArticlepeer-review

119 Scopus citations


The synthetic estrogen ethinylestradiol is extensively eliminated as glucuronide metabolites in humans, but the UDP-glucuronosyltransferases (UGTs) catalyzing this reaction have not been identified. Therefore, ethinylestradiol was tested as a substrate for cloned human UGTs stably expressed in V79 cell lines. Two cloned expressed human enzymes, a bilirubin UGT and a phenol UGT, were observed to catalyze the glucuronidation of ethinylestradiol. High performance liquid chromatographic analysis of the products formed revealed that the expressed bilirubin UGT specifically produced ethinylestradiol-3-glucuronide. In human liver microsomes the ratio of 3-glucuronide/17-glucuronide was 97:3. Subsequent study of the cloned expressed enzymes and human liver microsomes from Crigler-Najjar patients by kinetic analysis and by substrate inhibition strongly indicated that a human liver bilirubin UGT was largely responsible for glucuronidation of ethinylestradiol. These results may provide an explanation for jaundice caused by ethinylestradiol in certain susceptible individuals.

Original languageEnglish (US)
Pages (from-to)649-654
Number of pages6
JournalMolecular Pharmacology
Issue number4
StatePublished - 1993


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