Linoleic Acid Diols Are Novel Substrates for Human UDP-Glucuronosyltransferases

Linoleic acid diol glucuronides have been isolated previously from urine of patients suffering from generalized peroxisomal disorders. Glucuronidation of linoleic acid and linoleic acid diols by human liver microsomes was studied to investigate the role of glucuronide conjugation in the metabolism of linoleic acid diols. Glucuronide products were isolated and analyzed by TLC and HPLC-MS. HPLC-MS showed ions with (m/z) corresponding to singly glucuronidated linoleic acid diols while TLC revealed that the glucuronidation was at a hydroxyl position. Kinetic analysis gave apparent Km values in the range of 50–200 μM and Vmax rates from 5 to 12 nmol/mg × min. These rates are substantially higher than activities seen for most endogenous hydroxylated substrates. Assays using each of the four individually purified linoleic acid diol enantiomers suggest that glucuronidation occurs at only one of the two hydroxyl groups of each enantiomer. These results show for the first time that hydroxylated fatty acids are actively glucuronidated by human liver microsomes and suggest that glucuronidation may play a significant role in the biotransformation of linoleic acid diols in humans.