IN-VITRO GLUCURONIDATION OF PEROXISOMAL PROLIFERATORS - 2-ETHYLHEXANOIC ACID ENANTIOMERS AND THEIR STRUCTURAL ANALOGS

In order to investigate the glucuronidation of 2-ethylhexanoic acid (2 -EHA), a metabolite of the plasticizer di-(2-ethylhexyl) adipate, by l iver microsomes of several mammalian species including man, a gas chro matography method for the quantification of the corresponding glucuron ides was developed, The variation coefficients for intra- and interass ay repeatability were less than 3 and 7%, respectively. The rat liver UDP-glucuronosyl-transferase (UGT) presented similar K-m and V-max tow ard the two enantiomers. The glucuronidation of the racemate 2-EHA or its enantiomers was strongly increased up to six times by treatment of the rats with phenobarbital and, to a lesser extent, by 3-methylchola nthrene. In contrast, the treatment of the rats clofibrate did not mod ify the activity. The induction was not stereoselective. The Gunn rats , which present a genetic defect in the bilirubin UGT isoforms, were a ble to glucuronidate the drug as well as the congenic strain, Moreover , the UGT-2B1 isoform, stably expressed in V79 cells, glucuronidated 2 -EHA in an appreciable amount. Interspecies comparison indicated that the most active glucuronidation of 2-EHA occurred in the dog and the r at. The lowest activities were observed in the man and the rabbit. In all species considered, except rabbit and guinea pig which glucuronida ted the R isomer faster, the R and S enantiomers were glucuronidated t o a similar extent, The glucuronidation activity toward compounds chem ically related to 2-EHA increased as a function of molecular weight, b ut was not affected by the position of the methyl or the ethyl moiety on the hydrocarbon chain. A correlation between the glucuronidation ra te of 2-EHA and analogs and the activity of PCoA oxidase was observed. (C) 1995 Academic Press Inc.