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 liver microsomes of several mammalian species including man, a gas chromatography method for the quantification of the corresponding glucuronides was developed. The variation coefficients for intra- and interassay repeatability were less than 3 and 7%, respectively. The rat liver UDP-glucuronosyl-transferase (UGT) presented similar Km and Vmax toward 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-methylcholanthrene. In contrast, the treatment of the rats clofibrate did not modify the activity. The induction was not stereoselective. The Gunn rats, which present a genetic defect in the bilirubin UGT isoforms, were able 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 rat. The lowest activities were observed in the man and the rabbit. In all species considered, except rabbit and guinea pig which glucuronidated the R isomer faster, the R and S enantiomers were glucuronidated to a similar extent. The glucuronidation activity toward compounds chemically related to 2-EHA increased as a function of molecular weight, but was not affected by the position of the methyl or the ethyl moiety on the hydrocarbon chain. A correlation between the glucuronidation rate of 2-EHA and analogs and the activity of PCoA oxidase was observed.

Cyclosporine determinations in heart and liver transplant recipients: comparison of HPLC and FPIA methods on whole blood and plasma.

One hundred and eighty five whole blood samples were analysed for cyclosporine levels by fluorescence polarization immunoassay (FPIA) and high performance liquid chromatography (HPLC). 123 came from 4 heart transplant recipients (mean age +/- SD: 47.50 +/- 20.56 years) and 62 from 4 liver transplant recipients (44.50 +/- 16.52 years). FPIA was done on plasma and whole blood in heart transplant recipients, on plasma in the liver recipients. HPLC was always done on whole blood. The results show a good correlation between FPIA on plasma (y) and HPLC (x) in liver recipients (n = 62, r = 0.935, y = 1.23x + 70 ng/ml), slightly worse between FPIA on plasma (y) and HPLC (x) in heart recipients (n = 64, r = 0.610, y = 0.78x + 189 ng/ml) and mediocre for FPIA on whole blood (y) and HPLC (x) in heart recipients (n = 123, r = 0.566, y = 1.35x + 594 ng/ml).