CommentaryIn vitro–in vivo correlation for drugs and other compounds eliminated by glucuronidation in humans: Pitfalls and promises
Section snippets
The reaction phenotyping of glucuronidated compounds
Multiple approaches have been adopted for the reaction phenotyping of CYP substrates, most frequently using human liver microsomes as the enzyme source, including [1], [2], [3]: (i) impairment of metabolism by enzyme-selective chemical and antibody inhibitors; (ii) competitive inhibition of the metabolism of enzyme-selective substrates by the compound, with Km matching Ki; (iii) a significant correlation between rates of metabolism of the compound and immunoreactive enzyme contents or
The quantitative prediction of drug glucuronidation kinetics in vivo
Two approaches may be adopted for the calculation of in vitro CLint, which may subsequently be extrapolated to in vivo CLH and EH[4]. Measurement of product formation (e.g. a drug glucuronide) under initial rate conditions over an appropriate substrate concentration range allows calculation of Km and Vmax for that pathway (in the absence of atypical kinetics; see below), and then CLint (as Vmax/Km). The second approach measures the rate of substrate depletion with time (at a low substrate
Summary and conclusions
The reaction phenotyping of drugs and other chemicals metabolised by glucuronidation is currently feasible, but generally requires the application of multiple experimental approaches. Even so, problems with the interpretation of data may arise due to the dependence of UGT activity in vitro on incubation conditions, enzyme source and the occurrence of atypical glucuronidation kinetics, emphasising the need for careful experimental design. However, UGT reaction phenotyping with human liver
References (77)
- et al.
In vitro approaches for the prediction of human drug metabolism
Annu Rep Med Chem
(1994) - et al.
In vitro approaches can predict human drug metabolism
Trends Pharmacol Sci
(1993) - et al.
Prediction of in vivo drug metabolism in the human liver from in vitro metabolism data
Pharmacol Ther
(1997) - et al.
In vitro approaches to predicting drug interactions in vivo
Biochem Pharmacol
(1998) - et al.
Bilirubin UDP-glucuronosyltransferase-1. Is the only relevant bilirubin glucuronidating isoform in man
J Biol Chem
(1994) - et al.
Effect of fatty acid deficiency on microsomal membrane fluidity and cooperativity of the UDP-glucuronosyltransferase
Biochim Biophys Acta
(1983) - et al.
UDP-glucuronosyltransferase, the role of the amino terminus in dimerization
J Biol Chem
(1997) - et al.
Evidence for phosphorylation requirement for human bilirubin UDP-glucuronosyltransferase (UGT1A1) activity
Biochem Biophys Res Commun
(2003) The effect of N-linked glycosylation on the substrate preferences of UDP glucuronosyltransferases
Biochem Biophys Res Commun
(1990)- et al.
Towards integrated ADME prediction: past, present and future directions for modelling metabolism by UDP-glucuronosyltransferases
J Mol Graph Model
(2004)