title: Inter-individual variability in esterases in human liver.
abstract: Human liver has numerous hydrolytic enzymes involved in metabolism of endogenous and exogenous esters. Of these enzymes, carboxylesterases (EC 3.1.1.1) form an important group which hydrolyses many diverse ester substrates, including pro-ester drugs. Carboxylesterase activity was investigated in liver subcellular fractions from 22 individuals using the general carboxylesterase substrate phenylvalerate and the homologous series of esters methyl-, ethyl-, propyl-, butyl- and benzylparaben. The intra- and inter-individual variation in phenylvalerate and paraben metabolism was compared. Rates of hydrolysis were higher in microsomal fractions than cytosolic fractions for all compounds. The rate of paraben hydrolysis varied depending on the size of the paraben alcohol leaving group, showing a decrease with increasing leaving group size. Comparisons showed that individuals with high rates of hydrolysis towards methyl paraben also showed high rates of hydrolysis to the other parabens and phenylvalerate. Phenylvalerate as a non-specific carboxylesterase substrate was hydrolysed mainly by hCE1 in human livers and there was good correlation with small alcohol leaving group parabens, suggesting hCE1 involvement. Lower correlations with larger alcohol leaving group parabens are consistent with more hCE2 involvement.
authors.affiliation: Toxicology Unit, School of Clinical and Laboratory Sciences, 4th Floor, Devonshire Building, Devonshire Terrace, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4EA, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Jewell
authors.forename: Phillippa
authors.initials: P
authors.lastname: Bennett
authors.forename: Elaine
authors.initials: E
authors.lastname: Mutch
authors.forename: Chrisita
authors.initials: C
authors.lastname: Ackermann
authors.forename: Faith M
authors.initials: FM
authors.lastname: Williams
mesh_terms: D003600:Cytosol / Q000201:enzymology; D004950:Esterases / Q000032:analysis*; D004952:Esters / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D015203:Reproducibility of Results
chemical_list: D004952:Esters; D004950:Esterases