title: Study of the genetic determinants of UGT1A1 inducibility by phenobarbital in cultured human hepatocytes.
abstract: UGT1A1 is induced by phenobarbital. We investigated whether three common UGT1A1 variants are associated with the variability in UGT1A1 inducibility. Human hepatocytes were incubated with 2 mM phenobarbital for 2 and 6 days followed by 5 microM SN-38 (1 h), a UGT1A1 probe. SN-38 glucuronidation in the cell media was measured by high-performance liquid chromatography. Three UGT1A1 promoter variants [-53(TA)(6>7), -3156G > A and -3279T > G] were genotyped. Significant induction of UGT1A1 catalytic activity was observed in 82% and 100% of the cultures treated with phenobarbital for 2 days (median fold-induction = 1.6, range 1.3-2.8; n = 28) and 6 days (median fold-induction = 2.8, range 1.6-6.4; n = 16), respectively. After 2 days of treatment, a negative correlation was observed between the UGT1A1 basal activities and the fold-induction (Spearman r = -0.52, P < 0.005). By contrast, the UGT1A1 activities in the basal and induced states were highly correlated (Spearman r = 0.95, P < 0.0001). Similar results were observed after 6 days of treatment. The allele frequencies were not significantly different between induced (n = 22) and non-induced preparations (n = 6) (P > 0.05). The fold-induction was not associated with any variants (P > 0.05). The basal and induced activities were correlated with -53(TA)(6>7) (and with -3156G > A due to almost complete linkage with the -53 indel) (P = 0.001). No association was found with the -3279T > G single nucleotide polymorphism (P > 0.05). The indel at -53 affects the basal phenotype and appears to limit the hepatocyte capability of maximal induction after phenobarbital. However, variants at -53, -3156 and -3279 are not associated with variability in UGT1A1 inducibility.
authors.affiliation: Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Ramírez
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Komoroski
authors.forename: Snezana
authors.initials: S
authors.lastname: Mirkov
authors.forename: Andrea Yoder
authors.initials: AY
authors.lastname: Graber
authors.forename: Donna Lee
authors.initials: DL
authors.lastname: Fackenthal
authors.forename: Erin G
authors.initials: EG
authors.lastname: Schuetz
authors.forename: Soma
authors.initials: S
authors.lastname: Das
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Ratain
authors.forename: Federico
authors.initials: F
authors.lastname: Innocenti
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Strom
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D005260:Female; D014453:Glucuronosyltransferase / Q000235:genetics*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007223:Infant; D000077146:Irinotecan; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010597:Pharmacogenetics / Q000379:methods*; D010634:Phenobarbital / Q000494:pharmacology*; D020641:Polymorphism, Single Nucleotide; D000099148:UGT1A1 Enzyme
chemical_list: D002166:Camptothecin; D014453:Glucuronosyltransferase; D000077146:Irinotecan; D010634:Phenobarbital; D000099148:UGT1A1 Enzyme