Carcinogenesis Advance Access originally published online on July 17, 2007
Carcinogenesis 2007 28(11):2412-2418; doi:10.1093/carcin/bgm164
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Glucuronidation of PhIP and N-OH-PhIP by UDP-glucuronosyltransferase 1A10
1 Cancer Prevention and Control Program
2 Chemical Carcinogenesis and Chemoprevention Program, Penn State Cancer Institute
3 Department of Pharmacology
4 Department of Public Health Sciences, Penn State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
* To whom correspondence should be addressed. Tel: +1 717 531 5734; Fax: +1 717 531 0480; Email: plazarus{at}psu.edu
The UDP-glucuronosyltransferase (UGT) 1A10 is an extra-hepatic enzyme that plays an important role in the glucuronidation of a variety of endogenous and exogenous substances and is expressed throughout the aerodigestive and digestive tracts. Two classes of carcinogens that target the colon, heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons, are known to be detoxified by the UGT family of enzymes. Recently, our laboratory demonstrated that UGT1A10 has considerably more activity against polycyclic aromatic hydrocarbons in vitro than any other UGT family member. In this study, we focused on the glucuronidation of the HCA, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and its bioactivated metabolite, N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP). We demonstrated that UGT1A10 exhibited a significantly higher glucuronidation rate against PhIP and N-OH-PhIP than any other UGT family member in vitro using whole-cell homogenates of HEK293 cells over-expressing individual UGTs. Kinetic analysis revealed a 9- and 22-fold higher level of activity for UGT1A10 homogenates as compared with the next most active UGT, UGT1A1, against N-OH-PhIP as determined by maximum rate/apparent Michaelis constant (Vmax/KM) at the N3 and N2 positions, respectively. The polymorphic UGT1A10139Lys variant exhibited a 2- to 16-fold decrease in glucuronidation activity against PhIP and N-OH-PhIP, as compared with the wild-type UGT1A10139Glu isoform. These data suggest that UGT1A10 is the most active UGT against PhIP and N-OH-PhIP and that UGT1A10 may play an important role in susceptibility to HCA-induced colon cancer.
Abbreviations: HCA, heterocyclic amine; HPLC, high-pressure liquid chromatography; KM, apparent Michaelis constant; N-OH-PhIP, N-hydroxy 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine; UGT, UDP-glucuronosyltransferase; Vmax, maximum rate
Received March 7, 2007; revised June 29, 2007; accepted July 6, 2007.
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