title: Interception of benzo[a]pyrene-7,8-dione by UDP glucuronosyltransferases (UGTs) in human lung cells.
abstract: Polycyclic aromatic hydrocarbons (PAHs) are environmental and tobacco carcinogens. Proximate carcinogenic PAH trans-dihydrodiols are activated by human aldo-keto reductases (AKRs) to yield electrophilic and redox-active o-quinones. Interconversion among benzo[a]pyrene (B[a]P)-7,8-dione, a representative PAH o-quinone, and its corresponding catechol generates a futile redox-cycle with the concomitant production of reactive oxygen species (ROS). We investigated whether glucuronidation of B[a]P-7,8-catechol by human UDP glucuronosyltransferases (UGTs) could intercept the catechol in three different human lung cells. RT-PCR showed that UGT1A1, 1A3, and 2B7 were only expressed in human lung adenocarcinoma A549 cells. The corresponding recombinant UGTs were examined for their kinetic constants and product profile using B[a]P-7,8-catechol as a substrate. B[a]P-7,8-dione was reduced to B[a]P-7,8-catechol by dithiothreitol under anaerobic conditions and then further glucuronidated by the UGTs in the presence of uridine-5'-diphosphoglucuronic acid as a glucuronic acid group donor. UGT1A1 catalyzed the glucuronidation of B[a]P-7,8-catechol and generated two isomeric O-monoglucuronsyl-B[a]P-7,8-catechol products that were identified by RP-HPLC and by LC-MS/MS. By contrast, UGT1A3 and 2B7 catalyzed the formation of only one monoglucuronide, which was identical to that formed in A549 cells. The kinetic profiles of three UGTs followed Michaelis-Menten kinetics. On the basis of the expression levels of UGT1A3 and UGT2B7 and the observation that a single monoglucuronide was produced in A549 cells, we suggest that the major UGT isoforms in A549 cells that can intercept B[a]P-7,8-catechol are UGT1A3 and 2B7.
authors.affiliation: Center of Excellence in Environmental Toxicology and ‡Center for Cancer Pharmacology, Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6160, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Meng
authors.initials: M
authors.lastname: Huang
authors.forename: Ian A
authors.initials: IA
authors.lastname: Blair
authors.forename: Trevor M
authors.initials: TM
authors.lastname: Penning
mesh_terms: D001580:Benzopyrenes / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D002396:Catechols / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D004229:Dithiothreitol / Q000737:chemistry; D020719:Glucuronides / Q000737:chemistry / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008168:Lung / Q000201:enzymology; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D000099148:UGT1A1 Enzyme
chemical_list: D001580:Benzopyrenes; D002396:Catechols; D004229:Dithiothreitol; D020719:Glucuronides; D014453:Glucuronosyltransferase; D020033:Protein Isoforms; D011994:Recombinant Proteins; D000099148:UGT1A1 Enzyme; C000588520:benzo(a)pyrene-7,8-catechol; C076588:benzo(a)pyrene-7,8-dione
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