title: Detoxication of structurally diverse polycyclic aromatic hydrocarbon (PAH) o-quinones by human recombinant catechol-O-methyltransferase (COMT) via O-methylation of PAH catechols.
abstract: Polycyclic aromatic hydrocarbons (PAH) are environmental and tobacco carcinogens. Metabolic activation of intermediate PAH trans-dihydrodiols by aldo-keto reductases (AKRs) leads to the formation of electrophilic and redox-active o-quinones. We investigated whether O-methylation by human recombinant soluble catechol-O-methyltransferase (S-COMT) is a feasible detoxication step for a panel of structurally diverse PAH-catechols produced during the redox-cycling process. Classes of PAH non-K-region o-quinones (bay region, methylated bay region, and fjord region o-quinones) produced by AKRs were employed in the studies. PAH o-quinones were reduced to the corresponding catechols by dithiothreitol under anaerobic conditions and then further O-methylated by human S-COMT in the presence of S-[³H]adenosyl-l-methionine as a methyl group donor. The formation of the O-methylated catechols was detected by HPLC-UV coupled with in-line radiometric detection, and unlabeled products were also characterized by LC-MS/MS. Human S-COMT was able to catalyze O-methylation of all of the PAH-catechols and generated two isomeric metabolites in different proportions. LC-MS/MS showed that each isomer was a mono-O-methylated metabolite. ¹H NMR was used to assign the predominant positional isomer of benzo[a]pyrene-7,8-catechol as the O-8-monomethylated catechol. The catalytic efficiency (k(cat)/K(m)) varied among different classes of PAH-catechols by 500-fold. The ability of S-COMT to produce two isomeric products from PAH-catechols was rationalized using the crystal structure of the enzyme. We provide evidence that O-8-monomethylated benzo[a]pyrene-7,8-catechol is formed in three different human lung cell lines. It is concluded that human S-COMT may play a critical role in the detoxication of PAH o-quinones generated by AKRs.
authors.affiliation: Centers of Excellence in Environmental Toxicology and Cancer Pharmacology, Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Jin
authors.forename: Mo
authors.initials: M
authors.lastname: Chen
authors.forename: Meng
authors.initials: M
authors.lastname: Huang
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Harvey
authors.forename: Ian A
authors.initials: IA
authors.lastname: Blair
authors.forename: Trevor M
authors.initials: TM
authors.lastname: Penning
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002394:Catechol O-Methyltransferase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002396:Catechols / Q000737:chemistry*; D045744:Cell Line, Tumor; D018360:Crystallography, X-Ray; D006801:Humans; D008658:Inactivation, Metabolic; D007700:Kinetics; D008168:Lung / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D008745:Methylation; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism*; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics*; D011809:Quinones / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013552:Swine
chemical_list: D002396:Catechols; D011084:Polycyclic Aromatic Hydrocarbons; D011809:Quinones; D011994:Recombinant Proteins; D002394:Catechol O-Methyltransferase; D010100:Oxygen