title: Inhibition of human liver catechol-O-methyltransferase by tea catechins and their metabolites: structure-activity relationship and molecular-modeling studies.
abstract: (-)-Epigallocatechin-3-gallate (EGCG) is the major polyphenol present in green tea. We previously demonstrated that EGCG was both a substrate and potent inhibitor of human liver cytosolic catechol-O-methyltransferease (COMT). We now report the structure-activity relationship for the inhibition of COMT-catalyzed O-methylation of catecholestrogens in human liver cytosol by tea catechins and some of their metabolites. The most potent inhibitors were catechins with a galloyl-type D-ring, including EGCG (IC(50)=0.07 microM), 4''-O-methyl-EGCG (IC(50)=0.10 microM), 4',4''-di-O-methyl-EGCG (4',4''-DiMeEGCG) (IC(50)=0.15 microM), and (-)-epicatechin-3-gallate (ECG) (IC(50)=0.20 microM). Catechins without the D-ring showed two to three orders of magnitude less inhibitory potency. Enzyme kinetic analyses revealed that EGCG behaved as a mixed inhibitor, whereas 4',4''-di-O-methyl-EGCG exhibited competitive kinetics for the S-adenosylmethionine (SAM), and noncompetitive kinetics for the catechol binding site. These compounds may represent a new type of COMT inhibitor. In silico molecular-modeling studies using a homology model of human COMT were conducted to aid in the understanding the catalytic and inhibitory mechanisms. Either D-ring or B-ring of EGCG could be accommodated to the substrate binding pocket of human COMT. However, the close proximity (2.6A) of 4''-OH to the critical residue Lys144, the higher acidity of the hydroxyl groups of the D-ring, and the hydrophobic interactions between the D-ring and residues in the binding pocket greatly facilitated the interaction of the D-ring with the enzyme, and resulted in increased inhibitory potency. These results provide mechanistic insight into the inhibition of COMT by commonly consumed tea catechins.
authors.affiliation: Department of Chemical Biology, Ernest Mario School of Pharmacy, Rutgers University, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Dapeng
authors.initials: D
authors.lastname: Chen
authors.forename: Ching Y
authors.initials: CY
authors.lastname: Wang
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Lambert
authors.forename: Ni
authors.initials: N
authors.lastname: Ai
authors.forename: William J
authors.initials: WJ
authors.lastname: Welsh
authors.forename: Chung S
authors.initials: CS
authors.lastname: Yang
mesh_terms: D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002394:Catechol O-Methyltransferase / Q000737:chemistry; D065098:Catechol O-Methyltransferase Inhibitors; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D013662:Tea
chemical_list: D065098:Catechol O-Methyltransferase Inhibitors; D013662:Tea; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate; D002394:Catechol O-Methyltransferase; C057580:gallocatechol