Abstract
Catechins and procyanidins are major polyphenols in plant-derived foods. Despite intensive studies in recent years, neither their biochemical nor their toxicological properties have been clarified sufficiently. This study aimed to compare the methylation of catechins and procyanidins by the enzyme catechol-O-methyltransferase (COMT) in vitro. We conducted incubations with rat liver cytosol and human placental cytosol including S-adenosyl-l-methionine. The set of substrates comprised the catechins (−)-epicatechin (EC) and (+)-catechin (CAT), the procyanidin dimers B1, B2, B3, B4, B5, and B7 as well as procyanidin trimer C1. After extraction, metabolites were analyzed by means of liquid chromatography-electrospray ionization-mass spectrometry and liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry. EC and CAT were converted to two monomethylated metabolites each by human and rat COMT, with the 3′-O-methyl derivatives being consistently the main metabolites. Furthermore, the flavanyl units of procyanidins were methylated consecutively, leading to monomethylated and dimethylated dimeric metabolites as well as monomethylated, dimethylated, and trimethylated C1 metabolites. The methylation status of each flavanyl unit was determined by means of mass spectrometric quinone-methide fragmentation patterns. In addition, molecular modeling studies were performed with the aim to predict the preferred site of methylation and to verify the experimental data. In conclusion, our results indicate that the degree and position of methylation depend clearly on the three-dimensional structure of the entire substrate molecule.
Footnotes
This work was supported by the German Federal Ministry of Education and Research (BMBF) within the scope of the joint project “Dietary Procyanidins” [Grant 0313828A].
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- COMT
- catechol-O-methyltransferase
- EC
- (−)-epicatechin
- CAT
- (+)-catechin
- 3′-MeCAT
- 3′-O-methyl-(+)-catechin
- 3′-MeEC
- 3′-O-methyl-(−)-epicatechin
- 4′-MeCAT
- 4′-O-methyl-(+)-catechin
- 4′-MeEC
- 4′-O-methyl-(−)-epicatechin
- LC/MS
- liquid chromatography/mass spectrometry
- APCI
- atmospheric pressure chemical ionization
- DHBA
- 3,4-dihydroxybenzoic acid
- ESI
- electrospray ionization
- SAM
- S-adenosyl-l-methionine.
- Received July 20, 2011.
- Accepted November 9, 2011.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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