Methylation of Catechins and Procyanidins by Rat and Human Catechol-O-Methyltransferase: Metabolite Profiling and Molecular Modeling Studies

Abstract

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 ionizationmass 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.

Flavan‐3‐ol/Procyanidin Metabolomics in Rat Urine Using HPLC‐Quadrupole TOF/MS

“…However, few reports are available regarding PC conjugates. Recently, PC flavanyl units were reported as being methylated consecutively, together with (epi)catechin, leading to generation of monomethylated and dimethylated PC by the rat liver enzyme catechol‐O‐methyltransferase in vitro . Our results were consistent with an in vitro PC transformation study.…”

Comparative biokinetics and metabolism of pure monomeric, dimeric, and polymeric flavan‐3‐ols: A randomized cross‐over study in humans

“…The lack of phase II metabolism was also observed in the above-mentioned intervention studies [7,8,27]. The observed methylation to mono-methylated PC B1 confirms the results of an in vitro study [30]. In contrast, methylated PC B1 was only detectable in plasma and urine samples after glucuronidase/sulfatase treatment.…”

UHPLC‐ESI‐QTOF‐MS‐based metabolic profiling of Vicia faba L. (Fabaceae) seeds as a key strategy for characterization in foodomics

“…Their fragmentation pattern was characterized by the cleavage at the interflavanoid bond. Thus, depending of the dimer type, (epi)gallocatechin was detected at m / z 305.0670 or (epi)catechin at m / z 289.071762 from the terminal unit of the dimer, and the corresponding counterparts at m / z 304.0583, [(epi)gallocatechin–H 2 –H] − , or m / z 287.0561, [(epi)catechin–H 2 –H] − from the upper units . Other product ions derived from the fragmentation of flavanol units, as commented above, were also detected (e.g., Supporting Information Fig.…”