Catechin Is Metabolized by Both the Small Intestine and Liver of Rats

Abstract

Flavan-3-ols are the most abundant flavonoids in the human diet, but little is known about their absorption and metabolism. In this study, the absorption and metabolism of the monomeric flavan-3-ol, catechin, was investigated after the in situ perfusion of the jejunum + ileum in rats. Five concentrations of catechin were studied, ranging from 1 to 100 micromol/L. The absorption of catechin was directly proportional to the concentration, and 35 +/- 2% of the perfused catechin was absorbed during the 30-min period. Effluent samples contained only native catechin, indicating that intestinal excretion of metabolites is not a mechanism of catechin elimination. Catechin was absorbed into intestinal cells and metabolized extensively because no native catechin could be detected in plasma from the mesenteric vein. Mesenteric plasma contained glucuronide conjugates of catechin and 3'-O-methyl catechin (3'OMC), indicating the intestinal origin of these conjugates. Additional methylation and sulfation occurred in the liver, and glucuronide + sulfate conjugates of 3'OMC were excreted extensively in bile. Circulating forms were mainly glucuronide conjugates of catechin and 3'OMC. The data further demonstrate the role of the rat small intestine in the glucuronidation and methylation of flavonoids as well as the role of the liver in sulfation, methylation and biliary excretion.

The splanchnic metabolism of flavonoids highly differed according to the nature of the compound

“…In the present study, we did not determine the precise nature of the metabolites resulting from the respective intestinal and hepatic conjugation, but, as shown by the forms recovered in the bile, they may be quite different. As reported in our previous study, catechin was present in the mesenteric vein as glucuronides (methylated or nonmethylated), whereas it was recovered as glucurono/sulfoconjugates (methylated or nonmethylated) in the bile (10). Taken together, these data strongly suggest that hepatocytes are a site of deconjugation for the circulating forms coming from the mesenteric vein and that the conjugative activity of the liver produced metabolites available for the bile and peripheral tissues.…”

“…In a previous study, we have found that the catechin absorption was directly proportional to the amount perfused (10). Although the mechanism of catechin absorption in the small intestine is not established, it appears probable that catechin enters the enterocytes by a passive diffusion system or by a transporter that was not saturated at concentrations up to 100 M (10).…”

“…In this tissue, aglycones are metabolized by intestinal conjugation enzymes, and the resulting metabolites are then secreted toward the mucosal and/or serosal sides (5,6,10,13,37). Circulating forms of absorbed flavonoids have been identified as methylated and/or glucuronidated and/or sulfated metabolites (9,12,19,23,39), resulting from the conjugative activities of both liver and intestine (7).…”

Transformations of polyphenolic compounds in simulated human gastrointestinal tract

“…Z badań Donovan i wsp. [6] wynika, że w jelicie zachodzi glukuronidacja i metylacja (+)katechiny. Enzymy bakteryjne degradują też katechiny do prostszych cząsteczek, głównie do niskocząsteczko-wych kwasów fenolowych.…”

In vitroevaluation of the antioxidant and anti-inflammatory activities of sulphated metabolites of catechins Evaluaciónin vitrode las actividades antioxidante y antiinflamatoria de metabolitos sulfatados de catequinas

“…It has been shown that catechins are absorbed from the human intestinal tract, largely metabolised and distributed as conjugated derivatives in bloodstream (Baba et al, 2000). Methyl, sulphate and glucuronide conjugates have been described as circulating metabolites of catechins (Baba, Osakabe, & Natsume, 2001;Donovan et al, 1999Donovan et al, , 2001Natsume et al, 2003). Circulating metabolites would be those able to reach the biological targets and, therefore, they should be main actors to explain the health effects associated to the intake of catechins and flavonoids in general.…”