Studies on flavonoid metabolism: Absorption and metabolism of (+)-catechin in man

Abstract

Oral administration of (+)-catechin to man results in absorption, rapid metabolism and excretion of the compound largely within 24 hr. Eleven (+)-catechin metabolites are detected in the urine. The major phenolic acid metabolite is m-hydroxyphenylpropionic acid and the major lactone metabolites include δ-(3,4-dihydroxyphenyl)-γ-valerolactone and δ-(3-hydroxyphenyl)-γ-valerolactone. The phenolic compounds in the urine are excreted in both free and conjugated forms, including their glucuronides and to a lesser degree their ethereal sulphates. Absorption of (+)-catechin occurs in the gastrointestinal tract as early as 6 hr after the oral administration of the compound and appears in the urine together with several unidentified metabolites both in the free and conjugated forms. The amount excreted within 24 hr is about 7.5 per cent of the administered dose. The stomach gastric juice do not degrade (+)-catechin in vitro but prolonged contact with the gastric juice causes some polymerisation of the compound. Unchanged (+)-catechin amounts to about 18.6 per cent of the administered dose in the 48 hr faecal collection. In addition, m-hydroxyphenylpropionic acid and one unidentified metabolite are detected in the faeces. The rise in phenolic levels in the blood occurs as early as 6hr after the oral administration of (+)-catechin and parallel to the rise in urinary excretion of phenolic compounds.