Identification and antioxidant activity of flavonoid metabolites in plasmaand urine of eriocitrin-treated rats

Eriocitrin, a flavonoid glycoside present in lemon fruit, is metabolized in vivo to a series of eriodictyol, methylated eriodictyol, 3,4-dihydroxyhydr ocinnamic acid, and their conjugates. Plasma antioxidant activity increased following oral administration of aqueous eriocitrin solutions to rats. Eri ocitrin metabolites were found in plasma and renal excreted urine through H PLC and LC-MS analyses. Eriocitrin was not detected in plasma and urine, bu t eriodictyol, homoeriodictyol, and hesperetin in their conjugated forms we re detected in plasma of 4.0 h following administration of eriocitrin. In u rine for 24 h, both nonconjugates and conjugates of these metabolites were detected. 3,4-Dihydroxyhydrocinnamic acid, which is metabolized from eriodi ctyol by intestinal bacteria, was detected in slight amounts with each form in 4.0-h plasma and 24-h urine. Eriocitrin was suggested to be metabolized by intestinal bacteria, and then eriodictyol and 3,4-dihydroxyhydrocinnami c of its metabolite were absorbed. Following administration of eriocitrin, plasma exhibited an elevated resistance effect to lipid peroxidation. Erioc itrin metabolites functioning as antioxidant agents are discussed.