Identification and antioxidant activity of flavonoid metabolites in plasma and 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-dihydroxyhydrocinnamic acid, and their conjugates. Plasma antioxidant activity increased following oral administration of aqueous eriocitrin solutions to rats. Eriocitrin metabolites were found in plasma and renal excreted urine through HPLC and LC-MS analyses. Eriocitrin was not detected in plasma and urine, but eriodictyol, homoeriodictyol, and hesperetin in their conjugated forms were detected in plasma of 4.0 h following administration of eriocitrin. In urine for 24 h, both nonconjugates and conjugates of these metabolites were detected. 3,4-Dihydroxyhydrocinnamic acid, which is metabolized from eriodictyol 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-dihydroxyhydrocinnamic of its metabolite were absorbed. Following administration of eriocitrin, plasma exhibited an elevated resistance effect to lipid peroxidation. Eriocitrin metabolites functioning as antioxidant agents are discussed.