Bioavailability, Metabolism, and Possible Mechanism of Chemoprevention by Lutein and Lycopene in Humans

Abstract

Lutein and lycopene are among the most abundant dietary carotenoids found in fruits, vegetables, and human se-rum. Human absorption and bioavailability studies involving lutein and its structural isomer zeaxanthin have established in vivo oxidation of these carotenoids to four metabolites. Lyco-pene apparently undergoes oxidation to yield lycopene-5,6-epoxide followed by cyclization and enzymatic reduction to form two dihydroxylycopenes with a novel five-member ring end-group. These dihydroxylycopenes, which have been iden-tified as epimeric isomers of 2,6-cyclolycopene-1,5-diol, have been found in human serum. We present he re our most recent data concerning the identity of 24 carotenoids, including eight of their metabolites in human serum. Possible metabolic trans-formations and the antioxidant mechanism of action for lutein and lycopene that lead to the formation of the oxidative me-tabolites of these two promising chemopreventive agents are described.