Journal of Cellular Biochemistry, Supplement 22:236-246 (1995)
Lutein, Lycopene, and Their Oxidative Metabolites in Chemoprevention of Cancer
Frederick Khachik, Ph.D.1,2;
Gary R. Beecher, Ph.D.1; and
J. Cecil Smith, Jr., Ph.D.3
1 Food Composition Laboratory, Beltsville Human Nutrition Research
Center, United States Department of Agriculture, Beltsville, Maryland 20705
2 Department of Chemistry, The Catholic University of America,
Washington DC 20064
3 Nutrient Requirement and Function Laboratory, Beltsville Human
Nutrition Research Center, United States Department of Agriculture, Beltsville,
Maryland 20705
Abstract
Numerous epidemiological studies have demonstrated that consuming large
quantities of fruits and vegetables reduces the risk of several types of human
cancers. Carotenoids are abundant in fruits and vegetables and have been
extensively studied as cancer preventive agents. A proposed mechanism of action
for the protective effect of carotenoids against cancer is based on their
antioxidant capability. Recently, we have isolated and characterized 14 new
carotenoids, including seven metabolites from the extracts of human serum/plasma.
This brings the total number of identified blood carotenoids to 21. Lutein and
lycopene, abundant in most fruits and vegetables as well as human serum, have
been shown to possess strong antioxidant capability. Among the metabolites of
lutein, four result from oxidation and two from non-enzymatic dehydration. The
metabolite of lycopene has been identified as 5,6-dihydroxy-5,6-dihydrolycopene,
which apparently results from oxidation of lycopene to an intermediate lycopene
epoxide. This intermediate may undergo metabolic reduction to form the lycopene
metabolite. Although in vivo oxidation of lutein to its metobolites has
been demonstrated based on data obtained from two human studies, in vivo
oxidation of lycopene to its metabolite has not yet been established. Recent
preliminary studies involving healthy subjects ingesting purified lutein and
zeaxanthin (a dietary dehydroxycarotenoid isomeric to lutein) are presented. We
propose a possible antioxidant mechanism of action for lutein and lycopene that
leads to formation of the oxidation products of these promising chemopreventive
agents.
