Khachik F, Beecher G R, Smith J C
Food Composition Laboratory, Beltsville Human Nutrition Research Center, United States Department of Agriculture, Maryland 20705, USA.
J Cell Biochem Suppl. 1995;22:236-46. doi: 10.1002/jcb.240590830.
Numerous epidemiological studies have demonstrated that consuming large quantities of fruits and vegetables reduces the risk for 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 results 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 metabolites 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 dihydroxycarotenoid 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.
众多流行病学研究表明，大量食用水果和蔬菜可降低多种人类癌症的发病风险。类胡萝卜素在水果和蔬菜中含量丰富，作为癌症预防剂已得到广泛研究。类胡萝卜素对癌症具有保护作用的一种作用机制假说基于其抗氧化能力。最近，我们分离并鉴定了14种新的类胡萝卜素，其中包括7种来自人血清/血浆提取物的代谢产物。这使得已鉴定的血液类胡萝卜素总数达到21种。叶黄素和番茄红素在大多数水果、蔬菜以及人血清中含量丰富，已被证明具有强大的抗氧化能力。在叶黄素的代谢产物中，4种是氧化产物，2种是非酶促脱水产物。番茄红素的代谢产物已被鉴定为5,6 - 二羟基 - 5,6 - 二氢番茄红素，它显然是由番茄红素氧化为中间产物番茄红素环氧化物后形成的。该中间产物可能会发生代谢还原反应形成番茄红素代谢产物。尽管基于两项人体研究的数据已证实叶黄素在体内可氧化为其代谢产物，但番茄红素在体内氧化为其代谢产物的情况尚未得到证实。本文介绍了近期对健康受试者摄入纯化叶黄素和玉米黄质（一种与叶黄素同分异构的膳食二羟基类胡萝卜素）的初步研究。我们提出了一种叶黄素和番茄红素可能的抗氧化作用机制，该机制导致这些有前景的化学预防剂形成氧化产物。
