Nagao Akihiko, Maoka Takashi, Ono Hiroshi, Kotake-Nara Eiichi, Kobayashi Miyuki, Tomita Mie
National Food Research Institute, National Agriculture and Food Research Organization, Tsukuba, Ibaraki 305-8642, Japan.
Research Institute for Production and Development, Sakyo-ku, Kyoto 606-0805, Japan.
J Lipid Res. 2015 Feb;56(2):449-62. doi: 10.1194/jlr.P055459. Epub 2014 Dec 12.
We previously found that mice fed lutein accumulated its oxidative metabolites (3'-hydroxy-ε,ε-caroten-3-one and ε,ε-carotene-3,3'-dione) as major carotenoids, suggesting that mammals can convert xanthophylls to keto-carotenoids by the oxidation of hydroxyl groups. Here we elucidated the metabolic activities of mouse liver for several xanthophylls. When lutein was incubated with liver postmitochondrial fraction in the presence of NAD(+), (3'R,6'R)-3'-hydroxy-β,ε-caroten-3-one and (6RS,3'R,6'R)-3'-hydroxy-ε,ε-caroten-3-one were produced as major oxidation products. The former accumulated only at the early stage and was assumed to be an intermediate, followed by isomerization to the latter. The configuration at the C3' and C6' of the ε-end group in lutein was retained in the two oxidation products. These results indicate that the 3-hydroxy β-end group in lutein was preferentially oxidized to a 3-oxo ε-end group via a 3-oxo β-end group. Other xanthophylls such as β-cryptoxanthin and zeaxanthin, which have a 3-hydroxy β-end group, were also oxidized in the same manner as lutein. These keto-carotenoids, derived from dietary xanthophylls, were confirmed to be present in plasma of normal human subjects, and β,ε-caroten-3'-one was significantly increased by the ingestion of β-cryptoxanthin. Thus, humans as well as mice have oxidative activity to convert the 3-hydroxy β-end group of xanthophylls to a 3-oxo ε-end group.
我们之前发现，喂食叶黄素的小鼠会积累其氧化代谢产物（3'-羟基-ε,ε-胡萝卜素-3-酮和ε,ε-胡萝卜素-3,3'-二酮）作为主要类胡萝卜素，这表明哺乳动物可以通过羟基氧化将叶黄素转化为酮类胡萝卜素。在此，我们阐明了小鼠肝脏对几种叶黄素的代谢活性。当叶黄素在NAD(+)存在的情况下与肝脏线粒体后组分一起孵育时，会产生(3'R,6'R)-3'-羟基-β,ε-胡萝卜素-3-酮和(6RS,3'R,6'R)-3'-羟基-ε,ε-胡萝卜素-3-酮作为主要氧化产物。前者仅在早期积累，并被认为是一种中间体，随后异构化为后者。叶黄素ε-端基团C3'和C6'处的构型在这两种氧化产物中得以保留。这些结果表明，叶黄素中的3-羟基β-端基团优先通过3-氧代β-端基团氧化为3-氧代ε-端基团。其他具有3-羟基β-端基团的叶黄素，如β-隐黄质和玉米黄质，也以与叶黄素相同的方式被氧化。这些源自膳食叶黄素的酮类胡萝卜素在正常人类受试者的血浆中被证实存在，并且摄入β-隐黄质后β,ε-胡萝卜素-3'-酮显著增加。因此，人类和小鼠一样具有将叶黄素的3-羟基β-端基团转化为3-氧代ε-端基团的氧化活性。
