Identification of Lutein and Zeaxanthin
Oxidation Products in Human and Monkey Retinas.
Authors:
Khachik F , Bernstein PS , Garland DL
Beltsville Human Nutrition Research Center, Carotenoids Research Unit, US Department of
Agriculture, Beltsville, Maryland 20705, USA.
Invest Ophthalmol Vis Sci 1997 Aug;38(9):1802-11
PURPOSE: To characterize fully all
the major and minor carotenoids and their metabolites in human retina and probe for the
presence of the oxidative metabolites of lutein and zeaxanthin.
METHODS: Carotenoids of a composite of 58 pairs of human retinas and a monkey retina were elucidated by comparing their high-performance liquid chromatography (HPLC)-ultraviolet/visible absorption spectrophotometry (UV/Vis)-mass spectrometry (MS) profile with those of authentic standards prepared by organic synthesis.
RESULTS: In addition to lutein and zeaxanthin, several oxidation products of these compounds were present in the extracts from human retina. A major carotenoid resulting from direct oxidation of lutein was identified as 3-hydroxy-beta, epsilon-caroten-3'-one. Minor carotenoids were identified as: 3'-epilutein, epsilon,epsilon-carotene-3, 3'-diol, epsilon,epsilon-carotene-3, 3'-dione,3'-hydroxy-epsilon, epsilon-caroten- 3-one, and 2,6-cyclolycopene-1,5-diol. Several of the geometric isomers of lutein and zeaxanthin were also detected at low concentrations. These were as follows: 9-cis-lutein, 9'-cislutein, 13-cis-lutein, 13'-cis-lutein, 9-cis-zeaxanthin, and 13-cis-zeaxanthin. Similar results were also obtained from HPLC analysis of a freshly dissected monkey retina.
CONCLUSIONS: Lutein, zeaxanthin, 3'-epilutein, and 3-hydroxy-beta,epsilon-caroten-3'-one in human retina may be interconverted through a series of oxidation-reduction reactions similar to our earlier proposed metabolic transformation of these compounds in humans. The presence of the direct oxidation product of lutein and 3'-epilutein (metabolite of lutein and zeaxanthin) in human retina suggests that lutein and zeaxanthin may act as antioxidants to protect the macula against short-wavelength visible light. The proposed oxidative-reductive pathways for lutein and zeaxanthin in human retina, may therefore play an important role in prevention of age-related macular degeneration and cataracts.
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