ABSTRACT
In the mature retina, the components of the macular pigment, lutein (L), R,R-zeaxanthin (RRZ), R,S-zeaxanthin (RSZ, meso-zeaxanthin) are most concentrated in the central macula. L and RRZ are of dietary origin but RSZ is produced in situ from L. The relative proportions of L and Z isomers vary across the retina with eccentricity in the adult retina. Early reports have shown that during development, the proportions of L and Z isomers undergo changes as the total pigment levels increase. The methods described here demonstrate the unique utility of chiral phase HPLC to measure the amounts of L, RRZ, and RSZ, discriminating between the two zeaxanthin stereoisomers. In three concentric retinal sections of macaque retinas chiral phase HPLC has been employed to document the developmental changes in the distribution of each L, RSZ, and RRZ during the period just prior to full term gestation through 19 months after birth. The net rate of accumulation of carotenoids within the central retina during the first 20 months is quasi-linear and fit by a linear regression. During development, the rate of transport of L (0.12 (±0.033)ngmm-2mo-1 (SE)) into the central 2mm of the retina is double that of RRZ (0.062 (±0.02)ngmm-2mo-1 (SE)). The rate of accumulation of RSZ (0.06 (±0.01)ngmm-2mo-1 (SE)) is comparable to that of RRZ. In the peripheral retina, the rates of accumulation of L and RRZ are not correlated with increasing age, whereas accumulation of RSZ does correlate with age. The changing proportions of L to Z isomers in the central retina during development are explained by the rates for carotenoid accumulation within the central retina. At birth, the macular pigment in the central retina is dominated by L and RRZ, 0.35±0.11 and 0.21±0.054ngmm-2. In the central retina, RSZ was rarely detected in the youngest tissues analyzed. It can be estimated to represent 6% of the total macular pigment (0.033±0.11ngmm-2) at birth based on extrapolation from measurements in the peripheral retina and the ratio of L/(RRZ+RSZ) is ≈1.5. At maturity, the concentrations for L, RRZ, and RSZ in the central macaque retina are estimated to be 1.7, 1.8 and 1.08ngmm-2, with L/(RRZ+RSZ) being 0.6.
Subject(s)
Macular Pigment , Animals , Macaca , Retina , Zeaxanthins , beta CaroteneABSTRACT
BACKGROUND: Age-related macular degeneration (AMD) is a disease with multiple risk factors, many of which appear to involve oxidative stress. Macular pigment, with its antioxidant and light-screening properties, is thought to be protective against AMD. A result has been the appearance of dietary supplements containing the macular carotenoids, lutein and zeaxanthin. More recently, a supplement has been marketed containing, in addition, the third major carotenoid of the macular pigment, meso-zeaxanthin. The purpose of the study was to determine the effectiveness of such a supplement in raising macular pigment density in human subjects. METHODS: A 120 day supplementation study was conducted in which 10 subjects were given gel-caps that provided 20 mg/day of predominantly meso-zeaxanthin, with smaller amounts of lutein and zeaxanthin. A second group of 9 subjects were given gel caps containing a placebo for the same 120 day period. Prior to and during the supplementation period, blood serum samples were analyzed by high performance liquid chromatography for carotenoid content. Similarly, macular pigment optical density was measured by heterochromatic flicker photometry. Differences in response between the supplementation and placebo groups were tested for significance using a student's t-test. RESULTS: During supplementation with the carotenoids, blood samples revealed the presence of all three carotenoids. Macular pigment optical density, measured at 460 nm, rose at an average rate of 0.59 +/- 0.79 milli-absorbance unit/day in the 10 supplemented subjects. This was significantly different from the placebo group (9 subjects) for whom the average rate was -0.17 +/- 0.42 milli-absorbance units/day. CONCLUSION: We have shown for the first time that meso-zeaxanthin is absorbed into the serum following ingestion. The data indicate that a supplement containing predominantly meso-zeaxanthin is generally effective at raising macular pigment density, and may turn out to be a useful addition to the defenses against AMD.
