Abstract
Purpose::
Macular pigment is composed of the carotenoids lutein (L), zeaxanthin (RRZ) and meso-zeaxanthin (MZ). MZ is present in the fovea of the adult human and nonhuman primate retina in amounts comparable to dietary RRZ. A unique functional role for MZ has not been unambiguously established. It is formed by an unknown pathway from lutein, but preliminary study of MZ in the retinas of human neonates indicated that this pathway may not be functional in the young eye. The current study has investigated changes in the distribution of these carotenoids in the developing retina of macaque monkeys.
Methods::
HPLC was employed to study the distribution of carotenoids in 38 retinas from macaques ranging from 148 days of gestation to 19 mo in age. The carotenoids were measured in concentric punches of the retina having diameters of 2, 4, and 8 mm, centered on the fovea. L and total zeaxanthin (RRZ+MZ) were quantitatively measured after extraction from the retina through the use of reversed phase chromatography. Subsequent chromatography on a chiral normal-phase system allowed separation and quantitation of zeaxanthin stereoisomers.
Results::
The amounts of L, MZ, and RRZ in 2 mm punches were all found to vary significantly with age (P < 0.003). The ratio MZ to L in 2 mm punches increased significantly with age (P < 0.0001). The ratio of MZ to L for animals younger than 7 mo (n = 10, 14 retinas) was consistently less than 0.3, average value 0.09±0.03, whereas the ratio for older animals (n = 3, 5 retinas, age 12 - 19 mo) was consistently greater than 0.4, average 0.7±0.1. The amounts of L, MZ, and RRZ in 2 mm punches were significantly greater than in 2-4 mm annuli (P < 0.0001), and the amounts in 2-4 mm annuli were significantly greater than in 4-8 mm annuli (P < 0.002).
Conclusions::
These data are the first to define in detail the developmental course of macular pigment in the primate retina. The increase in the MZ/L ratio with age is consistent with a pathway in which L is converted MZ. MZ was not detected in the retinas of macaques younger than 25 days, indicating that retinal conversion of L to MZ begins soon after birth and increases in efficiency with the development of the retina.
Keywords: macular pigment • carotenoids/carotenoid binding proteins • macula/fovea