Effects of N–3 Fatty Acids, Lutein and Zeaxanthin on Photoreceptor Cell Densities in the Foveas of Rhesus Monkeys

Abstract

Abstract: : Purpose:To study the effects of dietary n–3 fatty acids, lutein and/or zeaxanthin levels on cone and rod cell density in the foveal region. Methods:Rhesus monkeys (7–16 yr, n = 17) were fed from birth xanthophyll–free semipurified diets with either adequate or low n–3 fatty acids; all animals had no macular pigment. Five monkeys then were supplemented with lutein and six with zeaxanthin for 6 to 24 months, while six remained xanthophyll–free until death. Retinas were embedded in methacrylate and serial 2 µm sections were cut along the vertical meridian. Rod and cone nuclei, and immunolabeled outer segments of rods, were reconstructed and counted in an 8 µm strip. The density profiles were compared with data from control monkeys (n = 7) fed a standard laboratory diet.Results: Cone densities were symmetrical along the vertical meridian and the densities decreased rapidly with retinal eccentricity. Rod densities were higher in the superior region than the inferior region in most of the control and experimental animals. Unlike the significant effects observed for retinal pigment epithelial cells of these same monkeys (Leung et al., IOVS. 45, 3244–3256), neither xanthophyll supplementation nor low dietary n–3 fatty acids produced consistent effects on cone or rod density profiles of the experimental animals. However, monkeys low in n–3 fatty acids had increased variability of cone density in the fovea, and those also lacking xanthophylls had exceptionally low density of foveal rod outer segments. Conclusions: The high variability of cell densities in the experimental groups suggests that the photoreceptors of some animals were resistant to the nutritional manipulations, while others may have been affected. Although more significant effects may merge over time or upon challenge with stressors such as high light levels, photoreceptors appear to be more resistant to the effects of these nutritional manipulations than the retinal pigment epithelium.

Keywords: carotenoids/carotenoid binding proteins • macula/fovea • photoreceptors