Long Term Dietary Supplementation with Zeaxanthin Reduces Photoreceptor Death in Light-damaged Japanese Quail

Abstract

The purpose of these studies was to evaluate the effects of light damage on Japanese quail whose retinal carotenoids had been experimentally manipulated through altered diets. The birds were raised 6 months on a commercial turkey diet (T), on a custom carotenoid-deficient diet (C−) containing 90% less carotenoid than the T diet, or on Z+ diet [the C− diet supplemented with natural zeaxanthin (35mgkg−1 food)]. Equal numbers of males and females on each diet were exposed to nine intervals (1hr on, 2hr off) of 3200lux cool white light, then placed in the dark for 14hr before tissue collection. One retina was immediately frozen for HPLC analysis; the other eye was immediately fixed and processed for microscopy. There were no significant differences in the retinal carotenoid concentrations in hatch-mates that were and were not exposed to light. Supplementation resulted in three- to four-fold increases in retinal zeaxanthin and no change in retinal lutein or α-tocopherol, but the C− diet did not reduce the retinal carotenoid concentration in C− birds below that in T birds. The light-exposed retinas had significant numbers of apoptotic photoreceptors and photoreceptor ghosts. The number of ghosts was negatively correlated with the number of dying photoreceptors (P<0.05), and with retinal concentrations of zeaxanthin, α-tocopherol or γ-tocopherol (P<0.04, 0.02, 0.04, respectively), but not with lutein. The number of dying photoreceptors was positively correlated with α-tocopherol and the sum α-tocopherol plus zeaxanthin (P<0.1; P0.04). Photoreceptor death was semi-quantitatively scored, assuming that ghosts were formed by removal of apoptotic photoreceptors with nuclear condensation. Stepwise regression produced a good model (r2=0.67;P<0.0001) for predicting death scores from retinal concentrations of zeaxanthin (Standard Coefficient=−0.76) and lutein (Standard Coefficients=+0.43). Absence of lutein in gender-specific analyses suggests lutein served as surrogate marker for gender. Combined analysis of the C− and T birds also demonstrated that dying photoreceptors were negatively correlated with retinal zeaxanthin. These data confirm our previous report that retinal carotenoids prevent photoreceptor cell death, and provide the first direct evidence that retinal zeaxanthin protects photoreceptors from light-induced death.