TEMPE, Ariz.—While domesticated species of birds have served as a model system for examining carotenoid uptake and macular deposition, wild species may also have a role in helping understand certain variations in retinal carotenoid accumulation, according to a new study (Arch Biochem Biophys. ePub 2010 Jul 2. DOI:10.1016/j.abb.2010.06.033). Researchers from Arizona State University examined the way variations in the levels and types of dietary carotenoids affect retinal accumulation in wild-caught house finches (Carpodacus mexicanus).
Three eight-week studies were conducted. The first found wild birds on a low carotenoid diet showed slower depletion of retinal carotenoids compared to other tissues; significant decreases were seen only after the full eight week period. In the second trial, birds were supplemented with lutein and zeaxanthin, common dietary carotenoids, to measure the effect on retinal accumulation; supplementation with the combination of these xanthophylls significantly increased retinal levels of galloxanthin and epsilon-carotene, leaving other carotenoid levels unchanged. For the final trial, birds were given high levels of zeaxanthin or astaxanthin, which is not commonly found in the diet. Retinal concentrations of zeaxanthin and astaxanthin were unaffected by the additional supplementation.
The researchers concluded there are highly specific mechanisms of retinal carotenoid metabolism, and differing turnover rates of all carotenoids in the retina, which may have implications for visual health maintenance and interventions in humans.
