School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA.
Arch Biochem Biophys. 2010 Dec 1;504(1):161-8. doi: 10.1016/j.abb.2010.06.033. Epub 2010 Jul 3.
Carotenoid pigments accumulate in the retinas of many animals, including humans, where they play an important role in visual health and performance. Recently, birds have emerged as a model system for studying the mechanisms and functions of carotenoid accumulation in the retina. However, these studies have been limited to a small number of domesticated species, and the effects of dietary carotenoid access on retinal carotenoid accumulation have not been investigated in any wild animal species. The purpose of our studies was to examine how variation in dietary carotenoid types and levels affect retinal accumulation in house finches (Carpodacus mexicanus), a common and colorful North American songbird. We carried out three 8-week studies with wild-caught captive birds: (1) we tracked the rate of retinal carotenoid depletion, compared to other body tissues, on a very low-carotenoid diet, (2) we supplemented birds with two common dietary carotenoids (lutein + zeaxanthin) and measured the effect on retinal accumulation, and (3) we separately supplemented birds with high levels of zeaxanthin--an important dietary precursor for retinal carotenoids--or astaxanthin--a dominant retinal carotenoid not commonly found in the diet (i.e. a metabolic derivative). We found that carotenoids depleted slowly from the retina compared to other tissues, with a significant (~50%) decline observed only after 8 weeks on a very low-carotenoid diet. Supplementation with lutein + zeaxanthin or zeaxanthin alone significantly increased only retinal galloxanthin and ε-carotene levels, while other carotenoid types in the retina remained unaffected. Concentrations of retinal astaxanthin were unaffected by direct dietary supplementation with astaxanthin. These results suggest highly specific mechanisms of retinal carotenoid metabolism and accumulation, as well as differential rates of turnover among retinal carotenoid types, all of which have important implications for visual health maintenance and interventions.
类胡萝卜素色素在许多动物的视网膜中积累，包括人类，在那里它们在视觉健康和表现中发挥着重要作用。最近，鸟类已成为研究视网膜中类胡萝卜素积累机制和功能的模型系统。然而，这些研究仅限于少数几种驯化物种，并且尚未在任何野生动物物种中研究饮食类胡萝卜素的获取对视网膜类胡萝卜素积累的影响。我们的研究目的是研究饮食中类胡萝卜素类型和水平的变化如何影响家雀（Carpodacus mexicanus）的视网膜积累，家雀是一种常见且色彩鲜艳的北美鸣禽。我们对圈养的野生捕获鸟类进行了三项为期 8 周的研究：（1）我们在极低类胡萝卜素饮食中追踪了与其他身体组织相比视网膜类胡萝卜素消耗的速度；（2）我们用两种常见的饮食类胡萝卜素（叶黄素+玉米黄质）补充鸟类，并测量了对视网膜积累的影响；（3）我们分别用高水平的玉米黄质（视网膜类胡萝卜素的重要饮食前体）或虾青素（一种在饮食中通常不发现的主要视网膜类胡萝卜素，即代谢衍生物）补充鸟类。我们发现与其他组织相比，类胡萝卜素从视网膜中缓慢消耗，只有在极低类胡萝卜素饮食 8 周后才会观察到显著（~50%）下降。单独补充叶黄素+玉米黄质或玉米黄质本身仅显著增加视网膜虾黄质和ε-胡萝卜素水平，而视网膜中其他类胡萝卜素类型则不受影响。直接用虾青素饮食补充不会影响视网膜虾青素的浓度。这些结果表明，视网膜类胡萝卜素代谢和积累具有高度特异性的机制，以及视网膜类胡萝卜素类型之间的周转率差异，所有这些都对视健康维护和干预具有重要意义。
