PDF(Pubmed)
Abstract：
In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis, this study determined that the bimolecular rate constants of scavenging cation radicals of retinoids by taurine are smaller than 2 × 107 M-1s-1 whereas lutein scavenges cation radicals of all three retinoids with the bimolecular rate constants approach the diffusion-controlled limits, while zeaxanthin is only 1.4-1.6-fold less effective. Despite that lutein exhibits greater scavenging rate constants of retinoid cation radicals than other antioxidants, the greater concentrations of ascorbate in the retina suggest that ascorbate may be the main protectant of all visual cycle retinoids from oxidative degradation, while α-tocopherol may play a substantial role in the protection of retinaldehyde but is relatively inefficient in the protection of retinol or retinyl palmitate. While the protection of retinoids by lutein and zeaxanthin appears inefficient in the retinal periphery, it can be quite substantial in the macula. Although the determined rate constants of scavenging the cation radicals of retinol and retinaldehyde by dopa-melanin are relatively small, the high concentration of melanin in the RPE melanosomes suggests they can be scavenged if they are in proximity to melanin-containing pigment granules.
摘要：
在视网膜上,与视力有关的类维生素A不断受到氧化的威胁，和它们的氧化产物表现出有害的性质。使用脉冲辐射分解，这项研究确定，牛磺酸清除类维生素A阳离子自由基的双分子速率常数小于2×107M-1s-1，而叶黄素清除所有三种类维生素A阳离子自由基的双分子速率常数接近扩散控制极限，而玉米黄质的效力仅为1.4-1.6倍。尽管叶黄素表现出比其他抗氧化剂更大的类维生素A阳离子自由基的清除速率常数，视网膜中更高浓度的抗坏血酸盐表明抗坏血酸盐可能是所有视觉周期视黄醇的主要保护剂，而α-生育酚可能在视黄醛的保护中起重要作用，但在视黄醇或棕榈酸视黄酯的保护方面相对无效。虽然叶黄素和玉米黄质对类维生素A的保护在视网膜周边似乎效率低下，它在黄斑中可能相当大。尽管确定的通过多巴黑色素清除视黄醇和视黄醛的阳离子自由基的速率常数相对较小，在RPE黑色素体中高浓度的黑色素表明，如果它们靠近含黑色素的色素颗粒，它们可以被清除。
