Aging may significantly modify antioxidant and photoprotective properties of melanin in retinal pigment epithelium (RPE). Here, photoreactivity of melanosomes (MS), isolated from younger and older human donors with and without added zeaxanthin and α-tocopherol, was analyzed by electron paramagnetic resonance oximetry, time-resolved singlet oxygen phosphorescence, and protein oxidation assay. The phototoxic potential of ingested melanosomes was examined in ARPE-19 cells exposed to blue light. Phagocytosis of FITC-labeled photoreceptor outer segments (POS) isolated from bovine retinas was determined by flow cytometry. Irradiation of cells fed MS induced significant inhibition of the specific phagocytosis with the effect being stronger for melanosomes from older than from younger human cohorts, and enrichment of the melanosomes with antioxidants reduced the inhibitory effect. Cellular protein photooxidation was more pronounced in samples containing older melanosomes, and it was diminished by antioxidants. This study suggests that blue light irradiated RPE melanosomes could induce substantial inhibition of the key function of the cells—their specific phagocytosis. The data indicate that while photoreactivity of MS and their phototoxic potential increase with age, they could be reduced by selected natural antioxidants.

中文翻译：

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衰老和抗氧化剂对人类黑素体光反应性和光毒性的影响：一项体外研究

衰老可能会显着改变视网膜色素上皮 (RPE) 中黑色素的抗氧化和光保护特性。在这里，通过电子顺磁共振血氧饱和度法、时间分辨单线态氧磷光和蛋白质氧化测定法分析了从年轻和年长的人类供体中分离出的添加和未添加玉米黄质和 α-生育酚的黑素体 (MS) 的光反应性。在暴露于蓝光的 ARPE-19 细胞中检查了摄入的黑素体的光毒性潜力。通过流式细胞术测定从牛视网膜中分离的 FITC 标记的光感受器外段 (POS) 的吞噬作用。对喂食 MS 的细胞进行辐照会显着抑制特定的吞噬作用，对来自较年长人群的黑素体的影响要强于来自较年轻人群的黑素体，并且用抗氧化剂富集黑素体降低了抑制作用。细胞蛋白质光氧化在含有较老黑素体的样品中更为明显，并且被抗氧化剂减少。这项研究表明，蓝光照射的 RPE 黑素体可以显着抑制细胞的关键功能——它们的特异性吞噬作用。数据表明，虽然 MS 的光反应性及其光毒性潜力随着年龄的增长而增加，但它们可以通过选择的天然抗氧化剂降低。