Departamento de Química Física, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Correo 22, Santiago de Chile.
Photochem Photobiol Sci. 2010 Oct 28;9(10):1351-8. doi: 10.1039/c0pp00048e. Epub 2010 Aug 24.
Exposure to light has been implicated as a risk factor during aging of the eye lens and in cataract generation. In order to visualize the actual effect of UVA-visible light on this tissue, we incubated water-soluble eye lens proteins with ascorbate in the presence and absence of UVA-visible light for 3, 6 and 9 days at low oxygen concentration. The samples incubated in the presence of light were characterized by an initially small but continuous increase over time of the protein crosslinking. This was not the result of more extensive glycation because the decrease in amino group content of the proteins and the decomposition of ascorbate was the same in both irradiated and unirradiated samples. The augmented crosslinking capacity observed in the presence of UVA-visible light is due to the generation of a chromophore from the decomposition of ascorbate. This chromophore, obtained after 3, 6 and 9 days of incubation of solutions containing only ascorbate, induces both protein-crosslinking and oxidation after exposure to UVA-visible light in the presence of lens proteins. The extent of the crosslinking was proportional to the amount of the chromophore present in the solution. The presence of this chromophore was also determined when ascorbate was incubated with four-fold higher concentrations of N-α-acetyl lysine and N-α-acetyl arginine. When these samples were used as photosensitizers, the crosslinking degree was conditioned by the presence of this chromophore; nonetheless, the ascorbate-mediated advanced glycation end product (AGE) generation also made a contribution. The results of this work indicate that ascorbate oxidation, which generates the AGEs responsible for the chemical crosslinking of the lens proteins, also simultaneously produces a chromophore that can act as a photosensitizer, further increasing the protein crosslinking.
光暴露已被认为是眼睛晶状体老化和白内障形成的一个风险因素。为了直观地观察 UVA-可见光对这种组织的实际影响，我们将水溶性眼晶状体蛋白与抗坏血酸在低氧浓度下孵育 3、6 和 9 天，同时存在和不存在 UVA-可见光。在光照下孵育的样品的特征是，蛋白质交联的初始小但持续增加。这不是更广泛的糖化的结果，因为蛋白质的氨基含量下降和抗坏血酸的分解在辐照和未辐照样品中是相同的。在 UVA-可见光存在下观察到的增强交联能力是由于抗坏血酸分解产生发色团的结果。这种发色团在仅含有抗坏血酸的溶液孵育 3、6 和 9 天后获得，在存在晶状体蛋白的情况下暴露于 UVA-可见光后诱导蛋白质交联和氧化。交联程度与溶液中存在的发色团的量成正比。当抗坏血酸与 N-α-乙酰赖氨酸和 N-α-乙酰精氨酸的浓度高四倍孵育时，也确定了这种发色团的存在。当这些样品用作光敏剂时，交联程度取决于发色团的存在；尽管如此，抗坏血酸介导的晚期糖基化终产物 (AGE) 的生成也做出了贡献。这项工作的结果表明，抗坏血酸氧化生成负责晶状体蛋白质化学交联的 AGEs，同时也会产生一种发色团，可作为光敏剂，进一步增加蛋白质交联。
