Schwab Christoph, Paar Margret, Fengler Vera Heike, Ivastinovic Domagoj, Haas Anton, Seidel Gerald, Glatz Wilfried, Malle Eva-Maria, Weger Martin, Velikay-Parel Michaela, Faustmann Gernot, Wedrich Andreas, Reibnegger Gilbert, Winklhofer-Roob Brigitte, Oettl Karl
Department of Ophthalmology, Medical University of Graz, Auenbruggerplatz 4, 8036 Graz, Austria.
Physiological Chemistry, Otto-Loewi Research Center, Medical University of Graz, Neue Stiftingtalstraße 6, 8010 Graz, Austria.
Free Radic Biol Med. 2020 Jan;146:257-263. doi: 10.1016/j.freeradbiomed.2019.11.008. Epub 2019 Nov 6.
Ascorbic acid is present at high concentrations in the vitreous and plays a central role in vitreous redox chemistry. Albumin is the main protein in the vitreous with antioxidant properties and occurs in different oxidation states, which can be used as redox indicators, but have not been studied in the vitreous. This study, therefore, addressed the vitreous redox state of cysteine-34 of albumin in relation to the ascorbic acid content, which has been suggested to exert a main function in detoxifying reactive oxygen in the vitreous. A total of 58 vitreous samples obtained from patients undergoing vitrectomy were analyzed for (i) human mercaptalbumin (HMA), the reduced thiol form; (ii) human non-mercaptalbumin1 (HNA1), a reversible oxidative modification with a disulfide at cysteine-34; and (iii) human non-mercaptalbumin2 (HNA2), a non-reversibly (highly) oxidized form of albumin; as well as (iv) ascorbic acid concentrations, to study possible relations. In addition, blood samples were taken to compare albumin redox state between plasma and the vitreous. Vitreous albumin showed greater variability in the redox state of cysteine-34 and a shift to the oxidized fractions compared to plasma albumin (P < 0.001). A strong positive relation was observed between the vitreous ascorbic acid concentrations and the reversibly oxidized form, HNA1 (P < 0.001), and a negative relation with the reduced form, HMA. Positive relations between ascorbic acid and HNA1 in the vitreous were stronger in men than in women. In contrast to HMA and HNA1, there was a distinct gender difference noted for the irreversibly oxidized form, HNA2. While males showed a positive relation between the vitreous ascorbic acid concentrations and HNA2, there was no correlation found with HNA2 in females. Our results support the view that ascorbic acid, by decreasing either directly or indirectly the concentrations of molecular oxygen, generates hydrogen peroxide, and that thiols, including HMA, are acting as antioxidants. This study for the first time provides evidence that vitreous albumin can be used as a marker molecule for the appearance of reactive oxygen species in the vitreous of patients undergoing vitrectomy. Moreover, it can be shown that there are gender differences in vitreous ascorbic acid and albumin concentrations as well as in oxidation state of vitreous albumin.
维生素C在玻璃体内以高浓度存在，在玻璃体内的氧化还原化学中起着核心作用。白蛋白是玻璃体内具有抗氧化特性的主要蛋白质，以不同的氧化态存在，可作为氧化还原指示剂，但尚未在玻璃体内进行研究。因此，本研究探讨了白蛋白半胱氨酸-34的玻璃体内氧化还原状态与维生素C含量的关系，维生素C被认为在玻璃体内活性氧解毒中发挥主要作用。对58例接受玻璃体切除术患者的玻璃体液样本进行了分析，检测了：（i）人巯基白蛋白（HMA），还原型硫醇形式；（ii）人非巯基白蛋白1（HNA1），半胱氨酸-34处有二硫键的可逆氧化修饰形式；（iii）人非巯基白蛋白2（HNA2）,白蛋白的不可逆（高度）氧化形式；以及（iv）维生素C浓度，以研究可能的关系。此外，采集血样以比较血浆和玻璃体内白蛋白的氧化还原状态。与血浆白蛋白相比，玻璃体内白蛋白在半胱氨酸-34氧化还原状态上表现出更大的变异性，且向氧化部分偏移（P<0.001）。观察到玻璃体内维生素C浓度与可逆氧化形式HNA1之间存在强正相关（P<0.001），与还原形式HMA呈负相关。玻璃体内维生素C与HNA1之间的正相关在男性中比在女性中更强。与HMA和HNA1不同，不可逆氧化形式HNA2存在明显的性别差异。男性玻璃体内维生素C浓度与HNA2呈正相关，而女性中未发现与HNA2相关。我们的结果支持这样的观点，即维生素C通过直接或间接降低分子氧浓度产生过氧化氢，包括HMA在内的硫醇作为抗氧化剂发挥作用。本研究首次提供证据表明，玻璃体内白蛋白可作为接受玻璃体切除术患者玻璃体内活性氧出现的标记分子。此外，可以证明，玻璃体内维生素C和白蛋白浓度以及玻璃体内白蛋白的氧化状态存在性别差异。
