Agus D B, Gambhir S S, Pardridge W M, Spielholz C, Baselga J, Vera J C, Golde D W
Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
J Clin Invest. 1997 Dec 1;100(11):2842-8. doi: 10.1172/JCI119832.
Vitamin C concentrations in the brain exceed those in blood by 10-fold. In both tissues, the vitamin is present primarily in the reduced form, ascorbic acid. We identified the chemical form of vitamin C that readily crosses the blood-brain barrier, and the mechanism of this process. Ascorbic acid was not able to cross the blood-brain barrier in our studies. In contrast, the oxidized form of vitamin C, dehydroascorbic acid (oxidized ascorbic acid), readily entered the brain and was retained in the brain tissue in the form of ascorbic acid. Transport of dehydroascorbic acid into the brain was inhibited by d-glucose, but not by l-glucose. The facilitative glucose transporter, GLUT1, is expressed on endothelial cells at the blood-brain barrier, and is responsible for glucose entry into the brain. This study provides evidence showing that GLUT1 also transports dehydroascorbic acid into the brain. The findings define the transport of dehydroascorbic acid by GLUT1 as a mechanism by which the brain acquires vitamin C, and point to the oxidation of ascorbic acid as a potentially important regulatory step in accumulation of the vitamin by the brain. These results have implications for increasing antioxidant potential in the central nervous system.
大脑中的维生素C浓度比血液中的高出10倍。在这两种组织中，维生素主要以还原形式即抗坏血酸存在。我们确定了易于穿过血脑屏障的维生素C的化学形式以及这一过程的机制。在我们的研究中，抗坏血酸无法穿过血脑屏障。相比之下，维生素C的氧化形式脱氢抗坏血酸（氧化型抗坏血酸）很容易进入大脑，并以抗坏血酸的形式保留在脑组织中。脱氢抗坏血酸进入大脑的过程受到d-葡萄糖的抑制，但不受l-葡萄糖的抑制。易化型葡萄糖转运体GLUT1在血脑屏障的内皮细胞上表达，负责葡萄糖进入大脑。这项研究提供了证据表明GLUT1也能将脱氢抗坏血酸转运到大脑中。这些发现将GLUT1对脱氢抗坏血酸的转运定义为大脑获取维生素C的一种机制，并指出抗坏血酸的氧化是大脑积累该维生素的一个潜在重要调节步骤。这些结果对提高中枢神经系统的抗氧化能力具有重要意义。
