VITAMIN-C CROSSES THE BLOOD-BRAIN-BARRIER IN THE OXIDIZED FORM THROUGH THE GLUCOSE TRANSPORTERS

Vitamin C concentrations in the brain exceed those in blood by 10-fold . In both tissues, the vitamin is present primarily in the reduced for m, ascorbic acid. We identified the chemical form of vitamin C that re adily crosses the blood-brain barrier, and the mechanism of this proce ss. 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 reta ined in the brain tissue in the form of ascorbic acid, Transport of de hydroascorbic acid into the brain was inhibited by D-glucose, but not by L-glucose. The facilitative glucose transporter, GLUT1, is expresse d on endothelial cells at the blood-brain barrier, and is responsible far glucose entry into the brain, This study provides evidence showing that GLUT1 also transports dehydroascorbic acid Into the brain. The f indings define the transport of dehydroascorbic acid by GLUT1 as a mec hanism by which the brain acquires vitamin C, and point to the oxidati on of ascorbic acid as a potentially important regulatory step in accu mulation of the vitamin by the brain. These results have implications for increasing antioxidant potential in the central nervous system.