Vitamin C transport in oxidized form across the rat blood-retinal barrier

Invest Ophthalmol Vis Sci. 2004 Apr;45(4):1232-9. doi: 10.1167/iovs.03-0505.


Purpose: To elucidate the mechanisms of vitamin C transport across the blood-retinal barrier (BRB) in vivo and in vitro. METHODS. [(14)C]Dehydroascorbic acid (DHA) and [(14)C]ascorbic acid (AA) transport in the retina across the BRB were examined using in vivo integration plot analysis in rats, and the transport mechanism was characterized using a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2) as an in vitro model of the inner BRB.

Results: The apparent influx permeability clearance (K(in)) per gram of retina of [(14)C]DHA and [(14)C]AA was found to be 2.44 x 10(3) microL/(min x g retina) and 65.4 microL/(min x g retina), respectively. In the retina and brain, the K(in) of [(14)C]DHA was approximately 38 times greater than that of [(14)C]AA, whereas there was no major difference in the heart. The K(in) of [(14)C]DHA in the retina was eight times greater than that in the brain. HPLC analysis revealed that most of the vitamin C accumulated in AA form in the retina. These results suggest that vitamin C is mainly transported in DHA form across the BRB and accumulates in AA form in the rat retina. In an in vitro uptake study in TR-iBRB2 cells, the initial uptake rate of [(14)C]DHA was 37 times greater than that of [(14)C]AA, which is in agreement with the results of the in vivo study. [(14)C]DHA uptake by TR-iBRB2 cells took place in an Na(+)-independent and concentration-dependent manner with a K(m) of 93.4 microM. This process was inhibited by substrates and inhibitors of glucose transporters. [(14)C]DHA uptake was inhibited by D-glucose in a concentration-dependent manner with a 50% inhibition concentration of 5.56 mM. Quantitative real-time PCR and immunostaining analyses revealed that expression of GLUT1 and -3 was greater than that of the Na(+)-dependent L-ascorbic acid transporter (SVCT)-2 in TR-iBRB2 cells.

Conclusions: Vitamin C is mainly transported across the BRB as DHA mediated through facilitative glucose transporters and accumulates as AA in the rat retina.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Ascorbic Acid / metabolism*
  • Biological Transport
  • Blood-Retinal Barrier / physiology*
  • Capillaries
  • Cell Line
  • Chromatography, High Pressure Liquid
  • Dehydroascorbic Acid / metabolism
  • Dose-Response Relationship, Drug
  • Endothelium, Vascular / metabolism*
  • Male
  • Monosaccharide Transport Proteins / antagonists & inhibitors
  • Monosaccharide Transport Proteins / metabolism
  • Organic Anion Transporters, Sodium-Dependent / antagonists & inhibitors
  • Organic Anion Transporters, Sodium-Dependent / metabolism
  • Permeability
  • Rats
  • Rats, Wistar
  • Retina / metabolism*
  • Retinal Vessels / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sodium-Coupled Vitamin C Transporters
  • Symporters / antagonists & inhibitors
  • Symporters / metabolism


  • Monosaccharide Transport Proteins
  • Organic Anion Transporters, Sodium-Dependent
  • Sodium-Coupled Vitamin C Transporters
  • Symporters
  • Ascorbic Acid
  • Dehydroascorbic Acid