TY - JOUR
T1 - Vitamin C transport in oxidized form across the rat blood-retinal barrier
AU - Hosoya, Ken Ichi
AU - Minamizono, Akito
AU - Katayama, Kazunori
AU - Terasaki, Tetsuya
AU - Tomi, Masatoshi
PY - 2004/4
Y1 - 2004/4
N2 - PURPOSE. To elucidate the mechanisms of vitamin C transport across the blood-retinal barrier (BRB) in vivo and in vitro. METHODS. [14C] Dehydroascorbic acid (DHA) and [14C]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 (Kin) per gram of retina of [14C]DHA and [ 14C]AA was found to be 2.44 × 103 μL/(min · g retina) and 65.4 μL/(min · g retina), respectively. In the retina and brain, the Kin of [14C]DHA was approximately 38 times greater than that of [14C]AA. whereas there was no major difference in the heart. The Kin of [14C]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 [14C]DHA was 37 times greater than that of [14C]AA, which is in agreement with the results of the in vivo study. [14C]DHA uptake by TR-iBRB2 cells took place in an Na +-independent and concentration-dependent manner with a Km of 93.4 μM. This process was inhibited by substrates and inhibitors of glucose transporters. [14C]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.
AB - PURPOSE. To elucidate the mechanisms of vitamin C transport across the blood-retinal barrier (BRB) in vivo and in vitro. METHODS. [14C] Dehydroascorbic acid (DHA) and [14C]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 (Kin) per gram of retina of [14C]DHA and [ 14C]AA was found to be 2.44 × 103 μL/(min · g retina) and 65.4 μL/(min · g retina), respectively. In the retina and brain, the Kin of [14C]DHA was approximately 38 times greater than that of [14C]AA. whereas there was no major difference in the heart. The Kin of [14C]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 [14C]DHA was 37 times greater than that of [14C]AA, which is in agreement with the results of the in vivo study. [14C]DHA uptake by TR-iBRB2 cells took place in an Na +-independent and concentration-dependent manner with a Km of 93.4 μM. This process was inhibited by substrates and inhibitors of glucose transporters. [14C]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.
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U2 - 10.1167/iovs.03-0505
DO - 10.1167/iovs.03-0505
M3 - Article
C2 - 15037592
AN - SCOPUS:2142819383
VL - 45
SP - 1232
EP - 1239
JO - Investigative Ophthalmology and Visual Science
JF - Investigative Ophthalmology and Visual Science
SN - 0146-0404
IS - 4
ER -