The role of ascorbic acid transporter in the lens of streptozotocin-induced diabetic rat

Ascorbic acid (AA) is found in high concentrations in the lens and protects the lens from photochemical events such as photo-oxidation. Diabetes reduces the concentration of AA in the lens, and it has been suggested that AA supplementation may rescue lens AA in diabetic patients. In the present study, the effects of dietary supplementation with AA were studied to assess changes in AA concentration and AA transporter expression in the lenses of streptozotocin (STZ)-induced diabetic rats. AA was lower in the aqueous humors and lenses of diabetic rats than in control rats, and low AA levels could be normalized with dietary AA supplementation. The sodium-dependent ascorbic acid transporter2, SVCT2, is transporter of AA, and glucose transporter 1 and 3 (GLUT1 and GLUT3) are transporters of dehydroascobic acid. Transcription of GLUT1 and GLUT3 was not changed as a result of diabetes or AA treatment, and the SVCT2 was increased in diabetic rats and normalized by AA supplementation in diabetic rats. Aquaporin 0 (AQP0) expression was increased in diabetic rats and by AA treatment. The rate of AA transport of vesicle originally from diabetic lens and that with AA treatment were greater than that from control rats with or without AA treatment. These results suggest that ascorbates are transported by AQP0 as well as by SVCT2, GLUT1 and GLUT3, and that supplementation with AA may help prevent diabetic cataracts.