UV light increases vitamin C uptake by bovine lens epithelialcells

[摘要] Purpose: To establish whether the oxidation of ascorbic acid (AA) inthe aqueous humor may contribute to maintain the high concentration ofAA of the anterior eye tissues during oxidative stress.Methods: Primary cultures of bovine lens epithelial cells (BLEC)were incubated in a medium with the concentration of AA, glutathione(GSH), and cysteine (Cys) found in the aqueous humor. The intracellularconcentration of AA was measured over time and compared to that ofcultures maintained in the same medium but exposed to UV light.Results: The uptake of extracellular AA by BLEC was 0.09±0.01nmol/mg protein/min, but rose to 0.53±0.02 nmol/mg protein/min whencell cultures were exposed to a dose of UV-C light (178μW/cm2)capable of oxidizing extracellular AA but not intracellular AA. Underthe same conditions, intracellular AA was oxidized when cell monolayerswere treated with 1,3-bis(2-Chloroethyl)-1-nitrosourea (BCNU), aninhibitor of glutathione reductase and thioredoxin reductase. The uptakeof the oxidized form of AA, dehydroascorbic acid (DHAA), wasapproximately 7 times quicker than that of AA; the uptake andintracellular reduction of DHAA to AA was inhibited by depletingintracellular GSH. Extracellula glucose inhibited the uptake of DHAA byBLEC, and the extent of this inhibition was dependent on theconcentration of extracellular glucose.Conclusions: During mild oxidative stress, AA contained in aqueoushumor may provide tissues of the anterior eye with a source of DHAAwhich is readily taken up and converted to intracellular AA, whileintracellular AA is maintained in the reduced status by intracellularantioxidant systems. Since glucose inhibited DHAA uptake, thisprotective mechanism could be impaired in diabetes.

[学科分类] 生物化学/生物物理