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At least 73 records · Page 4Linked to original sources
PubMed1995

A protective role for glutathione-dependent reduction of dehydroascorbic acid in lens epithelium.

PURPOSE: In view of the antioxidant role of ascorbic acid and the glutathione redox cycle in the lens, the authors have studied the relationship of the cycle to reduction of the oxidized product of ascorbic acid, dehydroascorbic acid (DHA), in lens epithelium. METHODS: Cultured dog lens epithelial cells and intact rabbit lenses were exposed to various concentrations of DHA in experiments performed at 20 degrees C to minimize hydrolysis of the compound (t1/2 of 5 minutes at 37 degrees C). Levels of glutathione (GSH) and oxidized glutathione (GSSG) were measured in lens cells and whole lens epithelial by electrochemical detection. RESULTS: Treatment of lens cells with 1 mM DHA for 0.5 to 3 hours in the absence of glucose (glucose is required for the reduction of GSSG through the glutathione redox cycle) produced from 60% to complete oxidation of GSH (controls contained negligible GSSG) and distinct morphologic changes (cell contraction and blebbing), as shown by scanning electron microscopy. Glucose prevented these effects and allowed nearly immediate recovery of GSH after DHA exposure in the absence of glucose. A dose-dependent response was observed for the formation of GSSG in cultured cells from 0.05 to 0.5 mM DHA in the absence of glucose. The results of experiments performed with DHA plus an inhibitor of glutathione reductase mimicked those obtained using DHA minus glucose. DHA produced a 3- to 10-fold stimulation of hexose monophosphate shunt activity in cultured lens cells and whole lenses, which was prevented by the inhibition of glutathione reductase. Treatment of whole lenses with DHA minus glucose also produced oxidation of epithelial GSH and was accompanied by the loss of lens transparency. No evidence was found for dehydroascorbate reductase activity in the lens epithelium. CONCLUSIONS: The exposure of lenses and lens epithelial cells to DHA under conditions in which the glutathione redox cycle was compromised resulted in the disappearance of GSH in the tissues and the appearance of GSSG. The reduction of DHA was shown to be linked to the glutathione redox cycle by a nonenzymatic interaction between GSH and DHA. Reduction of DHA in the lens is important because of the potential toxicity of this oxidant and/or its degradation products.

Animals↗
PubMed1990

Ascorbic and dehydroascorbic acids measured in plasma preserved with dithiothreitol or metaphosphoric acid.

We describe a rapid method for accurately and precisely measuring ascorbic acid and dehydroascorbic acid in plasma. Total analysis time is less than 10 min, replicate analyses of a single pool provide precision less than or equal to 2%, and values measured in supplemented samples agree with known concentrations of 4.68 and 11.83 mg/L. The stability and homogeneity of lyophilized plasma samples supplemented with ascorbic acid and dithiothreitol are documented. We also describe a procedure in which metaphosphoric acid (50 g/L) is used to prepare a reference material for the measurement of ascorbic acid and dehydroascorbic acid. The procedure for both acids consists of first measuring the native ascorbic acid, then reducing the dehydroascorbic acid, at neutral pH, with dithiothreitol, and finally measuring the total ascorbic acid; dehydroascorbic acid is then determined by difference. The metaphosphoric-acid-treated samples were stable at -70 degrees C, but stability decreased with temperature over the range examined, 4-50 degrees C.

Ascorbic Acid↗
PubMed1980

An improved method for determination of L-ascorbic acid and L-dehydroascorbic acid in blood plasma.

Various conditions for reducing L-dehydroascorbic acid were studied, using dithiothreitol. This led to an improved method for the separate determination of L-ascorbic acid and L-dehydroascorbic acid in blood plasma. The content of ascorbic acid was determined by an alpha,alpha'-dipyridyl method (A). Dehydroascorbic acid was reduced to ascorbic acid by incubation with dithiothreitol at room temperature for 10 min at pH 6.5 to 8.0. After removing the excess dithiothreitol with N-ethylmaleimide, total ascorbic acids, i.e. reduced plus original, were determined by the alpha,alpha'-dipyridyl method (B). The amount of dehydroascorbic acid could then be calculated from these results (B minus A).

2,2'-Dipyridyl↗
PubMed1999

Low levels of dehydroascorbic acid in uraemic serum and the partial correction of dehydroascorbic acid deficiency by haemodialysis.

BACKGROUND: Vitamin C is currently considered a potent water-soluble antioxidant and it appeared reasonable to study the metabolic changes of vitamin C in uraemia and during haemodialysis. METHODS: We measured the levels of ascorbic, dehydroascorbic and diketogulonic acids in sera of uraemic patients before and during haemodialysis, using the 2,4-dinitrophenylhydrazine method. RESULTS: The results indicate that the levels of ascorbic and dehydroascorbic acids in uraemic sera are low in comparison with controls, but the levels of diketogulonic acid are higher than in healthy persons. The comparison of ratios between levels of these substances in uraemic sera and in normal sera indicate that the oxidation of ascorbic acid to dehydroascorbic in uraemia proceeds much slower than in controls. We propose that uraemic patients are characterized by pronounced deficiency of dehydroascorbic acid. A marked decrease of ascorbic and diketogulonic acid plasma levels, and a pronounced increase of dehydroascorbic acid levels during haemodialysis was observed. Ratios between plasma levels of ascorbic and dehydroascorbic acids following haemodialysis are the same as in healthy persons. CONCLUSION: Uraemic patients are characterized by marked deficiency of dehydroascorbic acid and this deficiency can be partially corrected by haemodialysis.

Adolescent↗