Ascorbic Acid Determination by Hydrophobic Liquid Chromatography of the Osazone Derivative. Application to the Analysis of Aqueous Humor

Measurement of ascorbate and dehydroascorbate contents in biological fluids

Instabilities of ascorbate and dehydroascorbate throughout sample processing are clearly a significant aspect of quantifying of them. Contents of ascorbate in biological fluids decrease with measurable oxidation occurring within minutes to hours. Similarly, dehydroascorbate disappears with chemical or enzymatic degradation within minutes. The half-life of dehydroascorbate in human heparinized plasma was approximately 2 min. These results indicated that the amount of dehydroascorbate present in sample solutions is a function of both the oxidation of ascorbate and the degradation of dehydroascorbate during the processing of biological fluids. To quantify ascorbate and dehydroascorbate concentrations in biological fluids including circulating blood plasma and urine, we established a high-performance liquid chromatographic method, which requires no pretreatment of sample solutions.

Protection by ascorbic acid against oxidative injury of isolated hepatocytes

1. The ability of ascorbic acid to protect from prooxidant-induced toxic injury was investigated in isolated, intact rat hepatocytes, whose ascorbic acid content had been restored by means of exogenous supplementation. 2. Ascorbate-supplemented and ascorbate-non-supplemented cells in suspension were treated with a series of different prooxidants (allyl alcohol, diethyl maleate, carbon tetrachloride, menadione), and the development of lipid peroxidation and cell injury was evaluated. 3. With allyl alcohol and diethyl maleate, ascorbic acid was able to protect cells from both lipid peroxidation and cell injury. The same protection was offered by ascorbate also in hepatocytes obtained from vitamin E-deficient animals. 4. With carbon tetrachloride, ascorbate supplementation did not affect the initial steps of lipid peroxidation, but nevertheless provided a marked protection against lipid peroxidation and cell injury at later times of incubation. The protection was unaffected by the vitamin E content of cells. 5. With menadione, a toxin which does not induce lipid peroxidation, ascorbic acid did not protect cells against injury. 6. It is concluded that ascorbic acid can act as an efficient antioxidant in isolated rat liver cells, with protection against cell injury. The antioxidant effect appears primarily to involve membrane lipids, and can be independent from the cellular content of vitamin E, thus suggesting that ascorbic acid can play a direct and independent role in the intact cell, in addition to its synergistic interaction with vitamin E described in other models.

Measurement of ascorbic acid in human aqueous humour and plasma and bovine aqueous humour by high-performance liquid chromatography with electrochemical detection

High-performance liquid chromatography (HPLC) on ODS silica with cetyltrimethylammonium bromide as an ion-pairing reagent and electrochemical detection (ECD) was used to determine ascorbic acid in bovine and human aqueous humour and human plasma. Hydroquinone was used as the internal standard. A calibration curve plotted with ascorbic acid concentrations in the range 0.5-5 micrograms ml-1 for peak height versus internal standard peak height had a correlation coefficient of 0.998. The RSD (precision) between analyses of the same diluted sample was 1.5% and the RSD (reproducibility) between analyses of separate aliquots of the same sample of aqueous humour was 1.6%.

Lipid peroxidation and antioxidant systems in the liver injury produced by glutathione depleting agents

The mechanisms of the liver damage produced by three glutathione (GSH) depleting agents, bromobenzene, allyl alcohol and diethylmaleate, was investigated. The change in the antioxidant systems represented by alpha-tocopherol (vitamin E) and ascorbic acid were studied under conditions of severe GSH depletion. With each toxin liver necrosis was accompanied by lipid peroxidation that developed only after severe depletion of GSH. The hepatic level of vitamin E was decreased whenever extensive lipid peroxidation developed. In the case of bromobenzene intoxication, vitamin E decreased before the onset of lipid peroxidation. Changes in levels of the ascorbic and dehydroascorbic acid indicated a redox cycling of vitamin C with the oxidative stress induced by all the three agents. Such a change of the redox state of vitamin C (increase of the oxidized over the reduced form) may be an index of oxidative stress preceding lipid peroxidation in the case of bromobenzene. In the other cases, such a change is likely to be a consequence of lipid peroxidation. Experiments carried out with vitamin E deficient or supplemented diets indicated that the pathological phenomena occurring as a consequence of GSH depletion depend on hepatic levels of vitamin E. In vitamin E deficient animals, lipid peroxidation and liver necrosis appeared earlier than in animals fed the control diet. Animals fed a vitamin E supplemented diet had an hepatic vitamin E level double that obtained with a commercial pellet diet. In such animals, bromobenzene and allyl alcohol had only limited toxicity and diethylmaleate none in spite of comparable hepatic GSH depletion. Thus, vitamin E may largely modulate the expression of the toxicity by GSH depleting agents.

Ascorbic acid determination in serum and aqueous humour by high-performance liquid chromatography

High-performance liquid chromatography on a Supelcosil LC-HN2 analytical column in weak anion exchange mode has allowed separation of ascorbic acid, in less than 5 min, from other interfering substances in serum and aqueous humour. UV monitoring at 254 nm enables ascorbic acid to be detected at 20 pmol level. A method for determination of ascorbic acid concentration in serum and aqueous humour is described, and values from 10 cataract patients are reported.