Showing papers on "Dehydroascorbic acid published in 2000"

Simulating ozone detoxification in the leaf apoplast through the direct reaction with ascorbate.

Abstract: This paper presents a mathematical model which enables the semi-quantification of ozone (O3) detoxification, based upon the direct reaction of the pollutant with ascorbate (ASC) located in the aqueous matrix associated with the cell wall (i.e. the apoplast). The model describes the uptake of ozone into the leaf and its direct reaction with ASC, taking into consideration the regeneration of dehydroascorbic acid in the cytosol, the rate of replenishment of cell wall ASC and the distribution of ASC between sub-cellular compartments – based upon the permeability of biomembranes to the neutral species, ascorbic acid and the pH of various sub-cellular compartments. The importance of various physico-chemical characteristics (e.g. stomatal conductance, mesophyll cell wall thickness and tortuosity, chloroplast volume, apoplast pH, ASC:O3 reaction stoichiometry) in mediating the flux of ozone to the plasmalemma is analysed. Model simulations, supported by experimental observations, suggest that the ASC concentration in the leaf apoplast is high enough to scavenge a significant proportion of the O3 taken up into the leaf interior, under environmentally relevant conditions. However, there is considerable variation between taxa in the potential degree of protection afforded by apoplastic ASC, emphasizing the need for an improved understanding of the reaction chemistry of O3 in the cell wall.

Comparison of high-performance liquid chromatography and spectrofluorimetry for vitamin C analysis of green beans (Phaseolus vulgaris L.).

Abstract: A spectrofluorimetric method and a chromatographic method [high-performance liquid chromatography – ultraviolet (HPLC-UV) detection] were compared for vitamin C analysis of green beans For HPLC-UV, the determination was performed before [ascorbic acid (AA)] and after reduction with dithiothreitol [AA + dehydroascorbic acid (DHAA)]; for spectrofluorimetry, DHAA was determined after oxidation with activated charcoal The fluorimetric determination of DHAA before oxidation was also carried out, and showed good precision but poor accuracy (very high recovery percentages) HPLC-UV showed better linearity and sensitivity, while spectrofluorimetry was more precise Both methods were suitable for green bean samples, and the choice of which one to use depends on the particular interest of the analysis: spectrofluorimetry may be preferable when the total content of vitamin C is required, but not for individual analysis of each form HPLC-UV is more suitable when the interest of the analysis is the ascorbic acid form as a deterioration index of vegetable products

Apoptosis-inducing activity of vitamin C and vitamin K.

Abstract: Apoptosis-inducing activity of vitamins C and K and of their analogs are reviewed. Vitamin C shows both reducing and oxidizing activities, depending on the environment in which this vitamin is present. Higher concentrations of vitamin C induce apoptotic cell death in various tumor cell lines including oral squamous cell carcinoma and salivary gland tumor cell lines, possibly via its prooxidant action. The apoptosis-inducing activity of ascorbate is stimulated by Cu2+, lignin and ion chelator, and inhibited by catalase, Fe3+, Co2+ and saliva. On the other hand, at lower concentrations, ascorbic acid displays an antioxidant property, preventing the spontaneous and stress or antitumor agent-induced apoptosis. Sodium 5,6-benzylidene-L-ascorbate, intravenous administration of which induces degeneration of human inoperable tumors and rat hepatocellular carcinoma in vivo, induces apoptotic or non-apoptotic cell death, depending on the types of target cells. On the other hand, elevation of intracellular concentration of ascorbic acid by treatment with ascorbate 2-phosphate or dehydroascorbic acid makes the cells resistant to the oxidative stress-induced apoptosis. Vitamin K2, which has a geranylgeranyl group as a side chain,and vitamin K3 induces apoptosis of various cultured cells including osteoclasts and osteoblasts, by elevating peroxide and superoxide radicals. Synergistic apoptosis-inducing actions have been found between vitamins C and K, and between these vitamins and antiproliferative agents. The possible therapeutic application of these vitamins is discussed.

Glucose Modulates Vitamin C Transport in Adult Human Small Intestinal Brush Border Membrane Vesicles

Abstract: The uptake of L-ascorbate (vitamin C) and its oxidized form, dehydro-L-ascorbic acid (DHAA), was evaluated in brush border membrane vesicles isolated from adult human duodenum, jejunum and ileum. Ascorbate was taken up along the entire length of the small intestine with a threefold higher initial uptake rate in distal than proximal segments. Ascorbate uptake was Na(+)-dependent, potential-sensitive and saturable (K(m), 200 micromol/L), whereas DHAA transport involved facilitated diffusion (K(m), 800 micromol/L). Pharmacologic experiments were conducted to characterize further these transport mechanisms. DHAA uptake was not mediated by the fructose carrier GLUT5, the uridine transporter or the 4, 4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive anion exchanger of the apical membrane. DIDS and sulfinpyrazone, an inhibitor of the urate/lactate exchanger, both significantly reduced the initial rate of ascorbate uptake. Acidic pH inhibited ascorbate uptake, and this effect was not due to a transmembrane proton gradient. Increasing concentrations of glucose in the transport media also significantly inhibited ascorbate uptake, but no effect of glucose was seen when glucose internalization was blocked by phlorizin. Preloading the vesicles with glucose inhibited ascorbate uptake similarly, indicating that glucose interferes with the ascorbate transporter from the internal side of the membrane. The results of this study suggest that DHAA crosses the apical membrane by facilitated diffusion, whereas ascorbate transport is a Na(+)-dependent, electrogenic process modulated by glucose.

Ascorbate and dehydroascorbate influence cell cycle progression in a tobacco cell suspension.

Abstract: In addition to its well-known antioxidant properties, ascorbate (ASC) is capable of influencing normal cell cycle progression in plants. In this work we demonstrate that the oxidized molecule dehydroas-corbate (DHA) is the active redox form in this respect. Our results indicate that the reduction of

Reaction of ascorbic acid with S-nitrosothiols: clear evidence for two distinct reaction pathways

Abstract: Ascorbate reacts with S-nitrosothiols generally, in the pH range 3–13 by way of two distinct pathways, (a) at low [ascorbate], typically below ≈1 × 10−4 mol dm−3 which leads to the formation of NO and the disulfide, and (b) at higher [ascorbate] when the products are the thiol and NO. Reaction (a) is Cu2+-dependent, and is completely cut out in the presence of EDTA, whereas reaction (b) is totally independent of [Cu2+] and takes place readily whether EDTA is present or not. For S-nitrosoglutathione (GSNO) the two reactions can be made quite separate, although for some reactants the two reactions overlap. In reaction (a), ascorbate acts as a reducing agent, generating Cu+ from Cu2+, which in turn reacts with RSNO forming initially NO, Cu2+ and RS−. The latter can then play the role of reducing agent for Cu2+, leading to disulfide formation. Ascorbate will initiate reaction when the free thiolate has initially been reduced to a very low level by the synthesis of RSNO from a large excess of nitrous acid over the thiol. Reaction (b) is interpreted in terms of nucleophilic attack by ascorbate at the nitroso-nitrogen atom, leading to thiol and O-nitrosoascorbate which breaks up, by a free-radical pathway, to give dehydroascorbic acid and NO. A similar pathway is the accepted mechanism in the literature for the nitrosation of ascorbate by nitrous acid and alkyl nitrites. The rate constant for the Cu2+ -independent pathway increases sharply with pH and analysis of the variation of the rate constant with pH identifies a reaction pathway via both the mono- and di-anion forms of ascorbate, with the latter being the more reactive. As expected the entropy of activation is large and negative. Some aspects of structure–reactivity trends are discussed.

Intracellular Accumulation of Ascorbic Acid Is Inhibited by Flavonoids via Blocking of Dehydroascorbic Acid and Ascorbic Acid Uptakes in HL-60, U937 and Jurkat Cells

Abstract: In HL-60, U937 and Jurkat cells, the intracellular accumulation of ascorbic acid occurred via uptakes of both dehydroascorbic acid (an oxidized metabolite of ascorbic acid) and ascorbic acid (vitamin C). Dehydroascorbic acid and ascorbic acid were transported into cells by sodium-independent glucose transporters (GLUT 1 and GLUT 3) and sodium-dependent ascorbic acid transporters, respectively. Flavonoids inhibited the intracellular accumulation of ascorbic acid by blocking dehydroascorbic acid and ascorbic acid uptakes in the transformed cells. At flavonoid concentrations of 10-70 micromol/L, approximately 50% of dehydroascorbic acid uptake was inhibited in the cells. In Jurkat cells, two potent flavonoids (myricetin and quercetin) competitively inhibited dehydroascorbic acid uptake, and K(i) values were approximately 14 and 15 micromol/L, respectively. Because GLUT 1 and GLUT 3 transport dehydroascorbic acid, the inhibition of dehydroascorbic acid uptake by flavonoids was investigated by using Chinese hamster ovary cells overexpressing rat GLUT 1 or human GLUT 3. Myricetin at concentrations of 22 and 18 micromol/L, respectively, inhibited half of dehydroascorbic acid uptake in the cells overexpressing GLUT 1 and GLUT 3. Myricetin also inhibited ascorbic acid uptake; inhibition was noncompetitive with K(i) = 14 micromol/L in Jurkat cells. These data indicate that flavonoids inhibit both ascorbic acid and dehydroascorbic acid uptake but do so by different mechanisms. These data may contribute to new understanding of the biological effect of flavonoids on the intracellular accumulation of ascorbic acid in human cells.

Antioxidant status of anoxia-tolerant and -intolerant plant species under anoxia and reaeration

Abstract: The redox potential of the cell, as well as the antioxidant status of the tissue, are considered to be important regulatory constituents in an adaptive response in plants. Here the involvement of active antioxidants ascorbic acid (AA), reduced glutathione (GSH) and α- and β-tocopherols in reactive oxygen species scavenging, and the effect of anoxic stress on their reduction state were studied in 4 anoxia-tolerant and -intolerant plant species: Iris germanica L., Iris pseudacorus L., wheat (Triticum aestivum L. cv. Leningradka) and rice (Oryza sativa L. cv. VNIIR). The initial antioxidant content (both AA and GSH) was higher in the rhizomes of the more anoxia-tolerant Iris spp., as compared with that of the roots of the cereals. The predominant form of ascorbate was dehydroascorbic acid (DHA) in the cereals and AA in the Iris spp. Imposition of anoxia with subsequent reoxygenation resulted in an overall depletion of the reduced forms of antioxidants. No concurrent increase in oxidised forms (DHA and conjugated glutathione) was observed in anoxic samples. «-tocopherol content in Iris spp. was in the range 1-2 μg g -1 fresh weight, while β-tocopherol content was higher in the anoxia-intolerant I. germanica (7.2 μg g -1 fresh weight) as compared with the tolerant I. pseudacorus (1.5 μg g -1 fresh weight). In I. pseudacorus, a significant decrease in α- and β-tocopherol levels was observed only after long-term (45 days) anoxia. The results suggested exclusion of AA and GSH from the redox cycling under prolonged anoxia, and a concomitant decrease in the redox state, as well as an anoxia-induced depletion of α- and β-tocopherols.

Dehydroascorbic acid uptake in a human keratinocyte cell line (HaCaT) is glutathione-independent

Abstract: Vitamin C plays an important role in neutralizing toxic free radicals formed during oxidative metabolism or UV exposure of human skin. This study was performed to investigate the mechanisms that regulate the homoeostasis of vitamin C in HaCaT cells by identifying the events involved in the transport and in the reduction of dehydroascorbic acid. Dehydroascorbic acid accumulated to a greater extent and faster compared with ascorbic acid; its transport appeared to be mediated by hexose transporters and was entirely distinct from ascorbic acid transport. Dehydroascorbate reductase activity was unaffected by glutathione depletion, although it was sensitive to thiol protein reagents. These observations, as well as the subcellular distribution of this enzymic activity and the cofactor specificity, indicate that thioredoxin reductase and lipoamide dehydrogenase play an important role in this reduction process. HaCaT cells were able to enhance their dehydroascorbic acid reductase activity in response to oxidative stress.

NMR analytical approach to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of antioxidants in tea using 1,1-diphenyl-2-picrylhydrazyl.

Abstract: (+)-Catechin, ethyl gallate, ascorbic acid, and α-tocopherol were reacted with 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the reaction mixtures were subjected to 13C-nuclear magnetic resonance (NMR) analyses to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of each antioxidant. When ascorbic acid was reacted with DPPH, it was oxidized to dehydroascorbic acid by DPPH. When a mixture of ascorbic acid and (+)-catechin was reacted with DPPH, ascorbic acid scavenged DPPH radical faster than (+)-catechin. Ascorbic acid also scavenged DPPH radical faster than ethyl gallate and α-tocopherol. When (+)-catechin was reacted with DPPH, the B-ring of (+)-catechin changed to an o-quinone structure. However, it was reduced to (+)-catechin by ethyl gallate or α-tocopherol. α-Tocopherol and ethyl gallate had almost identical antioxidative activities. Therefore, the order of radical-scavenging ability (speed) suggested by our 13C NMR study was as follows: ascorbic acid > α-tocophero...

Dehydroascorbic acid irreversibly inhibits hexokinase activity.

Abstract: The oxidized form of vitamin C (dehydroascorbic acid, DHA) completely and irreversibly inactivates recombinant human hexokinase type I, in a pseudo-first order fashion. The inactivation reaction occurs without saturation, indicating that DHA does not form a reversible complex with hexokinase. Further characterization of this response revealed that the inactivation does not require oxygen and that dithiothreitol, while able to prevent the DHA-mediated loss of enzyme activity, failed to restore the activity of the DHA-inhibited enzyme. Inactivation was not associated with cleavage of the peptide chain or cross-linking. The decay in enzymatic activity was however both dependent on deprotonation of a residue with an alkaline pKa and associated with covalent binding of DHA to the protein. In addition, inactivation of hexokinase decreased or increased, respectively, in the presence of the substrates glucose or MgATP. Finally, amino acid analysis of the DHA-modified hexokinase revealed a decrease of cysteine residues. Taken together, the above results are consistent with the possibility that covalent binding of the reagent with a thiol group of cysteine is a critical event for the DHA-mediated loss of hexokinase activity.

Method for increasing the concentration of ascorbic acid in brain tissues of a subject

Abstract: This invention provides a method for increasing the concentration of ascorbic acid in the cells of a subject which comprises administering to the subject an amount of dehydroascorbic acid effective to increase the concentration of ascorbic acid in the subject's cells. This invention further provides a method for increasing the antioxidant potential of the cells of a subject which comprises administering to the subject an amount of dehydroascorbic acid effective to increase the antioxidant potential of the subject's cells. This invention also provides a method for increasing the concentration of ascorbic acid in brain tissue of a subject which comprises administering to the subject an amount of dehydroascorbic acid effective to increase the concentration of ascorbic acid in the subject's brain tissue. This invention also provides a method for increasing the antioxidant potential of brain tissue of a subject which comprises administering to the subject an amount of dehydroascorbic acid effective to increase the antioxidant potential of the subject's brain tissue.

Distinct mechanisms of transport of ascorbic acid and dehydroascorbic acid in intestinal epithelial cells (IEC-6).

Abstract: Ascorbic acid (AsA) is an essential nutrient for humans as they lack its biosynthesizing key enzyme. Its absorption mechanism in small intestinal epithelial cells still remains to be resolved. In this study, the transport mechanisms functioning on the uptake of AsA and its oxidized form, dehydroascorbic acid (DHA), were investigated using rat small intestinal epithelial cell line IEC-6. Both AsA and DHA were accumulated in the cells in time- and concentration-dependent manners, but their absorption kinetics were apparently different. The saturability of AsA uptake was shown at a considerably lower concentration in IEC-6 cells as well as other mammalian cells, indicating that this absorption was mediated by a specific transporting carrier. The absorption efficiency of AsA was about 1/5-1/10 that of DHA at the same concentration range and, moreover, the uptake of DHA was almost comparable to that of 2-deoxy-D-glucose, an alternative of glucose. The uptake of AsA was diminished by the removal of sodium ion, but not by the addition of glucose, whereas that of DHA was sodium ion-independent and effectively inhibited by glucose. In addition, phlorizin and cytochalasin B, which are blockers of glucose transporters, interfered the uptake of DHA more efficiently than that of AsA. These results indicate that there are at least two distinct transport systems of vitamin C in rat small intestinal epithelial cells; AsA is transported by a specific transporter and DHA is mainly transported by glucose transporter(s).

Mapping of the human genes (SLC23A2 and SLC23A1) coding for vitamin C transporters 1 and 2 (SVCT1 and SVCT2) to 5q23 and 20p12, respectively.

Abstract: Editor—Ascorbate or vitamin C (VC) is an essential reducing agent and antioxidant that participates in a variety of metabolic processes.1 Unlike rodents and other animals, humans depend on dietary intake of VC to meet their daily requirement.1 2 VC intracellular accumulation is mediated through two distinct pathways. In one pathway, vitamin C is transported as such by high affinity sodium dependent carriers. In a second pathway, oxidised vitamin C (dehydroascorbic acid) is transported on glucose transporters GLUT1 and GLUT3.3 4 Recently the coding sequences of the human Na+ dependent VC transporters types 1 and 2, hSVCT1 and hSVCT2, products of the SLC23A2 and SLC23A1 genes, respectively, were identified.5-7 Both genes were first identified as anonymous expression sequence tags (ESTs).8 9Subsequently, and based on homology, human SLC23A2 and SLC23A1 were identified as nucleobase transporters YSPL3 and YSPL2 , respectively.10 Their full length coding sequences, expression profile, and function were then identified.5-7 The EST location of YSPL3 and the physical location of the SLC23A2 gene on chromosome 5 were also recently confirmed.6 8-10 The known enzymatic roles of VC in collagen hydroxylation, carnitine biosynthesis, formation of the catecholamine norepinephrine, and as an inhibitor of oxidation make both SLC23A2 and SLC23A1 candidate genes for a variety of human disorders.1 2 These may include monogenic diseases affecting the skeleton, fat metabolism, and the endocrine glands, as well as polygenic conditions, such as osteoporosis, obesity, hypertension, and aging. Thus, the knowledge of the precise genetic and …

Flow injection spectrophotometric determination of ascorbic acid in soft drinks and beer.

Abstract: Two spectrophotometric methods, a photochemical and a non-photochemical, for the determination of ascorbic acid in soft drinks and beer using a flow-injection system are proposed The non-photochemical method is based on the redox reaction that takes place between ascorbic acid and Fe(III), yielding dehydroascorbic acid and Fe(II) Fe(II) reacts with 1,10-phenantroline, originating the reddish orange Fe(phen)3 2+ complex (ferroin) This complex is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of ascorbic acid in the sample The photochemical method has the same basis, nevertheless, uses the irradiation with visible light to enhance the redox reaction and so achieve higher sensitivities in the analysis The non-photochemical method shows a linear range between 5 and 80 μg mL−1, with a relative standard deviation of 16% (n = 11), a detection limit of 27 μg mL−1 and a sample throughput of ¶60 samples h−1 The photochemical method shows a linear range between 1 and 80 μg mL−1, with a relative standard deviation of 10% (n = 11), a detection limit of 05 μg mL−1 and a sample throughput of 40 samples h−1

Simultaneous Determination of l-Ascorbic Acid, Glutathione, and Their Oxidized Forms in Ozone-Exposed Vascular Plants by Capillary Zone Electrophoresis

Abstract: Simultaneous determination of ascorbic acid (AA), glutathione (GSH), and oxidized glutathione (GSSG) in vascular plants has been achieved by capillary zone electrophoresis. A background electrolyte containing a phosphate buffer of pH 7 and hexadimethrin bromide for dynamic control of electroosmotic flow was used. Separation was performed in less than 5 min. The signal was simultaneously monitored at 265 and 200 nm. Dehydroascorbic acid (DHA) was determined in another aliquot of the same plant extract upon reduction with dl-homocysteine. Limits of detection of AA, GSH, and GSSG ranged from 0.2 to 0.8 μg mL-1, which corresponded from 0.04 to 0.16 mg per 100 g fresh weight of tomato, watermelon, and potato leaves. Plants exposed to a high ozone concentration (1600 μg m-3) in a laboratory fumigation system during 1, 2, 3, and 5 h showed progressive ozone-induced oxidative stress. This could be seen as a simultaneous decrease of the AA/(AA+DHA) and GSH/(GSH+GSSG) ratios; however, the decline rate was higher fo...

A simple and rapid method for the routine assay of total ascorbic acid in serum and plasma using ascorbate oxidase and o-phenylenediamine.

Abstract: A simple and rapid analysis of total ascorbic acid (AsA) in serum and plasma and its automated analysis are described. AsA is oxidized by ascorbate oxidase (AsA oxi-dase) to dehydroascorbic acid that then reacts with o-phenylenediamine (OPDA) to form a quinoxaline derivative that absorbs at 340 nm. The change in absorbance is directly propor-tional to the total AsA concentration. The assay was validated with a linear concentration range of 0.8-80mg/L, and the within-day and between-day assays precision did not exceed 8.6% and 12.5%, respectively. On 47 sera, the manual enzymatic procedure gave 0.2mg/L on average lower values than those of an automated enzymatic procedure with a correla-tion coefficient of 0.847. On another 66 sera, results by automated enzymatic method cor-related well with the HPLC method and the regression equation is Y (enzymatic, automated)=0.97 X (HPLC)+0.1, r=0.980, Sy.x=0.6mg/L. An experienced analyst can perform about 24 manual assays per hour whereas the automated procedure gave a rate of 100 assays per hour.<

Ascorbic acid reduction of residual active chlorine in potable water prior to halocarboxylate determination

Abstract: In studies on the formation of disinfection byproducts (DBPs), it is necessary to scavenge residual active (oxidizing) chlorine in order to fix the chlorination byproducts (such as haloethanoates) at a point in time. Such research projects often have distinct needs from requirements for regulatory compliance monitoring. Thus, methods designed for compliance monitoring are not always directly applicable, but must be adapted. This research describes an adaptation of EPA Method 552 in which ascorbic acid treatment is shown to be a satisfactory means for reducing residual oxidizing chlorine, i.e., HOCl, ClO−, and Cl2, prior to determining concentrations of halocarboxylates. Ascorbic acid rapidly reduces oxidizing chlorine compounds, and it has the advantage of producing inorganic halides and dehydroascorbic acid as opposed to halogenated organic molecules as byproducts. In deionized water and a sample of chlorinated tap water, systematic biases relative to strict adherence to Method 552 were precise and could be corrected for using similarly treated standards and analyte-fortified (spiked) samples. This was demonstrated for the quantitation of chloroethanoate, bromoethanoate, 2,2-dichloropropanoate (dalapon), trichloroethanoate, bromochloroethanoate, and bromodichloroethanoate when extracted, as the acids, into tert-butyl methyl ether (MTBE) and esterified with diazomethane prior to gas chromatography with electron capture detection (GC-ECD). Recoveries for chloroethanoate, bromoethanoate, dalapon, dichloroethanoate, trichloroethanoate, bromochloroethanoate, bromodichloroethanoate, dibromoethanoate, and 2-bromopropanoate at concentrations near the lower limit of detection were acceptable. Ascorbic acid reduction appears to be the best option presently available when there is a need to quench residual oxidants fast in a DBP formation study without generating other halospecies but must be implemented cautiously to ensure no untoward interactions in the matrix.

Impaired reductive regeneration of ascorbic acid in the Goto-Kakizaki diabetic rat.

Abstract: Ascorbic acid (AA) is a naturally occurring major antioxidant that is essential for the scavenging of toxic free radicals in both plasma and tissues AA levels in plasma and tissues have been reported to be significantly lower than normal in diabetic animals and humans, and might contribute to the complications found at the late stages of diabetes In this study, plasma and hepatic AA levels and AA regeneration were studied in the Goto-Kakizaki diabetic rat (GK rat) to elucidate the mechanism of decreasing plasma and hepatic AA levels in diabetes AA concentrations in the plasma and liver were significantly lower in GK than in control rats AA levels in primary cultured hepatocytes derived from GK rats were lower than those derived from control Wistar rats with or without dehydroascorbic acid (DHA) in the medium Among various enzyme activities that reduce DHA to AA, the NADPH-dependent regeneration of AA in the liver was significantly suppressed in GK rats Northern blot analysis revealed that only the expression of 3-alpha-hydroxysteroid dehydrogenase (AKR) was significantly suppressed in these rats These results suggest that decreased AA-regenerating activity, probably through decreased expression of AKR, contributes to the decreased AA levels and increased oxidative stress in GK rats

The Effects of Antioxidants on Browning and on Degradation Products Caused by Dehydroascorbic Acid

Abstract: The efficiency of L-cysteine (cysteine) and sodium sulfite as antioxidants was examined in the browning of an aqueous solution of 100 mM dehydroascorbic acid (DHA). The browning was suppressed at 100 mM cysteine and at 40 mM and higher concentrations of sodium sulfite, but it increased in the presence of 10 mM of those agents. These agents did not allow the reduction of DHA to L-ascorbic acid (AA). These results suggest that the suppression or acceleration of browning is likely to be related to some degraded intermediates of DHA. The two colorless intermediates, which during DHA breakdown eventually transform into browning pigments, were discussed with regard to the browning regulation mechanism.

Dehydroascorbic acid formulations and uses thereof

Abstract: The invention provides improved dehydroascorbic acid compositions and methods for treatment of medical conditions The dehydroascorbic acid compositions are useful in the treatment of a variety of conditions which benefit from increased dehydroascorbic acid or ascorbic acid concentrations in tissues affected by the conditions