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PubMed1984

[Lipid peroxidation in patients with gastric ulcer and cancer].

Levels of certain metabolites of peroxidation of lipids such as diene conjugates malonic dialdehyde, ascorbic acid, dehydroascorbic acid and diketogulonic acid were compared in 39 cases of gastric ulcer, 25 patients with gastric cancer and 14 healthy subjects. Diene conjugates and malonic dialdehyde levels appeared to be increased in cases of gastric ulcer and cancer. This was matched by a decrease in ascorbic acid and dehydroascorbic acid levels. Ulcer patients revealed enhanced diketogulonic acid concentration.

2,3-Diketogulonic Acid↗

PubMedDate not supplied

Seminal plasma biochemistry. I. Preliminary report: a possible mechanism for the liquefaction of human seminal plasma and its relationship to spermatozoal motility.

Based on indirect evidence it has been suggested that the liquefaction of human seminal plasma involves fibrinolytic and proteolytic enzymes and that the coagulum is formed by proteins. In this preliminary investigation evidence is presented for the involvement of seminal plasma sialyltransferase in liquefaction which suggests that the coagulum may be composed of glycoproteins. It is proposed that the glycoproteins form a polymer by the chelation of divalent metal ions via the carboxylic acid moieties of the sialic acid groups of the glycoproteins. The glycoprotein polymer may then be dismantled by the reduction of the meal ions by the oxidation of L-ascorbic acid, possibly allowing enzymes to complete the liquefaction process. A total of 100 semen samples from 30 male subjects whose semen profiles were considered "normal" by an independent assessor, were examined for the following: (i) liquefaction time of the seminal plasma; (ii) seminal plasma sialyltransferase activity; (iii) spermatozoal motility, defined as directional or nondirectional; (iv) spermatozoal count, and (v) seminal plasma content of free L-ascorbic acid, dehydroascorbic acid and glutathione. Linear regression analysis showed a significant correlation between sialyltransferase activity and the liquefaction time for seminal plasma. Similarly, multilinear regression analysis of the data showed that as the seminal plasma levels of L-ascorbic acid, total dehydroascorbic acid and glutathione increase, there is a decrease in spermatozoal motility and a decrease in the liquefaction time of the seminal plasma. The possible metabolic relationship of seminal plasma L-ascorbic acid and glutathione is discussed and a metabolic pathway is suggested.

Ascorbic Acid↗

PubMed1997

Nutritional and toxic factors in selected wild edible plants.

Nutritional (ascorbic acid, dehydroascorbic acid and carotenes); antinutritional and toxic components (oxalic acid, nitrate and erucic acid) were determined in sixteen popular species of wild edible plants which are collected for human consumption in southeast Spain. Ascorbic + dehydroascorbic acids contents were very high in several species, especially in Chenopodium album L. (155 mg/100 g). Carotenoid content ranged from 4.2 mg/100 g (Stellaria media Villars) to 15.4 mg/100 g (Amaranthus viridis L.). A range of values was found for oxalic acid from absence to 1100 mg/100 g of plant material. Nitrate contents ranged from 47 mg/100 g (Salicornia europaea L.) to 597 mg/100 g (Amaranthus viridis L.). Low amounts of erucic acid were found in the Cruciferae family (Sisymbrium irio L. 1.73%; Cardaria draba L. 1.23%) and Plantago major L. 3.45%.

Ascorbic Acid↗

PubMed1998

Ascorbic acid oxidation by hydrogen peroxide.

The oxidative degradation of ascorbic acid by hydrogen peroxide was examined to determine routes of degradation and identify the initial products which form when ascorbic acid is oxidized. When reacted with hydrogen peroxide, solutions of ascorbic acid and dehydroascorbic acid are both ultimately oxidized to the same species, having a mass spectrum consistent with threonic acid. When the intermediate steps in the oxidation of ascorbic acid are examined in detail, ascorbic acid, dehydroascorbic acid, and solutions containing hydrolyzed dehydroascorbic acid are all oxidized through a six-carbon compound previously proposed to be tetrahydroxydiketohexanoic acid. Both dehydroascorbic acid and hydrolyzed dehydroascorbic acid (diketogulonic acid) are more susceptible to hydrogen peroxide oxidation than ascorbic acid. Based on mass spectral analysis, diketogulonic acid serves as an oxygen sink, implying that it may be a better reducing agent for toxic oxygen species than ascorbic acid. These data indicate that oxidation of ascorbic acid by hydrogen peroxide primarily proceeds through three major six-carbon intermediates, each with distinctive redox properties. The stable metabolite diketogulonic may be a critical antioxidant in ascorbic-acid-containing systems.

2,3-Diketogulonic Acid↗

PubMed1998

Oxidative stress: an important phenomenon with pathogenetic significance in the progression of acute pancreatitis.

BACKGROUND: Reactive oxygen species and related oxidative damage have been implicated in the initiation of acute pancreatitis. Changes in these parameters during disease progression merit further investigation. AIMS: To evaluate changes and the clinical relevance of superoxide radicals, endogenous antioxidants, and lipid peroxidation during the course of acute pancreatitis. PATIENTS AND METHODS: Superoxide radicals (measured as lucigenin amplified chemiluminescence), ascorbic acid, dehydroascorbic acid, alpha tocopherol, and lipid peroxidation (measured as thiobarbiturate reactive substances) were analysed in blood samples from 56 healthy subjects, 30 patients with mild acute pancreatitis, and 23 patients with severe acute pancreatitis. The association with grades of disease severity was analysed. Measurements were repeated one and two weeks after onset of pancreatitis. RESULTS: In the blood from patients with acute pancreatitis, there were increased levels of the superoxide radical as well as lipid peroxides. There was notable depletion of ascorbic acid and an increased fraction of dehydroascorbic acid. Changes in alpha tocopherol were not great except in one case with poor prognosis. Differences between severe and mild acute pancreatitis were significant (p < 0.01). Variable but significant correlations with disease severity scores were found for most of these markers. The normalisation of these indexes postdated clinical recovery one or two weeks after onset of disease. CONCLUSIONS: Heightened oxidative stress appears early in the course of acute pancreatitis and lasts longer than the clinical manifestations. The dependence of disease severity on the imbalance between oxidants and natural defences suggests that oxidative stress may have a pivotal role in the progression of pancreatitis and may provide a target for treatment.

Acute Disease↗

PubMed1986

Ascorbate in plasma as measured by liquid chromatography and by dichlorophenolindophenol colorimetry.

Ascorbic acid was measured in 125 plasma samples by an automated colorimetric method involving dichlorophenolindophenol and by a "high-performance" liquid-chromatographic procedure with electrochemical detection. The two methods gave comparable results for samples with ascorbate concentrations of 1 to 20 mg/L (r = 0.97). We also measured the amount of total ascorbate (ascorbic acid + dehydroascorbic acid) in the same samples by a liquid-chromatographic procedure with precolumn derivitization of ascorbic acid. We confirmed that plasma contains little dehydroascorbic acid.

2,6-Dichloroindophenol↗

PubMed1992

Sex variation in ascorbic acid catabolism.

Male and female albino rats of same age and body weight were pair fed with laboratory stock diet and ascorbic acid, dehydroascorbic acid and diketogulonic acid were determined in the liver and urine, while in blood only ascorbic acid was estimated. Male rats had concentration higher of ascorbic acid in liver and urine as compared with females, while there were no significant variations in the contents of dehydroascorbic acid and diketogulonic acid. Hepatic and renal 2, 3-diketoaldonate decarboxylase, and hepatic dehydroascorbatase were also found to be significantly higher in male rats. Similar sex variations were also observed in ascorbic acid catabolism in guinea pigs without any differences in urinary ascorbic acid contents.

Animals↗

PubMed1999

Inhibition by ascorbic acid of apoptosis induced by oxidative stress in HL-60 myeloid leukemia cells.

The human myeloid leukemia cell line HL-60 transports the oxidized form of ascorbic acid, dehydroascorbic acid (DHA), and accumulates reduced ascorbic acid. We studied the effect of ascorbic acid loading on apoptosis induced by serum- and glucose-free culture and by oxidative stress induced by H2O2. Uptake accumulation studies indicated that incubation of HL-60 cells with DHA resulted in the accumulation of intracellular ascorbic acid which decreased with time when cells were incubated in DHA-free medium. Exposure of HL-60 cells to increasing concentrations of H2O2 resulted in dose-dependent intracellular accumulation of peroxides, as determined by the use of the oxidation-sensitive fluorescent probe 2',7'-dichlorofluorescin-diacetate (DCFH-DA), which was accompanied by a decrease in intracellular ascorbic acid and an increase in apoptosis. A dramatic decrease in intracellular ascorbic acid was noted when preloaded HL-60 cells were exposed to 150 microM H2O2 (the concentration dropped from 5.2 +/- 0.6 mM to 3.6 +/- 0.1 mM in cells preincubated with 150 microM DHA). A dose-dependent protective effect of DHA was observed. Ascorbic acid loading also provided strong protection from apoptosis associated with serum- and glucose-free culture. Flow cytometry studies showed that exposure of HL-60 cells to 150 microM H2O2 resulted in decreased Bcl-2 expression that was associated with enhanced apoptosis (up to 33.6 +/- 2.6%). No significant variation of Bcl-2 expression was measured following exposure of HL-60 cells, loaded with ascorbic acid, to 150 microM H2O2 and only a slight increase (up to 10.1 +/- 3.1%) in apoptosis. These findings indicate that ascorbic acid can inhibit apoptosis induced by oxidative stress in HL-60 cells.

Antioxidants↗

PubMed2001

Mechanisms of ascorbic acid recycling in human erythrocytes.

Vitamin C, or ascorbic acid, is efficiently recycled from its oxidized forms by human erythrocytes. In this work the dependence of this recycling on reduced glutathione (GSH) was evaluated with regard to activation of the pentose cycle and to changes in pyridine nucleotide concentrations. The two-electron-oxidized form of ascorbic acid, dehydroascorbic acid (DHA) was rapidly taken up by erythrocytes and reduced to ascorbate, which reached intracellular concentrations as high as 2 mM. In the absence of D-glucose, DHA caused dose-dependent decreases in erythrocyte GSH, NADPH, and NADH concentrations. In the presence of 5 mM D-glucose, GSH and NADH concentrations were maintained, but those of NADPH decreased. Reduction of extracellular ferricyanide by erythrocytes, which reflects intracellular ascorbate recycling, was also enhanced by D-glucose, and ferricyanide activated the pentose cycle. Diethylmaleate at concentrations up to 1 mM was found to specifically deplete erythrocyte GSH by 75-90% without causing oxidant stress in the cells. Such GSH-depleted erythrocytes showed parallel decreases in their ability to take up and reduce DHA to ascorbate, and to reduce extracellular ferricyanide. These results show that DHA reduction involves GSH-dependent activation of D-glucose metabolism in the pentose cycle, but that in the absence of D-glucose DHA reduction can also utilize NADH.

Ascorbic Acid↗

PubMed1980

Effect of ascorbic acid in vitro on lymphocyte reactivity to mitogens.

The direct effects of ascorbic acid and dehydroascorbic acid in vitro on human lymphocyte proliferation to phytohemagglutinin (PHA) and concanavalin A (Con A) stimulation were determined. Cells exposed to physiologic and high concentrations of ascorbic acid and dehydroascorbic acid showed poorer tritiated thymidine ([3H]TdR) incorporation than controls without the vitamin. The inhibitory effect was dose-dependent, with the greatest inhibition occurring as the concentration of ascorbic acid and dehydroascorbic acid was increased. At supraoptimal concentrations of PHA and Con A, there was no recovery of the mitogen response, indicating that ascorbic acid did not inhibit the response by competition. Viability studies of cells in culture showed that concentrations of ascorbic acid and dehydroascorbic acid, which consistently inhibited mitogenic stimulation of lymphocytes, were noncytotoxic throughout the culture period. Timed addition of ascorbic acid to PHA-stimulated lymphocytes in culture demonstrated inhibition of [3H]TdR incorporation when ascorbic acid was added as late as 96 hours after initiation of culture. However, the greatest inhibitory effect was observed when ascorbic acid was added at initiation or early in culture. Inhibition was also evident when RNA and protein synthesis were determined. The results suggest that physiologic and high concentrations of ascorbic and dehydroascorbic acid affect early metabolic events in the process of mitogen-stimulated lymphocyte activation.

Ascorbic Acid↗

PubMed2002

Analysis of glycated and ascorbylated proteins by gas chromatography-mass spectrometry.

Proteins or poly-L-lysine which were incubated in the presence of ascorbic acid, dehydroascorbic acid (ascorbylation), or various sugars (glycation) were analyzed by gas chromatography-mass spectrometry (GC-MS). To also detect more labile reaction products, the Maillard modified proteins or poly-L-lysine were enzymatically hydrolyzed and reacted with N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide to form the N(O)-tert-butyldimethylsilyl (tBDMS) derivatives prior to GC analysis. Under these conditions, the known Maillard products N (epsilon)-(carboxymethyl)lysine (1), oxalic acid mono-N (epsilon)-lysinylamide (2), and N (epsilon)-(carboxyethyl)lysine (3) could be simultaneously detected and quantified in glycated and ascorbylated proteins. Additionally, N (epsilon)-(1-carboxy-3-hydroxypropyl)-L-lysine (4) was identified for the first time as a Maillard product of proteins. Under the conditions applied here, 4 was found only in ascorbylated proteins or poly-L-lysine, but not in glycated proteins. Maillard-modified poly-L-lysine was further subjected to high-performance liquid chromatography (HPLC) analysis after enzymatic hydrolysis and formation of the phenyl isothiocyanate derivatized amino acids. Using this method, N (epsilon)-formyl-L-lysine (5), which cannot be distinguished from 2 by GC-MS analysis, was identified for the first time as a glycation product. Compound 5 is mainly formed from ribose, lactose, and fructose. The indicated Maillard products were quantified in beta-lactoglobulin (GC-MS) or poly-L-lysine (HPLC) which were glycated or ascorbylated using different precursors.

Ascorbic Acid↗

PubMed1998

Histochemical observation and cellular distribution of ascorbic acid in persimmon leaves.

This study was carried out to resolve the discrepancy of data for the proportion of ascorbic acid and dehydroascorbic acid in persimmon leaves at the final stage of the season and to clarify their cellular distributions using histochemical and biochemical techniques. Fresh persimmon leaves were collected and used on July 31, September 5 and October 7, 1996. Ascorbic acid and dehydroascorbic acid in subcellular fractions were determined by the HPLC method that was found to be the most reliable for separation. The percent of dehydroascorbic acid in the total leaves was found to be almost constant (between 32 and 37%) in all preparations tested. In all preparations, more than 90% of the ascorbic acid and dehydroascorbic acid was found in the soluble fraction. The histochemical detection of ascorbic acid and an electron micrograph of persimmon leaf cells showed that the reactive color, after the reduction of silver nitrate under acidic conditions, in the leaves of all three preparations was mainly found on the face side of columned-type palisade parenchyma cells where chloroplasts were not rich and large vacuoles were seen. On the inner side of the palisade parenchyma cells where chloroplasts were the richest, only weak color development was observed. This study demonstrates that the percent of dehydroascorbic acid in persimmon leaves did not exceed 40% at least until October 7. It also shows that in persimmon leaf cells, ascorbic acid is mainly localized in the cytosol of palisade parenchyma tissue cells where large vacuoles are seen.

Ascorbic Acid↗

PubMed1987

In vitro oxidation of ascorbic acid and its prevention by GSH.

The interaction of glutathione (GSH) with ascorbic acid and dehydroascorbic acid was examined in in-vitro experiments in order to examine the role of GSH in protecting against the autoxidation of ascorbic acid and in regenerating ascorbic acid by reaction with dehydroascorbic acid. If a buffered solution (pH 7.4) containing 1.0 mM ascorbic acid was incubated at 37 degrees C, there was a rapid loss of ascorbic acid in the presence of oxygen. When GSH was added to this solution, ascorbic acid did not disappear. Maximum protection against ascorbic acid autoxidation was achieved with as little as 0.1 mM GSH. Cupric ions (0.01 mM) greatly accelerated the rate of autoxidation of ascorbic acid, an effect that was inhibited by 0.1 mM GSH. Other experiments showed that GSH complexes with cupric ions, resulting in in a lowering of the amount of GSH in solution as measured in GSH standard curves. These results suggest that the inhibition of ascorbic acid autoxidation by GSH involves complexation with cupric ions that catalyze the reaction. When ascorbic acid was allowed to autoxidize at 37 degrees C the subsequent addition of GSH (up to 10 mM) did not lead to the regeneration of ascorbic acid. This failure to detect a direct reaction between GSH and the dehydroascorbic acid formed by oxidation of ascorbic acid under this condition was presumably due to the rapid hydrolysis of dehydroascorbic acid. When conditions were chosen, i.e., low temperature, that promote stability of dehydroascorbic acid, the direct reaction between GSH and dehydroascorbic acid to form ascorbic acid was readily detected. The marked instability of dehydroascorbic acid at 37 degrees C raises questions regarding the efficiency of the redox couple between GSH and dehydroascorbic acid in maintaining the concentration of ascorbic acid in mammalian cells exposed to an oxidative challenge.

Ascorbic Acid↗

PubMed1986

Vitamin stability in a TPN mixture stored in an EVA plastic bag.

In order to examine the stability of vitamins in a TPN admixture stored in 3-litre plastic (EVA) bags, two different stability studies were performed. In the first experiment the TPN admixture was stored in darkness at 2-8 degrees C for 96 h and the stability of vitamins determined. The vitamins examined were retinyl palmitate, alpha-tocopherol, thiamine mononitrate, sodium ascorbate (analysed as reduced ascorbic acid and dehydroascorbic acid), sodium riboflavin-5'-phosphate, pyridoxine hydrochloride, nicotinamide, folic acid, biotin, sodium pantothenate and cyanocobalamin. In the second test the stability of vitamins was determined during simulated infusion from the bag containing the admixture. The vitamins examined were retinyl palmitate, alpha-tocopherol, sodium riboflavin-5'-phosphate and sodium ascorbate (analysed as reduced ascorbic acid and dehydroascorbic acid). The vitamin stability was found to be acceptable for all vitamins except ascorbic acid and folic acid. Total ascorbic acid is the sum of reduced ascorbic acid and dehydroascorbic acid (DHA). It is important to estimate the total ascorbic acid concentration because DHA is also biological active. About 50% of the nominal total ascorbic acid remained after 96 h of storage at 2-8 degrees C in darkness, or after 24 h of simulated infusion initiated immediately after mixing. With folic acid there appears to be assay interference which requires further investigation.

Drug Packaging↗

PubMed1982

The reversibility of the vitamin C redox system: electrochemical reasons and biological aspects.

The biological efficacy of vitamin C depends on its redox abilities as given by the relations between ascorbic acid, semidehydroascorbic acid, and dehydroascorbic acid. It is shown by means of proton magnetic resonance spectroscopy that the enzymatic (by ascorbate oxidase) as well as non-enzymatic (by iodine) oxidation of ascorbic acid is, in principle, reversible despite the hydration and structural changes during the formation of dehydroascorbic acid. The strong redox activity of semidehydroascorbic acid which results in a fast disproportionation to ascorbic acid and dehydroascorbic acid is inferred from an inversion of the electrochemical potentials of the vitamin C redox system. The capacity of this is maintained by a fast reduction of dehydroascorbic acid e.g. by reduced glutathione, preventing its delactonization and further degradation.

Animals↗

PubMed1989

Selected indices of micronutrient status in adult patients with sickle cell anemia (SCA).

In 24 adults with hemoglobin SS followed at the Duke University Comprehensive Sickle Cell Center, we have studied the following nutritional parameters: reduced ascorbic acid; dehydroascorbic acid; alpha and beta carotenes; cryptoxanthin; and alpha and gamma tocopherols in whole blood, washed red blood cells, plasma, or serum. In the same population we also examined reduced glutathione (GSH) and oxidized glutathione (GSSG). Fifteen of these 24 patients also were interviewed for usual dietary intakes using a 28-day dietary history. Data obtained from patients with hemoglobin SS, sickle cell anemia (SCA) were compared to those found for seven healthy normal black adults of similar age. Plasma alpha tocopherol levels were significantly lower in SCA individuals than those of the controls (P less than 0.004). Alpha and gamma tocopherol levels in sickle RBCs were significantly higher than those from RBC suspensions of control subjects (P less than 0.007, and P less than 0.001, respectively). All serum values for carotenoids examined, specifically, beta carotene, alpha carotene, and cryptoxanthin were also markedly depressed when compared to those of healthy controls (P less than 0.001, P less than 0.002, and P less than 0.001, respectively). No other statistically significant differences were found between the two groups for any of the remaining variables, including dietary estimates. Dietary analyses suggest that dietary intakes of SCA individuals exceeded the recommended daily allowances (RDA) of all macro- and micronutrients measured, and intakes of most nutrients exceeded those of black controls interviewed. These results suggest that in individuals with SCA, several micronutrients vital to maintaining reducing capacity are present in diminished quantities in plasma/serum. These anomalies exist in SCA patients even though their intake of these micronutrients are similar to those of healthy black men and women.

Adult↗

PubMed1987

[Quality changes in the storage of vegetable peas (Pisum sativum L.). 2. Nutritional physiologic quality].

In tests extending over several years the typical changes in the nutritional quality as occur during storage at defined temperatures (0 ... 18 degrees C) were determined in dependence on the duration of storage (chi in days). Due to the nutrient transfer from the pods to the seeds, a temporary major rise of the dry matter content (DM) is recorded in the latter together with a strongly inhibited reduction of the mono- and disaccharide content. Green peas stored without pods show a linear decrease in the DM content, degressively increasing DM losses and a more distinct reduction of saccharides. When stored with the pods, the typical decline of the vitamin C (ascorbic acid + dehydroascorbic acid) [changes in the content according to the equation y = alpha 0 + beta 1e-c theta chi and losses according to y = beta 1(1 - e-c theta chi)] goes back, mainly owing to an essentially lower coefficient for c theta. In addition, there are smaller losses in the total carotene content of such crops in the first stage of storage (losses of y = beta 1 chi 2). When storing peas without pods, we observe a a faster accumulation of the titratable total acid (up to 160%). The greatest influence on range and degree of the changes in the chemical constituents is exerted by the storage temperature. The form of the harvested crop, varietal characteristics and annual growing conditions have less bearing. Relationships and physiological causes are discussed.

Fabaceae↗

PubMed1998

Protection by vitamin C of loss of vitamin E in cultured rat hepatocytes.

Results from in vivo studies of the capacity of vitamin C to spare and/or recycle vitamin E are equivocal. While some in vitro and membrane models reveal an interaction between vitamins C and E, the characterization of this relationship in biologically relevant systems is lacking. Thus, we investigated this relationship using hepatocytes isolated from 3- to 6-month-old male Sprague-Dawley rats. Cells were incubated for 18-20 h in medium supplemented with 0.1-4 mM ascorbic acid. The loss of alpha-tocopherol and the formation of its primary oxidized metabolite, alpha-tocopherolquinone, was determined by HPLC. Levels of alpha-tocopherol in hepatocytes incubated without ascorbic acid declined from 390 to 35 pmol/mg protein; hepatocyte ascorbic acid levels declined from 9 to 0.5 nmol/mg protein. alpha-Tocopherolquinone was undetectable in freshly isolated hepatocytes but following incubation in ascorbate-free medium reached 10 pmol/mg protein. The formation of alpha-tocopherolquinone was not detected in hepatocytes incubated with ascorbic acid. Dehydroascorbic acid (DHA) levels represented 10-20% of the total ascorbate content in freshly isolated hepatocytes but after 3 h incubation the proportion of DHA increased to 50%; after 18-20 h incubation DHA was undetectable. Hepatocytes incubated with 1.0, 2.0, 2.5, or 4.0 mM ascorbic acid lost significantly less alpha-tocopherol (62, 69, 67, and 56%, respectively) than unsupplemented controls (90%). Twelve percent of the alpha-tocopherol lost from hepatocytes during incubation was detected in the medium of cells incubated with ascorbic acid, but vitamin E was undetectable in the medium of cells incubated without ascorbic acid. These results demonstrate an interaction between vitamins C and E in cell culture and are not inconsistent with a potential recycling of oxidized alpha-tocopherol by ascorbic acid.

Animals↗