Conversion of dehydroascorbic acid to a branched hexaric acid in neutral and alkaline aqueous solution.
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Ascorbic Acid↗
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Estimation of dehydroascorbic acid in blood of diabetic patients.
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Ascorbic Acid↗
Simultaneous determination of acetylsalicylic, salicylic, ascorbic and dehydroascorbic acid by HPLC.
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Ascorbic Acid↗
Automated fluorometric method for determination of total vitamin C in food products.
A specific microfluorometric method for the determination of ascorbic acid, dehydroascorbic acid, and total vitamin C in food products has been automated. The procedure developed is an adaptation of the official AOAC method (secs. 43.056-43.062), except that N-bromosuccinimide is used instead of Norit to oxidize vitamin C. Ascorbic acid is selectively oxidized by N-bromosuccinimide before other interfering substances that may be present, so this method is a highly sensitive and specific technique with extensive applicability. The proposed automated method is simple, rapid, reliable, and sufficiently sensitive to analyze as little as 2 x 10-3 to 0.1 mg ascorbic acid/ml. Analytical results obtained for ascorbic acid, dehydroascorbic acid, and total vitamin C in a wide variety of food products are reported. The analytical system developed has the capability of analyzing 50 samples/hr.
Ascorbic Acid↗
Inhibition of cyclic adenosine 3',5'-monophosphate phosphodiesterase from Walker carcinoma by ascorbic and dehydroascorbic acids.
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Animals↗
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↗
The influence of irradiation and packaging on the quality of prepacked vegetables.
During storage, transport and sale of prepacked vegetables, their quality deteriorates very quickly by microbiological decay, discolouration and desiccation. The experiments described were carried out with endive (Chichorium endiva L.) as a representative of the leaf vegetables. After processing (cutting, washing and drying), the product was packed in polythene bags without and with 4 perforations of 2 mm diameter. The endive was irradiated with 0 and 100 krad gammarays and afterwards stored at 10 degrees C, thus simulating the transport and sale temperature. The quality was studied on the basis of the following parameters. The gas composition in the bags, the microbiological composition, the Vitamin C (Ascorbic acid + Dehydroascorbic acid) content and the sensory quality. The experiments showed that the modified gas composition in the non-perforated bags, caused by the respiratory activity of the cut product, improved the quality. The low O2 and high CO2 content prevented discolouration, retarded the senescence and diminished the Vitamin C losses. The initial Total Viable Count of endive was 10(6) to 10(7) and the number of Enterobacteriaceae amounted to approx. 10(5) g-1 product, and increased in a couple of days to 10(8) and 10(7) g-1 respectively, resulting in decay of the product. The contamination with aerobic and anaerobic spores was low, viz. 10(1) to 10(2) g-1 and did not increase at 10 degrees C. An irradiation treatment of 100 krad reduced the Total Viable Count and the Enterobacteriaceae with 3-4 decimals, by which the shelf life increased with about 100% and almost all the Enterobacteriaceae were eliminated, so that the hygienic quality was improved. In prepacked endive nearly half of the Total Vitamin C content was lost within two days. The retention was strongly affected by the presence or absence of perforations; the effect of an irradiation treatment was slight.
Enterobacteriaceae↗
[On the mechanism of ascorbic acid induced methemoglobin reduction of human erythrocytes (author's transl)].
Ascorbic acid and dehydroascorbic acid penetrate the human erythrocyte membrane. In vitro methemoglobin is reduced nonenzymatically by both substances in concentrations of 10(-2) M to 10(-3) M. Dehydroascorbic acid is reduced nonenzymatically to ascorbic acid by GSH, even with low GSH-content of erythrocytes. Under physiological conditions ascorbic acid induced methemoglobin reduction is far less important than reduction by the NADH dependent methemoglobin reductase system. In methemoglobinemic conditions caused by toxic effects or by congenital methemoglobin reductase deficiency treatment with ascorbic acid is possible. However, critically increased methemoglobin content of the blood higher than 30% makes therapy with methylene blue necessary.
Ascorbic Acid↗
Compartmentation of redox metabolites in the anterior eye segment?
In bovine corneal epithelium, stroma, and aqueous humor the levels of ascorbic acid (ASC) and dehydroascorbic acid (DHA) were investigated. Two methods were used, the photometric assay with 2,6-dichlorophenolindophenol and the formation of osazone by 2,4-dinitrophenylhydrazine. The ASC levels in the corneal epithelium and aqueous humor were found to be in the millimolar range, the ASC/DHA ratio being about 10. The stromal ASC and DHA levels were much lower, with a ratio of 0.7. ASC and DHA had similar levels and ratios to those of reduced and oxidized glutathione (GSH/GSSG) reported in the literature. In the corneal epithelium the redox ratio of glutathione was higher than that of ascorbic acid. Therefore, glutathione was supposed to reduce dehydroascorbic acid.
Animals↗
Effect of organic mercurials and sulfhydryl compounds on the urease activity of Proteus: inhibition by urine and ascorbic acid.
Meralluride, mercaptomerin, ethacrynic acid, and penicillamine inhibited urease activity of Proteus mirabilis. The activity of the organic mercurials and ethacrynic acid was markedly inhibited by human and dog urine. Antiurease activity could not be detected in the urine of a human and a dog given meralluride by injection. Urine from patients receiving penicillamine also failed to inhibit urease activity. Ascorbic acid inhibited, whereas dehydroascorbic acid enhanced, the activity of the mercurials, but neither agent altered the inhibitory effect of urine. The lethal effect of meralluride against Proteus occurred at the same concentration at which urease activity was inhibited, but penicillamine inhibited the enzymatic activity without affecting viability of the organism. The data suggest that these sulfhydryl-reactive compounds will not be useful against Proteus infections of the urinary tract.
Animals↗
Ascorbic acid status in uremics.
Plasma levels of ascorbic acid (AA) and dehydroascorbic acid (DHA) were estimated in 27 patients of end stage renal failure (ESRF) on standard conservative therapy (group A) and 9 patients of ESRF on maintenance haemodialysis (MHD; group B). Fourteen healthy subjects matched for age and sex served as control (group C). The dietary intake of vitamin C was significantly decreased in group A than in group B compared to control. Similarly, plasma AA was significantly lowered to 0.801 +/- 0.283 mg per cent in group A compared to 1.421 +/- 0.47 mg per cent in control. While it was just lowered to 1.058 +/- 0.272 mg per cent in group B. Although plasma level of DHA was raised to 0.243 +/- 0.486 mg per cent and 0.166 +/- 0.54 mg per cent in groups A and B respectively, the increase was not statistically significant. In our present study, the DHA/AA ratio was found to be inversely proportional to the plasma AA. Further, this ratio has been claimed to be a better indicator of overall reducing atmosphere (i.e., profile of vitamin C) of the body.
Ascorbic Acid↗
Ascorbic acid and diabetes mellitus.
Dehydroascorbic acid, the oxidized form of vitamin C, causes diabetes when injected into animals and has been reported to be present in increased amounts in the blood of patients with diabetes mellitus and even in prediabetics. One of the earliest changes in diabetes mellitus is electron-microscopic evidence of damage to the inner endothelial lining of the blood vessels. Certain bioflavonoids, which are natural non-toxic food substances from plants, like rutin from buckwheat, prevent the oxidation of ascorbic acid and seem to protect the endothelium when given with vitamin C; it is therefore suggested that all vitamin C tablets should be combined with these flavonoids.
Animals↗
Effects of cortical ablation on apomorphine- and scopolamine-induced changes in dopamine turnover and ascorbic acid catabolism in the rat striatum.
Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid and dehydroascorbic acid (DHAA) were measured by HPLC in the striatum of rats whose fronto-parietal cortex had been unilaterally ablated after a single injection of apomorphine (1 mg/kg s.c.), scopolamine (0.6 mg/kg s.c.) or L-glutamate (500 mg/kg i.p.). Unilateral cortical ablation decreased striatal levels of glutamate in both striata ipsilateral (35%) and contralateral (17-25%) to the lesion. Apomorphine and scopolamine significantly increased (+94 and +122%, respectively) the DHAA/ascorbic acid ratio in the striata ipsilateral to the lesion in unoperated and sham-operated rats (+72 and +34%, respectively), but both drugs failed to increase it in ablated rats. L-Glutamate significantly increased the DHAA/ascorbic acid ratio in unoperated (+53%) and ablated rats (+37%). The increase in sham-operated rats (+34%) did not reach statistical significance. Apomorphine and scopolamine significantly decreased the DOPAC/DA ratio in the striata ipsilateral to the lesion of unoperated, sham-operated and ablated rats. The decrease in the DOPAC/DA ratio induced by apomorphine and scopolamine was greater in ablated rats than in sham-operated rats. L-Glutamate induced only minor changes in striatal DA and DOPAC levels. We conclude that the apomorphine- and scopolamine-induced increase in ascorbic acid oxidation in the striatum requires intact cortico-striatal glutamatergic pathways. Cortical ablation potentiates the apomorphine- and scopolamine-induced inhibition of striatal DA turnover.
3,4-Dihydroxyphenylacetic Acid↗
Effects of ascorbic acid and sodium ascorbate on cyclic nucleotide metabolism in human lymphocytes.
L-ascorbic acid (LAA) augmented cGMP many-fold in highly purified human peripheral blood lymphocytes. The cGMP response occurred within 10 sec and persisted for at least 60 min. D-ascorbic acid (DAA) and dehydroascorbic acid (DHAA) were also equally active in enhancing cGMP concentrations but metabolic precursors of ascorbic acid and other inorganic acids did not increase cGMP levels. Determination of the amount of DHAA contaminating the LAA precluded the possibility that it was solely responsible for the enhanced cGMP levels. The sodium or calcium salts of ascorbic acid did not increase cGMP concentrations. If these neutralized preparations were acidified, increased cGMP concentrations were then noted. In broken cell preparations, LAA, DAA, and DHAA and to a lesser extent sodium ascorbate (NaA) enhanced guanylate cyclase activity while neither inhibited cAMP or cGMP phosphodiesterase (PDE) activity. The possible role of H2O2, fatty acid liberation, prostaglandin production, oxidizing-reducing agents, and free radical formation in mediating the effects of ascorbic acid on cGMP levels were evaluated, but none of these potential mechanisms were definitively proven to be a required intermediary for the cGMP enhancing activity of ascorbic acid. LAA, DHAA or NaA did not induce lymphocyte transformation or modulate lectin-induced mitogenesis.
2',3'-Cyclic-Nucleotide Phosphodiesterases↗
The effects of cortical ablation on d-amphetamine-induced changes in striatal dopamine turnover and ascorbic acid catabolism in the rat.
Dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA) and dehydroascorbic acid (DHAA) levels were determined by HPLC in the striatal synaptosomal fraction and in the whole striatum of rats, whose fronto-parietal cortex had been bilaterally ablated, after a single injection of d-amphetamine (2.0 mg/kg i.p.). d-Amphetamine significantly increased the DHAA/AA ratio in unoperated and sham-operated rats, but failed to increase it in ablated rats, as compared to pertinent saline-treated groups. In the synaptosomal fraction, d-amphetamine significantly decreased the DHAA/AA ratio in unoperated, sham-operated and ablated rats. d-Amphetamine significantly decreased the DOPAC/DA ratio in the whole striatum and significantly increased it in the striatal synaptosomal fraction in all experimental groups. Cortical ablation greatly increased d-amphetamine-induced motor hyperactivity. We conclude that the d-amphetamine-induced increase in AA striatal oxidation requires integrity of the cortico-striatal glutamatergic pathways. Further, AA oxidation occurs in the extracellular space. The cortico-striatal glutamatergic pathways exert an inhibitory modulation on d-amphetamine behavioral effects.
3,4-Dihydroxyphenylacetic Acid↗
Automated analysis of vitamin C in pharmaceutical products.
The determination of total vitamin C in the form of both l-ascorbic acid (AA) and dehydroascorbic acid (DHAA) present in pharmaceutical preparations has been automated. Total vitamin C (completely oxidized to DHAA) was determined by reaction with 2,4-dinitrophenylhydrazine while blanks utilized the same reagent after reducing all DHAA to AA. The automated method was applicable to a variety of multivitamin preparations including those containing iron and copper. The mean recovery of L-ascorbic acid added to 11 multivitamin preparations was 99.4% with a coefficient of variation of 2.5%. In the analysis of these products, results obtained by the automated method were essentially the same as those obtained by the original manual method. For preparations containing no copper salts, the results were also comparable to those obtainable by titration with 2,6-dichloroindophenol except in 1 product which contained some DHAA.
Ascorbic Acid↗
Some studies on ascorbic acid metabolism in hydrazine-treated rats.
The metabolism of ascorbic acid was studied in hydrazine-treated rats. Hydrazine was administered i.p. at a dose of 1.28 mg/day (20% LD50) for each 100 g body weight for 7 days. Hydrazine administration at the present dose did not appear to have an effect on the total ascorbic acid level of liver, kidney, spleen and testis. The adrenal and plasma total ascorbic acid levels were, however, elevated. The activity of liver D-glucuronoreductase and that of liver and kidney dehydroascorbatases were diminished after hydrazine administration. The changes in the activities of liver enzymes were accompanied by a fall in the reduced ascorbic acid level and an elevation in the dehydroascorbic acid level. The uronolactonase activity of liver, on the other hand, remained independent of hydrazine treatment. It has been suggested that hydrazine treatment at the present dose reduced the biosynthesis of L-ascorbic acid from D-glucuronolactone as substrate. In spite of diminished synthesis, the normal level of total ascorbic acid in the liver of hydrazine-treated rats was maintained by reducing the degradation of L-ascorbic acid. The rise in the plasma total ascorbic acid level after hydrazine treatment was ascribed to reduced catabolism and urinary excretion of ascorbic acid, while the elevation in adrenal total ascorbic acid level might result from increased uptake of ascorbic acid by the gland from blood or from nonfunctional accumulation.
Alcohol Oxidoreductases↗
Stimulation of thiamine diphosphatase activity by ascorbic acid in rat brain microsomes.
The effect of ascorbic acid on microsomal thiamine diphosphatase activity in rat brain was examined. Ascorbic acid at 0.02--0.1 mM increased the thiamine diphosphatase activity by 20--600% and produced a significant amount of lipid peroxide, which was measured with thiobarbiturate under the same conditions as the enzyme. A lag period of about 10 min was observed in the process of stimulation of enzyme activity by ascorbic acid. The stimulation of enzyme activity and the lipid peroxidation induced by ascorbic acid were blocked by metal-binding compounds (EDTA, alpha,alpha'-dipyridyl, o-phenanthroline) and an antioxidant (N,N'-diphenyl p-phenylenediamine). GSH significantly enhanced the stimulation of enzyme activity and formation of lipid peroxide by 0.02--0.05 mM ascorbic acid. The effect of GSH was due in part to maintenance of the concentration of ascorbic acid in the medium, since GSH could convert dehydroascorbic acid, an oxidized form of ascorbic acid, to ascorbic acid.
Animals↗