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At least 307 records · Page 17Linked to original sources
PubMed1982

Effect of amino acids imbalance and ascorbic acid deficiency on carcinogenic action of N-nitrosopiperidine in guinea pigs.

The long-term maintenances of guinea pigs on diets with (a) lack of vitamin C, (b) lack of lysine, methionine and threonine or (c) with a deficiency of all the above nutrients led to the development of oesophageal hyperplasia and atrophic gastritis. These dietary insufficiences were found to favour oesophageal and gastric cancer production by NPIP with a greatly shortened tumour induction time. It seems likely that the observed features of NPIP carcinogenesis depend on the alteration of the chemistry and biochemistry of these organs provoked by the low intake of the above-mentioned nutrients.

Amino Acids↗
PubMed2002

Single preoperative oral application of ascorbic acid does not affect postoperative plasma levels of ascorbic acid.

BACKGROUND AND AIMS: A decrease in ascorbic acid (AA) plasma concentration is well known during the postoperative period and postulated to be caused by increased radical scavenging activity in response to surgical trauma. This often affects postoperative patients and is associated with multiple organ failure. Therefore, substitution of AA could potentially decrease the risk of postoperative complications. This study examines the effect of preoperative oral administration of 1,000 mg AA on the postoperative AA plasma concentration. METHODS: 54 patients were randomly split into two groups; patients in group 1 received no AA preoperatively while group 2 received oral AA (1,000 mg). Plasma samples were obtained preoperatively and on the first postoperative day for AA analysis (HPLC). RESULTS: In both groups the AA concentration was normal preoperatively and reduced postoperatively. CONCLUSION: A preoperative substitution of 1,000 mg AA is not sufficient to prevent postoperative lowered plasma concentration.

Administration, Oral↗
PubMed2001

Biosynthesis of L-ascorbic acid and conversion of carbons 1 and 2 of L-ascorbic acid to oxalic acid occurs within individual calcium oxalate crystal idioblasts.

L-Ascorbic acid (AsA) and its metabolic precursors give rise to oxalic acid (OxA) found in calcium oxalate crystals in specialized crystal idioblast cells in plants; however, it is not known if AsA and OxA are synthesized within the crystal idioblast cell or transported in from surrounding mesophyll cells. Isolated developing crystal idioblasts from Pistia stratiotes were used to study the pathway of OxA biosynthesis and to determine if idioblasts contain the entire path and are essentially independent in OxA synthesis. Idioblasts were supplied with various (14)C-labeled compounds and examined by micro-autoradiography for incorporation of (14)C into calcium oxalate crystals. [(14)C]OxA gave heavy labeling of crystals, indicating the isolated idioblasts are functional in crystal formation. Incubation with [1-(14)C]AsA also gave heavy labeling of crystals, whereas [6-(14)C]AsA gave no labeling. Labeled precursors of AsA (L-[1-(14)C]galactose; D-[1-(14)C]mannose) also resulted in crystal labeling, as did the ascorbic acid analog, D-[1-(14)C]erythorbic acid. Intensity of labeling of isolated idioblasts followed the pattern OxA > AsA (erythorbic acid) > L-galactose > D-mannose. Our results demonstrate that P. stratiotes crystal idioblasts synthesize the OxA used for crystal formation, the OxA is derived from the number 1 and 2 carbons of AsA, and the proposed pathway of ascorbic acid synthesis via D-mannose and L-galactose is operational in individual P. stratiotes crystal idioblasts. These results are discussed with respect to fine control of calcium oxalate precipitation and the concept of crystal idioblasts as independent physiological compartments.

Araceae↗
PubMed1993

Effect of eradication of Helicobacter pylori on gastric juice ascorbic acid concentrations.

Ascorbic acid, the reduced form of vitamin C, may protect against gastric cancer and is secreted by the normal stomach. Secretion is impaired in Helicobacter pylori (H pylori) associated chronic gastritis. This study examined if eradication of H pylori improves gastric juice ascorbate values. Fasting gastric juice and plasma samples were collected at endoscopy from patients participating in trials of H pylori eradication for duodenal ulcer disease and intestinal metaplasia before and up to 15 months after attempted eradication. Ascorbic acid and total vitamin C concentrations were determined by high performance liquid chromatography. In 12 patients in whom H pylori was successfully eradicated gastric juice ascorbate and total vitamin C concentrations and the ratio of juice to plasma vitamin C rose after treatment. Analysis after treatment suggested that the rise was greatest in patients with high final plasma vitamin C concentrations, even though these did not change with treatment. By contrast, in 22 patients in whom H pylori eradication was unsuccessful there were no significant changes in juice or plasma concentrations after treatment. It is concluded that successful eradication of H pylori improves secretion of vitamin C into gastric juice. It is speculated that this increases protection against gastric cancer.

Aged↗
PubMed1996

Effect on free radical processes of some ascorbic acid analogues.

Ascorbic acid, present in plasma from humans at concentrations of 50 to 200 mumol/l, has multiple antioxidant properties. Structural modification of this vitamin by the introduction of lipophilic moieties has allowed to the development of ascorbate esters and ethers active as free radical quenchers. Thus, a new series of ascorbic acid analogues possessing one or two aromatic rings was prepared in an attempt to synthesize potent antioxidants with lipophilic properties. Substituted 3-hydroxy furan-2 (5H)-ones and in some cases, dihydrofuro[3,4-b]pyrones were prepared. The synthesized compounds were evaluated for their antioxidant activity in vitro. So, 4-(4-methoxybenzoyl)-3-hydroxy-5-phenylfuran-2(5H)-one 3e (IC50 = 3.06 x 10(-4) M) was found to be the most effective in scavenging the superoxide anion, whereas 4-benzoyl-3-hydroxy-5-(3,4-dimethoxyphenyl)furan- 2(5H)-one 3d (IC50 = 1.38 x 10(-4) M) was the most active in inhibiting, lipid peroxidation.

Animals↗
PubMed1978

Biosynthesis of (+)-Tartaric Acid from l-[4-C]Ascorbic Acid in Grape and Geranium.

The metabolic fate of l-[4-(14)C]ascorbic acid has been examined in the grape (Vitis labrusca L.) and lemon geranium (Pelargonium crispum L. L'Hér. cv. Prince Rupert) under conditions comparable to data from l-[1-(14)C]ascorbic acid and l-[6-(14)C]ascorbic acid experiments. In detached grape leaves and immature berries, l-[4-(14)C]ascorbic acid and l-[1-(14)C]ascorbic acid were equivalent precursors to carboxyl labeled (+)-tartaric acid. In geranium apices, l-[4-(14)C]ascorbic acid yielded internal labeled (+)-tartaric acid while l-[6-(14)C]ascorbic acid gave an equivalent conversion to carboxyl labeled (+)-tartaric acid. These findings clearly show that two distinct processes for the synthesis of (+)-tartaric acid from l-ascorbic acid exist in plants identified as (+)-tartaric acid accumulators. In grape leaves and immature berries, (+)-tartaric acid synthesis proceeds via preservation of a four-carbon fragment derived from carbons 1 through 4 of l-ascorbic acid while carbons 3 through 6 yield (+)-tartaric acid in geranium apices.

Journal Article↗
PubMed2006

The oxidative damage of plasmid DNA by ascorbic acid derivatives in vitro: the first research on the relationship between the structure of ascorbic acid and the oxidative damage of plasmid DNA.

To study the structure-function relationship of the oxidative-damage effect of ascorbic acid, we have focused on the interaction between plasmid DNA pUC19 and a series of ascorbic acid derivatives modified on different OH groups in the presence of transition metal ions. Some ascorbic acid derivatives can selectively cleave plasmid DNA from Form I to Form II in the presence of low concentration of Cu2+ just like ascorbic acid itself, while other derivatives oxidatively damage plasmid DNA slightly. We found that those derivatives with unattached 2-OH and 3-OH groups retain the ability to cleave the plasmid DNA. The derivatives that have been methylated on 2-OH or 3-OH can only cleave plasmid DNA softly, and those derivatives that have been protected on both 2-OH and 3-OH can hardly exert an oxidative damage on plasmid DNA under the same condition. Form these results, we can draw the conclusion that 2-OH and 3-OH groups of the ascorbic acid molecule contribute most to this biological activity.

Ascorbic Acid↗
PubMed1989

Ascorbic acid in a New World monkey family: species difference and influence of stressors on ascorbic acid metabolism.

Like other simian primates, the New World monkey Callithrix jacchus, marmoset, and Saguinus fuscicollis, tamarin, require ascorbic acid as an essential nutrient. For adult marmosets, a daily intake of 15 mg/kg metabolic body weight was found to be necessary to obtain a serum level above the kidney threshold. A survey of the serum ascorbic acid level of marmosets and tamarins in a breeding colony resulted in a vast divergence between the two species, indicating a higher ascorbic acid requirement for tamarins. Unaccustomed trial conditions or additional stressors resulted in a higher catabolism of ascorbic acid to CO2 in both species, measured with 14C labeled material, compared to a higher rate of renal excretion when the animals were accustomed to the metabolic cage. These isotope excretion studies suggest a different metabolic behavior of ascorbic acid in the two species. This is supposedly caused by a higher sensitivity of the tamarins when subjected to the same conditions as marmosets.

Animals↗
PubMed1984

Structure of ascorbic acid and its biological function. Determination of the conformation of ascorbic acid and isoascorbic acid by infrared and ultraviolet investigations.

The four O-H bands of ascorbic acid could be assigned by means of infrared investigations. It could be shown by electron spin resonance and nuclear magnetic resonance measurements that the radical sodium ascorbate is formed by a cyclic side-chain structure resulting in a loss of C(6)-OH and C(3)-OH. The C(2) = C(3) double bond is still maintained as could be shown by infrared and ultraviolet absorption spectroscopy. In the case of complete oxidation of ascorbic acid to dehydroascorbic acid, C(6)-OH is reestablished (indicating the reopening of the furanoid ring), while C(2)-OH as well as the C(2) = C(3) double bond have disappeared due to the deprotonation of C(2)-OH and C(3)-OH. In the case of isoascorbic acid and its radical potassium isoascorbate similar results are obtained with one distinct difference: in the case of isoascorbic acid, C(2)-OH does not appear while C(3)-OH exhibits a shoulder.

Ascorbic Acid↗
PubMed1969

Studies on the structure of hyaluronic acid. Characterization of the product formed when hyaluronic acid is treated with ascorbic acid.

Physical and chemical methods were used to characterize hyaluronic acid before (fraction HAIIBI) and after (fraction HA-AA) treatment with ascorbic acid. Fraction HA-AA was recovered with an almost quantitative yield and was shown to be chemically identical with fraction HAIIBI by all the methods used. These two materials, however, differed markedly in their molecular sizes and degree of polydispersity. By using sedimentation, diffusion and sedimentation-equilibrium analyses, weight-average molecular weights of about 1.2x10(6) and 6.5x10(4) respectively were obtained for fractions HAIIBI and HA-AA. It is concluded from these results that hyaluronic acid has a molecular weight of about 65000 and that the polysaccharide chain of this molecule is not depolymerized by ascorbic acid. It is further proposed that hyaluronic acid molecules in the matrix of connective tissues are present either in an aggregated form or as subunits of heterogeneous macromolecules, and that it is the linkages responsible for the organization of these structures which are broken by ascorbic acid.

Animals↗
PubMed2005

Preparation of dehydro-L-ascorbic acid dimer by air oxidation of L-ascorbic acid in the presence of catalytic amounts of copper(II) acetate and pyridine.

The catalytic system Cu(AcO)2-pyridine 1:4 mol% in methanol, slowly catalyses the air oxidation of ascorbic acid to the 2-methyl hemi-ketal of dehydroascorbic acid 5, and hydrogen peroxide. However, with Cu(AcO)2-pyridine 3:4 mol% the air oxidation is quite fast and no hydrogen peroxide is present at the end of the reaction. Removal of the catalyst and refluxing the foamy 5 in MeCN gives the oxidized, dimeric, dehydroascorbic acid in very good yields (approximately 70%) contaminated by approximately 1-2% MeCN.

Ascorbic Acid↗