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At least 19 recordsLinked to original sources
PubMed1977

[Breakdown of linoleic and linolenic acid hydroperoxides in the presence of ascorbic acid analysis of the volatile aldehydes (author's transl)].

Hydroperoxide emulsions with 10(-3) mol ascorbic acid were stored for 19 h at 22 degrees C. Volatile aldehydes were formed in the presence of oxygen and traces of metals. The main compounds were identified as follows (mol-%): 2-pentenal [51] and 2-hexenal [22] from 13-hydroperoxioctadeca-9,11,15-trienoic acid; propanol [38] and 2-hexenal [25] from 9-hydroperoxioctadeca-10,12,15-trienoic acid; hexanal [82] respectively [66] from 13-hydroperoxioctadeca-9,11-respectively 9-hydroperoxioctadeca-10,12-dienoic acid. C9 and C10 aldehydes were only detected in very low concentrations as fragments of the 9-hydroperoxides.

Aldehydes↗
PubMed1975

Ascorbic acid for the common cold. A prophylactic and therapeutic trial.

Three hundred eleven employees of the National Institutes of Health volunteered to take 1 gm of ascorbic acid or lactose placebo in capsules three times a day for nine months. At the onset of a cold, the volunteers were given an additional 3 gm daily of either a placebo or ascorbic acid. One hundred ninety volunteers completed the study. Dropouts were defined as those who missed at least one month of drug ingestion. They represented 44% of the placebo group and 34% of those taking ascorbic acid. Analysis of these data showed that ascorbic acid had at best only a minor influence on the duration and severity of colds, and that the effects demonstrated might be explained equally well by a break in the double blind.

Adult↗
PubMed1979

Effects of ascorbic acid deficiency and of erythorbic acid on blood components in the Cynomolgus monkey.

Eight male Cynomolgus monkeys were fed an ascorbic acid-free total liquid diet until plasma levels decreased from a mean of 1.1 mg/dl to 0.04 mg/dl at 8 weeks. They showed no visible signs of scurvy. The animals were then given a daily oral dose of 10 mg ascorbic acid/kg body weight for 4 weeks, when the experiment was ended. Four of the animals were given, in addition, 200 mg erythorbic acid/kg body weight orally each day. In all animals repletion was accomplished in two to three weeks using return to initial plasma ascorbic acid levels as the criterion. During deficiency, blood cellular elements were found to be more resistant to depletion than plasma. For erythrocytes, this may be explained at least partially by the observation that in vitro uptake of ascorbic acid tended to be related inversely to blood ascorbic acid levels. However, no such relationship was seen in leucocytes or platelets. Other measurements made on blood did not vary in response to changing ascorbic acid levels. These include serum cholesterol; erythrocyte, leucocyte, or platelet counts; leucocyte differential; hemoglobin concentration; and hematocrit. Urinary hydroxyproline/creatinine ratios were also unchanged. Erythorbic acid, a stereoisomer of ascorbic acid and a common food additive, has been cited as a possible interferent in the determination of whole blood or plasma ascorbic acid, since in the guinea pig it is absorbed from the gut and no commonly used ascorbic acid analysis can distinguish between the isomers. Under conditions of the present experiment, however, no elevation of apparent whole blood or plasma ascorbic acid was produced by inclusion of high levels of erythorbic acid in the diet. Animals given erythorbic acid in addition to ascorbic acid during repletion did not differ from those given ascorbic acid alone in any aspect mentioned above.

Administration, Oral↗
PubMed1975

Relationship between levels of blood lipids, vitamins C, A, and E, serum copper compounds, and urinary excretions of tryptophan metabolites in women taking oral contraceptive therapy.

To evaluate which women using oral contraceptive agents might be at risk, biochemical indices known to be affected by the estrogens and progestogens were studied in women who take oral contraceptive agents, in women who do not use oral contraceptive agents, in women in third trimester of pregnancy and 6 weeks after parturition, and in men with normal and high blood lipid levels. The most consistent changes due to oral contraceptive agents were in serum levels of copper, triglycerides, and vitamin A and in the urinary excretion of xanthurenic acid and niacin derivatives before and after a tryptophan load test. There was only a slight suggestion, with no statistical significance, that serum vitamin C levels decreased when the serum levels of ceruloplasmin were high. The highest blood pressures and serum triglycerides and vitamin A levels were obtained in those women who ingested the highest level of estrogens. Pregnant women had the lowest levels of serum vitamin A. The oral contraceptive agents users had the lowest average levels of carotenoids corresponding to the highest average levels of vitamin A in the serum. Thus, estrogens not only increase the rate of change of tryptophan to niacin but may also increase the rate of conversion of carotene to vitamin A. Relative reactivity to oral contraceptive agents and possible risk to a patient might be evaluated by a profile of blood pressure and serum triglycerides, copper, and vitamin A.

Adult↗
PubMed1975

Oral contraceptives and ascorbic acid.

Plasma, leukocyte, and platelet ascorbic acid levels are decreased in women ingesting oral contraceptive steroids. Studies have shown that it is the estrogenic component of the oral contraceptive agents that is associated with the decresased ascorbic acid concentrations. Urinary excretion of ascorbic acid does not appear to be increased by the steroids. Although serum levels of copper are increased by estrogens and oral contraceptives, ascorbic acid catabolism does not appear to be increased (unpublished). Our preliminary data on tissue uptake of ascorbic acid suggest that changes in tissue distribution are one possible answer for the observed effects of the steroids on blood levels of ascorbic acid.

Adrenal Glands↗
PubMed1991

Ascorbic acid in mesencephalic cultures: effects on dopaminergic neuron development.

Ascorbic acid exists in high intracellular concentrations in fetal rat brain. In mesencephalic cultures the cellular ascorbic acid content drops sharply to undetectable levels when no ascorbic acid is added to the medium, thus creating a model of scorbutic neuronal tissue and affording the study of ascorbic acid's effects on mesencephalic cell development and function. Cultures treated with 0.2 mM ascorbic acid were compared with controls (scorbutic cultures) by using morphological and biochemical indices. Ascorbic acid cultures at 7 and 14 days in vitro showed a marked increase in glial proliferation on glial fibrillary acidic protein staining and increased neurite growth and number on tyrosine hydroxylase staining. Significantly higher dopamine uptake and levels of dopamine and 3,4-dihydroxyphenylacetic acid were also observed after 7 and 14 days of ascorbic acid treatment. The capacity to accumulate ascorbic acid and the ability to retain the intracellular ascorbic acid developed gradually as the cultures matured. Ascorbic acid reached the embryonal levels by day 14 in vitro. We conclude that although neuronal cultures can survive and grow in the absence of detectable levels of ascorbic acid, its presence exerts a broad effect on dopamine neuron morphology and biochemical functioning either directly or through increased glial proliferation, or possibly both.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Conformational stability of bovine alpha-crystallin. Evidence for a destabilizing effect of ascorbate.

Short-term incubation of bovine alpha-crystallin with ascorbate alters the protein conformational stability. The denaturation curves with urea and guanidinium-chloride show different patterns, suggesting a deviation from a two-state mechanism owing to the presence of one or more intermediates in the unfolding of ascorbate-modified alpha-crystallin. Furthermore, the latter protein profiles are shifted to lower denaturant concentrations indicating a destabilizing action of ascorbate, which is capable of facilitating protein dissociation into subunits as demonstrated by gel filtration with 1.5 M-urea. The decrease in conformational stability cannot be ascribed to any major structural alteration, but rather to localized changes in the protein molecule. In fact, no difference between native and ascorbate-treated alpha-crystallin can be detected by amino acid analysis but perturbation of the tryptophan and tyrosine environment is indicated by alterations in intrinsic fluorescence. Furthermore, turbidity and light-scattering measurements suggest an involvement of the lysine side chains, since aggregability patterns with acetylsalicylic acid are significantly altered. The ascorbate-destabilizing effect on the conformational stability of alpha-crystallin, probably exerted through oxidative modification of amino acid residues and/or the formation of covalent adducts, provokes unfavourable steric interactions between residues along the polypeptide chains, thus favouring aggregation and insolubilization of crystallins which can lead to cataract formation, as also demonstrated by proteolytic digestion patterns which show a lower rate of degradation of the ascorbate-modified alpha-crystallin.

Acrylamide↗
PubMed1991

Immunological monitoring of Fenton fragmentation of fibrinogen.

Fibrinogen is transformed into insoluble "neofibe" by reaction with up to 100 microM Cu(II) and 1.5 mM ascorbate. The soluble peptides which are released during the reaction can be monitored by amino acid analysis and by measuring released keto-carbonyl (with DNPH). Immunologic characterization of the soluble peptides, with antibodies directed against fibrino-peptide A (FPA) clearly show the release of this epitope, optimally at 50 microM Cu(II). Anti-FPB gives no evidence of that epitope. However, N-terminal amino acid analyses reveals the presence of 3 peptides terminating in ALA (alpha chain FPA), GLU (beta chain FPB) and SER/ASP (unknown). The release of fibrinopeptides is interpreted within the context of a general mechanism for OH'-induced peptide chain cleavage via intermediate Schiff-base hydrolysis.

Enzyme-Linked Immunosorbent Assay↗
PubMed1979

Lipid peroxidation of the microsomal fraction and extracted microsomal lipids from DAB-induced hepatomas.

NADPH- and ascorbic acid-induced microsomal lipid peroxidation was almost absent in subcutaneously implanted DAB-induced hepatomas D23, D30 and D192A, and present at greatly reduced levels in DAB-induced primary hepatomas when compared with normal liver controls. Fatty acid analysis of the microsomal lipid from passaged tumours demonstrated adequate levels of substrate in the phospholipid fractions to support lipid peroxidation. Lipid extracted from hepatoma microsomal fractions was shown to undergo ascorbic acid-induced lipid peroxidation, but to a lesser extent that the corresponding liver extract. This may be partially explained by a decrease in the phospholipid content of hepatoma microsomal membranes. However, phospholipid extracted from microsomal fractions of hepatoma and liver supported lipid peroxidation to a similar extent. The possible role of the non-lipid component of the membrane in the process of lipid peroxidation is discussed.

Animals↗
PubMed1990

Site-specific oxidation of angiotensin I by copper(II) and L-ascorbate: conversion of histidine residues to 2-imidazolones.

The reaction of a histidine-containing peptide (angiotensin I) with copper (II)/ascorbate under physiological conditions has been studied chemically. In the presence of a catalytic amount of copper(II) ion, ascorbate mediated the oxidative damage to the peptide via selective loss of the histidine residue. Furthermore, the reaction of copper(II)/ascorbate with the peptide gave two products (AGT-1 and AGT-2) selectively. From amino acid analysis of the modified peptides, it was found that either of the two histidine residues within the native peptide was modified. Amino-terminal sequence analysis indicated that AGT-1 and AGT-2 were modified at the His9 and the His6, respectively. In addition, the data of FAB-MS and 1H NMR suggested that the unknown residues (modified histidine) within AGT-1 and AGT-2 should have the 2-imidazolone structure. In order to confirm the 2-imidazolone residue in both modified peptides, they were hydrolyzed and analyzed by reverse-phase HPLC. The result demonstrated that the acid hydrolysis of modified peptides gave a product which was identical to authentic 2-imidazolone residue. Consequently, it was confirmed that the reaction of Cu(II)/ascorbate occurs specifically at the C-2 position of the imidazole ring of the histidine residue within a peptide.

Amino Acid Sequence↗
PubMed1977

Serum folates in man.

In an aseptic microbiological assay of folate compounds and their breakdown compounds, using Lactobacillus casei, Streptococcus faecalis, and Pediococcus cerevisiae, 4a-hydroxy-5methyl-4,5,6,7-tetrahydrofolate and 5-methyl-5,8-dihydrofolate were inactive under all conditions to all three organisms and 5-methyl-5,6-dihydrofolate was inactive unless ascorbate was present in the incubation medium, and then only to L. casei. 5-Methyltetrahydrofolate was active only for L. casei, and activity in purified samples to S. faecalis was due to trace amounts of folic acid. Analysis of S. faecalis values in the serum in normal subjects and in patients with various disorders showed that levels of 10-formyltetrahydrofolate are raised in coeliac disease, leukaemia, rheumatoid arthritis, and schizophrenia. 5-Methyltetrahydrofolate is readily absorbed by normal human subjects and by patients with pernicious anaemia but poorly absorbed by patients with coeliac disease or leukaemia. 5-Methyl-5,6-dihydrofolate was quickly absorbed by normal human subjects, being reflected by a considerably raised level of 5-methyltetrahydrofolate in serum when sodium bicarbonate was given by mouth before the 5-methyl-5,6-dihydrofolate. These higher levels were comparable to those in patients with pernicious anaemia after oral administration of 5-methyl-5,6-dihydrofolate. Oral 5-methyl-5,8-dihydrofolate and 4a-hydroxy-5-methyl-tetrahydrofolate did not appear as microbiologically active folates in the serum. The findings of this study suggest that the availability for biological utilisation of the major dietary folate compounds will depend on the amount of gastric acidity and of ascorbate in the intestinal chyme. Many may be unavailable for metabolic utilization in the body.

Anemia, Pernicious↗
PubMed1992

The glycation and cross-linking of isolated lens crystallins by ascorbic acid.

Individual lens crystallins were isolated from calf lens extracts and incubated in the presence of ascorbic acid for 3 weeks under aerobic conditions. Both alpha-crystallin and beta H-crystallin rapidly cross-linked to form high molecular weight proteins, which did not enter the resolving gel on SDS-PAGE. Beta L-crystallin was somewhat less reactive, but gamma-crystallin showed little or no crosslinking. Gamma-crystallin, however, was almost equivalent to the other crystallins as a substrate for glycation. This was measured by: (a) the binding of protein to a boronate affinity column; (b) the incorporation of 3H from NaB3H4 into protein; (c) amino acid analysis of the modified proteins to estimate the extent of lysine modification; and (d) the incorporation of [1-14C]ASA into individual crystallins. When the separated crystallins were combined with [125I]gamma-crystallin and incubated with ascorbic acid, radioactivity was readily incorporated into the cross-linked products with other crystallins, but again not with gamma-crystallin itself. Gel filtration chromatography of a mixture of [125I]gamma-crystallin and alpha-crystallin showed the formation of a complex between gamma- and alpha-crystallins. These data suggest that all crystallins are glycated, but that cross-linking occurs preferentially between proteins, which are already bound together non-covalently.

Amino Acids↗
PubMed1992

Glycation of MP26 and MP22 in bovine lens membranes.

Alkali treated membranes were isolated from mature bovine lenses and incubated with different sugars for 3 weeks to study the effect of glycation on the lens intrinsic membrane proteins, MP26 and MP22. The obtained results show that a) [1-14C] ascorbic acid (ASA) was able to glycate the intrinsic membrane proteins as rapidly as soluble lens proteins; b) on 15% acrylamide gels in SDS, glucose, fructose, galactose and ribose exhibited low activity for crosslinking membrane proteins; whereas ASA, dehydroascorbate (DHA), diketogulonate (DKG), xylosone and threose, all showed not only the formation of protein multimers, but also highly crosslinked products, which did not enter the spacer gel; c) except glycated MP22, all of the crosslinks of MP26 or MP22, and also the glycated MP26, showed cross reactivity with polyclonal MP26 antibody; d) the extent of crosslinking correlated with an equal loss of lysine and arginine contents by amino acid analysis.

Animals↗
PubMed1992

The extent of N epsilon-(carboxymethyl)lysine formation in lens proteins and polylysine by the autoxidation products of ascorbic acid.

The autoxidation of ascorbic acid (ASA) leads to the formation of compounds which are capable of glycating and crosslinking proteins in vitro. When the soluble crystallins from bovine lens were incubated with ASA in the presence of sodium cyanoborohydride, a single major adduct was observed, whose appearance correlated with the loss of lysine. When polylysine was reacted with equivalent amounts of ASA under the same conditions, this product represented half of the total lysine content after four weeks of incubation at 37 degrees C. This adduct was isolated and identified as N epsilon-(carboxymethyl)lysine (CML) by TLC, GC/MS and amino acid analysis. Several oxidation products of ASA were each reacted with polylysine in the presence of sodium cyanoborohydride to identify the reactive species. CML was the major adduct formed with either ASA and dehydroascorbic acid (DHA). Markedly diminished amounts were seen with L-2,3-diketogulonic acid (DKG), and L-threose, while no CML was formed with L-threo-pentos-2-ulose (L-xylosone). In the absence of sodium cyanoborohydride the yield of CML was similar with each of the ASA autoxidation products and required oxygen. Reactions with [1-14C]ASA gave rise to [14C]CML, but only with NaCNBH3 present. At least two routes of CML formation appear to be operating depending upon whether NaCNBH3 is present to reduce the putative Schiff base formed between lysine and DHA.

2,3-Diketogulonic Acid↗
PubMed1992

Site-specific glycation of lens crystallins by ascorbic acid.

The oxidation of ascorbic acid leads to the formation of several compounds which are capable of reacting with protein amino groups via a Maillard reaction. Radioactivity from [1-14C]ascorbic acid was linearly incorporated into lens crystallins over a 10 day period in the presence of NaCNBH3. This rate of incorporation was 6-7-fold more rapid than that obtained with [14C]glucose under the same conditions. SDS-PAGE showed a linear incorporation into all the crystallin subunits. [1-14C]Ascorbic acid-label led alpha-crystallin was separated into its component A and B subunits, and each was digested with chymotrypsin. HPLC peptide analysis showed a differential labelling of the various lysine residues. Analysis of the peptides by mass spectrometry allowed the identification of the sites and the extent of modification. These values ranged from 6% for Lys-78 to 36% for Lys-11 in the A subunit and from 5% for Lys-82 to an average of 38% for the peptide containing Lys-166, Lys-174 and Lys-175 in the B subunit. Amino acid analysis demonstrated a single modification reaction producing N epsilon-(carboxymethyl)lysine. This agreed with the mass increase of 58 observed for each modified peptide.

Amino Acid Sequence↗