Showing papers on "Ascorbic acid published in 1973"

Evolution and the biosynthesis of ascorbic acid

Abstract: The ability to synthesize ascorbic acid is absent in the insects, invertebrates, and fishes. The biosynthetic capacity started in the kidney of amphibians, resided in the kidney of reptiles, became transferred to the liver of mammals, and finally disappeared from the guinea pig, the flying mammals, monkey, and man. A similar transition in the biosynthetic ability was observed in the branched evolution of the birds.

Lipid peroxidation of rat-liver microsomes. Its effect on the microsomal membrane and some membrane-bound microsomal enzymes.

Abstract: Rat liver microsomes were peroxidized in vitro and chemical, physical and morphological changes in the membrane were related to the effects on certain membrane-bound microsomal enzymes. With increasing peroxidation, microsomal phospholipids revealed decreasing concentrations of 20:4 and 22:6 fatty acids. At a high level of peroxidation, where alterations in permeability and ultrastructural changes such as breakage and deformation of microsomal vesicles were apparent, there was also a decrease in the concentration of 18:2 fatty acids. Glucose-6-phosphatase, cytochrome P-450 and uridine-5′-diphosphate glucuronyltransferase (UDP glucuronyltransferase) (three microsomal enzymes known to be highly dependent on the integrity of the membrane for their function) responded differently to lipid peroxidation. Glucose-6-phosphatase showed an initial decrease in activity as well as in Km for glucose 6-phosphate, followed by a restoration to control values at an intermediate level of lipid peroxidation. At a high level of peroxidation, both kinetic parameters were again markedly decreased. Cytochrome P-450 concentration, on the other hand, revealed a continuous decrease with proceeding lipid peroxidation, which was only partly accounted for by a conversion to cytochrome P-420. The loss of cytochrome P-450 was paralleled by decreased rates of aminopyrine demethylation and 3,4-benzpyrene hydroxylation. Glucuronyltransferase activity, finally, was activated at low, but again normalized at high, levels of lipid peroxidation. It thus seems that although electron-microscopically observable changes in the microsomal membrane occurs only late in lipid peroxidation, chemical, physical and enzyme alterations are early phenomena during this process. The continuous loss of cytochrome P-450 and the final decrease in glucose-6-phosphatase late during peroxidation probably reflect damage to membrane lipids of vital importance for the integrity and function of these enzymes whereas the activation of UDP glucuronyltransferase early during peroxidation most likely can be ascribed to increased membrane permeability.

Carcinogen-Induced Chromosomal Breakage Decreased by Antioxidants

Abstract: Blood leukocyte cultures were incubated with antioxidants and the carcinogens sodium cyclamate and 7,12-dimethylbenz(α)anthracene in different combinations. There were 17.4% more chromosomal breaks in the group of cells treated with dimethylbenzanthracene only than in the untreated controls. The reductions in chromosomal breaks by the antioxidants were as follows: ascorbic acid, 31.7%; butylated hydroxytoluene, 63.8%; Na2SeO3, 42.0%; and dl-α-tocopherol, 63.2%. Multiple chromosomal breaks were distributed equally throughout the experimental groups. Sodium cyclamate had only slightly more chromosomal breaks than the controls (11.6 compared to 10.9%). In the cyclamate groups treated with Na2SeO3, 11.2% of chromosomes were broken. More acrocentric-type chromosomal breaks (21.7%) were seen in the untreated cells than the cells treated with cyclamate (3.4%) or dimethylbenzanthracene alone (4.8%). The carcinogen-treated groups had a higher percentage of meta breaks than the untreated controls.

The effects of ascorbic acid supplementation on the absorption of iron in maize, wheat and soya.

Abstract: Summary. The absorption of iron from three staple vegetables was measured by the red cell utilization method in iron deficient subjects. The food iron had been labelled with 55Fe by the hydroponic cultivation method. In addition, 59Fe was added with or without carrier iron in the form of ferric ammonium citrate, prior to cooking. The constant relationship reported by others between the absorption of the two isotopes was confirmed, suggesting that the extrinsic iron and the food iron were absorbed from a common pool. The addition of ascorbic acid to maize porridge before cooking significantly enhanced the absorption of both the intrinsic and the added iron. However, no effect was noted with soya biscuits or with whole wheat bread (100% extraction). Evidence was obtained that these differences were due to the oxidative destruction of the ascorbic acid by the high temperatures required for baking. If, therefore, a feasible method were found for supplementing vegetable foodstuffs with ascorbic acid and inorganic iron, nutritional benefit would only be anticipated with uncooked or boiled foods.

Changes in leucocyte ascorbic acid during the common cold.

Abstract: Summary. Leucocyte ascorbic acid was measured in 7 subjects during the common cold. There was a significant fall in L.A.A. to scorbutic levels within 24 hours of the onset of symptoms. By the fifth day the L.A.A. had returned to normal, which coincided with the cessation of symptoms. Absorption studies suggested 1g. ascorbic acid per day as a prophylactic dose and 6g. ascorbic acid per day as a therapeutic dose. The effect of such supplements of ascorbic acid in 4 episodes of the common cold in 3 subjects suggests that the L.A.A. pattern can be changed by this therapy. The implications are discussed. INCE the publication of the monograph Vitamin C and the Common Cold, by Linus Pauling (1970), there has been much discussion in the public press and elsewhere both in America and in this country on the prophylactic and therapeutic value of ascorbic acid in infections by the common cold virus. During the winter of 1971, we were able to observe the changes occurring in the leucocyte ascorbic acid levels (L.A.A.) in 7 individual members of the staff of one medical unit in a general hospital, during an outbreak of the common cold. Ascorbic acid saturation tests were also carried out to determine whether there was an optimum dose of ascorbic acid which would saturate both the white blood cells and the serum. The effect of 'optimum' doses of ascorbic acid during further episodes of the common cold was studied in 3 individuals. In view of the difficulty in carrying out detailed studies on individuals who are harbouring the common cold virus and who are taking supplements of ascorbic acid, we felt that these observations also were worth reporting. MATERIAL AND METHODS Subjectsmembers (2 males and 5 females) of the medical and nursing staff were studied while suffering from the common cold. By chance, 4 individuals had measurements of their L.A.A. performed during the week prior to the onset of symptoms. Six individuals had measurements performed on the first day of symptoms; 5 on the second day of symptoms; 7 on the third day of symptoms; 5 on the fourth day of symptoms; 3 on the f ifth day of symptoms and 7 on the tenth day of symptoms. Symptoms had usually subsided by the fifth day. ascorbic acid daily, increasing the amount at weekly intervals. During the first week 0.2 g. of ascorbic acid was taken daily, during the second week 1.0 g. of ascorbic acid was taken daily, during the third week 3.0 g. of ascorbic acid daily and during the fourth week 6.0 g. of ascorbic acid daily. Four individuals volunteered to take 10.0 g. of ascorbic acid daily, during the fifth week. The L.A.A. and the serum ascorbic acid (S.A.A.) were measured on 2 occasions each week in each individual and the mean of the 2 readings was used as the saturation level on that particular dose of

Ascorbic acid and the glycosaminoglycans. An orthomolecular approach to cancer and other diseases.

Abstract: A new concept of a basic mechanism involved in cell proliferation is presented. It is suggested that cells are normally restrained from proliferating by the highly viscous nature of the intercellular glycosaminoglycans. In order to proliferate, cells must escape from this restraint by depolymerizing the glycosaminoglycans in their immediate environment. This process is accomplished by the release of the enzyme hyaluronidase and is kept in check by physiological hyaluronidase inhibitor. There is some evidence that physiological hyaluronidase inhibitor is an oligoglycosaminoglycan that requires ascorbic acid for its synthesis, and perhaps incorporates residues of ascorbic acid. This hypothesis provides an explanation for the pathogenesis of scurvy. It explains the increased requirement for ascorbic acid that occurs in many cell proliferative diseases, including cancer. It indicates the existence of a basic underlying mechanism in many pathological states and suggests a common pattern of treatment. We conclude that ascorbic acid may have much greater therapeutic value than has been generally assigned to it.

Inhibition of histamine-induced airway constriction by ascorbic acid

Abstract: We studied the effect of ascorbic acid on histamine-induced airway constriction in 17 healthy subjects; we also investigated its effect on guinea pig tracheal strips in vitro . Ventilatory function was measured by recording partial expiratory flow-volume (PEFV) curves on which maximum flow rates at 50 per cent VC and at 25 per cent VC were calculated. Following oral administration of 500 mg. ascorbic acid, the mean reductions of V max at 50 per cent VC and V max at 25 per cent VC after histamine inhalation were significantly smaller in comparison with placebo administration (P in vitro relaxations of tracheal strips by ascorbic acid were reduced by 2.5 μg propranolol. Ascorbic acid probably has a direct effect on airway smooth muscle; in the guinea pig trachea its effect may be mediated by γ-adrenergic receptors.

Reducing Compounds in Radioprotection and Radio-sensitization: Model Experiments Using Ascorbic Acid

Abstract: SummaryAscorbic acid has been used in model experiments to investigate the possible roles of reducing agents in radioprotection and radiosensitization.The repair of organic radicals by their reaction with ascorbic acid has been demonstrated directly using pulse radiolysis. Absolute rate constants for the reaction of the vitamin with hydroxyl radicals and secondary inorganic radical anions have been determined. In the presence of ascorbic acid, the rapid reactions of the sensitizer triacetoneamine-N-oxyl (TAN), with the thymine hydroxyl adduct, or the isopropanol radical, were not observed. This was attributed to the rapid thermal reduction of the stable free radical. The resultant loss in radiosensitizing properties was confirmed by bacteriological studies using Serratia marcescens. In contrast, ascorbic acid had only an insignificant effect on the sensitizing action of the relatively stable compound p.nitroacetophenone (PNAP).

Protective Effect of Ascorbic Acid on Hepatotoxicity Caused by Sodium Nitrite Plus Aminopyrine

Abstract: The oral treatment of rats with sodium ascorbate in combination with sodium nitrite and aminopyrine prevents the rise in serum alanine aminotransferase (EC 2.6.1.2) observed when nitrite and aminopyrine are given alone. Ascorbic acid also affords protection, whereas dehydroascorbic acid exerts no protective effect.

Mucociliary function during experimentally induced rhinovirus infection in man.

Abstract: In conjunction with a controlled study of the effect of vitamin C on susceptibility to experimentally induced rhinovirus infections in man, we have conducted a study of nasal mucociliary function in the subjects volunteering for the study. In the 21 volunteers an average mucociliary flow rate (measured by the Quinlan tagged particle technique) of 7.5 mm/min was found in those with normal nasal morphology and 4.0 mm/min in those with abnormal nasal morphology. The rates decreased during infection in both groups but at different times after induction of infection. Ascorbic acid had no effect on either susceptibility to induced rhinovirus infection or mucociliary transport.

The meso-reactivity of porphyrins and related compounds. Part VI. Oxidative cleavage of the haem system. The four isomeric biliverdins of the IX series

Abstract: The oxidative cleavage of haemin in aqueous pyridine under various conditions (ascorbic acid–oxygen; hydrazine–oxygen; and ascorbic acid–hydrogen peroxide) gives four isomeric biliverdins of the IX series which have been isolated (from a much improved ascorbic acid–oxygen reaction) as their crystalline dimethyl esters. The properties of the four isomers are described. On the basis of mass and n.m.r. spectra, structures are assigned to all four isomers for the first time. A key observation in the n.m.r. spectra of these compounds is the chemical shift of the heteroaryl methyl group. The implications of these results are discussed.

Activation of Prolyl Hydroxylase in L-929 Fibroblasts by Ascorbic Acid

Abstract: The addition of ascorbate to the culture medium of early log-phase mouse fibroblasts (L-929 cells) resulted in a 5-fold increase of prolyl hydroxylase activity. Maximal activity was reached within 2 hr after addition of 5 μM ascorbate. The total amount of enzyme-related antigen did not change on treatment with ascorbate and the activation was shown to be independent of RNA and protein synthesis. The increase in activity caused by ascorbate is therefore due to the activation of a preformed precursor. Enzyme (molecular weight 260,000-300,000) and putative precursor (molecular weight 85,000-105,000) were separated by chromatography on DEAE-Sephadex. Treatment of intact cells with dithiothreitol resulted in an almost quantitative conversion of the enzyme to the smaller inactive protein. When these cells were treated with ascorbate or incubated overnight in fresh medium the enzyme reappeared and precursor concentrations decreased proportionately. Ascorbate may act by bringing about aggregation of enzymatically inactive subunits.

Degradation of thyroid hormones by phagocytosing human leukocytes.

Abstract: Thyroxine (T4) and triiodothyronine (T9) are rapidly degraded by a purified preparation of myeloperoxidase (MPO) and H2O2 with the formation of iodide and material which remains at the origin on paper chromatography. Deiodination by MPO and H2O2 occurs more readily at pH 7.0 than at pH 5.0 in contrast to iodination by this system which is known to occur more readily at pH 5.0 than at pH 7.0. Degradation is inhibited by azide, cyanide, ascorbic acid, and propylthiouracil. Methimazole stimulates deiodination by MPO and H2O2 but inhibits this reaction when MPO is replaced by lactoperoxidase or horseradish peroxidase. Intact human leukocytes, in the resting state, degrade T4 and T3 slowly: degradation, however, is increased markedly during phagocytosis of preopsonized particles. Serum inhibits this reaction. T3 can be detected as a minor product of T4 degradation. Proteolytic digestion of the reaction products increases the recovery of monoiodotyrosine. The fixation of iodine in the cytoplasm of leukocytes which contain ingested bacteria was detected radioautographically. Chronic granulomatous disease leukocytes, which are deficient in H2O2 formation, degrade T4 and T3 poorly during phagocytosis. MPO-deficient leukocytes degrade the thyroid hormones at a slower rate than do normal leukocytes although considerable degradation is still observed. Azide, cyanide, ascorbic acid, and propylthiouracil which inhibit certain peroxidasecatalyzed reactions inhibit degradation by normal leukocytes; however, inhibition is incomplete. Formation of iodinated origin material is inhibited to a greater degree by azide, cyanide, and propylthiouracil than is deiodination. Methimazole inhibits the formation of iodinated origin material by both normal and MPO-deficient leukocytes. However, deiodination by normal leukocytes is stimulated and that of MPO-deficient leukocytes is unaffected by methimazole. Hypoxia inhibits the degradation of T4 and T3 by untreated normal or MPO-deficient leukocytes and by normal leukocytes treated with azide or methimazole. These data suggest that both MPO-dependent and MPO-independent systems are involved in the degradation of T4 and T3 by phagocytosing leukocytes. The role of leukocytic degradation of T4 and T3 in thyroid hormone economy and in leukocytic microbicidal activity is considered.

Absence of ascorbic acid synthesis in channel catfish, Ictalurus punctatus and blue cat-fish, Ictalurus frucatus

Abstract: 1. 1. Ascorbic acid deficiency has been demonstrated in the channel catfish and the symptoms are described. 2. 2. The enzymes involved in ascorbic acid synthesis are apparently lacking in the liver and kidney of both the blue and channel catfish.

Studies on the reduction of tetrazolium salts. I. The isolation and characterisation of a half-formazan intermediate produced during the reduction of neotetrazolium chloride.

Abstract: 1. Chromatographically pure NT has been reduced by ascorbic acid at pH 10 to produce a red formazan. This material has been isolated and purified, and shown to be a half-reduced intermediate compound. 2. The intermediate can be reduced further to the purple di-formazan. It has been shown that one molecule of NT reacts with 2H to give one molecule of intermediate, and that one molecule of intermediate reacts with a further 2H to give one molecule of di-formazan. In addition, one molecule of NT also reacts with 4H to give one molecule of di-formazan. 3. The pH of the ascorbate reducing agent is critical. In the presence of excess ascorbate, there is no reduction at all at very acid pH values; at pH values up to about 8 only the red formazan is produced, at pH values up to about 10 both red formazan and purple di-formazan are produced; at pH values in excess of 11 only the purple di-formazan is produced.

PRIMARY CULTURES OF DISSOCIATED SYMPATHETIC NEURONS : II. Initial Studies on Catecholamine Metabolism

Abstract: Initial studies are reported on the catecholamine metabolism of low-density cultures of dissociated primary sympathetic neurons. Radioactive tyrosine was used to study the synthesis and breakdown of catecholamines in the cultures. The dependence of catecholamine synthesis and accumulation on external tyrosine concentration was examined and a concentration which is near saturation, 30 µM, was chosen for further studies. The free tyrosine pool in the nerve cells equilibrated with extracellular tyrosine within 1 h; the total accumulation of tyrosine (free tyrosine plus protein, catecholamines, and metabolites) was linear for more than 24 h of incubation. Addition of biopterin, the cofactor of tyrosine hydroxylase, only slightly enhanced catecholamine biosynthesis by the cultured neurons. However, addition of reduced ascorbic acid, the cosubstrate for dopamine β-hydroxylase, markedly stimulated the conversion of dopamine (DA) to norepinephrine (NE). Phenylalanine, like tyrosine, served as a precursor for some of the DA and NE produced by the cultures, but tyrosine always accounted for more than 90% of the catecholamines produced. The DA pool labeled rapidly to a saturation level characteristic of the age of the culture. The NE pool filled more slowly and was much larger than the DA pool. The disappearance of radioactive NE and DA during chase experiments followed a simple exponential curve. Older cultures showed both more rapid production and more rapid turnover of the catecholamines than did younger cultures, suggesting a process of maturation.