Showing papers on "Ascorbic acid published in 2001"
TL;DR: The TrxR-catalyzed regeneration of several antioxidant compounds, including ascorbic acid (vitamin C), selenium-containing substances, lipoic acid, and ubiquinone are summarized.
2,632 citations
TL;DR: It is now common to add antioxidant compounds to culture media, but maintaining the pro-oxidant-antioxidant equilibrium in embryos through such supplementation is a complex problem.
Abstract: Oxidative stress is involved in the aetiology of defective embryo development. Reactive oxygen species (ROS) may originate from embryo metabolism and/or embryo surroundings. Embryo metabolism generates ROS via several enzymatic mechanisms. The relative contribution of each source seems different depending on the species, the stage of development, and the culture conditions. Several exogenous factors and culture conditions can enhance the production of ROS by embryos. ROS can alter most types of cellular molecules, and also induce development block and retardation. Multiple mechanisms of embryo protection against ROS exist, and these have complementary actions. External protection, present in follicular and tubal fluids, mainly comprises non-enzymatic antioxidants such as hypotaurine, taurine and ascorbic acid. Internal protection mainly comprises antioxidant enzymes: superoxide dismutase, glutathione peroxidase and gamma-glutamylcysteine synthetase. Transcripts encoding for these enzymes are present in the oocyte, embryo and oviduct. It may be important that these transcripts are stored during oocyte maturation in order to allow the embryo to acquire the aptitude to develop. It is now common to add antioxidant compounds to culture media. Nevertheless, maintaining the pro-oxidant-antioxidant equilibrium in embryos through such supplementation is a complex problem. Further studies are necessary to limit oxidative stress during embryo culture.
1,198 citations
TL;DR: Fruits, specifically apples and cranberries, have phenol antioxidants that can enrich lower density lipoproteins and protect them from oxidation and, using the authors' assay, fruits had significantly better quantity and quality of Phenol antioxidants than vegetables.
Abstract: The free and bound phenols have been measured in 20 fruits commonly consumed in the American diet. Phenols were measured colorimetrically using the Folin-Ciocalteu reagent with catechin as the standard after correction for ascorbic acid contribution. On a fresh weight basis, cranberry had the highest total phenols, and was distantly followed by red grape. Free and total phenol quality in the fruits was analyzed by using the inhibition of lower density lipoprotein oxidation promoted by cupric ion. Ascorbate had only a minor contribution to the antioxidants in fruits with the exception of melon, nectarine, orange, white grape, and strawberry. The fruit extracts' antioxidant quality was better than the vitamin antioxidants and most pure phenols, suggesting synergism among the antioxidants in the mixture. Using our assay, fruits had significantly better quantity and quality of phenol antioxidants than vegetables. Fruits, specifically apples and cranberries, have phenol antioxidants that can enrich lower density lipoproteins and protect them from oxidation. The average per capita consumption of fruit phenols in the U.S. is estimated to be 255 mg/day of catechin equivalents.
1,153 citations
TL;DR: The ABTS/H2O2/HRP decoloration method as discussed by the authors is capable of determining both hydrophilic and lipophilic antioxidant properties, thus, it is possible estimate the antioxidant activity of both antioxidant types in the same sample.
1,142 citations
TL;DR: In this article, the authors developed and tested a sequential extraction procedure (SEP) for As by choosing extraction reagents commonly used for sequential extraction of metals, Se and P, including NH 4 NO 3, NaOAc, NH 2 OH·HCl, EDTA, NH 4 OH and NH 4 F, were shown to either have only low extraction efficiency for As, or to be insufficiently selective or specific for the phases targeted.
1,137 citations
TL;DR: An improvement in broodstock nutrition and feeding has been shown to greatly improve not only egg and sperm quality but also seed production, and protein component of cuttlefish and squid together with their optimal concentration of HUFA appear to be responsible for their positive effect on reproductive performance.
961 citations
TL;DR: The electrochemical behavior of a film of single-wall carbon nanotubes functionalized with carboxylic acid groups was studied extensively on a glassy carbon (GC) electrode and showed favorable electrocatalytic behavior toward the oxidation of biomolecules such as dopamine, epinephrine, and ascorbic acid.
Abstract: The electrochemical behavior of a film of single-wall carbon nanotubes (SWNTs) functionalized with carboxylic acid groups was studied extensively on a glassy carbon (GC) electrode. One stable couple corresponding to the redox of the carboxylic acid group, which was supported by XPS and IR experiments, was observed. The electrode process involved four electrons, while the rate-determining step was a one-electron reduction. The SWNT film-modified electrode showed favorable electrocatalytic behavior toward the oxidation of biomolecules such as dopamine, epinephrine, and ascorbic acid.
783 citations
TL;DR: It is unlikely that carotenoids actually act as prooxidants in biological systems; rather they exhibit a tendency to lose their effectiveness as antioxidants.
728 citations
TL;DR: The results compared favorably to results obtained when benzyl mercaptan was used as the trapping nucleophile, indicating that phloroglucinol is an effective reagent for this analysis.
Abstract: The analysis of proanthocyanidin cleavage products after acid-catalysis in the presence of excess phloroglucinol was investigated. In the developed analytical method, a solution of 0.1 N HCl in methanol, containing 50 g/L phloroglucinol and 10 g/L ascorbic acid was prepared. The proanthocyanidin of interest was reacted in this solution (5 g/L) at 50 °C for 20 min, and afterward combined with 5 volumes of 40 mM aqueous sodium acetate before analysis by reversed-phase HPLC using an aqueous acetic acid and methanol gradient. This procedure was used to investigate the composition of proanthocyanidins isolated from the seed and skin tissue of Vitis vinifera L. berries. The results compared favorably to results obtained when benzyl mercaptan was used as the trapping nucleophile, indicating that phloroglucinol is an effective reagent for this analysis. Keywords: Proanthocyanidin; tannin; flavan-3-ol; molar absorptivity; Vitis vinifera; grape; phloroglucinol; benzyl mercaptan; thiolysis; yield
716 citations
TL;DR: The results suggest a strong interaction between both cell compartments in the control of the apoplastic ASC content in pea leaves, but this anti-oxidative response does not seem to be sufficient to remove the harmful effects of high salinity.
Abstract: The present work describes, for the first time, the changes that take place in the leaf apoplastic antioxidant defenses in response to NaCl stress in two pea (Pisum sativum) cultivars (cv Lincoln and cv Puget) showing different degrees of sensitivity to high NaCl concentrations. The results showed that only superoxide dismutase, and probably dehydroascorbate reductase (DHAR), were present in the leaf apoplastic space, whereas ascorbate (ASC) peroxidase, monodehydroascorbate reductase (MDHAR), and glutathione (GSH) reductase (GR) seemed to be absent. Both ASC and GSH were detected in the leaf apoplastic space and although their absolute levels did not change in response to salt stress, the ASC/dehydroascorbate and GSH to GSH oxidized form ratios decreased progressively with the severity of the stress. Apoplastic superoxide dismutase activity was induced in NaCl-treated pea cv Puget but decreased in NaCl-treated pea cv Lincoln. An increase in DHAR and GR and a decrease in ASC peroxidase, MDHAR, ASC, and GSH levels was observed in the symplast from NaCl-treated pea cv Lincoln, whereas in pea cv Puget an increase in DHAR, GR, and MDHAR occurred. The results suggest a strong interaction between both cell compartments in the control of the apoplastic ASC content in pea leaves. However, this anti-oxidative response does not seem to be sufficient to remove the harmful effects of high salinity. This finding is more evident in pea cv Lincoln, which is characterized by a greater inhibition of the growth response and by a higher rise in the apoplastic hydrogen peroxide content, O(2)(.-) production and thiobarbituric acid-reactive substances, and CO protein levels. This NaCl-induced oxidative stress in the apoplasts might be related to the appearance of highly localized O(2)(.-)/H(2)O(2)-induced necrotic lesions in the minor veins in NaCl-treated pea plants. It is possible that both the different anti-oxidative capacity and the NaCl-induced response in the apoplast and in the symplast from pea cv Puget in comparison with pea cv Lincoln contributes to a better protection of pea cv Puget against salt stress.
702 citations
TL;DR: It is suggested that guard cells treated with ABA may close the stomata via a pathway with H(2)O(2), which may be an intermediate in ABA signaling, and H( 2)O
Abstract: One of the most important functions of the plant hormone abscisic acid (ABA) is to induce stomatal closure by reducing the turgor of guard cells under water deficit. Under environmental stresses, hydrogen peroxide (H 2 O 2 ), an active oxygen species, is widely generated in many biological systems. Here, using an epidermal strip bioassay and laser-scanning confocal microscopy, we provide evidence that H 2 O 2 may function as an intermediate in ABA signaling in Vicia faba guard cells. H 2 O 2 inhibited induced closure of stomata, and this effect was reversed by ascorbic acid at concentrations lower than 10 −5 m. Further, ABA-induced stomatal closure also was abolished partly by addition of exogenous catalase (CAT) and diphenylene iodonium (DPI), which are an H 2 O 2 scavenger and an NADPH oxidase inhibitor, respectively. Time course experiments of single-cell assays based on the fluorescent probe dichlorofluorescein showed that the generation of H 2 O 2 was dependent on ABA concentration and an increase in the fluorescence intensity of the chloroplast occurred significantly earlier than within the other regions of guard cells. The ABA-induced change in fluorescence intensity in guard cells was abolished by the application of CAT and DPI. In addition, ABA microinjected into guard cells markedly induced H 2 O 2 production, which preceded stomatal closure. These effects were abolished by CAT or DPI micro-injection. Our results suggest that guard cells treated with ABA may close the stomata via a pathway with H 2 O 2 production involved, and H 2 O 2 may be an intermediate in ABA signaling.
TL;DR: A randomized, controlled chemoprevention trial was conducted in subjects with confirmed histologic diagnoses of multifocal non-metaplastic atrophy and/or intestinal metaplasia, two precancerous lesions as discussed by the authors.
Abstract: Background: Previous research has identified a high risk of gastric carcinoma as well as a high prevalence of cancer precursor lesions in rural populations living in the province of Narino, Colombia, in the Andes Mountains. Methods: A randomized, controlled chemoprevention trial was con- ducted in subjects with confirmed histologic diagnoses of multifocal nonmetaplastic atrophy and/or intestinal meta- plasia, two precancerous lesions. Individuals were assigned to receive anti-Helicobacter pylori triple therapy and/or di- etary supplementation with ascorbic acid, -carotene, or their corresponding placebos. Gastric biopsy specimens taken at baseline were compared with those taken at 72 months. Relative risks of progression, no change, and regres- sion from multifocal nonmetaplastic atrophy and intestinal metaplasia were analyzed with multivariate polytomous lo- gistic regression models to estimate treatment effects. All statistical tests were two-sided. Results: All three basic inter- ventions resulted in statistically significant increases in the rates of regression: Relative risks were 4.8 (95% confidence interval (CI) = 1.6-14.2) for anti-H. pylori treatment, 5.1 (95% CI = 1.7-15.0) for -carotene treatment, and 5.0 (95% CI = 1.7-14.4) for ascorbic acid treatment in subjects with atrophy. Corresponding relative risks of regression in sub- jects with intestinal metaplasia were 3.1 (95% CI = 1.0-9.3), 3.4 (95% CI = 1.1-9.8), and 3.3 (95% CI = 1.1-9.5). Combi- nations of treatments did not statistically significantly in- crease the regression rates. Curing the H. pylori infection (which occurred in 74% of the treated subjects) produced a marked and statistically significant increase in the rate of regression of the precursor lesions (relative risks = 8.7 (95% CI = 2.7-28.2) for subjects with atrophy and 5.4 (95% CI = 1.7-17.6) for subjects with intestinal metaplasia). Con- clusions: In the very high-risk population studied, effective anti-H. pylori treatment and dietary supplementation with antioxidant micronutrients may interfere with the precan- cerous process, mostly by increasing the rate of regression of cancer precursor lesions, and may be an effective strategy to prevent gastric carcinoma. (J Natl Cancer Inst 2000;92: 1881-8)
TL;DR: In normotensive individuals, an earlier primary dysfunction of the NO system and a later production of oxidative stress cause age-related reduction in endothelium-dependent vasodilation, which is similar but anticipated in hypertensive patients compared withnormotensive subjects.
Abstract: Age-related endothelial dysfunction could be caused by an alteration in the L-arginine-NO system and the production of oxidative stress in both normotensive and hypertensive individuals. In 47 normotensive subjects and 49 patients with essential hypertension, we evaluated forearm blood flow (by strain-gauge plethysmography) modifications induced by intrabrachial sodium nitroprusside (1, 2, and 4 microg/100 mL per minute) and acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg/100 mL per minute), an endothelium-independent vasodilator and an endothelium-dependent vasodilator, respectively. Acetylcholine was repeated in the presence of the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 100 microg/100 mL per minute), the antioxidant vitamin C (8 mg/100 mL per minute), or both. Vasodilation to acetylcholine, but not to sodium nitroprusside, was lower (P 60 years). In young hypertensive patients (age 30 years, vitamin C enhanced endothelium-dependent vasodilation and restored the inhibiting effect of L-NMMA on response to acetylcholine. In normotensive individuals, an earlier primary dysfunction of the NO system and a later production of oxidative stress cause age-related reduction in endothelium-dependent vasodilation. These alterations are similar but anticipated in hypertensive patients compared with normotensive subjects.
26 Oct 2001
TL;DR: General Topics Food-Derived Antioxidants: How to Evaluate Their Importance in Food and In Vivo Measurement of Total Antioxidant Capacity in Nutritional and Clinical Studies Guohua Cao and Ronald L. Halliwell
Abstract: General Topics Food-Derived Antioxidants: How to Evaluate Their Importance in Food and In Vivo Barry Halliwell Measurement of Total Antioxidant Capacity in Nutritional and Clinical Studies Guohua Cao and Ronald L. Prior Quantification of Isoprostanes as Indicators of Oxidant Stress In Vivo Jason D. Morrow, William E. Zackert, Daniel S. Van der Ende, Erin E. Reich, Erin S. Terry, Brian Cox, Stephanie C. Sanchez, Thomas J. Montine, and L. Jackson Roberts Vitamin E Efficacy of Vitamin E in Human Health and Disease Sharon V. Landvick, Anthony T. Diplock, and Lester Packer Vitamin E Bioavailability, Biokinetics, and Metabolism Maret G. Traber Biological Activity of Tocotrienols Stefan U. Weber and Gerald Rimbach Vitamin C Vitamin C: From Molecular Mechanisms to Optimum Uptake Sebastian J. Padayatty, Rushad Daruwala, Yaohui Wang, Peter Eck, Jian Song, Woo S. Koh, and Mark Levine Vitamin C and Cardiovascular Diseases Anitra C. Carr and Balz Frei Epidemiological and Clinical Aspects of Ascorbate and Cancer James E. Enstrom Carotenoids Carotenoids: Linking Chemistry, Absorption, and Metabolism to Potential Roles in Human Health and Disease Denise M. Deming, Thomas W. M. Boileau, Kasey H. Heintz, Christine A. Atkinson, and John W. Erdman, Jr. Antioxidant Effects of Carotenoids: Implication in Photoprotection in Humans Wilhelm Stahl and Helmut Sies Oxidative Breakdown of Carotenoids and Biological Effects of Their Metabolites Werner G. Siems, Olaf Sommerburg, and Frederik J. G. M. van Kuijk Carotenoids in the Nutrition of Infants Olaf Sommerburg, Werner G. Siems, Kristina Meissner, and Michael Leichsenring Human Studies on Bioavailability and Serum Response of Carotenoids Elizabeth J. Johnson Polyphenols and Flavonoids Caffeic Acid and Related Antioxidant Compounds: Biochemical and Cellular Effects Joao Laranjinha Polyphenols and Flavonoids Protect LDL Against Atherogenic Modifications Bianca Fuhrman and Michael Aviram Phytoestrogen Content in Foods and Their Role in Cancer Anna H. Wu and Malcolm C. Pike Peroxynitrite Scavenging by Mitochondrial Reductants and Plant Polyphenols Alberto Boveris, Silvia Alvarez, Silvia Lores Arnaiz, and Laura B. Valdez Antioxidants in Beverages and Herbal Products Antioxidant and Other Properties of Green and Black Tea Philip J. Rijken, Douglas A. Balentine, C. A. J. van Mierlo, I. Paetau-Robinson, F. van de Put, Paul T. Quinlan, Ute M. Weisgerber, and Sheila A. Wiseman The Phenolic Wine Antioxidants Andrew L. Waterhouse French Maritime Pine Bark: Pycnogenol Gerald Rimbach, Fabio Virgili, and Lester Packer Spices as Potent Antioxidants with Therapeutic Potential Bharat B. Aggarwal, Nihal Ahmad, and Hasan Mukhtar Lipoic Acid and Glutathione Lipoic Acid: Cellular Metabolism, Antioxidant Activity, and Clinical Relevance Oren Tirosh, Sashwati Roy, and Lester Packer Cellular Effects of Lipoic Acid and Its Role in Aging Regis Moreau , Wei-Jian Zhang, and Tory M. Hagen Vascular Complications in Diabetes: Mechanisms and the Influence of Antioxidants Peter Rosen, Hans-Jurgen Tritschler, and Lester Packer Therapeutic Effects of Lipoic Acid on Hyperglycemia and Insulin Resistance Erik J. Henriksen Bioavailability of Glutathione Dean P. Jones Melatonin Antioxidant Capacity of Melatonin Russel J. Reiter, Dun-xian Tan, Lucien C. Manchester, and Juan R. Calvo Radical and Reactive Intermediate-Scavenging Properties of Melatonin in Pure Chemical Systems Maria A. Livrea, Luisa Tesoriere, Dun-xian Tan, and Russel J. Reiter Selenium Selenium: An Antioxidant? Regina Brigelius-Flohe, Matilde Maiorino, Fulvio Ursini, and Leopold Flohe Selenium Status and Prevention of Chronic Diseases Paul Kneckt Nitric Oxide Antioxidant Properties of Nitric Oxide Homero Rubbo and Rafael Radi
TL;DR: The results indicate that the generation of ROS plays a role in root gravitropism, and the scavenging of ROS by antioxidants (N-acetylcysteine, ascorbic acid, and Trolox) inhibited root gravItropism.
Abstract: We report our studies on root gravitropism indicating that reactive oxygen species (ROS) may function as a downstream component in auxin-mediated signal transduction. A transient increase in the intracellular concentration of ROS in the convex endodermis resulted from either gravistimulation or unilateral application of auxin to vertical roots. Root bending was also brought about by unilateral application of ROS to vertical roots pretreated with the auxin transport inhibitor N-1-naphthylphthalamic acid. Furthermore, the scavenging of ROS by antioxidants (N-acetylcysteine, ascorbic acid, and Trolox) inhibited root gravitropism. These results indicate that the generation of ROS plays a role in root gravitropism.
TL;DR: It is suggested that oxidative stress underlies early atrial electrophysiological remodeling and offer novel insight into the etiology and potential treatment of an enigmatic and difficult to control arrhythmia.
Abstract: Atrial fibrillation (AF), the most common chronic arrhythmia, increases the risk of stroke and is an independent predictor of mortality. Available pharmacological treatments have limited efficacy. Once initiated, AF tends to self-perpetuate, owing in part to electrophysiological remodeling in the atria; however, the fundamental mechanisms underlying this process are still unclear. We have recently demonstrated that chronic human AF is associated with increased atrial oxidative stress and peroxynitrite formation; we have now tested the hypothesis that these events participate in both pacing-induced atrial electrophysiological remodeling and in the occurrence of AF following cardiac surgery. In chronically instrumented dogs, we found that rapid (400 min(-1)) atrial pacing was associated with attenuation of the atrial effective refractory period (ERP). Treatment with ascorbate, an antioxidant and peroxynitrite decomposition catalyst, did not directly modify the ERP, but attenuated the pacing-induced atrial ERP shortening following 24 to 48 hours of pacing. Biochemical studies revealed that pacing was associated with decreased tissue ascorbate levels and increased protein nitration (a biomarker of peroxynitrite formation). Oral ascorbate supplementation attenuated both of these changes. To evaluate the clinical significance of these observations, supplemental ascorbate was given to 43 patients before, and for 5 days following, cardiac bypass graft surgery. Patients receiving ascorbate had a 16.3% incidence of postoperative AF, compared with 34.9% in control subjects. In combination, these studies suggest that oxidative stress underlies early atrial electrophysiological remodeling and offer novel insight into the etiology and potential treatment of an enigmatic and difficult to control arrhythmia. The full text of this article is available at http://www.circresaha.org.
TL;DR: In this paper, the relation between plasma ascorbic acid concentrations and mortality due to all causes, and to cardiovascular disease, ischaemic heart disease, and cancer in 19,496 men and women aged 45-79 years.
TL;DR: In this article, the antioxidant properties of lemons, oranges and grapefruits were evaluated and compared with their total radical-trapping antioxidative potential (TRAP), and the results showed that lemons possess the highest antioxidant potential among the studied citrus fruits and are preferable for dietary prevention of cardiovascular and other diseases.
TL;DR: The results indicate that endothelial function is impaired in women with previous preeclampsia and is not explained by established maternal risk factors but is reversed by antioxidant ascorbic acid administration.
Abstract: ContextPreeclampsia is believed to result from release of placental factors
that damage maternal vascular endothelium. However, because most studies have
been conducted during pregnancy, it has not been possible to separate maternal
from placental mechanisms underlying endothelial dysfunction in preeclampsia.ObjectiveTo determine whether endothelial function is impaired in nonpregnant
women with previous preeclampsia and whether endothelial dysfunction is mediated
by oxidative stress.Design and SettingCase-control study conducted at 3 hospital maternity units in London,
England, between July 1997 and June 2000.ParticipantsA total of 113 women with previous preeclampsia (n = 35 with recurrent
episodes; n = 78 with a single episode) and 48 women with previous uncomplicated
pregnancies, all of whom were at least 3 months (median, 3 years) postpartum.Main Outcome MeasuresBrachial artery flow-mediated (endothelium-dependent) and glyceryl trinitrate–induced
(endothelium-independent) dilatation were compared between previously preeclamptic
women and controls. To investigate oxidative stress, these measurements were
repeated after administration of ascorbic acid, 1 g intravenously, in 15 cases
and 15 controls.ResultsMean (SD) flow-mediated dilatation was lower in women with previous
preeclampsia compared with controls (recurrent group, 0.9% [4.1%]; single-episode
group, 2.7% [3.5%]; and control group, 4.7% [4.3%]; P<.001).
In contrast, glyceryl trinitrate–induced dilatation was similar in the
3 groups (recurrent, 19.5% [5.9%]; single-episode, 21.0% [8.0%]; and control,
21.0% [8.3%]; P = .65). Impaired flow-mediated dilatation
in previously preeclamptic women was not accounted for by recognized vascular
risk factors. Ascorbic acid administration increased flow-mediated dilatation
in previously preeclamptic women (baseline, 2.6% [3.3%]; after administration,
5.6% [3.0%]; P = .001) but not in controls (baseline,
6.2% [3.3%]; after administration, 6.7% [5.0%]; P
= .72).ConclusionsOur results indicate that endothelial function is impaired in women
with previous preeclampsia and is not explained by established maternal risk
factors but is reversed by antioxidant ascorbic acid administration.
TL;DR: Since no artificial feed formulation is yet available to completely substitute for Artemia, feeding live prey to young fish larvae still remains essential in commercial hatchery operations.
TL;DR: The application of a quantitative assay for the derivation of osteoblast lineage progenitors from pluripotent ES cells is demonstrated, which could be applied to obtain purified osteoblasts to analyze mechanisms of osteogenesis and for use of ES cells in skeletal tissue repair.
Abstract: Pluripotent embryonic stem (ES) cells have the potential to differentiate to all fetal and adult cell types and might represent a useful cell source for tissue engineering and repair. Here we show that differentiation of ES cells toward the osteoblast lineage can be enhanced by supplementing serum-containing media with ascorbic acid, beta-glycerophosphate, and/or dexamethasone/retinoic acid or by co-culture with fetal murine osteoblasts. ES cell differentiation into osteoblasts was characterized by the formation of discrete mineralized bone nodules that consisted of 50-100 cells within an extracellular matrix of collagen-1 and osteocalcin. Dexamethasone in combination with ascorbic acid and beta-glycerophosphate induced the greatest number of bone nodules and was dependent on time of stimulation with a sevenfold increase when added to ES cultures after, but not before, 14 days. Co-culture with fetal osteoblasts also provided a potent stimulus for osteogenic differentiation inducing a fivefold increase in nodule number relative to ES cells cultured alone. These data demonstrate the application of a quantitative assay for the derivation of osteoblast lineage progenitors from pluripotent ES cells. This could be applied to obtain purified osteoblasts to analyze mechanisms of osteogenesis and for use of ES cells in skeletal tissue repair.
TL;DR: Treatment with antioxidants alone resulted in reversal of oxidative stress without significant decline in tissue lead burden and responses to the treatment with different antioxidants were recorded in the parameters of oxidative damage viz. lipid peroxide level, antioxidant enzymes and thiol contents.
TL;DR: Long-term administration of antioxidants can inhibit the development of the early stages of diabetic retinopathy, and the mechanism by which this action occurs warrants further investigation.
Abstract: Antioxidants were administered to diabetic rats and experimentally galactosemic rats to evaluate the ability of these agents to inhibit the development of diabetic retinopathy. Alloxan diabetic rats and nondiabetic rats that were fed 30% galactose randomly received standard diets or the diets supplemented with ascorbic acid and alpha-tocopherol (vitamins C+E diet) or a more comprehensive mixture of antioxidants (multi-antioxidant diet), including Trolox, alpha-tocopherol, N-acetyl cysteine, ascorbic acid, beta-carotene, and selenium. Diabetes or galactose feeding of at least 12 months resulted in pericyte loss, acellular capillaries, and basement membrane thickening. Compared with diabetic controls, the development of acellular capillaries was inhibited by 50% (P < 0.05) in diabetic rats that received supplemental vitamins C+E, and the number of pericyte ghosts tended to be reduced. The vitamins C+E supplement had no beneficial effect in galactosemic rats, but these rats consumed only approximately half as much of the antioxidants as the diabetic rats. The multi-antioxidant diet significantly inhibited ( approximately 55-65%) formation of both pericyte ghosts and acellular capillaries in diabetic rats and galactosemic rats (P < 0.05 vs. controls), without affecting the severity of hyperglycemia. Parameters of retinal oxidative stress, protein kinase C activity, and nitric oxides remained elevated for at least 1 year of hyperglycemia, and these abnormalities were normalized by multi-antioxidant therapy. Thus, long-term administration of antioxidants can inhibit the development of the early stages of diabetic retinopathy, and the mechanism by which this action occurs warrants further investigation. Supplementation with antioxidants can offer an achievable and inexpensive adjunct therapy to help inhibit the development of retinopathy in diabetes.
TL;DR: The stability study demonstrated that GTC was stable in water at room temperature and suggested that other ingredients used in production of tea drinks might interact with GTC and affect its stability.
Abstract: Green tea cateachins (GTC). namely (-) epicatechin (EC), (-) epicatechin gallate (ECG), (-) epigallocatechin (EGC), and (-) epigallocatechin gallate (EGCG), have been studied extensively for their wide-ranging biological activities. The goal of the present study was to examine the stability of GTC as a mixture under various processing conditions. The stability study demonstrated that GTC was stable in water at room temperature. When it was brewed at 98 degrees C for 7 h, longjing GTC degraded by 20%. When longjing GTC and pure EGCG were autoclaved at 120 degrees C for 20 min, the epimerization of EGCG to (-) gallocatechin gallate (GCG) was observed. The relatively high amount of GCG found in some tea drinks was most likely the epimerization product of EGCG during autoclaving. If other ingredients were absent, the GTC in aqueous solutions was pH-sensitive: the lower the pH, the more stable the GTC during storage. When it was added into commercially available soft drinks or sucrose solutions containing citric acid and ascorbic acid, longjing GTC exhibited varying stability irrespective of low pH value. This suggested that other ingredients used in production of tea drinks might interact with GTC and affect its stability. When canned and bottled tea drinks are produced, stored, and transported, the degradation of GTC must be taken into consideration.
TL;DR: Results of a depletion–repletion study with healthy young women hospitalized for 186 +/− 28 days, using vitamin C doses of 30–2,500 mg daily indicate that the Recommended Dietary Allowance for young women should be increased to 90 mg daily.
Abstract: The recently released Recommended Dietary Allowance of vitamin C for women, 75 mg daily, was based on data for men. We now report results of a depletion–repletion study with healthy young women hospitalized for 186 +/− 28 days, using vitamin C doses of 30–2,500 mg daily. The relationship between dose and steady-state plasma concentration was sigmoidal. Only doses above 100 mg were beyond the linear portion of the curve. Plasma and circulating cells saturated at 400 mg daily, with urinary elimination of higher doses. Biomarkers of endogenous oxidant stress, plasma and urine F2-isoprostanes, and urine levels of a major metabolite of F2-isoprostanes were unchanged by vitamin C at all doses, suggesting this vitamin does not alter endogenous lipid peroxidation in healthy young women. By using Food and Nutrition Board guidelines, the data indicate that the Recommended Dietary Allowance for young women should be increased to 90 mg daily.
TL;DR: It is shown that ascorbic acid can reverse some alterations caused by in vivo selenium exposure, but not ALA-D inhibition, and this study suggests that vitamin C may have a protective role in organodiselenide intoxication.
Abstract: Sodium selenite (Na2SeO3) is the selenium form used in the composition of dietary supplements, and diphenyl diselenide (PhSe)2 is an important intermediate in organic synthesis, which increases the risk of human exposure to this chemical in the workplace. These compounds have been reported to inhibit the cerebral and hepatic aminolevulinic acid dehydratase (ALA-D) in vitro, and now we show that ascorbic acid can reverse some alterations caused by in vivo selenium exposure, but not ALA-D inhibition. The effect of Na2SeO3 or (PhSe)2 and ascorbic acid on selenium distribution, total non-protein thiol, ascorbic acid content (liver and brain) and haemoglobin was also examined. Mice were exposed to 250 micromol/kg (PhSe)2, or 18.75 micromol/kg Na2SeO3 subcutaneously, and to ascorbic acid, twice a day, 1 mmol/kg intraperitonially, for 10 days. Hepatic ALA-D of mice treated with (PhSe)2 was inhibited about 58% and similar results were observed in the animals that received ascorbic acid supplementation (P 0.10). Ascorbic acid treatment decreased significantly the hepatic and cerebral deposition of Se in (PhSe)2-exposed mice (P<0.01). Hepatic non-protein thiol content was not changed by treatment with (PhSe)2, ascorbic acid or (PhSe)2+ascorbic acid. Hepatic content of ascorbic acid was twice that in mice that received (PhSe)2, independent of ascorbic acid treatment (P<0.001). The results of this study suggest that vitamin C may have a protective role in organodiselenide intoxication.
01 Jun 2001
TL;DR: The description in 1996 of an Arabidopsis thaliana mutant deficient in ascorbic acid prompted renewed research effort in this area, and subsequently in 1998 a new pathway was discovered that is backed by strong biochemical and molecular genetic evidence.
Abstract: ▪ Abstract The structure of the familiar antioxidant L-ascorbic acid (vitamin C) was described in 1933 yet remarkably, its biosynthesis in plants remained elusive until only recently. It became clear from radioisotopic labeling studies in the 1950s that plant ascorbic acid biosynthesis does not proceed in toto via a route similar to that in mammals. The description in 1996 of an Arabidopsis thaliana mutant deficient in ascorbic acid prompted renewed research effort in this area, and subsequently in 1998 a new pathway was discovered that is backed by strong biochemical and molecular genetic evidence. This pathway proceeds through the intermediates GDP-D-mannose, L-galactose, and L-galactono-1,4-lactone. Much research has focused on the properties of the terminal enzyme responsible for conversion of the aldonolactone to ascorbate, and on related enzymes in both mammals and fungi. Two of the plant biosynthetic genes have been studied at the molecular level and additional ascorbate-deficient A. thaliana mutan...
TL;DR: It is determined that vit C induces lipid hydroperoxide decomposition to the DNA-reactive bifunctional electrophiles 4-oxo-2-nonenal, 4,5-epoxy-2(E)-decenal), and 4-hydroxy- 2-nonnal, a precursor of etheno- 2′-deoxyadenosine, a highly mutagenic lesion found in human DNA.
Abstract: Epidemiological data suggest that dietary antioxidants play a protective role against cancer. This has led to the proposal that dietary supplementation with antioxidants such as vitamin C (vit C) may be useful in disease prevention. However, vit C has proved to be ineffective in cancer chemoprevention studies. In addition, concerns have been raised over potentially deleterious transition metal ion-mediated pro-oxidant effects. We have now determined that vit C induces lipid hydroperoxide decomposition to the DNA-reactive bifunctional electrophiles 4-oxo-2-nonenal, 4,5-epoxy-2(E)-decenal, and 4-hydroxy-2-nonenal. The compound 4,5-Epoxy-2(E)-decenal is a precursor of etheno-2'-deoxyadenosine, a highly mutagenic lesion found in human DNA. Vitamin C-mediated formation of genotoxins from lipid hydroperoxides in the absence of transition metal ions could help explain its lack of efficacy as a cancer chemoprevention agent.
TL;DR: The addition of an anti-oxidant (0.5 mM ascorbic acid) to the root medium, prior to and during salt-treatment for 9 h, facilitated the subsequent recovery and long-term survival of c.
Abstract: The transition from reversible to permanent wilting, in whole tomato seedlings (Lycopersicon esculentum Mill. cv. M82) following severe salt-stress by root exposure to 300 mM NaCl, was investigated. Salinized seedlings wilted rapidly but recovered if returned to non-saline nutrient solution within 6 h. However, after 9 h of salt-treatment 100% of the seedlings remained wilted and died. Remarkably, the addition of an anti-oxidant (0.5 mM ascorbic acid) to the root medium, prior to and during salt-treatment for 9 h, facilitated the subsequent recovery and long-term survival of c .5 0% of the wilted seedlings. Other organic solutes without known anti-oxidant activity were not effective. Salt-stress increased the accumulation in roots, stems and leaves, of lipid peroxidation products produced by interactions with damaging active oxygen species. Additional ascorbic acid partially inhibited this response but did not significantly reduce sodium uptake or plasma membrane leakiness.
TL;DR: In this article, the authors introduce metabolic modeling as a new tool to analyze the network of redox reactions composing the superoxide dismutase-ascorbate (Asc)-glutathione (GSH) cycle.
Abstract: The present study introduces metabolic modeling as a new tool to analyze the network of redox reactions composing the superoxide dismutase-ascorbate (Asc)-glutathione (GSH) cycle. Based on previously determined concentrations of antioxidants and defense enzymes in chloroplasts, kinetic properties of antioxidative enzymes, and nonenzymatic rate constants of antioxidants with reactive oxygen, models were constructed to simulate oxidative stress and calculate changes in concentrations and fluxes of oxidants and antioxidants. Simulated oxidative stress in chloroplasts did not result in a significant accumulation of O2.− and H2O2 when the supply with reductant was sufficient. Model results suggest that the coupling between Asc- and GSH-related redox systems was weak because monodehydroascorbate radical reductase prevented dehydroascorbate (DHA) formation efficiently. DHA reductase activity was dispensable. Glutathione reductase was mainly required for the recycling of GSH oxidized in nonenzymatic reactions. In the absence of monodehydroascorbate radical reductase and DHA reductase, glutathione reductase and GSH were capable to maintain the Asc pool more than 99% reduced. This suggests that measured DHA/Asc ratios do not reflect a redox balance related to the Asc-GSH-cycle. Decreases in Asc peroxidase resulted in marked H2O2 accumulation without significant effects on the redox balance of Asc/DHA or GSH/GSSG. Simulated loss of SOD resulted in higher H2O2 production rates, thereby affecting all subsequent steps of the Asc-GSH-cycle. In conclusion, modeling approaches contribute to the theoretical understanding of the functioning of antioxidant systems by pointing out questions that need to be validated and provide additional information that is useful to develop breeding strategies for higher stress resistance in plants.