Showing papers on "Ascorbic acid published in 1998"
TL;DR: In this article, the kinetic behavior of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH).
Abstract: The kinetic behaviour of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH.). After addition of different standard concentrations to DPPH. (0.025 g litre-1), the percentage of remaining DPPH. was determined at different times from the absorbances at 515 nm. The percentage remaining DPPH. against reaction time followed a multiplicative model equation: In [DPPH.REM] = b 1n t + 1n a. The slopes of these equations may be useful parameters to define the antioxidant capacity. The steeper the slope, the lower the amount of antioxidant necessary to decrease by 50% the initial DPPH. concentration (EC50). This parameter, EC50, is widely used to measure antioxidant power, but it does not takes into account the reaction time. Time needed to reach the steady state to the concentration corresponding at EC50 (T(EC50)) was calculated, and antiradical efficiency (AE) was proposed as a new parameter to characterise the antioxidant compounds where AE = 1/EC50 T(EC50). It was shown that AE is more discriminatory than EC50. AE values are more useful because they also take into account the reaction time. The results have shown that the order of the AE (x 10(-3)) in the compounds tested was: ascorbic acid (11.44) > caffeic acid (2.75) greater than or equal to gallic acid (2.62) > tannic acid (0.57) greater than or equal to DL-alpha-tocopherol (0.52) > rutin (0.21) greater than or equal to quercetin (0.19) > ferulic acid (0.12) greater than or equal to 3-tert-butyl-4-hydroxyanisole, BHA (0.10) > resveratrol (0.05).
1,812 citations
TL;DR: This is the first completely biological TEBV to display a burst strength comparable to that of human vessels, and this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.
Abstract: Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.
1,403 citations
TL;DR: Different cultivars of four Vaccinium species were analyzed for total phenolics, total anthocyanins, and antioxidant capacity (oxygen radical absorbance capacity, ORAC).
Abstract: Different cultivars of four Vaccinium species [Vaccinium corymbosum L (Highbush), Vaccinium ashei Reade (Rabbiteye), Vaccinium angustifolium (Lowbush), and Vaccinium myrtillus L (Bilberry)] were analyzed for total phenolics, total anthocyanins, and antioxidant capacity (oxygen radical absorbance capacity, ORAC). The total antioxidant capacity of different berries studied ranged from a low of 13.9 to 45.9 μmol Trolox equivalents (TE)/g of fresh berry (63.2−282.3 μmol TE/g of dry matter) in different species and cultivars of Vaccinium. Brightwell and Tifblue cultivars of rabbiteye blueberries were harvested at 2 times, 49 days apart. Increased maturity at harvest increased the ORAC, the anthocyanin, and the total phenolic content. The growing location (Oregon vs Michigan vs New Jersey) did not affect ORAC, anthocyanin or total phenolic content of the cv. Jersey of highbush blueberries. A linear relationship existed between ORAC and anthocyanin (rxy = 0.77) or total phenolic (rxy = 0.92) content. In general,...
1,341 citations
TL;DR: An HPLC method using 1,1-diphenyl-2-picrylhydrazyl (DPPH) determined the free radical-scavenging activity of several antioxidants: ascorbic acid, alpha-tocopherol, Trolox, and cysteine, and the results well agree with those of previous reports.
Abstract: An HPLC method for evaluation of the free radical-scavenging activity of foods by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) is reported. The activity was evaluated by measuring the decrease of DPPH detected at 517 nm. By using this novel method, we determined the free radical-scavenging activity of several antioxidants: ascorbic acid, α-tocopherol, Trolox, and cysteine. The results gave good correlation between the radical-scavenging activity determined by HPLC and by conventional colorimetry. This methodology was applied to determine the free radical-scavenging activity of 8 beverages. The activity of coffee was the highest, followed by red wine, green tea, oolong tea, black tea, rose wine, white wine, and orange juice. The results well agree with those of previous reports. This method is expected to be useful for a simple and rapid determination of free radical-scavenging activity in colored foods, because coloring substances in foods do not interfere with the measurement.
1,075 citations
TL;DR: The definition of this biosynthetic pathway should allow engineering of plants for increased ascorbate production, thus increasing their nutritional value and stress tolerance.
Abstract: Vitamin C (L-ascorbic acid) has important antioxidant and metabolic functions in both plants and animals, but humans, and a few other animal species, have lost the capacity to synthesize it Plant-derived ascorbate is thus the major source of vitamin C in the human diet Although the biosynthetic pathway of L-ascorbic acid in animals is well understood, the plant pathway has remained unknown-one of the few primary plant metabolic pathways for which this is the case L-ascorbate is abundant in plants (found at concentrations of 1-5 mM in leaves and 25 mM in chloroplasts) and may have roles in photosynthesis and transmembrane electron transport We found that D-mannose and L-galactose are efficient precursors for ascorbate synthesis and are interconverted by GDP-D-mannose-3,5-epimerase We have identified an enzyme in pea and Arabidopsis thaliana, L-galactose dehydrogenase, that catalyses oxidation of L-galactose to L-galactono-1,4-lactone We propose an ascorbate biosynthesis pathway involving GDP-D-mannose, GDP-L-galactose, L-galactose and L-galactono-1,4-lactone, and have synthesized ascorbate from GDP-D-mannose by way of these intermediates in vitro The definition of this biosynthetic pathway should allow engineering of plants for increased ascorbate production, thus increasing their nutritional value and stress tolerance
1,029 citations
TL;DR: In essential hypertensive patients, impaired endothelial vasodilation can be improved by the antioxidant vitamin C, an effect that can be reversed by the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine, and these findings support the hypothesis thatNitric oxide inactivation by oxygen free radicals contributes to endothelial dysfunction in essential hypertension.
Abstract: Background—Essential hypertension is associated with impaired endothelium-dependent vasodilation. Inactivation of endothelium-derived nitric oxide by oxygen free radicals participates in endothelial dysfunction in experimental hypertension. To test this hypothesis in humans, we evaluated the effect of antioxidant vitamin C on endothelium-dependent responses in essential hypertensive patients. Methods and Results—In 14 healthy subjects (47.1±4.8 years; blood pressure, 120.6±4.5/80.9±3.5 mm Hg) and 14 essential hypertensive patients (47.3±5.1 years; blood pressure, 153.9±7.1/102.3±4.1 mm Hg), we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 μg · 100 mL−1 · min−1) or sodium nitroprusside (1, 2, and 4 μg/100 mL forearm tissue per minute), an endothelium-dependent and -independent vasodilator, respectively, in basal conditions and during infusion of intrabrachial vitamin C (2.4 mg/100 mL forearm tissue per minute). I...
739 citations
TL;DR: Post-slaughter carnosine addition may be an effective means of improving lipid stability in processed meats, perhaps in combination with dietary vitamin E supplementation, which appears to have little, if any, beneficial effects on meat stability.
713 citations
TL;DR: In this paper, the markers of lipid peroxidation and defenses against oxidative stress in patients with varying degrees of congestive heart failure were studied, and the prognosis of these patients was established by measuring the levels of soluble tumor necrosis factor-alpha receptors 1 and 2 (sTNF-R1 and sTNFR2).
536 citations
TL;DR: It is concluded that the consumption of strawberries, spinach or red wine, which are rich in antioxidant phenolic compounds, can increase the serum antioxidant capacity in humans.
Abstract: It is often assumed that antioxidant nutrients contribute to the protection afforded by fruits, vegetables, and red wine against diseases of aging. However, the effect of fruit, vegetable and red wine consumption on the overall antioxidant status in human is unclear. In this study we investigated the responses in serum total antioxidant capacity following comsumption of strawberries (240 g), spinach (294 g), red wine (300 ml) or vitamin C (1250 mg) in eight elderly women. Total antioxidant capacity was determined using different methods: oxygen radical absorbance capacity (ORAC) assay, Trolox equivalent antioxidant capacity (TEAC) assay and ferric reducing ability (FRAP) assay. The results showed that the total antioxidant capacity of serum determined as ORAC, TEAC and FRAP, using the area under the curve, increased significantly by 7-25% during the 4-h period following consumption of red wine, strawberries, vitamin C or spinach. The total antioxidant capacity of urine determined as ORAC increased (P < 0.05) by 9.6, 27.5, and 44.9% for strawberries, spinach, and vitamin C, respectively, during the 24-h period following these treatments. The plasma vitamin C level after the strawberry drink, and the serum urate level after the strawberry and spinach treatments, also increased significantly. However, the increased vitamin C and urate levels could not fully account for the increased total antioxidant capacity in serum following the consumption of strawberries, spinach or red wine. We conclude that the consumption of strawberries, spinach or red wine, which are rich in antioxidant phenolic compounds, can increase the serum antioxidant capacity in humans. J. Nutr. 2383-2390, 1998
512 citations
Book•
01 Feb 1998TL;DR: Fat-soluble vitamins Vitamin A and Carotenoids Review Properties Methods Method Protocols Vitamin D Review properties methods method protocols Vitamin E: Tocopherols and Tocotrienols Review Properties methods Method protocols Vitamin K Review properties Methods Method protocols 10:40:09 AM water-solvable vitamins Ascorbic Acid review Properties Methods Status of Vitamin C Analysis Method Protocol.
Abstract: Fat-soluble vitamins Vitamin A and Carotenoids Review Properties Methods Method Protocols Vitamin D Review Properties Methods Method Protocols Vitamin E: Tocopherols and Tocotrienols Review Properties Methods Method protocols Vitamin K Review Properties Methods Method protocols 10:40:09 AM Water-soluble vitamins Ascorbic Acid: Vitamin C Review Properties Methods Status of Vitamin C Analysis Method Protocols Thiamin Review Properties Methods Method Protocols Riboflavin Review Properties Methods Method Protocols Niacin Review Properties Methods Method Protocols Vitamin B6 Review Properties Methods Method Protocols Folate and Folic Acid Review Properties: The Microgram Dietary Folate Equivalents Method Protocols Vitamin B12 Review Properties Methods Method Protocols Biotin Review Properties Methods Pantothenic Acid Review Properties Methods Multianalyte Methods for Analysis of the Fat- and Water-Soluble Vitamins Fat-Soluble Vitamins Water-Soluble Vitamins
447 citations
TL;DR: The nutrient intakes of smokers differ substantially from those of nonsmokers, and some of these differences may exacerbate the deleterious effects of smoke components on cancer and coronary heart disease risk.
Abstract: The aim of this investigation was to assess the relationship between smoking status and nutrient intakes using a meta-analysis. Publications in English were sought through a Medline search using the following key words: food habits, eating, feeding behavior, diet, food, nutrition, nutritional status or assessment, tobacco use disorder, tobacco, nicotine and smoking. Scanning relevant reference lists of articles and hand searching completed the data collection. No attempt was made to search for unpublished results. Paper selection was based on nutritional surveys including comparisons of smokers with nonsmokers. Fifty-one published nutritional surveys from 15 different countries with 47,250 nonsmokers and 35,870 smokers were used in the analysis. The estimates of size effects were calculated with the mean and variance values of each nutrient intake and the size of the sample. Smokers declared significantly (all P < 10(-5)) higher intakes of energy (+4.9%), total fat (+3.5%), saturated fat (+8.9%), cholesterol (+10.8%) and alcohol (+77.5%) and lower intakes of polyunsaturated fat (-6.5%), fiber (-12.4%), vitamin C (-16.5%), vitamin E (-10.8%) and beta-carotene (-11.8%) than nonsmokers. Protein and carbohydrate intakes did not differ between smokers and nonsmokers. There was no evidence of heterogeneity among studies. In conclusion, the nutrient intakes of smokers differ substantially from those of nonsmokers. Some of these differences may exacerbate the deleterious effects of smoke components on cancer and coronary heart disease risk.
TL;DR: The results of this study indicate that ferritin formation by Caco-2 cell monolayers is highly sensitive and accurately measures food Fe availability in this in vitro system.
Abstract: We have adapted an in vitro digestion/Caco-2 cell model to assess Fe availability from foods, by using ferritin formation by Caco-2 cells as an indicator of Fe uptake. Ferritin formation by Caco-2 cells occurs in response to Fe uptake at concentrations of available Fe greater than that of the culture media to which the cells have been adapted. This methodology circumvents the need for using radioactive Fe and thus eliminates the costs and controversies associated with food radiolabeling. To validate this method, we measured ferritin formation in Caco-2 cells exposed to digests containing Fe of relatively high and low availability. Our objective was to determine if ferritin formation would be proportional to Fe uptake and sufficiently sensitive to be an indicator of Fe availability from food digests. Our model uses established in vitro digestion techniques coupled with uptake of Fe by Caco-2 cell monolayers. Measurement of cell ferritin was done by a commercially available RIA. Higher ferritin formation was observed in cells exposed to digests containing FeSO 4 plus ascorbic acid vs, digests containing FeSO 4 plus citric acid. Additional comparisons of Fe availability from digests of beef, fish, corn and green beans yielded results that demonstrate higher Fe availability (i.e., greater ferritin formation) from beef and fish digests than from digests of corn and green beans. Overall, the results document the promotional effects of ascorbic acid and animal tissue on Fe uptake as measured indirectly by ferritin formation. The results of this study indicate that ferritin formation by Caco-2 cell monolayers is highly sensitive and accurately measures food Fe availability in this in vitro system.
TL;DR: Control of the muscle enzyme systems, mainly proteases and lipases, is essential for the standardization of the processing and/or enhancement of flavor quality of dry-cured ham.
Abstract: The processing of dry-cured ham is very complex and involves numerous biochemical reactions that are reviewed in this article. Muscle proteins undergo an intense proteolysis, resulting in a great number of small peptides and high amounts of free amino acids. The enzymes responsible of these changes are proteinases (cathepsins B, D, H, and L and, to a less extent, calpains) and exopeptidases (peptidases and aminopeptidases). Muscle and adipose tissue lipids are also subject to intense lipolysis, generating free fatty acids by the action of lipases that, in a second stage, are transformed to volatiles as a result of oxidation. Sensory profiles of dry-cured ham are strongly affected by these enzymatic reactions. In addition, the activity levels of the muscle enzymes significantly depend on the properties of raw ham, such as age and crossbreeding as well as the process conditions such as temperature, time, water activity, redox potential, and salt content. Thus, the control of the muscle enzyme systems, mainly proteases and lipases, is essential for the standardization of the processing and/or enhancement of flavor quality of dry-cured ham.
TL;DR: It is demonstrated that an α2-integrin-collagen interaction is required for activation of Osf2 and induction of osteoblast-specific gene expression and matrix signals may regulate Osf 2 through a post-translational pathway or via an accessory factor.
TL;DR: It is found that SOD and EUK-8 compete more effectively with .NO for superoxide than does ascorbic acid and 3-nitrotyrosine formation (from peroxynitrite) is used as an indicator of .NO interaction with superoxide.
Abstract: The bioactivity of nitric oxide (.NO) depends, in part, on its interaction with superoxide. Usually, superoxide dismutase (SOD) preserves .NO bioactivity by limiting the availability of superoxide. Ascorbic acid also effectively scavenges superoxide, but the extent to which this interaction is necessary for intact .NO bioactivity is not known. Therefore, the present study examined the effect of ascorbic acid on .NO bioactivity with isolated rabbit arterial segments. A steady flux of superoxide (1.15 to 2.3 micromol . L-1 . min-1) produced either by pyrogallol autoxidation or a hypoxanthine/xanthine oxidase system inhibited endothelium-derived .NO-mediated arterial relaxation elicited by acetylcholine. This effect of superoxide was completely blocked by SOD (300 IU/mL) and the manganese SOD mimic EUK-8 (300 micromol/L) and partially inhibited by ascorbic acid (10 mmol/L). Lower concentrations of ascorbic acid were ineffective despite scavenging >90% of superoxide. We increased the endogenous flux of superoxide (3.2+/-0.3-fold) by inhibiting vascular copper-zinc SOD with diethyldithiocarbamate. This increased endogenous flux of superoxide produced an impairment of .NO-mediated arterial relaxation that was reversed by EUK-8 (300 micromol/L) but not ascorbic acid (10 mmol/L) despite equivalent scavenging of the endogenous superoxide flux. We used 3-nitrotyrosine formation (from peroxynitrite) as an indicator of .NO interaction with superoxide and found that SOD and EUK-8 compete more effectively with .NO for superoxide than does ascorbic acid. These data indicate that preservation of .NO bioactivity by superoxide scavengers depends not only on superoxide scavenging activity, but also on the rate of superoxide scavenging. Normal extracellular concentrations of ascorbic acid (30 to 150 micromol/L) are not likely to prevent the interaction of .NO with superoxide under physiological conditions.
TL;DR: Vitamin C improves FDD in patients with CHF as the result of increased availability of nitric oxide, and this observation supports the concept that endothelial dysfunction in patientswith CHF is, at least in part, due to accelerated degradation of Nitric oxide by radicals.
Abstract: Background—Chronic heart failure (CHF) is associated with endothelial dysfunction including impaired endothelium-mediated, flow-dependent dilation (FDD). There is evidence for increased radical formation in CHF, raising the possibility that nitric oxide is inactivated by radicals, thereby impairing endothelial function. To test this hypothesis, we determined the effect of the antioxidant vitamin C on FDD in patients with CHF. Methods and Results—High-resolution ultrasound and Doppler was used to measure radial artery diameter and blood flow in 15 patients with CHF and 8 healthy volunteers. Vascular effects of vitamin C (25 mg/min IA) and placebo were determined at rest and during reactive hyperemia (causing endothelium-mediated dilation) before and after intra-arterial infusion of N-monomethyl-l-arginine (L-NMMA) to inhibit endothelial synthesis of nitric oxide. Vitamin C restored FDD in patients with heart failure after acute intra-arterial administration (13.2±1.7% versus 8.2±1.0%; P<.01) and after 4 we...
TL;DR: Data on baseline characteristics of the participants suggest that the present sample is close to the national population in terms of geographic density, socioeconomic status, and the distribution of various major risk factors for the diseases under study.
TL;DR: Chitin-chitosan, when used as a food supplement, does lower plasma cholesterol and triglycerides and improves the HDL-cholesterol/total cholesterol ratio, but certain medical precautions should be observed with long-term ingestion of high doses to avoid potential adverse metabolic consequences.
TL;DR: It is concluded that sustained oxidation does not occur and that differential strategies of antioxidant response in Alg-S and AlG-R may contribute to pathogen sensitivity.
Abstract: Leaves of two barley ( Hordeum vulgare L.) isolines, Alg-R, which has the dominant Mla1 allele conferring hypersensitive race-specific resistance to avirulent races of Blumeria graminis , and Alg-S, which has the recessive mla1 allele for susceptibility to attack, were inoculated with B. graminis f. sp. hordei . Total leaf and apoplastic antioxidants were measured 24 h after inoculation when maximum numbers of attacked cells showed hypersensitive death in Alg-R. Cytoplasmic contamination of the apoplastic extracts, judged by the marker enzyme glucose-6-phosphate dehydrogenase, was very low (less than 2%) even in inoculated plants. Dehydroascorbate, glutathione, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase were present in the apoplast. Inoculation had no effect on the total foliar ascorbate pool size or the redox state. The glutathione content of Alg-S leaves and apoplast decreased, whereas that of Alg-R leaves and apoplast increased after pathogen attack, but the redox state was unchanged in both cases. Large increases in foliar catalase activity were observed in Alg-S but not in Alg-R leaves. Pathogen-induced increases in the apoplastic antioxidant enzyme activities were observed. We conclude that sustained oxidation does not occur and that differential strategies of antioxidant response in Alg-S and Alg-R may contribute to pathogen sensitivity.
TL;DR: To determine changes in chemokine and receptor expression in HIV infection, a large number of patients with or without HIV received chemotherapy for at least two weeks before and after treatment with antiretroviral drugs.
Abstract: Background: Three phenotypes of the antioxidant protein haptoglobin are known: Hp 1-1, Hp 2-1 and Hp 2-2. Objectives: To investigate the outcome of HIV infection according to haptoglobin type. Design and methods: Haptoglobin phenotypes were determined using starch gel electrophoresis in serum obtained from 653 HIV-infected Caucasians in the AIDS reference centers of Gent (n = 184), Antwerp (n = 309), and Luxembourg (n = 160). Survival was compared between haptoglobin types using Kaplan-Meier curves. Plasma HIV-1 RNA was quantified by reverse transcriptase PCR. Serum iron, transferrin saturation, ferritin, and vitamin C were assayed to evaluate iron-driven oxidative stress in 184 HIV-infected patients and 204 controls. Results: The haptoglobin type distribution amongst the patients (17.6% Hp 1-1, 49.9% Hp 2-1, 32.5% Hp 2-2) corresponded to that of the controls. Kaplan-Meier curves showed a higher mortality for the Hp 2-2 group (P = 0.0001; adjusted mortality risk ratio, 1.78; 95% confidence interval, 1.25-2.54). Median survival time was 11.0 years (Hp 1-1 and Hp 2-1) versus 7.33 years (Hp 2-2). Plasma HIV-1 RNA levels prior to antiviral therapy and their increase over 1 year were highest in Hp 2-2 patients (P = 0.03 and 0.003, respectively). The Hp 2-2 type was associated with higher serum iron, transferrin saturation, and ferritin levels and with low vitamin C concentrations. Furthermore, ferritin concentrations were higher in HIV-infected patients than in controls (P < 0.0001). Conclusion: HIV-infected patients carrying the Hp 2-2 phenotype show a worse prognosis, which is reflected by a more rapid rate of viral replication (in the absence of antiviral treatment). They also accumulate more iron and oxidize more vitamin C, suggesting that less efficient protection against haemoglobin/iron-driven oxidative stress may be a direct mechanism for stimulating viral replication.
TL;DR: A new, rapid, and reliable method for measuring the protective antioxidant potential of pure antioxidant solutions or biological tissues, and when incorporated into the microsomal membrane, alpha-tocopherol markedly enhances antioxidant protection against peroxyl radical, suitable for the assessment of fat-soluble antioxidants.
TL;DR: The highest concentration of antioxidants measured was 20.3 times that of the lowest, showing that great variation exists in the chemical nature of honey from different floral sources.
Abstract: SUMMARYThe water-soluble antioxidant capacity of 19 samples of honey from 14 different floral sources was determined by a spectrophotometric assay. The highest concentration of antioxidants measured was 20.3 times that of the lowest, showing that great variation exists in the chemical nature of honey from different floral sources. Antioxidant content was positively correlated with both water content and honey colour. Because of the health benefits of dietary antioxidants, floral source should be a factor in evaluating the potential of honey as an antioxidant-containing food supplement.
TL;DR: In this article, a spectrophotometric end-point method has been developed to evaluate L-ascorbic acid in aqueous media, and this represents an improvement over the lag-method previously reported.
Abstract: The 2,2’-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical can be generated by the enzymatic system formed by hydrogen peroxide and horseradish peroxidase. This ABTS radical (ABTS ∞a ), a chromogen, is stable at room temperature but is unstable above 35°C and/or at pH values of above 7.5. Nevertheless, the most important factor in its stability is the ABTS/ABTS ∞a concentration ratio in the medium. The radical reacts with the antioxidant, L-ascorbic acid, with a high rate constant, the stoichiometry of the reaction being 1 mol of L-ascorbic acid per 2 mol of ABTS ∞a reduced. Based on these considerations, a spectrophotometric end-point method has been developed to evaluate L-ascorbic acid in aqueous media, and this represents an improvement over the lag-method previously reported. Under optimal conditions of temperature, pH and reagent concentration, the end-point method was capable of determining L-ascorbic acid with a limit of quantification of 0.38 nmol. In the assay described here, this ability is used to evaluate the total antioxidant activity of commercial citrus juices, in which ascorbic acid is a principal component. In our opinion this procedure can quickly provide useful information on the antioxidant content of foods and plant extracts. # 1998 John Wiley & Sons, Ltd. Phytochem. Anal. 9, 196‐202, 1998
TL;DR: Results suggest that ascorbate within the erythrocyte protects α-tocopherol in the cell membrane by a direct recycling mechanism.
TL;DR: In this paper, the role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes and it was shown that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone.
Abstract: The role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes. Drought imposed at two different stages after anthesis resulted in an increase in H2O2 accumulation and lipid peroxidation and decrease in ascorbic acid content. Antioxidant enzymes like superoxide dismutase, ascorbate peroxidase and catalase significantly increased under water stress. Drought tolerant genotype C 306 which had highest ascorbate peroxidase and catalase activity and ascorbic acid content also showed lowest H2O2 accumulation and lipid peroxidation (malondialdehyde content) under water stress in comparison to susceptible genotype HD 2329 which showed lowest antioxidant enzyme activity and ascorbic acid content and highest H2O2 content and lipid peroxidation. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Superoxide dismutase activity, however, did not show significant differences among the genotypes under irrigated as well as water stress condition. It seems that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone.
TL;DR: Recent findings indicate several polyphenols and antioxidant drugs are effective in protecting the cells from ROS attack, and further development of these antioxidant molecules may be of value in preventing the development of neurodegenerative diseases.
Abstract: Oxidative insults, whether over-excitation, excessive release of glutamate or ATP caused by stroke, ischemia or inflammation, exposure to ionizing radiation, heavy-metal ions or oxidized lipoproteins may initiate various signaling cascades leading to apoptotic cell death and neurodegenerative disorders. Among the various reactive oxygen species (ROS) generated in the living organism, hydroxyl and peroxynitrite are the most potent and can damage proteins, lipids and nucleic acids. It appears that some natural antioxidants (tocopherol, ascorbic acid and glutathione) and defense enzyme systems (superoxide dismutase, catalase and glutathione peroxidase) may provide some protection against oxidative damage. Recent findings indicate several polyphenols and antioxidant drugs (probucol, seligilline) are effective in protecting the cells from ROS attack. Further development of these antioxidant molecules may be of value in preventing the development of neurodegenerative diseases.
TL;DR: The antioxidant activity of extracts of Du-zhong correlates to their polyphenol content, and the thiobarbituric acid reactive substances values for leaves, roasted cortex, and raw cortex were linked to their Polyphenol Content.
Abstract: The antioxidant effect of extracts from leaves, raw cortex, and roasted cortex of Du-zhong was evaluated using various lipid peroxidation models The inhibitory activity of extracts of Du-zhong (200 μg/mL) on the peroxidation of linoleic acid measured by thiocyanate method followed the order leaves (999%) > roasted cortex (959%) > raw cortex (772%) at 60 h of incubation The IC20 for leaves, roasted cortex, and raw cortex on the peroxidation of liposome, induced by Fe3+/H2O2/ascorbic acid, was <006, 024, and 081 mg/mL, respectively The thiobarbituric acid reactive substances values for leaves, roasted cortex, and raw cortex were 012, 154, and 181 μmol of malondialdehyde/mg of protein in enzyme-mediated microsomal peroxidation and 008, 069, and 088 μmol of malondialdehyde/mg of protein in the nonenzyme-mediated microsomal peroxidation, respectively The antioxidant activity of extracts of Du-zhong correlates to their polyphenol content The results presented herein indicate that extracts of Du
TL;DR: Vitamin C selectively restores the impaired endothelium-dependent vasodilation in the forearm resistance vessels of patients with insulin-dependent diabetes mellitus, and indicates that nitric oxide degradation by oxygen-derived free radicals contributes to abnormal vascular reactivity in humans with Diabetes mellitus.
TL;DR: According to these results, anoxia followed by re-aeration more severely impairs entire plant metabolism compared with hypoxia, thus leading to decreased viability.
Abstract: The response of the ascorbate-glutathione cycle was investigated in roots of young wheat (Triticum aestivum L.) seedlings that were deprived of oxygen either by subjecting them to root hypoxia or to entire plant anoxia and then re-aerated. Although higher total levels of ascorbate and glutathione were observed under hypoxia, only the total amount of ascorbate was increased under anoxia. Under both treatments a significant increase in the reduced form of ascorbate and glutathione was found, resulting in increased reduction states. Upon the onset of re-aeration the ratios started to decline rapidly, indicating oxidative stress. Hypoxia caused higher activity of ascorbate peroxidase, whereas activities of monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase were diminished or only slightly influenced. Under anoxia, activities of ascorbate peroxidase and glutathione reductase decreased significantly to 39 and 62%, respectively. However, after re-aeration of hypoxically or anoxically pretreated roots, activity of enzymes approached the control levels. This corresponds with the restoration of the high reduction state of ascorbate and glutathione within 16 to 96 h of re-aeration, depending on the previous duration of anoxia. Apparently, anoxia followed by re-aeration more severely impairs entire plant metabolism compared with hypoxia, thus leading to decreased viability.
TL;DR: Chronic gastritis is characterised by the accumulation of oxidative DNA damage with mutagenic and carcinogenic potential, and H pylori infection is the major determinant for DNA adduct formation.
Abstract: Background—Gastric carcinogenesis is a multifactorial, multistep process, in which chronic inflammation plays a major role.
Aims—In order to ascertain whether free radical mediated oxidative DNA damage is involved in such a process, concentrations of 8-hydroxydeoxyguanosine (8OHdG), a mutagenic/carcinogenic adduct, and thiobarbituric acid reactive substances (TBARS), as an indirect measure of free radical mediated damage, were determined in biopsy specimens from patients undergoing endoscopy.
Patients—Eighty eight patients were divided into histological subgroups as follows: 27 with chronic non-atrophic gastritis, 41 with atrophic gastritis, six with gastric cancer, and 14 unaffected controls.
Methods—Intestinal metaplasia, Helicobacter pylori infection, and disease activity were semiquantitatively scored. 8OHdG concentrations were assessed by HPLC with electrochemical detection, and TBARS concentrations were fluorimetrically assayed.
Results—8OHdG concentrations (mean number of adducts/105 dG residues) were significantly higher in chronic atrophic gastritis (p=0.0009). Significantly higher concentrations were also detected in the presence of severe disease activity (p=0.02), intestinal metaplasia (p=0.035), and H pylori infection (p=0.001). TBARS concentrations were also higher in atrophic gastritis, though not significantly so. In a multiple logistic regression analysis, 8OHdG concentrations correlated best with the presence and severity of H pylori infection (r=0.53, p=0.002).
Conclusions—Chronic gastritis is characterised by the accumulation of oxidative DNA damage with mutagenic and carcinogenic potential. H pylori infection is the major determinant for DNA adduct formation.
Keywords: free radicals; oxidative DNA damage; gastric carcinogenesis; precancerous changes; peroxidative damage