Rate Of Ascorbic Acid Oxidation Research Articles

Tumour Necrosis Factor Alpha and Oxidative Stress in the Breath Condensate of Those with Non-Small Cell Lung Cancer

Background and Aims: Lung cancer is a leading cause of cancer mortality worldwide and is associated with the release of tumour necrosis factor-α (TNF-α), subsequent cellular apoptosis and the generation of oxidative stress. Exhaled breath condensate (EBC) analysis is a non-invasive method for sampling biofluids from the lower respiratory tract. This study aimed to evaluate possible biomarkers of lung cancer by measuring the levels of TNF-α and the oxidation of ascorbic acid in EBC. Patients with lung cancer were enrolled into the study prior to treatment, during treatment and post-treatment, and results compared with an age-matched control population. Material and Methods: Patients with Stage II-IV non small cell lung cancer (NSCLC) were recruited prior to and at stages of their treatment. EBC levels of TNF-α, and rate of ascorbic acid oxidation were measured. Results: A total of 19 patients with NSCLC (mean age 71.37 ± 7.77 yrs) and 25 age-matched control subjects were enrolled. Levels of EBC TNF-α were elevated in the EBC of patients with lung cancer compared with control subjects (1.02 ± 0.07 pg/ml vs. 0.51 ± 0.06 pg/ml, p < 0.0001). Moreover, the rate of ascorbic acid oxidation was significantly greater in the EBC of patients with lung cancer compared with control subjects (2.20% [0.4 – 11.0] vs. 1.00% [0.1 – 8.5], p = 0.0244). Conclusion: TNF-α and the rate of ascorbic acid oxidation was elevated in the EBC of patients with lung cancer regardless of treatment. Longitudinal studies in a larger population are required to evaluate these markers for the effect of treatment and prognosis.

Liposomal stabilization of ascorbic acid in model systems and in food matrices

Ascorbic acid (AA) was encapsulated into dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylcholine/cholesterol (DPPC/chol) liposomes. We have shown that co-encapsulation of citric and ascorbic acids into liposomes results in considerable stabilization of the latter in model systems containing catalytic concentrations of copper ions. The rate of AA oxidation was decreased by up to 300-fold that of free AA. Incorporation of cholesterol into membranes resulted in lower stabilization efficacy at room temperature and better thermal stability at higher temperatures than pure DPPC liposomes. Total AA, extra-liposomal AA and leakage of AA out of liposomes during thermal treatment were evaluated using the free radical 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS). A modification of the ABTS based assay for liposome permeability makes it applicable to reducing agents and antioxidants as well as AA. Encapsulated AA was also stabilized in real food matrices. The rate of AA oxidation in apple juice, relative to that of free AA, was decreased by two orders of magnitude when encapsulated in DPPC liposomes and by more than one order of magnitude in DPPC/chol liposomes. Liposomal stabilization of AA in a fermented milk product was less pronounced.

Kinetic and Thermodynamic Investigation on Ascorbate Oxidase Activity and Stability of a Cucurbita maxima Extract

The kinetic and thermodynamic properties of ascorbate oxidase (AO) activity and stability of a Cucurbita maxima extract were investigated. Activity tests performed at 25 degrees C using initial ascorbic acid concentration in the range 50-750 M allowed estimating the Michaelis constant for this substrate (Km = 126 microM) and the maximum initial rate of ascorbic acid oxidation (A0,max = 1.57 mM min-1). The main thermodynamic parameters of the enzyme reaction (DeltaH* = 10.3 kJ mol-1; DeltaG* = 87.2 kJ mol-1; DeltaS* = -258 J mol-1 K-1) were estimated through activity tests performed at 25-48 C. Within such a temperature range, no decrease in the initial reaction rate was detected. The long-term thermostability of the raw extract was then investigated by means of residual activity tests carried out at 10-70 degrees C, which allowed estimating the thermodynamic parameters of the irreversible enzyme inactivation as well (DeltaH*D = 51.7 kJ mol-1; DeltaG*D = 103 kJ mol-1; S*D = -160 J mol-1 K-1). Taking into account the specific rate of AO inactivation determined at different temperatures, we also estimated the enzyme half-life (1047 min at 10 degrees C and 21.2 min at 70 degrees C) and predicted the integral activity of a continuous system using this enzyme preparation. This work should be considered as a preliminary attempt to characterize the AO activity of a C. maxima extract before its concentration by liquid-liquid extraction techniques.

Oxalic acid is available as a natural antioxidant in some systems

Oxalic acid is found in a wide variety of plants. This study showed that oxalic acid suppressed in vitro lipid peroxidation in a concentration-dependent manner. Furthermore, oxalic acid reduced the rate of ascorbic acid oxidation in the presence of hydrogen peroxide and Cu 2+. These results suggest that oxalic acid is available as a natural antioxidant.

Continuous Spectrophotometric Assay and Properties of Ascorbic Acid Oxidising Factors in Wheat

Abstract A continuous spectrophotometric assay was developed to measure ascorbic acid oxidation in crude Na 2 SO 4 extracts of flour. The rate of ascorbic acid oxidation in flour extracts measured using this method was similar to the rate in flour-water suspensions and 2–4 fold less than the rate in dough measured using an indophenol-xylene extraction method. Flour extracts appeared to contain two ascorbic acid oxidising factors; one with optimal activity at pH 6·3 and 30 °C and the other with optimal activity at pH 10 and 40 °C. The pH 6·3 factor had properties similar to those of ascorbate oxidase (EC 1·10·3·3) in its pH and temperature stability, strong inhibition by NaN 3 , KCN and diethyldithiocarbamate, inactivation by proteases, and greater stereospecificity towards l -ascorbic acid than d -isoascorbic acid. The pH 6·3 factor was most concentrated in the pollard milling fraction of wheat and was lowest in flour. The pH 10 factor had several properties indicating non-enzymic oxidation of ascorbic acid; it was not inactivated by proteases, it was inhibited poorly or not at all by the above ascorbate oxidase inhibitors, and it had low specificity for stereoisomers of ascorbic acid.

Destructive Effect of Aspartame on Ascorbic Acid in Cu‐catalyzed Solutions

ABSTRACTThe effect of aspartame on the early stage of ascorbic acid oxidation in solutions was studied by measuring ascorbic acid retention in an open system at 30°C and the oxygen uptake in a closed system at 33°C. Comparisons were also made between aspartame (0.06% and 0.12%) and sucrose (10% and 20%) in Cu‐catalyzed and noncatalyzed solutions at 30°C. Copper activity in aspartame solution was measured by using a cupric ion selective electrode. Aspartame increased the rate of ascorbic acid oxidation in all tested solutions. In the presence of copper the oxidation rate of ascorbic acid was significantly higher in aspartame solutions than in sucrose solutions despite the fact that aspartame showed Cu‐complex capacity in solution.

Subzero-temperature preservation of reactive fluids in the undercooled state: II. The effect on the oxidation of ascorbic acid of freeze concentration and undercooling

The rate of oxidation of ascorbic acid has been measured in both frozen and undercooled solutions. A new interpretation is advanced for changes in the rate of ascorbic acid oxidation in freeze-concentrated solutions. The results obtained with undercooled solutions indicate a rate reduction in line with that predicted by the Arrhenius equation. It is also demonstrated that undercoohng provides a method for greatly extending the shelf life of reactive fluids.

Chain ion molecular mechanism of ascorbic acid oxidation with hydrogen peroxide. Cu3+ ion as a chain carrier

AbstractThe kinetics and mechanism of ascorbic acid (DH2) oxidation have been studied under anaerobic conditions in the presence of Cu2+ ions. At 10−4 ≤ [Cu2+]0 &lt; 10−3M, 10−3 ≤ [DH2]0 &lt; 10−2M, 10−2 ≤ [H2O2] ≤ 0.1M, 3 ≤ pH &lt; 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: equation image where χ2 (25°C) = (6.5 ± 0.6) × 10−3 sec−1. The effective activation energy is E2 = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu+ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu+ initiation in the Cu2+ reaction with ascorbic acid by the expression equation image where C is a function of pH and of H2O2 concentration. The rate equation equation image where k1(25°C) = (5.3 ± 1) × 103M−1 sec−1 is true for the steady‐state catalytic reaction. The Cu+ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu2+–DH2–H2O2 system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu+ with H2O2, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme.Initiation: equation image Propagation: equation image equation image Termination: equation image

Influence of Organophosphate Insecticides on Ascorbic Acid Oxidation in Aqueous Systems

SUMMARY: Aqueous systems at four pH's containing ascorbic acid and various levels of organophosphate insecticides were prepared. The rate of ascorbic acid oxidation was measured polarographically. Organophosphate insecticides tested exhibited antioxidant activity. The antioxidant activity of malathion in the presence of copper ions was lost when EDTA was added. Oxygenated, oxidized and hydrolyzed samples of organophosphates still had antioxidant activity. Experimental evidence indicates that the phosphate moiety of malathion is responsible for this antioxidant activity. It is postulated that the antioxidant activity might be due to the phosphate's ability to chelate metal ions.

The reaction of benzoquinone with amines and proteins

It has been shown that benzoquinone will form 1,4 addition products with amines, amino acids, and proteins. The substituted quinones produced via this reaction have altered redox potentials. The quinone amine adduct can be reduced by ascorbate and oxidized by oxygen to produce hydrogen peroxide. This sequence of reactions can be conveniently monitored by following the oxygen consumption in the presence of excess ascorbate. Under appropriate experimental conditions the rate of oxygen consumption is proportional to the concentration of the quinoae adduct. Since benzoquinone alone will not react in this way, the reaction between the amines and benzoquinone can be followed by determining the rate of ascorbic acid oxidation. With this assay, it was shown that the glycine will react with benzoquinone at a very slow rate below pH 7.0, exhibiting an optimum rate at pH 8. All amino acids seemed to react with the benzoquinone in the same manner independent of their side chains. The reaction can be made an assay for an amino acid, and with this procedure quantities of glycine as low as 1 × 10 −7 m, could be readily detected. Both mono- and di-substituted benzoquinone amine products were formed. Proteins reacted with the benzoquinone in a manner similar to that described for the simple amino acids. The reaction with cytochrome c was studied in some detail. By using radioactively-labeled benzoquinone, it was shown that cytochrome c reacted readily to form a product containing two to four moles of benzoquinone per mole of cytochrome c. The position of the benzoquinone was such that it was not accessible to the heme groups, and did not cause denaturation or alteration of the structure of the cytochrome c. Other proteins vary with regard to their ability to form the quinone adduct, but all form adducts which are capable of catalyzing ascorbate oxidation. It has been suggested that quinone adducts of the type described here may be important in biological systems.

Copper-Catalyzed Oxidation of Ascorbic Acid in Gels and Aqueous Solutions of Polysorbate 80

The stability of ascorbic acid in aqueous solution has been studied as a function of polysorbate 80 concentration. The range of polysorbate concentrations studied was sufficiently wide to provide systems ranging from solutions of low viscosity to hydrogels. The study has been conducted at 30, 40, 50, and 60°. First-order rate constants for the oxidative reaction were calculated, and they appear to decrease as a function of polysorbate 80 concentration up to 10 percent, except at 30°, in which case the rate constants decreased up to 30 percent polysorbate 80. The rate generally leveled off at higher surfactant concentrations. It appears that this phenomenon is probably a result of micelle formation, or, more specifically, the increases in micellar aggregation number and micellar concentration which occur up to about 30 percent polysorbate 80. It does not appear that increased viscosity has a significant influence on the rate of ascorbic acid oxidation in these systems.

Oxidation of Milk Fat Globule Membrane Material. II. Relation of Ascorbic Acid and Membrane Concentrations

Summary The rate of development of oxidized flavor in model systems as influenced by the initial concentration of ascorbic acid was measured by the thiobarbituric acid reaction. At constant fat globule membrane material (FGMM) concentration, the rate of lipid oxidation increased with increasing initial concentration of ascorbic acid up to 20-40mg/liter. Further increases effected inhibition of lipid oxidation in relation to the concentration of ascorbic acid. At constant initial ascorbic acid concentration, the rate of lipid oxidation increased directly with FGMM concentration. The initial reaction rate appears to follow zero-order kinetics over-all. Energy of activation was 11.9 k cal/mole. The rate of ascorbic acid oxidation was proportional to the rate of lipid oxidation. Addition of copper in concentrations 0.1ppm increased ascorbic acid oxidation, but lipid oxidation was further inhibited. It is suggested that the lipid oxidative system is activated by association with ascorbic acid and inhibited by products of ascorbic acid oxidation.

Ascorbic acid and photosynthesis I. “Monodehydroascorbic acid” reductase of chloroplasts

An enzyme system catalyzing the oxidation of DPNH and TPNH in the presence of ascorbic acid and of an ascorbic acid-oxidizing agent such as Cu ++ ions or ascorbic acid oxidase has been extracted from the acetone powder of whole, washed spinach chloroplasts This system is unable to reduce dehydroascorbic acid, and closely corresponds to the reduced pyridine nucleotide-monodehydroascorbic acid reductase previously shown in several higher plant tissues. Its activity in the intact chloroplasts is shown by the marked activation induced by the addition of ascorbic acid plus an ascorbic acid-oxidizing agent on TPNH and DPNH oxidation by chlorplast suspensions. The probability of a physiological role of this enzyme, and of the ascorbic acid-monodehydro-ascorbic acid system, in photosynthesis is indicated by the finding that the illumination of chloroplast suspensions supplemented with ascorbic acid and an accorbic acid-oxidizing agent markedly slows down the rate of ascorbic acid oxidation. These results are interpreted as supporting the hypothesis of a participation of ascorbic acid, as an electron carrier, in the oxidative-phosphorylative chain functioning in the illuminated chloroplast.

Oxidation-reduction potential of modified cytochrome c.

THE presence of modified cytochrome c in the widely used Keilin and Hartree preparation was first reported by Margoliash1. Separation was effected by chromatography at pH 7.0 on a column of the resin ‘Amberlite IRC-50’ Modified material was present to the extent of 10–25 per cent and was characterized by having a lowered enzymatic activity in the cytochrome oxidase (heart muscle) and succinic oxidase (kidney) systems but an increased rate of ascorbic acid oxidation. Visual spectroscopy, however, did not show any difference between this and other cytochrome c fractions. Evidence was presented that the modification was caused by the action of trichloracetic acid on cytochrome c during the extraction procedure.