Kinetics of the competitive degradation of deoxyribose and other molecules by hydroxyl radicals produced by the Fenton reaction in the presence of ascorbic acid

As assessment of shelf life increasing competence of pectin (Zucchini) based edible coating on tomatoes

The most recent advancement in food packaging research involves improving the shelf life of perishable foods by utilising bio-based resources that are edible, eco-friendly, and biodegradable. The current study investigated the effect of edible pectin coating on mature green tomatoes to improve shelf life and storage properties. Zucchini pectin was used to make edible coating. The antimicrobial and antioxidant properties of extracted pectin were investigated. The findings indicated that the extracted pectin had antimicrobial (Staphylococcus aureus, Escherichia coli, and Aspergillus niger) and antioxidant (34.32% at 1 mg/mL) properties.Tomatoes were immersed in pectin solutions of varying concentrations, 1, 3, and 5% (w/v). Physiological evaluations of weight loss, total sugar content, titratable acidity pH, and ascorbic acid were performed on tomatoes during their maturing stages of mature green, light red, pure red, and breaking. Coating the tomatoes with pectin (5%) resulted in minimal weight loss while increasing the retention of total sugar, ascorbic acid, and titratable acidity. The shelf life of the pectin-coated tomatoes was extended to 11 days, while the uncoated control tomatoes lasted 9 days. Thus, a 5% edible pectin solution was found to be effective in coating tomatoes. The current study suggests that using 5% pectin as an edible coating on tomatoes can delay/slow the ripening/maturing process while also extending the shelf-life of tomatoes without affecting their physiochemical properties, which is scalable on a large scale for commercial purposes.

Complexes of Copper and Iron with Pyridoxamine, Ascorbic Acid, and a Model Amadori Compound: Exploring Pyridoxamine's Secondary Antioxidant Activity

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•-) or ascorbate (ASC^-). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of -35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of -58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•- and ASC^-. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 10³ and 4.09 × 10¹³ times, respectively. With iron, the rates become 1.78 × 10³ and 4.45 × 10¹⁵ times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

Ascorbate kills breast cancer cells by rewiring metabolism via redox imbalance and energy crisis

The idea to use megadoses of ascorbate (vitamin C) for cancer treatment has recently been revived. Despite clear efficacy in animal experimentation, our understanding of the cellular and molecular mechanisms of this treatment is still limited and suggests a combined oxidative and metabolic mechanism behind the selective cytotoxicity of ascorbate towards cancerous cells. To gain more insight into the cellular effects of high doses of ascorbate, we performed a detailed analysis of metabolic changes and cell survival of both luminal and basal-like breast cancer cells treated with ascorbate and revealed a distinctive metabolic shift virtually reversing the Warburg effect and triggering a severe disruption of redox homeostasis. High doses of ascorbate were cytotoxic against MCF7 and MDA-MB231 cells representing luminal and basal-like breast cancer phenotypes. Cell death was dependent on ascorbate-induced oxidative stress and accumulation of ROS, DNA damage, and depletion of essential intracellular co-factors including NAD⁺/NADH, associated with a multifaceted metabolic rewiring. This included a sharp disruption of glycolysis at the triose phosphate level, a rapid drop in ATP levels, and redirection of metabolites toward lipid droplet accumulation and increased metabolites and enzymatic activity in the pentose phosphate pathway (PPP). High doses of ascorbate also inhibited the TCA cycle and increased oxygen consumption. Together the severe disruptions of the intracellular metabolic homeostasis on multiple levels "redox crisis and energetic catastrophe" consequently trigger a rapid irreversible cell death.

Theoretical Study of the Iron Complexes with Aminoguanidine: Investigating Secondary Antioxidant Activity

A thorough analysis of the thermodynamic stability of various complexes of aminoguanidine (AG) with Fe(III) at a physiological pH is presented. Moreover, the secondary antioxidant activity of AG is studied with respect to its kinetic role in the Fe(III) reduction to Fe(II) when reacting with the superoxide radical anion or ascorbate. Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. Solvent effects (water) are taken into account in both geometry optimizations and frequency calculations employing the SMD solvation method. Even though the results of this study show that AG can form an extensive number of stable complexes with Fe(III), none of these can reduce the rate constant of the initial step of the Haber-Weiss cycle when the reducing agent is O2•-. However, when the reductant is the ascorbate anion, AG is capable of reducing the rate constant of this reaction significantly, to the point of inhibiting the production of •OH radicals. In fact, the most stable complex of Fe(III) with AG, having a ∆Gf° of -37.9 kcal/mol, can reduce the rate constant of this reaction by 7.9 × 105 times. Thus, AG possesses secondary antioxidant activity relative to the Fe(III)/Fe(II) reduction with ascorbate, but not with O2•-. Similar results have also been found for AG relative to the Cu(II)/Cu(I) reduction, in agreement with experimental results.

Silk Hydrogels Crosslinked by the Fenton Reaction

Here, the Fenton reaction is used to prepare silk hydrogels through oxidation of tyrosine residues in silk fibroin, leading to dityrosine crosslinking. At pH 5.7, gelation occurs rapidly within 30 s, and the resultant opaque gels show soft properties with a storage modulus of ≈100 Pa. The addition of ascorbic acid to the Fenton reaction increases the dityrosine bonds in the hydrogels but has little effect on the rheological or mechanical properties. The results indicate that Fe(III) ions significantly interacted with silk fibroin during the Fenton reaction, most likely binding to sites such as tyrosine, glutamate, and aspartate residues, triggering the formation of β-sheet structures that may impede dityrosine bond formation due to steric hindrance. The use of an iron chelator or the operation of the Fenton reaction at pH 9.2 enables control over the interaction of Fe(III) ions with silk fibroin, achieving a hydrogel with improved optical properties and enhanced dityrosine bond formation. Hydrogels prepared by the Fenton reaction are cytocompatible as L929 mouse fibroblasts remain viable and are proliferative when seeded on the hydrogels. The results offer a useful approach to generate chemically crosslinked silk fibroin hydrogels without the use of enzyme-catalyzed reactions for biomedical applications.

Structural, rheological and antioxidant properties of pectins from Equisetum arvense L. and Equisetum sylvaticum L

The pectins were isolated from sterile stems of E. arvense (EA, yield 5.9%) and E. sylvaticum (ES, yield 4.8%) (Equisetaceae) using ammonium oxalate extraction after preliminary treatment with dilute HCl (рH 4.0). The pectins possessed high molecular weight (Mw, 340-360 kDa), high GalA content (ca. 85%), low degrees of methyl-esterification (14-16%) and acetylation (3-8%). NMR analysis indicated extensive regions of partially methyl-etherified and 3-O-acetylated HG and minor regions of low branched RG in the fragment isolated after hydrolysis of pectin EA by pectinase. Pectin EA produced a higher viscosity solution, formed a stronger and more rigid ionotropic hydrogel than pectin ES. The pectins scavenged DPPH and hydroxyl radicals, but not the superoxide radical and hydrogen peroxide. Phenolic compounds (0.11 and 0.23%) associated with polysaccharide moieties were apparently responsible for the differences in the anti-DPPH scavenging activity of pectins EA and ES (63 and 49%). The findings suggested that pectin from E. arvense should be more perspective than pectin from E. sylvaticum on their use as components of wound healing remedies.

Effect of Allium hookeri Root on Physicochemical, Lipid, and Protein Oxidation of Longissimus Dorsi Muscle Meatball

The antioxidant effects of Allium hookeri root (AHR) were investigated by evaluating lipid and protein oxidation in meatballs during refrigerated storage at 4±1℃. AHR was mixed at concentrations of 0.5% (w/w, T2) and 1% (w/w, T3) with minced longissimus dorsi muscle. Meatballs containing AHR (T2 and T3) were compared to those containing 0.05% (w/w) ascorbic acid (T1) as a reference and without antioxidant as a control. The 2-thiobarbituric acid reactive substances (TBARS) value, disulfide bond formation, carbonyl contents, and volatile basic nitrogen (VBN) value of T2 were lower than those of the control during storage (p<0.05). The pH values of T2 and T3 were higher than that of the control (p<0.05). Texture profile analysis of T2 revealed a lower value compared to the control (p<0.05). Therefore, the VBN value, TBARS value, disulfide bond formation, and carbonyl content in meatball containing AHR were lower than those of the control meatball. These results indicate that AHR improves the quality of meat products and functions as an antioxidant.

Reactive oxygen species generation by copper(II) oxide nanoparticles determined by DNA damage assays and EPR spectroscopy

Copper(II) oxide nanoparticles (^NPCuO) have many industrial applications, but are highly cytotoxic because they generate reactive oxygen species (ROS). It is unknown whether the damaging ROS are generated primarily from copper leached from the nanoparticles, or whether the nanoparticle surface plays a significant role. To address this question, we separated nanoparticles from the supernatant containing dissolved copper, and measured their ability to damage plasmid DNA with addition of hydrogen peroxide, ascorbate, or both. While DNA damage from the supernatant (measured using an electrophoresis assay) can be explained solely by dissolved copper ions, damage by the nanoparticles in the presence of ascorbate is an order of magnitude higher than can be explained by dissolved copper and must, therefore, depend primarily upon the nanoparticle surface. DNA damage is time-dependent, with shorter incubation times resulting in higher EC₅₀ values. Hydroxyl radical (^•OH) is the main ROS generated by ^NPCuO/hydrogen peroxide as determined by EPR measurements; ^NPCuO/hydrogen peroxide/ascorbate conditions generate ascorbyl, hydroxyl, and superoxide radicals. Thus, ^NPCuO generate ROS through several mechanisms, likely including Fenton-like and Haber-Weiss reactions from the surface or dissolved copper ions. The same radical species were observed when ^NPCuO suspensions were replaced with the supernatant containing leached copper, washed ^NPCuO, or dissolved copper solutions. Overall, ^NPCuO generate significantly more ROS and DNA damage in the presence of ascorbate than can be explained simply from dissolved copper, and the ^NPCuO surface must play a large role.

The Antioxidant Properties of Pectin Fractions Isolated from Vegetables Using a Simulated Gastric Fluid

The antioxidant properties of vegetable pectin fractions against intraluminal reactive oxygen species were elucidated in vitro in conjunction with their structural features. The pectin fractions were isolated using a simulated gastric fluid (pH 1.5, pepsin 0.5 g/L, 37°C, 4 h) from fresh white cabbage, carrot, onion, and sweet pepper. The fraction from onion was found to inhibit the production of superoxide radicals by inhibiting the xanthine oxidase. The high molecular weight of onion pectin and a large number of galactose residues in its side chains appeared to participate in interaction with xanthine oxidase. All the isolated pectic polysaccharides were found to be associated with protein (2–9%) and phenolics (0.5–0.7%) as contaminants; these contaminants were shown to be responsible for the antioxidant effect of vegetable pectin fractions against the hydroxyl and 1,1-diphenyl-2-picrylhydrazyl radicals.

Measuring and Suppressing the Oxidative Damage to DNA During Cu(I)-Catalyzed Azide-Alkyne Cycloaddition

We have used the quantitative polymerase chain reaction (qPCR) to measure the extent of oxidative DNA damage under varying reaction conditions used for copper(I)-catalyzed click chemistry. We systematically studied how the damage depends on a number of key reaction parameters, including the amounts of copper, ascorbate, and ligand used, and found that the damage is significant under nearly all conditions tested, including those commonly used for bioconjugation. Furthermore, we discovered that the addition of dimethyl sulfoxide, a known radical scavenger, into the aqueous mixture dramatically suppresses DNA damage during the reaction. We also measured the efficiency of cross-linking two short synthetic oligonucleotides via click chemistry, and found that the reaction could proceed reasonably efficiently even with DMSO present. This approach for screening both DNA damage and reactivity under a range of reaction conditions will be valuable for improving the biocompatibility of click chemistry, and should help to extend this powerful synthetic tool for both in vitro and in vivo applications.

Use of green rooibos (Aspalathus linearis) extract and water-soluble nanomicelles of green rooibos extract encapsulated with ascorbic acid for enhanced aspalathin content in ready-to-drink iced teas

Heat-induced changes in aspalathin, iso-orientin, and orientin content of ready-to-drink (RTD) green rooibos iced tea formulations were investigated. An organic-solvent-based aspalathin-enriched extract prepared from green rooibos was used "as-is" or encapsulated with ascorbic acid in a water-soluble nanomicelle-based carrier system. The common iced tea ingredients, ascorbic acid, and/or citric acid were added to the iced tea containing green rooibos extract. Only citric acid was added to the iced tea containing the nanomicelles. Heat treatments consisted of pasteurization (93 °C/5 min and 93 °C/30 min), normal-temperature sterilization (NTS; 121 °C/15 min), and high-temperature sterilization (HTS; 135 °C/4 min). Pasteurization had little or no effect on the flavonoid content. NTS and HTS induced significant losses in the flavonoids. The addition of citric and ascorbic acids improved the stability of the flavonoids, but encapsulation of green rooibos extract with ascorbic acid in nanomicelles did not offer additional stability. The only benefit of using the water-soluble nanomicelles was the improved clarity of the RTD product. Iso-orientin and orientin contents were substantially less affected than aspalathin by the heat treatments, partially because of conversion of aspalathin to these flavones, which countered losses. 5-Hydroxymethylfurfural (HMF), a known dehydration product of hexoses under mild acidic conditions and also a degradation product of ascorbic acid, was observed in formulations containing citric and/or ascorbic acids.

Evaluation of Antioxidative Activity of Agrimonia pilosa-Ledeb Leaves on Non-lipid Oxidative Damage

Present study was conducted to evaluate the antioxidative activity of the Agrimonia pilosa-Ledeb leaves on non-lipid oxidative damage. The antioxidative activity of methanolic (MeOH) extract of the Agrimonia pilosa-Ledeb leaves on non-lipid oxidation, including liposome oxidation, deoxyribose oxidation, protein oxidation, chelating activity against metal ions, scavenging activity against hydrogen peroxide, scavenging activity against hydroxyl radical and 2'-deoxyguanosine (2'-dG) oxidation were investigated. The MeOH extract of the Agrimonia pilosa-Ledeb leaves exhibited high antioxidative activity in the liposome model system. Deoxyribose peroxidation was inhibited by the MeOH extract of the Agrimonia pilosa-Ledeb leaves and MeOH extract of the Agrimonia pilosa-Ledeb leaves provided remarkable protection against damage to deoxyribose. Protective effect of MeOH extracts of the Agrimonia pilosa-Ledeb leaves on protein damage was observed at 600 µg level (82.05%). The MeOH extracts of the Agrimonia pilosa-Ledeb leaves at 300 µg revealed metal binding ability (32.64%) for hydrogen peroxide. Furthermore, the oxidation of 2'-deoxyguanosine (2'-dG) to 8-hydroxy-2-deoxyguanosine (8-OH-2'dG) was inhibited by MeOH extracts of the Agrimonia pilosa-Ledeb leaves and scavenging activity for hydroxyl radical exhibited a remarkable effect. From the results in the present study on biological model systems, we concluded that MeOH extract of the Agrimonia pilosa-Ledeb leaves was effective in the protection of non-lipids against various oxidative model systems.

Free radical scavenging and antigenotoxic activities of natural phenolic compounds in dried flowers of Hibiscus sabdariffa L

The antioxidant and free radical scavenging effects of two fractions of the ethanolic extract (HSCF, chloroform soluble fraction and HSEA, ethyl acetate soluble fraction) obtained from the dried flowers of Hibiscus sabdariffa L were investigated. The total antioxidant activity of the extracts was estimated to be 4.6 and 8.6 mM of vitamin C for HSCF and HSEA, respectively. Both HSCF and HSEA scavenged hydrogen peroxide (H(2)O(2)) (79-94%) at the dose of 500 microg. Similarly, the extracts showed inhibitory (70-80%) effects on superoxide anions radicals (O(2) (- *)) at a dose of 1000 microg. The concentrations required for a 50% scavenging of hydroxyl radical (OH) (IC(50)) were 380 and 200 microg for HSCF and HSEA, respectively. HSEA and HSCF were better scavengers of O(2) (- *), *OH and H(2)O(2) as compared to BHA, quercetin and alpha-tocopherol. At a concentration of 25 microg/mL HSCF and HSEA exhibited 32 and 38% inhibition on CCl(4)-NADPH-induced lipid peroxidation, respectively, while both extracts exhibited 80 and 89% inhibitory effects at 100 microg/mL. Pretreatment with H. sabdariffa extracts orally with 100 mg/kg and 250 mg/kg simultaneously with intraperitoneal injection FeCl(2)-ascorbic acid-ADP mixture reduced (p < 0.01) the formation of malondialdehyde content. Treatment of rats with HSCF, HSEA and vitamin C (standard antioxidant) significantly inhibited the induction of micronucleated polychromatic erythrocytes by sodium arsenite (2.5 mg/kg) (p < 0.001) after 24 h by 60, 70 and 50%, respectively. The results indicate that extracts of H. sabdariffa showed strong antimutagenic activity and free radical scavenging effects on active oxygen species.

The antioxidant effect of tannic acid on the in vitro copper-mediated formation of free radicals

Tannic acid (TA) has well-described antimutagenic and antioxidant activities. The antioxidant activity of TA has been previously attributed to its capacity to form a complex with iron ions, interfering with the Fenton reaction [Biochim. Biophys. Acta 1472, 1999, 142]. In this work, we observed that TA inhibits, in the micromolar range, in vitro Cu(II) plus ascorbate-mediated hydroxyl radical (*OH) formation (determined as 2-deoxyribose degradation) and oxygen uptake, as well as copper-mediated ascorbate oxidation and ascorbate radical formation (quantified in EPR studies). The effect of TA against 2-deoxyribose degradation was three orders of magnitude higher than classic *OH scavengers, but was similar to several other metal chelators. Moreover, the inhibitory effectiveness of TA, by the four techniques used herein, was inversely proportional to the Cu(II) concentration in the media. These results and the observation of copper-induced changes in the UV spectra of TA are indications that the antioxidant activity of TA relates to its copper chelating ability. Thus, copper ions complexed to TA are less capable of inducing ascorbate oxidation, inhibiting the sequence of reactions that lead to 2-deoxyribose degradation. On the other hand, the efficiency of TA against 2-deoxyribose degradation declined considerably with increasing concentrations of the *OH detector molecule, 2-deoxyribose, suggesting that the copper-TA complex also possesses an *OH trapping activity.

Isolation of quercetin's salts and studies of their physicochemical properties and antioxidant relationships

Hydroxyflavones in alkaline solutions show high free radical scavenging activities. Quercetin, one of these hydroxyflavones may be submitted to chemical reactions yielding a mixture of mono-, di- and tri-sodium salts. These salts were recovered after solubilization and stepwise precipitation in methylalcohol/ethylacetate solvents. The different salts were analyzed using sodium emission spectrophotometry and nuclear magnetic resonance to determine the number of acid hydrogens at pH10 and the position of these acid hydrogens. Our study demonstrates that among the three salts of quercetin, the di-sodium compound is endowed with the more efficient scavenging properties in a phosphate buffer at physiological pH7.4. Physicochemical parameters and free hydroxyl radical scavenging activity relationships were also determined, allowing to explain the mechanisms whereby hydroxyl groups exert their radical scavenging activities.

Effects of Antioxidants on the Hydrogen Peroxide-Mediated Oxidation of Methionine Residues in Granulocyte Colony-Stimulating Factor and Human Parathyroid Hormone Fragment 13-34

PURPOSE

The effects and mechanisms of different antioxidants, methionine, glutathione, acetylcysteine, and ascorbic acid (AscH2), on the oxidation of methionine residues in granulocyte colony-stimulating factor (G-CSF) and human parathyroid hormone fragment 13-34 (hPTH 13-34) by hydrogen peroxide (H2O2) were quantified and analyzed.

METHODS

The rates of oxidation of methionine residues in G-CSF were determined by peptide mapping analyses, and the oxidation of methionine residue in hPTH 13-34 was quantified by reverse-phase HPLC.

RESULTS

At pH 4.5, free methionine reduces, glutathione and acetylcysteine have no obvious effect on, and AscH2 promotes the rates of oxidation of methionine residues in G-CSF. The H2O2-induced oxidation rate constants for free methionine, acetylcysteine, and glutathione at pH 4.5 were measured to be 32.07, 1.00, and 1.63 M(-1)h(-1), respectively, while the oxidation rate constant for Met1, the most readily oxidizable methionine residue in G-CSF, is 13.95 M(-1)h(-1). Therefore, the different effects of free methionine, acetylcysteine, and glutathione on the rates of oxidation of methionine residues in G-CSF are consistent with their different reactivity toward oxidation by H2O2. By using hPTH 13-34, the effect of AscH2 on the H2O2-induced oxidation of methionine residue was quantified, and the mechanisms involved were proposed. Because of the presence of trace transition metal ions in solution, at low concentrations, AscH2 is prone to be a prooxidant, increasing the hydroxyl radical (.OH) production rate via Fenton-type reactions. In addition to peroxide oxidation, these radicals lead to the degradation of hPTH 13-34 to smaller peptide fragments. At high concentrations, AscH2 tends to act as an OH scavenger. EDTA inhibits OH production and thus eliminates the degradation of hPTH 13-34 by forming complexes with transition metal ions. However, the rate of oxidation of the methionine residue in hPTH 13-34 increases as the concentration of AscH2 is increased from 0 to 200 mM, and the reason for this is still not clear.

CONCLUSIONS

Our results demonstrate that free methionine is an effective antioxidant to protect G-CSF against methionine oxidation at pH 4.5. Acetylcysteine and glutathione are not effective antioxidants at pH 4.5. Their oxidation rates at different pH values imply that they would be much more effective antioxidants than free methionine at alkaline conditions. AscH2 is a powerful electron donor. It acts as a prooxidant in the conditions in this study and is unlikely to prevent oxidation by H2O2 in protein formulation, whether or not EDTA is present.

Light-Induced Byproducts of Vitamin C in Multivitamin Solutions

Background: When solutions of multivitamin preparations (MVPs) are exposed to light, H2O2 as well as organic peroxides are generated and the concentration of vitamin C decreases. The aim of this study was to determine, using mass spectrometry, whether the generation of oxidative byproducts of vitamin C, such as dehydroascorbate (DHA) and 2,3-diketogulonic acid (DKG), accounted for the reported decrease in ascorbic acid in MVPs exposed to light.

Methods: Mass spectrometry was used to document the formation of byproducts of ascorbic acid in solutions containing a MVP, vitamin C + riboflavin, and vitamin C + H2O2 + Fe2+. The involvement of ascorbic acid and H2O2 in the formation of organic peroxides was tested by measuring peroxide concentrations in solutions containing H2O2 with or without ascorbic acid and with or without Fe2+ before and after addition of catalase.

Results: The loss of ascorbic acid in photo-exposed MVPs was associated with the concomitant generation of byproducts different from DHA and DKG. Among them, one mass fingerprint was particularly observed with solutions of vitamin C + riboflavin exposed to ambient light as well as with the solution of vitamin C + H2O2 + Fe2+, suggesting a Fenton-like reaction. This fingerprint was associated with the formation of catalase-resistant peroxides.

Conclusion: Exposure of MVPs to light leads to the rapid loss of ascorbic acid and generation of specific byproducts that differ from DHA and DKG. The conversion of vitamin C into byproducts could be of biological importance in accounting for the decrease in ascorbic acid concentrations and the generation of organic peroxides in light-exposed MVPs.

Anti- and pro-oxidant activity of rutin and quercetin derivatives

Some semi-synthetic flavonoids, particularly derivatives of rutin, are used as therapeutic agents in the treatment of diseases involving free radicals. Here, for the first time, a complete study has been made of the relationship between the structure of such molecules and their superoxide, hydroxyl and peroxyl radical scavenging activity. The molecules chosen for this study were rutin, its aglycone (quercetin), and their methyl ethyl and hydroxyl-ethyl derivatives. Our results are consistent with the general agreement on the structural requirements for free radical scavenging activity. Moreover, we have shown that alkylation of the hydroxyl in position 7 enhanced the scavenging, and also that in a Fenton reaction system, some quercetin derivatives with free catechol moiety or free hydroxyl in position 3 (or both) were pro-oxidant, through superoxide radical and hydrogen peroxide production. Although the structural features needed for pro-oxidant activity are not entirely clear, it appears that to avoid pro-oxidant behaviour, the hydroxyl group in position 3 should be blocked to prevent its auto-oxidation. Thus, flavonoids cannot only be considered purely as antioxidants, since under certain reaction conditions they can also display pro-oxidant activity. This unexpected behaviour could explain, in part, the observed toxicity of some flavonoids in-vivo.

Free radical scavenging and skin penetration of troxerutin and vitamin derivatives

BACKGROUND

By its 'protective function', human skin is a potential target for the production of free radicals. The role played by topically applied antioxidants as inhibitors of oxidative stress damage was felt to be worth investigation.

OBJECTIVE

To investigate the free radical scavenging (superoxide, hydroxyl and peroxyl radicals) and skin penetration of troxerutin in association with ascorbyl palmitate and alpha-tocopheryl succinate, esters of two vitamins commonly used in skin care products.

METHODS

The compounds' scavenging activities, in a concentration-dependent manner, were as follows: hydroxyl radicals in a Fenton-based assay; superoxide radicals in a hypoxanthine/xanthine oxidase system; and lipid peroxidation inhibition of liver microsomes was induced by 2,2'-azobis-(2-amidinopropane) dihydrochloride (ABAP).

RESULTS

A synergic action was observed between alpha-tocopheryl succinate and troxerutin for hydroxyl radical scavenging, between the three compounds for superoxide scavenging and between troxerutin and ascorbyl palmitate in lipid peroxidation inhibition.

CONCLUSION

Using a stripping method, it was shown that the three substances, incorporated in a pharmaceutical preparation, permeated through human epidermis. Thus, this association can improve skin care products for preventing free radical-mediated damage.

Developmental, cellular, and molecular basis of human breast cancer

Breast cancer, which is the most common neoplastic disease in females and accounts for up to one third of all new cases of women's cancer in North America, continues to rise in incidence. In addition, the mortality caused by this disease has remained almost unchanged for the past 5 decades, becoming only second to lung cancer as a cause of cancer-related death. The failure in eradicating this disease is largely due to the lack of identification of a specific etiologic agent, the precise time of initiation, and the molecular mechanisms responsible for cancer initiation and progression. Despite the numerous uncertainties surrounding the origin of cancer, there is substantial evidence that breast cancer risk relates to endocrinologic and reproductive factors. The development of breast cancer strongly depends on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. However, the specific hormone or hormone combinations responsible for cancer initiation have not been identified, and their role as protective or risk factors is still incompletely understood. A highly significant female hormone is estrogen, which is involved in the development of a variety of cancers, but it is still unclear whether estrogens are carcinogenic to the human breast. An understanding of whether estrogens cause mutations, and, if so, whether they act through hormonal effects activated by receptor binding, cytochrome P450-mediated metabolic activation, or compromise the DNA repair system, is essential for determining whether this steroid hormone is involved in the initiation or progression of breast cancer. This knowledge has to be based on a multidisciplinary approach encompassing studies of the development of the breast, influence of hormones on the differentiation of individual structures, and their interrelations in the pathogenesis of breast cancer. The analysis of the mechanisms involved would require confirmation in the adequate in vitro models and determination of the role played by genomic alterations in both cancer initiation and progression.

The iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and its analogues prevent damage to 2-deoxyribose mediated by ferric iron plus ascorbate

Iron chelating agents are essential for treating iron overload in diseases such as beta-thalassemia and are potentially useful for therapy in non-iron overload conditions, including free radical mediated tissue injury. Deferoxamine (DFO), the only drug available for iron chelation therapy, has a number of disadvantages (e.g., lack of intestinal absorption and high cost). The tridentate chelator pyridoxal isonicotinoyl hydrazone (PIH) has high iron chelation efficacy in vitro and in vivo with high selectivity and affinity for iron. It is relatively non-toxic, economical to synthesize and orally effective. We previously demonstrated that submillimolar levels of PIH and some of its analogues inhibit lipid peroxidation, ascorbate oxidation, 2-deoxyribose degradation, plasmid DNA strand breaks and 5,5-dimethylpyrroline-N-oxide (DMPO) hydroxylation mediated by either Fe(II) plus H(2)O(2) or Fe(III)-EDTA plus ascorbate. To further characterize the mechanism of PIH action, we studied the effects of PIH and some of its analogues on the degradation of 2-deoxyribose induced by Fe(III)-EDTA plus ascorbate. Compared with hydroxyl radical scavengers (DMSO, salicylate and mannitol), PIH was about two orders of magnitude more active in protecting 2-deoxyribose from degradation, which was comparable with some of its analogues and DFO. Competition experiments using two different concentrations of 2-deoxyribose (15 vs. 1.5 mM) revealed that hydroxyl radical scavengers (at 20 or 60 mM) were significantly less effective in preventing degradation of 2-deoxyribose at 15 mM than 2-deoxyribose at 1.5 mM. In contrast, 400 microM PIH was equally effective in preventing degradation of both 15 mM and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or NTA) caused a significant reduction in the protective effect of PIH towards 2-deoxyribose degradation. We also observed that PIH and DFO prevent 2-deoxyribose degradation induced by hypoxanthine, xanthine oxidase and Fe(III)-EDTA. The efficacy of PIH or DFO was inversely related to the EDTA concentration. Taken together, these results indicate that PIH (and its analogues) works by a mechanism different than the hydroxyl radical scavengers. It is likely that PIH removes Fe(III) from the chelates (either Fe(III)-EDTA or Fe(III)-NTA) and forms a Fe(III)-PIH(2) complex that does not catalyze oxyradical formation.

Iron-induced oxidative DNA damage in rat sperm cells in vivo and in vitro

We investigated whether acute iron intoxication causes oxidative DNA damage, measured in terms of 7-hydro-8-oxo-2'-deoxyguanosine, 8-oxodG, in nuclear DNA in testes and epididymal sperm cells in vivo and in vitro in rats. In addition, we investigated levels of the modified nucleoside in liver and kidney and measured its urinary excretion. Sperm cells were isolated from the epididymides and the testes cells were isolated after homogenisation. In vitro, the sperm and testes cells were incubated with increasing concentrations of FeCl2 ranging from 0 to 600 microM. The median (range) levels of 8-oxodG/10(5) dG in the epididymal sperm cells increased from 0.48 (0.42-0.90) to 15.1 (11.4-17.6) (p < 0.05), whereas the level rose from 0.63 (0.22-0.81) to 8.8 (4.5-11.6) (p < 0.05) at 0 and 600 microM, respectively, in the testicular cells. In vivo groups of 7-8 rats received 0, 200 or 400 mg iron/kg as dextran i.p. After 24 h, epididymal sperm cells, testes, kidneys and liver were collected for analysis. Kidney and sperm DNA showed a significant increase in 8-oxodG in the iron-treated animals. The median (range) values of the 8-oxodG/10(5) dG in the epididymal sperm cells rose from 0.66 (0.38-1.09) to 1.12 (0.84-5.88) (p < 0.05) at 0 and 400 mg iron/kg, respectively, whereas the values in the testes and liver showed no significant change. In the kidneys the 8-oxodG/10(5) dG median (range) values were 0.98 (0.73-1.24), 1.21 (1.13-1.69) and 1.34 (1.12-1.66) after 0, 200 and 400 mg iron/kg, respectively (p < 0.05). The 8-oxodG-excretion rate was measured in 24h urine before and after iron treatment. The rate of urinary 8-oxodG excretion increased from 129 (104-179) pmol/24 h before treatment to 147 (110-239) pmol/24 h after treatment in the group receiving 400 mg iron/kg (p < 0.05). The results indicate that acute iron intoxication may increase oxidative damage to sperm and kidney DNA.

Action of methanolic extract of mung bean hulls as inhibitors of lipid peroxidation and non-lipid oxidative damage

The antioxidant effects of methanolic extract of mung bean hulls (MEMBH) on lipids and non-lipids, including liposome, carbohydrate, protein and 2'-deoxyguanosine (2'-dG), were investigated. MEMBH exhibited a remarkable antioxidant effect in a liposome model system, indicating that the extract was an inhibitor of lipid peroxidation. The inhibitory effect of MEMBH on deoxyribose damage was amount-dependent and it afforded considerable protection against damage to deoxyribose. In addition, MEMBH at low amounts was more effective in protecting protein oxidation. Furthermore, the oxidation of 2'-dG to 8-hydroxy-2'-deoxyguanosine (8-OH-2'dG) was inhibited by MEMBH. These results show that the extract also was an inhibitor of non-lipid oxidation damage. The extract exhibited metal binding ability and scavenging activity for hydrogen peroxide and hydroxyl radical, which may explain the mechanism of their protecting lipids and non-lipids from oxidative damage.

Oxidative stress in microorganisms--I. Microbial vs. higher cells--damage and defenses in relation to cell aging and death

Oxidative stress in microbial cells shares many similarities with other cell types but it has its specific features which may differ in prokaryotic and eukaryotic cells. We survey here the properties and actions of primary sources of oxidative stress, the role of transition metals in oxidative stress and cell protective machinery of microbial cells, and compare them with analogous features of other cell types. Other features to be compared are the action of Reactive Oxygen Species (ROS) on cell constituents, secondary lipid- or protein-based radicals and other stress products. Repair of oxidative injury by microorganisms and proteolytic removal of irreparable cell constituents are briefly described. Oxidative damage of aerobically growing microbial cells by endogenously formed ROS mostly does not induce changes similar to the aging of multiplying mammalian cells. Rapid growth of bacteria and yeast prevents accumulation of impaired macromolecules which are repaired, diluted or eliminated. During growth some simple fungi, such as yeast or Podospora spp., exhibit aging whose primary cause seems to be fragmentation of the nucleolus or impairment of mitochondrial DNA integrity. Yeast cell aging seems to be accelerated by endogenous oxidative stress. Unlike most growing microbial cells, stationary-phase cells gradually lose their viability because of a continuous oxidative stress, in spite of an increased synthesis of antioxidant enzymes. Unlike in most microorganisms, in plant and animal cells a severe oxidative stress induces a specific programmed death pathway--apoptosis. The scant data on the microbial death mechanisms induced by oxidative stress indicate that in bacteria cell death can result from activation of autolytic enzymes (similarly to the programmed mother-cell death at the end of bacillary sporulation). Yeast and other simple eukaryotes contain components of a proapoptotic pathway which are silent under normal conditions but can be activated by oxidative stress or by manifestation of mammalian death genes, such as bak or bax. Other aspects, such as regulation of oxidative-stress response, role of defense enzymes and their control, acquisition of stress tolerance, stress signaling and its role in stress response, as well as cross-talk between different stress factors, will be the subject of a subsequent review.

Oxygen-accepting antioxidants which arise during ascorbate oxidation

To identify potential antioxidant compounds derived from ascorbate, the hydrogen peroxide-induced oxidation of ascorbate and dehydroascorbate was studied by gas-chromatography electron impact mass spectrometry and liquid-chromatography electrospray mass spectrometry in real time. Significant differences in ascorbate and dehydroascorbate oxidation occurred at pH 3.3 compared to pH 7.4. Of note, the primary species present in dehydroascorbate (DHA)-containing solutions at pH 7.4 had a spectrum consistent with diketogulonate. Hydrogen peroxide exposure of DHA-containing solutions formed threonate more rapidly at pH 7.4 than at pH 3.3. In these solutions, a 5-carbon species with mass spectral characteristics of a 3,4,5-trihydroxy-2-ketopentanoate appeared to be an intermediate between diketogulonate and threonate, and was more labile than other species in the presence of hydrogen peroxide. These data suggest that a 3,4,5-trihydroxy-2-ketopentanoate is potentially a key antioxidant compound in the ascorbate degradation cascade and in ascorbate-containing solutions at physiologic pH.

Spontaneous hydrolysis and dehydration of dehydroascorbic acid in aqueous solution

The interaction of water with dehydroascorbic acid was examined by incubating dehydroascorbic acid and ascorbic acid in 18O-labeled water for various amounts of time and then oxidizing the products with hydrogen peroxide or reducing the products with mercaptoethanol, with analysis by gas chromatography mass spectrometry. Based on mass changes, dehydroascorbic acid readily exchanged three oxygen atoms with H218O. When mercaptoethanol was used to reduce dehydroascorbic acid (which had been incubated in H218O) to ascorbic acid, the newly formed ascorbic acid also contained three labeled oxygen atoms. However, ascorbic acid incubated in H218O for the same amount of time under identical conditions exchanged only two labeled oxygen atoms. Electron impact mass spectrometry of derivatized ascorbic acid created a decarboxylation product which had only two labeled oxygen atoms, regardless if 3-oxygen-labeled or 2-oxygen-labeled ascorbic acid was the parent compound, isolating the extra oxygen addition to carbon 1. These data suggest that dehydroascorbic acid spontaneously hydrolyzes and dehydrates in aqueous solution and that the hydrolytic-hydroxyl oxygen is accepted by carbon 1. Ascorbic acid, on the other hand, does not show this same tendency to hydrolyze.

Ascorbic acid oxidation by hydrogen peroxide

The oxidative degradation of ascorbic acid by hydrogen peroxide was examined to determine routes of degradation and identify the initial products which form when ascorbic acid is oxidized. When reacted with hydrogen peroxide, solutions of ascorbic acid and dehydroascorbic acid are both ultimately oxidized to the same species, having a mass spectrum consistent with threonic acid. When the intermediate steps in the oxidation of ascorbic acid are examined in detail, ascorbic acid, dehydroascorbic acid, and solutions containing hydrolyzed dehydroascorbic acid are all oxidized through a six-carbon compound previously proposed to be tetrahydroxydiketohexanoic acid. Both dehydroascorbic acid and hydrolyzed dehydroascorbic acid (diketogulonic acid) are more susceptible to hydrogen peroxide oxidation than ascorbic acid. Based on mass spectral analysis, diketogulonic acid serves as an oxygen sink, implying that it may be a better reducing agent for toxic oxygen species than ascorbic acid. These data indicate that oxidation of ascorbic acid by hydrogen peroxide primarily proceeds through three major six-carbon intermediates, each with distinctive redox properties. The stable metabolite diketogulonic may be a critical antioxidant in ascorbic-acid-containing systems.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.