Plant phenolic antioxidant and prooxidant activities: phenolics-induced oxidative damage mediated by metals in plants (original) (raw)
Related papers
Phytochemistry, 2003
NAO is a natural water soluble antioxidant that was isolated and purified from spinach leaves. Using HPLC, NMR, and CMR spectroscopy, the main components were identified as flavonoids and p-coumaric acid derivatives. The NAO was found to be a very effective antioxidant in several in vivo and in vitro biological systems. In the present study, the antioxidant activity of the novel antioxidant glucurinated flavonoid (GF) isolated and characterized from NAO, is compared to well-known antioxidants. In addition, the direct free radical scavenging properties of the purified component GF were studied using the electron spin resonance (ESR) technique. GF and NAO were found to be superior to EGCG and NAC and to the Vitamin E homologue Trolox in inhibiting reactive oxygen species (ROS) formation in the autooxidation system of linoleic acid and in fibroblasts exposed to metal oxidation. GF and NAO were found to inhibit the ESR signal intensity of DMPO-O 2 radical formation during the riboflavin photodynamic reaction. 10 mM GF caused approximately 90% inhibition in the intensity of the ESR signal, while NAO at a concentration of 60 mg/ml caused an inhibition of about 50%. Using the Fenton reaction, GF and NAO were found to inhibit DMPO-OH radical formation. A concentration of 2 mM GF caused a 70% inhibition in the intensity of the DMPO-OH radical ESR signal, while propyl gallate at the same concentration caused only 50% inhibition. Furthermore, both GF and NAO also inhibited the 1 O 2 dependent TEMPO radical generated in the photoradiation TPPS4 system. About 80% inhibition was obtained by 4 mM GF. The results obtained indicate that the natural antioxidants derived from spinach may directly affect the scavenging of ROS and, as a consequence, may be considered as effective sources for combating oxidative damage.
Phenolic antioxidants â radical-scavenging and chain-breaking activity: A comparative study
European Journal of Lipid Science and Technology, 2009
Fifty phenolic antioxidants (AH) (42 individual compounds and 8 binary mixtures of two antioxidants) were chosen for a comparative analysis of their radical-scavenging (H-donating) and chain-breaking (antioxidant) activity. Correlations between experimental (antiradical and antioxidant) and predictable (theoretical) activities of 15 flavonoids, 15 hydroxy cinnamic acid derivatives, 5 hydroxy chalcones, 4 dihydroxy coumarins and 3 standard antioxidants (butylated hydroxytoluene, hydroquinone, DL-atocopherol) were summarized and discussed. The following models were applied to explain the structureactivity relationships of phenolic antioxidants of natural origin: (a) model 1, a DPPH assay used for the determination of the radical-scavenging capacity (AH 1 DPPH . ? A . 1 DPPH-H); (b) model 2, chemiluminescence of a model substrate RH (cumene or diphenylmethane) used for the determination of the rate constant of a reaction with model peroxyl radicals (AH 1 RO 2 . ? ROOH 1 A . ); (c) model 3, lipid autoxidation used for the determination of the chain-breaking antioxidant efficiency and reactivity (AH 1 LO 2 . ? LOOH 1 A . ; A . 1 LH (1O 2 ) ? AH 1 LO 2 . ); and (d) model 4, theoretical methods used for predicting the activity (predictable activity). The highest lipid oxidation stability was found for antioxidants with a catecholic structure and for their binary mixtures with DL-a-tocopherol, as a result of synergism between them.
Antioxidant Compounds and Their Antioxidant Mechanism
Antioxidants
An antioxidant is a substance that at low concentrations delays or prevents oxidation of a substrate. Antioxidant compounds act through several chemical mechanisms: hydrogen atom transfer (HAT), single electron transfer (SET), and the ability to chelate transition metals. The importance of antioxidant mechanisms is to understand the biological meaning of antioxidants, their possible uses, their production by organic synthesis or biotechnological methods, or for the standardization of the determination of antioxidant activity. In general, antioxidant molecules can react either by multiple mechanisms or by a predominant mechanism. The chemical structure of the antioxidant substance allows understanding of the antioxidant reaction mechanism. This chapter reviews the in vitro antioxidant reaction mechanisms of organic compounds polyphenols, carotenoids, and vitamins C against free radicals (FR) and prooxidant compounds under diverse conditions, as well as the most commonly used methods to evaluate the antioxidant activity of these compounds according to the mechanism involved in the reaction with free radicals and the methods of in vitro antioxidant evaluation that are used frequently depending on the reaction mechanism of the antioxidant.
Free radical scavenging and cytoprotective activities of phenolic antioxidants
The free radical scavenging activities of three flavonoids (quercetin, rutin and catechin) and four hydroxycinnamic acids (caffeic, ferulic, sinapic, and chlorogenic acids) were evaluated using both oxygen radical absorbance capacity (ORAC) and lipid peroxidation inhibition capacity (LPIC) assays. The cytoprotective effects of these compounds were also measured by the degree of protection against H 2 O 2-induced damage of human Jurkat cells. All compounds exhibited protection against H 2 O 2-mediated cytotoxicity in a dose-dependent manner. The concentrations required to result in a 50% reduction in cell death (EC 50 value) were calculated from their dose-response curves. These ranged from 0.15 – 2.65 lM. Overall, the four hydroxycinnamic acids tested were less effective than the three flavonoids, and of all compounds tested, quercetin offered the strongest protection against H 2 O 2-induced cell death. A comparison of the results showed that the ability to inhibit peroxidation of lipids in a liposomal system (LPIC) correlated well with the cytoprotective activities (EC 50), but not with the ability to protect an aqueous fluorescent substrate in the ORAC assays. The results suggest that the behavior of antioxidants in a liposomal membrane is to some extent similar to the mechanism involved in the protection of living cells from oxidative damage.
Dietary antioxidants protection against oxidative stress
Biochemical Education, 1995
Introduction Several lines of evidence indicate that the active oxygen-induced and free radicalmediated oxidation of biological molecules, membranes and tissues are closely related to a variety of pathological events. 1 Diverse biological processes such as inflammation, carcinogenesis, aging, stroke and photobiological effects, appears to involve reactive oxygen species. Oxidative metabolism, which is a normal biological process associated with a variety of metabolic activities in aerobes, is also capable of generating highly reactive oxygen flee radicals. 2 These active oxygen species include the superoxide anion radical, hydrogen peroxide, the hydroxyl radical, and singlet oxygen. Oxidative damage inflicted by these active free radicals is referred to as oxidative stress. Some of the major molecular targets of these agents are DNA, 3 proteins, 4 carbohydrates and lipids. 5 Transition metal ions are important in the production of radical species. The ability of these ions to move electrons is the basis for the formation and propagation of many of the most toxic radical reactions. For example, superoxide anion is relatively nonreactive in aqueous solution, but in the presence of hydrogen peroxide and a transition metal such as iron, the extremely reactive hydroxyl radical may be generated. This pathway, known as the iron-catalyzed Haber-Weiss reaction as represented by following reactions, is a Fenton chemistry and has been extensively studied. Although its role in pathology is not well established, the extensive measures taken by cells to minimize the presence of free metal ions such as iron and copper (ie the presence of iron-and copper-binding proteins) indirectly indicate that such reactions are detrimental to biological systems.
Toxicology, 2002
Dietary polyphenolics in fruits, vegetables, wines, spices and herbal medicines have beneficial antioxidant, anti-inflammatory and anticancer effects. However, we have observed that dietary polyphenolics with phenol rings were metabolized by peroxidase to form prooxidant phenoxyl radicals which, in some cases were sufficiently reactive to cooxidize GSH or NADH accompanied by extensive oxygen uptake and reactive oxygen species formation. The order of catalytic effectiveness found for oxygen activation when polyphenolics were metabolized by peroxidase in the presence of GSH was phloretin \phloridzin\ 4,2%-dihydroxy chalcone \ p-coumaric acid \ naringenin\ apigenin\ curcumin \resveratrol\ isoliquiritigenin\ capsaicin\ kaempferol. Ascorbate was also cooxidized by the phenoxyl radicals but without oxygen activation. Polyphenolics with catechol rings also cooxidized ascorbate, likely mediated by semiquinone radicals. The order of catalytic effectiveness found for ascorbate cooxidation was fisetin, luteolin, quercetin, \eriodictyol, caffeic acid, nordihydroguaiaretic acid \ catechin\taxifolin, catechol. NADH was stoichiometrically oxidized without oxygen uptake which, suggests that o-quinone metabolites were responsible. GSH was not cooxidized and GSH conjugates were formed, likely mediated by the o-quinone metabolites. Incubation of hepatocytes with dietary polyphenolics containing phenol rings was found to partially oxidize hepatocyte GSH to GSSG while polyphenolics with a catechol ring were found to deplete GSH through formation of GSH conjugates. Dietary polyphenolics with phenol rings also oxidized human erythrocyte oxyhemoglobin and caused erythrocyte hemolysis more readily than polyphenolics with catechol rings. It is concluded that polyphenolics containing a phenol ring are generally more prooxidant than polyphenolics containing a catechol ring.
Defense Mechanism of Natural Antioxidants Against Free Radicals
CENTRAL ASIAN JOURNAL OF MEDICAL AND NATURAL SCIENCE, 2022
Endogenous and exogenous antioxidants act as “free radical scavengers” by preventing and repairing damages caused by ROS and RNS, and therefore can enhance the immune defense and lower the risk of cancer and degenerative diseases. Free radicals reactive oxygen species and reactive nitrogen species are generated by our body by various endogenous systems, exposure to different physiochemical conditions or pathological states. A balance between free radicals and antioxidants is necessary for proper physiological function. If free radicals overwhelm the body's ability to regulate them, a condition known as oxidative stress ensues. Free radicals thus adversely alter lipids, proteins, and DNA and trigger a number of human diseases. Hence application of external source of antioxidants can assist in coping this oxidative stress. Synthetic antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole have recently been reported to be dangerous for human health. Thus, the search for effective, nontoxic natural compounds with antioxidative activity has been intensified in recent years. The present review provides a brief overview on oxidative stress mediated cellular damages and role of dietary antioxidants as functional foods in the management of human diseases.
Free Radicals and Antioxidants, 2014
Introduction: The antioxidant and radical scavenging properties of some of the hydroxy phenyl derivatives such as 4-Hydroxybenzoic acid (1), 3-Hydroxy-4-methoxycinnamic acid (2), 3-(4-Hydroxy-3,5-dimethoxyphenyl)prop-2enoic acid (Sinapic acid) (3), 4-Hydroxy-3,5-dimethoxybenzoic acid (4), 3,4-Dihydroxycinnamic acid (Caffeic acid) (5) and 5-Isopropyl-2-methylphenol (6), which are naturally present in fruits and vegetables, were investigated. Methods: The following analysis were conducted: The total antioxidant activity via the ferric thiocyanate method; 2,2'-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) radical scavenging activity; superoxide anion radical (O 2 •-) scavenging activity; the total reduction power through potassium ferricyanide reduction method; Cupric ions (Cu 2+) reduction capacity through Cuprac method; hydrogen peroxide scavenging activity and chelating activity of ferrous ions (Fe 2+). Furthermore, α-tocopherol, butylatedhydroxyanisole (BHA) and quercetin were used as the reference antioxidant compounds. Results: In the comparison of initial states and the products, it's observed that at the 50th hour the linoleic acid emulsion at 30 μg/mL concentration inhibited the lipid peroxidation by 85%, 60.7%, 69%, 45.4%, 80.4% and 31%, respectively. On the other hand, it's observed that the linoleic acid emulsion of α-tocopherol, (BHA) and quercetin inhibited the lipid peroxidation by 62.65%, 35.84% and 34.82% respectively, at the same concentration. Conclusions: It's found as a result of our studies that some of the phenolic compounds such as 4-Hydroxybenzoic acid (1), 3-Hydroxy-4-methoxycinnamic acid (2), 3-(4-Hydroxy-3,5-dimethoxyphenyl)prop-2-enoic acid (3), 4-Hydroxy-3,5dimethoxybenzoic acid (4), 3,4-Dihydroxycinnamic acid (5) and 5-Isopropyl-2-methylphenol (6) which are naturally present in foods. They have higher total antioxidant activity, radical scavenging and metal chelating activities than the widely used powerful antioxidant compounds such as BHA, Quercetin and α-tocopherol.
Biochemical …, 1989
The plant-derived phenolic compounds gossypol, quercetin and myricetin are powerful inhibitors of iron-induced lipid peroxidation in rat liver microsomes, under all five experimental conditions tested and at low micromolar concentrations (ICjo < 1.5 yM). However, they greatly accelerate the generation of hydroxyl radicals (*OH) from H,O, in the presence of Fe'+-EDTA at pH7.4, as measured by the deoxyribose assay. At 100 PM, the three phenolic compounds enhanced *OH formation up to eight-fold. The hydroxyi radical generation was inhibited by catalase and superoxide dismutase, suggesting a mechanism in which the phenols oxidize to produce superoxide radical, which then assists *OH generation from HzO, in the presence of Fe '+-EDTA. At concentrations up to 75 PM, quercetin and myricetin also accelerate bleomycin-dependent DNA damage in the presence of Fe3+, possibly by reducing the Fe 3+-bleomycin-DNA complex to the Fe 2t form. Hence these naturally-occurring substances can have nro-oxidant effects under some reaction conditions and cannot be classified simplistically as "antioxidants".