Pro‐oxidant effects of phenothiazine and phenoxazine on erythrocytes in the presence of peroxyl radical

Phenothiazine (PtzNH) and phenoxazine (PozNH) can protect human erythrocytes against hemolysis induced by 2,2′‐azobis(2‐amidinopropane hydrochloride) (AAPH), a peroxyl radical supplier. However, an antioxidant may be a pro‐oxidant to accelerate the oxidation in the presence of radicals. The aim of this work is to assess whether PtzNH and PozNH have the potential to be pro‐oxidants in AAPH‐induced hemolysis of human erythrocytes. It has been found that high concentrations of PtzNH and PozNH employed were able to initiate hemolysis even in the absence of AAPH. In the presence of AAPH, the period of PtzNH and PozNH to lag hemolysis (t_lag) decreased with the increase in the concentrations of PtzNH and PozNH, implicating that high concentration of PtzNH and PozNH accelerated hemolysis. So, PtzNH and PozNH played pro‐oxidants' role in this case. Furthermore, high concentrations of AAPH employed made the pro‐oxidant effect of PtzNH more remarkable. On the contrary, PozNH played a pro‐oxidant role if only low concentration of AAPH was employed. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:280–286, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20290     

Kinetics of ozone reaction with uric acid, ascorbic acid, and glutathione at physiologically relevant conditions

This study quantified the reaction kinetics of O3 with three low molecular weight antioxidants-uric acid (UA), ascorbic acid (AH2), and glutathione (GSH)-found in respiratory mucous. Using a semi-batch reactor in which a 500 ml/min flow of air containing 1-5 parts per million of O3 contacted 3 ml of well-stirred physiological saline solution containing 100-200 microM antioxidant, we found that: (1) mass transfer resistances in the gas and liquid phases were successfully eliminated by the reactor design; (2) the reaction of O3 with UA, AH2 and GSH had stoichiometries of 1:1, 1:1, and 1:2.5, respectively; (3) the reactivity between O3 and antioxidants was in the order UA approximately AH2>GSH. Simulating the measured amounts of O3 absorbed and antioxidant consumed with a mathematical model, reaction rate constants of O(3) with UA, AH2, and GSH were found to be 5.83 x 10(4) M(-1) s(-1), 5.5 x 10(4) M(-1) s(-1), and 57.5 M(-0.75) s(-1), respectively.     

Antioxidant effect of dipyridamole (DIP) and its derivative RA 25 upon lipid peroxidation and hemolysis in red blood cells

The antioxidant effects of dipyridamol (DIP), a coronary vasodilator, and its derivative RA-25 were compared in intact red blood cells (RBC) and in isolated ghost membranes. Both compounds are quite effective antioxidants in cumene hydroperoxide-induced lipid peroxidation of RBC, showing a much smaller effect for hydrogen peroxide oxidation. The antioxidant effect of DIP was considerably higher than that of RA25. For isolated ghost membranes, the apparent IC50 (the drug concentration that produces 50% inhibition of lipid peroxidation) in cumene hydroperoxide-induced peroxidation was 25 microM, while the maximum protective effect of RA-25 was around 30% in the drug concentration range of 50-100 microM. The drugs can protect the oxidative hemolysis induced by cumene hydroperoxide with a lower effect when the hemolysis is induced by H2O2. The significant antioxidant effect against damages induced by cumene hydroperoxide suggests that DIP, due to its lipophilic character, can interact with RBC membranes, and the protective effect is associated with the binding of the drug to the membrane. On the other hand, RA-25 is more hydrophilic than DIP, binds to the membrane to a smaller extent, and, for this reason, has a lower antioxidant effect.     

The antioxidant effect of hydroxyl-substituent Schiff bases on the free-radical-induced hemolysis of human erythrocytes

The major objectives of the present work were focused on assessing the antioxidant capacities of two hydroxyl-substituent Schiff bases, 2-((o-hydroxylphenylimino)methyl)phenol (OSAP) and 2-((p-hydroxylphenylimino)methyl)phenol (PSAP) either used alone or in combination with some familiar water-soluble antioxidants i.e. 6-hydroxyl-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) and L-ascorbic acid (VC), and lipophilic ones i.e. alpha-tocopherol (TOH) and L-ascorbyl-6-laurate (VC-12). 2,2'-Azobis(2-amidinopropane hydrochloride) (AAPH). Induced hemolysis of human erythrocytes functioned as the evaluation experimental system in this research. The present findings showed that either OSAP or PSAP not only was an antioxidant with high activity in protecting erythrocytes against AAPH-induced hemolysis concentration-dependently, but can also protect erythrocytes by acting with Trolox, TOH, VC and VC-12 synergistically. Based on chemical kinetic deduction, the number of trapping peroxyl radicals, n, of the above-mentioned antioxidants can be calculated in relation to Trolox that traps two peroxyl radicals; thus, TOH can trap 3.83 peroxyl radicals, VC-12 traps 2.87 and VC can only trap 1.08. As for OSAP and PSAP, 8.71 and 13.7 peroxyl radicals can be trapped, respectively, indicating that they were the most efficient inhibitors against AAPH-induced hemolysis. Moreover, the total number of peroxyl radicals trapped by OSAP+Trolox, OSAP+TOH, OSAP+VC and PSAP+VC were higher than the sum of the above individual antioxidant used alone, demonstrating that a mutual promotive effect existed in the above mixed antioxidants. In contrast, owing to the fact that the total number of peroxyl radicals trapped by OSAP+VC-12, PSAP+Trolox, PSAP+TOH and PSAP+VC-12 were less than the sum of the above individual antioxidant used alone, a mutual antagonistic effect was suggested in these combinative usages. This information may be helpful in the pharmaceutical application of two Schiff bases.     

Phenolic production and antioxidant properties of some Macedonian medicinal plants

Investigations have been made to study the production of phenolic compounds (total phenolics, flavonoids and phenylpropanoids) and total antioxidant capacity in 27 Macedonian traditional medicinal plants to improve its potential as a source of natural antioxidants. Antioxidant potential of plant extracts was analyzed by five different assays: cupric reducing antioxidant capacity (CUPRAC), phosphomolybdenum method (PM), reducing power (RP), 2,2-diphenyl-1-picrylhydrazyl (DPPH^·) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS^·+) radical scavenging activity. Origanum vulgare extract consistently exhibited the highest content of phenolic compounds and the strongest antioxidant capacity based on the tests performed, and can be proposed as a promising source of natural antioxidants. Melissa officinalis and Salvia ringens were also identified as valuable sources of antioxidant compounds. A positive linear correlation between antioxidant activity and total phenolics, flavonoids and phenylpropanoids indicates that these compounds are likely to be the main antioxidants contributing to the observed activities of evaluated plants. These findings suggest that the medicinal plants studied in this paper are good sources of bioactive compounds for the food and pharmaceutical industries.     

Influence of epithelial lining fluid lipids on NO(2)-induced membrane oxidation and nitration

Within the pulmonary epithelial lining layer (ELF), antioxidants such as ascorbic acid (AH(2)) and glutathione (GSH) react with inhaled nitrogen dioxide ((*)NO(2)) to produce reactive oxygen species (ROS) that induce cellular oxidation. Because the ELF contains unsaturated fatty acids (UFA), which potentially react with (*)NO(2) and/or the antioxidant-derived ROS, we studied the influence of aqueous phase model UFA [egg phosphatidylcholine (EggPC) liposomes] on exposure-induced oxidation and nitration of membranes. Our lung surface model used gas phase (*)NO(2) exposures of immobilized red cell membranes (RCM) overlaid with defined aqueous phases. Acetyl cholinesterase (AChE) activity, TBARS, and 3-nitrotyrosine (3-NT) were used to assess protein and lipid oxidation and RCM nitration, respectively. During (*)NO(2) exposure, AH(2) and GSH induced AChE loss and TBARS, which were unchanged with buffer only. Exposures of EggPC generated extensive TBARS but not AChE loss; addition of AH(2)/GSH to EggPC resulted in smaller AChE declines and fewer TBARS. 3-NT formation occurred with or without EggPC, low concentration antioxidants, SOD, catalase, or DTPA, but was inhibitable by desferrioxamine or high antioxidant concentrations. The data suggest that reaction/diffusion limitations govern (*)NO(2) distribution, that (*)NO(2) per se directly nitrates tyrosine residues within hydrophobic regions, and that the induction of secondary oxidative processes is dependent on nonlinear relationships among (*)NO(2) flux rates, antioxidant concentrations, and diffusivity of secondary reactive species.     

Antioxidant activity of caffeoyl-prolyl-histidine amide and its effects on PDGF-induced proliferation of vascular smooth muscle cells

Caffeic acid (CA) is one of the antioxidants found in plants, which protects vascular cells against vascular injuries from oxidative stress. In our previous study, caffeoyl-prolyl-histidine amide (CA-L-Pro-L-His-NH₂; CA-PH; a CA derivative) was synthesized, which exhibited a strong antioxidant activity with sufficient stability. In this study, we investigated the role of CA-PH in vascular smooth muscle cells (VSMCs) and confirmed the enhanced antioxidant activity of CA-PH compared with that of CA. In in vitro tube assays, CA-PH showed a higher free-radical-scavenging activity and lipid-peroxidation-inhibition activity than those of CA. In VSMCs, CA-PH significantly reduced hydrogen peroxide-induced ROS generation and increased the expression of heme oxygenase-1. Moreover, CA-PH effectively inhibited the platelet-derived growth factor-induced cellular proliferation of VSMCs, which was confirmed by a decrease in the expression of the proliferating cell nuclear antigen and the phosphorylation of Akt.     

Amelioration of glucose induced hemolysis of human erythrocytes by vitamin E

Cells under aerobic condition are always threatened with the insult of reactive oxygen species, which are efficiently taken care of by the highly powerful antioxidant systems of the cell. The erythrocytes (RBCs) are constantly exposed to oxygen and oxidative stress but their metabolic activity is capable of reversing the injury under normal conditions. In vitro hemolysis of RBCs induced by 5, 10 and 20 mM glucose was used as a model to study the free radical induced damage of biological membranes in hyperglycemic conditions and the protection rendered by vitamin E on the same. RBCs are susceptible to oxidative damage, peroxidation of the membrane lipids, release of hemoglobin (hemolysis) and alteration in activity of antioxidant enzymes catalase and superoxide dismutase. The glucose induced oxidative stress and the protective effect of vitamin E on cellular membrane of human RBCs manifested as inhibition of membrane peroxidation and protein oxidation and restoration of activities of superoxide dismutase and catalase, was investigated.Thiobarbituric acid reactive substances are generated from decomposition of lipid peroxides and their determination gives a reliable estimate of the amount of lipid peroxides present in the membrane. Vitamin E at 18 μg/ml (normal serum level) strongly enhanced the RBC resistance to oxidative lysis leading to only 50–55% hemolysis in 24 h, whereas RBCs treated with 10 and 20 mM glucose without vitamin E leads to 70–80% hemolysis in 24 h. Levels of enzymic antioxidants catalase, superoxide dismutase and nonenzymic antioxidants glutathione showed restoration to normal levels in presence of vitamin E. The study shows that vitamin E can protect the erythrocyte membrane exposed to hyperglycemic conditions and so a superior antioxidant status of a diabetic patient may be helpful in retarding the progressive tissue damage seen in chronic diabetic patients.     

Afamin is synthesized by cerebrovascular endothelial cells and mediates α-tocopherol transport across an in vitro model of the blood–brain barrier

α-Tocopherol (αTocH), a member of the vitamin E family, is essential for normal neurological function. Despite the importance of αTocH transport into the CNS, transfer mechanisms across the blood–brain barrier (BBB) are not entirely clear. We here investigate whether afamin, a known αTocH-binding protein, contributes to αTocH transport across an in vitro model of the BBB consisting of primary porcine brain capillary endothelial cells (BCEC) and basolaterally cultured astrocytoma cells. Exogenously added afamin had no adverse effects on BCEC viability or barrier function and was transported across BCEC Transwell cultures. Furthermore, αTocH transport across polarized BCEC cultures to astrocytoma cells is facilitated by afamin, though to a lesser extent than by high-density lipoprotein-mediated transport, an essential and in vivo operating αTocH import pathway at the cerebrovasculature. We also demonstrate that porcine BCEC endogenously synthesize afamin. In line with these in vitro findings, afamin was detected by immunohistochemistry in porcine, human postmortem, and mouse brain, where prominent staining was observed almost exclusively in the cerebrovasculature. The demonstration of afamin mRNA expression in isolated brain capillaries suggests that afamin might be a new family member of binding/transport proteins contributing to αTocH homeostasis at the BBB in vivo .     

Phenolic derivatives with free-radical-scavenging activities from Ixeridium gracile (DC.) Shih

Phytochemical investigation of the Tibetan medicinal plant Ixeridium gracile resulted in the isolation and identification of twelve flavonoids and two coumarins, compounds 1-14, the dimeric '2alpha,3alpha-epoxy-5,7,3',4'-tetrahydroxyflavan-(4beta-->8)-epicatechin' (1) being a new constituent. The free-radical-scavenging potentials of different extract fractions as well as of the pure compounds towards the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical were evaluated, and are discussed in terms of structure-activity relationship (SAR). The flavonoids were found to be the major constituents contributing to the free-radical-scavenging activity of I. gracile, but the high concentration of coumarins additionally contributed to the observed activity.     

The extraordinary antioxidant activity of vitamin E phosphate

The antioxidant activities of RRR-vitamin E (VE), all-rac-vitamin E (all-rac-VE), trolox, RRR-vitamin E acetate (VEA), all-rac-vitamin E phosphate (VEP) and RRR-vitamin E succinate (VES) were compared. In this study, the rank order in the inhibition of lipid peroxidation (LPO) of VE and its derivatives was trolox>VE approximately all-rac-VE>VEA>VES. VE and trolox inhibited LPO in non-heated and heated rat liver microsomes. It has generally been accepted that this is due to scavenging of free radicals by these antioxidants, and during this protection the antioxidants are oxidized. VEA and VES have to be converted into VE by esterases to obtain antioxidant activity against LPO. VEP, however, had a potent antioxidant effect of its own without conversion to VE. In contrast to VE, VEP is not consumed during this protection. Of the compounds tested, VEP is the most potent in induction of hemolysis of erythrocytes. EPR experiments using the spin label 16-doxylstearic acid showed that VEP reduces membrane fluidity, in contrast to VE. This indicates that VEP acts as a detergent and forms a barrier that might inhibit the transfer of radicals from one polyunsaturated fatty acid to another. This new mechanism may form the basis for a new class of antioxidants.     

Effect of exogenous antioxidants on erythrocyte redox status and hepcidin content in disorders of iron metabolism regulation

In many diseases associated with impairments in iron metabolism, erythrocytes exhibit an increased sensitivity to oxidative stress induced in vitro. In this study we have examined the antioxidant status of erythrocytes from healthy donors and from 12 patients with disorders of iron homeostasis by measuring the extent of hemolysis induced in vitro by tert-butyl hydroperoxide (t-BHP). The extent of hemolysis observed with patient erythrocytes was significantly higher than that observed in experiments with erythrocytes from healthy donors. After therapeutic infusions of the antioxidants mexidol or emoxypin, oxidative hemolysis in patients was restored to normal values and blood hepcidin increased significantly as compared with its initial level. A significant correlation was observed between hepcidin concentration after treatment and t-BHP-induced hemolysis before treatment. These data suggest that antioxidants may exert a favorable effect on those at risk for iron overload disease.     

Celastrus paniculatus seed oil and organic extracts attenuate hydrogen peroxide- and glutamate-induced injury in embryonic rat forebrain neuronal cells

Seed oil of Celastrus paniculatus Willd. (CP) has been reported to improve memory and the methanolic extract (ME) of CP was shown to exhibit free-radical-scavenging properties and anti-oxidant effects in human non-immortalized fibroblasts. In the present study, we have investigated the free-radical-scavenging capacity of CP seed oil (CPO) and two extracts, an ethanolic extract (EE) and a ME. CPO and EE showed dose-dependent, free-radical-scavenging capacity, but to a lesser degree than observed for ME. Oxidative stress involves the generation of free radicals and free radical scavenging is one of the mechanisms of neuroprotection. We therefore investigated the effects of CPO, ME, and EE for protection against hydrogen peroxide (H(2)O(2))- and glutamate-induced neurotoxicity in embryonic rat forebrain neuronal cells (FBNC). Pre-treatment of neuronal cells with CPO dose-dependently attenuated H(2)O(2)-induced neuronal death. Pre-treatment with ME and EE partially attenuated H(2)O(2)-induced toxicity, but these extracts were less effective than CPO for neuronal survival. In H(2)O(2)-treated cells, cellular superoxide dismutase (SOD) activity was unaffected, but catalase activity was decreased and levels of malondialdehyde (MDA) were increased. Pre-treatment with CPO, ME, or EE increased catalase activity and decreased MDA levels significantly. Also, CPO pre-treatment attenuated glutamate-induced neuronal death dose-dependently. The activity of cellular acetylcholinesterase (AChE) was not affected by CPO, ME, or EE, suggesting that the neuroprotection offered by CPO was independent of changes in AChE activity. Taken together, the data suggest that CPO, ME, and EE protected neuronal cells against H(2)O(2)-induced toxicity in part by virtue of their antioxidant properties, and their ability to induce antioxidant enzymes. However, CPO, which exhibited the least antioxidant properties, was the most effective in preventing neuronal cells against H(2)O(2)- and glutamate-induced toxicities. Thus, in addition to free-radical scavenging attributes, the mechanism of CP seed component (CP-C) neuroprotection must be elucidated.     

Comparison of Chemical Constituents and Pharmacological Effects of Different Varieties of Chrysanthemum Flos in China

Chrysanthemum Flos is the prestigious traditional Chinese medicinal material and the popular health drink. This article comprehensively evaluated the chemical constituents, antioxidant activity, and hepatoprotective effects of 25 common chrysanthemum varieties in China. Firstly, we analyzed the chemical compositions of water extracts of chrysanthemum using UPLC/Q-TOF-MS, and identified 29 chemical components. The results displayed that chrysanthemum was rich in chemical constituents, but there were significant differences in the contents of four phenolic acids and five flavonoids among different varieties, and the coefficient of variation (CVs) ranged from 35.96 % to 114.62 %. Then, the antioxidant activities of different chrysanthemums were investigated, respectively via 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and Ferric Reducing Antioxidant Power (FRAP) assays. The spectrum-effect relationships between nine main components and antioxidant activities were investigated to identify the antioxidant constitutes in chrysanthemums. Meanwhile, H₂O₂-induced hepatocyte injury testing showed wide variation in cultivar antioxidant capacity, with Tongchengju (TCJ) producing the best effect (90.32 %), followed by Chuju (CJ; 85.78 %). In addition, the hepatoprotective effects of 8 mainstream varieties were determined by the model of acute alcoholic liver injury. They protected liver from injury by affecting relevant liver function and antioxidant indexes. Huangshangongju (HSG) could decrease aspartate aminotransferase (AST) activity by 39.27 % in liver tissue; Hangju-Fubaiju (HJ-FBJ), Jinsihuangju (JSH), and Chuju (CJ) significantly decreased the malondialdehyde (MDA) content of liver tissue, which reduced by more than 40 %; Jinsihuangju (JSH) of used for tea could double the content of glutathione (GSH) and had the similar effect on superoxide dismutase (SOD) as the positive group, showing significant antioxidant capacity. Therefore, this study confirmed that chrysanthemums are potential resources as antioxidants, functional foods, and medicinal materials. Importantly, it may provide a scientific support for further development and utilization of chrysanthemum, and screen excellent varieties for different demands.     

Intermittent hypobaric hypoxia-induced oxidative stress in rat erythrocytes: protective effects of vitamin E, vitamin C, and carnitine

This study was aimed at determining the effect of vitamin E, vitamin C, and carnitine on intermittent hypobaric-hypoxia-induced oxidative stress (OS) in erythrocytes. For this purpose, male Wistar rats of 4 months of age were orally supplemented with one of the antioxidants prior to exposure to altitudes of 5700 m or 6300 m. Hemoglobin (Hb) and OS indices such as osmotic fragility and hemolysis were measured together with lipid peroxidation (LPO) and protein oxidation. The increase in Hb was accompanied by increase in activities of antioxidant enzymes, superoxide dismutase (SOD), and catalase (CAT) during exposure to both the altitudes without any further elevation by supplements. The extent of reduction in osmotic fragility and hemolysis by vitamin E and carnitine was greater at 6300 m than at 5700 m. Increase in LPO products, for example, malondialdehyde (MDA) and lipofuscin-like autofluorescent substances (AFS) was noticeable at both the altitudes, and vitamin E and carnitine were effective in reducing LPO. While protein oxidation products such as carbonyl content (PrC) and advanced oxidation protein products (AOPP) increased at 6300 m, protein sulphydryl (P-SH) content decreased. P-SH levels were restored on supplementation of antioxidants. Hence, our results indicate that vitamin E, vitamin C, and carnitine may be beneficial in overcoming OS and hemolysis under situations such as intermittent hypobaric hypoxia (IHH) and hypobarotherapy wherein hypoxia is used to correct many pathological situations in humans. Further, this study suggests that supplementation of vitamin E, vitamin C, and L-carnitine alone and not in combination can be beneficial in attenuating the OS associated with IHH compared to the unsupplemented rats exposed to two different altitudes.     

Comparison of the total antioxidant content of 30 widely used medicinal plants of New Mexico

Teas made from medicinal plants are commonly used by a majority of the inhabitants of New Mexico and Mexico to treat various ailments including infections, arthritis, heart disorders, headaches, fever, asthma and menstrual pain. However, little is known about the identity or chemical nature of the bioactive substances and compounds responsible for the therapeutic effects of the teas made from the leaves, seeds, flowers stems, and roots of these medicinal plants. Some of the beneficial effects of these teas may be attributable to antioxidants contained in the medicinal plants from which they are brewed. In the present study we collected 30 medicinal plants that are widely used in the Rio Grande Valley and, using a two-stage Trolox based assay, analyzed the total antioxidant capacity of aqueous extracts prepared from these plants. The antioxidant content of the aqueous extracts was substantial, ranging from 27 to 972 micromol Trolox equivalent per gram dry weight. An extract of the leaves of the plant Ilex paraguensis (Mate leaf) contained the highest amount of antioxidant, followed by the flowers of the Rosa sp. (Rosa de Castillo, 804 micromol/g), the bark of Chinchona sp. (Copalquin, 692 micromol/g), Rumex hymenosepalus stems (Cana Agria, 672 micromol/g) and the leaves of Marrubium vulgare (Mastranzo, 560 micromol/g). The plants that had the lowest antioxidant capacity were the seeds of Linum lewissii (Linasa, 29 micromol/g) and Yucca sp. plant root (Amole, 27 micromol/g). It will be useful to further analyze those plants that contain the most antioxidant activity in order to identify the active principles.     

Stress proteins as biomarkers of oxidative stress: effects of antioxidant supplements

The potential benefits to health of the supply of antioxidants, either through dietary intake or as supplements, is equivocal. There is a need to develop biomarkers that may act as monitors of cellular defense as influenced by antioxidant status. Thirty-two individuals participated in the project and 19 received supplements for 5 weeks in the form of a capsule containing a defined mixture of antioxidants. No change was noted in levels of superoxide dismutase and glutathione peroxidase following antioxidant supplementation. On the other hand, increase in total antioxidant status and decrease in malondialdehyde, protein carbonyl formation, and erythrocyte hemolysis were noted. In lymphocytes isolated from individuals receiving antioxidant supplements and subjected to a heat shock in the presence of the free radical generator 2, 2'-azobis-(2-amidinopropane)-dihydrochloride, enhanced synthesis of heat shock proteins hsp 105, hsp 90, hsp 70, and hsp 40 by contrast with decreased synthesis of heme oxygenase HO-1 (hsp 32) were noted. We conclude that antioxidant status modulates the synthesis of stress proteins.     

The effect of peroxynitrite and some antioxidants on the rate of osmotic hemolysis of bovine erythrocytes

Bovine erythrocytes treated with peroxynitrite (ONOO(-)), a cytotoxic species formed in vivo via the reaction of nitric oxide (NO(.)) and the superoxide anion (O2(-.)), show an increased rate of hemolysis on sudden osmotic stress. The increase in the rate was peroxynitrite concentration dependent. In the presence of some antioxidants (uric acid, ascorbic acid, glutathione, melatonin and albumin), this effect was significantly lower, with ascorbic acid as the most efficient antioxidant.     

Gallic acid, a metabolite of the antioxidant propyl gallate, inhibits gap junctional intercellular communication via phosphorylation of connexin 43 and extracellular-signal-regulated kinase1/2 in rat liver epithelial cells

Propyl gallate and its metabolite, gallic acid, are widely used as antioxidants in the food industry, but they have been shown to exhibit liver toxicity and enhance carcinogenesis. In the present study, we investigated the possible undesirable effects of propyl gallate and gallic acid on gap junctional intercellular communication (GJIC), inhibition of which is closely linked to carcinogenesis. Gallic acid and propyl gallate exhibited dose-dependent free-radical-scavenging activities as determined by 1,1-diphenyl-2-picrylhydrazyl- or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-radical-scavenging assays, and the free-radical-scavenging activity of gallic acid was stronger than that of propyl gallate. However, using WB-F344 rat liver epithelial cells, gallic acid inhibited GJIC in a dose-dependent manner, while propyl gallate had no significant effect compared with untreated controls. The gallic-acid-induced inhibition of GJIC was reversible, with a recovery of nearly 65% after 120 min. Gallic acid induced the phosphorylation of connexin 43 (Cx43) and phosphorylation of extracellular-signal-regulated kinase1/2 (ERK1/2). The gallic-acid-induced inhibition of GJIC was attenuated by treatment with mitogen-activated protein kinase kinase inhibitors (U0126 and PD098059). U0126 blocked the gallic-acid-induced phosphorylation of Cx43 and ERK1/2, indicating that the gallic-acid-induced inhibition of GJIC is mediated by phosphorylation of Cx43 via activation of ERK1/2. In addition, gallic-acid-induced inhibition of GJIC was protected by ascorbic acid and quercetin, which might represent a simple example of the different effects of natural antioxidants in carcinogenesis.     

Antioxidants characterization in selected cyanobacteria

Antioxidants—molecules that have the ability to inhibit the oxidation of other molecules and have many medicinal and industrial applications—are commonly found in algae. Due to the harmful effects of common synthetic antioxidants, their replacement with natural antioxidants would be advantageous. The goal of this study was to examine the efficacy of antioxidants (including antioxidant content, antioxidant activity and antioxidant enzymes) among 11 species of freshwater blue-green algae. Antioxidant activities were evaluated by assaying radical scavenging activity, reducing power and chelating activity. The results showed that Spirulina platensis has the highest radical scavenging activity and reducing power (524 and 244 % more than the control, respectively) and Nostoc linkia has the highest chelating activity (195 %). Examination of some antioxidant contents such as chlorophyll a, carotenoids and phenolic content revealed that S. platensis has the highest contents [10.6 mg/g dry weight (DW), 2.4 mg/g DW and 9.7 mg gallic acid equivalent /g DW, respectively]. The positive correlation (P <0.01) between algal content and antioxidant activity may be attributed to the potent antioxidant activity of these contents. Variation in the activity of three antioxidant enzymes (superoxide dismutase, catalase and peroxidase) was also reported. This study showed that the Cyanobacteria are promising sources of antioxidants.