Antioxidant and pro-oxidant properties of ascorbic acid and gallic acid

Antioxidant activity of selected plant species; potential new sources of natural antioxidants

The aim of this study was to examine six plants from Serbia for their potential antioxidant activity. Therefore, six antioxidant activity assays were carried out, including: total antioxidant capacity, DPPH free-radical scavenging, the inhibitory activity toward lipid peroxidation, Fe(3+)- reducing power, Fe(2+)- chelating ability and hydroxyl radical scavenging activity. Total phenolic and flavonoid contents were also determined for each alcoholic extract. Cotinus coggygria extract contained the highest amount of total phenols (413mg GAE /g dry extract), while the highest proportion of flavonoids was found in the Echium vulgare methanol extract (105 mg RU/g). Cotinus coggygria and Halacsya sendtneri alcoholic extracts showed the highest total antioxidant capacity (313 and 231 mg AA/g dry extract), as well as DPPH free-radical scavenging (IC(50)=9 and 99 μg/ml), inhibitory activity toward lipid peroxidation (IC(50)=3 and 17 μg/ml) and reducing power. Whereas, the greatest hydroxyl radical scavenging activity, as well as ferrous ion chelating ability showed Echium vulgare, Echium rubrum and Halacsya sendtneri.

Electrochemical detection of dopamine in the presence of ascorbic acid using graphene modified electrodes

Dopamine plays a significant role in the function of human metabolism. It is important to develop sensitive sensor for the determination of dopamine without the interference by ascorbic acid. This paper reports the synthesis of graphene using a modified Hummer's method and its application for the electrochemical detection of dopamine. Electrochemical measurements were performed at glassy carbon electrode modified with graphene via drop-casting method. Cyclic voltammogram of ferri/ferrocyanide redox couple at graphene modified electrode showed an increased current intensity compared with glassy carbon electrode and graphite modified electrode. The decrease of charge transfer resistance was also analyzed by electrochemical impedance spectroscopy. The capacity of graphene modified electrode for selective detection of dopamine was confirmed in a sufficient amount of ascorbic acid (1 mM). The observed linear range for the determination of dopamine concentration was from 4 microM to 100 microM. The detection limit was estimated to be 2.64 microM.

Chitosan gallate as a novel potential polysaccharide antioxidant: an EPR study

A novel biopolymer-based antioxidant, chitosan conjugated with gallic acid (chitosan galloylate, chitosan-GA), is proposed. Electron paramagnetic resonance (EPR) demonstrates a wide range of antioxidant activity for chitosan-GA as evidenced from its reactions with oxidizing free radicals, that is, 1,1-diphenyl-2-picryl-hydrazyl (DPPH), horseradish peroxidase (HRP)-H(2)O(2), carbon-centered alkyl radicals, and hydroxyl radicals. The EPR spectrum of the radical formed on chitosan-GA was attributed to the semiquinone radical of the gallate moiety. The stoichiometry and effective concentration (EC(50)) of the DPPH free radical with chitosan-GA show that the radical scavenging capacity is maintained even after thermal treatment at 100 degrees C for an hour. Although the degree of substitution of GA on chitosan was about 15%, its antioxidant capacity, that is, the reaction with carbon-centered and hydroxyl radicals, is comparable to that of GA.

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.

Interactions between PAMAM dendrimers and gallic acid molecules studied by spectrofluorimetric methods

Interactions between gallic acid molecules and different types of polyamidoamine (PAMAM) dendrimers with modified surfaces were studied by spectrofluorimetric methods. Changes in fluorescence intensity of gallic acid and in a position of spectrum were monitored. It was found that the extent of gallic acid incorporation into dendrimers depends on a type of a dendrimer.

Phenolic Phytochemicals Derived from Red Pine (Pinus densiflora) Inhibit the Invasion and Migration of SK-Hep-1 Human Hepatocellular Carcinoma Cells

Considerable attention has recently been focused on identifying chemopreventive phytochemicals derived from medicinal plants. Here, we analyzed phenolic phytochemicals from red pine (RP) leaves and found epigallocatechin gallate (EGCG) and epigallocatechin (EGC), and catechin gallate (CG) as their major phenolic phytochemicals. This article also investigated whether RP leaf extract and its phenolic phytochemicals inhibit the invasion of SK-Hep-1 human hepatocellular carcinoma cells (SK-Hep-1 cells). RP suppressed the invasion and the migration of SK-Hep-1 cells. EGCG and CG also inhibited the invasion and migration, with EGC exhibiting a lower efficacy. Matrix metalloproteinases (MMPs), particularly gelatinase-A (MMP-2) and gelatinase-B (MMP-9), degrade components of the basement membrane and are strongly implicated in invasion and metastasis formation of malignant tumors. RP suppressed both MMP-2 and MMP-9 activities. EGCG and CG reduced the activities of MMP-9 and MMP-2 in a dose-dependent manner, with EGC exhibiting a lower efficacy on both MMPs. Our results suggest that RP inhibits tumor invasion and migration, which may be attributed to the effects of EGCG and CG. In particular, EGCG plays a key role in the efficacy of RP against hepatocarcinogenesis.

Biphasic effects of dietary antioxidants on oxidative stress-mediated carcinogenesis

There is now strong evidence implicating the generation of reactive oxygen species (ROS) and the corresponding response to oxidative stress as key factors in the pathogenesis of several human diseases including cancer, atherosclerosis, and neurodegenerative disorders, and in ageing. The carcinogenicity of oxidative stress is primarily attributable to the genotoxicity of ROS, but ROS can promote cancer through diverse cellular processes. Therefore, dietary or pharmaceutical augmentation of the endogenous antioxidant defense capacity has been considered a plausible way to prevent ROS-mediated carcinogenicity, but actual antioxidant therapies have been equivocal at best. In fact, most free-radical scavengers act in reversible oxidation-reduction reactions, and some antioxidants can act both as antioxidants and prooxidants, depending on their structures and the conditions. This article summarizes the possible cancer-preventive and -enhancing mechanisms of dietary antioxidants, with an emphasis on epigenetic mechanisms.

In vitro antioxidant activity and scavenging effects of Cinnamomum verum leaf extract assayed by different methodologies

The free radical scavenging capacity and antioxidant activities of the methanolic extract of Cinnamomum verum leaf (CLE) were studied and compared to antioxidant compounds like trolox, butylated hydroxyl anisole, gallic acid and ascorbic acid. The CLE exhibited free radical scavenging activity, especially against DPPH radical and ABTS radical cation. They also exhibited reducing power and metal ion chelating activity, along with hydroxyl radical scavenging activity. The peroxidation inhibiting activity of CLE recorded using the linoleic acid emulsion system, showed very good antioxidant activity.

The roles of polyphenols in cancer chemoprevention

Oxidative stress imposed by reactive oxygen species (ROS) plays a crucial role in the pathophysiology associated with neoplasia, atherosclerosis, and neurodegenerative diseases. The ROS-induced development of cancer involves malignant transformation due to altered gene expression through epigenetic mechanisms as well as DNA mutations. Considerable attention has been focused on identifying naturally occurring antioxidative phenolic phytochemicals that are able to decrease ROS levels, but the efficacies of antioxidant therapies have been equivocal at best. Several studies have shown that some antioxidants exhibit prooxidant activity under certain conditions and potential carcinogenicity under others, and that dietary supplementation with large amounts of a single antioxidant may be deleterious to human health. This article reviews the intracellular signaling pathways that respond to oxidative stress and how they are modulated by naturally occurring polyphenols. The possible toxicity and carcinogenicity of polyphenols is also discussed.

Antioxidant properties of tea investigated by EPR spectroscopy

The antioxidant properties of green, black and mixed (fruit) tea samples of different origin were investigated by means of EPR spectroscopy. A six line EPR spectrum of solid tea samples indicates the presence of Mn(II) ions and it is superimposed with a sharp singlet line attributed to semiquinone radical species (Delta H(pp)=1 mT; g=2.0022). Antioxidant properties of aqueous tea extracts in H(2)O(2)/NaOH/dimethylsulfoxide system generating reactive radicals (*OH, O(2)*-), *CH(3)) were followed by spin trapping technique. In addition, antioxidant capacity of these samples was assessed using stable radicals 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL). Typically, the highest antioxidant potential to terminate superoxide radicals was found in green teas, followed by black and fruity teas. The pro-oxidant activity of green teas evidenced by spin traps was promoted in samples with higher Mn(II) and ascorbic acid concentrations. Various sources of free radicals used in the antioxidant tests due to their specific action show different termination rates in the presence of the individual tea samples.