RESUMO
Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here--in association with its reported signaling effects--could be an explanation to its beneficial effects observed in vivo.
Assuntos
Antioxidantes/farmacologia , Ácidos Cafeicos/farmacologia , Radicais Livres/química , Ferro/química , Peroxidação de Lipídeos/efeitos dos fármacos , Animais , Membrana Celular/metabolismo , Desoxirribose/química , Espectroscopia de Ressonância de Spin Eletrônica , Radical Hidroxila/química , Quelantes de Ferro/química , Compostos de Ferro/química , Masculino , Oxirredução/efeitos dos fármacos , Ratos , Ratos WistarRESUMO
We report elastic integral, differential and momentum transfer cross sections for low-energy electron scattering by the cellulose components ß-D-glucose and cellobiose (ß(1 â 4) linked glucose dimer), and the hemicellulose component ß-D-xylose. For comparison with the ß forms, we also obtain results for the amylose subunits α-D-glucose and maltose (α(1 â 4) linked glucose dimer). The integral cross sections show double peaked broad structures between 8 eV and 20 eV similar to previously reported results for tetrahydrofuran and 2-deoxyribose, suggesting a general feature of molecules containing furanose and pyranose rings. These broad structures would reflect OH, CO and/or CC σ* resonances, where inspection of low-lying virtual orbitals suggests significant contribution from anion states. Though we do not examine dissociation pathways, these anion states could play a role in dissociative electron attachment mechanisms, in case they were coupled to the long-lived π* anions found in lignin subunits [de Oliveira et al., Phys. Rev. A, 2012, 86, 020701(R)]. Altogether, the resonance spectra of lignin, cellulose and hemicellulose components establish a physical-chemical basis for electron-induced biomass pretreatment that could be applied to biofuel production.
Assuntos
Celulose/química , Polissacarídeos/química , Biomassa , Desoxirribose/química , Elétrons , Furanos/química , Modelos QuímicosRESUMO
Stryphnodendron rotundifolium is a phytotherapic used in the northeast of Brazil for the treatment of inflammatory processes which normally are associated with oxidative stress. Consequently, we have tested the antioxidant properties of hydroalcoholic (HAB) and aqueous extracts (AB) from the bark and aqueous extract (AL) from the leaves of Stryphnodendron rotundifolium to determine a possible association between antioxidant activity and the popular use of this plant. Free radical scavenger properties were assessed by the quenching of 1',1'-diphenil-2-picrylhydrazyl (DPPH) and the calculated IC(50) were: HAB = 5.4 ± 0.7, AB = 12.0 ± 2.6, and AL = 46.3 ± 12.3 µg/mL. Total phenolic contents were: HAB = 102.7 ± 2.8, AB = 114.4 ± 14.6, and AL = 93.8 ± 9.1 µg/mg plant). HPLC/DAD analyses indicated that gallic acid, catechin, rutin and caffeic acid were the major components of the crude extracts of S. rotundifolium. Plant extracts inhibited Fe(II)-induced lipid peroxidation in brain homogenates. Iron chelation was also investigated and only HBA exhibited a weak activity. Taken together, the results suggest that S. rotundifolium could be considered an effective agent in the prevention of diseases associated with oxidative stress.
Assuntos
Antioxidantes/farmacologia , Fabaceae/química , Casca de Planta/química , Extratos Vegetais/farmacologia , Folhas de Planta/química , Animais , Antioxidantes/química , Antioxidantes/isolamento & purificação , Compostos de Bifenilo/química , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encéfalo/fisiologia , Brasil , Cromatografia Líquida de Alta Pressão , Desoxirribose/química , Flavonoides/química , Flavonoides/isolamento & purificação , Quelantes de Ferro/química , Quelantes de Ferro/isolamento & purificação , Quelantes de Ferro/farmacologia , Masculino , Malondialdeído/metabolismo , Medicina Tradicional , Estresse Oxidativo , Fenóis/química , Fenóis/isolamento & purificação , Picratos/química , Extratos Vegetais/química , Extratos Vegetais/isolamento & purificação , Plantas Medicinais/química , Ratos Wistar , Substâncias Reativas com Ácido Tiobarbitúrico/metabolismoRESUMO
Some oxindole-Schiff base copper(II) complexes have already shown potential antitumor activity towards different cells, inducing apoptosis in a process modulated by the ligand, and having nuclei and mitochondria as main targets. Here, three novel copper(II) complexes with analogous ligands were isolated and characterized by spectroscopic techniques, having their reactivity compared to the so far most active complex in this class. Cytotoxicity experiments carried out toward human neuroblastoma SH-SY5Y cells confirmed its pro-apoptosis property. DNA cleavage studies were then performed in the presence of these complexes, in order to verify the influence of ligand structural features in its nuclease activity. All of them were able to cause double-strand DNA scissions, giving rise to nicked circular Form II and linear Form III species, in the presence of hydrogen peroxide. Additionally, DNA Form II was also detected in the absence of peroxide when the most active complex, [Cu(isaepy)2]2+ 1, was used. In an effort to better elucidate their interactions with DNA, solutions of the different complexes titrated with DNA had their absorption spectra monitored. An absorbance hyperchromism observed at 260 nm pointed to the intercalation of these complexes into the DNA structure. Further, investigations of 2-deoxy-d-ribose (DR) oxidation catalyzed by each of those complexes, using 2-thiobarbituric acid reactive species (TBARS) method, and detection of reactive oxygen species (ROS) formation by spin-trapping EPR, suggested that their mechanism of action in performing efficiently DNA cleavage occurs preferentially, but not only by oxidative pathways.
Assuntos
Antineoplásicos/química , Cobre/química , DNA/efeitos dos fármacos , Compostos Organometálicos/química , Bases de Schiff/química , Apoptose/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , DNA/química , Desoxirribonucleases/metabolismo , Desoxirribose/química , Humanos , Indóis/química , Oxindóis , Espectrofotometria Infravermelho , Células Tumorais CultivadasRESUMO
Chemoprevention by natural products is an emerging therapeutic approach for free radical-mediated diseases including cancer. This is a consequence of its wide applicability and acceptance. In the present study, the antioxidant activity of the soybean extract (Isoflavin Beta) and of formulations added with this extract were evaluated using stable free radical 2,2-diphenyl-1-pycrylhydrazyl (DPPH*) and deoxyribose as well as the lipid peroxidation inhibition assays. For all the assays the extract showed a dose-dependent activity, and IC50 of 21.03 microg/mL in lipid peroxidation inhibition, 161.8 microg/mL in DPPH*, and 33.5 ng/mL in hydroxyl radical scavenging assay. The antioxidant activity of the extract added in the formulations could not be assessed using the deoxyribose assay. However, the lipid peroxidation inhibition and DPPH* scavenging assays could be successfully applied for the antioxidant activity evaluation of the formulations added with soybean extract to protect the skin against free radicals, which can be generated by the ultraviolet radiation exposure.
Assuntos
Antioxidantes/farmacologia , Compostos de Bifenilo/química , Hidrazinas/química , Animais , Antioxidantes/química , Ácido Cítrico/química , Desoxirribose/química , Relação Dose-Resposta a Droga , Sequestradores de Radicais Livres , Radical Hidroxila , Concentração Inibidora 50 , Ferro/química , Peroxidação de Lipídeos , Masculino , Picratos , Ratos , Ratos Wistar , Glycine maxRESUMO
We studied mangiferin effects on the degradation of 2-deoxyribose induced by Fe(III)-EDTA/citrate plus ascorbate, in relation to ascorbate oxidation (measured at 265 nm). Results revealed that mangiferin was equally effective in preventing degradation of both 15 and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or citrate) caused a significant reduction in the protective effects of mangiferin. Interestingly, mangiferin strongly stimulated Fe(III)-EDTA ascorbate oxidation, but inhibited it when citrate was used as iron co-chelator. Mangiferin stimulated O2 consumption due to Fe(II) (formed by Fe(III) ascorbate reduction) autoxidation when the metal ligand was EDTA, but inhibited it when citrate was used. These results suggest that mangiferin removes iron from citrate, but not from EDTA, forming an iron-mangiferin complex that cannot induce ascorbate oxidation effectively, thus inhibiting iron-mediated oxyradical formation. Taken together, these results indicate that mangiferin works mainly by a mechanism different from the classical hydroxyl radical scavengers, keeping iron in its ferric form, by complexing Fe(III), or stimulating Fe(II) autoxidation.
Assuntos
Antioxidantes/química , Ácido Ascórbico/química , Desoxirribose/química , Compostos Férricos/química , Quelantes de Ferro/química , Xantonas/química , Ácido Edético/química , Modelos Químicos , OxirreduçãoRESUMO
The antioxidant activity of extracts of propolis and of formulations added with these extracts were measured by scavenging different radicals in different systems. For the ethanolic extract of propolis (EEP) and the glycolic extract of propolis (GEP) the IC50 observed were respectively of 0.024 and 0.035 microL/mL in scavenging hydroxyl radical, 0.016 and 0.012 microL/mL in inhibiting lipid peroxidation, 0.22 and 0.24 microL/mL in inhibiting chemiluminescence produced in the H2O2/luminol/horseradish peroxide (HRP) system and about 0.005 microL/mL for both extracts in inhibiting chemiluminescence produced in the xanthine/luminol/xanthine oxidase (XOD) system. The antioxidant activity of extracts of propolis in the formulations was not able to be assessed neither using the deoxyribose assay, since the formulation components interfered in the assay measurements, nor using chemiluminescence in the H2O2/luminol/HRP system, since this method did not show to be sensitive for the extract of propolis evaluation. However, the antioxidant activity of extracts of propolis could be successfully evaluated in the formulations using both lipid peroxidation and chemiluminescence generated in the xanthine/luminol/XOD system inhibitions.
Assuntos
Antioxidantes/farmacologia , Química Farmacêutica/métodos , Desoxirribose/química , Indústria Farmacêutica/métodos , Própole/química , Antioxidantes/química , Área Sob a Curva , Meios de Cultura/farmacologia , Relação Dose-Resposta a Droga , Etanol/química , Flavonoides/química , Sequestradores de Radicais Livres , Glicóis/química , Peróxido de Hidrogênio/química , Radical Hidroxila , Concentração Inibidora 50 , Ferro/química , Peroxidação de Lipídeos , Luminol/análise , Fenóis/química , Polifenóis , Xantina/análise , Xantina Oxidase/químicaRESUMO
It is widely believed that the iron chelator 1,10-phenanthroline (phen) is able to fully block the Fenton reaction by forming a complex (Fe(phen)3(2+), also known as ferroin) that cannot react with H2O2. We observed that phen cannot fully prevent 2-deoxyribose (5 mM) degradation induced by Fenton reagents (30 microM Fe(II) plus 100-500 microM H2O2); protection varied from 55% to 66% when the phen/Fe(II) ratio was 3:1 to 20:1. Inhibition of 2-deoxyribose damage was nearly unchanged if phen was pre-incubated with Fe(II). Moreover, preformed Fe(phen)3(2+) complex added to the solution containing H2O2 was able to induce 2-deoxyribose degradation and methane sulfinic acid formation from the oxidation of 5% DMSO. The partially protective effect of phen was unchanged with the use of either phosphate or HEPES as buffers (5 mM, pH 7.2), or in unbuffered media (pH 5.1). Both DMSO oxidation and 2-deoxyribose degradation correlated with the increase in Fe(phen)3(2+) concentration. Strand breaks in plasmid pTARGETtrade mark DNA induced by Fenton reagents (1 microM Fe(II) plus 25 microM H2O2) in HEPES buffer could only be partially prevented by phen, even when the chelator was 16 times more concentrated than Fe(II). In these experiments, Fe(phen)3(2+) and DNA were pre-incubated from 1 to 10 min before addition of H2O2. Moreover, a high level of DNA strand breakage was observed when iron and phen are added to the reaction immediately before H2O2. On the other hand, phen fully prevented 2-deoxyribose degradation induced by the autoxidation of 30 microM Fe(II) in phosphate-buffered (3 to 30 mM) media. Our data provide evidence that the Fe(phen)3(2+) complex induces in vitro oxidative damage in the presence of H2O2 (possibly by means of Fe(phen)3(2+) dissociation into Fe(phen)2(2+)), but they show that the complex cannot undergo autoxidation.
Assuntos
Dano ao DNA/efeitos dos fármacos , Compostos Ferrosos/química , Substâncias Intercalantes/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Fenantrolinas/farmacologia , Desoxirribose/química , Desoxirribose/metabolismo , Dimetil Sulfóxido/metabolismo , Peróxido de Hidrogênio , Ferro , Quelantes de Ferro/farmacologia , Oxirredução , Plasmídeos , Ácidos Sulfínicos/metabolismoRESUMO
Previous work from our laboratory demonstrated that pyridoxal isonicotinoyl hydrazone (PIH) has in vitro antioxidant activity against iron plus ascorbate-induced 2-deoxyribose degradation due to its ability to chelate iron; the resulting Fe(III)-PIH(2) complex is supposedly unable to catalyze oxyradical formation. A putative step in the antioxidant action of PIH is the inhibition of Fe(III)-mediated ascorbate oxidation, which yields the Fenton reagent Fe(II) [Biochim. Biophys. Acta 1523 (2000) 154]. In this work, we demonstrate that PIH inhibits Fe(III)-EDTA-mediated ascorbate oxidation (measured at 265 nm) and the formation of ascorbyl radical (in electron paramagnetic resonance (EPR) studies). The efficiency of PIH against ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation was dose dependent and directly proportional to the period of preincubation of PIH with Fe(III)-EDTA. The efficiency of PIH in inhibiting ascorbate oxidation and ascorbyl radical formation was also inversely proportional to the Fe(III)-EDTA concentration in the media. When EDTA was replaced by the weaker iron ligand nitrilotriacetic acid (NTA), PIH was much more effective in preventing ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation. Moreover, the replacement of EDTA with citrate, a physiological chelator with a low affinity for iron, also resulted in PIH having a higher efficiency in inhibiting iron-mediated ascorbate oxidation and 2-deoxyribose degradation. These results demonstrate that PIH removes iron from EDTA (or from either NTA or citrate), forming an iron-PIH complex that cannot induce ascorbate oxidation effectively, thus inhibiting iron-mediated oxyradical formation. These results are of pharmacological relevance because PIH has been considered for experimental chelating therapy in iron-overload diseases.
Assuntos
Ácido Ascórbico/química , Quelantes/farmacologia , Compostos Férricos/antagonistas & inibidores , Isoniazida/análogos & derivados , Isoniazida/farmacologia , Ácido Nitrilotriacético/análogos & derivados , Piridoxal/análogos & derivados , Piridoxal/farmacologia , Desoxirribose/química , Ácido Edético/antagonistas & inibidores , Espectroscopia de Ressonância de Spin Eletrônica , Radicais Livres/química , Radical Hidroxila/química , Ácido Nitrilotriacético/antagonistas & inibidores , Oxirredução/efeitos dos fármacos , Estresse OxidativoRESUMO
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.