Cyclic voltammetric analysis of 2-styrylchromones: relationship with the antioxidant activity

2-Styrylchromones (2-SC) are a chemical family of oxygen heterocyclic compounds, vinylogues of flavones (2-phenylchromones), whose occurrence in nature has been reported. Recently, several 2-SC derivatives were demonstrated to have antioxidant properties, namely, xanthine oxidase inhibition, hepatoprotection against pro-oxidant agents in cellular and non-cellular systems and scavenging activity against reactive oxygen and reactive nitrogen species (ROS and RNS). Considering these antioxidant properties, it may be hypothesised that the electrochemical redox behaviour of 2-SC contributes significantly to their activity. To test this hypothesis, the electrochemical behaviour of different 2-SC was studied, together with a number of flavonoids with well-known antioxidant activities, by cyclic voltammetry, and the results correlated to their ability to scavenge ROS and RNS. The results obtained showed that 2-SC with a catecholic B-ring have a low oxidation peak potential corresponding to the oxidation of the 3',4'-OH (catechol) moiety. The compounds with a phenolic B-ring have a common peak, with oxidation potential values of about +0.4/+0.5 V versus Ag/AgCl, corresponding to the oxidation of the 4'-OH. The oxidation of the hydroxyl substituents in the A-ring generated peaks of higher potentials (+0.7/+0.8 V vs Ag/AgCl). The results from the scavenging assays were in agreement with those obtained from the cyclic voltammetry, that is, higher scavenging effects corresponded to lower values of oxidation potentials, with significant correlation coefficients. The values obtained for the studied flavonoids are in accordance with the literature, and reflect their relative antioxidant activity, when compared to the studied 2-SC. Thus, in this family of compounds, oxidation potentials obtained by cyclic voltammetry seem to be applicable as a general indicator of radical scavenging activity.     

Novel 2-substituted nitronyl nitroxides as free radical scavengers: synthesis, biological evaluation and structure-activity relationship

To develop more potent small molecules with enhanced free radical scavenger properties, we designed and synthesized a series of nitronyl nitroxide derivatives 4a-h. A lead compound 4f was discovered based on Ach-induced vascorelaxation assay. Further chemical modification based on this scaffold provided a new series of 2-substituted phenylnitronyl nitroxide derivatives 6a-s. The newly synthesized compounds 6a-s possess improved radical scavenger's activity based on PC12 cell survival assay. Compounds 6g,n,o, and s are some of the most potent compounds in terms of NO, H(2)O(2), and OH scavenging ability. 2-Substitued phenylnitronyl nitroxides had a higher radical scavenging activity with the electron-donating group (EDG). In contrast, the introduction of electron-withdrawing group (EWG) to the aromatic ring led to a dramatic decrease in its radical scavenging activity. These results suggest that the electron-donating group (EDG) of the aromatic ring may be an important factor influencing the radical scavenging behavior of these compounds, and the potency of free radical scavenging activity largely depended on the position and electronic properties of the phenyl ring substituents. The enhanced radical scavenging capacities of the novel 2-substituted nitronyl nitroxides may be potential drug leads against the deleterious action of ROS (reactive oxygen species)/RNS (reactive nitrogen species).     

Protective role of new nitrogen compounds on ROS/RNS-mediated damage to PC12 cells

Reactive oxygen (ROS) and nitrogen (RNS) species are known to be involved in many degenerative diseases. This study reports four new nitrogen compounds from organic synthesis, identified as FMA4, FMA7, FMA762 and FMA796, which differ mainly by the number of hydroxyl groups within their phenolic unit. Their potential role as antioxidants was evaluated in PC12 cells by assessing their protection against oxidative and nitrosative insults. The four compounds, and particularly FMA762 and FMA796, were able to protect cells against lipid peroxidation and intracellular ROS/RNS formation to a great extent. Their protective effects were likely mediated by their free radicals scavenging ability, as they appeared to be involved neither in the induction of natural antioxidant enzymes like GSH-PX and SOD, nor in the inhibition of NOS. Nevertheless, these results suggest a promising potential for these compounds as ROS/RNS scavengers in pathologies where oxidative/nitrosative stress are involved.     

Antioxidant activity of β-blockers: An effect mediated by scavenging reactive oxygen and nitrogen species?

The therapeutic effects of beta-blockers are normally explained by their capacity to block the beta-adrenoceptors, however, some of the beneficial cardiovascular effects shown by this group of compounds have already been associated with the antioxidant properties that some of them seem to possess. The beta-blockers atenolol, labetalol, metoprolol, pindolol, propranolol, sotalol, timolol, and carvedilol were tested for their putative scavenging activity for ROS (O(2)(-), H(2)O(2), HO(.), HOCl, and ROO(.)) and RNS ((.)NO and ONOO(-)). Some of the studied compounds are effective ROS and/or RNS scavengers, these effects being possibly useful in preventing oxidative damage verified in hypertension as well as in other cardiovascular diseases that frequently emerge in association with oxidative stress.     

The protective and healing effects of a natural antioxidant formulation based on ubiquinol and Aloe vera against dextran sulfate-induced ulcerative colitis in rats

Oxygen/nitrogen reactive species (ROS/RNS) are currently implicated in the pathogenesis of ulcerative colitis, drawing attention on the potential prophylactic and healing properties of antioxidants, scavengers, chelators. We evaluated the possible protective/curative effects of a natural antioxidant preparation based on Aloe vera and ubiquinol, against intestinal inflammation, lesions, and pathological alterations of the intestinal electrophysiological activity and motility, in a rat model of DSS-induced colitis. 5% dextrane sulfate (DDS) (3 days), followed by 1% DSS (4 days) was administered in drinking water. The antioxidant formulation (25 mg/kg) was delivered with a pre-treatment protocol, or simultaneously or post-colitis induction. Spontaneous and acetylcholine-stimulated electrical activity were impaired in the small intestine and in distal colon, upon exposure to DSS only. Severe inflammation occurred, with increased myeloperoxidase activity, and significant alterations of the oxidant/antioxidant status in colonic tissue and peritoneal cells. Lipoperoxidation, superoxide production, glutathione peroxidase and glutathione-S-transferase activities, and reduced glutathione content increased, whilst superoxide dismutase and catalase activities were sharply suppressed in colon tissue. ROS/RNS formation in peritoneal cells was strongly inhibited. Inflammation, electrical/mechanical impairment in the gut, and a great majority of oxidative stress parameters were improved substantially by pre-treatment with the antioxidant preparation, but not by simultaneous administration or post-treatment.     

In vitro scavenging activity for reactive oxygen and nitrogen species by nonsteroidal anti-inflammatory indole, pyrrole, and oxazole derivative drugs

This study was undertaken to evaluate the scavenging activity for reactive oxygen species (ROS) and reactive nitrogen species (RNS) by several nonsteroidal anti-inflammatory drugs (NSAIDs), namely indole derivatives (indomethacin, acemetacin, etodolac), pyrrole derivatives (tolmetin and ketorolac), and an oxazole derivative (oxaprozin). The inhibition of prostaglandin synthesis constitutes the primary mechanism of the anti-inflammatory action of these drugs. Nevertheless, it has been suggested that the anti-inflammatory activity of NSAIDs may be also partly due to their ability to scavenge ROS and RNS and to inhibit the respiratory burst of neutrophils triggered by various activator agents. Thus, the scavenging activity of these NSAIDs was evaluated against an array of ROS (O(2)(-), HO, HOCl, and ROO) and RNS (NO and ONOO(-)) using noncellular in vitro systems. The results obtained demonstrated that tolmetin, ketorolac, and oxaprozin were not active against O(2)(-), while acemetacin, indomethacin, and etodolac exhibited concentration-dependent effects. Oxaprozin was also the least active scavenger for HO, among all the tested NSAIDs shown to be active. The scavenging effect for HOCl was not observed for any of the tested NSAIDs. The ROO was effectively scavenged by etodolac, with the other tested NSAIDs being much less active. NO and ONOO(-) were scavenged by all the tested NSAIDs. These effects may strongly contribute to the anti-inflammatory therapy benefits that may be attained with some of the studied NSAIDs.     

Free radical scavenging and antiproliferative properties of Biginelli adducts

A series of Biginelli adducts bearing different substituents at C-4 position were synthesized by using p-sulfonic acid calix[4]arene as a catalyst. The in vitro potential to scavenge reactive nitrogen/oxygen species (RNS and ROS) and the ability to inhibit cancer cells growth were then investigated. Four adducts were found to be potent scavengers of 2,2-diphenyl-1-picrylhydrazyl (RNS) and/or superoxide anion (ROS) radicals. The antiproliferative activity against cancer cells was disclosed for the first time for 16 monastrol analogs. The capacity of all compounds to inhibit cancer cells growth was dependent on the histological origin of cells, except for BA24, which was highly active against all cell lines. BA20 and BA33 were as potent as the reference drug doxorubicin against adriamycin-resistant ovarian and prostate cancer cells, respectively. These results highlight some monastrol analogs as lead compounds for the design of new free radical scavengers and anticancer agents.     

(E)-2-Styrylchromones as potential anti-norovirus agents

Human noroviruses (NoV) are now recognized as the most frequent cause of outbreaks and sporadic cases of acute gastroenteritis. Despite the significant economic impact and considerable morbidity of norovirus disease, no drug or vaccine is currently available to treat or prevent this disease, therefore the discovery of anti-norovirus drugs is urgent.In the present work, a total of 12 structure related chromone and (E)-2-styrylchromones were evaluated for their potential anti-norovirus activity using the murine norovirus (MNV) as a surrogate model for human NoV.From the 12 compounds studied, six (E)-2-styrylchromones were found to have with interesting anti-norovirus activity. The best compounds of the series were (E)-5-hydroxy-2-styrylchromone and (E)-4′-methoxy-2-styrylchromone with an IC₅₀ ≈ 7 μM. A first insight into the mechanism of action of these compounds was possible. An interesting relationship between the anti-norovirus activity and the chemical structure was observed. The present study points out that the (E)-2-styrylchromones skeleton is an important one which deserves to be developed and further explored as new antiviral drugs against NoV.     

Antioxidant activities of dihydroxylated salicylic acid derivatives

SUMMARY

The ability of hydroxylated metabolites of salicylic acid to scavenge reactive oxygen species and to inhibit arachidonic acid metabolism was investigated. The tested trihydroxybenzoic acids (THBAs) were potent scavengers of hydroxyl and superoxide anion radicals produced by Fenton reaction and xanthine/xanthine oxidase system or activated macrophages respectively. In the same tests, salicylic acid possessed moderate O₂^? and low OH'scavenging activities.

Our results demonstrate that adding two hydroxyl groups to salicylic acid strongly increases the reactive oxygen species (ROS) scavenging activities. Adding two hydroxyl groups at position 4 and 5 (2,4,5-THBA) affords the most active ROS scavenging activity probably due to the ortho unsubstituted catechol moiety. In fact, we can consider that the ROS scavenging properties of salicylic acid are essentially due to its metabolic products such as 2,3- and 2,5-DHBAs, catechol and also to THBAs.     

Reactive Oxygen,Nitrogen, Carbonyl and Sulfur Species and Their Roles in Plant Abiotic Stress Responses and Tolerance

Plants being sessile organisms are often exposed to various abiotic stress conditions, which greatly hamper the growth, yields as well as the quality of produce. Plants respond to abiotic stresses in an exceptionally complex and coordinated manner, involving the interactions and crosstalk with many metabolic-molecular pathways. One of the most common responses is generation of reactive chemical species including reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive carbonyl species (RCS) and reactive sulfur species (RSS). ROS and RNS have long attracted attention from the plant researchers for both their damaging as well as protective effects. However, several reports are emerging to confirm similar roles played by the relatively newer 'reactive' members, the RCS and RSS. Plant reactive species are also hailed as vivacious signaling molecules that play regulatory roles in many plant metabolic procedures. Undeniably, these reactive species are involved in virtually all aspects of plant cell functions. Reactive species and the antioxidant machinery maintain a delicate but critical cellular redox-balance which gets disturbed under stress conditions, where their biosynthesis, transportation, scavenging and the overall metabolism gets decisive for plant survival. The current review aims to highlight and discuss the role of ROS, RNS, RCS, and RSS in plants especially under abiotic stresses, cross-talks between them, current approaches and technological advents for their characterization, and a perspective view on exploration/manipulation of the pathways and check-points involved in biosynthesis, transport and scavenging of these reactive species for engineering abiotic stress tolerant crop plants.

     

Interaction of enkephalin derivatives with reactive oxygen species

The oxidation of opioid peptides by tyrosinase in the presence of an excess of a thiol gives rise to cysteinyldopa derivatives. The major products arising from the reaction between Leu-enkephalin and cysteine are represented by 5-S-cysteinyldopaenkephalin (5-CDenk) and 2-S-cysteinyldopaenkephalin (2-CDenk). The interaction of 5-CDenk and 2-CDenk with reactive oxygen species (ROS) has been studied. These compounds are able to scavenge superoxide anion, hydroxyl and peroxyl radicals as well as to reduce the lipid peroxidation rate induced by ABAP. The scavenging activities in all instances are dose-dependent. In some cases CDenks are more active than compounds recognized as strong radical scavengers, such as Trolox and mannitol. As a result of the action of the Fenton system, the CDenks (as well as the Enks) are oxidized into pigmented derivatives. The possible implications of the interaction of CDenks and Enks with ROS on melanization process in Parkinson's disease are discussed.     

Restorative and synergistic efficacy of Kalpaamruthaa, a modified Siddha preparation, on an altered antioxidant status in adjuvant induced arthritic rat model

BACKGROUND: Rheumatoid arthritis (RA) is a prevalent and debilitating disease that affects the joints. Infiltration of blood-derived cells in the affected joints upon activation generate reactive oxygen/nitrogen species, resulting in an oxidative stress. One approach to counteract this oxidative stress is the use of antioxidants as therapeutic agents. OBJECTIVES: Kalpaamruthaa (KA), a modified indigenous Siddha preparation constituting Semecarpus anacardium nut milk extract (SA), Emblica officinalis (EO) and honey was evaluated for its synergistic antioxidant potential in adjuvant induced arthritic rats than sole SA treatment. MATERIALS AND METHODS: Levels/activities of reactive oxygen species (ROS)/reactive nitrogen species (RNS), myeloperoxidase, lipid peroxide and enzymic and non-enzymic antioxidants were determined in control, arthritis induced, SA and KA treated (150 mg/kg b.wt.) animals. RESULTS AND CONCLUSION: The levels/activities of ROS/RNS, myeloperoxidase and lipid peroxide were increased significantly (p<0.05) and the activities of enzymic and non-enzymic antioxidants were in turn decreased in arthritic rats, whereas these changes were reverted to near normal levels upon SA and KA treatment. KA showed an enhanced antioxidant potential than sole treatment of SA in adjuvant induced arthritic rats. KA via enhancing the antioxidant status in adjuvant induced arthritic rats than sole SA treatment proves to be an important therapeutic modality in the management of RA and thereby instituting the role of oxidative stress in the clinical manifestation of the disease RA. The profound antioxidant efficacy of KA than SA alone might be due to the synergistic action of the polyphenols such as flavonoids, tannins and other compounds such as vitamin C and hydroxycinnamates present in KA.     

Natural and newly synthesized hydroxy-1-aryl-isochromans: a class of potential antioxidants and radical scavengers

We investigated the antioxidant and radical scavenging activity of polyphenolic isochromans. To assess the relation between structure and scavenging properties the natural occurring 1-(3'-methoxy-4'-hydroxy)phenyl-6,7-dihydroxy-isochroman (ISO-3, three OH groups) was compared with three newly synthesized derivatives that differ in their degree of hydroxylation by substitution with methoxy-groups (ISO-4: four OH groups; ISO-2: two OH groups and ISO-0: fully methoxylated). We found that ISO-4 is a 2-fold better scavenger for the artificial radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 100 microM) with an EC50=10.3 microM compared to the natural ISO-3 (EC50=22.4 microM) and to ISO-2 (EC50=25.1 microM), while ISO-0 did not react with DPPH. The scavenging capacity for superoxide enzymatically generated in a hypoxanthin-xanthinoxidase reaction was the highest for ISO-4 (EC50=34.3 microM) compared to those of ISO-3 (EC50=84.0 microM) and ISO-2 (EC50=91.8 microM), while ISO-0 was inactive. In analogy, ISO-4 scavenged peroxynitrite (ONOO-, EC25=23.0 microM) more effective than ISO-3, ISO-2 and ISO-0.When C6 rat glioma cells loaded with the reactive oxygen/nitrogen (ROS/RNS)-sensitive fluorochrome 2,7-dichlorodihydrofluorescein, were exposed to hydrogen peroxide, the lowest stress level as indicated by the fluorescence signal was detected when the cells were pretreated with ISO-4 or ISO-2 but to a much lesser extent with ISO-3, while ISO-0 did not show any effect. All tested hydroxyisochromans superceded the scavenging effect of trolox.The excellent radical and ROS/RNS scavenging features of the hydroxy-1-aryl isochromans and their simple synthesis let these compounds appear to be interesting candidates for pharmaceutical interventions that protect against the deleterious action of ROS/RNS.     

Antioxidant responses to oxidant-mediated lung diseases

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated throughout the human body. Enzymatic and nonenzymatic antioxidants detoxify ROS and RNS and minimize damage to biomolecules. An imbalance between the production of ROS and RNS and antioxidant capacity leads to a state of "oxidative stress" that contributes to the pathogenesis of a number of human diseases by damaging lipids, protein, and DNA. In general, lung diseases are related to inflammatory processes that generate increased ROS and RNS. The susceptibility of the lung to oxidative injury depends largely on its ability to upregulate protective ROS and RNS scavenging systems. Unfortunately, the primary intracellular antioxidants are expressed at low levels in the human lung and are not acutely induced when exposed to oxidative stresses such as cigarette smoke and hyperoxia. However, the response of extracellular antioxidant enzymes, the critical primary defense against exogenous oxidative stress, increases rapidly and in proportion to oxidative stress. In this paper, we review how antioxidants in the lung respond to oxidative stress in several lung diseases and focus on the mechanisms that upregulate extracellular glutathione peroxidase.     

Conjugation of catechins with cysteine generates antioxidant compounds with enhanced neuroprotective activity

Antioxidant compounds derived from the conjugation of (-)-epicatechin and (-)-epicatechin 3-O-gallate with cysteine and cysteine derivatives protected HT-22 nerve cells (EC50 between 36 and 65 microM) from death triggered by glutamate while underivatized (-)-epicatechin was almost inactive (EC50=610 microM). Differences in free radical scavenging capacity (DPPH assay) could not account for the improvement in neuroprotective activity upon derivatization of (-)-epicatechin with thiols. Moreover, while the gallate-containing compounds are more efficient radical scavengers than their non-galloylated counterparts, they are only equally or less potent as neuroprotective agents. Although all of the conjugates were able to scavenge mitochondrially generated reactive oxygen species (ROS) inside the cells, the majority of their neuroprotective activity appeared to be dependent upon their ability to maintain glutathione levels. These results suggest that a mechanism other than ROS scavenging is involved in the neuroprotective action exerted by the epicatechin conjugates.     

Antioxidant activities of agaro-oligosaccharides with different degrees of polymerization in cell-based system

The aim of the present study was to evaluate the antioxidant activity of agaro-oligosaccharides with different degrees of polymerizations (DPs) and establish a relationship between the activity and DPs. The attenuate effect of oligosaccharides on 1,1-diphenyl-2-picryl-hydrazyl (DPPH(*)) was initially assessed, and the result indicated that agarohexaose showed the highest scavenging DPPH(*) capability (IC(50)=1.85 mg/ml). Following that, the intracellular antioxidant ability of agaro-oligosacharides was investigated by using the dichlorofluorescein (DCF) assay in human liver cell L-02 system. Different levels of antioxidant activities of agaro-oligosaccharides with various DPs were observed, and their scavenging reactive oxygen species (ROS) capability was associated with the improvement of the cell viability. In these oligosaccharides, agarohexaose possessed the highest scavenging capability, which could reduce 50% of oxidants generated by H(2)O(2) at 1 mg/ml. Furthermore, the antioxidant effect of agarohexaose on the indirect oxidation of cells induced by antimycin A (AA) was also tested. The results showed that agarohexaose could scavenge ROS generated by electron leakage and protect cells against apoptosis induced by ROS. It is concluded that agaro-oligosaccharides are generally considered as novel antioxidants which could protect cell damage caused by reactive oxygen species, especially agarohexaose exhibiting most desirable effects.     

Evaluation of antioxidant activity of leafy vegetables and beans with myoglobin method

Key message

Antioxidant activity of seven leafy vegetables and four beans against five reactive oxygen species and reactive nitrogen species was clearly characterized with a protocol using myoglobin as a reporter probe.

Abstract

Antioxidant activity of seven leafy vegetables and four beans against peroxyl radical, hydroxyl radical, hypochlorite ion, and peroxynitrite ion has been measured using myoglobin as a reporter probe (myoglobin method). Conventional DPPH method was also used to evaluate antioxidant activity of the samples. Difference of activity against different reactive oxygen species (ROS) and reactive nitrogen species (RNS) was characterized by plotting the data in a 5-axe cobweb chart. This plot clearly showed the characteristics of the antioxidant activity of the leafy vegetables and the beans. The samples examined in this work were categorized into four groups. (1) The samples showed high antioxidant activity against all ROS and RNS: daikon sprout, spinach, Qing-geng-cai, and onion. (2) The samples showed high antioxidant activity against peroxyl radical: red bean and soy bean. (3) The samples showed high antioxidant against hypochlorite ion: broccoli floret, cabbage, and Chinese cabbage. (4) The samples showed weak antioxidant activity against all ROS and RNS: cowpea and common beans. Our protocol is probably useful to characterize antioxidant activity of the crops of different cultivars, the crops obtained in different growing environments and growing seasons, the crops harvested at different age, and the crops stored in the different conditions, as well as the changes of activity during cooking process of the crops.     

Dipyrone and aminopyrine are effective scavengers of reactive nitrogen species

Reactive nitrogen species (RNS), namely nitric oxide (NO*) and peroxynitrite (ONOO-) are produced in the inflammatory sites and may contribute to the deleterious effects of inflammation. The aim of the present study was to evaluate the putative scavenging effect of a particular group of non-steroidal anti-inflammatory drugs (NSAIDs), the pyrazolone derivatives dipyrone, aminopyrine, isopropylantipyrine, and antipyrine against RNS, using in vitro non-cellular screening systems. The results obtained showed that dipyrone and aminopyrine were highly potent scavengers of NO* and ONOO- while antipyrine exerted little effect and isopropylantipyrine no effect whatsoever against these two RNS and that, in the presence of bicarbonate, the scavenging potencies of both dipyrone and aminopyrine were slightly decreased. It could thus be inferred that the observed scavenging effects may be of therapeutic benefit for patients under anti-inflammatory treatment with dipyrone and aminopyrine in the case of overproduction of RNS. On the other hand, the possible depletion of physiological NO* concentrations, namely at the gastrointestinal tract as well as the formation of reactive derivatives of aminopyrine and/or dipyrone, resulting from their reaction with RNS, may otherwise be harmful for these patients.