Quercetin 3-O-methyl ether protects FL83B cells from copper induced oxidative stress through the PI3K/Akt and MAPK/Erk pathway

Quercetin is a bioflavonoid that exhibits several biological functions in vitro and in vivo. Quercetin 3-O-methyl ether (Q3) is a natural product reported to have pharmaceutical activities, including antioxidative and anticancer activities. However, little is known about the mechanism by which it protects cells from oxidative stress. This study was designed to investigate the mechanisms by which Q3 protects against Cu^2 +-induced cytotoxicity. Exposure to Cu^2 + resulted in the death of mouse liver FL83B cells, characterized by apparent apoptotic features, including DNA fragmentation and increased nuclear condensation. Q3 markedly suppressed Cu^2 +-induced apoptosis and mitochondrial dysfunction, characterized by reduced mitochondrial membrane potential, caspase-3 activation, and PARP cleavage, in Cu^2 +-exposed cells. The involvement of PI3K, Akt, Erk, FOXO3A, and Mn-superoxide dismutase (MnSOD) was shown to be critical to the survival of Q3-treated FL83B cells. The liver of both larval and adult zebrafish showed severe damage after exposure to Cu^2 + at a concentration of 5 μM. Hepatic damage induced by Cu^2 + was reduced by cotreatment with Q3. Survival of Cu^2 +-exposed larval zebrafish was significantly increased by cotreatment with 15 μM Q3. Our results indicated that Cu^2 +-induced apoptosis in FL83B cells occurred via the generation of ROS, upregulation and phosphorylation of Erk, overexpression of 14-3-3, inactivation of Akt, and the downregulation of FOXO3A and MnSOD. Hence, these results also demonstrated that Q3 plays a protective role against oxidative damage in zebrafish liver and remarked the potential of Q3 to be used as an antioxidant for hepatocytes.     

In vitro and intracellular antioxidant capacity of thymyl methyl ether as a major component in Blumea lanceolaria (Roxb.) Druce leaf oil

Thymyl methyl ether is a major component of Blumea lanceolaria (Roxb.) Druce leaves. In this study, the antioxidant capacity of thymyl methyl ether and its better known hydroxylated form thymol was examined using oxygen radical absorption capacity and intracellular antioxidant capacity assays. Thymol displayed stronger peroxyl radical and hydroxyl radical-scavenging capacity, as well as reducing capacity than those of thymyl methyl ether, which can be explained by its hydrogen or electron donating capacity. However, thymyl methyl ether exhibited potent protection against peroxyl radical and Cu²⁺-induced oxidative stress when compared to thymol in the intracellular antioxidant capacity and lipid peroxidation assays using HepG2 cells. These results illustrate the higher cell membrane permeability of thymyl methyl ether to thymol and its transformation to thymol, which results in potent intracellular antioxidant capacity contributing to protection against lipid peroxidation.     

Differential hepatoprotective mechanisms of rutin and quercetin in CCl4-intoxicated BALB/cN mice

Aim:

To investigate the mechanisms underlying the protective effects of quercetin-rutinoside (rutin) and its aglycone quercetin against CCl₄-induced liver damage in mice.

Methods:

BALB/cN mice were intraperitoneally administered rutin (10, 50, and 150 mg/kg) or quercetin (50 mg/kg) once daily for 5 consecutive days, followed by the intraperitoneal injection of CCl₄ in olive oil (2 mL/kg, 10% v/v). The animals were sacrificed 24 h later. Blood was collected for measuring the activities of ALT and AST, and the liver was excised for assessing Cu/Zn superoxide dismutase (SOD) activity, GSH and protein concentrations and also for immunoblotting. Portions of the livers were used for histology and immunohistochemistry.

Results:

Pretreatment with rutin and, to a lesser extent, with quercetin significantly reduced the activity of plasma transaminases and improved the histological signs of acute liver damage in CCl₄-intoxicated mice. Quercetin prevented the decrease in Cu/Zn SOD activity in CCl₄-intoxicated mice more potently than rutin. However, it was less effective in the suppression of nitrotyrosine formation. Quercetin and, to a lesser extent, rutin attenuated the inflammation in the liver by down-regulating the CCl₄-induced activation of nuclear factor-kappa B (NF-κB), tumor necrosis factor-α (TNF-α) and cyclooxygenase (COX-2). The expression of inducible nitric oxide synthase (iNOS) was more potently suppressed by rutin than by quercetin. Treatment with both flavonoids significantly increased NF-E2-related factor 2 (Nrf2) and heme oxygenase (HO-1) expression in injured livers, although quercetin was less effective than rutin at an equivalent dose. Quercetin more potently suppressed the expression of transforming growth factor-β1 (TGF-β1) than rutin.

Conclusion:

Rutin exerts stronger protection against nitrosative stress and hepatocellular damage but has weaker antioxidant and anti-inflammatory activities and antifibrotic potential than quercetin, which may be attributed to the presence of a rutinoside moiety in position 3 of the C ring.     

Comparative study of quercetin and its two glycoside derivatives quercitrin and rutin against methylmercury (MeHg)-induced ROS production in rat brain slices

The hypothesis that methylmercury (MeHg) potently induces formation of reactive oxygen species (ROS) in the brain is supported by observations on the neuroprotective effects of various classes of antioxidants. Flavonoids have been reported to possess divalent metal chelating properties, antioxidant activities and to readily permeate the blood–brain barrier. They can also provide neuroprotection in a wide array of cellular and animal models of neurological diseases. Paradoxically, in vivo administration of quercetin displays unexpected synergistic neurotoxic effect with MeHg. Considering this controversy and the limited data on the interaction of MeHg with other flavonoids, the potential protective effect of quercetin and two of its glycoside analogs (i.e., rutin and quercitrin) against MeHg toxicity were evaluated in rat cortical brain slices. MeHg (100 μM) caused lipid peroxidation and ROS generation. Quercitrin (10 μg/mL) and quercetin (10 μg/mL) protected mitochondria from MeHg (5 μM)-induced changes. In contrast, rutin did not afford a significant protective effect against MeHg (100 μM)-induced lipid peroxidation and ROS production in cortical brain slices. MeHg-generated ROS in cortical slices was dependent upon an increase in intracellular Ca²⁺ levels, because the over-production of MeHg-induced H₂O₂ in mitochondria occurred with a concomitant increase in Ca²⁺ transient. Here, we have extended the characterization of mechanisms associated with the neuroprotective effects of quercetin against MeHg-induced toxicity in isolated mitochondria, by performing an array of parallel studies in brain slices. We provide novel data establishing that (1) Ca²⁺ plays a central role in MeHg toxicity and (2) in brain slices MeHg induces mitochondrial oxidative stress both via direct interaction with mitochondria (as previously reported in in vitro studies) as well as via mitochondria-independent (or indirect) mechanisms.     

Involvement of oxidative stress-induced ERK/JNK activation in the Cu(2+)/pyrrolidine dithiocarbamate complex-triggered mitochondria-regulated apoptosis in pancreatic β-cells

Oxidative stress was demonstrated to promote the progression of diabetes mellitus (DM). It has been suggested that copper may play a specific role in the progression and pathogenesis of DM. Pyrrolidine dithiocarbamate (PDTC), a widely apply to the medicine, was known to be capable of enhancing copper accumulation. In this study, we investigated the effect of submicromolar-concentration Cu²⁺/PDTC complex on pancreatic β-cell damage and evaluated the role of oxidative stress in this effect. CuCl₂ (0.01-300 μM) did not affect the cell viability in β-cell line RIN-m5F cells. However, combination of CuCl₂ (0.5 μM) and PDTC (0.3 μM) markedly reduced RIN-m5F cell viability. Cu²⁺/PDTC complex could also increase the LPO and decrease the intracellular reduced GSH levels, and display several features of apoptosis signals including: increase in sub-G1 cell population, annexin-V binding, and caspase-3 activity, mitochondrial dysfunctions, and the activation of PARP and caspase cascades, which accompanied with the marked increase the intracellular Cu²⁺ levels. These apoptotic-related responses of Cu²⁺/PDTC complex-induced could be effectively prevented by antioxidant N-acetylcysteine (NAC). Furthermore, Cu²⁺/PDTC complex was capable of increasing the phosphorylations of ERK1/2 and JNK, and its upstream kinase MEK1/2 and MKK4, which could be reversed by NAC. Transfection with ERK2- and JNK-specific si-RNA and specific inhibitors SP600125 and PD98059 could inhibit ERK1/2 and JNK activation and attenuate MMP loss and caspase-3 activity induced by the Cu²⁺/PDTC complex. Taken together, these results are the first report to demonstrate that the Cu²⁺/PDTC complex triggers a mitochondria-regulated apoptosis via an oxidative stress-induced ERK/JNK activation-related pathway in pancreatic β-cells.     

Low micromolar zinc exerts cytotoxic action under H2O2-induced oxidative stress: Excessive increase in intracellular Zn concentration

The ability of zinc to retard oxidative processes has been recognized for many years. However, zinc is cytotoxic under certain oxidative stress. In this study, we investigated the effect of H₂O₂ on intracellular Zn²⁺ concentration of rat thymocytes and its relation to the cytotoxicity. Experiments were cytometrically performed by the use of fluorescent probes, propidium iodide, FluoZin-3-AM, and 5-chloromethylfluorescein diacetate. ZnCl₂ potentiated cytotoxicity of H₂O₂ while TPEN, a chelator for intracellular Zn²⁺, attenuated it. Results suggested an involvement of intracellular Zn²⁺ in the cytotoxicity of H₂O₂. H₂O₂ at concentrations of 30 μM or more (up to 1000 μM) significantly increased intracellular Zn²⁺ concentration. There were two mechanisms. (1) H₂O₂ decreased cellular content of nonprotein thiols, possibly resulting in release of Zn²⁺ from thiols as cellular Zn²⁺ binding sites. (2) H₂O₂ increased membrane Zn²⁺ permeability because external ZnCl₂ application further elevated intracellular Zn²⁺ concentration. Micromolar H₂O₂ may induce excessive elevation of intracellular Zn²⁺ concentration that is harmful to cellular functions. However, the incubation with micromolar ZnCl₂ alone increased cellular content of nonprotein thiols, one of the factors protecting cells against oxidative stress. Though zinc is generally considered to be protective with its antioxidant property, this study reveals the toxic effect of zinc even in micromolar range under oxidative stress induced by H₂O₂.     

Diarylheptanoid 7-(3,4 dihydroxyphenyl)-5-hydroxy-1-phenyl-(1E)-1-heptene from Curcuma comosa Roxb. protects retinal pigment epithelial cells against oxidative stress-induced cell death

Chronic exposure to oxidative stress causes damage to retinal pigment epithelial cells which may lead to the development of age-related macular degeneration, the major cause of vision loss in humans. Anti-oxidants provide a natural defense against retinal cell damage. The present study was designed to evaluate the potential anti-oxidant activity and protective effect of two diarylheptanoids isolated from a medicinal herb Curcuma comosa; 7-(3,4 dihydroxyphenyl)-5-hydroxy-1-phenyl-(1E)-1-heptene (compound A), and 1,7-diphenyl-4(E),6(E)-heptadien-3-ol (compound B) against oxidative stress (H₂O₂)-induced human retinal pigment epithelial (APRE-19) cell death. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay indicated that the anti-oxidant activity (IC₅₀) of compound A was similar to that of vitamin C. Pre-treatment of ARPE-19 cells with 20 μM compound A for 4 h afforded greater protection against the insult from 500 μM H₂O₂, compared to a similar protection period for compound B. Compound A lowered H₂O₂-induced lipid peroxidation, malondialdehyde formation and intracellular reactive oxygen species. Furthermore, compound A ameliorated the H₂O₂-induced decrease in anti-oxidant enzyme activities and subsequent apoptotic cell death in ARPE-19 cells in a dose and time-dependent manner. These results suggest that compound A protects ARPE-19 cells against oxidative stress, in part, by enhancing several anti-oxidant defense mechanisms. Therefore, compound A may have therapeutic potential for diseases associated with oxidative stress, particularly degenerative retinal diseases.     

Quercetin inhibits hydrogen peroxide-induced DNA damage and enhances DNA repair in Caco-2 cells

Flavonoids are known to have antioxidant activity that may limit DNA damage and help prevent degenerative diseases, including cancer. However, our knowledge of flavonoids’ role in DNA protection/repair mechanism(s) is limited. This study investigated the effects of quercetin on DNA oxidation and DNA repair in Caco-2 cells with or without oxidant (H₂O₂) challenge. Quercetin (1, 100 μM) significantly reduced oxidative DNA damage, as measured by the number of single-strand breaks identified by single cell gel electrophoresis. Quercetin treatment also caused a measurable increase in the mRNA expression of human 8-oxoguanine DNA glycosylase (hOGG1) at 0 and 4 h after H₂O₂ treatment (measured using RT-PCR). In addition, the highest level of quercetin tested (100 μM) maintained hOGG1 expression at basal levels or higher for up to 12 h after H₂O₂ treatment, while oxidant treatment alone resulted in significant reduction of hOGG1 at 8 h. Our study indicates that quercetin could protect DNA both by reducing oxidative DNA damage and by enhancing DNA repair through modulation of DNA repair enzyme expression.     

Quercetin protects the hydrogen peroxide-induced apoptosis via inhibition of mitochondrial dysfunction in H9c2 cardiomyoblast cells

Quercetin possesses a broad range of pharmacological properties, including protection of LDL from oxidation. However, little is known about the mechanism by which quercetin rescues cardiomyoblasts from oxidative damage. This study was designed to investigate the protective mechanism of quercetin on H(2)O(2)-induced toxicity of H9c2 cardiomyoblasts. Oxidative stress, such as H(2)O(2), ZnCl(2), and menadione, significantly decreased the viability of H9c2 cells, which was accompanied with apparent apoptotic features, including fragmentation of genomic DNA as well as activation of caspase protease. However, quercetin markedly inhibited the apoptotic characteristics via reduction of intracellular reactive oxygen species generation. Also, it prevented the H(2)O(2)-mediated mitochondrial dysfunction, including disruption of mitochondria membrane permeability transition as well as an increase in expression of apoptogenic Bcl-2 proteins, Bcl-2 and Bcl-X(L). Furthermore, pretreatment of quercetin inhibited the activation of caspase-3, thereby both cleavage of poly(ADP-ribose) polymerase and degradation of inhibitor of caspase-activated DNase/DNA fragmentation factor by H(2)O(2) were completely abolished. Taken together, these data suggest that protective effects of quercetin against oxidative injuries of H9c2 cardiomyoblasts may be achieved via modulation of mitochondrial dysfunction and inhibition of caspase activity.     

Thioredoxin-albumin fusion protein prevents copper enhanced zinc-induced neurotoxicity via its antioxidative activity

Zinc (Zn) is a co-factor for a vast number of enzymes, and functions as a regulator for immune mechanism and protein synthesis. However, excessive Zn release induced in pathological situations such as stroke or transient global ischemia is toxic. Previously, we demonstrated that the interaction of Zn and copper (Cu) is involved in the pathogenesis of Alzheimer’s disease and vascular dementia. Furthermore, oxidative stress has been shown to play a significant role in the pathogenesis of various metal ions induced neuronal death. Thioredoxin-Albumin fusion (HSA-Trx) is a derivative of thioredoxin (Trx), an antioxidative protein, with improved plasma retention and stability of Trx. In this study, we examined the effect of HSA-Trx on Cu²⁺/Zn²⁺-induced neurotoxicity. Firstly, HSA-Trx was found to clearly suppress Cu²⁺/Zn²⁺-induced neuronal cell death in mouse hypothalamic neuronal cells (GT1-7 cells). Moreover, HSA-Trx markedly suppressed Cu²⁺/Zn²⁺-induced ROS production and the expression of oxidative stress related genes, such as heme oxygenase-1. In contrast, HSA-Trx did not affect the intracellular levels of both Cu²⁺ and Zn²⁺ after Cu²⁺/Zn²⁺ treatment. Finally, HSA-Trx was found to significantly suppress endoplasmic reticulum (ER) stress response induced by Cu²⁺/Zn²⁺ treatment in a dose dependent manner. These results suggest that HSA-Trx counteracted Cu²⁺/Zn²⁺-induced neurotoxicity by suppressing the production of ROS via interfering the related gene expressions, in addition to the highly possible radical scavenging activity of the fusion protein. Based on these findings, HSA-Trx has great potential as a promising therapeutic agent for the treatment of refractory neurological diseases.     

Genetic toxicology evaluation of essential oil of Alpinia zerumbet and its chemoprotective effects against H2O2-induced DNA damage in cultured human leukocytes

Essential oil (EO) of Alpinia zerumbet leaves, at non-toxic concentrations (50–300 μg/mL), did not induce genotoxicity in human leukocytes. However, at the highest concentration (500 μg/mL) tested caused a reduction in cell proliferation and viability, and an increase in DNA damage. Moreover, in vivo experiments showed that EO (400 mg/kg) did not exert mutagenicity on peripheral blood cells and bone marrow in mice. In DPPH test, EO showed scavenging effects against DPPH radicals, and other free radicals (determination of intracellular GSH and lipid peroxidation assays). Furthermore, EO was able to reduce the intracellular levels of ROS, and prevented leukocytes DNA against oxidative damage. The ability of EO to reduce H₂O₂ toxicity was observed only when cells were treated with EO during and after exposure to H₂O₂. With the co- and post-treatment procedures, EO decreased the frequency of apoptotic and micronucleated leukocytes as well DNA strand breaks. However, a synergistic effect was observed in cultures exposed to 500 μg/mL EO. In conclusion, EO at concentrations up to 300 μg/mL or doses up to 400 mg/kg are not mutagenic in leukocytes and in mice, but do have antioxidative and protective effects against the cytotoxicity and clastogenesis induced by H₂O₂.     

Dietary quercetin exacerbates the development of estrogen-induced breast tumors in female ACI rats

Phytoestrogens are plant compounds that structurally mimic the endogenous estrogen 17β-estradiol (E₂). Despite intense investigation, the net effect of phytoestrogen exposure on the breast remains unclear. The objective of the current study was to examine the effects of quercetin on E₂-induced breast cancer in vivo. Female ACI rats were given quercetin (2.5 g/kg food) for 8 months. Animals were monitored weekly for palpable tumors, and at the end of the experiment, rats were euthanized, breast tumor and different tissues excised so that they could be examined for histopathologic changes, estrogen metabolic activity and oxidant stress. Quercetin alone did not induce mammary tumors in female ACI rats. However, in rats implanted with E₂ pellets, co-exposure to quercetin did not protect rats from E₂-induced breast tumor development with 100% of the animals developing breast tumors within 8 months of treatment. No changes in serum quercetin levels were observed in quercetin and quercetin + E₂-treated groups at the end of the experiment. Tumor latency was significantly decreased among rats from the quercetin + E₂ group relative to those in the E₂ group. Catechol-O-methyltransferase (COMT) activity was significantly downregulated in quercetin-exposed mammary tissue. Analysis of 8-isoprostane F_2α (8-iso-PGF_2α) levels as a marker of oxidant stress showed that quercetin did not decrease E₂-induced oxidant stress. These results indicate that quercetin (2.5 g/kg food) does not confer protection against breast cancer, does not inhibit E₂-induced oxidant stress and may exacerbate breast carcinogenesis in E₂-treated ACI rats. Inhibition of COMT activity by quercetin may expose breast cells chronically to E₂ and catechol estrogens. This would permit longer exposure times to the carcinogenic metabolites of E₂ and chronic exposure to oxidant stress as a result of metabolic redox cycling to estrogen metabolites, and thus quercetin may exacerbate E₂-induced breast tumors in female ACI rats.     

Protective effect of quercetin in gentamicin-induced oxidative stress in vitro and in vivo in blood cells. Effect on gentamicin antimicrobial activity

We have evaluated the effect of gentamicin and gentamicin plus quercetin on ROS production, endogenous antioxidant defenses (SOD and CAT) and lipid peroxidation in vitro on human leukocytes and in vivo on whole rat blood. Gentamicin generated ROS production in human leukocytes, produced a dual effect on both enzymes dosage-dependent and generated an increase in lipid peroxidation. Quercetin, in leukocytes stimulated by gentamicin, showed more inhibitory capacity in ROS production than the reference inhibitor (vitamin C) in mononuclear cells and a similar protective behavior at this inhibitor in polymorphonuclear cells. Quercetin, in both cellular systems, tend to level SOD and CAT activities, reaching basal values and could prevent lipidic peroxidation induced by gentamicin. The results in Wistar rats confirmed that therapeutic doses of gentamicin can induce oxidative stress in whole blood and that the gentamicin treatment plus quercetin can suppress ROS generation, collaborate with SOD and CAT and diminish lipid peroxidation. Finally, flavonoid and antibiotic association was evaluated on the antimicrobial activity in S. aureus and E. coli, showing that changes were not generated in the antibacterial activity of gentamicin against E. coli strains, while for strains of S. aureus a beneficial effect observes. Therefore, we have demonstrated that gentamicin could induce oxidative stress in human leukocytes and in whole blood of Wistar rats at therapeutic doses and that quercetin may to produce a protective effect on this oxidative stress generated without substantially modifying the antibacterial activity of gentamicin against E. coli strains, and it contributes to this activity against S. aureus strains.     

Protective effect of Mutellina purpurea polyphenolic compounds in doxorubicin-induced toxicity in H9c2 cardiomyocytes

The delayed cardiomyopathy caused by doxorubicin – an chemotherapeutic drug with broad spectrum of anticancer activity – is mainly triggered by oxidative stress. The aim of this study was to assess an effect of Mutellina purpurea methanolic extract fraction and other antioxidants of plant origin: rutin, quercetin and chlorogenic acid (all 1?mg% w/v) on oxidative stress and morphological changes induced by doxorubicin in cardiomyocytes H9c2. Mitochondrial oxidative stress in cardiomyocytes induced by 1?µM doxorubicin was evidenced by MitoTracker and RedoxSensor Red CC-1 dyes. Moreover, cardiomyocytes morphological changes and cell viability were evaluated. The tested fraction slightly reduced mitochondrial ROS fluorescence, similar to quercetin. Chlorogenic acid revealed concentration dependent prooxidative and antioxidative properties in the applied H9c2 model. The evaluation of the protective effect of tested compounds on doxorubicin-induced cytotoxicity was based on the examination of induced oxidative stress and morphology changes. The protective effect was described in the following order: rutin?>?chlorogenic acid (0.5?µM)?>?LH8 and quercetin. According to the MTT test, rutin seems to be the most promising compound that should be tested in a future studies.     

Liv.52 attenuate copper induced toxicity by inhibiting glutathione depletion and increased antioxidant enzyme activity in HepG2 cells

Altered copper metabolism plays a pivotal role in the onset of several hepatic disorders and glutathione (GSH) plays an important role in its homeostasis. Hepatic diseases are often implicated with decreased content of intracellular GSH. GSH depleted cells are prone to increased oxidative damage eventually leading to its death. Liv.52 is used to treat hepatic ailments since long time. Hence, in the present study the potential cytoprotective effect of Liv.52 against toxicity induced by copper (Cu²⁺) was evaluated in HepG2 cells. Cu²⁺ at 750 μM induced cytotoxicity to HepG2 cells as determined by MTT assay. The toxicity was brought about by increased lipid peroxidation, DNA fragmentation and decreased GSH content. But, upon treatment with Liv.52 cell death induced by Cu²⁺ was significantly abrogated by inhibition of lipid peroxidation by 58% and DNA fragmentation by 37%. Liv.52 increased the GSH content by 74%. Activities of the antioxidant enzymes catalase, glutathione peroxidase and superoxide dismutase were increased by 46%, 22% and 81% respectively in Liv.52 treated cells. Thus, it is apparent from these results that Liv.52 abrogates Cu²⁺ induced cytotoxicity in HepG2 cells by inhibiting lipid peroxidation and increased GSH content and antioxidant enzyme activity.     

Cardioprotective and Cardiotoxic Effects of Quercetin and Two of Its In Vivo Metabolites on Differentiated H9c2 Cardiomyocytes

Whilst mitotic rat embryonic cardiomyoblast‐derived H9c2 cells have been widely used as a model system to study the protective mechanisms associated with flavonoids, they are not fully differentiated cardiac cells. Hence, the aim of this study was to investigate the cardioprotective and cardiotoxic actions of quercetin and two of its major in vivo metabolites, quercetin 3‐glucuronide and 3′‐O‐methyl quercetin, using differentiated H9c2 cells. The differentiated cardiomyocyte‐like phenotype was confirmed by monitoring expression of cardiac troponin 1 after 7 days of culture in reduced serum medium containing 10 nM all‐trans retinoic acid. Quercetin‐induced cardiotoxicity was assessed by monitoring MTT reduction, lactate dehydrogenase (LDH) release, caspase 3 activity and reactive oxygen species production after prolonged flavonoid exposure (72 hr). Cardiotoxicity was observed with quercetin and 3′‐O‐methyl quercetin, but not quercetin 3‐glucuronide. Cardioprotection was assessed by pre‐treating differentiated H9c2 cells with quercetin or its metabolites for 24 hr prior to 2‐hr exposure to 600 μM H₂O_2, after which oxidative stress‐induced cell damage was assessed by measuring MTT reduction and LDH release. Cardioprotection was observed with quercetin and 3′‐O‐methyl quercetin, but not with quercetin 3‐glucuronide. Quercetin attenuated H₂O₂‐induced activation of ERK1/2, PKB, p38 MAPK and JNK, but inhibitors of these kinases did not modulate quercetin‐induced protection or H₂O₂‐induced cell death. In summary, quercetin triggers cardioprotection against oxidative stress‐induced cell death and cardiotoxicity after prolonged exposure. Further studies are required to investigate the complex interplay between the numerous signalling pathways that are modulated by quercetin and which may contribute to the cardioprotective and cardiotoxic effects of this important flavonoid.     

An in Vitro. Comparative Study on the Antioxidant Activity and Determination of Antibacterial Potential of Atorvastatin and Simvastatin

Abstract

Free radicals generated from oxidative stress (OS) have been depicted in the causation of cancerous and noncancerous diseases in humans. Increase in fat content of the body may favor the deleterious effect of free radical attack. The generation of free radicals is enhanced in respiratory burst during bacterial infection. The level of plasma membrane cholesterol appears to be critical in the regulation of microbial entry, intracellular trafficking, and exit. The current study was designed to compare the in vitro. antibacterial and antioxidant activities of hypocholesterolemic drugs atorvastatin and simvastatin. Agar-well diffusion assay was used to screen the antibacterial activity using Gram-positive and Gram-negative bacterial strains. Antioxidant activity was evaluated using Fe²⁺-induced lipid peroxidation inhibiting activity in whole rat liver homogenate and Fe³⁺ reducing activity using ferric-reducing antioxidant power (FRAP) assay. Atorvastatin and simvastatin inhibited the growth of all bacterial strains tested. The zone of inhibition produced by atorvastatin is higher than that of simvastatin. However, antioxidant activities of simvastatin were higher than those of atorvastatin. The exhibited pleiotropic activities of these statins suggest their clinical advantages against bacterial infection and oxidative stress–induced human ailments apart from their wide use for hypolipidemic effects.     

Ferrocenyl chalcones: antioxidants or prooxidants in radical-induced oxidation of DNA?

The effects of ferrocenyl chalcones including 1-acetyl-1′-(m-methoxy-p-hydroxycinnamoyl)ferrocene (AVF), 1,1′-di(m-methoxy-p-hydroxycinnamoyl)ferrocene (DVF), and 1-acetyl-1′-(m, p-dihydroxycinnamoyl)ferrocene (APF) on the oxidative damage of DNA were explored when glutathione (GSH) and Cu²⁺, hydroxyl radical (^?OH), and 2,2′-azobis(2-amidinopropanehydrochloride) (AAPH) acted as the oxidation-initiators. These ferrocenyl chalcones functioned as prooxidants in Cu²⁺/GSH- and ^?OH-induced oxidations of DNA. Ferrocene itself promoted AAPH-induced oxidative damage of DNA, and 1,1′-dicinnamoylferrocene (DCF) showed very weak inhibitive effect on AAPH-induced oxidation of DNA. On the other hand, APF, DVF, and AVF were able to trap 5.3, 5.5, and 5.7 radicals, respectively, in protecting DNA against AAPH-induced oxidation. Therefore, ferrocenyl chalcones were effective antioxidants to protect DNA against peroxyl radical-induced oxidation.     

YS 51, 1-(beta-naphtylmethyl)-6,7-dihydroxy-1,2,3,4,-tetrahydroisoquinoline, protects endothelial cells against hydrogen peroxide-induced injury via carbon monoxide derived from heme oxygenase-1

Oxidative stress plays an important role in the pathophysiology of several vascular diseases such as atherosclerosis, and great attention has been placed on the protective role of heme oxygenase-1 (HO-1) for vasculature against oxidant-induced injury. We tested whether the protective effects of YS 51, 1-(β-naphtyl-methyl)-6,7-dihydroxy-1,2,3,4,-tetrahydroisoquinoline, against hydrogen peroxide (H₂O₂)-induced cell injury is associated with HO-1 activity in bovine aortic endothelial cells (BAEC). YS 51 increased HO-1 expression and activity in concentration-dependent manners (10-100 μM) and time-dependent manners (1, 3, 6, 18 h), which were correlated well with its protective effect against H₂O₂-induced injury. Zinc protoporphyrin IX (ZnPP IX), a HO inhibitor, significantly inhibited the effect of YS 51 (50 μM). In contrast, [Ru(CO)₃(Cl)₂]₂ (CORM-2, a CO releasing molecule) but not bilirubin protected against H₂O₂-induced injury. Oxyhemoglobin (HbO₂) used as a CO scavenger significantly inhibited the protective effect of both YS 51 and CORM-2. Furthermore, both YS 51 and CORM-2 significantly reduced H₂O₂-induced intracellular reactive oxygen species (ROS) production; however, this was counteracted by ZnPP IX, HbO₂ and deferoxamine. We found evidence for the involvement of PI3/Akt kinase and ERK1/2 pathways in HO-1 induction by YS-51. Taken together, we conclude that CO is, at least, responsible for the YS 51-mediated protective action of endothelial cells against oxidant stress via HO-1 gene induction, involving the activation of the PI3/Akt and ERK1/2 kinase pathways. Thus, YS 51 may be useful in oxidative stress-induced vascular disorders.     

The dietary antioxidants resveratrol and quercetin protect cells from exogenous pro-oxidative damage.

In the colorectal epithelium oxidative stress is observed endogenously in premalignant adenoma cells or induced by nutritional factors like fatty acid hydroperoxides (LOOH). Bioactive phenols like resveratrol and quercetin can quench reactive oxygen species and protect from pro-oxidative damage. Our study used colorectal adenoma and carcinoma cell lines to assess antioxidant protective effects of resveratrol and quercetin. It demonstrated that both compounds efficiently protect from oxidative stress induced by LOOH. Effective concentrations (10 microM resveratrol and 1 microM quercetin) can easily be reached in the intestinal lumen after consumption of plant foods or food supplements. Both compounds prevent LOOH-induced formation of intracellular H2O2, stimulation of cyclooxygenase-2 and vascular endothelial growth factor. For reduction of endogenous H2O2 levels in colorectal tumor cells higher antioxidant-concentrations are needed in all cell lines. Quercetin (10 microM) alone even increased H2O2 in LT97 adenoma cells and stimulated VEGF production. Resveratrol and quercetin also induced 10-30% and 40-60% cell loss respectively by apoptosis. In summary, this indicates that resveratrol and quercetin have little protective capacity in absence of exogenous stress. They are however highly efficient in protecting against nutrition induced oxidative stress damage suggesting that this constitutes the major part of their tumor protective activity.