Phenolic compounds protect HepG2 cells from oxidative damage: relevance of glutathione levels

Rice protein improves oxidative stress by regulating glutathione metabolism and attenuating oxidative damage to lipids and proteins in rats

AIMS

To evaluate the effects of rice protein (RP) on glutathione metabolism and oxidative damage.

MAIN METHODS

Seven-week-old male Wistar rats were fed diets containing casein and RP without cholesterol for 3weeks. Plasma and liver lipid levels, hepatic accumulation of total glutathione (T-GSH), oxidized glutathione (GSSG), reduced glutathione (GSH), malondialdehyde (MDA) and protein carbonyl (PCO) were measured. In the liver, the total antioxidative capacity (T-AOC), mRNA levels of glutamate cysteine ligase catalytic subunit (GCLC) and glutamate cysteine ligase modulatory subunit (GCLM), and the activities of hepatic catalase (CAT), total superoxide dismutase (T-SOD), γ-glutamylcysteine synthetase (γ-GCS), glutathione S-transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GSHPx) were also measured.

KEY FINDINGS

T-AOC, GCLC and GCLM mRNA levels, antioxidative enzyme activities (T-SOD and CAT) and glutathione metabolism related enzyme activities (γ-GCS, GST, GR and GSHPx) were effectively stimulated by RP feeding compared to casein, and RP significantly reduced the hepatic accumulation of MDA and PCO in rats. These results indicate that lipid-lowering activity was induced by RP feeding.

SIGNIFICANCE

The present study demonstrates that RP improves oxidative stress primarily through enzymatic and non-enzymatic antioxidative defense mechanisms, reflected by enhancing the antioxidative status and attenuating the oxidative damage to lipids and proteins. These results suggest that RP can prevent hyperlipidemia in part through modifying glutathione metabolism, and sulfur amino acids may be the main modulator of this antioxidative mechanism.

Processed Panax ginseng, Sun Ginseng, Decreases Oxidative Damage Induced by tert-butyl Hydroperoxide via Regulation of Antioxidant Enzyme and Anti-apoptotic Molecules in HepG2 Cells

Potential antioxidant effect of processed ginseng (sun ginseng, SG) on oxidative stress generated by tert-butyl hydroperoxide (t-BHP) was investigated in HepG2 cells. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and lactate dehydrogenase (LDH) leakage test demonstrated that SG dose-dependently prevents a loss of cell viability against t-BHP-induced oxidative stress. Also, SG treatment dose-dependently relieved the increment of activities of hepatic enzymes, such as aspartate aminotrasferase and alanine aminotransferase, and lipid peroxidation mediated by t-BHP treatment in HepG2 cells. SG increased the gene expression of antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. However, high dose of SG treatment caused decrease in mRNA level of glutathione peroxidase as compared to low dosage of SG-treated cells. The gene expression of glutathione reductase was found to be slightly increased by SG treatment. In addition, SG extract attributed its hepaprotective effect by inducing the mRNA level of bcl-2 and bcl-xL but reducing that of bax. But, the gene expression of bad showed no significant change in SG-treated HepG2 cells. These findings suggest that SG has hepatoprotective effect by showing reduction of LDH release, activities of hepatic enzymes and lipid peroxidation and regulating the gene expression of antioxidant enzymes and apoptosis-related molecules against oxdative stress caused by t-BHP in HepG2 cells.

Protective effect of caffeic acid on paclitaxel induced anti-proliferation and apoptosis of lung cancer cells involves NF-κB pathway

Caffeic acid (CA), a natural phenolic compound, is abundant in medicinal plants. CA possesses multiple biological effects such as anti-bacterial and anti-cancer growth. CA was also reported to induce fore stomach and kidney tumors in a mouse model. Here we used two human lung cancer cell lines, A549 and H1299, to clarify the role of CA in cancer cell proliferation. The growth assay showed that CA moderately promoted the proliferation of the lung cancer cells. Furthermore, pre-treatment of CA rescues the proliferation inhibition induced by a sub-IC₅₀ dose of paclitaxel (PTX), an anticancer drug. Western blot showed that CA up-regulated the pro-survival proteins survivin and Bcl-2, the down-stream targets of NF-κB. This is consistent with the observation that CA induced nuclear translocation of NF-κB p65. Our study suggested that the pro-survival effect of CA on PTX-treated lung cancer cells is mediated through a NF-κB signaling pathway. This may provide mechanistic insights into the chemoresistance of cancer calls.

Keratin-based peptide: biological evaluation and strengthening properties on relaxed hair

A peptide based on a fragment of hair keratin type II cuticular protein, keratin peptide (KP), was studied as a possible strengthening agent for weakened relaxed hair. The peptide was prepared both in aqueous water formulation (WF) and organic solvent formulations (OF), to determine the effect of organic solvents on peptide interaction with hair and the differences in hair recovery. Both peptide formulations were shown to improve mechanical and thermal properties of weakened hair with peptide in OF showing the stronger effect. As a potential new hair care product, and so would necessitate contact with skin, the cytotoxicity and genotoxicity of the peptide were also evaluated through different methodologies (Alamar Blue assay, 2'-7'-dichlorofluorescein probe, cell morphology and growth and evaluation of DNA damage by an alkaline version of the comet assay) in skin fibroblasts. These tests are indicators of the potential of peptide to cause irritation on skin or to be carcinogenic, respectively. The peptide in WF did not cause cytotoxicity or genotoxicity in any of the concentrations tested. The presence of OF, however, induced a 20% decrease in cell viability in all of the range of concentrations used after 72-h incubation. Moreover, OF inhibited cell growth and was considered genotoxic at first contact with cells. The peptide was therefore considered a promising strengthening agent for hair and was shown to be innocuous when applied in WF.

Natural polyphenols may ameliorate damage induced by copper overload

The effect of the simultaneous exposure to transition metals and natural antioxidants frequently present in food is a question that needs further investigation. We aimed to explore the possible use of the natural polyphenols caffeic acid (CA), resveratrol (RES) and curcumin (CUR) to prevent damages induced by copper-overload on cellular molecules in HepG2 and A-549 human cells in culture. Exposure to 100μM/24h copper (Cu) caused extensive pro-oxidative damage evidenced by increased TBARS, protein carbonyls and nitrite productions in both cell types. Damage was aggravated by simultaneous incubation with 100μM of CA or RES, and it was also reflected in a decrease on cellular viability explored by trypan blue dye exclusion test and LDH leakage. Co-incubation with CUR produced opposite effects demonstrating a protective action which restored the level of biomarkers and cellular viability almost to control values. Thus, while CA and RES might aggravate the oxidative/nitrative damage of Cu, CUR should be considered as a putative protective agent. These results could stimulate further research on the possible use of natural polyphenols as neutralizing substances against the transition metal over-exposure in specific populations such as professional agrochemical sprayers and women using Cu-intrauterine devices.

Protective Effects of Emodin and Chrysophanol Isolated from Marine Fungus Aspergillus sp. on Ethanol-Induced Toxicity in HepG2/CYP2E1 Cells

Alcohol-induced liver injury progresses from fatty infiltration followed by a harmful cause of inflammation leading to an irreversible damage. In this study, two compounds (emodin and chrysophanol) isolated from marine fungus Aspergillus sp. were examined for their protective effects against ethanol-induced toxicity in vitro. Ethanol-induced HepG2/CYP2E1 cells were treated with the compounds at various concentrations, and the results showed that there was a dose-dependent decrease of gamma-glutamyl transpeptidase (GGT) activity and increase of glutathione (GSH) in the culture media with an increase in cell viability. Furthermore, the protective effects of the compounds were evaluated by protein expression levels of GGT, GSH, and CYP2E1 using Western blot. Among the compounds, emodin addressed to the ethanol-induced cytotoxicity more effectively compared to the chrysophanol. It could be suggested that emodin isolated from this genus would be a potential candidate for attenuating ethanol induced liver damage for further industrial applications such as functional food and pharmaceutical developments.

Pro- and anti-oxidant effects of polyunsaturated fatty acid supplementation in HepG2 cells

PUFA are bioactive nutrients thought to be effective in the prevention of many chronic diseases. PUFA susceptibility to free radical oxidation represents the other side of the coin, and the role of PUFA as pro- or anti-oxidants is still an unanswered question. In this study we supplemented HepG2 cells with different PUFA, and observed different effects on cytotoxicity, oxidation and modulation of antioxidant defenses. These were not simply related to the length of carbon chain, or to the number and position of double bonds. ARA supply evidenced the induction of oxidative damage, while DHA supplemented cells appeared richer in antioxidant defenses. To our knowledge, our study is the first evidencing the different pro- or anti-oxidant effect of different fatty acids when supplemented to cells. Overall, this points out the importance of not generalizing dietary recommendations considering PUFA as one category, but to extend them to the individual fatty acids.

Antioxidant and antigenotoxic effects of rosemary (Rosmarinus officinalis L.) extracts in Salmonella typhimurium TA98 and HepG2 cells

In the present study the chemopreventive effects of water soluble AquaROX(®) 15 and oil soluble VivOX(®) 40 rosemary extracts against 4-nitroquinoline-N-oxide (NQNO) and 2-amino-3-methyl-3H-imidazo[4,5-F]quinoline (IQ) induced mutagenicity in the reverse mutation assays with Salmonella typhimurium TA98 and against t-butyl hydroperoxide (t-BOOH), benzo(a)pyrene (BaP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced DNA damage in HepG2 cells were studied, applying the comet assay. The results showed comparable protective effect of AquaROX and VivOX against oxidative DNA damage, whereas protection against indirect active genotoxic carcinogens was more efficient by VivOX.

Alkyl hydroxytyrosyl ethers show protective effects against oxidative stress in HepG2 cells

Alkyl hydroxytyrosyl ethers (methyl, ethyl, propyl, and butyl ethers) have been synthesized from hydroxytyrosol (HTy) in response to the increasing food industry demand of new lipophilic antioxidants. Having confirmed that these compounds reach portal blood partially unconjugated and thus are effectively absorbed, their potential antioxidant activity was evaluated in the human hepatocarcinoma cell line (HepG2). The effects of 0.5-10 μM alkyl hydroxytyrosyl ethers on HepG2 cell integrity and redox status were assessed as well as the protective effect against oxidative stress induced by tert-butylhydroperoxide (t-BOOH). Cell viability (Crystal violet) and cell proliferation (BrdU assay) were measured as markers of cell integrity, concentration of reduced glutathione (GSH), generation of reactive oxygen species (ROS), and activity of antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR) as markers of redox status and determination of malondialdehyde (MDA) as a marker of lipid peroxidation. Direct treatment of HepG2 with alkyl hydroxytyrosyl ethers induced slight changes in cellular intrinsic antioxidants status, reducing ROS generation and inducing changes in GPx and GR activities. Pretreatment of HepG2 cells with alkyl hydroxytyrosyl ethers counteracted cell damage induced by t-BOOH, partially after 2 h and completely after 20 h, by increasing GSH and decreasing ROS generation, MDA levels, and antioxidant enzyme (GPx and GR) activity. According to these results the alkyl hydroxytyrosyl ethers show clear protective effects against oxidative stress, related to their lipophilic nature, that are similar to or even higher than those of their precursor, HTy.

Medicinal effects of peptides from marine microalgae

Nowadays, there are numerous commercial applications of microalgae, and they have been used to enhance the nutritional value of food and animal feed owing to their chemical composition. They are cultivated as a source of highly nutritional and valuable source. Recently, microalgae have been reported to use as a potent source for food additive, nutraceutical, or pharmaceuticals. According to the criteria of nutritional quality and cost, variety of marine organisms has been investigated for their suitability to be applied in the production of protein hydrolysates in functional foods. Recently, a great deal of interest has been expressed regarding marine-derived bioactive peptides because of their numerous health benefits. In addition, many studies have been reported that marine bioactive peptides can be used as functional foods, nutraceuticals, or pharmaceuticals due to their therapeutic potential in the treatment or prevention of various diseases. Hence, in this chapter, we discussed the importance of marine microalgae in relation to their medicinal value.

The anti-apoptotic action of 5-hydroxyindole: protection of mitochondrial integrity

5-Hydroxyindole (5HI), a metabolite of tryptophan, is involved in learning and memory, central neuron system regulation, and anti-oxidant activity. However, its protective action in mitochondrial function is not clear. Here, we tested whether 5HI protects against tert-butylhydroperoxide (t-BHP)-induced oxidative damage and mitochondrial dysfunction in human fibroblast cells. 5HI significantly suppressed t-BHP-induced cytotoxicity as determined by intracellular reactive species generation, lipid peroxidation, glutathione depletion, and peroxynitrite (ONOO(-)) generation. In addition, 5HI reduced t-BHP-induced DNA condensation. Pretreatment with 5HI significantly restored mitochondrial membrane potential (Deltapsim), suggesting that it protected cells against t-BHP-induced apoptosis. Western blot analysis also revealed that 5HI markedly inhibited cytochrome c release and caspase-3 activation, but not caspase-9 activation. Our data suggest that 5HI protects cells by attenuating oxidative stress and consequently protects against mitochondrial dysfunction.

Protective effects of ursolic acid and luteolin against oxidative DNA damage include enhancement of DNA repair in Caco-2 cells

Consumption of fruits and vegetables is associated with a reduced risk of developing a wide range of cancers including colon cancer. In this study, we evaluated the effects of two compounds present in fruits and vegetables, ursolic acid, a triterpenoid, and luteolin, a flavonoid, on DNA protection and DNA repair in Caco-2 cells using the comet assay. Ursolic acid and luteolin showed a protective effect against H(2)O(2)-induced DNA damage. Repair rate (rejoining of strand breaks) after treatment with H(2)O(2) was increased by pre-treatment of Caco-2 cells for 24h with ursolic acid or luteolin. To evaluate effects on induction of base oxidation, we exposed cells to the photosensitizer Ro 19-8022 plus visible light to induce 8-oxoguanine. Luteolin protected against this damage in Caco-2 cells after a short period of incubation. We also measured the incision activity of a cell extract from Caco-2 cells treated for 24h with test compounds, on a DNA substrate containing specific damage (8-oxoGua), to evaluate effects on base excision repair activity. Preincubation for 24h with ursolic acid enhanced incision activity in Caco-2 cells. In conclusion, we demonstrated for the first time that ursolic acid and luteolin not only protect DNA from oxidative damage but also increase repair activity in Caco-2 cells. These effects of ursolic acid and luteolin may contribute to their anti-carcinogenic effects.

Protective mechanism of quercetin and rutin on 2,2'-azobis(2-amidinopropane)dihydrochloride or Cu2+-induced oxidative stress in HepG2 cells

Protective effects of quercetin and rutin against oxidative stress were evaluated using in vitro and intracellular antioxidant assay. Quercetin showed higher peroxyl and hydroxyl radical-scavenging activity in a dose-dependent manner than did rutin in oxygen-radical absorbance capacity (ORAC). At 10 and 100 μM, quercetin had higher metal-chelating activity than rutin carrying rutinose at position C-3 and was also more efficient than rutin in reducing intracellular oxidative stress caused by peroxyl radicals and Cu(2+). The protective activities of 10 and 100 μM quercetin against Cu(2+)-induced intracellular oxidation were 13.8% and 44.8%, respectively. Rutin showed no protective activity against Cu(2+)-induced oxidative stress. Quercetin showed significantly lower intracellular Cu(2+)-chelating activity than did 1,10-phenanthroline but offered greater protection from Cu(2+)-induced oxidative stress. Thus, quercetin may diffuse through the cell membrane more efficiently than rutin because quercetin does not carry rutinose, is hydrophilic, and reduces Cu(2+)-induced oxidative stress by scavenging radicals instead of chelating with metal ions.

Effects of Melissa officinalis L. on oxidative status and DNA damage in subjects exposed to long-term low-dose ionizing radiation

The aim of this study was to determine the capability of Melissa officinalis L. (Lemon balm) infusion on improvement of oxidative stress status in radiology staff that were exposed to persistent low-dose radiation during work. The study was a before-after clinical trial performed on 55 radiology staff. They were asked to drink Lemon balm infusion which was prepared like a tea bag twice daily (1.5 g/100 mL) for 30 days. In the plasma, lipid peroxidation, DNA damage, catalase, superoxide dismutase, myeloperoxidase, and glutathione peroxidase activity were measured before and after using Lemon balm infusion.Use of Lemon balm infusion in radiology unit workers resulted in a significant improvement in plasma levels of catalase, superoxide dismutase, and glutathione peroxidase and a marked reduction in plasma DNA damage, myeloperoxidase, and lipid peroxidation. It is concluded that infusion of Lemon balm markedly improve oxidative stress condition and DNA damage in radiology staff when used as a dietary supplement for radiation protection.

Polyphenolic compounds from Salvia species protect cellular DNA from oxidation and stimulate DNA repair in cultured human cells

DNA damage can lead to carcinogenesis if replication proceeds without proper repair. This study evaluated the effects of the water extracts of three Salvia sp., Salvia officinalis (SO), Salvia fruticosa (SF), and Salvia lavandulifolia (SL), and of the major phenolic constituents, rosmarinic acid (RA) and luteolin-7-glucoside (L-7-G), on DNA protection in Caco-2 and HeLa cells exposed to oxidative agents and on DNA repair in Caco-2 cells. The comet assay was used to measure DNA damage and repair capacity. The final concentration of each sage extract was 50 microg/mL, and concentrations of RA and L-7-G were 50 and 20 microM, respectively. After a short incubation (2 h), L-7-G protected DNA in Caco-2 cells from damage induced by H(2)O(2) (75 microM); also, after a long incubation (24 h), SF, RA, and L-7-G had protective effects in Caco-2 cells. In HeLa cells, SO, SF, and RA protected against damage induced by H(2)O(2) after 24 h of incubation. Assays of DNA repair show that SO, SF, and L-7-G increased the rate of DNA repair (rejoining of strand breaks) in Caco-2 cells treated with H(2)O(2). The incision activity of a Caco-2 cell extract on a DNA substrate containing specific damage (8-oxoGua) was also measured to evaluate effects on base excision repair (BER) activity. Preincubation for 24 h with SO and L-7-G had a BER inductive effect, increasing incision activity in Caco-2 cells. In conclusion, SO, SF, and the isolated compounds (RA and L-7-G) demonstrated chemopreventive activity by protecting cells against oxidative DNA damage and stimulating DNA repair (SO, SF, and L-7-G).

Synthesis and evaluation of the platelet antiaggregant properties of phenolic antioxidants structurally related to rosmarinic acid

Polyphenols, such as rosmarinic acid, are widely distributed natural products with relevant antioxidant activity. Oxidative stress plays an important role in the pathogenesis of a number of disorders. Here, we report on the synthesis and biological effects of the polyphenolic esters hydroxytyrosyl gallate (1), hydroxytyrosyl protocatechuate (2) and hydroxytyrosyl caffeate (3), structurally related to rosmarinic acid. The three compounds showed a greater free radical scavenging activity than their precursors and also than rosmarinic acid. Esters 1 and 3 significantly reduced thrombin-evoked platelet aggregation, which is likely mediated to the attenuation of thrombin-stimulated Ca(2+) release and entry. The three compounds reduced the ability of platelets to accumulate Ca(2+) in the intracellular stores, probably by enhancing the Ca(2+) leakage rate and reduced store-operated Ca(2+) entry in these cells. These observations suggest that the structurally-simplified analogs to rosmarinic acid, compounds 1 and 3, might be the base of therapeutic strategies to prevent thrombotic complications associated to platelet hyperaggregability due to oxidative stress.

Ursolic acid and luteolin-7-glucoside improve lipid profiles and increase liver glycogen content through glycogen synthase kinase-3

In the present study, two phytochemicals - ursolic acid (UA) and luteolin-7-glucoside (L7G) - were assessed in vivo in healthy rats regarding effects on plasma glucose and lipid profile (total cholesterol, HDL and LDL), as well as liver glycogen content, in view of their importance in the aetiology of diabetes and associated complications. Both UA and L7G significantly decreased plasma glucose concentration. UA also significantly increased liver glycogen levels accompanied by phosphorylation of glycogen synthase kinase-3 (GSK3). The increase in glycogen deposition induced by UA (mediated by GSK3) could have contributed to the lower plasma glucose levels observed. Both compounds significantly lowered total plasma cholesterol and low-density lipoprotein levels, and, in addition, UA increased plasma high-density lipoprotein levels. Our results show that UA particularly may be useful in preventable strategies for people at risk of developing diabetes and associated cardiovascular complications by improving plasma glucose levels and lipid profile, as well as by promoting liver glycogen deposition.

Cytotoxic and antioxidant effects of methoxylated stilbene analogues on HepG2 hepatoma and Chang liver cells: Implications for structure activity relationship

Stilbenes possess a variety of biological activities including chemopreventive activity. This study was conducted to evaluate the structural activity relationships of six methoxylated stilbene analogues with respect to their cytotoxic effects and antioxidant activities on HepG2 hepatoma and Chang liver cells. The cytotoxic and total antioxidant activities of six stilbene analogues were determined by MTT and Ferric Reducing Antioxidant Power (FRAP) assays, respectively. We found that the cis-methoxylated stilbene: (Z)-3,4,4'-trimethoxystilbene was the most potent and selective antiproliferative agent (IC₅₀ 89 µM) in HepG2 cells. For the total antioxidant activity, compounds possessing hydroxyl groups at the 4' position namely (E)-3-methoxy-4'-hydroxystilbene, (E)-3,5-dimethoxy-4'-hydroxystilbene (pterostilbene), (E)-4-methoxy-4'-hydroxystilbene showed the highest antioxidant activity. Structure activity relationship studies of these compounds demonstrated that the cytotoxic effect and antioxidant activities of the tested compounds in this study were structurally dependent.

Antioxidant and antimutagenic effect of quercetin against DEN induced hepatotoxicity in rat

Diethylnitrosamine (DEN), a potent hepatocarcinogen, is found in tobacco smoke, processed meat as well as in different food products. Quercetin (QC), a naturally occurring flavonoid has excellent antioxidant properties. The present study was aimed to investigate the chemoprotective potential of QC against DEN induced hepatotoxicity in Sprague-Dawley (SD) rats. Quercetin was administered (10, 30 and 100 mg/kg) for 5 consecutive days after DEN (200 mg/kg) treatment. The animals were killed 24 h after the last dose of QC/saline treatment. The DEN induced hepatotoxicity was evident by elevated malondialdehyde (MDA) and decreased glutathione (GSH) levels in the liver. A significant increase in the levels of plasma aspartate transaminase (AST) and plasma alanine transaminase (ALT) was observed in the DEN treated group. The DEN induced DNA damage was evaluated using a single cell gel electrophoresis (SCGE) assay. A significant increase in the number of TUNEL positive cells was observed in the DEN treated group. Quercetin restored AST, ALT and GSH levels at all the tested doses. Restoration of the MDA level and cellular morphology was observed at doses of 10 and 30 mg/kg of QC. Further, DEN induced DNA damage and apoptosis was ameliorated by QC. The results indicate that QC ameliorates the DEN induced hepatotoxicity in rats and can be a candidate for a good chemoprotectant.

Protective effect of quercetin on the reproductive toxicity of 4-nitrophenol in diesel exhaust particles on male embryonic chickens

The 4-nitrophenol (PNP) in diesel exhaust particles (DEP) has been identified as a vasodilator and is a known degradation product of the insecticide parathion. In this study, the protective effect of quercetin, a potent oxygen free radical scavenger and metal chelator, against the oxidative damage of PNP on cultured testicular cells was studied in male embryonic chickens. Testicular cells from Day 18 embryos were cultured in serum-free McCoy's 5A medium and challenged with quercetin (1.0 microg/ml) alone or in combinations with PNP (10(-7)-10(-5) M) for 48 h. The oxidative damage was estimated by measuring cell viability, content of malondialdehyde (MDA), activity of superoxide dismutase (SOD) and glutathione peroxidation (GSH-Px) activity. The results showed that exposure to PNP (10(-5) M) induced condensed nuclei, vacuolated cytoplasm and a decrease in testicular cell viability and spermatogonial cell number. Exposure to PNP induced lipid peroxidation by elevation of the content of MDA. Exposure to PNP also decreased GSH-Px activity and SOD activity. However, simultaneous supplementation with quercetin restored these parameters to the same levels as the control. Consequently, PNP induced oxidative stress in spermatogonial cells, and dietary quercetin may attenuate the reproductive toxicity of PNP to restore the intracellular antioxidant system in the testicular cells of embryonic chickens.

Protective mechanism of quercetin and rutin using glutathione metabolism on HO-induced oxidative stress in HepG2 cells

The levels of cellular glutathione (GSH) and reactive oxygen species (ROS) simultaneously determined by fluorometric measurement, may provide important information on pro-oxidative and antioxidative balance. The dual effect of quercetin antioxidant and pro-oxidant activity was proposed from different studies. Our study demonstrated that quercetin acted as an antioxidant in HepG2 cells when cells were treated with 10 and 100 micromol/L quercetin for 30 min, but quercetin acted as a pro-oxidant when cells were incubated at 100 micromol/L quercetin for longer periods (12 and 24 h). Quercetin is capable of reducing H(2)O(2)-induced oxidative stress of HepG2 cells through different mechanisms, such as detoxification of H(2)O(2,) inhibition of ROS generation, and removal of generated ROS. We find that quercetin can block ROS generation through Fenton reaction to produce hydroxyl radicals by chelating with transition metal ions such as Cu(2+). Evidence that quercetin might exert an antioxidant effect by changing generated ROS into less reactive ROS suggests that when quercetin reacts with ROS, it becomes oxidized, which is less harmful but still reactive, and the oxidized quercetin interacts with thiol compounds as reduced GSH to return to the parent compound quercetin. In contrast, the prolonged treatment of quercetin in high concentrations (100 micromol/L) shows that quercetin may act as a pro-oxidant rather than as an antioxidant, resulting in cell death (apoptosis).

Sage tea drinking improves lipid profile and antioxidant defences in humans

Salvia officinalis (common sage) is a plant with antidiabetic properties. A pilot trial (non-randomized crossover trial) with six healthy female volunteers (aged 40–50) was designed to evaluate the beneficial properties of sage tea consumption on blood glucose regulation, lipid profile and transaminase activity in humans. Effects of sage consumption on erythrocytes’ SOD and CAT activities and on Hsp70 expression in lymphocytes were also evaluated. Four weeks sage tea treatment had no effects on plasma glucose. An improvement in lipid profile was observed with lower plasma LDL cholesterol and total cholesterol levels as well as higher plasma HDL cholesterol levels during and two weeks after treatment. Sage tea also increased lymphocyte Hsp70 expression and erythrocyte SOD and CAT activities. No hepatotoxic effects or other adverse effects were observed.

Luteolin, quercetin and ursolic acid are potent inhibitors of proliferation and inducers of apoptosis in both KRAS and BRAF mutated human colorectal cancer cells

KRAS and BRAF mutations are frequent in colorectal carcinoma (CRC) and have the potential to activate proliferation and survival through MAPK/ERK and/or PI3K signalling pathways. Because diet is one of the most important determinants of CRC incidence and progression, we studied the effects of the dietary phytochemicals quercetin (Q), luteolin (L) and ursolic acid (UA) on cell proliferation and apoptosis in two human CRC derived cell lines, HCT15 and CO115, harboring KRAS and BRAF activating mutations, respectively. In KRAS mutated HCT15 cells, Q and L significantly decreased ERK phosphorylation, whereas in BRAF mutated CO115 cells the three compounds decreased Akt phosphorylation but had no effect on phospho-ERK. Our findings show that these natural compounds have antiproliferative and proapoptotic effects and simultaneously seem to act on KRAS and PI3K but not on BRAF. These results shed light on the molecular mechanisms of action of Q, L and UA and emphasize the potential of dietary choices for the control of CRC progression.

Comparative mutagenic effects of structurally similar flavonoids quercetin and taxifolin on tester strains Salmonella typhimurium TA102 and Escherichia coli WP-2 uvrA

Quercetin (QT) and Taxifolin (TF) are structurally similar plant polyphenols. Both have been reported to have therapeutic potential as anti-cancer drugs and antioxidants. Mutagenic effects of QT and TF were evaluated using Salmonella typhimurium TA102 and Escherichia coli WP-2 uvrA tester strains. Either in the presence or absence of S9 mix, QT was mutagenic to TA102 and WP2 uvrA. However, the mutagenicity of QT was significantly enhanced in the presence of S9 mix. Likewise, in the presence of Iron (Fe2+) and NADPH generating system (NGS) and absence of S9 mix, QT induced significantly high mutations in both TA102 and WP-2 uvrA. Mutagenicity of QT decreased in both strains in the presence of Iron (Fe2+) or NGS alone. TF was not mutagenic in the presence or absence of S9 mix in both TA102 and WP-2 uvrA 2, regardless of the presence of iron or NGS. Incorporation of antioxidants (ascorbate, superoxide dismutase (SOD), catalase (CAT)) and/or iron chelators (desferroxamine (DF) and ethylenediamine-tetraacetate (EDTA)) in the test systems markedly decreased QT-induced mutations in both tester strains. These results suggest that QT but not TF, could induce mutations in the presence or absence of rat liver S9 or Iron (Fe2+) and NGS in both tester strains by redox cycling and Fenton reactions to produce oxygen free radicals. Our results indicate that a minor structural variation between the two plant polyphenols could elicit a marked difference in their genotoxicities. These results provide a basis for further study into the potential use of QT in combination with iron supplements.

Salvia fruticosa, Salvia officinalis, and rosmarinic acid induce apoptosis and inhibit proliferation of human colorectal cell lines: the role in MAPK/ERK pathway

Epidemiological studies have shown that nutrition is a key factor in modulating sporadic colorectal carcinoma (CRC) risk. Aromatic plants of the genus Salvia (sage) have been attributed many medicinal properties, which include anticancer activity. In the present study, the antiproliferative and proapoptotic effects of water extracts of Salvia fruticosa (SF) and Salvia officinalis (SO) and of their main phenolic compound rosmarinic acid (RA) were evaluated in two human colon carcinoma-derived cell lines, HCT15 and CO115, which have different mutations in the MAPK/ERK and PI3K/Akt signalling pathways. These pathways are commonly altered in CRC, leading to increased proliferation and inhibition of apoptosis. Our results show that SF, SO, and RA induce apoptosis in both cell lines, whereas cell proliferation was inhibited by the two sage extracts only in HCT15. SO, SF, and RA inhibited ERK phosphorylation in HCT15 and had no effects on Akt phosphorylation in CO115 cells. The activity of sage extracts seems to be due, at least in part, to the inhibition of MAPK/ERK pathway.

Oxidative DNA damage protection and repair by polyphenolic compounds in PC12 cells

Biological systems are frequently exposed to excessive reactive oxygen species, causing a disturbance in the cells natural antioxidant defence systems and resulting in damage to all biomolecules, including nucleic acids. In fact, oxidative DNA damage is described as the type of damage most likely to occur in neuronal cells. In this study, three polyphenolic compounds, luteolin, quercetin and rosmarinic acid, were investigated for their protective effects against oxidative DNA damage induced in PC12 cells, a neuronal cell model. Although luteolin and quercetin prevented the formation of strand breaks to a greater extent than rosmarinic acid, this last one presented the highest capacity to repair strand breaks formation. In addition, rosmarinic acid was the only compound tested that increased the repair of oxidized nucleotidic bases induced with the photosensitizer compound [R]-1-[(10-chloro-4-oxo-3-phenyl-4H-benzo[a]quinolizin-1-yl) carbonyl]-2-pyrrolidine-methanol (Ro 19-8022). The activity of repair enzymes was indicated by the in vitro base excision repair assay, using a cell-free extract obtained from cells previously treated with the compounds to incise DNA. The protective effect of rosmarinic acid was further confirmed by the increased expression of OGG1 repair gene, observed through real time RT-PCR. The data obtained is indicative that rosmarinic acid seems to act on the intracellular mechanisms responsible for DNA repair, rather than by a direct effect on reactive oxygen species scavenging, as deducted from the effects observed for luteolin and quercetin. Therefore, these results suggest the importance of these polyphenols, and in particular rosmarinic acid, as protectors of oxidative stress-induced DNA damage that commonly occurs in several pathological conditions, such as neurodegenerative diseases.

Luteolin suppresses cisplatin-induced apoptosis in auditory cells: possible mediation through induction of heme oxygenase-1 expression

Luteolin has been shown to possess antitumorigenic, antioxidant, and anti-inflammatory properties. In the present study, we investigated the protective mechanism of luteolin against cisplatin-induced apoptosis in auditory (House Ear Institute-Organ of Corti 1 [HEI-OC1]) cells. Luteolin was found to induce the expression of heme oxygenase-1 (HO-1) in a dose- and time-dependent manner. Luteolin also activated the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase pathway, which plays an important role in the expression of HO-1. Luteolin protected the cells against cisplatin-induced apoptotic cell death. The protective effect of luteolin was abrogated by zinc protoporphyrin IX (ZnPP IX), an HO inhibitor, and antisense oligodeoxynucleotides against the HO-1 gene. Furthermore, pretreatment with luteolin inhibited the activation of caspase-3 and the mitochondrial dysfunction, and the effect of luteolin on the activation of caspase-3 disappeared in the presence of ZnPP IX or PD098059. These results demonstrate that the expression of HO-1 by luteolin is mediated by the ERK pathway, and also that the activating of HO-1 inhibits cisplatin-induced apoptosis in HEI-OC1 1 cells.

Protection of human HepG2 cells against oxidative stress by cocoa phenolic extract

Cocoa is a rich source of flavanols and procyanidin oligomers with antioxidative properties, providing protection against oxidation and nitration. The present study investigated the potential protective effect of a polyphenolic extract from cocoa on cell viability and antioxidant defenses of cultured human HepG2 cells submitted to oxidative stress induced by tert-butylhydroperoxide (t-BOOH). Pretreatment of cells with 0.05-50 microg/mL of cocoa polyphenolic extract (CPE) for 2 or 20 h completely prevented cell damage and enhanced activity of antioxidant enzymes induced by a treatment with t-BOOH. Moreover, lower levels of GSH caused by t-BOOH in HepG2 cells were partly recovered by a pretreatment with CPE. Increased reactive oxygen species (ROS) induced by t-BOOH was dose-dependently prevented when cells were pretreated for 2 or 20 h with CPE. These results show that treatment of HepG2 in culture with CPE (within the physiological range of concentrations) confers a significant protection against oxidation to the cells.