Roles of catalase and hydrogen peroxide in green tea polyphenol-induced chemopreventive effects

Differential apoptosis by gallotannin in human colon cancer cells with distinct p53 status

Gallotannin (GT), a plant polyphenol, has shown anticarcinogenic activities in several animal models including colon cancer. In our previous study, we showed that GT inhibits 1,2-dimethylhydrazine-induced colonic aberrant crypt foci and tumors in Balb/c mice, thus supporting a role for GT as a chemopreventive agent in colon cancer. However, at the molecular level, GT's mechanism of chemoprevention is still unclear. In this study, we aim at identifying GT's potential molecular mechanisms of action in in vitro studies. We show that GT differentially inhibits the growth of two isogenic HCT-116 (p53+/+, p53-/-) human colon cancer cells versus normal human intestinal epithelial cells (FHs 74Int). DNA flow cytometric analysis showed that GT induced S-phase arrest in both HCT-116 cell lines. Cell-cycle arrest in p53 (+/+) cells was associated with an increase in p53 protein levels and p21 transcript and protein levels. The inhibition of cell-cycle progression of HCT-116 p53 (+/+) cells by GT correlated with a reduction in the protein levels of cyclin D(1), pRb, and the Bax/Bcl-2 ratio. Although GT did not induce apoptosis in p53 (+/+) cells, a significant induction of apoptosis was observed in p53 (-/-) cells as shown by TUNEL staining and flow cytometry analysis. Apoptosis induction in p53 (-/-) cells was associated with a significant increase in Bax/Bcl-2 protein levels. Our results demonstrate that GT inhibits the growth of HCT-116 colon cancer cells in a p53-independent manner but exhibits differential sensitivity to apoptosis induction in HCT-116 cells with distinct p53 status.

Green tea catechins inhibit bacterial DNA gyrase by interaction with its ATP binding site

Catechins are the main ingredients of green tea extracts and have been shown to possess versatile biological activities, including antimicrobial. We determined that the catechins inhibit bacterial DNA gyrase by binding to the ATP binding site of the gyrase B subunit. In the group of four tested catechins, epigallocatechin gallate (EGCG) had the highest activity, followed by epicatechin gallate (ECG) and epigallocatechin (EGC). Specific binding to the N-terminal 24 kDa fragment of gyrase B was determined by fluorescence spectroscopy and confirmed using heteronuclear two-dimensional NMR spectroscopy of the EGCG-15N-labeled gyrase B fragment complex. Protein residues affected by binding to EGCG were identified through chemical shift perturbation. Molecular docking calculations suggest that the benzopyran ring of EGCG penetrates deeply into the active site while the galloyl moiety anchors it to the cleft through interactions with its hydroxyl groups, which explains the higher activity of EGCG and ECG.

Photoprotective effects of green tea polyphenols

Non-melanoma skin cancer is the most common malignancy in humans and is equivalent to the incidence of malignancies in all other organs combined in the United States. Current methods of prevention depend on sunscreens in humans, efficacy of which is largely undetermined for non-melanoma skin cancers. Green tea polyphenols have the greatest effect with respect to chemoprevention and have been found to be most potent at suppressing the carcinogenic activity of UV radiation. They protect against many of the other damaging effects of UV radiation such as UV-induced sunburn response, UV-induced immunosuppression and photoaging of the skin. They exert their photoprotective effects by various cellular, molecular and biochemical mechanisms in in vitro and in vivo systems. Green tea polyphenols thus have the potential, when used in conjunction with traditional sunscreens, to further protect the skin against the adverse effects of ultraviolet radiation.

Hibernation, reversible cell growth inhibition by epigallocatechin-3-O-gallate

Epigallocatechin-3-O-gallate (EGCg) and related polyphenolic compounds found in tea are known to have antioxidative activities. However, they also have pro-oxidative activities such as generation of hydrogen peroxide. In this report, we investigated the effect on cells and showed the potential usage of EGCg in cell preservation. H(2)O(2) was generated from EGCg at concentrations of more than 300 microg/mL for 6 h at 37 degrees C, and high cytotoxicity for L929 cells were shown. In contrast, in the presence of 1 microg/mL catalase, the amount of generated H(2)O(2) was significantly low and cytotoxicity decreased markedly. This indicates that catalase eliminated H(2)O(2) generated by degradation of EGCg. Although H(2)O(2) generation was prevented, L929 cell proliferation was slightly inhibited in proportion to the concentrations of EGCg. L929 was exposed able to be 300 microg/mL to EGCg and 1 microg/mL catalase for maximum 18 days. EGCg inhibited the growth of L929 cells, and cell proliferation was restarted immediately after medium change for removing EGCg. We concluded that EGCg had a reversible growth inhibition when H(2)O(2) was eliminated from cell cultures.

Mixed-mode retention mechanism for (−)-epigallocatechin gallate on a 12% cross-linked agarose gel media

The adsorption behaviour of (-)-epigallocatechin gallate (EGCG), the major polyphenolic substance in green tea extracts, on the cross-linked agarose gel Superose 12 HR 10/30, has been studied using a variety of solvent systems and shown to be based on a mixture of hydrogen bonding and hydrophobic interaction. The hydrogen bonding was studied in acetonitrile in the presence of different co-solvents possessing varying hydrogen bond donor (HBD) and/or hydrogen bond acceptor (HBA) characteristics. The HBA-value of the co-solvent had the highest effect whereas the HBD-value played a subordinate role. Retention due to hydrophobic interaction could be demonstrated when mobile phases containing high water content were applied. The retention of EGCG, and its analogues (-)-epigallocatechin (EGC) and (-)-catechin (C) were thus shown to be dependent on the polarity of the organic modifiers added. However, the elution order of EGC and C, was inversed to that observed in reversed phase chromatography, indicating that some hydrogen bonding was still in effect. The retardation of EGCG in the presence of a wide concentration range of acetonitrile in water confirmed the interpretation that the retention mechanism is of mixed-mode character based on both hydrogen bonding and hydrophobic interaction.

Effects of oxidative stress on proliferation of rat hepatic stellate cells and antioxidation of reduced glutathione

AIM: To explore the effects of oxidative stress on the proliferation of rat hepatic stellate cells and the antioxidation of reduced glutathione.

METHODS: Rat hepatic stellate cells were incubated with different concentrations of ferric nitrilotriacetic acid (Fe-NTa). With 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphennylterazolium bromide (MTT) colorimetric assay, the effects of Fe-NTa on the proliferation of hepatic stellate cells at 6, 12, 24 and 48 h was detected, and malondialdehyde (MDA) contents and superoxide dismutase (SOD) activity were also detected. At the same time, hepatic stellate cells were incubated with different concentrations of reduced glutathione (0.5, 2.5, 10 mmol/L), and MTT assay was used to SOD activity again.

RESULTS: In comparison with that in the blank control group at 12 h, the proliferation of hepatic stellate cells was significantly increased when the ferric nitrilotriacetic acid concentrations were 500 and 1000 mmol/L, respectively (A value: 0.369 ± 0.124, 0.485 ± 0.101 vs 0.285 ± 0.044, both P < 0.01); the proliferation of cells incubated with different concentrations of Fe-NTa was also markedly increased at 24 and 48 h (P < 0.01). The proliferation of hepatic stellate cells without Fe-NTa interference at 12, 24 and 48 h was also increased as compared with that at 6 h (A value: 0.285 ± 0.044, 0.253 ± 0.033, 0.278 ± 0.037 vs 0.111 ± 0.005, all P < 0.01), while with the elevation of Fe-NTa concentration, the proliferation of hepatic stellate cells at 12, 24 and 48 h was markedly increased as compared with that at 6 h (P < 0.01). In comparison with those in the control group, SOD activity significantly reduced (156.95 ± 21.17, 100.92 ± 10.02 mkat/L vs 197.74 ± 17.59 mkat/L, all P < 0.01) and MDA contents significantly increased (1123 ± 217, 1549 ± 182 mmol/L vs 580 ± 332 mmol/L, all P < 0.01) when the concentrations of Fe-NTa were 200 and 500 mmol/L. As compared with the model group (200 mmol/L Fe-NTa), the SOD activities in the cells preincubated with reduced glutathione were significantly increased (5.42 ± 0.58, 6.67 ± 0.18, 8.75 ± 0.58 mkat/L vs 2.25 ± 0.35 mkat/L, all P < 0.01).

CONCLUSION: Oxidative stress can significantly promote the proliferation of rat hepatic stellate cells in time- and concentration-dependent manners. Oxidative stress can also lead to lipid peroxidation, while reduced glutathione may play an anti-oxidative role.

Comparative study of the cytotoxicity induced by antioxidant epicatechin conjugates obtained from grape

We studied the cytotoxicity of epicatechin conjugates obtained by depolymerization of grape polymeric flavanols in the presence of cysteamine or cysteine and the resulting conjugates purified by ion exchange and/or reversed-phase high-resolution chromatography and compared it to their antioxidant capacity. The studies were carried out on fibroblast and keratinocyte cell lines. The cytotoxic effects of these products were observed at concentrations 3-7-fold higher than the antioxidant concentration after exposure for 24, 48, and 72 h. The compounds with a gallate group were more toxic than the corresponding products without one. It is interesting to note that the esther ethyl derivative exhibited low cytotoxicity but had the most potent antioxidant activity. The results indicated that effective antioxidant activity can be obtained from these products in a concentration range that is safe for the normal cell. This finding suggests new pharmaceutical applications and may also help us to identify the potential therapeutic dose.

Regulation of inflammation and redox signaling by dietary polyphenols

Reactive oxygen species (ROS) play a key role in enhancing the inflammation through the activation of NF-kappaB and AP-1 transcription factors, and nuclear histone acetylation and deacetylation in various inflammatory diseases. Such undesired effects of oxidative stress have been found to be controlled by the antioxidant and/or anti-inflammatory effects of dietary polyphenols such as curcumin (diferuloylmethane, a principal component of turmeric) and resveratrol (a flavonoid found in red wine). The phenolic compounds in fruits, vegetables, tea and wine are mostly derivatives, and/or isomers of flavones, isoflavones, flavonols, catechins, tocopherols, and phenolic acids. Polyphenols modulate important cellular signaling processes such as cellular growth, differentiation and host of other cellular features. In addition, they modulate NF-kappaB activation, chromatin structure, glutathione biosynthesis, nuclear redox factor (Nrf2) activation, scavenge effect of ROS directly or via glutathione peroxidase activity and as a consequence regulate inflammatory genes in macrophages and lung epithelial cells. However, recent data suggest that dietary polyphenols can work as modifiers of signal transduction pathways to elicit their beneficial effects. The effects of polyphenols however, have been reported to be more pronounced in vitro using high concentrations which are not physiological in vivo. This commentary discusses the recent data on dietary polyphenols in the control of signaling and inflammation particularly during oxidative stress, their metabolism and bioavailability.

Beneficial effects of green tea--a review

Tea is the most consumed drink in the world after water. Green tea is a 'non-fermented' tea, and contains more catechins, than black tea or oolong tea. Catechins are in vitro and in vivo strong antioxidants. In addition, its content of certain minerals and vitamins increases the antioxidant potential of this type of tea. Since ancient times, green tea has been considered by the traditional Chinese medicine as a healthful beverage. Recent human studies suggest that green tea may contribute to a reduction in the risk of cardiovascular disease and some forms of cancer, as well as to the promotion of oral health and other physiological functions such as anti-hypertensive effect, body weight control, antibacterial and antivirasic activity, solar ultraviolet protection, bone mineral density increase, anti-fibrotic properties, and neuroprotective power. Increasing interest in its health benefits has led to the inclusion of green tea in the group of beverages with functional properties. However, although all the evidence from research on green tea is very promising, future studies are necessary to fully understand its contributions to human health, and advise its regular consumption in Western diets, in which green tea consumption is nowadays limited and sporadic.

In vitro cytotoxicity of a theaflavin mixture from black tea to malignant, immortalized, and normal cells from the human oral cavity

The growth inhibitory effects of a theaflavin mixture from black tea were more pronounced to malignant (CAL27; HSC-2; HSG1) and immortalized (S-G; GT1) cells than to normal (HGF-2) cells from the human oral cavity. Studies with malignant carcinoma CAL27 cells and immortalized GT1 fibroblasts showed that cytotoxicity of the theaflavin mixture was enhanced as the exposure time was increased, with the tumor CAL27 cells more sensitive than the GT1 cells. Hydrogen peroxide (H(2)O(2)) was detected in cell culture medium amended with the theaflavin mixture. The level of H(2)O(2) in cell culture medium amended with the theaflavin mixture was lessened in the presence of catalase and CoCl(2); the level of authentic H(2)O(2) was also lessened in the presence of CoCl(2), suggesting that Co(2+) led to the rapid catalytic decomposition of H(2)O(2). The cytotoxicity of the theaflavin mixture was due, in part, to the generation in the cell culture medium of H(2)O(2), which lessened the intracellular levels of glutathione in the CAL27 cells and, to a lesser extent, in the GT1 cells. For both cell types, coexposures of the theaflavin mixture with catalase or CoCl(2) afforded protection.

Epigallocatechin-3-gallate delivers hydrogen peroxide to induce death of ovarian cancer cells and enhances their cisplatin susceptibility

The green tea polyphenol epigallocatechin-3-gallate (EGCG) has cancer chemopreventive properties against various types of cancers. The compound is known to attack various targets in transformed cells. In this report, we examined the action of EGCG on ovarian cancer cells. Eight ovarian cancer cell lines were tested (SKOV3, CAOV3, OVCAR3, OVCAR10, A2780, CP70, C30, and C200) and showed IC50s for EGCG at the micromolar range, including ones that are resistant to the chemotherapeutic drug cisplatin. The ovarian cancer cells were sensitive to H2O2 at similar concentrations, and EGCG treatment led to enhanced intracellular H2O2. Neutralization with pyruvate, a scavenger of H2O2, suggests that the toxicity of EGCG may be mediated by oxidative stress from the free radical. Addition of Tempol, a superoxide dismutase mimetic, demonstrates that H2O2 might be generated endogenously from superoxide. The toxicity of cisplatin and the development of cisplatin resistance are major obstacles in treatment of ovarian cancer. We found that addition of EGCG amplified the toxicity of cisplatin. EGCG increased cisplatin potency by three to six-fold in SKOV3, CAOV3, and C200 cells, the latter being a cell line induced to have several hundred fold resistant to cisplatin above the parental line. Our findings suggest that EGCG may accentuate oxidative stress to inhibit growth of ovarian cancer cells and sensitize them to cisplatin.

Opposing action of curcumin and green tea polyphenol in human keratinocytes

Persistent environmental insult can convert a normal cell into a cancer cell. However, various natural chemopreventive agents called antioxidants can retard this progression. We have recently explored the effects of several chemopreventive agents, including green tea polyphenol and curcumin, on normal human keratinocyte function. Our findings suggest that a bioactive polyphenol from green tea, (-)-epigallocatechin-3-gallate (EGCG), acts to increase involucrin gene expression, suggesting that EGCG treatment enhances normal human keratinocyte differentiation. Mechanistic studies indicate that EGCG alters mitogen-activated protein kinase cascade function to activate involucrin gene transcription via a Ras, MEKK1, MEK3, ERK1/2-p38delta cascade that targets AP1 and CAATT enhancer binding protein transcription factors. These findings suggest that EGCG may inhibit disease progression by promoting keratinocyte differentiation. Parallel studies indicate that not all antioxidants produce a similar response. Curcumin, an antioxidant derived from the turmeric, antagonizes the EGCG-dependent response by interfering in this signaling pathway. These studies suggest that different antioxidant may produce antagonistic effects in tissues.

Redox properties of tea polyphenols and related biological activities

Plant polyphenolic compounds are known to be strong antioxidants. Because oxidative stress is believed to contribute to many acute and chronic diseases, these polyphenols have been postulated to have many beneficial health effects, such as the prevention of cancer and cardiovascular diseases. Indeed, some of these beneficial effects have been demonstrated in animal models and in some, but not all, epidemiological studies. Nevertheless, only some of these activities have been demonstrated to be associated with the antioxidative activities of polyphenols. In studies with cell lines in culture, some of the observed activities may be due to superoxide and hydrogen peroxide produced during the autooxidation of polyphenols. Such pro-oxidation-dependent reactions may not happen in tissues where the oxygen partial pressure is much lower than that in cell culture medium. This review will use the well-studied tea polyphenol, (-)-epigallocatechin-3-gallate, as an example to illustrate the redox properties of polyphenols and their influence on signaling pathways related to anti-cancer activities. Existing data suggest, however, that most of the relevant mechanisms of cancer prevention by tea polyphenols are not related to their redox properties, but are due to the direct binding of the polyphenol to target molecules, including the inhibition of selected protein kinases, matrix metalloproteinases, and DNA methyltransferases.

Blue light generates reactive oxygen species (ROS) differentially in tumor vs. normal epithelial cells

OBJECTIVES

Blue light of high intensity is commonly used in dentistry to activate polymerization of resin restorative materials. Other than its effects on the retina, the biological effects of blue light (380-500nm wavelengths) are poorly studied. Limited evidence suggests that blue light acts by forming intracellular reactive oxygen species (ROS) that then affect critical cell functions. If the biological effects of blue light are redox-mediated, antioxidants might be used to mitigate unwanted side effects of blue light during clinical use, or blue light might be used therapeutically to modulate redox-sensitive cell signaling responses.

METHODS

Intracellular ROS were estimated using HFLUOR-DA (dihydrofluorescein diacetate), a vital fluorescein-based, redox-sensitive dye. ROS were measured in normal (NHEK) and oral squamous carcinoma (OSC2) epithelial cells, shown previously to respond differentially to blue light irradiation. Two-hour cumulative levels of ROS and approximate ROS lifetimes were measured after irradiation doses of 5-30 J/cm(2). The blue light-induced generation of ROS was further tested by the ability of the antioxidants N-acetylcysteine (NAC) and vitamin E to mitigate intracellular ROS levels.

RESULTS

Dose-dependent ROS levels were generated in both NHEK and OSC2 cells, but cumulative levels were higher and persisted longer in the OSC2 cells. Both vitamin E and NAC significantly reduced blue-light-induced levels of ROS, but were more effective in the OSC2 cells.

SIGNIFICANCE

The induction of intracellular ROS by blue light implies that redox effects may mediate cellular responses to blue light. This result suggests the opportunity to mitigate any effects of direct or coincident exposure during dental treatment via antioxidants, and the opportunity to exploit differences in redox processing among cells for possible treatment of epithelial cancer or wound healing.

Epigallocatechin-3-gallate from green tea negatively affects swine granulosa cell function

The use of herbs as additives in livestock nutrition as an alternative to antibiotics is becoming a new goal in animal production. It is known that green tea exerts antimicrobial activity owing to specific flavonoid compounds named catechins, primarily represented by epigallocatechin-3-gallate (EGCG). Remarkably, despite many potential benefits of green tea and EGCG consumption, it is also important to get an insight on the possible reproductive-related consequences of feeding supplementation. To this purpose, granulosa cells were harvested from follicles > 5mm and treated with 5 and 50 microg/ml of EGCG in order to evaluate the effects on the main parameters of granulosa cell function: steroidogenesis, by measuring progesterone and estradiol-17beta production, and proliferation, one of the major feature of ovarian follicular growth. Moreover, as the genesis of new vessels has been demonstrated to be fundamental for follicle development, we evaluated the effect of EGCG on the production of the main angiogenetic factor, VEGF, by swine granulosa cells. Finally, since reactive oxygen species (ROS) might be involved in the control of female reproductive activity, we studied the effect of EGCG on superoxide anion (O2-) and hydrogen peroxide (H2O2) production by swine granulosa cells and on the activity of the scavenging enzyme superoxide dismutase (SOD). EGCG significantly (p < 0.05) inhibited proliferation, steroidogenesis, VEGF and O2- production by swine granulosa cells; on the contrary, H2O2 levels and SOD activity were stimulated (p < 0.05) by the catechin. Therefore, since our data demonstrate that EGCG has a negative effect on reproductive performances in swine, feeding supplementation should be carefully considered.

Differential in vitro cytotoxicity of (−)-epicatechin gallate (ECG) to cancer and normal cells from the human oral cavity

This study evaluated the biologic activity of epicatechin gallate (ECG), a polyphenol in tea, to carcinoma HSC-2 cells and normal HGF-2 fibroblasts cells from the human oral cavity. The relative cytotoxicity of ECG, as compared to five other polyphenols in tea, was evaluated. For the HSC-2 carcinoma cells, ECG, catechin gallate (CG), and epigallocatechin gallate (EGCG) grouped as highly toxic, epigallocatechin (EGC) as moderately toxic, and catechin (C) and epicatechin (EC) as least toxic. For the HGF-2 fibroblasts, ECG and CG grouped as highly toxic, EGCG as moderately toxic, and EGC, C, and EC as least toxic. The cytotoxic effects of the polyphenols were more pronounced to the carcinoma, than to the normal, cells. The addition of ECG to cell culture medium led to the generation of hydrogen peroxide (H2O2). However, ECG, as compared to EGCG, was a poor generator of H2O2 and, hence, the cytotoxicity of ECG was unaffected by the presence of the antioxidants, N-acetyl cysteine and glutathione, and catalase. The cytotoxicity of ECG was unaffected by a metabolic activating system, i.e., a hepatic microsomal S-9 mix. DNA fragmentation, caspase-3 activity, and nuclear staining, both with acridine orange and the TUNEL procedure, were used to assess ECG-induced apoptosis. ECG induced apoptosis in the carcinoma HSC-2 cells, but not in the normal HGF-2 fibroblasts. This research supports those studies suggesting that tea green is an effective chemopreventive agent of oral carcinoma.

Green tea extract and (-)-epigallocatechin-3-gallate, the major tea catechin, exert oxidant but lack antioxidant activities

Green tea is the most widely consumed beverage. It has attained high reputation as a health-promoting dietary component ascribed to the antioxidant activity of (-)-epigallocatechin-3-gallate (EGCG), its main polyphenolic constituent. Evidence is increasing that tea constituents can be cell damaging and pro-oxidant themselves. These effects were suggested to be due to spontaneous H2O2 generation by polyphenols in solution. In the present study, we investigated the oxidant and antioxidant properties of green tea extracts (GTE) and of EGCG by means of the rodent macrophage-like RAW 264.7 and human promyelocytic leukemic HL60 cell lines. The results obtained show that both under cell-free conditions and in the presence of cells the oxidant activities of GTE and EGCG exceeded those of spontaneously generated H2O2 (FOX assay). Increase of intracellular oxidative stress was indicated by 2',7'-dichlorofluorescin probing, and the enhanced genotoxicity was demonstrated by the alkaline comet assay and by the micronucleus assay (cytokinesis block). Time- and dose-dependent induction of cell death was monitored by trypan blue exclusion, MTT assay, and Hoechst staining. Furthermore, in our systems in vitro, EGCG neither directly scavenges H2O2 nor mediates other antioxidant activities but rather increased H2O2-induced oxidative stress and DNA damage. In conclusion, our data suggest that detailed mechanistic studies on the effects of GTE and EGCG should be performed in vivo before excessive intake and/or topical application of green tea products can be recommended to healthy and/or diseased persons.

Blue light differentially alters cellular redox properties

Blue light (lambda = 380-500 nm) historically has been used to initiate polymerization of biomaterials and recently has been proposed as a therapeutic agent. New evidence suggests that cell-type-specific responses result from redox changes induced by exposure to blue light. Cultured cells were exposed to defined doses of blue light, equivalent to exposure times of 10 s and 2 min, to achieve energies of 5 J/cm2 and 60 J/cm2, respectively, after which (a) viable cell number, (b) cellular protein profiles, (c) mitochondrial succinate dehydrogenase (SDH) activity, (d) total reactive oxygen species (ROS), and (e) induction of apoptosis were compared to that of nonexposed control cultures. Results showed that blue-light exposure arrested monocyte cell growth and increased levels of peroxiredoxins. SDH activity of normal epidermal keratinocytes (NHEK) was slightly enhanced by blue light, whereas identical treatment of OSC2 oral tumor cells resulted in significant suppression of SDH activity. Blue-light exposure generally induced higher levels of total ROS in OSC2 cells than in NHEK. Finally, only OSC2 cells exhibited signs of apoptosis via Annexin V staining following exposure to blue light. These data support the central hypothesis that blue light induces an oxidative stress response in cultured cells resulting in cell-type-specific survival outcomes. The identification of oxidative stress as a mediator of the effects of blue light is a critical first step in defining its biological risks and therapeutic opportunities.

ROS formation and glutathione levels in human oral fibroblasts exposed to TEGDMA and camphorquinone

Glutathione (GSH) is important for the self-protection of cells against oxidative stress and toxic xenobiotics, whereas reactive oxygen species (ROS) at elevated concentrations may cause detrimental alterations of cell membranes, DNA, and other cellular structures. The present investigation addressed the effects of triethylene-glycoldimethacrylate (TEGDMA) and camphorquinone (CQ) on glutathione metabolism and the formation of ROS in oral cells. Primary human pulp fibroblasts were exposed to various concentrations of TEGDMA and CQ (0.1-5 mM). Subsequently, GSH concentration and ROS formation were analyzed with the use of the monobromobimane assay (GSH) and 2',7'-dichlorofluorescein diacetate (DCFH-DA) (ROS). The endogenous ROS hydrogen peroxide (H2O2) was used as a positive control (0.02-2 mM). TEGDMA significantly decreased GSH at concentrations between 0.5 and 5 mM (p<0.05), but did not elevate ROS levels. Contrary, CQ increased ROS formation at concentrations>or=1 mM, but had only a moderate effect on GSH at the highest test concentration. Hydrogen peroxide increased ROS and simultaneously decreased GSH at concentrations of >or=0.2 mM. These data show that the investigated substances may cause cell damage due to various mechanisms, GSH decrease and/or ROS increase. As a consequence, TEGDMA and CQ released into an aqueous environment from resinous materials might interact, thus generating significant cytotoxic effects even at low concentrations.

In vitro Cytotoxicity of Epigallocatechin Gallate and Tea Extracts to Cancerous and Normal Cells from the Human Oral Cavity

This study compared the in vitro responses of malignant and normal cells from the human oral cavity to tea extracts and to its main polyphenolic component, (-)-epigallocatechin gallate (EGCG). The antiproliferative effects of tea polyphenolic extracts and EGCG were more pronounced towards immortalized, tumourigenic (CAL27, HSC-2, and HSG(1)) and non-tumourigenic (S-G) cells than towards normal (GN56 and HGF-1) fibroblasts and green tea was more toxic than black tea. As the addition of tea extract or EGCG to cell culture medium led to the formation of hydrogen peroxide (H(2)O(2)), the research then focused on EGCG as an inducer of oxidative stress, using CAL27, the cancerous cells most sensitive to EGCG, HSG(1), the cancerous cells least sensitive to EGCG, and GN56 cells. The toxicity of EGCG was decreased in the presence of catalase, an enzyme that degrades H(2)O(2), or of deferoxamine, a chelator of Fe(3+). Conversely, pretreatment of the cells with the glutathione depleters, 1-chloro-2,4-dinitrobenzene and 1,3-bis(2-chloroethyl)-N-nitrosourea, potentiated the toxicity of EGCG. A 4-hr exposure to EGCG lessened the intracellular level of reduced glutathione in the CAL27 and HSG(1) cells, but not in the GN56 fibroblasts. Whereas EGCG itself did not induce lipid peroxidation, Fe(2+)-induced lipid peroxidation was potentiated by EGCG. A 72-hr exposure to cytotoxic concentrations of EGCG induced significant cytoplasmic vacuolization in all cell types. The results presented herein are consistent with EGCG acting as a prooxidant, with the cancerous cells more sensitive to oxidative stress than the normal cells.

Antioxidants regulate normal human keratinocyte differentiation

Cancer begins with a normal cell that, due to persistent environmental insult, is transformed, via a series of progressively more insidious steps, into a cancer cell. A major goal of chemopreventive therapy is to alter the normal cell response to the environmental agent with the goal of inhibiting disease progression. (-)-Epigallocatechin-3-gallate (EGCG) is an important bioactive green tea antioxidant that possesses remarkable cancer chemopreventive properties. We have recently explored the hypothesis that EGCG prevents cancer by promoting keratinocyte differentiation. Based on our findings, we argue that EGCG acts to enhance the differentiation of normal keratinocytes. This is a potentially important finding, as it represents a novel mechanism of disease inhibition by EGCG--cancer preventive "differentiation therapy". However, not all antioxidant chemopreventive agents work by this mechanism. Curcumin, for example, inhibits the differentiation-promoting activity of EGCG. This report discusses the mechanism of EGCG and curcumin action in regulating expression of involucrin, a marker of keratinocyte differentiation.

Gene expression changes induced by green tea polyphenol (−)-epigallocatechin-3-gallate in human bronchial epithelial 21BES cells analyzed by DNA microarray

Many studies suggest green tea is a cancer chemopreventive agent. This effect has been attributed to its major constituent (−)-epigallocatechin-3-gallate (EGCG). EGCG is also observed to have cytotoxic anticancer effects, especially when used in combination with certain chemotherapeutic agents. The biochemical actions of EGCG in chemoprevention and anticancer effects have been studied; however, the mechanisms of action are not clearly understood. We show here by expression genomics the effects of EGCG (25 μmol/L) in the Ha-ras gene transformed human bronchial epithelial 21BES cells. We found induction of temporal changes in gene expression and the coalescence of specific genetic pathways by EGCG. In this experimental system, hydrogen peroxide (H2O2) was produced. By treating cells with EGCG in the presence or absence of catalase, we further distinguished gene expression changes that are mediated by H2O2 from those that are H2O2 independent. Many genes and cellular pathways, including genes of the transforming growth factor-β signaling pathway, were H2O2 dependent because the effects were abolished by catalase. Gene expression changes that were not affected by catalase included those of the bone morphogenetic protein signaling pathway, peptidylprolyl isomerase (cyclophilin)–like 2, alkylated DNA repair enzyme alkB, polyhomeotic-like 2, and homeobox D1. We show further that EGCG and H2O2 differentially transactivated the bone morphogenetic protein and the transforming growth factor-β response element promoter reporters, respectively, thus confirming results from DNA microarray analysis. The elucidation of gene expression changes between H2O2-dependent and H2O2-independent responses helps us better understand the cancer chemopreventive and anticancer actions of EGCG.