Effects of food factors on signal transduction pathways

Epigallocatechin Gallate Modulates Muscle Homeostasis in Type 2 Diabetes and Obesity by Targeting Energetic and Redox Pathways: A Narrative Review

Obesity is associated with the hypertrophy and hyperplasia of adipose tissue, affecting the healthy secretion profile of pro- and anti-inflammatory adipokines. Increased influx of fatty acids and inflammatory adipokines from adipose tissue can induce muscle oxidative stress and inflammation and negatively regulate myocyte metabolism. Muscle has emerged as an important mediator of homeostatic control through the consumption of energy substrates, as well as governing systemic signaling networks. In muscle, obesity is related to decreased glucose uptake, deregulation of lipid metabolism, and mitochondrial dysfunction. This review focuses on the effect of epigallocatechin-gallate (EGCG) on oxidative stress and inflammation, linked to the metabolic dysfunction of skeletal muscle in obesity and their underlying mechanisms. EGCG works by increasing the expression of antioxidant enzymes, by reversing the increase of reactive oxygen species (ROS) production in skeletal muscle and regulating mitochondria-involved autophagy. Moreover, EGCG increases muscle lipid oxidation and stimulates glucose uptake in insulin-resistant skeletal muscle. EGCG acts by modulating cell signaling including the NF-κB, AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase (MAPK) signaling pathways, and through epigenetic mechanisms such as DNA methylation and histone acetylation.

Therapeutic Potential of Epigallocatechin Gallate Nanodelivery Systems

Nowadays, the society is facing a large health problem with the rising of new diseases, including cancer, heart diseases, diabetes, neurodegenerative diseases, and obesity. Thus, it is important to invest in substances that enhance the health of the population. In this context, epigallocatechin gallate (EGCG) is a flavonoid found in many plants, especially in tea. Several studies support the notion that EGCG has several benefits in fighting cancer, heart diseases, diabetes, and obesity, among others. Nevertheless, the poor intestinal absorbance and instability of EGCG constitute the main drawback to use this molecule in prevention and therapy. The encapsulation of EGCG in nanocarriers leads to its enhanced stability and higher therapeutic effects. A comprehensive review of studies currently available on the encapsulation of EGCG by means of nanocarriers will be addressed.

Dietary phytochemicals alter epigenetic events and signaling pathways for inhibition of metastasis cascade: phytoblockers of metastasis cascade

Cancer metastasis is a multistep process in which a cancer cell spreads from the site of the primary lesion, passes through the circulatory system, and establishes a secondary tumor at a new nonadjacent organ or part. Inhibition of cancer progression by dietary phytochemicals (DPs) offers significant promise for reducing the incidence and mortality of cancer. Consumption of DPs in the diet has been linked to a decrease in the rate of metastatic cancer in a number of preclinical animal models and human epidemiological studies. DPs have been reported to modulate the numerous biological events including epigenetic events (noncoding micro-RNAs, histone modification, and DNA methylation) and multiple signaling transduction pathways (Wnt/β-catenin, Notch, Sonic hedgehog, COX-2, EGFR, MAPK-ERK, JAK-STAT, Akt/PI3K/mTOR, NF-κB, AP-1, etc.), which can play a key role in regulation of metastasis cascade. Extensive studies have also been performed to determine the molecular mechanisms underlying antimetastatic activity of DPs, with results indicating that these DPs have significant inhibitory activity at nearly every step of the metastatic cascade. DPs have anticancer effects by inducing apoptosis and by inhibiting cell growth, migration, invasion, and angiogenesis. Growing evidence has also shown that these natural agents potentiate the efficacy of chemotherapy and radiotherapy through the regulation of multiple signaling pathways. In this review, we discuss the variety of molecular mechanisms by which DPs regulate metastatic cascade and highlight the potentials of these DPs as promising therapeutic inhibitors of cancer.

Resveratrol antibacterial activity against Escherichia coli is mediated by Z-ring formation inhibition via suppression of FtsZ expression

Resveratrol exhibits a potent antimicrobial activity. However, the mechanism underlying its antibacterial activity has not been shown. In this study, the antibacterial mechanism of resveratrol was investigated. To investigate induction of the SOS response, a strain containing the lacZ⁺gene under the control of an SOS-inducible sulA promoter was constructed. DNA damage was measured by pulse-field gel electrophoresis (PFGE). After resveratrol treatment, the cells were observed by confocal microscopy. For the RNA silencing assay, ftsZ-specific antisense peptide nucleic acid (PNA) was used. Reactive oxygen species (ROS) production increased in Escherichia coli after resveratrol treatment; however, cell growth was not recovered by ROS quenching, indicating that, in this experiment, ROS formation and cell death following resveratrol treatment were not directly correlated. Resveratrol treatment increased DNA fragmentation in cells, while SOS response-related gene expression levels increased in a dose-dependent manner. Cell elongation was observed after resveratrol treatment. Elongation was induced by inhibiting FtsZ, an essential cell-division protein in prokaryotes, and resulted in significant inhibition of Z-ring the formation in E. coli. The expression of ftsZ mRNA was suppressed by resveratrol. Our results indicate that resveratrol inhibits bacterial cell growth by suppressing FtsZ expression and Z-ring formation.

Extracellular signal-regulated kinases 1/2 and Akt contribute to triclosan-stimulated proliferation of JB6 Cl 41-5a cells

Triclosan is a broad spectrum anti-bacterial agent widely used in many personal care products, household items, medical devices, and clinical settings. Human exposure to triclosan is mainly through oral and dermal routes. In previous studies, we found that sub-chronic dermal exposure of B6C3F1 mice to triclosan induced epidermal hyperplasia and focal necrosis; however, the mechanisms for these responses remain elusive. In this study, using mouse epidermis-derived JB6 Cl 41-5a cells, we found that triclosan stimulated cell growth in a concentration- and time-dependent manner. Enhanced cell proliferation was demonstrated by a substantial increase in the percentage of BrdU-positive cells, an elevation in the protein levels of cyclin D1 and cyclin A, and a reduction in the protein level of p27(Kip1). Western blotting analysis revealed that triclosan induced the activation of extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), p38, and Akt. Pre-treatment of the cells with PD184352, an inhibitor of the upstream kinase MEK1/2, or with wortmannin, an inhibitor of phosphoinositide 3-kinase, blocked triclosan-mediated phosphorylation of ERK1/2 and Akt, respectively, and substantially suppressed triclosan-stimulated cell proliferation, whereas the JNK inhibitor SP600125 or the p38 inhibitor SB203580 had little to no effect on triclosan-stimulated cell proliferation. The phosphorylation activation of ERK1/2 and Akt was further confirmed on the skin of mice dermally administered triclosan. These data suggest that the activation of ERK1/2 and Akt is involved in triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Recent advances in understanding the anti-diabetic actions of dietary flavonoids

Flavonoids are polyphenolic compounds that are abundant in fruits and vegetables, and increasing evidence demonstrates a positive relationship between consumption of flavonoid-rich foods and disease prevention. Epidemiological, in vitro and animal studies support the beneficial effects of dietary flavonoids on glucose and lipid homeostasis. It is encouraging that the beneficial effects of some flavonoids are at physiological concentrations and comparable to clinically-used anti-diabetic drugs; however, clinical research in this field and studies on the anti-diabetic effects of flavonoid metabolites are limited. Flavonoids act on various molecular targets and regulate different signaling pathways in pancreatic β-cells, hepatocytes, adipocytes and skeletal myofibers. Flavonoids may exert beneficial effects in diabetes by (i) enhancing insulin secretion and reducing apoptosis and promoting proliferation of pancreatic β-cells; (ii) improving hyperglycemia through regulation of glucose metabolism in hepatocytes; (iii) reducing insulin resistance, inflammation and oxidative stress in muscle and fat and (iv) increasing glucose uptake in skeletal muscle and white adipose tissue. This review highlights recent findings on the anti-diabetic effects of dietary flavonoids, including flavan-3-ols, flavanones, flavonols, anthocyanidins, flavones and isoflavones, with particular emphasis on the studies that investigated the cellular and molecular mechanisms involved in the beneficial effects of the compounds.

Suppression of free fatty acid-induced insulin resistance by phytopolyphenols in C2C12 mouse skeletal muscle cells

It was reported that increased plasma levels of free fatty acids (FFAs) are associated with profound insulin resistance in skeletal muscle and may also play a critical role in the insulin resistance of obesity and type 2 diabetes mellitus. Skeletal muscle is the major site for insulin-stimulated glucose uptake and is involved in energy regulation and homeostasis. In this study, we used 12-O-tetradecanoylphorbol 13-acetate (TPA), a protein kinase C (PKC) activator, and palmitate to induce insulin resistance in C2C12 mouse skeletal muscle cells. Our data show that epigallocatechin gallate (EGCG) and curcumin treatment reduce insulin receptor substrate-1 (IRS-1) Ser307 phosphorylation, and curcumin is more potent to increase Akt phosphorylation in TPA induction. Moreover, we found that after 5 h of palmitate incubation, epicatechin gallate (ECG) can suppress IRS-1 Ser307 phosphorylation and significantly promote Akt, ERK1/2, p38 MAPK, and AMP-activated protein kinase activation. With a longer incubation with palmitate, IRS-1 exhibited a dramatic depletion, and treatment with EGCG, ECG, and curcumin could reverse IRS-1 expression, Akt phosphorylation, and MAPK signaling cascade activation and improve glucose uptake in C2C12 skeletal muscle cells, especially ECG and curcumin. In addition, treatment with these polyphenols can suppress acetyl-CoA carboxylase activation, but only EGCG could inhibit lipid accumulation in the intracellular site. These findings may suggest that curcumin shows the best capacity to improve FFA-induced insulin resistance than the other two, and ECG was more effective than EGCG in attenuating insulin resistance.

Epigallocatechin gallate suppresses peritoneal fibrosis in mice

Long-term peritoneal dialysis (PD) leads to histological changes in the peritoneal membrane. Angiogenesis and inflammation caused by glucose degradation products (GDPs) play crucial roles in peritoneal fibrosis. One such GDP is methylglyoxal (MGO), which enhances the formation of advanced glycation end products (AGEs). AGEs bind to their receptor (RAGE) and activate nuclear factor-κB (NF-κB), which is a key regulator of angiogenesis and inflammation. Recent studies have indicated that (-)-epigallocatechin gallate (EGCG), a tea polyphenol, inhibits angiogenesis and inflammation. Here, we examined whether EGCG suppresses peritoneal fibrosis in mice. Based on preliminary examination, 2mL of 40mM MGO or PD fluid was injected intraperitoneally and EGCG (50mg/kg) or saline was injected subcutaneously for 3weeks. In comparison to PD fluid+saline-treated mice, the peritoneal tissues of MGO+saline-treated mice showed marked thickening of the submesothelial compact zone. In the submesothelial compact zone of the MGO+saline-treated mice, CD31-positive vessels and vascular endothelial growth factor-positive cells were significantly increased, as were inflammation, F4/80-positive macrophages, and monocyte chemotactic protein-1. Moreover, 8-hydroxydeoxyguanosine, a marker of reactive oxygen species, and NF-κB, determined by Southwestern histochemistry, in the submesothelial compact zone were also increased in MGO+saline-treated mice. These changes were attenuated in MGO+EGCG-treated mice. We demonstrated that EGCG treatment suppresses peritoneal fibrosis via inhibition of NF-κB. Furthermore, EGCG inhibits reactive oxygen species production. The results of this study indicate that EGCG is a potentially novel candidate for the treatment of peritoneal fibrosis.

Epigallocatechin gallate (EGCG) inhibits type II phosphatidylinositol 4-kinases: a key component in pathways of phosphoinositide turnover

Type II phosphatidylinositol (PtdIns) 4-kinases produce PtdIns 4-phosphate, an early key signaling molecule in phosphatidylinositol cycle, which is indispensable for T cell activation. Type II PtdIns 4-kinase alpha and beta have similar biochemical properties. To distinguish these isoforms Epigallocatechin gallate (EGCG) has been evaluated as a specific inhibitor. EGCG is the major active catechin in green tea having anti-inflammatory, antiatherogenic and cancer chemopreventive properties. The precise mechanism of actions and molecular targets of EGCG in early signaling cascades are not well understood. In the present study, we have shown that EGCG inhibits type II PtdIns 4-kinases (α and β isoforms) and PtdIns 3-kinase activity in vitro. EGCG directly bind to both alpha and beta isoforms of type II PtdIns 4-kinases with a Kd of 2.62 μM and 1.02 μM, respectively. Type II PtdIns 4-kinase-EGCG complex have different binding pattern at its excited state. Both isoforms showed significant change in helicity upon binding with EGCG. EGCG modulates its effect by interacting with ATP binding pocket; the residues likely to be involved in EGCG binding were predicted by Autodock. Our findings suggest that EGCG inhibits two isoforms and could be a key to regulate T cell activation.

Elevated phosphate activates N-ras and promotes cell transformation and skin tumorigenesis

Recent results suggest a paradigm shift from viewing inorganic phosphate as a passive requirement for basic cell functions to an active regulator of cell behavior. We have previously shown that elevated concentrations of phosphate increased cell proliferation and expression of protumorigenic genes such as Fra-1 and osteopontin in a preosteoblast cell line. Therefore, we hypothesized that elevated phosphate concentrations would promote cell transformation in vitro and tumorigenesis in vivo. Supplementation of medium with phosphate increased anchorage-independent transformation and proliferation of BALB/c mouse JB6 epidermal cells, activation of N-ras, ERK1/2, and activator protein-1, and increased gene expression of Fra-1, COX-2, and osteopontin in a dose-dependent manner. These in vitro results led to the hypothesis that varying the levels of dietary inorganic phosphate would alter tumorigenesis in the mouse model of skin carcinogenesis. Female FVB/N mice were treated with 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate and fed high- or low-phosphate diets (1.2% versus 0.2% of the diet) for 19 weeks. The high-phosphate diet increased skin papilloma number by approximately 50% without changing feed intake and body weights. High dietary phosphate increased serum concentrations of phosphate, parathyroid hormone, and osteopontin and decreased serum concentrations of calcium. Thus, we conclude that elevated phosphate promotes cell transformation and skin tumorigenesis partly by increasing the availability of phosphate for activation of N-ras and its downstream targets, which defines reducing dietary phosphate as a novel target for chemoprevention.

Evaluation of Resveratrol and Piceatannol Cytotoxicity in Macrophages, T Cells, and Skin Cells

The cytotoxicity of resveratrol and of piceatannol, a structural analog of resveratrol, was examined in cultured cells. Using a MTT-based assay, which measures the conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) to a colored formazan product in living cells, resveratrol was found to inhibit the viability of transformed mouse macrophages, tumor-derived human T cells and human epidermoid carcinoma cells in a concentration-dependent manner, with the effect decreasing in the order: T cells (LC50 ~27 μmol L-1, 24 h; ~9 μmol L-1; 48h) > macrophages (LC50~29 μmol L-1, 24 h; 39 μmol L-1, 48 h) > skin cells (LC50 ~91 μmol L-1, 24 h; ~66 μmol L-1, 48 h). Paradoxically, a high concentration of resveratrol (50 μmol L-1) inhibited the proliferation of all three cell types, and a low concentration (5 μmol L-1) stimulated the proliferation of macrophages. The viability of macrophages was also decreased by piceatannol in a concentration-dependent manner. The stimulation of macrophages with zymosan lowered the cytotoxicity of both resveratrol and piceatannol. Scanning electron microscopy of cells treated with resveratrol revealed changes in cellular morphology that were consistent with toxicity. In macrophages and skin cells, resveratrol (50 μmol L-1) induced a time-dependent increase in reduced glutathione levels but did not alter the background levels of thiobarbituric acid-reactive substances. Taken together, the present data indicate that resveratrol is toxic to cultured macrophages, T cells and skin cells at concentrations ≥25 μmol L-1, and that the cytotoxicity occurs via a mechanism that does not involve oxidative stress. Furthermore, the degree of toxicity of both resveratrol and piceatannol towards macrophages depends on the activation status of these cells, with zymosan-activated cells appearing more resistant than nonstimulated cells.

Predicting the physiological relevance of in vitro cancer preventive activities of phytochemicals

There is growing interest in the ability of phytochemicals to prevent chronic diseases, such as cancer and heart disease. However, some of these agents have poor bioavailability and many of the in-depth studies into their mechanisms of action have been carried out in vitro using doses which are unachievable in humans. In order to optimize the design of chemopreventive treatment, it is important to determine which of the many reported mechanisms of action are clinically relevant. In this review we consider the physiologically achievable doses for a few of the best studied agents (indole-3-carbinol, diindolylmethane, curcumin, epigallocatechin-3-gallate and resveratrol) and summarize the data derived from studies using these low concentrations in cell culture. We then cite examples of in vitro effects which have been observed in vivo. Finally, the ability of agent combinations to act synergistically or antagonistically is considered. We conclude that each of the compounds shows an encouraging range of activities in vitro at concentrations which are likely to be physiologically relevant. There are also many examples of in vivo studies which validate in vitro observations. An important consideration is that combinations of agents can result in significant activity at concentrations where any single agent is inactive. Thus, for each of the compounds reviewed here, in vitro studies have provided useful insights into their mechanisms of action in humans. However, data are lacking on the full range of activities at low doses in vitro and the benefits or otherwise of combinations in vivo.

T-Lymphokine–Activated Killer Cell–Originated Protein Kinase Functions as a Positive Regulator of c-Jun-NH2-Kinase 1 Signaling and H-Ras–Induced Cell Transformation

T-lymphokine-activated killer cell-originated protein kinase (TOPK) is overexpressed in highly proliferating tumors such as leukemias and myelomas, and seems to play a key role in tumorigenesis or metastasis. However, the precise role and regulatory mechanism explaining the effects of TOPK on tumor cells still remain elusive. Here, we reported that TOPK regulates UVB-induced c-Jun-NH2-kinase 1 (JNK1) activity, and is essential for H-Ras-induced activator protein-1 activity and cell transformation. We showed that TOPK associated with and phosphorylated JNK1 following UVB irradiation in vitro or in vivo. Moreover, UVB-induced JNK1 activity was greatly augmented in mouse epidermal JB6 Cl41 cells that stably expressed TOPK cDNA. On the other hand, JNK1 activity was markedly attenuated by stable expression of small interfering RNA against TOPK in malignant melanoma RPMI 7951 cells. Interestingly, TOPK interacted with JNK-interacting protein 1 and caused an elevation of JNK-interacting protein 1 scaffolding activity, thereby enhancing JNK1 activity. Furthermore, JNK1 was required for TOPK-mediated activator protein-1 transcriptional activity and transformed foci induced by UVB or H-Ras. Taken together, these findings showed that TOPK positively modulated UVB-induced JNK1 activity and played a pivotal role in JNK1-mediated cell transformation induced by H-Ras. These studies might also provide a novel molecular mechanism for the role of TOPK in UVB-mediated skin carcinogenesis.

Involvement of the paxillin pathway in JB6 Cl41 cell transformation

Paxillin is a substrate of the Src tyrosine onco-kinase and is involved in cell transformation, cell spreading, migration, and cancer development mediated through the mitogen-activated protein kinase signaling cascades. Here, we showed that paxillin plays a key role in skin cell transformation induced by epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA). To investigate the mechanism of paxillin's role in cell transformation, we established a paxillin knockdown stably transfected cell line by introducing small interfering RNA-paxillin (si-paxillin). The si-paxillin cells displayed a dramatic suppression of cell proliferation and anchorage-independent cell transformation induced by EGF or TPA compared with si-mock control cells. In si-paxillin cells, decreased activator protein-1 (AP-1)-dependent luciferase activity corresponded with suppressed AP-1 DNA binding activity. Importantly, knockdown of paxillin inhibited EGF- or TPA-induced c-Jun phosphorylation at Ser(63) and Ser(73). Furthermore, total c-Jun protein level was dramatically decreased in si-paxillin cells and was dependent on serum deprivation time. The down-regulation of c-Jun was restored in si-paxillin cells by treatment with the proteasome inhibitor lactacystin but not by the lysosome inhibitor leupeptin. These results clearly provided evidence that paxillin regulates c-Jun protein level and plays a key role in cell transformation most likely through the regulation of c-Jun stability.

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.

Molecular targets of dietary agents for prevention and therapy of cancer

While fruits and vegetables are recommended for prevention of cancer and other diseases, their active ingredients (at the molecular level) and their mechanisms of action less well understood. Extensive research during the last half century has identified various molecular targets that can potentially be used not only for the prevention of cancer but also for treatment. However, lack of success with targeted monotherapy resulting from bypass mechanisms has forced researchers to employ either combination therapy or agents that interfere with multiple cell-signaling pathways. In this review, we present evidence that numerous agents identified from fruits and vegetables can interfere with several cell-signaling pathways. The agents include curcumin (turmeric), resveratrol (red grapes, peanuts and berries), genistein (soybean), diallyl sulfide (allium), S-allyl cysteine (allium), allicin (garlic), lycopene (tomato), capsaicin (red chilli), diosgenin (fenugreek), 6-gingerol (ginger), ellagic acid (pomegranate), ursolic acid (apple, pears, prunes), silymarin (milk thistle), anethol (anise, camphor, and fennel), catechins (green tea), eugenol (cloves), indole-3-carbinol (cruciferous vegetables), limonene (citrus fruits), beta carotene (carrots), and dietary fiber. For instance, the cell-signaling pathways inhibited by curcumin alone include NF-kappaB, AP-1, STAT3, Akt, Bcl-2, Bcl-X(L), caspases, PARP, IKK, EGFR, HER2, JNK, MAPK, COX2, and 5-LOX. The active principle identified in fruit and vegetables and the molecular targets modulated may be the basis for how these dietary agents not only prevent but also treat cancer and other diseases. This work reaffirms what Hippocrates said 25 centuries ago, let food be thy medicine and medicine be thy food.

N-acetylcysteine conjugate of phenethyl isothiocyanate enhances apoptosis in growth-stimulated human lung cells

We previously showed that dietary treatment with the N-acetylcysteine conjugate of phenethyl isothiocyanate (PEITC-NAC) inhibited benzo(a)pyrene-induced lung tumorigenesis in A/J mice, and that tumor inhibition was associated with induction of activator protein-1 (AP-1) activity and stimulation of apoptosis in the lungs of mice. In the present study, we show that PEITC-NAC also induces apoptosis and AP-1 activity in human lung adenocarcinoma A549 cells, and that activation of AP-1 is important in PEITC-NAC induced apoptosis in these cells. PEITC-NAC induced AP-1 binding activity in A549 cells in a dose- and time-dependent manner; peak activity appeared at 10 micromol/L after 24 hours. At that time, flow cytometric analysis showed a sub-G1 peak, indicating that approximately 4.5% of the cells had undergone apoptosis. When wild-type c-jun cDNA was transfected into A549 cells, PEITC-NAC-mediated apoptosis was greatly increased in the c-jun-transfected cells compared with the control vector-transfected cells, based on cell morphology and analysis of DNA fragmentation. Furthermore, cells that were pretreated with 100 nmol/L 12-O-tetradecanoyl phorbol-13-acetate, and then treated with 25 micromol/L PEITC-NAC, underwent enhanced apoptosis compared with cells that were treated with PEITC-NAC alone; cells treated with 12-O-tetradecanoyl phorbol-13-acetate alone showed active cell growth without apoptosis. Bivariate flow cytometric analysis of DNA strand breaks versus DNA content showed that apoptosis induced by PEITC-NAC occurred predominantly in the G2-M phase. These findings suggest that growth-stimulated cells with an elevated basal AP-1 activity, i.e., A549 cells transfected with wild-type c-jun or treated with a tumor promoter, were more sensitive to PEITC-NAC-mediated apoptosis. The observation that PEITC-NAC induces apoptosis predominantly in growth-promoted cells, such as neoplastic cells, suggests a selective mechanism by which PEITC-NAC inhibits lung carcinogenesis.

Regulation of Nrf2, NF-kappaB, and AP-1 signaling pathways by chemopreventive agents

The inhibition of carcinogenesis by chemopreventive agents has been demonstrated in many tumorigenesis animal models. The chemopreventive mechanisms of those phytochemicals have been investigated extensively, though mostly in in vitro cell culture systems. The cellular signaling cascades mediated by transcription factors, including nuclear factor E2-related factor 2 (Nrf2), nuclear factor-kappaB (NF-kappaB), and activator protein-1 (AP-1), have been shown to play pivotal roles in tumor initiation, promotion, and progression processes. Thus, as demonstrated by previous substantive mechanistic studies, they appear to be ideal targets for cancer chemoprevention. In this review, we discuss the current progress and future challenges on our understanding of the molecular mechanisms in cancer chemoprevention by phytochemicals, focusing on the regulation of Nrf2, NF-kappaB, and AP-1 signaling pathways.

Synergistic effect of green tea catechins on cell growth and apoptosis induction in gastric carcinoma cells

(-)-Epigallocatechin gallate (EGCG), a major component of green tea catechins, is known to inhibit cell growth and to induce apoptosis in a variety of cultured cells. We examined effects of green tea catechins in cultured cells derived from human gastric carcinoma. The proliferation of four cell lines (MKN-1, MKN-45, MKN-74 and KATO-III) was inhibited with EGCG in a dose-dependent manner. The growth of MKN-45 cells was most efficiently inhibited by the treatment (IC(50): 40 muM EGCG) among the four cell lines, while KATO-III cells were most insensitive (IC(50): 80-150 muM) to the EGCG treatment. In addition, (-)-epicatechin (EC) had a major synergistic effect on the induction of apoptosis in MKN-45 cells treated with EGCG; however it had little effect on the inhibition of cell growth induced by EGCG. To study the molecular mechanisms behind the induction of apoptosis by EGCG, the activity of caspases in MKN-45 cells treated with EGCG was examined. Activity levels of caspases-3, -8 and -9 were elevated in EGCG-treated cells, suggesting that these caspases are involved in the apoptosis induced by EGCG. Furthermore, the synergistic effect of EC with EGCG on the induction of apoptosis was specifically canceled by catalase treatment, suggesting that the synergism involves the extracellular production of reactive oxygen species.

The intermediate filament protein vimentin is a new target for epigallocatechin gallate

Epigallocatechin gallate (EGCG) is the major active polyphenol in green tea. Protein interaction with EGCG is a critical step in the effects of EGCG on the regulation of various key proteins involved in signal transduction. We have identified a novel molecular target of EGCG using affinity chromatography, two-dimensional electrophoresis, and mass spectrometry for protein identification. Spots of interest were identified as the intermediate filament, vimentin. The identification was confirmed by Western blot analysis using an anti-vimentin antibody. Experiments using a pull-down assay with [3H]EGCG demonstrate binding of EGCG to vimentin with a Kd of 3.3 nm. EGCG inhibited phosphorylation of vimentin at serines 50 and 55 and phosphorylation of vimentin by cyclin-dependent kinase 2 and cAMP-dependent protein kinase. EGCG specifically inhibits cell proliferation by binding to vimentin. Because vimentin is important for maintaining cellular functions and is essential in maintaining the structure and mechanical integration of the cellular space, the inhibitory effect of EGCG on vimentin may further explain its anti-tumor-promoting effect.

Induction of apoptosis by epigallocatechin-3-gallate via mitochondrial signal transduction pathway

PURPOSE

To elucidate the apoptosis induction of Epigallocatechin-3-gallate (EGCG) on nasopharyngeal carcinoma (NPC) cells via mitochondrial signal transduction pathway regulated by EB-virus-encoded latent membrane protein 1 (LMP1).

METHODS

The survival rates of pTet-on-LMP1 HNE2 cells after the EGCG treatment were determined by MTT assay. Induction of apoptosis in pTet-on-LMP1 HNE2 cells after the EGCG treatment was analyzed by agarose gel electrophoresis. The activity of caspase-9 was determined by ApoAlert Caspase-9 Fluorescent Assay kit after the EGCG treatment. The protein expressions of cytochrome c and Bcl-2 were analyzed by Western blotting after the EGCG treatment.

RESULTS

EGCG inhibited the survival rates of pTet-on-LMP1 HNE2 cells and induced apoptosis of pTet-on-LMP1 HNE2 cells. EGCG raised the activities of caspase-9, enhanced the releasing of cytochrome c from the mitochondria, and suppressed the protein expression of Bcl-2. These are the key targets on the mitochondrial signal transduction pathway in apoptosis.

CONCLUSIONS

EGCG inhibited the survival rate of NPC cells and induced apoptosis of NPC cells via the mitochondrial signal transduction pathway. This study suggests that the interference effect of EGCG on targets of the mitochondrial signal transduction pathway plays an important role in the anticancer function.

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.

Transcriptional responses to epigallocatechin-3 gallate in HT 29 colon carcinoma spheroids

Catechins have been reported to possess anti-cancer activity in vitro and in vivo. To identify target genes that may be involved in the anti-tumorigenic effect of catechins, gene expression profiles in adherent human HT 29 colon carcinoma cells, in HT 29 spheroids and in epigallocatechin-3 gallate (EGCG)-treated HT 29 cells have been analysed by high-density oligonucleotide microarrays. Treatment of HT 29 cells with EGCG (2.5-50 microm) resulted in a dose-dependent inhibition of spheroid formation of HT 29 cells. Forty transcripts were induced at least twofold in 3-day-old spheroids relative to normal adherent cells using three replicates. Oncogenes like c-fos and c-jun are significantly up-regulated in spheroids. We identified several signal transduction and proliferation genes which are down-regulated in response to EGCG treatment. Increase in the mRNA expression profile of c-Fos correlated well with protein levels in HT 29 spheroids whereas EGCG did not affect protein formation. In agreement with the DNA chip data, IQGAP2 protein was not increased in spheroids but protein formation was totally blocked in EGCG-treated cells. Interestingly, no change in expression of cytotoxic or apoptotic related genes has been observed in EGCG-treated cells. Our findings suggest that EGCG may exert its anti-cancer activity through modulation of expression of a number of genes that are involved in cell proliferation, cell-cell contacts and cell-matrix interactions.

Chemopreventive potential of epigallocatechin gallate and genistein: evidence from epidemiological and laboratory studies

A wide array of antioxidative and anti-inflammatory substances derived from edible plants have been reported to possess chemopreventive and chemoprotective activities. Among the most extensively investigated and well-defined dietary chemopreventives are epigallocatechin gallate (EGCG), a principal antioxidant derived from green tea and genistein, a major pharmacologically active isoflavone widely present in soy products. Multiple lines evidence from epidemiologic studies indicate that frequent consumption of green tea is inversely associated with the risk of several types of human cancer, and studies with animal and in vitro cell culture models have revealed EGCG as a major chemopreventive ingredient of green tea. The lower frequencies of breast and prostate cancer in Asian population in general, compared to those in Western societies have been attributed to their consumption of relatively large amounts of soy products. Genistein, as a principal chemopreventive components of soy, exerts a wide array of chemopreventive activities in each stage of multistep carcinogenesis. The purpose of this review is to provide perspectives on the molecular basis of chemopreventive activities of EGCG and geneistein as representative functional food phytochemicals with emphasis on their ability to control intracellular signaling cascades responsible for regulating cell growth and differentiation.

Green tea polyphenol and curcumin inversely regulate human involucrin promoter activity via opposing effects on CCAAT/enhancer-binding protein function

Antioxidants are important candidate agents for the prevention of disease. However, the possibility that different antioxidants may produce opposing effects in tissues has not been adequately explored. We have reported previously that (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol antioxidant, stimulates expression of the keratinocyte differentiation marker, involucrin (hINV), via a Ras, MEKK1, MEK3, p38delta signaling cascade (Balasubramanian, S., Efimova, T., and Eckert, R. L. (2002) J. Biol. Chem. 277, 1828-1836). We now show that EGCG activation of this pathway results in increased CCAAT/enhancer-binding protein (C/EBPalpha and C/EBPbeta) factor level and increased complex formation at the hINV promoter C/EBP DNA binding site. This binding is associated with increased promoter activity. Mutation of the hINV promoter C/EBP binding site eliminates the regulation as does expression of GADD153, a dominant-negative C/EBP factor. In contrast, a second antioxidant, curcumin, inhibits the EGCG-dependent promoter activation. This is associated with inhibition of the EGCG-dependent increase in C/EBP factor level and C/EBP factor binding to the hINV promoter. Curcumin also inhibits the EGCG-dependent increase in endogenous hINV levels. The curcumin-dependent suppression of C/EBP factor level is inhibited by treatment with the proteasome inhibitor MG132, suggesting that the proteasome function is required for curcumin action. We conclude that curcumin and EGCG produce opposing effects on involucrin gene expression via regulation of C/EBP factor function. The observation that two antioxidants can produce opposite effects is an important consideration in the context of therapeutic antioxidant use.

Epigallocatechin-3-gallate is absorbed but extensively glucuronidated following oral administration to mice

Epigallocatechin-3-gallate (EGCG), the most abundant catechin in green tea (Camellia sinensis), has shown cancer preventive activity in animal models. The bioavailability of EGCG in the most commonly used animal species, mice, is poorly understood. Moreover, the pharmacokinetic parameters of EGCG have not been reported previously in mice. Here we report that after administration of EGCG intravenously at 21.8 micro mol/kg or intragastrically at 163.8 micro mol/kg, the peak plasma levels of EGCG in male CF-1 mice were 2.7 +/- 0.7 and 0.28 +/- 0.08 micro mol/L, respectively. EGCG was present mainly (50-90%) as the glucuronide. The plasma bioavailability of EGCG after intragastric administration was higher than previously reported in rats (26.5 +/- 7.5% vs. 1.6 +/- 0.6%). The conjugated EGCG displayed a shorter t(1/2) (82.8-211.5 vs 804.9-1102.3 min) than unconjugated EGCG (P < 0.01, Student's t test). EGCG was present in the unconjugated form in the lung, prostate and other tissues at levels of 0.31-3.56 nmol/g after intravenous administration. Although intragastric administration resulted in lower levels in most tissues compared with intravenous administration (e.g., 0.006 +/- 0.004 vs. 2.66 +/- 1.0 nmol/g in the lung), the levels in the small intestine and colon were high at 45.2 +/- 13.5 and 7.86 +/- 2.4 nmol/g, respectively. This is the first report of the pharmacokinetic parameters of EGCG in mice. Such information provides a basis for understanding the bioavailability of EGCG in mice and should aid in understanding the cancer preventive activity of EGCG.

Nutritional genomics: the next frontier in the postgenomic era

The interface between the nutritional environment and cellular/genetic processes is being referred to as “nutrigenomics.” Nutrigenomics seeks to provide a molecular genetic understanding for how common dietary chemicals (i.e., nutrition) affect health by altering the expression and/or structure of an individual’s genetic makeup. The fundamental concepts of the field are that the progression from a healthy phenotype to a chronic disease phenotype must occur by changes in gene expression or by differences in activities of proteins and enzymes and that dietary chemicals directly or indirectly regulate the expression of genomic information. We present a conceptual basis and specific examples for this new branch of genomic research that focuses on the tenets of nutritional genomics: 1) common dietary chemicals act on the human genome, either directly or indirectly, to alter gene expression or structure; 2) under certain circumstances and in some individuals, diet can be a serious risk factor for a number of diseases; 3) some diet-regulated genes (and their normal, common variants) are likely to play a role in the onset, incidence, progression, and/or severity of chronic diseases; 4) the degree to which diet influences the balance between healthy and disease states may depend on an individual’s genetic makeup; and 5) dietary intervention based on knowledge of nutritional requirement, nutritional status, and genotype (i.e., “individualized nutrition”) can be used to prevent, mitigate, or cure chronic disease.

Mechanisms of cancer prevention by tea constituents

Consumption of tea (Camellia sinensis) has been suggested to prevent cancer, heart disease and other diseases. Animal studies have shown that tea and tea constituents inhibit carcinogenesis of the skin, lung, oral cavity, esophagus, stomach, liver, prostate and other organs. In some studies, the inhibition correlated with an increase in tumor cell apoptosis and a decrease in cell proliferation. Studies with human cancer cell lines have demonstrated that epigallocatechin-3-gallate (EGCG), a major tea polyphenol, inhibits mitogen-activated protein kinases, cyclin-dependent kinases, growth factor-related cell signaling, activation of activator protein 1 (AP-1) and nuclear factor kappaB (NFkappaB), topoisomerase I and matrix metalloproteinases as well as other potential targets. Although some studies report effects of EGCG at submicromolar levels, most experiments require concentrations of >10 or 20 micromol/L to demonstrate the effect. In humans, tea polyphenols undergo glucuronidation, sulfation, methylation, and ring fission. The peak plasma concentration of EGCG is approximately 1 micromol/L. The possible relevance of each of the proposed mechanisms to human cancer prevention is discussed in light of current bioavailability data for tea polyphenols and the potential limitations of animal models of carcinogenesis. Such discussion, it is hoped, will clarify some misunderstandings of cancer prevention by tea and stimulate new research efforts.

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

The green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) possesses promising anticancer potential. Although in vivo studies unveiled the metabolic routes and pharmacokinetics of EGCG and showed no adverse effects, in vitro studies at high concentrations demonstrated oxidative stress. EGCG causes differential oxidative environments in tumor versus normal epithelial cells, but the roles that EGCG, hydrogen peroxide (H2O2), and intracellular catalase play in the epithelial system are largely unknown. The current study employed enzyme activity assays, reactive oxygen species quantification, and immunoblotting to investigate whether EGCG-induced differential effects correlate with levels of key antioxidant enzymes and H2O2. It was found that normal human keratinocytes with high catalase activity are least susceptible to H2O2, whereas H2O2 caused significant cytotoxicity in oral carcinoma cell lines. However, the EGCG-induced differential effects could not be duplicated by H2O2 alone. The addition of exogenous catalase failed to completely prevent the EGCG-induced cytotoxicity and rescue the EGCG-induced growth arrest in the tumor cells. The antioxidant N-acetyl-L-cysteine rescued the tumor cells from H2O2-induced damage only, but not from EGCG-induced mitochondrial damage. Finally, alterations in catalase or superoxide dismutase activities were not observed upon EGCG exposure. In conclusion, although endogenous catalase may play a role in response to H2O2-induced cytotoxicity, the EGCG-induced cytotoxic effects on tumor cells mainly result from sources other than H2O2.

Flavonoid effects relevant to cancer

Flavonoids, such as daidzein and genistein, present in dietary plants like soybean, have unique chemical properties with biological activity relevant to cancer. Many flavonoids and polyphenols, including resveratrol in red wine and epigallocatechin gallate in green tea, are known antioxidants. Some of these compounds have estrogenic (and antiestrogenic) activity and are commonly referred to as phytoestrogens. A yeast-based estrogen receptor (ER) reporter assay has been used to measure the ability of flavonoids to bind to ER and activate estrogen responsive genes. Recently, estrogenic compounds were also shown to trigger rapid, nongenomic effects. The molecular mechanisms, however, have not been completely detailed and little information exists regarding their relevance to cancer progression. As a preliminary step toward elucidating rapid phytoestrogen action on breast cancer cells, we investigated the effect of 17-beta estradiol (E2), genistein, daidzein and resveratrol on the activation status of signaling proteins that regulate cell survival and invasion, the cell properties underlying breast cancer progression. The effect of these estrogenic compounds on the activation, via phosphorylation, of Akt/protein kinase B (Akt) and focal adhesion kinase (FAK) were analyzed in ER-positive and -negative human breast cancer cell lines. E2, genistein and daidzein increased whereas resveratrol decreased both Akt and FAK phosphorylation in nonmetastatic ER-positive T47D cells. In metastatic ER-negative MDA-MB-231 cells, all estrogenic compounds tested increased Akt and FAK phosphorylation. The inhibitory action of resveratrol on cell survival and proliferation is ER dependent. Therefore, all estrogenic compounds tested, including resveratrol, may exert supplementary ER-independent nongenomic effects on cell survival and migration in breast cancer cells.

Attenuation of internal organ damages by exogenously administered epidermal growth factor (EGF) in burned rodents

Major burns are associated with multiple internal organ damages, including necrosis of the gastrointestinal mucosa. Failure of the intestinal barrier is a serious complication in burned patients. Epidermal growth factor (EGF) is a mitogenic polypeptide that stimulates wound repair and affords protection to the gastric mucosa. We examined whether a single systemic intervention with EGF prevents organ systems damages, following full-thickness scalds (25-30%) in rodents. Animals were randomly assigned to receive an intraperitoneal injection of EGF (30 microg/kg in mice, 10 microg/kg in rats) or saline solution, 30 min prior thermal injury in mice or after the cutaneous injury in rats. General clinical condition and mortality during 24h were recorded. Animals were autopsied and histopathological and histomorphometric studies were conducted. Mice treated with EGF exhibited a milder clinical evolution and acute lethality was significantly reduced as compared to saline counterparts (P<0.01). Histopathological and morphometric analysis showed that EGF significantly reduced intestinal necrosis and contributed to preserve jejunoileal architecture in mice (P<0.05) and rats (P<0.01). The onset of renal hemorrhagic foci was significantly reduced in EGF-treated groups (P<0.01). Lung damages appeared attenuated in EGF-treated animals. These data indicate the salutary effects of EGF by attenuating internal complications associated to thermal injuries. Further studies are warranted to fully elucidate the usefulness of this therapy.

Antimicrobial effect of resveratrol on dermatophytes and bacterial pathogens of the skin

The phytoalexin resveratrol is commonly found in food and drinks, including red wine, grapes, and peanuts. Many studies have shown that this compound has anti-inflammatory properties, and it has been ascribed as having health benefits that help to prevent cancer and coronary heart disease. A treatment that combines antimicrobial and anti-inflammatory actions may be desirable for alleviating many skin conditions that range in severity. Therefore, we evaluated the antimicrobial activity of resveratrol against bacteria and dermatophytes that are major etiologic agents of human skin infections. Using the broth microdilution protocol of the National Committee for Clinical Laboratory Standards (NCCLS) M7-A5, growth of the bacterial species Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa was inhibited at 171-342 microg/mL of resveratrol in the solvent dimethyl sulfoxide. Using the NCCLS protocol M38-P, activity against the fungal species Trichophyton mentagrophytes, Trichophyton tonsurans, Trichophyton rubrum, Epidermophyton floccosum, and Microsporum gypseum was also tested. The growth of dermatophytes was inhibited at 25-50 microg/mL of resveratrol. Thus, this study indicates a novel application for resveratrol, a molecule of plant defense, to combat human fungal pathogens. Resveratrol and its analogs may have wide application to skin conditions that afflict a significant portion of our population, and may also have promising clinical potentials in diabetic wounds.

Black tea polyphenols, theaflavins, prevent cellular DNA damage by inhibiting oxidative stress and suppressing cytochrome P450 1A1 in cell cultures

Tea polyphenols have been demonstrated as chemopreventive agents in a number of experimental models. However, less is known about the mechanism of chemoprevention by black tea compared with that of green tea. Some beneficial properties of theaflavins, the black tea polyphenols, were investigated in the present study. Theaflavins showed inhibitory effects on H(2)O(2)- and tert-butyl hydroperoxide (tBuOOH)-induced cytotoxicity (evaluated by tetrazolium bromide reduction), cellular oxidative stress (detected by oxidation of 2', 7'-dichlorofluorescin), and DNA damage (measured by amount of 8-OHdG and comet assay) in rat normal liver epithelium cell RL-34 cell lines. In addition, theaflavins also exhibited suppression of cytochrome P450 1A1 induced by omeprazole in the human hepatoma HepG2 cell line. Furthermore, when HepG2 cells were pretreated with omeprazole to induce CYP1A1, then exposed to benzo[a]pyrene (B[a]P), DNA damage was observed using the comet assay. However, theaflavins could inhibit this DNA damage. These results indicated that theaflavins could prevent cellular DNA damage by inhibiting oxidative stress and suppressing cytochrome P450 1A1 in cell cultures.