Differences of four catechins in cell cycle arrest and induction of apoptosis in LoVo cells

Induction of Apoptosis via Inactivating PI3K/AKT Pathway in Colorectal Cancer Cells Using Aged Chinese Hakka Stir-Fried Green Tea Extract

Food extract supplements, with high functional activity and low side effects, play a recognized role in the adjunctive therapy of human colorectal cancer. The present study reported a new functional beverage, which is a type of Chinese Hakka stir-fried green tea (HSGT) aged for several years. The extracts of the lyophilized powder of five HSGT samples with different aging periods were analyzed with high-performance liquid chromatography. The major components of the extract were found to include polyphenols, catechins, amino acids, catechins, gallic acid and caffeine. The tea extracts were also investigated for their therapeutic activity against human colorectal cancer cells, HT-29, an epithelial cell isolated from the primary tumor. The effect of different aging time of the tea on the anticancer potency was compared. Our results showed that, at the cellular level, all the extracts of the aged teas significantly inhibited the proliferation of HT-29 in a concentration-dependent manner. In particular, two samples prepared in 2015 (15Y, aged for 6 years) and 2019 (19Y, aged for 2 years) exhibited the highest inhibition rate for 48 h treatment (cell viability was 50% at 0.2 mg/mL). Further, all the aged tea extracts examined were able to enhance the apoptosis of HT-29 cells (apoptosis rate > 25%) and block the transition of G1/S phase (cell-cycle distribution (CSD) from <20% to >30%) population to G2/M phase (CSD from nearly 30% to nearly 10%) at 0.2 mg/mL for 24 h or 48 h. Western blotting results also showed that the tea extracts inhibited cyclin-dependent kinases 2/4 (CDK2, CDK4) and CylinB1 protein expression, as well as increased poly ADP-ribose polymerase (PRAP) expression and Bcl2-associated X (Bax)/B-cell lymphoma-2 (Bcl2) ratio. In addition, an upstream signal of one of the above proteins, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling, was found to be involved in the regulation, as evidenced by the inhibition of phosphorylated PI3K and AKT by the extracts of the aged tea. Therefore, our study reveals that traditional Chinese aged tea (HSGT) may inhibit colon cancer cell proliferation, cell-cycle progression and promoted apoptosis of colon cancer cells by inactivating PI3K/AKT signalling.

Differential Cytotoxicity of Rooibos and Green Tea Extracts against Primary Rat Hepatocytes and Human Liver and Colon Cancer Cells - Causal Role of Major Flavonoids

Differential anti-proliferative and pro-apoptotic effects of aqueous extracts of green rooibos (Rg; Aspalathus linearis) and green tea (GT; Camellia sinensis) and an aspalathin-enriched extract of green rooibos (GRE), were investigated in primary rat hepatocytes (PH) and human liver (HepG2) and colon (HT-29) cancer cells. Rooibos flavonoids, aspalathin and luteolin, and the green tea flavanol, epigallocatechin gallate (EGCG), were included to assess their contribution relative to their extract concentrations. GRE was the most effective in reducing cell growth parameters which was associated with a high total polyphenol content and high ferric reducing potential. Differential cell responses were noticed with HepG2 cells more sensitive than PH toward the induction of apoptosis by GRE. Luteolin induced apoptosis in PH and HepG2 cells while aspalathin lacked any effect. EGCG induced apoptosis in HepG2 cells while PH were resistant. HT-29 cells were resistant to apoptosis induction by the tea and pure flavonoids. Differences existed in the individual effects of the major rooibos and GT flavonoids against cell growth parameters compared to their equivalent concentrations in the extract mixtures. Diversity of the flavonoid constituents, physicochemical properties and cellular redox status governing cell survival are likely to explain the differential cell responses.

Antiproliferative activity of green, black tea and olive leaves polyphenols subjected to biosorption and in vitro gastrointestinal digestion in Caco-2 cells

Olive (Olea europaea L.) leaves and tea (Camellia sinensis) are rich sources of bioactive compounds, especially polyphenols. Our previous studies have evidenced the potential use of Saccharomyces cerevisiae as a natural delivery system for these antioxidants and a means to improve their bioaccessibility in the human gut. In the present work, the antiproliferative effect of green tea (GT), black tea (BT) and olive leaves (OL) infusions and suspensions of S. cerevisiae were evaluated, for the first time, in human colon cancer cells (Caco-2) after biosorption and in vitro gastrointestinal digestion. The bioaccessible fractions (BF) were not overtly cytotoxic, not affecting cell viability. ROS and mitochondrial membrane potential changes (Δψm) values were reduced compared with control cells. Moreover, all the BF after biosorption induced a significant (p < 0.05) increase in cell proportions in S-phase. The arrest of the cell cycle was reversible without induction of apoptosis, suggesting that the biosorbed phenolics in both infusions and suspensions act as cytostatic agents.

Epigallocatechin gallate inhibits dimethylhydrazine-induced colorectal cancer in rats

BACKGROUND

Epigallocatechin gallate (EGCG) is a polyhydroxy phenolic compound extracted from tea and its antitumor effect has received widespread attention. We explored the inhibitory effect of EGCG on dimethylhydrazine (DMH)-induced colorectal cancer (CRC) using a rat model, predicted the interaction between EGCG and CRC target genes using a database, and explained the EGCG associated target pathways and mechanisms in CRC.

AIM

To understand the inhibitory mechanisms of EGCG on CRC cell proliferation and identify its pharmacological targets by network pharmacology analysis.

METHODS

DMH (40 mg/kg, s.c., twice weekly for eight weeks) was used to induce CRC in rats. After model establishment, the rats were administered with EGCG (50, 100, or 200 mg/kg, p.o., once daily for eight weeks) and killed 12 and 20 wk after the start of the experiment. Formation of aberrant crypt foci and tumor was studied by histological analysis. Using network pharmacology analysis, candidate and collective targets of EGCG and CRC were identified, and Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes analyses were used to predict the pathways altered by EGCG.

RESULTS

At week 12, high-dose EGCG treatment significantly reduced the tumor formation rate, total number of tumors, cancerous and non-cancerous tumors, tumor volume, ascites formation, and aberrant crypt foci count. At week 20, all three doses of EGCG were effective. Seventy-eight collective targets of EGCG and CRC were identified, of which 28 genes were dysregulated in CRC. Kyoto Encyclopedia of Genes and Genomes and GO analyses showed that the dysregulated genes were enriched in hsa05210 (CRC), hsa04115 (p53 signaling pathway), and hsa04151 (PI3K-Akt signaling pathway), GO:0043124 (negative regulation of I-kappaB kinase/NF-kappaB signaling pathway), GO:0043409 (negative regulation of mitogen-activated protein kinase cascade), and GO:2001244 (positive regulation of intrinsic apoptotic signaling pathway) respectively.

CONCLUSION

EGCG inhibits the formation of DMH-induced CRC by regulating key pathways involved in tumorigenesis.

Apoptotic-Induced Effects of Acacia Catechu Willd. Extract in Human Colon Cancer Cells

The research for innovative treatments against colon adenocarcinomas is still a great challenge. Acacia catechu Willd. heartwood extract (AC) has health-promoting qualities, especially at the gastrointestinal level. This study characterized AC for its catechins content and investigated the apoptosis-enhancing effect in human colorectal adenocarcinoma HT-29 cells, along with its ability to spare healthy tissue. MTT assay was used to describe the time course, concentration dependence and reversibility of AC-mediated cytotoxicity. Cell cycle analysis and AV-PI and DAPI-staining were performed to evaluate apoptosis, together with ROS formation, mitochondrial membrane potential (MMP) changes and caspase activities. Rat ileum and colon rings were tested for their viability and functionality to explore AC effects on healthy tissue. Quantitative analysis highlighted that AC was rich in (±)-catechin (31.5 ± 0.82 mg/g) and (−)-epicatechin (12.5 ± 0.42 mg/g). AC irreversibly decreased cell viability in a concentration-dependent, but not time-dependent fashion. Cytotoxicity was accompanied by increases in apoptotic cells and ROS, a reduction in MMP and increases in caspase-9 and 3 activities. AC did not affect rat ileum and colon rings’ viability and functionality, suggesting a safe profile toward healthy tissue. The present findings outline the potential of AC for colon cancer treatment.

Cocoa tea (Camellia ptilophylla) induces mitochondria-dependent apoptosis in HCT116 cells via ROS generation and PI3K/Akt signaling pathway

Cocoa tea (Camellia ptilophylla), a natural gallocatechin gallate (GCG)-rich and low caffeine-containing tea species, has been recently reported to possess various bioactivities. However, the anti-colon cancer effects of Cocoa tea and its underlying mechanisms remain virtually unknown. This study aimed to assess the anti-proliferative and pro-apoptotic effects of water extract of Cocoa tea (CWE) on human colon cancer HCT116 cells compared with Yunnan Daye tea (YWE). Primarily, CWE showed stronger anti-proliferation and apoptosis induction than YWE. Moreover, reduction of mitochondrial membrane potential (MMP), up-regulation of Bax/Bcl-2 ratio, release of cytochrome c, activation of caspase-9 and -3, and cleavage of poly (ADP-ribose) polymerase (PARP) were observed, suggesting that mitochondrial apoptotic pathway was activated by CWE. Furthermore, CWE-induced apoptosis in HCT116 cells was dependent on the generation of intracellular reactive oxygen species (ROS) and down-regulation of phosphatidylinositol-3-kinase (PI3K)/Akt pathway. Pretreatment with ROS scavenger N-acetyl cysteine (NAC) attenuated the impact of CWE on mitochondria-related apoptosis proteins, and partially recovered the inhibition of Akt phosphorylation. These results indicated that ROS generation mediated mitochondrial dysfunction and inactivation of PI3K/Akt pathway in CWE-induced HCT116 cell apoptosis. Additionally, CWE significantly inhibited tumor growth in HCT116 tumor-bearing mice, suggesting that Cocoa tea could act as a potential functional beverage to prevent or treat colorectal cancer.

Polyphenol Polymerization by an Alternative Oxidative Microbial Enzyme and Characterization of the Biological Activity of Oligomers

The recombinant catalase-peroxidase HPI from E. coli was used as an alternative enzyme in polymerization reactions for the production of (−) epicatechin oligomers and their biological activity was characterized. The enzyme was prepared in two forms: a purified and an immobilized form. Both were tested for their activity in oxidative polymerization reactions, and their stability and reusability were assessed. The polymerization reactions were followed by SEC-HPLC analyses, and the substrate was completely converted into one or more polymerization products depending on the reactions conditions. Results showed that the utilized conditions allowed for the isolation of some oligomers of different molecular weight: the oligomers containing 6 and 7 units of epicatechin substrate are the heaviest ones. Epicatechin was also used in reactions catalyzed by HRP in the same reaction conditions for comparison. In addition, one selected oligomer obtained by HPI enzyme catalysis was shown to act as in vitro inhibitor of tumor cell growth, like one oligomer deriving from epicatechin by HRP catalysis. These data confirm that epicatechin oligomeric form is more effective than its monomer in biological activity and suggest the use of HPI as an alternative enzyme in reactions for the production of epicatechin oligomers.

Flavan-3-ols consumption and cancer risk: A meta-analysis of epidemiologic studies

Although numerous in vitro studies and animal model data have suggested that flavan-3-ols, the most common subclass of flavonoids in the diet, may exert protective effects against cancer, epidemiologic studies have reported inconclusive results for the association between flavan-3-ols intake and cancer risk. Therefore, we conducted this meta-analysis of epidemiologic studies to investigate the preventive effects of flavan-3-ols on various types of cancers. A total of 43 epidemiologic studies, consisting of 25 case-control and 18 prospective cohort studies, were included. A significant inverse association was shown between flavan-3-ols intake and the risk of overall cancer (relative risk (RR) 0.935, 95%CI: 0.891-0.981). When cancer types were separately analyzed, a statistically significant protective effect of flavan-3-ols consumption was observed in rectal cancer (RR 0.838, 95%CI: 0.733-0.958), oropharyngeal and laryngeal cancer (RR 0.759, 95%CI: 0.581-0.993), breast (RR 0.885, 95%CI: 0.790-0.991) in case-control studies and stomach cancer in women (RR 0.633, 95%CI: 0.468-0.858). Our analysis indicates the potential benefits of flavan-3-ols in cancer prevention.

Phytochemicals, Anti-Inflammatory, Antiproliferative, and Methylglyoxal Trapping Properties of Zijuan Tea

Zijuan tea (Camellia sinensis var. assamica) is a unique anthocyanin-rich tea cultivar in China. Although chemical component analysis of Zijuan tea and extraction technology of anthocyanins was widely documented, its functional properties have not been extensively explored. In this study, the anti-inflammatory, antiproliferative, and methylglyoxal (MGO) trapping activities of water extract (ZWE) and ethyl acetate extract (ZEE) of Zijuan tea were investigated for the 1st time. Results showed that ZWE and ZEE exhibited inhibitory effects on nitric oxide (NO), tumor necrosis factor (TNF)-α, and interleukin (IL)-6 production as well as inducible nitric oxide synthase protein (iNOS) expression in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. Moreover, Zijuan tea extracts exerted stronger antiproliferative activity against HCT-116 cells compared with HepG2 and MDA-MB-231 cells, and thus could induce apoptosis in HCT-116 cells in a dose-dependent manner. Furthermore, Zijuan tea extracts were effective in trapping MGO under simulated physiological conditions, and the T_1/2 (the time for 50% MGO remaining) values of ZWE and ZEE were 3.69 and 6.20 min, respectively. Additionally, the contents of total phenolics and catechins in ZEE were 685.43 ± 16.00 and 454.96 ± 4.21 mg/g extract, respectively, and in ZWE were 422.59 ± 12.09 and 307.29 ± 0.85 mg/g extract, respectively. Therefore, ZEE exhibited better anti-inflammatory, antiproliferative, and MGO trapping properties than ZWE may be mainly attributed to its higher (P < 0.05) content of total phenolics, expecially catechins. These results suggest that Zijuan tea could be a potential natural resource for the development of functional tea beverage.

PRACTICAL APPLICATION

This study revealed that Zijuan tea extracts possessed anti-inflammatory, antiproliferative, and methylglyoxal trapping potentials in vitro. With high anthocyanins and polyphenols, Zijuan tea can be developed into a healthy tea beverage or used as a natural component to reduce the level of methylglyoxal in Maillard reaction.

Antioxidant Activity and Cytotoxicity Effect of Cocoa Beans Subjected to Different Processing Conditions in Human Lung Carcinoma Cells

Lung cancer is a common malignancy in men and the second leading cause of cancer-related mortality in men in the western world. Phenolic cocoa ingredients have a strong antioxidative activity and the potential to have a protective effect against cancer. In the present study, we have evaluated the influence of cocoa beans subjected to different processing conditions on cell viability and apoptosis of human lung cancer cells (A549). We measured the viability of lung cells treated with cocoa beans, unroasted slates (US), roasted slates (RS), unroasted well fermented (UWF) cocoa, and roasted well fermented (RWF) cocoa for 24 h. Using an MTT assay, we observed a decrease in the viability of A549 cells after treatment with cocoa bean extracts. Flow cytometer analysis revealed that cocoa beans increased the percentage of cells in sub-G₁ phase and promoted up to twofold increase of apoptotic cells when compared to the control group. Taken together, the present study suggests that cocoa beans may have a protective effect against lung cancer.

Preventive Effects of Cocoa and Cocoa Antioxidants in Colon Cancer

Colorectal cancer is one of the main causes of cancer-related mortality in the developed world. Carcinogenesis is a multistage process conventionally defined by the initiation, promotion and progression stages. Natural polyphenolic compounds can act as highly effective antioxidant and chemo-preventive agents able to interfere at the three stages of cancer. Cocoa has been demonstrated to counteract oxidative stress and to have a potential capacity to interact with multiple carcinogenic pathways involved in inflammation, proliferation and apoptosis of initiated and malignant cells. Therefore, restriction of oxidative stress and/or prevention or delayed progression of cancer stages by cocoa antioxidant compounds has gained interest as an effective approach in colorectal cancer prevention. In this review, we look over different in vitro and in vivo studies that have identified potential targets and mechanisms whereby cocoa and their flavonoids could interfere with colonic cancer. In addition, evidence from human studies is also illustrated.

Epigallocatechin-3-gallate induces mesothelioma cell death via H2 O2 -dependent T-type Ca2+ channel opening

Malignant mesothelioma (MMe) is a highly aggressive, lethal tumour requiring the development of more effective therapies. The green tea polyphenol epigallocathechin-3-gallate (EGCG) inhibits the growth of many types of cancer cells. We found that EGCG is selectively cytotoxic to MMe cells with respect to normal mesothelial cells. MMe cell viability was inhibited by predominant induction of apoptosis at lower doses and necrosis at higher doses. EGCG elicited H₂O₂ release in cell cultures, and exogenous catalase (CAT) abrogated EGCG-induced cytotoxicity, apoptosis and necrosis. Confocal imaging of fluo 3-loaded, EGCG-exposed MMe cells showed significant [Ca²⁺]_i rise, prevented by CAT, dithiothreitol or the T-type Ca²⁺ channel blockers mibefradil and NiCl₂. Cell loading with dihydrorhodamine 123 revealed EGCG-induced ROS production, prevented by CAT, mibefradil or the Ca²⁺ chelator BAPTA-AM. Direct exposure of cells to H₂O₂ produced similar effects on Ca²⁺ and ROS, and these effects were prevented by the same inhibitors. Sensitivity of REN cells to EGCG was correlated with higher expression of Ca_v3.2 T-type Ca²⁺ channels in these cells, compared to normal mesothelium. Also, Ca_v3.2 siRNA on MMe cells reduced in vitro EGCG cytotoxicity and abated apoptosis and necrosis. Intriguingly, Ca_v3.2 expression was observed in malignant pleural mesothelioma biopsies from patients, but not in normal pleura. In conclusion, data showed the expression of T-type Ca²⁺ channels in MMe tissue and their role in EGCG selective cytotoxicity to MMe cells, suggesting the possible use of these channels as a novel MMe pharmacological target.

Grape seed procyanidin extract modulates proliferation and apoptosis of pancreatic beta-cells

Grape seed procyanidin extract (GSPE) modulates glucose homeostasis and insulinemia in several animal models. Under pathological conditions, insulin levels are dependent on pancreatic beta-cell functionality, as well as on the beta-cell mass expansion or apoptosis in the pancreas. In this study, we analysed the effects of GSPE on modulating apoptosis and proliferation in beta-cells. We tested the effects of GSPE in the INS-1E pancreatic beta-cell line, either under basal or altered conditions with high glucose, insulin or palmitate levels. GSPE enhanced the pro-apoptotic effect of high glucose and showed clear antiproliferative effects under high glucose, insulin and palmitate conditions. These antiproliferative effects are likely due to high molecular weight compounds contained in the extract. GSPE also modulated pro- and anti-apoptotic markers in the pancreas of rats fed a cafeteria diet, with the effect depending on the dose of GSPE and duration of treatment. Thus, GSPE is able to modulate apoptosis and proliferation of beta-cells under altered, but not basal, conditions.

A dry extract of Phyllanthus niruri protects normal cells and induces apoptosis in human liver carcinoma cells

The ability to induce apoptosis is an important marker for cytotoxic antitumor agents. Some natural compounds have been shown to modulate apoptosis pathways that are frequently blocked in human cancers, and therefore, these compounds provide novel opportunities for cancer drug development. Phyllanthus, a plant genus of the family Euphorbiaceae, exhibits multiple pharmacological actions. Of these, Phyllanthus niruri extracts exhibit significant antitumor activity, which is consistent with the traditional medicinal use of this plant. To examine the apoptotic effects of a spray-dried extract of P. niruri (SDEPN), human hepatocellular carcinoma cells (HepG2, Huh-7), colorectal carcinoma cells (Ht29) and keratinocytes (HaCaT) were exposed to the extract for 4, 8 and 24 h. Flow cytometry and caspase-3 immunostaining were used to detect apoptosis, while analysis of variance was applied to identify significant differences between groups ( P < 0.05). At all timepoints, the SDEPN induced significantly different cytotoxic effects for HepG2 and Huh-7 cells compared with control cells ( P < 0.001). In contrast, the SDEPN had a protective effect on HaCaT cells compared with control cells at all timepoints ( P < 0.001). In caspase-3 assays, activation was detected after cell death was induced in Huh-7 and HepG2 cancer cells by the SDEPN. In combination, these results indicate that the SDEPN is selectively toxic towards cancer cell lines, yet is protective towards normal cells.

Inhibitory effect and mechanisms of an anthocyanins- and anthocyanidins-rich extract from purple-shoot tea on colorectal carcinoma cell proliferation

One newly bred variety of tea cultivar, purple-shoot tea, was selected to evaluate its antiproliferative effects on colorectal carcinoma cells, as well as normal colon cells. The phytochemicals and identified catechins of purple-shoot tea extract (PTE) were significantly higher than that of ordinary tea, especially the anthocyanins (surpassed by 135-fold) and anthocyanidins (surpassed by 3.5-fold). PTE inhibited the proliferation of COLO 320DM (IC(50) = 64.9 μg/mL) and HT-29 (IC(50) = 55.2 μg/mL) by blocking cell cycle progression during the G(0)/G(1) phase and inducing apoptotic death. Western blotting indicated that PTE induced cell cycle arrest by reducing the expression of cyclin E and cyclin D1 in COLO 320DM and the upregulation of p21 and p27 cyclin-dependent kinase inhibitors in HT-29. Two cells treated with PTE also indicated the cleavage of PARP, activation of caspase 3, and an increased Bax/Bcl-2 ratio. Our results showed that PTE is a potential novel dietary agent for colorectal cancer chemoprevention.

Multistage carcinogenesis process as molecular targets in cancer chemoprevention by epicatechin-3-gallate

The consumption of green tea has long been associated with a reduced risk of cancer development. (-)-Epicatechin-3-gallate (ECG) or (-)-epigallocatechin-3-gallate (EGCG) are the major antioxidative polyphenolic compounds of green tea. They have been shown to exert growth-inhibitory potential of various cancer cells in culture and antitumor activity in vivo models. ECG or EGCG could interact with various molecules like proteins, transcription factors, and enzymes, which block multiple stages of carcinogenesis via regulating intracellular signaling transduction pathways. Moreover, ECG and EGCG possess pharmacological and physiological properties including induction of phase II enzymes, mediation of anti-inflammation response, regulation of cell proliferation and apoptosis effects and prevention of tumor angiogenesis, invasion and metastasis. Numerous review articles have been focused on EGCG, however none have been focused on ECG despite many studies supporting the cancer preventive potential of ECG. To develop ECG as an anticarcinogenic agent, more clear understanding of the cell signaling pathways and the molecular targets responsible for chemopreventive and chemotherapeutic effects are needed. This review summarizes recent research on the ECG-induced cellular signal transduction events which implicate in cancer management.

Epicatechin gallate suppresses oxidative stress-induced MUC5AC overexpression by interaction with epidermal growth factor receptor

The goal of this study was to investigate the effect of epicatechin gallate (ECG), a component of green tea polyphenols, on the signal pathway for oxidative stress-induced intracellular reactive oxygen species (ROS) generation and MUC5AC overexpression in normal human nasal epithelial (NHNE) cells. Passage-2 NHNE cells were used, and ECG was administered before stimulation with exogenous hydrogen peroxide (H(2)O(2)). MUC5AC gene and protein levels were measured by real-time PCR and dot blot analysis. Western blot analysis and immunocytofluorescence study were performed for detecting the activity of epidermal growth factor receptor (EGFR). Exogenous H(2)O(2) increases intracellular ROS generation, leading to the overexpression of MUC5AC. The phosphorylation and internalization of EGFR were associated with this ROS generation. ECG decreased the phosphorylation and internalization of EGFR at the cell surface of NHNE cells, resulting in the attenuation of exogenous H(2)O(2)-induced intracellular ROS generation and MUC5AC overexpression. ECG may be a therapeutic material against oxidative stress-induced ROS generation and mucus hypersecretion in airways.

Inhibitory effect of immature plum on PMA-induced MMP-9 expression in human hepatocellular carcinoma

The goal of this study was to evaluate the anticancer effect of Prunus salicina Lindl. cv. Soldam at three maturity stages (immature, midmature and mature). In search for anticancer effects of immature plum extract (IPE), we have found its antimigrative property in (phorbol 12-myristate 13-acetate) PMA-induced HepG2 cells, and this effect is associated with inhibition of MMP-9 activity. IPE appeared to have a strong inhibitory effect on the PMA-induced MMP-9 secretion through suppression of the transcriptional activity of the MMP-9 gene independently of the TIMP gene in HepG2 cells. PMA induced the translocation of c-jun and p65 to the nucleus; however, IPE inhibited their nuclear translocations induced by PMA in HepG2 cells. These results clearly indicate that IPE suppresses both AP-1- and NF-kappaB-mediated MMP-9 gene transcriptional activity through inhibiting the nuclear translocations of AP-1 and NF-kappaB. These findings suggest that AP-1 and NF-kappaB activations through the ERK, p38 MAPK and JNK pathways appears to be required for the induction of MMP-9 expression by PMA in IPE, and IPE regulates PMA-stimulated MMP-9 expression by suppressing the p38 MAPK, JNK and ERK pathways. IPE leads to a decrease in the migration potential of HepG2 cells in vitro, and this suggests that the migration inhibition is correlated well with its inhibition of MMP-9 expression.

Modulatory effects of polyphenols on apoptosis induction: relevance for cancer prevention

Polyphenols, occurring in fruit and vegetables, wine, tea, extra virgin olive oil, chocolate and other cocoa products, have been demonstrated to have clear antioxidant properties in vitro, and many of their biological actions have been attributed to their intrinsic reducing capabilities. However, it has become clear that, in complex biological systems, polyphenols exhibit several additional properties which are yet poorly understood. Apoptosis is a genetically controlled and evolutionarily conserved form of cell death of critical importance for the normal embryonic development and for the maintenance of tissue homeostasis in the adult organism. The malfunction of the death machinery may play a primary role in various pathological processes, since too little or too much apoptosis can lead to proliferative or degenerative diseases, respectively. Cancer cells are characterized by a deregulated proliferation, and/or an inability to undergo programmed cell death. A large body of evidence indicates that polyphenols can exert chemopreventive effects towards different organ specific cancers, affecting the overall process of carcinogenesis by several mechanisms: inhibition of DNA synthesis, modulation of ROS production, regulation of cell cycle arrest, modulation of survival/proliferation pathways. In addition, polyphenols can directly influence different points of the apoptotic process, and/or the expression of regulatory proteins. Although the bulk of data has been obtained in in vitro systems, a number of clinical studies suggesting a preventive and therapeutic effectiveness of polyphenols in vivo is available. However, a deeper knowledge of the underlying mechanisms responsible for the modulation of apoptosis by polyphenols, and their real effectiveness, is necessary in order to propose them as potential chemopreventive and chemotherapeutic candidates for cancer treatment.

The importance of polymerization and galloylation for the antiproliferative properties of procyanidin-rich natural extracts

Grape (Vitis vinifera) and pine (Pinus pinaster) bark extracts are widely used as nutritional supplements. Procyanidin-rich fractions from grape and pine bark extract showing different mean degrees of polymerization, percentage of galloylation (percentage of gallate esters) and reactive oxygen species-scavenging capacity were tested on HT29 human colon cancer cells. We observed that the most efficient fractions in inhibiting cell proliferation, arresting the cell cycle in G(2) phase and inducing apoptosis were the grape fractions with the highest percentage of galloylation and mean degree of polymerization. Additionally, the antiproliferative effects of grape fractions were consistent with their oxygen radical-scavenging capacity and their ability to trigger DNA condensation-fragmentation.

Comparative antioxidant and cytotoxic effect of procyanidin fractions from grape and pine

There is a great interest in characterizing the biological properties of natural compounds obtained from plants, especially polyphenols. We studied the structure-activity-cytotoxicity relationships of polyphenolic fractions obtained from grape pomace and pine bark. These fractions contained similar polymerised flavonoids but different percentages of pyrogallol groups that confer on them different biological properties. The human keratinocyte cell line HaCaT and the mouse fibroblast cell line 3T3 were used to study the cytotoxicity of the different fractions after 24, 48, and 72 h of exposure. Antioxidant activity of the fractions was evaluated by measuring the inhibition of hemolysis mediated by AAPH. Our results demonstrate that the polyphenolic fractions studied show high antioxidant capacity in a concentration range that is not harmful to normal human cells. Pine fractions presented slightly lower antioxidant activity than grape fractions but are less cytotoxic. This data provides useful information to help design safe antioxidant products that act without altering critical cell functions.

Effects of dietary flavonoids on apoptotic pathways related to cancer chemoprevention

Epidemiological studies have described the beneficial effects of dietary polyphenols (flavonoids) on the reduction of the risk of chronic diseases, including cancer. Moreover, it has been shown that flavonoids, such as quercetin in apples, epigallocatechin-3-gallate in green tea and genistein in soya, induce apoptosis. This programmed cell death plays a critical role in physiological functions, but there is underlying dysregulation of apoptosis in numerous pathological situations such as Parkinson's disease, Alzheimer's disease and cancer. At the molecular level, flavonoids have been reported to modulate a number of key elements in cellular signal transduction pathways linked to the apoptotic process (caspases and bcl-2 genes), but that regulation and induction of apoptosis are unclear. The aim of this review is to provide insights into the molecular basis of the potential chemopreventive activities of representative flavonoids, with emphasis on their ability to control intracellular signaling cascades responsible for regulating apoptosis, a relevant target in cancer-preventive approach.

Identification of two biologically crucial hydroxyl groups of (−)-epigallocatechin gallate in osteoclast culture

(-)-Epigallocatechin gallate (EGCG) induces cell death of osteoclasts in an Fe(2+)- and H(2)O(2)-dependent manner. In the present study, we further explore the cytotoxic mechanism of EGCG using four EGCG analogues. Molecules methylated at position 4' in the B ring (EGCG-4'-O-Me) or at position 4'' in the D-ring (EGCG-4''-O-Me) showed markedly decreased cytotoxicity to osteoclasts, indicating that hydroxyl groups at these two positions of EGCG are crucial for inducing cell death of osteoclasts. EGCG-4'-O-Me also showed the lowest Fe(3+)-reducing activity among five EGCGs. The Fe(3+)-reducing activity of EGCG was enhanced under conditions whereby protonated EGCG levels were increased, indicating that the protonated status of EGCG was involved in the Fe(3+)-reducing activity. The hydroxyl group at position 4'' in the D-ring was shown by quantum chemical calculation to be preferentially deprotonated among all of the hydroxyl groups in EGCGs. It was also shown that the highest occupied molecular orbital (HOMO) was localized to the B-ring of EGCGs, except for EGCG-4'-O-Me. We report here that the HOMO on the B-ring plays crucial roles in both the Fe(3+)-reducing activity of EGCG and the cytotoxicity of EGCG to osteoclasts, while deprotonation of the hydroxyl group at position 4'' in the D-ring plays a supplementary role.

Mechanism of apoptosis with the involvement of calpain and caspase cascades in human malignant neuroblastoma SH-SY5Y cells exposed to flavonoids

Neuroblastoma is the most common extracranial solid tumor in children causing death at pre-school age, as no cure has yet been developed. We investigated the proteolytic mechanisms for apoptosis in human malignant (N-type) neuroblastoma SH-SY5Y cells following exposure to flavonoids such as apigenin (APG), (-)-epigallocatechin (EGC), (-)-epigallocatechin-3-gallate (EGCG) and genistein (GST). We found decrease in viability of SH-SY5Y cells with an increase in dose of APG, EGC, EGCG and GST. Predominantly apoptosis occurred following exposure of SH-SY5Y cells to 50 microM APG, 50 microM EGC, 50 microM EGCG and 100 microM GST for 24 hr. Apoptosis was associated with increases in intracellular free [Ca(2+)] and Bax:Bcl-2 ratio, mitochondrial release of cytochrome c and activation of caspase-9, calpain and caspase-3. Induction of apoptosis with APG and GST showed activation of caspase-12 as well. Activation of caspase-3 could cleave the inhibitor-of-caspase-activated DNase (ICAD) to release and translocate caspase-3-activated DNase (CAD) to the nucleus. Activation of caspase-8 cleaved Bid to truncated Bid (tBid) in cells treated with EGC and EGCG. EGC and EGCG induced apoptosis with caspase-8 activation and mitochondria-mediated pathway, whereas APG and GST caused apoptosis via an increase in intracellular free [Ca(2+)] with calpain activation and mitochondria-mediated pathway. Activation of different proteases for cell death was confirmed using caspase-8 inhibitor II, calpeptin (calpain inhibitor), caspase-9 inhibitor I and caspase-3 inhibitor IV. Thus, plant-derived flavonoids cause cell death with activation of proteolytic activities of calpain and caspases in SH-SY5Y cells, and therefore serve as potential therapeutic agents for controlling the growth of neuroblastoma.

Epicatechins Purified from Green Tea (Camellia sinensis) Differentially Suppress Growth of Gender-Dependent Human Cancer Cell Lines

The anticancer potential of catechins derived from green tea is not well understood, in part because catechin-related growth suppression and/or apoptosis appears to vary with the type and stage of malignancy as well as with the type of catechin. This in vitro study examined the biological effects of epicatechin (EC), epigallocatechin (EGC), EC 3-gallate (ECG) and EGC 3-gallate (EGCG) in cell lines from human gender-specific cancers. Cell lines developed from organ-confined (HH870) and metastatic (DU145) prostate cancer, and from moderately (HH450) and poorly differentiated (HH639) epithelial ovarian cancer were grown with or without EC, EGC, ECG or EGCG. When untreated cells reached confluency, viability and doubling time were measured for treated and untreated cells. Whereas EC treatment reduced proliferation of HH639 cells by 50%, EGCG suppressed proliferation of all cell lines by 50%. ECG was even more potent: it inhibited DU145, HH870, HH450 and HH639 cells at concentrations of 24, 27, 29 and 30 µM, whereas EGCG inhibited DU145, HH870, HH450 and HH639 cells at concentrations 89, 45, 62 and 42 µM. When compared with EGCG, ECG more effectively suppresses the growth of prostate cancer and epithelial ovarian cancer cell lines derived from tumors of patients with different stages of disease.

Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies

Experimental studies have supported tea as a chemopreventive agent for colorectal cancer. No quantitative summary of the epidemiologic evidence on tea and colorectal cancer risk has ever been performed. The current meta-analysis included 25 papers conducted in 11 countries across three continents (North America, Asia and Europe). Summary odds ratios (ORs) for highest versus non/lowest tea consumption levels were calculated based on fixed and random effects models. The meta-regression and stratified methods were used to examine heterogeneity across studies. For green tea, the combined results from eight studies indicated a reduced risk of colorectal cancer with intake [summary OR = 0.82, 95% confidence interval (CI) = 0.69-0.98]. The protective effect is mainly found among the three case-control studies of colon cancer (summary OR = 0.74, 95% CI = 0.60-0.93). Results from studies of rectal cancer irrespective of study design (case-control versus cohort) (summary OR = 0.99, 95% CI = 0.71-1.37) and cohort studies of colon cancer (summary OR = 0.99, 95% CI = 0.79-1.24) were compatible with the null hypothesis. For black tea, the summary OR derived from 20 studies was 0.99 (95% CI = 0.87-1.13). There is wide divergence in results across the 20 individual studies; formal tests for homogeneity across studies revealed statistically significant differences in findings across all studies (P < 0.001), amongst the 7 cohort studies (P = 0.002), and amongst the 13 case-control studies (P < 0.001). Despite the strong evidence from in vitro and non-human in vivo studies in support of green and black tea as potential chemopreventive agents against colorectal cancer, available epidemiologic data are insufficient to conclude that either tea type may protect against colorectal cancer in humans.

Protective effects of tea polyphenols and caffeine

Compounds derived from botanical sources, such as polyphenols from tea, have been of interest as possible therapeutic agents. Their benefits in terms of cancer chemoprevention have also been investigated primarily through in vitro and animal in vivo studies. Ultraviolet light from solar radiation has been proven to initiate and promote skin cancer, which is the most common malignancy in light-skinned populations. This review discusses the effects of tea polyphenols in preventing cutaneous carcinogenesis. Although many of the mechanisms and pathways discussed may be applicable to other carcinogens, this review focuses mainly on those related to ultraviolet light-induced processes and potential action sites for tea polyphenols. Since caffeine is a component of tea, and has also been suggested as a possible chemoprotective agent, it is included in this review. Based on data from numerous studies published in the scientific literature, tea polyphenols are promising chemopreventive agents against ultraviolet-induced skin cancers. Their antioxidant properties, inhibitory effects on signal transduction pathways, cell proliferation, angiogenesis and capacity for apoptosis induction, as well as possible immune protective effects, are among the mechanisms that contribute to skin cancer prevention.

Anti-proliferative effects of green tea polyphenol EGCG on Ha-Ras-induced transformation of intestinal epithelial cells

Oncogenic Ras mutations are frequently observed in colorectal cancer and participate in neoplastic transformation of intestinal epithelial cells. Accumulating evidence demonstrates the chemopreventive properties of green tea on colon carcinogenesis. Here we investigated the major green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), to inhibit proliferation of intestinal epithelial cells (RIE-1) transfected with an inducible Ha-Ras(Val12) cDNA. EGCG inhibited cell proliferation induced by oncogenic Ras and blocked cell cycle transition at G1 phase via inhibition of cyclin D1 expression. The EGCG IC(50) was 42microM in transformed cells and 81microM in non-transformed cells. EGCG also promoted E-cadherin expression, which is downregulated by Ras transformation. This study demonstrates the potential of the natural compound EGCG as an effective adjuvant therapy for colon tumors bearing Ras mutations.

Effect of new antioxidant cysteinyl-flavanol conjugates on skin cancer cells

Novel catechin derivatives obtained from grape procyanidins and l-cysteine scavenge free radicals by hydrogen atom donation, rather than electron transfer, and reduce cell viability in A375 and M21 melanoma cells. In particular, 4beta-(S-cysteinyl)epicatechin 3-O-gallate has a free radical scavenging capacity as strong as that of tea (-)-epigallocatechin gallate and causes a significant S-phase cell-cycle arrest in both cell lines at doses higher than 100 microM. The other cysteinyl compounds do not affect normal cell cycle distribution. The gallate derivative also induces apoptosis in melanoma cells more strongly than the other derivatives and the parent (-)-epicatechin do. The gallate compound seems to trigger nuclear condensation and fragmentation, which is confirmed by DNA laddering. Interestingly, they do not induce apoptosis in keratinocytes (HaCaT).

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.

Effects of tea constituents on cell cycle progression of human leukemia U937 cells

Tea and tea constituents are known to induce apoptosis in a variety of cancerous cells, suggesting their beneficial effects as chemopreventive agents. Previous studies have shown that low molecular weight constituent catechins and high molecular weight fractions of tea have the apoptosis-inducing activity, but that their action mechanisms may be different. Since cell cycle arrest is known to be one of the underlying mechanisms of apoptosis, we examined the effects of these tea constituents on cell cycle progression of human leukemia U937 cells. The results showed that the high molecular weight fractions of green tea and black tea caused G2/M arrest associated with up-regulation of p21/Waf1, but that epigallocatechin gallate, a major component of green tea catechins, gave little effects of cell cycle progression and p21/Waf1 expression. Thus, the present results suggest the difference in the apoptosis-induction mechanism between the two types of tea constituents.

Studies in polyphenol chemistry and bioactivity. 4.(1) Synthesis of trimeric, tetrameric, pentameric, and higher oligomeric epicatechin-derived procyanidins having all-4beta,8-interflavan connectivity and their inhibition of cancer cell growth through cell cycle arrest

We report an improved synthesis of bis(5,7,3',4'-tetra-O-benzyl)epicatechin 4beta,8-dimer (3) from 5,7,3',4'-tetra-O-benzylepicatechin (1) and 5,7,3',4'-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4beta,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3',4'-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4beta,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent.

Epicatechin-copper 9II) complexes: Damage of small intestinal epithelium

Four epicatechins [(−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg)] and their corresponding copper complexes were compared with regard to their effect on the viability of Caco-2 colon cancer cells in vitro, measured by 3-(4,5-dimethylthyazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay. The viability of Caco-2 cells exposed to EC (1 mM), ECg (1 mM) or EGC (1mM) respectively, for 30 min, was comparable to that of the saline control group, while EGCg (1 mM) apparently enhanced cellular activity. in contrast, the cells treated with epicatechin-copper complexes were killed. Bivalent copper 91 mM), in similar conditions, did not affect the cells. No cell leakage or other histological differences were observed, implying a rapid cell death. The suggested mechanism of killing is by OH radical attack, produced in the presence of epicatechin-copper complexes, but not in the presence of either of the epicatechins or copper alone. The reaction sites are discussed.

Topical applications of caffeine or (-)-epigallocatechin gallate (EGCG) inhibit carcinogenesis and selectively increase apoptosis in UVB-induced skin tumors in mice

SKH-1 hairless mice were irradiated with ultraviolet B (UVB) twice weekly for 20 weeks. These tumor-free mice, which had a high risk of developing skin tumors during the next several months, were then treated topically with caffeine (6.2 micromol) or (-)-epigallocatechin gallate (EGCG; 6.5 micromol) once a day 5 days a week for 18 weeks in the absence of further treatment with UVB. Topical applications of caffeine to these mice decreased the number of nonmalignant and malignant skin tumors per mouse by 44% and 72%, respectively. Topical applications of EGCG decreased the number of nonmalignant and malignant tumors per mouse by 55% and 66%, respectively. Immunohistochemical analysis showed that topical applications of caffeine or EGCG increased apoptosis as measured by the number of caspase 3-positive cells in nonmalignant skin tumors by 87% or 72%, respectively, and in squamous cell carcinomas by 92% or 56%, respectively, but there was no effect on apoptosis in nontumor areas of the epidermis. Topical applications of caffeine or EGCG had a small inhibitory effect on proliferation in nonmalignant tumors as measured by BrdUrd labeling (16-22%), and there was also a similar, but nonsignificant, inhibitory effect on proliferation in malignant tumors. The results suggest a need for further studies to determine whether topical applications of caffeine or EGCG can inhibit sunlight-induced skin cancer in humans.

Primary prevention: phytoprevention and chemoprevention of colorectal cancer

Considering the various stages of carcinogenesis and the numerous tumor types and available chemoprevention agents, knowledge of the etiology and the type of cancer to be treated, or possibly prevented, and understanding of the mechanisms by which agents exert their chemoprevention benefits may provide for improved strategy in designing therapeutic regimens. Because cancer usually develops over a 10- to 20-year period, it may be necessary for some agents to be provided before or early in the initiation steps of carcinogenesis to have beneficial effects. On the other hand, some agents may be more suitable for CRC prevention if provided at a later stage of carcinogenesis. Gene array, genomics, and proteomics are useful tools in advancing our understanding of the molecular events involved in carcinogenesis and in identifying markers of risk and surrogate end-points for colorectal cancer progression. These techniques may also serve for screening, identifying, and providing treatment targets for high-risk patients populations. Treatment could be developed depending on a patient's individual needs and genomic tumor profile. Clinical markers and surrogate end-points should be considered, together with molecular measurements, to more accurately assess risk. NSAIDs and COXIBs are clinically recognized as chemoprevention agents, and clinical trials evaluating their efficacy are ongoing. Treatment protocols, including dose and timing, remain to be determined, however. DFMO may best be used in combination with other chemoprevention agents. Dietary fiber and calcium supplements, as part of an overall low-fat diet, may decrease CRC risk. Long-term compliance with this regimen may be necessary to effect a beneficial outcome. Folate holds promise but needs further investigation, especially because its beneficial effects may depend on cancer type. Phytochemicals have been identified as strong candidates for use as agents to prevent colorectal cancer in cell culture and in rodent models of carcinogenesis. Their potential as chemoprevention agents must be demonstrated in clinical trials. In vitro and animal studies indicated that combination therapy may be a promising strategy over the monotherapy approach; clinical trials addressing the safety and efficacy of some combinations (DFMO/sulindac, fiber/calcium) are underway. The gastrointestinal tract and other organs are constantly exposed to a mixture of potentially toxic compounds and molecules considered favorable to health. Homeostasis between stress-mediated by toxic compounds and defensive mechanisms, is key for the maintenance of health and the prevention of disease. Whereas aggressive pharmacologic treatment may be necessary for patients at high risk for cancer, dietary supplements may be useful for populations at normal risk. The message for cancer prevention in the general population may well remain: keep a balanced healthy diet, eating a variety from all food groups, as part of a healthy lifestyle that includes moderate exercise.

Cysteinyl-flavan-3-ol conjugates from grape procyanidins. Antioxidant and antiproliferative properties

New bio-based antioxidant compounds have been obtained by depolymerisation of grape polymeric flavanols in the presence of cysteine. Their preparation and purification, as well as their antiradical/antioxidant and antiproliferative properties are reported. 4beta-(S-cysteinyl)epicatechin 5, 4beta-(S-cysteinyl)catechin 6 and 4beta-(S-cysteinyl)epicatechin 3-O-gallate 7 were efficiently purified from the crude depolymerised mixture by cation-exchange chromatography and preparative reversed-phase chromatography. The new compounds were more efficient than the underivatised (-)-epicatechin 1 as scavengers of the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH) and weak growth inhibitors of human colon carcinoma HT29 cells. The order of antiradical and antiproliferative efficiency was 7 >5 approximately 6 >1, the same for both assays.