Theaflavin-3,3'-digallate, a component of black tea: an inducer of oxidative stress and apoptosis

Research advancements on theaflavins: Isolation, purification, synthesis, gut microbiota interactions, and applications potentials

Theaflavins (TFs), specific polyphenolic compounds found in tea, including TF, TF-3-G, TF-3'-G, and TFDG, are renowned for their health-promoting effects. The growing interest in TFs among researchers necessitates a comprehensive review of their properties and impacts. This review systematically examines the chemical and physical properties of TFs, covering their isolation, purification, synthesis, safety, and bioavailability, as well as their implications for health. Special attention is paid to the dynamic interactions between TFs and gut microbiota (GM), exploring how GM metabolizes TFs and the consequent effects on the microbial community. An in-depth understanding of these interactions is crucial for realizing the full health benefits of TFs. Additionally, this review summarizes the well-documented health benefits of TFs, including their roles in ameliorating metabolic diseases, exhibiting anti-inflammatory properties, reducing viral infections, and potential applications in treating cancer and neurological diseases. It also explores the potential industrial applications of TFs, underscoring the need for further research to enhance their benefits for human health and well-being. The primary goal of this review is to support and inspire further detailed investigations into TFs.

Theaflavins Applications to Ameliorate Implant Failure and Eradicate Microbial Infections and Foodborne Pathogens: A Comprehensive Review

Theaflavins, powerful antioxidants found in black tea ( Camellia sinensis ), have garnered increasing interest for their promising therapeutic potential. Experimental studies have contributed to enlightening about the advantages of theaflavins, including their antioxidant, anti-inflammatory, anticancer, antiosteoporosis, and antimicrobial properties. Theaflavin and its derivatives, particularly theaflavin-3,3'-digallate, have been particularly noted for their enhanced action in different areas. These compounds have found an important role as alternatives or adjuvants in the pharmaceutical sector, food industry, and in the improvement of health conditions. This review focuses on the antioxidant and anti-inflammatory aspects of theaflavins, particularly their potential in addressing peri-implant osteolysis. We explore mechanisms and pathways involved in this therapeutic action. Furthermore, we cover some of the relevant studies on the antimicrobial action of theaflavins in both the health and food sectors. Specifically, we explore the use of theaflavins for the treatment of dental infections, where these compounds have shown particular efficacy against several bacterial strains and their antimicrobial application in food matrices. Given the low solubility and stability of theaflavins in physiological conditions, we emphasize the benefits of the development of biocompatible and biodegradable nanoformulations to enhance the stability, bioavailability, and efficacy of these polyphenols, to promote their broader research and application. Given the potential demonstrated so far by in vitro and in vivo studies, the application of theaflavins stands as a promising alternative to enhance the existing strategies and fight prosthetic failure and antimicrobial resistance in the health and food sectors.

Flexion of Nrf2 by tea phytochemicals: A review on the chemopreventive and chemotherapeutic implications

Nuclear factor erythroid 2 [NF-E2]-related factor 2 (Nrf2), the redox-sensitive transcription factor, plays a key role in stress-defense and detoxification. Nrf2 is tightly controlled by its negative regulator cum sensor Kelch-[ECH]-associated protein 1 (Keap1). Nrf2 is well known for its dual nature owing to its cancer preventive and cancer promoting abilities. Modulation of this biphasic nature of Nrf2 signaling by phytochemicals may be a potential cancer preventive and anticancer therapeutic strategy. Phytocompounds may either act as Nrf2-activator or Nrf2-inhibitor depending on their differential concentration and varied cellular environment. Tea is not just the most popular global beverage with innumerable health-benefits but has well-established chemopreventive and chemotherapeutic effects. Various types of tea infusions contain a wide range of bioactive compounds, such as polyphenolic catechins and flavonols, which are endowed with potent antioxidant properties. Despite of their rapid biotransformation and poor bioavailability, regular tea consumption is risk-reductive for several cancer forms. Tea catechins show their dual Nrf2-modulatory effect by directly acting on Nrf2-Keap1 or their upstream regulators and downstream effectors in a highly case-specific manner. In this review, we have tried to present a comprehensive evaluation of the Nrf2-mediated chemopreventive and chemotherapeutic applications of tea in various preclinical cancer models, the Nrf2-modulatory mechanisms, and the limitations which need to be addressed in future research.

DK, Ragunathan V, Tiwari P, A. S, P BD. Molecular docking, validation, dynamics simulations, and pharmacokinetic prediction of natural compounds against the SARS-CoV-2 main-protease

The study aims to evaluate the potency of two hundred natural antiviral phytocompounds against the active site of the Severe Acquired Respiratory Syndrome - Coronavirus - 2 (SARS-CoV-2) Main-Protease (Mpro) using AutoDock 4.2.6. The three- dimensional crystal structure of the Mpro (PDB Id: 6LU7) was retrieved from the Protein Data Bank (PDB), the active site was predicted using MetaPocket 2.0. Food and Drug Administration (FDA) approved viral protease inhibitors were used as standards for comparison of results. The compounds theaflavin-3-3'-digallate, rutin, hypericin, robustaflavone, and (-)-solenolide A with respective binding energy of -12.41 (Ki = 794.96 pM); -11.33 (Ki = 4.98 nM); -11.17 (Ki = 6.54 nM); -10.92 (Ki = 9.85 nM); and -10.82 kcal/mol (Ki = 11.88 nM) were ranked top as Coronavirus Disease - 2019 (COVID-19) Mpro inhibitors. The interacting amino acid residues were visualized using Discovery Studio 3.5 to elucidate the 2-dimensional and 3-dimensional interactions. The study was validated by i) re-docking the N3-peptide inhibitor-Mpro and superimposing them onto co-crystallized complex and ii) docking decoy ligands to Mpro. The ligands that showed low binding energy were further predicted for and pharmacokinetic properties and Lipinski's rule of 5 and the results are tabulated and discussed. Molecular dynamics simulations were performed for 50 ns for those compounds using the Desmond package, Schrödinger to assess the conformational stability and fluctuations of protein-ligand complexes during the simulation. Thus, the natural compounds could act as a lead for the COVID-19 regimen after in-vitro and in- vivo clinical trials.Communicated by Ramaswamy H. Sarma.

Taking leads out of nature, can nano deliver us from COVID-like pandemics?

The COVID-19 crisis has alerted the research community to re-purpose scientific tools that can effectively manage emergency pandemic situations. Researchers were never so desperate to discover a 'magic bullet' that has significant clinical benefits with minimal or no side effects. At the beginning of the pandemic, due to restricted access to traditional laboratory techniques, many research groups delved into computational screening of thousands of lead molecules that could inhibit SARS-CoV-2 at one or more stages of its infectious cycle. Several in silico studies on natural derivatives point out their potency against SARS-CoV-2 proteins. However, theoretical predictions and existing knowledge on related molecules reflect their poor oral bioavailability due to biotransformation in the gut and liver. Nanotechnology has evolved into a key field for precise and controlled delivery of various drugs that lack aqueous solubility, have low oral bioavailability and possess pronounced toxicity in their native form. In this review, we discuss various nanoformulations of natural products with favorable ADME properties, and also briefly explore nano-drug delivery to lungs, the primary site of SARS-CoV-2 infection. Natural products are also envisioned to augment nanotechnology-based 1) personnel protective equipment for ex vivo viral inactivation and 2) wearable sensors that perform rapid and non-invasive analysis of volatile organic compounds in exhaled breath of the infected person after therapeutic food consumption.

Anticancer Effects and Molecular Target of Theaflavins from Black Tea Fermentation in Vitro and in Vivo

Black tea is one of the most popular beverages in the world, and numerous epidemiological studies have shown that drinking black tea is good for health. As a natural tea pigment formed during the fermentation of black tea, the content of theaflavins accounts for only 2-6% of the dry weight of black tea, but they have a great impact on the color and taste of black tea soup. Recently, a large number of studies have shown that theaflavins have a significant anticancer effect. In this Perspective, we first state the physical and chemical properties, separation and purification methods, and biological formation pathways of theaflavins and analyze their safety and oral bioavailability and the structure-activity relationship of their antioxidant and anticancer activities; then, we describe in detail their anticancer effect in vitro and in vivo and highlight their various molecular targets involved in cancer inhibition. The anticancer molecular targets of theaflavins are mainly cell-cycle regulatory proteins, apoptosis-related proteins, cell-migration-related proteins, and growth transcription factors. Finally, the possibility of developing new health-care food based on theaflavins is discussed. This Perspective is expected to provide a theoretical basis for the anticancer application of theaflavins in the future.

Theaflavin Chemistry and Its Health Benefits

Huge epidemiological and clinical studies have confirmed that black tea is a rich source of health-promoting ingredients, such as catechins and theaflavins (TFs). Furthermore, TF derivatives mainly include theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3'-gallate (TF2B), and theaflavin-3,3'-digallate (TF3). All of these TFs exhibit extensive usages in pharmaceutics, foods, and traditional medication systems. Various indepth studies reported that how TFs modulates health effects in cellular and molecular mechanisms. The available literature regarding the pharmacological activities of TFs has revealed that TF3 has remarkable anti-inflammatory, antioxidant, anticancer, antiobesity, antiosteoporotic, and antimicrobial properties, thus posing significant effects on human health. The current manuscript summarizes both the chemistry and various pharmacological effects of TFs on human health, lifestyle or aging associated diseases, and populations of gut microbiota. Furthermore, the biological potential of TFs has also been focused to provide a deeper understanding of its mechanism of action.

Cellular Defensive Mechanisms of Tea Polyphenols: Structure-Activity Relationship

Tea is particularly rich in polyphenols, including catechins and theaflavins, thearubigins, flavonols, and phenolic acids, which are believed to contribute to the health benefits of tea. The health-promoting effects of tea polyphenols are believed to be related to their cellular defensive properties. This review is intended to briefly summarize the relationship between the chemical structures of tea polyphenols and their biological activities. Tea polyphenols appear as direct antioxidants by scavenging reactive oxygen/nitrogen species; chelating transition metals; and inhibiting lipid, protein, and DNA oxidations. They also act directly by suppressing “pro-oxidant” enzymes, inducing endogenous antioxidants, and cooperating with vitamins. Moreover, tea polyphenols regulate cellular signaling transduction pathways, importantly contributing to the prevention of chronic diseases and the promotion of physiological functions. Apparently, the features in the chemical structures of tea polyphenols are closely associated with their antioxidant potentials.

Progress in Drug and Formulation Development for the Chemoprevention of Oral Squamous Cell Carcinoma: A Review

BACKGROUND

Cancer is a life-threatening global problem with high incidence rates. Prioritizing the prevention of cancer, chemopreventive agents have drawn much attention from the researchers.

OBJECTIVE

This review focuses on the discussion of the progress in the development of chemopreventive agents and formulations related to the prevention of oral cancer.

METHODS

In this perspective, an extensive literature survey was carried out to understand the mechanism, control and chemoprevention of oral cancer. Different patented agents and formulations have also exhibited cancer preventive efficacy in experimental studies. This review summarizes the etiology of oral cancer and developments in prevention strategies.

RESULTS

The growth of oral cancer is a multistep activity necessitating the accumulation of genetic as well as epigenetic alterations in key regulatory genes. Many risk factors are associated with oral cancer. Genomic technique for sequencing all tumor specimens has been made available to help detect mutations. The recent development of molecular pathway and genetic tools has made the process of diagnosis easier, better forecast and efficient therapeutic management. Different chemical agents have been studied for their efficacy to prevent oral cancer and some of them have shown promising results.

CONCLUSION

Use of chemopreventive agents, either synthetic or natural origin, to prevent carcinogenesis is a worthy concept in the management of cancers. Preventive measures are helpful in controlling the occurrence or severity of the disease. The demonstrated results of preventive agents have opened an arena for the development of promising chemopreventive agents in the management of oral squamous cell carcinoma.

Development of a Time-Resolved Fluorescence Resonance Energy Transfer Ultrahigh-Throughput Screening Assay for Targeting the NSD3 and MYC Interaction

Epigenetic modulators play critical roles in reprogramming of cellular functions, emerging as a new class of promising therapeutic targets. Nuclear receptor binding SET domain protein 3 (NSD3) is a member of the lysine methyltransferase family. Interestingly, the short isoform of NSD3 without the methyltransferase fragment, NSD3S, exhibits oncogenic activity in a wide range of cancers. We recently showed that NSD3S interacts with MYC, a central regulator of tumorigenesis, suggesting a mechanism by which NSD3S regulates cell proliferation through engaging MYC. Thus, small molecule inhibitors of the NSD3S/MYC interaction will be valuable tools for understanding the function of NSD3 in tumorigenesis for potential cancer therapeutic discovery. Here we report the development of a cell lysate-based time-resolved fluorescence resonance energy transfer (TR-FRET) assay in an ultrahigh-throughput screening (uHTS) format to monitor the interaction of NSD3S with MYC. In our TR-FRET assay, anti-Flag-terbium and anti-glutathione S-transferase (GST)-d2, a paired fluorophores, were used to indirectly label Flag-tagged NSD3 and GST-MYC in HEK293T cell lysates. This TR-FRET assay is robust in a 1,536-well uHTS format, with signal-to-background >8 and a Z' factor >0.7. A pilot screening with the Spectrum library of 2,000 compounds identified several positive hits. One positive compound was confirmed to disrupt the NSD3/MYC interaction in an orthogonal protein-protein interaction assay. Thus, our optimized uHTS assay could be applied to future scaling up of a screening campaign to identify small molecule inhibitors targeting the NSD3/MYC interaction.

Theaflavin-3,3'-Digallate Suppresses Biofilm Formation, Acid Production, and Acid Tolerance in Streptococcus mutans by Targeting Virulence Factors

As one of the most important cariogenic pathogens, Streptococcus mutans has strong abilities to form biofilms, produce acid and tolerate acid. In present study, we found that theaflavin-3,3'-digallate (TF3) had an inhibitory effect on S. mutans UA159 in vitro. Visualized by field emission-scanning electron microscopy, the suppressed formation of S. mutans biofilms grown with TF3 at sub-inhibitory concentrations could be attributed to the reduced biofilm matrix, which was proven to contain glucans and extracellular DNA (eDNA). Glucan-reduced effect of TF3 was achieved by down-regulating expression levels of gtfB, gtfC, and gtfD encoding glucosyltransferases. Besides, TF3 reduced eDNA formation of S. mutans by negatively regulating lrgA, lrgB, and srtA, which govern cell autolysis and membrane vesicle components. Furthermore, TF3 also played vital roles in antagonizing preformed biofilms of S. mutans. Bactericidal effects of TF3 became significant when its concentrations increased more than twofold of minimum inhibitory concentration (MIC). Moreover, the capacities of S. mutans biofilms to produce acid and tolerate acid were significantly weakened by TF3 at MIC. Based on real-time PCR (RT-PCR) analysis, the mechanistic effects of TF3 were speculated to comprise the inhibition of enolase, lactate dehydrogenase, F-type ATPase and the agmatine deiminase system. Moreover, TF3 has been found to downregulate LytST, VicRK, and ComDE two component systems in S. mutans, which play critical roles in the regulatory network of virulence factors. Our present study found that TF3 could suppress the formation and cariogenic capacities of S. mutans biofilms, which will provide new strategies for anti-caries in the future.

Theaflavins prevent cartilage degeneration via AKT/FOXO3 signaling in vitro

Theaflavins (TFs) are the main bioactive polyphenols in tea and contribute to protection against oxidative stress. Excessive reactive oxygen species (ROS) accumulation can lead to the disruption of cartilage homeostasis. The present study examined the potential effects of TFs on H₂O₂-induced cartilage degeneration in vitro. Cell Counting kit (CCK-8) was used to determine cell viability, and flow cytometric analysis was used to detect ROS, apoptosis and DNA damage. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to detect the expression levels of target factors. The present study revealed that TFs effectively reduced the expression of catabolic factors, including matrix metalloproteinase-13, interleukin-1 and cartilage glycoprotein 39. TFs inhibited ROS generation in cartilage degeneration, and suppressed apoptosis and DNA damage caused by oxidative stress. TFs also downregulated the expression levels of cleaved caspase-3 and B-cell lymphoma 2-associated X protein, and the DNA damage-related genes, ATR serine/threonine kinase and ATM serine/threonine kinase. Furthermore, TFs enhanced the activity of glutathione peroxidase 1 and catalase, but reduced the expression levels of phosphorylated (p)-AKT serine/threonine kinase (AKT) and p-Forkhead box O3 (FOXO3)a. Conversely, the effects of TFs on apoptosis and DNA damage were reversed by persistent activation of AKT. In conclusion, TFs prevented cartilage degeneration via AKT/FOXO3 signaling in vitro. The present study suggested that TFs may be a potential candidate drug for the prevention of cartilage degeneration.

Theaflavin-3,3'-Digallate Enhances the Inhibitory Effect of Cisplatin by Regulating the Copper Transporter 1 and Glutathione in Human Ovarian Cancer Cells

Ovarian cancer has the highest fatality rate among the gynecologic cancers. The side effects, high relapse rate, and drug resistance lead to low long-term survival rate (less than 40%) of patients with advanced ovarian cancer. Theaflavin-3,3'-digallate (TF3), a black tea polyphenol, showed less cytotoxicity to normal ovarian cells than ovarian cancer cells. We aimed to investigate whether TF3 could potentiate the inhibitory effect of cisplatin against human ovarian cancer cell lines. In the present study, combined treatment with TF3 and cisplatin showed a synergistic cytotoxicity against A2780/CP70 and OVCAR3 cells. Treatment with TF3 could increase the intracellular accumulation of platinum (Pt) and DNA-Pt adducts and enhanced DNA damage induced by cisplatin in both cells. Treatment with TF3 decreased the glutathione (GSH) levels and upregulated the protein levels of the copper transporter 1 (CTR1) in both cells, which led to the enhanced sensitivity of both ovarian cancer cells to cisplatin. The results imply that TF3 might be used as an adjuvant to potentiate the inhibitory effect of cisplatin against advanced ovarian cancer.

Research progress on theaflavins: efficacy, formation, and preparation

Background: Theaflavins (TFs) are a category of natural compounds characterized with the benzotropolone skeleton. The prominent benefits of TFs have been well documented. Amount of research were conducted and excellent achievements were disclosed during the past years. However, as far as we know, there is no comprehensive review about TFs. Scope and approach: This review summarized the recent research progress. The activity of TFs on anti-oxidation, anti-mutagenicity, hypolipidemic, anti-inflammatory, anti-cancer, anti-viral effect as well as the epidemiological cure were sorted. Converging pioneer literature and deduction, the underlying formation mechanism of TFs was proposed. Subsequently, acquisition of TFs was pointed out to be the fundament for further research. Accelerated by enzyme, bio-synthesis of TFs were reviewed simultaneously. At the end, employing modern analysis instrument and technology, isolations of TFs were enumerated. Key findings and conclusions: Structure of the skeleton as well as functional groups were paramount related with the bio-activity of TFs. Meanwhile, oxidation pathway of two catechin molecules to form TFs were hypothesized. Also, ascertainment of the several therapeutic efficiency of the family members of TFs would be the next step in the future.

Polyphenol compounds and PKC signaling

BACKGROUND

Naturally occurring polyphenols found in food sources provide huge health benefits. Several polyphenolic compounds are implicated in the prevention of disease states, such as cancer. One of the mechanisms by which polyphenols exert their biological actions is by interfering in the protein kinase C (PKC) signaling pathways. PKC belongs to a superfamily of serine-threonine kinase and are primarily involved in phosphorylation of target proteins controlling activation and inhibition of many cellular processes directly or indirectly.

SCOPE OF REVIEW

Despite the availability of substantial literature data on polyphenols' regulation of PKC, no comprehensive review article is currently available on this subject. This article reviews PKC-polyphenol interactions and its relevance to various disease states. In particular, salient features of polyphenols, PKC, interactions of naturally occurring polyphenols with PKC, and future perspective of research on this subject are discussed.

MAJOR CONCLUSIONS

Some polyphenols exert their antioxidant properties by regulating the transcription of the antioxidant enzyme genes through PKC signaling. Regulation of PKC by polyphenols is isoform dependent. The activation or inhibition of PKC by polyphenols has been found to be dependent on the presence of membrane, Ca(2+) ion, cofactors, cell and tissue types etc. Two polyphenols, curcumin and resveratrol are in clinical trials for the treatment of colon cancer.

GENERAL SIGNIFICANCE

The fact that 74% of the cancer drugs are derived from natural sources, naturally occurring polyphenols or its simple analogs with improved bioavailability may have the potential to be cancer drugs in the future.

Theaflavin-3, 3'-digallate induces apoptosis and G2 cell cycle arrest through the Akt/MDM2/p53 pathway in cisplatin-resistant ovarian cancer A2780/CP70 cells

Ovarian cancer is the most lethal gynecological cancer among women worldwide. Adverse side effects and acquired resistance to conventional platinum based chemotherapy are major impediments in ovarian cancer treatment, and drive the development of more selective anticancer drugs that target cancer-specific defects. In this study, theaflavin-3, 3′-digallate (TF3), the major theaflavin monomer in black tea, exhibited a potent growth inhibitory effect on the cisplatin-resistant ovarian cancer A2780/CP70 cells (IC₅₀, 23.81 μM), and was less cytotoxic to a normal ovarian IOSE-364 cells (IC₅₀, 59.58 μM) than to the cancer cells. Flow cytometry analysis indicated that TF3 induced preferential apoptosis and G2 cell cycle arrest in A2780/CP70 cells with respect to IOSE-364 cells. TF3 induced apoptosis through both the intrinsic and extrinsic apoptotic pathways, and caused G2 cell cycle arrest via cyclin B1 in A2780/CP70 cells. The p53 protein played an important role in TF3-induced apoptosis and G2 cell cycle arrest. TF3 might upregulate the p53 expression via the Akt/MDM2 pathway. Our findings help elucidate the mechanisms by which TF3 may contribute to the prevention and treatment of platinum-resistant ovarian cancer.

Theaflavin-3, 3'-digallate decreases human ovarian carcinoma OVCAR-3 cell-induced angiogenesis via Akt and Notch-1 pathways, not via MAPK pathways

Theaflavin-3, 3'-digallate (TF3) is a black tea polyphenol produced from polymerization and oxidization of the green tea ployphenols epicatechin gallate and (-)-epigallocatechin-3-gallate (EGCG) during fermentation of fresh tea leaves. TF3 has been reported to have anticancer properties. However, the effect of TF3 on tumor angiogenesis and the underlying mechanisms are not clear. In the present study, TF3 was verified to inhibit tumor angiogenesis. Compared with EGCG, TF3 was more potent. TF3 inhibited human ovarian carcinoma OVCAR-3 cell-induced angiogenesis in human umbilical vein endothelial cell model and in chick chorioallantoic membrane model. TF3 reduced tumor angiogenesis by downregulating HIF-1α and VEGF. One of the mechanisms was TF3 inactivated Akt/mTOR/p70S6K/4E-BP1 pathway and Akt/c-Myc pathway. Besides, TF3 suppressed the cleavage of Notch-1, subsequently decreased the expression of c-Myc, HIF-1α and VEGF, and finally the impaired cancer cells induced angiogenesis. Nevertheless, TF3 did not have any influence on the MAPK pathways. Taken together, these findings suggest that TF3 might serve as a potential anti-angiogenic agent for cancer treatment.

Protection of dietary polyphenols against oral cancer

Oral cancer represents a health burden worldwide with approximate 275,000 new cases diagnosed annually. Its poor prognosis is due to local tumor invasion and frequent lymph node metastasis. Better understanding and development of novel treatments and chemo-preventive approaches for the preventive and therapeutic intervention of this type of cancer are necessary. Recent development of dietary polyphenols as cancer preventives and therapeutic agents is of great interest due to their antioxidant and anti-carcinogenic activities. Polyphenols may inhibit carcinogenesis in the stage of initiation, promotion, or progression. In particular, dietary polyphenols decrease incidence of carcinomas and exert protection against oral cancer by induction of cell death and inhibition of tumor growth, invasion, and metastasis. In this review, we discuss current progress of dietary polyphenols against oral cancers in vitro, in vivo, and at population levels.

Diet and risk of oral potentially malignant disorders in rural Sri Lanka

BACKGROUND

While the protective role of antioxidant nutrients against cancer is well established, data on Asian diets in patients with oral cancer are meagre.

METHODS

A total of 1029 subjects over 30 years of age were investigated on their dietary practices in the Sabaragamuwa province (Sri Lanka) in 2006-07. Data collection tools were an interviewer-administered questionnaire, a three-day food diary and an examination of the oral cavity. Subjects identified with Oral Potentially Malignant Disorders (OPMD) and disease-free controls were analysed in a case-control fashion. Among the OPMDs, those with leukoplakia were separately considered. A further subgroup analysis was undertaken for β-carotene-rich foods. The analysis was stratified by portions of fruit/vegetables consumed as five or more portions and two or more portions daily.

RESULTS

A low BMI (<18.5) was a significant independent risk factor for the development of OPMD. More than half of both cases and controls consumed less than two portions of fruit/vegetables per day and only 20 subjects consumed more than five portions per day. Intake of more than two portions per day of β-carotene-containing fruits/vegetables significantly reduced the risk of having an OPMD and leukoplakia (OR = 0.5; 95% CI, 0.3-0.9). The significant differences observed with BMI and fruits/vegetables were attenuated when adjusted for betel quid chewing, smoking and alcohol use.

CONCLUSIONS

This study discloses prevailing under-nutrition in this rural population with very low daily consumption of fruit/vegetables. Cancer preventive properties in their diets are limited and are swamped by the known carcinogenic agents associated with use of betel quid, tobacco and alcohol.

Anti-proliferative and pro-apoptotic activities of hydroxytyrosol on different tumour cells: the role of extracellular production of hydrogen peroxide

PURPOSE

Several recently published data suggest that the anti-proliferative and pro-apoptotic properties of hydroxytyrosol [3,4-dihydroxyphenyl ethanol (3,4-DHPEA)] on HL60 cells may be mediated by the accumulation of hydrogen peroxide (H₂O₂) in the culture medium. The aim of this study was to clarify the role played by H₂O₂ in the chemopreventive activities of 3,4-DHPEA on breast (MDA and MCF-7), prostate (LNCap and PC3) and colon (SW480 and HCT116) cancer cell lines and to investigate the effects of cell culture medium components and the possible mechanisms at the basis of the H₂O₂-producing properties of 3,4-DHPEA.

METHODS

The proliferation was measured by the MTT assay and the apoptosis by both fluorescence microscopy and flow cytometry. The concentration of H₂O₂ in the culture medium was measured by the ferrous ion oxidation-xylenol orange method.

RESULTS

It was found that the H₂O₂-inducing ability of 3,4-DHPEA is completely prevented by pyruvate and that the exposure of cells to conditions not supporting the H₂O₂ accumulation (addition of either catalase or pyruvate to the culture medium) inhibited the anti-proliferative effect of 3,4-DHPEA. Accordingly, the sensitivity of the different cell lines to the anti-proliferative effect of 3,4-DHPEA was inversely correlated with their ability to remove H₂O₂ from the culture medium. With regard to the mechanism by which 3,4-DHPEA causes the H₂O₂ accumulation, it was found that superoxide dismutase increased the H₂O₂ production while tyrosinase, slightly acidic pH (6,8) and absence of oxygen (O₂) completely prevented this activity. In addition, different transition metal-chelating compounds did not modify the H₂O₂-producing activity of 3,4-DHPEA.

CONCLUSIONS

The pro-oxidant activity of 3,4-DHPEA deeply influences its 'in vitro' chemopreventive activities. The main initiation step in the H₂O₂-producing activity is the auto-oxidation of 3,4-DHPEA by O₂ with the formation of the semiquinone, superoxide ions (O₂(-)) and 2H(+).

Research strategies in the study of the pro-oxidant nature of polyphenol nutraceuticals

Polyphenols of phytochemicals are thought to exhibit chemopreventive effects against cancer. These plant-derived antioxidant polyphenols have a dual nature, also acting as pro-oxidants, generating reactive oxygen species (ROS), and causing oxidative stress. When studying the overall cytotoxicity of polyphenols, research strategies need to distinguish the cytotoxic component derived from the polyphenol per se from that derived from the generated ROS. Such strategies include (a) identifying hallmarks of oxidative damage, such as depletion of intracellular glutathione and lipid peroxidation, (b) classical manipulations, such as polyphenol exposures in the absence and presence of antioxidant enzymes (i.e., catalase and superoxide dismutase) and of antioxidants (e.g., glutathione and N-acetylcysteine) and cotreatments with glutathione depleters, and (c) more recent manipulations, such as divalent cobalt and pyruvate to scavenge ROS. Attention also must be directed to the influence of iron and copper ions and to the level of polyphenols, which mediate oxidative stress.

Molecular binding of black tea theaflavins to biological membranes: relationship to bioactivities

Molecular dynamics simulations were used to study the interactions of three theaflavin compounds with lipid bilayers. Experimental studies have linked theaflavins to beneficial health effects, some of which are related to interactions with the cell membrane. The molecular interaction of theaflavins with membranes was explored by simulating the interactions of three theaflavin molecules (theaflavin, theaflavin-3-gallate, and theaflavin-3,3'-digallate) with a mixed bilayer composed of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE). The simulations show that the theaflavins evaluated have an affinity for the lipid bilayer surface via hydrogen bonding. The molecular structure of theaflavins influenced their configuration when binding to the bilayer surface, as well as their ability to form hydrogen bonds with the lipid headgroups. The theaflavin-bilayer interactions studied here help to define structure-function relationships of the theaflavins and provide a better understanding of the role of theaflavins in biological processes. The significance of the results are discussed in the context of black tea composition and bioactivity.

Acute and subchronic oral toxicities of Pu-erh black tea extract in Sprague-Dawley rats

ETHNOPHARMACOLOGICAL RELEVANCE

Pu-erh black tea, which is obtained by first parching crude green tea leaves and then undergoes secondary fermentation with microorganisms, has been believed to be beneficial beverages for health for nearly 2000 years in China, Japan and Taiwan area. But its potential toxicity when administered at a high dose as concentrated extracts has not been completely investigated.

THE AIM OF THE STUDY

The present study was aimed at evaluating potential toxicity of Pu-erh black tea extracts (BTE) from acute and sub-chronic administration to male and female Sprague-Dawley (SD) rats.

MATERIALS AND METHODS

A single BTE dose of 10,000 mg/kg of body weight was administered by oral gavage for acute toxicity in SD rats. Four groups (10 males and 10 females per group) of dose levels of 1250, 2500, and 5,000 mg/kg/day of the test article, as well as controls (distilled water) were tested as the subchronic toxicity study.

RESULTS

No deaths and signs of toxicity occurred during the 14 days of the study. There were no test article related mortalities, body weight gain, feed consumption, clinical observation, organ weight changes, gross finding, clinical or histopathological alterations during the 91-day administration.

CONCLUSIONS

The LD(50) of BTE can be defined as more than 10,000 mg/kg, and a dose of 5,000 mg/kg/day was identified as the no-observed-adverse-effect-level (NOAEL) in this study.

Role of fatty acid chain length on the induction of apoptosis by newly synthesized catechin derivatives

The catechins, a family of polyphenols found in tea, can evoke various responses, including apoptosis. In this study we investigated whether the chemical modification of (-)-epigallocatechin gallate (EGCG) could enhance its apoptosis activity. We found that one of the catechin conjugated with capric acid [(2R,3S)-3',4',5,7-tetrahydroxyflavan-3-yl decanoate; catechin-C10] was most potent to induce apoptosis in U937 cells. C10 treatment resulted in a significant increase in reactive oxygen species (ROS) formation, mitochondrial membrane potential (MMP) loss, cytochrome c release caspase-9 and caspase-3 activation. In addition to this C10 also activated extrinsic pathway significantly as evident by time-dependent increase in Fas expression and caspase-8 activity. C10 mediated cleavage of Bid may be an important event for cross talk between intrinsic and extrinsic signaling. Moreover, pre-treatment of cells with anti-oxidant N-acetyl-L-cysteine (NAC) significantly prevented C10-induced apoptosis but did not protect MMP loss. Treatment of cells with pan-caspase inhibitor significantly inhibited apoptosis indicating that caspases are playing key role. In addition to this C10 was found to induce apoptosis in human colon cancer (HCT116) cells while it showed resistance to human keratinocytes (HaCat). In short our results showed that the optimal fatty acid side chain length is required for the apoptosis inducing activity of catechin derivatives in U937 cells.

Inhibition of mammalian thioredoxin reductase by black tea and its constituents: implications for anticancer actions

Black tea is recently reported to have anti-carcinogenic effects through pro-oxidant property, but the underlying mechanisms remain unclear. Mammalian cytosolic thioredoxin reductase (TrxR1) is well -known for its anti-oxidation activity. In this study, we found that black tea extract (BTE) and theaflavins (TFs), the major black tea polyphenols, inhibited the purified TrxR1 with IC(50) 44 microg/ml and 21+/-1 microg/ml, respectively. Kinetics of TFs exhibited a mixed type of competitive and non-competitive inhibition, with K(is) 4+/-1 microg/ml and K(ii) 26+/-5 microg/ml against coenzyme NADPH, and with K(is) 12+/-3 microg/ml and K(ii) 27+/-5 microg/ml against substrate DTNB. In addition, TFs inhibited TrxR1 in a time-dependent manner. In an equilibrium step, a reversible TrxR1-TFs complex (E*I) forms, which is followed by a slow irreversible first-order inactivation step. Rate constant of the inactivation was 0.7 min(-1), and dissociation constant of E*I was 51.9 microg/ml. Treatment of NADPH-reduced TrxR1 with TFs decreased 5-(Iodoacetamido) fluorescein incorporation, a fluorescent thiol-reactive reagent, suggesting that Sec/Cys residue(s) in the active site may be involved in the binding of TFs. The inhibitory capacity of TFs depends on their structure. Among the TFs tested, gallated forms had strong inhibitory effects. The interactions between TFs and TrxR1 were investigated by molecular docking, which revealed important features of the binding mechanism of theaflavins. An inhibitory effect of BTE on viability of HeLa cells was observed with IC(50) 29 microg/ml. At 33 microg/ml of BTE, TrxR1 activity in HeLa cells was decreased by 73% at 22 h after BTE treatment. TFs inhibited cell viability with IC(50) 10+/-4 microg/ml for HeLa cells and with IC(50) 20+/-5 microg/ml for EAhy926 cells. The cell susceptibility to TFs was inversely correlated to cellular levels of TrxR1. The inhibitory actions of TFs on TrxR1 may be an important mechanism of their anti-cancer properties.

Chemoprotective properties of rooibos (Aspalathus linearis), honeybush (Cyclopia intermedia) herbal and green and black (Camellia sinensis) teas against cancer promotion induced by fumonisin B1 in rat liver

The chemoprotective properties of unfermented and fermented rooibos (Aspalathus linearis) and honeybush (Cyclopia intermedia) herbal teas, and green and black teas (Camellia sinensis) were investigated against fumonisin B1 (FB1) promotion in rat liver utilizing diethylnitrosamine (DEN) as cancer initiator. The various teas differently affected the clinical chemical parameters associated with liver and kidney damage associated with FB1 suggesting specific FB1/iron/polyphenolic interactions. Green tea enhanced (P<0.05) the FB1-induced reduction of the oxygen radical absorbance capacity, while fermented herbal teas and unfermented honeybush significantly (P<0.05) decreased FB1-induced lipid peroxidation in the liver. The teas exhibited varying effects on FB1-induced changes in the activities of catalase, glutathione peroxidase (GPx) glutathione reductase (GR) as well as the glutathione (GSH) status. Unfermented rooibos and honeybush significantly (P<0.05) to marginally (P<0.1) reduced the total number of foci (>10microm), respectively, while all the teas reduced the relative amount of the larger foci. Fermentation seems to reduce the protective effect of the herbal teas. Differences in the major polyphenolic components and certain FB1/polyphenolic/tissue interactions may explain the varying effects of the different teas on the oxidative parameters, hepatotoxic effects and cancer promotion in rat liver.