Reduced prostate cancer risk with green tea and epigallocatechin 3-gallate intake among Hong Kong Chinese men

The efficacy of natural bioactive compounds against prostate cancer: Molecular targets and synergistic activities

Globally, prostate cancer (PCa) is regarded as a challenging health issue, and the number of PCa patients continues to rise despite the availability of effective treatments in recent decades. The current therapy with chemotherapeutic drugs has been largely ineffective due to multidrug resistance and the conventional treatment has restricted drug accessibility to malignant tissues, necessitating a higher dosage resulting in increased cytotoxicity. Plant-derived bioactive compounds have recently attracted a great deal of attention in the field of PCa treatment due to their potent effects on several molecular targets and synergistic effects with anti-PCa drugs. This review emphasizes the molecular mechanism of phytochemicals on PCa cells, the synergistic effects of compound-drug interactions, and stem cell targeting for PCa treatment. Some potential compounds, such as curcumin, phenethyl-isothiocyanate, fisetin, baicalein, berberine, lutein, and many others, exert an anti-PCa effect via inhibiting proliferation, metastasis, cell cycle progression, and normal apoptosis pathways. In addition, multiple studies have demonstrated that the isolated natural compounds: d-limonene, paeonol, lanreotide, artesunate, and bicalutamide have potential synergistic effects. Further, a significant number of natural compounds effectively target PCa stem cells. However, further high-quality studies are needed to firmly establish the clinical efficacy of these phytochemicals against PCa.

Green Tea Epigallocatechin-3-Gallate Regulates Autophagy in Male and Female Reproductive Cancer

With a rich abundance of natural polyphenols, green tea has become one of the most popular and healthiest nonalcoholic beverages being consumed worldwide. Epigallocatechin-3-gallate (EGCG) is the predominant catechin found in green tea, which has been shown to promote numerous health benefits, including metabolic regulation, antioxidant, anti-inflammatory, and anticancer. Clinical studies have also shown the inhibitory effects of EGCG on cancers of the male and female reproductive system, including ovarian, cervical, endometrial, breast, testicular, and prostate cancers. Autophagy is a natural, self-degradation process that serves important functions in both tumor suppression and tumor cell survival. Naturally derived products have the potential to be an effective and safe alternative in balancing autophagy and maintaining homeostasis during tumor development. Although EGCG has been shown to play a critical role in the suppression of multiple cancers, its role as autophagy modulator in cancers of the male and female reproductive system remains to be fully discussed. Herein, we aim to provide an overview of the current knowledge of EGCG in targeting autophagy and its related signaling mechanism in reproductive cancers. Effects of EGCG on regulating autophagy toward reproductive cancers as a single therapy or cotreatment with other chemotherapies will be reviewed and compared. Additionally, the underlying mechanisms and crosstalk of EGCG between autophagy and other cellular processes, such as reactive oxidative stress, ER stress, angiogenesis, and apoptosis, will be summarized. The present review will help to shed light on the significance of green tea as a potential therapeutic treatment for reproductive cancers through regulating autophagy.

Another look at dietary polyphenols: challenges in cancer prevention and treatment

Cancer is a pathology that impacts in a profound manner people all over the world. The election strategy against cancer often uses chemotherapy and radiotherapy, which more often than not can present many side effects and not always reliable efficacy. By contrast, it is widely known that a diet rich in fruit and vegetables has a protective effect against cancer insurgence and development. Polyphenols are generally believed to be responsible for those beneficial actions, at least partially. In this review, we highlight the metabolic interaction between polyphenols and our metabolism and discuss their potential for anticancer prevention and therapy.

Dietary flavonoid patterns and prostate cancer: evidence from a Mexican population-based case-control study

Flavonoids are a broad group of bioactive compounds with anticarcinogenic effects on the prostate that have been scarcely evaluated in Latin American populations. Our objective was to evaluate the association between dietary patterns of flavonoid intake and prostate cancer (PC) in a population-based case-control study carried out in Mexico City. Based on a semi-quantitative FFQ with a frame reference of 3 years before diagnosis or interview, we used an updated database for estimating the daily intake (mg/d) of flavones, flavonols and flavanols for 395 confirmed incident PC cases and 797 population controls matched by age (± 5 years). Histological PC differentiation was evaluated using the Gleason score at diagnosis. Flavonoid dietary intake patterns (FDIP) were determined through principal component analysis, and their association with PC was estimated using logistic regression models. Three FDIP were identified: gallate pattern (GP) characterised by (-)-epicatechin-3-O-gallate, (-)-epigallocatechin-3-O-gallate and (+)-gallocatechin; luteolin pattern (LP) characterised by luteolin and (-)-epigallocatechin-3-O-gallate; and a mixed pattern (MP) that included (+)-catechin, (-)-epicatechin and quercetin. A higher GP (ORT3 v.T1 = 0·47; 95 % CI 0·33, 0·66) and LP intake (ORT3 v. T1 = 0·39; 95 % CI 0·27, 0·59) were associated with a decreased PC likelihood. In contrast, a higher MP intake (ORT3 v. T1 = 2·32; 95 % CI 1·67, 3·23) increased PC likelihood. The possible differential and synergistic anticarcinogenic role of flavonoid compounds in PC deserves further study.

Nutraceuticals: Transformation of Conventional Foods into Health Promoters/Disease Preventers and Safety Considerations

Nutraceuticals are essential food constituents that provide nutritional benefits as well as medicinal effects. The benefits of these foods are due to the presence of active compounds such as carotenoids, collagen hydrolysate, and dietary fibers. Nutraceuticals have been found to positively affect cardiovascular and immune system health and have a role in infection and cancer prevention. Nutraceuticals can be categorized into different classes based on their nature and mode of action. In this review, different classifications of nutraceuticals and their potential therapeutic activity, such as anti-cancer, antioxidant, anti-inflammatory and anti-lipid activity in disease will be reviewed. Moreover, the different mechanisms of action of these products, applications, and safety upon consumers including current trends and future prospect of nutraceuticals will be included.

The effect of green tea on prostate specific antigen (PSA): A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Prostate cancer is a major malignancy, affecting men, worldwide. The protective effect of green tea consumption on prostate cancer has been reported in several studies; however, the findings are equivocal.

OBJECTIVE

The aim of this study was to evaluate the effects of green tea on PSA level, by conducting a systematic review and meta-analysis of randomized controlled trials.

METHODS

We searched online databases, including PubMed, Scopus, and Web of Science, up to 11 Aug 2020, to obtain relevant publications. The publication search was not limited by language or date.

RESULTS

A total of 2488 records were identified in the systematic search; from these, seven were included in the meta-analysis. The overall analysis showed no significant changes in PSA levels in subjects treated with green tea, (WMD: ‒0.60 ng/mL; 95 % CI: ‒1.32, 0.12 ng/mL; P = 0.104, I² = 93.80 %, P heterogeneity<0.001). Subgroup analysis based on geographical location showed that green tea significantly reduced PSA level in the USA population (WMD: ‒1.02 pg/mL, 95 % CI: ‒1.30, ‒0.73, P < 0.001) compared to non-USA populations (WMD: ‒0.22 pg/mL, 95 % CI: ‒0.95, 0.50, P = 0.539) (P < 0.001).

CONCLUSION

The results of this review show that green tea has no significant effect on PSA level. However, due to the heterogeneity among studies more consistent clinical trials, with larger sample sizes are required.

Revisiting prostate cancer metabolism: From metabolites to disease and therapy

Prostate cancer (PCa), one of the most commonly diagnosed cancers worldwide, still presents important unmet clinical needs concerning treatment. In the last years, the metabolic reprogramming and the specificities of tumor cells emerged as an exciting field for cancer therapy. The unique features of PCa cells metabolism, and the activation of specific metabolic pathways, propelled the use of metabolic inhibitors for treatment. The present work revises the knowledge of PCa metabolism and the metabolic alterations that underlie the development and progression of the disease. A focus is given to the role of bioenergetic sources, namely, glucose, lipids, and glutamine sustaining PCa cell survival and growth. Moreover, it is described as the action of oncogenes/tumor suppressors and sex steroid hormones in the metabolic reprogramming of PCa. Finally, the status of PCa treatment based on the inhibition of metabolic pathways is presented. Globally, this review updates the landscape of PCa metabolism, highlighting the critical metabolic alterations that could have a clinical and therapeutic interest.

Epigallocatechin-3-gallate sensitises multidrug-resistant oral carcinoma xenografts to vincristine sulfate

Oral squamous cell carcinoma (OSCC) is a very aggressive malignancy, and 50% of patients who receive curative treatment die from the disease or related complications within 5 years. Epigallocatechin‐3‐gallate (EGCG) is the most abundant bioactive ingredient of tea polyphenols in green tea and has anticancer properties. Here, we evaluated the preclinical efficacy of EGCG combined with vincristine sulfate (VCR) on the growth, angiogenic activity and vascular endothelial growth factor (VEGF) expression in xenograft nude mice inoculated with KBV200 cells. Compared with VCR alone, the combined use of EGCG and VCR strongly inhibited tumour growth and angiogenesis (P < 0.01). VEGF mRNA and protein levels were lower in the KBV200 xenograft group treated with the combined regime (P < 0.01) than those in the VCR alone group. EGCG sensitises multidrug‐resistant OSCC to VCR, and this may occur through the inhibition of angiogenesis via VEGF down‐regulation.

Prospective randomized trial evaluating blood and prostate tissue concentrations of green tea polyphenols and quercetin in men with prostate cancer

We evaluated if chronic consumption of quercetin (Q) with green tea extract (GTE) enhances the bioavailability of GT polyphenols (GTPs) and reduces methylation activity as previously observed in mouse xenograft tumors. In this prospective, randomized, parallel design, placebo controlled study, thirty-one men with prostate cancer consumed daily 1 gram of GTE (830 mg of GTP) with 800 mg of Q (GT + Q) or placebo (GT + PL) for four weeks before prostatectomy. First morning voided urine was collected at baseline, 3 weeks and the day of surgery, and prostate tissue on the day of surgery. In week 3, plasma concentration of GTPs and Q was measured in blood collected before and 2 hours after the morning dose. Prostate tissue epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) were detected in 67 and 93% of participants in the GT + Q group and 75 and 94% of participants in the GT + PL group. Q was increased 14-fold, 12-fold and 4.5-fold in plasma, urine, and prostate tissue, respectively, in the GT + Q compared to the GT + PL-group. There was a trend for decreased EGC levels in urine collected prior to prostatectomy in the GT + Q compared to GT + PL-group (p = 0.053). Plasma epigallocatechin (EGC) showed a trend to increase (p = 0.066) two hours after capsule intake in the GT + Q vs. the GT + PL-group. There was no significant difference between the groups in GTP content or methylation activity in prostate tissue or RBCs. No liver toxicity was observed. Although our findings are suggestive, further studies are warranted evaluating if Q alters GTP metabolism.

Flavonoids as Epigenetic Modulators for Prostate Cancer Prevention

Prostate cancer (PCa) is a multifactorial disease with an unclear etiology. Due to its high prevalence, long latency, and slow progression, PCa is an ideal target for chemoprevention strategies. Many research studies have highlighted the positive effects of natural flavonoids on chronic diseases, including PCa. Different classes of dietary flavonoids exhibit anti-oxidative, anti-inflammatory, anti-mutagenic, anti-aging, cardioprotective, anti-viral/bacterial and anti-carcinogenic properties. We overviewed the most recent evidence of the antitumoral effects exerted by dietary flavonoids, with a special focus on their epigenetic action in PCa. Epigenetic alterations have been identified as key initiating events in several kinds of cancer. Many dietary flavonoids have been found to reverse DNA aberrations that promote neoplastic transformation, particularly for PCa. The epigenetic targets of the actions of flavonoids include oncogenes and tumor suppressor genes, indirectly controlled through the regulation of epigenetic enzymes such as DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC). In addition, flavonoids were found capable of restoring miRNA and lncRNA expression that is altered during diseases. The optimization of the use of flavonoids as natural epigenetic modulators for chemoprevention and as a possible treatment of PCa and other kinds of cancers could represent a promising and valid strategy to inhibit carcinogenesis and fight cancer.

Green tea (Camellia sinensis) for the prevention of cancer

BACKGROUND

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (2009, Issue 3).Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea, and drinking habits vary cross-culturally. C sinensis contains polyphenols, one subgroup being catechins. Catechins are powerful antioxidants, and laboratory studies have suggested that these compounds may inhibit cancer cell proliferation. Some experimental and nonexperimental epidemiological studies have suggested that green tea may have cancer-preventative effects.

OBJECTIVES

To assess possible associations between green tea consumption and the risk of cancer incidence and mortality as primary outcomes, and safety data and quality of life as secondary outcomes.

SEARCH METHODS

We searched eligible studies up to January 2019 in CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, and reference lists of previous reviews and included studies.

SELECTION CRITERIA

We included all epidemiological studies, experimental (i.e. randomised controlled trials (RCTs)) and nonexperimental (non-randomised studies, i.e. observational studies with both cohort and case-control design) that investigated the association of green tea consumption with cancer risk or quality of life, or both.

DATA COLLECTION AND ANALYSIS

Two or more review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. We summarised the results according to diagnosis of cancer type.

MAIN RESULTS

In this review update, we included in total 142 completed studies (11 experimental and 131 nonexperimental) and two ongoing studies. This is an additional 10 experimental and 85 nonexperimental studies from those included in the previous version of the review. Eleven experimental studies allocated a total of 1795 participants to either green tea extract or placebo, all demonstrating an overall high methodological quality based on 'Risk of bias' assessment. For incident prostate cancer, the summary risk ratio (RR) in the green tea-supplemented participants was 0.50 (95% confidence interval (CI) 0.18 to 1.36), based on three studies and involving 201 participants (low-certainty evidence). The summary RR for gynaecological cancer was 1.50 (95% CI 0.41 to 5.48; 2 studies, 1157 participants; low-certainty evidence). No evidence of effect of non-melanoma skin cancer emerged (summary RR 1.00, 95% CI 0.06 to 15.92; 1 study, 1075 participants; low-certainty evidence). In addition, adverse effects of green tea extract intake were reported, including gastrointestinal disorders, elevation of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin/subcutaneous reactions. Consumption of green tea extracts induced a slight improvement in quality of life, compared with placebo, based on three experimental studies. In nonexperimental studies, we included over 1,100,000 participants from 46 cohort studies and 85 case-control studies, which were on average of intermediate to high methodological quality based on Newcastle-Ottawa Scale 'Risk of bias' assessment. When comparing the highest intake of green tea with the lowest, we found a lower overall cancer incidence (summary RR 0.83, 95% CI 0.65 to 1.07), based on three studies, involving 52,479 participants (low-certainty evidence). Conversely, we found no association between green tea consumption and cancer-related mortality (summary RR 0.99, 95% CI 0.91 to 1.07), based on eight studies and 504,366 participants (low-certainty evidence). For most of the site-specific cancers we observed a decreased RR in the highest category of green tea consumption compared with the lowest one. After stratifying the analysis according to study design, we found strongly conflicting results for some cancer sites: oesophageal, prostate and urinary tract cancer, and leukaemia showed an increased RR in cohort studies and a decreased RR or no difference in case-control studies.

AUTHORS' CONCLUSIONS

Overall, findings from experimental and nonexperimental epidemiological studies yielded inconsistent results, thus providing limited evidence for the beneficial effect of green tea consumption on the overall risk of cancer or on specific cancer sites. Some evidence of a beneficial effect of green tea at some cancer sites emerged from the RCTs and from case-control studies, but their methodological limitations, such as the low number and size of the studies, and the inconsistencies with the results of cohort studies, limit the interpretability of the RR estimates. The studies also indicated the occurrence of several side effects associated with high intakes of green tea. In addition, the majority of included studies were carried out in Asian populations characterised by a high intake of green tea, thus limiting the generalisability of the findings to other populations. Well conducted and adequately powered RCTs would be needed to draw conclusions on the possible beneficial effects of green tea consumption on cancer risk.

Natural Compounds in Prostate Cancer Prevention and Treatment: Mechanisms of Action and Molecular Targets

Prostate cancer (PCa) represents a major cause of cancer mortality among men in developed countries. Patients with recurrent disease initially respond to androgen-deprivation therapy, but the tumor eventually progresses into castration-resistant PCa; in this condition, tumor cells acquire the ability to escape cell death and develop resistance to current therapies. Thus, new therapeutic approaches for PCa management are urgently needed. In this setting, natural products have been extensively studied for their anti-PCa activities, such as tumor growth suppression, cell death induction, and inhibition of metastasis and angiogenesis. Additionally, numerous studies have shown that phytochemicals can specifically target the androgen receptor (AR) signaling, as well as the PCa stem cells (PCSCs). Interestingly, many clinical trials have been conducted to test the efficacy of nutraceuticals in human subjects, and they have partially confirmed the promising results obtained in vitro and in preclinical models. This article summarizes the anti-cancer mechanisms and therapeutic potentials of different natural compounds in the context of PCa prevention and treatment.

Evaluation of the neuroprotective effect of EGCG: a potential mechanism of mitochondrial dysfunction and mitochondrial dynamics after subarachnoid hemorrhage

(-)-Epigallocatechin-3-gallate (EGCG), the main bioactive component of tea catechins, exhibits broad-spectrum health efficacy against mitochondrial damage after subarachnoid hemorrhage (SAH). The mechanisms, however, are largely unknown. Here, the ability of EGCG to rescue mitochondrial dysfunction and mitochondrial dynamics following the inhibition of cell death was investigated by using in vitro and in vivo SAH models. EGCG blocked the cytosolic channel ([Ca2+])i influx via voltage-gated calcium channels (VGCCs), which induced mitochondrial dysfunction, including mitochondrial membrane potential depolarization and reactive oxygen species (ROS) release. As expected, EGCG ameliorated oxyhemoglobin (OxyHb)-induced impairment of mitochondrial dynamics by regulating the expression of Drp1, Fis1, OPA1, Mfn1, and Mfn2. As a result, EGCG restored the increases in fragmented mitochondria and the mtDNA copy number in the OxyHb group to almost the normal level after SAH. In addition, the normal autophagic flux induced by EGCG at both the initiation and formation stages regulated Atg5 and Beclin-1 after SAH for the timely elimination of damaged mitochondria. In the end, EGCG increased the neurological score by decreasing cell death through the cyt c-mediated intrinsic apoptotic pathway. The results revealed the mechanisms behind the neuroprotective effects of EGCG via inhibition of the overloaded [Ca2+]i-induced mitochondrial dysfunction and the imbalanced mitochondrial fusion and fission cycle. Therefore, the simultaneous inhibition and timely elimination of damaged mitochondria could determine the therapeutic effect of EGCG.

Anti-Cancer Effects of Green Tea Polyphenols Against Prostate Cancer

Prostate cancer is the most common cancer among men. Green tea consumption is reported to play an important role in the prevention of carcinogenesis in many types of malignancies, including prostate cancer; however, epidemiological studies show conflicting results regarding these anti-cancer effects. In recent years, in addition to prevention, many investigators have shown the efficacy and safety of green tea polyphenols and combination therapies with green tea extracts and anti-cancer agents in in vivo and in vitro studies. Furthermore, numerous studies have revealed the molecular mechanisms of the anti-cancer effects of green tea extracts. We believe that improved understanding of the detailed pathological roles at the molecular level is important to evaluate the prevention and treatment of prostate cancer. Therefore, in this review, we present current knowledge regarding the anti-cancer effects of green tea extracts in the prevention and treatment of prostate cancer, with a particular focus on the molecular mechanisms of action, such as influencing tumor growth, apoptosis, androgen receptor signaling, cell cycle, and various malignant behaviors. Finally, the future direction for the use of green tea extracts as treatment strategies in patients with prostate cancer is introduced.

Tea Polyphenols in Promotion of Human Health

Tea is the most widely used beverage worldwide. Japanese and Chinese people have been drinking tea for centuries and in Asia, it is the most consumed beverage besides water. It is a rich source of pharmacologically active molecules which have been implicated to provide diverse health benefits. The three major forms of tea are green, black and oolong tea based on the degree of fermentation. The composition of tea differs with the species, season, leaves, climate, and horticultural practices. Polyphenols are the major active compounds present in teas. The catechins are the major polyphenolic compounds in green tea, which include epigallocatechin-3-gallate (EGCG), epigallocatechin, epicatechin-3-gallate and epicatechin, gallocatechins and gallocatechin gallate. EGCG is the predominant and most studied catechin in green tea. There are numerous evidences from cell culture and animal studies that tea polyphenols have beneficial effects against several pathological diseases including cancer, diabetes and cardiovascular diseases. The polyphenolic compounds present in black tea include theaflavins and thearubigins. In this review article, we will summarize recent studies documenting the role of tea polyphenols in the prevention of cancer, diabetes, cardiovascular and neurological diseases.

Tea Polyphenols in Promotion of Human Health

Tea is the most widely used beverage worldwide. Japanese and Chinese people have been drinking tea for centuries and in Asia, it is the most consumed beverage besides water. It is a rich source of pharmacologically active molecules which have been implicated to provide diverse health benefits. The three major forms of tea are green, black and oolong tea based on the degree of fermentation. The composition of tea differs with the species, season, leaves, climate, and horticultural practices. Polyphenols are the major active compounds present in teas. The catechins are the major polyphenolic compounds in green tea, which include epigallocatechin-3-gallate (EGCG), epigallocatechin, epicatechin-3-gallate and epicatechin, gallocatechins and gallocatechin gallate. EGCG is the predominant and most studied catechin in green tea. There are numerous evidences from cell culture and animal studies that tea polyphenols have beneficial effects against several pathological diseases including cancer, diabetes and cardiovascular diseases. The polyphenolic compounds present in black tea include theaflavins and thearubigins. In this review article, we will summarize recent studies documenting the role of tea polyphenols in the prevention of cancer, diabetes, cardiovascular and neurological diseases.

Leukemia therapy by flavonoids: Future and involved mechanisms

Flavonoids are a varied family of phytonutrients (plant chemicals) usually are detected in fruits and vegetables. In this big family, there exist more than 10,000 members that is separated into six chief subtypes: isoflavonols, flavonoenes, flavones, flavonols, anthocyanins, and chalcones. The natural compounds, such as fruits, have visible positive effects in regulating of survival involved signaling pathways that performance as the regulator of cell survival, growth, and proliferation. Researchers have established that commonly consumption up flavonoids decreases incidence and development risk of certain cancers, especially leukemia. Flavonoids have been able to induce apoptosis and stimulate cell cycle arrest in cancer cells via different pathways. Similarly, they have antiangiogenesis and antimetastasis capability, which were shown in wide ranges of cancer cells, particularly, leukemia. It seems that flavonoid because of their widespread approval, evident safety and low rate of side effects, have hopeful anticarcinogenic potential for leukemia therapy. Based on the last decade reports, the most important acting mechanisms of these natural compounds in leukemia cells are stimulating of apoptosis pathways by upregulation of caspase 3, 8, 9 and poly ADP-ribose polymerase (PARP) and proapoptotic proteins, particularly Bax activation. As well, they can induce cell cycle arrest in target cells not only via increasing of activated levels of p21 and p53 but also by inhibition of cyclins and cyclin-dependent kinases. Furthermore, attenuation of neclear factor-κB and signal transducer and activator of transcription 3 activation, suppression of signaling pathway and downregulation of intracellular antiapoptotic proteins are other significant antileukemic function mechanism of flavonoids. Overall, it appears that flavonoids are promising and effective compounds in the field of leukemia therapy. In this review, we tried to accumulate and revise most promising flavonoids and finally declared their major working mechanisms in leukemia cells.

Perspectives on the recent developments with green tea polyphenols in drug discovery

INTRODUCTION

Increasing evidence has expanded the role of green tea from a traditional beverage to a source of pharmacologically active molecules with diverse health benefits. However, conclusive clinical results are needed to better elucidate the cancer-preventive and therapeutic effects of green tea polyphenols (GTPs). Areas covered: The authors describe GTPs' chemical compositions and metabolic biotransformations, and their recent developments in drug discovery, focusing on their cancer chemopreventive and therapeutic effects. They then review the recent development of GTP-loaded nanoparticles and GTP prodrugs. Expert opinion: GTPs possess potent anticarcinogenic activities through interfering with the initiation, development and progression phases of cancer. There are several challenges (e.g. poor bioavailability) in developing GTPs as therapeutic agents. Use of nanoparticle-based delivery systems has provided unique advantages over purified GTPs. However, there is still a need to determine the actual magnitude and pharmacological mechanisms of GTPs encapsulated in nanoparticles, in order to address newly emerging safety issues associated with the potential 'local overdose' effect. The use of Pro- epigallocatechin gallate (Pro-EGCG) as a prodrug appears to offer improved in vitro stability as well as better in vivo bioavailability and efficacies in a number of animal studies, suggesting its potential as a therapeutic agent for further study and development.

GPCR6A Is a Molecular Target for the Natural Products Gallate and EGCG in Green Tea

SCOPE

The molecular mechanisms whereby gallates in green tea exert metabolic effects are poorly understood.

METHODS AND RESULTS

We found that GPRC6A, a multi-ligand-sensing G-protein-coupled receptor that regulates energy metabolism, sex hormone production, and prostate cancer progression, is a target for gallates. Sodium gallate (SG), gallic acid (GA) > ethyl gallate (EG) > octyl gallate (OG) dose dependently activated ERK in HEK-293 cells transfected with GPRC6A but not in non-transfected controls. SG also stimulated insulin secretion in β-cells isolated from wild-type mice similar to the endogenous GPRC6A ligands, osteocalcin (Ocn) and testosterone (T). Side-chain additions to create OG resulted in loss of GPRC6A agonist activity. Another component of green tea, epigallocatechin 3-gallate (EGCG), dose-dependently inhibited Ocn activation of GPRC6A in HEK-293 cells transfected with GPRC6A and blocked the effect of Ocn in stimulating glucose production in CH10T1/2 cells. Using structural models of the venus fly trap (VFT) and 7-transmembrane (7-TM) domains of GPRC6A, calculations suggest that l-amino acids and GA bind to the VFT, whereas EGCG is calculated to bind to sites in both the VFT and 7-TM.

CONCLUSION

GA and EGCG have offsetting agonist and antagonist effects on GPRC6A that may account for the variable metabolic effect of green tea consumption.

REDUCTION OF PM2.5 TOXICITY ON HUMAN ALVEOLAR EPITHELIAL CELLS A549 BY TEA POLYPHENOLS

Tea-derived polyphenols have anticancer and antioxidant properties, and they can regulate oxidative stress. This study was designed to quantify both the toxic effects of fine particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5) and determine whether tea polyphenols could provide a protective effect against PM2.5 toxicity on human alveolar epithelial A549 cells in vitro. Cytotoxic effects of the PM2.5 on A549 cells were measured by means of cell viability, the expression of caspase-3, bax/bcl-2 and C/EBP-homologous protein (CHOP), and the generation of intracellular reactive oxygen species, malondialdehyde and superoxide dismutase. The results showed that tea polyphenols ameliorated some of the adverse effects of PM2.5 on A549 cell viability and superoxide dismutase levels. In addition, tea polyphenols decreased the production of reactive oxygen species, malondialdehyde generation, and apoptosis in response to PM2.5 exposure. Therefore, our results support a role for tea polyphenols in reducing the toxicity of PM2.5, particularly with regard to targeting oxidative stress and apoptosis.

Oxidative stress-induced Akt downregulation mediates green tea toxicity towards prostate cancer cells

Green tea consumption has been shown to possess cancer chemopreventive activity. Polyphenol E (PE) is a widely used standardized green tea extract formulation. This study was designed to investigate the impact of PE on prostate cancer cells (PC3), analyze the potential signals involved and elucidate whether anti- or pro-oxidant effects may be implicated. Treatment of PC3 cells with 30 and 100μg/ml PE significantly decreased cell viability and proliferation. At the tested concentrations, PE did not exert any antioxidant activity, eliciting instead a pro-oxidant effect at concentrations 30 and 100μg/ml, which was consistent with the observed PE cytotoxicity. PE-induced cell death was associated with mitochondrial dysfunction and downregulation of Akt activation, thus suggesting their implication in the PE-elicited cell dysfunction. Cell exposure to the ROS scavenger N-Acetyl Cysteine prevented PE-induced ROS increase, pAkt impairment, and cell death, clearly indicating the causative role of ROS in the observed phenomena. Failure of PE to induce PC3 damage in cells overexpressing Akt further confirms its implication in the PE-elicited cell death. Our findings showed an association between the antiproliferative and the pro-oxidant effect elicited by PE on PC3 cells and delineates a molecular signaling pattern potentially implicated in the toxicity of PE towards prostate cancer cells.