cancer-prevention

Author: Helena Malhomme de la Roche and Susan Seagrove and Anisha Mehta and Preshita Divekar and Sandra Campbell and Alison Curnow

Oral ingestion of green tea is a potent dietary source of antioxidant polyphenols. These compounds are of interest as they may be able to provide additional protection to the body to help prevent the deleterious effects of ultraviolet A and visible radiation (UVA/VIS) produced indirectly via reactive oxygen species (ROS) in sunlight exposed skin. A small clinical study was conducted in ten healthy adult volunteers. Samples of whole blood were obtained from each before and 30, 60 and 90 min following ingestion of three breakfast cups of green tea (540 ml in total) prepared in a standardised manner. Peripheral leucocytes were isolated from each blood sample and exposed to increasing periods of UVA/VIS irradiation in the laboratory (0, 9, 12 or 18 min). Alkaline single cell gel electrophoresis (the comet assay) was then conducted to determine the level of DNA damage in each sample from each individual. The findings support those of our previous pilot study and indicate that drinking green tea did significantly reduce the genotoxic effects observed in peripheral blood cells 60 min following ingestion when artificially exposed to 12 min of UVA/VIS irradiation in the laboratory. It is postulated that this protection is afforded by the polyphenol compounds (known to be contained within green tea) via scavenging or quenching of the damaging ROS induced by this form of light exposure. Further investigation should consider whether this dietary-induced protection could be extended to cells of the skin.

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Author: Draženka Komes and Dunja Horžić and Ana Belščak and Karin Kovačević Ganić and Ivana Vulić

The effect of different extraction conditions and storage time of prepared infusions on the content of bioactive compounds of green teas and their antioxidant capacity were investigated. The content of total phenols, total flavonoids and total non-flavonoids in green teas was determined spectrophotometrically, while 7 flavan-3-ols, 6 phenolic acids and 3 methylxanthines were identified and quantified by using high performance liquid chromatography (HPLC–PDA). Among the tested green teas bagged green tea Twinings of London was recognized as the richest source of phenolic compounds (3585 mg/L GAE of total phenols). The most abundant phenolic constituents of green tea were flavan-3-ols, of which EGCG was prevailing in all teas (94.54–357.07 mg/L). The highest content of caffeine, as the most abundant methylxanthine, was determined in powdered green tea. The findings of this investigation suggest that extraction efficiency of studied bioactive compounds from green tea depends on the extraction conditions and that maximum extraction efficiency is achieved during aqueous extraction at 80 °C, for 5′ (powder), 15′ (bagged) and 30′ (loose leaf). In order to determine the antioxidant capacity of teas the DPPH, ABTS and FRAP assays were applied. Regardless of the extraction conditions all green teas exhibited significant antioxidant capacity in vitro, which was in correlation with their phenolic content, confirming that green tea is one of the best dietary sources of antioxidants.

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Author: J.J. Johnson and H.H. Bailey and H. Mukhtar

Every year nearly 200,000 men in the United States are diagnosed with prostate cancer (PCa), and another 29,000 men succumb to the disease. Within certain regions of the world population based studies have identified a possible role for green tea in the prevention of certain cancers, especially PCa. One constituent in particular, epigallocatechin-3-gallate also known as EGCG has been shown in cell culture models to decrease cell viability and promote apoptosis in multiple cancer cell lines including PCa with no effect on non-cancerous cell lines. In addition, animal models have consistently shown that standardized green tea polyphenols when administered in drinking water delay the development and progression of PCa. Altogether, three clinical trials have been performed in PCa patients and suggest that green tea may have a distinct role as a chemopreventive agent. This review will present the available data for standardized green tea polyphenols in regard to PCa chemoprevention that will include epidemiological, mechanism based studies, safety, pharmacokinetics, and applicable clinical trials. The data that has been collected so far suggests that green tea may be a promising agent for PCa chemoprevention and further clinical trials of participants at risk of PCa or early stage PCa are warranted.

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Author: Márcia Carvalho and Carmen Jerónimo and Patrícia Valentão and Paula B. Andrade and Branca M. Silva

Renal cell carcinoma (RCC) is one of the most lethal amongst the urologic malignancies, comprising three percent of all human neoplasms, and its incidence appears to be rising. RCC is refractory to both chemotherapy and radiotherapy. Therefore, the discovery of new strategies for therapeutic intervention remains a priority. Green tea (Camellia sinensis) and tea polyphenols have been proposed to exert protective effects against several types of cancer, based on preclinical and clinical trial data; however, the anticarcinogenic activity of green tea towards RCC is unknown. In this study, a targeted metabolite analysis on a green tea leaves methanolic extract was performed by HPLC/DAD and the antiproliferative activity of the extract was assayed using human renal cancer cell lines A-498 and 769-P. The total phenolic content was very high (31.8% of methanolic extract), and the main compounds were flavan-3-ols (94.3% of the total phenolic content), and especially (−)-epigallocatechin-3-gallate (35.9% of the total phenolic content). In addition, two methylxanthines – theophylline and caffeine – were also present in the extract, caffeine being the most abundant. Green tea extract strongly inhibited the growth of both RCC cell lines in a concentration-dependent manner, with IC50 values of 54 ± 10 and 129 ± 28 μg/ml for A-498 and 769-P cells, respectively. This is the first report showing that green tea is likely to be an effective anticancer agent for renal cell carcinoma.

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Author: M.S. Westerterp-Plantenga

The global prevalence of obesity has increased considerably in the last decade. Tools for obesity management including caffeine, and green tea have been proposed as strategies for weight loss and weight maintenance. These ingredients may increase energy expenditure and have been proposed to counteract the decrease in metabolic rate that is present during weight loss. Positive effects on body-weight management have been shown using green tea mixtures. Green tea, by containing both tea catechins and caffeine, may act through inhibition of catechol O-methyl-transferase, and inhibition of phosphodiesterase. Here the mechanisms may also operate synergistically. A green tea–caffeine mixture improves weight maintenance, through thermogenesis, fat oxidation, and sparing fat free mass. The sympathetic nervous system is involved in the regulation of lipolysis, and the sympathetic innervation of white adipose tissue may play an important role in the regulation of total body fat in general. Taken together, these functional ingredients have the potential to produce significant effects on metabolic targets such as thermogenesis, and fat oxidation. An ethnic or genetic effect, and habitual caffeine or green tea catechin intake may act as confounders; this remains to be revealed.

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Author: Rashmi Singh and Nahid Akhtar and Tariq M. Haqqi

A number of factors including inflammation and oxidative stress are believed to play a role in the development of chronic joint diseases. Green tea has become a popular drink and is consumed throughout the world. Extracts of green tea and polyphenols present therein have been shown to inhibit the inflammatory responses in vitro in different cell types and the development of arthritis in animal model studies. There is considerable evidence that (−)-epigallocatechin-3-gallate (EGCG), the predominant green tea polyphenol which mimic its effects, inhibits enzyme activities and signal transduction pathways that play important roles in inflammation and joint destruction in arthritis. After oral consumption EGCG become bioavailable and proteomic studies suggest that EGCG may directly interact with a large set of protein targets and alter the physiological response of the cells. Taken together these and other studies identify and support the use of EGCG as a possible chemopreventive agent with a potential to inhibit the development of arthritis. Here we review the biological effects of EGCG in an attempt to understand its pivotal molecular targets that directly affect the inflammation and joint destruction process for prevention and/or for the development of new therapeutics for arthritis in humans.

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Author: Jonathan M. Hodgson and Kevin D. Croft

The two main types of tea are green and black. Both green and black teas are rich dietary sources of flavonoids. Available evidence suggests that regular tea consumption may reduce the risk of cardiovascular disease. The cardiovascular health benefits of drinking tea are thought to be largely due to flavonoids. Tea intake and intake of flavonoids found in tea have been associated with reduced risk of cardiovascular disease in cross-sectional and prospective population studies. Isolated flavonoids found in tea have also been consistently shown to inhibit the development of atherosclerosis in animal models. A number of possible pathways and mechanisms have been investigated. There is now consistent data indicating that tea and tea flavonoids can enhance nitric oxide status and improve endothelial function, which may be at least partly responsible for benefits on cardiovascular health. There is also evidence, although limited, to suggest benefits of green tea (flavonoids) on body weight and body fatness. Data supporting reduced oxidative damage, inflammation, platelet activation, blood pressure, and risk of type 2 diabetes with tea (flavonoids) remains inadequate to draw any conclusions.

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Author: Stéphane Bastianetto and Slavica Krantic and Rémi Quirion

Background: It has been suggested that accumulation of amyloid-beta (Aß) peptides into senile plaques plays a pivotal role in neuronal cell death occuring in Alzheimer's disease (AD). Aß produces two major types of programmed cell death (PCD) in vitro which requires the activation of effectors of caspase-dependent and -independent cell death pathways, namely caspase-3 and apoptosis inducing factor (AIF). Published data comparing the expression of AIF in post-mortem brains from AD patients and neurologically normal subjects in the course of aging suggest the relevance of AIF in the pathogenesis of AD Reix et al, Neurobiol Aging 28:351, 2007; Yu et al., Am. J. Path., in press). Recent epidemiological studies have reported that elderly people have a lower risk (up to 50%) to develop AD if they regularly eat fruits and vegetables and drink a moderate amount of tea and red wine. Numerous studies indicate that polyphenols derived from these foods and beverages account for the observed neuroprotective effects. In particular, polyphenols extracted from green tea (i.e. epigallocatechin gallate or EGCG) or red wine (i.e. resveratrol) blocked hippocampal cell death against Aß-induced toxicity (Bastianetto et al, Eur J Neurosci 23:55, 2006; Han et al, Br J Pharmacol 141:997, 2004). Our main objective is to determine whether concurrent inactivation of both main types of PCD may have additive therapeutic benefit in AD. Methods: Mixed hippocampal cell cultures were prepared from E19 fetuses obtained from Sprague-Dawley rats. They were grown in D-MEM high glucose containing 10% (v/v) fetal bovine serum. Experiments were performed in 6-day-old cultures. Results: The 24-hour exposure of cultured hippocampal cells to Aß1-42 (15 μM) alone or in combination with either resveratrol (20 μM) or EGCG (10 μM) reduced Aß1-42-mediated increased expression of the 57 kDa death-inducing form of AIF. Moreover, EGCG completely inhibited the activation of the key apoptotic executioner, caspase-3, and reduce the number of apoptotic cells, whereas resveratrol was less effective. Conclusions: Our findings show that these polyphenols do not share the same mechanism of action, suggesting that a combination of EGCG and resveratrol might provide additional neuroprotection against Aß-associated cell death.

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Author: Ian T Johnson

Despite being one of the most widely consumed beverages in the world, green tea is often seen by the media as a so-called superfood, attributed with various health benefits including protective effects against cancer. This reputation rests primarily on the fact that green tea is a rich source of polyphenols, which provide much of the colour and aroma of tea. Both green and black varieties are aqueous infusions of the plant Camellia sinensis, but whereas the constituent polyphenols of black tea are allowed to become oxidised to theaflavins during processing, green tea leaves are heat-treated to inactivate their polyphenol oxidase activity, enabling the native catechins to remain intact.

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Author: Yoshinori Fujimura and Shuntaro Tsukamoto and Miho Irie and Daisuke Miura and Hiroyuki Miura and Hirofumi Tachibana

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