Antiobesity effects of green tea catechins: a mechanistic review

Plant-derived food ingredients for stimulation of energy expenditure

The development of obesity is related to the regulation of energy intake, energy expenditure, and energy storage in the body. Increasing energy expenditure by inducing lipolysis followed by fat oxidation is one of the alternatives which could help to reverse this increasingly widespread condition. Currently, there is no approved drug targeting on stimulation of energy expenditure available. The use of herbal medicines has become a preferred alternative, supported by the classical consensus on the innocuity of herbal medicine vs synthetic drugs, something that often lacks a scientific basis (ban on Ephedra, for example). The inclusion of functional food in the daily diet has also been promoted although its efficacy requires further investigation. This review summarizes the results of recent work focused on the investigation of edible plant materials targeted at various important pathways related to stimulation of energy expenditure. The aim is to evaluate a number of plants that may be of interest for further studies because of their potential to provide novel lead compounds or functional foods which may be used to combat obesity, but require further studies to evaluate their antiobesity activity in humans.

Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials

PURPOSE

Although previous literature has reported that regular green tea consumption may improve blood pressure, the evidence from these studies is not consistent. The present study systematically reviewed randomised controlled trials and examined the effect of green tea consumption on blood pressure using meta-analysis.

METHODS

Search of ProQuest, PubMed, Scopus and Cochrane Library (CENTERAL) was conducted, to identify eligible articles. Articles from 1995 to 2013 were included. A random-effect model was chosen to calculate the effect of combined trials.

RESULT

Thirteen studies were included in the meta-analysis. Green tea consumption significantly changed systolic blood pressure, by -2.08 mm Hg (95% CI -3.06, -1.05), and diastolic blood pressure, by -1.71 mm Hg (95% CI -2.86, -0.56), compared to the control. Changes in lipid profile, blood glucose and body mass index were also assessed in the meta-analysis. A significant reduction was found in total cholesterol (-0.15 mmol/L [95% CI -0.27, -0.02]) and low-density lipoprotein cholesterol (-0.16 mmol/L [95% CI -0.22, -0.09]). Changes in other parameters did not reach statistical significance. Subgroup analysis suggested a greater reduction in both systolic and diastolic blood pressure in studies that included participants with a baseline mean systolic blood pressure of ≥ 130 mm Hg, and studies involving consuming green tea as an extract.

CONCLUSION

The present meta-analysis suggests that green tea and its catechins may improve blood pressure, and the effect may be greater in those with systolic blood pressure ≥ 130 mm Hg. The meta-analysis also suggests that green tea catechins may improve total and low-density lipoprotein cholesterol.

The chalcones cardamonin and flavokawain B inhibit the differentiation of preadipocytes to adipocytes by activating ERK

AIM

We searched for polyphenols capable of inhibiting the lipid accumulation in 3T3-L1 cells, and investigated the mechanisms of two effective chalcones cardamonin and flavokawain B on differentiation of preadipocytes.

METHOD AND RESULTS

We treated 3T3-L1 cells with a panel of 46 polyphenols and measured intracellular lipid accumulation by Sudan II staining. Four of them, including cardamonin and flavokawain B, inhibited lipid accumulation. In the further study, cardamonin and flavokawain B inhibited lipid accumulation by downregulating the expression of CCAAT/enhancer binding protein (C/EBP)-β, C/EBPα, and peroxisome proliferator-activated receptor-γ (PPARγ) at both mRNA and protein levels. Cardamonin and flavokawain B also increased phosphorylation of extracellular signal-regulated kinase (ERK) in the early phase of adipocyte differentiation. PD98059, an ERK inhibitor, restored C/EBPβ, PPARγ expression and intracellular lipid accumulation in adipocytes. Moreover, cardamonin and flavokawain B also modulated the secretion of C-reactive protein, dipeptidyl peptidase IV, interleukin-6, tumor necrosis factor-α and fibroblast growth factor-21 in mature adipocytes.

CONCLUSIONS

These results indicate that ERK activation and consequent downregulation of adipocyte-specific transcription factors are involved in the inhibitory effects of the chalcones cardamonin and flavokawain B on adipocyte differentiation. Moreover, cardamonin and flavokawain B are able to modulate secretion of adipokines in mature adipocytes.

Flavan-3-ol fraction from cocoa powder promotes mitochondrial biogenesis in skeletal muscle in mice

BACKGROUND

Numerous clinical studies have reported that ingestion of chocolate has reduced risk of metabolic syndrome. In order to elucidate the mechanism, we evaluated the influence of flavan-3-ols derived from cocoa powder on energy metabolism in mice using an indirect calorimetric method.

METHOD

The mice were divided into two groups, and administered either distilled water or 50 mg/kg of flavan-3-ol fraction for 2 weeks. At the end of the experimental period, animals were sacrificed after blood pressure and the mean respiratory exchange ratio (RER) over 24 hours were measured.

RESULTS

The mean respiratory exchange ratio (RER) over 24 hours was reduced significantly in the flavan-3-ols group. The mean blood pressure was significantly decreased in flavan-3-ols treatment group compared with control group. The protein level of carnitine palmitoyltransferase 2 (CPT2) was increased significantly by flavan-3-ols in skeletal muscle, but not in liver. Uncoupling protein (UCP) 1 was increased significantly in brown adipose tissue by flavan-3-ols. The mitochondria copy number in gastrocnemius and soleus muscles and brown adipose tissue were increased significantly by administration of flavan-3-ol fraction.

CONCLUSION

These results suggest that flavan-3-ols enhances lipolysis and promotes mitochondrial biogenesis. We conclude that improvement of metabolic syndrome risk factors following ingestion of chocolate may be induced, in part, by the mitochondrial biogenesis-promoting effect of flavan-3-ols.

Diets naturally rich in polyphenols improve fasting and postprandial dyslipidemia and reduce oxidative stress: a randomized controlled trial

BACKGROUND

The postprandial triglyceride-rich lipoprotein (TRL) concentration is a recognized independent cardiovascular disease risk factor. Diet is the natural approach for these postprandial alterations. Dietary polyphenols and long chain n-3 polyunsaturated fatty acids (LCn3s) are associated with a lower cardiovascular disease risk.

OBJECTIVE

This randomized controlled study evaluated, in persons with a high risk of cardiovascular disease, the effects of diets naturally rich in polyphenols and/or marine LCn3s on plasma TRLs and urinary 8-isoprostane concentrations, a biomarker of oxidative stress.

DESIGN

According to a 2 × 2 factorial design, 86 overweight/obese individuals with a large waist circumference and any other component of the metabolic syndrome were randomly assigned to an isoenergetic diet 1) poor in LCn3s and polyphenols, 2) rich in LCn3s, 3) rich in polyphenols, or 4) rich in LCn3s and polyphenols. The diets were similar in all other components. Before and after the 8-wk intervention, fasting and postmeal TRLs and 8-isoprostane concentrations in 24-h urine samples were measured.

RESULTS

Dietary adherence was good in all participants. Polyphenols significantly reduced fasting triglyceride concentrations (2-factor ANOVA) in plasma (P = 0.023) and large very-low-density lipoproteins (VLDLs) (P = 0.016) and postprandial triglyceride total area under the curve in plasma (P = 0.041) and large VLDLs (P = 0.004). LCn3s reduced postprandial chylomicron cholesterol and VLDL apolipoprotein B-48. The concentrations of urinary 8-isoprostane decreased significantly with the polyphenol-rich diets. Lipoprotein changes induced by the intervention significantly correlated with changes in 8-isoprostane.

CONCLUSIONS

Diets naturally rich in polyphenols positively influence fasting and postprandial TRLs and reduce oxidative stress. Marine LCn3s reduce TRLs of exogenous origin. Through their effects on postprandial lipemia and oxidative stress, polyphenols may favorably affect cardiovascular disease risk.

Green tea decoction improves glucose tolerance and reduces weight gain of rats fed normal and high-fat diet

Green tea containing polyphenols exerts antidiabetic and antiobesity effects, but the mechanisms involved are not fully understood. In this study, we first analyzed and compared polyphenol compounds [epigallocatechin gallate (EGCG), epigallocatechin (EGC)] in decoction of green tea leaves versus usual green tea extracts. Second, the effects of acute (30 min) or chronic (6 weeks) oral administration of green tea decoction (GTD) on intestinal glucose absorption were studied in vitro in Ussing chamber, ex vivo using isolated jejunal loops and in vivo through glucose tolerance tests. Finally, we explore in rat model fed normal or high-fat diet the effects of GTD on body weight, blood parameters and on the relative expression of glucose transporters SGLT-1, GLUT2 and GLUT4. GTD cooked for 15 min contained the highest amounts of phenolic compounds. In fasted rats, acute administration of GTD inhibited SGLT-1 activity, increased GLUT2 activity and improved glucose tolerance. Similarly to GTD, acute administration of synthetic phenolic compounds (2/3 EGCG+1/3 EGC) inhibited SGLT-1 activity. Chronic administration of GTD in rat fed high-fat diet reduced body weight gain, circulating triglycerides and cholesterol and improved glucose tolerance. GTD-treated rats for 6 weeks display significantly reduced SGLT-1 and increased GLUT2 mRNA levels in the jejunum mucosa. Moreover, adipose tissue GLUT4 mRNA levels were increased. These results indicate that GTD, a traditional beverage rich in EGCG and EGC reduces intestinal SGLT-1/GLUT2 ratio, a hallmark of regulation of glucose absorption in enterocyte, and enhances adipose GLUT4 providing new insights in its possible role in the control of glucose homeostasis.

Acute effect on satiety, resting energy expenditure, respiratory quotient, glucagon-like peptide-1, free fatty acids, and glycerol following consumption of a combination of bioactive food ingredients in overweight subjects

OBJECTIVE

A combination of bioactive food ingredients (capsaicinoids, epigallocatechin gallate, piperin, and l-carnitine, CBFI) may promote satiety and thermogenesis. The study was conducted in order to assess whether there is any effect on satiety, resting energy expenditure (REE), respiratory quotient, glucagon-like peptide-1 (GLP-1), free fatty acids (FFA) and glycerol release, following a standardized mixed meal with or without single consumption of a CBFI.

DESIGN

An 8-week randomized double-blind placebo-controlled trial.

SETTING

Dietetic and Metabolic Unit, Azienda di Servizi alla Persona, University of Pavia and "Villa delle Querce" Clinical Rehabilitation Institute, Rome, Italy.

PARTICIPANTS

Thirty-seven overweight adults (body mass index [BMI]: 25-35).

INTERVENTION

Nineteen overweight subjects were included in the supplemented group (14 women, 5 men; age 46.4 ± 6.4; BMI: 30.5 ± 3.3) and 18 in the placebo group (13 women, 5 men; age 40.8 ± 11.5; BMI: 30.1 ± 2.6). Satiety was assessed using 100-mm visual analogue scales (VAS) and the area under the curve was calculated.

RESULTS

All measured parameters increased significantly in comparison with baseline in response to meal, both with CBFI and with placebo. However, throughout the study day, the supplemented group experienced a significantly greater increase than the placebo group in their sensation of satiety following acute administration of the supplement.

CONCLUSION

CBFI may therefore be of great value in the treatment of overweight patients by increasing satiety and stimulating thermogenesis.

Green tea and vitamin E enhance exercise-induced benefits in body composition, glucose homeostasis, and antioxidant status in elderly men and women

OBJECTIVE

To investigate the effects of green tea plus vitamin E in addition to exercise on body composition and metabolic and antioxidant parameters in healthy elderly individuals.

DESIGN

Interventional randomized controlled prospective trial.

METHODS

For 12 weeks, 22 elderly men and women (age: 71.1 ± 1.2 years; body mass index: 28.3 ± 0.5 kg/m(2) [mean ± SE]) undertook 30 minutes of moderately intense walking 6 d/wk. They were randomly assigned to ingest either green tea plus vitamin E (GTVE; 3 cups and 400 IU, respectively; n = 11) or placebo (n = 11). Data on anthropometrics, fasting insulin and glucose levels, physical fitness, dietary intake, safety parameters, and biomarkers of oxidation status were recorded and analyzed at the start and end of the study.

RESULTS

Though dietary intake was unchanged, improved exercise capacity was followed by a significant reduction in body weight and fasting insulin levels in all participants. Additional consumption of GTVE resulted in a twofold increase in serum vitamin E (from 20.4 to 40.6 μmol/L, p < 0.001) and a decrease of men's and women's waist circumferences (from 100.8 and 95.7 to 96.9 and 85.0 cm, p < 0.05 and p < 0.01, respectively) and fasting glucose levels (from 5.30 to 4.98 mmol/L, p < 0.01). Plasma protein carbonyls dropped (from 0.93 to 0.77 nmol/mg protein, p < 0.05), whereas erythrocyte catalase activities increased (from 26.7 to 29.7 U/g hemoglobin, p < 0.05) in the GTVE group only. Oral peroxidase activities were increased in both groups.

CONCLUSIONS

A daily dose of GTVE in healthy elderly men and women may improve exercise-induced benefits in body composition and glucose tolerance and may also lower oxidative burden.

Effects of dietary supplementation with epigallocatechin-3-gallate on weight loss, energy homeostasis, cardiometabolic risk factors and liver function in obese women: randomised, double-blind, placebo-controlled clinical trial

The aim of the present study was to examine the effects of green tea epigallocatechin-3-gallate (EGCG) on changes in body composition, energy and substrate metabolism, cardiometabolic risk factors and liver function enzymes after an energy-restricted diet intervention in obese women. In the present randomised, double-blind, placebo-controlled study, eighty-three obese (30 kg/m² > BMI < 40 kg/m²) pre-menopausal women consumed 300 mg/d of EGCG or placebo (lactose). We measured body weight and adiposity (dual-energy X-ray absorptiometry), energy expenditure and fat oxidation rates (indirect calorimetry), blood lipid levels (TAG, total cholesterol, LDL-cholesterol and HDL-cholesterol), insulin resistance, C-reactive protein and liver function markers (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, γ-glutamyltransferase, urea, bilirubin and 2-keto[1-¹³C]isocaproate oxidation) before and after the intervention in the EGCG and control groups. We did not find any significant difference in the changes in body weight (-0.3 kg, 95% CI -5.0, 4.3), fat mass (-0.7 kg, 95% CI -3.5, 2.1), energy (0.3 kJ/kg per d, 95% CI -3.1, 2.7) and fat (-0.1 g/min, 95% CI -0.03, 0.01) metabolism, homeostasis assessment model for insulin resistance (0.2, 95% CI -0.2, 0.7), total cholesterol (-0.21 mmol/l, 95% CI -0.55, 0.13), LDL-cholesterol (-0.15 mmol/l, 95% CI -0.50, 0.20), TAG (-0.4 mmol/l, 95% CI -0.56, 0.29) and liver function markers between the EGCG and control groups. In conclusion, the present results suggest that dietary supplementation with 300 mg/d of EGCG for 12 weeks did not enhance energy-restricted diet-induced adiposity reductions, and did not improve weight-loss-induced changes in cardiometabolic risk factors in obese Caucasian women. The intake of 300 mg/d of EGCG for 12 weeks did not cause any adverse effect on liver function biomarkers.

Plaster body wrap: effects on abdominal fat

BACKGROUND

Abdominal fat is associated with metabolic disorders, leading to cardiovascular risk factors and numerous diseases. This study aimed to analyze the effect of plaster body wrap in combination with aerobic exercise on abdominal fat.

METHODS

Nineteen female volunteers were randomly divided into intervention group (IG; n = 10) performing aerobic exercise with plaster body wrap, and control group (CG; n = 9) performing only exercise. Subcutaneous and visceral fat were measured using ultrasound; subcutaneous fat was also estimated on analysis of skinfolds and abdominal perimeters.

RESULTS

At the end of the 10-sessions protocol, the IG demonstrated a significant decrease (p ≤ 0.05) in subcutaneous fat at the left anterior superior iliac spine (ASIS) level and in iliac crest perimeter measurements. A large intervention effect size strength (0.80) was found in subcutaneous fat below the navel and a moderate effect size strength on the vertical abdominal skinfold (0.62) and the perimeter of the most prominent abdominal point (0.57). Comparing the initial and final data of each group, the IG showed a significant decrease in numerous variables including visceral and subcutaneous fat above and below the navel measured by ultrasound (p ≤ 0.05).

CONCLUSION

Plaster body wrap in combination with aerobic exercise seems to be effective for abdominal fat reduction.

Consumption of wheat bran modified by autoclaving reduces fat mass in hamsters

PURPOSE

To investigate the effect that wheat bran modified by autoclaving (MWB) had on reducing fat accumulation in hamsters fed a hypercholesterolemia- and obesity-inducing diet.

METHODS

Male hamsters (n = 45) were randomized into 3 groups and fed a hypercholesterolemia- and obesity-inducing diet with or without 10% standard wheat bran or MWB for 28 days. Our outcome measures included body composition measured by DXA, oxygen consumption and plasma lipids and glucose concentrations.

RESULTS

Animals fed the MWB diet had lower % fat mass (49.8 vs. 53.4%; p = 0.02) and higher % lean body mass (47.2 vs. 44.1%; p = 0.02) compared with controls despite no differences in food intake or weight gain. Additionally, plasma glucose tended to be lower (6.9 vs. 8.5 mmol/l; p < 0.08) in the MWB animals compared with controls.

CONCLUSIONS

Our data suggest that the compositional changes in autoclaved wheat bran, specifically solubility of phenolic antioxidants and fiber, may have contributed to the lower fat accumulation in our animals. Further study is needed to determine whether the exact mechanism involved increased lipolysis and energy utilization from adipose.

Improvement in insulin resistance and favourable changes in plasma inflammatory adipokines after weight loss associated with two months' consumption of a combination of bioactive food ingredients in overweight subjects

This randomized, double blind, placebo-controlled, 8 week trial assessed the efficacy on metabolic changes produced by a consumption of a combination of bioactive food ingredients (epigallocatechin gallate, capsaicins, piperine and L-carnitine) versus a placebo, as part of a therapeutic 'lifestyle change' diet, in 86 overweight subjects. Forty-one patients (2/14 F/M; age 43.7 ± 8.5; BMI 30.3 ± 3.5 kg/m(2)) were randomized to the supplemented group and 45 (29/16; age 40.7 ± 10.2; BMI 30.0 ± 2.7) to the control group. We observed that consumption of the dietary supplement was associated with a significantly greater decrease in insulin resistance, assessed by homostasis model assessment (p < 0.001), leptin/adiponectin ratio (p < 0.04), respiratory quotient (p < 0.008). LDL-cholesterol levels (p < 0.01). Moreover, statistically significant differences were recorded between the two groups in relation to urinary norepinephrine levels (p < 0.001). Leptin, ghrelin, C-reactive protein decreased and resting energy expenditure increased significantly in the supplemented group (p < 0.05, 0.03, 0.02 and 0,02 respectively), but not in the placebo group; adiponectin decreased significantly in the placebo group (0.001) but not in the supplemented group, although no statistical significance between the groups was elicited. BMI, fat mass (assessed by DXA) and vascular endothelial growth factor significantly decreased, whilst the resting energy expenditure/free fat mass significantly increased in both groups. In general, a greater change was recorded in the supplemented group compared to the placebo, although no statistically significant difference between the two groups was recorded. These results suggest that the combination of bioactive food ingredients studied might be useful for the treatment of obesity-related inflammatory metabolic dysfunctions.

A review on botanical species and chemical compounds with appetite suppressing properties for body weight control

As obesity has reached epidemic proportions, the management of this global disease is of clinical importance. The availability and popularity of natural dietary supplements for the treatment of obesity has risen dramatically in recent years. The purpose of this paper was to review the effect of commonly available over the counter plant-derived supplements used to suppress appetite for obesity control and management. The data were obtained from the electronic databases PubMed, SpringerLink, Google Scholar, ScienceDirect, and MEDLINE with full text (via EBSCOHost) and the databases were accessed during late 2012 - early January 2013. The botanical species discussed in this review include Camellia sinensis, Caralluma fimbriata, Citrus aurantium, Coleus forskohlii, Garcinia cambogia and Phaseolus vulgaris. This review found that many botanical species including crude extracts and isolated compounds from plants have been shown to provide potentially promising therapeutic effects including appetite control and weight loss. However, many of these crude extracts and compounds need to be further investigated to define the magnitude of the effects, optimal dosage, mechanisms of action, long term safety, and potential side effects.

Green tea polyphenol epigallocatechin-3-gallate enhance glycogen synthesis and inhibit lipogenesis in hepatocytes

The beneficial effects of green tea polyphenols (GTP) against metabolic syndrome and type 2 diabetes by suppressing appetite and nutrient absorption have been well reported. However the direct effects and mechanisms of GTP on glucose and lipid metabolism remain to be elucidated. Since the liver is an important organ involved in glucose and lipid metabolism, we examined the effects and mechanisms of GTP on glycogen synthesis and lipogenesis in HepG2 cells. Concentrations of GTP containing 68% naturally occurring (−)-epigallocatechin-3-gallate (EGCG) were incubated in HepG2 cells with high glucose (30 mM) under 100 nM of insulin stimulation for 24 h. GTP enhanced glycogen synthesis in a dose-dependent manner. 10 μM of EGCG significantly increased glycogen synthesis by 2fold (P < 0.05) compared with insulin alone. Western blotting revealed that phosphorylation of Ser9 glycogen synthase kinase 3β and Ser641 glycogen synthase was significantly increased in GTP-treated HepG2 cells compared with nontreated cells. 10 μM of EGCG also significantly inhibited lipogenesis (P < 0.01). We further demonstrated that this mechanism involves enhanced expression of phosphorylated AMP-activated protein kinase α and acetyl-CoA carboxylase in HepG2 cells. Our results showed that GTP is capable of enhancing insulin-mediated glucose and lipid metabolism by regulating enzymes involved in glycogen synthesis and lipogenesis.

Developing 'integrative' zebrafish models of behavioral and metabolic disorders

Recently, the pathophysiological overlap between metabolic and mental disorders has received increased recognition. Zebrafish (Danio rerio) are rapidly becoming a popular model organism for translational biomedical research due to their genetic tractability, low cost, quick reproductive cycle, and ease of behavioral, pharmacological or genetic manipulation. High homology to mammalian physiology and the availability of well-developed assays also make the zebrafish an attractive organism for studying human disorders. Zebrafish neurobehavioral and endocrine phenotypes show promise for the use of zebrafish in studies of stress, obesity and related behavioral and metabolic disorders. Here, we discuss the parallels between zebrafish and other model species in stress and obesity physiology, as well as outline the available zebrafish models of weight gain, metabolic deficits, feeding, stress, anxiety and related behavioral disorders. Overall, zebrafish demonstrate a strong potential for modeling human behavioral and metabolic disorders, and their comorbidity.

Dietary Chinese quince polyphenols suppress generation of α-dicarbonyl compounds in diabetic KK-A(y) mice

Many dietary polyphenols can provide health benefits, such as antioxidant and antidiabetic effects, and can down-regulate the progression of glycation (one cause of diabetic complications). Chinese quince (CQ) is rich in polyphenols, especially procyanidins. A few studies have indicated that CQ has an effect on diabetes. In this study, a procyanidin-rich extract was prepared from Chinese quince fruit (CQE), and its effects were investigated and compared with those of green tea extract (GTE) in type 2 diabetes model KK-A(y) mice. Mice were provided one of two high-fat (HF) diets for 4 weeks: a HF diet containing 0.5% CQE or a HF diet containing 0.5% GTE. Blood glucose was suppressed in mice fed CQE and GTE during the experimental period (p < 0.05), although the effect of CQE was weaker than that of GTE. Intake of CQE had no effect on the blood insulin level, whereas GTE decreased the insulin level. Body weight gain was suppressed in mice fed CQE similarly to mice fed GTE (p < 0.05). Hepatic lipid content and α-dicarbonyl compounds in the kidney were reduced in mice fed CQE and GTE (p < 0.05). These results suggest that intake of CQE could moderate type 2 diabetes and diabetic complications.

The relationship between the structure and biological actions of green tea catechins

Catechins and their gallate esters are a class of polyphenolic compounds. The catechin subclass known as flavan-3-ols have recently attracted much attention with regards to their beneficial effect on human health. Their biological actions are dependent on the structure of the compounds and vary according to cell type. They are best known as powerful antioxidants; however depending on the doses they also exhibit prooxidant effects. The anti- or prooxidant effects of green tea catechins have been implicated in the modulation of several cellular functions often associated with strong chemoprotective properties. This review summarises the benefit catechins to human health, the main molecular pathways modulated by catechins. The relationship between the structure and activity of the catechins needs to be studied further. In the future, the structure of catechins could be modified so as to synthesise novel compounds with more specific beneficial properties and higher bioavailability.

Active extracts of black tea (Camellia Sinensis) induce apoptosis of PC-3 prostate cancer cells via mitochondrial dysfunction

Cancer of the prostate gland is the most common invasive malignancy and the second leading cause of cancer-related death in human males. Many studies have shown that black tea reduces the risk of several types of cancer. We studied the effects of active extracts of black tea and the black tea polyphenols theaflavins (TFs), on the cellular proliferation and mitochondria of the human prostate cancer cell line PC-3. Our studies revealed that Yinghong black tea extracts (YBT), Assam black tea extracts (ABT) and TFs inhibited cell proliferation in a dose-dependent manner. We also showed that TFs, YBT and ABT affected the morphology of PC-3 cells and induced apoptosis or even necrosis in PC-3 cells. In addition, it was observed that the samples significantly caused loss of the mitochondrial membrane potential, release of cytochrome c from the intermembrane space into the cytosol, decrease of the ATP content and activation of caspase-3 compared with the control. Taken together, these findings suggest that black tea could act as an effective anti-proliferative agent in PC-3 cells, and TFs, YBT and ABT induced apoptosis of PC-3 cells through mitochondrial dysfunction.

The effect of green tea extract on fat oxidation at rest and during exercise: evidence of efficacy and proposed mechanisms

Green tea is made from the leaves of the Camellia sinensis L plant, which is rich in polyphenol catechins and caffeine. There is increasing interest in the potential role of green tea extract (GTE) in fat metabolism and its influence on health and exercise performance. A number of studies have observed positive effects of GTE on fat metabolism at rest and during exercise, following both shorter and longer term intake. However, overall, the literature is inconclusive. The fact that not all studies observed effects may be related to differences in study designs, GTE bioavailability, and variation of the measurement (fat oxidation). In addition, the precise mechanisms of GTE in the human body that increase fat oxidation are unclear. The often-cited in vitro catechol-O-methyltransferase mechanism is used to explain the changes in substrate metabolism with little in vivo evidence to support it. Also, changes in expression of fat metabolism genes with longer term GTE intake have been implicated at rest and with exercise training, including the upregulation of fat metabolism enzyme gene expression in the skeletal muscle and downregulation of adipogenic genes in the liver. The exact molecular signaling that activates changes to fat metabolism gene expression is unclear but may be driven by PPAR-γ coactivator 1-α and PPARs. However, to date, evidence from human studies to support these adaptations is lacking. Clearly, more studies have to be performed to elucidate the effects of GTE on fat metabolism as well as improve our understanding of the underlying mechanisms.

Dietary intake of green tea polyphenols regulates insulin sensitivity with an increase in AMP-activated protein kinase α content and changes in mitochondrial respiratory complexes

SCOPE

The intake of food rich in polyphenols is related to a lower incidence in almost all chronic degenerative diseases. However, relatively little is known about the molecular mechanisms involved in its antioxidant properties. The aim of this study was to determine whether the mechanism of action of polyphenols could be related to a modulation in energy uptake and metabolism, and further induced mitochondrial changes.

METHODS AND RESULTS

For this purpose, male C57BL6 mice were fed during 3 months with a tea-based beverage rich in polyphenols. Insulin sensitivity, tissue oxidative damage biomarkers, as well as energy-related signaling pathways were determined to evaluate its mechanism of action. As a result, a tissue- and protein-specific subtle reduction in oxidative damage was observed. Skeletal muscle showed mitochondrial changes in respiratory complexes and an increase in AMP-activated protein kinase α levels, suggesting reduced energy availability. These changes were also associated with adipose tissue cellular metabolism. This was confirmed by a decline in the potential of energy uptake, evidenced by a diminished intestinal and systemic absorption of carbohydrates together with an inhibition of insulin sensitivity.

CONCLUSIONS

Our results suggest that the mechanisms of action of green tea polyphenols may be related to their ability to modulate energy uptake leading to mitochondrial adaptations possibly responsible for the changes in protein oxidative damage.

Green tea for weight loss and weight maintenance in overweight or obese adults

BACKGROUND

Preparations of green tea are used as aids in weight loss and weight maintenance. Catechins and caffeine, both contained in green tea, are each believed to have a role in increasing energy metabolism, which may lead to weight loss. A number of randomised controlled trials (RCTs) evaluating the role of green tea in weight loss have been published; however, the efficacy of green tea preparations in weight loss remains unclear.

OBJECTIVES

To assess the efficacy and safety of green tea preparations for weight loss and weight maintenance in overweight or obese adults.

SEARCH METHODS

We searched the following databases from inception to specified date as well as reference lists of relevant articles: The Cochrane Library (Issue 12, 2011), MEDLINE (December 2011), EMBASE (December 2011), CINAHL (January 2012), AMED (January 2012), Biological Abstracts (January 2012), IBIDS (August 2010), Obesity+ (January 2012), IPA (January 2012) and Web of Science (December 2011). Current Controlled Trials with links to other databases of ongoing trials was also searched.

SELECTION CRITERIA

RCTs of at least 12 weeks' duration comparing green tea preparations to a control in overweight or obese adults.

DATA COLLECTION AND ANALYSIS

Three authors independently extracted data, assessed studies for risk of bias and quality, with differences resolved by consensus. Heterogeneity of included studies was assessed visually using forest plots and quantified using the I(2) statistic. We synthesised data using meta-analysis and descriptive analysis as appropriate; subgroup and sensitivity analyses were conducted. Adverse effects reported in studies were recorded.

MAIN RESULTS

Due to the level of heterogeneity among studies, studies were divided into two groups; those conducted in Japan and those conducted outside Japan. Study length ranged between 12 and 13 weeks. Meta-analysis of six studies conducted outside Japan showed a mean difference (MD) in weight loss of -0.04 kg (95% CI -0.5 to 0.4; P = 0.88; I(2) = 18%; 532 participants). The eight studies conducted in Japan were not similar enough to allow pooling of results and MD in weight loss ranged from -0.2 kg to -3.5 kg (1030 participants) in favour of green tea preparations. Meta-analysis of studies measuring change in body mass index (BMI) conducted outside Japan showed a MD in BMI of -0.2 kg/m(2) (95% CI -0.5 to 0.1; P = 0.21; I(2) = 38%; 222 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed a reduction in BMI ranging from no effect to -1.3 kg/m(2) (1030 participants), in favour of green tea preparations over control. Meta-analysis of five studies conducted outside Japan and measuring waist circumference reported a MD of -0.2 cm (95% CI -1.4 to 0.9; P = 0.70; I(2) = 58%; 404 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed effects on waist circumference ranging from a gain of 1 cm to a loss of 3.3 cm (1030 participants). Meta-analysis for three weight loss studies, conducted outside Japan, with waist-to-hip ratio data (144 participants) yielded no significant change (MD 0; 95% CI -0.02 to 0.01). Analysis of two studies conducted to determine if green tea could help to maintain weight after a period of weight loss (184 participants) showed a change in weight loss of 0.6 to -1.6 kg, a change in BMI from 0.2 to -0.5 kg/m(2) and a change in waist circumference from 0.3 to -1.7 cm. In the eight studies that recorded adverse events, four reported adverse events that were mild to moderate, with the exception of two (green tea preparations group) that required hospitalisation (reported as not associated with the intervention). Nine studies reported on compliance/adherence, one study assessed attitude towards eating as part of the health-related quality of life outcome. No studies reported on patient satisfaction, morbidity or cost.

AUTHORS' CONCLUSIONS

Green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important. Green tea had no significant effect on the maintenance of weight loss. Of those studies recording information on adverse events, only two identified an adverse event requiring hospitalisation. The remaining adverse events were judged to be mild to moderate.

Effects of green tea supplementation on elements, total antioxidants, lipids, and glucose values in the serum of obese patients

The consumption of green tea has been associated with cardiovascular and metabolic diseases. There have been some studies on the influence of green tea on the mineral status of obese subjects, but they have not yielded conclusive results. The aim of the present study is to examine the effects of green tea extract on the mineral, body mass, lipid profile, glucose, and antioxidant status of obese patients. A randomized, double-blind, placebo-controlled study was conducted. Forty-six obese patients were randomly assigned to receive either 379 mg of green tea extract, or a placebo, daily for 3 months. At baseline, and after 3 months of treatment, the anthropometric parameters, blood pressure, and total antioxidant status were assessed, as were the levels of plasma lipids, glucose, calcium, magnesium, iron, zinc, and copper. We found that 3 months of green tea extract supplementation resulted in decreases in body mass index, waist circumference, and levels of total cholesterol, low-density cholesterol, and triglyceride. Increases in total antioxidant level and in zinc concentration in serum were also observed. Glucose and iron levels were lower in the green tea extract group than in the control, although HDL-cholesterol and magnesium were higher in the green tea extract group than in the placebo group. At baseline, a positive correlation was found between calcium and body mass index, as was a negative correlation between copper and triglycerides. After 3 months, a positive correlation between iron and body mass index and between magnesium and HDL-cholesterol, as well as a negative correlation between magnesium and glucose, were observed. The present findings demonstrate that green tea influences the body's mineral status. Moreover, the results of this study confirm the beneficial effects of green tea extract supplementation on body mass index, lipid profile, and total antioxidant status in patients with obesity.

Flavonoids and metabolic syndrome

Increasing evidence indicates that several mechanisms, associated or not with antioxidant actions, are involved in the effects of flavonoids on health. Flavonoid-rich beverages, foods, and extracts, as well as pure flavonoids are studied for the prevention and/or amelioration of metabolic syndrome (MS) and MS-associated diseases. We summarize evidence linking flavonoid consumption with the risk factors defining MS: obesity, hypertriglyceridemia, hypercholesterolemia, hypertension, and insulin resistance. Nevertheless, a number of molecular mechanisms have been identified; the effects of flavonoids modifying major endpoints of MS are still inconclusive. These difficulties are explained by the complex relationships among the risk factors defining MS, the multiple biological targets controlling these risk factors, and the high number of flavonoids (including their metabolites) present in the diet and potentially responsible for the in vivo effects. Consequently, extensive basic and clinical research is warranted to assess the final relevance of flavonoids for MS.

Metabolic response to green tea extract during rest and moderate-intensity exercise

BACKGROUND

Green tea catechins have been hypothesized to increase energy expenditure and fat oxidation by inhibiting catechol-O-methyltransferase (COMT) and thus promoting more sustained adrenergic stimulation. Metabolomics may help to clarify the mechanisms underlying their putative physiological effects.

OBJECTIVE

The study investigated the effects of 7-day ingestion of green tea extract (GTE) on the plasma metabolite profile at rest and during exercise.

METHODS

In a placebo-controlled, double-blind, randomized, parallel study, 27 healthy physically active males consumed either GTE (n=13, 1200 mg catechins, 240 mg caffeine/day) or placebo (n=14, PLA) drinks for 7 days. After consuming a final drink (day 8), they rested for 2 h and then completed 60 min of moderate-intensity cycling exercise (56% ± 4% VO(2)max). Blood samples were collected before and during exercise. Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines.

RESULTS

Using the metabolomic approach, we observed that GTE did not enhance adrenergic stimulation (adrenaline and noradrenaline) during rest or exercise. At rest, GTE led to changes in metabolite concentrations related to fat metabolism (3-β-hydroxybutyrate), lipolysis (glycerol) and tricarboxylic acid cycle (TCA) cycle intermediates (citrate) when compared to PLA. GTE during exercise caused reductions in 3-β-hydroxybutyrate concentrations as well as increases in pyruvate, lactate and alanine concentrations when compared to PLA.

CONCLUSIONS

GTE supplementation resulted in marked metabolic differences during rest and exercise. Yet these metabolic differences were not related to the adrenergic system, which questions the in vivo relevance of the COMT inhibition mechanism of action for GTE.

Effect of lignin-derived lignophenols on hepatic lipid metabolism in rats fed a high-fat diet

The effect of lignin-derived lignophenols on lipid metabolism in the livers of rats fed a high-fat diet was investigated. Rats fed a diet providing 45% of energy from fat were divided into 2 groups, namely 0% and 0.5% lignophenols-containing diets. The controls were fed a diet providing 10% of energy from fat. Plasma blood parameters, protein expression of acetyl-CoA carboxylase (ACC) and sterol regulatory element-binding protein (SREBP)-1, and SREBP-1c mRNA expression in the livers were examined. The plasma triglyceride levels in the rats fed lignophenols-containing diets were decreased. SREBP-1c mRNA expression in the rats fed lignophenols-containing diets was significantly reduced compared with the rats fed high-fat diets, and phosphorylated ACC protein in the rats fed lignophenols-containing diets was significantly increased. Our results suggested that lignophenols suppress the expression of SREBP-1c mRNA and the phosphorylation of ACC in the liver, and may lead to a decrease in plasma triglyceride levels.

Green tea polyphenols reduce body weight in rats by modulating obesity-related genes

Beneficial effects of green tea polyphenols (GTP) against obesity have been reported, however, the mechanism of this protection is not clear. Therefore, the objective of this study was to identify GTP-targeted genes in obesity using the high-fat-diet-induced obese rat model. A total of three groups (n = 12/group) of Sprague Dawley (SD) female rats were tested, including the control group (rats fed with low-fat diet), the HF group (rats fed with high-fat diet), and the HF+GTP group (rats fed with high-fat diet and GTP in drinking water). The HF group increased body weight as compared to the control group. Supplementation of GTP in the drinking water in the HF+GTP group reduced body weight as compared to the HF group. RNA from liver samples was extracted for gene expression analysis. A total of eighty-four genes related to obesity were analyzed using PCR array. Compared to the rats in the control group, the rats in the HF group had the expression levels of 12 genes with significant changes, including 3 orexigenic genes (Agrp, Ghrl, and Nr3c1); 7 anorectic genes (Apoa4, Cntf, Ghr, IL-1β, Ins1, Lepr, and Sort); and 2 genes that relate to energy expenditure (Adcyap1r1 and Adrb1). Intriguingly, the HF+GTP group restored the expression levels of these genes in the high-fat-induced obese rats. The protein expression levels of IL-1β and IL-6 in the serum samples from the control, HF, and HF+GTP groups confirmed the results of gene expression. Furthermore, the protein expression levels of superoxide dismutase-1 (SOD1) and catechol-O-methyltransferase (COMT) also showed GTP-regulated protective changes in this obese rat model. Collectively, this study revealed the beneficial effects of GTP on body weight via regulating obesity-related genes, anti-inflammation, anti-oxidant capacity, and estrogen-related actions in high-fat-induced obese rats.

Green tea polyphenols benefits body composition and improves bone quality in long-term high-fat diet-induced obese rats

This study investigates the effects of green tea polyphenols (GTPs) on body composition and bone properties along with mechanisms in obese female rats. Thirty-six 3-month-old Sprague Dawley female rats were fed either a low-fat (LF) or a high-fat (HF) diet for 4 months. Animals in the LF diet group continued on an LF diet for additional 4 months, whereas those in the HF diet group were divided into 2 groups: with GTP (0.5%) or without in drinking water, in addition to an HF diet for another 4 months. Body composition, femur bone mass and strength, serum endocrine and proinflammatory cytokines, and liver glutathione peroxidase (GPX) protein expression were determined. We hypothesized that supplementation of GTP in drinking water would benefit body composition, enhance bone quality, and suppress obesity-related endocrines in HF diet-induced obese female rats and that such changes are related to an elevation of antioxidant capacity and a reduction of proinflammatory cytokine production. After 8 months, compared with the LF diet, the HF diet increased percentage of fat mass and serum insulin-like growth factor I and leptin levels; reduced percentage of fat-free mass, bone strength, and GPX protein expression; but had no effect on bone mineral density and serum adiponectin levels in the rats. Green tea polyphenol supplementation increased percentage of fat-free mass, bone mineral density and strength, and GPX protein expression and decreased percentage of fat mass, serum insulin-like growth factor I, leptin, adiponectin, and proinflammatory cytokines in the obese rats. This study shows that GTP supplementation benefited body composition and bone properties in obese rats possibly through enhancing antioxidant capacity and suppressing inflammation.

Low doses of grape seed procyanidins reduce adiposity and improve the plasma lipid profile in hamsters

OBJECTIVE

Procyanidins are polyphenolic compounds with beneficial effects on health in relation to cardiovascular disease and metabolic syndrome. In this study, we evaluated the potential beneficial effects of low doses of a grape seed procyanidin extract (GSPE) on body weight and fat deposition.

DESIGN

Four groups of hamsters were fed either a standard diet (STD) or a high-fat diet (HFD) for 30 days and supplemented with either GSPE at 25 mg per kg of body weight per day (STD-GSPE and HFD-GSPE groups) or vehicle (STD and HFD groups) during the last 15 days of the study.

RESULTS

A significant decrease in body weight gain was observed in both GSPE-treated animals at the end of the experiment. GSPE treatment significantly reduced the adiposity index and the weight of all the white adipose tissue depots studied (retroperitoneal (RWAT), mesenteric (MWAT), epididymal (EWAT) and inguinal (IWAT)) in both GSPE-treated groups. GSPE administration reversed the increase in plasma phospholipids induced by the HFD feeding. In the RWAT, GSPE treatment increased the mRNA expression of genes related to β-oxidation and the glycerolipid/free fatty acid (GL/FFA) cycle, mainly in HFD-GSPE animals. In the MWAT, the effects of GSPE at the transcriptional level were not as evident as in the RWAT. Moreover, GSPE treatment induced heparin-releasable lipoprotein lipase activity in the RWAT and MWAT depots. The alterations in the lipid metabolic pathways induced by GSPE were accompanied by lower FFA levels in the plasma and decreased lipid and triglyceride accumulation in the MWAT.

CONCLUSION

The use of GSPE at low doses protects against fat accumulation and improves the plasma lipid profile in hamsters. We suggest that GSPE exerts these effects in part through the activation of both β-oxidation and the GL/FFA cycle, mainly in the RWAT.

Leucine signaling in the pathogenesis of type 2 diabetes and obesity

Epidemiological evidence points to increased dairy and meat consumption, staples of the Western diet, as major risk factors for the development of type 2 diabetes (T2D). This paper presents a new concept and comprehensive review of leucine-mediated cell signaling explaining the pathogenesis of T2D and obesity by leucine-induced over-stimulation of mammalian target of rapamycin complex 1 (mTORC1). mTORC1, a pivotal nutrient-sensitive kinase, promotes growth and cell proliferation in response to glucose, energy, growth factors and amino acids. Dairy proteins and meat stimulate insulin/insulin-like growth factor 1 signaling and provide high amounts of leucine, a primary and independent stimulator for mTORC1 activation. The downstream target of mTORC1, the kinase S6K1, induces insulin resistance by phosphorylation of insulin receptor substrate-1, thereby increasing the metabolic burden of β-cells. Moreover, leucine-mediated mTORC1-S6K1-signaling plays an important role in adipogenesis, thus increasing the risk of obesity-mediated insulin resistance. High consumption of leucine-rich proteins explains exaggerated mTORC1-dependent insulin secretion, increased β-cell growth and β-cell proliferation promoting an early onset of replicative β-cell senescence with subsequent β-cell apoptosis. Disturbances of β-cell mass regulation with increased β-cell proliferation and apoptosis as well as insulin resistance are hallmarks of T2D, which are all associated with hyperactivation of mTORC1. In contrast, the anti-diabetic drug metformin antagonizes leucine-mediated mTORC1 signaling. Plant-derived polyphenols and flavonoids are identified as natural inhibitors of mTORC1 and exert anti-diabetic and anti-obesity effects. Furthermore, bariatric surgery in obesity reduces increased plasma levels of leucine and other branched-chain amino acids. Attenuation of leucine-mediated mTORC1 signaling by defining appropriate upper limits of the daily intake of leucine-rich animal and dairy proteins may offer a great chance for the prevention of T2D and obesity, as well as other epidemic diseases of civilization with increased mTORC1 signaling, especially cancer and neurodegenerative diseases, which are frequently associated with T2D.

Green tea extract supplementation gives protection against exercise-induced oxidative damage in healthy men

The purpose of this study was to evaluate the effects of a long-term (4-week) green tea extract (GTE) supplementation in combination with strength training on selected blood markers of oxidative stress and muscular damage after a short-term exercise in previously untrained men. We hypothesized that GTE supplementation would elevate antioxidant potential and attenuate exercise-induced oxidative stress and muscular damage. Thirty-five male students were exposed to 4 weeks of strength training and received (in a randomized, double-blind design) GTE (n = 17; 640 mg polyphenols/d) or placebo (P; n = 18). Before (term I) and after 4 weeks of strength training and supplementation (term II), students performed a short-term muscular endurance test. Blood samples were collected at rest, 5 minutes after the muscular endurance test, and after 24 hours of recovery. Supplementation with GTE enhanced plasma total polyphenols at rest and 5 minutes after the muscular endurance test. Supplementation also contributed to the rise of resting total antioxidant status in plasma. Throughout the experiment (terms I and II), a reduction in plasma lipid hydroxyperoxides was observed 24 hours after the muscular endurance test. Four weeks of strength training resulted in an increase in plasma lipid hydroxyperoxides at rest, but only in the P group. In term I, the muscular endurance test induced an increase in activity of creatine kinase in plasma after 24 hours of recovery in both the P and GTE groups. In term II, plasma creatine kinase activity after 24 hours of recovery was elevated only in the P group. In conclusion, in previously untrained men, dietary supplementation with GTE (in combination with strength training) enhances the antioxidant defense system in plasma at rest and, in turn, may give protection against oxidative damage induced by both short-term muscular endurance test and long-term strength training.

The effects of green tea consumption on cardiometabolic alterations induced by experimental diabetes

We evaluated cardiac autonomic modulation by heart rate (HRV), and arterial pressure variability (APV), and metabolic response in streptozotocin diabetic rats treated with green tea. Male Wistar rats were separated in groups: control, drinking tap water (C), green tea-treated (GT) group, diabetic, drinking tap water (D), and diabetic, treated with green tea (DGT). Kidney mass was greater in D and DGT than in C and GT, but reduced in DGT compared to D. Green tea prevented the increase in creatinine clearance and reduced hyperglycemia in DGT compared to D. Arterial pressure was increased in GT and decreased in D compared to C. HRV was reduced in D compared with all groups. APV was decreased in D compared to C and recovery in DGT. Sympathetic modulation of APV was decreased in D compared with all groups. Green tea reduced hyperglycemia, prevented renal injury and autonomic dysfunction, suggesting reduced cardiovascular risk and target organ damage in diabetes.

Target molecules of food phytochemicals: food science bound for the next dimension

Phytochemicals are generally defined as secondary metabolites in plants that play crucial roles in their adaptation to a variety of environmental stressors. There is a great body of compelling evidence showing that these metabolites have pronounced potentials for regulating and modulating human health and disease onset, as shown by both experimental and epidemiological approaches. Concurrently, enormous efforts have been made to elucidate the mechanism of actions underlying their biological and physiological functions. For example, the pioneering work of Tachibana et al. uncovered the receptor for (-)-epigallocatechin-3-gallate (EGCg) as the 67 kDa laminin receptor, which was shown to partially mediate the functions of EGCg, such as anti-inflammatory, anti-allergic, and anti-proliferative activities. Thereafter, several protein kinases were identified as binding proteins of flavonoids, including myricetin, quercetin, and kaempferol. Isothiocyanates, sulfur-containing phytochemicals present in cruciferous plants, are well known to target Keap1 for activating the transcription factor Nrf2 for inducing self-defensive and anti-oxidative gene expression. In addition, we recently identified CD36 as a cell surface receptor for ursolic acid, a triterpenoid ubiquitously occurring in plants. Importantly, the above mentioned target proteins are indispensable for phytochemicals to exhibit, at least in part, their bioactivities. Nevertheless, it is reasonable to assume that some of the activities and potential toxicities of metabolites are exerted via their interactions with unidentified, off-target proteins. This notion may be supported by the fact that even rationally designed drugs occasionally display off-target effects and induce unexpected outcomes, including toxicity. Here we update the current status and future directions of research related to target molecules of food phytochemicals.

Obesity: the preventive role of the pomegranate (Punica granatum)

Obesity represents a rapidly growing threat to the health of populations in an increasing number of countries. Diet intervention has been proposed as one of the strategies for weight loss and weight maintenance. Traditionally, the pomegranate, including its roots, tree bark, fruit juice, leaves, and flowers, has been used to treat some conditions such as diarrhea, hemorrhage, acidosis, and microbial infections. Pomegranate extracts have been found to have strong anti-inflammatory, antioxidant, and even antitumor properties in vivo and in vitro. More recently, positive effects on fat reduction have been shown using the pomegranate and its extracts. Many of the beneficial effects are related to the presence of anthocyanins, tannins, and very high levels of antioxidants, including polyphenols and flavonoids. Many studies have explored the effects of the pomegranate in obesity, and various mechanisms have been proposed as to how these different extracts help in fat reduction. This article provides an overview of the work done addressing the potential benefits of the pomegranate on obesity and assesses the efficacy of intervention by means of the pomegranate and its extracts. Human studies in this field are still limited and need more attention that would help in understanding the preventive and protective roles pomegranate extracts have on obesity.

Nutraceutical approach for preventing obesity-related colorectal and liver carcinogenesis

Obesity and its related metabolic abnormalities, including insulin resistance, alterations in the insulin-like growth factor-1 (IGF-1)/IGF-1 receptor (IGF-1R) axis, and the state of chronic inflammation, increase the risk of colorectal cancer (CRC) and hepatocellular carcinoma (HCC). However, these findings also indicate that the metabolic disorders caused by obesity might be effective targets to prevent the development of CRC and HCC in obese individuals. Green tea catechins (GTCs) possess anticancer and chemopreventive properties against cancer in various organs, including the colorectum and liver. GTCs have also been known to exert anti-obesity, antidiabetic, and anti-inflammatory effects, indicating that GTCs might be useful for the prevention of obesity-associated colorectal and liver carcinogenesis. Further, branched-chain amino acids (BCAA), which improve protein malnutrition and prevent progressive hepatic failure in patients with chronic liver diseases, might be also effective for the suppression of obesity-related carcinogenesis because oral supplementation with BCAA reduces the risk of HCC in obese cirrhotic patients. BCAA shows these beneficial effects because they can improve insulin resistance. Here, we review the detailed relationship between metabolic abnormalities and the development of CRC and HCC. We also review evidence, especially that based on our basic and clinical research using GTCs and BCAA, which indicates that targeting metabolic abnormalities by either pharmaceutical or nutritional intervention may be an effective strategy to prevent the development of CRC and HCC in obese individuals.

Health-promoting effects of green tea

Green tea is manufactured from the leaves of the plant Camellia sinensis Theaceae and has been regarded to possess anti-cancer, anti-obesity, anti-atherosclerotic, anti-diabetic, anti-bacterial, and anti-viral effects. Many of the beneficial effects of green tea are related to the activities of (-)-epigallocatechin gallate (EGCG), a major component of green tea catechins. For about 20 years, we have engaged in studies to reveal the biological activities and action mechanisms of green tea and EGCG. This review summarizes several lines of evidence to indicate the health-promoting properties of green tea mainly based on our own experimental findings.