Green tea polyphenols improve cardiac muscle mRNA and protein levels of signal pathways related to insulin and lipid metabolism and inflammation in insulin-resistant rats

Myocardial insulin resistance, metabolic stress and autophagy in diabetes

Clinical studies in humans strongly support a link between insulin resistance and non-ischaemic heart failure. The occurrence of a specific insulin-resistant cardiomyopathy, independent of vascular abnormalities, is now recognized. The progression of cardiac pathology linked with insulin resistance is poorly understood. Cardiac insulin resistance is characterized by reduced availability of sarcolemmal Glut-4 transporters and consequent lower glucose uptake. A shift away from glycolysis towards fatty acid oxidation for ATP supply is apparent and is associated with myocardial oxidative stress. Reliance of cardiomyocyte excitation-contraction coupling on glycolytically derived ATP supply potentially renders cardiac function vulnerable to the metabolic remodelling adaptations observed in diabetes development. Findings from Glut-4-knockout mice demonstrate that cardiomyocytes with extreme glucose uptake deficiency exhibit cardiac hypertrophy and marked excitation-contraction coupling abnormalities characterized by reduced sarcolemmal Ca(2+) influx and sarcoplasmic reticulum Ca(2+) uptake. The 'milder' phenotype fructose-fed mouse model of type 2 diabetes does not show evidence of cardiac hypertrophy, but cardiomyocyte loss linked with autophagic activation is evident. Fructose feeding induces a marked reduction in intracellular Ca(2+) availability with myofilament adaptation to preserve contractile function in this setting. The cardiac metabolic adaptations of two load-independent models of diabetes, namely the Glut-4-deficient mouse and the fructose-fed mouse are contrasted. The role of autophagy in diabetic cardiopathology is evaluated and anomalies of type 1 versus type 2 diabetic autophagic responses are highlighted.

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.

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.

Cocoa flavonoids improve insulin signalling and modulate glucose production via AKT and AMPK in HepG2 cells

SCOPE

Cocoa and (-)-epicatechin (EC), a main cocoa flavanol, have been suggested to exert beneficial effects in diabetes, but the mechanism for their insulin-like effects remains unknown. In this study, the modulation of insulin signalling by EC and a cocoa phenolic extract (CPE) on hepatic HepG2 cells was investigated by analysing key proteins of the insulin pathways, namely insulin receptor, insulin receptor substrate (IRS) 1 and 2, PI3K/AKT and 5'-AMP-activated protein kinase (AMPK), as well as the levels of the glucose transporter GLUT-2 and the hepatic glucose production.

METHODS AND RESULTS

EC and CPE enhanced the tyrosine phosphorylation and total insulin receptor, IRS-1 and IRS-2 levels and activated the PI3K/AKT pathway and AMPK in HepG2 cells. CPE also enhanced the levels of GLUT-2. Interestingly, EC and CPE modulated the expression of phosphoenolpyruvate carboxykinase, a key protein involved in the gluconeogenesis, leading to a diminished glucose production. In addition, EC- and CPE-regulated hepatic gluconeogenesis was prevented by the blockage of AKT and AMPK.

CONCLUSION

Our data suggest that EC and CPE strengthen the insulin signalling by activating key proteins of that pathway and regulating glucose production through AKT and AMPK modulation in HepG2 cells.

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.

Molecular Mechanism Underlying the Antidiabetic Effects of a Siddha Polyherbal Preparation in the Liver of Type 2 Diabetic Adult Male Rats

A siddha polyherbal preparation consisting of 5 medicinal plants, namely, Asparagus racemosus, Emblica officinalis, Salacia oblonga, Syzygium aromaticum, and Tinospora cordifolia, in equal ratio, was formulated to examine the molecular mechanism by which it exhibits antidiabetic effects in the liver of high-fat and fructose-induced type 2 diabetic rats. The polyherbal preparation treated type 2 diabetic rats showed an increase in insulin receptor, Akt, and glucose transporter2 mRNA levels compared with diabetic rats. Insulin receptor, insulin receptor substrate-2, Akt, phosphorylated Akt substrate of 160kDaThreonine642, α-Actinin-4, β-arrestin-2, and glucose transporter2 proteins were also markedly decreased in diabetic rats, whereas the polyherbal preparation treatment significantly improved the expression of these proteins more than that of metformin-treated diabetic rats. The expression pattern of insulin signaling molecules analyzed in the present study signifies the therapeutic efficacy of the siddha polyherbal preparation.

Obesity and hepatocellular carcinoma: targeting obesity-related inflammation for chemoprevention of liver carcinogenesis

Obesity and related metabolic abnormalities, including a state of chronic inflammation, increase the risk of hepatocellular carcinoma (HCC). Adipose tissue constitutively expresses the proinflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), which are important tumor promoters in inflammation-related carcinogenesis. Dysregulation of TNF-α and IL-6 is associated with the development of steatosis and inflammation within the liver. These cytokines also lie at the core of the association between obesity and insulin resistance, which is a key factor in the development of obesity-related HCC. Here we present a detailed review of the relationship between metabolic abnormalities and the development of HCC, focusing on the role played by inflammation. Drawing from our basic and clinical research, the present report also reviews evidence that targeting metabolic abnormalities, such as attenuation of chronic inflammation and improvement of insulin resistance by either pharmaceutical or nutritional intervention, may be an effective strategy in preventing the development of HCC in obese individuals.

Nonalcoholic beer reduces inflammation and incidence of respiratory tract illness

PURPOSE

Strenuous exercise significantly increases the incidence of upper respiratory tract illness (URTI) caused by transient immune dysfunction. Naturally occurring polyphenolic compounds present in food such as nonalcoholic beer (NAB) have strong antioxidant, antipathogenic, and anti-inflammatory properties.The objective of this study was to determine whether ingestion of NAB polyphenols for 3 wk before and 2 wk after a marathon would attenuate postrace inflammation and decrease URTI incidence.

METHODS

Healthy male runners (N = 277, age = 42 ± 9 yr) were randomly assigned to 1-1.5 L · d(-1) of NAB or placebo (PL) beverage (double-blind design) for 3 wk before and 2 wk after the Munich Marathon. Blood samples were collected 4 and 1 wk before the race and immediately and 24 and 72 h after the race and analyzed for inflammation measures (interleukin-6 and total blood leukocyte counts). URTI rates, assessed by the Wisconsin Upper Respiratory Symptom Survey, were compared between groups during the 2-wk period after the race.

RESULTS

Change in interleukin-6 was significantly reduced in NAB compared with PL immediately after the race (median (interquartile range) = 23.9 (15.9-38.7) vs 31.6 (18.5-53.3) ng · L(-1), P = 0.03). Total blood leukocyte counts were also reduced in NAB versus PL by approximately 20% immediately and 24 h after the race (P = 0.02). Incidence of URTI was 3.25-fold lower (95% confidence interval = 1.38-7.66) (P = 0.007) in NAB compared with PL during the 2-wk postmarathon period.

CONCLUSIONS

Consumption of 1-1.5 L · d(-1) of NAB for 3 wk before and 2 wk after marathon competition reduces postrace inflammation and URTI incidence.

Multiple factors and pathways involved in hepatic very low density lipoprotein-apoB100 overproduction in Otsuka Long-Evans Tokushima Fatty rats

AIMS

Overproduction of hepatic very low-density lipoprotein (VLDL) particles is a major abnormality of lipoprotein dysregulation in type 2 diabetes (T2D). We sought to examine the relationship between systemic/hepatic inflammation associated with insulin resistance and apolipoprotein (apo)B100-containing VLDL production.

METHODS AND RESULTS

At the age of 19 wks, Otsuka Long-Evans Tokushima Fatty (OLETF) rats showed systemic inflammation (plasma TNF-α and interleukin (IL)-6 levels increased), insulin resistance (plasma retinol binding protein 4 and soluble CD36 levels were higher), dyslipidemia and fatty liver (plasma and liver triglyceride and cholesterol levels were higher as well as total VLDL-, VLDL(1)-, VLDL(2)-apoB100 and VLDL-triglycerides were overproduced), compared with the control rats. In livers of OLETF rats, mRNA levels of tnf, il1b and il6 were increased, but an anti-inflammatory protein, zinc finger protein 36, and its mRNA expression were decreased. We also found that the liver mRNA, protein levels, and tyrosine phosphorylation (pY) of insulin receptor (InsR) substrate (IRS) 2, but not IRS1, were decreased in OLETF rats; pY of InsR and Akt protein and phospho-Akt (ser437) were also reduced; but protein tyrosine phosphatase-1B protein was overexpressed. The gene expressions of glucose transporters 1 and 2, and glycogen synthase were decreased, but phosphatase and tensin homolog deleted on chromosome ten and glycogen synthase kinase 3β mRNAs were overexpressed, compared with the controls. Sterol regulatory element binding protein-1c mRNA, ATP-binding cassette transporter A1 mRNA, microsomal triglyceride transfer protein mRNA/protein, and CD36 mRNA/protein levels were increased and lipoprotein lipase and Niemann-Pick c1-like1 mRNA levels were decreased, which are all involved in lipogenesis. Decreased sirtuins1-3 mRNA levels were also observed in OLETF rats.

CONCLUSIONS

These abnormal genes, proteins expression and phosphorylation of multiple pathways related to inflammatory, insulin signaling and lipogenesis may be important underlying factors in VLDL-apoB100 particles overproduction observed in T2D. Our data contribute to the further understanding of an association of dyslipoproteinemia with systemic metabolic disorders, fatty liver and dysregulated hepatic metabolic pathways.

Suppression of hypoxia-inducible factor-1α contributes to the antiangiogenic activity of red propolis polyphenols in human endothelial cells

Polyphenol-enriched fractions from natural sources have been proposed to interfere with angiogenesis in pathological conditions. We recently reported that red propolis polyphenols (RPP) exert antiangiogenic activity. However, molecular mechanisms of this activity remain unclear. Here, we aimed at characterizing molecular mechanisms to explain the impact of RPP on endothelial cells' (EC) physiology. We used in vitro and ex and in vivo models to test the hypothesis that RPP inhibit angiogenesis by affecting hypoxia-inducible factor-1α (HIF1α) stabilization in EC. RPP (10 mg/L) affected angiogenesis by reducing migration and sprouting of EC, attenuated the formation of new blood vessels, and decreased the differentiation of embryonic stem cells into CD31-positive cells. Moreover, RPP (10 mg/L) inhibited hypoxia- or dimethyloxallylglycine-induced mRNA and protein expression of the crucial angiogenesis promoter vascular endothelial growth factor (VEGF) in a time-dependent manner. Under hypoxic conditions, RPP at 10 mg/L, supplied for 1-4 h, decreased HIF1α protein accumulation, which in turn attenuated VEGF gene expression. In addition, RPP reduced the HIF1α protein half-life from ~58 min to 38 min under hypoxic conditions. The reduced HIF1α protein half-life was associated with an increase in the von Hippel-Lindau (pVHL)-dependent proteasomal degradation of HIF1α. RPP (10 mg/L, 4 h) downregulated Cdc42 protein expression. This caused a corresponding increase in pVHL protein levels and a subsequent degradation of HIF1α. In summary, we have elucidated the underlying mechanism for the antiangiogenic action of RPP, which attenuates HIF1α protein accumulation and signaling.

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.

Effects of the aqueous extract of white tea (Camellia sinensis) in a streptozotocin-induced diabetes model of rats

White tea (WT) is very similar to green tea (GT) but it is exceptionally prepared only from the buds and young tea leaves of Camelia sinensis plant while GT is prepared from the matured tea leaves. The present study was investigated to examine the effects of a 0.5% aqueous extract of WT in a streptozotocin-induced diabetes model of rats. Six-week-old male Sprague-Dawley rats were divided into 3 groups of 6 animals in each group namely: normal control (NC), diabetic control (DBC) and diabetic white tea (DWT). Diabetes was induced by an intraperitoneal injection of streptozotocin (65 mg/kg BW) in DBC and DWT groups except the NC group. After 4 weeks feeding of 0.5% aqueous extracts of WT, the drink intake was significantly (P<0.05) increased in the DWT group compared to the DBC and NC groups. Blood glucose concentrations were significantly decreased and glucose tolerance ability was significantly improved in the DWT group compared to the DBC group. Liver weight and liver glycogen were significantly increased and serum total cholesterol and LDL-cholesterol were significantly decreased in the DWT group compared to the DBC group. The food intake, body weight gain, serum insulin and fructosamine concentrations were not influenced by the consumption of WT. Data of this study suggest that the 0.5% aqueous extract of WT is effective to reduce most of the diabetes associated abnormalities in a steptozotocin-induced diabetes model of rats.

An extract of chokeberry attenuates weight gain and modulates insulin, adipogenic and inflammatory signalling pathways in epididymal adipose tissue of rats fed a fructose-rich diet

Chokeberries are a rich source of anthocyanins, which may contribute to the prevention of obesity and the metabolic syndrome. The aim of the present study was to determine if an extract from chokeberries would reduce weight gain in rats fed a fructose-rich diet (FRD) and to explore the potential mechanisms related to insulin signalling, adipogenesis and inflammatory-related pathways. Wistar rats were fed a FRD for 6 weeks to induce insulin resistance, with or without chokeberry extract (CBE) added to the drinking-water (100 and 200 mg/kg body weight, daily: CBE100 and CBE200). Both doses of CBE consumption lowered epididymal fat, blood glucose, TAG, cholesterol and LDL-cholesterol. CBE consumption also elevated plasma adiponectin levels and inhibited plasma TNF-α and IL6, compared with the control group. There were increases in the mRNA expression for Irs1, Irs2, Pi3k, Glut1, Glut4 and Gys1, and decreases in mRNA levels of Gsk3β. The protein and gene expression of adiponectin and Pparγ mRNA levels were up-regulated and Fabp4, Fas and Lpl mRNA levels were inhibited. The levels of gene expression of inflammatory cytokines, such as Il1β, Il6 and Tnfα were lowered, and protein and gene expression of ZFP36 (zinc finger protein) were enhanced in the epididymal adipose tissue of the rats that consumed the CBE200 extract. In summary, these results suggest that the CBE decreased risk factors related to insulin resistance by modulating multiple pathways associated with insulin signalling, adipogenesis and inflammation.

Chemical compositions and bioactivities of crude polysaccharides from tea leaves beyond their useful date

The chemical compositions and bioactivities of crude tea polysaccharides (TPS) from the out-of-date tea leaves (beyond their useful date), namely Xihu Longjing (XTPS), Anxi Tieguanyin (TTPS), Chawentianxia (CTPS) and Huizhoulvcha (HTPS), in market were investigated. These TPS showed similar neutral sugar content and different distribution of molecular weight (1-800 kD). These crude TPS were mainly composed of rhamnose, arabinose, galactose, glucose, xylose, mannose, and galacturonic acid. IR spectra confirmed that these crude TPS were composed of polysaccharide, protein and uronic acids. These TPS showed similar DPPH scavenging activity and exhibited lower DPPH scavenging activities than Vc within 25-200 μg/mL. However, these TPS with higher concentrations (200-400 μg/mL) showed similar DPPH scavenging activity with Vc. HTPS exhibited significant higher superoxide anion scavenging activity than others TPS and gallic acid. XTPS showed significant higher inhibitory effects on α-glucosidase and α-amylase with inhibitory percentages of 64.35% and 82.24% than others TPS. TTPS, XTPS, and HTPS exhibited similar inhibition ability on α-d-glucosidase and α-amylase. The overdue tea leaves can be a resource of tea polysaccharides as function food.

Effects of green tea polyphenol (-)-epigallocatechin-3-gallate on newly developed high-fat/Western-style diet-induced obesity and metabolic syndrome in mice

The aim of this study was to investigate the effects of (-)-epigallocatechin-3-gallate (EGCG) on newly developed high-fat/Western-style diet-induced obesity and symptoms of metabolic syndrome. Male C57BL/6J mice were fed a high fat/Western-style (HFW; 60% energy as fat and lower levels of calcium, vitamin D(3), folic acid, choline bitartrate, and fiber) or HFW with EGCG (HFWE; HFW with 0.32% EGCG) diet for 17 wks. As a comparison, two other groups of mice fed a low-fat diet (LF; 10% energy as fat) and high-fat diet (HF; 60% energy as fat) were also included. The HFW group developed more body weight gain and severe symptoms of metabolic syndrome than the HF group. The EGCG treatment significantly reduced body weight gain associated with increased fecal lipids and decreased blood glucose and alanine aminotransferase (ALT) levels compared to those of the HFW group. Fatty liver incidence, liver damage, and liver triglyceride levels were also decreased by the EGCG treatment. Moreover, the EGCG treatment attenuated insulin resistance and levels of plasma cholesterol, monocyte chemoattractant protein-1 (MCP-1), C-reactive protein (CRP), interlukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF). Our results demonstrate that the HFW diet produces more severe symptoms of metabolic syndrome than the HF diet and that the EGCG treatment can alleviate these symptoms and body fat accumulation. The beneficial effects of EGCG are associated with decreased lipid absorption and reduced levels of inflammatory cytokines.

Administration of rosmarinic acid reduces cardiopathology and blood pressure through inhibition of p22phox NADPH oxidase in fructose-fed hypertensive rats

Rosmarinic acid (RA), a caffeic acid ester, has insulin-sensitizing and antioxidant effects in high fructose-fed model of insulin resistance (IR). This study investigated whether RA supplementation prevents cardiac abnormalities and hypertension in fructose-fed rats (FFR). Rats fed with fructose diet (60 g/100 g) for 60 days exhibited metabolic abnormalities and rise in plasma and cardiac lipids and whole body IR. The levels of cardiac antioxidants and plasma ferric reducing antioxidant power were significantly reduced in FFR concomitant with increased levels of lipid peroxidation and protein oxidation products. A significant rise in troponin T, creatine kinase-MB, aspartate transaminase, and lactate dehydrogenase in plasma of FFR was noted. RA supplementation to FFR (10 mg/kg from the 16th day) significantly improved insulin sensitivity, reduced lipid levels, oxidative damage, and the expression of p22phox subunit of nicotinamide adenine dinucleotide phosphate reduced oxidase, and prevented cardiac hypertrophy. Fructose-induced rise in blood pressure was also lowered by RA through decrease in endothelin-1 and angiotensin-converting enzyme activity and increase in nitric oxide levels. Histology revealed a reduction in myocardial damage in RA-supplemented FFR. These findings suggest that RA acts as a vasoactive substance and a cardioprotector through its antioxidant property. Thus, RA may be useful in reducing the cardiovascular risk associated with IR.

Noncovalent interaction of dietary polyphenols with common human plasma proteins

Common human plasma proteins (CHPP), also called blood proteins, are proteins found in blood plasma. The molecular structure/property-affinity relationships of dietary polyphenols noncovalently binding to CHPP were investigated by comparing the binding constants obtained from the fluorescence titration method. An additional methoxy group in flavonoids increased their binding affinities for CHPP by 1.05 to 72.27 times. The hydroxylation on the 4' position (ring B) of flavones and flavonols and the 5 position (ring A) of isoflavones weakened the binding affinities; however, the hydroxylation on other positions of flavonoids slightly enhanced or little affected the binding affinities for CHPP. The glycosylation of flavonoids weakened or slightly affected the affinities for CHPP by 1 order of magnitude. The hydrogenation of the C2═C3 double bond of flavone, 6-hydroxyflavone, 6-methoxyflavone and myricetin decreased the binding affinities about 10.02 to 17.82 times. The galloylation of catechins significantly improved the binding affinities with CHPP about 10 to 1000 times. The esterification of gallic acid increased its binding affinity. The binding affinities with CHPP were strongly influenced by the structural differences of dietary polyphenols. Polyphenols with higher affinities for purified HSA also showed stronger affinities with CHPP. The hydrophobic force played an important role in binding interaction between polyphenols and CHPP.

Preventive effects of (-)-epigallocatechin gallate on diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BL/KsJ-db/db Mice

Obesity and related metabolic abnormalities, including insulin resistance and a state of chronic inflammation, increase the risk of hepatocellular carcinoma. Abnormal activation of the insulin-like growth factor (IGF)/ IGF-1 receptor (IGF-1R) axis is also involved in obesity-related liver tumorigenesis. In the present study, we examined the effects of (-)-epigallocatechin gallate (EGCG), a major biologically active component of green tea, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-db/db (db/db) obese mice. Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks and then they received drinking water containing 0.1% EGCG for 34 weeks. At sacrifice, drinking water with EGCG significantly inhibited the development of liver cell adenomas in comparison with the control EGCG-untreated group. EGCG inhibited the phosphorylation of the IGF-1R, ERK (extracellular signal-regulated kinase), Akt, GSK-3β (glycogen synthase kinase-3β), Stat3, and JNK (c-Jun NH(2)-terminal kinase) proteins in the livers of experimental mice. The serum levels of insulin, IGF-1, IGF-2, free fatty acid, and TNF-α were all decreased by drinking EGCG, which also decreased the expression of TNF-α, interleukin (IL)-6, IL-1β, and IL-18 mRNAs in the livers. In addition, EGCG improved liver steatosis and activated the AMP-activated kinase protein in the liver. These findings suggest that EGCG prevents obesity-related liver tumorigenesis by inhibiting the IGF/IGF-1R axis, improving hyperinsulinemia, and attenuating chronic inflammation. EGCG, therefore, may be useful in the chemoprevention of liver tumorigenesis in obese individuals. Cancer Prev Res; 4(3); 396-403. ©2011 AACR.

Grape seed extract supplementation prevents high-fructose diet-induced insulin resistance in rats by improving insulin and adiponectin signalling pathways

Recent evidence strongly supports the contention that grape seed extract (GSE) improves hyperglycaemia and hyperinsulinaemia in high-fructose-fed rats. To explore the underlying molecular mechanisms of action, we examined the effects of GSE on the expression of muscle proteins related to the insulin signalling pathway and of mRNA for genes involved in the adiponectin signalling pathway. Compared with rats fed on a normal diet, high-fructose-fed rats developed pathological changes, including insulin resistance, hyperinsulinaemia, hypertriacylglycerolaemia, a low level of plasma adiponectin and a high level of plasma fructosamine. These disorders were effectively attenuated in high-fructose-fed rats supplemented with GSE. A high-fructose diet causes insulin resistance by significantly reducing the protein expression of insulin receptor, insulin receptor substrate-1, Akt and GLUT4, and the mRNA expression of adiponectin, adiponectin receptor R1 (AdipoR1) and AMP-activated protein kinase (AMPK)-α in the skeletal muscle. Supplementation of GSE enhanced the expression of insulin signalling pathway-related proteins, including Akt and GLUT4. GSE also increased the mRNA expression of adiponectin, AdipoR1 and AMPK-α. In addition, GSE increased the mRNA levels of glycogen synthase and suppressed the mRNA expression of glycogen synthase kinase-3-α, causing an increase in glycogen accumulation in the skeletal muscle. These results suggest that GSE ameliorates the defective insulin and adiponectin signalling pathways in the skeletal muscle, resulting in improved insulin resistance in fructose-fed rats.

A high fructose diet does not affect amphetamine self-administration or spatial water maze learning and memory in female rats

High energy diets can have a detrimental effect on brain plasticity. For example, a high fructose diet impairs spatial memory in male rats. The aim of the present study was to determine whether a high fructose diet impairs another form of learning and memory: drug reinforcement learning. Female Sprague-Dawley rats were fed a high fructose diet (60%) from weaning at postnatal day (PND) 21, then allowed to acquire lever-pressing maintained by intravenous (i.v.) amphetamine at PND 68, 109, or 165. Acquisition was tested on a fixed ratio one (FR1) schedule of reinforcement (0.025 mg/kg/infusion, 1h daily sessions, 10 sessions over 14 days), followed by testing for reinforcing efficacy on a progressive ratio (PR) schedule (0.025, 0.01, and 0.1mg/kg/infusion), 14 days of abstinence, and within-session extinction and reinstatement tests. Subsequently, water maze acquisition and retention were tested in these subjects as well as a separate cohort tested in the water maze only. The diet had no effect on acquisition, reinforcing efficacy, extinction, or reinstatement of amphetamine seeking. Nor did the diet alter any measures of spatial memory. The high fructose diet did decrease body mass and increase relative liver and spleen mass, but did not affect plasma triglyceride concentrations consistently. Together with prior research on males, these results suggest that the metabolism of fructose and the effects of a high fructose diet on learning and memory may be sex-dependent.

Soluble CD36- a marker of the (pathophysiological) role of CD36 in the metabolic syndrome?

CD36 is a class B scavenger receptor observed in many cell types and tissues throughout the body. Recent literature has implicated CD36 in the pathogenesis of metabolic dysregulation such as found in obesity, insulin resistance, and atherosclerosis. Genetic variation at the CD36 loci have been associated with obesity and lipid components of the metabolic syndrome, with risk of heart disease and type 2 diabetes. Recently, non-cell bound CD36 was identified in human plasma and was termed soluble CD36 (sCD36). In this review we will describe the functions of CD36 in tissues and address the role of sCD36 in the context of the metabolic syndrome. We will also highlight recent findings from human genetic studies looking at the CD36 locus in relation to metabolic profile in the general population. Finally, we present a model in which insulin resistance, oxLDL, low-grade inflammation and liver steatosis may contribute to elevated levels of sCD36.

A grape polyphenol extract modulates muscle membrane fatty acid composition and lipid metabolism in high-fat--high-sucrose diet-fed rats

Accumulation of muscle TAG content and modification of muscle phospholipid fatty acid pattern may have an impact on lipid metabolism, increasing the risk of developing diabetes. Some polyphenols have been reported to modulate lipid metabolism, in particular those issued from red grapes. The present study was designed to determine whether a grape polyphenol extract (PPE) modulates skeletal muscle TAG content and phospholipid fatty acid composition in high-fat-high-sucrose (HFHS) diet-fed rats. Muscle plasmalemmal and mitochondrial fatty acid transporters, GLUT4 and lipid metabolism pathways were also explored. The PPE decreased muscle TAG content in HFHS/PPE diet-fed rats compared with HFHS diet-fed rats and induced higher proportions of n-3 PUFA in phospholipids. The PPE significantly up-regulated GLUT4 mRNA expression. Gene and protein expression of muscle fatty acid transporter cluster of differentiation 36 (CD36) was increased in HFHS diet-fed rats but returned to control values in HFHS/PPE diet-fed rats. Carnitine palmitoyltransferase 1 protein expression was decreased with the PPE. Mitochondrial β-hydroxyacyl CoA dehydrogenase was increased in HFHS diet-fed rats and returned to control values with PPE supplementation. Lipogenesis, mitochondrial biogenesis and mitochondrial activity were not affected by the PPE. In conclusion, the PPE modulated membrane phospholipid fatty acid composition and decreased muscle TAG content in HFHS diet-fed rats. The PPE lowered CD36 gene and protein expression, probably decreasing fatty acid transport and lipid accumulation within skeletal muscle, and increased muscle GLUT4 expression. These effects of the PPE are in favour of a better insulin sensibility.

Weight control and prevention of metabolic syndrome by green tea

Green tea (Camellia sinensis, Theaceace) is the second most popular beverage in the world and has been extensively studied for its putative disease preventive effects. Green tea is characterized by the presence of a high concentrations of polyphenolic compounds known as catechins, with (-)-epigallocatechin-3-gallate (EGCG) being the most abundant and most well-studied. Metabolic syndrome (MetS) is a complex condition that is defined by the presence of elevated waist circumference, dysglycemia, elevated blood pressure, decrease serum high-density lipoprotein-associated cholesterol, and increased serum triglycerides. Studies in both in vitro and laboratory animal models have examined the preventive effects of green tea and EGCG against the symptoms of MetS. Overall, the results of these studies have been promising and demonstrate that green tea and EGCG have preventive effects in both genetic and dietary models of obesity, insulin resistance, hypertension, and hypercholesterolemia. Various mechanisms have been proposed based on these studies and include: modulation of dietary fat absorption and metabolism, increased glucose utilization, decreased de novo lipogenesis, enhanced vascular responsiveness, and antioxidative effects. In the present review, we discuss the current state of the science with regard to laboratory studies on green tea and MetS. We attempt to critically evaluate the available data and point out areas for future research. Although there is a considerable amount of data available, questions remain in terms of the primary mechanism(s) of action, the dose-response relationships involved, and the best way to translate the results to human intervention studies.