Dose-Dependent Suppression of Tea Catechins with a Galloyl Moiety on Postprandial Hypertriglyceridemia in Rats

Evaluating the appropriate oral lipid tolerance test model for investigating plasma triglyceride elevation in mice

The oral lipid tolerance test (OLTT) has been known to assess intestinal fat metabolism and whole-body lipid metabolism, but rodent models for OLTT are not yet established. Differences in OLTT methodology preclude the generation of definitive results, which may cause some confusion about the anti-hypertriglyceridemia effects of the test materials. To standardize and generate more appropriate methodology for the OLTT, we examined the effects of mice strain, dietary lipid sources, fasting period, and gender on lipid-induced hypertriglyceridemia in mice. First, lipid-induced hypertriglyceridemia was more strongly observed in male ddY mice than in C57BL/6N or ICR mice. Second, the administration of olive and soybean oils remarkably represented lipid-induced hypertriglyceridemia. Third, fasting period before the OLTT largely affected the plasma triglyceride elevation. Fasting for 12 h, but less than 48 h, provoked lipid-induced hypertriglyceridemia. Fourth, we explored the suppressive effects of epigallocatechin gallate (EGCG), a green tea polyphenol, on lipid-induced hypertriglyceridemia. The administration of 100 mg/kg of EGCG suppressed lipid-induced hypertriglyceridemia and intestinal lipase activity. Fifth, EGCG-induced suppressive effects were observed after lipid-induced hypertriglyceridemia was observed in male mice, but not in female mice. Lastly, lipid-induced hypertriglyceridemia could be more effectively induced in mice fed a high-fat diet for 1 week before the OLTT. These findings indicate that male ddY mice after 12 h fasting displayed marked lipid-induced hypertriglyceridemia in response to soybean oil. Hence, the defined experiment condition may be a more appropriate OLTT model for evaluating lipid-induced hypertriglyceridemia.

Separationless and Adsorptionless Quantification of Individual Catechins in Green Tea with a Carbon Nanotube-Carboxymethylcellulose Electrode

We demonstrate the electrochemical quantification of individual catechins (epicatechin, EC; epigallocatechin, EGC; epicatechingallate, ECG; and epigallocatechingallate, EGCG) in a green tea infusion without a separation process nor any adsorption complication. In the detection of catechins, long-length carbon nanotube (CNT)-carboxymethylcellulose (CMC) thin-film electrodes have attractive properties, such as well-defined current peaks, high reproducibility from sample to sample, high repeatability, and low background current. Cyclic voltammograms (CVs) for real green tea, which is mainly composed of a mixture of the four catechins, are produced by the sum of those catechins. A set of three specific peaks in the CVs of the real green tea samples, as catechin-mixture solutions, was used for quantification of the individual catechins. The CVs of the real samples are similar to the CVs of intentionally prepared mixture solutions with the catechin-component ratios determined by high-performance liquid chromatography (HPLC). The values for the real samples determined from the CVs show good agreement with those obtained by HPLC. The novelty of the work is the demonstration of the usefulness of the CNT-CMC electrode and the separationless quantification of individual catechins in green tea for the first time.

Enrichment of Biscuits with Matcha Green Tea Powder: Its Impact on Consumer Acceptability and Acute Metabolic Response

Matcha green tea powder (MGTP) is made with finely ground green tea leaves that are rich in phytochemicals, most particularly catechins. Shortbread biscuits were enriched with MGTP and evaluated for consumer acceptability and potential functional health properties. Baking decreased the content of total catechins by 19% compared to dough, although epimerization increased the amount of (+)-gallocatechin gallate at the expense of other catechins such as (−)-epigallocatechin gallate. Consumer acceptability tests using a 9-point hedonic scale showed that consumers preferred enriched biscuits with low content of MGTP (2 g of MGTP 100 g⁻¹ of flour), and an increase of sugar content did not significantly improve the acceptability of MGTP-enriched biscuits. Overall, enrichment of biscuits with MGTP did not significantly affect the postprandial glucose or triglyceride response (area under curve) compared to non-enriched biscuits consumed with water or MGTP drink. Enriching biscuits with Matcha green tea is acceptable to consumers, but may not bring significant postprandial effects.

Oxidized tea polyphenols prevent lipid accumulation in liver and visceral white adipose tissue in rats

BACKGROUND

Tea polyphenols are the prominent component in tea. After the fermentation process, tea polyphenols are oxidized by polyphenol oxidase to form oxidized tea polyphenols (OTPs). OTPs contain a significant amount of hydrophobic phenyl groups that can bind with non-aqueous materials. Here, we determined whether OTPs can bind with lipids and reduce fat uptake and assessed the effect of OTPs on decreasing obesity and alleviating hyperlipidaemia and other metabolic syndromes.

METHODS

Rats were divided into three groups: control, high-fat diet (HFD) and OTP groups. The control and HFD groups were fed a chow diet and a high-fat diet, respectively, for 12 weeks; the OTP group was fed a high-fat diet for 6 weeks and then a high-fat diet containing 2 % OTP for 6 weeks. The serum and excrement triglyceride (TAG) and total cholesterol (CHOL) concentrations were determined, and liver tissue and white adipose tissue were collected to detect the expression levels of genes involved in lipid metabolism.

RESULTS

Our results revealed that OTPs failed to decrease the serum concentrations of TAG and CHOL. OTPs alleviated the accumulation of lipids in the liver tissue and changed the expression levels of the regulators of lipid metabolism, i.e., peroxisome proliferation-activated receptors (ppars), compared with the rats fed a high-fat diet alone. We also observed a significantly decreased reduction of weight in the visceral white adipose, enhanced regulation of fatty acid β-oxidation by PPARα and enhanced biosynthesis of mitochondria in the visceral white adipose of the OTP rats compared with the HFD rats. Additionally, OTPs promoted the excretion of lipids.

CONCLUSION

Our results suggest that OTPs alleviate the accumulation of lipids in liver and visceral white adipose tissue and promote lipid excretion in rats in vivo.

Inhibitory effect of catechin-related compounds on renin activity

Renin is a crucial enzyme in the renin-angiotensin system, and the inhibition of its activity is considered as a useful approach to the treatment of hypertension. The inhibitory effect of catechin-related compounds on renin was investigated in this work. It was found that epigallocatechin gallate (EGCg) possessed the strongest activity with an IC₅₀ value of 44.53 μM and acted in an uncompetitive manner. Gallated catechins exerted higher inhibition than the ungallated forms, and gallic acid exhibited an inhibitory potency close to that of epicatechin gallate (ECg). Results indicated that the galloyl moiety and ortho-trihydroxy phenyl structures might be favorable for the renin-inhibitory activity of these compounds.

Theflavins and theasinensin A derived from fermented tea have antihyperglycemic and hypotriacylglycerolemic effects in KK-A(y) mice and Sprague-Dawley rats

Although tea polyphenols are reported to improve serum glucose and lipid levels by inhibiting amylase activity and reducing lipid absorption, in vivo data are lacking. We evaluated in vivo the antihyperglycemic and hypotriacylglycerolemic effects of theaflavins (TFs) and theasinensin A (TSA) refined from fermented tea to purities of 12 and 59%, respectively. Feeding male KK-A(y) mice diets with 0.1% TFs or TSA for 6 weeks reduced serum glucose levels by >30% compared to a control diet. Rats fed diets containing 0.2% TFs or TSA for 4 weeks had higher fecal fat excretion and 33% lower hepatic triacylglycerol; hepatic fatty acid synthase activity was not affected. Oral administration of TFs or TSA reduced the increase in serum triacylglycerol after an oral bolus of a fat emulsion. These results indicate TFs and TSA induce antihyperglycemic responses in diabetic mice and are hypotriacylglycerolemic in rats by suppressing intestinal fat absorption.

Acute effects of epigallocatechin gallate from green tea on oxidation and tissue incorporation of dietary lipids in mice fed a high-fat diet

OBJECTIVE

To examine in mice the acute effects of epigallocatechin gallate (EGCG), a green tea bioactive polyphenol on substrate metabolism with focus on the fate of dietary lipids.

METHODS

Male C57BL/6 mice were fed high-fat diets supplemented with EGCG extracted from green tea (TEAVIGO, DSM Nutritional Products Ltd, Basel, Switzerland) at different dosages up to 1% (w/w). Effects of EGCG on body composition (quantitative magnetic resonance), food intake and digestibility, oxidation and incorporation of exogenous lipids (stable isotope techniques: (13)C-labeled palmitate and diet supplemented with corn oil as a natural source of (13)C-enriched lipids) as well as gene expression (quantitative real-time PCR) in liver and intestinal mucosa were investigated.

RESULTS

Short-term supplementation (4-7 days) of dietary EGCG increased energy excretion, while food and energy intake were not affected. Fecal energy loss was accompanied by increased fat and nitrogen excretion. EGCG decreased post-prandial triglyceride and glycogen content in liver, increased oxidation of dietary lipids and decreased incorporation of dietary 13C-enriched lipids into fat tissues, liver and skeletal muscle. EGCG dose dependently reversed high-fat diet-induced effects on intestinal substrate transporters (CD36, FATP4 and SGLT1) and downregulated lipogenesis-related genes (ACC, FAS and SCD1) in liver in the post-prandial state.

CONCLUSIONS

Anti-obesity effects of EGCG can be explained by a decreased food digestibility affecting substrate metabolism of intestinal mucosa and liver, leading to increased post-prandial fat oxidation and reduced incorporation of dietary lipids into tissues.

Differences and similarities of postprandial lipemia in rodents and humans

Background

The rat has been a mainstay of physiological and metabolic research, and more recently mice. This study aimed at characterizing the postprandial triglyceride profile of two members of the Muridae family: the Wistar rats (Rattus norvegicus albinus) and C57BL/6 mice (Mus musculus) plus comparing them to the profile obtained in humans.

Methods

Thirty-one male and twelve female Wistar rats, ten C57BL/6 male and nine female mice received a liquid meal containing fat (17%), protein (4%) and carbohydrates (4%), providing 2 g fat/Kg. Thirty-one men and twenty-nine women received a standardized liquid meal containing fat (25%), dextromaltose (55%), protein (14%), and vitamins and minerals (6%), and providing 40 g of fat per square meter of body surface. Serial blood samples were collected at 2, 4, 6, 8 and 10 h after the ingestion in rats, at 1, 2, 3, 4, 5 and 6 h in mice and in humans at 2, 4, 6 and 8 h. Wilcoxon and Mann-Whitney tests were used.

Results/Discussion

The triglyceride responses were evaluated after the oral fat loads. Fasting and postprandial triglyceridemia were determined sequentially in blood sample. AUC, AUIC, AR, RR and late peaks were determined.

Conclusions

Rats are prone to respond in a pro-atherogenic manner. The responses in mice were closer to the ones in healthy men. This study presents striking differences in postprandial triglycerides patterns between rats and mice not correlated to baseline triglycerides, the animal baseline body weight or fat load in all animal groups.

Oolong tea theasinensins attenuate cyclooxygenase-2 expression in lipopolysaccharide (LPS)-activated mouse macrophages: structure-activity relationship and molecular mechanisms

Oolong tea theasinensins are a group of tea polyphenols different from green tea catechins and black tea theaflavins. The present study reports the inhibitory effects of oolong tea theasinensins on the expression of cyclooxygenase-2 (COX-2) and underlying molecular mechanisms in lipopolysaccharide (LPS)-activated murine macrophage RAW264 cells. The structure-activity data revealed that the galloyl moiety of theasinensins played an important role in the inhibitory actions. Theasinensin A, a more potent inhibitor, caused a dose-dependent inhibition of mRNA, protein, and promoter activity of COX-2. An electrophoretic mobility shift assay (EMSA) revealed that theasinensin A reduced the complex of NF-κB- and AP-1-DNA in the promoter of COX-2. Signaling analysis demonstrated that theasinensin A attenuated IκB-α degradation, nuclear p65 accumulation, and c-Jun phosphorylation. Furthermore, theasinensin A suppressed the phosphorylation of MAPKs, IκB kinase α/β (IKKα/β), and TGF-β activated kinase (TAK1). These data demonstrated that the down-regulation of TAK1-mediated MAPKs and NF-κB signaling pathways might be involved in the inhibition of COX-2 expression by theasinensin A. These findings provide the first molecular basis for the anti-inflammatory properties of oolong tea theasinensins.

[Inhibitory effects of "Goishi-tea" as a post-fermented-tea on dietary-induced hypercholesteremia and atherosclerosis in rabbits]

Since lipid oxidation is involved in the deterioration of hypercholesterolemia-related atherosclerosis, ingestion of drinks and foods with antioxidant actions is useful for preventing lipid oxidation. Goishi-tea is a post-fermented-tea manufactured by a unique method in Japan, and may be useful for preventing various disorders. However, there is no scientific evidence. In this study, we compared the radical scavenging activity of goishi-tea with that of other teas, and administered this tea to a rabbit model of hypercholesteremia to evaluate its usefulness in the inhibition of hypercholesteremia and atherosclerosis. The radical scavenging activity of goishi-tea was similar to that of green-tea, and was higher than that of other types of fermented-teas. On the other hand, some difference of components was found between goishi-tea and green-tea. In cholesterol-fed rabbits, low-density lipoprotein (LDL)-cholesterol level in the goishi-tea-group was lower than that in the green-tea-group. Plasma lipidperoxide value was also lower in the goishi-tea-group than in the green-tea and tap-water-groups. On aortic endothelial staining, fat area in the goishi-tea-group was lower than that in the tap-water-group. Furthermore, fat accumulation in the aortic intima in the goishi-tea-group was very low. Goishi-tea has higher antioxidant activities than the other fermented-teas tested, which were generally low, and decreased serum lipid levels, suggesting that goishitea is a very peculiar fermented-tea with usefulness in the prevention of hypercholesterolemia and atherosclerosis.

Effects of green tea and EGCG on cardiovascular and metabolic health

Since ancient times green tea has been considered a health-promoting beverage. In recent years, scientists throughout the world have investigated the potential benefits of green tea and its most abundant catechin, epigallocatechin gallate (EGCG). The anti-cancer effects of green tea and EGCG were the focus of early research, and encouraging data from in vitro, animal model, and human studies have emerged. Due to the dominant role of cardiovascular disease and the dramatic rise of obesity and type 2 diabetes mellitus as major and interlinked healthcare problems, green tea and EGCG are increasingly being investigated in these areas. Dose-response relationships observed in several epidemiological studies have indicated that pronounced cardiovascular and metabolic health benefits can be obtained by regular consumption of 5-6 or more cups of green tea per day. Furthermore, intervention studies using similar amounts of green tea, containing 200-300 mg of EGCG, have demonstrated its usefulness for maintaining cardiovascular and metabolic health. Additionally, there are numerous in vivo studies demonstrating that green tea and EGCG exert cardiovascular and metabolic benefits in these model systems. Therefore, green tea and EGCG can be regarded as food components useful for the maintenance of cardiovascular and metabolic health. To prove the effectiveness for disease prevention or treatment, several multi-center, long-term clinical studies investigating the effects of one precisely-defined green tea product on cardiovascular and metabolic endpoints would be necessary. The aim of this manuscript is to provide an overview of the research investigating the effects of green tea and green tea catechins on cardiovascular and metabolic health.

Green tea proanthocyanidins inhibit cyclooxygenase-2 expression in LPS-activated mouse macrophages: molecular mechanisms and structure-activity relationship

The inhibitory effects of green tea proanthocyanidins on cyclooxygenase-2 (COX-2) expression and prostaglandin E(2) (PGE(2)) release were investigated in lipopolysaccharide (LPS)-activated murine macrophage RAW264 cells. Prodelphinidin B2 3,3' di-O-gallate (PDGG) caused a dose-dependent inhibition of COX-2 at both mRNA and protein levels with the attendant release of PGE(2). Molecular evidence revealed that PDGG inhibited the degradation of Ikappa-B, nuclear translocation of p65 and CCAAT/enhancer-binding protein (C/EBP)delta, and phosphorylation of c-Jun, but not CRE-binding protein (CREB), which regulate COX-2 expression. Moreover, PDGG suppressed the activations of mitogen-activated protein kinase (MAPK) including c-Jun NH(2)-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38 kinase. The results demonstrated that PDGG suppressed COX-2 expression via blocking MAPK-mediated activation of nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) and C/EBPdelta. Furthermore, studies on structure-activity relationship using five kinds of proanthocyanidins revealed that the galloyl moiety of proanthocyanidins appeared important to their inhibitory actions. Thus, our findings provide the first molecular basis that green tea proanthocyanidins with the galloyl moiety might have anti-inflammatory properties through blocking MAPK-mediated COX-2 expression.