The Inhibition of α-Amylase by Tea Polyphenols

The inhibition of α-amylase from human saliva by polyphenolic components of tea and its specificity was investigated in vitro. Four kinds of green tea catechins, and their isomers and four kinds of their dimeric compounds (theaflavins) produced oxidatively during black tea production were isolated. They were (?)-epicatechin (EC), (?)-epigallocatechin (EGC), (?)-epicatechin gallate (ECg), (?)-epigallocatechin gallate (EGCg), (?)-catechin (C), (?)-gallocatechin (GC), (?)-catechin gallate (Cg), (?)-gallocatechin gallate (GCg), theaflavin (TF1), theaflavin monogallates (TF2A and TF2B), and theaflavin digallate (TF3). Among the samples tested, EC, EGC, and their isomers did not have significant effects on the activity of α-amylase. All the other samples were potent inhibitors and the inhibitory effects were in the order of TF3>TF2A>TF2B>TFl>Cg> GCg > ECg > EGCg. The inhibitory patterns were noncompetitive except for TF3.     

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

Tea has long been believed to be a healthy beverage, and its beneficial effects are almost all attributed to catechins. The effect of catechins on postprandial hypertriglyceridemia in rats was investigated in this study. A lipid emulsion administered orally to rats with (?)-epigallocatechin gallate at a dose of 100 mg/kg resulted in the increase in plasma triacylglycerol being significantly inhibited after 1 and 2 h compared to the case without (?)-epigallocatechin gallate. The effect of (?)-epigallocatechin was weaker than that of (?)-epigallocatechin gallate. A tea extract (THEA-FLAN 90S), mainly composed of catechins with a galloyl moiety, dose-dependently suppressed postprandial triacylglycerol after the administration of a lipid emulsion at doses of 50–200 mg/kg. The administration of the tea extract alone at a dose of 200 mg/kg had no effect on the plasma triacylglycerol level. These results strongly suggest that catechins with a galloyl moiety would be promising agents for suppressing dietary fat absorption through the small intestine.     

Browning Reaction between Phospholipids and Acetaldehyde

Tea catechins have strong bitterness and influence the taste of tea. Among the 25 human bitter-taste receptors (TAS2Rs), we found that hTAS2R14 responded to catechins, in addition to hTAS2R39, a known catechin receptor. Although hTAS2R14 responded to (?)-epicatechin gallate and (?)-epigallocatechin gallate, it did not respond to (?)-epicatechin and (?)-epigallocatechin.     

Antioxidants from Steamed Used Tea Leaves and Their Reaction Behavior

The most efficient steaming conditions below 200 °C for extracting antioxidants from used tea leaves and their reaction behavior during the steaming treatment were investigated. The antioxidative activity of the steamed extracts increased with increasing steaming temperature, and the yield of the ethyl acetate extract fraction from each steamed extract showing the greatest antioxidative activity also increased. Caffeine, (?)-catechin, (?)-epicatechin, (?)-gallocatechin, (?)-epigallocatechin, (?)-catechin gallate, (?)-epicatechin gallate, (?)-gallocatechin gallate, (?)-epigallocatechin gallate and gallic acid were identified from the ethyl acetate extract fraction. Quantitative analyses demonstrated that the catechins with a 2,3-cis configuration decreased with increasing steaming temperature, whereas the corresponding epimers at the C-2 position increased. Each pair of epimers showed similar antioxidative activity to each other, indicating that the epimerization reaction did not contribute to the improved antioxidative activity. It is concluded from these results that the improvement in antioxidative activity at higher steaming temperatures was due to the increased yield of catechins and other antioxidants.     

The theaflavin monomers inhibit the cancer cells growth in vitro

The biological effects of tea and tea constituents havebeen studied and reviewed in many publications. Teaand its components have been demonstrated to inhibitchemically induced carcinogenesis in animal models,including cancers of the skin, lung, esophagus…     

The relationship between the antioxidant and the antibacterial properties of galloylated catechins and the structure of phospholipid model membranes

The effects of four catechins, (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), on the physical properties of phospholipid model membranes and the correlation to their antioxidant and antibacterial capacities have been studied by using differential scanning calorimetry (DSC), fluorescence spectroscopy, infrared spectroscopy (IR), AAPH-induced oxidation, and leakage experiments. DSC data revealed that galloylated catechins, especially ECG, affected the physical properties of both the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) bilayers dramatically. Galloylated catechins showed higher phospholipid/water partition coefficients than their homologues and were immersed in the phospholipid palisade intercalating within the hydrocarbon chains, ECG being at the deepest position. In contrast, nongalloylated catechins presented a shallow location close to the phospholipid/water interface. ECG also exhibited the highest antioxidant capacity against lipid peroxidation, which correlated with its strong effect on DPH fluorescence anisotropy (as observed by the increase of the lipid order of fluid PC bilayers) and with the presence of highly cooperative transitions as seen by DSC. We propose that the high antioxidant capacity of some galloylated catechins such as ECG could be partially due to the formation of membrane structures showing resistance to detergent solubilization and in which the phospholipids have tightly packed acyl chains and highly hydrated phosphate groups. Significantly, PE was found to be essential to the promotion of carboxyfluorescein leakage from bacterial model membranes by galloylated catechins, indicating that their bactericidal activity, at least at the membrane level, could be due to the specific effect of these catechins on PE.     

Tea catechins reduce inflammatory reactions via mitogen-activated protein kinase pathways in toll-like receptor 2 ligand-stimulated dental pulp cells

AimsIn this study, we evaluated whether catechins could inhibit the expression of pro-inflammatory mediators induced by dental caries-related bacteria, Streptococci, or pathogen-associated molecular patterns (PAMPs) stimulation in human dental pulp fibroblasts (HDPF). We further determined the mechanisms of the anti-inflammatory activity of catechins.Main methodsStreptococci or PAMP-stimulated HDPF were treated with catechin, and then the expression and production of pro-inflammatory mediators were determined by RT-PCR and ELISA. Furthermore, the signal transduction pathways activated with toll-like receptor (TLR)2 ligand were assessed by Immunoblot and ELISA using blocking assay with specific inhibitors.Key findingsIncreased expressions of pro-inflammatory mediators are found in inflamed dental pulp, especially in HDPF. We recently reported that dental pulpal innate immune responses may mainly result from the predominantly-expressed TLR2 signaling. Catechins, polyphenolic compounds in green tea, exert protective and healing effects through multiple mechanisms, including antioxidative and anti-inflammatory effects. However, there are no reports concerning the effects of catechins on dental pulp. In this study, we demonstrated that the up-regulated expressions of IL-8 or PGE₂ in Streptococci or PAMP-stimulated HDPF were inhibited by catechins, (?)-epicatechin gallate (ECG) and (?)-epigallocatechin gallate (EGCG). In TLR2 ligand-stimulated HDPF, specific inhibitors of extracellular signal regulated kinase (ERK)1/2, p38, c-jun NH₂-terminal kinase (SAP/JNK), NF-κB or catechins markedly reduced the level of pro-inflammatory mediators and the phosphorylation of these signal transduction molecules was suppressed by catechins.SignificanceThese findings suggest that catechins might be useful therapeutically as an anti-inflammatory modulator of dental pulpal inflammation.     

Interaction of Tea Catechins with Lipid Bilayers Investigated by a Quartz-Crystal Microbalance Analysis

The quartz-crystal microbalance (QCM) technique was applied to investigate the interaction of tea catechins with lipid bilayers. The association constants obtained from the frequency changes of QCM revealed that (?)epicatechin gallate and (?)epigallocatechin gallate interacted with 1,2-dimyristoyl-sn-glycero-3-phosphocholine ca. 1000 times more strongly than (?)epicatechin and (?)epigallocatechin. The results exhibited good correlation with the strength of biological activity.     

Green tea extracts reduce leukocyte cell–Derived chemotaxin 2 and selenoprotein P levels in the livers of C57BL/6J mice fed a high-fat diet

Epidemiological studies suggest that green tea extracts (GTEs), including catechins such as epigallocatechin gallate and epicatechin gallate, have a beneficial effect on obesity, hyperglycemia, insulin resistance, endothelial dysfunction, and inflammation. Although several studies have shown that catechins directly modulate the cellular and molecular alterations in the liver tissue, the contributions of indirect mechanisms underlying these systemic effects of catechins remain unclear. In this study, we report that, in the C57BL/6J mouse liver, GTEs reduce high-fat diet-induced increases in the levels of hepatokines, liver-derived secretary proteins such as leukocyte cell-derived chemotaxin 2 and selenoprotein P production, which have been shown to induce systemic adverse effects, including several metabolic diseases. These findings suggest that the systemic effects of GTEs involve the regulation of hepatokine production as an indirect mechanism.     

Single GUV method reveals interaction of tea catechin (-)-epigallocatechin gallate with lipid membranes

Tea catechins, which are flavonoids and the main components of green tea extracts, are thought to have antibacterial and antioxidant activity. Several studies indicate that lipid membranes are one of the targets of the antibacterial activity of catechins. Studies using a suspension of large unilamellar vesicles (LUVs) indicate that catechin causes gradual leakage of internal contents from LUVs. However, the detailed characteristics of the interaction of catechins with lipid membranes remain unclear. In this study, we investigated the interaction of (-)-epigallocatechin gallate (EGCg), a major catechin in tea extract, with single giant unilamellar vesicles (GUVs) of egg phosphatidylcholine (egg PC) using phase-contrast fluorescence microscopy and the single GUV method. We prepared GUVs of lipid membranes of egg PC in a physiological ion concentration ( approximately 150 mM NaCl) using the polyethylene glycol-lipid method. Low concentrations of EGCg at and above 30 muM induced rapid leakage of a fluorescent probe, calcein, from the inside of single egg PC-GUVs; after the leakage, the GUVs changed into small lumps of lipid membranes. On the other hand, phase-contrast microscopic images revealed the detailed process of the EGCg-induced burst of GUVs, the decrease in their diameter, and their transformation into small lumps. The dependence of the fraction of burst GUVs on EGCg concentration was almost the same as that of the fraction of leaked GUV. This correlation strongly indicates that the leakage of calcein from the inside to the outside of the GUV occurred as a result of the burst of the GUV. The fraction of completely leaked GUV and the fraction of the burst GUV increased with time and also increased with increasing EGCg concentration. We compared the EGCg-induced leakage from single GUVs with EGCg-induced leakage from a LUV suspension. The analysis of the EGCg-induced shape changes shows that the binding of EGCg to the external monolayer of the GUV increases its membrane area, inducing an increase in its surface pressure. Small angle x-ray scattering experiments indicate that the intermembrane distance of multilamellar vesicles of PC membrane greatly decreased at EGCg concentrations above the threshold, suggesting that neighboring membranes came in close contact with each other. On the basis of these results, we discuss the mechanism of the EGCg-induced bursting of vesicles.     

Antimicrobial Activities of Tocklai Vegetative Tea Clones

Thirty-one Tocklai vegetative (TV) tea clones contained caffeine and total catechin 44.39 and 227.55 mg/g dry weight of leaves, respectively. The (−)-epigallocatechin gallate (EGCG) was the most abundant (109.60 mg/g) followed by -(−)-epigallocatechin (EGC, 44.54 mg/g), (−)-epicatechin gallate (ECG, 41.74 mg/g), (−)-epicatechin (EC, 27.42 mg/g) and +catechin (4.25 mg/g). Total catechins were highest in TV 20 (509.7 mg/g) and lowest in TV 6 (71.7 mg/g). The tea clones that contain high level of total catechin exhibited the strongest antimicrobial activity. Among caffeine and flavanol compounds, theaflavins (TF) present in black tea possess a similar antimicrobial potency as EC present in fresh leaves, and that the conversion of catechins to TF during fermentation in making black tea tends to alter their antimicrobial activities. The bioactive molecules other than catechins present in tea leaves may also contribute towards antimicrobial activity.     

Distinct effects of tea catechins on 6-hydroxydopamine-induced apoptosis in PC12 cells.

Green tea polyphenols have aroused considerable attention in recent years for preventing oxidative stress related diseases including cancer, cardiovascular disease, and degenerative disease. Neurodegenerative diseases are cellular redox status dysfunction related diseases. The present study investigated the different effects of the five main components of green tea polyphenols on 6-hydroxydopamine (6-OHDA)-induced apoptosis in PC12 cells, the in vitro model of Parkinson's disease (PD). When the cells were treated with five catechins respectively for 30 min before exposure to 6-OHDA, (-)-epigallocatechins gallate (EGCG) and (-)-epicatechin gallate (ECG) in 50-200 microM had obvious concentration-dependent protective effects on cell viability, while (-)-epicatechin (EC), (+)-catechin ((+)-C), and (-)-epigallocatechin (EGC) had almost no protective effects. The five catechins also showed the same pattern described above of the different effects against 6-OHDA-induced cell apoptotic characteristics as analyzed by cell viability, fluorescence microscopy, flow cytometry, and DNA fragment electrophoresis methods. The present results indicated that 200 microM EGCG or ECG led to significant inhibition against typical apoptotic characteristics of PC12 cells, while other catechins had little protective effect against 6-OHDA-induced cell death. Therefore, the classified protective effects of the five catechins were in the order ECG> or = EGCG>EC> or = (+)-C>EGC. The antiapoptotic activities appear to be structurally related to the 3-gallate group of green tea polyphenols. The present data indicate that EGCG and ECG might be potent neuroprotective agents for PD.     

The synaptonemal complex is assembled by a polySUMOylation-driven feedback mechanism in yeast

During meiotic prophase I, proteinaceous structures called synaptonemal complexes (SCs) connect homologous chromosomes along their lengths via polymeric arrays of transverse filaments (TFs). Thus, control of TF polymerization is central to SC formation. Using budding yeast, we show that efficiency of TF polymerization closely correlates with the extent of SUMO conjugation to Ecm11, a component of SCs. HyperSUMOylation of Ecm11 leads to highly aggregative TFs, causing frequent assembly of extrachromosomal structures. In contrast, hypoSUMOylation leads to discontinuous, fragmented SCs, indicative of defective TF polymerization. We further show that the N terminus of the yeast TF, Zip1, serves as an activator for Ecm11 SUMOylation. Coexpression of the Zip1 N terminus and Gmc2, a binding partner of Ecm11, is sufficient to induce robust polySUMOylation of Ecm11 in nonmeiotic cells. Because TF assembly is mediated through N-terminal head-to-head associations, our results suggest that mutual activation between TF assembly and Ecm11 polySUMOylation acts as a positive feedback loop that underpins SC assembly.     

Dose-dependent suppression of tea catechins with a galloyl moiety on postprandial hypertriglyceridemia in rats

Tea has long been believed to be a healthy beverage, and its beneficial effects are almost all attributed to catechins. The effect of catechins on postprandial hypertriglyceridemia in rats was investigated in this study. A lipid emulsion administered orally to rats with (-)-epigallocatechin gallate at a dose of 100 mg/kg resulted in the increase in plasma triacylglycerol being significantly inhibited after 1 and 2 h compared to the case without (-)-epigallocatechin gallate. The effect of (-)-epigallocatechin was weaker than that of (-)-epigallocatechin gallate. A tea extract (THEA-FLAN 90S), mainly composed of catechins with a galloyl moiety, dose-dependently suppressed postprandial triacylglycerol after the administration of a lipid emulsion at doses of 50-200 mg/kg. The administration of the tea extract alone at a dose of 200 mg/kg had no effect on the plasma triacylglycerol level. These results strongly suggest that catechins with a galloyl moiety would be promising agents for suppressing dietary fat absorption through the small intestine.     

ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers

The purpose of this study is to examine the relationship between the free radical scavenging activities and the chemical structures of tea catechins ((-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)) and their corresponding epimers ((-)-gallocatechin gallate (GCG), (-)-gallocatechin (GC) and (+)-catechin ((+)-C)). With electron spin resonance (ESR) we investigated their scavenging effects on superoxide anions (O-.2) generated in the irradiated riboflavin system, singlet oxygen(1O2) generated in the photoradiation-hemoporphyrin system, the free radicals generated from 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. The results showed that the scavenging effects of galloylated catechins (EGCG and GCG) on the four free radicals were stronger than those of nongalloylated catechins (EGC, GC, EC, (+)-C), and the scavenging effects of EGC and GC were stronger than those of EC and (+)-C. Thus, it is suggested that the presence of the gallate group at the 3 position plays the most important role in their free radical-scavenging abilities and an additional insertion of the hydroxyl group at the 5' position in the B ring also contributes to their scavenging activities. Moreover, the corresponding phenoxyl radicals formed after the reaction with O-.2 were trapped by DMPO and the ESR spectra of DMPO/phenoxyl radical adducts were observed (aN=15.6 G and aHbeta=21.5 G). No significant differences were found between the scavenging effects of the catechins and their epimers when their concentrations were high. However, significant differences were observed at relatively low concentrations, and the lower their concentrations, the higher the differences. The scavenging abilities of GCG, GC and (+)-C were stronger than those of their corresponding epimers (EGCG, EGC and EC). The differences between their sterical structures played a more important role in their abilities to scavenge large free radicals, such as the free radicals generated from AAPH and the DPPH radical, than to scavenge small free radicals, such as O-.2 and 1O2, especially in the case with EGCG and GCG with more bulky steric hindrance.     

Alternative pathway implicated as an influencing factor in the synthesis of theaflavin

The principal pigments present in black tea, theaflavins (TF), have been indicated to be of potential clinical significance in various fields of research which has been hampered by the very low levels of TFs from black tea extractions, being the original method employed to acquire TFs. Forelle pear (44?µM TF/g dry weight/h) and Yacon leaf (65?µM TF/g dry weight/h) homogenates were tested for their TF synthesis capacity and found to have a larger TF synthesis capacity than a green tea leaf homogenate (26?µM TF/g dry weight/h) based upon the flavognost method. In an incubation system of green tea leaf extract utilizing endogenous enzymes present in Forelle pear and Yacon homogenates to synthesize TF, the formation of an unknown peak [m/z 563.1349; (23.95)⁵; C₂₆H₂₈O₁₄] was detected by mass spectrometry with a molecular mass similar to TF. This is in contrast to TF being solely synthesized in an in vitro model incubation system using isolated catechins and purified Forelle pear polyphenol oxidase. The preferential formation of the unknown compound could explain the low levels of TFs in black tea.     

Effects of external factors on the interaction of tea catechins with lipid bilayers

Green tea contains a high concentration of such catechins as (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg). Their biological activities have been evaluated by in vitro experiments using cultured cells or bacteria, but the order of activity of the various catechins differed with the study. We have been studying the interaction of tea catechins with lipid bilayers, and clarified that the number of hydroxyl groups on the B-ring, the presence of the galloyl moiety, and the stereochemical structure of each catechin govern their affinity for lipid bilayers. We investigated in this present study the effects of various external factors on the affinity of tea catechins for lipid bilayers by using liposomes as model membranes. The amount of tea catechins incorporated into the lipid bilayers increased with increasing salt concentration in an aqueous medium and decreased with increasing negative electric charge of the lipid bilayers. Furthermore, the amount of EGCg or ECg incorporated into the lipid bilayers increased with increasing EC concentration. These results reveal that the salt concentration in an aqueous medium, the electric charge of the membrane, and the presence of other catechins governed the affinity of tea catechins for the lipid bilayers.     

双液相系统酶化学技术制取茶色素

应用双液相酶化学技术研究茶色素的形成与制取,并以单液（水）相系统进行茶多酚酶促氧化制取茶色素为对照,引入氧载体后,构成了双液相酶化学氧化系统,对其中溶解氧浓度,PPO活性,TFs,TRs含量的变化和HPLC图谱等分析研究,制品中TFs的HPLC图谱可知：TOP－1中TFs的峰高和峰面积均高于TOP－2制品中TFs,尤以TFG与TFDG较高,TOP－1制品中儿茶素类残留量较对照少,尤其是简单儿茶素的列留量（如DL－C（－）－EC）少得更多。     

O-methylated catechins from tea leaves inhibit multiple protein kinases in mast cells

Tea contains a variety of bioactive compounds. In this study, we show that two O-methylated catechins, (-)-epigallocatechin-3-O-(3-O-methyl) gallate and (-)-epigallocatechin-3-O-(4-O-methyl) gallate, inhibit in vivo mast cell-dependent allergic reactions more potently than their nonmethylated form, (-)-epigallocatechin-3-O-gallate. Consistent with this, these O-methylated catechins inhibit IgE/Ag-induced activation of mouse mast cells: histamine release, leukotriene release, and cytokine production and secretion were all inhibited. As a molecular basis for the catechin-mediated inhibition of mast cell activation, Lyn, Syk, and Bruton's tyrosine kinase, the protein tyrosine kinases, known to be critical for early activation events, are shown to be inhibited by the O-methylated catechins. In vitro kinase assays using purified proteins show that the O-methylated catechins can directly inhibit the above protein tyrosine kinases. These catechins inhibit IgE/Ag-induced calcium response as well as the activation of downstream serine/threonine kinases such as Akt and c-Jun N-terminal kinase. These observations for the first time have revealed the molecular mechanisms of antiallergic effects of tea-derived catechins.