Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction.

Theanine (γ-glutamylethylamide) characteristically present in tea leaves (Camellia sinensis). It has a similar chemical structure to glutamate, which is a neurotransmitter related to memory. Theanine passes through the blood-brain barrier and has been shown to have a cerebroprotective effect and a preventive effect on neuronal cell death after transient cerebral ischemia. The neuroprotective effect is partly due to the antagonistic action of theanine on glutamate receptor subtype AMPA and kainate receptors, but the affinity is very low. Theanine also acted on glutamine (Gln) transporter strongly and inhibited the incorporation of extracellular Gln into neurons, which in turn suppressed the conversion of Gln to glutamate by glutaminase, a reaction required for condensation into synaptic vesicles to form a neurotransmitter pool responsible for subsequent exocytotic release upon stimuli. In an investigation of elderly persons with normal or slight cognitive dysfunction, volunteers who ingested powdered green tea containing a high theanine concentration (equivalent to 47.5mgday(-1) of theanine) showed significantly lower decline in cognitive function compared with that of the placebo group. This result suggested that theanine might have improved a slight cognitive dysfunction in elderly persons.

Black-tea polyphenols suppress postprandial hypertriacylglycerolemia by suppressing lymphatic transport of dietary fat in rats.

Administration of black-tea polyphenols (BTP) at 100 and 200 mg/kg of body weight in rats suppressed postprandial hypertriacylglycerolemia in a dose-dependent manner. Administration of BTP also suppressed lymphatic recovery of (14)C-trioleoylglycerol in rats that were cannulated in the thoracic duct. BTP dose-dependently inhibited the activity of pancreatic lipase in vitro with an IC50 of 0.254 mg/mL. When purified theaflavins, which are components of BTP, were used, theaflavins with galloyl moieties, but not those without galloyl moiety, inhibited the activity of pancreatic lipase. Theaflavin-3,3'-digallate (TFDG) was more effective in inhibiting the activity of pancreatic lipase than epigallocatechin gallate (EGCG), epicatechin gallate (ECG), and a mixture of EGCG and ECG. BTP and TFDG had a similar effect in inhibiting the activity of pancreatic lipase when the total polyphenol amount was adjusted to the same. BTP had no effect on micellar solubility of hydrolysis products of triacylglycerol. These results suggest that BTP suppressed postprandial hypertriacylglycerolemia by reducing triacylglycerol absorption via the inhibition of pancreatic lipase activity.

Endothelium-dependent vasorelaxation effect of rutin-free tartary buckwheat extract in isolated rat thoracic aorta.

The aim of this study was to point out the potential of tartary buckwheat on vascular functions. A nonabsorbed fraction of hot-water extract of tartary buckwheat on a SP70 column (TBSP-T), which was free from rutin, was used for this aim. In a contractile experiment using Sprague-Dawley rat thoracic aorta rings contracted by 1.0 microM phenylephrine (PE) or 50 mM KCl, TBSP-T evoked a significant vasorelaxation [EC50 (mg/ml): PE; 2.2; KCl, 1.9]. By a further fractionation of TBSP-T by liquid-liquid partitioning into basic, neutral and acidic fractions, a marked enhancement of vasorelaxation effect was observed only for acidic fraction (EC50, 0.25 mg/ml). The action of acidic fraction was significantly attenuated in endothelium-denuded aortic rings and in the presence of nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (100 microM). The fraction also enhanced the cyclic guanosine monophosphate (cGMP) production in aortic rings contracted with PE [cGMP (pmol/mg protein): PE, 7.2+/-2.3; PE+Acidic fraction, 35+/-8]. These results indicate that acidic fraction could mediate NO/cGMP pathways, thereby exerting endothelium-dependent vasorelaxation action. In conclusion, tartary buckwheat was proven to regulate vascular tones and have latent acidic candidates except for rutin.

Theanine, an ingredient of green tea, inhibits [3H]glutamine transport in neurons and astroglia in rat brain.

We have previously shown that theanine (=gamma-glutamylethylamide), an ingredient of green tea, has a protective effect against ischemic neuronal death in the hippocampal CA1 region of the gerbil brain without affecting ligand binding to ionotropic receptor subtypes of the neurotransmitter glutamate structurally related to theanine. The neurotransmitter pool of glutamate is thought to be fueled by the entry of the other structural analog glutamine (Gln) and subsequent cleavage by glutaminase. Although theanine did not inhibit [3H]glutamate accumulation, [3H]theanine was actively accumulated in a temperature-dependent and saturable manner in rat brain synaptosomal fractions. The accumulation of [3H]theanine was markedly inhibited by Gln in a concentration-dependent manner, whereas [3H]Gln accumulation was inhibited by theanine vice versa. Both [3H]theanine and [3H]Gln accumulations were decreased after the replacement of sodium chloride with choline chloride, along with similarly high distribution profiles in telencephalic structures. A similar equilibrium was observed within 30 min at 30 degrees C for the accumulations of both [3H]theanine and [3H]Gln in cultured rat neocortical astroglia as well as neurons, whereas theanine inhibited [3H]Gln accumulation in a concentration-dependent manner at 0.1-10 mM. Furthermore, sustained exposure to 10 mM theanine led to a significant decrease in the level of extracellular glutamate released from cultured neurons. These results suggest that the green tea ingredient theanine would be an inhibitor of different transporters capable of transporting Gln across plasma membranes toward the modulation of the glutamate/Gln cycle required for the neurotransmitter pool of glutamate in neurons.

Analysis of tea catechins in human plasma by high-performance liquid chromatography with solid-phase extraction.

Accurate monitoring of tea catechins in biological samples might provide a means of better evaluation of their benefits. The aim of the present study was to develop a rapid method for extracting tea catechins from human plasma samples with a solid-phase extraction technique and to subsequently measure their concentrations using an HPLC system. A human plasma sample spiked with known concentrations of the analyte standards was passed through a Waters Oasis HLB cartridge. After repeated washing, tea catechins were eluted with 70% dimethylformamide containing 0.1% phosphoric acid, and the resulting eluate was injected into an HPLC system. Analytes were separated on a reverse-phase C18 column using an isocratic mobile phase and detected electrochemically. The coefficient of variation for inter- and intraday reproducibility was less than 5.0% and 6.4%, respectively. Linearity was established for the concentration range of 0.01-1.0 microM. The method was successfully applied to measure tea catechin concentrations in the plasma of two healthy subjects who received a single ingestion of a green tea beverage. The proposed method enables the rapid and accurate quantitation of plasma tea catechins and might prove useful for the evaluation of beneficial health effects of tea consumption.

Heat-epimerized tea catechins have the same cholesterol-lowering activity as green tea catechins in cholesterol-fed rats.

Tea catechins are known to be epimerized by heat treatment. The effect of heat-epimerized tea catechins on serum cholesterol concentration was compared with that of green tea catechins. Our observations strongly suggest that both tea catechins and heat-epimerized tea catechins lower serum cholesterol concentration by inhibiting cholesterol absorption in the intestine. There was no differential effect between the two catechin preparations.

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.

Sedative effects of the jasmine tea odor and (R)-(-)-linalool, one of its major odor components, on autonomic nerve activity and mood states.

We investigated the effects of the odor of jasmine tea on autonomic nerve activity and mood states in a total of 24 healthy volunteers. We used the odor of jasmine tea at the lowest concentration that could be detected by each subject but that did not elicit any psychological effects. R-R intervals and the POMS test were measured before and after inhalation of the odors for 5 min. Both jasmine tea and lavender odors at perceived similar intensity caused significant decreases in heart rate and significant increases in spectral integrated values at high-frequency component in comparison with the control (P < 0.05). In the POMS tests, these odors produced calm and vigorous mood states. We also examined the effects of (R)-(-)-linalool, one of its major odor components, at the same concentration as in the tea, and (S)-(+)-linalool. Only (R)-(-)-linalool elicited a significant decrease in heart rate (P < 0.05) and an increase in high-frequency component in comparison with the controls, and produced calm and vigorous mood states. Thus, the low intensity of jasmine tea odor has sedative effects on both autonomic nerve activity and mood states, and (R)-(-)-linalool, one of its components, can mimic these effects.

Effect of tea catechins on postprandial plasma lipid responses in human subjects.

Epidemiological surveys suggest that a higher intake of tea may be associated with a lower risk of CHD. There is accumulating evidence that postprandial lipaemia makes a substantial contribution to the incidence of CHD. Our aim was, therefore, to evaluate the effect of tea catechins (major ingredients in green tea) on postprandial lipid responses in human subjects after the consumption of test meals. In a randomized triple-crossover design, nine male subjects with mild or borderline hypertriacylglycerolaemia consumed 10 (control), 224 (moderate dose) and 674 mg (high dose) of the assigned tea catechins three times each along with a standardized light meal consisting of a piece of bread spread with 20 g butter. Plasma lipids were measured in the fasting state and 1, 2, 3, 4 and 6 h after consuming the light meal. Results showed that, compared with the control, moderate and high doses of tea catechins reduced the incremental area under the plasma triacylglycerol curves by 15.1 and 28.7%, respectively. Next, the rapid elevation of remnant-like particle cholesterol was significantly inhibited by a high dose of tea catechins 2 h after consuming the light meal (P<0.01). In the range of tea catechin dosages, no significant differences were observed in the postprandial responses for plasma total cholesterol or NEFA at any time point. In conclusion, this trial demonstrated that tea catechins attenuated the postprandial increase in plasma triacylglycerol levels following a fat load. These results may provide evidence for one of the possible mechanisms involved in lowering the incidence of CVD, and may prove useful in further studies on the beneficial health effects of tea drinking.

Dietary gallate esters of tea catechins reduce deposition of visceral fat, hepatic triacylglycerol, and activities of hepatic enzymes related to fatty acid synthesis in rats.

Tea catechins, rich in (-)-epigallocatechin gallate and (-)-epicatechin gallate, or heat-treated tea catechins in which about 50% of the (-)-epigallocatechin gallate and (-)-epicatechin gallate in tea catechins was epimerized to (-)-gallocatechin gallate and (-)-catechin gallate, were fed to rats at 1% level for 23 d. Visceral fat deposition and the concentration of hepatic triacylglycerol were significantly lower in the tea catechin and heat-treated tea catechin groups than in the control group. The activities of fatty acid synthase and the malic enzyme in the liver cytosol were significantly lower in the two catechin groups than in the control group. In contrast, the activities of carnitine palmitoyltransferase and acyl-CoA oxidase in the liver homogenate were not significantly different among the three groups. These results suggest that the reduction in activities of enzymes related to hepatic fatty acid synthesis by the feeding of tea catechins or heat-treated tea catechins can cause reductions of hepatic triacylglycerol and possibly of visceral fat deposition.

Tea catechins with a galloyl moiety suppress postprandial hypertriacylglycerolemia by delaying lymphatic transport of dietary fat in rats.

Tea catechins, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), have been shown to be epimerized to (-)-catechin (C), (-)-gallocatechin (GC), (-)-catechin gallate (CG), and (-)-gallocatechin gallate (GCG), respectively, during heat treatment. In this study, we examined the effect of tea catechins rich in ECG and EGCG and heat-treated tea catechins rich in CG and GCG on postprandial hypertriacylglycerolemia in rats. Both tea catechins and heat-treated tea catechins suppressed postprandial hypertriacylglycerolemia. Lymphatic recovery of (14)C-trioleoylglycerol in rats cannulated in the thoracic duct was delayed by the administration of tea catechins and heat-treated tea catechins. Tea catechins and heat-treated tea catechins had the same effect on all variables tested. These catechin preparations dose-dependently inhibited the activity of pancreatic lipase in vitro. When purified catechins were used, only those with a galloyl moiety inhibited the activity of pancreatic lipase. These results suggest that catechins with a galloyl moiety suppress postprandial hypertriacylglycerolemia by slowing down triacylglycerol absorption through the inhibition of pancreatic lipase. Because postprandial hypertriacylglycerolemia is a risk factor for coronary heart disease, our results suggest that catechins with a galloyl moiety may prevent this disease.

Xanthine oxidase inhibitors from the leaves of Lagerstroemia speciosa (L.) Pers.

Xanthine oxidase (XOD) is a key enzyme playing a role in hyperuricemia, catalyzing the oxidation of hypoxanthine to xanthine and then to uric acid. This study aimed to identify the XOD inhibitors from the leaves of Lagerstroemia speciosa (L.) Pers. (Lythraceae), which was traditionally used as a folk medicine in the Philippines. Using a bioassay-guided fractionation technique, two active compounds were isolated from the aqueous extracts of the Lagerstroemia speciosa leaves, namely valoneic acid dilactone (VAD) and ellagic acid (EA). The result demonstrated that the XOD-inhibitory effect of VAD was a stronger than that of allopurinol, a clinical drug used for XOD inhibitor, with a non-competitive mode for the enzyme with respect to xanthine as the substrate. These results may explain and support the dietary use of the aqueous extracts from Lagerstroemia speciosa leaves for the prevention and treatment of hyperuricemia.

Pigments in green tea leaves (Camellia sinensis) suppress transformation of the aryl hydrocarbon receptor induced by dioxin.

Environmental contaminants such as dioxins enter the body mainly through diet and cause various toxicities through transformation of the aryl hydrocarbon receptor (AhR). We previously reported that certain natural flavonoids at the dietary level suppress the AhR transformation induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In this study, we identified lutein and chlorophyll a and b from green tea leaves as the novel antagonists for AhR. These active compounds suppressed AhR transformation dose-dependently with the 50% inhibitory concentration (IC(50)) values against 0.1 nM TCDD-induced AhR transformation at 3.2, 5.0, and 5.9 microM, respectively. (-)-Epigallocatechin gallate, which is the most abundant flavonoid in green tea leaves, also showed stronger suppressive effects than did other major tea components, with the IC(50) value of 1.7 microM. Thus, these pigments of green tea leaves have the potential to protect from dioxin toxicity through the suppression of AhR transformation.

Heat-epimerized tea catechins rich in gallocatechin gallate and catechin gallate are more effective to inhibit cholesterol absorption than tea catechins rich in epigallocatechin gallate and epicatechin gallate.

It has been known that tea catechins, (-)-epicatechin (1), (-)-epigallocatechin (2), (-)-epicatechin gallate (3), and (-)-epigallocatechin gallate (4) are epimerized to(-)-catechin (5), (-)-gallocatechin (6), (-)-catechin gallate (7), and (-)-gallocatechin gallate (8), respectively, during retort pasteurization. We previously reported that tea catechins, mainly composed of 3 and 4, effectively inhibit cholesterol absorption in rats. In this study, the effect of heat-epimerized catechins on cholesterol absorption was compared with tea catechins. Both tea catechins and heat-epimerized catechins lowered lymphatic recovery of cholesterol in rats cannulated in the thoracic duct and epimerized catechins were more effective than tea catechins. The effect of purified catechins on micellar solubility of cholesterol was examined in an in vitro study. The addition of gallate esters of catechins reduced micellar solubility of cholesterol by precipitating cholesterol from bile salt micelles. Compounds 7 and 8 were more effective to precipitate cholesterol than 3 and 4, respectively. These observations strongly suggest that heat-epimerized catechins may be more hypocholesterolemic than tea catechins.

Autonomic nervous responses according to preference for the odor of jasmine tea.

The effect of jasmine tea odor on the autonomic nervous system was investigated by a power spectral analysis of the heart rate variability. We assigned eight volunteers to two groups with either a predilection for or antipathy toward the jasmine tea odor. We tested both high- and low-intensity jasmine tea odors. The low-intensity odor was produced by diluting 20-fold the jasmine tea used for the high-intensity odor test. The low-intensity odor produced an increase in parasympathetic nervous activity in both the predilection and antipathy groups. The high-intensity odor produced an increase in parasympathetic nervous activity in the predilection group, but an increase in sympathetic nervous activity in the antipathy group. The odor of Chinese green tea, a basic ingredient of jasmine tea, produced no effects similar to those of the jasmine tea odor. These results suggest that the jasmine tea odor activated the parasympathetic nerve, whereas the higher-intensity odor activated the sympathetic nerve in those subjects who disliked the odor.

[Isolation and quantitative analysis of the alpha-amylase inhibitor in Lagerstroemia speciosa (L.) Pers. (Banaba)].

Banaba [Lagerstroemia speciosa (L.) Pers.] has been used as a folk medicine for diabetes in the Philippines. Using bioassay-guided separation, valoneaic acid dilactone (1) was isolated from the leaves as a potent alpha-amylase inhibitor. A simple and efficient method for the quantitative determination of valoneaic acid and its derivatives in Banaba extract was established. Valoneaic acid exists as the structural part of the polyphenols, which like flosin A, reginin A, and lagerstroemin, are characteristic constituents of Banaba. These derivatives were hydrolyzed to valoneaic acid by HCl and extracted with 2-butanone. This extract was subjected to HPLC analysis, and the contents of valoneaic acid determined as the whole valoneaic acid contents. Using this method, the whole valoneaic acid contents were measured in eight Banaba leaf decoctions. The alpha-amylase-inhibiting activities of the decoctions were dependent on the whole valoneaic acid contents. In addition, a strong linear correlation was observed between the whole valoneaic acid contents and total polyphenol contents. This analytical procedure is applicable to the chemical evaluation of Banaba.

Neuroprotective effects of the green tea components theanine and catechins.

The neuroprotective effects of theanine and catechins contained in green tea are discussed. Although the death of cultured rat cortical neurons was induced by the application of glutamic acid, this neuronal death was suppressed with exposure to theanine. The death of hippocampal CA1 pyramidal neurons caused by transient forebrain ischemia in the gerbil was inhibited with the ventricular preadministration of theanine. The neuronal death of the hippocampal CA3 region by kainate was also prevented by the administration of theanine. Theanine has a higher binding capacity for the AMPA/kainate receptors than for NMDA receptors, although the binding capacity in all cases is markedly less than that of glutamic acid. The results of the present study suggest that the mechanism of the neuroprotective effect of theanine is related not only to the glutamate receptor but also to other mechanisms such as the glutamate transporter, although further studies are needed. One of the onset mechanisms for arteriosclerosis, a major factor in ischemic cerebrovascular disease, is probably the oxidative alteration of low-density lipoprotein (LDL) by active oxygen species. The oxidative alterations of LDL were shown to be prevented by tea catechins. Scavenging of *O(2)(-) was also exhibited by tea catechins. The neuroprotective effects of theanine and catechins contained in green tea are a focus of considerable attention, and further studies are warranted.

Identification of potent odorants in Chinese jasmine green tea scented with flowers of Jasminum sambac.

The odorants in Chinese jasmine green tea scented with jasmine flowers (Jasminum sambac) were separated from the infusion by adsorption to Porapak Q resin. Among the 66 compounds identified by GC and GC/MS, linalool (floral), methyl anthranilate (grape-like), 4-hexanolide (sweet), 4-nonanolide (sweet), (E)-2-hexenyl hexanoate (green), and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (sweet) were extracted as potent odorants by an aroma extract dilution analysis and sensory analysis. The enantiomeric ratios of linalool in jasmine tea and Jasminum sambac were determined by a chiral analysis for the first time in this study: 81.6% ee and 100% ee for the (R)-(-)-configuration, respectively. The jasmine tea flavor could be closely duplicated by a model mixture containing these six compounds on the basis of a sensory analysis. The omission of methyl anthranilate and the replacement of (R)-(-)-linalool by (S)-(+)-linalool led to great changes in the odor of the model. These two compounds were determined to be the key odorants of the jasmine tea flavor.