Takami Kakuda

Inhibiting Effects of Theanine on Caffeine Stimulation Evaluated by EEG in the Rat

In this study, the inhibiting action of theanine on the excitation by caffeine at the concentration regularly associated with drinking tea was investigated using electroencephalography (EEG) in rats. First, the stimulatory action by caffeine i.v. administration at a level higher than 5 μmol/kg (0.970 mg/kg) b.w. was shown by means of brain wave analysis, and this level was suggested as the minimum dose of caffeine as a stimulant. Next, the stimulatory effects of caffeine were inhibited by an i.v. administration of theanine at a level higher than 5 μmol/kg (0.781 mg/kg) b.w., and the results suggested that theanine has an antagonistic effect on caffeine’s stimulatory action at an almost equivalent molar concentration. On the other hand, the excitatory effects were shown in the rat i.v. administered 1 and 2 μmol/kg (0.174 and 0.348 mg/kg) b.w. of theanine alone. These results suggested two effects of theanine, depending on its concentration.

Inhibition by Theanine of Binding of [3H]AMPA, [3H]Kainate, and [3H]MDL 105,519 to Glutamate Receptors

In an investigation of the mechanisms of the neuroprotective effects of theanine (γ-glutamylethylamide) in brain ischemia, inhibition by theanine of the binding of [3H](RS)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), [3H]kainate, and [3H](E)-3-(2-phenyl-2-carboxyethenyl)-4,6-dichloro-1-H-indole-2-carboxylic acid (MDL 105,519) to glutamate receptors was studied in terms of its possible inhibiting effects on the three receptor subtypes (AMPA, kainate, and NMDA glycine), with rat cortical neurons. Theanine bound the three receptors, but its IC50 of theanine was 80- to 30,000-fold less than that of L-glutamic acid.

Scavenging effect of tea catechins and their epimers on superoxide anion radicals generated by a hypoxanthine and xanthine oxidase system

Catechins are a major group of polyphenolic compounds contained in abundance in green tea. Using electron spin resonance spectroscopy along with a spin-trapping agent, the scavenging effect of tea catechins and their corresponding epimers against superoxide anion radicals generated by a hypoxanthine and xanthine oxidase reaction system was evaluated. The presence of 3′,4′,5′-trihydroxyl groups attached to the B-ring of the flavan skeleton of tea catechins elevated their radical-scavenging efficiency in comparison to those with 3′,4′-dihydroxyl groups. There were no significant differences between the four dominant tea catechins and their corresponding epimers with regard to radical-scavenging ability. Under the different spin-trapping agent concentrations, the sigmoid curves of reducing spin-trapping adducts produced by tea catechins were shifted leftward, suggesting that a likely possible action of tea catechins is to scavenge superoxide anion radicals directly, not to inhibit the function of xanthine oxidase. Although caffeine is also known as a major ingredient of tea, its superoxide anion radical-scavenging effect was much weaker than that of the catechin family. It is concluded that tea catechins and their epimers serve as powerful antioxidants for directly eliminating superoxide anion radicals, and may be useful in the prevention of diseases relating to in vivo oxidative stress. © 2000 Society of Chemical Industry

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.

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

We have previously shown that theanine (=γ‐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°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.

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.

Theanine, γ-glutamylethylamide, is metabolized by renal phosphate-independent glutaminase

Abstract The distribution of theanine-degrading activity in Wistar rats was examined and this activity was detected only in the kidney. Judging from polyacrylamide gel electrophoresis, theanine-degrading enzyme from rat kidney was purified almost to homogeneity. Theanine-degrading activity was co-purified with glutaminase activity, and the relative activity for theanine was about 85% of that for l -glutamine throughout purification. Substrate specificity of purified enzyme preparation coincided well with the data of phosphate-independent glutaminase [EC 3.5.1.2], which had been previously reported. It was very curious that γ-glutamyl methyl and ethyl esters were more effectively hydrolyzed than theanine and l -glutamine, in view of relative activity and K m value. It was suggested that γ-glutamyl moiety in theanine molecule was transferred to form γ-glutamylglycylglycine with relative ease in the presence of glycylglycine. On the other hand, purified phosphate-dependent glutaminase did not show theanine-degrading activity at all. Thus, it was concluded that theanine was hydrolyzed by phosphate-independent glutaminase in kidney and suggested that, as for the metabolic fate of theanine, its glutamyl moiety might be transferred by means of γ-glutamyl transpeptidase reaction to other peptides in vivo.

Antioxidative Activity of Water Extracts of Lagerstroemia speciosa Leaves

In order to develop naturally occurring antioxidants from edible plants, the antioxidative effect of hot water extracts of Lagerstroemia speciosa leaves, known by the Tagalog name of banaba in the Phillipines, was studied. The content of tannin in banaba extract was 36.8% in dry weight. Banaba extract showed strong antioxidative activity in a linoleic acid autoxidation system. Banaba extract was found to have a potent radical scavenging action on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and superoxide radicals (O(2-) ) generated by a hypoxanthine (HPX)/xanthine oxidase (XOD) system. In vitro lipid peroxidation of rat liver homogenate induced by tert-butyl hydroperoxide (BHP) was inhibited by the addition of banaba extract in a dose-dependent manner. From these results, banaba extract was demonstrated to be useful as an antioxidant or free radical scavenger to protect biological systems against oxidative stress.

バナバLagerstroemia speciosa (L.) Pers. のα-アミラーゼ阻害活性成分の単離, 及び定量分析

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.

Promotion of Both Proliferation and Neuronal Differentiation in Pluripotent P19 Cells with Stable Overexpression of the Glutamine Transporter slc38a1

Background We previously demonstrated the functional expression in newborn rat neocortical astrocytes of glutamine transporter (GlnT = slc38a1) believed to predominate in neurons over astroglia in the brain. In order to evaluate the possible role of this transporter in neurogenesis, we attempted to establish stable transfectants of GlnT in mouse embryonal carcinoma P19 cells endowed to proliferate for self-renewal and differentiate into progeny cells such as neurons and astroglia, in addition to in vitro pharmacological profiling of the green tea ingredient theanine, which is shown to be a potent inhibitor of glutamine transport mediated by GlnT in cultured neurons and astroglia. Methodology/Principal Findings The full-length coding region of rat GlnT was inserted into a vector for gene transfection along with selection by G418, followed by culture with all-trans retinoic acid under floating conditions and subsequent dispersion for spontaneous differentiation under adherent conditions. Stable overexpression of GlnT led to marked increases in the size of round spheres formed during the culture for 4 days and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide reduction, with concomitant promotion of subsequent differentiation into cells immunoreactive for a neuronal marker protein. In these stable GlnT transfectants before differentiation, drastic upregulation was seen for mRNA expression of several proneural genes with a basic helix-loop-helix domain such as NeuroD1. Although a drastic increase was seen in NeuroD1 promoter activity in stable GlnT transfectants, theanine doubled NeuroD1 promoter activity in stable transfectants of empty vector (EV), without affecting the promoter activity already elevated in GlnT transfectants. Similarly, theanine promoted cellular proliferation and neuronal differentiation in stable EV transfectants, but failed to further stimulate the acceleration of both proliferation and neuronal differentiation found in stable GlnT transfectants. Conclusions/Significance GlnT would promote both proliferation and neuronal differentiation through a mechanism relevant to the upregulation of particular proneural genes in undifferentiated P19 cells.