Akio Sugimoto

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

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.

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.

Pectic Enzymes Related with the Formation of Coagulum in Carrot Juice

This study was conducted to investigate the relationship between several blanching conditions and remaining enzyme activities, especially pectinesterase (PE) and polygalacturonase (PG), on the formation of coagulum. Eight commercial enzyme preparations were added to carrot juice, and PE or PG caused coagulum formation while the other six enzymes had no effect. Since the endogenous activities of PE and PG were also observed in carrots, these activities were believed to be a major cause of coagulum formation. Coagulum formation was prevented under blanching conditions above 70°C, at this temperature, PE activity was inactivated, and PG activity was reduced about 60% in relation to the non-blanching juice. Since blanching in a 0.02 M citric acid solution (pH 2.4) at 60°C prevented the formation of coagulum, blanching under low pH conditions was more effective. Although PE activity was not reduced in relation to blanching in water at 60°C, the reduction of PG activity was 14%. These results lead to the conclusion that coagulum formation in carrot juice depended on the remaining activities of both PE and PG and that to prevent coagulum these enzyme activities must be suppressed.