Yuko Yamazaki

Jumonji University, Saitama, Saitama, Japan

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Publications (5)8.15 Total impact

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    ABSTRACT: In an attempt to develop d-sorbose as a new sweetener that could help in preventing lifestyle-related diseases, we investigated the inhibitory effect of d-sorbose on disaccharidase activity, using the brush border membrane vesicles of rat small intestines. The inhibitory effect was compared with that of l-sorbose and other rare sugars, and the small intestinal disaccharidases in rats was compared with that of humans as well. In humans and the small intestines of rats, d-sorbose strongly inhibited sucrase activity and weakly inhibited maltase activity. Inhibition by d-sorbose of sucrase activity was similar to that of l-arabinose, and the Ki of d-sorbose was 7.5 mM. Inhibition by d-sorbose was very strong in comparison with that of l-sorbose (Ki, 60.8 mM), whereas inhibition of d-tagatose was between that of d-sorbose and l-sorbose. The inhibitory mode of d-sorbose for sucrose and maltase was uncompetitive, and that of l-sorbose was competitive. To determine a suppressive effect on postprandial blood levels of glucose and insulin via inhibition of sucrase activity, sucrose solution with or without d-sorbose was administered to rats. Increments in the blood levels of glucose and insulin were suppressed significantly after administration of sucrose solution with d-sorbose to rats, in comparison to administration of sucrose solution without d-sorbose. In contrast, the suppressive effect of l-sorbose on postprandial blood levels of glucose and insulin was very weak. These results suggest that d-sorbose may have an inhibitory effect on disaccharidase activity and could be used as a sweetener to suppress the postprandial elevation of blood levels of glucose and insulin. The use of d-sorbose as a sweetener may contribute to the prevention of lifestyle-related diseases, such as type 2 diabetes mellitus.
    Nutrition research (New York, N.Y.). 09/2014;
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    ABSTRACT: Coleus forskohlii root extract (CFE) is popular for use as a weight loss dietary supplement. In this study, the influence of standardized CFE containing 10% active component forskolin on the hepatic drug metabolizing system was investigated to evaluate the safety through its drug interaction potential. Male ICR mice were fed AIN93G-based diets containing 0-5% CFE or 0.05% pure forskolin for 2-3 weeks. Intake of two different sources of 0.5% CFE significantly increased the relative liver weight, total content of hepatic cytochrome P450 (CYP) and induced CYPs (especially 2B, 2C, 3A types) and glutathione S-transferase (GST) activities. CFE significantly increased mRNA expression of CYPs and GST with dose related responses. However, unlike the CFE, intake of 0.05% pure forskolin was found to be associated with only weak induction in CYP3A and GST activities with no significant increases in relative liver weight, total hepatic content or other CYPs activities. The inductions of CYPs and GST by CFE were observed at 1 week of feeding and rapidly recovered by discontinuation of CFE. These results indicated the induction potential of CFE on CYPs, and that this effect was predominantly due to other, as yet unidentified constituents, and not forskolin contained in CFE.
    Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association 12/2011; 50(3-4):750-5. · 2.99 Impact Factor
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    ABSTRACT: A single dose by gavage of bilobalide (30 mg/kg) was found to produce a time-dependent induction of hepatic cytochrome P450 (CYP) enzyme activity and protein expression in rats. An RT-PCR study further showed that mRNA expression of CYP2B was maximal at 6 h. Plasma and liver bilobalide concentration in rats following administration of Ginkgo biloba extract equivalent to bilobalide of approximately 40 mg/kg showed a similar response to that exhibited by mRNA expression. These findings suggest that bilobalide markedly induced hepatic CYPs, but the induction could be mitigated due to rapid elimination from the liver.
    Journal of Pharmacological Sciences 04/2009; 109(3):459-62. · 2.15 Impact Factor
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    ABSTRACT: Commercial products containing the kava plant (Piper methysticum), known to have the anxiolytic activity, are banned in several European countries and Canada because of the suspicion of a potential liver toxicity. In some reports, kava and kavalactones (major constituents of kava) inhibited activities of cytochrome P450 (CYP) isoforms including CYP1A2. On the other hand, a few studies showed that administration of kava to rats moderately increased CYP1A2 proteins in the liver. CYP1A isoforms are likely responsible for the metabolic activation of potent carcinogenic environmental toxins such as aflatoxins, benzo[a]pyrene, and others. On these bases, we have investigated the effects of administration of commercial kava products on gene expression of hepatic CYP1A isoforms in rats. A high dose (equivalent to approximately 380 mg kavalactones/kg/day; 100 times of the suggested dosage for human use) of two different types of kava products for 8 days significantly increased liver weights. CYP1A2 mRNA expression was moderately increased (2.8–7.3 fold). More importantly, the high dose of kava markedly enhanced CYP1A1 mRNA expression (75–220 fold) as well as ethoxyresorufin O-deethylase activities and CYP1A1 immunoreactivities. Thus, no observed adverse effect levels of kavalactones would be lower than 380 mg/kg/day. When the safety factor of kavalactones is assumed to be 100, a value most often used upon the risk analysis of chemicals and designed to account for interspecies and intraspecies variations, a number of kava product users likely ingest more kavalactones than acceptable daily intakes. Based on overall evidence, we should pay considerable attention to the possibility that kava products induce hepatic CYP1A1 expression in human especially in sensitive individuals.
    Food and Chemical Toxicology 01/2008; · 3.01 Impact Factor
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    ABSTRACT: Currently, adverse reactions to herbal remedies as the result of herb-drug interactions have received a great deal of attention. GBE, one of popular herbal medicine, is used by elderly people for treatment such as dementia. People who take GBE tend to be elderly, and GBE-drug interactions are a matter of concern. Our previous studies showed existence of GBE-drug interaction via induction of hepatic CYPs [1,2]. As GBE is a natural product, exact components of GBE may vary among products. For clear understanding of GBE-drug interactions and better use of GBE, it is necessary to identify and characterize the mode of action of substance responsible for inducing CYPs. In this study, fractionated GBE samples were prepared and orally given to mice to identify the substance inducing CYPs. It was found that terpenoid fraction, particularly bilobalide rich fraction, showed highest CYP inducing activity. When several terpenoids of GBE (ginkgolide A, B, C and bilobalide) were orally given to mice for 5 days, marked induction of CYPs was detected by bilobalide, but not by other terpenoids. Details of enzyme induction by bilobalide were examined in rats by analyzing hepatic CYPs activity and mRNA expression. Oral administration of bilobalide increased CYPs activity at 6-24 hr post treatment, and increased mRNA expression at 6 hr. When bilobalide in blood was monitored in rats given excess GBE, the concentration increased about 1-2 hr and decreased to the undetectable level at 24 hr. These findings suggest that bilobalide in GBE cause a remarkable induction of CYPs and may cause interaction with drugs, but the interaction could be easily eliminated by stopping the intake. It will be necessary to standardize bilobalide content in GBE products to avoid GBE-drug interaction. 1. Sugiyama T et al., Life Sci; 75: 1113-22(2004). 2. Uchida S et al., J Clin Pharmacol; 46: 1290-8(2006).
    2nd Asian Pacific Regional International society for the study of xenobiotics Meeting;