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Articles by Y Nagamatsu
Total Records ( 6 ) for Y Nagamatsu
  Y Shitara , Y Nagamatsu , S Wada , Y Sugiyama and T. Horie
 

Cyclosporin A (CsA) is a well known inhibitor of the organic anion-transporting polypeptide (OATP/Oatp) family transporters, causing a large number of transporter-mediated drug-drug interactions in clinical situations. In the present study, we examined the inhibitory effect of CsA on the hepatic uptake of sulfobromophthalein (BSP) in rats, focusing on a long-lasting inhibition. Twenty-one hours after the subcutaneous administration of CsA, the hepatic clearance of BSP was decreased. The liver uptake index study revealed that hepatic uptake of BSP was reduced in CsA-treated rats for at least 3 days. Comparison of uptake studies using isolated hepatocytes prepared from control and CsA-treated rats showed that hepatic uptake in CsA-treated rats was decreased. In primary cultured hepatocytes, after preincubation with CsA, the uptake of [3H]BSP was reduced even after removal of CsA from the incubation buffer although a preincubation time dependence was not observed. However, the expression of Oatp1a1 and Oatp1b2, which are involved in the hepatic uptake of BSP, and the amount of intrahepatic glutathione, a driving force of Oatp1a1, did not change in CsA-treated rats. Thus, we can conclude that CsA modulates the transporter function sustainably. It can cause a potent in vivo drug-drug interaction. The modulation of transporters is not caused by reduced expression or driving force of transporters. It may be affected by CsA accumulated in the liver or its metabolites. The inhibitory effect of CsA on the transporter-mediated uptake of BSP cannot be explained by a simple competitive mechanism and a novel mechanism should be considered.

  Y Shitara , Y Nagamatsu , S Wada , Y Sugiyama and T. Horie
 

Cyclosporin A (CsA) is a well known inhibitor of the organic anion-transporting polypeptide (OATP/Oatp) family transporters, causing a large number of transporter-mediated drug-drug interactions in clinical situations. In the present study, we examined the inhibitory effect of CsA on the hepatic uptake of sulfobromophthalein (BSP) in rats, focusing on a long-lasting inhibition. Twenty-one hours after the subcutaneous administration of CsA, the hepatic clearance of BSP was decreased. The liver uptake index study revealed that hepatic uptake of BSP was reduced in CsA-treated rats for at least 3 days. Comparison of uptake studies using isolated hepatocytes prepared from control and CsA-treated rats showed that hepatic uptake in CsA-treated rats was decreased. In primary cultured hepatocytes, after preincubation with CsA, the uptake of [3H]BSP was reduced even after removal of CsA from the incubation buffer although a preincubation time dependence was not observed. However, the expression of Oatp1a1 and Oatp1b2, which are involved in the hepatic uptake of BSP, and the amount of intrahepatic glutathione, a driving force of Oatp1a1, did not change in CsA-treated rats. Thus, we can conclude that CsA modulates the transporter function sustainably. It can cause a potent in vivo drug-drug interaction. The modulation of transporters is not caused by reduced expression or driving force of transporters. It may be affected by CsA accumulated in the liver or its metabolites. The inhibitory effect of CsA on the transporter-mediated uptake of BSP cannot be explained by a simple competitive mechanism and a novel mechanism should be considered.

  Y Ishibashi , Y Nagamatsu , S Meyer , A Imamura , H Ishida , M Kiso , N Okino , R Geyer and M. Ito
 

Although 6-gala series glycosphingolipids possessing R-Gal (/β) 1-6Galβ1-1'Cer have been found in some mollusks, pathogenic parasites, and fungi, their physiological functions and metabolic pathway are not fully understood. We described a novel method of detecting 6-gala series glyco- sphingolipids utilizing the specificity of endogalactosylceramidase (EGALC), which is capable of hydrolyzing 6-gala series glycosphingolipids to produce intact oligosaccharides and ceramides. EGALC catalyzes not only hydrolysis but also a transglycosylation reaction. In the latter reaction, EGALC transfers oligosaccharides from the glycosphingolipids to acceptors such as fluorescent 1-alkanols. Based on the transglycosylation reaction of EGALC, a specific, easy, fast, sensitive, and reproducible method of detecting 6-gala series glycosphingolipids was developed using NBD-pentanol as an acceptor. The fluorescent products, NBD-pentanol-conjugated 6-gala oligosaccharides, were separated and detected by TLC or HPLC with a fluorescent detector. Moreover, it was revealed that as well as glycosphingolipids, a glycoglycerolipid, digalactosyldiacylglycerol, was utilized by EGALC as a donor substrate. This method was successfully applied to detect 6-gala series glycosphingolipids in a fungus, Rhizopus oryzae, and a parasite, Taenia crassiceps. The method would be useful for studying glycosphingolipids and galactosyl glycerolipids which share the Gal (/β) 1-6Gal structure.

 
 
 
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