Results in the present study indicate that all MDR1 stably expressing cells have efflux activity for various P-gp substrates, and that interspecies differences and similarities of the P-gp substrate efflux activity may exist.

TAK-875 is a selective G-protein-coupled receptor 40 agonist in development for the treatment of type 2 diabetes mellitus. This randomized, double-blind, placebo-controlled study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of TAK-875 following administration of a single oral dose of TAK-875 (25-800 mg) in 60 healthy volunteers. TAK-875 was eliminated slowly with a mean terminal elimination t(1/2) of approximately 28.1 to 36.6 hours. Systemic exposure of TAK-875 did not exhibit dose-proportional increases across the dose range evaluated due to a greater than proportional increase in exposure at doses greater than 200 mg. A preliminary food effect assessment indicated that coadministration of TAK-875 with a high-fat meal decreased C(max) of TAK-875 by 40% and AUC by 17%. Clinical adverse experiences were generally mild and transient. No dose-dependent pattern was observed. In healthy volunteers, no glucose-lowering effect and no increase in insulin or c-peptide secretion were evident following administration of TAK-875; the frequency of plasma glucose concentrations <70 mg/dL was similar in the TAK-875 and pooled placebo groups. TAK-875 was well tolerated in the study and has pharmacokinetic characteristics suitable for a once-daily regimen. The pharmacodynamic data support the notion that TAK-875, if effective in diabetic patients, may bear a low risk of hypoglycemia.

No abstract

ABSTRACT:CYP2C9 and CYP2C19 are clinically important drug-metabolizing enzymes. The expression level of CYP2C9 is much higher than that of CYP2C19, although the factor(s) responsible for the difference between the expression levels of these genes is still unclear. It has been reported that hepatocyte nuclear factor 4␣ (HNF4␣) plays an important role in regulation of the expression of liver-enriched genes, including P450 genes. Thus, we hypothesized that HNF4␣ contributes to the difference between the expression levels of these genes. Two direct repeat 1 (DR1) elements were located in both the CYP2C9 and CYP2C19 promoters. The upstream and downstream elements in these promoters had the same sequences, and HNF4␣ could bind to both elements in vitro. The transactivation levels of constructs containing two DR1 elements of the CYP2C9 promoter were increased by HNF4␣, whereas those of the CYP2C19 promoter were not increased. The introduction of mutations into either the upstream or downstream element in the CYP2C9 gene abolished the responsiveness to HNF4␣. We also examined whether HNF4␣ could bind to the promoter regions of the CYP2C9 and the CYP2C19 genes in vivo. The results of chromatin immunoprecipitation assays showed that HNF4␣ could bind to the promoter region of the CYP2C9 gene but not to that of the CYP2C19 promoter in the human liver. Taken together, our results suggest that HNF4␣ is a factor responsible for the difference between the expression levels of CYP2C9 and CYP2C19 in the human liver.

No abstract

The absorption, distribution, metabolism, and excretion of fasiglifam were investigated in rats, dogs, and humans. The absolute oral bioavailability of fasiglifam was high in all species (>76.0%). After oral administration of [C]fasiglifam, the administered radioactivity was quantitatively recovered and the major route of excretion of radioactivity was via feces in all species. Fasiglifam was a major component in the plasma and feces in all species. Its oxidative metabolite (M-I) was observed as a minor metabolite in rat and human plasma (<10% of plasma radioactivity). In human plasma, hydroxylated fasiglifam (T-1676427), the glucuronide of fasiglifam (fasiglifam-G), and the glucuronide of M-I were detected as additional minor metabolites (<2% of plasma radioactivity). None of these metabolites were specific to humans. Fasiglifam-G was the major component in the rat and dog bile. In vitro cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) reaction phenotyping indicated that oxidation (to form M-I and T-1676427) and glucuronidation of fasiglifam are mainly mediated by CYP3A4/5 and UGT1A3, respectively. Fasiglifam and fasiglifam-G are substrates of BCRP and Mrp2/MRP2, respectively. Glucuronidation of fasiglifam-G was found to be the predominant elimination pathway of fasiglifam in all species tested, including humans.

No abstract

ABSTRACT:The ligand-binding domain of human pregnane X receptor (hPXR) is highly hydrophobic and flexible, allowing promiscuity in accepting structurally diverse ligands. However, little information is available regarding the critical substituents of compounds involved in the activation of hPXR. The aim of this study was to determine the structure-activity relationships for hPXR-mediated transactivation by barbiturates, hydantoins, and macrolide antibiotics. Most of the barbiturates studied (mephobarbital, pentobarbital, phenobarbital, etc.) activated hPXR. However, barbital, which has a low hydrophobic moiety at the 5-position, and primidone, which has no carbonyl moiety at the 2-position, did not activate hPXR. Therefore, a hydrophobic moiety at the 5-position and a hydrogen-bond acceptor being sufficiently separated from the phenyl-ring are responsible for activation of hPXR by barbiturates. In the case of hydantoins, only mephenytoin and ethotoin, which have an alkylchain at the R1-position, strongly activated hPXR at 300 M. Phenytoin and 5-(4-methylphenyl)-5-phenylhydantoin, which contain a phenyl or methylphenyl group at both R2-and R3-positions, also activated hPXR, whereas 5-(4-hydroxyphenyl)-5-phenylhydantoin did not activate the receptor. These results suggest that the presence of an alkyl-chain at the R1-position and the presence of bulky and hydrophobic moieties at both R2-and R3-positions are important factors for activation of hPXR by hydantoins. In the case of macrolide antibiotics, troleandomycin, but not oleandomycin, showed significant activation of hPXR. Therefore, triacetate esterification of oleandomycin might increase the hydrophobicity and enhance the activation of hPXR. These findings suggest that hydrophobicity of the ligand and adequate distance between the hydrogen-bond acceptor and the hydrophobic group are important for hPXR activation.