Multidrug and toxin extrusion (MATE) 1 and MATE2-K, H⁺/organic cation antiporters, are located at the brush-border membrane of renal proximal tubules. The present study aimed to clarify the role of MATE transporters in tubular secretion of varenicline. Varenicline at a dose of 5 mg/kg was administered to wild-type and Mate1-knockout mice via the jugular vein, and its uptake was measured by high-performance liquid chromatography. The renal secretory clearance of and systemic exposure to varenicline were significantly decreased (54.6%, p < 0.05) and increased (116%, p < 0.05) respectively, by the genetic disruption of Mate1 in mice. Uptake of varenicline and [¹⁴C]tetraethylammonium (TEA) was examined in HEK293 cells transiently expressing the human (h) MATE1, hMATE2-K, mouse (m) MATE1, and hOCT2 basolateral organic cation transporter. [¹⁴C]TEA uptake in HEK293 cells expressing MATE transporters and hOCT2 was decreased in the presence of varenicline. The calculated IC₅₀ values for hMATE1, hMATE2-K, mMATE1, and hOCT2 were 62.2 ± 6.5, 122.3 ± 67.6, 255.0 ± 37.9, and 1,003.9 ± 135.8 (µM; mean ± S.E. for three separate experiments), respectively. Varenicline uptake was significantly increased in HEK293 cells expressing mMATE1, hMATE1, or hMATE2-K cDNA as well as hOCT2 compared to empty vector-transfected cells. In conclusion, renal MATE transporters were found to be responsible for renal tubular secretion of varenicline.

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In this study, we elucidated the effect of poly(amino acid)s such as poly-L-ornithine (PLO) on FITC-insulin uptake in cultured alveolar type II epithelial cells, RLE-6TN. FITC-insulin uptake by RLE-6TN cells as well as its cell surface binding was markedly increased by PLO without cytotoxicity. The uptake of FITC-insulin in the presence of PLO was shown to be mediated by endocytosis, but in contrast to the uptake in the absence of PLO, the contribution of macropinocytosis emerged. Colocalization of FITC-insulin and LysoTracker Red was observed by confocal laser scanning microscopy both in the absence and presence of PLO, indicating that FITC-insulin was partly targeted to lysosomes in the cells and degraded. The half-life of the intracellular degradation of FITC-insulin was, however, prolonged by the presence of PLO. PLO also stimulated the uptake of other FITC-labeled compounds. Among them, the enhancement effects of PLO on FITC-albumin and FITC-insulin uptake were prominent. The effect of PLO on insulin absorption was also examined in in-vivo pulmonary administration in rats, and co-administration of PLO enhanced the hypoglycemic action of insulin. These findings suggest that co-administration of poly(amino acid)s such as PLO is a useful strategy for enhancing insulin uptake by alveolar epithelial cells and subsequent absorption from the lung.

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Glucuronidation is an important pathway in the elimination of salvianolic acid A (Sal A); however the mechanism of UDP-glucuronosyltransferases (UGTs) in this process remains to be investigated. In this study, the kinetics of Sal A glucuronidation by pooled human liver microsomes (HLMs), pooled human intestinal microsomes (HIMs) and 12 recombinant UGT isozymes were investigated. The glucuronidation of Sal A can be shown both in HLMs and HIMs with K_m values of 39.84 ± 3.76 and 54.04 ± 4.36 µM, respectively. Among the 12 human UGTs investigated, UGT1A1 and UGT1A9 were the major isoforms that catalyzed the glucuronidation of Sal A (K_m values of 29.72 ± 2.20 and 24.40 ± 2.60 µM). UGT1A9 showed the highest affinity of Sal A glucuronidation. Furthermore, a significant correlation between Sal A glucuronidation and propofol glucuronidation (a typical UGT1A9 substrate) was observed. The chemical inhibition study showed that the IC₅₀ for phenylbutazone inhibition of Sal A glucuronidation was 50.3 ± 4.3 and 39.4 ± 2.9 µM by HLMs and UGT1A9, respectively. Mefenamic acid inhibited Sal A glucuronidation in UGT1A1 and HLMs with IC₅₀ values of >200 and 12.4 ± 2.2 µM, respectively.

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Astragaloside IV (AIV) is the most abundant saponin and a marker compound in Astragali Radix, a Chinese herb notable for its anti-aging and immune-enhancing effects. The present study investigated the role of intestinal bacterial conversion in the in vivo fate of AIV administered through a traditional oral route for the first time. When incubated anaerobically with rat intestinal bacteria, AIV generated five metabolites with three [monoglycosides brachyoside B and cyclogaleginoside B, the aglycone cycloastragenol (CA)] via stepwise deglycosylation and two from further epimerization (CA-iso) and dehydrogenation (CA-2H). Hydrolytic removal of C-6 glucose was a rate-limiting step for formations of CA and its derivatives. When AIV was orally administered to the rat, CA and CA-iso presented as the main components in plasma following AIV, and the AUC_0–∞ were 88.60 ± 9.66 (CA), 179.06 ± 28.53 (CA-iso) and 452.28 ± 43.33 nM·h (AIV). CA-2H was the predominant form in feces but was not detected in urine or plasma. This agreed well with in vitro data including rapid hepatic metabolism of CA-2H to form CA and CA-iso and reversible conversions between CA-2H and CA/CA-iso by intestinal bacteria. These findings support a crucial role of gut bacterial conversion of AIV in the traditional application of Astragali herb and warrant further investigational emphasis on CA and CA-iso.

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There is a great deal of interest in differentiation of human embryonic stem cells (hESCs) into hepatocyte-like cells for application in pharmaceutical screening. Cytochrome P450 (CYP) 1A is involved in the metabolic activation of procarcinogenic compounds as well as in detoxification of drugs. We differentiated hESCs into hepatocyte-like cells (hESC-derived hepatocyte-like cells) and examined whether CYP1A was induced in these cells by typical inducers of CYP1A. hESC-derived hepatocyte-like cells expressed albumin, α-fetoprotein, CYP3A4, CYP3A7, CYP1A1, CYP1A2, and UDP-glucuronyl transferase (UGT) 1A1 mRNA. The levels of CYP1A1, CYP1A2, and UGT1A1 mRNA expression were increased by omeprazole and 3-methylcholanthrene. Furthermore, the enzyme activity of CYP1A was also increased by these compounds. In conclusion, hESC-derived hepatocyte-like cells are available for the detection of CYP1A inducers.

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3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is a ring-substituted amphetamine widely used for recreational purposes. MDMA is predominantly O-demethylenated in humans by cytochrome P450 (CYP) 2D6, and is also a potent mechanism-based inhibitor of the enzyme. After assessing the inhibition and recovery of CYP2D6 in a previous study, the aim of this work was to study in humans the activity of CYP1A2 in vivo after CYP2D6 had been inhibited by MDMA, using caffeine as a probe drug. Twelve male and nine female recreational MDMA users were included. In session 1, 100 mg of caffeine was given at 0 h. In session 2, a 1.5 mg/kg MDMA dose (range 75–100 mg) was given at 0 h followed by a 100 mg dose of caffeine 4 h later. Aliquots of plasma were assayed for caffeine (137X) and paraxanthine (17X) and statistically significant differences were assessed with a one-way ANOVA. There were significant gender differences at basal condition, which persisted after MDMA administration. CYP1A2 activity was higher in both genders after drug administration, with an increase in 40% in females and 20% in males. Results show an increase in CYP1A2 activity when CYP2D6 is inhibited by MDMA in both genders, being more pronounced in females.

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Peg-interferon-alpha-2a (PEG-IFN) has been used all over the world including Japan as the standard of care for chronic hepatitis C (CHC). PEG-IFN causes platelet count decrease, while CHC patients with compensated liver cirrhosis have a low baseline of platelets. To use PEG-IFN more safely in these patients, we analyzed the effect of PEG-IFN on the longitudinal platelet profile with a pharmacokinetic-pharmacodynamic model. Platelet count and serum PEG-IFN concentration obtained from a Japanese clinical study on 40 patients were analyzed. The serum PEG-IFN concentration profile was fitted with an open 1-compartment model and the platelet profile was fitted with a turnover model. After the final model was fixed, the platelet profiles were simulated with various platelet baselines. The simulation revealed that according to PEG-IFN administration platelets decreased gradually and reached steady state within 12 weeks, and almost subjects would not have a lower platelet count than the criteria for discontinuation of the treatment. Once administration was discontinued, platelets recovered up to the baseline within several weeks. In conclusion, platelet count was predicted to be about a 30% (5th–95th percentiles in 1,000 simulation: 11–66%) decrease and to return to the baseline value in 4 to 8 weeks after the last administration of PEG-IFN.

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Drug-induced liver injury (DILI) is thought to be involved in the participation of drugs that either directly affect the cell viability or elicit an immune response. However, there is limited information about the immune responses induced by drugs, including those drugs that are metabolically activated. In this study, we constructed an in vitro assay system to assess the involvement of immune-related factors induced by metabolic activation of drugs. To investigate whether CYP3A4-mediated metabolism of 10 hepatotoxic drugs is associated with immune-related responses, human monocytic leukemia THP-1 cells were co-incubated with CYP3A4 Supersomes. Cluster of differentiation (CD) 86 and CD54 expression levels on THP-1 cells were upregulated by treatment with albendazole and amiodarone (AMD), respectively, in the presence of CYP3A4. Additionally, N-desethylamiodarone (DEA), a major metabolite of AMD, upregulated the CD54 expression of THP-1 cells with CYP3A4. The release of interleukin (IL)-8 and tumor necrosis factor (TNF) α from THP-1 cells was significantly increased by the treatment of AMD or DEA with CYP3A4. Similarly, IL-8 and TNFα were also upregulated by the treatment of AMD and DEA with human liver microsomes, but were inhibited by adding ketoconazole to the cell culture. In this study, we first report that albendazole, AMD and DEA activate immune reaction when metabolically activated.

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To elucidate the impact of genetic variations in breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (MDR1/ABCB1) on the pharmacokinetics of sunitinib, we carried out a pharmacogenetic study in a clinical setting and pharmacokinetic analysis using Abcg2^−/−, Abcb1a/1b^−/− and Abcb1a/1b;Abcg2^−/− mice. Nineteen renal cell carcinoma patients were enrolled in this study. The plasma concentrations of sunitinib and its active metabolite were determined and the area under the concentration-time curve (AUC) was calculated. Genetic polymorphisms in ABCG2 (421C>A) and ABCB1 (1236C>T, 2677G>T/A and 3435C>T) were examined. The dose-adjusted AUC_0–24 of sunitinib was significantly higher in patients with a heterozygous variant for ABCG2 421C>A than in wild-type patients (p = 0.02), and one homozygous patient showed the highest dose-adjusted AUC_0–24. The ABCB1 polymorphisms were not associated with the dose-adjusted AUC_0–24. The maximum concentration and AUC_0–4 of sunitinib were significantly higher in Abcg2^−/−, Abcb1a/1b^−/− and Abcb1a/1b;Abcg2^−/− mice than wild-type mice when sunitinib was given orally but not intraperitoneally. Incidence of thrombocytopenia and hypertension and poor compliance were associated with the systemic exposure to sunitinib and its active metabolite. These results suggest that the loss of protein expression of ABCG2 by genetic polymorphism is associated with an increase in the systemic exposure to sunitinib and sunitinib-induced toxicity.

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The objective of this study was to compare RT-PCR, Western blot and determination of enzyme activity in the assessment of the induction of cytochromes P450 (CYPs) 1A1 and 1A2 by benzo[a]pyrene (BaP) in Sprague-Dawley and Wistar rats. Inhibition studies and kinetic analyses confirmed literature data indicating that methoxyresorufin is a specific CYP1A2 substrate in both uninduced and BaP-treated rats, whereas ethoxyresorufin is a specific CYP1A1 substrate only in BaP-treated rats. BaP treatment increased mRNA and protein expressions of both CYP1A enzymes to a greater extent in Wistar than Sprague-Dawley rats. It consistently caused a higher increase in mRNA and protein expression of the aryl hydrocarbon receptor in the former rats. By contrast, CYP1A2 enzyme activity was much more markedly increased in Sprague-Dawley than Wistar rats and CYP1A1 activity was induced to similar levels. A BaP-induced increase in the turnover number of CYP1A enzymes in Sprague-Dawley rats, relative to Wistar rats, may provide a plausible explanation for the differential effect of BaP on gene expression and enzyme activity. These results have methodological implications, since they show that RT-PCR and Western blot may not provide a quantitative measure of induction of CYP1A activity, which is the actual measure of the change in CYP1A-mediated metabolism.

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Human fetal liver (HFL) cells express major drug metabolic enzymes CYP3A4, CYP3A5 and CYP3A7. In the fetal hepatocytes, betamethasone and dexamethasone (DEX) markedly enhanced the expression levels of CYP3A4 and CYP3A7 mRNAs and slightly increased the expression level of CYP3A5 mRNA. Interestingly, a high correlation between the CYP3A induction ability and the intensity of anti-inflammatory effect was observed. Human glucocorticoid receptor (GR)–small interfering RNA clearly attenuated the expression level of GR mRNA, and diminished the DEX-stimulated CYP3A4, CYP3A5 and CYP3A7 expression in HFL cells. These findings indicate that GR mediates the induction of CYP3A4 and CYP3A7 expression in human fetal hepatocytes as well as the CYP3A5.

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In regulatory guidelines for bioequivalence (BE) assessment, the definitions of AUC for primary assessment are different in ICH countries, i.e., AUC from zero to the last sampling point (AUCall) in Japan, AUC from zero to infinity (AUCinf) or AUC from zero to the last measurable point (AUClast) in the US, and AUClast in the EU. To assure sufficient accuracy of truncated AUC for BE assessment, the ratio of truncated AUC (AUCall or AUClast) to AUCinf should be more than 80% both in Japanese and EU guidelines. We investigated how the difference in the definition of truncated AUC affects BE assessment of sustained release (SR) formulation. Our simulation result demonstrated that AUCall/AUCinf could be ≥80% despite AUClast/AUCinf being <80% and AUCall failed to detect formulation difference. In Japanese package inserts of generic drugs in SR formulation, there were products for which AUCall/AUCinf was ≥80% though AUClast/AUCinf was <80%. In conclusion, it was confirmed that the difference in definition of truncated AUC affected the judgment of validity of truncated AUC for BE assessment, and AUCall could fail to detect the substantially different in vivo dissolution profile of generic drugs with SR formulation from the original drug.

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CYP3A4 and CYP3A5 require cytochrome b5 (b5) and NADPH-cytochrome P450 oxidoreductase (CPR) for optimum metabolism, but little is known about the specific requirements for b5 and CPR to produce optimal activities for these enzymes. The metabolism of testosterone (TT) by CYP3A4 and CYP3A5 was analyzed by various combinations of b5 and CPR using a fixed amount of recombinant P450 which had been purified from an Escherichia coli expression system. CYP3A4 and CYP3A5 required 4- and 8-fold more of CPR than of the P450s, respectively, for optimal activity. The requirement of b5 for optimal activity showed the same pattern for both CYP3A4 and CYP3A5, exhibiting a gradual stimulation of the activity reaching a maximum at 16 fold more b5 than P450. Although CYP3A4 exhibited higher activities than CYP3A5 in all combinations, both enzymes exhibited the same dependency profile for b5 and CPR. Therefore, the stronger activity of CYP3A4 compared to CYP3A5 appears to be intrinsic to the CYP3A4 protein itself and not to different requirements for b5 and CPR. Since the relative amounts of b5 and CPR are important in the maintenance of CYP3A4 and CYP3A5 activities, different levels of these proteins in vitro and in vivo may cause altered metabolism of their substrates or misinterpretation of enzyme properties.

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