The aim of this study was to investigate the effect of the dipeptidyl peptidase-4 inhibitor linagliptin on the pharmacokinetics of glyburide (a CYP2C9 and CYP3A4 substrate) and vice versa. This randomized, open-label, three-period, two-way crossover study examined the effects of co-administration of multiple oral doses of linagliptin (5 mg/day × 6 days) and single doses of glyburide (1.75 mg/day × 1 day) on the relative bioavailability of either compound in healthy subjects (n = 20, age 18–55 years). Coadministration of glyburide did not alter the steady-state pharmacokinetics of linagliptin. Geometric mean ratios (GMRs) [90% CI] for (linagliptin + glyburide)/linagliptin AUC_τ,ss and C_max,ss were 101.7% [97.7–105.8%] and 100.8% [89.0–114.3%], respectively. For glyburide, there was a slight reduction in exposure of ∼14% when coadministered with linagliptin (GMRs [90% CI] for (glyburide + linagliptin)/glyburide AUC_0–∞ and C_max were 85.7% [79.8–92.1%] and 86.2% [79.6–93.3%], respectively). However, this was not seen as clinically relevant due to the absence of a reliable dose–response relationship and the known large pharmacokinetic interindividual variability of glyburide. These results further support the assumption that linagliptin is not a clinically relevant inhibitor of CYP2C9 or CYP3A4 in vivo. Coadministration of linagliptin and glyburide had no clinically relevant effect on the pharmacokinetics of linagliptin or glyburide. Both agents were well tolerated and can be administered together without the need for dosage adjustments.

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  Warfarin exhibits wide interpatient variability in dosing requirements. Recent studies have shown a novel polymorphism (rs2108622, V433M) in the CYP4F2 gene to be associated with variability in warfarin requirements in Caucasians. The purpose of this study was to evaluate the impact of rs2108622 on warfarin dose requirements in the Asian population. The mean warfarin dose was found to be significantly lower in patients carrying homozygous wild-type allele CC when compared with patients carrying variant alleles CT and TT (CC vs CT+TT: 3.0 mg/day vs 3.75 mg/day, p = 0.033). In patients harboring VKORC1 diplotypes associated with low warfarin requirements, a linear regression model which included age, weight, CYP2C9 and CYP4F2 variants accounted for 38% of the variability in warfarin dose. Approximately 11% of the dose variation was explained by CYP4F2 rs2108622 (p = 0.004). The influence of rs2108622 in patients harboring VKORC1 diplotypes associated with high warfarin requirements was not significant. This study suggests that CYP4F2 rs2108622 may significantly affect warfarin dose requirements in carriers of VKORC1 low-dose-associated diplotypes.

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  We evaluated a novel three-dimensional primary culture system using micro-space plates to determine the expression levels of 61 target (drug-metabolizing enzymes, transporters, and nuclear receptors) mRNAs in human hepatocytes. We measured mRNA expression levels of many target genes in four lots of cryopreserved human hepatocyte primary cells after 120 h of culture and compared differences in mRNA expression levels between cultures using traditional plates and those using micro-space plates. In this study, we show that the mRNA levels of many experimental targets in human hepatocytes before inoculation resemble the levels inside the human liver. Furthermore, we show that the rate of change of expression levels of many target mRNAs relative to the value before inoculation of the hepatocytes into micro-space plates was relatively smaller than the rate of change in hepatocytes inoculated into traditional plates. Pharmacokinetics-related examinations using this system are possible within a time frame of 120 h. We report that this novel three-dimensional culture system reproduces mRNA expression levels that are nearer to those in the liver in vivo and is an excellent platform for maintaining mRNA expression levels of drug-metabolizing enzymes and transporters when compared to common monolayer cultures.

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  Caco-2 and T84 cells are intestinal epithelial model cells. Caco-2 cells are more commonly used in drug transport studies, whereas only a few studies have used T84 cells, and the two cell lines have not been compared. We cultured Caco-2 and T84 cells on plastic dishes or polycarbonate Transwell filters and compared the expression and function of ATP binding cassette (ABC) transporters, including multidrug resistance protein (MDR) 1 and multidrug resistance-associated protein (MRP) 2 and MRP3, in response to various compounds. Overall, the pattern of change in transporter mRNA expression in response to compounds was very similar regardless of culture conditions (plastic dish or polycarbonate filter) and cell line (Caco-2 or T84), and changes in MDR1 function was accompanied by expression changes. The cells cultured on Transwell filters were more sensitive to the tested compounds, regardless of the cell line. On comparing the two cell lines, the intrinsic function of MDR1 was stronger in Caco-2 cells, while sensitivity to the tested compounds was more prominent in T84 cells. These results suggest that Caco-2 cells are more suitable for identifying whether MDR1 mediates drug transport, while T84 cells are more useful for assessing the induction capacity of compounds.

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  Phyllanthus amarus has long been used as a herbal medicine in several countries. Phytochemicals in herbal medicine may interact with cytochromes P450 (CYP) and thus raise the potential of herb-drug interactions; therefore, the inhibitory effects of P. amarus and its major phytochemicals phyllanthin and hypophyllanthin on CYP isoforms were determined using human liver microsomes and selective substrates. Both ethanolic and aqueous extracts of P. amarus inhibited CYP1A2, CYP2D6, CYP2E1 and CYP3A4 in a dose-dependent manner. Compared to known CYP3A inhibitors, the IC₅₀ values of the ethanolic and aqueous extracts on testosterone 6β-hydroxylation were higher than that of ketoconazole but were lower than those of erythromycin and clarithromycin. Both extracts were weak inhibitors of CYP1A2, CYP2D6 and CYP2E1. In addition, phyllanthin and hypophyllanthin were potent mechanism-based inhibitors of CYP3A4 with K_I values of 1.75 ± 1.20 µM and 2.24 ± 1.84 µM and k_inact values of 0.18 ± 0.05 min⁻¹ and 0.15 ± 0.06 min⁻¹, respectively. The k_inact/K_I ratios of these lignans were higher than those reported for some therapeutic drugs that act as mechanism-based inhibitors of CYP3A4. These results suggest that co-administration of P. amarus with drugs that are metabolized by CYP3A4 may potentially result in herb-drug interactions.

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  We investigated the effects of lauroylcarnitine and palmitoylcarnitine on major tight junction proteins such as claudins in Caco-2 cell monolayers and also examined the involvement of cholesterol in the effects induced by both acylcarnitines on these proteins. We investigated the effects of lauroylcarnitine and palmitoylcarnitine on the barrier function of tight junctions by measuring transepithelial electrical resistance (TEER) and fluorescein isothiocyanate dextran 40,000 (FD-40) flux. A decrease in the TEER value and an increase in FD-40 flux were observed after incubating Caco-2 cell monolayers with lauroylcarnitine and palmitoylcarnitine for 1 h, suggesting the loss of the barrier function of tight junctions. In addition, lauroylcarnitine and palmitoylcarnitine decreased the protein levels of claudin 1, 4, and 5 but not those of claudin 2, 3, 6, or 7. In addition, palmitoylcarnitine and methyl-β-cyclodextrin increased cholesterol release from the plasma membrane. It is suggested that the effects of palmitoylcarnitine and methyl-β-cyclodextrin on claudin 4 and 5 may be associated with cholesterol leakage from the plasma membrane into the apical side. These results indicate that the protein levels of claudin 4 and 5 are decreased by treatment with palmitoylcarnitine and lauroylcarnitine, and that this change is involved in the absorption-enhancing mechanism.

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  The purpose of this study was to investigate the involvement of organic anion transporting polypeptide (OATP/Oatp) and P-glycoprotein (P-gp)/multidrug resistance 1 (MDR1/Mdr1) in intestinal absorption of pitavastatin. Pitavastatin was found to be a substrate for human OATP1A2, OATP2B1, and MDR1 and rat Oatp1a5, Oatp2b1, and Mdr1a in experiments using transporter-expressing Xenopus oocytes and LLC-PK1 cell systems. Naringin inhibited Oatp1a5- and Mdr1a-mediated transport of pitavastatin with IC₅₀ values of 18.5 and 541 µM, respectively. The difference in the IC₅₀ values of naringin for Oatp1a5 and Mdr1a-mediated pitavastatin transport may account for the complex concentration-dependent effect of naringin on the intestinal absorption of pitavastatin. Rat intestinal permeability of pitavastatin measured by the in situ closed-loop perfusion method was indeed significantly reduced by 200 µM naringin, but was significantly increased by 1000 µM naringin. Furthermore, the permeability was significantly increased by elacridar, a potent inhibitor of Mdr1, while the permeability was significantly decreased in the presence of both elacridar and naringin, suggesting that Oatp1a5 and Mdr1a are both involved in intestinal absorption of pitavastatin. Our present results indicate that OATP/Oatp and MDR1/Mdr1 play roles in the intestinal absorption of pitavastatin as influx and efflux transporters, respectively.

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  Correlation analysis between food effects on oral drug absorption (food effect) and physicochemical properties is important for efficient drug discovery and contributes to drug design. This study focused on micelle binding and solubilization considering bile micelles in the intestinal fluid. Profiling using about 40 launched drugs demonstrated that those in a high solubilization area (area 1) tended to have a positive food effect, and that drugs exhibiting negative/no food effect tended to coexist in a no/low solubilization area (area 2). In area 1, the solubilization effect by bile micelles was demonstrated quantitatively as an important factor that indicates a positive food effect. In area 2, the relative and quantitative relationships among the membrane permeation rate, dissolution rate, micelle binding and food effect could be clarified by simulation. The improvement of membrane permeability and the suppression of micelle binding are considered to be required to avoid a negative food effect. In conclusion, important factors contributing to the food effect were clarified relatively and quantitatively. Data generated from this profiling may be beneficial to find a solution for negative food effects. Furthermore, this risk assessment of food effects is considered to be a useful tool in rational drug design for drug discovery.

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  A novel phosphodiesterase-4 inhibitor, 2-aryl-7(3′,4′-dialkoxyphenyl)-pyrazolo[1,5-alpha] pyrimidine (PDE-310), has been synthesized for the treatment of respiratory diseases. We conducted in vitro and in vivo studies to characterize the pharmacokinetics of PDE-310. The high liver microsomal stability and low inhibitory potency against CYP isoforms of PDE-310 suggested a low first-pass effect and high bioavailability. PDE-310 exhibited high Caco-2 cell permeability in the absorptive direction (apparent permeability coefficients, ∼20 × 10⁻⁶ cm/s), with higher transport in the secretory direction, giving efflux ratios of 3.9 and 2.6 at 5 and 10 µM, respectively. In addition, the high efflux ratio and improved absorption on treatment with efflux transporter inhibitors such as verapamil and MK-571 indicated the involvement of P-gp, BCRP and MRP2 in intestinal transport. PDE-310 bound strongly to human plasma proteins, whereas significantly more PDE-310 (27–34%) was free in rat plasma. Following intravenous administration, nonlinear elimination of PDE-310 was observed at the tested dose ranges (K_m, 0.87 µg/mL; V_max, 0.3 mg·h⁻¹·kg⁻¹). Following oral PDE-310 administration, dose-normalized AUC and T_max increased significantly in a dose-dependent manner. PDE-310 exhibited high oral bioavailability (>70%) and was distributed well to various tissues except brain and testis.

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  Ginseng is one of the most commonly used herbal medicines worldwide. Ginsenosides are believed to be responsible for the therapeutic activities of ginseng; however, co-administration of prescription drugs with ginseng products may give rise to ginseng-drug interactions. Cytochrome P450 enzymes are major phase I enzymes involved in the metabolism of most currently used drugs. Inhibition or induction of P450 enzymes can lead to pharmacokinetic drug interactions. Previous reports on ginseng-drug interactions have been controversial and confusing. In the present study, we examined the effects of thirteen ginsenosides on the expression of CYP1A1, CYP1A2 and CYP3A4 in HepG2 cells. We found that eight ginsenosides and aglycones potently induced CYP1A1 expression, and that structure-activity relationships existed for these effects. Moreover, we discovered that deglycosylated ginsenosides, some of which are putative ginsenoside metabolites, were more potent inducers of CYP1A1, CYP1A2 and CYP3A4 than glycosylated ginsenosides. This finding indicates that ginsenoside metabolites may partially account for ginseng-drug interactions, and that differences in the composition of intestinal bacteria and the extent of deglycosylation of the ginsenosides could be a contributing factor to the inconsistencies observed in previous clinical and pre-clinical studies with regard to ginseng-drug interactions.

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  The genetic variability, haplotype profile and ethnic differences of MDR1 polymorphisms in healthy Roma and Hungarian populations were analyzed and the results were compared with those of other populations available from the literature. Healthy subjects (465 Roma and 503 Hungarian) were genotyped for C1236T, G2677T/A and C3435T variants of MDR1 by PCR-RFLP assay. Differences were found between the Roma and Hungarian populations in the frequencies of MDR1 1236 CC (20.7 vs. 33.2%) and TT genotypes (30.8 vs. 21.9%), in T allele frequency (0.551 vs. 0.443) (p < 0.002), and in 3435T allele frequency (0.482 vs. 0.527, p < 0.04). Furthermore, the frequency of CGC, CGT and CTT haplotypes was significantly higher in the Hungarian population than in Roma (41.4 vs. 35.3%, 9.04 vs. 6.02% and 2.88 vs. 1.08%, respectively; p < 0.009), whereas the frequency of TGC and TTC haplotypes was higher in the Roma population than in the Hungarian (7.31 vs. 1.68% and 6.67 vs. 2.08%, respectively; p < 0.001). The prevalence of MDR1 polymorphisms in the Hungarian population is similar to that of other European populations; however, some differences were observed in the haplotype structures. In contrast, the Roma population differs from Hungarians, from Caucasians and from populations from India in the incidence of MDR1 common variants and haplotypes.

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