Resveratrol, a natural polyphenol found in grapes, berries and other plants, has been proposed as an ideal chemopreventative agent due to its plethora of health promoting activities. However, despite its lofty promise as a cancer prevention agent its success in human clinical trials has been limited due to its poor bioavailability. Thus, interest in other natural polyphenols is intensifying including the naturally occurring dimethylated analog of resveratrol, pterostilbene. The UDP-glucuronosyltransferase (UGT) family of enzymes plays a vital role in the metabolism of both resveratrol and pterostilbene. The current study sought to elucidate the UGT family members responsible for the metabolism of pterostilbene and to examine gender differences in the glucuronidation of resveratrol and pterostilbene. We demonstrate that UGT1A1 and UGT1A3 are mainly responsible for pterostilbene glucuronidation although UGT1A8, UGT1A9 and UGT1A10 also had detectable activity. Intriguingly, UGT1A1 exhibits the highest activity against both resveratrol and pterostilbene despite altered hydroxyl group specificity. Using pooled human liver microsomes, enzyme kinetics were determined for pterostilbene and resveratrol glucuronides. In all cases females were more efficient than males, indicating potential gender differences in stilbene metabolism. Importantly, the glucuronidation of pterostilbene is much less efficient than that of resveratrol, indicating that pterostilbene will have dramatically decreased metabolism in humans.
A model for drug interaction between amlodipine and simvastatin was developed using concentration data obtained from a multiple-dose study consisting of single- and co-administration of amlodipine and simvastatin conducted in healthy Koreans. Amlodipine concentrations were assumed to influence the clearance of simvastatin and simvastatin acid, which as well as the oral bioavailability was allowed to vary depending on genetic polymorphisms of metabolic enzymes. Covariate effects on drug concentrations were also considered. The developed model yielded a 46% increase in simvastatin bioavailability and a 13% decrease in simvastatin clearance when amlodipine 10 mg was co-administered. When CYP3A4/5 polymorphisms were assessed by a mixture model, extensive metabolizers yielded a decrease in simvastatin bioavailability of 81% and a decrease in simvastatin clearance by 4.6 times as compared to poor metabolizers. Sixty percent of the usual dose was the optimal simvastatin dose that can minimize the interaction with amlodipine 10 mg. Age and weight had significant effects on amlodipine concentrations. In conclusion, this study has quantitatively described the pharmacokinetic interaction between simvastatin and amlodipine using a modeling approach. Given that the two drugs are often prescribed together, the developed model is expected to contribute to more efficient and safer drug treatment when they are co-administered.
Rat sandwich-cultured hepatocytes (SCH) were used to correlate the in vitro hepatic disposition of mycophenolic acid (MPA) with published in vivo data, as well as mechanistic studies on drug-drug interaction. The major metabolite of MPA in SCH was 7-O-glucuronide (MPAG) followed by acyl-glucuronide (AcMPAG). MPAG and AcMPAG, but not MPA, showed significant in vitro biliary excretion with biliary excretion indexes (BEI) of 40% for MPAG and 45% for AcMPAG. While these BEIs were similar, the biliary excretion amount (BEA) of MPAG (120 pmol/mg protein) was orders of magnitude higher than that of AcMPAG (0.34 pmol/mg protein). Since MPAG is the major metabolite in in vivo bile, we propose that BEA is a better qualifier of biliary excretion. Quercetin inhibited MPAG and AcMPAG production, while chrysin inhibited only MPAG production, showing that chrysin is not a pan-glucuronidation inhibitor. Cyclosporin A (CysA) reduced the BEI of MPAG and increased intracellular MPA accumulation without changing MPAG amounts. These results suggest that CysA causes inhibition of biliary excretion of MPAG, as well as a mixed inhibition of glucuronidation of MPA and sinusoidal efflux of MPA/MPAG. In conclusion, the present study demonstrates a good agreement of hepatic MPA disposition between SCH and in vivo rats.
Fraxetin, a major constituent of the traditional medicine plant Fraxinus rhynchophylla Hance (Oleaceae), has been found to possess multiple bioactivities. However, the metabolic pathway(s) of fraxetin in human tissues has not been reported yet. This study aimed to characterize the glucuronidation pathway(s) of fraxetin in human tissues. Fraxetin could be metabolized to two glucuronides in human liver microsomes (HLMs). These two glucuronides were biosynthesized and characterized as 7-O-glucuronide (7-O-G) and 8-O-glucuronide (8-O-G). UGT1A1, -1A6, -1A7, -1A8, -1A9 and -1A10 participated in the formation of 7-O-G, while the formation of 8-O-G was catalyzed selectively by UGT1A6 and UGT1A9. UGT1A9 showed the highest catalytic activities in the formation of 7-O-G and 8-O-G. Both kinetic characterization and inhibition assays demonstrated that UGT1A9 played important roles in fraxetin glucuronidations in HLMs, especially in the formation of the major metabolite 8-O-G. Furthermore, the intrinsic clearance of fraxetin in both human liver microsomes and UGT1A9 was greater than that of 7,8-dihydroxylcoumarin, revealing that the addition of a C-6 methoxy group led to the higher metabolic clearance. In summary, the glucuronidation pathways of fraxetin in human liver microsomes were well-characterized, and UGT1A9 was the major isoform responsible for the glucuronidations of fraxetin.
To investigate the pharmacokinetics of mericitabine in healthy Caucasian and Japanese subjects, healthy Caucasian (n = 32) and Japanese (n = 32) subjects were randomized to receive single 500, 1,000, or 2,000 mg doses of mericitabine or a placebo, after which plasma and urine samples were collected for 72 h. Mericitabine (prodrug), RO4995855 (parent), and RO5012433 (uridine metabolite) concentrations were quantified by tandem mass spectrometry. Pharmacokinetics were estimated by non-compartmental methods, and pharmacokinetic parameters of RO4995855 were normalized by body weight. Exposure to RO4995855 was similar in both populations after administration of mericitabine 500, 1,000, and 2,000 mg. Mean AUCinf of RO4995855 increased in a dose-proportional manner from 28.8 to 52.3, and 113.0 µg·h/mL in Caucasian subjects, and from 32.5 to 57.1 and 119 µg·h/mL in Japanese subjects. A linear relationship was observed between the weight-adjusted dose of mericitabine and Cmax (r2 = 0.83 and 0.80) and AUC (r2 = 0.94 and 0.74) for RO4995855 in Caucasian and Japanese subjects, respectively. Mean half-life and renal clearance of RO4995855 were similar and independent of dose in both populations. The results support the use of the same dosing regimens in Caucasian and Asian subjects.
Purpose: Pemetrexed transport by human organic anion transporters, hOAT1 (SLC22A6) and hOAT3 (SLC22A8), were characterized in comparison with methotrexate. Methods: Accumulation of pemetrexed and methotrexate in hOAT1- and hOAT3-expressing cells were evaluated. Pemetrexed and methotrexate were determined by HPLC. Kinetic parameters were calculated by Eadie-Hofstee plot. Results: When HEK-hOAT3 and -hOAT1 cells were incubated with 100 µM pemetrexed for 30 min, pemetrexed was accumulated at 14- and 1.7-fold greater than that in control cells, respectively. Pemetrexed and methotrexate transport by hOAT3 was saturated at high concentrations with apparent Km values 28.2 µM and 76.6 µM, respectively. In addition, intrinsic activity (Vmax/Km) of pemetrexed and methotrexate transport by hOAT3 was 4.82 and 0.42 µl/min/mg protein, respectively, suggesting 11-fold higher transport of pemetrexed than methotrexate by hOAT3. Furthermore, loxoprofen, ibuprofen, pravastatin, and cefazolin, transport substrates of hOAT3, inhibited pemetrexed transport by hOAT3 with IC50 values, 34.2, 27.9, 76.3 and 650 µM, respectively. Conclusions: Pemetrexed is a superior substrate to methotrexate for hOAT3. Loxoprofen, ibuprofen, and cefazolin could cause drug-drug interactions when attaining high blood concentrations.
The aim of this study was to present a deductive compartment pharmacokinetic (PK) model to predict the concentration profiles of drugs in plasma and peritoneal fluid in peritoneal dialysis (PD) rats. PK parameters of model drugs in normal and experimentally induced acute renal failure (ARF) rats not undergoing PD were obtained inductively in a common regression manner with a two-compartment model. In PD normal and ARF rats, PK parameters relating to the transfer of drugs to the peritoneal dialysate and the progress of renal failure were deductively modified to simulate the drug concentration-time profiles in plasma and in the peritoneal fluid in PD rats. The deductively introduced modifiers were the volume of distribution in the peripheral compartment, plasma protein binding, and solvent movement factor to the peritoneal fluid. Predicted profiles of tolbutamide, propranolol and cefazolin in PD normal and ARF rats were compared with the corresponding observed data. This minimal deductive approach yielded satisfactory accuracy in the prediction of both the plasma and peritoneal fluid concentrations of tolbutamide and propranolol.
We previously reported that aging and/or cytochrome P450 2D6 polymorphism are responsible for the interindividual variability in the systemic clearance (CL) and bioavailability (F) of metoprolol. The aim of the present study was to evaluate the residual variability of F of metoprolol in routinely treated Japanese patients and to investigate the intestinal absorption mechanism of the drug using human intestinal epithelial LS180 cells. We first re-analyzed the blood concentration data for metoprolol in 34 Japanese patients using a nonlinear mixed effects model. The oral clearance (CL/F) of metoprolol was positively correlated with the apparent volume of distribution (V/F), suggesting the residual variability of F. The uptake of metoprolol into LS180 cells was significantly decreased by the acidification of extracellular medium pH, and was dependent on temperature and intracellular pH. Furthermore, the cellular uptake of metoprolol was saturable, and was significantly decreased in the presence of hydrophobic cationic drugs such as diphenhydramine, procainamide, bisoprolol, and quinidine. These findings indicate that residual variability of F is one of the causes of the interindividual pharmacokinetic variability of metoprolol, and that the interindividual variability of not only presystemic first-pass metabolism, but also intestinal absorption, may be responsible for the variable F of the drug.
An in vitro–in vivo correlation analysis between observed and predicted metabolic clearance in multiple preclinical species including dogs and monkeys constitutes an integral part of prediction for the pharmacokinetics in humans by using liver-derived in vitro preparations. Empirical values of the scaling factor for the extrapolation of metabolic (intrinsic) clearance in the in vitro preparation to that for whole liver were calculated for each preparation of 8 and 5 cryopreserved dog and monkey hepatocytes, respectively, by optimizing the objective function of average fold error between predicted and observed metabolic (intrinsic) clearance for eight and 11 standard compounds for dogs and monkeys, respectively. Thus obtained values of the scaling factor ranged from 5.46 × 109 to 19.9 × 109 cells/kg body weight with an average of 10.3 × 109 cells/kg body weight in dogs, and the value ranged from 2.36 × 109 to 4.21 × 109 cells/kg body weight with an average of 3.17 × 109 cells/kg body weight in monkeys, which were both consistent with biologically calculated values in corresponding species. These results demonstrated the utility of commercially available cryopreserved preparations of dog and monkey hepatocytes for the in vitro–in vivo correlation analyses with the aid of empirically or biologically obtained scaling factors at the early development stage of new drug candidates.
Bupropion is widely used as an antidepressant drug and also as a smoking cessation aid. In humans, this drug is extensively metabolized to form several metabolites. Oxidised hydroxybupropion and two reduced metabolites, threohydrobupropion and erythrohydrobupropion, are major metabolites. All of these metabolites are considered to be active. Although the oxidative metabolic pathway and the central role of CYP2B6 are known, the enzymes that participate in the reduction have not been identified to date. The aim of this study was to confirm the role of human liver subcellular fractions in the metabolism of bupropion and elucidate the contribution of particular carbonyl-reducing enzymes. An HPLC method for the determination of bupropion metabolites was utilised. Bupropion is reduced to threohydrobupropion and less to erythrohydrobupropion in human liver cytosol, microsomes and also mitochondria. Surprisingly, intrinsic clearance for formation of both metabolites is the highest in mitochondrial fraction. Moreover this study provides the first direct evidence that 11β-hydroxysteroid dehydrogenase 1, AKR1C1, AKR1C2, AKR1C3 and CBR1 participate in the reducing biotransformation of bupropion in vitro. The enzyme kinetics of all of these reductases was investigated and kinetic parameters were calculated.
The purpose of this study is to assess the impact of human epidermal growth factor receptor 2 (HER2) status on the antitumor activity of CH5164840, an orally available heat shock protein 90 (HSP90) inhibitor, using pharmacokinetic–pharmacodynamic modeling. Athymic mice, each implanted with one of eight human tumor xenografts, were treated with CH5164840 once daily at doses of 3.13 to 50 mg/kg. Plasma concentrations of CH5164840 were described by a one-compartment model with first-order absorption rate. Time profiles of tumor growth inhibition in the eight xenograft models were well captured by an indirect response model with a maximum tumor-killing rate constant (Emax model). Threshold plasma concentrations for tumor stasis, which are determined by multiple pharmacodynamic parameters, Emax, EC50 and tumor growth rate constant, were significantly lower in HER2-positive tumors (1.96–3.85 µM) than in HER2-negative tumors (4.48–23.4 µM). The results suggest that CH5164840 was more efficacious in HER2-positive tumors than in HER2-negative tumors in terms of the lower effective concentration of the drug in preclinical animal models.
Using two breeds (Meishan and Landrace) of pigs and their crossbred offspring (ML, Meishan × Landrace; LM, Landrace × Meishan), of which males have genetically different serum androgen levels, we examined whether or not serum androgen plays a crucial role in the constitutive gene expression of hepatic sulfotransferases (SULTs) and UDP-glucuronosyltransferases (UGTs). Real-time RT-PCR analyses showed that in Meishan, ML, and LM pigs, SULT1A1 and SULT2A1 mRNA levels were lower in males having high levels of serum androgen (>38 ng/ml) than in females, whereas those of UGT1A1, UGT1A6, and UGT2B31 were just the opposite. In Landrace pigs having low levels of serum androgen (<22 ng/ml), no such sex differences in expression levels were observed. Moreover, castration of male Meishan pigs altered the gene expression patterns of SULTs and UGTs to female levels. Testosterone-treatment to the castrated males and intact females of either pig breed resulted in decreased SULT1A1 and SULT2A1 and increased UGT1A1, UGT1A6, and UGT2B31 mRNA levels. These findings demonstrate that androgen is one of the physiological factors that determine sexual dimorphism on the constitutive gene expression of SULTs and UGTs in the pig liver.
Avoiding drug-drug interactions (DDIs) mediated through inhibition of cytochrome P450 (CYP) activity is highly desirable. Direct inhibition (DI) of CYP through new chemical entities (NCEs) or time-dependent inhibition (TDI) through reactive metabolites should be elucidated at an early stage of drug discovery research. In particular, TDI of CYP occurring through reactive metabolites may be irreversible and even sustained, causing far more serious DDIs for TDIs than for DIs. Furthermore, it is important to ascertain whether an NCE inhibits multiple CYP isoforms. Hence, using a cocktail-substrate approach that we previously established (in which the activity of 8 CYP isoforms is simultaneously evaluated in a single run), we evaluated the IC50 values of direct inhibitors and TDI parameters (kobs, shifted IC50, KI and kinact) of time-dependent inhibitors that affect multiple CYP isoforms. The IC50 values for 8 CYP isoforms obtained using the cocktail-substrate approach were nearly identical to values previously reported. The TDI parameters for CYP1A2, 2C9, 2C19, 2D6, and CYP3A4/5 obtained using the cocktail-substrate approach were also nearly identical to those obtained using a single-substrate approach. Thus, the cocktail-substrate approach is useful for evaluating DI and TDI in the early stages of drug discovery and development processes.
Gout, a common disease, is a consequence of hyperuricemia, and increases the risks of hypertension, cardiovascular diseases, cerebrovascular diseases and renal failure. Gout can be classified into 3 types: the renal underexcretion (RUE) type, renal overload type and combined type. RUE type is a major type of gout; however, its genetic causes are still unclear. Since human organic anion transporter 4 (OAT4/SLC22A11) is expressed in the kidney and mediates urate transport, we investigated the effects of a common variant of OAT4/SLC22A11 on the susceptibility to gout. Five hundred and forty-five Japanese male gout cases and 1,115 male individuals as a control group were genotyped with rs17300741, a single nucleotide polymorphism in the OAT4/SLC22A11 gene. The association analysis of rs17300741 showed no significant association for all gout cases; however, there was a slight but significant association for RUE type gout cases (p = 0.049). These results also suggest that OAT4 contributes to urate transport at the apical membrane of renal proximal tubule cells in humans. Our findings make it clear for the first time that a common variant of OAT4/SLC22A11 is associated with RUE type gout, a major gout subtype.
Ribavirin is a purine nucleoside analogue that possesses potent anti-hepatitis C virus activity, and it has long been considered likely that ribavirin undergoes a first-pass metabolism at the small intestine. Although purine nucleoside phosphorylase (PNP) is assumed to be involved in this metabolism, this has not been conclusively demonstrated. Furthermore, no pharmacogenomic studies related to PNP-mediated ribavirin phosphorolysis have previously been conducted. In this study, we sought to identify the role of PNP in ribavirin phosphorolysis in the human small intestine, and to clarify the effect of the single nucleotide polymorphism (rs1049564) on PNP's ribavirin phosphorolysis activity. The results of our investigations show that PNP is abundantly expressed in the human small intestine, and that intestinal ribavirin phosphorolysis is severely inhibited by ganciclovir, a PNP-inhibitor. Therefore, PNP is likely to play a primary role in the ribavirin phosphorolysis in the human small intestine. On the other hand, the results of our attempt to clarify the function of rs1049564 show that it does not affect PNP's ribavirin phosphorolysis activity. We believe that the present study will facilitate further pharmacogenomic and biochemical characterization of PNP as a key metabolic enzyme of ribavirin.
Cytochrome P450 2B6 (CYP2B6) is responsible for the initial biotransformation of profol, an extensively metabolized intravenous anesthetic. In this study we examined the effect of the apparently functional CYP2B6 c.516G>T polymorphism on the distribution of propofol concentrations, quantified by GC/MS analysis following a single bolus dose, in the blood of 44 Greek women undergoing oocyte retrieval. Univariate analysis using age, height, weight and smoking status as covariates, as well as the Mann-Whitney non-parametric test, revealed a strong trend of association of the T allele with high propofol concentrations determined in whole blood, shortly after a single bolus dose. Propofol concentrations which were higher than one standard deviation of the mean were almost invariably associated with carriage of the T allele.
Isoniazid (INH), a first-line drug for tuberculosis control, frequently causes liver injury. Multiple previous reports suggest that CYP3A is involved in INH metabolism, bioactivation and hepatotoxicity, although direct evidence is unavailable. In the current study, wild-type and Cyp3a-null mice were used to determine the potential role of Cyp3a in INH metabolism in vivo. Compared to wild-type mice, there were no significant differences in the pharmacokinetic profiles of INH or acetyl-isoniazid in Cyp3a-null mice after an oral administration of 50 mg/kg INH. With the same treatment, distribution of INH and its major metabolites was similar in the liver of wild-type and Cyp3a-null mice. A reactive metabolite of INH was trapped by N-α-acetyl-L-lysine in mouse liver microsomes, but Cyp3a does not contribute to this bioactivation pathway. In addition, no liver injury was observed in wild-type or Cyp3a-null mice treated with 60 or 120 mg/kg INH. In summary, Cyp3a has no effect on systemic pharmacokinetics of INH in mice. Further studies are needed to determine whether and how exactly CYP3A is involved in INH bioactivation and hepatotoxicity.
Caco-2 is a widely used cell model in drug absorption and P-glycoprotein (P-gp, MDR1) substrate identification. Long-term vinblastine treatment of Caco-2 cells could increase the expression of P-gp; thus, the vinblastine resistant Caco-2 (Caco-2 vbl) cells can be used as a rapid and sensitive alternative model in identifying P-gp substrates. The mechanism of P-gp induction in this model is not clear; this study was therefore intended to clarify the possible factors involved in P-gp up-regulation in Caco-2 vbl cells. Since vinblastine is the inducer of both activator protein-1 (AP-1) and nuclear factor kappa B (NF-κB), we investigated the role of AP-1 and NF-κB in the regulation of MDR1 gene expression. Our results indicated that the AP-1 and NF-κB luciferase activity was higher in Caco-2 vbl cells than that in Caco-2 cells according to reporter gene assay. The mRNA expression of AP-1 subunit c-Jun and NF-κB was increased in Caco-2 vbl cells. The c-Jun inhibitor SP600125 and NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) suppressed the expression of MDR1 mRNA in Caco-2 vbl cells. In conclusion, this study provides the evidence that AP-1 and NF-κB are involved in the P-gp induction in Caco-2 vbl cells.