Lack of interaction between metoclopramide and morphine in vitro and in mice

1.?This study examined interactions via common metabolism or via common pharmacodynamic pathways between frequently co-prescribed metoclopramide (a prokinetic) and morphine (an opioid analgesic).

2.?In human liver microsomes, morphine 3-glucuronide and morphine 6-glucuronide formation had V_max estimates of 6.2 ± 0.07 and 0.75 ± 0.01 (nmole min^?1 mg^?1 protein) and K_m estimates of 1080 ± 37 and 665 ± 55 (µM), respectively. The in vitro K_i for morphine 3-glucuronide formation in the presence of metoclopramide in human liver microsomes or recombinant uridine diphosphoglucuronosyltransferase 2B7 predicted a lack of in vivo interaction.

3.?Morphine (2 mg kg^?1 subcutaneously) delayed gastrointestinal meal transit in mice, metoclopramide (10 mg kg^?1 subcutaneously) had no effect on meal transit, and metoclopramide did not alter this effect of morphine.

4.?Morphine (2 or 5 mg kg^?1 subcutaneously) was antinociceptive in mice (hot plate test) and metoclopramide (10 mg kg^?1 subcutaneously) did not alter the antinociceptive effects of morphine.

5.?Together, the data suggest a lack of interaction between morphine and metoclopramide.     

The different metabolism of morusin in various species and its potent inhibition against UDP-glucuronosyltransferase (UGT) and cytochrome p450 (CYP450) enzymes

1.?The aim of this study was to investigate the inhibitory effect of morusin on Glucuronosyltransferase (UGT) isoforms and cytochrome P450 enzymes (CYP450s). We also investigated the metabolism of morusin in human, rat, dog, monkey, and minipig liver microsomes.

2.?100?μM of morusin exhibited strong inhibition on all UGTs and CYP450s. The half inhibition concentration (IC₅₀) values for CYP3A4, CYP1A2, CYP2C9, CYP2E1, UGT1A6, UGT1A7, and UGT1A8 were 2.13, 1.27, 3.18, 9.28, 4.23, 0.98, and 3.00?μM, and the inhibition kinetic parameters (K_i) were 1.34, 1.16, 2.98, 6.23, 4.09, 0.62, and 2.11?μM, respectively.

3.?Metabolism of morusin exhibited significant species differences. The quantities of M₁ from minipig, monkey, dog, and rat were 7.8, 11.9, 2.0, and 6.3-fold of human levels. The K_m values in HLMs, RLMs, MLMs, DLMs, and PLMs were 7.84, 22.77, 14.32, 9.13, and 22.83?μM, and V_max for these species were 0.09, 1.23, 1.43, 0.15, and 0.75?nmol/min/mg, respectively. CL_int (intrinsic clearance) values (V_max/K_m) for morusin obeyed the following order: monkey?>?rat?>?minipig?>?dog?>?human. CL_H (hepatic clearance) values for humans, dogs, and rats were calculated to be 8.28, 17.38, and 35.12?mL/min/kg body weight, respectively.

4.?This study provided vital information to understand the inhibitory potential and metabolic behavior of morusin among various species.     

Raloxifene glucuronidation in liver and intestinal microsomes of humans and monkeys: contribution of UGT1A1, UGT1A8 and UGT1A9

1.?Raloxifene is an antiestrogen that has been marketed for the treatment of osteoporosis, and is metabolized into 6- and 4′-glucuronides by UDP-glucuronosyltransferase (UGT) enzymes. In this study, the in vitro glucuronidation of raloxifene in humans and monkeys was examined using liver and intestinal microsomes and recombinant UGT enzymes (UGT1A1, UGT1A8 and UGT1A9).

2.?Although the K_m and CL_int values for the 6-glucuronidation of liver and intestinal microsomes were similar between humans and monkeys, and species differences in V_max values (liver microsomes, humans?>?monkeys; intestinal microsomes, humans?<?monkeys) were observed, no significant differences were noted in the K_m or S₅₀, V_max and CL_int or CL_max values for the 4′-glucuronidation of liver and intestinal microsomes between humans and monkeys.

3.?The activities of 6-glucuronidation in recombinant UGT enzymes were UGT1A1?>?UGT1A8?>UGT1A9 for humans, and UGT1A8?>?UGT1A1?>?UGT1A9 for monkeys. The activities of 4′-glucuronidation were UGT1A8?>?UGT1A1?>?UGT1A9 in humans and monkeys.

4.?These results demonstrated that the profiles for the hepatic and intestinal glucuronidation of raloxifene by microsomes were moderately different between humans and monkeys.     

Investigation of the role of organic cation transporter 2 (OCT2) in the renal transport of guanfacine,a selective α2A-adrenoreceptor agonist

Abstract

1.?Guanfacine is a selective α_2A-adrenoreceptor agonist primarily excreted as its unchanged form through urine in human. This study was to investigate the involvement of organic cation transporter 2 (OCT2) in the renal tubular secretion of guanfacine.

2.?Transport of guanfacine was characterized using human embryonic kidney (HEK293) cells expressing human OCT2 (hOCT2). The inhibitory effect of cimetidine on guanfacine uptake was also examined. In addition, in vivo pharmacokinetic study was conducted in rats to assess the effects of cimetidine on the pharmacokinetics of guanfacine.

3.?The accumulation of guanfacine in hOCT2-transfected HEK293 cells was both time- and concentration-dependent, and markedly higher than that in mock cells. The apparent K_m and V_max values of guanfacine uptake by hOCT2 were 96.19?±?7.49?μM and 13.03?±?0.49?nmol/mg protein/min, respectively. Guanfacine transport mediated by hOCT2 was significantly inhibited by a typical OCT2 inhibitor cimetidine with an IC₅₀ value of 93.82?±?1.13?μM. Co-administration of cimetidine significantly decreased the plasma clearance (CL_p) as well as the renal clearance (CL_r) of guanfacine in rats in a dose-dependent manner, resulting in a noticeable increase in the systemic exposure of guanfacine.

4.?These results indicated that OCT2 may be involved in the renal disposition of guanfacine.     

In vitro inhibition of UGT1A3, UGT1A4 by ursolic acid and oleanolic acid and drug–drug interaction risk prediction

1.?Ursolic acid (UA) and oleanolic acid (OA) may have important activity relevant to health and disease prevention. Thus, we studied the activity of UA and OA on UDP-glucuronosyltransferases (UGTs) and used trifluoperazine as a probe substrate to test UGT1A4 activity. Recombinant UGT-catalyzed 4-methylumbelliferone (4-MU) glucuronidation was used as a probe reaction for other UGT isoforms.

2.?UA and OA inhibited UGT1A3 and UGT1A4 activity but did not inhibit other tested UGT isoforms.

3.?UA-mediated inhibition of UGT1A3 catalyzed 4-MU-β-d-glucuronidation was via competitive inhibition (IC₅₀ 0.391?±?0.013?μM; K_i 0.185?±?0.015?μM). UA also competitively inhibited UGT1A4-mediated trifluoperazine-N-glucuronidation (IC₅₀ 2.651?±?0.201?μM; K_i 1.334?±?0.146?μM).

4.?OA offered mixed inhibition of UGT1A3-mediated 4-MU-β-d-glucuronidation (IC₅₀ 0.336?±?0.013?μM; K_i 0.176?±?0.007?μM) and competitively inhibited UGT1A4-mediated trifluoperazine-N-glucuronidation (IC₅₀ 5.468?±?0.697?μM; K_i 6.298?±?0.891?μM).

5.?Co-administering OA or UA with drugs or products that are substrates of UGT1A3 or UGT1A4 may produce drug-mediated side effects.     

Comparison of intrinsic metabolic clearance in fresh and cryopreserved human hepatocytes

1. We compared the intrinsic clearance (CL_int) of a number of substrates in suspensions of fresh and cryopreserved human hepatocytes from seven donors.

2. CL_int values for a cocktail incubation of phenacetin, diclofenac, diazepam, bufuralol, midazolam, and hydroxycoumarin were 4.9?±?3.4, 18?±?7.2, 5.1?±?4.9, 6.3?±?3.3, 9.8?±?5.8 and 22?±?14?μl min^?1/10⁶ cells, respectively, and they correlated well with corresponding CL_int values using cryopreserved hepatocytes from 25 different donors.

3. CL_int values of each cocktail substrate and 20 AstraZeneca new chemical entities were compared in fresh and cryopreserved hepatocytes from the same three donors. There was a statistically significant correlation between CL_int in fresh and cryopreserved hepatocytes for each of the three livers (p?int values was 1.03.

4. In conclusion, the results add further support to the use of cryopreserved human hepatocytes as a screening model for the intrinsic clearance of new chemical entities.

     

Single concentration loss of activity assay provides an improved assessment of drug–drug interaction risk compared to IC50-shift

1.?The utility of two abbreviated, higher-throughput assays [IC50-shift and the loss of activity (LOA) assay] to evaluate time-dependent inhibition (TDI) of 24 structurally related compounds was compared.

2.?Good correlation (R² =?0.90) between % inhibition and k_inact/K_I suggested that the LOA assay has utility as an indicator of TDI potential. Weaker correlation was observed for the shifted IC50 (IC50_(T?=?30)) (R²?=?0.61) and the fold-shift in IC50 (R²?=?0.17).

3.?Primary mechanism for poor correlation was depletion of active enzyme at concentrations?>?1?μM leading to greater than predicted inhibition in the IC50-shift assay.

4.?Previously reported strong correlations between IC50_(T?=?30) and k_inact/K_I were found to be dependent on potent TDI compounds with k_inact/K_I?>?30; correlation was reduced for moderate inhibitors (k_inact/K_I?<?30). LOA assay maintained good correlation even when strong TDI compounds were excluded.

5.?LOA assay (% Inhibition at 30?min, 10?μM) was a good predictor of in vivo DDI (AUCr), providing a graded response with low potential for false negatives or positives. IC50-shift assay had bias for over-predicting in vivo DDI and was more likely to identify false positives.     

Retrospective use of PBPK modelling to understand a clinical drug–drug interaction between dextromethorphan and GSK1034702

1.?In a clinical trial, a strong drug–drug interaction (DDI) was observed between dextromethorphan (DM, the object or victim drug) and GSK1034702 (the precipitant or perpetrator drug), following single and repeat doses. This study determined the inhibition parameters of GSK1034702 in vitro and applied PBPK modelling approaches to simulate the clinical observations and provide mechanistic hypotheses to understand the DDI.

2.?In vitro assays were conducted to determine the inhibition parameters of human CYP2D6 by GSK1034702. PBPK models were populated with the in vitro parameters and DDI simulations conducted and compared to the observed data from a clinical study with DM and GSK1034702.

3.?GSK1034702 was a potent direct and metabolism-dependent inhibitor of human CYP2D6, with inhibition parameters of: IC_50?=_?1.6?μM, K_inact?=?3.7?h^?1 and K_I?=?0.8?μM. Incorporating these data into PBPK models predicted a DDI after repeat, but not single, 5?mg doses of GSK1034702.

4.?The DDI observed with repeat administration of GSK1034702 (5?mg) can be attributed to metabolism-dependent inhibition of CYP2D6. Further, in vitro data were generated and several potential mechanisms proposed to explain the interaction observed following a single dose of GSK1034702.     

Hepatic metabolism of diallyl disulphide in rat and man

1.?The metabolism of diallyl disulphide was investigated in vitro with rat and human liver cell subfractions and ex vivo with an isolated perfused rat liver.

2.?Diallyl disulphide was oxidized to diallylthiosulphinate by rat liver microsomes with an apparent K_m = 0.86 ± 0.1?mM and an apparent V_max = 0.47 ± 0.12 nmol?min^?1?mg^?1 protein (mean ± SE). Both cytochrome P450 (CYP) and flavin-containing monooxygenases were involved, with CYP2B1/2 and CYP2E1 being the most active CYP enzymes.

3.?In rat and man, microsomal oxidation of allylmethyl sulphide to allylmethyl sulphoxide and allylmethyl sulphone also occurred, although at a low rate. Diallyl disulphide was also metabolized to allylglutathione sulphide and allylmercaptan. In addition, diallylthiosulphinate reacted non-enzymatically with glutathione to form allylglutathione sulphide.

4.?When an isolated rat liver was perfused with diallyl disulphide, the metabolites allyl mercaptan, allylmethyl sulphide, allylmethyl sulphoxide, allylmethyl sulphone and allylglutathione sulphide were detected primarily within the liver tissue, with only small amounts of metabolites found in the bile and perfusion medium. The pharmacokinetic parameters for diallyl disulphide were t_1/2 = 6.09?min; AUC_0–∞ = 4.77?min?mmol?l^?1; clearance = 34.22 ml?min^?1.

5.?A scheme for the metabolism of diallyl disulphide in rat and man is proposed.     

Interaction of isoflavonoids with human liver microsomal cytochromes P450: inhibition of CYP enzyme activities

1.?The possibility of interaction of isoflavonoids with concomitantly taken drugs to determined isoflavonoids safety was studied. Inhibition of nine forms of cytochrome P450 (CYP3A4, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2C9, CYP2D6 and CYP2E1) by 12 isoflavonoids (daidzein, genistein, biochanin A, formononetin, glycitein, equol and six glucosides, daidzin, puerarin, genistin, sissotrin, ononin and glycitin) was studied systematically.

2.?The most potent inhibitors were genistein and daidzein inhibiting noncompetitively the CYP2C9 with K_i of 35.95?±?6.96 and 60.56?±?3.53?μmol/l and CYP3A4 (inhibited by genistein with K_i of 23.25?±?5.85?μmol/l also by a noncompetitive mechanism). Potent inhibition of CYP3A4 was observed also with biochanin A (K_i of 57.69?±?2.36?μmol/l) and equol (K_i of 38.47?±?2.32?μmol/l).

3.?Genistein and daidzein inhibit noncompetitively CYP3A4 and CYP2C9. With plasma levels in micromolar range, a clinically important interaction with concomitantly taken drugs does not seem to be probable.     

A novel in vitro allometric scaling methodology for aldehyde oxidase substrates to enable selection of appropriate species for traditional allometry

1.?Failure to predict human pharmacokinetics of aldehyde oxidase (AO) substrates using traditional allometry has been attributed to species differences in AO metabolism.

2.?To identify appropriate species for predicting human in vivo clearance by single-species scaling (SSS) or multispecies allometry (MA), we scaled in vitro intrinsic clearance (CL_int) of five AO substrates obtained from hepatic S9 of mouse, rat, guinea pig, monkey and minipig to human in vitro CL_int.

3.?When predicting human in vitro CL_int, average absolute fold-error was ≤2.0 by SSS with monkey, minipig and guinea pig (rat/mouse >3.0) and was <3.0 by most MA species combinations (including rat/mouse combinations).

4.?Interspecies variables, including fraction metabolized by AO (F_m,AO) and hepatic extraction ratios (E) were estimated in vitro. SSS prediction fold-errors correlated with the animal:human ratio of E (r²?=?0.6488), but not F_m,AO (r²?=?0.0051).

5.?Using plasma clearance (CL_p) from the literature, SSS with monkey was superior to rat or mouse at predicting human CL_p of BIBX1382 and zoniporide, consistent with in vitro SSS assessments.

6.?Evaluation of in vitro allometry, F_m,AO and E may prove useful to guide selection of suitable species for traditional allometry and prediction of human pharmacokinetics of AO substrates.     

In vitro metabolism of the epoxide substructure of cryptophycins by cytosolic glutathione S-transferase: Species differences and stereoselectivity

The enzyme kinetics of the glutathione (GSH) conjugation of cryptophycin 52 (C52, R-stereoisomer) and cryptophycin 53 (C53,?S-stereoisomer) by cytosolic glutathione S-transferases (cGSTs) from human, rat, mouse, dog and monkey liver were studied. V_max, K_m, and CL_int values for glutathione conjugation of C52 (R-stereoisomer) were 0.10?±?0.01?nmol?min^?1?mg^?1, 3.24?±?0.23?µM, and (3.15?±?0.09)?×?10^?2?ml?min^?1?mg^?1, respectively, in human cytosol. Due to limited solubility relative to the K_m, only CL_int values were determined in rat ((7.76?±?0.10)?×?10^?2?ml?min^?1?mg^?1) and mouse ((7.61?±?0.50)?×?10^?2?ml?min^?1?mg^?1) cytosol. Enzyme kinetic parameters could not be determined for C53 (S-stereoisomer). Microsomal GSH conjugation in human, rat, and mouse was attributed to cytosolic contamination. No GSH conjugation was seen in any biological matrix from dog or monkey. There was little GSH conjugation of C53 by cytosol or microsomes from any species. The metabolism of C52 and C53 by epoxide hydrolase was also investigated. No diol product was observed in any biological matrix from any species. Thus, cGSTs are primarily responsible for C52 metabolism.     

Prediction of clinical pharmacokinetic parameters of linezolid using animal data by allometric scaling: applicability for the development of novel oxazolidinones

1.?Allometric scaling has previously been used as an effective tool for the prediction of human pharmacokinetic data. The pharmacokinetic data for linezolid, a novel oxazolidinone to treat Gram-positive pathogens, in mice, rats and dogs were subjected to simple allometric scaling. Generated allometric equations for parameters such as clearance (CL), volume of distribution (V_ss) and elimination rate constant (K₁₀) were used to predict human pharmacokinetic parameters including elimination half-lives. In addition, the human plasma concentration–time curve was simulated using a one-compartmental model.

2.?Application of simple allometry (Y?=?aW^b) for animal parameters such as CL, V_ss, and K₁₀ showed excellent allometric fit (r?≥?0.98). The allometric equations for CL, V_ss, and K₁₀ were??0.5465W^0.6595,??0.1369W^0.9246, and??0.4117W^–0.3139, respectively. The confidence in predictability of CL and V_ss parameters was particularly high since the allometric exponents of CL and V_ss almost approached the suggested values of 0.75 and 1.00, respectively.

3.?Animal pharmacokinetic parameters generated in the present authors’?laboratories for linezolid were in close agreement with reported literature values. The predicted human values for CL (4.68?l?h^?1), V_ss (37.07 litres), and K₁₀ (0.10?h^?1) were within the range observed for linezolid in the literature (CL?=?4?10.5 l?h^?1; V_ss?=?21???53 litres; K₁₀?=?0.09???0.3?h^?1). The human half-life (t_1/2) predicted using allometry (6.9?h) was similar to reported values in humans of 5?h. In summary, the retrospective analysis for linezolid suggests that allometric scaling can be used as a prospective tool for predicting human pharmacokinetic parameters of novel oxazolidinones.     

Effect of grapefruit juice and food on the pharmacokinetics of pirfenidone in healthy Chinese volunteers: a diet–drug interaction study

1.?Ingestion of grapefruit juice and food could be factors affecting the pharmacokinetics of pirfenidone, a promising drug for treatment of idiopathic pulmonary fibrosis.

2.?A randomized, open-label, three-period crossover study was carried out in 12 healthy Chinese male volunteers who were randomized to one of the three treatments: pirfenidone tablets (0.4?g) were orally administered to fasted or fed subjects, or with grapefruit juice. The washout period was 7 d.

3.?Significantly reduced maximum plasma concentration (C_max, 5.0 5?±?1.39 versus 10.9 0?±?2.94?mg·L^{? 1}), modestly affected area-under-the-plasma concentration–time curve (AUC) from time zero to 12?h post dosing (AUC_0–12?h, 21.8 9?±?6.47 versus 26.1 6?±?7.32?mg·h·L^{? 1}) and delayed time to reach C_max (T_max) were observed in fed group compared with fasted group. Similar effects on C_max (5.8 2?±?1.23 versus 10.9 0?±?2.94?mg·L^{? 1}) and AUC_0–12?h (modest but not statistically significant, 24.4 4?±?7.40 versus 26.1 6?±?7.32?mg·h·L^{? 1}) were observed for grapefruit juice compared to fasted subjects.

4.?Co-administration of pirfenidone with grapefruit juice resulted in modestly reduced overall oral absorption and significantly reduced peak concentrations compared to fasting, which was similar to effect of food ingestion. No adverse events were observed in the study, but relatively dramatic reduction of peak concentrations should raise concerns for clinical efficacy and safety.     

In vitro glucuronidation of aprepitant: a moderate inhibitor of UGT2B7

Abstract

1.?Aprepitant, an oral antiemetic, commonly used in the prevention of chemotherapy-induced nausea and vomiting, is primarily metabolized by CYP3A4. Aprepitant glucuronidation has yet to be evaluated in humans. The contribution of human UDP-glucuronosyltransferase (UGT) isoforms to the metabolism of aprepitant was investigated by performing kinetic studies, inhibition studies and correlation analyses. In addition, aprepitant was evaluated as an inhibitor of UGTs.

2.?Glucuronidation of aprepitant was catalyzed by UGT1A4 (82%), UGT1A3 (12%) and UGT1A8 (6%) and K_ms were 161.6?±?15.6, 69.4?±?1.9 and 197.1?±?28.2?µM, respectively. Aprepitant glucuronidation was significantly correlated with both UGT1A4 substrates anastrazole and imipramine (r_s?=?0.77, p?<?0.0001 for both substrates; n?=?44), and with the UGT1A3 substrate thyroxine (r_s?=?0.58, p?<?0.0001; n?=?44).

3.?We found aprepitant to be a moderate inhibitor of UGT2B7 with a K_i of ～10?µM for 4-MU, morphine and zidovudine. Our results suggest that aprepitant can alter clearance of drugs primarily eliminated by UGT2B7. Given the likelihood for first-pass metabolism by intestinal UGT2B7, this is of particular concern for oral aprepitant co-administered with oral substrates of UGT2B7, such as zidovudine and morphine.     

Effects of CYP3A5 genotypes,ABCB1 C3435T and G2677T/A polymorphism on pharmacokinetics of Tacrolimus in Chinese adult liver transplant patients

Abstract

1.?The purpose of this study was to establish a population pharmacokinetic (PK) model of tacrolimus and evaluate the influence of clinical covariates, including the genetic polymorphisms of the cytochrome P450 3A5 gene (CYP3A5) and gene-encoding P-glycoprotein (ABCB1), on the PK parameters in Chinese adult liver transplant recipients.

2.?Details of drug dose, sampling times and concentrations were collected retrospectively from routine therapeutic drug monitoring data early after liver transplant. Tacrolimus PKs was studied by a non-linear mixed-effect modeling (NONMEM) method. CYP3A5 genotypes, ABCB1 C3435T and G2677T/A polymorphism and a number of clinical covariates were tested for their influence on TAC PKs.

3.?A one-compartment model with first-order absorption and elimination adequately described the data. Apparent clearance (CL/F) and apparent volumes of distribution (V/F) in final population model were 17.6?L/h and 225?L, respectively. The absorption rate constant (K_a) was fixed at 4.48?h^?1. The inter-individual variability in CL/F and V/F was 53.9 and 68%, respectively. In the final model, CYP3A5 genotype, post-operative day, alanine aminotransferase, total bilirubin, hematocrit and blood urea nitrogen were found to significantly influence the CL/F, whereas POD and HB influence V/F.

4.?Population PK analysis of tacrolimus in Chinese adult liver transplant patients resulted in identification of the CYP3A5 genotype, POD, BUN, ALP, HCT, TBIL and HB as significant covariates on the PK parameters of tacrolimus.     

Mechanistic investigations into the species differences in pinometostat clearance: impact of binding to alpha-1-acid glycoprotein and permeability-limited hepatic uptake

1.?The plasma clearance of the first-in-class DOT1L inhibitor, EPZ-5676 (pinometostat), was shown to be markedly lower in human compared to the preclinical species, mouse, rat and dog.

2.?This led to vertical allometry where various interspecies scaling methods were applied to the data, with fold-errors between 4 and 13. We had previously reported the elimination and metabolic pathways of EPZ-5676 were similar across species. Therefore, the aim of this work was to explore the mechanistic basis for the species difference in clearance for EPZ-5676, focusing on other aspects of disposition.

3.?The protein binding of EPZ-5676 in human plasma demonstrated a non-linear relationship suggesting saturable binding at physiologically relevant concentrations. Saturation of protein binding was not observed in plasma from preclinical species. Kinetic determinations using purified serum albumin and alpha-1-acid glycoprotein (AAG) confirmed that EPZ-5676 is a high affinity ligand for AAG with a dissociation constant (K_d) of 0.24?μM.

4.?Permeability limited uptake was also considered since hepatocyte CL_int was much lower in human relative to preclinical species. Passive unbound CL_int for EPZ-5676 was estimated using a correlation analysis of logD and data previously reported on seven drugs in sandwich cultured human hepatocytes.

5.?Incorporation of AAG binding and permeability limited hepatic uptake into the well-stirred liver model gave rise to a predicted clearance for EPZ-5676 within 2-fold of the observed value of 1.4?mL min^?1?kg^?1. This analysis suggests that the marked species difference in EPZ-5676 clearance is driven by high affinity binding to human AAG as well as species-specific hepatic uptake invoking the role of transporters.     

A unified strategy in selection of the best allometric scaling methods to predict human clearance based on drug disposition pathway

1.?It is critical to develop a unified strategy to select the best allometric scaling (AS) method for a given group of drugs.

2.?A total of 446 drugs with known human CL_iv, clear disposition pathway and animal (rat, dog, monkey) CL_iv were analyzed. All drugs were stratified based on their disposition pathway, liver extraction ratio (ER_H) and ratios of unbound clearance to renal glomerular filtration rate (R_GFR). Up to 22 AS methods were applied and compared in prediction of human CL_iv to each group of drugs.

3.?AS methods that give the best prediction of human CL_iv, were identified for drugs primarily eliminated through liver with a fraction of renal elimination (f_renal) within 0.3–0.5 or ER_H?>?0.3, where human CL_iv of more than 80% or 90% drugs could be accurately (within 2- or 3-fold error) predicted. For drugs with ER_H?<?0.3, acceptable accuracy could be achieved by a two species method TS_R,D resulting more than 60% or 75% drugs were predicted within 2- or 3-fold error.

4.?By stratified analysis of drugs, according to their disposition pathway and organ extraction ratio, a unified strategy was developed to select the best AS method in prediction of human CL_iv.     

Effect of piperine on CYP2E1 enzyme activity of chlorzoxazone in healthy volunteers

1.?The purpose of the present study was to investigate the effect of piperine (PIP) on CYP2E1 enzyme activity and pharmacokinetics of chlorzoxazone (CHZ) in healthy volunteers.

2.?An open-label, two period, sequential study was conducted in 12 healthy volunteers. A single dose of PIP 20?mg was administered daily for 10 days during treatment phase. A single dose of CHZ 250?mg was administered during control and after treatment phases under fasting conditions. The blood samples were collected at predetermined time intervals after CHZ dosing and analyzed by HPLC.

3.?Treatment with PIP significantly enhanced maximum plasma concentration (C_max) (3.14–4.96?μg/mL)_, area under the curve (AUC) (10.46–17.78?μg h/mL), half life (T_1/2) (1.26–1.82?h) and significantly decreased elimination rate constant (K_el) (0.57–0.41?h?^??¹), apparent oral clearance (CL/F) (24.76–13.65?L/h) of CHZ when compared to control. In addition, treatment with PIP significantly decreased C_max (0.22–0.15?μg/mL), AUC (0.94–0.68?μg h/mL), T_1/2 (2.54–1.68?h) and significantly increased K_el (0.32–0.43?h?^??¹) of 6-hydroxychlorzoxazone (6-OHCHZ) as compared to control. Furthermore, treatment with PIP significantly decreased metabolite to parent (6-OHCHZ/CHZ) ratios of C_max, AUC, T_1/2 and significantly increased K_el ratio of 6-OHCHZ/CHZ, which indicate the decreased formation of CHZ to 6-OHCHZ.

4.?The results suggest that altered pharmacokinetics of CHZ might be attributed to PIP mediated inhibition of CYP2E1 enzyme, which indicate significant pharmacokinetic interaction present between PIP and CHZ. The inhibition of CYP2E1 by PIP may represent a novel therapeutic benefit for minimizing ethanol induced CYP2E1 enzyme activity and results in reduced hepatotoxicity of ethanol.     

Pharmacokinetic analysis of factors determining elimination pathways for sulfate and glucuronide metabolites of xenobiotics. iii: mechanisms for sinusoidal efflux of 4-methylumbelliferone sulfate

1.?To elucidate the mechanisms involved in the sinusoidal efflux of sulfate and glucuronide metabolites of 4-methylumbelliferone (4MU), isolated rat liver perfusion studies were performed under several conditions.

2.?The effect of sodium azide on the hepatic handling of both conjugates was examined. The net sinusoidal efflux clearance (CL_eff) based on the unbound concentration in the liver did not change for 4MU glucuronide (4MUG) or significantly increase for 4MU sulfate (4MUS), suggesting that the sinusoidal efflux of both conjugates is not mediated by the transport systems dependent on adenosine triphosphate.

3.?Under Cl^?-depleted conditions, the CL_eff of 4MUG significantly decreased, but the saturation of its sinusoidal efflux rather than the transport system dependent on Cl^? might be involved because the hepatic concentration of 4MUG was extensively higher than that of the control study due to the extremely attenuated biliary excretion. The CL_eff of 4MUS also significantly decreased, but its hepatic concentration was not different from that in the control study, suggesting that the transport system using Cl^? is involved in the sinusoidal efflux of 4MUS.

4.?The effect of glutathione was examined. CL_eff of 4MUG was not affected by the additional glutathione, but CL_eff of 4MUS decreased significantly, suggesting that some transport system sensitive to glutathione is involved in the sinusoidal efflux of 4MUS, but not of 4MUG.

5.?Transporters such as Oatp1, Oatp2 and/or Npt1 might be involved in the sinusoidal efflux of 4MUS, but 4MUG is secreted from the sinusoidal membrane via the systems that are totally different from those for 4MUS.