A convenient five-drug cocktail for the assessment of major drug metabolizing enzymes: a pilot study

Critical Assessment of Phenotyping Cocktails for Clinical Use in an African Context

Interethnic and interindividual variability in in vivo cytochrome P450 (CYP450)-dependent metabolism and altered drug absorption via expressed transport channels such as P-glycoprotein (P-gp) contribute to the adverse drug reactions, drug-drug interaction and therapeutic failure seen in clinical practice. A cost-effective phenotyping approach could be advantageous in providing real-time information on in vivo phenotypes to assist clinicians with individualized drug therapy, especially in resource-constrained countries such as South Africa. A number of phenotyping cocktails have been developed and the aim of this study was to critically assess the feasibility of their use in a South African context. A literature search on library databases (including AccessMedicine, BMJ, ClinicalKey, MEDLINE (Ovid), PubMed, Scopus and TOXLINE) was limited to in vivo cocktails used in the human population to phenotype phase I metabolism and/or P-gp transport. The study found that the implementation of phenotyping in clinical practice is currently limited by multiple administration routes, the varying availability of probe drugs, therapeutic doses eliciting side effects, the interaction between probe drugs and extensive sampling procedures. Analytical challenges include complicated sample workup or extraction assays and impractical analytical procedures with low detection limits, analyte sensitivity and specificity. It was concluded that a single time point, non-invasive capillary sampling, combined with a low-dose probe drug cocktail, to simultaneously quantify in vivo drug and metabolite concentrations, would enhance the feasibility and cost-effectiveness of routine phenotyping in clinical practice; however, future research is needed to establish whether the quantitative bioanalysis of drugs in a capillary whole-blood matrix correlates with that of the standard plasma/serum matrixes used as a reference in the current clinical environment.

Evaluation of a six-probe cocktail (caffeine, tolbutamide, omeprazole, dextromethorphan, midazolam, and digoxin) approach to estimate hepatic drug detoxification capability and dosage requirements after a single oral dosing in healthy Chinese volunteers

The primary objectives of this study were to investigate the suitability of a 6-probe cocktail (caffeine, tolbutamide, omeprazole, dextromethorphan, midazolam, and digoxin) to be used as a tool for assessing the activity of drug metabolizing enzymes and transporters, and examine differences in the way drugs are handled among groups with different genetic regulation of these processes. This was a single-center, open-label, phase I clinical study involving 20 young, healthy Chinese volunteers (equal gender distribution). The subjects were administered a single, oral dose of the 6-probe cocktail and serum samples were collected to assess the disposition of the different probe substrates and produced metabolites. The serum samples were analyzed using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry technology. The DNA samples were subjected to whole exome sequencing. Nineteen healthy volunteers completed the study. The 6-probe cocktail was safe and well-tolerated by all the subjects. The parent substrates and metabolites-caffeine (paraxanthine), dextromethorphan (dextrorphan), digoxin, midazolam (1-hydroxy-midazolam), omeprazole (5-hydroxy-omeprazole), and tolbutamide (4-hydroxy-tolbutamide)-were within the detectable window. Genetic variations known to alter drug metabolism (CYP2D6*10, CYP2C19*2, CYP2C19*3, and CYP2C9*3) were identified and generally correlated with phenotypic status. The 6-probe cocktail appeared to be suitable for assessing drug metabolizing activities. This, in conjunction with individual genetics, will pave the way for the implementation of personalized medicine in clinical practice. This will hopefully improve efficacy and reduce the incidence of adverse drug reactions.

Limited Sampling Modeling for Estimation of Phenotypic Metrics for CYP Enzymes and the ABCB1 Transporter Using a Cocktail Approach

Plasma concentration data points (n = 2,640) from 16 healthy adults were used to develop and validate limited sampling strategies (LSS) for estimation of phenotypic metrics for CYP enzymes and the ABCB1 transporter, using a cocktail of subtherapeutic doses of the selective probes caffeine (CYP1A2), metoprolol (CYP2D6), midazolam (CYP3A), losartan (CYP2C9), omeprazole (CYP2C19), and fexofenadine (ABCB1). All-subsets linear regression modelling was applied to estimate the AUC_0–12h for caffeine, fexofenadine, and midazolam, and the AUC_0–12h ratio of metoprolol: α-OH metoprolol and omeprazole:5-OH omeprazole. LSS-derived metrics were compared with the parameters’ ‘best estimates’ obtained by non-compartmental analysis using all plasma concentration data points. The correlation coefficient (R²) was used to identify the LSS equations that provided the best fit for n timed plasma samples, and the jack-knife statistics was used as an additional validation procedure for the LSS models. Single time-point LSS models provided R² values greater than 0.95 (R² > 0.95) for the AUC_0–12h ratio of metoprolol:α-OH metoprolol and omeprazole:5-OH omeprazole, whereas 2 time-point models were required for R² > 0.95 for the AUC_0–12h of caffeine, fexofenadine, and midazolam. Increasing the number of sampling points to three led to minor increases in R² and/or the bias or prediction of the estimates. In conclusion, the LSS models provided accurate prediction of phenotypic indices for CYP1A2, CYP2C19, CYP2D6, CYP3A, and ABCB1, when using subtherapeutic doses of selective probes for these enzymes and transporter.

Use of Cocktail Probe Drugs for Indexing Cytochrome P450 Enzymes in Clinical Pharmacology Studies - Review of Case Studies

BACKGROUND

The cocktail approach of probing drug metabolizing enzymes, in particular cytochrome P450 (CYP) enzymes, is a cornerstone in clinical pharmacology studies. The first report of the famous "Pittsburg cocktail" has led the way for the availability of numerous cocktail substrate mixtures that provide options for indexing of CYP enzymes and/or evaluating the perpetrator capacity of the drug.

OBJECTIVE

The key objectives were: 1) To collate, tabulate, and discuss the various cocktail substrates to determine specific CYP enzyme activity in clinical pharmacology studies with specific case studies; 2) To introspect on how the cocktail approach has withstood the test of time and evolved for enabling key decision(s); 3) To provide some futuristic views on the use of cocktail in drug discovery and development.

METHOD

The review was compiled after consultation with databases such as PubMed (NCBI database) and Google scholar to source various published literature on cocktail approaches in drug development.

RESULTS

In the reviewed case studies, CYP indexing was achieved using a single time point (differing for specific CYP enzyme) plasma determination of the metabolite to parent ratio for all CYP enzymes with the exception of CYP3A4/5, where multiple time points were required for exposure measurement of midazolam and its metabolite. Likewise, a single void of urine, for a specific time duration, has been utilized for the recovery measurements of parent and metabolite for CYP indexing purposes.

CONCLUSION

The review provides a comprehensive list of various types of cocktail approaches and discusses some key considerations including the evolution of the cocktail approaches over time, perspectives and futuristic views for the use of probe drugs to aid the execution of clinical pharmacology studies and data interpretation.

Pharmacokinetics and phenotyping properties of the Basel phenotyping cocktail combination capsule in healthy male adults

AIMS

We compared the phenotyping metrics of a combination capsule formulation to its individual components of the newly composed Basel phenotyping cocktail. Moreover, we investigated a reduced sampling regimen for clinical applications.

METHODS

We performed in vitro experiments and a crossover pharmacokinetic study in twelve healthy male subjects to compare the Basel phenotyping cocktail capsule containing 6 cytochrome P450 (CYP) probe drugs with individual administration of the same drugs. Parent compounds and selected metabolites were determined by liquid chromatography-tandem mass spectrometry. Metabolic ratios (MR) for are under the curve (AUC) and single time point measurements and their correlation were determined.

RESULTS

Experiments with human liver microsomes and primary human hepatocytes in 3D co-culture confirmed that flurbiprofen is a suitable CYP2C9 substrate. Both cocktail formulations (capsule and individual probe drug administration) were well-tolerated and yielded reproducible MRs, which were almost identical. Correlations between single time point ratios and the corresponding AUC ratios depended on the sampling time point and the concentration time curve of the probe drugs. The MR of the capsule (Spearman rank correlation coefficient, R_s : 0.77-0.97) as well as the individual components (R_s : 0.69-0.99) correlated best at 6 h post-treatment considering all 6 CYPs. Moreover, the 2-h time points of the capsule agreed suitably with the AUC; however, the MR of omeprazole could not be determined for 10 out of 12 subjects.

CONCLUSION

The capsule is easy to swallow, well tolerated and provides reliable estimates for CYP activity. The optimal sampling point for the capsule formulation is 6 h after intake.

Non randomized study on the potential of nitisinone to inhibit cytochrome P450 2C9, 2D6, 2E1 and the organic anion transporters OAT1 and OAT3 in healthy volunteers

PURPOSE

Nitisinone inhibits the cytochrome P450 (CYP) subfamilies CYP2C9, CYP2D6, and CYP2E1 and the organic anion transporter (OAT) isoforms OAT1 and OAT3 in vitro. Since the effect of nitisinone on these enzymes and transporters in humans is still unknown, the purpose of this study was to evaluate the effect of nitisinone on these CYP subfamilies and OAT isoforms.

METHODS

This was an open-label, nonrandomized, two-arm, phase 1 study (EudraCT: 2016-004297-17) in healthy volunteers. The substrates (tolbutamide, metoprolol, and chlorzoxazone for the respective CYPs and furosemide for the OATs) were administered as single doses, before and after 15 days of once daily dosing of 80 mg nitisinone, to determine the AUC_∞ ratios ([substrate+nitisinone]/[substrate]). Nitisinone pharmacokinetics, safety, and tolerability were also assessed, and blood and urine were collected to determine substrate and nitisinone concentrations by LC-MS/MS.

RESULTS

Thirty-six subjects were enrolled with 18 subjects included in each arm. The least square mean ratio (90% confidence interval) for AUC_∞ was 2.31 (2.11-2.53) for tolbutamide, 0.95 (0.88-1.03) for metoprolol, 0.73 (0.67-0.80) for chlorzoxazone, and 1.72 (1.63-1.81) for furosemide. Clinically relevant nitisinone steady-state concentrations were reached after 12 days: mean C_av,ss of 94.08 μM. All treatments were well tolerated, and no safety concerns were identified.

CONCLUSIONS

Nitisinone did not affect CYP2D6 activity, was a weak inducer of CYP2E1, and was a weak inhibitor of OAT1 and OAT3. Nitisinone was a moderate inhibitor of CYP2C9, and treatment may therefore result in increased plasma concentrations of comedications metabolized primarily via this enzyme.

CLINICAL TRIAL REGISTRY IDENTIFICATION

EudraCT 2016-004297-17.

Effects of shuanghuanglian injection on the activities of CYP1A2, 2C11, 2D1 and 3A1/2 in rats in vivo and in vitro

Shuanghuanglian Injection (SHLI), one of the most popular herbal prescription in China, has been commonly used to treat pneumonia, tonsillitis, and other respiratory diseases caused by bacterium and virus. This study is to investigate the effects of SHLI on the activities of Cytochrome P450 (CYP) 1A2, 2C11, 2D1 and 3A1/2 in rats. Sixteen rats were randomly divided into two groups (SHLI-treated and blank control). They were administered SHLI or physiological saline for consecutive seven days. On day eight, 16 animals were administrated cocktail drugs as probe substrates of the four CYP in vivo. In addition, other four probe drugs were added, respectively, into incubation systems of rat liver microsomes (RLM) to assess the effects of SHLI on the four CYP isoforms in vitro. SHLI exhibited an inductive effect on CYP2C11 in vivo by decreasing C_max, t_1/2 and AUC_0-∞ of tolbutamide, while the main pharmacokinetic parameters of caffeine, metoprolol and dapsone have no significant changes. In vitro study, SHLI showed no significant effects on the activities of CYP1A2, 2D1 and 3A1/2, but increasing the metabolism of tolbutamide in RLM. SHLI induced the activities of CYP2C11, but had no significant effects on the activities of CYP1A2, CYP2D1 and CYP3A1/2 in rats.

Cytochrome P450 Enzymes Involved in Metoprolol Metabolism and Use of Metoprolol as a CYP2D6 Phenotyping Probe Drug

Metoprolol is used for phenotyping of cytochrome P450 (CYP) 2D6, a CYP isoform considered not to be inducible by inducers of the CYP2C, CYP2B, and CYP3A families such as rifampicin. While assessing CYP2D6 activity under basal conditions and after pre-treatment with rifampicin in vivo, we surprisingly observed a drop in the metoprolol/α-OH-metoprolol clearance ratio, suggesting CYP2D6 induction. To study this problem, we performed in vitro investigations using HepaRG cells and primary human hepatocytes (before and after treatment with 20 μM rifampicin), human liver microsomes, and CYP3A4-overexpressing supersomes. While mRNA expression levels of CYP3A4 showed a 15- to 30-fold increase in both cell models, mRNA of CYP2D6 was not affected by rifampicin. 1'-OH-midazolam formation (reflecting CYP3A4 activity) increased by a factor of 5-8 in both cell models, while the formation of α-OH-metoprolol increased by a factor of 6 in HepaRG cells and of 1.4 in primary human hepatocytes. Inhibition studies using human liver microsomes showed that CYP3A4, 2B6, and 2C9 together contributed 19.0 ± 2.6% (mean ± 95%CI) to O-demethylation, 4.0 ± 0.7% to α-hydroxylation, and 7.6 ± 1.7% to N-dealkylation of metoprolol. In supersomes overexpressing CYP3A4, metoprolol was α-hydroxylated in a reaction inhibited by the CYP3A4-specific inhibitor ketoconazole, but not by the CYP2D6-specific inhibitor quinidine. We conclude that metoprolol is not exclusively metabolized by CYP2D6. CYP3A4, 2B6, and 2C9, which are inducible by rifampicin, contribute to α-hydroxylation, O-demethylation, and N-dealkylation of metoprolol. This contribution is larger after CYP induction by rifampicin but is too small to compromise the usability of metoprolol α-hydroxylation for CYP2D6 phenotyping.

Integration of pharmacometabolomics with pharmacokinetics and pharmacodynamics: towards personalized drug therapy

Personalized medicine, in modern drug therapy, aims at a tailored drug treatment accounting for inter-individual variations in drug pharmacology to treat individuals effectively and safely. The inter-individual variability in drug response upon drug administration is caused by the interplay between drug pharmacology and the patients' (patho)physiological status. Individual variations in (patho)physiological status may result from genetic polymorphisms, environmental factors (including current/past treatments), demographic characteristics, and disease related factors. Identification and quantification of predictors of inter-individual variability in drug pharmacology is necessary to achieve personalized medicine. Here, we highlight the potential of pharmacometabolomics in prospectively informing on the inter-individual differences in drug pharmacology, including both pharmacokinetic (PK) and pharmacodynamic (PD) processes, and thereby guiding drug selection and drug dosing. This review focusses on the pharmacometabolomics studies that have additional value on top of the conventional covariates in predicting drug PK. Additionally, employing pharmacometabolomics to predict drug PD is highlighted, and we suggest not only considering the endogenous metabolites as static variables but to include also drug dose and temporal changes in drug concentration in these studies. Although there are many endogenous metabolite biomarkers identified to predict PK and more often to predict PD, validation of these biomarkers in terms of specificity, sensitivity, reproducibility and clinical relevance is highly important. Furthermore, the application of these identified biomarkers in routine clinical practice deserves notable attention to truly personalize drug treatment in the near future.

Evaluation of the synergistic effect of Allium sativum, Eugenia jambolana, Momordica charantia, Ocimum sanctum, and Psidium guajava on hepatic and intestinal drug metabolizing enzymes in rats

Aims/Background:

This study was to investigated the synergistic effect of polyherbal formulations (PHF) of Allium sativum L., Eugenia jambolana Lam., Momordica charantia L., Ocimum sanctum Linn., and Psidium guajava L. in the inhibition/induction of hepatic and intestinal cytochrome P450 (CYPs) and Phase-II conjugated drug metabolizing enzymes (DMEs). Consumption of these herbal remedy has been extensively documented for diabetes treatment in Ayurveda.

Methodology:

PHF of these five herbs was prepared, and different doses were orally administered to Sprague–Dawley rats of different groups except control group. Expression of mRNA and activity of DMEs were examined by real-time polymerase chain reaction and high performance liquid chromatography in isolated liver and intestine microsomes in PHF pretreated rats.

Results:

The activities of hepatic and intestinal Phase-II enzyme levels increased along with mRNA levels except CYP3A mRNA level. PHF administration increases the activity of hepatic and intestinal UDP-glucuronyltransferase and glutathione S-transferase in response to dose and time; however, the activity of hepatic sulfotransferase increased at higher doses.

Conclusions:

CYPs and Phase-II conjugated enzymes levels can be modulated in dose and time dependent manner. Observations suggest that polyherbal formulation might be a possible cause of herb-drug interaction, due to changes in pharmacokinetic of crucial CYPs and Phase-II substrate drug.

A liquid chromatography-tandem mass spectrometry analysis of nine cytochrome P450 probe drugs and their corresponding metabolites in human serum and urine

Cocktail phenotyping using specific probe drugs for cytochrome P450 (CYP) enzymes provides information on the real-time activity of multiple CYPs. We investigated different sample preparation techniques and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with simple protein precipitation for the analysis of nine CYP probe drugs and their metabolites in human serum and urine. Specific CYP probe drugs (melatonin, CYP1A2; nicotine, CYP2A6; bupropion, CYP2B6; repaglinide, CYP2C8; losartan, CYP2C9; omeprazole, CYP2C19 and CYP3A4; dextromethorphan, CYP2D6; chlorzoxazone, CYP2E; midazolam, CYP3A4) and their main metabolites, with the exception of 3'-hydroxyrepaglinide, were quantified in human serum and urine using the developed LC-MS/MS method. The analytical method was fully validated showing high selectivity, linearity, acceptable accuracy (85-115 %) and precision (2-19 %) and applied to a pharmacokinetic study in four healthy volunteers after oral administration of drugs given as a cocktail. All probe drugs and their metabolites (totally 19 analytes) were detected and quantified from human serum and urine over the time range of 1 to 6 h after oral administration. Therefore, the proposed method is applicable for drug interaction and CYP phenotyping studies utilizing a cocktail approach. Graphical Abstract Workflow overwiew of cocktail CYP-phenotyping study.

Effects of notoginsenoside R1 on CYP1A2, CYP2C11, CYP2D1, and CYP3A1/2 activities in rats by cocktail probe drugs

CONTEXT

Notoginsenoside R1 (NGR1) is the main component with cardiovascular activity in Panax notoginseng (Burk.) F. H. Chen, an herbal medicine that is widely used to enhance blood circulation and dissipate blood stasis.

OBJECTIVE

The objective of this study is to investigate NGR1's effects on CYP1A2, CYP2C11, CYP2D1, and CYP3A1/2 activities in rats in vivo through the use of the Cytochrome P450 (CYP450) probe drugs.

MATERIALS AND METHODS

After pretreatment with NGR1 or physiological saline, the rats were administered intraperitoneally with a mixture solution of cocktail probe drugs containing caffeine (10 mg/kg), tolbutamide (15 mg/kg), metoprolol (20 mg/kg), and dapsone (10 mg/kg). The bloods were then collected at a set of time-points for the ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) analysis.

RESULTS

NGR1 was shown to exhibit an inhibitory effect on CYP1A2 by increased caffeine Cmax (43.13%, p < 0.01) and AUC0 - ∞ (40.57%, p < 0.01), and decreased CL/F (62.16%, p < 0.01) in the NGR1-treated group compared with those of the control group, but no significant changes in pharmacokinetic parameters of tolbutamide, metoprolol, and dapsone were observed between the two groups, indicating that NGR1 had no effects on rat CYP2C11, CYP2D1, and CYP3A1/2.

DISCUSSION AND CONCLUSION

When NGR1 is co-administered with drugs that are metabolized by CYP1A2, the pertinent potential herb-drug interactions should be monitored.

Effects of Guanxinning injection on rat cytochrome P450 isoforms activities in vivo and in vitro

1. We aimed to investigate the regulatory effects of Guanxinning injection (GXNI) on activities of cytochrome P1A2 (CYP1A2), CYP2C11, CYP2D1 and CYP3A1/2 by probe drugs in rats in vivo and in vitro. 2. GXNI-treated and blank control groups were administered GXNI and physiological saline by caudal vein for 14 days consecutively, then they were given the probe drugs of caffeine (10 mg/kg), tolbutamide (10 mg/kg), metoprolol (20 mg/kg) and dapsone (10 mg/kg) by intraperitoneal injection. The blood samples were collected at different times for ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. Changes of the pharmacokinetics parameters between the GXNI-treated and the blank control groups were used to evaluate the effects of GXNI on the four CYP450 isoforms in rats in vivo. After blood collection, the livers of rats were taken and made microsomes for in vitro tests. The relevant metabolites of phenacetin, tolbutamide, dextromethorphan and testosterone were analyzed quantitatively by high-performance liquid chromatography (HPLC) after microsome incubation. The statistical differences between the two groups were observed to detect the effects of GXNI on the four CYP450 isoforms in rats in vitro. 3. The in vivo and in vitro results demonstrated that GXNI could induce CYP1A2 activity in rats, but had no significant effects on CYP2C11, CYP2D1 and CYP3A1/2.

The basel cocktail for simultaneous phenotyping of human cytochrome P450 isoforms in plasma, saliva and dried blood spots

BACKGROUND AND OBJECTIVE

Phenotyping cocktails use a combination of cytochrome P450 (CYP)-specific probe drugs to simultaneously assess the activity of different CYP isoforms. To improve the clinical applicability of CYP phenotyping, the main objectives of this study were to develop a new cocktail based on probe drugs that are widely used in clinical practice and to test whether alternative sampling methods such as collection of dried blood spots (DBS) or saliva could be used to simplify the sampling process.

METHODS

In a randomized crossover study, a new combination of commercially available probe drugs (the Basel cocktail) was tested for simultaneous phenotyping of CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4. Sixteen subjects received low doses of caffeine, efavirenz, losartan, omeprazole, metoprolol and midazolam in different combinations. All subjects were genotyped, and full pharmacokinetic profiles of the probe drugs and their main metabolites were determined in plasma, dried blood spots and saliva samples.

RESULTS

The Basel cocktail was well tolerated, and bioequivalence tests showed no evidence of mutual interactions between the probe drugs. In plasma, single timepoint metabolic ratios at 2 h (for CYP2C19 and CYP3A4) or at 8 h (for the other isoforms) after dosing showed high correlations with corresponding area under the concentration-time curve (AUC) ratios (AUC0-24h parent/AUC0-24h metabolite) and are proposed as simple phenotyping metrics. Metabolic ratios in dried blood spots (for CYP1A2 and CYP2C19) or in saliva samples (for CYP1A2) were comparable to plasma ratios and offer the option of minimally invasive or non-invasive phenotyping of these isoforms.

CONCLUSIONS

This new combination of phenotyping probe drugs can be used without mutual interactions. The proposed sampling timepoints have the potential to facilitate clinical application of phenotyping but require further validation in conditions of altered CYP activity. The use of DBS or saliva samples seems feasible for phenotyping of the selected CYP isoforms.

Evaluation on activity of cytochrome p450 enzymes in turbot via a probe drug cocktail

Cytochrome P450s (CYPs) are the main catalytic enzymes for metabolism by a variety of endogenous and exogenous substrates in mammals, fish, insects, etc. We evaluated the application of a multidrug cocktail on changes in CYP1, CYP2, and CYP3 activity in Turbot Scophthalmus maximus. The probe drugs were a combination of caffeine (5 mg/kg body weight), dapsone (5 mg/kg), and chlorzoxazone (10 mg/kg). After a single intraperitoneal injection of the cocktail, the concentration of all three probe drugs in the plasma increased quickly to a peak and then decreased gradually over 24 h. Pharmacokinetic profiles of the three probe drugs were determined using a noncompartmental analysis, and the typical parameters were calculated. In the assay for CYP induction, pretreatment with rifampicin significantly reduced the typical pharmacokinetic metrics for caffeine and chlorzoxazone, but not dapsone, indicating that the activity of CYP1 and CYP2 in turbot were induced by rifampicin.

Multianalyte determination of the kinetic rate constants of drug-cyclodextrin supermolecules by high performance affinity chromatography

The kinetics of the dissociation is fundamental to the formation and the in vivo performance of cyclodextrin supramolecules. The individual determination of the apparent dissociation rate constant (kd,app) using high performance affinity chromatography (HPAC) is a tedious process requiring numerous separate studies and massive data fitting. In this study, the multianalyte approach was employed to simultaneously measure the kd,app values of three drugs through one injection based on the investigation of the dependence of drug-cyclodextrin interaction kinetics on the mobile phase composition. As a result, the kd,app values increased when decreasing the ion strength, increasing the ionization of drugs and adding extra organic solvents. The values of kd,app for acetaminophen, phenacetin and S-flurbiprofen estimated by the multianalyte approach were 8.54±1.81, 5.36±0.94 and 0.17±0.02s(-1), respectively, which were in good agreement with those determined separately (8.31±0.58, 5.01±0.42 and 0.15±0.01s(-1)). For both of the single and multiple flow rate peak profiling methods, the results of the multianalyte approach were statistically equivalent with that of the single compound analysis for all of the three drugs (p>0.05). The multianalyte approach can be employed for the efficient evaluation of the drug-cyclodextrin kinetics with less variance caused by cyclodextrin column bleeding.

Biochemical and analytical development of the CIME cocktail for drug fate assessment in humans

Phenotyping based on drug metabolism activity appears to be informative regarding mechanism-based interactions during drug development. We report here the first steps of the development of the innovative CIME cocktail. This cocktail is designed not only for the major cytochrome P450, with caffeine, amodiaquine, tolbutamide, omeprazole, dextromethorphan and midazolam as substrates of CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A, respectively, but also phase II enzymes UGT 1A1/6/9 with acetaminophen, P-gp and OATP1B1 with digoxin and rosuvastatin, and renal function with memantine. An assay combining ultra-performance liquid chromatography using a 1.7 microm particle size column with tandem mass spectrometry (UPLC/MS/MS) was set up for the simultaneous quantification of the 20 substrates and metabolites after extraction from human plasma using solid-phase extraction. The method was validated in the spirit of the FDA guidelines. Mean accuracy ranged from 87.7 to 115%, the coefficient of variance (CV%) of intra- and inter-run from 1.7 to 16.4% and from 1.6 to 14.9%, respectively, and for the limit of quantification (LOQ) with ten lots of plasma, accuracy ranged from 84 to 115% and CV% precision was <16%. Short-term stability was evaluated in eluate (4 h, room temperature), plasma (24 h, room temperature), the autosampler (24 h, 4 degrees C) and in three freeze/thaw cycles in plasma. All except three analytes were stable under these conditions. For the three others a specific process can be followed. This robust, fast and sensitive assay in human plasma provides an analytical tool for ten-probe drugs of the CIME cocktail. Clinical samples will be assayed in the near future using this new assay method.

Effects of fluoroquinolones on CYP4501A and 3A in male broilers

The inhibitory effects of fluoroquinolones on the enzyme activity, protein levels and mRNA expression of liver cytochrome P450 (CYP) 1A and 3A were investigated in male broiler chicks. Enrofloxacin (20 mg/kg), sarafloxacin (8 mg/kg) and marbofloxacin (5.5 mg/kg) were administrated in drinking water for 7 consecutive days. A cocktail of the probe drugs caffeine and dapsone was used to determine CYP1A and 3A activity. Western blot analysis and real-time PCR were used to determine the effects on protein levels of CYP1A and 3A, and on CYP1A4, 1A5, 3A37 mRNA levels. Enrofloxacin increased the half-life of elimination for both caffeine and dapsone, and decreased expression of CYP1A and 3A protein. Marbofloxacin decreased the metabolism of caffeine and expression of CYP1A protein. However, no change in mRNA expression was observed for any treatment group. This suggested that high doses of enrofloxacin and marbofloxacin, but not sarafloxacin, inhibit CYP in chick liver raising the possibility of drug-drug interaction when using these compounds.

Simultaneous HPLC determination of tolbutamide, phenacetin and their metabolites as markers of cytochromes 1A2 and 2C6/11 in rat liver perfusate

A new, simple, rapid, sensitive, and repeatable reversed-phase HPLC method was developed and validated for the simultaneous determination of tolbutamide, phenacetin and their metabolites in rat liver perfusate. Chlorpropamide was used as an internal standard to ensure the precision and accuracy of this method. Analytes were extracted into diethyl ether using a two-step liquid-liquid extraction. A C18 analytical column and a mobile phase composed of acetonitrile and potassium phosphate buffer were used for the chromatographic separation with UV detection. Limits of detection varied between 20 and 46ng/mL for phenacetin, tolbutamide and their metabolites. The overall extraction recovery for the analytes varied from 65.4% in paracetamol to 88.0% in tolbutamide for concentrations within the expected range of concentrations from previous experimental samples. In terms of precision, the intra- and inter-day variation at three different concentrations in all analytes never exceeded 7.6 and 11.4%, respectively. This method is applicable for the modeling and description of possible pharmacological interactions on rat cytochromes P450 1A2 and 2C6/11 or can be used for in vitro evaluation of both cytochromes 1A2 and 2C.

Evaluation of protective effects of Chi-Zhi-Huang decoction on Phase I drug metabolism of liver injured rats by cocktail probe drugs

AIM OF THE STUDY

Chi-Zhi-Huang decoction (PGR) is one of the traditional Chinese medicine (TCM) preparations with unique effect on withdrawing jaundice and has been used to treat icteric patients in China for many years. In this research, we aim at to evaluate the potential activity of PGR in restoring hepatic drug metabolism in a damaged liver.

MATERIALS AND METHODS

A cocktail approach with caffeine (10mg/kg), dapsone (10mg/kg) and chlorzoxazone (20mg/kg) respectively as probe drug of cytochrome P450 (CYP) isoform of CYP 1A2, 3A4 and 2E1 was used to evaluate its possible effects on Phase I oxidative metabolism. Pretreated with three dosages of PGR water extract (0.75, 1.5 and 3g/kg, po) for 5 days, male Wistar rats (220-240 g) were intoxicated by phenylisothiocyanate (PITC, 100mg/kg, po) 24h before probes intravenous injection. The pharmacokinetics of the probes in the blood was determined simultaneously by HPLC, and their non-compartmental parameters were used to evaluate the metabolic difference among the groups. Moreover, the levels of liver enzymes (ALT, AST, ALP) and bilirubins were also measured for insight of liver function.

RESULTS

The findings in this study suggest that PGR induces CYP 3A4, does not have much effect on CYP 2E1, and inhibits CYP 1A2 at high dosage.

CONCLUSION

The current pharmacokinetic approach allowed the protective effects of PGR on oxidative drug metabolism in damaged liver to be systemically examined and will certainly help in the explanation of synergistic effect of the composites formula.

Simultaneous analysis of cytochrome P450 probes—dextromethorphan, flurbiprofen and midazolam and their major metabolites by HPLC-mass-spectrometry/fluorescence after single-step extraction from plasma

Cytochrome P450 enzymes catalyze oxidative metabolism of most pharmaceutical compounds. Consequently dextromethorphan, flurbiprofen, midazolam and other compounds are commonly used as probe substrates to evaluate cytochrome P450 function in humans. A "cocktail" approach employing simultaneous administration of two or more of the probe substrates has been used by various investigators in recent years. An analytical strategy to simultaneously extract and analyze dextromethorphan, flurbiprofen and midazolam and their major metabolites (dextrorphan, 4'-hydroxy-flurbiprofen and 1'-hydroxy-midazolam) by HPLC-MS/fluorescence was developed and is described here. The three probe substrates and their major metabolites were extracted simultaneously by means of a solid-phase (Bond Elut Certify cartridges) extraction procedure from 200 microl of pig plasma. The extraction efficiency was more than 79.5% for each of the six analytes. The extracted compounds were chromatographically separated on a Luna C8(II) column (50 mm Lx3 mm ID) in a single run of 20 min and analyzed by either fluorescence (flurbiprofen and 4'-hydroxy-flurbiprofen) or selective ion monitoring (dextromethorphan, dextrorphan, midazolam and 1'-hydroxy-midazolam) with positive electrospray ionization. The limit of quantification was 2.5 ng/ml for midazolam and 5 ng/ml for the other five analytes. The assay was precise and accurate (error: -9.1 to 12.1) with total CVs of 13.9% or better for each of the 6 analytes. This method was used to analyze concentrations of the three probes and their metabolites in plasma after intravenous administration to a healthy pig.

Appropriate phenotyping procedures for drug metabolizing enzymes and transporters in humans and their simultaneous use in the "cocktail" approach

Phenotyping for drug metabolizing enzymes and transporters is used to assess quantitatively the effect of an intervention (e.g., drug therapy, diet) or a condition (e.g., genetic polymorphism, disease) on their activity. Appropriate selection of test drug and metric is essential to obtain results applicable for other substrates of the respective enzyme/transporter. The following phenotyping metrics are recommended based on the level of validation and on practicability: CYP1A2, paraxanthine/caffeine in plasma 6 h after 150 mg caffeine; CYP2C9, tolbutamide plasma concentration 24 h after 125 mg tolbutamide; CYP2C19, urinary excretion of 4'-OH-mephenytoin 0-12 h after 50 mg mephenytoin; CYP2D6, urinary molar ratio debrisoquine/4-OH-debrisoquine 0-8 h after 10 mg debrisoquine; and CYP3A4, plasma clearance of midazolam after 2 mg midazolam (all drugs given orally).