Publications by authors named "Hege Christensen"

26 Publications

  • Page 1 of 1

Clinical application of intrathecal gadobutrol for assessment of cerebrospinal fluid tracer clearance to blood.

JCI Insight 2021 May 10;6(9). Epub 2021 May 10.

Division of Radiology and Nuclear Medicine, Department of Radiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway.

BACKGROUNDMethodology for estimation of cerebrospinal fluid (CSF) tracer clearance could have wide clinical application in predicting excretion of intrathecal drugs and metabolic solutes from brain metabolism and for diagnostic workup of CSF disturbances.METHODSThe MRI contrast agent gadobutrol (Gadovist) was used as a CSF tracer and injected into the lumbar CSF. Gadobutrol is contained outside blood vessels of the CNS and is eliminated along extravascular pathways, analogous to many CNS metabolites and intrathecal drugs. Tracer enrichment was verified and assessed in CSF by MRI at the level of the cisterna magna in parallel with obtaining blood samples through 48 hours.RESULTSIn a reference patient cohort (n = 29), both enrichment within CSF and blood coincided in time. Blood concentration profiles of gadobutrol through 48 hours varied between patients diagnosed with CSF leakage (n = 4), idiopathic normal pressure hydrocephalus dementia (n = 7), pineal cysts (n = 8), and idiopathic intracranial hypertension (n = 4).CONCLUSIONAssessment of CSF tracer clearance is clinically feasible and may provide a way to predict extravascular clearance of intrathecal drugs and endogenous metabolites from the CNS. The peak concentration in blood (at about 10 hours) was preceded by far peak tracer enhancement at MRI in extracranial lymphatic structures (at about 24 hours), as shown in previous studies, indicating a major role of the spinal canal in CSF clearance capacity.FUNDINGThe work was supported by the Department of Neurosurgery, Oslo University Hospital; the Norwegian Institute for Air Research; and the University of Oslo.
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http://dx.doi.org/10.1172/jci.insight.147063DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8262318PMC
May 2021

Influence of Proteome Profiles and Intracellular Drug Exposure on Differences in CYP Activity in Donor-Matched Human Liver Microsomes and Hepatocytes.

Mol Pharm 2021 04 19;18(4):1792-1805. Epub 2021 Mar 19.

Department of Pharmacy and Science for Life Laboratory, Uppsala University, 752 37 Uppsala, Sweden.

Human liver microsomes (HLM) and human hepatocytes (HH) are important systems for studies of intrinsic drug clearance (CL) in the liver. However, the CL values are often in disagreement for these two systems. Here, we investigated these differences in a side-by-side comparison of drug metabolism in HLM and HH prepared from 15 matched donors. Protein expression and intracellular unbound drug concentration (Kp) effects on the CL were investigated for five prototypical probe substrates (bupropion-CYP2B6, diclofenac-CYP2C9, omeprazole-CYP2C19, bufuralol-CYP2D6, and midazolam-CYP3A4). The samples were donor-matched to compensate for inter-individual variability but still showed systematic differences in CL. Global proteomics analysis outlined differences in HLM from HH and homogenates of human liver (HL), indicating variable enrichment of ER-localized cytochrome P450 (CYP) enzymes in the HLM preparation. This suggests that the HLM may not equally and accurately capture metabolic capacity for all CYPs. Scaling CL with CYP amounts and Kp could only partly explain the discordance in absolute values of CL for the five substrates. Nevertheless, scaling with CYP amounts improved the agreement in rank order for the majority of the substrates. Other factors, such as contribution of additional enzymes and variability in the proportions of active and inactive CYP enzymes in HLM and HH, may have to be considered to avoid the use of empirical scaling factors for prediction of drug metabolism.
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http://dx.doi.org/10.1021/acs.molpharmaceut.1c00053DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8041379PMC
April 2021

Correlation of Body Weight and Composition With Hepatic Activities of Cytochrome P450 Enzymes.

J Pharm Sci 2021 01 19;110(1):432-437. Epub 2020 Oct 19.

Section for Pharmacology and Pharmaceutical Biosciences, Department of Pharmacy, University of Oslo, Oslo, Norway. Electronic address:

Obesity is associated with comorbidities of which pharmacological treatment is needed. Physiological changes associated with obesity may influence the pharmacokinetics of drugs, but the effect of body weight on drug metabolism capacity remains uncertain. The aim of this study was to investigate ex vivo activities of hepatic drug metabolizing CYP enzymes in patients covering a wide range of body weight. Liver biopsies from 36 individuals with a body mass index (BMI) ranging from 18 to 63 kg/m were obtained. Individual hepatic microsomes were prepared and activities of CYP3A, CYP2B6, CYP2C8, CYP2D6, CYP2C9, CYP2C19 and CYP1A2 were determined. The unbound intrinsic clearance (CL) values for CYP3A correlated negatively with body weight (r = -0.43, p < 0.01), waist circumference (r = -0.47, p < 0.01), hip circumference (r = -0.51, p < 0.01), fat percent (r = -0.41, p < 0.05), fat mass (r = -0.48, p < 0.01) and BMI (r = -0.46, p < 0.01). Linear regression analysis showed that CL values for CYP3A decreased with 5% with each 10% increase in body weight (r = 0.12, β = -0.558, p < 0.05). There were no correlations between body weight measures and CL values for the other CYP enzymes investigated. These results indicate reduced hepatic metabolizing capacity of CYP3A substrates in patients with increasing body weight.
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http://dx.doi.org/10.1016/j.xphs.2020.10.027DOI Listing
January 2021

Chronic Inhibition of CYP3A is Temporarily Reduced by Each Hemodialysis Session in Patients With End-Stage Renal Disease.

Clin Pharmacol Ther 2020 10 1;108(4):866-873. Epub 2020 Jun 1.

Section for Pharmacology and Pharmaceutical Biosciences, Department of Pharmacy, University of Oslo, Oslo, Norway.

Drug dosing is challenging in patients with end-stage renal disease. Not only is renal drug elimination reduced, but nonrenal clearance pathways are also altered. Increasing evidence suggest that uremia impacts drug metabolizing enzymes and transporters leading to changes in nonrenal clearance. However, the exact mechanisms are not yet fully understood, and the acute effects of dialysis are inadequately investigated. We prospectively phenotyped cytochrome P450 3A (CYP3A; midazolam) and P-glycoprotein (P-gp)/organic anion-transporting proteins (OATP; fexofenadine) in 12 patients on chronic intermittent hemodialysis; a day after ("clean") and a day prior to ("dirty") dialysis. Unbound midazolam clearance decreased with time after dialysis; median (range) reduction of 14% (-3% to 41%) from "clean" to "dirty" day (P = 0.001). Fexofenadine clearance was not affected by time after dialysis (P = 0.68). In conclusion, changes in uremic milieu between dialysis sessions induce a small, direct inhibitory effect on CYP3A activity, but do not alter P-gp/OATP activity.
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http://dx.doi.org/10.1002/cpt.1875DOI Listing
October 2020

A Comparative Analysis of Cytochrome P450 Activities in Paired Liver and Small Intestinal Samples from Patients with Obesity.

Drug Metab Dispos 2020 01 4;48(1):8-17. Epub 2019 Nov 4.

Section for Pharmacology and Pharmaceutical Biosciences, Department of Pharmacy, University of Oslo, Oslo, Norway (V.K., I.R., A.Å., H.C.); Department of Transplantation Medicine, Oslo University Hospital, Rikshospitalet, Oslo, Norway (V.K., A.Å.); Research and Early Development, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca Gothenburg, Gothenburg, Sweden (A.P., C.W., S.A., T.B.A.); Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway (M.K.K.); Department of Health Sciences, OsloMet-Oslo Metropolitan University, Oslo, Norway (M.K.K.); Department of Pharmacy, Uppsala University, Uppsala, Sweden (C.W., P.A.); The Morbid Obesity Centre, Vestfold Hospital Trust, Tønsberg, Norway (P.C.A., J.H.); Department of Surgery, Vestfold Hospital Trust, Tønsberg, Norway (P.C.A.); Department of Endocrinology, Morbid Obesity and Preventive Medicine, Institute of Clinical Medicine, University of Oslo, Oslo, Norway (J.H.); Late-Stage Development, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca Gothenburg, Gothenburg, Sweden (C.K.); Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden (C.K.); and Department of Physiology and Pharmacology, Section of Pharmacogenetics, Karolinska Institutet, Stockholm, Sweden (T.B.A.).

The liver and small intestine restrict oral bioavailability of drugs and constitute the main sites of pharmacokinetic drug-drug interactions. Hence, detailed data on hepatic and intestinal activities of drug metabolizing enzymes is important for modeling drug disposition and optimizing pharmacotherapy in different patient populations. The aim of this study was to determine the activities of seven cytochrome P450 (P450) enzymes in paired liver and small intestinal samples from patients with obesity. Biopsies were obtained from 20 patients who underwent Roux-en-Y gastric bypass surgery following a 3-week low-energy diet. Individual hepatic and intestinal microsomes were prepared and specific probe substrates in combined incubations were used for determination of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A activities. The activities of CYP2C8, CYP2C9, CYP2D6, and CYP3A were quantified in both human liver microsomes (HLM) and human intestinal microsomes (HIM), while the activities of CYP1A2, CYP2B6, and CYP2C19 were only quantifiable in HLM. Considerable interindividual variability was present in both HLM (9- to 23-fold) and HIM (5- to 55-fold). The median metabolic HLM/HIM ratios varied from 1.5 for CYP3A to 252 for CYP2C8. The activities of CYP2C9 in paired HLM and HIM were positively correlated ( = 0.74, < 0.001), while no interorgan correlations were found for activities of CYP2C8, CYP2D6, and CYP3A ( > 0.05). Small intestinal CYP3A activities were higher in females compared with males ( < 0.05). Hepatic CYP2B6 activity correlated negatively with body mass index ( = -0.72, < 0.001). These data may be useful for further in vitro-in vivo predictions of drug disposition in patients with obesity. SIGNIFICANCE STATEMENT: Hepatic and intestinal drug metabolism is the key determinant of oral drug bioavailability. In this study, paired liver and jejunum samples were obtained from 20 patients with obesity undergoing gastric bypass surgery following a 3-week low-energy diet. We determined the hepatic and small intestinal activities of clinically important P450 enzymes and provide detailed enzyme kinetic data relevant for predicting in vivo disposition of P450 substrates in this patient population.
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http://dx.doi.org/10.1124/dmd.119.087940DOI Listing
January 2020

Impact of body weight, low energy diet and gastric bypass on drug bioavailability, cardiovascular risk factors and metabolic biomarkers: protocol for an open, non-randomised, three-armed single centre study (COCKTAIL).

BMJ Open 2018 05 29;8(5):e021878. Epub 2018 May 29.

Cardiovascular, Renal and Metabolism Translational Medicine Unit, Early Clinical Development, IMED Biotech Unit, AstraZeneca Gothenburg, Gothenburg, Sweden.

Introduction: Roux-en-Y gastric bypass (GBP) is associated with changes in cardiometabolic risk factors and bioavailability of drugs, but whether these changes are induced by calorie restriction, the weight loss or surgery per se, remains uncertain. The COCKTAIL study was designed to disentangle the short-term (6 weeks) metabolic and pharmacokinetic effects of GBP and a very low energy diet (VLED) by inducing a similar weight loss in the two groups.

Methods And Analysis: This open, non-randomised, three-armed, single-centre study is performed at a tertiary care centre in Norway. It aims to compare the short-term (6 weeks) and long-term (2 years) effects of GBP and VLED on, first, bioavailability and pharmacokinetics (24 hours) of probe drugs and biomarkers and, second, their effects on metabolism, cardiometabolic risk factors and biomarkers. The primary outcomes will be measured as changes in: (1) all six probe drugs by absolute bioavailability area under the curve (AUC/AUC) of midazolam (CYP3A4 probe), systemic exposure (AUC) of digoxin and rosuvastatin and drug:metabolite ratios for omeprazole, losartan and caffeine, levels of endogenous CYP3A biomarkers and genotypic variation, changes in the expression and activity data of the drug-metabolising, drug transport and drug regulatory proteins in biopsies from various organs and (2) body composition, cardiometabolic risk factors and metabolic biomarkers.

Ethics And Dissemination: The COCKTAIL protocol was reviewed and approved by the Regional Committee for Medical and Health Research Ethics (Ref: 2013/2379/REK sørøst A). The results will be disseminated to academic and health professional audiences and the public via presentations at conferences, publications in peer-reviewed journals and press releases and provided to all participants.

Trial Registration Number: NCT02386917.
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http://dx.doi.org/10.1136/bmjopen-2018-021878DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988193PMC
May 2018

Determination of Tacrolimus Concentration and Protein Expression of P-Glycoprotein in Single Human Renal Core Biopsies.

Ther Drug Monit 2018 06;40(3):292-300

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo.

Background: Tacrolimus (TAC) is currently the cornerstone of immunosuppressive protocols for renal transplant recipients. Despite therapeutic whole blood monitoring, TAC is associated with nephrotoxicity, and it has been hypothesized that intrarenal accumulation of TAC and/or its metabolites are involved. As TAC is a substrate of P-glycoprotein (P-gp), the expression and activity of this efflux transporter could influence the levels of TAC in renal tissue. The primary aim of this study was to develop and validate a method for quantification of TAC in tissue homogenates from single human renal core biopsies. The secondary aim was to provide measures of P-gp expression and of the demethylated metabolites of TAC in the same renal biopsy.

Methods: Human renal tissue, with and without clinical TAC exposure, was used for method development and validation. Homogenates were prepared with bead-beating, and concentrations of TAC and its demethylated metabolites were analyzed with liquid chromatography tandem mass spectrometry after protein precipitation. A Western blot method was used for semiquantification of P-gp expression in the homogenates. The final methods were applied to renal core biopsies from 2 transplant patients.

Results: The TAC assay showed within- and between-run mean accuracy between 99.7% and 107% and coefficients of variation ≤6.7%. Matrix effects were nonsignificant, and samples were stable for 3 months preanalytically when stored at -80°C. TAC concentrations in the renal core biopsies were 62.6 and 43.7 pg/mg tissue. The methods for measurement of desmethyl-TAC and P-gp expression were suitable for semiquantification in homogenates from renal core biopsies.

Conclusions: These methods may be valuable for the elucidation of the pharmacokinetic mechanisms behind TAC-induced nephrotoxicity in renal transplant recipients.
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http://dx.doi.org/10.1097/FTD.0000000000000510DOI Listing
June 2018

Closer to the Site of Action: Everolimus Concentrations in Peripheral Blood Mononuclear Cells Correlate Well With Whole Blood Concentrations.

Ther Drug Monit 2015 Oct;37(5):675-80

*Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo; and Departments of †Pharmacology, and ‡Transplantation Medicine, Oslo University Hospital, Rikshospitalet, Oslo, Norway.

Background: Everolimus (EVE) is an immunosuppressive drug dosed according to therapeutic drug monitoring in renal transplant recipients. The primary site of action is within activated lymphocytes. EVE is a substrate of the efflux transporter ABCB1 also known as P-glycoprotein. Limited data exist regarding a possible association between whole blood and intralymphocyte concentrations of EVE and the potential influence of ABCB1.

Methods: Twelve renal transplant recipients (5 men and 7 women) treated with EVE underwent a pharmacokinetic investigation where EVE concentrations in whole blood and in peripheral blood mononuclear cells (PBMC) were determined within a dosing interval. In addition, the activity of ABCB1 in PBMC was determined using the Rhodamine123 efflux assay and the patients' genotypes of ABCB1 were determined.

Results: There was a significant correlation between EVE AUC0-12 in whole blood and in PBMC (r = 0.90, P < 0.01), and no association was demonstrated between the ABCB1 activity and EVE PBMC/whole blood ratio of trough concentrations (r = 0.23, P = 0.76). Furthermore, ABCB1 1236C>T, 3435C>T, and 2677G>T/A polymorphism did not influence EVE AUC0-12 PBMC/whole blood ratio.

Conclusions: The results revealed a significant association between EVE whole blood and PBMC concentrations, suggesting that ABCB1-mediated efflux from PBMC to be of minor importance for the distribution of EVE.
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http://dx.doi.org/10.1097/FTD.0000000000000185DOI Listing
October 2015

The influence of CYP3A, PPARA, and POR genetic variants on the pharmacokinetics of tacrolimus and cyclosporine in renal transplant recipients.

Eur J Clin Pharmacol 2014 Jun;70(6):685-93

Purpose: Tacrolimus (Tac) and cyclosporine (CsA) are mainly metabolized by CYP3A4 and CYP3A5. Several studies have demonstrated an association between the CYP3A5 genotype and Tac dose requirements. Recently, CYP3A4, PPARA, and POR gene variants have been shown to influence CYP3A metabolism. The present study investigated potential associations between CYP3A5*3, CYP3A4*22, PPARA c.209- 1003G>A and c.208+3819A>G, and POR*28 alleles and dose-adjusted concentrations (C/D) of Tac and CsA in 177 renal transplant patients early post-transplant.

Methods: All patients (n=177) were genotyped for CYP3A4*22, CYP3A5*3, POR*28, PPARA c.209-1003G>A, and PPARA c.208+3819A>G using real-time polymerase chain reaction (PCR) and melting curve analysis with allelespecific hybridization probes or PCR restriction fragment length polymorphisms (RFLP) methods. Drug concentrations and administered doses were retrospectively collected from patient charts at Oslo University Hospital, Rikshospitalet, Norway. One steady-state concentration was collected for each patient.

Results: We confirmed a significant impact of the CYP3A5*3 allele on Tac exposure. Patients with POR*28 and PPARA variant alleles demonstrated 15 % lower (P=0.04) and 19 % higher (P=0.01) Tac C0/D respectively. CsA C2/D was 53 % higher among CYP3A4*22 carriers (P=0.03).

Conclusion: The results support the use of pre-transplant CYP3A5 genotyping to improve initial dosing of Tac, and suggest that Tac dosing may be further individualized by additional POR and PPARA genotyping. Furthermore, initial CsA dosing may be improved by pre-transplant CYP3A4*22 determination.
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http://dx.doi.org/10.1007/s00228-014-1656-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4025175PMC
June 2014

Endomyocardial, intralymphocyte, and whole blood concentrations of ciclosporin A in heart transplant recipients.

Transplant Res 2013 Apr 8;2(1). Epub 2013 Apr 8.

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, P,O, Box 1068, Blindern, Oslo, 0316, Norway.

Background: In the early phases following heart transplantation a main challenge is to reduce the impact of acute rejections. Previous studies indicate that intracellular ciclosporin A (CsA) concentration may be a sensitive acute rejection marker in renal transplant recipients. The aims of this study were to evaluate the relationships between CsA concentrations at different target sites as potential therapeutic drug monitoring (TDM) tools in heart transplant recipients.

Methods: Ten heart transplant recipients (8 men, 2 women) on CsA-based immunosuppression were enrolled in this prospective single-center pilot study. Blood samples were obtained once to twice weekly up to 12 weeks post-transplant. One of the routine biopsies was allocated to this study at each sampling time. Whole blood, intralymphocyte, and endomyocardial CsA concentrations were determined with validated HPLC-MS/MS-methods. Mann-Whitney U test was used when evaluating parameters between the two groups of patients. To correlate whole blood, intralymphocyte, and endomyocardial CsA concentrations linear regression analysis was used.

Results: Three patients experienced mild rejections. In the study period, the mean (range) intralymphocyte CsA trough concentrations were 10.1 (1.5 to 39) and 8.1 (1.3 to 25) ng/106 cells in the rejection and no-rejection group, respectively (P=0.21). Corresponding whole blood CsA concentrations were 316 (153 to 564) and 301 (152 to 513) ng/mL (P=0.33). There were no correlations between whole blood, intralymphocyte, or endomyocardial concentrations of CsA (P >0.11).

Conclusions: The study did not support an association between decreasing intralymphocyte CsA concentrations and acute rejections. Further, there were no association between blood concentrations and concentrations at sites of action, potentially challenging TDM in these patients.
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http://dx.doi.org/10.1186/2047-1440-2-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3643826PMC
April 2013

In vitro inhibition of cytochrome P450 3A4 by Aronia melanocarpa constituents.

Planta Med 2013 Jan 18;79(2):137-41. Epub 2012 Dec 18.

School of Pharmacy, Department of Pharmaceutical Chemistry, University of Oslo, Blindern, Oslo, Norway.

Extracts, subfractions, isolated anthocyanins and procyanidins, and two phenolic acids from aronia [Aronia melanocarpa] were investigated for their CYP3A4 inhibitory effects, using midazolam as the probe substrate and recombinant insect cell microsomes expressing CYP3A4 as the enzyme source. Procyanidin B5 was a considerably stronger CYP3A4 inhibitor in vitro than the isomeric procyanidin B2 and comparable to bergamottin, a known CYP3A4 inhibitor from grapefruit juice. The inhibitory activity of proanthocyanidin-containing fractions was correlated to the degree of polymerization. Among the anthocyanins, cyanidin 3-arabinoside showed stronger CYP3A4 inhibition than cyanidin 3-galactoside and cyanidin 3-glucoside. Thus, the ability to inhibit CYP3A4 in vitro seems to be influenced by the sugar unit linked to the anthocyanidin.
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http://dx.doi.org/10.1055/s-0032-1328055DOI Listing
January 2013

Long-term effects of gastric bypass and duodenal switch on systemic exposure of atorvastatin.

Surg Endosc 2013 Jun 18;27(6):2094-101. Epub 2012 Dec 18.

Morbid Obesity Centre, Vestfold Hospital Trust, P.O. Box 2168, 3103, Tønsberg, Norway.

Background: A previous study of 22 patients undergoing either gastric bypass or duodenal switch showed increased systemic exposure of atorvastatin acid 3-8 weeks after surgery in the majority of patients. This study aimed to investigate the long-term effects on systemic exposure of atorvastatin acid in the same group of patients.

Methods: An 8-h pharmacokinetic investigation was performed a median of 27 months (range 21-45 months) after surgery. Systemic exposure was measured as the area under the plasma concentration versus the time curve from 0 to 8 h postdose (AUC0-8). Linear mixed models with AUC0-8 as the dependent variable were implemented to assess the effect of time, surgical procedure, and body mass index (BMI) as explanatory variables.

Results: The study enrolled 20 patients. The systemic exposure of atorvastatin acid changed significantly over time (p = 0.001), albeit there was substantial variation between subjects. The effect of time was attenuated but remained significant after adjustment for surgical procedure and BMI (p = 0.048). The initial AUC0-8 increase seen in the majority of patients 3-8 weeks after surgery was normalized long term, with 7 of the 12 gastric bypass patients and 6 of the 8 duodenal switch patients showing decreased AUC0-8 compared with preoperative values.

Conclusions: The systemic exposure of atorvastatin showed a significant change over time after bariatric surgery, albeit with large inter- and intraindividual variations. The findings indicate that patients using atorvastatin or drugs with similar pharmacokinetic properties should be monitored closely for both therapeutic effects and adverse events the first years after gastric bypass and duodenal switch.
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http://dx.doi.org/10.1007/s00464-012-2716-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3661042PMC
June 2013

Immunological response as a source to variability in drug metabolism and transport.

Front Pharmacol 2012 10;3. Epub 2012 Feb 10.

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo Oslo, Norway.

Through the last decades it has become increasingly evident that disease-states involving cytokines affect the pharmacokinetics of drugs through regulation of expression and activity of drug metabolizing enzymes, and more recently also drug transporters. The clinical implication is however difficult to predict, since these effects are dependent on the degree of inflammation and may be changed when the diseases are treated. This article will give an overview of the present understanding of the effects of cytokines on cytochrome P450 enzymes and drug transporters, and highlight the importance of considering these issues in regard to increasing use of the relatively new class of drugs, namely therapeutic proteins.
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http://dx.doi.org/10.3389/fphar.2012.00008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277081PMC
October 2012

Cyclosporine A- and tacrolimus-mediated inhibition of CYP3A4 and CYP3A5 in vitro.

Drug Metab Dispos 2012 Apr 28;40(4):655-61. Epub 2011 Dec 28.

University of Oslo, School of Pharmacy, P.O. Box 1068 Blindern, 0316 Oslo, Norway.

Cyclosporine A (CsA) and tacrolimus (Tac) are immunosuppressive drugs used in the majority of patients with solid organ transplants, generally in combination with a wide range of drugs. CsA and Tac seem not only to be substrates of CYP3A but have also been described as inhibitors of CYP3A. For CsA, in particular, inhibition of CYP3A has been suggested as the main mechanism of interactions seen clinically with various drugs. The aim of this study was to investigate the inhibitory effect and inhibition characteristics of CsA and Tac on CYP3A4 and CYP3A5 in vitro and to evaluate its clinical relevance. Inhibition by CsA and Tac was studied using midazolam as the probe substrate in coincubation and preincubation investigations using human liver microsomes (HLMs) as well as specific CYP3A4- and CYP3A5-expressing insect microsomes (Supersomes). In vitro-in vivo extrapolations (IVIVEs) were performed to evaluate the clinical relevance of the inhibition. Both CsA and Tac competitively inhibited CYP3A in HLMs, showing inhibition constants (K(i)) of 0.98 and 0.61 μM, respectively. Experiments in Supersomes revealed that Tac inhibited both CYP3A4 and CYP3A5, whereas CsA only inhibited CYP3A4. In contrast to the HLM experiments, studies in Supersomes showed inhibition by Tac to be NADPH- and time-dependent, with a 5-fold reduction in IC(50) after preincubation, supporting a time-dependent inhibition mechanism in recombinant microsomes. By application of HLM data, IVIVE estimated the area under the concentration versus time curve of midazolam to increase by 73 and 27% with CsA and Tac, respectively. The inhibitory effect was predominantly on the intestinal level, whereas hepatic intrinsic clearance seemed unaffected.
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http://dx.doi.org/10.1124/dmd.111.043018DOI Listing
April 2012

CYP3A5-mediated metabolism of midazolam in recombinant systems is highly sensitive to NADPH-cytochrome P450 reductase activity.

Xenobiotica 2011 Jan 18;41(1):1-5. Epub 2010 Oct 18.

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Norway.

Data from in vitro drug metabolism studies with recombinant enzyme systems are frequently used to predict human drug metabolism in vivo. However, for the CYP3A probe substrate midazolam (MDZ), considerable variability in enzyme kinetic parameters has been observed in different in vitro studies. The aim of this study was to explore the effect of varying activities of the electron donor NADPH-cytochrome P450 reductase (CPR) on CYP3A5-mediated metabolism of MDZ. Microsomes with similar levels of CYP3A5 but 12-fold difference in CPR activity showed a 30-fold difference in intrinsic clearance for the formation of 1'-OH-MDZ. Significantly higher K(m) and lower V(max) for the formation of 1'-OH-MDZ were found in microsomes with low CPR activity compared with microsomes with higher CPR activity (P = 0.024 and 0.001). In the microsomes with lowest CPR activity, the formation of 1'-OH-MDZ displayed Michaelis-Menten kinetics, whereas substrate inhibition was observed in the two preparations with higher CPR activity. The present study shows that the CPR activity in different recombinant enzyme preparations is crucial for in vitro CYP3A5-mediated clearance of MDZ. This suggests that the CPR activity of enzyme preparations could be an important factor for the ability of in vitro data to predict human drug metabolism in vivo.
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http://dx.doi.org/10.3109/00498254.2010.523734DOI Listing
January 2011

Cyclosporine A, but not tacrolimus, shows relevant inhibition of organic anion-transporting protein 1B1-mediated transport of atorvastatin.

Drug Metab Dispos 2010 Sep 2;38(9):1499-504. Epub 2010 Jun 2.

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Blindern, Oslo, Norway.

The aim of this study was to investigate the potential of calcineurin inhibitors [cyclosporine A (CsA) and tacrolimus (Tac)] to inhibit cellular uptake of atorvastatin mediated by the liver-specific organic anion-transporting polypeptide 1B1 (OATP1B1) in vitro. Patients with solid organ transplants are frequently treated with HMG-CoA reductase inhibitors (statins). CsA increases atorvastatin systemic exposure severalfold, an effect not observed with Tac. The effect of CsA and Tac on atorvastatin transport via OATP1B1 was investigated in transfected human embryonic kidney 293 cells. An in vitro-in vivo extrapolation (IVIVE) was performed to estimate the clinical potential for CsA and Tac to inhibit OATP1B1-mediated transport. CsA inhibited OATP1B1-mediated uptake of atorvastatin approximately 90-fold more efficiently than Tac, with half-maximal inhibitory concentration (IC(50)) values of 0.021 +/- 0.004 and 1.99 +/- 0.42 muM, respectively. Coincubation compared with preincubation with CsA showed a 20-fold lower inhibitory capacity, with an IC(50) value of 0.47 +/- 0.34 muM. The IVIVE showed that clinically obtainable concentrations of CsA, but not Tac, inhibit OATP1B1 transport of atorvastatin. CsA inhibition ranged from 28 to 77% within a dosing interval, whereas it was less than 1% for Tac, considering free concentrations and assuming competitive inhibition. This does not fully explain the clinically observed interaction with CsA, suggesting that a more complex inhibitory mechanism may be present. This is also supported by the decreased IC(50) value of CsA after preincubation. This study provides evidence that OATP1B1 inhibition is a relevant mechanism for the interaction observed between CsA and atorvastatin.
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http://dx.doi.org/10.1124/dmd.110.032268DOI Listing
September 2010

Different enzyme kinetics of midazolam in recombinant CYP3A4 microsomes from human and insect sources.

Drug Metab Pharmacokinet 2009 ;24(3):261-8

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway.

In vitro drug metabolism techniques with human CYP c-DNA expressed systems are frequently used to predict human drug metabolism in vivo. The aim of this study was to compare midazolam enzyme kinetics in recombinant expressed CYP3A4 microsomes from human and insect cells. The amounts of 1'- hydroxymidazolam and 4-hydroxymidazolam formed in CYP3A4 microsomes from transfected human liver epithelial cells (T5-3A4 microsomes) and baculovirus-infected insect cells (with and without coexpressed cytochrome b(5)) were analysed by LC-MS. Enzyme kinetic parameters were estimated by nonlinear regression. Mean K(m) for the formation of 1'-hydroxymidazolam was 3- and 4-fold higher in T5-3A4 microsomes than in insect microsomes (p<0.05), with and without coexpressed cytochrome b(5), respectively. Only minor differences in V(max) were observed and the higher K(m) in T5-3A4 microsomes was reflected by significantly lower Cl(int) compared to insect microsomes (p<0.001). For formation of 1'-hydroxymidazolam, human microsomes displayed Michaelis-Menten kinetics, while insect microsomes showed substrate inhibition kinetics. The different enzyme kinetics of midazolam observed in recombinant CYP3A4 microsomes from human and insect sources, especially the substantially higher K(m) obtained in human microsomes compared to insect microsomes, should be further evaluated since it may have implications for correlations to in vivo situation.
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http://dx.doi.org/10.2133/dmpk.24.261DOI Listing
October 2009

Influence of comedication on serum concentrations of aripiprazole and dehydroaripiprazole.

Ther Drug Monit 2009 Apr;31(2):233-8

Department of Psychopharmacology, Diakonhjemmet Hospital, School of Pharmacy, University of Oslo, Vinderen, Oslo, Norway.

Aripiprazole, a relatively new antipsychotic drug, is metabolized by cytochrome P450 3A4 (CYP3A4) and CYP2D6 to an active metabolite, dehydroaripiprazole. As studies on pharmacokinetic drug interactions with aripiprazole are so far limited, the aim of the present study was to investigate the impact of comedication on serum concentrations of aripiprazole and dehydroaripiprazole in psychiatric patients in a clinical setting. A therapeutic drug monitoring database was screened for patients receiving aripiprazole tablets as part of their treatment. Of the 361 samples included, 78% were from patients receiving comedication. The remaining 79 samples constituted the control group. Steady-state dose-adjusted serum concentrations (concentration to dose ratios, C:D ratios) of aripiprazole, dehydroaripiprazole and the sum of aripiprazole and dehydroaripiprazole, and the metabolic ratio (dehydroaripiprazole/aripiprazole) in the different comedication groups were compared with controls. Coadministration of a CYP3A4 inducer resulted in approximately 60% lower mean C:D ratios of aripiprazole, dehydroaripiprazole, and the sum of aripiprazole and dehydroaripiprazole (P < 0.05, P < 0.01, and P < 0.01, respectively). Combination with a CYP2D6 inhibitor resulted in a 45% higher mean C:D ratio of aripiprazole (P < 0.05), with no effect on the C:D ratio of dehydroaripiprazole. When aripiprazole was coadministered with alimemazine or lithium, a 56% (P < 0.01) and 43% (P = 0.05) higher mean C:D ratio of aripiprazole, respectively, was observed. Olanzapine, risperidone injections, escitalopram, or lamotrigine also had statistically significant effects on aripiprazole disposition but to a lesser extent. In conclusion, concurrent treatment with CYP3A4 inducers, CYP2D6 inhibitors, alimemazine, or lithium resulted in changes in the systemic exposure of aripiprazole between 40% and 60%. This is of such a magnitude that dose adjustments of aripiprazole may be required.
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http://dx.doi.org/10.1097/FTD.0b013e3181956726DOI Listing
April 2009

Metabolism of quetiapine by CYP3A4 and CYP3A5 in presence or absence of cytochrome B5.

Drug Metab Dispos 2009 Feb 20;37(2):254-8. Epub 2008 Nov 20.

Department of Psychopharmacology, Diakonhjemmet Hospital, P.O. Box 85, Vinderen, N-0319 Oslo, Norway.

The antipsychotic drug quetiapine is extensively metabolized by CYP3A4, but little is known about the possible influence of the polymorphic enzyme CYP3A5. This in vitro study investigated the relative importance of CYP3A4 and CYP3A5 in the metabolism of quetiapine and compared the metabolic pattern by the two enzymes, in the presence or absence of cytochrome b(5). Intrinsic clearance (CL(int)) of quetiapine was determined by the substrate depletion approach in CYP3A4 and CYP3A5 insect cell microsomes with or without coexpressed cytochrome b(5). Formation of the metabolites quetiapine sulfoxide, N-desalkylquetiapine, O-desalkylquetiapine, and 7-hydroxyquetiapine by CYP3A4 and CYP3A5 were compared in the different microsomal preparations. CL(int) of quetiapine by CYP3A5 was less than 35% relative to CYP3A4. CL(int) was higher (3-fold) in CYP3A4 microsomes without cytochrome b(5) compared with CYP3A4 microsomes with coexpressed cytochrome b(5), whereas in CYP3A5 microsomes CL(int) was similar for both microsomal preparations. Metabolism of quetiapine by CYP3A5 revealed a different metabolic pattern compared with CYP3A4. The results indicated that O-desalkylquetiapine constituted a higher proportion of the formed metabolites by CYP3A5 compared with CYP3A4. In conclusion, the present study indicates that CYP3A5 is of minor importance for the overall metabolism of quetiapine, regardless of the presence of cytochrome b(5). However, a different metabolic pattern by CYP3A5 compared with CYP3A4 could possibly result in different pharmacological and/or toxicological effects of quetiapine in patients expressing CYP3A5.
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http://dx.doi.org/10.1124/dmd.108.023291DOI Listing
February 2009

Prediction of plasma protein binding displacement and its implications for quantitative assessment of metabolic drug-drug interactions from in vitro data.

J Pharm Sci 2006 Dec;95(12):2778-87

Academic Unit of Clinical Pharmacology, The University of Sheffield, Sheffield, UK.

Although displacement from plasma protein binding (dPB) is usually of little clinical significance, it should be taken into account when interpreting changes in total plasma concentrations of drugs subject to metabolically based drug-drug interactions (mDDI). The aim of this study was to develop an approach to predict changes in the free fractions (fu) of pairs of drugs that compete for plasma binding, knowing their binding affinity constants, and to consider the implications of associated concentration- and time-dependence of such changes with respect to drug exposure. Experimental fu values of valproic acid and phenytoin in the presence of ibuprofen, diflunisal, or naproxen were predicted successfully (within 0.99- to 1.36-fold) by the model. In addition, the simulation of time-dependent changes in fu of valproic acid following administration of ibuprofen indicated different extents of dPB during 'first-pass' through the liver after oral absorption and on systemic recirculation. To understand the impact of the time-dependent change in fu, a full physiologically based pharmacokinetic model, that accounts for concentration-time profile of displacee and displacer and their mutual effect on each other, is required. The approach developed in this study is a first step towards the development of such a model.
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http://dx.doi.org/10.1002/jps.20733DOI Listing
December 2006

Evaluation of microsomal incubation conditions on CYP3A4-mediated metabolism of cyclosporine A by a statistical experimental design.

Curr Drug Metab 2006 Apr;7(3):265-71

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Norway.

The effect of changes in microsomal incubation conditions (NADPH, Mg(2+), Cl(-), NADPH-regenerating system and pH) on the formation of the CYP3A4 metabolites AM1 and AM9 from CsA were studied by application of a fractional factorial design. Metabolism was studied in microsomes of transfected human liver epithelial (THLE) cells specifically expressing CYP3A4. Within the conditions tested, a 3-4-fold difference in formation of CsA metabolites was observed. Formation of both AM1 and AM9 was favoured by a low Mg(2+) concentration (0.5 mM) and no addition of Cl(-) to the incubation matrix. However, while a high NADPH concentration (1.75 mM) was the single most important factor for the formation of AM1, changes in NADPH concentration between 0.25 and 1.75 mM had no influence on AM9 formation. Formation of the two metabolites also differed in their influence by pH changes, as a change in pH from 7.2 to 7.5 significantly increased the formation of AM9, while formation of AM1 was unaffected by this change. The present study showed that relatively small changes in the incubation matrix had a significant influence on the microsomal CYP3A4-mediated metabolism of CsA. Systematic studies on microsomal incubation conditions could be a key to improve metabolic in vitro-in vivo extrapolations in drug development.
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http://dx.doi.org/10.2174/138920006776359275DOI Listing
April 2006

Atorvastatin does not affect the pharmacokinetics of cyclosporine in renal transplant recipients.

Eur J Clin Pharmacol 2005 Mar 12;61(1):59-62. Epub 2005 Feb 12.

Department of Pharmacology, School of Pharmacy, University of Oslo, PB 1068, Blindern, N-0316 Oslo, Norway.

Objective: The aim of the present study was to evaluate the possible influence of atorvastatin on the pharmacokinetics of cyclosporine (INN ciclosporin) and its main metabolites, AM1 and AM9, in renal transplant recipients.

Methods: Whole blood samples from 18 renal transplanted patients on cyclosporine-based immunosuppressive therapy were collected prior to and after 4 weeks of treatment with atorvastatin (10 mg/day) and analysed with regard to both cyclosporine and its main metabolites, AM1 and AM9, using a specific chromatographic method with ultraviolet detection.

Results: On average, AUC(0-12) [area under the whole blood concentration versus time curve in the dosing interval (0-12 h)] of cyclosporine was 5% (-16, 5) (90% confidence interval) lower upon co-administration with atorvastatin. No statistically significant changes in any of the calculated pharmacokinetic variables [AUC(0-12), maximum whole blood concentration (C(max)), whole blood concentration 12 h post dose (C(12)), time to C(max) (t(max)), terminal half-life (t(1/2))] for cyclosporine or the two metabolites, AM1 and AM9, upon atorvastatin treatment were observed. On average, atorvastatin did not affect the ratio between the CYP3A4-mediated metabolite AM9 and cyclosporine, suggesting that atorvastatin does not affect the CYP3A4 metabolism of cyclosporine to any significant extent. However, the influence of atorvastatin on the ratio between AM9 and cyclosporine showed large interindividual variability.

Conclusion: The results of this study indicate that atorvastatin does not, on average, affect cyclosporine pharmacokinetics in renal transplant recipients.
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http://dx.doi.org/10.1007/s00228-004-0874-5DOI Listing
March 2005

High-performance liquid chromatography-mass spectrometry analysis of diltiazem and 11 of its phase I metabolites in human plasma.

J Pharm Biomed Anal 2003 Sep;33(2):275-85

Department of Pharmacology, School of Pharmacy, University of Oslo, Oslo, Norway.

The aim of the present work was to develop a high-performance liquid chromatography-mass spectrometry method for analysis of diltiazem (DTZ) and metabolites in human plasma after single dose administration (120 mg). Human plasma samples (1 ml) were cleaned up by a solid phase extraction procedure (C18 cartridges) using codeine as an internal standard. Reconstituted extracts were separated on a reversed-phase C8 column with a linear gradient mobile phase system. The run time per sample analysis was 11 min. Detection was performed using selected ion monitoring following atmospheric pressure chemical ionization. The lower limit of quantification was estimated to be 1 microg/l (in spiked plasma) for all available reference compounds (i.e. DTZ and five metabolites). Validation of the method showed good linearity, precision and accuracy for quantification of these six reference compounds. In addition, tandem MS analyses of human plasma sampled from healthy individuals after peroral intake of 120 mg DTZ revealed that the method enabled detection of six additional metabolites for which reference compounds were not available.
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http://dx.doi.org/10.1016/s0731-7085(03)00259-0DOI Listing
September 2003

Coadministration of grapefruit juice increases systemic exposure of diltiazem in healthy volunteers.

Eur J Clin Pharmacol 2002 Nov 16;58(8):515-20. Epub 2002 Oct 16.

Department of Pharmacology, School of Pharmacy, University of Oslo, PO Box 1068 Blindern, 0316 Oslo, Norway.

Objectives: Grapefruit juice has been reported to increase the bioavailability of several calcium-channel antagonists, i.e. the dihydropyridines and verapamil, which are cytochrome P450 3A4 (CYP3A4) substrates. The objective of the present study was to investigate the effect of grapefruit juice on the pharmacokinetics of diltiazem and the metabolites N-demethyl-diltiazem (MA) and desacetyl-diltiazem (M1).

Methods: Ten healthy male volunteers were included in a randomised, open, crossover study, comparing the effect of a single oral dose of non-retard formulated diltiazem (120 mg) administered with 250 ml grapefruit juice or water. The study was performed on two investigation days separated by 13-38 days (median 28 days). Plasma samples were collected for measurement of diltiazem and the metabolites MA and M1. Blood pressure and heart rate were monitored throughout the study.

Results: Grapefruit juice intake resulted in a statistically significant average individual increase in the area under the plasma diltiazem concentration-time curve (AUC(0-24)) of 20+/-25% ( P=0.02) compared with water. The average individual increase in peak plasma concentration (C(max)) of diltiazem after grapefruit juice administration was 22+/-37%, but this effect was not statistically significant ( P=0.14). The time to C(max) (t(max)) or terminal half-life was not affected by grapefruit juice. Considerable interindividual variability in the interaction was observed. There were no statistically significant differences in blood pressure and heart rate between the two treatments.

Conclusion: The present study demonstrated that a single intake of grapefruit juice (250 ml) caused a slight but statistically significant increase in the systemic exposure of diltiazem. Inhibition of intestinal metabolism and/or P-glycoprotein efflux transport may be responsible for this effect.
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http://dx.doi.org/10.1007/s00228-002-0516-8DOI Listing
November 2002

Pharmacokinetics of diltiazem and its metabolites in relation to CYP2D6 genotype.

Clin Pharmacol Ther 2002 Sep;72(3):333-42

Department of Pharmacology and Pharmaceutical Analysis, School of Pharmacy, University of Oslo, Norway.

Objectives: Recently, it was shown in vitro that the polymorphic enzyme cytochrome P450 (CYP) 2D6 mediates O-demethylation of diltiazem. The aim of this study was to compare the pharmacokinetics of diltiazem and its major metabolites in healthy human volunteers representing different CYP2D6 genotypes.

Methods: Norwegians of Caucasian origin were screened for their CYP2D6 genotype on the LightCycler (Roche Diagnostics, Mannheim, Germany) by melting-curve analysis of allele-specific fluorescence resonance energy transfer probes hybridized to polymerase chain reaction-amplified deoxyribonucleic acid. The first 5 individuals identified with genotypes corresponding to a homozygous extensive, heterozygous extensive, or homozygous poor CYP2D6-metabolizing phenotype, respectively, were voluntarily enrolled in the pharmacokinetic study. The participants received diltiazem, 120 mg, as a single oral dose, and plasma samples were collected up to 24 hours after administration. Plasma samples were purified by solid phase extraction. Diltiazem and 7 phase I metabolites were analyzed by liquid chromatography-mass spectrometry.

Results: The pharmacokinetics of diltiazem was not significantly different between the subgroups. However, the systemic exposure of the pharmacologically active metabolites desacetyl diltiazem and N-demethyldesacetyl diltiazem was > or = 5 times higher in poor CYP2D6 metabolizers than in extensive CYP2D6 metabolizers (P <.01).

Conclusions: CYP2D6 activity does not have a major impact on the disposition of diltiazem. In contrast, desacetyl diltiazem and N-demethyldesacetyl diltiazem are markedly accumulated in individuals expressing a deficient CYP2D6 phenotype. Because these metabolites exhibit pharmacologic properties of possible importance, individual CYP2D6 activity might be an aspect to consider in the clinical use of diltiazem.
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http://dx.doi.org/10.1067/mcp.2002.127396DOI Listing
September 2002

Desacetyl-diltiazem displays severalfold higher affinity to CYP2D6 compared with CYP3A4.

Drug Metab Dispos 2002 Jan;30(1):1-3

Department of Pharmacology, School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, N-0316 Oslo, Norway.

It has earlier been shown that the isoenzymes CYP2D6 and CYP3A4 are involved in O- and N-demethylation of diltiazem (DTZ), respectively. Apparently, CYP3A4 plays a more prominent role than CYP2D6 in the overall metabolism of DTZ. However, previous observations indicate that the opposite might be true for the pharmacologically active metabolite desacetyl-DTZ (M1). Thus, the aim of the present in vitro investigation was to study the relative affinity of M1 to CYP2D6 and CYP3A4. Immortalized human liver epithelial cells transfected with either CYP2D6 or CYP3A4 were used as a model system, and the presence of M1 and its metabolites in the cell culture medium was analyzed by high-performance liquid chromatography/UV detection both before and following 90 min of incubation. The estimated K(m) value for the CYP2D6-mediated O-demethylation of M1 was approximately 5 microM. In comparison, the affinity of M1 to CYP3A4 (N-demethylation) was about 100 times lower (K(m), approximately 540 microM) than to CYP2D6. These in vitro data suggest that M1 metabolism via CYP2D6, in contrast to the parent drug, probably is the preferred pathway in vivo. Metabolism mediated through CYP2D6 is associated with a substantial interindividual variability, and since M1 expresses pharmacological activity, individual CYP2D6 metabolic capacity might be an aspect to consider when using DTZ.
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http://dx.doi.org/10.1124/dmd.30.1.1DOI Listing
January 2002