Publications by authors named "Marianne K Kringen"

20 Publications

  • Page 1 of 1

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

The Influence of Combined CYP2D6 and CYP2C19 Genotypes on Venlafaxine and O-Desmethylvenlafaxine Concentrations in a Large Patient Cohort.

J Clin Psychopharmacol 2020 Mar/Apr;40(2):137-144

From the Center for Psychopharmacology, Diakonhjemmet Hospital.

Purpose: The antidepressant venlafaxine is largely O-desmethylated by CYP2D6, whereas CYP2C19 mediates an alternative metabolic route of venlafaxine through N-desmethylation. The aim of this study was to investigate the combined effect of genotype-predicted CYP2D6 and CYP2C19 phenotypes on serum concentrations of venlafaxine and metabolites in a large patient population.

Methods: Patients were retrospectively included from a therapeutic drug monitoring service at Diakonhjemmet Hospital in Oslo (Norway) between January 01, 2007, and December 31, 2017. The study population was divided into different phenotype subgroups according to the combinations of CYP2D6/CYP2C19 phenotypes; intermediate metabolizers (IMs), poor metabolizers (PMs) and ultrarapid metabolizers, and compared using combined normal metabolizers (NMs) as reference.

Findings: The dose-adjusted serum concentration of venlafaxine was 4- and 13-fold increased in combined CYP2D6 IM/CYP2C19 PMs and combined PMs, respectively, compared with combined NMs (P < 0.001). The sum concentration of venlafaxine + ODV (pharmacological active moiety) was increased 1.9 and 3.6-fold, respectively, in the same phenotype groups. Furthermore, the dose-adjusted active moiety exposure was similar in combined IMs as combined CYP2D6 PM/CYP2C19 NMs. CYP2D6 and CYP2C19 phenotypes explained 46% of the interindividual variability in dose-adjusted venlafaxine serum concentrations, whereas CYP2D6 alone explained 24%.

Conclusions: The combined CYP2D6/CYP2C19 phenotype has a significant impact on serum concentrations of venlafaxine and also on the active moiety of venlafaxine + ODV, than CYP2D6 alone. In clinical practice, it is therefore important to take into account phenotype variabilities of both enzymes when assessing the risk of dose-dependent adverse effects during venlafaxine treatment.
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http://dx.doi.org/10.1097/JCP.0000000000001174DOI Listing
December 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 CYP2C19 genotype on sertraline exposure in 1200 Scandinavian patients.

Neuropsychopharmacology 2020 02 24;45(3):570-576. Epub 2019 Oct 24.

Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway.

Sertraline is an (SSRI-)antidepressant metabolized by the polymorphic CYP2C19 enzyme. The aim of this study was to investigate the impact of CYP2C19 genotype on the serum concentrations of sertraline in a large patient population. Second, the proportions of patients in the various CYP2C19 genotype-defined subgroups obtaining serum concentrations outside the therapeutic range of sertraline were assessed. A total of 2190 sertraline serum concentration measurements from 1202 patients were included retrospectively from the drug monitoring database at Diakonhjemmet Hospital in Oslo. The patients were divided into CYP2C19 genotype-predicted phenotype subgroups, i.e. normal (NMs), ultra rapid (UMs), intermediate (IMs), and poor metabolisers (PMs). The differences in dose-harmonized serum concentrations of sertraline and N-desmethylsertraline-to-sertraline metabolic ratio were compared between the subgroups, with CYP2C19 NMs set as reference. The patient proportions outside the therapeutic concentration range were also compared between the subgroups with NMs defined as reference. Compared with the CYP2C19 NMs, the sertraline serum concentration was increased 1.38-fold (95% CI 1.26-1.50) and 2.68-fold (95% CI 2.16-3.31) in CYP2C19 IMs and PMs, respectively (p < 0.001), while only a marginally lower serum concentration (-10%) was observed in CYP2C19 UMs (p = 0.012). The odds ratio for having a sertraline concentration above the therapeutic reference range was 1.97 (95% CI 1.21-3.21, p = 0.064) and 8.69 (95% CI 3.88-19.19, p < 0.001) higher for IMs and PMs vs. NMs, respectively. CYP2C19 IMs and PMs obtain significantly higher serum concentrations of sertraline than NMs. Based on the relative differences in serum concentrations compared to NMs, dose reductions of 60% and 25% should be considered in PMs and IMs, respectively, to reduce the risk of sertraline overexposure in these patients.
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http://dx.doi.org/10.1038/s41386-019-0554-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6969041PMC
February 2020

Effect of CYP4F2, VKORC1, and CYP2C9 in Influencing Coumarin Dose: A Single-Patient Data Meta-Analysis in More Than 15,000 Individuals.

Clin Pharmacol Ther 2019 06 17;105(6):1477-1491. Epub 2019 Feb 17.

Department of Clinical Pharmacology & Genetics, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.

The cytochrome P450 (CYP)4F2 gene is known to influence mean coumarin dose. The aim of the present study was to undertake a meta-analysis at the individual patients level to capture the possible effect of ethnicity, gene-gene interaction, or other drugs on the association and to verify if inclusion of CYP4F2*3 variant into dosing algorithms improves the prediction of mean coumarin dose. We asked the authors of our previous meta-analysis (30 articles) and of 38 new articles retrieved by a systematic review to send us individual patients' data. The final collection consists of 15,754 patients split into a derivation and validation cohort. The CYP4F2*3 polymorphism was consistently associated with an increase in mean coumarin dose (+9% (95% confidence interval (CI) 7-10%), with a higher effect in women, in patients taking acenocoumarol, and in white patients. The inclusion of the CYP4F2*3 in dosing algorithms slightly improved the prediction of stable coumarin dose. New pharmacogenetic equations potentially useful for clinical practice were derived.
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http://dx.doi.org/10.1002/cpt.1323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6542461PMC
June 2019

Combined Effect of CYP2B6 Genotype and Other Candidate Genes on a Steady-State Serum Concentration of Methadone in Opioid Maintenance Treatment.

Ther Drug Monit 2017 10;39(5):550-555

*Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo; †Department of Addiction Medicine, Haukeland University Hospital, Bergen; ‡Norwegian National Advisory Unit on Concurrent Substance Abuse and Mental Health Disorders, Innlandet Hospital Trust, Hamar; §Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo; ¶Department of Forensic Sciences, Oslo University Hospital, Oslo; and ‖Norwegian Center for Addiction Research, University of Oslo, Oslo, Norway.

Background: A considerable interindividual variability in methadone pharmacokinetics is seen in patients on methadone maintenance treatment. The aim of this study was to clarify the impact of the reduced function CYP2B6*6 variant allele together with variants in other candidate genes on a steady-state methadone concentration in a naturalistic setting.

Methods: Information of methadone serum concentration, dose, age, sex, and CYP2C9, CYP2C19, and CYP2D6 genotypes were collected from a routine therapeutic drug monitoring database, whereas variant alleles in CYP2B6 and CYP3A5 were retrospectively genotyped. Linear mixed model analyses were used to study the impact of gene variants on methadone serum concentration/dose (C/D) ratios, including age, sex, and time since the last dose intake as covariates.

Results: Overall, 155 serum samples from 62 patients were included in this study. The estimated mean methadone C/D ratios was 17.8 nmol·L·mg for homozygous carriers of CYP2B6*6, which was significantly (P < 0.001) higher than noncarriers (9.2 nmol·L·mg). There was no difference in C/D ratios between heterozygous carriers of CYP2B6*6 (9.1 nmol·L·mg) and noncarriers. An increase in mean methadone C/D ratios was also seen for homozygous carriers of CYP3A5*3 and heterozygous carriers of CYP2C9*2 or *3 and CYP2C19*2 or *3.

Conclusions: Patients homozygous for CYP2B6*6 had a >90% higher methadone C/D ratio. Genotyping of CYP2B6 may therefore be of value when assessing dose requirements in methadone maintenance treatment.
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http://dx.doi.org/10.1097/FTD.0000000000000437DOI Listing
October 2017

Distinct DNA methylation profiles in bone and blood of osteoporotic and healthy postmenopausal women.

Epigenetics 2017 08 26;12(8):674-687. Epub 2017 Jun 26.

b Lovisenberg Diakonale Hospital, Unger-Vetlesen Institute , Oslo , Norway.

DNA methylation affects expression of associated genes and may contribute to the missing genetic effects from genome-wide association studies of osteoporosis. To improve insight into the mechanisms of postmenopausal osteoporosis, we combined transcript profiling with DNA methylation analyses in bone. RNA and DNA were isolated from 84 bone biopsies of postmenopausal donors varying markedly in bone mineral density (BMD). In all, 2529 CpGs in the top 100 genes most significantly associated with BMD were analyzed. The methylation levels at 63 CpGs differed significantly between healthy and osteoporotic women at 10% false discovery rate (FDR). Five of these CpGs at 5% FDR could explain 14% of BMD variation. To test whether blood DNA methylation reflect the situation in bone (as shown for other tissues), an independent cohort was selected and BMD association was demonstrated in blood for 13 of the 63 CpGs. Four transcripts representing inhibitors of bone metabolism-MEPE, SOST, WIF1, and DKK1-showed correlation to a high number of methylated CpGs, at 5% FDR. Our results link DNA methylation to the genetic influence modifying the skeleton, and the data suggest a complex interaction between CpG methylation and gene regulation. This is the first study in the hitherto largest number of postmenopausal women to demonstrate a strong association among bone CpG methylation, transcript levels, and BMD/fracture. This new insight may have implications for evaluation of osteoporosis stage and susceptibility.
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http://dx.doi.org/10.1080/15592294.2017.1345832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5687328PMC
August 2017

Mortality among head trauma patients taking preinjury antithrombotic agents: a retrospective cohort analysis from a Level 1 trauma centre.

BMC Emerg Med 2016 08 2;16(1):29. Epub 2016 Aug 2.

Centre for Psychopharmacology, Diakonhjemmet Hospital, PO Box 85 Vinderen, N-0319, Oslo, Norway.

Background: Bleeding represents the most well-known and the most feared complications caused by the use of antithrombotic agents. There is, however, limited documentation whether pre-injury use of antithrombotic agents affects outcome after head trauma. The aim of this study was to define the relationship between the use of preinjury antithrombotic agents and mortality among elderly people sustaining blunt head trauma.

Methods: A retrospective cohort analysis was performed on the hospital based trauma registry at Oslo University Hospital. Patients aged 55 years or older sustaining blunt head trauma between 2004 and 2006 were included. Multivariable logistic regression analyses were used to identify independent predictors of 30-day mortality. Separate analyses were performed for warfarin use and platelet inhibitor use.

Results: Of the 418 patients admitted with a diagnosis of head trauma, 137 (32.8 %) used pre-injury antithrombotic agents (53 warfarin, 80 platelet inhibitors, and 4 both). Seventy patients died (16.7 %); 15 (28.3 %) of the warfarin users, 12 (15.0 %) of the platelet inhibitor users, and two (50 %) with combined use of warfarin and platelet inhibitors, compared to 41 (14.6 %) of the non-users. There was a significant interaction effect between warfarin use and the Triage Revised Trauma Score collected upon the patients' arrival at the hospital. After adjusting for potential confounders, warfarin use was associated with increased 30-day mortality among patients with normal physiology (adjusted OR 8,3; 95 % CI, 2.0 to 34.8) on admission, but not among patients with physiological derangement on admission. Use of platelet inhibitors was not associated with increased mortality.

Conclusions: The use of warfarin before trauma was associated with increased 30-day mortality among a subset of patients. Use of platelet inhibitors before trauma was not associated with increased mortality. These results indicate that patients on preinjury warfarin may need closer monitoring and follow up after trauma despite normal physiology on admission to the emergency department.
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http://dx.doi.org/10.1186/s12873-016-0094-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4971754PMC
August 2016

Changes of 5-hydroxymethylcytosine distribution during myeloid and lymphoid differentiation of CD34+ cells.

Epigenetics Chromatin 2016 31;9:21. Epub 2016 May 31.

Nordic European Molecular Laboratory (EMBL) Partnership, Centre for Molecular Medicine Norway, University of Oslo, Blindern, P.O. Box 1137, 0318 Oslo, Norway ; Department of Haematology, Oslo University Hospital, Oslo, Norway ; Norwegian Center for Stem Cell Research, University of Oslo, Oslo, Norway.

Background: Hematopoietic stem cell renewal and differentiation are regulated through epigenetic processes. The conversion of 5-methylcytosine into 5-hydroxymethylcytosine (5hmC) by ten-eleven-translocation enzymes provides new insights into the epigenetic regulation of gene expression during development. Here, we studied the potential gene regulatory role of 5hmC during human hematopoiesis.

Results: We used reduced representation of 5-hydroxymethylcytosine profiling (RRHP) to characterize 5hmC distribution in CD34+ cells, CD4+ T cells, CD19+ B cells, CD14+ monocytes and granulocytes. In all analyzed blood cell types, the presence of 5hmC at gene bodies correlates positively with gene expression, and highest 5hmC levels are found around transcription start sites of highly expressed genes. In CD34+ cells, 5hmC primes for the expression of genes regulating myeloid and lymphoid lineage commitment. Throughout blood cell differentiation, intragenic 5hmC is maintained at genes that are highly expressed and required for acquisition of the mature blood cell phenotype. Moreover, in CD34+ cells, the presence of 5hmC at enhancers associates with increased binding of RUNX1 and FLI1, transcription factors essential for hematopoiesis.

Conclusions: Our study provides a comprehensive genome-wide overview of 5hmC distribution in human hematopoietic cells and new insights into the epigenetic regulation of gene expression during human hematopoiesis.
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http://dx.doi.org/10.1186/s13072-016-0070-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4888655PMC
June 2016

Copy number variation in the ATP-binding cassette transporter ABCC6 gene and ABCC6 pseudogenes in patients with pseudoxanthoma elasticum.

Mol Genet Genomic Med 2015 May 8;3(3):233-7. Epub 2015 Mar 8.

Furst Medical Laboratory Oslo, Norway.

Single mutations in the ATP-binding cassette transporter (ABCC6) gene (OMIM 603234) are known to cause the rare autosomal recessive disease pseudoxanthoma elasticum (PXE). Recently, we have found that copy number variations (CNVs) in pseudogenes of the ABCC6 gene are quite common. The aim of this study was to investigate the frequency and possible contribution of CNV in ABCC6 and its pseudogenes in PXE. Genomic DNA from 212 PXE individuals were examined for copy number by pyrosequencing and quantitative polymerase chain reaction (PCR) and compared with healthy individuals. The frequency of PXE individuals with any CNV was higher than in healthy individuals. The majority of variation comprised known and possibly new deletions in the ABCC6 gene and duplications of the ABCC6P1 and ABCC6P2 genes. ABCC6 deletions and ABCC6P2 duplications were not observed in 142 healthy individuals. In conclusion, by pyrosequencing and quantitative PCR, we were able to detect known and possibly new deletions in the ABCC6 gene that may have caused the PXE phenotype. Pyrosequencing may be used in PXE patients who have obtained incomplete genotype from conventional techniques. The frequency of ABCC6P2 pseudogene duplication was more common in PXE patients than healthy individuals and may affect the PXE phenotype.
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http://dx.doi.org/10.1002/mgg3.137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4444165PMC
May 2015

RNA-sequencing analysis of HepG2 cells treated with atorvastatin.

PLoS One 2014 25;9(8):e105836. Epub 2014 Aug 25.

Fürst Medical Laboratory, Oslo, Norway.

The cholesterol-lowering drug atorvastatin is among the most prescribed drug in the world. Alternative splicing in a number of genes has been reported to be associated with variable statin response. RNA-seq has proven to be a powerful technique for genome-wide splice variant analysis. In the present study, we sought to investigate atorvastatin responsive splice variants in HepG2 cells using RNA-seq analysis to identify novel candidate genes implicated in cholesterol homeostasis and in the statin response. HepG2 cells were treated with 10 µM atorvastatin for 24 hours. RNA-seq and exon array analyses were performed. The validation of selected genes was performed using Taqman gene expression assays. RNA-seq analysis identified 121 genes and 98 specific splice variants, of which four were minor splice variants to be differentially expressed, 11 were genes with potential changes in their splicing patterns (SYCP3, ZNF195, ZNF674, MYD88, WHSC1, KIF16B, ZNF92, AGER, FCHO1, SLC6A12 and AKAP9), and one was a gene (RAP1GAP) with differential promoter usage. The IL21R transcript was detected to be differentially expressed via RNA-seq and RT-qPCR, but not in the exon array. In conclusion, several novel candidate genes that are affected by atorvastatin treatment were identified in this study. Further studies are needed to determine the biological significance of the atorvastatin responsive splice variants that have been uniquely identified using RNA-seq.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0105836PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4143339PMC
November 2015

Serum bilirubin concentration in healthy adult North-Europeans is strictly controlled by the UGT1A1 TA-repeat variants.

PLoS One 2014 28;9(2):e90248. Epub 2014 Feb 28.

Department of Medical Biochemistry, Oslo University Hospital, Ullevål, Oslo, Norway ; Institute of Clinical Medicine, University of Oslo, Oslo, Norway.

The major enzyme responsible for the glucuronidation of bilirubin is the uridine 5'-diphosphoglucose glucuronosyltransferase A1 (UGT1A1) enzyme, and genetic variation in the UGT1A1 gene is reported to influence the bilirubin concentration in the blood. In this study, we have investigated which gene-/haplotype variants may be useful for genetic testing of Gilbert's syndrome. Two groups of samples based on serum bilirubin concentrations were obtained from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA): the 150 individuals with the highest bilirubin (>17.5 µmol/L) and the 150 individuals with normal bilirubin concentrations (<17.5 µmol/L). The individuals were examined for the TA6>TA7 variant in the UGT1A1 promoter and 7 tag-SNPs in an extended promoter region of UGT1A1 (haplotype analysis) and in selected SNPs in candidate genes (SLCO1B3, ABCC2 and NUP153). We found significant odds ratios for high bilirubin level for all the selected UGT1A1 variants. However, in stepwise multivariate logistic regression analysis of all genetic variants together with age, sex, country of origin and fasting time, the repeat variants of UGT1A1 TA6>TA7 and SLCO1B3 rs2117032 T>C were the only variants significantly associated with higher bilirubin concentrations. Most individuals with high bilirubin levels were homozygous for the TA7-repeat (74%) while only 3% were homozygous for the TA7-repeat in individuals with normal bilirubin levels. Among individuals heterozygous for the TA7-repeat, a low frequent UGT1A1-diplotype harboring the rs7564935 G-variant was associated with higher bilirubin levels. In conclusion, our results demonstrate that in testing for Gilbert's syndrome, analyzing for the homozygous TA7/TA7-genotype would be appropriate.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0090248PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938665PMC
October 2014

UGT1A1*28 is associated with decreased systemic exposure of atorvastatin lactone.

Mol Diagn Ther 2013 Aug;17(4):233-7

Department of Medical Biochemistry, Oslo University Hospital, University of Oslo, Nydalen, P.O. Box 4956, 0424, Oslo, Norway.

Background: Atorvastatin is commonly used to reduce cholesterol. Atorvastatin acid is converted to its corresponding lactone form spontaneously or via glucuronidation mediated by uridine diphosphate glucuronosyltransferase (UGT) 1A1 and 1A3. Atorvastatin lactone is pharmacologically inactive, but is suspected to be muscle toxic and cause statin-induced myopathy (SIM). A several fold increase in systemic exposure of atorvastatin lactone has previously been observed in patients with SIM compared with healthy control subjects. In this study we aimed to investigate the association between polymorphisms in the UGT1A gene locus and plasma atorvastatin lactone levels.

Methods: DNA was extracted from whole blood obtained from a previous pharmacokinetic study of patients carefully diagnosed as having true SIM (n = 13) and healthy control subjects (n = 15). The UGT1A1*28(TA) 7 , UGT1A3*2, UGT1A3*3, and UGT1A3*6 polymorphisms were detected by pyrosequencing.

Results: Carriers of the low-expression allele UGT1A1*28(TA) 7 tended to have lower levels of atorvastatin lactone (p < 0.05) than carriers with the normal-activity allele (TA) 6 .

Conclusion: The low-expression UGT1A1*28(TA) 7 allele seems to be associated with decreased systemic exposure of the suspected muscle-toxic metabolite atorvastatin lactone.
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http://dx.doi.org/10.1007/s40291-013-0031-xDOI Listing
August 2013

A novel 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) splice variant with an alternative exon 1 potentially encoding an extended N-terminus.

BMC Mol Biol 2012 Sep 18;13:29. Epub 2012 Sep 18.

Department of Medical Biochemistry, University of Oslo and Oslo University Hospital, Ullevål, P,O box 4956, Nydalen, Oslo, 0424, Norway.

Background: The major rate-limiting enzyme for de novo cholesterol synthesis is 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). HMGCR is sterically inhibited by statins, the most commonly prescribed drugs for the prevention of cardiovascular events. Alternative splicing of HMGCR has been implicated in the control of cholesterol homeostasis. The aim of this study was to identify novel alternatively spliced variants of HMGCR with potential physiological importance.

Results: Bioinformatic analyses predicted three novel HMGCR transcripts containing an alternative exon 1 (HMGCR-1b, -1c, -1d) compared with the canonical transcript (HMGCR-1a). The open reading frame of the HMGCR-1b transcript potentially encodes 20 additional amino acids at the N-terminus, compared with HMGCR-1a. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to examine the mRNA levels of HMGCR in different tissues; HMGCR-1a was the most highly expressed variant in most tissues, with the exception of the skin, esophagus, and uterine cervix, in which HMGCR-1b was the most highly expressed transcript. Atorvastatin treatment of HepG2 cells resulted in increased HMGCR-1b mRNA levels, but unaltered proximal promoter activity compared to untreated cells. In contrast, HMGCR-1c showed a more restricted transcription pattern, but was also induced by atorvastatin treatment.

Conclusions: The gene encoding HMGCR uses alternative, mutually exclusive exon 1 sequences. This contributes to an increased complexity of HMGCR transcripts. Further studies are needed to investigate whether HMGCR splice variants identified in this study are physiologically functional.
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http://dx.doi.org/10.1186/1471-2199-13-29DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3526503PMC
September 2012

Copy number variations of the ATP-binding cassette transporter ABCC6 gene and its pseudogenes.

BMC Res Notes 2012 Aug 9;5:425. Epub 2012 Aug 9.

Department of Pharmacology, Oslo University Hospital, Ullevål, Oslo, Norway.

Background: The ATP-binding cassette transporter ABCC6 gene is located on chromosome 16 between its two pseudogenes (ABCC6P1 and ABCC6P2). Previously, we have shown that ABCC6P1 is transcribed and affects ABCC6 at the transcriptional level. In this study we aimed to determine copy number variations of ABCC6, ABCC6P1 and ABCC6P2 in different populations. Moreover, we sought to study the transcription pattern of ABCC6 and ABCC6 pseudogenes in 39 different human tissues.

Findings: Genomic DNA from healthy individuals from five populations, Chinese (n = 24), Middle East (n = 20), Mexicans (n = 24), Caucasians (n = 50) and Africans (n = 24), were examined for copy number variations of ABCC6 and its pseudogenes by pyrosequencing and quantitative PCR. Copy number variation of ABCC6 was very rare (2/142; 1.4%). However, one or three copies of ABCC6P1 were relatively common (3% and 8%, respectively). Only one person had a single copy of ABCC6P2 while none had three copies. In Chinese, deletions or duplications of ABCC6P1 were more frequent than in any other population (9/24; 37.5%). The transcription pattern of ABCC6P2 was highly similar to ABCC6 and ABCC6P1, with highest transcription in liver and kidney. Interestingly, the total transcription level of pseudogenes, ABCC6P1 + ABCC6P2, was higher than ABCC6 in most tissues, including liver and kidney.

Conclusions: Copy number variations of the ABCC6 pseudogenes are quite common, especially in populations of Chinese ancestry. The expression pattern of ABCC6P2 in 39 human tissues was highly similar to that of ABCC6 and ABCC6P1 suggesting similar regulatory mechanisms for ABCC6 and its pseudogenes.
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http://dx.doi.org/10.1186/1756-0500-5-425DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3434077PMC
August 2012

Genetic variation of VKORC1 and CYP4F2 genes related to warfarin maintenance dose in patients with myocardial infarction.

J Biomed Biotechnol 2011 24;2011:739751. Epub 2010 Nov 24.

Department of Pharmacology, Oslo University Hospital, Ullevål, Oslo, Norway.

The aim of this study was to investigate whether the VKORC1*3 (rs7294/9041 G > A), VKORC1*4 (rs17708472/6009 C > T), and CYP4F2 (rs2108622/1347 C > T) polymorphisms were associated with elevated warfarin maintenance dose requirements in patients with myocardial infarction (n = 105) from the Warfarin Aspirin Reinfarction Study (WARIS-II). We found significant associations between elevated warfarin dose requirements and VKORC1*3 and VKORC1*4 polymorphisms (P = .001 and P = .004, resp.), whereas CYP4F2 (1347 C > T) showed a weak association on higher warfarin dose requirements (P = .09). However, analysing these variant alleles in a regression analysis together with our previously reported data on VKORC1*2, CYP2C9*2 and CYP2C9*3 polymorphisms, gave no significant associations for neither VKORC1*3, VKORC1*4 nor CYP4F2 (1347 C > T). In conclusion, in patients with myocardial infarction, the individual contribution to warfarin dose requirements from VKORC1*3, VKORC1*4, and CYP4F2 (1347 C > T) polymorphisms was negligible. Our results indicate that pharmacogenetic testing for VKORC1*2, CYP2C9*2 and CYP2C9*3 is more informative regarding warfarin dose requirements than testing for VKORC1*3, VKORC1*4, and CYP4F2 (1347 C > T) polymorphisms.
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http://dx.doi.org/10.1155/2011/739751DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992873PMC
March 2011

Reduced platelet function and role of drugs in acute gastrointestinal bleeding.

Basic Clin Pharmacol Toxicol 2011 Mar 30;108(3):194-201. Epub 2010 Nov 30.

Department of Pharmacology, Oslo University Hospital, Ullevål, Kirkeveien 166, Oslo, Norway.

Gastrointestinal (GI) bleeding may be caused by a constitutive bleeding disposition or drug-induced inhibition of hemostasis. Platelet function in patients with ongoing GI bleeding is unknown. The aim of this study was to investigate platelet function in patients with acute GI bleeding. Patients (n=35) presenting with acute GI bleeding (hematemesis or melena) were recruited. For comparison, 13 patients treated with aspirin and 11 patients treated with clopidogrel without GI bleeding and 27 healthy controls were studied. Platelet function was measured by whole-blood aggregation and flow cytometry. Coagulation function was measured with calibrated automated thrombography. Platelet aggregation and P-selectin expression were significantly lower after arachidonic acid stimulation in GI bleeding patients than in healthy subjects (p≤0.05). Collagen-induced P-selectin expression was significantly reduced in patients using anti-platelet drugs (p=0.02) and in many patients not using anti-platelet drugs. Thrombin generation, measured by calibrated automated thrombography, was only reduced in patients on warfarin treatment. In conclusion, platelet function is reduced in acute GI bleeding patients and a considerable proportion appears to be related to drug use.
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http://dx.doi.org/10.1111/j.1742-7843.2010.00643.xDOI Listing
March 2011

No link between X chromosome inactivation pattern and simple goiter in females: evidence from a twin study.

Thyroid 2009 Feb;19(2):165-9

Department of Endocrinology and Metabolism, Odense University Hospital, Odense, Denmark.

Background: Simple goiter (SG) comprises diffuse (DG) and nodular (NG) benign nonautoimmune nontoxic goiter. In nonendemic goiter areas, the ratio of females to males may exceed 5:1, indicating that gender and/or sex hormones may play a role in the etiology of SG in these areas. Theoretically, as shown for autoimmune thyroid disease, X chromosome inactivation (XCI) and resultant tissue chimerism could offer a novel explanation for the female preponderance of SG. To examine whether skewed XCI is associated with SG, we first compared XCI in 71 twin individuals with SG with that in 142 unrelated healthy control twin individuals, and then performed a within-pair comparison of XCI in 48 twin pairs discordant for SG.

Methods: DNA was extracted from peripheral blood cells. XCI analysis was performed by predigestion of DNA using the methylation-sensitive enzyme Hpall, followed by polymerase chain reaction of the polymorphic CAG repeat of the androgen receptor gene. A polymerase chain reaction product is obtained from the inactive X chromosome only. The XCI pattern was classified as skewed when 80% or more of the cells preferentially inactivated the same X chromosome. Twin zygosity was established by DNA fingerprinting.

Results: The frequency of skewed XCI in female twins with SG, DG, and NG was 11% (8/71), 13% (6/46), and 8% (2/25), respectively, which was not significantly different from the prevalences in the corresponding control populations, 14% (20/142, p = 0.56), 14% (13/92, p = 1.00), and 14% (7/50, p = 0.71), respectively. Essentially, similar results were obtained when comparing the prevalence of skewed XCI in twin pairs discordant for SG (48 pairs), DG (30 pairs), and NG (18 pairs).

Conclusion: In a sample of Danish female twins, we did not find evidence for involvement of skewed XCI in the etiology or the female preponderance of SG.
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http://dx.doi.org/10.1089/thy.2008.0380DOI Listing
February 2009

Warfarin dose and INR related to genotypes of CYP2C9 and VKORC1 in patients with myocardial infarction.

Thromb J 2008 Jun 17;6. Epub 2008 Jun 17.

R&D, Department of Clinical Chemistry, Ulleval University Hospital, Kirkeveien 166, O407 Oslo, Norway.

Background: Warfarin treatment has a narrow therapeutic range, requiring meticulous monitoring and dosage titration. Individual dosage requirement has recently partly been explained by genetic variation of the warfarin metabolizing enzyme CYP2C9 and the Vitamin K-activating enzyme VKORC1. In the WARIS-II study, comparing three different antithrombotic regimens after myocardial infarction, warfarin treatment reduced thrombotic events, but was associated with more frequent bleeding than use of acetylsalisylic acid (ASA) alone.

Aims: The primary aim of the present study was to investigate the relation between genotypes of CYP2C9 and VKORC1 and warfarin maintenance dose in myocardial infarction. The secondary aim was to relate the genotypes to international normalized ratio (INR).

Methods: Genotyping was performed in 212 myocardial infarction patients from the WARIS-II study by robotic isolation of DNA from EDTA whole blood (MagNa Pure LC) before PCR amplification (LightCycler) and melting point analysis.

Results: The 420 C>T substitution of CYP2C9*2, the 1075 A>C substitution of CYP2C9*3 and the 1173 C>T substitution of VKORC1 had minor allele frequencies of, 11.3%, 5.7% and 36.6% respectively. Warfarin weekly dose varied between 17 mg and 74 mg among the patients. INR did not vary between genotypes. Warfarin dosage requirement was significantly associated with CYP2C9 and VKORC1 genotypes, treatment group and age. The VKORC1 genotype contributed 24.5% to the interindividual variation in warfarin dosage, whereas the combined CYP2C9 genotypes were only responsible for 7.2% of the dose variation.

Conclusion: CYP2C9 and VKORC1 genotype frequencies in myocardial infarction patients appear similar to other patient groups and have similar impact on warfarin maintenance dose.
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http://dx.doi.org/10.1186/1477-9560-6-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440373PMC
June 2008
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