ȕ-Hydroxycholesterol as biomarker for variation in CYP3A activity Dissertation for the Degree of Philosophiae Doctor (Ph.D.) Kristine Hole 2018 Center for Psychopharmacology Diakonhjemmet Hospital Oslo Department of Pharmaceutical Biosciences School of Pharmacy Faculty of Mathematics and Natural Sciences University of Oslo © Kristine Hole, 2018 Series of dissertations submitted to the Faculty of Mathematics and Natural Sciences, University of Oslo No. ISSN 1501-7710 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Cover: Hanne Baadsgaard Utigard. Print production: Reprosentralen, University of Oslo. TABLE OF CONTENTS ACKNOWLEDGEMENTS ...................................................................................................... II LIST OF PUBLICATIONS ..................................................................................................... III ABBREVIATIONS..................................................................................................................IV ABSTRACT.............................................................................................................................. V 1 INTRODUCTION.............................................................................................................. 1 1.1 Variability in drug response ....................................................................................... 1 1.2 Drug metabolism ........................................................................................................ 1 1.2.1 CYP enzymes ......................................................................................................... 2 1.3 CYP3A metabolism.................................................................................................... 3 1.3.1 CYP3A enzymes .................................................................................................... 3 1.3.2 CYP3A variability.................................................................................................. 4 1.4 CYP3A biomarkers .................................................................................................... 6 1.4.1 ȕ-hydroxycholesterol............................................................................................ 7 2 AIM OF THE THESIS..................................................................................................... 11 3 SUMMARY OF RESULTS............................................................................................. 12 4 DISCUSSION .................................................................................................................. 16 4.1 ȕ-hydroxycholesterol as biomarker for CYP3A variability ................................... 16 4.1.1 CYP3A induction and inhibition.......................................................................... 16 4.1.2 Genetic polymorphism ......................................................................................... 18 4.1.3 Renal function and CYP3A activity..................................................................... 19 4.1.4 Body weight and body mass index....................................................................... 20 4.1.5 Future perspectives............................................................................................... 21 4.2 Methodological considerations ................................................................................ 21 5 CONCLUSIONS.............................................................................................................. 23 REFERENCES......................................................................................................................... 24 I ACKNOWLEDGEMENTS The present work was performed at Center for Psychopharmacology, Diakonhjemmet Hospital, during the years 2014-2018. First and foremost, I would like to thank my supervisors Espen Molden and Tore Haslemo for inspiration and motivation throughout this work. I am so privileged to have been part of your research group. Thank you for all the valuable input, encouragement, and never ending research enthusiasm. I would also like to thank my third supervisor, Helge Refsum, for facilitating the scientific work at Center for Psychopharmacology. Thank you to all my collaborators and co-authors for great input during the work of the different papers. To all my colleagues at Center for Psychopharmacology, thank you for your contributions and support, and for providing a great working environment. A special thanks to Caroline, I am so grateful for having shared this PhD run with you. And finally, huge thanks to my family and friends, for your interest and support during these years. Oslo, December 2018 Kristine Hole II LIST OF PUBLICATIONS I. Hole K, Gjestad C, Heitmann KM, Haslemo T, Molden E, Bremer S. Impact of genetic and nongenetic factors on interindividual variability in 4ȕ-hydroxycholesterol concentration. Eur J Clin Pharmacol. 2017 Mar;73(3):317-324. II. Hole K, Størset E, Olastuen A, Haslemo T, Kro GB, Midtvedt K, Åsberg A, Molden E. Recovery of CYP3A Phenotype after Kidney Transplantation. Drug Metab Dispos. 2017 Dec;45(12):1260-1265. III. Hole K, Wollmann BM, Nguyen C, Haslemo T, Molden E. Comparison of CYP3A4- inducing capacity of enzyme-inducing antiepileptic drugs using 4ȕ-hydroxycholesterol as biomarker. Ther Drug Monit. 2018 Aug;40(4):463-468. IV. Hole K, Heiberg PL, Gjestad C, Mehus LL, Rø Ø, Molden E. (OHYDWHG ȕ- hydroxycholesterol/cholesterol ratio in anorexia nervosa patients. Pharmacol Res Perspect. 2018 Sep 11;6(5):e00430. III ABBREVIATIONS 4ȕOHC 4ȕ-hydroxycholesterol 4ȕOHC/C 4ȕ-hydroxycholesterol/cholesterol AUC Area under the concentration versus time curve BMI Body mass index CYP Cytochrome P450 EIAED Enzyme-inducing antiepileptic drug GFR Glomerular filtration rate IL Interleukin P-gp P-glycoprotein POR Cytochrome P450 oxidoreductase TDM Therapeutic drug monitoring IV ABSTRACT Individual differences in drug metabolism can cause extensive variability in drug exposure and efficacy. Better characterization of the different factors influencing drug metabolism can contribute to individualizing and optimizing drug therapy. The overall objective of this thesis was to investigate the suitability of 4ȕ-hydroxycholesterol (4ȕOHC) as biomarker for the variability in the activity of CYP3A-mediated drug metabolism. In a large naturalistic study of psychiatric patients, we reported 120-fold variation of 4ȕOHC levels. Impact of enzyme-inducing drugs was the factor with greatest quantitative effect on 4ȕOHC levels, and the findings support the suitability of 4ȕOHC as a biomarker for hepatic CYP3A induction. 4ȕOHC was also responsive to long-term treatment with moderate CYP3A inhibitors, but its suitability as a biomarker for CYP3A inhibition is yet to be established. Genetic polymorphism is known to be important for CYP3A5 activity, and to contribute to the total CYP3A activity. The contribution of CYP3A5 to in vivo formation of 4ȕOHC was, however, inconclusive in the present studies. Impact of other genetic polymorphisms on 4ȕOHC levels was limited. End-VWDJH UHQDO GLVHDVH LV DVVRFLDWHG ZLWK UHGXFHG ȕ2+& OHYHOV DQG Uecovery of renal function after kidney transplantation was associated with recovery of CYP3A activity. The clinical impact of this is yet to be established, but might indicate higher dose requirements of CYP3A-metabolized drugs after vs. before kidney transplantation. Body weight and body mass index (BMI) impacted CYP3A activity both in kidney transplant and anorexic patients, with increasing level of 4ȕOHC levels with decreasing body weight and BMI. This suggests that clearance of CYP3A substrates increases with decreasing body weight/BMI. The present thesis supports the suitability of 4ȕOHC as a hepatic CYP3A biomarker since the factors which in these studies describe variation in 4ȕOHC levels coincide with previous findings on variation in CYP3A phenotype. Further studies should investigate 4ȕOHC as a potential biomarker for personalized dosing of CYP3A substrates. V VI 1 INTRODUCTION 1.1 Variability in drug response A major problem during drug therapy is variability in drug response. Standard doses of a given drug can lead to the desired effect in some patients, while others experience subtherapeutic response or side effects. Personalized dosing can therefore improve the outcome of drug treatment by reducing the occurrence of adverse effects and lack of effect. However, personalized dosing is not a straightforward procedure. The effect a drug dose will produce in a given patient is influenced by pharmacokinetic and pharmacodynamic processes, which describe the interaction between the body and the drug. Pharmacodynamics is the study of the effects of drugs on the body, and variability can be caused by e.g. genetic differences in target receptors, drug-drug interactions at the target site or disease status. Pharmacokinetic variability is one of the main sources for variation in drug response. Pharmacokinetic variability comprises variation in drug exposure due to differences in e.g. absorption, distribution, metabolism and excretion of a given drug. These processes influence drug concentration at the target site, and therefore lead to variations in drug response. Several factors are known to impact pharmacokinetic processes, such as age, sex, body weight, disease status, kidney function, genetics and drug-drug interactions. Better characterization of the different factors influencing