caa a22 4500 477058035 CHVBK 20180405111352.0 cr unu---uuuuu 170330e19960101xx s 000 0 eng 10.1007/BF00226333 doi (NATIONALLICENCE)springer-10.1007/BF00226333 Biotransformation of caffeine by cDNA-expressed human cytochromes P-450 [Elektronische Daten] [H. Ha, F. Follath, J. Chen, S. Krähenbühl] Objectives: The biotransformation of caffeine has been studied in vitro using human cytochrome P-450 isoenzymes (CYPs) expressed in human B-lymphoblastoid cell lines, namely CYP1A1, 1A2, 2A6, 2B6, 2D6-Val, 2E1 and 3A4, and microsomal epoxide hydroxylase (EH). In addition, CYP 2D6-Met was also studied, in which a valine in the wild type (CYP2D6-Val) has been replaced by a methionine due to a G to A mutation in position 112. Results: At caffeine 3 mmol·l-1, five CYPs (1A1, 1A2, 2D6-Met, 2E1 and 3A4) catalysed the biotransformation of caffeine. Among the enzymes studied, CYP1A2, which predominantly catalysed paraxanthine formation, had the highest intrinsic clearance (160 l h-1·mmol-1 CYP). Together with its high abundance in liver, it should be considered, therefore, to be the most important isoenzyme in caffeine metabolism. The affinity of caffeine for CYP1A1 was comparable to that of its homologue 1A2. CYP2D6-Met, which catalysed caffeine metabolism by demethylation and 8-hydroxylation, also had a relatively high intrinsic clearance (3.0 l·h-1mmol-1 CYP), in particular for theophylline and paraxanthine formation, with kM values between 9-16 mmol·l-1. In contrast, the wild type, CYP2D6-Val, had no detectable activity. In comparison, CYP2E1 played a less important role in in vitro caffeine metabolism. CYP3A4 predominantly catalysed 8-hydroxylation with a kM value of 46 mmol·l-1 and an intrinsic clearance of 0.60 l·h-1·mmol-1 CYP. Due to its high abundance in human liver, the latter CYP may contribute significantly to the in vivo formation of TMU. Conclusion: The findings of this study indicate that i) microsomes from transfected human B-lymphoblastoid cell lines give results close to those obtained with microsomes isolated from human liver, ii) at least four CYP isoforms are involved in caffeine metabolism, iii) at a substrate concentration <0.1 mmol·l-1, CYP1A2 and 1A1 are the most important isoenzymes, iv) at higher concentrations the participation of other isoenzymes, in particular CYP3A4, 2E1 and possibly also CYP2D6-Met, are important in caffeine metabolism, and v) the nucleotide composition at position 1120 of CYP2D6 determines the activity of this isoenzyme in caffeine metabolism. Springer-Verlag, 1996 Caffeine nationallicence Biotransformation nationallicence CYP1A2 nationallicence CYP1A1 nationallicence CYP2D6-Met CYP2D6-Val nationallicence CYP2E1 nationallicence cDNA-expressed microsomes nationallicence AFMU : 5-acetylamino-6-formylamino-3-methyluracil nationallicence CYP : human cytochrome P-450 nationallicence PAH : polycyclic aromatic hydrocarbon nationallicence 17X : paraxanthine nationallicence 37X : theobromine nationallicence 13X : theophylline nationallicence 137U : trimethyluric acid nationallicence Ha H. Cardiovascular Therapy Research Unit, Cardiology Division, University Hospital Zuerich, CH-8091, Zurich, Switzerland aut Follath F. Cardiovascular Therapy Research Unit, Cardiology Division, University Hospital Zuerich, CH-8091, Zurich, Switzerland aut Chen J. Huadong Hospital, Shanghai, P. R. China aut Krähenbühl S. Division of Clinical Pharmacology and Toxicology, Department of Internal Medicine, University Hospital Zurich, CH-8091, Zurich, Switzerland aut European Journal of Clinical Pharmacology Springer-Verlag 49/4(1996-01-01), 309-315 0031-6970 49:4<309 1996 49 228 https://doi.org/10.1007/BF00226333 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00226333 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Ha H. Cardiovascular Therapy Research Unit, Cardiology Division, University Hospital Zuerich, CH-8091, Zurich, Switzerland aut NATIONALLICENCE 700 1- Follath F. Cardiovascular Therapy Research Unit, Cardiology Division, University Hospital Zuerich, CH-8091, Zurich, Switzerland aut NATIONALLICENCE 700 1- Chen J. Huadong Hospital, Shanghai, P. R. China aut NATIONALLICENCE 700 1- Krähenbühl S. Division of Clinical Pharmacology and Toxicology, Department of Internal Medicine, University Hospital Zurich, CH-8091, Zurich, Switzerland aut NATIONALLICENCE 773 0- European Journal of Clinical Pharmacology Springer-Verlag 49/4(1996-01-01), 309-315 0031-6970 49:4<309 1996 49 228 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer