title: Evaluation of caffeine as a test drug for CYP1A2, NAT2 and CYP2E1 phenotyping in man by in vivo versus in vitro correlations.
abstract: Caffeine is used to phenotype subjects in vivo for the cytochrome P450 isoforms CYP1A2 and CYP2E1, and for N-acetyltransferase type 2 (NAT2). However, how much of the variation in phenotyping parameters may be attributed to variations in CYP1A2 and CYP2E1 activities has not been determined. Therefore, this study intraindividually compared enzyme activities and/or content in liver samples with pharmacokinetic parameters of caffeine in vivo after administration of a test dose in 25 patients undergoing hepatectomy. Parameters measured in vitro were the high affinity components of caffeine 3-demethylation and phenacetin 0-deethylation, microsomal CYP1A2 and CYP2E1 immunoreactivity, and cytosolic sulfamethazine N-acetylation. Caffeine parameters in vivo included caffeine clearance from plasma and/or saliva, paraxanthine/caffeine ratios in plasma and saliva, plasma theophylline/caffeine ratio, and several metabolite ratios from spot urine sampled 6 h postdose. Correlations between parameters were determined using weighted linear regression analyses. Caffeine clearance and paraxanthine/caffeine ratios correlated most highly to intrinsic clearance of caffeine 3-demethylation and to CYP1A2 immunoreactivity (r= 0.584-0.82), whereas urinary CYP1A2 ratios correlated less strongly with CYP1A2 parameters in vitro. Assignment of acetylator phenotype by urinary NAT2 ratios was concordant with sulfamethazine-N-acetylation in vitro. In contrast to CYP1A2 parameters in vitro, CYP2E1 immunoreactivity was not related to the theophylline/caffeine plasma ratio. CYP1A2 activity, thus, is the major determinant of caffeine clearance and the paraxanthine/caffeine ratios in vivo, of which the saliva ratio 6 h postdose appears as the most advantageous parameter. The results confirm that phenotyping using caffeine provides valid estimates of CYP1A2 and NAT2 activity.
authors.affiliation: Department of Clinical Pharmacology, University Hospital Frankfurt am Main, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Fuhr
authors.forename: K L
authors.initials: KL
authors.lastname: Rost
authors.forename: R
authors.initials: R
authors.lastname: Engelhardt
authors.forename: M
authors.initials: M
authors.lastname: Sachs
authors.forename: D
authors.initials: D
authors.lastname: Liermann
authors.forename: C
authors.initials: C
authors.lastname: Belloc
authors.forename: P
authors.initials: P
authors.lastname: Beaune
authors.forename: S
authors.initials: S
authors.lastname: Janezic
authors.forename: D
authors.initials: D
authors.lastname: Grant
authors.forename: U A
authors.initials: UA
authors.lastname: Meyer
authors.forename: A H
authors.initials: AH
authors.lastname: Staib
mesh_terms: D000368:Aged; D001191:Arylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism*; D002110:Caffeine / Q000097:blood / Q000378:metabolism* / Q000652:urine; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics / Q000378:metabolism*; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005838:Genotype; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D010641:Phenotype; D012463:Saliva / Q000378:metabolism; D013806:Theophylline / Q000097:blood / Q000378:metabolism
chemical_list: D002110:Caffeine; D013806:Theophylline; D019392:Cytochrome P-450 CYP2E1; D019388:Cytochrome P-450 CYP1A2; D001191:Arylamine N-Acetyltransferase; C478900:NAT2 protein, human; C021183:1,7-dimethylxanthine