Objective: Metabolism of the atypical antipsychotic olanzapine (OLA) is partially catalyzed by cytochrome P450 (CYP) 1A2, a target of aryl hydrocarbon receptor (AHR)-mediated induction. We investigated the influence of four cis-acting polymorphisms (rs2470893C>T and rs2472297C>T between CYP1A1 and CYP1A2 loci, and rs762551C>A and rs2472304A>G within CYP1A2) as well as one trans-acting polymorphism upstream of the AHR locus (rs4410790C>T) on interindividual variation in systemic OLA exposure.
Methods: A cohort of 342 Caucasian psychiatric patients on long-term OLA treatment was genotyped using Illumina GoldenGate assays. The influence of haplotype and genotype was evaluated in terms of dose-adjusted steady-state serum concentrations (C/Ds) of OLA and the 4'-desmethyl OLA (DMO) to OLA ratio, a marker for CYP1A2-mediated metabolism of OLA.
Results: The CYP1A haplotype [rs2470893 (T)-rs2472297 (T)-rs762551 (A)] was associated with an increased DMO/OLA ratio and decreased C/Ds of OLA. This haplotype could not be tagged by rs762551 (A) but was tagged by rs2472297C>T, a single nucleotide polymorphism further identified as a significant covariate of the DMO/OLA ratio (P=0.0001) and OLA C/D (P=0.01). AHR rs4410790C>T influenced only the DMO/OLA ratio (P=0.02). Among nonsmokers, patients carrying rs2472297 (T) and homozygous for rs4410790 (C) [n=26; mean=0.22, 95% confidence interval (CI) 0.19-0.26] showed a 1.7-fold higher mean DMO/OLA ratio compared with those carrying rs4410790 (T) and homozygous for rs2472297 (C) (n=50; mean=0.13, 95% CI 0.12-0.16, P=0.0001), together with a nonsignificant decrease in the mean OLA C/D.
Conclusion: The reported influence of CYP1A2*1F (also known as CYP1A2-163A, rs762551C>A) on systemic OLA exposure could not be verified. CYP1A1/CYP1A2 rs2472297C>T and AHR rs4410790C>T are potentially useful genetic markers associated with variability in CYP1A2-mediated metabolism, but are of minor quantitative importance for systemic OLA exposure.