CYP1A2 mRNA Expression Rather than Genetic Variants Indicate Hepatic CYP1A2 Activity

Abstract

CYP1A2, one of the most abundant hepatic cytochrome P450 enzymes, is involved in metabolism of several drugs and carcinogenic compounds. Data on the significance of CYP1A2 genetic polymorphisms in enzyme activity are highly inconsistent; therefore, the impact of CYP1A2 genetic variants (−3860G>A, −2467delT, −739T>G, −163C>A, 2159G>A) on mRNA expression and phenacetin O-dealkylation selective for CYP1A2 was investigated in human liver tissues and in psychiatric patients belonging to Caucasian populations. CYP1A2*1F, considered to be associated with high CYP1A2 inducibility, is generally identified by the presence of −163C>A polymorphism; however, we demonstrated that −163C>A existed in several haplotypes (CYP1A2*1F, CYP1A2*1L, CYP1A2*1M, CYP1A2*1V, CYP1A2*1W), and consequently, CYP1A2*1F was a much rarer allelic variant (0.4%) than reported in Caucasian populations. Of note, −163C>A polymorphism was found to result in an increase of neither mRNA nor the activity of CYP1A2. Moreover, hepatic CYP1A2 activity was associated with hepatic or leukocyte mRNA expression rather than genetic polymorphisms of CYP1A2. Consideration of non-genetic phenoconverting factors (co-medication with CYP1A2-specific inhibitors/inducers, tobacco smoking and non-specific factors, including amoxicillin+clavulanic acid therapy or chronic alcohol consumption) did not much improve genotype–phenotype estimation. In conclusion, CYP1A2-genotyping is inappropriate for the prediction of CYP1A2 function; however, CYP1A2 mRNA expression in leukocytes can inform about patients’ CYP1A2-metabolizing capacity.

CYP1A2 expression rather than genotype is associated with olanzapine concentration in psychiatric patients

“…2 A). We have previously demonstrated that CYP1A2 expression rather than CYP1A2 genotype indicated hepatic CYP1A2 activity 35 ; therefore, the association between CYP1A2 mRNA levels in the patients’ leukocytes and olanzapine concentration was also established. Due to the low number of high CYP1A2 expressers, in statistical analysis, high and normal expressers were combined.…”

“…Genomic DNA was isolated from peripheral blood samples by Quick-DNA™ Universal Kit (Zymo Research, Irvine, CA). Hydrolysis SNP analyses were performed by TaqMan assays for CYP1A2 SNPs [− 3860G > A (rs2069514), − 2467delT (rs35694136), − 739T > G (rs2069526), − 163C > A (rs762551) and 2159G > A (rs2472304)] and for CYP2D6 SNPs [2549delA (rs35742686), 1846G > A (rs3892097), 1707delT (rs5030655), 2615-2617delAAG (rs5030656), 100C > T (rs1065852) and 2988G > A (rs28371725)] 34 , 35 . CYP2D6 gene deletion and CYP2D6 allele specific duplication/multiplication were determined as previously described 34 .…”

“…The quantities of the CYP1A2 mRNA relative to that of the housekeeping gene glyceraldehyde 3-phosphate dehydrogenase ( GAPDH ) were determined 43 . Patients were classified as low, normal and high CYP1A2 expressers on the basis of CYP1A2 mRNA levels in leukocytes with the cut-off expression values of 10 −5 and 5 * 10 −4 as previously determined 35 .…”

“…For CYP1A2, the identification of single nucleotide polymorphisms (SNPs) in CYP1A2 gene provides a relatively weak prediction for CYP1A2 phenotype 35 . Some of the CYP1A2 SNPs, such as − 3860G > A (rs2069514), − 2467delT (rs35694136), − 739T > G (rs2069526), − 163C > A (rs762551) and 2159G > A (rs2472304), are present in several CYP1A2 haplotypes, which makes the identification of allelic variants laborious; furthermore, the functional relevance of a particular SNP to CYP1A2 activity may differ from that of the haplotype 35 , 36 .…”

“…For CYP1A2, the identification of single nucleotide polymorphisms (SNPs) in CYP1A2 gene provides a relatively weak prediction for CYP1A2 phenotype 35 . Some of the CYP1A2 SNPs, such as − 3860G > A (rs2069514), − 2467delT (rs35694136), − 739T > G (rs2069526), − 163C > A (rs762551) and 2159G > A (rs2472304), are present in several CYP1A2 haplotypes, which makes the identification of allelic variants laborious; furthermore, the functional relevance of a particular SNP to CYP1A2 activity may differ from that of the haplotype 35 , 36 . Decreased CYP1A2 activity has been reported to be associated with the nucleotide change of − 3860G > A and − 2467delT 37 , 38 , whereas the SNP at the position − 163C > A has been suggested to be associated with high inducibility of CYP1A2 transcription in smokers; however, the effect of − 163C > A SNP itself on CYP1A2 activity is highly inconsistent 37 , 39 , 40 .…”