From Genotype to Phenotype: Content and Activities of Cytochromes P450 2A6 in Human Liver In Vitro and Predicted In Vivo

Abstract

Unraveling the molecular mechanisms by which genetic variants of cytochrome P450 2A6 lead to different metabolic phenotypes remains a long-standing but important challenge. CYP2A6 is an enzyme involved in the metabolism of several clinical drugs as well as the metabolic activation of carcinogenic nitrosamines. Herein, CYP2A6 genotypes and phenotypes, as indicated by protein content [by liquid chromatography-mass spectrometry (MS)/MS] and metabolic activities [V max , clearance (CL)], were determined for 90 human liver samples. We determined the median, range, and interindividual and intraindividual variation of CYP2A6 content and activity at the microsomal, liver tissue, and whole liver level and predicted hepatic in vivo clearance by in vitro-in vivo extrapolation based on CYP2A6-mediated coumarin metabolism by each CYP2A6 genotype. These results reveal how different CYP2A6 genotypes yield different phenotypic traits in protein content and enzyme activity. For relative V max , CL, and protein content, the intraindividual percentage coefficients of variation (ICVs) were 41.0% (18.8%-125.1%), 28.5% (2.39%-133.5%), and 27.8% (2.68%-88.0%), respectively. The high ICVs implied large intraindividual variation at different levels, sometimes in a genotype-dependent manner. Intergenotype analysis revealed that the CYP2A6*4 allele demonstrated the most obvious effect on phenotypic outcomes, both in protein content and in metabolic activity. Indeed, decreased CYP2A6 protein content with the CYP2A6*4 genotype might explain the decreased metabolic activity from the molecular to the organismal level. These findings may allow useful predictions for CYP2A6-mediated drug metabolism on an individual patient basis in accord with the goal of achieving personalized medicine. SIGNIFICANCE STATEMENT We provide the median, range, and interindividual and intraindividual variation in CYP2A6 content at the microsomal, liver tissue, and whole liver level by liquid chromatography-mass spectrometry (MS)/MS as well as activities at the protein, microsomal, liver tissue, and whole liver level both in vitro and at the organismal level based on CYP2A6-mediated coumarin metabolism with each CYP2A6 genotype, thereby allowing us to elucidate how different CYP2A6 genotypes yield differing phenotypic traits (protein content and enzyme activity), facilitating the development of personalized medicine.

The POR rs10954732 polymorphism decreases susceptibility to hepatocellular carcinoma and hepsin as a prognostic biomarker correlated with immune infiltration based on proteomics

“…During the past several years, increasing evidence indicated that genes that encode metabolic enzymes can serve as tumor susceptibility genes and/or prognostic signatures, in part through their roles in activation of carcinogens; these genes include cytochrome P450 2E1 (CYP2E1) [ 8 , 9 ], CYP2D6 [ 10 ], GSTP1 [ 11 ], NAT2 and GSTM1 [ 12 ]. Our previous systematic studies on 10 major CYP enzymes responsible for hepatic drug metabolism showed significant changes in CYP polymorphism incidence [ 10 ] and enzyme activity [ 13 – 15 ] in HCC patients, some of which were confirmed as related to increased susceptibility to hepatofibrosis and HCC [ 16 , 17 ], especially for increased activity of CYP2D6 and CYP2E1, decreased activity of CYP2C8, and decreased frequency of the CYP2D6*2 allele.…”