Novel independent trans- and cis-genetic variants associated with CYP2D6 expression and activity in human livers .

Cytochrome P450 2D6 (CYP2D6) is a critical hepatic drug-metabolizing enzyme in humans, responsible for metabolizing approximately 20-25% of commonly used medications, such as codeine, desipramine, fluvoxamine, paroxetine, and tamoxifen. The CYP2D6 gene is highly polymorphic, resulting in substantial interindividual variability in its catalytic function and the pharmacokinetics and therapeutic outcomes of its substrate drugs. Though many functional CYP2D6 variants have been discovered and validated, a significant portion of the variability in the expression and activity of CYP2D6 remains unexplained. In this study, we performed a genome-wide association study (GWAS) to identify novel variants associated with CYP2D6 protein expression in individual human livers, followed by a conditional analysis to control for the effect of functional CYP2D6 star alleles. We also examined their impact on hepatic CYP2D6 activity. Genotyping on a genome-wide scale was achieved using the Illumina Multi-Ethnic Genotyping Array (MEGA). A Data Independent Acquisition (DIA)-based proteomics method was utilized to quantify CYP2D6 protein concentrations. CYP2D6 activity was determined by measuring the Dextromethorphan O-demethylation in individual human liver s9 fractions. The GWAS identified 44 SNPs that are significantly associated with CYP2D6 protein expressions with a p-value threshold of 5.0×10 -7 Following the conditional analysis, five SNPs, including the cis-variants rs1807493 and rs1062753, and the trans-variants rs4073010, rs729559, and rs80274432, emerged as independent variants significantly correlated with hepatic CYP2D6 protein expressions. Notably, four of these SNPs, except for rs80274432, also exhibited a significant association with CYP2D6 activities in human livers, suggesting their potential as novel and independent cis- and trans-variants regulating CYP2D6. Significance Statement We identified four novel cis- and trans- pQTLs/aQTLs of CYP2D6 using individual human livers, which are independent from known functional CYP2D6 star alleles. This study connects the CYP2D6 gene, expression and activity, enhancing our understanding into the genetic variants associated with CYP2D6 protein expression and activity, potentially advancing our insight of the interindividual variability in CYP2D6 substrate medication response.