The impact of genetics, environmental, and geographical factors on inter-individual and inter-ethnic differences in CYP2C9-catalysed drug metabolism

Abstract

Inter-individual and inter-ethnic variations in drug metabolism are creating an obstacle in providing efficient and effective drug treatments especially for drugs with narrow therapeutic windows. This thesis is contributes to the understanding of the molecular mechanism of these variations.

Paper I is an introduction to the inter-individual and inter-ethnic differences in CYP2C9 catalysed drug metabolism. Wide inter-individual differences were observed in the metabolic ratio of losartan to E-3174 metabolite even among individuals who were not carrying defective alleles CYP2C9*2 and CYP2C9*3. Inter-ethnic variation was observed in the metabolism of losartan between CYP2C9 wild type Koreans and Swedes. An allelic variation in the intronic region between exon 8 and 9 of CYP2C9, IVS8-109A>T was observed to cause a lower CYP2C9 activity in Swedes but not Koreans.

Paper II studied the combination of age, CYP2C9 genotype, ethnicity, smoking habit, weight and sex as a predictor of CYP2C9 metabolic ratio variability. Ethnicity was the main significant factor influencing between subject-variability in CYP2C9 enzyme activity. Additionally, CYP2C9 genotype and smoking were significant contributors to the variation. Grouping the subjects based on their ethnicity, we found that CYP2C9 genotype is a major predictor for both Koreans and Swedes (27% and 40% of the variability respectively). The smoking effect was non-significant in the Swedes but remains as a factor in the Koreans. The reason behind the smoking effect in Koreans is unidentified.

Paper III investigated the possibility of Behcet’s disease as a CYP2C9 inducer. A Swedish ultra-rapid CYP2C9 metaboliser was diagnosed with this disease and this study tested the possibility in Turkish healthy subjects to have a lower CYP2C9 activity than Behcet’s disease patients. Interestingly, the Behcet’s disease patients were shown to have a significantly low CYP2C9 metabolic activity. The factors of genetics, medication and inflammation-related biomolecules are suspected to have caused this down-regulation. We did not find evidence of CYP2C9 genotype and typical Behcet’s disease medication, colchicine having any influence on the observed low CYP2C9 metabolic activity. It is very possible that inflammation response agent caused this inhibitory effect on CYP2C9 activity.

Paper IV investigated the effect of the P450 oxidoreductase (POR)*28 variant on the metabolic activity of CYP2C9. We screened all Swedish and Koreans CYP2C9*1/*1 subjects for POR* 5, *13 and *28. No subject was found to carry *5 or *13. Interestingly, Swedish individuals who carry POR*28 allele were observed to display a 1.40 fold increase in CYP2C9 enzyme activity compared to none-POR*28 carriers. We screened the ultra-rapid metaboliser for this variant and she was also a carrier of this variant. More studies should be done to investigate the effect of other SNPs in POR gene to the metabolic activity of drug metabolising enzymes.