Interindividual Variability of Cytochromes P450 2B Mediated Oxidation in Human Liver

The cytochromes P450 (CYPs) are a group of enzymes that are primarily responsible for oxidative drug biotransformation in people. CYP2B6, which metabolizes numerous drugs including bupropion, propofol and other drug shows great variability in rates of drug oxidation between individuals. In this chapter we discuss the contribution of selected genetic and environmental factors to this variability. Several studies identified and quantified the most common CYP2B6 mRNA splice such as deletion of exons 4 to 6 and of exon 4 which were significantly and negatively correlated with CYP2B6 protein and enzyme activity. CYP2B6 gene expression is highly inducible by phenobarbital. Alcohol ingestion has been associated with increased CYP2B6 levels this involves the constitutive androstane receptor (CAR) and/or the pregnane X receptor (PXR). CYP2B7 is considered a pseudogene because of the presence of a single premature stop codon (TGA) in exon 7. In 10 out of 24 African-Americans (but none out of 48 European-Americans) there is a single nucleotide polymorphism that results in an arginine codon instead of a stop codon (X378R). The results of these studies identify certain CYP2B6 genetic polymorphisms, mRNA splicing variants, and alcohol ingestion as significant factors that determine interindividual variability of CYP2B-mediated oxidation of drugs in people.