Related Experiment Videos
Identification of a new variant CYP2D6 allele lacking the codon encoding Lys-281: possible association with the poor
1Department of Pharmacology, University of Toronto, Medical Sciences Center, Canada.
Abstract:
A variant CYP2D6(C) P450 protein was found in a liver characterized by deficient microsomal metabolism of bufuralol and sparteine, prototypical substrates for the debrisoquine-sparteine drug oxidation polymorphism. This protein was present at decreased levels in liver and had a slightly different relative mobility on SDS-polyacrylamide gels. The cDNA cloning and sequencing of the variant, designated CYP2D6(C), revealed that its mRNA lacked a single codon resulting in deletion of Lys281. This was the result of a three base pair deletion at the 3' end of CYP2D6 exon 5. The CYP2D6(C) P450, produced in HepG2 cells using vaccinia virus mediated cDNA expression displayed Km values toward bufuralol, debrisoquine and sparteine that were not significantly different from wild type CYP2D6. These data suggest that the poor metabolizer phenotype in livers expressing CYP2D6(C) is not due to a catalytically defective enzyme but perhaps due to decreased levels of the P450 protein in microsomal membranes. Low microsomal CYP2D6(C) contents could result from deficient membrane insertion or decreased stability of the P450 protein. A polymerase chain reaction-based procedure, developed to detect CYP2D6(C) alleles, indicates that this variant probably represents less than 1.5% of all CYP2D6 alleles.
Insights
A novel CYP2D6(C) variant protein, found at lower levels, causes deficient drug metabolism. This poor metabolizer phenotype is linked to reduced protein levels, not enzyme defects, impacting drug oxidation polymorphism.
Area of Science:
- Pharmacogenomics
- Enzyme kinetics
- Molecular biology
Background:
- The debrisoquine-sparteine drug oxidation polymorphism is a critical area in pharmacogenetics.
- Cytochrome P450 2D6 (CYP2D6) is a key enzyme involved in the metabolism of many drugs.
- Understanding genetic variations in CYP2D6 is essential for personalized medicine.
Purpose of the Study:
- To characterize a novel variant CYP2D6(C) protein associated with deficient microsomal metabolism.
- To elucidate the molecular basis of the poor metabolizer phenotype linked to CYP2D6(C).
- To develop a method for detecting CYP2D6(C) alleles.
Main Methods:
- Microsomal metabolism assays using bufuralol and sparteine.
- cDNA cloning and sequencing of the variant CYP2D6(C).
- Expression of CYP2D6(C) in HepG2 cells via vaccinia virus, followed by kinetic analysis.
- Polymerase chain reaction (PCR) for allele detection.
Main Results:
- A variant CYP2D6(C) P450 protein was identified with decreased levels and altered electrophoretic mobility.
- cDNA sequencing revealed a single codon deletion (Lys281) due to a three base pair deletion in exon 5.
- Expressed CYP2D6(C) showed no significant difference in Km values for bufuralol, debrisoquine, and sparteine compared to wild-type CYP2D6.
- The CYP2D6(C) variant accounts for less than 1.5% of all CYP2D6 alleles.
Conclusions:
- The poor metabolizer phenotype associated with CYP2D6(C) is likely due to decreased protein levels rather than catalytic enzyme deficiency.
- Reduced microsomal CYP2D6(C) content may result from impaired membrane insertion or protein instability.
- The findings contribute to understanding the genetic basis of drug metabolism variability and the debrisoquine-sparteine polymorphism.