Semester

Fall

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Robert L. Haining.

Abstract

Human CYP2D6 is one of the most important human P450s based on the number of its drug substrates. It shows an extensive genetic polymorphism that influences its expression and function. There are more than 80 different CYP2D6 alleles and allelic variants that have been identified in human. However, only a part of alleles have been characterized with respect to enzyme activity and substrate specificity. In the first project, three alleles CYP2D6*24 (1297L), CYP2D6*27 (E410K) and CYP2D6*26 (I369T) were constructed and expressed. The enzymatic activities were evaluated by the metabolic rates for dextromethorphan O-demethylation and N-demethylation; codeine O-demethylation and N-demethylation. For DXM O-demethylation, CYP2D6*24 has the highest intrinsic clearance value, as estimated by Vmax/Km ratio, followed by *1, *26 and *27; For DXM N-demethylation, three allelic variants showed almost the same intrinsic clearance values as the wild type CYP2D6. For codeine O-demethylation, 2D6*26 and *27 have the same intrinsic clearance, it is around 2-fold higher than 2D6*1 as estimated by Vmax/Km ratio. For codeine N-demethylation, the variant CYP2D6*26 exhibited higher enzyme efficiency for codeine O-demethylation than codeine N-demethylation compared to the wild type and other alleles.;The human CYP2D subfamily includes CYP2D6, CYP2D7 and CYP2D8P, which locate at the CYP2D locus of chromosome 22. It was found that alternatively splicing of CYP2D pre-mRNA could occur and these splicing variants are tissue-specific. However, it is still unknown whether and how these alternatively splicing variants play important physiological or pathological roles in these tissues. In the second project, a human brain CYP2D7 variant was successfully constructed and expressed.;CYP2D6 polymorphism has been associated with various human cancer susceptibilities such as lung, breast, skin and prostate cancers. It has hypothesized that the existence of these alternatively splicing variants may impact the expression and functions of CYP2D6 in extrahepatic tissues, and the alternation of CYP2D6 might play an important role in determining cancer risk. However, the genotypes and function of these extrahepatic CYP2D6 are still unknown. In the third project, several alternatively splicing variants derived from different human tissues including liver, brain, skin, eye and prostate have been cloned and sequenced. Among these variants, a full-length skin variant were constructed and, expressed. (Abstract shortened by UMI.).

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