DRUG METABOLIZING ENZYMES IN ANIMAL MODELS AND HUMAN TISSUE

这个项目是新项目，所以工作总结代表计划，

This project is new so the summary of work represent plans, objectives and some preliminary findings. Cytochrome P-450 is the principal monooxygenase system which catalyzes foreign chemicals to mutagens and carcinogens as well as inactivating them. This system is perturbed dramatically by exposure to hormones and foreign chemicals. The system consists of a large number of isozymes each with its own substrate specificity. Some P-450 enzymes are constitutive and some appear to be polymorphic (present or absent, active or inactive) in outbred strains of rats and in man. The polymorphisms can result in dramatic differences in the ability to metabolize certain drugs (e.g., a polymorphism for debrisoquine metabolism and sparteine metabolism in man). Antibodies and cDNA probes to the P-450 proteins are useful for determining the effects of chemicals on these enzymes and for studying polymorphisms in these enzymes. One objective of these studies is to examine phenotypic variability of P-450g, a constitutive enzyme, in male rats and humans. Our data suggest that the CD rat is a good model to study polymorphism of this cytochrome in humans. These studies revealed that rats could be divided into two distinct phenotypes containing high P-450g (10-20% of total P-450) or low P-450g (greater than 0.5%). Surprisingly, both phenotypes of male rats appeared to contain a translatable mRNA for this enzyme although it was absent in females suggesting that the defect might be defective or labile enzyme in the low phenotype. P-450g was shown to metabolize aflatoxin to mutagens in a reconstituted system. A cDNA library was constructed from high phenotype P- 450g in rats, and several putative cDNA clones for this protein have been selected with antibody and rescreening with a positive clone. If human tissue is available, we plan to analyze the DNA by Southern blots and restriction analysis to determine whether the phenotypic variability in one or more human P-450s is associated with liver or lung tumors.