Abstract:
Enzymes of the cytochrome P450 (P450) superfamily metabolize a variety of foreign compounds, or xenobiotics. In turn, many environmental and therapeutic chemicals modulate the expression of specific P450 genes and to some degree microsomal epoxide hydrolase (EH). Therefore, P450 and EH expression profiles may serve as useful biomarkers of exposure and susceptibility to certain classes of chemicals. The primary hypothesis of this project is that human and rat P450 and EH mRNA expression patterns can be reliably measured in various tissues with competitive reverse transcriptase-polymerase chain reaction (RT-PCR). An additional hypothesis is that Phenobarbital-like chemicals are capable of modifying P450 expression patterns in certain regions of the central nervous system. To address these hypothesis and others, a quantitative competitive RT-PCR assay was developed to simultaneously measure a battery of P450 and EH mRNA molecules. Using this assay, P450 and EH mRNA abundance were quantified for the first time in adult human livers. A rat-specific assay was used to assess time-dependent changes in P450 abundance in vitro using a primary hepatocyte model. Furthermore, the inducibility of P450 and EH expression in extraheptatic tissues was demonstrated in the brains of rats treated with multiple does of Phenobarbital and other related compounds. In summary, this project focused on the implementation of quantitative RT-PCR technology to address research hypotheses regarding P450 and EH expression. Aberrant gene expression profiles may be important determinants in an individual's response to drugs and environmental chemicals. The studies described herein may allow expanded use of the cytochrome P450 system as a bioindicator of chemical exposure and biological effects in humans exposed to xenobiotic agents.