Expression and regulation of human genes central to drug disposition in the brain

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The study of the regulation of human genes is inherently difficult. It is difficult or impossible to gain access to many body tissues in either healthy or sick individuals to examine coordinated gene function (or dysfunction). This is particularly true for the brain, where live human tissue is unavailable. For this reason, it is often the case that we have a much better understanding of gene function in species such as rats and mice, the most common animal environments for biomedical research. However, findings in animals often fail to meaningfully mirror what occurs in man. To progress our understanding of human genes in brain we need to develop models that more faithfully reproduce the human situation in an environment that is amenable to both manipulation and close examination, such as the novel 'humanized' mouse models described in this application. This application deals with the genes that control enzymes belonging to the human cytochrome P450 3A (CYP3A) subfamily and the drug transporter MDR1. These genes are present in several tissues including liver, gut, lung and brain. They form the main disposal pathway for foreign chemicals such as drugs, environmental pollutants and some cancer causing chemicals. In addition they are involved in the breakdown of several important internally produced substances, such as steroid hormones. We postulate that altered formation of CYP3A enzymes and MDR1 in brain can have a dramatic impact on the action of many important drugs and may affect the way the brain responds in a behavioral sense to hormones, such as sex steroids. In addition, this work will provide a new and useful information relevant to the design and development of the plethora of drugs that act on the central nervous system.