Hormonal regulation of human CYP3A

描述（由申请人提供）：小肠粘膜上皮中CYP3A4表达和活性的个体间差异导致许多CYP3A底物药物的口服生物利用度低且多变。这种高度的可变性似乎是人十二指肠肠细胞中CYP3A4和CYP3A5特异性含量的巨大个体间差异的结果。从治疗的角度来看，患者间首次通过肠道提取效率的巨大差异可能导致母体药物及其代谢物的全身暴露和口服剂量对平均患者的药理学作用的差异，从而增加治疗失败和不良毒性的风险。肠道CYP3A表达变化的原因在很大程度上是未知的，但被认为涉及遗传和环境/生理因素。例如，我们之前已经证明，最具生物活性的维生素D形式，1,25-(OH)2-维生素D3，以vdr依赖的方式增强主要药物代谢酶CYP3A4的转录，而CYP3A4反过来可以催化1,25-(OH) 2-D3的代谢清除。本拨款提案的总体目标是确定1,25-(OH)2-D3是否在体内调节人小肠中CYP3A4的表达，以及通过酶诱导或抑制影响CYP3A4功能的药物的施用是否通过改变粘膜肠细胞内1,25-(OH)2-D3的配置来改变肠钙转运蛋白的合成和功能。具体来说，我们将通过评估口服1,25-(OH)2-D3对激活维生素D受体的十二指肠基因靶点和cyp3a依赖性药物清除的影响来验证1,25-(OH)2-D3增强肠道CYP3A4表达和功能的假设。我们还将通过评估CYP3A4抑制剂和诱导剂对人肠细胞对1,25-(OH)2-D3的反应性的影响，来测试CYP3A4转录的激活是否提供了vdr介导的基因组效应的自反馈控制。最后，我们将测试已知激动剂激活hPXR是否会增强依赖cyp3a4的肠道1,25-(OH)2-D3代谢，从而导致肠道VDR基因靶点转录减少，并改变钙稳态的全身指标。阐明CYP3A依赖性药物代谢个体间差异的分子基础，可以通过更清楚地了解其他药物、环境和疾病状态如何影响肠道CYP3A底物的新候选药物的处置，从而增强制药行业开发安全有效药物的能力。此外，如果我们关于CYP3A4参与小肠肠细胞内1,25-(OH)2-D3基因组效应负反馈控制的假设被证明是正确的，那么它可以指出相对简单的方法（例如，每天适量饮用葡萄柚汁）来预防强效hPXR激动剂对高危患者骨骼健康的不良影响。完成本资助申请中提出的具体目标将提高我们对cyp3a4依赖性药物代谢个体间差异的分子基础的理解，并有可能提高现有和新药物用于治疗疾病的安全性和有效性。为有效预防某些导致骨质疏松的药物不良反应提供科学依据。

DESCRIPTION (provided by applicant): Inter-individual differences in the expression and activity of CYP3A4 in the mucosal epithelium of the small intestine contribute to a low and variable oral bioavailability that is observed for many drugs that are CYP3A substrates. This high degree of variability appears to be the result of large inter-individual differences in the specific content of CYP3A4 and CYP3A5 in human duodenal enterocytes. From a therapeutic perspective, large inter-patient differences in first-pass intestinal extraction efficiency can lead to differences in systemic exposure to the parent drug and its metabolites and pharmacological effects following oral administration of doses that are appropriate for the }average} patient, increasing the risk of therapeutic failure and adverse toxicity. The cause of variable intestinal CYP3A expression is largely unknown, but thought to involve both genetic and environmental/physiological factors. For example, we have shown previously that the most biologically active form of vitamin D, 1,25-(OH)2-vitamin D3, enhances transcription of the major drug metabolizing enzyme CYP3A4 in a VDR-dependent manner, and that CYP3A4 in turn can catalyze the metabolic clearance of 1,25- (OH)2-D3. The overall objectives of this grant proposal are to determine whether 1,25-(OH)2-D3 regulates the expression of CYP3A4 in the human small intestine in vivo, and whether the administration of drugs that affect CYP3A4 function through enzyme induction or inhibition alter the synthesis and function of intestinal calcium transport proteins through changes in 1,25-(OH)2-D3 disposition within the mucosal enterocyte. Specifically, we will test the hypothesis that 1,25-(OH)2-D3 enhances intestinal CYP3A4 expression and function by assessing the effects of oral 1,25-(OH)2-D3 administration on duodenal gene targets of the activated vitamin D receptor and CYP3A-dependent drug clearance. We will also test whether activation of CYP3A4 transcription provides auto-feedback control of VDR-mediated genomic effects by assessing the effects of CYP3A4 inhibitors and inducers on the responsiveness of human enterocytes to 1,25-(OH)2-D3. Finally, we will test whether activation of hPXR by known agonists enhances CYP3A4-dependent intestinal 1,25-(OH)2-D3 metabolism, resulting in a decrease in the transcription of intestinal VDR gene targets and a change in systemic indices of calcium homeostasis. Elucidating the molecular basis of inter-individual differences in CYP3A-dependent drug metabolism could enhance the ability of the drug industry to develop safe and efficacious drugs through a clearer understanding of how other medications, the environment, and disease states might impinge on the disposition of new drug candidates that are intestinal CYP3A substrates. In addition, if our hypothesis about the participation of CYP3A4 in negative feedback control of 1,25-(OH)2-D3 genomic effects within enterocytes of the small intestine proves to be correct, it could point to relatively simple ways (e.g., moderate daily grapefruit juice consumption) to prevent the adverse effects of potent hPXR agonists on bone health in }at-risk} patients. PROJECT NARRATIVE Completion of the specific aims proposed in this grant application should improve our understanding of the molecular basis for inter-individual differences in CYP3A4-dependent drug metabolism and potentially enhance the safety and efficacy of existing and new drugs used to treat disease. Moreover, it may provide a scientific basis for the effective prevention of some adverse drug effects that lead to osteoporosis. Public Health Relevance: Completion of the specific aims proposed in this grant application should improve our understanding of the molecular basis for inter-individual differences in CYP3A4-dependent drug metabolism and potentially enhance the safety and efficacy of existing and new drugs used to treat disease. Moreover, it may provide a scientific basis for the effective prevention of some adverse drug effects that lead to osteoporosis.