Hormonal regulation of human CYP3A

描述(由申请人提供)：在小肠粘膜上皮细胞中，细胞色素P3A4的表达和活性的个体间差异导致口服生物利用度低且可变，这在许多作为细胞色素P3A底物的药物中观察到。这种高度的变异性似乎是人类十二指肠肠上皮细胞中细胞色素P3A4和细胞色素P3A5的特定含量的个体间差异很大的结果。从治疗的角度来看，患者之间首过肠道提取效率的巨大差异可能会导致全身暴露于母药及其代谢物的差异，以及口服适用于一般患者的剂量后的药理效应，从而增加治疗失败和不良毒性的风险。肠道细胞色素P3A表达变异的原因很大程度上尚不清楚，但被认为涉及遗传和环境/生理因素。例如，我们以前已经证明，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。这项拨款提案的总体目标是确定1，25-(OH)2-D3是否在体内调节人体小肠中CYP3A4的表达，以及通过酶诱导或抑制影响CYP3A4功能的药物的给药是否通过改变粘膜肠细胞内1，25-(OH)2-D3的处置来改变肠道钙转运蛋白的合成和功能。具体地说，我们将通过评估口服1，25-(OH)2-D3对激活的维生素D受体的十二指肠基因靶标和依赖于CYP3A的药物清除的影响来检验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道细胞对1，25-(OH)2-D3的反应性的影响，来测试CYP3A4转录的激活是否为VDR介导的基因组效应提供自动反馈控制。最后，我们将测试已知激动剂激活hPXR是否增强了依赖细胞色素P3A4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，全身钙稳态指标发生变化。阐明细胞色素P3A依赖的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、环境和疾病状态可能如何影响作为肠道细胞色素P3A底物的新药候选药物的处置，从而提高制药业开发安全有效药物的能力。此外，如果我们关于CYP3A4参与小肠细胞内1，25-(OH)2-D3基因组效应的负反馈控制的假设被证明是正确的，那么它可能指向相对简单的方法(例如，每天适量食用西柚汁)，以防止有效的hPXR激动剂对高危患者骨健康的不利影响。项目简介完成这一赠款申请中提出的具体目标将提高我们对依赖于CYP3A4的药物代谢个体间差异的分子基础的理解，并有可能提高用于治疗疾病的现有药物和新药的安全性和有效性。为有效预防某些导致骨质疏松症的药物不良反应提供科学依据。 公共卫生相关性：完成这项拨款申请中提出的具体目标将提高我们对依赖细胞色素P3A4的药物代谢个体间差异的分子基础的理解，并有可能提高用于治疗疾病的现有药物和新药的安全性和有效性。为有效预防某些导致骨质疏松症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.