Hormonal Regulation of Human CYP3A

性状（由申请方提供）：小肠中CYP 3A 4活性的个体间差异导致许多CYP 3A底物药物的口服生物利用度较低且可变。这种变异性似乎是由于十二指肠上皮细胞中CYP 3A 4的具体含量存在很大差异。从治疗的角度来看，首过肠道提取效率的巨大差异可能导致口服给药适合“普通”患者的剂量后全身药物暴露和药理学效应的变化，增加治疗失败和不良毒性的风险。肠道CYP 3A表达可变的原因在很大程度上是未知的，但认为涉及遗传和环境因素。重要的是，我们之前已经表明，维生素D的最具生物活性的形式，1，25-二羟基维生素D3（1，25（OH）2D 3），以VDR依赖性方式增强CYP 3A 4基因的转录，CYP 3A 4反过来可以催化1，25（OH）2D 3的代谢清除。本资助申请的总体目标是确定肠道CYP 3A 4是否在体内通过以下顺序过程进行调节：25（OH）D3-葡糖苷酸结合物的形成和胆汁排泄，结合物在近端肠腔中水解为25（OH）D3，并吸收至原代肠细胞，在原代肠细胞中通过CYP 27 B1转化为1，25（OH）2D 3。以这种方式在肠上皮细胞中产生的活性激素可以调节CYP 3A 4和其他VDR靶基因的表达，包括钙转运蛋白TRPV 6和钙结合蛋白D9 k。我们将通过鉴定和表征参与人体维生素D结合物胆汁排泄的肝转运蛋白，并测试这些结合物是否会影响培养的人肠上皮细胞中VDR靶基因的表达和功能，来验证这一假设。由于CYP 3A 4可以催化1，25（OH）2D 3的氧化代谢，我们还提出，已知受体激动剂激活小肠中的hPXR可增强肠道1，25（OH）2D 3清除，导致钙转运蛋白形成减少，并可能改变钙稳态的全身指数。我们将使用培养的人肝细胞，肠上皮细胞和原代肾小管上皮细胞，一种新的微流体，三维模型的人肠粘膜和在健康志愿者体内进行的CYP 3A 4相互作用研究来测试这一假设。阐明CYP 3A依赖性药物代谢的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作为肠道CYP 3A底物的新药候选物的处置，提高制药行业开发安全有效药物的能力。此外，如果我们关于CYP 3A 4参与小肠内1，25（OH）2D 3基因组效应的负反馈控制的假设被证明是正确的，那么它可以指向相对简单的方法（例如，葡萄柚汁消耗），以防止有效的hPXR激动剂对“高危”患者骨骼健康的不良影响。

DESCRIPTION (provided by applicant): Inter-individual differences in the activity of CYP3A4 in the small intestine contribute to the low and variable oral bioavailability observed for many drugs that are CYP3A substrates. This variability appears to be the result of large differences in the specific content of CYP3A4 in duodenal enterocytes. From a therapeutic perspective, large differences in first-pass intestinal extraction efficiency can lead to variable systemic drug exposure and variable 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 factors. Importantly, we have shown previously that the most biologically active form of vitamin D, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3), enhances transcription of the CYP3A4 gene in a VDR-dependent manner and that CYP3A4 in turn can catalyze the metabolic clearance of 1,25(OH)2D3. The overall objectives of this grant proposal are to determine whether or not intestinal CYP3A4 is regulated in vivo by the following sequential process: formation and biliary excretion of a 25(OH)D3-glucuronide conjugate, hydrolysis of the conjugate to 25(OH)D3 in the proximal intestinal lumen and its absorption into the primary enterocytes, where it is converted to 1,25(OH)2D3 by CYP27B1. Active hormone produced in the enterocyte in this manner can regulate the expression of CYP3A4 and other VDR target genes, including the calcium transport proteins TRPV6 and calbindin D9k. We will test this hypothesis by identifying and characterizing the hepatic transporters involved in the biliary excretion of vitamin D conjugates in humans and testing whether or not these conjugates can affect the expression and function of VDR target genes in cultured human enterocytes. Because CYP3A4 can catalyze the oxidative metabolism of 1,25(OH)2D3, we also propose that activation of hPXR in the small intestine by known receptor agonists enhances intestinal 1,25(OH)2D3 clearance, resulting in a decrease in the formation of calcium transporters, and a potential change in systemic indices of calcium homeostasis. We will test this hypothesis with the use of cultured human hepatocytes, enterocytes and primary tubular epithelial cells, a novel microfluidic, 3-dimensional model of the human intestinal mucosa and the conduct of an in vivo CYP3A4 interaction study in healthy volunteers. 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)2D3 genomic effects within the small intestine proves correct, it could point to relatively simple ways (e.g., grapefruit juice consumption) to prevent the adverse effects of potent hPXR agonists on bone health in "at-risk" patients.