P450 Metabolism of Glucocorticoids in Lungs of Pediatric Asthmatics

描述（由申请人提供）：在过去的几十年里，儿童哮喘的发病率不断增加，这是现代医学治疗的一个主要挑战。然而，一种重要的治疗方式是使用吸入糖皮质激素（GC），它针对哮喘的炎症成分，同时最大限度地减少全身GC不良反应。这些药物大大降低了死亡率、哮喘症状的发病率和严重程度，但估计对GCs的耐药性高达50%的儿童哮喘患者。高达90%的吸入GCs被吞咽和吸收，但通过首过肝脏代谢将全身效应降至最低。据推测，吸入的GCs在其浓度最高的肺内局部起作用，然后被细胞色素P450酶就地代谢。三种主要的CYP3A酶（3A4, 3A5, 3A7）是人肝脏中GC氧化的主要催化剂，其中关于这些酶的个体发生和发育表达的了解很多。然而，对于CYP3A在儿童肺部的相对表达水平，以及GC药物作用和氧化代谢的重要呼吸细胞在儿童时期的发育变化，基本上一无所知。在GCs代谢中，cyp3a酶催化的确切化学途径也不清楚。遗传多态性、器官选择性表达和CYP3A基因的自身诱导是预测个体间代谢多样性的已知机制，导致对GCs的耐药性或超敏性。这些过程都没有在哮喘儿童中进行过研究。本研究的主要长期目标是显著改善哮喘儿童的GC治疗，该应用的假设是儿童哮喘患者对吸入GC的耐药性或超敏性主要由P450 3A基因的发育表达模式、遗传多态性和环境反应性控制。我们将通过以下具体目标来解决这一假设：1)通过三种主要CYP3A酶分别表征五种最常用的、治疗相关的gc的代谢物和代谢途径；2)评估3A基因在肺和肝细胞中的诱导作用；3)将气相色谱诱导的P450 3A转录物与类固醇代谢增加联系起来，并在气管吸引样本中建立P450 3A基因表达的发育模式；4) CYP3A5和CYP3A7多态性与儿童哮喘患者GC耐药或超敏反应的相关性。这个实验计划的结果将提供基本的遗传和生化因素的重要信息，导致有效的GC治疗。这些知识可以与基因型分析一起用于指导GC产品的临床选择，并为替代哮喘治疗方式提供更有力的理论依据。

DESCRIPTION (provided by applicant): A major therapeutic challenge of modern medicine is the ever-increasing incidence of asthma in children during the past several decades. However, one significant therapeutic modality that has provided considerable progress is the use of inhaled glucocorticoids (GC) that target the inflammatory component of asthma while minimizing systemic GC adverse effects. These drugs provide considerable reduction in mortality and in incidence and severity of asthma symptoms, but estimates of resistance to GCs are as high as 50% of the pediatric asthmatic population. As much as 90% of inhaled GCs are swallowed and absorbed, but systemic effects are minimized through first pass hepatic metabolism. Presumably, inhaled GCs act locally within the lung where their concentrations are highest and are then metabolized by cytochrome P450 enzymes in situ. The three major CYP3A enzymes (3A4, 3A5, 3A7) are the primary catalysts of GC oxidation in human liver, where much is known about the ontogeny and developmental expression of the enzymes. However, essentially nothing is known about the relative levels of CYP3A expression in lungs of children, or the developmental changes during childhood in the important respiratory cells where GC drugs act and undergo oxidative metabolism. The exact chemical pathways catalyzed by the CYP 3A enzymes in the metabolism of GCs are also not known. Genetic polymorphisms, organ-selective expression, and autoinduction of the CYP3A genes are known mechanisms that predict dramatic interindividual metabolic diversity, resulting in resistance or hypersensitivity to GCs. None of these processes has been studied in asthmatic children. The major long-term goal of this research is to significantly improve GC therapy in asthmatic children, and the hypothesis of this application is resistance or hypersensitivity to inhaled GCs in pediatric asthmatics is predominantly controlled by developmental expression patterns, genetic polymorphisms, and environmental responsiveness of P450 3A genes. We will address this hypothesis with the following specific aims: 1) characterize the metabolites and metabolic pathways of the five most frequently used, therapeutically relevant GCs by each of the three major CYP3A enzymes; 2) evaluate the induction of the 3A genes in lung and liver cells; 3) correlate GC-induced P450 3A transcripts to increased metabolism of the steroids and establish developmental patterns of P450 3A gene expression in pediatric pulmonary cells from tracheal suctioning samples; and 4) correlate CYP3A5 and CYP3A7 polymorphisms with GC resistance or hypersensitivity from a cohort of pediatric asthma patients. The results of this experimental plan will provide essential information on the basic genetic and biochemical factors that lead to effective GC therapy. This knowledge can be used with genotype analysis to guide the clinical choice of GC products, and provide a more robust rationale for alternative asthmatic treatment modalities.