P450 Metabolism of Glucocorticoids in Lungs of Pediatric Asthmatics

描述（由申请人提供）：现代医学的一个主要治疗挑战是在过去几十年中儿童哮喘的发病率不断增加。然而，一个重要的治疗方式，提供了相当大的进展是使用吸入糖皮质激素（GC）的目标哮喘的炎症成分，同时最大限度地减少全身GC的不良反应。这些药物提供了相当大的降低死亡率和哮喘症状的发生率和严重程度，但估计对GC的耐药性高达50%的儿科哮喘人群。多达90%的吸入GC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GC在其浓度最高的肺内局部作用，然后被细胞色素P450酶原位代谢。三种主要的CYP 3A酶（3A 4、3A 5、3A 7）是人肝脏中GC氧化的主要催化剂，其中关于酶的个体发生和发育表达的了解很多。然而，对于儿童肺中CYP 3A表达的相对水平，或儿童时期GC药物作用和进行氧化代谢的重要呼吸细胞中的发育变化，基本上一无所知。GC代谢中由β 3A酶催化的确切化学途径也是未知的。CYP 3A基因的遗传多态性、器官选择性表达和自身诱导是预测显著个体间代谢多样性的已知机制，导致对GC的抗性或超敏反应。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，并且本申请的假设是儿科哮喘患者对吸入GC的抗性或超敏性主要受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CYP 3A酶中的每一种来表征五种最常用的治疗相关GC的代谢物和代谢途径; 2）评价肺和肝细胞中3A基因的诱导; 3）关联GC-诱导P450 3A转录增加类固醇的代谢，并建立P450 3A基因在小儿气管肺细胞中表达的发育模式。抽吸样品;以及4）将CYP 3A 5和CYP 3A 7多态性与来自一组儿童哮喘患者的GC抗性或超敏性相关联。该实验计划的结果将提供关于导致有效GC治疗的基本遗传和生化因素的重要信息。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可靠的理论依据。 公共卫生相关性：吸入性糖皮质激素药物（GC）为哮喘儿童提供了有效的治疗，但多达50%的哮喘儿童对吸入性GC没有帮助，即他们对这些药物产生耐药性。基本上对儿童肺中P450酶表达的相对水平或儿童时期GC试剂作用和清除的重要呼吸细胞中的发育变化一无所知。本研究的主要长期目标是显著改善哮喘儿童的GC治疗。

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. PUBLIC HEALTH RELEVANCE: Inhaled glucocorticoid medicines (GC) provide effective therapy for children with asthma, but as many as 50% of children with asthma are not helped by inhaled GCs, i.e. they are resistant to these medicines. Essentially nothing is known about the relative levels of P450 enzyme expression in lungs of children, or the developmental changes during childhood in the important respiratory cells where GC agents act and are cleared. The major long-term goal of this research is to significantly improve GC therapy in asthmatic children.