P450 Metabolism of Glucocorticoids in Lungs of Pediatric Asthmatics

描述(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，一个重要的治疗方法已经提供了相当大的进步是使用吸入性糖皮质激素(GC)，它针对哮喘的炎症成分，同时将全身GC的不良反应降至最低。这些药物显著降低了死亡率，降低了哮喘症状的发生率和严重性，但据估计，儿童哮喘人群中对GCs的耐药性高达50%。多达90%的吸入GC被吞噬和吸收，但通过首次通过肝脏代谢，全身影响被降至最低。据推测，吸入的GC在其浓度最高的肺内局部发挥作用，然后被细胞色素P450酶在原位代谢。3A4、3A5、3A7这三种主要的细胞色素P3A酶是人体肝脏中GC氧化的主要催化剂，人们对这些酶的个体发生和发育表达有很多了解。然而，对于儿童肺部细胞色素P3A的相对表达水平，以及儿童时期重要的呼吸道细胞的发育变化，GC药物在这些细胞中的作用和进行氧化代谢，基本上一无所知。CYP 3A酶在GCs代谢中催化的确切化学途径也尚不清楚。CYP3A基因的遗传多态、器官选择性表达和自身诱导是已知的预测个体间代谢差异显著的机制，导致对GCs的抵抗或超敏。所有这些过程都没有在哮喘儿童身上进行过研究。这项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GCs的抵抗或超敏主要由P450 3A基因的发育表达模式、遗传多态和环境反应性控制。我们将针对这一假说提出以下具体目标：1)分析三种主要CYP3A酶各自对五种最常用、有治疗意义的GC的代谢物和代谢途径；2)评估对肺和肝细胞中3A基因的诱导作用；3)将GC诱导的P450 3A转录本与激素代谢增加相关联，并建立一组儿童哮喘患者气管抽吸样本中P450 3A基因表达的发育模式；以及4)将一组儿童哮喘患者的CYP3A5和CYP3A7基因多态性与GC耐药或超敏反应关联起来。这一实验计划的结果将提供有关导致有效GC治疗的基本遗传和生化因素的基本信息。这一知识可用于基因分析，以指导临床选择GC产品，并为替代哮喘治疗方式提供更可靠的理论基础。 公共卫生相关性：吸入型糖皮质激素药物(GC)为哮喘儿童提供了有效的治疗方法，但多达50%的哮喘儿童无法通过吸入GCs获得帮助，即他们对这些药物具有抗药性。基本上，对儿童肺部P450酶表达的相对水平，或者儿童时期重要的呼吸系统细胞的发育变化一无所知，GC制剂在这些细胞中发挥作用并被清除。这项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.