Pharmacogenetics of sulfamethoxazole in HIV/AIDS patients

说明(由申请人提供)：复方新诺明(甲氧苄氨嘧啶-磺胺甲恶唑，TMP-SMX)是预防与艾滋病毒/艾滋病相关的机会性感染和其他免疫受损状态的首选药物。然而，SMX介导的超敏反应限制了其应用。该项目的目标是了解对SMX毒性的可变敏感性的遗传基础，这是许多药物观察到的特殊不良反应的一个例子。有几个途径决定了SMX的过敏性：N-乙酰转移酶1和2(NAT1和NAT2)的代谢失活；CYP2C9和其他(肝外)酶将代谢氧化成有毒的羟胺衍生物；谷胱甘肽(GSH)氧化防御系统保护活性氧物种(ROS)；以及免疫反应性(重点是人类白细胞抗原，HL A)。编码药物代谢酶、GSH相关酶和HLA蛋白的基因是多态的，但遗传因素在SMX超敏反应中的作用仍不确定。我们建议，需要一种综合的方法来澄清特殊反应中的遗传因素。具体目的1利用高通量方法对参与SMX代谢和毒性以及免疫应答的候选基因(35个候选基因和149个多态)进行靶向基因分型。基因分析将通过比较患有和不患有SMX过敏症的一组艾滋病毒/艾滋病患者，来检验基因和临床结果之间的关联。为了增加临床遗传关联分析的能力，这项研究包括系统地寻找新的功能多态。虽然大多数候选基因已经被广泛研究，主要集中在改变蛋白质结构的非同义SNPs上，但调节性多态似乎更普遍，但大多数仍有待发现。特定的目标2是在Nat1-一个高度多态的基因中发现新的调节SNPs，因为它在SMX新陈代谢中扮演着重要的角色。该方法依赖于测量目标组织(150例肝脏尸检)中候选基因的基因组DNA和mRNA中的等位基因比率。任何偏离相等的DNA和信使核糖核酸比率，称为等位基因表达失衡，揭示了顺式作用因子的存在，提供了精确的定量表型。扫描基因位点寻找连锁的SNPs揭示了新的调控多态。综上所述，这项拟议的研究将阐明遗传因素是否与艾滋病毒/艾滋病患者的SMX过敏有关，并确定Nat1基因的新功能多态。这种结合的方法对特殊药物不良反应的一般研究很有希望。 公共卫生相关性：该项目旨在发现预测磺胺甲恶唑严重不良反应的遗传生物标记物，该药广泛用于预防与艾滋病相关的机会性感染和其他免疫损害情况。这种特殊的不良反应可能涉及到活性氧中间体和免疫反应作为致病因素，与许多药物有关，但仍知之甚少。这项研究的结果将评估导致磺胺甲恶唑不良反应的遗传成分，揭示一般特殊的药物反应，并指导针对个别患者选择优化的治疗方案。

DESCRIPTION (provided by applicant): Cotrimoxazole (Trimethoprim-sulfamethoxazole, TMP-SMX) is the agent of choice for prophylaxis against opportunistic infections associated with HIV/AIDS and other immuno-compromised states. However, hypersensitivity mediated by SMX limits its use. The goal of this project is to understand the genetic basis for variable sensitivity to SMX toxicity, an example of idiosyncratic adverse reactions observed with many drugs. Several pathways determine SMX hypersensitivity: Metabolic inactivation by N-acetyltransferases 1 and 2 (NAT1 and NAT2); metabolic oxidation to toxic hydroxylamine derivatives by CYP2C9 and other (extra-) hepatic enzymes; protection from reactive oxygen species (ROS) by the glutathione (GSH) oxidative defense system, and immune responsiveness (focus on human leukocyte antigen, HLA). Genes encoding the drug metabolizing enzymes, GSH -related enzymes, and HLA proteins are polymorphic, but the role of genetic factors in SMX hypersensitivity remains uncertain. We propose that a comprehensive approach is needed to clarify genetic factors in idiosyncratic reactions. Specific Aim 1 focuses on targeted genotyping of candidate genes (35 candidate genes and 149 polymorphisms) involved in SMX metabolism and toxicity, and in immune response (HLA) using high throughput methods. Genetic analyses will test association between genotype and clinical outcomes, comparing a cohort of HIV/AIDS patients with and without SMX hypersensitivity. To increase the power of clinical genetic association analysis, this study includes a systematic search for novel functional polymorphisms. While most of the candidate genes have been extensively studied with focus on non-synonymous SNPs that change protein structure, regulatory polymorphisms appear to be more prevalent but most remain to be discovered. Specific Aim 2 is to identify novel regulatory SNPs in NAT1 - a highly polymorphic gene - because of its important role in SMX metabolism. The approach relies on measuring allelic ratios in genomic DNA and mRNA of candidate genes in target tissues (150 liver autopsies). Any deviation from equal DNA and mRNA ratios, termed allelic expression imbalance, reveals the presence of cis-acting factors, providing a precise quantitative phenotype. Scanning the gene locus for linked SNPs reveal novel regulatory polymorphisms. Taken together, the proposed study will clarify whether genetic factors contribute to SMX hypersensitivity in HIV/AIDS patients, and identify novel functional polymorphisms in NAT1. This combined approach has promise for the general study of idiosyncratic adverse drug reactions. PUBLIC HEALTH RELEVANCE: This project aims at discovering genetic biomarkers for predicting severe adverse reactions to sulfamethoxazole, widely used in prophylaxis against opportunistic infections associated with AIDS and other immune-compromised conditions. This type of idiosyncratic adverse reactions, likely involving reactive oxygen intermediates and immune response as a causative factor, is associated with many drugs but remains poorly understood. The results of this study will assess the genetic component contributing to adverse sulfamethoxazole reaction, shed light on idiosyncratic drug reactions in general, and guide the selection of optimized therapies for individual patients.