Pharmacogenetics of sulfamethoxazole in HIV/AIDS patients

描述（由申请方提供）：复方新诺明（甲氧苄啶-磺胺甲恶唑，TMP-SMX）是预防与HIV/AIDS和其他免疫功能低下状态相关的机会性感染的首选药物。然而，SMX介导的超敏反应限制了其使用。该项目的目标是了解SMX毒性敏感性的遗传基础，SMX毒性是许多药物观察到的特异质不良反应的一个例子。几种途径决定SMX超敏反应：N-乙酰基转移酶1和2（NAT 1和NAT 2）的代谢失活; CYP 2C 9和其他（外）肝酶对毒性羟胺衍生物的代谢氧化;谷胱甘肽（GSH）氧化防御系统对活性氧（ROS）的保护以及免疫反应性（重点是人类白细胞抗原，HLA）。编码药物代谢酶、GSH相关酶和HLA蛋白的基因具有多态性，但遗传因素在SMX超敏反应中的作用仍不确定。我们建议，需要一个全面的方法来澄清特异质反应的遗传因素。具体目标1侧重于使用高通量方法对参与SMX代谢和毒性以及免疫应答（HLA）的候选基因（35个候选基因和149个多态性）进行靶向基因分型。遗传分析将测试基因型和临床结果之间的关联，比较一组有和没有SMX超敏反应的HIV/AIDS患者。为了增加临床遗传关联分析的能力，本研究包括对新的功能多态性的系统搜索。虽然大多数候选基因已被广泛研究，重点是改变蛋白质结构的非同义SNP，但调节多态性似乎更普遍，但大多数仍有待发现。具体目标2是识别NAT 1（一种高度多态性基因）中的新型调节SNP，因为它在SMX代谢中发挥重要作用。该方法依赖于测量靶组织中候选基因的基因组DNA和mRNA中的等位基因比率（150例肝脏尸检）。任何偏离相等的DNA和mRNA比例，称为等位基因表达不平衡，揭示了顺式作用因子的存在，提供了一个精确的定量表型。扫描基因位点的连锁SNPs揭示了新的调控多态性。综上所述，拟议的研究将澄清遗传因素是否有助于SMX超敏反应在艾滋病毒/艾滋病患者，并确定新的功能多态性NAT 1。这种联合方法有望用于特异质药物不良反应的一般研究。 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志物，磺胺甲恶唑广泛用于预防与艾滋病和其他免疫受损疾病相关的机会性感染。这种类型的特异质不良反应，可能涉及活性氧中间体和免疫反应作为致病因素，与许多药物相关，但仍知之甚少。这项研究的结果将评估遗传成分有助于不良磺胺甲恶唑反应，阐明特异质药物反应一般，并指导个体患者的最佳治疗选择。

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.