Does the extreme variability of methadone metabolism have an epigenetic cause?

美沙酮代谢的极端变异性是否有表观遗传原因？

• 批准号: 7772587
• 负责人: GAVIN R SCHNITZLER
• 金额: $ 15.9万
• 依托单位: TUFTS MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7772587
• 关键词: Accounting; Alleles; Attention; Biological Assay; Cell Culture Techniques; Cell Nucleus; Centers for Disease Control and Prevention (U.S.); Cessation of life; Chemicals; Chromatin; Clinical; Collaborations; CpG dinucleotide; Cytochrome P450; Cytochrome P450 3A4; DNA; DNA Methyltransferase; DNA Modification Methylases; DNA Packaging; DNA Sequence; Data; Dose; Drug Prescriptions; Effectiveness; Enzymes; Epigenetic Process; Gene Mutation; Genes; Genetic; Genetic Polymorphism; Genetic Transcription; Genetic Variation; Genetic screening method; Genomics; Genotype; Heroin; Heroin Abuse; Heroin Dependence; Histone Acetylation; Histone Deacetylase Inhibitor; Histone Deacetylation; Histones; Human; Individual; Intestines; Laboratories; Lead; Libraries; Life; Liver; Measures; Messenger RNA; Metabolism; Methadone; Methylation; Modification; Mutation; Nucleic Acid Regulatory Sequences; Opiates; Patients; Pharmaceutical Preparations; Pharmacogenomics; Pilot Projects; Play; Poisoning; Production; Proteins; Regulation; Relapse; Reporting; Repression; Research; Research Personnel; Retinoblastoma Protein; Role; Sampling; System; Testing; Tissue Sample; Tumor Suppressor Genes; Tumor-Suppressor Gene Inactivation; United States; Variant; Withdrawal Symptom; Work; base; carcinogenesis; court; derepression; drug metabolism; drug of abuse; drug production; histone modification; human disease; mRNA Expression; malignant breast neoplasm; methadone maintenance; novel; promoter; public health relevance; response; success

DESCRIPTION (provided by applicant): Heroin is one of the most addictive and dangerous drugs of abuse. Indeed, a recent CDC report indicated that heroin and other opiates account for ~30% of all inadvertent poisoning deaths in the United States. Treatment with methadone is one of the few effective ways to treat heroin addicts, keeping them from relapsing while allowing them to carry on mostly normal lives. Unfortunately, the rate of methadone metabolism differs hugely between individuals, which complicates dosing decisions in maintenance methadone treatment. Moreover, many prescription drugs and other substances can greatly alter methadone metabolism, which can lead to withdrawal symptoms and relapse to heroin abuse. Interindividual variation in methadone metabolism also likely contributes to the dramatic, recent rise in deaths due to illicit methadone use. Much of the variability in methadone metabolism is due to the greater than 40-fold range of inter-individual expression variability, in the liver and intestines, of the drug metabolizing enzyme cytochrome P450 3A4 (CYP3A4). Over the past two decades, researchers have systematically examined the CYP3A4 gene to try to identify genetic polymorphisms that could explain the observed variability in CYP3A4 mRNA production. While some polymorphisms have been found, however, they could only explain a small fraction of the CYP3A4 variability. This has suggested that some other "epigenetic" mechanism (as distinguished from genetic mechanisms by not being directly based on DNA sequence) might result in variable CYP3A4 mRNA production. In the work described here, we will test this novel hypothesis by examining whether three epigenetic chemical modifications that are commonly associated with reduced mRNA production correlate with reduced CYP3A4 mRNA levels in a bank of 54 human liver samples. The first of these epigenetic marks is the covalent methylation of the C base in CG dinucleotides in genomic DNA. The other two are chemical modifications of the histone proteins that serve as packaging for DNA inside cell nuclei (hypoacetylation and trimethylation of H3K9). Each of these modifications have been shown to promote reduced mRNA production in other systems. For instance, these modifications are often associated with the aberrant loss of mRNA for important tumor suppressor genes, including retinoblastoma protein (pRB) and breast cancer associated protein 1 (BRCA1). Surprisingly, however, their connection to variable production of drug metabolizing gene mRNA has never been tested. PUBLIC HEALTH RELEVANCE: If these studies show that CYP3A4 mRNA levels are controlled by these epigenetic modifications, it will suggest new ways to predict an individual patient's response to methadone (e.g. by testing whether the CYP3A4 gene shows epigenetic modifications associated with repression). In a larger context, it will establish a new paradigm for understanding the causes of variable mRNA expression for other drug metabolizing genes, as well as for other genes whose variability is associated with human disease. If we find that epigenetic modifications do not play a role in CYP3A4 mRNA variability, this will also be an important discovery, that will encourage further research into the genetic or long-term environmental causes of this variability.

描述（由申请人提供）：海洛因是最容易上瘾和最危险的滥用药物之一。事实上，CDC最近的一份报告表明，海洛因和其他阿片类药物占美国所有意外中毒死亡的30%。美沙酮治疗是治疗海洛因成瘾者的少数有效方法之一，可以防止他们复发，同时让他们继续正常的生活。不幸的是，美沙酮代谢率在个体之间差异很大，这使得维持美沙酮治疗的剂量决定变得复杂。此外，许多处方药和其他物质可以大大改变美沙酮的代谢，这可能导致戒断症状和海洛因滥用的复发。美沙酮代谢的个体间差异也可能导致最近因非法使用美沙酮而死亡的人数急剧上升。美沙酮代谢的大部分变异性是由于肝脏和肠道中药物代谢酶细胞色素P450 3A 4（CYP 3A 4）的个体间表达变异性范围超过40倍。在过去的二十年里，研究人员系统地研究了CYP3A4基因，试图确定可以解释CYP3A4 mRNA产生中观察到的变异性的遗传多态性。虽然已经发现了一些多态性，但它们只能解释CYP3A4变异的一小部分。这表明其他一些“表观遗传”机制（与遗传机制不同，不直接基于DNA序列）可能导致CYP3A4 mRNA产生的变化。在本文所述的工作中，我们将通过检查通常与mRNA产生减少相关的三种表观遗传化学修饰是否与54份人类肝脏样本库中CYP3A4 mRNA水平降低相关来验证这一新假设。这些表观遗传标记中的第一个是基因组DNA中CG二核苷酸中C碱基的共价甲基化。另外两个是组蛋白的化学修饰，作为细胞核内DNA的包装（H3K9的低乙酰化和三甲基化）。这些修饰中的每一种都显示出在其他系统中促进mRNA产生的减少。例如，这些修饰通常与重要肿瘤抑制基因的mRNA异常丢失有关，包括视网膜母细胞瘤蛋白（pRB）和乳腺癌相关蛋白1（BRCA 1）。然而，令人惊讶的是，它们与药物代谢基因mRNA的可变产生的联系从未被测试过。公共卫生相关性：如果这些研究表明CYP3A4 mRNA水平受这些表观遗传修饰的控制，则将提出预测个体患者对美沙酮的反应的新方法（例如，通过测试CYP3A4基因是否显示与抑制相关的表观遗传修饰）。在更大的背景下，它将建立一个新的范式，以了解其他药物代谢基因的可变mRNA表达的原因，以及其变异性与人类疾病相关的其他基因。如果我们发现表观遗传修饰在CYP3A4 mRNA变异性中不起作用，这也将是一个重要的发现，这将鼓励进一步研究这种变异性的遗传或长期环境原因。