Ah Receptor-Mediated Ligand Toxicity

描述(申请人提供)：2，3，7，8-四氯二苯并对二恶英(TCDD)和相关化合物在许多体外和动物模型以及人类中引起广泛的生化和毒性效应。这些效应中的许多是由于芳烃受体(AHR)介导的基因表达中断，AHR是一种配体依赖的基本螺旋-环-螺旋PAS DNA结合转录因子。尽管有毒配体的作用与它们与AHR的结合亲和力密切相关，但越来越多的合成化学品、天然饮食产品和内源性物质也表现出高结合亲和力，但不会引起毒性。流行的教条认为，有毒和无毒的AHR配体之间的差异是由于更大的配体结合亲和力和有毒化学物质的不可代谢持久性。尽管这些因素的重要性没有争议，但初步数据和核受体的类似物表明，配体依赖的AHR对基因表达的调节在TCDD及其相关化合物的毒性效应中也起着不可或缺的作用。这项提议将使用毒理学、分子、基因组和生物信息学方法进一步研究有毒和无毒配体之间的机理差异。具体地说，两种有毒的AHR配体TCDD和3，3‘，4，4’，5-五氯联苯(PCB126)，以及两种无毒的配体(-萘黄酮(BNF)和吲哚[3，2-b]-咔唑(ICZ))在体外和体内的人类、小鼠和大鼠模型中，将考察它们在全球基因表达谱中的异同。我们假设，与非毒性配体相比，有毒的AHR配体引起基因表达的独特变化，这是由于二恶英反应元件(DRE)调节的基因表达的配体结构依赖的调节。统计学上严格的方法将被用来识别AHR配体引起的全球基因表达的显著变化，并将这些变化与毒性相关联，以确定因果关系。这些研究的结果将通过将基因表达的变化与毒性效应相关联来阐明毒性AHR配体在受体结合后的作用机制。该提案还将解决与风险评估相关的问题，包括评估从体外模型到整个动物的外推机制的有效性，跨物种的全球基因表达反应的比较，以及使用啮齿动物数据预测人类风险的适当性。

DESCRIPTION (provided by applicant): 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds elicit a broad spectrum of biochemical and toxic effects in a number of in vitro and animal models as well as humans. Many of these effects are due to the disruption of gene expression mediated by the aryl hydrocarbon receptor (AHR), a ligand-dependent basic helix-loop-helix PAS DNA-binding transcription factor. Although the effects of toxic ligands correlate well with their binding affinity for the AHR, there are an increasing number of synthetic chemicals, natural dietary products, and endogenous substances that also exhibit high binding affinity but do not elicit toxicity. The prevailing dogma suggests that the difference between toxic and non-toxic AHR ligands is due to greater ligand binding affinity and to the non-metabolizable persistent nature of toxic chemicals. Although the importance of these factors is not disputed, preliminary data and analogies to nuclear receptors indicate that ligand-dependent AHR modulation of gene expression also plays an integral role in the toxic effects elicited by TCDD and related compounds. This proposal will further examine the mechanistic differences between toxic and non-toxic ligands using toxicological, molecular, genomic and bioinformatic approaches. Specifically, the similarities and differences in global gene expression profiles elicited by two toxic AHR ligands, TCDD and 3,3',4,4',5-pentachlorobiphenyl (PCB126), and two non-toxic ligands, (-naphthoflavone (BNF) and indolo[3,2-b]-carbazole (ICZ), will be examined in vitro and in vivo using human, mouse and rat models. We hypothesize that toxic AHR Iigands elicit unique changes in gene expression compared to non-toxic ligands, due to ligand structure-dependent modulation of dioxin response element (DRE)-regulated gene expression. Statistically rigorous approaches will be used to identify significant changes in global gene expression elicited AHR ligands, and to correlate these changes to toxicity in order to identify causal relationships. Results from these studies will elucidate the mechanisms of action of toxic AHR ligands following receptor binding by correlating changes in gene expression with toxic effects. This proposal will also address concerns relevant to risk assessment, including an evaluation of the validity of extrapolating mechanisms from in vitro models to whole animals, a comparison of global gene expression responses across species, and the appropriateness of using rodent data m predict human risk.