Ah Receptor-Mediated Ligand Toxicity

描述（由申请人提供）：2,3,7,8-四氯二苯并-对二恶英（TCDD）及其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作用。许多这些影响是由于芳烃受体（AHR）介导的基因表达中断，AHR是一种依赖配体的碱性螺旋-环-螺旋PAS dna结合转录因子。尽管有毒配体的作用与其对AHR的结合亲和力密切相关，但越来越多的合成化学品、天然膳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。普遍的观点认为，有毒和无毒AHR配体之间的差异是由于配体结合亲和力更大，以及有毒化学物质的不可代谢持久性。虽然这些因素的重要性没有争议，但初步数据和与核受体的类比表明，配体依赖性AHR基因表达调节在TCDD和相关化合物引起的毒性作用中也起着不可或缺的作用。本提案将使用毒理学、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制差异。具体来说，两种有毒AHR配体TCDD和3,3',4,4'，5-五氯联苯（PCB126）以及两种无毒配体（-萘黄酮（BNF）和吲哚[3,2-b]-卡唑（ICZ））引发的全球基因表达谱的异同将通过人、小鼠和大鼠模型在体外和体内进行检测。我们假设，与无毒配体相比，有毒AHR配体引起基因表达的独特变化，这是由于配体结构依赖于二恶英反应元件（DRE）调控基因表达的调节。统计上严谨的方法将用于确定引起AHR配体的全球基因表达的显著变化，并将这些变化与毒性联系起来，以确定因果关系。这些研究的结果将通过将基因表达变化与毒性作用联系起来，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.