溴代二噁英的鸟类相对毒性效力及其种间敏感性差异的分子动力学机制研究

Brominated dioxins are an important class of highly toxic dioxin-like environmental pollutants with effumability, high lipophilicity and environmental persistence. They have recently been detected to be widespread in various environmental and biological samples with high detection rates and levels. They have been increasingly concerned by the scientific community and the government in recent years. Recently, they were recommended to be included in the existing toxicity equivalency factor (TEF) scheme by World Health Organization. However, very few data were available concerning the toxicity of brominated dioxins in birds, thus the avian TEFs could not be determined, thereby leading to the inability to conduct ecological risk assessment of brominated dioxins for birds. In this project, a recently developed avian aryl hydrocarbon receptor 1 (AHR1)-mediated luciferase report gene assay will be employed to assess the avian species-specific relative potencies (RePs) of 16 brominated dioxins and to compare the inter-species sensitivity among different avian species. In addition, the research effort will also be focused on the molecular- and atomic-level interactions between compound ligands and avian AHR1s to reveal mechanisms of the avian inter-species sensitivity variations to dioxin-like toxicity. Thus, a cell-based binding affinity assay and a molecular dynamics simulation method will be used to study the potential relations between ligand-receptor binding affinities, kinetic and thermodynamic parameters of three-dimensional conformational transformation of ligand-receptor complexes, and avian inter-species sensitivity variations. The outcome of this project will not only provide fundamental scientific knowledge and novel technologies for the TEFs derivation and the ecological risk assessment, but also further elucidate the underlying mechanisms of inter-species sensitivity variations for dioxin-like compounds including brominated dioxins in birds.

溴代二噁英是一类具有易挥发性、强亲脂性和环境持久性的高毒类二噁英环境污染物，在各种环境基质中的检出率和检出浓度均较高，近年来备受科学界和政府关注。世卫组织最近建议将其纳入毒性当量因子方法，但鸟类毒性数据的严重不足导致鸟纲特异毒性当量因子无法推导，不利于其鸟类生态风险评价的开展。因此，拟选取16种溴代二噁英为目标化合物，通过一种新型鸟类芳香烃受体荧光报告基因实验，研究其鸟类物种特异的相对毒性效力及其类二噁英毒性的鸟类种间敏感性差异。另外，为了探究种间差异的微观机制，以分子和原子水平上的相互作用为出发点，通过细胞内结合亲和力试验和分子动力学模拟，探究配体-受体结合亲和力及其复合体三维构象变化的动力学和热力学等参数与鸟类种间相对敏感性的关系。该研究不仅能为溴代二噁英鸟类毒性当量因子的推导和生态风险评价的开展提供科学依据和新技术方法，而且将进一步阐明类二噁英毒性鸟类种间敏感性差异的更深层次机制。

PBDD/Fs和PBBs是具有易挥发性、强亲脂性和环境持久性的高毒类二噁英环境污染物，在各种环境基质中的检出率和检出浓度均较高。世卫组织最近建议将其纳入毒性当量因子方法，但鸟类毒性数据的严重不足导致鸟纲特异毒性当量因子无法推导，不利于其鸟类生态风险评价的开展。因此，本项目首先通过鸟纲AHR1-LRG实验测定了PBDD/Fs和PBBs的鸟纲生态风险评价亟需的物种特异的相对毒性效力及化合物特异的鸟纲种间相对敏感性。结果表明，PBDD/Fs和PBBs类二噁英毒性的鸟纲物种特异的相对毒性效力并不总是遵循世界卫生组织公布的其氯化单体的毒性当量因子。然后，通过分子动力学模拟和分子力学-泊松玻尔兹曼表面积方法计算了结合自由能以及各PBDD/Fs和PBBs与AHR1-LBD内各氨基酸间的分子间作用能EMM。这些EMM值可以精细地表征各配体化合物物种特异的AHR1-LBD的最终活性构象。在此基础上，我们基于机器学习算法经特征筛选后构建了黑箱预测模型，并采用样条近似方法获得了解释性更强的广义线性模型，可实现毒性和敏感性高低的分类预测，且模型预测准确率（大于87%）和泛化能力（受试者工作特征曲线下面积大于88%）都很高。这些预测模型是基于分子致毒机制构建的，且提取了配体和物种特异的AHR1-LBD构象信息，并融合了机器学习算法的高预测精度和广义线性模型可解释性强的优点。此外，我们发现特征筛选可准确识别决定物种相对敏感性的差异氨基酸所在区域。因此总的来讲，本项目的研究结果为PBDD/Fs和PBBs类二噁英毒性鸟类毒性当量因子的推导及其鸟类生态风险的评价提供了科学依据，为优控类二噁英化合物的筛查提供了新工具，为揭示其它脊椎动物对类二噁英毒性种间敏感性差异的氨基酸层面的机制提供了新策略，为化学品安全性评价预测模型的开发提供了新思路。