Project 2: An Integrated Experimental and Computational Approach to Understand t

项目总结(见说明)； 美国国家研究委员会(NRC)最近发布的一份题为《科学与决策》的报告表明，在存在被毒物加剧的功能障碍的背景发病率的情况下，即使个人的剂量-反应曲线是非线性的或显示出阈值，人类的变异性也会有效地使群体剂量-反应曲线线性化。人类变异性导致的剂量-反应曲线线性化的论点在很大程度上是理论上的，只有有限的实验数据，对非癌症终点使用阈值方法已经是几十年来化学风险评估的标准做法。改变为线性方法，没有阈值方法将对超级基金站点的清理水平产生重大影响，任何取代非癌症终点的传统阈值方法的决定都应该基于可靠的科学和足够的实验数据，2，3，7，8-四氯二苯并-对二恶英(TCDD)被广泛接受通过受体介导的作用模式和相关的非线性剂量反应。我们建议使用TCDD作为模型化学品，对NRC报告中提出的想法进行实验评估。该项目的主要假设是，对TCDD免疫抑制和胚胎毒性的剂量-反应曲线的表征将表明，该反应符合非线性模型，并且纳入种群变异性不会以NRC建议的方式线性化基于种群的剂量-反应曲线。这一假设将通过一组近亲交配的小鼠来验证，该小组提供了人类种群遗传异质性的体内模型和体外人类模型。这项建议的具体目的是：(1)以近交系小鼠基因组多样性小组为模型，评估遗传异质性对TCDD介导的胚胎毒性和血清激素变化的群体剂量反应曲线的影响；(2)评估人类个体间差异对TCDD介导的抑制B细胞IgM分泌的群体剂量反应曲线的影响；(3)鉴定和表征与TCDD介导的胚胎毒性的品系间差异相关的基因和途径，以了解作用模式。将构建TCDD介导的胚胎毒性和B细胞抑制的计算模型，并用于了解该系统在低环境相关剂量下的行为。通过这些特定的目标，将在两个不同物种(小鼠和人类)的多个非癌症终点(早期胚胎毒性、类固醇激素改变和B细胞免疫抑制)上产生大量科学数据和分析，并使用体内和体外模型来评估NRC报告所依据的假设。

PROJECT SUMMARY (See Instructions); A recent report released by the National Research Council (NRC) entitled "Science and Decisions" has suggested that in cases where there is a background incidence of a dysfunction which is augmented by a toxicant, human variability would effectively linearize the population dose-response curve even if the dose response curve in an individual person was non-linear or showed a threshold. The arguments for linearization of the dose-response curve due to human variability are largely theoretical with a limited amount of experimental data and the use of a threshold approach for non-cancer endpoints has been standard practice in chemical risk assessment for decades. Changing to a linear, no threshold approach would have a major impact on clean up levels at Superfund sites and any decision to replace the traditional threshold approach for non-cancer endpoints should be based on sound science with adequate experimental data 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is widely accepted to act through a receptor-mediated mode-of action with an associated non-linear dose response. We propose to use TCDD as a model chemical to experimentally evaluate the ideas laid out in the NRC report. The primary hypothesis of the project is that characterization of the dose-response curves for the immunosuppression and embryotoxicity of TCDD will demonstrate that the response is consistent with a non-linear model and the incorporation of population variability will not linearize the population-based dose-response curve in the manner proposed by the NRC. This hypothesis will be tested using a panel of inbred mice that provides an In vivo model of the genetic heterogeneity in the human population and an in vitro human model. The specific aims of this proposal are: (1) evaluate the effects of genetic heterogeneity on the population dose-response curve for TCDD-mediated embryotoxicity and serum hormone alterations using the Mouse Phenome Diversity Panel of inbred mice as a model; (2) evaluate the effects of human inter-individual variability on the population dose-response curve for TCDD-mediated suppression of B-cell IgM secretion; (3) Identify and characterize the genes and pathways associated with the inter-strain differences in TCDD-mediated embryotoxicity to understand the mode-of-action. Computational models of TCDD-mediated embryotoxicity and B-cell suppression will be constructed and used to understand behavior of the system at low, environmentally-relevant doses. Through these specific aims, a substantial amount of scientific data and analysis will be generated across multiple non-cancer endpoints (early embryotoxicity, steroid hormone alterations, and B-cell immunosuppression), in two different species (mice and humans), and using both in vivo and in vitro models to evaluate the assumption underlying the NRC report.