砷的睾丸毒作用模式和男性不育替代终点标志物研究

Abstract: To establish the environmental health risk assessment on the direct use of human exposure biomonitoring data is the cutting-edge approach, while the biggest challenge is to have the ready surrogate endpoint biomarkers. To investigate the biomarkers' sensitively response to the pollution exposure and their predictively descriptions of the adverse outcomes, we proposed the following project. Taking the male reproduction toxicity of arsenic as the example, we will use rat as the testing model to illustrate the toxic effects and mode of actions (MOA) of arsenic on testis; in the same time the methodology of the adverse outcome pathway (AOP) analysis will be applied to extend the MOA by involving the reference of oligozoospermic infertile rats model and the health improved counterparts. By analysis the AOP related key molecular events using high-throughput OMICs techniques, we will screen the rat biomarkers (esp., the markers in body fluids) that can specific response to arsenic exposure and surrogate the adverse endpoints including the decreased sperm quality and infertile. In further, we will screen the potential biomarkers from human urine and blood samples using both of arsenic dosages and oligozoospermic infertile-health control as classifiers, then by using Bayesian network analysis and biological pathway analysis we will identify the biomarkers which can be supported by the rat toxicological results. Finally, a tentative risk assessment model will be established on the human arsenic body burden and the surrogate endpoint biomarkers, in which the threshold values will be derived from the arsenic dose dependent biomarker changes.

摘要：直接基于人群体液中污染物残留水平和替代终点标志物构建健康风险评估模型是目前环境健康研究领域的前沿，主要面临的挑战是筛选具有污染暴露特异性和不良结局预期性能力的易达性标志物。以典型环境污染物砷的男（雄）性生殖毒性为例，项目拟基于不良结局通路分析的理念，首先利用大鼠模型阐明砷对睾丸的毒作用模式和效应；通过比较寡精症造模大鼠和症状改善大鼠的效应和健康结局变化，构建从暴露到结局的主要风险通路；从与通路相关的体液标志物中甄别替代终点标志物。进而基于暴露剂量和健康-疾病对照，选人群体液中的潜在替代终点标志物；基于贝叶斯网络模型和生物通路分析，横向比较大鼠体液标志物与人群体液标志物的关联，甄别人群体液中的替代终点标志物。最终利用人群内暴露剂量和标志物的变化阈值构建风险评估模型。

本项目基于有害结局通路（Adverse Outcome Pathway, AOP）的理念，利用体液代谢标志物重构从暴露到不良结局的路径，初步探讨了生物监测数据直接用于健康风险评估的方法学基础。基于典型的饮用水暴露方式，项目选择典型的砷污染物暴露和雄（男）性不育结局展开。研究主要从模式动物暴露的视角设计了一系列实验，收集了砷暴露诱导的一系列分子事件的发生和发展，并进一步通过合笼实验考察了雄性SD大鼠的受孕能力。另外，实验室研究之外，首次通过人群流行病学考察了砷污染事件从暴露相关的代谢性毒作用模式（MOA）发展到以男性不育为不良结局的通路，验证了人体有害结局通路（hAOP）研究框架的可行性。项目结果（1）验证了MIMA（meet-in-metabolite analysis）模型能够高效地重构砷的代谢毒性（标志物、通路和毒理学机制）与男性不孕的代谢病理特征（标志物、通路和病理学机制）之间通路；（2）观察到砷的起始毒作用模式为砷的甲基化代谢（methylation）和氧化胁迫，这两个分子事件通过一碳代谢通路（one-carbon metabolism）和脂质代谢（尤其是脂肪酸氧化）通路影响了与男（雄）性生殖密切相关的甾醇类激素合成；（3）睾酮作为男性生殖能力的指示性激素，沟通了砷暴露事件和男性不孕之间的代谢性通路。总之，考虑到物种间差异使实验室的毒理学结果难以通过简单剂量-效应关系外推到人群，且砷的毒性效应和睾酮因素可能仅是男性不育病因中的部分因果性关系，在现实环境污染背景下基于hAOP重构人群的直接风险，MIMA模型能高效追索到睾酮扮演了统计学显著和机制合理的替代性标志物的角色。