Leveraging comparative physiology and genomics to predict species sensitivity: A novel framework for interspecies extrapolation in ecotoxicology

矿工拿着金丝雀作为有毒气体的警报；根据经验，他知道金丝雀会在毒气造成持久伤害之前停止鸣叫。“矿工的金丝雀”这个成语在毒理学风险评估中被广泛使用，无论是测试对人类健康的潜在风险还是对环境的影响。有限范围的生物被用作“金丝雀”或哨兵，以评估化学品对整个生态系统构成的风险。然而，与“金丝雀和矿工”不同，我们通常不知道化学物质对哨兵和其他生物的相对影响。为了解释风险评估中的这种不确定性，一个“安全系数”，即任意100或1000倍的调整，适用于对哨兵物种观察到的最低毒理学效应，以试图保护更敏感的物种。这种外推没有机械基础，它本身完全是对进入环境的化学物质数量和存在的生物体种类的实际反应。在这个应用中，我们建议开发一个新的框架，可以用来提供比较物种敏感性的客观测量。该框架基于三个组成部分；1)测量化学物质进入生物体后的去向；Ii)化学物质与其生物受体分子的特定相互作用，以及这种相互作用如何受到物种之间观察到的受体的细微差异的影响；iii)化学物质的影响从与受体的相互作用传递到最终对生物体的影响的途径。为了计算目标组织中存在的化学物质的数量，我们将使用放射性标记化合物和详细化学来确定化学物质积累（进入生物体），分布（特别是到目标部位），代谢（形成或多或少有毒的代谢物）和排泄（从体内）的速率。这些测量将使我们能够确定在精确的暴露水平下，化合物的相对位置和含量。许多化学物质通过与被称为受体的特定生物分子相互作用来影响生物系统。就像推动一张多米诺骨牌可以产生奇异的图案一样，化学物质与受体的相互作用可以作为“分子启动事件”，最终产生一连串的生物反应。这意味着化学物质与受体相互作用的精确特性对化学作用的传递至关重要。不同物种的受体分子结构不同，这显著影响了化学物质对生物体的效力。我们将使用为制药行业开发的基因组学工具和建模技术来预测化学-受体相互作用的相对强度，从而预测传递其影响的有效性。化学效应是通过一系列复杂的生物学途径，从与受体的分子相互作用传递到最终观察到的生物学效应，现在称为Adverse Outcome pathways （AOP）。我们将使用计算方法推导出我们化学链接的有效AOP，暴露量及其传输生物影响的效力。案例研究：选择化学品和蚯蚓我们选择了不同种类的蚯蚓作为哨兵，因为它们被广泛用于土壤中的化学品风险评估，它们是关键的生态系统工程师，并且它们对一系列化学品的敏感性表现出显著的多样性。我们选择研究的化学物质：a)在不同种类的蚯蚓之间表现出显著的敏感性差异；B)代表一系列的化学作用模式；&, c)具有不同复杂性的受体。此外，所选择的化学类别具有重要的环境相关性，特别是因为这涉及到对陆地生态系统的“非目标”影响。

The idiom of a 'miner's canary'A miner holds a canary as an alert for toxic gas; from experience he knows that the canary will stop singing before the gas causes lasting harm. The idiom of a 'miner's canary' is used throughout toxicological risk assessment, whether testing for potential risks to human health or for environmental impacts. A restricted range of organisms are used as 'canaries' or sentinels to assess the risk chemicals pose to entire ecosystems. However, unlike 'the canary and the miner' we often do not know the relative affect of the chemical on the sentinels in relation to other organisms. To account for this uncertainty in risk assessment, a 'safety factor', an arbitrary 100 or 1000-fold adjustment, is applied to the lowest observed toxicological effect on sentinel species in an attempt to protect more sensitive species. This extrapolation has no mechanistic grounding being itself entirely a pragmatic response to the number of chemicals entering the environment & variety of organisms present. In this application we propose to develop a novel framework that may be used to provide an objective measure of comparative species sensitivity. The framework is based on three components; i) the measurement of where a chemical goes when it enters an organism; ii) the specific interactions of the chemical with its biological receptor molecules & how this is affected by subtle differences in the receptors observed between species, & iii) the pathways that transmit the affect of the chemical from the interactions with receptor through to eventual impact on the organism.The where & the how muchTo calculate the amount of a chemical that resides in a target tissue we will use radio-labelled compounds & also detailed chemistry to determine the rates of chemical Accumulation (into the organism), Distribution (especially to the target site), Metabolism (to form more or less toxic metabolites) & Excretion (from the body). These measurements will allow us to determine the relative where & how much of a compound is present in response to a precise level of exposure.Pushing the first dominoMany chemicals affect a biological system through interaction with specific biomolecules termed receptors. In the same way as pushing on a single domino can lead to exotic patterns, a chemical-receptor interaction can act as a "Molecular Initiating Event" that ultimately produces a cascade of biological responses. This means that the precise characteristics of the chemical-receptor interaction are crucial to transmission of chemical affect. The structure of receptor molecules differs between species & this significantly influences the potency of the chemical to the organism. We will use genomics tools & modelling techniques developed for the pharmaceutical industry to predict the relative strength of the chemical-receptor interaction & therefore the effectiveness to transmit its affect.Mapping affect pathwaysChemical affect is transmitted from a molecular interaction with receptor(s) to the final observed biological effect through a complex series of biological pathways, now termed the Adverse Outcome Pathways (AOP). We will use computational approaches to derive the effective AOP for our chemical linking the exposure amount & its potency to transmit the biological impact.Case studies: Selecting chemicals & earthwormsWe have selected different earthworm species as sentinels because they are widely used for chemical risk assessment in soils, they are key ecosystem engineers & they show a significant diversity of sensitivity to a range of chemicals. The chemical we have selected to study: a) show significant differential sensitivity amongst earthworm species; b) represent a range of chemical modes-of-action; &, c) have receptors of varying complexities. Furthermore, the chemical classes selected have significant environmental relevance especially as this relates to 'non-target' impacts in terrestrial ecosystems.