Structure-activity relationships for alkyl-phenanthrenes support two independent but interacting synergistic models for PAC mixture potency Science of The Total Environment

Multiple lines of evidence at whole animal, cellular and molecular levels implicate polycyclic aromatic compounds (PACs) with three rings as drivers of crude oil toxicity to developing fish. Phenanthrene (P0) and its alkylated homologs (C1- through C4-phenanthrenes) comprise the most prominent subfraction of tricyclic PACs in crude oils. Among this family, P0 has been studied intensively, with more limited detail available for the C4-phenanthrene 1-methyl-7-isopropyl-phenanthrene (1-M,7-IP, or retene). While both compounds are cardiotoxic, P0 impacts embryonic cardiac function and development through direct blockade of K+ and Ca2+ currents that regulate cardiomyocyte contractions. In contrast, 1-M,7-IP dysregulates aryl hydrocarbon receptor (AHR) activation in developing ventricular cardiomyocytes. Although no other compounds have been assessed in detail across the larger family of alkylated phenanthrenes, increasing alkylation might be expected to shift phenanthrene family member activity from K+/Ca2+ ion current blockade to AHR activation. Using embryos of two distantly related fish species, zebrafish and Atlantic haddock, we tested 14 alkyl-phenanthrenes in both acute and latent developmental cardiotoxicity assays. All compounds were cardiotoxic, and effects were resolved into impacts on multiple, highly specific aspects of heart development or function. Craniofacial defects were clearly linked to developmental cardiotoxicity. Based on these findings, we suggest a novel framework to delineate the developmental toxicity of petrogenic PAC mixtures in fish, which incorporates multi-mechanistic pathways that produce interactive synergism at the organ level. In addition, relationships among measured embryo tissue concentrations, cytochrome P4501A mRNA induction, and cardiotoxic responses suggest a two-compartment toxicokinetic model that independently predicts high potency of PAC mixtures through classical metabolic synergism. These two modes of synergism, specific to the sub-fraction of phenanthrenes, are sufficient to explain the high embryotoxic potency of crude oils, independent of as-yet unmeasured compounds in these complex environmental mixtures.

多项基于整体动物、细胞及分子水平的研究证据表明，三环多环芳烃化合物（polycyclic aromatic compounds, PACs）是原油对发育鱼类产生毒性的关键驱动因子。菲（phenanthrene, P0）及其烷基同系物（C1至C4烷基菲）构成了原油中三环PACs最主要的亚组分。在该类化合物家族中，P0的研究最为深入，而对于C4烷基菲中的1-甲基-7-异丙基菲（1-M,7-IP，又称惹烯retene）的相关研究则相对有限。尽管两种化合物均具有心脏毒性，但P0可通过直接阻断调控心肌细胞收缩的钾离子（K+）与钙离子（Ca2+）电流，影响胚胎心脏功能与发育过程；与之相反，1-M,7-IP则会干扰发育中心室心肌细胞的芳香烃受体（aryl hydrocarbon receptor, AHR）激活通路。目前尚未对烷基菲家族中其他化合物开展系统性详细评估，但可以推测，随着烷基化程度升高，菲类化合物的活性可能会从阻断K+/Ca2+离子电流转向激活AHR通路。本研究选取亲缘关系较远的两种鱼类——斑马鱼（zebrafish）与大西洋黑线鳕（Atlantic haddock）的胚胎为实验对象，在急性与潜在发育性心脏毒性检测模型中，对14种烷基菲类化合物开展了测试。结果显示，所有受试化合物均表现出心脏毒性，且其毒性效应可归结为对心脏发育或功能多个高度特异性环节的影响；颅面畸形与发育性心脏毒性存在明确关联。基于上述研究结果，我们提出了一套全新的研究框架，用于阐释石油源PACs混合物对鱼类的发育毒性，该框架纳入了可在器官层面产生交互协同效应的多机制通路。此外，对胚胎组织中污染物浓度、细胞色素P4501A信使核糖核酸（cytochrome P4501A mRNA）诱导水平与心脏毒性反应之间关联的分析，提示可构建双室毒代动力学模型，该模型可通过经典代谢协同效应，独立预测PACs混合物的高毒性潜能。这两种特异性针对菲类亚组分的协同作用模式，足以解释原油复杂混合物所展现出的高胚胎毒性，而无需依赖其中尚未被检测到的其他化合物。