Scott Jason A, Hodson Peter V
Department of Biology, Queen's University, Kingston, ON, Canada.
Aquat Toxicol. 2008 Jul 7;88(3):200-6. doi: 10.1016/j.aquatox.2008.04.007. Epub 2008 Apr 22.
Alkylated polycyclic aromatic hydrocarbons, such as retene (7-isopropyl-1-methylphenanthrene), induce cytochrome P450 1A (CYP1A) enzymes and produce dioxin-like toxicity in the embryo-larval stages of fish characterized by the signs of blue sac disease (BSD). The signs of toxicity are well characterized; however, the mechanism is not well understood. To elucidate the role of CYP1A in retene toxicity, larval rainbow trout (Oncorhynchus mykiss) were co-treated with a range of concentrations of alpha-naphthoflavone (ANF), a known CYP1A inhibitor. The co-treatment produced synergistic toxicity at 3.2-100 microg/L ANF, after which toxicity at 180 microg/L ANF dropped to levels typical of retene-only. At 320 microg/L ANF, toxicity increased with or without retene, indicating that ANF alone was capable of inducing BSD. In addition, the additive toxicity of retene-only and 320 microg/L ANF-only approximately equalled that of the co-exposed larvae (100 microg/L retene+320 microg/L ANF), indicating response addition. Thus, two mechanisms of action occurred in co-exposed larvae at different concentrations of ANF. In trout larvae, there was a correlation between toxicity and CYP1A protein concentrations, and in juvenile trout, ANF produced a concentration-dependent inhibition of ethoxyresorufin-O-deethylase (EROD) activity without a measurable drop in CYP1A protein. Taken together, the mechanism underlying the synergistic toxicity is EROD-independent and may be AhR-dependent. This study demonstrated that multiple, exposure-dependent mechanisms can occur in mixture toxicity, suggesting that current risk assessment models may drastically underestimate toxicity, particularly of mixtures containing both CYP1A inducers and inhibitors.
烷基化多环芳烃，如惹烯（7-异丙基-1-甲基菲），可诱导细胞色素P450 1A（CYP1A）酶，并在鱼类胚胎-幼体阶段产生二噁英样毒性，其特征为蓝囊病（BSD）症状。毒性症状已得到充分表征；然而，其机制尚不清楚。为阐明CYP1A在惹烯毒性中的作用，将一系列浓度的α-萘黄酮（ANF，一种已知的CYP1A抑制剂）与虹鳟幼鱼（Oncorhynchus mykiss）共同处理。在3.2 - 100μg/L的ANF浓度下，共同处理产生了协同毒性，之后在180μg/L的ANF浓度下，毒性降至仅使用惹烯时的典型水平。在320μg/L的ANF浓度下，无论有无惹烯，毒性均增加，表明单独的ANF能够诱导BSD。此外，仅使用惹烯和仅使用320μg/L的ANF的相加毒性大致等同于共同暴露幼虫（100μg/L惹烯 + 320μg/L ANF）的毒性，表明是反应相加。因此，在不同浓度的ANF共同暴露的幼虫中发生了两种作用机制。在虹鳟幼鱼中，毒性与CYP1A蛋白浓度之间存在相关性，而在虹鳟幼鱼中，ANF对乙氧异吩唑酮 - O - 脱乙基酶（EROD）活性产生了浓度依赖性抑制，而CYP1A蛋白没有可测量的下降。综合来看，协同毒性的潜在机制不依赖于EROD，可能依赖于芳烃受体（AhR）。本研究表明，在混合物毒性中可能会出现多种依赖于暴露的机制，这表明当前的风险评估模型可能会大幅低估毒性，尤其是对于同时含有CYP1A诱导剂和抑制剂的混合物。
