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Acetylcholinesterase in zebrafish embryos as a tool to identify neurotoxic effects in sediments

Kais, Britta, Stengel, Daniel, Batel, Annika, Braunbeck, Thomas
Environmental science and pollution research international 2015 v.22 no.21 pp. 16329-16339
Danio rerio, acetylcholinesterase, bisphenol A, chemical analysis, chlorpyrifos, extracts, fish, mechanism of action, mercuric chloride, methylmercury compounds, models, neurotoxicity, pollutants, polycyclic aromatic hydrocarbons, quinoline, sediments, water policy
In order to clarify the suitability of zebrafish (Danio rerio) embryos for the detection of neurotoxic compounds, the acetylcholinesterase assay was adapted and validated with a series of priority pollutants listed as relevant for the European water policy (Aroclor 1254, 2,3-benzofuran, bisphenol A, chlorpyrifos, paraoxon-methyl, quinoline, and methyl mercury chloride) as well as acetonic extracts from three sediments of known contamination. The acute toxicities of the model substances and the sediment extracts were determined by means of the fish embryo test as specified in OECD TG 236, and concentrations as low as the effective concentration at 10 % inhibition (EC₁₀) were used as the highest test concentration in the acetylcholinesterase test in order to avoid nonspecific systemic effects mimicking neurotoxicity. Among the model compounds, only the known acetylcholinesterase inhibitors paraoxon-methyl and chlorpyrifos produced a strong inhibition to about 20 and 33 %, respectively, of the negative controls. For the sediment extracts, a reduction of acetylcholinesterase activity to about 60 % could only be shown for the Vering Canal sediment extracts; this could be correlated to high contents of acetylcholinesterase-inhibiting polycyclic aromatic hydrocarbons (PAHs) as identified by chemical analyses. Co-incubation of the Vering Canal sediment extracts with chlorpyrifos at EC₁₀ concentrations each did not significantly increase the inhibitory effect of chlorpyrifos, indicating that the mode of action of acetylcholinesterase inhibition by the sediment-borne PAHs is different to that of the typical acetylcholinesterase blocker chlorpyrifos. Overall, the study documents that zebrafish embryos represent a suitable model not only to reveal acetylcholinesterase inhibition, but also to investigate various modes of neurotoxic action.