Toxicity identification and evaluation of neuro-active chemicals in zebrafish

During the production and after therapeutic use pharmaceutical compounds can enter the aquatic environment through industrial and household discharges. Indeed, pharmaceuticals are continually released into the environment wherever humans live. But until recently, very little attention has been paid on what happens to these these compounds after their administration or use. Human pharmaceuticals have ‘enjoyed’ several decades of unrestricted discharge to the environment. Over the last decade, the increasing number of reports on the occurrence of human pharmaceuticals in the aquatic environment has raised public concern on the environmental risk of these compounds. The big unknown however, is whether the presence of low concentrations of human pharmaceuticals in the aquatic environment can cause a serious threat. Currently, very little is known on the potential adverse effects of human pharmaceuticals on aquatic organisms, and there is a great need for relevant and specific ecotoxicological effect data in order to correctly assess the environmental risk of pharmaceutical compounds.

The principal aim of this research is to identify and evaluate the possible impact of exposure to selected human neuro-endocrine active substances, and the development of relevant gene expression assays for the early detection of neurotoxic effects in the zebrafish (Danio rerio).
The following research goals are addressed: (1) Development of LC/EC-MS-MS protocols for the sensitive and specific detection of selected neuro-endocrine active pharmaceuticals in sewage and surface water in Belgium, (2) molecular characterization of 4 selected neuro-endocrine active pharmaceuticals by isolation of genes that were differentially expressed in zebrafish brain after exposure to diazepam, chlorpromazine, mianserin or 17β-estradiol, (3) development of a custom brain-specific cDNA microarray containing most important affected genes, (4) application and evaluation of gene expression analysis – using the custom cDNA and oligo microarrays – for studying the molecular mechanisms underlying the toxic effects of exposure to the selected model pharmaceuticals in zebrafish, and (4) investigation of the ecological relevance of observed effects on gene expression by evaluating the impact of exposure to the model compounds on reproductive parameters in zebrafish.
Through this approach we want to illustrate the potential of a toxicogenomics approach – specifically gene expression analysis using microarrays – on the effect evaluation of neuro-endocrine active pharmaceuticals. This will lead to a better understanding of the ecotoxicological risk of these pharmaceuticals and may lead to the development of specific assays for the detection of toxic effects to the neuro-endocrine system in fish.