Comparative embryotoxicity and proteotoxicity of three carrier solvents to zebrafish (Danio rerio) embryos

The present study examines the effects of ethanol (ETOH), dimethyl sulfoxide (DMSO), and acetone on zebrafish embryos and the implications of the observed results on the use of these solvents to zebrafish early life stage tests. The embryos were exposed to different concentrations (0.0, 0.0001, 0.001, 0.01, 0.1, 0.05, 1, 1.5, and 2.0% v/v) of the respective solvents by diluting reagent-grade solvent with reconstituted water [DIN 38415-6-Suborganismische Testverfahren (Gruppe T) Teil 6: Giftigkeit gegenüber Fischen. Deutsches Institute für Normung e.V]. The following endpoints were investigated (mortality, hatching rate, abnormalities, heart rate, and hsp 70 induction). No effect on survival was recorded for both acetone and DMSO even up to the highest concentration. On the other hand, embryos exposed to 1.5% and 2.0% ethanol showed a significant reduction in survival rate. No developmental defects occurred with any of the solvents at the 0.1% concentration. However, starting with 1.0%, weak to very pronounced abnormalities (weak pigmentation, edema, crooked bodies, eye defect, tail defect, reduced heartbeat, and abnormal hatching) were observed depending on the solvent type and the concentration used. Ethanol has been shown to be the most embryotoxic solvent while DMSO and acetone have comparably lesser effects. Heat shock protein 70 was induced by all solvents but at different concentration ranges. DMSO has been shown to be the most potent inducer of stress proteins. Based on the study, the chemicals tested here may be used as carrier solvents in the zebrafish embryo assay at levels below 1.5, 1.5, and 1% v/v for acetone, DMSO, and ethanol, respectively. For stress protein analysis of the exposed embryos, however, the solvent levels should be below 0.1%, 0.01%, and 1.5%, respectively. Additional and separate investigations utilizing other biomarkers should be carried out to further validate the suitability of using these solvents in a typical zebrafish embryo assay.