A systems toxicological analysis of oxybenzone effects on the metabolic physiology of embryo-larval zebrafish (Danio rerio)

Oxybenzone is an emerging aquatic pollutant whose widespread use has contributed to its detection in the surface waters and body-burdens of exposed biota. In this study, the sub-lethal toxicity effects of oxybenzone were studied at the environmentally relevant concentrations of 0.6 and 5.2 µg/L (including 0.01% DMSO as the solvent control). An integrative in vivo and in silico experimental approach was taken to study the effects of exposure on the metabolic physiology of larval zebrafish (Danio rerio) after 7 days of exposure (from 2 to 9 days post fertilization). The use of whole-organism respirometry showed a statistically significant ∼2x increase in metabolic rate for the 0.6 µg/L treatment group, with no significant differences between the solvent control versus 5.2 µg/L oxybenzone treatment level. The analysis of whole-transcriptome RNA-sequencing data showed functional categories related to metabolism (metabolic enzymes) and biological regulation (genome regulation, cell signaling) to be highly dysregulated. The transcriptomics changes for metabolic enzyme genes were used to parameterize in silico stoichiometric metabolic models for each treatment group. Flux balance analysis (FBA) simulations for each metabolic model revealed glycerolipid metabolism to be highly affected under the low dose oxybenzone exposure. The further analysis of core metabolic pathways revealed elevated flux through the esterification reactions of glycerolipid metabolism, producing triglycerides. The elevated in vivo metabolic rate observed for 0.6 µg/L oxybenzone is explainable by the elevated catalytic activities of the esterification reactions. Furthermore, the disruption of glycerolipid metabolism predicted by our in silico analysis agrees with the results of non-targeted metabolomics studies performed by other authors, and which demonstrate oxybenzone exposure to cause dyslipidemia and affect glycerophospholipid metabolism. Therefore, the methods of our study provide a framework for integrated biological pathways-based toxicological analysis.