Metformin disrupts Danio rerio metabolism at environmentally relevant concentrations: A generational study

Abstract

Metformin (MET) is an anti-diabetic pharmaceutical with a large-scale consumption, which is increasingly detected in surface waters. However, current knowledge on the generational effects of MET exposure in the metabolism of non-target organisms is limited. The present study aimed at investigating the effects of MET in the model freshwater teleost Danio rerio, following a generational exposure (from egg up to 9 months exposure) to environmentally relevant concentrations ranging from 361 ng/L to 13 000 ng/L. Biochemical markers were used to determine cholesterol and triglycerides levels, as well as mitochondrial complex I activity in males and females zebrafish liver. mRNA transcript changes were also assessed in the liver of both sexes by means of an exploratory RNA-seq analysis and expression levels of key genes involved in the energy metabolism and lipid homeostasis, i.e. acaca, acadm, cox5aa, idh3a, hmgcra, prkaa1, were determined using qRT-PCR analysis. The findings here reported revealed that MET was able to significantly disrupt critical biochemical and molecular processes involved in zebrafish metabolism, such as cholesterol and fatty acid biosynthesis, the mitochondrial electron transport chain and the tricarboxylic acid cycle, concomitantly to changes on the hepatosomatic index. Non-monotonic dose response curves were frequently detected in the gene expression profile, with higher effects observed for 361 ng/L and 2 166 ng/L concentrations. Collectively, the obtained results suggest that environmentally relevant concentrations of MET are able to severely disrupt D. rerio metabolism, with potential impacts at the ecological level, supporting the need to update the environmental quality standard (EQS) and predicted no-effect concentration (PNEC) for MET.