Dysregulatory effects of retinoic acid isomers in late zebrafish embryos

Dysregulation of lipid metabolism in PLHC-1 and ZFL cells exposed to tributyltin an all-trans retinoic acid

There is increasing awareness that exposure to endocrine disrupters interferes with lipid homeostasis in vertebrates, including fish. Many of these compounds exert their action by binding to nuclear receptors, such as peroxisome proliferator-activated receptors and retinoid X receptor. This work investigates the use of fish liver cells (PLHC-1 and ZFL cells) for the screening of metabolic and lipid disrupters in the aquatic environment by assessing changes in the cell's lipidome after exposure to the model compounds, tributyltin chloride and all-trans retinoic acid. Lipid extracts, analyzed by FIA-ESI (+/-) Orbitrap, evidenced the intracellular accumulation of triglycerides and diglycerides in both cell models after exposure to 100 and 200 nM tributyltin chloride for 24 h. Exposure to 1 μM all-trans retinoic acid led to a significant accumulation of triglycerides in PLHC-1 cells, while few triglycerides were accumulated in ZFL cells. Retinoic acid (cyp26b1, cyp3a65, lrata) and lipid metabolism (fasn, scd, elovl6) related genes were up-regulated by tributyltin chloride and all-trans retinoic acid, while only all-trans retinoic acid down-regulated the expression of dgat1a. The two cell models show sensitivity and responses to tributyltin chloride and all-trans retinoic acid comparable to those previously reported in mammalian cells. These results support the use of fish liver cells as alternative models for the detection of contaminants that act as lipid disrupters in the aquatic environment.

Neurobehavioral effects of cyanobacterial biomass field extracts on zebrafish embryos and potential role of retinoids

Cyanobacteria are known for their ability to produce and release mixtures of up to thousands of compounds into the environment. Recently, the production of novel metabolites, retinoids, was reported for some cyanobacterial species along with teratogenic effects of samples containing these compounds. Retinoids are natural endogenous substances derived from vitamin A that play a crucial role in early vertebrate development. Disruption of retinoid signalling- especially during the early development of the nervous system- might lead to major malfunctions and malformations. In this study, the toxicity of cyanobacterial biomass samples from the field containing retinoids was characterized by in vivo and in vitro bioassays with a focus on the potential hazards towards nervous system development and function. Additionally, in order to identify the compounds responsible for the observed in vitro and in vivo effects the complex cyanobacterial extracts were fractionated (C18 column, water-methanol gradient) and the twelve obtained fractions were tested in bioassays. In all bioassays, all-trans retinoic acid (ATRA) was tested along with the environmental samples as a positive control. Retinoid-like activity (mediated via the retinoic acid receptor, RAR) was measured in the transgenic cell line p19/A15. The in vitro assay showed retinoid-like activity by specific interaction with RAR for the biomass samples. Neurotoxic effects of selected samples were studied on zebrafish (Danio rerio) embryos using the light/dark transition test (Viewpoint, ZebraLab system) with 120 hpf larvae. In the behavioural assay, the cyanobacterial extracts caused significant hyperactivity in zebrafish at 120 hpf after acute exposure (3 h prior to the measurement) at concentrations below the teratogenicity LOEC (0.2 g dw L^-1). Similar effect was observed after exposure to fractions of the extracts with detected retinoid-like activity and additive effect was observed after combining the fractions. However, the effect on behaviour was not observed after exposure to ATRA only. To provide additional insight into the behavioural effects and describe the underlying mechanism gene expression of selected biomarkers was measured. We evaluated an array of 28 genes related to general toxicity, neurodevelopment, retinoid and thyroid signalling. We detected several affected genes, most notably, the Cyp26 enzymes that control endogenous ATRA concentration, which documents an effect on retinoid signalling.

Dose-dependent transcriptomic responses of zebrafish eleutheroembryos to Bisphenol A

Despite the abundant literature on the adverse effects of Bisphenol A (BPA) as endocrine disruptor, its toxicity mechanisms are still poorly understood. We present here a study of its effects on the zebrafish eleutheroembryo transcriptome at concentrations ranging from 0.1 to 4 mg L^-1, this latter representing the lowest observed effect concentration (LOEC) found in our study at three different macroscopical endpoints (survival, hatching and swim bladder inflation). Multivariate data analysis methods identified both monotonic and bi-phasic patterns of dose-dependent responses. Functional analyses of genes affected by BPA exposure suggest an interaction of BPA with different signaling pathways, being the estrogenic and retinoid receptors two likely targets. In addition, we identified an apparently unrelated inhibitory effect on, among others, visual function genes. We interpret our data as the result of a sum of underlying, independent molecular mechanisms occurring simultaneously at the exposed animals, well below the macroscopic LOEC, but related to at least some of the observed morphological alterations, particularly in eye size and yolk sac resorption. Our data supports the idea that the physiological effects of BPA cannot be only explained by its rather weak interaction with the estrogen receptor, and that multivariate analyses are required to analyze the effects of toxicants like BPA, which interact with different cellular targets producing complex phenotypes.