An assay to determine the sensitive window of embryos to chemical exposure usingXenopus tropicalis

Microscopic photoplethysmography-based evaluation of cardiotoxicity in whitefish larvae induced by acute exposure to cadmium and phenol

Toxic environmental pollutants pose a health risk for both humans and animals. Accumulation of industrial contaminants in freshwater fish may become a significant threat to biodiversity. Comprehensive monitoring of the impact of environmental stressors on fish functional systems is important and use of non-invasive tools that can detect the presence of these toxicants in vivo is desirable. The blood circulatory system, by virtue of its sensitivity to the external stimuli, could be an informative indicator of chemical exposure. In this study, microscopic photoplethysmography-based approach was used to investigate the cardiac activity in broad whitefish larvae (Coregonus nasus) under acute exposure to cadmium and phenol. We identified contamination-induced abnormalities in the rhythms of the ventricle and atrium. Our results allow introducing additional endpoints to evaluate the cardiac dysfunction in fish larvae and contribute to the non-invasive evaluation of the toxic effects of industrial pollutants on bioaccumulation and aquatic life.

Cadmium significantly changes major morphometrical points and cardiovascular functional parameters during early development of zebrafish

Living organisms are commonly exposed to cadmium and other toxic metals. A vast body of research has shown the significant effects of these toxic metals on developmental processes. In order to study the role of toxic metals on early developmental stages of eukaryotes, we explored the effect of cadmium (Cd²⁺) contaminant on zebrafish. Thus, zebrafish embryos were exposed to 3 mg/L (16.7 μM) Cd²⁺ for 96 h and imaged every 24 h from the exposure onwards. Hatching rates of the eggs were determined at 72 h, followed by analyses at 96 h for: survival rate, morphometrical factors, and functional parameters of the cardiovascular system. Interestingly enough, significant hatching delays along with smaller cephalic region and some morphological abnormalities were observed in the treatment group. Moreover, substantial changes were noticed in the length of notochord and embryo, absorption of yolk sac with shorter extension, area of swimming bladder, as well as pericardium sac after Cd²⁺ treatment. Cadmium also caused significant abnormalities in heart physiology which could be the leading cause of mentioned morphological deformities. Herein, our results shine light on systematic acute embryological effects of cadmium in the early development of zebrafish for the first time.

Evaluation of the potential teratogenic and toxic effect of the herbicide 2,4-D (DMA® 806) in bullfrog embryos and tadpoles (Lithobates catesbeianus)

The objective of this work was to evaluate the potential teratogenic and toxic effect of the herbicide 2,4-D (DMA® 806) on bullfrog embryos and tadpoles (Lithobates catesbeianus). We used the FETAX (Frog Embryo Teratogenesis Assay Xenopus) assay for embryos, and for tadpoles, we used acute (96 h) and chronic (49 days) toxicity tests and evaluated aspects of healthiness, hematology, and histopathology. The LC_50-144h (Median Lethal Concentration), EC_50-144h (Median Effective Concentration), MCIG (Minimum Concentration to Inhibit Growth) and TI (Teratogenic Index) for embryos were 792 mg/L, 593 mg/L, 150 mg/L of 2,4-D (DMA) and 1.34, respectively. For tadpoles, the LC_50-96h was 700 mg/L of 2,4-D (DMA) and chronic test indicated an inflammatory process and erythrocytosis (with possible polycythemia), with consequent reduction of the spleen. This demonstrates physiological stress probably due to dehydration, which can be proven by the gill tufts widening intercellular space and gill tuft fusions. We also found injuries to the kidneys and skin of the animals even in the lowest concentration tested. Our results indicated that this pesticide is minimally teratogenic and has a low toxicity on L. catesbeianus embryos and tadpoles, but it can inhibit embryo growth in concentrations lower than those tested in this study. We hypothesized that the herbicide 2,4-D (DMA® 806) may be a respiratory allergen for L. catesbeianus tadpoles and recommend precautionary measures for prolonged exposure of aquatic organisms to this pesticide.

The unexpected teratogenicity of RXR antagonist UVI3003 via activation of PPARγ in Xenopus tropicalis

The RXR agonist (triphenyltin, TPT) and the RXR antagonist (UVI3003) both show teratogenicity and, unexpectedly, induce similar malformations in Xenopus tropicalis embryos. In the present study, we exposed X. tropicalis embryos to UVI3003 in seven specific developmental windows and identified changes in gene expression. We further measured the ability of UVI3003 to activate Xenopus RXRα (xRXRα) and PPARγ (xPPARγ) in vitro and in vivo. We found that UVI3003 activated xPPARγ either in Cos7 cells (in vitro) or Xenopus embryos (in vivo). UVI3003 did not significantly activate human or mouse PPARγ in vitro; therefore, the activation of Xenopus PPARγ by UVI3003 is novel. The ability of UVI3003 to activate xPPARγ explains why UVI3003 and TPT yield similar phenotypes in Xenopus embryos. Our results indicate that activating PPARγ leads to teratogenic effects in Xenopus embryos. More generally, we infer that chemicals known to specifically modulate mammalian nuclear hormone receptors cannot be assumed to have the same activity in non-mammalian species, such as Xenopus. Rather they must be tested for activity and specificity on receptors of the species in question to avoid making inappropriate conclusions.