Geometric Morphometrics as a Tool to Evaluate Teratogenic Effects in Zebrafish (Danio rerio)

Protocol of Geometric Morphometrics for Teratogenicity Testing

Geometric morphometrics (GM) enables a quantitative study of shapes and forms allowing the identification and characterization of teratogenic malformations. The GM methodology offers several advantages in comparison to traditional biometric methods, such as higher detail and precision analysis. In this chapter, we describe the recent application of the Procrustes method with ImageJ and MorphoJ programs in the characterization of developmental malformations. With this methodology, we are a step closer to being able to assign molecular pathways or unique signatures to a specific teratogen according to the produced phenotypes or to cluster unknown compounds.

Morphometric analysis of developing zebrafish embryos allows predicting teratogenicity modes of action in higher vertebrates

The early identification of teratogens in humans and animals is mandatory for drug discovery and development. Zebrafish has emerged as an alternative model to traditional preclinical models for predicting teratogenicity and other potential chemical-induced toxicity hazards. To prove its predictivity, we exposed zebrafish embryos from 0 to 96 h post fertilization to a battery of 31 compounds classified as teratogens or non-teratogens in mammals. The teratogenicity score was based on the measurement of 16 phenotypical parameters, namely heart edema, pigmentation, body length, eye size, yolk size, yolk sac edema, otic vesicle defects, otoliths defects, body axis defects, developmental delay, tail bending, scoliosis, lateral fins absence, hatching ratio, lower jaw malformations and tissue necrosis. Among the 31 compounds, 20 were detected as teratogens and 11 as non-teratogens, resulting in 94.44 % sensitivity, 90.91 % specificity and 87.10 % accuracy compared to rodents. These percentages decreased slightly when referred to humans, with 87.50 % sensitivity, 81.82 % specificity and 74.19 % accuracy, but allowed an increase in the prediction levels reported by rodents for the same compounds. Positive compounds showed a high correlation among teratogenic parameters, pointing out at general developmental delay as major cause to explain the physiological/morphological malformations. A more detailed analysis based on deviations from main trends revealed potential specific modes of action for some compounds such as retinoic acid, DEAB, ochratoxin A, haloperidol, warfarin, valproic acid, acetaminophen, dasatinib, imatinib, dexamethasone, 6-aminonicotinamide and bisphenol A. The high degree of predictivity and the possibility of applying mechanistic approaches makes zebrafish a powerful model for screening teratogenicity.

Embryonic exposure to environmentally relevant concentrations of triclosan impairs foraging efficiency in zebrafish larvae

The ubiquitous and persistent contaminant triclosan is known to cause developmental and behavioral toxicity in fish, but few studies have evaluated the long-term effects of these responses. We used a phenotypically anchored approach to evaluate the behavioral responses caused by early exposure to environmentally relevant concentrations of triclosan to better understand the risk triclosan poses to fish. Zebrafish were exposed to 0, 0.4, 4, or 40 μg triclosan/L (nominal concentrations) for 5 d followed by depuration for 16 d to assess effects on mortality, development, and foraging efficiency. Because foraging efficiency can be impacted by neurological and structural alterations, we assessed morphological and behavioral indicators of neurotoxicity and morphology of craniofacial features associated with gape to identify potential underlying mechanisms associated with altered foraging behaviors. To our knowledge, we are the first to show that early exposure to environmentally relevant concentrations of triclosan impairs foraging efficiency in larval fish by 10%, leading to emaciation and reduced growth and survival. The cause of the impacts of triclosan on foraging efficiency remains unknown, because effects were not associated with overt indicators of neurotoxicity or grossly malformed craniofacial structures. Our results suggest that early exposure to triclosan has the potential to impact the sustainability of wild fish populations, and thus the mechanism underlying behavioral alterations following exposure to triclosan warrants further study. Environ Toxicol Chem 2018;37:3124-3133. © 2018 SETAC.