Teratogenicity assay in the zebrafish alternative model under the ICH S5 (R3) Guideline on reproductive toxicology perspective

By 2035 the American Environmental Protection Agency (EPA) aims to eliminate all mammal studies requests and funding. The current ICH S5 (R3) Guideline on reproductive toxicology for novel compounds supports the use of alternative models for animal testing in an attempt to comply with the 3Rs principle in which a Reduction, Refinement, and Replacement of animals are sought. 

The zebrafish embryo model is widely used in reproductive and developmental toxicity studies because it offers an ethical alternative to the use of mammals and provides a good throughput at a small scale but with complexity of a whole organ.

The ICH S5 (R3) Guideline includes a compound list that serves as a reference for the developmental toxicity in a rodent animal model. Our aim has therefore been to pursue the correlation of this reproductive toxicity in the zebrafish embryo model with regards to this reference Compound List.  

To do this, potential morphological alterations of zebrafish embryos treated with these compounds were analyzed at two different stages establishing a teratogenic index (TI) based on the ratio between LC50/EC50. Out of the 29 teratogenic compounds included in the list, 5 of them showed study limitations such as poor water solubility or acidification, and 1 showed no teratogenicity in this animal model. The 3 negative controls included in this guidance also showed to be not teratogenic for the zebrafish embryos. 

In summary, although further replicates to reproduce this work are needed to improve its reproducibility, these promising results show a zebrafish animal model for teratogenicity with a Sensitivity close to 80% and a Specificity of 100%. Further work is also needed to evaluate the internal concentration of these chemicals inside the zebrafish embryos and compare the results with the mammalian exposures provided in the ICH S5 (R3) guide to determine the ability of this assay to predict mammalian embryotoxicity exposure. This would allow using the zebrafish teratogenicity assay in the circumstances mentioned on the updated Guideline version to complement or even substitute current mammalian teratogenicity assays for positive compounds.

Presenter: Roberto Henan (Biobide)

Dr. Hernan holds the position of Business Development Manager at Biobide, a leading Contract Research Organization (CRO) in the field of zebrafish animal model that helps predicting the toxicity and efficacy of novel compounds. Dr. Hernan has previous experience as an entrepreneur in several biotech companies including a startup company working in zebrafish named ZFbiotox where he held the position of Chief Scientific Officer. He graduated in 1993 with a bachelor´s degree in biology at the University of Basque Country (Spain). Shortly after, he worked in UK and USA for 6 years and in 2005 he obtained a Ph.D. researching on tumors of the Central Nervous System (CNS) under the University of Newcastle Upon Tyne, UK.