Fertilized Avian Egg Fetal Liver Assays for Assessing DNA Damaging Potential of Chemicals: A Comparative Analysis...

The ability to produce direct DNA damage (genotoxicity), which underlies the carcinogenicity of various chemicals, is typically evaluated in a regulatory-approved battery of in vitro tests with potential in vivo follow-up. Growing concerns for animal welfare and implementation of regulations restricting the use of animal testing necessitate the introduction of New Approach Methodologies (NAMs). The avian egg-based (in ovo) models were developed as metabolically competent NAMs capable of bioactivation, detoxication, and elimination of xenobiotics to potentially replace short-term in vivo genotoxicity assays for chemicals that are genotoxic in vitro. These models utilize avian (chicken or turkey) fetal livers for the evaluation of endpoints indicative of DNA damage produced by either direct or indirect mechanisms, the formation of nuclear DNA adducts and strand breaks. Avian embryos have genetic and morphologic resemblance to mammals and can be used for the evaluation of other endpoints including histopathology and genomic profiling. A concordance analysis of 87 and 59 chemicals assessed in the chicken and turkey models, respectively, revealed a stronger correlation with the results from in vivo genotoxicity assays (76% and 67% sensitivity, 79% and 72% specificity for chicken and turkey, respectively) compared to in vitro assays (58% and 56% sensitivity, 45% and 63% specificity for chicken and turkey, respectively). These results demonstrate that in ovo models detect the genotoxic potential of a broader range of compounds compared to in vitro assays with S9 supplementation. In conclusion, fertilized avian egg fetal liver assays offer a promising alternative to traditional in vivo genotoxicity assays.