Biochemical Studies to Understand Teratogenicity and Lethality Outcomes in Modified-FETAX

The frog embryo teratogenesis assay-Xenopus (FETAX) is a standardized test used to assess the toxic and teratogenic effects of xenobiotics. With this test, toxic and/or teratogenic concentrations of xenobiotic substances can be determined using morphological parameters such as lethality, length, and malformations in stage 8-11 Xenopus laevis embryos after 96 h exposure. These parameters enable the determination of the median lethal and effective concentrations (LC₅₀ and EC₅₀), minimum concentration to inhibit growth (MCIG), and teratogenic index of the tested chemical to reveal the short-term effects of relatively high concentrations. On the other hand, although FETAX provides quantitative and qualitative data on teratogenicity and toxicity, the biochemical and molecular mechanisms of these effects cannot be explained. Recent studies have tried to elucidate the mechanisms causing malformations and to explain the underlying causes of toxicity and teratogenicity by biochemical marker analysis. This chapter describes methods to analyze modified-FETAX and some detoxification and oxidative stress-related biomarkers during the early embryonic development of X. laevis.