Validation of a new protocol for a zebrafish MEFL (malformation or embryo-fetal lethality) test method that conforms to the ICH S5 (R3) guideline

Detecting the toxic effects of chemicals on reproduction and development without using mammalian animal models is crucial in the exploitation of pharmaceuticals for human use. Zebrafish are a promising animal model for investigating pharmacological effects and toxicity during vertebrate development. Several studies have suggested the use of zebrafish embryos for the assessment of malformations or embryo-fetal lethality (MEFL). However, a reproducible protocol as a standard for the zebrafish MEFL test method that fulfills global requests has not been established based on the International Council of Harmonisation (ICH) S5 (R3) guidelines. To establish such a toxicity test method, we developed a new and easy protocol to detect MEFL caused by chemicals, especially those with teratogenic potential, using fertilized zebrafish eggs (embryos) within 5 days of development. Our toxicity test trials using the same protocol in two to four different laboratories corroborated the high inter-laboratory reproducibility. Our test method enabled the detection of 18 out of 22 test compounds that induced rat MEFL. Thus, the prediction rate of our zebrafish test method for MEFL was almost 82% compared with that of rat MEFL. Collectively, our study proposes the establishment of an easy and reproducible protocol for the zebrafish MEFL test method for reproductive and developmental toxicity that meets ICH guideline S5 (R3), which can be further considered in combination with information from other sources for regulatory use.