Quantitative prediction of teratogenicity based on teratogen concentrations in larvae of the zebrafish embryotoxicity test

Abstract

Zebrafish embryotoxicity test (ZET) is useful for the evaluation of teratogenic potential at the drug discovery stage, but it is limited to qualitative evaluation. Concentration-response relationship is ususually observed for survival and morphology scores of larvae in ZET; therefore, the present study was conducted with the hypothesis that an evaluation of teratogenic risk based on exposure levels would be possible.

We used already known rat teratogens to compare exposures (rCmax and rAUC) at the lowest-observed-adverse-effect-level in rats to the lowest-effect-concentration of formulations (zCOF) or the teratogen concentration in larvae (zCIL) in ZET. Fertilized eggs of zebrafish were continuously exposed to teratogen formulations from 5 hours post fertilization (hpf) to 120 hpf. On 120 hpf, morphological abnormalities of the larvae were scored and determined the positive concentrations. zCIL was measured by a high-performance liquid chromatography. zCOF or zCIL as zCmax was compared to rCmax, respectively. In addition, zAUC calculated from zCmax was also compared to rAUC.

As a result, the ratios of zCmax (zCOF or zCIL) to rCmax were almost ranging from10^-1 to 10¹-folds. Meanwhile, zAUC calculated from zCIL was almost equivalent to rAUC, indicating that the rAUC could be estimated with high predictability from the ZET results. This study suggests that ZET is a useful evaluation system that can accurately and quantitatively assess teratogenic risk at the drug discovery stage.