Chicken embryo as animal model to study drug distribution to the developing brain

Rodent models are routinely used to assess the safety and developmental toxicity of pharmaceuticals, along with analysis of their distribution. These models require sacrifice of parent females, have challenges in the estimation of the number of embryos and stage of development, and are expensive and time-consuming. In this study, we used fertilized chicken eggs as an alternative model to address drug distribution to the developing brain of two antiepileptic drugs, valproic acid (VPA) and lamotrigine (LTG) at two developmental stages.

VPA or LTG was injected into the allantois of the egg on embryonic day 13 (E13) or E16. Whole chicken brains were harvested at time-points of 5 min to 24 h and the concentrations of the drugs determined using GC/MS and LC-MS/MS, for VPA and LTG, respectively.

VPA and LTG had distinct absorption and elimination phases and were found in the brain as early as 5-15 min after injection. Both drugs reached the brain in clinically relevant concentrations, with C_max 10-30% of the calculated concentration assuming uniform distribution throughout the egg. LTG concentrations were higher when injected at E13 compared to E16.

The chicken embryo model may be a suitable alternative animal model for preclinical drug distribution studies. It enables to easily approach antenatal development on an individual level, with a precise number of experimental animals, high reproducibility and low time and cost. Knowledge of the concentrations reaching the brain at different developmental stages with different drugs is important for the planning and interpretation of neurodevelopmental toxicity studies.