Adult health can be programmed by conceptus adaptations to environmental conditions during pre-implantation development. During IVF the embryo is exposed to conditions which may impact viability including temperature and toxin build-up (e.g. ammonium). Ammonium levels can increase in culture media due to deamination of amino-acids, decreasing embryo quality, implantation and fetal development, however its impact on offspring health is unknown. Therefore the aim of this study was to investigate the impact of ammonium exposure on offspring phenotype.
Zygotes from CBAF1 mice were cultured in sequential media ± 300µM ammonium. Blastocysts were transferred to recipient mothers. From d18 of pregnancy, females were housed individually and monitored for live birth. Pups were tattooed on d3 for tracking and weighed on d3 to d21. At d21, pups were sexed, weaned and weighed weekly until 17weeks when post mortems were performed.
Exposure to 300µM ammonium significantly decreased embryo viability, with reductions in viable offspring/embryo transferred (46% vs. 36%, p<0.05). Ammonium exposure increased female pre-weaning weights at d14 (6.8g±0.4 vs. 7.9g±0.4) and d21 (8.2g±0.5 vs. 9.7g±0.6, p>0.05) and this difference was maintained until 5 weeks of age. Although no change in weight was seen by 17 weeks, post mortem analysis revealed female mice had significantly increased retro-peritoneal and gonadal fat deposits and increased total adipose tissue, both in mass (0.59g±0.8 vs. 0.92g±0.9) and percentage body weight (2.6%±0.3 vs. 3.9±0.5, p<0.01). No difference was seen in male weight however male mice exposed to ammonium showed signs of insulin resistance, evidenced by a decreased AUC after ITT (p<0.05).
Exposure to ammonium throughout embryo development results in female offspring with increased adipose accumulation and male offspring with early evidence of insulin resistance. This demonstrates how the preimplantation environment influences offspring phenotype and that culture media used in IVF should contain stable forms of amino-acids to minimise ammonium build-up.