In vitro cultured embryos have significantly poorer development than their in vivo counterparts, developing more slowly and fewer reaching the blastocyst stage. In vitro culture of preimplantation embryos alters their metabolism, increases ATP production and reduces pyruvate oxidation. This study used LC/MS to measure metabolite concentrations in pre-implantation cultured embryos compared to fresh embryos. Expression of genes involved in redox signalling pathways were examined by RT-qPCR to determine if any differences in metabolites were correlated to changes in gene expression.
In vitro embryo culture caused changes in metabolite concentrations at all stages of development, with 25-45% of detected metabolites being significantly altered, with the largest alterations occurring post-compaction embryos. Metabolite concentrations affected by in vitro culture included common amino acids. Concentrations of essential amino acids were decreased or maintained, with maintenance potentially occurring via autophagy. Non-essential amino acids concentrations were increased in vitro presumably due to endogenous upregulation of production resulting from activation of the amino acid response pathway. There were also changes in concentrations of metabolites involved in the pentose phosphate pathway, glucose metabolism and the TCA cycle.
In vitro culture also caused a downregulation of genes critical in redox regulation and GSH production suggesting oxidative distress in in vitro cultured embryos.
These results highlight the significant physiological differences between in vivo and in vitro developed embryos, indicating that the in vivo environment is not fully mimicked in vitro. These results highlight the need for improvement in embryo culture media to improve the success of in vitro embryo production.