404. Repercussions of a transient decrease in pH on embryo viability and subsequent fetal development

Abstract

Changes in the environment to which the preimplantation embryo is exposed can significantly influence fetal outcomes, indicative of ‘embryo programming'. Although many previous in vitro stress models have demonstrated programming changes using high dose stress effects, it is possible to induce similar effects with a physiologically relevant stress model. This study investigates the effect of a subtle transient pH change, during the first cleavage division, on blastocyst viability and fetal outcomes after embryo transfer. Zygotes from F1 hybrid mice (C57BL6xCBA F1) were cultured to the 2-cell stage (19h) in either control G1 medium or in G1 containing a weak acid, 2 mM DMO (5,5-Dimethyl-2,4-oxazolidinedione), then cultured to the blastocyst stage in control media G1/G2 (72h). Exposure to DMO induced a decrease in intracellular pH from 7.25 (control) to 7.10 (DMO). At the blastocyst stage, inner cell mass (ICM) cell number and cellular apoptosis were assessed, or embryos were transferred to pseudopregnant recipients to assess implantation and fetal outcomes. Differences were assessed using Student's t-test or generalised linear modelling followed by post-hoc tests. Exposure to DMO during the first cleavage division significantly reduced total blastocyst cell number from 83.0 ± 6.4 to 63.6 ± 3.8 (P < 0.05), reduced ICM number from 30.6 ± 3.6 to 20.2 ± 1.8 (P < 0.05) and significantly increased the apoptotic cell index from 1.9% to 3.2% (for control verses DMO embryos respectively) (P < 0.05). Blastocyst development was unchanged. Exposure to DMO during the first cleavage division did not alter implantation rates however fetal weight was decreased from 1058.9 mg ± 25.2 (control) to 949.1 mg ± 26.7 (DMO) (P < 0.05) and crown–rump length decreased from 21.9 mm ± 0.4 (control) to 20.6 mm ± 0.5 (DMO) (P < 0.05). In conclusion, this study demonstrates that a transient reduction in pH of only 0.15 units during early preimplantation embryo development significantly reduces resultant blastocyst viability and perturbs fetal growth, indicative of altered embryo programming. The mechanism behind this permanent change however is currently unknown.