Increased cell death in mouse blastocysts exposed to high D-glucose in vitro: implications of an oxidative stress and alterations in glucose metabolism.

AIMS/HYPOTHESIS: Signs of apoptosis have been observed in rodent blastocysts exposed to high d-glucose concentrations in vitro. The mechanism underlying the detrimental influence of glucose remains to be identified. It has been postulated that high d-glucose concentrations induced oxidative stress in rat post-implantation embryos in vitro. A decreased glucose uptake has also been implicated in the embryotoxicity of glucose in pre-implantation mouse embryos. We examined whether the high incidence of cell death in high d-glucose-treated embryos was associated with a disrupted redox status and with alterations in glucose transport and metabolism.
METHODS: After blastocysts were incubated in different concentrations of d-glucose for 24 h, they were examined for the proportion of nuclei showing signs of chromatin degradation using the TUNEL technique, for the generation of reactive oxygen species and for the mitochondrial membrane potential using specific fluoroprobes and the confocal microscopy. Glucose transport and metabolism were assessed using radiolabelled 3-O-methylglucose and glucose, respectively.
RESULTS: Compared to the control blastocysts, high d-glucose-treated embryos showed a higher incidence of TUNEL-positive nuclei and reactive oxygen species generation principally in the inner cell mass cells. Decreased glucose transport and glycolytic activity but unmodified pentose phosphate pathway activity were detected in these embryos. CONCLUSION/
INTERPRETATION: Incubation in high d-glucose concentrations in vitro increased cell death, induced oxidative stress and decreased glucose transport and metabolism in mouse blastocysts. As only glycolysis was affected, however, we suggest that metabolic inhibition occurred downstream glucose transport and glucose-6-phosphate formation.