Importance of gestational hypoglycaemia for foetal malformations and skeletal development in rats

Prolonged insulin-induced hypoglycaemia reduces ß-cell activity rather than number in pancreatic islets in non-diabetic rats

Pancreatic β-cells have an extraordinary ability to adapt to acute fluctuations in glucose levels by rapid changing insulin production to meet metabolic needs. Although acute changes have been characterised, effects of prolonged metabolic stress on β-cell dynamics are still unclear. Here, the aim was to investigate pancreatic β-cell dynamics and function during and after prolonged hypoglycaemia. Hypoglycaemia was induced in male and female rats by infusion of human insulin for 8 weeks, followed by a 4-week infusion-free recovery period. Animals were euthanized after 4 or 8 weeks of infusion, and either 2 days and 4 weeks after infusion-stop. Total volumes of pancreatic islets and β-cell nuclei, islet insulin and glucagon content, and plasma c-peptide levels were quantified. Prolonged hypoglycaemia reduced c-peptide levels, islet volume and almost depleted islet insulin. Relative β-cell nuclei: total pancreas volume decreased, while being unchanged relative to islet volume. Glucagon: total pancreas volume decreased during hypoglycaemia, whereas glucagon: islet volume increased. Within two days after infusion-stop, plasma glucose and c-peptide levels normalised and all remaining parameters were fully reversed after 4 weeks. In conclusion, our findings indicate that prolonged hypoglycaemia inactivates β-cells, which can rapidly be reactivated when needed, demonstrating the high plasticity of β-cells even following prolonged suppression.

Disruption of Fetal Eye Development Caused by Insulin-induced Maternal Hypoglycemia in Rats

We previously revealed that insulin-induced severe and long-lasting maternal hypoglycemia in rats caused anophthalmia and microphthalmia in fetuses; however, it remained unclear whether hypoglycemia-induced eye anomalies were developmental retardation or disruption, and when and how they developed. Hence, we induced hypoglycemia in pregnant Sprague-Dawley rats by injecting insulin from Days 6 to 11 of pregnancy and performed periodical histopathological examination of fetal eyes from embryonic days (E)10 to 20. On E10, optic vesicle had developed normally both in the control and insulin-treated group; however, on E11, optic cup (OC) had developed in the control group but not in the insulin-treated group. On E12, neural retina (NR), retinal pigmented epithelium (RPE), lens, and presumptive cornea had been observed in the control group. In contrast, lens pit and OC with remaining space between RPE and NR had developed in the insulin-treated group. From E13 to E15, developmental disruption characterized by defects, hypoplasia, and degeneration in the retina, lens, and cornea was observed in the insulin-treated group, resulting in anophthalmia or microphthalmia on E20. Moreover, the expression of MITF and chx10, which are essential for early eye development by expressing in the presumptive retina and lens and regulating each other's expression level, was ectopic and suppressed on E11. In conclusion, insulin-induced maternal hypoglycemia caused developmental disruption, but not simple developmental retardation of fetal eyes, and its trigger might be a failure of presumptive retina and lens to interact on E11.

Placental nutrient transporters adapt during persistent maternal hypoglycaemia in rats

Maternal malnutrition is associated with decreased nutrient transfer to the foetus, which may lead to foetal growth restriction, predisposing children to a variety of diseases. However, regulation of placental nutrient transfer during decreased nutrient availability is not fully understood. In the present study, the aim was to investigate changes in levels of placental nutrient transporters accompanying maternal hypoglycaemia following different durations and stages of gestation in rats. Maternal hypoglycaemia was induced by insulin-infusion throughout gestation until gestation day (GD)20 or until end of organogenesis (GD17), with sacrifice on GD17 or GD20. Protein levels of placental glucose transporters GLUT1 (45/55 kDa isotypes) and GLUT3, amino acid transporters SNAT1 and SNAT2, and insulin receptor (InsR) were assessed. On GD17, GLUT1-45, GLUT3, and SNAT1 levels were increased and InsR levels decreased versus controls. On GD20, following hypoglycaemia throughout gestation, GLUT3 levels were increased, GLUT1-55 showed the same trend. After cessation of hypoglycaemia at end of organogenesis, GLUT1-55, GLUT3, and InsR levels were increased versus controls, whereas SNAT1 levels were decreased. The increases in levels of placental nutrient transporters seen during maternal hypoglycaemia and hyperinsulinemia likely reflect an adaptive response to optimise foetal nutrient supply and development during limited availability of glucose.

Effects of glucokinase activator, DS-7309, on embryo-fetal developmental toxicity in rats and rabbits

The toxicological effects of DS-7309, a glucokinase activator, on pregnancy and embryo-fetal development in rats and rabbits and maternal blood glucose levels were examined. DS-7309 was administered at 3, 10, or 100 mg/kg to rats from Days 7-17 of pregnancy or at 10, 30, or 100 mg/kg to rabbits from Days 6-18 of pregnancy. In rats, maternal hypoglycemia (approximately 50 mg/dL) was seen at 3 and 10 mg/kg, but it recovered 7 h after dosing, leading to no toxic changes. In contrast, continuous severe maternal hypoglycemia (approximately 40 mg/dL, ≥7 h), fetal eye anomalies, and decreased fetal body weight were noted at 100 mg/kg. In rabbits, no fetal anomalies were seen at 10 and 30 mg/kg where maternal blood glucose level dropped to approximately 60-90 mg/dL, but recovered by 7 h after dosing at the latest. In contrast, at 100 mg/kg, severe hypoglycemia (around 60 mg/dL) was maintained and did not recover until 24 h after dosing; it resulted in decreased fetal viability and increased fetal skeleton anomalies. These findings indicate that DS-7309 could lead to embryo-fetal toxicity in rats and rabbits, with such toxicity considered to be related to continuous severe maternal hypoglycemia.

Inner histopathologic changes and disproportionate zone volumes in foetal growth plates following gestational hypoglycaemia in rats

Maternal hypoglycaemia throughout gestation until gestation day (GD)20 delays foetal growth and skeletal development. While partially prevented by return to normoglycaemia after completed organogenesis (GD17), underlying mechanisms are not fully understood. Here, we investigated the pathogenesis of these changes and significance of maternal hypoglycaemia extending beyond organogenesis in non-diabetic rats. Pregnant rats received insulin-infusion until GD20 or GD17, with sacrifice on GD20. Hypoglycaemia throughout gestation increased maternal corticosterone levels, which correlated with foetal levels. Growth plates displayed central histopathologic changes comprising disrupted cellular organisation, hypertrophic chondrocytes, and decreased cellular density; expression of pro-angiogenic factors, HIF-1α and VEGF-A increased in surrounding areas. Disproportionately decreased growth plate zone volumes and lower expression of the structural protein MATN-3 were seen, while bone ossification parameters were normal. Ending maternal/foetal hypoglycaemia on GD17 reduced incidence and severity of histopathologic changes and with normal growth plate volume. Compromised foetal skeletal development following maternal hypoglycaemia throughout gestation is hypothesised to result from corticosterone-induced hypoxia in growth plates, where hypoxia disrupts chondrocyte maturation and growth plate structure and volume, decreasing long bone growth. Maternal/foetal hypoglycaemia lasting only until GD17 attenuated these changes, suggesting a pivotal role of glucose in growth plate development.