Placental Inositol Reduced in Gestational Diabetes as Glucose Alters Inositol Transporters and IMPA1 Enzyme Expression.

Abstract

Perturbed inositol physiology in insulin-resistant conditions has led to proposals of inositol supplementation for gestational diabetes (GDM) prevention, but placental inositol biology is poorly understood. Investigate associations of maternal glycemia with placental inositol content, determine glucose effects on placental expression of inositol enzymes and transporters, and examine relations with birthweight. Case-control study of placentae from term singleton pregnancies (GDM n = 24, non-GDM n = 26), and culture of another 9 placentae in different concentrations of glucose and myo-inositol for 48 hours. Placental inositol was quantified by the Megazyme assay. Relative expression of enzymes involved in myo-inositol metabolism and plasma membrane inositol transport was determined by quantitative RT-PCR and immunoblotting. Linear regression analyses were adjusted for maternal age, body mass index, ethnicity, gestational age, and sex. Placental inositol content was 17% lower in GDM compared with non-GDM. Higher maternal mid-gestation glycemia were associated with lower placental inositol. Increasing fasting glycemia was associated with lower protein levels of the myo-inositol synthesis enzyme, IMPA1, and the inositol transporters, SLC5A11 and SLC2A13, the expression of which also correlated with placental inositol content. In vitro, higher glucose concentrations reduced IMPA1 and SLC5A11 mRNA expression. Increasing fasting glycemia positively associated with customized birthweight percentile as expected in cases with low placental inositol, but this association was attenuated with high placental inositol. Glycemia-induced dysregulation of placental inositol synthesis and transport may be implicated in reduced placental inositol content in GDM, and this may in turn be permissive to accelerated fetal growth.