Metformin and insulin exacerbate one-carbon metabolism deficits in pregnant growth restricted rats and impacts the placenta, fetal liver and pancreas.

Fetal growth restriction increases the risk of metabolic conditions such as gestational diabetes mellitus (GDM). One-carbon metabolite and nutrient concentrations are dysregulated in GDM and influenced by antihyperglycaemic medications. However, it remains unclear whether disrupted one-carbon metabolism contributes to GDM onset in growth restricted offspring and whether antihyperglycaemic medications exacerbate this dysregulation. We investigated the effects of growth restriction and antihyperglycaemic treatment on one-carbon metabolism in pregnant rats and their fetuses. Uteroplacental insufficiency (Restricted) or sham (Control) surgery was performed on embryonic day (E)18 in Wistar-Kyoto rats. Female F1 offspring were mated and Restricted dams received daily metformin, insulin or vehicle from E13. Although restricted dams did not develop metabolic dysfunction during pregnancy, they exhibited reduced one-carbon metabolism and a lower S-adenosylmethionine:S-adenosylhomocysteine (SAM:SAH) ratio, indicating reduced methylation capacity. These changes were exacerbated by both metformin and insulin. In F2 fetuses, plasma one-carbon metabolites were unaffected despite changes in expression of genes involved in one-carbon metabolism and DNA methylation in the placenta and fetal liver. F2 fetuses displayed an elevated pancreatic β-cell:islet ratio. Antihyperglycaemic medications altered the expression of multiple one-carbon metabolising enzymes in the maternal liver, the placenta junctional zone and the fetal liver. Metformin also increased pancreatic α-cell area. This study suggests disrupted one-carbon metabolism may underly programmed metabolic dysfunction and highlights the need for monitoring females born small. Both metformin and insulin induced similar physiological changes indicating that one is not safer than the other. Treatment decisions should consider potential impacts on long-term health. KEY POINTS: Being born growth restricted predisposes females to develop gestational diabetes (GDM) contributing to intergenerational transmission of disease. GDM is often treated with metformin or insulin. Disruptions to one-carbon metabolism caused by growth restriction, insulin or metformin may explain transmission of disease. This study investigated the effects of growth restriction, metformin and insulin on one-carbon metabolism and subsequent fetal outcomes in rats. Growth restriction impaired one-carbon metabolism in mothers resulting in a reduced S-adenosylmethionine:S-adenosylhomocysteine ratio, changes to expression of associated enzymes in the placenta and fetal liver and an increase in the fetal β-cell: pancreatic islet ratio. Metformin and insulin exacerbated deficits in one-carbon metabolism in growth restricted dams and their fetuses, whereas metformin also increased pancreatic α-cell area. This study demonstrates one-carbon metabolism as a key regulator of programmed metabolic disease in pregnancy and informs about the appropriate treatment of GDM in women born growth restricted.