Excess folic acid supplementation impairs placental development and alters tryptophan metabolism in a mouse model of diabetes in pregnancy

Background: The relationship between excess folic acid supplementation and gestational diabetes (GDM) risk is unclear, with observational studies reporting both increased and decreased risk. While supplementation with 0.4 mg folic acid/day is recommended to prevent neural tube defects, high-risk women, including those with obesity (BMI≥30 kg/m2), may supplement with up to 10x this amount. In a C57BL/6J model of diet-induced GDM, we previously identified sex-dependent effects of excess folic acid supplementation on offspring metabolic health. The mechanisms underlying these outcomes are unclear but may involve effects of folic acid intake and/or GDM on placental development. The objective of my thesis was to determine the effect of maternal excess folic supplementation in GDM on placental development and maternal metabolism. Methods: Female C57BL/6J mice were fed a control (10% kcal fat; CD) or Western diet (45% kcal fat; WD), with (10 mg/kg diet) or without (2 mg/kg diet) supplemental folic acid for 8-10 weeks prior to mating with males fed the unsupplemented CD. The WD induced a phenotype modelling obesity and glucose intolerance before and during pregnancy resulting in a metabolic state that resembles key features of gestational diabetes mellitus (GDM). At embryonic day (ED) 18.5, male and female placentas were collected for morphology, vascular density (CD31+ staining), and metabolic gene expression analyses (NanoString) (n=6/sex/group). Maternal serum and hepatic kynurenine metabolite concentrations were quantified at ED18.5, and hepatic SLC7A5 protein expression was assessed by Western blot. Results: Both folic acid supplementation (p<0.05) and GDM (p<0.05) independently reduced labyrinth zone area and vascular density in male placentas, while female placentas were unaffected. Placental mRNA expression of 3-hydroxyanthranilate 3,4-dioxygenase (Haao) was increased in male offspring from supplemented dams (p<0.05). In GDM dams, folic acid supplementation increased hepatic kynurenine concentrations (p<0.05), whereas GDM alone reduced hepatic SLC7A5 expression (p<0.05). Conclusion: Excess maternal folic acid supplementation interacts with GDM to alter placental development, in a sex-dependent manner, and maternal metabolism. These findings suggest that maternal folate status modulates placental adaptation to metabolic stress, with implications for fetal development and long-term offspring metabolic health.