(P11-043-23) High 5-Methyltetrahydrofolate Concentrations Impair Glucose-Stimulated Insulin Secretion in a Pancreatic Islet Cell Line

Objectives: Many pregnant individuals consume folic acid, the synthetic form of folate, at higher levels than recommended. This may be of concern given higher maternal folate levels during pregnancy are associated with metabolic dysfunction in offspring, and divergent evidence exists on the relationship between folic acid supplementation and gestational diabetes. The mechanisms mediating these effects are not understood. The objective of this study is to determine how folate impacts insulin secretion by islets.

Methods: Murine insulinoma cells (MIN6), a pancreatic islet cell line, were treated with folic acid-free RPMI for 3 days to deplete intracellular folates. The cells were then incubated with folic acid or 5-methyltetrahydrofolate (5MTHF, circulating form of folate) for 24 hours at levels (in μM) ranging from murine physiological (0.16), intermediary (0.8, 6.4), to supraphysiological (20) levels. Cell proliferation was assessed by MTT assays, and glucose-stimulated insulin secretion (GSIS) in response to low (2 mM) vs high (20 mM) glucose, and insulin stimulatory conditions (40 mM KCl), were conducted.

Results: Folic acid depletion decreased (p < 0.001) cell proliferation. Following depletion and acute folate replacement, greater proliferation was observed in cells incubated with 5MTHF vs folic acid (p = 0.059); no effect of dose was observed. Under high glucose conditions, cells treated with 5MTHF at high levels (6.4 or 20 μM) secreted lower (p < 0.05) insulin compared to those treated with 0.16 μM, indicating impaired GSIS. A similar effect of folic acid was observed but at a lower concentration where cells treated with 0.8 and 6.4 μM folic acid had lower insulin secretion compared to those treated with 0.16 μM (p < 0.01). Both forms of folate affected KCl-induced insulin secretion. Cells treated with moderate or high folic acid or 5MTHF (0.8, 6.4 or 20 μM) secreted less (p < 0.05) insulin than those treated with 0.16 μM folic acid or 5MTHF, respectively. Folic acid treated cells released more (p < 0.001) insulin than 5-MTHF treated cells under KCl stimulation. 

Conclusions: High folate concentrations perturb GSIS and stimulatory insulin release in MIN6 cells. These finding suggest high folate may impact beta-cell insulin production.

Funding Sources: Canadian Institutes of Health Research