| Valproic acid (VPA) during pregnancy leads to congenital anomalies, possibly by disrupting folate metabolism. Mild deficiency of methylenetetrahydrofolate reductase (MTHFR), an enzyme of folate-dependent homocysteine metabolism, is common due to a polymorphism at bp 677, and may influence response to VPA. To examine interactions between VPA and MTHFR in vivo and in vitro, VPA-induced teratogenicity was studied in Mthfr -deficient mice, and the effects of VPA on MTHFR expression in HepG2 cells were investigated. Mthfr+/+ and Mthfr+/- pregnant mice were injected with VPA on gestational day 8.5; resorption rates and occurrence of neural tube defects (NTDs) were examined on gestational day 14.5. MTHFR expression in HepG2 cells was studied by promoter assays, quantitative RT-PCR and Western analysis. Mthfr+/+ mice had increased resorption rates (36%) after VPA treatment, compared to saline treatment (10%), whereas resorption rates were similar with Mthfr+/- mice with the 2 treatments (25-27%). NTDs were only observed in one group (VPA-treated Mthfr+/+). VPA increased activity of both MTHFR promoters (1.8- and 3.5-fold), and levels of MTHFR mRNA and protein (2.5- and 3.7-fold, respectively) in HepG2 cells. Consistent with MTHFR upregulation in vitro, plasma homocysteine decreased in mice one hour after VPA injection. VPA increases MTHFR expression and may have lower teratogenicity in MTHFR deficiency. These phenomena underscore the importance of folate interconversion in VPA teratogenicity. |
