Reduction in Valproic Acid–Induced Neural Tube Defects by Maternal Immune Stimulation: Role of Apoptosis

Abstract

Teratogenic deregulation of apoptosis during development is a possible mechanism for birth defects. Administration of valproic acid (VA) during first trimester of pregnancy causes neural tube defects (NTDs). Nonspecific stimulation of the mother's immune system has been shown to reduce various teratogen-induced fetal malformations including NTDs in rodents. This present study investigated the role of reduced apoptosis by maternal immune stimulation in prevention of VA-induced NTDs in CD-1 mice. Prevention of VA-induced NTDs by nonspecific maternal immune stimulation using IFNγ was employed to evaluate the role of reduced apoptosis by IFNγ in this protective mechanism. Apoptosis was quantified using flow cytometry. Terminal Transferase dUTP Nick End Labeling assay was used to localize the apoptosis. Increased apoptosis, suggesting involvement in VA teratogenicity, was observed along the neural tube in both normal and abnormal embryos from VA-exposed dams. Increased apoptosis in normal VA-exposed embryos suggests that VA may alter other cellular processes such as cell proliferation and differentiation in addition to apoptosis. Apoptotic levels in embryos with closed neural tubes from IFNγ + VA dams were similar to controls indicating resistance to VA-induced apoptosis and protection against teratogenicity of VA. In IFNγ + VA exposed embryos with open neural tubes, maternal immune stimulation failed to regulate apoptosis resulting in an NTD. Overall, these results suggest that VA alters several biological processes including apoptosis in the developing embryos to induce fetal malformations. Resistance to VA-induced apoptosis in embryos resulting from maternal immune stimulation may be involved in protective mechanism.