Inhibition of valproic acid-induced neural tube defects through Nrf2 signaling

Abstract

Valproic acid (VPA) is an effective antiepileptic drug but is also a known human teratogen that causes neural tube defects (NTDs). The mechanisms responsible for VPA-induced embryopathy remain poorly understood, but various studies suggest that VPA-induced oxidative stress is central to its involvement in its developmental toxicity. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a transcription factor that activates the cellular antioxidant response and upregulates detoxification enzymes, potentially preventing the disruption of redox-sensitive signaling. The aim of this study is to elucidate if VPA-induced NTDs can be attenuated though Nrf2 induction using both in vivo and ex vivo mouse models. Gestational day 8.0 mice were treated with or without 5 μM D3T, a Nrf2 inducer, and were then treated with 600 μM VPA on GD 8.6 and collected periodically over an 18 h period for glutathione (GSH) redox potential (Eh) and morphology assessment on GD 9.0. In embryos treated with VPA only, GSH Eh increased by over +20 mV at 2 h post VPA treatment and then slowly rebounded, nearing untreated control GSH Eh levels by 18 h. Pretreatment with D3T prevented any changes to GSH Eh. At 24 h, 58% of embryos treated with only VPA exhibited NTDs, but NTD rates dropped to 5% with D3T pretreatment. Embryos from WT mice treated on GD 8.0 in utero and evaluated on GD 9.0 demonstrated similar NTD rates, but the prevalence of NTDs nearly doubled in Nrf2 KO embryos. To further understand the role of Nrf2 in NTDs, both WT and Nrf2 KO mice were treated with D3T (i.p. 5 mg/kg) on GD 7.12, followed by treatment with VPA (s.c. 400mg/kg) on gestational day 8.0. D3T pretreatments significantly reduced NTDs in WT embryos but failed to reduce rates in KO mice treated with VPA. These data suggest that mitigation of VPA-induced redox imbalance in the early organogenesis stage mouse embryo is critical for NTD prevention and that Nrf2 is a protective factor during development that requires further investigation.