Abstract

Valproic acid (VPA) is a commonly prescribed antiepileptic drug that causes negative neurodevelopmental outcomes, including neural tube defects (NTDs) and neurodevelopmental disorders, in fetuses exposed to it. While the exact mechanism by which VPA causes defects is unknown, research has shown that VPA increases the production of reactive oxygen species (ROS) that lead to redox dysregulation. We hypothesize that VPA causes negative neurodevelopmental outcomes through the disruption of redox-sensitive signaling pathways that are critical for proper embryonic development, and that protection from the VPA-induced redox disruption may decrease the prevalence of the observed defects. Time-bred mice were treated with 3H-1,2-dithiole-3-thione (D3T) -- an inducer of the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant pathway which protects against redox disruptions. Embryos were collected from the pregnant mice and treated with VPA in vitro over an 18-h culture period. Embryos treated with VPA exhibited a transiently oxidizing glutathione (GSH) redox potential, a measure of the intracellular redox environment, while those that received D3T pretreatment prior to VPA exposure displayed no significant redox potential changes compared to controls. Subsequently, time-bred mice were pretreated with D3T and exposed to VPA in utero, after which their embryos were analyzed for morphological differences. The prevalence of NTDs in VPA-treated embryos significantly decreased with D3T pretreatment, demonstrating that NRF2 induction protects against VPA-induced redox disruption and decreases the prevalence of NTDs. The effectiveness of NRF2 induction in combating VPA-induced neurodevelopmental disorders has not yet been evaluated. To assess whether VPA affects proper neuronal differentiation and consequently proper neurodevelopment, stem cells were treated with VPA at various time points during their four-day-long differentiation into neurons. Cells exposed to VPA early in the differentiation process did not undergo normal neurogenesis as measured by OCT4 and βIII-tubulin, markers of cell stemness and neuronal differentiation, respectively. Neurogenesis was improved with D3T pretreatment prior to VPA exposure. Furthermore, undifferentiated stem cells were more susceptible to VPA-induced sulfenic acid formation, an oxidative protein modification, and less prone to S-glutathionylation, a protective modification that prevents protein overoxidation, than fully differentiated neurons. Pretreatment with D3T prevented all VPA-induced protein modifications. These data suggest that periods during early neurodevelopment are more susceptible to VPA-induced oxidative protein modifications, highlighting the need for developmental therapeutics to target redox-sensitive proteins during early embryogenesis. In conclusion, D3T pretreatment inhibits VPA-induced negative neurodevelopmental outcomes and proposes NRF2 induction as a means to potentially mitigate the negative effects of other oxidative toxicants in the developing embryo.

Degree

PhD

College and Department

Life Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2022-03-29

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd12675

Keywords

valproic acid, NRF2, fetal valproate syndrome, neural tube defects, D3T, P19

Language

english

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