Phenytoin-induced teratogenesis: A molecular basis for the observed developmental delay during neurulation

Purpose: We wished to determine whether chronic phenytoin (PHT) exposure could impair neural development and if any morphological alterations could be linked to changes in gene expression. Methods: Pregnant SWV mice were chronically administered PHT 40 mg/kg/day from gestational day (GD) 0:12 (day:h) until they were killed at various timepoints throughout neural tube closure (NTC). At each timepoint, embryos from both treated and control dams were collected and scored for their progression through NTC. The neural tubes were then isolated and subjected to in situ transcription (IST) and antisense RNA amplification procedures. Using these techniques, we examined the expression of 10 genes: N-cadherin (Ncad), collagen type IV (col-IV), bcl-2, c-jun, PAX-3, cellular retinol binding protein-2 (CRBP-2), retinoic acid receptor alpha (RAR alpha), transforming growth factor(beta 2), (TGF(beta 2)), wee-1, and EMX-2. Results: Chronic PHT exposure not only caused a delay in NTC whereby exposed embryos lagged behind the controls at each collection timepoint, but also significantly altered the expression of specific genes at distinct times during NTC. Early in NTC, PHT induced a significant reduction in the expression of N-cad, col-IV, and c-jun in exposed embryos as compared with controls. In contrast, during the midstages of NTC, the only significant molecular alterations observed in the PHT-exposed embryos was the continued decreased expression of col-IV and an increase in CRBP-2 expression. Finally, in the latter stages of NTC, PHT caused a significant reduction in the expression of bcl-2, RAR(alpha), TGF(beta 2), EMX-2, and PAX-3. Conclusions: These results show that although the effects of PHT are morphologically subtle, causing a delay in the development of the neural tube, this delay is accompanied by alterations in critical genes at crucial times of neural development that may account for the observed neurological deficits often associated with PHT exposure.