Teratogenic effects on the neuroepithelium of the CD‐1 mouse embryo exposed in utero to sodium valproate

Abstract

A causal association has now been recognized between the use of the anticonvulsant drug sodium valproate during pregnancy and the increased incidence of spina bifida in the human population. The objective of this study was to investigate the teratogenic effects of sodium valproate on the cephalic 1) neuroepithelium, 2) extracellular matrix, and 3) embryonic protein content in the CD-1 mouse embryo. Nulliparous female CD-1 mice were dosed intraperitoneally on day 8 of gestation with 340 mg/kg of sodium valproate. On day 10 of gestation, females were killed by cervical dislocation, and all live embryos were assigned to one of the following groups and processed accordingly for: 1) head measurements, 2) scanning electron microscopy, 3) total protein determination, 4) two-dimensional polyacrylamide gel electrophoresis, 5) immunohistochemistry, and 6) light microscopy. Exposure to sodium valproate at the selected dosage resulted in a 30% incidence of neural tube defects in the cranial region of these embryos. Treated embryos showed a significant reduction in head size, indicating a drug-induced microcephaly. No major differences were seen in the total embryonic protein patterns between control and treated embryos. Immunoreactivity to laminin and fibronectin showed a similar distribution in control and treated embryos except in the vasculature pattern of the hindbrain neuroepithelium. The neuroepithelium of the treated embryos showed marked disorganization when it was examined histologically, particularly in the forebrain region. Cells were disoriented, and there was a noticeable loss of intercellular adhesion in the juxtaluminal region. Increased cellular blebbing was apparent at the ependymal surface, and large protrusions of cells were seen invading the neural tube lumen. The lumen was distorted in shape and frequently contained blood cells. Irregularities and gaps were observed in the underlying basal lamina. These results suggest that treatment with sodium valproate during a critical time in neurogenesis in the CD-1 mouse embryo alters the normal architecture of the neuroepithelium, with a loss of integrity at both the basal and apical surfaces. The alterations seen in the neuroepithelium at any of these sites in this animal model could help explain the increased incidence of spina bifida seen in children of epileptic mothers receiving sodium valproate.

The teratology of autism

“…Skeletal abnormalities have been reported in mice (Brown et al, 1980; Bruckner et al, 1983), rats (Mengola et al, 1998), rabbits (Petrere et al, 1986), and rhesus monkeys (at doses 10‐fold above therapeutic levels in humans) (Mast et al, 1986). Cardiac abnormalities (e.g., Sonoda et al, 1993) and neural tube defects, including induction of spina bifida in mice (Ehlers et al, 1992) and cranial neural tube defects in rats (Turner et al, 1990) have also been reported in animal models. Most importantly, VPA exposure in utero also leads to behavioral abnormalities in rats (e.g., Vorhees, 1987).…”

Animal models of neural tube defects

“…In contrast, the genetic cause of spontaneous NTD in the TO strain does not lead to exceptionally high frequencies of NTD, the risk (30%) being similar to that of normal strains at the same dose of valproic acid [Padmanabhan and Ahmed, 1996;Padmanabhan and Hameed, 1994;Hall et al, 1997]. Valproic acid in genetically normal embryos causes disorganization of the cellular structure of the neuroepithelium [Turner et al, 1990;Ehlers et al, 1992b]. Interference with folate metabolism may be involved [Nau, 1994], and various transcription factors and cell cycle genes, including p53, may be overexpressed [Wlodarczyk et al, 1996].…”

Epigenetics of psychoactive drugs

“…A severe foetal valproate syndrome has also been documented [101] . Experimental studies also support the effect of VPA on reprogramming and intrauterine development [102,103] …”