A rat model of valproate teratogenicity from chronic oral treatment during pregnancy

Abstract

Objective: Sodium valproate (VPA), the most effective antiepileptic drug for patients with genetic generalized epilepsy (GGE), is a potent human teratogen that increases the risk of a range of congenital malformations, including spina bifida. The mechanisms underlying this teratogenicity are not known, but may involve genetic risk factors. This study aimed to develop an animal model of VPA-induced birth defects. Methods: We used three different rat strains: inbred Genetic Absence Epilepsy Rats From Strasbourg (GAERS), a model of GGE with absence seizures; inbred Non-Epileptic Controls (NEC); and outbred nonepileptic Wistars. Female rats were fed standard chow or VPA (20 g/kg food) mixed in standard chow for 2 weeks prior to conception, and then mated with same-strain males. Treatment continued throughout pregnancy. Fetuses were extracted via C-section on gestational day 21 and examined for birth defects, including external assessment and spinal measurements. Results: VPA-exposed pups showed significant reductions in weight, length, and whole-body development compared with controls of all three strains (P < .0001).Gestational VPA treatment altered intravertebral distances, and resulted in underdeveloped vertebral arches between thoracic region T11 and caudal region C2 in most pups (GAERS, 100%; NEC, 95%; Wistar, 80%), more frequently than in controls (9%, 13%, 19%). Significance: Gestational VPA treatment results in similar developmental and morphological abnormalities in three rat strains, including one with GGE, indicating that the genetic underpinnings of epilepsy do not contribute markedly to VPA-induced birth defects. This model may be used in future studies to investigate mechanisms involved in the pathogenesis of antiepileptic drug-induced birth defects.

Entry of antiepileptic drugs (valproate and lamotrigine) into the developing rat brain

“…Animals assigned to the chronic group were treated with a feed containing 20 g/kg valproate (see Methods and Jazayeri et al ., 2020 ) for at least 3 weeks for non-pregnant adults, and at least 2 weeks prior to mating followed by a further 19 days for E19 experiments and 25–26 days for P4 experiments. They were compared with animals fed chronically with food not containing valproate.…”

“…The chronic treatment used in the present study was that developed by Jazayeri et al . (2020) who showed that a feed containing 20 g/kg valproate resulted in blood levels in pregnant rats similar to those in pregnant mothers on treatment with this antiepileptic drug.…”

“…For chronic experiments, female rats were fed for two weeks prior to mating on a feed premixed with 20 g/kg valproate (Specialty Feeds, Sigma Aldrich). This feed has been shown to achieve consistent blood concentrations of ~220 μmol/L (approaching human clinical range of 300–600 μmol/L) of valproate across a sustained period ( Jazayeri et al ., 2020 ). For successfully time-mated females, feeding continued up until the point of fetus or postnatal (P4) sample collection.…”

“…The chronic treatment used in the present study was that developed by Jazayeri et al (2020) who showed that a feed containing 20 g/kg valproate resulted in blood levels in pregnant rats similar to those in pregnant mothers on treatment with this antiepileptic drug. At E19 there was a small but significant (p<0.05) decrease in cortical brain plasma ratios following injection of a dose of 100 mg/kg that included 3 H-valproate compared with an acute injection (Figure 8).…”

“…by the US Federal Drug Administration) that all new drugs before being used in any patients should be tested in animals (usually rodents) for possible teratogenic effects. Such tests have shown that a well-established antiepileptic drug, valproate causes a significant number of congenital abnormalities in animals ( Jazayeri et al ., 2020 ) but also in humans; Tomson et al (2018) found that the risk for congenital malformation in children of mothers exposed to valproate was increased by 4–5-times especially at higher valproate doses, and particularly when used in the first trimester (see also Abou-Khalil, 2019 ; Vajda, 2012 ). The most common problems associated with gestational valproate use are cardiac malformations, hypospadias, renal defects, and neural tube defects, with higher doses increasing the risk of spina bifida ( Jentink et al ., 2010 ).…”