Valproic Acid-Induced Teratogenesis in Japanese Rice Fish (Oryzias Latipes) Embryogenesis
Date of Award
M.S. in Pharmaceutical Science
Asok K. Dasmahapatra
Valproic acid (VPA) was introduced as an antiepileptic in 1967 in France and it has become the most prescribed anticonvulsive drug therapy worldwide since then. In the clinic, valproic acid is selected to treat absence seizures, myoclonic seizures, generalized tonic-clonic seizures, atonic attacks and partial seizures. Epilepsy is the second most common neurologic disorder that affects pregnant women (0.5%–1%). Approximately 1 out of 250 pregnant women are taking antiepileptic drugs. Valproic acid is designated as a human teratogen, which induces major congenital anomalies, facial dysmorphic features, and autistic-like behaviors, which affect verbal, cognitive, communicative, and social abilities of affected children. We are developing the Japanese rice fish (Oryzias latipes), also known as Japanese medaka, as an animal model to study valproate-induced teratogenesis during the period of embryogenesis. Fertilized embryos of Japanese rice fish at three developmental stages (group A: 0–2 dpf; group B: 1–3 dpf; group C: 4–6 dpf) were exposed to VPA (0–80 mM) for 48 hrs. The amounts of VPA to cause 50% mortality (LC50), which were observed on 14 day post fertilization (dpf), are found to be developmental stage-specific. The LC50 for group A (Iwamatsu developmental stage 4–10) is 1.68 ± 1.55 mM which is much lower than the LC50s for groups B (26.45 ±1.64 mM) and C (20.37 ± 3.3 mM) (Iwamatsu developmental stages 17–32). The development of the cardiovascular system was disrupted by VPA in each treatment group, displaying increased incidence of thrombus, reduced heart rates, and inhibited or delayed onset of circulation. The hatching efficiency was also reduced by VPA in each treatment group. The higher the concentration of VPA the embryos were treated with, the more severe the results were. The earlier developmental stages the treatments were targeted at, the more deleterious the effects of VPA were. VPA also caused malformation of neurocranial and splanchnocranial cartilages of hatchlings that had been exposed prenatally. The length of neurocranium, quadrate, ceratohyal and basibranchial 1–3 were all reduced in hatchlings of both groups E (0–2 pdf) and L (4–6 dpf). Trabeculae, epiphyseal bar, anterior orbital cartilage and basilar plate displayed reduction in length only in hatchlings of group E. In addition, the significant reduction in the linear length of polar cartilage and ceratobranchials 1–5 were manifested only in hatchlings of group L. Other cartilages remained unaltered in both groups E and L. It was indicated that the length of the neurocranium was reduced due to cumulative reduction of the component cartilages. mRNA analyses of nine genes demonstrated that the genes involved with oxidative stress remained unaltered after valproate exposure. However, the genes involved with neurogenesis (wnt1, otx2 and nlgn3b) and regulation of cell division (shh and ccna2) showed developmental stage-specific alteration after valproate exposure. This study indicates that valproate is able to induce some phenotypic features in Japanese rice fish which are analogous to human fetal valproate syndrome (FVS), and Japanese rice fish can be used as a unique alternatively non-mammalian vertebrate model to study valproate-induced teratogenesis, including FVS.
Wu, Mengmeng, "Valproic Acid-Induced Teratogenesis in Japanese Rice Fish (Oryzias Latipes) Embryogenesis" (2012). Electronic Theses and Dissertations. 319.