Possible teratogenic effect of valproic acid

The treatment of epilepsy in pregnancy: The neurodevelopmental risks associated with exposure to antiepileptic drugs

A number of antiepileptic drugs (AEDs) have been confirmed as teratogens due to their association with an increased malformation rate. The majority of research to date does not find an association between prenatal exposure to monotherapy carbamazepine, lamotrigine or phenytoin and neurodevelopmental outcome in comparison to control children and noted higher abilities in comparison to children exposed to valproate; but further work is needed before conclusions can be drawn. Data for levetiracetam was limited to one study, as was the evidence for topiramate. Sodium valproate exposure appeared to carry a dose dependent risk to the developing brain, with evidence of reduced levels of IQ, poorer verbal abilities and increased rate of autistic spectrum disorder both in comparison to control children and children exposed to other AEDs. The severity of the neurodevelopmental deficits associated with prenatal exposure to valproate highlight the critical need to consider neurodevelopmental outcomes as a central aspect of teratological research.

A role for protein kinase C and its substrates in the action of valproic acid in the brain: implications for neural plasticity

Valproic acid (VPA) is a broad-spectrum anticonvulsant with well-documented teratogenic effects, but whose mechanism of action is largely unknown. In the present study we have examined the effects of VPA on the expression of two prominent substrates for protein kinase C (PKC) in the brain, MARCKS and GAP-43, which have been implicated in actin-membrane plasticity and neurite outgrowth during neuronal differentiation, respectively, and are essential to normal brain development. Immortalized hippocampal HN33 cells exposed to VPA exhibited reduced MARCKS protein expression and demonstrated increased GAP-43 protein expression, with concomitant alterations in cellular morphology, including an increase in the number and length of neurites and accompanied by a reduction in cell growth rate. The effects of VPA were observed at clinically relevant concentrations following chronic (>1 day) VPA exposure. We also present evidence for a VPA-induced alteration in PKC activity, as well as temporal changes in individual PKC isozyme expression. Inhibition of PKC with the PKC-selective inhibitor, LY333531, prevented the VPA-induced down-regulation of membrane-associated MARCKS, but had no effect on the cytosolic MARCKS reduction or the GAP-43 up-regulation. Inhibition of PKC by LY333531 enhanced the differentiating effects of VPA; additionally, LY333531 alone induced greater neurite outgrowth in this cell line. Collectively, these data indicate that VPA induces neuronal differentiation, associated with a reduction in MARCKS expression and an increase in GAP-43 expression, consistent with the hypothesis that a reduction in MARCKS at the membrane may be permissive for cytoskeletal plasticity during neurite outgrowth.

Morphological alterations induced by sodium valproate on somites and spinal nerves in rat embryos

The antiepileptic drug valproic acid is a well-known teratogenic agent; its main target organ is the neural tube, though skeletal malformations have also been described. In our recent work, respecifications of vertebrae were described in rat fetuses after treatment with 400 mg/kg of sodium valproate at specific somitogenic stages. The observed malformations were stage-dependent. Morphological segmental respecification was observed at the level of segments in formation at the moment of exposure and at the level of more posterior segments. Recently, specific alterations in the development of cranial nerves and ganglia were described in mouse embryos after in vitro exposure to VPA. The aim of the present work was to analyze dysmorphogenetic effects of VPA on embryonic metameric structures: somites, spinal and cranial nerves, and ganglia. Sodium valproate (400 mg/kg) was subcutaneously injected at specific gestational times corresponding to embryonic stages: presomitic or at about 2, 6, 10, 14, 18, or 22 somites. Females were sacrificed on the day 12 post coitum, and embryos were examined. Morphological examination of somites was performed by staining with acridine orange. Morphological examination of nerves and ganglia was performed by immunostaining, using monoclonal antibodies to the 160-kD neurofilament protein. No abnormalities were observed in the cranial nerves and ganglia. Specific and stage-dependent alterations were observed both at the level of the somites and at the level of the spinal nerves. The following characteristic malformations were observed: fusions, duplications, and reductions of somites and corresponding spinal nerves and ganglia. Our morphological data suggest a morphogenetic action of VPA at the level of the axial segments, with a possible respecification of the identity of the interested segments and their derivatives.

In vitro neuroteratogenicity of valproic acid and 4-en-VPA

Mouse embryos displaying 8 to 9 pairs of somites were cultured during 26 h in presence of 0.75 mM of VPA, or of 1 mM of 4-en-VPA. These concentrations induced approximately 50% of dysmorphogenic embryos. Irregular suture of caudal neural tube, abnormal head shape, cranial neural tube defects, and deformed optic vesicles were the most common defects observed with both compounds. The main differences in the types of dysmorphogeneses detected between the two compounds concerned the suture of the caudal neural tube and the telencephalic region. Other macroscopic effects induced by the two compounds were similar. Several of the observed abnormalities can be correlated with defects reported after in vivo exposure. The major alteration of the histological structure of the neural tube concerned a specific area in the hindbrain : VPA and 4-en-VPA induced an abnormal and irregular budding of the neuroepithelium at this level. Immunohistology with an antibody specific for radial glial fibers (RC-2) as well as SEM analysis showed a moderate effect on glial development, mainly after exposure to VPA.

Developmental toxicity of valproic acid

Valproic acid is a very effective anticonvulsant agent widely used in the management of various forms of epilepsy. Administration of the drug during pregnancy results in increased incidence of congenital abnormalities in both humans and experimental animals. In recent years, a significant number of research efforts have attempted to define the contributory role of valproic acid to the impairment of normal prenatal growth and development. The present report summarizes current knowledge that has emerged from clinical and research studies. The specific topics include: the placental transfer of valproic acid; the teratogenic potential; structure-teratogenicity and dose-response relationships; species and strain differences; biochemical changes evoked by the drug in the fetus.

Parental epilepsy, anticonvulsant drugs, and reproductive outcome: epidemiologic and experimental findings spanning three decades; 2: Human studies

Evidence accumulated over the past three decades has established AEDs as human teratogens. Important developments in the delineation of these compounds as human teratogens include: the demonstration of a consistent association between in utero exposure to AEDs and an increased occurrence of single major malformations, the description of AED-induced dysmorphogenic syndromes; demonstration of a dose-response relationship, both in terms of the number and dosage of AEDs; and evidence that pharmacogenetic differences in the metabolism of AEDs are strongly correlated with the occurrence of congenital malformations. Furthermore, the experimental animal findings, having accumulated in parallel to those of human studies, strongly support the teratogenic role of AEDs. Areas that require further amplification and clarification in future studies are the relative contribution of AEDs and other factors, such as genetic predisposition and maternal seizures, particularly with respect to the occurrence of minor anomalies, growth retardation, and developmental outcome; the relative teratogenicity of specific monotherapies and polytherapies; the predictive role of pharmacogenetic differences in the metabolism of AEDs in the occurrence of structural and functional abnormalities; and characterization of the precise nature of the pharmacogenetic defect underlying the aforementioned differences in AED metabolism. Attempts should also be made in future prospective studies to monitor metabolite levels of AEDs, particularly the oxidative metabolites, in order to further elucidate the relative contribution of individual differences in metabolism in the determination of adverse fetal outcome. Similarly, further efforts should be made to assess the clinical significance of decreased growth parameters in terms of mental and neurologic development, and to ascertain whether there is any risk for such abnormalities in children who do not display overt or persistent reductions in physical growth parameters. This is critically important in light of the animal studies that have shown functional abnormalities at doses that do not necessarily produce structural defects. Future investigations would be conducted through collaborative studies that would encompass sufficiently large numbers of women to provide adequate power to the statistical analyses of the data obtained. Care would have to be exercised to establish a uniform protocol for the collaborating centers. Regionally based investigations would be preferable to studies based at special centers, in order to assess the relative role of risk factors associated with abnormal pregnancy outcomes in the epileptic population at large.(ABSTRACT TRUNCATED AT 400 WORDS)

Teratogenic effects of sodium valproate in the Jcl: ICR mouse fetus

Sodium valproate was administered to Jcl:ICR mice in order to evaluate its teratogenicity. A single dose of 600 mg/kg of sodium valproate was injected intraperitoneally on gestational day 6, 7, 8 or 9. On day 18 of gestation, dams were laparotomized, and live fetuses were inspected for the presence of external and internal abnormalities. Exencephaly and urogenital abnormalities showed the highest frequency in the group treated on day 8, being recognized in about 60% and 10% of live fetuses, respectively. Cardiovascular abnormalities were found in the highest frequency in the group treated on day 7 (in about 30% of live fetuses). Incidence of tail abnormality was found to increase with delay in day of drug administration. Other abnormalities observed were cleft palate and digital malformation. Our study showed that a constellation of major abnormalities similar to the congenital valproate syndrome suspected in humans could be produced in the Jcl:ICR mouse fetus.

Clinical manifestation of prenatal exposure to valproic acid using case reports and epidemiologic information

The present study includes 28 patients prenatally exposed to valproic acid (VPA) monitored by the Spanish Collaborative Study of Congenital Malformations (ECEMC), from April 1976 to December 1988. Among the 28 cases, 15 (53.6%) were exposed only to VPA and 13 (46.4%) to VPA plus other anticonvulsant drugs. The clinical manifestations observed in those prenatally exposed only to VPA, are compared with the abnormalities observed in those with prenatal exposure to VPA plus other anticonvulsant drugs. To better define the spectrum of clinical manifestation of the prenatal exposure to VPA we used, besides our clinical observations and those from the literature, all available epidemiological data. We consider that a "valproate embryofetopathy (VPEF)" could exist, because different anomalies have been observed in children prenatally exposed to VPA in monotherapy. A facial phenotype of VPA exposure has been reported, and epidemiologic studies have shown an increased risk for congenital defects. However, from a review of published cases as well as those in the present study, it appears that the spectrum of VAE in monotherapy may not include oral clefts.

Proximal phocomelia and radial ray aplasia in fetal valproic syndrome

We describe a child with multiple congenital anomalies born to a women treated with valproic acid (1000 mg/day) for post traumatic epilepsy. Defects included the typical dysmorphism of the "fetal valproic syndrome", bilateral radial ray aplasia, unilateral proximal phocomelia of the upper limb, kidney hypoplasia and brain atrophy. A direct teratogenic effect of valproic acid is suspected on an experimental basis, and validated by two previous reports of radial defects after valproic acid exposure.

Strain differences in the teratogenicity induced by sodium valproate in cultured mouse embryos

Strain differences in the teratogenicity of valproic acid (VPA) have been reported in mice. Finnell and Chernoff (Proc. Grnwd. Genet. Ctr. 5:162-163, 1985) showed that 300 mg/kg of VPA twice a day on days 6-8 of gestation induced exencephaly in 82% of SWV embryos but in 0% of C57BL/6J embryos. In the present experiment, we have collected similar results and investigated this strain difference using whole embryo culture in an attempt to determine whether maternal or embryonic factors are responsible for the difference. Mouse embryos were explanted on day 8.5 (plug day 0), and embryos at the 6-8-somite stage were cultured for 48 hours in rat serum containing various doses of sodium valproate (NaVP). All the embryos died within 24 hours with 4.5-mM and higher doses of NaVP in C57BL/6NCr1BR (C57) and with 3.0-mM and higher doses in SWV. Unfused brain folds were recognized in embryos treated with 3.0-mM and higher doses in C57, and with 1.0-mM and higher doses in SWV. Irregular somite formation was observed in many embryos treated with 1.6-mM and higher doses in C57 and with 1.0-mM and higher doses in SWV. These results indicate that SWV embryos have 1.5-3 times the sensitivity of C57 embryos to the embryolethal and teratogenic effects of NaVP. Furthermore, the results suggest that the basis of the strain difference resides within the embryo rather than the mother.

Verification of the fetal valproate syndrome phenotype

We have evaluated 19 children who were exposed to valproic acid (VPA) in utero to look for manifestations of a fetal valproate syndrome (FVS), as proposed by Di Liberti et al. [1984]. We found no consistent alterations of pre- or postnatal growth with exposure to VPA monotherapy. Postnatal growth deficiency and microcephaly were present however, in two thirds of children exposed to VPA in combination with other anticonvulsants. Developmental delay or neurologic abnormality was found in 71% of those exposed to VPA monotherapy, and in 90% of those exposed to VPA and other anticonvulsants. Craniofacial anomalies, which can be seen with other anticonvulsant exposures, including midface hypoplasia, short nose with a broad and/or flat bridge, epicanthal folds, minor abnormalities of the ear, philtrum or lip, and micrognathia were also found in infants whose mothers used VPA. Prominent metopic ridge and outer orbital ridge deficiency or bifrontal narrowing and certain major anomalies such as tracheomalacia, talipes equinovarus (with intact spine) and lumbosacral meningomyelocele seem to be peculiar to infants with VPA exposure. Other defects such as urogenital anomalies, inguinal or umbilical hernias, and minor digital anomalies that are common to other prenatal anticonvulsant exposures are also occasionally found in those exposed to VPA. Heart defects have been found in infants exposed to nearly every class of anticonvulsant although the types of defects associated with maternal VPA use may be clarified when classified by pathogenetic mechanism. Our findings overall are in agreement with the report of Di Liberti et al. [1984].

Congenital malformations associated with maternal use of valproic acid

Two children born with birth defects after intrauterine exposure to valproic acid are reported. The mothers took the drug throughout pregnancy as sole treatment for primary generalized epilepsy. The first baby showed facial dysmorphism, arachnodactyly and triphalangeal thumbs. The second had facial dysmorphism, severe laryngeal hypoplasia, tracheomalacia and an aberrant innominate artery that caused tracheal compression. A left superior vena cava, abnormal pulmonary lobulation, and unilateral hydronephrosis were also found at autopsy. Valproic acid has probable teratogenic potential in humans but the number of reported cases is few and the spectrum of anomalies is broad so it is not possible to delineate a definite fetal valproate syndrome.

Teratogen update: valproic acid

Valproic acid use during pregnancy results in an absolute risk for spina bifida of 1-2%. This increased risk is comparable to the recurrence risk for neural tube defects and warrants informed counselling and access to prenatal diagnosis. There is no substantial evidence that valproic acid use increases the risk for other specific major malformations above the increased risk due to maternal epilepsy. Valproic acid may cause a characteristic pattern of minor facial malformations. Further definition and confirmation are required, and the magnitude of the risk needs to be determined. There are inadequate data to assess the magnitude, if any, of the risks for postnatal growth abnormalities and developmental disabilities associated with the use of valproic acid during pregnancy. Birth-defect monitoring programs and international collaboration among the staffs of monitoring programs played a major role in determining that valproic acid is a human teratogen.

Studies in neural tube defects. I. Epidemiologic and etiologic aspects

In the NIH Collaborative Perinatal Project, a prospective study of over 53,000 pregnant women and their offspring, 71 single-born children (13.33/10,000) were found to have a non-syndromal neural tube defect (NTD). A family history was present in only one case. The group of individuals with NTD was compared to a group of 400 randomly selected non-malformed control infants. Of over 50 maternal factors studied the following showed significant association with NTD in the offspring: diabetes mellitus; organic heart disease; lung disease; and diuretic, antihistamine, and sulfonamide use. The interval between the termination of the immediately previous pregnancy and the start of the proband pregnancy was significantly shorter in mothers of NTD children than in mothers of control infants. The risk for NTD was also significantly increased if the immediately previous pregnancy was a spontaneous abortion. There was no increased risk for NTDs among sibs of children with major malformations such as tracheo-esophageal "dysraphism," cleft lip/palate, or renal agenesis. NTDs are apparently etiologically heterogeneous.

Fetal growth, major malformations, and minor anomalies in infants born to women receiving valproic acid

The association of fetal and neonatal distress, birth measurements, major malformations, and minor anomalies was studied prospectively in 14 infants of women with epilepsy who were receiving valproic acid (VPA) monotherapy and in 12 infants of women with epilepsy who were receiving VPA in combination with other anticonvulsant drugs. Comparison was made with 26 matched-pair controls and 116 controls from a larger study of antiepileptic drugs. During the first trimester, total VPA serum concentrations were well above therapeutic levels (100 to 184 micrograms/ml) in two women receiving high VPA doses (2000 and 1500 mg daily). Although dosage remained the same, serum concentrations decreased during pregnancy to therapeutic levels (33.9 to 57.0 micrograms/ml). The VPA percent free fraction increased in the third trimester and was threefold higher at birth. Almost half of the infants exposed to VPA monotherapy were distressed during labor, and 28% had low Apgar scores. Fetal and neonatal distress may be caused by the high VPA percent free fraction during labor and at birth. Mean body measurements at birth after VPA monotherapy were comparable to those in the matched control group, but were reduced in the group of infants receiving VPA combination therapy. Four infants exposed to VPA monotherapy were born with major malformations. The median number of minor anomalies was four times higher in infants whose mothers received VPA alone or VPA combination therapy than in controls. Seven infants had a pattern of craniofacial and digital anomalies that was distinctly different from that observed after in utero exposure to other anticonvulsant medications. The occurrence of major malformations and the number of minor anomalies may be dose related.

Predicting the human teratogenic potential of the anticonvulsant, valproic acid, from a non-human primate model

The anticonvulsant, valproic acid (VPA) is a suspected human teratogen. This study, employing the rhesus monkey as an animal model, demonstrates that VPA has a significant teratogenic potential in the monkey. Timed pregnant monkeys were exposed orally to VPA at approx. 1X, 10X, and 30X (20, 200, and 600 mg/kg/day, respectively) the human therapeutic dose, daily, during organogenesis (gestation days 21-50). All fetuses of mothers exposed to greater than 1X exhibited some form of embryotoxicity. The highest dose, 30X, was 100% embryolethal, while offspring of the 10X dose group exhibited craniofacial and skeletal defects, and low body weights. Maternal pharmacokinetic parameters and plasma metabolites were determined for VPA on the first and last day of dosing for the 10X dose group. Comparison of the kinetic and metabolite data with that obtained for man indicates that the rhesus monkey is a good model for predicting the teratogenic potential of VPA in the human.

An update on sodium valproate

Sodium valproate has been in clinical use for the treatment of epilepsy in Great Britain since 1973 and in the United States since 1978. It is chemically quite different from the existing antiepileptic drugs. Although most authorities concentrate on its modification of GABAergic inhibitory transmission in the central nervous system, its mechanism of action remains obscure. It has been shown to be an effective antiepileptic drug in a wide variety of seizure types, but clinically, its major use to date has been in generalized seizures. It is particularly effective in photosensitive epilepsy and myoclonus. Most adverse reactions to sodium valproate are mild and reversible, but with increasing experience, the drug's rare, idiosyncratic, adverse effects are becoming apparent, particularly hepatotoxicity and teratogenicity. The role of therapeutic drug monitoring in the management of patients taking sodium valproate is controversial.

The fetal valproate syndrome

We evaluated seven children who had been exposed to sodium valproate (or valproic acid) in utero. A consistent facial phenotype was observed in all seven in addition to other birth defects in four. The facial changes consisted of epicanthal folds which continued inferiorly and laterally to form a crease or groove just under the orbit, flat nasal bridge, small upturned nose, long upper lip with a relatively shallow philtrum, a thin upper vermillion border, and downturned angles of the mouth. Hypospadias, strabismus, and psychomotor delay were found in two males; two children had nystagmus and two had low birth weight.

Non-dose-related side effects of valproate

The clinical and histological findings in 88 patients in whom hepatotoxicity with valproate has been reported were reviewed. The characteristic lesion is microvesicular steatosis. Hepatotoxicity appears to be an idiosyncratic reaction and is most likely to appear within 6 months from the start of therapy, especially in young patients on comedication. The condition may be reversible if the drug is immediately withdrawn in patients who show acute gastrointestinal symptoms, drowsiness or lethargy, jaundice, or change in seizure pattern. Clinical monitoring is more important than laboratory monitoring. The outcome of pregnancies in 344 women who received valproate in the first trimester was reviewed. There were 225 normal babies and 68 abnormal babies. The role of valproate in the aetiology of neural tube defects remains uncertain, but mothers treated with valproate should receive prenatal counselling.

Fetal drug exposure-behavioral teratogenesis

This paper reviews the neurobehavioral and developmental effects of fetal drug exposure. The drugs most commonly associated with adverse developmental outcome include alcohol, anticonvulsants (particularly phenytoin and trimethadione), narcotics, and some environmental toxins. Major limitations of studies examining the consequences of prenatal drug exposure on development include inadequate control of other confounding factors, uncertain accuracy of drug histories, and outcome criteria that provide insufficient delineation of subtle developmental delays.