Pharmacology of neural tube defects

Elucidation of the cytogenotoxic potential of vigabatrin and its in silico computer-assisted DNA interaction

Vigabatrin (VGB) is a gammaaminobutyric acid-ergic (GABA-ergic) antiepileptic drug (AED) and is one of 2 approved drugs available to treat infantile spasms (IS). The aim of this study is to elucidate conflicting data on the toxic effects of VGB and to obtain detailed information about its possible cytogenotoxic effects in human lymphocytes. For this purpose, in vitro Chromosomal Aberration (CA), Sister Chromatid Exchange (SCE), Micronucleus (MN) tests, and Comet Assay were performed to determine possible genotoxic and cytotoxic effects of VGB. In addition, the binding energy level of VGB to DNA was determined in silico by molecular docking. The highest concentration (80 μg/ml) of VGB increased the SCE, CA, MN and micronucleated binuclear cell (BNMN) frequency significantly compared to the control after 24 and 48 hours of treatment. In the tail density and tail length parameters, the dose-dependent increase was found to be statistically significant compared to the control. At the 40 and 80 μg/ml concentrations of VGB for 48 hours caused a statistically significant increase in both CA/Cell and AC percentages, while MI and NDI decreased only significantly at the highest concentration (80 µg/ml) causing. In the Comet Assay head density, tail density and tail length parameters, the dose-dependent increase was found to be statistically significant compared to the control. Also, the in silico molecular docking analysis showed that VGB interacts with B-DNA close to the threshold binding energy. The lowest negative free binding energy (ΔG binding) was found as -5.13 kcal/mol. In conclusion, all results are evaluated together, it has been determined that VGB has cytogenotoxic effects in vitro and binds to DNA in silico with significant free binding energy.

Antiseizure medication in early nervous system development. Ion channels and synaptic proteins as principal targets

The main strategy for the treatment of epilepsy is the use of pharmacological agents known as antiseizure medication (ASM). These drugs control the seizure onset and improves the life expectancy and quality of life of patients. Several ASMs are contraindicated during pregnancy, due to a potential teratogen risk. For this reason, the pharmacological treatments of the pregnant Women with Epilepsy (WWE) need comprehensive analyses to reduce fetal risk during the first trimester of pregnancy. The mechanisms by which ASM are teratogens are still under study and scientists in the field, propose different hypotheses. One of them, which will be addressed in this review, corresponds to the potential alteration of ASM on ion channels and proteins involved in relevant signaling and cellular responses (i.e., migration, differentiation) during embryonic development. The actual information related to the action of ASM and its possible targets it is poorly understood. In this review, we will focus on describing the eventual presence of some ion channels and synaptic proteins of the neurotransmitter signaling pathways present during early neural development, which could potentially interacting as targets of ASM. This information leads to elucidate whether these drugs would have the ability to affect critical signaling during periods of neural development that in turn could explain the fetal malformations observed by the use of ASM during pregnancy.

Hematological Consequences of Valproic Acid in Pediatric Patients: A Systematic Review with a Mechanistic Approach

PURPOSE

Although valproate (VPA) has several advantages in controlling seizures, it may cause serious hematological consequences. Hematotoxicity of VPA is particularly important in pediatrics because patients at this age are at a growing risk of leukemia. For a conclusive agreement about the toxicity of VPA, in this study, we systematically reviewed the literature in which the hematological consequences of VPA had been emphasized. <P> Methods: A systematic literature search was performed in June 2021 on electronic databases to find original research on the association between VPA therapy and hematotoxicity in pediatric patients. For this purpose, the following search terms "hematotoxicity", "valproic acid" and "pediatrics" with different spellings and similar terms, were searched in the title, keywords, and abstracts of articles. The data were collected and used for qualitative data description. <P> Results: A total of 36 relevant articles with an overall 1381 study population were included. The results showed that VPA could cause severe hematotoxicity in children even at therapeutic doses. Neutropenia, thrombocytopenia, and bone marrow depression are the most common complications associated with VPA therapy. Also, findings showed that after discontinuation of VPA and starting other antiepileptic drugs or reducing the administered VPA dose, hematologic damages were entirely resolved, and all the hematological parameters improved during two weeks. <P> Conclusions: This review showed that VPA therapy could cause hematotoxicity in children; hence, it is recommended to monitor hematological indices during VPA therapy. Also, according to the suggested mechanistic pathways of VPA side effects, a combination of VPA with antioxidants may reduce hematological side effects.

Effect of gabapentin on fetal rat brain and its amelioration by ginger

Intrauterine exposure to antiepileptic drugs (AEDs) is associated with neurodevelopmental alterations causing postnatal behavioral and cognitive alterations. These disorders are associated with the interference of these AEDs with the developing cerebral cortex and hippocampal neurons. Therefore, it is crucial to identify the drugs that should be avoided during pregnancy in order to prevent AED mediated developmental alterations. The present study was conducted to investigate the effects of prenatal exposure to the antiepileptic drug gabapentin (GBP) on the rat fetal brain during the organogenesis phase and to examine the potential ameliorative effect of ginger (Zingiber officinale). Consequently, the current study addressed the developmental neural changes on the histological, immuno-histochemical and ultrastructural levels. The brain of fetuses from the GBP group showed a highly significant decrease in their weight. Histologically, the cerebral cortex and hippocampus regions of fetuses maternally injected with GBP showed layer disorganization, vacuolated neuropil and massive cell degeneration. The expression of Caspase 3 was significantly increased in the brain of GBP fetuses, unlike the expression of Bcl-2 which was significantly decreased. On the ultrastructure level, the neurons showed pyknotic and chromatolytic nuclei. The cytoplasm was rarefied with swollen organelles. Co-administration of ginger evidently ameliorated most of these effects. In conclusion, GBP administration during pregnancy could possibly affect the developing fetal brain and ginger may have ameliorating effect against the induced GBP neurotoxicity and should be taken in parallel.

The Role of Oxidative Stress in the Pathomechanism of Congenital Malformations

Congenital anomalies are significant causes of mortality and morbidity in infancy and childhood. Embryogenesis requires specific signaling pathways to regulate cell proliferation and differentiation. These signaling pathways are sensitive to endogenous and exogenous agents able to produce several structural changes of the developing fetus. Oxidative stress, due to an imbalance between the production of reactive oxygen species and antioxidant defenses, disrupts signaling pathways with a causative role in birth defects. This review provides a basis for understanding the role of oxidative stress in the pathomechanism of congenital malformations, discussing the mechanisms related to some congenital malformations. New insights in the knowledge of pathomechanism of oxidative stress-related congenital malformations, according to experimental and human studies, represent the basis of possible clinical applications in screening, prevention, and therapies.

Evaluation of apoptotic cell death on liver and kidney tissues following administration of levetiracetam during prenatal period

OBJECTIVE

Levetiracetam is a new generation antiepileptic drug used in treatment of patients with epilepsy and has adverse effects on different tissues. We aimed to evaluate the apoptotic effects of levetiracetam exposure during pregnancy on liver and kidney tissues of rat pups.

METHODS

We analyzed the newborn rat pups exposed to levetiracetam during prenatal period. Fifteen pregnant female rats were divided into three groups. The group 1 and 2 rats were treated with different doses of levetiracetam (25 mg/kg/d and 50 mg/kg/d, respectively) from gestational days 1-22 during pregnancy. Group 3 (control group) was treated with the same volume of saline. Apoptosis was evaluated by the terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) method. Liver and kidney tissues from rat pups were used for investigation.

RESULTS

The percent of TUNEL positive apoptotic cells in group 1 were 22 and 17.5 for kidney and liver, respectively. The percent of TUNEL positive apoptotic cells in group 2 were 20.9 and 20.9 for kidney and liver, respectively. The percent of TUNEL positive apoptotic cells in group 3 were 18.4 and 17.1, respectively, for kidney and liver. The apoptotic index was the same in kidney and liver tissues of all groups.

CONCLUSION

Our results demonstrate that the prenatal exposure of levetiracetam has no apoptotic effects on liver and kidney of rat pups and, it has biosafety in pregnancy in terms of apoptosis. The first study evaluating the apoptotic effects on liver and kidney tissues following administration of levetiracetam during prenatal period.

Novel single nucleotide polymorphisms in the superoxide dismutase 1 and 2 genes among children with myelomeningocele

OBJECTIVE

Excessive oxidative stress has been demonstrated as a mechanism for neural tube defects (NTDs). The current exploratory study sought to examine sequence variations in the superoxide dismutase 1 (SOD1) and 2 (SOD2) genes in patients with myelomeningocele and to identify variants altering risk for myelomeningocele.

STUDY DESIGN

We sequenced deoxyribonucleic acid from 96 patients with myelomeningocele. The 11 exons were amplified by polymerase chain reaction, and the products were sequenced with the Sanger method. Results were compared with reference sequences (NM_000454, NM_000636, and NM_001024466) obtained from University of California Santa Cruz Genome Browser. Observed alleles that differed from the reference sequences were considered novel variants.

RESULTS

We found 1 novel variant and 1 variant only recently described in phase 1 of the 1000 Genomes Project but not yet validated. The novel variant is located in the 3'-untranslated region (UTR) of SOD2 and is present in 2 of 96 patients (1.0% allele frequency). The other variant is located in the 3'-UTR of SOD1 and is present in 2 of 96 patients (1.0% allele frequency). Minor allele frequencies of known single nucleotide polymorphisms were compared with unaffected population controls.

CONCLUSION

We identified 1 novel variant and made the second report of an additional variant in the SOD genes studied. The variant located in the 3'-UTR of SOD1 is predicted to alter microribonucleic acid (miRNA) binding. The variant located in the 3'-UTR of SOD2 is predicted to alter 2 miRNA binding sites and potentially affects messenger ribonucleic acid production. We also identified 2 known single-nucleotide polymorphisms that occur in significantly different frequency compared with the unaffected population controls.

Neural tube defects and their significance in clinical dentistry: a mini review

Neural tube defects are common congenital malformations that could be apparent at birth or manifested in later stages of life. Morbidity is high in anencephaly, whereas in spina bifida, there are neurological and motor disorders. These defects deserve paramount importance in clinical dentistry. Latex allergy, dental caries, difficulty in mouth opening, and sitting in a dental chair are common problems. There is a high risk of anaphylactic response during anaesthesia. There could be associated craniosynostosis causing maxillary deficiency, and malformed sella turcica might be seen. An association of the defects has been linked with orofacial clefts and Down syndrome.

Association of copper-zinc superoxide dismutase (SOD1) and manganese superoxide dismutase (SOD2) genes with nonsyndromic myelomeningocele

BACKGROUND

A common and severe neural tube defect (NTD) phenotype, myelomeningocele (MM), results from the defective closure of the caudal end of the neural tube with herniation of the spinal cord and meninges through the vertebral column. The exact mechanisms for NTDs are unknown, but excessive oxidative stress, particularly in association with maternal diabetes, has been postulated as a mechanism for MM.

METHODS

The SNPlex Genotyping (ABI, Foster City, CA) platform was used to investigate single nucleotide polymorphisms (SNPs) across the superoxide dismutase (SOD) 1 and 2 genes to assess their association with MM risk. The study population included 329 trio (affected child and both parents) and 281 duo (affected child and one parent) families. Only cases with documented MM were studied. Seventeen SNPs across the SOD1 and SOD2 genes met the quality-control criteria to be considered for statistical analysis. Genetic association was assessed using the family-based transmission disequilibrium test in PLINK (a genome association analysis toolset).

RESULTS

Four SNPs in the SOD1 gene (rs 202446, rs202447, rs4816405, and rs2070424) and one SNP in the SOD2 gene ( rs5746105) [corrected] appeared to be associated with MM risk in our population. After adjusting for multiple testing, these SNPs remained significant.

CONCLUSION

This study provides the first genetic evidence to support association of myelomeningocele with superoxide scavenging. The rare alleles of the five specific SNPs within SOD1 and SOD2 appear to confer a protective effect on the susceptibility for MM risk in the MM population tested. Further evaluation of the roles of superoxide scavenging and neural tube development is warranted.

The effect of antiepileptic drugs administered in pregnancy on micronucleus frequency in cord blood lymphocytes

OBJECTIVES

Epidemiological data indicate that the pregnancies of epileptic women constitute about 1% of all pregnancies. A large group of antiepileptic drugs (AEDs) applied in long-term monotherapy or polytherapy produce toxic metabolites as well as free radicals and reactive oxygen species. The aim of this study was to assess the potential genotoxic effect of AED therapy in pregnancy on DNA structure of umbilical cord blood lymphocytes.

MATERIAL AND METHODS

The study group were 30 newborns (14 males and 16 females) of mothers receiving long-term AED therapy during pregnancy. The AED considered were carbamazepine, valproic acid, phenyltriazine, benzodiazepine, gamma-aminobutyric acid and sulfonamide analogues. The controls were infants born to mothers not exposed to any medication in pregnancy (n = 20). Positive controls were the same infants, but in this case Nitrogranulogen (Sigma) was added to the collected cord blood samples (n = 11). Micronucleus (MN) assay was used as an indicator of chromosome damage. The frequency (%) of MN/1000 binucleated cells and the nuclear division index (NDI) were calculated.

RESULTS

Mean MN frequency and NDI were respectively 0.110 (+/-0.152), 1.592 (+/-0.206) in the study group and 0.050 (+/-0.061), 1.628 (+/-0.178) in the controls (statistically non-significant difference, p > 0.1).

CONCLUSION

The findings did not reveal any genotoxic effect or inhibition of nuclear division in cord blood lymphocytes by AED metabolites. This was reflected by the absence of significant between-group differences in the mean MN frequency and NDI.

Folate-responsive neurologic diseases

Folate is a water-soluble vitamin of the B complex group, and is required for optimal health, growth, and development. In humans, it cannot be synthesized de novo. As a cofactor or coenzyme, folate plays key biological roles in a variety of physiologic processes: maintenance and repair of the genome, regulation of gene expression, amino-acid metabolism, neurotransmitter synthesis, and the formation of myelin. Dietary folates must undergo multiple, tightly regulated absorption and metabolic processes before their cellular utilization occurs. Clinical conditions associated with abnormal body folate status are very diverse. They range from genetic syndromes defined prior to conception, to malformations that develop during embryogenesis (neural tube defects), to disorders that are postnatally acquired and progressive (e.g., cerebral folate deficiency, or folinic acid-responsive seizures). Central nervous system folate deficiency or impaired availability can occur in the settings of normal or decreased systemic folate levels. Because the majority of patients respond to treatment with folinic acid, pediatric neurologists should remain vigilant to the possibility of deficiencies of folate in patients with unexplained neurologic disorders. The deleterious outcomes of untreated patients underscore the importance of making an early diagnosis.

Schizophrenia and neural tube defects: comparisons from an epidemiological perspective

In this review, we examine and compare epidemiological studies of schizophrenia and neural tube defects (NTDs). Although there is no apparent link between these 2 disparate disorders in terms of clinical manifestation or phenotypes, overlapping patterns in the variation of incidence of schizophrenia with that of NTDs indicate the existence of one or more shared etiological risk factors. Evidence in support of such a phenomenon may enhance our understanding of underlying pathological mechanisms and may guide future studies of etiology and prevention. The similarities that occur in a number of epidemiological observations for these disorders are in keeping with a hypothesis of nutritional deficiencies in utero acting as a risk factor for both schizophrenia and NTDs. Programes of periconceptual folate and multivitamin supplementation aimed to reduce the risk of NTDs are already in place in many countries. Nevertheless, evidence of additional effects of specific maternal micronutrient deficiency on risk of schizophrenia may not only increase enthusiasm for expansion of such programes but also enhance understanding of etiology of this disorder and offer the potential for targeted interventions in high-risk groups.

Effect of maternal exposure to homocystine on sodium valproate-induced neural tube defects in the mouse embryos

BACKGROUND

Neural tube defects (NTD) are mainly of multifactorial origin. Maternal treatment with valproic acid (VPA) during pregnancy induces NTD in susceptible fetuses. Elevated levels of homocysteine are observed in pregnancies with NTD. The mechanism by which homocysteine might cause NTD is unknown.

AIM OF THE STUDY

The aim of this study was to determine if homocystine would augment VPA-induced exencephaly in an experimental model.

METHODS

Groups of mice were injected (IP) on gestational day 8 (GD) with a single dose of 75 mg/kg of L: -Homocystine (HC) or a proportionate volume of saline, followed by a single dose of 600 mg/kg of VPA or an equal volume of saline. In a second experiment, mice were treated with a daily dose of 75 mg/kg of HC or an equal volume of saline (IP) from GD 5 and continued through GD 10. These animals had a single exposure to 600 mg/kg of VPA or saline (IP) on GD 8. All animals were killed by cervical dislocation on GD 18. Plasma homocysteine, folate and vitamin B12 were determined on GD 8 and GD 10 from single and multiple dose groups of mice, respectively, from additional experiments.

RESULTS

The VPA and HC+VPA induced significantly higher rates of embryonic resorption and intrauterine growth retardation (IUGR) than HC or saline alone. HC + VPA groups had significantly more numerous fetuses with severe IUGR than HC alone or VPA alone groups. Both single and multiple doses of HC augmented VPA-induced reduction in fetal body weight. Successive doses of HC did not augment the rate of IUGR more significantly than a single dose of HC. Incidence of exencephaly was significantly enhanced in the HC + VPA groups compared to that in the HC or VPA alone groups. HC alone was not teratogenic. Plasma homocysteine levels increased several fold both in HC and HC + VPA groups and the increase was not particularly more marked in multiple dose groups than in the single dose groups. VPA did not elevate homocysteine concentration. Both FA and vitamin B12 concentrations were reduced by VPA, HC and HC + VPA, but HC and VPA when combined did not produce an additive effect on vitamin levels.

CONCLUSION

These data indicate that HC and VPA interact in neurulation stage embryos, affect fundamental processes of closure of the neural tube and lead to enhanced incidence of NTD.

Pregnancy in women who have epilepsy

Ideal, comprehensive care of women who have epilepsy during the reproductive years must include effective preconceptional counseling and preparation. The importance of planned pregnancies with effective birth control should be emphasized, with consideration of the effects of the enzyme-inducing AEDs on lowering efficacy of hormonal contraceptive medications and the need for back-up barrier methods. Before pregnancy occurs, the patient's diagnosis and treatment regimen should be reassessed. Once the diagnosis of epilepsy is confirmed, it is important to verify if the individual patient continues to need medications and if she is taking the most appropriate AED to balance control of her seizures with teratogenic risks. For most women who have epilepsy, withdrawal of all AEDs before pregnancy is not a realistic option. A decision to undergo a trial while not taking AEDs before a planned pregnancy should be based on the same principles used for AED withdrawal in any person who has epilepsy. The taper should be completed at least 6 months before planned conception to provide some reassurance that seizures are not going to recur. If a woman who has epilepsy is in the more prevalent category of needing AEDs for seizure control, then monotherapy at the lowest effective dosage should be used. If large daily doses are needed, then frequent smaller doses or extended-release formulations may be helpful to avoid high peak levels. Some of the newest information about differential risks between AEDs also should be considered. The woman's AED regimen should be optimized and folate supplementation should begin before pregnancy. Given that 50% of pregnancies are unplanned in the United States, folate supplementation should be encouraged in all women of childbearing age who are taking any AED for any indication. Dosing recommendations vary from 0.4 mg/d to 5 mg/d. It is not uncommon for a physician to consider changing AED regimens when the patient first reports that she is pregnant. In many cases, she already is in or past the critical period of organogenesis (Table 3). If a woman who has epilepsy presents after conception and is taking a single AED that is effective, her medication usually should not be changed. Exposing the fetus to a second agent during a crossover period of AEDs only increases the teratogenic risk, and seizures are more likely to occur with any abrupt medication changes. If a woman is on polytherapy, it may be possible to switch to monotherapy safely. Seizure control remains an important goal during pregnancy. In particular, convulsive seizures place the mother and fetus at risk. Nonconvulsive seizures also may be harmful, especially if they involve falling or other forms of trauma. Monitoring serum AED levels during pregnancy can be helpful in optimizing seizure control. Prenatal screening can detect major malformations in the first and second trimesters. Vitamin K1 is given 10 mg/d orally during the last month of pregnancy followed by 1 mg intramuscularly or intravenously to the new-born. Although women who have epilepsy and women who are taking AEDs for other indications do have increased risks for maternal and fetal complications, these risks can be reduced considerably with effective preconceptional planning and careful management during pregnancy and the postpartum period.

Spina bifida

Spina bifida results from failure of fusion of the caudal neural tube, and is one of the most common malformations of human structure. The causes of this disorder are heterogeneous and include chromosome abnormalities, single gene disorders, and teratogenic exposures. However, the cause is not known in most cases. Up to 70% of spina bifida cases can be prevented by maternal, periconceptional folic acid supplementation. The mechanism underlying this protective effect is unknown, but it is likely to include genes that regulate folate transport and metabolism. Individuals with spina bifida need both surgical and medical management. Although surgical closure of the malformation is generally done in the neonatal period, a randomised clinical trial to assess in utero closure of spina bifida has been initiated in the USA. Medical management is a lifelong necessity for individuals with spina bifida, and should be provided by a multidisciplinary team.