Valproic acid-induced alterations in growth and neurotrophic factor gene expression in murine embryos [corrected]

Dynamic regulation of BDNF gene expression by estradiol and lncRNA HOTAIR

Brain derived neurotrophic factor (BDNF) is a major neurotransmitter that controls growth and maintenance of neurons and its misregulation is linked to neurodegeneration and human diseases. Estradiol (E2) is well-known to regulate the process of differentiation and plasticity of hippocampal neurons. Here we examined the mechanisms of BDNF gene regulation under basal conditions and under stimuli such as E2. Our results demonstrated that BDNF expression is induced by E2 in vitro in HT22 cells (hippocampal neuronal cells) and in vivo (in ovariectomized mouse brain under E2-treatment). Using chromatin immunoprecipitation assay, we demonstrated that estrogen receptors (ERα, ERβ) were enriched at the BDNF promoter in presence of E2. Additionally, ER-coregulators (e.g., CBP/p300, MLL3), histone acetylation, H3K4-trimethylation, and RNA polymerase II levels were also elevated at the BDNF promoter in an E2-dependent manner. Additionally, under the basal conditions (in the absence of E2), the long noncoding RNA HOTAIR and its interacting partners PRC2 and LSD1 complexes binds to the promoter of BDNF and represses its expression. HOTAIR knockdown -relieves the repression resulting in elevation of BDNF expression. Further, levels of HOTAIR-interacting partners, EZH2 and LSD1 were reduced at the BDNF promoter upon HOTAIR-knockdown revealing that HOTAIR plays a regulatory role in BDNF gene expression by modulating promoter histone modifications. Additionally, we showed that E2 induced-BDNF expression is mediated by the displacement of silencing factors, EZH2 and LSD1 at BDNF promoter and subsequent recruitment of active transcription machinery. These results reveal the mechanisms of BDNF gene regulation under the basal condition and in presence of a positive regulator such as E2 in neuronal cells.

The early overgrowth theory of autism spectrum disorder: Insight into convergent mechanisms from valproic acid exposure and translational models

The development of new approaches for the clinical management of autism spectrum disorder (ASD) can only be realized through a better understanding of the neurobiological changes associated with ASD. One strategy for gaining deeper insight into the neurobiological mechanisms associated with ASD is to identify converging pathogenic processes associated with human idiopathic clinicopathology that are conserved in translational models of ASD. In this chapter, we first present the early overgrowth theory of ASD. Second, we introduce valproic acid (VPA), one of the most robust and well-known environmental risk factors associated with ASD, and we summarize the rapidly growing body of animal research literature using VPA as an ASD translational model. Lastly, we will detail the mechanisms of action of VPA and its impact on functional neural systems, as well as discuss future research directions that could have a lasting impact on the field.

Neuropsychopathology of Autism Spectrum Disorder: Complex Interplay of Genetic, Epigenetic, and Environmental Factors

Autism spectrum disorder (ASD) is a complex heterogeneous consortium of pervasive development disorders (PDD) which ranges from atypical autism, autism, and Asperger syndrome affecting brain in the developmental stage. This debilitating neurodevelopmental disorder results in both core as well as associated symptoms. Core symptoms observed in autistic patients are lack of social interaction, pervasive, stereotyped, and restricted behavior while the associated symptoms include irritability, anxiety, aggression, and several comorbid disorders.ASD is a polygenic disorder and is multifactorial in origin. Copy number variations (CNVs) of several genes that regulate the synaptogenesis and signaling pathways are one of the major factors responsible for the pathogenesis of autism. The complex integration of various CNVs cause mutations in the genes which code for molecules involved in cell adhesion, voltage-gated ion-channels, scaffolding proteins as well as signaling pathways (PTEN and mTOR pathways). These mutated genes are responsible for affecting synaptic transmission by causing plasticity dysfunction responsible, in turn, for the expression of ASD.Epigenetic modifications affecting DNA transcription and various pre-natal and post-natal exposure to a variety of environmental factors are also precipitating factors for the occurrence of ASD. All of these together cause dysregulation of glutamatergic signaling as well as imbalance in excitatory: inhibitory pathways resulting in glial cell activation and release of inflammatory mediators responsible for the aberrant social behavior which is observed in autistic patients.In this chapter we review and provide insight into the intricate integration of various genetic, epigenetic, and environmental factors which play a major role in the pathogenesis of this disorder and the mechanistic approach behind this integration.

Multi-target drug repositioning by bipartite block-wise sparse multi-task learning

Background

Finding potential drug targets is a crucial step in drug discovery and development. Recently, resources such as the Library of Integrated Network-Based Cellular Signatures (LINCS) L1000 database provide gene expression profiles induced by various chemical and genetic perturbations and thereby make it possible to analyze the relationship between compounds and gene targets at a genome-wide scale. Current approaches for comparing the expression profiles are based on pairwise connectivity mapping analysis. However, this method makes the simple assumption that the effect of a drug treatment is similar to knocking down its single target gene. Since many compounds can bind multiple targets, the pairwise mapping ignores the combined effects of multiple targets, and therefore fails to detect many potential targets of the compounds.

Results

We propose an algorithm to find sets of gene knock-downs that induce gene expression changes similar to a drug treatment. Assuming that the effects of gene knock-downs are additive, we propose a novel bipartite block-wise sparse multi-task learning model with super-graph structure (BBSS-MTL) for multi-target drug repositioning that overcomes the restrictive assumptions of connectivity mapping analysis.

Conclusions

The proposed method BBSS-MTL is more accurate for predicting potential drug targets than the simple pairwise connectivity mapping analysis on five datasets generated from different cancer cell lines.

Availability

The code can be obtained at http://gr.xjtu.edu.cn/web/liminli/codes.

Effect of early postnatal exposure to valproate on neurobehavioral development and regional BDNF expression in two strains of mice

Valproate has been used for over 30years as a first-line treatment for epilepsy. In recent years, prenatal exposure to valproate has been associated with teratogenic effects, limiting its use in women that are pregnant or of childbearing age. However, despite its potential detrimental effects on development, valproate continues to be prescribed at high rates in pediatric populations in some countries. Animal models allow us to test hypotheses regarding the potential effects of postnatal valproate exposure on neurobehavioral development, as well as identify potential mechanisms mediating observed effects. Here, we tested the effect of early postnatal (P4-P11) valproate exposure (100mg/kg and 200mg/kg) on motor and affective development in two strains of mice, SVE129 and C57Bl/6N. We also assessed the effect of early valproate exposure on regional BDNF protein levels, a potential target of valproate, and mediator of neurodevelopmental outcomes. We found that early life valproate exposure led to significant motor impairments in both SVE129 and C57Bl/6N mice. Both lines of mice showed significant delays in weight gain, as well as impairments in the righting reflex (P7-8), wire hang (P17), open field (P12 and P21), and rotarod (P25 and P45) tasks. Interestingly, some of the early locomotor effects were strain- and dose-dependent. We observed no effects of valproate on early markers of anxiety-like behavior. Importantly, early life valproate exposure had significant effects on regional BDNF expression, leading to a near 50% decrease in BDNF levels in the cerebellum of both strains of mice, while not impacting hippocampal BDNF protein levels. These observations indicate that postnatal exposure to valproate may have significant, and region-specific effects, on neural and behavioral development, with specific consequences for cerebellar development and motor function.

Use of antiepileptic drugs in pregnancy

Babies born to mothers exposed to antiepileptic drugs (AEDs) are at increased risk for major congenital malformations, cognitive impairment and fetal death. For the millions of women with epilepsy, maintaining the safest drug that will successfully prevent seizures during pregnancy remains a primary consideration. The recent development of collaborative international registries to examine the differential and dose-dependent effects of the expanding number of old and new AEDs, have shed light upon potential differences during pregnancy. Valproic acid appears to be associated with the highest risk of overall, as well as AED-specific, birth defects, becoming more evident as doses exceed 1000 mg/day. Lamotrigine may be less teratogenic to humans than other AEDs, although orofacial clefts have recently been reported. The effects of polytherapy appear to carry greater risks compared with monotherapy. Limited data exist for many of the newer AEDs. Furthermore, AED effects may persist during postnatal development. Although no class 1 outcome data are available, prepregnancy counseling to optimize patient-specific treatment is recommended for women of childbearing potential with epilepsy.

Alterations of neocortical development and maturation in autism: insight from valproic acid exposure and animal models of autism

Autism spectrum disorder (ASD) is a behaviourally defined brain disorder affecting approximately 1 in 88 children. Many pathological studies have shown that ASD is frequently associated with grey and white matter changes that can be described by their deviations from the normal trajectory of cortical maturation. For example, during the early (i.e. <2 years) postnatal period there is marked and selective tissue overgrowth in the higher-order temporal and frontal networks involved in emotional, social, and communication functions. In this focused review we first summarize some basic principles of neocortical neural organization and how they are disrupted in ASD. We will then highlight some of the potential mechanisms by which the normal developmental trajectory and organization of neocortical networks can be altered based on animal studies of valproic acid, a teratogen widely used in animal models of ASD. We argue that the trajectory of postnatal cerebral neocortex development may be influenced by several cellular and molecular mechanisms that may all converge to produce a neuropathology characterized by premature or accelerated neuronal growth.

Antiepileptic drugs and pregnancy outcomes

The treatment of epilepsy in women of reproductive age remains a clinical challenge. While most women with epilepsy (WWE) require anticonvulsant drugs for adequate control of their seizures, the teratogenicity associated with some antiepileptic drugs (AEDs) is a risk that needs to be carefully addressed. Antiepileptic medications are also used to treat an ever broadening range of medical conditions such as bipolar disorder, migraine prophylaxis, cancer, and neuropathic pain. Despite the fact that the majority of pregnancies of WWE who are receiving pharmacological treatment are normal, studies have demonstrated that the risk of having a pregnancy complicated by a major congenital malformation is doubled when comparing the risk of untreated pregnancies. Furthermore, when AEDs are used in polytherapy regimens, the risk is tripled, especially when valproic acid (VPA) is included. However, it should be noted that the risks are specific for each anticonvulsant drug. Some investigations have suggested that the risk of teratogenicity is increased in a dose-dependent manner. More recent studies have reported that in utero exposure to AEDs can have detrimental effects on the cognitive functions and language skills in later stages of life. In fact, the FDA just issued a safety announcement on the impact of VPA on cognition (Safety Announcement 6-30-2011). The purpose of this document is to review the most commonly used compounds in the treatment of WWE, and to provide information on the latest experimental and human epidemiological studies of the effects of AEDs in the exposed embryos.

Chronic divalproex sodium to attenuate agitation and clinical progression of Alzheimer disease

CONTEXT

Agitation and psychosis are common in Alzheimer disease and cause considerable morbidity. We attempted to delay or to prevent agitation and psychosis with the use of divalproex sodium (valproate).

OBJECTIVE

To determine whether treatment with valproate could delay or prevent emergence of agitation or psychosis.

DESIGN, SETTING, AND PATIENTS

A multicenter, randomized, double-blind, placebo-controlled trial of flexible-dose valproate in 313 (of 513 screened) individuals with moderate Alzheimer disease who had not yet experienced agitation or psychosis. The study was conducted from November 1, 2005, through March 31, 2009, at 46 sites in the United States.

INTERVENTION

Participants were randomly assigned to valproate treatment at a target dose of 10 to 12 mg per kilogram of body weight per day or identical-appearing placebo for 24 months followed by a 2-month period of single-blind placebo treatment.

MAIN OUTCOME MEASURE

Time to emergence of clinically significant agitation or psychosis.

RESULTS

A total of 122 participants (59 receiving valproate and 63 receiving placebo) completed 24 months of treatment while taking study medication; 42 (27 receiving valproate and 15 receiving placebo) reached 24 months having discontinued study medication; 150 reached month 26. There was no difference between groups in time to emergence of agitation or psychosis (Cox proportional hazard ratio, 0.96; P = .88). There was no difference between groups in change on any secondary outcome. The valproate group had higher rates of somnolence, gait disturbance, tremor, diarrhea, and weakness. Eighty-eight participants underwent magnetic resonance imaging scans at baseline and 12 months; the valproate group showed greater loss in hippocampal and whole-brain volume, accompanied by greater ventricular expansion (P < .001).

CONCLUSION

Valproate treatment did not delay emergence of agitation or psychosis or slow cognitive or functional decline in patients with moderate Alzheimer disease and was associated with significant toxic effects.

Teratogenic effects of antiepileptic drugs

Many antiepileptic drugs (AEDs) have therapeutic applications that extend beyond epilepsy to include neuropathic pain, migraine headaches and psychiatric disorders. The risk of some AEDs has been clearly established, but for newer drugs, small sample sizes and polytherapy exposures preclude a conclusive determination of their teratogenic potential. Most women with epilepsy will require AED therapy throughout their entire pregnancy to control seizures; the vast majority of pregnancies in women with epilepsy have positive outcomes. A conservative estimate suggests that AED monotherapy doubles, and polytherapy triples, the risk for major congenital malformations. Furthermore, while evidence is still accruing, recent investigations suggest that exposure to select AEDs results in altered cognitive function later in development. There is no evidence to suggest that additional folic acid supplementation ameliorates the increased risk of congenital malformations conferred by in utero AED exposure.

Effects of the brain-derived neurotrophic growth factor val66met variation on hippocampus morphology in bipolar disorder

Histological and behavioral research in bipolar disorder (BD) implicates structural abnormalities in the hippocampus. Brain-derived neurotrophic growth factor (BDNF) protein is associated with hippocampal development and plasticity, and in mood disorder pathophysiology. We tested the hypotheses that both the BDNF val66met polymorphism and BD diagnosis are associated with decreased hippocampus volume, and that individuals with BD who carry the met allele have the smallest hippocampus volumes compared to individuals without BD and val/val homozygotes. We further explored localization of morphological differences within hippocampus in BD associated with the met allele. Twenty individuals with BD and 18 healthy comparison (HC) subjects participated in high-resolution magnetic resonance imaging scans from which hippocampus volumes were defined and measured. We used linear mixed model analysis to study effects of diagnosis and BDNF genotype on hippocampus volumes. We then employed three-dimensional mapping to localize areas of change within the hippocampus associated with the BDNF met allele in BD. We found that hippocampus volumes were significantly smaller in BD compared to HC subjects, and presence of the BDNF met allele was associated with smaller hippocampus volume in both diagnostic groups. The BD subgroup who carried the BDNF met allele had the smallest hippocampus volumes, and three-dimensional mapping identified these decreases as most prominent in left anterior hippocampus. These results support effects of BD diagnosis and BDNF genotype on hippocampus structure and suggest a genetic subgroup within BD who may be most vulnerable to deficits in hippocampus and may most benefit from interventions that influence BDNF-mediated signaling.

Valproic acid-induced fetal malformations are reduced by maternal immune stimulation with granulocyte-macrophage colony-stimulating factor or interferon-gamma

Valproic acid, a drug commonly used to treat seizures and other psychiatric disorders, causes neural tube defects (NTDs) in exposed fetuses at a rate 20 times higher than in the general population. Failure of the neural tube to close during development results in exencephaly or anencephaly, as well as spina bifida. In mice, nonspecific activation of the maternal immune system can reduce fetal abnormalities caused by diverse etiologies, including diabetes-induced NTDs. We hypothesized that nonspecific activation of the maternal immune system with interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF) could reduce valproic acid (VA)-induced defects as well. Female CD-1 mice were given immune stimulant prebreeding: either IFN-gamma or GM-CSF. Approximately half of the control and immune-stimulated pregnant females were then exposed to 500 mg/kg VA on the morning of gestational day 8. The incidence of developmental defects was determined on gestational day 17 from at least eight litters in each of the following treatment groups: control, VA only, IFN-gamma only, IFN-gamma+VA, GM-CSF only, and GM-CSF+VA. The incidence of NTDs was 18% in fetuses exposed to VA alone, compared to 3.7% and 2.9% in fetuses exposed to IFN-gamma+VA, or GM-CSF+VA respectively. Ocular defects were also significantly reduced from 28.0% in VA exposed groups to 9.8% in IFN-gamma+VA and 12.5% in GM-CSF+VA groups. The mechanisms by which maternal immune stimulation prevents birth defects remain unclear, but may involve maternal or fetal production of cytokines or growth factors which protect the fetus from the dysregulatory effects of teratogens.

Failure of homocysteine to induce neural tube defects in a mouse model

BACKGROUND

Folate deficiencies have been associated with many adverse congenital abnormalities. It is not clear, however, whether these defects are due to a folate deficiency or to an increase in homocysteine. Homocysteine has been shown to be teratogenic in the chicken-embryo model and it has been suggested that homocysteine-induced defects are mediated by inhibiting the N-methyl-D-aspartate (NMDA) receptor on neural crest cells. The majority of the teratology studies have been carried out using the chicken embryo model. In an effort to develop a murine model of homocysteine-induced neural tube defects, several inbred mouse strains were treated with homocysteine or the NMDA inhibitor MK801 and the fetuses examined for any induced-NTD.

METHODS

Several in-bred mouse strains were administered homocysteine once on gestational day (GD) E8.5 or once daily on GD 6.5-10.5. Additionally, because homocysteine was been reported to mediate its effects through the NMDA receptor, the effect of MK801, an antagonist of this receptor, was also investigated.

RESULTS

Regardless of the mouse treatment time, homocysteine failed to induce neural tube defects in our in-bred mouse strains. Homocysteine also failed to increase the number of neural tube defects in the splotch strain, regardless of the genotype.

CONCLUSIONS

Irrespective of the mouse strain or treatment, homocysteine failed to induce neural tube defects in our mouse models, which is in contrast to what has been reported in the chicken embryo models.

Molecular approaches to developmental malformations using analogous forms of valproic acid

The teratogenic potential of valproic acid has been well established both in experimental models and in human clinical studies. Evidence from many previous studies has shown that VPA is an appropriate drug model for studying chemical structure-teratogenicity relationships. Using molecular techniques of DNA microarray (GeneChip system) or quantitative real-time polymerase chain reaction with low teratogenic VPA analogs as comparative control drugs, we attempted to identify the genes involved with the molecular mechanisms of VPA teratogenicity in the neural tube and the axial skeleton of the mouse embryo. The recent development of DNA microarray enables a genome-wide approach to the identification of genes correlated with the teratogenicity of chemicals (teratogenomics). The VPA-induced changes in gene expression seen during mouse embryogenesis provides information for understanding how VPA disrupts normal embryonic development, and also provides leads for the development of safer medicines.

Myo-inositol enhances teratogenicity of valproic acid in the mouse

BACKGROUND

Valproic acid (VPA) is an anticonvulsant drug that is widely used therapeutically for a variety of neurological conditions. VPA is also well known for its teratogenic potential in both humans and experimental animal models. The typical malformations observed following VPA exposure include neural tube defects (NTDs) and craniofacial and skeletal malformations. Nevertheless, the mechanisms underlying VPA's anticonvulsant efficacy or its teratogenicity remain to be elucidated. It was recently suggested that a relationship exists between VPA exposure and the cellular depletion of myo-inositol (INO). Furthermore, INO has been shown to rescue NTDs in the curly tail mouse. The aim of this study was to investigate the interactions of VPA and INO in the developing embryo.

METHODS

For this purpose, 2 strains of mice were used: SWV/Fnn (known to be sensitive to VPA) and LM/Bc (known to be resistant to VPA-induced NTDs). Pregnant females were randomly assigned to 4 experimental groups: control, VPA (600 mg/kg), INO (400 mg/kg), and VPA plus INO. VPA was injected IP at 8.5 days postcoitum (dpc). INO was administered PO twice a day from 6.5 to 10.5 dpc. At term the dams were killed, the uteri were removed, and all of the general toxicological parameters (number of implants, resorptions, dam weight, and fetus weight) were recorded and statistically analyzed.

RESULTS

Postimplantation loss in the SWV/Fnn strain and NTDs in the LM/Bc strain were significantly increased after the coadministration of VPA and INO.

CONCLUSIONS

This work clearly indicates that INO enhances VPA-induced teratogenicity in the mouse.

The effects of valproic acid, vitamin E and folic acid on ribs of rat fetuses in the prenatal period

The present study was undertaken to determine histopathologic differences in the ribs of Wistar-albino rat fetuses prenatally exposed to valproic acid (VPA), folic acid (FA) and vitamin E (Vit E), and to compare their differential developmental susceptibility and morphological association with skeletal anomalies. VPA (300 mg/ kg), FA (300mg/kg) and Vit E (250mg/kg) were administered to rats on each of gestation days (GD) 7-9. Fetuses were collected on GD 21 and their ribs were examined for malformations. The fetuses were divided into four groups: blind-trial group, VPA group (vpa), VPA and Vit E group (vpa+vit e), valproic and FA group (vpa+fa). In each group; drug procedure, surgical procedure and histological methods were performed. Later, weights and lengths of fetuses in each group were compared and analyzed by one-way Anova test. As a result, maLformations in fetuses were determined and photographed by Nikon SMZ-2 steromicroscopy, using 2 x objective. Administration of single doses of VPA (300 mg/kg) resulted in weight and length loss between blind-trial and vpa group. However, length and weight differences between the other groups were not significant. The objective of the present study is to analyze morphological and histopathologic changes which may occur in a high-risk experimental model after the administration of VPA. In addition, protective roles of the administration of FA and Vit E are assessed.

Identification of early-responsive genes correlated to valproic acid-induced neural tube defects in mice

BACKGROUND

Valproic acid (VPA) causes the failure of neural tube closure in newborn mice. However, the molecular mechanism of its teratogenesis is unknown. This study was conducted to investigate the genomewide effects of VPA disruption of normal neural tube development in mice.

METHODS

Microarray analysis was performed on the head part of NMRI mouse embryos treated for 1 hr with VPA on gestational day (GD) 8. Subsequently, we attempted to isolate genes that changed in correlation with the teratogenic action of VPA by employing reduced teratogenic VPA analogs, valpromide (VPD) and valnoctamide (VCD), in a real-time PCR study.

RESULTS

Microarray results demonstrated that during neurulation, many genes, some of whose functions are known and some unknown, were either increased or decreased after VPA injection. Some genes were affected by VPD or VCD in the same way as VPA, but others were not changed by the analogs. In this way, our system identified 11 increased and 20 decreased genes. Annotation analysis revealed that the increased genes included gadd45b, ier5, per1, phfl3, pou3f1, and sox4, and the decreased genes included ccne2, ccnl, gas5, egr2, sirt1, and zfp105.

CONCLUSIONS

These findings demonstrate that expression changes in genes having roles in the cell cycle and apoptosis pathways of neural tube cells were strongly expected to relate to the teratogenic, but not antiepileptic, activity of VPA. Our approach has allowed the expansion of the catalog of molecules immediately affected by VPA in the developing neural tube.

Experimental studies on cervical and lumbar ribs in mouse embryos

In humans, the presence of cervical and lumbar ribs is of particular clinical significance. However, the relevance of their occurrence in the offspring of experimental animals in reproductive toxicologic studies is poorly understood. Maternal toxicity has been implicated in the etiology but conclusive evidence is lacking. The present study was undertaken to determine the incidence of supernumerary ribs (SNR) in mouse fetuses prenatally exposed to valproic acid (VPA) and retinoic acid (RA), and to compare their differential developmental susceptibility and morphological association with other axial skeletal anomalies. Single doses of valproic acid (VPA) or retinoic acid (RA) were administered to groups of mice on one of gestation days (GD) 7-12. Fetuses were collected on GD 18 and their skeletons examined for SNR. VPA treatment on GD 7 and GD 8 resulted in a high incidence of cervical and lumbar ribs, respectively. Cervical neural arch anomalies in the GD 7 group, and eight pairs of sternal ribs and seven sternebrae in the GD 8 group were observed in excess of the background SNR suggesting a direct effect of VPA on the developing mouse skeletal system. In the RA groups, GD 8-12 were susceptible for lumbar rib induction but increased incidence of cervical ribs was observed only from GD 9-12. Peak incidence of cervical ribs was found in the GD 10 and 11 groups and that of the lumbar ribs in the GD 8 and 11 groups. Although SNR incidence generally increased with increasing dose of RA, a strict dose-response relationship was lacking. Cervical arch anomalies were observed in as many embryos as those with cervical ribs, but eight pairs of sternal ribs and seven sternebrae did not correlate well with the lumbar ribs in the peak day groups. Interrupted cervical neural arches correlated well with lumbar ribs. The reduction in the frequency of presacral vertebrae from 26 to 25 in the VPA groups was limited to GD 7 (30%) and 8 (18%) groups. RA-induced reduction in presacral vertebral number extended to GD 9 and was greater in the GD 8 than in the GD 9 groups. Sternal anomalies occurred both in VPA and RA experiments and did not strictly correlate with the frequency of SNR. VPA had a narrow window of susceptibility, whereas RA effects on sternum extended from GD 9-12. The incidence of sternal anomalies generally increased with increasing dose and advancing developmental stage at which RA exposure occurred. These developmental susceptibility windows and associated malformations, when considered in the context of the ability of these drugs to induce alterations in gene expression in mouse embryos suggest that SNR are polygenic in origin and greatly influenced by environmental toxicants.

Gene-Teratogen Interactions in Chemically Induced Congenital Malformations

Exposure of the embryo to environmental chemicals can result in congenital malformations or abortion. Although experimental teratology data are considered sufficient for risk assessment, only knowledge of their mechanisms of action permits a justifiable extrapolation of animal data to humans. Mechanistic studies of some teratogenic agents such as retinoic acids, valproic acid, diethylstilbestrol, and cyclopamine provided evidence of interference with regulation of genes controlling the embryonic development. The new genomic technologies are important tools in this field and may represent a real improvement in understanding the mechanisms of action of chemical teratogens.

Mood stabilizers in Alzheimer's disease: symptomatic and neuroprotective rationales

OBJECTIVE

This paper provides a case study of 'reverse translational research', in which empirical clinical trials focused on relieving psychopathological symptoms of Alzheimer's disease (AD) ultimately led to mechanism-based trials addressing aspects of the underlying pathophysiology of Alzheimer's disease. AD is multi-dimensional in nature, characterized not only by cognitive and functional decline but by neuropsychiatric symptoms that develop commonly and are associated with considerable morbidity. There have been a large number of empirical trials of various pharmacological agents to reduce these symptoms, such as agitation. Although antipsychotics are used most frequently for agitation, the usual effect size is modest, and there is a range of tolerability and/or safety issues, leading to the hope that alternatives can be found. Furthermore, most clinical trials addressing psychopathology have not been mechanism-based and none have attempted an alternative approach, namely, to delay or prevent the emergence of psychopathology.

FINDINGS

The evidence of clinical trials is reviewed regarding the safety, tolerability, and apparent efficacy of the mood stabilizers carbamazepine and valproate for agitation associated with AD. Possible mechanisms of action of valproate are reviewed, leading to the surprising conclusion that neuroprotective properties may account for some of its clinical effects. These mechanisms (including activation of wnt-dependent signaling and upregulation of bcl-2, among others) may be particularly relevant for long-term treatment of AD.

CONCLUSIONS

These clinical and mechanistic findings were combined in the development of a novel clinical trial examining whether chronic valproate therapy can attenuate the clinical progression of AD, which will be implemented by the Alzheimer's Disease Cooperative Study. The design addresses valproate's potential to delay or prevent the onset of agitation in patients lacking agitation to begin with, as well as to slow progressive decline in cognition and daily functioning.

Neural crest cell motility in valproic acid

Neural crest cells (NCCs) exit the dorsal neural tube and migrate to sites where they form diverse tissues. Valproic acid (VPA) is an anticonvulsant drug that induces neural tube and related defects. Altered NCC migration and proliferation have been proposed as mechanisms of teratogenicity. We cultured neural tube segments from chick embryos in 0.75-3.0mM VPA. We used image analysis, proliferation assays, and fluorescence localization to investigate NCCs during VPA exposure. VPA inhibited attachment of explants and the number that produced migrating cells. VPA markedly decreased the proportion of cells migrating individually, promoting migration as epithelial sheets. VPA at 3mM decreased cellular spreading. Area and perimeter change per minute were reduced, but migration velocity was not. VPA at 2mM reduced proliferation 11% and 3mM arrested proliferation. Immunostaining of VPA-exposed explants revealed N-cadherin-positive cell boundaries within sheets, but independent NCCs did not stain. F-actin staining was reduced in independent NCCs. The data support a VPA mechanism involving interference with epithelial-mesenchymal transition.

Gene expression profiling within the developing neural tube

The developing mammalian nervous system is subject to devastating congenital malformations with clinical significance that extends into the billions of health care dollars annually worldwide. Neural tube defects (NTDs) are among the most common of all human congenital defects, yet their etiology remains poorly understood. This is largely due to the complexity of the genetic factors regulating the intricate events involved in neurulation. Using mouse model systems and the application of modern molecular biological technologies, we have recently gained a greater appreciation for the factors that not only regulate normal neural tube closure (NTC), but those genetic factors that predispose an embryo to significant birth defects such as anencephaly or spina bifida. We have selected prominent murine mutants, both spontaneous and genetically modified, as well as the use of teratogenic agents, to examine the impact of altering the normal pattern of gene expression in the developing neural tube.

Molecular basis of environmentally induced birth defects

Exposure of the developing conceptus to selected environmental agents can lead to deleterious and often times lethal birth defects. These malformations result in serious emotional and financial consequences to families and societies worldwide. As we continue to progress technologically, we face challenges from the introduction of new pharmacological agents and chemical compounds into the environment. This results in a concomitant need to more fully understand the relationship between in utero exposure to environmental teratogens and the risk of congenital malformations. The goal of this review is to provide a current perspective of the major concepts related to the molecular basis of environmentally induced birth defects. Starting with a discussion of commonly occurring birth defects, we consider important fundamental facets of embryonic development, teratology, and gene-environment interactions. The review then summarizes our current understanding of the molecular mechanisms involved in selected birth defects following exposure to pharmacological compounds, including thalidomide, retinoids, and valproic acid. Understanding these signaling pathways may lead to the development of safer pharmaceutical compounds and a reduction in the number of infants born with preventable birth defects.

Maternal immune stimulation in mice decreases fetal malformations caused by teratogens

For unknown reasons, non-specific stimulation of the maternal immune system in pregnant mice has what appears to be a broad-spectrum efficacy for reducing birth defects. Immune stimulation by diverse procedures has proven effective, including footpad injection with Freund's complete adjuvant (FCA), intraperitoneal (IP) injection with inert particles to activate resident macrophages, IP injection with attenuated Bacillus Calmette-Guerin (BCG), and intrauterine injection with allogeneic or zenogeneic lymphocytes. Morphologic lesions that were significantly reduced included cleft palate and associated craniofacial defects, digit and limb defects, tail malformations, and neural tube defect (NTD). Teratogenic stimuli to induce these lesions included chemical agents (2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], ethyl carbamate [urethane], methylnitrosourea [MNU], cyclophosphamide [CP], and valproic acid [VA]), physical agents (X-rays, hyperthermia), and streptozocin (STZ)-induced diabetes mellitus. Limited information is available regarding mechanisms by which such immune stimulation reduced fetal dysmorphogenesis. The collective literature suggests the possibility that immunoregulatory cytokines of maternal origin may be the effector molecules in this phenomenon.