Reduction in diabetes-induced craniofacial defects by maternal immune stimulation

Single Cell Multimodal Analyses Reveal Epigenomic and Transcriptomic Basis for Birth Defects in Maternal Diabetes

Maternal diabetes mellitus is among the most frequent environmental contributors to congenital birth defects, including heart defects and craniofacial anomalies, yet the cell types affected and mechanisms of disruption are largely unknown. Using multi-modal single cell analyses, here we show that maternal diabetes affects the epigenomic landscape of specific subsets of cardiac and craniofacial progenitors during embryogenesis. A previously unrecognized cardiac progenitor subpopulation expressing the homeodomain-containing protein ALX3 showed prominent chromatin accessibility changes and acquired a more posterior identity. Similarly, a subpopulation of neural crest-derived cells in the second pharyngeal arch, which contributes to craniofacial structures, displayed abnormalities in the epigenetic landscape and axial patterning defects. Chromatin accessibility changes in both populations were associated with increased retinoic acid signaling, known to establish anterior-posterior identity. This work highlights how an environmental insult can have highly selective epigenomic consequences on discrete cell types leading to developmental patterning defects.

Maternal serum CFHR4 protein as a potential non-invasive marker of ventricular septal defects in offspring: evidence from a comparative proteomics study

Background

Despite advances in diagnosis of congenital heart defects, there is no non-invasive biomarker clinically available for the early detection of fetal ventricular septal defects (VSD).

Methods

This study was to profile differentially expressed proteins (DEP) in the first trimester maternal plasma samples that were collected in the 12th–14th week of gestation and identify potential biomarkers for VSD. Maternal plasma samples of ten case–control pairs of women (who had given birth to an isolated VSD infant or not) were selected from a birth cohort biospecimen bank for identifying DEPs by using high-performance liquid chromatography-tandem mass spectrometry-based comparative proteomics.

Results

There were 35 proteins with significantly different levels between cases and controls, including 9 upregulated and 26 downregulated proteins. With Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and protein–protein interaction analyses, most of the DEPs were clustered in pathways related to B cell-mediated immune responses, complement activation, and phagocytosis. Three DEPs were validated using enzyme-linked immunosorbent assay in another set of samples consisting of 31 cases and 33 controls. And CFHR4, a key regulator in complement cascades, was found to be significantly upregulated in cases as compared to controls.

Conclusions

Subsequent logistic regression and receiver operating characteristic analysis suggested maternal serum CFHR4 as a promising biomarker of fetal VSD. Further studies are warranted to verify the findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-022-09356-y.

Complement factors and alpha-fetoprotein as biomarkers for noninvasive prenatal diagnosis of neural tube defects

Neural tube defects (NTDs) are serious congenital malformations. In this study, we aimed to identify more specific and sensitive maternal serum biomarkers for noninvasive NTD screenings. We collected serum from 37 pregnant women carrying fetuses with NTDs and 38 pregnant women carrying normal fetuses. Isobaric tags for relative and absolute quantitation were conducted for differential proteomic analysis, and an enzyme-linked immunosorbent assay was used to validate the results. We then used a support vector machine (SVM) classifier to establish a disease prediction model for NTD diagnosis. We identified 113 differentially expressed proteins; of these, 23 were either up- or downregulated 1.5-fold or more, including five complement proteins (C1QA, C1S, C1R, C9, and C3); C3 and C9 were downregulated significantly in NTD groups. The accuracy rate of the SVM model of the complement factors (including C1QA, C1S, and C3) was 62.5%, with 60% sensitivity and 67% specificity, while the accuracy rate of the SVM model of alpha-fetoprotein (AFP, an established biomarker for NTDs) was 62.5%, with 75% sensitivity and 50% specificity. Combination of the complement factor and AFP data resulted in the SVM model accuracy of 75%, and receiver operating characteristic curve analysis showed 75% sensitivity and 75% specificity. These data suggest that a disease prediction model based on combined complement factor and AFP data could serve as a more accurate method of noninvasive prenatal NTD diagnosis.

Congenital nasal pyriform aperture stenosis: Analysis of twenty cases at a single institution

OBJECTIVES

Congenital nasal pyriform aperture stenosis (CNPAS) is a rare cause of neonatal respiratory distress that is difficult to treat. The primary objective of this study was to identify factors that predict the need for initial and revision surgery for CNAPS. The secondary objective is to identify risk factors in maternal history associated with the development of CNPAS.

METHODS

Infants with CNPAS between 2010 and 2017 were identified by ICD- 9 and 10 codes. Demographics, maternal history, anatomic features on imaging and medical and/or surgical management were reviewed. Frequencies, means and standard deviations were calculated. A p-value <.05 was considered significant.

RESULTS

Twenty infants were included. All underwent flexible nasal endoscopy with inability to pass the scope in either nostril in 65% of infants. Nineteen had a CT scan and 13 had a MRI with midline defects in 76.3% and 53.8%, respectively. Solitary central mega-incisor was present in 65%. Half underwent surgical intervention at a mean age of 74.8 days, with 90% requiring revision surgery. There was no difference in pyriform aperture distance in the surgical and non-surgical patient subgroups (5.4 mm and 5.2 mm, p = .6 respectively). No specific variables were predictive of need for initial or revision surgery. Maternal diabetes mellitus (MDM) was found in 55% of mothers of infants with CNPAS.

CONCLUSION

Pyriform aperture distance was not a predictor of surgical intervention. MRI should be considered in all infants with CNPAS as the rate of intracranial complications is high. MDM may be a risk factor for CNPAS.

Diabetes mellitus and drug abuse during pregnancy and the risk for orofacial clefts and related abnormalities

Objective:

to assessed the prevalence of diabetes mellitus (DM) and drug abuse in mothers of children with orofacial clefts (OFC).

Methods:

325 women who had children (0-3y) with clefts were interviewed. Data regarding type of diabetes, use of legal/illegal drugs during pregnancy, waist girth and fasting blood sugar at the first prenatal consult were collected.

Results:

twenty seven percent of the women had DM, out of these, 89% had gestational DM, 5,5% type 1 DM and 5,5% type 2 DM. The prevalence of DM in mothers of children with OFC was 27%, it is significantly higher than the average Brazilian population which is 7.6% (p<0.01) (OR=4.5, 95%CI=3.5-5.8). Regarding drug abuse during pregnancy, 32% of the mothers used drugs and a significant positive correlation was observed between drug abuse and the occurrence of clefts and other craniofacial anomalies (p=0.028) (OR=2.87; 95%CI=1.1-7.4).

Conclusions:

DM and drug abuse during pregnancy increases the risk for OFC and related anomalies and early diagnosis of DM and prevention of drug abuse, especially in pregnant women, should be emphasized.

Ambient and Dosed Exposure to Quaternary Ammonium Disinfectants Causes Neural Tube Defects in Rodents

Background

Quaternary ammonium compounds are a large class of chemicals used for their antimicrobial and antistatic properties. Two common quaternary ammonium compounds, alkyldimethylbenzyl ammonium chloride (ADBAC) and didecyldimethyl ammonium chloride (DDAC), are combined in common cleaners and disinfectants. Introduction of a cleaner containing ADBAC+DDAC in the vivarium caused neural tube defects (NTDs) in mice and rats.

Methods

To further evaluate this finding, male and female mice were dosed in the feed at 60 or 120 mg/kg/day, or by oral gavage at 7.5, 15, or 30 mg/kg ADBAC+DDAC. Mice also received ambient exposure to ADBAC+DDAC from the disinfectant used in the mouse room. Embryos were evaluated on gestational day 10 for NTDs, and fetuses were evaluated on gestational day 18 for gross and skeletal malformations.

Results

We found increased NTDs with exposure to ADBAC+DDAC in both rats and mice. The NTDs persisted for two generations after cessation of exposure. Notably, male exposure alone was sufficient to cause NTDs. Equally significant, ambient exposure from disinfectant use in the vivarium, influenced the levels of NTDs to a greater extent than oral dosing. No gross or significant axial skeletal malformations were observed in late gestation fetuses. Placental abnormalities and late gestation fetal deaths were increased at 120 mg/kg/day, which might explain the lack of malformations observed in late gestation fetuses.

Conclusion

These results demonstrate that ADBAC+DDAC in combination are teratogenic to rodents. Given the increased use of these disinfectants, further evaluation of their safety in humans and their contribution to health and disease is essential.

Modulation of lipid metabolic defects rescues cleft palate in Tgfbr2 mutant mice

Mutations in transforming growth factor beta (TGFβ) receptor type II (TGFBR2) cause Loeys-Dietz syndrome, characterized by craniofacial and cardiovascular abnormalities. Mice with a deletion of Tgfbr2 in cranial neural crest cells (Tgfbr2(fl/fl);Wnt1-Cre mice) develop cleft palate as the result of abnormal TGFβ signaling activation. However, little is known about metabolic processes downstream of TGFβ signaling during palatogenesis. Here, we show that Tgfbr2 mutant palatal mesenchymal cells spontaneously accumulate lipid droplets, resulting from reduced lipolysis activity. Tgfbr2 mutant palatal mesenchymal cells failed to respond to the cell proliferation stimulator sonic hedgehog, derived from the palatal epithelium. Treatment with p38 mitogen-activated protein kinase (MAPK) inhibitor or telmisartan, a modulator of p38 MAPK activation and lipid metabolism, blocked abnormal TGFβ-mediated p38 MAPK activation, restoring lipid metabolism and cell proliferation activity both in vitro and in vivo. Our results highlight the influence of alternative TGFβ signaling on lipid metabolic activities, as well as how lipid metabolic defects can affect cell proliferation and adversely impact palatogenesis. This discovery has broader implications for the understanding of metabolic defects and potential prevention of congenital birth defects.

Reduction in valproic acid-induced neural tube defects by maternal immune stimulation: role of apoptosis

Teratogenic deregulation of apoptosis during development is a possible mechanism for birth defects. Administration of valproic acid (VA) during first trimester of pregnancy causes neural tube defects (NTDs). Nonspecific stimulation of the mother's immune system has been shown to reduce various teratogen-induced fetal malformations including NTDs in rodents. This present study investigated the role of reduced apoptosis by maternal immune stimulation in prevention of VA-induced NTDs in CD-1 mice. Prevention of VA-induced NTDs by nonspecific maternal immune stimulation using IFNγ was employed to evaluate the role of reduced apoptosis by IFNγ in this protective mechanism. Apoptosis was quantified using flow cytometry. Terminal Transferase dUTP Nick End Labeling assay was used to localize the apoptosis. Increased apoptosis, suggesting involvement in VA teratogenicity, was observed along the neural tube in both normal and abnormal embryos from VA-exposed dams. Increased apoptosis in normal VA-exposed embryos suggests that VA may alter other cellular processes such as cell proliferation and differentiation in addition to apoptosis. Apoptotic levels in embryos with closed neural tubes from IFNγ + VA dams were similar to controls indicating resistance to VA-induced apoptosis and protection against teratogenicity of VA. In IFNγ + VA exposed embryos with open neural tubes, maternal immune stimulation failed to regulate apoptosis resulting in an NTD. Overall, these results suggest that VA alters several biological processes including apoptosis in the developing embryos to induce fetal malformations. Resistance to VA-induced apoptosis in embryos resulting from maternal immune stimulation may be involved in protective mechanism.

Effect of maternal immunopotentiation on apoptosis-associated molecules expression in teratogen-treated embryos

PROBLEM

Potentiation of the maternal immune system was shown by us to affect the embryonic response to teratogenic insults. In order to understand better the mechanisms underlying that phenomenon, we explored the effect of maternal immunopotentiation by rat splenocytes on the early stages of the embryonic response to cyclophosphamide (CP).

METHOD OF STUDY

Immunopotentiated CP-treated embryos were analysed for cell cycle changes by flow cytometry, while cell proliferation and apoptosis were assessed by 5'-bromo-2'-deoxyuridine (BrdU) incorporation and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL) respectively. The expression of the p65 subunit of NF-kappaB, IkappaBalpha, Bax, bcl-2 and p53 was assessed by flow cytometry.

RESULTS

Exposure to CP resulted in significant growth retardation and in the appearance of cellular damage, a reduction in cell proliferation and the appearance of apoptotic cells, which were all found to be delayed in immunopotentiated embryos. In parallel, CP-treated embryos demonstrated a reduction in the percentage of p65- or IkappaBalpha-positive cells, while the percentage of bcl-2- or p53-positive cells increased initially and decreased later. Those changes were normalized by maternal immunopotentiation when tested at 24 hrs after exposure to the teratogen.

CONCLUSION

Our data implicate maternal immunopotentiation to protect the embryo against teratogenic insults, possibly through its effect on the expression of p65, bcl-2 or p53.

Production of a type 2 maternal diabetes rodent model using the combination of high-fat diet and moderate dose of streptozocin

INTRODUCTION

Pregnancy may be complicated by maternal diabetes. The following experiments were performed in an attempt to produce mouse models of insulin-resistant maternal diabetes.

METHODS

CD1 females received 200 mg/kg streptozocin (STZ) to model insulin-dependent diabetes (T1 group). Another group of females (T2 group) was put on a HFD 4 weeks before receiving 100 mg/kg STZ. After 4 additional weeks of HFD, hyperglycemic females were separated and bred. In another experiement, CD1 females were fed a HFD for 4 weeks before receiving an intravenous (GDM1 group) or intraperitoneal (GDM2 group) injection of 100 mg/kg STZ. Females from GDM2 group were bred at the same day of the STZ injection. Females from GDM1 group were bred 4 weeks after the STZ injection.

RESULTS AND CONCLUSION

About 25% of the females from T2 group became hyperglycemic after 4 weeks of the injection of STZ. Fifty percent of the females from GDM1 group reached hyperglycemic levels greater than 250 mg/dl during pregnancy. The combination of HFD and moderate STZ in CD1 mice therefore produced hyperglycemic females; however numbers of these mice were somewhat low.

Late-gestation ventricular myocardial reduction in fetuses of hyperglycemic CD1 mice is associated with increased apoptosis

BACKGROUND

Previous work in our laboratory showed reduced myocardium and dilated ventricular chambers in gestation day (GD) 17 hearts that were collected from hyperglycemic CD1 mouse dams. Pre-breeding maternal immune stimulation, using Freund's complete adjuvant (FCA), diminished the severity of these fetal heart lesions. The following experiments were performed to detect possible changes in fetal heart apoptotic cell death, under hyperglycemic conditions and with or without maternal immune stimulation.

METHODS

Female CD1 mice were injected with 200 mg/kg of streptozocin (STZ) to induce insulin-dependent diabetes mellitus. Half of these mice received prior FCA injection. Fetal hearts were collected on GD 17 and myocardial apoptotic cells were quantified using flow cytometry. A panel of apoptosis regulatory genes (Bcl2, p53, Casp3, Casp9, PkCe) was then examined in the fetal myocardium using RT-PCR.

RESULTS

Early apoptotic cells and late apoptotic/necrotic cells were significantly increased in fetal hearts from STZ or STZ+FCA dams. Pre-treatment with FCA reduced late apoptotic/necrotic cells to control level, suggesting some cell death protection was rendered by FCA. Paradoxically in the face of such increased cell death, the expression of pro-apoptotic genes Casp3 and Casp9 was decreased by diabetes, while the anti-apoptotic gene Bcl2 was increased.

CONCLUSIONS

Maternal hyperglycemia causes dys-regulated apoptosis of fetal myocardial cells. Such effect may be prevented by maternal immune stimulation.

Modulation of diabetes-induced palate defects by maternal immune stimulation

Maternal diabetes can induce a number of developmental abnormalities in both laboratory animals and humans, including deformities of the face and palate. The incidence of birth defects in newborns of women with diabetes is approximately 3 to 5 times higher than among nondiabetics. In mice, nonspecific activation of the maternal immune system can reduce fetal abnormalities caused by various etiologies including hyperglycemia. This study was conducted to determine whether nonspecific maternal immune stimulation could reduce diabetes-induced palate defects and orofacial clefts. Female ICR mice were immune stimulated before induction of hyperglycemia with Freund's complete adjuvant (FCA), granulocyte-macrophage colony-stimulating factor (GM-CSF), or interferon-gamma (IFNgamma). Streptozocin was used to induce hyperglycemia (26-35 mmol blood glucose) in females before breeding. Fetuses from 12 to 18 litters per treatment group were collected on Day 17 of gestation. Palate width and length were measured, and the incidence of orofacial clefts was determined. Palate length and width were both decreased by maternal hyperglycemia. Maternal immune stimulation with GM-CSF or FCA limited the degree of palate shortening from the hyperglycemia. Each of the three immune stimulants attenuated significant narrowing of the palate. Rates of orofacial clefts were not significantly different between treatment groups. Palatogenesis is a complex process driven by cellular signals, which regulate cell growth and apoptosis. Dysregulation of cellular signals by maternal hyperglycemia can result in fetal malformations. Maternal immune stimulation may prevent dysregulation of these signaling pathways thus reducing fetal malformations and normalizing palate growth.

Heart changes in 17-day-old fetuses of diabetic ICR (Institute of Cancer Research) mothers: improvement with maternal immune stimulation

Maternal diabetes mellitus is associated with increased fetal teratogenesis, including cardiovascular defects. Non-specific maternal immune stimulation with Freund's complete adjuvant (FCA) or interferon gamma (IFNgamma) has been associated with protection against birth malformations. Using a diabetic mouse model, late-gestation fetal heart and great vessel morphology were analyzed. Four groups of mice were used: non-diabetic females as a control group, hyperglycemic females induced by streptozotocin as a diabetic group, and diabetic females injected either with FCA or IFNgamma. At day 17 of gestation, females were euthanized and one fetus was arbitrarily selected per litter for fixation and sectioning. Treatment-induced changes in cardiac development were assessed from digital images of serial sections taken at standardized levels in the thorax. One-way parametric and non-parametric ANOVA and ordinal logistic regression were performed to compare the difference among groups (P<0.05). Maternal hyperglycemia altered morphology of the late-gestation fetal mouse heart by causing ventricular chamber dilation, sectional myocardial reduction, and an increase in transversal aortic area. FCA protected the fetal heart from cavitary dilation in diabetic mothers. FCA and IFNgamma protected the fetal heart against reduction of myocardial area, and ascending thoracic aorta dilation. Consequences of late gestation heart chamber dilation and myocardial reduction are not yet known. Maternal immune stimulation partially protected against these developmental defects by mechanisms that remain unclear.

Aortic and ventricular dilation and myocardial reduction in gestation day 17 ICR mouse fetuses of diabetic mothers

BACKGROUND

Maternal diabetes mellitus is associated with increased fetal teratogenesis, including cardiovascular defects. Information regarding cardiovascular changes in late-gestation fetal mice, related to maternal hyperglycemia, is not present in the literature.

METHODS

Late-gestation fetal heart and great vessel morphology were analyzed in fetuses from control and diabetic mice. Female ICR mice were injected with streptozocin (200 mg/kg IP) prior to mating to induce diabetes (n = 8). Nonhyperglycemic females were used as controls (n = 8). At day 17 of gestation, females were euthanized and one fetus was arbitrarily selected per litter to analyze the heart and great vessels. Six additional fetuses from different litters, showing external malformations (spina bifida and/or exencephaly), were also evaluated from the diabetic group. Fetal thoraxes were processed using routine histopathologic techniques, and 7-mum transversal sections were stained with hematoxylin-eosin. Digital images of sections were made and analyzed using NIH Image J software to compare regional cardiac development. Student's t tests for means were performed to determine differences between groups (p < .05).

RESULTS

Maternal hyperglycemia caused a dilation of late-gestation fetal ventricular chambers, a reduction of total ventricular myocardial area, and an increase in transversal ascending thoracic aortic area. Three of six fetuses that displayed external malformations showed an overt cardiac defect, beyond the ventricular and myocardial changes.

CONCLUSIONS

Maternal hyperglycemia altered morphology of the late-gestation fetal mouse heart. Postnatal persistence or consequences of late-gestation heart chamber dilation and myocardial reduction are not yet known.

Palatal fusion - where do the midline cells go? A review on cleft palate, a major human birth defect

Formation of the palate, the organ that separates the oral cavity from the nasal cavity, is a developmental process characteristic to embryos of higher vertebrates. Failure in this process results in palatal cleft. During the final steps of palatogenesis, two palatal shelves outgrowing from the sides of the embryonic oronasal cavity elevate above the tongue, meet in the midline, and rapidly fuse together. Over the decades, multiple mechanisms have been proposed to explain how the superficial mucous membranes disappear from the contact line, thus allowing for normal midline mesenchymal confluence. A substantial body of experimental evidence exists for cell death, cell migration, epithelial-to-mesenchymal transdifferentiation (EMT), replacement through new tissue intercalation, and other mechanisms. However, the most recent use of gene recombination techniques in cell fate tracking disfavors the EMT concept, and suggests that apoptosis is the major fate of the midline cells during physiological palatal fusion. This article summarizes the benefits and drawbacks of histochemical and molecular tools used to determine the fates of cells within the palatal midline. Mechanisms of normal disintegration of the midline epithelial seam are reviewed together with pathologic processes that prevent this disintegration, thus causing cleft palate.

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.

Valproic Acid: second generation

The manuscript focuses on structure-activity relationship studies of CNS-active compounds derived from valproic acid (VPA) that have the potential to become second-generation VPA drugs. Valproic acid is one of the four most widely prescribed antiepileptic drugs (AEDs) and is effective (and regularly approved) in migraine prophylaxis and in the treatment of bipolar disorders. Valproic acid is also currently undergoing clinical trials in cancer patients. Valproic acid is the least potent of the established AEDs and its use is limited by two rare but potentially life-threatening side effects, teratogenicity and hepatotoxicity. Because AEDs treat the symptoms (seizure) and not the cause of epilepsy, epileptic patients need to take AEDs for a long period of time. Consequently, there is a substantial need to develop better and safer AEDs. To become a successful second-generation VPA, the new drug should possess the following characteristics: broad-spectrum antiepileptic activity, better potency than VPA, lack of teratogenicity and hepatotoxicity, and a favorable pharmacokinetic profile compared with VPA including a low potential for drug interactions.

New antiepileptic drugs that are second generation to existing antiepileptic drugs

In the last decade, 10 new antiepileptic drugs (AEDs) have been introduced that offer appreciable advantages in terms of their favourable pharmacokinetics, improved tolerability and lower potential for drug interactions. However, despite the large therapeutic range of old and new AEDs, approximately 30% of the patients with epilepsy are still not seizure free and, consequently, there is a substantial need to develop new AEDs. The new AEDs currently in development can be divided into two categories: drugs with completely new chemical structures such as lacosamide (formally harkoseride), retigabine, rufinamide and talampanel; and drugs that are derivatives or analogues of existing AEDs that can be regarded as second-generation or follow-up compounds of established AEDs. This article focuses on the second category and thus critically reviews the following second-generation compounds: eslicarbazepine acetate or BIA-2-093 and 10-hydroxy carbazepine (carbamazepine derivatives); valrocemide and NPS 1776 (isovaleramide; valproic acid derivatives); pregabalin and XP13512 (gabapentin derivatives); brivaracetam (ucb 34714) and seletracetam (ucb 44212; levetiracetam derivatives); and fluorofelbamate (a felbamate derivative). In addition, a series of valproic acid derivatives that are currently in preclinical stage has also been evaluated because some lead compounds of this series have a promising potential to become new antiepileptics and CNS drugs. For any of these follow-up compounds to become a successful second generation to an existing AED, it has to be more potent, safer and possess favourable pharmacokinetics, including low potential for pharmacokinetic and pharmacodynamic drug interactions.