Phenytoin-induced cleft palate: evidence for embryonic cardiac bradyarrhythmia due to inhibition of delayed rectifier K+ channels resulting in hypoxia-reoxygenation damage

Involvement of microRNA-4680-3p against phenytoin-induced cell proliferation inhibition in human palate cells

Cleft palate (CP) is one of the most common birth defects and is caused by a combination of genetic and/or environmental factors. Environmental factors such as pharmaceutical exposure in pregnant women are known to induce CP. Recently, microRNA (miRNA) was found to be affected by environmental factors. The aim of the present study was to investigate the involvement of miRNA against phenytoin (PHE)-induced inhibition of proliferation in human embryonic palatal mesenchymal (HEPM) cells. We demonstrated that PHE inhibited HEPM cell proliferation in a dose-dependent manner. We found that treatment with PHE downregulated cyclin-D1 and cyclin-E expressions in HEPM cells. Furthermore, PHE increased miR-4680-3p expression and decreased two downstream genes (ERBB2 and JADE1). Importantly, an miR-4680-3p-specific inhibitor restored HEPM cell proliferation and altered expression of ERBB2 and JADE1 in cells treated with PHE. These results suggest that PHE suppresses cell proliferation via modulation of miR-4680-3p expression.

Dexamethasone Suppresses Palatal Cell Proliferation through miR-130a-3p

Cleft lip with or without cleft palate (CL/P) is one of the most common congenital birth defects. This study aims to identify novel pathogenic microRNAs associated with cleft palate (CP). Through data analyses of miRNA-sequencing for developing palatal shelves of C57BL/6J mice, we found that miR-449a-3p, miR-449a-5p, miR-449b, miR-449c-3p, and miR-449c-5p were significantly upregulated, and that miR-19a-3p, miR-130a-3p, miR-301a-3p, and miR-486b-5p were significantly downregulated, at embryonic day E14.5 compared to E13.5. Among them, overexpression of the miR-449 family (miR-449a-3p, miR-449a-5p, miR-449b, miR-449c-3p, and miR-449c-5p) and miR-486b-5p resulted in reduced cell proliferation in primary mouse embryonic palatal mesenchymal (MEPM) cells and mouse cranial neural crest cell line O9-1. On the other hand, inhibitors of miR-130a-3p and miR-301a-3p significantly reduced cell proliferation in MEPM and O9-1 cells. Notably, we found that treatment with dexamethasone, a glucocorticoid known to induce CP in mice, suppressed miR-130a-3p expression in both MEPM and O9-1 cells. Moreover, a miR-130a-3p mimic could ameliorate the cell proliferation defect induced by dexamethasone through normalization of Slc24a2 expression. Taken together, our results suggest that miR-130-3p plays a crucial role in dexamethasone-induced CP in mice.

The effect of phenytoin on embryonic heart rate in Vivo

Phenytoin is a known human teratogen with unknown etiology. Several mechanisms have been proposed including disturbances in folate metabolism, induction of embryonic hypoxia following phenytoin-induced bradycardia, free radical formation following re-oxygenation and phenytoin-induced maternal hyperglycemia. Using high frequency ultrasound, we demonstrated that phenytoin induced a dramatic decrease in the heart rate of embryos. This coincided with a moderate transient decrease in maternal heart rate and blood glucose levels. Embryonic heart rate had not fully recovered 24 h later in some embryos despite normal maternal physiological parameters. In a separate study, extent of hypoxia was measured using the marker pimonidazole. Phenytoin-exposed embryos did not demonstrate increased hypoxia compared to control embryos at 2, 4, 8 or 24 h dosing. Together our results show that phenytoin induces malformations as a result of a combination of insults: embryonic bradycardia, maternal bradycardia and maternal hyperglycemia. However, this does not appear to result in measurable embryonic hypoxia in our animal model.

Environmental mechanisms of orofacial clefts

Orofacial clefts (OFCs) are among the most common birth defects and impart a significant burden on afflicted individuals and their families. It is increasingly understood that many nonsyndromic OFCs are a consequence of extrinsic factors, genetic susceptibilities, and interactions of the two. Therefore, understanding the environmental mechanisms of OFCs is important in the prevention of future cases. This review examines the molecular mechanisms associated with environmental factors that either protect against or increase the risk of OFCs. We focus on essential metabolic pathways, environmental signaling mechanisms, detoxification pathways, behavioral risk factors, and biological hazards that may disrupt orofacial development.

Msx1 Heterozygosity in Mice Enhances Susceptibility to Phenytoin-Induced Hypoxic Stress Causing Cleft Palate

OBJECTIVE

Cleft palate is among the most frequent congenital defects in humans. While gene-environment multifactorial threshold models have been proposed to explain this cleft palate formation, only a few experimental models have verified this theory. This study aimed to clarify whether gene-environment interaction can cause cleft palate through a combination of specific genetic and environmental factors.

METHODS

Msx1 heterozygosity in mice (Msx1^+/-) was selected as a genetic factor since human MSX1 gene mutations may cause nonsyndromic cleft palate. As an environmental factor, hypoxic stress was induced in pregnant mice by administration of the antiepileptic drug phenytoin, a known arrhythmia inducer, during palatal development from embryonic day (E) 11 to E14. Embryos were dissected at E13 for histological analysis or at E17 for recording of the palatal state.

RESULTS

Phenytoin administration downregulated cell proliferation in palatal processes in both wild-type and Msx1^+/- embryos. Bone morphogenetic protein 4 (Bmp4) expression was slightly downregulated in the anterior palatal process of Msx1^+/- embryos. Although Msx1^+/- embryos do not show cleft palate under normal conditions, phenytoin administration induced a significantly higher incidence of cleft palate in Msx1^+/- embryos compared to wild-type littermates.

CONCLUSION

Our data suggest that cleft palate may occur because of the additive effects of Bmp4 downregulation as a result of Msx1 heterozygosity and decreased cell proliferation upon hypoxic stress. Human carriers of MSX1 mutations may have to take more precautions during pregnancy to avoid exposure to environmental risks.

Msx1 deficiency interacts with hypoxia and induces a morphogenetic regulation during mouse lip development

Nonsyndromic clefts of the lip and palate are common birth defects resulting from gene-gene and gene-environment interactions. Mutations in human MSX1 have been linked to orofacial clefting and we show here that Msx1 deficiency causes a growth defect of the medial nasal process (Mnp) in mouse embryos. Although this defect alone does not disrupt lip formation, Msx1-deficient embryos develop a cleft lip when the mother is transiently exposed to reduced oxygen levels or to phenytoin, a drug known to cause embryonic hypoxia. In the absence of interacting environmental factors, the Mnp growth defect caused by Msx1 deficiency is modified by a Pax9-dependent 'morphogenetic regulation', which modulates Mnp shape, rescues lip formation and involves a localized abrogation of Bmp4-mediated repression of Pax9 Analyses of GWAS data revealed a genome-wide significant association of a Gene Ontology morphogenesis term (including assigned roles for MSX1, MSX2, PAX9, BMP4 and GREM1) specifically for nonsyndromic cleft lip with cleft palate. Our data indicate that MSX1 mutations could increase the risk for cleft lip formation by interacting with an impaired morphogenetic regulation that adjusts Mnp shape, or through interactions that inhibit Mnp growth.

Fetal hypoxia and hyperglycemia in the formation of phenytoin-induced cleft lip and maxillary hypoplasia

OBJECTIVE

Phenytoin exposure during the first trimester of pregnancy increases the risk of maxillary hypoplasia and cleft lip. The etiology of phenytoin embryopathy is unknown. Interestingly, phenytoin is also known to induce hyperglycemia in humans as well as rats. This study uses a rat model of fetal phenytoin syndrome to examine the role of hyperoxia, hyperglycemia, and arachidonic acid deficiency in the development of cleft lip and maxillary hypoplasia.

METHODS

Pregnant rats were dosed with phenytoin during the critical period of lip development (day 11 of pregnancy) with or without supplemental oxygen, insulin, or arachidonic acid. The fetuses from all studies were examined at term.

RESULTS

The frequency of cleft lip and maxillary hypoplasia was reduced by treating dams at the time of phenytoin exposure with either increased oxygen or insulin. However, in fetuses from phenytoin-treated dams dosed with arachidonic acid, the incidence of severe lip deformities remained the same although there was an increase in normal and mildly affected fetuses. Interestingly, this occurred in embryos from hyperglycemic dams.

SIGNIFICANCE

Together, the results from these experiments suggest phenytoin-induced malformations may be a multifactorial process as malformations were not solely linked to a hyperglycemic state of the dam.

Knockdown of Crispld2 in zebrafish identifies a novel network for nonsyndromic cleft lip with or without cleft palate candidate genes

Orofacial development is a multifaceted process involving tightly regulated genetic signaling networks, that when perturbed, lead to orofacial abnormalities including cleft lip and/or cleft palate. We and others have shown an association between the cysteine-rich secretory protein LCCL domain containing 2 (CRISPLD2) gene and nonsyndromic cleft lip with or without cleft palate (NSCLP). Further, we demonstrated that knockdown of Crispld2 in zebrafish alters neural crest cell migration patterns resulting in abnormal jaw and palate development. In this study, we performed RNA profiling in zebrafish embryos and identified 249 differentially expressed genes following knockdown of Crispld2. In silico pathway analysis identified a network of seven genes previously implicated in orofacial development for which differential expression was validated in three of the seven genes (CASP8, FOS, and MMP2). Single nucleotide variant (SNV) genotyping of these three genes revealed significant associations between NSCLP and FOS/rs1046117 (GRCh38 chr14:g.75746690 T > C, p = 0.0005) in our nonHispanic white (NHW) families and MMP2/rs243836 (GRCh38 chr16:g.55534236 G > A; p = 0.002) in our Hispanic families. Nominal association was found between NSCLP and CASP8/rs3769825 (GRCh38 chr2:g.202111380 C > A; p < 0.007). Overtransmission of MMP2 haplotypes were identified in the Hispanic families (p < 0.002). Significant gene-gene interactions were identified for FOS-MMP2 in the NHW families and for CASP8-FOS in the NHW simplex family subgroup (p < 0.004). Additional in silico analysis revealed a novel gene regulatory network including five of these newly identified and 23 previously reported NSCLP genes. Our results demonstrate that animal models of orofacial clefting can be powerful tools to identify novel candidate genes and gene regulatory networks underlying NSCLP.

Association of JARID2 polymorphisms with non-syndromic orofacial clefts in northern Chinese Han population

OBJECTIVES

Non-syndromic orofacial clefts (NSOC) are the most common human craniofacial malformation in all worldwide populations. Recently, the jumoji AT-rich interaction domain 2 (JARID2) had been reported to be a novel candidate gene for non-syndromic cleft lip with or without cleft palate (CL/P). The SNPs rs2076056, rs2237138 and rs2299043 in JARID2 were highly significant in Italian families.

MATERIAL AND METHODS

In the current research, a case-control study was conducted to examine the association between these three SNPs and NSOC in a northern Chinese Han population. Genotyping of the three SNPs were performed using SNaPshot minisequencing technique.

RESULTS

Distribution of rs2237138 genotypes in CL/P group was different from those in the control group (P = 0.04), but significant results did not persist after Benjamini and Hochberg false discovery rate (FDR) correction for multiple tests. Further logistic regression analysis showed that rs2237138 GG genotypes were associated with decreased CL/P susceptibility (OR = 0.34, 95% CI = 0.13-0.84), compared with the AA wild-type homozygote. For the haplotype CGT, a statistically difference was identified between the CL/P group and controls (P = 0.04). And carriers of GAT haplotype were considered to be less frequent among cleft palate only group as compared to controls (P = 0.02). However, both of the haplotypes association did not remain statistically significant after Benjamini and Hochberg FDR correction.

CONCLUSION

We got a weak association between these polymorphisms and NSOC in both single-marker and haplotype analyses. Our data further strengthen the conclusion that JARID2 polymorphisms are associated with NSOC susceptibility.

Otorhinolaryngology/maxillofacial disorders

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Upper respiratory infections are ubiquitous

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Voice changes may herald laryngeal cancer

The teratogenic effect of dofetilide during rat limb development and association with drug-induced bradycardia and hypoxia in the embryo

BACKGROUND

Dofetilide is an antiarrhythmic drug that blocks the cardiac repolarizing current IKr ((IKr, rapid component of the delayed rectifying potassium current). Previous studies have shown that (a) IKr is essential for normal cardiac function of the embryonic heart and (b) dofetilide is teratogenic in rodents. This study was undertaken to examine the mechanism by which dofetilide causes limb defects on gestational day 13 (GD 13) in the rat.

METHODS

Rats were treated with dofetilide (single oral dose, 5 mg/kg) on GD 13 and embryonic heart rates assessed by ultrasound (Vevo770, VisualSonics, Toronto, Ontario, Canada) 2 hr later. Fetuses were examined for malformations on GD 20. In a separate experiment, dofetilide treatment of GD 13 rats was followed 2, 4, 12, or 24 hr with iv dosing with the hypoxia marker, pimonidazole (60 mg/kg). Embryos were collected and heart rates were assessed in vitro and hypoxia in embryo limbs analyzed.

RESULTS

A teratogenic dose of dofetilide at a susceptible stage of development (GD 13) resulted in a period of bradycardia and arrhythmia of the embryonic heart and hypoxia in the developing limbs (GD 13) resulting in limb malformations (GD 20).

CONCLUSIONS

Drugs that induce periods of bradycardia and/or arrhythmia of the embryonic heart and cause the embryo to become hypoxic are potential human teratogens.

Nonsyndromic cleft lip and palate: CRISPLD genes and the folate gene pathway connection

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common birth defect that has a multifactorial etiology. Despite having substantial genetic liability, <15% of the genetic contribution to NSCLP has been delineated. In our efforts to dissect the genetics of NSCLP, we found that variation in the CRISPLD2 (cysteine-rich secretory protein LCCL domain containing 2) gene is associated with NSCLP and that the protein is expressed in the developing murine craniofacies. In addition, we found suggestive linkage of NSCLP (LOD > 1.0) to the chromosomal region on 8q13.2-21.13 that contains the CRISPLD1 gene. The protein products of both CRISPLD1 and CRISPLD2 contain more cysteine residues than comparably sized proteins. Interestingly, the folic acid pathway produces endogenous cysteines, and variation in genes in this pathway is associated with NSCLP. Based on these observations, we hypothesized that variation in CRISPLD1 contributes to NSCLP and that both CRISPLD genes interact with each other and genes in the folic acid pathway.

METHODS

Single nucleotide polymorphisms (SNPs) in CRISPLD1 were genotyped in our non-Hispanic white and Hispanic multiplex and simplex NSCLP families.

RESULTS

There was little evidence for a role of variation for CRISPLD1 alone in NSCLP. However, interactions were detected between CRISPLD1/CRISPLD2 SNPs and variation in folate pathway genes. Altered transmission of one CRISPLD1 SNP was detected in the NHW simplex families. Importantly, interactions were detected between SNPs in CRISPLD1 and CRISPLD2 (15 interactions, 0.0031 ≤p < 0.05).

CONCLUSION

These novel findings suggest that CRISPLD1 plays a role in NSCLP through the interaction with CRISPLD2 and folate pathway genes.

CRISPLD2: a novel NSCLP candidate gene

Non-syndromic cleft lip with or without cleft palate (NSCLP) results from the complex interaction between genes and environmental factors. Candidate gene analysis and genome scans have been employed to identify the genes contributing to NSCLP. In this study, we evaluated the 16q24.1 chromosomal region, which has been identified by multiple genome scans as an NSCLP region of interest. Two candidate genes were found in the region: interferon regulatory factor 8 (IRF8) and cysteine-rich secretory protein LCCL domain containing 2 (CRISPLD2). Initially, Caucasian and Hispanic NSCLP multiplex families and simplex parent-child trios were genotyped for single nucleotide polymorphisms (SNPs) in both IRF8 and CRISPLD2. CRISPLD2 was subsequently genotyped in a data set comprised of NSCLP families from Colombia, South America. Linkage disequilibrium analysis identified a significant association between CRISPLD2 and NSCLP in both our Caucasian and Hispanic NSCLP cohorts. SNP rs1546124 and haplotypes between rs1546124 and either rs4783099 or rs16974880 were significant in the Caucasian multiplex population (P=0.01, P=0.002 and P=0.001, respectively). An altered transmission of CRISPLD2 SNPs rs8061351 (P=0.02) and rs2326398 (P=0.06) was detected in the Hispanic population. No association was found between CRISPLD2 and our Colombian population or IRF8 and NSCLP. In situ hybridization showed that CRISPLD2 is expressed in the mandible, palate and nasopharynx regions during craniofacial development at E13.5-E17.5, respectively. Altogether, these data suggest that genetic variation in CRISPLD2 has a role in the etiology of NSCLP.

Polytherapy withhERG-blocking antiepileptic drugs: Increased risk for embryonic cardiac arrhythmia and teratogenicity

BACKGROUND

The antiepileptic drugs (AEDs) phenytoin, phenobarbital, dimethadione, and carbamazepine cause a similar pattern of malformations in humans, with an increased risk after polytherapy. The teratogenicity has been linked to cardiac rhythm disturbances and hypoxic damage as a consequence of their common potential to inhibit a specific potassium ion current (IKr). The IKr is of major importance for embryonic cardiac repolarization and rhythm regulation. This study investigated whether these AEDs cause irregular rhythm and if various combinations of AEDs result in higher arrhythmia risk than exposure to a single AED.

METHODS

The effects on heart rhythm of a single AED (monotherapy), and of various combinations (polytherapy) of AEDs, in gestational day 10 C57BL mouse embryos in culture were analyzed and graphically illustrated during a 25 s recording with a digitalization technique.

RESULTS

All of the studied AEDs caused increased intervals between heartbeats (resulting in bradycardia) and large variations in the interval between heartbeats (resulting in irregular rhythm) in a concentration-dependent manner in cultured mouse embryos. Dimethadione caused irregular rhythm at concentrations within and phenytoin slightly above the therapeutic ranges. Polytherapy resulted in more substantial prolongation of the mean interval between heartbeats (>60 ms) than monotherapy at clinically relevant concentrations.

CONCLUSIONS

The results suggest that polytherapy more than monotherapy causes substantial prolongation of the cardiac repolarization, a marker associated with high risk of developing irregular rhythm during longer exposure periods (days to months). This supports the idea that the increased risk for malformations following polytherapy is linked to an increased risk for cardiac rhythm disturbances.

Embryonic cardiac arrhythmia and generation of reactive oxygen species: common teratogenic mechanism for IKr blocking drugs

In the adult organism, it is well established that hypoxia followed by reperfusion may be fatal and result in generation of reactive oxygen species (ROS) and subsequent tissue damage. There is also considerable evidence that temporary decrease or interruption in oxygen supply to the embryo and ROS generation during reperfusion result in tissue damage in embryonic tissues. A wide spectrum of different malformations by transient embryonic hypoxia could be produced, depending on the duration, extent, and timing of the hypoxic event. It is the contention of this paper that drugs that block the potassium channel IKr, either as an intended pharmacologic effect or as an unwanted side-effect, are potentially teratogenic by a common ROS related mechanism. Drugs blocking the IKr channel, such as almokalant, dofetilide, phenytoin, cisapride and astemizole, do all produce a similar pattern of hypoxia-related malformations. Mechanistic studies show that the malformations are preceded by embryonic cardiac arrhythmia and periods of hypoxia/reoxygenation in embryonic tissues. Pretreatment or simultaneous treatment with radical scavengers with capacity to capture ROS, markedly decrease the teratogenicity of different IKr blocking drugs. A second aim of this review is to demonstrate that the conventional design of teratology studies is not optimal to detect malformations caused by IKr blocking drugs. Repeated high doses result in high incidences of embryonic death due embryonic cardiac arrhythmia, thus masking their teratogenic potential. Instead, single dosing on specific days is proposed to be a better way to characterize the teratogenic potential of Ikr blocking drugs.

Tessier 3 cleft with clinical anophthalmia: two case reports and a review of the literature

Tessier 3 cleft with clinical anophthalmia is one of the rarest craniofacial clefts, and hence little has been published about its management and treatment. This article presents two cases of Tessier 3 cleft with clinical anophthalmia. A review of the literature helps to diagnose these complex facial deformities. The treatment and etiopathogenesis are discussed.

Increased Susceptibility to Phenytoin Teratogenicity: Excessive Generation of Reactive Oxygen Species or Impaired Antioxidant Defense?

Phenytoin is a human and animal teratogen. Accumulating evidence suggests that the teratogenicity is associated with a potential of phenytoin to cause embryonic cardiac arrhythmia and resultant generation of toxic reactive oxygen species via hypoxia-reoxygenation mechanisms. The A/J mouse is more susceptible to phenytoin teratogenicity than other mouse strains. The aim of this study was to investigate whether A/J mice have other antioxidant enzyme activities than C57BL/6J and CD-1 mice. Also, strain differences in phenytoin effects on embryonic heart rate and rhythm were determined. Another objective was to determine whether a spin trapping agent with capacity to capture reactive oxygen species alter the developmental toxicity of phenytoin. Treatment with this agent resulted in a marked decrease in phenytoin teratogenicity, which supports the idea that reactive oxygen species are important mediators for the teratogenic action of phenytoin. The A/J mice embryos were most susceptible to the adverse cardiac effects of phenytoin and had the highest activity of superoxide dismutase and glutathione peroxidase, while the activity of catalase was the same in embryos of the three different strains. The high activities of antioxidant enzymes in the A/J stain indicate that the sensitivity to develop malformations is caused by excessive arrhythmia-related generation of reactive oxygen species rather than impaired antioxidant defense.

Maternal antioxidant supplementation does not reduce the incidence of phenytoin-induced cleft lip and related malformations in rats

There is considerable evidence that phenytoin-induced birth defects in the rat are a consequence of a period of bradycardia and hypoxia in the embryos. Experiments were designed to test the hypothesis that phenytoin-induced birth defects result from free-radical damage to the embryos during the reoxygenation period posthypoxia. Female rats (>9 per group) were fed either a control diet or a diet high in antioxidants (vitamins C and E and coenzyme Q(10)) both before and during pregnancy and were then given a teratogenic dose of phenytoin (180 mg/kg) on GD 11. The rats were killed on GD 20 and the fetuses were examined for malformations. The initial results showed that the antioxidant diet had a significant protective effect, with far fewer antioxidant-group fetuses showing cleft lip or maxillary hypoplasia compared with the control group. However, this result was confounded by reduced food intake by the rats fed the antioxidant diet and a significantly lower maternal body weight at the time of phenytoin administration. Since the phenytoin was administered by intraperitoneal injection (i.p.) the control rats received higher absolute doses of phenytoin and it is speculated that this results in higher fetal exposure. A second experiment, in which the rats were pair-fed, failed to demonstrate any protective effect of the high antioxidant diet. These results do not support the reoxygenation hypothesis for phenytoin teratogenesis. An alternative explanation would be hypoxia-induced transcription-related changes resulting in cell cycle arrest and apoptosis.

Phenytoin teratogenicity: Hypoxia marker and effects on embryonic heart rhythm suggest an hERG-related mechanism

BACKGROUND

The antiepileptic drug phenytoin (PHT) is a human and animal teratogen. The teratogenicity has been linked to PHT-induced embryonic cardiac arrhythmia and hypoxic damage during a period when regulation of embryonic heart rhythm is highly dependent on a specific K(+) ion current (I(Kr)). PHT has been shown to inhibit I(Kr). The aims of this study were to investigate whether teratogenic doses cause embryonic hypoxia during and after the I(Kr) susceptible period and to further characterize PHT effects on embryonic heart rhythm.

METHODS

Pregnant C57BL mice were administered the hypoxia marker pimonidazole followed by PHT or saline (controls) on GD 10 or GD 15. The embryos were fixed and sectioned, and the immunostained sections were analyzed with a computer assisted image analysis. Effects of PHT (0-250 microM) on heart rhythm in GD 10 embryos cultured in vitro were videotaped and then analyzed by using a digitalization technique.

RESULTS

PHT dose-dependently increased the hypoxia staining (6- and 11-fold after maternal dosing of 100 and 150 mg/kg, respectively) during the period I(Kr) is expressed and functional (GD 10). In contrast, there were no differences between the PHT doses in hypoxia staining, and much less pronounced hypoxia after this period (GD 15). With increasing PHT concentrations, increased length of the interval (bradycardia) and large variations in length between individual heartbeats (arrhythmia) were recorded.

CONCLUSIONS

PHT induced bradycardia/arrhythmia and severe embryonic hypoxia during the I(Kr) susceptible period, supporting the idea of an I(Kr)-arrhythmia-hypoxia-related teratogenic mechanism.

Effect of ENU (ethylnitrosourea) mutagenesis in cleft lip and/or palate pathogenesis in mice

Cleft lip and/or palate (CL/P) are caused by many factors. The aim of this study was to investigate the effects of genetic point mutations in CL/P pathogenesis. ICR and AJ strain mice were used. Ethylnitrosourea (ENU) was injected into 10-week-old male mice (G0) intraperitoneally at a dose of 250 mg/kg. The males were bred with two untreated virgin females of the same strain on day 100 after injection. The uterine contents (G1) of one female were examined on day 18.5 of pregnancy. From the other female, the offspring were delivered naturally, and F3 mice (G3) were also examined in the same way. In ICR strain mice, cleft palate only (CPO) was increased in both the G1 and G3. The frequency was significantly higher in the G3 than the G1 generation. Cleft lip was not observed. In AJ strain mice, CL/P increased in both the G1 and G3. In the G3, the frequency of CPO was increased significantly. Genes related to CPO may be recessive in phenotype. CPO and cleft lip differ from a genetic viewpoint. Point mutations play a significant role in cleft lip and palate.

Electrophysiological effects of anthopleurin-Q on rat hepatocytes

AIM: To study the effects of AP-Q on CCl₄-induced acute liver injury, delayed outward potassium current (I_K), inward rectifier potassium current (I_K1) and calcium release-activated calcium current (I_CRAC) in isolated rat hepatocytes.

METHODS: A single dose of CCl₄ (10 μg/mL, ip) was injected to induce acute liver injury in rats. Serum aminotransferase activities were determined. Whole cell patch-clamp techniques were used to investigate the effects of AP-Q on delayed outward potassium current (I_K), inward rectifier potassium current (I_K1) and calcium release-activated calcium current (I_CRAC).

RESULTS: AP-Q (3.5 and 7 μg/kg) pretreatment significantly reduced ALT and AST activities. AP-Q 0.1-100 nM produced a concentration-dependent increase of I_K with EC₅₀ value of 5.55±1.8 nM (n=6). AP-Q 30 nM shifted the I-V curve of I_K leftward and upward. CCl₄ 4 mM decreased I_K current 28.6±6.5% at 140 mV. After exposure to CCl₄ for 5 min, AP-Q 30 nM attenuated the decrease of I_K induced by CCl₄ close to normal amplitude. AP-Q 0.01-100 nM had no significant effect on either inward or outward components of I_K1 at any membrane potential examined. AP-Q 0.1-100 nM had no significant influence on the peak amplitude of I_CRAC, either, and did not affect the shape of its current voltage curve.

CONCLUSION: AP-Q has a protective effect on CCl₄-induced liver injury, probably through selectively increased I_K in hepatocytes.

Multiple congenital anomalies associated with in utero exposure of phenytoin: Possible hypoxic ischemic mechanism?

BACKGROUND

The characteristics of the phenotype of the malformed phenytoin-exposed infant can help to clarify the mechanism of the drug's teratogenesis. One postulated mechanism is vascular disruption.

CASE

An infant who was exposed to phenytoin as monotherapy throughout pregnancy was born with the following abnormalities: midface hypoplasia, digit hypoplasia with syndactyly in the hands and feet, meningomyelocele, talipes equinovarus, and a long skin pedicle on the back. The mother was also exposed to cigarette smoking and alcohol during the pregnancy.

CONCLUSIONS

The malformations of the hands and feet, and the talipes deformity are potential effects of vascular disruption, a postulated fetal effect of both phenytoin and cigarette smoking. The mechanism of the teratogenicity of phenytoin may have included episodes of bradyarrhythmia in the fetus; however, no such episodes were documented.

Teratogenicity by the hERG potassium channel blocking drug almokalant: use of hypoxia marker gives evidence for a hypoxia-related mechanism mediated via embryonic arrhythmia

The rapid component of the delayed rectifying potassium ion current (IKr), plays an important role in cardiac repolarization. In rats, potent IKr channel blocking drugs cause similar stage-specific malformations (such as orofacial clefts and digital reductions) on gestational days (GDs) 10-14 as after periods of embryonic oxygen deprivation (hypoxia). The idea of a hypoxia-related teratogenic mechanism is supported by studies using rat embryos cultured in vitro. These studies show that the embryonic heart reacts with concentration-dependent bradycardia, arrhythmia, and cardiac arrest when exposed to IKr blockers on GDs 10-14. The main purpose of this study was to investigate whether previously shown teratogenic doses on GD 11 and 13 of the selective IKr blocker almokalant (ALM) induce hypoxia in rat embryos in vivo by using the hypoxia marker pimonidazole hydrochloride (PIM). Rats were orally dosed with almokalant or tap water on GD 11 (150 micromol/kg), 13 (50 micromol/kg), or 16 (800 micromol/kg), followed by PIM intravenously 30 min later. Two hours after the PIM dose, the embryonic heart activity was videotaped and analysed, and the embryos were fixed, sectioned, and immunostained. Computer-assisted image analysis showed a two- and threefold increase in hypoxia staining in embryos exposed to teratogenic doses of ALM on GDs 11 and 13. Embryonic arrhythmia was observed in almokalant groups on these GDs, but not in controls. In contrast, dosing on GD 16, with a much higher dose (800 micromol/kg), caused neither hypoxia nor any effects on heart rhythm. The results support the IKr-related arrhythmia-hypoxia hypothesis, by showing that the potent IKr-blocking drug, almokalant, (1) causes severe embryonic hypoxia and arrhythmia at stages (GDs 11 and 13) when developmental toxicity could be induced and IKr is functional and (2) does not cause hypoxia or affect heart rhythm at a developmental stage when IKr is suppressed (GD 16) and potent IKr blockers do not induce developmental toxicity.

Impact of cleft lip and/or palate on nutritional health and oral-motor development

Infants born with a cleft may require modifications in feeding practices prior to surgical closure of the defect; however, few changes in dietary recommendations are necessary. Often, the delivery method of breast milk or formula can be altered in order to require less effort by the infant and decrease caloric output, thereby increasing the calories ingested to facilitate weight gain and growth. This adaptation may not be necessary when the cleft does not include the palate but can be implemented fairly easily when the baby appears to have difficulty obtaining adequate nutritional intake. Before and after any surgical intervention, the goal remains to continue to supply the infant with sufficient caloric intake to heal and to continue to grow. Although some surgeons may demand modifications in how the baby is fed postoperatively, many advocate cautious reinstitution of normal feeding practices. Early referral for dental care should be encouraged in children born with clefts because these children (even the very young) demonstrate higher dental needs. Education provided to parents regarding causes of and methods to reduce dental disease could help decrease its incidence and help these children require less invasive and difficult rehabilitation therapy.

Epilepsy and pregnancy: Report of an Epilepsy Research Foundation Workshop

Pregnancy in women with epilepsy (WWE) is known to be associated with a higher risk of congenital malformations than is associated with pregnancy in non-epileptic women. Several factors have been identified to account for the increased risk, including the direct teratogenic effects of antiepileptic drug (AED) therapy, indirect effects of these drugs by interfering with folate metabolism, genetic abnormalities in drug or folate metabolism, and possibly an arrhythmogenic effect of maternal drug therapy on the embryonic heart, leading to ischaemia in developing tissues. A harmful effect of maternal seizures on the developing embryo has not been proven, although seizures and status epilepticus account for most of the excess maternal mortality in women with epilepsy. Abrupt withdrawal of drug therapy by the mother may be an important contributory factor. Less is known about the psychomotor development of children born to mothers with epilepsy because few studies have been designed to follow their progress throughout childhood. Retrospective studies suggest that impaired cognitive development may be associated with maternal drug therapy, particularly valproate. There is an urgent need to evaluate these risks and, with this in mind, several prospective registers have been set up to collect data from pregnancies in women with epilepsy.

Effect of Prenatal Phenytoin Administration on the Fine Structure of Rat Myocardium and Aorta

Phenytoin (PHT) is an antiepileptic drug known to have teratogenic effects. The aim of this study was to examine the ultrastructure of the left ventricle, the left atrium, and the aorta of 3-month-old offspring and 4-month-old mother animals after oral PHT (150 mg/kg/day) administration to Wistar/DV rats on days 7-18 of gestation. Electron microscopy of the myocardium revealed a heterogeneous population of cardiomyocytes with conventional architecture, and hypoxia/ischemia-like subcellular changes. Cardiomyocytes of offspring hearts were more vulnerable to PHT administration compared with the mother animals. Atrial cardiomyocytes of both mother animals and offspring were less affected by PHT than the ventricular ones. In the myocardium, both interstitial fibrosis and injury of capillaries were noted. Electron microscopy of the aorta revealed a higher resistance of maternal endothelial and smooth muscle cells to PHT compared with offspring cells. Nuclei of endothelial and smooth muscle cells showed pronounced mitotic activity with one and/or two hyperactive nucleoli, more frequently observed in offspring. PHT administration resulted in aortic arteriogenesis in both offspring and mother animals. Interestingly, bundles of myocardial fibers consisting of ischemia-like altered cardiomyocytes with own capillary network were noted in off-spring aortic adventitia. These results are indicative of harmful effects of PHT on rat myocardium and aorta.

Teratogen-induced limb defects

Limb abnormalities are one of the most common and visible phenotypic effects of several human teratogens. The specific effects are different for most teratogens and include effects on limb morphogenesis (thalidomide, warfarin, phenytoin, valproic acid) and the effect of vascular disruption on a limb that had formed normally (misoprostol, chorionic villus sampling, and phenytoin). Either duplication (preaxial polydactyly of hands and feet) or deficiency (absence of thumb) is a common effect of thalidomide; no other human teratogen identified to date has this effect on the developing limb. Procedures during pregnancy, including chorionic villus sampling and dilation and curettage, produce defects of vascular disruption. For common exposures, such as alcohol and cocaine, it has been difficult to confirm objectively the exposure during embryogenesis and to ascribe specific limb defects that are produced. The molecular basis for the limb defects produced by the recognized human teratogens remains unknown.

Effects on toes from prenatal exposure to anticonvulsants

BACKGROUND

Changes in the distal phalanges of the fingers, including coned epiphyses and hypoplasia of the phalanges, are recognized teratogenic effects of the anticonvulsant drugs phenytoin and phenobarbital. We hypothesized that the frequency of these changes would also be increased in the toes of children exposed to these drugs in comparison to unexposed children.

METHODS

We report on the findings in an analysis of radiographs of the feet of 63 children exposed in utero to either phenytoin alone, phenobarbital alone or both drugs and 56 unexposed comparison children.

RESULTS

Only subtle changes were identified. The frequency of coned epiphyses and hypoplasia of phalanges of the toes was the same in both the anticonvulsant and unexposed children. Among the anticonvulsant-exposed children, however, there was a strong association between the presence of coned epiphyses in the feet and in the hands: all five children with coned epiphyses in the hands, as described previously in the same individuals by Lu et al. ([2000] Teratology 61:277-283) had coned epiphyses in their feet (P = 0.0012). Measurements showed a shortening of metatarsals in all three treatment groups, but this was significant only in the phenytoin monotherapy-exposed children.

CONCLUSIONS

Subtle changes are present in the phalanges and metatarsals of the feet of anticonvulsant-exposed children, but the overall frequency is much less than occurred in the hands of the same children. We conclude that the presence of either coned epiphyses or hypoplasia of the phalanges of the toes cannot be considered a distinctive feature of the teratogenicity of the anticonvulsant drugs phenytoin and phenobarbital.

Teratogenicity of the I(Kr)-blocker cisapride: relation to embryonic cardiac arrhythmia

Cisapride and mosapride are structurally and pharmacologically related prokinetic agents. In contrast to mosapride, cisapride causes embryonic lethality in teratology studies, and has been related to fatal cardiac arrhythmia in the adult. The arrhythmogenic potential of cisapride is linked to its potential to inhibit a specific ion channel (I(Kr)) as a side effect. Mosapride lacks I(Kr)-blocking properties. The aims of this study were (1) to compare the effects of cisapride and mosapride on embryonic heart rhythm in vitro and (2) to investigate if cisapride in vivo, has potential to induce hypoxia-related teratogenic effects as has been shown for selective I(Kr)-blockers. Cisapride induced severe embryonic bradycardia (approximately 60% decrease), and arrhythmia in 94% of the cultured rat embryos at 1000 ng/ml. Mosapride did not induce any bradycardia or arrhythmia up to 2000 ng/ml. In vivo, single dose administration of cisapride to rats on gestational day (GD) 13 caused digital reductions (8/108 fetuses, 4/9 litters) at 75 mg/kg and high incidence of embryonic death (55-82%) at 100-200 mg/kg. Identical developmental toxic effects have been described after temporary interruption of oxygen supply, and after single dose administration of selective I(Kr)-blockers, on the same GD. The results support the idea that all potent I(Kr)-blocking agents have the potential to cause embryolethality and teratogenicity, and that the adverse effects are mediated via hypoxic episodes due to embryonic arrhythmia.

Embryonic arrhythmia by inhibition of HERG channels: a common hypoxia-related teratogenic mechanism for antiepileptic drugs?

PURPOSE

There is evidence that drug-induced embryonic arrhythmia initiates phenytoin (PHT) teratogenicity. The arrhythmia, which links to the potential of PHT to inhibit a specific potassium channel (Ikr), may result in episodes of embryonic ischemia and generation of reactive oxygen species (ROS) at reperfusion. This study sought to determine whether the proposed mechanism might be relevant for the teratogenic antiepileptic drug trimethadione (TMO).

METHODS

Effects on embryonic heart rhythm during various stages of organogenesis were examined in CD-1 mice after maternal administration (125-1,000 mg/kg) of dimethadione (DMO), the pharmacologically active metabolite of TMO. Palatal development was examined after administration of a teratogenic dose of DMO and after simultaneous treatment with DMO and a ROS-capturing agent (alpha-phenyl-N-tert-butyl-nitrone; PBN). The Ikr blocking potentials of TMO and DMO were investigated in HERG-transfected cells by using voltage patch-clamping tests.

RESULTS

DMO caused stage-specific (gestation days 9-13 only) and dose-dependent embryonic bradycardia and arrhythmia at clinically relevant maternal plasma concentrations (3-11 mM). Hemorrhage in the nasopharyngeal part of the embryonic palate (within 24 h) preceded cleft palate in fetuses at term. Simultaneous treatment with PBN significantly reduced the incidence of DMO-induced cleft palate, from 40 to 13%. Voltage patch-clamping studies showed that particularly DMO (70% inhibition), but also TMO, had Ikr blocking potential at clinically relevant concentrations.

CONCLUSIONS

TMO teratogenicity, in the same way as previously shown for PHT, was associated with Ikr-mediated episodes of embryonic cardiac arrhythmia and hypoxia/reoxygenation damage.

Stage-specific skeletal and visceral defects of the I(Kr)-blocker almokalant: further evidence for teratogenicity via a hypoxia-related mechanism

BACKGROUND

As a class effect, potent I(Kr)-blockers have been shown to induce stage-specific external malformations. The aim of this study was to investigate whether I(Kr)-blockers also induce stage-specific visceral and skeletal defects and to further elucidate a proposed arrhythmia-hypoxia hypothesis.

METHODS

Single oral doses of the selective I(Kr)-blocker almokalant (ALM) 25-150 micromol/kg, 7-14 dams/group, were given to Sprague-Dawley rats on gestation days (GD) 10-14, and the fetuses were examined for malformations on GD 21. One group was pretreated with the spin-trapping agent, alpha-phenyl-N-t-butylnitrone (PBN), given intraperitoneally 1 hr before ALM on GD 11.

RESULTS

Cardiac ventricular septum defects and vascular malformations were observed after dosing on GD 10-11 and, to a lesser degree, on GD 12-13. Urogenital defects, absence/malposition of the postcaval lung lobe, and attenuated diaphragm were observed mainly on GD 10-11. Skeletal examination showed a high incidence of vertebral abnormalities on thoracic level on GD 10, on lower thoracic to caudal level on GD 11, and sternebral defects were observed all days. On GD 13 brachy-, oligo-, and syndactyly of the forepaw were induced, and of the hindpaw on GD 14. PBN reduced the incidence of both visceral and skeletal defects.

CONCLUSIONS

The stage specificity of observed visceral and skeletal defects correlates well with what has been reported in the literature after temporary interruption of oxygen supply during the same stages of development. The protective effect by PBN present further evidence that the teratogenicity of potent I(Kr)-blockers is related to induction of hypoxia- reoxygenation injury due to embryonic cardiac arrhythmia.

The genetics and epigenetics of orofacial clefts

Orofacial clefts (cleft lip, cleft palate) are among the most common of all major birth defects, but very little is known about their causation. Genetic factors are thought to play a major role, and there has been considerable recent effort to map and identify genes that constitute risk factors for clefts. This review will put into perspective the frequently-conflicting results of these studies.

Maternal antiepileptic drug use and effects on fetal development

Many pregnant women take antiepileptic medications, and concern has arisen about the risks this poses to the fetus. It has been debated whether the causative agent is the medication or the underlying maternal disorder. Review of the recent literature indicates that the effects seem to be from the medications themselves. The frequency of malformations is about two to three-fold above the background rate and is dose-related for some of the medications. There seem to be effects on birth weight, length, and head circumference caused by at least some of the medications. The risks are greater when more than one medication is used. Cognitive effects from the medications have been shown, although these effects are of lower magnitude than previously reported. More investigation needs to be done to determine the exact risks of each individual medication, especially the newer ones. Studies on underlying mechanisms indicate potential genetic susceptibility and altered developmental gene expression patterns.

An in vitro screening system for characterizing the cleft palate-inducing potential of chemicals and underlying mechanisms

An in vitro organ culture system with developing mouse palates was improved to characterize the cleft palate (CP)-inducing potential of chemicals and underlying mechanisms. Palatal explants collected from gestation day 12 mouse fetuses were cultured with various concentrations of teratogens and examined for palatal development after 48 and 72 h of culture to assess effects of the chemicals on growth and/or fusion of palatal shelves. When the explants were exposed to diphenylhydantoin or 5-fluorouracil, palatal growth was inhibited in a concentration-dependent manner at 48 h. Suppression of the expression of proliferative cell nuclear antigen revealed poor cell proliferation. At 72 h, the incidence of explants with CP was significantly increased in the high-dose groups, suggesting that CP induction is mainly attributable to inhibition of palatal growth. By contrast, retinoic acid and hydrocortisone significantly lowered the rates of fused palates at 72 h in all treated groups, while they exhibited no effects on palatal growth at 48 h even at the highest concentration. Because no apoptosis was found in the epithelial cells at the tip of these palates, these chemicals are suggested to inhibit palatal fusion process by preventing apoptosis.