Arrhenius thermodynamics and birth defects: Chemical teratogen synergy. Untested,testable, and projected relevance

This article addresses the issue of hyperthermia‐induced birth defects with an accompanying additional teratogen, be it a chemical or a physical agent (i.e., a simultaneous “combinational” exposure to two teratogens, one of which is hyperthermia). Hyperthermia per se is a recognized human and animal teratogen. An excellent example of such combinational exposures is an epileptic woman who becomes pregnant while taking valproic acid (VPA) to control seizures. VPA is a recognized chemical teratogen, and fever (hyperthermia) is not an uncommon event during pregnancy. While VPA also may occasionally induce fever as a side effect, we are concerned here with fevers arising from other, unrelated causes. There is a small but internally consistent literature on these combinational‐teratogen exposures involving hyperthermia plus a chemical teratogen; in each instance, the effect level has been observed to be synergistically elevated above levels induced by the separate teratogenic components. The data were empirical. The observed synergy is, however, consistent with Arrhenius thermodynamics, a well‐known chemical rate equation. The need for information about combinational teratogen exposures is acute; fever is a common occurrence during pregnancy; and there are many instances whereby there is also the simultaneous presence of some other teratogen(s). Given that the rate of autism spectrum disorders in the United States was recently presented as 1 in 88 births, it seems reasonable to suspect that such combinational regimens are much more prevalent than previously thought. Our hypothesis is that synergistic birth defect levels from combinational regimens are consistent with Arrhenius thermodynamics. Birth Defects Research (Part C) 99:50–60, 2013. © 2013 Wiley Periodicals, Inc.     

Periconceptional maternal alcohol consumption and neural tube defects

BACKGROUND: Neural tube defects (NTD)s, which occur when the neural tube fails to close during early gestation, are some of the most common birth defects worldwide. Alcohol is a known teratogen and has been shown to induce NTDs in animal studies, although most human studies have failed to corroborate these results. Using data from the National Birth Defects Prevention Study, associations between maternal reports of periconceptional (1 month prior through 2 months postconception) alcohol consumption and NTDs were examined. METHODS: NTD cases and unaffected live born control infants, delivered from 1997 through 2005, were included. Interview reports of alcohol consumption (quantity, frequency, variability, and type) were obtained from 1223 case mothers and 6807 control mothers. Adjusted odds ratios (aOR)s and 95% confidence intervals were estimated using multivariable logistic regression analysis. RESULTS: For all NTDs combined, most aORs for any alcohol consumption, one or more binge episodes, and different type(s) of alcohol consumed were near unity or modestly reduced (≥0.7<aOR≤1.1) and were not statistically significant. Findings were similar for individual NTD subtypes. CONCLUSIONS: These findings suggest no elevated association between maternal periconceptional alcohol consumption and NTDs. Underreporting of alcohol consumption, due to negative social stigma associated with alcohol consumption during pregnancy, and limited reports for mothers with early pregnancy loss of a fetus with an NTD may have affected the estimated odds ratios. Future studies should aim to increase sample sizes for less prevalent subtypes, reduce exposure misclassification, and improve ascertainment offetal deaths and elective terminations. Birth Defects Research (Part A), 2013. © 2013 Wiley Periodicals, Inc.     

Review: Hyperthermia and fever during pregnancy

An episode of hyperthermia is not uncommon during pregnancy. The consequences depend on the extent of temperature elevation, its duration, and the stage of development when it occurs. Mild exposures during the preimplantation period and more severe exposures during embryonic and fetal development often result in prenatal death and abortion. Hyperthermia also causes a wide range of structural and functional defects. The central nervous system (CNS) is most at risk probably because it cannot compensate for the loss of prospective neurons by additional divisions by the surviving neuroblasts and it remains at risk at stages throughout pre- and postnatal life. In experimental animals the most common defects are of the neural tube, microphthalmia, cataract, and micrencephaly, with associated functional and behavioral problems. Defects of craniofacial development including clefts, the axial and appendicular skeleton, the body wall, teeth, and heart are also commonly found. Nearly all these defects have been found in human epidemiological studies following maternal fever or hyperthermia during pregnancy. Suggested future human studies include problems of CNS function after exposure to influenza and fever, including mental retardation, schizophrenia, autism, and cerebral palsy.     

Prenatal exposure to fluconazole: an identifiable dysmorphic phenotype

BACKGROUND: Fluconazole is a triazole antifungal used to treat mycotic infections. Fluconazole is reported to act as a teratogen when used continuously at a dosage of 400-800 mg daily. Fluconazole embryopathy was previously reported in 4 cases. The common features that were also seen in the current case include multiple synostosis (including craniosynostosis and digital synostosis), congenital heart defects, skeletal anomalies, and recognizable dysmorphic facial features. CASE: We report the case of a 9-month-old male born to a 30-year-old woman following a 37-week pregnancy. The pregnancy was complicated by maternal human immunodeficiency virus (HIV) infection and multiple drug exposures, including fluconazole (400 mg/day) until the fifth month and then from 6 months to term, efavirenz, nevirapine, methadone, dapsone, pentamidine, and trimethoprim-sulfamethoxazole. At birth the infant had seizures related to neonatal abstinence syndrome and was noted to have multiple congenital anomalies. On examination at age 9 months, he had craniosynostosis secondary to coronal and lambdoidal suture closures, shallow orbital region, hypoplastic supraorbital ridges, hypertelorism, and mild ptosis. He had radioulnar synostosis and metacarpophalangeal-proximal interphalangeal symphalangism of D2-D5 bilaterally. CONCLUSIONS: The findings of cranial synostosis, multiple symphalangism, and long-bone abnormalities in our case are typical of other reported cases of fluconazole embryopathy. Our patient showed no evidence of embryopathy due to efavirenz, and he did not have the features of Antley-Bixler or other craniosynostosis syndromes. We review the literature regarding the teratogenic effects of prenatal exposure to fluconazole and provide additional evidence that prenatal fluconazole exposure has a clearly identifiable phenotype.     

Strain differences in heat-induced neural tube defects in mice

Neural tube defects are common congenital anomalies affecting approximately 0.1% of liveborn infants. It is widely accepted that these disorders are of a multifactorial origin, having both a genetic and an environmental component to their development. In a study designed to elucidate the genetic factors involved in a mouse model of hyperthermia-induced neural tube defects, it is apparent that a hierarchy of susceptibility exists among various inbred mouse strains. Female SWV mice were extremely sensitive to a 10-minute hyperthermic treatment on day 8.5 of gestation, with 44.3% of their offspring having exencephaly. The other strains used in these studies (LM/Bc, SWR/J, C57BL/6J, and DBA/2J) all had less than 14% affected offspring. In experimental situations where the environment is held constant and the only difference between the strains is their genotype, it is assumed that the difference in response to a teratogen is genetically mediated. To test the hypothesis that several genes are involved, reciprocal crosses were made between strains of high, moderate, and low sensitivity. When this was done, the high sensitivity of the SWV strain was lost in the F1 hybrid, implying not only that multiple genes are involved, but that it is the embryo's genotype and not the maternal genotype that is the major factor in determining susceptibility to heat-induced neural tube defects.     

Deciduous enamel defects in prehistoric Americans from Dickson Mounds: prenatal and postnatal stress

The month of onset, duration, and incidence of dental enamel hypoplasia and hypocalcification was determined in sub-adults from the Dickson Mounds (Illinois) skeletal series (A.D. 950-1300). The onset of enamel defects occurred predominantly during the intrauterine period, suggesting maternal stress. There are marked differences in survivorship and the duration of enamel disruption in those affected prenatally and postnatally. The relationship between these data and studies of adult dentition is examined.     

Limb reduction defects in humans associated with prenatal isotretinoin exposure.

Retinoic acid has long been used to induce limb reductions defects in experimental animal studies. No limb malformations, however, have been reported among malformed retinoic acid-exposed human fetuses from case reports or epidemiologic studies. We report a child and a fetus with limb reduction malformations following maternal use of isotretinoin (13-cis-retinoic acid) during the first trimester of pregnancy. The child had a unilaterally absent clavicle and nearly absent scapula, with a short humerus and short, synostotic forearm bones. He also had ventriculomegaly and developmental delay, minor dysmorphic facial features, and a short sternum with a sterno-umbilical raphe. The fetus had a unilaterally absent thumb with normal proximal bony structures. Other findings included hydrocephalus, craniofacial anomalies, thymic agenesis, supracristal ventricular septal defect, single umbilical artery, anal and vaginal atresia, and urethral agenesis with dysplastic, multicystic kidneys. Although the limb malformations were quite dissimilar, a number of anomalies that are frequently found among isotretinoin-exposed fetuses/infants were present in both cases. This increases the probability that retinoic acid caused these limb defects, but a causal association cannot be conclusively drawn on the basis of these two retrospective case reports.     

Proteomics data mining

Marc Wilkins completed his undergraduate and doctoral studies at Macquarie University, Sydney, Australia. During his doctoral studies, he defined the concept of the proteome and coined the term. After postdoctoral studies in Geneva, Switzerland, during which he co-edited the first book on proteomics, he returned to Australia, where he cofounded the company Proteome Systems. More recently, Marc took a position as Professor of Systems Biology at the University of New South Wales. He has established and directs the NSW Systems Biology Initiative, and is currently researching the role that protein post-translational modifications play in the regulation of protein-interaction networks.     

The effect of fever, febrile illnesses, and heat exposures on the risk of neural tube defects in a Texas-Mexico border population

BACKGROUND: Hyperthermia produces neural tube defects (NTDs) in a variety of animal species. Elevated maternal body temperatures may also place the developing human embryo at risk. We examined the relation between maternal hyperthermia and the development of NTDs in a high-risk Mexican-American population. METHODS: Case-women were Mexican-American women with NTD-affected pregnancies who resided and delivered in any of the 14 Texas counties bordering Mexico, during 1995-2000. Control-women were randomly selected from study area residents delivering normal live births, frequency-matched to cases by hospital and year. Information on maternal fevers, febrile illnesses, exposures to heat generated from external sources, and hyperthermia-inducing activities was gathered through in-person interviews, conducted about six weeks postpartum. RESULTS: The risk effect (OR) associated with maternal fever in the first trimester, compared to no fever, was 2.9 (95% CI, 1.5-5.7). Women taking fever-reducing medications showed a lower risk effect (OR, 2.4; 95% CI, 1.0-5.6) than those who did not (OR, 3.8; 95% CI, 1.4-10.9). First-trimester maternal exposures to heat devices such as hot tubs, saunas, or electric blankets were associated with an OR of 3.6 (95% CI, 1.1-15.9). Small insignificant effects were observed for activities such as cooking in a hot kitchen (OR, 1.6; 95% CI, 1.0-2.6) and working or exercising in the sun (OR, 1.4; 95% CI, 0.9-2.2). CONCLUSIONS: Maternal hyperthermia increases the risk for NTD-affected offspring. Women intending to become pregnant should avoid intense heat exposures, carefully monitor and manage their febrile illnesses, and routinely consume folic acid supplements.     

Teratogenic interaction of ethanol and hyperthermia in mice

Alcohol and maternal hyperthermia have been implicated in human birth defects. Both ethanol and heat can induce neural tube defects (NTDs) and other developmental abnormalities in mice when large doses are given during pregnancy. To explore the teratogenic interaction of both agents, pregnant ICR mice were injected with a single dose of 25% ethanol and/or were heat-stressed in a water bath at 42 degrees C on the morning of Day 8 of gestation. Combined treatment with ethanol (0.01-0.02 ml/g) and heat (10 min), when they were given concurrently or 1 hr apart, resulted in a significant increase of resorptions and externally malformed fetuses. Skeletal malformations and visceral variations also increased significantly following a concurrent exposure to both agents. These results indicate that ethanol and heat can be synergistically teratogenic in mice when the doses of each agent are below the teratogenic threshold. It was also suggested that pretreatment with a small dose of ethanol may not enhance the teratogenicity of heat when the hyperthermic stress is strong enough and teratogenic by itself.     

Reduced birth defects caused by maternal immune stimulation in methylnitrosourea-exposed mice: association with placental improvement

BACKGROUND: Methylnitrosourea (MNU) is a potent carcinogen and teratogen that is associated with central nervous system, craniofacial, skeletal, ocular, and appendicular birth defects following transplacental exposure at critical time points during development, and preliminary studies have suggested that nonspecific maternal immunostimulation may offer protection against development of these birth defects. METHODS: Our study examined morphologic alterations in fetal limb and digital development and placental integrity following maternal exposure to MNU on GD 9 in CD-1 mice, and characterized the improvement in placental integrity and abrogation of fetal defects following maternal immune stimulation with interferon-gamma (IFN-gamma) on GD 7. RESULTS: Fetal limbs were significantly shortened (p < 0.0001) and incidence of limb and digital defects (syndactyly, polydactyly, oligodactyly, clubbing, and webbing) was dramatically increased following mid-gestational maternal MNU exposure. Maternal immune stimulation with IFN-gamma on GD 7 lessened incidence of fetal limb shortening and maldevelopment on GD 12 and 14. Further, disruption of placental spongiotrophoblast integrity, increased cell death in placental trophoblasts with increased intercellular spaces in the spongiotrophoblast layer and minimal inflammation, and increased loss of fetal labyrinthine endothelial cells from MNU-exposed dams suggested that MNU-induced placental breakdown may contribute to fetal limb and digital maldevelopment. MNU + IFN-gamma was associated with diminished cell death within all layers of the placenta, especially in the labyrinthine layer. CONCLUSIONS: These data verify improved distal limb development in MNU-exposed mice as a result of maternal IFN-gamma administration, and suggest a link between placental integrity and proper fetal development.     

Case fatality among infants with congenital malformations by lethality

OBJECTIVE: Infant mortality rates continue to show that congenital anomalies are the leading cause of infant death in the United States. However, studies of factors contributing to increased mortality across different types of congenital anomalies have been limited. The objective of this study was to assess whether the likelihood of infant mortality varied by maternal race and ethnic group while considering the severity of the birth defect. METHODS: A retrospective cohort analysis was conducted using data from Colorado's statewide, population-based birth defects surveillance system (CRCSN). The cohort included infants, born between 1995 and 2000 to Colorado resident mothers, who were diagnosed with major congenital malformations stratified by degree of lethality. Multiple logistic regression was performed for each level of lethality, and included the following potential explanatory variables: maternal race/ethnicity, clinical gestation, birth weight, maternal education level, maternal age, and sex of child. RESULTS: Within the low/very low lethality cohort, maternal race/ethnicity of Black/non-Hispanic was associated with increased risk of infant mortality, OR 2.81 (1.41-5.19), as were low and very low birth weight, OR 2.21 (1.12-4.04) and 19.31 (11.84-31.01), respectively. Maternal race/ethnicity was not a significant risk factor in either high or very high lethality groups; however, the interaction between birth weight and gestational age significantly increased the risk of mortality. CONCLUSIONS: Through the use of statewide, population-based birth defects surveillance data, a disparity in infant mortality has been identified in a specific subset of the population that could be investigated further and targeted for prevention activities.     

Can folic acid protect against congenital heart defects in down syndrome?

BACKGROUND: Several studies have suggested a protective effect of folic acid (FA) on congenital heart anomalies. Down syndrome (DS) infants are known to have a high frequency of heart anomalies. Not all children with DS suffer from heart anomalies, which raises the question whether maternal factors might affect the risk of these anomalies. Our objectives were to investigate whether first-trimester FA use protects against heart anomalies among DS children. METHODS: Women with liveborn DS children participating in the Slone Epidemiology Center Birth Defects Study between 1976 and 1997 were included. We performed case-control analyses using DS, with heart anomalies as cases and DS, without heart anomalies as controls. Subanalyses were performed for defects that have been associated with FA in non-DS populations (conotruncal, ventricular septal [VSD]) and for those that are associated with DS (ostium secundum type atrial septal defects [ASD] and endocardial cushion defects [ECD]). Exposure was defined as the use of any FA-containing product for an average of at least 4 days per week during the first 12 weeks of pregnancy, whereas no exposure was defined as no use of FA in these 12 weeks. RESULTS: Of the 223 cases, 110 (49%) were exposed versus 84 (46%) of the 184 controls. After adjustment for possible confounders, no protective effect of FA was found on heart anomalies overall (OR 0.95, 95% CI: 0.61-1.47) nor separately for conotruncal defects, VSDs, ASDs, or ECDs. CONCLUSIONS: Our study does not show a protective effect of FA on heart anomalies among infants with DS.     

磷酸化的JNK和p38在高温致神经管畸形上皮细胞中的表达变化

目的 探讨高温致神经管畸形（neural tube defects,NTD）的分子机制,为防治神经管畸形提供理论依据.方法 利用高温致金黄地鼠NTD动物模型,应用免疫荧光染色技术,观察NTD发生过程中磷酸化c-Jun氨基末端活化蛋白激酶（p-JNK）和磷酸化p38（p-p38）在胚胎神经管上皮的表达变化.结果 p-JNK和p-p38的免疫阳性产物表达于胚胎神经管上皮细胞及其周围间充质细胞的胞浆中,高温后不同时间点胚胎神经管上皮细胞内的p-JNK和p-p38的表达量均较对照组减弱.结论 磷酸化JNK和p38参与了神经管的正常发育,其表达量降低可能是高温致NTD发生的重要途径之一.     

Impact of intra- and interstrain cross-fostering on mouse maternal care

The importance of maternal care in shaping an individual's phenotype in health and disease is becoming more and more apparent in both human and animal studies. However, in mouse studies using inbred strains or knockout mice to analyze the genetic influences on the development of normal and aberrant behavioral phenotypes, maternal behavior is very poorly characterized and often ignored. This study provides an extensive analysis of spontaneous maternal behavior of inbred mice in three conditions: (1) comparing two commonly used strains, (2) analyzing the impact of adopting pups from the same strain (intrastrain cross-fostering) and (3) analyzing the impact of adopting pups from a different strain (interstrain cross-fostering). For each condition, maternal behavior was analyzed continuously over 23-h periods on postnatal days 2, 4, 6 and 9. We report that (1) the maternal behavior of C57BL/6J and DBA/2J dams toward their biological offspring is highly similar, (2) intrastrain cross-fostering has minimal impact on maternal behavior of C57BL/6J and DBA/2J dams, (3) interstrain cross-fostering does not modify the strain differences in maternal care observed between AKR and C3H/He mothers and (4) the pup strain does influence the amount of maternal behavior shown by both mothers in interstrain cross-fostering. These latter findings demonstrate that both mother strain and pup strain are key determinants of maternal behavior.     

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.     

Fetal cardiac effects of maternal hyperglycemia during pregnancy

Maternal diabetes mellitus is associated with increased teratogenesis, which can occur in pregestational type 1 and type 2 diabetes. Cardiac defects and with neural tube defects are the most common malformations observed in fetuses of pregestational diabetic mothers. The exact mechanism by which diabetes exerts its teratogenic effects and induces embryonic malformations is unclear. Whereas the sequelae of maternal pregestational diabetes, such as modulating insulin levels, altered fat levels, and increased reactive oxygen species, may play a role in fetal damage during diabetic pregnancy, hyperglycemia is thought to be the primary teratogen, causing particularly adverse effects on cardiovascular development. Fetal cardiac defects are associated with raised maternal glycosylated hemoglobin levels and are up to five times more likely in infants of mothers with pregestational diabetes compared with those without diabetes. The resulting anomalies are varied and include transposition of the great arteries, mitral and pulmonary atresia, double outlet of the right ventricle, tetralogy of Fallot, and fetal cardiomyopathy. A wide variety of rodent models have been used to study diabetic teratogenesis. Both genetic and chemically induced models of type 1 and 2 diabetes have been used to examine the effects of hyperglycemia on fetal development. Factors such as genetic background as well as confounding variables such as obesity appear to influence the severity of fetal abnormalities in mice. In this review, we will summarize recent data on fetal cardiac effects from human pregestational diabetic mothers, as well as the most relevant findings in rodent models of diabetic cardiac teratogenesis. Birth Defects Research (Part A), 2009. © 2009 Wiley‐Liss, Inc.     

Common hierarchies of susceptibility to the induction of neural tube defects in mouse embryos by valproic acid and its 4-propyl-4-pentenoic acid metabolite

The teratogenic effects of valproic acid and its 4-propyl-4-pentenoic acid (4-en) metabolite were investigated in three inbred mouse strains that were known to possess differing sensitivity to heat-induced neural tube defects. In the heat-resistant DBA/2J strain, administration of either valproic acid or the metabolite during the critical period of neural tube development failed to produce any abnormal offspring. Similar treatment in the moderately heat-sensitive LM/Bc strain resulted in up to 19.8% exencephalic fetuses. The highly heat-sensitive SWV strain was also very susceptible to the induction of neural tube defects by either valproic acid or its 4-en metabolite. When administered on gestational day 8 plus 12 hours, the parent compound produced 35% exencephalic fetuses, while the metabolite had a response frequency of 32.4%. Thus, the hierarchy of susceptibility for the induction of neural tube defects in these inbred mouse strains was exactly the same whether the teratogen was a physical agent such as hyperthermia or a chemical compound such as valproic acid. If such diverse agents as these should interact to produce malformations, then it is possible that a wide variety of other agents might interact in a similar manner to produce neural tube defects.     

Neural tube defects: a review of human and animal studies on the etiology of neural tube defects

Although neural tube defects are a common congenital anomaly, their etiology is not known. Human studies have emphasized the pathology and epidemiology of the defects and suggest that in the majority of cases the etiology is multifactorial. Factors which appear possibly to be important are genetic predisposition, maternal illness, and fetal drug exposure. Animal studies have utilized naturally occurring neural tube defects and teratologically induced lesions. No animal model has been convincingly established as the equivalent of human neural tube defects. However, animal models have allowed investigation of the mechanisms of suggested human teratogens and determination of the pathogenesis of naturally occurring animal defects. Their most important contribution has been in furthering the understanding of the normal mechanisms of neural tube closure. It may be through this understanding that the etiology of human neural tube defects will be determined.     

Gastrulating chick embryo as a model for evaluating teratogenicity: a comparison of three approaches

BACKGROUND: Teratology studies must be carefully designed to minimize potential secondary effects of vehicle and delivery routes. A systematic method to evaluate chick models of early embryogenesis is lacking. METHODS: We investigated 3 experimental approaches that are popular for studies of early avian development, in terms of their utility for teratogen assessment starting at gastrulation. These included in vitro embryo culture, egg windowing followed by direct application of a carrier vehicle to the embryo, and injection of a carrier vehicle into the egg yolk. We also developed a morphologically based scoring system to assess development of the early embryo. RESULTS: The in vitro culture and egg windowing approaches both caused an unacceptably high incidence of central nervous system and cardiac abnormalities in vehicle-treated embryos, which made it difficult to identify teratogen-specific defects. In contrast, exposing chick embryos to vehicle via direct egg yolk injection did not induce developmental anomalies. CONCLUSIONS: Optimization of the exposure route of potential toxicants to the embryo is critical because control treatments can cause developmental anomalies. In ovo yolk injection minimizes perturbation of young embryos and may be appropriate for teratogen delivery.