Indoor air pollution and neural tube defects: effect modification by maternal genes

Transcriptional Signature of Valproic Acid-Induced Neural Tube Defects in Human Spinal Cord Organoids

In vertebrates, the entire central nervous system is derived from the neural tube, which is formed through a conserved early developmental morphogenetic process called neurulation. Although the perturbations in neurulation caused by genetic or environmental factors lead to neural tube defects (NTDs), the most common congenital malformation and the precise molecular pathological cascades mediating NTDs are not well understood. Recently, we have developed human spinal cord organoids (hSCOs) that recapitulate some aspects of human neurulation and observed that valproic acid (VPA) could cause neurulation defects in an organoid model. In this study, we identified and verified the significant changes in cell-cell junctional genes/proteins in VPA-treated organoids using transcriptomic and immunostaining analysis. Furthermore, VPA-treated mouse embryos exhibited impaired gene expression and NTD phenotypes, similar to those observed in the hSCO model. Collectively, our data demonstrate that hSCOs provide a valuable biological resource for dissecting the molecular pathways underlying the currently unknown human neurulation process using destructive biological analysis tools.

Association between cooking fuel and folate insufficiency among pregnant women in Northern China

This study explored whether using a coal or biomass stove for cooking was associated with a greater risk of red blood cell (RBC) folate insufficiency among pregnant women compared to using clean energy. A researcher-designed questionnaire was used to collect information on exposure-related factors and confounding factors. RBC folate concentrations were examined by microbiological assay. Binary logistic regression analysis was used to identify factors related to RBC folate insufficiency. The use of coal or firewood for cooking was associated with an increased risk of RBC folate insufficiency (<906 nmol/L) compared to gas. In subgroup analyses, associations between the use of polluting cooking fuels and folate insufficiency were positive for both urban and rural residents and statistically significant for rural women. Efforts to promote the use of clean energy and proper ventilation, especially in rural areas, are recommended to improve the health of pregnant women and their offspring.

Indoor air pollution from coal combustion and tobacco smoke during the periconceptional period and risk for neural tube defects in offspring in five rural counties of Shanxi Province, China, 2010-2016

Indoor air pollution may increase the risk for neural tube defects (NTDs) in Chinese rural populations. However, this association remains a subject of debate. We conducted a population-based case-control study of 222 NTD and 517 control mothers recruited between 2010 and 2016 in five rural areas in northern China. An indoor air pollution exposure evaluation index (IAPEEI) was used to evaluate mothers' exposure to tobacco-sourced and coal-sourced indoor air pollution. Essential characteristics were collected using structured questionnaires within 10 days of delivery. We found that exposure to indoor air pollution (IAPEEI ≥ 1) can lead to 3.41 times the risk of conceiving NTD fetuses compared with the no-exposure group (IAPEEI = 0) (adjusted odds ratio and 95 % confidence interval: 3.41 [2.34-5.02]). The risk increased with increasing IAPEEI score, indicating a clear dose-response trend (P < 0.001). Using a coal stove for heating (especially in the bedroom) and passive smoking are significantly associated with an increased likelihood of NTD occurrence. Exposure to indoor air pollution is a daily reality for rural women in China, and its impact on reproductive health deserves extensive attention.

Gene-environment interactions underlying the etiology of neural tube defects

Neural tube defects (NTDs) consist of severe structural malformations of the brain and spinal cord and are the second most common structural birth defect in humans, accounting for approximately 2700 affected pregnancies every year in the United States. These numbers are highly significant, considering that birth defects remain a leading cause of infant mortality in the United States, affecting approximately 120,000 babies born annually. Survivors of these congenital malformations face long-term disability and lifelong challenges imposed by severe physical burdens compromising the afflicted individual's overall quality of life. Clearly, birth defects, and especially NTDs remain a global public health challenge, and the source of significant financial repercussions for healthcare systems worldwide. In order to better understand the role gene-environment interactions play in the etiology of NTDs, this chapter provides an overview of NTD phenotypes and their embryonic origins, discusses the genetic landscape of NTDs as it is currently understood, with a focus on experimental models that best illustrate how environmental factors modulate individual susceptibility to these birth defects. As folic acid interventions have proven to be effective in reducing the prevalence of NTDs, the chapter ends with a discussion on the impact that maternal dietary status has on NTD prevalence from a population perspective.

Cooking stoves and risk of congenital heart disease in Northwest China: A case-control study

Congenital heart disease (CHD) has become the most common birth defect in recent decades. The aim of our study was to examine the association between stove cooking by women during pregnancy and congenital heart disease in their offspring. To address this question, we conducted a case-control study from 2014 to 2016 in Xi'an, Shaanxi, Northwest China, investigating 326 cases and 1071 controls. The cases included fetuses or newborns diagnosed with CHD based on the International Classification of Disease (ICD)-10. Controls consisted of healthy newborns without birth defects. Multivariate unconditional logistic regression was applied to analyze the effects of stove cooking before and during pregnancy on CHD in offspring. After adjusting for confounding factors, we found that, compared to cooking with gas stoves, electromagnetic, coal, and firewood stoves during pregnancy was associated with increased risk of CHD in offspring [electromagnetic stove (odds ratio (OR): 2.89, 95% confidence interval (CI): 2.02, 4.12); coal stove (OR: 3.94, 95% CI: 2.33, 6.65); firewood stove (OR: 6.74, 95% CI: 3.03, 15.00)]. Additionally, higher cooking frequency was associated with increased risk of CHD [total stoves (OR: 2.27, 95% CI: 1.57, 3.28); gas stove (OR: 2.38, 95% CI: 1.43, 3.95); electromagnetic stove (OR: 2.46, 95% CI: 1.32, 4.58); coal and firewood stoves (OR: 3.09, 95% CI: 1.01, 9.46)]. Our study suggests that using electromagnetic, coal, and firewood stoves for cooking during pregnancy and greater cooking frequency increased the risk of CHD in offspring. More attention to the choice of fuels in cooking by pregnant women would help to reduce the incidence of CHD in children.

Gene-environment interactions between air pollution and biotransformation enzymes and risk of birth defects

Genetic and environmental factors have been observed to influence risks for birth defects, though few studies have investigated gene-environment interactions. Our aim was to examine the interaction terms of gene variants in biotransformation enzyme pathways and air pollution exposures in relation to risk of several structural birth defects. We evaluated the role of ambient air pollutant exposure (nitrogen dioxide [NO2 ], nitrogen oxide, carbon monoxide, particulate matter <10 [PM10 ] and <2.5 [PM2.5 ] microns) during pregnancy and 104 gene variants of biotransformation enzymes from infant bloodspots or buccal cells in a California population-based case-control study in 1997-2006. Cases included cleft lip with or without cleft palate (N = 206), gastroschisis (N = 94), tetralogy of Fallot (N = 69), and dextro-transposition of the great arteries (d-TGA; N = 40) and were compared to 208 nonmalformed controls. Overall, the results were not consistent, though did highlight some associations for further investigation as indicated by Wald chi-square test p value <.1. Increased risk of cleft lip was associated with exposure to high PM10 and two CYP gene variants. High PM2.5 and the variant of SLCO1B1 was associated with increased risk of teratology of Fallot. Higher NO2 and two gene variants, CYP2A6 and SLC01B1, were associated with increased risk of d-TGA. Results for gastroschisis were inconsistent in direction and across pollutants. These exploratory results suggest that some individuals based on their genetic background may be more susceptible to the adverse effects of air pollution.

Gene Environment Interactions in the Etiology of Neural Tube Defects

Human structural congenital malformations are the leading cause of infant mortality in the United States. Estimates from the United States Center for Disease Control and Prevention (CDC) determine that close to 3% of all United States newborns present with birth defects; the worldwide estimate approaches 6% of infants presenting with congenital anomalies. The scientific community has recognized for decades that the majority of birth defects have undetermined etiologies, although we propose that environmental agents interacting with inherited susceptibility genes are the major contributing factors. Neural tube defects (NTDs) are among the most prevalent human birth defects and as such, these malformations will be the primary focus of this review. NTDs result from failures in embryonic central nervous system development and are classified by their anatomical locations. Defects in the posterior portion of the neural tube are referred to as meningomyeloceles (spina bifida), while the more anterior defects are differentiated as anencephaly, encephalocele, or iniencephaly. Craniorachischisis involves a failure of the neural folds to elevate and thus disrupt the entire length of the neural tube. Worldwide NTDs have a prevalence of approximately 18.6 per 10,000 live births. It is widely believed that genetic factors are responsible for some 70% of NTDs, while the intrauterine environment tips the balance toward neurulation failure in at risk individuals. Despite aggressive educational campaigns to inform the public about folic acid supplementation and the benefits of providing mandatory folic acid food fortification in the United States, NTDs still affect up to 2,300 United States births annually and some 166,000 spina bifida patients currently live in the United States, more than half of whom are now adults. Within the context of this review, we will consider the role of maternal nutritional status (deficiency states involving B vitamins and one carbon analytes) and the potential modifiers of NTD risk beyond folic acid. There are several well-established human teratogens that contribute to the population burden of NTDs, including: industrial waste and pollutants [e.g., arsenic, pesticides, and polycyclic aromatic hydrocarbons (PAHs)], pharmaceuticals (e.g., anti-epileptic medications), and maternal hyperthermia during the first trimester. Animal models for these teratogens are described with attention focused on valproic acid (VPA; Depakote). Genetic interrogation of model systems involving VPA will be used as a model approach to discerning susceptibility factors that define the gene-environment interactions contributing to the etiology of NTDs.

The role of Vitamin B12 and genetic risk factors in the etiology of neural tube defects: A systematic review

Neural tube defects (NTDs) are birth defects that arise during embryogenesis when normal neural tube closure fails to occur. According to the World Health Organization, NTDs are detected annually in approximately 300,000 neonates worldwide. The exact etiology of NTDs remains complex and poorly understood. It is generally agreed that most NTD cases are of multifactorial origin, having a combination of multiple genes and a number of environmental risk factors. The role of folic acid, vitamin B12 deficiency, genetics and other risk factors, in the etiology of NTDs, has also been extensively studied. This knowledge synthesis brings together different types of evidence to update the role of vitamin B12 deficiency, genetics and other risk factors, in the etiology of NTDs. Following a PubMed search and screening for relevant articles, we included 40 studies in our review (30 case-control studies, 3 cross-sectional studies, 5 cohort studies, and 2 case reports). The available data showed that vitamin B12 levels were decreased in mothers and infants in NTD groups compared with control groups. Holo-transcobalamin, the active form of vitamin B12, was also found in lower levels in mothers with NTD-affected infants. Several studies reported elevated homocysteine levels in mothers and infants in NTD groups. Additionally, numerous studies reported links between genetic variants and increased NTD risk. These genes include GIF, LRP2, CUBN, TCb1R, MTHFR, and others. Several maternal factors have also been linked with significant NTD risk such as BMI, maternal diet, air pollutants, low maternal age, and many others. The majority of studies on NTDs have focused on the role of folic acid, hence there is a need for well-designed studies on the role of other risk factors like vitamin B12 deficiency in the etiology of NTDs.

Cell non-autonomy amplifies disruption of neurulation by mosaic Vangl2 deletion in mice

Post-zygotic mutations that generate tissue mosaicism are increasingly associated with severe congenital defects, including those arising from failed neural tube closure. Here we report that neural fold elevation during mouse spinal neurulation is vulnerable to deletion of the VANGL planar cell polarity protein 2 (Vangl2) gene in as few as 16% of neuroepithelial cells. Vangl2-deleted cells are typically dispersed throughout the neuroepithelium, and each non-autonomously prevents apical constriction by an average of five Vangl2-replete neighbours. This inhibition of apical constriction involves diminished myosin-II localisation on neighbour cell borders and shortening of basally-extending microtubule tails, which are known to facilitate apical constriction. Vangl2-deleted neuroepithelial cells themselves continue to apically constrict and preferentially recruit myosin-II to their apical cell cortex rather than to apical cap localisations. Such non-autonomous effects can explain how post-zygotic mutations affecting a minority of cells can cause catastrophic failure of morphogenesis leading to clinically important birth defects.

Prenatal exposure to traffic-related air pollution and risk of congenital diseases in South Korea

BACKGROUND

Previous studies have suggested links between exposure to ambient air pollutants and increased risk of congenital heart defects. However, few studies have investigated the association between other congenital diseases and traffic-related air pollution. In this study, we assessed the relationship between prenatal exposure to fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) with congenital diseases in South Korea.

METHODS

Patients with one or more congenital diseases and a control group of patients with non-infective gastroenteritis and colitis with a case:control ratio of 1:3 were obtained from the National Health Insurance Service data for 2008-2013 in South Korea. We estimated the associations of PM_2.5 and NO₂ exposures with congenital diseases using generalized estimation equations after controlling for covariates.

RESULTS

Maternal PM_2.5 exposure during the first and second trimester showed positive associations with overall congenital diseases, with changes of 14.7% (95% confidence intervals (CI), 9.3%, 20.3%) and 16.2% (95% CI, 11.0%, 21.7%), respectively, per 11.1 μg/m³ and 10.2 μg/m³ increase of PM_2.5 interquartile range (IQR). Similarly, NO₂ exposure during the first and second trimester was associated with increased numbers of overall congenital anomalies, with 8.2% (95% CI, 4.2%, 12.3%) and 15.6% (95% CI, 9.3%, 22.2%) more cases, respectively, per 10.6 ppb increase of NO₂. We found that maternal PM_2.5 exposure during the first and second trimesters of pregnancy was significantly associated with increased risk of specific congenital diseases, including subtypes affecting the circulatory, genitourinary, and musculoskeletal system. However, no significant associations were observed during the third trimester. Maternal NO₂ exposure across the entire pregnancy was associated with malformations of the musculoskeletal system.

CONCLUSIONS

Our study identified significant links between in utero exposure to PM_2.5 and NO₂ and certain congenital diseases, and suggests that stricter controls on PM_2.5 and NO₂ concentrations are required.

Integrating Autism Spectrum Disorder Pathophysiology: Mitochondria, Vitamin A, CD38, Oxytocin, Serotonin and Melatonergic Alterations in the Placenta and Gut

BACKGROUND

A diverse array of data has been associated with autism spectrum disorder (ASD), reflecting the complexity of its pathophysiology as well as its heterogeneity. Two important hubs have emerged, the placenta/prenatal period and the postnatal gut, with alterations in mitochondria functioning crucial in both.

METHODS

Factors acting to regulate mitochondria functioning in ASD across development are reviewed in this article.

RESULTS

Decreased vitamin A, and its retinoic acid metabolites, lead to a decrease in CD38 and associated changes that underpin a wide array of data on the biological underpinnings of ASD, including decreased oxytocin, with relevance both prenatally and in the gut. Decreased sirtuins, poly-ADP ribose polymerase-driven decreases in nicotinamide adenine dinucleotide (NAD+), hyperserotonemia, decreased monoamine oxidase, alterations in 14-3-3 proteins, microRNA alterations, dysregulated aryl hydrocarbon receptor activity, suboptimal mitochondria functioning, and decreases in the melatonergic pathways are intimately linked to this. Many of the above processes may be modulating, or mediated by, alterations in mitochondria functioning. Other bodies of data associated with ASD may also be incorporated within these basic processes, including how ASD risk factors such as maternal obesity and preeclampsia, as well as more general prenatal stressors, modulate the likelihood of offspring ASD.

CONCLUSION

Such a mitochondria-focussed integrated model of the pathophysiology of ASD has important preventative and treatment implications.

Choline, not folate, can attenuate the teratogenic effects ofdibutyl phthalate (DBP) during early chick embryo development

Dibutyl phthalate (DBP), a persistent environmental pollutant, can induce neural tube abnormal development in animals. The possible effects of DBP exposure on human neural tube defects (NTDs) remain elusive. In this study, the distribution of DBP in the body fluid of human NTDs was detected by GC-MS. Then, chick embryos were used to investigate the effects of DBP on early embryonic development. Oxidative stress indicators in chick embryos and the body fluid of human NTDs were detected by ELISA. The cell apoptosis and total reactive oxygen species (ROS) level in chick embryos were detected by whole-mount TUNEL and oxidized DCFDA, respectively. The study found that the detection ratio of positive DBP and its metabolites in maternal urine was higher in the NTD population than that in normal controls. 8-hydroxy-2 deoxyguanosine (8-OHDG) and malondialdehyde (MDA) were evidently upregulated and superoxide dismutase (SOD) was observably downregulated in amniotic fluid and urine. Animal experiments indicated that DBP treatment induced developmental toxicity in chick embryos by enhancing the levels of oxidative stress and cell apoptosis. MDA was increased and SOD was decreased in DBP-treated embryos. Interestingly, the supplement of high-dose choline (100 μg/μL), not folic acid, could partially restore the teratogenic effects of DBP. Our data collectively suggest that the incidence of NTDs is closely associated with DBP exposure. This study may provide new insight for NTD prevention.

Genetic variation in biotransformation enzymes, air pollution exposures, and risk of spina bifida

Spina bifida is a birth defect characterized by incomplete closure of the embryonic neural tube. Genetic factors as well as environmental factors have been observed to influence risks for spina bifida. Few studies have investigated possible gene-environment interactions that could contribute to spina bifida risk. The aim of this study is to examine the interaction between gene variants in biotransformation enzyme pathways and ambient air pollution exposures and risk of spina bifida. We evaluated the role of air pollution exposure during pregnancy and gene variants of biotransformation enzymes from bloodspots and buccal cells in a California population-based case-control (86 cases of spina bifida and 208 non-malformed controls) study. We considered race/ethnicity and folic acid vitamin use as potential effect modifiers and adjusted for those factors and smoking. We observed gene-environment interactions between each of the five pollutants and several gene variants: NO (ABCC2), NO₂ (ABCC2, SLC01B1), PM₁₀ (ABCC2, CYP1A1, CYP2B6, CYP2C19, CYP2D6, NAT2, SLC01B1, SLC01B3), PM_2.5 (CYP1A1 and CYP1A2). These analyses show positive interactions between air pollution exposure during early pregnancy and gene variants associated with metabolizing enzymes. These exploratory results suggest that some individuals based on their genetic background may be more susceptible to the adverse effects of pollution.

Indoor air pollution affects hypertension risk in rural women in Northern China by interfering with the uptake of metal elements: A preliminary cross-sectional study

Coal combustion and passive smoking are two important contributors to indoor air pollution (IAP) in rural areas of northern China. Although the association between outdoor air pollutants and hypertension risk had been widely reported, fewer studies have examined the relationship between IAP and hypertension risk. This study evaluated the association between IAP and hypertension risk in housewives in rural areas of northern China and the potential mediation pathway of metal elements. Our cross-sectional study, conducted in Shanxi Province, China, enrolled 367 subjects without taking anti-hypertensive drugs, including 142 subjects with hypertension (case group) and 225 subjects without hypertension (control group). We collected information on energy use characteristics and lifestyle using questionnaires. An IAP exposure index was developed to indicate the population exposure to coal combustion and passive smoking. Scalp hair samples were collected from the housewives and various trace and major metal elements were measured. Our results revealed that the IAP index was positively correlated with systolic and diastolic blood pressure. A significant association between the IAP index and hypertension risk was found both without [odds ratio (95% confidence interval, CI) = 2.08 (1.30-3.31)] and with [OR (95% CI) = 2.52 (1.46-4.36)] adjustment for confounders. We also observed that the IAP index was positively correlated with the arsenic, lead, and rare earth element levels in hair samples, and negatively correlated with the levels of some other trace elements (i.e., chromium, cobalt, nickel, and tin) and alkaline earth elements (i.e., calcium, magnesium, and barium) with an overall p value of <0.01. We concluded that IAP may contribute to the development of hypertension in rural housewives in northern China, possibly by interfering with the uptake of metal elements.

Assessment of interaction between maternal polycyclic aromatic hydrocarbons exposure and genetic polymorphisms on the risk of congenital heart diseases

The major causes of congenital heart diseases (CHDs) are the interactions of genetic and environmental factors. We conducted a case–control study in 357 mothers of CHDs fetuses and 270 control mothers to investigate the association of maternal PAHs exposure, AHR, CYP1A1, CYP1A2, CYP1B1 and CYP2E polymorphisms, the interaction between PAHs exposure and genetic variants with the risk of CHDs. The higher level PAHs exposure was associated with the risk of CHDs (aOR = 2.029, 95% CI: 1.266, 3.251) or subtypes. The haplotypes of AHR or CYP1A2 were associated with the risk of CHDs: AHR: C-G-A-C: aOR = 0.765; T-A-G-A: aOR = 1.33; CYP1A2: A-T:aOR = 1.75; C-C: aOR = 0.706. When exposed to higher level PAHs, the risk of CHDs among the mothers carrying rs2158041 “C/T or T/T” genotype or rs7811989 “G/A or A/A” genotype in AHR was 1.724 (χ² = 7.209, P = 0.007) or 1.735 (χ² = 7.364, P = 0.007) times greater than the aOR in the mothers carrying wild genotype. The multiplicative-scale interactions between PAHs exposure and polymorphisms of CYP1A2 rs4646425 (P = 0.03) or CYP2E1 rs915908 (P = 0.0238) on the risk of CHDs were observed. Our study suggests that maternal AHR polymorphisms may modify the association of PAHs exposure with CHDs, CYP1A2 or CYP2E1 polymorphisms significantly interact with PAHs exposure on CHDs.

Are concentrations of alkaline earth elements in maternal hair associated with risk of neural tube defects?

The relationship between maternal intake of alkaline earth elements (AEEs) during the period of neural tube closure and the risk of neural tube defects (NTDs) is still unclear. We propose that AEE deficiency during the early period of pregnancy is associated with an elevated risk of NTDs in the offspring. In this study, we recruited 191 women with NTD-affected pregnancies (cases) and 261 women who delivered healthy infants (controls). The concentrations of four AEEs (Ca, Mg, Sr, Ba) in maternal hair sections that grew during early pregnancy were analyzed. Information on the dietary habits of the mothers was also collected by questionnaire. Higher concentrations of the four AEEs in hair had protective effects against the risk of total NTDs, with odds ratios with 95% confidence interval (comparing groups separated by each median level) of 0.44 (0.28-0.68) for Mg, 0.56 (0.36-0.87) for Ca, 0.45 (0.28-0.70) for Sr, and 0.41 (0.26-0.65) for Ba. Significant negative dose-response trends were identified for the relationships between the four AEE concentrations in maternal hair and the risks of anencephaly and spina bifida, but not for encephalocele. The frequencies of maternal consumption of fresh green vegetables, fresh fruit, and meat or fish were positively correlated with the concentrations of AEEs in hair. We concluded that the maternal intake of AEEs may play an important role in preventing NTD formation in offspring, and that this intake is related to maternal dietary habits of consuming fresh green vegetables, fresh fruit, and fish or meat.

Indoor air pollution and the risk of orofacial clefts in a rural population in Shanxi province, China

BACKGROUND

Shanxi Province is a region in China with a high incidence of orofacial clefts (OFCs). Our objective is to investigate the effect of maternal exposure to indoor air pollution (IAP) from coal combustion and tobacco smoke on the risk of an infant being born with orofacial clefts.

METHODS

Data were derived from an ongoing population-based case-control study of major external structural birth defects in Shanxi Province. Subjects included 213 cases with OFCs and 1319 healthy babies born between November 2002 and December 2014 in four rural counties. Exposure information was collected by face-to-face interview with mothers within 1 week of delivery or pregnancy termination. The authors derived an exposure index by integrating a series of IAP-related characteristics concerning dwelling and lifestyle.

RESULTS

Increased odds of OFC were associated with IAP exposure from heating (adjusted odds ratio [aOR] = 2.4; 95% confidence interval [CI], 1.2-4.5) and from smoking (aOR = 1.8; 95% CI: 1.3, 2.5), but not with exposure from cooking (aOR = 0.9; 95% CI, 0.6-1.4). Compared with women without IAP exposure, the aORs of OFC for children of women with exposure indices of 1, 2, 3 and ≥ 4 were 1.1 (95% CI, 0.6-1.8), 1.4 (95% CI, 0.8-2.4), 1.8 (95% CI, 1.0-3.2), and 3.4 (95% CI, 1.6-7.4), respectively, demonstrating a clear dose-response trend (p < 0.001).

CONCLUSION

Periconceptional exposure to IAP from coal combustion and tobacco smoking may increase the risk of OFCs in offsprings of women in Shanxi Province. Birth Defects Research (Part A) 106:708-715, 2016. © 2016 Wiley Periodicals, Inc.