Overview of developmental heart defects by dioxins, PCBs, and pesticides

TCDD‑induced chick cardiotoxicity is abolished by a selective cyclooxygenase‑2 (COX‑2) inhibitor NS398

Halogenated aromatic hydrocarbons, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are known to cause severe heart defects in avian species. However, the mechanism of TCDD-induced chick cardiovascular toxicity is unclear. In this study, we investigated cyclooxygenase-2 (COX-2) as a possible mechanism of TCDD-induced cardiotoxicity. Fertile chicken eggs were injected with TCDD and a COX-2 selective inhibitor, NS398, and we investigated chick heart failure on day 10. We found that the chick heart to body weight ratio and atrial natriuretic factor mRNA expression were increased, but this increase was abolished with treatment of NS398. In addition, the morphological abnormality of an enlarged ventricle resulting from TCDD exposure was also abolished with co-treatment of TCDD and NS398. Our results suggested that TCDD-induced chick heart defects are mediated via the nongenomic pathway and that they do not require the genomic pathway.

Parental occupational exposures to endocrine disruptors and the risk of simple isolated congenital heart defects

This study aims to explore the associations between parental occupational exposures to endocrine disruptors (EDs) and simple isolated congenital heart defects (CHDs). A case-control study with standardized data collection involving 761 children with isolated CHDs and 609 children without any congenital malformations was conducted in Sichuan Province of China from March in 2012 to August in 2013. An adjusted job exposure matrix was used for occupational EDs exposure assessment. Logistic regression analysis was performed to assess the associations between parental occupational EDs exposures and CHDs. Maternal age at births, maternal education level, gravity, parity, induced abortion, folic acid use, medication use, drinking capacity and area of residence periconceptionally were selected as confounding factors for mothers. For fathers, we selected the following confounding factors: paternal education level, smoking, drinking frequencies and drinking capacity periconceptionally. Maternal occupational exposures to phthalates are associated with perimembranous ventricular septal defect (PmVSD) (P = 0.001, adjusted OR 3.7, 95 % CI 1.7-8.0), patent ductus arteriosus (PDA) (P = 0.002, adjusted OR 3.8, 95 % CI 1.6-8.9), secundum atrial septal defect (s-ASD) (P = 0.008, adjusted OR 3.5, 95 % CI 1.4-8.7) and pulmonary valve stenosis (PS) (P = 0.035, adjusted OR 4.2, 95 % CI 1.1-16.0), to alkylphenolic compounds and PmVSD (P = 0.003, adjusted OR 2.2, 95 % CI 1.3-3.6), PDA (P = 0.005, adjusted OR 2.0, 95 % CI 1.1-3.5) and PS (P = 0.004, adjusted OR 3.8, 95 % CI 1.5-9.4), to heavy metals with PmVSD (P = 0.003, adjusted OR 7.3, 95 % CI 2.0-27.6) and s-ASD (P = 0.034, adjusted OR 6.5, 95 % CI 1.1-36.7). Paternal occupational exposures to phthalates are associated with PmVSD (P = 0.035, adjusted OR 1.6, 95 % CI 1.0-2.4) and PS (P = 0.026, adjusted OR 2.4, 95 % CI 1.1-5.2), to alkylphenolic compounds (P = 0.027, adjusted OR 1.5, 95 % CI 1.0-2.2) with PmVSD. In conclusion, parental occupational exposures to some specific EDs, in particular phthalates and alkylphenolic compounds, are associated with an increased risk of some CHD phenotypes. However, the findings need to be considered more circumspectly regarding a crude measure of exposure probabilities and small numbers.

Complexity of bioindicator selection for ecological, human, and cultural health: Chinook salmon and red knot as case studies

There is considerable interest in developing bioindicators of ecological health that are also useful indicators for human health. Yet, human health assessment usually encompasses physical/chemical exposures and not cultural well-being. In this paper, we propose that bioindicators can be selected for all three purposes. We use Chinook or king salmon (Oncorhynchus tshawytscha) and red knot (Calidris canutus rufa, a sandpiper) as examples of indicators that can be used to assess human, ecological, and cultural health. Even so, selecting endpoints or metrics for each indicator species is complex and is explored in this paper. We suggest that there are several endpoint types to examine for a given species, including physical environment, environmental stressors, habitat, life history, demography, population counts, and cultural/societal aspects. Usually cultural endpoints are economic indicators (e.g., number of days fished, number of hunting licenses), rather than the importance of a fishing culture. Development of cultural/societal endpoints must include the perceptions of local communities, cultural groups, and tribal nations, as well as governmental and regulatory communities (although not usually so defined, the latter have cultures as well). Endpoint selection in this category is difficult because the underlying issues need to be identified and used to develop endpoints that tribes and stakeholders themselves see as reasonable surrogates of the qualities they value. We describe several endpoints for salmon and knots that can be used for ecological, human, and cultural/societal health.

Feathers as a source of RNA for genomic studies in avian species

Dioxins and dioxin-like chemicals (DLCs) cause a suite of adverse effects in terrestrial species. Most of the adverse effects occur subsequent to binding to the aryl hydrocarbon receptor. Avian species vary in their sensitivity to the effects of DLCs and current research indicates that this is mediated by variations in the amino acid sequence within the ligand binding domain (LBD) of the aryl hydrocarbon receptor 1 (AHR1). Eighty-eight avian species have been classified into three broad categories of sensitivity, based on the amino acid variations within the AHR1 LBD: sensitive type 1 (Ile324_Ser380), moderately sensitive type 2 (Ile324_Ala380), and relatively insensitive type 3 (Val324_Ala380). Risk assessment of avian species can be complicated due to the variability in sensitivity among species. A predictive tool for selecting the priority species at a given site would have broad implications for the risk assessment community. We present a method for AHR1 genotyping using plucked feathers as a source of RNA. The method is extremely robust, requires minimal sample processing and handling, and eliminates the need for blood sampling or tissue collection from the species of interest. Using this method we were able to determine the amino acid sequence of the AHR LBD of three avian species: the chicken, the herring gull, and the zebra finch, and to categorize them based on the identity of amino acids at key sites within the LBD.

Internal exposure to organochlorine pollutants and cadmium and self-reported health status: a prospective study

In this paper, based on the Flemish biomonitoring programs, we describe the associations between internal exposure to organochlorine pollutants and to cadmium (measured in 2004-2005 for adults aged 50-65 years) and self-reported health status obtained through a questionnaire in November 2011. Dioxin-like activity in serum showed a significant positive association with risk of cancer for women. After adjustment for confounders and covariates, the odds ratio for an exposure equal to the 90th percentile was 2.4 times higher than for an exposure equal to the 10th percentile. For both men and women dioxin-like activity and serum hexachlorobenzene (HCB) showed a significant positive association with risk of diabetes and of hypertension. Detailed analysis suggested that an increase in BMI might be part of the mechanism through which HCB contributes to diabetes and hypertension. Serum dichlorodiphenyldichloroethylene (p,p'-DDE) concentration showed a significant positive association with diabetes and hypertension in men, but not in women. Serum polychlorinated biphenyl (PCB) 118 showed a significant positive association with diabetes in both men and women, and after adjustment for correlated exposures, also with hypertension in men. Urinary cadmium concentrations showed a significant positive association with hypertension. Urinary cadmium concentrations were (in 2004-2005) significantly higher in persons who felt in less than good health (in 2011) than in persons who felt in very good health. After adjustment for correlated exposures (to HCB, p,p'-DDE and PCB118) marker PCBs showed a significant negative association with diabetes and hypertension. Serum p,p'-DDE showed in men a significant negative association with risk of diseases based on atheromata. Our findings suggest that exposure to pollutants can lead to an important increase in the risk of diseases such as cancer, diabetes and hypertension. Some pollutants may possibly also decrease the risk of some health problems, although this requires confirmation by other approaches.

Residential agricultural pesticide exposures and risk of selected congenital heart defects among offspring in the San Joaquin Valley of California

BACKGROUND

Pesticide exposures are ubiquitous and of substantial public concern. We examined the potential association of congenital heart defects with residential proximity to commercial agricultural pesticide applications in the San Joaquin Valley, California.

METHODS

Study subjects included 569 heart defect cases and 785 non-malformed controls born from 1997 to 2006 whose mothers participated in a population-based case-control study. Associations with any versus no exposure to physicochemical groups of pesticides and specific chemicals were assessed using logistic regression adjusted for relevant covariates, for 8 heart defect phenotypes that included ≥ 50 cases and pesticide exposures with ≥ 5 exposed cases and controls, which resulted in 235 comparisons.

RESULTS

38% of cases and controls were classified as exposed to pesticides within a 500 m radius of mother's address during a 3-month periconceptional window. Adjusted odds ratios (AORs) with 95% CIs excluding 1.0 were observed for 18 comparisons; all were >1 and ranged from 1.9 to 7.1. They included tetralogy of Fallot (n=101 cases) and neonicotinoids; hypoplastic left heart syndrome (n=59) and strobins; coarctation of the aorta (n=74) and pyridazinones; pulmonary valve stenosis (n=53) and bipyridyliums and organophosphates; ventricular septal defects (n=93) and avermectins and pyrethroids; and atrial septal defects (n=132) and dichlorphenoxy acid or esters, organophosphates, organotins, and pyrethroids. No AORs met both of these criteria for d-transposition of the great arteries (n=58) or heterotaxia (n=53).

CONCLUSIONS

Most pesticides were not associated with increased risk of specific heart defect phenotypes. For the few that were associated, results should be interpreted with caution until replicated in other study populations.

Higher urinary heavy metal, arsenic, and phthalate concentrations in people with high blood pressure: US NHANES, 2009-2010

BACKGROUND

A link between environmental chemicals and human health has emerged but not complete in risk factors. This work aimed to study the relationships of different sets of urinary environmental chemical concentrations and risk of high blood pressure (BP) in a national, population-based study.

METHODS

Data was retrieved from United States National Health and Nutrition Examination Surveys, 2009-2010, including demographics, BP readings and urinary environmental chemical concentrations. Analyses included t-test and survey-weighted logistic regression models.

RESULTS

Urinary mercury concentrations were not associated with high BP (OR = 1.19, 95% CI 0.97-1.48, p = 0.095). Urinary cobalt (OR = 1.35, 95% CI 1.01-1.81, p = 0.044), lead (OR = 1.77, 95% CI 1.31-2.38, p = 0.001), antimony (OR = 1.37, 95% CI 1.09-1.72, p = 0.010) and tungsten (OR = 1.52, 95% CI 1.27-1.81, p < 0.001) concentrations were observed to increase the risk of high BP. There are no clear associations between environmental parabens and high BP. The effect of environmental bisphenol A (OR = 1.14, 95% CI 1.00-1.30, p = 0.051) disappeared after additionally adjusting for subsample weighting (OR = 1.12, 95% CI 0.93-1.35, p = 0.225). People with higher urinary mono-2-ethyl-5-carboxypentyl phthalate (OR = 1.26, 95% CI 1.00-1.58, p = 0.051), mono-n-butyl phthalate (OR = 1.19, 95% CI 1.01-1.41, p = 0.042) and mono-n-methyl phthalate metabolites (OR = 1.16, 95% CI 1.03-1.32, p = 0.021) tended to have high BP. Moreover, urinary o-phenyl phenol concentrations (OR = 1.49, 95% CI 1.25-1.77, p < 0.001) and dimethylarsonic acid concentrations (OR = 1.35, 95% CI 1.06-1.73, p = 0.019) were also seen to be associated with high BP.

CONCLUSIONS

Urinary environmental chemical concentrations were associated with risk of high BP, although the causal effect cannot be established. Elimination of environmental chemicals in humans would need to be continued.

Disruption of aryl hydrocarbon receptor homeostatic levels during embryonic stem cell differentiation alters expression of homeobox transcription factors that control cardiomyogenesis

BACKGROUND

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of xenobiotic detoxification genes and is a critical mediator of gene-environment interactions. Many AHR target genes identified by genome-wide gene expression profiling have morphogenetic functions, suggesting that AHR may play a role in embryonic development.

OBJECTIVES

To characterize the developmental functions of the AHR, we studied the consequences of AHR activation by the agonist 2,3,7,8-tetrachlorodibenzo-p-doxin (TCDD), and the result of its repression by the antagonists 6,2,4-trimethoxyflavone and CH 223191 or by short-hairpin RNA (shRNA)-mediated Ahr knockdown during spontaneous differentiation of embryonic stem (ES) cells into cardiomyocytes.

METHODS

We generated an AHR-positive cardiomyocyte lineage differentiated from mouse ES cells that expresses puromycin resistance and enhanced green fluorescent protein (eGFP) under the control of the Cyp1a1 (cytochrome P450 1a1) promoter. We used RNA sequencing (RNA.Seq) to analyze temporal trajectories of TCDD-dependent global gene expression in these cells during differentiation.

RESULTS

Activation, inhibition, and knockdown of Ahr significantly inhibited the formation of contractile cardiomyocyte nodes. Global expression analysis of AHR-positive cells showed that activation of the AHR/TCDD axis disrupted the concerted expression of genes that regulate multiple signaling pathways involved in cardiac and neural morphogenesis and differentiation, including dozens of genes encoding homeobox transcription factors and Polycomb and trithorax group proteins.

CONCLUSIONS

Disruption of AHR expression levels resulted in gene expression changes that perturbed cardiomyocyte differentiation. The main function of the AHR during development appears to be the coordination of a complex regulatory network responsible for attainment and maintenance of cardiovascular homeostasis.

Application of high-throughput sequencing for studying genomic variations in congenital heart disease

Congenital heart diseases (CHD) represent the most common birth defect in human. The majority of cases are caused by a combination of complex genetic alterations and environmental influences. In the past, many disease-causing mutations have been identified; however, there is still a large proportion of cardiac malformations with unknown precise origin. High-throughput sequencing technologies established during the last years offer novel opportunities to further study the genetic background underlying the disease. In this review, we provide a roadmap for designing and analyzing high-throughput sequencing studies focused on CHD, but also with general applicability to other complex diseases. The three main next-generation sequencing (NGS) platforms including their particular advantages and disadvantages are presented. To identify potentially disease-related genomic variations and genes, different filtering steps and gene prioritization strategies are discussed. In addition, available control datasets based on NGS are summarized. Finally, we provide an overview of current studies already using NGS technologies and showing that these techniques will help to further unravel the complex genetics underlying CHD.

Epicardium Formation as a Sensor in Toxicology

Zebrafish (Danio rerio) are an excellent vertebrate model for studying heart development, regeneration and cardiotoxicity. Zebrafish embryos exposed during the temporal window of epicardium development to the aryl hydrocarbon receptor (AHR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibit severe heart malformations. TCDD exposure prevents both proepicardial organ (PE) and epicardium development. Exposure later in development, after the epicardium has formed, does not produce cardiac toxicity. It is not until the adult zebrafish heart is stimulated to regenerate does TCDD again cause detrimental effects. TCDD exposure prior to ventricular resection prevents cardiac regeneration. It is likely that TCDD-induced inhibition of epicardium development and cardiac regeneration occur via a common mechanism. Here, we describe experiments that focus on the epicardium as a target and sensor of zebrafish heart toxicity.

The effects of an environmentally relevant 58-congener polychlorinated biphenyl (PCB) mixture on cardiac development in the chick embryo

Chicken (Gallus domesticus) embryonic exposure in ovo to a 58-congener polychlorinated biphenyl (PCB) mixture resulted in teratogenic heart defects in chick embryos at critical heart developmental stages Hamburger-Hamilton (HH) stages 10, 16, and 20. The 58-congener mixture contained relative proportions of primary congeners measured in belted sandpiper (Megaceryle alcyon) and spotted sandpiper (Actitis macularia) eggs collected along the upper Hudson River, New York, USA, and chicken doses were well below observed environmental exposure levels. Embryos were injected with 0.08 µg PCBs/g egg weight and 0.50 µg PCBs/g egg weight (0.01 and 0.064 ng toxic equivalent/g, respectively) at embryonic day 0, prior to incubation. Mortality of exposed embryos was increased at all developmental stages, with a marked rise in cardiomyopathies at HH16 and HH20 (p < 0.05). Heart abnormalities occurred across all treatments, including abnormal elongation and expansion of the heart tube at HH10, improper looping and orientation, indentations in the emerging ventricular wall (HH16 and HH20), and irregularities in overall heart shape (HH10, HH16, and HH20). Histology was conducted on 2 cardiac proteins critical to embryonic heart development, ventricular myosin heavy chain and titin, to investigate potential mechanistic effects of PCBs on heart development, but no difference was observed in spatiotemporal expression. Similarly, cellular apoptosis in the developing heart was not affected by exposure to the PCB mixture. Conversely, cardiomyocyte proliferation rates dramatically declined (p < 0.01) at HH16 and HH20 as PCB exposure concentrations increased. Early embryonic cardiomyocyte proliferation contributes to proper formation of the morphology and overall thickness of the ventricular wall. Therefore, in ovo exposure to this 58-congener PCB mixture at critical stages adversely affects embryonic heart development.

Effects of an environmentally relevant polychlorinated biphenyl (PCB) mixture on embryonic survival and cardiac development in the domestic chicken

A 58-congener polychlorinated biphenyl (PCB) mixture based on contaminant analysis of spotted sandpiper eggs collected along the upper Hudson River, New York, USA, in 2004 was used to study in ovo PCB effects on cardiac development in the domestic chicken. Fertile eggs were injected prior to incubation with the following doses of the PCB mixture: untreated, sham, 0, 0.03, 0.08, 0.3, 0.5, 0.7, and 2.06 µg PCBs/g egg weight (toxic equivalent quotient [TEQ] range of 0.004-0.266 ng/g). In addition, there were untreated and sham-control groups. Embryonic development was monitored throughout incubation and chicks were necropsied at hatch. Hatchability followed a dose-dependent curve with significant (p < 0.05) mortality above the 0.5 µg PCBs/g egg weight treatment compared with controls. The median lethal dose (LD50) of this PCB mixture in hatchling chicks was estimated as 0.4 µg/g egg weight (0.052 ng TEQ/g egg wt) based on the lethality curve. Cardiac arrhythmia was observed at embryonic day 14 of development in embryos treated at concentrations of 0.5 µg/g egg weight and above. Histological analysis was utilized to characterize any cardiac abnormalities. Cardiomyopathies increased across treatments in a dose-dependent manner compared with control groups. Identified abnormalities included the absence of the trabeculated layer of the ventricular wall, ventricular dilation, thinning of the ventricular walls, malformation of the septal wall, and most commonly, absence of the compact layer of the ventricular wall. Chick heart width, depth, total area, compact layer depth, septal width, chamber area, and ventricular wall dimensions did not differ across treatments. The present study supports prior reports of adverse developmental effects of PCBs on cardiovascular systems in birds. Although the eggs hatched, measured cardiomyopathies suggest potential deleterious long-term impacts on individual health and fitness.

Genetics of congenital heart disease: the glass half empty

Congenital heart disease (CHD) is the most common congenital anomaly in newborn babies. Cardiac malformations have been produced in multiple experimental animal models, by perturbing selected molecules that function in the developmental pathways involved in myocyte specification, differentiation, or cardiac morphogenesis. In contrast, the precise genetic, epigenetic, or environmental basis for these perturbations in humans remains poorly understood. Over the past few decades, researchers have tried to bridge this knowledge gap through conventional genome-wide analyses of rare Mendelian CHD families, and by sequencing candidate genes in CHD cohorts. Although yielding few, usually highly penetrant, disease gene mutations, these discoveries provided 3 notable insights. First, human CHD mutations impact a heterogeneous set of molecules that orchestrate cardiac development. Second, CHD mutations often alter gene/protein dosage. Third, identical pathogenic CHD mutations cause a variety of distinct malformations, implying that higher order interactions account for particular CHD phenotypes. The advent of contemporary genomic technologies including single nucleotide polymorphism arrays, next-generation sequencing, and copy number variant platforms are accelerating the discovery of genetic causes of CHD. Importantly, these approaches enable study of sporadic cases, the most common presentation of CHD. Emerging results from ongoing genomic efforts have validated earlier observations learned from the monogenic CHD families. In this review, we explore how continued use of these technologies and integration of systems biology is expected to expand our understanding of the genetic architecture of CHD.

Dietary exposure of mink (Mustela vison) to fish from the upper Hudson River, New York, USA: effects on organ mass and pathology

The authors evaluated effects of feeding ranch mink (Mustela vison) diets containing polychlorinated biphenyl (PCB)-contaminated fish from the upper Hudson River (New York, USA) on adult and offspring organ mass and pathology. Diets contained 2.5 to 20% Hudson River fish, providing 0.72 to 6.1 µg ΣPCBs/g feed (4.8-38 pg toxic equivalents [TEQWHO 2005 ]/g feed). Absolute thyroid and adrenal gland masses were increased in adult females and 31-week-old juveniles, respectively, and absolute liver and heart masses were decreased in six-week-old kits exposed to dietary PCBs. Dietary concentrations of 0.72 µg ΣPCBs/g feed (4.8 pg TEQWHO 2005 /g feed) and greater induced mandibular and maxillary squamous epithelial proliferation in adult animals. The dietary concentration of ΣPCBs predicted to result in 20% incidence of the jaw lesion (EC20) was 2.3 µg ΣPCBs/g feed (15 pg TEQWHO 2005 /g feed), and the hepatic concentration was 2.8 µg ΣPCBs/g liver (89 pg TEQWHO 2005 /g liver). The EC20 values were greater than the dietary and hepatic concentrations predicted to result in a 20% increase in kit mortality (LC20) at six weeks of age (0.34 µg ΣPCBs/g feed or 2.6 pg TEQWHO 2005 /g feed and 0.80 µg ΣPCBs/g liver or 13 pg TEQWHO 2005 /g liver). However, the EC20 values reflect exposure of adults to PCBs for approximately six months, and the LC20 values reflect exposure of offspring from conception onward.

Differential expression profile of MicroRNAs during differentiation of cardiomyocytes exposed to polychlorinated biphenyls

Exposure to persistent environmental pollutants, such as polychlorinated biphenyls (PCBs), is a risk factor for the development of congenital heart defects. MicroRNAs (miRNAs) have been shown to be involved in cardiac development. The objective of this study was to investigate changes in miRNA expression profiles during the differentiation of cardiomyocytes exposed to PCBs. For that purpose, PCBs (Aroclor 1254) at a concentration of 2.5 μmol/L were added on day 0 of differentiation of P19 mouse embryonal carcinoma cells into cardiac myocytes. The relative expression of miRNA genes was determined by miRNA microarray and real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR) analyses. The microarray results revealed that 45 miRNAs, of which 14 were upregulated and 31 were downregulated, were differentially expressed in P19 cells treated with PCBs compared with control cells. The miRNA expression data was validated with real-time RT-PCR. The expression of certain potential target genes (Wnt1) was found to be reduced in P19 cells treated with PCBs, whereas the expression of other potential predicted target genes (GSK3β) was increased. Our results demonstrate a critical role of miRNAs in mediating the effect of PCBs during the differentiation of P19 cells into cardiac myocytes.

Toxic effects of PCB126 and TCDD on shortnose sturgeon and Atlantic sturgeon

Exposure to chemical contaminants is often invoked to explain recruitment failures to populations of sturgeon worldwide, but there is little empirical evidence to support the idea that young sturgeon are sensitive at environmentally relevant concentrations. The authors used shortnose sturgeon (Acipenser brevirostum) and Atlantic sturgeon (Acipenser oxyrinchus) as models to investigate the sensitivities of sturgeon to early-life-stage toxicities from embryonic exposures to graded doses of polychlorinated biphenyl 126 (PCB126) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Survival to hatching of shortnose sturgeon decreased with increasing dose, although the duration of the embryonic period was not significantly altered by exposure in either species. Morphometric features of larvae of both species were affected by dose, including shortening of the body, reduction in head size, reduction in quantity of yolk reserves, and reduction in eye size. Eye development in both species was delayed with increasing dose for both chemicals. The persistence of larvae in a food-free environment decreased inversely with dose in both species, with sharp declines occurring at PCB126 and TCDD doses of ≥1 ppb and ≥0.1 ppb, respectively. Dose-responsive early-life-stage toxicities reported here are among the more sensitive found in fish and occurred at burdens similar to those found in situ in a sympatric bottom-dwelling bony fish in the Hudson River Estuary. The present study is among the first demonstrating the sensitivity of any sturgeon to the hallmark early-life-stage toxicities induced by aryl hydrocarbon receptor agonists.

Differential gene expression and a functional analysis of PCB-exposed children: understanding disease and disorder development

The goal of the present study is to understand the probable molecular mechanism of toxicities and the associated pathways related to observed pathophysiology in high PCB-exposed populations. We have performed a microarray-based differential gene expression analysis of children (mean age 46.1 months) of Central European descent from Slovak Republic in a well-defined study cohort. The subset of children having high blood PCB concentrations (>75 percentile) were compared against their low PCB counterparts (<25 percentile), with mean lipid-adjusted PCB values of 3.02±1.3 and 0.06±0.03 ng/mg of serum lipid, for the two groups, respectively (18.1±4.4 and 0.3±0.1 ng/ml of serum). The microarray was conducted with the total RNA from the peripheral blood mononuclear cells of the children using an Affymetrix platform (GeneChip Human genome U133 Plus 2.0 Array) and was analyzed by Gene Spring (GX 10.0). A highly significant set of 162 differentially expressed genes between high and low PCB groups (p value <0.00001) were identified and subsequently analyzed using the Ingenuity Pathway Analysis tool. The results indicate that Cell-To-Cell Signaling and Interaction, Cellular Movement, Cell Signaling, Molecular Transport, and Vitamin and Mineral Metabolism were the major molecular and cellular functions associated with the differentially altered gene set in high PCB-exposed children. The differential gene expressions appeared to play a pivotal role in the development of probable diseases and disorders, including cardiovascular disease and cancer, in the PCB-exposed population. The analyses also pointed out possible organ-specific effects, e.g., cardiotoxicity, hepatotoxicity and nephrotoxicity, in high PCB-exposed subjects. A few notable genes, such as BCL2, PON1, and ITGB1, were significantly altered in our study, and the related pathway analysis explained their plausible involvement in the respective disease processes, as mentioned. Our results provided insight into understanding the associated molecular mechanisms of complex gene-environment interactions in a PCB-exposed population. Future endeavors of supervised genotyping of pathway-specific molecular epidemiological studies and population biomarker validations are already underway to reveal individual risk factors in these PCB-exposed populations.

Modeling geographic risk of complex congenital heart defects in Eastern Wisconsin

BACKGROUND

Geographic variation may be an indicator of risk factors for birth defects. This study models the geographic distribution of three complex congenital heart defects (CHDs) in eastern Wisconsin, and evaluates effects of demographic census variables linked to geographic location.

METHODS

Cases of Hypoplastic Left Heart Syndrome (HLHS), Tetralogy of Fallot (TOF) and d-Transposition of the Great Arteries (d-TGAs) born between1995 and 2004 were identified from three medical centers serving eastern Wisconsin. Case diagnoses were assigned by a pediatric cardiologist using echocardiographic records. Births by ZIP code were obtained from the State of Wisconsin. ZIP Code demographic variables were derived from 2000 census data. Numbers of cardiac defects by ZIP code were modeled using cluster analysis and Poisson generalized additive models (GAMs) for spatial coordinates including all and white only cases (excluding trisomies). GAM analyses were repeated adjusting for census variables.

RESULTS

Four hundred forty-eight cases were ascertained. A significant south-to-north spatial gradient for HLHS, TOF, and combined CHDs, but not d-TGAs was identified. This gradient remained significant when census variables were included in the model for the full sample. In the analysis excluding non-white cases, findings were the same for TOF, combined CHDs, and d-TGAs. However, the geographic gradient for HLHS was not significant in the adjusted model.

CONCLUSIONS

A south-to-north gradient was apparent for two of three complex CHDs in eastern Wisconsin. For white cases, demographic variation seems to explain some of this spatial gradient in HLHS. Further studies are needed to confirm demographic and other risk factors underlying this geographic gradient.

Genetic architecture of susceptibility to PCB126-induced developmental cardiotoxicity in zebrafish

Variability in risk of developmental defects caused by dioxin-like compounds (DLCs) has been demonstrated within and among several vertebrate species. Beyond our knowledge of the aryl hydrocarbon receptor (AHR) and its role in mediating toxicity for this class of compounds, little else is known concerning precise downstream targets influencing this vulnerability. In the present study, zebrafish with divergent genetic backgrounds were screened for susceptibility to developmental cardiotoxicity caused by the prototypical DLC, 3,3',4,4',5-pentachlorobiphenyl (PCB126); a range up to ∼40-fold differences was observed. Differentially sensitive zebrafish were chosen for a genetic cross, and the recombinant generation was used for genome-wide quantitative trait loci (QTL) mapping. Multiple QTLs were identified--several acting alone, one additively, and two others via epistatic interaction. Together, these QTLs account for 24% of the phenotypic variance observed in cardioteratogenicity resulting from PCB126 exposure (logarithm of the odds = 13.55, p = 1.89 × 10⁻¹⁰). Candidate genes in these QTL regions include the following: ahr2, bcor, and capn1 (Chr 22); e2f1 and pdyn (Chr 23); ctnnt2, plcg1, eno3, tgm1, and tgm2 (interacting on Chr 23); and vezf1 (Chr 15). These data demonstrate that DLC-induced cardiac teratogenicity is a multifactorial complex trait influenced by gene × gene and gene × environment interactions. The identified QTLs harbor many DLC-responsive genes critical to cardiovascular development and provide insight into the genetic basis of susceptibility to AHR-mediated developmental toxicity.

Comparative study of teratogenic potentials of crude ethanolic root bark and leaf extract of Rauwolfia vomitoria (apocynaceae) on the fetal heart

BACKGROUND

Rauwolfia vomitoria, a tropical shrub, is a medicinal plant used in the treatment of a variety of ailments. It is popular to the locals because of its anti-hypertensive and sedative properties.

AIM

This is to find the probable teratogenic effects of ethanolic leaf and root bark extracts of Rauwolfia vomitoria on the morphological and histological features of the fetal heart.

MATERIAL AND METHODS

Twenty five female rats weighing between 170-200g were used for this study. The rats were divided into five groups labeled A, B, C, D and E, with each group consisting of five rats. Pregnancy was induced by caging the female rats with sexually matured males. The presence of vaginal plug and tail structures in the vaginal smear the following morning confirmed coition, and it was regarded as day 0 of pregnancy. Group A was given sham treatment of distilled water. Group B and C received respectively 150mg/kg and 250mg/kg body weight doses of ethanolic leaf extract of Rauwolfia vomitoria, and those in groups D and E received respectively 150mg/kg and 250mg/kg body weight doses of ethanolic root bark extract of Rauwolfia vomitoria. These treatments were on days 7-11 of gestation (5 days) with the aid of an orogastric tube. On the day 20 of gestation, the rats were sacrificed and the fetuses examined for gross anomalies, preserved and latter process for histological studies.

RESULTS

There were no mortality in this study, and no obvious gross malformations in the fetuses. Histological observations of the fetal heart showed marked distortion of the cardiac muscle nuclei and myocardial fibers in the treated groups particularly those whose mothers received 250mg/kg of the extracts. These effects were more pronounced in the groups whose mothers received the root extract when compared with the control and the groups whose mothers received the leaf extract.

CONCLUSION

This result suggests that high doses of ethanolic leaf and root extracts of Rauwolfia vomitoria may be cardiotoxic to the developing rat's heart.

Photodegradation of selected PCBs in the presence of Nano-TiO2 as catalyst and H2O2 as an oxidant

Photodegradation of five strategically selected PCBs was carried out in acetonitrile/water 80:20. Quantum chemical calculations reveal that PCBs without any chlorine on ortho-positions are closer to be planar, while PCBs with at least one chlorine atoms at the ortho-positions causes the two benzene rings to be nearly perpendicular. Light-induced degradation of planar PCBs is much slower than the perpendicular ones. The use of nano-TiO₂ speeds up the degradation of the planar PCBs, but slows down the degradation of the non-planar ones. The use of H₂O₂ speeds up the degradation of planar PCBs greatly (by >20 times), but has little effect on non-planar ones except 2,3,5,6-TCB. The relative photodegradation rate is: 2,2′,4,4′-TCB > 2,3,5,6-TCB > 2,6-DCB ≈ 3,3′,4,4′-TCB > 3,4′,5-TCB. The use of H₂O₂ in combination with sunlight irradiation could be an efficient and “green” technology for PCB remediation.

TCDD induced pericardial edema and relative COX-2 expression in medaka (Oryzias Latipes) embryos

Exposure to dioxin and other aryl hydrocarbon receptor (AhR) ligands results in multiple, specific developmental cardiovascular phenotypes including pericardial edema and circulatory failure in small aquarium fish models. Although phenotypes are well described, mechanistic underpinnings for such toxicities remain elusive. Here we suggest that AhR activation results in stimulation of inflammation and "eicosanoid" pathways, which contribute to the observed developmental, cardiovascular phenotypes. We demonstrate that medaka embryos exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.05-1 ppb) during early development result in a dose-related increase in the prevalence of pericardial edema and that this phenotype correlates with an increase in cyclooxygenase-2 (COX-2) gene expression. Those individuals exhibiting the edema phenotype had significantly greater COX-2 mRNA than their nonedematous cohort. Selective pharmacological inhibition of COX-2, with NS-398, and genetic knock down of COX-2 with a translation initiation morpholino significantly attenuated prevalence and severity of edema phenotype. Subsequently, exposures of medaka embryos to arachidonic acid (AA) resulted in recapitulation of the pericardial edema phenotype and significantly increased COX-2 expression only in those individuals exhibiting the edema phenotype compared with their nonedematous cohort. AA exposure does not result in significant induction of cytochrome P450 1A expression, suggesting that pericardial edema can be induced independent of AhR/aryl hydrocarbon receptor nuclear translocator/dioxin response element interactions. Results from this study demonstrate that developmental exposure to TCDD results in an induction of inflammatory mediators including COX-2, which contribute to the onset, and progression of heart dysmorphogenesis in the medaka model.