Inorganic arsenic as a developmental toxicant: in utero exposure and alterations in the developing rat lungs

Study on the Mechanism of Arsenic-Induced Lung Injury Based on SWATH Proteomics Technology

Chronic arsenic poisoning is a global health problem that affects millions of people, and studies have found that long-term ingestion of arsenic-containing compounds can lead to lung damage, but the exact mechanism is unknown. In this study, Sprague-Dawley (SD) rats were used as the research object, and the proteomic analysis method based on sequential window acquisition of all theoretical fragment ions (SWATH) was used to detect the changes in the expression levels of related proteins in the lung tissue of arsenic-exposed rats, and to explore the mechanism of arsenic compound-induced lung injury. The results showed that arsenic exposure resulted in the abnormal expression of collagen type III and proteins involved in metabolic, immune, and cellular processes, leading to the dysfunction of important pathways associated with these proteins, resulting in lung injury. It suggested that the underlying mechanism of arsenic-induced lung injury may be related to oxidative stress, immune injury, cell junction, and collagen type III. This result provides a new research idea for revealing the mechanism of lung injury caused by arsenic exposure.

Non-malignant respiratory illness associated with exposure to arsenic compounds in the environment

Arsenic (As), a toxic metalloid, primarily originates from both natural and anthropogenic activities. Reports suggested that millions of people globally exposed to high levels of naturally occurring As compounds via inhalation and ingestion. There is evidence that As is a well-known lung carcinogen. However, there has been relatively little evidence suggesting its non-malignant lung effects. This review comprehensively summarises current experimental and clinical studies implicating the association of As exposure and the development of several non-malignant lung diseases. Experimental studies provided evidence that As exposure induces redox imbalance, apoptosis, inflammatory response, epithelial-to-mesenchymal transition (EMT), and affected normal lung development through alteration of the components of intracellular signaling cascades. In addition, we also discuss the sources and possible mechanisms of As influx and efflux in the lung. Finally, current experimental studies on treatment strategies using phytochemicals and our perspective on future research with As are also discussed.

Serum intracellular adhesion molecule-1 and interleukin-8 as predictors of pulmonary impairment among workers in secondary copper smelters

OBJECTIVE

Copper smelter workers are exposed to harmful chemical agents in dust and fumes which contain harmful metals such as copper and arsenic. These substances are known to be respiratory irritants.

METHODS

This study aimed at investigating the effect of occupational exposure to copper and arsenic on the respiratory system. A group of 75 male exposed workers, and 75 male administrative employees (control group) were recruited from a secondary copper smelting factory. Full history, complete clinical examination, ventilatory function parameters (FVC, FEV1, FVC/FEV1 and FEF), and chest X-ray were done for both groups. Serum levels of ICAM-1 and IL8 (as markers of epithelial injury) were measured by ELISA. Serum copper and arsenic were measured by atomic absorption spectrophotometer.

RESULTS

The exposed group was associated with increased respiratory symptoms, higher serum copper, arsenic, and ICAM-1and Il-8 as compared to the control group. There was a significant decrease in ventilatory parameters among the exposed group: 58.7% of the exposed group had restrictive lung impairment, 40% had obstructive impairment. In the exposed group a positive correlation between serum copper, arsenic and serum ICAM and IL8 was found. While a negative correlation was observed between both serum ICAM, IL8 and ventilatory parameters among the exposed group. Moreover, 36% of the exposed group had radiological infiltrates on chest X.ray.

CONCLUSION

Occupational exposure to copper and arsenic was associated with ventilatory and radiological impairment, with a corresponding increase in the serum level of ICAM-1 and IL8, which can be used as biomarkers for pulmonary impairment among copper smelter workers.

Arsenic represses airway epithelial mucin expression by affecting retinoic acid signaling pathway

Arsenic is a ubiquitous environmental toxicant, found in high concentrations worldwide. Although abundant research has dealt with arsenic-induced cancers, studies on mechanisms of non-malignant lung diseases have not been complete. In addition, decades of research have mostly concentrated on high-dose arsenic exposure, which has very limited use in modeling the biological effects of today's low-dose exposures. Indeed, accumulated evidence has shown that low-dose arsenic exposure (i.e. ≤100 ppb) may also alter lung homeostasis by causing host susceptibility to viral infection. However, the underlying mechanism of this alteration is unknown. In this study, we found that low-dose sodium arsenite (As (III)) repressed major airway mucins-MUC5AC and MUC5B at both mRNA and protein levels. We further demonstrated that this repression was not caused by cellular toxicity or mediated by the reduction of a common mucin-inducing pathway-EGFR. Other established mucin activators- dsRNA, IL1β or IL17 were not able to override As (III)-induced mucin repression. Interestingly, the suppressing effect of As (III) appeared to be partially reversible, and supplementation of all trans retinoic acid (t-RA) doses dependently restored mucin gene expression. Further analyses indicated that As (III) treatment significantly reduced the protein level of retinoic acid receptors (RARα, γ and RXRα) as well as RARE promoter reporter activity. Therefore, our study fills in an important knowledge gap in the field of low-dose arsenic exposure. The interference of RA signaling, and mucin gene expression may be important pathogenic factors in low-dose arsenic induced lung toxicity.

Early life inhalation exposure to mine tailings dust affects lung development

Exposure to mine tailings dust from active and abandoned mining operations may be a very significant health hazard, especially to sensitive populations living in arid and semi-arid climates like the desert southwest of the US. It is anticipated that early life exposures during sensitive times of development can lead to adult disease. However, very few studies have investigated the effects of inhalation exposure to real world dusts during lung development. Using a mouse model, we have examined the effect(s) of inhalation of real world mine tailing dusts under three separate conditions: (1) Exposure only during in utero development (exposure of the pregnant moms) (2) exposure only after birth and (3) exposures that occurred continuously during in utero development, through gestation and birth until the mice reached adulthood (28 days old). We found that the most significant changes in lung structure and function were observed in male mice when exposure occurred continuously throughout development. These changes included increased airway hyper-reactivity, increased expression of epithelial to mesenchymal (EMT) transition protein markers and increased expression of cytokines related to eosinophils. The data also indicate that in utero exposures through maternal inhalation can prime the lung of male mice for more severe responses to subsequent postnatal exposures. This may be due to epigenetic alterations in gene regulation, immune response, molecular signaling, and growth factors involved in lung development that may make the neonatal lung more susceptible to continued dust exposure.

Impact of prenatal arsenic exposure on chronic adult diseases

Exposure to environmental stressors during susceptible windows of development can result in negative health outcomes later in life, a concept known as the Developmental Origins of Health and Disease (DOHaD). There is a growing body of evidence that exposures to metals early in life (in utero and postnatal) increase the risk of developing adult diseases such as cancer, cardiovascular disease, non-alcoholic fatty liver disease, and diabetes. Of particular concern is exposure to the metalloid arsenic, a drinking water contaminant and worldwide health concern. Epidemiological studies of areas with high levels of arsenic in the drinking water, such as some regions in Chile and Bangladesh, indicate an association between in utero arsenic exposure and the development of adult diseases. Therefore, the need for experimental models to address the mechanism underlining early onset of adult diseases have emerged including the in utero and whole-life exposure models. This review will highlight the epidemiological events and subsequent novel experimental models implemented to study the impact of early life exposure to arsenic on the development of adult diseases. In addition, current research using these models will be discussed as well as possible underlying mechanism for the early onset of disease. Abbreviations: ALT: alanine aminotransferase; AMI: acute myocardial infarction; AST: aspartate aminotransferase; ATSDR: Agency for Toxic Substances and Disease Registry; CVD: cardiovascular disease; DMA: dimethylarsinate; DOHaD: Developmental Origins of Health and Disease; EPA: U.S. Environmental Protection Agency; ER-α: estrogen receptor alpha; HDL: high-density lipoprotein; HOMA-IR: homeostatic model assessment of insulin resistance; iAs: inorganic arsenic; LDL: low-density lipoprotein; MetS: metabolic syndrome; MMA: monomethylarsonate; NAFLD: non-alcoholic fatty liver disease; PND: postnatal day; ppb: parts per billion; ppm: parts per million; SAM: S-adenosylmethionine; USFDA: United States Food and Drug Administration.

Metabolism and disposition of arsenic species from oral dosing with sodium arsenite in neonatal CD-1 mice. IV. Toxicokinetics following gavage administration and lactational transfer

Arsenic is a ubiquitous contaminant, with typical human dietary intake below 1 μg/kg bw/d and extreme drinking water exposures up to ∼50 μg/kg bw/d. The formation and binding of trivalent metabolites are central to arsenic toxicity and strong human evidence suggests special concern for early life exposures in the etiology of adult diseases, especially cancer. This study measured the metabolism and disposition of arsenite in neonatal mice to understand the role of maturation in metabolic activation and detoxification of arsenic. Many age-related differences were observed after gavage administration of arsenite, with consistent evidence in blood and tissues for higher exposures to trivalent arsenic species in neonatal mice related to the immaturity of metabolic and/or excretory functions. The evidence for greater tissue binding of arsenic species in young mice is consistent with enhanced susceptibility to toxicity based on metabolic and toxicokinetic differences alone. Lactational transfer from arsenite-dosed dams to suckling mice was minimal, based on no dosing-related changes in the levels of arsenic species in pup blood or milk collected from the dams. Animal models evaluating whole-life exposure to inorganic arsenic must use direct dosing in early neonatal life to predict accurately potential toxicity from early life exposures in children.

Arsenic and Immune Response to Infection During Pregnancy and Early Life

PURPOSE OF REVIEW

Arsenic, a known carcinogen and developmental toxicant, is a major threat to global health. While the contribution of arsenic exposure to chronic diseases and adverse pregnancy and birth outcomes is recognized, its ability to impair critical functions of humoral and cell-mediated immunity-including the specific mechanisms in humans-is not well understood. Arsenic has been shown to increase risk of infectious diseases that have significant health implications during pregnancy and early life. Here, we review the latest research on the mechanisms of arsenic-related immune response alterations that could underlie arsenic-associated increased risk of infection during the vulnerable periods of pregnancy and early life.

RECENT FINDINGS

The latest evidence points to alteration of antibody production and transplacental transfer as well as failure of T helper cells to produce IL-2 and proliferate. Critical areas for future research include the effects of arsenic exposure during pregnancy and early life on immune responses to natural infection and the immunogenicity and efficacy of vaccines.

Arsenite Effects on Mitochondrial Bioenergetics in Human and Mouse Primary Hepatocytes Follow a Nonlinear Dose Response

Arsenite is a known carcinogen and its exposure has been implicated in a variety of noncarcinogenic health concerns. Increased oxidative stress is thought to be the primary cause of arsenite toxicity and the toxic effect is thought to be linear with detrimental effects reported at all concentrations of arsenite. But the paradigm of linear dose response in arsenite toxicity is shifting. In the present study we demonstrate that arsenite effects on mitochondrial respiration in primary hepatocytes follow a nonlinear dose response. In vitro exposure of primary hepatocytes to an environmentally relevant, moderate level of arsenite results in increased oxidant production that appears to arise from changes in the expression and activity of respiratory Complex I of the mitochondrial proton circuit. In primary hepatocytes the excess oxidant production appears to elicit adaptive responses that promote resistance to oxidative stress and a propensity to increased proliferation. Taken together, these results suggest a nonlinear dose-response characteristic of arsenite with low-dose arsenite promoting adaptive responses in a process known as mitohormesis, with transient increase in ROS levels acting as transducers of arsenite-induced mitohormesis.

Infant Infections and Respiratory Symptoms in Relation to in Utero Arsenic Exposure in a U.S. Cohort

BACKGROUND

Arsenic has been linked to disrupted immune function and greater infection susceptibility in highly exposed populations. Well arsenic levels above the U.S. EPA limit occur in our U.S. study area and are of particular concern for pregnant women and infants.

OBJECTIVES

We investigated whether in utero arsenic exposure affects the risk of infections and respiratory symptoms over the first year of life.

METHODS

We prospectively obtained information on infant infections and symptoms, including their duration and treatment (n = 412) at 4, 8, and 12 months using a parental telephone survey. Using generalized estimating equation models adjusted for potential confounders, we evaluated the association between maternal pregnancy urinary arsenic and infant infections and symptoms over the first year.

RESULTS

Each doubling of maternal urinary arsenic was related to increases in the total number of infections requiring prescription medication in the first year [relative risk (RR) = 1.1; 95% CI: 1.0, 1.2]. Urinary arsenic was related specifically to respiratory symptoms (difficulty breathing, wheezing, and cough) lasting ≥ 2 days or requiring prescription medication (RR = 1.1; 95% CI: 1.0, 1.2; and RR = 1.2; 95% CI: 1.0, 1.5, respectively), and wheezing lasting ≥ 2 days, resulting in a doctor visit or prescription medication treatment (RR = 1.3; 95% CI: 1.0, 1.7; RR = 1.3; 95% CI: 1.0, 1.8, and RR = 1.5; 95% CI: 1.0, 2.2, respectively). Associations also were observed with diarrhea (RR = 1.4; 95% CI: 1.1, 1.9) and fever resulting in a doctor visit (RR = 1.2; 95% CI: 1.0, 1.5).

CONCLUSIONS

In utero arsenic exposure was associated with a higher risk of infection during the first year of life in our study population, particularly infections requiring medical treatment, and with diarrhea and respiratory symptoms.

CITATION

Farzan SF, Li Z, Korrick SA, Spiegelman D, Enelow R, Nadeau K, Baker E, Karagas MR. 2016. Infant infections and respiratory symptoms in relation to in utero arsenic exposure in a U.S.

COHORT

Environ Health Perspect 124:840-847; http://dx.doi.org/10.1289/ehp.1409282.

Arsenic inhibits stem cell differentiation by altering the interplay between the Wnt3a and Notch signaling pathways

data indicates that arsenic exposure inhibits stem cell differentiation. This study investigated whether arsenic disrupted the Wnt3a signaling pathway, critical in the formation of myotubes and neurons, during the differentiation in P19 mouse embryonic stem cells. Cells were exposed to 0, 0.1, or 0.5 μM arsenite, with or without exogenous Wnt3a, for up to 9 days of differentiation. Arsenic exposure alone inhibits the differentiation of stem cells into neurons and skeletal myotubes, and reduces the expression of both β-catenin and GSK3β mRNA to ~55% of control levels. Co-culture of the arsenic-exposed cells with exogenous Wnt3a rescues the morphological phenotype, but does not alter transcript, protein, or phosphorylation status of GSK3β or β-catenin. However, arsenic exposure maintains high levels of Hes5 and decreases the expression of MASH1 by 2.2-fold, which are anti- and pro-myogenic and neurogenic genes, respectively, in the Notch signaling pathway. While rescue with exogenous Wnt3a reduced Hes5 levels, MASH1 levels stay repressed. Thus, while Wnt3a can partially rescue the inhibition of differentiation from arsenic, it does so by also modulating Notch target genes rather than only working through the canonical Wnt signaling pathway. These results indicate that arsenic alters the interplay between multiple signaling pathways, leading to reduced stem cell differentiation.

Lung tumors in mice induced by "whole-life" inorganic arsenic exposure at human-relevant doses

In mice, inorganic arsenic in the drinking water in the parts per million range via the dam during in utero life or with whole-life exposure is a multi-site carcinogen in the offspring. However, human arsenic exposure is typically in the parts per billion (ppb) range. Thus, we studied "whole-life" inorganic arsenic carcinogenesis in mice at levels more relevant to humans. Breeder male and female CD1 mice were exposed to 0, 50, 500 or 5,000 ppb arsenic (as sodium arsenite) in the drinking water for 3 weeks prior to breeding, during pregnancy and lactation, and after weaning (at week 3) groups of male and female offspring (initial n = 40) were exposed for up to 2 years. Tumors were assessed in these offspring. Arsenic exposure had no effect on pregnant dam weights or water consumption, litter size, offspring birthweight or weight at weaning compared to control. In male offspring mice, arsenic exposure increased (p < 0.05) bronchiolo-alveolar tumor (adenoma or carcinoma) incidence at 50-ppb group (51 %) and 500-ppb group (54 %), but not at 5,000-ppb group (28 %) compared to control (22 %). These arsenic-induced bronchiolo-alveolar tumors included increased (p < 0.05) carcinoma at 50-ppb group (27 %) compared to controls (8 %). An increase (p < 0.05) in lung adenoma (25 %) in the 50-ppb group compared to control (11 %) occurred in female offspring. Thus, in CD1 mice whole-life arsenic exposure induced lung tumors at human-relevant doses (i.e., 50 and 500 ppb).

Arsenic exposure and impaired lung function. Findings from a large population-based prospective cohort study

RATIONALE

Exposure to arsenic through drinking water has been linked to respiratory symptoms, obstructive lung diseases, and mortality from respiratory diseases. Limited evidence for the deleterious effects on lung function exists among individuals exposed to a high dose of arsenic.

OBJECTIVES

To determine the deleterious effects on lung function that exist among individuals exposed to a high dose of arsenic.

METHODS

In 950 individuals who presented with any respiratory symptom among a population-based cohort of 20,033 adults, we evaluated the association between arsenic exposure, measured by well water and urinary arsenic concentrations measured at baseline, and post-bronchodilator-administered pulmonary function assessed during follow-up.

MEASUREMENTS AND MAIN RESULTS

For every one SD increase in baseline water arsenic exposure, we observed a lower level of FEV1 (-46.5 ml; P < 0.0005) and FVC (-53.1 ml; P < 0.01) in regression models adjusted for age, sex, body mass index, smoking, socioeconomic status, betel nut use, and arsenical skin lesions status. Similar inverse relationships were observed between baseline urinary arsenic and FEV1 (-48.3 ml; P < 0.005) and FVC (-55.2 ml; P < 0.01) in adjusted models. Our analyses also demonstrated a dose-related decrease in lung function with increasing levels of baseline water and urinary arsenic. This association remained significant in never-smokers and individuals without skin lesions, and was stronger in male smokers. Among male smokers and individuals with skin lesions, every one SD increase in water arsenic was related to a significant reduction of FEV1 (-74.4 ml, P < 0.01; and -116.1 ml, P < 0.05) and FVC (-72.8 ml, P = 0.02; and -146.9 ml, P = 0.004), respectively.

CONCLUSIONS

This large population-based study confirms that arsenic exposure is associated with impaired lung function and the deleterious effect is evident at low- to moderate-dose range.

In utero and early life arsenic exposure in relation to long-term health and disease

BACKGROUND

There is a growing body of evidence that prenatal and early childhood exposure to arsenic from drinking water can have serious long-term health implications.

OBJECTIVES

Our goal was to understand the potential long-term health and disease risks associated with in utero and early life exposure to arsenic, as well as to examine parallels between findings from epidemiological studies with those from experimental animal models.

METHODS

We examined the current literature and identified relevant studies through PubMed by using combinations of the search terms "arsenic", "in utero", "transplacental", "prenatal" and "fetal".

DISCUSSION

Ecological studies have indicated associations between in utero and/or early life exposure to arsenic at high levels and increases in mortality from cancer, cardiovascular disease and respiratory disease. Additional data from epidemiologic studies suggest intermediate effects in early life that are related to risk of these and other outcomes in adulthood. Experimental animal studies largely support studies in humans, with strong evidence of transplacental carcinogenesis, atherosclerosis and respiratory disease, as well as insight into potential underlying mechanisms of arsenic's health effects.

CONCLUSIONS

As millions worldwide are exposed to arsenic and evidence continues to support a role for in utero arsenic exposure in the development of a range of later life diseases, there is a need for more prospective studies examining arsenic's relation to early indicators of disease and at lower exposure levels.

In utero exposure to low dose arsenic via drinking water impairs early life lung mechanics in mice

BACKGROUND

Exposure to arsenic via drinking water is a significant environmental issue affecting millions of people around the world. Exposure to arsenic during foetal development has been shown to impair somatic growth and increase the risk of developing chronic respiratory diseases. The aim of this study was to determine if in utero exposure to low dose arsenic via drinking water is capable of altering lung growth and postnatal lung mechanics.

METHODS

Pregnant C57BL/6 mice were given drinking water containing 0, 10 (current World Health Organisation (WHO) maximum contaminant level) or 100 μg/L arsenic from gestational day 8 to birth. Birth outcomes and somatic growth were monitored. Plethysmography and the forced oscillation technique were used to collect measurements of lung volume, lung mechanics, pressure-volume curves and the volume dependence of lung mechanics in male and female offspring at two, four, six and eight weeks of age.

RESULTS

In utero exposure to low dose arsenic via drinking water resulted in low birth weight and impaired parenchymal lung mechanics during infancy. Male offspring were more susceptible to the effects of arsenic on growth and lung mechanics than females. All alterations to lung mechanics following in utero arsenic exposure were recovered by adulthood.

CONCLUSIONS

Exposure to arsenic at the current WHO maximum contaminant level in utero impaired somatic growth and the development of the lungs resulting in alterations to lung mechanics during infancy. Deficits in growth and lung development in early life may contribute to the increased susceptibility of developing chronic respiratory disease in arsenic exposed human populations.

In utero exposure to arsenic alters lung development and genes related to immune and mucociliary function in mice

BACKGROUND

Exposure to arsenic via drinking water is a global environmental health problem. In utero exposure to arsenic via drinking water increases the risk of lower respiratory tract infections during infancy and mortality from bronchiectasis in early adulthood.

OBJECTIVES

We aimed to investigate how arsenic exposure in early life alters lung development and pathways involved in innate immunity.

METHODS

Pregnant BALB/c, C57BL/6, and C3H/HeARC mice were exposed to 0 (control) or 100 μg/L arsenic via drinking water from gestation day 8 until the birth of their offspring. We measured somatic growth, lung volume, and lung mechanics of mice at 2 weeks of age. We used fixed lungs for structural analysis and collected lung tissue for gene expression analysis by microarray.

RESULTS

The response to arsenic was genetically determined, and C57BL/6 mice were the most susceptible. Arsenic-exposed C57BL/6 mice were smaller in size, had smaller lungs, and had impaired lung mechanics compared with controls. Exposure to arsenic in utero up-regulated the expression of genes in the lung involved in mucus production (Clca3, Muc5b, Scgb3a1), innate immunity (Reg3γ, Tff2, Dynlrb2, Lplunc1), and lung morphogenesis (Sox2). Arsenic exposure also induced mucous cell metaplasia and increased expression of CLCA3 protein in the large airways.

CONCLUSIONS

Alterations in somatic growth, lung development, and the expression of genes involved in mucociliary clearance and innate immunity in the lung are potential mechanisms through which early life arsenic exposure impacts respiratory health.

Delayed temporal increase of hepatic Hsp70 in ApoE knockout mice after prenatal arsenic exposure

Prenatal arsenic exposure accelerates atherosclerosis in ApoE(-/-) mice by unknown mechanism. Arsenic is a hepatotoxicant, and liver disease increases atherosclerosis risk. Prenatal arsenic exposure may predispose to liver disease by priming for susceptibility to other environmental insults. Earlier microarray analyses showed prenatal arsenic exposure increased Hsc70 (HspA8) and Hsp70 (HspA1a) mRNAs in livers of 10-week-old mice. We determined effects of prenatal arsenic exposure on hepatic Hsp70 and Hsc70 expression by Western blot and on DNA methylation by methyl acceptance assay during prenatal and postnatal development. Pregnant ApoE(-/-) mice were given drinking water containing 85 mg/l NaAsO(2) (49 ppm arsenic) from gestation day (GD) 8 to 18. Hsp70 and Hsc70 expression and DNA methylation were determined in GD18 fetuses and 3-, 10-, and 24-week-old mice. Hsc70 expression was unchanged at all ages. Hsp70 induction was observed at 3 and 10 weeks, but was unchanged in GD18 fetuses and 24-week livers of mice. Global DNA methylation increased with age; arsenic had no effects. Bisulfite sequencing of DNA from livers of 10-week-old mice showed Hsp70 promoter region methylation was unchanged, but methylation was increased within the transcribed region. Hsf1 and Nrf2 nuclear translocation were investigated as potential mechanisms of Hsp70 induction and found unaltered. Putative binding sites were identified in HSP70 for in utero arsenic exposure-suppressed microRNAs suggesting a possible mechanism. Thus, prenatal arsenic exposure causes delayed temporal hepatic Hsp70 induction, suggesting a transient state of stress in livers which can predispose the mice to developing liver disease.

Arsenic exposure to killifish during embryogenesis alters muscle development

Epidemiological studies have correlated arsenic exposure in drinking water with adverse developmental outcomes such as stillbirths, spontaneous abortions, neonatal mortality, low birth weight, delays in the use of musculature, and altered locomotor activity. Killifish (Fundulus heteroclitus) were used as a model to help to determine the mechanisms by which arsenic could impact development. Killifish embryos were exposed to three different sodium arsenite concentrations and were collected at 32 h post-fertilization (hpf), 42 hpf, 168 hpf, or < 24 h post-hatch. A killifish oligo microarray was developed and used to examine gene expression changes between control and 25-ppm arsenic-exposed hatchlings. With artificial neural network analysis of the transcriptomic data, accurate prediction of each group (control vs. arsenic-exposed embryos) was obtained using a small subset of only 332 genes. The genes differentially expressed include those involved in cell cycle, development, ubiquitination, and the musculature. Several of the genes involved in cell cycle regulation and muscle formation, such as fetuin B, cyclin D-binding protein 1, and CapZ, were differentially expressed in the embryos in a time- and dose-dependent manner. Examining muscle structure in the hatchlings showed that arsenic exposure during embryogenesis significantly reduces the average muscle fiber size, which is coupled with a significant 2.1- and 1.6-fold upregulation of skeletal myosin light and heavy chains, respectively. These findings collectively indicate that arsenic exposure during embryogenesis can initiate molecular changes that appear to lead to aberrant muscle formation.

Arsenic toxicology: translating between experimental models and human pathology

BACKGROUND

Chronic arsenic exposure is a worldwide health problem. How arsenic exposure promotes a variety of diseases is poorly understood, and specific relationships between experimental and human exposures are not established. We propose phenotypic anchoring as a means to unify experimental observations and disease outcomes.

OBJECTIVES

We examined the use of phenotypic anchors to translate experimental data to human pathology and investigated research needs for which phenotypic anchors need to be developed.

METHODS

During a workshop, we discussed experimental systems investigating arsenic dose/exposure and phenotypic expression relationships and human disease responses to chronic arsenic exposure and identified knowledge gaps. In a literature review, we identified areas where data exist to support phenotypic anchoring of experimental results to pathologies from specific human exposures.

DISCUSSION

Disease outcome is likely dependent on cell-type-specific responses and interaction with individual genetics, other toxicants, and infectious agents. Potential phenotypic anchors include target tissue dosimetry, gene expression and epigenetic profiles, and tissue biomarkers.

CONCLUSIONS

Translation to human populations requires more extensive profiling of human samples along with high-quality dosimetry. Anchoring results by gene expression and epigenetic profiling has great promise for data unification. Genetic predisposition of individuals affects disease outcome. Interactions with infectious agents, particularly viruses, may explain some species-specific differences between human pathologies and experimental animal pathologies. Invertebrate systems amenable to genetic manipulation offer potential for elaborating impacts of specific biochemical pathways. Anchoring experimental results to specific human exposures will accelerate understanding of mechanisms of arsenic-induced human disease.

Phenotypic changes in cultured smooth muscle cells: limitation or opportunity for tissue engineering of hollow organs?

Smooth muscle cells (SMCs) are typically used as a cell source for the reconstruction of hollow organs by conventional tissue engineering techniques. However, the necessity for and advantage of the use of tissue-specific SMCs are unknown. The present study investigated the phenotypic changes that occur following isolation and in vitro expansion of rat SMC populations isolated from three different tissues: the aorta, oesophagus and urinary bladder. rSMCs were isolated by enzymatic dispersion and expanded by conventional cell culture techniques, yielding microscopically homogeneous populations. SMC phenotypes were monitored according to their expression of marker proteins during the first two passages. Two of the three SMC populations (rSMC-a and rSMC-e) showed a marked change in their marker protein profiles during the first two passages, which resulted in a homogeneous phenotype that was neither fully contractile nor fully synthetic. SMCs from the urinary bladder did not show such a shift. Differences between the three rSMC populations were observed with regard to proliferative activity and gene expression patterns, suggesting the retention of some tissue-specific cell characteristics. In summary, phenotypic changes in SMCs occur as a result of conventional cell isolation and expansion techniques, thus questioning the necessity for a tissue-specific cell source for regenerative medicine applications.

Impact of environmental chemicals on lung development

BACKGROUND

Disruption of fundamental biologic processes and associated signaling events may result in clinically significant alterations in lung development.

OBJECTIVES

We reviewed evidence on the impact of environmental chemicals on lung development and key signaling events in lung morphogenesis, and the relevance of potential outcomes to public health and regulatory science .

DATA SOURCES

We evaluated the peer-reviewed literature on developmental lung biology and toxicology, mechanistic studies, and supporting epidemiology.

DATA SYNTHESIS

Lung function in infancy predicts pulmonary function throughout life. In utero and early postnatal exposures influence both childhood and adult lung structure and function and may predispose individuals to chronic obstructive lung disease and other disorders. The nutritional and endogenous chemical environment affects development of the lung and can result in altered function in the adult. Studies now suggest that similar adverse impacts may occur in animals and humans after exposure to environmentally relevant doses of certain xenobiotics during critical windows in early life. Potential mechanisms include interference with highly conserved factors in developmental processes such as gene regulation, molecular signaling, and growth factors involved in branching morphogenesis and alveolarization.

CONCLUSIONS

Assessment of environmental chemical impacts on the lung requires studies that evaluate specific alterations in structure or function-end points not regularly assessed in standard toxicity tests. Identifying effects on important signaling events may inform protocols of developmental toxicology studies. Such knowledge may enable policies promoting true primary prevention of lung diseases. Evidence of relevant signaling disruption in the absence of adequate developmental toxicology data should influence the size of the uncertainty factors used in risk assessments.

Arsenic exposure perturbs epithelial-mesenchymal cell transition and gene expression in a collagen gel assay

Arsenic is a naturally occurring metalloid and environmental contaminant. Arsenic exposure in drinking water is reported to cause cancer of the liver, kidneys, lung, bladder, and skin as well as birth defects, including neural tube, facial, and vasculogenic defects. The early embryonic period most sensitive to arsenic includes a variety of cellular processes. One key cellular process is epithelial-mesenchymal transition (EMT) where epithelial sheets develop into three-dimensional structures. An embryonic prototype of EMT is found in the atrioventricular (AV) canal of the developing heart, where endothelia differentiate to form heart valves. Effects of arsenic on this cellular process were examined by collagen gel invasion assay (EMT assay) using explanted AV canals from chicken embryo hearts. AV canals treated with 12.5-500 ppb arsenic showed a loss of mesenchyme at 12.5 ppb, and mesenchyme formation was completely inhibited at 500 ppb. Altered gene expression in arsenic-treated explants was investigated by microarray analysis. Genes whose expression was altered consistently at exposure levels of 10, 25, and 100 ppb were identified, and results showed that 25 ppb in vitro was particularly effective. Three hundred and eighty two genes were significantly altered at this exposure level. Cytoscape analysis of the microarray data using the chicken interactome identified four clusters of altered genes based on published relationships and pathways. This analysis identified cytoskeleton and cell adhesion-related genes whose disruption is consistent with an altered ability to undergo EMT. These studies show that EMT is sensitive to arsenic and that an interactome-based approach can be useful in identifying targets.

In utero and postnatal exposure to arsenic alters pulmonary structure and function

In addition to cancer endpoints, arsenic exposures can also lead to non-cancerous chronic lung disease. Exposures during sensitive developmental time points can contribute to the adult disease. Using a mouse model, in utero and early postnatal exposures to arsenic (100 ppb or less in drinking water) were found to alter airway reactivity to methacholine challenge in 28 day old pups. Removal of mice from arsenic exposure 28 days after birth did not reverse the alterations in sensitivity to methacholine. In addition, adult mice exposed to similar levels of arsenic in drinking water did not show alterations. Therefore, alterations in airway reactivity were irreversible and specific to exposures during lung development. These functional changes correlated with protein and gene expression changes as well as morphological structural changes around the airways. Arsenic increased the whole lung levels of smooth muscle actin in a dose dependent manner. The level of smooth muscle mass around airways was increased with arsenic exposure, especially around airways smaller than 100 microm in diameter. This increase in smooth muscle was associated with alterations in extracellular matrix (collagen, elastin) expression. This model system demonstrates that in utero and postnatal exposure to environmentally relevant levels of arsenic can irreversibly alter pulmonary structure and function in the adults.