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

A Clinical Perspective on Arsenic Exposure and Development of Atherosclerotic Cardiovascular Disease

Cardiovascular risk has traditionally been defined by modifiable and non-modifiable risk factors, such as tobacco use, hyperlipidemia, and family history. However, chemicals and pollutants may also play a role in cardiovascular disease (CVD) risk. Arsenic is a naturally occurring element that is widely distributed in the Earth's crust. Inorganic arsenic (iAs) has been implicated in the pathogenesis of atherosclerosis, with chronic high-dose exposure to iAs (> 100 µg/L) being linked to CVD; however, whether low-to-moderate dose exposures of iAs (< 100 µg/L) are associated with the development of CVD is unclear. Due to limitations of the existing literature, it is difficult to define a threshold for iAs toxicity. Studies demonstrate that the effect of iAs on CVD is far more complex with influences from several factors, including diet, genetics, metabolism, and traditional risk factors such as hypertension and smoking. In this article, we review the existing data of low-to-moderate dose iAs exposure and its effect on CVD, along with highlighting the potential mechanisms of action.

Benzophenone-3 induced abnormal development of enteric nervous system in zebrafish through MAPK/ERK signaling pathway

Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of enteric neurons, which is derived from the failure of the proliferation, differentiation or migration of the enteric neural crest cells (ENCCs). HSCR is associated with multiple risk factors, including polygenic inheritance factors and environmental factors. Genetic studies have been extensively performed, whereas studies related to environmental factors remain insufficient. Benzophenone-3 (BP-3), one important component of the ultraviolet (UV) filters, has been proved to have cytotoxicity and neurotoxicity which might be associated with HSCR. In this study, we used zebrafish as a model to investigate the relationship between BP-3 exposure and the development of the enteric nervous system (ENS) in vivo. Embryos exposed to BP-3 showed an average of 46% reduction of the number of the enteric neurons number. Besides, the ENCCs specific markers (ret and hand2) were downregulated upon BP-3 exposure. Moreover, we identified potential targets of BP-3 through Network Pharmacology Analysis and Autodock and demonstrated that the attenuation of the MAPK/ERK signaling might be the potential mechanism underlying the inhibition of the ENS development by BP-3. Importantly, MAPK/ERK signaling agonist could be used to rescue the ENS defects of zebrafish induced by BP-3. Overall, we characterized the influence of BP-3 on ENS development in vivo and explored possible molecular mechanisms.

Single-cell RNA-seq Analysis Reveals That Prenatal Arsenic Exposure Results in Long-term, Adverse Effects on Immune Gene Expression in Response to Influenza A Infection

Arsenic exposure via drinking water is a serious environmental health concern. Epidemiological studies suggest a strong association between prenatal arsenic exposure and subsequent childhood respiratory infections, as well as morbidity from respiratory diseases in adulthood, long after systemic clearance of arsenic. We investigated the impact of exclusive prenatal arsenic exposure on the inflammatory immune response and respiratory health after an adult influenza A virus (IAV) lung infection. C57BL/6J mice were exposed to 100 ppb sodium arsenite in utero, and subsequently infected with IAV (H1N1) after maturation to adulthood. Assessment of lung tissue and bronchoalveolar lavage fluid at various time points post-IAV infection reveals greater lung damage and inflammation in arsenic-exposed mice versus control mice. Single-cell RNA sequencing analysis of immune cells harvested from IAV-infected lungs suggests that the enhanced inflammatory response is mediated by dysregulation of innate immune function of monocyte-derived macrophages, neutrophils, natural killer cells, and alveolar macrophages. Our results suggest that prenatal arsenic exposure results in lasting effects on the adult host innate immune response to IAV infection, long after exposure to arsenic, leading to greater immunopathology. This study provides the first direct evidence that exclusive prenatal exposure to arsenic in drinking water causes predisposition to a hyperinflammatory response to IAV infection in adult mice, which is associated with significant lung damage.

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.

Validation of control genes and a standardised protocol for quantifying gene expression in the livers of C57BL/6 and ApoE-/- mice

The liver plays a critical role in food and drug metabolism and detoxification and accordingly influences systemic body homeostasis in health and disease. While the C57BL/6 and ApoE−/− mouse models are widely used to study gene expression changes in liver disease and metabolism, currently there are no validated stably expressed endogenous genes in these models, neither is it known how gene expression varies within and across liver lobes. Here we show regional variations in the expression of Ywhaz, Gak, Gapdh, Hmbs and Act-β endogenous genes across a liver lobe; Using homogeneous samples from the four liver lobes of 6 C57BL/6 mice we tested the stability of 12 endogenous genes and show that Act-β and Eif2-α are the most stably expressed endogenous genes in all four lobes and demonstrate lobular differences in the expression of Abca1 cholesterol efflux gene. These results suggest that sampling from a specified homogeneous powdered liver lobe is paramount in enhancing data reliability and reproducibility. The stability of the 12 endogenous genes was further tested using homogeneous samples of left liver lobes from 20 ApoE−/− mice on standard or high polyphenol diets. Act-β and Ywhaz are suitable endogenous genes for gene expression normalisation in this mouse model.

The relationship between prenatal exposure to BP-3 and Hirschsprung's disease

Hirschsprung's disease (HSCR) is neonatal intestinal abnormality which derived from the faliure of enteric neural crest cells migration to hindgut during embryogenesis from 5 to 12 weeks. Currenly, the knowledge of environmental factors contributing to HSCR is still scarce. Benzophenone-3 (BP-3) is one of the most widely used UV filters, and has weak estrogen and strong anti-androgenic effects. In order to examine the effect of maternal BP-3 exposure on development of offspring and explore the potential mechanism, we conducted case and control study and in vitro study. In this work, BP-3 concertrations in maternal urine was detected by ultra-high performance liquid chromatography. Besides, we investigated the cytotoxicity and receptor tyrosine kinase (RET) expression in cells exposed to BP-3. The results showed that maternal BP-3 exposure was associated with offspring's HSCR in the population as well as inhibited migration of 293T and SH-SY5Y cells. What's more, we discovered dose-response relationship between RET expression and BP-3 exposure dose, and miR-218 and some other genes involved in SLIT2/ROBO1-miR-218-RET/PLAG1 pathway were also related to BP-3 exposure. Therefore, we deduced that BP-3 influenced cell migration via SLIT2/ROBO1-miR-218-RET/PLAG1 pathway. Our study firstly revealed the relationship between maternal BP-3 exposure and HSCR as well as its potential mechanism.

Mechanisms of action for arsenic in cardiovascular toxicity and implications for risk assessment

The possibility of an association between inorganic arsenic (iAs) exposure and cardiovascular outcomes has received increasing attention in the literature over the past decade. The United States Environmental Protection Agency (US EPA) is currently revising its Integrated Risk Assessment System (IRIS) review of iAs, and one of the non-cancer endpoints of interest is cardiovascular disease (CVD). Despite the increased interest in this area, substantial gaps remain in the available information, particularly regarding the mechanism of action (MOA) by which iAs could cause or exacerbate CVD. Few studies specifically address the plausibility of an association between iAs and CVD at the low exposure levels which are typical in the United States (i.e., below 100 μg As/L in drinking water). We have conducted a review and evaluation of the animal, mechanistic, and human data relevant to the potential MOAs of iAs and CVD. Specifically, we evaluated the most common proposed MOAs, which include disturbance of endothelial function and hepatic dysfunction. Our analysis of the available evidence indicates that there is not a well-established MOA for iAs in the development or progression of CVD. Few human studies of the potential MOAs have addressed plausibility at low doses and the applicability of extrapolation from animal studies to humans is questionable. However, the available evidence indicates that regardless of the specific MOA, the effects of iAs on physiological processes at the cellular level appear to operate via a threshold mechanism. This finding is consistent with the lack of association of CVD with iAs exposure in humans at levels below 100 μg/L, particularly when considering important exposure and risk modifiers such as nutrition and genetics. Based on this analysis, we conclude that there are no data supporting a linear dose-response relationship between iAs and CVD, indicating this relationship has a threshold.

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 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.