Epigenetics in metal carcinogenesis: nickel, arsenic, chromium and cadmium

Cadmium transport by mammalian ATP-binding cassette transporters

Cellular responses to toxic metals depend on metal accessibility to intracellular targets, reaching interaction sites, and the intracellular metal concentration, which is mainly determined by uptake pathways, binding/sequestration and efflux pathways. ATP-binding cassette (ABC) transporters are ubiquitous in the human body-usually in epithelia-and are responsible for the transfer of indispensable physiological substrates (e.g. lipids and heme), protection against potentially toxic substances, maintenance of fluid composition, and excretion of metabolic waste products. Derailed regulation and gene variants of ABC transporters culminate in a wide array of pathophysiological disease states, such as oncogenic multidrug resistance or cystic fibrosis. Cadmium (Cd) has no known physiological role in mammalians and poses a health risk due to its release into the environment as a result of industrial activities, and eventually passes into the food chain. Epithelial cells, especially within the liver, lungs, gastrointestinal tract and kidneys, are particularly susceptible to the multifaceted effects of Cd because of the plethora of uptake pathways available. Pertinent to their broad substrate spectra, ABC transporters represent a major cellular efflux pathway for Cd and Cd complexes. In this review, we summarize current knowledge concerning transport of Cd and its complexes (mainly Cd bound to glutathione) by the ABC transporters ABCB1 (P-glycoprotein, MDR1), ABCB6, ABCC1 (multidrug resistance related protein 1, MRP1), ABCC7 (cystic fibrosis transmembrane regulator, CFTR), and ABCG2 (breast cancer related protein, BCRP). Potential detoxification strategies underlying ABC transporter-mediated efflux of Cd and Cd complexes are discussed.

Genome-wide DNA methylation profiles and breast cancer among World Trade Center survivors

Background

Increased incidence of cancer has been reported among World Trade Center (WTC)-exposed persons. Aberrant DNA methylation is a hallmark of cancer development. To date, only a few small studies have investigated the relationship between WTC exposure and DNA methylation. The main objective of this study was to assess the DNA methylation profiles of WTC-exposed community members who remained cancer free and those who developed breast cancer.

Methods

WTC-exposed women were selected from the WTC Environmental Health Center clinic, with peripheral blood collected during routine clinical monitoring visits. The reference group was selected from the NYU Women's Health Study, a prospective cohort study with blood samples collected before 9 November 2001. The Infinium MethylationEPIC array was used for global DNA methylation profiling, with adjustments for cell type composition and other confounders. Annotated probes were used for biological pathway and network analysis.

Results

A total of 64 WTC-exposed (32 cancer free and 32 with breast cancer) and 32 WTC-unexposed (16 cancer free and 16 with prediagnostic breast cancer) participants were included. Hypermethylated cytosine-phosphate-guanine probe sites (defined as β > 0.8) were more common among WTC-exposed versus unexposed participants (14.3% vs. 4.5%, respectively, among the top 5000 cytosine-phosphate-guanine sites). Cancer-related pathways (e.g., human papillomavirus infection, cGMP-PKG) were overrepresented in WTC-exposed groups (breast cancer patients and cancer-free subjects). Compared to the unexposed breast cancer patients, 47 epigenetically dysregulated genes were identified among WTC-exposed breast cancers. These genes formed a network, including Wnt/β-catenin signaling genes WNT4 and TCF7L2, and dysregulation of these genes contributes to cancer immune evasion.

Conclusion

WTC exposure likely impacts DNA methylation and may predispose exposed individuals toward cancer development, possibly through an immune-mediated mechanism.

Emerging insights into the impacts of heavy metals exposure on health, reproductive and productive performance of livestock

Heavy metals, common environmental pollutants with widespread distribution hazards and several health problems linked to them are distinguished from other toxic compounds by their bioaccumulation in living organisms. They pollute the food chain and threaten the health of animals. Biologically, heavy metals exhibit both beneficial and harmful effects. Certain essential heavy metals such as Co, Mn, Se, Zn, and Mg play crucial roles in vital physiological processes in trace amounts, while others like As, Pb, Hg, Cd, and Cu are widely recognized for their toxic properties. Regardless of their physiological functions, an excess intake of all heavy metals beyond the tolerance limit can lead to toxicity. Animals face exposure to heavy metals through contaminated feed and water, primarily as a result of anthropogenic environmental pollution. After ingestion heavy metals persist in the body for an extended duration and the nature of exposure dictates whether they induce acute or chronic, clinical or subclinical, or subtle toxicities. The toxic effects of metals lead to disruption of cellular homeostasis through the generation of free radicals that develop oxidative stress. In cases of acute heavy metal poisoning, characteristic clinical symptoms may arise, potentially culminating in the death of animals with corresponding necropsy findings. Chronic toxicities manifest as a decline in overall body condition scoring and a decrease in the production potential of animals. Elevated heavy metal levels in consumable animal products raise public health concerns. Timely diagnosis, targeted antidotes, and management strategies can significantly mitigate heavy metal impact on livestock health, productivity, and reproductive performance.

Effects of hexavalent chromium on mitochondria and their implications in carcinogenesis

Hexavalent chromium (Cr(VI)) is a well-known occupational and environmental human carcinogen. The cellular effect of Cr(VI) is complex and often nonspecific due to its ability to modulate multiple cellular targets. The toxicity of Cr(VI) is strongly linked to the generation of reactive oxygen species (ROS) during its reduction process. ROS can cause oxidation of cellular macromolecules, such as proteins, lipids, and DNA, thereby altering their functions. A major genotoxic effect of Cr(VI) that contributes to carcinogenesis is the formation of DNA adducts, which can lead to DNA damage. Modulations of cellular signaling pathways and epigenetics may also contribute to the carcinogenic effects of Cr(VI). Cr(VI) has a major impact on many aspects of mitochondrial biology, including oxidative phosphorylation, mitophagy, and mitochondrial biogenesis. These effects have the potential to alter the trajectory of Cr(VI)-induced carcinogenic process. This perspective article summarizes current understandings of the effect of Cr(VI) on mitochondria and discusses the future directions of research in this area, particularly with regard to carcinogenesis.

Synthesis of Plant-Mediated Iron Oxide Nanoparticles and Optimization of Chemically Modified Activated Carbon Adsorbents for Removal of As, Pb, and Cd Ions from Wastewater

This research study was designed with the aim to prepare plant extract-mediated iron oxide nanoparticles (IONPs) and different chemically modified carbon adsorbents from the Parthenium hysterophorus plant and then optimize the carbon adsorbents by evaluating their adsorption applications in wastewater for the selected metal ions like arsenic (As3+), lead (Pb2+), and cadmium (Cd2+). The Fourier transform infrared spectroscopy (FTIR) technique was used to highlight functional groups in plant-mediated IONPs and chemically modified carbon adsorbents. A scanning electron microscopy study was conducted to explain the surface morphology of the adsorbents. Energy-dispersive X-rays was used for elemental analysis and X-ray diffraction for particle size and crystallinity of the adsorbents. From the study, it was found that the best optimum conditions were pH = 5-6, initial concentration of adsorbate of 10 mg/L, dose of adsorbent of 0.01 g, contact time of 90-120 min of adsorbent and adsorbate, and temperature of 25 °C. At optimum conditions, the adsorption capacities of IONPs for arsenic (As) 144.7 mg/g, lead (Pb) 128.01 mg/g, and cadmium (Cd) ions 122.1 mg/g were recorded. The activated carbon at optimum conditions showed adsorption capacities of 46.35 mg/g for As, 121.95 mg/g for Pb, and 113.25 mg/g for Cd ion. At equilibrium, Langmuir, Freundlich Temkin, and Dubinin-Radushkevich isotherms were applied on the experimental adsorption data having the best R2 values (0.973-0.999) by the Langmuir isotherm. High-correlation coefficient R2 values (0.996-0.999) were obtained from the pseudo-second-order for all cases, showing that the adsorption process proceeds through pseudo second-order kinetics. The apparent adsorption energy E value was in the range of 0.24-2.36 kJ/mol. The adsorption capacity of regenerated IONPs for As gradually decreased from 144.8 to 45.67 mg/g, for lead 128.15 to 41.65 mg/g, and cadmium from 122.10 to 31.20 mg/g in 5 consecutive cycles. The study showed that the synthesized IONPs and acid-activated carbon adsorbent were successfully used to remove selected metal ions from wastewater.

World Trade Center Exposure, DNA Methylation Changes, and Cancer: A Review of Current Evidence

Introduction: Known carcinogens in the dust and fumes from the destruction of the World Trade Center (WTC) towers on 9 November 2001 included metals, asbestos, and organic pollutants, which have been shown to modify epigenetic status. Epigenome-wide association analyses (EWAS) using uniform (Illumina) methodology have identified novel epigenetic profiles of WTC exposure. Methods: We reviewed all published data, comparing differentially methylated gene profiles identified in the prior EWAS studies of WTC exposure. This included DNA methylation changes in blood-derived DNA from cases of cancer-free "Survivors" and those with breast cancer, as well as tissue-derived DNA from "Responders" with prostate cancer. Emerging molecular pathways related to the observed DNA methylation changes in WTC-exposed groups were explored and summarized. Results: WTC dust exposure appears to be associated with DNA methylation changes across the genome. Notably, WTC dust exposure appears to be associated with increased global DNA methylation; direct dysregulation of cancer genes and pathways, including inflammation and immune system dysregulation; and endocrine system disruption, as well as disruption of cholesterol homeostasis and lipid metabolism. Conclusion: WTC dust exposure appears to be associated with biologically meaningful DNA methylation changes, with implications for carcinogenesis and development of other chronic diseases.

The Role of Trace Elements in Cardiovascular Diseases

Essential trace elements play an important role in human physiology and are associated with various functions regulating cellular metabolism. Non-essential trace elements, on the other hand, often have well-documented toxicities that are dangerous for the initiation and development of diseases due to their widespread occurrence in the environment and their accumulation in living organisms. Non-essential trace elements are therefore regarded as serious environmental hazards that are harmful to health even in low concentrations. Many representatives of these elements are present as pollutants in our environment, and many people may be exposed to significant amounts of these substances over the course of their lives. Among the most common non-essential trace elements are heavy metals, which are also associated with acute poisoning in humans. When these elements accumulate in the body over years of chronic exposure, they often cause severe health damage in a variety of tissues and organs. In this review article, the role of selected essential and non-essential trace elements and their role in the development of exemplary pathophysiological processes in the cardiovascular system will be examined in more detail.

Impact of Heavy Metals on Glioma Tumorigenesis

Recently, an increase in the incidence of brain tumors has been observed in the most industrialized countries. This event triggered considerable interest in the study of heavy metals and their presence in the environment (air, water, soil, and food). It is probable that their accumulation in the body could lead to a high risk of the onset of numerous pathologies, including brain tumors, in humans. Heavy metals are capable of generating reactive oxygen, which plays a key role in various pathological mechanisms. Alteration of the homeostasis of heavy metals could cause the overproduction of reactive oxygen species and induce DNA damage, lipid peroxidation, and the alteration of proteins. A large number of studies have shown that iron, cadmium, lead, nickel, chromium, and mercury levels were significantly elevated in patients affected by gliomas. In this study, we try to highlight a possible correlation between the most frequently encountered heavy metals, their presence in the environment, their sources, and glioma tumorigenesis. We also report on the review of the relevant literature.

Characterization of histone chaperone MCM2 as a key regulator in arsenic-induced depletion of H3.3 at genomic loci

Arsenic exposure is associated with an increased risk of many cancers, and epigenetic mechanisms play a crucial role in arsenic-mediated carcinogenesis. Our previous studies have shown that arsenic exposure induces polyadenylation of H3.1 mRNA and inhibits the deposition of H3.3 at critical gene regulatory elements. However, the precise underling mechanisms are not yet understood. To characterize the factors governing arsenic-induced inhibition of H3.3 assembly through H3.1 mRNA polyadenylation, we utilized mass spectrometry to identify the proteins, especially histone chaperones, with reduced binding affinity to H3.3 under conditions of arsenic exposure and polyadenylated H3.1 mRNA overexpression. Our findings reveal that the interaction between H3.3 and the histone chaperon protein MCM2 is diminished by both polyadenylated H3.1 mRNA overexpression and arsenic treatment in human lung epithelial BEAS-2B cells. The increased binding of MCM2 to H3.1, resulting from elevated H3.1 protein levels, appears to contribute to the reduced availability of MCM2 for H3.3. To further investigate the role of MCM2 in H3.3 deposition during arsenic exposure and H3.1 mRNA polyadenylation, we overexpressed MCM2 in BEAS-2B cells overexpressing polyadenylated H3.1 or exposed to arsenic. Our results demonstrate that MCM2 overexpression attenuates H3.3 depletion at several genomic loci, suggesting its involvement in the arsenic-induced displacement of H3.3 mediated by H3.1 mRNA polyadenylation. These findings suggest that changes in the association between histone chaperone MCM2 and H3.3 due to polyadenylation of H3.1 mRNA may play a pivotal role in arsenic-induced carcinogenesis.

Nano/micro-cellulose-based materials as remarkable sorbents for the remediation of agricultural resources from chemical pollutants

Overusing pesticides, fertilizers, and synthetic dyes has significantly increased their presence in various parts of the environment. The transportation of these pollutants into agricultural soil and water through rivers, soils, and groundwater has seriously threatened human and ecosystem health. Applying techniques and materials to clean up agricultural sources from pesticides, heavy metals (HMs), and synthetic dyes (SDs) is one of the major challenges in this century. The sorption technique offers a viable solution to remediate these chemical pollutants (CHPs). Cellulose-based materials have become popular in nano and micro scales because they are widely available, safe to use, biodegradable, and have a significant ability to absorb substances. Nanoscale cellulose-based materials exhibit greater capacity in absorbing pollutants compared to their microscale counterparts because they possess a larger surface area. Many available hydroxyl groups (-OH) and chemical and physical modifications enable the incorporation of CHPs on to cellulose-based materials. Following this potential, this review aims to comprehensively summarize recent advancements in the field of nano- and micro-cellulose-based materials as effective adsorbents for CHPs, given the abundance of cellulosic waste materials from agricultural residues. The recent developments pertaining to the enhancement of the sorption capacity of cellulose-based materials against pesticides, HMs, and SDs, are deliberated.

Interactions between chromium species and DNA in vitro and their potential role in the toxicity of hexavalent chromium

Epidemiological and animal studies have supported the carcinogenicity of hexavalent chromium [Cr(VI)]; however, molecular changes responsible for the induction of cancer by Cr(VI) are not entirely understood. Numerous mechanistic studies suggested the role of oxidative stress and genotoxicity in Cr(VI)-mediated carcinogenesis; however, specific types of DNA damage have not yet been conclusively attributed to specific chromium species or other reactive byproducts generated in biological systems exposed to Cr(VI). Due to the remarkably complex chemistry and biological effects of chromium species generated through the intracellular reduction of Cr(VI), their relevance for Cr(VI)-mediated carcinogenesis has not yet been fully elucidated and continues to be a subject of ongoing discussions in the field. In this report, we describe a complex world of chromium species and their reactivity with DNA and other biologically relevant molecules in vitro to inform a more complete understanding of Cr(VI)-mediated toxicity. In addition, we discuss previous results in the context of in vitro models and analytical methods to reconcile some conflicting findings on the biological role of chromium species.

A review of chromium (Cr) epigenetic toxicity and health hazards

Carcinogenic metals affect a variety of cellular processes, causing oxidative stress and cancer. The widespread distribution of these metals caused by industrial, residential, agricultural, medical, and technical activities raises concern for adverse environmental and human health effects. Of these metals, chromium (Cr) and its derivatives, including Cr(VI)-induced, are of a public health concern as they cause DNA epigenetic alterations resulting in heritable changes in gene expression. Here, we review and discuss the role of Cr(VI) in epigenetic changes, including DNA methylation, histone modifications, micro-RNA changes, biomarkers of exposure and toxicity, and highlight prevention and intervention strategies to protect susceptible populations from exposure and adverse occupational health effects. Cr(VI) is a ubiquitous toxin linked to cardiovascular, developmental, neurological, and endocrine diseases as well as immunologic disorders and a high number of cancer types in humans following inhalation and skin contact. Cr alters DNA methylation levels as well as global and gene-specific histone posttranslational modifications, emphasizing the importance of considering epigenetics as a possible mechanism underlying Cr(VI) toxicity and cell-transforming ability. Our review shows that determining the levels of Cr(VI) in occupational workers is a crucial first step in shielding health problems, including cancer and other disorders. More clinical and preventative measures are therefore needed to better understand the toxicity and safeguard employees against cancer.

Insufficient evidence to link human exposure to heavy metals with biomarkers of glioma

Information on molecular mechanisms has implicated potential association between the concentrations of heavy metals and incidences of glioma, but experimental data on human brain tissue remain sparse. To address this data gap, 13 heavy metals were measured in 137 glioma and 35 non-glioma samples collected from 161 alive patients in Guangdong Province, China in 2019 - 2020. All target heavy metals were detected, suggesting they could cross the blood-brain barrier. Concentrations of Mn, Cu, and Zn were higher in glioma than in non-glioma samples, while those of Ni and Se were higher in non-glioma samples, probably suggesting that these five heavy metals are more prone to be altered by changing pathological conditions. In addition, Cu/Zn, Cr/Mn, Cr/Se, Ni/Se, Pb/Mn, and Pb/Se were statistically different between glioma and non-glioma samples by a difference test and a multiple logistic regression model. These concentration ratios may serve as chemical markers to assist pathological analysis for differentiating between tumor and healthy tissues. However, no direct link between heavy metal concentrations or concentration ratios and biomarkers of glioma (i.e., tumor grade, P53, and Ki-67) was observed. No sufficient evidence was obtained to implicate the role of heavy metals in inducing glioma, largely caused by the limited number of samples. Different concentrations and concentration ratios of heavy metals may be the consequence rather than the cause of pathological changes in brain tumors.

Nutriepigenomics in Environmental-Associated Oxidative Stress

Complex molecular mechanisms define our responses to environmental stimuli. Beyond the DNA sequence itself, epigenetic machinery orchestrates changes in gene expression induced by diet, physical activity, stress and pollution, among others. Importantly, nutrition has a strong impact on epigenetic players and, consequently, sustains a promising role in the regulation of cellular responses such as oxidative stress. As oxidative stress is a natural physiological process where the presence of reactive oxygen-derived species and nitrogen-derived species overcomes the uptake strategy of antioxidant defenses, it plays an essential role in epigenetic changes induced by environmental pollutants and culminates in signaling the disruption of redox control. In this review, we present an update on epigenetic mechanisms induced by environmental factors that lead to oxidative stress and potentially to pathogenesis and disease progression in humans. In addition, we introduce the microenvironment factors (physical contacts, nutrients, extracellular vesicle-mediated communication) that influence the epigenetic regulation of cellular responses. Understanding the mechanisms by which nutrients influence the epigenome, and thus global transcription, is crucial for future early diagnostic and therapeutic efforts in the field of environmental medicine.

Effect of Gene 33/Mig6/ERRFI1 on hexavalent chromium-induced transformation of human bronchial epithelial cells depends on the length of exposure

Hexavalent chromium (Cr(VI)) compounds are environmental and occupational lung carcinogens. The present study followed the chronic effect of Cr(VI) on the neoplastic transformation of BEAS-2B lung bronchial epithelial cells with or without deletion of Gene 33 (Mig6, EFFRI1), a multifunctional adaptor protein. We find that Gene 33-deleted cells exhibit increased anchorage-independent growth compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure. Gene 33-deleted cells show a higher level of cell proliferation and are more resistant to acute Cr(VI) toxicity compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure, despite that 24-week-transformed cells have increased resistance to acute Cr(VI) toxicity. However, Gene 33-deleted cells show increased migration after transformed by both 8-week and 24-week Cr(VI) exposures. Furthermore, only cells transformed by 24 weeks of Cr(VI) exposure can form subcutaneous tumors in nude mice. Although no significant difference in the size of tumors formed by the two cell types, there is a marked difference in the histological manifestation and more MMP3 expression in tumors from Gene 33-deleted cells. Our results demonstrate progressive neoplastic transformation of BEAS-2B cells and the adaptation of these cells to Gene 33 deletion during chronic exposure to Cr(VI).

Prognostic biomarker prediction for glioma induced by heavy metals and their mixtures: An in-silico study

Although there is an association between heavy metals and glioma, the molecular mechanisms involved in glioma development remain unclear. Therefore, this study aimed to assess the molecular mechanisms implicated in glioma development induced by heavy metals and their mixtures using various methodologies and databases (CTD, Google Scholar, PubMed, ScienceDirect, SpringerLink, miRNAsong, GeneMANIA, Metascape, MIENTURNET, UALCAN). I found that heavy metals, particularly arsenic, mercury, lead, and cadmium, as well as their mixtures, have substantial influences on the etiology of gliomas. "glioblastoma signaling pathways," "integrated cancer pathway," "central carbon metabolism in cancer," "microRNAs in cancer," "p53 signaling pathway," "chemical carcinogenesis-DNA adducts," "glioma," "TP53 network," and "MAPK signaling pathway" were the predominant molecular pathways implicated in the glioma development induced by the studied heavy metals and their mixtures. Five genes (SOD1, CAT, GSTP1, PTGS2, TNF), two miRNAs (hsa-miR-26b-5p and hsa-miR-143-3p), and transcription factors (DR1 and HNF4) were identified as key components related to combined heavy metal and glioma development. Physical interactions were found to be the most common among the heavy metals and their mixtures studied (ranging from 45.2% to 77.6%). The expression level of SOD1 was significantly lower in glioblastoma multiforma samples compared to normal samples, whereas GSTP1 and TP53 expression levels were significantly higher. Brain lower and grade glioma patients who had higher levels of TP53, hsa-miR-25, hsa-miR-34, hsa-miR-222, and hsa-miR-143 had a reduced likelihood of survival. Our findings suggest that further priority should be given to investigating the impact of specific heavy metals or their mixtures on these molecular processes.

Interstrand crosslinking oligonucleotides elucidate the effect of metal ions on the methylation status of repetitive DNA elements

DNA methylation plays an important physiological function in cells, and environmental changes result in fluctuations in DNA methylation levels. Metal ions have become both environmental and health concerns, as they have the potential to disrupt the genomic DNA methylation status, even on specific sequences. In the current research, the methylation status of two typical repetitive DNA elements, i.e., long-interspersed nuclear element-1 (LINE-1) and alpha satellite (α-sat), was imaged and assessed using methylation-specific fluorescence in situ hybridization (MeFISH). This technique elucidated the effect of several metal ions on the methylation levels of repetitive DNA sequences. The upregulation and downregulation of the methylation levels of repetitive DNA elements by various metal ions were confirmed and depended on their concentration. This is the first example to investigate the effects of metal ions on DNA methylation in a sequence-specific manner.

Cadmium nitrate and DNA methylation in gastropods: comparison between ovotestis and hepatopancreas

Dietary ingestion is the main route of exposure to hazardous contaminants in land animals. Cadmium, a high-profile toxic metal, affects living systems at different organismal levels, including major storage organs (liver, kidneys), key organs for species survival (gonads), and epigenetic networks regulating gene expression. 5-methylcytosine (5mC) is the most common and best-characterized epigenetic mark among different modified nucleosides in DNA. This important player in methylation-driven gene expression is impacted by cadmium in sentinel terrestrial vertebrates. However, limited information exists regarding its impact on macroinvertebrates, especially land snails commonly used as (eco)toxicological models. We first investigate the methylomic effects of dietary cadmium given as cadmium nitrate on terrestrial mollusks. Mature specimens of the common brown garden snail, Cornu aspersum, were continuously exposed for four weeks to environmentally-relevant cadmium levels. We determined global genomic DNA methylation in hepatopancreas and ovotestis, as well as changes in the methylation status of CG pairs at the 5' region close to the transcription site of gene encoding the Cd-selective metallothionein (Cd-MT). Weight gain/loss, hypometabolism tendency, and survival rates were also assessed. Although this exposure event did not adversely affect survival, gastropods exposed to the highest Cd dose revealed a significant reduction in body weight and a significant increase in hypometabolic behavior. The hepatopancreas, but not the ovotestis, displayed significant hypermethylation, but only for the aforementioned specimens. We also found that the 5' end of the Cd-MT gene was unmethylated in both organs and its methylation status was insensitive to cadmium exposure. Our results are important since they provide scientists, for the first time, with quantitative data on DNA methylation in gastropod ovotestis and refine our understanding of Cd epigenetic effects on terrestrial mollusks.

Nickel-induced alterations to chromatin structure and function

Nickel (Ni), a heavy metal is prevalent in the atmosphere due to both natural and anthropogenic activities. Ni is a carcinogen implicated in the development of lung and nasal cancers in humans. Furthermore, Ni exposure is associated with a number of chronic lung diseases in humans including asthma, chronic bronchitis, emphysema, pulmonary fibrosis, pulmonary edema and chronic obstructive pulmonary disease (COPD). While Ni compounds are weak mutagens, a number of studies have demonstrated the potential of Ni to alter the epigenome, suggesting epigenomic dysregulation as an important underlying cause for its pathogenicity. In the eukaryotic nucleus, the DNA is organized in a three-dimensional (3D) space through assembly of higher order chromatin structures. Such an organization is critically important for transcription and other biological activities. Accumulating evidence suggests that by negatively affecting various cellular regulatory processes, Ni could potentially affect chromatin organization. In this review, we discuss the role of Ni in altering the chromatin architecture, which potentially plays a major role in Ni pathogenicity.

A pilot study that provides evidence of epigenetic changes among mother-child pairs living proximal to mining in the US

Environmental exposures to chemicals can disrupt gene expression, and the effects could be mediated by methylation. This investigation focused on methylation of genes associated with exposure to metals. Mother-child pairs from three locations in Montana were recruited, and buccal cells were collected for genome-wide methylation assay. Four pairs were from Butte, where there is mining and a Superfund site, four pairs were from Anaconda with a Superfund site, and four pairs were from Missoula with neither a mine nor a Superfund site. Principal component analysis, linear mixed models, hierarchical clustering and heatmap, and gene set enrichment analysis were used to visualize the profiles, identify the top associated methylation loci, and investigate the involved pathways. Distinctly higher or lower methylation in samples from Butte were found at the top differentially methylated loci. The 200 genes harboring the most hypermethylated loci were significantly enriched in genes involved in actin cytoskeleton regulation, ABC transporters, leukocyte transendothelial migration, focal adhesion, and adherens junction, which plays a role in pathogenesis of disease, including autism spectrum disorders. This study lays a foundation for inquiry about genetic changes associated with environmental exposure to metals for people living in proximity to Superfund and open pit mining.

Chromium as a Risk Factor for Breast Cancer: A Meta-Analysis

BACKGROUND

Chromium (Cr) is a transition metal, natural element. Chromium is the 21st most abundant element in Earth's crust. Cr is found in soil, rocks and living organisms. It may have various oxidation states, from -2 to +6, but most of these states are too unstable to exist in any significant quantities. The purpose of this review and meta-analysis is to critically assess the scientific evidence on the carcinogenic effects of chromium (Cr) and to determine whether there is currently sufficient evidence to suggest that that there is a link between chromium levels in hair and blood serum and breast cancer in women.

MATERIAL AND METHODS

Research on the relationship between heavy metal chromium and the risk of developing breast cancer has been searched in PubMed, EMBASE, Web of Science, Scopus among papers published between January 2000 and September 2020. The search used the following terms (MeSH): breast cancer, women, trace elements, metals, chromium, chemically-induced, hair, serum using additional terms.

RESULTS

In the second group of comparisons of women from "ecologically clean" districts of Aktobe Region, there were significantly lower indicators of the microelements in tumor tissue. The amount of Fe ranges from 38.46 to 65.39 ug/g (average 49.56±5.81 ug/g), Cu from 2.8 to 6.69 ug/g (average 5.06±1.01 ug/g), Zn from 1.89 to 5.38 ug/g (average 3.88±0.89 ug/g), Cr from zero to 6,1 ug/g (average 2.13±1.29 ug/g), Ni from 0.11 to 0.42 ug/g (average 0.28±0.067 ug/g) и Pb from zero to 0.19 ug/g (average 0.098±0.06 ug/g).

CONCLUSION

The article established that women who live or work in ecologically polluted areas or have problems with micronutrient exchange need in-depth screening and more frequent screening for early detection of pre- and breast cancer.

Epigenetic Dysregulations in Arsenic-Induced Carcinogenesis

Arsenic is a crucial environmental metalloid whose high toxicity levels negatively impact human health. It poses significant health concerns to millions of people in developed and developing countries such as the USA, Canada, Bangladesh, India, China, and Mexico by enhancing sensitivity to various types of diseases, including cancers. However, how arsenic causes changes in gene expression that results in heinous conditions remains elusive. One of the proposed essential mechanisms that still has seen limited research with regard to causing disease upon arsenic exposure is the dysregulation of epigenetic components. In this review, we have extensively summarized current discoveries in arsenic-induced epigenetic modifications in carcinogenesis and angiogenesis. Importantly, we highlight the possible mechanisms underlying epigenetic reprogramming through arsenic exposure that cause changes in cell signaling and dysfunctions of different epigenetic elements.

Nickel oral bioavailability in contaminated soils using a mouse urinary excretion bioassay: Variation with bioaccessibility

To assess the health risk of nickel (Ni) in contaminated soils, studies rarely evaluated Ni bioavailability in the gastrointestinal (GI) tract, limiting the accurate regulation of contaminated sites. Here, for 15 soil samples contaminated by Ni-electroplating, Ni oral relative bioavailability (RBA, relative to NiSO₄) was measured using a mouse urinary excretion bioassay. Nickel-RBA varied from 7.89% to 33.8% at an average of 19.1 ± 18.6%. The variation was not explained well by variation in soil properties including Ni speciation and co-contamination of other metals, which showed weak correlation with Ni-BRA (R² < 0.36). In comparison, the Ni-RBA variation was explained well by the variation of soil-Ni solubility in simulated human gastric or gastrointestinal fluids, i.e., Ni bioaccessibility. Determined using the gastric (GP) and intestinal phases (IP) of solubility bioaccessibility research consortium (SBRC), physiologically based extraction test methods (PBET), and unified BARGE method (UBM), Ni bioaccessibility explained 54-71% variation of the Ni-RBA, suggesting that Ni oral bioavailability was predominantly controlled by Ni solubility in the GI tract. The results highlight the suitability of using simple, fast, and cost-effective bioaccessbility assays to predict site-specific Ni oral bioavailability.

Environmental and occupational exposure of metals and female reproductive health

Untainted environment promotes health, but the last few decades experienced steep upsurge in environmental contaminants posing detrimental physiological impact. The responsible factors mainly include the exponential growth of human population, havoc rise in industrialization, poorly planned urbanization, and slapdash environment management. Environmental degradation can increase the likelihood of human exposure to heavy metals, resulting in health consequences such as reproductive problems. As a result, research into metal-induced causes of reproductive impairment at the genetic, epigenetic, and biochemical levels must be strengthened further. These metals impact upon the female reproduction at all strata of its regulation and functions, be it development, maturation, or endocrine functions, and are linked to an increase in the causes of infertility in women. Chronic exposures to the heavy metals may lead to breast cancer, endometriosis, endometrial cancer, menstrual disorders, and spontaneous abortions, as well as pre-term deliveries, stillbirths. For example, endometriosis, endometrial cancer, and spontaneous abortions are all caused by the metalloestrogen cadmium (Cd); lead (Pb) levels over a certain threshold can cause spontaneous abortion and have a teratogenic impact; toxic amounts of mercury (Hg) have an influence on the menstrual cycle, which can lead to infertility. Impact of environmental exposure to heavy metals on female fertility is therefore a well-known fact. Thus, the underlying mechanisms must be explained and periodically updated, given the growing evidence on the influence of increasing environmental heavy metal load on female fertility. The purpose of this review is to give a concise overview of how heavy metal affects female reproductive health.

Arsenic exposure increases susceptibility to Ptpn11-induced malignancy in mouse embryonic fibroblasts through mitochondrial hypermetabolism

OBJECTIVE

To explore the synergistic effect and metabolic mechanism of chronic arsenic exposure and PTPN11 gain-of-function mutation on tumorigenesis.

METHODS

Arsenic-transformed Ptpn11^+/+ (WT-As) and Ptpn11^D61G/+ -mutant (D61G-As) mouse embryonic fibroblasts (MEFs) were established by chronic treatment of low-dose arsenic. We used cell counting, plate colony and soft agar colony formation, and a nude mouse xenograft model to detect malignant transformation and tumorigenesis in vitro and in vivo. To detect mitochondrial oxidative phosphorylation (OXPHOS), we used Seahorse real-time cell metabolic analysis as well as adenosine triphosphate (ATP) and ROS production assays. Lastly, we examined mTOR signaling pathway changes by western blotting.

RESULTS

Low-dose arsenic exposure promoted WT MEFs proliferation and exacerbated malignancy driven by Ptpn11^D61G/+ mutation. Additionally, Ptpn11^D61G/+ -mutant MEFs exhibited increased mitochondrial metabolism and low-dose arsenic amplified this malignant metabolic activity. Mechanistically, the mTOR signaling pathway was activated in Ptpn11^D61G/+ -mutant MEFs and was further phosphorylated in arsenic-treated MEFs expressing Ptpn11^D61G/+ . Critically, tumorigenesis induced by the synergistic effect of low-dose arsenic and Ptpn11^D61G/+ mutation was prevented by mTOR pathway inhibition via rapamycin.

CONCLUSION

This study found that metabolic reprogramming, particularly mitochondrial hyperactivation, is a core mechanism underlying tumorigenesis induced by the synergistic effect of Ptpn11^D61G/+ mutation and arsenic exposure. Furthermore, these findings suggested mTOR is a therapeutic target for Ptpn11-associated cancers.

Mechanism of chromium-induced toxicity in lungs, liver, and kidney and their ameliorative agents

Heavy metal Chromium (Cr), can adversely affect humans and their health if accumulated in organs of the body, such as the lungs, liver, and kidneys. Cr (VI) is highly toxic and has a higher solubility in water than Cr (III). One of the most common routes for Cr exposure is through inhalation and is associated with liver, lung, kidney damage, widespread dermatitis, GI tract damage, human lung cancer, cardiomyopathies, and cardiovascular disease. The increase in ROS production has been attributed to most of the damage caused by Cr toxicity. Cr-induced ROS-mediated oxidative stress has been seen to cause a redox imbalance affecting the antioxidant system balance in the body. The Nrf2 pathway dysregulation has been implicated in the same. Deregulation of histone acetylation and methylation has been observed, together with gene methylation in genes such as p16, MGMT, APC, hMLH1, and also miR-143 repression. Several ultra-structural changes have been observed following Cr (VI)-toxicity, including rough ER dilation, alteration in the mitochondrial membrane and nuclear membrane, pycnotic nuclei formation, and cytoplasm vacuolization. A significant change was observed in the metabolism of lipid, glucose, and the metabolism of protein after exposure to Cr. Cr-toxicity also leads to immune system dysregulations with changes seen in the expression of IL-8, IL-4, IgM, lymphocytes, and leukocytes among others. P53, as well as pro-and anti-apoptotic proteins, are involved in apoptosis. These Cr-induced damages can be alleviated via agents that restore antioxidant balance, regulate Nrf-2 levels, or increase anti-apoptotic proteins while decreasing pro-apoptotic proteins.

Association between urinary cadmium concentrations and liver function in adolescents

Evidence from previous studies has shown that exposure to cadmium (Cd) is associated with cardiovascular disease, kidney disease, and osteoporosis, but the effects of Cd on liver toxicity in adolescents are unclear. The data of 4411 adolescents who participated in the US The National Health and Nutrition Examination Survey (NHANES) during 1999-2016 was analyzed. Liver function was indicated by the levels of alanine aminotransferase (ALT) and aspartate amino transferase (AST). The associations between the levels of urinary Cd and liver function were evaluated using multivariate logistic regression models adjusted for covariates. The results showed that the odds ratios of ALT and AST in the highest quartiles of urinary Cd were 1.40 (95% confidence interval [CI], 1.07-1.82) and 1.64 (95% CI, 1.10-2.44), respectively, compared with the lowest quartiles, which were similar to using urinary creatinine as the covariate. We also found linear regression of associations of urinary Cd with elevated ALT and AST levels in boys. In addition, one augmented urinary Cd concentration unit (Log₁₀) was associated with a 0.04-mg/dL increase in C-reactive protein and a 0.53-mg/dL decrease in HDL cholesterol in the fully adjusted model. Our results add novel evidence that exposure to Cd might be positively associated with indicators of liver injury, indicating the potential toxic effect of Cd exposure on the adolescent liver. Further confirmatory studies are needed.

Impact of Nano- and Micro-Sized Chromium(III) Particles on Cytotoxicity and Gene Expression Profiles Related to Genomic Stability in Human Keratinocytes and Alveolar Epithelial Cells

Exposure to Cr(VI) compounds has been consistently associated with genotoxicity and carcinogenicity, whereas Cr(III) is far less toxic, due to its poor cellular uptake. However, contradictory results have been published in relation to particulate Cr₂O₃. The aim of the present study was to investigate whether Cr(III) particles exerted properties comparable to water soluble Cr(III) or to Cr(VI), including two nano-sized and one micro-sized particles. The morphology and size distribution were determined by TEM, while the oxidation state was analyzed by XPS. Chromium release was quantified via AAS, and colorimetrically differentiated between Cr(VI) and Cr(III). Furthermore, the toxicological fingerprints of the Cr₂O₃ particles were established using high-throughput RT-qPCR and then compared to water-soluble Cr(VI) and Cr(III) in A549 and HaCaT cells. Regarding the Cr₂O₃ particles, two out of three exerted only minor or no toxicity, and the gene expression profiles were comparable to Cr(III). However, one particle under investigation released considerable amounts of Cr(VI), and also resembled the toxicity profiles of Cr(VI); this was also evident in the altered gene expression related to DNA damage signaling, oxidative stress response, inflammation, and cell death pathways. Even though the highest toxicity was found in the case of the smallest particle, size did not appear to be the decisive parameter, but rather the purity of the Cr(III) particles with respect to Cr(VI) content.

Epigenetic mechanisms in metal carcinogenesis

Many metals exhibit genotoxic and/or carcinogenic effects. These toxic metals can be found ubiquitously - in drinking water, food, air, general use products, in everyday and occupational settings. Exposure to such carcinogenic metals can result in serious health disorders, including cancer. Arsenic, cadmium, chromium, nickel, and their compounds have already been recognized as carcinogens by the International Agency for Research on Cancer. This review summarizes a wide range of epigenetic mechanisms contributing to carcinogenesis induced by these metals, primarily including, but not limited to, DNA methylation, miRNA regulation, and histone posttranslational modifications. The mechanisms are described and discussed both from a metal-centric and a mechanism-centric standpoint. The review takes a broad perspective, putting the mechanisms in the context of real-life exposure, and aims to assist in guiding future research, particularly with respect to the assessment and control of exposure to carcinogenic metals and novel therapy development.

Nickel's Role in Pancreatic Ductal Adenocarcinoma: Potential Involvement of microRNAs

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancer types with a limited overall survival rate due to the asymptomatic progression of symptoms in metastatic stages of the malignancy and the lack of an early reliable diagnostic biomarker. MicroRNAs (miRs/miRNAs) are small (~18–24 nucleotides), endogenous, non-coding RNAs, which are closely linked to the development of numerous malignancies comprising PDAC. Recent studies have described the role of environmental pollutants such as nickel (Ni) in PDAC, but the mechanisms of Ni-mediated toxicity in cancer are still not completely understood. Specifically, Ni has been found to alter the expression and function of miRs in several malignancies, leading to changes in target gene expression. In this study, we found that levels of Ni were significantly higher in cancerous tissue, thus implicating Ni in pancreatic carcinogenesis. Hence, in vitro studies followed by using both normal and pancreatic tumor cell lines and increasing Ni concentration increased lethality. Comparing LC50 values, Ni-acetate groups demonstrated lower values needed than in NiCl₂ groups, suggesting greater Ni-acetate. Panc-10.05 cell line appeared the most sensitive to Ni compounds. Exposure to Ni-acetate resulted in an increased phospho-AKT, and decreased FOXO1 expression in Panc-10.05 cells, while NiCl₂ also increased PTEN expression in Panc-10.05 cells. Specifically, following NiCl₂ exposure to PDAC cells, the expression levels of miR-221 and miR-155 were significantly upregulated, while the expression levels of miR-126 were significantly decreased. Hence, our study has suggested pilot insights to indicate that the environmental pollutant Ni plays an important role in the progression of PDAC by promoting an association between miRs and Ni exposure during PDAC pathogenesis.

The Acute Toxicity of Mineral Fibres: A Systematic In Vitro Study Using Different THP-1 Macrophage Phenotypes

Alveolar macrophages are the first line of defence against detrimental inhaled stimuli. To date, no comparative data have been obtained on the inflammatory response induced by different carcinogenic mineral fibres in the three main macrophage phenotypes: M0 (non-activated), M1 (pro-inflammatory) and M2 (alternatively activated). To gain new insights into the different toxicity mechanisms of carcinogenic mineral fibres, the acute effects of fibrous erionite, crocidolite and chrysotile in the three phenotypes obtained by THP-1 monocyte differentiation were investigated. The three mineral fibres apparently act by different toxicity mechanisms. Crocidolite seems to exert its toxic effects mostly as a result of its biodurability, ROS and cytokine production and DNA damage. Chrysotile, due to its low biodurability, displays toxic effects related to the release of toxic metals and the production of ROS and cytokines. Other mechanisms are involved in explaining the toxicity of biodurable fibrous erionite, which induces lower ROS and toxic metal release but exhibits a cation-exchange capacity able to alter the intracellular homeostasis of important cations. Concerning the differences among the three macrophage phenotypes, similar behaviour in the production of pro-inflammatory mediators was observed. The M2 phenotype, although known as a cell type recruited to mitigate the inflammatory state, in the case of asbestos fibres and erionite, serves to support the process by supplying pro-inflammatory mediators.

Metal Bioaccumulation, Cytogenetic and Clinico-Biochemical Alterations in Rattus norvegicus Exposed In Situ to a Municipal Solid Waste Landfill in Lagos, Nigeria

This study aimed at determining in animal model the health effects of in situ exposure to landfill chemicals. We evaluated metal concentrations in tissues and cytogenetic and clinico-biochemical effects in Wistar rats (Rattus norvegicus) exposed in situ at Olusosun landfill in Lagos, Nigeria. Male rats (n = 30/point) were exposed at three different points to ambient air and underground water (via drinking) at the landfill for 4-, 8-, 12-, 16-, 20- and 24-week periods. Rats concurrently sited at a residential area, 17.3 km from the landfill site served as control. There was significantly (p < 0.05) time-dependent: accumulation of lead, cadmium, chromium, copper and zinc in the liver and kidney and increase in body weight gain, in exposed rats compared to control. There was significant induction of micronuclei and cytotoxicity (reduced PCE/NCE ratios) in exposed rats. Haematological parameters (RBC, PCV, Hb and WBC) and serum biomarkers of hepato-renal damage [aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) activities; creatinine and urea levels] revealed significant increases. There was significant increase in hepatic levels of reduced glutathione, malondialdehyde, catalase activities, and decrease in superoxide dismutase, at all periods. Chromium and copper concentrations in the liver and kidney revealed significant positive correlations with either one or more of AST, ALT, LDH and urea. Significant metal concentrations in the underground water and tissues suggest that heavy metals are responsible for the observed alterations, and this may have been via oxidative stress. These findings suggest potential health risk due to occupational and residential exposure to landfill pollutants.

Epigenetic modifications from arsenic exposure: A comprehensive review

Arsenic is a notorious element with the potential to harm exposed individuals in ways that include cancerous and non-cancerous health complications. Millions of people across the globe (especially in South and Southeast Asian countries including China, Vietnam, India and Bangladesh) are currently being unknowingly exposed to precarious levels of arsenic. Among the diverse effects associated with such arsenic levels of exposure is the propensity to alter the epigenome. Although a large volume of literature exists on arsenic-induced genotoxicity, cytotoxicity, and inter-individual susceptibility due to active research on these subject areas from the last millennial, it is only recently that attention has turned on the ramifications and mechanisms of arsenic-induced epigenetic changes. The present review summarizes the possible mechanisms involved in arsenic induced epigenetic alterations. It focuses on the mechanisms underlying epigenome reprogramming from arsenic exposure that result in improper cell signaling and dysfunction of various epigenetic components. The mechanistic information articulated from the review is used to propose a number of novel therapeutic strategies with a potential for ameliorating the burden of worldwide arsenic poisoning.

Hepatotoxicity-Related Oxidative Modifications of Thioredoxin 1/Peroxiredoxin 1 Induced by Different Cadmium-Based Quantum Dots

The hepatotoxicity of cadmium-based quantum dots (Cd-QDs) has become the focus with their extensive applications in biomedicine. Previous reports have demonstrated that high oxidative stress and consequent redox imbalance play critical roles in their toxicity mechanisms. Intracellular antioxidant proteins, such as thioredoxin 1 (Trx1) and peroxiredoxin 1 (Prx1), could regulate redox homeostasis through thiol-disulfide exchange. Herein, we hypothesized that the excessive reactive oxygen species (ROS) induced by Cd-QD exposure affects the functions of Trx1 or Prx1, which further causes abnormal apoptosis of liver cells and hepatotoxicity. Thereby, three types of Cd-QDs, CdS, CdSe, and CdTe QDs, were selected for conducting an intensive study. Under the same conditions, the H₂O₂ level in the CdTe QD group was much higher than that of CdS or CdSe QDs, and it also corresponded to the higher hepatotoxicity. Mass spectrometry (MS) results show that excessive H₂O₂ leads to sulfonation modification (-SO₃H) at the active sites of Trx1 (Cys32 and Cys35) and Prx1 (Cys52 and Cys173). The irreversible oxidative modifications broke their cross-linking with the apoptosis signal-regulating kinase 1 (ASK1), resulting in the release and activation of ASK1, and activation of the downstream JNK/p38 signaling finally promoted liver cell apoptosis. These results highlight the key effect of the high oxidative stress, which caused irreversible oxidative modifications of Trx1 and Prx1 in the mechanisms involved in Cd-QD-induced hepatotoxicity. This work provides a new perspective on the hepatotoxicity mechanisms of Cd-QDs and helps design safe and reliable Cd-containing nanoplatforms.

Effect of Environmental Stressors, Xenobiotics, and Oxidative Stress on Male Reproductive and Sexual Health

This article examines the environmental factor-induced oxidative stress (OS) and their effects on male reproductive and sexual health. There are several factors that induce OS, i.e. radition, metal contamination, xenobiotic compounds, and cigarette smoke and lead to cause toxicity in the cells through metabolic or bioenergetic processes. These environmental factors may produce free radicals and enhance the reactive oxygen species (ROS). Free radicals are molecules that include oxygen and disbalance the amount of electrons that can create major chemical chains in the body and cause oxidation. Oxidative damage to cells may impair male fertility and lead to abnormal embryonic development. Moreover, it does not only cause a vast number of health issues such as ageing, cancer, atherosclerosis, insulin resistance, diabetes mellitus, cardiovascular diseases, ischemia-reperfusion injury, and neurodegenerative disorders but also decreases the motility of spermatozoa while increasing sperm DNA damage, impairing sperm mitochondrial membrane lipids and protein kinases. This chapter mainly focuses on the environmental stressors with further discussion on the mechanisms causing congenital impairments due to poor sexual health and transmitting altered signal transduction pathways in male gonadal tissues.

Mitochondria damage and ferroptosis involved in Ni-induced hepatotoxicity in mice

Nickel (Ni) is an environmental toxicant that can cause toxic damage to humans and animals. Although the hepatotoxicity of Ni has been confirmed, its precise mechanism is still unclear. In this study, the results showed that nickel chloride (NiCl₂)-treatment could induce mice hepatotoxicity including hepatic histopathological alterations and up-regulation of serum AST and ALT. According to the results, NiCl₂ increased malondialdehyde (MDA) production while reducing total antioxidant capacity (T-AOC) activity and glutathione (GSH) content. Additionally, NiCl₂ induced mitochondrial damage which was featured by increase in mitochondrial ROS (mt-ROS) and mitochondrial membrane potential (MMP) depolarization. The mitochondrial respiratory chain complexes I-IV and ATP content were decreased in the liver of NiCl₂-treated mice. Meanwhile, NiCl₂ caused hepatic ferroptosis accompanied by increased iron content in the liver and up-regulation of cyclooxygenase 2 (COX-2) protein and mRNA expression levels, down-regulation of glutathione eroxidase 4 (GPX4), ferritin heavy chain 1 (FTH1) and nuclear receptor coactivator 4 (NCOA4) protein and mRNA expression levels. Altogether, the above mentioned results indicate that NiCl₂ treatment may induce hepatic damage through mitochondrial damage and ferroptosis.

Inferred inactivation of the Cftr gene in the duodena of mice exposed to hexavalent chromium (Cr(VI)) in drinking water supports its tumor-suppressor status and implies its potential role in Cr(VI)-induced carcinogenesis of the small intestines

Carcinogenicity of hexavalent chromium [Cr (VI)] has been supported by a number of epidemiological and animal studies; however, its carcinogenic mode of action is still incompletely understood. To identify mechanisms involved in cancer development, we analyzed gene expression data from duodena of mice exposed to Cr(VI) in drinking water. This analysis included (i) identification of upstream regulatory molecules that are likely responsible for the observed gene expression changes, (ii) identification of annotated gene expression data from public repositories that correlate with gene expression changes in duodena of Cr(VI)-exposed mice, and (iii) identification of hallmark and oncogenic signature gene sets relevant to these data. We identified the inactivated CFTR gene among the top scoring upstream regulators, and found positive correlations between the expression data from duodena of Cr(VI)-exposed mice and other datasets in public repositories associated with the inactivation of the CFTR gene. In addition, we found enrichment of signatures for oncogenic signaling, sustained cell proliferation, impaired apoptosis and tissue remodeling. Results of our computational study support the tumor-suppressor role of the CFTR gene. Furthermore, our results support human relevance of the Cr(VI)-mediated carcinogenesis observed in the small intestines of exposed mice and suggest possible groups that may be more vulnerable to the adverse outcomes associated with the inactivation of CFTR by hexavalent chromium or other agents. Lastly, our findings predict, for the first time, the role of CFTR inactivation in chemical carcinogenesis and expand the range of plausible mechanisms that may be operative in Cr(VI)-mediated carcinogenesis of intestinal and possibly other tissues.

Effects of Cadmium Sulfate on the Brown Garden Snail Cornu aspersum: Implications for DNA Methylation

An extensive literature exists regarding the cellular, physiological, and genetic effects of cadmium (Cd)—A highly toxic, but commonly used trace metal in modern industry. However, limited data are available on its epigenetic effects, especially for terrestrial sentinel invertebrates. We determined Cd retention, total DNA methylation, and the methylation status of 5′ end of the Cd-MT gene in the hepatopancreas of the brown garden snail, Cornu aspersum, fed Cd sulfate for four weeks. Bodyweight changes and survival were also measured. Hepatopancreas cadmium increased in a dose-dependent manner from the third-lowest dose onward, with very large amounts being found for the highest treatment group. However, no mortalities occurred, irrespective of dietary Cd dose. We identified significant genome-wide hypermethylation in specimens given the highest dose, which overlapped with a significant bodyweight decrease. The Cd-MT gene showed an unmethylated 5′ end of the Cd-MT gene and this status was not affected by cadmium exposure. Hepatopancreas DNA methylation is as sensitive as bodyweight to non-lethal concentrations of dietary Cd given as cadmium sulfate but less responsive than tissue accumulation. Such an exposure event, by contrast, does not affect the methylation status of the Cd-MT gene 5′ end.

Global DNA (LINE-1) methylation is associated with lead exposure and certain job tasks performed by electronic waste workers

OBJECTIVE

This study assessed the associations between blood and urine levels of toxic metals; cadmium (Cd) and lead (Pb), and methylation levels of the LINE-1 gene among e-waste and control populations in Ghana.

METHODS

The study enrolled 100 male e-waste workers and 51 all-male non-e-waste workers or controls. The concentrations of Cd and Pb were measured in blood and urine using inductively coupled plasma mass spectrometry, while LINE1 methylation levels were assessed by pyrosequencing of bisulfite-converted DNA extracted from whole blood. Single and multiple metals linear regression models were used to determine the associations between metals and LINE1 DNA methylation.

RESULTS

Blood lead (BPb) and urine lead (UPb) showed higher median concentrations among the e-waste workers than the controls (76.82 µg/L vs 40.25 µg/L, p ≤ 0.001; and 6.89 µg/L vs 3.43 µg/L, p ≤ 0.001, respectively), whereas blood cadmium (BCd) concentration was lower in the e-waste workers compared to the controls (0.59 µg/L vs 0.81 µg/L, respectively, p = 0.003). There was no significant difference in LINE1 methylation between the e-waste and controls (85.16 ± 1.32% vs 85.17 ± 1.11%, p = 0.950). In our single metal linear regression models, BPb was significantly inversely associated with LINE1 methylation in the control group (βBPb = - 0.027, 95% CI - 0.045, - 0.010, p = 0.003). In addition, a weak association between BPb and LINE1 was observed in the multiple metals analysis in the e-waste worker group (βBPb = - 0.005, 95% CI - 0.011, 0.000, p = 0.058).

CONCLUSION

Continuous Pb exposure may interfere with LINE1 methylation, leading to epigenetic alterations, thus serving as an early epigenetic marker for future adverse health outcomes.

Concentration of heavy metals and rare earth elements in patients with brain tumours: Analysis in tumour tissue, non-tumour tissue, and blood

Inorganic elements have been associated with brain tumours for long. The blood concentration of 47 elements was assessed by ICP-MS in 26 brain tumour patients and 21 healthy subjects from Bucharest (Romania). All 47 elements were detected in the brain tumour tissue, and 22 were detected in > 80% of samples; this implies that these elements can cross the blood-brain barrier. Median blood levels of cadmium, lead, and nickel were higher than the reference values (1.14, 53.3, and 2.53 ng/mL). Gadolinium and tantalum showed significantly higher concentrations among cases. We observed considerable differences and different profiles of the presence of inorganic elements between the tumour and non-tumour brain tissue and between tissue from the primary tumour and tissue from brain metastasis. Our data suggest that similar to heavy metals, other elements - commonly used in high tech devices and rare earth elements - can also influence brain tumour.

Environmentally induced ribosomal DNA (rDNA) instability in human cells and populations exposed to hexavalent chromium [Cr (VI)]

Hexavalent Chromium [Cr (VI)] is an established toxicant, carcinogen, and a significant source of public health concern. The multicopy ribosomal DNA (rDNA) array is mechanistically linked to aging and cancer, is the most evolutionarily conserved segment of the human genome, and gives origin to nucleolus, a nuclear organelle where ribosomes are assembled. Here we show that exposure to Cr (VI) induces instability in the rDNA, triggering cycles of rapid, specific, and transient amplification and contraction of the array in human cells. The dynamic of environmentally responsive rDNA copy number (CN) amplification and contraction occurs at doses to which millions of individuals are regularly exposed. Finally, analyses of human populations occupationally exposed to Cr (VI) indicate that environmental exposure history and drinking habits but not age shape extensive naturally occurring rDNA copy number variation. Our observations identify a novel pathway of response to hexavalent chromium exposure and raise the prospect that a suite of environmental determinants of rDNA copy number remain to be discovered.

Metallomic profile in non-cirrhotic hepatocellular carcinoma supports a phenomenon of metal metabolism adaptation in tumor cells

We have previously described a form of hepatocellular carcinoma (HCC) in non-cirrhotic liver (HCC-NC) developed by Peruvian patients. We analyzed the metallomic profile in hepatic tissues from two independent cohorts exhibiting HCC-NC. Clinical, histopathological data, and HCC and non-tumoral liver (NTL) samples of 38 Peruvian and 38 French HCC-NC patients, were studied. Twelve metals were quantified using ICP/MS: Mn, Fe, Cu, Co, Zn, As, Se, Rb, Mo, Cd, Pb, and Sn. Associations between metals and survival were assessed. Our data showed significant differences between cohorts. Mean ages were 40.6 ± 20, 67.5 ± 9 years old for Peruvians and French, respectively. Fifty percent of the Peruvian patients were positive for the HBsAg, versus 3% in French patients. Mn, Cu, Zn, As, Se, Rb, Mo, Cd, Sn metal concentrations were higher in NTL of Peruvians. Importantly, metal concentrations were lower in HCC areas compared to NTL tissues in both cohorts, except for Cu for which mean concentration was higher in HCC (p < 0.05). Se concentration in HCC was associated with extended survival only in Peruvians. Our data, obtained in Peruvian and French HCC-NC cohorts, highlights similarity in the metallomic profile of HCC compared to NTL during the hepatic tumorigenesis in these specific groups of patients.

The Effect of Global DNA Methylation on PDCD5 Expression in the PBMC of Occupational Chromate Exposed Workers

OBJECTIVES

To evaluate the alteration of protein of programmed cell death 5 (PDCD5) in peripheral blood mononuclear cells (PBMC) and DNA methylation caused by hexavalent chromium exposure.

METHODS

There were 112 workers and 56 controls in this study. The chromium in RBC and urine, PBMC with PDCD5+, DNA methylation, urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and score of DNA damage were measured.

RESULTS

In chromate exposed workers, the percent of PBMC with PDCD5+, urine 8-OHdG, and score of DNA damage were significantly higher, whereas global DNA methylation was significantly lower. The binary logistic regression and generalized linear mixed model analysis showed that the percent of PBMC with PDCD5+ was significantly associated with global DNA hypomethylation.

CONCLUSIONS

The aberrant DNA hypomethylation plays an important role in PBMC apoptosis of occupational hexavalent chromium exposure.

A study on water quality monitoring of Buddha Nullah, Ludhiana, Punjab (India)

Diverse genotoxic agents, entering the aquatic environment through natural and anthropogenic events, pose serious threats to its biotic components. The present study involves the monitoring of water quality by assessing the genotoxic effects and physico-chemical parameters including heavy metals of 10 surface water samples collected from different locations of Buddha Nullah, a tributary of Sutlej flowing through Ludhiana, Punjab (India). Genotoxicity was evaluated following Allium cepa root chromosomal aberration assay and DNA nicking assay using plasmid (pBR322) whilst the metal (cadmium, chromium, cobalt, copper, lead, nickel and zinc) analysis was conducted using atomic absorption spectrophotometer. All water samples collected from the study area had cobalt and lead content more than the permissible limits (0.04 and 0.01, respectively) recommended by the Bureau of Indian Standards and the World Health Organization. The samples also induced genotoxicity following both bioassays. The water samples collected from Gaunspur (GP), a site approx. 75.53 km upstream of the Sutlej-Buddha Nullah joining point, has shown the maximum genotoxic effect, i.e. 38.62% in terms of per cent total aberrant cells during A. cepa assay and 100% DNA damage during DNA nicking assay. The Pearson correlation indicated that genotoxicity had a significant positive correlation with the content of cobalt (at p ≤ 0.5). During cluster analysis, the samples from 10 sites formed four statistically significant clusters based on the level of pollution that was dependent on two factors like similarity in physico-chemical characteristics and source of pollution at a specific site.

Potential environmental toxicant exposure, metabolizing gene variants and risk of PCOS-A systematic review

Exposure of environmental toxicants such as potentially toxic metals and pesticides have largely been attributed to produce adverse effects on general women's health and to be more precise on the reproductive system. In order to explore exposure of toxicants and metabolizing gene variants as risk factor for polycystic ovarian syndrome (PCOS), literature search was carried out using the databases PubMed, Central Cochrane Library, Google Scholar, Science Direct with appropriate keywords upto 6 December 2020. While most of the studies indicate higher serum Cu concentration and lower concentration of Mn as risk factor, studies also report presence of higher pesticide concentration in PCOS women. Genes such as MTHFR, CYPs participate in the metabolism of toxicants and may show different response due to underlying genetic variants. Thus, toxicant exposure are to some extent responsible for the pathogenesis of syndrome through oxidative stress and endocrine disruption, but the susceptibility may vary due to the underlying genetic polymorphism of the exposed population.

Mechanisms of the synergistic lung tumorigenic effect of arsenic and benzo(a)pyrene combined- exposure

Humans are often exposed to mixtures of environmental pollutants especially environmental chemical carcinogens, representing a significant environmental health issue. However, our understanding on the carcinogenic effects and mechanisms of environmental carcinogen mixture exposures is limited and mostly relies on the findings from studying individual chemical carcinogens. Both arsenic and benzo(a)pyrene (BaP) are among the most common environmental carcinogens causing lung cancer and other types of cancer in humans. Millions of people are exposed to arsenic via consuming arsenic-contaminated drinking water and even more people are exposed to BaP via cigarette smoking and consuming BaP-contaminated food. Thus arsenic and BaP combined-exposure in humans is common. Previous epidemiology studies indicated that arsenic-exposed people who were cigarette smokers had significantly higher lung cancer risk than those who were non-smokers. Since BaP is one of the major carcinogens in cigarette smoke, it has been speculated that arsenic and BaP combined-exposure may play important roles in the increased lung cancer risk observed in arsenic-exposed cigarette smokers. In this review, we summarize important findings and inconsistencies about the co-carcinogenic effects and underlying mechanisms of arsenic and BaP combined-exposure and propose new areas for future studies. A clear understanding on the mechanism of co-carcinogenic effects of arsenic and BaP combined exposure may identify novel targets to more efficiently treat and prevent lung cancer resulting from arsenic and BaP combined-exposure.

The role of autophagy in metal-induced urogenital carcinogenesis

Environmental and/or occupational exposure to metals such as Arsenic (As), Cadmium (Cd), and Chromium (Cr) have been shown to induce carcinogenesis in various organs, including the urogenital system. However, the mechanisms responsible for metal-induced carcinogenesis remain elusive. We and others have shown that metals are potent inducers of autophagy, which has been suggested to be an adaptive stress response to allow metal-exposed cells to survive in hostile environments. Albeit few, recent experimental studies have shown that As and Cd promote tumorigenesis via autophagy and that inhibition of autophagic signaling suppressed metal-induced carcinogenesis. In light of the newly emerging role of autophagic involvement in metal-induced carcinogenesis, the present review focuses explicitly on the mechanistic role of autophagy and potential signaling pathways involved in As-, Cd-, and Cr-induced urogenital carcinogenesis.

A review on epigenetic effects of environmental factors causing and inhibiting cancer

Epigenetic modifications refer to reversible changes in gene expression. Epigenetic changes include DNA methylation, histone modification, and non-coding RNAs that are collectively called epigenome. Various epigenetic effects account for the main impacts of environment and lifestyle on multifactorial diseases such as cancers. The environment's impacts on cancers act as double-edged swords. While some of them are involved in cancer development, some others contribute to preventing it. In this review article, the keywords 'cancer', 'epigenetic', 'lifestyle', 'carcinogen', ' cancer inhibitors" and related words were searched to finding a link between environmental factors and epigenetic mechanisms influencing cancer in ISI, PUBMED, SCOPUS, and Google Scholar databases. Based on the literature environmental factors that are effective in cancer development or cancer prevention in this review will be divided into physical, chemical, biological, and lifestyle types. Different types of epigenetic mechanisms known for each of these agents will be addressed in this review. Unregulated changes in epigenome play roles in tumorigenicity and cancer development. The action mechanism and genes targeted which are related to the signaling pathway for epigenetic alterations determine whether environmental agents are carcinogenic or prevent cancer. Having knowledge about the effective factors and related mechanisms such as epigenetic on cancer can help to prevent and better cancers treatment.

Adenine derivatization for LC-MS/MS epigenetic DNA modifications studies on monocytic THP-1 cells exposed to reference particulate matter

The aim of this study was to explore the impact of three different standard reference particulate matter (ERM-CZ100, SRM-1649, and SRM-2975) on epigenetic DNA modifications including cytosine methylation, cytosine hydroxymethylation, and adenine methylation. For the determination of low levels of adenine methylation, we developed and applied a novel DNA nucleobase chemical derivatization and combined it with liquid chromatography tandem mass spectrometry. The developed method was applied for the analysis of epigenetic modifications in monocytic THP-1 cells exposed to the three different reference particulate matter for 24 h and 48 h. The mass fraction of epigenetic active elements As, Cd, and Cr was analyzed by inductively coupled plasma mass spectrometry. The exposure to fine dust ERM-CZ100 and urban dust SRM-1649 decreased cytosine methylation after 24 h exposure, whereas all 3 p.m. increased cytosine hydoxymethylation following 24 h exposure, and the epigenetic effects induced by SRM-1649 and diesel SRM-2975 were persistent up to 48 h exposure. The road tunnel dust ERM-CZ100 significantly increased adenine methylation following the shorter exposure time. Two-dimensional scatters analysis between different epigenetic DNA modifications were used to depict a significantly negative correlation between cytosine methylation and cytosine hydroxymethylation supporting their possible functional relationship. Metals and polycyclic aromatic hydrocarbons differently shapes epigenetic DNA modifications.

Developmental toxicity of cadmium in infants and children: a review

Several millions of people are exposed to cadmium worldwide due to natural and anthropogenic activities that led to their widespread distribution in the environment and have shown potential adverse effects on the kidneys, liver, heart and nervous system. Recently human and animal-based studies have been shown that In utero and early life exposure to cadmium can have serious health issues that are related to the risk of developmental disabilities and other outcomes in adulthood. Since, cadmium crosses the placental barrier and reaches easily to the fetus, even moderate or high-level exposure of this metal during pregnancy could be of serious health consequences which might be reflected either in the children’s early or later stages of life. Mortality from various diseases including cancer, cardiovascular, respiratory, kidney and neurological problems, correlation with In utero or early life exposure to cadmium has been found in epidemiological studies. Animal studies with strong evidence of various diseases mostly support for the human studies, as well as suggested a myriad mechanism by which cadmium can interfere with human health and development. More studies are needed to establish the mechanism of cadmium-induced toxicity with environmentally relevant doses in childhood and later life. In this review, we provide a comprehensive examination of the literature addressing potential long- term health issues with In utero and early life exposure to cadmium, as well as correlating with human and animal exposure studies.