Tumor suppressor gene inactivation during cadmium-induced malignant transformation of human prostate cells correlates with overexpression of de novo DNA methyltransferase

Exosome-transmitted circ_0004664 suppresses the migration and invasion of cadmium-transformed human bronchial epithelial cells by regulating PTEN expression via miR-942-5p

Exosomes play a crucial role in regulating extracellular communication between normal and cancer cells within the tumor microenvironment, thereby affecting tumor progression through their cargo molecules. However, the specific impact of exosomal circular RNAs (circRNAs) on the development of cadmium-induced carcinogenesis remains unclear. To address this, we investigated whether exosomes derived from normal human bronchial epithelial BEAS-2B (N-B2B) cells could transmit circRNA to cadmium-transformed BEAS-2B (Cd-B2B) cells and the potential effects on Cd-B2B cells. Our findings demonstrated a significant downregulation of circ_0004664 in Cd-B2B cells compared to N-B2B cells (P < 0.01). Overexpression of circ_0004664 in Cd-B2B cells led to a significant inhibition of cell migration and invasion (P < 0.01 or P < 0.05). Furthermore, N-B2B cells could transfer circ_0004664 into recipient Cd-B2B cells via exosomes, subsequently inhibiting cell migration and invasion (P < 0.05 or P < 0.01). Mechanistic investigations revealed that exosomal circ_0004664 functioned as a competitive endogenous RNA for miR-942-5p, resulting in an upregulation of PTEN (P < 0.05). Our study highlights the involvement of exosomal circ_0004664 in cell-cell communication during cadmium carcinogenesis, providing a novel insight into the role of exosomal circRNA in this process.

Epigenetic toxicity of heavy metals - implications for embryonic stem cells

Exposure to heavy metals, such as cadmium, nickel, mercury, arsenic, lead, and hexavalent chromium has been linked to dysregulated developmental processes, such as impaired stem cell differentiation. Heavy metals are well-known modifiers of the epigenome. Stem and progenitor cells are particularly vulnerable to exposure to potentially toxic metals since these cells rely on epigenetic reprogramming for their proper functioning. Therefore, exposure to metals can impair stem and progenitor cell proliferation, pluripotency, stemness, and differentiation. In this review, we provide a comprehensive summary of current evidence on the epigenetic effects of heavy metals on stem cells, focusing particularly on DNA methylation and histone modifications. Moreover, we explore the underlying mechanisms responsible for these epigenetic changes. By providing an overview of heavy metal exposure-induced alterations to the epigenome, the underlying mechanisms, and the consequences of those alterations on stem cell function, this review provides a foundation for further research in this critical area of overlap between toxicology and developmental biology.

Non-nucleoside inhibitors of DNMT1 and DNMT3 for targeted cancer therapy

DNA methylation can deactivate tumor suppressor genes thus causing cancers. Two DNA methylation inhibitors have been approved by the Food and Drug Administration (FDA) and have entered clinical use. However, these inhibitors are nucleoside analogues that can be incorporated into DNA or RNA and induce significant side effects. DNMT1 and DNMT3 are key enzymes involved in DNA methylation. In the acute myeloid leukemia model, a non-nucleoside DNMT1-specific inhibitor has shown lower toxicity and improved pharmacokinetics compared to traditional nucleoside drugs. DNMT3 is also implicated in certain specific cancers. Thus, developing non-nucleoside inhibitors for DNMT1 or DNMT3 can help in understanding their roles in carcinogenesis and provide targeted treatment options in certain cancers. Although no non-nucleoside inhibitors have yet entered clinical trials, in this review, we focus on DNMT1 or DNMT3 selective inhibitors. For DNMT1 selective inhibitors, we have compiled information on the repurposed drugs, derivative compounds and selective inhibitors identified through virtual screening. Additionally, we have outlined potential targets for DNMT1, including protein-protein complex, RNA mimics and aptamers. Compared to DNMT1, research on DNMT3-specific inhibitors has been less extensive. In this context, our exploration has identified a limited number of molecular inhibitors, and we have proposed specific long non-coding RNAs (lncRNAs) as potential contributors to the selective inhibition of DNMT3. This collective effort aims to offer valuable insights into the development of non-nucleoside inhibitors that selectively target DNMT1 or DNMT3.

Prostate Cancer: Emerging Modifiable Risk Factors and Therapeutic Strategies in the Management of Advanced Cancer

Prostate cancer (PCa) is the third highest cause of cancer death in men. PCa is a very heterogeneous tumor form in terms of grade, phenotypes, and genetics, often accompanied by complex networks. PCa is characterized by slow growth that does not compromise the patient's quality of life, unlike more aggressive forms showing rapid growth and progression. Early diagnosis, even for the most aggressive forms, increases the possibilities of cure with less aggressive treatments and fewer side effects. However, it is important to know how to decrease the exposure to modifiable risk factors, including diet, sedentary life, smoking and alcohol, can represent an effective tool to reduce the incidence of PCa. In addition, the chronic exposure to environmental factors, most of which act as endocrine disruptors, is the focus of recent studies for their potential role in promoting the onset and progression of PCa. Although molecular therapies and clinical trials for biomarker identification have been introduced into the management of PCa, these still lag behind research performed in other solid tumors. This review provides an overview of the modifiable factors of PCa, linked to lifestyle and environmental pollutants, which together with the development of new therapeutic targets, can reduce the incidence of PCa and improve the quality of life of patients.

The dynamic face of cadmium-induced Carcinogenesis: Mechanisms, emerging trends, and future directions

Cadmium (Cd) is a malleable element with odorless, tasteless characteristics that occurs naturally in the earth's crust, underground water, and soil. The most common reasons for the anthropological release of Cd to the environment include industrial metal mining, smelting, battery manufacturing, fertilizer production, and cigarette smoking. Cadmium-containing products may enter the environment as soluble salts, vapor, or particle forms that accumulate in food, soil, water, and air. Several epidemiological studies have highlighted the association between Cd exposure and adverse health outcomes, especially renal toxicity, and the impact of Cd exposure on the development and progression of carcinogenesis. Also highlighted is the evidence for early-life and even maternal exposure to Cd leading to devastating health outcomes, especially the risk of cancer development in adulthood. Several mechanisms have been proposed to explain how Cd mediates carcinogenic transformation, including epigenetic alteration, DNA methylation, histone posttranslational modification, dysregulated non-coding RNA, DNA damage in the form of DNA mutation, strand breaks, and chromosomal abnormalities with double-strand break representing the most common DNA form of damage. Cd induces an indirect genotoxic effect by reducing p53's DNA binding activity, eventually impairing DNA repair, inducing downregulation in the expression of DNA repair genes, which might result in carcinogenic transformation, enhancing lipid peroxidation or evasion of antioxidant interference such as catalase, superoxide dismutase, and glutathione. Moreover, Cd mediates apoptosis evasion, autophagy activation, and survival mechanisms. In this review, we decipher the role of Cd mediating carcinogenic transformation in different models and highlight the interaction between various mechanisms. We also discuss diagnostic markers, therapeutic interventions, and future perspectives.

Source, toxicity and carcinogenic health risk assessment of heavy metals

Heavy metals are chemical elements with unique properties that are toxic even in low concentrations and affect human health with different functions. Agricultural and industrial activities, improper disposal of household solid waste and residues related to industrial producers, discharge of household wastewater and agricultural fertilizers are the most important ways in which toxic heavy metals enter the environment, which harms human health and life. A narrative review of the literature was done from 2000 to 2022 based on searched databases included Google Scholar, PubMed, Springer, Web of Science, and Science Direct (Scopus). All relevant studies published 2000 until 2022 gathered. According to the databases, 820 articles were retrieved. 186 and 50 articles were found and selected based on records identified through database searching and additional records identified through other sources. In the next stage, 97 studies were screened after review and 64 full-text articles entered into the analysis process. Finally, 45 articles were selected in this study. Adverse effects of heavy metals on various conditions in the body depend on a number of factors, including dose, route of exposure and chemical species, as well as age, sex, genetics, nutritional status, and duration of exposure to the heavy metal. The existence of significant relationships between long-term and short-term exposure to toxic heavy metals and their adverse effects, including carcinogenicity, has been extensively studied and proven through numerous experiments. However, the mechanisms associated with this complication have not been properly identified, so in future research, there is a great need for comprehensive studies on the carcinogenicity of heavy metals.

Arsenic-induced prostate cancer: an enigma

Arsenic exhibits varying degrees of toxicity depending on its many chemical forms. The carcinogenic properties of arsenic have already been established. However, the precise processes underlying the development of diseases following acute or chronic exposure to arsenic remain poorly known. Most of the existing investigation has focused on studying the occurrence of cancer following significant exposure to elevated levels of arsenic. Nevertheless, multiple investigations have documented diverse health consequences from prolonged exposure to low levels of arsenic. Inorganic arsenic commonly causes lung, bladder, and skin cancer. Some investigations have shown an association between arsenic in drinking water and prostate cancer, but few investigations have focused on exploring this connection. There is currently a lack of relevant animal models demonstrating a clear link between inorganic arsenic exposure and the development of prostate cancer. Nevertheless, studies using cellular model systems have demonstrated that arsenic can potentially promote the malignant transformation of human prostate epithelial cells in vitro. The administration of elevated levels of arsenic has been demonstrated to elicit cell death in instances of acute experimental exposure. Conversely, in cases of chronic exposure, arsenic prompts cellular proliferation and sustains cellular viability, thereby circumventing the constraints imposed by telomere shortening and apoptosis. Furthermore, cells consistently exposed to the stimulus exhibit an augmented ability to invade surrounding tissues and an enhanced potential to form tumors. This review aims to portray mechanistic insights into arsenic-induced prostate cancer.

Environment factors, DNA methylation, and cancer

Today, the rapid development of science and technology and the rapid change in economy and society are changing the way of life of human beings and affecting the natural, living, working, and internal environment on which human beings depend. At the same time, the global incidence of cancer has increased significantly yearly, and cancer has become the number one killer that threatens human health. Studies have shown that diet, living habits, residential environment, mental and psychological factors, intestinal flora, genetics, social factors, and viral and non-viral infections are closely related to human cancer. However, the molecular mechanisms of the environment and cancer development remain to be further explored. In recent years, DNA methylation has become a key hub and bridge for environmental and cancer research. Some environmental factors can alter the hyper/hypomethylation of human cancer suppressor gene promoters, proto-oncogene promoters, and the whole genome, causing low/high expression or gene mutation of related genes, thereby exerting oncogenic or anticancer effects. It is expected to develop early warning markers of cancer environment based on DNA methylation, thereby providing new methods for early detection of cancers, diagnosis, and targeted therapy. This review systematically expounds on the internal mechanism of environmental factors affecting cancer by changing DNA methylation, aiming to help establish the concept of cancer prevention and improve people's health.

Impacts of heavy metal exposure on the prostate of murine models: Mechanisms of toxicity

Heavy metals are elements found into the environment mainly due to anthropogenic activities. Naturally occurring and higher released doses cause disorders in the prostate, which depends on appropriate hormonal regulation, and exposure to heavy metals may impair prostate homeostasis. The current work highlighted the main mechanisms of toxicity of different environmental heavy metal contaminants, such as aluminum, arsenic, cadmium, chromium, lead, mercury, and nickel, and their impacts found in the prostate morphophysiology of murine models. The repercussions triggered by heavy metals on the prostate include hormonal imbalance and oxidative damage, leading to morphological alterations, which can vary according to the chemical properties of each element, exposure time and concentration, and age. The information of altered biological pathways and its impacts on the prostate of exposed murines are related to human outcomes being useful in the real context of human exposure.

The environment and male reproductive system: the potential role and underlying mechanisms of cadmium in testis cancer

Cadmium is a known human carcinogen, and has been shown to profoundly affect male reproductive function, at multiple levels, by exerting both endocrine and non-endocrine actions. Nevertheless, the potential role of cadmium in the etiology of testis cancer has been scantly investigated in humans, and, currently, available epidemiological observational studies are insufficient to draw definitive conclusions in this regard. On the contrary, experimental studies in laboratory animals demonstrated that cadmium is a strong inducer of testis tumors, mostly represented by benign Leydig cell adenoma; moreover, malignant transformation was also reported in few animals, following cadmium treatment. Early experimental studies in animals proposed an endocrine-dependent mechanism of cadmium-induced testis tumorigenesis; however, more recent findings from cell-free assays, in vitro studies, and short-term in vivo studies, highlighted that cadmium might also contribute to testis tumor development by early occurring endocrine-independent mechanisms, which include aberrant gene expression within the testis, and genotoxic effects, and take place well before the timing of testis tumorigenesis. These endocrine-independent mechanisms, however, have not been directly investigated on testis tumor samples retrieved from affected, cadmium-treated animals so far. The present review focuses on the relationship between cadmium exposure and testis cancer, by reporting the few epidemiological observational human studies available, and by providing animal-based experimental evidences of cadmium implication in the pathogenesis and progression of testis tumor. Moreover, the relevance of experimental animal studies to human cadmium exposure and the translational potential of experimental findings will be extensively discussed, by critically addressing strengths and weaknesses of available data.

The emerging role of N6-methyladenine RNA methylation in metal ion metabolism and metal-induced carcinogenesis

N⁶-methyladenine (m⁶A) is the most common and abundant internal modification in eukaryotic mRNAs, which can regulate gene expression and perform important biological tasks. Metal ions participate in nucleotide biosynthesis and repair, signal transduction, energy generation, immune defense, and other important metabolic processes. However, long-term environmental and occupational exposure to metals through food, air, soil, water, and industry can result in toxicity, serious health problems, and cancer. Recent evidence indicates dynamic and reversible m⁶A modification modulates various metal ion metabolism, such as iron absorption, calcium uptake and transport. In turn, environmental heavy metal can alter m⁶A modification by directly affecting catalytic activity and expression level of methyltransferases and demethylases, or through reactive oxygen species, eventually disrupting normal biological function and leading to diseases. Therefore, m⁶A RNA methylation may play a bridging role in heavy metal pollution-induced carcinogenesis. This review discusses interaction among heavy metal, m⁶A, and metal ions metabolism, and their regulatory mechanism, focuses on the role of m⁶A methylation and heavy metal pollution in cancer. Finally, the role of nutritional therapy that targeting m⁶A methylation to prevent metal ion metabolism disorder-induced cancer is summarized.

A cross-sectional study of the association between heavy metals and pan-cancers associated with sex hormones in NHANES 1999-2018

Given the complexity of tumorigenesis, numerous studies have also shown that excessive exposure to heavy metals increases the risk of cancers and disrupts the secretion of sex hormones. However, the specific effects of heavy metals on cancers remain to be proven. To confirm the association between heavy metals and pan-cancer sex hormone levels among adults, 94,337 individuals from the National Health and Nutrition Examination Survey were assessed. We examined the associations between pan-cancers associated with sex hormones (ovarian, testicular, breast, and prostate cancers) and heavy metals in blood/urine. The methods (the WQS (weighted quantile sums) and SVYGLM (survey generalized linear model) regressions) were used to evaluate the association between sex hormone-related cancers and each metal category by incorporating covariates. To evaluate the overall effect of heavy metals and detect the dose-response relationship between the prevalence of pan-cancers associated with sex hormones and heavy metals, RCS (restricted cubic splines) were applied. Environmental exposure to heavy metals may be associated with pan-cancers associated with sex hormones in adults in the USA. Prostate cancer was inversely associated with blood cadmium while positively associated with blood lead, urinary tin, and thallium. Breast cancer was inversely associated with blood lead. Ovarian cancer was positively associated with blood cadmium. We also found a non-linear dose-response relationship between pan-cancers associated with sex hormones and heavy metals, which was non-parametric, using RCS models. The OR for breast cancer decreased along with the increase in lead concentration under approximately 20 µg/dl, while the OR for prostate cancer increased between urine thallium levels of approximately 0.17-1.1 ng/ml. Pan-cancers associated with sex hormones are associated with exposure to heavy metals. Considering the design of the NHANES study, further studies need to be conducted on other nationally representative surveys.

Epigenetic mechanisms of cadmium-induced nephrotoxicity

Cadmium (Cd) is a widespread toxic pollutant that affects millions of individuals worldwide. Cd exposure in humans occurs primarily through consumption of contaminated food and water, cigarette smoking, and industrial applications. The kidney proximal tubular (PT) epithelial cells are the primary target of Cd toxicity. Cd-induced injury to PT cells impedes tubular reabsorption. Despite the many long-term sequelae of Cd exposure, molecular mechanisms of Cd toxicity are poorly understood, and no specific therapies exist to mitigate the effects of Cd exposure. In this review, we summarize recent work linking Cd-mediated damage to epigenetic perturbations - DNA methylation, and levels of histone modifications, including methylation and acetylation. New insights into the links between Cd intoxication and epigenetic damage will contribute to an improved understanding of Cd's pleiotropic impacts on cells, and perhaps lead to new, mechanism-based treatments for this condition.

Epigenetic Regulation in Chromium-, Nickel- and Cadmium-Induced Carcinogenesis

Environmental and occupational exposure to heavy metals, such as hexavalent chromium, nickel, and cadmium, are major health concerns worldwide. Some heavy metals are well-documented human carcinogens. Multiple mechanisms, including DNA damage, dysregulated gene expression, and aberrant cancer-related signaling, have been shown to contribute to metal-induced carcinogenesis. However, the molecular mechanisms accounting for heavy metal-induced carcinogenesis and angiogenesis are still not fully understood. In recent years, an increasing number of studies have indicated that in addition to genotoxicity and genetic mutations, epigenetic mechanisms play critical roles in metal-induced cancers. Epigenetics refers to the reversible modification of genomes without changing DNA sequences; epigenetic modifications generally involve DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs. Epigenetic regulation is essential for maintaining normal gene expression patterns; the disruption of epigenetic modifications may lead to altered cellular function and even malignant transformation. Therefore, aberrant epigenetic modifications are widely involved in metal-induced cancer formation, development, and angiogenesis. Notably, the role of epigenetic mechanisms in heavy metal-induced carcinogenesis and angiogenesis remains largely unknown, and further studies are urgently required. In this review, we highlight the current advances in understanding the roles of epigenetic mechanisms in heavy metal-induced carcinogenesis, cancer progression, and angiogenesis.

DNMT1 Gene Expression in Patients with Helicobacter pylori Infection

DNMT1, as a critical enzyme affecting epigenetics through methylation of DNA cytosine-rich sequences, regulates gene expression. Exterior factors including long-term infections, in this study Helicobacter pylori infection, could change host cells' epigenetics by affecting DNMT1 gene expression. This study investigated the statistical correlation between H. pylori virulence genes and DNMT1 gene expression in gastric antral epithelial cells of gastric adenocarcinoma and gastritis patients. In a case-control study, 50 and 53 gastritis and gastric adenocarcinoma antral biopsies, including 23 and 21 patients with H. pylori infection, respectively, were collected from hospitals in the west of Iran. Having extracted total RNA from gastric biopsy samples, cDNA was synthesized and virulence genes of H. pylori were detected by using the PCR method. Relative real-time RT PCR was used to detect ΔΔCt fold changes of the DNMT1 gene expression in divided groups of patients based on H. pylori infection and clinical manifestations. The results showed that along with increasing patients' age, the DNMT1 gene expression will increase in gastric antral epithelial cells of gastric cancer patients (P ≤ 0.05). On the other hand, the biopsy samples with infection of H. pylori cagA, cagY, and cagE genotypes revealed a direct correlation along with increased DNMT1 gene expression. This study revealed the correlations of H. pylori cag pathogenicity island genes with increased DNMT1 gene expression.

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.

Maternal exposure to cadmium during pregnancy is associated with changes in DNA methylation that are persistent at 9 years of age

BACKGROUND

Cadmium (Cd) exposure during gestation has been associated with altered DNA methylation at birth, but it is not known if the changes in methylation persist into childhood.

OBJECTIVES

To evaluate whether gestational Cd-related changes of DNA methylation persist from birth to 9 years of age.

METHODS

We studied mother-child dyads in a longitudinal cohort in rural Bangladesh. Cadmium concentrations in maternal blood (erythrocyte fraction; Ery-Cd) at gestational week 14 and in child urine (U-Cd, long-term exposure marker) at 9 years were measured using inductively coupled plasma mass spectrometry. The epigenome-wide DNA methylation was measured in mononuclear cells (PBMCs) prepared from cord blood and peripheral blood at 9 years in 71 children (hereafter referred to as the explorative group) by Infinium HumanMethylation450K BeadChip. Replication of one differentially methylated region (DMR; 9 CpG sites) was performed in PBMCs of 160 9-year-old children (validation group) by EpiTyper MALDI-TOF mass spectrometry.

RESULTS

The median maternal Ery-Cd concentration was 1.24 µg/kg (range 0.35, 4.55) in the explorative group and 0.83 µg/kg (0.08, 2.97) in the validation group. The median U-Cd concentration in the 9-year-old children was 0.26 µg/L (0.09, 1.06) in the explorative group and 0.32 µg/L (0.07, 1.33) in the validation group. In the explorative group, we identified ten DMRs, both in cord blood and in PBMCs at 9 years, that were associated with maternal Ery-Cd. Eight out of the ten DMRs were hypomethylated and three of the hypomethylated DMRs were located in the HLA region on chromosome 6. One of the DMRs (hypomethylated) in the HLA region (upstream of the zinc finger protein 57 homolog, ZFP57 gene) was replicated in the validation group, and we found that it was hypomethylated in relation to maternal Ery-Cd, but not child U-Cd.

CONCLUSION

Gestational exposure to Cd appears to be associated with regional changes, especially hypomethylated, in DNA methylation that linger from birth up to prepubertal age.

Epigenetic Inheritance: Intergenerational Effects of Pesticides and Other Endocrine Disruptors on Cancer Development

Parental environmental experiences affect disease susceptibility in the progeny through epigenetic inheritance. Pesticides are substances or mixtures of chemicals-some of which are persistent environmental pollutants-that are used to control pests. This review explores the evidence linking parental exposure to pesticides and endocrine disruptors to intergenerational and transgenerational susceptibility of cancer in population studies and animal models. We also discuss the impact of pesticides and other endocrine disruptors on the germline epigenome as well as the emerging evidence for how epigenetic information is transmitted between generations. Finally, we discuss the importance of this mode of inheritance in the context of cancer prevention and the challenges ahead.

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.

Common mechanisms cannot explain time- and dose-dependent DNA methylation changes in earthworms exposed to cadmium

DNA hypermethylation caused by environmental pollutants like cadmium (Cd) has already been demonstrated in many invertebrates, including earthworms. However, the exact epigenetic mechanisms that drive this hypermethylation are largely unknown and even basic DNA methylation and demethylation processes are hardly characterized. Therefore, we used an important bioindicator, the earthworm Lumbricus terrestris, as a model organism to determine time- and dose-dependent effects of Cd on global and gene-specific DNA methylation and its underlying mechanisms. We revealed Cd-induced adenine and cytosine hypermethylation using specific antibodies in dot blots and found that the methylation level of adenine compared to cytosine changed even to a bigger extent. However, the levels of hydroxymethylated cytosine did not differ between treatment groups. General methylation and demethylation components like methyltransferases (DNMT1 and 3), and ten-eleven translocation (TET) genes were confirmed in L. terrestris by quantitative RealTime PCR. However, neither gene expression, nor DNMT and TET enzyme activity showed significant differences in the Cd exposure groups. Using bisulfite conversion and sequencing, gene body methylation (gbm) of metallothionein 2 (MT2), one of the most important detoxification proteins, was characterized. Cd-dependent changes in MT2 gbm could, however, not be correlated to MT2 gene activity evaluated by quantitative RealTime PCR. Future directions as well as missing links are discussed in the present study hinting towards the importance of studying epigenetic marks and mechanistic insights in a broad variety of species to deepen our knowledge on the effects of changing environmental conditions.

Prenatal Cadmium Exposure Alters Proliferation in Mouse CD4+ T Cells via LncRNA Snhg7

Objective

Prenatal cadmium (Cd) exposure leads to immunotoxic phenotypes in the offspring affecting coding and non-coding genes. Recent studies have shown that long non-coding RNAs (lncRNAs) are integral to T cell regulation. Here, we investigated the role of long non-coding RNA small nucleolar RNA host gene 7 (lncSnhg7) in T cell proliferation.

Methods

RNA sequencing was used to analyze the expression of lncRNAs in splenic CD4+ T cells with and without CD3/CD28 stimulation. Next, T cells isolated from offspring exposed to control or Cd water throughout mating and gestation were analyzed with and without stimulation with anti-CD3/CD28 beads. Quantitative qPCR and western blotting were used to detect RNA and protein levels of specific genes. Overexpression of a miR-34a mimic was achieved using nucleofection. Apoptosis was measured using flow cytometry and luminescence assays. Flow cytometry was also used to measure T cell proliferation in culture. Finally, lncSnhg7 was knocked down in splenic CD4+ T cells with lentivirus to assess its effect on proliferation.

Results

We identified 23 lncRNAs that were differentially expressed in stimulated versus unstimulated T cells, including lncSnhg7. LncSnhg7 and a downstream protein, GALNT7, are upregulated in T cells from offspring exposed to Cd during gestation. Overexpression of miR-34a, a regulator of lncSnhg7 and GALNT7, suppresses GALNT7 protein levels in primary T cells, but not in a mouse T lymphocyte cell line. The T cells isolated from Cd-exposed offspring exhibit increased proliferation after activation in vitro, but Treg suppression and CD4+ T cell apoptosis are not affected by prenatal Cd exposure. Knockdown on lncSnhg7 inhibits proliferation of CD4+ T cells.

Conclusion

Prenatal Cd exposure alters the expression of lncRNAs during T cell activation. The induction of lncSnhg7 is enhanced in splenic T cells from Cd offspring resulting in the upregulation of GALNT7 protein and increased proliferation following activation. miR-34a overexpression decreased GALNT7 expression and knockdown of lncSnhg7 inhibited proliferation suggesting that the lncSnhg7/miR-34a/GALNT7 is an important pathway in primary CD4+ T cells. These data highlight the need to understand the consequences of environmental exposures on lncRNA functions in non-cancerous cells as well as the effects in utero.

The preferential accumulation of cadmium ions among various tissues in mice

Cadmium (Cd) is hazardous to human health because of its toxicity and long half-life of clearance. Many studies have explored the relationship between chronic Cd exposure and different human diseases. However, most of the studies limited the study targets of Cd toxicity to two or three organ systems. The goal of this study was to establish a mouse model of Cd accumulation in most organ systems and to particularly investigate the potential toxic effects of Cd to the cardiovascular system. Mice were divided into three groups: the control group, Cd-100 group, and Cd-200 group. In the control group, Cd was detected in the kidney, lung, liver, heart and urine but was undetectable in the aorta, intestine, thigh bone, spinal bone and serum. Upon chronic exposure in the Cd-100 and Cd-200 groups, Cd accumulated in all tissues, with a dramatic increase in concentration. We confirmed that Cd could accumulate significantly in the heart and aorta upon chronic exposure. This finding might help to explain the potential toxic effects of Cd on these organs. In addition, the calcium concentration in the bones and kidney declined when the exposure to Cd increased. This finding aligned with the negative effects of Cd on bony mineralization and the potential direct toxic effects of Cd on bones. The impacts of Cd on the cardiovascular system were explored. Histologically, chronic Cd exposure led to myocytes hypertrophy and myocardial architecture disarray in the Cd-100 group compared to those in the control group. Our research confirms that Cd can accumulate in all of the organs studied upon chronic exposure, and suggests that the toxicity of Cd accumulation may play important roles in mediating the pathophysiologic effects in these target organs, especially the bone and heart.

Down-regulation of lncRNA MEG3 promotes chronic low dose cadmium exposure-induced cell transformation and cancer stem cell-like property

Cadmium (Cd) is a toxic heavy metal and one of carcinogens that cause lung cancer. However, the exact mechanism of Cd carcinogenesis remains unclear. To investigate the mechanism of Cd carcinogenesis, we exposed human bronchial epithelial cells (BEAS-2B) to a low dose of Cd (2.5 μM, CdCl₂) for 9 months, which caused cell malignant transformation and generated cancer stem cell (CSC)-like cells. The goal of this study is to investigate the underlying mechanism. The long non-coding RNA (lncRNA) microarray analysis showed that the expression level of a tumor suppressive lncRNA maternally expressed 3 (MEG3) is significantly down-regulated in Cd-transformed cells, which is confirmed by further q-PCR analysis. Mechanistically, it was found that chronic Cd exposure up-regulates the levels of DNA methyltransferases (DNMTs), which increases the methylation of the differentially methylated region (DMR) 1.5 kb upstream of MEG3 transcription start site to reduce MEG3 expression. Functional studies showed that stably overexpressing MEG3 in Cd-transformed cells significantly reduces their transformed phenotypes. Moreover, stably overexpressing MEG3 in parental non-transformed human bronchial epithelial cells significantly impaired the capability of chronic Cd exposure to induce cell transformation and CSC-like property. Further mechanistic studies revealed that the cell cycle inhibitor p21 level is reduced and retinoblastoma protein (Rb) phosphorylation is increased in Cd-transformed cells to promote cell cycle progression. In addition, Cd-transformed cells also expressed higher levels of Bcl-xL and displayed apoptosis resistance. In contrast, stably overexpressing MEG3 increased p21 levels and reduced Rb phosphorylation and Bcl-xL levels in Cd-exposed cells and reduced their cell cycle progression and apoptosis resistance. Together, these findings suggest that MEG3 down-regulation may play important roles in Cd-induced cell transformation and CSC-like property by promoting cell cycle progression and apoptosis resistance.

DNA methylation changes induced by prenatal toxic metal exposure: An overview of epidemiological evidence

Accumulating evidence suggests that exposure to unfavorable conditions early in life can substantially contribute to the risk of chronic disorders later in life ('developmental programming' phenomenon). The mechanistic basis for this phenomenon remains poorly understood so far, although epigenetic mechanisms such as DNA methylation, histone modifications and microRNA-mediated gene regulation apparently play a crucial role. The key role of epigenetic modifications triggered by unfavorable environmental cues during sensitive developmental periods in linking adverse early-life events to later-life health outcomes is evident from a large body of studies, including methylome-wide association studies and research of candidate genes. Toxic metals (TMs), such as heavy metals, including lead, chromium, cadmium, arsenic, mercury, etc., are among environmental contaminants currently most significantly impacting human health status. Since TMs can cross the placental barrier and accumulate in fetal tissues, exposure to high doses of these xenobiotics early in development is considered to be among important factors contributing to the developmental programming of adult-life diseases in modern societies. In this mini-review, we summarize epidemiological findings indicating that prenatal TM exposure can induce epigenetic dysregulation, thereby potentially affecting adult health outcomes.

Epigenetic Effects of Benzene in Hematologic Neoplasms: The Altered Gene Expression

Simple Summary

Benzene is produced by diverse petroleum transformation processes and it is widely employed in industry despite its oncogenic effects. In fact, occupational exposure to benzene may cause hematopoietic malignancy. The leukemogenic action of benzene is particularly complex. Possible processes of onset of hematological malignancies have been recognized as a genotoxic action and the provocation of immunosuppression. However, benzene can induce modifications that do not involve alterations in the DNA sequence, the so-called epigenetics changes. Acquired epigenetic modification may also induce leukemogenesis, as benzene may alter nuclear receptors, and cause changes at the protein level, thereby modifying the function of regulatory proteins, including oncoproteins and tumor suppressor proteins.

Abstract

Benzene carcinogenic ability has been reported, and chronic exposure to benzene can be one of the risk elements for solid cancers and hematological neoplasms. Benzene is acknowledged as a myelotoxin, and it is able to augment the risk for the onset of acute myeloid leukemia, myelodysplastic syndromes, aplastic anemia, and lymphomas. Possible mechanisms of benzene initiation of hematological tumors have been identified, as a genotoxic effect, an action on oxidative stress and inflammation and the provocation of immunosuppression. However, it is becoming evident that genetic alterations and the other causes are insufficient to fully justify several phenomena that influence the onset of hematologic malignancies. Acquired epigenetic alterations may participate with benzene leukemogenesis, as benzene may affect nuclear receptors, and provoke post-translational alterations at the protein level, thereby touching the function of regulatory proteins, comprising oncoproteins and tumor suppressor proteins. DNA hypomethylation correlates with stimulation of oncogenes, while the hypermethylation of CpG islands in promoter regions of specific tumor suppressor genes inhibits their transcription and stimulates the onset of tumors. The discovery of the systems of epigenetic induction of benzene-caused hematological tumors has allowed the possibility to operate with pharmacological interventions able of stopping or overturning the negative effects of benzene.

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.

DNMT1 and DNMT3B regulate tumorigenicity of human prostate cancer cells by controlling RAD9 expression through targeted methylation

Prostate cancer is the second most common type of cancer and the second leading cause of cancer death in American men. RAD9 stabilizes the genome, but prostate cancer cells and tumors often have high quantities of the protein. Reduction of RAD9 level within prostate cancer cells decreases tumorigenicity of nude mouse xenographs and metastasis phenotypes in culture, indicating that RAD9 overproduction is essential for the disease. In prostate cancer DU145 cells, CpG hypermethylation in a transcription suppressor site of RAD9 intron 2 causes high-level gene expression. Herein, we demonstrate that DNA methyltransferases DNMT1 and DNMT3B are highly abundant in prostate cancer cells DU145, CWR22, LNCaP and PC-3; yet, these DNMTs bind primarily to the transcription suppressor in DU145, the only cells where methylation is critical for RAD9 regulation. For DU145 cells, DNMT1 or DNMT3B shRNA reduced RAD9 level and tumorigenicity, and RAD9 ectopic expression restored this latter activity in the DNMT knockdown cells. High levels of RAD9, DNMT1, DNMT3B and RAD9 transcription suppressor hypermethylation were significantly correlated in prostate tumors, and not in normal prostate tissues. Based on these results, we propose a novel model where RAD9 is regulated epigenetically by DNMT1 and DNMT3B, via targeted hypermethylation, and that consequent RAD9 overproduction promotes prostate tumorigenesis.

Epigenetic influence of environmentally neurotoxic metals

Continuous globalization and industrialization have ensured metals are an increasing aspect of daily life. Their usefulness in manufacturing has made them vital to national commerce, security and global economy. However, excess exposure to metals, particularly as a result of environmental contamination or occupational exposures, has been detrimental to overall health. Excess exposure to several metals is considered environmental risk in the aetiology of several neurological and neurodegenerative diseases. Metal-induced neurotoxicity has been a major health concern globally with intensive research to unravel the mechanisms associated with it. Recently, greater focus has been directed at epigenetics to better characterize the underlying mechanisms of metal-induced neurotoxicity. Epigenetic changes are those modifications on the DNA that can turn genes on or off without altering the DNA sequence. This review discusses how epigenetic changes such as DNA methylation, post translational histone modification and noncoding RNA-mediated gene silencing mediate the neurotoxic effects of several metals, focusing on manganese, arsenic, nickel, cadmium, lead, and mercury.

Exposure to microplastics cause gut damage, locomotor dysfunction, epigenetic silencing, and aggravate cadmium (Cd) toxicity in Drosophila

The interactions of microplastics (MPs) with other chemicals and the range of outcomes are of great importance to enhance understanding of their environmental impacts and health risks. Cadmium (Cd) and cadmium compounds are widely used as pigments and stabilizers in plastics, but they readily leach out. Here we addressed the impacts of MPs, Cd, and their joint exposure in a tractable Drosophila melanogaster model. We show that exposure to MPs lead to extensive particle size depended gut damage early in life and an enhancement of Cd-induced inhibition of locomotor-behavioral function in adult flies. In addition, we show that Cd exposure induces epigenetic gene silencing via position-effect variegation (PEV) in somatic tissues that was dramatically enhanced by co-exposure with MPs. The results indicate that MPs can aggravate the toxicity of other environmental contaminants and induce adverse effects across a range of diverse outcomes in a tractable and widely used model organism. These observations raise the prospects of using Drosophila as a tool for the rapid assessment of MP-mediated toxicity.

Metals and molecular carcinogenesis

Many metals are essential for living organisms, but at higher doses they may be toxic and carcinogenic. Metal exposure occurs mainly in occupational settings and environmental contaminations in drinking water, air pollution and foods, which can result in serious health problems such as cancer. Arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr) and nickel (Ni) are classified as Group 1 carcinogens by the International Agency for Research on Cancer. This review provides a comprehensive summary of current concepts of the molecular mechanisms of metal-induced carcinogenesis and focusing on a variety of pathways, including genotoxicity, mutagenesis, oxidative stress, epigenetic modifications such as DNA methylation, histone post-translational modification and alteration in microRNA regulation, competition with essential metal ions and cancer-related signaling pathways. This review takes a broader perspective and aims to assist in guiding future research with respect to the prevention and therapy of metal exposure in human diseases including cancer.

Cadmium chloride enhances cisplatin sensitivity in osteosarcoma cells by reducing FOXM1 expression

Osteosarcoma is a highly malignant disease and is associated with a poor patient prognosis and a high mortality rate. Disease prognosis significantly correlates with chemotherapeutic responses. Cadmium is a heavy metal with specific effects on bone, but its benefits for osteosarcoma treatment have not been characterized. In the present study, cadmium chloride was used to treat MG63 osteosarcoma cells, and their gene expression profiles were assessed by GeneChip technology. We found that forkhead box protein M1 (FOXM1) was downregulated by cadmium chloride, and lentiviral‑mediated silencing of FOXM1 confirmed a role for this factor in the cisplatin resistance of MG63 cells. In nude mice, cadmium chloride enhanced the sensitivity of osteosarcoma to cisplatin, an effect mediated by FOXM1. Collectively, these data indicate that cadmium chloride can alter the sensitivity of osteosarcoma cells to cisplatin through FOXM1, highlighting it as a potential therapeutic target and prognostic factor for osteosarcoma.

Metals and Mechanisms of Carcinogenesis

Metal exposure is pervasive and not limited to sporadic poisoning events or toxic waste sites. Hundreds of millions of people around the globe are affected by chronic metal exposure, which is associated with serious health concerns, including cancer, as demonstrated in a variety of studies at the molecular, systemic, and epidemiologic levels. Metal-induced toxicity and carcinogenicity are sophisticated and complex in nature. This review provides a broad context and holistic view of currently available studies on the mechanisms of metal-induced carcinogenesis. Specifically, we focus on the five most prevalent carcinogenic metals, arsenic, nickel, cadmium, chromium, and beryllium, and their potential to drive carcinogenesis in humans. A comprehensive understanding of the mechanisms behind the development of metal-induced cancer can provide valuable insights for therapeutic intervention involving molecular targets in metal-induced carcinogenesis.

Cadmium, Smoking, and Human Blood DNA Methylation Profiles in Adults from the Strong Heart Study

BACKGROUND

The epigenetic effects of individual environmental toxicants in tobacco remain largely unexplored. Cadmium (Cd) has been associated with smoking-related health effects, and its concentration in tobacco smoke is higher in comparison with other metals.

OBJECTIVES

We studied the association of Cd and smoking exposures with human blood DNA methylation (DNAm) profiles. We also evaluated the implication of findings to relevant methylation pathways and the potential contribution of Cd exposure from smoking to explain the association between smoking and site-specific DNAm.

METHODS

We conducted an epigenome-wide association study of urine Cd and self-reported smoking (current and former vs. never, and cumulative smoking dose) with blood DNAm in 790,026 CpGs (methylation sites) measured with the Illumina Infinium Human MethylationEPIC (Illumina Inc.) platform in 2,325 adults 45-74 years of age who participated in the Strong Heart Study in 1989-1991. In a mediation analysis, we estimated the amount of change in DNAm associated with smoking that can be independently attributed to increases in urine Cd concentrations from smoking. We also conducted enrichment analyses and in silico protein-protein interaction networks to explore the biological relevance of the findings.

RESULTS

At a false discovery rate (FDR)-corrected level of 0.05, we found 6 differentially methylated positions (DMPs) for Cd; 288 and 17, respectively, for current and former smoking status; and 77 for cigarette pack-years. Enrichment analyses of these DMPs displayed enrichment of 58 and 6 Gene Ontology and Kyoto Encyclopedia of Genes and Genomes gene sets, respectively, including biological pathways for cancer and cardiovascular disease. In in silico protein-to-protein networks, we observed key proteins in DNAm pathways directly and indirectly connected to Cd- and smoking-DMPs. Among DMPs that were significant for both Cd and current smoking (annotated to PRSS23, AHRR, F2RL3, RARA, and 2q37.1), we found statistically significant contributions of Cd to smoking-related DNAm.

CONCLUSIONS

Beyond replicating well-known smoking epigenetic signatures, we found novel DMPs related to smoking. Moreover, increases in smoking-related Cd exposure were associated with differential DNAm. Our integrative analysis supports a biological link for Cd and smoking-associated health effects, including the possibility that Cd is partly responsible for smoking toxicity through epigenetic changes. https://doi.org/10.1289/EHP6345.

The Effects of Cadmium Toxicity

Cadmium (Cd) is a toxic non-essential transition metal that poses a health risk for both humans and animals. It is naturally occurring in the environment as a pollutant that is derived from agricultural and industrial sources. Exposure to cadmium primarily occurs through the ingestion of contaminated food and water and, to a significant extent, through inhalation and cigarette smoking. Cadmium accumulates in plants and animals with a long half-life of about 25-30 years. Epidemiological data suggest that occupational and environmental cadmium exposure may be related to various types of cancer, including breast, lung, prostate, nasopharynx, pancreas, and kidney cancers. It has been also demonstrated that environmental cadmium may be a risk factor for osteoporosis. The liver and kidneys are extremely sensitive to cadmium's toxic effects. This may be due to the ability of these tissues to synthesize metallothioneins (MT), which are Cd-inducible proteins that protect the cell by tightly binding the toxic cadmium ions. The oxidative stress induced by this xenobiotic may be one of the mechanisms responsible for several liver and kidney diseases. Mitochondria damage is highly plausible given that these organelles play a crucial role in the formation of ROS (reactive oxygen species) and are known to be among the key intracellular targets for cadmium. When mitochondria become dysfunctional after exposure to Cd, they produce less energy (ATP) and more ROS. Recent studies show that cadmium induces various epigenetic changes in mammalian cells, both in vivo and in vitro, causing pathogenic risks and the development of various types of cancers. The epigenetics present themselves as chemical modifications of DNA and histones that alter the chromatin without changing the sequence of the DNA nucleotide. DNA methyltransferase, histone acetyltransferase, histone deacetylase and histone methyltransferase, and micro RNA are involved in the epigenetic changes. Recently, investigations of the capability of sunflower (Helianthus annuus L.), Indian mustard (Brassica juncea), and river red gum (Eucalyptus camaldulensis) to remove cadmium from polluted soil and water have been carried out. Moreover, nanoparticles of TiO2 and Al2O3 have been used to efficiently remove cadmium from wastewater and soil. Finally, microbial fermentation has been studied as a promising method for removing cadmium from food. This review provides an update on the effects of Cd exposure on human health, focusing on the cellular and molecular alterations involved.

Epigenomic regulation of OTU5 in Arabidopsis thaliana

Epigenetic regulation by DNA methylation and histone marks is crucial to plant development. In Arabidopsis, the otu5 mutant exhibited altered root phenotypes resembling those of phosphate-deficient plants. In low phosphate (Pi) conditions, altered H3K4 and H3K27 trimethylation were associated with the expression of Pi homeostasis-related genes. However, the genetic effect of OTU5 on the epigenomes was left unexplored. We assessed genome-wide DNA methylation, gene expression and histone modifications of roots from both Col-0 and otu5 mutants. We found that OTU5 altered DNA methylation profile with a context-specific effect through targeting local genomic regions. Our analysis showed that in otu5 the abundance of H3K4me3 was clearly associated with the changes of DNA methylation, leading to the transcriptional difference from wildtype. We concluded that OTU5 induced cross-talks among epigenomes that altogether impacted the regulation of approximately 7060 genes. Of which 186 genes associated with root development were likely to be epigenetically regulated.

Cyanidin-3-O-glucoside restores spermatogenic dysfunction in cadmium-exposed pubertal mice via histone ubiquitination and mitigating oxidative damage

Cadmium (Cd) is an environmental contaminant found in soil, water, and food, and can cause oxidative stress and male reproductive damage. During puberty, the male reproductive system is very vulnerable to interference, however, the dysregulation of Cd on spermatogenesis in this period is ambiguous. The anthocyanin cyanidin-3-O-glucoside (C3G) is phytochemical rich in plants and fruits and has been shown to have remarkable anti-oxidant activity, making it an ideal nutrient for nutritional intervention. By modeling Cd-induced damage in male pubertal mice and feeding with C3G, we demonstrated that the C3G could rescue the amount and activity of sperm predominantly. Furthermore, C3G showed partial resistance to Cd-induced histone modification during spermiogenesis and prevented oxidative damage of the DNA in the sperm nucleus. Additionally, C3G mitigated the oxidative stress of testis to achieve the level coinciding with the control group. Meanwhile, Cd-induced mitochondrial apoptosis of sperm cells was reduced significantly via the MAPK signaling pathway in the presence of C3G. Collectively, our findings can offer a potential intervention for combating Cd-induced reproductive damage during puberty by taking anthocyanin as a dietary supplement.

Multigenerational effects of cadmium on the lifespan and fertility of Drosophila melanogaster

Although the damage and tolerance mechanisms of Cd stress are known, the data on genetic risk are limited. The aim of this study was to assess the chronic toxicity of Cd, genetic responses, and multigenerational effects in five generations of Drosophila melanogaster. For each generation, lifespan and fertility were statistically analysed and the expression of apoptosis- (p53 and caspase-3) and epigenesis-related (dDnmt2 and dMBD2/3) genes was examined. Lifespan and fertility significantly declined under Cd stress and these effects were maintained for two generations and one generation, respectively, when Cd stress was removed. The expression of p53 and caspase-3 was significantly up-regulated after exposure, suggesting that apoptosis contributes to the resistance mechanism. Their altered expression was retained for two generations. Furthermore, high expression of dDnmt2 and dMBD2/3 accompanied Cd exposure, which was passed on to three generations, suggesting that genetic modifications in apoptosis-related genes are carried to the offspring through epigenetic regulation.

Dynamic Signatures of the Epigenome: Friend or Foe?

Highly dynamic epigenetic signaling is influenced mainly by (micro)environmental stimuli and genetic factors. The exact mechanisms affecting particular epigenomic patterns differ dependently on the context. In the current review, we focus on the causes and effects of the dynamic signatures of the human epigenome as evaluated with the high-throughput profiling data and single-gene approaches. We will discuss three different aspects of phenotypic outcomes occurring as a consequence of epigenetics interplaying with genotype and environment. The first issue is related to the cases of environmental impacts on epigenetic profile, and its adverse and advantageous effects related to human health and evolutionary adaptation. The next topic will present a model of the interwoven co-evolution of genetic and epigenetic patterns exemplified with transposable elements (TEs) and their epigenetic repressors Krüppel-associated box zinc finger proteins (KRAB–ZNFs). The third aspect concentrates on the mitosis-based microevolution that takes place during carcinogenesis, leading to clonal diversity and expansion of tumor cells. The whole picture of epigenome plasticity and its role in distinct biological processes is still incomplete. However, accumulating data define epigenomic dynamics as an essential co-factor driving adaptation at the cellular and inter-species levels with a benefit or disadvantage to the host.

Hypomethylation of LINE-1 repeat elements and global loss of DNA hydroxymethylation in vapers and smokers

The outbreak of vaping-related severe lung injuries and deaths and the epidemic of teen vaping in the U.S. underscore the urgent need for determining the biological consequences of electronic cigarette (e-cig) use. We have investigated the association between vaping and epigenetic changes by quantifying DNA methylation levels in Long Interspersed Nucleotide Element 1 (LINE-1) and global DNA hydroxymethylation (5-hmC) levels and measuring the expression level of enzymes catalysing the respective processes in peripheral blood of exclusive vapers, smokers, and controls, matched for age, gender, and race (n = 45). Both vapers and smokers showed significant loss of methylation in LINE-1 repeat elements in comparison to controls (P = 0.00854 and P = 0.03078, respectively). Similarly, vapers and smokers had significant reductions in 5-hmC levels relative to controls (P = 0.04884 and P = 0.0035, respectively). Neither the LINE-1 methylation levels nor the global 5-hmC levels were different between vapers and smokers. There was a direct correlation between methylation levels in the LINE-1 elements and global 5-hmC levels in the study subjects (r = 0.31696, P = 0.03389). Inverse and statistically significant correlations were found between both the LINE-1 methylation levels and the global 5-hmC levels and various vaping/smoking metrics in the study subjects. There were modest but not statistically significant changes in transcription of DNA methyltransferases and ten-eleven translocation enzymes in both vapers and smokers relative to controls. Our findings support follow-up genome-wide investigations into the epigenetic effects of vaping, which may further clarify the health consequences of e-cig use.

ABBREVIATIONS

5-mC: 5-methylcytosine; 5-hmC: 5-hydroxymethylcytosine; 8-OHdG: 8-hydroxy-2'-deoxyguanosine; ACTIN: actin beta; ANOVA: Analysis of Variance; BER: base excision repair; BMI: body mass index; CO: carbon monoxide; COHb: carboxyhaemoglobin; COBRA: combined bisulphite restriction analysis; COPD: chronic obstructive pulmonary disease; DNMT1: DNA methyltransferase 1; DNMT3A: DNA methyltransferase 3A; DNMT3B: DNA methyltransferase 3B; e-cigs: electronic cigarettes; ELISA: enzyme-linked immunosorbent assay; ENDS: electronic nicotine delivery systems; FDA: Food and Drug Administration; GAPDH; glyceraldehyde-3-phosphate dehydrogenase; HPLC: high-performance liquid chromatography; LINE-1: Long Interspersed Nucleotide Element 1; PBS: phosphate-buffered saline; RFU: relative fluorescence units; RT-qPCR: quantitative reverse-transcription polymerase chain reaction; ROS: reactive oxygen species; SAM, S-adenosylmethionine; SE: standard error; TET1: ten-eleven translocation 1; TET2: ten-eleven translocation 2; TET3: ten-eleven translocation 3.

Association of liver and kidney functions with Klotho gene methylation in a population environment exposed to cadmium in China

Exposure to the heavy metal cadmium has adverse effects on human health, including DNA methylation. This study aimed to investigate the effects of cadmium on liver and kidney functions and Klotho gene methylation and to explore the relationship of methylation level with indicators of liver and kidney functions. Graphite furnace atomic absorption spectrometry was conducted to determine urinary cadmium, and an automatic biochemical analyzer was used to detect indices of liver and kidney functions. PCR pyrosequencing was performed to detect the methylation rate of Klotho. One-way ANOVA was adopted to compare the differences between groups, and the linear correlation to variables was analyzed. Cadmium exposure was negatively correlated with albumin level (r=-0.143, p=0.021) and positively correlated with urinary β₂-microglobulin level (r=0.229, p<0.001). However, the methylation levels of Klotho gene was decreased and increased by low and high doses of cadmium exposure, respectively. And Klothomethylation levels were negatively correlated with albumin levels and positively correlated with β₂-microglobulin levels.In this study, cadmium exposure affects liver and kidney functions as well as Klotho methylation levels, but the effect on Klotho methylation levels is not linear. Klotho methylation levels also influence liver and kidney functions.

Inhibition of DNA demethylation enhances plant tolerance to cadmium toxicity by improving iron nutrition

Although the alteration of DNA methylation due to abiotic stresses, such as exposure to the toxic metal cadmium (Cd), has been often observed in plants, little is known about whether such epigenetic changes are linked to the ability of plants to adapt to stress. Herein, we report a close linkage between DNA methylation and the adaptational responses in Arabidopsis plants under Cd stress. Exposure to Cd significantly inhibited the expression of three DNA demethylase genes ROS1/DML2/DML3 (RDD) and elevated DNA methylation at the genome-wide level in Col-0 roots. Furthermore, the profile of DNA methylation in Cd-exposed Col-0 roots was similar to that in the roots of rdd triple mutants, which lack RDD, indicating that Cd-induced DNA methylation is associated with the inhibition of RDD. Interestingly, the elevation in DNA methylation in rdd conferred a higher tolerance against Cd stress and improved cellular Fe nutrition in the root tissues. In addition, lowering the Fe supply abolished improved Cd tolerance due to the lack of RDD in rdd. Together, these data suggest that the inhibition of RDD-mediated DNA demethylation in the roots by Cd would in turn enhance plant tolerance to Cd stress by improving Fe nutrition through a feedback mechanism.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

One year exposure to Cd- and Pb-contaminated soil causes metal accumulation and alteration of global DNA methylation in rats

Metal pollution has been associated with anthropogenic activities, such as effluents and emissions from mines. Soil could be exposure route of wild rats to metals, especially in mining areas. The aim of this study was to verify whether soil exposure under environmentally relevant circumstances results in metal accumulation and epigenetic modifications. Wistar rats were divided to three groups: 1) control without soil exposure, 2) low-metal exposure group exposed to soil containing low metal levels (Pb: 75 mg/kg; Cd: 0.4), and 3) high-metal exposure group exposed to soil (Pb: 3750; Cd: 6). After 1 year of exposure, the metal levels, Pb isotopic values, and molecular indicators were measured. Rats in the high-group showed significantly greater concentrations of Pb and Cd in tissues. Higher accumulation factors (tissue/soil) of Cd than Pb were observed in the liver, kidney, brain, and lung, while the factor of Pb was higher in the tibia. The obtained results of metal accumulation ratios (lung/liver) and stable Pb isotope ratios in the tissues indicated that the respiratory exposure would account for an important share of metal absorption into the body. Genome-wide methylation status and DNA methyltransferase (Dnmt 3a/3b) mRNA expressions in testis were higher in the high-group, suggesting that exposure to soil caused metal accumulation and epigenetic alterations in rats.

Mass Spectrometry for Investigating the Effects of Toxic Metals on Nucleic Acid Modifications

The extensive use of toxic metals in industry and agriculture leads to their wide distribution in the environment, which raises critical concerns over their toxic effects on human health. Many toxic metals are reported to be mildly mutagenic or non-mutagenic, indicating that genetic-based mechanisms may not be primarily responsible for toxic metal-induced carcinogenesis. Increasing evidence has demonstrated that exposure to toxic metals can alter epigenetic modifications, which may lead to the dysregulation of gene expression and disease susceptibility. It is now becoming clear that a full understanding of the effects of toxic metals on cellular toxicity and carcinogenesis will need to consider both genetic- and epigenetic-based mechanisms. Uncovering the effects of toxic metals on epigenetic modifications in nucleic acids relies on the detection and quantification of these modifications. Mass spectrometry (MS)-based methods for deciphering epigenetic modifications have substantially advanced over the past decade, and they are now becoming widely used and essential tools for evaluating the effects of toxic metals on nucleic acid modifications. This Review provides an overview of MS-based methods for analysis of nucleic acid modifications. In addition, we also review recent advances in understanding the effects of exposure to toxic metals on nucleic acid modifications.

Aberrant gene expression profiles in Mediterranean sea urchin reproductive tissues after metal exposures

Marine organisms are simultaneously exposed to numerous pollutants, among which metals probably represent the most abundant in marine environments. In order to evaluate the effects of metal exposure at molecular level in reproductive tissues, we profiled the sea urchin transcriptional response after non-lethal exposures using pathway-focused mRNA expression analyses. Herein, we show that exposures to relatively high concentrations of both essential and toxic metals hugely affected the gonadic expression of several genes involved in stress-response, detoxification, transcriptional and post-transcriptional regulation, without significant changes in gonadosomatic indices. Even though treatments did not result in reproductive tissues visible alterations, metal exposures negatively affected the main mechanisms of stress-response, detoxification and survival of adult P. lividus. Additionally, transcriptional changes observed in P. lividus gonads may cause altered gametogenesis and maintenance of heritable aberrant epigenetic effects. This study leads to the conclusion that exposures to metals, as usually occurs in polluted coastal areas, may affect sea urchin gametogenesis, thus supporting the hypothesis that parental exposure to environmental stressors affects the phenotype of the offspring.

Chronic cadmium exposure aggravates malignant phenotypes of nasopharyngeal carcinoma by activating the Wnt/β-catenin signaling pathway via hypermethylation of the casein kinase 1α promoter

BACKGROUND

Our previous study has shown that cadmium (Cd) exposure is not only a risk factor for nasopharyngeal carcinoma (NPC), but also correlated with the clinical stage and lymph node metastasis. However, the underlying molecular events of Cd involved in NPC progression remain to be elucidated.

PURPOSE

The objective of this study was to decipher how Cd impacts the malignant phenotypes of NPC cells.

METHODS

NPC cell lines CNE-1 and CNE-2 were continuously exposed with 1 μM Cd chloride for 10 weeks, designating as chronic Cd treated NPC cells (CCT-NPC). MTT assay, colony formation assay and xenograft tumor growth were used to assess cell viability in vitro and in vivo. Transwell assays were performed to detect cell invasion and migration. The protein levels of E-cadherin, N-cadherin, Vimentin as well as β-catenin and casein kinase 1α(CK1α) were measured by Western blot. Immunofluorescence staining was used to observe the distribution of filament actin (F-actin), β-catenin and CK1α. The mRNA levels of downstream target genes of β-catenin were detected by RT-PCR. Wnt/β-catenin signaling activity was assessed by TOPFlash/FOPFlash dual luciferase report system. MS-PCR was used to detect the methylation status of CK1α. Finally, the activation of Wnt/β-catenin pathway and cell biological properties were examined following treatment of CCT-NPC cells with 5-aza-2-deoxy-cytidine(5-aza-CdR).

RESULTS

CCT-NPC cells showed an increase in cell proliferation, colony formation, invasion and migration compared to the parental cells. Cd also induced cytoskeleton reorganization and epithelial-to-mesenchymal transition. Upregulation and nuclear translocation of β-catenin and increased luciferase activity accompanied with transcription of downstream target genes were found in CCT-NPC cells. Treatment of CCT-CNE1 cells with 5-aza-CdR could reverse the hypermethylation of CK1α and attenuate the cell malignancy.

CONCLUSION

These results support a role for chronic Cd exposure as a driving force for the malignant progression of NPC via epigenetic activation of the Wnt/β-catenin pathway.