The carcinogen cadmium elevates CpG-demethylation and enrichment of NFYA and E2F1 in the promoter of oncogenic PRMT5 and EZH2 methyltransferases resulting in their elevated expression in vitro

Mechanisms of Heavy Metal Cadmium (Cd)-Induced Malignancy

The environmental pollution of cadmium is worsening, and its significant carcinogenic effects on humans have been confirmed. Cadmium can induce cancer through various signaling pathways, including the ERK/JNK/p38MAPK, PI3K/AKT/mTOR, NF-κB, and Wnt. It can also cause cancer by directly damaging DNA and inhibiting DNA repair systems, or through epigenetic mechanisms such as abnormal DNA methylation, LncRNA, and microRNA. However, the detailed mechanisms of Cd-induced cancer are still not fully understood and require further investigation.

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.

Expression and function of NF-Y subunits in cancer

NF-Y is a Transcription Factor (TF) targeting the CCAAT box regulatory element. It consists of the NF-YB/NF-YC heterodimer, each containing an Histone Fold Domain (HFD), and the sequence-specific subunit NF-YA. NF-YA expression is associated with cell proliferation and absent in some post-mitotic cells. The review summarizes recent findings impacting on cancer development. The logic of the NF-Y regulome points to pro-growth, oncogenic genes in the cell-cycle, metabolism and transcriptional regulation routes. NF-YA is involved in growth/differentiation decisions upon cell-cycle re-entry after mitosis and it is widely overexpressed in tumors, the HFD subunits in some tumor types or subtypes. Overexpression of NF-Y -mostly NF-YA- is oncogenic and decreases sensitivity to anti-neoplastic drugs. The specific roles of NF-YA and NF-YC isoforms generated by alternative splicing -AS- are discussed, including the prognostic value of their levels, although the specific molecular mechanisms of activity are still to be deciphered.

Transition metals in angiogenesis - A narrative review

The aim of this paper is to offer a narrative review of the literature regarding the influence of transition metals on angiogenesis, excluding lanthanides and actinides. To our knowledge there are not any reviews up to date offering such a summary, which inclined us to write this paper. Angiogenesis describes the process of blood vessel formation, which is an essential requirement for human growth and development. When the complex interplay between pro- and antiangiogenic mediators falls out of balance, angiogenesis can quickly become harmful. As it is so fundamental, both its inhibition and enhancement take part in various diseases, making it a target for therapeutic treatments. Current methods come with limitations, therefore, novel agents are constantly being researched, with metal agents offering promising results. Various transition metals have already been investigated in-depth, with studies indicating both pro- and antiangiogenic properties, respectively. The transition metals are being applied in various formulations, such as nanoparticles, complexes, or scaffold materials. Albeit the increasing attention this field is receiving, there remain many unanswered questions, mostly regarding the molecular mechanisms behind the observed effects. Notably, approximately half of all the transition metals have not yet been investigated regarding potential angiogenic effects. Considering the promising results which have already been established, it should be of great interest to begin investigating the remaining elements whilst also further analyzing the established effects.

Cadmium modulates steatosis, fibrosis, and oncogenic signaling in liver cancer cells by activating notch and AKT/mTOR pathways

Cadmium (Cd) is an environmental pollutant that increases hepatotoxicity and the risk of liver diseases. In the current study, we investigated the effect of a physiologically relevant, low concentration of Cd on the regulation of liver cancer cell proliferation, steatosis, and fibrogenic/oncogenic signaling. Exposure to low concentrations of Cd increased endogenous reactive oxygen species (ROS) production and enhanced cell proliferation in a human bipotent progenitor cell line HepaRG and hepatocellular carcinoma (HCC) cell lines. Acute exposure of Cd increased Jagged-1 expression and activated Notch signaling in HepaRG and HCC cells HepG2 and SK-Hep1. Cd activated AKT/mTOR signaling by increasing phosphorylation of AKT-S473 and mTOR-S-4448 residues. Moreover, a low concentration of Cd also promoted cell steatosis and induced fibrogenic signaling in HCC cells. Chronic exposure to low concentrations of Cd-activated Notch and AKT/mTOR signaling induced the expression of pro-inflammatory cytokines tumor necrosis factor-alpha (TNFα) and its downstream target TNF-α-Induced Protein 8 (TNFAIP8). RNA-Seq data revealed that chronic exposure to low concentrations of Cd modulated the expression of several fatty liver disease-related genes involved in cell steatosis/fibrosis in HepaRG and HepG2 cells. Collectively, our data suggest that low concentrations of Cd modulate steatosis along with fibrogenic and oncogenic signaling in HCC cells by activating Notch and AKT/mTOR pathways.

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.

Characterization of primary canine Sertoli cells as a model to test male reproductive toxicant

Sertoli cells play critical roles in regulating spermatogenesis and testis development by providing structural and nutritional support. This study aimed to develop a standard protocol for canine Sertoli cell isolation and culture; and characterize its biological features, functionality, and application of compound toxicity testing. Canine testicles were received from the neuter clinic, and three-step of enzymatic digestion was applied to isolate Sertoli cells. We characterized the growth and purity of Sertoli cells with the expression of SOX9, GATA4, and Clusterin. In addition, we selected cadmium as a model toxicant to evaluate the toxic responses in the newly established Sertoli cells using High-content Analysis (HCA). With our optimized protocol, the purity of isolated Sertoli cells was above 95%, as determined with Sertoli cell-specific protein markers of SOX9 and GATA4. More importantly, primary Sertoli cell populations could be expanded rapidly in vitro, passaged (up to seven), and cryopreserved. The HCA-based assay revealed that cadmium at 1 μM induced both disruptions of cytoskeletal and DNA damage responses. Furthermore, we established an HCA assay with the newly isolated and optimized culture of canine Sertoli cells to evaluate the epigenetic markers of histone modification. We found cadmium-induced differential changes in histone modifications H3Me3K9, H3Me3K36, H4Me3K20, and H4acK5. In summary, we have established the standardized protocol to produce canine Sertoli cells with Sertoli cell-specific phenotype. The isolation and expansion of large quantities of canine Sertoli cells will provide broad applications in studying male infertility, reproductive toxicology, testicular cancer, and cell therapy.

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.

Di-(2-ethylhexyl) phthalate triggers DNA methyltransferase 1 expression resulting in elevated CpG-methylation and enrichment of MECP2 in the p21 promoter in vitro

Leaching of the plastic constituents leading to their chronic exposure to humans is a major concern for our environmental and occupational health. Our previous and other numerous studies have demonstrated that environmental chemicals like di (2-Ethylhexyl)-phthalate (DEHP) could pose a risk towards the epigenetic mechanisms. Yet, the mechanisms underlying its possible epigenotoxicity are poorly understood. We aimed to assess the impact of DEHP exposure to the human breast cancer cells (MCF-7) and resultant changes in DNA methylation regulators ultimately altering the expression of the cell cycle regulator p21 as a model gene. The MCF-7 cells were exposed to environmentally relevant concentrations (50-500 nM) for 24 h. The results showed that DEHP was proliferative towards the MCF-7 cells while it induced global DNA hypermethylation with selective upregulation of DNMT1 and MECP2. In addition, DEHP significantly reduced p53 protein and its enrichment to the DNMT1 promoter binding site, while elevating SP1 and E2F1 transcription factor levels, stimulating their binding to the promoter DNA. Coincidently, increased DNMT1 level was highly associated with loss of p21 expression and increased cyclin D1 levels. Importantly, the p21, but not cyclin D1 promoter CpG-dinucleotides were hypermethylated after exposure to 500 nM DEHP for 24 h. Furthermore, it was observed that DEHP significantly enriched DNMT1 and MECP2 to the p21 promoter to induce DNA methylation-based epigenetic silencing of p21, resulting in increased cell proliferation. Our results suggest DEHP could potentially induce the epigenetic alterations that might increase the risk of breast cancer, given that the underlying mechanisms should be fully elucidated.

Sevoflurane Offers Neuroprotection in a Cerebral Ischemia/Reperfusion Injury Rat Model Through the E2F1/EZH2/TIMP2 Regulatory Axis

Cerebral ischemia/reperfusion (I/R) injury contributes considerably to the poor prognosis in patients with ischemic stroke. This study is aimed to delineate the molecular mechanistic actions by which sevoflurane protects against cerebral I/R injury. A rat model of cerebral I/R injury was established and pre-treated with sevoflurane, in which hippocampal neuron apoptosis was found to be repressed and the level of E2F transcription factor 1 (E2F1) was observed to be down-regulated. Then, the up-regulated expression of E2F1 was validated in rats with cerebral I/R injury, responsible for stimulated neuron apoptosis. Further, the binding of E2F1 to enhancer of zeste homolog 2 (EZH2) and EZH2 to tissue inhibitor of metalloproteinases-2 (TIMP2) was identified. The stimulative effect of the E2F1/EZH2/TIMP2 regulatory axis on neuron apoptosis was subsequently demonstrated through functional assays. After that, it was substantiated in vivo that sevoflurane suppressed the apoptosis of hippocampal neurons in rats with cerebral I/R injury by down-regulating E2F1 to activate the EZH2/TIMP2 axis. Taken together, our data elucidated that sevoflurane reduced neuron apoptosis through mediating the E2F1/EZH2/TIMP2 regulatory axis, thus protecting rats against cerebral I/R injury.

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.

Rapamycin antagonizes cadmium-induced breast cancer cell proliferation and metastasis through directly modulating ACSS2

Cadmium (Cd) is a carcinogen that stimulates breast cancer (BC) progression. Rapamycin is a macrolide antibiotic produced by Streptomyces hygroscopicus that possesses a wide array of pharmacological activities, including anti-BC activity. However, the effects of rapamycin on Cd-increased BC progression and the underlying mechanism have not been fully elucidated. Here, we hypothesize that rapamycin antagonizes Cd-induced BC cell proliferation and metastasis by directly modulating ACSS2. In this study, we found that rapamycin efficiently inhibited Cd-induced proliferation, invasion and migration in MCF-7 and T47-D cells. Moreover, a surface plasmon resonance (SPR) assay confirmed that rapamycin directly binds to the ACSS2 protein with a calculated equilibrium dissociation constant (KD) of 18.3 μM. Molecular docking showed that there are three binding sites in the ACSS2 protein and that rapamycin binds at the coenzyme A (COA) binding site with a docking score of - 12.26 and a binding free energy of - 26.34 kcal/mol. More importantly, rapamycin suppresses Cd-induced BC progression by activating ACSS2. After cells were cotreated with an ACSS2 inhibitor, the effects of rapamycin were abolished. In conclusion, our findings suggest that rapamycin suppresses Cd-augmented BC progression by upregulating ACSS2, and ACSS2 may serve as a direct target of rapamycin for inhibiting xenobiotic (e.g., Cd)-mediated BC progression.

Gestational cadmium exposure impairs placental angiogenesis via activating GC/GR signaling

Gestational exposure to environmental Cd caused placental angiogenesis impairment and fetal growth restriction (FGR). However, its mechanism remained unclear. This study was to investigate the effects of Cd exposure during pregnancy on placental angiogenesis and its mechanism. Pregnant mice were exposed to CdCl2 (4.5 mg/kg) on gestational day (GD) 8 with or without melatonin (MT) (5.0 mg/kg), an anti-endoplasmic reticulum stress agent, from GD7 to GD15. Human primary placental trophoblasts and JEG-3 cells were stimulated using CdCl2 (20 μM) after MT (1 mM) preprocessing. We firstly found MT treatment obviously mitigated environmental Cd-induced placental angiogenesis disorder and reduction of the VEGF-A level. Mechanistically, MT reversed environmental Cd-downregulated the protein expression of VEGF-A via inhibiting glucocorticoid receptor (GR) activation. Notably, our data showed MT treatment antagonized Cd-activated GC/GR signaling via blocking PERK signaling and thereby upregulated VEGF-A and 11β-HSD2 protein expression. Based upon the population case-control study, the levels of VEGF-A and 11β-HSD2 protein in small-for-gestational-age placentae were significantly reduced when compared to appropriate-for-gestational-age placentae. Overall, environmental Cd exposure during gestation impaired placental angiogenesis via PERK-regulated GC/GR signaling in placental trophoblasts. Our findings will provide a basis for prevention and treatment of placental impairments and fetal growth restriction caused by environment toxicants in future.

Role of Autophagy in Cadmium-Induced Hepatotoxicity and Liver Diseases

Cadmium (Cd) is a toxic pollutant that is associated with several severe human diseases. Cd can be easily absorbed in significant quantities from air contamination/industrial pollution, cigarette smoke, food, and water and primarily affects the liver, kidney, and lungs. Toxic effects of Cd include hepatotoxicity, nephrotoxicity, pulmonary toxicity, and the development of various human cancers. Cd is also involved in the development and progression of fatty liver diseases and hepatocellular carcinoma. Cd affects liver function via modulation of cell survival/proliferation, differentiation, and apoptosis. Moreover, Cd dysregulates hepatic autophagy, an endogenous catabolic process that detoxifies damaged cell organelles or dysfunctional cytosolic proteins through vacuole-mediated sequestration and lysosomal degradation. In this article, we review recent developments and findings regarding the role of Cd in the modulation of hepatotoxicity, autophagic function, and liver diseases at the molecular level.

C-myc promotes miR-92a-2-5p transcription in rat ovarian granulosa cells after cadmium exposure

Cadmium (Cd) can induce ovarian injury by microRNAs (miRNAs), however, the molecular mechanism of miRNAs after Cd exposure have not known. In this study, 56-day-old adult female Sprague-Dawley (SD) rats were injection with PMSG, after 48 h, ovarian granulosa cells (GCs) were extracted and cultured for 24 h, then treated with 0, 2.5, 5, 10 and 20 μM Cd for 24 h. The results showed that expression levels of miR-92a-2-5p (upregulated) and Bcl2 (downregulated) changed significantly after Cd exposure. The messenger RNA (mRNA) and protein expression levels of DNMT1, DNMT3A, and DNMT3B had changed, but no obvious differences were found in miR-92a-2-5p single site methylation. The transcription factors C-MYC (upregulated), E2F1 (downregulated), and SP1 (downregulated), which target miRNAs significantly changed after exposure to Cd. The human ovarian GC tumor line (COV434) was used to knocked down C-myc, and the expression of miR-92a-2-5p was downregulated in the COV434-C-myc + 10 μM Cd group compared with COV434 cells. The N6-methyladenosine (m6A) methylation modification levels of long noncoding RNA (lncRNA) MT1JP and lncRNA CDKN2B-AS, which regulate miR-92a-2-5p were detected. In the 10 μM Cd group, m6A methylation levels at MT1JP-84, CDKN2B-AS-257, and CDKN2B-AS-329 were reduced. In summary, after Cd exposure, expression of miR-92a-2-5p, which targets the antiapoptotic gene Bcl2, was upregulated, which may be primarily related to upregulation of C-myc. MiR-92a-2-5p promoter DNA methylation may has no obvious effect on miR-92a-2-5p. Otherwise, the role of m6A methylation modified lncRNA MT1JP and lncRNA CDKN2B-AS in the regulation of miR-92a-2-5p needs further study.

Cadmium-Associated Molecular Signatures in Cancer Cell Models

The exposure of cancer cells to cadmium and its compounds is often associated with the development of more malignant phenotypes, thereby contributing to the acceleration of tumor progression. It is known that cadmium is a transcriptional regulator that induces molecular reprogramming, and therefore the study of differentially expressed genes has enabled the identification and classification of molecular signatures inherent in human neoplastic cells upon cadmium exposure as useful biomarkers that are potentially transferable to clinical research. This review recapitulates selected studies that report the detection of cadmium-associated signatures in breast, gastric, colon, liver, lung, and nasopharyngeal tumor cell models, as specifically demonstrated by individual gene or whole genome expression profiling. Where available, the molecular, biochemical, and/or physiological aspects associated with the targeted gene activation or silencing in the discussed cell models are also outlined.

Epimutational effects of electronic cigarettes

Electronic cigarettes (e-cigarettes), since they do not require tobacco combustion, have traditionally been considered less harmful than conventional cigarettes (c-cigarettes). In recent years, however, researchers have found many toxic compounds in the aerosols of e-cigarettes, and numerous studies have shown that e-cigarettes can adversely affect the human epigenome. In this review, we provide an update on recent findings regarding epigenetic outcomes of e-cigarette aerosols. Moreover, we discussed the effects of several typical e-cigarette ingredients (nicotine, tobacco-specific nitrosamines, volatile organic compounds, carbonyl compounds, and toxic metals) on DNA methylation, histone modifications, and noncoding RNA expression. These epigenetic effects could explain some of the diseases caused by e-cigarettes. It also reminds the public that like c-cigarettes, inhaling e-cigarette aerosols could also be accompanied with potential epigenotoxicity on the human body.

Facile synthesis and application of cellulosic coagulant from banana peels in cadmium-spiked water

Cellulosic coagulant with low crystallinity and surface charge of -19.2 mV were extracted from wet banana peels (WBE) using kitchen-blending method. Functionalization with ferric chloride and aluminium chloride yielded higher surface charge of -23.8 mV (mWBE). Both WBE and mWBE coagulants were used to target cadmium ions from aqueous solution. Coagulants and the floccules (WBEA and mWBEA) were characterized by XRD, FT-IR, zeta sizer nano series, and SEM/EDs. The amount of cadmium ion coagulated was determined using ICP-OES. The FTIR analysis revealed the functional groups involved in the coordination and subsequent removal of the metals ions around 1634 cm-1, ascribed to the C = O vibrational band of carbonyl group. Microscopic analysis revealed that the mWBE is porous and exhibited microfibers with rod-like morphology. The effects of parameters such as the initial concentration, coagulant dosage and solution pH were investigated. Coagulation results showed that 10 mg of WBE and mWBE could remove about 80% and 90% of the Cd2+ ions respectively. However; the difference in the performance of both materials does not justify the essence of surface modification. Therefore, WBE is considered more efficient and environmentally friendly. Notwithstanding, the performance of these coagulants in real environmental samples will confirm their robustness.

Toxicological Effects of Cadmium on Mammalian Testis

Cadmium is a heavy metal, and people are exposed to it through contaminated foods and smoking. In humans and other mammals, cadmium causes damage to male testis. In this review, we summarize the effects of cadmium on the development and function of the testis. Cadmium causes severe structural damage to the seminiferous tubules, Sertoli cells, and blood-testis barrier, thus leading to the loss of sperm. Cadmium hinders Leydig cell development, inhibits Leydig cell function, and induces Leydig cell tumors. Cadmium also disrupts the vascular system of the testis. Cadmium is a reactive oxygen species inducer and possibly induces DNA damage, thus epigenetically regulating somatic cell and germ cell function, leading to male subfertility/infertility.