Elevated tissue Cr levels, increased plasma oxidative markers, and global hypomethylation of blood DNA in male Sprague-Dawley rats exposed to potassium dichromate in drinking water

Oxidative damage, genetic and epigenetic alterations in hexavalent chromium exposed workers - A cross-sectional study within the SafeChrom project

BACKGROUND

Hexavalent chromium (Cr(VI)) is a lung cancer carcinogen. However, the genotoxic and mutagenic effects of Cr(VI) in humans at low-to-moderate occupational exposure levels are unknown. This study aims to investigate the relationship between occupational exposure to Cr(VI) and the presence of oxidative damage, genetic and epigenetic alterations.

METHODS

We included 113 Cr(VI) exposed workers in 14 companies and 72 controls recruited within the SafeChrom project. Cr(VI) was measured in inhalable dust and total chromium in urine (U-Cr) and red blood cells (RBC-Cr). Analysed effect biomarkers included urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), micronuclei in peripheral blood reticulocytes (MNRET), blood relative mitochondrial DNA copy number (mtDNA-cn), relative telomere length (TL), and blood DNA methylation of four lung cancer-related genes (F2RL3, LINE-1, MGMT promoter and SEMA4B).

RESULTS

The median inhalable Cr(VI) concentration among the exposed workers was 0.11 μg/m3 (5th-95th percentile: 0.02-8.44). Exposed workers showed higher 8-OHdG, TL, and MGMT promoter methylation levels and lower mtDNA-cn and MNRET compared with controls. Company-based differences in biomarkers were observed. Univariate analysis showed that TL was positively correlated with U-Cr, and 8-OHdG and MGMT promoter methylation were positively correlated with RBC-Cr. Multivariate analyses with adjustment for possible confounders showed higher 8-OHdG, TL, and MGMT promoter methylation in exposed workers compared with controls.

CONCLUSIONS

Low-to-moderate Cr(VI) exposure was associated with higher oxidative stress, longer telomeres and epigenetic alterations, changes that previously have been linked to lung cancer risk. This study highlights the molecular impacts of Cr(VI) exposure, underscoring the importance of reducing the exposure to Cr(VI).

Chromate Affects Gene Expression and DNA Methylation in Long-Term In Vitro Experiments in A549 Cells

Chromate has been shown to dysregulate epigenetic mechanisms such as DNA methylation, leading to changes in gene expression and genomic instability. However, most in vitro studies are limited to short incubation periods, although chronic exposure may be more relevant for both environmental and occupational exposure. In this study, human adenocarcinoma A549 cells were treated with 1, 2 or 5 µM chromate for 24 h and compared with incubations with 0.2, 0.5 or 1 µM chromate for 1 to 5 weeks. Chromium accumulated in a pronounced time- and concentration-dependent manner after short-term treatment, whereas a plateau of intracellular chromium content was observed after long-term treatment. While short-term treatment induced a G2 arrest of the cell cycle, this effect was not observed after long-term treatment at lower concentrations. The opposite was observed for global DNA methylation: while short-term treatment showed no effect of chromate, significant dose-dependent hypomethylation was observed in the long-term experiments. Time-dependent effects were also observed in a high-throughput RT-qPCR gene expression analysis, particularly in genes related to the inflammatory response and DNA damage response. Taken together, the results suggest specific differences in toxicity profiles when comparing short-term and long-term exposure to chromate in A549 cells.

An Update Overview on Mechanistic Data and Biomarker Levels in Cobalt and Chromium-Induced Neurodegenerative Diseases

There is increasing evidence that the imbalance of metals as cobalt (Co) and chromium (Cr) may increase the risk of development and progression of neurodegenerative diseases (NDDs). The human exposure to Co and Cr is derived mostly from industry, orthopedic implants, and polluted environments. Neurological effects of Co and Cr include memory deficit, olfactory dysfunction, spatial disorientation, motor neuron disease, and brain cancer. Mechanisms of Co and Cr neurotoxicity included DNA damage and genomic instability, epigenetic changes, mitochondrial disturbance, lipid peroxidation, oxidative stress, inflammation, and apoptosis. This paper seeks to overview the Co and Cr sources, the mechanisms by which these metals induce NDDs, and their levels in fluids of the general population and patients affected by NDDs. To this end, evidence of Co and Cr unbalance in the human body, mechanistic data, and neurological symptoms were collected using in vivo mammalian studies and human samples.

Effects of the SEMA4B gene on hexavalent chromium [Cr(VI)]-induced malignant transformation of human bronchial epithelial cells

Our previous study identified the potential of SEMA4B methylation level as a biomarker for hexavalent chromium [Cr(VI)] exposure. This study aimed to investigate the role of the SEMA4B gene in Cr(VI)-mediated malignant transformation of human bronchial epithelial (BEAS-2B) cells. In our population survey of workers, the geometric mean [95% confidence intervals (CIs)] of Cr in blood was 3.80 (0.42, 26.56) μg/L. Following treatment with various doses of Cr(VI), it was found that 0.5 μM had negligible effects on the cell viability of BEAS-2B cells. The expression of SEMA4B was observed to decrease in BEAS-2B cells after 7 days of treatment with 0.5 μM Cr(VI), and this downregulation continued with increasing passages of Cr(VI) treatment. Chronic exposure to 0.5 μM Cr(VI) enhanced the anchorage-independent growth ability of BEAS-2B cells. Furthermore, the use of a methylation inhibitor suppressed the Cr(VI)-mediated anchorage-independent growth in BEAS-2B cells. Considering that Cr levels exceeding 0.5 μM can be found in human blood due to occupational exposure, the results suggested a potential carcinogenic risk associated with occupational Cr(VI) exposure through the promotion of malignant transformation. The in vitro study further demonstrated that Cr(VI) exposure might inhibit the expression of the SEMA4B gene to promote the malignant transformation of BEAS-2B cells.

Geniposide alleviated hydrogen peroxide-induced apoptosis of human hepatocytes via altering DNA methylation

Geniposide (GP) is the homology of medicine and food with bioactive effects of antioxidation and resistance to apoptosis in the liver. It's of great significance to explore the biosafety exposure limits and action mechanisms of GP. This study detected the global DNA methylation microenvironment and the regulation of specific genes in GP against cellular apoptosis induced by hydrogen peroxide (H2O2) of human hepatocyte L-02 cells. The half inhibitory concentration (IC50) of GP on normal L-02 cells was 57.7 mg/mL. GP exerted new epigenetic activity, increased DNMT1, decreased TET1 and TET2 expression, and reversed the demethylation effect to some extent, thereby increasing the overall genomic DNA methylation level at the concentration of 900 μg/mL. GP pretreatment could also adjust the level of P53, Bcl-2 and AKT altered by H2O2, reducing their specific DNA methylation levels in the promoter regions of AKT and Bcl-2 to inhibit apoptosis. Taken together, GP regulates the global DNA methylation level and controls the expression changes of P53, Bcl-2 and AKT, jointly inhibiting the occurrence of apoptosis in human hepatocytes and providing the newly theoretical references for its safety evaluation.

Mechanisms of chromate carcinogenesis by chromatin alterations

In a dynamic environment, organisms must constantly mount an adaptive response to new environmental conditions in order to survive. Novel patterns of gene expression, driven by attendant changes in chromatin architecture, aid in adaptation and survival. Critical mechanisms in the control of gene transcription govern new spatiotemporal chromatin-chromatin interactions that make regulatory DNA elements accessible to the transcription factors that control the response. Consequently, agents that disrupt chromatin structure are likely to have a direct impact on the transcriptional programs of cells and organisms and to drive alterations in fundamental physiological processes. In this regard, hexavalent chromium (Cr(VI)) is of special interest because it interacts directly with cellular proteins, DNA, and other macromolecules, and is likely to upset cell functions that may cause generalized damage to the organism. Here, we will highlight chromium-mediated mechanisms that disrupt chromatin architecture and discuss how these mechanisms are integral to its carcinogenic properties. Emerging evidence indicates that Cr(VI) targets euchromatin, particularly in genomic locations flanking the binding sites of the essential transcription factors CTCF and AP1, and, in so doing, they disrupt nucleosomal architecture. Ultimately, the ensuing changes, if occurring in critical regulatory domains, may establish a new chromatin state, either toxic or adaptive, that will be governed by the corresponding gene transcription changes in key biological processes associated with that state.

The role of ageing and oxidative stress in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the primary cause of intervertebral disc (IVD) disease. With the increased ageing of society, an increasing number of patients are plagued by intervertebral disc disease. Ageing not only accelerates the decreased vitality and functional loss of intervertebral disc cells but also increases intracellular oxidative stress. Moreover, the speed of intervertebral disc ageing is also linked to high levels of reactive oxygen species (ROS) production. Not only is the production of ROS increased in ageing intervertebral disc cells, but antioxidant levels in degenerative intervertebral discs also decrease. In addition to the intervertebral disc, the structural components of the intervertebral disc matrix are vulnerable to oxidative damage. After chronic mitochondrial dysfunction, ROS can be produced in large quantities, while autophagy can eliminate these impaired mitochondria to reduce the production of ROS. Oxidative stress has a marked impact on the occurrence of IDD. In the future, IDD treatment is aiming to improve oxidative stress by regulating the redox balance in intervertebral disc cells. In summary, ageing and oxidative stress promote the degeneration of IVD, but further basic and clinical trials are needed to determine how to treat oxidative stress. At present, although there are many in-depth studies on the relationship between oxidative stress and degeneration of intervertebral disc cells, the specific mechanism has not been elucidated. In this paper, the main causes of intervertebral disc diseases are studied and summarized, and the impact of oxidative stress on intervertebral disc degeneration is studied.

Countrywide Spatial Variation of Potentially Toxic Element Contamination in Soils of Turkey and Assessment of Population Health Risks for Nondietary Ingestion

Countrywide surface soil concentrations of potentially toxic elements (PTEs) in Turkey were reviewed in the Web of Science database. A total of 93 papers were investigated to compose a PTE dataset for determining spatial variations and estimating exposure and health risks. Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were selected as PTEs in surface soil. A compiled PTE concentration dataset was used to estimate chronic toxic risks (CTRs) and carcinogenic risks (CRs) according to the deterministic and probabilistic approaches. While the CTR and CR levels of age and sex groups were estimated using a deterministic approach, population risks were estimated using a probabilistic approach. CTR and CR levels in lower age groups and female sex groups were estimated to be higher than those in higher age groups and associated male sex groups. The average CTR levels of the nondietary ingestion of As-containing soil in <11 year age groups were near/just above the threshold level, while As-associated average CR levels of adults and other age groups were estimated to be in the acceptable risk range (10^-6 < CR < 10^-5) and low priority risk range (10^-5 < CR < 10^-4), respectively. As-, Cr(VI)-, and Pb-associated upper-bound CR levels of the Turkish population were simulated to be 5.14 × 10^-4, 6.23 × 10^-5, and 2.34 × 10^-6, respectively. Health risk models show the significance of As in both chronic toxic and carcinogenic effects.

Epigenetic and epitranscriptomic mechanisms of chromium carcinogenesis

Hexavalent chromium [Cr(VI)], a Group I carcinogen classified by the International Agency for Research on Cancer (IARC), represents one of the most common occupational and environmental pollutants. The findings from human epidemiological and laboratory animal studies show that long-term exposure to Cr(VI) causes lung cancer and other cancer. Although Cr(VI) is a well-recognized carcinogen, the mechanism of Cr(VI) carcinogenesis has not been well understood. Due to the fact that Cr(VI) undergoes a series of metabolic reductions once entering cells to generate reactive Cr metabolites and reactive oxygen species (ROS) causing genotoxicity, Cr(VI) is generally considered as a genotoxic carcinogen. However, more and more studies have demonstrated that acute or chronic Cr(VI) exposure also causes epigenetic dysregulations including changing DNA methylation, histone posttranslational modifications and regulatory non-coding RNA (microRNA and long non-coding RNA) expressions. Moreover, emerging evidence shows that Cr(VI) exposure is also capable of altering cellular epitranscriptome. Given the increasingly recognized importance of epigenetic and epitranscriptomic dysregulations in cancer initiation and progression, it is believed that Cr(VI) exposure-caused epigenetic and epitranscriptomic changes could play important roles in Cr(VI) carcinogenesis. The goal of this chapter is to review the epigenetic and epitranscriptomic effects of Cr(VI) exposure and discuss their roles in Cr(VI) carcinogenesis. Better understanding the mechanism of Cr(VI) carcinogenesis may identify new molecular targets for more efficient prevention and treatment of cancer resulting from Cr(VI) exposure.

Dynamic Alteration Profile and New Role of RNA m6A Methylation in Replicative and H2O2-Induced Premature Senescence of Human Embryonic Lung Fibroblasts

N6-methyladenosine (m6A) methylation is one of the most common RNA modifications, regulating RNA fate at the posttranscriptional level, and is closely related to cellular senescence. Both models of replicative and premature senescence induced by hydrogen peroxide (H₂O₂) were used to detect m6A regulation during the senescence of human embryonic lung fibroblasts (HEFs). The ROS level accumulated gradually with senescence, leading to normal replicative senescence. H₂O₂-treated cells had dramatically increased ROS level, inducing the onset of acute premature senescence. Compared with replicative senescence, ROS changed the expression profiles for m6A-related enzymes and binding proteins, including higher levels of METTL3, METTL14, WTAP, KIAA1429, and FTO, and lower levels of METTL16, ALKBH5, YTHDC1, and YTHDF1/2/3 in the premature senescence persistence group, respectively. Meanwhile, senescent cells decreased total m6A content and RNA methylation enzymes activity, regardless of replicative or premature senescence. Moreover, specific m6A methylation levels regulated the expression of SIRT3, IRS2, and E2F3 between replicative and premature senescence separately. Taken together, differential m6A epitranscription microenvironment and the targeted genes can be used as epigenetic biomarkers to cell senescence and the related diseases, offering new clues for the prevention and intervention of cellular senescence.

Low-dose hexavalent chromium(VI) exposure promotes prostate cancer cell proliferation by activating MAGEB2-AR signal pathway

Hexavalent chromium [Cr(VI)], one common environmental contaminant, has long been recognized as a carcinogen associated with several malignancies, such as lung cancer, but little information was available about the effects of its low-dose environmental exposure in prostate cancer. Our previous study has shown that low-dose Cr(VI) exposure could promote prostate cancer(PCa) cell growth in vitro and in vivo. In the present study, we furthermore found that low-dose Cr(VI) exposure could induce DNA demethylation in PCa cells. Based on our transcriptome sequencing data and DNA methylation database, we further identified MAGEB2 as a potential effector target that contributed to tumor-promoting effect of low-dose Cr(VI) exposure in PCa. In addition, we demonstrated that MAGEB2 was upregulated in PCa and its knockdown restrained PCa cell proliferation and tumor growth in vitro and in vivo. Moreover, Co-IP and point mutation experiments confirmed that MAGEB2 could bind to the NH₂-terminal NTD domain of AR through the F-box in the MAGE homology domain, and then activated AR through up-regulating its downstream targets PSA and NX3.1. Together, low-dose Cr(VI) exposure can induce DNA demethylation in prostate cancer cells, and promote cell proliferation via activating MAGEB2-AR signaling pathway. Thus, inhibition of MAGEB2-AR signaling is a novel and promising strategy to reverse low-dose Cr(VI) exposure-induced prostate tumor progression, also as effective adjuvant therapy for AR signaling-dependent PCa.

Children Environmentally Exposed to Agrochemicals in Rural Areas Present Changes in Oxidative Status and DNA Damage

Rural children are exposed to several chemicals. This study evaluated the environmental co-exposure of rural children to cholinesterase inhibitor insecticides and metals/metalloids, and the resulting oxidative stress and DNA damage. Seventy-two children (5 to 16 years old) were studied at two different moments: period 1, when agrochemicals were less used, and period 2, when agrochemicals were extensively used in agriculture. Biomonitoring was performed by evaluating butyrylcholinesterase (BuChE) activity in serum; arsenic (As), chromium (Cr), lead (Pb), and nickel (Ni) levels in blood; malondialdehyde (MDA) in plasma; glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) activities in whole blood; non-protein thiol levels in erythrocytes; and micronuclei (MN) assay in exfoliated buccal cells. Cr and As levels were higher than the reference values in both periods, and Ni levels were higher than the reference values in period 2 alone. BuChE activity was inhibited in period 2 compared with period 1. In period 2, there was an increase in endogenous antioxidants and a decrease in MDA, probably demonstrating a compensatory mechanism as a response to increasing xenobiotics. Also in period 2, the MN frequency increased and BuChE and As were positively associated, suggesting co-exposure. On the other hand, in period 1, it was observed that Cr, Ni, and Pb blood levels were negatively associated with GSH-Px and GST, while MDA was positively associated with As levels. Our findings demonstrated an imbalance in endogenous antioxidants, contributing to genotoxicity and lipoperoxidation, probably in response to exposure to xenobiotics, especially carcinogenic elements (Cr, As, and Ni).

Redox sensitive miR-27a/b/Nrf2 signaling in Cr(VI)-induced carcinogenesis

Hexavalent chromium [Cr(VI)] is a well-known carcinogen that can cause several types of cancer including lung cancer. NF-E2-related factor 2 (Nrf2), the redox sensitive transcription factor, can protect normal cells from a variety of toxicants and carcinogens by inducing the expression of cellular protective genes and maintaining redox balance. However, Nrf2 also protects cancer cells from radio- and chemo-therapies and facilitates cancer progression. Although Cr(VI) treatment has been demonstrated to upregulate Nrf2 expression, the mechanisms for Nrf2 regulation upon chronic Cr(VI) exposure remain to be elucidated. We found that Nrf2 was upregulated in BEAS-2B cells exposed to Cr(VI) from 1 to 5 months, and also in Cr(VI)-induced transformed (Cr-T) cells with Cr(VI) treatment for 6 months. We showed that KEAP1, the classic negative regulator of Nrf2, was downregulated after Cr(VI) exposure for 4 months, suggesting that Nrf2 induction by Cr(VI) treatment is through KEAP1 decrease at late stage. To further decipher the mechanisms of Nrf2 upregulation at early stage of Cr(VI) exposure, we demonstrated that miR-27a and miR-27b were redox sensitive miRNAs, since reactive oxygen species (ROS) scavengers induced miR-27a/b expression. After Cr(VI) exposure for 1 month, the expression levels of miR-27a/b was dramatically decreased. The changes of miR-27a/b and their target Nrf2 were confirmed in vivo by mouse model intranasally exposed to Cr(VI) for 12 weeks. Nrf2 was a direct target of miR-27a/b, which acted as tumor suppressors in vitro and in vivo to inhibit tumorigenesis and cancer development of Cr-T cells. The results suggested that the inhibition of miR-27a/b was responsible for Nrf2 upregulation at both early stage and late stage of Cr(VI) exposure. This novel regulation of Nrf2 upon chronic Cr(VI) exposure through redox-regulated miR-27a/b will provide potential targets for preventing and treating Cr(VI)-induced carcinogenesis in the future.

The Role of Oxidative Stress in Intervertebral Disc Degeneration

Intervertebral disc degeneration is a very common type of degenerative disease causing severe socioeconomic impact, as well as a major cause of discogenic low back pain and herniated discs, placing a heavy burden on patients and the clinicians who treat them. IDD is known to be associating with a complex process involving in extracellular matrix and cellular damage, and in recent years, there is increasing evidence that oxidative stress is an important activation mechanism of IDD and that reactive oxygen and reactive nitrogen species regulate matrix metabolism, proinflammatory phenotype, autophagy and senescence in intervertebral disc cells, apoptosis, autophagy, and senescence. Despite the tremendous efforts of researchers within the field of IDD pathogenesis, the proven strategies to prevent and treat this disease are still very limited. Up to now, several antioxidants have been proved to be effective for alleviating IDD. In this article, we discussed that oxidative stress accelerates disc degeneration by influencing aging, inflammation, autophagy, and DNA methylation, and summarize some antioxidant therapeutic measures for IDD, indicating that antioxidant therapy for disc degeneration holds excellent promise.

Hexavalent chromium disrupts chromatin architecture

Accessibility of DNA elements and the orchestration of spatiotemporal chromatin-chromatin interactions are critical mechanisms in the regulation of gene transcription. Thus, in an ever-changing milieu, cells mount an adaptive response to environmental stimuli by modulating gene expression that is orchestrated by coordinated changes in chromatin architecture. Correspondingly, agents that alter chromatin structure directly impact transcriptional programs in cells. Heavy metals, including hexavalent chromium (Cr(VI)), are of special interest because of their ability to interact directly with cellular protein, DNA and other macromolecules, resulting in general damage or altered function. In this review we highlight the chromium-mediated mechanisms that promote disruption of chromatin architecture and how these processes are integral to its carcinogenic properties. Emerging evidence shows that Cr(VI) targets nucleosomal architecture in euchromatin, particularly in genomic locations flanking binding sites of the essential transcription factors CTCF and AP1. Ultimately, these changes contribute to an altered chromatin state in critical gene regulatory regions, which disrupts gene transcription in functionally relevant biological processes.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Assessment of Mechanistic Data for Hexavalent Chromium-Induced Rodent Intestinal Cancer Using the Key Characteristics of Carcinogens

Oral exposure to hexavalent chromium (Cr[VI]) induces intestinal tumors in mice. Mutagenic and nonmutagenic modes of action (MOAs) have been accepted by different regulatory bodies globally, the latter involving cytotoxicity-induced regenerative cell proliferation. However, concerns persist that all possible MOAs have not been fully considered. To address the potential for alternative MOAs, mechanistic data not represented in the existing two MOAs were evaluated. Relevant data were identified and organized by key characteristics of carcinogens (KCCs); literature related to epigenetics, immunosuppression, receptor-mediated effects, and immortalization were reviewed to identify potential key events associated with an alternative MOA. Over 200 references were screened for these four KCCs and further prioritized based on relevance to the research objective (ie, in vivo, oral exposure, gastrointestinal tissue). Minimal data were available specific to the intestine for these KCCs, and there was no evidence of any underlying mechanisms or key events that are not already represented in the two proposed MOAs. For example, while epigenetic dysregulation of DNA repair genes has been demonstrated, epigenetic effects were not measured in intestinal tissue, and it has been shown that Cr(VI) does not cause DNA damage in intestinal tissue. High-throughput screening data related to the KCCs were also evaluated, with activity generally limited to the two recognized MOAs. Collectively, no plausible alternative MOAs (or key events) were identified in addition to those previously proposed for Cr(VI) small intestine tumors.

Novel DNA methylation biomarkers for hexavalent chromium exposure: an epigenome-wide analysis

Aim: We aimed to identify differential methylation of genes that could illuminate the biological mechanisms of chromium (VI) toxicity in this exposure-control study. Materials & methods: DNA methylation was measured in blood samples collected from electroplating workers and controls using a combination of Infinium Methylation450K Chip and targeted-bisulfite sequencing. QuantiGene assay was used to detect the mRNA expression of differentially methylated genes. Inductively coupled plasma–mass spectrometry was used to quantify metals in blood and urine samples. The cytosine–phosphate–guanine sites methylation and gene expression were confirmed in a human lymphoblastoid cell line. Results & conclusion: A total of 131 differentially methylated cytosine–phosphate–guanine sites were found between exposures and controls. DNA methylation of SEMA4B may serve as a potential biomarker for chromium (VI) exposure.

Body burdens of heavy metals associated with epigenetic damage in children living in the vicinity of a municipal waste incinerator

To evaluate the body burdens of heavy metals correlated with health impact on school-age children living around a waste incinerator. A total of 81 children from the exposure area and 95 from the control area were recruited in our study. We measured the blood levels of chromium (Cr), cadmium (Cd) and lead (Pb) by an inductively coupled plasma mass spectrometer (ICP-MS), conducted comet assays, calculated the percentage of 5-methylcytosine (5 mC) and 5-hydroxymethylcytosine (5hmC) by MethylFlash methylated and a hydroxymethylated DNA quantification kit, and performed the flow cytometry to detect the expressions of surface antigens (including CD3⁺, CD19⁺, CD3⁺CD4⁺, CD3⁺CD8⁺, and CD3^-CD16⁺ and/or CD56⁺) in peripheral lymphocytes. Besides, we measured hormonal levels, including triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH), and analyzed several regular hematological parameters. In addition, concentrations of heavy metals in environmental samples including rice, soils, vegetables, and drinking water were detected by ICP-MS. The mean blood levels of Cr, Cd, and Pb in the exposure group were all statistically higher than in the control group (2.57 vs. 0.79 μg/L; 1.83 vs. 1.81 μg/L; 44.00 vs. 32.31 μg/L, p < 0.01). The 5 mC and 5hmC levels in the exposure group were statistically lower (1.15% vs. 4.14%; 0.22% vs. 0.30%, p < 0.01), whereas the mean level of % tail DNA was statistically higher (10.10% vs. 8.62%, p < 0.01). Furthermore, the mean blood level of Cr and Pb was negatively correlated with the level of 5 mC (r = -0.279, r = -0.190, P < 0.05) in total population. In conclusion, children living in the vicinity of the municipal waste incinerator suffered increased body burdens of heavy metals (Cr, Cd, and Pb) associated with genotoxicity and epigenetic modifications.

Chromium exposure disrupts chromatin architecture upsetting the mechanisms that regulate transcription

IMPACT STATEMENT

This mini-review highlights current evidence on the mechanisms through which hexavalent chromium (Cr(VI)) disrupts transcriptional regulation, an emerging area of interest and one of the central processes by which chromium induces carcinogenesis. Several studies have shown that Cr(VI) causes widespread DNA damage and disrupts epigenetic signatures, suggesting that chromatin may be a direct Cr(VI) target. The findings discussed here suggest that Cr(VI) disrupts transcriptional regulation by causing genomic architecture changes.

Mechanisms of Chromium-Induced Toxicity

Chromium is a pervasive environmental contaminant that is of great importance because of its toxicity. Hexavalent chromium is a classified group 1 carcinogen with multiple complex mechanisms by which it triggers cancer development. Increased levels of oxidative stress, chromosome breaks, and DNA-adduct formation are some of the major mechanisms by which C(VI) causes cellular damage. Trivalent chromium is another species of chromium that is described as a non-essential metal, and is used in nutritional supplementation. Evidence on nutritional benefit is conflicting which could suggest that humans absorb enough Cr(III) from diet alone, and that extra supplementation is not necessary. This review highlights the differences between Cr(VI) and Cr(III) from a chemical and toxicological perspective, describes short-comings in nutritional research of Cr(III), and explains the multiple mechanisms by which Cr(VI) is involved in the process of carcinogenesis.

DNA methylation modifications induced by hexavalent chromium

Hexavalent chromium [Cr (VI)] contributes a significant health risk and causes a number of chronic diseases and cancers. While the genotoxic and carcinogenic effects of hexavalent chromium exposure are explicit and better-characterized, the exact mechanism underlying the carcinogenic process of Cr (VI) is still a matter of debate. In recent years, studies have shown that epigenetic modifications, especially DNA methylation, may play a significant role in Cr (VI)-induced carcinogenesis. The aim of this review is to summarize our understanding regarding the effects of Cr (VI) on global and gene-specific DNA methylation.

Concentration of chromium in whole blood and erythrocytes showed different relationships with serum apolipoprotein levels in Cr(VI) exposed subjects

OBJECTIVE

To explore the effects of hexavalent chromium [Cr(VI)] on apolipoprotein(Apo) metabolism.

METHODS

One hundred and six long-term Cr(VI) exposed subjects and fifty five non-exposed individuals were recruited. The blood metals, glucose and lipid parameters were measured to evaluate the effects of hexavalent chromium on the apolipoproteins.

RESULTS

The quantity and homeostasis of multi-elements were significantly different between Cr(VI)exposed subjects and the controls(P < 0.05). The levels of serum TG, FPG, LDL-C, Apo AI, AII, CII, CIII, E and Lp(a) also changed significantly (P < 0.05). Concentration of chromium in whole blood and erythrocytes had different relationships with serum apolipoprotein levels in Cr(VI)exposed subjects.

CONCLUSIONS

Exposure of hexavalent chromium could significantly change the homeostasis of multi-elements as well as the levels of serum apolipoproteins. Cr(III) and Cr(VI)may have different effects on the apolipoproteins.

Cr(VI)-induced methylation and down-regulation of DNA repair genes and its association with markers of genetic damage in workers and 16HBE cells

To examine the mechanism of hexavalent chromium [Cr(VI)]-induced carcinogenesis, a cross-sectional study in workers with or without exposure to Cr(VI) as well as in vitro administration of Cr(VI) in 16HBE cells was conducted. We explored the associations between Cr(VI) exposure, methylation modification of DNA repair genes and their expression levels, and genetic damage. Results showed that hypermethylation of CpG sites were observed in both occupationally exposed workers and 16HBE cells administrated Cr(VI). DNA damage markers including 8-hydroxydeoxyguanosine (8-OHdG) and micronucleus frequency in Cr(VI)-exposed workers were significantly higher than the control group. Among workers, blood Cr concentration was positively correlaed with the methylation level of CpG sites in DNA repair genes including CpG6,7, CpG8, CpG9,10,11 of MGMT, CpG11 of HOGG1; CpG15,16,17, CpG19 of RAD51, and genetic damage markers including 8-OHdG and micronucleus frequency. Significant negative association between methylation levels of CpG sites in DNA repair genes and corresponding mRNA was also observed in 16HBE cells. This indicated that Cr(VI) exposure can down-regulate DNA repair gene expression by hypermethylation, which leads to enhanced genetic damage. The methylation level of these CpG sites of DNA repair genes can be potential epigenetic markers for Cr(VI)-induced DNA damage.

ROS, Cell Senescence, and Novel Molecular Mechanisms in Aging and Age-Related Diseases

The aging process worsens the human body functions at multiple levels, thus causing its gradual decrease to resist stress, damage, and disease. Besides changes in gene expression and metabolic control, the aging rate has been associated with the production of high levels of Reactive Oxygen Species (ROS) and/or Reactive Nitrosative Species (RNS). Specific increases of ROS level have been demonstrated as potentially critical for induction and maintenance of cell senescence process. Causal connection between ROS, aging, age-related pathologies, and cell senescence is studied intensely. Senescent cells have been proposed as a target for interventions to delay the aging and its related diseases or to improve the diseases treatment. Therapeutic interventions towards senescent cells might allow restoring the health and curing the diseases that share basal processes, rather than curing each disease in separate and symptomatic way. Here, we review observations on ROS ability of inducing cell senescence through novel mechanisms that underpin aging processes. Particular emphasis is addressed to the novel mechanisms of ROS involvement in epigenetic regulation of cell senescence and aging, with the aim to individuate specific pathways, which might promote healthy lifespan and improve aging.