Role of reactive oxygen species in arsenic-induced transformation of human lung bronchial epithelial (BEAS-2B) cells

Arsenic-Induced Inflammatory Response via ROS-Dependent Activation of ERK/NF-kB Signaling Pathways: Protective Role of Natural Polyphenol Tannic Acid

Arsenic (As), a highly toxic metalloid, is present throughout our environment as a result of both natural and human-related activities. Furthermore, As exposure could lead to a persistent inflammatory response, which may facilitate the pathogenesis of several diseases in various organs. This study was performed to investigate the As-induced inflammatory response and the underlying molecular mechanisms in vitro. Further, the anti-inflammatory effects of a natural dietary polyphenol tannic acid (TA) were also explored. In human normal bronchial (BEAS-2B), adenocarcinoma alveolar basal (A549), and murine macrophages (J774) cell lines, a trivalent form of As (as As3+) exposure markedly induced the expression of various pro-inflammatory mediators (cytokines and chemokines). Additionally, it was found that As3+ exposure induced reactive oxygen species (ROS) generation and activation of the nuclear factor-kappa B (NF-kB) p65 and extracellular signal-regulated kinase (ERK)1/2 pathways in BEAS-2B cells. As expected, the blockade of either ERK1/2 (PD98059) or NF-kB p65 (IMD0354), or both pathways attenuated As3+-induced pro-inflammatory mediators release. Interestingly, pre-treatment with ROS inhibitor N-acetylcysteine (NAC) attenuated activation of ERK/NF-kB pathways, suggesting that ROS have a critical role in pathway's activation and subsequent inflammatory response. Further, TA pre-treatment effectively attenuated As3+-induced inflammatory response by suppressing ROS production and ERK/NF-kB signaling pathways activation. Therefore, this study provides scientific evidence for the anti-inflammatory activities of TA and the underlying molecular mechanisms.

Environmental contamination of arsenic: pathway analysis through water-soil-feed-livestock in Nadia District (India) and potential human health risk

This study investigated arsenic (As) concentrations in diverse environmental components and their potential impact on the health risks faced by residents of the arsenic (As)-contaminated Nadia district in West Bengal, India. A random selection of 182 cattle and 255 goats from 40 livestock farmers in the district revealed that both animals and humans were naturally exposed to elevated arsenic levels through contaminated drinking water, foods, grasses, concentrate feeds, various fodder tree leaves, and other food/feed resources. The mean As concentration in roughages (483.18 µg/kg DM) was significantly higher (p < 0.001) than in tree leaves (391.53 µg/kg DM), and concentrate feed/ingredients (186.66 µg/kg DM). Pond water exhibited higher arsenic levels (106.11 µg/L) compared to shallow tube well water (47.96 µg/L) and deep tube well water/tap water (10.64 µg/L and 10.04 µg/L, respectively). The mean arsenic concentration in soils DM of fodder fields, crop fields, and grassland was 10.25, 10.58, and 10.20 mg/kg, respectively. It was observed that protein-rich feeds had lower levels of arsenic accumulation (p < 0.048), while fiber-rich feeds containing more cellulose, hemicellulose, and lignin had higher arsenic levels (p < 0.017). Goats consumed 73.46% more arsenic per kg body weight compared to dairy cows. Although chronic and sub-chronic arsenic exposure in the district did not typically manifest symptoms or visible signs in ruminant animals, concentrations in the hair and feces of both cattle and goats exceeded normal values. Cattle feces had significantly higher arsenic (410.43 µg/kg DM) levels (p < 0.001) than goat feces (227.00 µg/kg DM), and arsenic concentration in cattle hair (1917.74 µg/kg DM) was also significantly greater (p < 0.001) than goat hair (1435.74 µg/kg DM). Arsenic levels in milk samples from both species were below 10 µg/kg. Liver (356.02 µg/kg DM) and kidney (317.22 µg/kg DM) contained significantly higher (p < 0.001) levels of arsenic compared to muscle (204.23 µg/kg DM), and bone (161.98 µg/kg DM) in local meat-type adult male goats. The skin accumulated the highest amount of arsenic (576.24 µg/kg DM) among the non-edible parts of the goat carcass. The cumulative cancer risk value for adults was 4.96 × 10-3, exceeding the threshold value (1 × 10-6). This suggests a significant risk of cancer development for the population in arsenic-affected areas. Non-cancer risks (hazard indexes) were estimated at 11.01 for adults. Our observations revealed that the highest bioaccumulation of arsenic occurred in the hair of cows, and goats in the examined localities. The biotransformation factor (BTF) for hair was much higher compared to other excreted samples from both species. The calculated BTF followed the order: hair > feces > milk for cows and goats. Livestock farmers in Nadia district are advised to carefully select feed resources, prioritizing those high in crude protein and low in neutral detergent fiber, and they should provide drinking water from deep aquifers to ensure the safety of milk and meat for human consumption.

Oral arsenite exposure induces inflammation and apoptosis in pulmonary tissue: acute and chronic evaluation in young and adult mice

Inorganic arsenic is a well-known environmental toxicant, and exposure to this metalloid is strongly linked with severe and extensive toxic effects in various organs including the lungs. In the present study, we aimed to investigate the acute and chronic effects of arsenite exposure on pulmonary tissue in young and adult mice. In brief, young and adult female Balb/C mice were exposed to 3 and 30 ppm arsenite daily via drinking water for 30 and 90 days. Subsequently, the animals were sacrificed and various histological and immunohistochemistry (IHC) analyses were performed using lung tissues. Our findings showed arsenite was found to cause dose-dependent pathological changes such as thickening of the alveolar septum, inflammatory cell infiltrations and lung fibrosis in young and adult mice. In addition, arsenite exposure significantly increased the expression of inflammatory markers NF-κB and TNF-α, indicating that arsenite-exposed mice suffered from severe lung inflammation. Moreover, the IHC analysis of fibrotic proteins demonstrated an increased expression of TGF-β1, α-SMA, vimentin and collagen-I in the arsenite-exposed mice compared to the control mice. This was accompanied by apoptosis, which was indicated by the upregulated expression of caspase-3 in arsenite-exposed mice compared to the control. Adult mice were generally found to be more prone to arsenite toxicity during chronic exposure relative to their younger counterparts. Overall, our findings suggest that arsenite in drinking water may induce dose-dependent and age-dependent structural and functional impairment in the lungs through elevating inflammation and fibrotic proteins.

N6-methyladenosine promotes aberrant redox homeostasis required for arsenic carcinogenesis by controlling the adaptation of key antioxidant enzymes

N6-methyladenosine (m6A), a high-profile RNA epigenetic modification, responds to oxidative stress and temporal-specifically mediates arsenic carcinogenesis. However, how m6A affects aberrant redox homeostasis required for arsenic carcinogenesis is poorly understood. Here, we established arsenic-carcinogenic models of different stages, including As-treated, As-transformed, and As-tumorigenic cell models. We found that arsenic-induced reactive oxygen species (ROS) elevated m6A levels, thus triggering m6A-dependent antioxidant defenses. During arsenic-induced cell transformation, METTL3-upregulated m6A on the mRNAs of SOD1, SOD2, CAT, TXN, and GPX1 promoted the mRNA translation and protein expressions of these antioxidant enzymes by increasing YTHDF1-mediated mRNA stability. Meanwhile, FTO-downregulated m6A on PRDX5 mRNA increased PRDX5 translation and expression by reducing YTHDF2-mediated mRNA decay. After upregulated antioxidant defenses balanced with high levels of ROS induced by arsenic, the m6A balance formed in mRNAs of six key antioxidant enzymes (SOD1, SOD2, CAT, TXN, GPX1, and PRDX5) and promoted high expressions of these antioxidant enzymes to maintain aberrant redox homeostasis. METTL3 inhibitor STM2457, FTO inhibitor FB23-2, or YTHDF1 knockdown disturbed the aberrant redox homeostasis by breaking the m6A balance, causing cell death in arsenic-induced tumors. Our results demonstrated that m6A promotes the formation and maintenance of aberrant redox homeostasis required for arsenic carcinogenesis by time-dependently orchestrating the adaptive expressions of six key m6A-targeted antioxidant enzymes. This study advances our understanding of arsenic carcinogenicity from the novel aspect of m6A-dependent adaptation to arsenic-induced oxidative stress.

Dose-Dependent Effect of Mitochondrial Superoxide Dismutase Gene Overexpression on Radioresistance of HEK293T Cells

Over the last two decades, a multitude of gain-of-function studies have been conducted on genes that encode antioxidative enzymes, including one of the key enzymes, manganese superoxide dismutase (SOD2). The results of such studies are often contradictory, as they strongly depend on many factors, such as the gene overexpression level. In this study, the effect of altering the ectopic expression level of major transcript variants of the SOD2 gene on the radioresistance of HEK293T cells was investigated using CRISPRa technology. A significant increase in cell viability in comparison with the transfection control was detected in cells with moderate SOD2 overexpression after irradiation at 2 Gy, but not at 3 or 5 Gy. A further increase in the level of SOD2 ectopic expression up to 22.5-fold resulted in increased cell viability detectable only after irradiation at 5 Gy. Furthermore, a 15-20-fold increase in SOD2 expression raised the clonogenic survival of cells after irradiation at 5 Gy. Simultaneous overexpression of genes encoding SOD2 and Catalase (CAT) enhanced clonogenic cell survival after irradiation more effectively than separate overexpression of both. In conjunction with the literature data on the suppression of the procarcinogenic effects of superoxide dismutase overexpression by ectopic expression of CAT, the data presented here suggest the potential efficacy of simultaneous overexpression of SOD2 and CAT to reduce oxidative stress occurring in various pathological processes. Moreover, these results illustrate the importance of selecting the degree of SOD2 overexpression to obtain a protective effect.

Malignant growth of arsenic-transformed cells depends on activated Akt induced by reactive oxygen species

Arsenic is an identified carcinogen for humans.In this study, chronic exposure of human hepatocyte L-02 to low-doses of inorganic arsenic caused cell malignant proliferation. Meanwhile, compared with normal L-02 cells, arsenic-transformed malignant cells, L-02-As displayed more ROS and significantly higher Cyclin D1 expression as well as aerobic glycolysis. Moreover, Akt activation is followed by the upregulation of Cyclin D1 and HK2 expression in L-02-As cells, since inhibition of Akt activity by Ly294002 attenuated the colony formation in soft agar and decreased the levels of Cyclin D1 and HK2. In addition, scavenging of ROS by NAC resulted in a decreased expression of phospho-Akt, HK2 and Cyclin D1, and attenuates the ability of anchorage-independent growth ofL-02-As cells, suggested that ROS mediated the Akt activation in L-02-As cells. In summary, our results demonstrated that ROS contributes to the malignant phenotype of arsenic-transformed human hepatocyte L-02-As via the activation of Akt pathway.

Arsenic trioxide promotes ERK1/2-mediated phosphorylation and degradation of BIMEL to attenuate apoptosis in BEAS-2B cells

Inorganic arsenic is highly toxic, widely distributed in the human environment and may result in multisystem diseases and several types of cancers. The BCL-2-interacting mediator of cell death protein (BIM) is a key modulator of the intrinsic apoptosis pathway. Interestingly, in the present study, we found that arsenic trioxide (As₂O₃) decreased BIM_EL levels in human bronchial epithelial cell line BEAS-2B and increased BIM_EL levels in human lung carcinoma cell line A549 and mouse Sertoli cell line TM4. Mechanismly, the 26S proteasome inhibitors MG132 and bortezomib could effectively inhibit BIM_EL degradation induced by As₂O₃ in BEAS-2B cells. As₂O₃ activated extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways, but only the ERK1/2 MAPK inhibitor PD98059 blocked BIM_EL degradation induced by As₂O₃. Furthermore, As₂O₃ induced-phosphorylation of BIM_EL at multiple sites was inhibited by ERK1/2 MAPK inhibitor PD98059. Inhibition of As₂O₃-induced ERK1/2 MAPK phosphorylation increased the levels of BIM_EL and cleaved-caspase-3 proteins and decreased BEAS-2B cell viability. As₂O₃ also markedly mitigated tunicamycin-induced apoptosis of BEAS-2B cells by increasing ERK1/2 phosphorylation and BIM_EL degradation. Our results suggest that As₂O₃-induced activation of the ERK1/2 MAPK pathway increases phosphorylation of BIM_EL and promotes BIM_EL degradation, thereby alleviating the role of apoptosis in As₂O₃-induced cell death. This study provides new insights into how to maintain the survival of BEAS-2B cells before malignant transformation induced by high doses of As₂O₃.

Effects of Antioxidant Gene Overexpression on Stress Resistance and Malignization In Vitro and In Vivo: A Review

Reactive oxygen species (ROS) are normal products of a number of biochemical reactions and are important signaling molecules. However, at the same time, they are toxic to cells and have to be strictly regulated by their antioxidant systems. The etiology and pathogenesis of many diseases are associated with increased ROS levels, and many external stress factors directly or indirectly cause oxidative stress in cells. Within this context, the overexpression of genes encoding the proteins in antioxidant systems seems to have become a viable approach to decrease the oxidative stress caused by pathological conditions and to increase cellular stress resistance. However, such manipulations unavoidably lead to side effects, the most dangerous of which is an increased probability of healthy tissue malignization or increased tumor aggression. The aims of the present review were to collect and systematize the results of studies devoted to the effects resulting from the overexpression of antioxidant system genes on stress resistance and carcinogenesis in vitro and in vivo. In most cases, the overexpression of these genes was shown to increase cell and organism resistances to factors that induce oxidative and genotoxic stress but to also have different effects on cancer initiation and promotion. The last fact greatly limits perspectives of such manipulations in practice. The overexpression of GPX3 and SOD3 encoding secreted proteins seems to be the "safest" among the genes that can increase cell resistance to oxidative stress. High efficiency and safety potential can also be found for SOD2 overexpression in combinations with GPX1 or CAT and for similar combinations that lead to no significant changes in H₂O₂ levels. Accumulation, systematization, and the integral analysis of data on antioxidant gene overexpression effects can help to develop approaches for practical uses in biomedical and agricultural areas. Additionally, a number of factors such as genetic and functional context, cell and tissue type, differences in the function of transcripts of one and the same gene, regulatory interactions, and additional functions should be taken into account.

Urinary Arsenic Concentration and Its Relationship with Bronchial Asthma in Children from Arica, Chile

In the city of Arica, northern Chile, the population has been involuntarily exposed to arsenic of natural and anthropogenic origin. This study aims to evaluate the association between urinary arsenic concentration and bronchial asthma diagnosis in the children of Arica. A cross-sectional analysis of a database of 1892 subjects under 18 years of age enrolled in the Environmental Health Centre between 2009 and 2021 was carried out. Arsenic exposure was obtained from a urine sample and bronchial asthma diagnosis from the database of the system for the management of explicit health guarantees. Logistic regression models were used to assess the association between inorganic arsenic and asthma. The median inorganic arsenic was 15 μg/L, and the prevalence of asthma was 7.4%. After adjusting for sex, age, ethnicity, and urinary creatinine, children with the highest tertile of urinary arsenic concentration (≥21.4 μg/L) had a greater chance of developing asthma (odds ratio (OR) 1.90; 95% confidence interval (CI) [1.13-3.18]). When exploring the modifying effect of ethnicity, the association increased among children belonging to any ethnic group (OR 3.51, 95%CI [1.43-8.65]). These findings suggest a relationship between arsenic exposure and bronchial asthma in children. While further studies are needed to assess the impact of arsenic on respiratory health, mitigation efforts to reduce arsenic exposure should be maintained.

PIN1-mediated ROS production is involved in antagonism of N-acetyl-L-cysteine against arsenic-induced hepatotoxicity

Arsenic, a widely existing environmental contaminant, is recognized to be toxic to multiple organs. Exposure to arsenic results in liver damage via excessive production of reactive oxidative species (ROS). PIN1 regulates the levels of ROS. N-acetyl-L-cysteine (NAC) is an ROS scavenger that protects the hepatic functions. Whether PIN1 plays a regulatory role in NAC-mediated antagonism against arsenic hepatotoxicity remains largely unknown. In our study, the protective effects of NAC against arsenic (NaAsO2)-induced hepatotoxicity were evaluated in vitro and in vivo. Arsenic exposure induced cytotoxicity by increasing the intracellular ROS production, impairing mitochondrial function and inducing apoptosis in L02 hepatocytes. Overexpression of PIN1 markedly protected against arsenic cytotoxicity, decreased ROS levels, and mitigated mitochondrial dysfunction and apoptosis in L02 cells. However, loss of PIN1 further aggravated arsenic-induced cytotoxicity and abolished the protective effects of NAC in L02 cells. An in vivo study showed that pretreatment with NAC rescued arsenic-induced liver injury by restoring liver function and suppressing hepatic oxidative stress. Overexpression of PIN1 in mice transfected with AAV-Pin1 relieved arsenic-induced liver dysfunction and hepatic oxidative stress. Taken together, our study identified PIN1 as a novel intervention target for antagonizing arsenic-induced hepatotoxicity, highlighting a new pharmacological mechanism of NAC targeting PIN1 in antagonism against arsenic toxicity.

Arsenate and arsenite differential toxicity in Tetrahymena thermophila

A comparative analysis of toxicities of both arsenic forms (arsenite and arsenate) in the model eukaryotic microorganism Tetrahymena thermophila (ciliate protozoa) has shown the presence of various detoxification mechanisms and cellular effects comparable to those of animal cells under arsenic stress. In the wild type strain SB1969 arsenate is almost 2.5 times more toxic than arsenite. According to the concentration addition model used in binary metallic mixtures their toxicities show an additive effect. Using fluorescent assays and flow cytometry, it has been detected that As(V) generates elevated levels of ROS/RNS compared to As(III). Both produce the same levels of superoxide anion, but As(V) also causes greater increases in hydrogen peroxide and peroxynitrite. The mitochondrial membrane potential is affected by both As(V) and As(III), and electron microscopy has also revealed that mitochondria are the main target of both arsenic ionic forms. Fusion/fission and swelling mitochondrial and mitophagy, together with macroautophagy, vacuolization and mucocyst extruction are mainly associated to As(V) toxicity, while As(III) induces an extensive lipid metabolism dysfunction (adipotropic effect). Quantitative RT-PCR analysis of some genes encoding antioxidant proteins or enzymes has shown that glutathione and thioredoxin metabolisms are involved in the response to arsenic stress. Likewise, the function of metallothioneins seems to be crucial in arsenic detoxification processes, after using both metallothionein knockout and knockdown strains and cells overexpressing metallothionein genes from this ciliate. The analysis of the differential toxicity of As(III) and As(V) shown in this study provides cytological and molecular tools to be used as biomarkers for each of the two arsenic ionic forms.

Flaxseed Ethanol Extract Effect in Acute Experimental Inflammation

Background and Objectives: Previous studies demonstrated antioxidant activities for flaxseed and flaxseed oil. The aim of the present study was to evaluate the prophylactic and therapeutic anti-inflammatory and antioxidant effects of flaxseed ethanol extract in acute experimental inflammation. Materials and Methods: The in vivo anti-inflammatory and antioxidant activity was evaluated on a turpentine-induced acute inflammation (6 mL/kg BW, i.m.) by measuring serum total oxidative status, total antioxidant reactivity, oxidative stress index, malondialdehyde, total thiols, total nitrites, 3-nitrotyrosine, and NFkB. The experiment was performed on nine groups (n = 5) of male rats: negative control; inflammation; three groups with seven days of flaxseed extract (100%, 50%, 25%) pretreatment followed by inflammation on day eight; three groups of inflammation followed by seven days of treatment with flaxseed extract (100%, 50%, 25%); inflammation followed by seven days of treatment with diclofenac (20 mg/kg BW). Results: Flaxseed extract anti-inflammatory activity was better in the therapeutic plan than in the prophylactic one, and consisted of NO, 3NT, and NF-κB reduction in a dose dependent way. ROS was reduced better in the therapeutic flaxseed extracts administration, and antioxidants were increased by the prophylactic flaxseed extracts administration. Both, ROS and antioxidants were influenced more by the total flaxseed extract, which was also more efficient than diclofenac. Conclusions: flaxseed extract prophylaxis has a useful antioxidant activity by increasing the antioxidants, and flaxseed extract therapy has anti-inflammatory and antioxidant activities by reducing NF-κB, RNS, and ROS.

Quercetin attenuates the proliferation of arsenic-related lung cancer cells via a caspase-dependent DNA damage signaling

Exposure to arsenic (As) mainly through contaminated drinking water enhances the lung tumor progression, invasion, and metastasis. The carcinogenic effect of As is due to the generation of reactive oxygen species (ROS) and DNA damage, and interference with DNA repair machinery. Herein, we investigated the potential therapeutic function of quercetin on As-treated lung cancer cells. Quercetin is a natural product with antioxidative, anti-inflammatory, and antiproliferative properties. We showed that quercetin induced cell death in the As-exposed lung cancer cells in a dose-dependent manner. Quercetin was able to significantly inhibit the proliferation of the As-treated cells over a period of 5 weeks. In addition, quercetin induced ROS-mediated DNA double-strand breaks in the As-treated lung cancer cells. We also showed that ROS generation induced by quercetin activated caspase-3 to a sufficient level to induce DNA damage but insufficient to induce death in As-treated lung cancer cells. Moreover, transient activation of caspase-2 was detected in quercetin- and As-cotreated cells. The flow cytometry-based cell cycle analysis showed that the antiproliferative function of quercetin was mediated by S-phase cell cycle arrest, which was associated with upregulation of the Ataxia Telangiectasia-mutated (ATM), but not ATM and RAD3-related. In conclusion, quercetin synergized the As-driven ROS generation and DNA damage, and induced the S-phase arrest, thus inhibiting the proliferation of As-exposed lung cancer cells. This data suggested that quercetin is an alternative reagent to chemo-drugs to prevent the growth of As-exposed lung cancer cells.

Curcumin prevents As3+-induced carcinogenesis through regulation of GSK3β/Nrf2

Background

Arsenic (As³⁺) is a carcinogen with considerable environmental and occupational relevancy. Its mechanism of action and methods of prevention remain to be investigated. Previous studies have demonstrated that ROS is responsible for As³⁺-induced cell transformation, which is considered as the first stage of As³⁺ carcinogenesis. The NF-E2 p45-related factor-2 (Nrf2) signaling pathway regulates the cellular antioxidant response, and activation of Nrf2 has recently been shown to limit oxidative damage following exposure to As³⁺

Methods and results

In this study, molecular docking was used to virtually screen natural antioxidant chemical databases and identify molecules that interact with the ligand-binding site of Keap1 (PDB code 4L7B). The cell-based assays and molecular docking findings revealed that curcumin has the best inhibitory activity against Keap1-4L7B. Co-immunoprecipitation (Co-IP) results indicated that curcumin is a potent Keap1 Kelch domain-dependent Nrf2 activator that stabilizes Nrf2 by hindering its ubiquitination. The increased activation of Nrf2 and its target antioxidant genes by curcumin could significantly decrease As³⁺-generated ROS. Moreover, curcumin induced autophagy in As³⁺-treated BEAS-2B via inducing autophagy by the formation of a p62/LC-3 complex and increasing autophagic flux by promoting transcription factor EB (TFEB) and lysosome-associated membrane protein 1 (LAMP1) expression. Knockdown of Nrf2 abolished curcumin-induced autophagy and downregulated ROS. Further studies showed that inhibition of autophagosome and lysosome fusion with bafilomycin a1 (BafA1) could block curcumin and prevented As³⁺-induced cell transformation. These results demonstrated that curcumin prevents As³⁺-induced cell transformation by inducing autophagy via the activation of the Nrf2 signaling pathway in BEAS-2B cells. However, overexpression of Keap-1 showed a constitutively high level of Nrf2 in As³⁺-transformed BEAS-2B cells (AsT) is Keap1-independent regulation. Overexpression of Nrf2 in AsT demonstrated that curcumin increased ROS levels and induced cell apoptosis via the downregulation of Nrf2. Further studies showed that curcumin decreased the Nrf2 level in AsT by activating GSK-3β to inhibit the activation of PI3K/AKT. Co-IP assay results showed that curcumin promoted the interaction of Nrf2 with the GSK-3β/β-TrCP axis and ubiquitin. Moreover, the inhibition of GSK-3β reversed Nrf2 expression in curcumin-treated AsT, indicating that the decrease in Nrf2 is due to activation of the GSK-3β/β-TrCP ubiquitination pathway. Furthermore, in vitro and in vivo results showed that curcumin induced cell apoptosis, and had anti-angiogenesis and anti-tumorigenesis effects as a result of activating the GSK-3β/β-TrCP ubiquitination pathway and subsequent decrease in Nrf2.

Conclusions

Taken together, in the first stage, curcumin activated Nrf2, decreased ROS, and induced autophagy in normal cells to prevent As³⁺-induced cell transformation. In the second stage, curcumin promoted ROS and apoptosis and inhibited angiogenesis via inhibition of constitutive expression of Nrf2 in AsT to prevent tumorigenesis. Our results suggest that antioxidant natural compounds such as curcumin can be evaluated as potential candidates for complementary therapies in the treatment of As³⁺-induced carcinogenesis.

p62 functions as a signal hub in metal carcinogenesis

A number of metals are toxic and carcinogenic to humans. Reactive oxygen species (ROS) play an important role in metal carcinogenesis. Oxidative stress acts as the converging point among various stressors with ROS being the main intracellular signal transducer. In metal-transformed cells, persistent expression of p62 and erythroid 2-related factor 2 (Nrf2) result in apoptosis resistance, angiogenesis, inflammatory microenvironment, and metabolic reprogramming, contributing to overall mechanism of metal carcinogenesis. Autophagy, a conserved intracellular process, maintains cellular homeostasis by facilitating the turnover of protein aggregates, cellular debris, and damaged organelles. In addition to being a substrate of autophagy, p62 is also a crucial molecule in a myriad of cellular functions and in molecular events, which include oxidative stress, inflammation, apoptosis, cell proliferation, metabolic reprogramming, that modulate cell survival and tumor growth. The multiple functions of p62 are appreciated by its ability to interact with several key components involved in various oncogenic pathways. This review summarizes the current knowledge and progress in studies of p62 and metal carcinogenesis with emphasis on oncogenic pathways related to oxidative stress, inflammation, apoptosis, and metabolic reprogramming.

Connections between endoplasmic reticulum stress-associated unfolded protein response, mitochondria, and autophagy in arsenic-induced carcinogenesis

Arsenic exposure in contaminated drinking water is a global health issue, as more than 200 million people are affected globally. Arsenic has been known to cause skin, liver, lung, bladder and prostate cancers. Accordingly, it has been categorized as a group I human carcinogen by the International Agency for Research on Cancer (IARC). Various natural and anthropogenic activities lead to the release of arsenic in the environment, contaminating air, water and food sources. Traditionally, genetic mutations have been the center of cancer research. However, emerging studies have now focused on the importance of epigenetics, metabolism and endoplasmic reticulum (ER) stress in cancer. Arsenic is highly capable of inducing stress in the cells via the generation of free radicals causing oxidative stress, epigenetic and genetic alterations, mitochondrial dysfunction, activation of intracellular signaling pathways, and impairment of autophagy and DNA repair systems. The cancer cells are able to utilize the unfolded protein response (UPR) to overcome these internal stresses in various stages of arsenic-induced carcinogenesis, from cancer growth to immune responses. The UPR is an evolutionarily conserved stress response that has both survival and apoptotic outcomes. PERK, IRE1α and ATF6α are the three ER stress sensors that are activated to maintain cellular proteostasis, which can also promote apoptosis on prolonged ER stress. The dual nature of UPR in different cancer types and stages is a challenge for researchers. We must investigate the role and the connections among ER stress-associated UPR, mitochondrial dysfunction and autophagy in arsenic malignancies to identify key targets for cancer prevention and therapeutics.

Paradoxical effects of arsenic in the lungs

High levels (> 100 ug/L) of arsenic are known to cause lung cancer; however, whether low (≤ 10 ug/L) and medium (10 to 100 ug/L) doses of arsenic will cause lung cancer or other lung diseases, and whether arsenic has dose-dependent or threshold effects, remains unknown. Summarizing the results of previous studies, we infer that low- and medium-concentration arsenic cause lung diseases in a dose-dependent manner. Arsenic trioxide (ATO) is recognized as a chemotherapeutic drug for acute promyelocytic leukemia (APL), also having a significant effect on lung cancer. The anti-lung cancer mechanisms of ATO include inhibition of proliferation, promotion of apoptosis, anti-angiogenesis, and inhibition of tumor metastasis. In this review, we summarized the role of arsenic in lung disease from both pathogenic and therapeutic perspectives. Understanding the paradoxical effects of arsenic in the lungs may provide some ideas for further research on the occurrence and treatment of lung diseases.

Dichloromethane increases mutagenic DNA damage and transformation ability in cholangiocytes and enhances metastatic potential in cholangiocarcinoma cell lines

Dichloromethane (DCM), a widely used chlorinated solvent, is classified by IARC (2017) as probably carcinogenic to humans. Exposure to DCM has been associated with increased incidence of cholangiocarcinoma (CCA) in humans. This study aimed to investigate how DCM could contribute to CCA development by investigating the effects of DCM on DNA damage and cell transformation in cholangiocytes (MMNK-1) and on metastatic potential as measured by invasion and cell migration in malignant CCA cell lines (HuCCA-1 and RMCCA-1). MMNK-1 cells treated with the non-cytotoxic concentration of DCM (25 μM, 24 h) significantly increased the levels of mutagenic DNA adducts including 8-hydroxydeoxyguanosine, 8-OHdG, (1.84-fold, p < 0.01) and 8-nitroguanine (1.96-fold, p < 0.01) and enhanced cell transformation by 1.47-fold (p < 0.01). In addition, the expression of various genes involved in carcinogenesis, namely, NFE2L2 (antioxidative response), CXCL8 (inflammation), CDH1 (cell adhesion), MMP9 (tissue remodeling) and MKI67 (cell proliferation) were altered in cholangiocytes treated with DCM. When MMNK-1 cells were transformed by DCM, the expression of all the aforementioned genes was also increased. In malignant cell lines (HuCCA-1 and RMCCA-1), DCM treatment resulted in increased CXCL8 and MMP9 transcription and decreased CDH1 transcription accompanied by increased invasion and migration capabilities of these cells. Taken together, this study demonstrated that DCM exposure could be linked to the development of CCA.

The Beneficial Effects of QIAPI 1® against Pentavalent Arsenic-Induced Lung Toxicity a Hypothetical Model for SARS CoV2-Induced Lung Toxicity

Exposure to environmental toxicants such as Arsenic (As) can result in As-induced alterations in immune regulators. Consequently, people who are more prone to viral infections like influenza A or B, H1N1, SARS CoV (Severe Acute Respiratory Syndrome Coronavirus), and SARS CoV2 may develop susceptibility to immune responses in their lungs because our previous reports delineated the ability of QIAPI 1®, a melanin precursor, to dissociate water molecules with simultaneous therapeutic efficacy against central nervous system (CNS) diseases, retinopathy, and As-induced renal toxicity. Given the commonalities of lung pathology of SARS CoV and As-induced toxicity, the aim of this study is to decipher the efficacy of QIAPI 1® against pentavalent As-induced lung toxicity by examining the pulmonary pathology. Hematoxylin & Eosin (H&E) staining was used for ascertaining the lung pathology in Wistar rat models. Animals were divided into 3 groups: control group, group treated with pentavalent As, and a group treated with pentavalent As and QIAPI 1®. There were no significant changes in lung histopathology in the control group as indicated by intact morphology. As-treated group revealed damage to the histoarchitecture with pulmonary edema, interstitial fibrosis, diffuse alveolar damage, Bronchiolitis obliterans organizing pneumonia (BOOP)-lesions, formation of hyaline membrane, multinucleated giant pneumocytes, atypical pneumocytes, inflammatory cell infiltration, and interstitial edema. The group treated with As and QIAPI 1® significantly associated with mitigated histological signs of lung inflammation induced by Arsenic. Therefore, QIAPI 1® can be recommended as antagonistic to As-induced lung toxicity. In conclusion, this model could be preferred as a hypothetical model to examine the efficacy of QIAPI 1® in SARS CoV2-induced pulmonary damage. Future studies are warranted to delineate the efficacy of QIAPI 1® against SARS CoV and SARS CoV2 lung pathology.

Ethanol extract of Vitellaria paradoxa (Gaertn, F) leaves protects against sodium arsenite - induced toxicity in male wistar rats

The inadvertent exposure to arsenic has been associated with diverse diseases such as cancers. Vitellaria paradoxa is a medicinal plant with antidiabetic and antiproliferative properties. Here, we assessed the ameliorative role of Ethanol Leaf extract of Vitellaria paradoxa (ELVp) in Sodium Arsenite (SA) - induced toxicity in rats after oral treatment for two weeks as follows: Group 1 (Control, distilled water), Group 2 (Vitamin E, 100 mg/kg), Groups 3 and 4 (ELVp, 100 & 200 mg/kg respectively), Group 5 (SA, 2.5 mg/kg), Group 6 (SA + Vit E) and Group 7 (SA + ELVp (100 mg/kg) and Group 8 (SA + ELVp (200 mg/kg). The results indicated that SA significantly increased liver and kidney function markers and elevated platelet, white blood cell (WBC) count and malondialdehyde levels in rats. Additionally, SA decreased Red Blood Cell (RBC), Hemoglobin (HGB) and Hematocrit (HCT) levels in rats (p < 0.05). Sodium arsenite caused mild expression of BCL-2 protein> NF-Kb = p53 in the kidney of rats. However, ELVp ameliorated SA-induced toxicity in the liver and kidney of rats with respect to these markers. Overall, ELVp has hepatoprotective, nephroprotective and apoptotic properties against sodium arsenite-induced toxicity.

Underlying mechanisms of cytotoxicity in HepG2 hepatocarcinoma cells exposed to arsenic, cadmium and mercury individually and in combination

BACKGROUND

Toxicity data regarding combinational exposure of humans to arsenic, cadmium and mercury is scarce. Although hepatotoxicity has been reported, limited information is available on their mechanistic underpinnings. The cytotoxic mechanisms of these metals were determined in HepG2 hepatocarcinoma cell lines after individual and combinational exposure.

METHODS

HepG2 cells were exposed to heavy metals (sodium arsenite, cadmium chloride, and mercury chloride) individually or in combination for 24 h, after which cell density, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), reduced glutathione (GSH), adenosine triphosphate (ATP) and caspase-3/7 activity was assessed.

RESULTS AND DISCUSSION

Cadmium (IC₅₀ = 0.43 mg/L) and the combination (0.45 mg/L, arsenic reference) were most cytotoxic, followed by arsenic (6.71 mg/L) and mercury (28.23 mg/L). Depolarisation of the ΔΨm and reductions in ROS, GSH and ATP levels occurred. Arsenic, cadmium and the combination increased caspase-3/7 activity, while mercury reduced it.

CONCLUSION

The combination produced a greater, albeit mechanistically similar, cytotoxicity compared to individual metals. Cytotoxicity was dependent on altered mitochondrial integrity, redox-status, and bioenergetics. Although the combination's cytotoxicity was associated with caspase-3/7 activity, this was not true for mercury. Heavy metal interactions should be assessed to elucidate molecular underpinnings of cytotoxicity.

Estimating seasonal variations of realistic exposure doses and risks to organs due to ambient particulate matter -bound metals of Delhi

This study aims to calculate deposition of PM_2.5 -bound hazardous metals in different organs after inhalation of particulate matter for the Delhi (India), and to estimate risks to organs following inhalation. Bio-accessible fractions of three PM-associated carcinogenic metals (As, Pb &Cd) were calculated using the metal values in simulated lung fluids. Depositions of metals in different organs were calculated using an integrated model consists of HRT and PBPK models. The calculation indicates that the major or significant deposition of metal Pb occurs in tissues, such as bone, muscle and blood. Most of the depositions of Cd happens in lung whereas most of the depositions of As happens in lung, muscle and skin. Most of the deposition of studied metals was found in lung (45% for arsenic and 70% for cadmium of their bio -dissolved contents). The following order of depositions of metals in different tissues were found (from highest deposition to smallest deposition): As: Lung > muscle = liver; Pb: bone > blood > muscle; Cd: lung > intestine. The combined exposures of PM_2.5 and its associated metals were found to give interaction-based hazard index greater than 1 for several months of the year, indicating a chance of health risk. Hazard quotient (HQ) <1 was seen for ingestion and dermal pathways, indicating no cause of concern. Findings indicate the need for doing periodic monitoring and estimating deposition doses and exposure risks of PM-associated metals to lungs and other organs for protecting human health.

Transformed ALDH2-/- hepatocytes by ethanol could serve as a useful tool for studying alcoholic hepatocarcinogenesis

Alcohol is a well-recognized hepatic carcinogen. Alcohol is metabolized into genotoxic acetaldehyde in hepatocytes, which is catalyzed by aldehyde dehydrogenase 2 (ALDH2). The detailed underlying mechanisms of alcohol-related hepatocellular carcinoma (HCC) remains unclear, at least partially, due to the absence of appropriate experimental models. Current studies suggest that rodents are not good models of the most common liver diseases that trigger HCC including alcoholic liver injury. We hypothesize that ethanol could induce transformation of immortalized normal liver cells, which may serve as a versatile tool for studying alcoholic HCC. Besides, we believe that knockout of ALDH2 will help to shorten the time course of transformation, as ALDH2 deficiency will significantly increase the accumulation of acetaldehyde in hepatocytes. Using this model, the dynamic changes of carcinogenesis-related molecular events could be easily examined. Furthermore, the transformed cells isolated from soft agar could be inoculated to mice for studying invasion, metastasis, and also for screening prophylactics.

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.

Autophagy mediates bronchial cell malignant transformation induced by chronic arsenic exposure via MEK/ERK1/2 pathway

Chronic exposure to arsenic increases the risk of developing a variety of human cancers including lung carcinomas. However, the exact molecular mechanism underlying arsenic carcinogenicity remains largely unknown. Autophagy is a conserved catabolic process for maintaining cellular protein homeostasis whose defects might result in accumulation of dysfunctional organelles and damaged proteins thus promoting tumorigenesis. In the present study, we found that chronic exposure of human bronchial epithelial BEAS-2B cells to sub-lethal dose of sodium arsenite led to autophagy activation and induced an epithelial-to-mesenchymal transition (EMT) to enhance cell migratory and invasive capability. The malignant transformation was mediated via activation of MEK/ERK1/2 signaling. Importantly, inhibition of autophagy in these arsenic-exposed cells by pharmacological intervention or genetic deletion further promoted the EMT and increased the generation of inflammasomes. Both autophagy inhibitor and genetic deletion of autophagy core gene Beclin-1 produced similar effects. These results may suggest the important role of autophagy in sodium arsenite-induced lung tumorigenesis which may serve as a potential target in prevention and treatment of arsenic-imposed lung cancer.

Grape seed proanthocyanidin extract alleviates arsenic-induced lung damage through NF-κB signaling

IMPACT STATEMENT

Arsenic-induced respiratory inflammatory damage is an important occupational hazard in many areas of the world, particularly in underdeveloped and developing countries. Effective treatments are lacking and expensive. Therefore, the aim of the study was to examine the anti-inflammatory effects of proanthocyanidin (PC) and the molecular mechanisms in vivo and in vitro. The present study showed that PC extracted from grape seed could attenuate the lung damage in a mouse model of arsenic poisoning. The effects were observed at the level of lung histology and inflammasome expression. This study suggests that a natural compound is effective in mitigating the toxic effects of arsenic in the lungs, providing an inexpensive and more readily accessible method for treating arsenic exposure in some parts of the world.

Constitutive Activation of NAD-Dependent Sirtuin 3 Plays an Important Role in Tumorigenesis of Chromium(VI)-Transformed Cells

Chronic exposure of human bronchial epithelial BEAS-2B cells to hexavalent chromium [Cr(VI)] causes malignant cell transformation. Sirtuin-3 (SIRT3) regulates mitochondrial adaptive response to stress, such as metabolic reprogramming and antioxidant defense mechanisms. In Cr(VI)-transformed cells, SIRT3 was upregulated and mitochondrial adenosine triphosphate (ATP) production and proton leak were reduced. Knockdown of SIRT3 by its shRNA further decreased mitochondrial ATP production, proton leak, mitochondrial mass, and mitochondrial membrane potential, indicating that SIRT3 positively regulates mitochondrial oxidative phosphorylation and maintenance of mitochondrial integrity. Mitophagy is critical to maintain proper cellular functions. In Cr(VI)-transformed cells expressions of Pink 1 and Parkin, two mitophagy proteins, were elevated, and mitophagy remained similar as that in passage-matched normal BEAS-2B cells, indicating that in -Cr(VI)-transformed cells mitophagy is suppressed. Knockdown of SIRT3 induced mitophagy, suggesting that SIRT3 plays an important role in mitophagy suppression of Cr(VI)-transformed cells. In Cr(VI)-transformed cells, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) was constitutively activated, and protein levels of p62 and p-p62Ser349 were elevated. Knockdown of SIRT3 or treatment with carbonyl cyanide m-chlorophenyl hydrazone (CCCP) decreased the binding of p-p62Ser349 to Keap1, resulting in increased binding of Keap1 to Nrf2 and consequently reduced Nrf2 activation. The results from CHIP assay showed that in Cr(VI)-transformed cells binding of Nrf2 to antioxidant response element (ARE) of SIRT3 gene promoter was dramatically increased. Knockdown of SIRT3 suppressed cell proliferation and tumorigenesis of Cr(VI)-transformed cells. Overexpression of SIRT3 in normal BEAS-2B cells exhibited mitophagy suppression phenotype and increased cell proliferation and tumorigenesis. The present study demonstrated that upregulation of SIRT3 causes mitophagy suppression and plays an important role in cell survival and tumorigenesis of Cr(VI)-transformed cells.

Arsenic-Induced Carcinogenesis: The Impact of miRNA Dysregulation

Arsenic is a toxic metalloid widely present in the earth's crust, and is a proven human carcinogen. Chronic arsenic exposure mainly through drinking water causes skin, lung, and urinary bladder cancers, and is associated with liver, prostate, and kidney cancers, cardiovascular and neurological disorders, and diabetes. Several modes of action have been suggested in arsenic carcinogenesis. However, the molecular etiology of arsenic-induced cancer remains unclear. Recent evidence clearly indicates that gene expression modifications induced by arsenic may involve epigenetic alterations, including miRNA dysregulation. Many miRNAs have been implicated in different human cancers as a consequence of losses and or gains of miRNA function that contribute to cancer development. Progress in identifying miRNA dysregulation induced by arsenic has been made using different approaches and models. The present review discusses the recent data regarding dysregulated expression of miRNA in arsenic-induced malignant transformation in vitro, gaps in current understanding and deficiencies in current models for arsenic-induced carcinogenesis, and future directions of research that would improve our knowledge regarding the mechanisms involved in arsenic-induced carcinogenesis.

Co-Exposure to SiO2 Nanoparticles and Arsenic Induced Augmentation of Oxidative Stress and Mitochondria-Dependent Apoptosis in Human Cells

Widespread application of silica nanoparticles (nSiO₂) and ubiquitous metalloid arsenic (As) may increase their chances of co-exposure to human beings in daily life. Nonetheless, studies on combined effects of nSiO₂ and As in human cells are lacking. We investigated the co-exposure effects of nSiO₂ and As in human liver (HepG2) and human fibroblast (HT1080) cells. Results showed that nSiO₂ did not cause cytotoxicity. However, exposure of As caused oxidative stress and apoptosis in both types of cells. Interesting results were that co-exposure of a non-cytotoxic concentration of nSiO₂ significantly augmented the As induced toxicity in both cells. Intracellular level of As was higher in the co-exposure group (nSiO₂ + As) than the As group alone, suggesting that nSiO₂ facilitates the cellular uptake of As. Co-exposure of nSiO₂ and As potentiated oxidative stress indicated by pro-oxidants generation (reactive oxygen species, hydrogen peroxide and lipid peroxidation) and antioxidants depletion (glutathione level, and glutathione reductase, superoxide dismutase and catalase activities). In addition, co-exposure of nSiO₂ and As also potentiated mitochondria-mediated apoptosis suggested by increased expression of p53, bax, caspase-3 and caspase-9 genes (pro-apoptotic) and decreased expression of bcl-2 gene (anti-apoptotic) along with depleted mitochondrial membrane potential. To the best of our knowledge, this is the first study showing that co-exposure of nSiO₂ and As induced augmentation of oxidative stress and mitochondria-mediated apoptosis in HepG2 and HT1080 cells. Hence, careful attention is required for human health assessment following combined exposure to nSiO₂ and As.

Overexpression of hsa-miR-186 induces chromosomal instability in arsenic-exposed human keratinocytes

The mechanism of arsenic-induced skin carcinogenesis is not yet fully understood. Chromosomal instability contributes to aneuploidy and is a driving force in carcinogenesis. Arsenic causes mitotic arrest and induces aneuploidy. hsa-miR-186 overexpression is associated with metastatic cancers as well as arsenic-induced squamous cell carcinoma and is reported to target several mitotic regulators. Decreased levels of these proteins can dysregulate chromatid segregation contributing to aneuploidy. This work investigates the potential aneuploidogenic role of hsa-miR-186 in arsenic carcinogenesis. Clones of immortalized human keratinocytes (HaCaT) stably transfected with a hsa-miR-186 expression or empty vector were isolated. Three clones with high and low hsa-miR-186 expression determined by RT-qPCR were selected for further analysis and cultured with 0 or 100 nM NaAsO2 for 8 weeks. Analysis of mitoses revealed that chromosome number and structural abnormalities increased in cells overexpressing hsa-miR-186 and were further increased by arsenite exposure. Double minutes were the dominant structural aberrations. The peak number of chromosomes also increased. Cells with >220 to >270 chromosomes appeared after 2 months in hsa-miR-186 overexpressing cells, indicating multiple rounds of endomitosis had occurred. The fraction of cells with increased chromosome number or structural abnormalities did not increase in passage matched control cells. Levels of selected target proteins were determined by western blot. Expression of BUB1, a predicted hsa-miR-186 target was suppressed in hsa-miR-186 overexpressing clones, but increased with arsenite exposure. CDC27 remained constant under all conditions. These results suggest that overexpression of miR-186 in arsenic exposed tissues likely induces aneuploidy contributing to arsenic-induced carcinogenesis.

Characterization of the cellular effects and mechanism of arsenic trioxide-induced hepatotoxicity in broiler chickens

To characterize the cellular effects and mechanism of arsenic trioxide (ATO)-induced hepatotoxicity in broiler chickens, increasing concentrations of ATO (0, 0.6, 1.2, 2.4, and 4.8 μM) were added to chicken hepatocyte cultures in vitro. The changes in hepatocyte morphology, oxidative stress and apoptosis were evaluated using fluorescence microscopy and flow cytometry. The effects of ATO on mRNA or protein expression of antioxidant enzymes, especially methionine sulfoxide reductase (Msr), were analyzed using qRT-PCR and western blotting assays. Increased apoptosis were concomitant with increased reactive oxygen species (ROS) accumulation and upregulation of antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) with increasing ATO concentrations. Moreover, G₁ phase arrest and dysregulation of the balance between antiapoptotic versus proapoptotic factors were noted. Furthermore, upregulation of HO-1, SOD-1, and TRX in the ATO groups were consistent with ATO-induced oxidative damage. High Msr, SOD-1, TRX, Bak1, Bax, and p53 protein levels in the ATO groups indicate that these proteins may have accumulated to counter ATO-induced oxidative stress. ROS scavenger N-acetyl-l-cysteine (NAC) could reverse ATO-induced oxidative damage and restore hepatocyte viability, even with compromised Msr function. Our findings suggest that Msr can protect broiler hepatocytes against ATO-induced oxidative stress. Furthermore, NAC-mediated reversal of oxidative damage may represent a strategy to mitigate potential economic losses associated with arsenic poisoning in the poultry industry.

Study of arsenic (III) removal by monolayer protected silver nanoadsorbent and its execution on prokaryotic system

This work deals with the removal of arsenic by nanoadsorbent from aqueous environment that is subsequently applied to the biological system for the evaluation of its efficiency. We started our aspiration by the modification of carboxylate functionalized silver nanoparticle (nanoadsorbent) fabrication process. Batch mode arsenic uptake study by the nanoadsorbent was conducted considering several altering parameters and the reactants in addition to products were evaluated by several analytical techniques for the interpretation of the interaction mechanism. It was found nanoadsorbent, Ag@MSA is an efficient system for the exclusion of arsenic (III) from the aqueous system and due to the alteration in the ratio of silver content and protective agent, the characteristic profile of silver nanoparticles with an average diameter of 15 nm also became changed in respect of reported results. Here the low pH range (4-6) favors the interaction between nanoparticle and arsenic and it was found that the interaction was chemical in nature through adsorption or complex formation with surface carboxylate groups of the protecting agent (MSA). Following the interaction, a successful removal of arsenic (III) was achieved at a percentage of 94.16 with an initial concentration of 45 mg/L and equilibrium time of 60 min. Hence nanoparticles were executed against the toxic effect of arsenic in E. coli, an important gut microbe of higher animals, for the restoration of bacterial growth in arsenic pre-removed media. In this context the validation of this removal efficiency against arsenic induced toxicity was proved through several morphological studies, degree of oxidative damages and other biochemical attributes.

Health effects inflicted by chronic low-level arsenic contamination in groundwater: A global public health challenge

Groundwater arsenic (As) contamination is a global public health concern. The high level of As exposure (100-1000 μg/L or even higher) through groundwater has been frequently associated with serious public health hazards, e.g., skin disorders, cardiovascular diseases, respiratory problems, complications of gastrointestinal tract, liver and splenic ailments, kidney and bladder disorders, reproductive failure, neurotoxicity and cancer. However, reviews on low-level As exposure and the imperative health effects are far less documented. The World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) has set the permissible standard of As in drinking water at 10 μg/L. Considering the WHO and USEPA guidelines, most of the developed countries have established standards at or below this guideline. Worldwide many countries including India have millions of aquifers with low-level As contamination (≤50 μg/L). The exposed population of these areas might not show any As-related skin lesions (hallmark of As toxicity particularly in a population consuming As contaminated groundwater >300 μg/L) but might be subclinically affected. This review has attempted to encompass the wide range of health effects associated with chronic low-level As exposure ≤50 μg/L and the probable mechanisms that might provide a better insight regarding the underlying cause of these clinical manifestations. Therefore, there is an urgent need to create mass awareness about the health effects of chronic low-level As exposure and planning of proper mitigation strategies.

Carnosic Acid, a Natural Diterpene, Attenuates Arsenic-Induced Hepatotoxicity via Reducing Oxidative Stress, MAPK Activation, and Apoptotic Cell Death Pathway

The present studies have been executed to explore the protective mechanism of carnosic acid (CA) against NaAsO₂-induced hepatic injury. CA exhibited a concentration dependent (1–4 μM) increase in cell viability against NaAsO₂ (12 μM) in murine hepatocytes. NaAsO₂ treatment significantly enhanced the ROS-mediated oxidative stress in the hepatic cells both in in vitro and in vivo systems. Significant activation of MAPK, NF-κB, p53, and intrinsic and extrinsic apoptotic signaling was observed in NaAsO₂-exposed hepatic cells. CA could significantly counteract with redox stress and ROS-mediated signaling and thereby attenuated NaAsO₂-mediated hepatotoxicity. NaAsO₂ (10 mg/kg) treatment caused significant increment in the As bioaccumulation, cytosolic ATP level, DNA fragmentation, and oxidation in the liver of experimental mice (n = 6). The serum biochemical and haematological parameters were significantly altered in the NaAsO₂-exposed mice (n = 6). Simultaneous treatment with CA (10 and 20 mg/kg) could significantly reinstate the NaAsO₂-mediated toxicological effects in the liver. Molecular docking and dynamics predicted the possible interaction patterns and the stability of interactions between CA and signal proteins. ADME prediction anticipated the drug-likeness characteristics of CA. Hence, there would be an option to employ CA as a new therapeutic agent against As-mediated toxic manifestations in future.

Alleviation of Arsenic-Induced Pulmonary Oxidative Damage by GSPE as Shown during In vivo and In vitro Experiments

A long-term exposure to arsenic may lead to lung damage due to oxidative stress. In this context, GSPE can play a major role as a strong antioxidant. Our study attempted to reveal the connection between arsenic-induced lung injury and the antagonistic effect of GSPE. For this purpose, BEAS-2B cells and Kunming mice were exposed to different dosages of As₂O₃ and GSPE. Oxidative stress indicators were detected both in vivo and in vitro. Cell survival rate and morphological changes in the lung tissue (H&E staining) were evaluated as well. It was exhibited that As₂O₃ increased oxidative stress both in vivo and in vitro and decreased cells viability. In contrast, higher cell survival rate was revealed in the group treated with arsenic plus GSPE after 24 h as compared to that in the arsenic group. GSPE effectively reduced oxidative stress levels, along with increasing antioxidant capacity. In vivo experiments in arsenic-exposed group showed alveolar septum to be significantly thickened with considerable capillary congestion and invasion by inflammatory cells. After the intervention with GSPE, there seemed to be a dramatic reversal of morphology with thinning of the alveolar septum, decrease in capillary congestion, and number of inflammatory cells. This had shown that GSPE can effectively reduce the levels of oxidative stress, induced by arsenic in mice lung tissue. Conversely, antioxidant enzymes or products were increased. The experiment proved that GSPE can protect the lungs from oxidative damage induced by arsenic, and it may also be used as an antagonist against arsenic injuries.

Fetal bovine serum induces sustained, but reversible, epithelial-mesenchymal transition in the BEAS-2B cell line

BEAS-2B is a non-malignant, immortalized human cell line that has been used extensively as a model of lung epithelium. Despite ATCC recommendations to culture BEAS-2B in defined, serum-free media, many publications describe culturing BEAS-2B in fetal bovine serum (FBS)-containing media. The objective of this study was to define the effects of FBS on BEAS-2B cells. FBS exposure resulted in increased nuclear levels of transcription factors responsible for regulating epithelial-mesenchymal transition (EMT), increased cell invasiveness and increased anchorage-independent growth. FBS-exposed BEAS-2B cells exhibited a decrease of the epithelial markers, E-cadherin and claudin-1 at the mRNA and protein levels, along with a corresponding increase of the mesenchymal marker, vimentin, at the protein level. Fractionation studies implicated an active moiety in FBS with a molecular weight larger than 30 kD. The mesenchymal phenotype was persistent provided FBS exposure was maintained. Upon FBS removal, both epithelial and mesenchymal markers began to revert toward an epithelial phenotype. Transforming growth factor β1 (TGFβ1) exposure to BEAS-2B recapitulated some key features of FBS-induced EMT. Our data suggest that FBS-exposed BEAS-2B cells do not accurately model the epithelial phenotype. Interpretation of data from BEAS-2B should include careful consideration of the effect of culture conditions.

Arjunolic Acid Improves the Serum Level of Vitamin B12 and Folate in the Process of the Attenuation of Arsenic Induced Uterine Oxidative Stress

Continuation of prolonged treatment against arsenicosis with conventional chelating therapy is a global challenge. The present study was intended to evaluate the defensive effect of arjunolic acid against arsenic-induced oxidative stress and female reproductive dysfunction. Wistar strain adult female rats were given sodium arsenite (10 mg/kg body weight) in combination with arjunolic acid (10 mg/kg body weight) orally for two estrous cycles. Electrozymographic analysis explored that arjunolic acid co-treatment counteracted As³⁺-induced ROS production in uterine tissue by stimulating the activities of endogenous enzymatic antioxidants. Arjunolic acid was able to enhance the protection against mutagenic uterine DNA breakage, necrosis, and ovarian-uterine tissue damages in arsenicated rats by improving the ovarian steroidogenesis. The mechanisms might be coupled with the augmentation of antioxidant defense system, partly through the elimination of arsenic with the involvement of S-adenosyl methionine pool where circulating levels of vitamin B₁₂, folic acid, and homocysteine play critical roles as evidenced from our present investigation.

Dual Roles of Oxidative Stress in Metal Carcinogenesis

It has been well established that environmental and occupational exposure to heavy metal causes cancer in several organs. Although the exact mechanism of heavy metal carcinogenesis remains elusive, metal-generated reactive oxygen species (ROS) are essential. ROS can play two roles in metal carcinogenesis; two stages in the process of metal carcinogenesis differ in the amounts of ROS activating a dual redox-mediated mechanism. In the early stage of metal carcinogenesis, ROS acts in an oncogenic role. However, in the late stage of metal carcinogenesis, ROS plays an antioncogenic role. Similarly, NF-E2-related factor 2 (Nrf2) also has two different roles, which makes it a key molecule for separating metal carcinogenesis into two different stages. In the early stage, inducible Nrf2 fights against elevated ROS to decrease cell transformation by its antioxidant protection property. In the late stage, constitutively activated Nrf2 manipulates reduced ROS to perform a comfortable environment for apoptosis resistance through an oncogenic role. Interestingly, a cunning carcinogenic mechanism takes advantage of the dual role of Nrf2 to implement the dual role of ROS through a series of redox adaption mechanisms. In this review, we discuss the paradox in the rationales behind the two opposite ROS roles and focus on their potential pharmacological application. The dual role of ROS represents a 'double-edged sword' with many possible novel ROS-mediated strategies in cancer therapy in metal carcinogenesis.

MicroRNA-124 alleviates hyperoxia-induced inflammatory response in pulmonary epithelial cell by inhibiting TLR4/NF-κB/CCL2

BACKGROUND

Lung epithelial cell dysfunction induced by hyperoxia-associated oxidative stress is a prominent feature involved in the development of acute lung injury (ALI). How the underlying molecular mechanisms contributed to this process are poorly defined. In the present study, we sought to identify the role of miR-124 in hyperoxia-induced cell apoptosis and excessive inflammatory response in pulmonary epithelial cell.

METHODS

The miR-124 levels in pulmonary epithelial cell were assayed by qRT-PCR. MiR-124 mimics and inhibitors were transfected to gain or loss of miR-124 function. Cell proliferation was analyzed by CCK8 assay. Cell apoptosis was analyzed by flow cytometry. The targeted genes were predicted by a bioinformatics algorithm and confirmed by a dual luciferase reporter assay. The protein levels were assayed by western blotting.

RESULTS

The results showed that miR-124 was significantly down-regulated in Beas2B cells and primary LECs upon hyperoxia exposure conditions. However, overexpression of miR-124 dramatically attenuated hyperoxia-provoked TLR4, NF-κB and pro-inflammatory cytokines production. In vitro, the cell viability and apoptosis was significantly reversed following transfection with miR-124 mimics in the presence of hyperoxia. Furthermore, the 3'-untranslated region (3'-UTR) of CCL2 was bound by miR-124.

CONCLUSION

It was concluded that miR-124 inhibited hyperoxia-induced apoptosis and excessive inflammatory response in Beas2B cells and primary LECs, at least partially, through the inhibition of TLR4/NF-κB/CCL2 signaling cascades.

Arsenite renal apoptotic effects in chickens co-aggravated by oxidative stress and inflammatory response

The kidney is the most crucial site for the excretion of arsenic and its metabolites.

Oxidative Stress and Metabolic Reprogramming in Cr(VI) Carcinogenesis

Cr(VI)-containing compounds are well-established lung carcinogens. Chronic exposure of the normal human epithelial cells is able to induce malignant cell transformation, the first stage of metal carcinogenesis. These Cr(VI)-transformed cells exhibit increased level of antioxidants, reduced capacity of generating reactive oxygen species (ROS), and development of apoptosis resistance, promoting tumorigenesis of Cr(VI)-transformed cells, the second stage of metal carcinogenesis. The mechanism of Cr(VI) induced carcinogenesis is still under investigation. Recent studies indicate that ROS play a positive role in the first stage while a negative role in the second stage. Transformed cells adapt metabolism to support tumor initiation and progression. Altered metabolic activities directly participate in the process of cell transformation or support a large requirement for nucleotides, amino acids, and lipids for tumor growth. In malignantly Cr(VI)-transformed cells, mitochondrial oxidative phosphorylation is defective, and pentose phosphate pathway, glycolysis, and glutaminolysis are upregulated. These metabolic reprogramming supports rapid cell proliferation and contributes to tumorigenesis of Cr(VI)-transformed cells. This article summarizes the current progress in the studies of metabolic reprogramming and Cr(VI) carcinogenesis with emphasis on the metabolic enzymes and oxidative stress related major oncogenic pathways.

Transient and permanent changes in DNA methylation patterns in inorganic arsenic-mediated epithelial-to-mesenchymal transition

Chronic low dose inorganic arsenic exposure causes cells to take on an epithelial-to-mesenchymal phenotype, which is a crucial process in carcinogenesis. Inorganic arsenic is not a mutagen and thus epigenetic alterations have been implicated in this process. Indeed, during the epithelial-to-mesenchymal transition, morphologic changes to cells correlate with changes in chromatin structure and gene expression, ultimately driving this process. However, studies on the effects of inorganic arsenic exposure/withdrawal on the epithelial-to-mesenchymal transition and the impact of epigenetic alterations in this process are limited. In this study we used high-resolution microarray analysis to measure the changes in DNA methylation in cells undergoing inorganic arsenic-induced epithelial-to-mesenchymal transition, and on the reversal of this process, after removal of the inorganic arsenic exposure. We found that cells exposed to chronic, low-dose inorganic arsenic exposure showed 30,530 sites were differentially methylated, and with inorganic arsenic withdrawal several differential methylated sites were reversed, albeit not completely. Furthermore, these changes in DNA methylation mainly correlated with changes in gene expression at most sites tested but not at all. This study suggests that DNA methylation changes on gene expression are not clear-cut and provide a platform to begin to uncover the relationship between DNA methylation and gene expression, specifically within the context of inorganic arsenic treatment.

Mechanisms underlying the toxic effects of antimony species in human embryonic kidney cells (HEK-293) and their comparison with arsenic species

Antimony cytotoxicity was assessed in human embryonic kidney cells (HEK-293). Uptake, mitochondrial respiratory activity, ROS generation and diffusional kinetics were measured using fluorescence recovery after photobleaching (FRAP). Furthermore, the toxic effect induced by Sb was compared with As toxicity in regard to ROS generation and diffusional kinetics, which provides information on the protein aggregation process. Our results show a favored uptake of Sb(III) and a more severe effect, decreasing the mitochondrial activity more than in the presence of Sb(V). In comparison with As, the Sb species did not generate a significant increase in ROS generation, which was observed with As(III) and As(V). FRAP analysis yielded important information on the diffusion and binding dynamics of live cells in presence of these metalloids. The mobile fraction showed a strong decrease with the As species and Sb(III). The diffusion rate and the k_off-rate were significantly decreased for the As and Sb species but were more strong in the presence of As(III).

Epigenomic reprogramming in inorganic arsenic-mediated gene expression patterns during carcinogenesis

Arsenic is a ubiquitous metalloid that is not mutagenic but is carcinogenic. The mechanism(s) by which arsenic causes cancer remain unknown. To date, several mechanisms have been proposed, including the arsenic-induced generation of reactive oxygen species (ROS). However, it is also becoming evident that inorganic arsenic (iAs) may exert its carcinogenic effects by changing the epigenome, and thereby modifying chromatin structure and dynamics. These epigenetic changes alter the accessibility of gene regulatory factors to DNA, resulting in specific changes in gene expression both at the levels of transcription initiation and gene splicing. In this review, we discuss recent literature reports describing epigenetic changes induced by iAs exposure and the possible epigenetic mechanisms underlying these changes.

Assessment of arsenic trioxide in the heart of Gallus gallus: alterations of oxidative damage parameters, inflammatory cytokines, and cardiac enzymes

The aim of this study was to assess the effects of arsenic trioxide (As₂O₃) in the chicken heart, and 72 1-day-old male Hy-line chickens were fed either a commercial diet (C group) or an arsenic supplement diet containing 7.5 mg/kg (L group), 15 mg/kg (M group), or 30 mg/kg (H group) As₂O₃ for 90 days. The results showed that exposure to As₂O₃ merely lowered (P < 0.05) the activities of catalase (CAT) and glutathione peroxidase (GSH-Px) in M and H groups at 90 days, significantly downregulated the inhibition ability of hydroxyl radicals (OH·), and upregulated (P < 0.05) the contents of malondialdehyde (MDA) in As₂O₃ exposure groups at 30, 60, and 90 days. Meanwhile, the messenger RNA levels of inflammatory cytokines (tumor necrosis factor-α (TNF-α), nuclear factor-kappa B (NF-κB), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and prostaglandin E synthase (PTGEs)) significantly increased (P < 0.05) in As₂O₃ exposure groups at 30, 60, and 90 days, and histological and ultrastructural damage was observed in As₂O₃ exposure groups. Additionally, As₂O₃-induced cardiac enzyme (aspartate transaminase (AST), creatine kinase (CK), creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and α-hydroxybutyrate dehydrogenase (α-HBDH)) levels increased (P < 0.05) at 90 days. These findings suggested that As₂O₃ exposure led to oxidative stress, inflammatory response, and histological and ultrastructural damage and altered the levels of cardiac enzymes in chicken heart tissues. This result may be helpful for further studies on the toxicological mechanisms of As₂O₃ in the chicken heart.

Oncogenic transformation of human lung bronchial epithelial cells induced by arsenic involves ROS-dependent activation of STAT3-miR-21-PDCD4 mechanism

Arsenic is a well-documented human carcinogen. The present study explored the role of the onco-miR, miR-21 and its target protein, programmed cell death 4 (PDCD4) in arsenic induced malignant cell transformation and tumorigenesis. Our results showed that treatment of human bronchial epithelial (BEAS-2B) cells with arsenic induces ROS through p47phox, one of the NOX subunits that is the key source of arsenic-induced ROS. Arsenic exposure induced an upregulation of miR-21 expression associated with inhibition of PDCD4, and caused malignant cell transformation and tumorigenesis of BEAS-2B cells. Indispensably, STAT3 transcriptional activation by IL-6 is crucial for the arsenic induced miR-21 increase. Upregulated miR-21 levels and suppressed PDCD4 expression was also observed in xenograft tumors generated with chronic arsenic exposed BEAS-2B cells. Stable shut down of miR-21, p47phox or STAT3 and overexpression of PDCD4 or catalase in BEAS-2B cells markedly inhibited the arsenic induced malignant transformation and tumorigenesis. Similarly, silencing of miR-21 or STAT3 and forced expression of PDCD4 in arsenic transformed cells (AsT) also inhibited cell proliferation and tumorigenesis. Furthermore, arsenic suppressed the downstream protein E-cadherin expression and induced β-catenin/TCF-dependent transcription of uPAR and c-Myc. These results indicate that the ROS-STAT3-miR-21-PDCD4 signaling axis plays an important role in arsenic -induced carcinogenesis.

Progress and prospects of reactive oxygen species in metal carcinogenesis

Carcinogenesis induced by environmental metal exposure is a major public health concern. The exact mechanisms underlying metal carcinogenesis remain elusive. In the past few decades, the relationship between metal induced generation of reactive oxygen species (ROS) and the mechanism of metal carcinogenesis has been established. The carcinogenic process is a very complex one. In the early stage of metal carcinogenesis or cell transformation high levels of ROS are oncogenic by causing DNA damage, genetic instability, epigenetic alteration, and metabolic reprogramming, leading to malignant transformation. In the second stage of metal carcinogenesis or the cancer development of metal-transformed cells, low levels of ROS are carcinogenic by promoting apoptosis resistance. The metal-transformed cells have the property of autophagy deficiency, resulting in accumulation of p62 and constitutive activation of Nrf2, and leading to higher levels of antioxidants, decreased levels of ROS, apoptosis resistance, inflammation, and angiogenesis. This review summarizes the most recent development in the field of metal carcinogenesis with emphasis on the difference in cellular events between early (cell transformation) and late (after cell transformation) stages of metal carcinogenesis.