Effects of Arsenic in Drinking Water on Risk of Hepatitis or Cirrhosis in Persons With and Without Chronic Viral Hepatitis

The activation of TLR4-MyD88 signaling promotes hepatic dysfunction and fibrotic changes in SD rats resulting from prolonged exposure to sodium arsenite

Arsenic, a poisonous metalloid element, is linked to liver diseases, but the exactmechanisms for this process are not yet to be completely elucidated. Toll like receptor 4 (TLR4), acting as a pathogenic pattern recognition receptor, plays a pivotal role in various inflammatory diseases via the myeloid differentiation factor 88 (MyD88) pathway. This study aims to investigate the involvement of the TLR4-MyD88 signaling pathway in liver injury induced by prolonged exposure to sodium arsenite (NaAsO2) in Sprague-Dawley rats. Our research findings demonstratethe activation of TLR4-MyD88 signaling pathway in long-term NaAsO2-exposed rat liver tissues, leading to a significant release of inflammatory factors, which suggests its potential involvement in the pathogenesis of NaAsO2-induced liver injury. We further administered lipopolysaccharide (LPS), a natural ligand of TLR4, and TAK-242, a specific inhibitor of TLR4, to rats in order to validate the specific involvement of the TLR4-MyD88 signaling pathway in NaAsO2-induced liver injury. The results showed that, 1 mg/kg.bw LPS treatment significantly activated TLR4-MyD88 signalling pathway and its mediated pro-inflammatory factors, leading to up-regulation of activation indicators in hepatic stellate cells (HSCs) as well as increased secretion levels of extracellular matrix (ECM) in the liver, and ultimately induced liver fibrosis and dysfunction in rats. Relevantly, subsequent administration of 0.5 mg/kg.bw TAK-242 significantly attenuated the expression levels of TLR4 and its associated proteins, mitigated collagen deposition, and partially improved liver fibrosis and dysfunction caused by NaAsO2 in rats. Our study fully confirms the pivotal role of the TLR4-MyD88 signaling in promoting liver injury induced by NaAsO2, thereby providing a novel molecular target for preventing and treating patients with arsenic poisoning-related liver injury.

Resveratrol Alleviates Arsenic Exposure-Induced Liver Fibrosis in Rats by Inhibiting Hepatocyte Senescence

Arsenic is an environmental pollutant that has garnered considerable attention from the World Health Organization. Liver fibrosis is an advanced pathological stage of liver injury that can be caused by chronic arsenic exposure and has the potential to be reversed to prevent cirrhosis and hepatic malignancies. However, effective treatment options are currently limited. Given the profibrogenic effect of hepatocyte senescence, we established a rat model of sub-chronic sodium arsenite exposure and investigated the ability of resveratrol (RSV), a potential anti-senescence agent, to ameliorate arsenic-induced liver fibrosis and elucidate the underlying mechanism from the perspective of hepatocyte senescence. The results demonstrated that RSV was capable of mitigating fibrosis phenotypes in rat livers, including the activation of hepatic stellate cell (HSC), the generation of extracellular matrix, and the deposition of collagen fibers in the liver vascular zone, which are all induced by arsenic exposure. Furthermore, as an activator of the longevity factor SIRT1, RSV antagonized the arsenic-induced inhibition of SIRT1 expression, thereby restoring the suppression of the senescence protein p16 by SIRT1. This prevented arsenic-induced hepatocyte senescence, manifesting as a decrease in telomere shortening and a reduction in the release of senescence-associated secretory phenotype (SASP)-related proteins. In conclusion, this study demonstrated that RSV counteracts arsenic-induced hepatocyte senescence and the release of SASP-related proteins by restoring the inhibitory effect of SIRT1 on p16, thereby suppressing the activation of fibrotic phenotypes and mitigating liver fibrosis. These findings provide new insights for understanding the mechanism of arsenic-induced liver fibrosis, and more importantly, they reveal novel potential interventional approaches.

Arsenic trioxide impacts hepatitis B virus core nuclear localization and efficiently interferes with HBV infection

The key to a curative treatment of hepatitis B virus (HBV) infection is the eradication of the intranuclear episomal covalently closed circular DNA (cccDNA), the stable persistence reservoir of HBV. Currently, established therapies can only limit HBV replication but fail to tackle the cccDNA. Thus, novel therapeutic approaches toward curative treatment are urgently needed. Recent publications indicated a strong association between the HBV core protein SUMOylation and the association with promyelocytic leukemia nuclear bodies (PML-NBs) on relaxed circular DNA to cccDNA conversion. We propose that interference with the cellular SUMOylation system and PML-NB integrity using arsenic trioxide provides a useful tool in the treatment of HBV infection. Our study showed a significant reduction in HBV-infected cells, core protein levels, HBV mRNA, and total DNA. Additionally, a reduction, albeit to a limited extent, of HBV cccDNA could be observed. Furthermore, this interference was also applied for the treatment of an established HBV infection, characterized by a stably present nuclear pool of cccDNA. Arsenic trioxide (ATO) treatment not only changed the amount of expressed HBV core protein but also induced a distinct relocalization to an extranuclear phenotype during infection. Moreover, ATO treatment resulted in the redistribution of transfected HBV core protein away from PML-NBs, a phenotype similar to that previously observed with SUMOylation-deficient HBV core. Taken together, these findings revealed the inhibition of HBV replication by ATO treatment during several steps of the viral replication cycle, including viral entry into the nucleus as well as cccDNA formation and maintenance. We propose ATO as a novel prospective treatment option for further pre-clinical and clinical studies against HBV infection.

IMPORTANCE

The main challenge for the achievement of a functional cure for hepatitis B virus (HBV) is the covalently closed circular DNA (cccDNA), the highly stable persistence reservoir of HBV, which is maintained by further rounds of infection with newly generated progeny viruses or by intracellular recycling of mature nucleocapsids. Eradication of the cccDNA is considered to be the holy grail for HBV curative treatment; however, current therapeutic approaches fail to directly tackle this HBV persistence reservoir. The molecular effect of arsenic trioxide (ATO) on HBV infection, protein expression, and cccDNA formation and maintenance, however, has not been characterized and understood until now. In this study, we reveal ATO treatment as a novel and innovative therapeutic approach against HBV infections, repressing viral gene expression and replication as well as the stable cccDNA pool at low micromolar concentrations by affecting the cellular function of promyelocytic leukemia nuclear bodies.

Effects of dietary arsenic exposure on liver metabolism in mice

Arsenic, a ubiquitous environmental toxicant with various forms and complex food matrix interactions, can reportedly exert differential effects on the liver compared to drinking water exposure. To examine its specific liver-related harms, we targeted the liver in C57BL/6 J mice (n=48, 8-week-old) fed with arsenic-contaminated food (30 mg/kg) for 60 days, mimicking the rice arsenic composition observed in real-world scenarios (iAsV: 7.3%, iAsIII: 72.7%, MMA: 1.0%, DMA: 19.0%). We then comprehensively evaluated liver histopathology, metabolic changes, and the potential role of the gut-liver axis using human hepatocellular carcinoma cells (HepG2) and microbiota/metabolite analyses. Rice arsenic exposure significantly altered hepatic lipid (fatty acids, glycerol lipids, phospholipids, sphingolipids) and metabolite (glutathione, thioneine, spermidine, inosine, indole-derivatives, etc.) profiles, disrupting 33 metabolic pathways (bile secretion, unsaturated fatty acid biosynthesis, glutathione metabolism, ferroptosis, etc.). Pathological examination revealed liver cell necrosis/apoptosis, further confirmed by ferroptosis induction in HepG2 cells. Gut microbiome analysis showed enrichment of pathogenic bacteria linked to liver diseases and depletion of beneficial strains. Fecal primary and secondary bile acids, short-chain fatty acids, and branched-chain amino acids were also elevated. Importantly, mediation analysis revealed significant correlations between gut microbiota, fecal metabolites, and liver metabolic alterations, suggesting fecal metabolites may mediate the impact of gut microbiota and liver metabolic disorders. Gut microbiota and its metabolites may play significant roles in arsenic-induced gut-liver injuries. Overall, our findings demonstrate that rice arsenic exposure triggers oxidative stress, disrupts liver metabolism, and induces ferroptosis.

Reduced burden of Arsenic-Related cancers after water mitigation in Taiwan

BACKGROUND

Epidemiological evidence has demonstrated an association between arsenic in drinking water and increased cancer incidence. This population-based study investigates the impact of a tap water supply system installation in Blackfoot disease-endemic regions of Taiwan on cancer incidence.

METHODS

By using the Taiwan Cancer Registry dataset, we enrolled patients aged 40-84 diagnosed with arsenic-related cancers, including hepatocellular carcinoma, small and squamous cell lung cancer, Bowen's disease, basal and squamous cell skin cancer, urothelial bladder cancer, and upper tract urothelial carcinoma between 1995 and 2019. Random-effects age-period-cohort models were used to estimate the cancer incidence data, and a stabilized kriging method was employed to interpolate incidence rates to more precise spatiotemporal units.

RESULTS

The results showed that the age-standardized incidence rates of all six types of studied cancers were consistently higher in Blackfoot disease-endemic areas than those in other areas from 1995 to 2019. However, the gap in incidence rates between Blackfoot disease-endemic areas and the remaining regions began to narrow approximately after the 1960 birth cohort when the tap water supply system installation commenced. For small and squamous cell lung cancer, Bowen's disease, and urothelial bladder cancer, the excess incidence rates sharply declined to null for those born after the year of arsenic mitigation. For upper tract urothelial carcinoma, the excess incidence rates decreased more gradually for those born after the year of arsenic mitigation. For hepatocellular carcinoma and basal and squamous cell skin cancer, the excess incidence rates remained constant. Spatiotemporal clusters of high incidence rates were identified in the core townships of Blackfoot disease-endemic areas. These clusters began to dissipate mainly after the 1960 birth cohort.

CONCLUSION

Arsenic mitigation from drinking water in Taiwan is associated with a reduced burden of small and squamous cell lung cancers, Bowen's disease, urothelial bladder cancer, and upper tract urothelial carcinoma.

Assessing the mechanisms and adjunctive therapy for arsenic-induced liver injury in rats

Environmental arsenic exposure is a significant global public health concern. Previous studies have demonstrated the association between arsenic-induced liver injury and oxidative stress as well as ferroptosis. However, the knowledge of the interactions among these mechanisms remains limited. Moreover, there is a lack of research on potential therapeutic interventions for liver injury resulting from arsenic exposure. To address these limitations, we established a rat model with liver injury caused by arsenic exposure and investigated the impact of the nuclear factor E2-related factor 2 (Nrf2)/glutathione peroxidase 4 (GPx4) signaling pathway and ferroptosis on arsenic-induced liver injury. Our findings revealed that arsenic increased Nrf2 expression and decreased GPx4 expression in the rat liver. This was accompanied by a substantial generation of reactive oxygen species and disruption of the antioxidant defense system, ultimately promoting liver injury through ferroptosis. Subsequently, we conducted intervention experiments using Rosa roxburghii Tratt (RRT) in rats exposed to arsenic. The results showed that the detrimental effects mentioned earlier were partially alleviated following RRT intervention. This study offers preliminary evidence that persistent activation of Nrf2 by arsenic triggers an adaptive antioxidant response, leading to liver injury through the promotion of ferroptosis. Additionally, we discovered that RRT inhibits Nrf2-mediated adaptive antioxidant responses by reducing hepatic ferroptosis, thereby mitigating liver injury caused by arsenic exposure in rats. Our study contributes to a deeper understanding of the molecular mechanisms underlying liver injury resulting from arsenic exposure. Furthermore, our findings may facilitate the identification of a potential edible and medicinal plant extracts that could be utilized to develop a more effective adjunctive treatment approach.

Assessing the health risks of coal-burning arsenic-induced skin damage: A 22-year follow-up study in Guizhou, China

Risk assessment of arsenic-induced skin damage has always received significant global attention. Theories derived from arsenic exposure in drinking water may not be applicable to the coal-burning type to arsenic-exposed area. Furthermore, very few studies have successfully determined the reference value of cumulative arsenic (CA) exposure that leads to specific skin lesions. In this study, we conducted a 22-year follow-up investigation to assess the risk of skin lesions and cancer resulting from long-term, multi-channel arsenic exposure from hazard identification, dose-response assessment, exposure assessment, and risk characterization. The results show that the arsenic exposure can significantly increase the prevalence of skin lesions. For each interquartile range increase of hair arsenic (HA) and CA, the risk of skin damage increased by 1.91 and 3.90 times, respectively. The lower confidence limit of the benchmark dose of HA of arsenic-induced various skin lesions ranged from 0.07 to 0.12 μg·g-1, and 932.57 to 1368.92 mg for CA. The chronic daily intake, lifetime average daily dose in the arsenic-exposed area after the comprehensive prevention and control measures have decreased significantly, but remained higher than the daily baseline level of 3.0 μg·kg-1·d-1. Even as recently as 2020, the hazard quotients and hazard index still exceeded 1, measuring 155.33 and 55.20, and the lifetime excess risk of skin cancer (2.80 × 10-3) remains significantly higher than the acceptable level of 10-6. Our study underscores the effectiveness of comprehensive prevention and control measures in managing high arsenic exposure in coal-burning arsenic poisoning areas. However, it is crucial to acknowledge that the risk of both non-carcinogenic and carcinogenic effects on the skin remains substantially higher than the acceptable level. We recommend setting reference limits for monitoring skin damage among individuals exposed to arsenic, with a recommended upper limit of 0.07 μg·g-1 for HA and a maximum acceptable level of 935.57 mg for CA.

Depletion of S-adenosylmethionine induced by arsenic exposure is involved in liver injury of rat through perturbing histone H3K36 trimethylation dependent bile acid metabolism

Long-term exposure to arsenic, a common environmental pollutant, can induce various types of liver injury, but the mechanism and treatment measures remain unclear. This study constructed a rat model of arsenic-induced liver injury, with methyl group donor S-adenosylmethionine (SAM) supplementation and Rosa roxburghii Tratt juice intervention, to explore the epigenetic mechanism and intervention method of arsenic-induced liver injury from the perspective of hepatic bile acid metabolism. The results showed that arsenic exposure induced the accumulation of total bile acids (TBA) in the liver and serum of rats, and the abnormalities in liver function and liver histopathology. Arsenic reduced histone H3K36 trimethylation (H3K36me3) in the liver via consuming methyl group donor SAM. The reduction of H3K36me3 was involved in arsenic-induced bile acid accumulation by inhibiting the transcription of negative feedback regulators Fxr and Fgfr4 for hepatic bile acid synthesis. SAM supplementation reversed arsenic-induced bile acid accumulation and liver injury by reactivating H3k36me3-dependent transcription of Fxr and Fgfr4. Moreover, this study found that Rosa roxburghii Tratt juice could rescue arsenic-induced SAM consumption, recover H3K36me3-dependent negative feedback regulation of hepatic bile acid synthesis, and alleviate arsenic-induced bile acid accumulation and liver injury. In conclusion, arsenic exposure perturbed H3K36me3-dependent hepatic bile acid metabolism via depleting SAM, thereby inducing hepatic bile acid accumulation and liver injury, which was ameliorated by the supporting effect of Rosa roxburghii Tratt juice on SAM. This study contributes to understanding the mechanism of arsenic-induced liver injury from the perspective of SAM-dependent epigenetics, providing new insight into its prevention and treatment.

Integrated metabolomics and network pharmacology revealing the mechanism of arsenic-induced hepatotoxicity in mice

Endemic arsenic (As) poisoning is a severe biogeochemical disease that endangers human health. Epidemiological investigations and animal experiments have confirmed the damaging effects of As on the liver, but there is an urgent need to investigate the underlying mechanisms. This study adopted a metabolomic approach using UHPLC-QE/MS to identify the different metabolites and metabolic mechanisms associated with As-induced hepatotoxicity in mice. A network pharmacology approach was applied to predict the potential target of As-induced hepatotoxicity. The predicted targets of differential metabolites were subjected to a deep matching for elucidating the integration mechanisms. The results demonstrate that the levels of ALT and AST in plasma significantly increased in mice after As exposure. In addition, the liver tissue showed disorganized liver lobules, lax cytoplasm and inflammatory cell infiltration. Metabolomic analysis revealed that As exposure caused disturbance to 40 and 75 potential differential metabolites in plasma and liver, respectively. Further investigation led to discovering five vital metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis and nicotinate and nicotinamide metabolism pathways. These pathways may responded to As-induced hepatotoxicity primarily through lipid metabolism, apoptosis, and deoxyribonucleic acid damage. The network pharmacology suggested that As could induce hepatotoxicity in mice by acting on targets including Hsp90aa1, Akt2, Egfr, and Tnf, which regulate PI3K Akt, HIF-1, MAPK, and TNF signaling pathways. Finally, the integrated metabolomics and network pharmacology revealed eight key targets associated with As-induced hepatoxicity, namely DNMT1, MAOB, PARP1, MAOA, EPHX2, ANPEP, XDH, and ADA. The results also suggest that nicotinic acid and nicotinamide metabolisms may be involved in As-induced hepatotoxicity. This research identified the metabolites, targets, and mechanisms of As-induced hepatotoxicity, offering meaningful insights and establishing the groundwork for developing antidotes for widespread As poisoning.

Carcinogenic effect of arsenic in digestive cancers: a systematic review

BACKGROUND

The carcinogenic effect of arsenic (As) has been documented in lung, bladder and skin cancers but remains unclear for digestive cancers, although metabolic pathways of As and recent data suggest that it may be an important determinant in these malignancies as well.

OBJECTIVE

This study aimed to systematically review the available literature investigating the potential association between As and digestive cancers.

METHODS

An extensive search was conducted in Medline Ovid SP, Cochrane, PubMed, Embase.com, Cochrane Library Wiley, Web of Science and Google Scholar. Studies providing original data in humans, with As measurement and analysis of association with digestive cancers including esogastric cancers (esophagus and stomach), hepato-pancreatico-biliary (HPB) cancers (including biliary tract, liver and pancreas) and colorectal cancers were eligible.

RESULTS

A total of 35 studies were identified, 17 ecological, 13 case-control and 5 cohort studies. Associations between As and digestive cancers were reported for both risks of incidence and cancer-related mortality. Overall, 43% (3/7) and 48% (10/21) studies highlighted an association between As and the incidence or the mortality of digestive cancers, respectively.

CONCLUSIONS

A substantial proportion of studies exploring the potential link between As and digestive cancers suggested an association, particularly in HPB malignancies. These findings emphasize the need to further investigate this topic with dedicated and high-quality studies, as it may have an important impact, including for prevention strategies.

The lncRNA HOTAIR via miR-17-5p is involved in arsenite-induced hepatic fibrosis through regulation of Th17 cell differentiation

Arsenic compounds are toxins that are widely distributed in the environment. Chronic exposure to low levels of these compounds can cause hepatic fibrosis and other damage. Th17 differentiation of CD4⁺ T cells and the secretion of IL-17 activates hepatic stellate cells (HSCs), which are involved in hepatic fibrosis, but their mechanisms in arsenic-induced hepatic fibrosis are unclear. We found, in arsenite-induced fibrotic livers of mice, increases of CD4⁺ T cell infiltration, Th17 cell nuclear receptor retinoic acid receptor-related orphan receptor γt (RORγt), and secretion of the pro-inflammatory cytokine IL-17. There were also elevated levels of the lncRNA, HOTAIR. For Jurkat cells, arsenite elevated levels of HOTAIR and protein levels of RORγt and IL-17A, decreased miR-17-5p, promoted Th17 cell differentiation, and released IL-17. The culture medium of arsenite-treated Jurkat cells activated LX-2 cells. Down-regulation of HOTAIR or up-regulation of miR-17-5p blocked arsenite-induced Th17 cell differentiation, which inhibited the LX-2 cell activation. However, down-regulation of HOTAIR and miR-17-5p reversed this inhibitory effect. For mice, silencing of HOTAIR diminished the hepatic levels of RORγt and IL-17A and alleviated arsenite-induced hepatic fibrosis. These results demonstrate that, for CD4⁺ T cells, arsenite promotes RORγt-mediated Th17 cell differentiation through HOTAIR down-regulation of miR-17-5p, and increases the secretion of cytokine IL-17A, which activates HSCs; the activated HSCs facilitate hepatic fibrosis. The findings reveal a new mechanism and a potential therapeutic target for arsenite-induced hepatic fibrosis.

Thymoquinone supplementation mitigates arsenic-induced cytotoxic and genotoxic alterations in rat liver

Arsenic, a widespread environmental toxin, produces multiple organ toxicity, including hepatotoxicity. Thymoquinone (TQ) is known to restore liver functions in several hepatic injury models. This study aims to assess the mitigative potential of TQ against sodium arsenate (NaAs)-induced cytotoxic and genotoxic alterations in the liver. Rats were randomly distributed to control, NaAs, TQ, and NaAs+TQ groups. NaAs+TQ and TQ group of rats were pre-treated with TQ (1.5 mg/kg bwt, orally) for 14 days, and the treatment was further continued for 30 days, with and without NaAs treatment (5 mg/kg bwt, orally), respectively. The deleterious histological alterations in the liver of arsenic intoxicated animals were accompanied by an upsurge in the activities of serum ALT and AST, the diagnostic indicators of liver injury. NaAs caused pronounced alterations in the activities of membrane marker and carbohydrate metabolic enzymes and the enzymatic and non-enzymatic components of hepatic antioxidant defense. Significant hepatocyte DNA damage and hepatic arsenic accumulation were also observed in arsenic-exposed rats. TQ supplementation alleviated these adverse alterations and improved the overall hepatic metabolic and antioxidant status in NaAs-administered rats. Prevention of oxidative injury could be the key mechanism of TQ-elicited protective effects. TQ may have an excellent scope as a dietary supplement in the management of arsenic-induced hepatic pathophysiology.

Investigation of arsenic contamination in groundwater using hydride generation atomic absorption spectrometry

The validated hydride generation atomic absorption spectrometry (HG-AAS) method has been used to investigate total arsenic in groundwater. Under optimal experimental conditions, the concentration of arsenic in groundwater can be analysed in the range of 0.5 to 50 µg/L, with a method detection limit of 0.15 µg/L. Its recovery in the field is from 96.3 to 99.8%, with high repeatability. The method was used to observe the total arsenic pollution in groundwater collected in Phu Tho Province, Vietnam. A total of 364 groundwater samples were analysed. The results showed that arsenic pollution was significant, with 15.93% of the samples higher than the maximum permissible level of arsenic. About 20.69% of the contaminated samples had a total arsenic ten times higher (100 µg/L) than the maximum permissible level of arsenic. The pollution source was also considered by comparing the arsenic level in the groundwater with arsenic in the surface water in the same areas. Thus, the use of the high-accuracy and sensitive method, HG-AAS, supplies valuable data on groundwater pollution for water resources management and environmental protection.

Hypermethylation of Mig-6 gene promoter region inactivates its function, leading to EGFR/ERK signaling hyperphosphorylation, and is involved in arsenite-induced hepatic stellate cells activation and extracellular matrix deposition

Arsenic is a widespread naturally contaminant. Previous studies have highlighted the issue of liver fibrosis induced by arsenic exposure, while the exact mechanisms are not yet fully understood. Recent studies suggest that Mig-6/EGFR/ERK signaling appear to play important roles in fibrosis caused by various factors. In this study, we focused on the epigenetic modification combined with the signaling dysregulation to validate the role of Mig-6 in regulating EGFR/ERK signaling in arsenite-induced human hepatic stellate cells (HSCs) activation. Our results revealed that arsenite exposure induced HSCs activation and extracellular matrix (ECM) deposition. The EGFR/ERK signaling was significantly hyperphosphorylated in arsenite-exposed HSCs, and Mig-6 inactivation was involved in arsenite induced hyperphosphorylation of EGFR and activation of HSCs. Additionally, we further illustrated that hypermethylation of Mig-6 gene promoter region was responsible for the downregulation of Mig-6 induced by arsenite exposure. Moreover, 5-Aza-dC (a DNA methyltransferase inhibitor) can efficiently rescue hypermethylation of Mig-6 gene, decrease the hyperphosphorylation of EGFR/ERK signaling, then reverse arsenite induced HSCs activation. Taken together, the present study strongly suggests that inactivating of Mig-6 function by hypermethylation of its promoter region leading to hyperphosphorylation of EGFR/ERK signaling, and is involved in arsenite-induced HSCs activation and ECM deposition.

Arsenic-Induced Injury of Mouse Hepatocytes through Lysosome and Mitochondria: An In Vitro Study

BACKGROUND AND AIMS

The cellular mechanism of liver injury related to arsenic toxicity is ill defined. It is thought that oxidative stress and mitochondrial dysfunction may play some role in arsenic-induced liver damage. In this study, we evaluated subcellular events within the primary cultured mouse hepatocytes when exposed to inorganic arsenic.

METHODS

Primary cultured mouse hepatocytes were treated with 10 μM arsenic for different time periods. Reactive oxygen species (ROS) formation, functional changes of the lysosome and mitochondria, and mode of hepatocytes death were studied by laser confocal microscopy, fluorescence spectroscopy, and flow cytometry. Expression of proapoptotic member of the BCL-2 family of genes BAX and antiapoptotic BCL-2 mRNA expression were studied by real-time PCR. Cytochrome c expression was studied by Western blotting.

RESULTS

Fluorescence spectroscopy as well as flow cytometric analysis revealed that arsenic-induced formation of ROS was time dependent. Confocal microscopy showed initiation of ROS formation from periphery of the hepatocytes at 30 min of arsenic exposure that progressed to central part of the hepatocytes at 3 h of arsenic exposure. The ROS formation was found to be NADPH oxidase (NOX) dependent. This low level of intracellular ROS induced lysosomal membrane permeabilization (LMP) and subsequently released cathepsin B to the cytosol. The LMP further increased intracellular ROS which in turn triggered induction of mitochondrial permeability transition (MPT). Pretreatment of hepatocytes with LMP inhibitor bafilomycin A (BafA) significantly decreased, and LMP inducer chloroquine (ChQ) significantly increased the production of ROS suggesting that LMP preceded enhanced ROS generation in response to arsenic. MPT was accompanied with increase in BAX : BCL2 mRNA ratio resulting in upregulation of caspase 3 and increased hepatocyte apoptosis.

CONCLUSION

Although arsenic-related oxidative liver injury is well established, neither the site of origin of ROS nor the early sequence of events in arsenic toxicity due to ROS is known. We believe that our study provides evidences elucidating the early sequence of events that culminates in the death of the mouse hepatocytes during arsenic exposure.

Assessing the Role of Nrf2/GPX4-Mediated Oxidative Stress in Arsenic-Induced Liver Damage and the Potential Application Value of Rosa roxburghii Tratt [Rosaceae]

Arsenic poisoning is a geochemical disease that seriously endangers human health. The liver is one of the important target organs for arsenic poisoning, several studies have shown that oxidative stress plays an important role in arsenic-induced liver damage. However, the specific mechanism of arsenic-induced oxidative stress has not yet been fully elucidated, and currently, there are no effective intervention measures for the prevention and treatment of arsenic-induced liver damage. In this study, the effect of the Nrf2/GPX4 signaling pathway and oxidative stress in the arsenic-induced liver damage was first evaluated. The results show that arsenic can activate the Nrf2/GPX4 signaling pathway and increase the oxidative stress, which in turn promotes arsenic-induced liver damage in MIHA cells. Moreover, when we applied the Nrf2 inhibitor, the promoting effect of arsenic on liver damage was alleviated by inhibiting the activation of the Nrf2/GPX4 signaling pathway. Subsequently, the Rosa roxburghii Tratt [Rosaceae] (RRT) intervention experiments in cells and arsenic poisoning population were designed. The results revealed that RRT can inhibit Nrf2/GPX4 signaling pathway to reduce oxidative stress, thereby alleviates arsenic-induced liver damage. This study provides some limited evidence that arsenite can activate Nrf2/GPX4 signaling pathway to induce oxidative stress, which in turn promotes arsenic-induced liver damage in MIHA cells. The second major finding was that Kaji-ichigoside F1 may be a potential bioactive compound of RRT, which can inhibit Nrf2/GPX4 signaling pathway to reduce oxidative stress, thereby alleviates arsenic-induced liver damage. Our study will contribute to a deeper understanding of the mechanisms in arsenic-induced liver damage, these findings will identify a possible natural medicinal food dual-purpose fruit, RRT, as a more effective prevention and control strategies for arsenic poisoning.

Arsenic exposure and non-carcinogenic health effects

Inorganic arsenic (iAs) exposure is a serious health problem that affects more than 140 million individuals worldwide, mainly, through contaminated drinking water. Acute iAs poisoning produces several symptoms such as nausea, vomiting, abdominal pain, and severe diarrhea, whereas prolonged iAs exposure increased the risk of several malignant disorders such as lung, urinary tract, and skin tumors. Another sensitive endpoint less described of chronic iAs exposure are the non-malignant health effects in hepatic, endocrine, renal, neurological, hematological, immune, and cardiovascular systems. The present review outlines epidemiology evidence and possible molecular mechanisms associated with iAs-toxicity in several non-carcinogenic disorders.

Persistence and reversibility of arsenic-induced gut microbiome and metabolome shifts in male rats after 30-days recovery duration

The metabolites of gut microbiome are important host-health regulating factors and can be interrupted when the host is exposed to environmental pollutant via ingestion route. Arsenic contaminated drinking water is one of the most serious environmental health problems worldwide. Therefore, the arsenic-induced alterations of gut microbiome and metabolome, especially the persistence and reversibility of the alterations after the long-term arsenic exposure will be interesting to know. In this study, we investigated the relationship between gut microbiota and metabolites in male rats both after the 30-days arsenic treatment and 30-days recovery duration. The composition and diversity of gut microbiota were affected significantly by the treatment, but they presented partial improvement in recovery duration. Moreover, arsenic exposure induced the significant changes of 73 metabolites, which involved in the metabolism of glycerophospholipid, linoleic acid, as well as the biosynthesis of phenylalanine, tyrosine and tryptophan. Although it had a persistent effect, the restoration of glycerophospholipid metabolism was observed in the 30-days recovery. Integration analysis further correlated the arsenic impacting microbes with some important differential metabolites. Lactobacillus associated with the decreases of phosphatidylethanolamine(34:1), 16alpha-hydroxydehydroepiandrosterone 3-sulfate, seryltryptophan and alanyltyrosine in recovery duration. Lactobacillus strains have potential to work as protective agents against arsenic toxicity by restoring perturbed glycerophospholipid metabolism. In summary, arsenic significantly disrupted gut microbiome and metabolome, but the disruptions are reversible to some extent after a 30-days recovery.

GT-Repeat Polymorphism in the HO-1 Gene Promoter Is Associated with Risk of Liver Cancer: A Follow-Up Study from Arseniasis-Endemic Areas in Taiwan

The induction of heme oxygenase-1 (HO-1) has been shown to have therapeutic potential in experimental models of hepatitis and liver fibrosis, which are closely related to liver cancer. In humans, HO-1 induction is transcriptionally modulated by the length of a GT-repeat [(GT)n] in the promoter region. We aimed to investigate the effect of HO-1 (GT)n variants on liver cancer in a human population. We determined the HO-1 genotype in 1153 study subjects and examined their association with liver cancer risk during a 15.9-year follow-up. Allelic polymorphisms were classified as short [S, <27 (GT)n] or long [L, ≥27 (GT)n]. Newly developed cancer cases were identified through linkage to the National Cancer Registry of Taiwan. Multivariate Cox regression analysis was used to evaluate the effect of the HO-1 (GT)n variants. Alpha-fetoprotein (AFP) and cirrhosis history were also examined. The S/S genotype was found to be significantly associated with liver cancer risk, compared to the L/S and L/L genotypes. The S/S genotype group also had a higher percentage of subjects with abnormal AFP levels than other groups. There were significant percentages of cirrhosis among groups who carried S-alleles. Our findings indicate that short (GT)n variants in the HO-1 gene may confer susceptibility to rather than protection from liver cirrhosis/cancer.

Protective efficacy of thymoquinone or ebselen separately against arsenic-induced hepatotoxicity in rat

Arsenic (As) exposure is associated with adverse health outcomes to the living organisms. In the present study, the hepato-protective ability of thymoquinone (TQ), the active principle of Nigella sativa seed, or ebselen (Eb), an organoselenium compound, against As intoxication in female rats was investigated. For this purpose, animals were allocated randomly into control, As (20 mg/kg), TQ (10 mg/kg), Eb (5 mg/kg), As+TQ, and As+Eb groups that were orally administered for 28 consecutive days. Arsenic exposure resulted in hepatic oxidative damage which was evidenced by marked decreases in antioxidant parameters (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione (GSH)) concomitant with high malondialdehyde (MDA) level. Furthermore, As toxicity induced significant elevations in liver accumulation of As, serum hepatic indices (aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and total bilirubin (TB)), and apoptotic marker (B cell lymphoma 2(Bcl2), Bcl-2-associated X protein (Bax), and caspase 3) levels. Additionally, notable increments in hepatic fibrotic markers (epidermal growth factor (EFG) and transforming growth factor beta 1 (TGF-β1)) associated with high nitric oxide, interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and myeloperoxidase (MPO) levels were noticed following As intoxication. Biochemical findings were well-supported by hepatic histopathological screening. The co-treatment of As-exposed rats with TQ or Eb considerably improved liver function and antioxidant status together with lessened hepatic As content, inflammation, apoptosis, and fibrosis. The overall outcomes demonstrated that TQ or Eb ameliorates As-induced liver injury through their favorable antioxidant, anti-inflammatory, anti-apoptotic, and fibrolytic properties.

miR-21-regulated M2 polarization of macrophage is involved in arsenicosis-induced hepatic fibrosis through the activation of hepatic stellate cells

Arsenicosis induced by chronic exposure to arsenic is recognized as one of the main damaging effects on public health. Exposure to arsenic can cause hepatic fibrosis, but the molecular mechanisms by which this occurs are complex and elusive. It is not known if miRNAs are involved in arsenic-induced liver fibrosis. We found that in the livers of mice exposed to arsenite, there were elevated levels of microRNA-21 (miR-21), phosphorylated mammalian target of rapamycin (p-mTOR), and arginase 1 (Arg1); low levels of phosphatase and tensin homolog (PTEN); and more extensive liver fibrosis. For cultured cells, arsenite-induced miR-21, p-mTOR, and Arg1; decreased PTEN; and promoted M2 polarization of macrophages derived from THP-1 monocytes (THP-M), which caused secretion of fibrogenic cytokines, including transforming growth factor-β1. Coculture of arsenite-treated, THP-M with LX-2 cells induced α-SMA and collagen I in the LX-2 cells and resulted in the activation of these cells. Downregulation of miR-21 in THP-M inhibited arsenite-induced M2 polarization and activation of LX-2 cells, but cotransfection with PTEN siRNA or a miR-21 inhibitor reversed this inhibition. Moreover, knockout of miR-21 in mice attenuated liver fibrosis and M2 polarization compared with WT mice exposed to arsenite. Additionally, LN, PCIII, and HA levels were higher in patients with higher hair arsenic levels, and levels of miR-21 were higher than controls and positively correlated with PCIII, LN, and HA levels. Thus, arsenite induces the M2 polarization of macrophages via miR-21 regulation of PTEN, which is involved in the activation of hepatic stellate cells and hepatic fibrosis. The results establish a previously unknown mechanism for arsenicosis-induced fibrosis.

Epigenetic effects of low-level sodium arsenite exposure on human liver HepaRG cells

Chronic exposure to inorganic arsenic is associated with a variety of adverse health effects, including lung, bladder, kidney, and liver cancer. Several mechanisms have been proposed for arsenic-induced tumorigenesis; however, insufficient knowledge and many unanswered questions remain to explain the integrated molecular pathogenesis of arsenic carcinogenicity. In the present study, using non-tumorigenic human liver HepaRG cells, we investigated epigenetic alterations upon prolonged exposure to a noncytotoxic concentration of sodium arsenite (NaAsO₂). We demonstrate that continuous exposure of HepaRG cells to 1 µM sodium arsenite (NaAsO₂) for 14 days resulted in substantial cytosine DNA demethylation and hypermethylation across the genome, among which the claudin 14 (CLDN14) gene was hypermethylated and the most down-regulated gene. Another important finding was a profound loss of histone H3 lysine 36 (H3K36) trimethylation, which was accompanied by increased damage to genomic DNA and an elevated de novo mutation frequency. These results demonstrate that continuous exposure of HepaRG cells to a noncytotoxic concentration of NaAsO₂ results in substantial epigenetic abnormalities accompanied by several carcinogenesis-related events, including induction of epithelial-to-mesenchymal transition, damage to DNA, inhibition of DNA repair genes, and induction of de novo mutations. Importantly, this study highlights the intimate mechanistic link and interplay between two fundamental cancer-associated events, epigenetic and genetic alterations, in arsenic-associated carcinogenesis.

State of the science review of the health effects of inorganic arsenic: Perspectives for future research

Human exposure to inorganic arsenic (iAs) is a global health issue. Although there is strong evidence for iAs-induced toxicity at higher levels of exposure, many epidemiological studies evaluating its effects at low exposure levels have reported mixed results. We comprehensively reviewed the literature and evaluated the scientific knowledge on human exposure to arsenic, mechanisms of action, systemic and carcinogenic effects, risk characterization, and regulatory guidelines. We identified areas where additional research is needed. These priority areas include: (1) further development of animal models of iAs carcinogenicity to identify molecular events involved in iAs carcinogenicity; (2) characterization of underlying mechanisms of iAs toxicity; (3) assessment of gender-specific susceptibilities and other factors that modulate arsenic metabolism; (4) sufficiently powered epidemiological studies to ascertain relationship between iAs exposure and reproductive/developmental effects; (5) evaluation of genetic/epigenetic determinants of iAs effects in children; and (6) epidemiological studies of people chronically exposed to low iAs concentrations.

Autophagy upregulation as a possible mechanism of arsenic induced diabetes

The key features of type 2 diabetes mellitus (T2DM) caused by high fat diet (HFD) in combination with arsenic (As) exposure (pronounced glucose intolerance despite a significant decrease in insulin resistance) are different from those expected for T2DM. Autophagy has been considered as a possible link between insulin resistance and obesity. Therefore in this study, we utilized autophagy gene expression profiling via real-time RT-PCR array analysis in livers of NMRI mice exposed to an environmentally relevant and minimally cytotoxic concentration of arsenite (50 ppm) in drinking water while being fed with a HFD for 20 weeks. Out of 84 genes associated with autophagy under study, 21 genes were related to autophagy machinery components of which 13 genes were downregulated when HDF diet was applied. In this study, for the first time, it was shown that the exposure to arsenic in the livers of mice chronically fed with HFD along with increased oxidative stress resulted in the restoration of autophagy [upregulation of genes involved in the early phase of phagophore formation, phagophore expansion and autophagosome-lysosome linkage stages]. Considering the role of arsenic in the induction of autophagy; it can be argued that reduced insulin resistance in HFD - As induced diabetes may be mediated by autophagy upregulation.

Identification and Characterization of Cadmium-Related Genes in Liver Carcinoma

Evidence indicates that exposure to heavy trace element might be a risk factor for liver carcinoma. Cadmium has been supposed to be a carcinogen that has a correlation with the risk of a number of cancers, including liver cancer. However, the mechanisms underlying Cadmium-induced malignant transformation in liver cells are not fully understood. In the present study, we aimed to screen the differentially expressed genes (DEGs) that might play a role in both the Cadmium-related liver cell transformation and the development of liver cancer. Microarray-based gene expression profiles concerning liver carcinoma vs non-cancerous tissue (GSE64041) and Cadmium-treated liver cells vs controls (GSE8865 and GSE31286), respectively, were retrieved from Gene Expression Omnibus (GEO) database. Then, DEGs of each profile were calculated and screened. The intersection of each DEGs was obtained by Venn analysis. Afterwards, the possible roles of the selected genes in cancer development were evaluated by using Oncomine database and TCGA cohort analysis. Consequently, three DEGs, LRAT, SLC7A11, and ITGA2, were selected for further analysis. SLC7A11 and ITGA2, but not LRAT, were upregulated in liver cancer compared with those in normal tissues, respectively. After using a TCGA cohort analysis, results failed to show a significant correlation between SLC7A11 or ITGA2 expression and clinical parameters. However, the survival analysis showed that patients with high expression levels of SLC7A11 had a shorter overall survival time relative to those of the patients with low levels. In conclusion, SLC7A11 and ITGA2 might play a role in the Cadmium-induced liver cell damage or transformation, and the development of liver carcinoma. SLC7A11 might be a prognostic factor for patients with liver carcinoma. Future validation experiments are needed to verify the results.