Antimony-trioxide- and arsenic-trioxide-induced apoptosis in myelogenic and lymphatic cell lines, recruitment of caspases, and loss of mitochondrial membrane potential are enhanced by modulators of the cellular glutathione redox system

Low-dose antimony exposure promotes prostate cancer proliferation by inhibiting ferroptosis via activation of the Nrf2-SLC7A11-GPX4 pathway

Antimony (Sb) is a typical environmental pollutant. With the development of industrialization, antimony is widely used in daily life and enters the human body through the food chain, water source, air pollution, and other channels. The risk of antimony exposure has emerged as one of the public's major health concerns. Current research on antimony shows that antimony has certain biological toxicity, and antimony exposure may be one of the carcinogenic risk factors for bladder cancer, prostate cancer (PCa), and other cancers. But the molecular mechanism of antimony exposure in PCa is still unclear. Our results showed that serum antimony levels were significantly higher in PCa patients than in benign prostatic hyperplasia (BPH), and high levels of serum antimony were associated with poorer prognosis in PCa. We demonstrate that antimony exposure promotes PCa progression in vivo and in vitro. In addition, our results also showed that low-dose antimony exposure resulted in increased GSH, increased GPX4 expression, and decreased Fe2+. Since GPX4 and Fe2+ are important molecular features in the mechanism of ferroptosis, we further found that low-dose antimony exposure can inhibit RSL3-induced ferroptosis and promote PCa proliferation. Finally, our study demonstrates that low-dose antimony exposure promotes Nrf2 expression, increases the expression level of SLC7A11, and then increases the expression of GPX4, inhibits ferroptosis, and promotes PCa progression. Taken together, our experimental results suggest that low-dose antimony exposure promotes PCa cell proliferation by inhibiting ferroptosis through activation of the Nrf2-SLC7A11-GPX4 pathway. These findings highlight the link between low-dose antimony exposure and the Nrf2-SLC7A11-GPX4 ferroptosis pathway, providing a new potential direction for the prevention and treatment of PCa.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Cardiovascular Effects of Environmental Metal Antimony: Redox Dyshomeostasis as the Key Pathogenic Driver

Significance: Cardiovascular diseases (CVDs) are the leading cause of death worldwide, which may be due to sedentary lifestyles with less physical activity and over nutrition as well as an increase in the aging population; however, the contribution of pollutants, environmental chemicals, and nonessential metals to the increased and persistent CVDs needs more attention and investigation. Among environmental contaminant nonessential metals, antimony has been less addressed. Recent Advances: Among environmental contaminant nonessential metals, several metals such as lead, arsenic, and cadmium have been associated with the increased risk of CVDs. Antimony has been less addressed, but its potential link to CVDs is being gradually recognized. Critical Issues: Several epidemiological studies have revealed the significant deleterious effects of antimony on the cardiovascular system in the absence or presence of other nonessential metals. There has been less focus on whether antimony alone can contribute to the pathogenesis of CVDs and the proposed mechanisms of such possible effects. This review addresses this gap in knowledge by presenting the current available evidence that highlights the potential role of antimony in the pathogenesis of CVDs, most likely via antimony-mediated redox dyshomeostasis. Future Directions: More direct evidence from preclinical and mechanistic studies is urgently needed to evaluate the possible roles of antimony in mitochondrial dysfunction and epigenetic regulation in CVDs. Antioxid. Redox Signal. 38, 803-823.

Disruption of mitochondrial redox homeostasis as a mechanism of antimony-induced reactive oxygen species and cytotoxicity

Occupational and environmental Sb exposure has been associated with increased risk of respiratory diseases and lung cancer, but the toxicities and molecular mechanisms of Sb have been less investigated. In the present study, we first analyzed the Sb toxicity profile of lung adenocarcinoma A549 cells, and found that Sb dose-dependently decreased the cell viability and arrested cell cycle at G2/M but did not induce apoptosis. We next investigated the role of reactive oxygen species (ROS) involved in Sb-induced cytotoxicity. The results showed that Sb did not significantly induce cytosolic ROS production by NADPH oxidase (NOX) and the NOX inhibitors did not ameliorate the Sb-induced cell viability loss in A549 cells. However, the level of mitochondrial ROS (mtROS) was significantly increased in Sb-exposed cells and the mitochondria-targeted antioxidant significantly improved cell viability. These results suggested that mitochondria but not NOX is the major source of ROS production and mtROS plays a critical role in Sb-induced cytotoxicity. Furthermore, we found that Sb induced mitochondria dysfunction including the significant decrease of ATP level and mitochondrial membrane potential. Finally, Sb exposure decreased the activity of complex I and complex III, the level of -SH and GSH in mitochondria, and the activity of mitochondrial GR, GPx and TrxR, but increased the mitochondrial SOD activity, suggesting the disruption of mitochondrial redox homeostasis. Taken together, these findings suggested that Sb impaired mitochondrial redox homeostasis, resulting in formation of mtROS, thereby inhibited mitochondrial function and led to cytotoxicity.

NaAsO2 decreases GSH synthesis by inhibiting GCLC and induces apoptosis through Hela cell mitochondrial damage, mediating the activation of the NF-κB/miR-21 signaling pathway

BACKGROUND

Cervical cancer is the fourth most common cancer in women worldwide, and arsenic has a certain effect in solid tumor chemotherapy. As the rate-limiting enzyme subunit of GSH synthesis, GCLC may be an important target for arsenic to induce apoptosis through mitochondrial apoptosis pathway to exert anti-tumor effect. NF-κB plays an important role in the occurrence and development of cervical cancer and can regulate the expression of GCLC. miR-21 is a potential biomarker of cervical cancer, which can induce apoptosis through ROS regulated the mitochondrial pathway of cells. However, the role of miR-21 in the mitochondrial pathway of cervical cancer cells induced by NaAsO2 through NF-κB/GCLC and GSH synthesis regulated oxidative stress is rarely reported. Therefore, the purpose of this study was to investigate whether NaAsO2 might induce mitochondrial damage and apoptosis of cervical cancer cells through NF-κB/ miR-21 /GCLC induced oxidative stress, and play the anti-tumor role of arsenic as a potential drug for the treatment of cervical cancer.

METHODS

Hela cells were treated with different concentrations of NaAsO2, D, L-Buthionine-(SR)-sulfoximine (BSO), IκBα inhibitor (BAY 11-7082) and miR-21 Inhibitor. CCK-8 assay, Western Blot, qRT PCR, immunofluorescence, transmission electron microscopy, mitochondrial Membrane Potential Assay Kit with JC-1,2',7'-Dichlorofluorescin diacetate fluorescent probe and Annexin V-FITC were used to measure cell activity, GSH and ROS, mitochondrial morphology and membrane potential (ΔΨm), protein and mRNA expression of GCLC, GCLM, p65, IκBα, p-P65, p-I κBα, Bcl-2, BAX, Caspase3, cleaved-caspase3 and miR-21.

RESULTS

Compared with the control group, with the gradual increasing dose of NaAsO2, cell viability was considerable reduced, and increased rate of apoptosis, intracellular GSH level was decreased significantly, ROS was increased, mitochondrial structure was damaged, mitochondrial membrane potential ΔΨm and Bcl2/BAX lowered, the expression of Caspase3 and cleaved-caspase3 were significantly increased, resulting in mitochondrial apoptosis. When Hela cells were treated with 15, 20, and 25 μmol/L NaAsO2, the mRNA and protein levels of GCLC and GCLM were reduced, the expression of p65 in the nucleus was increased, the expression of p-p65/p65, p-IκBα/IκBα and miR-21 were significantly increased. When BSO increased the inhibitory effect of NaAsO2 on GCLC, Compared with NaAsO2 group, the ΔΨm and protein of Bcl-2/BAX, caspase3 and cleaved-capsase3 were increased. When BAY 11-7082 combined with NaAsO2 co-treated, compared with the NaAsO2 group, the protein and mRNA expression of GCLC was increased, NaAsO2-increased expression level of miR-21 was suppressed, and the ΔΨm and cell viability were higher. In addition, compared with the combination of NaAsO2 and miR-21NC, the protein expression of GCLC was increased, the ΔΨm and cell viability reduction were alleviated by miR-21 Inhibitor combined with NaAsO2.

CONCLUSION

NaAsO2 may lead to ROS accumulation in Hela cells and trigger mitochondrial apoptosis. The mechanism may be related to the activation of NF-κB signaling pathway and the promotion of miR-21 expression which leads to the inhibition of GCLC expression and the significant decrease of intracellular reductive GSH synthesis.

LncRNA PCA3 promotes antimony-induced lipid metabolic disorder in prostate cancer by targeting MIR-132-3 P/SREBP1 signaling

Antimony is a common environmental contaminant that causes biological toxicity in exposed populations worldwide. Previous studies have revealed that antimony promotes prostate cancer growth by stabilizing the c-Myc protein and mimicking androgen activity. However, the role of lncRNAs in the regulation of antimony-induced carcinogenesis remains unknown, and the precise mechanisms need to be explored. In the present study, we found that chronic exposure to antimony promoted cell growth and lipid metabolic disequilibrium in prostate cancer. Mechanistically, we identified a long noncoding RNA molecule, PCA3, that was substantially upregulated in LNCaP cells in response to long-term antimony exposure. Functional studies indicated that abnormal PCA3 expression modulated antimony-induced proliferation and cellular triglyceride and cholesterol levels. In addition, PCA3 levels were found to be inversely correlated with MIR-132-3 P levels by acting as a decoy for MIR-132-3P. Besides, SREBP1 directly interacted with MIR-132-3 P to increase cell growth and disrupt lipid metabolism by targeting its 3'UTR regions. Taken together, our results revealed that lncRNA PCA3 promotes antimony-induced lipid metabolic disorder in prostate cancer by targeting MIR-132-3 P/SREBP1 signaling.

Mechanistic effects of arsenic trioxide on acute promyelocytic leukemia and other types of leukemias

Acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia characterized with a translocation between promyelocytic leukemia gene (PML) on chromosome 15 and retinoic acid receptor alpha gene (RARα) on chromosome 17. Transcription of this fusion gene results in PML/RARα fusion protein blocking expression of critical genes involved in differentiation of myeloid cells through interaction with RAR element. PML/RARα fusion protein prevents normal function of PML and RARα as well as inhibiting apoptosis. Arsenic trioxide (ATO) is an important agent for the treatment of relapsed and newly diagnosed APL. ATO induces apoptosis, autophagy, and partial cellular differentiation as well as inhibiting cell growth and angiogenesis. Recognition of signaling pathways and molecular mechanisms induced by ATO can be effective for discovering novel treatment strategies to target leukemia cells. Also, it can be developed for the treatment of a variety of cancer cells. This review provides a perspective on anticancerous effects of ATO on APL and leukemia cells.

Occupational exposure to antimony trioxide: a risk assessment

OBJECTIVES

The US National Toxicology Program (NTP) recently recommended in its Report on Carcinogens Monograph for Antimony Trioxide that antimony trioxide be listed as 'reasonably anticipated to be a human carcinogen' based on sufficient evidence of carcinogenicity in experimental animals and supporting evidence from mechanistic studies. Our goal was to estimate the possible human cancer risk from occupational exposure to antimony trioxide.

METHODS

We selected data from 2-year inhalation studies in male and female mice conducted by the NTP and performed cancer dose-response analyses using cancer models and benchmark dose methods developed by the US Environmental Protection Agency. In these analyses, we generated benchmark doses and cancer slope factors for antimony trioxide, and then estimated human cancer risk under various exposure scenarios. Typical and worst-case inhalation scenarios in multiple occupational settings were used in risk estimation.

RESULTS

In typical case scenarios, the occupational cancer risk from antimony trioxide was estimated to be 0.025 (25 in 1000) for persons working with flame retardants in plastics and textiles for 40 years. Under worst-case scenarios, the occupational cancer risk was estimated to be 0.11 (110 in 1000) for persons working with flame retardants in plastics and textiles. At the current Occupational Safety and Health Administration Permissible Exposure Limit, the cancer risk for occupational inhalation exposure of antimony trioxide was estimated to be 0.096 (96 in 1000).

CONCLUSION

The risk estimates calculated in this study suggest that exposure to antimony trioxide at levels present in certain occupational settings results in a large increase in the risk of developing cancer.

The potential DNA toxic changes among workers exposed to antimony trioxide

Occupational exposure to antimony has gained much interest when specific toxic effects were noticed among workers processing antimony. Thus, the aim of the present work was to investigate the potential DNA oxidative damage occurring among Egyptian workers occupationally exposed to antimony trioxide. The study was conducted on 25 subjects exposed to antimony trioxide while working in the polymerization process of polyester in Misrayon and Polyester Fiber Company, KafrEldawwar, Beheira, Egypt. Urinary antimony levels were assessed using inductive coupled plasma-optical emission spectrometry (ICP-OES) and considered as a biological exposure index. DNA damage and total oxidant capacity (TOC) were assessed using ELISA. DNA damage was detected in the form of increased apurinic/apyrimidinic (AP) sites among antimony trioxide-exposed workers compared to control subjects, but it could not be explained by oxidative mechanisms due to lack of significant correlation between DNA damage and measured TOC. Antimony trioxide might have a genotoxic impact on occupationally exposed workers which could not be attributed to oxidative stress in the studied cases.

Ameliorative Effects of Dietary Selenium Against Cadmium Toxicity Is Related to Changes in Trace Elements in Chicken Kidneys

The ameliorative effects of selenium (Se) against cadmium (Cd)-induced toxicity have been reported extensively. However, few studies have assessed the effects of multiple ions simultaneously on the variations of elements. In this study, the changes in Se, Cd, and 26 other element concentrations were investigated in chicken kidneys. One hundred and twenty-eight 31-week-old laying hens were fed a diet supplemented with either Se, Cd, or both Se and Cd for 90 days. The ion content was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). We found that the Se, Cd, and combined Se and Cd treatments significantly affected the trace elements in the chicken kidneys. The Cd supplement caused ion profile disorders, including reduced concentrations of V, Cr, Mn, Mo, As, Ba, Hg, Ti, and Pb and increased Si, Cu, Li, Cd, and Sb. The Se supplement reduced the contents of Co, Mo, and Pb and increased the contents of Cr, Fe, and Se. Moreover, Se also increased the concentrations of Cr, Mn, Zn, and Se and decreased those of Li and Pb, which in contrast were induced by Cd. Complex interactions between elements were analyzed, and both positive and negative correlations among these elements are presented. The present study indicated that Se can help against the negative effects of Cd and may be related to the homeostasis of the trace elements in chicken kidneys.

Urinary antimony and leukocyte telomere length: An analysis of NHANES 1999-2002

Telomeres are repetitive DNA sequences (TTAGGG) at the end of chromosomes. Cells with critically short telomeres enter replicative senescence and apoptosis. Several in vitro studies report that antimony causes cell apoptosis in human leukocyte cell lines. The goal of this analysis was to investigate whether there is an association between antimony exposure and leukocyte telomere length (LTL) among US adults aged 20 and older based on the National Health and Nutrition Examination Survey (NHANES) 1999-2002. We used multivariate linear regression to analyze the association of urinary antimony with LTL. LTL was log-natural transformed and the results were re-transformed and presented as percent differences. After adjustment for potential confounders, individuals in the 3rd and 4th quartiles of urinary antimony had statistically significantly shorter LTL (-4.78%, 95% CI: -8.42,-0.90; and -6.11%, 95% CI: -11.04,-1.00, respectively) compared to the lowest referent quartile, with evidence of a dose-response relationship (p-value for trend =0.03). Shorter LTL with antimony was driven by middle aged (40-59 years) and older (60-85 years) adult groups. The association may be biologically plausible because of reported oxidative stress and apoptosis effects of antimony on blood cells, effects known to shorten telomere length.

The protective role of Nrf2-Gadd45b against antimony-induced oxidative stress and apoptosis in HEK293 cells

Antimony (Sb) is one of the most prevalent heavy metals and frequently causes biological toxicity. However, the specific mechanisms by which Sb elicits its toxic effects remains to be fully elucidated. In this study, we found antimony trioxide (Sb2O3) caused a dose-dependent cytotoxicity against HEK293 cells, and Sb2O3-induced excessive reactive oxygen species (ROS) was closely correlated with increased cell apoptosis. Mechanistic investigation manifested that nuclear factor NF-E2-related factor 2 (Nrf2) expression and nuclear translocation were significantly induced under Sb2O3 treatment in HEK293 cells, and Nrf2 knockdown aggregated Sb2O3-induced cell apoptosis. Moreover, elevated Gadd45b expression actives the phosphorylation of MAPKs upon Sb2O3 exposure, whereas Gadd45b knockdown diminished Sb2O3-induced activation of MAPKs and promoted cell apoptosis. In the meantime, however, the antioxidant N-acetylcysteine (NAC) was found to ameliorate Nrf2 expression and nuclear translocation as well as Gadd45b expression and MAPKs activation by repressing Sb2O3-induced ROS production. More importantly, we found Gadd45b was transcriptionally enhanced by Nrf2 through binding to three canonical antioxidant response elements (AREs) within its promoter region. Either Sb2O3 or TBHQ (a selective Nrf2 activator) treatment, Gadd45b expression was significantly increased by luciferase assay. Nrf2 inhibition greatly diminished Gadd45b expression due to reduced binding of Nrf2 in Gadd45b promoter under Sb2O3 treatment. To summarize, this study demonstrated the Nrf2-Gadd45b signaling axis exhibited a protective role in Sb-induced cell apoptosis.

Hepatotoxicity of pentavalent antimonial drug: possible role of residual Sb(III) and protective effect of ascorbic acid

Pentavalent antimonial drugs such as meglumine antimoniate (Glucantime [Glu; Sanofi-Aventis, São Paulo, Brazil]) produce severe side effects, including cardiotoxicity and hepatotoxicity, during the treatment of leishmaniasis. We evaluated the role of residual Sb(III) in the hepatotoxicity of meglumine antimoniate, as well as the protective effect of the antioxidant ascorbic acid (AA) during antimonial chemotherapy in a murine model of visceral leishmaniasis. BALB/c mice infected with Leishmania infantum were treated intraperitoneally at 80 mg of Sb/kg/day with commercial meglumine antimoniate (Glu) or a synthetic meglumine antimoniate with lower Sb(III) level (MA), in association or not with AA (15 mg/kg/day), for a 20-day period. Control groups received saline or saline plus AA. Livers were evaluated for hepatocytes histological alterations, peroxidase activity, and apoptosis. Increased proportions of swollen and apoptotic hepatocytes were observed in animals treated with Glu compared to animals treated with saline or MA. The peroxidase activity was also enhanced in the liver of animals that received Glu. Cotreatment with AA reduced the extent of histological changes, the apoptotic index, and the peroxidase activity to levels corresponding to the control group. Moreover, the association with AA did not affect the hepatic uptake of Sb and the ability of Glu to reduce the liver and spleen parasite loads in infected mice. In conclusion, our data supports the use of pentavalent antimonials with low residue of Sb(III) and the association of pentavalent antimonials with AA, as effective strategies to reduce side effects in antimonial therapy.

Synergistic apoptosis of CML cells by buthionine sulfoximine and hydroxychavicol correlates with activation of AIF and GSH-ROS-JNK-ERK-iNOS pathway

Background

Hydroxychavicol (HCH), a constituent of Piper betle leaf has been reported to exert anti-leukemic activity through induction of reactive oxygen species (ROS). The aim of the study is to optimize the oxidative stress –induced chronic myeloid leukemic (CML) cell death by combining glutathione synthesis inhibitor, buthionine sulfoximine (BSO) with HCH and studying the underlying mechanism.

Materials and Methods

Anti-proliferative activity of BSO and HCH alone or in combination against a number of leukemic (K562, KCL22, KU812, U937, Molt4), non-leukemic (A549, MIA-PaCa2, PC-3, HepG2) cancer cell lines and normal cell lines (NIH3T3, Vero) was measured by MTT assay. Apoptotic activity in CML cell line K562 was detected by flow cytometry (FCM) after staining with annexinV-FITC/propidium iodide (PI), detection of reduced mitochondrial membrane potential after staining with JC-1, cleavage of caspase- 3 and poly (ADP)-ribose polymerase proteins by western blot analysis and translocation of apoptosis inducing factor (AIF) by confocal microscopy. Intracellular reduced glutathione (GSH) was measured by colorimetric assay using GSH assay kit. 2′,7′-dichlorodihydrofluorescein diacetate (DCF-DA) and 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) were used as probes to measure intracellular increase in ROS and nitric oxide (NO) levels respectively. Multiple techniques like siRNA transfection and pharmacological inhibition were used to understand the mechanisms of action.

Results

Non-apoptotic concentrations of BSO significantly potentiated HCH-induced apoptosis in K562 cells. BSO potentiated apoptosis-inducing activity of HCH in CML cells by caspase-dependent as well as caspase-independent but apoptosis inducing factor (AIF)-dependent manner. Enhanced depletion of intracellular GSH induced by combined treatment correlated with induction of ROS. Activation of ROS- dependent JNK played a crucial role in ERK1/2 activation which subsequently induced the expression of inducible nitric oxide synthase (iNOS). iNOS- mediated production of NO was identified as an effector molecule causing apoptosis of CML cells.

Conclusion/Significance

BSO synergizes with HCH in inducing apoptosis of CML cells through the GSH-ROS-JNK-ERK-iNOS pathway.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.