Arsenite enhances tumor necrosis factor-α-induced expression of vascular cell adhesion molecule-1

Metabolic Derangement by Arsenic: a Review of the Mechanisms

Studies have implicated arsenic exposure in various pathological conditions, including metabolic disorders, which have become a global phenomenon, affecting developed, developing, and under-developed nations. Despite the huge risks associated with arsenic exposure, humans remain constantly exposed to it, especially through the consumption of contaminated water and food. This present study provides an in-depth insight into the mechanistic pathways involved in the metabolic derangement by arsenic. Compelling pieces of evidence demonstrate that arsenic induces metabolic disorders via multiple pathways. Apart from the initiation of oxidative stress and inflammation, arsenic prevents the phosphorylation of Akt at Ser473 and Thr308, leading to the inhibition of PDK-1/Akt insulin signaling, thereby reducing GLUT4 translocation through the activation of Nrf2. Also, arsenic downregulates mitochondrial deacetylase Sirt3, decreasing the ability of its associated transcription factor, FOXO3a, to bind to the agents that support the genes for manganese superoxide dismutase and PPARg co-activator (PGC)-1a. In addition, arsenic activates MAPKs, modulates p53/ Bcl-2 signaling, suppresses Mdm-2 and PARP, activates NLRP3 inflammasome and caspase-mediated apoptosis, and induces ER stress, and ox-mtDNA-dependent mitophagy and autophagy. More so, arsenic alters lipid metabolism by decreasing the presence of 3-hydroxy-e-methylglutaryl-CoA synthase 1 and carnitine O-octanoyl transferase (Crot) and increasing the presence of fatty acid-binding protein-3 mRNA. Furthermore, arsenic promotes atherosclerosis by inducing endothelial damage. This cascade of pathophysiological events promotes metabolic derangement. Although the pieces of evidence provided by this study are convincing, future studies evaluating the involvement of other likely mechanisms are important. Also, epidemiological studies might be necessary for the translation of most of the findings in animal models to humans.

Contaminant Metals and Cardiovascular Health

A growing body of research has begun to link exposure to environmental contaminants, such as heavy metals, with a variety of negative health outcomes. In this paper, we sought to review the current research describing the impact of certain common contaminant metals on cardiovascular (CV) health. We reviewed ten metals: lead, barium, nickel, chromium, cadmium, arsenic, mercury, selenium, zinc, and copper. After a literature review, we briefly summarized the routes of environmental exposure, pathophysiological mechanisms, CV health impacts, and exposure prevention and/or mitigation strategies for each metal. The resulting article discloses a broad spectrum of pathological significance, from relatively benign substances with little to no described effects on CV health, such as chromium and selenium, to substances with a wide-ranging and relatively severe spectrum of CV pathologies, such as arsenic, cadmium, and lead. It is our hope that this article will provide clinicians with a practical overview of the impact of these common environmental contaminants on CV health as well as highlight areas that require further investigation to better understand how these metals impact the incidence and progression of CV diseases.

Regulation of the Inflammatory Response, Proliferation, Migration, and Epithelial-Mesenchymal Transition of Human Lens Epithelial Cells by the lncRNA-MALAT1/miR-26a-5p/TET1 Signaling Axis

Background

The ocular inflammatory microenvironment has been reported to be closely associated with the occurrence and progression of highly myopic cataract (HMC). Long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) could alter the biological properties of mammalian cells by modulating the expression of inflammatory mediators; therefore, it may contribute to the development of HMC.

Objective

To investigate the function of MALAT1 in the inflammatory response, proliferation, migration, and epithelial-mesenchymal transition (EMT) of inflammatory and injured human lens epithelial cells (HLECs) and to reveal the underlying molecular signals.

Methods

Patients with HMC and age-related cataract (ARC) with an axial length of more than 26 mm were selected, and the anterior capsular tissue was obtained during cataract surgery. TNF-α (20 ng/mL) was chosen to induce inflammatory damage in HLECs to simulate the inflammatory microenvironment in HMC eyes. Specific siRNAs, inhibitors, and mimics were used to suppress or enhance the functions of MALAT1 and miR-26a-5p. RT-qPCR and Western blot analysis were performed to measure gene and protein expression, respectively.

Results

The expression of MALAT1 and the inflammatory mediators IL-6, MMP-2, and MMP-9 were significantly higher in HMC anterior capsule tissues than in ARC. TNF-α treatment increased the expression of MALAT1, while it also promoted the proliferation, migration, and EMT of HLECs. MALAT1 interference decreased the expression of IL-6 and MMP-2 and inhibited the aforementioned processes. Furthermore, MALAT1 negatively regulated the expression of miR-26a-5p and then promoted TET1 expression. TET1 was identified as a direct target of miR-26a-5p, and the promoting effect of MALAT1 on TET1 expression could be reversed by miR-26a-5p mimics.

Conclusion

The inflammatory environment and MALAT1 expression could be reciprocally induced in HLECs. MALAT1 may act as a ceRNA via the "sponge" miR-26a-5p and target TET1 to regulate the inflammatory response, proliferation, migration, and EMT processes in HLECs.

The Association Between Arsenic Levels and Oxidative Stress in Myocardial Infarction: A Case-Control Study

Cardiovascular diseases (CVDs) are known as the first causes of death throughout the world, and mainly myocardial infarction (MI), lead to 7.4 million deaths annually. Atherosclerosis is the major underlying cause of most CVDs. However, exposure to heavy metals, among other factors, deserves further attention as a risk factor for CVDs. This study was designed to evaluate the levels of arsenic (Ars) in myocardial infarction (MI) patients and healthy individuals as well as assess the association between the incidence of MI and Ars, total antioxidant capacity (TAC), and oxidative stress. This case-control study was conducted among patients with MI (n = 164) and normal individuals (n = 61) at Shafa Hospital in Kerman, Iran. Patients were classified into two groups, including coronary artery blocks above 50% (CAB > 50%, n = 83) and coronary artery blocks less than 50% (CAB < 50%, n = 83) based on their angiography findings. The demographic characteristics, clinical history, biochemical parameters, and serum Ars and TAC levels were evaluated. In the present study, both CAB groups had significantly reduced levels of TAC compared with the control. Furthermore, TAC was lower in the CAB > %50 group compared to the CAB < %50 group. Ars levels were significantly higher in both CAB groups compared with the control. There was a significant positive relationship between CAB and Ars, BG, HbA1c, urea, creatinine, TG, TC, and LDL-c, as well as a negative relationship between HDL-c and TAC. Moreover, TAC levels showed a significant inverse correlation with Ars, HbA1c, and creatinine, and a positive correlation with HDL-c. As risk factors, Ars, hs-CRP, TG, TC, and LDL-c enhance the severity of the disease, and HDL-c and TAC decrease the disease severity. Moreover, ROC curve analysis revealed that the highest AUC for the CAB > %50 (AUC = 78.29), and cytotoxic levels for both CAB groups (Ars ≥ 0.105 ppm), and no significant differences were found between the two groups. Our findings suggest that Ars at ≥ 0.105 ppm is able to increase the risk of MI through the increased OS and decreased TAC.

Pesticide exposure and risk of cardiovascular disease: A systematic review

The increase in pesticide consumption has a negative health impact. Studies point to an association between exposure to pesticides and cardiovascular disease (CVD), one of the leading causes of world mortality. This review synthesize evidence on the association between occupational exposure and environmental contamination by pesticides with CVDs from 1750 references databases (EBSCO, Medline, Science Direct, Scielo, Lilacs and Ovid) without date or language restriction. Selected 24 articles by PRISMA and Downs & Black methodologies, were included from inclusion criteria: original studies (case-control, cohort or cross-sectional design); clear CVD definition and exposure to pesticides; representative sample of the target population. The results show the occupational exposure to pesticides chlorpyrifos, coumafos, carbofuran, ethylene bromide, mancozeb, ziram, metalaxyl, pendimethalin and trifluralin was associated a risk of 1.8 to 3.2 for acute myocardial infarction. Primaphos, fenitrothion, malathion and deltamethrin pesticides were associated with a blood pressure increase. Environmental contamination by tetrachlorodibenzo-p-dioxin was associated with CVD with risk of 1.09 to 2.78 and organochlorine, 1.19 to 4.54; heavy metals, arsenic, trimethylarsine and dimethylarsinic acid with atherosclerosis and systemic arterial hypertension. These findings point to the association between exposure to pesticides and CVD, signaling the importance of greater rigor in the public policy related to pesticides.

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.

Role of Pigment Epithelium-Derived Factor in Arsenic-Induced Vascular Endothelial Dysfunction in a Rat Model

Water-borne arsenicosis is caused by the consumption of excess levels of inorganic arsenic from drinking water and is a worldwide public health issue. Arsenic exposure has recently attracted extensive attention due to its damage to the cardiovascular system. Vascular endothelial dysfunction (VED) is recognized as an important cause of cardiovascular diseases. Pigment epithelium-derived factor (PEDF) plays an important role in maintaining endothelial function, and our previous studies suggested that PEDF may have role in arsenic-induced damage. In the present study, we established subchronic arsenic exposure (3 months) rat model from drinking water at doses of 0, 2 mg/L, 10 mg/L, and 50 mg/L, respectively. The results showed that the endothelial cells of the aortic arch were obviously damaged, the apoptosis rate increased, the vWF and iNOS levels increased, and the NO and TNOS levels significantly decreased in the arsenic exposure groups. Regardless of serum or aortic arch endothelium, PEDF levels in the arsenic exposure groups decreased compared to the control group. The oxidative stress level and key proteins associated with apoptosis such as Fas, FasL, P53, and p-p38 were then detected to explore the detailed mechanisms. The results showed that the P53 and p-p38 levels significantly increased in the 10 mg/L and 50 mg/L groups compared to the control group. The MDA content in the arsenic exposure groups increased markedly, whereas the SOD activity decreased significantly with the increased arsenic dose. Taken together, our study is the first to find that PEDF plays a protective role in arsenic-induced endothelial dysfunction through anti-oxidation and anti-apoptosis, and p38 and P53 may be promising target proteins.

Arsenite exposure potentiates apoptosis-inducing effects of tumor necrosis factor-alpha- through reactive oxygen species

Tumor necrosis factor-alpha (TNF-α) is a proinflammatory cytokine released by immune cells during inflammation process. Sodium arsenite (NaAsO₂) is an environmental toxic metal. The effects of excess NaAsO₂ on TNF-α response and its intracellular signaling are not well understood. We hypothesized that NaAsO₂ exposure might affect cellular response to TNF-α. Using HeLa cell model, we found that the combination of NaAsO₂ and TNF-α clearly decreased cell viability and mitochondrial membrane potential, but increased percentage of early and late apoptotic cells and cleaved-poly (ADP-ribose) polymerase (PARP). Moreover, the combination prolonged the phosphorylation of mitogen-activated protein kinase (MAPK) members, including c-Jun-N-terminal kinase (JNK), p38, and extracellular signal related kinases (ERK), and increased intracellular reactive oxygen species (ROS), in comparison to treatment of NaAsO₂ or TNF-α alone. We further investigated the role of ROS and MAPK signaling on this event by inhibiting ROS production and MAPK. An antioxidant N-acetylcysteine pretreatment diminished the apoptosis-inducing effect of NaAsO₂ and TNF-α combination and also inhibited MAPK signaling. Using specific inhibitor of p38 (SB203580) and siRNA-p38 surprisingly increased cell apoptosis and this effect was not observed by JNK and ERK inhibition. This study suggests that p38 may possibly be a survival mediator in response to environmental toxicant-related inflammation. In conclusion, NaAsO₂ exposure might amplify inflammation-related tissue injury by potentiating the apoptosis-inducing effect of TNF-α through ROS-dependent mechanism.

Crucial role of Toll-like receptors in the zinc/nickel-induced inflammatory response in vascular endothelial cells

Our previous studies indicated that zinc induced inflammatory response in both vascular endothelial cells and promonocytes. Here, we asked if other metals could cause the similar effect on vascular endothelial cells and tried to determine its underlying mechanism. Following screening of fifteen metals, zinc and nickel were identified with a marked proinflammatory effect, as determined by ICAM-1 and IL-8 induction, on human umbilical vein endothelial cells (HUVECs). Inhibiting protein expression of myeloid differentiation primary response protein-88 (MyD88), a Toll-like receptor (TLR) adaptor acting as a TLR-signaling transducer, significantly attenuated the zinc/nickel-induced inflammatory response, suggesting the critical roles of TLRs in the inflammatory response. Blockage of TLR-4 signaling by CLI-095, a TLR-4 inhibitor, completely inhibited the nickel-induced ICAM-1 and IL-8 expression and NFκB activation. The same CLI-095 treatment significantly blocked the zinc-induced IL-8 expression, however with no significant effect on the ICAM-1 expression and a minor inhibitory effect on the NFκB activation. The finding demonstrated the differential role of TLR-4 in regulation of the zinc/nickel-induced inflammatory response, where TLR-4 played a dominant role in NFκB activation by nickel, but not by zinc. Moreover, inhibition of NFκB by adenovirus-mediated IκBα expression and Bay 11-7025, an inhibitor of cytokine-induced IκB-α phosphorylation, significantly attenuated the zinc/nickel-induced inflammatory responses, indicating the critical of NFκB in the process. The study demonstrates the crucial role of TLRs in the zinc/nickel-induced inflammatory response in vascular endothelial cells and herein deciphers a potential important difference in NFκB activation via TLRs. The study provides a molecular basis for linkage between zinc/nickel exposure and pathogenesis of the metal-related inflammatory vascular disease.

Arsenic exposure from drinking water, arsenic methylation capacity, and carotid intima-media thickness in Bangladesh

We conducted a cross-sectional study to evaluate the interrelationships between past arsenic exposure, biomarkers specific for susceptibility to arsenic exposure, and carotid intima-media thickness (cIMT) in 959 subjects from the Health Effects of Arsenic Longitudinal Study in Bangladesh. We measured cIMT levels on average 7.2 years after baseline during 2010-2011. Arsenic exposure was measured in well water at baseline and in urine samples collected at baseline and during follow-up. Every 1-standard-deviation increase in urinary arsenic (357.9 µg/g creatinine) and well-water arsenic (102.0 µg/L) concentration was related to a 11.7-µm (95% confidence interval (CI): 1.8, 21.6) and 5.1-µm (95% CI: -0.2, 10.3) increase in cIMT, respectively. For every 10% increase in monomethylarsonic acid (MMA) percentage, there was an increase of 12.1 µm (95% CI: 0.4, 23.8) in cIMT. Among participants with a higher urinary MMA percentage, a higher ratio of urinary MMA to inorganic arsenic, and a lower ratio of dimethylarsinic acid to MMA, the association between well-water arsenic and cIMT was stronger. The findings indicate an effect of past long-term arsenic exposure on cIMT, which may be potentiated by suboptimal or incomplete arsenic methylation capacity. Future prospective studies are needed to confirm the association between arsenic methylation capacity and atherosclerosis-related outcomes.

Arsenic exposure and cardiovascular disease: an updated systematic review

In epidemiologic studies, high-chronic arsenic exposure has been associated with cardiovascular disease, despite methodological limitations. At low-moderate arsenic levels, the evidence was inconclusive. Here, we update a previous systematic review (Am J Epidemiol 2005;162:1037-49) examining the association between arsenic exposure and cardiovascular disease. Eighteen studies published since 2005 were combined with 13 studies from the previous review. We calculated pooled relative risks by comparing the highest versus the lowest exposure category across studies. For high exposure (arsenic in drinking water > 50 μg/L), the pooled relative risks (95 % confidence interval) for cardiovascular disease, coronary heart disease, stroke, and peripheral arterial disease were 1.32 (95 % CI:1.05-1.67), 1.89 (95 % CI:1.33-2.69), 1.08 (95 % CI:0.98-1.19), and 2.17 (95 % CI:1.47-3.20), respectively. At low-moderate arsenic levels, the evidence was inconclusive. Our review strengthens the evidence for a causal association between high-chronic arsenic exposure and clinical cardiovascular endpoints. Additional high quality studies are needed at low-moderate arsenic levels.

Zinc induces chemokine and inflammatory cytokine release from human promonocytes

Our previous studies found that zinc oxide (ZnO) particles induced expression of intercellular adhesion molecule-1 (ICAM-1) protein in vascular endothelial cells via NF-κB and that zinc ions dissolved from ZnO particles might play the major role in the process. This study aimed to determine if zinc ions could cause inflammatory responses in a human promonocytic leukemia cell line HL-CZ. Conditioned media from the zinc-treated HL-CZ cells induced ICAM-1 protein expression in human umbilical vein endothelial cells (HUVEC). Zinc treatment induced chemokine and inflammatory cytokine release from HL-CZ cells. Inhibition of NFκB activity by over-expression of IκBα in HL-CZ cells did not block the conditioned medium-induced ICAM-1 protein expression in HUVEC cells. Zinc treatment induced activation of multiple immune response-related transcription factors in HL-CZ cells. These results clearly show that zinc ions induce chemokine and inflammatory cytokine release from human promonocytes, accompanied with activation of multiple immune response-related transcription factors. Our in vitro evidence in the zinc-induced inflammatory responses of vascular cells provides a critical linkage between zinc exposure and pathogenesis of those inflammatory vascular diseases.

Atherosclerosis induced by arsenic in drinking water in rats through altering lipid metabolism

Arsenic in drinking water is a global environmental health problem, and the exposure may increase cardiovascular and cerebrovascular diseases mortalities, most likely through causing atherosclerosis. However, the mechanism of atherosclerosis formation after arsenic exposure is still unclear. To study the mechanism of atherosclerosis formation after arsenic exposure and explore the role of high cholesterol diet (HCD) in this process, we fed spontaneous hypertensive rats and Wistar Kyoto rats with basal diet or HCD and provided with them drinking water containing arsenic at different ages and orders for 20 consecutive weeks. We measured high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), total cholesterol, triglycerides, heat shock protein 70 (HSP 70), and high sensitive C-reactive protein (hs-CRP) at predetermined intervals and determined expressions of cholesteryl ester transfer protein-1 (CETP-1) and liver X receptor β (LXRβ) in the liver. Atherosclerosis was determined by examining the aorta with hematoxylin and eosin stain. After 20 weeks, we found arsenic, alone or combined with HCD, may promote atherosclerosis formation with transient increases in HSP 70 and hs-CRP. Early combination exposure decreased the HDL-C/LDL-C ratio without changing the levels of total cholesterol and triglyceride until 30 weeks old. Both CETP-1 and LXRβ activities were suppressed, most significantly in early combination exposure. In conclusion, arsenic exposure may induce atherosclerosis through modifying reverse cholesterol transport in cholesterol metabolism and suppressing LXRβ and CEPT-1 expressions. For decreasing atherosclerosis related mortality associated with arsenic, preventing exposure from environmental sources in early life is an important element.

Zinc ions induce inflammatory responses in vascular endothelial cells

Using one particulate zinc oxide (ZnO) and two soluble zinc compounds (Zn(NO(3))(2) and Zn(CH(3)COO)(2)), we aimed to clarify if zinc ions (Zn(2+)), like particulate ZnO, caused inflammatory responses in vascular endothelial cells. Treatments of human umbilical vein endothelial cells (HUVECs) with 368.6 μM of each zinc compound caused marked increases in IκBα phosphorylation and intercellular adhesion molecule-1 (ICAM-1) expression. Treatments with Zn(CH(3)COO)(2) (50-350 μM) induced a dose-dependent ICAM-1 expression. These results show that Zn(2+) alone is sufficient to induce similar levels of ICAM-1 expression as ZnO particles, suggesting that dissolved Zn(2+) may play the major role in inflammatory effect of ZnO particles on vascular endothelial cells.

Arsenic: toxicity, oxidative stress and human disease

Arsenic (As) is a toxic metalloid element that is present in air, water and soil. Inorganic arsenic tends to be more toxic than organic arsenic. Examples of methylated organic arsenicals include monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. Reactive oxygen species (ROS)-mediated oxidative damage is a common denominator in arsenic pathogenesis. In addition, arsenic induces morphological changes in the integrity of mitochondria. Cascade mechanisms of free radical formation derived from the superoxide radical, combined with glutathione-depleting agents, increase the sensitivity of cells to arsenic toxicity. When both humans and animals are exposed to arsenic, they experience an increased formation of ROS/RNS, including peroxyl radicals (ROO•), the superoxide radical, singlet oxygen, hydroxyl radical (OH•) via the Fenton reaction, hydrogen peroxide, the dimethylarsenic radical, the dimethylarsenic peroxyl radical and/or oxidant-induced DNA damage. Arsenic induces the formation of oxidized lipids which in turn generate several bioactive molecules (ROS, peroxides and isoprostanes), of which aldehydes [malondialdehyde (MDA) and 4-hydroxy-nonenal (HNE)] are the major end products. This review discusses aspects of chronic and acute exposures of arsenic in the etiology of cancer, cardiovascular disease (hypertension and atherosclerosis), neurological disorders, gastrointestinal disturbances, liver disease and renal disease, reproductive health effects, dermal changes and other health disorders. The role of antioxidant defence systems against arsenic toxicity is also discussed. Consideration is given to the role of vitamin C (ascorbic acid), vitamin E (α-tocopherol), curcumin, glutathione and antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase in their protective roles against arsenic-induced oxidative stress.

Zinc oxide particles induce inflammatory responses in vascular endothelial cells via NF-κB signaling

This study investigated inflammatory effects of zinc oxide (ZnO) particles on vascular endothelial cells. The effects of 50 and 100-nm ZnO particles on human umbilical vein endothelial cells (HUVECs) were characterized by assaying cytotoxicity, cell proliferation, and glutathione levels. A marked drop in survival rate was observed when ZnO concentration was increased to 45 μg/ml. ZnO concentrations of ≤3 μg/ml resulted in increased cell proliferation, while those of ≤45 μg/ml caused dose-dependent increases in oxidized glutathione levels. Treatments with ZnO concentrations ≤45 μg/ml were performed to determine the expression of intercellular adhesion molecule-1 (ICAM-1) protein, an indicator of vascular endothelium inflammation, revealing that ZnO particles induced a dose-dependent increase in ICAM-1 expression and marked increases in NF-κB reporter activity. Overexpression of IκBα completely inhibited ZnO-induced ICAM-1 expression, suggesting NF-κB plays a pivotal role in regulation of ZnO-induced inflammation in HUVECs. Additionally, TNF-α, a typical inflammatory cytokine, induced ICAM-1 expression in an NF-κB-dependent manner, and ZnO synergistically enhanced TNF-α-induced ICAM-1 expression. Both 50 and 100-nm ZnO particles agglomerated to similar size distributions. This study reveals an important role for ZnO in modulating inflammatory responses of vascular endothelial cells via NF-κB signaling, which could have important implications for treatments of vascular disease.

Induction of heme oxygenase 1 by arsenite inhibits cytokine-induced monocyte adhesion to human endothelial cells

Heme oxygenase-1 (HO-1) is an oxidative stress responsive gene upregulated by various physiological and exogenous stimuli. Arsenite, as an oxidative stressor, is a potent inducer of HO-1 in human and rodent cells. In this study, we investigated the mechanistic role of arsenite-induced HO-1 in modulating tumor necrosis factor alpha (TNF-alpha) induced monocyte adhesion to human umbilical vein endothelial cells (HUVEC). Arsenite pretreatment, which upregulated HO-1 in a time- and concentration-dependent manner, inhibited TNF-alpha-induced monocyte adhesion to HUVEC and intercellular adhesion molecule 1 protein expression by 50% and 40%, respectively. Importantly, knockdown of HO-1 by small interfering RNA abolished the arsenite-induced inhibitory effects. These results indicate that induction of HO-1 by arsenite inhibits the cytokine-induced monocyte adhesion to HUVEC by suppressing adhesion molecule expression. These findings established an important mechanistic link between the functional monocyte adhesion properties of HUVEC and the induction of HO-1 by arsenite.

Glutathione regulation of redox-sensitive signals in tumor necrosis factor-α-induced vascular endothelial dysfunction

We investigated the regulatory role of glutathione in tumor necrosis factor-alpha (TNF-alpha)-induced vascular endothelial dysfunction as evaluated by using vascular endothelial adhesion molecule expression and monocyte-endothelial monolayer binding. Since TNF-alpha induces various biological effects on vascular cells, TNF-alpha dosage could be a determinant factor directing vascular cells into different biological fates. Based on the adhesion molecule expression patterns responding to different TNF-alpha concentrations, we adopted the lower TNF-alpha (0.2 ng/ml) to rule out the possible involvement of other TNF-alpha-induced biological effects. Inhibition of glutathione synthesis by l-buthionine-(S,R)-sulfoximine (BSO) resulted in down-regulations of the TNF-alpha-induced adhesion molecule expression and monocyte-endothelial monolayer binding. BSO attenuated the TNF-alpha-induced nuclear factor-kappaB (NF-kappaB) activation, however, with no detectable effect on AP-1 and its related mitogen-activated protein kinases (MAPKs). Deletion of an AP-1 binding site in intercellular adhesion molecule-1 (ICAM-1) promoter totally abolished its constitutive promoter activity and its responsiveness to TNF-alpha. Inhibition of ERK, JNK, or NF-kappaB attenuates TNF-alpha-induced ICAM-1 promoter activation and monocyte-endothelial monolayer binding. Our study indicates that TNF-alpha induces adhesion molecule expression and monocyte-endothelial monolayer binding mainly via activation of NF-kappaB in a glutathione-sensitive manner. We also demonstrated that intracellular glutathione does not modulate the activation of MAPKs and/or their downstream AP-1 induced by lower TNF-alpha. Although AP-1 activation by the lower TNF-alpha was not detected in our systems, we could not rule out the possible involvement of transiently activated MAPKs/AP-1 in the regulation of TNF-alpha-induced adhesion molecule expression.

ATM/ATR-related checkpoint signals mediate arsenite-induced G2/M arrest in primary aortic endothelial cells

Epidemiological studies have demonstrated a high association of inorganic arsenic exposure with vascular disease. Our recent in vitro studies have linked this vascular damage to vascular endothelial dysfunction induced by arsenic exposure. However, cell-cycle arrest induced by arsenic and its involvement in vascular dysfunction remain to be clarified. In this study, we employed primary porcine aortic endothelial cells to investigate regulatory mechanisms of G2/M phase arrest induced by arsenite. Our study revealed that lower concentrations of arsenite (1 and 3 microM) increased cell proliferation, whereas higher concentrations of arsenite (10, 20, and 30 microM) inhibited cell proliferation together with correlated increases in G2/M phase arrest. We found that this arsenite-induced G2/M phase arrest was accompanied by accumulation and/or phosphorylation of checkpoint-related molecules, including p53, Cdc25B, Cdc25C, and securin. Inhibition of activations of these checkpoint-related molecules by caffeine significantly attenuated the 30-microM arsenite-induced G2/M phase arrest by 93%. Our data suggest that the DNA damage responsive kinases ATM (ataxia-telangiectasia mutated) and ATR (ATM and Rad3-related) play critical roles in arsenite-induced G2/M phase arrest in aortic endothelial cells possibly via regulation of checkpoint-related signaling molecules including p53, Cdc25B, Cdc25C, and securin.

Arsenic and cigarette smoke synergistically increase DNA oxidation in the lung

Epidemiological evidence has indicated that arsenic and cigarette smoking exposure act synergistically to increase the incidence of lung cancer. Since oxidative damage of DNA has been linked to cancer, our hypothesis is that aerosolized arsenic and cigarette smoke work synergistically to increase oxidative stress and increase DNA oxidation in the lung. To test this hypothesis male Syrian golden hamsters were exposed to room air (control), aerosolized arsenic compounds (3.2 mg/m3 for 30 minutes), cigarette smoke (5 mg/m3 for 30 minutes), or both smoke and arsenic. Exposures were for 5 days/week for 5 or 28-days. Animals were sacrificed one day after the last exposure. In the 28-day group, glutathione levels and DNA oxidation (8-oxo-2'-deoxyguanosine (8-oxo-dG)) were determined. Our results show that in the 28-day arsenic/smoke group there was a significant decrease in both the reduced and total glutathione levels compared with arsenic or smoke alone. This correlated with a 5-fold increase in DNA oxidation as shown by HPLC. Immunohistochemical localization of 8-oxo-dG showed increase staining in nuclei of airway epithelium and subadjacent interstitial cells. These results show that dual exposure of arsenic and cigarette smoke at environmentally relevant levels can act synergistically to cause DNA damage.