Microvascular dysfunction with increased vascular leakage response in mice systemically exposed to arsenic

Long-term exposure to arsenic in drinking water leads to myocardial damage by oxidative stress and reduction in NO

Chronic arsenic exposure causes myocardial damage. The aim of this study is to investigate if oxidative stress and reduction in NO is involved in the myocardial damage induced by arsenic in drinking water. Rats were divided into a control group and different doses of sodium arsenite. With increasing sodium arsenite concentrations in drinking water, localised inflammatory foci and necrotic myocardial tissues were gradually observed. Compared to the control group, the activities and gene expression of antioxidant enzymes in arsenic-exposed rats decreased. NO content and the NOS activity as well as the expression of NOS mRNA in the myocardial tissue of exposed rats, decreased, and the extracellular NO content of cardiomyocytes treated with sodium arsenite also decreased. The rate of cell apoptosis induced by sodium arsenite decreased after treatment with sodium nitroprusside (an NO donor). In conclusion, arsenic exposure in drinking water can lead to myocardial injury and cardiomyocyte apoptosis through oxidative stress and a reduction in NO content.

Arsenic induces the global hypophosphorylation of insulin receptor substrate proteins in differentiated human neuroblastoma SH-SY5Y cells

We recently reported that arsenic disrupted neuronal insulin signaling. Here, we further investigated the effect of arsenic on insulin receptor substrate (IRS) proteins, which are crucial downstream signaling molecules of insulin in differentiated human neuroblastoma SH-SY5Y cells. We also found that prolonged arsenic treatment accelerated the migration of IRS1 and IRS2 on SDS-PAGE. Treatment with phosphatases abolished the arsenic-induced increased mobility of IRS, suggesting that the electrophoretic mobility shift of IRS on SDS-PAGE by arsenic was phosphorylation-dependent. By using label-free mass spectrometry, the phosphorylation sites of IRS1 were found to be S24, S345, S636, T774, S1057, S1058, and S1070, while those of IRS2 were at S645, Y653, T657, S665, S667, S669, S672, S915, and S1203, which were at least 2-fold lower than found in the control. These findings indicated a global hypophosphorylation of IRS proteins after prolonged arsenic treatment. In addition, four novel phosphorylation sites were identified on IRS1 (T774, S1057, S1058, and S1070), with another two on IRS2 (S665 and S667). As basal IRS phosphorylation plays an important role in insulin signaling, the reduction of IRS phosphorylation on multiple residues may underlie arsenic-impaired insulin signaling in neurons.

Vascular Hyperpermeability Response in Animals Systemically Exposed to Arsenic

The mechanisms underlying cardiovascular diseases induced by chronic exposure to arsenic remain unclarified. The objectives of this study were to investigate whether increased vascular leakage is induced by inflammatory mustard oil in mice systemically exposed to various doses of arsenic and whether an increased vascular leakage response is still present in arsenic-fed mice after arsenic discontinuation for 2 or 6 months. ICR mice were fed water or various doses of sodium arsenite (10, 15, or 20 mg/kg/day; 5 days/week) for 8 weeks. In separate experiments, the mice were treated with sodium arsenite (20 mg/kg) for 2 or 8 weeks, followed by arsenic discontinuation for 2 or 6 months. Vascular permeability to inflammatory mustard oil was quantified using Evans blue (EB) techniques. Both arsenic-exposed and water-fed (control) mice displayed similar basal levels of EB leakage in the ears brushed with mineral oil, a vehicle of mustard oil. The levels of EB leakage induced by mustard oil in the arsenic groups fed with sodium arsenite (10 or 15 mg/kg) were similar to those of water-fed mice. However, increased levels of EB leakage in response to mustard oil stimulation were significantly higher in mice treated with sodium arsenite (20 mg/kg; high dose) than in arsenic-fed (10 or 15 mg/kg; low and middle doses) or control mice. After arsenic discontinuation for 2 or 6 months, mustard oil-induced vascular EB leakage in arsenic-fed (20 mg/kg) mice was similar to that in control mice. Dramatic increases in mustard oil-induced vascular leakage were only present in mice systemically exposed to the high arsenic dose, indicating the synergistic effects of the high arsenic dose and mustard oil.

The Green Tea Component (-)-Epigallocatechin-3-Gallate Sensitizes Primary Endothelial Cells to Arsenite-Induced Apoptosis by Decreasing c-Jun N-Terminal Kinase-Mediated Catalase Activity

The green tea component (-)-epigallocatechin-3-gallate (EGCG) has been shown to sensitize many different types of cancer cells to anticancer drug-induced apoptosis, although it protects against non-cancerous primary cells against toxicity from certain conditions such as exposure to arsenic (As) or ultraviolet irradiation. Here, we found that EGCG promotes As-induced toxicity of primary-cultured bovine aortic endothelial cells (BAEC) at doses in which treatment with each chemical alone had no such effect. Increased cell toxicity was accompanied by an increased condensed chromatin pattern and fragmented nuclei, cleaved poly(ADP-ribose) polymerase (PARP), activity of the pro-apoptotic enzymes caspases 3, 8 and 9, and Bax translocation into mitochondria, suggesting the involvement of an apoptotic signaling pathway. Fluorescence activated cell sorting analysis revealed that compared with EGCG or As alone, combined EGCG and As (EGCG/As) treatment significantly induced production of reactive oxygen species (ROS), which was accompanied by decreased catalase activity and increased lipid peroxidation. Pretreatment with N-acetyl-L-cysteine or catalase reversed EGCG/As-induced caspase activation and EC toxicity. EGCG/As also increased the phosphorylation of c-Jun N-terminal kinase (JNK), which was not reversed by catalase. However, pretreatment with the JNK inhibitor SP600125 reversed all of the observed effects of EGCG/As, suggesting that JNK may be the most upstream protein examined in this study. Finally, we also found that all the observed effects by EGCG/As are true for other types of EC tested. In conclusion, this is firstly to show that EGCG sensitizes non-cancerous EC to As-induced toxicity through ROS-mediated apoptosis, which was attributed at least in part to a JNK-activated decrease in catalase activity.

Effect of trivalent arsenicals on cell proliferation in mouse and human microvascular endothelial cells

Chronic exposure to high levels of inorganic arsenic (iAs) has been associated with cancerous and non-cancerous health effects, including cardiovascular effects. However, the mechanism for a presumed toxic effect of arsenic on vascular tissue is not clear. Our working hypothesis is that inorganic trivalent arsenic and its methylated metabolites react with cysteine-containing cellular proteins and alter their function leading to adverse events such as cytotoxicity or proliferation. In this study, human microvascular endothelial cells (HMEC1) and mouse microvascular endothelial cells (MFP-MVEC) were exposed to arsenite (iAs^III), monomethylarsonous acid (MMA^III), or dimethylarsinous acid (DMA^III) for 72 h to evaluate cytotoxicity, and for 24, 48 or 72 h to evaluate cell proliferation. Both cell lines showed similar LC₅₀ values, from 0.1 to 2.4 μM, for all three trivalent arsenicals. The endothelial cells treated with1 nM to 1 μM concentrations of the three trivalent arsenicals did not show increased cell proliferation at 24, 48 or 72 h or increased rate of proliferation at 72 h of exposure. Overall, cytotoxicity of trivalent arsenicals to microvascular endothelial cells is similar to their cytotoxicity to epithelial cells, and that these compounds are not mitogenic.