Chromium genotoxicity as influenced by complexation and rate effects

Conclusions as to the mutagenicity and carcinogenicity of metal salts can be ambiguous and misleading, especially for metal ions having a high charge/radius ratio, hence a strong tendency to hydrolyze. Using the rec-assay, we determined whether the mutagenicity of chromium salts was reduced by complexation, as in the case of Cr(VI), or induced in the case of Cr(III). We find that several chelants, in proportion to concentration, reduce or eliminate the mutagenicity of Cr2O32-. These include EDTA, salicylate (SA), and Tiron (disodium 1,2-dihydroxylbenzene-3,5-disulfonate). Cr(III) was rendered slightly mutagenic by salicylate and citrate. None of the chelating agents or their combinations were mutagenic.     

Effectiveness of chelation therapy with time after acute vanadium intoxication

The effect of increasing the time interval between vanadium exposure and chelation therapy was studied in male Swiss mice. The following chelating or reducing agents were administered i.p. at 0, 0.5, 2 and 8 h after i.p. administration of 0.16 mmol kg-1 sodium metavanadate: ascorbic acid, deferoxamine mesylate (DFOA) and 4,5-dihydroxy-1,3-benzene-disulphonic acid (Tiron). These agents were given at doses equal to one-quarter of their respective LD50 values. Daily elimination of vanadium into urine and faeces was determined for four days. The excretion of vanadium was especially rapid in the first 24 h. Treatment with Tiron increased significantly the urinary elimination of vanadium in all four groups during Day 1, whereas DFOA significantly increased the faecal excretion during the same period. Treatment with DFOA or Tiron resulted in a significant decrease in the concentration of vanadium in the kidney four days after sodium metavanadate administration. The magnitude of the increased elimination of vanadium, as well as the decreased tissue concentration of the metal, was remarkably attenuated by increasing the time interval between vanadium injection and administration of the chelators.     

Re-evaluation of the relationship between catechol-O-methyl transferase and the binding of norepinephrine to brown adipocyte membranes.

The binding of labeled norepinephrine to brown adipose tissue intact microsomes or solubilized microsomal proteins was studied in vitro.The effects of incubation in oxygenated Krebs-Ringer bicarbonate buffer, pH 7.4, on the physicochemical state of norepinephrine was investigated. After 10 minutes of incubation, the recovery of norepinephrine (0.5 μM) by alumina adsorption technique was found to be only about 40 per cent and no oxidation was detected by polarography. The recovery could be increased to over 90 per cent by adding metal chelators to the Krebs-Ringer bicarbonate buffer or by incubation in a phosphate buffer, which suggests that contaminating metals can cause considerable complexation of the hormone. The assays with unmodified norepinephrine were therefore performed under the following conditions: 10 min incubation in 50 mM phosphate buffer, pH 7.4. 25°.In both intact microsomes and solubilized microsmal proteins, the binding of norephinephrine was found to be sensitive to substances affecting catechol-O-methyl transferase activity such as tropolone, normeta nephrine, dithiothreitol, Ca²⁺ and Ca²⁺ chelators; agents that inhibited catechol-O-methly transferase activity were shown to stimulate norepinephrine binding and vice versa.After separation of solubilized microsomal proteins by Ultrogel AcA 34 filtration, both norepinephrine binding and catechol-O-methly transferase activity were found in the same protein fraction. Separation by polyacrylamide gel electrophoresis revealed congruent migration of norepinephrine binding, catechol-O-methyl transferase activity and S-adenosyl methionine binding.     

Nitric oxide donor-induced increase in permeability of the blood–brain barrier

The goal of the present study was to determine the effect of nitric oxide (NO) donors on the permeability of the blood–brain barrier in vivo. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood–brain barrier was quantitated by calculating the clearance of fluorescent-labeled dextran (M_w=10 000 Da; FITC–dextran-10K) during suffusion with vehicle, S-nitroso-N-acetylpenicillamine (SNAP; 100 μM) and 3-morpholinosydnonimin (SIN-1; 100 μM). In addition, we examined changes in arteriolar diameter during suffusion with vehicle, SNAP and SIN-1. During suffusion with vehicle, clearance of FITC–dextran-10K from pial vessels and diameter of pial arterioles remained relatively constant during the experimental period. In contrast, suffusion with SNAP or SIN-1 markedly increased clearance of FITC–dextran-10K from the cerebral microcirculation and produced a rapid, sustained dilatation of pial arterioles. Thus, NO donors increase the permeability of the blood–brain barrier and produce pronounced dilatation of cerebral arterioles. In light of evidence suggesting that NO donors may produce their effect by the simultaneous release of NO and superoxide anion to form peroxynitrite, we elected to examine the role of superoxide anion in increases in permeability of the blood–brain barrier in response to SNAP and SIN-1. We found that suffusion with tiron (1 mM) did not alter basal permeability of the blood–brain barrier, but significantly inhibited increases in permeability of the blood–brain barrier in response to SNAP and SIN-1. In addition, tiron did not alter baseline diameter of cerebral arterioles, or SNAP- and SIN-1-induced cerebrovasodilatation. The findings of the present study suggest that NO donors produce an increase in permeability of the blood–brain barrier which appears to be related to the presence of NO and superoxide anion, to presumably form peroxynitrite. We suggest that increases in NO formation observed during brain trauma may contribute to disruption of the blood–brain barrier.     

Critical roles for nitric oxide and ERK in the completion of prosurvival autophagy in 4OHTAM-treated estrogen receptor-positive breast cancer cells

Autophagy is a mechanism of tamoxifen (TAM) resistance in ER-positive (ER+) breast cancer cells. In this study, we showed in ER+ MCF7 cells that 4-hydroxytamoxifen (4OHTAM) induced cellular nitric oxide (NO) that negatively regulates cellular superoxide (O2−) and cytotoxicity. 4OHTAM stimulated LC3 lipidation and formation of monodansylcadaverine (MDC)-labeled autophagic vesicles dependent on O2−. Depletion of NO increased O2− and LC3 lipidation, yet reduced formation of MDC-labeled autophagic vesicles. Instead, NO-depleted cells formed remarkably large vacuoles with rims decorated by LC3. The vacuoles were not labeled by MDC or the acidic lysosome-specific fluorescence dye acridine orange (AO). The vacuoles were increased by the late stage autophagy inhibitor chloroquine, which also increased LC3 lipidation. These results suggest NO is required for proper autophagic vesicle formation or maturation at a step after LC3 lipidation. In addition, 4OHTAM induced O2−-dependent activation of ERK, inhibition of which destabilized lysosomes/autolysosomes upon 4OHTAM treatment and together with depletion of NO led to necrotic cell death. These results suggest an essential role for endogenous NO and ERK activation in the completion of pro-survival autophagy.     

原钒酸钠对大鼠的毒性及1,2-二羟基苯3,5-二磺酸钠对钒蓄积和排泄的影响

钒(Vanadium)可能成为有前途的治疗糖尿病(DM)药物[1-3],但钒酸盐具有一定的毒性[4],目前尚缺乏疗效显著又便于普及应用的抗钒中毒的药物.1,2-二羟基苯3,5-二磺酸钠(Tiron)是一种螯合剂,对钒中毒的预防和治疗可能会具有一定的作用 , 本实验研究是观察饮钒大鼠的毒性,大鼠血液、肝、肾、骨组织中的钒蓄积量及1,2-二羟基苯3,5-二磺酸钠Tiron驱钒效果.     

Tiron protects against UVB-induced senescence-like characteristics in human dermal fibroblasts by the inhibition of superoxide anion production and glutathione depletion

Background/Objectives: Free radicals and reactive oxygen species (ROS), which are generated by UV irradiation, may induce an irreversible growth arrest similar to senescence. Tiron, 4,5-dihydroxy-1,3-benzene disulfonic acid, is a widely used antioxidant to rescue ROS-evoked cell death. The aim of the article was to explore the effects of tiron on skin photoaging and associated mechanisms. Methods: The effects of tiron on cell proliferation were determined using 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide. Senescent cells were determined by morphology and senescence-associated β-galactosidase activity analysis. Intracellular hydrogen peroxide, superoxide anion and glutathione concentration were analysed by a fluorescent probe. The concomitant changes of protein expression were analysed with Western blot. Results: Human dermal fibroblasts were induced to premature senescence by sub-cytotoxic doses of irradiated UVB. Strong senescence-associated β-galactosidase activity and increased intracellular superoxide anion were observed in human dermal fibroblasts irradiated by UVB. Tiron blocks UVB-induced glutathione depletion and increase of superoxide anion and protects against UVB-induced senescence-like characteristics in human dermal fibroblasts. Compared with normal fibroblasts, UVB-irradiated human dermal fibroblasts showed a higher ratio of active (hypophosphorylated) to inactive (phosphorylated) forms of Rb and p38, upregulation of p53 or p16 and c-Myc and insulin-like growth factor 1 (IGF-1) downregulation. After treatment with tiron, p53, p16 c-Myc and IGF-1 as well as phosphorylation Rb and p38 could partially recover. Conclusion: These results indicate that tiron protects against UVB-induced senescence-like characteristics in human dermal fibroblasts via the inhibition of production of superoxide anion and glutathione depletion, and modulation of related senescence proteins.     

Tiron对抗外源性过氧化氢对离体培养小鼠耳蜗Corti器损伤研究

目的：探讨Tiron能否有效地对抗过氧化氢（H2O2）对离体培养小鼠Corti器内、外毛细胞的损伤。方法：采用新生小鼠Corti器体外培养技术，建立外源性H2O2损伤内外毛细胞模型，给予不同浓度的Tiron，观察对H2O2损伤的保护作用。结果：H2O2浓度大于1.0mmol/L时，基底膜顶回、中回和底回毛细胞损伤程度不同，底回较重，预回和中回损伤程度在统计学上无差别。在低于0.5mmol/L时毛细胞损伤与位置无关。在培养液中加入Tiron(10mmol/L)可以明显减轻H2O2对毛细胞的损伤程度。当H2O2浓度在0.01-1.0mmol/L之间时，Tiron几乎可以完全抑制毛细胞的损伤和缺失。结论：Tiron对于小鼠离体培养的Corti器具有明显的保护作用，其对抗H2O2损伤的机制可能通过清除超氧阴离子O2^-和螯合铁离子共同发挥作用。     

Electrochemical preparation of polypyrrole-molybdenum trisulfide-tetrathiomolybdate electrode with various amounts of molybdenum species

Polypyrrole films doped with molybdenum trisulfide and tetrathiomolybdate anions have been prepared from an aqueous solution containing pyrrole and ammonium tetrathiomolybdate in the presence of tiron, (4, 5-dihydroxy-1, 3-benzenedisulfonic acid), in the deposition solution. In such a solution the electrodeposition of polypyrrole doped with tetrathiomolybdate anions is in competition with the electrodeposition of molybdenum trisulfide by oxidation of tetrathiomolybdate anions. Our results indicate that the relative amounts of polypyrrole and molybdenum species can be varied over larger ratios when tiron is present in the deposition solution. The variation of the amount of molybdenum species can be explained by considering the number of electrons required to generate one mole of tetrathiomolybdate as dopant for polypyrrole and one mole of molybdenum trisulfide; 14 electrons are required per mole of tetrathiomolybdate incorporated in the polymer in comparison to 2 electrons per mole of molybdenum trisulfide generated directly by electrochemical oxidation of tetrathiomolybdate. Tiron acts as a catalyst for the deposition of polypyrrole and in this case the relative amount of polypyrrole in the composite film electrode is larger. For higher tetrathiomolybdate concentration, the direct formation of molybdenum trisulfide occurs preferentially and the catalytic effect of tiron is less important.