维生素C在Cr(Ⅵ)诱导L-02肝细胞氧化损伤中的双面作用

铬是人类环境中最常见的重金属污染物之一,可通过污染食物或饮用水对人类健康带来严重危害.铬有多种不同的化合价态,其化学性质较为稳定的有六价铬[Cr(Ⅵ)]和三价铬(Cr(Ⅲ)).普遍认为,Cr(Ⅵ)的细胞毒性比Cr(Ⅲ)大,其主要原因是Cr(Ⅲ)不易通过细胞膜,Cr(Ⅵ)则以Cr2 O2-7形式借助于细胞膜SO3-4、HPO2-4阴离子通道进入细胞内,在细胞内易被还原性物质逐步还原成Cr(V)、Cr(Ⅳ)与Cr(Ⅲ),在其还原过程中产生含氧自由基,后者在Cr(Ⅵ)诱导的细胞毒效应中起重要作用[1～3].维生素C(VC)是一个良好的电子供体,易失去电子,在生物体内具有较好的还原性[4].VC对Cr(Ⅵ)细胞毒性的影响可能存在"双面性",一方面,VC在细胞外可将Cr(Ⅵ)还原成Cr(Ⅲ),从而通过影响Cr(Ⅵ)透过细胞膜的能力使其毒性降低.另一方面,VC在细胞内将Cr(Ⅵ)还原成Cr(Ⅲ)过程中可产生自由基,后者对细胞生物大分子产生氧化损伤,而从增加Cr(Ⅵ)的细胞毒性[5].本研究用VC预处理L-02肝细胞一定时间后,通过洗脱与不洗脱VC两种处理方式,测定细胞内与细胞外总铬含量及细胞氧化损伤程度,以了解VC对Cr(Ⅵ)透过细胞膜以及诱导细胞氧化损伤的作用.     

N-乙酰半胱氨酸在有或无caspase抑制条件下对Cr(Ⅵ)诱导的肝细胞凋亡的拮抗作用

目的探讨N-乙酰半胱氨酸(NAC)在有或无caspase抑制条件下,对Cr(Ⅵ)诱导的肝细胞线粒体依赖性凋亡的拮抗作用。方法将L-02肝细胞随机分成对照组、Cr(Ⅵ)处理组、Z-VAD-fmk预处理组[Z-VAD-fmk预处理细胞1h,加入Cr(Ⅵ)]、NAC预处理组[NAC预处理细胞1h,加入Cr(Ⅵ)]、联合预处理组[Z-VAD-fmk和NAC分别预处理细胞1h,加入Cr(Ⅵ)],Cr(Ⅵ)终浓度为20μmol/L,处理6h。流式细胞仪检测细胞凋亡率,荧光分光光度法检测线粒体膜电位(△ψm)和通透性转运孔(PTP)的改变,单细胞凝胶电泳法观察细胞凋亡形态及细胞DNA损伤情况。结果终浓度20μmol/L的Cr(Ⅵ),处理6h,可诱导细胞凋亡,在有或无caspase抑制条件下,NAC均明显减轻了Cr(Ⅵ)引起的肝细胞线粒体膜电位下降及PTP孔开放(P<0.05),使细胞DNA损伤程度减轻(P<0.05),从而对细胞凋亡有明显拮抗作用(P<0.05),但与非caspase抑制条件下相比,caspase抑制条件下NAC的保护效果有明显降低(P<0.05)。结论在有或无caspase抑制条件下,NAC对Cr(Ⅵ)诱导的L-02肝细胞凋亡具有重要拮抗作用,caspase在该凋亡过程中不起决定性作用。     

葡萄糖介质中铬(V)化合物诱导DNA损伤的机理探讨

目的初步探索铬[Cr(V)]中间化合物在葡萄糖介质中对DNA损伤的反应机理。方法共研究了在4种糖类及3种不同pH值条件下DNA损伤的情况。DNA的损伤通过凝胶电泳测定;反应体系中各物种的寿命及新物种的测定用顺次共振波谱仪检测。结果Cr(V)在葡萄糖介质中具有毒性并可能导致癌症,但不同糖类对DNA的损伤不同,同时随着pH值的增高,DNA的损伤相对较小,这是由于反应体系的酸性增加,Cr(V)化合物发生歧化反应的速度加快以及还原剂氢原子浓度的增加所造成的,同时Cr(V)化合物与葡萄糖产生配位体交换使反应体系产生新的物种,而新物种对DNA也产生损伤。结论根据实验结果初步推断葡萄糖介质中铬(V)化合物诱导DNA损伤的机理。     

探讨六价铬对人体健康的影响及防治措施

[目的]探讨六价铬Cr(Ⅵ)对人体健康的影响及有效的防治措施. [方法]分析人体受Cr(Ⅵ)影响的途径、Cr(Ⅵ)在体内代谢方式及对人体健康的影响和有效的防治措施. [结果]通过严格执行有效的管理、防护及治疗措施,可明显降低铬中毒发生率和致残率. [结论]有效的防护及治疗措施对控制铬中毒发生率和致残率具有非常重要的作用.     

职业接触铬化合物生物标志物的研究进展

铬化合物是已证实可致人类肿瘤的化合物。以铬化合物代谢为基础研究了一系列体内可以测量的指标，并试图寻找铬化合物的生物标志物。理想的铬化合物生物标志物应该既能反映铬的摄入，又能区分不同价态的铬[即Cr(Ⅲ)、Cr(Ⅵ)]，因为这两种价态的铬具有不同的生物学效应。本就职业接触铬化合物的人群接触生物标志物、效应生物标志物进行综述，并对今后研究工作的发展方向进行展望。     

铬化合物对健康影响的研究进展

综述了铬化合物 (Cr)在自然界的存在形式 ,工业用途及其对健康的影响 ,尤其是讨论了铬中间产物Cr(V IV)的形成及其毒性 ,以及它们对DNA损伤的机理 ,进而得出结论 :铬中间产物是造成DNA损伤的主要化合物 ,但活性自由基的作用也不可忽视     

铬(Ⅵ)-谷胱甘肽配合物诱导DNA构象变化的作用机制

目的研究重铬酸钾和还原型谷胱甘肽(GSH)反应所形成的配合物与DNA的作用机制,了解Cr(Ⅵ)在体内的致癌过程.方法用1:10的K2Cr2O7和GSH溶液形成Cr(Ⅵ)-GSH中间态配合物,配制1.4×10-3 mol/L的DNA溶液,以溴化乙锭(EB)为DNA荧光探针,用紫外光谱、荧光光谱、Scatchard图及DNA热变性等方法研究Cr(Ⅵ)-GSH配合物对DNA构象变化的影响.结果在pH=7.4的4-(2-羟乙基)哌嗪乙磺酸(Hepes)缓冲溶液中,Cr(Ⅵ)与GSH反应后很快形成Cr(Ⅵ)-GSH中间态配合物.配合物与DNA不发生嵌插作用,也不与DNA磷酸骨架产生静电结合,而是在DNA碱基部位作用,破坏DNA二级结构.中间态配合物配合物不稳定,最终分解产物Cr(Ⅲ)可以和DNA进行交联,整个过程约1 h进行完全.结论重铬酸钾和还原型谷胱甘肽(GSH)反应所形成的Cr(Ⅴ)配合物在诱导DNA变性中起重要作用.     

Cr(Ⅵ)-CAS-CPB体系光度法测定水中痕量Cr(Ⅵ)

[目的]采用Cr(Ⅵ)-CAS-CPB体系建立快速、简便测定河水中痕量Cr(Ⅵ)的新方法。[方法]在表面活性剂溴化十六烷基吡啶(CPB)存在下,Cr(Ⅵ)与CAS沸水浴中加热显色反应10 min,在620 nm处用3 cm比色皿空试剂,白为参比,测量吸光度。[结果]络合物的组成比为Cr(Ⅵ)∶CAS∶CPB=1∶2∶2,Cr(Ⅵ)含量在0~1.6μg/25 ml范围内符合比尔定律,相关系数为0.9998,表观摩尔吸光系数ε620=1.03×105L/(mol.cm)。[结论]此法用于河水样中痕量铬的测定结果满意。     

083 职业接触铬化合物生物标志物的研究进展

铬化合物是已证实可致人类肿瘤的化合物.以铬化合物代谢为基础研究了一系列体内可以测量的指标,并试图寻找铬化合物的生物标志物.理想的铬化合物生物标志物应该既能反映铬的摄入,又能区分不同价态的铬[即Cr(Ⅲ)、Cr(Ⅵ)],因为这两种价态的铬具有不同的生物学效应.本文就职业接触铬化合物的人群接触生物标志物、效应生物标志物进行综述,并对今后研究工作的发展方向进行展望.     

阴离子对零价铁修复铬污染水体的影响

目的研究阴离子存在对零价铁去除水体中Cr(Ⅵ)污染的影响。方法向200 ml含2.0 mmol/L阴离子[NO3-和(或)H2PO4-]的Cr(Ⅵ)(10 mg/L)溶液中加入3.5 g铁粉,以235 r/min分别振荡5、10、15、20、25、30、40、50、60 min后,测定水中Cr(Ⅵ)浓度并计算其去除率。结果反应0~10min,所有待测体系Cr(Ⅵ)去除率迅速上升,10min后上升速率减慢。铁粉+NO3-、铁粉+H2PO4-、铁粉+NO3-+H2PO4-体系Cr(Ⅵ)去除率达到100%的时间分别为40、15、15 min。结论 NO3-与H2PO4-单独存在及共存都可以促进零价铁去除水体中Cr(Ⅵ)污染。其中,H2PO4-单独存在体系的促进作用最强。     

Hexavalent chromium-induced DNA damage and repair mechanisms

Hexavalent chromium is a commonly used industrial metal that has been shown to induce lung cancer in workers having long term exposure. In the particulate form, Cr(VI) dissolves slowly in vivo, leading to an extended exposure of lung cells. Hexavalent chromium is taken into the cell and rapidly reduced to Cr(V), Cr(IV), Cr(III), and reactive oxygen species. Cells treated with Cr(VI) are subject to several types of DNA damage resulting from this reduction, including base modification, single-strand breaks, double-strand breaks, Cr-DNA adducts, DNA-Cr-DNA adducts, and protein-Cr-DNA adducts. These types of damage, if left unrepaired or are misrepaired, can lead to growth arrest, cytotoxicity, and apoptosis, as well as mutations leading to neoplastic transformation and ultimately tumorigenesis. Here we review the current literature on Cr-induced DNA damage and its repair.     

低剂量铬暴露工人铬鼻病调查分析

六价铬 [hexavalent chromium,Cr（VI）] 是通过将矿物中的三价铬在有氧条件下加热得到 ,其广泛应用在工业生产中,研究表明,Cr（VI）可诱导机体氧化应激、DNA损伤和染色体不稳定,产生细胞毒性并造成遗传损伤,增加肺癌、鼻咽癌、肝和肾的毒性损伤、心脏功能障碍、过敏性接触性皮炎或铬溃疡等相关疾病的风险,长期职业接触Cr（VI）可导致肺癌的发生。近年,六价铬化合物先后被列入我国《优先控制化学品名录（第一批）》和《有毒有害水污染物名录（第一批）》的危险化学物质。本文就近年的相关文献报道,从Cr（VI）的细胞毒性、Cr（VI）暴露的动物和接触Cr（VI）的人群3个方面概述Cr（VI）诱发肺癌的潜在分子机制,为后续的相关研究提供参考。     

Effect of available nitrogen on phytoavailability and bioaccumulation of hexavalent and trivalent chromium in hankow willows (Salix matsudana Koidz)

The effect of available nitrogen in nutrient solution on removal of two chemical forms of chromium (Cr) by plants was investigated. Pre-rooted hankow willows (Salix matsudana Koidz) were grown in a hydroponic solution system with or without nitrogen, and amended with hexavalent chromium [Cr (VI)] or trivalent chromium [Cr (III)] at 25.0±0.5 °C for 192 h. The results revealed that higher removal of Cr by plants was achieved from the hydroponic solutions without any nitrogen than those containing nitrogen. Although faster removal of Cr (VI) than Cr (III) was observed, translocation of Cr (III) within plant materials was more efficient than Cr (VI). Substantial difference existed in the distribution of Cr in different parts of plant tissues due to the nitrogen in nutrient solutions (p<0.05): lower stems were the major sink for both Cr species in willows grown in the N-free nutrient solutions and more Cr was accumulated in the roots of plants in N-containing ones. No significant difference was found in the removal rate of Cr (VI) between willows grown in the N-free and N-containing solutions (p>0.05). Removal rates of Cr (III) decreased linearly with the strength of nutrient solutions with or without N addition (p<0.01). Translocation efficiencies of both Cr species increased proportionally with the strength of N-containing nutrient solutions and decreased with the strength of N-free nutrient solutions. Results suggest that uptake and translocation mechanisms of Cr (VI) and Cr (III) are apparently different in hankow willows. The presence of easily available nitrogen and other nutrient elements in the nutrient solutions had a more pronounced influence on the uptake of Cr (III) than Cr (VI). Nitrogen availability and quantities in the ambient environment will affect the translocation of both Cr species and their distribution in willows in phytoremediation.     

Speciation of hexavalent chromium in welding fumes interference by air oxidation of chromium

The determination of various chromium species in welding fume normally involves digestion in a hot alkaline solution. This work confirms that Cr(III) can be oxidized to Cr(VI) during this digestion. However, only dissolved forms of Cr(III), such as the hydroxochromate(III) ion, [Cr(OH)4], are susceptible to oxidation under these conditions. The air oxidation of Cr(III) can be prevented by hydrolytic destabilization of the hydroxochromate(III) complex by the presence of magnesium hydroxide precipitate. The procedure has been used successfully in the determination of insoluble chromium(VI) in welding fumes. Excellent reproducibility is documented for soluble and insoluble chromium(VI) fractions in the analysis of a bulk sample of welding fume.     

Oxidative stress-related mechanisms are associated with xenobiotics exerting excess toxicity to Fanconi anemia cells

An extensive body of evidence has demonstrated the sensitivity of Fanconi anemia (FA) cells to redox-active xenobiotics, such as mitomycin C, diepoxybutane, cisplatin, and 8-methoxypsoralen plus ultraviolet irradiation, with toxicity mechanisms that are consistent with a deficiency of FA cells in coping with oxidative stress. A recent study has reported on excess sensitivity of FA complementation A group cells to chromium VI [Cr(VI)] toxicity, by postulating that a deficiency in Cr-DNA cross-link removal by FA cells and formation of Cr(VI)-associated cross-links may be the mechanism of Cr(VI)-induced cytotoxicity. However, the report failed to demonstrate any enhanced Cr uptake or, especially, any increase in Cr-DNA adducts. Thus, well-established findings on Cr(VI)-induced oxidative stress may explain excess sensitivity of FA cells to Cr(VI) in terms of its inability to cope with the Cr(VI)-induced prooxidant state.     

Biochemical and spectroscopic studies of the response of Convolvulus arvensis L. to chromium(III) and chromium(VI) stress

The objective of the present study was to determine the oxidative stress caused by hexavalent chromium (Cr[VI]), the chromium (Cr) uptake, and the Cr speciation in Convolvulus arvensis L. plants grown in hydroponics media containing either Cr(VI) or Cr(III). The results demonstrated that C. arvensis plants exposed to Cr(VI) concentrations ranging from 0 to 40 mg/L expressed higher ascorbate peroxidase specific activity in roots than in shoots. On the other hand, catalase activity monitored in plants exposed to 2 mg/L of Cr(VI) for 24 h increased in roots after a few hours of exposure. However, catalase activity in shoots revealed a decrement almost immediately after treatment was initiated. The results from x-ray absorption spectroscopic studies indicated that the oxidation state of the supplied Cr(III) remained the same in plant tissues. The supplied Cr(VI), however, was reduced to the trivalent form in plant tissues. The results of inductively coupled plasma/optical emission spectroscopy demonstrated that after 5 d, the roots of plants exposed to 40 mg/L of Cr(III) or Cr(VI) accumulated approximately 25,000 and 3,500 mg/kg dry weight of Cr, respectively. Nevertheless, shoots concentrated 1,500 and 2,000 mg/kg dry weight of Cr from Cr(III) and Cr(VI), respectively, which indicated that Cr moved faster into C. arvensis plants when supplied as Cr(VI).     

The simultaneous detection of trivalent & hexavalent chromium in exhaled breath condensate: A feasibility study comparing workers and controls

The analytical method outlined in this feasibility study has been used to show that trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) can be detected and measured in exhaled breath condensate (EBC) samples. EBC samples and urine samples were collected from a cohort of 58 workers occupationally exposed to hexavalent chromium compounds and 22 unexposed volunteers (control group). Levels of Cr(III) and Cr(VI) were determined in EBC samples and total chromium levels were determined in urine samples. Pre and post working week samples for both EBC and urine were collected in tandem. Total chromium in urine samples was analysed by inductively coupled plasma mass spectrometry (ICP-MS). Analysis of Cr(III) and Cr(VI) in EBC samples used a hyphenated micro liquid chromatography (μLC) system coupled to an ICP-MS. Separation was achieved using an anion exchange micro-sized column. The results showed that the occupationally exposed workers had significantly higher levels of Cr(III) and Cr(VI) in their EBC samples than the control group, as well as higher levels of total chromium in their urine samples. However, for the exposed workers no significant difference was found between pre and post working week EBC samples for either Cr(III) or Cr(VI). This study has established that Cr(III) and Cr(VI) can simultaneously be detected and measured in ‘real’ EBC samples and will help in understanding inhalation exposure.     

Reduction of hexavalent chromium concentration in fumes from metal cored arc welding by addition of reactive metals

Previous work has demonstrated that both the mass and composition of fumes produced during metal arc welding can be influenced by changes in the welding wire composition, the flux or gas shielding used and by changes in the process parameters, including voltage, adopted. The present paper describes modifications directed at reducing the concentration of hexavalent chromium [Cr(VI)] in welding fume by the addition of active metals—zinc, magnesium and aluminium to metal cored arc welding wires containing 10% Cr. There were marked changes in both the Cr(VI) concentration in the fume and the fume formation rate and hence in the Cr(VI) formation rate over the range of voltages used (18–24 V). Fume from wires containing the addition of 1% zinc contained Cr(VI) concentrations in the fume below those in the control and in wires with 1% magnesium and wires with 1% aluminium additions. Also, at 18 V, the Cr(VI) formation rate was at a minimum compared to the other wires. This advantage was not sustained as the voltage was increased and above 21 V the Cr(VI) formation rate for all the three wires containing active metal additions was higher than the control. These results demonstrate that at 18 V a significant reduction of Cr(VI) in welding fume can be produced by the addition of 1% zinc to the welding wire.     

Hexavalent chromium reduces larval growth and alters gene expression in mummichog (Fundulus heteroclitus)

Hexavalent chromium [Cr(VI)] is a common bioavailable metal ion that causes oxidative stress, DNA adducts, and perturbs gene expression. Changes in gene expression are useful biomarkers of toxicant exposure that provide information about an organism's health, adaptability, and toxicant-specific effects. Therefore, we developed a cDNA array for the estuarine sentinel species mummichog (Fundulus heteroclitus). Mummichog larvae were exposed to concentrations ranging from 0 to 24 mg/L (462 microM) of Cr(VI) for 30 d, and growth was measured to determine the no-observable-effect concentration (1.5 mg/L) and the lowest-observable-effect concentration (3 mg/L). Body burdens from Cr(VI)-exposed fish showed a dose-dependent increase and were inversely correlated to body weight. Mummichog larvae exposed to Cr(VI) differentially expressed 16 genes in a dose-dependent manner, including GLUT-2, L-FABP, ATPase synthase 8, type II keratin, TBT-binding protein, and complement component C3-2. Many of these genes are involved in energy metabolism or growth, which is consistent with the reduced growth observed. In subsequent experiments, adults were exposed to Cr(VI) for 7 d at 0, 1.5, or 3 mg/L, because adult mummichog are used in monitoring Superfund sites. Hexavalent chromium altered the expression of 10 genes in adult liver, including HGFA, H-FABP, and complement component C3-2. Many of these genes also are involved in energy metabolism. The mummichog arrays provide a potential mechanism for the effects of Cr(VI) on growth. We anticipate using these arrays and the data they provide to monitor effects at polluted sites, to assess the bioavailability of chromium at these sites, and to investigate the efficacy of remediation in chromium-polluted estuaries.     

Chromium(III)-induced 8-hydroxydeoxyguanosine in DNA and its reduction by antioxidants: comparative effects of melatonin, ascorbate, and vitamin E

Chromium compounds are well documented carcinogens. Cr(III) is more reactive than Cr(VI) toward DNA under in vitro conditions. In the present study, we investigated the ability of Cr(III) to induce oxidative DNA damage by examining the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in calf thymus DNA incubated with CrCl(3) plus H(2)O(2). We measured 8-OH-dG using HPLC with electrochemical detection. In the presence of H(2)O(2), we observed that Cr(III)-induced formation of 8-OH-dG in isolated DNA was dose and time dependent. Melatonin, ascorbate, and vitamin E (Trolox), all of which are free radical scavengers, markedly inhibited the formation of 8-OH-dG in a concentration-dependent manner. The concentration that reduced DNA damage by 50% was 0.51, 30.4, and 36.2 microM for melatonin, ascorbate, and Trolox, respectively. The results show that melatonin is 60- and 70-fold more effective than ascorbate or vitamin E, respectively, in reducing oxidative DNA damage in this in vitro model. These findings also are consistent with the conclusion that the carcinogenic mechanism of Cr(III) is possibly due to Cr(III)-mediated Fenton-type reactions and that melatonin's highly protective effects against Cr(III) relate, at least in part, to its direct hydroxyl radical scavenging ability.