羟基自由基与DNA中腺嘌呤碱基间反应的AM1研究

UV诱发的羟基自由基，引起了DNA互补碱对间的交联。本文论证了UV引起的互补碱对交联是UV诱发基因突变的主要根源。UV与化学致癌剂不同，可以引起双氢键AT对转化成叁氢键GC或CG对的点突变，这与腺嘌呤A在UV作用下转化成2－羟基腺嘌呤有关。本文采用高级半经验AM1方法，对UV诱发产生的羟基自由基在腺嘌呤8－位及2－位的羟基化反应，进行了计算探讨。证明在两个位置上的反应均经两步完成，反应的活化能较小并且焓变为负值、反应无论在动力学或热力学上均有利于发生。8－羟基腺嘌呤或8－羟基鸟嘌呤的存在，虽然是羟基自由基作用于DNA的标志性产物，但因其不影响小沟槽的氢键键合，很易被修复而不影响基因变异。但DNA双股中的2－羟基腺嘌呤碱或其互变异构体，则引起AT→GC或AT→CG的双氢键键合向叁氢键键合的突变。     

一些致突变剂与致癌剂分子流行病学的研究进展

分子流行病学是一种新兴的并迅速发展的研究领域。它结合了内剂量、生物有效剂量、生物效应和个体易感性效应等流行病方法学的实验检测方法，如接触性生物标记：尿中的代谢物、DNA加合物；蛋白质加合物和彗星实验参数检测的DNA损伤；效应性生物标记：染色体畸变、姊妹染色单体交换、策核、次黄嘌呤－鸟嘌呤磷酸核糖转移酶基因（HPRT）的突变，编码p53或p21蛋白的肿瘤基因的活化；易感性生物标记：CYP1A1、GSTM1、GSTT1、NAT2等基因的多态性。但无论什么实验都需要人类监测的可靠根据。直到现在仍不能解释基因型、接触性生物标记与效应性生物标记之间的关系。     

对二氯苯的毒理学研究进展

对二氯苯是一种含卤素的挥发性有机污染物,是钢铁烧结烟气中的主要芳烃类化合物之一.该化合物也是合成药物、人造树脂及精细化学品的重要原料,可用于制备家用防蛀防霉剂.对二氯苯挥发性较强,可通过大气传输,已经广泛出现在人和动物的食物链中,对于人体和生态环境具有潜在的危害.体外毒理学研究证实,对二氯苯主要是通过线粒体凋亡途径引起细胞损伤.对二氯苯不具有遗传毒性,其致突变作用仍需进一步研究.体内毒理学研究表明,对二氯苯会引起肝脏和神经系统的损害,并且会出现抽搐、贫血、厌食和皮肤色素沉积等一系列症状,对人致癌的证据不充分.活体动物的研究表明,在大剂量灌胃条件下,对二氯苯可诱发动物的肝细胞增殖,并可能引发肿瘤.当小鼠暴露于极低浓度的对二氯苯时,小鼠海马神经元中相关的基因表达被强烈抑制.对二氯苯在哺乳动物体内的Ⅰ相代谢产物主要是2,5-二氯苯酚,Ⅱ相代谢产物为2,5-二氯苯酚的硫酸盐和葡萄糖醛酸等形式.在代谢中产生的环氧化物和二氯氢醌中间体是该化合物体内毒性的来源之一.对二氯苯生态毒性研究表明,对二氯苯对环境中的动植物具有毒害作用.低浓度的对二氯苯会抑制植物根际微域土壤脱氢酶和脲酶活性,而高浓度的对二氯苯则表现为促进作用.对二氯苯可以通过抑制细胞生长的G1期来抑制植物细胞分裂,从而影响植物的生长.本文综述了对二氯苯在体内外的毒性、代谢转化及生态毒理效应,为对二氯苯的污染控制及毒害作用的阻控研究提供依据.     

1,3-丁二烯与DNA交联致癌机理的研究——代谢产物与鸟嘌呤反应及与DNA交联作用的AM1计算

采用AMI方法计算了环境致癌物1.2-环氧3,4-丁烯(EB)和1,2,3,4二环氧丁烷(DEB)与DNA鸟嘌呤反应过程速率控制步骤的活化能及DEB与DNA片段生成烷化交联产物的结构和能量、结果得出:用烷化反应的难易程度难以解释DEB的致突性比EB大100倍的实验事实;强致突的DEB可与鸟嘌吟发生两次烷化反应,生成DNA交联产物,交联后的DNA结构稳定、变形小:而EB则不能交联.这可能为两者基因毒性差异巨大的分子机制.     

Mutagenicity of polyaromatic hydrocarbons by chemical models for cytochrome P450 in Ames assay

DNA damage is an important step in carcinogenesis. The Ames assay is a short-term screening of carcinogens that induce DNA damage. Most carcinogens require enzymatic activation through oxidation by cytochrome P450 (CYP450) in the presence of S9 mix. A combination of iron (Fe)(III) porphyrin and an oxidant is also able to oxidize compounds as an alternative metabolic pathway to CYP450. Previously it was reported that a chemical model containing a water-soluble 5,10,15,20-tetrakis(1-methylpyridinium4-yl)porphyrinatoiron(III) chloride (4-MPy) and tert-butyl hydroperoxide (t-BuOOH) activated aromatic amines and amides. In this study, a chemical model composed of an Fe porphyrin, water-insoluble 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinatoiron(III) chloride (F₅P) or water-soluble 4-MPy was optimized with an oxidant – t-BuOOH, magnesium monoperoxyphthalate (MPPT), or iodosylbenzene (PhIO). Subsequently the mutagenicity of benzo[a]pyrene (B[a]P) and chrysene in Salmonella typhimurium TA strains was compared. B[a]P was activated by a combination of F₅P or 4-MPy plus MPPT or PhIO in S. typhimurium TA1538. The B[a]P-induced mutagenicity with F₅P plus oxidant was higher than 4-MPy plus oxidant. Mutagenicity of chrysene, a tetracyclic aromatic hydrocarbon, was not detected in the presence of F₅P/PhIO in S. typhimurium TA98, but was activated in the presence of F₅P/MPPT. The F₅P/MPPT activated other polyaromatic hydrocarbons (PAH) in the S. typhimurium TA98 assay including dibenz[a,c]anthracene, dibenz[a,h]anthracene, 3-methylcholanthrene, and benzo[a]anthracene. The results indicated that the F₅P/MPPT was the most efficient model for detecting PAH-induced mutagenicity in the Ames assay.     

Testicular DNA synthesis inhibition—an in vivo system for the detection of mutagenic and carcinogenic chemicals

By binding covalently to DNA chemical mutagens and carcinogens inhibit replication, which can be measured as a decrease in thymidine incorporation into DNA. This DNA synthesis inhibition (DSI) has been determined in testicular cells of mice for a large number of compounds and has been found to correlate very well with their known mutagenic and carcinogenic properties.

Not only could this test give a qualitative answer about potential carcinogenicity or mutagenicity, but, with regard to its in vivo characteristics, could furthermore give an indication of the carcinogenic and mutagenic potency and thus be of use in the risk evaluation of chemical substances; the relationship between the DNA synthesis inhibition and the underlying alkylation of guanine ‐0⁶ by different methylating agents is demonstrated.

As toxic effects decrease thymidine incorporation, too, means are discussed for distinguishing between “true”;, mutagenic, and “false”;, cytotoxic, DNA synthesis inhibition.

In conclusion, the implications of including the DSI‐test in a battery of mutagenicity tests are outlined.     

人血淋巴细胞检测浊漳河地表水的遗传毒性

为评价浊漳河水体中有机污染物的致突变性,采用单细胞凝胶电泳(SCGE)技术,研究了浊漳河水体3个不同样点的有机提取物对人外周血淋巴细胞DNA损伤效应。结果显示,各水样中的有机提取物均能引起DNA损伤,且随剂量的增高,有机物对DNA的损伤加重;细胞DNA损伤与对照组相比均有显著性差异(p<0.01)。这表明人外周血淋巴细胞对水体有机污染物的毒作用非常敏感。细胞彗星尾部DNA含量(%DNAT)和染毒剂量呈极显著正相关(R2>0.8547,p<0.01)。以上结果表明,浊漳河水体受到一定程度的有机物污染,这些有机污染物可诱导淋巴细胞DNA损伤,具有遗传毒性。SCGE技术作为一种简便、快速和灵敏的检测方法在水环境遗传毒性监测方面具有较大的应用价值。     

2-硝基芴的致突变性受共存多环芳烃的影响

本文以Ames试验的TA_(98)菌株研究了2-硝基芴(2-Nitroflurene)在其它多环芳烃共存时,其致突变性的变化.结果显示:它与其它硝基多环芳烃共存时.直接致突变性增强;而与其它无直接致突变性的多环芳烃共存时,其直接致突变性减弱,且多环芳烃的环数越多、减弱作用越强,这可能是因为硝基多环芳烃具有亲电子性,DNA的碱基有亲核性,易于结合,造成DNA的损伤;而多环芳烃一般具有供电子性,阻碍了硝基多环芳烃与DNA碱基的结合.     

利用彗星实验检测丙烯酰胺对小鼠两种细胞的DNA损伤和修复

为了研究丙烯酰胺致小鼠睾丸细胞和外周血淋巴细胞DNA的损伤及修复情况,同时比较这两种细胞对丙烯酰胺的敏感性,将雄性昆明种小鼠一次性腹腔注射丙烯酰胺(50mg·kg-1(bw)),在暴露后第1、2、4、6、8、10、12d,分别对其睾丸组织细胞和外周血淋巴细胞DNA损伤进行彗星实验分析.结果表明,暴露结束后每个时间点小鼠睾丸组织细胞、外周血淋巴细胞DNA的迁移率均显著高于阴性对照组,随时间推移两种细胞DNA迁移距离逐渐降低,同一时间点睾丸组织细胞DNA损伤较外周血淋巴细胞DNA损伤更为严重,两者差异显著(p<0.05).以上结果表明,睾丸组织和外周血淋巴细胞可能是丙烯酰胺的作用位点;机体对丙烯酰胺造成的遗传损伤有一定的修复能力;与淋巴细胞相比,睾丸细胞对丙烯酰胺导致的遗传损伤更为敏感.     

Assessment of mutagenic potency of source water treated by ozone and adsorption processes

This research utilized the Ames test to determine the mutagenicity of water treated by advanced processes, including ozonation and granular activated carbon (GAC). Raw water samples for this research included those obtained from the Pan Hsin waterworks as well as samples containing humic acids. Treated samples were collected from the pilot‐scale advanced treatment plant. The Ames test was used to measure the mutagenicity of the water after each treatment process. For the Pan Hsin raw water samples treated with ozone or GAC, it was indicated that, regardless of whether samples were preozonated or not, they all showed a mutagenic potency less than 2 once the S9 enzyme was added. This level of mutagenicity is insignificant. The prepared humic acid samples, on the other hand, demonstrated a significant reduction in mutagenicity after the pre‐ozonation process, indicating that preozonation can lower the degree of mutagenicity. Furthermore, the mutagenicity of the prepared humic acid samples gradually decreased after the advanced treatment process. However, when chlorine was added later to these samples, the mutagenicity increased again. This research shows that the use of O3/GAC processes to treat water can successfully lower mutagenicity, indicating a great potential for applications in the treatment of drinking water.     

Uptake and genotoxicity of micromolar concentrations of cobalt chloride in mammalian cells

Literature data concerning the genotoxicity of cobalt salts have been conflicting. To establish appropriate incubation conditions, we conducted a series of uptake studies, before genotoxicity was determined by DNA strand break induction in HeLa cells and mutagenicity in V79 Chinese hamster cells. Co(II) is taken up by HeLa cells in a concentration‐dependent manner and is accumulated inside the cell. The uptake is preceded by a fast association step to the outer membrane, with no saturation up to 24 h. DNA strand breaks as determined by nucleoid sedimentation are induced at concentrations as low as 50μMCoCl₂. The induction is time‐dependent, showing the highest number of breaks after 4h incubation with no further increase up to 24h. CoCl₂ is mutagenic at the HPRT‐locus, enhancing the spontaneous mutation frequency 4.2‐fold at 100μ?. Besides direct interactions with DNA, the mutagenicity of CoCl₂ could also be due to a decrease in the Fidelity of DNA polymerisation.     

生物样品体外致突变高通量检测方法研究进展

评述了几种常用的体外致突变检测方法及其用于生物样品检测的可行性,有些方法经改进可用于高通量检测生物样品体外致突变性.经典Ames实验受生物样品中组氨酸的影响,易产生假阳性结果,尽管经过修正可以排除组氨酸的干扰,但操作繁琐,不适合高通量检测.基于SOS反应的检测体系避开了组氨酸的影响,且简单易行,适合高通量检测:以β-半乳糖苷酶基因(lacZ)作为报告基因的检测体系灵敏度高,且经过离心洗涤或后培养的方式可降低样品颜色的影响;以绿色荧光蛋白(GFP)基因作为报告基因的检测体系避开了颜色的干扰,但这类方法灵敏度普遍不高,可以寻找信号更强的荧光蛋白以替代GFP;荧光素酶(lux)基因集lacZ和GFP的优点于一身,但检测时需要额外添加辅助因子,限制了其应用.也对单细胞凝胶电泳、tk基因突变实验、染色体损伤检测等方法进行了分析,有些适合生物样品高通量检测,但由于缺少国际通用的标准,很难推广使用.     

Humic substances. Part III. sorptive interactions with environmental chemicals†

The formation of covalent binding to DNA of a carcinogen is now widely accepted to represent a classical mechanism of tumour induction in mammals. This mechanism does not operate with metals since no covalent binding of these agents to DNA does occur. Nevertheless, somatic mutations as typical consequences of DNA‐damage have been reported to be induced by metals in various model systems. Beside DNA‐alkylation such damages can be caused by changes in the conformation of DNA or in the fidelity of DNA‐repair. The activity of the repair enzymes DNA‐polymerases is indeed impaired by many metal ions at least in vitro. It is not yet established whether these mechanisms are also important in the intact mammalian organism. Much evidence has accumulated during the last years that a disturbance of the balance of cations and especially metal ions represents another possible mechanism of tumour induction. The tumours found with high doses of chelating agents such as nitrilo‐triacetic acid (NTA) have to be discussed in this context. Since most—if not—all of the speculative mechanisms of metal carcinogenesis resemble classical pharmacological reactions the existence of a threshold level is likely. So metal carcinogenesis will not be a problem of the environmental contamination at trace levels but a problem of occupational medicine.