Chem oprevention of 2-amino-1-methyl-6-phenyli-midazo[4,5-b]pyridine-induced carcinogen-DNA adducts by Chinese cabbage in rats

AIM The food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces colon and mammary gland tumors in rats and has been implicated in the etiology of human colorectal cancer. This study was conducted to examine the potentially preventive effect of Chinese cabbage (Brassica chinensis), a brassica vegetable most commonly consumed in China, against this carcinogen-induced DNA adduct formation in rats and its possible mechanisms.METHODS Sprague-Dawley rats were maintained for 10 days on basal diet or diet containing 20% (w/ w) freeze-dried cabbage powder prior to administration of a single dose of PhIP (10 mg/ kg) by oral gavage. Rats were sacrificed at 20 h after PhIP treatment and PhIP-DNA adducts in the colon, heart, lung and liver were analyzed using 32P-postlabeling technique. Levels of hepatic cytochrome P450 (CYP) 1A1 and 1A2, as indicated by 7-ethoxyresorufin O-deethylase and 7-methlxyresorufin O-demethylase activity, and cytosolic glutathione S-transferases (GSTs) towards 1-chloro-2, 4-dinitrobenzene (CDNB) in the liver, lung and colon were measured.RESULTS Rats pre-treated with Chinese cabbage and given a single dose of PhIP had reduced levels of PhIP-DNA adducts in the colon, heart, lung and liver, with inhibition rates of 82.3%, 60.6%, 48.4% and 48.9%, respectively (P＜0.01). The enzyme assays revealed that Chinese cabbage induced both CYP1A1 and 1A2 activity, but the induction was preferential for CYP1A1 over 1A2 (81% vs 51%). GST activity towards CDNB in the liver and lung, but not colon, was also significantly increased by cabbage treatment.CONCLUSION The results indicate that Chinese cabbage has a preventive effect on PhIP-initiated carcinogenesis in rats and the mechanism is likely to involve the induction of detoxification enzymes.

GSTM1 and XRCC3 Polymorphisms:Effects on Levels of Aflatoxin B1-DNA Adducts

Objective： Aflatoxin B1 （AFB1）, which can cause the formation of AFB1-DNA adducts, is a known human carcinogen. AFB1-exposure individuals with inherited susceptible carcinogen-metabolizing or repairing genotypes may experience an increased risk of genotoxicity. This study was designed to investigate whether the polymorphisms of two genes, the metabolic gene Glutathione S-transferase M1 （GSTM1） and DNA repair gene x-ray repair cross-complementing group 3 （XRCC3）, can affect the levels of AFB1-DNA adducts in Guangxi Population （n= 966） from an AFB1-exposure area. Methods： AFB1-DNA adducts were measured by ELISA, and GSTM1 and XRCC3 codon 241 genotypes were identified by PCR-RFLP. Results： The GSTM1-null genotype [adjusted odds ratio （OR） = 2.09; 95% confidence interval （CI） = 1.61-2.71] and XRCC3 genotypes with 241 Met alleles [i.e., XRCC3-TM and -MM, adjusted ORs （95% CI） were 1.43 （1.08-1.89） and 2.42 （1.13-5.22）, respectively] were significantly associated with higher levels of AFB1-DNA adducts. Compared with those individuals who did not express any putative risk genotypes as reference （OR = 1）, individuals featuring all of the putative risk genotypes did experience a significantly higher DNA-adduct levels （adjusted ORs were 2.87 for GSTM1-null and XRCC3-TM; 5.83 for GSTM1-null and XRCC3-MM）. Additionally, there was a positive joint effect between XRCC3 genotypes and long-term AFB1 exposure in the formation of AFB1-DNA adducts. Conclusion： These results suggest that individuals with susceptible genotypes GSTM1-null, XRCC3-TM, or XRCC3-MM may experience an increased risk of DNA damage elicited by AFB1 exposure.

Improved preparation and identification of aristolochic acid-DNA adducts by solid-phase extraction with liquid chromatography-tandem mass spectrometry

Aristolochic acid （AA） is a known nephrotoxin and potential carcinogen, which can form covalent DNA adducts after metabolic activation in vivo and in vitro. A simple method for preparation and characterization of aristolochic acid-DNA adducts was developed. Four AA-adducts were synthesized by a direct reaction of AAI/AAII with 2′-deoxynucleosides. The reaction mixture was first cleaned-up and pre-concentrated using solid phase extraction （SPE）, and further purified by a reversed-phase high performance liquid chromatography （HPLC）. By the application of developed SPE procedure, matrices and byproducts in reaction mixture could be greatly reduced and adducts of high purity （more than 94% as indicated by HPLC） were obtained. The purified AA-DNA adducts were identified and characterized with liquid-electrospray ionization-quadrupole-time of flight-mass spectrometry （LC-ESI-Q-TOF-MS/MS） and LC-Diode array detector-fluorescence （LC-DAD-FL） analysis. This work provides a robust tool for possible large-scale preparation of AA-DNA adduct standards, which can promote the further studies on carcinogenic and mutagenic mechanism of aristolochic acids.

STUDY ON GMA-DNA ADDUCTS

Objective. DNA modification fixed as mutations in the cells may be an essential factor in the initiation step of chemical carcinogenesis. In order to explore the mechanism of gene mutation and cell transformation induced by glycidyl methacrylate (GMA), the current test studied the characteristics of GMA DNA adducts formation in vitro. Methods. In vitro test, dAMP, dCMP, dGMP, dTMP and calf thymus DNA were allowed to react with GMA (Glycidyl Methacrylate). After the reaction, the mixtures were detected by UV and subjected to reversed phase HPLC on ultrasphere ODS reversed phase column, the reaction products were eluted with a linear gradients of methanol (solvent A) and 10mmol/L ammonium formate, pH5 0 (solvent B). The synthesized adducts were then characterized by UV spectroscopy in acid (pH1 0), neutral (pH7 2), alkaline (pH11 0) and by mass spectroscopy. Results. The results showed that GMA could bind with dAMP, dCMP, dGMP and calf thymus DNA by covalent bond, and the binding sites were specific (N 6 of adenine, N 3 of cytosine). Meanwhile, a main GMA DNA adduct in the reaction of GMA with calf thymus DNA was confirmed as N 3 methacrylate 2 hydroxypropy1 dCMP. Conclusions. GMA can react with DNA and /or deoxynucleotide monophosphate and generate some adducts such as N 6 methacrylate 2 hydroxypropyl dAMP and N 3 methacrylate 2 hydroxypropyl dCMP, ets. Formation of GMA DNA adducts is an important molecular event in gene mutation and cell transformation induced by GMA.

氮芥与DNA体外加合物及其质谱裂解规律

氮芥作为两用物质,不仅是禁止化学武器公约清单物,其衍生物至今仍是临床化疗药物。该文应用高效液相色谱-四极杆静电场轨道阱高分辨质谱法分析并鉴定了3种典型氮芥(HN1、HN2、HN3)分别与4种碱基、4种脱氧核糖核苷、4种脱氧核糖核苷酸和鲑鱼精DNA孵育后形成的加合产物。所有39个孵育体系中的HN-DNA加合产物经色谱分离,采用Full MS/dd-MS2模式进行数据采集获得其质谱特征信息。结果表明,在各孵育体系中均可鉴定到3种氮芥与鸟嘌呤、腺嘌呤和胞嘧啶特定碱基位点形成的单加合产物,并可鉴定到其与鸟嘌呤或腺嘌呤形成的双加合产物。在碱基孵育体系中虽可检测到3种氮芥与胸腺嘧啶形成的单加合产物,但在鲑鱼精DNA中并未检测到,表明其并非DNA的显著加合产物。通过探究各加合物的质谱裂解规律和特征加合离子,优化并给出了鉴定的系列DNA加合物的质谱多反应监测离子对,为氮芥暴露潜在生物标志物的鉴定和定量分析提供了重要的技术支撑,为复杂生物样品中氮芥DNA加合物的结构分析、准确溯源以及快速定量奠定了基础。

A STUDY ON DNA ADDUCTION WITH NICOTINE－DERIVED NITROSAMINE BY ACCELERATOR MASS SPECTROMETRY

DNA adduction with nicotine-derived nitrosamine, 4-(methylnitrosamino)-1-(3- pyridy1)-1 -butanone (NNK) in mice at doses equivalent to human exposure has been studied using 14C-label by accelerator mass spectrometry(AMS). A detection limit of DNA adducts of 1 adduct Per 1010 nucleotides has been achieved. This sensitivity of AMS measurement is 3 or more orders of magnitude improved than that of radioimmunoassay.Formation of DNA adducts is linearly dependent on dose down to an exposure of 100 ng Per kg of body weight .The ultimate cheeical form of carcinogen NNK binding to DNA is speculated.

Leptin influences estrogen metabolism and increases DNA adduct formation in breast cancer cells

Objective: The elevated incidence of obesity has been paralleled with higher risks of breast cancer. High adiposity increases leptin secretion from adipose tissue, which in turn increases cancer cell proliferation. The interplay between leptin and estrogen is one of the mechanisms through which leptin influences breast carcinogenesis. An unbalanced estrogen metabolism increases the formations of catechol estrogen quinones, DNA adducts, and cancer mutations. This study aims to investigate the effect of leptin on some estrogen metabolic enzymes and DNA adduction in breast cancer cells.Methods: High performance liquid chromatography(HPLC) was performed to analyze the DNA adducts 4-OHE1[E2]-1-N3 adenine and 4-OHE1[E2]-1-N7 guanine. Reporter gene assay, real time reverse transcription polymerase chain reaction(real time RT-PCR), and Western blot were used to assess the expression of estrogen metabolizing genes and enzymes: Cytochrome P-4501B1(CYP1B1), Nicotinamide adenine dinucleotide phosphate-quinone oxidoreductase1(NQO1), and Catechol-O-methyl transferase(COMT).Results: Leptin significantly increased the DNA adducts 4-OHE1[E2]-1-N3 adenine and 4-OHE1[E2]-1-N7 guanine.Furthermore, leptin significantly upregulated CYP1B1 promoter activity and protein expression. The luciferase promoter activities of NQO1 and m RNA levels were significantly reduced. Moreover, leptin greatly reduced the reporter activities of the COMT-P1 and COMT-P2 promoters and diminished the protein expression of COMT.Conclusions: Leptin increases DNA adduct levels in breast cancer cells partly by affecting key genes and enzymes involved in estrogen metabolism. Thus, increased focus should be directed toward leptin and its effects on the estrogen metabolic pathway as an effective approach against breast cancer.

Carcinogen-Macromolecular Adducts As Biomarkers in Human Cancer Risk Assessment

Substantial data have been generated during the past 5 years in both experimental systems and human populations which shed light on the potential role of carcinogen-macromolecular adducts in human cancer risk assessment. The use of DNA and protein adducts is based on the fundamental concept in chemical carcinogenesis that most genotoxins are metabolized to electrophilic 'ultimate' carcinogens that are capable of forming covalent adducts with cellular macromolecules. This report examines the relative usefulness and limitations of using DNA and protein adducts and related techniques for assessing human exposure to genotoxic carcinogens. Data discussed in this report clearly demonstrate that these biomarkers not only allow early detection of potential cancer hazard in humans, but they can also significantly increase the power of conventional cancer epidemiological studies in determining true causal relationships. In addition, such biomarkers can improve extrapolation of cancer risks from laboratory animals to humans or from one human population to another.

Inhibition of nicotine-DNA adduct formation by polyphenolic compounds in vitro

Nicotine [3-(1-methyl-2-pyrrolidinyl)-pyridine], a major alkaloid in tobacco products, has proven to be a potential genotoxic compound. Some polyphenolic compounds can suppress the DNA adduction, and hence act as the potential inhibitors of carcinogenesis. In this study, the inhibitory effects of three polyphenolic compounds, curcumin (diferuloylmethane), resveratrol (trans-3, 5, 4-trihydroxystilbene) and tea polyphenols, on the nicotine-DNA adduction have been investigated in vitro using radiolabelled nicotine and liquid scintillation counting (LSC) technique. Also, the inhibition mechanism of these chemopreventive agents in regard to the activity of the biotransformation enzymes, including cytochrome P450 (CYP450), cytochrome b5 (CYb5) and glutathione S-transferase (GST), has been studied. The results demonstrated that these three polyphenols induced marked dose-dependent decrease in nicotine-DNA adducts as compared with the controls. The elimination rate of adducts reached above 46% at the highest dose for all the three agents with 51.6% for resveratrol. Correspondingly, three polyphenols all suppressed CYP450 and CYb5, whereas curcumin and resveratrol induced GST. We may arrive at a point that the three polyphenols are beneficial to prevent the nicotine adduct formation, and thus may be used to block the potential carcinogenesis induced by nicotine.

应用紫外及荧光光谱法研究三种醛类污染物对牛腺DNA的损伤作用

应用紫外光谱移动法和溴乙锭荧光法对三种醛类化合物与牛腺DNA的加合以及它们引起的DNA-DNA交联进行了检测 结果表明,甲醛和乙醛能够与DNA形成共价加合物,与四种脱氧核苷加合顺序分别为dG>dC>dA>dT和dA>dG>dC>dT,丙烯醛与DNA的加合不能用紫外光谱移动法测定 甲醛能够显著地引起DNA-DNA的交联;乙醛也有这种作用,但不显著;丙烯醛的交联作用未测出,可能是由于羰基碳正电性较弱。

克百威与DNA之间作用的光谱学研究

利用吸收光谱法和荧光光谱法研究了克百威与ctDNA之间的相互作用。结果表明,ctDNA可使克百威的吸收光谱发生减色以及红移现象;ctDNA对克百威的荧光存在静态的荧光猝灭。两种光谱都支持克百威是以嵌插方式与ctDNA形成两者的加合物。溶剂以及离子强度对于两者加合作用存在不同的影响。

典型醛类污染物与细胞DNA分子的结合作用

为了研究甲醛、乙醛和丙烯醛等 3种典型醛类污染物与细胞DNA的结合作用 ,探讨其遗传毒性效应和机制 ,采用体外测试系统 ,应用紫外光谱移动法和高效液相色谱法研究结合位点 .结果表明 ,醛类污染物染毒细菌DNA紫外吸收峰位移不显著 ;但提取的细菌DNA与甲醛进行试管反应体系紫外位移显著 ;醛类污染物染毒真核细胞致DNA分子紫外吸收峰位移显著 ;乙醛与脱氧鸟苷酸的试管反应经NaBH4 还原后经HPLC分离检测 ,产物初步定性为N2 -乙基鸟苷加合物 .说明 3种醛类污染物能够与细胞DNA结合而体现遗传毒性 ,鸟苷的N2位可能是共价加合的位点 .

三种氨基甲酸酯类农药化合物对DNA的潜在损伤作用

应用紫外光谱法研究了3种氨基甲酸酯类农药对DNA的损伤作用。结果显示,这3种氨基甲酸酯类农药能够引起ctDNA的紫外吸收光谱发生发射波长以及吸收强度的变化,从而说明3种氨基甲酸酯类农药能够与ctDNA进行作用。即意味着3种氨基甲酸酯类农药进入生物有机体后有可能通过形成DNA加合物的形式而进一步导致基因突变,最终对生物体的DNA产生化学损伤。

肺癌组织中DNA修复基因ERCC1的表达与多环芳烃 -DNA加合物的关系

目的 :探讨核苷酸切除修复基因ERCC1在肺癌中的表达及其与多环芳烃 (PAH) -DNA加合物的关系。方法 :用RT -PCR技术检测 15 0例肺癌、12 0例癌旁肺组织、4 0例肺良性病变和 4 0例正常肺组织中ERCC1基因mRNA的表达 ;用免疫法检测PAH -DNA加合物 ;分析有关暴露因素对修复基因ERCC1的表达和PAH -DNA加合物的影响 ,并探讨ERCC1与PAH -DNA加合物的关系。结果 :30 7% (4 6 / 15 0 )的肺癌组织和 2 5 % (1/ 4 0 )的正常肺组织存在ERCC1基因的表达低下 ;吸烟可抑制ERCC1基因的表达。肺组织中PAH -DNA加合物的水平与ERCC1基因表达呈显著负相关 ,Spearman相关系数为 - 0 6 4 8,P <0 0 1。结论 :ERCC1是参与修复DNA加合物等损伤的一个重要的核苷酸切除修复基因 。

涕灭威及其有毒代谢产物对DNA潜在损伤研究

采用生物遗传监测系统,研究了涕灭威及其两个有毒代谢产物(涕灭威亚砜,涕灭威砜)对蚕豆及大蒜根尖细胞微核率的影响,以及对小牛胸腺DNA的加合作用．结果表明,两种植物根尖细胞微核试验测得的高浓度剂量诱导的微核率与对照组相比有显著性差异(p<0．05),说明涕灭威、涕灭威亚砜及涕灭威砜可能对蚕豆及大蒜根尖细胞有致突变性．并且配对资料差异的显著性检验表明,蚕豆根尖微核试验的敏感性明显高于大蒜根尖微核试验的敏感性．涕灭威及其两个有毒代谢产物与小牛胸腺DNA结合引起吸收光谱波峰的移位,而且存在着剂量关系,说明涕灭威、涕灭威亚砜及涕灭威砜可能对小牛胸腺DNA造成加合作用．

天然抗氧化剂丹参酮Ⅱ—A对肝细胞脂质过氧化产物与DNA相互作用的影响

［３Ｈ］花生四烯酸标记的肝细胞，经ＦｅＣｌ２－ＤＴＰＡ启动脂质过氧化后，细胞ＤＮＡ出现放射性，并随保温时间增加而逐渐增高，表明在细胞内脂质过氧化产物与ＤＮＡ发生相互作用，生成了一种ＤＮＡ加成物，经测定它具有特征荧光光谱，显示较低的增色效应和Ｔｍ值。用高度敏度荧光图象显微镜直接观察发现丹参酮Ⅱ－Ａ经细胞摄取后主要滞留在细胞膜与胞浆中。它能有效地抑制细胞脂质过氧化，减少脂质－ＤＮＡ加成物的产生，并阻止了细胞存活率和Ｏ６甲基鸟嘌呤转移酶活性的降低，其抑制率与ＶｉｔＥ，ＢＨＴ相近，但显著高于ＮａＮ３，甘露醇和ＳＯＤ。上述结果提示丹参酮Ⅱ－Ａ是一种新的有效的细胞内脂质过氧化产物与ＤＮＡ相互作用的抑制剂。它对ＤＮＡ的保护作用可能是通过清除脂类自由基而阻断脂质过氧化的链式反应，抑制ＤＮＡ加成物的生成，从而减少了细胞毒性。

灭幼脲光解产物DNA加合物的研究

灭幼脲(邻氯苯甲酰基-对氯苯基-脲)本身是一种低毒、低残留、没有致突、致癌性的农药.但是它的某些分解产物,如:氯苯、对氯苯、对氯苯基脲等有一定的毒性.邻氯苯甲酰胺(灭幼脲的主要光解产物——CBA)和未经分离的灭幼脲光解产物的混合物,在试管反应条件下能与小牛胸腺DNA反应形成多种DNA加合物,用P_1加强灵敏度的^(32)P后标记方法分析,有四种DNA加合物被检出(DNA-CBA),实验证明,邻氯苯甲酸胺和灭幼脲光解产物的混合物在Ames实验中也均呈阳性结果,初步说明两者都可能具有一定的致突性.经单独碱基和邻氯苯甲酰胺试管反应的加合物鉴定,验证出其中较强的一种加合物是邻氯苯甲酸酰与2’-脱氧腺嘌吟-3’-单磷酸碱基(dAMP)反应所形成的加合物(dA-CBA),已占所形成加合物总量的57%.从^(32)P后标记方法所测的DNA加合物的自显影指纹图上可以看出,邻氯苯甲酰胺和灭幼脲光解产物混合物的DNA加合物具有相同的迁移特性.初步说明,尽管灭幼脲原体化合物没有致突性,但它的主要光解产物邻氯苯甲酰胺具有一定基因突变性,所以不仅应对原体化合物进行评价,而且还必须对它的分解物和代谢物同时进行安全评价.

DNA加合物8-羟基脱氧鸟苷特性研究

作为DNA氧化损伤的生物学标志物,8-羟基脱氧鸟苷(8-OH-dG)的特性研究,对稳定、灵敏、准确地定量8-OH-dG,进而研究有毒化学物质对生物体内的氧化损伤很重要。该文研究了氧化损伤后DNA中8-OH-dG的分析、水解、储存、稳定性等方面的问题。采用Fenton型产羟自由基系统如螯合剂Fe2+-H2O2为氧化源,与脱氧鸟苷和小牛胸腺DNA反应,生成的8-OH-dG用高压液相色谱-电化学法检测,并对8-OH-dG的分析条件进行优化。该法最低检出限为32fmol,比光学吸收法高2～3个数量级,线性范围可高达4个数量级,从0.32pmol到3.2nmol,相关系数0.9996。并对酶水解DNA的条件、储存酸度、介质环境及其稳定性等进行了探讨,结果表明8-OH-dG储存在中性偏酸的缓冲溶液中损失较少,其形成与所处介质环境有关,在氧化源存在或有氧环境中一定时间内有累积作用,添加抗氧化剂等干预措施后,能灵敏而稳定地对DNA中的8-OH-dG进行测定。

肠胃清逆转结肠癌HCT116/L-OHP细胞草酸铂耐药作用及对Pt-DNA加合物的影响

目的探讨中药复方肠胃清(黄芪、白术、党参、猪苓、薏苡仁、八月札、野葡萄藤、红藤等)对结肠癌HCT116/L-OHP细胞草酸铂耐药的逆转作用及对Pt-DNA加合物的影响。方法将HCT116/L-OHP细胞种植于裸小鼠皮下,建立肿瘤耐药模型,随机分为5组,A组为对照组,B组为草酸铂组,C组为肠胃清组,D组为草酸铂+肠胃清低剂量组,E组为草酸铂+肠胃清高剂量组,治疗前后测量移植瘤体积及荷瘤鼠体质量;采用细胞增殖抑制实验MTT法观察肠胃清药物血清对HCT116/L-OHP细胞株耐药性的逆转作用,并采用原子吸收分光光度法检测细胞内铂(Platinum,Pt)药物及核内Pt-DNA水平。结果肠胃清联合草酸铂组与肠胃清或草酸铂单独用药组相比,有更高的肿瘤抑制率(P<0.01),其中肠胃清高剂量联合草酸铂组抑瘤率最高;与对照组相比,含肠胃清组荷瘤鼠体质量减轻好于单用草酸铂;MTT结果显示7.5%肠胃清药物血清能够增加耐药细胞株HCT116/L-OHP对草酸铂敏感性,逆转指数为2.74;肠胃清药物血清可以增加HCT116/L-OHP细胞内草酸铂水平,并能使细胞核内Pt-DNA加合物水平增加15.74%。结论肠胃清能够逆转HCT116/L-OHP细胞对草酸铂的耐药性,其机制与肠胃清增加细胞内Pt-DNA加合物水平有关。

免疫毛细管电泳-激光诱导荧光分析DNA加合物的方法学研究

DNA加合物是一类重要的生物标志物,可应用于人体致癌物暴露监测、癌症风险评价和人群易感性研究。DNA加合物作为生物标志物的应用需要安全、灵敏、快速的先进分析技术。我们利用免疫毛细管电泳-激光诱导荧光分析,发展了高灵敏的DNA加合物分析方法和技术。本文主要介绍了相关的仪器研制及方法学研究。方法学研究涉及DNA加合物荧光探针的合成和表征、抗体与DNA加合物的相互作用及其结合计量学、抗原-抗体复合物的稳定化和DNA驱动电泳聚焦技术。