Detection of DNA damage in peripheral lymphocytes by 7 compounds using comet assay

目的：检测过氧化氢（Ｈ２Ｏ２）、甲磺酸乙酯（ＥＭＳ）、丝裂霉素Ｃ（ＭＭＣ）、二甲基亚硝胺（ＤＭＮＡ）、苯并（ａ）芘（ＢａＰ）、２氨基芴（２ＡＦ）和环磷酰胺（ＣＰ）诱发小鼠、大鼠及人外周血淋巴细胞ＤＮＡ单链断裂．方法：体外单细胞微量凝胶碱性电泳试验（慧星试验）．结果：除ＥＭＳ０９７ｍｍｏｌ·Ｌ－１在小鼠淋巴细胞，ＭＭＣ３０μｍｏｌ·Ｌ－１在小鼠、人淋巴细胞中呈阴性外，其余均为阳性．最低可检测浓度分别为Ｈ２Ｏ２１μｍｏｌ·Ｌ－１，ＥＭＳ０４８ｍｍｏｌ·Ｌ－１，ＢａＰ５０μｍｏｌ·Ｌ－１，ＣＰ２０ｍｍｏｌ·Ｌ－１，ＭＭＣ１０μｍｏｌ·Ｌ－１，ＤＭＮＡ２７３ｍｍｏｌ·Ｌ－１，２ＡＦ６２５μｍｏｌ·Ｌ－１．ＣＰ、ＢａＰ、２ＡＦ需经Ｓ９Ｍｉｘ代谢活化才显示毒性．结论：彗星试验检测出ＭＭＣ诱导大鼠，ＥＭＳ诱导大鼠和人，以及Ｈ２Ｏ２、ＤＭＮＡ、ＢａＰ、ＣＰ和２ＡＦ诱导小鼠、大鼠和人外周血淋巴细胞ＤＮＡ单链断裂损伤．     

人白细胞髓过氧化物酶代谢活化致癌物4－氨基联苯

本文研究人白细胞髓过氧化物酶（ＭＰＯ）体外代谢芳胺类致癌物４－氨基联苯（４－ＡＢＰ〕在Ｈ２Ｏ２存在下，ＭＰＯ代谢活化４－ＡＢＰ生成二种可与ＤＮＡ共价结合的代谢产物。高效液相色谱和质谱分析表明。在没有ＤＮＡ存在时４－ＡＢＰ的主要代谢产物是偶氮二联苯。抗坏血酸和谷胱甘肽显著抑制活化的４－ＡＢＰ与ＤＮＡ结合。而且可将活化产物还原成４－ＡＢＰ．这些结果结合质谱资料提示活性中间产物可能是４－ＡＢＰ自由基。３２Ｐ－后标记实验证实ＤＮＡ加合物形成，用此种方法检测出８个４－ＡＢＰ－ＤＮＡ加合物。并表明ＭＰＯ介导产生的４－ＡＢＰ－ＤＮＡ加合物与细胞色素Ｐ４５０代谢产物Ｎ－羟基－４－ＡＢＰ和ＤＮＡ反应产生的加合物性质不同．这些结果提示。ＭＰＯ代谢活化途径可能在４－ＡＢＰ诱发肝外组织肿瘤过程中起一定的作用．     

人白细胞髓过氧化物酶代谢活化致癌物4－氨基联苯

本文研究人白细胞髓过氧化物酶（ＭＰＯ）体外代谢芳胺类致癌物４－氨基联苯（４－ＡＢＰ〕在Ｈ２Ｏ２存在下，ＭＰＯ代谢活化４－ＡＢＰ生成二种可与ＤＮＡ共价结合的代谢产物。高效液相色谱和质谱分析表明。在没有ＤＮＡ存在时４－ＡＢＰ的主要代谢产物是偶氮二联苯。抗坏血酸和谷胱甘肽显著抑制活化的４－ＡＢＰ与ＤＮＡ结合。而且可将活化产物还原成４－ＡＢＰ．这些结果结合质谱资料提示活性中间产物可能是４－ＡＢＰ自由基。３２Ｐ－后标记实验证实ＤＮＡ加合物形成，用此种方法检测出８个４－ＡＢＰ－ＤＮＡ加合物。并表明ＭＰＯ介导产生的４－ＡＢＰ－ＤＮＡ加合物与细胞色素Ｐ４５０代谢产物Ｎ－羟基－４－ＡＢＰ和ＤＮＡ反应产生的加合物性质不同．这些结果提示。ＭＰＯ代谢活化途径可能在４－ＡＢＰ诱发肝外组织肿瘤过程中起一定的作用．     

氰戊菊酯对细胞色素P450 2B1/2B2的诱导

１５只ＳＤ大鼠随机分为氰戊菊酯（Ｆｅｎ）组（１２０ｍｇ·ｋｇ－１·ｄ－１×７,ｉｇ）,苯巴比妥（ＰＢ）诱导组（８０ｍｇ·ｋｇ－１·ｄ－１×３,ｉｐ）及溶剂对照组（给予Ｆｅｎ组等体积的二甲亚砜,处理同Ｆｅｎ组）．应用不连续ＳＤＳ－ＰＡＧＥ电泳分离细胞色素Ｐ４５０,用ＣＯ差示光谱法和细胞色素Ｃ还原法测定Ｐ４５０含量及ＮＡＤＰＨ－细胞色素Ｐ４５０还原酶活性,用ＣＹＰ２Ｂ１／２Ｂ２抗体及ＣＹＰ３Ａ１／３Ａ２抗体进行Ｗｅｓｔｅｒｎ印迹法分析,用免疫组化和半定量ＲＴ－ＰＣＲ等技术观察Ｆｅｎ影响大鼠脑,肝组织细胞色素Ｐ４５０亚型的特异性．结果显示,与溶剂对照组相比Ｆｅｎ可使脑和肝中Ｐ４５０含量及ＮＡＤＰＨ－Ｐ４５０还原酶活性增高;Ｐ４５０２Ｂ１／２Ｂ２增加,Ｐ４５０３Ａ１／３Ａ２未见改变;Ｐ４５０２Ｂ１／２Ｂ２ｍＲＮＡ含量相应增加．由于正常大鼠脑,肝组织中Ｐ４５０２Ｂ１／２Ｂ２表达很低,Ｆｅｎ对该亚型Ｐ４５０的诱导可能会干扰机体对内,外源化合物的正常代谢,从而产生毒作用．     

胸腺因子D对复发性口疮的免疫调节作用

采用双育法将１０６例ＲＡＮ患者随机分为Ａ、Ｂ两组。分别用ＴＦＤ２ｍＬ（５ｍｇ）或核酷２ｍＬ,隔日１次,连续肌注６０ｄ。在治疗前后测定细胞免疫和体液免疫指标。结果与正常对照组比较ＲＡＵ患者外周血淋巴细胞数减少,ＥＲＦＣ、ＣＤ４＋、ＣＤ８＋值降低;ＩｇＧ、ＩｇＡ、ＩｇＭ、Ｃ３水平升高。ＴＦＤ可使淋巴细胞数、ＥＲＦＣ、ＡＲＦＣ、ＣＤ３＋、ＣＤ４＋、ＣＤ８＋值升高;ＩｇＧ、ＩｇＡ、ＩｇＭ、Ｃ３值复常。     

Inhibitory effects of α-methyl-4-(3-oxo-2H-1,2-benzoisoselenazol-2-yl)benzeneacetic acid on Cu~(2+) and Fe~(2+) induced oxidative modification of human low density lipoprotein

为观察α－甲基－４－（３－氧－２Ｈ－１，２－苯并异硒唑－２－基）苯乙酸（ＭＢＢＡ）对Ｃｕ２＋及Ｆｅ２＋氧化修饰低密度脂蛋白（ＬＤＬ）的保护作用及其作用机理，采用分光光度法测定ＬＤＬ中丙二醛（ＭＤＡ）和共轭双烯（ＣＤ）的产生量．ＭＢＢＡ（０．２－２μｍｏｌ·Ｌ－１）能以剂量依赖性抑制Ｃｕ２＋及Ｆｅ２＋诱导的ＭＤＡ和ＣＤ生成．２μｍｏｌ·Ｌ－１的ＭＢＢＡ对Ｃｕ２＋诱导ＬＤＬ产生ＭＤＡ和ＣＤ的抑制率分别为８９．７％和６０．３％．０．５ｍｍｏｌ·Ｌ－１ＧＳＨ对ＬＤＬ产生ＭＤＡ无影响，但能显著增强ＭＢＢＡ对ＭＤＡ生成的抑制作用．上述结果表明ＭＢＢＡ对ＬＤＬ氧化修饰的抑制作用可能依赖于其ＧＳＨ－Ｐｘ样活性的作用和（或）直接还原脂质氢过氧化物的作用．     

胸腺α1和干扰素α1b联合治疗慢性病毒性乙型,丙型肝炎

选取慢性病毒性乙型肝炎５０例及丙型肝炎２０例，应用胸腺α１和干扰素α１ｂ联合治疗６个月，治疗后其ＰＣＲ－ＨＢＶ－ＤＮＡ的阴转率为６８．０％，ＰＣＲ－ＨＣＶ－ＲＮＡ的阴转率为７０．０％，较对照组（干扰素α１ｂ）的ＰＣＲ－ＨＢＶ－ＤＮＡ阴转率４４０％及ＰＣＲ－ＨＣＶ－ＲＮＡ的阴转率３０．０％为高（Ｐ〈０．０５）。通过治疗前，后检测Ｔ细胞亚群，ｓＩＬ－２Ｒα及ＴＮＦα发现，治疗前ＣＤ８，ｓＩＬ－２Ｒα和     

氯通道阻断剂对α1—肾上腺素受体亚型引起的Ca^2＋内流的影响

目的探讨氯通道阻断剂在α１Ａ、α１Ｂ、α１Ｄ肾上腺素受体（ＡＲ）亚型触发的Ｃａ２＋内流中的作用。方法采用Ｆｕｒａ－２荧光探针双波长测定胞浆游离Ｃａ２＋浓度（［Ｃａ２＋］ｉ）。结果在３种亚型的细胞上,肾上腺素（Ａｄｒ）触发的Ｃａ２＋内流均不受ｎｉｆｅｄｉｐｉｎｅ影响; ＳＫ＆Ｆ９６３６５可部分抑制α１Ａ、α１Ｂ－ＡＲ介导的Ｃａ２＋内流,而对ａ１Ｄ－ＣＨＯ细胞无影响。在ＢＢ－ＣＨＯ细胞上,ｎｉｆｌｕｍｉｃ　ａｃｉｄ（ＮＦＡ）和ｆｕｒｏｓｅｍｉｄｅ呈浓度依赖性抑制Ｃａ２＋内流;当Ｃａ２＋内流被ＳＫ＆Ｆ９６３６５最大限度抑制后,ＮＦＡ和ｆｕｒｏｓｅｍｉｄｅ可进一步抑制Ｃｄ２＋内流。α１Ａ－ＡＲ介导的Ｃａ２＋内流可被ｆｕｒｏｓｅｍｉｄｅ抑制,抑制率达 １４％ １５％。 ＮＦＡ可抑制ａ１Ｄ－ＡＲ引起的Ｃａ２＋内流,抑制率为３９％±９％。结论氯通道参与α１Ａ、α１Ｂ及α１Ｄ－ＡＲ引起的经非电压依赖性Ｃａ２＋通道介导的Ｃａ２＋内流,其间存有异同。ＮＦＡ敏感Ｃａ２＋内流及ｆｕｒｏｓｅｍｉｄｅ敏感的Ｃａ２＋内流与ＳＫ＆Ｆ９６３６５敏感的Ｃａ２＋内流存在非同一性。     

~(19)F体内核磁共振技术观测5-氟尿嘧啶在小鼠肝脏中的代谢

应用１９Ｆ体内核磁共振技术（１９ＦＮＭＲ）直接观测了５－氟尿嘧啶（５－ＦＵ）在小鼠肝脏中的代谢产物和代谢动力学，昆明种（ＫＭ）小鼠和Ｃ５７小鼠ｉｖ５－ＦＵ２００ｍｇ·ｋｇ－１后，用１９Ｆ表面线圈测得５－ＦＵ在肝脏中依次代谢为α－氟－β－脲基丙酸（ＦＵＰＡ）和α－氟－β－丙氨酸（ＦＢＡＬ）．在荷Ｓ１８０瘤ＫＭ小鼠肝脏中还可检测到活化产物氟代核苷／核苷酸（ＦＮＵＣ）．５－ＦＵ在ＫＭ和Ｃ５７小鼠肝脏中清除较快，消除半衰期分别为１６．７±３．０和３６．６±２．４ｍｉｎ，其主要产物ＦＢＡＬ的最大生成ｒｍａｘ（相对强度比）分别为８４±１４和９２±１０．但在ＫＭ小鼠肝脏中由ＦＵＰＡ进一步降解为ＦＢＡＬ的速率明显快于Ｃ５７小鼠，ｔ１／２ｒ分别为３１±８和５７±１３ｍｉｎ．相应地，在Ｃ５７小鼠肝脏中ＦＵＰＡ能维持一定的水平并达到ｒｍａｘ２６．２±２．２．     

2，4，5－三氯苯胺体外代谢生成一氧化碳的途径与三卤苯胺的构效关系研究

实验证明，２，４，５－三氯苯胺（ＴＦＡ）与大鼠肝微粒体、ＮＡＤＰＨ和分子氧共存时可经历脱氟、对位羟化和氧化释放一氧化碳（ＣＯ）等代谢过程。与对照组（Ｃｏｎｔｒｏｌ）微粒体相比，苯巴比妥（ＰＢ）或地塞米松（ＤＥＸ）诱导的微粒体，使２，４，５－ＴＦＡ代谢降解为ＣＯ的速度分别提高３～８倍，脱氟速度提高１～４倍，对位羟化速度提高１．９～１．５倍，底物消失速度提高２～２．５倍。而２，４，６－ＴＦＡ，２，４，５－与２，４，６－三氯苯胺（ＴＣＡ）和１，２，４－三氟苯（ＴＦＢ）等经一般代谢几乎不产生ＣＯ，ＰＢ或ＤＥＸ诱导的微粒体使其转化为ＣＯ的能力也低至可忽略不计。同时，在Ｃｏｎｔｒｏｌ或ＰＢ微粒体中，２，４，５－ＴＦＡ的底物消失与脱氟两种速度比平均约为１：１，在ＤＥＸ微粒体中，两种速度比则为１：２，而２，４，６－ＴＦＡ在ＰＢ微粒体中的两种速度比为１：０．６。两个ＴＦＡ的对位羟化速度相对较慢，而两个ＴＣＡ几乎不能进行对位羟化。     

DNA-damaging effects of genotoxins in mixture: modulation of covalent binding to DNA.

Modulation of DNA adduct formation by pre-existing adducts was examined in synthetic oligonucleotides and genomic DNA (calf thymus); genotoxins studied were N-acetoxy-acetylaminofluorene (N-AcO-AAF), aminofluorene (AF), aflatoxin B1-8,9-epoxide (AFB1-8,9-epoxide), and dimethylsulfate (DMS). Oligodeoxynucleotides containing either guanine-C8-AAF (Gua-C8-AAF) or Gua-C8-AF adducts and a neighboring unadducted guanine (G) (target G), located 1, 2, or 4 nucleotides from the adduct, were reacted, as single- (ss) or double-stranded (ds) substrates, with dimethylsulfate (DMS) or AFB1-8,9-epoxide. A modified Maxam-Gilbert technique showed that the presence of the AAF adduct lowered the extent to which AFB1-8,9-epoxide, but not DMS, reacted with target G. Binding of AFB1-8,9-epoxide to the target G was attenuated (> or =5-fold) when the target was located immediately adjacent to an AAF, but not AF, adduct in ds-DNA. Reaction with AFB1-8,9-epoxide increased when the target G was located 2 or 4 nucleotides from the AAF adduct. Pretreatment of calf thymus DNA with AAF (0-1.8% nucleotides modified) reduced levels of Gua-N7-AFB1 adducts formed after subsequent treatment with AFB1-8,9-epoxide. Pretreatment of calf thymus DNA with AFB1 did not alter levels of adducts formed after subsequent treatment with N-AcO-AAF. The supposition that aflatoxin B1-binding to DNA may be altered by conformational changes in the helix, due to the presence of a pre-existing AAF adduct, is supported by the absence of an effect by AF and confirmation of local denaturation of the oligomer helix by use of chemical probes hydroxylamine and diethylpyrocarbonate. Nonetheless, the importance of changes in the nucleophilicity of neighboring nucleotides and local steric effects cannot be ruled out.     

Effects of intermittent exposure to aflatoxin B1 on DNA and RNA adduct formation in rat liver: dose-response and temporal patterns.

We studied the effects of intermittent exposure to aflatoxin B1 (AFB1) on hepatic DNA and RNA adduct formation. Fisher-344 male rats were fed 0.01, 0.04, 0.4, or 1.6 ppm of AFB1 intermittently for 8, 12, 16, and 20 weeks, alternating with 4 weeks of dosing and 4 weeks of rest. Other groups of rats were fed 1.6 ppm of AFB1 continuously for 4, 8, 12, and 16 weeks. Control rats received AFB1-free NIH-31 meal diet. AFB1-DNA and -RNA adducts were measured by HPLC with fluorescence detection. The data are presented as total DNA or RNA adducts. The DNA and RNA adduct levels increased or decreased depending on the cycles of dosing and rest. Rats removed from treatment 1 month after 1 or 2 dosing cycles (8 and 16 weeks of intermittent exposure) showed approximately a twofold decrease in DNA adduct levels and a two- to elevenfold decrease in RNA adduct levels compared with rats euthanized immediately after the last dosing cycle (12 and 20 weeks of intermittent exposure). Our data indicate that DNA and RNA adducts increased linearly, from 0.01 ppm to 1.6 ppm of AFB1 after 12 and 20 weeks of intermittent treatment. A linear dose response was also apparent for DNA but not for RNA adducts after 8 and 16 weeks of treatment. As biomarkers of exposure, AFB1-RNA adducts were three to nine times more sensitive than AFB1-DNA adducts but showed greater variability. These results suggest that binding of AFB1 to hepatic DNA is a linear function of the dose, regardless of the way this is administered. The dose-response relationship for RNA adducts depends on the length of the no-dosing cycles and on the turnover rate of RNA.     

Potential Application of Benzo(a)Pyrene-Associated Adducts (Globin or Lipid) as Blood Biomarkers for Target Organ Exposure and Human Risk Assessment

In order to investigate the potential application of blood biomarkers as surrogate indicators of carcinogen–adduct formation in target-specific tissues, temporal formation of benzo[a]pyrene (BaP)-associated DNA adducts, protein adducts, or lipid damage in target tissues such as lung, liver, and kidney was compared with globin adduct formation or plasma lipid damage in blood after continuous intraperitoneal (ip) injection of [³H]BaP into female ICR mice for 7 d. Following treatment with [³H]BaP, formation of [³H]BaP–DNA or –protein adducts in lung, liver, and kidney increased linearly, and persisted thereafter. This finding was similar to the observed effects on globin adduct formation and plasma lipid damage in blood. The lungs contained a higher level of DNA adducts than liver or kidneys during the treatment period. Further, the rate of cumulative adduct formation in lung was markedly greater than that in liver. Treatment with a single dose of [³H]BaP indicated that BaP–globin adduct formation and BaP–lipid damage in blood reached a peak 48 h after treatment. Overall, globin adduct formation and lipid damage in blood were significantly correlated with DNA adduct formation in the target tissues. These data suggest that peripheral blood biomarkers, such as BaP–globin adduct formation or BaP–lipid damage, may be useful for prediction of target tissue-specific DNA adduct formation, and for risk assessment after exposure.     

DNA adduct formation of 4-aminobiphenyl and heterocyclic aromatic amines in human hepatocytes

DNA adduct formation of the aromatic amine, 4-aminobiphenyl (4-ABP), a known human carcinogen present in tobacco smoke, and the heterocyclic aromatic amines (HAAs), 2-amino-9H-pyrido[2,3-b]indole (AαC), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), potential human carcinogens, which are also present in tobacco smoke or formed during the high-temperature cooking of meats, was investigated in freshly cultured human hepatocytes. The carcinogens (10 μM) were incubated with hepatocytes derived from eight different donors for time periods up to 24 h. The DNA adducts were quantified by liquid chromatography-electrospray ionization mass spectrometry with a linear quadrupole ion trap mass spectrometer. The principal DNA adducts formed for all of the carcinogens were N-(deoxyguanosin-8-yl) (dG-C8) adducts. The levels of adducts ranged from 3.4 to 140 adducts per 10(7) DNA bases. The highest level of adduct formation occurred with AαC, followed by 4-ABP, then by PhIP, MeIQx, and IQ. Human hepatocytes formed dG-C8-HAA-adducts at levels that were up to 100-fold greater than the amounts of adducts produced in rat hepatocytes. In contrast to HAA adducts, the levels of dG-C8-4-ABP adduct formation were similar in human and rat hepatocytes. These DNA binding data demonstrate that the rat, an animal model that is used for carcinogenesis bioassays, significantly underestimates the potential hepatic genotoxicity of HAAs in humans. The high level of DNA adducts formed by AαC, a carcinogen produced in tobacco smoke at levels that are up to 100-fold higher than the amounts of 4-ABP, is noteworthy. The possible causal role of AαC in tobacco-associated cancers warrants investigation.     

Synthesis, characterization, and 32P-postlabeling of N-(deoxyguanosin)-4-aminobiphenyl 3'-phosphate adducts

The (32)P-postlabeling assay is an extremely sensitive technique for detecting carcinogen-DNA adducts. However, for the assignment of DNA adduct structures and the accurate determination of DNA adduct levels by (32)P-postlabeling, authentic adduct standards are needed. For most (32)P-postlabeling applications, such verified synthetic standard compounds are required in the form of their deoxynucleoside 3'-phosphates because they represent substrates for the polynucleotide kinase for transfer of [(32)P]phosphate from [gamma-(32)P]ATP. Three N-(deoxyguanosin)-4-aminobiphenyl 3'-phosphate adducts were prepared and fully characterized by (1)H NMR and mass spectroscopy to serve as standards for the (32)P-postlabeling assay. Apart from the C8- and the N(2)-deoxyguanosine 3'-phosphate adducts of the mutagenic human bladder carcinogen 4-aminobiphenyl (dG3'p-C8-4-ABP and dG3'p-N(2)-4-ABP), the C8-deoxyguanosine 3'-phosphate adduct of the nonmutagenic 4'-tert-butyl-4-aminobiphenyl (dG3'p-C8-4'tBu-4-ABP) was included in the study. Both C8-deoxyguanosine 3'-phosphate adducts were prepared by the in situ formation of deoxyguanosine 3'-phosphate and its subsequent reaction with the appropriate electrophilic amination agent (N-acetoxy compound). The N(2)-deoxyguanosine 3'-phosphate adduct was obtained by a modification of a previously described procedure for the synthesis of N(2)-deoxyguanosine adducts of aromatic amines. The three adduct standards were added at different concentrations to calf thymus DNA, and adduct recoveries were determined by the (32)P-postlabeling assay under conditions routinely used in the standard methodology, enhancement by nuclease P1 digestion and enhancement by butanol extraction. The dG3'p-C8-4-ABP adduct was recovered irrespective of the concentration with approximately 30% in both the standard and the butanol extraction version of the assay. Both C8-deoxyguanosine 3'-phosphate adducts were sensitive to nuclease P1 digestion resulting in recoveries of only 1-3%. In contrast, the dG3'p-N(2)-4-ABP adduct was resistant to nuclease P1 digestion; however, recovery in all three versions was poor (1-2%) resulting in a detection limit of one adduct/10(6) nucleotides. These results demonstrate that the (32)P-postlabeling assay underestimates the level of DNA adducts formed by 4-ABP and indicates that there is a need to determine the recovery for each adduct to be analyzed by the (32)P-postlabeling technique.     

Synthesis, characterization, and comparative 32P-postlabeling efficiencies of 2,6-dimethylaniline-DNA adducts

2,6-Dimethylaniline (2,6-diMeA) is a ubiquitous environmental pollutant that is used in industry as a synthetic intermediate. It is also found in tobacco smoke and as a major metabolite of lidocaine. Although the potential carcinogenicity of 2,6-diMeA in humans is presently uncertain, this aromatic amine has been classified as a rodent carcinogen. In addition, it is known to form hemoglobin adducts in humans, which indicates a profile of metabolic activation similar to that of typical arylamine carcinogens. Like other aromatic amines, 2,6-diMeA has been shown to yield N-(deoxyguanosin-8-yl)-2,6-dimethylaniline (dG-C8-2,6-diMeA) as a major DNA adduct in vitro. In this study, we show that 2,6-diMeA yields an unusual pattern of DNA adducts. In addition to dG-C8-2,6-diMeA, we have isolated two new adducts, 4-(deoxyguanosin-N(2)-yl)-2,6-dimethylaniline (dG-N(2)-2,6-diMeA) and 4-(deoxyguanosin-O(6)-yl)-2,6-dimethylaniline (dG-O(6)-2,6-diMeA), from the reaction of N-acetoxy-2,6-dimethylaniline with deoxyguanosine. A similar reaction conducted with deoxyadenosine yielded 4-(deoxyadenosin-N(6)-yl)-2,6-dimethylaniline (dA-N(6)-2,6-diMeA). All four adducts were detected in DNA reacted with N-acetoxy-2,6-dimethylaniline, with the relative yields being 46% for dA-N(6)-2,6-diMeA, 22% for dG-N(2)-2,6-diMeA, 20% for dG-O(6)-2,6-diMeA, and 12% for dG-C8-2,6-diMeA. This product profile contrasts markedly with the usual pattern of adducts obtained with aromatic amines, where C8-substituted deoxyguanosine products typically predominate. We further analyzed the kinetics of the T(4) polynucleotide kinase (PNK)-catalyzed phosphorylation of the C8 and N(2) deoxyguanosine 3'-phosphate adducts from 2,6-diMeA. The kinetic parameters obtained with these two structurally different adducts are compared to those determined with the parent nucleotide (dG3'p), and with (+/-)-anti-10-(deoxyguanosin-N(2)-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene 3'-phosphate, the major adduct derived from the environmental pollutant benzo[a]pyrene. The results indicate that all the adducts were labeled with lower efficiencies than dG3'p, stressing the likely underestimation of adduct levels in typical 32P-postlabeling protocols. Nonetheless, the N(2) adducts derived from 2,6-diMeA and benzo[a]pyrene were both labeled with higher efficiencies than the C8 adduct derived from 2,6-diMeA, with the benzo[a]pyrene adduct being the best substrate for PNK. Thus, the data suggest that N(2) adducts from dG3'p are intrinsically better substrates than their C8 analogues for PNK, and that bulkier aromatic fragments may favor the enzyme-substrate interaction during the labeling step.     

The relationship between DNA adduct formation by benzo[a]pyrene and expression of its activation enzyme cytochrome P450 1A1 in rat

Benzo[a]pyrene (BaP) is a human carcinogen requiring metabolic activation prior to reaction with DNA. Cytochrome P450 (CYP) 1A1 is the most important hepatic and intestinal enzyme in both BaP activation and detoxification. CYP1A2 is also capable of oxidizing BaP, but to a lesser extent. The induction of CYP1A1/2 by BaP and/or β-naphthoflavone in liver and small intestine of rats was investigated. Both BaP and β-naphthoflavone induced CYP1A expression and increased enzyme activities in both organs. Moreover, the induction of CYP1A enzyme activities resulted in an increase in formation of BaP–DNA adducts detected by ³²P-postlabeling in rat liver and in the distal part of small intestine in vivo. The increases in CYP1A enzyme activity were also associated with bioactivation of BaP and elevated BaP–DNA adduct levels in ex vivo incubations of microsomes of both organs with DNA and BaP. These findings indicate a stimulating effect of both compounds on BaP-induced carcinogenesis.     

Role of phenoxyl radicals in DNA adduction by chlorophenol xenobiotics following peroxidase activation

Chlorophenol (CP) toxins are classified as probable human carcinogens and are known to undergo bioactivation to generate benzoquinone (BQ) electrophiles that react covalently with biopolymers. Recently, we characterized the ability of pentachlorophenol (PCP) to react covalently with deoxyguanosine (dG) following treatment with horseradish peroxidase (HRP)/H2O2 or myeloperoxidase to yield a C8-dG oxygen (O)-adduct that suggested the intermediacy of the pentachlorophenoxyl radical in covalent bond formation [Dai, J., Wright, M. W., and Manderville, R. A. (2003) Chem. Res. Toxicol. 16, 817-821]. Investigations currently focus on a wider range of CP substrates (PCP, 2,4,6-trichlorophenol (2,4,6-TCP), 2,4,5-TCP, and 2,4-dichlorophenol (2,4-DCP)) to establish their reactivity toward dG and duplex DNA (calf thymus (CT)) following activation by HRP/H2O2, as a representative peroxidase system. Our data show that chlorophenoxyl radicals may either react directly with dG and CT-DNA to form C8-dG O-adducts in an irreversible process or couple to yield 1,4-BQ electrophiles that react with dG to afford adducts of the benzetheno variety. These results are the first to establish the in vitro relevance of C8-dG O-adducts of phenolic toxins. The 1H NMR chemical shifts and reactivity of the benzetheno adducts favor 4' '-hydroxy-1,N2-benzetheno-dG adduct assignment, which is in contrast to other literature which has assigned the 1,4-BQ-dG adduct as 3' '-hydroxy-1,N2-benzetheno-dG. Overall, the results from this current study have provided new insights into peroxidase-mediated activation of CP substrates and have strengthened the hypothesis that direct reactions of phenoxyl radicals with DNA contribute to peroxidase-driven toxic effects of phenolic xenobiotics.     

Effect of caloric restriction on hepatic nuclear DNA damage in male Fischer 344 rats treated with aflatoxin B1.

Caloric restriction is known to reduce chemically-induced tumor incidence in laboratory animals. The effect is believed to be mediated in part by modification of hepatic drug metabolism, including both phase I and phase II enzymes. Using aflatoxin B1 (AFB1) as a model carcinogen, we studied the effect of caloric restriction on the modification of rat liver nuclear DNA by AFB1 and DNA damage due to the formation of apurinic sites from the AFB1-DNA adduct removal process. Caloric restriction reduced the metabolic activation of AFB1 which resulted in a decrease of AFB1-DNA binding by more than 50%. The results of the study of the effect of caloric restriction on the AFB1-induced DNA strand breakage assayed by the alkaline unwinding technique showed that caloric restriction protected the formation of apurinic sites from the AFB1-DNA adducts and reduced the double strand DNA breakages by 1.3-2.5-fold. Thus, the lower initial AFB1-DNA binding and less DNA damage, presumably by the less apurinic sites formed during the depurination process of AFB1-DNA adducts, contributed to the protective effect of caloric restriction.     

Low hepatic glutathione S-transferase and increased hepatic DNA adduction contribute to increased tumorigenicity of aflatoxin B1 in newborn and partially hepatectomized mice

Low levels of hepatic glutathione S-transferase and increased formation of aflatoxin B1 (AFB1)-DNA adducts correlate with hepatocyte proliferation and increased hepatocarcinogenesis in both newborn mice and partially hepatectomized adult mice, as compared to normal, adult C57BL/6J mice. Newborn mice, which are highly susceptible to the hepatocarcinogenic effects of AFB1, have active proliferation of hepatocytes until 3 weeks of age, when hepatocyte proliferation abruptly ceases. At about this time, the mice become highly resistant to AFB1. In adult mice, AFB1 carcinogenicity is increased after stimulation of liver proliferation by partial hepatectomy. To become carcinogenic, AFB1 is activated in the liver by the P450 enzyme system to electrophilic intermediates, some of which form DNA adducts believed to be responsible for mutations leading to cancer. The most carcinogenic intermediate, AFB(1)-8,9-epoxide, is detoxified by glutathione S-transferase-mediated conjugation to glutathione. Glutathione levels, glutathione S-transferase levels, and AFB1-DNA adduct formation were measured at 4, 10, 30, 120, 245 and 365 days of age in C57BL/6J mice. There was a 5-fold increase in hepatic glutathione S-transferase levels and 13-fold decrease in hepatic AFB1-DNA adduct formation over these ages. Induction of hepatocyte proliferation following partial hepatectomy of 120-day-old mice lowered hepatic glutathione S-transferase levels and increased the extent of hepatic AFB1-DNA formation to levels similar to those measured in 4-day-old mice. These results indicate that increased susceptibility to AFB1 hepatocarcinogenesis in newborn mice, and in adult mice following partial hepatectomy, is due to decreased GST and increased adduct formation in proliferating liver.