限量饮食对黄曲霉素B1—DNA加成物生成的影响

本实验用黄曲霉霉素Ｂ１（ＡＦＢ１）作为致癌物代表，研究限量饮食（ＦＲ）对雄性Ｆ３４４大鼠和Ｂ６Ｃ３Ｆ１小鼠代谢活化ＡＦＢ１的影响。ＡＦＢ１－ＤＮＡ加合物（ＡＤＡ）作为ＡＦＢ１代谢活化的生物指标。结果显示ＦＲ降低大鼠和小鼠对ＡＦＢ１的代谢活化，ＡＤＡ的生成在大鼠和小鼠中分别减少４３％和３１％。ＡＤＡ的两种主要加合物的生成、分布和清除以及它们与ＡＦＢ１致癌作用的关系也作了讨论。     

尿液中黄曲霉毒素—DNA加合物与肝癌关系的前瞻性研究

应用单克隆抗体系和层析柱结合高效液相色谱法测定了５０例肝瘤及２６７名对照尿液中ＡＦＢ１及其代谢物，ＡＦＰ１、ＡＦＭ１及ＡＦ－Ｎ７－乌嘌呤加合物，同时用ＲＩＡ试剂检测其血清中ＨＢｓＡｇ．肝癌病例尿液中含一种或一种以上ＡＦ标志物的检测率显著高于对照，ＲＲ＝４．０．肝癌病例尿液中ＡＦ－Ｎ７－乌嘌呤加成物的检出率也显著高于对照，ＲＲ＝７．６．尿液中如只检出ＡＦＭ１、ＡＦＰ１或ＡＦＢ１，不同时伴有ＡＦ－Ｎ７－乌嘌呤加合物。其发生肝癌的相对危险度比同时伴有ＡＦ－Ｎ７－乌嘌呤加合物者低得多。而且在调整ＨＢｓＡｇ及吸烟等混杂因素后，尿液中ＡＦＰ１或ＡＦＢ１阳性与肝癌的关系无统计学上显著性联系。过表明尿液中ＡＦ标志物，尤其是ＡＦ－Ｎ７－乌嘌呤加合物与肝癌的发生有较强联系并在个体水平上提供了ＡＦ暴露与ＨＢＶ感染对肝癌发生有明显协同作用的证据。在上海，花生及酱油是饮食中ＡＦＢ１的最主要来源，队列对象摄入ＡＦＢ１总量的８０％以上均来自这二种食品。     

大、小鼠摄入AFB_1和羧乙基锗倍半氧化物体内超氧化物歧化酶变化研究

本实验通过观察摄入ＡＦＢ１及Ｇｅ－１３２后Ｗｉｓｔａｒ大鼠和昆明小鼠体内ＳＯＤ活力的变化，进一步了解ＡＦＢ１代谢途径和Ｇｅ－１３２与自由基的关系。实验表明，摄入ＡＦＢ１的ＳＯＤ活力受到抑制，而摄入Ｇｅ－１３２后ＳＯＤ活力得到提高，且一次性摄入ＡＦＢ１后ＳＯＤ活力最终得到恢复，其中大鼠对ＡＦＢ１敏感性相对较大。     

人B7—1（CD80）转染的PA317细胞对小鼠H22肝癌抑制作用的初步探讨

人Ｂ７－１（ＣＤ８０）转染的ＰＡ３１７细胞对小鼠Ｈ２２肝癌抑制作用的初步探讨黄晋生１杨金亮１严明山２连慕兰２张海荣１郭启煜１周正谋１房殿春关键词ＰＡ３１７Ｂ７－１（ＣＤ８０）Ｈ２２肝癌小鼠中图号Ｒ７３－３５Ｂ７是Ｂ细胞上的活化抗原，导入Ｂ７基因的肿瘤...     

骨髓增生异常综合征诊断与分期的探讨：附116例临床分析

报告ＭＤＳ１６６例，其中ＲＡ１２２例（７３．５％），ＲＡＳ５例（３％），ＲＡＥＢ２５例（１５％），ＣＭＭＬ１例（０．６％），ＲＡＥＢ－Ｔ１３例（７．９％）。并对其诊断标准，分期和治疗等进行了讨论。Ｂｅｎｎｅｔｔ改良的ＦＡＢ诊断与分型标准已被广泛应用，本文虽按此标准进行统计，但本文认为：①ＦＡＢ的５个亚型不是独立的，而是同一疾病病程发展的不同阶段；②ＣＭＭＬ实际为白血病，不宜划入ＭＤＳ范畴；③ＲＡＳ     

骨髓增生异常综合征亚型分型标准的商榷

就１９８９￣１９９１年３１例诊断ＭＤＳ病例，按ＦＡＢ分型标准（即原粒Ｉ型＋Ⅱ型）及改良标准（原始粒＋早幼粒）分别进行亚型分型研究。结果，按ＦＡＢ分型ＲＡ型２２例，ＲＡＥＢ型８例，ＲＡＥＢ－Ｔ１例。按改良标准分型，则ＲＡ６例，ＲＡＥＢ１７例，ＲＡＥＢ－Ｔ６例，白血病２例。即按ＦＡＢ分型，ＲＡ型比例高，占７１％。按改良标准则ＲＡ型仅占１９％。前者２９％符合ＲＡＥＢ、ＲＡＥＢ－Ｔ，而按改良标准则８１％符     

C－erbB－2，人表皮生长因子及其受体在大肠癌中表达的意义

用ＡＢＣ免疫组化法测定２００例大肠癌组织中Ｃ－ｅｒｂＢ－２，人表皮生长因子（ｈＥＧＦ）及其受体（ＥＧＦＲ）。结果发现：１）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ，ＥＧＦＲ在２００例大肠癌中阳性表达分别为３６％、４４％、４７％，三者共同阳性为１６．５％。２）ｈＥＧＦ，ＥＧＦＲ在大肠癌ＤｕｋｅｓＣ、Ｄ期，肿瘤＞２ｃｍ、低分化腺癌，有深度浸润和淋巴结转移者阳性率显著高于其它各型（Ｐ＜０．０１）。３）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ和ＥＧＦＲ阳性病例存活率明显低于这些阴性病例（Ｐ＜０．０１）。结果表明，Ｃ－ｅｒｂＢ－２，ｈＥＧＦ和ＥＧＦＲ在大肠癌的侵袭性生长中起重要作用，ｈＥＧＦ和ＥＧＦＲ可作为大肠癌患者高度恶性的生物学指标。     

肝细胞癌p53基因特异点突变的分子流行病学意义

目的研究肝细胞癌（ＨＣＣ）ｐ５３基因突变热点的特异性及其分子流行病学意义。方法取广西高、中、低流行区ＨＣＣ样品，进行ＤＮＡ测序，并用限制性片段长度多态性（ＲＦＬＰ）分析。结果ＤＮＡ测序结果为２４９密码子第３碱基Ｇ→Ｔ颠换占５７％（２０／３５）。ＲＦＬＰ分析表明ＨａｅⅢ酶切点丢失占６９％（３６／５２），与低发区的１０％（１／１０）和２０％（２／１０）比较，差异有显著意义（Ｐ＜０．０１）。结论广西ＨＣＣ高发主要原因为黄曲霉毒素（ＡＦＢ１）高污染。ｐ５３基因突变集中于２４９第３碱基Ｇ→Ｔ颠换。这个由ＡＦＢ１介导的特异位点、固定形式（Ｇ→Ｔ）和高频率的ｐ５３突变，应称为“ＡＦＢ１突变点”，具有分子流行病学意义，可用于确定流行区不同个体ＨＣＣ由ＡＦＢ１介导和某些地区受ＡＦＢ１污染的情况。用ＲＦＬＰ替代ＤＮＡ测序可获同样效果。     

单剂量黄曲霉毒素B1致大鼠肝癌作用的短期实验模型

本文报告单剂量黄曲霉毒素Ｂ１（ＡＦＢ１）致大鼠肝癌作用短期实验模型的研究。６周龄、雄性Ｗｉｓｔａｒ大鼠，经腹腔一次性注射不同剂量（０、０．５０、０．７５、１．００和１．５０ｍｇ／ｋｇ体重）的ＡＦＢ１，作为启动剂，两周后，饲以含０．０１５％的２－乙酰氨基芴（２－ＡＡＦ）饲料４周，实验第三周末，施行肝大部分切除术（ＰＨ）。所有动物于实验第６周处死，取肝组织作Ｇａｍｍａ－谷氨酰转肽酶（ＧＧＴ）化学染色，     

骨髓增生异常综合征亚型分型标准的商榷

就１９８９～１９９１年３１例诊断ＭＤＳ病例，按ＦＡＢ分型标准（即原粒Ⅰ型＋Ⅱ型）及改良标准（原始粒＋早幼粒）分别进行亚型分型研究。结果，按ＦＡＢ分型ＲＡ型２２例，ＲＡＥＢ型８例，ＲＡＥＢ－Ｔ１例。按改良标准分型，则ＲＡ６例，ＲＡＥＢ１７例，ＲＡＥＢ－Ｔ６例，白血病２例。即按ＦＡＢ分型，ＲＡ型比例高，占７１％。按改良标准则ＲＡ型仅占１９％，前者２９％符合ＲＡＥＢ、ＲＡＥＢ－Ｔ，而按改良标准则８１％符合ＲＡＥＢ、ＲＡＥＢ－Ｔ，甚至白血病的诊断，二者相差均非常显著，亚型分型直接影响治疗，因此作者主张以ＦＡＢ分型标准来进行亚型分型为宜。     

Effect of sex difference on the in vitro and in vivo metabolism of aflatoxin B1 by the rat.

Hepatic microsome-catalyzed metabolism of aflatoxin B1 (AFB1) to aflatoxin M1 and aflatoxin Q1 and the "metabolic activation" of AFB1 to DNA-alylating metabolite(s) were studied in normal male and female Sprague-Dawley rats, in gonadectomized animals, and in castrated males and normal females treated with testosterone. Microsomes from male animals formed 2 to 5 times more aflatoxin M1, aflatoxin Q1, and DNA-alkylating metabolite(s) than those from females. Castration reduced the metabolism of AFB1 by the microsomes from males by about 50%, whereas ovariectomy had no significant effect on AFB1 metabolism by the microsomes from females. Testosterone treatment (4 mg/rat, 3 times/week for about 6 weeks) of castrated immature males and immature females enhanced the metabolism of AFB1 by their microsomes. A sex difference in the metabolism of AFB1 by liver microsomes was also seen in other strains of rats tested: Wistar, Long-Evans, and Fischer. The activity of kidney microsomes for metabolic activation was 1 to 4% that of the liver activity and was generally lower in microsomes from male rats as compared to those from female rats of Sprague-Dawley, Wistar, and Long-Evans strains. The in vitro results obtained with hepatic microsomes correlated well with the in vivo metabolism of AFB1, in that more AFB1 became bound in vivo to hepatic DNA isolated from male rats and from a female rat treated with testosterone than that isolated from control female rats. These data suggest that the differences in hepatic AFB1 metabolism may be the underlying cause of the sex difference in toxicity and carcinogenicity of AFB1 observed in rats.     

Grapefruit juice intake does not enhance but rather protects against aflatoxin B1-induced liver DNA damage through a reduction in hepatic CYP3A activity

Influence of grapefruit juice intake on aflatoxin B1 (AFB1)-induced liver DNA damage was examined using a Comet assay in F344 rats given 5 mg/kg AFB1 by gavage. Rats allowed free access to grapefruit juice for 5 days prior to AFB1 administration resulted in clearly reduced DNA damage in liver, to 65% of the level in rats that did not receive grapefruit juice. Furthermore, rats treated with grapefruit juice extract (100 mg/kg per os) for 5 days prior to AFB1 treatment also reduced the DNA damage to 74% of the level in rats that did not receive grapefruit juice. No significant differences in the portal blood and liver concentrations of AFB1 were observed between grapefruit juice intake rats and the controls. In an Ames assay with AFB1 using Salmonella typhimurium TA98, lower numbers of revertant colonies were detected with hepatic microsomes prepared from rats administered grapefruit juice, compared with those from control rats. Microsomal testosterone 6beta-hydroxylation was also lower with rats given grapefruit juice than with control rats. Immunoblot analyses showed a significant decrease in hepatic CYP3A content, but not CYP1A and CYP2C content, in microsomes of grapefruit juice-treated rats than in non-treated rats. No significant difference in hepatic glutathione S-transferase (GST) activity and glutathione content was observed in the two groups. GSTA5 protein was not detected in hepatic cytosol of the two groups. In microsomal systems, grapefruit juice extract inhibited AFB1-induced mutagenesis in the presence of a microsomal activation system from livers of humans as well as rats. These results suggest that grapefruit juice intake suppresses AFB1-induced liver DNA damage through inactivation of the metabolic activation potency for AFB1 in rat liver.     

Effect of dietary protein level on aflatoxin B1 actions in the liver of weanling rats.

The hepatocarcinogenic responses of rats to aflatoxin B1 (AFB1) are believed to depend on microsomal activation of the toxin, followed by macromolecular binding. Dietary protein insufficiency is reported to reduce the level of microsomal metabolism, and therefore would be expected to reduce the AFB1-induced carcinogenicity. Indeed, diminished hepatocarcinogenicity in low-protein diet fed weanling rats that had received AFB1 has been reported. In the present study, carcinogenicity and other toxic effects of AFB1 (0.5 p.p.m.) fed to weanling male Fischer F344 rats on a low-protein diet (5%) or normal-protein (20%) diet for up to 8 weeks were examined. In our study, in contrast with the previous report, all animals that had survived some initial toxicity were found to have developed hepatic tumors or hyperplastic gamma-glutamyltransferase-positive foci a year later. The low-protein diet also produced sub-acute toxicity after AFB1 exposure in the weanling rats, leading to severe histological changes, and the death of about half the animals after 3-4 weeks of exposure. Animals fed an AFB1-containing normal-protein diet also exhibited AFB1-induced hepatocarcinogenicity, but not the sub-acute toxicity. The levels of hepatic enzymes involved in AFB1 metabolism were examined in animals fed the low- or normal-protein diets in the absence of AFB1. The low-protein diet, fed to 3 week weanlings for the subsequent 5 weeks, decreased hepatic cytochrome P450 levels, as well as the in vitro capacity of microsomal fractions to form AFB1-8,9-dihydrodiol, an index of AFB1-8,9-epoxide formation. Rats on a normal-protein diet did not show these changes. This discrepancy between the observed increase in sub-acute toxicity and decrease in microsomal activities in the low-protein fed animals implies that the toxic effects observed in these rats were not directly related to metabolic activation of the toxin. In contrast to the diminished microsomal in vitro AFB1 activation, however, in vivo AFB1-DNA adduct formation ability in rats receiving the low-protein diet in the absence of AFB1 was found to become elevated more rapidly during the 5 week experimental feeding period, compared with animals receiving the normal-protein diet. This was accompanied by a more rapid fall in the levels of AFB1-glutathione S-transferase isozyme activity in the low-protein fed animals. The results of this study on weanling rats support the importance of AFB1-GSH in protecting against the carcinogenic responses to AFB1, and probably also the sub-acute toxicity of the latter.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lack of influence of butylated hydroxytoluene on modification of lung microsome mediated aflatoxin B1-DNA binding: role of pulmonary glutathione S-transferase

Phenolic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are known to inhibit tumor formation due to several chemical carcinogens including aflatoxin B1 (AFB1). Metabolic activation of AFB1 by lung microsomes and possible modification by dietary BHA was reported in an earlier communication (Allameh et al. (1988) Cancer Lett., 40, 49). Here we report the effect of dietary BHA at a high dose (0.75% for 15 days) and a low dose (0.06% for 180 days) on the activation and inactivation of AFB1 by subcellular preparations of lung. BHT at high dose alone induced hepatic cytosolic glutathione (GSH) S-transferases activity while the pulmonary enzyme was unaffected by BHT feeding. This observation was substantiated when the addition of lung cytosol from control and BHT-treated rats showed similar inhibition (50%) in the microsome mediated AFB1-DNA binding. Thus BHT appears to have little influence on the pulmonary metabolism of AFB1.     

Efficient activation of aflatoxin B1 by cytochrome P450 2A13, an enzyme predominantly expressed in human respiratory tract

The worldwide human exposure to aflatoxin B1 (AFB1), particularly in developing countries, remains to be a serious public health concern. Although AFB1 is best known as a hepatocarcinogen, epidemiological studies have shown a positive association between human lung cancer occurrence and inhalation exposure to AFB1. Cytochrome P450 (CYP)-catalyzed metabolic activation is required for AFB1 to exert its carcinogenicity. Previous studies have identified CYP1A2 and CYP3A4 as the major enzymes for AFB1 activation in human liver. However, the key CYP enzymes in human lung that can efficiently activate AFB1 in situ are unknown. In the present study, we demonstrate that CYP2A13, an enzyme predominantly expressed in human respiratory tract, has a significant activity in metabolizing AFB1 to its carcinogenic/toxic AFB1-8,9-epoxide and AFM1-8,9-epoxide at both low (15 microM) and high (150 microM) substrate concentrations. Under the same conditions, there was no detectable AFB1 epoxide formation by CYP2A6, which was also reported to be involved in the metabolic activation of AFB1. Consistent with the activity data, there was an approximately 800-fold difference in LC50 values of AFB1 (48-hr treatment) between Chinese hamster ovary (CHO) cells expressing CYP2A13 and CYP2A6 (50 nM versus 39 microM). We further demonstrate that amino acid residues Ala117 and His372 in CYP2A13 protein are important for AFB1 epoxidation and its related cytotoxicity. Our results suggest that CYP2A13-catalyzed metabolic activation in situ may play a critical role in human lung carcinogenesis related to inhalation exposure to AFB1.     

Liver DNA adducts in methyl-deficient rats administered a single dose of aflatoxin B1.

Using an 8 week Solt-Farber protocol with selection pressure (2-acetylaminofluorene/partial hepatectomy) applied during weeks 6 and 7, we have observed that a single oral administration of aflatoxin B1 (AFB1) to Fischer 344 rats on day 1 of the study, followed by a 3 week feeding regimen of either a methyl-deficient (CMD) or a basal (CMS) diet, results in a relative increase in hepatic preneoplastic lesions in CMD diet fed rats. It has previously been shown that a multiple dosing regimen with AFB1, started after 3 weeks of CMD diet, enhances tumor incidence. In the present study, the role of metabolic activation in the induction of preneoplastic lesions, and liver DNA adduct levels after the first dose of AFB1 in the tumorigenesis model have been investigated. AFB1-DNA adducts were determined at 2-168 h following a single non-necrogenic (100 micrograms/kg body wt) or necrogenic (600 micrograms/kg body wt) dose of AFB1 on day 1 or day 21 of a 3 week treatment with a complete basal or CMD diet. In all rats irrespective of dose, dietary treatment or time of AFB1 dosing, the patterns of adduct formation and repair did not change. In rats receiving AFB1 on day 1, total DNA adduct levels between the diet or dose groups were not significantly different, and quantitatively did not correlate with the observed increase in preneoplastic lesions, suggesting a contribution by additional factors in the initiation of these lesions. Administration of AFB1 on day 21, however, resulted in significantly reduced levels of total adducts at both dose levels in CMD diet fed rats compared to controls. Serum biochemistry data suggest that a prolonged exposure to CMD diet may cause pathological and/or biochemical alterations in hepatocytes with a resultant decrease in metabolic activation of AFB1, thus making it difficult to evaluate whether DNA damage is directly related to tumorigenesis.     

Effect of (+)-catechin, dimethyl sulfoxide and ethanol on the microsome-mediated metabolism of two hepatocarcinogens, N-nitrosodimethylamine and aflatoxin B1

Effects of catechin, a plant phenolic flavonoid, and of the commonly used organic solvents dimethyl sulfoxide (DMSO) and ethanol (EtOH) on the microsome-mediated metabolism of two hepatocarcinogens, N-nitrosodimethylamine (NDMA) and aflatoxin B1 (AFB1), are presented. Using hamster liver microsomes as a source of mixed-function oxidases, it was shown that catechin at 0.1-0.2 mM levels had no effect on the oxidation of either carcinogen. However, at 1-5 mM levels it caused a concentration-dependent inhibition (38-70%) of the formation of formaldehyde from NDMA, and at the 5 mM level it caused a 40% inhibition of AFB1-DNA binding. DMSO and EtOH totally inhibited NDMA demethylase activity but had little effect on the binding of AFB1 to DNA. These observations indicate that the mixed-function oxidases (cytochrome P450) essential for the metabolic activation of these carcinogens exhibit different sensitivities to different inhibitors.     

Comparative action of aflatoxin B1 in mammalian airway epithelium

Aflatoxin B1 (AFB1) is thought to be an occupational risk factor for airway carcinogenesis where exposure to AFB1-laden grain dusts is common. Since activation of AFB1 is catalyzed by cytochromes P-450 associated with the smooth endoplasmic reticulum, we compared the response to AFB1 in cultured tracheal epithelium from species with abundant (rabbit and hamster) and scarce (rat and monkey) distributions of smooth endoplasmic reticulum in nonciliated tracheal epithelial cells. Explants from each species, incubated in medium containing 0.5 microM [14C]-AFB1 for selected intervals up to 24 h, were compared on the basis of binding of [14C]-AFB1 to tracheal DNA, amount and type of AFB1 metabolites in the medium, ultrastructurally determined population densities of epithelial cells, and distribution of bound material in epithelium as determined by autoradiographic grain densities. Cultures derived from rabbits were most active in metabolic conversion and formation of AFB1-DNA adducts, followed by those from hamsters, rats, and monkeys. Rabbit tracheal epithelium formed a significantly greater proportion of glutathione conjugates, while that from hamster formed a greater amount of AFB1-dihydrodiol, compared to rats and monkeys. The monkey formed significantly greater proportions of aflatoxin Q1 and the rabbit more aflatoxicol, compared to other species. There was selective degeneration and accumulation of labeled material in nonciliated cells in both rabbits and hamsters but not in rats or monkeys. Explants from rabbit tracheas were much more susceptible to cytotoxic injury and had higher autoradiographic grain densities than explants from hamsters. We conclude that the presence of smooth endoplasmic reticulum-containing nonciliated epithelial cells is qualitatively associated with the activation and toxicity of AFB1.     

Effect of allixin, a phytoalexin produced by garlic, on mutagenesis, DNA-binding and metabolism of aflatoxin B1

Allixin, a phytoalexin isolated from garlic, was examined for its effects on aflatoxin B1(AFB1)-induced mutagenesis using Salmonella typhimurium TA100 as the bacterial tester strain and rat liver S9 fraction as the metabolic activation system. The effects of allixin on the binding of [3H]AFB1 to calf thymus DNA and on the formation of metabolites of [3H]AFB1 were also determined. Allixin showed a dose-related inhibition of Histidine+ revertants induced by AFB1. Allixin at 75 micrograms/ml inhibited [3H]AFB1 binding to calf thymus DNA and reduced formation of AFB1-DNA adducts. In addition, allixin exhibited a concentration-dependent inhibition of the formation of organosoluble metabolites and the glutathione conjugates of [3H]AFB1. The data indicate that the effect of allixin on AFB1-induced mutagenesis and binding of metabolites to DNA may be mediated through an inhibition of microsomal P-450 enzymes. Allixin may thus be useful in the chemoprevention of cancer.