Gupta R C, Earley K, Becker F F
Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030.
Cancer Res. 1988 Sep 15;48(18):5270-4.
Exposure of rats to a standard four-cycle feeding regimen of 0.06% 2-acetylaminofluorene (AAF) results in the formation of putatively premalignant hepatic nodules, but the types and magnitude of DNA adducts formed in these nodules has not been previously examined. By using a sensitive 32P-adduct assay (R. C. Gupta, Cancer Res., 45: 5656-5662, 1985), we analyzed the DNA adduct lesions in individual hepatic nodules at various times during and after exposure to AAF. Kidney, spleen, and testis were included as nontarget tissues. No qualitative difference was observed in the DNA adducts found in hepatic nodules and nontarget tissues; however, quantitative differences occurred. At least one unknown and two known (dG-C8-AF and dG-N2-AAF) DNA adducts were detected, with dG-C8-AF being predominantly (96-98%) formed, in all tissues examined. At the end of the first three weeks of AAF feeding, the concentration of the deacetylated adduct dG-C8-AF in liver (223 fmol/micrograms DNA) was found to be about 2, 6, and 5 times higher than in kidney, spleen, and testis, respectively. The concentration of the N2-acetylated adduct in liver (4.5 fmol/micrograms DNA) was 4-fold higher than in kidney and strikingly higher (51- and 42-fold, respectively) than in spleen and testis. At the end of the fourth feeding cycle, total DNA adducts measured in the hepatic nodules ranged from 30-100 fmol/micrograms DNA, while the "surrounding liver," kidney, spleen, and testis showed 235, 218, 62, and 28 fmol adducts/micrograms DNA, respectively. Sixty days following the cessation of AAF, the binding in both the persistent nodules and liver had decreased to 7% of their respective levels measured at the end of the fourth cycle, while adducts in kidney, spleen, and testis were 32%, 18% and 19%. After 88 days, the binding levels in the nontarget tissues declined further, but no additional adduct removal occurred in the nodules. Our data indicate that (a) although the metabolic apparatus for activation of AAF is diminished in the hepatic nodules, a significant level of adduct formation occurs in the cells of this putative, premalignant lesion, and (b) unlike in the nontarget tissues, repair processes in the premalignant nodules may not be operative several weeks after the cessation of AAF exposure.
将大鼠暴露于含0.06% 2-乙酰氨基芴（AAF）的标准四周期喂养方案下会导致形成推定的癌前肝结节，但此前尚未检测这些结节中形成的DNA加合物的类型和数量。通过使用灵敏的32P加合物检测法（R.C.古普塔，《癌症研究》，45: 5656 - 5662，1985），我们分析了在暴露于AAF期间及之后不同时间点各个肝结节中的DNA加合物损伤情况。将肾、脾和睾丸作为非靶组织纳入研究。在肝结节和非靶组织中发现的DNA加合物在定性上没有差异；然而，存在定量差异。在所有检测的组织中均检测到至少一种未知的以及两种已知的（dG-C8-AF和dG-N2-AAF）DNA加合物形成，其中dG-C8-AF占主导（96 - 98%）。在AAF喂养的前三周结束时，发现肝脏中去乙酰化加合物dG-C8-AF的浓度（223 fmol/μg DNA）分别比肾、脾和睾丸中的浓度高约2倍、6倍和5倍。肝脏中N2-乙酰化加合物的浓度（4.5 fmol/μg DNA）比肾中的浓度高4倍，比脾和睾丸中的浓度显著更高（分别高51倍和42倍）。在第四个喂养周期结束时，肝结节中测得的总DNA加合物范围为30 - 100 fmol/μg DNA，而“周围肝脏”、肾、脾和睾丸中分别显示235、218、62和28 fmol加合物/μg DNA。停止给予AAF 60天后，持续存在的结节和肝脏中的结合量已降至第四个周期结束时各自测量水平的7%，而肾、脾和睾丸中的加合物分别为32%、18%和19%。88天后，非靶组织中的结合水平进一步下降，但结节中没有发生额外的加合物清除。我们的数据表明：（a）尽管肝结节中AAF活化的代谢机制有所减弱，但在这个推定的癌前病变的细胞中仍发生了显著水平的加合物形成；（b）与非靶组织不同，在停止AAF暴露数周后，癌前结节中的修复过程可能不起作用。
