Staretz M E, Foiles P G, Miglietta L M, Hecht S S
American Health Foundation, Valhalla, New York 10595, USA.
Cancer Res. 1997 Jan 15;57(2):259-66.
The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), selectively induces lung tumors in F344 rats. NNK is metabolically activated to intermediates that methylate and pyridyloxobutylate DNA. To explore the importance of pyridyloxobutyl DNA adducts in NNK-induced rat lung tumorigenesis, the first study in this report examined levels of these adducts in whole lung and pulmonary cells of F344 rats treated with different doses of NNK (0.3, 1.0, 10.0, and 50 mg/kg; 3 x weekly for 2 weeks). Pyridyloxobutyl DNA adducts were highest in Clara cells compared to alveolar Type II cells, alveolar macrophages, and small cells, suggesting that enzymes involved in the formation of the pyridyloxobutylating species are concentrated in Clara cells. When we compared lung tumor incidence at the different doses of NNK (S. A. Belinsky et al., Cancer Res., 50: 3772-3780, 1990) versus pyridyloxobutyl DNA adducts in Type II cells, we observed a significant correlation. Because NNK-induced lung tumors arise from the Type II cells, this suggests an important role for pyridyloxobutyl DNA adducts. In the second study presented in this report, we examined the effect of dietary phenethyl isothiocyanate (PEITC), an inhibitor of lung tumor induction in F344 rats by NNK, on O6-methyldeoxyguanosine (O6-mG) and pyridyloxobutyl DNA adducts in whole lung and lung cells of F344 rats treated with NNK. F344 rats were fed control or PEITC-containing diets (3 micromol/g diet) before and throughout NNK treatment (1.76 mg/kg, three times weekly for 4, 8, 12, 16, or 20 weeks). PEITC inhibited formation of pyridyloxobutyl DNA adducts in whole lung and all lung cells except macrophages. There was also inhibition of O6-mG, but it varied with cell type and length of NNK treatment. Overall, PEITC treatment decreased pyridyloxobutyl DNA adducts by 57% in Clara cells, 51% in Type II cells, 40% in small cells, and 44% in whole lung. PEITC treatment decreased O6-mG levels by 52% in Clara cells, 19% in Type II cells and small cells, and 36% in whole lung. These results support the hypothesis that PEITC inhibition of NNK-induced lung tumors is a result of decreased metabolic activation and DNA binding of NNK. The 50% reduction of pyridyloxobutyl DNA adducts in Type II cells agreed well with the 50% reduction of NNK-induced lung tumors by PEITC. Because NNK-induced tumors arise from Type II cells, these results suggest an important role for pyridyloxobutyl DNA adducts in NNK-induced rat lung tumorigenesis.
烟草特异性亚硝胺4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁酮(NNK)可选择性地诱导F344大鼠发生肺肿瘤。NNK经代谢活化生成可使DNA甲基化和吡啶氧丁酰化的中间体。为探究吡啶氧丁酰化DNA加合物在NNK诱导的大鼠肺肿瘤发生中的重要性，本报告中的第一项研究检测了不同剂量NNK(0.3、1.0、10.0和50mg/kg；每周3次，共2周)处理的F344大鼠全肺和肺细胞中这些加合物的水平。与Ⅱ型肺泡细胞、肺泡巨噬细胞和小细胞相比，克拉拉细胞中的吡啶氧丁酰化DNA加合物水平最高，这表明参与形成吡啶氧丁酰化物质的酶集中在克拉拉细胞中。当我们比较不同剂量NNK( S. A. 贝林斯基等人，《癌症研究》，50: 3772 - 3780, 1990)处理组的肺肿瘤发生率与Ⅱ型细胞中吡啶氧丁酰化DNA加合物水平时，发现二者存在显著相关性。由于NNK诱导产生的肺肿瘤源自Ⅱ型细胞，这表明吡啶氧丁酰化DNA加合物具有重要作用。在本报告中的第二项研究中，我们检测了饮食中的异硫氰酸苯乙酯(PEITC)，一种可抑制NNK诱导F344大鼠发生肺肿瘤的物质，对经NNK处理的F344大鼠全肺和肺细胞中O6-甲基脱氧鸟苷(O6-mG)和吡啶氧丁酰化DNA加合物的影响。在整个NNK处理期间(1.76mg/kg，每周3次，共4、8、12、16或20周)及之前，给F344大鼠喂食对照饮食或含PEITC的饮食(3μmol/g饮食)。PEITC抑制了全肺和除巨噬细胞外所有肺细胞中吡啶氧丁酰化DNA加合物的形成。对O6-mG也有抑制作用，但因细胞类型和NNK处理时间的不同而有所差异。总体而言，PEITC处理使克拉拉细胞中的吡啶氧丁酰化DNA加合物减少了57%，Ⅱ型细胞中减少了51%，小细胞中减少了40%，全肺中减少了44%。PEITC处理使克拉拉细胞中的O6-mG水平降低了52%，Ⅱ型细胞和小细胞中降低了19%，全肺中降低了36%。这些结果支持了以下假说：PEITC对NNK诱导的肺肿瘤的抑制作用是由于NNK的代谢活化及与DNA的结合减少所致。Ⅱ型细胞中吡啶氧丁酰化DNA加合物减少50%与PEITC使NNK诱导的肺肿瘤减少50%的结果非常吻合。由于NNK诱导的肿瘤源自Ⅱ型细胞，这些结果表明吡啶氧丁酰化DNA加合物在NNK诱导的大鼠肺肿瘤发生中具有重要作用。
