中华猕猴桃的防癌作用(三)在模拟人胃液中对N-亚硝酰胺合成的阻断作用——Ames试验

本文用Ames试验的方法研究了中华猕猴桃汁对N-亚硝酰胺体外合成的阻断作用。 在模拟人胃液的条件下,亚硝酸钠和甲基硝基胍能反应生成N-甲基-N′-硝基-N亚硝基胍,在Ames氏平皿掺入试验中引起鼠伤寒沙门氏菌TA100菌株的突变反应,有明显的剂量反应关系。当亚硝酸钠浓度为50mM,甲基硝基胍为100mM时,突变菌落数高达4327个/皿,为自发回变的19.94倍。中华猕猴桃汁能阻断N-甲基-N′-硝基-N-亚硝基胍合成,抑制突变反应。在亚硝酸钠浓度为22.2mM,甲基硝基胍为44.4mM时,猕猴桃汁能完全阻断N-甲基-N′-硝基-N-亚硝基胍的合成,致突变反应为阴性。而不加猕猴桃汁的同浓度反应体系引起的突变反应为自发回变的12.59倍。桃汁组低于此浓度的反应体系结果皆是阴性,而对高于此浓度的反应体系,猕猴桃汁不能完全阻断N-甲基-N′-硝基-N-亚硝基胍合成,但能明显抑制突变反应。对中等浓度的反应体系,与桃汁含量相同的抗坏血酸溶液亦能部分阻断N-甲基-N′-硝基-N-亚硝基胍的合成,但作用低于猕猴桃汁。实验结果证明猕猴桃汁阻断N-甲基-N′-硝基-N-亚硝基胍体外合成的作用明显优于同浓度抗坏血酸溶液。 在相同实验条件下,单独的亚硝酸钠或甲基硝基胍均无致突变作用。经薄层层析方法定性分析,反应生成物是N-甲基-N′-硝基-N-亚硝基胍。

THE EFFECTS OF ACTINIDIA CHINENSIS PLANCH ON THE PREVENTION OF CANCERIII. The Blocking Effect of Fruit Juice on the Formation of N-Methyl-N'-Nitro-N- Nitrosoguanidine in VitroAmes Test

A model system which simulated the conditions of the human stomach was used in the experiments. Precursors NaNO2 and MNG formed MNNG and resulted in the positive mutagenic response to Salmonella typhimurium TA 100. When the concentration of the precursors was 50 mM NaNO2 and 100 mM MNG, the induced average number of revertant per plate was 4327 showed an approximate twenty fold spontaneous revertants. With diluting of the precursors, the mutagenic response was lower, showing a dose-response relationship between the mutagenic activity and the precursors concentration. It was found that, when precursor concentration was lower than 22.2 mM NaNO2 and 44.4 mM MNG, the formation of MNNG was blocked completely by the Chinese Kiwi fruit juice and mutation was inhibited. In the same concentration without the Chinese Kiwi fruit juice, the induced revertant was an approximate 13 fold of the spontaneous revertant. The Chinese Kiwi fruit could not block the formation of the MNNG when the precursors concentration was higher than 33.3 mM NaNO2, but it inhibited the mutagenic activity partly. Compared with the Chinese Kiwi fruit juice, the effect of the ascorbic acid solution in the same concentration was much less.It was demonstrated with TLC that MNNG was formed in the model system.