中华猕猴桃汁的防癌作用——(二)在体外模拟胃液中对亚硝胺合成的阻断作用—Ames试验方法检测

本文研究了猕猴桃汁对N-二甲基亚硝胺体外合成的阻断作用,以鼠伤寒沙门氏菌致突变试验检验。 将二甲基亚硝胺的前体物质-亚硝酸钠和氨基比林,在体外模拟胃液条件下(pH3.3,37％℃)保温一小时,以鼠伤寒沙门氏菌变异株TA100,按常规方法(平皿掺入试验)检验致突变性。当两种前体浓度达5mg/ml以上时,如不加阻断剂,均显示出突变阳性反应,提示反应体系中形成了有致突变性的亚硝胺。如果同时加入猕猴桃汁,可以阻断亚硝胺合成,在5mg/ml和8mg/ml两个浓度的测定结果均未出现致突变作用。在5mg/ml反应体系中,分别加入桃汁和维生素C溶液进行对比,发现桃汁的阻断效率高于维生素C,每皿菌落数均值分别为252±4.2(桃汁),和445±81.2(同浓度维生素C),两者差异有显著性(P<0.01)。结果证明猕猴桃汁对体外亚硝胺合成的阻断作用优于同浓度的维生素C溶液。同样条件下单独保温的亚硝酸钠氨基比林或磷酸缓冲液均无致突变作用。 同样条件下处理的样品(亚硝酸钠,氨基比林各5mg/ml,加到pH3.3磷酸缓冲液中,37℃混合保温1小时)经水蒸气蒸馏,二氯甲烷萃取,浓缩后用气相色谱—质谱联机分析,确认为N-二甲基亚硝胺(NDMA)。

THE BLOCKING EFFECTS OF CHINESE ACTINIDIA SINENSIS PLANCH JUICE ON THE FORMATION OF N-NITROSAMINE

The present investigation was undertaken to evaluate the role of the Chinese fruit juice in blocking nitrosamine formation in vitro.A model system simulated the conditions (pH 3.3, 37℃) known, to exist in the stomach, was used in the experiments. Different amount of nitrite and aminopyrine was incubated with Chinese fruit juice or vitamin C solution or buffer solution for 1 hr. 0.1 ml samples were taken and then subjected to the Ames mutagenicity test. The tester strain TA100 of Salmonella typhi-murium was employed for the detection of mutagenicity due to the N-nitro-samine formed from sodium nitrite and aminopyrine. Test samples and bacteria with or without S-9 mixed with molten top agar and poured onto the minimal agar plates. After incubation, the sample, that gave at least a 2-fold increase in induced revertants, compared to spontaneous revertants, was considered to have mutagenic activity.It showed that the concentration of the precursors was at or above 5 mg/ ml with S-9 and without juice. the samples exhibited mutagenic activity. It suggested that the nitrosamine was formed in this system. While the incorporation of Chinese fruit juice was found to inhibit the formation of nitrosamine at 5mg/ml and 8mg/ml. The cultures did not show mutagenic activity. The induced revertant colonies per plate was 252 ± 4.2. The Chin esefruit juice is more effective than that of vitamin C, the induced revertant colonies per plate was 445 ± 81.2, which shows mutagenic. The difference between the cultures of Chinese fruit juice and vitamin C is significant (P<0.01).