Wu Hui-Ju, Chi Chin-Wen, Liu Tsung-Yun
Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.
J Toxicol Environ Health A. 2005 Sep;68(17-18):1511-23. doi: 10.1080/15287390590967478.
Epidemiological evidence suggests that chewing betel quid and smoking have synergistic potential in the development of oral squamous-cell carcinoma in Taiwan. Chewing betel quid produces alkalization of saliva. This study investigated the response of human oral cancer OEC-M1 cells to nicotine in different pH environments (6.5 and 8) by examining its effects on DNA damage as evidenced by single-cell gel electrophoresis. Nicotine (1 and 10 muM) significantly induced DNA strand breakage when cultured at pH 8 for 6 h but did not induce DNA damage at pH 6.5. Nicotine-induced DNA damage was also time dependent. When cells were pretreated with catalase or N-acetylcysteine, a significant reduction in nicotine-induced DNA damage was observed. Flow cytometric analyses showed that the production of 8-oxoguanine was significantly increased following nicotine (10 muM) treatment. Posttreatment of nicotine-damaged DNA by endonuclease III and formamidopyrimidine-DNA glycosylase, recognizing oxidized DNA bases, increased the extent of DNA damage. These results suggest that nicotine-induced DNA strand breakage is pH dependent, and oxidative stress might be involved in nicotine-induced DNA damage. Finally, cigarette smoke condensate (equivalent to 8 muM nicotine) induced significant DNA strand breaks in OEC-M1 cells at pH 8 and correlated with the generation of oxidative DNA damage. Thus, alkaline saliva generated by chewing betel quid plays an important role in cigarette-related nicotine-induced DNA damage, and reactive oxygen species may be involved in generating this DNA damage.
流行病学证据表明，在台湾，嚼食槟榔与吸烟在口腔鳞状细胞癌的发生发展中具有协同作用的可能性。嚼食槟榔会使唾液碱化。本研究通过单细胞凝胶电泳检测尼古丁对DNA损伤的影响，从而探究人口腔癌OEC-M1细胞在不同pH环境（6.5和8）下对尼古丁的反应。尼古丁（1和10μM）在pH 8条件下培养6小时后可显著诱导DNA链断裂，但在pH 6.5时不会诱导DNA损伤。尼古丁诱导的DNA损伤也具有时间依赖性。当细胞用过氧化氢酶或N-乙酰半胱氨酸预处理时，观察到尼古丁诱导的DNA损伤显著减少。流式细胞术分析表明，尼古丁（10μM）处理后8-氧代鸟嘌呤的产生显著增加。用识别氧化DNA碱基的核酸内切酶III和甲酰胺嘧啶-DNA糖基化酶对尼古丁损伤的DNA进行后处理，增加了DNA损伤的程度。这些结果表明，尼古丁诱导的DNA链断裂是pH依赖性的，氧化应激可能参与了尼古丁诱导的DNA损伤。最后，香烟烟雾冷凝物（相当于8μM尼古丁）在pH 8时可诱导OEC-M1细胞显著的DNA链断裂，且与氧化性DNA损伤的产生相关。因此，嚼食槟榔产生的碱性唾液在香烟相关的尼古丁诱导的DNA损伤中起重要作用，活性氧可能参与了这种DNA损伤的产生。
