title: Effects of pH on nicotine-induced DNA damage and oxidative stress.
abstract: 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.
authors.affiliation: Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Hui-Ju
authors.initials: HJ
authors.lastname: Wu
authors.forename: Chin-Wen
authors.initials: CW
authors.lastname: Chi
authors.forename: Tsung-Yun
authors.initials: TY
authors.lastname: Liu
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D017610:Calcium Compounds / Q000737:chemistry; D002374:Catalase / Q000494:pharmacology; D045744:Cell Line, Tumor / Q000187:drug effects*; D020552:Comet Assay; D004249:DNA Damage; D004357:Drug Synergism; D006147:Guanine / Q000031:analogs & derivatives / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009062:Mouth Neoplasms; D009538:Nicotine / Q000737:chemistry / Q000633:toxicity*; D018384:Oxidative Stress; D010087:Oxides / Q000737:chemistry; D031701:Piper; D010936:Plant Extracts / Q000737:chemistry; D012906:Smoke; D013624:Taiwan; D014026:Nicotiana / Q000737:chemistry
chemical_list: D017610:Calcium Compounds; D010087:Oxides; D010936:Plant Extracts; D012906:Smoke; C495400:lime-piper betel quid; C024829:8-hydroxyguanine; D006147:Guanine; D009538:Nicotine; D002374:Catalase; D000111:Acetylcysteine