Prevention of the Areca Nut Extract-Induced Unscheduled DNA Synthesis of Gingival Keratinocytes by Vitamin C and Thiol Compounds

There are about 600 million betel quid (BQ) chewers in the world. BQ chewing is the major risk factor of oral cancer in India, Taiwan, South Africa and numerous other countries. Areca nut (AN) extract, the main component of BQ, exerts cytotoxicity and genotoxicity to several types of cells. In the present study, AN extract induced the unscheduled DNA synthesis (UDS) of gingival keratinocytes (GK). Vitamin C, at concentration of 50 and 200 mug ml prevented the AN- induced UDS by 89 100 and 76-90%. These preventive effects were not due to cytotoxicity as analyzed by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Deferoxamine (20 and 30 mM), an iron chelator and a free radical scavenger, also prevented AN extract induced UDS of GK by 30-55%. On the contrary, banthocuproine (50-200 muM, a copper chelator) and 1,10- phenanthroline (50, 100 muM, a lipid permeable iron chelator), lacked preventive effects. Specific reactive oxygen species scavengers such as dimethylsulfoxide (2%), mannitol (10-20 mM), dimethylthiourea (10-20 mM), pyruvate (10 mM), catalase (200 and 400 U, ml), and super-oxide dismutase (50 and 200 U, ml ) also lacked these preventive effects. Moreover, higher concentrations of H2O2 (0.5-1 mM) inhibited the basal levels of UDS by 19 37%. Interestingly, NAC, GSH, Vitamin C and deferoxamine cannot prevent the AN-induced morphological changes of GK at similar concentrations. These results reveal that AN extract-induced UDS of GK is associated with free radical reactions. Possibly different ingredients of AN is responsible for genotoxicity and cytotoxicity. Vitamin C , GSH and NAC may be potentially used in the future for chemoprevention of BQ chewing related oral mucosal lesions.( C) 2002 Elsevier Science Ltd. All rights reserved