Effects of areca nut on growth, differentiation and formation of DNA damage in cultured human buccal epithelial cells.
Because the high incidence of oral cancers in South-East Asia is causally linked to the common habit of betel quid chewing, the effects of an aqueous extract of areca nut, one of the main ingredients of the quid, on growth, differentiation, morphology and DNA damage were studied in cultured human buccal epithelial cells. An acute exposure (3 hr) of the cells to the extract altered their morphology and induced ridges in the plasma membrane, with indications of internalization of extract particles. Such exposure also caused formation of DNA single-strand breaks which accumulated during post-treatment culture, indicating continuous exposure to residual particles and/or the possibility of inhibited DNA repair. The extract accelerated terminal differentiation of the cells, measured as involucrin expression at relatively non-toxic levels. The extract caused similar loss of colony-forming efficiency in normal cells and in a buccal carcinoma cell line (SqCC/YI) which was defective in its ability to undergo differentiation, indicating that extract toxicity could occur independently from this response. Finally, the genotoxicity of the salivary areca-nut-specific carcinogen 3-(N-nitrosomethyl-amino)propionaldehyde, was demonstrated by the formation of DNA protein cross-links and DNA single-strand breaks in normal buccal epithelial cells. These findings in vitro suggest that betel quid carcinogenesis in the human oral cavity may involve cytopathic alterations of normal cell morphology, growth and differentiation, as well as formation of DNA damage by areca-nut-related agents extracted or formed in saliva.