stract
Chewing betel quid (BQ) is a popular habit worldwide. A causal association between BQ chewing and oral cancer has been well
documented. Emerging evidence indicates that sustained exposure to stress induces epigenetic reprogramming of some mammalian
cells and increases the mutation rate to accelerate adaptation to stressful environments. In this study, we first confirmed that 24-h
treatment with areca nut extracts (ANE; a major component of BQ) at doses over 40 g/ml induced mutations at the hypoxanthine
phosphoribisyltransferase (HPRT) locus in human keratinocytes (HaCaT cells). We then investigated whether the stress of long-term
exposure to sublethal doses of ANE (0, 5 and 20 g/ml for 35 passages) could enhance genetic damage to HaCaT cells. Compared
to cells exposed to 0 or 5 g/ml ANE, cells exposed to 20 g/ml ANE were slightly but significantly more resistant to a 72-h
treatment with ANE and its major ingredients, arecoline and arecaidine, but did not develop cross-resistance to other BQ ingredients
or alcohol. The cells that received 20 g/ml ANE for 35 passages also had a significantly increased mutation frequency at the HPRT
locus and an increased frequency in the appearance of micronuclei compared to lower doses. Moreover, increased intracellular levels
of reactive oxygen species and 8-hydroxyguanosine in cells exposed to 20 g/ml ANE suggested that long-term ANE exposure
results in the accumulation of oxidative damage. However, cells subjected to long-term treatment of 20 g/ml ANE contained higher
levels of glutathione than unexposed cells. Therefore, after long-term exposure to sublethal doses of ANE, intracellular antioxidative
activity may also be enhanced in response to increased oxidative stress. These results suggest that stress caused by long-term ANE
exposure enhances oxidative stress and genetic damage in human keratinocytes.
© 2006 Elsevier B.V. All rights reserved.