Induction of unscheduled DNA synthesis in cultured human oral keratinocytes by sodium fluoride.

The effect of treatment of cultured human oral keratinocytes with sodium fluoride (NaF) has been investigated with respect to induction of unscheduled DNA synthesis (UDS). Oral keratinocytes were isolated from excised buccal mucosa of normal individuals by trypsinization at 4 degrees C overnight, followed by separation of the epithelium of mucosa from lamina propria mucosae with forceps. Isolated cells were cultured in vitro and all experiments were performed with secondary cultures. For detection of UDS, the keratinocytes were cultivated with medium containing 1% fetal calf serum (FCS) for 2 days and then treated with 100-300 micrograms/ml NaF for 4 h in medium containing 1% FCS and 10 mM hydroxyurea (1% FCS-HU medium). Following treatment with NaF, UDS was measured by direct scintillation counting of [3H]thymidine incorporated into DNA of the cells in 1% FCS-HU medium. Significant levels of UDS were induced in a dose-related fashion by NaF treatment. The results suggest that NaF causes DNA damage in cultured human oral keratinocytes.