TiF4 and NaF varnishes induce low levels of apoptosis in murine and human fibroblasts through mitochondrial Bcl-2 family and death receptor signalling

Objectives: This study evaluated the level and mechanism of apoptosis in human gingival fibroblasts (HGF) and murine fibroblasts (NIH/3T3) treated with a titanium tetrafluoride (TiF4) varnish compared those treated with a sodium fluoride (NaF) varnish. Methods: Cells were treated with a TiF4, NaF (both 2.45%F) or placebo varnish for 6 h and were then examined using the TUNEL method. The activities of caspase-3, -8 and -9 were assessed. cDNA for Bax, Bad, Bcl-2 and Fas-L was amplified by quantitative PCR. Bax, Bcl-2 and Fas-L were further detected by western blot analysis. Results: Both fluorides similarly increased the percentage of apoptosis, while they failed to activate caspases. The Bax/Bcl-2 gene expression ratio was not altered by either fluoride treatment regardless of the type of cell. NaF varnish increased the amplification of the Fas-L gene in NIH/3T3 and HGF cells, while treatment with the TiF4 varnish resulted in a lower Bad/Bcl-2 expression ratio compared to that of the control for NIH/3T3 cells, but not for HGF cells. No effect of the fluorides was detected in the protein analysis. Conclusions: NaF and TiF4, at the studied conditions, similarly induce a low level of apoptosis, with consequent modest activation of the Bcl-2 and Fas-L-dependent signalling pathways. Generally, HGF cells are more susceptible to the fluoride effect than NIH/3T3 cells.