Involvement of both mitochondrial- and death receptor-dependent apoptotic pathways regulated by Bcl-2 family in sodium fluoride-induced apoptosis of the human gingival fibroblasts

Sodium fluoride (NaF) has been shown to be cytotoxic and produces inflammatory responses in humans. However, the cellular mechanisms underlying the NaF-induced cytotoxicity in periodontal tissues are unclear. This study examined whether or not NaF induces apoptosis in human gingival fibroblasts (HGF), and its underlying mechanisms by monitoring various apoptosis-associated processes. NaF reduced the cell viability of HGF in a dose- and time-dependent manner. NaF increased TUNEL-positive cell and induced apoptosis with concomitant chromatin condensation and DNA fragmentation in HGF. In addition, NaF increased the level of cytochrome c released from the mitochondria into the cytosol, enhanced the caspase-9, -8 and -3 activities, the cleavage of poly (ADP-ribose) polymerase (PARP), and up-regulated the voltage-dependent anion channel (VDAC) 1. However, NaF did not affect the production of reactive oxygen species (ROS) which is a strong apoptotic inducer. Furthermore, NaF up-regulated the Fas-ligand (Fas-L), a ligand of death receptor. Bcl-2, a member of the anti-apoptotic Bcl-2 family, was down-regulated, whereas the expression of Bax, a member of the pro-apoptotic Bcl-2 family, was unaffected in the NaF-treated HGF. These results suggest that NaF induces apoptosis in HGF through both the mitochondria-mediated pathways regulated by the Bcl-2 family and death receptor-mediated pathway.