Metabolomic profiling of sodium fluoride-induced cytotoxicity in an oral squamous cell carcinoma cell line

Sodium fluoride (NaF) is used in dentistry as a preventive agent for dental caries because of its ability to remineralize the tooth surface and its antibacterial effect. Although one of its target molecules in bacteria is enolase, its site of action in human cells has not been identified. The aim of this study was to identify target metabolites that are coupled to NaF-induced cytotoxicity in the HSC-2 human oral squamous cell carcinoma cell line. Cell viability, membrane integrity and apoptosis induction were analyzed by MTT assay, trypan blue exclusion and caspase-3 activation, respectively. Cells were treated with a minimal cytotoxic concentration of NaF for various times and subjected to comprehensive metabolomics analysis using capillary electrophoresis-mass spectrometry. In the early stages, inhibition of the enolase reaction in glycolysis pathway was observed. This was coupled with rapid inhibition of the progression of TCA cycle. In the later stages, gradual increases in the AMP/ATP ratio (a putative marker of apoptosis) and oxidized products (e.g. GSSH, and methionine sulfoxide), and marginal changes in polyamine levels (putative marker of necrosis) were observed. This manuscript provides the new insight into the global impact of NaF on metabolic pathways in human oral squamous cell carcinoma cells.