Introduction
Fluorine compounds are common environmental pollutants and may excessively penetrate the human body, especially the brain (fluoride penetrates the blood-brain barrier). Some of the latest studies have shown that fluoride may interfere with some of the metabolic pathways involved in the development of invasive potential in many types of cancer (eg Wnt/catenin or NF-κB). One of the stages of tumor invasion is the degradation of the extracellular matrix by metalloproteinases (MMP-2 and MMP-9), which allows the migration and metastasis of cancer cells. Taking into account the above facts, we decided to check whether low concentrations of fluoride affect the expression level of genes encoding MMP-2, MMP-9, and their TIMP-2 and TIMP-3 inhibitors in human glioblastoma cells.

Methods
U-87MG human glioblastoma cells were cultured with EMEM medium (10% FBS, 2 mM glutamine, 1% NEAA), 1 mM sodium pyruvate, 100 IU / ml penicillin, 10 μg / ml streptomycin) under optimal conditions (at 37 ° C, in an atmosphere of 5% CO₂, with 95% humidity). Cells were treated with sodium fluoride (NaF; 1-5 µM) for 24, 48 and 72 hours.
The analysis of the expression level of the MMP-2, MMP-9, Timp-2, and Timp-3 genes was carried out by RT-PCR.

Results
The results indicate that NaF (0.1-5 µM) can disrupt the expression of MMP-2, MMP-9, Timp-2, and Timp-3. In the case of MMP-2, there was an approx. 2-fold increase in expression in 48h (5 µM NaF) and about 2.5-fold increase in expression in 72h (0.1-5 µM NaF). For MMP-9, an approximately 3-fold increase in expression was observed in 24h (0.1 µM NaF) and 48h (5 µM NaF). Both Timp-2 and Timp-3 showed a significant increase in expression observed at all time points especially at the highest concentration of NaF (5 µM).

Conclusions
The obtained results may suggest that even low concentrations of fluorine compounds may have an undesirable influence promoting the invasive potential of human glioblastoma cells.

Acknowledgments
The project was implemented with the use of funds for science granted by the Pomeranian Medical University in Szczecin.