Effects of fluorosis on osteoclasts's quantity and bone resorption function in vitro

Objective To determine the effects of fluoride on osteoclasts's quantity and bone resorption function in vitro and its mechanisms. Methods The osteoclasts and bone marrow stromal cells(BMSCs) isolated from long bone of new born rats were cultured respectively in TC199 medium (containing 10% fetal bovine serum) with fluoride. The osteoclasts were inoculated in 96-well culture plate and ivory slice, BMSCs were inoculated in 6- well culture plate, respectively, medium were changed after 2 hours incubation. They were divided into control group, low-dose fluoride, medium-dose fluoride and high-dose fluoride groups, the doses of sodium fluoride were 0,2.5 × 10-5,5.0 × 10-5,10.0 × 10-5 mol/L, respectively. Tartrate-resistant acid phosphatase(TRAP) staining positive cells were counted under light microscope after TRAP staining on the 2nd and the 5th day and the pit formed in ivory slices were measured by histomorphometry after staining with toludine blue. The expression of receptor activator of NK-κβ ligand(RANKL) and osteoprotegerin(OPC) was detected by real-time fluorescence quantitative (337.5 ± 70.5), (447.5 ± 43.4), (472.9 ± 34.8), (475.3 ± 24.3)/well in the control group, the low-dose, mediumdose and high-dose fluoride groups, respectively. The differences were statistically significant between these groups and the control group (all P < 0.05). After in vitro culture for 5 days, the numbers of osteoclasts were (92.5 ± 22.1), (123.0 ± 26.4), (135.5 ± 22.2), (136.9 ± 23.0) per well in the control group, the low-dose, medium-dose and high-dose fluoride groups, respectively. The differences were statistically significant between these groups and the (0.088 ± 0.030), (0.100 ± 0.018), (0.152 ± 0.015), (0.242 ± 0.031 )mm2 per piece in the control group, the lowdose, medium-dose and high-dose fluoride groups, respectively. The values of medium-dose and high-dose fluoride BMSCs in the control group, the low-dose, medium-dose and high-dose fluoride groups were 100.00 ± 56.02, 144.95 ± 97.21,223.25 ± 184.48,193.98 ± 137.93, respectively. The values of medium-dose and high-dose fluoride groups were significantly higher than that of control group (all P < 0.05). Conclusions Fluoride can cause increase in the number of osteoclasts in vitro and promote their cell differentiation and bone resorption activity, which may be related to increased expression ratio of RANKL/OPG mRNA in BMSCs. Key words: Fluoride poisoning;  Osteoclasts;  Cell culture techniques;  Receptor activator of NK-κβ ligand;  Osteoprotegerin