Effects of fluoride on bone mass of tibia and lumbar in BALB/c mice

Abstract

Objective To investigate the effects of fluoride on trabecular bone of the tibia and lumbar in BALB/c mice. Methods Totally 64 four-week-old BALB/c mice were randomly divided into 4 groups by weight, 16 per group: control group (treated with distilled water) and 3 sodium fluoride (NaF) exposure groups (treated with NaF at 25, 50 and 100 mg/L F-), respectively. At 12 weeks, mice were killed and blood, two hind limbs and lumbar were collected. Bone fluoride content and incidence rates of dental fluorosis were determined. Serum content of alkaline phosphatase (AKP) and acid phosphatase (ACP) were detected by micro enzyme labeled method. The ultrastructure of osteoblasts and osteoclasts in lumbar were observed via transmission electron microscope. The pathological changes of the trabecular bone of the tibia and the lumbar were observed under optical microscope, the percentage of trabecular area (%Tb.Ar) was measured with Image-Pro Plus (IPP) software. Results Bone fluoride contents of low, middle and high fluoride groups [(1 828.62 ± 102.93), (3 308.27 ± 185.63), (4 933.36 ± 301.16) mg/kg] were higher than that of the control group [(775.23 ± 92.56) mg/kg, all P < 0.05]. The incidences of dental fluorosis in the 4 groups were 0 (0/16) , 47% (7/15) , 93% (14/15) and 100% (16/16) , respectively; the difference was statistically significant (χ2= 27.23, P < 0.05). In middle and high fluoride groups, serum AKP [(18.30 ± 1.99), (24.50 ± 3.14) king unit/100 ml] and ACP [(11.97 ± 1.73), (11.31 ± 1.46) king unit/100 ml] were significantly higher than those of control [(14.63 ± 1.21), (9.07 ± 1.47) king unit/100 ml, respectively, all P < 0.05]. Under the electron microscope, osteoblast had developed organelles in each fluoride group, rough endoplasmic reticulum, Golgi body, and mitochondria were abundant, and nucleolus was obvious in the osteoblast. Osteoclast was rich in mitochondria, ruffled border clear and distributed phagocytic vacuoles in low fluoride group and middle fluoride group. Compared with the control group (17.03 ± 3.73), HE staining of tibia % Tb.Ar in high fluoride group (28.79 ± 8.26) was significantly increased (P < 0.05). The lumbar spine %Tb.Ar in low, middle and high fluoride groups (15.87 ± 2.59, 18.28 ± 0.89, 21.99 ± 1.81) were higher than that of the control group (12.06 ± 1.76, all P < 0.05]. Conclusions BALB/c mice could be used as a model of skeletal fluorosis. Osteoblast and osteoclast are activated in BALB/c mice with skeletal fluorosis. Bone formation is more obvious than bone resorption and bone mass is increased. What is more, bone mass has increased more significantly in the lumbar spine of mice. Key words: Fluorides; Bone and bone tissue; Osteoblast; Osteoclast