Combined effects of fluoride exposure and low nutrition on osteogenesis and osteoclastic differentiation in rats

Menglan YANG; Hongwei DING; Ruiqi ZHOU; Xueli PAN

ABSTRACT

Objective:

To investigate the combined effect of fluoride exposure and low nutrition on osteogenesis and osteoclastic differentiation in rats.

Methods:

SD rats were divided into four groups by the method of random number table, namely normal nutrition group, low nutrition treatment group, fluoride exposure group and co-treatment of fluoride and low nutrition group according to 2 × 2 factorial experimental design, 8 rats in each group, half male and half female. Five months after the experiment, immunohistochemistry was used to test the expression levels of femoral alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL). Analysis of variance of factorial design was used to determine the interaction between fluoride exposure and low nutrition on osteogenesis and osteoclastic differentiation.

Results:

The immunohistochemical results of bone tissue showed that there were significant differences in the expression levels of osteogenesis differentiation markers ALP and Runx2 between different groups ( F = 25.98, 17.77, P < 0.001). Compared with normal nutrition group (0.005 2 ± 0.002 7, 0.003 1 ± 0.001 4), the expression levels of ALP and Runx2 in fluoride exposure group were higher (0.019 5 ± 0.005 0, 0.014 4 ± 0.004 4, P < 0.05). There was no significant difference between low nutrition treatment group (0.002 6 ± 0.001 8, 0.004 4 ± 0.003 2) and co-treatment of fluoride and low nutrition group (0.003 6 ± 0.000 7, 0.002 9 ± 0.000 8, P > 0.05). The expression levels of ALP and Runx2 in co-treatment of fluoride and low nutrition group were lower than those of fluoride exposure group ( P < 0.05). There were significant differences in the expression level osteoclastic differentiation marker of RANKL and the ratio of RANKL/OPG ( F = 10.50, 31.05, P < 0.001). Among them, the RANKL/OPG ratio (0.115 3 ± 0.039 5) in fluoride exposure group was lower than that in normal nutrition group (1.426 3 ± 0.777 2), and the RANKL expression level and RANKL/OPG ratio (0.019 5 ± 0.007 7, 7.258 7 ± 3.674 3) in co-treatment of fluoride and low nutrition group were higher than those in normal nutrition group (0.004 4 ± 0.002 5, 1.426 3 ± 0.777 2, P < 0.05). However, there was no significant difference in the RANKL expression level and RANKL/OPG ratio (0.004 0 ± 0.001 9, 2.022 3 ± 0.753 7) in low nutrition treatment group ( P > 0.05). The expression level of RANKL and the ratio of RANKL/OPG in the co-treatment of fluoride and low nutrition group were higher than those in low nutrition treatment group and fluoride exposure group ( P < 0.05). The 2 × 2 analysis of variance of factorial design showed that fluoride exposure and low nutrition had interaction on ALP, Runx2, RANKL expression levels and RANKL/OPG ratio ( F = 4.38, 19.39, 22.12, 108.00, P < 0.05), antagonistic effect on ALP and Runx2 expression, synergistic effect on RANKL expression and RANKL/OPG ratio.

Conclusions:

In rat bone tissue, fluoride exposure promotes osteogenesis differentiation, inhibits osteoclastic differentiation dominated by active osteogenic function. The interaction between fluoride and low nutrition on osteogenesis and osteoclastic differentiation is antagonistic osteogenesis differentiation and synergistic promotion of osteoclastic differentiation. Normal nutrition conditions are material basis of osteogenesis differentiation, and low nutrition is the inducement of enhanced osteoclastic differentiation.