Objective To investigate the effects of different doses of sodium fluoride exposure on histomorphometric change of bone and miRNA-23a expression in rats at different developmental stages.
Methods Ninety-six SD rats were randomly divided into control (0 mg/L) and low (50 mg/L), moderate (150 mg/L), and high (250 mg/L) fluoride treated groups. The animals were executed after 2, 4, and 6 months of the treatment via drinking water to determine bone and dental fluoride levels in left lower limb and teeth by ashing-fluoride ion selective eletrode method. The rat femoral metaphysis samples were stained with hematoxylin-eosin (HE) after decalcification, and observed under optical microscope for evaluating morphological changes in trabeculae, epiphyseal plate, and osteoblasts. The expression levels of miRNA-23a in total RNA extracted by RNAiso Plus from bone meal of left rat forelimb were detected by real-time fluorescence quantitative PCR.
Results Except the low NaF group at 2 months, the dental fluorosis incidence rates of each NAF group at different time points were statistically higher than those of the control group (P < 0.05). The bone and dental fluoride concentrations of each NaF group were increased over exposure time. At different time points, the trabecular area and epiphyseal area of both moderate and high NaF groups were statistically higher than those of the control group (P < 0.05), while the trabecular area of the low NaF group was statistically lower (P < 0.05). Both trabecular area and epiphyseal area showed rising trends with the increase of NaF dose, with statistical differences among the groups after 2, 4, and 6 months of treatment (P < 0.01). After the treatment for different time, the numbers of osteoblasts of each NaF group were statistically lower than that of the control group (P < 0.05), and showed a decreasing trend with the increase of NaF dose. The trabecular area, epiphyseal area, and number of osteoblasts all showed downward trends with prolonged time of the NaF treatment (P < 0.05). After the treatment for different time, the miRNA-23a expression levels of each NaF group were statistically higher than that of the control group (P < 0.05); the expression level after 6 months was statistically higher than the levels after 2 and 4 months in each NaF group, showing an upward trend.
Conclusion Excessive and long-term fluoride intake will affect bone formation and development, indicating that miRNA-23a is involved in the abnormal bone transformation in rats caused by fluorosis, and that the systematic damage induced by fluoride exposure is potentially linked to miRNA-23a, but the relevant mechanism is not yet clear and needs further study.
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