Effect of Fluoride in Drinking Water on Fecal Microbial Community in Rats.

Intestinal nutrition has a close association with the onset and development of fluorosis. Intestinal microbes play a major role in intestinal nutrition. However, the effect of fluoride on intestinal microbes is still not fully understood. This study aimed to evaluate the dose-response of fluoride on fecal microbes as well as the link between fluorosis and fecal microbes. The results showed that fluoride did not significantly alter the diversity of fecal microbiota, but richness estimators (ACE and Chao) increased first, and then decreased with the increase of water fluoride. At the genus level, 150 mg/L fluoride significantly reduced the abundances of Roseburia and Clostridium sensu stricto, and 100 mg/L and 150 mg/L fluoride obviously increased the abundances of Unclassified Ruminococcaceaes and Unclassified Bdellovibrionales, respectively. The correlation analysis showed fluoride exposure had a negative association with Roseburia and Turicibacter and was positively associated with Pelagibacterium, Unclassified Ruminococcaceae, and Unclassified Bdellovibrionales. Dental fluorosis was negatively associated with Clostridium sensu stricto, Roseburia, Turicibacter, and Paenalcaligenes and had a positive association with Pelagibacterium, Unclassified Ruminococcaceae, and Unclassified Bdellovibrionales. In conclusion, this study firstly reports fluoride in drinking water has a remarkable biphasic effect on fecal microbiota in rats, and some bacteria are significantly associated with fluoride exposure and dental fluorosis. These results indicate the gut microbiota may play an important role in fluorosis, and some bacteria are likely to be developed as biomarkers for fluorosis.

miR-21-5p and canonical Wnt signaling pathway promote osteoblast function through a feed-forward loop induced by fluoride.

Long-term excessive exposure to fluoride from environmental sources can cause serious public health problems such as dental fluorosis and skeletal fluorosis. The aberrant activation of osteoblasts in the early stage is one of the critical steps during the pathogenesis of skeletal fluorosis and canonical Wnt signaling pathway participate in the progress. However, the specific mechanism that how canonical Wnt signaling pathway was mediated is not yet clear. In this study, we found that miR-21-5p induced the activation of canonical Wnt signaling pathway via targeting PTEN and DKK2 during fluoride induced osteoblasts activation and firstly demonstrated the forward loop between canonical Wnt signaling and miR-21-5p in the process. These findings suggested an important regulatory role of miR-21-5p on canonical Wnt signaling pathway during skeletal fluorosis and miR-21-5p might be a potential therapeutic target for skeletal fluorosis.

sKlotho is associated with the severity of brick tea-type skeletal fluorosis in China.

The change of serum soluble Klotho (sKlotho) content is related to a variety of osteoarthropathy. However, its association with the severity of skeletal fluorosis (SF) is not clear. Here, the association of tea fluoride exposure with serum sKlotho levels and the severity of SF were investigated and further verified in a rat model of fluorosis. A cross sectional case control study was conducted in residents over 50 years old from brick-tea drinking areas in Qinghai and Xinjiang Provinces, China. Concentrations of fluoride in brick tea water and urine were determined by ion selective electrode method, and the levels of serum sKlotho were determined by ELISA method. Linear regression and ordered logistic regression models were constructed to examine the relationship among fluoride exposure, serum sKlotho levels and the severity of SF. The kidney and small intestine of Wistar rats were isolated for detection of Klotho by immunohistochemistry (IHC), and femoral artery blood was sampled to measure the serum levels of sKlotho. An increase of 1 mg/day in tea fluoride intake (TFI) was associated with a 12.070 pg/mL (95% CI: 0.452-23.689) increase in serum sKlotho levels and a 1.163-fold (95% CI: 1.007-1.342) increase in the severity of SF after adjusting for age, gender, and ethnicity. Serum sKlotho levels were also positively associated with the severity of SF (P < 0.05). The mediation analysis showed that serum sKlotho levels mediated 17.76% of the increase in the severity of SF caused by an increase of 1 mg/day of TFI. Moreover, a significant increase of serum sKlotho levels in fluoride-exposed groups was also seen in the rat model. The present study suggests that serum sKlotho may be a potential mediator of SF in brick tea-type fluorosis endemic areas.