Fluoride Action Network

home // Researchers // Study Tracker //

Abstract

Fluoride is a common element in nature and our daily life, and excessive intake of this element can cause fluorosis and irreversible brain damage. The toxic effects of fluoride on the central nervous system may be attributed to the release of inflammatory cytokines and ROS. GSK3B is a key protein that modulates NF-kB activity and inflammatory cytokine levels and plays an important role in the Wnt signaling pathway. In this study, we found that fluoride altered the inflammatory status and oxidative stress by inhibiting Wnt signaling pathway activity. This study thus provides a valid basis for the fluorine-induced neuroinflammation injury theory.

Keywords: DKK1; GSK3B; NaF; Wnt signaling pathway; neuroinflammation.

*Original abstract online at https://link.springer.com/article/10.1007/s10753-017-0556-y

 

Excerpt:

Fluoride exposure increases IL-1B and TNF-a production and changes the cellular oxidation and antioxidation status [5, 19]. Neuroinflammation seems to be an important mediator of the effects of fluoride. Neuroinflammation, which is mediated by microglia, contributes to most pathological neurologic processes, including CNS infections, ischemic stroke, neurodegenerative disease, and anesthetic neurotoxicity. Increased pro-inflammatory mediator production is thought to cause neuronal cell death. As previously mentioned, inflammation is characterized by activation of the pro-inflammatory transcription factor NF-kB, a process mediated by GSK3B, a critical protein in the Wnt signaling pathway [9]. Therefore, we conducted the present study to investigate the changes in the Wnt signaling pathway in BV2 cells exposed to NaF.

Microglia are the resident macrophages in the brain and play critical roles in the development and maintenance of the neural environment [20]. To exclude the possibility that NaF directly affects microglial viability and proliferation, we examined the effects of different NaF concentrations on BV2 viability at different time points. As shown in Fig. 1, BV2 cell viability increased after treatment with lower concentrations of NaF for 6 h. This increase in cell viability was likely caused by a stress response to NaF. However, cell viability decreased significantly when the NaF concentration increased, indicating that high NaF concentrations are toxic to cells.

Microglia can be activated in response to perturbations in the brain microenvironment or changes in neuronal structure. Activated microglia cells break the balance between oxidation and antioxidation. MDA levels reflect the degree of lipid peroxidation and indirectly reflect the degree of cell damage. SOD, an antioxidant, can defend against ROS activity and reduce theMDA level. ROS can cause oxidative damage to cells and DNA structure [2]. As shown in Fig. 2, the MDA levels increased in the NaF groups. SOD activity decreased significantly at higher NaF concentrations. The intracellular ROS levels increased as the NaF concentration increased. Activated microglia also produce various inflammatory mediators, including IL-6 and TNF-a, which are the two main pro-inflammatory cytokines produced by these cells. As shown in Fig. 3, higher NaF concentrations stimulated IL-6 and TNF-a production in BV2 cells. This result could indicate that NaF-induced oxidative stress and inflammation play an important role in fluorosis.

Previous studies have shown that the Wnt signaling pathway can affect cognitive function by regulating the proliferation, differentiation, and migration of neural stem cells…

Wnt/B-catenin signaling in the rat hippocampus [9]. DKK1 has been described as an extracellular antagonist of the Wnt pathway, and studies have shown that DKK1 is required for the pathogenesis of many neurodegenerative diseases, including AD in patients and animal models [24], frontotemporal dementia in transgenic mice [25], ischemic insults [26], and mesial temporal lobe epilepsy with hippocampal sclerosis [27]. However, the relationship between DKK1 level and fluorosis remains unknown. In this study, we established a model of NaF-induced neuroinflammation to measure DKK1 expression and found increased DKK1 levels in BV2 cells treated with various concentrations of NaF. This result suggested that DKK1, an inhibitor of the canonical Wnt signaling pathway, might be involved in NaF-induced neuroinflammation.

References

  1. 1.

    Liu, F., et al. 2014. Fluoride exposure during development affects both cognition and emotion in mice. Physiology & Behavior 124: 1–7. CAS  Article  Google Scholar

  2. 2.

    Zhang, C., et al. 2013. The analog of Ginkgo biloba extract 761 is a protective factor of cognitive impairment induced by chronic fluorosis. Biological Trace Element Research 153 (1–3): 229–236. CAS  Article  PubMed  Google Scholar

  3. 3.

    Long, Y.G., et al. 2002. Chronic fluoride toxicity decreases the number of nicotinic acetylcholine receptors in rat brain. Neurotoxicology and Teratology 24 (6): 751–757. CAS  Article  PubMed  Google Scholar

  4. 4.

    Khan, S.A., et al. 2015. Relationship between dental fluorosis and intelligence quotient of school going children in and around Lucknow District: a cross-sectional study. Journal of Clinical and Diagnostic Research 9 (11): ZC10–ZC15.
    PubMed  PubMed Central  Google Scholar

  5. 5.

    Shuhua, X., et al. 2012. A role of fluoride on free radical generation and oxidative stress in BV-2 microglia cells. Mediators of Inflammation 2012: 102954. Article  PubMed  PubMed Central  Google Scholar

  6. 6.

    Abeti, R., and M.R. Duchen. 2012. Activation of PARP by oxidative stress induced by beta-amyloid: implications for Alzheimer’s disease. Neurochemical Research 37 (11): 2589–2596. CAS  Article  PubMed  Google Scholar

  7. 7.

    Zhou, J., et al. 2008. Complement C3 and C4 expression in C1q sufficient and deficient mouse models of Alzheimer’s disease. Journal of Neurochemistry 106 (5): 2080–2092. CAS  Article  PubMed  PubMed Central  Google Scholar

  8. 8.

    Cortese, G.P. and C. Burger, Neuroinflammatory challenges compromise neuronal function in the aging brain: postoperative cognitive delirium and Alzheimer’s disease. Behav Brain Res, 2016.

  9. 9.

    Orellana, A.M., et al. 2015. Age-related neuroinflammation and changes in AKT-GSK-3beta and WNT/ beta-CATENIN signaling in rat hippocampus. Aging (Albany NY) 7 (12): 1094–1111. Article  Google Scholar

  10. 10.

    Ajmone-Cat, M.A., et al. 2016. Glycogen synthase kinase 3 is part of the molecular machinery regulating the adaptive response to LPS stimulation in microglial cells. Brain, Behavior, and Immunity 55: 225–235. CAS  Article  PubMed  Google Scholar

  11. 11.

    Chen, J., C.S. Park, and S.J. Tang. 2006. Activity-dependent synaptic Wnt release regulates hippocampal long term potentiation. The Journal of Biological Chemistry 281 (17): 11910–11916. CAS  Article  PubMed  Google Scholar

  12. 12.

    Margarit, C., et al. 1998. Efficacy and safety of oral low-dose tacrolimus treatment in liver transplantation. Transplant International 11 (Suppl 1): S260–S266. Article  PubMed  Google Scholar

  13. 13.

    Esposito, G., et al. 2008. S100B induces tau protein hyperphosphorylation via Dickopff-1 up-regulation and disrupts the Wnt pathway in human neural stem cells. Journal of Cellular and Molecular Medicine 12 (3): 914–927. CAS  Article  PubMed  PubMed Central  Google Scholar

  14. 14.

    Ke, L., et al. 2016. Effects of sodium fluoride on lipid peroxidation and PARP, XBP-1 expression in PC12 cell. Biological Trace Element Research 173 (1): 161–167. CAS  Article  PubMed  Google Scholar

  15. 15.

    Ghosh, S., and M. Karin. 2002. Missing pieces in the NF-kappaB puzzle. Cell 109 (Suppl): S81–S96. CAS  Article  PubMed  Google Scholar

  16. 16.

    Chioca, L.R., et al. 2008. Subchronic fluoride intake induces impairment in habituation and active avoidance tasks in rats. European Journal of Pharmacology 579 (1–3): 196–201. CAS  Article  PubMed  Google Scholar

  17. 17.

    Ando, M., et al. 1998. Health effects of indoor fluoride pollution from coal burning in China. Environmental Health Perspectives 106 (5): 239–244. CAS  Article  PubMed  PubMed Central  Google Scholar

  18. 18.

    Choi, A.L., et al. 2012. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environmental Health Perspectives 120 (10): 1362–1368. CAS  Article  PubMed  PubMed Central  Google Scholar

  19. 19.

    Yan, L., et al. 2013. JNK and NADPH oxidase involved in fluoride-induced oxidative stress in BV-2 microglia cells. Mediators of Inflammation 2013: 895975. Article  PubMed  PubMed Central  Google Scholar

  20. 20.

    Kraft, A.D., and G.J. Harry. 2011. Features of microglia and neuroinflammation relevant to environmental exposure and neurotoxicity. International Journal of Environmental Research and Public Health 8 (7): 2980–3018. Article  PubMed  PubMed Central  Google Scholar

  21. 21.

    Teo, J.L., and M. Kahn. 2010. The Wnt signaling pathway in cellular proliferation and differentiation: a tale of two coactivators. Advanced Drug Delivery Reviews 62 (12): 1149–1155. CAS  Article  PubMed  Google Scholar

  22. 22.

    Die, L., et al. 2012. Glycogen synthase kinase-3 beta inhibitor suppresses Porphyromonas gingivalis lipopolysaccharide-induced CD40 expression by inhibiting nuclear factor-kappa B activation in mouse osteoblasts. Molecular Immunology 52 (1): 38–49. CAS  Article  PubMed  Google Scholar

  23. 23.

    Du, Q., and D.A. Geller. 2010. Cross-regulation between Wnt and NF-kappaB signaling pathways. For Immunopathol Dis Therap 1 (3): 155–181. Article  PubMed  PubMed Central  Google Scholar

  24. 24.

    Caricasole, A., et al. 2004. Induction of Dickkopf-1, a negative modulator of the Wnt pathway, is associated with neuronal degeneration in Alzheimer’s brain. The Journal of Neuroscience 24 (26): 6021–6027. CAS  Article  PubMed  Google Scholar

  25. 25.

    Rosi, M.C., et al. 2010. Increased Dickkopf-1 expression in transgenic mouse models of neurodegenerative disease. Journal of Neurochemistry 112 (6): 1539–1551. CAS  Article  PubMed  Google Scholar

  26. 26.

    Cappuccio, I., et al. 2005. Induction of Dickkopf-1, a negative modulator of the Wnt pathway, is required for the development of ischemic neuronal death. The Journal of Neuroscience 25 (10): 2647–2657. CAS  Article  PubMed  Google Scholar

  27. 27.

    Busceti, C.L., et al. 2007. Induction of the Wnt inhibitor, Dickkopf-1, is associated with neurodegeneration related to temporal lobe epilepsy. Epilepsia 48 (4): 694–705. CAS  Article  PubMed  Google Scholar

Download references

Acknowledgements

This study was supported by BK20151159 from the Natural Science Foundation of Jiangsu Province, China, Project 81501185 of National Natural Science Foundation of China, Jiangsu Provincial Medical Youth Talent No.QNRC2016369, Xuzhou Medical Talents Project and Xuzhou technological and scientific project No. KC14SH050.

Print Friendly Version of this pagePrint Get a PDF version of this webpagePDF