Fluoride (F) is a naturally exists in nature but several studies have indicated it as an environmental toxicant to all leaving beings. Human F exposure has increased over the years since this ion has been used by industry on foods, beverages, toothpastes and on water supply. Although F is safe at optimal concentrations in water supply, human exposure to high levels could trigger neurofunctional deficits.
Materials and methods
In this study, human glial-like (U87) and neuronal-like (IMR-32) cells lineages were used to access F toxicity and CNS cell sensibility on both cell facing the same protocol. Cells were exposed to F over 3, 5 and 10 days on two different F concentrations. Fluoride exposed cells were evaluated by standard toxicity assays to cell viability, apoptosis, necrosis and general cell metabolism. Oxidative stress parameters were evaluated by ATP and ROS levels, lipid peroxidation, GSH/GSSG ratio and comet assay.
No changes were observed in IMR-32 at any given time while after 10 days of exposure to 0.22?g/mL, U87 glial-like cells showed signs of toxicity such as decreased cell viability by necrosis while general cell metabolism was increased. Oxidative stress parameters were next evaluated only on U87 glial-like cells after 10 days of exposure. F induced a decrease on ATP levels while no changes were observed on reactive oxygen species and lipid peroxidation. GSH/GSSG ratio was decreased followed by DNA damage both on 0.22?g/mL F.
Our results suggest an important differential behavior of the distinct types of cells exposed to the different fluoride concentrations, pointing that the U87 glial-like cells as more susceptible to damage triggered by this ion.
*Full-text article online at https://doi.org/10.1371/journal.pone.0251200
When comparing the F-induced toxicity on neurons and glial cells, it is important to highlight that most studies have used neurons and only two have investigate de glial cells behavior after F exposure [21, 36]. The effect of F on neuronal cell viability is inconsistent across the studies with doses ranging from 18.09 ?g/mL to 36.18 ?g/mL while glia/astrocytes seems to shown decreased cell viability above 19 ?g/mL. As our study is the first one to compare both types of cells facing the same parameters we may suggest that at those conditions presented here, U87 glial cells may respond worse to F toxicity than IMR-32 cells.
21. Flores-Mendez M., et al., Fluoride exposure regulates the elongation phase of protein synthesis in cultured Bergmann glia cells. Toxicol Lett, 2014. 229(1): p. 126–33. pmid:24954634. View Article – PubMed/NCBI
36. Li H., et al., [Toxic effects of fluoride on rat cerebral cortex astrocytes in vitro]. Wei Sheng Yan Jiu, 2010. 39(1): p. 86–8. pmid:20364598. View Article – PubMed/NCBI