Abstract
Although the literature does not provide evidence of health risks from exposure to fluoride (F) in therapeutic doses, questions remain about the effects of long-term and high-dose use on the function of the central nervous system. The objective of this study was to investigate the effect of long-term exposure to F at levels similar to those found in areas of artificial water fluoridation and in areas of endemic fluorosis on biochemical, proteomic, cell density, and functional parameters associated with the cerebellum. For this, mice were exposed to water containing 10 mg F/L or 50 mg F/L (as sodium fluoride) for 60 days. After the exposure period, the animals were submitted to motor tests and the cerebellum was evaluated for fluoride levels, antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (MDA), and nitrite levels (NO). The proteomic profile and morphological integrity were also evaluated. The results showed that the 10 mg F/L dose was able to decrease the ACAP levels, and the animals exposed to 50 mg F/L presented lower levels of ACAP and higher levels of MDA and NO. The cerebellar proteomic profile in both groups was modulated, highlighting proteins related to the antioxidant system, energy production, and cell death, however no neuronal density change in cerebellum was observed. Functionally, the horizontal exploratory activity of both exposed groups was impaired, while only the 50 mg F/L group showed significant changes in postural stability. No motor coordination and balance impairments were observed in both groups. Our results suggest that fluoride may impair the cerebellar oxidative biochemistry, which is associated with the proteomic modulation and, although no morphological impairment was observed, only the highest concentration of fluoride was able to impair some cerebellar motor functions.
Highlights
Fluoride is naturally present in the earth’s crust and is frequent in a variety of environments [1]
According to the recommendations of the World Health Organization (WHO), the optimal fluoride concentration in supply waters is in the range of 0.5–1 mg/L, which can be adjusted between 0.7–1.2 mg/L depending on the mean local temperature [3,4]
The prolonged exposure to fluoride promoted significant differences in the levels of fluoride in the cerebellum of animals exposed to 50 mg F/L (0.10 ± 0.014 μg/g) compared to the control group (0.05 ± 0.01 μg/g; p = 0.03) and 10 mg F/L group (0.05 ± 0.009 μg/g; p = 0.02)
Summary
Fluoride is naturally present in the earth’s crust and is frequent in a variety of environments [1]. This ion does not exist in an isolated form, always being associated with other elements constituting fluoridated compounds, which are found in rock minerals and volcanic soil [2]. Water is one of the main sources of systemic exposure to fluoride. This ion can be naturally present in the water, due to the geological sources, or can be artificially added to public water distribution systems, with anticariogenic purposes, at controlled concentrations [2]. It is important to consider that some regions naturally present high levels of fluoride for natural or anthropogenic reasons; in this way, it is necessary to control the artificial fluoridation levels in order to assure efficacy for caries control and safety [5]
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