Fluoride exposure alters Ca ²⁺ signaling and mitochondrial function in enamel cells

Abstract

Fluoride ions are highly reactive, and their incorporation in forming dental enamel at low concentrations promotes mineralization. In contrast, excessive fluoride intake causes dental fluorosis, visually recognizable enamel defects that can increase the risk of caries. To investigate the molecular bases of dental fluorosis, we analyzed the effects of fluoride exposure in enamel cells to assess its impact on Ca2+ signaling. Primary enamel cells and an enamel cell line (LS8) exposed to fluoride showed decreased internal Ca2+ stores and store-operated Ca2+ entry (SOCE). RNA-sequencing analysis revealed changes in gene expression suggestive of endoplasmic reticulum (ER) stress in fluoride-treated LS8 cells. Fluoride exposure did not alter Ca2+ homeostasis or increase the expression of ER stress–associated genes in HEK-293 cells. In enamel cells, fluoride exposure affected the functioning of the ER-localized Ca2+ channel IP3R and the activity of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pump during Ca2+ refilling of the ER. Fluoride negatively affected mitochondrial respiration, elicited mitochondrial membrane depolarization, and disrupted mitochondrial morphology. Together, these data provide a potential mechanism underlying dental fluorosis.

Comparison of hydroxyapatite and fluoride oral care gels for remineralization of initial caries: a pH-cycling study

“…Caries preventive agents should preferably be used on a daily basis to maintain a preventive concentration of the agent in oral cavity at all times. 47 Furthermore, on a risk/benefit ratio, while high fluoride concentration dentifrices can only be used by adults due to the risk of fluorosis in children, 20,50 HAP-based dentifrices and gels at any concentration can be used by all ages since no adverse effect has been reported in previous clinical studies. 4,12,35 This would go further to eliminate having different dosages for infants, children and adults, as it is the case with fluoride at the moment.…”

“…are combined. 20,21 Consequently, highly concentrated fluoride gels should not be used on a daily basis as daily oral care routine at home. However, daily oral health care regimen has been shown to have positive effects on oral health.…”

Impact of a toothpaste with microcrystalline hydroxyapatite on the occurrence of early childhood caries: a 1-year randomized clinical trial

“…sodium monofluorophosphate (Na 2 PO 3 F), or stannous fluoride (SnF 2 ) are well-known for their caries preventing effect and consequently they are frequently used in many toothpaste formulations 6,14,[16][17][18] . However, it is known that infants and toddlers swallow a substantial proportion of the applied toothpaste during toothbrushing [19][20][21][22][23][24] , which can increase the systemic uptake of fluorides beyond a threshold associated with the occurrence of dental fluorosis and other unwanted side effects 19,25 . Therefore, in many countries toothpastes for children contain a reduced amount of fluorides compared to toothpastes for adults 17 .…”

Calcium Transport in Specialized Dental Epithelia and Its Modulation by Fluoride

“…A recent study using rat primary ameloblasts and LS8 cells exposed to various concentrations of fluoride in vitro showed decreased internal Ca 2+ in the ER and SOCE ( 76 ). These effects were observed when using high NaF concentrations (0.5 mM, 1 mM), equivalent to ~9 ppm and 18 ppm, respectively.…”

“…These effects were observed when using high NaF concentrations (0.5 mM, 1 mM), equivalent to ~9 ppm and 18 ppm, respectively. In primary ameloblasts, these fluoride treatments decreased the ER Ca 2+ within 30 minutes of incubation, and resulted in ER stress ( 76 ). LS8 cells exposed to bromide (NaBr) did not change these functions.…”