A Bayesian benchmark concentration analysis for urinary fluoride and intelligence in adults in Guizhou, China

Low Fluoride Regulates Macrophage Polarization Through Mitochondrial Autophagy Mediated by PINK1/Parkin Axis

Fluoride exposure has been shown to affect immune cell subsets and immune function, but its impact on macrophage polarization remains unclear. This study investigates the effects of low fluoride exposure on macrophage polarization and its underlying mechanisms through epidemiological surveys, animal experiments, and in vitro cell experiments. In the population-based epidemiological survey, we used mass cytometry to assess the impact of low fluoride exposure (0.570-2.027 mg/L) in the environment on human immune cell populations following the current water improvement and fluoride reduction measures. A rat fluorosis model was established by treating rats with sodium fluoride (NaF) in drinking water at concentrations of 0 mg/L, 5 mg/L, 10 mg/L, 25 mg/L, and 50 mg/L for 90 days., and morphological changes were assessed by hematoxylin-eosin (H&E) staining and transmission electron microscopy in the spleen of rats. Flow cytometry was used to analyze the proportion of macrophage subtypes in the spleen, while Western blot and immunofluorescence were performed to detect the expression of mitochondrial autophagy-related proteins. An M1 macrophage model was constructed in vitro by inducing THP-1 cells, and the effects of fluoride on macrophage-related cell markers and cytokines were assessed using flow cytometry and ELISA, respectively, following intervention with an autophagy inhibitor. Mitochondrial membrane potential and mitochondrial-lysosomal colocalization are analyzed through flow cytometry and confocal microscopy. The study aims to investigate the role of mitophagy in sodium fluoride-induced macrophage polarization. Epidemiological investigations revealed that low fluoride increases the proportion of blood monocytes, as well as the expression levels of CD68 (a macrophage surface marker), CD86 (an M1 macrophage marker), and the inflammatory cytokine IFN-γ in peripheral blood mononuclear cells (PBMCs). In the rats of NaF-treated groups, splenic tissues exhibited inflammatory infiltration, mitochondrial swelling, and increased autophagosome formation. Moreover, low fluoride activated the PINK1/Parkin-mediated mitophagy pathway, promoting an increase in the M2/M1 macrophage ratio. In vitro experiments further confirmed that autophagy inhibitors reversed the NaF-induced increase in the M2/M1 macrophage ratio. This study demonstrates that low fluoride induces inflammatory responses in the body and drives M1 macrophage polarization toward M2 macrophages via mitophagy. These findings highlight the potential immunological risks associated with low fluoride and provide mechanistic insights into the interplay among fluoride, mitophagy, and macrophage polarization.

Impact of high lodine and fluoride intake on children's IQ in rural China

BACKGROUND

Excessive intake of both fluorine and iodine can lead to various health effects. The potential influence of excessive fluorine and iodine intake on the intelligence of school-age children has become a notable concern.

OBJECTIVES

To investigate the relationship between urinary fluoride (UF) levels, urinary iodine (UI) levels, and intelligence quotient (IQ).

METHODS

This study involved 711 children aged 8 to 12 from rural Jiangsu, China. Water iodine levels were measured using As3+-Ce4+ catalytic spectrophotometry, while UI levels were determined using inductively coupled plasma mass spectrometry. Fluoride levels in urine and drinking water were measured using the ion-selective electrode method. Children's cognitive function, evaluated through IQ scores, was assessed using the Combined Raven's Test. The results were considered significant at the P < 0.05 level.

RESULTS

The average IQ score was 107.6, the median UF was 281 µg/L, and the median UI was 1.39 mg/L. The correlation coefficient (β) and confidence interval (95%CI) for UF and UI on IQ were - 3.34 (-4.14, -2.43) and - 3.31 (-4.19, -2.41), respectively (P < 0.001, P < 0.001). UF > 1.4 mg/L and UI ≥ 300 µg/L were negatively correlated with IQ scores in all school-age children (P < 0.001, P < 0.001), with β and 95% CIs of -3.59 (-5.45, -1.74), -4.06 (-5.91, -2.21), respectively. The interaction term (UF > 1.4 mg/L: UI ≥ 300 µg/L) was negatively correlated with IQ scores in all (P = 0.041) and female school-age children (P = 0.007), with β and 95%CIs of -4.43 (-8.66, -0.19) and - 8.87 (-15.16, -2.40), respectively.

CONCLUSIONS

High levels of both fluoride and iodine intake negatively affect the IQ of school-age children. Monitoring and regulating these elements in children's diets is essential to prevent cognitive impairment.

Fluoride-Mediated Immune Damage Through Cytokine Network Regulation of Tregs

Long-term fluoride exposure can induce inflammatory responses in various tissues of the body, thereby affecting the inflammatory microenvironment. To explore how fluoride induces changes in immune function within this microenvironment, this study collected baseline information and biological samples from participants in areas with the drinking water type of fluorosis, and simultaneously established Wistar rat models with a 12-week and 24-week fluoride exposure, as well as a 12-week fluoride exposure followed by 12-week pure water feeding regimen. Luminex multiplex assays and enzyme-linked immunosorbent assays (ELISAs) were used to measure cytokine expression levels. Subsequently, correlation analysis, multiple linear regression, and mediation analysis were employed to explore the long-term effects induced by the complex cytokine network during fluoride exposure. The population survey results indicated that fluoride suppressed the expression of pro-inflammatory factors such as Interleukin-2 (IL-2), Interleukin-12 (IL-12), Interferon-γ (IFN-γ), Tumor necrosis factor-α (TNF-α), and anti-inflammatory factors such as Interleukin-4 (IL-4), Interleukin-13 (IL-13), and Interleukin-37 (IL-37), while promoting an increase in the proportion of regulatory T cells (Tregs) in peripheral blood. Among these, IL-2 and IFN-γ mediated the fluoride-induced peripheral Tregs expansion. Animal experiments indicate that the proportion of Tregs in peripheral blood and immune organs increases in a time-dependent manner with fluoride exposure. After reducing the fluoride concentration in the drinking water of rats, the number of Tregs remained significantly elevated. The changes in Treg numbers in the 12-week fluoride feeding group, 24-week fluoride feeding group, and 12-week fluoride feeding followed by 12-week water improvement group were related to the cytokine levels. Therefore, the impact of fluoride on the immune homeostasis has cumulative and long-term effects, and may be related to the accumulation and migration of Tregs induced by fluoride in an inflammatory environment, mediated by cytokines.

Analysis of Acute and Short-Term Fluoride Toxicity in Zebrafish Embryo and Sac-Fry Stages Based on Bayesian Model Averaging

Acute and short-term toxicity tests are foundational to toxicology research. These tests offer preliminary insights into the fundamental toxicity characteristics of the chemicals under evaluation and provide essential data for chronic toxicity assessments. Fluoride is a common chemical in aquatic environments; however, the findings of toxicological data, such as LC50 for aquatic organisms, often exhibit inconsistency. Consequently, this study employed zebrafish as a model organism during their early life stages to assess the acute and short-term toxicity of fluoride exposure. Bayesian model averaging was utilized to calculate the LC50/EC50 values and establish baseline concentrations. The results indicated a dose-response relationship between water fluoride concentration and harmful outcomes. The 20 mg/L group was identified as the lowest observed adverse effect level (LOAEL) for the majority of toxicity indicators and warrants special attention. Based on the BBMD model averages, the LC50 of fluoride for 1 to 5 days post-fertilization (dpf) zebrafish was 147.00, 80.80, 61.25, 56.50, and 37.50 mg/L, while the EC50 of cumulative malformation rate for 5 dpf zebrafish was 59.75 mg/L. As the benchmark response (BMR) increased, both the benchmark concentrations (BMCs) and benchmark dose levels (BMDLs) also increased. The research aims to provide essential data for the development of environmental water guidelines and to mitigate ecological risks associated with fluoride in aquatic ecosystems.