Disruption of the core intestinal microbiota contributes to fluoride-induced neurotoxicity in the host organisms.

Excessive fluorine intake has received increasing global attention due to its widespread environmental occurrence and well-documented adverse effects on human health. Fluoride commonly occurs in nature as fluorite, primarily composed of CaF₂. In addition, synthetic organic fluorides, such as per– and polyfluoroalkyl substances (PFASs), are widely applied as surface protectants in both household and industrial products. Due to the high stability of the CF bond, PFASs exhibit remarkable resistance to environmental degradation (Wu et al., 2022; Chen et al., 2015). Fluoride concentrations in groundwater across North and South America, China, India, Italy, Spain, and Holland frequently exceed recommended safety thresholds for human consumption (Kumar et al., 2024). Fluoride exposure occurs through multiple pathways, including fluoridated water, pharmaceuticals, toothpaste, cosmetics, dental products, beverages such as tea, and animal-derived foods from fluoride-contaminated environments. Moreover, pesticides, fertilizers, industrial effluents, and atmospheric emissions further contribute to fluoride exposure through both direct and indirect routes (Sharma et al., 2022).

Accumulating epidemiological evidence indicates that fluorosis is associated with impairments in cognitive functions, including attention, learning, and memory, as well as neuropsychiatric manifestations such as anxiety, tension, and depression (Ren et al., 2022). Mechanistic studies have demonstrated that excessive fluoride intake can cross the blood–brain barrier, accumulate in neural tissues, and induce neurotoxicity (Bartos et al., 2022). Fluoride accumulation affects the synthesis and receptor expression of neurotransmitters, which are critical regulators of nervous system function (Reddy et al., 2014; Reddy et al., 2021). Fluoride-induced neurotoxicity likely involves neurotransmitters such as acetylcholine, glutamate, epinephrine, serotonin, norepinephrine, and dopamine (Ren et al., 2022). Both in vitro and in vivo studies demonstrated that fluoride exposure increases reactive oxygen species (ROS) levels by inducing lipid peroxidation, reducing GSH levels, and inhibiting antioxidant enzyme activity (Shuhua et al., 2012; Adedara et al., 2017; Dec et al., 2020). Fluoride neurotoxicity appears to be dose–dependent. Chronic exposure to low-dose fluoride disrupts amino acid and lipid metabolism (Dec et al., 2020), whereas acute high-dose exposure may lead to severe neurological outcomes, including seizures, coma, and even death (Kumar et al., 2024). Nevertheless, the precise molecular mechanisms underlying fluoride-induced neurotoxicity remain incompletely elucidated.

Recently, gut microbiota has been increasingly recognized as a critical modulator of fluorosis–related pathophysiology. The gut microbiota influences various physiological processes through the microbiota–gut–neuraxis, a bidirectional communication system linking the gut microbiome and the nervous system (Wang et al., 2023; Loh et al., 2024). Disruptions in gut microecology may contribute to fluoride neurotoxicity, thereby highlighting a potential microbiota-targeted strategy for mitigating cognitive impairment (Xin et al., 2020). Fluoride exposure has been shown to impair intestinal barrier function and cause microbiota dysbiosis in insects, laying hens, ducks, and mice (Li et al., 2022; Miao et al., 2020; Li et al., 2021; Fu et al., 2022). However, the mechanistic role of the gut microbiota in fluoride–induced neurotoxicity remains poorly understood, particularly in relation to neurotransmitter regulation. Therefore, elucidating microbiota–nervous system interactions under fluoride exposure is essential for advancing our understanding of fluoride-induced neurotoxicity.

The silkworm (Bombyx mori L.), an interspecies insect model, has been extensively utilized in various fields, including drug screening and evaluation, physiology, medicine, and toxicology (Li et al., 2020). As an experimental model, silkworms offer several advantages, such as low rearing costs, large progeny size, short generation time, and minimal ethical concerns (Meng et al., 2017; Ullah et al., 2025; Matsumoto and Sekimizu, 2019). In the present study, we utilized the silkworm model to systematically investigate the mechanisms underlying fluoride-induced neurotoxicity using an integrative approach, including enzyme activity assays, histopathological examination, real-time quantitative PCR (qPCR), and dual-omics analyses. This study aims to identify potential biomarkers and provide mechanistic insights into the prevention and intervention of fluoride-induced neural damage.