The role of PERK and IRE1 signaling pathways in excessive fluoride mediated impairment of lymphocytes in rats' spleen in vivo and in vitro

Fluoride induces immunotoxicity by regulating riboflavin transport and metabolism partly through IL-17A in the spleen

The impairment of the immune system by fluoride is a public health concern worldwide, yet the underlying mechanism is unclear. Both riboflavin and IL-17A are closely related to immune function and regulate the testicular toxicity of fluoride. However, whether riboflavin or IL-17A is involved in fluoride-induced immunotoxicity is unknown. Here, we first established a male ICR mouse model by treating mice with sodium fluoride (NaF) (100 mg/L) via the drinking water for 91 days. The results showed that fluoride increased the expression of the proinflammatory factors IL-1β and IL-17A, which led to splenic inflammation and morphological injury. Moreover, the expression levels of the riboflavin transporters SLC52A2 and SLC52A3; the transformation-related enzymes RFK and FLAD1; and the key mitochondrial functional determinants SDH, COX, and ATP in the spleen were measured via real-time PCR, Western blotting, and ELISA. The results revealed that fluoride disrupted riboflavin transport, transformation, metabolism, and mitochondrial function. Furthermore, wild-type (WT) and IL-17A knockout (IL-17A-/-) C57BL/6 J male mice of the same age were treated with NaF (24 mg/kg·bw, equivalent to 100 mg/L) and/or riboflavin sodium phosphate (5 mg/kg·bw) via gavage for 91 days. Similar parameters were evaluated as above. The results confirmed that fluoride increased riboflavin metabolism through RFK but not through FLAD1. Fluoride also affected mitochondrial function and activated neutrophils (marked with Ly6g) and macrophages (marked with CD68) in the spleen. Interestingly, IL-17A partly mediated fluoride-induced riboflavin metabolism disorder and immunotoxicity in the spleen. This work not only reveals a novel toxic mechanism for fluoride but also provides new clues for exploring the physiological function of riboflavin and for diagnosing and treating the toxic effects of fluoride in the environment.

Combined exposure of PS-MPs with NaF induces Sertoli cell death and dysfunction via ferroptosis and apoptosis

The individual toxicity of sodium fluoride (NaF) and microplastics (MPs) has been extensively documented. Owing to their high specific surface area, widespread presence and durability, MPs can adsorb a broad spectrum of environmental contaminants into the organism. However, the combined toxicity of NaF and MPs has not been investigated. This study aimed to assess the effects of combined exposure to NaF and MPs on the function of testicular Sertoli cells (SCs) in male mice, and to investigate the underlying molecular mechanisms. The study revealed that combined exposure to NaF and MPs resulted in a decrease in the negative surface charge of MPs, along with an increase in the number of MPs entering the SCs. Through in vivo observation of the testicular pathological structure, spermatogenesis, and cell apoptosis in 180-day-old male mice, we discovered that combined exposure to NaF (80 mg/L) and MPs (10 mg/L) heightened reproductive toxicity compared to the individual exposure groups. This was evidenced by testicular structural defects, impaired spermatogenesis, and increased testicular cell apoptosis. Our in vitro studies showed that NaF (21 μg/mL) and MPs (100 μg/mL) synergistically induced SCs apoptosis and ferroptosis, leading to a reduction in SCs number and dysfunction. This ultimately resulted in structural and functional damage to the testes. Our findings demonstrate, for the first time, the synergistic effects of NaF and MPs on reproductive toxicity in mammals. These insights may provide valuable contributions to co-toxicity studies involving MPs and other environmental pollutants.

Progress in research on the role of fluoride in immune damage

Excessive fluoride intake from residential environments may affect multiple tissues and organs; however, the specific pathogenic mechanisms are unclear. Researchers have recently focused on the damaging effects of fluoride on the immune system. Damage to immune function seriously affects the quality of life of fluoride-exposed populations and increases the incidence of infections and malignant tumors. Probing the mechanism of damage to immune function caused by fluoride helps identify effective drugs and methods to prevent and treat fluorosis and improve people's living standards in fluorosis-affected areas. Here, the recent literature on the effects of fluoride on the immune system is reviewed, and research on fluoride damage to the immune system is summarized in terms of three perspectives: immune organs, immune cells, and immune-active substances. We reviewed that excessive fluoride can damage immune organs, lead to immune cells dysfunction and interfere with the expression of immune-active substances. This review aimed to provide a potential direction for future fluorosis research from the perspective of fluoride-induced immune function impairment. In order to seek the key regulatory indicators of fluoride on immune homeostasis in the future.

Preparation, characterization and immune response of chitosan‑gold loaded Myricaria germanica polysaccharide

In this study, a novel nano-drug delivery system (CS-Au NPs) based on gold nanoparticles (Au NPs) and chitosan (CS) that modified Myricaria germanica polysaccharide (MGP) was developed to enhance immune responses. At a MGP to CS Au ratio of 5:1, CS-Au-MGP NPs had a loading capacity of 78.27 %. The structure of CS-Au-MGP NPs were characterized by Transmission electron microscope, TEM-energy dispersive spectroscopy mapping, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer, particle size and zeta-potential distribution analysis. Under weakly acidic conditions, in vitro CS-Au-MGP NPs release was most effective. In vivo showed that co-immunization with CS-Au-MGP NPs and PCV2 significantly increased the organ index of the thymus, spleen, and liver in mice. Additionally, CS-Au-MGP NPs significantly increased the levels of IgG, IgG1, and IgG2a antibodies, as well as IFN-γ and IL-6 levels. Furthermore, the CS-Au-MGP NPs promoted proliferation of spleen T and B lymphocytes, increased the number of CD3+, CD4+, and CD8+ cells, and increased the CD4+/CD8+ T cell ratio. Meanwhile, CS-Au-MGP NPs remarkably TLR2/IRAK4 pathway activation and mRNA levels of cytokines (IFN-γ and IL-6). These results indicated that CS-Au-MGP NPs could enhance the immune activity, and it could be potentially used as an MGP delivery system for the induction of strong immune responses.

Fluoride-induced apoptosis in non-skeletal tissues of experimental animals: A systematic review and meta-analysis

Different studies have suggested that fluoride can induce apoptosis in non-skeletal tissues, however, evidence from these experimental studies is still controversial. This meta-analysis aims to clarify the mechanism of fluoride-induced apoptosis in non-skeletal tissues of experimental animals. Primary studies which measured apoptosis were identified through exhaustive database searching in PubMed, Embase, Web of Science Core Collection, Scopus, and references of included studies. A random effects model with standardized mean difference (SMD) was used for meta-analyses. The heterogeneity of the studies was evaluated using Higgin's I2 statistics. The risk of bias and publication bias were assessed using the SYRCLE's risk of bias tool and Egger's test, respectively. There was an increase in total apoptotic cells, and the expression of Bax, Bax/Bcl-2 ratio, caspase-3, caspase-8, caspase-9, Cyt c, and p53, and a decrease in the expression of Bcl-2 in the fluoride-treated groups as compared to the control groups. However, there was no evidence of a difference in the expression of APAF-1 in the two groups. The subgroup analysis highlighted the role of the intervention period in modification of the apoptotic effect of fluoride and that the susceptibility and tolerance of different animal species and tissues vary. Meta-regression analysis indicated that the studies' effect size for total apoptotic cells was influenced by animal species and that of Bax by the sample source. The results of this meta-analysis revealed that fluoride causes apoptosis by up-regulating caspase-3, -8, and -9, Cyt c, p53, Bax, and down-regulating Bcl-2 with a concomitant up-regulation of the Bax/Bcl-2 ratio.

Necessity to Pay Attention to the Effects of Low Fluoride on Human Health: an Overview of Skeletal and Non-skeletal Damages in Epidemiologic Investigations and Laboratory Studies

Due to the implementation of water improvement and fluoride reduction plans supported by central and local governments in recent years, areas with high fluoride exposure are being gradually decreased. Therefore, it is of practical importance to study the effect of low fluoride on human health. Epidemiologic investigations and in vivo and in vitro studies based on low fluoride have also confirmed that fluoride not only causes skeletal damage, such as dental fluorosis, but also causes non-skeletal damage involving the cardiovascular system, nervous system, hepatic and renal function, reproductive system, thyroid function, blood glucose homeostasis, and the immune system. This article summarizes the effects of low fluoride on human and animal skeletal and non-skeletal systems. A preliminary exploration of corresponding mechanisms that will help to fully understand the harm of low fluoride on human health was undertaken to provide the basis for establishing new water fluoride standards and help to implement individual guidance.

Polystyrene nanoplastics aggravates lipopolysaccharide-induced apoptosis in mouse kidney cells by regulating IRE1/XBP1 endoplasmic reticulum stress pathway via oxidative stress

Nanoplastics (NPs) pollution poses a huge threat to the ecosystem and has become one of the environmental pollutants that have attracted much attention. There is increasing evidence that both oxidative stress and endoplasmic reticulum stress (ERS) are associated with polystyrene nanoplastics (PS-NPs) exposure. Lipopolysaccharide (LPS) has been shown to induce apoptotic damage in various tissues, but whether PS-NPs can aggravate LPS-induced apoptosis in mouse kidneys through oxidative stress-regulated inositol-requiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) ERS pathway remains unclear. In this study, based on the establishment of in vitro and in vivo PS-NPs and LPS exposure models alone and in combination in mice and HEK293 cells, the effects and mechanisms of PS-NPs on LPS-induced renal cell apoptosis were investigated. The results showed that PS-NPs could aggravate LPS-induced apoptosis. PS-NPs/LPS can induce ERS through oxidative stress, activate the IRE1/XBP1 pathway, and promote the expression of apoptosis markers (Caspase-3 and Caspase-12). Kidney oxidative stress, ERS, and apoptosis in PS-NPs + LPS combined exposure group were more severe than those in the single exposure group. Interestingly, 4-phenylbutyric acid-treated HEK293 cells inhibited the expression of the IRE1/XBP1 ERS pathway and apoptotic factors in the PS-NPs + LPS combined exposure group. N-acetyl-L-cysteine effectively blocked the activation of the IRE1/XBP1 ERS pathway, suggesting that PS-NPs-induced oxidative stress is an early event that triggers ERS. Collectively, these results confirmed that PS-NPs aggravated LPS-induced apoptosis through the oxidative stress-induced IRE1/XBP1 ERS pathway. Our study provides new insights into the health threats of PS-NPs exposed to mammals and humans.

Role of oxidative stress-mediated cell death and signaling pathways in experimental fluorosis

Free radicals and other oxidants have enticed the interest of researchers in the fields of biology and medicine, owing to their role in several pathophysiological conditions, including fluorosis (Fluoride toxicity). Radical species affect cellular biomolecules such as nucleic acids, proteins, and lipids, resulting in oxidative stress. Reactive oxygen species-mediated oxidative stress is a common denominator in fluoride toxicity. Fluorosis is a global health concern caused by excessive fluoride consumption over time. Fluoride alters the cellular redox homeostasis, and its toxicity leads to the activation of cell death mechanisms like apoptosis, autophagy, and necroptosis. Even though a surfeit of signaling pathways is involved in fluorosis, their toxicity mechanisms are not fully understood. Thus, this review aims to understand the role of reactive species in fluoride toxicity with an outlook on the effects of fluoride in vitro and in vivo models. Also, we emphasized the signal transduction pathways and the mechanism of cell death implicated in fluoride-induced oxidative stress.

Effect of Fluoride on Cytotoxicity Involved in Mitochondrial Dysfunction: A Review of Mechanism

Fluoride is commonly found in the soil and water environment and may act as chronic poison. A large amount of fluoride deposition causes serious harm to the ecological environment and human health. Mitochondrial dysfunction is a shared feature of fluorosis, and numerous studies reported this phenomenon in different model systems. More and more evidence shows that the functions of mitochondria play an extremely influential role in the organs and tissues after fluorosis. Fluoride invades into cells and mainly damages mitochondria, resulting in decreased activity of mitochondrial related enzymes, weakening of protein expression, damage of respiratory chain, excessive fission, disturbance of fusion, disorder of calcium regulation, resulting in the decrease of intracellular ATP and the accumulation of Reactive oxygen species. At the same time, the decrease of mitochondrial membrane potential leads to the release of Cyt c, causing a series of caspase cascade reactions and resulting in apoptosis. This article mainly reviews the mechanism of cytotoxicity related to mitochondrial dysfunction after fluorosis. A series of mitochondrial dysfunction caused by fluorosis, such as mitochondrial dynamics, mitochondrial Reactive oxygen species, mitochondrial fission, mitochondrial respiratory chain, mitochondrial autophagy apoptosis, mitochondrial fusion disturbance, mitochondrial calcium regulation are emphasized, and the mechanism of the effect of fluoride on cytotoxicity related to mitochondrial dysfunction are further explored.

The potential risks of herbicide butachlor to immunotoxicity via induction of autophagy and apoptosis in the spleen

Butachlor being an important member of chloroacetanilide herbicides, is frequently used in agriculture to control unwanted weeds. Exposure to butachlor can induce cancer, human lymphocyte aberration, and immunotoxic effects in animals. The current experimental trial was executed to determine the potential risks of herbicide butachlor to immunotoxicity and its mechanism of adverse effects on the spleen. For this purpose, mice were exposed to 8 mg/kg butachlor for 28 days, and the toxicity of butachlor on the spleen of mice was evaluated. We found that butachlor exposure led to an increase in serum ALB, GLU, TC, TG, and TP and changes in the morphological structure of the spleen of mice. More importantly, results showed that butachlor significantly increased the expression level of ATG-5, decreased the protein expression of LC3B and M-TOR, and significantly decreased the mRNA content of M-TOR and p62. Results revealed that the mRNA contents of APAF-1, CYTC, and CASP-9 related genes were significantly decreased after butachlor treatment. Subsequently, the mRNA levels of inflammatory cytokines (IL-1β, TNF-α, IL-10) were reduced in the spleen of treated mice. This study suggested that butachlor induce spleen toxicity and activate the immune response of spleen tissue by targeting the CYTC/BCL2/M-TOR pathway and caspase cascading activation of spleen autophagy and apoptosis pathways which may ultimately lead to immune system disorders.

Upregulation of miR-200c-3p induced by NaF promotes endothelial apoptosis by activating Fas pathway

Fluoride has been considered as a risk factor of cardiovascular disease due to its endothelial toxicology. However, the mechanism underlying the endothelial toxicity of fluoride has not been clearly illustrated. MiR-200c-3p was strongly linked with endothelial function and its level is increased in serum of fluorosis patients, but it is unclear the role of miR-200c-3p in the fluoride induced endothelial dysfunction. In this study, we confirmed that fluoride exposure induced the apoptosis of endothelial cells both in established rats model and cultured human umbilical vein endothelial cells (HUVECs). And miR-200c-3p was found to be upregulated in NaF treated HUVECs. Fluoride stimulation increased caspase-dependent apoptosis through miR-200c-3p upregulation, with repressing expression of its target gene Fas-associated phosphatase 1 (Fap-1), which functioned as Fas inhibitor. This resulted in activation of Fas-associated extrinsic apoptosis via interaction with increased Fas, Fadd, Cleaved Caspase-8 and Cleaved Caspase-3. The activation of Fas-associated extrinsic apoptosis was abrogated by miR-200c-3p inhibitor. Furthermore, the antiapoptotic effect of downregulated miR-200c-3p was restored by Fap-1 siRNA. These results suggested a determinant role of the miR-200c-3p/Fap-1 axis in fluoride induced endothelial apoptosis.

Sodium fluoride exposure triggered the formation of neutrophil extracellular traps

In recent years, numerous studies paid more attention to the molecular mechanisms associated with fluoride toxicity. However, the detailed mechanisms of fluoride immunotoxicity in bovine neutrophils remain unclear. Neutrophil extracellular traps (NETs) is a novel immune mechanism of neutrophils. We hypothesized that sodium fluoride (NaF) can trigger NETs activation and release, and investigate the related molecular mechanisms during the process. We exposed peripheral blood neutrophils to 1 mM NaF for 120 min in bovine neutrophils. The results showed that NaF exposure triggered NET-like structures decorated with histones and granule proteins. Quantitative measurement of NETs content correlated positively with the concentration of NaF. Mechanistically, NaF exposure increased reactive oxygen species (ROS) levels and phosphorylation levels of ERK, p38, whereas inhibiting the activities of superoxide dismutase (SOD) and catalase (CAT) compared with control neutrophils. NETs formation is induced by NaF and this effect was inhibited by the inhibitors diphenyleneiodonium chloride (DPI), U0126 and SB202190. Our findings described the potential importance of NaF-triggered NETs related molecules, which might help to extend the current understanding of NaF immunotoxicity.

Effect of Peptides from Alaska Pollock on Intestinal Mucosal Immunity Function and Purification of Active Fragments

The intestinal mucosal barrier plays an important role in systemic immune functions. This study aimed to find the mechanism of peptide from Alaska Pollock (APP) on intestinal mucosal immunity in mice induced by cyclophosphamide (Cy). Cy-induced decreases of body weight and index of immune organ were significantly improved by APP as compared with Cy group (p < 0.05). APP could promote the secretion of SIgA and IgA on intestinal mucosa (p < 0.05) and mainly had an impact on the final differentiation of IgA⁺ B cell, thereby promoting the secretion of plasma cells, which can be corroborated by the increases of IL-6 and IL-10 (p < 0.05). APP with high immune activity was separated and two peptides were purified and identified as Gly–Val–Ile–Lys and Ala–Cys–Asn–Gly–Arg. Therefore, APP can be considered as beneficial ingredients to protect the intestinal barrier disruption induced by Cy.