Bone cell mitogenic action of fluoroaluminate and aluminum fluoride but not that of sodium fluoride involves upregulation of the insulin-like growth factor system

Principles of fluoride toxicity and the cellular response: a review

Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.

The Effects of Fluoride on the Gap-Junctional Intercellular Communication of Rats' Osteoblast

The gap junction protein plays an important role in the bone formation and alteration of these proteins leading to cause bone development. Aim to determine the effects of different concentration of fluoride on gap-junctional intercellular communication (GJIC) related genes and proteins in the rats' osteoblast cells. We treated the osteoblast cells with various concentrations (0, 0.01, 0.1, 0.5, and 1.0 mM) NaF for 24 and 72 h. We used the scrape loading and dye transfer technique to research the intracellular connectivity. Moreover, the mRNA expression levels of connexin 43 (Cx43), connexin45 (Cx45), collagen I, and osteocalcin (OCN) were analyzed by qRT-PCR, the protein expression levels of connexin43 (Cx43) were analyzed by western blotting and immunofluorescence. Our results suggested that the osteoblast proliferations were decreased in the 0.5 and 1 mM NaF groups, after 24 and 72 treatments. The scrape loading and dye transfer experiment showed that the GJIC were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In addition, the mRNA expressions of Cx43, Cx45, and OCN, and the protein expressions of Cx43 were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In summary, these results suggest that the low concentration NaF is good for the GJIC, but the high concentration NaF damages the GJIC.

Analysis of the Role of Insulin Signaling in Bone Turnover Induced by Fluoride

The role of insulin signaling on the mechanism underlying fluoride induced osteopathology was studied. We analyzed the expression of genes related with bone turnover and insulin signaling in rats treated by varying dose of fluoride with or without streptozotocin (STZ) in vivo. Furthermore, insulin receptor (InR) expression in MC3T3-E1 cells (pre-osteoblast cell line) was interfered with small interfering RNA (siRNA), and genes related with osteoblastic and osteoclastic differentiation were investigated in cells exposed to fluoride in vitro for 2 days. The in vivo study indicated the possible role of insulin in bone lesion induced by excessive amount of fluoride. Fluoride activated the InR and Insulin-like growth factor 1 (IGF1) signaling, which were involved in the mechanism underlying fluoride induced bone turnover. The TGFβ1 and Wnt10/β-catenin pathway took part in the mechanism of bone lesion induced by fluoride, and insulin probably modulated the TGFβ1 and β-catenin to exert action on bone turnover during the development of bone lesion. The in vitro study showed the concomitant decrease of OPG, osterix and OCN with inhibition of InR expression in osteoblast, and three genes still was low in cells co-treated with fluoride and InR siRNA, which suggested that fluoride probably stimulated the expression of OPG, osterix and OCN through InR signaling. In conclusion, insulin played the important role in bone lesion induced by excessive amount of fluoride through mediating InR receptor signaling, and IGF1 signaling probably exerted action on bone turnover caused by overdose of fluoride.

Effects of thirty elements on bone metabolism

The human skeleton, made of 206 bones, plays vital roles including supporting the body, protecting organs, enabling movement, and storing minerals. Bones are made of organic structures, intimately connected with an inorganic matrix produced by bone cells. Many elements are ubiquitous in our environment, and many impact bone metabolism. Most elements have antagonistic actions depending on concentration. Indeed, some elements are essential, others are deleterious, and many can be both. Several pathways mediate effects of element deficiencies or excesses on bone metabolism. This paper aims to identify all elements that impact bone health and explore the mechanisms by which they act. To date, this is the first time that the effects of thirty minerals on bone metabolism have been summarized.

Fluoride's effects on the formation of teeth and bones, and the influence of genetics

Fluorides are present in the environment. Excessive systemic exposure to fluorides can lead to disturbances of bone homeostasis (skeletal fluorosis) and enamel development (dental/enamel fluorosis). The severity of dental fluorosis is also dependent upon fluoride dose and the timing and duration of fluoride exposure. Fluoride's actions on bone cells predominate as anabolic effects both in vitro and in vivo. More recently, fluoride has been shown to induce osteoclastogenesis in mice. Fluorides appear to mediate their actions through the MAPK signaling pathway and can lead to changes in gene expression, cell stress, and cell death. Different strains of inbred mice demonstrate differential physiological responses to ingested fluoride. Genetic studies in mice are capable of identifying and characterizing fluoride-responsive genetic variations. Ultimately, this can lead to the identification of at-risk human populations who are susceptible to the unwanted or potentially adverse effects of fluoride action and to the elucidation of fundamental mechanisms by which fluoride affects biomineralization.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.

The effect of fluoride contents in fluoridated hydroxyapatite on osteoblast behavior

Fluoridated hydroxyapatite (FHA) discs with various fluoride contents (0-0.567 mol F(-)/mol) [corrected] have been used to investigate the effect of fluoride content on osteoblastic cell behavior. SAOS-3 rat osteosarcoma cells were cultured on FHA discs for different time periods. The cell behavior was examined in terms of cell attachment, proliferation, morphology and differentiation. The fluoride content in FHA discs strongly affected the cell activities. More cell attachment and proliferation were observed on the fluoride-containing FHA discs than on pure hydroxyapatite (HA). The fluoride content also affected the differentiation behavior of osteoblastic cells. Cells on FHA discs demonstrated a higher alkaline phosphatase (ALP) activity than those on pure HA after 2 [corrected] weeks of culturing. These results suggested that fluoride ions have a significant impact on different osteoblastic cell activities.

Fluid shear stress synergizes with insulin-like growth factor-I (IGF-I) on osteoblast proliferation through integrin-dependent activation of IGF-I mitogenic signaling pathway

This study tested the hypothesis that shear stress interacts with the insulin-like growth factor-I (IGF-I) pathway to stimulate osteoblast proliferation. Human TE85 osteosarcoma cells were subjected to a steady shear stress of 20 dynes/cm(2) for 30 min followed by 24-h incubation with IGF-I (0-50 ng/ml). IGF-I increased proliferation dose-dependently (1.5-2.5-fold). Shear stress alone increased proliferation by 70%. The combination of shear stress and IGF-I stimulated proliferation (3.5- to 5.5-fold) much greater than the additive effects of each treatment alone, indicating a synergistic interaction. IGF-I dose-dependently increased the phosphorylation level of Erk1/2 by 1.2-5.3-fold and that of IGF-I receptor (IGF-IR) by 2-4-fold. Shear stress alone increased Erk1/2 and IGF-IR phosphorylation by 2-fold each. The combination treatment also resulted in synergistic enhancements in both Erk1/2 and IGF-IR phosphorylation (up to 12- and 8-fold, respectively). Shear stress altered IGF-IR binding only slightly, suggesting that the synergy occurred primarily at the post-ligand binding level. Recent studies have implicated a role for integrin in the regulation of IGF-IR phosphorylation and IGF-I signaling. To test whether the synergy involves integrin-dependent mechanisms, the effect of echistatin (a disintegrin) on proliferation in response to shear stress +/- IGF-I was measured. Echistatin reduced basal proliferation by approximately 60% and the shear stress-induced mitogenic response by approximately 20%. It completely abolished the mitogenic effect of IGF-I and that of the combination treatment. Shear stress also significantly reduced the amounts of co-immunoprecipitated SHP-2 and -1 with IGF-IR, suggesting that the synergy between shear stress and IGF-I in osteoblast proliferation involves integrin-dependent recruitment of SHP-2 and -1 away from IGF-IR.

Synthesis and characterization of fluorine-containing hydroxyapatite by a pH-cycling method

Different fluorine-containing hydroxyapatite (FHA) powders were synthesized through a pH-cycling method by varying sodium fluoride (NaF) concentration in hydroxyapatite (HA) suspensions. The powders were then calcined at 1200 ( composite function)C for 1 h. Both uncalcined and calcined powders were characterized using X-ray diffraction (XRD), Fourier transform infra-red (FTIR), and F-electrode. It was discovered that fluorine incorporation increased with the fluorine content in the initial solution and the number of pH cycles employed. A relatively low fluorine incorporation efficiency, approximately 60%, was attained for most of the FHA samples, and it did not vary significantly after calcination. It was also revealed that the FHA particles produced by the pH-cycling method were inhomogeneous. They were a mixture of hydroxyapatite and F-rich apatite (or FA) particles. After calcination, however, these FHA particles were homogenized and became single phased FHA.

The biochemistry and physiology of metallic fluoride: action, mechanism, and implications

Fluoride is a well-known G protein activator. Activation of heterotrimeric GTP-binding proteins by fluoride requires trace amounts of Al3+ or Be2+ ions. AlFx mimics a gamma-phosphate at its transition state in a Galpha protein and is therefore able to inhibit its GTPase activity. AlFx also forms complexes with small GTP-binding proteins in the presence of their GTPase-activating proteins (GAP). As phosphate analogs, AlFx or BeFx affect the activity of a variety of phosphoryl transfer enzymes. Most of these enzymes are fundamentally important in cell signal transduction or energy metabolism. Al3+ and F- tend to form stable complexes in aqueous solution. The exact structure and concentration of AlFx depend on the pH and the amount of F- and Al3+ in the solution. Humans are exposed to both F and Al. It is possible that Al-F complexes may be formed in vivo, or formed in vitro prior to their intake by humans. Al-F complexes may play physiological or pathological roles in bone biology, fluorosis, neurotoxicity, and oral diseases such as dental caries and periodontal disease. The aim of this review is to discuss the basic chemical, biochemical, and toxicological properties of metallic fluoride, to explore its potential physiological and clinical implications.