Fluoride increases rat osteoblast function and population after in vivo administration but not after in vitro exposure

Oral health knowledge, attitudes, and practices among female public health and nutrition university students in Qatar

Objectives

The present study aimed to determine oral health (OH) related knowledge, attitudes, and practices among Public Health (PH) and Nutrition (NU) students at Qatar University.

Method

A cross-sectional study was conducted using a pre-validated questionnaire comprising 36 items covering demographics, knowledge, attitudes and perception of oral health practices. Data were analyzed descriptively (means, standard deviations, proportions) and inferentially using statistical tests including t-tests for comparing means, and chi-square tests for examining associations between categorical variables.

Results

A total of 112 female undergraduate students participated, including 41 from PH and 71 from NU programs (response rate for both courses = 59.5%). The mean age was 21.8, while 23% were Qataris and 77% non-Qataris. Overall, students demonstrated good knowledge of OH (67.65%), with the PH group scoring higher (70.7%) than NU (65.35%). Knowledge regarding dental plaque was low for both groups (31.0%). Attitudes toward OH varied among participants. Most students reported practicing brushing with fluoridated toothpaste and demonstrated high knowledge regarding the association between poor OH and general health (95%).

Conclusion

Overall, PH and NU undergraduate students exhibited relatively good knowledge of OH, however, demonstrated a range of attitudes and practices, including suboptimal ones. Integration of OH education into the PH and NU curriculum is warranted, along with enhanced interprofessional education to promote self-awareness and improve patient oral health outcomes.

A Porous Fluoride-Substituted Bovine-Derived Hydroxyapatite Scaffold Constructed for Applications in Bone Tissue Regeneration

Hydroxyapatite is widely used in bone implantation because of its similar mineral composition to natural bone, allowing it to serve as a biocompatible osteoconductive support. A bovine-derived hydroxyapatite (BHA) scaffold was developed through an array of defatting and deproteinization procedures. The BHA scaffold was substituted with fluoride ions using a modified sol-gel method to produce a bovine-derived fluorapatite (BFA) scaffold. Fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that fluoride ions were successfully substituted into the BHA lattice. According to energy dispersive X-ray analysis, the main inorganic phases contained calcium and phosphorus with a fluoride ratio of ~1-2 wt%. Scanning electron microscopy presented a natural microporous architecture for the BFA scaffold with pore sizes ranging from ~200-600 μm. The BHA scaffold was chemically stable and showed sustained degradation in simulated-body fluid. Young's modulus and yield strength were superior in the BFA scaffold to BHA. In vitro cell culture studies showed that the BFA was biocompatible, supporting the proliferative growth of Saos-2 osteoblast cells and exhibiting osteoinductive features. This unique technique of producing hydroxyapatite from bovine bone with the intent of producing high performance biomedically targeted materials could be used to improve bone repair.

Absence of DNA damage in multiple organs (blood, liver, kidney, thyroid gland and urinary bladder) after acute fluoride exposure in rats

Fluoride has been widely used in dentistry as a caries prophylactic agent. However, there has been some speculation that excess fluoride could cause an impact on genome integrity. In the current study, the potential DNA damage associated with exposure to fluoride was assessed in cells of blood, liver, kidney, thyroid gland and urinary bladder by the single cell gel (comet) assay. Male Wistar rats aging 75 days were distributed into seven groups: Groups 1 (control), 2, 3, 4, 5, 6 and 7 received 0 (deionized water), 10, 20, 40, 60, 80 and 100 mgF/Kg body weight from sodium fluoride (NaF), respectively, by gastrogavage. These groups were killed at 2 h after the administration of the fluoride doses. The level of DNA strand breaks did not increase in all organs evaluated and at all doses of NaF tested, as depicted by the mean tail moment. Taken together, our results suggest that oral exposure to NaF did not result in systemic genotoxic effect in multiple organs related to fluoride toxicity. Since DNA damage is an important step in events leading to carcinogenesis, this study represents a relevant contribution to the correct evaluation of the potential health risk associated with chemical exposure. Human & Experimental Toxicology ( 2007) 26, 435—440

Differential effects of fluoride during osteoblasts mineralization in C57BL/6J and C3H/HeJ inbred strains of mice

The behavior of fluoride ions in biological systems has advantages and problems. On one hand, fluoride could be a mitogenic stimulus for osteoblasts. However, high concentrations of this element can cause apoptosis in rat and mouse osteoblasts. Toward an understanding of this effect, we examined the role of sodium fluoride (NaF) in two mouse calvaria osteoblasts during the mineralization process. The animals used were C3H/HeJ (C3) and C57BL/6J (B6) mice. The calvaria cells were cultured for 28 days in the presence of several doses of NaF (0, 5, 10, 25, 50, and 75 μM), and we performed the assays: mineralized nodule measurements, alkaline phosphatase (ALP) activity, determination of type I collagen, and matrix metalloproteinase-2 (MMP-2) activity. The results showed no effects on alkaline phosphatase activity but decreased mineralized nodule formation. In B6 cells, the NaF effect was already seen with 10 μM of NaF and a greater increase of cellular type I collagen, and MMP-2 activity was upregulated after 7 days of NaF exposure. C3 osteoblasts showed a reduction in the mineralization pattern only after 50 μM of NaF with a slight increase of type I collagen and downregulation of MMP-2 activity during the mineralization period. In conclusion, fluoride affects the production and degradation of the extracellular matrix during early onset and probably during the mineralization period. Additionally, the genetic factors may contribute to the variation in cell response to fluoride exposure, and the differences observed between the two strains could be explained by an alteration of the bone matrix metabolism (synthesis and degradation).

Effects of fluoride and cadmium co-exposure on bone in male rats

Although cadmium (Cd) and fluoride may both have adverse effects on bone, most studies focus on a single agent. In this study, we investigated the effects of cadmium and fluoride on bone at a relative low level. Sprague-Dawley male rats were assigned randomly into four groups which were given sodium chloride, cadmium (50mg/L), and fluoride (20mg/L) alone, or in combination via drinking water. At the 12th week, urine, blood, and bone tissues were collected for biomarker assay, biomechanical assay, and histological assay. Cadmium had significantly adverse effects on bone mineral density, bone biomechanical property, and bone microstructure. Fluoride slightly increased vertebral bone mineral density but negatively affected bone biomechanical property and bone microstructure. Fluoride could reverse the decrease of vertebral bone mineral density caused by cadmium but could not improve the damage of bone biomechanical property and microstructure caused by cadmium. Tartrate-resistant acid phosphatase 5b levels in rats treated with cadmium and fluoride or in combination were 1-2.5 folds higher than the control. Our data suggest that low level of fluoride could reverse the decrease of vertebral bone mineral density caused by cadmium exposure but has no influence on appendicular skeleton damage caused by cadmium.

Surface properties and ion release from fluoride-containing bioactive glasses promote osteoblast differentiation and mineralization in vitro

Bioactive glasses (BG) are suitable for bone regeneration applications as they bond with bone and can be tailored to release therapeutic ions. Fluoride, which is widely recognized to prevent dental caries, is efficacious in promoting bone formation and preventing osteoporosis-related fractures when administered at appropriate doses. To take advantage of these properties, we created BG incorporating increasing levels of fluoride whilst holding their silicate structure constant, and tested their effects on human osteoblasts in vitro. Our results demonstrate that, whilst cell proliferation was highest on low-fluoride-containing BG, markers for differentiation and mineralization were highest on BG with the highest fluoride contents, a likely effect of a combination of surface effects and ion release. Furthermore, osteoblasts exposed to the dissolution products of fluoride-containing BG or early doses of sodium fluoride showed increased alkaline phosphatase activity, a marker for bone mineralization, suggesting that fluoride can direct osteoblast differentiation. Taken together, these results suggest that BG that can release therapeutic levels of fluoride may find use in a range of bone regeneration applications.

Fluoride and calcium-phosphate coated sponges of the magnesium alloy AX30 as bone grafts: a comparative study in rabbits

Biocompatibility and degradation of magnesium sponges (alloy AX30) with a fluoride (MgF(2) sponge, n = 24, porosity 63 ± 6 %, pore size 394 ± 26 μm) and with a fluoride and additional calcium-phosphate coating (CaP sponge, n = 24, porosity 6 ± 4 %, pore size 109 ± 37 μm) were evaluated over 6, 12 and 24 weeks in rabbit femurs. Empty drill holes (n = 12) served as controls. Clinical and radiological examinations, in vivo and ex vivo μ-computed tomographies and histological examinations were performed. Clinically both sponge types were tolerated well. Radiographs and XtremeCT evaluations showed bone changes comparable to controls and mild gas formation. The μCT80 depicted a higher and more inhomogeneous degradation of the CaP sponges. Histomorphometrically, the MgF(2) sponges resulted in the highest bone and osteoid fractions and were integrated superiorly into the bone. Histologically, the CaP sponges showed more inflammation and lower vascularization. MgF(2) sponges turned out to be better biocompatible and promising, biodegradable bone replacements.

Substituted hydroxyapatites for bone repair

Calcium phosphates such as hydroxyapatite have a wide range of applications both in bone grafts and for the coating of metallic implants, largely as a result of their chemical similarity to the mineral component of bone. However, to more accurately mirror the chemistry, various substitutions, both cationic (substituting for the calcium) and anionic (substituting for the phosphate or hydroxyl groups) have been produced. Significant research has been carried out in the field of substituted apatites and this paper aims to summarise some of the key effect of substitutions including magnesium, zinc, strontium, silicon and carbonate on physical and biological characteristics. Even small substitutions have been shown to have very significant effects on thermal stability, solubility, osteoclastic and osteoblastic response in vitro and degradation and bone regeneration in vivo.

Osteoporosis and trace elements--an overview

More than 200 million people are affected by osteoporosis worldwide, as estimated by 2 million annual hip fractures and other debilitating bone fractures (vertebrae compression and Colles' fractures). Osteoporosis is a multi-factorial disease with potential contributions from genetic, endocrine functional, exercise related and nutritional factors. Of particular considerations are calcium (Ca) status, vitamin D, fluoride, magnesium and other trace elements. Several trace elements such as zinc and copper are essential for normal development of the skeleton in humans and animals. Fluoride accumulates in new bone and results in a net gain in bone mass, but may be associated with a tissue of poor quality. Aluminum induces impairment of bone formation. Gallium and cadmium suppresses bone turnover. However, exact involvements of the trace elements in osteoporosis have not yet been fully clarified. Numerous investigators have evaluated the role of medications and supplementations with minerals and trace substances to reverse the progression of this disease. Although bisphosphonates are still the drugs of choice, low-dosed fluoride and strontium salts have shown promise for the future.

Simultaneous incorporation of carbonate and fluoride in synthetic apatites: Effect on crystallographic and physico-chemical properties

The mineral in bone is an impure hydroxyapatite, with carbonate as the chief minor substituent. Fluoride has been shown to stimulate osteoblastic activity and inhibit osteoclastic resorption in vitro. CO(3)- and F-substituted apatite (CFA) has been considered as potential bone graft material for orthopedic and dental applications. The objective of this study was to determine the effects of simultaneously incorporated CO(3) and F on the crystallographic physico-chemical properties of apatite. The results showed that increasing CO(3) and Na content in apatites with relatively constant F concentration caused a decrease in crystallite size and an increase in the extent of calcium release; increasing F content in apatites with relatively constant CO(3) concentration caused an increase in crystallite size and a decrease in the extent of Ca release. These findings suggest that CFAs as bone graft materials of desired solubility can be prepared by manipulating the relative concentrations of CO(3) and F incorporated in the apatite.

Fluoride effects on bone formation and mineralization are influenced by genetics

INTRODUCTION

A variation in bone response to fluoride (F(-)) exposure has been attributed to genetic factors. Increasing fluoride doses (0 ppm, 25 ppm, 50 ppm, 100 ppm) for three inbred mouse strains with different susceptibilities to developing dental enamel fluorosis (A/J, a "susceptible" strain; SWR/J, an "intermediate" strain; 129P3/J, a "resistant" strain) had different effects on their cortical and trabecular bone mechanical properties. In this paper, the structural and material properties of the bone were evaluated to explain the previously observed changes in mechanical properties.

MATERIALS AND METHODS

This study assessed the effect of increasing fluoride doses on the bone formation, microarchitecture, mineralization and microhardness of the A/J, SWR/J and 129P3/J mouse strains. Bone microarchitecture was quantified with microcomputed tomography and strut analysis. Bone formation was evaluated by static histomorphometry. Bone mineralization was quantified with backscattered electron (BSE) imaging and powder X-ray diffraction. Microhardness measurements were taken from the vertebral bodies (cortical and trabecular bones) and the cortex of the distal femur.

RESULTS

Fluoride treatment had no significant effect on bone microarchitecture for any of the strains. All three strains demonstrated a significant increase in osteoid formation at the largest fluoride dose. Vertebral body trabecular bone BSE imaging revealed significantly decreased mineralization heterogeneity in the SWR/J strain at 50 ppm and 100 ppm F(-). The trabecular and cortical bone mineralization profiles showed a non-significant shift towards higher mineralization with increasing F(-) dose in the three strains. Powder X-ray diffraction showed significantly smaller crystals for the 129P3/J strain, and increased crystal width with increasing F(-) dose for all strains. There was no effect of F(-) on trabecular and cortical bone microhardness.

CONCLUSION

Fluoride treatment had no significant effect on bone microarchitecture in these three strains. The increased osteoid formation and decreased mineralization heterogeneity support the theory that F(-) delays mineralization of new bone. The increasing crystal width with increasing F(-) dose confirms earlier results and correlates with most of the decreased mechanical properties. An increase in bone F(-) may affect the mineral-organic interfacial bonding and/or bone matrix proteins, interfering with bone crystal growth inhibition on the crystallite faces as well as bonding between the mineral and organic interface. The smaller bone crystallites of the 129P3/J (resistant) strain may indicate a stronger organic/inorganic interface, reducing crystallite growth rate and increasing interfacial mechanical strength.

Role of oxidative stress in osteoblasts exposed to sodium fluoride

We investigated the relationship between oxidative stress and osteoblasts viability in osteoblasts exposed to various concentrations of fluoride in this study. Primary calvarial osteoblasts from neonatal Kunming mice were cultured and subcultured to the third generation. Osteoblasts were incubated with sodium fluoride (0, 0.5, 1, 2, 4, 8, 12, and 20 mgF(-)/L) for 24, 48, and 72 h. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) analysis showed cell viability significantly increased after osteoblasts exposed to low concentrations of fluoride (0.5 to approximately 2 mgF(-)/L) for 24 to approximately 72 h. Oxidative stress analysis showed that low concentration of fluoride excited lipid peroxidation in osteoblasts and increased activity of antioxidant enzymes in varying degrees. We demonstrated that changes of osteoblasts viability of the low-dose fluoride groups are different from those of high-dose fluoride groups; however, both low and high doses of fluoride caused active state of oxidative stress in osteoblasts, which suggesting that oxidative stress may be excited by the active osteoblasts viability induced by a low dose of fluoride.

Fluoride-induced oxidative stress of osteoblasts and protective effects of baicalein against fluoride toxicity

The key role of osteoblasts in skeletal fluorosis makes the exploration of the possible mechanisms of the fluoride-induced oxidative stress of osteoblasts of great importance. In this article, the in vitro effects of fluoride on the oxidative stress of osteoblasts are presented. To study the inhibitory effect of baicalein on the oxidative stress of osteoblasts, the antioxidant activity of baicalein was evaluated for osteoblasts exposed to fluoride. Calvarial osteoblasts were prepared and respectively treated with alpha-MEM (5% calf serum) containing 0.5, 1.0, 2.0, 4.0, 8.0, 12.0, and 20.0 mg/L fluoride for 48 h. Baicalein (10 micromol/L) was added to the cells for the same period of time as that of the fluoride treatment. Low concentrations of fluoride (0.5-2 mg F-/L) stimulated the mitochondrial activity of osteoblasts and produced significant reaction to the oxidative stress, whereas high concentrations of fluoride (>or=12 mg F-/L) inhibited cell proliferation and the activity of antioxidant enzymes. This suggests that the oxidative stress induced by low concentrations of fluoride might mediate or participate in the process of fluoride inducing the proliferation of osteoblasts. The viability of osteoblasts in the high concentrations of fluoride with the addition of 10 mumol/L baicalein (>or=12 mg/L) was higher than those of the same level of fluoride- treated groups without the addition of baicalein. The protective role of baicalein is obvious as an inhibitor of lipid peroxidation against the damage induced by the high concentration of fluoride.

Health effects of fluoride pollution caused by coal burning

Recently a huge amount of fluoride in coal has been released into indoor environments by the combustion of coal and fluoride pollution seems to be increasing in some rural areas in China. Combustion of coal and coal bricks is the primary source of gaseous and aerosol fluoride and these forms of fluoride can easily enter exposed food products and the human respiratory tract. Major human fluoride exposure was caused by consumption of fluoride contaminated food, such as corn, chilies and potatoes. For each diagnostic syndrome of dental fluorosis, a log-normal distribution was observed on the logarithm of urinary fluoride concentration in students in China. Urinary fluoride content was found to be a primary health indicator of the prevalence of dental fluorosis in the community. In the fluorosis areas, osteosclerosis in skeletal fluorosis patients was observed with a high prevalence. A biochemical marker of bone resorption, urinary deoxypyridinoline content was much higher in residents in China than in residents in Japan. It was suggested that bone resorption was stimulated to a greater extent in residents in China and fluoride may stimulate both bone resorption and bone formation. Renal function especially glomerular filtration rate was very sensitive to fluoride exposure. Inorganic phosphate concentrations in urine were significantly lower in the residents in fluorosis areas in China than in non-fluorosis area in China and Japan. Since airborne fluoride from the combustion of coal pollutes extensively both the living environment and food, it is necessary to reduce fluoride pollution caused by coal burning.

Health effects of indoor fluoride pollution from coal burning in China

The combustion of high fluoride-content coal as an energy resource for heating, cooking, and food drying is a major exhaust emission source of suspended particulate matter and fluoride. High concentrations of these pollutants have been observed in indoor air of coal-burning families in some rural areas in China. Because airborne fluoride has serious toxicological properties, fluoride pollution in indoor air and the prevalence of fluorosis have been analyzed in a fluorosis area and a healthy nonfluorosis area in China and in a rural area in Japan. For human health, fluoride in indoor air has not only been directly inhaled by residents but also has been absorbed in stored food such as corn, chilies, and potatoes. In the fluorosis area in China, concentrations of urinary fluoride in the residents have been much higher than in the nonfluorosis area in China and in the rural area in Japan. In the fluorosis area, almost all elementary and junior high school students 10-15 years of age had dental fluorosis. Osteosclerosis in the skeletal fluorosis patients was very serious. Urinary deoxypyridinoline in rural residents in China was much higher than in rural residents in Japan. Data suggest that bone resorption was extremely stimulated in the residents in China and that fluoride may stimulate both bone resorption and bone formation. Because indoor fluoride from combustion of coal is easily absorbed in stored food and because food consumption is a main source of fluoride exposure, it is necessary to reduce airborne fluoride and food contamination to prevent serious fluorosis in China.