Detection of dental fluorosis-associated quantitative trait Loci on mouse chromosomes 2 and 11

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.

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.

Review of Fluoride Intake and Appropriateness of Current Guidelines

Since the classical epidemiological studies by Dean, it has been known that there should be an optimum level of exposure to fluoride that would be able to provide the maximum protection against caries, with minimum dental fluorosis. The "optimal" daily intake of fluoride for children (0.05-0.07 mg per kilogram bodyweight) that is still accepted worldwide was empirically determined. In the present review, we discuss the appropriateness of the current guidance for fluoride intake, in light of the windows of susceptibility to caries and fluorosis, the modern trends of fluoride intake from multiple sources, individual variations in fluoride metabolism, and recent epidemiological data. The main conclusion is that it is very difficult to think about a strict recommendation for an "optimal" range of fluoride intake at the individual level in light of existing knowledge of 1) the mechanisms of action of fluoride to control caries, 2) the mechanisms involved in dental fluorosis development, 3) the distinct factors that interfere in the metabolism of fluoride, and 4) the windows of susceptibility to both dental caries and fluorosis development. An "optimal" range of fluoride intake is, however, desirable at the population level to guide programs of community fluoridation, but further research is necessary to provide additional support for future decisions on guidance in this area. This list includes the effect of factors affecting fluoride metabolism, clinical trials on the effectiveness of low-fluoride dentifrices to prevent caries in the primary dentition, and validation of biomarkers of exposure to fluoride.

Evaluation of genetic polymorphisms in MMP2, MMP9 and MMP20 in Brazilian children with dental fluorosis

Recent studies suggested that genetics contribute to differences in dental fluorosis (DF) susceptibility among individuals having the same environmental exposure. This study evaluated if MMP2, MMP9 and MMP20 are expressed during enamel development and assessed the association between polymorphisms in these genes with DF. Mice susceptible and resistant to DF were used to evaluate if MMPs were candidate genes for DF. The animals received fluoride and their enamels were used for immunohistochemistry. Additionally, 481 subjects from a city with fluoridation of public water supplies were recruited. Genotyping was performed using real time PCR. Allele/genotype frequencies were compared between groups. MMP2, MMP9 and MMP20 immunostaining was detected in both animal groups. DF was observed in 22.4% of the subjects. A borderline association was observed in MMP2 (rs243865), MMP9 (rs17576) and in MMP20 (rs1784418) (p = 0.06, p = 0.08 and p = 0.06 respectively). Briefly, MMPs were expressed during enamel maturation and genetic polymorphisms were not associated with DF.

Investigation on Anti-Autofluorescence, Osteogenesis and Long-Term Tracking of HA-Based Upconversion Material

Hydroxyapatite (HA) material will be long-standing once implanted in bone tissue of the body. It should be considered to endow the osteogenic HA material with traceable fluorescence to realize a lifelong in vivo tracking. We prepared and utilized lanthanides-doped HA upconversion material, and revealed for the first time that the lanthanides (ytterbium (Yb) and holmium (Ho)) co-doped HA upconversion material was suitable for long-term or lifelong in vivo tracking, the lanthanide ions doped in the HA matrix would not affect the biocompatibility and osteogenesis, and the tissue autofluorescence could be effectively avoided by the HA:Yb/Ho upconversion material. Also the distribution in bone and osteointegration with bone of the HA:Yb/Ho material could be clearly discriminated by its bright fluorescence under NIR irradiation. The upconversion characteristic of the HA:Yb/Ho material provides a feasibility and promising prospect for lifelong in vivo tracking, and has an advantage in revealing the material-tissue interrelation. The material has important clinical application value in addition to its usefulness for scientific investigation.

FRZB1 rs2242070 polymorphisms is associated with brick tea type skeletal fluorosis in Kazakhs, but not in Tibetans, China

Skeletal fluorosis is a metabolic bone and joint disease caused by excessive accumulation of fluoride in the bones. Compared with Kazakhs, Tibetans are more likely to develop moderate and severe brick tea type skeletal fluorosis, although they have similar fluoride exposure. Single nucleotide polymorphisms (SNPs) in frizzled-related protein (FRZB) have been associated with osteoarthritis, but their association with the risk of skeletal fluorosis has not been reported. In this paper, we investigated the association of three SNPs (rs7775, rs2242070 and rs9288087) in FRZB1with brick tea type skeletal fluorosis risk in a cross-sectional case-control study conducted in Sinkiang and Qinghai, China. A total of 598 individuals, including 308 Tibetans and 290 Kazakhs, were enrolled in this study, in which cases and controls were 221 and 377, respectively. The skeletal fluorosis was diagnosed according to the Chinese diagnostic criteria of endemic skeletal fluorosis (WS192-2008). The fluoride content in tea water or urine was detected using the fluoride ion electrode. SNPs were assessed using the Sequenom MassARRAY system. Binary logistic regressions found evidence of association with rs2242070 AA genotype in only Kazakh participants [odds ratio (OR) 0.417, 95% CI 0.216-0.807, p = 0.009], but not in Tibetans. When stratified by age, this protective effect of AA genotype in rs2242070 was pronounced in Kazakh participants aged 46-65 (OR 0.321, 95% CI 0.135-0.764, p = 0.010). This protective association with AA genotype in rs2242070 in Kazakhs also appeared to be stronger with tea fluoride intake > 3.5 mg/day (OR 0.396, 95% CI 0.182-0.864, p = 0.020). Our data suggest there might be differential genetic influence on skeletal fluorosis risk in Kazakh and Tibetan participants and that this difference might be modified by tea fluoride intake.

Polymorphisms in Nonamelogenin Enamel Matrix Genes Are Associated with Dental Fluorosis

The aim of this study was to evaluate whether genetic polymorphisms in AMELX, AMBN, ENAM, TFIP11, and TUFT1 genes are associated with dental fluorosis (DF). A total of 1,017 children from 2 Brazilian cohorts were evaluated. These populations lived in cities with fluoridation of public water supplies. DF was assessed in erupted permanent teeth using the modified Dean index. The polymorphisms rs946252, rs12640848, rs4694075, rs5997096, and rs4970957 were analyzed by real-time PCR from genomic DNA. Associations between DF, genotype, and allele distribution were evaluated using the χ2 test, with an alpha of 5%. The polymorphisms rs4694075, rs5997096, and rs4970957 in AMBN, TFIP11, and TUFT1 were associated with DF (p < 0.05). In conclusion, enamel matrix genes are associated with DF.

The genetic influence in fluorosis

Fluorosis, caused by ingestion of excess fluoride, is endemic in at least 25 countries across the globe, China and India being the worst affected among them. Dental, skeletal and non-skeletal are the major types of fluorosis affecting millions of people in these countries. A number of genetic epidemiological studies carried out by investigators have shown the evidence for association between genetic polymorphisms in candidate genes and differences in the susceptibility pattern of different types of fluorosis among individuals living in the same community and having the same environmental exposure. These studies have pointed out that genetic variants in some candidate genes like COL1A2 (Collagen type 1 alpha 2), CTR (Calcitonin receptor gene), ESR (Estrogen receptor), COMT (Catechol-o-methyltransferase), GSTP1 (Glutathione S-transferase pi 1), MMP-2 (Matrix metallopeptidase 2), PRL (Prolactin), VDR (Vitamin D receptor) and MPO (Myeloperoxidase) could increase or decrease the risk of fluorosis among the exposed individuals in endemic areas. So, it is increasingly becoming evident that an individual's genetic background could play a major role in influencing the risk to fluorosis when other factors like specific environmental exposures including dietary patterns of fluoride intake and other nutrients remain the same. The current manuscript presents an up-to-date critical review on fluorosis, focusing mainly on the genetic association studies that have looked at the possible involvement of genetic factors in fluorosis.

Liver proteome of mice with different genetic susceptibilities to the effects of fluoride

OBJECTIVE

In this study, we investigated the differential pattern of protein expression in the liver of these mice to provide insights on why they have different responses to F.

MATERIAL AND METHODS

Weanling male A/J and 129P3/J mice (n=10 from each strain) were pared and housed in metabolic cages with ad libitum access to low-F food and deionized water for 42 days. Liver proteome profiles were examined using nLC-MS/MS. Protein function was classified by GO biological process (Cluego v2.0.7 + Clupedia v1.0.8) and protein-protein interaction network was constructed (PSICQUIC, Cytoscape).

RESULTS

Most proteins with fold change were increased in A/J mice. The functional category with the highest percentage of altered genes was oxidation-reduction process (20%). Subnetwork analysis revealed that proteins with fold change interacted with Disks large homolog 4 and Calcium-activated potassium channel subunit alpha-1. A/J mice had an increase in proteins related to energy flux and oxidative stress.

CONCLUSION

This could be a possible explanation for the high susceptibility of these mice to the effects of F, since the exposure also induces oxidative stress.

Association between vitamin D receptor gene FokI polymorphism and skeletal fluorosis of the brick-tea type fluorosis: a cross sectional, case control study

BACKGROUND

Brick-tea type fluorosis is a public health concern in the north west area of China. The vitamin D receptor (VDR)-FokI polymorphism is considered to be a regulator of bone metabolism and calcium resorption. However, the association of VDR-FokI polymorphism with the risk of brick-tea type fluorosis has not been reported.

MATERIALS AND METHODS

A cross sectional, case control study was conducted in three provinces (Inner Mongolia, Qinghai and Sinkiang) in China. The fluoride content of Brick-tea water and urine was tested using the standards GB 1996-2005 and WS/T89-2006 (China), respectively. Skeletal fluorosis was diagnosed using the standard WS/192-2008 (China). The VDR-FokI polymorphism was detected by the Sequenom MassARRAY system.

RESULT

Compared with carriers of the CC genotype, participants with the CT/TT genotype had a significantly decreased risk of skeletal fluorosis (OR=0.761 (95% CI 0.580 to 0.997)), after adjustment for risk factors. When investigated among ethnic groups, the protective effect of the CT/TT genotype was limited in the Mongolian participants (OR=0.525 (95% CI 0.278 to 0.991)). Moreover, the interaction of VDR-FokI with risk factors was only found in Mongolian participants: the protective effect of the CT/TT genotype was limited to participants with >7.0 mg/day daily intake of tea fluoride (OR=0.085 (95% CI 0.009 to 0.851), participants with >3.2 mg/L urine fluoride (OR=0.103 (95% CI 0.017 to 0.633)) or participants aged 46-65 years (OR=0.404 (95% CI 0.177 to 0.922).

CONCLUSIONS

Our data suggest that the CT/TT genotype of VDR-FokI may be a protective factor for brick-tea type skeletal fluorosis, and this effect is pronounced in Mongolian participants.

P38/JNK signaling pathway mediates the fluoride-induced down-regulation of Fam83h

BACKGROUND/AIM

The similar clinical and pathological feature in fluorosis and amelogenesis imperfect with FAM83H mutations imply that excess fluoride could have effects on the expression of FAM83H and could elaborate this process by some signal pathways regulation. The present study aims to investigate the effects of fluoride on Fam83h expression and try to explore the molecular signaling regulation between them as well as the association of high concentration fluoride with mineralization in ameloblast lineage cells.

METHODS

Protein expression and signaling pathways of mouse ameloblast-like LS8 cells, exposed to fluoride or MAPK inhibitors, were compared to control cells without exposure. Fam83h, proteins of MAPK signal pathways (ERK, P38 and JNK) were examined by Quantitative real-time PCR and/or Western-blot. ALP activity and ALP staining were used to detect the mineralization in the cells with exposure during 7-day mineralization inducing differentiation.

RESULTS

The results showed that Fam83h protein level in LS8 cells decreased in the presence of fluoride and MAPK inhibitors. Down-regulation of Fam83h by fluoride was related to suppression of JNK and P38 phosphorylation, and the descending degree of P38 was more obvious. Fluoride and MAPK inhibitors treatment significantly decreased the mineralization level in LS8 cells.

CONCLUSION

The findings suggest that JNK and P38 could be key regulatory element for Fam83h expression, and that LS8 cells can respond to fluoride by down-regulating Fam83h expression through the regulation of JNK and p38 signaling pathways.

Proteomics of Secretory-Stage and Maturation-Stage Enamel of Genetically Distinct Mice

The mechanisms by which excessive ingestion of fluoride (F) during amelogenesis leads to dental fluorosis (DF) are still not precisely known. Inbred strains of mice vary in their susceptibility to develop DF, and therefore permit the investigation of underlying molecular events influencing DF severity. We employed a proteomic approach to characterize and evaluate changes in protein expression from secretory-stage and maturation-stage enamel in 2 strains of mice with different susceptibilities to DF (A/J, i.e. ‘susceptible' and 129P3/J, i.e. ‘resistant'). Weanling male and female susceptible and resistant mice fed a low-F diet were divided into 2 F-water treatment groups. They received water containing 0 (control) or 50 mg F/l for 6 weeks. Plasma and incisor enamel was analyzed for F content. For proteomic analysis, the enamel proteins extracted for each group were separated by 2-dimensional electrophoresis and subsequently characterized by liquid-chromatography electrospray-ionization quadrupole time-of-flight mass spectrometry. F data were analyzed by 2-way ANOVA and Bonferroni's test (p < 0.05). Resistant mice had significantly higher plasma and enamel F concentrations when compared with susceptible mice in the F-treated groups. The proteomic results for mice treated with 0 mg F/l revealed that during the secretory stage, resistant mice had a higher abundance of proteins than their susceptible counterparts, but this was reversed during the maturation stage. Treatment with F greatly increased the number of protein spots detected in both stages. Many proteins not previously described in enamel (e.g. type 1 collagen) as well as some uncharacterized proteins were identified. Our findings reveal new insights regarding amelogenesis and how genetic background and F affect this process.

Modifying Role of GSTP1 Polymorphism on the Association between Tea Fluoride Exposure and the Brick-Tea Type Fluorosis

Background

Brick tea type fluorosis is a public health concern in the north-west area of China. The association between SNPs of genes influencing bone mass and fluorosis has attracted attention, but the association of SNPs with the risk of brick-tea type of fluorosis has not been reported.

Objective

To investigate the modifying roles of GSTP1 rs1695 polymorphisms on this association.

Methods

A cross-sectional study was conducted. Brick-tea water was tested by the standard of GB1996-2005 (China). Urinary fluoride was tested by the standard of WS/T 89-2006 (China). Skeletal fluorosis was diagnosed by X-ray, the part we scheduled was forearm, shank, and pelvic, then diagnosed the skeletal fluorosis by the standard of WS/192-2008 (China). Gene polymorphism was tested by Sequenom MassARRAY system.

Result

The prevalence rate in different ethnical participants was different: Tibetan individuals had the highest prevalence rate of skeletal fluorosis. There were significant differences in genotype frequencies of GSTP1 Rs1695 among different ethnical participants (p<0.001): Tibetan, Mongolian and Han subjects with homozygous wild type (GSTP1-AA) genotype were numerically higher than Kazakh and Russian subjects (p<0.001). Compared to Tibetan participants who carried homozygous A allele of GSTP1 Rs1695, Tibetan participants who carried G allele had a significantly decreased risk of skeletal fluorosis (OR = 0.558 [95% CI, 0.326-0.955]). For Kazakh participants, a decreased risk of skeletal fluorosis among carriers of the G allele was limited to non high-loaded fluoride status (OR = 0. 166 [95% CI, 0.035–0.780] vs. OR = 1.478 [95% CI, 0.866–2.552] in participants with high-loaded fluoride status). Neither SNP-IF nor SNP-age for GSTP1 Rs1695 was observed.

Conclusion

The prevalence rate of the brick tea type fluorosis might have ethnic difference. For Tibetan individuals, who had the highest prevalence rate, G allele of GSTP1 Rs1695 might be a protective factor for brick tea type skeletal fluorosis.

Enamel crystals of mice susceptible or resistant to dental fluorosis: an AFM study

Objective

This study aimed to assess the overall apatite crystals profile in the enamel matrix of mice susceptible (A/J strain) or resistant (129P3/J strain) to dental fluorosis through analyses by atomic force microscopy (AFM).

Material and Methods

Samples from the enamel matrix in the early stages of secretion and maturation were obtained from the incisors of mice from both strains. All detectable traces of matrix protein were removed from the samples by a sequential extraction procedure. The purified crystals (n=13 per strain) were analyzed qualitatively in the AFM. Surface roughness profile (Ra) was measured.

Results

The mean (±SD) Ra of the crystals of A/J strain (0.58±0.15 nm) was lower than the one found for the 129P3/J strain (0.66±0.21 nm) but the difference did not reach statistical significance (t=1.187, p=0.247). Crystals of the 129P3/J strain (70.42±6.79 nm) were found to be significantly narrower (t=4.013, p=0.0013) than the same parameter measured for the A/J strain (90.42±15.86 nm).

Conclusion

Enamel crystals of the 129P3/J strain are narrower, which is indicative of slower crystal growth and could interfere in the occurrence of dental fluorosis.

Ameloblasts require active RhoA to generate normal dental enamel

RhoA plays a fundamental role in regulation of the actin cytoskeleton, intercellular attachment, and cell proliferation. During amelogenesis, ameloblasts (which produce the enamel proteins) undergo dramatic cytoskeletal changes and the RhoA protein level is up-regulated. Transgenic mice were generated that express a dominant-negative RhoA transgene in ameloblasts using amelogenin gene-regulatory sequences. Transgenic and wild-type (WT) molar tooth germs were incubated with sodium fluoride (NaF) or sodium chloride (NaCl) in organ culture. Filamentous actin (F-actin) stained with phalloidin was elevated significantly in WT ameloblasts treated with NaF compared with WT ameloblasts treated with NaCl or with transgenic ameloblasts treated with NaF, thereby confirming a block in the RhoA/Rho-associated protein kinase (ROCK) pathway in the transgenic mice. Little difference in quantitative fluorescence (an estimation of fluorosis) was observed between WT and transgenic incisors from mice provided with drinking water containing NaF. We subsequently found reduced transgene expression in incisors compared with molars. Transgenic molar teeth had reduced amelogenin, E-cadherin, and Ki67 compared with WT molar teeth. Hypoplastic enamel in transgenic mice correlates with reduced expression of the enamel protein, amelogenin, and E-cadherin and cell proliferation are regulated by RhoA in other tissues. Together these findings reveal deficits in molar ameloblast function when RhoA activity is inhibited.

Renal proteome in mice with different susceptibilities to fluorosis

A/J and 129P3/J mouse strains have different susceptibilities to dental fluorosis due to their genetic backgrounds. They also differ with respect to several features of fluoride (F) metabolism and metabolic handling of water. This study was done to determine whether differences in F metabolism could be explained by diversities in the profile of protein expression in kidneys. Weanling, male A/J mice (susceptible to dental fluorosis, n = 18) and 129P3/J mice (resistant, n = 18) were housed in pairs and assigned to three groups given low-F food and drinking water containing 0, 10 or 50 ppm [F] for 7 weeks. Renal proteome profiles were examined using 2D-PAGE and LC-MS/MS. Quantitative intensity analysis detected between A/J and 129P3/J strains 122, 126 and 134 spots differentially expressed in the groups receiving 0, 10 and 50 ppmF, respectively. From these, 25, 30 and 32, respectively, were successfully identified. Most of the proteins were related to metabolic and cellular processes, followed by response to stimuli, development and regulation of cellular processes. In F-treated groups, PDZK-1, a protein involved in the regulation of renal tubular reabsorption capacity was down-modulated in the kidney of 129P3/J mice. A/J and 129P3/J mice exhibited 11 and 3 exclusive proteins, respectively, regardless of F exposure. In conclusion, proteomic analysis was able to identify proteins potentially involved in metabolic handling of F and water that are differentially expressed or even not expressed in the strains evaluated. This can contribute to understanding the molecular mechanisms underlying genetic susceptibility to dental fluorosis, by indicating key-proteins that should be better addressed in future studies.

Fine mapping of dental fluorosis quantitative trait loci in mice

Genetic factors underlie the susceptibility and the resistance to dental fluorosis (DF). The A/J (DF susceptible) and 129P3/J (DF resistant) mouse strains have previously been used to detect quantitative trait loci (QTLs) associated with DF on chromosome (Chr) 2 and Chr 11. In the present study, increased marker density genotyping followed by interval mapping was performed to narrow the QTL intervals and improve the logarithm of the odds (to the base 10) (LOD) scores. Narrower intervals were obtained on Chr 2 where LOD ≥ 6.0 (57-84 cM or ≈ 51 Mb), LOD ≥ 7.0 (62-79 cM or ≈ 32 Mb), and LOD ≥ 8.0 (65-74 cM or ≈ 17 Mb); and on Chr 11 where LOD ≥ 6.0 (18-51 cM or ≈ 53 Mb), LOD ≥ 7.0 (28-48 cM or ≈ 34 Mb), and LOD ≥ 8.0 (31-45 cM or ≈ 22 Mb). Haplotype analysis between A/J and 129P3/J mice further reduced the QTL intervals. Accn1 was selected as a candidate gene based upon its location near the peak LOD score on Chr 11 and distant homology with the Caenorhabditis elegans fluoride-resistance gene, flr1. The severity of DF between Accn1(-/-) and wild-type mice was not significantly different. Hence, the loss of ACCN1 function does not modify DF severity in mice. Narrowing the DF QTL intervals will facilitate additional candidate gene selections and interrogation.

The relationship of PTH Bst BI polymorphism, calciotropic hormone levels, and dental fluorosis of children in China

The aim of this study was to explore the association of parathyroid hormone (PTH) gene Bst BI polymorphism, calciotropic hormone levels, and dental fluorosis of children. A case-control study was conducted in two counties (Kaifeng and Tongxu) in Henan Province, China in 2005-2006. Two hundred and twenty-five children were recruited and divided into three groups including dental fluorosis group (DFG), non-dental fluorosis group (NDFG) from high fluoride areas, and control group (CG). Urine fluoride content was determined using fluoride ion selective electrode; PTH Bst BI were genotyped using PCR-RFLP; osteocalcin (OC) and calcitonin (CT) levels in serum were detected using radioimmunoassay. Genotype distributions were BB 85.3% (58/68), Bb 14.7% (10/68) for DFG; BB 77.6% (52/67), Bb 22.4% (15/67) for NDFG; and BB 73.3% (66/90), Bb 27.7% (24/90) for CG. No significant difference of Bst BI genotypes was observed among three groups (P > 0.05). Serum OC and urine fluoride of children were both significantly higher in DFG and NDFG than in CG (P < 0.05, respectively), while a similar situation was not observed between DFG and NDFG in high fluoride areas (P > 0.05). Serum OC level of children with BB genotype was significantly higher compared to those with Bb genotype in high fluoride areas (P < 0.05). However, no significant difference of serum CT or calcium (Ca) was observed. In conclusion, there is no correlation between dental fluorosis and PTH Bst BI polymorphism. Serum OC might be a more sensitive biomarker for detecting early stages of dental fluorosis, and further studies are needed.

Association of dental fluorosis with polymorphisms of estrogen receptor gene in Chinese children

Dental fluorosis (DF) is one of the important performances of endemic fluorosis. Some studies indicated that estrogen receptor (ESR) gene polymorphisms were associated with bone metabolism-related diseases. Therefore, it is possible that the variation in ESR genotypes will be associated with DF status. A case-control study was conducted among children aged 8-12 years with (n = 75) or without (n = 165) DF in China to investigate the relationship between ESR gene polymorphisms and DF. Gene polymorphisms were genotyped using the PCR-RFLP procedure. Children carrying R allele of ER RsaI had significantly increased risk of DF (Odds ratio (OR) = 1.821; 95% confidence interval (CI), 1.013-3.274) compared to children carrying r allele of ER RsaI in endemic fluorosis villages. For children with high-loaded fluoride status, carrying X allele of ESRα XbaI had a significantly decreased risk of DF (OR = 0.542; 95% CI, 0.314-0.936) compared to carrying x allele. This study provides the first evidence of an association between polymorphisms in the ESR gene with DF in high-fluoride-exposed populations. Further studies are needed to confirm the association.

Chronic fluoride toxicity: dental fluorosis

Dental fluorosis occurs as a result of excess fluoride ingestion during tooth formation. Enamel fluorosis and primary dentin fluorosis can only occur when teeth are forming, and therefore fluoride exposure (as it relates to dental fluorosis) occurs during childhood. In the permanent dentition, this would begin with the lower incisors, which complete mineralization at approximately 2-3 years of age, and end after mineralization of the third molars. The white opaque appearance of fluorosed enamel is caused by a hypomineralized enamel subsurface. With more severe dental fluorosis, pitting and a loss of the enamel surface occurs, leading to secondary staining (appearing as a brown color). Many of the changes caused by fluoride are related to cell/matrix interactions as the teeth are forming. At the early maturation stage, the relative quantity of amelogenin protein is increased in fluorosed enamel in a dose-related manner. This appears to result from a delay in the removal of amelogenins as the enamel matures. In vitro, when fluoride is incorporated into the mineral, more protein binds to the forming mineral, and protein removal by proteinases is delayed. This suggests that altered protein/mineral interactions are in part responsible for retention of amelogenins and the resultant hypomineralization that occurs in fluorosed enamel. Fluoride also appears to enhance mineral precipitation in forming teeth, resulting in hypermineralized bands of enamel, which are then followed by hypomineralized bands. Enhanced mineral precipitation with local increases in matrix acidity may affect maturation stage ameloblast modulation, potentially explaining the dose-related decrease in cycles of ameloblast modulation from ruffle-ended to smooth-ended cells that occur with fluoride exposure in rodents. Specific cellular effects of fluoride have been implicated, but more research is needed to determine which of these changes are relevant to the formation of fluorosed teeth. As further studies are done, we will better understand the mechanisms responsible for dental fluorosis.

Fluoride effect on the secretory-stage enamel organic extracellular matrix of mice

The formation of an ordered enamel organic extracellular matrix (EOECM) seems to be a crucial step for the proper formation of the enamel mineral phase. The ordered supramolecular structure of the EOECM in the secretory stage can be analyzed using polarizing microscopy, as it is strongly birefringent. Excessive fluoride (F) ingestion during tooth development can cause enamel fluorosis, leading to increased porosity in mature enamel. We analyzed the effects of F on the birefringence of the EOECM in the A/J, CBA, and DBA/2 strains of mice given 0, 11.25, and 45 ppm of fluoride in drinking water. In the CBA and DBA/2 strains, the 11.25 and 45 ppmF groups presented a significant decrease in optical retardation (OR) when compared with the respective 0 (CBA 11.25 ppmF p = 0.0056 and 45 ppmF p < 0.0001; DBA/2 11.25 and 45 ppmF p < 0.05). ORs in A/J 0 ppmF were significantly higher than in 45 (p < 0.0001). The enamel of the A/J strain was more severely affected by fluoride than it was in the other strains of mice and exhibited the lowest levels of fluoride in plasma, whereas its normal secretory enamel presented a significantly higher protein absorbance than it did in CBA and DBA mice (p = 0.0099 and p = 0.0025, respectively). The results showed that experimental fluorosis can alter the supramolecular organization of EOECM in the secretory stage of amelogenesis and that the susceptibility to dental fluorosis seems to be influenced by the inherent characteristics of the developing enamel.

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.

The impact of fluoride on ameloblasts and the mechanisms of enamel fluorosis

Intake of excess amounts of fluoride during tooth development cause enamel fluorosis, a developmental disturbance that makes enamel more porous. In mild fluorosis, there are white opaque striations across the enamel surface, whereas in more severe cases, the porous regions increase in size, with enamel pitting, and secondary discoloration of the enamel surface. The effects of fluoride on enamel formation suggest that fluoride affects the enamel-forming cells, the ameloblasts. Studies investigating the effects of fluoride on ameloblasts and the mechanisms of fluorosis are based on in vitro cultures as well as animal models. The use of these model systems requires a biologically relevant fluoride dose, and must be carefully interpreted in relation to human tooth formation. Based on these studies, we propose that fluoride can directly affect the ameloblasts, particularly at high fluoride levels, while at lower fluoride levels, the ameloblasts may respond to local effects of fluoride on the mineralizing matrix. A new working model is presented, focused on the assumption that fluoride increases the rate of mineral formation, resulting in a greater release of protons into the forming enamel matrix.

Modulation of murine bone marrow-derived CFU-F and CFU-OB by in vivo bisphosphonate and fluoride treatments

OBJECTIVES

Bisphosphonates (BPN) have actions on a variety of cell types including: osteoclasts, osteoblasts, osteocytes, and endothelial cells. The objectives of this report are to review the current state of understanding of the effects of BPNs on orthodontic tooth movement and to provide evidence on BPN's in vivo effects on bone marrow-derived osteoprogenitor cells.

MATERIAL AND METHODS

Mice from the C3H/HeJ (C3H), C57BL/6J (B6), FVB/NJ (FVB), and BALB/cByJ (BALB) strains were treated for 3 weeks with 0, 3, 30, or 150 mcg/kg/week alendronate (ALN) administered subcutaneous alone or in combination with 50 ppm fluoride (F). Bone marrow cells were harvested and subjected to in vitro colony-forming unit fibroblast (CFU-F) and colony-forming unit osteoblasts (CFU-OB) assays.

RESULTS

Baseline differences in CFU-F, CFU-OB/ALP+, and CFU-OB/total were observed among the four strains. Strain-specific responses to ALN and F treatments were observed for CFU-F, CFU-OB/ALP+, and CFU-OB/total. F treatment alone resulted in decreases in CFU-F (p = 0.013), CFU-OB/ALP+ (p = 0.005), and CFU-OB/total (p = 0.003) in the C3H strain. CFU-F (p = 0.036) were decreased by F in the B6 strain. No significant (NS) effects of F were observed for FVB and BALB. ALN treatment resulted in a significant decrease in CFU-F (p = 0.0014) and CFU-OB/total (p = 0.028) in C3H only. ALN treatment had NS effect on CFU-OB/ALP+ in all four strains.

CONCLUSION

Genetic factors appear to play a role in ALN's effects on CFU-F and CFU-OB/total but not on CFU-OB/ALP+.