Studies of fluoride metabolism in man. A review and report of original data

Correlations between bone metabolism biomarkers and fluoride exposure in adults and children

Increased exposure to fluoride, which notably affects bone metabolism, is a global concern. However, the correlations and sensitivity of bone metabolism to fluoride remain controversial. In this cross-sectional study, 549 children (aged 7-12 years) and 504 adults (≥ 18 years old) were recruited in the high-fluoride areas of the Henan Province. Urinary fluoride (UF) level was determined using a fluoride electrode. Fasting venous blood serum was collected to measure bone metabolism biomarkers. The selected bone metabolism biomarkers for children included bone alkaline phosphatase (BALP), serum alkaline phosphatase (ALP), osteocalcin (OCN), calcitonin (CT), parathyroid hormone (PTH), phosphorus (P5+), and calcium (Ca2+). For adults, the biomarkers included ALP, CT, PTH, β-CrossLaps (β-CTX), P5+, and Ca2+. The correlations between UF and bone metabolism biomarkers were analyzed using binary logistic regression, a trend test, a generalized additive model, and threshold effect analysis. Regression analysis indicated a significant correlation between serum OCN, PTH, and UF levels in children aged 7-9 years. Serum OCN, PTH, and BALP contents were significantly correlated with UF in boys (P < 0.05). Furthermore, the interaction between age and UF affected serum P5+ and PTH (P < 0.05). The generalized additive model revealed nonlinear dose-response relationships between P5+, BALP, and UF contents in children (P < 0.05). Serum OCN level was linearly correlated with the UF concentration (P < 0.05). Similarly, a significant correlation was observed between β-CTX and UF levels in adults. In addition, significant correlations were observed between UF-age and serum Ca2+, β-CTX, and PTH contents. There was a non-linear correlation between serum Ca2+, P5+, and β- CTX and UF levels (P < 0.05). Overall, serum OCN, BALP, and P5+ levels can serve as sensitive bone metabolism biomarkers in children, while β-CTX, P5+, and Ca2+ can be considered fluoride-sensitive bone metabolism biomarkers in adults.

Association between dental fluorosis prevalence and inflammation levels in school-aged children with low-to-moderate fluoride exposure

Inflammation mediates the neurological deficits caused by fluoride. Thus, whether inflammation is the underlying mechanism of dental fluorosis (DF) in school-aged children is worth exploring. A cross-sectional study was conducted to investigate the association between inflammation and the prevalence and severity of DF with low-to-moderate fluoride exposure. Fasting morning urine and venous blood samples were collected from 593 children aged 7-14 years. The fluoride content in the water and urine samples was measured using a fluoride ion-selective electrode assay. The levels of interleukin-1β (IL-1β) and C-reactive protein (CRP) were detected using an enzyme-linked immunosorbent assay. The Dean's index was used when performing dental examinations. Regression, stratified, and mediation analyses were performed to analyze the association between fluoride exposure, inflammation, and DF prevalence. In the adjusted regression models, the prevalence of mild DF was 1.723-fold (95% confidence interval [CI]:1.612, 1.841) and 1.594-fold (1.479, 1.717) greater than that of normal DF for each 1 mg/L increase in water and urinary fluoride content, respectively. The prevalence of mild DF increased by 3.3% for each 1 pg/mL increase in the IL-1β level and by 26.0% for each 1 mg/L increase in the CRP level. Stratified analysis indicated a weaker association between fluoride concentration and DF prevalence in boys than in girls, and susceptibility in the boys was reflected by the association of IL-1β with very mild and moderate DF prevalence. For every 1 mg/L increase in water and urinary fluoride levels, the proportion of IL-1β-mediated effects on the prevalence of mild DF was 10.0% (6.1%, 15.8%) and 8.7% (4.8%, 15.2%), respectively, and the proportion of CRP-mediated effects was 9.2% (5.5%, 14.9%) and 6.1% (3.3%, 11.0%), respectively. This study indicates that the DF prevalence may be sex-specific. Inflammatory factors may partially mediate the increased prevalence of mild DF in school-aged children with low-to-moderate fluoride exposure.

Periarticular calcifications containing giant pseudo-crystals of francolite in skeletal fluorosis from 1,1-difluoroethane "huffing"

Inhalant use disorder is a psychiatric condition characterized by repeated deliberate inhalation from among a broad range of household and industrial chemical products with the intention of producing psychoactive effects. In addition to acute intoxication, prolonged inhalation of fluorinated compounds can cause skeletal fluorosis (SF). We report a young woman referred for hypophosphatasemia and carrying a heterozygous ALPL gene variant (c.457T>C, p.Trp153Arg) associated with hypophosphatasia, the heritable metabolic bone disease featuring impaired skeletal mineralization, who instead suffered from SF. Manifestations of her SF included recurrent articular pain, axial osteosclerosis, elevated bone mineral density, maxillary exostoses, and multifocal periarticular calcifications. SF was suspected when a long history was discovered of 'huffing' a computer cleaner containing 1,1-difluoroethane. Investigation revealed markedly elevated serum and urine levels of F^-. Histopathology and imaging techniques including backscattered electron mode scanning electron microscopy, X-ray microtomography, energy dispersive and wavelength dispersive X-ray emission microanalysis, and polarized light microscopy revealed that her periarticular calcifications were dystrophic deposition of giant pseudo-crystals of francolite, a carbonate-rich fluorapatite. Identifying unusual circumstances of F^- exposure is key for diagnosing non-endemic SF. Increased awareness of the disorder can be lifesaving.

Rate normalization for sweat metabolomics biomarker discovery

As the demand for real-time exercise performance feedback increases, excreted sweat has become a biosource of interest for continuous human performance assessment. For sweat to truly fulfill this requirement, analyte concentrations must be normalized to adequately assess day-to-day differences within and among individuals. In this manuscript, data are presented highlighting the use of accurate localized sweat rate as a means for ion and global metabolomic data normalization. The results illustrate large sweat rate variability among individuals over the course of two distinct exercises protocols. Furthermore, the data show sweat rate is not symmetrical at similar locations among right and left forearms of individuals (p = 0.0007). Sweat ion conductivity analysis suggest overall sweat rate normalization reduces variability collectively among ion values and participants with principal component analysis showing 77.8% of variation in the data set attributable to sweat rate normalization. Global metabolomic analysis of sweat illustrated overall rate normalization increases the variability among test subjects with 72.7% of the variation explained by sweat rate normalization. Finally, overall rate normalized metabolomic features of sweat significantly correlated (ρ ≥ 0.7, ρ ≤ -0.7) with measured performance metrics of the individual, establishing the potential for sweat to be used as a biosource for performance monitoring. Collectively, these data illustrate the importance of accurate localized sweat rate determination, for analyte data normalization, in support for the use of sweat in biomarker discovery efforts to predict human performance.

Effect of altitude on urinary, plasma and nail fluoride levels in children and adults in Nepal

INTRODUCTION

A greater prevalence of dental fluorosis has been reported in higher- versus lower-altitude communities. This study, for the first time, examined several aspects of fluoride metabolism in children, aged 4-5 years, and their parent, living at lower altitude (<78 m) and higher altitude (>1487) areas in Nepal.

METHODS

The study assessed total daily fluoride intake (TDFI), 24 h urinary fluoride excretion (UFE), and fluoride concentrations of toe- and finger-nail (FC_toenail, FC_fingernail) in children and parents as well as fluoride concentration of plasma (FC_plasma) in parents. Fractional urinary fluoride excretion (FUFE) was calculated as the ratio between UFE and TDFI. FC_toenail, FC_fingernail and FC_plasma were normalised for TDFI by dividing the variables by TDFI and the ratio was reported as the percentage.

RESULTS

In total, 89 children and 80 parents took part in the study: 42 children and 41 parents from the lower altitude area; 47 children and 39 parents from the higher altitude area. Fluoride concentration of drinking water was significantly (P < 0.001) higher at lower altitude (0.395 mg F/l) than at higher altitude (0.104 mg F/l). TDFI was significantly (p < 0.001) higher in both children and parents living in lower altitude than those living at higher altitude. There was a statistically significant (p = 0.044) difference in the mean FUFE of children living at lower altitude (53%) and higher altitude (46%). However, no significant difference in FUFE was found between parents living at lower altitude (47%) compared with higher altitude (41%). In both children and parents, no statistically significant differences in normalised FC_toenail, FC_fingernail were found between the two altitude areas. However, normalised FC_plasma was statistically significantly (P = 0.005) higher in parents living at higher altitude (0.15%) compared with those living at lower altitude (0.11%).

CONCLUSION

The results suggest that higher altitude living results in decreased urinary fluoride excretion, and consequently increased fluoride retention in children for a given dose (amount) of fluoride.

Inhaled magnesium fluoride reverse bronchospasma

Asthma is a global health problem. Asthma attacks are becoming more severe and more resistant to usual treatment by beta(2) agonists nebulisation. The search for a new product that could reduce the morbidity of asthmatic disease seems necessary. The objective of this study was to compare the effectiveness of inhaled magnesium fluoride (MgF(2)) with that of magnesium sulphate (MgSO(4)) 15% alone and sodium fluoride (NaF) 0.5 M alone in rats pre-contracted by methacholine (MeCh). Fifty six adult male Wistar rats of medium weight 259 +/- 15 g were divided randomly into five groups. They inhaled respectively: MeCh, MgF(2) + NaCl 0.9%, MgF(2) + acetic acid, MgSO(4) 15% single and NaF (0.5 M) single. Airway resistances were measured after each dose of MeCh by pneumomultitest equipment. Results indicated that (1) MgF(2) + NaCl 0.9%, MgF(2) + acetic acid and MgSO(4) reversed significantly the methacholine-induced bronchial constriction in rats and had a bronchodilating effect at the moment of its administration (2) MgF(2) + acetic acid led to a greater decrease (P<0.05) of bronchial resistances when compared to that obtained from MgF(2) + NaCl 0.9%, NaF exclusively and MgSO(4) alone (3) inhaled NaF alone led to a significant bronchorelaxing effect (P<0.05) that starts at the sixth dose of MeCh (17 mg/L). As a matter of fact, MgF(2) dissolved in acetic acid and delivered in aerosol form reduces significantly bronchial spasm. In conclusion, MgF(2) can be used as a bronchodilator for diseases with bronchospasma such as asthma and chronic obstructive pulmonary disease (COPD).

Serum ionic fluoride concentrations are related to renal function and menopause status but not to age in a Japanese general population

BACKGROUND

There have been no studies in which fasting serum ionic fluoride (SIF) concentrations in a general population were investigated despite the fact that SIF has various activities in humans.

METHODS

A total of 332 healthy subjects (167 men and 165 women aged 40 to 69years) were selected from residents of 2 towns in Iwate Prefecture, Japan using sex-specific and age-specific stratified random sampling methods. Overnight fasting blood samples were collected from all subjects. Serum levels of creatinine, bone alkaline phosphatase and urinary deoxypyridinoline levels were determined in one laboratory. SIF concentrations were measured using highly sensitive methods. Estimated glomerular filtration rate (eGFR) was calculated using serum creatinine level, age and sex.

RESULTS

Mean SIF concentrations were 0.495mumol/l in men and 0.457mumol/l in women. SIF concentrations were independently related to eGFR in both sexes and to menopause status in women. SIF concentrations in women were significantly higher in the post-menopausal group than in the pre-menopausal group.

CONCLUSION

SIF concentrations in middle-aged healthy subjects were increased with an age-related degeneration in renal function. SIF concentrations in post-menopausal women arise from the increased fluoride release from bone after menopause. Age is not related to SIF concentrations.

Oral administration of fluoride in pregnant women, and the relation between concentration in maternal plasma and in amniotic fluid

The aim was to measure the ionic fluoride concentration in maternal plasma and in amniotic fluid after oral administration of different doses of sodium fluoride (NaF) to 121 pregnant women. They were divided into six groups, according to the dose administered; 0 for the control group and 0.25, 0.50, 0.75, 1.00 or 1.25 mg of F- for the others. The subjects were instructed to take the corresponding NaF dose both 24 and 3 h before amniocentesis. Amniotic fluid (5 ml) and venous blood (5 ml) were obtained from each subject. Ionic fluoride concentration was measured with an expanded-scale potentiometer and a selective fluoride electrode. The results showed that F- concentration in amniotic fluid and, presumably, in fetal circulation, was not significantly different in groups taking 0.25, 0.50, 0.75 or 1.00 mg/day of F-. The F- concentration in amniotic fluid of the 1.25 mg/day group was, however, significantly higher than in all the other groups.

The changing patterns of systemic fluoride intake

Fluorosis prevalence has increased in North America since the 1930's-1940's. It may also have increased since 1970, though the evidence for that is less clear. Continued monitoring will help determine whether increased fluorosis prevalence in children in the United States is a cohort effect from the 1970's. This review considers the evidence for an increase in fluoride ingestion from all sources since the 1970's. If an increase has occurred, the most likely sources are fluoride dietary supplements, inadvertent swallowing of fluoride toothpastes, and increased fluoride in food and beverages. For adults, there is no evidence from dietary surveys to show that fluoride intake has increased over the last generation. Dietary surveys for children aged six months to two years are similarly inconclusive, though the great variation in fluoride content of various infant foods might be obscuring real effects. The data on fluoride intake by children from food and beverages, infant foods included, are not strong enough to conclude that an increase in fluoride ingestion has occurred since the 1970's. However, the suggested upper limit of fluoride intake is substantially being reached in many children by ingestion of fluoride from food and drink (0.2-0.3 mg per day) and from fluoride toothpaste (0.2-0.3 mg per day). Two public health issues that arise from this review are: (a) the need for a downward revision in the schedule for fluoride supplementation, and (b) education on the potential for high fluoride concentration of soft drinks and processed fruit juices.

An experimental study of bio-availability of fluoride from dietary sources in man

After single, oral doses, 8 h profiles of fluoride (F) concentrations in plasma and saliva, and 24 h urinary excretions were determined in healthy adult volunteers. Bio-availability of F from dietary sources was evaluated in relation to that of NaF. Between 2 and 10 mg of F administered all 3 variables were dose-dependent. However, digestion, the chemical state of F, and interaction with accompanying foods may modify the kinetics of F passage through the human body. Low bio-availabilities were observed for most solid foods such as fish and algal flour and for mammalian and fish bones, when used as typical components of fluoride-rich foods such as meat- and fish-products. This data is important in the determination of optimum levels of F supplementation in human nutrition for caries-prevention programmes.