Aberrant methylation-induced dysfunction of p16 is associated with osteoblast activation caused by fluoride

Chronic exposure to fluoride continues to be a public health problem worldwide, affecting thousands of people. Fluoride can cause abnormal proliferation and activation of osteoblast and osteoclast, leading to skeletal fluorosis that can cause pain and harm to joints and bones and even lead to permanent disability. Nevertheless, there is no recognized mechanism to explain the bone lesions of fluorosis. In this work, we performed a population study and in vitro experiments to investigate the pathogenic mechanism of skeletal fluorosis in relation to methylation of the promoter of p16. The protein coded by the p16 gene inhibits cdk (cyclin-dependent kinase) 4/cdk6-mediated phosphorylation4 of retinoblastoma gene product and induces cell cycle arrest. The results showed that hypermethylation of p16 and reduced gene expression was evident in peripheral blood mononuclear cells of patients with fluorosis and correlated with the level of fluoride exposure. Studies with cell cultures of osteoblasts revealed in response to sodium fluoride (NaF) treatment, there was an induction of p16 hypermethylation and decreased expression, leading to increased cell proliferation, a longer S-phase of the cell cycle, and development of skeletal fluorosis. Further, the methylation inhibitor, 5-aza-2-deoxycytidine, reversed the p16 hypermethylation and expression in response to NaF. These results reveal a regulatory role of p16 gene methylation on osteoblasts activation during the development of skeletal fluorosis.

[Caries prevention with fluoridated and iodinated salt in school-aged children living in areas with fluoride and iodine deficiency]

The aim of the study was to evaluate the efficacy of dental caries prevention program with 3 years follow-up in children living in areas with fluoride and iodine deficiency. The study involved 625 school-aged children aged 6, 12 and 15 years receiving endogenous prevention with fluoridated and iodinated salt (300±50 mgF/kg and 40±10 mgI/kg). Enamel and dentine concentrations of CA, P, F and I were measured in 98 intact deciduous teeth by X-ray microanalysis before and after prevention program. Enamel and dentin microhardness was assessed in the same 98 teeth by Vickers Hardness Test. Obtained reduction of DMFT growth, positive changes of mineral composition and dental hard tissues microhardness prove high clinical efficacy of applied prevention program.

Comparison of the Biological Impacts of the Fluoride Compounds by Graphical Risk Visualization Map Technique

Various fluoride compounds are widely used in industry. The present risk assessment study was conducted using a series of inorganic binary fluorides of the type XFn, where X(n) = Na(+), K(+), Li(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Al(3+), Nd(3+), La(3+), Ce(3+), Sm(3+), Gd(3+), Y(3+), Yb(2+), and Zn(2+). The aqueous solutions of these salts were orally administrated to 16 experimental groups (one for each of the salts tested). The levels of fluoride, N-acetyl-β-D-glucosaminidase in cumulative 24-h urine samples and creatinine clearance were measured to assess possible acute renal damages. The levels of fluoride, alanine aminotransferase, and aspartate aminotransferase were also determined in serum samples to assess possible acute hepatic damages. The results reveal that sodium fluoride (NaF), potassium fluoride (KF), and zinc fluoride tetrahydrate (ZnF2 (.)4H2O) can carry the fluoride ion into the bloodstream and that it is excreted via urine more readily than the other compounds tested. These fluorides were assigned the highest risk impact factor. Most of the rare earth fluorides are insoluble in water while those groups 2 and 13 of the periodic table are slightly soluble, so that they do not have a significant negative risk. These findings suggest that the biological impact of fluoride depends on the accompanying counter ion and its solubility. The risk map obtained in the present study shows that the graphical visualization map technique employed is a valuable new tool to assess the toxicological risk of chemical compounds.

Effects of selenium and zinc on renal oxidative stress and apoptosis induced by fluoride in rats

OBJECTIVE

To study the effects of selenium and zinc on oxidative stress, apoptosis, and cell cycle changes in rat renal cells induced by fluoride.

METHODS

Wistar rats were given distilled water containing sodium fluoride (50 mg/L NaF) and were gavaged with different doses of selenium-zinc preparation for six months. Four groups were used and each group had eight animals (four males and four females). Group one, sham-handled control; group two, 50 mg/L NaF; group three, 50 mg/L NaF with a low dose of selenium-zinc preparation (0.1 mg/kg Na2 SeO3 and 14.8 mg/kg ZnSO4 x 7H2O); and group four, 50 mg/L NaF with a high dose of selenium-zinc preparation (0.2 mg/kg Na2 SeO3 and 29.6 mg/kg ZnSO4 x 7H2O). The activities of serum glutathione peroxidase (GSH-Px), kidney superoxide dismutase (SOD), and the levels of malondialdehyde (MDA) and glutathione (GSH) in the kidney were measured to assess the oxidative stress. Kidney cell apoptosis and cell cycle were detected by flow cytometry.

RESULTS

NaF at the dose of 50 mg/L increased excretion of fluoride in urine, promoted activity of urine gamma-glutamyl transpeptidase (gamma-GT), inhibited activity of serum GSH-PX and kidney SOD, reduce kidney GSH content, and increased kidney MDA. NaF at the dose of 50 mg/L also induced rat renal apoptosis, reduced the cell number of G2/M phase in cell cycle, and decreased DNA relative content significantly. Selenium and zinc inhibited effects of NaF on oxidative stress and apoptosis, promoted the cell number of G2/M phase in cell cycle, but failed to increase relative DNA content significantly.

CONCLUSION

Sodium fluoride administered at the dose of 50 mg/L for six months induced oxidative stress and apoptosis, and changes the cell cycle in rat renal cells. Selenium and zinc antagonize oxidative stress, apoptosis, and cell cycle changes induced by excess fluoride.

[Fluoride metabolism in children and caries prevention]

Basal mineral elements content in superficial dental enamel layers and daily urine fluoride excretion have been investigated in children using water with various level of this trace element. The investigation was carried out before and after sodium fluoride intake in the doses 1.1-1.6 mg/day. The results give evidence that differential approach to dental caries prevention with fluoride is required.

A case of nonfatal sodium fluoride ingestion

A nonfatal case of sodium fluoride ingestion is presented. The quantity of sodium fluoride ingested is unknown. Initial serum and urine samples were taken 24 h after ingestion and contained 3.4 and 21.3 mg/L fluoride, respectively. At that time the patient was essentially asymptomatic, but it is clear that he survived a plasma concentration greater than that usually considered lethal, 3 mg/L serum fluoride. The case illustrates the lack of correlation between plasma fluoride concentration and toxic effects and the importance of obtaining a history of fluoride ingestion.

Experimental acute sodium fluoride poisoning in sheep: renal, hepatic, and metabolic effects

Sheep received a single intragastric dose of 0.5, 1.0, 1.5, or 2.0 mmol F-/kg. Mild signs occurred at 1.5 mmol F-/kg and the animals recovered 2 days later. With the 2.0 mmol F-/kg dose all animals showed dullness, anorexia, and mild diarrhea which decreased from the third day. Dose-related congestion of duodenum, liver, kidney, and lung was observed in all animals. For the two higher doses kidney degeneration and tubular necrosis were associated with glomerular inflammation. Serum fluoride had a dose-related increase and was still significantly elevated on Day 7 for sheep given doses higher than or equal to 1.0 mmol F-/kg. Serum calcium and glucose levels were significantly lowered for all doses on the first day and the decrease was dose-related. In sheep given 2.0 mmol F-/kg total proteins and sodium were significantly lowered, whereas potassium and urea were increased (p less than 0.05); alkaline phosphatase (ALP) and lactic dehydrogenase (LDH) were both lowered (p less than 0.01) on the first day and ALP was still lowered on Day 7. For the highest dose glutamate dehydrogenase (GDH) was increased on Days 1 and 7 and gamma-glutamyl transferase (GGT) was increased on Day 1 and lowered on Day 7. Diuresis was increased for the two higher doses in Day 3 or 4 following dosage. A dose-related increase of daily fluoride excretion occurred for all doses on Day 1 and fluoride excretion was still significantly elevated on Day 7 except for the lowest dose.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro release and in vivo serum fluoride levels and urinary excretion after different sodium fluoride tablets

Various sodium fluoride tablets used for the treatment of osteoporosis were evaluated. The tablets were characterized in vitro by determining the release curves. The serum levels and urinary recovery of fluoride were determined after a single oral dose either of rapidly soluble (conventional), sustained release or enterocoated tablets. The in vivo study showed that administration of sustained release tablets eliminated high serum peaks and prolonged the duration of an elevated serum level as compared to conventional tablets. The biovailability of the fluoride was lower after intake of sustained release and enterocoated tablets, and there was an increase in the interindividual variance of biovailability.