The status of sulphated isomers of glycosaminoglycans in fluorosed human teeth

Prevention & control of fluorosis & linked disorders: Developments in the 21st Century - Reaching out to patients in the community & hospital settings for recovery

The review on fluorosis addresses the genesis of the disease, diagnostic protocols developed, mitigation and recovery through nutritional interventions. It reveals the structural and functional damages caused to skeletal muscle and erythrocytes, leading to clinical manifestations in fluorosis. Hormonal derangements resulting in serious abnormalities in the health of children and adults are discussed. Fluoride toxicity destroys the probiotics in the gut, resulting in vitamin B₁₂ depletion, an essential ingredient in haemoglobin (Hb) biosynthesis. The article provides an overview of National Technology Mission on Safe Drinking Water and its contributions to fluorosis control. National Programme for Prevention and Control of Fluorosis is presently in operation in India and its focus cited. Major emphasis has been laid on a variety of disorders surfacing in India due to fluoride toxicity/fluorosis as ‘fluorosis-linked disorders’, viz. anaemia in pregnancy, schoolchildren, thyroid hormone abnormalities, hypertension, iodine deficiency disorders/goitre, renal failure and calcium+vitamin D-resistant rickets in children. The major action taken by the Indian Council of Medical Research (ICMR), Government of India in establishing a Centre of Excellence for Fluorosis Research in India and its contributions are highlighted.

Fluoride-induced changes to proteoglycan structure synthesised within the dentine–pulp complex in vitro

Fluoride is known to influence mineralisation patterns within dentine, where alterations in the post-translational modification of proteoglycans (PG) have been proposed as an implicating factor. In light of recent studies elucidating changing PG profiles in the transition of predentine to mineralised dentine, this study investigates the influence of fluoride on the major PG populations (decorin, biglycan and versican) within the pulp, predentine and dentine. Tooth sections from rat incisors were cultured for 14 days in the presence 0, 1 and 6 mM sodium fluoride and the PG extracted from the pulp, predentine and dentine matrices. PG species and corresponding metabolites were identified by their immuno-reactivity to antibodies against decorin, biglycan and versican. Component glycosaminoglycan chains were characterised with respect to their nature, chain length and disaccharide composition. Levels of PG extracted from pulp and predentine were reduced, particularly for biglycan. Fluoride did not influence levels of decorin or versican within predentine or dentine, although the processing of these macromolecules within pulp and predentine was affected, particularly at higher fluoride concentrations. Levels of dermatan sulfate were reduced within pulp and predentine, although the effect was less pronounced for predentine. Fluoride reduced sulfation of glycosaminoglycan chains within pulp and predentine tissues, with a notable reduction in Deltadi6S evident. In all three tissues, glycosaminoglycan chain length was reduced. Considering the various roles for PG in the dentine-pulp complex, either directly or indirectly in the mineralisation process, changes in the synthesis, structure and processing of the different PG species within the pulp, predentine and dentine matrices provides a further molecular explanation for the altered mineralisation patterns witnessed during fluorosis.

Odontoblast transport of sulphate--the in vitro influence of fluoride

The present study reports the development of a culture system for the analysis of 35S-sulphate release from odontoblasts in vitro. Pulpless longitudinally split rat incisors were cultured in supplemented minimum essential medium (alphaMEM) with 20 microCi 35S-sulphate per ml, 20 microCi 3H-mannitol per ml for 1h. Teeth were then transferred to fresh unlabelled media and aliquots of media were removed and the level of 35S-sulphate 3H-mannitol determined. Results indicated a two phase release of 35S-sulphate into the media, and comparison with pulp tissue indicated a specific release pattern. Transport of sulphate is essential for correct synthesis and glycosylation of macromolecules such as proteoglycans (PG). Previous studies have shown that post-translational modifications of these proteins can be influenced by excess fluoride, resulting in decreased sulphation and elongation of glycosaminoglycan (GAG) chains. Therefore the influence of fluoride on sulphate transport, using the optimised culture system was also investigated. Inclusion of 6mM fluoride during pulse labelling caused a significant decrease of 35S-sulphate (P<0.0001) during the initial release phase. Inclusion of 3 and 6mM fluoride only in the post-labelling incubation media resulted in a significant decrease in the release of 35S-sulphate (P<0.0001), during the total time course. The influence of fluoride was not dose dependent. Inclusion of a specific chloride channel blocker SITS, into the culture system indicated that 35S-sulphate transport may in part be via this route. Fluoride would therefore appear to influence the transport of 35S-sulphate across the odontoblast membrane, potentially via a chloride channel.

The influence of fluoride on the cellular morphology and synthetic activity of the rat dentine-pulp complex in vitro

Exposure to high fluoride concentrations in the immediate environment of the tissue is recognized to result in the post-translational modification of non-collagenous dentine extracellular matrix (ECM) components, potentially altering dentine mineralization. However, less is known about the effects of fluoride exposure on the morphology or metabolism of the cells associated with the dentine-pulp complex. This study examined the effects of fluoride exposure at defined concentrations on the cellular morphology and ECM synthetic activities of odontoblasts and pulpal fibroblasts by the culture of tooth sections from male Wistar rat incisors in Trowel-type cultures for up to 14 days, in the presence and absence of 6mM sodium fluoride. Histomorphometric analysis of the dentine-pulp complex of sodium fluoride-exposed tooth sections demonstrated no obvious gross morphological differences with respect to the odontoblasts and pulpal fibroblasts throughout the 14-day culture period, in comparison with unexposed tooth sections. No significant differences in odontoblast and pulpal fibroblast cell numbers were determined in the absence and presence of fluoride. Image analysis examination of odontoblast cytoplasmic:nuclear (C/N) ratios also showed no significant differences in fluoride-exposed and unexposed tooth sections, although reductions in the C/N ratios of pulpal fibroblasts were evident in fluoride-exposed sections at days 10 and 14. No significant differences in predentine width were observed in fluoride-exposed and unexposed tooth sections over the 14-day culture period. Autoradiography following [3H]proline incorporation into the dentine-pulp complex demonstrated inhibition of collagen synthesis, particularly by the odontoblasts in tooth sections exposed to 6mM sodium fluoride. These findings, in association with those from previous studies, imply that dentine ECM alterations may contribute to the altered mineralization of dentine during fluorosis, rather than secretory-related changes in odontoblast morphology.

Proteoglycans in dentinogenesis

The predominant proteoglycans present in predentin and dentin are the chondroitin-sulphate-rich decorin and biglycan and the keratan-sulphate-rich lumican and fibromodulin. These are small, interstitial, leucine-rich proteoglycans which have recently been shown to exist in gradients across the predentin. Antibodies recognizing chondroitin sulphate show a decreasing gradient from the pulpal aspect toward the mineralizing front, the converse being true for keratan sulphate. Antidecorin shows an increase toward the mineralization front. Evidence from biochemical, autoradiographic, and immunohistochemical studies implies that such changes may be brought about by gradients of metalloproteinases. This offers the possibility that the proteoglycans organize the collagen network for receipt of phosphoproteins and phospholipids, the former being evident only at the onset of dentin formation. The suggestion is raised that glycosaminoglycan-depleted leucine-rich protein cores act as sequester points for receipt of phosphoproteins in particular. The rigid, spatially oriented glycosaminoglycan chains on decorin and biglycan are known to bind calcium and may feature directly in mineral initiation.

Fluoride alters casein kinase II and alkaline phosphatase activity in vitro with potential implications for dentine mineralization

Dentine phosphoprotein (DPP), a major non-collagenous acidic protein of dentine, undergoes altered phosphorylation in vivo in the presence of high fluoride concentrations. This has major implications for the altered mineralization patterns found during fluorosis. In dentine, casein kinase II is involved in phosphorylating DPP, and alkaline phosphatase (ALP) is ascribed roles in the dephosphorylation of DPP, increasing the inorganic phosphate at the mineralization front and the removal of pyrophosphate. Here the influence of fluoride in vitro on the activity of purified casein kinase II and ALP and its relation to altered patterns of mineralization were examined. Kinetic analysis showed that casein kinase II activity was completely inhibited at 0.04 M NaF. Vmax when compared to the control assay was significantly decreased (P < 0.0001) between concentrations 4 x 10(-4)-4 x 10(-8) M NaF. Significant changes to the Km (P < 0.0001) were also observed. ALP activity was inhibited by NaF (0.09-9 x 10(-8) M), with Vmax significantly decreased (P < 0.0001) at 0.09 M NaF. Alterations in the activity of these enzymes in the presence of fluoride may in part explain the decreased phosphorylation observed in DPP isolated from fluorotic dentine and may aid understanding of the altered matrix mediated mineralization patterns found during fluorosis.

Structural analysis of proteoglycans synthesized by mineralizing bone cells in vitro in the presence of fluoride

This study investigated the biochemical structure of proteoglycans synthesized during matrix maturation by mineralizing bone cells in vitro, in the presence and absence of fluoride. Bone cells were obtained from rat femur washes and cultured in alpha MEM media supplemented with fetal calf serum, ascorbic acid, beta-glycerophosphate and dexamethasone. Cells were characterized as osteoblast-like by the expression of alkaline phosphatase activity and the synthesis of collagen type I and osteocalcin. Fluoride, present in the culture media at concentrations of 10(-5) M or 10(-7) M, had negligible effect on cell viability. However, calcium deposition was increased in cell cultures incubated in the presence of fluoride. Proteoglycans were extracted from the extracellular matrix with 4 M guanidinium chloride and purified by anion exchange chromatography. Biochemical analysis identified the presence of the small leucine rich proteoglycan, decorin and biglycan, in addition to degradation products relating to the larger chondroitin sulphate protoeglycan, versican. Fluoride had little effect on the size or amino acid composition of the protein core, but resulted in significant alterations to the GAG chains, including a dramatic reduction in chain length, reduction in sulphation and decrease in the proportion of dermatan sulphate compared to chondroitin sulphate. The influence of fluoride on proteoglycan structure synthesized by mineralizing bone cells provides valuable information, indicating specific roles for dermatan sulphate and chondroitin sulphate proteoglycans. The results suggested that fluoride affected the post-translational assembly of the GAG chains which may be an influential factor in the mineralization process.

Modification of the proteoglycans of rat incisor dentin-predentin during in vivo fluorosis

Proteoglycans (PGs) were isolated from the dentin-predentin of fluorotic and control rat incisor teeth using demineralization in EDTA, followed by extraction with 4 M guanidinium chloride in the presence of protease inhibitors. Differences in the behaviour of fluorotic and control PG were evident during purification by anion exchange chromatography on Q-Sepharose and MONO-Q interfaced with fast protein liquid chromatography. The PG from fluorotic teeth exhibited a more anionic profile, due to changes in glycosaminoglycan characteristics, since no apparent differences were evident between the respective core proteins, both of which were 45 kDa. The constituent glycosaminoglycan chains of fluorotic dentin were of lower molecular size and showed the additional presence of dermatan sulfate and heparan sulfate by comparison to nonfluorotic controls, where only chondroitin-4-sulfate was detected.

The influence of fluoride on the adsorption of proteoglycans and glycosaminoglycans to hydroxyapatite

Proteoglycans and their spatial arms, the glycosaminoglycans, are known to interact with hydroxyapatite, and are considered to have a role in the regulation of mineralization. This study investigates the interactive mechanisms, with particular attention directed at the influence of fluoride on the adsorption process. Proteoglycans and glycosaminoglycans were adsorbed to hydroxyapatite in the presence of fluoride (1-20 ppm range). The adsorbates included a chondroitin 4-sulfate-rich proteoglycan extracted from rat incisor dentine, hyaluronan, chondroitin 4-sulfate, and dermatan sulfate. The order of glycosaminoglycan in decreasing affinity for hydroxyapatite was chondroitin 4-sulfate, dermatan sulfate, and hyaluronan, and the individual glycosaminoglycans showed different responses to the presence of fluoride. Graded increases in fluoride (1-4 ppm) led to 5-40% reduction of glycosaminoglycan adsorption to hydroxyapatite. The proteoglycan showed less affinity for hydroxyapatite, and demonstrated a reduction in adsorption of up to 22% with 20 ppm fluoride. The inhibitory effect of fluoride indicated an electrostatic mechanism, presumably via the calcium sites in the hydroxyapatite lattice.

Fluoride toxicity: a biochemical and scanning electron microscopic study of enamel surface of rabbit teeth

The present study has been carried out to investigate the effect of fluoride toxicity on the morphology as well as inorganic chemical constituents of rabbit teeth. Rabbits were administered sodium fluoride at a dose of 10 mg NaF/kg body weight every 24 h for 18 and 23 months. The incisor and molar teeth (whole tooth) were investigated for fluoride, calcium and phosphorus content in 18- and 23-month treated animals. The enamel surfaces of incisor teeth of 23-month treated animals were examined under scanning electron microscope. A significant increase in fluoride levels and significant decrease in calcium content was found following fluoride administration for 18 and 23 months as compared to control. Ca/P ratio was significantly increased only in 23-month treated animals. The scanning electron micrographs revealed hypoplastic, rough, uneven, pitted and cracked enamel surfaces covered with granular deposits as a result of excessive intake of fluoride. It can be concluded that long term fluoride administration leads to severe structural alterations on the enamel surface, possibly through defective mineralization.

The influence of fluoride on proteoglycan structure using a rat odontoblast in vitro system

Using an in vitro rat incisor odontoblast system, the effect of fluoride on proteoglycans was investigated at both the metabolic and structural level. Incisors were removed from 4-week-old rats, split longitudinally, and the pulps removed. Teeth were incubated at 37 degrees C, 5% CO2 in Eagle's Minimum Essential Medium containing 35S-sulfate for 7 hours in the presence of 0 mM, 3 mM, or 6 mM sodium fluoride. Teeth were demineralized in EDTA, proteoglycan was extracted from the residue with 4 M guanidinium chloride, and further purified by anion exchange chromatography. Uptake of radiolabel was monitored by liquid scintillation counting. The resultant products were examined by cellulose acetate electrophoresis, SDS-PAGE, chondroitinase digestion, and amino acid analysis. Differential effects of fluoride were observed in both metabolism and biochemical characterization of proteoglycans following incubation at the two concentrations. Fluoride decreased uptake of the radiolabel but led to an accumulation of glycosaminoglycan within the proteoglycan of the matrix. Chondroitin sulfate was the predominant glycosaminoglycan identified, with the additional presence of dermatan sulfate and heparan sulfate identified. Dermatan sulfate levels increased in 3 mM-treated teeth. Fluoride-treated proteoglycans had a reduced molecular weight (200-90K to 180-79K); this reduction is primarily a result of smaller glycosaminoglycan chains, with limited reduction in the size of the core protein of 6 mM-treated teeth occurring. Such alterations in the biochemical metabolism and hence structure and function of proteoglycan may be implicated in the hypomineralization seen in fluorosis.

Fluoride-induced changes in the tooth glycosaminoglycans: an in vivo study in the rabbit

Effect of high fluoride ingestion on the tooth matrix glycosaminoglycans was studied in rabbits administered 10 mg NaF/kg body weight orally at 24-h intervals for a period of 9 months. Fluoride-treated tooth showed a significant reduction in glycosaminoglycan content as compared to the normal tooth. Sephadex G-75 chromatography and DEAE-cellulose ion exchange chromatography revealed the presence of small molecular weight glycosaminoglycan molecules and an increase in the charge density heterogeneity in the sulphated glycosaminoglycans of the fluoride-treated rabbit tooth as compared to the controls. These changes may be related to the dedifferentiated tooth matrix and an increase in the dermatan sulphate content in the fluoride-treated tooth matrix reported earlier.