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Biomedical subjects

T van den Bos

Publications and source records attributed to T van den Bos.

At least 19 recordsLinked to original sources
PubMed2005

Cementum and dentin in hypophosphatasia.

Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum.

Adolescent↗
PubMed2000

Response of periodontal ligament fibroblasts and gingival fibroblasts to pulsating fluid flow: nitric oxide and prostaglandin E2 release and expression of tissue non-specific alkaline phosphatase activity.

The capacity of the periodontal ligament to alter its structure and mass in response to mechanical loading has long been recognized. However, the mechanism by which periodontal cells can detect physical forces and respond to them is largely unknown. Besides transmission of forces via cell-matrix or cell-cell interactions, the strain-derived flow of interstitial fluid through the periodontal ligament may mechanically activate the periodontal cells, as well as ensure transport of cell signaling molecules, nutrients and waste products. Mechanosensory cells, such as endothelial and bone cells, are reported to respond to a flow of fluid with stimulated prostaglandin E2 (PGE2) and nitric oxide production. Therefore, we examined the PGE2 and nitric oxide response of human periodontal ligament and gingival fibroblasts to pulsating fluid flow and assessed the expression of tissue non-specific alkaline phosphatase activity. Periodontal ligament and gingival fibroblasts were subjected to a pulsating fluid flow (0.7 +/- 0.02 Pa, 5 Hz) for 60 min. PGE2 and nitric oxide concentrations were determined in the conditioned medium after 5, 10, 30 and 60 min of flowing. After fluid flow the cells were cultured for another 60 min without mechanical stress. Periodontal ligament fibroblasts, but not gingival fibroblasts, responded to fluid flow with significantly elevated release of nitric oxide and decreased expression of tissue non-specific alkaline phosphatase activity. In both periodontal ligament and gingival fibroblasts, PGE2 production was significantly increased after 60 min of flowing. Periodontal ligament fibroblasts, but not gingival fibroblasts, produced significantly higher levels of PGE2 during the postflow culture period. We conclude that human periodontal ligament fibroblasts are more responsive to pulsating fluid flow than gingival fibroblasts. The similarity of the early nitric oxide and PGE2 responses to fluid flow in periodontal fibroblasts with bone cells and endothelial cells suggests that these three cell types possess a similar sensor system for fluid shear stress.

Adolescent↗
PubMed1999

Alkaline phosphatase activity in human periodontal ligament: age effect and relation to cementum growth rate.

Recently, a relationship was demonstrated between the thickness of the cementum layer in rat molars and the activity of alkaline phosphatase (ALP) in the adjoining periodontal ligament (PDL). It was the aim of the present study to investigate whether such a relationship also exists in the periodontium of man. Healthy deciduous and permanent teeth free from periodontitis were obtained from 74 patients, varying in age from 3 to 78 yr, and their PDL dissected from the middle one-third of the roots. ALP activity was measured in PDL extracts and expressed per hydroxyproline content. It was shown that ALP activity was relatively high in children. After puberty its concentration decreased to level off at about half the concentration found in the younger age groups. The activity of the enzyme in the PDL correlated positively with the yearly cementum thickness increment as calculated from data published previously.

Adolescent↗
PubMed1998

[Survey of 50 years of veterinary remedy provision in the Netherlands].

This article gives an overview of a half century of veterinary product provision in the Netherlands, and describes the availability of veterinary products from 1945 and onwards. The development of antibiotics, sulfonamides, anthelmintics, endocrine products, vaccines, and other product groups is discussed briefly. The importance of the research carried out by leading pharmaceutical companies in collaboration with the Faculty of Veterinary Medicine Utrecht and other governmental research institutes is stressed. This article also emphasizes the importance of good and responsible product information for veterinarians. The introduction of the veterinary drug law in 1986 has had great consequences for the industry, distributors, and wholesalers as well as for practising veterinarians.

Animals↗
PubMed1998

Formation of reparative acellular extrinsic fiber cementum in relation to implant materials installed in rat periodontium.

The aim of the present study was to determine the nature of the cells associated with the formation of reparative acellular extrinsic fiber cementum (AEFC). Calcifying collagen membranes, hydroxyapatite particles and/or non-resorbable ePTFE membranes were implanted in lesions made in the periodontium of the rat mandibular incisor. The incisor was prevented from erupting further, and the animals were killed after 1-8 wk. In the first week, next to cells with a fibroblastic phenotype, epithelial cells (ECs) migrating out of the reduced enamel epithelium were among the cells colonizing the wounds. From 2 wk on, the ECs showed regressive changes and disappeared. Along mineralized implant surfaces, a basophilic layer enriched in osteopontin (but without detectable amelogenin) was deposited. After 3 wk (when ECs were no longer present) the healing tissue transformed into a well-organized PDL-like tissue, and AEFC started to develop. Along the non-mineralizing ePTFE membranes, AEFC did not form except in regions where small calcified bodies were present. It is concluded that reparative AEFC layers are formed only along calcified surfaces. The cells associated with this reparative activity are periodontal ligament cells with a fibroblastic phenotype.

Animals↗
PubMed1997

Degradable bisphosphonate-alkaline phosphatase-complexed hydroxyapatite implants in vitro.

Degradable hydroxyapatite (HA) implants complexed with the resorption inhibiting agent bisphosphonate (PCP) and the mineralizing agent alkaline phosphatase (ALP) can theoretically maintain alveolar bone mass directly after extraction of teeth. The present in vitro study investigated the surface properties of PCP-ALP-complexed HA implants in relation to the requirements of implant behavior and action. Adsorbed PCP (pH 3.49) resulted in a flattening and broadening of the phosphate peaks and the formation of carbonate peaks in the HA pattern of the implant indicating a chemical alteration of the HA surface. Adsorption of ALP onto PCP-altered HA surfaces was 26% lower than onto HA implant blank surfaces. PCP-ALP-complexed HA implants released the PCP and ALP steadily and continuously over observation periods of, respectively, 75 and 14 days. During these observation periods, the ceramic grains of the HA implant became smaller and intergrain boundaries became broader. These morphologic characteristics suggested preconditioning of the HA implant surface for future bonding and degradation in vivo. Individual grains were no longer bonded to other grains and detached from the implant which had become rounded in shape. From in vitro mice experiments we found that PCP concentrations between 10(-4) and 10(-3) M resulted in 45Ca-release from the bone HA. Our calculations showed, however, that only a total concentration of 1.4 x 10(-4) M PCP was gradually released over the whole observation period. In another experiment, it appeared that a PCP concentration in solution < 10(-3) M did not reduce ALP activity. It is concluded that release of PCP by the PCP-ALP-complexed implants is maintained at levels in the range to impair osteoclast bone resorption but not high enough to block osteoblast activity. The amount of ALP released can lead to induction of bone formation onto implant surfaces. pH-induced alterations in the microstructure and chemistry of the HA surface allow for controlled degradation of the HA implants in vitro. A PCP-ALP-complexed HA implant acting as temporary scaffolding for alveolar bone growth enhancement, mineralization, and maintenance seems to be a reasonable concept for preservation of the edentulous alveolus.

Absorption↗
PubMed1995

Mineralization of alkaline phosphatase-complexed collagen implants in the rat in relation to serum inorganic phosphate.

The present study was designed to determine the relationship between mineralization of collagenous matrices and serum levels of calcium and inorganic phosphate. Collagen slices were prepared from bovine dentin or cortical bone and complexed with varying amounts of intestinal alkaline phosphatase (ALP). The enzyme was added to induce de novo mineralization. The ALP-complexed slices were implanted subcutaneously over the skull and in the dorsolateral aspect of the abdominal wall in female Wistar rats of various ages (5-, 10-, 20-, or 35-week-old) and in young male rats fed on a low-P diet. After 1-4 weeks, the implants were removed and analyzed for calcium and phosphate content. In addition, serum levels of calcium and phosphate (total and inorganic) were determined. It was shown that the highest mineral influx occurred in the younger rats (which were also highest in serum P(i)), whereas almost no mineral uptake occurred in the older ones. Also in rats fed on a low-P diet (which were low in serum P(i), a strongly decreased mineral influx was noted. In all animal groups a positive correlation was found between the degree of mineralization and serum P(i). No distinct relationship was found between serum Ca/organic phosphate levels and mineral influx in the implants. In vitro incubation of ALP-collagen conjugates in serum from younger and older rats confirmed our view that serum P(i), besides local levels of ALP, is important in de novo mineral deposition. For accretion of mineral in partially remineralized collagenous carriers, ALP activity was not required.

Aging↗
PubMed1994

Mineralization of alkaline phosphatase-complexed collagenous implants in the rat: relation with age, sex, and site of implantation.

This study was designed to determine the effects of age, sex, and site of implantation on the extent of alkaline phosphatase-complexed collagen sheets mineralization in the animal body. Collagen sheets were prepared from bovine dentin and cortical bone and complexed with varying amounts of intestinal alkaline phosphatase (ALP). Controls were without enzyme or with heat-inactivated enzyme. Sheets were implanted subcutaneously over the skull and in the dorsolateral abdominal wall in 5- or 20-week-old male and female Wistar rats. After 2-3 weeks the implants were removed and analyzed for phosphate and calcium content. Our findings have shown that alkaline phosphatase-induced mineralization of collagenous implants is influenced to a considerable extent by age, sex, and site of implantation. Highest mineral influx was seen in the younger males. Implants in younger females and older males contained less mineral, whereas those installed in the older females were almost free of calcium phosphate deposits. Dentinal implants in the skull region contained more mineral than those in the abdominal wall.

Abdominal Muscles↗
PubMed1994

Bound phosphoproteins enhance mineralization of alkaline phosphatase-collagen complexes in vivo.

Phosphoproteins (PP) covalently bound to a collagenous matrix have been reported to promote its mineralization in vitro. It was the aim of the present study to determine whether PP also enhance the mineralization of collagen in vivo. To this end, collagen slices were prepared from demineralized bovine cortical bone. Following immobilization of rat dentin phosphoprotein (PP) to the slices, bovine intestinal alkaline phosphatase (ALP) was bound according to the SATA-MHS coupling method. Controls were without enzyme. The slices were implanted into skin pockets prepared over the skull of female Wistar rats (6-10 weeks old). After 3-31 days the implants were removed and analyzed for calcium and phosphate content. It was shown that slices of PP-treated bone collagen mineralized more rapidly and to a greater extent than bone collagen slices without PP. Controls remained free of mineral. It is concluded that mineralization of collagenous matrices, induced by alkaline phosphatase, is enhanced by bound phosphoproteins following implantation in subcutaneous connective tissue.

Alkaline Phosphatase↗
PubMed1993

Mineralization of dentinal collagen sheets complexed with alkaline phosphatase and integration with newly formed bone following subperiosteal implantation over osseous defects in rat calvaria.

We addressed the question to what extent alkaline phosphatase (ALP) can induce mineralization of a collagenous matrix implanted subperiosteally, and how the graft interacts with the underlying bone. Bovine intestinal ALP was bound to sheets of guanidine-extracted, demineralized bovine dentin by using the crosslinking agent 1-ethyl-3(3-dimethylaminopropyl)carbodiimide.HCl. The complexes (with active enzyme) and control grafts (no enzyme) were implanted over osseous defects in opposite halves of rat calvaria. After time intervals varying from 3-12 weeks, the calvaria were processed for light and electron microscopic examination and histomorphometric analysis. The ALP-containing sheets (but not their controls) rapidly accumulated mineral crystals. As the complexes mineralized, osteoblasts appeared and formed a layer of bone in direct contact with the grafted material. The results indicate that ALP induced the deposition of mineral crystals, and strongly suggest that it is this mineral component which influenced the formation of bone.

Alkaline Phosphatase↗
PubMed1993

Effect of bound phosphoproteins and other organic phosphates on alkaline phosphatase-induced mineralization of collagenous matrices in vitro.

The aim of the present study was to determine to what extent the rate at which collagen mineralizes correlates with the amount and nature of bound phosphate groups. Sheets of collagen prepared from demineralized bovine dentin or cortical bone were complexed with various concentrations of phosphoserine [(P)Ser] or rat dentin phosphoproteins (PP; lowly or highly phosphorylated PP, LPP or HPP). Alternatively, phosphate groups were removed from the collagenous carrier material by treatment with phosphatases. Mineralization was achieved by incubation in culture medium supplemented with 45Ca, alkaline phosphatase and 10 mM beta-glycerophosphate. The sheets were monitored for uptake of 45Ca and lag times calculated and plotted against the amount of bound phosphate. It was observed that dephosphorylation of the carrier causes an increase in lag time and that rat PP decreases lag times in a concentration-dependent way. HPP were more effective than LPP. (P)Ser or other small organic P-containing molecules had hardly any influence on lag time. It is concluded that next to the amount of bound phosphate, the nature of phosphorylated substances has considerable influence on the rate of mineralization of a collagenous carrier.

Alkaline Phosphatase↗
PubMed1992

Alkaline phosphatase induces the mineralization of sheets of collagen implanted subcutaneously in the rat.

To determine whether alkaline phosphatase (ALP) can cause the mineralization of collagenous matrices in vivo, bovine intestinal ALP was covalently bound to slices of guanidine-extracted demineralized bovine dentin (DDS). The preparations were implanted subcutaneously over the right half of the rat skull. Control slices not treated with the enzyme were implanted over the left half of the skull of the same animals. Specimens were harvested after periods varying from 1 to 4 wk. It was shown that ALP-coupled DDS rapidly accumulated hydroxyapatite crystals. 4 wk after implantation, the content of calcium and phosphate per microgram of hydroxyproline amounted up to 80 and 60%, respectively, of that found in normal bovine dentin. Our observations present direct evidence that ALP may play a crucial role in the induction of hydroxyapatite deposition in collagenous matrices in vivo.

Alkaline Phosphatase↗
PubMed1990

The possible relationship between the mineralization of dentin and the composition of its organic matrix.

Using the rat incisor as a model, evidence is presented that enamel-related (ERD) and cementum-related (CRD) dentins exhibit differences in composition. Whereas the ERD is rich in highly phosphorylated phosphoproteins, the CRD is rich in lowly phosphorylated phosphoproteins. These differences are accompanied by and possibly related to differences in composition and physical properties of the mineral phase.

Animals↗
PubMed1989

Differences between enamel-related and cementum-related dentin in the rat incisor with special emphasis on the phosphoproteins.

In order to determine whether qualitative and quantitative differences exist between the non-collagenous proteins of crown and root dentin, rat incisors were separated into their enamel- and cementum-related dentin portions (ERD and CRD, respectively). Isolation of the mineral-bound proteins was performed under nondegradative conditions. Analytical procedures included DEAE-chromatography on high pressure liquid chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and determination of phosphate, protein, and hydroxyproline. The results have shown that considerable differences exist among the two dentins with respect to the quantity of the various phosphoproteins. For this group of proteins as a whole, the ERD contains about 2 times the amount of organic phosphate found in the CRD and about 1.4 times the amount of protein. The content of higher phosphorylated phosphoproteins was about 4 times higher in the ERD than in the CRD, whereas the reverse was shown for the lower phosphorylated phosphoproteins. All differences were found to be statistically significant. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that while the ERD contains phosphoproteins with an apparent molecular mass of 98 kDa, the CRD contains two classes of phosphoproteins one of 98 and one of 88 kDa. The relevance of the observed differences in phosphoprotein distribution is discussed in relation to their possible role in mineralization.

Aging↗
PubMed1989

Calcification of dentinal collagen by cultured rabbit periosteum: the role of alkaline phosphatase.

Periostea were dissected from 1-2 weeks old rabbit calvaria and folded around decalcified and extracted bovine dentin matrix slices (DMS). The cocultures were grown in serum-containing medium supplemented with beta-glycerophosphate or other organic phosphate esters. [45Ca]-uptake measurements indicated that the DMS calcified. Initiation of the calcification process was associated with alkaline phosphatase activity and could be prevented by adding the inhibitor L-levamisole to the culture medium. Using [32P]-adenosine-monophosphate as a substrate for phosphatase activity it was demonstrated that very little, if any, phosphate was utilized for the phosphorylation of higher molecular weight substances. The results suggest that over 99% of the phosphate produced was laid down in inorganic form. Further, it was noted that mineral deposition in the DMS was accompanied by the simultaneous inclusion of methylene blue and PAS-positive substances whose nature, origin and function remain to be determined. The results lend support to the theory that alkaline phosphatase is involved in the initiation of calcification processes by raising the local concentration of phosphate ions.

Alkaline Phosphatase↗
PubMed1987

Effects of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) on the synthesis of dentin matrix proteins in the mouse.

The drug 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) is known to inhibit the mineralization of bone and dentin. Its mechanism of action, however, has not yet been elucidated. In order to study its effects on dentinogenesis, mice were supplied with either physiological saline or HEBP in a dose of 10 mg P/kg body weight. This dose is known to interfere with the deposition of mineral crystallites in dentin matrix. The animals were then given a combined injection of [3H]-serine and [14C]-proline (or [14C]-glycine) and killed 8-9 days thereafter. The dentin proteins were isolated and fractionated in soluble proteins among which phosphoproteins, CNBr-peptides of collagen and collagen-associated phosphoproteins. It was found that HEBP had a strong inhibitory effect on the synthesis of phosphoproteins and to a lesser extent on that of collagen. The inhibition of the formation of these proteins is supposed to be related to the impaired calcification of dentin under the influence of the bisphosphonate.

Animals↗
PubMed1985

Glycosaminoglycans in myxoma of the jaw: a biochemical study.

Myxoma of the jaw is classified as an odontogenic tumor although final proof for an odontogenic origin is lacking. In the present study glycosaminoglycans (GAG's) in the extracellular matrix of a jaw myxoma were analyzed and compared with known data on GAG's in dental tissues. It was noted that the GAG's formed approximately 1% of the total tumor weight and 17% of the dry weight. Hyaluronic acid formed 72.4% of the GAG-fraction. Neither this high GAG-content nor the high fraction of hyaluronic acid are found in dental tissues and it is concluded that the myxoma matrix differs from the matrix in dental pulp and periodontal ligament.

Adult↗