Biomedical subjects

E H Burger

Publications and source records attributed to E H Burger.

At least 91 records · Page 5Linked to original sources

PubMed1995

Sensitivity of osteocytes to biomechanical stress in vitro.

It has been known for more than a century that bone tissue adapts to functional stress by changes in structure and mass. However, the mechanism by which stress is translated into cellular activities of bone formation and resorption is unknown. We studied the response of isolated osteocytes derived from embryonic chicken calvariae to intermittent hydrostatic compression as well as pulsating fluid flow, and compared their response to osteoblasts and periosteal fibroblasts. Osteocytes, but not osteoblasts or periosteal fibroblasts, reacted to 1 h pulsating fluid flow with a sustained release of prostaglandin E2. Intermittent hydrostatic compression stimulated prostaglandin production to a lesser extent: after 6 and 24 h in osteocytes and after 6 h in osteoblasts. These data provide evidence that osteocytes are the most mechanosensitive cells in bone involved in the transduction of mechanical stress into a biological response. The results support the hypothesis that stress on bone causes fluid flow in the lacunar-canalicular system, which stimulates the osteocytes to produce factors that regulate bone metabolism.

Animals↗

PubMed1994

Opposite effects of osteogenic protein and transforming growth factor beta on chondrogenesis in cultured long bone rudiments.

Osteogenic protein-1 (OP-1, also called BMP-7) is a bone morphogenetic member of the TGF-beta superfamily. In the present study, we examined the effect of recombinant human OP-1 on cartilage and bone formation in organ cultures of metatarsal long bones of mouse embryos and compared the OP-1 effects with those of human TGF-beta 1 and porcine TGF-beta 1 and beta 2. Cartilage formation was determined by measurement of longitudinal growth of whole bone rudiments during culture and by the incorporation of 35SO4 into glycosaminoglycans. Mineralization was monitored by 45Ca incorporation in the acid-soluble fraction and by measuring the length of the calcifying center of the rudiment. Toluidine blue-stained histologic sections were used for quantitative histomorphometric analysis. We found that OP-1 stimulated cartilage growth as determined by sulfate incorporation and that it increased remarkably the width of the long bones ends compared with controls. This effect was partly caused by differentiation of perichondrial cells into chondrocytes, resulting in increased appositional growth. In contrast to OP-1, TGF-beta 1 and beta 2 inhibited cartilage growth and reduced the length of whole bone rudiments compared with controls. In the ossifying center of the bone rudiments, both OP-1 and TGF-beta inhibited cartilage hypertrophy, growth of the bone collar, and matrix mineralization. These data demonstrate that OP-1 and TGF-beta exhibit opposite effects on cartilage growth but similar effects on osteogenesis in embryonic mouse long bone cultures. Since both OP-1 and TGF-beta have been demonstrated in embryonic cartilage and bone, these results suggest that they act as autocrine or paracrine regulators of embryonic bone development.

Animals↗

PubMed1994

Function of osteocytes in bone.

Although the structural design of cellular bone (i.e., bone containing osteocytes that are regularly spaced throughout the bone matrix) dates back to the first occurrence of bone as a tissue in evolution, and although osteocytes represent the most abundant cell type of bone, we know as yet little about the role of the osteocyte in bone metabolism. Osteocytes descend from osteoblasts. They are formed by the incorporation of osteoblasts into the bone matrix. Osteocytes remain in contact with each other and with cells on the bone surface via gap junction-coupled cell processes passing through the matrix via small channels, the canaliculi, that connect the cell body-containing lacunae with each other and with the outside world. During differentiation from osteoblasts to mature osteocyte the cells lose a large part of their cell organelles. Their cell processes are packed with microfilaments. In this review we discuss the various theories on osteocyte function that have taken in consideration these special features of osteocytes. These are 1) osteocytes are actively involved in bone turnover; 2) the osteocyte network is through its large cell-matrix contact surface involved in ion exchange; and 3) osteocytes are the mechanosensory cells of bone and play a pivotal role in functional adaptation of bone. In our opinion, especially the last theory offers an exciting concept for which some biomechanical, biochemical, and cell biological evidence is already available and which fully warrants further investigations.

Animals↗

PubMed1994

An analysis of the orientation of the radiographic trabecular pattern in the distal radius of children.

A digital image processing system was used to study changes in orientation of the radiographic trabecular pattern of bone in children aged 4-14 years. The radiographs originated from a mixed-longitudinal growth study (The Nijmegen Growth Study), which comprised of three birth cohorts and which was carried out between 1971 and 1975. Of 3075 left hand-forearm radiographs of 426 children, the orientation of the trabecular pattern of the radius was analysed in twelve directions on a standard area of 10 x 10 millimetres. It was demonstrated that the trabecular pattern of the radius shows two predominant directions of orientation: along and perpendicular to the long axis of the radius. Spearman's Rank Correlations were calculated between direction of orientation and age of the children for the total population as well as for the cohorts separately, because the existence of cohorts-effects. The cohort of the youngest children showed more and higher significant correlations than the other cohorts, indicating that the trabecular pattern of young children is more subjected to changes. The results indicate that the prevalence of trabeculae orientated perpendicular to the long axis of the radius decreases. We speculate that this development reflects the effects of changes in mechanical loading in that direction during growth and development resulting in functional adaptation of the trabecular bone.

Adaptation, Biological↗

PubMed1994

Longitudinal changes in the orientation of trabecular bone in relation to the location in the distal radius.

The aim of this study was to examine changes in orientation of trabecular bone during growth and development in relation to the location of trabeculae between the epiphysial growth plate and the marrow cavity. Five annual hand-wrist radiographs of 57 children between 4-9 years of age, originating from the Nijmegen Growth Study, were analysed by a digital image processing system. Analysis was carried out on four adjacent areas of 7 mm x 7 mm located in the distal head of the radius between the epiphyseal growthplate and the marrow cavity. The orientation of the trabecular pattern was measured in twelve directions. The orientation of trabeculae at a standardized distance from the epiphysial growth plate did not change significantly during growth and development. The orientation in directions perpendicular to the long axis of the radius was higher in newly formed trabecular bone, which is located just below the epiphysial growthplate, than in older trabecular bone at a larger distance from the epiphysial growth plate. Observation of one single area during five years of growth and development showed a comparable development.

Aging↗

PubMed1993

Effect of mechanical stimulation on the production of soluble bone factors in cultured fetal mouse calvariae.

Mechanical stimulation by intermittent compressive force (ICF) stimulates bone formation and inhibits bone resorption in cultured fetal mouse bone. Fetal bone tissue can produce autocrine factors that stimulate bone cell replication and matrix formation, and paracrine factors that increase the formation of osteoclast precursor-like cells from bone marrow. In the present study, we have tested whether ICF affects the production of such local factors in fetal mouse calvariae. Calvariae were cultured for 4 days in the presence and absence of ICF (130 mbar, 0.3 Hz). Conditioned medium was collected daily and pooled. We found that conditioned medium from ICF-exposed cultures stimulated [3H]-TdR incorporation into DNA, and [3H]-proline incorporation into collagenase digestible protein but not into non-collagen protein in fresh calvarial cultures. Treatment with conditioned medium from ICF-exposed cultures had earlier effects on [3H]-TdR and [3H]-proline incorporation than direct treatment with ICF. Conditioned medium from ICF-exposed cultures decreased the number of osteoclast precursor-like cells in bone marrow cultures stained for tartrate-resistant acid phosphatase. We conclude that ICF stimulates the release (activity) of an autocrine growth-factor from bone. In addition, ICF can stimulate the release (activity) of a paracrine factor, inhibiting the growth and/or differentiation of osteoclast precursor-like cells. These data suggest that mechanical forces may modulate skeletal (re)modeling by affecting the production of local growth factors.

Animals↗

PubMed1992

Bone induction by demineralized bone particles: long-term observations of the implant-connective tissue interface.

Allogeneic demineralized bone (DB) powder was applied to subcutaneous pockets and cranial defects of rats and histological, histomorphometrical, and radiological evaluation was performed one to 52 weeks after implantation. In both type of implants cartilage formation was observed after 1 week between DB particles and in former vascular channels and cervices within the particles. Foci of bone formation were observed after 2 weeks in the center of the implant. Remineralization of DB particles only occurred in close contact with the new bone tissue by which they became incorporated, indicating that remineralization of DB is a continuation of a process which has started in live bone. At all times, the interface between implant and connective tissue of the host consisted of a layer of non-remineralized DB particles embedded in fibrous connective tissue. This rim was thinner at the dura-mater-side in the cranial implants, compared with the skin-side of the same implants as well as all sides of the subcutaneous implants. The rim became thinner with time but never disappeared completely. The outer contour of the mineralized implant sometimes ran right through a DB particle. A critical concentration of bone-inducing agent leaking from DB particles seems to be necessary for bone induction. We suggest that at the interface of the implant and loose connective tissue this concentration is never reached, which results in maintenance of the rim.

Animals↗

PubMed1992

Mechanical stress and osteogenesis in vitro.

The use of hydrostatic pressure to apply mechanical stress to bone organ cultures is reviewed. Ossifying long bones and calvarial rudiments are sensitive to this type of stress. Intermittent hydrostatic compression of near physiologic magnitude (ICF) has anabolic effects on mineral metabolism in such rudiments, and continuous hydrostatic stress of high magnitude (CCP) has catabolic effects. The effects of ICF may be ascribed to shear stress generated at tissue interphases of different chemical and mechanical properties. Local factors, such as prostaglandins and growth factors, seem to be involved in the tissue response to mechanical stress.

Adaptation, Physiological↗

PubMed1991

Inhibiting and stimulating effects of TGF-beta 1 on osteoclastic bone resorption in fetal mouse bone organ cultures.

The effects of TGF-beta 1 on osteoclastic resorption of fetal mouse calvaria and long bones at various stages of development was studied in organ culture. In resorbing calvariae and long bones with an established marrow cavity TGF-beta 1 (4-10 ng/ml) had a stimulating effect on 45Ca release that was partially inhibited by indomethacin. In primitive long bones, however, which were explanted before osteoclast invasion and excavation of a marrow cavity had started, TGF-beta 1 (1-4 ng/ml) inhibited 45Ca release by an indomethacin-insensitive mechanism. Histomorphometry of long bones after staining for tartrate-resistant acid phosphatase (TRAP) revealed that TGF-beta 1 treatment inhibited the migration of TRAP-positive cells from periosteum to developing marrow cavity and inhibited cell fusion. However, the formation of (mononuclear) TRAP-positive cells in the periosteum-perichondrium was strongly enhanced. These data suggest that TGF-beta 1 modulates various steps in the cascade of osteoclast development, recruitment, and activation in different ways, involving both prostaglandin-mediated and prostaglandin-independent pathways. Therefore the net effect of exogenous TGF-beta 1 on osteoclastic resorption in bone organ cultures depends on the relative prevalence of osteoclast progenitors, precursors, and mature osteoclasts in the tissue under study.

Animals↗

PubMed1991

Modulation of osteogenesis in fetal bone rudiments by mechanical stress in vitro.

Studies of organ cultures of developing bone subjected to intermittent mechanical stress are reviewed. Mineral metabolism in these bones is modulated by exposure to dynamic stress of physiological magnitude. Finite element stress analysis of long bone rudiments shows that hydrostatic pressure during organ culture produces significant shear stresses at mineralized/non-mineralized tissue interfaces, in addition to dilatational stress. Both matrix producing cells (chondrocytes, osteoblasts) and matrix resorbing cells (osteoclasts) are affected by mechanical stress in vitro. The organ culture model offers certain opportunities for studying effects of mechanical stress on skeletal tissue at the cell and tissue level.

Animals↗

PubMed1990

Inhibition of osteoclastic bone resorption by mechanical stimulation in vitro.

The influence of mechanical stimulation by intermittent compressive force (ICF) of physiologic magnitude on osteoclastic bone resorption was investigated in cultures of fetal mouse cartilaginous long bones. Exposure to ICF resulted in a significant decrease in mineral resorption, as indicated by the decreased release of 45Ca and a decreased number of osteoclasts in the diaphysis. Conditioned medium (CM) from ICF-exposed periosteum-free cultures (ICF-CM), but not from control cultures (Co-CM), inhibited mineral resorption in fresh bones cultured under control conditions. Co-CM increased, but ICF-CM decreased, the number of tartrate-resistant acid phosphatase-positive cells in 7-day bone marrow cultures. Direct exposure of bone marrow cultures to ICF yielded the same results. Thus, osteoclastic bone resorption in cartilaginous long bones is inhibited by ICF in vitro. A soluble factor(s) acting on tartrate-resistant acid phosphatase-positive, osteoclast precursor-like cells seems to play a role in this effect.

Acid Phosphatase↗

PubMed1990

Bacteroides gingivalis stimulates bone resorption via interleukin-1 production by mononuclear cells. The relative role for B. gingivalis endotoxin.

Supernatants of human peripheral blood mononuclear cells cultured in the presence of B. gingivalis, showed a strong osteoclast stimulating activity as measured by 45Ca release from fetal mouse long bones in vitro. These supernatants also contained a high concentration of bioactive and immunoreactive interleukin-1 (IL-1), but tumor necrosis factor (TNFa), another osteoclast-activating cytokine, was not detected. Osteoclast activation by the supernatants was inhibited by an antibody against IL-1, whereas ultrapure human IL-1 mimicked the effect of the supernatant. The ability of B. gingivalis to induce IL-1 and OAF production was heat sensitive, as 20 min heating of the bacteria at 120 degrees C caused a 50% loss of activity. In addition, purified B. gingivalis lipopolysaccharide (LPS) had little IL-1 inducing capacity, compared with LPS of Escherichia coli. These data suggest that human peripheral blood cells confronted with B. gingivalis produce large amounts of IL-1 which has strong osteoclast stimulating activity. However, in contrast with E. coli LPS, B. gingivalis LPS does not seem to be the major inducing agent. Thus other bacterial components must be responsible for the observed IL-1 and OAF induction.

Animals↗

PubMed1989

Mechanical stimulation by intermittent compression stimulates sulfate incorporation and matrix mineralization in fetal mouse long-bone rudiments under serum-free conditions.

Mechanical stimulation evoked by intermittent hydrostatic compression (IC) in a closed culture system has been shown to stimulate calcification of fetal long-bone rudiments in the presence of serum [6]. We have studied effects of IC on sulfate metabolism and matrix mineralization under serum-free conditions, in short-term (24 hours) cultures of mineralizing long-bone rudiments in alpha minimum essential medium (MEM) + 0.2% bovine serum albumen (BSA). Exposure to IC for 24 hours stimulated radiosulfate incorporation into the papain-digestible pool in the noncalcifying epiphyses and, to a larger extent, in the calcifying diaphysis. The percentage release of 35S from prelabeled rudiments was stimulated in the epiphyses, but inhibited in the diaphyses. The changes in sulfate metabolism of matrix mineralization, in hypertrophic cartilage, and the diaphyseal bone collar, were judged from the increase in length of the diaphysis. This study shows that under serum-free conditions, mechanical stimulation by IC increases sulfate content while stimulating mineralization in calcifying cartilage of fetal long-bone rudiments. Mechanical stimulation seems to be an important regulator of cartilage calcification.

Animals↗

PubMed1989

Conditioned medium of fetal mouse long bone rudiments stimulates the formation of osteoclast precursor-like cells from mouse bone marrow.

We studied the influence of skeletal tissue on expression of the osteoclastic phenotype in the mouse, in vivo and in vitro. In various soft and hard tissues of adult and fetal mice the distribution of mono- and multinucleate cells showing tartrate-resistant acid phosphatase was studied, using enzyme histochemistry on undecalcified plastic sections. Cells with strong TRAcP activity were only observed in mineralized tissues. Multinucleate TRAcP cells were exclusively found in close correlation with mineral resorption. In fetal bones mononuclear TRAcP cells appeared in the surrounding soft tissue prior to osteoclast formation. In addition, conditioned media of fetal long bone rudiments (FBCM) increased the number of mononuclear cells showing strong TRAcP activity in 7 d cultures of adult bone marrow. FBCM stimulated DNA synthesis in TRAcP cells and induced their multi-nuclearity. Pretreatment with FBCM increased the capacity of bone marrow cultures to form osteoclasts in coculture with fetal bone rudiments. However, FBCM did not change the number of cells with tartrate-sensitive acid phosphate activity (TSAcP cells). The activity of FBCM was heat labile and was not detectable in CM of killed bones. CM of embryonic mouse fibroblasts which contains M-CSF activity, strongly increased the number of TSAcP cells but reduced the number of TRAcP cells. These data suggest that fetal mouse bone tissue induces the differentiation of osteoclast precursors. In addition, fetal bone rudiments but not embryonic fibroblasts seem to produce a factor(s) which stimulate(s) the formation of cells showing characteristics of osteoclast precursor cells. Osteoclasts and macrophages seem to have different growth requirements, indicating that they represent separate cell lines which may nevertheless derive from a common progenitor.

Acid Phosphatase↗

PubMed1989

Direct and immune-cell-mediated effects of Bacteroides gingivalis on bone metabolism in vitro.

We investigated direct and immune-cell-mediated effects of Bacteroides gingivalis on bone metabolism in vitro. Fetal mouse long-bone rudiments were cultured under aerobic conditions in the presence of (a) intact bacteria, (b) low molecular weight (MW less than 1000) metabolic products of the bacteria, or (c) conditioned media of mouse spleen cells activated by whole bacteria. A suspension of intact bacteria, added directly to the bone culture, had no effect on bone resorption or bone formation. Low molecular weight (MW less than 1000) excretion products of the bacteria inhibited bone resorption and transiently reduced mineralization of the diaphysis, while the growth in length of the bones was not affected. However, conditioned media of bacteria-activated spleen cells strongly enhanced bone resorption and increased osteoclast numbers in the bone culture, while inhibiting mineral formation in the diaphysis. This led to a strongly negative mineral balance. These data do not support a direct effect of either bacteria or bacterial products on bone tissue as a likely explanation for bone loss in periodontal disease. Rather, they favour the concept that the loss of bone in this disease is an indirect effect of the host response, resulting from the contact of immune cells with the bacteria. This implies that bacterial invasion of the connective tissue of the gingiva may not be a prerequisite for alveolar bone loss.

Animals↗

PubMed1989

A clinical, radiographic, and histological evaluation of permucosal dental implants of dense hydroxylapatite in dogs.

A clinical, histological, and radiographic examination was performed on 77 permucosal dental implants, made of dense sintered hydroxylapatite: 34 solid cylinders and 43 hollow cylinders. The hollow cylinders were pre-compressed between two titanium caps. The implants were placed in partly edentulous mandibles of dogs, and were physiologically loaded. Healing was clinically and radiographically evaluated during a six-month to five-year period. At various times, implants with their surrounding tissues were removed and prepared for light and electron microscopy. All implants showed a good initial fit and were maintained in place without undercut or mechanical stabilization. After 18 months, 76% of the solid cylinders had fractured at the implant/bone junction due to fatigue. However, the submerged portions of the solid cylinders were preserved without clinical problems, and became entirely embedded in bone. The pre-stressed implants did not fracture, and 91% were functioning 24 months after placement. The average scores of pocket depths and gingival bleeding showed no significant differences between implants and surrounding natural teeth. Bone deposition occurred on the entire surface of the implant below the crest of the alveolar bone, and intimate bone contact was confirmed by electron microscopy. It was also observed that a layer of bone tissue was deposited on the implant surface in the permucosal area just above the alveolar bone level. Embedding of gingival fibers in this layer resulted in gingival attachment to the implant, comparable with that of natural teeth.

Alveolar Process↗

PubMed1989

Osteoclastic invasion and mineral resorption of fetal mouse long bone rudiments are inhibited by culture under intermittent compressive force.

To study the effect of low-magnitude mechanical stimuli on mineralized matrix metabolism, fetal mouse long bone rudiments were cultured for 5d in the absence or presence of intermittent (0.3 Hz) compressive force (ICF) of 132 g/cm2. ICF treatment stimulated mineralization of the diaphyseal bone collar as well as hypertrophic cartilage, but inhibited the release of 45Ca from prelabeled rudiments. ICF also inhibited the migration of osteoclasts and their precursors from the periosteum into the diaphysis and the subsequent excavation of a primitive marrow cavity. These data suggest that osteoclasts are sensitive to mechanical stimuli. Mechanical stimulation seems to protect the bone rudiment against osteoclastic attack and has a strong anabolic effect on mineral metabolism.

Animals↗

PubMed1988

Role of mineralizing cartilage in osteoclast and osteoblast recruitment.

Periost-free, live and/or devitalized cartilaginous long bone rudiments of fetal mice were transplanted under the renal capsule of adult syngeneic mice to study the role of cells and intercellular matrix in the recruitment and formation of osteoclasts and osteoblasts, both identified by means of enzyme- and immunohistochemical methods. Live bone rudiments recruited host-derived osteoclasts within 5 days after transplantation. Osteoblasts developed as rapidly as osteoclasts and participated in the modeling of the rudiments into hemopoietic bone marrow containing ossicles. Devitalized bone rudiments, killed before osteoclastic invasion had occurred, did not recruit osteoclasts or osteoblasts, and were not resorbed up till 35 days after transplantation. Co-transplantation of live and devitalized bone rudiments however resulted in osteoclastic resorption of the killed rudiments, starting 9 days after transplantation. Again the live rudiments were modeled into ossicles. Devitalized bone rudiments which had been invaded by osteoclasts before killing and transplantation, did recruit host osteoclasts, but at a slower rate than live rudiments, and depending on the number of resorption sites at the time of transplantation. Osteoblasts were not formed. These data suggest that in developing long bones chondrocyte activity is involved in the recruitment of osteoclasts as well as osteoblasts. Matrix components diffusing from resorbing surfaces seem to be involved in osteoclast recruitment.

Acid Phosphatase↗