Search PubMed⌕ Search

Biomedical subjects

T J Chambers

Publications and source records attributed to T J Chambers.

At least 199 records · Page 11Linked to original sources
PubMed1984

Failure of cells of the mononuclear phagocyte series to resorb bone.

Monocytes, peritoneal macrophages, inflammatory polykaryons, and myeloid cell lines were incubated on slices of human cortical bone and assessed for their capacity to resorb bone by scanning electron microscopy. None of these cell types, mononuclear or multinucleate, induced any detectable change in the bone surface, even after prolonged incubation, and even in the presence of macrophage activators. These findings emphasise the inadequacies of mononuclear phagocytes as surrogate osteoclasts, and expose a discrepancy between 45Ca release and bone resorption.

Animals↗
PubMed1984

Resorption of bone by isolated rabbit osteoclasts.

A carborundum wheel was used to prepare slices of cortical bone that demonstrate a predictable surface appearance in the scanning electron microscope. Osteoclasts were mechanically disaggregated from neonatal rabbit long bones and settled onto these slices. After 24h in culture osteoclasts were associated with areas of excavation in the bone surface. These excavated areas typically showed a well-defined outline and a distinctive fibrillar base, which resembled the pattern of collagen fibrils in bone. The majority of such concavities were of approximately circular outline and of smaller diameter than the associated osteoclast, but other excavations were elongated or of complex morphology, and may have been produced by osteoclasts that were resorbing bone while they migrated. Irregular concavities tended to be more shallow but to occupy a greater area of the bone surface than circular concavities. Roughening of the bone surface without detectable excavation was also seen adjacent to osteoclasts. Calcitonin and cytochalasin B, which inhibit osteoclastic motility, also inhibited bone resorptive activity by these cells. The techniques described in this paper represent a model system with which to assess the direct and indirect effects of hormones, cells and substrate composition on the induction, stimulation and inhibition of osteoclastic bone resorption and to investigate the mechanisms by which cells degrade extracellular matrices.

Animals↗
PubMed1984

Effect of substrate composition on bone resorption by rabbit osteoclasts.

Slices of human femoral cortical bone were prepared with a carborundum wheel. Osteoclasts were isolated from neonatal rabbit long bones and incubated on either untreated, demineralized or anorganic preparations of these bone slices. Anorganic bone showed extensive tracts of uninterrupted surface excavation after incubation, while untreated bone tended to show discontinuous excavations of smaller total volume; demineralized bone was not resorbed. The endosteal surface of adult rat calvaria was also used as a substrate for osteoclastic bone resorption. The endosteal surface was exposed and rendered acellular, and was used either without further treatment or after incubation in collagenase. Bone resorption occurred only in those calvaria pre-treated with collagenase. These experiments imply that osteoclastic contact with bone mineral rather than the endosteal surface is the stimulus that initiates bone-resorptive behaviour in osteoclasts. The mechanism by which osteoblasts induce osteoclastic bone resorption may be through the known ability of osteoblasts to secrete collagenase, which, by digestion of the unmineralized lamina limitans of endosteal surfaces, exposes bone mineral to osteoclastic contact.

Animals↗
PubMed1984

Effect of parathyroid hormone and calcitonin on the cytoplasmic spreading of isolated osteoclasts.

Osteoclasts, the major agents of bone resorption, were isolated from neonatal rat bone, and the cytoplasmic spreading of these cells was measured after incubation in the presence or absence of hormones or other cell types. Salmon calcitonin, which inhibits osteoclastic bone resorption, reduced spreading in a dose-dependent manner and caused significant inhibition at concentrations as low as 6.7 pg/ml. Parathyroid hormone (PTH) had no effect on the spreading of isolated osteoclasts but if osteoblasts and osteoclasts were co-cultured the addition of PTH caused a marked increase in spreading at concentrations of 0.025 i.u./ml and above. The results suggest that while calcitonin is a direct inhibitor of osteoclastic activity, PTH may stimulate osteoclasts through a primary action on osteoblasts.

Animals↗
PubMed1984

The effect of prostaglandins I2, E1, E2 and dibutyryl cyclic AMP on the cytoplasmic spreading of rat osteoclasts.

We isolated osteoclasts from neonatal rat bone and assessed the effects of prostaglandins (PGs) I2, E1 and E2 on osteoclastic spreading. We found that although the PGs and dibutyryl cyclic AMP (DB-cAMP) acted as direct inhibitors of osteoclastic spreading, if osteoblasts and osteoclasts were co-cultured, the addition of PGs or DB-cAMP caused a considerable increase in spreading. This suggests that the PGs and DB-cAMP induce osteoblasts to stimulate osteoclasts. Osteoblasts are known to produce PGs, and thus possess the capacity to either inhibit (through PGs) or stimulate osteoclasts. Our results suggest that the balance between stimulation and inhibition of osteoclasts by osteoblasts may be determined by osteoblastic cyclic AMP levels.

Alprostadil↗
PubMed1983

Inhibition of osteoclastic motility by prostaglandins I2, E1, E2 and 6-oxo-E1.

We have recently found that calcitonin (CT), a hormone which inhibits osteoclastic bone resorption, completely abolishes the normally intense cytoplasmic motility of isolated osteoclasts. Here we report that prostaglandin (PG)I2, PGE1, PGE2 and 6-oxo-PGE1 cause an identical change in behaviour to that induced by CT. The order of potency was PGI2 greater than PGE1 greater than 6-oxo-PGE1 greater than PGE2. We found that, unlike CT which causes prolonged immotility in osteoclasts, the effect of these PGs was transient. The transient nature of the inhibition was not caused by their decay or inactivation, nor was it due to production in the cultures of a stimulator of osteoclast motility. Osteoclasts refractory to one PG were also less sensitive to the others, but showed no loss of sensitivity to CT, suggesting that the PGs share a common receptor system, distinct from that for CT. The PGs, like CT, appear to operate by increasing the cyclic AMP level in osteoclasts. The identical nature of the response of osteoclasts to PGs and CT, and the shared use of cyclic AMP as second messenger, suggest that the PGs, like CT, act directly on osteoclasts to inhibit bone resorption by these cells. Osteoblasts are known to make PGs, and we suggest that osteoblasts make them as agents of the local control of osteoclastic bone resorption. Paradoxically, when PGs are added to bone in organ culture they stimulate bone resorption. Like PTH they increase osteoblastic cyclic AMP levels, and the effect of adding PGs to bone may be a transient direct inhibition of osteoclasts followed by a sustained PTH-like stimulation of osteoclasts through osteoblasts. This mechanism may account for the bone resorption seen in inflammatory and malignant disease.

Alprostadil↗
PubMed1983

Pharmacological control of osteoclastic motility.

We separated osteoclasts from bone and observed the effect of several known and potential mediators of the control of bone resorption on their cytoplasmic motility. We already found that calcitonin (CT), a hormone that inhibits bone resorption, regularly causes complete inhibition of cytoplasmic motility, specific for osteoclasts, through a trypsin-sensitive membrane receptor [1]. We report here that prostaglandin I2 (PGI2) and dibutyryl cyclic AMP induce an identical change in osteoclastic behavior. We found that theophylline, which inhibits intracellular cyclic AMP degradation, and which itself had no effect on osteoclastic motility, potentiated the cytoplasmic inhibition caused by CT, PGI2, and cyclic AMP. This suggests that PGI2 and CT cause cytoplasmic quiescence by increasing the intracellular level of cyclic AMP, a view compatible with the known ability of CT to increase cyclic AMP in bone [2]. Parathyroid hormone (PTH), PGE2, and 1,25 dihydroxycholecalciferol (1,25 (OH)2D3), hormones known to stimulate osteoclasts, did not stimulate the activity of either active or quiescent isolated osteoclasts. The undoubted ability of these hormones to stimulate osteoclastic activity in vivo may therefore be mediated through a primary hormonal interaction with another cell type.

Animals↗
PubMed1983

The effect of prostaglandin I2 and 6a-Carba-PGI2 on the motility of isolated osteoclasts.

We have recently found that calcitonin (CT), a hormone which inhibits osteoclastic bone resorption, completely abolishes the normally intense cytoplasmic movement of isolated osteoclasts. We have also found that prostaglandin (PG)I2 causes an identical change in behaviour. In this paper we extend our investigations into the mode of action of PGI2 and a stable analogue, 6a-Carba-PGI2. We found that, unlike CT which causes prolonged immotility in osteoclasts, the effect of PGI2 and 6a-Carba-PGI2 were transient. Our results suggest that the transient nature of the inhibition was neither caused by inactivation of these compounds, nor was it due to production in the cultures of an osteoclastic stimulator. CT, PGI2 and 6a-Carba-PGI2 all appear to operate by increasing the intracellular cyclic AMP level. We found no refractoriness to either CT, dibutyryl cyclic AMP or 8-bromo cyclic AMP, and neither PGI2 nor 6a-Carba-PGI2 affected the sensitivity of osteoclasts to CT or dibutyryl cyclic AMP. This implies that refractoriness of osteoclasts to PGI2 and 6a-Carba-PGI2 develops at some stage in the interaction between PG and cell proximal to cyclic AMP production. We also found that there was cross-tachyphylaxis between PGI2 and 6a-Carba-PGI2, and this suggests that these two compounds share a receptor site on osteoclasts.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Merkel cell tumour: report of a case.

We report the case of a 75-year-old lady with recurrent primary cutaneous Merkel cell tumours. The condition can be misdiagnosed as lymphoma or anaplastic carcinoma, and the definitive diagnosis can be made only by electron microscopy of fresh tissue. This is the first reported case in the British literature.

Aged↗
PubMed1983

The sensitivity of isolated osteoclasts to morphological transformation by calcitonin.

We recently developed a technique for isolating osteoclasts from other bone cells which allows the direct effect of hormones on these cells to be assessed. We found that calcitonin (CT), which inhibits osteoclastic bone resorption, abolished cytoplasmic movement in these cells. In this paper we use the shape-change which accompanies immotility to define the sensitivity of osteoclasts to human and salmon CT. Concentrations of human CT above 62 pg/ml and salmon CT above 3 pg/ml regularly induced the shape-change in osteoclasts which corresponds to complete inhibition of cytoplasmic motility. Morphological transformation of osteoclasts by such low concentrations implies that CT may inhibit bone resorption by inhibiting the motility of the bone-resorptive cell. Even relatively high concentrations of other hormones had no effect on the sensitivity of osteoclasts to CT. This suggests that the response of isolated osteoclasts to CT is sufficiently specific and sensitive to be used as a bioassay, and we used the response to compare the biological potency of several samples of known immunoassayable CT content.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Calcitonin alters behaviour of isolated osteoclasts.

Osteoclasts were incubated on a glass or plastic substrate and the effect of calcitonin (CT) on their behaviour was observed. Before exposure to CT the osteoclasts were actively motile, the cytoplasm advancing behind broad pseudopodial (lamellipodial) processes which showed intense ruffling activity. CT caused cessation of lamellipodial activity within minutes, followed by gradual fragmentation and retraction of lamellipodia. Complete osteoclast quiescence was regularly induced by concentrations of CT above 50 pg/ml, and lesser degrees of quiescence were induced at concentrations down to 10 pg/ml. This quiescent state was reversed on removing CT from the medium, and was abrogated by prior treatment of osteoclasts with trypsin. The quiescent state did not reduce the longevity of the cells in culture, nor did it affect their resistance to removal from glass by trypsin. CT showed no influence on the pseudopodial activity of osteoclasts, peritoneal macrophages or inflammatory giant cells. Osteoclast quiescence seems to be a reversible state induced by the interaction of CT with a trypsin-sensitive CT receptor, present on osteoclasts. The range of concentrations which induce partial osteoclast quiescence are within the physiological range of serum concentrations in man, and this suggests that CT plays a physiological role in the regulation of osteoclasts may help to identify the precursor cell of the osteoclast and may assist investigations into the mechanism of control of osteoclasis.

Animals↗
PubMed1982

Inflammatory giant cells.

Giant cells are commonly seen in granulomas produced by a wide variety of known and unknown agents. It is widely accepted that giant cell formation results from fusion of mononuclear phagocytes. Both experimental and circumstantial evidence suggests that fusion takes place following the attachment of more than one macrophage to the same endocytic material. This view is in keeping with the consistent observation of giant cell formation in granulomas, where macrophages are actively ingesting material in close apposition to other macrophages. The experimental evidence for this view derives from the finding that if more than one macrophage is attached simultaneously to the same endocytic material in vitro, fusion results. Study of the phagocytic capacity of giant cells formed in vivo suggests that the same mechanism of fusion operates in granulomatous inflammation. Giant cell formation in granulomas thus appears to be the incidental result of macrophages ingesting material in close apposition to other macrophages. The material responsible for fusion may either be the visible particulate cause of granuloma formation or the denatured macromolecules formed by the inflammatory process.

Animals↗
PubMed1982

Osteoblasts release osteoclasts from calcitonin-induced quiescence.

There is an increasing body of indirect evidence that suggests that the localization and activity of osteoclasts, the major agents of bone resorption, are controlled by osteoblasts. In this paper I provide direct evidence that osteoblasts are indeed able to alter the behaviour of osteoclasts. I used calcitonin (CT) to suppress the cytoplasmic activity of osteoclasts isolated on glass or plastic substrates, and found that, while isolated osteoclasts remain quiescent in CT for as long as the hormone is present, they regain activity when osteoblasts are added to the culture. 'Escape' from CT-induced quiescence could not be transmitted by supernatants from cultures of osteoblasts, was not due to inactivation of CT by osteoblasts, and did not occur if osteoblasts were separated from osteoclasts by a Millipore filter. When osteoblasts and osteoclasts were cultured together at low cell density in CT, I found that while those osteoclasts in the culture that remained isolated also remained inactive, osteoclasts that were in contact with osteoblasts showed a return to activity. This return to activity was most marked in the portion of osteoclast periphery in direct contact with an adjacent osteoblast. Although contact with osteoblasts did not abrogate the sensitivity of osteoclasts to added calcitonin, osteoclasts were found to escape inhibition by calcitonin at a rate proportional to the number of osteoblasts with which they were in contact.

Alkaline Phosphatase↗
PubMed1981

Phagocytic recognition of bone by macrophages.

There is now persuasive evidence that osteoclasts are formed by the fusion of mononuclear phagocytes. The presence of osteoclasts on bone thus infers the phagocytic recognition bone by mononuclear phagocytes. I compared the phagocytic recognition by macrophages of hydroxyapatite, and native, demineralised and deproteinated bone powder. Removal of mineral resulted in loss of phagocytic recognition by macrophages, while removal of the organic component resulted in avid binding of bone fragments to a similar degree to that observed for hydroxyapatite crystals. The organic component of bone therefore protects the hydroxyapatite crystals of the mineral component from phagocytic recognition by macrophages. A simple model for bone resorption would be that resident bone-lining cells (active and resting osteoblasts) remove the organic protection under appropriate stimuli and thus allow phagocytic recognition of the underlying mineral by macrophages, which accumulate, fuse and commence digestion.

Animals↗
PubMed1981

Resorption of bone by mouse peritoneal macrophages.

An experimental system is described in which mononuclear phagocytes are shown to cause contact-dependent resorption of bone powder in vitro. Endotoxin, which is known to stimulate macrophage functions, and which has also been shown to increase bone resorption in organ culture, increased bone dissolution by mononuclear phagocytes. On the other hand, parathyroid hormone and prostaglandin E2, hormones which increase th number and activity of osteoclasts, had no effect on resorption of bone powder by mononuclear phagocytes. This suggests that the osteoclast, which is probably derived from mononuclear phagocytes, is induced to respond to these hormones indirectly, following a primary hormonal effect on osteoblasts.

Animals↗