THE EFFECT OF ANTISERUM, ALONE AND WITH HYDROCORTISONE, ON FOETAL MOUSE BONES IN CULTURE

Prostaglandin synthesis in the pathogenesis of fronto-ethmoidal mucoceles

The fronto-ethmoidal mucocele is a rare condition capable of expansion and erosion of bone. Its etiology is attributed to obstruction of the fronto-nasal duct and inflammation. To elucidate the role of inflammation, mucocele fragments and fibroblasts cultured from them were examined in vitro to assess prostaglandin E2 synthesis. The cultured fibroblasts when stimulated with mononuclear cell culture supernatant produced significant levels of prostaglandin E2 and collagenase, compared with normal frontal sinus mucosa fibroblasts removed at craniotomy. These significantly elevated mucocele levels of prostaglandin E2 (p = less than 0.001) suggest that lining fibroblasts are a major source of bone-resorbing factors, acting under the stimulus of lymphocytes and monocytes and which operate at the mucocele-bone interface, facilitating expansion. This situation closely parallels that already established in odontogenic cysts.

Evidence for fibroblasts as the major source of prostacyclin and prostaglandin synthesis in dental cyst in man

Periodontal cysts synthesize large amounts of prostaglandins and collagenase which probably cause the localized bone destruction essential for intraosseous cyst growth. Fragments of cyst wall, and fibroblasts cultured from them, synthesized prostacyclin (PGI2) in addition to prostaglandin E2 (PGE2), PGF2 alpha and collagenase in vitro. Soluble products from cultures of unstimulated and phytohaemagglutinin-stimulated blood mononuclear cells enhanced the synthesis of these prostaglandins in monolayer cultures of cyst-wall fibroblasts. It is therefore proposed that cyst capsule fibroblasts are the major source of these bone-resorbing factors, acting under the stimulus of lymphocytes and monocytes in chronically inflamed cysts. Cysts which were not infiltrated by chronic inflammatory cells (follicular cysts, a keratocyst, an ameloblastoma, and an aneurysmal bone cyst) also produced prostaglandins and collagenase, indicating that the stimulatory mechanism for the production of bone-resorbing factors in these cysts may differ from that in periodontal cysts.

The effect of cortisol on porcine articular tissues in organ culture

(1) The effects of hydrocortisone succinate (1.0--0.01 micrograms HC/ml of medium) on porcine articular tissues in organ culture have been studied by histological and biochemical methods. (2) 1.0 and 0.1 micrograms HC/ml considerably inhibited the severe breakdown of matrix that occurs in living and dead cartilage explained in contact with synovial tissue. (3) The depletion of matrix in living cartilage cultivated in the same dish as but not in contact with synovial tissue, is much diminished when the medium contains 1.0 or 0.1 micrograms HC/ml. (4) Cartilage grown in the used medium of synovial tissue loses both proteoglycan and hydroxyproline; the addition of HC to the used medium has little (1.0 microgram HC/ml) or 0.1 microgram HC/ml) no inhibitory effect. If, however, the used medium is from synovial tissue that has been cultured in the presence of 1.0 or 0.1 micrograms HC/ml, loss of proteoglycan and collagen from the cartilage is much reduced. (5) In isolated cartilage in normal medium there is outgrowth of cells from the cut surface and some loss of proteoglycan and collagen; outgrowth is completely, and loss of matrix components partially suppressed by 1.0 micrograms HC/ml. (6) Isolated synovial tissue cultured in normal medium shrinks to about one-third of its original size, loses much of its collagen and secretes neutral metallo-proteinases into the medium; in the presence of 1.0 microgram HC/ml these changes are largely prevented. The explants also secrete an inhibitor of metallo-proteinases the production of which is not reduced by HC.

Activation of serum complement inhibits collagen synthesis in fetal rat bone in organ culture

Activation of rabbit serum complement caused a marked reduction in collagen synthesis but a much smaller change in noncollagen protein synthesis in fetal rat calvaria maintained in organ culture. In the periosteum of the fetal rat calvarium, both collagen and noncollagen protein synthesis were reduced, whereas in the central bone, presumably enriched in osteoblasts, only collagen synthesis was inhibited. This large decrease in bone collagen synthesis could not be attributed to enhanced degradation of newly synthesized collagen or its release into the culture medium. Activation of complement also stimulated the production of PGE in fetal rat calvaria. Antagonists of prostaglandin cyclooxygenase decreased prostaglandin synthesis but did not restore collagen synthesis in complement-treated bones, suggesting that complement decreases osteoblast collagen synthesis by a mechanism largely independent of prostaglandin production.

Cartilage growth inhibition and necrosis in vitro caused by prostaglandin A1

This paper details experiments using the Fell technique of organ culture of 8-day chick embryo femoral and tibial rudiments to test the effects of prostaglandin A1 (PGA1) on cartilage growth. Growth was studied during 8 days in vitro by measurement of rudiment length and wet and dry weight, and by histology. PGA1 inhibited explant growth in a dose-related manner. Linear growth was significantly decreased by 20 and 25 microgram/ml PGA1 at 2, 4, 6 and 8 days, and by 15 microgram/ml at 6 and 8 days. Linear growth was unaffected by 1 and 10 microgram/ml doses. Weight measurements were significantly reduced by 25 microgram/ml PGA1 (2, 4 and 8 days) and by 20 microgram/ml (8 days). Chondroblast degeneration was caused by doses of 15, 20 and 25 microgram/ml PGA1. Progressive degeneration was seen at the 25 microgram/ml concentration after 2 days in vitro. Cellular changes as early as 27 h in vitro were seen using electron microscopy. Tritiated thymidine autoradiography confirmed reduced chondroblast proliferation in the presence of PGA1 (25 microgram/ml). The mechanisms of prostaglandin-induced changes in embryonic cartilage remain uncertain. The possible role of intracellular cyclic nucleotides in the reaction is discussed.

The effects of prostaglandin A1 and prostaglandin B1 on the differentiation of cartilage in the chick embryo

In organ cultures of chick embryonic limb rudiments the mean length of explants treated with 25 microgram/ml prostaglandin B1 (PGB1) was significantly smaller than that of paired controls (P < 0.001) after 4, 6 and 8 days in vitro. The deceleration of linear growth was constant during 8 days in vitro. Growth inhibition was confirmed by a statistically significant decrease in explant dry weight after 8 days of culture. However, PGB1 caused no observable alteration in the histological structure of the explants. The possible role of PGB1 in the physiological control of cartilage growth is postulated. Explants similarly treated with prostaglandin A1 (PGA1) at concentrations of 15 microgram/ml for 8 days or 20 microgram/ml for 4 and 8 days exhibited "comma" and "inverted commas" phenomena, caused by the intermingling of chondroblasts from the epiphyseal and flattened-cell zones, which thus ceased to be distinct entities. Adenylate cyclase in the plasma membrane may be involved in this disturbance of cartilage differentiation.

Glucocorticoids and lysosomes

Steroids in general and glucocorticoids in particular affect lysosomes in various ways. The explanation of these effects remains in dispute, however. Theories include the view that steroids interact directly with lysosomal membranes, that steroids provoke induced changes in lysosomes, and that classical steroid receptors originate in lysosomes. Experiments pertaining to these views are discussed, particularly with respect to steroid specificity and tissue specificity of effects and to dose-response considerations.

A cat model for the evaluation of mechanisms of bone resorption: induction of bone loss by simulated immune complexes and inhibition by indomethacin

When simulated immune complexes (SIC) (heat-aggregated IgG) possessing many of the properties of true antigen-antibody complexes were injected via the root canal into the periapical tissues of cat maxillary cuspids, radiographically and histologically evident bone resorption occurred at these sites within 7 days. Bone loss was accompanied in all cases by inflammation of the surrounding collagenous connective tissues and was characterized by the presence of osteoclasts. Bone resorption, but not the accumulation of inflammatory cells, was blocked by the systemic administration of indomethacin, an inhibitor of prostaglandin synthetase. The most likely explanation is that SIC-activated mechanisms such as the complement cascade, prostaglandin synthesis, and neutrophil degranulation were responsible for the bone loss. The minor inflammation and bone loss that followed the repeated injections of BSA and of monomeric IgG can best be explained as a response to trauma. The data presented establish that the cat maxillary cuspid is a useful model in which to explore the mechanism underlying pathological bone resorption.

Destruction of joint homografts. An experimental study

The host synovium undergoes a striking transformation at about 26 weeks after joint homografting. Histologically the synovium invaded and destroyed the graft with which it came in contact, becoming markedly hypercellular; the infiltrate consisted mainly of plasma cells and lymphocytes. The synovium at this stage closely resembled a rheumatoid pannus. The cartilage in contact with this invasive synovium lost its staining qualities, failed to take up S-35, and was gradually destroyed. The mechanism causing this transformation remains unclear. It is postulated that these changes could be due to an inflammatory or immune response.

Direct resorption of bone by human monocytes

Cultured human peripheral blood monocytes stimulate the release of bone mineral and matrix from killed long bones of fetal rats. These effects were inhibited by cortisol but were not altered by hormones that normally stimulate osteoclastic bone resorption. There was no evidence of morphologic differentiation of the monocytes into osteoclasts during bone resorption.

The effect of complement-sufficient antiserum against pig erythrocytes on pig articular tissues in organ culture

Pig cartilage devoid of marrow or synovium is virtually unaffected by rabbit complement-sufficient antiserum to pig erythrocytes (AS + C'), probably because normal cartilage matrix excludes immunoglobulins. When synovium or invading marrow is present, AS + C' causes depletion of the proteoglycan, with consequent entry of IgG into the cartilage, followed by the breakdown of collagen; the chondrocytes assume a fibroblastic form and their reaction with the antiserum is greatly reduced. If degradation of the matrix has not advanced too far, new matrix is regenerated when the explant is transferred to control medium. Experiments on the depletion of pure cartilage by exposure to retinol, indicate that articular cartilage produces enzymes capable of degrading protoglycan but not collagen. The work was done in collaboration with colleagues at the Strangeways Laboratory and in the Division of Immunology, Pathology Department, University of Cambridge.

The effect of D-penicillamine of the skeletal development of rat foetuses

Rats received 20, 50 or 100 mg/animal D-penicillamine i.p. twice daily on days 15, 16, 17, 18, and 19 of gestation, i.e. a total dose of 200, 500 resp. 1000 mg/animal. At all dosages the number of fetal resorptions did not increase significantly. Weight of the 20 day old embryos as well as length of the long bones in the extremities in the 100 mg-group showed a significant decrease. Numerous skeletal alterations could be observed in the 1000 mg-group such as absence, deformations or incomplete mineralisation of bones. Light microscopic examinations revealed an inhibition of the ossification as well as a decrease of number and size of the trabecula and of the thickness of the perichondrial bone sheath. A swelling of the collagenous fibrils can be demonstrated with the electron microscope. The first apatite crystals aggregate in collagen-free areas. The fusion of these aggregates to homogenously mineralized trabecula is inhibitied. In contrast to bones from untreated embryos, mineralized areas show varying content of collagen and apatide crystals. A regular spatial relationship between apatite crystals and collagenous fibrils does not develop. These findings show that even after the so-called "critical period" malformations can be pproduced by substances which disturb synthesis and maturation of the mesenchymal intercellular substance.

Complement-dependent stimulation of prostaglandin synthesis and bone resorption

Complement-sufficient heterologous serum induced prostaglandin synthesis and resultant resorption in cultures of fetal rat long bones. Bone resorption was enhanced with unheated normal rabbit serum as compared to heated serum or serum from rabbits lacking the sixth component of complement (C6). Addition of functionally purified C6 restored resorptive activity in C6-deficient serum. Concentrations of prostaglandin E were increased in the culture media of bones incubated with complement-sufficient serum. The resorptive effects of active serum as well as the appearance of prostaglandin E in the media were inhibited by indomethacin.

Endotoxin: stimulation of bone resorption in tissue culture

Bacterial endotoxins can stimulate the release of previously incorporated calcium-45 and tritiated proline from fetal rat bone in tissue culture. Endotoxin from Bacteroides melaninogenicus, an organism regularly found in the gingival crevice of man, produces a response similar to parathyroid hormone and is effective at doses as low as 0.1 microgram per milliliter. This response is inhibited by serum and dependent upon the presence of albumin. Endotoxins may play a role in the bone loss characteristic of human periodontal disease.

The effects of heparin and dextran sulphate on cultured mouse limb bones

Heparin and the synthetic substitute dextran sulphate induce osteoporisis following prolonged administration to man or experimental animals. The possibility that this is brought about by a direct toxic effect on bone has been studied in tissue culture using explants of mouse radii, ulnae and tibiae. Fifty-three bones from new born or day old mice were cultured as controls, 73 with added heparin and 74 with added dextran sulphate at concentrations 0·1, 1·0 and 5·0 mg. per ml. Cultures were continued for 6 days. Control bones increased in length by approximately 22 per cent during this period and although little endochondral ossification occurred there was considerable periosteal and endosteal new bone formation.

When heparin or dextran sulphate was added to the culture medium there was progressive impairment of linear growth with increasing concentrations of these substances. Thus at a concentration of 0·1 mg. per ml. there was little impairment of linear growth but at 5·0 mg. per ml. the bones increased in length by only approximately 15 per cent.

With 1·0 and 5·0 mg. per ml. of heparin or dextran sulphate there was increased resorption of bone and impaired new bone formation. At the highest concentration of 5 mg. per ml. both substances almost completely inhibited new bone formation. Undecalcified sections showed no loss of mineral from the remaining diaphyseal bone and there was no impairment of alkaline phosphatase activity demonstrated histochemically.

The concentrations of heparin or dextran sulphate required in the present tissue culture experiments to produce bone changes were higher than those achieved in the blood and tissue fluids of experimental animals even after prolonged administration. For the in vivo changes to be brought about by a direct effect of heparin or dextran sulphate on bone it would be necessary to postulate a selective accumulation of these substances in bone tissues.

Role of biological membranes in some skeletal reactions

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