Collagenous bone matrix-induced endochondral ossification hemopoiesis

Dissociative extraction and reconstitution of extracellular matrix components involved in local bone differentiation

Subcutaneous implantation of demineralized diaphyseal bone matrix in allogeneic rats results in the local induction of endochondral bone differentiation. We have explored the potential of three dissociative extractants, 4 M guanidine hydrochloride (Gdn . HCl), 8 M urea/1 M NaCl, and 1% NaDodSO4 at pH 7.4, containing protease inhibitors to solubilize putative inductive molecules in the bone matrix. Extraction of bone matrix with any one of these extracts resulted in the loss of the bone inductive property. The solubilized extracts were then reconstituted with the residue by dialysis against water. The various reconstituted matrices were bioassayed for bone inductive potential by quantitation of alkaline phosphatase activity and 45Ca incorporation on day 12 after implantation. There was complete recovery of biological activity after reconstitution of the residues with each of the three extracts. Polyacrylamide gel electrophoresis of the extracts revealed similar protein profiles. Gel filtration of the 4 M Gdn. HCl extract on Sepharose CL-4B showed a heterogeneous broad peak. When fractions of that peak containing proteins less than 50,000 daltons were reconstituted with inactive 4 M Gdn . HCl-treated bone matrix and then implanted, new bone was induced. These observations demonstrate the dissociative extraction and successful biological reconstitution of bone inductive macromolecules in demineralized bone matrix.

The bone inductive capacity of decalcified bone matrix modified by diphenylhydantoin

Decalcified bone matrix was prepared from cortical bones of rats premedicated with I) Diphenylhydantoin (DPH), II) DPH + Vitamin D3, III) Vitamin D3 or IV) no premedication for 10 days. In the donor animals, DPH lowered the serum calcium level, caused a weight loss of 10 per cent, and stopped the growth of the long bones. Vitamin D3 supplementation normalized the serum calcium concentration but had no effect on the other parameters. Vitamin D3 alone caused hypertrophy of the growth cartilage, while the bone growth and structure was normal. The bone inductive capacity of decalcified bone matrix was highest in the DPH group, and the DPH + D3 group also showed significantly higher values than the D3, and control groups. The results of the present study show that the bone inductive capacity of the decalcified bone matrix is independent of Vitamin D3 metabolism.

Calcitonin stimulates bone formation when administered prior to initiation of osteogenesis

The influence of calcitonin (CT) on various stages of bone formation was investigated. A demineralized collagenous bone matrix-induced bone forming system in rats was used to temporally segregate chondrogenesis and osteogenesis. Administration of CT (15 Medical Research Council Units [MRCU]) daily) at the initiation of matrix-induced bone formation (BF) resulted in a 76% stimulation of BF as measured by 45Ca incorporation and alkaline phosphatase activity. This increase was due, in part, to a stimulation of cartilage and bone precursor cell proliferation monitored by the rate of [3H]thymidine incorporation and ornithine decarboxylase activity. Chondrogenesis on day 7 as measured by 35SO4 incorporation was increased by 52% with CT treatment. To rule out the possibility of a secondary response due to parathyroid hormone, similar studies were done in parathyroidectomized animals and CT stimulation of BF was still observed. However, when CT injections were started after cartilage formation (day 8) there was no stimulation of BF but a significant decrease in 45Ca incorporation was observed. These results indicate CT has two actions: (a) when CT is administered during the initial phases of bone formation, it increases BF due to a stimulation of proliferation of cartilage and bone precursor cells; and (b) when CT is administered after bone formation has been initiated, subsequent bone formation is suppressed.

Changes in intracellular enzymes of collagen biosynthesis during matrix-induced cartilage and bone development

The activities of five intracellular enzymes of collagen biosynthesis were determined during cartilage and bone formation induced in rats by demineralized bone matrix. The five enzymes, prolyl 4-hydroxylase, prolyl 3-hydroxylase, lysyl hydroxylase, hydroxylysyl galactosyltransferase and galactosyl-hydroxylysyl glucosyltransferase, exhibited broadly parallel profiles; the activities rising steeply from day one to reach their highest values on day nine and decreasing gradually thereafter. The maximal enzyme activity correlated with the period of chondrogenesis and hypertrophic cartilage characterized by the synthesis of cartilage-specific type II collagen. Prolyl 4-hydroxylase was also studied in respect of its tissue distribution and cellular location using indirect immunofluorescence. The enzyme was mainly located in the mesenchymal cells on day three, in the chondrocytes and hypertrophic chondrocytes on days seven to nine, and in the osteoblasts on day eleven and thereafter.

Somatostatin can locally inhibit proliferation and differentiation of cartilage and bone precursor cells

The influence of somatostatin on discrete stages of collagenous-matrix-induced endochondral bone formation has been investigated. Local injection of somatostatin, i.e., without any measurable systemic effect, resulted in a 75% reduction of cell proliferation as measured by [3H]thymidine incorporation and ornithine decarboxylase activities. The minimum effective inhibitory dose of somatostatin was 0.25 microgram/day. Twice daily local injections of the hormone during cartilage formation also resulted in an inhibition, but this was shown to be due to impaired cell proliferation rather than to a direct effect of somatostatin on differentiation. Injection of somatostatin into developing bone tissue after the cartilage stage impaired osteogenesis, assessed by 45Ca incorporation and alkaline phosphatase activity. Concurrent injections of insulin and somatostatin obliterated the inhibitory effect of the latter on cell proliferation. Somatostatin can locally regulate the proliferation and differentiation of chondroprogenitor and osteoprogenitor cells in vivo and may directly contribute to the regulation of bone growth by its ability to counteract the stimulatory effect of insulin.

The role of connective tissue in craniofacial development, function and disease

The connective tissue, composed of cells, fibers and ground substance, plays a vital role in the processes of craniofacial development, growth, wound healing and disease. This article reviews current knowledge of connective tissue biology and relates it to certain clinical situations of relevance in oral surgery.

Bone-forming cell line derived from embryonal carcinoma cells

The use of established cell lines of various types has provided information on the properties of certain stem cells and on the conditions of their differentiation. No bone-forming cell line has so far been described. We report here the isolation, from in vitro differentiating teratocarcinoma cells, of a line which, on subcutaneous injection into syngeneic mice, gives rise to ossicles. The appearance of ossicles is preceded by the formation of a cartilaginous matrix, thus reproducing what has been described as endochondral differentiation. The ossicles obtained are rapidly colonized by host marrow, are non-malignant and stop growing 2 weeks after injection of the cells. In certain conditions, however, osteosarcomas, chondroosteosarcomas and fibrosarcomas can be obtained. From these tumours, cell lines have been isolated which retain in vitro the properties of the cells found in the tumour.

Heterotopically induced osteogenesis in osteopetrotic rat mutants. A preliminary report

Heterotopic osteogenesis was induced in three groups of Fatty Orl-op strain of rats, i.e., osteopetrotic (op/op) mutants, op/op mutants cured by previous transplants of normal bone marrow, and phenotypically normal littermates. Allogenic decalcified bone matrix was used as inductor. The osteopetrotic mutants from heterotopic ossicles containing bone and bone marrow under the influence of inductor. After four weeks the signs of remodelling processes of induced bone tissue are observed: osteoclasts are found in the Howship lacunae, and bone marrow is formed in the spaces adjacent to the bone trabeculae. The induced bone marrow contains megakaryocytes, cells of the erythropoietic and granulopoietic lines as well as some infiltrating lymphocytes. The important finding is that the amount and the histological structure of bone tissue and bone marrow induced heterotopically in the osteopetrotic animals were similar to that observed in both control groups. It is concluded that 1) osteopetrotic mutants have the same potency to form heterotopic bone tissue under the influence of inductor as the control animals, and 2) remodelling processes in four-week-old, induced ossicles are normal and differ in this respect from defective rebuilding of the orthotopic bones of op/op hosts.

Stimulation by a low-molecular-weight angiogenic factor of capillary endothelial cells in culture

A low-mol.-wt compound isolated from rat Walker 256 carcinoma and found to induce neovascularization in vivo was tested on cultures of cow brain-derived endothelial cells (CBEC) growing on plastic and collagen substrates. This factor had a mitogenic effect on CBEC cultured on native collagen gels and for this reason has been called "endothelial-cell-stimulating angiogenesis factor" (ESAF). CBEC growing on plastic culture dishes or denatured collagen films were not stimulated by ESAF. The mitogenic effect of ESAF was equally apparent when added to cells already attached to the native collagen substrate or when the collagen substrate was pre-incubated with ESAF before plating the cells. A floating collagen gel pre-incubated with ESAF in cultures of CBEC growing on plastic dishes did not stimulate cell growth. Our data indicate that the substrate influences cell behaviour and that CBEC only respond to ESAF when growing on a native collagen substrate.

Synthesis and localization of fibronectin during collagenous matrix-mesenchymal cell interaction and differentiation of cartilage and bone in vivo

The biosynthesis of fibronectin during the in vivo development of matrix-induced endochondral bone was investigated by using [35S]methionine in rats. The dmineralized bone matrix that was implanted subcutaneously to induce local bone formation bound circulating fibronectin. This may be an important initial requirement for cell attachment to the matrix. Fibronectin was present throughout the development of bone but accounted for the largest percentage of total protein synthesized during mesenchymal cell proliferation and hematopoiesis. Fibronectin was identified in tissue extracts by its (i) comigration on electrophoretic NaDodSO4/polyacrylamide gels with human and rat plasma fibronectin, (ii) affinity for denatured collagen, (iii) crossreactivity with purified antibody of rat plasma fibronectin, and (iv) insensitivity to collagenase digestion. Fibronectin was localized by immunofluorescence in the extracellular matrix during the period of mesenchymal cell proliferation. During chondrogenesis, fibronectin was demonstrated in the differentiating chondrocytes. Fibronectin was detectable in the cartilage matrix only after hyaluronidase treatment. During vascular invasion, prior to osteogenesis, fibronectin was localized in association with endothelial cells. These observations demonstrate a possible role of fibronectin in collagenous matrix-mesenchymal cell interaction in vivo.

Changes in synthesis of types-I and -III collagen during matrix-induced endochondral bone differentiation in rat

The changes in rates of hydroxyproline formation and biosynthesis of types-I and -III collagen during bone matrix-induced sequential differentiation of cartilage, bone and bone marrow in rat were investigated. Biosynthesis of types-I and -III collagen at different stages of this sequence was studied by labelling in vivo and in vitro with [2,3-3H]proline. Pepsin-solubilized collagens were separated by sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis. The results revealed that maximal amounts of type-III collagen were synthesized on day 3 during mesenchymal-cell proliferation. Thereafter, there was a gradual decline in type-III collagen synthesis. On days 9--20 during bone formation predominantly type-I collagen was synthesized. Similar results were obtained by the use of labelling techniques both in vivo and in vitro.

Influence of experimental diabetes and insulin on matrix-induced cartilage and bone differentiation

The influence of streptozotocin-induced diabetes on discrete stages of matrix-induced endochondral bone formation has been investigated. Mesenchymal cell proliferation was inhibited in diabetic rats as evidenced by a 65% reduction of ornithine decarboxylase (ODC) activity and a 56% reduction of [3H]thymidine incorporation per microgram DNA compared to nondiabetic controls; the inhibition was prevented by insulin treatment. In diabetic animals, chondrogenesis on day 7 was reduced by 49% compared to control animals as assessed by 35SO4 incorporation. Exogenous insulin was stimulatory to cartilage development when present during days 0 through 4 (mesenchymal cell proliferation). Calcification of cartilage and osteogenesis were reduced by more than 50% in diabetic rats and corrected by insulin as measured by alkaline phosphatase activity and 45Ca incorporation. Decreased in vivo endochondral bone growth and development during diabetes is the result of 1) inhibition of insulin-dependent mesenchymal cell proliferation, 2) decreased and delayed cartilage formation due to impaired mesenchymal cell proliferation, 3) decreased and delayed vascular invasion prior to chondrolysis and osteogenesis, and 4) reduced insulin-dependent calcification and ossification.

Bone formation in cartilage produced by transplanted epiphyseal chondrocytes

Chondrocytes were isolated from rat epiphyseal cartilage, cultured in vitro, and exposed to exogenous tracers which accumulated in their lysosomes. The cells were then injected into the posterior tibial muscle of animals from the same outbred strain, where they reconstructed calcifying hyaline cartilage. The mineralization of the tissue was followed by ingrowth of blood capillaries from the host bed. Macrophage-like cells surrounding the vessels phagocytized degenerated chondrocytes and unmineralized matrix, whereas multinucleated chondroclasts removed some of the mineralized cartilage matrix. Mesenchyme-like cells accompanying the invading vessels attached to the remaining septa of calcified cartilage matrix and developed into osteoblasts depositing bone matrix on the surface of these septa. The apparent lack of inherent tracer labeling of the lysosomes in the different bone cells indicate that they were derived from the host. No signs of transformation of chondrocytes into bone cells were observed. When isolated rat epiphyseal chondrocytes were injected into the wall of the hamster cheek pouch, calcifying cartilage was reconstructed without signs of subsequent ossification. Transplantation of cartilage reconstructed in the hamster into the dorsal muscles of rats was, however, followed by formation of bone by a sequence analogous to that described above. Such an osteogenetic response was also obtained when the cartilage had been devitalized before transplantation. These experiments show that calcified cartilage, developing in or grafted into an intramuscular site, is able to induce and serve as a substrate for endochondral bone formation, similar to that occurring during normal development. They further indicate that bone induction by calcified cartilage does not require the presence of living chondrocytes.

Influence of magnesium depletion on matrix-induced endochondral bone formation

The effect of magnesium deficiency on bone cell differentiation and bone formation was investigated using in vivo matrix-induced endochondral ossification as a test system. Demineralized bone matrix was implanted subcutaneously in young (35-day-old) male Long-Evans rats that had been fed a semisynthetic Mg-deficient diet (50 ppm Mg) for 7 days. Plasma Mg levels were reduced to 25-30% of control values at that time. Control rats were paired the same diet, supplemented to contain 1000 ppm Mg. The implants were harvested 7, 9, 11, 15, and 20 days after implantation and analyzed for Mg and Ca content, 45Ca incorporation, and alkaline phosphatase levels. At each stage, plaques (implants) removed from Mg-deficient rats showed retardation in cartilage and bone differentiation and matrix calcification. Magnesium content was markedly reduced when compared to the control plaques. Histological appearance of the matrix-induced plaques confirmed the retardation in bone development and mineralization suggested by the chemical indicators. Most marked was the virtual absence of bone marrow in 20-day-old plaques in Mg-depleted rats. These data show that bone cell differentiation can occur in a severely Mg-depleted environment, although the onset of mineralization and bone remodeling was delayed and bone marrow differentiation was impaired.

Changes in proline synthetic and degradative enzymes during matrix-induced cartilage and bone formation

Proline biosynthetic and degradative enzymes are unevenly distributed in differentiated mammalian tissues. Activities of the synthetic enzymes are relatively high in collagenous tissues, whereas activities of the degradative enzymes are high in noncollagenous tissues. In order to further characterize tissue-specific proline biosynthesis and degradation, we have determined proline enzyme activities during cartilage and bone formation induced by demineralized bone matrix. We can thus follow temporal changes in enzyme activity in a single tissue as different cell types develop. Ornithine aminotransferase and pyrroline-5-carboxylate reductase have peaks of activity which correlate with maximal type II collagen synthesis by chondrocytes. Both enzymes also are active during bone formation. In contrast, proline oxidase and pyrroline-5-carboxylate dehydrogenase are present at low levels and do not change as new cell types appear. Arginase activity peaks during the first 3 days and then rapidly decreases by the time cartilage and bone formation begin. These observations further substantiate the importance of proline biosynthesis in collagenous tissues. The close correlation between ornithine aminotransferase activity and type II collagen synthesis suggests that the pathway from ornithine to proline may be especially important during formation of type II collagen.

Poly-HEMA sponge: a biocompatible calcification implant

Poly-hydroxyethyl methacrylate (Poly-HEMA) was investigated for biocompatibility and calcification potential. S.C. and I.M. implants and transplants to subperiosteal sites were examined. The material was judged to be tolerated by the host tissue since no inflammatory or degenerative changes were observed. This study established that calcification does occur. This calcification does not simulate bone formation; osteoblasts were not observed. The x-ray diffraction pattern resembles that of calcium hydroxyapatite.

Formation of an atypical collagen and cartilage pattern in limb bud cultures by highly sulfated GAG

Addition of 1 mg/ml or higher doses of the highly sulfated pentosanpolysulfoester SP54 or the mucopolysaccharidepolysulfoester Arteparon to limb bud cultures from 11-day-old mouse embryos caused a marked reduction in the growth of the distal parts of the cartilage anlagen. The most striking effect, however, was the change in the collagen structure of the cartilaginous intercellular substance. After more than 0.05 mg/ml SP54 or Arteparon no collagen filaments were seen but collagen aggregates with an altered cross-striation occurred. They were produced by an antiparallel arrangement of collagen molecules caused by the highly sulfated substances. By immunofluorescence microscopy it was shown that SP54 and Arteparon did not influence the distribution of the collagen types but only affected the aggregation of collagen type II. From the morphological point of view the production of endogenous PG seemed to be uneffected by SP54 and Arteparon. The effect of SP54 and Arteparon was reversible. After removal of these substances characteristic collagen filaments re-formed. The collagen aggregates were decomposed extracellularly or phagocytosed by chondroblasts and decomposed intracellularly.

Transitions in collagen types during matrix-induced cartilage, bone, and bone marrow formation

The localization of types I, II, and III collagens during bone matrix-induced sequential differentiation of cartilage, bone, and bone marrow was studied by specific immunofluorescence. Subcutaneous transplantation of coarse powders of demineralized rat bone matrix into allogeneic recipients resulted in new bone formation. After a transient appearance of polymorphonuclear leukocytes in the implant, fibroblasts appeared in close continguity to the matrix on day 3. Type III collagen was then localized as a fine network around the invading fibroblasts. On days 4--6 smaller amounts of type I were also detected around these proliferating cells. With the onset of chondrogenesis, type II collagen was detected in the cartilage matrix on day 6 and persisted until the early stages of bone formation. Vascular invasion of the implant was accompanied by osteogenesis on day 10. Type I collagen was demonstrated in the newly deposited bone matrix coating the surfaces of cartilage spicules and particles of implanted bone powder. On day 17 and thereafter, type III collagen was localized as a fibrous array around nests of hematopoietic cells.