[Influences of induced membranes on heterotopic bone formation within an osteo-inductive complex. Experimental study in rabbits]. / Influence des membranes induites sur l'ostéogenèse hétérotopique au sein d'un complexe ostéo-inducteur. Etude expérimentale chez le lapin.

UNLABELLED: Based on a new concept, a procedure combining induced membranes and cancellous autografts allows the reconstruction of wide diaphyseal defects. To date, this procedure is limited by the amount of cancellous bone available from the patient and by the related morbidity at the donor site. The aim of this study was to evaluate the biological effect of induced membranes on a cylindrical-shaped ceramic implants loaded with OP-1 in heterotopic site. MATERIALS AND METHODS: Sixty hydroxyapatite tricalcium phosphate (HA-TCP) implants, 20 of which being loaded with a bone growth factor (rhOP-1) were inserted either in a subcutaneous tunnel or within a previously induced membrane on the back of rabbits. There were two time-points at four and 16 weeks. Implants were investigated at three different levels (extremities and middle). RESULTS: None of the untreated implants showed any evidence of bone formation. Implants inserted in an induced membrane presented with less resorption. Bone ingrowth within the pores of the materials was significantly higher when the implants were inserted into the induced membrane whatever the time-point considered. CONCLUSION: The membrane seems to play the role it was assigned, i.e. to protect and revascularize the implant, thus favouring osteogenesis that occurs in 80% of the implants after four months.

Human bone marrow stromal cells express an osteoblastic phenotype in culture.

This study reports the selection and characterization of osteogenic precursors from human bone marrow which were isolated by two "clonings" and successive subculturing. These cell lines express alkaline phosphatase activity. Gel electrophoresis of [3H]-proline labeled cultures showed that the cloned cells produce only type I collagen. They synthetize osteocalcin and osteonectin. They respond to 1,25 dihydroxy vitamin D3 by increasing osteocalcin synthesis and secretion, and to parathyroid hormone by increasing cyclic AMP synthesis. After the third subculture in the absence of beta-glycerophosphate, these cell lines formed lots of clusters which exhibit high alkaline phosphatase activity and positive von Kossa staining. X-ray energy spectrum shows that these cells are surrounded by "budding" structures containing calcium and phosphorus with a ratio Ca:P identical to those of pure hydroxyapatite. This process was associated with 45Ca uptake into the cells. All these data support the selection of osteogenic cells which may be of considerable clinical importance.

Biodistribution study of a monoclonal antibody specific to link proteins from human cartilage.

We report the use of monoclonal antibody 6F3 prepared against link proteins from human articular cartilage to elucidate the distribution of these glycoproteins within connective and other tissues. By immunohistochemical analysis, we showed that only the Fab fragment could reach the antigenic site in human articular sections. Cross-reactivity of the antibody 6F3 with link proteins purified from rat articular cartilage allowed us to carry out a biodistribution analysis in vivo in the rat. The time course of whole blood and plasma showed maximal activity 6 h after the 20 micrograms i.v. injection of [125I]Fab-6F3. Urinary excretion seems to be a high route of elimination. Moreover, we noticed no radioactive uptake across the blood-brain barrier. A significant fixation of labeled antibody Fab-6F3 was observed in noncartilaginous connective tissues such as aorta, skin and lung. As expected, specific and increased radioactivity was observed in all cartilage tissues, this increase was significantly higher 6 h after the [125I]Fab-6F3 injection than in the other connective tissues.

Osteoarthritis-related changes in human articular cartilage. An immunologic study.

We report the use of immunologic methods for detecting specific alterations in human osteoarthritic cartilage. Monoclonal antibodies with specificities for proteoglycans and link proteins have been used to define immunogenic sites in these molecules. We have identified 1 site in the protein core, 1 site in the link proteins, and another site that is common to both proteoglycan and link proteins, which are not modified in osteoarthritic cartilage. In addition, an antigenic determinant in link proteins that is altered in osteoarthritic cartilage has been identified. These results suggest that the structure of the ternary complex (hyaluronic acid binding region-link proteins-hyaluronic acid) could be altered in osteoarthritic cartilage. These modifications may be due to a genetic defect or to partial enzymatic degradation of these sites.

Biochemical analysis of normal and osteoarthritic human cartilage.

Non-collagenous proteins from the articular cartilage of normal subjects and patients with degenerative joint disease were extracted sequentially. Proteoglycans and the other glycoproteins were more extractable from the osteoarthritic cartilage at lower ionic strength than those from the normal cartilage. A 50-kD protein which seems specific to osteoarthritic cartilage was identified. Three different populations of proteoglycans were purified from normal and only two from osteoarthritic cartilage. Moreover, greater amounts of albumin and fibronectin were found in the pathological cartilage. No differences were observed between link proteins from normal and osteoarthritic cartilage, nor in their molecular weight or the amounts extracted.