Changes in proteoglycan types during matrix-induced cartilage and bone development

Bone marrow aspiration: technique, grafts, and reports

This article describes a technique for obtaining adult stem cells from bone marrow aspirate. Case reports show how this procedure might replace the gold standard for bone grafts with the platinum standard of obtaining stem cells. The bone marrow aspirate and transplantation of adult stem cells within the resorbable) matrix and under the influence of soluble regulators have the potential for introducing the platinum standard for bone grafts. There are several advantages to using bone marrow aspirate. The technique is simple, a second surgical site is not needed, there is minimal postoperative morbidity, and adult stem cells populate the graft site with osteoblasts.

Increased accumulation of superficial zone protein (SZP) in articular cartilage in response to bone morphogenetic protein-7 and growth factors

The purpose of this study was to investigate the role of bone morphogenetic proteins (BMPs), such as BMP-7, growth factors, and cytokines, in the accumulation of superficial zone protein (SZP) in bovine articular cartilage. Calf superficial articular cartilage discs and chondrocytes were obtained for explant and monolayer culture systems, respectively. Dose- and time-dependent actions of BMP-7 on SZP accumulation were investigated in both explant and monolayer culture systems. In addition, actions of various morphogens and growth factors [BMP-2, BMP-4, fibroblast growth factor 2 (FGF-2), insulin-like growth factor 1 (IGF-1), platelet-derived growth factor (PDGF), and transforming growth factor beta (TGF-beta1)], and cytokines [interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF-alpha)] alone, and in combination with BMP-7, on SZP accumulation were investigated in monolayer culture systems. SZP accumulation was quantified in both the cartilage and the medium using SDS-PAGE and subsequent immunoblotting. In both explant and monolayer cultures, BMP-7 increased SZP accumulation in a dose- and time-dependent fashion (p < 0.05). Furthermore, SZP accumulation was significantly increased in monolayer cultures by FGF-2, IGF-1, PDGF, and TGF-beta1 (p < 0.05). Both IL-1alpha and TNF-alpha significantly reduced SZP accumulation (p < 0.05). The inhibition of SZP accumulation by TNF-alpha was partially alleviated by concurrent treatment with BMP-7. The results of this investigation provide novel insights into the role of morphogens, especially BMP-7, growth factors, and cytokines in the accumulation of SZP in articular cartilage. This information has clinical implications because stimulation of SZP may ameliorate the pathology of joint function in arthritis. Furthermore, tissue engineering approaches to articular cartilage may depend on the optimal synthesis and assembly of SZP in the superficial zone to ensure functional tissue architecture.

The Bone-Grafting Decision Tree: A Systematic Methodology for Achieving New Bone

Successful bone grafting requires that the clinician select the optimal bone grafting material and surgical technique from among a number of alternatives. This article reviews the biology of bone growth and repair, and presents a decision-making protocol in which the clinician first evaluates the bone quality at the surgical site to determine which graft material should be used. Bone quantity is then evaluated to determine the optimal surgical technique. Choices among graft stabilization techniques are also reviewed, and cases are presented to illustrate the use of this decision tree.

Low frequency EMF regulates chondrocyte differentiation and expression of matrix proteins

This study describes the enhancement of chondrogenic differentiation in endochondral ossification by extremely low frequency pulsed electric/magnetic fields (EMFs). The demineralized bone matrix (DBM)-induced endochondral ossification model was used to examine the effects of EMF stimulation. [35S]-Sulfate and [3H]-thymidine incorporation and glycosaminoglycan (GAG) content were determined by standard methods. Proteoglycan (PG) and GAG molecular size and composition were determined by gel chromatography and sequential enzyme digestion. Immunohistochemical and Western blot analysis of PGs were done with antibodies 2B6, 3B3, 2D3 and 5D4. Northern analysis of total RNA extracts was performed for aggrecan, and type II collagen. All data was compared for significance by Student's t- or analysis of variance (ANOVA)-tests. The EMF field accelerated chondrogenesis as evidenced by an increase in: (1) 35SO4 incorporation and GAG content, (2) the number of chondrocytes at day 8 of development, (3) the volumetric density of cartilage and (4) the extent of immunostaining for 3B3 and 5D4. No differences in DNA content or [3H]-thymidine incorporation were observed between control and stimulated ossicles, suggesting the absence of enhanced cell proliferation or recruitment as a mechanism for the acceleration. PG and GAG molecular sizes and GAG chemical composition were similar in stimulated and control ossicles, indicating that stimulation resulted in an accelerated synthesis of normal cartilage molecules. The increased expression of PG and type II collagen mRNA as well as a greater immunoreactivity of 3B3 and 5D4 suggest an increase in the rate of differentiation of chondrocytes and enhanced phenotypic maturation.

Arthrodesis of lumbar spine transverse processes using nacre in rabbit

This study compares the osteogenic effects of nacre and autogenous bone grafts in a rabbit model of lumbar spine transverse process arthrodesis. A total of 15 rabbits were processed for arthrodesis between the fifth and sixth lumbar vertebrae using nacre powder mixed with autologous blood or autogenous iliac crest bone. Control rabbits were sham operated. Sample vertebrae were removed from the nacre-implanted rabbits at 2, 5, and 11 weeks postsurgery. The autogenous bone graft and sham-operated groups were processed for histological study 11 weeks postsurgery. The results for the three groups were compared at 11 weeks. The nacre-implanted samples taken at 2 weeks showed that the nacre was well tolerated by the host tissue. Endochondral bone formation was seen in the region of the dissolving nacre particles by 5 weeks. The newly formed bone formed a solid fusion between the transverse processes in one-third of the rabbits. There was still new bone formation at 11 weeks at the nacre implant site. Two-thirds of the rabbits had formed a solid fusion. Light microscopy also showed new bone formation 11 weeks after the autologous bone graft. All rabbits had a solid fusion. This initial study indicates that nacre can induce spinal fusion in an acceptable percentage of cases.

Basement membrane composition of cartilage canals during development and ossification of the epiphysis

BACKGROUND

Cartilage canals are perichondral invaginations of blood vessels and connective tissue that are found within the epiphyses of most mammalian long bones. Functionally, they provide a means of transport of nutrients to the hyaline cartilage, a mechanism for removal of metabolic wastes, and a conduit for stem cells that are capable of initiating and sustaining ossification of the chondroepiphysis. Morphological and biomolecular changes of the chondroepiphyses appear to potentiate ossification within the chondroepiphyses of developing bones.

METHODS

As both cell migration and vascular invasion are anchorage dependent processes, antibodies to laminin and Type IV collagen were used to assess compositional changes in the basement membrane of cartilage canals accompanying epiphyseal ossification.

RESULTS

Differences in chronological appearance, as well as, in distribution between the two components were noted in the chondroepiphysis. Laminin was distributed throughout the connective tissue of cartilage canal at all stages of development, and not limited to an association with the vascular lumen. Type IV collagen was not present during the initial perichondral invagination. Although staining for Type IV collagen was later acquired, its distribution was restricted to a discontinuous rimming of the periphery of the canal, and a diffuse presence within the intra-canalicular mesenchyme.

CONCLUSIONS

Concurrent with chondrocyte hypertrophy and mineralization of the hyaline matrix, rapid changes in both the morphology of the vessel and distribution of the antibodies were detected. In addition to the presence of laminin at the interface of the endothelium and the hyaline matrix, a wide distribution within the connective tissue components of the newly ossifying matrix of epiphyseal bone could be detected. Type IV collagen remained closely associated with the lumens of the intra-canalicular vessels throughout the transition. Following ossification of the secondary center, staining for Type IV collagen could then be detected in the bone-forming regions of transforming matrix as well, clearly delineating the individual vessels within the newly formed marrow spaces. This suggests that bone formation is intimately related to vessel staining for collagen type IV, and that acquired vessel competence is a facet of endochondral bone formation that results from provisional matrix changes. Furthermore, the data suggests that during bone formation under tension, basement membrane deposition can be demonstrated without an intermediary hyaline matrix hypertrophic chondrocyte phase. This data was interpreted to suggest that chondrocyte hypertrophy at the growth plate may be a reaction to vascular invasion, that in turn, stimulates adjacent chondrocyte proliferation.

Vitamin B6 deficiency experimentally-induced bone and joint disorder: microscopic, radiographic and biochemical evidence

In the present study the effect of pyridoxine deficiency on the ultrastructure and morphology of bone and its metabolism was examined in the rapidly growing chick. Pyridoxine-deficient animals had tibias of reduced dry weight and cortical thickness. Histomorphometry demonstrated a disproportionately high eroded surface, lower amount of osteoid tissue and reduced mineralized trabecular width. Anterior-posterior radiographs of the tibiotarsometatarsal joint showed reduced secondary ossification centres and coarse trabeculation. Decalcified metaphyseal cartilage showed irregular trabeculas and a markedly reduced amount of Fast-green counterstain matrix suggesting that there is less collagen present and in turn less availability for matrix to be laid down for later calcification. Plasma activity of the bone alkaline phosphatase isoenzyme (EC 3.1.3.1) was decreased. Plasma Ca and PO4 levels did not vary. The present bone study referring to a pseudo-lathyritic state in which collagen maturation is not completely achieved supports the hypothesis that pyridoxine is an essential nutrient for the connective tissue matrix.

The control of chondrocyte differentiation during endochondral bone growth in vivo: changes in TGF-beta and the proto-oncogene c-myc

The expression of transforming growth factor-beta and the c-myc proto-oncogene was studied in situ in the chondrocytes of the tibial growth plate of normal chicks and those with avian tibial dyschondroplasia in which the chondrocytes are developmentally arrested in the transitional phase between proliferation and differentiation. This results in an accumulation of unmineralised and avascular cartilage. Dyschondroplastic chicks showed reduced c-myc expression in the transitional chondrocytes but unaltered levels in the proliferating chondrocytes. Transforming growth factor-beta expression was reduced in the transitional chondrocytes of dyschondroplastic chicks. In areas where the lesion was being repaired there was evidence of increased expression of both c-myc protein and transforming growth factor-beta. Addition of 1,25-dihydroxyvitamin D to the diet, which is known to reduce the incidence of dyschondroplasia, resulted in an increase in c-myc production. These results suggest that both transforming growth factor-beta and the proto-oncogene c-myc may be important elements of the cascade of events that lead to chondrocyte differentiation, hypertrophy and mineralisation.

Sequential appearance of macromolecules in bone induction in the rat

The appearance of noncollagenous proteins and proteoglycans during induction of cartilage and bone by implanted demineralized bone powder was studied by immunohistochemistry with polyclonal antibodies. Three bone proteins (osteopontin, sialoprotein, and a 62 kDa protein) were present in the bone powder grains before implantation. They appeared to be lost slowly from the granulation tissue but reappeared when bone formation started. The raw powder also contained a cartilage protein, biglycan (S1), chondrocalcin, cartilage oligomeric matrix protein, and the large proteoglycan aggrecan. The amounts of these molecules, however, increased significantly both within and outside the grains on cartilage formation. Cartilage matrix protein (148 kDa protein) appeared sparsely. The 58 kDa protein and fibromodulin (59 kDa protein), particularly the latter, were prevalent in fibrillar bundles. Antibodies against the laminin-staining vessel basement membranes showed an abundant occurrence of capillaries within the matrix grains in the granulation tissue and in the precartilaginous tissue. Bone powder made noninductive by 4 M guanidine HCl did not induce cartilage and did not stain for antibodies against bone proteins or for molecules restricted to cartilage.

The concept of osseointegration and bone matrix expression

Osseointegration has been defined as the direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant. To date, this concept has been described by descriptive histological and ultrastructural criteria but not by biochemical means. This review evaluates the basic science work performed on this concept and then applies the concept to the principle of osseous healing. Specific studies are cited where alterations in the healing response are due to clinical management of implant placement and how studies of surface properties may lead to further insights on implant design and prognosis. In addition, a review of bone expression as a function of in vitro stress applications is given. This is followed by an indepth review of the collagens and noncollagenous proteins, described to date, within isolated bone matrix. It is this collagenous matrix (especially type I) that is described as being close to and oriented with a glycoprotein component next to the implant surface. In turn, the large family of noncollagenous proteins are important in mediating bone proliferation, matrix accumulation, orientation, mineralization, and turnover. This section is followed by a discussion of specific growth factors as they may relate to osseous healing around an implant.

Matrix vesicles as a marker of endochondral ossification

Endochondral ossification in bone development and repair, and in induced bone formation in mesenchymal tissues, involves recruitment of mesenchymal cells, their differentiation into chondrocytes, and calcification of the cartilagenous matrix. Stimulation of proteoglycan synthesis is used as a biochemical marker of chondrogenesis, however it does not distinguish among chondrogenic phenotypes. Chondrocytes derived from the resting zone and adjacent growth zone cartilage of the costochondral junction of young rats, produce matrix vesicles in culture which are enriched in alkaline phosphatase specific activity with respect to the plasma membrane. Matrix vesicles isolated from cultures of neonatal rat muscle mesenchymal cells are not enriched in this enzyme activity. Alkaline phosphatase in matrix vesicles produced by growth zone chondrocytes is stimulated by 1,25(OH)2D3; enzyme in matrix vesicles produced by resting zone chondrocytes is stimulated by 24,25(OH)2D3; enzyme in matrix vesicles isolated from mesenchymal cell cultures is responsive to neither metabolite. Matrix vesicle phospholipase A2 is stimulated by 1,25(OH)2D3 in growth zone chondrocytes cultures; inhibited by 24,25(OH)2D3 in resting zone chondrocyte cultures; and is unaffected by either metabolite in mesenchymal cell cultures. These observations suggest that matrix vesicle production, as defined by alkaline phosphatase enrichment, and responsiveness of matrix vesicle enzymes to vitamin D metabolites, can be used as markers of phenotypic maturation during chondrogenesis in vivo and in vitro.

Stimulation of experimental endochondral ossification by low-energy pulsing electromagnetic fields

Pulsed electromagnetic fields (PEMFs) of certain configuration have been shown to be effective clinically in promoting the healing of fracture nonunions and are believed to enhance calcification of extracellular matrix. In vitro studies have suggested that PEMFs may also have the effect of modifying the extracellular matrix by promoting the synthesis of matrix molecules. This study examines the effect of one PEMF upon the extracellular matrix and calcification of endochondral ossification in vivo. The synthesis of cartilage molecules is enhanced by PEMF, and subsequent endochondral calcification is stimulated. Histomorphometric studies indicate that the maturation of bone trabeculae is also promoted by PEMF stimulation. These results indicate that a specific PEMF can change the composition of cartilage extracellular matrix in vivo and raises the possibility that the effects on other processes of endochondral ossification (e.g., fracture healing and growth plates) may occur through a similar mechanism.

Neutral protein-degrading enzymes in experimental fracture callus: a preliminary report

The process of endochondral fracture healing is biochemically similar to growth plate calcification. Recent studies have identified potentially important roles for proteoglycan-degrading enzymes in the growth plate. The purpose of the study described herein was to identify, in healing fractures, neutral enzyme activities capable of degrading proteoglycans and other matrix proteins. Two sets of 60 male Sprague-Dawley rats underwent the production of closed femoral fractures. Calluses were retrieved at timed intervals, and cell and matrix vesicle fractions were prepared for electron microscopy, neutral peptidase, and alkaline phosphatase assays. In another group of 10 animals, fractions were prepared from 14-day calluses and examined for proteoglycanase activity. In the cell fractions, alkaline phosphatase, alanyl-beta-naphthylamidase, aminopeptidase, and endopeptidase activities showed somewhat parallel distributions peaking at approximately 14-17 days. In the matrix vesicle fractions, similar relative distributions were observed for alkaline phosphatase and endopeptidase. However, here the peak activities occurred up to 3 days later than they did in the cell fractions. Significant proteoglycanase activity was confirmed in both cell and matrix vesicle fractions. These findings are consistent with the hypotheses that (a) neutral peptidases, by virtue of their temporal expression in parallel with alkaline phosphatase, may be involved in preparing fracture callus matrix for calcification; and (b) matrix vesicles may convey certain of these enzymes to sites of both matrix degradation and calcification, since the same activities found in cells are found in matrix vesicles a few days later. The possibility that some of these enzymes are involved in growth factor activation remains to be investigated.

A comparative ultrahistochemical study of glycosaminoglycans with cuprolinic blue in bone formed in vivo and in vitro

Histochemical and morphological studies have shown that proteoglygans (PG) are involved in mineralization process in vivo but such studies have not yet been conducted in vitro. A comparative histochemical study in electronic microscopy of the localization, organization, and morphology of the PG was performed with bones of calvaria rat formed in vivo and bone nodules formed in vitro from osteoblastic cells in culture. For this investigation, we used a cationic phthalocyanin dye, cuprolinic blue, in a critical electrolyte concentration which simultaneously stained the glycosaminoglycans and demineralized the bone. This histochemical technique demonstrated (1) osteoblast cells in vitro synthesized PG which were included in the matrix formed. (2) These PG were found in the calcified and uncalcified matrix both in vivo and in vitro. In the uncalcified matrix, PG were either free with a granular or rodlike structure or tightly connected to the periphery of the collagen fiber. Contrarily, in the calcified matrix, PG formed dense filamentous reticular patches between the collagen fibers. (3) Similarities in localization, organization, and morphology were noted in PG of bone formed de novo in vitro and in vivo with the exception of the mineralization front, where the staining in vivo compared with in vitro was faint or absent.

A histochemical method for the demonstration of calcifying cartilage

The demonstration of histochemical characteristics in calcifying cartilage is fraught with methodological difficulties including the distinction of mineralized from unmineralized cartilage and the demonstration of cell detail in relatively hard tissue. This study uses the decalcified bone matrix-induced enchondral (endochondral) ossification system to demonstrate a technique of methylmethacrylate embedding, thin sections, and a combination of histochemical stains that distinguishes mineralized from unmineralized cartilage while preserving excellent cell detail. These techniques are applicable to other areas of enchondral ossification and are exemplified by the staining of growth plates.

Mitogenic response of cells in culture to demineralized bone matrix

In this study the mitogenic effect of demineralized bone powder (DBP) on cells in tissue culture was evaluated. The cells studied have osteoblastic properties. At a DBP concentration of 100 micrograms/well, rat osteosarcoma cells (ROS) 17/2.8 cells, ROS 24/1 cells, and periosteal fibroblasts (POF) all showed a significant increase in proliferation in comparison to controls. The peak effect was on day two for ROS 17/2.8 (125% of control), on day three for ROS 24/1 (139% of control), and on day four for POF (145% of control). The results indicate that this in vitro system may be useful for evaluating the osteoinductive activity of DBP preparations.

Biochemistry of fusion mass consolidation in the sheep spine

We report here the biochemistry of fusion mass consolidation in sheep spines during a 1-year period following autogenous cortical-cancellous bone grafting and stabilization with Harrington distraction rods. Biochemical analysis of vertebral fusion mass included determination of wet weight and dry weight and quantification of glycosaminoglycan, collagen, calcium, and phosphate following extraction with neutral EDTA and proteolytic hydrolysis with papain. Our results showed that at 1 week after surgery, the fusion mass consisted of original cortical and cancellous bone graft material. The cortical bone graft was partially resistant to EDTA-papain treatment, resulting in a residue containing hydroxyproline and mineral. At 12 weeks after surgery, the fusion mass had become a homogeneous material, which, like cancellous bone graft, was completely susceptible to treatment by EDTA-papain. Collagen content of consolidating fusion mass was highest at 16 weeks after surgery when normalized to dry weight; glycosaminoglycan content was highest within 6 weeks after surgery. Mineral content was lowest at the 6-week stage but by 12 weeks after surgery, it was comparable with original bone grafting material. At 24 and 52 weeks after surgery, fusion mass consolidation was characterized by an increase in the proportion of organic and mineral components resistant to EDTA-papain. The appearance of the EDTA-papain-resistant material in the fusion mass coincided with formation of lamellar bone and successful consolidation.

Differentiation of the organic matrix in bone repair

This study describes the sequence of production and distribution of collagen, collagen types, proteoglycans, and calcium during bone repair in rabbits utilizing histologic and biochemical techniques. Proteoglycan content peaked 11 days following surgery and total collagen peaked 19 days after surgery, after which both levels decreased. Collagen Types I and III were present in the bone defect throughout the healing process but Type II was found only in the mid stages of repair. In the surrounding external callus Types I, II, and III were present, but Type III was not noted in the later stages of healing. These results are similar to those found in studies of fracture repair and developing bone.

Loss of proteoglycans during decalcification of fresh metaphyses with disodium ethylenediaminetetraacetate (EDTA)

Recent immunofluorescent and histochemical data did not detect changes in the concentration of proteoglycans between noncalcified and calcified cartilage in fetal bovine growth plate or metaphyseal bone. These findings were constant, regardless of prior fixation before demineralization with disodium ethylenediaminetetraacetate (EDTA) or prior demineralization before fixation. Previous experience has shown that EDTA can extract proteoglycans from calcified cartilage. With this in mind, we determined the amount of proteoglycan extracted from calcified cartilage in metaphyseal bone and uncalcified growth plate cartilages during decalcification of unfixed fresh tissues with EDTA. To this end, fresh growth plate cartilages and metaphyses were decalcified at 5 degrees C for 48 hours in a buffered solution of EDTA to which several protease inhibitors were added. Under these conditions 20-25% of the total proteoglycan (measured as uronic acid and hexosamine) was extracted from mineralized cartilage but only about 1% from the uncalcified (growth plate) cartilages. Thus, histochemical and immunohistochemical studies appear to be insensitive measures of proteoglycan concentrations in histological sections of mineralized tissue and may not give quantitative information.

Comparison of the stimulation of glycosaminoglycan synthesis in cultures of mononuclear cells from blood and of fibroblastic cells

A small molecular weight factor, derived from bovine bone ('matrigenin'), stimulated glycosaminoglycan and proteoglycan synthesis of cultured human fibroblastic cells but not of mononuclear cells from human blood. However, proteoglycan synthesis and secretion by the mononuclear cells was stimulated by the addition of concanavalin A. The proteoglycan from the concanavalin-A-stimulated mononuclear cells was of smaller molecular weight than the proteoglycan from the 'matrigenin'-stimulated fibroblastic cells. The major increase in proteoglycan synthesis and secretion occurred much later during the culture period for concanavalin-A-stimulated mononuclear cells than for 'matrigenin'-stimulated fibroblastic cells.

Proteoglycan synthesis during intramembranous bone regeneration following avulsive wounding in guinea pig long bones

Information on proteoglycan synthesis by bone cells and tissue is largely limited to studies of developing fetal bone. The present investigation focuses on proteoglycan synthesis during the intramembranous type of bone regeneration seen within avulsive (puncture-type) defects placed in guinea pig tibiae. [35S] Sulfate-labeled proteoglycans were extracted from tissue within regenerating tibial avulsive defects seven days following surgical wounding and also from xiphisternal cartilage utilized as an internal control. Labeled proteoglycans in 4M guanidine HCl extracts of regenerating bone and cartilage were purified by DEAE-Sephacel chromatography and further analyzed by chromatography and appropriate enzyme digestions. Regenerating bone tissue contained a proteoglycan relatively small in size (Kav = 0.56 following chromatography on Sepharose CL-2B) compared to proteoglycan from xiphisternal cartilage (Kav = 0.17). Alkaline borohydride treatment degraded this bone proteoglycan (Kav = 0.4 on Sepharose CL-6B), indicating an average molecular weight of glycosaminoglycan chains approximating 50,000. Enzymatic digestions followed by Sepharose CL-6B chromatography showed that glycosaminoglycan side chains of regenerating bone proteoglycan contained dermatan sulfate, with 60% chondroitinase AC II-resistant but chondroitinase ABC-sensitive material. This bone proteoglycan did not interact with hyaluronic acid to form aggregates under conditions where such aggregates were formed by xiphisternal cartilage proteoglycan. The regenerating bone proteoglycans are therefore similar to other bone proteoglycans in hydrodynamic size and glycosaminoglycan chain size, but differ in the per cent of iduronic acid within glycosaminoglycan side chains. This guinea pig bone proteoglycan may be associated with the large mesenchymal cell population noted histologically within the bone defects at seven days of regeneration.

Biochemical characterization of fracture callus proteoglycans

The changes in proteoglycan molecules during the initial stages of fracture healing in rats were characterized. Following extraction of callus proteoglycan components with dissociative solvents, the components were purified in a cesium chloride density gradient. The recovered proteoglycans were characterized with respect to their molecular size distribution using gel filtration chromatography and a centrifugal transport methodology. During this early healing period, a decrease was observed in the relative proportion of the aggregate and in the hydrodynamic size and sedimentation coefficients of these molecules. While some molecular degradation could have occurred during the early stages of fracture healing, the dominant change of the proteoglycan molecules seemed to be disaggregation. No significant difference was observed in the proportion of aggregates reformed when exogenous hyaluronate and link glycoproteins were allowed to interact with the two corresponding monomer preparations. The molecular changes of the proteoglycan molecules seem to parallel those occurring during endochondral calcification of rat epiphyseal cartilage.

The effects of mechanical stability on the macromolecules of the connective tissue matrices produced during fracture healing. II. The glycosaminoglycans

The glycosaminoglycans secreted into the matrices associated with fractures of the rabbit tibia healing under stable and unstable mechanical conditions have been characterized histochemically using the dye Alcian Blue at pH 5.7 in the presence of increasing concentrations of magnesium chloride, and after enzymatic extractions. These results are compared with those of immunohistochemical experiments using monoclonal antibodies which recognize epitopes specific to various glycosaminoglycans. The results indicate that the fibrous tissues, including those of the cavities of the cancellous bone and periosteum, possess hyaluronate and chondroitin sulphate, but the amounts present are small. The glycosaminoglycans detected in the cortical bone are located mainly around the osteocyte lacunae where chondroitin and keratan sulphates are found. The developing trabeculae of cancellous bone in the callus contain chondroitin and keratan sulphates, but as the trabeculae mature, these glycosaminoglycans are no longer present throughout the matrix; they are found particularly around the osteocyte lacunae. The cartilage in the callus of mechanically unstable fractures contains chondroitin, chondroitin-4- and 6-sulphates and keratan sulphate, through their distribution is variable. The small, transient areas of cartilage in the callus of mechanically stable fractures also contain those glycosaminoglycans, but they appear to be less highly sulphated. The mechanical stability of the fractures appears to affect the amount and degree of sulphation of the glycosaminoglycans, rather than the types of glycosaminoglycan produced. The glycosaminoglycans produced during fracture healing are compared with those produced during embryonic development and other healing processes.

Changes in cartilage proteoglycans associated with calcification

The purposes of these experiments were to study the biosynthetic and postbiosynthetic relationships between proteoglycans in noncalcified growth cartilage and calcified cartilage in metaphysis from the costochondral junctions of immature rabbits. Based on in vivo experiments in which 35 S-sodium sulfate was injected into rabbits, it is shown that proteoglycans from the hypertrophic region becomes part of the calcified cartilage matrix which is to be incorporated into the metaphysis. The proteoglycan aggregates in the growth apparatus undergo partial disaggregation and degradation. There is approximately a 25% decrease in aggregation from regions of the rib distal to the metaphyseal-growth plate junction (69%) to the region proximal to it (50%). In contrast, in their final state in calcified cartilage, the proteoglycans are more completely disaggregated and the proteoglycans subunits are smaller, as adjudged from gel chromatography. Control experiments indicate that although some artifactual disaggregation is produced by the extraction process, it is not of the same magnitude as that seen in the actual isolation experiments nor are the subunits reduced in size.

Biosynthesis and fate of proteoglycans in cartilage and bone during development and mineralization

Subcutaneous implantation of demineralized bone matrix in rats induces migration of host cells into the site and results in the sequential development of cartilage and bone. The biosynthesis and metabolic fate of proteoglycans in the plaques at the bone matrix implantation site were investigated by [35S]sulfate labeling in vivo. 35S-Labeled proteoglycans were extracted with 4 M guanidine HCl and purified by DEAE-Sephacel chromatography. Analysis of proteoglycans on Sepharose CL-2B chromatography showed two major peaks at Kd = 0.28 and 0.68 (peaks I and II, respectively). Peak I proteoglycan has a high buoyant density and contains chondroitin sulfate chains of average Mr = 20,000. Peak II proteoglycan has a lower average buoyant density and contains dermatan sulfate chains of average Mr = 33,000. Throughout the endochondral bone development sequence, peak II proteoglycan predominates. Peak I was low on Day 3, became prominent on Day 7 (approximately 30% of the total radioactivity), and declined after Day 9. The calculated half-lives of peak I and II proteoglycans labeled on Day 7 were about 1.8 and 2.8 days, respectively. After the initiation of osteogenesis, a species of mineral-associated proteoglycan was extracted with a 4 M guanidine HCl solvent containing 0.5 M EDTA. This proteoglycan has a small hydrodynamic size (Kd = 0.38 on Sepharose CL-6B chromatography) and shows a long half-life, about 6 days.

Primary glial cells and brain fibroblasts: interactions in culture

Primary glial-enriched cultures were prepared from newborn mouse cerebral hemispheres. The cultures were grown in Dulbecco's Modified Eagle Medium in which L-valine was substituted with D-valine; this medium selectively inhibits the growth of fibroblasts. Using glutamine synthetase and glial fibrillary acidic protein as immunocytochemical markers, cultures in D-valine medium were characterized as being over 80% astrocytic. However, these cultures exhibited a suppressed growth rate and lagged behind in their differentiation as assessed biochemically using DNA content and glutamine synthetase activity as markers for growth and differentiation. Growth was restored when D-valine cultures were grown in medium containing conditioned medium derived from brain fibroblast cultures when grown on matrix or killed substrata derived from brain fibroblast cultures. This in vitro approach offers the possibility of purifying factors and developing immunological probes to investigate the possible role of brain fibroblasts in influencing glial cell function.

Control of repair in articular tissues and the development of osteoarthritis

Bones from different mammalian species, including man, contain a low molecular weight extractable activity which stimulates proteoglycan synthesis by connective tissue cells in culture ("matrigenin" activity). Partial purification of matrigenin activity has been achieved from bovine bone. The activity shows a strong tendency for reversible physical associations in low ionic strength solutions and binds tightly to collagenous and other bone matrix proteins. It is speculated that the pathophysiological role of matrigenins may be to initiate repair during injury to bone. Chronic repair reactions are more likely to occur at sites of repeated anatomical stress at the ligamentous, tendon and synovial attachments at the ends of bones, in the subchondral bone and in the articular cartilage regions abbuting to subchondral bone. At these sites, repair reactions may be broadly viewed as the development of osteophytes and fibrocartilage and the progression of subchondral bone sclerosis. Repeated anatomical stress leads to the activation of extracellular, small molecular weight factors, which in turn, stimulate the biosynthesis of matrix macromolecules that are an important feature of these repair reactions of osteoarthritis.

Comparative distribution of glycosaminoglycans and proteoglycans in the reproductive tissues of the female fowl

The objective of this work was to survey and compare the composition of the parts of the reproductive system of the female fowl in glycosaminoglycans and proteoglycans. Those parts analyzed were ovary, infundibulum, magnum, isthmus, shell gland and vagina. Methods of analysis included cellulose acetate electrophoresis, infrared spectroscopy, colorimetry, amino acid determination and scanning electron microscopy. Concentrations of glycosaminoglycans were higher in vagina, ovary, infundibulum and isthmus than in shell gland and magnum. Glycosaminoglycans may be important in those parts of the reproductive tract which contribute membraneous and mucosal material to the descending egg, and where fertilization of the egg occurs.

Implant-stimulated interface reactions during collagenous bone matrix-induced bone formation

The sequential cellular reactions in the interface of collagenous bone matrix implants are described. The multistep cascade in response to bone matrix implantation include: binding of fibrin and fibronectin to the implanted matrix, chemotaxis of cells, proliferation of fibroblasts, differentiation into chondroblasts, cartilage formation, vascular invasions, bone formation, remodeling, and bone marrow differentiation. The mechanisms of action is not known. However, several properties governing the implant-cell interface are described. It is possible that bone matrix is a suitable biomaterial with potential applications in periodontal and orthopedic practice.

Proteoglycans of adult bovine compact bone

Proteoglycans of bovine compact bone were purified by chromatography of the formic acid precipitate of an EDTA extract. The sequential chromatographic steps consisted of gel filtration on Sepharose CL-6B in 4-M guanidine HCl, ion-exchange chromatography on DEAE-Sephacel in 4-M urea and rechromatography on Sepharose CL-6B in 4-M guanidine HCl. The preparation consisted of a relatively small proteoglycan (Kav = 0.4 on Sepharose CL-6B) containing about 40% protein, 21% hexuronic acid, 23% galactosamine and lesser amounts of other monosaccharides. The core protein was shown by gradient NaDodSO4 gel electrophoresis, electrotransfer and immunodetection to be monodispersed with an Mr = 45,000. Analysis of glycopeptides obtained after papain digestion of the proteoglycan and separation from glycosaminoglycan chains by gel chromatography, indicated that both N-linked and O-linked oligosaccharides were present. The glycosaminoglycan chains liberated by papain digestion eluted from Sepharose CL-6B as a broad peak with Kav = 0.50, slightly ahead of the position of elution of bovine nasal cartilage glycosaminoglycans (Kav = 0.52); the bone glycosaminoglycans are thus slightly larger than those from cartilage and smaller than the ones attached to fetal bone proteoglycans. These chains were totally susceptible to chondroitinase AC II, a procedure that yielded unsaturated disaccharides corresponding predominantly to chondroitin-4-sulfate, and to a lesser extent chondroitin-6-sulfate. Antisera raised against adult bone proteoglycans cross-reacted with core protein of bone proteoglycan (obtained after chondroitinase digestion) but not with papain digested proteoglycan. In addition, they cross-reacted with core protein and trypsin-liberated, chondroitin sulfate rich region (AlTAl) derived from cartilage proteoglycans and, to a lesser extent, rat bone proteoglycans. No cross-reactivity could be detected to Smith-degraded cartilage proteoglycans, bone acidic glycoproteins or serum proteins.

Induced osteogenesis--the biological principle and clinical applications

Complex orthopedic and craniofacial surgical procedures have stimulated renewed interest in the physiology of bone grafting. The experimental and clinical evidence that a nonvital implant can stimulate local host cells to become bone-forming cells (osteoinduction) is reviewed. Studies of induced osteogenesis were derived from old clinical observations of heterotopic ossification in scars and muscle. When demineralized bone is placed within soft tissues of a rat, a remarkable sequence of endochondral ossification occurs. In contrast, mineral-containing bone particles stimulate obligatory resorption by host mono- and multinucleated cells. The biochemical, endocrine, and physicochemical aspects of induced osteogenesis are actively being investigated. Present understanding of the mechanism of bone induction is discussed along with descriptions of preliminary clinical trials with allogeneic demineralized implants.

Glycosaminoglycan synthesis by rat fibroblast monolayers: effects of serum and solubilized bone matrix fractions

Glycosaminoglycan synthesis by fibroblasts, from skeletal muscle of the neonatal rat, is stimulated by a bone matrix preparation, soluble in isotonic medium, obtained by extracting decalcified rat bone with 4 M guanidine HCl. The stimulation in glycosaminoglycan synthesis is dependent on the presence of serum in the culture, but the stimulatory effect can be clearly distinguished from that of serum. The stimulatory activity in the bone matrix has been fractionated by ion-exchange chromatography and coelutes largely with anionic, non-collagenous matrix glycoproteins.

The inhibitory effect of cartilage proteoglycans on hydroxyapatite growth

The calcification of connective tissues, including cartilage, is under the control of many interacting systems. Proteoglycans are thought to retard the deposition of hydroxyapatite crystals, and modification of the proteoglycans presumably facilitates mineralization in those tissues that are actively calcifying. The mechanism underlying these regulations remains speculative. This study investigates this question by comparing the inhibitory effectiveness of several macromolecules at neutral pH and approximately physiological ionic strengths. Inhibitors tested include bovine nasal proteoglycan monomer A1D1D1 and aggregate-containing A1 fractions, glycosaminoglycan chains (chondroitin 4-sulfate), and neutral dextran (as an uncharged analog). Hydroxyapatite growth was assessed either by measuring the time-dependent decreases in solution calcium and phosphate concentrations, or by determining utilization of hydroxyl ion in a pH-Stat. All species studied inhibit hydroxyapatite growth, and the extent of inhibition for each class is concentration-dependent. The proteoglycan aggregate-containing A1 fraction is more effective than the proteoglycan monomer at the same concentration, and the proteoglycan monomer is more effective than chondroitin 4-sulfate. Neutral dextran inhibits hydroxyapatite growth less effectively than proteoglycans. These results suggest that inhibition of hydroxyapatite growth by proteoglycans critically depends on both status (aggregate, monomer, etc.) and hydrodynamic size of this macromolecule, supporting the hypothesis that modification of proteoglycans in vivo functions to modulate the effectiveness of proteoglycans as a hydroxyapatite growth inhibitor.

Proteoglycan synthesis and deposition in fetal rat bone

A pulse-labeling approach has been used to study proteoglycan metabolism in fetal rat bone. Pregnant rats were injected with [35S]sulfate and sacrificed 6, 24, or 48 h later. Fetal calvaria were dissected and extracted sequentially with 4 M guanidine hydrochloride and 4 M guanidine hydrochloride/0.5 M ( ethylenedinitrilo )tetraacetic acid (EDTA). With time after injection, the proportion of total incorporated radioactivity decreased in the guanidine pool (corresponding to nonmineralized bone and associated soft tissues) and increased in the guanidine/EDTA pool (mineralized bone). Chromatographic analysis of the proteoglycan species present in these pools after different labeling times indicated that three species of proteoglycan are synthesized in fetal rat calvaria. A large chondroitin sulfate (CS) proteoglycan and a smaller dermatan sulfate (DS) proteoglycan are located in the nonmineralized compartment. A CS proteoglycan similar in size to the DS proteoglycan is initially present in the nonmineralized bone but subsequently is located in the mineralized matrix. A fraction of the small CS proteoglycan is strongly associated with collagen.

The effect of solubilized bone matrix fractions from different mammalian species on glycosaminoglycan synthesis by cultured fibroblasts

Human and bovine bone matrices were extracted with salt solutions of different composition and the extracts tested for stimulation of incorporation of radioactivity from [3H]glucosamine and [35S]SO4 into the hyaluronic acid and chondroitin sulfate of the cell pellet, the cell surface and the medium fractions of human synovial cells in culture. Stimulatory activity was extracted with a solution of 0.3 M EDTA in 2.5 M NaCl from bovine but not human bone. Subsequent extraction of the residues with 4 M guanidinium hydrochloride yielded activity from both matrices. A major stimulation of incorporation of radioactivity was observed in the cell surface fractions. Human synovial cells constitute a more sensitive assay system for the stimulatory activity than rabbit synovial cells.

The effect of vitamin A deficiency and fluoride on glycosaminoglycan metabolism in bone

The effects of fluoride intake and vitamin A deficiency on glycosaminoglycan metabolism in vivo were investigated. Weanling female rats were fed either a vitamin A deficient diet ad libitum, a vitamin A supplemented diet pair-fed to the deficient animals, or the vitamin A supplemented diet ad libitum. Additionally, each vitamin A dietary group was divided into three subgroups with the animals receiving water containing 0, 10 or 50 ppm fluoride. The results showed that the groups receiving 10 and 50 ppm fluoride at all dietary levels of vitamin A had significantly higher in vivo 35SO4 incorporation in both the epiphyseal and diaphyseal regions of the bone than the animals receiving 0 ppm fluoride. The vitamin A deficient animals incorporated significantly less 35SO4 into glycosaminoglycans in the epiphyseal and diaphyseal regions of the bone compared to the pair-fed, vitamin A sufficient animals for all three fluoride receiving groups. There was no interaction between fluoride intake and dietary vitamin A levels on 35SO4 incorporation into glycosaminoglycans. Fluoride either increased sulfation or turnover of glycosaminoglycans.

Influence of vitamin A on matrix-induced endochondral bone formation

The influence of retinoic acid on matrix-induced endochondral bone differentiation was determined. Retinoic acid was administered during discrete stages of endochondral bone formation, specifically, mesenchymal cell proliferation, chondrogenesis, bone formation, and mineralization. In retinoic acid-treated rats examined on day 3 following matrix implantation, biochemical markers for mesenchymal cell proliferation were about 50% of the controls. Chondrogenesis on day 7, assessed by 35 SO4 incorporation into proteoglycans, was 27% of the control. In addition, dissociative extraction of proteoglycans with 4.0 M guanidine-HCl and chromatography on Sepharose CL-2B revealed the synthesis of a smaller molecular weight proteoglycan when compared to controls which exhibited the cartilage-specific type. Osteogenesis and bone mineralization were monitored by alkaline phosphatase activity and 45Ca incorporation. On day 11 alkaline phosphatase activity was decreased by 40% and 45Ca incorporation was 48% of the control. These results revealed the multiple foci of the actions of excess vitamin A.