Collagenous bone matrix is a local mitogen

Biocatalysis by Transglutaminases: A Review of Biotechnological Applications

The biocatalytic activity of transglutaminases (TGs) leads to the synthesis of new covalent isopeptide bonds (crosslinks) between peptide-bound glutamine and lysine residues, but also the transamidation of primary amines to glutamine residues, which ultimately can result into protein polymerisation. Operating with a cysteine/histidine/aspartic acid (Cys/His/Asp) catalytic triad, TGs induce the post-translational modification of proteins at both physiological and pathological conditions (e.g., accumulation of matrices in tissue fibrosis). Because of the disparate biotechnological applications, this large family of protein-remodelling enzymes have stimulated an escalation of interest. In the past 50 years, both mammalian and microbial TGs polymerising activity has been exploited in the food industry for the improvement of aliments' quality, texture, and nutritive value, other than to enhance the food appearance and increased marketability. At the same time, the ability of TGs to crosslink extracellular matrix proteins, like collagen, as well as synthetic biopolymers, has led to multiple applications in biomedicine, such as the production of biocompatible scaffolds and hydrogels for tissue engineering and drug delivery, or DNA-protein bio-conjugation and antibody functionalisation. Here, we summarise the most recent advances in the field, focusing on the utilisation of TGs-mediated protein multimerisation in biotechnological and bioengineering applications.

Expression of Bone Morphogenetic Proteins in Stromal Cells from Human Bone Marrow Long-term Culture

Highly purified primitive hemopoietic stem cells express BMP receptors but do not synthesize bone morphogenetic proteins (BMPs). However, exogenously added BMPs regulate their proliferation, differentiation, and survival. To further explore the mechanism by which BMPs might be involved in hemopoietic differentiation, we tested whether stromal cells from long-term culture (LTC) of normal human bone marrow produce BMPs, BMP receptors, and SMAD signaling molecules. Stromal cells were immunohistochemically characterized by the presence of lyzozyme, CD 31, factor VIII, CD 68, S100, alkaline phosphatase, and vimentin. Gene expression was analyzed by RT-PCR and the presence of BMP protein was confirmed by immunohistochemistry (IHC). The supportive role of the stromal cell layer in hemopoiesis in vitro was confirmed by a colony assay of clonogenic progenitors. Bone marrow stromal cells express mRNA and protein for BMP-3, -4, and -7 but not for BMP-2, -5, and -6 from the first to the eighth week of culture. Furthermore, stromal cells express the BMP type I receptors, activin-like kinase-3 (ALK-3), ALK-6, and the downstream transducers SMAD-1, -4, and -5. Thus, human bone marrow stromal cells synthesize BMPs, which might exert their effects on hemopoietic stem cells in a paracrine manner through specific BMP receptors.

Effect of Storage Temperature on Allograft Bone

BACKGROUND: The recommendations for storage temperature of allogeneic bone are varying between -20 °C and -70 °C and down to -80 °C. The necessary temperature of storage is not exactly defined by scientific data, and the effect of different storage temperatures onto the biomechanical and the biological behavior is discussed controversially. METHODS: The historical development of storage temperature of bone banks is described. A survey on literature concerning the biomechanical and biological properties of allograft bone depending on the procurement and storage temperature is given as well as on national and international regulations on storage conditions of bone banks (European Council, American Association of Tissue Banks (AATB), European Association of Tissue Banks (EATB)). RESULTS: Short-term storage up to 6 months is recommended with -20 °C and -40 °C for a longer period (AATB), and EATB recommends storage at -40 °C and even -80 °C while the regulations of the German German Medical Association (Bundesärztekammer) from 2001 recommend storage at -70 °C. Duration of storage at -20 °C can be maintained at least for 2 years. The potential risk of proteolysis with higher storage temperatures remains, but a definite impairment of bone ingrowth due to a storage at -20 °C was not shown in clinical use, and no adverse biomechanical effects of storage at -20 °C could be proven. CONCLUSION: Biomechanical studies showed no clinically relevant impairment of biomechanical properties of cancellous bone due to different storage temperatures. Sterilization procedures bear the advantage of inactivating enzymatic activity though reducing the risk of proteolysis. In those cases a storage temperature of -20 °C can be recommended for at least a period of 2 years, and the risk of undesired effects seems to be low for native unprocessed bone.

Modeling dynamic reciprocity: engineering three-dimensional culture models of breast architecture, function, and neoplastic transformation

In order to understand why cancer develops as well as predict the outcome of pharmacological treatments, we need to model the structure and function of organs in culture so that our experimental manipulations occur under physiological contexts. This review traces the history of the development of a prototypic example, the three-dimensional (3D) model of the mammary gland acinus. We briefly describe the considerable information available on both normal mammary gland function and breast cancer generated by the current model and present future challenges that will require an increase in its complexity. We propose the need for engineered tissues that faithfully recapitulate their native structures to allow a greater understanding of tissue function, dysfunction, and potential therapeutic intervention.

An assessment of the osteoinductive potential of commercial demineralized freeze-dried bone in the murine thigh muscle implantation model

Early studies have demonstrated that implantation of laboratory preparations of demineralized freeze dried bone (DFDB) into the thigh muscle of mice induces ectopic osteoinduction. However, with the development of commercial preparations of DFDB for clinical use, concerns have been raised as to the osteoinductive properties of such preparations. The aim of this study was to investigate the osteoinductive potential of some commercial preparations of DFDB compared to a newly developed product which incorporates DFDB into a collagen sponge. Commercial preparations of DFDB or the DFDB/collagen sponge were inserted into the thigh muscles of 60 adult Swiss CD-1 mice. At the completion of each experimental period (7, 14, 30, 90 and 180 days), the animals were sacrificed, and the hindquarters of the mice were radiographed. The area where each graft had been placed was then excised, processed for light microscopy, and stained with hematoxylin and eosin or von Kossa's stain. Histological analysis of the DFDB/collagen sponges demonstrated significant remineralization which increased with time. Remineralization of the DFDB/collagen sponges was verified by radiographs which showed a significant increase in radiopacity over time. There was no radiographic evidence of mineralized tissue formation or remineralization in any of the commercial DFDB samples studied. At all time points studied, histological analyses failed to show evidence of bone formation for any of the preparations. The results suggest that commercially available DFDB is not osteoinductive in the murine model and question the use of such materials in clinical periodontics. The results found for the DFDB/collagen sponge indicate a different mechanism of activity from DFDB as evidenced by its rapid remineralization. The role this remineralization process has in osteoinduction is unknown and requires further study.

A quantitative assessment of osteoinductivity of human demineralized bone matrix

Demineralized bone matrix (DBM) is widely used in the repair of pathologies associated with skeletal defects and periodontal diseases. The present study was directed at establishing in vivo and in vitro models for a quantitative assessment of the osteoinductivity of DBM before clinical use. Athymic mice were used in an in vivo assay to overcome the species limitations (for human DBM) found in xenogeneic animal models. Calcium contents of explants, as an indicator of new bone formation, were assayed and expressed as a change in the weight percent calcium in the explant as compared to the weight percent of calcium in the implanted material. A total of 82 mice (2 implants per mouse) were used in this study. Significant amounts of new bone were induced in this animal model in response to implantation of DBM. Muscular implantation was found to be more osteoinductive (increases of 10.0 +/- 0.4 calcium weight percent of explant) than subcutaneous implantation (increases of 1.62 +/- 0.27 calcium weight percent of explant) and new bone formation in muscular implantation sites of athymic mice mimics endochondral bone formation. Between weeks 1 to 4, the weight of explanted materials did not significantly differ from the weight of the implanted material; however, by week 5 the explant weight began to increase. Calcium deposition over the 5 weeks of implantation increased in a nearly linear fashion. Consequently week 4 was chosen as the optimum time for explantation in the in vivo assay in that sufficient calcium levels had been achieved without a significant increase in explant dry weight. Aliquots of 10, 20, 30, and 40 mg per implantation site were used in dose response studies in the in vivo bioassay. Dose response curves with DBM exhibited maximal activity at the 20 mg DBM implant dose in the in vivo bioassay. An in vitro bioassay was also developed where human periosteal (HPO) cells were chosen because osteoprogenitor cells found in bone repair typically come from periosteal tissue. Alkaline phosphatase (ALP) activity in confluent cell cultures of HPO cells exposed to DBM, as an indicator of osteoblast induction, reached its highest level on day 5 of DBM treatment. Aliquots of 2, 5, 10, 20, 30, and 40 mg DBM per flask were chosen in dose response studies using the in vitro bioassay. These dose response studies with DBM revealed that quantities approximating 5 to 10 mg DBM in the in vitro model provided for maximal levels of ALP in cell extracts. A linear correlation (R2 = 0.7397) was demonstrated between the in vivo calcium remineralization assay and the in vitro ALP assay of osteoinductivity of DBM, suggesting that the in vitro assay can be used to quantitatively assess the osteoinductive potential of DBM where production and distribution of clinically usable DBM dictates rapid analysis.

Bone morphogenetic proteins: background and implications for oral reconstruction. A review

For over 30 years now, research has been carried out to isolate and purify bone morphogenetic protein (BMP), a substance which has been shown to induce heterotopic bone formation in various animal species. Recent advances in the fields of developmental biology, molecular biology, genetics and wound healing, have shown that the BMPs are not only responsible for postfetal bone induction (including normal bone remodeling, healing and repair), but are also critical during embryogenesis, not only in regards to the skeletal system, but quite possibly in the morphogenesis and pattern formation of other tissues and organs as well. Therefore, BMPs have the potential as a therapeutic utility in orthopedic and dento-alveolar reconstruction.

Bone induction using demineralized bone in the rabbit femur: a long-term study

While traditional bone grafting is the standard for replacement of segmental bony defects, alternative options (avoiding morbidity of autologous grafts) are attractive and continue to be sought. This study attempted to determine whether demineralized bone powder could be used reliably to replace a significant bony deficit at a weight-bearing site. The long-term functional characteristics of this induced bone were analyzed to determine whether it maintained its strength and shape and reacted normally to physiologic stress over an extended period of time (12 months). In 55 New Zealand White rabbits, a 1-cm length of femur was removed (approximately 20 percent of the total length of the rabbit femur). The femur was then reconstructed with a titanium mandibular plate, leaving the gap intact. In 38 of the animals, this gap was filled with demineralized bone powder in an attempt to induce bone to form across the defect. In group 1 (n = 23), the mandibular plate remained in place for the duration of the study (12 months). In group 2 (n = 15), the plate was removed 8 weeks after placement of the demineralized bone powder, and the animals were followed for an additional 12 months. In group 3 (n = 10), nothing was placed within the bony gap. In group 4 (n = 7), the gap was repaired with autologous bone graft. All the animals that received demineralized bone powder completely filled the osteotomy gap with new bone within 6 to 8 weeks after implantation. None of control group 3 formed bone across the gap (p < 0.001). Eighty-six percent of control group 4 (autologous bone graft) successfully formed bone across the osteotomy gap. In addition, 90 percent of control group 3 had hardware failure within 8 weeks after surgery compared with 0 percent (0 of 38) of the group that received demineralized bone powder (p < 0.001). In group 1, analysis after 12 months revealed that the bone formed ultimately became thin and easily fractured, most likely because of shielding from stress loading by the mandibular plate. In contrast, in group 2 (in which the plate was removed after 8 weeks), the bone remodeled and hypertrophied in response to the physiologic stress of weight bearing and at the end of the 12-month period was essentially identical to normal femur. In certain circumstances, reconstruction of bony defects using bone-induction techniques may be as good as autologous bone grafting, with the advantage of limiting the donor-site morbidity for the patient.

Bone morphogenetic proteins: an unconventional approach to isolation of first mammalian morphogens

It is conventional to identify morphogens from fly and frog embryos during morphogenesis using gene-screens, subtractive hybridizations, differential displays and expression cloning. This information is then extended to mice and men. The bone morphogenetic proteins (BMPs) are a family of pleiotropic morphogens/cytokines isolated and cloned from the demineralized extracellular matrix of adult bone. Thus, BMPs were isolated from mammalian bone by an unconventional approach. BMPs initiate the sequential developmental cascade of bone morphogenesis in ectopic sites. The pleiotropic effects of BMPs on chemotaxis, mitosis and differentiation are based on concentration-dependent thresholds. Recent work has demonstrated the critical role of BMPs in pattern formation in amphibian and chick limb development. Targeted disruption of gene function by homologous recombination has demonstrated the actions of BMPs beyond bone in such disparate tissues as kidney, eye, testis, teeth, skin and heart. The successful isolation of first mammalian morphogens has laid the foundation for the elucidation of molecular signalling during morphogenesis in bones and beyond.

[Osteoinduction and -reparation]

Traumata, diseases, developmental deformities, and tumor resections frequently cause bone defects and atrophies. In general, three different mechanisms exist by which bone restoration can be achieved: (1) osteogenesis initiated by vital, osteoblastic cells of autografts; (2) osteoconduction (or creeping substitution); and (3) osteoinduction. The latter mechanism means the differentiation of pluripotent, mesenchymal-type cells (located in a recipient bed with strong regenerative capacity) into cartilage- and bone-forming progenitor cells under the influence of inductive bone morphogenetic proteins (BMPs). Some BMPs are physiologically included in low concentrations as organic components in bone tissue. They can diffuse from demineralized bone implants into the recipient bed and induce a differentiation into new bone tissue. Nine different BMPs have been isolated, characterized, and cloned. Some of these possess inductive properties and can initiate new bone formation in muscle tissue or in bone defects. In the future recombinant BMPs will be available in unlimited quantities. This will lead to completely new therapeutic concepts in reconstructive bone surgery.

The effect of insulin-like growth factor 1 on craniofacial bone healing

Human insulin-like growth factor 1, a known regulator of bone formation, was investigated for its possible effect on membranous bone formation in a rat model. Full-thickness bone defects (10 x 10 x 1 mm) were created in the rat calvarium, and insulin-like growth factor 1 was administered by an osmotic minipump directly into the defect enclosed by the periosteum and dura mater. The dose of insulin-like growth factor 1 was 100 micrograms every 2 weeks. The defects were studied radiographically, macroscopically, and microscopically at 3, 6, 9, and 12 weeks. The group treated with insulin-like growth factor 1 showed qualitative and quantitative differences when compared with the control group. The amount of new bone formation in the group treated with insulin-like growth factor 1 was significantly larger than that of the control group. In the insulin-like growth factor 1 group, the location of new bone formation occurred in the center and at the margin of the bone defect. In the control group, bone was formed only around the margin of the bone defect. This study suggests that insulin-like growth factor 1 improved membranous bone healing in vivo and that insulin-like growth factor 1 makes mesenchymal precursor cells of bone differentiate directly into bone-forming cells.

Basic fibroblast growth factor for stimulation of bone formation in osteoinductive or conductive implants

Basic Fibroblast Growth Factor (bFGF) is one of the endogenous factors found in bone matrix. bFGF is a mitogen for many cell types, including osteoblasts and chondrocytes. It can stimulate angiogenesis and osteoblast gene expression. The purpose of this study was to investigate whether exogenous bFGF can stimulate the formation of bone in bone grafts and in a bone graft substitute. In a model using demineralized bone matrix implants for bone induction, a dose of 15 ng bFGF per implant increased the number of chondrocytes and the amount of bone, whereas 1900 ng greatly inhibited cartilage and bone formation. These results are consistent with previous studies with this model, showing that a lower dose of bFGF increased bone calcium content and a higher dose reduced it. Thus, exogenous bFGF can stimulate proliferation during early phases of bone induction. A new device, the bone conduction chamber, was developed for the application of bFGF to bone conductive materials. This model made it possible to demonstrate a difference between the conductive properties of bone grafts and porous hydroxyapatite. bFGF increased bone ingrowth into bone graft inside the chamber and showed a biphasic dose-response curve, so that 8-200 ng per implant (0.4-10 ng/mm3) increased bone ingrowth, but higher or lower doses had no effect. The same doses had the same effects in porous hydroxyapatite. In both bone grafts and porous hydroxyapatite, the highest dose still caused an increase in ingrowth of fibrous tissue. The effect on bone ingrowth was first detected after 6 weeks, regardless if administration of bFGF started at implantation or 2 weeks later, using an implanted minipump. Hyaluronate gel was effective as a slow-release carrier for bFGF. In conclusion, bFGF stimulates bone formation in bone implants, depending on dose and method for administration.

Periodontal regeneration: potential role of bone morphogenetic proteins

Initiation of osteogenesis and cementogenesis is a problem central to periodontal regeneration. A major advance in the understanding of bone formation has been the identification of an entirely new family of protein initiators, the bone morphogenetic proteins, that regulate cartilage and bone differentiation in vivo. The purification, genetic cloning and expression of recombinant human bone morphogenetic proteins (BMPs) have laid the foundation for the cellular and molecular dissection of bone development and regeneration. The striking evolutionary conservation of the BMP genes indicates that they are critical in the normal development and function of animals. In addition to postfetal osteogenesis, the BMPs may play multiple roles in embryonic development and organogenesis, including skeletogenesis and the development of craniofacial and dental tissues. The availability of recombinant human BMPs provides several challenges and opportunities to gain insights into the mechanisms regulating the regeneration of bone and cementum for optimal outcome in the periodontal patient.

Reconstruction of the growing cricoid with a composite graft of demineralized bovine bone and autogenous perichondrium; a comparative study in rabbits

In growing rabbits, the feasibility of a new type of composite graft for the reconstruction of defects in the cricoid ring is studied. This graft consists of Demineralized Bovine Bone matrix (DBBM) enfolded in a perichondrial flap. The cartilage formed in the DBBM by cells, derived from the perichondrium, is demonstrated to provide a valuable substitute for resected parts of the cricoid. A specific feature of this reconstruction is that it allows further growth and does not result in a secondary stenosis during later development.

Growth and morphogenetic factors in bone induction: role of osteogenin and related bone morphogenetic proteins in craniofacial and periodontal bone repair

Bone has considerable potential for repair as illustrated by the phenomenon of fracture healing. Repair and regeneration of bone recapitulate the sequential stages of development. It is well known that demineralized bone matrix has the potential to induce new bone formation locally at a heterotopic site of implantation. The sequential development of bone is reminiscent of endochondral bone differentiation during bone development. The collagenous matrix-induced bone formation is a prototype model for matrix-cell interactions in vivo. The developmental cascade includes migration of progenitor cells by chemotaxis, attachment of cells through fibronectin, proliferation of mesenchymal cells, and differentiation of bone. The bone inductive protein, osteogenin, was isolated by heparin affinity chromatography. Osteogenin initiates new bone formation and is promoted by other growth factors. Recently, the genes for osteogenin and related bone morphogenetic proteins were cloned and expressed. Recombinant osteogenin is osteogenic in vivo. The future prospects for bone induction are bright, and this is an exciting frontier with applications in oral and orthopaedic surgery.

Transforming growth factor beta type 1 binds to collagen IV of basement membrane matrix: implications for development

The interaction of transforming growth factor beta (TGF beta) with extracellular matrix macromolecules was examined by using radiolabeled TGF beta and various matrix macromolecules immobilized on nitrocellulose. TGF beta bound to collagen IV with greater affinity than to other extracellular matrix macromolecules tested. Neither laminin nor fibronectin, both of which bind type IV collagen, interfered with the binding of TGF beta to type IV collagen. TGF beta 2 competed effectively with TGF beta 1 for binding to type IV collagen. The biological effect of TGF beta was tested by an assay based on inhibition of proliferation of an osteoblast cell line, MC3T3-E1. The results demonstrated that the effect of TGF beta 1 was sustained when cells were grown on type IV collagen compared to cells grown on laminin, collagen type I, and plastic. These results demonstrate that extracellular matrix components may function as an affinity matrix for binding and immobilizing soluble growth and differentiation factors. In view of the demonstrated role of basement membranes in development the present results imply an important function for transforming growth factor beta bound to collagen IV in local regulation of cell proliferation and differentiation.

Osteogenin inhibits proliferation and stimulates differentiation in mouse osteoblast-like cells (MC3T3-E1)

Osteogenin, a novel bone differentiation factor, was recently purified and characterized. We examined its effect on the proliferation and differentiation of MC3T3-E1 osteoblast-like cells. Cell proliferation was inhibited the first 48 h after addition of osteogenin, and this effect was independent of serum. Osteogenin did not influence the cell morphology. Alkaline phosphatase promptly increased in a dose and time-dependent manner and appeared to be specific. Treatment with TGF-beta 1 resulted in inhibition of alkaline phosphatase activity, and was reversed by osteogenin within 48 h. Cell cultures treated with osteogenin for 72 h after confluence became responsive to parathyroid hormone. Synthesis of collagenous proteins was stimulated by osteogenin. The present results demonstrate a significant influence of osteogenin on the differentiation of osteogenic phenotype in MC3T3-E1 cells in vitro.

The role of cells versus matrix in bone induction

Earlier observations indicated that epithelial cells of urinary bladder, and transformed epithelial cells from human amnion (FL), epidermal carcinoma (HeLa), etc. can induce ectopic endochondral bone formation when implanted into the skeletal muscle of immunosuppressed or autologous animals. Such epithelial cells are associated with little matrix. Bone-inducing activity was also demonstrated in cultured osteosarcoma cells of murine and human origin or extracts thereof, and it is notable that these bone-inducing osteosarcoma cells grow in vitro with little matrix production. Finally, electron microscopy of in vitro cartilage induction showed that decalcified rodent bone that had been extensively extracted to remove cells still contained devitalized cells and cell fragments some of which made contact with inducible, cartilage-forming mesenchymal cells that had migrated in from cocultured muscle. Suggestions: These observations suggest that: 1) the bone-inducing agent(s) of both epithelial and mesenchymal cells may reside mostly in cells rather than matrix. Thus it may be premature to assume that bone "matrix" is the major source of bone-inducing agent in decalcified bone until the osteoinductive activity of residual bone cells has been assessed; and 2) that the osteoinductive agent, whether residing in epithelial cells or bone cells, may be the same or a similar factor operating through the same mechanism.

Influence of whole body irradiation and local shielding on matrix-induced endochondral bone differentiation

Subcutaneous implantation of demineralized bone matrix into allogeneic rats induces endochondral bone formation. We have investigated the effects of irradiation on the sequelae of the interaction of collagenous matrix and mesenchymal cells and on cartilage and bone differentiation. Rats were irradiated in a vertical direction with a midline dose of 850 rad. Radiation entered the rats ventrally while a small area of the upper thorax was locally shielded. After irradiation, bone matrix was implanted in shielded and nonshielded sites, and the implants were studied at various stages. On day 3, [3H]thymidine incorporation, an index of cell proliferation, was inhibited by 70% in the nonshielded sites compared to nonirradiated control rats. The degree of inhibition (35%) was less pronounced in shielded sites. Furthermore, there was recovery of cell proliferation in the shielded sites as opposed to the nonshielded contralateral site. A similar pattern was observed on day 7 as assessed by 35SO4 incorporation into proteoglycans during chondrogenesis. Bone formation and mineralization were quantified on day 11 by alkaline phosphatase activity and 45Ca incorporation. In nonshielded sites, there was a 73% inhibition of alkaline phosphatase activity. In conclusion, radiation impaired progenitor cell proliferation which resulted in decreased cartilage and bone differentiation. These findings imply that local mesenchymal cells proliferate and differentiate into bone in response to implanted collagenous matrix.

In vivo analysis of the half-life of the osteoinductive potential of demineralized bone matrix using diffusion chambers

Subcutaneous implantation of demineralized bone matrix (DBM) from rat initiates a sequence of developmental events that results in endochondral bone formation. This investigation examined the modification of the osteoinductive potential of DBM during the initial stages of this developmental cascade. Diffusion chambers (DC), constructed with filters of known pore size, permitting or excluding cells from entering the chambers, and containing DBM were subcutaneously implanted into Long-Evans male rats for specific time periods (1-7 days). DC were recovered and the osteoinductive potential of the matrix from these chambers was then tested by subcutaneous implantation and assaying the resulting day 11 plaque tissue enzymatically for alkaline phosphatase activity, and histologically for evidence of chondrogenesis and osteogenesis. The possible modification of DBM by local systemic factors (enzymatic degradation) or contact by polymorphonuclear leukocytes (PMNs) was also investigated. We have concluded from this study that the osteoinductive potential of DBM has a half-life of 5-7 days following implantation and although the enzymes collagenase, elastase, and trypsin abolished this activity, pepsin significantly enhanced it. Culture of PMNs with matrix prior to its implantation appeared to have little effect. Furthermore, during the initial stages of matrix-induced endochondral bone formation, DBM serves as both the instructive inducer and permissive substratum required in this process.

Stimulation of the expression of osteogenic and chondrogenic phenotypes in vitro by osteogenin

Osteogenin was recently purified and the amino acid sequences of tryptic peptides were determined. Osteogenin in conjunction with insoluble collagenous bone matrix induces cartilage and bone formation in vivo. To understand the mechanism of action of osteogenin, we examined its influence on periosteal cells, osteoblasts, fibroblasts, chondrocytes, and bone marrow stromal cells in vitro. Osteogenin stimulated alkaline phosphatase activity and collagen synthesis in periosteal cells. The cAMP response to parathyroid hormone in periosteal cells was increased by osteogenin. In primary cultures of calvarial osteoblasts, osteogenin stimulated alkaline phosphatase activity, the cAMP response to parathyroid hormone, and the synthesis of collagenous and noncollagenous proteins; however, cell proliferation was not affected. Osteogenin increased the production of sulfated proteoglycans in fetal rat chondroblasts and in rabbit articular chondrocytes. The present experiments demonstrate the significant influence of osteogenin in the stimulation of osteogenic and chondrogenic phenotypes in vitro.

Initiation of bone development by osteogenin and promotion by growth factors

The cellular and molecular basis of bone development and its regulation by differentiation and growth factors is an exciting area of current research. This article briefly reviews the historical progress in the isolation of osteogenin, a novel bone differentiation factor, and its modulation by well known growth factors. Endochondral bone development is a multistep sequential cascade and the process must be operationally dissected. It has been accomplished with the demineralized bone matrix-induced bone formation model. The reproducible development of cartilage and bone in an extraskeletal site permits the study of the initiation of the first cycle of endochondral bone formation and mineralization. Recent progress in the isolation of osteogenin, a specific bone differentiation factor, by heparin affinity chromatography permits the further investigation of the commitment and clonal expansion of the putative osteoprogenitor stem cells. Once initiated, bone formation is promoted by growth factors such as platelet derived growth factor, fibroblast growth factor, insulin like growth factor, transforming growth factor beta and a plethora of non specific cytokines. Finally bone development is further modulated by systemic hormones and nutrition and a host of physical signals including electrical, gravitational and mechanical forces.

Dose-dependence of and threshold for optimal bone induction by collagenous bone matrix and osteogenin-enriched fraction

Subcutaneous implantation of demineralized collagenous bone matrix results in local induction of new bone formation. The dose dependence of bone induction was investigated using different amounts of rat demineralized bone matrix (DBM) and also osteogenin-enriched fraction with and without inactive collagenous bone matrix (ICBM). There is a threshold for bone induction; at least 10 mg of DBM is required. There is a dose dependent increase in bone induction between 10 to 25 mg. Exogenous type I collagen was found to be stimulatory to bone induction when suboptimal doses of DBM are employed. The activity of osteogenin-enriched dissociative extract was enhanced by addition of ICBM. These results imply that optimal bone induction requires the combined action of soluble osteogenin-enriched fraction and insoluble collagenous substratum.

Platelet-derived growth factor enhances demineralized bone matrix-induced cartilage and bone formation

Subcutaneous implantation of demineralized bone matrix induces the local formation of cartilage and bone. In this study we have investigated the influence of adding various growth factors to the implant. Cartilage formation was monitored by measuring collagen II mRNA levels, and bone formation in the implant was assessed from alkaline phosphatase activity and calcium content. Supplements of the platelet-derived growth factor to implants in older rats increased and production of mRNA for collagen II, alkaline phosphatase activity, and the calcium content of the implant, whereas the other growth factors tested were without effect. The data suggest that under some conditions bone induction is submaximal and can be increased by local supplement of platelet-derived growth factor (PDGF). The present observations may have important therapeutic implications in the treatment of nonunions of fractures and impaired bone formation in the aged.

Changes in the extracellular matrix and glycosaminoglycan synthesis during the initiation of regeneration in adult newt forelimbs

The extracellular matrix (ECM) of the distal tissues in a newt limb stump is completely reorganized in the 2-3-week period following amputation. In view of numerous in vitro studies showing that extracellular material influences cellular migration and proliferation, it is likely that the changes in the limb's ECM are important activities in the process leading to regeneration of such limbs. Using biochemical, autoradiographic, and histochemical techniques we studied temporal and spatial differences in the synthesis of glycosaminoglycans (GAGs) during the early, nerve-dependent phase of limb regeneration. Hyaluronic acid synthesis began with the onset of tissue dedifferentiation, became maximal within 1 weeks, and continued throughout the period of active cell proliferation. Chondroitin sulfate synthesis began somewhat later, increased steadily, and reached very high levels during chondrogenesis. During the first 10 days after amputation, distributions of sulfated and nonsulfated GAGs were both uniform throughout dedifferentiating tissues, except for a heavier localization near the bone. Since nerves are necessary to promote the regenerative process, we examined the neural influence on synthesis and accumulation of extracellular GAGs. Denervation decreased GAG production in all parts of the limb stump by approximately 50%. Newt dorsal root ganglia and brain-derived fibroblast growth factor each produced twofold stimulation of GAG synthesis in cultured 7-day regenerates. The latter effect was primarily on synthesis of hyaluronic acid. The results indicate that the trophic action of nerves on amphibian limb regeneration includes a positive influence on synthesis and extracellular accumulation of GAGs. Since the ECM exerts a major influence on cellular proliferation and migration, the effect of nerves on GAG metabolism may have considerable importance for growth and development of the early regenerate.

Induction of chondrogenesis in muscle, skin, bone marrow, and periodontal ligament by demineralized dentin and bone matrix in vivo and in vitro

Induction of chondrogenesis in vivo by rolls of demineralized dentin implanted in muscle, subcutaneous connective tissue of skin, medullary cavity of femur, and periodontal ligament of rat was investigated. Specimens were examined at various times up to 21 days after implantation, using light microscopy and morphometric analysis. Induction of cartilage occurred most quickly in muscle, followed by subcutaneous connective tissue of skin and medullary cavity of femur, and most slowly in periodontal ligament. Significantly more cartilage was found in muscle than in subcutaneous connective tissue of skin and medullary cavity of femur at the times examined, and least of all in periodontal ligament. Outgrowth of cells from rat muscle, dermis and subcutaneous tissue, bone marrow and periodontal ligament cultured in vitro on demineralized bone matrix for up to 35 days produced similar results.

Induction of endochondral bone by demineralized bone matrix from diabetic rats

In this investigation we examined the osteoinductive potential of demineralized bone matrix derived from chronically diabetic (streptozotocin-induced) rats. Long-Evans rats (28-31 days) were made diabetic with a single injection of streptozotocin (65 mg/kg) and provided food and water ad lib for 2 months. Diaphyseal shafts of femurs and tibias removed from the diabetic rats and their sibling controls were dehydrated, pulverized, sieved to 74-420 micron particles, and demineralized. Matrix was then bioassayed for its ability to induce endochondral bone on day 11 following subcutaneous implantation over the thorax of Long-Evans rats. The resulting plaques of tissue were subjected to histological analysis, determination of alkaline phosphatase activity, and calcium content. Bone matrix derived from diabetic animals proved to be a significantly better inducer of endochondral bone than did control matrix.

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.

Colony forming cell-fibroblast development in extracellular matrix-induced bone and bone marrow formation in rat

The development of murine endochondral bone and bone marrow as a result of demineralized bone matrix implantation is preceded by the accumulation and proliferation of colony forming cell fibroblasts. These cells appear first at 24 hours post-implantation, after which they increase in 2 swells, achieving peak number between days 10-14. The observed differences in developmental kinetics of colony forming cell fibroblasts in culture were not found to be related to qualitative differences in the synthesis of collagens, fibronectin, laminin or proteoglycans. The colony forming cell fibroblasts were shown to be radiosensitive, with the Do = 339 +/- 63.

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.

Injury to nerves and the initiation of amphibian limb regeneration

The possibility has been investigated that nerves, which promote mitotic activity during the growth phase of limb regeneration, may also release factors upon injury to stimulate the cellular events during the initiation of regeneration. These events have been compared in control, innervated limb stumps and in limbs denervated for various periods before amputation. Wound closure occurred in an essentially normal manner in limbs denervated at the time of amputation but frequently occurred at reduced rates or not at all in limb stumps denervated 5 days before amputation. Tissue loss and various degrees of morphological regression were seen in many of the predenervated limb stumps, including all of those denervated for 6 days or more before amputation. Evidence is presented which suggests that regression may result from a combination of the denervated state and disturbance to the limb's vascular system. Limbs predenervated 2-10 days before amputation were fixed 7 days after amputation and examined histologically. All limb stumps, including those involved in regression, showed tissue dissociation and cellular dedifferentiation. Autoradiography revealed that the dedifferentiation involved DNA synthesis in both denervated and innervated limbs. Seven days after amputation, DNA-labeling indices in limb stumps predenervated 2 or 4 days were similar to those of control limbs, but labeling indices were significantly reduced in limbs predenervated 6 or more days. The results are assessed in light of the state of nerve degeneration in the limbs at the time of amputation and are discussed in terms of what is known regarding nerve-derived growth-promoting substances.

Bone-derived factors active on bone cells

Effects of systemic calcium regulating hormones have been studied extensively, yet mechanisms of bone volume regulation at the local level are poorly understood. Our laboratory has reported evidence for two locally mediated processes of bone volume regulation which function independently of systemic control: (1) coupling of bone formation and resorption and (2) repletion of resorbed bone. These local regulatory mechanisms have been shown to occur in vivo and in vitro. We have reported that embryonic chick tibiae in culture, stimulated to resorb, release a factor in the serum-free culture medium that stimulates bone cell proliferation and bone matrix formation in vitro. We have postulated that this factor could be involved in the coupling mechanism. Subsequently, a similar factor which stimulates bone cell proliferation, collagen synthesis and bone formation in vitro was extracted from embryonic and adult bones. The factor partially purified from human bone, designated as human skeletal growth factor, has molecular weight, heat sensitivity and biological activity similar to the factor found in bone conditioned medium. Many other biologically active factors have also been extracted from bone cells or demineralized bone by different laboratories. Their actions on bone cells range from chemotactic to mitogenic. These recently discovered bone factors emphasize that there is important regulation of bone metabolism at the local level.

Fibronectin mediated human gingival fibroblasts attachment to bone

Experiments were undertaken to examine the effects of acid and fibronectin treatments on the human gingival fibroblast attachment to bone in vitro. The binding of [125I]fibronectin to bone powders was dependent on concentration of fibronectin and incubation time. The optimum pH of [125I]fibronectin attachment to bone powders was 6.0 using phosphate buffer. Acid treatment on bone powders in low concentration such as 10 mM of citric acid enhanced [125I]fibronectin binding. The attachment of [3H]thymidine labelled human gingival fibroblasts to bone was enhanced 1.5, 2.0 and 2.5-fold by citric acid, fibronectin and citric acid + fibronectin treatment, respectively. Scanning electron microscopic observations confirm that citric acid and/or fibronectin treatment enhanced the cell number and rapidity of fibroblast attachment to bone surfaces.

Changes in tissue concentration of prostaglandins during endochondral bone differentiation

Prostaglandins are known to be involved in bone metabolism as evidenced by the ability of PGE2 to induce bone resorption. It was, therefore, of interest to determine if there was an association of specific prostaglandin metabolites with the various stages of developing bone by utilizing the matrix-induced endochondral bone formation system. During mesenchymal cell proliferation a peak of endogenous thromboxane B2 was detected. In the subsequent stages of chondrogenesis and chondrolysis PGF2 alpha was in high concentration, whereas during bone formation PGE2, 6-Keto-PGF1 alpha and thromboxane B2 were elevated. These changes in the peak levels of the various prostaglandin metabolites may reflect differences in the cell populations and function associated with various stages of endochondral bone formation.

Effect of tanning agent on tissue reaction to tissue implanted collagen sponge

Pure collagen, isolated from bovine skin, was reconstituted into the form of a sponge in the presence of either glutaraldehyde (GTA) or hexamethylene diisocyanate (DIC). Extensively washed sponges were implanted subcutaneously in rats and harvested 5 and 17 days later. Histology showed that at 5 days, the GTA-crosslinked sponge induced more cellular reaction at the outer layer of the sponge than the DIC-tanned sponge. After 17 days, the cellular infiltration of the GTA-tanned sponge remained at the periphery of the implant while the DIC-tanned sponge was completely infiltrated by inflammatory cells, including fibroblasts. Quantitative morphometry and determination of cellular DNA in sponges harvested at 17 days support the morphological finding. We conclude that GTA-tanned sponges are cytotoxic as evidenced by more pronounced tissue reaction soon after tissue implantation, and no cellular infiltration at later stages into the implant. Hexamethylene diisocyanate seems to be a more adequate tanning agent for sponges designed as a tissue substitute.

Structural analysis of three subunits of laminin from teratocarcinoma-derived parietal endoderm cells

The structure of the three polypeptide chains of the laminin subunits and the number of glycosylation sites in each polypeptide chain were determined using peptide mapping by high-performance liquid chromatography. Analysis of the [35S]methionine-labeled underglycosylated laminin isolated from tunicamycin (TM)-treated cells revealed that the three subunits of laminin contain unique polypeptide chains. Analysis of [3H]glucosamine-labeled glycosylated laminin subunits showed that they are sialylated and that each subunit has 11-14 glycosylation sites.

Bone cell differentiation and growth factors

Bone morphogenetic protein and bone-derived growth factors are biochemical tools for research on induced cell differentiation and local mechanisms controlling cell proliferation. Bone morphogenetic protein irreversibly induces differentiation of perivascular mesenchymal-type cells into osteoprogenitor cells. Bone-derived growth factors are secreted by and for osteoprogenitor cells and stimulate DNA synthesis. Bone generation and regeneration are attributable to the co-efficiency of bone morphogenetic protein and bone-derived growth factors.

Considerations on manufacturing principles of a synthetic burn dressing: a review

This review presents various considerations on the construction of a synthetic burn dressing, based mainly on collagen protein. Membranous wound covers are compared with sponge-felt types, monocomponental with composite. The importance of collagen crosslinking agent and the nonextractibility of any component from the dressing material are discussed. According to the type of the burn the dressing should be used dry or wet, plain or medicated, and changed often to reduce substantially the presence of necrotic tissue, inflammatory cell of the granulation tissue, and bacterial contamination.