[Comparison of the osteogenic activity of bone morphogenetic protein (BMP) mutants]. / Vergleich der osteogenen Potenz gentechnisch modifizierter BMP.

BACKGROUND: Modification of the heparin binding site by alteration of the amino acid sequence of bone morphogenetic protein-2 (BMP-2) results in a change in the local retention time. The purpose of this study was to compare the osteogenic activity of T3 and T4, two mutants with increased binding capacity to heparin, and B2GDF-5 a mutant resulting from the fusion of the n-terminal amino acid sequence of BMP-2 and the c-terminal sequence of GDF-5 with wild-type BMP-2 in vivo. MATERIAL AND METHODS: The proteins were coupled to an equine-derived collagen carrier and implanted in standardized critical size calvarial defects in adult rats. After 28 days, bone formation was evaluated radiographically and the new bone was characterized histologically. RESULTS: Proteins T3 and T4 showed a higher osteogenic activity than BMP-2. Less new bone formation was observed with GDF-5 and B2GDF-5 than with-type BMP-2. No difference in bone formation was observed between GDF-5 and B2GDF-5. CONCLUSION: Increased heparin binding capacity enhances osteogenic activity of BMP-2 in vivo. This might be due to a longer retention period in the tissue and thus better bioavailability. Replacement of the N-terminal amino acid sequence of GDF-5 by the corresponding sequence of BMP-2 did not result in an increased osteogenic activity as heparin binding capacity is not the main reason for the bioavailability of GDF-5.

[Genioplasty alone and in combination. Long-term results with emphasis on sensitivity and photoanalysis]. / Kinnosteotomie isoliert und in Kombination. Langzeitergebnisse unter besonderer Berücksichtigung der Sensibilität und der Fotoanalyse.

PURPOSE: Striving for beauty and expressiveness is a deeply rooted human attitude. The lower jaw-especially the mentum-plays an important role in the perception of the face as an instrument of communication. According to Grammer a distinctive lower jaw is an essential characteristic feature of male attractiveness. MATERIAL AND METHODS: During a period of 10 years 58 patients underwent genioplasty. A follow-up examination was performed in 49 patients (complete sensitivity evaluation: 33 patients, complete photoanalysis: 30 patients). To reduce radiation due to cephalometric radiography a simple photometric method for cephalometry was developed and applied. Particular attention was directed at sensitivity of the mental nerve after genioplasty. RESULTS: To the best of our knowledge, this is the first time that photos of the right profile were compared with those of the left side. Unexpectedly, intraindividual differences dependent on the facial side (right and left) could be found in the relationship of the lower to the upper face and in the proportion of the profile angle and the nasomental angle. After three-dimensional genioplasty these differences were reduced and facial asymmetry was improved. Comparing the right with the left side the average difference of the nasomental angle was reduced from 2.5 degrees to 0.6 degrees on average. The profile angle was changed by genioplasty from 19 degrees on average to 15 degrees ("ideally" 10 degrees , the so-called upright face). According to Schwarz the ideal height of the mentum (stomion-menton) should amount to 66% of the total lower face. Especially by combined dorsal and cranial positioning of the mentum a reduction from 85 to 68% was achieved. Postoperatively 24 of 33 patients (73%) showed disturbances of the mental nerve. After at least 1 year following the operation, normal sensitivity of the lower lip and chin of both sides was evaluated by almost all of these patients (19 of 24 = 79%). Especially all patients having had only a single genioplasty recovered totally from a neurosensory deficit. CONCLUSIONS: Genioplasty can be considered to be a reliable procedure to achieve harmony of the lower face.

[Mandibular reconstruction with autologous bone and osseoinductive implant in the Göttingen minipig]. / Unterkieferrekonstruktion mit autologem Knochen und einem induktiven Implantat beim Göttinger Minischwein.

BACKGROUND: Direct mandibular reconstruction with an autologous bone transplant was compared with an osteoinductive implant following an extensive continuity resection of the lower jaw in Göttinger mini-pigs. METHOD: In nine full-grown mini-pigs a one-sided continuity defect (5 cm) was created in the lower jaw. In four animals it was filled with a 50 x 25 x 15 mm(3) collagenous carrier enhanced by rhBMP-2 (400 micro g/cm(3) rhBMP-2). In two animals only the carrier was implanted as a control. Three animals received the resected autologous bone as a free transplant. Bone regeneration and consolidation of the defects was analyzed radiographically and histologically. RESULTS: Following implantation of the osteoinductive implant, complete osseous consolidation of the continuity defect in the lower jaw was observed in all animals. The defects were completely filled with a biomechanically stable bone which showed signs of functional adaptation. The replantation of the orthotopic autologous bone did not lead to functional stability quickly enough. In the periphery only an incomplete bony bridge was formed which was interrupted by large pseudarthrosis. No consolidation of the defects was found in the control group (carrier alone). CONCLUSION: Direct reconstruction of an extensive, biomechanically loaded defect with an osteoinductive implant proved to be the superior method. The osseous regeneration observed shows an immediate functional orientation. The necessity for extensive adaptive remodeling is thus minimized.

[Evaluation of the osteoinductive potential of genetically modified BMP-2 variants]. / Evaluation der osteoinduktiven Potenz von gentechnisch modifizierten BMP-2-Varianten.

BACKGROUND: The alteration of the N-terminal amino acid sequence of BMP-2 allows modification of heparin binding of the new protein. This leads to a change in the local retention time at the site of implantation. Mutants with increased (T3, T4) and with no binding (EHBMP-2) to heparin were assessed for their osteoinductivity in vivo and compared with the wild type BMP-2. METHODS: Cylindrical collagenous carriers (diameter = 5 mm, height = 10) were loaded with different concentrations (0.25-4 micro g) of the proteins. Following intramuscular implantation into the hind legs, the bone formation was measured in radiographic follow-ups. After 28 days the newly formed bone was characterized histologically. RESULTS: Elimination of the heparin binding leads to massive reduction in osteoinductivity. On the other hand, an increase in the heparin binding leads to enhancement in the osteoinductive properties, resulting in faster bone formation with a higher yield. CONCLUSION: It could be shown for the first time that modifications of BMP-2 by gene technology can lead to proteins with enhanced binding to components of the extracellular matrix. The resulting prolonged retention time at the implantation site results in an increased osteoinductivity compared with the wild type.

Influence of platelet-rich plasma (PRP) on osteogenic differentiation of rat bone marrow stromal cells. An in vitro study.

Recent clinical reports suggest that the application of an autologous blood plasma enriched with thrombocytes by centrifugal concentration (platelet-rich plasma: PRP) can enhance the formation of new bone. There are very fewin vitro or in vivo studies published on the efficiency of PRP. In this project a three dimensional cell culture system was used to compare PRP and rhBMP-2 in vitro. Marrow derived bone forming cells from Spraque-Dawley (SD) rats were seeded on porous collagenous carriers (d=5mm, h=3mm) at a density of 4 x 10(4) cells/carrier and exposed to different concentrations of PRP (platelet counts from 2.5 x 10(8)-1.6 x 10(7) platelets/culture), rhBMP-2 (300 ng) or plasma poor in thrombocytes (platelet-poor plasma, PPP). Cultures without additional supplements were used as controls. During a culture period of 21 days cell proliferation, alkaline phosphatase activity (ALP) and calcium content (days 18, 21) were measured in 3 day intervals.PRP showed a dose dependent stimulation of cell proliferation, while reducing ALP activity and calcium deposition in the culture. BMP-2 led to an opposite cell response and induced the highest ALP activity and mineral deposition. These data suggest that PRP inhibited osteogenic differentiation of marrow derived pre-osteoblasts in a dose dependent manner. PRP is not a substitute for BMP-2 in osteogenic induction.

[Effect of periosteum on induced bone formation by autolyzed, antigen-extracted, allogeneic bone. Determination of the extent of bone formation using quantitative computerized tomography]. / Einfluss des Periosts auf die induzierte Knochenneubildung durch autolysierten, antigenextrahierten, allogenen Knochen. Bestimmung des Ausmasses der Knochenneubildung mittels quantitativer Computertomographie.

Autolyzed, antigen-extracted, allogenic (AAA) bone is an osteoinductive preparation of completely demineralized bone matrix. It has been clinically applied for years. In an experimental study in rabbits, we evaluated the influence of cortical bone and periosteum on the amount of bone formation following augmentation with AAA bone. Two implants of standardized size were placed on the femoral bone of rabbits. A cell-excluding PTFE membrane was wrapped circularly around the femur as well as the anterior implant shielding the implant from the surrounding periosteum. The posterior implant was exposed directly to the periosteum while being shielded from the cortical bone by the membrane. Thus, two compartments were created selectively, preventing contact between the periosteum or cortical bone and the implants. For each compartment the area and volume of the induced new bone were evaluated by computerized radiograph analysis and quantitative CT (pQCT) scans. Implantation of AAA bone led to new bone formation in both compartments. Contact of the periosteum and the implant led to an almost four-fold increase in bone volume. Although bone formation showed interindividual variations, the difference of both compartments was highly significant using the Student's t-test for paired samples (P < 0.0001). The data show that periosteum is the primary source of new bone formation in augmentations with osteoinductive materials as it is rich in inducible progenitor cells and is well vascularized. In osseous augmentations with AAA bone, the periosteum should be preserved in order to achieve a close contact of the osteoinductive implant. Shielding from the periosteum, e.g., by cell-excluding membranes, leads to significantly less bone formation following implantation of AAA bone and should therefore be avoided.

[Effect of different factors on the bone forming properties of recombinant BMPs]. / Einfluss unterschiedlicher Faktoren auf die knochenbildenden Eigenschaften von rekombinanten BMPs.

The extent of BMP-induced new bone formation is mainly determined by the number of mesenchymal target cells in the recipient bed as well as by the biological half-life of the BMP molecules within the tissue. While the number of inducible cells is determined by the age and vascularization of the tissue, the retention time of the BMP molecules can be influenced. One possibility is the coupling of BMPs to suitable carriers, which significantly increases the osteoinductive effect. The reason for this is the physical binding of BMPs to the carrier material, which delays the resorption of the proteins. Other factors are the composition of the carrier materials, their structural stability, and possible dislocations of carrier particles. The local tissue concentration of BMPs can also be increased by an enhanced binding of the proteins to the extracellular matrix. A BMP-2 mutant (BMP-2xa) was produced by the specific modification of the amino acid sequence using recombinant technologies. BMP-2xa induces heterotopic bone formation at significantly lower concentrations than natural BMP-2. Furthermore, BMP-2xa-induced bone tissue possesses a higher bone density.

Radiation-induced impairment of bone healing can be overcome by recombinant human bone morphogenetic protein-2.

Radiotherapy of head and neck tumors very often results in impaired healing of craniomaxillofacial bones in the vicinity. Management of radionecrosis of bones after radiotherapy is an important clinical challenge. Bone morphogenetic proteins (BMPs) induce new bone differentiation. The aim of this study is to investigate the potential of BMPs in ameliorating radiation-induced impaired bone repair. Two 3-mm diameter defects were created in the calvaria of rats. The defects were treated with different doses of recombinant human (rh) BMP-2 using collagen type I as a carrier. Irradiation with a single dose of 1,200 rad was performed 2 or 7 days preoperatively. Unirradiated animals served as controls. New bone formation was assessed by quantitation of radiographs of the calvaria and histology on day 21 after surgery. Untreated, unirradiated defects showed a spontaneous osseous regeneration of 90 +/- 7% of the defect area within 21 days. Irradiation of the site (1,200 rad 2 days preoperatively) resulted in a profound decrease in the bone fill of the untreated defect (5 +/- 2%). Recombinant human BMP-2 in soluble collagen type I carrier delivered to the defect resulted in a significant increase of new bone formation (34 +/- 14%, P < 0.01 for 25 micrograms rhBMP-2; 77 +/- 19% for 35 micrograms rhBMP-2, P < 0.01). Type I collagen carrier alone resulted in only 7 +/- 2% healing. In conclusion, radiation-induced impairment of calvarial repair can be overcome by rhBMP-2. Thus, the concept of BMP-2-induced regeneration has potential applications in reconstructive craniomaxillofacial surgery after irradiation.