The role in cell binding of a beta-bend within the triple helical region in collagen alpha 1 (I) chain: structural and biological evidence for conformational tautomerism on fiber surface

Clinical evaluation of anorganic bovine-derived hydroxyapatite matrix/cell-binding peptide (P-15) in the treatment of human infrabony defects

The purpose of the present study was to compare the clinical outcomes of infrabony periodontal defects following treatment with an anorganic bovine-derived hydroxyapatite matrix/cell-binding peptide (ABM/P-15) flow to open flap debridement. Twenty-six patients, each displaying one infrabony defect with probing depth>or=6 mm and vertical radiographic bone loss>or=3 mm participated in the present study. Patients were allocated randomly to be treated with ABM/P-15 flow (test group) or open flap debridement (control group). At baseline and at 12 months after surgery, the following clinical parameters were recorded by a blinded examiner: plaque index, gingival index, probing depth (PD), clinical attachment level (CAL), and gingival recession. Both treatments resulted in significant improvements between baseline and 12 months, in terms of PD reduction and CAL gain (p<0.001). At 12 months following therapy, the test group showed a reduction in mean PD from 7.8+/-1.6 mm to 3.5+/-1.0 mm and a change in mean CAL from 8.5+/-2.1 mm to 4.6+/-1.2 mm, whereas in the control group the mean PD decreased from 7.5+/-0.8 mm to 4.9+/-0.7 mm and mean CAL from 8.2+/-1.2 mm to 6.4+/-1.4 mm. The test group demonstrated significantly greater PD reductions (p=0.002) and CAL gains (p=0.001) compared to the control group. In conclusion, treatment of infrabony periodontal defects with ABM/P-15 flow significantly improved clinical outcomes compared to open flap debridement.

A review of bone substitutes

The use of bone grafts in the repair of defects has a long history of success, primarily with the use of autologous bone. With increasing technologic advances, researchers have been able to broaden the spectrum of grafting materials to allografts, xenografts, and synthetic materials, which provide the surgeon and patient with options, each with unique advantages. It is with the knowledge of each material that the clinician can present and suggest the best material and tailor treatment plans to fit each individual. In this article, we present an overview of the principles of bone grafting, the types of graft materials available, and an outlook to what the future holds in this area of medicine and dentistry.

A mineralization-associated membrane protein plays a role in the biological functions of the peptide-coated bovine hydroxyapatite

BACKGROUND AND OBJECTIVE

Anorganic bovine mineral coated with a cell-binding peptide (P-15) is superior to anorganic bovine mineral alone in the treatment of periodontal osseous defects. However, the molecular interactions between P-15 and periodontal ligament fibroblasts remain unclear.

MATERIAL AND METHODS

We first compared the in vitro osteogenic activities between periodontal ligament fibroblasts cultured with anorganic bovine mineral alone and with the P-15/anorganic bovine mineral combination. We then harvested the periodontal ligament cell lysate, incubated it with various graft materials, and then washed it to remove unbound proteins. The bound proteins were eluted from graft materials and analyzed using electrophoresis, followed by mass spectrometry and then western blotting. Finally, a neutralizing antibody against one bound protein was added to the cell cultures to repeat the osteogenic assays to clarify its role in the in vitro effects of the P-15/anorganic bovine mineral combination.

RESULTS

Cells treated with P-15/anorganic bovine mineral were more viable and showed greater osteogenic activities than cells treated with anorganic bovine mineral alone and the no-graft control. Annexin II, a mineralization-associated protein, bound to P-15/anorganic bovine mineral significantly more than to anorganic bovine mineral alone. The addition of neutralizing antibody for annexin II decreased the osteogenic activities of the P-15/anorganic bovine mineral combination.

CONCLUSION

Annexin II of periodontal ligament fibroblasts interacted with the peptide of P-15, and was partially responsible for better in vitro osteogenesis in the P-15 graft.

An Integrin-Specific Collagen-Mimetic Peptide Approach for Optimizing Hep3B Liver Cell Adhesion, Proliferation, and Cellular Functions

This study focused on mimicking collagen structurally and biologically using various peptide sequences toward realizing an artificial collagen-like biomaterial. Collagen-mimetic peptides (CMPs) incorporating integrin-specific glycine-phenylalanine-hydroxyproline-glycine-glutamate-arginine (GFOGER) sequence from residues 502 to 507 of collagen alpha(1)(I) were used as a bioadhesive matrix and grafted onto poly(3-hydroxybutyrate-co3-hydroxyvalerate) microspheres to optimize cell adhesion, proliferation, and functions. Cell recognition of these biomolecules appeared to be conformation dependent, with the CMP1 of higher triple helix stability being preferred. Absence of the GFOGER hexapeptide in the CMP1' and CMP2' caused an adverse effect on the level of cell adhesion (<10%). The GFOGER-containing triple-helical CMPs effectively inhibited cell adhesion to collagen in a competition assay. The cell-adhesion activity of the CMP1 was approximately 50% of that of collagen. The cell spreading on the CMP1 was comparable with that observed on collagen. The presence of the CMP1 promoted cell attachment and spreading on the microspheres and extensive cell proliferation and bridging. Slower cell proliferation was observed on the blank microspheres. Live-dead assay showed that most cells are viable after 10-day culture. The presence of CMP1 on the microspheres maintained the albumin secretion and P-450 activity levels of the liver cells for up to 14 days. Our results established the potential of CMP1 to create a collagen-like microenvironment for optimizing cellular responses for liver tissue engineering.

Differences in osteoblast miRNA induced by cell binding domain of collagen and silicate-based synthetic bone

PerioGlas (PG) is an silicate-based (i.e. anorganic) material used for grafting periodontal osseous defects since the ninety whereas P-15 is an analog of the cell binding domain of collagen (i.e. organic material) that is successfully used in clinical trial to promote bone formation. However, how PG (i.e anorganic material) and P-15 (i.e. collagen) differentially alter osteoblast activity to promote bone formation is unknown. We therefore attempted to get more insight by using microRNA microarray techniques to investigate the translation process in osteoblasts differentially exposed to PG and P-15. We identified 3 up-regulated miRNA (i.e. mir-30b, mir-26a, mir-92) and 8 down-regulated miRNA (i.e. mir-337, mir-377, mir-25, mir-200b, mir-129, mir-373, mir-133b, mir-489). The data reported are, to our knowledge, the first study on translation regulation in osteoblatsts differentially exposed to cell binding domain of collagen and to silicate-based material. Both enhance the translation of several miRNA belonging to osteogenetic genes, but P-15 acts preferentially on homeobox genes.

Biomimetic scaffolds for tissue engineering

A major goal of tissue engineering is to generate living cellular constructs with 3-D, tissue-like organization of cells and matrices. The generation of mechanical forces by the cellular cytoskeleton plays a critical role in the organization of matrix and of cellular colonies. The anchorage of the cytoskeleton to a substrate is essential for cellular tractional processes. We show that placing cells in scaffolds which contain a collagen-related synthetic peptide P-15 allows them to generate highly organized 3-D colonies and matrices. These observations suggest that P-15 may replicate cells' physiological collagen anchorage.

Augmentation of osseous phenotypes in vivo with a synthetic peptide

The synthetic peptide B2A2-K-NS augmented the in vitro expression of osseous phenotypes when cells were stimulated with BMP-2, an osteoinductive growth factor. B2A2-K-NS significantly enhanced the effects of BMP-2-induced alkaline phosphatase activity and mineralization. In the absence of BMP-2, B2A2-K-NS did not have an effect on these endpoints. Based on these observations, in vivo studies were conducted to evaluate if B2A2-K-NS could augment osseous phenotypes in an osteoinductive environment in which BMP-2 should be present. In one study, human demineralized bone matrix (DBM) was used to generate an osteoinductive environment and the effects of B2A2-K-NS on ectopic mineralization of subcutaneous implants evaluated. In the second study, a noncritical sized defect in rabbit ulnas with inherent reparative capacity was used as the osteoinductive environment and was treated with or without B2A2-K-NS. In the DBM studies, B2A2-K-NS augmented mineralization as determined using a combination of radiographic analysis and von Kossa staining at 4 weeks postimplant. In the rabbit ulna model, B2A2-K-NS significantly increased the radiographic bone density in the defects compared to carrier-only or no-treatment controls after 6 weeks. Histological staining confirmed that B2A2-K-NS generated a pronounced bone repair response. The results are consistent with the hypothesis that B2A2-K-NS augments osseous phenotypes in an osteoinductive environment, and suggests that B2A2-K-NS may have clinical utility.

Osteopromotion with synthetic oligopeptide-coated bovine bone mineral in vivo

BACKGROUND

Recombinant human bone morphogenetic protein (rhBMP)-2 has been shown to stimulate significant regeneration of alveolar bone and cementum in periodontal defects clinically. The aim of this study was to evaluate the osteopromotive effect of oligopeptide domain-coated bovine bone mineral granules in a rabbit calvarial defect model.

METHODS

The peptide-coated bovine bone was fabricated by incubating the graft material in a solution of oligopeptide domain. The cell attachment and proliferation were measured in vitro. Peptide-coated (test group) or uncoated (control group) bone minerals were implanted into 10-mm calvarial defects in rabbits, and the animals were sacrificed at 1, 2, or 4 weeks post-surgery.

RESULTS

The cells grown with peptide-coated bone showed significantly higher proliferation activity at all times compared to cells grown with peptide-uncoated bone mineral. At 2 weeks post-surgery, the control wounds showed a limited amount of osteoid formation in a centripetal pattern around the grafted bone, but the oligopeptide domain-coated grafted bone had formed new bone around the grafted area. At 4 weeks post-surgery, the control sites showed increased new bone formation, but they still showed a significant difference from the peptide-coated bone-implanted sites.

CONCLUSIONS

At 2 and 4 weeks, accelerated new bone formation was observed within the experimental sites compared to control groups. The use of deproteinized bovine bone combined with a synthetic oligopeptide seems to be a more beneficial material for bone regeneration in the early healing period.

Augmentation of demineralized bone matrix (DBM) mineralization by a synthetic growth factor mimetic

These studies evaluated whether F2A4-K-NS, a peptide mimetic of FGF-2, could augment ectopic bone production following the subcutaneous implant of human demineralized bone matrix (DBM). DBM was formulated into a gel with and without F2A4-K-NS, and injected subcutaneously into athymic rats. After 28 days the resultant tissue was excised and fixed. The tissue was examined with soft X-rays and microcomputerized tomography (micro-CT), and by histological methods. Inclusion of F2A4-K-NS with DBM resulted in an increased mineral deposition as determined by soft X-ray and micro-CT analysis and von Kossa staining. DBM-containing tissues showed extensive mineralization compared to the carrier alone, which was poorly mineralized. The mineralization was qualitatively and quantitatively the most extensive in the samples containing F2A4-K-NS plus DBM. Additionally, the highest amount of von Kossa staining for calcium was observed in tissues from animals that had received DBM plus F2A4-K-NS. In these studies, 100 ng of peptide per 0.2 mL of injectable DBM gel generated the most optimal results. The synthetic peptide F2A4-K-NS augmented DBM-induced ectopic mineralization in athymic animals.

Experimental Intrabony and Periodontal Defects Treated With Natural Mineral Combined With a Synthetic Cell-Binding Peptide in the Canine: Morphometric Evaluations

BACKGROUND

A synthetic peptide (P-15) analog of collagen added to anorganic bovine bone mineral (ABM) has recently been used as an enhanced bone graft material (ABM/P-15). The objective of this study was to test the contribution of ABM/P-15 in a new putty form (PEP) in two experimental membrane-protected defects: periodontal and intrabony. Its efficacy as filler biomaterial in guided tissue regeneration (GTR) and guided bone regeneration (GBR) procedures was evaluated histologically and morphometrically.

METHODS

In the maxillary canines, a facial mucoperiosteal flap was raised bilaterally in nine dogs. Two circular defects, 5 mm in diameter and 2 mm in depth, were made on each side: a fenestrated periodontal on the canine root and an intrabony in the alveolar diastema, anteriorly. PEP particles filled both defects on one side; the contralateral side was blood filled (control). All surgical sites were covered with a bioabsorbable membrane. Histologically, at 4 months, tissue blocks were made using the cutting/grinding non-decalcification method followed by morphometric analysis. In the periodontal fenestration root surface, the linear percentage of new cementum (%CEM), area percentage of new bone (%NB), and residual biomaterial particles (%PEP) were calculated. These same measurements were calculated at the intrabony sites, except cementum. The amount of direct NB to PEP contact was measured to assess the osteoconductivity level (OSC). The Pearson correlation test was used to evaluate any significant relationship between the different measured parameters.

RESULTS

In the grafted and non-grafted fenestration root surface defects, %CEM averaged 59.5% and 73.9% (P <0.02), respectively; %NB averaged 36.1% and 31.4%, respectively; and %PEP averaged 20.6%. The mean percentage of OSC was 52.4%. In the intrabony grafted and non-grafted sites, %NB averaged 50.7% and 60.1%, respectively (P <0.02). Residual %PEP averaged 26.1%, and OSC averaged 35.6%. At the intrabony sites, higher %NB and lower %OSC were found compared to the fenestration sites (P <0.001 and P <0.03, respectively). Correlation analysis showed a negative correlation between %NB and %PEP at the fenestration defects. In between the two defect types, %OSC was significantly correlated (P <0.05).

CONCLUSIONS

ABM/P-15 putty showed osteoconductive and biocompatible qualities. However, at 4 months in this model, no enhanced regeneration was present compared to a higher CEM and NB growth detected at non-grafted membrane-protected sites.

Anorganic bovine matrix/p-15 "flow" in the treatment of periodontal defects: case series with 12 months of follow-up

BACKGROUND

Nowadays there is a trend in developing biologic modalities that may enhance wound healing of specific sites. In this regard, a cell-binding activity of type I collagen provided by a synthetic peptide (P-15) was incorporated in a scaffold (anorganic bovine matrix [ABM]) to facilitate the attachment, migration, and differentiation of cells. This case series describes a surgical protocol for the placement of ABM/P-15 "flow" during regenerative procedures.

METHODS

Wide periodontal defects were treated with sulcular incisions preserving the papillae, full-thickness flap reflection, granulation tissue debridement, mechanical and chemical root surface treatment, placement of the ABM/P-15 "flow," and wound-closure sutures. Weekly, and then monthly, deplaquing was performed until the 12-month postoperative recall, in which the clinical parameters were reevaluated.

RESULTS

Significant clinical changes, including probing depth reduction and relative clinical attachment level gain, were achieved after the 12-month period. The radiographs demonstrated increase in radiopacity when compared to those taken initially, suggesting hard tissue improvements.

CONCLUSIONS

The topography of the defects described here could be understood as a challenge for regeneration, once the previous breakdown of the supporting tissues had diminished the source of cells for the healing process and reduced the number of residual walls to retain the graft material. Thus, it seems that the ABM/P-15 "flow" contributed to the clinical success achieved. Based on this result, ABM/P-15 "flow" could be a useful and beneficial material for the treatment of periodontal defects.

Maxillary sinus augmentation with different biomaterials: a comparative histologic and histomorphometric study in man

OBJECTIVE

Rehabilitation of the edentulous posterior maxilla with dental implants can be difficult because of insufficient bone volume caused by pneumatization of the maxillary sinus and crestal bone resorption. Different biomaterials have been used for sinus augmentation. The aim of the study was to compare different materials in maxillary sinus augmentation in man.

METHODS

A total of 94 patients participated in this study. Inclusion criteria were maxillary partial (unilateral or bilateral) edentulism involving the premolar/molar areas, and the presence of 3-5-mm crestal bone between the sinus floor and alveolar ridge. A total of 362 implants were inserted. There were 9 biomaterials used in the sinus augmentation procedures. Each patient underwent 1 biopsy after 6 months. A total of 144 specimens were retrieved.

RESULTS

None of the 94 patients had complications. All implants were stable, and x-ray examination showed dense bone around the implants. Mean follow-up was 4 years. There were 7 implants that failed. Histologic resultsshowed that almost all the particles of the different biomaterials (i.e., autologous bone, demineralized freeze-dried bone allograft Biocoral [Inoteb, St. Gonnery, France], Bioglass [US Biomaterials, Alachua, FL], Fisiograft [Ghimas, Bologna, Italy], PepGen P-15 [Dentsply Friadent CeraMed, Lakewood, CO], calcium sulfate, Bio-Oss [Geistlich Pharma AG, Wohlhusen, Switzerland], and hydroxyapatite) were surrounded by bone. Some biomaterials were more resorbable than others. Included are the histomorphometry clarified features of the newly formed bone around the different grafted particles.

CONCLUSION

All biomaterials examined resulted in being biocompatible and seemed to improve new bone formation in maxillary sinus lift. No signs of inflammation were present. The data are very encouraging because of the high number of successfully treated patients and the good quality of bone found in the retrieved specimens.

P-15 small peptide bone graft substitute in the treatment of non-unions and delayed union. A pilot clinical trial

Treatment of non-unions and delayed unions often requires osteogenic material. Recently, a biomimetic bone matrix that simulates the cellular environment of hard tissue, identified as P-15, was introduced to the orthopaedic community. A total of 22 patients with mal-union or delayed union fractures was treated from June 2000 to October 2003 with P15- bone graft substitute (P15-BGS) in the site of fracture and mostly with internal fixation. Patients were examined by independent radiographic analysis. Assessment criteria included time elapsed until bone bridging and time to full consolidation. In addition, histological assessment of the callus was done at the time of recovery of metal implants in five patients. Full consolidation was achieved in 90% (20 out of 22) of the patients treated with P15-BGS. The average time for full consolidation was 4.2 months. Histological assessment of the fracture callus in five of the patients confirmed the positive clinical and radiographic results. P15-BGS appears to offer a safe, economical and clinically useful alternative to autograft in the repair of ununited fractures. These results compare favourably with those in the published literature as an alternative to autograft.

Comparison of bone grafting materials in human extraction sockets: clinical, histologic, and histomorphometric evaluations

PURPOSE

Although there are a number of bone replacement graft materials that are currently available for clinical use, there are few studies that directly compare efficacy among graft treatments before implant placement. The purpose of this report was to compare 3 bone replacement graft materials (PepGen P-15 228 FLOW [DENTSPLY Friadent CeraMed, Lakewood, CO], Puros [Zimmer Dental, Carlsbad, CA], and C-Graft 228 [Clinician's Preference, Golden, CO]) for bone formation by clinical, histologic, and histomorphometric evaluation.

MATERIALS AND METHODS

In this prospective, intraoral pilot study, 13 maxillary sockets in 2 patients (both smokers) were grafted immediately after tooth extraction with C-Graft 228, Puros, or PepGen P-15 228 FLOW (containing additional PepGen P-15 228 particles; FLOW PUTTY). After 4 months, bone cores were retrieved and analyzed histologically.

RESULTS

PepGen P-15 228 FLOW PUTTY produced a significantly (P <0.01) higher amount of vital bone than C-Graft 228 or Puros. The amount of vital bone for FLOW PUTTY was 12-fold higher than for C-Graft 228 and 4-fold higher than Puros. Of 7 FLOW PUTTY treated sites, 7 showed >14% vital bone versus 0 of 3 C-Graft 228 and 0 of 3 Puros treated sites. FLOW PUTTY treated sites showed new vital bone between particles of residual graft. C-Graft 228 treated sites showed residual particles in a background of connective tissue with very little bone. Puros treated sites showed nonvital bone particles in a background of connective tissue, with some new vital bone forming around the nonvital bone.

CONCLUSION

PepGen P-15 228 FLOW PUTTY produced significantly greater vital bone as compared to Puros and C-Graft 228 after 4 months. A larger clinical study is required to confirm these results.

Treatment of Class III Furcation Defects With Expanded Polytetrafluoroethylene Membrane Associated or Not With Anorganic Bone Matrix/Synthetic Cell-Binding Peptide: A Histologic and Histomorphometric Study in Dogs

BACKGROUND

Up until now, no predictable periodontal regeneration of Class III furcation defects has been demonstrated after treatment with different available techniques. Recently, a bone graft enriched with a peptide was developed and has shown satisfactory results when applied in intrabony defects. The aim of this study was to compare the use of expanded polytetrafluoroethylene (ePTFE) membrane associated (test group) or not (control group) with anorganic bovine-derived bone matrix (ABM)/synthetic peptide, in the treatment of Class III furcation defects in dogs.

METHODS

Six mongrel dogs were used in this study, and the second and fourth mandibular lower premolars were extracted. Class III furcation defects were surgically created in the third premolars and filled with impression material. Afterwards, the defects were surgically assessed for debridement and root planing. Teeth were randomly assigned into test and control groups. The membranes were removed after 4 weeks, and the animals were sacrificed 12 weeks later.

RESULTS

Comparisons between groups by the Wilcoxon signed rank test showed no statistically significant differences in the parameters evaluated. In the control group, a new bone area (NBA) of 41.71%+/-24.07%, connective tissue area (CTA) of 36.34%+/-15.50%, and epithelium tissue area (ETA) of 9.39%+/-5.85% were observed. The new cementum extension (NCE) was 24.16%+/-13.18%. The test group presented an NBA of 31.84%+/-12.58%, CTA of 47.72%+/-11.33%, ETA of 9.17%+/-6.81%, and an NCE of 30.13%+/-16.43%.

CONCLUSION

There was no statistically significant difference between the two therapies: ePTFE membrane associated with ABM/synthetic peptide flow or ePTFE membrane only.

A study of biologically active peptide sequences (P-15) on the surface of an ABM scaffold (PepGen P-15) using AFM and FTIR

Cellular response to any biomaterial surface is governed by a number of factors including topography, surface chemistry, surface charge, structural heterogeneity, and physiological conditions. Understanding these factors at the nanoscale level is crucial to develop improved biomaterials. Any changes in these properties due to surface modifications need to be addressed properly, as they could have significant impact on the cellular interaction with biomaterials. In this study, the topography and surface chemistry of commercially available tissue engineered xenograft, PepGen P-15 [comprised of a synthetic peptide P-15 irreversibly attached to anorganic bovine bone mineral (OsteoGraf/-N)] was studied using Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR). FTIR confirmed the presence of the peptide on the surface of PepGen P-15. Changes in the peptide conformation, which includes a decrease in the beta-strand accompanied by an increase in unordered structures/random coil structures after attachment on OsteoGraf/-N is observed. Specific functional groups, which are involved in the binding mechanism, are identified. The results suggest that the attachment of the peptide on OsteoGraf/-N occurs via a specific surface docking ionic interaction involving the C-terminal carboxylic group on the peptide with positive domains generated by hydroxyl vacancies on the apatite surface.

Periodontal Regeneration With Peptide-Enhanced Anorganic Bone Matrix in Particulate and Putty Form in Dogs

BACKGROUND

Peptide-enhanced (using the peptide 15 [P-15] synthetic peptide) anorganic bone matrix (ABM) particulate (PPart) grafts have demonstrated clinical and histologic success in human periodontal defects. Dispersion of ABM/P-15 in sodium hyaluronate carrier (PPutty) improves the handling properties of the graft material. The healing of ABM/P-15 particulate and ABM/P-15 putty was compared in critical-sized fenestration defects in 16 mongrel dogs.

METHODS

After full thickness flap reflection, 7 mm diameter fenestrations were made with a trephine in the mid-root of both maxillary canines in each dog. Bone, periodontal ligament, and cementum were removed as completely as possible with hand root planing within the trephine-produced notches. By random allocation, each defect was filled with PPart or PPutty, and the flaps were closed with sutures. One dog contributing two defects served as a negative control. Block sections were retrieved at 3 and 8 weeks for histologic processing. Three 6-mu step serial sections in the center of the defects were used for analysis. Parameters measured included the original length of the wound, linear amount of periodontal regeneration including new cementum, bone and connective tissue, and area measurements of new bone and remaining particles. PPutty and PPart results were compared for significant differences using the Wilcoxon rank sum test.

RESULTS

Clinical healing was uneventful in all cases. There was no evidence of inflammation or adverse tissue reactions with either material. The controls showed minimal regeneration at the periphery of the defect. Histomorphometric evaluation of the grafted defects revealed the following: at 3 weeks, there was minimal new bone formation (occupying 4.2% of the grafted area for the PPutty and 1.2% for the PPart). The grafted particles occupied 21.2% and 35.6% of the area for the PPutty and PPart, respectively (P = 0.039). At 8 weeks, there was a tendency for greater new bone formation compared to 3 weeks with both materials. There was significantly more new bone with the PPutty (49.3%) compared to the PPart (14.8%) (P = 0.045). The grafted particles occupied 7.9% and 17% of the grafted area for the PPutty and PPart, respectively (no significant difference). There were no significant differences for any of the linear measurements. ABM/P-15 PPutty had superior handling characteristics.

CONCLUSIONS

Both ABM/P-15 materials yielded satisfactory healing and resulted in the greater regeneration of fenestration defects in dogs at 8 weeks compared to controls. In addition, AMB/P-15 putty resulted in more bone formation compared to ABM/P-15 particulate.

Maxillary sinus augmentation using a peptide-modified graft material in three mixtures: a prospective human case series of histologic and histomorphometric results

This prospective study assessed vital bone quality and quantity after grafting maxillary sinuses with anorganic bone mineral containing a cell binding peptide (ABM/P-15) in combination with DFDBA (Mix I), hydrogel/ABM/P-15 (Mix II), or PRP (Mix III). Fifteen maxillary sinuses in 12 patients were grafted with the ABM/P-15 mixtures and after 4 to 5 months, cores were taken and analyzed histologically and histomorphometrically. Fifty-nine screw-type implants were placed. Mixes containing a spacer material (Mix I and II) produced greater average vital bone, more mature bone, and more interconnected bone bridges from the cortical (oral) end to the most apical portion, compared to a mix that lacked a spacer material (Mix III). None of the 59 implants failed with any graft material up to 5 months following implant placement. The study demonstrates that new trabecular bone is formed after grafting ABM/P-15 in the sinus floor; that more vital bone is formed when ABM/P-15 is mixed with a spacer material than without; and that implants can be successfully placed.

Maxillary Sinus Augmentation With a Synthetic Cell-Binding Peptide: Histological and Histomorphometrical Results in Humans

Bone substitutes should be used when sufficient amounts of autologous bone cannot be harvested from intraoral donor sites. P-15 is a highly conserved linear peptide with a 15 amino acid sequence identical to the sequence contained in the residues 766 to 780 of the alpha-chain of type I collagen. PepGen P-15 (Dentsply Friadent, Mannheim, Germany) is a combination of the mineral component of bovine bone (Osteograf/N 300) with P-15. Bio-Oss (Geistlich, Mannheim, Germany) is a deproteinized sterilized bovine bone with 75% to 80% porosity and a crystal size of approximately 10 μm in the form of cortical granules. The purpose of the present histological and histomorphometrical study was to compare maxillary sinus augmentation procedures in humans performed with PepGen P-15 with procedures associated with Bio-Oss and autologous bone. Seven patients participated in this study (3 men and 4 women; ages between 48 and 69 years, mean of 58 years) and were categorized into 3 groups. In group 1, a mixture of 50% autologous bone from an intraoral source and 50% Bio-Oss was used. In group 2, the graft materials used were 50% Bio-Oss and 50% PepGen P-15. In group 3, 50% autologous bone and 50% PepGen P-15 were used. Group 1 histomorphometry showed that the percentage of newly formed bone was 38.7% ± 3.2%, marrow spaces represented 45.6% ± 5%, and residual graft particles constituted the remaining 14.4% ± 2.1%. Group 2 histomorphometry showed that newly formed bone represented 36.7% ± 3.3%, marrow spaces represented 39.7% ± 3.4%, and residual graft particles represented 19.6% ± 2.1%. In group 3, newly formed bone represented 32.2% ± 3.2%, marrow spaces represented 38% ± 2.5%, and residual graft particles represented 28.8% ± 1.1%. Nonstatistically significant differences were found in the percentage of newly formed bone in the different groups (P = .360). Statistically significant differences were found in the percentage of residual graft materials among the different groups (group 1 vs groups 2 and 3) (P = .0001). These data demonstrate that the use of bone-replacement materials, without the addition of autologous bone, could be an alternative in sinus augmentation procedures. Such treatment would increase patient satisfaction, decrease surgical complications, and save the clinician substantial operating time.

Receptor technology--cell binding to P-15: a new method of regenerating bone quickly and safely-preliminary histomorphometrical and mechanical results in sinus floor augmentations

Modern implantology involves the application and optimization of bone engineering biomaterials and scaffolds to achieve predictability in quality and quantity of the regeneration result and to avoid the high morbidity factor of the present gold standard. In this respect, acceleration of (woven) bone formation and completeness of the regeneration result seems to be an reasonable attempt by multiplication of the whole cascades by duplicating all phases of cell binding, migration, proliferation and differentiation. Collagen I is an extracellular matrix protein with multiple main binding domains for osteogenic progenitor cells and therefore plays a crucial role in osteogenesis. PepGen P15 is the first man engineered collagen I binding domain for potential osteoblasts and is able to multiply the complete regeneration cascade. The article explains the principles of micromolecular receptor engineering and its application in sinus floor augmentations as a preliminary report. It presents the first clinical and histomorphometrical results of this new technology in sinus floor elevations. The future potential of individual bone regeneration will be discussed.

Growth and proliferation of human osteoblasts on different bone graft substitutes: an in vitro study

The purpose of this study was to investigate the effect of different bone graft substitutes onto the growth and proliferation pattern of bone cells derived from human iliac cancellous bone. Five different bone graft materials were used to investigate the effect on the proliferation of osteoblasts in vitro: phytogene hydroxyapatite (Algipore), alpha-Tricalcium phosphate (Bio-Base), bovine hydroxyapatite (low temperature) (Bio-Oss), bovine hydroxyapatite (high temperature) (Osteograf), and bovine hydroxyapatite (high temperature) enhanced with p-15, synthetic peptide (PepGen p-15). The osteoblasts were derived from human iliac cancellous bone and seeded with the different bone substitutes. The cell proliferation and viability (WST-1), alkaline phosphatase as an early marker of osteoblast proliferation, was evaluated after 6 and 9 days. The cultures were examined for cell growth pattern and morphology by normal light and scanning electron microscopy. The human osteoblasts showed a different proliferation pattern according to the type of applied bone graft substitute. PepGen P-15 showed the highest proliferation and differentiation rate followed by Osteograf, Algipore, and Bio-base. Bio-Oss showed the lowest. These results were confirmed by electron microscopy and light microscopy evaluation in which similar growth pattern were observed. Distinct bone graft materials have different impact onto the proliferation pattern of human osteoblasts in vitro.

Biomimetic Collagen Scaffolds for Human Bone Cell Growth and Differentiation

Type I collagen provides a structural framework for connective tissues and plays a central role in the temporal cascade of events leading to the formation of new bone from progenitors. The aim of this study was to examine the ability of the cell-binding domain of type I collagen (P-15 peptide) to promote human bone marrow stromal cell adhesion, proliferation, and differentiation on three-dimensional scaffolds. Human bone marrow stromal cells were selected, expanded, and cultured on particulate microporous ABM ("pure" hydroxyapatite) phase adsorbed with or without P-15 under basal or osteogenic conditions. Immobilized P-15 increased alkaline phosphatase activity and bone morphogenetic protein 2 (BMP-2) gene expression after 1 and 5 days as determined by real-time polymerase chain reaction. P-15 promoted human bone marrow stromal cell attachment, spreading, and alignment on ABM as well as alkaline phosphatase-specific activity in basal and osteogenic cultures. The presence of mineralized bone matrix, extensive cell ingrowth, and cellular bridging between three-dimensional matrices adsorbed with P-15 was confirmed by confocal microscopy, scanning electron microscopy, and alizarin red staining. Negligible cell growth was observed on ABM alone. In vivo diffusion chamber studies using MF1-nu/nu mice showed bone matrix formation and organized collagen formation after 6 weeks. These studies indicate the potential of P-15 to generate appropriate biomimetic microenvironments for osteoblasts and demonstrate the potential for the exploitation of extracellular matrix cues for osteogenesis and, ultimately, bone regeneration.

P-15 cell-binding domain derived from collagen: analysis of MG63 osteoblastic-cell response by means of a microarray technology

BACKGROUND

P-15 is an analog of the cell-binding domain of collagen. P-15 has been shown to facilitate physiological processes in a way similar to collagen; to serve as an anchorage for cells; and to promote the binding, migration, and differentiation of cells.

METHODS

Expression profiling by DNA microarray is a molecular technology that allows the analysis of gene expression in a cell system. By using DNA microarrays containing 19,200 genes, we identified in osteoblast-like cell line (MG-63) cultured with P-15 several genes whose expression was significantly up- or downregulated.

RESULTS

The differentially expressed genes cover a broad range of functional activities: 1) signaling transduction, 2) differentiation, 3) apoptosis, and 4) cell-cycle regulation. It was also possible to detect some genes whose function is unknown.

CONCLUSIONS

The data reported are, to our knowledge, the first genetic portrait of P-15 effects. They can help us to better understand the molecular mechanism of osteogenesis and can serve as a model for comparing different cell cultures and/or other materials with similar effect.

Cortical bone regeneration with a synthetic cell-binding peptide: a histologic and histomorphometric pilot study

PepGen P-15 is a combination natural anorganic bovine-derived hydroxyapatite matrix (ABM) coupled with a synthetic cell-binding peptide (P-15). This material has been reported to enhance bone formation in periodontal osseous defects. The aim of this study was to assess the effect of ABM/P-15 on the healing of cortical bone defects in rabbits. Five New Zealand rabbits were used. Two 8-mm bone defects were created in each tibia. Eight defects were filled with PepGen P-15, 8 defects with PepGen P-15 Flow, and 4 defects were used as a control group. A total of 20 defects were created. All rabbits were killed at 4 weeks. Block sections containing the defects were retrieved and the specimens processed for light microscopy examination. Newly formed bone was present in both test groups, whereas, in the control-group, only a scarce quantity of newly formed bone was present and the cortical defects had not been filled by the regenerated bone. Statistical evaluation showed that there were statistically significant differences between control sites and sites treated with P-15 and P-15 Flow (P = 0.0001), and also between sites treated with P-15 and P-15 Flow (P = 0.0001), respectively. No acute inflammatory infiltrate cells were visible in both of these groups. Both PepGen P-15 and PepGen P-15 Flow enhanced new bone formation in the cortical drilled defects, whereas control defects showed very little newly formed bone.

In vitro study of cell-promoting multiple-armed peptides

The purpose of this study was to compare the effectiveness of several linear and branch cell-binding peptides to promote cell growth in prosthetic vascular grafts. In this in vitro study, the peptides were covalently immobilized onto expanded polytetrafluoroethylene (ePTFE) vascular grafts. Cell-growth properties were studied using primary human umbilical vein endothelial cells (HUVECs) and primary human umbilical artery smooth muscle cells (HUASMCs). Linear peptides (P15 and P15') and multiple-armed peptides (MAP4-I and MAP4-II) were covalently bonded onto ePTFE grafts by an atmospheric plasma coating method. X-ray photoelectron spectroscopy and amino acid analysis were used to analyze the surface characteristics of the peptide-coated samples. Cell adhesion, proliferation, and morphology were evaluated by culturing HUVECs and HUASMCs onto the surfaces of different samples: ePTFE control, chemically activated ePTFE, P15-coated ePTFE, and MAP4-coated ePTFE. The cell culture experiments were repeated several times to obtain statistically reliable cell-growth data. Cell-growth data were statistically analyzed by the two-way statistical analysis of variance. The study showed that multiple-armed MAP4 peptides were significantly more effective in promoting endothelial cells than the structurally similar linear P15 peptides. There were 800% more HUVECs proliferated on the MAP4-coated ePTFE samples compared with the ePTFE control. MAP4 peptides were 80% more effective for promoting HUVECs than P15 peptides. In contrast, MAP4 peptides were significantly less effective for promoting HUASMCs than HUVECs. There were only about 100% more HUASMCs proliferated on the MAP4-coated ePTFE samples compared with the ePTFE control. MAP4 and P15 peptides had similar cell-promoting characteristics for SMCs.

Enhanced cell attachment and osteoblastic activity by P-15 peptide-coated matrix in hydrogels

The cells in bone grow on a composite matrix made up of mineral and organic (mainly type-I collagen) components. In this study, anorganic bone mineral (ABM) particles were coated with a cell-binding domain of type-I collagen (P-15 peptide) to mimic the bone matrix components and suspended in injectable hyaluronate (Hy) hydrogels. The ABM/P-15/Hy was compared to ABM/Hy-the same matrix without P-15 peptide. Osteoblast-like HOS cells migrated through the hydrogels around ABM/P-15 or ABM particles; however, more cells adhered to ABM/P-15/Hy particles, and the cells formed better surface coverage and had more stress fibers on ABM/P-15/Hy. HOS cells cultured on ABM/P-15/Hy had increased osteogenic gene expression for alkaline phosphatase and bone morphogenetic proteins, and deposited more mineralized matrix. Studies with two different hydrogels (carboxymethylcellulose and sodium alginate) showed similar enhanced cell attachment and mineralization. The studies suggest that the ABM/P-15 in hydrogels can be used as an injectable biomimetic matrix to facilitate bone repair.

Clinical, radiographic, histologic, and histomorphometric comparison of PepGen P-15 particulate and PepGen P-15 flow in extraction sockets: a same-mouth case study

PURPOSE

Although the efficacy of PepGen P-15 particulate has been conclusively demonstrated in two multicenter clinical studies, the effect of a new hydrogel formulation containing PepGen P-15 on bone repair has not been previously demonstrated.

MATERIALS AND METHODS

PepGen P-15 Flow contains PepGen P-15 particulate in a biocompatible hydrogel, which provides spacing between the particles. In this case study, bone repair of both PepGen P-15 particles and PepGen P-15 Flow was compared to natural bone in same-mouth extraction sockets.

RESULTS

The radiographic, histologic, and histomorphometric evaluations showed enhanced bone formation and faster particle resorption with PepGen P-15 Flow compared to the PepGen P-15 particulate.

CONCLUSION

The accelerated bone formation by PepGen P-15 Flow may provide faster implant placement.

The putative collagen-binding peptide P-15 promotes fibroblast attachment to root shavings but not hydroxyapatite

BACKGROUND

Regenerative periodontal treatment aims to restore the attachment of the periodontal ligament and gingival collagen fibers to both the cementum of the root surface and alveolar bone. Fibroblasts are the predominant cells of the periodontal ligament and gingiva and have important roles in the function and regeneration of the tooth-supporting apparatus. This study investigated whether a putative collagen-based cell-binding peptide (P-15) increases gingival fibroblast attachment to root shavings and bone replacement graft (BRG) materials.

METHODS

Gingival and dermal fibroblast attachment to root shavings and BRG materials, and cell proliferation on root shavings and sections were measured fluorometrically. Root shavings and root sections obtained from periodontally healthy teeth were treated with P-15 at 2 concentrations (200 ng/g or 400 ng/g). Citric acid (CA)-treated root materials were also compared to untreated root shavings and root sections that served as negative control groups.

RESULTS

Attachment of all cells to bone fragments (whether freeze-dried or demineralized) was significantly greater than to hydroxyapatite (HA)-based BRG materials. The addition of P-15 to HA did not significantly increase gingival or dermal fibroblast attachment. At a concentration of 400 ng/g, P-15 significantly increased gingival and dermal fibroblast attachment to root shavings as compared to untreated shavings. Bone fragments, HA-based BRG materials, and untreated root shavings inhibited gingival fibroblast proliferation. Treatment of root sections with P-15 did not have any effect on gingival fibroblast proliferation.

CONCLUSIONS

P-15 is a potential alternative to CA for promoting fibroblast attachment to root surfaces. However, P-15 did not enhance fibroblast proliferation on root sections.

Bone regeneration of localized chronic alveolar defects utilizing cell binding peptide associated with anorganic bovine-derived bone mineral: a clinical and histological study

BACKGROUND

Osteoinduction to treat osseous defects has been attempted by several means. Some clinical studies have demonstrated that a synthetic cell binding peptide (P-15) with anorganic bovine derived bone matrix (ABM) has the ability to enhance bone regeneration. These studies suggest that more histological data are necessary to better understand this process. We have developed a Class III chronic alveolar defect animal model to investigate space-maintaining regenerative materials. The objective of this study was to clinically and histologically evaluate the use of P-15/ABM with or without a bioabsorbable membrane (M) to regenerate localized chronic alveolar ridge defects in dogs.

METHODS

Six adult, male mongrel dogs were used in this study. Bilateral, Class III, alveolar defects were surgically produced following extraction of the mandibular second premolar teeth and local reduction of the alveolar ridge. After an 8-week healing interval, mucoperiosteal flaps were elevated. P-15/ABM with or without bioabsorbable membranes were implanted into contralateral defects in 10 sites. Two sites received no biomaterial (controls). Mucoperiosteal flaps were advanced over the P-15/ABM or P-15/ABM/M constructs and sutured. Pre- and postaugmentation clinical evaluation was done utilizing periodontal probes and calipers. The animals were sacrificed 12 weeks postaugmentation and block specimens processed for histologic evaluation.

RESULTS

Clinical results showed no significant statistical augmentation on the control group (0.0 +/- 0.6 mm). In all experimental sites utilizing P-15/ABM or P-15/ABM/M, relevant ridge augmentation was observed (3.6 +/- 2.0 mm and 2.9 +/- 1.9 mm, respectively). Histologically, all experimental sites showed active bone formation with plump osteoblast and osteoid matrix deposition in the treated area. Bone ingrowth filled the area of the defects treated with P-15/ABM/M. Few P-15/ABM particles were seen in the cellular fibrous tissue surrounding the new formed bone trabeculae.

CONCLUSIONS

P-15/ABM with or without membranes can produce a significant clinical ridge augmentation. Bone formation was histologically observed in all test areas. The association of a membrane with P-15/ABM seemed to enhance the process of bone formation.

Thirty-six month follow-up of 25 patients treated with combination anorganic bovine-derived hydroxyapatite matrix (ABM)/cell-binding peptide (P-15) bone replacement grafts in human infrabony defects. I. Clinical findings

BACKGROUND

Long-term evaluation of periodontal therapy is important for clinical decision making.

METHODS

A synthetic cell-binding peptide (P-15) combined with anorganic bovine-derived hydroxyapatite bone matrix (ABM) was evaluated as a bone replacement graft in human periodontal osseous defects. Following initial preparation and reevaluation, flap surgery was performed. A variety of 1-, 2-, 3-wall bony defects were curetted and root surfaces subjected to mechanical debridement only. The bone defects were grafted with ABM/P-15, and the host flaps replaced or slightly coronally positioned. Weekly, then monthly deplaquing was performed until surgical reentry at 6 to 7 months. Patients were then followed on approximate 3-month recalls for 3 years. Twenty-five of the original 31 patients qualified for long-term evaluation in that their ABM/P-15 treated sites did not receive any additional therapy at the time of reentry.

RESULTS

Significant clinical changes for the overall group of bony defects included improvement in mean clinical attachment level from 5.4 mm at surgery to 4.5 mm at the 6-month reentry to 3.8 mm at 3 years. There was also a decrease in mean probing depth from 5.3 mm at surgery to 3.1 mm at the 6-month reentry to 2.9 mm at 3 years. The mean gingival recession changed from +0.1 mm at surgery to 1.4 mm at the 6-month reentry to 0.9 mm at 3 years. All of these differences were at least P <0.05 from surgery to the 6-month reentry, and surgery to 3 years, but were not significant from reentry to 3 years via repeated measures analysis of variance.

CONCLUSIONS

These favorable 3-year results with ABM/P-15 suggest that it may have a beneficial effect in the long-term clinical management of infrabony defects. Further long-term randomized controlled studies are needed to better assess the role of ABM/P-15 in long-term healing of periodontal osseous defects.

The putative collagen binding peptide hastens periodontal ligament cell attachment to bone replacement graft materials

BACKGROUND

Bone replacement graft (BRG) materials are often used to treat periodontal defects, to promote cellular invasion, and to encourage bone regrowth. Periodontal ligament fibroblasts (PDLF) incorporate these materials and form the basis of the renewed connection between the existing and newly formed alveolar bone and the tooth surface. A peptide (P-15) that mimics the putative cell-binding domain of collagen has been reported to promote dermal fibroblast attachment and proliferation.

METHODS

PDLF were quantitatively examined for their ability to adhere to a variety of BRG materials fluorometrically. In addition, scanning electron microscopy was used to examine the changes in morphology exhibited by these cells as they attached and spread on several BRG materials. Finally, BRG materials containing the P-15 peptide were quantitatively examined for their ability to promote PDLF attachment and proliferation.

RESULTS

Freeze-dried allograft bone supports greater PDLF attachment than does several xenograft and alloplastic anorganic bone replacement materials. An anorganic BRG material containing the P-15 peptide promoted more rapid cell attachment and spreading than a similar anorganic BRG material lacking this peptide. Finally, none of the BRG materials examined promoted PDLF proliferation.

CONCLUSIONS

Our data indicate that the addition of the P-15 peptide increases the rapidity of PDLF attachment to xenogeneic bone replacement materials. This increase in the rate of attachment may have clinical significance in the context of the dynamic regulation of cell attachment during periodontal regeneration. However, this peptide does not promote an increase in stable cell attachment or proliferation in vitro.

Multi-center clinical comparison of combination anorganic bovine-derived hydroxyapatite matrix (ABM)/cell binding peptide (P-15) and ABM in human periodontal osseous defects. 6-month results

BACKGROUND

Intraosseous periodontal defects present a particular treatment problem. New bone replacement grafts offer promise for improved results.

METHODS

The role of a synthetic cell-binding peptide (P-15), combined with anorganic [corrected] bovine-derived hydroxyapatite bone matrix (ABM), was compared to ABM alone in human periodontal osseous defects in a controlled, monitored, multi-center trial. Following appropriate initial preparation procedures, flap surgery with defect and root debridement was performed. Two osseous defects per patient were treated randomly with each procedure after surgical preparation. Appropriate periodontal maintenance schedules were followed, and at 6 to 7 months, re-entry flap surgery was performed for documentation and finalization of treatment.

RESULTS

T test and Mann-Whitney U analyses of patient mean values from 33 patients revealed that the combination ABM/P-15 grafts demonstrated significantly better mean defect fill of 2.9 +/- 1.2 mm (72.9%) versus a mean defect fill of 2.2 +/- 1.4 mm (50.67%) for defects treated with ABM (P<0.05). Other hard tissue findings showed similar clinically superior results with the use of ABM/P-15. Relative defect fill results showed 81% positive (50% to 100% defect fill) responses with ABM/P-15 and 67% positive responses with ABM. There were 3.5 times as many optimal results (> or = 90% defect fill) with ABM/P-15 and twice as many failures (minimal response) with ABM. Soft tissue findings showed no significant differences between treatments.

CONCLUSIONS

These results suggest that the use of the P-15 synthetic cell-binding peptide combined with ABM yields better clinical results than the ABM alone in intrabony periodontal defects.

Molecular modeling of the collagen-like tail of asymmetric acetylcholinesterase

The asymmetric form of acetylcholinesterase comprises three catalytic tetramers attached to ColQ, a collagen-like tail responsible for the anchorage of the enzyme to the synaptic basal lamina. ColQ is composed of an N-terminal domain which interacts with the catalytic subunits of the enzyme, a central collagen-like domain and a C-terminal globular domain. In particular, the collagen-like domain of ColQ contains two heparin-binding domains which interact with heparan sulfate proteoglycans in the basal lamina. A three-dimensional model of the collagen-like domain of the tail of asymmetric acetylcholinesterase was constructed. The model presents an undulated shape that results from the presence of a substitution and an insertion in the Gly-X-Y repeating pattern, as well as from low imino-acid regions. Moreover, this model permits the analysis of interactions between the heparin-binding domains of ColQ and heparin, and could also prove useful in the prediction of interaction domains with other putative basal lamina receptors.

Conformational analysis and stability of collagen peptides by CD and by 1H- and 13C-NMR spectroscopies

Four small type I collagen CNBr peptides containing complete natural sequences were purified from bovine skin and investigated by CD and 1H- and 13C-nmr spectroscopies to obtain information concerning their conformation and thermal stability. CD showed that a triple helix was formed at 10 degrees C in acidic aqueous solution by peptide alpha l(I) CB2 only, and to lesser extent, by alpha 1(I) CB4, whereas peptides alpha 1(I) CB5 and alpha 2(I) CB2 remained unstructured. Analytical gel filtration confirmed that peptides alpha 1(I) CB2 and alpha 1(I) CB4 only were able to form trimeric species at temperature between 14 and 20 degrees C, and indicated that the monomer = trimer equilibrium was influenced by the chaotropic nature of the salt present in the eluent, by its concentration, and by temperature variations. CD measurements at increasing temperatures showed that alpha 1(I) CB2 was less stable than its synthetic counterpart due to incomplete prolyl hydroxylation of the preparation from the natural source. 1H- and 13C-nmr spectra acquired in the temperature range 0-47 and 0-27 degrees C, respectively, indicated that with decreasing temperature the most abundant from of alpha 1(I) CB2 was in slow exchange with an assembled form, characterized by broad lines, as expected for the triple-helical conformation. A large number of trimer cross peaks was observed both in the proton and carbon spectra, and these were most likely due to the nonequivalence of the environments of the three chains in the triple helix. This nonequivalence may have implications for the aggregation of collagen molecules and for collagen binding to other molecules. The thermal transition from trimer to monomer was also monitored by 1H-nmr following the change in area of the signal belonging to one of the two beta protons of the C-terminal homoserine. The unfolding process was found to be fully reversible with a melting temperature of 13.4 degrees C, in agreement with CD results. The qualitative superposition of the melting curves obtained by CD for the peptide bond characteristics and by nmr for a side chain suggests that triple-helical backbone and side chains constitute a single unit.

Design of biomimetic habitats for tissue engineering with P-15, a synthetic peptide analogue of collagen

In tissues, collagen forms the scaffold for cell attachment and migration, and it modulates cell differentiation and morphogenesis by mediating the flux of chemical and mechanical stimuli. We are constructing biomimetic environments by immobilizing a collagen-derived high-affinity cell-binding peptide P-15 in three-dimensional (3-D) templates. The cell-binding peptide can be expected to transduce mechanical forces. In their physiological environment, periodontal ligament fibroblasts (PDLF) are subject to significant mechanical forces. We have examined the behavior of human PDLF in culture on particulate bovine anorganic bone mineral (ABM) coated with P-15 (ABM-P-15). Greater numbers of cells associated with ABM-P-15 compared to ABM alone. Higher levels of incorporation of radiolabeled precursors in DNA and protein were consistent with the presence of larger numbers of cells on ABM-P-15 compared to ABM cultures. Scanning electron microscopic examination showed that cultures on ABM-P-15 generated highly oriented 3-D colonies of elongated cells and formed copious amounts of fibrous as well as membranous matrix reminiscent of ligamentous structures. PDLF cultured on ABM formed sparse monolayers with little order and a meager matrix. Alizarin Red stained the matrix of particle associated cells and inter-particle cellular bridges in P-15-associated cultures, indicating mineralization. 3-D colony formation and ordering of cells along with increased mineralization suggests that the coupling of cells to the ABM matrix through P-15 may provide a biomimetic environment permissive for cell differentiation and morphogenesis. Our studies suggest that ABM-P-15 templates may be effective as endosseous grafts, and, when seeded with PDLF, these matrices may serve as tissue engineered substitutes for autologous bone grafts.

Recombinant procollagen II: Deletion of D period segments identifies sequences that are required for helix stabilization and generates a temperature-sensitive N-proteinase cleavage site

A cDNA cassette system was used to synthesize recombinant versions of procollagen II in which one of the four blocks of 234 amino acids that define a repeating D periods of the collagen triple helix were deleted. All the proteins were triple helical and all underwent a helix-to-coil transition between 25 and 42 degreesC as assayed by circular dichroism. However, the details of the melting curves varied. The procollagen lacking the D1 period unfolded 3 degreesC lower than a full-length molecule. With the procollagen lacking the D4 period, the first 25% of unfolding occurred at a lower temperature than the full-length molecule, but the rest of the structure unfolded at the same temperature. With the procollagen lacking the terminal D0.4 period, the protein unfolded 3 degreesC lower than the full-length molecule and a smaller fraction of the protein was secreted by stably transfected clones than with the other recombinant procollagens. The results confirmed previous suggestions that the collagen triple helix contains regions of varying stability and they demonstrated that the two D periods at the end of the molecule contain sequences that serve as clamps for folding and for stabilizing the triple helix. Reaction of the recombinant procollagens with procollagen N-proteinase indicated that in the procollagen lacking the sequences, the D1 period assumed an unusual temperature-sensitive conformation at 35 degreesC that allowed cleavage at an otherwise resistant Gly-Ala bond between residues 394 and 395 of the alpha1(II) chain.

Inhibition of the self-assembly of collagen I into fibrils with synthetic peptides. Demonstration that assembly is driven by specific binding sites on the monomers

A series of experiments were carried out to test the hypothesis that the self-assembly of collagen I monomers into fibrils depends on the interactions of specific binding sites in different regions of the monomer. Six synthetic peptides were prepared with sequences found either in the collagen triple helix or in the N- or C-telopeptides of collagen I. The four peptides with sequences found in the telopeptides were found to inhibit self-assembly of collagen I in a purified in vitro system. At concentrations of 2.5 mM, peptides with sequences in the C-telopeptides of the alpha1(I) and alpha2(I) chain inhibited assembly at about 95%. The addition of the peptide with the alpha2-telopeptide sequence was effective in inhibiting assembly if added during the lag phase and early propagation phase but not later in the assembly process. Experiments with biotinylated peptides indicated that both the N- and C-telopeptides bound to a region between amino acid 776 and 822 of the alpha(I) chain. A fragment of nine amino acids with sequences in the alpha2-telopeptide was effective in inhibiting fibril assembly. Mutating two aspartates in the 9-mer peptide to serine had no effect on inhibition of fibril assembly, but mutating two tyrosine residues and one phenylalanine residue abolished the inhibitory action. Molecular modeling of the binding sites demonstrated favorable hydrophobic and electrostatic interactions between the alpha2telopeptide and residues 781-794 of the alpha(I) chain.

Multi-center clinical evaluation of combination anorganic bovine-derived hydroxyapatite matrix (ABM)/cell binding peptide (P-15) as a bone replacement graft material in human periodontal osseous defects. 6-month results

A synthetic cell-binding peptide (P-15) combined with anorganic bovine-derived hydroxyapatite bone matrix (ABM) was compared to demineralized freeze-dried bone allograft (DFDBA) and open flap debridement (DEBR) in human periodontal osseous defects in a controlled, monitored, multi-center trial. Following appropriate initial preparation procedures, flap surgery with defect and root debridement was performed. Three osseous defects per patient were treated randomly with one of three procedures after surgical preparation. Appropriate periodontal maintenance schedules were followed, and at 6 to 7 months re-entry flap surgery was performed for documentation and finalization of treatment. Analysis of variation (ANOVA) and t test analyses of patient mean values from 31 patients revealed that the combination ABM/P-15 grafts demonstrated significantly better mean defect fill of 2.8 +/- 1.2 mm (72.3%) versus a mean defect fill of 2.0 +/- 1.4 mm (51.4%) for defects treated with DFDBA (P <0.05) and a mean defect fill of 1.5 +/- 1.3 mm (40.3%) (P <0.05) for defects treated with DEBR. Other hard tissue findings showed similar clinically superior results with the use of ABM/P-15. Relative defect fill results showed 87% positive (50% to 100% defect fill) responses with ABM/P-15, 58% positive responses with DFDBA, and 41% positive responses with DEBR. There were 8 to 9 times more failures (minimal response) with DFDBA and DEBR (26% to 29% frequency) than with ABM/P-15. Soft tissue findings showed no significant differences among treatments except for greater clinical attachment level gain with ABM/P-15 compared to DEBR. These results suggest that the use of the P-15 synthetic cell-binding peptide combined with ABM yields better clinical results than either DFDBA or DEBR. Further studies are needed to determine the relative roles of the ABM and/or the P-15 in these improved results.