The combination of platelet-derived growth factor-BB and insulin-like growth factor-I stimulates bone repair in adult Yucatan miniature pigs

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Insulin-like growth factor-I enhances proliferation and differentiation of human mesenchymal stromal cells in vitro

Human mesenchymal stromal cells (hMSCs) offer great potential for bone tissue engineering applications, but their in vivo performance remains limited. Preconditioning of these cells with small molecules to improve their differentiation before implantation, or incorporation of growth factors are possible solutions. Insulin-like growth factor-1 (IGF-1) is one of the most abundant growth factors in bone, involved in growth, development, and metabolism, but its effects on hMSCs are still subject of debate. Here we examined the effects of IGF-1 on proliferation and differentiation of hMSCs in vitro and we found that serum abolished the effects of IGF-1. Only in the absence of serum, IGF-1 increased proliferation, alkaline phosphatase expression, and osteogenic gene expression of hMSCs. Furthermore, we examined synergistic effects of bone morphogenetic protein-2 (BMP-2) and IGF-1 and, although IGF-1 enhanced BMP-2-induced mineralization, IGF-1 only slightly affected in vivo bone formation.

Sustained platelet-derived growth factor receptor alpha signaling in osteoblasts results in craniosynostosis by overactivating the phospholipase C-gamma pathway

The development and growth of the skull is controlled by cranial sutures, which serve as growth centers for osteogenesis by providing a pool of osteoprogenitors. These osteoprogenitors undergo intramembranous ossification by direct differentiation into osteoblasts, which synthesize the components of the extracellular bone matrix. A dysregulation of osteoblast differentiation can lead to premature fusion of sutures, resulting in an abnormal skull shape, a disease called craniosynostosis. Although several genes could be linked to craniosynostosis, the mechanisms regulating cranial suture development remain largely elusive. We have established transgenic mice conditionally expressing an autoactivated platelet-derived growth factor receptor alpha (PDGFRalpha) in neural crest cells (NCCs) and their derivatives. In these mice, premature fusion of NCC-derived sutures occurred at early postnatal stages. In vivo and in vitro experiments demonstrated enhanced proliferation of osteoprogenitors and accelerated ossification of osteoblasts. Furthermore, in osteoblasts expressing the autoactivated receptor, we detected an upregulation of the phospholipase C-gamma (PLC-gamma) pathway. Treatment of differentiating osteoblasts with a PLC-gamma-specific inhibitor prevented the mineralization of synthesized bone matrix. Thus, we show for the first time that PDGFRalpha signaling stimulates osteogenesis of NCC-derived osteoblasts by activating the PLC-gamma pathway, suggesting an involvement of this pathway in the etiology of human craniosynostosis.

The use of autologous concentrated growth factors to promote syndesmosis fusion in the Agility total ankle replacement. A preliminary study

BACKGROUND

The Agility (DePuy, Warsaw, Indiana) total ankle replacement has been in use since 1984. One of the most common complications continues to be delayed union or nonunions of the distal tibiofibular syndesmosis. In the reported studies on the Agility ankle the delayed union and nonunion rate can be as high as 38%.

METHODS

Since 1999, 114 Agility total ankle replacements were done at two centers in the United States without the use of autologous concentrated growth factors. Since July of 2001, 66 Agility ankles were implanted with Symphony (DePuy, Warsaw, Indiana) augmented bone grafting. The standard operative technique was followed in all the patients. Prospective data was collected on all patients. The standard ankle radiographs were taken preoperatively and postoperative at 8 weeks, 12 weeks, 16 weeks, 6 months, and yearly. CT scans were obtained at 6 months if fusion at the syndesmosis was questionable. The Graphpad Instat software (Graphpad Software Inc., San Diego, CA) was used for statistical analysis. The two-tailed unpaired t-test was used, and the value <0.05 was considered significant.

RESULTS

There was no statistical difference in the demographic data for the two groups. In 114 ankle replacements without autologous concentrated growth factors 70 fused at 8 weeks (61%), 14 fused at 12 weeks (12%), 13 fused at 6 months (12%). There were 17 nonunions (15%); delayed unions (3 to 6 months) and nonunions, therefore, equaled 27%. The syndesmosis fused in 50 of the 66 ankle replacements (76%) that had autologous concentrated growth fractures at 8 weeks (76%); 12 fused at 3 months (18%), 2 fused at 6 months (3%), 2 had nonunions (3%). Delayed unions (3 to 6 months) and nonunions equaled 6%. There was a statistically significant improvement in the 8- and 12-week fusion rates, and a statistically significant reduction in delayed unions and nonunions.

CONCLUSION

Autologous concentrated growth factors appear to make a significant positive difference in the syndesmosis union rate in total ankle replacements.

A Comparative Study of Bilateral Sinus Lifts Performed with Platelet-Rich Plasma Alone Versus Alloplastic Graft Material Reconstituted with Blood

The objective of this study was to compare the alveolar bone growth in the 2 sides of the maxillary sinus after bilateral sinus lift procedures were performed with the simultaneous placement of dental implants in 20 consecutive patients. After elevation of the Schneiderian membrane, one side had only platelet-rich plasma (PRP) gel applied, while the other had placed only alloplastic graft material reconstituted with blood. Both open window and closed window techniques were used in ridges with > or =9 mm residual crest of bone. Results indicate that using PRP alone in cases with >7 mm residual crest can produce bone growth. Preliminary results indicate that in cases with a minimum of 7-mm crestal bone, it is possible to use a crestal approach for sinus grafting, with PRP alone and implant placement for bone growth.

Enhancement of syndesmotic fusion rates in total ankle arthroplasty with the use of autologous platelet concentrate

BACKGROUND

One of the challenges of total ankle arthroplasty continues to be achieving a solid distal fusion of the tibiofibular joint. Delayed union rates of 29% to 38% and the nonunion rates of 9% to 18% for syndesmotic fusion have been documented. The risk of tibial component migration has been reported to increase 8.5 times if a solid syndesmotic fusion is absent. Growth factors have been shown to accelerate bone healing and may enhance the fusion of the syndesmosis and, thereby, decrease the frequency of nonunion and subsequent tibial component migration.

METHODS

An autologous platelet concentrate was used to increase the amount of growth factors at the site of the distal tibiofibular joint fusion in 20 total ankle arthroplasties.

RESULTS

Our 6-month fusion rate was 100%. When compared to historical controls (6-month fusion rate of 62%) the difference was statistically significant (p < 0.0001).

CONCLUSION

The improved rate of distal tibiofibular fusion may be attributable to the increased presence of growth factors provided by an autologous platelet concentrate.

Use of a polymeric device to deliver growth factors to a healing fracture

BACKGROUND

Fracture healing is a cascade of events regulated by systemic and local factors. Local growth factors are believed to play an integral role. The present study evaluates the effects of basic fibroblast growth factor (bFGF) and insulin-like growth factor-1 (IGF-1) using a controlled delivery system in a closed rodent femoral fracture model.

METHODS

Female Wistar rats (n = 144) were used in the present study. Animals were randomly allocated to six groups, with each group divided into three time-points of 2, 4 and 8 weeks. Two groups had growth factor administered. The others had no operation or sham operations. Growth factors were delivered to the fracture site using a specialised delivery system. This consisted of a Kirschner-wire coated with ethylene vinyl acetate co-polymer embedded with growth factors, inserted as an intramedullary nail. Fractures were effected with a three-point bending device. Femurs were tested in four-point bending and structural properties of peak load and stiffness were obtained from the load-displacement graphs. Specimens were prepared for qualitative analysis under a light microscope and using immunohistochemistry, specimens were analysed for expression of bFGF, IGF-1 and transforming growth factor beta (TGF-beta).

RESULTS

The growth factor-treated groups exhibited larger calluses at 2 and 4 weeks. Four-point bending showed weaker structural properties (stiffness and peak load) at 4 weeks in both growth factor-treated groups. Administration of bFGF or IGF-1 increased the ratio of cartilaginous to mesenchymal tissues in the fracture callus compared with non-treated animals at 2 and 4 weeks. Immunostaining intensity and distribution of both growth factors in the treated groups was greater than the non-treated groups.

CONCLUSION

Exogenous delivery of bFGF or IGF-1 alters the course of fracture healing.

Growth factors regulate expression of osteoblast-associated genes

BACKGROUND

The goal of periodontal regenerative therapies is to reconstruct periodontal tissues such as bone, cementum, and periodontal ligament cells (PDL). The need to establish predictable treatment modalities is important for reconstruction of these tissues. The aim of this study was to determine the effects of a low molecular extract of bovine bone protein (BP) containing bone morphogenetic proteins (BMPs) 2, 3, 4, 6, 7, 12, and 13, alone or in combination with platelet-derived growth factor (PDGF) and/or insulin-like growth factor (IGF) on osteoblast differentiation in vitro.

METHODS

BP, mixed with a collagen matrix, was added to a poly (DL-lactide-co-glycolide) polymer (PLG) and placed at orthotopic sites in the skullcaps of Sprague-Dawleys rats. At day 28, rats were sacrificed for histological analysis. All sites treated with the polymer/BP produced bone while control sites (without BP) showed no bone formation. Having established the biological activity of BP, in vitro studies were initiated using MC3T3-E1 cells, a mouse osteoprogenitor cell line. The ability of BP and other growth factors to alter cell proliferation was determined by Coulter counter, and differentiation was determined by Northern analysis for specific genes.

RESULTS

When compared with cells treated with 2% serum alone, PDGF enhanced cell numbers at 10 and 20 ng/ml; IGF produced no significant effect at these doses; and BP at 10 and 20 microg/ml decreased cell proliferation. Northern analysis revealed that PDGF blocked gene expression of osteopontin (OPN) and osteocalcin (OCN), while BP and IGF promoted gene expression of bone sialoprotein (BSP) and OPN. The combination of BP and IGF enhanced expression of OPN beyond that of either BP or IGF alone. PDGF was able to block the effects of IGF on gene expression, but not those of BP.

CONCLUSIONS

These results indicate that BP, PDGF, and IGF influence cell activity differently, and thus raise the possibility that combining factors may enhance the biological activity of cells.

Gene therapy for osteoinduction

One application of gene therapy that holds great promise is the stimulation of bone formation. Gene therapy offers several potential advantages over other methods of osteoinduction and current research suggests that it may be a feasible treatment option for the orthopedic surgeon in the near future. This article reviews the basic concepts and strategies of gene therapy and evaluates the current research using gene therapy to induce bone formation and enhance healing.

Potential role of insulinlike growth factors in fracture healing

Several lines of evidence suggest that the insulinlike growth factors play a role in fracture healing. They promote cell proliferation and matrix synthesis by chondrocytes and osteoblasts, the two cell types largely responsible for the formation of fracture callus. Circulating levels of insulinlike growth factor I and bone mineral density decrease with increasing age, and administration of insulinlike growth factor I increases bone turnover in patients with low bone mineral density. Insulinlike growth factor I may accelerate the normal healing of intramembranous bone defects, inducing the healing of defects that otherwise would not heal. An important role of insulinlike growth factor I is to mediate many of the actions of growth hormone on the skeleton. Considerable effort has been devoted to testing the effect of growth hormone and, thereby, indirectly that of insulinlike growth factor I on fracture healing. These studies have yielded such disparate results that no general conclusions regarding the effect of growth hormone (or of growth hormone dependent insulinlike growth factor I) on fracture healing currently can be drawn. Additional studies are needed to clarify the role of the insulinlike growth factors in the fracture healing process and to determine how their anabolic actions can be enlisted in the clinical enhancement of fracture healing.

A phase I/II clinical trial to evaluate a combination of recombinant human platelet-derived growth factor-BB and recombinant human insulin-like growth factor-I in patients with periodontal disease

The primary objective of this study was to assess the safety of recombinant human (rh) platelet-derived growth factor-BB (PDGF-BB) and (rh) insulin-like growth factor-I (IGF-I) when applied to periodontal osseous defects in humans; a secondary objective was to begin to accrue data on the therapeutic dose of these growth factors (GFs) required to stimulate periodontal regeneration. Thirty-eight human subjects possessing bilateral osseous periodontal lesions were assigned to one of two treatment groups in a split-mouth design. Following full-thickness flap reflection, test sites received local application of the therapeutic drug delivered in coded syringes by a "masked" investigator. Two dose levels were tested, 50 micrograms/ml each of rhPDGF-BB and rhIGF-I in a gel vehicle (LD-PDGF/IGF-I) and 150 micrograms/ml each of rhPDGF-BB and rhIGF-I plus vehicle (HD-PDGF/IGF-I). Control treatment consisted of either conventional periodontal flap surgery or surgery plus vehicle. Safety analyses included physical examination, hematology, serum chemistry, urinalysis, antibody titers, and radiographic evaluation of bony changes. The primary therapeutic assessment was bone fill measured at re-entry 6 to 9 months after treatment. No local or systemic safety issues were found as a result of GF administration. No patients developed antibodies to the rhGF proteins. In subjects treated with LD-PDGF/IGF-I, there were no enhancements in periodontal regeneration compared to controls. However, in patients treated with HD-PDGF/IGF-I, statistically significant increases in alveolar bone formation were noted as measured by surgical re-entry 9 months following drug delivery (P < 0.05). This corresponded to an increase of 2.08 mm of new vertical bone height and 42.3% osseous defect fill in the HD-PDGF/IGF-I subjects versus only 0.75 mm and 18.5% gains in new bone height and osseous fill, respectively, in the controls. Furcation lesions, although limited in number, responded most favorably to treatment, with 2.8 mm horizontal osseous fill. The results from this study suggest that the local application of rhPDGF-BB and rhIGF-I to periodontal lesions is safe at the dose levels studied. LD-PDGF/IGF-I did not elicit increased defect fill compared to the control; however, HD-PDGF/IGF-I resulted in a significant promotion in bone regeneration. Additional studies are warranted to more fully characterize the effects of PDGF/IGF-I on periodontal regeneration in humans.

Non-coordinate control of bone formation displayed by growth factor combinations with IGF-I

Polypeptide growth factors (GFs) promote osteogenesis by enhancing the mitogenesis, migration, and matrix synthesis of osteoblasts. Most previous investigators have evaluated only the effects of single GFs on these parameters. Studies on single GFs might overlook large biological responses comparable with those documented in the cell cycle literature when GFs are used in combinations that interact synergistically. In this study, we screened for synergistic interactions between IGF-I and three additional GFs (PDGF-BB, TGF-beta 1, and bFGF) on the regulation of bone growth and differentiation. Fetal bovine osteoblasts were assessed for osteoblast mitogenesis, collagenous and non-collagenous protein synthesis, and alkaline phosphatase activity (ALP). Our results show synergistic interactions between IGF-I and the other GFs on osteoblast mitogenic activity and protein synthesis. In contrast to synergistic mitogenic and protein synthesis. In contrast to synergistic mitogenic and protein synthesis effects, IGF-I failed to increase ALP activity when combined with TGF-beta 1, PDGF-BB, and bFGF in bovine osteoblast-like cells.

Platelet derived growth factor stimulates chondrocyte proliferation but prevents endochondral maturation

Platelet-derived growth factor (PDGF) is a cytokine released by platelets at sites of injury to promote mesenchymal cell proliferation. Since many bone wounds heal by endochondral bone formation, we examined the response of chondrocytes in the endochondral lineage to PDGF. Confluent cultures of rat costochondral resting zone cartilage cells were incubated with 0-300 ng/mL PDGF-BB for 24 h to determine whether dose-dependent changes in cell proliferation (cell number and [3H]-thymidine incorporation), alkaline phosphatase specific activity, [35S]-sulfate incorporation, or [3H]-proline incorporation into collagenase-digestible protein (CDP) or noncollagenase-digestible protein (NCP), could be observed. Long-term effects of PDGF were assessed in confluent cultures treated for 1, 2, 4, 6, 8, or 10 d with 37.5 or 150 ng/mL PDGF-BB. To determine whether PDGF-BB could induce resting zone chondrocytes to change maturation state to a growth zone chondrocyte phenotype, confluent resting zone cell cultures were treated for 1, 2, 3, or 5 d with 37.5 or 150 ng/ml PDGF-BB and then challenged for an additional 24 h with 1,25-(OH)2D3. PDGF-BB caused a dose-dependent increase in cell number and [3H]-thymidine incorporation at 24 h. The proliferative effect of the cytokine decreased with time. PDGF-BB had no effect on alkaline phosphatase at 24 h, but at later times, the cytokine prevented the normal increase in enzyme activity seen in post-confluent cultures. This effect was primarily on the cells and not on the matrix. PDGF-BB stimulated [35S]-sulfate incorporation at all times examined, but had no effect on [3H]-proline incorporation into either the CDP or NCP pools. Thus, percent collagen production was not changed. Treatment of the cells for up to 5 d with PDGF-BB failed to elicit a 1,25-(OH)2D3 responsive phenotype typical of rat costochondral growth zone cartilage cells. These results show that committed chondrocytes can respond to PDGF-BB with increased proliferation. The effect of the cytokine is to enhance cartilage matrix production, but at the same time to prevent progression of the cells along the endochondral maturation pathway.

Comparative effects of platelet-derived growth factor-BB and insulin-like growth factor-I, individually and in combination, on periodontal regeneration in Macaca fascicularis

Platelet-derived growth factor (PDGF) and insulin-like growth factor I (IGF-I) in combination have previously been shown to enhance periodontal regeneration. The objective of this study was to further characterize the biological effects of this combination of growth factors in non-human primates and compare the effects to those of each growth factor individually. Ligature-induced periodontitis was initiated in 10 cynomolgus monkeys. After periodontal lesions were established, surgery was performed, and either a methylcellulose gel vehicle or vehicle containing 10 micrograms each of either PDGF-BB, IGF-I or both PDGF-BB and IGF-I was applied to exposed root surfaces. Biopsies were taken 4 and 12 wk after treatment and the extent of periodontal regeneration was assessed by histomorphometry. At both 4 and 12 wk vehicle-treated lesions generally revealed minimal osseous defect fill (ODF) (8.5 +/- 2.1% and 14.5 +/- 5.7%, respectively) and new attachment (NA) (34.1 +/- 5.2% and 26.6 +/- 10.5%, respectively). IGF-I treatment did not significantly alter healing compared to vehicle in any parameter at both 4 and 12 wk. PDGF-BB-treated sites exhibited significant (p < 0.05) regeneration of NA (69.6 + 12.0%) at 12 wk; trends for PDGF-BB treatment effect were also observed in other parameters at 4 and 12 wk, although these increases were not statistically significant. Treatment with PDGF-BB/IGF-I resulted in 21.6 +/- 5.1% and 42.5 +/- 8.3% ODF at 4 and 12 wk, respectively, and 64.1 +/- 7.7% and 74.6 +/- 7.4% NA at 4 and 12 wk, respectively (all significantly greater than vehicle, p < 0.05). The results from this study demonstrated that: 1) IGF-I alone at the dose tested did not significantly alter periodontal wound healing; 2) PDGF-BB alone significantly stimulated NA, with trends of effect on other parameters; and 3) the PDGF-BB/IGF-I combination resulted in significant increases in NA and ODF above vehicle at both 4 and 12 wk.