Samuel E. Lynch

Role of Growth Factors in Cutaneous Wound Healing: A Review

The well-orchestrated, complex series of events resulting in the repair of cutaneous wounds are, at least in part, regulated by polypeptide growth factors. This review provides a detailed overview of the known functions, interactions, and mechanisms of action of growth factors in the context of the overall repair process in cutaneous wounds. An overview of the cellular and molecular events involved in soft tissue repair is initially presented, followed by a review of widely studied growth factors and a discussion of commonly utilized preclinical animal models. The article concludes with a summary of the preliminary results from human clinical trials evaluating the effects of growth factors in the healing of chronic skin ulcers. Throughout, the interactions among the growth factors in the wound-healing process are emphasized.

Gel Matrix Vehicles for Growth Factor Application in Nerve Gap Injuries Repaired with Tubes: A Comparison of Biomatrix, Collagen, and Methylcellulose

The repair of nerve gap injuries with tubular nerve guides has been used extensively as an in vivo test model in identifying substances which may enhance nerve regeneration. The model has also been used clinical nerve repair. The objective of this study was to compare three different gel matrix-forming materials as potential vehicles for growth factors in this system. The vehicles included a laminin containing extracellular matrix preparation (Biomatrix), collagen, and a 2% methylcellulose gel. The growth factor test substance consisted of a combination of platelet-derived growth factor BB (PDGF-BB) and insulin-like growth factor I (IGF-I). An 8-mm gap in rat sciatic nerve was repaired with a silicone tube containing each of the vehicles alone or with a combination of each vehicle plus PDGF-BB and IGF-I. At 4 weeks after injury, the application of the growth factor combination significantly stimulated axonal regeneration when applied in methylcellulose or collagen, but not in Biomatrix. A similar trend was present between the vehicle control groups. By 8 weeks after injury, nerves repaired with methylcellulose as a vehicle had significantly greater conduction velocity than either collagen or Biomatrix. It was concluded that a 2% methylcellulose gel was the best of the three matrices tested, both in its effects on nerve regeneration and flexibility of formulation.

Platelet-derived growth factor applications in periodontal and peri-implant bone regeneration

Introduction: Achieving successful tissue regeneration following traditional therapeutic protocols, combining bone grafts and barrier membranes, may be challenging in certain clinical scenarios. A deeper understanding of periodontal and peri-implant wound healing and recent advances in the field of tissue engineering have provided clinicians with novel means to obtain predictable clinical outcomes. The use of growth factors such as recombinant human platelet-derived growth factor-BB (rhPDGF) with biocompatible matrices to promote tissue regeneration represents a promising approach in the disciplines of periodontology and implantology. Areas covered: This review covers the basic principles of bone and periodontal regeneration, and provides an overview of the biology of PDGF and its potential to predictably and reproducibly promote bone regeneration in regular clinical practice. The results of preclinical and clinical human studies evaluating the effectiveness of growth-factor-enhanced matrices are analyzed and discussed. Expert opinion: Current available evidence supports the use of rhPDGF-enhanced matrices to promote periodontal and peri-implant bone regeneration.

Nanofibrous Scaffolds Incorporating PDGF-BB Microspheres Induce Chemokine Expression and Tissue Neogenesis In Vivo

Platelet-derived growth factor (PDGF) exerts multiple cellular effects that stimulate wound repair in multiple tissues. However, a major obstacle for its successful clinical application is the delivery system, which ultimately controls the in vivo release rate of PDGF. Polylactic-co-glycolic acid (PLGA) microspheres (MS) in nanofibrous scaffolds (NFS) have been shown to control the release of rhPDGF-BB in vitro. In order to investigate the effects of rhPDGF-BB release from MS in NFS on gene expression and enhancement of soft tissue engineering, rhPDGF-BB was incorporated into differing molecular weight (MW) polymeric MS. By controlling the MW of the MS over a range of 6.5 KDa–64 KDa, release rates of PDGF can be regulated over periods of weeks to months in vitro. The NFS-MS scaffolds were divided into multiple groups based on MS release characteristics and PDGF concentration ranging from 2.5–25.0 µg and evaluated in vivo in a soft tissue wound repair model in the dorsa of rats. At 3, 7, 14 and 21 days post-implantation, the scaffold implants were harvested followed by assessments of cell penetration, vasculogenesis and tissue neogenesis. Gene expression profiles using cDNA microarrays were performed on the PDGF-releasing NFS. The percentage of tissue invasion into MS-containing NFS at 7 days was higher in the PDGF groups when compared to controls. Blood vessel number in the HMW groups containing either 2.5 or 25 µg PDGF was increased above those of other groups at 7d (p<0.01). Results from cDNA array showed that PDGF strongly enhanced in vivo gene expression of the CXC chemokine family members such as CXCL1, CXCL2 and CXCL5. Thus, sustained release of rhPDGF-BB, controlled by slow-releasing MS associated with the NFS delivery system, enhanced cell migration and angiogenesis in vivo, and may be related to an induced expression of chemokine-related genes. This approach offers a technology to accurately control growth factor release to promote soft tissue engineering in vivo.

Platelet-Derived Growth Factor Promotes Periodontal Regeneration in Localized Osseous Defects: 36-Month Extension Results From a Randomized, Controlled, Double-Masked Clinical Trial

BACKGROUND Recombinant human platelet-derived growth factor (rhPDGF) is safe and effective for the treatment of periodontal defects in short-term studies up to 6 months in duration. We now provide results from a 36-month extension study of a multicenter, randomized, controlled clinical trial evaluating the effect and long-term stability of PDGF-BB treatment in patients with localized severe periodontal osseous defects. METHODS A total of 135 participants were enrolled from six clinical centers for an extension trial. Eighty-three individuals completed the study at 36 months and were included in the analysis. The study investigated the local application of β-tricalcium phosphate scaffold matrix with or without two different dose levels of PDGF (0.3 or 1.0 mg/mL PDGF-BB) in patients possessing one localized periodontal osseous defect. Composite analysis for clinical and radiographic evidence of treatment success was defined as percentage of cases with clinical attachment level (CAL) ≥2.7 mm and linear bone growth (LBG) ≥1.1 mm. RESULTS The participants exceeding this composite outcome benchmark in the 0.3 mg/mL rhPDGF-BB group went from 62.2% at 12 months, 75.9% at 24 months, to 87.0% at 36 months compared with 39.5%, 48.3%, and 53.8%, respectively, in the scaffold control group at these same time points (P <0.05). Although there were no significant increases in CAL and LBG at 36 months among all groups, there were continued increases in CAL gain, LBG, and percentage bone fill over time, suggesting overall stability of the regenerative response. CONCLUSION PDGF-BB in a synthetic scaffold matrix promotes long-term stable clinical and radiographic improvements as measured by composite outcomes for CAL gain and LBG for patients possessing localized periodontal defects ( ClinicalTrials.gov no. CT01530126).

Methods for Evaluation of Regenerative Procedures

A multitude of new procedures and materials are being tested for their ability to promote periodontal wound healing. This review provides an overview of the most wellaccepted methods for evaluating periodontal wound healing procedures/materials. Topics discussed include appropriate patient selection, general principles in non-surgical and surgical therapy as they relate to wound healing trials, clinical soft and hard tissue measurements which are generally obtained, an overview of radiographic assessments, and a discussion of the methods and role of histological evaluations in clinical trials. The advantages and disadvantages of the various methodologies are presented. The review concludes with the potential endpoints which can be used in periodontal wound healing studies. J Periodontol 1992; 63:1085-1092.

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

The combination of insulin‐like growth factor‐I and platelet‐derived growth factor‐BB has previously been shown to stimulate healing of soft tissue wounds and the formation of bone and ligament around teeth. The purpose of the present study was to evaluate the effects of platelet‐derived growth factor‐BB and insulin‐like growth factor‐I individually and in combination on the healing of osseous wounds. Four standardized cortical wounds were created in each tibia of 11 adult Yucatan miniature pigs. The wounds in one tibia per animal were treated with either purified recombinant human insulin‐like growth factor‐I, platelet‐derived growth factor‐BB, or both in a methylcellulose gel. The wounds in each contralateral tibia received placebo gel alone. Coded serial sections of each wound were evaluated by computer‐aided histomorphometry 21 days after surgery. The area and perimeter of the newly formed mineralized callus, the thickness of the total callus, and the percentage of mineralized tissue within the callus were significantly increased compared with the values of matched controls only in wounds treated with a combination of insulin‐like growth factor‐I and platelet‐derived growth factor‐BB. No significant differences in the measured parameters of callus formation were found in wounds treated with either insulin‐like growth factor‐I or platelet‐derived growth factor‐BB alone. Cartilage was present only in sites treated with insulin‐like growth factor‐I alone. These results suggest that the combination of platelet‐derived growth factor‐BB and insulin‐like growth factor‐I stimulates bone formation in wounds in long bones of adult animals and that these growth factors act via different pathways during the repair process.

Augment bone graft products compare favorably with autologous bone graft in an ovine model of lumbar interbody spine fusion.

Study Design. This study was designed to determine whether Augment Bone Graft (Augment, Biomimetic Therapeutics, Inc., Franklin, TN) and Augment Injectable Bone Graft (Augment Injectable, Biomimetic Therapeutics, Inc., Franklin, TN), 2 combination devices comprising recombinant human platelet-derived growth factor-BB and &bgr;-tricalcium phosphate–containing matrices, promote bone bridging in an ovine model of lumbar spine fusion. Autologous bone graft (autograft) was used as a positive control. Objective. The purpose of this study was to determine the ability of Augment products to promote fusion of the L2–L3 and L4–L5 vertebral bodies in an ovine model. Summary of Background Data. In interbody spine fusion, the intervertebral disc is removed and a spacer is inserted for support and to facilitate bone growth. The fusion is commonly enhanced with grafts. Autograft is the “gold standard” but it has limitations including availability and donor-site morbidity. Synthetic graft substitutes eliminate these complications. Augment products are combination devices including recombinant human platelet-derived growth factor-BB, a well-characterized chemotactic, mitogenic, and proangiogenic protein essential in wound and bone healing. Methods. Twenty-two sheep received an uninstrumented, double-level, interbody lumbar spinal fusion procedure using a polyetheretherketone spacer, which was either empty or packed with iliac crest autograft, Augment or Augment Injectable. The same treatment was used at both levels. Animals were 24 weeks after surgery, and fusion was assessed by micro-computed tomography (micro-CT) and histology. Results. Micro-CT and histologic assessment of fusion revealed that empty controls had significantly lower fusion rates. No differences were detected among autografts, Augment, and Augment Injectable–treated specimens. Residual &bgr;-tricalcium phosphate particles embedded in the newly formed bone were visible in Augment- and Augment Injectable–treated specimens. Conclusion. Augment-treated specimens had the highest fusion scores. Treatment with either of the Augment products significantly promoted interbody spine fusion compared with empty spacers and was equivalent to autograft-induced fusion. No adverse events were noted.

Growth factors and craniofacial surgery

Abstract The specialty of craniofacial surgery is broad and includes trauma, aesthetics, reconstruction of congenital deformities, and regeneration of tissues. Moreover, craniofacial surgery deals with a diverse range of tissues including both “soft” and “hard” tissues. Technological advances in materials and biological sciences and improved surgical techniques have remarkably improved clinical outcomes. The quest to raise the bar for patient care continues to inspire advances for predictable biological regeneration of soft and hard tissues. As a consequence of this quest for advancement, a wide spectrum of biologicals is becoming available to surgeons. Is the use of recombinant DNA engineered biologicals daring? Sensible? Logical? Timely? Safe? It is crucial for the practicing craniofacial surgeon to take a step back periodically and carefully review the biological factors that have the potential for dramatically altering the discipline of craniofacial surgery. With this emphasis, the coauthors of this article will focus on growth factor technology underscoring bone tissue regeneration. As the 21st-century matures, recombinant human biologicals will have an overwhelming impact on the practice of craniofacial surgery.

Combination of platelet-derived growth factor-BB and insulin-like growth factor-I is more effective than platelet-derived growth factor-BB alone in stimulating complete healing of full-thickness wounds in "older" diabetic mice.

Platelet‐derived growth factor and insulin‐like growth factor‐I have been shown to interact synergistically to enhance repair of skin wounds in normal healing swine. Platelet‐derived growth factor alone has shown promise in treating human chronic ulcers. The objective of this study was to compare the wound healing effects of platelet‐derived growth factor‐BB alone with those of a combination of platelet‐derived growth factor‐BB and insulin‐like growth factor‐I in an improved model with the use of “older” animals with diabetes. Older diabetic (db/db) mice (>15 weeks of age) have less elevated insulin levels compared with young db/db mice. The serum insulin levels in the older animals is 1.0 to 2.5 times that of the nondiabetic animals, a similar increase to that which occurs in human patients with type II diabetes. Healing was evaluated in two studies involving a total of 104 animals. Treatment groups included the following: 4.0 µg/cm2 of platelet‐derived growth factor‐BB, 40.0 µg/cm2 of platelet‐derived growth factor‐BB, 4.0 µg/cm2 of both platelet‐derived growth factor‐BB and insulin‐like growth factor‐I or vehicle. All growth factors were applied topically in a methylcellulose vehicle to full‐thickness wounds every other day for 24 days. Efficacy end points were median and mean time to complete healing and rate of wound closure. The median time to complete healing for animals receiving the platelet‐derived growth factor‐BB/insulin‐like growth factor‐I combination was 38% and 33% faster (p < 0.001) than animals receiving 4.0 µg/cm2 and 40.0 µg/cm2 of platelet‐derived growth factor‐BB, respectively. The mean time to complete healing for platelet‐derived growth factor/insulin‐like growth factor‐I treated animals was 31% and 29% faster (p < 0.001) than 4.0 µg/cm2 and 40.0 µg/cm2 platelet‐derived growth factor‐BB treated animals, respectively. Wounds treated with 4.0 µg/cm2 platelet‐derived growth factor‐BB/insulin‐like growth factor‐I healed, on average, in 22 days compared with 31 days for 40.0 µg/cm2 platelet‐derived growth factor‐BB alone and 38 days for vehicle. Also, platelet‐derived growth factor‐BB/insulin‐like growth factor‐I significantly improved the rate of wound closure throughout the duration of the studies compared with either dose of platelet‐derived growth factor‐BB alone (p < 0.005) or vehicle (p < 0.001). In conclusion, the data show that the combination of platelet‐derived growth factor‐BB and insulin‐like growth factor‐I is more effective than platelet‐derived growth factor‐BB alone at the doses tested or vehicle treatment in stimulating cutaneous wound healing in older, diabetic mice.