Plain Language Summary of Work
This research centered on investigating the effects of the local application of a known growth factor, recombinant-human platelet-derived growth factor BB (rhPDGF-BB), on compromised bone healing in diabetic rats. Our study revealed for the first time that the local application of rhPDGF-BB around the fracture site increased the number of callus cells in diabetic rats, which increases the mechanical strength of bone 8 weeks post-fracture. We demonstrated for the first time in the literature that local rhPDGF-BB treatment significantly enhances bone fracture healing in the presence of diabetes mellitus. Furthermore, our findings indicate that local rhPDGF-BB treatment is highly targeted and therefore unlikely to have significant off-target effects (side effects).
We further investigated the histology of fractured femora 12 weeks post-fracture to identify the long-term effects of local rhPDGF on bone formation. If the rats were treated with the high dose rhPDGF-BB (75 µg) an increased bone formation was observed at the fracture site. This support the hypothesis that local treatment of rhPDGF-BB ultimately leads to more bone formation. Our findings showed a dose-dependent effect. As such, our study provides a blueprint for determining which dose of rhPDGF-BB should be used locally to enhance early and late stages of bone fracture healing in the presence of diabetes mellitus as well as identifying other possible applications for rhPDGF in bone metabolism and repair.
Resulting Publication
Ph.D. Dissertation:
- Rutgers University (Formerly: University of Medicine and Dentistry of New Jersey). Newark, NJ, USA. Biomedical Engineering, April 2008 Ph.D. Dissertation: The Role of Local Growth Factor Delivery on BoneFracture Healing: Recombinant Human Platelet Derived Growth Factor and Insulin.
Journal Articles:
- Al-Zube, Loay; Breitbart, Eric A.; O’Connor, J. Patrick; Parsons, J. Russell; Bradica, Gino; Hart, Charles E.; Lin, Sheldon S. Recombinant Human Platelet-Derived Growth Factor BB (rhPDGF-BB) and Beta-Tricalcium Phosphate/Collagen Matrix Enhance Fracture Healing in a Diabetic Rat Model. Journal of Orthopaedic Research. 2009 Aug;27(8):1074-81.
Technical Summary of Work
This work involved evaluating the dose-dependent effect of rhPDGF-BB delivered in a b-TCP/Type I bovine collagen matrix on fracture healing in the diabetic BB Wistar rat model. Low (22 µg) and high (75 µg) doses of recombinant human PDGF-BB (rhPDGF-BB) were applied directly to femur fracture sites in BB Wistar diabetic rats that were then compared to untreated or vehicle-treated animals. Using diabetic-prone BB Wistar rats that had become diabetic and that were treated with insulin implants to maintain blood glucose levels between 300 and 500 mg/dl, we demonstrated that fracture callus cell proliferation was significantly higher in the diabetic rats treated with rhPDGF-BB, indicating that rhPDGF-BB treatment can ameliorate the deficit in callus cell proliferation observed in diabetic animals. Torsional mechanical testing also indicated that low dose rhPDGF-BB treatment (22 µg) significantly increased fracture callus peak torque (p<0.05) at 8 weeks after healing as compared to controls, supporting the hypothesis that rhPDGF-BB induced fracture callus cell proliferation and led to a subsequent increase in the structural properties of the callus in the diabetic rat.
We also prepared and analyzed histological sections of fractured femora. While histomorphometric analysis at 12 weeks post-fracture showed no significant difference in callus area, a significant increase in percent mineralized area was observed in the calluses treated with high dose rhPDGF-BB as compared to low dose rhPDGF-BB or control groups. These data suggest that rhPDGF-BB treatment may have a long-term effect that enhances the later stages of fracture healing in diabetic animals. High dose rhPDGF-BB treatment significantly increased early callus cell proliferation but had no effect later on callus mechanical properties. In contrast, low dose rhPDGF-BB increased early callus cell proliferation and later on callus biomechanical properties. We interpret these data to indicate that in this model, high dose rhPDGF-BB treatment may delay differentiation of mesenchymal cells into chondrocytes and osteoblasts by extending the proliferative phase.
Summary of the Significance of the Work
Twenty million Americans have diabetes mellitus (diabetes) and 500,000 to 1,000,000 new cases are diagnosed each year. The prevalence of diabetes is estimated to exceed 30 million patients in the United States by 2010 (currently 30.2 million patients, National Diabetes Statistics Report, 2017). The association between diabetes and impaired osseous healing has been documented in clinical and experimental settings. In 2012, the US faced over $ 245 billion in direct and indirect medical costs as a result of diabetes (National Diabetes Statistics Report, 2017), and therefore any research that helps to mitigate health outcomes associated with diabetes is very valuable to the US in particular. Our research is especially valuable because we demonstrated that local delivery of growth factors (such as rhPDGF-BB), which had previously not been widely used as a therapeutic option due to technology/carrier limitations, can be utilized to significantly reverse compromised bone fracture healing in diabetes patients. We also demonstrated that local rhPDGF treatment has dose dependent effects on early and late stages of fracture healing in diabetic animals. Overall our study promotes the use of biological growth factors and proteins locally as a therapeutic option to reverse compromised fracture healing in diabetes patients, and strongly supports continued research in the use of rhPDGF-BB delivered locally via suitable possible drug-delivery systems to significantly enhance fracture healing and bone regeneration. Further research in developing and validating biomaterials as carriers for local, long-term, and sustainable release of rhPDGF-BB is relevant to further enhance bone fracture healing, which will help further reduce healthcare costs.
Summary of the Implementation/Influence of the Work
BioMimetic Therapeutics, Inc. (Franklin, TN) supported my research. Based on my pre-clinical research findings, BioMimetic Therapeutics conducted clinical trials. The clinical trials resulted in acquiring BioMimetic Therapeutics by Wright Medical. A clinical product named AUGMENT® BONE GRAFT was developed. Augment ® Bone Graft combines recombinant human platelet-derived growth factor B homodimer (rhPDGF-BB) with a bioresorbable synthetic bonematrix (beta-tricalciumphosphate or β-TCP).
My paper has been widely cited, with a total of 81 citations. For specific citation details, please refer to my google scholar profile. A few notable citations include:
- I. Caplan and D. Correa. 2011. “PDGF in bone formation and regeneration: New insights into a novel mechanism involving MSCs”. Journal of Orthopaedic Research. 2011 December; 29(12):1795-1803. – This is an NIH-funded paper that explains how PDGF functions as a powerful therapeutic agent for bone formation and repair. These researchers from Case Western Reserve University (OH, USA) cited my paper and specifically mentioned our study in the context of demonstrating that exogenously delivered PDGF‐BB improved both the rate of bone formation and the bone volume spanning the fracture in rodent models in the presence of diabetes.
- Jäger et al. 2011. “Bridging the gap: Bone marrow aspiration concentrate reduces autologous bone grafting in osseous defects”. Journal of Orthopaedic Research. 2011 February; 29(2):173-180. – These researchers from Heinrich-Heine University (Duesseldorf, Germany) ran a study to investigate the potency of bone marrow aspiration concentrate (BMAC) to augment bone grafting and support bone healing. They cited my paper as their 1st reference. They cited my paper to demonstrated that different orthobiologics such as platelet derived growth factor (PDGF) can promote healing in critical sized bone defects and even in the healing of avascular osteonecrosis.
- K Hee et al. 2011. “Augmentation of a Rotator Cuff Suture Repair Using rhPDGF-BB and a Type I Bovine Collagen Matrix in an Ovine Model”. The American Journal of Sports Medicine. 2011; 39(8): 1630-1639. – These researchers from Colorado State University (USA) investigated implanting an interpositional graft consisting of rhPDGF-BB and a type I collagen matrix in an ovine model of rotator cuff repair. They cited my paper to demonstrated that exogenous addition of rhPDGF-BB to animal models of bone injury has shown beneficial effects on tissue repair in vivo, suggesting that augmentation of rotator cuff repair with rhPDGF-BB may lead to improved tendon repair and tendon-to-bone integration