The Kuhn lab’s research mission is to bring regenerative and anti-cancer biomaterials technologies closer to patient use through pre-clinical testing and research.

Bone morphogenetic protein-2 (BMP-2) is now used clinically in patients to enhance bone regeneration during spinal fusion, fracture healing and dental bone implant procedures. While BMP-2 has been demonstrated to significantly enhance bone repair, the complication profile, likely related to the supraphysiologic dose of BMP-2 delivered in its current formulation, has lead to safety concerns and has limited its clinical use. Reported complications include early inflammatory reaction and osteolysis, ectopic bone formation sometimes leading to compression of neural elements, seroma formation and a possible increase in the risk of malignancy. Thus, there is a need to refine the delivery and improve the efficacy of BMP-2 so that it can be delivered in lower doses with less risk of complications. The Kuhn lab is addressing the BMP-2 problem by developing a better delivery system. We are designing and testing polyelectrolyte multi-layer coated scaffolds to achieve controlled delivery of BMP-2 in conjunction with other growth factors to regenerate bone for dental and orthopaedic applications.

Many older adults have a compromised ability to repair fractures or replace lost bone. It has been suggested that a decrease in numbers of osteogenic progenitor cells in elderly patients contributes to the decrease in skeletal bone formation and rate of fracture repair observed with aging and in osteoporotic patients. Further, mesenchymal stem cells in post-menopausal women have a lower growth rate and are deficient in their ability to differentiate along the osteogenic lineage. The problem of reduced bone formation in the aging mammalian body remains unsolved. While the biology of aging is complex, strategies that improve the number and function of osteoprogenitor cells in elderly patients is likely to contribute to increased bone formation; thus that is our research focus.

Fibroblast growth factor-2 (FGF-2) regulates the proliferation and differentiation of many cell types, including osteoblasts, and is stored in the extracellular matrix. In mice, FGF receptor 2 loss of function results in progressive osteopenia and decreased bone formation rates, suggesting a role for FGF-2 in maintaining bone mass, especially with aging. Several studies by our co-investigator Dr. Hurley at our institute and others have shown that FGF-2 is a potent stimulator of preosteoblast replication. FGF-2 and platelet-derived growth factor (PDGF) were observed to be the only growth factors that increased mineralized nodule formation in calvarial osteoblasts from aged rats, and FGF-2 was twice as potent as PDGF. Whereas chronic exposure to FGF-2 can also stimulate osteoclast formation, and increase bone resorption, intermittent FGF-2 treatment stimulates bone formation in vitro and in vivo. FGF-2 has great potential to increase the activity and function of osteoprogenitor cells in elderly patients and thus we are developing biomaterial scaffolds that can delivery it locally, in combination with BMP-2 to stimulate more rapid bone healing.

FGF-2 and BMP-2 have synergistic bone enhancing effects resulting in increased bone volume as a function of dose in ectopic sites and in rat calvaria parietal bones, but the combination has been primarily testing in young animals, not old. Our current research thus studies effects of these two factors in old animals. Too much FGF-2 has been shown to reduce the amount of in vivo bone formation with BMP-2 because it can maintain cells in an undifferentiated state too long thus dose optimization is mandatory. FGF-2 enhances BMP-2 stimulated bone formation and may be the solution for reducing the dose and complications associated with BMP-2 use.

We have a major research effort investigating polyelectrolyte multi-layer (PEM) technology applied to bone substitute materials to enable sequential delivery of FGF-2 and BMP-2. The PEM technology is a thin film deposition technique that forms nanoreservoirs for drug delivery and antimicrobial protection. Bioactive proteins can be directly integrated into PEM coatings in the absence of covalent bonding and thus keep secondary structures close to their native form. The growth factors are released through cell-based PEM degradation, rather than by the undesirable non-cell initiated polymer hydrolysis which leads to burst release and may degrade the growth factor or initiate inflammation. Our work, and that of others, indicates that sequential delivery of FGF-2 followed by BMP-2, rather than co-delivery of FGF-2/BMP-2, produces the maximal osteogenic effect. Our work in this area is currently funded by the NIH NIDCR and has been presented at the Society For Biomaterials and Orthopaedic Research Society annual meetings.

Recent publications in this area include:

L Kuhn*, G Ou, L Charles, M Hurley, C Rodner and G Gronowicz, Fibroblast growth factor-2 and Bone Morphogenetic Protein-2 Have a Synergistic Stimulatory Effect on Bone Formation in Cell Cultures from Aging Mouse and Human Bone, J Gerontol A Biol Sci Med Sci. 2013 Oct;68(10):1170-80. doi: 10.1093/gerona/glt018.

L Xiao, D Ueno, S Catros, L Charles, L Kuhn, MM Hurley. Exported 18-kDa Isoform of Fibroblast Growth Factor-2 Improved Bone Regeneration in Critical Size Mice Calvarial Defects. Endocrinology, 2014 Mar;155(3):965-74. doi: 10.1210/en.2013-1919.