Comparing variable-length polyglutamate domains to anchor an osteoinductive collagen-mimetic peptide to diverse bone grafting materials.
OBJECTIVE
Allografts, xenografts, and alloplasts are commonly used in craniofacial medicine as alternatives to autogenous bone grafts; however, these materials lack important bone-inducing proteins. A method for enhancing the osteoinductive potential of these commercially available materials would provide a major clinical advance. In this study, a calcium-binding domain, polyglutamate, was added to an osteoinductive peptide derived from collagen type I, Asp-Gly-Glu-Ala (DGEA), to anchor the peptide onto four different materials: freeze-dried bone allograft (FDBA); anorganic bovine bone (ABB); β-tricalcium phosphate (β-TCP); and a calcium sulfate bone cement (CaSO4). The authors also examined whether peptide binding and retention could be tuned by altering the number of glutamate residues within the polyglutamate domain.


METHODS
DGEA or DGEA modified with diglutamate (E2DGEA), tetraglutamate (E4DGEA), or heptaglutamate (E7DGEA) were evaluated for binding and release to the grafting materials. Peptides were conjugated with a fluorescein isothiocyanate (FITC) tag to allow monitoring by fluorescent microscopy or through measurements of solution fluorescence. In vivo retention was evaluated by implanting graft materials coated with FITC-peptides into rat subcutaneous pouches.


RESULTS
Significantly more peptide was loaded onto the four graft materials as the number of glutamates increased, with E7DGEA exhibiting the greatest binding. There was also significantly greater retention of peptides with longer glutamate domains following a 3-day incubation with agitation. Importantly, E7DGEA peptides remained on the grafts after a 2-month implantation into skin pouches, a sufficient interval to influence bony healing.


CONCLUSIONS
Variable-length polyglutamate domains can be added to osteoinductive peptides to control the amount of peptide bound and rate of peptide released. The lack of methods for tunable coupling of biologics to commercial graft sources has been a major barrier toward developing materials that approach the clinical efficacy of autogenous bone. Modification of osteoinductive factors with polyglutamate domains constitutes a technically straightforward and cost-effective strategy for enhancing osteoinductivity of diverse graft products.
Jennifer L
JL
Bain
Bonnie K
BK
Culpepper
Michael S
MS
Reddy
Susan L
SL
Bellis
D064591:Allografts / Q000737:chemistry; D000818:Animals; D040761:Biomimetic Materials / Q000737:chemistry*; D001843:Bone Cements / Q000737:chemistry; D018786:Bone Substitutes / Q000737:chemistry*; D016025:Bone Transplantation / Q000379:methods; D001842:Bone and Bones / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry; D002133:Calcium Sulfate / Q000737:chemistry; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002417:Cattle; D024042:Collagen Type I / Q000737:chemistry; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D005456:Fluorescent Dyes; D005612:Freeze Drying; D064593:Heterografts / Q000737:chemistry; D008297:Male; D009842:Oligopeptides / Q000737:chemistry*; D010012:Osteogenesis / Q000502:physiology*; D011099:Polyglutamic Acid / Q000737:chemistry*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D040521:Subcutaneous Tissue / Q000601:surgery
D001843:Bone Cements; D018786:Bone Substitutes; D002130:Calcium Phosphates; D002135:Calcium-Binding Proteins; D024042:Collagen Type I; D005456:Fluorescent Dyes; D009842:Oligopeptides; C113781:aspartyl-glycyl-glutamyl-alanine; C485817:beta-tricalcium phosphate; D011099:Polyglutamic Acid; D016650:Fluorescein-5-isothiocyanate; D002133:Calcium Sulfate