title: Peri-implant reactivity and osteoinductive potential of immobilized rhBMP-2 on titanium carriers.
abstract: Recombinant human BMP-2 (rhBMP-2) was immobilized non-covalently and covalently as a monolayer on plasma vapour deposited (PVD) porous commercially pure titanium surfaces in amounts of 5-8 μg cm(-2), providing a ca. 10-fold increase vs. previously reported values. Dissociation of the immobilized [125I]rhBMP-2 from the surface occurred in a two-phase exponential decay: a first rapid phase (ca. 15% of immobilized BMP-2) with a half-life of 1-2 days and a second slow sustained release phase (ca. 85% of immobilized BMP-2) with a half-life of 40-60 days. Dissociation rate constants of sustained release of k(-1)=1.3-1.9 x 10(-7)s(-1) were determined, allowing an estimation of the binding constants (K(A)) for the adsorbed rhBMP-2 monolayer, to be around 10(12) M(-1). The rhBMP-2-coated surfaces showed a high level of biological activity, as demonstrated by in vitro epifluorescence tests for alkaline phosphatase with MC3T3-E1 cells and in vivo experiments. In vivo osteoinductivity of rhBMP-2-coated implants was investigated in a gap-healing model in the trabecular bone of the distal femur condylus of sheep. Healing occurred without inflammation or capsule formation. The calculated concentration of released rhBMP-2 in the 1mm gap ranged from 20 to 98 nM--well above the half-maximal response concentration (K(0.5)) for inducing alkaline phosphatase in MC3T3-E1 cells. After 4, 9 and 12 weeks the bone density (BD) and bone-to-implant contact (BIC) of the explanted implants were assessed histomorphometrically. Implants with immobilized rhBMP-2 displayed a significant (2- to 4-fold) increase in BD and BIC values vs. negative controls after 4-9 weeks. Integration of implants by trabecular bone was achieved after 4 weeks, indicating a mean "gap-filling rate" of ∼250 μm week(-1). Integration of implants by cortical bone was observed after 9 weeks. Control implants without rhBMP-2 were not osseointegrated. This study demonstrates the feasibility of enhancing peri-implant osseointegration and gap bridging by immobilized rhBMP-2 on implant surfaces which may serve as a model for future clinical applications.
authors.affiliation: Institut für Physiologische Chemie, Abtlg. Biochemische Endokrinologie, Universität Duisburg-Essen, Hufelandstrasse 55, D-45122 Essen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Chatzinikolaidou
authors.forename: T K
authors.initials: TK
authors.lastname: Lichtinger
authors.forename: R T
authors.initials: RT
authors.lastname: Müller
authors.forename: H P
authors.initials: HP
authors.lastname: Jennissen
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001681:Biological Assay; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D005269:Femur / Q000187:drug effects / Q000473:pathology; D005453:Fluorescence; D006207:Half-Life; D006801:Humans; D055767:Immobilized Proteins / Q000494:pharmacology*; D020007:Implants, Experimental; D007700:Kinetics; D051379:Mice; D049329:Nanostructures / Q000648:ultrastructure; D016348:Osseointegration / Q000187:drug effects*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D011994:Recombinant Proteins / Q000494:pharmacology*; D012756:Sheep; D013499:Surface Properties / Q000187:drug effects; D054457:Tissue Scaffolds / Q000737:chemistry*; D014025:Titanium / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D017155:Wettability / Q000187:drug effects; D014945:Wound Healing / Q000187:drug effects
chemical_list: D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D055767:Immobilized Proteins; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D014025:Titanium; D000469:Alkaline Phosphatase