title: Imparting bone mineral affinity to osteogenic proteins through heparin-bisphosphonate conjugates.
abstract: Although numerous growth factors can promote the regeneration of bone upon parenteral administration, all exhibit undesirable side-effects that prevent their clinical utility. These side-effects arise due to the growth factors' inherent lack of bone affinity. The goal of this study was to develop a means to enhance the bone mineral affinity of osteogenic growth factors so as to minimize their extra-skeletal distribution. Heparin, a glycosaminoglycan that exhibits a high affinity to numerous growth factors, was modified with bisphosphonates to enhance its affinity to bone mineral (i.e. hydroxyapatite, HA). To this end, conjugation of 1-amino-1,1-diphosphonate methane (aminoBP) onto periodate-oxidized heparin using 4-(maleimidomethyl)cyclohexane-1-carboxyl-hydrazide was attempted. Using this chemistry, the number of aminoBPs conjugated onto heparin was modulated by varying the reacting reagent concentrations (to a maximum of 7 aminoBPs per heparin). Increasing the number of aminoBPs resulted in a more than twofold increase in heparin's affinity for HA in vitro. Subsequently, the ability of aminoBP-heparin conjugates to enhance the mineral affinity of basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) was explored. The results revealed that the complexation between the conjugates and growth factors had occurred and that the conjugates increased the bone mineral affinity of bFGF and BMP-2 in an aminoBP-dependent manner. In conclusion, the conjugation of aminoBP onto heparin is a feasible approach to enhance the affinity of heparin-binding, osteogenic growth factors to HA.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Sébastien A
authors.initials: SA
authors.lastname: Gittens
authors.forename: Keith
authors.initials: K
authors.lastname: Bagnall
authors.forename: John R
authors.initials: JR
authors.lastname: Matyas
authors.forename: Raimar
authors.initials: R
authors.lastname: Löbenberg
authors.forename: Hasan
authors.initials: H
authors.lastname: Uludag
mesh_terms: D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000737:chemistry / Q000378:metabolism*; D004164:Diphosphonates / Q000737:chemistry*; D004337:Drug Carriers / Q000138:chemical synthesis / Q000737:chemistry; D016503:Drug Delivery Systems / Q000379:methods*; D017886:Durapatite / Q000737:chemistry / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000737:chemistry / Q000378:metabolism*; D006493:Heparin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D008301:Maleimides / Q000737:chemistry; D010504:Periodic Acid / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D011485:Protein Binding / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism*
chemical_list: C113054:4-(4-N-maleimidomethyl)cyclohexane-1-carboxyl hydrazide; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D004164:Diphosphonates; D004337:Drug Carriers; D008301:Maleimides; D010710:Phosphates; D016212:Transforming Growth Factor beta; C411447:aminomethane diphosphonate; D016222:Fibroblast Growth Factor 2; D010504:Periodic Acid; D006493:Heparin; D017886:Durapatite; C009288:metaperiodate