title: Novel Protamine-Based Polyelectrolyte Carrier Enhances Low-Dose rhBMP-2 in Posterolateral Spinal Fusion.
abstract: METHODS
  A rodent posterolateral spinal fusion model.
  
  
  OBJECTIVE
  This study evaluated a protamine-based polyelectrolyte complex (PEC) developed to use heparin in enhancing the biological activity of low-dose recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion.
  
  
  BACKGROUND
  rhBMP-2 is commonly regarded as the most potent bone-inducing molecule. However, poor pharmacokinetics and short in vivo half-life means that large amounts of the bioactive growth factor are required for consistent clinical outcomes. This has been associated with a number of adverse tissue reactions including seroma and heterotopic ossification. Glycosaminoglycans including heparin are known to stabilize rhBMP-2 bioactivity. Previous studies with poly-L-lysine (PLL) and heparin-based PEC carriers amplified the therapeutic efficacy of low-dose BMP-2. However, questions remained on the eventual clinical applicability of relatively cytotoxic PLL. In the present study, a protamine-based PEC carrier was designed to further enhance the safety and efficacy of BMP-2 by delivering lower dose within the therapeutic window.
  
  
  METHODS
  A polyelectrolyte shell was deposited on the surface of alginate microbead templates using the polycation (protamine)/polyanion (heparin) layer-by-layer polyelectrolyte self-assembly protocol. rhBMP-2 was loaded onto the outermost layer via heparin affinity binding. Loading and release of rhBMP-2 were evaluated in vitro. The bone-inductive ability of 20-fold reduction of rhBMP-2 with the different carrier vehicle was evaluated using a posterolateral spinal fusion model in rats.
  
  
  RESULTS
  In vitro uptake and release analysis, protamine-based PEC showed higher uptake and significantly enhanced control release than PLL-based PEC (P < 0.05). In vivo implantation with protamine-based and PLL-based PEC showed better fusion performances than absorbable collagen sponge-delivered same dose of rhBMP-2, and negative control group through manual palpation, micro-computed tomography, and histological analyses.
  
  
  CONCLUSIONS
  Solid posterolateral spinal fusion was achieved with 20-fold reduction of rhBMP-2 when delivered using protamine-based PEC carrier in the rat posterolateral spinal fusion model.
  
  
  METHODS
  N/A.
authors.affiliation: *Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore †Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore ‡Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore; and §Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore.
authors.forename: Tao
authors.initials: T
authors.lastname: Hu
authors.forename: Sunny Akogwu
authors.initials: SA
authors.lastname: Abbah
authors.forename: Ming
authors.initials: M
authors.lastname: Wang
authors.forename: Soo Yein
authors.initials: SY
authors.lastname: Toh
authors.forename: Raymond Wing Moon
authors.initials: RW
authors.lastname: Lam
authors.forename: Mathanapriya
authors.initials: M
authors.lastname: Naidu
authors.forename: Gajadhar
authors.initials: G
authors.lastname: Bhakta
authors.forename: Simon M
authors.initials: SM
authors.lastname: Cool
authors.forename: Kishore
authors.initials: K
authors.lastname: Bhakoo
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: James Cho-Hong
authors.initials: JC
authors.lastname: Goh
authors.forename: Hee-Kit
authors.initials: HK
authors.lastname: Wong
mesh_terms: D000464:Alginates / Q000737:chemistry; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics*; D004337:Drug Carriers / Q000737:chemistry*; D020723:Glucuronic Acid / Q000737:chemistry; D006493:Heparin / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D008297:Male; D008863:Microspheres; D011479:Protamines / Q000737:chemistry*; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics; D013123:Spinal Fusion / Q000379:methods*; D023822:Tissue Engineering; D016212:Transforming Growth Factor beta / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D000464:Alginates; D055396:Bone Morphogenetic Protein 2; D004337:Drug Carriers; D006603:Hexuronic Acids; D011479:Protamines; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D020723:Glucuronic Acid; D006493:Heparin