title: Full-length spp24, but not its 18.5-kDa proteolytic fragment, inhibits bone-healing in a rodent model of spine fusion.
abstract: BACKGROUND
  Growth factors like bone morphogenetic protein (BMP) are used as bone-graft substitutes to enhance bone growth in clinical situations. However, adverse reactions have been associated with BMP use. We developed a synthetic adjuvant therapy based on the sequence of a BMP-binding protein, secreted phosphoprotein-24 (spp24), which enhances the effects of BMPs and ameliorates the adverse reactions. Our hypothesis is that a natural proteolytic fragment of spp24 is identical to an osteogenic protein previously described independently by two investigators. To test this hypothesis, spp24 and a truncated form of spp24 were separately implanted with recombinant human BMP-2 (rhBMP-2) in a rodent model of spine fusion.
  
  
  METHODS
  Two isoforms of spp24 were constructed with use of DNA recombinant technology. Spp24 with or without rhBMP-2 were added to collagen sponges and implanted bilaterally between L4 and L5 transverse processes. Radiographs were made biweekly, and spines were explanted after eight weeks. Gross evaluation, microquantitative computed tomography study, and histological analysis were performed to evaluate bone growth.
  
  
  RESULTS
  Animals that received full-length spp24 and rhBMP-2 exhibited a complete obliteration of bone growth, while animals with the truncated form in combination with rhBMP-2 exhibited a mild inhibition to bone growth, with bone area measured from radiographs. Manual assessment and gross evaluation of all spines confirmed the results obtained from the bone-area measurements. Microquantitative computed tomography provided three-dimensional visual images of representative specimens, while histological staining of spine tissue displayed cellular evidence of bone formation.
  
  
  CONCLUSIONS
  Results from this investigation confirm that the various isoforms of spp24 affect the bone-healing activity of rhBMP-2 in the rat spine fusion model. Thus, proteolytic modification of this protein is a likely mechanism for the regulation of BMP availability in the physiological environment. Future studies will define the roles of these proteins in controlling the activity of BMPs and other members of the transforming growth factor-beta family of cytokines. This information will increase the understanding of normal bone-healing, allowing for the engineering of more effective orthopaedic treatment.
authors.affiliation: Biomedical Engineering Interdepartmental Program, School of Engineering and Applied Science, University of California Los Angeles, 5121 Engineering V, Los Angeles, CA 90095, USA.
authors.forename: Chananit
authors.initials: C
authors.lastname: Sintuu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Simon
authors.forename: Masashi
authors.initials: M
authors.lastname: Miyazaki
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Morishita
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Hymanson
authors.forename: Cyrus
authors.initials: C
authors.lastname: Taghavi
authors.forename: Elsa J
authors.initials: EJ
authors.lastname: Brochmann
authors.forename: Samuel S
authors.initials: SS
authors.lastname: Murray
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Wang
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D023421:Models, Animal; D010012:Osteogenesis / Q000187:drug effects*; D010750:Phosphoproteins / Q000494:pharmacology / Q000627:therapeutic use*; D020033:Protein Isoforms / Q000494:pharmacology / Q000627:therapeutic use*; D011859:Radiography; D051381:Rats; D011917:Rats, Inbred Lew; D011994:Recombinant Proteins / Q000494:pharmacology / Q000627:therapeutic use; D013123:Spinal Fusion / Q000379:methods; D013131:Spine / Q000000981:diagnostic imaging / Q000187:drug effects / Q000601:surgery; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000627:therapeutic use*; D014945:Wound Healing / Q000187:drug effects*
chemical_list: D055396:Bone Morphogenetic Protein 2; D010750:Phosphoproteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; C091340:secreted phosphoprotein 24