title: 11 kGy gamma irradiated demineralized bone matrix enhances osteoclast activity.
abstract: BACKGROUND
  Demineralized bone matrix (DBM) allografts are widely used in orthopaedic clinics. However, the biological impact on its osteoinductivity after its sterilization process by gamma irradiation is not well studied. Furthermore, little is known about the relationship between residual calcium levels on osteoinductivity.
  
  
  OBJECTIVE
  We hypothesize that low-dose gamma irradiation retains the osteoinducitivity properties of DBM and causes ectopic bone formation.
  
  
  METHODS
  A randomised animal trial was performed to compare tissue and molecular responses of low-dose (11 kGy) gamma irradiated and non-irradiated human DBM at 6 weeks post-intramuscular implantation using an athymic rat model. In addition, we correlated residual calcium levels and bone formation in gamma irradiated DBM.
  
  
  RESULTS
  A modified haematoxylin and eosin stain identified ectopic bony capsules at all implanted sites with no significant difference on the amount of new bone formed between the groups. Statistically significantly lower ratio of alkaline phosphatase expression over tartrate-resistant acid phosphatase and/or cathepsin K expressions was found between the groups.
  
  
  CONCLUSIONS
  This study found that low-dose gamma irradiated DBM, which provides a sterility assurance level of 10(-6) for bone allografts, retained osteoinductivity but exhibited significantly enhanced osteoclastic activity. Furthermore, this is the first study to find a positive correlation between residual calcium levels and bone formation in gamma irradiated DBM.
authors.affiliation: Surgical and Orthopaedic Research Laboratories, Prince of Wales Clinical School, University of New South Wales, Sydney, NSW, 2031, Australia, wong.may.yw@gmail.com.
authors.forename: May Y W
authors.initials: MY
authors.lastname: Wong
authors.forename: Yan
authors.initials: Y
authors.lastname: Yu
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Yang
authors.forename: Tracey
authors.initials: T
authors.lastname: Woolford
authors.forename: David A F
authors.initials: DA
authors.lastname: Morgan
authors.forename: William R
authors.initials: WR
authors.lastname: Walsh
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001857:Bone Matrix / Q000378:metabolism / Q000528:radiation effects*; D016025:Bone Transplantation / Q000379:methods; D002118:Calcium / Q000378:metabolism; D056657:Cathepsin K / Q000378:metabolism; D005720:Gamma Rays; D064593:Heterografts / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D010010:Osteoclasts / Q000378:metabolism / Q000528:radiation effects*; D011897:Random Allocation; D051381:Rats; D014183:Transplantation, Heterologous
chemical_list: D000469:Alkaline Phosphatase; D056657:Cathepsin K; D002118:Calcium