Ability of recombinant human bone morphogenetic protein 2 to enhance bone healing in the presence of tobramycin: evaluation in a rat segmental defect model.
OBJECTIVE
To determine whether locally applied tobramycin influences the ability of recombinant human bone morphogenetic protein 2 (rhBMP-2) to heal a segmental defect in the rat femur.


METHODS
The influence of tobramycin on the osteogenic differentiation of mesenchymal stem cells was first evaluated in vitro. For the subsequent, in vivo experiments, a 5-mm segmental defect was created in the right femur of each of 25 Sprague-Dawley rats and stabilized with an external fixator and four Kirschner wires. Rats were divided in four groups: empty control, tobramycin (11 mg)/absorbable collagen sponge, rhBMP-2 (11 microg)/absorbable collagen sponge, and rhBMP-2/absorbable collagen sponge with tobramycin. Bone healing was monitored by radiography at 3 and 8 weeks. Animals were euthanized at 8 weeks and the properties of the defect were compared with the intact contralateral femur. Bone formation in the defect region was assessed by dual-energy x-ray absorptiometry, microcomputed tomography, histology, and mechanical testing.


RESULTS
Tobramycin exerted a dose-dependent inhibition of alkaline phosphatase induction and calcium deposition by mesenchymal stem cells cultured under osteogenic conditions. The inhibition was reversed in the presence of 500 ng/mL of rhBMP-2. Segmental defects in the rat femora failed to heal in the absence of rhBMP-2. Tobramycin exerted no inhibitory effects on the ability of rhBMP-2 to heal these defects and increased the bone area of the defects treated with rhBMP-2. Data obtained from all other parameters of healing, including dual-energy x-ray absorptiometry, microcomputed tomography, histology, and mechanical testing, were unaffected by tobramycin.


CONCLUSIONS
Although our in vitro results suggested that tobramycin inhibits the osteogenic differentiation of mesenchymal stem cells, this could be overcome by rhBMP-2. Tobramycin did not impair the ability of rhBMP-2 to heal critical-sized femoral defects in rats. Indeed, bone area was increased by nearly 20% in the rhBMP-2 group treated with tobramycin. This study shows that locally applied tobramycin can be used in conjunction with rhBMP-2 to enhance bone formation at fracture sites.
Orthopaedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
Vaida
V
Glatt
Francois N
FN
Kwong
Kichul
K
Park
Nicola
N
Parry
Damian
D
Griffin
Mark
M
Vrahas
Christopher H
CH
Evans
Mitchel
M
Harris
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D004359:Drug Therapy, Combination; D005264:Femoral Fractures / Q000175:diagnosis / Q000628:therapy*; D005592:Fracture Fixation; D017102:Fracture Healing / Q000187:drug effects*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000627:therapeutic use*; D014031:Tobramycin / Q000008:administration & dosage*; D016212:Transforming Growth Factor beta / Q000627:therapeutic use*; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D014031:Tobramycin