Rapamycin affects early fracture healing in mice.
OBJECTIVE
The immunosuppressive drug rapamycin (RAPA) prevents rejection in organ transplantation by inhibiting interleukin-2-stimulated T-cell division. Rapamycin has also been suggested to possess strong anti-angiogenic activities linked to a decrease in production of vascular endothelial growth factor (VEGF). Angiogenesis and VEGF are thought to play a crucial role in fracture healing and as osteoporotic and traumatic fractures are common complications in immunosuppressed, organ transplantation patients, we conducted this study to analyze the effect of rapamycin treatment on bone repair.


METHODS
We investigated the effect of rapamycin treatment on bone repair in a murine closed femur fracture model using radiological, histomorphometric, immunohistochemical, biomechanical and protein biochemical analyses.


RESULTS
X-ray analyses demonstrated that rapamycin treatment inhibits callus formation after two weeks of fracture healing. The radiologically observed lack of callus formation was confirmed by histomorphometric analyses, which revealed a significantly diminished callus size and a reduced amount of bone formation when compared with vehicle-treated controls. Biomechanical testing further demonstrated that rapamycin significantly reduces torsional stiffness of the callus. Interestingly, this effect was associated with decreased vessel formation; a diminished proliferation of osteoblasts, endothelial cells and periosteal cells; and a reduced VEGF expression in hypertrophic chondrocytes. After five weeks treatment, however, the negative impact of rapamycin on fracture healing was overcome.


CONCLUSIONS
Thus, rapamycin initially delays fracture healing, most probably by inhibiting cell proliferation and neovascularization in the callus. These undesirable effects should be considered when rapamycin is administered to patients sustaining bone fractures.
Holstein
J H
JH
Department of Trauma, Hand and Reconstructive Surgery, Homburg/Saar, Germany. chjhol@uniklinikum-saarland.de
Klein
M
M
Garcia
P
P
Histing
T
T
Culemann
U
U
Pizanis
A
A
Laschke
M W
MW
Scheuer
C
C
Meier
C
C
Schorr
H
H
Pohlemann
T
T
Menger
M D
MD
D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D001696:Biomechanical Phenomena; D015153:Blotting, Western; D002146:Bony Callus / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D049109:Cell Proliferation / Q000187:drug effects; D019902:Chondrocytes / Q000187:drug effects; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D005264:Femoral Fractures / Q000473:pathology / Q000503:physiopathology*; D017102:Fracture Healing / Q000187:drug effects*; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*; D051379:Mice; D018919:Neovascularization, Physiologic / Q000187:drug effects; D010006:Osteoblasts / Q000187:drug effects; D010012:Osteogenesis / Q000187:drug effects*; D020123:Sirolimus / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors
D020533:Angiogenesis Inhibitors; D007166:Immunosuppressive Agents; D020123:Sirolimus