Fri., 10/19/07 Basic Science, Paper #39, 4:11 pm OTA-2007
The Role of Leptin in the Local Control of Fracture Healing
Safdar N. Khan, MD1 (n); Mark A. Lee, MD1 (n); Grayson DuRaine, BS1 (n);
Jennifer Fung, BS2 (n); Douglas Rowland, PhD2 (n); A. Hari Reddi, PhD1 (n);
1Department of Orthopaedic Surgery, University of California, Davis, California, USA;
2Center for Molecular and Genomic Imaging, University of California, Davis, California, USA
Hypothesis: Leptin is a cytokine-like hormone with pleiotropic actions including regulating body mass, bone formation, and angiogenesis. Osteoblasts are under dual leptin-dependent regulation: central antiosteogenic negative regulation acting via the hypothalamus and local pro-osteogenic positive regulation. We hypothesized that leptin is expressed during fracture healing and leptin deficiency leads to impaired healing that can be rescued by local application of either recombinant leptin or vascular endothelial-derived growth factor (VEGF).
Methods: 10-week-old wild type C57BL/6 control mice and leptin knockout (ob/ob) mice were used. Leptin expression in normal fracture healing (on days 1, 3, 5, 7, 10, 14, and 21 postfracture by RT-PCR analysis) was determined by creating closed middiaphyseal femur fractures stabilized with intramedullary fixation in 56 wild type mice. The effect of leptin deficiency on fracture healing was determined by optimizing an open model of stabilized middiaphyseal femur fracture healing. A total of 84 mice underwent fractures: 42 wild type controls and 42 ob/ob mice; tissues were harvested at 14, 21, and 42 days and analyzed by radiograph, histology, and qCT. Recombinant leptin in a collagen carrier was drip-applied at the fracture site in two separate groups (group I used 10 μg and group II used 100-μg leptin doses) of 42 ob/ob mice each and tissue analyzed at 4, 21, and 42 days postfracture by radiograph, histology, and qCT. 2 μg of recombinant VEGF was drip-applied at the fracture site in 12 separate ob/ob mice and tissue harvested and analyzed as above at 14 and 21 days postfracture. Two-factor analysis of variance and Student t test was used for statistical analysis.
Results: Leptin mRNA was detected at the fracture site and in the fracture callus at multiple time points. Delay in callus maturation was demonstrated radiographically in the ob/ob mice compared to the controls. Histologically, ob/ob fractures demonstrated delay in callus organization with significantly greater hypertrophic chondrocytes (P <0.05) compared with controls at 14 and 21 days. ob/ob fractures demonstrated increase in total callus height and total callus volume by qCT (P <0.05). Application of local leptin at both doses and the VEGF reversed the delay seen in the ob/ob fractures radiographically and histologically at 14 and 21 days.
Conclusions: Leptin is expressed locally during fracture healing. Leptin deficiency leads to a delay in fracture healing that can be reversed by local application of leptin or VEGF protein.
Significance: We describe an unrecognized role of leptin as a potential angiogenic factor in the program of fracture healing.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing.