Association of Bone Morphogenetic Protein (BMP)/Smad Signaling Pathway with Fracture Healing and Osteogenic Ability in Senile Osteoporotic Fracture in Humans and Rats

Background

To investigate the effect of the BMP/Smad signaling pathway on fracture healing and osteogenic ability in senile osteoporotic fracture on humans and rats.

Material/Methods

Sixty-two patients and well-matched normal controls were enrolled for clinical observation. A rat model of senile osteoporotic fracture was established. Serum BMP2 and Smad4 levels, as well as alkaline phosphatase (ALP) activity, were detected by ELISA. Fracture healing was observed by X-ray radiography and bone formation was analyzed by micro-CT.

Results

Serum BMP2 and Smad4 levels in patients with senile osteoporotic fracture were significantly lower than those in normal controls (all P<0.01). BMP2 was highly positively correlated with Smad4 in patients with senile osteoporotic fracture (r=0.738). Compared with patients with low serum BMP2 and Smad4 levels, visual analog scale scores decreased, bone mineral density (BMD) increased, and duration of fracture healing was shortened in patients with high levels (all P<0.05). Compared with the Model group, serum BMP2 and Smad4 levels increased, fracture healing was improved, BMD, trabecular bone volume (TBV), tissue volume (TV), bone volume fraction (BV/TV), mean trabecular thickness (Tb. Th), and mean number of trabecular bone (Tb. N) were increased, and ALP activity increased in the BMP2 overexpression group (all P<0.05), while each index in the NC group showed no statistical difference relative to rats in the Model group (all P>0.05).

Conclusions

BMP2 overexpression can promote fracture healing and osteogenic ability in senile osteoporotic fractures through activating the BMP/Smad signaling pathway.

Ovariectomy-Induced Osteopenia Influences the Middle and Late Periods of Bone Healing in a Mouse Femoral Osteotomy Model

OBJECTIVE

It is known that bone healing is delayed in the presence of osteoporosis in humans. However, due to the complexities of the healing of osteoporotic fractures, animal models may be more appropriate for studying the effects of osteoporosis in more detail and for testing drugs on the fracture repair process. The purpose of this study was to investigate the influence of ovariectomy-induced osteopenia in bone healing in an open femoral osteotomy model, and to test the feasibility of this model for evaluating the healing process under osteopenic conditions.

METHODS

Ovariectomized (OVX) mouse models were employed to assess the effects of osteopenia on fracture healing, A mid-shaft femur osteotomy model was also established 3 weeks after ovariectomy as an osteopenic fracture group (OVX group). Femurs were then harvested at 2 weeks and 6 weeks after fracture for X-ray radiography, micro-computed tomography (micro-CT), histology, and biomechanical analysis. A sham-operated group (sham group) was used for comparison.

RESULTS

The OVX mice had significantly lower bone volume density (BVF), volumetric bone mineral density (vBMD), and tissue mineral density (TMD) in the fracture calluses at 6 weeks (p<0.05), and similar trend was observed in 2 weeks. Additionally, larger calluses in OVX animals were observed via micro-CT and X-ray, but these did not result in better healing outcomes, as determined by biomechanical test at 6 weeks. Histological images of the healing fractures in the OVX mice found hastening of broken end resorption and delay of hard callus remodeling. The impaired biomechanical measurements in the OVX group (p<0.05) were consistent with micro-CT measurements and radiographic scoring, which also indicated delay in fracture healing of the OVX group.

CONCLUSIONS

This study provided evidence that ovariectomy-induced osteopenia impair the middle and late bone healing process. These data also supported the validity of the mouse femoral osteotomy model in evaluating the process of bone healing under osteopenic conditions.

Bone morphogenetic protein-7 accelerates fracture healing in osteoporotic rats

BACKGROUND

Osteoporosis is characterized by low bone mass, bone fragility and increased susceptibility to fracture. Fracture healing in osteoporosis is delayed and rates of implant failure are high with few biological treatment options available. This study aimed to determine whether a single dose of bone morphogenetic protein-7 (BMP-7) in a collagen/carboxy-methyl cellulose (CMC) composite enhanced fracture healing in an osteoporotic rat model.

MATERIALS AND METHODS

An open femoral midshaft osteotomy was performed in female rats 3 months post-ovarectomy. Rats were randomized to receive either BMP-7 composite (n = 30) or composite alone (n = 30) at the fracture site during surgery. Thereafter calluses were collected on days 12, 20 and 31. Callus cross-sectional area, bone mineral density, biomechanical stiffness and maximum torque, radiographic bony union and histological callus maturity were evaluated at each time point.

RESULTS

There were statistically significant increases in bone mineral density and callus cross-section area at all time points in the BMP-7 group as compared to controls and biomechanical readings showed stronger bones at day 31 in the BMP-7 group. Histological and radiographic evaluation indicated significant acceleration of bony union in the BMP-7 group as compared to controls.

CONCLUSION

This study demonstrated that BMP-7 accelerates fracture healing in an oestrogen-deficient environment in a rat femoral fracture healing model to scientific relevance level I. The use of BMP-7 composite could offer orthopedic surgeons an advantage over oestrogen therapy, enhancing osteoporotic fracture healing with a single, locally applied dose at the time of surgery, potentially overcoming delays in healing caused by the osteoporotic state.

BMP-7 stimulates early diaphyseal fracture healing in estrogen deficient rats

Estrogen deficiency causes postmenopausal osteoporosis. The relationship between estrogen deficiency and the high failure rate after osteoporotic fracture treatment is unclear, as is the effect of possible interventions, either with anti-resorptive agents or with anabolic agents such as bone morphogenetic proteins (BMPs). To investigate the influence of estrogen deficiency as well as the effect of early intervention, forty female wistar rats underwent ovarectomy (OVX) followed by low calcium diet. Ten rats underwent sham operations, followed by normal diet. After 6 weeks, a closed midshaft femoral fracture was induced. Ten animals received a systemic bisphosphonate injection, 10 injection of BMP-7 in the fracture, and 10 a combination. All then received a normal diet. After 2 weeks healing was evaluated using radiographs, CT, biomechanical testing, and histology. Radiography showed significant increase of bridging in groups treated with BMP-7. Callus volume was higher in these groups. Bending stiffness and strength were similar between OVX and sham, and not influenced by bisphosphonates. Significant increase was seen in groups treated with BMP-7. Histology was in accordance with other endpoints. Early fracture healing was not affected by estrogen deficiency. While no beneficiary effect of bisphosphonate treatment was found, injection of BMP-7 stimulated healing in ovarectomized rats.