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Nell-1 Enhances Bone Regeneration in a Rat Critical-Sized Femoral Segmental Defect Model

Li, Weiming M.D.; Zara, Janette N. M.D.; Siu, Ronald K. M.S.; Lee, Min Ph.D.; Aghaloo, Tara M.D.; Zhang, Xinli M.D., Ph.D.; Wu, Benjamin M. D.D.S., Ph.D.; Gertzman, Arthur A. M.S.; Ting, Kang M.D.; Soo, Chia M.D.

Plastic and Reconstructive Surgery: February 2011 - Volume 127 - Issue 2 - p 580-587
doi: 10.1097/PRS.0b013e3181fed5ae
Experimental: Original Articles

Background: Effective regeneration of bone is critical for fracture repair and incorporation and healing of bone grafts used during orthopedic, dental, and craniofacial reconstructions. Nel-like molecule-1 (Nell-1) is a secreted protein identified from prematurely fused cranial sutures of craniosynostosis patients that has been found to specifically stimulate osteogenic cell differentiation and bone formation. To test the in vivo osteoinductive capacity of Nell-1, a critical-sized femoral segmental defect model in athymic rats was used.

Methods: A 6-mm defect, which predictably leads to nonunion if left untreated, was created in the left femur of each rat. Three treatment groups (n = 8 each) were created consisting of rats treated with (1) 1.5 mg/ml Nell-1, (2) 0.6 mg/ml Nell-1, and (3) phosphate-buffered saline only as a Nell-free control. Phosphate-buffered saline or Nell-1 was mixed with demineralized bone matrix as a carrier before implantation. All animals were euthanized 12 weeks after surgery, and bone regeneration was evaluated using radiographic, three-dimensional micro–computed tomographic, and histologic analysis.

Results: Both Nell-1–treated groups had significantly greater bone formation compared with the Nell-free group, with bone volume increasing with increasing Nell-1 concentration.

Conclusions: Nell-1 in a demineralized bone matrix carrier can significantly improve bone regeneration in a critical-sized femoral segmental defect in a dose-dependent manner. The results of this study demonstrate that Nell-1 is a potent osteospecific growth factor that warrants further investigation. Results also support the potential application of Nell-1 as a bone graft substitute in multiple clinical scenarios involving repair of critical bone loss when autograft bone is limited or unavailable.

Los Angeles, Calif.; Harbin, China; and Edison, N.J.

From the Dental and Craniofacial Research Institute, the Department of Bioengineering, the Division of Advanced Prosthodontics, Biomaterials, and Hospital Dentistry, and the Department of Orthopedic Surgery, University of California, Los Angeles; the Department of Orthopedics, First Clinical Hospital, Harbin Medical University; and the Musculoskeletal Transplant Foundation.

Received for publication May 10, 2010; accepted July 22, 2010.

The first three authors should be considered co–first authors.

The last two authors should be considered co–senior authors.

Disclosure:Bone Biologics, Inc., licensed Nell-1–related patents from the University of California, Los Angeles. Drs. Soo, Ting, Wu, and Zhang are founders of Bone Biologics, Inc., and inventors of the related patents. Mr. Gertzman is a member of the scientific advisory board of Bone Biologics, Inc.

Chia Soo, M.D., Department of Orthopaedic Surgery, University of California, Los Angeles, 675 Charles E. Young Drive South, Room 2641A MRL, Los Angeles, Calif. 90095-1759, bsoo@ucla.edu

©2011American Society of Plastic Surgeons