SPINE Volume 31, Number 22, pp 2550 –2555 ©2006, Lippincott Williams & Wilkins, Inc. Osteogenic Protein-1 Induced Gene Expression: Evaluation in a Posterolateral Spinal Pseudarthrosis Model Andrew P. White, MD,* Travis G. Maak, BS,* Daniel Prince, MD,* Alexander R. Vaccaro, MD,† Todd J. Albert, MD,† Alan S. Hilibrand, MD,† and Jonathan N. Grauer, MD* Study Design. Molecular study of gene expression in rabbit lumbar pseudarthrosis repairs using reverse tran- scriptase polymerase chain reaction. Objective. To evaluate differential gene expression of no graft, autograft, and osteogenic protein-1 treated pseudarthroses. Summary of Background Data. Osteogenic protein-1 is a potential bone graft alternative that has achieved high fusion rates in a rabbit lumbar fusion model, including in the repair of nicotine-induced pseudarthroses. A previous study established a correlation between osteogenic pro- tein-1 fusion outcomes and an enhanced level of cytokine gene expression. The expression of such cytokines is known to be decreased in nicotine-exposed rabbit fusion masses. Methods. Messenger ribonucleic acid was isolated from nicotine-exposed New Zealand white rabbit lumbar pseudarthroses following attempted no graft, autograft, and osteogenic protein-1 pseudarthrosis repairs. Reverse transcriptase polymerase chain reaction was used to as- sess the expression of angiogenin, angiopoietin, intercel- lular adhesion molecule, platelet-derived growth factor-, vascular endothelial growth factor, bone morphogenetic proteins 2 and 7, type I collagen, and osteonectin. Glyc- eraldehyde-3-phosphate dehydrogenase was used as a constitutively expressed control. Results. Levels of gene expression in the osteogenic protein-1 group were higher than those of the autograft group, which were higher than the no graft group for the majority of the genes studied. Conclusions. In the rabbit pseudarthrosis model, gene expression data supported the hypothesis that successful pseudarthrosis repair is related to the induction of osteo- genic and angiogenic cytokines by osteogenic protein-1. Key words: animal models, bone morphogenetic pro- tein, nicotine, pseudarthrosis, rabbit, spinal fusion, gene expression. Spine 2006;31:2550 –2555 Autologous bone, supplying live osteogenic progenitor cells, resident growth factors, and a histocompatible struc- tural scaffolding to support tissue ingrowth, has served as a gold standard material to achieve lumbar arthrodesis. Nev- ertheless, and despite the routine use of autologous iliac crest bone graft to induce spinal arthrodesis, it is associated with well-defined shortcomings and complications. 1,2 The recovery of autograft is associated with significant donor site morbidity, 3,4 and donor tissue may be limited because of poor bone quality or previous graft harvest. Moreover, the harvest of autograft requires additional operative time. For these reasons, there is great interest in developing and characterizing effective bone graft alternatives. Marshall Urist 5 first reported the osteogenic potential of demineralized bone in 1965. Subsequently, individual bone morphogenetic proteins (BMPs) were isolated from demin- eralized bone and identified as the osteoinductive agent. Individual recombinant human BMPs (rhBMPs) have more recently been shown to induce spinal fusion without au- tograft in preclinical and clinical models, potentially avoid- ing the complications of iliac bone harvest. 6,7 Cigarette smoking is an established risk factor for the development of pseudarthrosis following fusion surgery. Clinical studies have reported a 2–5-fold increase in the rate of lumbar pseudarthrosis in smokers as compared to non- smokers 8 as well as a significant decrease (81% to 62%) in the success of anterior cervical arthrodesis in smokers as compared to nonsmokers. 9 Nicotine has been documented to inhibit neovascularization 10 and to impede the incorpo- ration of bone graft in an animal model. 11 Nicotine admin- istration increases the rate of pseudarthrosis in the New Zealand white rabbit model. Silcox et al 12 reported an au- tograft fusion rate decrease from 56% to 0% with the in- troduction of nicotine exposure, while other groups re- ported a 54% to 0% decrease 13 and a 63% to 25% decrease. 14 Osteogenic protein-1, also known as rhBMP-7, has been shown to induce single-level lumbar intertransverse fusions in a number of preclinical animal studies. Grauer et al 15 found osteogenic protein-1 to induce fusion in 100% of rabbits, as compared to 63% for autograft. This high fusion rate was maintained even when rabbits were exposed to systemic nicotine (100% fusion as com- pared to 25% for autograft fusions). 14 Pseudarthrosis repair in the lumbar spine is a chal- lenging surgical problem, and high failure rates have From the *Department of Orthopaedics and Rehabilitation, Yale Uni- versity School of Medicine, New Haven, CT, and †Rothman Institute at Thomas Jefferson University, Philadelphia. PA. Acknowledgment date: April 8, 2005. First revision date: August 15, 2005. Second revision date: October 17, 2005. Third revision date: January 9, 2006. Acceptance date: January 10, 2006. The device(s)/drug(s) is/are FDA-approved or approved by correspond- ing national agency for this indication. Corporate/Industry No funds were received in support of this work. One or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related di- rectly or indirectly to the subject of this manuscript: e.g., honoraria, gifts, consultancies. Address correspondence and reprint requests to Jonathan N. Grauer, MD, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, PO Box 208071, New Haven, CT 06520-8071; E-mail: jonathan.grauer@yale.edu 2550