Rat spinal fusion model.
This study aimed to assess the ability of rat bone marrow cells (RBMCs) transfected with bone morphogenetic protein (BMP)-2-containing lentivirus to induce a posterolateral spinal fusion in a rat model.
Spinal arthrodesis is a commonly performed spinal procedure and autograft remains the standard for achieving spinal fusion. However, its procurement is associated with significant morbidity, and the rate of pseudoarthrosis has been reported to be 5% to 43%. Nonunion frequently leads to an unsatisfactory resolution of clinical symptoms and usually results in high medical costs and morbidity as well as the need for additional surgeries. These problems have led surgeons to search for alternative solutions to stimulate bone formation. Recombinant BMPs have also been used successfully in clinical trials. However, large doses of BMPs were required to induce adequate bone repair. The development of a regional gene therapy may be a more efficient method to deliver proteins to a specific anatomic site. Furthermore, adeno-BMP-2-producing rat bone marrow-derived cells have been used successfully to induce posterior spinal fusion. Recently, lentiviral vectors on the basis of human immunodeficiency virus have been developed for gene therapy. Lentiviruses are capable of insertion into the host genome, ensuring a prolonged gene expression. However, safety issues are a major concern when adopting these vectors for clinical use.
In vitro study, we used RBMCs transfected with lentivirus vectors encoding BMP-2 (Lenti-BMP-2), RBMCs transfected with lentivirus vectors encoding the green fluorescent protein (GFP) (Lenti-GFP), and untransfected RBMCs; the latter 2 were used as controls. Alkaline phosphatase (ALP) staining and ALP activity were compared between the groups to assess the ability of the Lenti-BMP-2-transfected RBMCs to stimulate osteoblastic differentiation. In the rat posterolateral spine fusion model, the experimental study comprised 4 groups. Group 1 comprised 6 animals that were implanted with a collagen sponge containing 5 million RBMCs transfected with Lenti-BMP-2. Group 2 comprised 3 animals that were implanted with a collagen sponge containing 5 million RBMCs transfected with Lenti-GFP. Group 3 comprised 6 animals that were implanted with a collagen sponge containing 5 million untransfected RBMCs. Group 4 comprised 3 animals that were implanted with a collagen sponge alone. The rats were assessed by radiographs obtained at 4, 6, and 8 weeks. After death, their spines were explanted and assessed by manual palpation, high-resolution microcomputerized tomography, and histologic analysis.
The ALP staining was significantly greater in the Lenti-BMP-2-transfected RBMCs than in the untransfected RBMCs and the Lenti-GFP-transfected RBMCs. The ALP activity was 3-fold greater in the Lenti-BMP-2-transfected RBMCs than in the untransfected RBMCs and the Lenti-GFP-transfected RBMCs. In the rat spine fusion model, radiographic evaluation, high-resolution microcomputerized tomography, and manual palpation revealed spinal fusion in all the rats in Group 1 at 8 weeks. Groups 2, 3, and 4 comprised the control group. None of the rats in the control group (0 of 12) developed fusion at L4-L5.
The present study demonstrated that BMP-2-producing RBMCs, created through lentiviral gene transfer, induced sufficient spinal fusion. The use of lentiviral vectors that contain the cDNA for BMP-2 will be a novel and promising approach for a spinal fusion strategy.
Journal of Spinal Disorders & Techniques 08/2008; 21(5):372-9. DOI:10.1097/BSD.0b013e31814cf51d · 1.89 Impact Factor
A prospective 8-week interventional trial employing a rat model of spinal fusion to test the effect on bone morphogenetic protein binding peptide (BBP) on rhBMP-2 induced bone healing.
To determine if the addition of BBP to the collagen sponges used as a carrier for rhBMP-2 reduces the amount of rhBMP-2 required to achieve a satisfactory clinical outcome.
Bone morphogenetic proteins (BMPs) although effective in promoting osseous growth and spinal fusion have limitations in their extensive use because of higher costs and possible adverse effects including ectopic bone formation and local inflammatory reaction, particularly in the cervical spine.
Posterolateral intertransverse process spinal fusion at L4-L5 was performed in Lewis rats. Two doses of BBP (500 microg, and 1000 microg) were tested with or without "low dose" (1 microg) rhBMP-2 and the results were compared with the low dose (1 microg) rhBMP-2. Fusion was evaluated by radiology, histology, and manual palpation tests.
Radiology revealed significant earlier fusion with 1000 microg BBP + 1 microg BMP-2 combination when compared with low dose BMP-2 (1 microg) only (P < 0.05). Manual palpation and histology at eighth week revealed higher rate of fusion with the same combination with a nearly significant difference (P = 0.057).
Specific growth factor binding agents, such as BBP, can be compounded into carriers used in fusion procedures to decrease the dosage of BMP and possibly decrease the side effects which are most likely dose-related. This may also decrease costs and improve clinical outcomes.
Spine 07/2008; 33(16):1709-13. DOI:10.1097/BRS.0b013e31817e9dfd · 2.45 Impact Factor
The Spine Journal 09/2007; 7(5). DOI:10.1016/j.spinee.2007.07.369 · 2.80 Impact Factor
The safety of allograft material has come under scrutiny because of recent reports of allograft-associated bacterial and viral infections in tissue recipients. Gamma irradiation, although being one of the most effective ways of terminal sterilization, has been shown to affect the biomechanical properties of allograft bone. It may also have detrimental effects on the osteoinductivity of allograft material such as demineralized bone matrix (DBM) by the denaturation of proteins because of heat generated by irradiation. Sterilization of DBM material is an important variable in processing graft materials. This is considered to be one of the factors leading to different fusion rates observed with different commercially available DBM products, as the sterilization procedure itself may affect the osteoinductivity of the material. Currently, there is no ideal sterilization technique that limits the detrimental effect on osteoinductivity and fusion rates.
To evaluate the effects of a range of hydrogen peroxide exposures with or without the controlled high-dose gamma irradiation after processing with radioprotectant solutions (Clearant radiation sterilization procedure) on the fusion rates of human DBM.
A prospective in vivo animal study.
Eighty mature athymic nude female rats were used for this study, which formed 10 equal groups. Human DBM exposed to hydrogen peroxide for different time periods (0, 1, 6, and 24 hours) was divided into two major subgroups. One group was further treated with controlled high-dose radiation using radioprotectants (radiation treated), whereas the other group was frozen immediately without specific treatment (non-radiation treated). Both radiation-treated and non-radiation-treated DBM material from each group of hydrogen peroxide exposure times were implanted between L4 and L5 transverse processes of the rats forming eight test groups including eight animals in each. The remaining 16 rats were divided into two additional groups to form negative (only decortication, n=8) and positive (bone morphogenetic protein [BMP]-2, n=8) control groups. The rats were evaluated for fusion by radiographs (2, 4, and 8 weeks), manual palpation (8 weeks), and histological analysis after sacrificing. Comparison of fusion rate among all groups was made using these three evaluation methods.
Increasing the time period of hydrogen peroxide (0, 1, 6, or 24 hours) exposure for preparation of DBM from bone allograft did not affect the fusion rates significantly (p<.05), although there was a trend toward decreasing fusion rates with longer exposure times. When the hydrogen peroxide washed DBM preparations were also radiation treated, the resulting fusion rates were again not significantly different (p<.05). Agreement among fusion detection methods was found to be high.
Hydrogen peroxide processing was not detrimental to fusion rates. The additional terminal sterilization technique with special gamma irradiation protocols (Clearant process) also did not decrease the fusion rates but could provide an additional margin of safety.
The Spine Journal 08/2007; 8(5):789-95. DOI:10.1016/j.spinee.2007.06.009 · 2.80 Impact Factor
Recombinant growth factors bone morphogenetic protein-2 (BMP-2) and BMP-7 are currently approved for human use but are associated with various adverse effects including ectopic bone formation and local inflammatory reaction. The development of alternative growth factors may help minimize the adverse effects of current osteoinductive therapeutics. Nell-1 (Nel-like molecule-1; Nel [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]) is a novel secretory molecule that appears to act more specifically on osteoblasts than the BMPs, which can act on multiple cell types. From a molecular point of view, Nell-1 is directly regulated by runt-related transcription factor 2 (Runx2/Cbfa1), a master regulatory gene controlling bone formation. Previous studies showed that Nell-1 accelerates osteogenic differentiation in vitro and calvarial bone formation in vivo. We hypothesize that Nell-1 may also effectively form bone in spinal fusion.
Our primary aim was to assess if direct adenoviral gene delivery with Nell-1 in a demineralized bone matrix (DBM) carrier can improve spinal fusion in a rat model. Because adenoviral vectors allow for sustained growth factor delivery, they were used for initial feasibility testing before protein studies.
Two groups of 20 athymic rats underwent posterolateral intertransverse process spinal fusion at L4-L5 with implanted DBM carrier containing either adenovirus coding for Nell-1 (AdNell-1) or control, Lac Z (AdLacZ). No cells were implanted. The 20 rats were sacrificed at 6 weeks for evaluation of spinal fusion.
All animals underwent Faxitron radiographs at 2, 4, and 6 weeks, manual spine palpation at 6 weeks, and high-resolution micro computerized tomography (microCT) at 6 weeks. Spinal fusion rate was assessed by: 1) 6-week Faxitron images; 2) manual palpation by three independent observers; 3) microCT; and 4) histology. New bone formation was assessed by hematoxylin-eosin and Masson trichrome staining on decalcified, coronally sectioned spine segments.
All differences achieved statistical significance. After 6 weeks, direct application of adenoviral Nell-1 in a DBM carrier achieved significantly higher rates of spinal fusion over Lac Z controls: 60% Nell-1 versus 20% Lac Z by manual palpation and 70% Nell-1 versus 20% Lac Z by microCT and histology. Histological assessment of bone quality and maturity revealed more mature, higher quality bone in all the Nell-1 treated specimens relative to Lac Z at 6 weeks.
Spinal fusion is more accurately assessed by microCT and histology than manual palpation. Direct application of adenoviral Nell-1 in a DBM carrier achieved significantly higher rates of spinal fusion over Lac Z controls at 6 weeks. Direct application of adenoviral Nell-1 in a DBM carrier also achieved significantly higher rates of spinal fusion over other reports in the literature using direct adenoviral BMP application. Direct application of adenoviral BMP in an allograft carrier achieved 8% fusion for BMP-2 and 16% fusion for BMP-7 at 8 weeks. These results indicate that Nell-1 may be a potent osteoinductive molecule. In addition, the regulation of Nell-1 by the master bone regulatory gene, Runx2 suggests that Nell-1 may exert its effects more specifically in osteoblastic cells than BMPs which affect multiple cell types. Overall, Nell-1 may fulfil a current need for an osteoinductive factor.
The Spine Journal 01/2007; 7(1):50-60. DOI:10.1016/j.spinee.2006.04.020 · 2.80 Impact Factor