Lactoferrin Mediates Enhanced Osteogenesis of Adipose-Derived Stem Cells: Innovative Molecular and Cellular Therapy for Bone Repair.

A prospective source of stem cells for bone tissue engineering is adipose-derived stem cells (ADSCs), and BMP-2 has been proven to be highly effective in promoting the osteogenic differentiation of stem cells. Rarely has research been conducted on the impact of lactoferrin (LF) on ADSCs' osteogenic differentiation. As such, in this study, we examined the effects of LF and BMP-2 to assess the ability of LF to stimulate ADSCs' osteogenic differentiation. The osteogenic medium was supplemented with the LF at the following concentrations to culture ADSCs: 0, 10, 20, 50, 100, and 500 µg/mL. The Cell Counting Kit-8 (CCK-8) assay was used to measure the proliferation of ADSCs. Calcium deposition, alkaline phosphatase (ALP) staining, real-time polymerase chain reaction (RT-PCR), and an ALP activity assay were used to establish osteogenic differentiation. RNA sequencing analysis was carried out to investigate the mechanism of LF boosting the osteogenic development of ADSCs. In the concentration range of 0-100 µg/mL, LF concentration-dependently increased the proliferative vitality and osteogenic differentiation of ADSCs. At a dose of 500 µg/mL, LF sped up and enhanced differentiation, but inhibited ADSCs from proliferating. LF (100 and 500 µg/mL) produced more substantial osteoinductive effects than BMP-2. The PI3 kinase/AKT (PI3K/AKT) and IGF-R1 signaling pathways were significantly activated in LF-treated ADSCs. The in vitro study results showed that LF could effectively promote osteogenic differentiation of ADSCs by activating the PI3K/AKT and IGF-R1 pathways. In our in vitro investigation, an LF concentration of 100 µg/mL was optimal for osteoinduction and proliferation. Our study suggests that LF is an attractive alternative to BMP-2 in bone tissue engineering. As a bioactive molecule capable of inducing adipose stem cells to form osteoblasts, LF is expected to be clinically used in combination with biomaterials as an innovative molecular and cellular therapy to promote bone repair.

The Effect of Smoking on the Outcome of Matrix-Based Autologous Chondrocyte Implantation: Data from the German Cartilage Registry.

Smoking is known to have various deleterious effects on health. However, it is not clear whether smoking negatively affects the postoperative outcome following matrix-based autologous cartilage implantation (MACI) in the knee. The purpose of this study was to evaluate the effect of smoking on the outcome of MACI in the knee. A total of 281 patients receiving MACI in the knee between 2015 and 2018 were registered in the German Cartilage Database. The cohort was divided into ex-smokers, smokers, and nonsmokers. Data regarding the Knee Injury and Osteoarthritis Outcome Score (KOOS), the numeric rating scale (NRS) for pain, and satisfaction with the outcome were analyzed and compared. Follow-ups were performed at 6, 12, and 24 months after surgery. Of the 281 patients, 225 (80.1%) were nonsmokers, 43 (15.3%) were smokers, and 13 (4.6%) were ex-smokers. The three groups were comparable with respect to age, sex, body mass index (BMI), height, defect size, the need for additional reconstruction of the subchondral bone defect, number of previous knee surgeries, and defect location. However, nonsmokers had a significantly lower weight as compared with smokers. Besides a significantly lower preoperative NRS of nonsmokers as compared with smokers, there were no significant differences between the three groups with respect to KOOS, NRS, and satisfaction at 6, 12, and 24 months of follow-ups. The present study of data retrieved from the German Cartilage Registry suggests that the smoking status does not influence the outcome of MACI in the knee.

Osteogenic Differentiation of Human Adipose-Derived Stem Cells Seeded on a Biomimetic Spongiosa-like Scaffold: Bone Morphogenetic Protein-2 Delivery by Overexpressing Fascia.

Human adipose-derived stem cells (hADSCs) have the capacity for osteogenic differentiation and, in combination with suitable biomaterials and growth factors, the regeneration of bone defects. In order to differentiate hADSCs into the osteogenic lineage, bone morphogenetic proteins (BMPs) have been proven to be highly effective, especially when expressed locally by route of gene transfer, providing a constant stimulus over an extended period of time. However, the creation of genetically modified hADSCs is laborious and time-consuming, which hinders clinical translation of the approach. Instead, expedited single-surgery gene therapy strategies must be developed. Therefore, in an in vitro experiment, we evaluated a novel growth factor delivery system, comprising adenoviral BMP-2 transduced fascia tissue in terms of BMP-2 release kinetics and osteogenic effects, on hADSCs seeded on an innovative biomimetic spongiosa-like scaffold. As compared to direct BMP-2 transduction of hADSCs or addition of recombinant BMP-2, overexpressing fascia provided a more uniform, constant level of BMP-2 over 30 days. Despite considerably higher BMP-2 peak levels in the comparison groups, delivery by overexpressing fascia led to a strong osteogenic response of hADSCs. The use of BMP-2 transduced fascia in combination with hADSCs may evolve into an expedited single-surgery gene transfer approach to bone repair.

Gene activated adipose tissue fragments as advanced autologous biomaterials for bone regeneration: osteogenic differentiation within the tissue and implications for clinical translation.

Cost-effective, expedited approaches for bone regeneration are urgently needed in an ageing population. Bone Morphogenetic Proteins (BMPs) stimulate osteogenesis but their efficacy is impeded by their short half-life. Delivery by genetically modified cells can overcome this problem. However, cell isolation and propagation represent significant obstacles for the translation into the clinic. Instead, complete gene activated fragments of adipose tissue hold great potential for bone repair. Here, using an in-vitro culture system, we investigated whether adenoviral transduction with human BMP-2 can promote osteogenic differentiation within adipose tissue fragments. Osteoinduction in adipose tissue fragments was evaluated by quantitative reverse transcriptase polymerase chain reaction, immunohistology and histomorphometry. BMP-2 transduced adipose tissue synthesized BMP-2 protein over 30 days peaking by day six, which significantly promoted osteogenic differentiation as indicated by increased calcium depositions, up-regulation of bone marker genes, and bone-related protein expression. Our results demonstrate that cells within adipose tissue fragments can differentiate osteogenically after BMP-2 transduction of cells on the surface of the adipose tissue. BMP-2 gene activated adipose tissue represents an advanced osteo-regenerative biomaterial that can actively contribute to osteogenesis and potentially enable the development of a novel, cost-effective, one-step surgical approach to bone repair without the need for cell isolation.

Osteoinduction within BMP-2 transduced muscle tissue fragments with and without a fascia layer: implications for bone tissue engineering.

Bone can be engineered in vivo by implantation of gene-activated muscle tissue fragments. This expedited approach may be further improved by use of muscle tissue with attached fascia. The aim of this in vitro study was to provide an in depth comparison of the osteogenic differentiation capacity of muscle alone and muscle with fascia after BMP-2 transduction. Skeletal muscle tissue from rats was cut into pieces with and without a fascia layer on the surface. Adenoviral BMP-2 or GFP vectors were used for transduction. Osteogenic differentiation within the tissue fragments was evaluated and compared by qRT-PCR, alizarin red S staining, histomorphometry and immunohistology. Transduction efficiency and level of transgene expression were higher for muscle with fascia than muscle alone. Transduction with BMP-2 led to a significant upregulation of bone marker genes, proteins, and calcium deposition in both groups. Interestingly, histological evaluation revealed that osteoinduction did not occur within the fascia layer itself. The upregulation of bone marker genes in muscle with fascia was significantly lower after 2 weeks but similar after 4 weeks of in vitro culture in comparison to muscle alone. The fascia layer led to higher transduction efficiency and enhanced BMP-2 expression. Despite fascia's lower capacity for osteogenic differentiation, muscle implants may benefit from the fascia layer by the improved ability to deliver BMP-2. The presented data may contribute to the development of a novel, cost-effective, single-surgery bone engineering technology and encourage the evaluation of the osteoregenerative potential of muscle with fascia in an animal model.

Gene-activated tissue grafts for sustained bone morphogenetic protein-2 delivery and bone engineering: Is muscle with fascia superior to muscle and fat?

Previously, we have presented an expedited strategy for sustained delivery of bone morphogenetic protein-2 (BMP-2) to bone lesions based on the implantation of gene-activated fat and muscle fragments. The aim of the present in vitro experiments was to evaluate the potential of muscle with fascia as a BMP-2 delivering osteo-regenerative implant in comparison to fat tissue and muscle alone. Subcutaneous fat, muscle, and muscle with fascia were harvested from Fischer 344 rats. The tissues were cut into small pieces and cultured for up to 90 days after direct transduction with adenoviral BMP-2 or green fluorescence protein vectors. Different vector doses were applied, and proliferation, long-term BMP-2 production, and osteogenic differentiation of the 3 different tissues were investigated in vitro. Muscle with fascia produced the largest amounts of BMP-2. Expression of the transgene was detected for up to 90 days. Proliferation was reduced with increased vector doses. Muscle with fascia showed a higher potential for osteogenic differentiation than fat, but it was not improved as compared to muscle alone. A dose of 4 × 108 plaque forming units of the adenoviral BMP-2 vector appeared to be the optimal dose for transduction of muscle with fascia. Because muscle with fascia produced higher amounts of BMP-2 as compared to muscle alone or fat tissue grafts, showing a high potential for osteogenic differentiation, it might represent an improved osteo-regenerative implant facilitating endogenous repair. Future studies should investigate the effect of muscle with fascia transduced with 4 × 108 plaque forming units on bone healing in vivo.

BMP-2 gene activated muscle tissue fragments for osteochondral defect regeneration in the rabbit knee.

BACKGROUND: Previously published data indicate that BMP-2 gene activated muscle tissue grafts can repair large bone defects in rats. This innovative abbreviated ex vivo gene therapy is appealing because it does not require elaborative and time-consuming extraction and expansion of cells. Hence, in the present study, we evaluated the potential of this expedited tissue engineering approach for regenerating osteochondral defects in rabbits. METHODS: Autologous muscle tissue grafts from female White New Zealand rabbits were directly transduced with an adenoviral BMP-2 vector or remained unmodified. Osteochondral defects in the medial condyle of rabbit knees were treated with either BMP-2 activated muscle tissue implants or unmodified muscle tissue or remained empty. After 13 weeks, repair of osteochondral defects was examined by biomechanical indentation testing and by histology/imunohistochemistry applying an extended O'Driscoll scoring system and histomorphometry. RESULTS: Biomechanical investigations revealed a trend towards slightly improved mechanical properties of the group receiving BMP-2 activated muscle tissue compared to unmodified muscle treatment and empty defect controls. However, a statistically significant difference was noted only between BMP-2 muscle and unmodified muscle treatment. Also, histological evaluation resulted in slightly higher histological scores and improved collagen I/II ratio without statistical significance in the BMP-2 treatment group. Histomorphometry indicated enhanced repair of subchondral bone after treatment with BMP-2 muscle, with a significantly larger bone area compared to untreated defects. CONCLUSIONS: Gene activated muscle tissue grafts showed potential for osteochondral defect repair. There is room for improvement via the use of appropriate growth factor combinations.

An expedited approach for sustained delivery of bone morphogenetic protein-7 to bone defects using gene activated fragments of subcutaneous fat.

BACKGROUND: Delivery of bone morphogenetic protein-7 (BMP-7) to bone defects can be improved by applying gene transfer methods. However, traditional ex vivo gene therapy approaches are cumbersome and costly, requiring the extraction and culturing of cells. Therefore, we evaluated a novel, expedited ex vivo BMP-7 gene transfer technology based on the use of fragments of subcutaneous fat tissue. METHODS: We created 5-mm mid-femoral bone defects in the right femora of 23 male, syngeneic Fischer 344 rats. Adipose tissue was harvested from the subcutaneous fat depot of two donor rats. Bone defects were treated with either unmodified fat (control group) or adenovirally BMP-7 transduced fat fragments (treatment group). Healing of bone defects was assessed by radiographs, microcomputed tomography (µCT) and histology at 6 weeks after the implantation of fat tissue fragments. RESULTS: Radiographs, µCT-imaging and histology revealed relevant bone formation in six out of 10 rats treated with BMP-7 activated fat grafts. Two of the defects were bridged. By contrast, femora of the control group receiving unmodified fat did not display signs of osseous healing. BMP-7 gene activated fat treatment led to a significantly higher bone volume (11.18 ± 9.48 mm(3) ) than treatment with unmodified fat grafts (3.19 ± 1.68 mm(3) ) (p = 0.008). CONCLUSIONS: Implantation of BMP-7 gene activated fat tissue fragments can elicit regeneration of large bone defects in rats and could become a clinically expeditious strategy for in vivo bone tissue engineering. However, gene expression must be improved in order to reliably induce osseous bridging of critical-size bone defects. Copyright © 2016 John Wiley & Sons, Ltd.

Gene-activated fat grafts for the repair of spinal cord injury: a pilot study.

BACKGROUND: Spinal cord injury (SCI) is a complex disease requiring a concerted multi-target approach. The most appropriate combination of therapeutic gene, cellular vehicle, and space filling scaffold still has to be determined. We present an approach that employs syngeneic adipose tissue serving as a three-dimensional biological implant, source of progenitor cells, and delivery system for therapeutic genes. In this pilot experiment, we evaluated the feasibility and short-term effects using gene-activated autologous fat grafts after SCI. METHODS: An experimental SCI model was established in syngeneic Fischer 344 rats by a T9-T10 hemimyelonectomy. Fat tissue was harvested from two donor rats. Animals were divided into four groups and treated with either (i) fat grafts activated by an adenoviral vector carrying the human NT-3 cDNA, (ii) or BDNF, (iii) or with untreated fat grafts or (iv) remained untreated. Animals were euthanized either 7 or 21 days after surgery, and spinal cord tissue was investigated by histological and immunohistochemical methods. RESULTS: NT-3 and BDNF were produced by gene-activated fat grafts for at least 21 days in vitro and in vivo. Fat tissue grafts remained stable at the site of implantation at 7 days and at 21 days. Neither BDNF-activated nor NT-3-activated fat graft had a detectable limiting effect on the neuronal degeneration. BDNF recruited microglia to perilesional site and attenuated their inflammatory response. CONCLUSIONS: Gene-activated syngeneic fat tissue serves as a three-dimensional biological material delivering therapeutic molecules to the site of SCI over an extended period of time. The BDNF-fat graft attenuated the inflammatory response. Whether these findings translate into functional recovery will require extended observation times.

The effect of BMP-7 gene activated muscle tissue implants on the repair of large segmental bone defects.

BACKGROUND: This study was conducted in order to investigate the effect of Bone Morphogenetic Protein-7 (BMP-7) transduced muscle cells on bone formation and to further develop an innovative abbreviated ex vivo gene therapy for bone repair. As conventional ex vivo gene therapy methods require an elaborative and time-consuming extraction and expansion of cells we evaluated an expedited approach. Fragments of muscle tissue were directly activated by BMP-7 cDNA and implanted into bone defects. METHODS: 25 male, syngeneic Fischer 344 rats were used in the present study. Muscle tissue was harvested from two donor rats and either transduced with an adenovirus carrying the BMP-7 cDNA or remained unmodified. 5mm osseous defects in the right femora of 23 rats were treated with either unmodified muscle tissue (control group) or BMP-7 activated muscle tissue (treatment group). Six weeks after surgery, rat femora were evaluated by radiographs, micro-computed tomography (µCT) and histology. RESULTS: Implantation of BMP-7 activated muscle grafts led to bony bridging in 5 out of 12 defects (41.7%) and to bone formation without bridging in 2 out of 12 defects. In 2 femoral defects of this group radiographs, µCT-imaging and histology did not reveal significant mineralization. Three animals of the BMP-7 treatment group had to be euthanized due to serious wound infection. The bone volume of the treatment group was significantly (p=0.007) higher compared to the control group. CONCLUSION: This study shows that BMP-7 gene activated muscle fragments have the potential to regenerate critical-size segmental bone defects in rats. However, further development of this promising expedited treatment modality is required to improve the healing rate and to investigate if the high infection rate is related to treatment with BMP-7 activated muscle grafts.

Repair of large segmental bone defects: BMP-2 gene activated muscle grafts vs. autologous bone grafting.

BACKGROUND: Common cell based strategies for the treatment of osseous defects require the isolation and expansion of autologous cells. Since this makes such approaches time-consuming and expensive, we developed a novel expedited technology creating gene activated muscle grafts. We have previously shown that large segmental bone defects in rats can be regenerated by implantation of muscle tissue fragments activated by BMP-2 gene transfer. RESULTS: In the present study, we compared the bone healing capacities of such gene activated muscle grafts with bone isografts, mimicking autologous bone grafting, the clinical gold standard for treatment of bone defects in patients. Two of 14 male, syngeneic Fischer 344 rats used for this experiment served as donors for muscle and bone. Muscle tissue was harvested from both hind limbs and incubated with an adenoviral vector carrying the cDNA encoding BMP-2. Bone was harvested from the iliac crest and long bone epiphyses. Bone defects (5 mm) were created in the right femora of 12 rats and were filled with either BMP-2 activated muscle tissue or bone grafts. After eight weeks, femora were evaluated by radiographs, micro-computed tomography (µCT), and biomechanical testing. In the group receiving BMP-2 activated muscle grafts as well as in the bone-grafting group, 100% of the bone defects were healed, as documented by radiographs and µCT-imaging. Bone volume was similar in both groups and biomechanical stability of the two groups was statistically indistinguishable. CONCLUSIONS: This study demonstrates that treatment of large bone defects by implantation of BMP-2 gene activated muscle tissue leads to similar bone volume and stability as bone isografts, mimicking autologous bone grafting.

Improvement of tendon repair using muscle grafts transduced with TGF-ß1 cDNA.

Tendon rupture is a common injury. Inadequate endogenous repair often leaves patients symptomatic, with tendons susceptible to re-rupture. Administration of certain growth factors improves tendon healing in animal models, but their delivery remains a challenge. Here we evaluated the delivery of TGF-ß1 to tendon defects by the implantation of genetically modified muscle grafts. Rat muscle biopsies were transduced with recombinant adenovirus encoding TGF-ß1 and grafted onto surgically transected Achilles tendons in recipient animals. Tissue regenerates were compared to those of controls by biomechanical testing as well as histochemical and immunohistochemical analyses. Healing was greatly accelerated when genetically modified grafts were implanted into tendon defects, with the resulting repair tissue gaining nearly normal histological appearance as early as 2 weeks postoperatively. This was associated with decreased deposition of type III collagen in favour of large fibre bundles indicative of type I collagen. These differences in tendon composition coincided with accelerated restoration of mechanical strength. Tendon thickness increased in gene-treated animals at weeks 1 and 2, but by week 8 became significantly lower than that of controls suggesting accelerated remodelling. Thus localised TGF-ß1 delivery via adenovirus-modified muscle grafts improved tendon healing in this rat model and holds promise for clinical application.

The repair of critical-sized bone defects using expedited, autologous BMP-2 gene-activated fat implants.

The repair of bone defects can be induced experimentally with bone morphogenetic protein-2 (BMP-2) producing fat-derived stem cells, but this ex vivo tissue engineering method requires the isolation and long-term culture of autologous cells. To develop an expedited bone repair strategy, we transferred BMP-2 cDNA directly to autologous fat tissue fragments that were held in culture for only 24 h before implantation. We evaluated the ability of such gene-activated fat grafts to regenerate large segmental bone defects in rats. Fat tissue was harvested from 2 of 35 male Fischer 344 rats used for this study. The fat tissue fragments were incubated with an adenoviral vector carrying the cDNA encoding either BMP-2 or green florescent protein (GFP), or they remained unmodified. According to their group, the segmental femoral bone defects of 33 rats were filled press fit with either BMP-2-activated fat tissue, GFP-transduced fat tissue, or unmodified fat tissue. Another control group remained untreated. Femora were evaluated by radiographs, microcomputed tomography, biomechanical torsional testing, and histology. Radiographically and histologically, 100% of the femora treated with BMP-2-activated fat grafts were bridged at 6 weeks after surgery. The femora of this group exceeded the bone volume and the biomechanical stability of intact, contralateral femora. Control defects receiving no treatment, unmodified fat tissue, or GFP-transduced fat were filled with fibrous or adipose tissue, as evaluated by histology. The use of BMP-2 gene-activated fat tissue grafts represents an expedited and effective bone repair strategy that does not require the extraction and expansion of stem cells.

Healing of large segmental bone defects induced by expedited bone morphogenetic protein-2 gene-activated, syngeneic muscle grafts.

Numerous preclinical studies have shown that osseous defects can be repaired by implanting bone morphogenetic protein (BMP)-2-transduced muscle cells. However, the drawback of this treatment modality is that it requires the isolation and long-term (approximately 3 weeks) culture of transduced autologous cells, which makes this approach cumbersome, time-consuming, and expensive. Therefore, we transferred BMP-2 cDNA directly to muscle tissue fragments that were held in culture for only 24 hr before implantation. We evaluated the ability of such gene-activated muscle grafts to induce bone repair. Two of 35 male, syngeneic Fischer 344 rats used in this study served as donors for muscle tissue. The muscle fragments remained unmodified or were incubated with an adenoviral vector carrying the cDNA encoding either green fluorescent protein (GFP) or BMP-2. Critical-size defects were created in the right femora of 33 rats and remained untreated or were filled (press fitted) with either unmodified muscle tissue or GFP-transduced muscle tissue or with BMP-2-activated muscle tissue. After 6 weeks, femora were evaluated by radiography, microcomputed tomography (muCT), histology, and biomechanical testing. Six weeks after implantation of BMP-2-activated muscle grafts, 100% of the bone defects were bridged, as documented by radiographs and muCT imaging, and showed formation of a neocortex, as evaluated by histology. Bone volumes of the femora repaired by BMP-2-transduced muscle were significantly (p = 0.006) higher compared with those of intact femora and the biomechanical stability was statistically indistinguishable. In contrast, control defects receiving no treatment, unmodified muscle, or GFP-transduced muscle did not heal. BMP-2 gene-activated muscle grafts are osteoregenerative composites that provide an expedited means of treating and subsequently healing large segmental bone defects.

Healing of segmental bone defects by direct percutaneous gene delivery: effect of vector dose.

Previous studies have demonstrated the ability of direct adenoviral BMP-2 (Ad.BMP-2) gene delivery to enhance bone repair. Nevertheless, in studies using a rat segmental defect model, it has not proved possible to achieve reliably full osseous union in all animals. To address this issue, we evaluated the effect of vector dose on healing. Critical-size defects were created in the right femora of 27 Sprague-Dawley rats. The defects received a single, intralesional, percutaneous injection of 2.7 x 10(7) (low dose), 2.7 x 10(8) (medium dose), or 2.7 x 10(9) (high dose) plaque-forming units of Ad.BMP-2. After 8 weeks, femora were evaluated by X-ray, dual-energy X-ray absorptiometry, microcomputed tomography (microCT), and histology. The high dose of vector bridged 100%, the medium dose 11%, and the low dose 25% of the defects, as evaluated by X-ray and microCT imaging. Bone mineral content and bone volume of the defects receiving the high dose of vector were significantly higher than those of both groups receiving lower doses. Histologically, defects treated with the high dose were filled by trabecular bone and small amounts of cartilage, whereas large areas of fibrous tissue and cartilage remained in the defects receiving lower doses. However, the newly formed bone lacked the structural organization of native bone, suggesting that further maturation is necessary.

Direct percutaneous gene delivery to enhance healing of segmental bone defects.

BACKGROUND: Healing of segmental bone defects can be induced experimentally with genetically modified osteoprogenitor cells, an ex vivo strategy that requires two operative interventions and substantial cost. Direct transfer of osteogenic genes offers an alternative, clinically expeditious, cost-effective approach. We evaluated its potential in a well-established, critical-size, rat femoral defect model. METHODS: A critical-size defect was created in the right femur of forty-eight skeletally mature Sprague-Dawley rats. After twenty-four hours, each defect received a single, intralesional, percutaneous injection of adenovirus carrying bone morphogenetic protein-2 (Ad.BMP-2) or luciferase cDNA (Ad.luc) or it remained untreated. Healing was monitored with weekly radiographs. At eight weeks, the rats were killed and the femora were evaluated with dual-energy x-ray absorptiometry, micro-computed tomography, histological analysis, histomorphometry, and torsional mechanical testing. RESULTS: Radiographically, 75% of the Ad.BMP-2-treated femora showed osseous union. Bone mineral content was similar between the Ad.BMP-2-treated femora (0.045 +/- 0.020 g) and the contralateral, intact femora (0.047 +/- 0.003 g). Histologically, 50% of the Ad.BMP-2-treated defects were bridged by lamellar, trabecular bone; the other 50% contained islands of cartilage. The control (Ad.luc-treated) defects were filled with fibrous tissue. Histomorphometry demonstrated a large difference in osteogenesis between the Ad.BMP-2 group (mean bone area, 3.25 +/- 0.67 mm(2)) and the controls (mean bone area, 0.65 +/- 0.67 mm(2)). By eight weeks, the Ad.BMP-2-treated femora had approximately one-fourth of the strength (mean, 0.07 +/- 0.04 Nm) and stiffness (mean, 0.5 +/- 0.4 Nm/rad) of the contralateral femora (0.3 +/- 0.08 Nm and 2.0 +/- 0.5 Nm/rad, respectively). CONCLUSIONS: A single, percutaneous, intralesional injection of Ad.BMP-2 induces healing of critical-size femoral bone defects in rats within eight weeks. At this time, the repair tissue is predominantly trabecular bone, has normal bone mineral content, and has gained mechanical strength.