Ultrasound enhances recombinant human BMP-2 induced ectopic bone formation in a rat model.

Two methods to improve bone repair include the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) and low-intensity pulsed ultrasound (LIPUS). The present study was designed to determine if LIPUS enhances the effect of rhBMP-2-induced bone formation in a well characterized ectopic implant model. Absorbable collagen sponges loaded with 0-, 1-, 2.5- or 5-microg doses of rhBMP-2 were implanted subcutaneously in 11-week-old, male Long Evans rats, followed by daily 20-min LIPUS or sham LIPUS treatment beginning 1 d after surgery. Explanted sponges were assessed for bone volume, mineral density and mineral content by microcomputed tomography (microCT). At two weeks, LIPUS had no effect on rhBMP-2-induced bone formation, but at four weeks, LIPUS increased bone volume in the 1-microg rhBMP-2-treated implants 117.7-fold (0.02 +/- 0.04 mm(3)vs. 2.07(S.E.M.) +/- 1.67 mm(3);p = 0.028), and 2.3-fold in the 5-microg dose implants (5.96 +/- 3.68 mm(3)vs. 13.52 +/- 6.81 mm(3);p = 0.077) compared with sham LIPUS. Bone mineral density was not affected by LIPUS treatment. Total mineral content followed the same pattern as bone volume. Histologic staining for mineralized tissue was consistent with the microCT observations. The present study is the first to demonstrate that LIPUS enhances bone formation induced by rhBMP-2.

Assessment of axonal growth into collagen nerve guides containing VEGF-transfected stem cells in matrigel.

The early events associated with axonal growth into 10-mm nerve gaps were studied histologically in the rat sciatic nerve model to determine if the outgrowth of blood vessels, Schwann cells, and axons could be enhanced. In the first two experimental groups, collagen nerve guides were filled with either saline or Matrigel. Marrow-derived mesenchymal stem cells (MSCs) were added to Matrigel in two other groups, one of which contained cells transfected with VEGF (MSC/VEGF). After 21 days, the injury site was exposed, fixed, sectioned, and volume fractions of the conduit contents were determined by point counting. The bioresorbable collagen conduits appropriately guided the axons and vessels in a longitudinal direction. The volume fraction of axons was significantly greater in the group with saline when compared with all three groups with Matrigel. This measure had a significant positive correlation with actual counts of myelinated axons. The blood vessel volume fraction in the Matrigel group decreased compared with the saline group, but was restored in the MSC/VEGF group. All Matrigel groups had comparable cellularity and showed a distribution of residual Matrigel in acellular zones. The saline group, by contrast, sustained a network of delicate fibroblastic processes that compartmentalized the nerve and its natural matrix as it became infiltrated by axons as minifascicles. In conclusion, the reduction of axonal outgrowth in the Matrigel groups, when compared with the saline group, suggests that Matrigel may impede the early regenerative process even when enriched by the addition of MSCs or VEGF-transfected cells.

Microstructural and strength evaluation of regenerate tissue during the consolidation period after vertical mandibular ramus distraction.

Mandibular ramus height restoration by distraction osteogenesis (DO) is a key procedure in mandibular hypoplasia reconstruction. The objective of this study was to evaluate short-term skeletal changes in the regenerated bone after vertical mandibular ramus DO using a buried distraction device. Eight subadult beagle dogs underwent bilateral vertical mandibular ramus DO. After a 7-day latency period, distraction was performed at a rate of 0.5 mm twice a day for 12 days. Four dogs were killed at 1 month and four dogs at 2 months after the end of distraction. One intact beagle was included as an unoperated control. After sacrifice, micro computed tomography (muCT) and mechanical testing of distracted sites were used to measure bone volume (BV), total volume (TV), and mechanical peak load strength, respectively. The muCT images showed wide variation in the response, with some animals demonstrating considerable bone formation and reconstitution of the canal for the inferior alveolar nerve. Quantitatively, BV was no more than 67% and BV/TV was less than 25% of the intact control, and strength was approximately 33% of the intact control value. The 1 and 2 month values were similar. These results suggest that internal distractors can successfully reconstitute bone but that the regenerated tissue did not regain structural and mechanical characteristics of native bone within the 2 month study period.

Effect of low intensity pulsed ultrasound and BMP-2 on rat bone marrow stromal cell gene expression.

To determine how low intensity pulsed ultrasound alters gene expression in rat bone marrow stromal cells and to see if combining this stimulation with BMP-2, cells were pre-cultured for eight days in the presence of 50 microg/ml ascorbic acid and then exposed to either low intensity US or 100 ng/ml BMP-2 or both combined, beginning on the first, third fifth or seventh day of culture so that cells were exposed to the stimuli for one, three, five or seven days. Real time PCR was used to determine the effect of these treatments on gene expression of several genes associated with osteogenesis. The expression of some of the genes (Cbfa-1/Runx2, IGF-receptor, Alk-3, alkaline phosphatase, osteopontin, TGF-beta1, BMP-7) was increased compared to untreated controls. Combination of US and BMP-2 treatment did not lead to synergy of the two stimuli. Cbfa-1 stimulation occurred more quickly with US than with BMP-2. Increases in gene expression were greatest after 3 days exposure to US, with similar results for BMP-2 treatment implying that there may be a time dependence for the stimulus of osteogenic gene expression in stromal cells.

Local application of rhTGF-beta2 enhances peri-implant bone volume and bone-implant contact in a rat model.

Orthopedic and dental implant fixation depends upon bone regeneration. Growth factors such as transforming growth factor-beta (TGF-beta) have been shown to enhance bone repair and strengthen the mechanical connection between implant and host skeleton in canine models. To provide a platform for studying molecular mechanisms of growth factor stimulated bone regeneration and implant fixation, the present study examined peri-implant bone volume as a response to TGF-beta treatment in a rodent model. The rat femoral ablation model in which an implant is placed in the medullary cavity of the femur was used to examine the dose response to TGF-beta2 applied to the implant (0, 0.1, 1.0, or 10 microg). The study included a total of 40 rats (10 per dose) examined at 28 days. Peri-implant bone volume and bone-implant contact were assessed through microcomputed tomography and implant fixation strength was determined by a mechanical pullout test. Treatment of the implant with 10 microg TGF-beta2 led to a 2-fold increase in bone volume (P<0.001) and a 1.5-fold increase in bone-implant contact (P<0.01) with a trend of increasing fixation strength (non-significant increase of 1.4-fold). TGF-beta2 treatment with 10 microg led to uniform peri-implant bone volume and bone-implant contact along the length of the implant, whereas the other groups had less bone at the mid-point compared to the proximal and distal aspects of the implant. About 50% of the variance in implant fixation strength was explained by a regression model involving both bone-implant contact and peri-implant bone volume.

Early gene response to low-intensity pulsed ultrasound in rat osteoblastic cells.

The aim of the current research was to quantify the changes in gene expression in rat bone marrow derived stromal cells (BMSC) to low intensity pulsed ultrasound (LIPUS) during early time points after the ultrasound application. LIPUS at 1.5 MHz, 30 mW/cm(2) was applied to BMSC for a single 20 min treatment. Real-time PCR was carried out to quantify the expression of early response genes and bone differentiation marker genes 0.5, 1, 3, 6 and 12 h after the end of the LIPUS treatment. Compared with the controls, LIPUS treatment resulted in elevated transient expression of early response genes (c-jun, c-myc, COX-2, Egr-1, TSC-22) as well as the bone differentiation marker genes, osteonectin and osteopontin, at 3 h. This induction of early response genes as well as extracellular matrix genes associated with cell proliferation and differentiation may represent the effect of LIPUS to cells of osteoblastic lineage.

Patterns of gene expression in rat bone marrow stromal cells cultured on titanium alloy discs of different roughness.

Rat bone marrow stromal cells were cultured on either Ra (0.14 microm) or Ra (5.8 microm) Ti6Al4V discs for 24 or 48 h. Cells on the Ra (0.14 microm) surface showed typical fibroblastic morphology, whereas cells on the Ra (5.8 microm) surface were in clusters with a more epithelial appearance. RNA was extracted from the cells at both time points, and gene expression was analyzed by using a rat gene microarray. At 24 and 48 h, a similar number of genes were both up- and down-regulated at least twofold on the Ra (5.8 microm) surface compared to the Ra (0.14 microm) surface. We analyzed the relative level of specific groups of genes related to bone and cartilage development, cell adhesion and extracellular matrix proteins, transcription factors, bone morphogenetic proteins, phospholipases, and protein kinases. Roughness did not appear to be a specific stimulator of osteogenesis because genes of both the bone and cartilage lineage were up-regulated on the Ra (5.8 microm) surface. The most prominent change among transcription factors was up-regulation of Hox 1.4 on the Ra (5.8 microm) surface. Up-regulation of phospholipase A2 and SMAD 4 indicate these genes are also involved in the response of cells to an Ra (5.8 microm) surface. Our data show surface roughness alters the expression of a large number of genes in marrow stromal cells, which are related to multiple pathways of mesenchymal cell differentiation.