The influence of hyperbaric oxygen treatment on the healing of experimental defects filled with different bone graft substitutes

Bone Graft Substitutes and Enhancement in Craniomaxillofacial Surgery

Critical-sized bone defects are a reconstructive challenge, particularly in the craniomaxillofacial (CMF) skeleton. The "gold standard" of autologous bone grafting has been the work horse of reconstruction in both congenital and acquired defects of CMF skeleton. Autologous bone has the proper balance of the protein (or organic) matrix and mineral components with no immune response. Organic and mineral adjuncts exist that offer varying degrees of osteogenic, osteoconductive, osteoinductive, and osteostimulative properties needed for treatment of critical-sized defects. In this review, we discuss the various mostly organic and mostly mineral bone graft substitutes available for autologous bone grafting. Primarily organic bone graft substitutes/enhancers, including bone morphogenic protein, platelet-rich plasma, and other growth factors, have been utilized to support de novo bone growth in setting of critical-sized bone defects. Primarily mineral options, including various calcium salt formulation (calcium sulfate/phosphate/apatite) and bioactive glasses have been long utilized for their similar composition to bone. Yet, a bone graft substitute that can supplant autologous bone grafting is still elusive. However, case-specific utilization of bone graft substitutes offers a wider array of reconstructive options.

Functional regulation of osteoblastic MC3T3E-1 cells by hyperbaric oxygen treatment

OBJECTIVES

The purpose of the present study was to examine the influence of hyperbaric oxygen (HBO) on the function of osteoblastic MC3T3-E1 cells.

DESIGN

Murine MC3T3-E1 cells were exposed to HBO treatment (at 2.5 absolute atmospheric pressure with 100% oxygen, 90 min per day) for 28 days. Alkaline phosphatase (ALP) staining, activity, and calcium (Ca) content were measured. Gene expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), hypoxia-inducible factor-1α (HIF-1α), type 1 collagen (COL1), and osteocalcin (OCN) was assessed using real-time quantitative polymerase chain reaction after a single HBO exposure for 1.5, 6, and 12 h. Furthermore, adenosine triphosphate (ATP) levels were measured using a luminescent cell viability assay.

RESULTS

ALP activity and Ca content were higher in the HBO group compared to those in the control group. Gene expression of bFGF, COL1, and OCN was upregulated in the HBO group; however, that of VEGF and HIF-1α significantly decreased in the HBO group in comparison with that in the control group. ATP levels were significantly higher in the HBO group compared to those in the control group.

CONCLUSIONS

These findings suggest that HBO accelerates bone formation by increasing the ATP levels of osteoblasts, and bFGF can act as a substitute for VEGF in vascularization by HBO application.

Impact of Hyperbaric Oxygen on the Healing of Teeth Extraction Sockets and Alveolar Ridge Preservation

OBJECTIVES

The purpose of this study was to investigate the role of hyperbaric oxygen (HBO) in the healing of teeth extraction sockets and in alveolar ridge preservation. This may provide an experimental basis for the widespread application of HBO in oral implantation.

METHODS

A total of 32 beagle dogs were included in the study and randomly divided equally between an HBO group treated with hyperbaric oxygen (100% O₂, 2.4 atm, 90 min/day, 5 times/week, 6 weeks) and a normobaric oxygen (NBO) group treated with normal air in the same chamber. The lateral incisors of the maxillary and mandible of each dog were extracted, and the right upper and lower incisor extraction sockets (A2C2) were allowed to heal naturally, while left upper and lower incisor sockets (B2D2) received implants of a commercial bone substitute. At 4 and 8 weeks after surgery, clinical observation, cone-beam computerized tomography (CBCT), histomorphology observation, and expression levels of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) were analyzed to evaluate new bone formation, mineralization, and reconstruction.

RESULTS

After 4 and 8 weeks, bone width and lip contour of the extraction socket in the NBO group were significantly reduced and collapsed in comparison with the HBO group. CBCT showed that the difference in vertical height between the alveolar crest of the labial tongue and palatal side of the extraction sockets was smaller in the HBO than NBO group. There was a significant difference in new bone formation (P < 0.05) and bone mineral density (P < 0.05) between the HBO and NBO groups, and the HBO group showed significantly greater new bone and bone reconstruction based on histology. Furthermore, the expression levels of VEGF and BMP-2 were higher in the HBO group.

CONCLUSION

HBO reduced bone resorption and promoted early bone formation, bone mineralization, and reconstruction in the extraction sockets. HBO greatly reduced the healing time of the extraction sockets and promoted alveolar ridge preservation, thus showing promise for the clinic.

Eight-week healing of grafted calvarial bone defects with hyperbaric oxygen therapy in rats

Purpose

The purpose of this study was to evaluate the synergistic effect of adjunctive hyperbaric oxygen (HBO) therapy on new bone formation and angiogenesis after 8 weeks of healing.

Methods

Sprague-Dawley rats (n=28) were split into 2 groups according to the application of adjunctive HBO therapy: a group that received HBO therapy (HBO group [n=14]) and another group that did not receive HBO therapy (NHBO group [n=14]). Each group was divided into 2 subgroups according to the type of bone graft material: a biphasic calcium phosphate (BCP) subgroup and an Escherichia coli-derived recombinant human bone morphogenetic protein-2-/epigallocatechin-3-gallate-coated BCP (mBCP) subgroup. Two identical circular defects with a 6-mm diameter were made in the right and left parietal bones of each rat. One defect was grafted with bone graft material (BCP or mBCP). The other defect was not grafted. The HBO group received 2 weeks of adjunctive HBO therapy (1 hour, 5 times a week). The rats were euthanized 8 weeks after surgery. The specimens were prepared for histologic analysis.

Results

New bone (%) was higher in the NHBO-mBCP group than in the NHBO-BCP and control groups (P<0.05). Blood vessel count (%) and vascular endothelial growth factor staining (%) were higher in the HBO-mBCP group than in the NHBO-mBCP group (P<0.05).

Conclusions

HBO therapy did not have a positive influence on bone formation irrespective of the type of bone graft material applied after 8 weeks of healing. HBO therapy had a positive effect on angiogenic activity.

Adjunctive hyperbaric oxygen therapy for irradiated rat calvarial defects

Purpose

The aim of this study was to conduct a histologic evaluation of irradiated calvarial defects in rats 4 weeks after applying fibroblast growth factor-2 (FGF-2) with hyaluronan or biphasic calcium phosphate (BCP) block in the presence or absence of adjunctive hyperbaric oxygen (HBO) therapy.

Methods

Twenty rats were divided into HBO and non-HBO (NHBO) groups, each of which was divided into FGF-2 and BCP-block subgroups according to the grafted material. Localized radiation with a single 12-Gy dose was applied to the calvaria of rats to simulate radiotherapy. Four weeks after applying this radiation, 2 symmetrical circular defects with a diameter of 6 mm were created in the parietal bones of each animal. The right-side defect was filled with the materials mentioned above and the left-side defect was not filled (as a control). All defects were covered with a resorbable barrier membrane. During 4 weeks of healing, 1 hour of HBO therapy was applied to the rats in the HBO groups 5 times a week. The rats were then killed, and the calvarial specimens were harvested for radiographic and histologic analyses.

Results

New bone formation was greatest in the FGF-2 subgroup, and improvement was not found in the BCP subgroup. HBO seemed to have a minimal effect on new bone formation. There was tendency for more angiogenesis in the HBO groups than the NHBO groups, but the group with HBO and FGF-2 did not show significantly better outcomes than the HBO-only group or the NHBO group with FGF-2.

Conclusions

HBO exerted beneficial effects on angiogenesis in calvarial defects of irradiated rats over a 4-week healing period, but it appeared to have minimal effects on bone regeneration. FGF-2 seemed to enhance new bone formation and angiogenesis, but its efficacy appeared to be reduced when HBO was applied.

Synergistic effect of hyperbaric oxygen therapy with PTH [1-34] on calvarial bone graft in irradiated rat

OBJECTIVE

To determine the synergistic effect of parathyroid hormone (PTH) [1-34] in combination with hyperbaric oxygen (HBO) on bone graft in a rat calvarial bone defect model under impaired osteogenic conditions.

MATERIALS AND METHODS

Twenty-four rats were divided into three groups. Localized radiation with a single 12 Gy dose was administered to the calvaria. Four weeks after radiation, calvarial circular defects were created in the parietal bones. All defects were filled with biphasic calcium phosphate. After the bone graft, PTH [1-34] was injected subcutaneously, and HBO was administered. At 6 weeks after the bone graft, the rats were sacrificed, and specimens were harvested.

RESULTS

Histomorphometric evaluation showed that the percentage of new bone area was higher in the PTH and PTH/HBO groups than in the control group. The percent residual material area was decreased in the PTH/HBO group compared with the control group. The percentage blood vessel number was highest in the PTH group. Micro-CT evaluation showed that the new bone volume was highest in the PTH/HBO group. The residual material volume was lowest in the PTH/HBO group.

CONCLUSION

Within the limitations of this study, our data indicate that PTH combined with HBO may reverse radiation-induced impairment of bone healing.

Delayed bone healing by collagen membrane in early phase of 4 weeks

OBJECTIVE

Barrier membranes are important in maintaining space in guided bone regeneration process by preventing downgrowth of epithelial or connective tissue. In this study, the effects of resorbable membranes during the early stages of bone regeneration in rats with impaired bone healing capacity were investigated.

STUDY DESIGN

Twenty-eight rats were selected for this study. Half of the animals were selected for radiation therapy before surgical procedure (G3, G4). Animals were assigned into 4 groups (G1-G4). A circular defect was created in the central parietal bone. It was covered with resorbable membrane in G2 and G4. After 4 weeks, the animals were sacrificed.

RESULTS

At week 4, the new bone formation was observed around the margin of old bone in G1, G2 and G4 groups. Osteoclast was most abundant in the G1 group (18.3 ± 7.7) and least abundant in the G4 group (7.9 ± 4.7). The mean of osteocalcin levels in blood was the highest in the G2 group and lowest in the G3 group. Only G4 group showed significant difference in Runx2 levels between before-treatment and after- treatment.

CONCLUSIONS

Bone healing is adversely affected after radiation therapy. In addition, resorbable membranes can delay healing in the early stages of bone regeneration.

Four-week histologic evaluation of grafted calvarial defects with adjunctive hyperbaric oxygen therapy in rats

Purpose

The aim of this study was to characterize the healing in the grafted calvarial defects of rats after adjunctive hyperbaric oxygen therapy.

Methods

Twenty-eight male Sprague-Dawley rats (body weight, 250–300 g) were randomly divided into two treatment groups: with hyperbaric oxygen therapy (HBO; n=14) and without HBO (NHBO; n=14). Each group was further subdivided according to the bone substitute applied: biphasic calcium phosphate (BCP; n=7) and surface-modified BCP (mBCP; n=7). The mBCP comprised BCP coated with Escherichia-coli-derived recombinant human bone morphogenetic protein-2 (ErhBMP-2) and epigallocatechin-3-gallate (EGCG). Two symmetrical circular defects (6-mm diameter) were created in the right and left parietal bones of each animal. One defect was assigned as a control defect and received no bone substitute, while the other defect was filled with either BCP or mBCP. The animals were allowed to heal for 4 weeks, during which those in the HBO group underwent 5 sessions of HBO. At 4 weeks, the animals were sacrificed, and the defects were harvested for histologic and histomorphometric analysis.

Results

Well-maintained space was found in the grafted groups. Woven bone connected to and away from the defect margin was formed. More angiogenesis was found with HBO and EGCG/BMP-2 (P<0.05). None of the defects achieved complete defect closure. Increased new bone formation with HBO or EGCG/BMP-2 was evident in histologic evaluation, but it did not reach statistical significance in histometric analysis. A synergic effect between HBO and EGCG/BMP-2 was not found.

Conclusions

Within the limitations of this study, the present findings indicate that adjunctive HBO and EGCG/BMP-2 could be beneficial for new bone formation in rat calvarial defects.

The effect of bone marrow concentrate and hyperbaric oxygen therapy on bone repair

Neoangiogenesis represents an essential part of bone regeneration. Therefore the improvement of neovascularization is the subject of various research approaches. In addition autologous mesenchymal stem cells concentrate in combination with bone substitute materials have been shown to support bone regeneration. In a rabbit model we examined the proposed synergistic effect of hyperbaric oxygen therapy (HBOT) and bone marrow concentrate (BMC) with porous calcium phosphate granules (CPG) on neoangiogenesis and osseous consolidation of a critical- size defect. The animal groups treated with HBOT showed a significantly higher microvessel density (MVD) by immunhistochemistry. Furthermore HBOT groups presented a significantly larger amount of new bone formation histomorphometrically as well as radiologically. We conclude that the increase in perfusion as a result of increased angiogenesis may play a key role in the effects of HBOT and consequently promotes bone healing.

Effective immobilization of BMP-2 mediated by polydopamine coating on biodegradable nanofibers for enhanced in vivo bone formation

Although bone morphogenic proteins (BMPs) have been widely used for bone regeneration, the ideal delivery system with optimized dose and minimized side effects is still active area of research. In this study, we developed bone morphogenetic protein-2(BMP-2) immobilized poly(l-lactide) (PLLA) nanofibers inspired by polydopamine, which could be ultimately used as membranes for guided bone regeneration, and investigated their effect on guidance of in vitro cell behavior and in vivo bone formation. Surface chemical analysis of the nanofibers confirmed successful immobilization of BMP-2 mediated by polydopamine, and about 90% of BMP-2 was stably retained on the nanofiber surface for at least 28 days. The alkaline phosphatase activity and calcium mineralization of human mesenchymal stem cells (hMSCs) after 14 days of in vitro culture was significantly enhanced on nanofibers immobilized with BMP-2. More importantly, BMP-2 at a relatively small dose was highly active following implantation to the critical-sized defect in the cranium of mice; radiographic analysis demonstrated that 77.8 ± 11.7% of newly formed bone was filled within the defect for a BMP-2-immobilized groups at the concentration of 124 ± 9 ng/cm(2), as compared to 5.9 ± 1.0 and 34.1 ± 5.5% recovery, for a defect-only and a polydopamine-only group, respectively. Scanning and transmission electron microscopy of samples from the BMP-2 immobilized group showed fibroblasts and osteoblasts with nanofiber strands in the middle of regenerated bone tissue, revealing the importance of interaction between implanted nanofibers and the neighboring extracellular environment. Taken together, our data support that the presentation of BMP-2 on the surface of nanofibers as immobilized by utilizing polydopamine chemistry may be an effective method to direct bone growth at relatively low local concentration.

Mechanisms of action of hyperbaric oxygenation in stroke: a review

This article outlines the therapeutic mechanisms of hyperbaric oxygenation in acute stroke, based on information obtained from peer-reviewed medical literature. Hyperbaric oxygen is an approved treatment modality for ischemia-reperfusion injury in several conditions. It maintains the viability of the marginal tissue, reduces the mitochondrial dysfunction, metabolic penumbra, and blocks inflammatory cascades observed in acute stroke. Basic and clinical data suggest that hyperbaric oxygen could be a safe and effective treatment option in the management of acute stroke. Further work is needed to clarify its clinical utility when applied within the treatment window of "gold standard" treatments (<3-5 hours).