Zongping Xie

Treatment of osteomyelitis and repair of bone defect by degradable bioactive borate glass releasing vancomycin.

The effectiveness of a degradable and bioactive borate glass has been compared with the clinically used calcium sulfate in the treatment of osteomyelitis of rabbits, as a carrier for vancomycin. The bone infections were induced in the tibias of 65 rabbits by injecting methicillin-resistant Staphylococcus aureus (MRSA). After 3 weeks, these rabbits were distributed into 4 groups and treated by debridement. Pure borate glass (BG), vancomycin-loaded calcium sulfate (VCS) and vancomycin-loaded borate glass (VBG) were implanted into the infection sites of groups 2 to 4 respectively. After 8 weeks, the effectiveness of treatment was assessed radiographically, bacteriologically, and histopathologically. The results showed that the negative rates of MRSA examination for rabbits were 36.36%, 18.18%, 73.33% and 81.25% respectively for groups 1 to 4. Significant differences were observed radiographically, bacteriologically, and histopathologically between groups 1 and 4, groups 2 and 3, and between groups 2 and 4. The best result of treatment was observed in group 4. Radiographically, VBG was found to be mostly reabsorbed and replaced by lots of new bones, whereas, VCS was completely reabsorbed and replaced by modest new bones. Histopathologically, there were lots of newly formed bones around VBG without any foreign body response, and only modest new bones around VCS with obvious foreign body response. VBG proved to have excellent biocompatibility and to be very effective in eradicating osteomyelitis and simultaneously stimulating bone regeneration, avoiding the disadvantages of VCS.

Exosomes/tricalcium phosphate combination scaffolds can enhance bone regeneration by activating the PI3K/Akt signaling pathway

BackgroundRecently, accumulating evidence has shown that exosomes, the naturally secreted nanocarriers of cells, can exert therapeutic effects in various disease models in the absence of parent cells. However, application of exosomes in bone defect repair and regeneration has been rarely reported, and little is known regarding their underlying mechanisms.MethodsExosomes derived from human-induced pluripotent stem cell-derived mesenchymal stem cells (hiPS-MSC-Exos) were combined with tricalcium phosphate (β-TCP) to repair critical-sized calvarial bone defects, and the efficacy was assessed by histological examination. We evaluated the in vitro effects of hiPSC-MSC-Exos on the proliferation, migration, and osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) by cell-counting, scratch assays, and qRT-PCR, respectively. Gene expression profiling and bioinformatics analyses were also used to identify the underlying mechanisms in the repair.ResultsWe found that the exosome/β-TCP combination scaffolds could enhance osteogenesis as compared to pure β-TCP scaffolds. In vitro assays showed that the exosomes could release from β-TCP and could be internalized by hBMSCs. In addition, the internalization of exosomes into hBMSCs could profoundly enhance the proliferation, migration, and osteogenic differentiation of hBMSCs. Furthermore, gene expression profiling and bioinformatics analyses demonstrated that exosome/β-TCP combination scaffolds significantly altered the expression of a network of genes involved in the PI3K/Akt signaling pathway. Functional studies further confirmed that the PI3K/Akt signaling pathway was the critical mediator during the exosome-induced osteogenic responses of hBMSCs.ConclusionsWe propose that the exosomes can enhance the osteoinductivity of β-TCP through activating the PI3K/Akt signaling pathway of hBMSCs, which means that the exosome/β-TCP combination scaffolds possess better osteogenesis activity than pure β-TCP scaffolds. These results indicate that naturally secreted nanocarriers-exosomes can be used as a bioactive material to improve the bioactivity of the biomaterials, and that hiPS-MSC-Exos combined with β-TCP scaffolds can be potentially used for repairing bone defects.

Gentamicin-Loaded Borate Bioactive Glass Eradicates Osteomyelitis Due to Escherichia coli in a Rabbit Model

ABSTRACT The treatment of osteomyelitis induced by Gram-negative bacilli is rarely reported in the literature. This study established a rabbit tibia model of osteomyelitis induced by the Gram-negative bacillus Escherichia coli. Using this model, pellets composed of a chitosan-bonded mixture of borate bioactive glass and gentamicin were evaluated in vitro and in vivo for the treatment of osteomyelitis induced by Escherichia coli. Our results showed that the pellets in phosphate-buffered saline released gentamicin continuously over 26 days. Without the simultaneous use of a systemic antibiotic, the implantation of the gentamicin-loaded pellets into the osteomyelitis region of the tibia resulted in the eradication of 81.82% of infections, as determined by microbiological, histological and radiographic evaluation, and supported the ingrowth of new bone into the tibia defects after 6 weeks of implantation. The results indicate that the gentamicin-loaded borate bioactive glass implant, combining sustained drug release with the ability to support new bone formation, could provide a method for treating osteomyelitis induced by Gram-negative bacilli.

In vivo study effect of particulate Bioglass® in the prevention of infection in open fracture fixation

There are many in vitro experiments showing that particulate bioactive glasses have a broad and certain antibacterial effect, but there is no report about this antibacterial effect in vivo so far. The aim of this study is to examine the efficacy of particulate Bioglass in reducing the rate of infection with Staphylococcus aureus after the fixation of open tibial fractures in rabbits. The test in vivo was carried out with male rabbits split into two groups infected with Staphylococcus aureus at the right tibial fracture sites fixed with plate and screw, either with or without bioactive glass respectively. Culture results show that six of ten rabbits from the control group had a positive culture for the strain of Staphylococcus aureus ATCC25923, compared with six of the nine rabbits from the Bioglass group. The median radiographic score is 4.5 points for the rabbits from the control group and 4 points for the rabbits from the Bioglass group. The median histopathological score was 2.5 points for the rabbits in the control group and 3 points for the rabbits in the Bioglass group. In conclusion, this study showed no significant difference between the rates of infection of two groups. Particulate Bioglass did not reduce the rate of infection with Staphylococcus aureus after the fixation of open tibial fractures in rabbits.

Dimethyloxaloylglycine Promotes the Angiogenic Activity of Mesenchymal Stem Cells Derived from iPSCs via Activation of the PI3K/Akt Pathway for Bone Regeneration

The vascularization of tissue-engineered bone is a prerequisite step for the successful repair of bone defects. Hypoxia inducible factor-1α (HIF-1α) plays an essential role in angiogenesis-osteogenesis coupling during bone regeneration and can activate the expression of angiogenic factors in mesenchymal stem cells (MSCs). Dimethyloxaloylglycine (DMOG) is an angiogenic small molecule that can inhibit prolyl hydroxylase (PHD) enzymes and thus regulate the stability of HIF-1α in cells at normal oxygen tension. Human induced pluripotent stem cell-derived MSCs (hiPSC-MSCs) are promising alternatives for stem cell therapy. In this study, we evaluated the effect of DMOG on promoting hiPSC-MSCs angiogenesis in tissue-engineered bone and simultaneously explored the underlying mechanisms in vitro. The effectiveness of DMOG in improving the expression of HIF-1α and its downstream angiogenic genes in hiPSC-MSCs demonstrated that DMOG significantly enhanced the gene and protein expression profiles of angiogenic-related factors in hiPSC-MSCs by sustaining the expression of HIF-1α. Further analysis showed that DMOG-stimulated hiPSC-MSCs angiogenesis was associated with the phosphorylation of protein kinase B (Akt) and with an increase in VEGF production. The effects could be blocked by the addition of the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. In a critical-sized calvarial defect model in rats, DMOG-treated hiPSC-MSCs showed markedly improved angiogenic capacity in the tissue-engineered bone, leading to bone regeneration. Collectively, the results indicate that DMOG, via activation of the PI3K/Akt pathway, promotes the angiogenesis of hiPSC-MSCs in tissue-engineered bone for bone defect repair and that DMOG-treated hiPSC-MSCs can be exploited as a potential therapeutic tool in bone regeneration.

Failure of particulate bioglass to prevent experimental staphylococcal infection of open tibial fractures

range from 355 to 500 mm, consisting of 45 wt% SiO2/24.5 wt% Na2O/24.5 wt% CaO/6 wt% P2O5) in vivo by examining its efficacy in reducing the rate of infection by Staphylococcus aureus after the fixation of open tibial fractures in rabbits. An in vivo test was carried out with male rabbits split into two groups infected with S. aureus ATCC 25923 at the right tibial fracture sites fixed with plates and screws, with 300 mg of particulate Bioglass w implanted in the fracture and surrounding area for the Bioglass w group, in accordance with the guidelines of the Local Animal Welfare Committee. Six weeks after the operation, the anteroposterior and lateral radiographs of the right tibia were taken and scored, the specimens from the plate and the bone were collected for microbiological evaluation, and the tibias were cut off for histopathological examination and scoring. There was no significant difference between the rates of infection in the control group (60%) and the Bioglass w group (66.7%) (P ¼ 0.35; Table 1). Similarly, there were no significant differences between the radiographic and histological scores of the control group (4.5 and 2.5, respectively) and the Bioglass w group (4 and 3, respectively) (P ¼ 0.96 and 0.32, respectively; Wilcoxon test). It has been suggested that bioglass exerts antibacterial activity by increasing pH, osmotic effects and calcium ion concentrations. 4,5 The failure of Bioglass w to prevent infection in this model may reflect the difference between in vitro and in vivo environments. For example, when bioglass particles are released into local body fluids in vivo, the local pH may not change due to the buffering capacity of the fluids. One possible limitation of the current study is that only a single strain of S. aureus was used, and a single body site was investigated. Although the initial results presented here showed no evidence for efficacy of bioglass in vivo, scope remains for studies with other strains or species of bacteria and other body sites.

Bioactive borate glass promotes the repair of radius segmental bone defects by enhancing the osteogenic differentiation of BMSCs.

Bioactive borate glass (BG) has emerged as a promising alternative for bone regeneration due to its high osteoinductivity, osteoconductivity, compressive strength, and biocompatibility. However, the role of BG in large segmental bone repair is unclear and little is known about the underlying mechanism of BGs osteoinductivity. In this study, we demonstrated that BG possessed pro-osteogenic effects in an experimental model of critical-sized radius defects. Transplanting BG to radius defects resulted in better repair of bone defects as compared to widely used β-TCP. Histological and morphological analysis indicated that BG significantly enhanced new bone formation. Furthermore, the degradation rate of the BG was faster than that of β-TCP, which matched the higher bone regeneration rate. In addition, ions from BG enhanced cell viability, ALP activity, and osteogenic-related genes expression. Mechanistically, the critical genes Smad1/5 and Dlx5 in the BMP pathway and p-Smad1/5 proteins were significantly elevated after BG transplantation, and these effects could be blocked by the BMP/Smad specific inhibitor. Taken together, our findings suggest that BG could repair large segmental bone defects through activating the BMP/Smad pathway and osteogenic differentiation in BMSCs.