Duohong Zou

The synergistic effect of hierarchical micro/nano-topography and bioactive ions for enhanced osseointegration

Both surface chemistry and topography have significant influence on good and fast osseointegration of biomedical implants; the main goals in orthopeadic, dental and maxillofacial surgeries. A surface modification strategy encompassing the use of bioactive trace elements together with surface micron/nano-topographical modifications was employed in this study in an attempt to enhance the osseointegration of Ti alloy (Ti-6Al-4V), a commonly used implant. Briefly, we developed strontium-substituted hardystonite (Sr-HT) ceramic coating with a hierarchical topography where the nanosized grains were superimposed in the micron-rough coating structure. Its ability to induce new bone formation was evaluated by an in vivo animal model (beagle dogs). Hardystonite (HT), classic hydroxyapatite (HAp) coated and uncoated Ti-alloy implants were parallelly investigated for comparison. In addition, we investigated the effects of surface topography and the dissolution products from the coatings on the in vitro bioactivity using canine bone marrow mesenchymal stem cells (BMMSCs) cultured on the implant surface as well as using extracts of the coated implants. Micro-CT evaluation, histological observations, biomechanical test (push-out test) and sequential fluorescent labeling and histomorphometrical analysis consistently demonstrated that our developed Sr-HT-coated Ti-alloy implants have the highest osseointegration, while the uncoated implants had the lowest. The osseointegration ability of HAp-coated Ti alloy was inferior to that seen for HT- and Sr-HT-coated Ti alloy. We demonstrated that the dissolution products, particularly strontium (Sr) from the Sr-HT-coated implants, enhanced the ALP activity and in vitro mineralization ability, while the micro/nano-topography was more related to the promotion of cell adhesion. Those results suggest that our developed Sr-HT coatings have the potential for future use as coatings for orthopedic/dental and maxillofacial devices.

Repair of Critical-Sized Rat Calvarial Defects Using Genetically Engineered Bone Marrow-Derived Mesenchymal Stem Cells Overexpressing Hypoxia-Inducible Factor-1ᆇ§

The processes of angiogenesis and bone formation are coupled both temporally and spatially during bone repair. Bone marrow‐derived mesenchymal stem cells (BMSCs) have been effectively used to heal critical‐size bone defects. Enhancing their ability to undergo angiogenic and osteogenic differentiation will enhance their potential use in bone regeneration. Hypoxia‐inducible factor‐1α (HIF‐1α) has recently been identified as a major regulator of angiogenic‐osteogenic coupling. In this study, we tested the hypothesis that HIF‐1α gene therapy could be used to promote the repair of critical‐sized bone defects. Using lentivirus‐mediated delivery of wild‐type (HIF) or constitutively active HIF‐1α (cHIF), we found that in cultured BMSCs in vitro, HIF and cHIF significantly enhanced osteogenic and angiogenic mRNA and protein expression when compared with the LacZ group. We found that HIF‐1α‐overexpressing BMSCs dramatically improved the repair of critical‐sized calvarial defects, including increased bone volume, bone mineral density, blood vessel number, and blood vessel area in vivo. These data confirm the essential role of HIF‐1α modified BMSCs in angiogenesis and osteogenesis in vitro and in vivo. STEM CELLS 2011;29:1380–1390

The Bone-Forming Effects of HIF-1α-Transduced BMSCs Promote Osseointegration with Dental Implant in Canine Mandible

The presence of insufficient bone volume remains a major clinical problem for dental implant placement to restore the oral function. Gene-transduced stem cells provide a promising approach for inducing bone regeneration and enhancing osseointegration in dental implants with tissue engineering technology. Our previous studies have demonstrated that the hypoxia-inducible factor-1α (HIF-1α) promotes osteogenesis in rat bone mesenchymal stem cells (BMSCs). In this study, the function of HIF-1α was validated for the first time in a preclinical large animal canine model in term of its ability to promote new bone formation in defects around implants as well as the osseointegration between tissue-engineered bone and dental implants. A lentiviral vector was constructed with the constitutively active form of HIF-1α (cHIF). The ectopic bone formation was evaluated in nude mice. The therapeutic potential of HIF-1α-overexpressing canine BMSCs in bone repair was evaluated in mesi-implant defects of immediate post-extraction implants in the canine mandible. HIF-1α mediated canine BMSCs significantly promoted new bone formation both subcutaneously and in mesi-implant defects, including increased bone volume, bone mineral density, trabecular thickness, and trabecular bone volume fraction. Furthermore, osseointegration was significantly enhanced by HIF-1α-overexpressing canine BMSCs. This study provides an important experimental evidence in a preclinical large animal model concerning to the potential applications of HIF-1α in promoting new bone formation as well as the osseointegration of immediate implantation for oral function restoration.

Long-Term Results for Maxillary Rehabilitation with Dental Implants after Tumor Resection

BACKGROUND Defects of the maxilla due to tumor extirpation can create accordingly high levels of psychological and physical trauma for patients and their families. However, the reconstruction of maxillary defects remains very challenging. Today, using autogenous bone grafts and dental implants is an effective method to restore maxillary defects. PURPOSE The purpose of this study was to evaluate the long-term clinical outcomes of maxillary rehabilitation with dental implants after tumor resection. Patient satisfaction after maxillary reconstruction was also assessed with regard to function and comfort. MATERIALS AND METHODS Over a 6-year period (2000-2005), 24 patients with maxillary tumors underwent resection with either immediate (n = 18) or delayed reconstruction or underwent prosthetic rehabilitation (n = 6).The patients received 88 implants in total, including 9 zygomatic and 79 conventional implants, for maxillary rehabilitation of the defective areas. RESULTS Autogenous bone grafts were successful in all patients, although partial loss of the graft was observed in one patient who received an iliac graft. Patient follow-up was started at the point of the prosthetic loading of implants. The median treatment time was 99.1 months (range:18-137 months). One patient died after 18 months of follow-up due to tumor recurrence, and two patients were lost to follow-up after 3 years of observation. Ten conventional dental implants were removed due to peri-implantitis. Six patients chose implant-supported obturators. The cumulative survival and success rates of the implants were 88.6 and 86.3%, respectively. CONCLUSIONS This study demonstrated that the rehabilitation of maxillary defects following tumor resection using implant-supported fixed prostheses with autogenous bone grafts or prosthetic rehabilitation is successful and is associated with high patient satisfaction. Oral function can be restored using dental implants for patients with maxillary defects.

A pH-Responsive Yolk-Like Nanoplatform for Tumor Targeted Dual-Mode Magnetic Resonance Imaging and Chemotherapy

Incorporation of T1 and T2 contrast material in one nanosystem performing their respective MR contrast role and simultaneously serving as an efficient drug delivery system (DDS) has a significant potential application for clinical diagnosis and chemotherapy of cancer. However, inappropriate incorporation always encountered many issues, such as low contact area of T1 contrast material with water-proton, inappropriate distance between T2 contrast material and water molecule, and undesirable disturbance of T2 contrast material for T1 imaging. Those issues seriously limited the T1 or T2 contrast effect. In this work, we developed a yolk-like Fe3O4@Gd2O3 nanoplatform functionalized by polyethylene glycol and folic acid (FA), which could efficiently exert their tumor targeted T1-T2 dual-mode MR imaging and drug delivery role. First, this nanoplatform possessed a high longitudinal relaxation rate (r1) (7.91 mM-1 s-1) and a stronger transverse relaxation rate (r2) (386.5 mM-1 s-1) than that of original Fe3O4 (268.1 mM-1 s-1). Second, cisplatin could be efficiently loaded into this nanoplatform (112 mg/g) and showed pH-responsive release behavior. Third, this nanoplatform could be effectively internalized by HeLa cells with time and dosage dependence. Fourth, the FA receptor-mediated nanoplatform displayed excellent T1-T2 dual mode MR contrast enhancement and anticancer activity both in vitro and in vivo. Fifth, no apparent toxicity for vital organs was observed with systemic delivery of the nanoplatform in vivo. Thus, this nanoplatform could be a potential nanotheranostic for tumor targeted T1-T2 dual-mode MR imaging and chemotherapy.

Autologous Ilium Grafts: Long-Term Results on Immediate or Staged Functional Rehabilitation of Mandibular Segmental Defects Using Dental Implants after Tumor Resection

BACKGROUND It is a challenge for clinicians to restore oral function in patients with segmental defects of the mandible because of tumor extirpation. Dental implant therapy following vascularized autologous ilium grafts is an effective method to restore oral function in patients with mandibular segmental defects. PURPOSE The aim of this retrospective study was to investigate the long-term clinical outcomes of ilium grafts combined with immediate or staged mandibular dental implant therapy to restore craniofacial defects resulting from tumor resection. MATERIALS AND METHODS Over a 5-year period (2000-2004), 32 patients who underwent mandibular segmental resection for tumors were treated with vascularized ilium grafts to augment bone volume. Seventeen patients received phase I therapy (immediate placement of implants), and 15 patients underwent phase II therapy (delayed placement of implants). A total of 110 dental implants were placed in these patients for mandibular restoration of the defective areas. Information regarding implant success and survival rates, marginal bone loss, soft tissue inflammation, complications of prosthesis, and patient satisfaction for the 8 to 12 years following oral reconstruction was obtained from patient records. RESULTS Although there was mild evidence of bone graft resorption, the vascularized autogenous ilium bone grafts were successful in all patients. The cumulative patient survival and success rate of the implants were 96.4% and 91.8%, respectively. The mean peri-implant bone resorption ranged from 1.0 to 1.2 mm over the 8- to 12-year follow-up period. The annual mean number of complications/repairs was from 0.11 to 0.07 per patient during the 8- to 12-year follow-up. Over 80% of the patients were fully satisfied with their restoration of oral function. CONCLUSIONS This study demonstrates that reconstruction of mandibular segmental defects because of resection of mandibular tumors using dental implants therapy combined with vascularized autogenous ilium grafts is an effective method to restore oral function.

Comprehensive Evaluation of Cryopreserved Bone-Derived Osteoblasts for the Repair of Segmental Mandibular Defects in Canines

BACKGROUND The repair of segmental mandibular defects remains challenging in the clinic. Previous studies have shown that cryopreserved bone-derived osteoblasts (CBOs) have good proliferation and osteogenicity. However, whether these cells can be used in the repair of segmental mandibular defects is largely unknown. PURPOSE In this study, we applied CBOs combined with beta-tricalcium phosphate (β-TCP) to repair a segmental mandibular defect in canines and thus established the feasibility of using this type of tissue-bank cell for the repair of large bone defects in the future. MATERIAL AND METHODS Sixteen segmental mandibular defects in 16 animals were made on the right side. Sequential radiographs, computer tomography, polychrome fluorescent labeling, immunohistochemical staining, and histological analysis were used to evaluate the effects of tissue-engineered bone for segmental mandibular defects. RESULTS Our results demonstrated that CBOs combined with β-TCP promoted bone mineralization and deposition at the early stage, and bony union was achieved in the CBO and fresh bone-derived osteoblast (FBO) groups. However, nonunion and minimal callus were present in the β-TCP group. Furthermore, there was a large amount of newly formed bone in the CBO and FBO groups and in the autogenous bone group. Additionally, osteocalcin immunohistochemistry showed intensive osteocalcin immunoreactivity in the bone matrix of the CBO and FBO groups. CONCLUSIONS These data indicate that CBOs implanted in a scaffold can promote new bone formation, and this tissue-engineered bone can repair critically sized segmental mandibular defects in canines. The use of CBOs combined with β-TCP may be an effective approach for the reconstruction of segmental mandibular defects in the clinic.

Comparison of Intraoral Bone Regeneration with Iliac and Alveolar BMSCs

This study compared the osteogenic potential of bone marrow mesenchymal stem cells (BMSCs) of iliac and alveolar origins (I-BMSCs and Al-BMSCs, respectively), which were transplanted in combination with β tricalcium phosphate (β-TCP) in peri-implant bone defects to investigate the osseointegration between dental implants and tissue-engineered bone in dogs. Specifically, I-BMSCs and Al-BMSCs were cultured, characterized, and seeded on β-TCP and subjected to immunoblotting analyses and alkaline phosphatase activity assays. Subsequently, these cell-seeded scaffolds were implanted into defects that were freshly generated in the mandibular premolar areas of 4 dogs. The defects were covered with β-TCP + Al-BMSCs (n = 6), β-TCP + I-BMSCs (n = 6), or β-TCP (n = 6) or served as the blank control (n = 6). After healing for 12 wk, the formation and mineralization of new bones were assessed through micro–computed tomographic, histologic, and histomorphometric analyses, and bone-to-implant contacts were measured in the specimens. It was evident that in this large animal model, I-BMSCs and Al-BMSCs manifested similarly strong osteogenic potential, as significantly more new bone was formed in the Al-BMSC and I-BMSC groups than otherwise (P < 0.01). Therefore, Al-BMSCs are emerging as an efficient alternative for autologous mesenchymal stem cells in regenerative dental and maxillofacial therapies. I-BMSCs, if not restricted in their bioavailability, can also be of great utility in bone tissue–engineering applications.

Superhero Rictor promotes cellular differentiation of mouse embryonic stem cells

Embryonic stem cells (ESCs) hold great promise for regenerative medicine. To harness the full therapeutic potential of ESCs, better understanding of the molecular mechanisms underlying the maintenance and differentiation of ESCs is required. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that integrates growth factor receptor signaling with cellular growth and proliferation. Dysregulation of mTOR signaling has been linked to various human diseases including cancer and metabolic syndromes. However, little is known regarding the function of mTOR signaling in the regulation of ES cell differentiation. Here we report that Rictor, a key component of mTORC2, functions as a novel ES cell differentiation promoting factor. Mechanistically, Rictor is able to interact with Prkch and facilitate Prkch phosphorylation at Ser-642. Upon phosphorylation, Prkch promotes Klf4 phosphorylation and inhibits Klf4-dependent E-cadherin expression, thereafter leading to the ES cell differentiation. These findings reveal a novel Rictor–Prkch–Klf4 pathway that plays an important role in the regulation of ES cell differentiation.

Functional reconstruction of critical-sized load-bearing bone defects using a Sclerostin-targeting miR-210-3p-based construct to enhance osteogenic activity

A considerable amount of research has focused on improving regenerative therapy strategies for repairing defects in load-bearing bones. The enhancement of tissue regeneration with microRNAs (miRNAs) is being developed because miRNAs can simultaneously regulate multiple signaling pathways in an endogenous manner. In this study, we developed a miR-210-based bone repair strategy. We identified a miRNA (miR-210-3p) that can simultaneously up-regulate the expression of multiple key osteogenic genes in vitro. This process resulted in enhanced bone formation in a subcutaneous mouse model with a miR-210-3p/poly-l-lactic acid (PLLA)/bone marrow-derived stem cell (BMSC) construct. Furthermore, we constructed a model of critical-sized load-bearing bone defects and implanted a miR-210-3p/β-tricalcium phosphate (β-TCP)/bone mesenchymal stem cell (BMSC) construct into the defect. We found that the load-bearing defect was almost fully repaired using the miR-210-3p construct. We also identified a new mechanism by which miR-210-3p regulates Sclerostin protein levels. This miRNA-based strategy may yield novel therapeutic methods for the treatment of regenerative defects in vital load-bearing bones by utilizing miRNA therapy for tissue engineering. STATEMENT OF SIGNIFICANCE The destroyed maxillofacial bone reconstruction is still a real challenge for maxillofacial surgeon, due to that functional bone reconstruction involved load-bearing. Base on the above problem, this paper developed a novel miR-210-3p/β-tricalcium phosphate (TCP)/bone marrow-derived stem cell (BMSC) construct (miR-210-3p/β-TCP/BMSCs), which lead to functional reconstruction of critical-size mandible bone defect. We found that the load-bearing defect was almost fully repaired using the miR-210-3p construct. In addition, we also found the mechanism of how the delivered microRNA activated the signaling pathways of endogenous stem cells, leading to the defect regeneration. This miRNA-based strategy can be used to regenerate defects in vital load-bearing bones, thus addressing a critical challenge in regenerative medicine by utilizing miRNA therapy for tissue engineering.