Amir Kamali

Potential mechanisms and applications of statins on osteogenesis: Current modalities, conflicts and future directions

Statins are known for their beneficial effects on cardiovascular diseases. Besides the lipid-lowering properties, statins exert their anabolic effects on the bone by differentiating mesenchymal cells to osteoblasts via upregulating BMP-2 and protecting osteoblasts from apoptosis. In addition, statins have been suggested to be anti-osteoclastic by reducing the osteoclast differentiation and activity. Several in vivo and clinical studies have confirmed the beneficial effects of statins in the treatment of osteoporosis and fracture injuries. However, controversial results exist showing statins may have no benefit and in some instances, they may retard bone repair. Different factors such as type, route of administration, dose and dosage of statins, and the injury model seem to be involved for such controversies. In the present study, the most important issues regarding statins have been reviewed to find out how statins may be beneficial and statin therapy can be improved for treating osteoporosis and fracture injuries. The lipophilic statins particularly simvastatin and atorvastatin are the most investigated statins with beneficial results on bone healing and turnover. Most of the in vivo and clinical studies performed systemic route of administration for treating osteoporosis, with much higher clinical doses than the lipid lowering therapy, which increases the statin related side and out of target effects. In contrast, most of the in vivo studies that used statins for fracture repair have applied local delivery methods with much lower doses via tissue engineering approaches. However, local delivery of statins and statin therapy for fracture repair both have low application in the clinical setting and such methods are still under in vivo investigation. Future clinical trials are needed to elucidate how delivery systems and tissue engineering technologies are able to improve the outcome of statin therapy.

Role of Mesenchymal Stem Cells in Bone Regenerative Medicine: What Is the Evidence?

Healing and regeneration of bone injuries, particularly those that are associated with large bone defects, are a complicated process. There is growing interest in the application of osteoinductive and osteogenic growth factors and mesenchymal stem cells (MSCs) in order to significantly improve bone repair and regeneration. MSCs are multipotent stromal stem cells that can be harvested from many different sources and differentiated into a variety of cell types, such as preosteogenic chondroblasts and osteoblasts. The effectiveness of MSC therapy is dependent on several factors, including the differentiating state of the MSCs at the time of application, the method of their delivery, the concentration of MSCs per injection, the vehicle used, and the nature and extent of injury, for example. Tissue engineering and regenerative medicine, together with genetic engineering and gene therapy, are advanced options that may have the potential to improve the outcome of cell therapy. Although several in vitro and in vivo investigations have suggested the potential roles of MSCs in bone repair and regeneration, the mechanism of MSC therapy in bone repair has not been fully elucidated, the efficacy of MSC therapy has not been strongly proven in clinical trials, and several controversies exist, making it difficult to draw conclusions from the results. In this review, we update the recent advances in the mechanisms of MSC action and the delivery approaches in bone regenerative medicine. We will also review the most recent clinical trials to find out how MSCs may be beneficial for treating bone defects.

Chemical crosslinking of biopolymeric scaffolds: Current knowledge and future directions of crosslinked engineered bone scaffolds

Bone tissue scaffolds made from either natural or synthetic polymers are employed to promote bone healing. However, lack of sufficient or poor mechanical properties such as low integrity and stability reduces their medical applications. Crosslinking, defined as induction of chemical or physical links among polymer chains, is a simple method generally used to modify mechanical, biological and degradation properties of hydrogels. Although crosslinking through chemical reactions improves the mechanical properties of bone substitutes, most of the reagents used for this aim demonstrate undesirable effects and may exert toxic reactions. Glutaraldehyde is a widely-used chemical crosslinker with unique ability to crosslink a wide variety of biomaterials; however, many contradictory views have been recently raised on its cytotoxic effects. By keeping this limit in mind, green chemicals or natural crosslinking agents have been shown to provide desired improvements in mechanical properties of bone scaffolds. Therefore, developing more efficient crosslinking materials and methods are desirable to obtain crosslinked scaffolds with perfect properties in bone tissue engineering from different biopolymers such as collagen, gelatin, cellulose, chitosan, alginate, etc. In this review, we focused on developed or developing modalities used to improve mechanical properties of various bone scaffolds and matrices based on common crosslinking reagents.

Effectiveness of tissue engineered chitosan-gelatin composite scaffold loaded with human platelet gel in regeneration of critical sized radial bone defect in rat

&NA; Although many strategies have been utilized to accelerate bone regeneration, an appropriate treatment strategy to regenerate a new bone with optimum morphology and mechanical properties has not been invented as yet. This study investigated the healing potential of a composite scaffold consisting of chitosan (CS), gelatin (Gel) and platelet gel (PG), named CS‐Gel‐PG, on a bilateral critical sized radial bone defect in rat. Eighty radial bone defects were bilaterally created in 40 Sprague‐Dawley rats and were randomly divided into eight groups including untreated, autograft, CS, Gel, CS‐PG, Gel‐PG, CS‐Gel, and CS‐Gel‐PG treated defects. The bone defects were evaluated clinically and radiologically during the study and their bone samples were assessed by gross and histopathology, histomorphometry, CT‐scan, scanning electron microscopy, and biomechanical testing after 8 weeks of bone injury. The autograft and CS‐Gel‐PG groups showed significantly higher new bone formation, density of osseous and cartilaginous tissues, bone volume, and mechanical performance than the defect, CS and Gel‐PG groups (P < 0.05). In addition, bone volume, density of osseous and cartilaginous tissues, and numbers of osteons in the CS‐Gel‐PG group were significantly superior to the CS‐PG, CS‐Gel and Gel groups (P < 0.05). Increased mRNA levels of alkaline phosphatase, runt‐related transcription factor 2, osteocalcin, collagen type 1 and CD31, vascular endothelial growth factor as osteogenic and angiogenic differentiation markers were found with the CS‐Gel‐PG scaffold by quantitative real‐time PCR in vitro after 30 days of culturing on bone marrow‐derived mesenchymal stem cells. In conclusion, the healing potential of CS‐Gel scaffold embedded with PG was comparable to autografting and therefore, it can be offered as an appropriate scaffold in bone tissue engineering and regenerative applications.

Synergistic effect of strontium, bioactive glass and nano-hydroxyapatite promotes bone regeneration of critical-sized radial bone defects: SYNERGISTIC EFFECT OF STRONTIUM, BIOACTIVE GLASS AND NANO-HYDROXYAPATITE ON BONE REGENERATION

Critical-sized bone defects constitute a major health issue in orthopedics and usually cause mal-unions due to an inadequate number of migrated progenitor cells into the defect site or their incomplete differentiation into osteogenic precursor cells. The current study aimed to develop an optimized osteoinductive and angiogenic scaffold by incorporation of strontium (Sr) and bioglass (BG) into gelatin/nano-hydroxyapatite (G/nHAp) seeded with bone marrow mesenchymal stem cells to enhance bone regeneration. The scaffolds were fabricated by a freeze-drying technique and characterized in terms of morphology, structure, porosity and degradation rate. The effect of fabricated scaffolds on cell viability, attachment and differentiation into osteoblastic lineages was evaluated under in vitro condition. Micro computed tomography scan, histological and histomorphometric analysis were performed after implantation of scaffolds into the radial bone defects in rat. RT-PCR analysis showed that G/nHAp/BG/Sr scaffold significantly increased the expression level of osteogenic and angiogenic markers in comparison to other groups (P < 0.05). Moreover, the defects treated with the BMSCs-seeded scaffolds showed superior bone formation and mechanical properties compared to the cell-free scaffolds 4 and 12 weeks post-implantation. Finally, the BMSCs-seeded G/nHAp/BG/Sr scaffold showed the greatest bone regenerative capacity which was more similar to autograft. It is concluded that combination of Sr, BG, and nHAp can synergistically enhance the bone regeneration process. In addition, our results demonstrated that the BMSCs have the potential to considerably increase the bone regeneration ability of osteoinductive scaffolds.

In vitro and in vivo investigation of PLA/PCL scaffold coated with metformin-loaded gelatin nanocarriers in regeneration of critical-sized bone defects

Large bone defects constitute a major challenge in bone tissue engineering and usually fail to heal due to the incomplete differentiation of recruited mesenchymal stem cells (MSCs) into osteogenic precursor cells. As previously proposed, metformin (MET) induces differentiation of MSCs into osteoblastic lineages in vitro. We fabricated a Poly (lactic acid) and Polycaprolactone (PLA/PCL) scaffold to deliver metformin loaded gelatin nanocarriers (MET/GNs) to critical-sized calvarial bone defects in a rat model. The scaffolds were evaluated regarding their morphology, porosity, contact angle, degradation rate, blood compatibility, biomechanical, cell viability and their osteogenic differentiation. In animal study, the defects were filled with autograft, scaffolds and a group was left empty. qRT-PCR analyses showed the expression level of osteogenic and angiogenic markers considerably increased in MET/GNs-PLA/PCL. The in vivo results showed that MET/GNs-PLA/PCL improved bone ingrowth, angiogenesis and defect reconstruction. Our results represent the applicability of MET/GNs-PLA/PCL for successful bone regeneration.

Comparative impact of systemic delivery of atorvastatin, simvastatin, and lovastatin on bone mineral density of the ovariectomized rats

PurposeIn addition to lipid-lowering properties, statins have been suggested to affect bone turnover by increasing the osteoblastic bone formation and blocking the osteoclastogenesis. However, there are many controversial reports regarding the beneficial effect of statins on osteoporosis. In this study, we investigated the therapeutic effects of the most important lipophilic statins administered orally for 60 days to the ovariectomized (OVX) female Sprague–Dawley rats and compared the effects on different harvested trabecular and compact bones.MethodsThirty female rats were divided into five equal groups including the normal rats, untreated OVX rats (negative control), and the OVX rats treated with atorvastatin (20 mg/kg/day), simvastatin (25 mg/kg/day), and lovastatin (20 mg/kg/day). The osteoporotic animals were treated daily for 60 days and euthanized at the end of experiments. The effectiveness of these treatments was evaluated by biomechanical testing, histopathologic, histomorphometric, micro-CT scan, real-time PCR, and serum biochemical analysis. Moreover, the hepatotoxicity and rhabdomyolysis related with these treatments were assessed by biochemistry analysis and histopathological evaluation.ResultsThe results and statistical analysis showed that systemic delivery of simvastatin and lovastatin significantly increased serum calcium level, expression of osteogenic genes, bone mineral density (BMD), and biomechanical properties in comparison to the untreated OVX rats, especially in trabecular bones (P < 0.05). The results of different analysis also indicated that there was no statistical difference between the atorvastatin-treated animals and the negative control. Among all treatments, only atorvastatin showed an evident hepatotoxicity and myopathy.ConclusionsIt was concluded that the lovastatin and simvastatin efficiently ameliorated the OVX-induced osteoporosis. Moreover, the simvastatin-treated animals showed more resemblance to the normal group in terms of BMD, expression of osteogenic genes, serum biochemical parameters, histomorphometric findings, and biomechanical performance with no significant side-effects.

The concurrent use of probiotic microorganism and collagen hydrogel/scaffold enhances burn wound healing: An in vivo evaluation

Treatment of burn wounds is technically demanding and several attempts have been taken to improve wound healing. Silver sulfadiazine antibiotic has been shown to have some beneficial effects on wound healing via reduction in infection. This study was designed to investigate the impact of collagen hydrogel-scaffold dressing with or without topical use of Saccharomyces cerevisiae on cutaneous burn wound healing in rat. Four circular 1cm cutaneous wounds were created in the dorsum back of rats, 48h post-burning. Thirty male rats were divided into the three major groups (1-3, n=10), then the wounds in each group were equally divided into two subgroup treatments (6 treatments), (1) including (a) silver sulfadiazine (SSD) as positive control (PC) and (b) untreated wounds as negative control (NC) (2) including (c) S. cerevisiae and (S.C.) and (d) collagen scaffold (CS), (3) including (e) collagen hydrogel-scaffold (CH-S) and (f) S. cerevisiae with collagen hydrogel-scaffold (CH-S-S). In each group, the animals were euthanized at 12 and 22 days post-injury (DPI) and the skin samples were used for histopathological and biomechanical investigations. Collagen scaffold and hydrogel modulated the inflammation, especially when combined together. Moreover, they increased wound healing, epithelialization and biomechanical performance of wound area and also reduced the scar size. The best results gained when the combination of collagen scaffold and hydrogel were mixed with probiotic. The CH-S biological dressing along with probiotic microorganism (S.C.) significantly increased collagen content compared to the negative controls. Moreover, the CH-S-S treated lesions demonstrated greater ultimate load and stiffness compared to the untreated wounds. In conclusion, application of S. cerevisiae with a bi-phase biological dressing (CH-S) improved the morphological and biomechanical characteristics of the healing burned wounds in rats and the results were comparable to the positive control.

The role of nanomedicine, nanotechnology, and nanostructures on oral bone healing, modeling, and remodeling

Abstract Several conditions may alter the bone health in the oral cavity. These include a variety of bone fractures, tumors, infections, osteoporosis, and degenerative diseases, which may lead to bone loss, dental loosening, and development of large defects. Such defects should immediately be reconstructed by classic grafts. However, the auto- and allografts have significant limitations. Tissue-engineered based bone graft substitutes are the alternative option. In the recent years, nanomedicine has been developed and many nanostructures have been designed and synthesized to optimize the tissue-engineered based treatment strategies. These nanostructures vary based on the shape, structure, type of material, and several other factors. Nanoceramics, nanometals, and nanopolymers are the common nanomaterials used in bone healing. Different nanostructures, such as nanospheres, nanocrystals, and nanofibers have been used alone, or in combination with stem cells for numerous applications, such as increasing the scaffold bioactivity, controlling the infection and drug, gene and cell delivery. Although nanostructures may have value on bone health and repair, presence of some controversies and biases make the results difficult to conclude. This chapter covers the most important information regarding the manufacturing methods, available and future options, and the role of nanostructures on bone health, healing, and repair based on their basic to clinical evidences.