Selective local delivery of RANK siRNA to bone phagocytes using bone augmentation biomaterials

Implications of siRNA Therapy in Bone Health: Silencing Communicates

The global statistics of bone disorders, skeletal defects, and fractures are frightening. Several therapeutic strategies are being used to fix them; however, RNAi-based siRNA therapy is starting to prove to be a promising approach for the prevention of bone disorders because of its advanced capabilities to deliver siRNA or siRNA drug conjugate to the target tissue. Despite its 'bench-to-bedside' usefulness and approval by food and drug administration for five siRNA-based therapeutic medicines: Patisiran, Vutrisiran, Inclisiran, Lumasiran, and Givosiran, its use for the other diseases still remains to be resolved. By correcting the complications and complexities involved in siRNA delivery for its sustained release, better absorption, and toxicity-free activity, siRNA therapy can be harnessed as an experimental tool for the prevention of complex and undruggable diseases with a personalized medicine approach. The present review summarizes the findings of notable research to address the implications of siRNA in bone health for the restoration of bone mass, recovery of bone loss, and recuperation of bone fractures.

Harnessing Nucleic Acids Nanotechnology for Bone/Cartilage Regeneration

The effective regeneration of weight-bearing bone defects and critical-sized cartilage defects remains a significant clinical challenge. Traditional treatments such as autologous and allograft bone grafting have not been successful in achieving the desired outcomes, necessitating the need for innovative therapeutic approaches. Nucleic acids have attracted significant attention due to their ability to be designed to form discrete structures and programmed to perform specific functions at the nanoscale. The advantages of nucleic acid nanotechnology offer numerous opportunities for in-cell and in vivo applications, and hold great promise for advancing the field of biomaterials. In this review, the current abilities of nucleic acid nanotechnology to be applied in bone and cartilage regeneration are summarized and insights into the challenges and future directions for the development of this technology are provided.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Insights into oxidative stress in bone tissue and novel challenges for biomaterials

The presence of Reactive Oxygen Species (ROS) in bone can influence resident cells behaviour as well as the extra-cellular matrix composition and the tissue architecture. Aging, in addition to excessive overloads, unbalanced diet, smoking, predisposing genetic factors, lead to an increase of ROS and, if it is accompanied with an inappropriate production of scavengers, promotes the generation of oxidative stress that encourages bone catabolism. Furthermore, bone injuries can be triggered by numerous events such as road and sports accidents or tumour resection. Although bone tissue possesses a well-known repair and regeneration capacity, these mechanisms are inefficient in repairing large size defects and bone grafts are often necessary. ROS play a fundamental role in response after the implant introduction and can influence its success. This review provides insights on the mechanisms of oxidative stress generated by an implant in vivo and suitable ways for its modulation. The local delivery of active molecules, such as polyphenols, enhanced bone biomaterial integration evidencing that the management of the oxidative stress is a target for the effectiveness of an implant. Polyphenols have been widely used in medicine for cardiovascular, neurodegenerative, bone disorders and cancer, thanks to their antioxidant and anti-inflammatory properties. In addition, the perspective of new smart biomaterials and molecular medicine for the oxidative stress modulation in a programmable way, by the use of ROS responsive materials or by the targeting of selective molecular pathways involved in ROS generation, will be analysed and discussed critically.

Top-Down Fabricated microPlates for Prolonged, Intra-articular Matrix Metalloproteinase 13 siRNA Nanocarrier Delivery to Reduce Post-traumatic Osteoarthritis

Post-traumatic osteoarthritis (PTOA) associated with joint injury triggers a degenerative cycle of matrix destruction and inflammatory signaling, leading to pain and loss of function. Here, prolonged RNA interference (RNAi) of matrix metalloproteinase 13 (MMP13) is tested as a PTOA disease modifying therapy. MMP13 is upregulated in PTOA and degrades the key cartilage structural protein type II collagen. Short interfering RNA (siRNA) loaded nanoparticles (siNPs) were encapsulated in shape-defined poly(lactic-co-glycolic acid) (PLGA) based microPlates (μPLs) to formulate siNP-μPLs that maintained siNPs in the joint significantly longer than delivery of free siNPs. Treatment with siNP-μPLs against MMP13 (siMMP13-μPLs) in a mechanical load-induced mouse model of PTOA maintained potent (65-75%) MMP13 gene expression knockdown and reduced MMP13 protein production in joint tissues throughout a 28-day study. MMP13 silencing reduced PTOA articular cartilage degradation/fibrillation, meniscal deterioration, synovial hyperplasia, osteophytes, and pro-inflammatory gene expression, supporting the therapeutic potential of long-lasting siMMP13-μPL therapy for PTOA.

Potential of Carbon-Based Nanocomposites for Dental Tissue Engineering and Regeneration

While conventional dental implants focus on mechanical properties, recent advances in functional carbon nanomaterials (CNMs) accelerated the facilitation of functionalities including osteoinduction, osteoconduction, and osseointegration. The surface functionalization with CNMs in dental implants has emerged as a novel strategy for reinforcement and as a bioactive cue due to their potential for mechanical reinforcing, osseointegration, and antimicrobial properties. Numerous developments in the fabrication and biological studies of CNMs have provided various opportunities to expand their application to dental regeneration and restoration. In this review, we discuss the advances in novel dental implants with CNMs in terms of tissue engineering, including material combination, coating strategies, and biofunctionalities. We present a brief overview of recent findings and progression in the research to show the promising aspect of CNMs for dental implant application. In conclusion, it is shown that further development of surface functionalization with CNMs may provide innovative results with clinical potential for improved osseointegration after implantation.

Osteoporosis and Its Nanotechnology-Based Advanced Treatment-An Overview

Human Immunodeficiency Virus (HIV) is a global pandemic that has contributed to the burden of disease, and the synergistic interaction between Herpes Simplex Virus (HSV) and HIV has assisted further in the spread of the HIV disease. Moreover, several chemotherapeutic treatment options from antiviral monotherapy to highly active antiretroviral therapy (HAART) have been adopted to manage the infection; however, HIV has developed new mechanisms against these active pharmaceutical agents (APAs), limiting the effect of the drugs. In this article, we reviewed different nanoparticles and their antiviral potency against HSV and HIV infection as well as the effect of drug encapsulated nanoparticles using different drug delivery systems as they palliate to some flaws or deficiencies that the stand-alone drugs present. Drug encapsulated nanoparticles show better treatment outcomes of HSV and HIV infection. The nanoparticles can transverse the anatomic privilege sites to exert their therapeutic effect, and a prolonged and higher dose of the encapsulated therapeutic agent can ease the dosage frequency, thus palliating low drug compliance which the stand-alone drugs fail to perform. Therefore, it is clear that nanoparticles prevent antiviral drug resistance by maintaining sustained drug release over an extended period, improving the therapeutic effect of the entrapped drug.

RNA-based scaffolds for bone regeneration: application and mechanisms of mRNA, miRNA and siRNA

Globally, more than 1.5 million patients undergo bone graft surgeries annually, and the development of biomaterial scaffolds that mimic natural bone for bone grafting remains a tremendous challenge. In recent decades, due to the improved understanding of the mechanisms of bone remodeling and the rapid development of gene therapy, RNA (including messenger RNA (mRNA), microRNA (miRNA), and short interfering RNA (siRNA)) has attracted increased attention as a new tool for bone tissue engineering due to its unique nature and great potential to cure bone defects. Different types of RNA play roles via a variety of mechanisms in bone-related cells in vivo as well as after synthesis in vitro. In addition, RNAs are delivered to injured sites by loading into scaffolds or systemic administration after combination with vectors for bone tissue engineering. However, the challenge of effectively and stably delivering RNA into local tissue remains to be solved. This review describes the mechanisms of the three types of RNAs and the application of the relevant types of RNA delivery vectors and scaffolds in bone regeneration. The improvements in their development are also discussed.

Calcium Phosphate Nanoparticles-Based Systems for RNAi Delivery: Applications in Bone Tissue Regeneration

Bone-related injury and disease constitute a significant global burden both socially and economically. Current treatments have many limitations and thus the development of new approaches for bone-related conditions is imperative. Gene therapy is an emerging approach for effective bone repair and regeneration, with notable interest in the use of RNA interference (RNAi) systems to regulate gene expression in the bone microenvironment. Calcium phosphate nanoparticles represent promising materials for use as non-viral vectors for gene therapy in bone tissue engineering applications due to their many favorable properties, including biocompatibility, osteoinductivity, osteoconductivity, and strong affinity for binding to nucleic acids. However, low transfection rates present a significant barrier to their clinical use. This article reviews the benefits of calcium phosphate nanoparticles for RNAi delivery and highlights the role of surface functionalization in increasing calcium phosphate nanoparticles stability, improving cellular uptake and increasing transfection efficiency. Currently, the underlying mechanistic principles relating to these systems and their interplay during in vivo bone formation is not wholly understood. Furthermore, the optimal microRNA targets for particular bone tissue regeneration applications are still unclear. Therefore, further research is required in order to achieve the optimal calcium phosphate nanoparticles-based systems for RNAi delivery for bone tissue regeneration.

Nanoparticles to Knockdown Osteoporosis-Related Gene and Promote Osteogenic Marker Expression for Osteoporosis Treatment

Osteoporosis is the most common disease involving bone degeneration. Current clinical treatments are not able to offer a satisfying curative effect, so the development of effective treatments is desired. Gene silencing through siRNA delivery has gained great attention as a potential treatment in bone diseases. SOST gene inhibits the Wnt signaling pathway reducing osteoblast differentiation. Consequently, silencing SOST genes with a specific siRNA could be a potential option to treat osteoporosis. Generally, siRNAs have a very short half-life and poor transfection capacity, so an effective carrier is needed. In particular, mesoporous silica nanoparticles (MSNs) have attracted great attention for intracellular delivery of nucleic acids. We took advantage of their high loading capacity to further load the pores with osteostatin, an osteogenic peptide. In this study, we developed a system based on MSNs coated with poly(ethylenimine), which can effectively deliver SOST siRNA and osteostatin inside cells, with the consequent augmentation of osteogenic markers with a synergistic effect. This established the potential utility of MSNs to co-deliver both biomolecules to promote bone formation, this being a potential alternative to treat osteoporosis.

Current advances for bone regeneration based on tissue engineering strategies

Bone tissue engineering (BTE) is a rapidly developing strategy for repairing critical-sized bone defects to address the unmet need for bone augmentation and skeletal repair. Effective therapies for bone regeneration primarily require the coordinated combination of innovative scaffolds, seed cells, and biological factors. However, current techniques in bone tissue engineering have not yet reached valid translation into clinical applications because of several limitations, such as weaker osteogenic differentiation, inadequate vascularization of scaffolds, and inefficient growth factor delivery. Therefore, further standardized protocols and innovative measures are required to overcome these shortcomings and facilitate the clinical application of these techniques to enhance bone regeneration. Given the deficiency of comprehensive studies in the development in BTE, our review systematically introduces the new types of biomimetic and bifunctional scaffolds. We describe the cell sources, biology of seed cells, growth factors, vascular development, and the interactions of relevant molecules. Furthermore, we discuss the challenges and perspectives that may propel the direction of future clinical delivery in bone regeneration.

Development of PEI-RANK siRNA Complex Loaded PLGA Nanocapsules for the Treatment of Osteoporosis

Osteoporosis, which is characterized by low bone mineral density and susceptibility to fracture, is caused by increased osteoclastic activity. Receptor activator of nuclear factor kappa B ligand (RANKL)/RANK signaling plays an important role in osteoclast differentiation and activation. The current treatment strategies for osteoporosis do not directly address this underlying cause and generates undesired side effects. This led to emergence of controlled delivery systems to increase drug bioavailability and efficacy specifically at the bone tissue. With better understanding of molecular pathology of bone, the use of small interfering RNA (siRNA) to inhibit translation of abnormal gene expression in cells is becoming a promising approach. In this study, we report a siRNA delivery system consisting of PEI:RANK siRNA complex entrapped in nanosized poly(lactic acid-co-glycolic acid) (PLGA) capsules intended to be used in the treatment of osteoporosis. The nanosize will enable the nanoparticles to be administered by intravenous injection. The RANK siRNA was complexed with polyethylenimine (PEI) and loaded into biodegradable PLGA nanocapsules (NCs). The PEI:RANK siRNA loaded nanocapsules significantly reduced (47%) RANK mRNA levels. The differentiation of osteoclast precursors to mature osteoclasts was significantly suppressed (∼54%). The reduction in the osteoclastic activity of the differentiated osteoclasts (55%) was found to be statistically significant. The siRNA delivery system developed in the study is planned to be tested i.v. in mouse and has the potential to be used as a novel alternative approach for the systemic treatment of osteoporosis.

Small non-coding RNAs-based bone regulation and targeting therapeutic strategies

Small non-coding RNAs, which are 20-25 nucleotide ribonucleic acids, have emerged as an important transformation in the biological evolution over almost three decades. microRNAs (miRNAs) and short interfering RNAs (siRNAs) are two significant categories of the small RNAs that exert important effects on bone endocrinology and skeletology. Therefore, clarifying the expression and function of these important molecules in bone endocrine physiology and pathology is of great significance for improving their potential therapeutic value for metabolism-associated bone diseases. In the present review, we highlight the recent advances made in understanding the function and molecular mechanism of these small non-coding RNAs in bone metabolism, especially their potentially therapeutic values in bone-related diseases.

Dual-Functionalized Graphene Oxide Based siRNA Delivery System for Implant Surface Biomodification with Enhanced Osteogenesis

Surface functionalization by small interfering RNA (siRNA) is a novel strategy for improved implant osseointegration. A gene delivery system with safety and high transfection activity is a crucial factor for an siRNA-functionalized implant to exert its biological function. To this end, polyethylene glycol (PEG) and polyethylenimine (PEI) dual-functionalized graphene oxide (GO; nGO-PEG-PEI) may present a promising siRNA vector. In this study, nanosized nGO-PEG-PEI was prepared and optimized for siRNA delivery. Titania nanotubes (NTs) fabricated by anodic oxidation were biomodified with nGO-PEG-PEI/siRNA by cathodic electrodeposition, designated as NT-GPP/siRNA. NT-GPP/siRNA possessed benign cytocompatibility, as evaluated by cell adhesion and proliferation. Cellular uptake and knockdown efficiency of the NT-GPP/siRNA were assessed by MC3T3-E1 cells, which exhibited high siRNA delivery efficiency and sustained target gene silencing. Casein kinase-2 interacting protein-1 (Ckip-1) is a negative regulator of bone formation. siRNA-targeting Ckip-1 (siCkip-1) was introduced to the implant, and a series of in vitro and in vivo experiments were carried out to evaluate the osteogenic capacity of NT-GPP/siCkip-1. NT-GPP/siCkip-1 dramatically improved the in vitro osteogenic differentiation of MC3T3-E1 cells in terms of improved osteogenesis-related gene expression, and increased alkaline phosphatase (ALP) production, collagen secretion, and extracellular matrix (ECM) mineralization. Moreover, NT-GPP/siCkip-1 led to apparently enhanced in vivo osseointegration, as indicated by histological staining and EDX line scanning. Collectively, these findings suggest that NT-GPP/siRNA represents a practicable and promising approach for implant functionalization, showing clinical potential for dental and orthopedic applications.

Biomaterials to Facilitate Delivery of RNA Agents in Bone Regeneration and Repair

Bone healing after traumatic injuries or pathological diseases remains an important worldwide problem. In search of safer and more effective approaches to bone regeneration and repair, RNA-based therapeutic agents, specifically microRNAs (miRNAs) and short interfering RNA (siRNA), are beginning to be actively explored. In this review, we summarize current attempts to employ miRNAs and siRNAs in preclinical models of bone repair. We provide a summary of current limitations when attempting to utilize bioactive nucleic acids for therapeutic purposes and position the unique aspects of RNA reagents for clinical bone repair. Delivery strategies for RNA reagents are emphasized and nonviral carriers (biomaterial-based) employed to deliver such reagents are reviewed. Critical features of biomaterial carriers and various delivery technologies centered around nanoparticulate systems are highlighted. We conclude with the authors' perspectives on the future of the field, outlining main critical issues important to address as RNA reagents are explored for clinical applications.

Small Players Ruling the Hard Game: siRNA in Bone Regeneration

Silencing gene expression through a sequence-specific manner can be achieved by small interfering RNAs (siRNAs). The discovery of this process has opened the doors to the development of siRNA therapeutics. Although several preclinical and clinical studies have shown great promise in the treatment of neurological disorders, cancers, dominant disorders, and viral infections with siRNA, siRNA therapy is still gaining ground in musculoskeletal tissue repair and bone regeneration. Here we present a comprehensive review of the literature to summarize different siRNA delivery strategies utilized to enhance bone regeneration. With advancement in understanding the targetable biological pathways involved in bone regeneration and also the rapid progress in siRNA technologies, application of siRNA for bone regeneration has great therapeutic potential. High rates of musculoskeletal injuries and diseases, and their inevitable consequences, impose a huge financial burden on individuals and healthcare systems worldwide.

Inhibition of osteoclastogenesis through siRNA delivery with tunable mesoporous bioactive nanocarriers

Gene silencing through siRNA delivery has shown great promise for treating diseases and repairing damaged tissues, including bone. This report is the first to develop siRNA delivery system in the inhibition of osteoclastic functions which in turn can help turn-over bone mass increase in the diseases like osteoporosis. For this reason, biocompatible and degradable nanocarriers that can effectively load and deliver genetic molecules to target cells and tissues are being actively sought by researchers. In this study, mesoporous bioactive glass nanospheres (MBG), a novel unique biocompatible degradable inorganic nanocarrier, is introduced. Furthermore, siRNA was designed to function by inhibiting the expression of the receptor activator of nuclear factor kappa B (RANK) in order to suppress osteoclastogenesis. Amine-functionalized MBG were synthesized with tunable mesoporosities, showing a strong complexation with siRNA. An in vitro release profile indicated that the siRNA from the MBG was able to achieve a highly sustainable liberation for up to 4 days, confirming a temporary delivery system can be designed to function for that period of time. The intracellular uptake capacity of the complex siRNA(RANK)-MBG was recorded to be around 70%. Furthermore, the RANK-expressing cell population declined down to 29% due to the delivery of siRNA(RANK)-MBG (vs. 86% in control). The expression of osteoclastogenesis-related genes, including c-fos, cathepsin-K, tartrate-resistant acid phosphatase (TRAP), and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), was substantially down-regulated by the siRNA delivery system. This study reports for the first time on the use of a novel MBG delivery system for siRNA that aims to suppress osteoclastic actions. MBGs may be a potential gene delivery platform for hard tissue repair and disease treatment due to the collective results which indicate a high loading capacity, temporary release kinetics, high intracellular uptake rate, and sufficient gene silencing effects, together with the intrinsic beneficial properties like bone-bioactivity and degradability.

STATEMENT OF SIGNIFICANCE

This report is the first to develop siRNA delivery system of biocompatible and degradable nanocarriers made from a unique composition, i.e., mesoporous bioactive glass that can effectively load and deliver genetic molecules to osteoclastic cells. We proved through a series of studies that the biocompatible nanocarriers are effective for the delivery of siRNA in the inhibition of osteoclastic functions which thus might be considered as a nanocarrier platform to help turn-over bone mass increase in the diseases like osteoporosis.

Bone site-specific delivery of siRNA

Small interfering RNAs (siRNA) have enormous potential as therapeutics to target and treat various bone disorders such as osteoporosis and cancer bone metastases. However, effective and specific delivery of siRNA therapeutics to bone and bone-specific cells in vivo is very challenging. To realize the full therapeutic potential of siRNA in treating bone disorders, a safe and efficient, tissue- and cell-specific delivery system must be developed. This review focuses on recent advances in bone site-specific delivery of siRNA at the tissue or cellular level. Bone-targeted nanoparticulate siRNA carriers and various bone-targeted moieties such as bisphosphonates, oligopeptides (Asp)₈ and (AspSerSer)₆, and aptamers are highlighted. Incorporation of these bone-seeking targeting moieties into siRNA carriers allows for recognition of different sub-tissue functional domains of bone and also specific cell types residing in bone tissue. It also provides a means for bone-formation surface-, bone-resorption surface-, or osteoblast-specific targeting and transportation of siRNA therapeutics. The discussion mainly focuses on systemic and local bone-specific delivery of siRNA in osteoporosis and bone metastasis preclinical models.

MicroRNA-mediated immune modulation as a therapeutic strategy in host-implant integration

The concept of implanting an artificial device into the human body was once the preserve of science fiction, yet this approach is now often used to replace lost or damaged biological structures in human patients. However, assimilation of medical devices into host tissues is a complex process, and successful implant integration into patients is far from certain. The body's immediate response to a foreign object is immune-mediated reaction, hence there has been extensive research into biomaterials that can reduce or even ablate anti-implant immune responses. There have also been attempts to embed or coat anti-inflammatory drugs and pro-regulatory molecules onto medical devices with the aim of preventing implant rejection by the host. In this review, we summarize the key immune mediators of medical implant reaction, and we evaluate the potential of microRNAs to regulate these processes to promote wound healing, and prolong host-implant integration.

Osteoblastic NF-κB pathway is involved in 1α, 25(OH)2D3-induced osteoclast-like cells formation in vitro

1α, 25-dihydroxyvitamin D3 (1α, 25(OH)2D3) acts on the osteoblasts to enhance the expressions of receptor activator of nuclear factor κB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF) and induce the formation of osteoclasts. However, the mechanism in osteoblasts by which 1α, 25(OH)2D3 promotes osteoclastogenesis has not yet been completely understood. This study aimed to select the first generation of murine osteoblasts to explore the underlying mechanism of 1α, 25(OH)2D3-induced osteoclastic formation from bone marrow mononuclear cells (BMMNCs). We discovered the activation of osteoblastic NF-κB pathway under 10(-8) mol/L 1α, 25(OH)2D3 treatment, as evidenced by the transfer of NF-κB p65 from cytoplasm to nuclei. Then, the NF-κB p65-siRNA was designed, constructed, and transfected into osteoblastic cells. Immunofluorescence assay confirmed the successfully silenced NF-κB p65 gene in osteoblasts. In the co-culture system of osteoblasts and BMMNCs with 1α, 25(OH)2D3 added, the multinucleated osteoclast-like cells containing 2-3 nuclei were observed in BMMNCs co-cultured with non-transfection osteoblasts, conversely, silencing osteoblastic NF-κB p65 resulted in failed differentiation of BMMNCs along with substantial vacuolar degeneration in cytoplasm. In addition, the expressions of RANKL and M-CSF were notably decreased in NF-κB p65-silenced osteoblasts. Taken together, our data indicated that osteoblastic NF-κB pathway was involved in 1α, 25(OH)2D3-induced osteoclast-like cells formation from BMMNCs through regulating the expression of RANKL and M-CSF. Therefore, our findings further identified the mechanism of 1α, 25(OH)2D3-induced osteoclastogenesis on the basis of prior studies.

Inhibition of osteolysis and increase of bone formation after local administration of siRNA-targeting RANK in a polyethylene particle-induced osteolysis model

Receptor activator of nuclear factor kappa-B (RANK) and RANK-ligand are relevant targets for the treatment of polyethylene particle-induced osteolysis. This study assessed the local administration of siRNA, targeting both human RANK and mouse Rank transcripts in a mouse model. Four groups of mice were implanted with polyethylene (PE) particles in the calvaria and treated locally with 2.5, 5 and 10 μg of RANK siRNA or a control siRNA delivered by the cationic liposome DMAPAP/DOPE. The tissues were harvested at day 9 after surgery and evaluated by micro-computed tomography, tartrate-resistant acid phosphatase (TRAP) immunohistochemistry for macrophages and osteoblasts, and gene relative expression of inflammatory and osteolytic markers. 10 μg of RANK siRNA exerted a protective effect against PE particle-induced osteolysis, decreasing the bone loss and the osteoclastogenesis, demonstrated by the significant increase in the bone volume (P<0.001) and by the reduction in both the number of TRAP(+) cells and osteoclast activity (P<0.01). A bone anabolic effect demonstrated by the formation of new trabecular bone was confirmed by the increased immunopositive staining for osteoblast-specific proteins. In addition, 5 and 10 μg of RANK siRNA downregulated the expression of pro-inflammatory cytokines (P<0.01) without depletion of macrophages. Our findings show that RANK siRNA delivered locally by a synthetic vector may be an effective approach for reducing osteolysis and may even stimulate bone formation in aseptic loosening of prosthetic implants.

Co-delivery of siRNA and doxorubicin to cancer cells from additively manufactured implants

Tumors in load bearing bones are a major clinical problem as recurrence is common after surgery. Void filling scaffolds that kill residual cancer cells by releasing chemotherapy and siRNA/chitosan nanoparticles may offer a solution to this problem.

Foreign body response to subcutaneous biomaterial implants in a mast cell-deficient Kit(w-Sh) murine model

Mast cells (MCs)_are recognized for their functional role in wound-healing and allergic and inflammatory responses - host responses that are frequently detrimental to implanted biomaterials if extended beyond acute reactivity. These tissue reactions impact especially on the performance of sensing implants such as continuous glucose monitoring (CGM) devices. Our hypothesis that effective blockade of MC activity around implants could alter the host foreign body response (FBR) and enhance the in vivo lifetime of these implantable devices motivated this study. Stem cell factor and its ligand c-KIT receptor are critically important for MC survival, differentiation and degranulation. Therefore, an MC-deficient sash mouse model was used to assess MC relationships to the in vivo performance of CGM implants. Additionally, local delivery of a tyrosine kinase inhibitor (TKI) that inhibits c-KIT activity was also used to evaluate the role of MCs in modulating the FBR. Model sensor implants comprising polyester fibers coated with a rapidly dissolving polymer coating containing drug-releasing degradable microspheres were implanted subcutaneously in sash mice for various time points, and the FBR was evaluated for chronic inflammation and fibrous capsule formation around the implants. No significant differences were observed in the foreign body capsule formation between control and drug-releasing implant groups in MC-deficient mice. However, fibrous encapsulation was significantly greater around the drug-releasing implants in sash mice compared to drug-releasing implants in wild-type (e.g. MC-competent) mice. These results provide insights into the role of MCs in the FBR, suggesting that MC deficiency provides alternative pathways for host inflammatory responses to implanted biomaterials.

Local strategies to prevent and treat osteoporosis

Despite advances in systemic osteoporosis therapeutic outcomes, management of fragility fractures and implant fixation in osteoporotic bone remain difficult clinical challenges. Low initial bone density and a prolonged healing response can lead to fracture nonunion and aseptic implant loosening. Local treatment strategies could be used to prevent fracture, accelerate healing, and increase implant fixation by locally stimulating anabolic pathways or inhibiting catabolic pathways. Local strategies under investigation include direct drug release from injectable materials or implant surface coatings. Common locally delivered drugs include bisphosphonates, parathyroid hormone, and bone morphogenetic proteins, yet additional compounds targeting novel pathways in bone biology are also being actively explored. Mechanical stimulation via low intensity pulsed ultrasound, alone or in combination with drug therapy, may also prove effective to promote local bone healing and implant fixation within osteoporotic bone.

Endothelial targeting of nanocarriers loaded with antioxidant enzymes for protection against vascular oxidative stress and inflammation

Endothelial-targeted delivery of antioxidant enzymes, catalase and superoxide dismutase (SOD), is a promising strategy for protecting organs and tissues from inflammation and oxidative stress. Here we describe Protective Antioxidant Carriers for Endothelial Targeting (PACkET), the first carriers capable of targeted endothelial delivery of both catalase and SOD. PACkET formed through controlled precipitation loaded ~30% enzyme and protected it from proteolytic degradation, whereas attachment of PECAM monoclonal antibodies to surface of the enzyme-loaded carriers, achieved without adversely affecting their stability and functionality, provided targeting. Isotope tracing and microscopy showed that PACkET exhibited specific endothelial binding and internalization in vitro. Endothelial targeting of PACkET was validated in vivo by specific (vs IgG-control) accumulation in the pulmonary vasculature after intravenous injection achieving 33% of injected dose at 30 min. Catalase loaded PACkET protects endothelial cells from killing by H2O2 and alleviated the pulmonary edema and leukocyte infiltration in mouse model of endotoxin-induced lung injury, whereas SOD-loaded PACkET mitigated cytokine-induced endothelial pro-inflammatory activation and endotoxin-induced lung inflammation. These studies indicate that PACkET offers a modular approach for vascular targeting of therapeutic enzymes.

C3 rho-inhibitor for targeted pharmacological manipulation of osteoclast-like cells

The C3 toxins from Clostridium botulinum (C3bot) and Clostridium limosum (C3lim) as well as C3-derived fusion proteins are selectively taken up into the cytosol of monocytes/macrophages where the C3-catalyzed ADP-ribosylation of Rho results in inhibition of Rho-signalling and characteristic morphological changes. Since the fusion toxin C2IN-C3lim was efficiently taken up into and inhibited proliferation of murine macrophage-like RAW 264.7 cells, its effects on RAW 264.7-derived osteoclasts were investigated. C2IN-C3lim was taken up into differentiated osteoclasts and decreased their resorption activity. In undifferentiated RAW 264.7 cells, C2IN-C3lim-treatment significantly decreased their differentiation into osteoclasts as determined by counting the multi-nucleated, TRAP-positive cells. This inhibitory effect was concentration- and time-dependent and most efficient when C2IN-C3lim was applied in the early stage of osteoclast-formation. A single-dose application of C2IN-C3lim at day 0 and its subsequent removal at day 1 reduced the number of osteoclasts in a comparable manner while C2IN-C3lim-application at later time points did not reduce the number of osteoclasts to a comparable degree. Control experiments with an enzymatically inactive C3 protein revealed that the ADP-ribosylation of Rho was essential for the observed effects. In conclusion, the results indicate that Rho-activity is crucial during the early phase of osteoclast-differentiation. Other bone cell types such as pre-osteoblastic cells were not affected by C2IN-C3lim. Due to their cell-type selective and specific mode of action, C3 proteins and C3-fusions might be valuable tools for targeted pharmacological manipulation of osteoclast formation and activity, which could lead to development of novel therapeutic strategies against osteoclast-associated diseases.

Developing siRNA therapies to address osteoporosis

Osteoporosis is a skeletal system pathology characterized by low bone mineral density and tissue structural deterioration. This malady is associated with high fracture risk that severely compromises quality of life. Osteoporosis incidence is becoming more significant with increasing lifespan worldwide. However, current approaches for treating osteoporosis cannot and do not treat the disease in the most ideal manner for diverse reasons. Substantial research has sought both the discovery of new targets and new therapies. In this review, emerging possible RNAi-mediated therapeutic opportunities for osteoporosis are identified and associated challenges discussed. Targeted delivery strategies capable of more reliable and efficient delivery to skeletal tissue are described, as well as possibilities to treat bone-forming cells with siRNA to produce cell-based therapy.

Calcium phosphate cements with strontium halides as radiopacifiers

High radiopacity is required to monitor the delivery and positioning of injectable implants. Inorganic nonsoluble radiopacifiers are typically used in nondegradable bone cements; however, their usefulness in resorbable cements is limited due to their low solubility. Strontium halides, except strontium fluoride, are ionic water-soluble compounds that possess potential as radiopacifiers. In this study, we compare the radiopacity, mechanical properties, composition, and cytotoxicity of radiopaque brushite cements prepared with strontium fluoride (SrF2 ), strontium chloride (SrCl2 ·6H2 O), strontium bromide (SrBr2 ), or strontium iodide (SrI2 ). Brushite cements containing 10 wt % SrCl2 ·6H2 O, SrBr2 , or SrI2 exhibited equal to or higher radiopacity than commercial radiopaque cements. Furthermore, the brushite crystal lattice in cements that contained the ionic radiopacifiers was larger than in unmodified cements and in cements that contained SrF2 , indicating strontium substitution. Despite the fact that the strontium halides increased the solubility of the cements and affected their mechanical properties, calcium phosphate cements containing SrCl2 ·6H2 O, SrBr2 , and SrI2 showed no significant differences in Saos-2 cell viability and proliferation with respect to the control. Strontium halides: SrCl2 ·6H2 O, SrBr2 , and SrI2 may be potential candidates as radiopacifiers in resorbable biomaterials although their in vivo biocompatibility, when incorporated into injectable implants, is yet to be assessed.

Drug carriers in osteoporosis: preparation, drug encapsulation and applications

Carriers are largely used to enhance therapy efficiency via the encapsulation of active molecules. The encapsulation enhances the stability of drug molecules, improves the targeting properties and prolongs pharmacological activity via continuous local release of active molecules. The aim of this review is to report the carrier systems used in osteoporosis therapy. This state of the art research has mainly focused on describing all types of carriers used in this area, their elaboration and properties, the drug characteristics used in such specific application, and drug release and efficiency. In this field, various processes have been used in order to obtain well-defined capsules, spheres and more complex carriers. In this exhaustive review, each process is described, illustrated and discussed.