Bone targeting for the treatment of osteoporosis

Ångstrom-scale gold particles loaded with alendronate via alpha-lipoic acid alleviate bone loss in osteoporotic mice

Osteoporosis is a highly prevalent metabolic disease characterized by low systemic bone mass and deterioration of bone microarchitecture, resulting in reduced bone strength and increased fracture risk. Current treatment options for osteoporosis are limited by factors such as efficacy, cost, availability, side effects, and acceptability to patients. Gold nanoparticles show promise as an emerging osteoporosis therapy due to their osteogenic effects and ability to allow therapeutic delivery but have inherent constraints, such as low specificity and the potential for heavy metal accumulation in the body. This study reports the synthesis of ultrasmall gold particles almost reaching the Ångstrom (Ång) dimension. The antioxidant alpha-lipoic acid (LA) is used as a dispersant and stabilizer to coat Ångstrom-scale gold particles (AuÅPs). Alendronate (AL), an amino-bisphosphonate commonly used in drug therapy for osteoporosis, is conjugated through LA to the surface of AuÅPs, allowing targeted delivery to bone and enhancing antiresorptive therapeutic effects. In this study, alendronate-loaded Ångstrom-scale gold particles (AuÅPs-AL) were used for the first time to promote osteogenesis and alleviate bone loss through regulation of the WNT signaling pathway, as shown through in vitro tests. The in vivo therapeutic effects of AuÅPs-AL were demonstrated in an established osteoporosis mouse model. The results of Micro-computed Tomography, histology, and tartrate-resistant acid phosphatase staining indicated that AuÅPs-AL significantly improved bone density and prevented bone loss, with no evidence of nanoparticle-associated toxicity. These findings suggest the possible future application of AuÅPs-AL in osteoporosis therapy and point to the potential of developing new approaches for treating metabolic bone diseases using Ångstrom-scale gold particles.

Transdermal drug delivery via microneedles for musculoskeletal systems

As the population is ageing and lifestyle is changing, the prevalence of musculoskeletal (MSK) disorders is gradually increasing with each passing year, posing a serious threat to the health and quality of the public, especially the elderly. However, currently prevalent treatments for MSK disorders, mainly administered orally and by injection, are not targeted to the specific lesion, resulting in low efficacy along with a series of local and systemic adverse effects. Microneedle (MN) patches loaded with micron-sized needle array, combining the advantages of oral administration and local injection, have become a potentially novel strategy for the administration and treatment of MSK diseases. In this review, we briefly introduce the basics of MNs and focus on the main characteristics of the MSK systems and various types of MN-based transdermal drug delivery (TDD) systems. We emphasize the progress and broad applications of MN-based transdermal drug delivery (TDD) for MSK systems, including osteoporosis, nutritional rickets and some other typical types of arthritis and muscular damage, and in closing summarize the future prospects and challenges of MNs application.

Irisin as an agent for protecting against osteoporosis: A review of the current mechanisms and pathways

BACKGROUND

Osteoporosis is recognized as a skeletal disorder characterized by diminished bone tissue quality and density. Regular physical exercise is widely acknowledged to preserve and enhance bone health, but the detailed molecular mechanisms involved remain unclear. Irisin, a factor derived from muscle during exercise, influences bone and muscle. Since its discovery in 2012, irisin has been found to promote bone growth and reduce bone resorption, establishing a tangible link between muscle exertion and bone health. Consequently, the mechanism by which irisin prevents osteoporosis have attracted significant scientific interest.

AIM OF THE REVIEW

This study aims to elucidate the multifaceted relationship between exercise, irisin, and bone health. Focusing on irisin, a muscle-derived factor released during exercise, we seek to understand its role in promoting bone growth and inhibiting resorption. Through a review of current research article on irisin in osteoporosis, Our review provides a deep dive into existing research on influence of irisin in osteoporosis, exploring its interaction with pivotal signaling pathways and its impact on various cell death mechanisms and inflammation. We aim to uncover the molecular underpinnings of how irisin, secreted during exercise, can serve as a therapeutic strategy for osteoporosis.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

Irisin, secreted during exercise, plays a vital role in bridging muscle function to bone health. It not only promotes bone growth but also inhibits bone resorption. Specifically, Irisin fosters osteoblast proliferation, differentiation, and mineralization predominantly through the ERK, p38, and AMPK signaling pathways. Concurrently, it regulates osteoclast differentiation and maturation via the JNK, Wnt/β-catenin and RANKL/RANK/OPG signaling pathways. This review further delves into the profound significance of irisin in osteoporosis and its involvement in diverse cellular death mechanisms, including apoptosis, autophagy, ferroptosis, and pyroptosis.

Brief review: Applications of nanocomposite in electrochemical sensor and drugs delivery

The recent advancement of nanoparticles (NPs) holds significant potential for treating various ailments. NPs are employed as drug carriers for diseases like cancer because of their small size and increased stability. In addition, they have several desirable properties that make them ideal for treating bone cancer, including high stability, specificity, higher sensitivity, and efficacy. Furthermore, they might be taken into account to permit the precise drug release from the matrix. Drug delivery systems for cancer treatment have progressed to include nanocomposites, metallic NPs, dendrimers, and liposomes. Materials’ mechanical strength, hardness, electrical and thermal conductivity, and electrochemical sensors are significantly improved using nanoparticles (NPs). New sensing devices, drug delivery systems, electrochemical sensors, and biosensors can all benefit considerably from the NPs’ exceptional physical and chemical capabilities. Nanotechnology is discussed in this article from a variety of angles, including its recent applications in the medical sciences for the effective treatment of bone cancers and its potential as a promising option for treating other complex health anomalies via the use of anti-tumour therapy, radiotherapy, the delivery of proteins, antibiotics, and vaccines, and other methods. This also brings to light the role that model simulations can play in diagnosing and treating bone cancer, an area where Nanomedicine has recently been formulated. There has been a recent uptick in using nanotechnology to treat conditions affecting the skeleton. Consequently, it will pave the door for more effective utilization of cutting-edge technology, including electrochemical sensors and biosensors, and improved therapeutic outcomes.

A novel biologically hierarchical hydrogel with osteoblast precursor-targeting extracellular vesicles ameliorates bone loss in vivo via the sequential action of antagomiR-200b-3p and antagomiR-130b-3p

Osteoporotic fracture is a major health problem plaguing the ageing society, and improving its treatment is an urgent challenge. How to ameliorate bone loss determines the recovery of such fractures. Extracellular vesicle (EV)-loaded hydrogel has the capacity to treat osteoporotic fractures due to its pro-osteogenic property. And balancing proliferation and maturation of osteoblast precursors (OBPs) is of great significance to avoid OBP depletion, which is lacking in current treatment. Based on osteoblastogenic miRNAs, this study aimed to explore the efficacies of the combination of hierarchical hydrogel and EVs altering functional miRNAs level in bone loss. Through bioinformatics analyses, we screened out proliferative gene-targeting miR-200b-3p and osteogenic gene-targeting miR-130b-3p. And antagomiR-200b-3p (ant-200b) enhanced OBP proliferation, and antagomiR-130b-3p (ant-130b) promoted OBP differentiation. After confirming the directional effect of Fibronectin (Fn1) on OBPs, we prepared OBP-targeting EVs. Furthermore, encapsulation of two antagomiRNAs in EVs enhanced the respective effect of ant-200b and ant-130b. Notably, hierarchically injectable hydrogel exerted an effective function in promoting the sequential delivery of EVs-200b and EVs-130b. Importantly, hierarchical hydrogel containing dual EVs effectively ameliorated bone loss. Overall, hierarchical hydrogel based on two antagomiRNAs effectively improves bone loss in vivo due to its role in promoting OBP proliferation and maturation sequentially.

Mesoporous Bioactive Nanoparticles for Bone Tissue Applications

Research in nanomaterials with applications in bone regeneration therapies has experienced a very significant advance with the development of bioactive mesoporous nanoparticles (MBNPs). These nanomaterials consist of small spherical particles that exhibit chemical properties and porous structures that stimulate bone tissue regeneration, since they have a composition similar to that of conventional sol-gel bioactive glasses and high specific surface area and porosity values. The rational design of mesoporosity and their ability to incorporate drugs make MBNPs an excellent tool for the treatment of bone defects, as well as the pathologies that cause them, such as osteoporosis, bone cancer, and infection, among others. Moreover, the small size of MBNPs allows them to penetrate inside the cells, provoking specific cellular responses that conventional bone grafts cannot perform. In this review, different aspects of MBNPs are comprehensively collected and discussed, including synthesis strategies, behavior as drug delivery systems, incorporation of therapeutic ions, formation of composites, specific cellular response and, finally, in vivo studies that have been performed to date.

Application and Molecular Mechanisms of Extracellular Vesicles Derived from Mesenchymal Stem Cells in Osteoporosis

Osteoporosis (OP) is a chronic bone disease characterized by decreased bone mass, destroyed bone microstructure, and increased bone fragility. Accumulative evidence shows that extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) (MSC-EVs), especially exosomes (Exos), exhibit great potential in the treatment of OP. However, the research on MSC-EVs in the treatment of OP is still in the initial stage. The potential mechanism has not been fully clarified. Therefore, by reviewing the relevant literature of MSC-EVs and OP in recent years, we summarized the latest application of bone targeted MSC-EVs in the treatment of OP and further elaborated the potential mechanism of MSC-EVs in regulating bone formation, bone resorption, bone angiogenesis, and immune regulation through internal bioactive molecules to alleviate OP, providing a theoretical basis for the related research of MSC-EVs in the treatment of OP.

Advanced Glycation End Products, Bone Health, and Diabetes Mellitus

Advanced glycation end products (AGEs), the compounds resulting from the non-enzymatic glycosylation between reducing sugars and proteins, are derived from food or produced de novo. Over time, more and more endogenous and exogenous AGEs accumulate in various organs such as the liver, kidneys, muscle, and bone, threatening human health. Among these organs, bone is most widely reported. AGEs accumulating in bone reduce bone strength by participating in bone structure formation and breaking bone homeostasis by binding their receptors to alter the proliferation, differentiation, and apoptosis of cells involved in bone remodeling. In this review, we summarize the research about the effects of AGEs on bone health and highlight their associations with bone health in diabetes patients to provide some clues toward the discovery of new treatment and prevention strategies for bone-related diseases caused by AGEs.

Bone-Targeting Nanoparticles of a Dendritic (Aspartic acid)3-Functionalized PEG-PLGA Biopolymer Encapsulating Simvastatin for the Treatment of Osteoporosis in Rat Models

Simvastatin (SIM) is a lipid-lowering drug that also promotes bone formation, but its high liver specificity may cause muscle damage, and the low solubility of lipophilic drugs limits the systemic administration of SIM, especially in osteoporosis (OP) studies. In this study, we utilized the bone-targeting moiety of dendritic oligopeptides consisting of three aspartic acid moieties (_dAsp₃) and amphiphilic polymers (poly(ethylene glycol)-block-poly(lactic-co-glycolic acid); PEG-PLGA) to create _dAsp₃-PEG-PLGA (APP) nanoparticles (NPs), which can carry SIM to treat OP. An in vivo imaging system showed that gold nanocluster (GNC)-PLGA/APP NPs had a significantly higher accumulation rate in representative bone tissues. In vivo experiments comparing low-dose SIM treatment (0.25 mg/kg per time, 2 times per week) showed that bone-targeting SIM/APP NPs could increase the bone formation effect compared with non-bone-targeting SIM/PP NPs in a local bone loss of hindlimb suspension (disuse) model, but did not demonstrate good bone formation in a postmenopausal (ovariectomized) model of systemic bone loss. The APP NPs could effectively target high mineral levels in bone tissue and were expected to reduce side effects in other organs affected by SIM. However, in vivo OP model testing showed that the same lower dose could not be used to treat different types of OP.

Dual Targeting Anti-Osteoporotic Therapy through Potential Nanotherapeutic Approaches

Osteoporosis is characterised by a major public health burden, particularly taking into account the ageing global population. Therapeutic modalities for osteoporosis are categorised on the basis of their effect on bone remodeling: antiresorptive agents and anabolic agents. Anabolic drugs are favoured as they promote the formation of new bone, whereas antiresorptive drugs terminate the further deterioration of bone. Non-specific delivery of anabolic agents results in prolonged kidney exposure causing malignant hypercalcemia, whereas antiresorptive agents and bisphosphonates may produce osteonecrosis of the jaw. Several clinical trials have been reported for combinational therapy of anabolic agents and antiresorptive agents for osteoporosis. However, none of them have proven their cumulative effectiveness in the treatment of disease. The present work emphasizes on dual-targeting drug delivery approach comprising of bone anabolic and antiresorptive agents that would deliver the therapeutic agents to both the zones of bone simultaneously. The anticipated pioneering delivery approach will intensify the explicit interaction between the therapeutic agent and bone surfaces separately without developing severe adverse effects and improve the osteoporotic therapy effectively compared to non-targeted drug delivery.

Antiosteoporosis Effects, Pharmacokinetics, and Drug Delivery Systems of Icaritin: Advances and Prospects

Osteoporosis is a systemic skeletal disorder affecting over 200 million people worldwide and contributes dramatically to global healthcare costs. Available anti-osteoporotic drug treatments including hormone replacement therapy, anabolic agents, and bisphosphonates often cause adverse events which limit their long-term use. Therefore, the application of natural products has been proposed as an alternative therapy strategy. Icaritin (ICT) is not only an enzyme-hydrolyzed product of icariin but also an intestinal metabolite of eight major flavonoids of the traditional Chinese medicinal plant Epimedium with extensive pharmacological activities, such as strengthening the kidney and reinforcing the bone. ICT displays several therapeutic effects, including osteoporosis prevention, neuroprotection, antitumor, cardiovascular protection, anti-inflammation, and immune-protective effect. ICT inhibits bone resorption activity of osteoclasts and stimulates osteogenic differentiation and maturation of bone marrow stromal progenitor cells and osteoblasts. As for the mechanisms of effect, ICT regulates relative activities of two transcription factors Runx2 and PPARγ, determines the differentiation of MSCs into osteoblasts, increases mRNA expression of OPG, and inhibits mRNA expression of RANKL. Poor water solubility, high lipophilicity, and unfavorable pharmacokinetic properties of ICT restrict its anti-osteoporotic effects, and novel drug delivery systems are explored to overcome intrinsic limitations of ICT. The paper focuses on osteogenic effects and mechanisms, pharmacokinetics and delivery systems of ICT, and highlights bone-targeting strategies to concentrate ICT on the ideal specific site of bone. ICT is a promising potential novel therapeutic agent for osteoporosis.

A bone-targeted engineered exosome platform delivering siRNA to treat osteoporosis

The complex pathogenesis of osteoporosis includes excessive bone resorption, insufficient bone formation and inadequate vascularization, a combination which is difficult to completely address with conventional therapies. Engineered exosomes carrying curative molecules show promise as alternative osteoporosis therapies, but depend on specifically-functionalized vesicles and appropriate engineering strategies. Here, we developed an exosome delivery system based on exosomes secreted by mesenchymal stem cells (MSCs) derived from human induced pluripotent stem cells (iPSCs). The engineered exosomes BT-Exo-siShn3, took advantage of the intrinsic anti-osteoporosis function of these special MSC-derived exosomes and collaborated with the loaded siRNA of the Shn3 gene to enhance the therapeutic effects. Modification of a bone-targeting peptide endowed the BT-Exo-siShn3 an ability to deliver siRNA to osteoblasts specifically. Silencing of the osteoblastic Shn3 gene enhanced osteogenic differentiation, decreased autologous RANKL expression and thereby inhibited osteoclast formation. Furthermore, Shn3 gene silencing increased production of SLIT3 and consequently facilitated vascularization, especially formation of type H vessels. Our study demonstrated that BT-Exo-siShn3 could serve as a promising therapy to kill three birds with one stone and implement comprehensive anti-osteoporosis effects.

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A bone-targeted engineered exosome platform BT-Exo-siShn3 could deliver siRNA to osteoblasts specifically.

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Comprehensive anti-osteoporosis effects were implemented based on the synchronization of exosome-carrier and siRNA-cargo.

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The BT-Exo-siShn3 platform was the first drug delivery system using exosomes produced by iPSC-derivatives.

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This study proposed a versatile paradigm of targeted therapies for different diseases based on iPSC-derivatives.

Osteoporosis Remission and New Bone Formation with Mesoporous Silica Nanoparticles

Nanotechnology changed the concept of treatment for a variety of diseases, producing a huge impact regarding drug and gene delivery. Among the different targeted diseases, osteoporosis has devastating clinical and economic consequences. Since current osteoporosis treatments present several side effects, new treatment approaches are needed. Recently, the application of small interfering RNA (siRNA) has become a promising alternative. Wnt/β-catenin signaling pathway controls bone development and formation. This pathway is negatively regulated by sclerostin, which knock-down through siRNA application would potentially promote bone formation. However, the major bottleneck for siRNA-based treatments is the necessity of a delivery vector, bringing nanotechnology as a potential solution. Among the available nanocarriers, mesoporous silica nanoparticles (MSNs) have attracted great attention for intracellular delivery of siRNAs. The mesoporous structure of MSNs permits the delivery of siRNAs together with another biomolecule, achieving a combination therapy. Here, the effectiveness of a new potential osteoporosis treatment based on MSNs is evaluated. The proposed system is effective in delivering SOST siRNA and osteostatin through systemic injection to bone tissue. The nanoparticle administration produced an increase expression of osteogenic related genes improving the bone microarchitecture. The treated osteoporotic mice recovered values of a healthy situation approaching to osteoporosis remission.

Strategies for transdermal drug delivery against bone disorders: A preclinical and clinical update

The transdermal drug delivery system is an exceptionally safe and well-tolerable therapeutic approach that has immense potential for delivering active components against bone-related pathologies. However, its use is limited in the current clinical practices due to the low skin permeability of most active drugs in the formulation. Thus, innovations in the methodologies of skin permeation enhancement techniques are suggested to overcome this limitation. Although various transdermal drug delivery systems are studied to date, there are insufficient studies comparing the therapeutic efficacy of transdermal delivery systems to oral delivery systems. Thus, creating a decision-making dilemma between oral or transdermal therapies. Therefore, a timely review is inevitable to develop a platform for future researchers to develop next-generation transdermal drug delivery strategies against skeletal diseases that must be convenient and cost-effective for the patients with improved therapeutic efficacy. Here, we will outline the most recent strategies that can overcome the choice limitation of the drug and enhance the transdermal adsorption of various types of drugs to treat bone disorders. For the first time, in this review paper, we will highlight the preclinical and clinical studies on the different transdermal delivery methods. Thus, providing insight into the current therapeutic approaches and suggesting new directions for the advancements in transdermal drug delivery systems against bone disorders.

Calcium Chelidonate: Semi-Synthesis, Crystallography, and Osteoinductive Activity In Vitro and In Vivo

Calcium chelidonate [Ca(ChA)(H₂O)₃]_n was obtained by semi-synthesis using natural chelidonic acid. The structure of the molecular complex was determined by X-ray diffraction analysis. The asymmetric unit of [Ca(ChA)(H₂O)₃]_n includes chelidonic acid coordinated through three oxygen atoms, and three water ligands. The oxygen atoms of acid and oxygen atoms of water from each asymmetric unit are also coordinated to the calcium of another one, forming an infinite linear complex. Calcium geometry is close to the trigonal dodecahedron (D2d). The intra-complex hydrogen bonds additionally stabilize the linear species, which are parallel to the axis. In turn the linear species are packed into the 3D structure through mutual intercomplex hydrogen bonds. The osteogenic activity of the semi-synthetic CaChA was studied in vitro on 21-day hAMMSC culture and in vivo in mice using ectopic (subcutaneous) implantation of CaP-coated Ti plates saturated in vitro with syngeneic bone marrow. The enhanced extracellular matrix ECM mineralization in vitro and ectopic bone tissue formation in situ occurred while a water solution of calcium chelidonate at a dose of 10 mg/kg was used. The test substance promotes human adipose-derived multipotent mesenchymal stromal/stem cells (hAMMSCs), as well as mouse MSCs to differentiate into osteoblasts in vitro and in vivo, respectively. Calcium chelidonate is non-toxic and can stimulate osteoinductive processes.

Genetically Modified Ferritin Nanoparticles with Bone-Targeting Peptides for Bone Imaging

Bone homeostasis plays a major role in supporting and protecting various organs as well as a body structure by maintaining the balance of activities of the osteoblasts and osteoclasts. Unbalanced differentiation and functions of these cells result in various skeletal diseases, such as osteoporosis, osteopetrosis, and Paget’s disease. Although various synthetic nanomaterials have been developed for bone imaging and therapy through the chemical conjugation, they are associated with serious drawbacks, including heterogeneity and random orientation, in turn resulting in low efficiency. Here, we report the synthesis of bone-targeting ferritin nanoparticles for bone imaging. Ferritin, which is a globular protein composed of 24 subunits, was employed as a carrier molecule. Bone-targeting peptides that have been reported to specifically bind to osteoblast and hydroxyapatite were genetically fused to the N-terminus of the heavy subunit of human ferritin in such a way that the peptides faced outwards. Ferritin nanoparticles with fused bone-targeting peptides were also conjugated with fluorescent dyes to assess their binding ability using osteoblast imaging and a hydroxyapatite binding assay; the results showed their specific binding with osteoblasts and hydroxyapatite. Using in vivo analysis, a specific fluorescent signal from the lower limb was observed, demonstrating a highly selective affinity of the modified nanoparticles for the bone tissue. These promising results indicate a specific binding ability of the nanoscale targeting system to the bone tissue, which might potentially be used for bone disease therapy in future clinical applications.

Alendronate Sodium Intercalation in Layered Double Hydroxide/Poly (ε-caprolactone): Application in Osteoporosis Treatment

Background:

Osteoporosis is a bone disease alters the amount and variety of proteins in bone tissue and increases the potential of bone fracture. Antiresorptive therapy is one of the most popular treatment methods for osteoporosis. To reduce side effects and enhance the bioavailability of drug agents, the controlled delivery of drug is commonly utilized.

Objectives:

We investigated the controlled release of Alendronate in different composites of layered double hydroxide (LDH) using poly (ε-caprolactone) (PCL) as a matrix.

Materials and Methods:

We prepared different microsphere composites of ALD intercalated in various amounts of LDH, using PCL as a matrix. The controlled release of ALD from these composites is subsequently investigated. Samples are characterized and in vitro cell cytotoxicity, attachment, osteogenic activity including alkaline phosphatase activity and mineralization are examined using MG-63 human osteosarcoma cells.

Results:

The results showed that the release of ALD is more desirable and controlled in the samples having a higher amount of LDH incorporated into the PCL matrix. MG63 cells show a significant increase in viability, attachment, and mineralization while alkaline phosphatase activity remains almost at a constant level after 3 weeks.

Conclusions:

Overall, the findings showed that by incorporation of 15 wt% of LDH, the composite microsphere is capable of holding the antiresorptive drug longer and release it in a more controlled manner. This is an advantageous and promising characteristic for a carrier that could be used as a potential candidate for osteoporosis treatment.

Ipriflavone-Loaded Mesoporous Nanospheres with Potential Applications for Periodontal Treatment

The incorporation and effects of hollow mesoporous nanospheres in the system SiO₂-CaO (nanoMBGs) containing ipriflavone (IP), a synthetic isoflavone that prevents osteoporosis, were evaluated. Due to their superior porosity and capability to host drugs, these nanoparticles are designed as a potential alternative to conventional bioactive glasses for the treatment of periodontal defects. To identify the endocytic mechanisms by which these nanospheres are incorporated within the MC3T3-E1 cells, five inhibitors (cytochalasin B, cytochalasin D, chlorpromazine, genistein and wortmannin) were used before the addition of these nanoparticles labeled with fluorescein isothiocyanate (FITC-nanoMBGs). The results indicate that nanoMBGs enter the pre-osteoblasts mainly through clathrin-dependent mechanisms and in a lower proportion by macropinocytosis. The present study evidences the active incorporation of nanoMBG-IPs by MC3T3-E1 osteoprogenitor cells that stimulate their differentiation into mature osteoblast phenotype with increased alkaline phosphatase activity. The final aim of this study is to demonstrate the biocompatibility and osteogenic behavior of IP-loaded bioactive nanoparticles to be used for periodontal augmentation purposes and to shed light on internalization mechanisms that determine the incorporation of these nanoparticles into the cells.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Osteoblast-n-Osteoclast: Making Headway to Osteoporosis Treatment

Background:

Bone is a dynamic tissue that continuously undergoes the modeling and remodeling process to maintain its strength and firmness. Bone remodeling is determined by the functioning of osteoblast and osteoclast cells. The imbalance between the functioning of osteoclast and osteoblast cells leads to osteoporosis. Osteoporosis is divided into primary and secondary osteoporosis. Generally, osteoporosis is diagnosed by measuring bone mineral density (BMD) and various osteoblast and osteoclast cell markers.

Methods:

Relevant literature reports have been studied and data has been collected using various search engines like google scholar, scihub, sciencedirect, pubmed, etc. A thorough understanding of the mechanism of bone targeting strategies has been discussed and related literature has been studied and compiled.

Results:

Bone remodeling process has been described in detail including various approaches for targeting bone. Several bone targeting moieties have been stated in detail along with their mechanisms. Targeting of osteoclasts and osteoblasts using various nanocarriers has been discussed in separate sections. The toxicity issues or Biosafety related to the use of nanomaterials have been covered.

Conclusion:

The treatment of osteoporosis targets the inhibition of bone resorption and the use of agents that promote bone mineralization to slow disease progression. Current osteoporosis therapy involves the use of targeting moieties such as bisphosphonates and tetracyclines for targeting various drugs. Nanotechnology has been used for targeting various drug molecules such as RANKLinhibitors, parathyroid hormone analogues, estrogen agonists and antagonists, Wnt signaling enhancer and calcitonin specifically to bone tissue (osteoclast and osteoblasts). So, a multicomponent treatment strategy targeting both the bone cells will be more effective rather than targeting only osteoclasts and it will be a potential area of research in bone targeting used to treat osteoporosis. The first section of the review article covers various aspects of bone targeting. Another section comprises details of various targeting moieties such as bisphosphonates, tetracyclines; and various nanocarriers developed to target osteoclast and osteoblast cells and summarized data on in vivo models has been used for assessment of bone targeting, drawbacks of current strategies and future perspectives.

Bone-Specific Drug Delivery for Osteoporosis and Rare Skeletal Disorders

PURPOSE OF REVIEW

The skeletal system provides an important role to support body structure and protect organs. The complexity of its architecture and components makes it challenging to deliver the right amount of the drug into bone regions, particularly avascular cartilage lesions. In this review, we describe the recent advance of bone-targeting methods using bisphosphonates, polymeric oligopeptides, and nanoparticles on osteoporosis and rare skeletal diseases.

RECENT FINDINGS

Hydroxyapatite (HA), a calcium phosphate with the formula Ca10(PO4)6(OH)2, is a primary matrix of bone mineral that includes a high concentration of positively charged calcium ion and is found only in the bone. This unique feature makes HA a general targeting moiety to the entire skeletal system. We have applied bone-targeting strategy using acidic amino acid oligopeptides into lysosomal enzymes, demonstrating the effects of bone-targeting enzyme replacement therapy and gene therapy on bone and cartilage lesions in inherited skeletal disorders. Virus or no-virus gene therapy using techniques of engineered capsid or nanomedicine has been studied preclinically for skeletal diseases. Efficient drug delivery into bone lesions remains an unmet challenge in clinical practice. Bone-targeting therapies based on gene transfer can be potential as new candidates for skeletal diseases.

Targeting nanoparticles for diagnosis and therapy of bone tumors: Opportunities and challenges

A variety of targeted nanoparticles were developed for the diagnosis and therapy of orthotopic and metastatic bone tumors during the past decade. This critical review will focus on principles and methods in the design of these bone-targeted nanoparticles. Ligands including bisphosphonates, aspartic acid-rich peptides and synthetic polymers were grafted on nanoparticles such as PLGA nanoparticles, liposomes, dendrimers and inorganic nanoparticles for bone targeting. Besides, other ligands such as monoclonal antibodies, peptides and aptamers targeting biomarkers on tumor/bone cells were identified for targeted diagnosis and therapy. Examples of targeted nanoparticles for the early detection of bone metastatic tumors and the ablation of cancer via chemotherapy, photothermal therapy, gene therapy and combination therapy will be intensively reviewed. The development of multifunctional nanoparticles to break down the "vicious" cycle between tumor cell proliferation and bone resorption, and the challenges and perspectives in this area will be discussed.

Osteoblast-Based Therapy-A New Approach for Bone Repair in Osteoporosis: Pre-Clinical Setting

BACKGROUND

Osteoporosis is a metabolic bone disease characterized by low bone density resulting in increased fracture susceptibility. This research was constructed to uncover the potential therapeutic application of osteoblasts transplantation, generated upon culturing male rat bone marrow-derived mesenchymal stem cells (BM-MSCs) in osteogenic medium (OM), OM containing gold (Au-NPs) or gold/hydroxyapatite (Au/HA-NPs) nanoparticles, in ovariectomized rats to counteract osteoporosis.

METHODS

Forty rats were randomized into: (1) negative control, (2) osteoporotic rats, whereas groups (3), (4) and (5) constituted osteoporotic rats treated with osteoblasts yielded from culturing BM-MSCs in OM, OM plus Au-NPs or Au/HA-NPs, respectively. After 3 months, osterix (OSX), bone alkaline phosphatase (BALP), sclerostin (SOST) and bone sialoprotein (BSP) serum levels were assessed. In addition, gene expression levels of cathepsin K, receptor activator of nuclear factor-κb ligand (RANKL), osteoprotegerin (OPG) and RANKL/OPG ratio were evaluated using real-time PCR. Moreover, histological investigation of femur bone tissues in different groups was performed. The homing of implanted osteoblasts to the osteoporotic femur bone of rats was documented by Sex determining region Y gene detection in bone tissue.

RESULTS

Our results indicated that osteoblasts infusion significantly blunted serum BALP, BSP and SOST levels, while significantly elevated OSX level. Also, they brought about significant down-regulation in gene expression levels of cathepsin K, RANKL and RANKL/OPG ratio versus untreated osteoporotic rats. Additionally, osteoblasts nidation could restore bone histoarchitecture.

CONCLUSION

These findings offer scientific evidence that transplanting osteoblasts in osteoporotic rats regains the homeostasis of the bone remodeling cycle, thus providing a promising treatment strategy for primary osteoporosis.

Pamidronate-Encapsulated Electrospun Polycaprolactone-Based Composite Scaffolds for Osteoporotic Bone Defect Repair

Bone fractures associated with osteoporosis are a major concern all over the world especially among the elderly population and postmenopausal women. Bisphosphonates (BPs) are widely used clinically for both treatment and prevention of osteoporosis despite their poor oral bioavailability and undesired side effects. Local delivery of BPs from polymeric scaffolds can improve the efficacy and overcome the undesirable side effects associated with oral bisphosphonate therapy. The aim of the present study is to explore the effectiveness of pamidronate (PDS) encapsulated electrospun polycaprolactone/polycaprolactone-polyethyleneglycol-polycaprolactone/nanohydroxyapatite (PCH) scaffolds in healing critical-size calvarial defects in an osteoporotic rat animal model. Prior to implantation studies, the effect of PDS on the fiber architecture, mechanical properties, and in vitro degradation behavior was evaluated. The in vitro release of PDS from PCH scaffolds in phosphate buffer saline (PBS) at 37 °C was monitored for a period of 21 days. An osteoporotic animal model was successfully developed in Wistar rats by bilateral ovariectomy. Results of micro CT (computed tomography) and blood serum analysis confirmed the osteoporotic model induction in rats. Critical-size calvarial defects of 8 mm size were created in osteoporotic rats, and the in vivo osteogenic efficacy of PCH-PDS scaffolds was evaluated by micro CT, histology, and histomorphometry. Micro CT analysis showed improved osseous tissue integration with the use of PDS-loaded PCH scaffolds after 12 week post implantation. Histology, density measurement using micro CT, and histomorphometry further substantiate that PCH-PDS scaffolds have the potential to be used for the repair of osteoporotic bone defects. Our findings revealed that incorporation of PDS onto PCH scaffolds provides a promising biomaterial that could be used for regenerating osteoporosis-related fractures.

Green nanotechnology-based drug delivery systems for osteogenic disorders

Introduction: Current treatments for osteogenic disorders are often successful, however they are not free of drawbacks, such as toxicity or side effects. Nanotechnology offers a platform for drug delivery in the treatment of bone disorders, which can overcome such limitations. Nevertheless, traditional synthesis of nanomaterials presents environmental and health concerns due to its production of toxic by-products, the need for extreme and harsh raw materials, and their lack of biocompatibility over time.Areas covered: This review article contains an overview of the current status of treating osteogenic disorders employing green nanotechnological approaches, showing some of the latest advances in the application of green nanomaterials, as drug delivery carriers, for the effective treatment of osteogenic disorders.Expert opinion: Green nanotechnology, as a potential solution, is understood as the use of living organisms, biomolecules and environmentally friendly processes for the production of nanomaterials. Nanomaterials derived from bacterial cultures or biomolecules isolated from living organisms, such as carbohydrates, proteins, and nucleic acids, have been proven to be effective composites. These nanomaterials introduce enhancements in the treatment and prevention of osteogenic disorders, compared to physiochemically-synthesized nanostructures, specifically in terms of their improved cell attachment and proliferation, as well as their ability to prevent bacterial adhesion.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Pamidronate-encapsulated electrospun polycaprolactone as a potential bone regenerative scaffold

This study explores the potential of electrospun polycaprolactone scaffolds for the controlled delivery of pamidronate disodium pentahydrate, an amino-bisphosphonate drug used for the treatment of osteoporosis. Major drawbacks associated with oral bisphosphonate therapy are its poor bioavailability and gastrointestinal side-effects. Herein, we used polycaprolactone, a well-known Food and Drug Administration–approved biomaterial, as the delivering vehicle for pamidronate disodium pentahydrate. Scaffolds based on polycaprolactone with three different formulations (1, 3, and 5 wt%) of pamidronate disodium pentahydrate were fabricated by electrospinning, and a comparative study was carried out to evaluate the effect of pamidronate disodium pentahydrate on physico-mechanical and biological properties of polycaprolactone. The observations from Fourier-transform infrared spectra and thermogravimetric analysis confirmed the successful incorporation of pamidronate disodium pentahydrate into polycaprolactone scaffolds. The study also revealed that pamidronate disodium pentahydrate–loaded scaffolds exhibited improved hydrophilicity as well as superior mechanical properties as depicted by the contact angle measurements and mechanical property evaluation. In vitro drug release studies of pamidronate disodium pentahydrate–loaded scaffolds in phosphate buffer saline at 37°C showed that all the scaffolds exhibited controlled release of pamidronate disodium pentahydrate. In vitro degradation studies further revealed that pamidronate disodium pentahydrate incorporated polycaprolactone scaffolds degraded faster as depicted by the fiber rupture and drop in mechanical properties. In vitro cell culture studies using human osteosarcoma cell lines demonstrated that pamidronate disodium pentahydrate–loaded polycaprolactone scaffolds were cytocompatible. The human osteosarcoma cells had favorable interaction with the scaffolds, and the viability of adhered cells was depicted by the fluorescein diacetate/propidium iodide staining. MTT assay further revealed enhanced cell viability on PCL/PDS3 scaffolds. Our findings bespeak that the pamidronate disodium pentahydrate–encapsulated electrospun polycaprolactone scaffolds have the potential to serve as a promising drug delivery vehicle for osteoporotic bone defect repair.

The Osteogenic Potential of Brown Seaweed Extracts

Marine drugs hold significantly more promise than their terrestrial counterparts, which could help to solve the current shortfall in treatments for osteoporosis and other bone related diseases. Fucoxanthin is the main carotenoid found in brown seaweed, and has many perceived health benefits, including potential bone therapeutic properties. This study assessed the osteogenic potential of pure fucoxanthin and crude extracts containing both fucoxanthin and phenolic fractions (also cited to have osteogenic potential) isolated from two intertidal species of brown seaweed, Laminaria digitata and Ascophyllum nodosum. In vitro studies were performed using a human foetal osteoblast cell line (hFOBs) and primary human bone marrow stromal cells (hBMSCs). The results found pure fucoxanthin inhibitory to cell proliferation in hFOBs at higher concentrations, whereas, the crude extracts containing both polyphenols and fucoxanthin showed the ability to scavenge free radicals, which masked this effect. None of the extracts tested showed strong pro-osteogenic effects in either cell type tested, failing to support previously reported positive effects.

Strontium Alleviates Endoplasmic Reticulum Stress in a Nonalcoholic Fatty Liver Disease Model

The purpose of this study was to explore the effects of strontium on fatty liver, and to clarify the possible mechanisms by which strontium improves nonalcoholic fatty liver disease (NAFLD). We also evaluated how strontium affected the endoplasmic reticulum stress (ERS) pathways. We established an in vitro model of NAFLD using a human hepatocyte cell line (L02) treated with 0.2 mM palmitic acid. The Sprague-Dawley rats were fed with a high-fat diet (HFD) to establish NAFLD model in vivo. After strontium treatment, the total cholesterol (TC), triglyceride (TG), and lipid deposition in L02 cells and liver tissues were determined. Strontium treatment suppressed intracellular TC and TG levels and lipid accumulation in L02 cells, and the effect of high concentrations of strontium were more obvious. Strontium significantly reduced the mRNA and protein expression of glucose-regulated protein 78 (GRP78), activating transcription factor 6 (ATF6), inositol requiring enzyme 1 (IRE1), SREBP cleavage activator protein (SCAP), sterol regulatory element binding protein 1c (SREBP-1c), and SREBP-2 in L02 cells. In HFD-fed rats, strontium treatment reduced serum TC, TG, and low density lipoprotein cholesterol (LDL-C) levels, concurrent with a decrease in hepatic lipid accumulation. Furthermore, strontium treatment reduced the expression of GRP78 and SREBP-2 protein in liver tissues. Overall, strontium alleviated hepatic steatosis by decreasing ERS-related protein expression in vivo and in vitro models. The results indicated that strontium has the potential to become a new therapy for the prevention and treatment of NAFLD.

The facile synthesis of copper oxide quantum dots on chitosan with assistance of phyto-angelica for enhancing the human osteoblast activity to the application of osteoporosis

Osteoblasts are an important key factor for the pathogenesis of several bone-related diseases, notably in osteoporosis. Osteoporosis is a disorder categorized based on the bone mineral density (BMD) and an alteration in the bone micro-architecture had been considered as the major determinant for increasing the fracture risk. The available medicine for curing the osteoporosis shows a minimal or no activity against the genesis or function of osteoblasts. The present study was conducted to determine the influence of phyto Angelica species (Ang.) mediated synthesized copper quantum dots decorated chitosan on human osteoblast cells for application of osteoporosis. The phyto compound of Angelica sp. was extracted by ethanol as solvent and it has been characterized through spectral analyses. An Angelica sp. mediated synthesized copper oxide quantum dots (CuO QDs) and the presence of CuO QDs on chitosan have been analyzed and exhibited by important spectral investigations. The morphological observation of CuO QDs on the chitosan (CS) was visualized by the microscopic analyses. The MTT assay results showed that cell growth of CuO QDs/CS-Ang. by the concentration dependent. The highest cell growth (87%) was noted at 5 μg/mL followed by 80 and 77% at 15 and 25 μg/mL respectively. The functional groups and potential compounds of Angelica sp. with CuO QDs/CS has been improved the osteoblast cell activity as prophylactic potentials against osteoporosis.

Incorporation and effects of mesoporous SiO2-CaO nanospheres loaded with ipriflavone on osteoblast/osteoclast cocultures

Mesoporous nanospheres in the system SiO₂-CaO (NanoMBGs) with a hollow core surrounded by a radial arrangement of mesopores were characterized, labeled with FITC (FITC-NanoMBGs) and loaded with ipriflavone (NanoMBG-IPs) in order to evaluate their incorporation and their effects on both osteoblasts and osteoclasts simultaneously and maintaining the communication with each other in coculture. The influence of these nanospheres on macrophage polarization towards pro-inflammatory M1 or reparative M2 phenotypes was also evaluated in basal and stimulated conditions through the expression of CD80 (as M1 marker) and CD206 (as M2 marker) by flow cytometry and confocal microscopy. NanoMBGs did not induce the macrophage polarization towards the M1 pro-inflammatory phenotype, favoring the M2 reparative phenotype and increasing the macrophage response capability against stimuli as LPS and IL-4. NanoMBG-IPs induced a significant decrease of osteoclast proliferation and resorption activity after 7 days in coculture with osteoblasts, without affecting osteoblast proliferation and viability. Drug release test demonstrated that only a fraction of the payload is released by diffusion, whereas the rest of the drug remains within the hollow core after 7 days, thus ensuring the local long-term pharmacological treatment beyond the initial fast IP release. All these data ensure an appropriate immune response to these nanospheres and the potential application of NanoMBG-IPs as local drug delivery system in osteoporotic patients.

Bone-targeted delivery of simvastatin-loaded PEG-PLGA micelles conjugated with tetracycline for osteoporosis treatment

This study aimed to investigate the improved therapeutic efficacy and pharmacokinetic profiles of simvastatin (SIM) with imparted bone targeting potential using tetracycline-mediated PEG-PLGA (TC-PEG-PLGA) micelles in osteoporotic rats. The SIM-loaded TC-PEG-PLGA (TC-PEG-PLGA/SIM) micelles were evaluated for particle size, morphology, stability, loading efficiency, cell viability, bone mineral binding ability in vitro, mineralization, pharmacokinetics, and pharmacodynamics. TC-PEG-PLGA conjugates were successfully and could self-assembly form micelles in aqueous medium with a 19.4 μg/mL critical micelle concentration. Then, TC-PEG-PLGA/SIM micelles were prepared with solvent diffusion method, and the obtained micelles (56.21 ± 7.39 nm average size; 81.8 ± 3.1% encapsulation efficiency; and 7.56 ± 0.27% drug loading) led to the prolonged release of SIM from micelles. Cellular uptake test indicated that TC had no effects on micellar internalization and micellar internalization was mainly involved with clathrin-mediated endocytic pathway. In vivo pharmacokinetic results indicated that TC-PEG-PLGA/SIM micelles exhibited a significantly prolonged time in systemic circulation and were preferentially accumulated in bone tissue. TC-PEG-PLGA/SIM micelles showed better therapeutic effects, as reflected by the improved bone mineral density, bone mineral content, and bone mechanical strength. Overall, these results suggested that TC-PEG-PLGA/SIM micelles provide several advantages, including prolonged systemic circulation, enhanced bone tissue distribution, and improved therapeutic outcomes in osteoporotic rats.

Effects of a mesoporous bioactive glass on osteoblasts, osteoclasts and macrophages

A mesoporous bioactive glass (MBG) of molar composition 75SiO₂-20CaO-5P₂O₅ (MBG-75S) has been synthetized as a potential bioceramic for bone regeneration purposes. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption studies and transmission electron microscopy (TEM) demonstrated that MBG-75S possess a highly ordered mesoporous structure with high surface area and porosity, which would explain the high ionic exchange rate (mainly calcium and silicon soluble species) with the surrounded media. MBG-75S showed high biocompatibility in contact with Saos-2 osteoblast-like cells. Concentrations up to 1 mg/ml did not lead to significant alterations on either morphology or cell cycle. Regarding the effects on osteoclasts, MBG-75S allowed the differentiation of RAW-264.7 macrophages into osteoclast-like cells but exhibiting a decreased resorptive activity. These results point out that MBG-75S does not inhibit osteoclastogenesis but reduces the osteoclast bone-resorbing capability. Finally, in vitro studies focused on the innate immune response, evidenced that MBG-75S allows the proliferation of macrophages without inducing their polarization towards the M1 pro-inflammatory phenotype. This in vitro behavior is indicative that MBG-75S would just induce the required innate immune response without further inflammatory complications under in vivo conditions. The overall behavior respect to osteoblasts, osteoclasts and macrophages, makes this MBG a very interesting candidate for bone grafting applications in osteoporotic patients.

Bone-seeking agents for the treatment of bone disorders

The targeting and delivery of therapeutic and diagnostic agents to bone tissue presents both a challenge and opportunity. Osteoporosis, Paget's disease, cancer, and bone metastases are all skeletal diseases whose treatment would benefit from new targeted therapeutic strategies. Osteoporosis, in particular, is a very prevalent disease, affecting over one in three women and one in five men in Canada alone with the cost to the healthcare system estimated at over $2.3 billion in 2010. Bone tissue is often considered a rigid structure when in reality there is a process of continuous remodeling that takes place via complex endocrine-regulated cell signaling pathways in addition to the signaling pathways unique to bone tissue. It is these specific boneremodeling processes that provide unique targeting opportunities but also present a number of challenges.

Atorvastatin-loaded micelles with bone-targeted ligand for the treatment of osteoporosis

Osteoporosis is a common bone disorder where the declined bone mass is far more than normal physiological status and usually associated with enhanced fracture risk, reduced bone strength and even deteriorated quality of life. Recent studies showed that statins could exert beneficial effects on bones via promoting osteoblastic activity mediated by increased expression of bone morphogenetic protein 2 and also by suppressing osteoclast proliferation. In this study, we developed atorvastatin-loaded tetracycline-poly (ethylene glycol)-poly(lactic-co-glycolic acid) (TC-PEG-PLGA/ATO) micelles for the targeted treatment of osteoporosis. The TC-PEG-PLGA was synthesized under the action of coupling reagents and then ATO was encapsulated through solvent diffusion method with encapsulation efficiency and drug loading of 89.32 ± 2.48% and 8.20 ± 0.53%, respectively. The release of ATO from micelles could be maintained for more than 48 h in pH 7.4 PBS. Pharmacokinetic results further demonstrated that TC-PEG-PLGA micelles could effectively shield ATO leakage from micelles and prolong their circulation time. Benefiting from TC specifically binding to hydroxyapatite (HAp), TC-PEG-PLGA/ATO micelles exerted good bone-targeted ability, as demonstrated by in vitro HAp affinity assay and biodistribution. Pharmacodynamic studies showed that TC-PEG-PLGA/ATO micelles could effectively improve bone mineral density and bone mechanical strength in osteoporotic rats. These results suggest that TC-PEG-PLGA/ATO micelles hold significant promise for the targeted treatment of osteoporosis.

Targeting to the Bone: Alendronate-Directed Combretastatin A-4 Bearing Antiangiogenic Polymer-Drug Conjugates

Selective targeting of tumor site with chemotherapeutic agents appears to be one of the most effective methods to address many of the problems encountered with conventional chemotherapy. In this work, poly(oligoethylene glycol)methacrylate (POEGMA) based bone-targeting polymers bearing an antiangiogenic drug combretastatin A4 (CA4) were synthesized using free radical polymerization. Targeted and nontargeting copolymers were evaluated for their bone targeting efficiency, cytotoxicities against endothelial cells, namely, HUVECs and U2-OS and Saos-2 cancerous cell lines, as well as their antiangiogenic activity against endothelial cell tube formation by HUVECs. It is observed that the drug conjugated polymers conjugated with the bisphosphonate groups containing drug alendronate (ALN) have remarkably high affinity for bone mineral when compared to the polymer-drug conjugates devoid of the bisphosphonate groups. Both targeted and nontargeted polymer-drug conjugates show a sustained drug release in rat plasma with an overall release of 80-93% over 5 days. In vitro studies revealed high levels of cytotoxicity of the polymer-drug conjugates against HUVECs and U2-OS, and moderate cytotoxicity toward Saos-2. Importantly, the CA4 conjugated copolymers displayed excellent level of antiangiogenic activity as deduced from in vitro endothelial cell tube formation assay using HUVECs. Overall, a novel bone-targeting antiangiogenic polymer-drug conjugate that can be further elaborated to carry additional anticancer drugs is disclosed.

Effects of Osteo-F, a new herbal formula, on osteoporosis via up-regulation of Runx2 and Osterix

Osteo-F, a new herbal formula, ameliorates osteoporosis by up-regulating Runx2 and Osterix.

Study of a new bone-targeting titanium implant-bone interface

New strategies involving bone-targeting titanium (Ti) implant–bone interface are required to enhance bone regeneration and osseointegration for orthopedic and dental implants, especially in osteoporotic subjects. In this study, a new dual-controlled, local, bone-targeting delivery system was successfully constructed by loading tetracycline-grafted simvastatin (SV)-loaded polymeric micelles in titania nanotube (TNT) arrays, and a bone-targeting Ti implant–bone interface was also successfully constructed by implanting the delivery system in vivo. The biological effects were evaluated both in vitro and in vivo. The results showed that Ti surfaces with TNT–bone-targeting micelles could promote cytoskeletal spreading, early adhesion, alkaline phosphatase activity, and extracellular osteocalcin concentrations of rat osteoblasts, with concomitant enhanced protein expression of bone morphogenetic protein (BMP)-2. A single-wall bone-defect implant model was established in normal and ovariectomized rats as postmenopausal osteoporosis models. Microcomputed tomography imaging and BMP-2 expression in vivo demonstrated that the implant with a TNT-targeting micelle surface was able to promote bone regeneration and osseointegration in both animal models. Therefore, beneficial biological effects were demonstrated both in vitro and in vivo, which indicated that the bone-targeting effects of micelles greatly enhance the bioavailability of SV on the implant–bone interface, and the provision of SV-loaded targeting micelles alone exhibits the potential for extensive application in improving local bone regeneration and osseointegration, especially in osteoporotic subjects.

Advances in Controlled Drug Delivery for Treatment of Osteoporosis

Osteoporosis, which is characterized by resorption of bone exceeding formation, remains a significant human health concern, and the impact of this condition will only increase with the "graying" of the worldwide population. This review focuses on current and emerging approaches for delivering therapeutic agents to restore bone remodeling homeostasis. Well-known antiresorptive and anabolic agents, such as estrogen, estrogen analogs, bisphosphonates, calcitonin, and parathyroid hormone, along with newer modulators and antibodies, are primarily administered orally, intravenously, or subcutaneously. Although these treatments can be effective, continuing problems include patient noncompliance and adverse systemic or remote-site effects. Controlled drug delivery via polymeric, targeted, and active release systems extends drug half-life by shielding against premature degradation and improves bioavailability while also providing prolonged, sustained, or intermittent release at therapeutic doses to more effectively treat osteoporosis and associated fracture risk.

Local and targeted drug delivery for bone regeneration

While experimental bone regeneration approaches commonly employ cells, technological hurdles prevent translation of these therapies. Alternatively, emulating the spatiotemporal cascade of endogenous factors through controlled drug delivery may provide superior bone regenerative approaches. Surgically placed drug depots have clinical indications. Additionally, noninvasive systemic delivery can be used as needed for poorly healing bone injuries. However, a major hurdle for systemic delivery is poor bone biodistribution of drugs. Thus, peptides, aptamers, and phosphate-rich compounds with specificity toward proteins, cells, and molecules within the regenerative bone microenvironment may enable the design of targeted carriers with bone biodistribution greater than that achieved by drug alone. These carriers, combined with osteoregenerative drugs and/or stimuli-sensitive linkers, may enhance bone regeneration while minimizing off-target tissue effects.

On-chip synthesis of fine-tuned bone-seeking hybrid nanoparticles

Aims: Here we report a one-step approach for reproducible synthesis of finely tuned targeting multifunctional hybrid nanoparticles (HNPs). Materials & methods: A microfluidic-assisted method was employed for controlled nanoprecipitation of bisphosphonate-conjugated poly(D,L-lactide-co-glycolide) chains, while coencapsulating superparamagnetic iron oxide nanoparticles and the anticancer drug Paclitaxel. Results: Smaller and more compact HNPs with narrower size distribution and higher drug loading were obtained at microfluidic rapid mixing regimen compared with the conventional bulk method. The HNPs were shown to have a strong affinity for hydroxyapatite, as demonstrated in vitro bone-binding assay, which was further supported by molecular dynamics simulation results. In vivo proof of concept study verified the prolonged circulation of targeted microfluidic HNPs. Biodistribution as well as noninvasive bioimaging experiments showed high tumor localization and suppression of targeted HNPs to the bone metastatic tumor. Conclusion: The hybrid bone-targeting nanoparticles with adjustable characteristics can be considered as promising nanoplatforms for various theragnostic applications.