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Montana State University, Department of Mechanical and Industrial Engineering and Xtant Medical Holdings created a 3D printer capable of printing resorbable bone grafts. The grafts produced can be broken down and absorbed into the body. The personalized bone grafts are custom made and the material used for MSU can minimize the material limitations.
The ability to bioprint usable bone and joint material has seen progress from all over the world and now MSU has contributed their breakthrough research in the medical race to 3D print reconstructive parts for the human body.
This post is in the second part of the reviews that focuses on the current status of drug delivery to bone and the issues facing this field. The first part can be accessed here
Annual treatment costs for musculoskeletal diseases in the US are roughly 7.7% (~ $849 billion) of total gross domestic product. Such disorders are the main cause of physical disability in US. Almost half of all chronic conditions in people can be attributed to bone and joint disorders. In addition there is increasing ageing population and associated increases in osteoporosis and other diseases, rising incidences of degenerative intervertebral disk diseases and numbers of revision orthopedic arthroplasty surgeries, and increases in spinal fusions. All these factors contribute towards the increasing requirement of bone regeneration and reconstruction methods and products. Delivery of therapeutic grade products to bone has various challenges. Parenteral administration limits the efficient delivery of drugs to the required site of injury and local delivery methods are often expensive and invasive. The theme issue of Advance Drug Delivery reviews focuses on the current status of drug delivery to bone and the issues facing this field. Here is the second part of these reviews and research articles.
An aging population in the developing world has led to an increase in musculoskeletal diseases such as osteoporosis and bone metastases. Left untreated many bone diseases cause debilitating pain and in the case of cancer, death. Many potential drugs are effective in treating diseases but result in side effects preventing their efficacy in the clinic. Bone, however, provides a unique environment of inorganic solids, which can be exploited in order to effectively target drugs to diseased tissue. By integration of bone targeting moieties to drug-carrying water-soluble polymers, the payload to diseased area can be increased while side effects decreased. The realization of clinically relevant bone targeted polymer therapeutics depends on (1) understanding bone targeting moiety interactions, (2) development of controlled drug delivery systems, as well as (3) understanding drug interactions. The latter makes it possible to develop bone targeted synergistic drug delivery systems.
Rheumatoid arthritis (RA) is a chronic autoimmune disease that is considered to be one of the major public health problems worldwide. The development of therapies that target tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and co-stimulatory pathways that regulate the immune system have revolutionized the care of patients with RA. Despite these advances, many patients continue to experience symptomatic and functional impairment. To address this issue, more recent therapies that have been developed are designed to target intracellular signaling pathways involved in immunoregulation. Though this approach has been encouraging, there have been major challenges with respect to off-target organ side effects and systemic toxicities related to the widespread distribution of these signaling pathways in multiple cell types and tissues. These limitations have led to an increasing interest in the development of strategies for the macromolecularization of anti-rheumatic drugs, which could target them to the inflamed joints. This approach enhances the efficacy of the therapeutic agent with respect to synovial inflammation, while markedly reducing non-target organ adverse side effects. In this manuscript, we provide a comprehensive overview of the rational design and optimization of macromolecular prodrugs for treatment of RA. The superior and the sustained efficacy of the prodrug may be partially attributed to their Extravasation through Leaky Vasculature and subsequent Inflammatory cell-mediated Sequestration (ELVIS) in the arthritic joints. This biologic process provides a plausible mechanism, by which macromolecular prodrugs preferentially target arthritic joints and illustrates the potential benefits of applying this therapeutic strategy to the treatment of other inflammatory diseases.
Peptides are attractive as novel therapeutic reagents, since they are flexible in adopting and mimicking the local structural features of proteins. Versatile capabilities to perform organic synthetic manipulations are another unique feature of peptides compared to protein-based medicines, such as antibodies. On the other hand, a disadvantage of using a peptide for a therapeutic purpose is its low stability and/or high level of aggregation. During the past two decades, numerous peptides were developed for the treatment of bone diseases, and some peptides have already been used for local applications to repair bone defects in the clinic. However, very few peptides have the ability to form bone themselves. We herein summarize the effects of the therapeutic peptides on bone loss and/or local bone defects, including the results from basic studies. We also herein describe some possible methods for overcoming the obstacles associated with using therapeutic peptide candidates.
Biomaterial scaffolds have been extensively used to deliver growth factors to induce new bone formation. The pharmacokinetics of growth factor delivery has been a critical regulator of their clinical success. This review will focus on the surface interactions that control the non-covalent incorporation of growth factors into scaffolds and the mechanisms that control growth factor release from clinically relevant biomaterials. We will focus on the delivery of recombinant human bone morphogenetic protein-2 from materials currently used in the clinical practice, but also suggest how general mechanisms that control growth factor incorporation and release delineated with this growth factor could extend to other systems. A better understanding of the changing mechanisms that control growth factor release during the different stages of preclinical development could instruct the development of future scaffolds for currently untreatable injuries and diseases.
Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.
Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.
The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitroand in vivoapplications for bone tissue engineering.
Reconstruction of complex craniofacial deformities is a clinical challenge in situations of injury, congenital defects or disease. The use of cell-based therapies represents one of the most advanced methods for enhancing the regenerative response for craniofacial wound healing. Both somatic and stem cells have been adopted in the treatment of complex osseous defects and advances have been made in finding the most adequate scaffold for the delivery of cell therapies in human regenerative medicine. As an example of such approaches for clinical application for craniofacial regeneration, Ixmyelocel-T or bone repair cells are a source of bone marrow derived stem and progenitor cells. They are produced through the use of single pass perfusion bioreactors for CD90+ mesenchymal stem cells and CD14+ monocyte/macrophage progenitor cells. The application of ixmyelocel-T has shown potential in the regeneration of muscular, vascular, nervous and osseous tissue. The purpose of this manuscript is to highlight cell therapies used to repair bony and soft tissue defects in the oral and craniofacial complex. The field at this point remains at an early stage, however this review will provide insights into the progress being made using cell therapies for eventual development into clinical practice.
Bone formation and regeneration therapies continue to require optimization and improvement because many skeletal disorders remain undertreated. Clinical solutions to nonunion fractures and osteoporotic vertebral compression fractures, for example, remain suboptimal and better therapeutic approaches must be created. The widespread use of recombinant human bone morphogenetic proteins (rhBMPs) for spine fusion was recently questioned by a series of reports in a special issue of The Spine Journal, which elucidated the side effects and complications of direct rhBMP treatments. Gene therapy – both direct (in vivo) and cell-mediated (ex vivo) – has long been studied extensively to provide much needed improvements in bone regeneration. In this article, we review recent advances in gene therapy research whose aims are in vivo or ex vivo bone regeneration or formation. We examine appropriate vectors, safety issues, and rates of bone formation. The use of animal models and their relevance for translation of research results to the clinical setting are also discussed in order to provide the reader with a critical view. Finally, we elucidate the main challenges and hurdles faced by gene therapy aimed at bone regeneration as well as expected future trends in this field.
Gene delivery to bone is useful both as an experimental tool and as a potential therapeutic strategy. Among its advantages over protein delivery are the potential for directed, sustained and regulated expression of authentically processed, nascent proteins. Although no clinical trials have been initiated, there is a substantial pre-clinical literature documenting the successful transfer of genes to bone, and their intraosseous expression. Recombinant vectors derived from adenovirus, retrovirus and lentivirus, as well as non-viral vectors, have been used for this purpose. Both ex vivoand in vivostrategies, including gene-activated matrices, have been explored. Ex vivodelivery has often employed mesenchymal stem cells (MSCs), partly because of their ability to differentiate into osteoblasts. MSCs also have the potential to home to bone after systemic administration, which could serve as a useful way to deliver transgenes in a disseminated fashion for the treatment of diseases affecting the whole skeleton, such as osteoporosis orosteogenesis imperfecta. Local delivery of osteogenic transgenes, particularly those encoding bone morphogenetic proteins, has shown great promise in a number of applications where it is necessary to regenerate bone. These include healing large segmental defects in long bones and the cranium, as well as spinal fusion and treating avascular necrosis.
RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing technique developed with dramatically increasing utility for both scientific and therapeutic purposes. Short interfering RNA (siRNA) is currently exploited to regulate protein expression relevant to many therapeutic applications, and commonly used as a tool for elucidating disease-associated genes. Osteoporosis and their associated osteoporotic fragility fractures in both men and women are rapidly becoming a global healthcare crisis as average life expectancy increases worldwide. New therapeutics are needed for this increasing patient population. This review describes the diversity of molecular targets suitable for RNAi-based gene knock down in osteoclasts to control osteoclast-mediated excessive bone resorption. We identify strategies for developing targeted siRNA delivery and efficient gene silencing, and describe opportunities and challenges of introducing siRNA as a therapeutic approach to hard and connective tissue disorders.
Annual treatment costs for musculoskeletal diseases in the US are roughly 7.7% (~ $849 billion) of total gross domestic product. Such disorders are the main cause of physical disability in US. Almost half of all chronic conditions in people can be attributed to bone and joint disorders. In addition there is increasing ageing population and associated increases in osteoporosis and other diseases, rising incidences of degenerative intervertebral disk diseases and numbers of revision orthopedic arthroplasty surgeries, and increases in spinal fusions. All these factors contribute towards the increasing requirement of bone regeneration and reconstruction methods and products. Delivery of therapeutic grade products to bone has various challenges. Parenteral administration limits the efficient delivery of drugs to the required site of injury and local delivery methods are often expensive and invasive. The theme issue of Advance Drug Delivery reviews focuses on the current status of drug delivery to bone and the issues facing this field. Here is the first part of these reviews and research articles.
Demineralized bone matrix (DBM) is an osteoconductive and osteoinductive commercial biomaterial and approved medical device used in bone defects with a long track record of clinical use in diverse forms. True to its name and as an acid-extracted organic matrix from human bone sources, DBM retains much of the proteinaceous components native to bone, with small amounts of calcium-based solids, inorganic phosphates and some trace cell debris. Many of DBM’s proteinaceous components (e.g., growth factors) are known to be potent osteogenic agents. Commercially sourced as putty, paste, sheets and flexible pieces, DBM provides a degradable matrix facilitating endogenous release of these compounds to the bone wound sites where it is surgically placed to fill bone defects, inducing new bone formation and accelerating healing. Given DBM’s long clinical track record and commercial accessibility in standard forms and sources, opportunities to further develop and validate DBM as a versatile bone biomaterial in orthopedic repair and regenerative medicine contexts are attractive.
The regeneration of large bone defects caused by trauma or disease remains a significant clinical problem. Although osteoinductive growth factors such as bone morphogenetic proteins have entered clinics, transplantation of autologous bone remains the gold standard to treat bone defects. The effective treatment of bone defects by protein therapeutics in humans requires quantities that exceed the physiological doses by several orders of magnitude. This not only results in very high treatment costs but also bears considerable risks for adverse side effects. These issues have motivated the development of biomaterials technologies allowing to better control biomolecule delivery from the solid phase. Here we review recent approaches to immobilize biomolecules by affinity binding or by covalent grafting to biomaterial matrices. We focus on biomaterials concepts that are inspired by extracellular matrix (ECM) biology and in particular the dynamic interaction of growth factors with the ECM. We highlight the value of synthetic, ECM-mimicking matrices for future technologies to study bone biology and develop the next generation of ‘smart’ implants.
Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.
Silk fibroin (SF) is a biopolymer with distinguishing features from many other bio- as well as synthetic polymers. From a biomechanical and drug delivery perspective, SF combines remarkable versatility for scaffolding (solid implants, hydrogels, threads, solutions), with advanced mechanical properties and good stabilization and controlled delivery of entrapped protein and small molecule drugs, respectively. It is this combination of mechanical and pharmaceutical features which renders SF so exciting for biomedical applications. This pattern along with the versatility of this biopolymer has been translated into progress for musculoskeletal applications. We review the use and potential of silk fibroin for systemic and localized delivery of therapeutics in diseases affecting the musculoskeletal system. We also present future directions for this biopolymer as well as the necessary research and development steps for their achievement.
As a unique human bone extract approved for implant use, demineralized bone matrix (DBM) retains substantial amounts of endogenous osteoconductive and osteoinductive proteins. Commercial preparations of DBM represent a clinically accessible, familiar, widely used and degradable bone-filling device, available in composite solid, strip/piece, and semi-solid paste forms. Surgically placed and/or injected, DBM releases its constituent compounds to bone sites with some evidence for inducing new bone formation and accelerating healing. Significantly, DBM also has preclinical history as a drug carrier by direct loading and delivery of several important classes of therapeutics. Exogenous bioactive agents, including small molecule drugs, protein and peptide drugs, nucleic acid drugs and transgenes and therapeutic cells have been formulated within DBM and released to bone sites to enhance DBM’s intrinsic biological activity. Local release of these agents from DBM directly to surgical sites in bone provides improved control of dosing and targeting of both endogenous and exogenous bioactivity in the context of bone healing using a clinically familiar product. Given DBM’s long clinical track record and commercial accessibility in standard forms and sources, opportunities to formulate DBM as a versatile matrix to deliver therapeutic agents locally to bone sites in orthopedic repair and regenerative medicine contexts are attractive.
Biodegradable nanofibers are important scaffolding materials for bone regeneration. In this paper, the basic concepts and recent advances of self-assembly, electrospinning and thermally induced phase separation techniques that are widely used to generate nanofibrous scaffolds are reviewed. In addition, surface functionalization and bioactive factor delivery within these nanofibrous scaffolds to enhance bone regeneration are also discussed. Moreover, recent progresses in applying these nanofiber-based scaffolds to deliver stem cells for bone regeneration are presented. Along with the significant advances, challenges and obstacles in the field as well as the future perspective are discussed.
Bone is one of the few tissues in the human body with high endogenous healing capacity. However, failure of the healing process presents a significant clinical challenge; it is a tremendous burden for the individual and has related health and economic consequences. To overcome such healing deficits, various concepts for a local drug delivery to bone have been developed during the last decades. However, in many cases these concepts do not meet the specific requirements of either surgeons who must use these strategies or individual patients who might benefit from them. We describe currently available methods for local drug delivery and their limitations in therapy. Various solutions for drug delivery to bone focusing on clinical applications and intra-operative constraints are discussed and drug delivery by implant coating is highlighted. Finally, a new set of design and performance requirements for intra-operatively customized implant coatings for controlled drug delivery is proposed. In the future, these requirements may improve approaches for local and intra-operative treatment of patients.
Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.
Many surgical procedures require the placement of an inert or tissue-derived implant deep within the body cavity. While the majority of these implants do not become colonized by bacteria, a small percentage develops a biofilm layer that harbors invasive microorganisms. In orthopaedic surgery, unresolved periprosthetic infections can lead to implant loosening, arthrodeses, amputations and sometimes death. The focus of this review is to describe development of an implant in which an antibiotic tethered to the metal surface is used to prevent bacterial colonization and biofilm formation. Building on well-established chemical syntheses, studies show that antibiotics can be linked to titanium through a self-assembled monolayer of siloxy amines. The stable metal–antibiotic construct resists bacterial colonization and biofilm formation while remaining amenable to osteoblastic cell adhesion and maturation. In an animal model, the antibiotic modified implant resists challenges by bacteria that are commonly present in periprosthetic infections. While the long-term efficacy and stability is still to be established, ongoing studies support the view that this novel type of bioactive surface has a real potential to mitigate or prevent the devastating consequences of orthopaedic infection.
Non-invasive treatment of injuries and disorders affecting bone and connective tissue remains a significant challenge facing the medical community. A treatment route that has recently been proposed is nitric oxide (NO) therapy. Nitric oxide plays several important roles in physiology with many conditions lacking adequate levels of NO. As NO is a radical, localized delivery via NO donors is essential to promoting biological activity. Herein, we review current literature related to therapeutic NO delivery in the treatment of bone, skin and tendon repair.
A new study in JBMR highlights a novel glucocorticoid receptor modulator Compound A (CpdA) with the potential for an improved risk/benefit profile. They tested the effects of CpdA on bone in a mouse model of GC‐induced bone loss.
PRED reduced the total and trabecular bone density in the femur by 9% and 24% and in the spine by 11% and 20%, respectively, whereas CpdA did not influence these parameters. Histomorphometry confirmed these results and further showed that the mineral apposition rate was decreased by PRED whereas the number of osteoclasts was increased. Decreased bone formation was paralleled by a decline in serum P1NP, reduced skeletal expression of osteoblast markers, and increased serum levels of the osteoblast inhibitor dickkopf‐1 (DKK‐1). In addition, serum CTX‐1 and the skeletal RANKL/OPG ratio were increased by PRED. None of these effects were observed with CpdA. Consistent with the in vivo data, CpdA did not increase the RANKL/OPG ratio in MLO‐Y4 cells. Finally, CpdA also failed to transactivate DKK‐1 expression in bone tissue, BMSCs and osteocytes.
METHODS
Bone loss was induced in FVB/N mice by implanting slow‐release pellets containing either vehicle, prednisolone (PRED) (3.5 mg), or CpdA (3.5 mg). After 4 weeks, mice were killed to examine the effects on the skeleton using quantitative computed tomography, bone histomorphometry, serum markers of bone turnover, and gene expression analysis. To assess the underlying mechanisms, in vitro studies were performed with human bone marrow stromal cells (BMSCs) and murine osteocyte‐like cells (MLO‐Y4 cells).
Nitric oxide (NO) is a short-lived, highly reactive, free radical which is ubiquitously present in the human body. Physiologically, it is widely used as a second messenger both an inter-cellular and intra-cellular signaling molecule. NO is produced when L-arginine is converted to L-citruline in the presence of NO synthase (NOS) enzyme, molecular oxygen, NADPH, and other cofactors. Principally, three isoenzymes of NOS are present in the body to catalyse the production of NO in various anatomic locations and under various physiological conditions. Three distinct genes encode for the three types of NOS i.e. endothelial (eNOS or NOS-3), neuronal (nNOS or NOS-1), and inducible (iNOS or NOS-2) NOS. Neuronal NOS and endothelial NOS are calcium-dependent enzymes, whereas inducible NOS is a calcium-independent inducible enzyme, that is activated and upregulated by cytokines during inflammatory processes. The tissue-specificity indicated in the names is not absolute as these subtypes have been discovered in wider locations in the body.
In bone, NO plays a vital role in mechanosensation and mechanotransduction. Osteocytes are widely accepted as the ‘professional’ mechanosensors in bone. They sense external mechanical loads on bone and produce chemical signals such as NO and prostaglandins. NO in turn has been shown to modulate the activity of both bone forming osteoblasts and bone resorbing osteoclasts. NO is essential for load-induced bone formation in vivo. Studies using single gene deletions have shown that NO is an important cog in the wheel for bone metabolism and bone remodelling. Although eNOS isotype is widely implicated in NO production in bone, but recent studies indicate that iNOS isotype might also be involved in NO production in bone in response to mechanical loading. Targeted deletion of eNOS shows mild osteoporotic phenotype in mice and iNOS pathway has been implicated in L-1-induced osteoclastic bone resorption. Hence both NOS isoforms have important role in bone remodelling.
Challenges to study NO: NO is a small, short-lived signalling molecule. It has a half life of less than 5 sec, which makes its online detection very difficult. Predominantly, the more stable metabolites of NO such as nitrites and nitrates are detected by using techniques such as Greiss reagent. They are however lited by the sensitivity levels and their inability to detect actual levels of NO. However, fluorescent dyes such as DAR 4M and DAF dyes are potent tools to detect online NO production at single cell level. These dyes are membrane-permeable, hence are taken up readily by the cells. Once inside the cell they are metabolised and rendered membrane-impermeable. When cell produces NO these dyes trap NO and get converted into fluorescent product, which can then be detected by using fluorescence microscopy. Moreover, by using these techniques, quantitative analyses of NO production (not only its metabolites) is feasible in live, single cells.
Molecular methods to investigate mRNA or protein levels of NOS enzymes are also used to corroborate with the changes in NO production levels.
A new study by Stern et al reports a technique where in the authors have isolated primary osteocytes from mature and aged mice.
Osteocytes are deeply embedded in the mineralised matrix of bone. They form the majority cell types of bone and play vital function in maintenance of bone homeostasis. However their study has been limited by their location in the bone and that they are terminally differentiated cells.
“Osteocytes are the most abundant of the three bone cell types; however, the least is known about them. While their location deep within the bone matrix makes them ideally situated to sense bone strain, it also makes their observation and study in vivo difficult. Additionally, primary osteocytes, particularly those within the long bones of skeletally mature animals, have proven difficult to obtain and study ex vivo. Furthermore, once primary osteocytes are obtained, their study is often limited by their inability to proliferate as they are considered terminally differentiated cells. ”
As a result majority of the studies on osteocytes in vitro have used either cell lines and/or primary cells from new-born animals such as chicken, rat and mouse.
“The MLO-Y4 cell line is well-characterized and represents the phenotype of early osteocytes ”
“Although the MLO-Y4 cell line is a very powerful tool for the study of osteocytes in vitro, there are known differences between primary osteocytes and the immortalized MLO-Y4 cell line. For example, MLO-Y4 cells express low to undetectable levels of Dentin matrix protein 1 (Dmp1) and Sclerostin (Sost), while osteocytes are known to express these genes in vivo .”
“Primary osteocytes have most commonly been isolated from 16- or 18-day-old chick calvaria or from newborn through 4-day-old rat calvaria, 12-day-old mouse calvaria, and 3- to 4-week-old mouse calvaria and long bones.”
“Studies utilizing these primary osteocytes can provide insight to the behavior of osteocytes during development but do not aid in the study of osteocytes from skeletally mature animals or enable the comparison between osteocytes isolated from skeletally mature but relatively young mice (4- to 6-month) and aged mice (>22-month-old).”
To circumvent the above mentioned limitations the authors utilised multi-step digestion technique. They subjected mouse long bone pieces (from 4-month old mouse and 22-month old mouse) to collagenase and EDTA alternatively for 25 minutes and collected the aspirate after each step for plating and culture of cells. (as described in the table, which has been taken from the study).
Table 1. Osteocyte isolation from murine long bone (courtesy: Stern et al)
They collected cells from nine such alternate steps in total and also the left over bone. These cells were then cultured for 7 days. Following parameters were tested to characterise the osteocytes.
E11/GP38 staining – early osteocyte specific protein
Alkaline Phosphatase (ALP) staining – indicator of osteoblastic state
COL 1 – major component of bone and produced by osteoblasts
Gene expression of E11, SOST, MEPE, Dmp1 – markers of osteogencity in different stages of osteogenesis
“Osteoid osteocytes are known to express E11, Phex, and Mepe, while mineralizing osteocytes express Dmp1, and mature osteocytes encased in a mineralized matrix express Sost and Fgf23”
The authors were able to demonstrate that the isolated cells indeed expressed osteogenic markers. It was observed that cells isolated from later digestion steps (6-9) were more osteocyte like. This was also the case with the cells isolated from the left over bone pieces.
“In this study, we were able to success fully isolate primary cells displaying several characteristics of osteocytes from the long bones of skeletally mature 4-month-old and 22-month-old mice through a process of sequential digestions and the use of a tissue homogenizer. From both the 4-month-old and 22-month-old mice, approximately 250,000 cells per osteocyte-enriched digestion (digestions 7–9) were obtained. These cells expressed E11/GP38 protein, and they lacked ALP and COL1A1 expression found in osteoblasts. Furthermore, several genes known to be expressed in osteocytes were also expressed in the cells obtained using our methodology. These include E11/gp38, Sost, Cox2, Mepe, Phex, and Dmp1.”
Limitations:
As the authors pointed out, their study characterised the cells ensemble from separate digestion steps. This could lead to having a mixed population from each step.
The authors did not mention about the proliferation (or the absence of it) of the isolated cells. Since osteocytes are terminally differentiated cells, theoretically they should not proliferate. In addition when such primary cells are co-cultured with dividing cells, such as osteoblasts and fibroblasts in this case, the dividing population tends to over grow in culture leaving behind very few primary osteocytes. A detailed characterisation of these cells at different stages of digestion along with progressive time points will be very helpful.
Possibilities:
As authors claim, in future, this technique can help scientists to answer tricky questions about osteocytes such as comparing osteocytes from animals grouped on the basis of age, disease, bone characteristics, and therapies.
2012pharmaceutical
Amandeep Kaur
Aashir Awan, Phd
Abhisar Anand
Adina Hazan
Alan F. Kaul, PharmD., MS, MBA, FCCP
alexcrystal6
anamikasarkar
apreconasia
aviralvatsa
David Orchard-Webb, PhD
danutdaagmailcom
Demet Sag, Ph.D., CRA, GCP
Dror Nir
dsmolyar
Ethan Coomber
evelinacohn
FrasonKalapurackal
Gail S Thornton
Irina Robu
jayzmit48
jdpmd
jshertok
kellyperlman
Ed Kislauskis
larryhbern
Madison Davis
marzankhan
megbaker58
ofermar2020
Dr. Pati
pkandala
ritusaxena
Rick Mandahl
sjwilliamspa
Srinivas Sriram
stuartlpbi
Dr. Sudipta Saha
tildabarliya
zraviv06
zs22