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Posts Tagged ‘mesenchymal stem cells (MSCs)’


Stem Cell Therapy for Coronary Artery Disease (CAD)

Author and Curator: Larry H. Bernstein, MD, FCAP

and

Curator: Aviva Lev-Ari, PhD, RN

 

There is great interest and future promise for stem cell therapy in ischemic heart disease.  This is another report for the active work in cardiology with stem cell therapy by MA Gaballa and associates at University of Arizona.

Stem Cell Therapy for Coronary Heart Disease

Julia N. E. Sunkomat and Mohamed A. Gaballa

The University ofArizona Sarver Heart Center, Section of Cardiology, Tucson, Ar
Cardiovascular Drug Reviews 2003: 21(4): 327–342

Keywords: Angiogenesis — Cardiac therapy — Coronary heart disease — Heart failure — Myoblasts — Myocardial ischemia — Myocardial regenera­tion — Stem cells

ABSTRACT

Coronary artery disease (CAD) remains the leading cause of death in the Western world. The high impact of its main sequelae, acute myocardial infarction and congestive heart failure (CHF), on the quality of life of patients and the cost of health care drives the search for new therapies. The recent finding that

stem cells contribute to neovascularization and possibly improve cardiac function after myocardial infarction makes stem cell therapy the most highly active research area in cardiology. Although the concept of stem cell therapy may revolutionize heart failure treatment, several obstacles need to be ad­dressed. To name a few:

  1.  Which patient population should be considered for stem cell therapy?
  2.  What type of stem cell should be used?
  3.  What is the best route for cell de­livery?
  4.  What is the optimum number of cells that should be used to achieve functional effects?
  5.  Is stem cell therapy safer and more effective than conventional therapies?

The published studies vary significantly in design, making it difficult to draw conclusions on the efficacy of this treatment. For example, different models of

  1. ischemia,
  2. species of donors and recipients,
  3. techniques of cell delivery,
  4. cell types,
  5. cell numbers and
  6. timing of the experiments

have been used. However, these studies highlight the landmark concept that stem cell therapy may play a major role in treating cardiovascular diseases in the near future. It should be noted that stem cell therapy is not limited to the treatment of ischemic cardiac disease.

  • Non-ischemic cardiomyopathy,
  • peripheral vascular disease, and
  • aging may be treated by stem cells.

Stem cells could be used as vehicle for gene therapy and eliminate the use of viral vectors. Finally, stem cell therapy may be combined with phar­macological, surgical, and interventional therapy to improve outcome. Here we attempt a systematic overview of the science of stem cells and their effects when transplanted into ischemic myocardium.

INTRODUCTION

Background

Congestive heart failure (CHF) is the leading discharge diagnosis in patients over the age of 65 with estimates of $24 billion spent on health care in the US (1,11). The number one cause of CHF is coronary artery diseases (CAD). Coronary care units, reperfusion therapy (lytic and percutaneous coronary intervention) and medical therapy with anti-pla­telet agents, statins, ACE-inhibitors and â-adrenoceptor antagonists all significantly reduce morbidity and mortality of CAD and CHF (9), but it is very difficult to regenerate new viable myocardium and new blood vessels.

Identification of circulating endothelial progenitor cells in peripheral blood that incor­porated into foci of neovascularization in hindlimb ischemia (4) and the successful engraftment of embryonic stem cells into myocardium of adult dystrophic mice (31) intro­duced a new therapeutic strategy to the field of cardiovascular diseases: tissue regeneration. This approach is supported by the discovery of primitive cells of extracardiac origin in cardiac tissues after sex-mismatched transplants suggesting that an endogenous repair mechanism may exist in the heart (35,45,54). The number of recruited cells varied significantly from 0 (19) to 18% (54), but the natural course of ischemic cardiomyopathy implies that cell recruitment for tissue repair in most cases is insufficient to prevent heart failure. Therefore, investigational efforts are geared towards

  • augmenting the number of multipotent stem cells and endothelial and myocardial progenitor cells at the site of ischemia to induce clinically significant angiogenesis and potentially myogenesis.

Stem and Progenitor Cells

Stem cells are defined by their ability to give rise to identical stem cells and progenitor cells that continue to differentiate into a specific tissue cell phenotype (23,33). The po­tential of mammalian stem cells varies with stage of development and age (Table 1).

In mammals, the fertilized oocyte and blastomere cells of embryos of the two to eight cell stage can generate a complete organism when implanted into the uterus; they are called totipotent stem cells. After the blastocyst stage, embryonic stem cells retain the ability to differentiate into all cell types, but

  • cannot generate a complete organism and thus are denoted pluripotent stem cells.

Other examples of pluripotent stem cells are embryo­nic germ cells that are derived from the gonadal ridge of aborted embryos and embryonic carcinoma cells that are found in gonadal tumors (teratocarcinomas) (23,33). Both these cell types can also differentiate into cells of all three germ layers, but are not as well inves­tigated as embryonic stem cells.

It is well established that embryonic stem cells can differentiate into cardiomyocytes (7,10,13,14,31,37,76), endothelial cells (55), and smooth muscle cells (5,22,78) in vitro, but it is unclear whether

  • pure populations of embryonic stem cell-derived cardiomyocytes can integrate and function appropriately in the heart after transplantation.
  • one study reported arrhythmogenic potential of embryonic stem cell-derived cardiomyocytes in vitro (80).

Adult somatic stem cells are cells that have already committed to one of the three germ layers: endoderm, ectoderm, or mesoderm (76). While embryonic stem cells are defined by their origin (the inner cell mass of the blastocyst), the origin of adult stem cells in mature tissues is still unknown. The primary role of adult stem cells in a living organism is thought to be maintaining and repairing the tissue in which they reside. They are the source of more identical stem cells and cells with a progressively more distinct phenotype of specialized tissue cells (progenitor and precursor cells) (Fig. 1). Until recently adult stem cells were thought to be lineage-specific, meaning that they can only differentiate into the cell-type of their original tissue. This concept has now been challenged with the discovery of multipotent stem and progenitor cells (26, 50, 51).

The presence of multipotent stem and progenitor cells in adult mammals has vast im­plications on the availability of stem cells to research and clinical medicine. Recent publi­cations, however, have questioned whether the adaptation of a phenotype in those dogma-challenging studies is really a result of trans-differentiation or rather a result of cell and nuclear fusion (60,68,75,79). Spontaneous fusion between mammalian cells was first re­ported in 1961 (8), but how frequently fusion occurs and whether it occurs in vivo is not clear.

The bone marrow is a known source of stem cells. Hematopoietic stem cells are fre­quently used in the field of hematology. Surface receptors are used to differentiate hematopoietic stem and progenitor cells from mature cells. For example, virtually all

  • hematopoietic stem and progenitor cells express the CD34+ glycoprotein antigen on their cell membrane (73),

though a small proportion of primitive cells have been shown to be CD34 negative (58).

The function of the CD34+ receptor is not yet fully understood. It has been suggested that it may act as a regulator of hematopoietic cell adhesion in the bone marrow microenvironment. It also appears to be involved in the maintenance of the hematopoietic stem/progenitor cell phenotype and function (16,21). The frequency of immature CD34+ cells in peripheral circulation diminishes with age.

  • It is the highest (up to 11%) in utero (69) and decreases to 1% of nucleated cells in term cord blood (63).
  • This equals the per­centage of CD34+ cells in adult bone marrow.
  • The number of circulating stem cells in adult peripheral blood is even lower at 0.1% of nucleated cells.

Since hematopoietic stem cells have been identified as endothelial progenitor cells (29,30,32) their low density in adult bone marrow and blood could explain the inadequacy of endogenous recruitment of cells to injured organs such as an ischemic heart. The bone marrow is also home to another stem cell population the so-called mesenchymal stem cells. These may constitute a subset of the bone marrow stromal cells (2,43). Bone marrow stromal cells are a mixed cell popu­lation that generates

  1. bone,
  2. cartilage,
  3. fat,
  4. connective tissue, and
  5. reticular network that sup­ports cell formation (23).

Mesenchymal stem cells have been described as multipotent (51,52) and as a source of myocardial progenitor cells (41,59). They are, however, much less defined than the hematopoietic stem cells and a characteristic antigen constellation has not yet been identified (44).

Another example of an adult tissue containing stem cells is the skeletal muscle. The cells responsible for renewal and growth of the skeletal muscle are called satellite cells or myoblasts and are located between the sarcolemma and the basal lamina of the muscle fiber (5). Since skeletal muscle and cardiac muscle share similar characteristics such as they both are striated muscle cells, satellite cells are considered good candidates for the repair of damaged myocardium and have been extensively studied (20,25,38–40,48,56, 64–67). Myoblasts are particularly attractive, because they can be autotransplanted, so that issues of donor availability, ethics, tumorigenesis and immunological compatibility can be avoided. They also have been shown to have a high growth potential in vitro and a strong resistance to ischemia in vivo (20). On the down side

  • they may have more arrhythmogenic potential when transplanted into myocardium than bone marrow or peripheral blood de­rived stem cells and progenitor cells (40).

Isolation of Cells Prior to Transplantation

Hematopoietic stem and progenitor cells are commonly identified by the expression of a profile of surface receptors (cell antigens). For example, human hematopoietic stem cells are defined as CD34+/CD59+/Thy-1+/CD38low//c-kit/low/lin, while mouse hema-topoietic stem cells are defined as CD34low//Sca-1+/Thy-1+/low/CD38+/c-kit+/lin (23). Additional cell surface receptors have been identified as markers for subgroups of hema-topoietic stem cells with the ability to differentiate into non-hematopoetic tissues, such as endothelial cells (57,78). These can be specifically targeted by isolation methods that use the receptors for cell selection (positive selection with antibody coated magnetic beads or fluorescence-activated cell sorting, FACS). Other stem cell populations are identified by their behavior in cell culture (mesenchymal stem cells) or dye exclusion (SP cells). Finally, embryonic stem cells are isolated from the inner cell mass of the blastocyst and skeletal myoblasts are mechanically and enzymatically dissociated from an easily acces­sible skeletal muscle and expanded in cell culture.

FIG. 1. Maturation process of adult stem cells: with acquisition of a certain phenotype the cell gradually loses its self-renewal capability.  (unable to transfer)

METHODICAL APPROACHES 

j.1527-3466.2003.tb00125.x  fig stem cell

FIG. 2. Intramyocardial injection:

the cells are injected directly into the myocardium through the epicardium. Usually a thoracotomy or sternotomy is required. Transendocardial injection: access can be gained from the ar­terial vasculature. Cells are injected through the endocardium into the myocardium, ideally after identifying the ischemic myocardium by perfusion studies and/or electromechanical mapping. Intracoronary injection: the coronary artery is accessed from the arterial vasculature. Stem cells are injected into the lumen of the coronary artery. Proximal washout is prevented by inflation of a balloon. Cells are then distributed through the capillary system. They eventually cross the endothelium and migrate towards ischemic areas.

The intracoronary delivery of stem cells (Fig. 2) and distribution through the coronary system has also been explored (6,62,74). This approach was pioneered by Robinson et al. (56), who demonstrated successful engraftment within the coronary distribution after intracoronary delivery of genetically labeled skeletal myoblasts. The risk of intracoronary injection is comparable to that of a coronary angiogram and percutaneous transluminal coronary angioplasty (PTCA) (62), which are safe and clinically well established.

RESULTS IN ANIMAL STUDIES AND HUMAN TRIALS

Dif­ferentiation into cardiomyocytes was observed after transplantation of embryonic stem cells, mesenchymal stem cells, lin/c-kit+ and SP cells. The induction of angiogenesis was observed after transplantation of embryonic stem cells, mesenchymal stem cells, bone marrow-derived mononuclear cells, circulating endothelial progenitor cells, SP cells and lin/c-kit+ cells.

The use of embryonic stem cells in ischemia was examined in two studies (42,43). These studies demonstrated that mice embryonic stem cells transplanted into rat myo­cardium exhibited cardiomyocyte phenotype at 6 weeks after transplantation. In addition, generation of myocardium and angiogenesis were observed at 32 weeks after allogenic transplantation in rats. In these two studies no arrhythmias or cardiac tumors were reported.

Several studies have shown retardation of LV remodeling and improvement of cardiac function after administration of bone marrow-derived mononuclear cells. For example, decreases in infarct size, and increase in ejection fraction (EF), and left ventricular (LV) time rate change of pressure (dP/dtmax) were observed after direct injection of bone marrow-derived mononuclear cells 60 min after ischemia in swine (28). In humans, intra-coronary delivery and transendocardial injection of mononuclear cells leads to a decrease in LV dimensions and improvement of cardiac function and perfusion (49,62). A decrease in end systolic volume (ESV) and an increase in EF as well as regional wall motion were observed following intracoronary administration of CD34+/CD45+ human circulating en­dothelial cells (6). Injection of circulating human CD34+/CD117+ cells into infarcted rat myocardium induced neoangiogenesis and improved cardiac function (32). This study suggests that the improvement in LV remodeling after infarction appears to be in part me­diated by a decrease in apoptosis within the noninfarcted myocardium. Two other studies reported increased fractional shortening, improved regional wall motion and decreased left ventricular dimensions after transplantation of human CD34+ cells (29,30). Improved global left ventricular function and infarct perfusion was demonstrated after intramyo-cardial injection of autologous endothelial progenitor cells in humans (61).

DISCUSSION AND OUTLOOK

The idea of replacing damaged myocardium by healthy cardiac tissue is exciting and has received much attention in the medical field and the media. Therefore, it is important for the scientist to know what is established and what is based on premature conclusions. Currently, there are data from animal studies and human trials (Table 2). However, some of these data are not very concrete. For example,

  • many animal studies do not report the level of achieved neoangiogenesis and/or regeneration of myocardium.
  • In studies where the numbers of neovessels and new cardiomyocytes are specified, these numbers are often very low.

While these experiments confirm the concept that bone marrow and peripheral blood-derived stem and progenitor cells can differentiate into cardiomyocytes and endo­thelial cells when transplanted into ischemic myocardium, they also raise the question how effective this treatment is.

The results of the clinical trials that have been conducted are encouraging, but they need to be interpreted with caution. The common endpoints of these studies include left ventricular dimensions, perfusion, wall motion and hemodynamic function. While all studies report improvement after mononuclear cell, myoblast or endothelial progenitor cell transplantation, it is difficult to separate the effects of stem cell transplantation from the effects of the state-of-the art medical care that the patients typically received.

CONCLUSION

While the majority of studies demonstrate neoangiogenesis and some studies also show regeneration of myocardium after stem/progenitor cell transplantation, it remains unclear whether the currently achieved level of tissue regeneration is sufficient to affect clinical outcome. Long-term follow-up of patients that received stem/progenitor cells in clinical trials will provide important information on the potential risks of neoplasm and arrhythmias and, therefore, safety of this treatment. Ultimately, postmortem histological confirmation of scar tissue repair by transplanted cells and randomized placebo control trials with long-term follow-up are required to prove efficacy of this treatment.

REFERENCES (10)

1. American Heart Association Disease and Stroke Statistics-2003 Update, Dallas TX, American Heart Associ­ation; 2002 http://http://www.americanheart.org/downloadable/heart/10461207852142003HDSStatsBook.pdf

2. Arai A, Sheikh F, Agyeman K, et al. Lack of benefit from cytokine mobilized stem cell therapy for acute myocardial infarction in nonhuman primates. J Am Coll Cardiol 2003;41(Suppl 6A):371.

3. Asahara T, Masuda H, Takahashi T, et al. Bone marrow origin of endothelial progenitor cells responsible for postnatal vasculogenesis in physiological and pathological neovascularization. Circ Res 1999;85:221–228.

4. Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997;275:964–967.

5. Asakura A, Seale P, Girgis-Gabardo A, Rudnicki M. Myogenic specification of side population cells in skeletal muscle. J Cell Biol 2002;159(1):123–134.

6. Assmus B, Schaechinger V, Teupe C, et al. Transplantation of progenitor cells and regeneration en­hancement in acute myocardial infarction (TOPCARE-AMI). Circulation 2002;106:r53–r61.

7. Bader A, Al-Dubai H, Weitzer G. Leukemia inhibitory factor modulates cardiogenesis in embryoid bodies in opposite fashions. Circ Res 2000;86(7):787–794.

8. Barski G, Sorieul S, Cornefert F. “Hybrid” type cells in combined cultures of two different mammalian cell strains. J Natl Cancer Inst 1961;26:1269–1291.

9. Boersma E, Mercado N, Poldermans D, Gardien M, Vos J, Simoons M. Acute myocardial infarction. Lancet 2003;361:847–58.

  1. 10.          Boheler K, Czyz J, Tweedie D, Yang H, Anisimov S, Wobus A. Differentiation of pluripotent embryonic stem cells into cardiomyocytes. Circ Res 2002;91:189–201.
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Author: Tilda Barliya PhD

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 (I). The challenges of drug delivery for bone regeneration and reconstruction has been previously reported here by Dr. Aviral Vatsa (I-IV), herein, we will discussed the different needs for bone regeneration and the potential use if nanotechnology.

Bone regeneration is a complex, well-orchestrated physiological process of bone formation, which can be seen during normal fracture healing, and is involved in continuous remodelling throughout adult life. However, there are complex clinical conditions in which bone regeneration is required in large quantity, such as for skeletal reconstruction of large bone defects created by trauma, infection, tumour resection and skeletal abnormalities, or cases in which the regenerative process is compromised, including avascular necrosis, atrophic non-unions and osteoporosis (1,2).

Regenerative medicine offers a way to improve  ‘local’ strategies in terms of tissue engineering and gene therapy, or even ‘systemic’ enhancement of bone repair. To make regenerative medicine successful, three elements are required: stem cells, scaffolds, and growth factors (3).

Bones

Bone is a tough supporting tissue and functions in both movement and the maintenance of postural stability by working cooperatively with muscles as well as play a role in calcium metabolism. Despite its hard structure it exist in a dynamic turnover known as bone remodeling. There are two types of bone structures that naturally remodel during the a year:

  • cortical bone (~3%/year)
  • cancellous bone (~30%/year)
148261.fig.001

Jimi J et al. The schematic outlines of the bone remodeling cycle and the balance of bone resorption and bone formation

At the remodeling sites, osteoblasts produce new bone, while osteoclasts resorb existing bone. Each cell type seems to be regulated by a variety of hormones and by local factors. If the balance between bone formation and resorption is lost by uncontrolled production of these regulators, the bone structure will be damaged, and the subject would be susceptible to osteoporosis and osteopetrosis (2).

Current Clinical approaches:

Standard approaches widely used in clinical practice to stimulate or augment bone regeneration include distraction osteogenesis and bone transport.

As well as the use of a number of different bone-grafting methods, such as (1):

  • Autologous bone grafts – considered as the ‘gold standard‘ bone-grafting material, as it combines all properties required in a bone-graft material: osteoinduction (bone morphogenetic proteins (BMPs) and other growth factors), osteogenesis (osteoprogenitor cells) and osteoconduction (scaffold)
  • Allografts – obtained from human cadavers or living donors, which bypasses the problems associated with harvesting and quantity of graft material. Allogeneic bone is available in many preparations, including demineralised bone matrix (DBM), morcellised and cancellous chips, corticocancellous and cortical grafts, and osteochondral and whole-bone segments, depending on the recipient site requirements.
  • Bone-graft substitutes or growth factors – developed as alternatives to autologous or allogeneic bone grafts. They consist of scaffolds made of synthetic or natural biomaterials that promote the migration, proliferation and differentiation of bone cells for bone regeneration. Commonly performed surgical procedure to augment bone regeneration in a variety of orthopaedic and maxillofacial procedures.

The Masquelet technique is a two-step procedure for bone regeneration and reconstruction of long-bone defects. It is based on the concept of a “biological” membrane, which is induced after application of a cement spacer at the first stage and acts as a ‘chamber’ for the insertion of non-vascularised autograft at the second stage (2, 4).

There are  non-invasive methods of biophysical stimulation, such as low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic fields (PEMF) (1).

Limitations of Current approaches: Most of the current strategies for bone regeneration exhibit relatively satisfactory results. However, there are associated drawbacks and limitations to their use and availability, and even controversial reports about their efficacy and cost-effectiveness.

New Approaches:

New methods for studying this process, such as quantitative three-dimensional microcomputed tomography analyses, finite element modelling, and nanotechnology have been developed to further evaluate the mechanical properties of bone regenerate at the microscopic level. Here are some examples of the latest developments as reviewed by Dimitriou R at el (1).

BMPs and growth factors – They induce the mitogenesis of mesenchymal stem cells (MSCs) and other osteoprogenitors, and their differentiation towards osteoblasts. BMP-2 and BMP-7 have been licensed for clinical use since 2002 and 2001 respectively (5). These two molecules have been used in a variety of clinical conditions including non-union, open fractures, joint fusions, aseptic bone necrosis and critical bone defects. Platelet-derived growth factor (PDFG), transforming growth factor-β (TGF-b), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) have been also implicated in bone regeneration, with different functions in terms of cell proliferation, chemotaxis and angiogenesis. One current approach to enhance bone regeneration and soft-tissue healing by is local application of growth factors is the use of platelet-rich plasma alongside the autograph. BMPs are also being used in bone-tissue engineering.

MSCs – The current approach of delivering osteogenic cells directly to the regeneration site includes use of bone-marrow aspirate from the iliac crest, which also contains growth factors. It is a minimally invasive procedure to enhance bone repair, and produces satisfactory results (1). Overall, however, there are significant ongoing issues with quality control with respect to delivering the requisite number of MSCs/osteoprogenitors to effect adequate repair responses. Issues of quantity and alternative sources of MSCs are being extensively investigated. Novel approaches in terms of cell harvesting, in vitro expansion and subsequent implantation are promising.

Scaffolds and Bone substitutes – synthetic bone substitutes and biomaterials are already widely used in clinical practice for osteoconduction. DBM (Demineralized bone matrix)  and collagen are biomaterials, used mainly as bone-graft extenders, as they provide minimal structural support. A large number of synthetic bone substitutes are currently available, such as HA, β-TCP and calcium-phosphate cements, and glass ceramics. These are being used as adjuncts or alternatives to autologous bone grafts. Especially for regeneration of large bone defects, where the requirements for grafting material are substantial, these synthetics can be used in combination with autologous bone graft, growth factors or cells (6). Improved biodegradable and bioactive three-dimensional porous scaffolds are being investigated, as well as novel approaches using nanotechnology, such as magnetic biohybrid porous scaffolds acting as a crosslinking agent for collagen for bone regeneration guided by an external magnetic field or injectable scaffolds for easier application.

Tissue Engineering – The tissue-engineering approach is a promising strategy added in the field of bone regenerative medicine, which aims to generate new, cell-driven, functional tissues, rather than just to implant non-living scaffolds. In essence, bone-tissue engineering combines progenitor cells, such as MSCs (native or expanded) or mature cells (for osteogenesis) seeded in biocompatible scaffolds and ideally in three-dimensional tissue-like structures (for osteoconduction and vascular ingrowth), with appropriate growth factors (for osteoinduction), in order to generate and maintain bone (7). Bone-tissue engineering is in its early stages, and there are many issues of efficacy, safety and cost to be addressed before general clinical application can be achieved.

Gene Therapy – This involves the transfer of genetic material into the genome of the target cell, allowing expression of bioactive factors from the cells themselves for a prolonged time. Gene transfer can be performed using a viral (transfection) or a non-viral (transduction) vector, and by either an in vivo or ex vivo gene-transfer strategy. There are issues of cost, efficacy and biological safety that need to be answered.

Nanotechnology and Bone Regeneration

Nanotechnology has been greatly utilized for bone tissue engineering strategies. It has been employed to overcome some of the current limitations associated with bone regeneration methods including insufficient mechanical strength of scaffold materials, ineffective cell growth and osteogenic differentiation at the defect site, as well as unstable and insufficient production of growth factors to stimulate bone cell growth (8,9).

To mimic the natural bone nanocomposite architecture, novel biomaterials and nanofabrication techniques are currently being employed and many different nanostructures have already been designed and tested. Electrospinning has been extensively applied to create bone nanofiber scaffolds and biomaterials typically used for this purpose, including synthetic organic polymers such as PCL, PLGA, PLLA, Chitosan, and silk fibroin.

Among the materials used for bone-reconstruction, PLLA is a biocompatible polymer with the advantage of being highly. biodegradable. For this reason, PLLA have received the approval of the Food and Drug Administration (FDA) to be use in bone reconstructive surgery (10).

PLLA nanofibers are often functionalized to improve their biological performance with peptides such as RGD (Arg-Gly-Asp); with osteogenic molecules such as hydroxyapatite; or with proteins such as collagen and the growth factor bone morphogenic protein 2 (BMP-2). It was found that direct incorporation of BMP-2 into PLLA nanofibers enhances the osteoinductivity of the scaffolds.

Current orthopedic implants fail in an appropriate osteo-integration limiting implant lifespan. Titanium, as a biocompatible material, has been used to enhance implant incorporation in bone for dental, craniofacial, and orthopedic applications. Studies have demonstrated that nanoporous titanium dioxide (TiO2) surface modification alters nanoscale topography improving soft tissue attachment on titanium implants surface (11). For example, the uses of nanoporous TiO2 surface-modified implants, in a human dental clinical study, showed that TiO2 thin film increased adherence in early healing of the human oral mucosa and reduced marginal bone resorption (11).

Another example are rosette nanotubes. Bioactive helical rosette nanotubes are self-assembled nanomaterials, formed in water from synthetic DNA base analogs that mimic the helical nanostructure of collagen in bone. This technology has been used to create a biomimetic nanocomposite combined with nanocrystalline hydroxyapatite, and biocompatible hydrogels which increased osteoblast adhesion.

Carbon nanotubes (CNTs) are other suitable scaffold materials that have proved to support osteoblast proliferation. CNTs possess exceptional mechanical, thermal, and electrical properties, facilitating their use as reinforcements or, in combination with other biomaterials, to improve and to support bone growth.

Nanotechnology and clinical trials

Clinical therapies implying the use of nanotechnology in bone regeneration are still in the beginning stages.

BDSint –  Recently, the bone healing ability of a nanocomposite (DBSint®), approved for clinical use, constituted by biomimetic nanostructured Mg-hydroxyapatite and human demineralized bone matrix has been investigated.  The clinical-radiographic and histomorphometry study in subjects undergoing high tibial osteotomy, demonstrated that these nanocomposites are safe and effective. Yet the long term outcome is still to be defined (8, 12).

BioOsss and BioGides –  Schwarz et al. undertook a four-year study of patients treated of moderate intrabony peri-implantitis defects using either a nanocrystalline hydroxyapatite or a natural bone mineral (BioOsss spongiosa granules) in combination with a collagen membrane (BioGides) and found bone reconstruction (8, 13).

Here are some of the ongoing clinical trials for use of nanotechnology in bone regeneration (Perán M et al (8)):

NCT00729716 – Comparison of BioCart™II With Microfracture for Treatment of Cartilage Defects of the Femoral Condyle BioCart™II scaffold Cartilage ————Phase 2.

NCT01183637  – Evaluation of “Kensey Nash Corp” an Acellular Osteochondral Graft for Cartilage Lesions Pilot Trial (EAGLE Pilot) bioresorbable scaffold Bone/ Cartilage————-Phase 2

NCT01218945 –  Development of Bone Grafts Using Adipose-Derived Stem Cells and Different Scaffolds Bone scaffold Bone——– recruiting participants

NCT01435434 – Mononucleotide Autologous Stem Cells and Demineralized Bone Matrix in the Treatment of Non-Union/Delayed Fractures Ignite®ICS injectable scaffold Bone——————Not yet recruiting

Summary:

The advantages of nanomaterials as therapeutic and diagnostic tools are vast, due to design flexibility, small sizes, large surface-to-volume ratio, and ease of surface modification.  The potential of these bio-devices has shown promising results in vitro, and some of them have also been successfully tested in vivo with animal models. Nevertheless, the gap between laboratory and medical application of these nanotechnological advances is still wide (8).

Although some successful devises have already being tested in clinical trials and the data produced by these studies is highly encouraging, the safety of nanomedicine is not yet fully defined and more clinical studies still need to be conducted to translate nanotechnological devices to the clinic.

Reference:

1. Dimitriou R, Jones E, McGonagle D and Giannoudis P.V. Bone regeneration: current concepts and future directions. BMC Medicine 2011, 9:66. http://www.biomedcentral.com/1741-7015/9/66

2. Jimi E.,  Hirata S., Osawa K.,  Terashita M., Kitamura C.,  and Fukushima H. The Current and Future Therapies of Bone Regeneration to Repair Bone Defects. International Journal of Dentistry Volume 2012 (2012), Article ID 148261. doi:10.1155/2012/148261. http://www.hindawi.com/journals/ijd/2012/148261/

3. G. C. Gurtner, M. J. Callaghan, and M. T. Longaker, “Progress and potential for regenerative medicine,” Annual Review of Medicine, vol. 58, pp. 299–312, 2007. http://www.ncbi.nlm.nih.gov/pubmed/17076602

4. Masquelet AC, Begue T: The concept of induced membrane for reconstruction of long bone defects. Orthop Clin North Am 2010, 41(1):27-37. http://www.ncbi.nlm.nih.gov/pubmed/19931050

5. Food and Drug Administration: Medical devices. [http:/ / www.fda.gov/ MedicalDevices/ ProductsandMedicalProcedures/ DeviceApprovalsandClearances/ Recently-ApprovedDevices/ default.htm

6. Giannoudis PV, Dinopoulos H, Tsiridis E: Bone substitutes: an updateInjury 2005, 36(Suppl 3):S20-27. http://www.ncbi.nlm.nih.gov/pubmed/16188545

7. Jones E, English A, Churchman SM, Kouroupis D, Boxall SA, Kinsey S, Giannoudis PG, Emery P, McGonagle D: Large-scale extraction and characterization of CD271+ multipotential stromal cells from trabecular bone in health and osteoarthritis: implications for bone regeneration strategies based on uncultured or minimally cultured multipotential stromal cells. Arthritis Rheum 2010, 62(7):1944-1954.  http://onlinelibrary.wiley.com/doi/10.1002/art.27451/abstract;jsessionid=4573A69E4561194C83A97EC302CD20CB.d04t02

8. Perán M., García MA., Lopez-Ruiz E., Jiménez G and Marchal JA. How Can Nanotechnology Help to Repair the Body?Advances in Cardiac, Skin, Bone, Cartilage and Nerve Tissue Regeneration. Materials 2013, 6, 1333-1359; doi:10.3390/ma6041333 http://www.mdpi.com/1996-1944/6/4/1333

9. Kim K and Fisher JP. Nanoparticle technology in bone tissue engineering. J Drug Target. 2007 May;15(4):241-52.  http://www.ncbi.nlm.nih.gov/pubmed/17487693

10.  Schofer, M.D.; Roessler, P.P.; Schaefer, J.; Theisen, C.; Schlimme, S.; Heverhagen, J.T.; Voelker, M.; Dersch, R.; Agarwal, S.; Fuchs-Winkelmann, S.; Paletta, J.R. Electrospun PLLA nanofiber scaffolds and their use in combination with BMP-2 for reconstruction of bone defects. PLoS One 2011, 6, e25462. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3182232/

11.  Wennerberg, A.; Frojd, V.; Olsson, M.; Nannmark, U.; Emanuelsson, L.; Johansson, P.; Josefsson, Y.; Kangasniemi, I.; Peltola, T.; Tirri, T.; et al. Nanoporous TiO(2) thin film on titanium oral implants for enhanced human soft tissue adhesion: a light and electron microscopy study. Clin. Implant. Dent. Relat. Res. 2011, 13, 184–196. http://www.ncbi.nlm.nih.gov/pubmed/19681943

12. Dallari, D.; Savarino, L.; Albisinni, U.; Fornasari, P.; Ferruzzi, A.; Baldini, N.; Giannini, S. A prospective, randomised, controlled trial using a Mg-hydroxyapatite-demineralized bone matrix nanocomposite in tibial osteotomy. Biomaterials 2012, 33, 72–79. http://www.ncbi.nlm.nih.gov/pubmed/21955688

13. Schwarz, F.; Sahm, N.; Bieling, K.; Becker, J. Surgical regenerative treatment of peri-implantitis lesions using a nanocrystalline hydroxyapatite or a natural bone mineral in combination with a collagen membrane: a four-year clinical follow-up report. J. Clin. Periodontol. 2009, 36, 807–814.  http://www.ncbi.nlm.nih.gov/pubmed/19637997

Other articles from our Open Access Journal

I. By: Aviral Vatsa PhD MBBS. Targeted delivery of therapeutics to bone and connective tissues: current status and challenges- Part I. https://pharmaceuticalintelligence.com/2012/09/23/targeted-delivery-of-therapeutics-to-bone-and-connective-tissues-current-status-and-challenges-part-i/

II. By: Aviral Vatsa PhD MBBS. Targeted delivery of therapeutics to bone and connective tissues: current status and challenges- Part II. https://pharmaceuticalintelligence.com/2012/09/30/targeted-delivery-of-therapeutics-to-bone-and-connective-tissues-current-status-and-challenges-part-ii/

III. By: Aviral Vatsa PhD MBBS. Osteocytes: A Special Issue in Bone.  https://pharmaceuticalintelligence.com/2013/02/06/osteocytes-a-special-issue-in-bone/

IV. By: Aviral Vatsa PhD MBBS. Bone remodelling in a nutshell. https://pharmaceuticalintelligence.com/2012/06/22/bone-remodelling-in-a-nutshell/

V. By: Ritu Saxena PhD. Dual protection of bone by Sema3a. https://pharmaceuticalintelligence.com/2012/05/10/dual-protection-of-bone-by-sema3a-2/

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