Prospects of stem cell therapy in osteoarthritis

Impact of olive leaf extract on pain management and functional improvement in elderly patients with knee osteoarthritis: A randomized controlled trial

INTRODUCTION

Osteoarthritis is a progressive joint disease that affects one or more joints, leading to restricted movement, pain, and eventual disability. Despite the availability of various treatments and supportive care, managing osteoarthritis symptoms remains challenging. This study aimed to evaluate the effect of Hydroalcoholic olive leaf extract on pain reduction and daily functioning in elderly patients with knee osteoarthritis.

METHOD

A randomized, controlled, factorial clinical trial was conducted in 2022-2023 with 100 elderly participants suffering from knee osteoarthritis. Participants were selected through consecutive sampling and randomly assigned to four groups using block-stratified randomization. In addition to routine treatment, participants in group I received topical olive leaf extract ointment, Group II received oral olive leaf extract capsules, and Group III received a combination of both treatments. The intervention was administered three times daily for eight weeks. The control group did not receive any olive leaf extract-based interventions. Pain intensity was assessed using a visual analog scale, and daily functioning and joint stiffness were measured using the Western Ontario and McMaster Universities Osteoarthritis Index questionnaire. Data were analyzed using SPSS software.

RESULTS

The intervention groups showed significantly more significant reductions in mean pain scores than the control group (p < 0.05). The combination of oral capsules and topical ointment among the intervention groups demonstrated the most pronounced pain reduction. The mean score for daily functioning improved significantly over time in all groups (p = 0.007). A decrease of 1.19 units per time increment was observed in the group using the ointment, while the oral capsule group showed a decrease of 0.89 units, both statistically significant (p = 0.006).

CONCLUSION

Hydroalcoholic olive leaf extract effectively reduces pain and improves physical functioning in elderly patients with knee osteoarthritis, offering a promising complementary treatment option for managing osteoarthritis symptoms.

Extracellular Vesicles: A Novel Diagnostic Tool and Potential Therapeutic Approach for Equine Osteoarthritis

Osteoarthritis (OA) is a chronic progressive degenerative joint disease that affects a significant portion of the equine population and humans worldwide. Current treatment options for equine OA are limited and incompletely curative. Horses provide an excellent large-animal model for studying human OA. Recent advances in the field of regenerative medicine have led to the exploration of extracellular vesicles (EVs)-cargoes of microRNA, proteins, lipids, and nucleic acids-to evaluate their diagnostic value in terms of disease progression and severity, as well as a potential cell-free therapeutic approach for equine OA. EVs transmit molecular signals that influence various biological processes, including the inflammatory response, apoptosis, proliferation, and cell communication. In the present review, we summarize recent advances in the isolation and identification of EVs, the use of their biologically active components as biomarkers, and the distribution of the gap junction protein connexin 43. Moreover, we highlight the role of mesenchymal stem cell-derived EVs as a potential therapeutic tool for equine musculoskeletal disorders. This review aims to provide a comprehensive overview of the current understanding of the pathogenesis, diagnosis, and treatment strategies for OA. In particular, the roles of EVs as biomarkers in synovial fluid, chondrocytes, and plasma for the early detection of equine OA are discussed.

Intra-Articular Injection of Human Umbilical Cord-Derived Mesenchymal Stromal Cells Reduces Radiographic Osteoarthritis in an Ovine Model

OBJECTIVE

To determine if mesenchymal stromal cells (MSCs) derived from human umbilical cords (hUC) could reduce degeneration developing when injected into the knee of a large animal model of osteoarthritis (OA).

DESIGN

Ten million culture-expanded UC-MSCs (pooled from 3 human donors) were injected in 50 μL of tissue culture medium into the left stifle joints of 7 sheep whose medial meniscus was transected 4 weeks previously. Seven other sheep had only 50 μL of medium injected as the no treatment "control" group. After 8 weeks the sheep underwent euthanasia, the joints were excised and examined macroscopically, via x-ray and magnetic resonance imaging (MRI), both via histology for degenerative and inflammatory changes and immunohistochemically to identify any human cells within the joint tissues. Activity monitoring both before meniscus transection and euthanasia was also undertaken.

RESULTS

There was a significant reduction in the Kellgren-Lawrence x-ray score for joints injected with hUC-MSCs compared with the control joints. Likewise, macroscopic, MRI, synovitis and OARSI histology scores were all lower (better) in the joints injected with hUC-MSCs than in the control arm, but not significantly. Activity levels and synovitis scores were similar in both groups of animals.

CONCLUSIONS

hUC-MSCs appear to modify and reduce the development of osteoarthritic changes in the ovine stifle joint after meniscal destabilization, an injury which commonly leads to OA in humans. These results are encouraging for the potential benefit of culture expanded UC-MSCs as an allogeneic cell therapy in patients who may have early OA following a meniscal injury of the knee.

Assessing the advantages of 3D bioprinting and 3D spheroids in deciphering the osteoarthritis healing mechanism using human chondrocytes and polarized macrophages

The molecular niche of an osteoarthritic microenvironment comprises the native chondrocytes, the circulatory immune cells, and their respective inflammatory mediators. Although M2 macrophages infiltrate the joint tissue during osteoarthritis (OA) to initiate cartilage repair, the mechanistic crosstalk that dwells underneath is still unknown. Our study established a co-culture system of human OA chondrocytes and M2 macrophages in 3D spheroids and 3D bioprinted silk-gelatin constructs. It is already well established that Silk fibroin-gelatin bioink supports chondrogenic differentiation due to upregulation of the Wnt/β-catenin pathway. Additionally, the presence of anti-inflammatory M2 macrophages significantly upregulated the expression of chondrogenic biomarkers (COL-II, ACAN) with an attenuated expression of the chondrocyte hypertrophy (COL-X), chondrocyte dedifferentiation (COL-I) and matrix catabolism (MMP-1 and MMP-13) genes even in the absence of the interleukins. Furthermore, the 3D bioprinted co-culture model displayed an upper hand in stimulating cartilage regeneration and OA inhibition than the spheroid model, underlining the role of silk fibroin-gelatin in encouraging chondrogenesis. Additionally, the 3D bioprinted silk-gelatin constructs further supported the maintenance of stable anti-inflammatory phenotype of M2 macrophage. Thus, the direct interaction between the primary OAC and M2 macrophages in the 3D context, along with the release of the soluble anti-inflammatory factors by the M2 cells, significantly contributed to a better understanding of the molecular mechanisms responsible for immune cell-mediated OA healing.

Mechanobiology-based physical therapy and rehabilitation after orthobiologic interventions: a narrative review

PURPOSE

This review aims to summarize the evidence for the role of mechanotherapies and rehabilitation in supporting the synergy between regeneration and repair after an orthobiologic intervention.

METHODS

A selective literature search was performed using Web of Science, OVID, and PubMed to review research articles that discuss the effects of combining mechanotherapy with various forms of regenerative medicine.

RESULTS

Various mechanotherapies can encourage the healing process for patients at different stages. Taping, bracing, cold water immersion, and extracorporeal shockwave therapy can be used throughout the duration of acute inflammatory response. The regulation of angiogenesis can be sustained with blood flow restriction and resistance training, whereas heat therapy and tissue loading during exercise are recommended in the remodeling phase.

CONCLUSION

Combining mechanotherapy with various forms of regenerative medicine has shown promise for improving treatment outcomes. However, further studies that reveal a greater volume of evidence are needed to support clinical decisions.

Accentuating the sources of mesenchymal stem cells as cellular therapy for osteoarthritis knees-a panoramic review

The large economic burden on the global health care systems is due to the increasing number of symptomatic osteoarthritis (OA) knee patients whereby accounting for greater morbidity and impaired functional quality of life. The recent developments and impulses in molecular and regenerative medicine have paved the way for inducing the biological active cells such as stem cells, bioactive materials, and growth factors towards the healing and tissue regenerative process. Mesenchymal stem cells (MSCs) act as a minimally invasive procedure that bridges the gap between pharmacological treatment and surgical treatment for OA. MSCs are the ideal cell-based therapy for treating disorders under a minimally invasive environment in conjunction with cartilage regeneration. Due to the worldwide recognized animal model for such cell-based therapies, global researchers have started using the various sources of MSCs towards cartilage regeneration. However, there is a lacuna in literature on the comparative efficacy and safety of various sources of MSCs in OA of the knee. Hence, the identification of a potential source for therapeutic use in this clinical scenario remains unclear. In this article, we compared the therapeutic effects of various sources of MSCs in terms of efficacy, safety, differentiation potential, durability, accessibility, allogenic preparation and culture expandability to decide the optimal source of MSCs for OA knee.

Mesenchymal Stem Cells: Current Concepts in the Management of Inflammation in Osteoarthritis

Osteoarthritis (OA) has traditionally been known as a “wear and tear” disease, which is mainly characterized by the degradation of articular cartilage and changes in the subchondral bone. Despite the fact that OA is often thought of as a degenerative disease, the catabolic products of the cartilage matrix often promote inflammation by activating immune cells. Current OA treatment focuses on symptomatic treatment, with a primary focus on pain management, which does not promote cartilage regeneration or attenuate joint inflammation. Since articular cartilage have no ability to regenerate, thus regeneration of the tissue is one of the key targets of modern treatments for OA. Cell-based therapies are among the new therapeutic strategies for OA. Mesenchymal stem cells (MSCs) have been extensively researched as potential therapeutic agents in cell-based therapy of OA due to their ability to differentiate into chondrocytes and their immunomodulatory properties that can facilitate cartilage repair and regeneration. In this review, we emphasized current knowledge and future perspectives on the use of MSCs by targeting their regeneration potential and immunomodulatory effects in the treatment of OA.

Biomolecular phenotyping and heterogeneity assessment of mesenchymal stromal cells using label-free Raman spectroscopy

Easy, quantitative measures of biomolecular heterogeneity and high-stratified phenotyping are needed to identify and characterise complex disease processes at the single-cell level, as well as to predict cell fate. Here, we demonstrate how Raman spectroscopy can be used in the difficult-to-assess case of clonal, bone-derived mesenchymal stromal cells (MSCs) to identify MSC lines and group these according to biological function (e.g., differentiation capacity). Biomolecular stratification is achieved using high-precision measures obtained from representative statistical sampling that also enable quantified heterogeneity assessment. Application to primary MSCs and human dermal fibroblasts shows use of these measures as a label-free assay to classify cell sub-types within complex heterogeneous cell populations, thus demonstrating the potential for therapeutic translation, and broad application to the phenotypic characterisation of other cells.

Mesenchymal Stem Cell Implantation in Knee Osteoarthritis: Midterm Outcomes and Survival Analysis in 467 Patients

Background

A cell-based tissue engineering approach that uses mesenchymal stem cells (MSCs) has addressed the issue of articular cartilage repair in knees with osteoarthritis (OA).

Purpose

To evaluate the midterm outcomes, analyze the survival rates, and identify the factors affecting the survival rate of MSC implantation to treat knee OA.

Study Design

Case series; Level of evidence, 4.

Methods

We retrospectively evaluated 467 patients (483 knees) who underwent MSC implantation on a fibrin glue scaffold for knee OA with a minimum 5-year follow-up. Clinical outcomes were determined based on the International Knee Documentation Committee (IKDC) and Tegner activity scale results measured preoperatively and during follow-up. Standard radiographs were evaluated using Kellgren-Lawrence grading. Statistical analyses were performed to determine the survival rate and the effect of different factors on the clinical outcomes.

Results

The mean IKDC scores (baseline, 39.2 ± 7.2; 1 year, 66.6 ± 9.6; 3 years, 67.2 ± 9.9; 5 years, 66.1 ± 9.7; 9 years, 62.8 ± 8.5) and Tegner scores (baseline, 2.3 ± 1.0; 1 year, 3.4 ± 0.9; 3 years, 3.5 ± 0.9; 5 years, 3.4 ± 0.9; 9 years, 3.2 ± 0.9) were significantly improved until 3 years postoperatively and gradually decreased from 3- to 9-year follow-up (P < .05 for all, except for Tegner score at 5 years vs 1 year [P = .237]). Gradual deterioration of radiological outcomes according to the Kellgren-Lawrence grade was found during follow-up. Survival rates based on either a decrease in IKDC or an advancement of radiographic OA with Kellgren-Lawrence scores were 99.8%, 94.5%, and 74.5% at 5, 7, and 9 years, respectively. Based on multivariate analyses, older age and the presence of bipolar kissing lesion were associated with significantly worse outcomes (P = .002 and .013, respectively), and a larger number of MSCs was associated with significantly better outcomes (P < .001) after MSC implantation.

Conclusion

MSC implantation provided encouraging outcomes with acceptable duration of symptom relief at midterm follow-up in patients with early knee OA. Patient age, presence of bipolar kissing lesion, and number of MSCs were independent factors associated with failure of MSC implantation.

Injected human umbilical cord-derived mesenchymal stromal cells do not appear to elicit an inflammatory response in a murine model of osteoarthritis

Objective

This study investigated the effect of hUC-MSCs on osteoarthritis (OA) progression in a xenogeneic model.

Design

Male, 10 week-old C57BL/6 mice underwent sham surgery (n = 15) or partial medial meniscectomy (PMM; n = 76). 5x10⁵ hUC-MSCs (from 3 donors: D1, D2 and D3) were phenotyped via RT-qPCR and immunoprofiling their response to inflammatory stimuli.

They were injected into the mouse joints 3 and 6 weeks post-surgery, harvesting joints at 8 and 12 weeks post-surgery, respectively. A no cell ‘control’ group was also used (n = 29). All knee joints were assessed via micro-computed tomography (μCT) and histology and 10 plasma markers were analysed at 12 weeks.

Results

PMM resulted in cartilage loss and osteophyte formation resembling human OA at both time-points. Injection of one donor's hUC-MSCs into the joint significantly reduced the loss of joint space at 12 weeks post-operatively compared with the PMM control.

This ‘effective’ population of MSCs up-regulated the genes, IDO and TSG6, when stimulated with inflammatory cytokines, more than those from the other two donors.

No evidence of an inflammatory response to the injected cells in any animals, either histologically or with plasma biomarkers, arose.

Conclusion

Beneficial change in a PMM joint was seen with only one hUC-MSC population, perhaps indicating that cell therapy is not appropriate for severely osteoarthritic joints. However, none of the implanted cells appeared to elicit an inflammatory response at the time-points studied. The variability of UC donors suggests some populations may be more therapeutic than others and donor characterisation is essential in developing allogeneic cell therapies.

Combination Therapy of Mesenchymal Stromal Cells and Interleukin-4 Attenuates Rheumatoid Arthritis in a Collagen-Induced Murine Model

Rheumatoid arthritis (RA) is a disease of the joints that causes decreased quality of life. Mesenchymal stromal cells (MSCs) have immunosuppressive properties, with possible use in the treatment of RA. Similarly, interleukin (IL)-4 has been shown as a potential RA treatment. However, their combination has not been explored before. Therefore, this study aimed to investigate the effect of a combination therapy of MSCs and IL-4 in the treatment of RA, using a murine collagen-induced arthritis (CIA) model. Arthritis was induced in Balb/c mice by two intradermal injections of type II collagen (CII), at days 0 and 21. CIA mice were randomly assigned to four groups; group I received an intravenous injection of mouse bone marrow-derived MSCs, while group II received an intraperitoneal injection of IL-4. Group III received a combined treatment of MSC and IL-4, while group IV served as a CIA diseased control group receiving phosphate buffer saline (PBS). A fifth group of healthy mice served as the normal healthy control. To assess changes induced by different treatments, levels of RA-associated inflammatory cytokines and biomarkers were measured in the serum, knee joints, and synovial tissue, using ELISA and Real Time-qPCR. Histopathological features of knee joints were analyzed for all groups. Results showed that combined MSC and IL-4 treatment alleviated signs of synovitis in CIA mice, reverting to the values of healthy controls. This was evident by the decrease in the levels of rheumatic factor (RF), C-reactive protein (CRP) and anti-nuclear antibodies (ANA) by 64, 80, and 71%, respectively, compared to the diseased group. Moreover, tumor necrosis factor-alpha (TNF- α) and monocyte chemoattractant protein-1 (MCP-1) levels decreased by 63 and 68%, respectively. Similarly, our gene expression data showed improvement in mice receiving combined therapy compared to other groups receiving single treatment, where cartilage oligomeric matrix protein (Comp), tissue inhibitor metalloproteinase-1 (Timp1), matrix metalloproteinase1 (Mmp-1), and IL-1 receptor (Il-1r) gene expression levels decreased by 75, 70, and 78%, respectively. Collectively, treatment with a combined therapy of MSC and IL-4 might have an efficient therapeutic effect on arthritis. Thus, further studies are needed to assess the potential of different MSC populations in conjugation with IL-4 in the treatment of experimental arthritis.

Regenerative Medicine: "Are We There Yet?"

Translation of regenerative therapies to the patient-bench-to-bedside-is one of the global multidisciplinary challenges of our time. New cell-based therapies are reaching the clinic through staged trials leading eventually to routine adoption. The roots of stem cell therapy lie in surgical practice and transplantation medicine with multiple multidisciplinary challenges emerging to support the new therapies. Control of stem cell behavior in line with regulatory confidence is an example of these challenges. One successful journey from bench-to-bedside is the generation of cartilage through autologous cell-based approaches for use in the repair of the knee joint. An analysis of this journey in Europe reveals success and failure; new initiatives include adopting more quantitative modelling and "organ on a chip" approaches to be used in clinical translation reducing experimental time and redressing the lack of preclinical models. The current state and challenges for the field are outlined with the question posed, "are we there yet?"

A mathematical model of cartilage regeneration after chondrocyte and stem cell implantation - II: the effects of co-implantation

We present a mathematical model of cartilage regeneration after cell therapy, to show how co-implantation of stem cells (mesenchymal stem cells) and chondrocytes into a cartilage defect can impact chondral healing. The key mechanisms involved in the regeneration process are simulated by modelling cell proliferation, migration and differentiation, nutrient diffusion and Extracellular Matrix (ECM) synthesis at the defect site, both spatially and temporally. In addition, we model the interaction between mesenchymal stem cells and chondrocytes by including growth factors. In Part I of this work, we have shown that matrix formation was enhanced at early times when mesenchymal stem cell-to-chondrocyte interactions due to the effects of growth factors were considered. In this article, we show that the additional effect of co-implanting mesenchymal stem cells and chondrocytes further enhances matrix production within the first year in comparison to implanting only chondrocytes or only mesenchymal stem cells. This could potentially reduce healing time allowing the patient to become mobile sooner after surgery.

Rehabilitation following regenerative medicine treatment for knee osteoarthritis-current concept review

The purpose of this manuscript is to provide a current concept review for the rehabilitative management of knee osteoarthritis (KOA) following regenerative medicine intervention. A proposed comprehensive regenerative rehabilitative program has been created, based on a literature review of the current best practices of rehabilitative methods and non-operative management in KOA patients with an emphasis on the goals of regenerative medicine: to optimize self-healing and functional tissue recovery. Regenerative medicine promotes regeneration and joint restoration by using blood-based procedures such as platelet rich plasma, stem cell and cell-based or tissue engineering. Regenerative medicine procedures are variable and lack of standardization in product preparation, administration, and different treatment protocols. The lack of standardization imposes challenges in regenerative rehabilitation. Over the last decade, there is growing evidence in regenerative medicine and its uses in non-operative management of various pathologies. Advances in regenerative medicine technologies brings radical innovations to establish new and effective rehabilitation protocols promoting restoration of function through tissue regeneration and repair optimizing the standard of care, specifically in rehabilitation when combined with regenerative protocols for patients with KOA is the most common degenerative disease in the knee and can affect any synovial joint in the body. It is a leading cause of disability affecting the quality of lives of millions of people world-wide. Conventional methods of mild to moderate KOA are focused on short-term symptomatic relief and do not promote joint homeostasis or regeneration of injured tissue. Regenerative medicine emphasizes a paradigm shift in patient-centered care promoting regeneration and joint restoration by using blood-based procedures such as platelet rich plasma, stem cell and cell-based or tissue engineering. The purpose of this current concept review is to outline a comprehensive post-regenerative rehabilitative program in the management of KOA based on the best available evidence. Our proposed regenerative rehabilitation program is intended to align the goals of regenerative medicine with the current, high-level evidence of non-operative management for KOA, to optimize self-healing and functional tissue recovery.

Analysis of the Intrinsic Self-Organising Properties of Mesenchymal Stromal Cells in Three-Dimensional Co-Culture Models with Endothelial Cells

Mesenchymal stem/stromal cells (MSCs) are typically characterised by their ability to differentiate into skeletal (osteogenic, chondrogenic and adipogenic) lineages. MSCs also appear to have additional non-stem cell functions in coordinating tissue morphogenesis and organising vascular networks through interactions with endothelial cells (ECs). However, suitable experimental models to examine these apparently unique MSC properties are lacking. Following previous work, we have developed our 3D in vitro co-culture models to enable us to track cellular self-organisation events in heterotypic cell spheroids combining ECs, MSCs and their differentiated progeny. In these systems, MSCs, but not related fibroblastic cell types, promote the assembly of ECs into interconnected networks through intrinsic mechanisms, dependent on the relative abundance of MSC and EC numbers. Perturbation of endogenous platelet-derived growth factor (PDGF) signalling significantly increased EC network length, width and branching. When MSCs were pre-differentiated towards an osteogenic or chondrogenic lineage and co-cultured as mixed 3D spheroids, they segregated into polarised osseous and chondral regions. In the presence of ECs, the pre-differentiated MSCs redistributed to form a central mixed cell core with an outer osseous layer. Our findings demonstrate the intrinsic self-organising properties of MSCs, which may broaden their use in regenerative medicine and advance current approaches.

Evaluating the Current Literature on Treatments Containing Adipose-Derived Stem Cells for Osteoarthritis: a Progress Update

PURPOSE OF REVIEW

Recent studies have investigated the effect of treatments containing adipose-derived mesenchymal stem cells (ADMSCs) on human osteoarthritis. These have mostly used biologic adjuvants which may influence results. Thus, the purpose of this systematic review is to evaluate the current literature on these treatments when used in isolation.

RECENT FINDINGS

Five studies in this review used cultured ADMSCs, while four studies used stromal vascular fraction and three used micro-fragmented adipose tissue to deliver ADMSCs. No studies reported serious treatment-related adverse effects and all reported improvements in clinical measures for at least one dose. This was not necessarily reflected in imaging evaluations nor were improvements always maintained. Current low-level evidence is limited due to variability in study methodology but indicates that treatments containing ADMSCs, when used in isolation, are safe and have the potential to reduce pain and improve function. Randomized controlled trials are now needed.

Exosomes and Stem Cells in Degenerative Disease Diagnosis and Therapy

Stroke can cause death and disability, resulting in a huge burden on society. Parkinson’s disease (PD) is a chronic neurodegenerative disorder characterized by motor dysfunction. Osteoarthritis (OA) is a progressive degenerative joint disease characterized by cartilage destruction and osteophyte formation in the joints. Stem cell therapy may provide a biological treatment alternative to traditional pharmacological therapy. Mesenchymal stem cells (MSCs) are preferred because of their differentiation ability and possible derivation from many adult tissues. In addition, the paracrine effects of MSCs play crucial anti-inflammatory and immunosuppressive roles in immune cells. Extracellular vesicles (EVs) are vital mediators of cell-to-cell communication. Exosomes contain various molecules such as microRNA (miRNA), which mediates biological functions through gene regulation. Therefore, exosomes carrying miRNA or other molecules can enhance the therapeutic effects of MSC transplantation. MSC-derived exosomes have been investigated in various animal models representing stroke, PD, and OA. Exosomes are a subtype of EVs. This review article focuses on the mechanism and therapeutic potential of MSC-derived exosomes in stroke, PD, and OA in basic and clinical aspects.

Stem cell-based therapeutic strategies for cartilage defects and osteoarthritis

The gold standard cell therapy for repair of articular cartilage defects is autologous chondrocyte implantation, with good outcomes long-term. Mesenchymal stromal/stem cells (MSCs) from bone marrow or connective tissues such as fat are being pursued as alternatives for cartilage repair, and are trialled via intra-articular administration in patients with knee osteoarthritis. Early-phase clinical studies concur on safety and provide some promising insight into efficacy, but the mechanism of action remains unclear. Recent studies implicate extracellular vesicles as important mediators of MSC action, offering exciting therapeutic prospects. Our increasing understanding of the mechanisms underlying intrinsic articular cartilage maintenance and repair fosters hope that novel/repurposed therapeutics could elicit repair through activation of endogenous stem/progenitor cells to maintain healthy joints and prevent osteoarthritis.

Therapeutic Benefit for Late, but Not Early, Passage Mesenchymal Stem Cells on Pain Behaviour in an Animal Model of Osteoarthritis

Background

Mesenchymal stem cells (MSCs) have a therapeutic potential for the treatment of osteoarthritic (OA) joint pathology and pain. The aims of this study were to determine the influence of a passage number on the effects of MSCs on pain behaviour and cartilage and bone features in a rodent model of OA.

Methods

Rats underwent either medial meniscal transection (MNX) or sham surgery under anaesthesia. Rats received intra-articular injection of either 1.5 × 10⁶ late passage MSCs labelled with 10 μg/ml SiMAG, 1.5 × 10⁶ late passage mesenchymal stem cells, the steroid Kenalog (200 μg/20 μL), 1.5 × 10⁶ early passage MSCs, or serum-free media (SFM). Sham-operated rats received intra-articular injection of SFM. Pain behaviour was quantified until day 42 postmodel induction. Magnetic resonance imaging (MRI) was used to localise the labelled cells within the knee joint.

Results

Late passage MSCs and Kenalog attenuated established pain behaviour in MNX rats, but did not alter MNX-induced joint pathology at the end of the study period. Early passage MSCs exacerbated MNX-induced pain behaviour for up to one week postinjection and did not alter joint pathology.

Conclusion

Our data demonstrate for the first time the role of a passage number in influencing the therapeutic effects of MSCs in a model of OA pain.

Targeting subchondral bone mesenchymal stem cell activities for intrinsic joint repair in osteoarthritis

Osteoarthritis (OA) is a common age-related disease with complex pathophysiology. It is characterized by wide-ranging tissue damage and ultimate biomechanical failure of the whole joint. However, signs of tissue adaptation and attempted repair responses are evident in OA-affected osteochondral tissues. Highlighted in this review article is the role of bone-resident mesenchymal stem cells (MSCs) in these bone remodeling responses, and a proposal that targeting MSC activities in OA subchondral bone could represent a novel approach for intrinsic joint regeneration in OA. The development of these therapies will require better understanding of MSC proliferation, migration and differentiation patterns in relation to OA tissue damage and further clarification of the molecular signaling events in these MSCs during disease progression.

Osteoarthritis (OA) is a joint disorder, in which the cartilage, the underlying bone and other joint tissues are affected. Recent evidence demonstrating attempted repair responses in these OA tissues challenges the traditional view of OA as a degenerative disorder. Signs of tissue regeneration are particularly evident in the bone located directly underneath the damaged cartilage, where increased stem cell activity has been observed. Targeting these stem cells could represent a novel approach for intrinsic joint regeneration in OA. To progress with developing these novel therapies, a better understanding of stem cell function in normal and OA joint tissues is needed.

Transplantation of human skeletal muscle-derived progenitor cells ameliorates knee osteoarthritis in streptozotocin-induced diabetic mice

The epidemiological and experimental evidence suggests that diabetes can be an independent risk factor for osteoarthritis. The osteoarthritis-like cartilage damage has been shown in streptozotocin-induced diabetic mice. The therapeutic effects of human skeletal muscle-derived progenitor cells (HSMPCs) on diabetic osteoarthritis still remain unclear. Here, we investigated the therapeutic potential of HSMPCs on diabetic knee osteoarthritis. The in vitro chondrogenic ability of HSMPCs was determined by pellet culture assay. Male mice were used to develop the model of streptozotocin-induced type 1 diabetes and its related osteoarthritis. HSMPCs were injected intra-articularly to rescue osteoarthritis. Protein expressions of advanced glycation end-products, cyclooxygenase-2, and type-2 collagen in tissues were determined by immunohistochemistry. The pellet culture assay showed that HSMPCs cultured in differentiation medium for chondrogenesis significantly produced larger pellets with an overproduction of extracellular matrix than in growth medium. In in vivo experiments, intra-articular injection of HSMPCs for 4 weeks significantly prevented the progression of degenerative changes in the cartilage of streptozotocin-induced diabetic mice, including an obvious increase of total articular cartilage thickness and a decrease of fibrous cartilage thickness. HSMPCs transplantation also exerted the decline in advanced glycation end-products and cyclooxygenase-2 protein expression, but increased the type-2 collagen protein expression in streptozotocin-induced osteoarthritic cartilages. Moreover, HSMPCs transplantation also inhibited the increased serum interleukin-6 and matrix metalloproteinase-3 levels in diabetic mice. These results demonstrated for the first time that HSMPCs transplantation ameliorates cartilage degeneration in diabetes-related osteoarthritis mice. These findings suggest that HSMPCs transplantation may apply as a potential therapeutic use of diabetes-related osteoarthritis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1886-1893, 2017.

Inflammation affects the viability and plasticity of equine mesenchymal stem cells: possible implications in intra-articular treatments

Mesenchymal stem cells (MSCs) are gaining relevance for treating equine joint injuries because of their ability to limit inflammation and stimulate regeneration. Because inflammation activates MSC immunoregulatory function, proinflammatory priming could improve MSC efficacy. However, inflammatory molecules present in synovial fluid or added to the culture medium might have deleterious effects on MSCs. Therefore, this study was conducted to investigate the effects of inflammatory synovial fluid and proinflammatory cytokines priming on viability and plasticity of equine MSCs. Equine bone marrow derived MSCs (eBM-MSCs) from three animals were cultured for 72 h in media supplemented with: 20% inflammatory synovial fluid (SF); 50 ng/mL IFN-γ and TNF-α (CK50); and 20 ng/mL IFN-γ and TNF-α (CK20). Proliferation assay and expression of proliferation and apoptosis-related genes showed that SF exposed-eBM-MSCs maintained their viability, whereas the viability of CK primed-eBM-MSCs was significantly impaired. Tri-lineage differentiation assay revealed that exposure to inflammatory synovial fluid did not alter eBM-MSCs differentiation potential; however, eBM-MSCs primed with cytokines did not display osteogenic, adipogenic or chondrogenic phenotype. The inflammatory synovial environment is well tolerated by eBM-MSCs, whereas cytokine priming negatively affects the viability and differentiation abilities of eBM-MSCs, which might limit their in vivo efficacy.

Role of mesenchymal stem cells in osteoarthritis treatment

As the most common form of joint disorder, osteoarthritis (OA) imposes a tremendous burden on health care systems worldwide. Without effective cure, OA represents a unique opportunity for innovation in therapeutic development. In contrast to traditional treatments based on drugs, proteins, or antibodies, stem cells are poised to revolutionize medicine as they possess the capacity to replace and repair tissues and organs such as osteoarthritic joints. Among different types of stem cells, mesenchymal stem cells (MSCs) are of mesoderm origin and have been shown to generate cells for tissues of the mesoderm lineage, thus, raising the hope for them being used to treat diseases such as OA. However, given their ability to differentiate into other cell types, MSCs have also been tested in treating a myriad of conditions from diabetes to Parkinson's disease, apparently of the ectoderm and endoderm lineages. There are ongoing debates whether MSCs can differentiate into lineages outside of the mesoderm and consequently their effectiveness in treating conditions from the ectoderm and endoderm lineages. In this review, we discuss the developmental origin of MSCs, their differentiation potential and immunomodulatory effects, as well as their applications in treating OA. We suggest further investigations into new therapies or combination therapies that may provide more effective treatment for bone and joint diseases. Furthermore, cell-based therapy and its associated safety and effectiveness should be carefully evaluated before clinical translation. This review provides updated information on recent approval of clinical trials and related applications of MSCs, and discusses additional efforts on cell-based therapy for treating OA and other joint and bone diseases.

Mesenchymal Stem Cells and Their Clinical Applications in Osteoarthritis

Osteoarthritis is a chronic degenerative joint disorder characterized by articular cartilage destruction and osteophyte formation. Chondrocytes in the matrix have a relatively slow turnover rate, and the tissue itself lacks a blood supply to support repair and remodeling. Researchers have evaluated the effectiveness of stem cell therapy and tissue engineering for treating osteoarthritis. All sources of stem cells, including embryonic, induced pluripotent, fetal, and adult stem cells, have potential use in stem cell therapy, which provides a permanent biological solution. Mesenchymal stem cells (MSCs) isolated from bone marrow, adipose tissue, and umbilical cord show considerable promise for use in cartilage repair. MSCs can be sourced from any or all joint tissues and can modulate the immune response. Additionally, MSCs can directly differentiate into chondrocytes under appropriate signal transduction. They also have immunosuppressive and anti-inflammatory paracrine effects. This article reviews the current clinical applications of MSCs and future directions of research in osteoarthritis.

Lack of anti-inflammatory and anti-catabolic effects on basal inflamed osteoarthritic chondrocytes or synoviocytes by adipose stem cell-conditioned medium

OBJECTIVE

To define whether good manufacturing practice (GMP)-clinical grade adipose stem cell (ASC)-derived conditioned medium (CM) is as effective as GMP-ASC in modulating inflammatory and catabolic factors released by both osteoarthritis (OA) chondrocytes or synoviocytes.

METHODS

OA chondrocytes and synoviocytes were treated with ASC-CM or co-cultured with ASC. Inflammatory factors (IL6, CXCL1/GROα,CXCL8/IL8, CCL2/MCP-1, CCL3/MIP-1α and CCL5/RANTES) and proteinases, such as metalloproteinase (MMP13), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS4, ADAMTS5) and their tissue metalloproteinase inhibitors (TIMP1, TIMP3) were evaluated by qRT-PCR or immunoassays. The involvement of prostaglandin E2 (PGE2) was also analyzed.

RESULTS

Most ASC-CM ratios tested did not decrease IL6, CCL2/MCP-1, CCL3/MIP1-α, CCL5/RANTES on basal inflamed chondrocytes or synoviocytes in contrast to what we found using ASC in co-culture. CXCL8/IL8 and CXCL1/GROα were not decreased by ASC-CM on synoviocytes but were only partially reduced on chondrocytes. Moreover, ASC-CM was less efficient both on basal inflamed OA chondrocytes and synoviocytes in reducing proteinases, such as MMP13, ADAMTS4, ADAMTS5 and increasing TIMP1 and TIMP3 compared to ASC in co-culture. The different ratios of ASC-CM contain lower amounts of PGE2 which were not sufficient to reduce inflammatory factors.

CONCLUSIONS

These data show that ASC-CM has a limited ability to decrease inflammatory and proteinases factors produced by OA chondrocytes or synoviocytes. ASC-CM is not sufficient to recapitulate the beneficial effect demonstrated using ASC in co-culture with inflamed OA chondrocytes and synoviocytes and shows that their use in clinical trials is fundamental to counteract OA progression.

Overcoming translational challenges - The delivery of mechanical stimuli in vivo

Despite major medical advances, non-union bone fractures and skeletal defects continue to place significant burden on the patient, the clinicians and the healthcare system as a whole. Current bone substitute approaches are still limited in effectiveness and to date no adequate bone substitute material has been developed for routine clinical application. Tissue engineering presents a novel approach to tackling this clinical burden and developing an acceptable solution for the treatment of skeletal defects. Over the past three decades the field has evolved to appreciate the key biological, material and physical parameters influencing the development of a cell-based tissue engineered therapy and to create associated technologies to exploit such parameters. In recent years a number of therapies have started progressing along the pre-clinical pipeline to build a case for regulatory approval and ultimately clinical adoption. However, little emphasis has been given to the translational challenges faced when moving from "bench-to-bedside". One particular challenge lies in the delivery of functional mechanical stimuli to implanted cell populations to activate and promote osteogenic activities. This review introduces novel bio-magnetic approaches to overcoming this challenge.

Potential benefits and limitations of utilizing chondroprogenitors in cell-based cartilage therapy

Chondroprogenitor cells are a subpopulation of multipotent progenitors that are primed for chondrogenesis. They are believed to have the biological repertoire to be ideal for cell-based cartilage therapy. In addition to summarizing recent advances in chondroprogenitor cell characterization, this review discusses the projected pros and cons of utilizing chondroprogenitors in regenerative medicine and compares them with that of pre-existing methods, including autologous chondrocyte implantation (ACI) and the utilization of bone marrow derived mesenchymal stem cells (MSCs) for the purpose of cartilage tissue repair.

Hip osteoarthritis in dogs: a randomized study using mesenchymal stem cells from adipose tissue and plasma rich in growth factors

Purpose: The aim of this study was to compare the efficacy and safety of a single intra-articular injection of adipose mesenchymal stem cells (aMSCs) versus plasma rich in growth factors (PRGF) as a treatment for reducing symptoms in dogs with hip osteoarthritis (OA). Methods: This was a randomized, multicenter, blinded, parallel group. Thirty-nine dogs with symptomatic hip OA were assigned to one of the two groups, to receive aMSCs or PRGF. The primary outcome measures were pain and function subscales, including radiologic assessment, functional limitation and joint mobility. The secondary outcome measures were owners’ satisfaction questionnaire, rescue analgesic requirement and overall safety. Data was collected at baseline, then, 1, 3 and 6 months post-treatment. Results: OA degree did not vary within groups. Functional limitation, range of motion (ROM), owner’s and veterinary investigator visual analogue scale (VAS), and patient’s quality of life improved from the first month up to six months. The aMSCs group obtained better results at 6 months. There were no adverse effects during the study. Our findings show that aMSCs and PRGF are safe and effective in the functional analysis at 1, 3 and 6 months; provide a significant improvement, reducing dog’s pain, and improving physical function. With respect to basal levels for every parameter in patients with hip OA, aMSCs showed better results at 6 months.

Effect of self-assembled peptide-mesenchymal stem cell complex on the progression of osteoarthritis in a rat model

PURPOSE

To evaluate the efficacy of mesenchymal stem cells (MSCs) encapsulated in self-assembled peptide (SAP) hydrogels in a rat knee model for the prevention of osteoarthritis (OA) progression.

MATERIALS AND METHODS

Nanostructured KLD-12 SAPs were used as the injectable hydrogels. Thirty-three Sprague Dawley rats were used for the OA model. Ten rats were used for the evaluation of biotin-tagged SAP disappearance. Twenty-three rats were divided into four groups: MSC (n=6), SAP (n=6), SAP-MSC (n=6), and no treatment (n=5). MSCs, SAPs, and SAP-MSCs were injected into the knee joints 3 weeks postsurgery. Histologic examination, immunofluorescent staining, measurement of cytokine levels, and micro-computed tomography analysis were conducted 6 weeks after injections. Behavioral studies were done to establish baseline measurements before treatment, and repeated 3 and 6 weeks after treatment to measure the efficacy of SAP-MSCs.

RESULTS

Concentration of biotinylated SAP at week 1 was not significantly different from those at week 3 and week 6 (P=0.565). Bone mineral density was significantly lower in SAP-MSC groups than controls (P=0.002). Significant differences in terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling staining between the control group and all other groups were observed. Caspase-8, tissue inhibitor of metalloproteinases 1, and matrix metalloproteinase 9 were diffusely stained in controls, whereas localized or minimal staining was observed in other groups. Modified Mankin scores were significantly lower in the SAP and SAP-MSC groups than in controls (P=0.001 and 0.013). Although not statistically significant, synovial inflammation scores were lower in the SAP (1.3±0.3) and SAP-MSC (1.3±0.2) groups than in controls (2.6±0.2). However, neither the cytokine level nor the behavioral score was significantly different between groups.

CONCLUSION

Injection of SAP-MSC hydrogels showed evidence of chondroprotection, as measured by the histologic grading and decreased expression of biochemical markers of inflammation and apoptosis. It also lowered subchondral bone mineral density, which can be increased by OA. This suggests that the SAP-MSC complex may have clinical potential to inhibit OA progression.

Regenerative medicine interventions for orthopedic disorders: ethical issues in the translation into patients

Regenerative medicine (RM) technologies, such as cell therapy, gene transfer and tissue engineering, are expected to move the field of orthopedics into a new era. Now that more and more attempts are underway to translate preclinical research into clinical studies, it is time to proactively discuss the ethical issues associated with first-in-human applications of RM interventions for musculoskeletal disorders. The design and launch of early clinical trials will be ethically challenging due to the specific features of RM in general, and the application for musculoskeletal disorders specifically. In this paper, we identify three sets of ethical issues that need to be addressed when considering initiating early clinical trials: assessment of risks and benefits; designing a study in terms of outcome measures and comparators; and participant selection. These issues are particularly emphasized in RM research that aims to apply these approaches in an early stage of degenerative musculoskeletal disorders.

Inflammatory stimuli differentially modulate the transcription of paracrine signaling molecules of equine bone marrow multipotent mesenchymal stromal cells

OBJECTIVE

Osteoarthritis (OA) is a degenerative disease of joint tissues that causes articular cartilage erosion, osteophytosis and loss of function due to pain. Inflammation and inflammatory cytokines in synovial fluid (SF) contribute to OA progression. Intra-articular (IA) injections of multipotent mesenchymal stromal cells (MSCs) are employed to treat OA in both humans and animals. MSCs secrete paracrine pro-inflammatory and anabolic signaling molecules that promote tissue repair. The objective of this study was to investigate the effects of OASF on the gene expression of paracrine signaling molecules by MSCs.

METHODS

The effects of Lipopolysaccharide (LPS) and interleukin (IL)-1β as well as both normal (N) and osteoarthritis (OA) SF stimulations on the expression of paracrine pro-inflammatory (tumor necrosis factor (TNF)-α, IL-1β, IL-8), modulatory (IL-6) and anabolic (vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β1 and insulin-like growth factor (IGF)-1) signaling molecules by equine bone marrow multipotent mesenchymal stromal cells (eBM-MSCs) was investigated employing reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

In contrast with NSF, OASF significantly up-regulated the expression of VEGF in eBM-MSCs. Both NSF and OASF significantly down-regulated the expression of IL-1β. LPS and IL-1β significantly increased the expression of pro-inflammatory cytokines (TNF-α, IL-8 and IL-6; and IL-1β and IL-8 respectively).

DISCUSSION

We conclude that the transcription of paracrine signaling molecules in eBM-MSCs is modulated by SF. Furthermore, OA alters the properties of SF and the response of eBM-MSCs. Finally, the effects of LPS or IL-1β stimulation are distinct to that observed following stimulations with OASF.

Cell-based approaches to joint surface repair: a research perspective

Repair of lesions of the articular cartilage lining the joints remains a major clinical challenge. Surgical interventions include osteochondral autograft transfer and microfracture. They can provide some relief of symptoms to patients, but generally fail to durably repair the cartilage. Autologous chondrocyte implantation has thus far shown the most promise for the durable repair of cartilage, with long-term follow-up studies indicating improved structural and functional outcomes. However, disadvantages of this technique include the need for additional surgery, availability of sufficient chondrocytes for implantation, and maintenance of their phenotype during culture-expansion. Mesenchymal stem cells offer an attractive alternative cell-source for cartilage repair, due to their ease of isolation and amenability to ex vivo expansion while retaining stem cell properties. Preclinical and clinical studies have demonstrated the potential of mesenchymal stem cells to promote articular cartilage repair, but have also highlighted several key challenges. Most notably, the quality and durability of the repair tissue, its resistance to endochondral ossification, and its effective integration with the surrounding host tissue. In addition, challenges exist related to the heterogeneity of mesenchymal stem cell preparations and their quality-control, as well as optimising the delivery method. Finally, as our knowledge of the cellular and molecular mechanisms underlying articular cartilage repair increases, promising studies are emerging employing bioactive scaffolds or therapeutics that elicit an effective tissue repair response through activation and mobilisation of endogenous stem and progenitor cells.

Chitosan for gene delivery and orthopedic tissue engineering applications

Gene therapy involves the introduction of foreign genetic material into cells in order exert a therapeutic effect. The application of gene therapy to the field of orthopaedic tissue engineering is extremely promising as the controlled release of therapeutic proteins such as bone morphogenetic proteins have been shown to stimulate bone repair. However, there are a number of drawbacks associated with viral and synthetic non-viral gene delivery approaches. One natural polymer which has generated interest as a gene delivery vector is chitosan. Chitosan is biodegradable, biocompatible and non-toxic. Much of the appeal of chitosan is due to the presence of primary amine groups in its repeating units which become protonated in acidic conditions. This property makes it a promising candidate for non-viral gene delivery. Chitosan-based vectors have been shown to transfect a number of cell types including human embryonic kidney cells (HEK293) and human cervical cancer cells (HeLa). Aside from its use in gene delivery, chitosan possesses a range of properties that show promise in tissue engineering applications; it is biodegradable, biocompatible, has anti-bacterial activity, and, its cationic nature allows for electrostatic interaction with glycosaminoglycans and other proteoglycans. It can be used to make nano- and microparticles, sponges, gels, membranes and porous scaffolds. Chitosan has also been shown to enhance mineral deposition during osteogenic differentiation of MSCs in vitro. The purpose of this review is to critically discuss the use of chitosan as a gene delivery vector with emphasis on its application in orthopedic tissue engineering.

Chondrogenic differentiation of amniotic fluid stem cells and their potential for regenerative therapy

Chronic articular cartilage defects are the most common disabling conditions of humans in the western world. The incidence for cartilage defects is increasing with age and the most prominent risk factors are overweight and sports associated overloading. Damage of articular cartilage frequently leads to osteoarthritis due to the aneural and avascular nature of articular cartilage, which impairs regeneration and repair. Hence, patients affected by cartilage defects will benefit from a cell-based transplantation strategy. Autologous chondrocytes, mesenchymal stem cells and embryonic stem cells are suitable donor cells for regeneration approaches and most recently the discovery of amniotic fluid stem cells has opened a plethora of new therapeutic options. It is the aim of this review to summarize recent advances in the use of amniotic fluid stem cells as novel cell sources for the treatment of articular cartilage defects. Molecular aspects of articular cartilage formation as well as degeneration are summarized and the role of growth factor triggered signaling pathways, scaffolds, hypoxia and autophagy during the process of chondrogenic differentiation are discussed.

Anti-inflammatory role and immunomodulation of mesenchymal stem cells in systemic joint diseases: potential for treatment

INTRODUCTION

Mesenchymal stem cells (MSCs) are multipotent stromal cells characterized by their ability to differentiate into adipocytes, chondrocytes, osteocytes and a number of other lineages. Investigation into their use has increased in recent years as characterization of their immunomodulatory properties has developed, and their role in the pathophysiology of joint disease has been suggested.

AREAS COVERED

MSCs demonstrate immunosuppressive functionality by suppressing T- and B-cell responses following activation by cytokines such as IL-6 and IL-1α. They also can be induced to exert pro-inflammatory effects in the presence of acute inflammatory environment due to the actions of TNF-α and IFN-γ. In inflammatory joint diseases such as rheumatoid arthritis, MSCs in bone marrow migrate to joints by a TNF-α-dependent mechanism and may be in part responsible for the disease process. MSCs have also been demonstrated in increased numbers in periarticular tissues in osteoarthritis, which may reflect an attempt at joint regeneration.

EXPERT OPINION

Clinical applications for MSCs have shown promise in a number of inflammatory and autoimmune disorders. Future work is likely to further reveal the immunosuppressive characteristics of MSCs, their role in the pathophysiology of joint diseases and provide the basis for new avenues for treatment.

Cell sources for the regeneration of articular cartilage: the past, the horizon and the future

Avascular, aneural articular cartilage has a low capacity for self-repair and as a consequence is highly susceptible to degradative diseases such as osteoarthritis. Thus the development of cell-based therapies that repair focal defects in otherwise healthy articular cartilage is an important research target, aiming both to delay the onset of degradative diseases and to decrease the need for joint replacement surgery. This review will discuss the cell sources which are currently being investigated for the generation of chondrogenic cells. Autologous chondrocyte implantation using chondrocytes expanded ex vivo was the first chondrogenic cellular therapy to be used clinically. However, limitations in expansion potential have led to the investigation of adult mesenchymal stem cells as an alternative cell source and these therapies are beginning to enter clinical trials. The chondrogenic potential of human embryonic stem cells will also be discussed as a developmentally relevant cell source, which has the potential to generate chondrocytes with phenotype closer to that of articular cartilage. The clinical application of these chondrogenic cells is much further away as protocols and tissue engineering strategies require additional optimization. The efficacy of these cell types in the regeneration of articular cartilage tissue that is capable of withstanding biomechanical loading will be evaluated according to the developing regulatory framework to determine the most appropriate cellular therapy for adoption across an expanding patient population.

Translational research and therapeutic applications of stem cell transplantation in periodontal regenerative medicine

Stem cells have received a great deal of interest from the research community as potential therapeutic "tools" for a variety of chronic debilitating diseases that lack clinically effective therapies. Stem cells are also of interest for the regeneration of tooth-supporting tissues that have been lost to periodontal disease. Indeed, substantial data have demonstrated that the exogenous administration of stem cells or their derivatives in preclinical animal models of periodontal defects can restore damaged tissues to their original form and function. As we discuss here, however, considerable hurdles must be overcome before these findings can be responsibly translated to novel clinical therapies. Generally, the application of stem cells for periodontal therapy in clinics will not be realized until the best cell(s) to use, the optimal dose, and an effective mode of administration are identified. In particular, we need to better understand the mechanisms of action of stem cells after transplantation in the periodontium and to learn how to preciously control stem cell fates in the pathological environment around a tooth. From a translational perspective, we outline the challenges that may vary across preclinical models for the evaluation of stem cell therapy in situations that require periodontal reconstruction and the safety issues that are related to clinical applications of human stem cells. Although clinical trials that use autologous periodontal ligament stem cells have been approved and have already been initiated, proper consideration of the technical, safety, and regulatory concerns may facilitate, rather than inhibit, the clinical translation of new therapies.

Orthopaedic applications of nanoparticle-based stem cell therapies

Stem cells have tremendous applications in the field of regenerative medicine and tissue engineering. These are pioneering fields that aim to create new treatments for disease that currently have limited therapies or cures. A particularly popular avenue of research has been the regeneration of bone and cartilage to combat various orthopaedic diseases. Magnetic nanoparticles (MNPs) have been applied to aid the development and translation of these therapies from research to the clinic. This review highlights contemporary research for the applications of iron-oxide-based MNPs for the therapeutic implementation of stem cells in orthopaedics. These MNPs comprise of an iron oxide core, coated with a choice of biological polymers that can facilitate the uptake of MNPs by cells through improving endocytic activity. The combined use of these oxides and the biological polymer coatings meet biological requirements, effectively encouraging the use of MNPs in regenerative medicine. The association of MNPs with stem cells can be achieved via the process of endocytosis resulting in the internalisation of these particles or the attachment to cell surface receptors. This allows for the investigation of migratory patterns through various tracking studies, the targeting of particle-labelled cells to desired locations via the application of an external magnetic field and, finally, for activation stem cells to initiate various cellular responses to induce the differentiation. Characterisation of cell localisation and associated tissue regeneration can therefore be enhanced, particularly for in vivo applications. MNPs have been shown to have the potential to stimulate differentiation of stem cells for orthopaedic applications, without limiting proliferation. However, careful consideration of the use of active agents associated with the MNP is suggested, for differentiation towards specific lineages. This review aims to broaden the knowledge of current applications, paving the way to translate the in vitro and in vivo work into further orthopaedic clinical studies.