Cell therapy for the treatment of tendinopathy – A systematic review on the pre-clinical and clinical evidence

Cerium oxide nanoparticles-carrying human umbilical cord mesenchymal stem cells counteract oxidative damage and facilitate tendon regeneration

BACKGROUND

Tendon injuries have a high incidence and limited treatment options. Stem cell transplantation is essential for several medical conditions like tendon injuries. However, high local concentrations of reactive oxygen species (ROS) inhibit the activity of transplanted stem cells and hinder tendon repair. Cerium oxide nanoparticles (CeONPs) have emerged as antioxidant agents with reproducible reducibility.

RESULTS

In this study, we synthesized polyethylene glycol-packed CeONPs (PEG-CeONPs), which were loaded into the human umbilical cord mesenchymal stem cells (hUCMSCs) to counteract oxidative damage. H2O2 treatment was performed to evaluate the ROS scavenging ability of PEG-CeONPs in hUCMSCs. A rat model of patellar tendon defect was established to assess the effect of PEG-CeONPs-carrying hUCMSCs in vivo. The results showed that PEG-CeONPs exhibited excellent antioxidant activity both inside and outside the hUCMSCs. PEG-CeONPs protect hUCMSCs from senescence and apoptosis under excessive oxidative stress. Transplantation of hUCMSCs loaded with PEG-CeONPs reduced ROS levels in the tendon injury area and facilitated tendon healing. Mechanistically, NFκB activator tumor necrosis factor α and MAPK activator dehydrocrenatine, reversed the therapeutic effect of PEG-CeONPs in hUCMSCs, indicating that PEG-CeONPs act by inhibiting the NFκB and MAPK signaling pathways.

CONCLUSIONS

The carriage of the metal antioxidant oxidase PEG-CeONPs maintained the ability of hUCMSCs in the injured area, reduced the ROS levels in the microenvironment, and facilitated tendon regeneration. The data presented herein provide a novel therapeutic strategy for tendon healing and new insights into the use of stem cells for disease treatment.

Wetspun Polymeric Fibrous Systems as Potential Scaffolds for Tendon and Ligament Repair, Healing and Regeneration

Tendon and ligament traumatic injuries are among the most common diagnosed musculoskeletal problems. Such injuries limit joint mobility, reduce musculoskeletal performance, and most importantly, lower people's comfort. Currently, there are various treatments that are used to treat this type of injury, from surgical to conservative treatments. However, they're not entirely effective, as reinjures are frequent and, in some cases, fail to re-establish the lost functionality. Tissue engineering (TE) approaches aim to overcome these disadvantages by stimulating the regeneration and formation of artificial structures that resemble the original tissue. Fabrication and design of artificial fibrous scaffolds with tailored mechanical properties are crucial for restoring the mechanical function of the tissues. Recently, polymeric nanofibers produced by wetspinning have been largely investigated to mimic, repair, and replace the damaged tissue. Wetspun fibrous structures are extensively used due to their exceptional properties, such as the ability to mimic the native tissue, their biodegradability and biocompatibility, and good mechanical properties. In this review, the tendon and ligament structure and biomechanics are presented. Then, promising wetspun multifunctional fibrous structures based on biopolymers, more specifically polyhydroxyalkanoates (PHA), polycaprolactone (PCL), and polyethylenes, will be discussed, as well as reinforcing agents such as cellulose nanocrystals (CNC), nanoparticles, and growth factors.

Cell therapy efficacy and safety in treating tendon disorders: a systemic review of clinical studies

Purpose

Despite substantial animal evidence, cell therapy in humans remains in its infancy. The purpose of this study was to examine the potential therapeutic effects and safety of cell therapy in the treatment of tendon disorders.

Methods

According to the PRISMA guideline, a systematic review was performed on clinical studies concerning cell therapy in tendon disorders. A comprehensive search including the 5 databases of MEDLINE, Embase, Scopus, Web of Science, and Cochrane Library until December 2021 was carried out and associated with hand searching. The quality of the eligible studies was assessed using the tools suggested by Cochrane recommendations. Qualitative synthesis was performed in 2 tables and discussed separately for rotator cuff, elbow, patella, Achilles, and gluteal tendons.

Results

Through 6017 records, 22 studies were included in the qualitative synthesis, including 658 patients. All the studies administered autologous cells, except one that used allogenic adipose-derived mesenchymal stem cells (Allogenic AD-MSC). Almost all studies demonstrated the safety of cell injection in their follow-up period with no serious side effects or immunologic reactions, with only a few related minor adverse events in some cases.

The included studies showed the effectiveness of cell injection in tendinopathies of different sites, rotator cuff, elbow, patella, Achilles, and gluteal tendons. Among the rotator cuff studies, 4 comparative studies claimed that cell therapy is a more efficient treatment with a lower retear rate and pain level compared to the control group. However, one study found no differences between the groups. No controlled study has been performed on elbow tendinopathies, but 5 case series demonstrated the effectiveness of cell injection in elbow tendon disorders. For Achilles tendinopathies, only one randomized controlled trial (RCT) found that both cell therapy and control groups showed significant pain reduction and functional improvement with no statistical differences at the 6 months follow-up, but the cell therapy group had improved faster at earlier follow-ups. Patellar tendinopathy was studied in 2 RCTs, one did not show a significant difference and the other showed superior improvement compared to controls.

Conclusion

Cell therapy showed promising results and the available evidence suggests that it is safe at several sites of tendon disease. Based on available evidence, cell therapy should be suggested in specific conditions at each site. To approve cell therapy for tendon diseases, randomized clinical trials are required with a large sample size and long-term follow-ups.

Level of evidence

IV

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00520-9.

Tendon tissue engineering: Cells, growth factors, scaffolds and production techniques

Tendon injuries are a global health problem that affects millions of people annually. The properties of tendons make their natural rehabilitation a very complex and long-lasting process. Thanks to the development of the fields of biomaterials, bioengineering and cell biology, a new discipline has emerged, tissue engineering. Within this discipline, diverse approaches have been proposed. The obtained results turn out to be promising, as increasingly more complex and natural tendon-like structures are obtained. In this review, the nature of the tendon and the conventional treatments that have been applied so far are underlined. Then, a comparison between the different tendon tissue engineering approaches that have been proposed to date is made, focusing on each of the elements necessary to obtain the structures that allow adequate regeneration of the tendon: growth factors, cells, scaffolds and techniques for scaffold development. The analysis of all these aspects allows understanding, in a global way, the effect that each element used in the regeneration of the tendon has and, thus, clarify the possible future approaches by making new combinations of materials, designs, cells and bioactive molecules to achieve a personalized regeneration of a functional tendon.

The Effect of L-Ascorbic Acid and Serum Reduction on Tenogenic Differentiation of Human Mesenchymal Stromal Cells

Background and Objectives

Despite significant improvement in the treatment of tendon injuries, the full tissue recovery is often not possible because of its limited ability to auto-repair. The transplantation of mesenchymal stromal cells (MSCs) is considered as a novel approach in the treatment of tendinopathies. The question about the optimal culture conditions remains open. In this study we aimed to investigate if serum reduction, L-ascorbic acid supplementation or a combination of both factors can induce tenogenic differentiation of human adipose-derived MSCs (ASCs).

Methods and Results

Human ASCs from 3 healthy donors were used in the study. The tested conditions were: 0.5 mM of ascorbic acid 2-phosphate (AA-2P), reduced serum content (2% FBS) or combination of these two factors. The combination of AA-2P and 2% FBS was the only experimental condition that caused a significant increase of the expression of all analyzed genes related to tenogenesis (SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3, DECORIN) in comparison to the untreated control (evaluated by RT-PCR, 5^th day of experiment). Moreover, this treatment significantly increased the synthesis of SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3 proteins at the same time point (evaluated by Western blot method). Double immunocytochemical staining revealed that AA-2P significantly increased the extracellular deposition of both types of collagens. Semi-quantitative Electron Spin Resonance analysis of ascorbyl free radical revealed that AA-2P do not induce harmful transition metals-driven redox reactions in cell culture media.

Conclusions

Obtained results justify the use of reduced content of serum with the addition of 0.5 mM of AA-2P in tenogenic inducing media.

Orthobiologics for the Hip Region: A Narrative Review

Management of hip region disorders is challenging. Orthobiologic treatments including platelet rich plasma (PRP), mesenchymal stem cells, and amniotic injectables have gained popularity as promising treatments despite a lack of robust evidence for their effectiveness. We review rationale and current evidence for orthobiologics for three common hip region conditions: hip osteoarthritis, gluteal tendinopathy, and proximal hamstring tendinopathy. Overall, the current state of evidence is extremely limited for orthobiologic treatments and is predominantly relevant to PRP injections. There is currently a lack of data to support the use of mesenchymal stem cells or amniotic injectables in these conditions of the hip.

Tendinopathy in diabetes mellitus patients-Epidemiology, pathogenesis, and management

Chronic tendinopathy is a frequent and disabling musculo-skeletal problem affecting the athletic and general populations. The affected tendon is presented with local tenderness, swelling, and pain which restrict the activity of the individual. Tendon degeneration reduces the mechanical strength and predisposes it to rupture. The pathogenic mechanisms of chronic tendinopathy are not fully understood and several major non-mutually exclusive hypotheses including activation of the hypoxia-apoptosis-pro-inflammatory cytokines cascade, neurovascular ingrowth, increased production of neuromediators, and erroneous stem cell differentiation have been proposed. Many intrinsic and extrinsic risk/causative factors can predispose to the development of tendinopathy. Among them, diabetes mellitus is an important risk/causative factor. This review aims to appraise the current literature on the epidemiology and pathology of tendinopathy in diabetic patients. Systematic reviews were done to summarize the literature on (a) the association between diabetes mellitus and tendinopathy/tendon tears, (b) the pathological changes in tendon under diabetic or hyperglycemic conditions, and (c) the effects of diabetes mellitus or hyperglycemia on the outcomes of tendon healing. The potential mechanisms of diabetes mellitus in causing and exacerbating tendinopathy with reference to the major non-mutually exclusive hypotheses of the pathogenic mechanisms of chronic tendinopathy as reported in the literature are also discussed. Potential strategies for the management of tendinopathy in diabetic patients are presented.

No evidence for the use of stem cell therapy for tendon disorders: a systematic review

INTRODUCTION

Stem cells have emerged as a new treatment option for tendon disorders. We systematically reviewed the current evidence for stem cell therapy in tendon disorders.

METHODS

Randomised and non-randomised controlled trials, cohort studies and case series with a minimum of 5 cases were searched in MEDLINE, CENTRAL, EMBASE, CINAHL, PEDro and SPORTDiscus. In addition, we searched grey literature databases and trial registers. Only human studies were included and no time or language restrictions were applied to our search. All references of included trials were checked for possibly eligible trials. Risk of bias assessment was performed using the Cochrane risk of bias tool for controlled trials and the Newcastle-Ottawa scale for case series. Levels of evidence were assigned according to the Oxford levels of evidence.

RESULTS

4 published and three unpublished/pending trials were found with a total of 79 patients. No unpublished data were available. Two trials evaluated bone marrow-derived stem cells in rotator cuff repair surgery and found lower retear rates compared with historical controls or the literature. One trial used allogenic adipose-derived stem cells to treat lateral epicondylar tendinopathy. Improved Mayo Elbow Performance Index, Visual Analogue Pain scale and ultrasound findings after 1-year follow-up compared with baseline were found. Bone marrow-derived stem cell-treated patellar tendinopathy showed improved International Knee Documentation Committee, Knee injury and Osteoarthritis Outcome Score subscales and Tegner scores after 5-year follow-up. One trial reported adverse events and found them to be mild (eg, swelling, effusion). All trials were at high risk of bias and only level 4 evidence was available.

CONCLUSIONS

No evidence (level 4) was found for the therapeutic use of stem cells for tendon disorders. The use of stem cell therapy for tendon disorders in clinical practice is currently not advised.

Retinoic acid receptor signaling preserves tendon stem cell characteristics and prevents spontaneous differentiation in vitrox

Background

Previous studies have reported that adult mesenchymal stem cells (MSCs) tend to gradually lose their stem cell characteristics in vitro when placed outside their niche environment. They subsequently undergo spontaneous differentiation towards mesenchymal lineages after only a few passages. We observed a similar phenomenon with adult tendon stem cells (TSCs) where expression of key tendon genes such as Scleraxis (Scx), are being repressed with time in culture. We hypothesized that an environment able to restore or maintain Scleraxis expression could be of therapeutic interest for in vitro use and tendon cell-based therapies.

Methods

TSCs were isolated from human cadaveric Achilles tendon and expanded for 4 passages. A high content imaging assay that monitored the induction of Scx protein nuclear localization was used to screen ~1000 known drugs.

Results

We identified retinoic acid receptor (RAR) agonists as potent inducers of nuclear Scx in the small molecule screen. The upregulation correlated with improved maintenance of tendon stem cell properties through inhibition of spontaneous differentiation rather than the anticipated induction of tenogenic differentiation. Our results suggest that histone epigenetic modifications by RAR are driving this effect which is not likely only dependent on Scleraxis nuclear binding but also mediated through other key genes involved in stem cell self-renewal and differentiation. Furthermore, we demonstrate that the effect of RAR compounds on TSCs is reversible by revealing their multi-lineage differentiation ability upon withdrawal of the compound.

Conclusion

Based on these findings, RAR agonists could provide a valid approach for maintaining TSC stemness during expansion in vitro, thus improving their regenerative potential for cell-based therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0306-3) contains supplementary material, which is available to authorized users.

A practical guide for the isolation and maintenance of stem cells from tendon

Stem cells are unspecialized cells that can self-renew and have the ability to develop into cells of highly specialized functions. The study of stem cells holds enormous promise in the medical field ranging from their uses in cell therapies to their uses for greater understanding of tissue development and disease pathologies. Stem cells have been isolated from tendon tissue recently. These tendon-derived stem cells (TDSCs) are particularly relevant for tendon repair and the study of the potential roles of stem cells in tendon pathology as they are isolated from tendon tissues. This paper aims to describe the step-by-step protocol and the practical tips for the isolation and verification of stem cell characteristics of TDSCs. The cell seeding density and hence cell-cell contact has a significant impact on the isolation and expansion of TDSCs. Hence, I also describe our established protocol for the determination of the optimal seeding density for TDSC isolation and culture.

Restricted differentiation potential of progenitor cell populations obtained from the equine superficial digital flexor tendon (SDFT)

The aim of this study was to characterize stem and progenitor cell populations from the equine superficial digital flexor tendon, an energy-storing tendon with similarities to the human Achilles tendon, which is frequently injured. Using published methods for the isolation of tendon-derived stem/progenitor cells by low-density plating we found that isolated cells possessed clonogenicity but were unable to fully differentiate towards mesenchymal lineages using trilineage differentiation assays. In particular, adipogenic differentiation appeared to be restricted, as assessed by Oil Red O staining of stem/progenitor cells cultured in adipogenic medium. We then assessed whether differential adhesion to fibronectin substrates could be used to isolate a population of cells with broader differentiation potential. However we found little difference in the stem and tenogenic gene expression profile of these cells as compared to tenocytes, although the expression of thrombospondin-4 was significantly reduced in hypoxic conditions. Tendon-derived stem/progenitor cells isolated by differential adhesion to fibronectin had a similar differentiation potential to cells isolated by low density plating, and when grown in either normoxic or hypoxic conditions. In summary, we have found a restricted differentiation potential of cells isolated from the equine superficial digital flexor tendon despite evidence for stem/progenitor-like characteristics.

Assessment of stem cell carriers for tendon tissue engineering in pre-clinical models

Tendon injuries are prevalent and problematic, especially among young and otherwise healthy individuals. The inherently slow innate healing process combined with the inevitable scar tissue formation compromise functional recovery, imposing the need for the development of therapeutic strategies. The limited number of low activity/reparative capacity tendon-resident cells has directed substantial research efforts towards the exploration of the therapeutic potential of various stem cells in tendon injuries and pathophysiologies. Severe injuries require the use of a stem cell carrier to enable cell localisation at the defect site. The present study describes advancements that injectable carriers, tissue grafts, anisotropically orientated biomaterials, and cell-sheets have achieved in preclinical models as stem cell carriers for tendon repair.

Progress in cell-based therapies for tendon repair

The last decade has seen significant developments in cell therapies, based on permanently differentiated, reprogrammed or engineered stem cells, for tendon injuries and degenerative conditions. In vitro studies assess the influence of biophysical, biochemical and biological signals on tenogenic phenotype maintenance and/or differentiation towards tenogenic lineage. However, the ideal culture environment has yet to be identified due to the lack of standardised experimental setup and readout system. Bone marrow mesenchymal stem cells and tenocytes/dermal fibroblasts appear to be the cell populations of choice for clinical translation in equine and human patients respectively based on circumstantial, rather than on hard evidence. Collaborative, inter- and multi-disciplinary efforts are expected to provide clinically relevant and commercially viable cell-based therapies for tendon repair and regeneration in the years to come.

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

Viability of equine mesenchymal stem cells during transport and implantation

INTRODUCTION

Autologous mesenchymal stem cell (MSC) injection into naturally-occurring equine tendon injuries has been shown to be safe and efficacious and protocols inform translation of the technique into humans. Efficient transfer of cells from the laboratory into tissue requires well-validated transport and implantation techniques.

METHODS

Cell viability in a range of media was determined over 72 hours and after injection through a 19G, 21G or 23G needle. Viability, proliferation and apoptosis were analysed using TrypanBlue, alamarBlue® and AnnexinV assays.

RESULTS

Cell viability was similar in all re-suspension media following 24 hour storage, however cell death was most rapid in bone marrow aspirate, platelet-rich plasma and serum after longer storage. Cryogenic media exhibited greatest viability regardless of storage time. Cell proliferation after 24 and 72 hour storage was similar for all media, except after 24 hours in serum wherein proliferation was enhanced. MSC tri-lineage differentiation and viability did not significantly change when extruded through 19G, 21G or 23G needles, but 21G and 23G needles significantly increased apoptotic cells compared to 19G and non-injected controls. All gauges induced a decrease in metabolic activity immediately post-injection but cells recovered by 2 hours.

CONCLUSIONS

These data indicate storage and injection influence viability and subsequent cell behaviour and provide recommendations for MSC therapy that implantation of cells should occur within 24 hours of recovery from culture, using larger needle bores.

Repairing damaged tendon and muscle: are mesenchymal stem cells and scaffolds the answer?

Mesenchymal stem cells (MSCs) have become an area of intense interest in the treatment of musculoskeletal conditions, such as muscle and tendon injury, as various animal and human trials have demonstrated that implantation with MSCs leads to improved healing and function. However, these trials have usually been relatively small scale and lacking in adequate controls. Additionally, the optimum source of these cells has yet to be determined, partly due to a lack of understanding as to how MSCs produce their beneficial effects when implanted. Scaffolds have been shown to improve tissue-engineering repairs but require further work to optimize their interactions with both native tissue and implanted MSCs. Robust, well-controlled trials are therefore required to determine the usefulness of MSCs in musculoskeletal tissue repair.