Clinical Trials with Mesenchymal Stem Cell Therapies for Osteoarthritis: Challenges in the Regeneration of Articular Cartilage

Optimizing bone marrow harvesting sites for enhanced mesenchymal stem cell yield and efficacy in knee osteoarthritis treatment

Knee osteoarthritis (OA) is a debilitating condition with limited long-term treatment options. The therapeutic potential of mesenchymal stem cells (MSCs), particularly those derived from bone marrow aspirate concentrate, has garnered attention for cartilage repair in OA. While the iliac crest is the traditional site for bone marrow harvesting (BMH), associated morbidity has prompted the exploration of alternative sites such as the proximal tibia, distal femur, and proximal humerus. This paper reviews the impact of different harvesting sites on mesenchymal stem cell (MSC) yield, viability, and regenerative potential, emphasizing their relevance in knee OA treatment. The iliac crest consistently offers the highest MSC yield, but alternative sites within the surgical field of knee procedures offer comparable MSC characteristics with reduced morbidity. The integration of harvesting techniques into existing knee surgeries, such as total knee arthroplasty, provides a less invasive approach while maintaining therapeutic efficacy. However, variability in MSC yield from these alternative sites underscores the need for further research to standardize techniques and optimize clinical outcomes. Future directions include large-scale comparative studies, advanced characterization of MSCs, and the development of personalized harvesting strategies. Ultimately, the findings suggest that optimizing the site of BMH can significantly influence the quality of MSC-based therapies for knee OA, enhancing their clinical utility and patient outcomes.

Cathepsin K Inhibitors as Potential Drugs for the Treatment of Osteoarthritis

Links between cathepsin K and the pathophysiology of osteoarthritis (OA) can be established, not least because of the overabundance of cathepsin K in the serum of OA patients and the upregulation of cathepsin K in degraded cartilage in animal models of OA. Chondrocytes, chondroclasts, or osteoclasts contribute to the accumulated cathepsin K at the diseased osteochondral junction. After a general presentation of OA and cartilage physiology, as well as its degradation processes, we describe the function of cathepsin K and its effect on cartilage degradation via type II collagen cleavage. An overview of the most promising cathepsin K inhibitors is then presented, together with their in vitro effects. Although intensive research on cathepsin K inhibitors initially focused on bone resorption, there is growing interest in the potential of these drugs to prevent cartilage degradation. In this review, we summarize the pre-clinical and clinical trials that support the use of cathepsin K inhibitors in the treatment of OA. To date, no molecules of this type are commercially available, although a few have undergone clinical trials, but we believe that the development of cathepsin K inhibitors could broaden the therapeutic arsenal for the treatment of OA.

Inhibition of TGF-β signaling enhances osteogenic potential of iPSC-derived MSCs

Mesenchymal stem cells (MSCs) represent the most commonly utilized type of stem cell in clinical applications. However, variability in quality and quantity between different tissue sources and donors presents a significant challenge to their use. Induced pluripotent stem cells (iPSCs) are a promising and abundant alternative source of MSCs, offering a potential solution to the limitations of adult MSCs. Nevertheless, a standardized protocol for the differentiation of iPSCs into iPSC-derived mesenchymal stem cells (iMSCs) has yet to be established, as the existing methods vary significantly in terms of complexity, duration, and outcome. Many straightforward methods induce differentiation by culturing iPSCs in MSC media which are supplemented with fetal bovine serum (FBS) or human platelet lysate (hPL), followed by selection of MSC-like cells by passaging. However, in our hands, this approach yielded inconsistent quality of iMSCs, particularly in terms of osteogenic potential and premature senescence. This study examines the impact of the selective TGF-β inhibitor SB431542 on iMSC differentiation, demonstrating that TGF-β inhibition enhances osteogenic potential and reduces premature senescence. Additionally, we present a reliable, xeno-free method for producing high-quality iMSCs that can be adapted for Good Manufacturing Practice (GMP) compliance, thus enhancing the potential for clinical applications.

Efficacy of a single dose of cryopreserved human umbilical cord mesenchymal stromal cells for the treatment of knee osteoarthritis:a randomized, controlled, double-blind pilot study

BACKGROUND

Knee osteoarthritis (OA) is the most prevalent degenerative musculoskeletal disorder, which is particularly common in older population. While conventional treatments have limited effectiveness, the development of more effective therapeutic strategies is necessary to address this primary source of pain and disability. Umbilical cord mesenchymal stromal cells (UC-MSCs) offer a promising therapeutic approach for treating knee OA.

AIM

This randomized, prospective, double-blind and controlled pilot study was carried out to evaluate and compare the safety and therapeutic efficacy of a single intra-articular injection of a standardized product CellistemOA (5 × 106 ± 5 × 105 UC-MSCs), vs. triamcinolone (a synthetic corticosteroid) (10 mg/mL) in thirty patients with symptomatic knee OA (Kellgren-Lawrence grade II or III).

METHODS

The outcomes included changes in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores based on a Likert scale, numerical rating score (NRS) for pain, Magnetic Resonance Imaging (MRI), and quality of life (SF-36 questionnaire), from baseline and throughout 12-months of follow-up.

RESULTS

Patients treated with CellistemOA showed significant improvement in WOMAC score (including the three subscale scores (pain, stiffness and function), NRS in pain, and SF-36 profile from baseline to 12 months (p < 0.05) compared to the triamcinolone group, and no severe adverse events were reported. There were no significant differences in MRI WORMS scores between the two groups. However, patients who received the cellular treatment experienced a significant improvement in their SF-36 profile (p < 0.05).

CONCLUSIONS

This pilot study revealed that a single dose of CellistemOA is safe and superior to the active comparator in knee OA at 1-year of follow-up, making it a compelling therapeutic alternative to treat symptomatic OA patients.

Subchondral Cellular Density Decreases with Increasing Grade of Cartilage Degeneration in Knee Osteoarthritis - An Ex vivo Histopathological Analysis

Introduction

Subchondral milieu has been the region of interest in recent clinical trials demonstrating it as an effective treatment focus in knee osteoarthritis (OA). However, a systematic analysis of the subchondral cell population density is lacking in knee OA. Hence, this study aims to analyze the cell population density of the subchondral zone for every stage of cartilage degeneration to analyze the rationale behind this evolving treatment method for knee OA.

Materials and Methods

This is an ex vivo histopathological analysis of the distal femur and proximal tibia articular specimens from the patients undergoing total knee replacement for primary knee OA between November 2023 and March 2024. Two pathologists independently graded and analyzed the subchondral cell density based on the International Cartilage Repair Society cartilage injury grading system.

Results

We noted a significant association between the grade of cartilage degeneration and the subchondral cell density (r = 0.831, P < 0.001). We noted a statistically significant decrease in the cell density for every stage of cartilage injury compared to the control (P < 0.001). We also noted a significant decrease in cell density between the early and late stages of cartilage degeneration (P < 0.001). We did not note any significant difference in the cell density between the tibial and femoral articular cartilage for every grade of cartilage degeneration analyzed (P = 0.432).

Conclusion

Subchondral cell density decreases significantly with increasing grade of degeneration in knee OA. Subchondral milieu warrants attention to be considered as a potential treatment focus that could alter the disease progression in knee OA.

Substitution of liposomal bupivacaine for lidocaine reduces incidence of injection-emergent adverse events after intraarticular therapies for knee osteoarthritis: a prospective cohort study

BACKGROUND

Local anesthetics as a part of intraarticular therapies (IATs) are widely used for treating knee osteoarthritis (KOA). Whether the substitution of liposomal bupivacaine (LB) for lidocaine is safe and effective in reducing the incidence of injection-emergent adverse events (AEs) after IATs remains unclear.

METHODS

We recruited outpatients who had a clinical diagnosis of KOA and decided to receive IATs from November 2023 to April 2024. The type of IATs (glucocorticoids, platelet-rich plasma, and hyaluronic acid) for each participant was decided by the preference of patients after consulting with his or her treating physicians. Using lidocaine or LB as local anesthetics was determined by enrollment timing due to considerations of safety. The primary outcome was injection-emergent AEs after IATs. Secondary outcome measures included the Visual Analog Scale (VAS) pain scores and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale score.

RESULTS

In this study, 123 and 103 patients, respectively, received lidocaine and LB according to their enrollment date. Compared with lidocaine, using LB yielded a reduced incidence of AEs in the overall 2 weeks (LB vs. lidocaine, 30.1% vs. 45.5%, P = 0.018) and week 1 (LB vs. lidocaine, 23.3% vs. 39.8%, P = 0.008). After adjusting for sex, baseline body mass index, age, baseline WOMAC pain subscale score, and K-L grade, the substitution of LB for lidocaine was significantly associated with the reduced incidence of AEs in 2 weeks (OR, 0.484; 95% CI, 0.274-0.853; P = 0.012). In the initial 3 days, the LB groups reported better outcomes in terms of VAS pain score (change from baseline of VAS pain, LB vs. lidocaine, day 1 -8.3 ± 8.9 vs. -1.9 ± 9.3, P < 0.001; day 2 -20.6 ± 16.1 vs. -13.7 ± 19.4, P = 0.005; day 3 -22.3 ± 18.5 vs. -16.3 ± 19.3, P = 0.020). The changes from the baseline of the WOMAC pain subscale at day 14 were similar between the two groups (LB vs. lidocaine, -32.2 ± 11.7 vs. -29.4 ± 11.3, P = 0.073).

CONCLUSION

With the substitution of LB for lidocaine, patients might have reported reduced incidence of AEs, mainly derived from the superiority in week 1. The substitution of LB for lidocaine was safe in different scenarios of IATs, and future randomized clinical trials were warranted by the current study.

Efficiently directing differentiation and homing of mesenchymal stem cells to boost cartilage repair in osteoarthritis via a nanoparticle and peptide dual-engineering strategy

Mesenchymal stem cells (MSCs) are expected to be useful therapeutics in osteoarthritis (OA), the most common joint disorder characterized by cartilage degradation. However, evidence is limited with regard to cartilage repair in clinical trials because of the uncontrolled differentiation and weak cartilage-targeting ability of MSCs after injection. To overcome these drawbacks, here we synthesized CuO@MSN nanoparticles (NPs) to deliver Sox9 plasmid DNA (favoring chondrogenesis) and recombinant protein Bmp7 (inhibiting hypertrophy). After taking up CuO@MSN/Sox9/Bmp7 (CSB NPs), the expressions of chondrogenic markers were enhanced while hypertrophic markers were decreased in response to these CSB-engineered MSCs. Moreover, a cartilage-targeted peptide (designated as peptide W) was conjugated onto the surface of MSCs via a click chemistry reaction, thereby prolonging the residence time of MSCs in both the knee joint cavity of mice and human-derived cartilage. In a surgery-induced OA mouse model, the NP and peptide dual-modified W-CSB-MSCs showed an enhancing therapeutic effect on cartilage repair in knee joints compared with other engineered MSCs after intra-articular injection. Most importantly, W-CSB-MSCs accelerated cartilage regeneration in damaged cartilage explants derived from OA patients. Thus, this new peptide and NPs dual engineering strategy shows potential for clinical applications to boost cartilage repair in OA using MSC therapy.

Intra-Articular Injection of Human Bone Marrow-Derived Mesenchymal Stem Cells in Knee Osteoarthritis: A Randomized, Double-Blind, Controlled Trial

To assess the impact of a single intra-articular (IA) injection of bone marrow-derived mesenchymal stem cells (BM-MSCs) in patients with knee osteoarthritis (OA), a randomized, double-blind, placebo-controlled study was conducted. The study included 24 patients with knee OA who were randomly assigned to receive either a single IA injection of BM-MSCs or normal saline. Changes in the visual analog scale (VAS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Injury and Osteoarthritis Outcome Score (KOOS) after IA injection were assessed at 3, 6, 9, and 12 months. Magnetic resonance imaging (MRI) with T2 mapping sequences was conducted for knee cartilage assessment at baseline and at 3 and 12 months. The MSC group showed between-group improvement in WOMAC (-5.0 ± 3.6 vs. -0.1 ± 5.5, P = 0.02) and KOOS (23.9 ± 18.3 vs. 7.2 ± 15.9, P = 0.028) scores at 9 months compared with the control group. The MSC group exhibited a less sharp increase in the mean T2 value of the medial compartment than the control group at 12 months, with no serious adverse events observed during follow-up. A single IA injection of allogeneic BM-MSCs provided satisfactory pain relief for patients with knee OA compared with the control group at 9 months. Quantitative T2 MRI mapping of the cartilage showed that IA BM-MSCs could have a preventive effect on OA progression for 12 months. Our findings suggest the potential of allogeneic BM-MSCs IA injection as a pain-relieving and disease-modifying treatment for patients with knee OA in the outpatient setting.

Advancements in the treatment of osteochondral lesions of the talus

Osteochondral lesions of the talus (OLT) are common ankle joint pathologies, often caused by traumatic or non-traumatic factors. Due to the anatomical characteristics and limited blood supply of the talus, the spontaneous healing capacity of OLT is poor, posing challenges for clinical treatment. Traditional treatments include conservative therapy and surgical interventions, but their efficacy is limited. In recent years, significant advancements in OLT treatment have been achieved with developments in biomaterials science, cell biology, and tissue engineering. This article summarizes the latest research progress in various treatment methods, including conservative treatment, bone marrow stimulation, chondrocyte transplantation, and osteochondral grafting, and evaluates the role of biological augmentation agents such as platelet-rich plasma (PRP) and concentrated bone marrow aspirate (CBMA) in promoting cartilage repair. Additionally, the application of biological scaffold technology offers new prospects for cartilage regeneration. Although emerging therapies show potential in clinical practice, further research is needed to evaluate their long-term efficacy, indications, and safety. This article aims to provide valuable references for clinicians, researchers, and policymakers, promoting the development and refinement of OLT treatment strategies.

A comprehensive review of phase 2/3 trials in osteoarthritis: an expert opinion

INTRODUCTION

Osteoarthritis (OA) is a chronic, degenerative, and debilitating disease associated with significant long-term morbidity and disability. The pathogenesis of OA is not completely understood but involves an interplay between environmental risk factors, joint mechanics, abnormal pain pathways and upregulation of inflammatory signaling pathways. Current therapeutic options for patients are limited to conservative management, minimal pharmacological options or surgical management, with significant caveats to all approaches.

AREAS COVERED

In this review, we have set out to investigate current phase II/III clinical trials by undertaking a PubMed search. Examined clinical trials have explored a myriad of potential therapeutics from conventional disease-modifying anti-rheumatic drugs and biologics usually used in the treatment of inflammatory arthritides, to more novel approaches targeting inflammatory pathways implicated in OA, cartilage degeneration or pain pathways.

EXPERT OPINION

Unfortunately, most completed phase II/III clinical trials have shown little impact on patient pain scores, with the exception of the traditional DMARD methotrexate and Sprifermin. Methotrexate has been shown to be beneficial when used in the correct patient cohort (MRI proven synovitis). Sprifermin has the longest follow-up data of 5 years and has been shown to reduce loss of MRI-measured cartilage thickness and pain scores.

Mesenchymal Stromal Cells for Aging Cartilage Regeneration: A Review

Cartilage degeneration is a key feature of aging and osteoarthritis, characterized by the progressive deterioration of joint function, pain, and limited mobility. Current treatments focus on symptom relief, not cartilage regeneration. Mesenchymal stromal cells (MSCs) offer a promising therapeutic option due to their capability to differentiate into chondrocytes, modulate inflammation, and promote tissue regeneration. This review explores the potential of MSCs for cartilage regeneration, examining their biological properties, action mechanisms, and applications in preclinical and clinical settings. MSCs derived from bone marrow, adipose tissue, and other sources can self-renew and differentiate into multiple cell types. In aging cartilage, they aid in tissue regeneration by secreting growth factors and cytokines that enhance repair and modulate immune responses. Recent preclinical studies show that MSCs can restore cartilage integrity, reduce inflammation, and improve joint function, although clinical translation remains challenging due to limitations such as cell viability, scalability, and regulatory concerns. Advancements in MSC delivery, including scaffold-based approaches and engineered exosomes, may improve therapeutic effectiveness. Potential risks, such as tumorigenicity and immune rejection, are also discussed, emphasizing the need for optimized treatment protocols and large-scale clinical trials to develop effective, minimally invasive therapies for cartilage regeneration.

Regenerative Inflammation: The Mechanism Explained from the Perspective of Buffy-Coat Protagonism and Macrophage Polarization

The buffy-coat, a layer of leukocytes and platelets obtained from peripheral blood centrifugation, plays a crucial role in tissue regeneration and the modulation of inflammatory responses. This article explores the mechanisms of regenerative inflammation, highlighting the critical role of the buffy-coat in influencing macrophage polarization and its therapeutic potential. Macrophage polarization into M1 and M2 subtypes is pivotal in balancing inflammation and tissue repair, with M1 macrophages driving pro-inflammatory responses and M2 macrophages promoting tissue healing and regeneration. The buffy-coat's rich composition of progenitor cells, cytokines, and growth factors-such as interleukin-10, transforming growth factor-β, and monocyte colony-stimulating factor-supports the transition from M1 to M2 macrophages, enhancing tissue repair and the resolution of inflammation. This dynamic interaction between buffy-coat components and macrophages opens new avenues for therapeutic strategies aimed at improving tissue regeneration and managing inflammatory conditions, particularly in musculoskeletal diseases such as osteoarthritis. Furthermore, the use of buffy-coat-derived therapies in conjunction with other regenerative modalities, such as platelet-rich plasma, holds promise for more effective clinical outcomes.

Cell-based therapy in the treatment of musculoskeletal diseases

A limited number of tissues can spontaneously regenerate following injury, and even fewer can regenerate to a state comparable to mature, healthy adult tissue. Mesenchymal stem cells (MSCs) were first described in the 1960s-1970s by Friedenstein et al as a small population of bone marrow cells with osteogenic potential and abilities to differentiate into chondrocytes. In 1991, Arnold Caplan coined the term "mesenchymal cells" after identifying these cells as a theoretical precursor to bone, cartilage, tendon, ligament, marrow stroma, adipocyte, dermis, muscle, and connective tissues. MSCs are derived from periosteum, fat, and muscle. Another attractive property of MSCs is their immunoregulatory and regenerative properties, which result from crosstalk with their microenvironment and components of the innate immune system. Collectively, these properties make MSCs potentially attractive for various therapeutic purposes. MSCs offer potential in sports medicine, aiding in muscle recovery, meniscal tears, and tendon and ligament injuries. In joint disease, MSCs have the potential for chondrogenesis and reversing the effects of osteoarthritis. MSCs have also demonstrated potential application to the treatment of degenerative disc disease of the cervical, thoracic, and lumbar spine.

Advances in Mesenchymal Stem Cell Research Applications for Female Infertility-Mechanisms, Efficacy Parameters, Challenges and Future Roadmap

Infertility affects approximately 15-20% of couples globally, with female factors contributing to nearly half of cases. Conditions such as polycystic ovary syndrome, endometriosis, tubal damage and premature ovarian failure are leading causes of female infertility. Current treatments like in vitro fertilization (IVF) have limitations and risks. Mesenchymal stem cells (MSCs) have shown therapeutic potential due to their ability to differentiate, secrete trophic factors, and exhibit immunomodulatory and anti-inflammatory properties. They have been demonstrated to repair and regenerate reproductive organs in various preclinical models of infertility related conditions. MSCs have reduced endometriotic lesions, regenerated lost follicles in premature ovarian failure (POF) models, and promoted tubal repair in damage models. Some clinical and preclinical studies have reported improved outcomes with MSC therapy in endometriosis and premature ovarian failure patients. This review discusses the properties and sources of MSCs, their mechanisms of action, preclinical evidence for applications in conditions like POF, polycystic ovary syndrome (PCOS), endometriosis, Asherman syndrome, and preeclampsia, and preliminary clinical data on MSC therapy for female infertility management.

Roles of Microenvironment on Mesenchymal Stem Cells Therapy for Osteoarthritis

Osteoarthritis (OA) induced microenvironmental alterations are a common and unavoidable phenomenon that greatly exacerbate the pathologic process of OA. Imbalances in the synthesis and degradation of cartilage extracellular matrix (ECM) have been reported to be associated with an adverse microenvironment. Stem cell therapy is a promising treatment for OA, and mesenchymal stem cells (MSCs) are the main cell sources for this therapy. With multispectral differentiation and immunomodulation, MSCs can effectively regulate the microenvironment of articular cartilage, ameliorate inflammation, promote regeneration of damaged cartilage, and ultimately alleviate OA symptoms. However, the efficacy of MSCs in the treatment of OA is greatly influenced by articular cavity microenvironments. This article reviews the five microenvironments of OA articular cavity, including inflammatory microenvironment, senescence microenvironment, hypoxic microenvironment, high glucose microenvironment and high lipid environment, focus on the positive and negative effects of OA microenvironments on the fate of MSCs. In this regard, we emphasize the mechanisms of the current use of MSCs in OA treatment, as well as its limitations and challenges.

Stanniocalcin 2 Promotes Neuronal Differentiation in Neural Stem/Progenitor Cells of the Mouse Subventricular Zone Through Activation of AKT Pathway

Neural stem/progenitor cells (NSPCs) persist in the mammalian subventricular zone (SVZ) throughout life, responding to various pathophysiological stimuli and playing a crucial role in central nervous system repair. Although numerous studies have elucidated the role of stanniocalcin 2 (STC2) in regulating cell differentiation processes, its specific function in NSPCs differentiation remains poorly understood. Clarifying the role of STC2 in NSPCs is essential for devising novel strategies to enhance the intrinsic potential for brain regeneration postinjury. Our study revealed the expression of STC2 in NSPCs derived from the SVZ of the C57BL/6N mouse. In cultured SVZ-derived NSPCs, STC2 treatment significantly increased the number of Tuj1 and DCX-positive cells. Furthermore, STC2 injection into the lateral ventricle promoted the neuronal differentiation of NSPCs and migration to the olfactory bulb. Conversely, the STC2 knockdown produced the opposite effect. Further investigation showed that STC2 treatment enhanced AKT phosphorylation in cultured NSPCs, whereas STC2 inhibition hindered AKT activation. Notably, the neuronal differentiation induced by STC2 was blocked by the AKT inhibitor GSK690693, whereas the AKT activator SC79 reversed the impact of STC2 knockdown on neuronal differentiation. Our findings indicate that enhancing STC2 expression in SVZ-derived NSPCs facilitates neuronal differentiation, with AKT regulation potentially serving as a key intracellular target of STC2 signaling.

Melatonin enhances therapeutic outcomes of adipose tissue-derived mesenchymal stem cell therapy in rat osteoarthritis by reducing TNF-α and IL-1β-induced injuries

Although adipose tissue-derived mesenchymal stem cell (ADSC) transplantation has been effectively used to treat osteoarthritis (OA), the low cell survival rate induced by the inflammatory and oxidative stress, severely affects the therapeutic efficiency of ADSC transplantation in OA. This study was designed to evaluate whether melatonin pretreatment could improve ADSC survival and its therapeutic efficacy in OA. The papain-induced OA rats were pretreated with melatonin via intra-articular injection and then intra-articular injected with indocyanine green (ICG)-labeled ADSCs (3 × 106/rat). Afterward, ADSC retention was evaluated by NIR-II fluorescence imaging. The tibia and synovial fluid were collected for histopathological examination and ELISA assay, respectively. To confirm the anti-inflammatory effect of melatonin, a TNF-α and IL-1β-induced cell model was used to evaluate the protective effects of melatonin on ADSC viability, cell apoptosis, and migration. Our results showed that melatonin pretreatment enhanced ADSC survival and improved the therapeutic effects of ADSC transplantation on cartilage repair, and anti-inflammation by reducing TNF-α, IL-6, IL-1β, and IL-12 in vivo. In particular, we also found that melatonin promoted ADSC viability and migration, and reduced cell apoptosis in vitro. In conclusion, this study supports that melatonin pretreatment can effectively improve ADSC survival and therapeutic efficiency in OA by reducing inflammatory injuries, which provides a novel strategy for enhancing ADSC therapy.

Control of articular degeneration by extracellular vesicles from stem/stromal cells as a potential strategy for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint condition that contributes to years lived with disability. Current therapeutic approaches are limited as there are no disease-modifying interventions able to delay or inhibit the progression of disease. In recent years there has been an increasing interest in the immunomodulatory and regenerative properties of mesenchymal stem/stromal cells (MSCs) to develop new OA therapies. Extracellular vesicles (EVs) mediate many of the biological effects of these cells and may represent an alternative avoiding the limitations of cell-based therapy. There is also a growing interest in EV modifications to enhance their efficacy and applications. Recent preclinical studies have provided strong evidence supporting the potential of MSC EVs for the development of OA treatments. Thus, MSC EVs may regulate chondrocyte functions to avoid cartilage destruction, inhibit abnormal subchondral bone metabolism and synovial tissue alterations, and control pain behavior. EV actions may be mediated by the transfer of their cargo to target cells, with an important role for proteins and non-coding RNAs modulating signaling pathways relevant for OA progression. Nevertheless, additional investigations are needed concerning EV optimization, and standardization of preparation procedures. More research is also required for a better knowledge of possible effects on different OA phenotypes, pharmacokinetics, mechanism of action, long-term effects and safety profile. Furthermore, MSC EVs have a high potential as vehicles for drug delivery or as adjuvant therapy to potentiate or complement the effects of other approaches.

Development of scaffold-free tissue-engineered constructs derived from mesenchymal stem cells with serum-free media for cartilage repair and long-term preservation

Synovial mesenchymal stem cells (sMSCs) have great potential for cartilage repair, but their therapeutic design to avoid adverse effects associated with unknown factors remains a challenge. In addition, because long-term preservation is indispensable to maintain high quality levels until implantation, it is necessary to reduce their fluctuations. This study aimed to investigate the properties and feasibility of novel scaffold-free tissue-engineered constructs using serum-free media and to develop long-term preservation methods. sMSCs were cultured in serum-free media, seeded at high density in a monolayer, and finally developed as a sheet-like construct called "gMSC1". The properties of frozen gMSC1 (Fro-gMSC1) were compared with those of refrigerated gMSC1 (Ref-gMSC1) and then examined by their profile. Chondrogenic differentiation potential was analyzed by quantitative real-time polymerase chain reaction and quantification of glycosaminoglycan content. Xenografts into the cartilage defect model in rats were evaluated by histological staining. gMSC1 showed nearly similar properties independent of the preservation conditions. The animal experiment demonstrated that the defect could be filled with cartilage-like tissue with good integration to the adjacent tissue, suggesting that gMSC1 was formed and replaced the cartilage. Furthermore, several chondrogenesis-related factors were significantly secreted inside and outside gMSC1. Morphological analysis of Fro-gMSC1 revealed comparable quality levels to those of fresh gMSC1. Thus, if cryopreserved, gMSC1, with no complicated materials or processes, could have sustained cartilage repair capacity. gMSC1 is a prominent candidate in novel clinical practice for cartilage repair, allowing for large quantities to be manufactured at one time and preserved for a long term by freezing.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-024-00637-y.

Aptamer-Modified Tetrahedral Framework Nucleic Acid Synergized with TGF-β3 to Promote Cartilage Protection in Osteoarthritis by Enhancing Chondrogenic Differentiation of MSCs

Characterized by progressive and irreversible degeneration of the articular cartilage (AC), osteoarthritis (OA) is the most common chronic joint disease, and there is no cure for OA at present. Recent studies suggest that enhancing the recruitment of endogenous mesenchymal stem cells (MSCs) to damaged cartilage is a promising therapeutic strategy for cartilage repair. Tetrahedral framework nucleic acid (tFNA) is a novel DNA nanomaterial and has shown great potential in the field of biomedical science. Transforming growth factor-beta 3 (TGF-β3), a vital member of the highly conserved TGF-β superfamily, is considered to induce chondrogenesis. A 66-base DNA aptamer named HM69 is reported to identify and recruit MSCs. In this study, aptamer HM69-modified tFNAs were successfully self-assembled and used to load TGF-β3 when the disulfide bonds combined. We confirmed the successful synthesis of the final composition, HM69-tFNA@TGF-β3 (HTT), by PAGE, dynamic light scattering, and atomic force microscopy. The results of in vitro experiments showed that HTT effectively induced MSC proliferation, migration, and chondrogenic differentiation. In addition, HTT-treated MSCs were shown to protect the OA chondrocytes. In DMM mice, the injection of HTT improved the therapeutic outcome of mouse pain symptoms and AC degeneration. In conclusion, this study innovatively used the disulfide bonds combined with TGF-β3 and tFNA, and an additional sequence HM69 was loaded on tFNA for the better-targeted recruitment of MSCs. HTT demonstrated its role in promoting the chondrogenesis of MSCs and cartilage protection, indicating that it might be promising for OA therapy.

Therapeutic effect of three-dimensional hanging drop cultured human umbilical cord mesenchymal stem cells on osteoarthritis in rabbits

BACKGROUND

Mesenchymal stem cells (MSCs) have shown a positive effect on Osteoarthritis (OA), but the efficacy is still not significant in clinical. Conventional two-dimensional (2D) monolayer culture method is prone to cause MSCs undergoing replication senescence, which may affect the functions of MSCs. Three-dimensional (3D) culture strategy can sustain cell proliferative capacity and multi-differentiation potential. This study aimed to investigate the therapeutic potential of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) cultured by 3D hanging drop method on OA.

METHODS

hUC-MSCs were isolated from umbilical cord and cultured by 3D hanging drop method for 48 h. Scanning electron microscopy (SEM) was used to observe gross morphology 2D and 3D hUC-MSCs. Transcriptome comparison of gene expression differences between 2D and 3D hUC-MSCs. GO enrichment analysis, KEGG pathway enrichment analysis and GSEA enrichment analysis were used to analyze the impact of 3D hanging drop culture on the biological functions of hUC-MSCs. Female New Zealand rabbits (n = 12) were divided into 4 groups: Normal group, Model group, 2D hUC-MSCs treatment group and 3D hUC-MSCs treatment group. After 8 weeks, the gross and histological appearance of the cartilage was evaluated by safranin O-fast green staining and Mankin scoring system. The expression of type I collagen and type II collagen was detected by immunohistochemistry. The levels of IL-6, IL-7, TNFα, TGFβ1 and IL-10 in the knee joint fluid were tested by ELISA.

RESULTS

3D hanging drop culture changed cell morphology but did not affect phenotype. The MSCs transcriptome profiles showed that 3D hanging drop culture method enhanced cell-cell contact, improved cell responsiveness to external stimuli and immunomodulatory function. The animal experiment results showed that hUC-MSCs could promote cartilage regeneration compared with Model group. 3D hUC-MSCs treatment group had a higher histological score and significantly increased type II collagen secretion. In addition, 3D hUC-MSCs treatment group increased the expression of anti-inflammatory factors TGFβ1 and IL-10.

CONCLUSION

The above experimental results illustrated that 3D hanging drop culture method could enhance the therapeutic effect of hUC-MSCs, and showed a good clinical application prospect in the treatment of OA.

Rat Tracheal Cartilage Regeneration Using Mesenchymal Stem Cells Derived From Human iPS Cells

Tracheal cartilage provides structural support to the airways to enable breathing. However, it can become damaged or impaired, sometimes requiring surgical resection and reconstruction. Previously, we clinically applied an artificial trachea composed of a polypropylene mesh and collagen sponge, with a favorable postoperative course. However, the artificial trachea presents a limitation, as the mesh is not biodegradable and cannot be used in pediatric patients. Compared to a polypropylene mesh, regenerated cartilage represents an ideal material for reconstruction of the damaged trachea. The use of mesenchymal stem cells (MSCs) as a source for cartilage regeneration has gained widespread acceptance, but challenges such as the invasiveness of harvesting and limited cell supply persist. Therefore, we focused on the potential of human-induced pluripotent stem cell (hiPSC)-derived mesenchymal stem cells (iMSCs) for tracheal cartilage regeneration. In this study, we aimed to regenerate tracheal cartilage on an artificial trachea as a preliminary step to replace the polypropylene mesh. iMSCs were induced from hiPSCs through neural crest cells and transplanted with a polypropylene mesh covered with a collagen sponge into the damaged tracheal cartilage in immunodeficient rats. Human nuclear antigen (HNA)-positive cells were observed in all six rats at 4 weeks and in six out of seven rats at 12 weeks after transplantation, indicating that transplanted iMSCs survived within the tracheal cartilage defects of rats. The HNA-positive cells coexpressed SOX9, and type II collagen was detected around HNA-positive cells in four of six rats at 4 weeks and in three of seven rats at 12 weeks after transplantation, reflecting cartilage-like tissue regeneration. These results indicate that the transplanted iMSCs could differentiate into chondrogenic cells and promote tracheal cartilage regeneration. iMSC transplantation thus represents a promising approach for human tracheal reconstruction.

Delivering Microrobots in the Musculoskeletal System

Disorders of the musculoskeletal system are the major contributors to the global burden of disease and current treatments show limited efficacy. Patients often suffer chronic pain and might eventually have to undergo end-stage surgery. Therefore, future treatments should focus on early detection and intervention of regional lesions. Microrobots have been gradually used in organisms due to their advantages of intelligent, precise and minimally invasive targeted delivery. Through the combination of control and imaging systems, microrobots with good biosafety can be delivered to the desired area for treatment. In the musculoskeletal system, microrobots are mainly utilized to transport stem cells/drugs or to remove hazardous substances from the body. Compared to traditional biomaterial and tissue engineering strategies, active motion improves the efficiency and penetration of local targeting of cells/drugs. This review discusses the frontier applications of microrobotic systems in different tissues of the musculoskeletal system. We summarize the challenges and barriers that hinder clinical translation by evaluating the characteristics of different microrobots and finally point out the future direction of microrobots in the musculoskeletal system.

Glycosphingolipids in Osteoarthritis and Cartilage-Regeneration Therapy: Mechanisms and Therapeutic Prospects Based on a Narrative Review of the Literature

Glycosphingolipids (GSLs), a subtype of glycolipids containing sphingosine, are critical components of vertebrate plasma membranes, playing a pivotal role in cellular signaling and interactions. In human articular cartilage in osteoarthritis (OA), GSL expression is known notably to decrease. This review focuses on the roles of gangliosides, a specific type of GSL, in cartilage degeneration and regeneration, emphasizing their regulatory function in signal transduction. The expression of gangliosides, whether endogenous or augmented exogenously, is regulated at the enzymatic level, targeting specific glycosyltransferases. This regulation has significant implications for the composition of cell-surface gangliosides and their impact on signal transduction in chondrocytes and progenitor cells. Different levels of ganglioside expression can influence signaling pathways in various ways, potentially affecting cell properties, including malignancy. Moreover, gene manipulations against gangliosides have been shown to regulate cartilage metabolisms and chondrocyte differentiation in vivo and in vitro. This review highlights the potential of targeting gangliosides in the development of therapeutic strategies for osteoarthritis and cartilage injury and addresses promising directions for future research and treatment.

Mesenchymal Stem/Progenitor Cells and Their Derivates in Tissue Regeneration-Part II

During the last three decades, mesenchymal stem/stromal cells (MSCs) were extensively studied, and are mainly considered within the setting of their regenerative and immunomodulatory properties in tissue regeneration [...].

Expansion of human umbilical cord derived mesenchymal stem cells in regenerative medicine

BACKGROUND

Stem cells are undifferentiated cells that possess the potential for self-renewal with the capacity to differentiate into multiple lineages. In humans, their limited numbers pose a challenge in fulfilling the necessary demands for the regeneration and repair of damaged tissues or organs. Studies suggested that mesenchymal stem cells (MSCs), necessary for repair and regeneration via transplantation, require doses ranging from 10 to 400 million cells. Furthermore, the limited expansion of MSCs restricts their therapeutic application.

AIM

To optimize a novel protocol to achieve qualitative and quantitative expansion of MSCs to reach the targeted number of cells for cellular transplantation and minimize the limitations in stem cell therapy protocols.

METHODS

Human umbilical cord (hUC) tissue derived MSCs were obtained and re-cultured. These cultured cells were subjected to the following evaluation procedures: Immunophenotyping, immunocytochemical staining, trilineage differentiation, population doubling time and number, gene expression markers for proliferation, cell cycle progression, senescence-associated β-galactosidase assay, human telomerase reverse transcriptase (hTERT) expression, mycoplasma, cytomegalovirus and endotoxin detection.

RESULTS

Analysis of pluripotent gene markers Oct4, Sox2, and Nanog in recultured hUC-MSC revealed no significant differences. The immunophenotypic markers CD90, CD73, CD105, CD44, vimentin, CD29, Stro-1, and Lin28 were positively expressed by these recultured expanded MSCs, and were found negative for CD34, CD11b, CD19, CD45, and HLA-DR. The recultured hUC-MSC population continued to expand through passage 15. Proliferative gene expression of Pax6, BMP2, and TGFb1 showed no significant variation between recultured hUC-MSC groups. Nevertheless, a significant increase (P < 0.001) in the mitotic phase of the cell cycle was observed in recultured hUC-MSCs. Cellular senescence markers (hTERT expression and β-galactosidase activity) did not show any negative effect on recultured hUC-MSCs. Additionally, quality control assessments consistently confirmed the absence of mycoplasma, cytomegalovirus, and endotoxin contamination.

CONCLUSION

This study proposes the development of a novel protocol for efficiently expanding stem cell population. This would address the growing demand for larger stem cell doses needed for cellular transplantation and will significantly improve the feasibility of stem cell based therapies.

A novel, microfluidic high-throughput single-cell encapsulation of human bone marrow mesenchymal stromal cells

The efficacy of stem-cell therapy depends on the ability of the transplanted cells to escape early immunological reactions and to be retained at the site of transplantation. The use of tissue engineering scaffolds or injectable biomaterials as carriers has been proposed, but they still present limitations linked to a reliable manufacturing process, surgical practice and clinical outcomes. Alginate microbeads are potential candidates for the encapsulation of mesenchymal stromal cells with the aim of providing a delivery carrier suitable for minimally-invasive and scaffold-free transplantation, tissue-adhesive properties and protection from the immune response. However, the formation of stable microbeads relies on the cross-linking of alginate with divalent calcium ions at concentrations that are toxic for the cells, making control over the beads' size and a single-cell encapsulation unreliable. The present work demonstrates the efficiency of an innovative, high throughput, and reproducible microfluidic system to produce single-cell, calcium-free alginate coatings of human mesenchymal stromal cells. Among the various conditions tested, visible light and confocal microscopy following staining of the cell nuclei by DAPI showed that the microfluidic system yielded an optimal single-cell encapsulation of 2000 cells/min in 2% w/v alginate microcapsules of reproducible morphology and an average size of 28.2 ± 3.7 µm. The adhesive properties of the alginate microcapsules, the viability of the encapsulated cells and their ability to escape the alginate microcapsule were demonstrated by the relatively rapid adherence of the beads onto tissue culture plastic and the cells' ability to gradually disrupt the microcapsule shell after 24 h and proliferate. To mimic the early inflammatory response upon transplantation, the encapsulated cells were exposed to proliferating macrophages at different cell seeding densities for up to 2 days and the protection effect of the microcapsule on the cells assessed by time-lapse microscopy showing a shielding effect for up to 48 h. This work underscores the potential of microfluidic systems to precisely encapsulate cells by good manufacturing practice standards while favouring cell retention on substrates, viability and proliferation upon transplantation.

Stable Housekeeping Genes in Bone Marrow, Adipose Tissue, and Amniotic Membrane-Derived Mesenchymal Stromal Cells for Orthopedic Regenerative Medicine Approaches

The therapeutic effect of mesenchymal stromal cells (MSCs) has been described for a variety of disorders, including those affecting musculoskeletal tissues. In this context, the literature reports several data about the regenerative effectiveness of MSCs derived from bone marrow, adipose tissue, and an amniotic membrane (BMSCs, ASCs, and hAMSCs, respectively), either when expanded or when acting as clinical-grade biologic pillars of products used at the point of care. To date, there is no evidence about the superiority of one source over the others from a clinical perspective. Therefore, a reliable characterization of the tissue-specific MSC types is mandatory to identify the most effective treatment, especially when tailored to the target disease. Because molecular characterization is a crucial parameter for cell definition, the need for reliable normalizers as housekeeping genes (HKGs) is essential. In this report, the stability levels of five commonly used HKGs (ACTB, EF1A, GAPDH, RPLP0, and TBP) were sifted into BMSCs, ASCs, and hAMSCs. Adult and fetal/neonatal MSCs showed opposite HKG stability rankings. Moreover, by analyzing MSC types side-by-side, comparison-specific HKGs emerged. The effect of less performant HKG normalization was also demonstrated in genes coding for factors potentially involved in and predicting MSC therapeutic activity for osteoarthritis as a model musculoskeletal disorder, where the choice of the most appropriate normalizer had a higher impact on the donors rather than cell populations when compared side-by-side. In conclusion, this work confirms HKG source-specificity for MSCs and suggests the need for cell-type specific normalizers for cell source or condition-tailored gene expression studies.

Housekeeping Gene Stability in Adipose Mesenchymal Stromal Cells Cultivated in Serum/Xeno-Free Media for Osteoarthritis

Among the available therapeutics for the conservative treatment of osteoarthritis (OA), mesenchymal stromal cells (MSCs)-based products appear to be the most promising. Alongside minimally manipulated cell-based orthobiologics, where MSCs are the engine of the bioactive properties, cell expansion under good manufacturing practice (GMP) settings is actively studied to obtain clinical-grade pure populations able to concentrate the biological activity. One of the main characteristics of GMP protocols is the use of clinical-grade reagents, including the recently released serum-free/xeno-free (SFM/XFM) synthetic media, which differ significantly from the traditional reagents like those based on fetal bovine serum (FBS). As SFM/XFM are still poorly characterized, a main lack is the notion of reliable housekeeping genes (HKGs) for molecular studies, either standalone or in combination with standard conditions. Indeed, the aim of this work was to test the stability of five commonly used HKGs (ACTB, EF1A, GAPDH, RPLP0, and TBP) in adipose-derived MSCs (ASCs) cultivated in two commercially available SFM/XFM and to compare outcomes with those obtained in FBS. Four different applets widely recognized by the scientific community (NormFinder, geNorm, comparative ΔCt method, and BestKeeper) were used and data were merged to obtain a final stability order. The analysis showed that cells cultured in both synthetic media had a similar ranking for HKGs stability (GAPDH being best), albeit divergent from FBS expanded products (EF1A at top). Moreover, it was possible to identify specific HKGs for side by side studies, with EF1A/TBP being the most reliable normalizers for single SFM/XFM vs. FBS cultured cells and TBP the best one for a comprehensive analysis of all samples. In addition, stability of HKGs was donor-dependent. The normalization effect on selected genes coding for factors known to be involved in OA pathology, and whose amount should be carefully considered for the selection of the most appropriate MSC-based treatment, showed how HKGs choice might affect the perceived amount for the different media or donor. Overall, this work confirms the impact of SFM/XFM conditions on HKGs stability performance, which resulted similarly for both synthetic media analyzed in the study.

CD146-positive adipose-derived stem cells subpopulation enriched by albumin magnetic sphere ameliorates knee osteoarthritis pain and promotes cartilage repair

BACKGROUND

The use of adipose stem cell (ADSCs) subpopulations in cartilage repair remains poorly characterized. In this study, we constructed an albumin magnetic sphere with specific targeting of CD146 (CD146-AMs) for sorting a subpopulation of CD146-positive ADSCs (CD146 + ADSCs) and explored the role of CD146 + ADSCs on joint pain and cartilage repair in rats with knee osteoarthritis (KOA).

METHODS

CD146-AMs were prepared and analyzed in materialistic characterization tests. Subpopulations of CD146 + ADSCs were sorted using CD146-AMs. Surface labeling, viability, and proliferation of a subpopulation of CD146 + ADSCs were evaluated in vitro. Molecular characterization of mRNA and protein expression profiles was analyzed by microarray. A rat KOA pain model was established by the iodoacetic acid method, and KOA pain and the promotion of cartilage repair were assessed after treatment with bilateral joint cavity injections of CD146 + ADSCs.

RESULTS

The CD146-AMs prepared in this study had an average particle size of 242.63 ± 6.74 nm, an average potential of 33.82 ± 3.53 mv, and high CD146 targeting and low cytotoxicity. The positive rate of enriched CD146 + ADSCs was 98.21% and showed a high level of stem cell marker expression and good cell viability. Gene and protein expression profiles showed that CD146 + ADSCs have different cellular functions, especially in regulating inflammation. In the KOA model, low, medium and high concentrations of CD146 + ADSCs were able to improve KOA pain and promote cartilage repair in a concentration-dependent trend.

CONCLUSIONS

The CD146-AMs prepared in this study were able to safely and efficiently sort out the CD146 + ADSCs subpopulation. The subpopulation of CD146 + ADSCs has a unique molecular profile that ameliorates KOA pain and repairs cartilage damage in rats, providing a new idea for KOA treatment.

Shoulder replacement surgery's rising demand, inequality of provision, and variation in outcomes: cohort study using Hospital Episode Statistics for England

BACKGROUND

The aim of this study was to forecast future patient demand for shoulder replacement surgery in England and investigate any geographic and socioeconomic inequalities in service provision and patient outcomes.

METHODS

For this cohort study, all elective shoulder replacements carried out by NHS hospitals and NHS-funded care in England from 1999 to 2020 were identified using Hospital Episode Statistics data. Eligible patients were aged 18 years and older. Shoulder replacements for malignancy or acute trauma were excluded. Population estimates and projections were obtained from the Office for National Statistics. Standardised incidence rates and the risks of serious adverse events (SAEs) and revision surgery were calculated and stratified by geographical region, socioeconomic deprivation, sex, and age band. Hospital costs for each admission were calculated using Healthcare Resource Group codes and NHS Reference Costs based on the National Reimbursement System. Projected rates and hospital costs were predicted until the year 2050 for two scenarios of future growth.

RESULTS

A total of 77,613 elective primary and 5847 revision shoulder replacements were available for analysis. Between 1999 and 2020, the standardised incidence of primary shoulder replacements in England quadrupled from 2.6 to 10.4 per 100,000 population, increasing predominantly in patients aged over 65 years. As many as 1 in 6 patients needed to travel to a different region for their surgery indicating inequality of service provision. A temporal increase in SAEs was observed: the 30-day risk increased from 1.3 to 4.8% and the 90-day risk increased from 2.4 to 6.0%. Patients from the more deprived socioeconomic groups appeared to have a higher risk of SAEs and revision surgery. Shoulder replacements are forecast to increase by up to 234% by 2050 in England, reaching 20,912 procedures per year with an associated annual cost to hospitals of £235 million.

CONCLUSIONS

This study reports a rising incidence of shoulder replacements, regional disparities in service provision, and an overall increasing risk of SAEs, especially in more deprived socioeconomic groups. These findings highlight the need for better healthcare planning to match local population demand, while more research is needed to understand and prevent the increase observed in SAEs.

Bioadhesive and Injectable Hydrogels and Their Correlation with Mesenchymal Stem Cells Differentiation for Cartilage Repair: A Mini-Review

Injectable bioadhesive hydrogels, known for their capacity to carry substances and adaptability in processing, offer great potential across various biomedical applications. They are especially promising in minimally invasive stem cell-based therapies for treating cartilage damage. This approach harnesses readily available mesenchymal stem cells (MSCs) to differentiate into chondrocytes for cartilage regeneration. In this review, we investigate the relationship between bioadhesion and MSC differentiation. We summarize the fundamental principles of bioadhesion and discuss recent trends in bioadhesive hydrogels. Furthermore, we highlight their specific applications in conjunction with stem cells, particularly in the context of cartilage repair. The review also encompasses a discussion on testing methods for bioadhesive hydrogels and direct techniques for differentiating MSCs into hyaline cartilage chondrocytes. These approaches are explored within both clinical and laboratory settings, including the use of genetic tools. While this review offers valuable insights into the interconnected aspects of these topics, it underscores the need for further research to fully grasp the complexities of their relationship.

Cartilage Defect Treatment Using High-Density Autologous Chondrocyte Implantation (HD-ACI)

Hyaline cartilage's inability to self-repair can lead to osteoarthritis and joint replacement. Various treatments, including cell therapy, have been developed for cartilage damage. Autologous chondrocyte implantation (ACI) is considered the best option for focal chondral lesions. In this article, we aimed to create a narrative review that highlights the evolution and enhancement of our chondrocyte implantation technique: High-Density-ACI (HD-ACI) Membrane-assisted Autologous Chondrocyte Implantation (MACI) improved ACI using a collagen membrane as a carrier. However, low cell density in MACI resulted in softer regenerated tissue. HD-ACI was developed to improve MACI, implanting 5 million chondrocytes per cm2, providing higher cell density. In animal models, HD-ACI formed hyaline-like cartilage, while other treatments led to fibrocartilage. HD-ACI was further evaluated in patients with knee or ankle defects and expanded to treat hip lesions and bilateral defects. HD-ACI offers a potential solution for cartilage defects, improving outcomes in regenerative medicine and cell therapy. HD-ACI, with its higher cell density, shows promise for treating chondral defects and advancing cartilage repair in regenerative medicine and cell therapy.

Relations between Structure/Composition and Mechanics in Osteoarthritic Regenerated Articular Tissue: A Machine Learning Approach

In the context of a large animal model of early osteoarthritis (OA) treated by orthobiologics, the purpose of this study was to reveal relations between articular tissues structure/composition and cartilage viscoelasticity. Twenty-four sheep, with induced knee OA, were treated by mesenchymal stem cells in various preparations-adipose-derived mesenchymal stem cells (ADSCs), stromal vascular fraction (SVF), and amniotic endothelial cells (AECs)-and euthanized at 3 or 6 months to evaluate the (i) biochemistry of synovial fluid; (ii) histology, immunohistochemistry, and histomorphometry of articular cartilage; and (iii) viscoelasticity of articular cartilage. After performing an initial analysis to evaluate the correlation and multicollinearity between the investigated variables, this study used machine learning (ML) models-Variable Selection Using Random Forests (VSURF) and Extreme Gradient Boosting (XGB)-to classify variables according to their importance and employ them for interpretation and prediction. The experimental setup revealed a potential relation between cartilage elastic modulus and cartilage thickness (CT), synovial fluid interleukin 6 (IL6), and prostaglandin E2 (PGE2), and between cartilage relaxation time and CT and PGE2. SVF treatment was the only limit on the deleterious OA effect on cartilage viscoelastic properties. This work provides indications to future studies aiming to highlight these and other relationships and focusing on advanced regeneration targets.