Effect of Intra-Articular Sprifermin vs Placebo on Femorotibial Joint Cartilage Thickness in Patients With Osteoarthritis: The FORWARD Randomized Clinical Trial

Emerging injectable therapies for osteoarthritis

Osteoarthritis (OA) affects more than 240 million people worldwide. In 2016, the Osteoarthritis Research Society International submitted a report to the United States Food and Drug Administration highlighting OA as a 'serious' disease, and appealed for the urgent development and review of new therapies to address a significant unmet need. Despite this, international guidelines for the treatment of OA have been largely unchanged for over a decade. There is now an updated understanding that OA is more than simply a non-inflammatory 'wear-and-tear' process involving articular cartilage. Based on this, potential emerging therapies are being developed that target novel inflammatory, pain, and regeneration pathways. Drugs targeting the latter are being lauded as 'Disease-Modifying Osteoarthritis Drugs' - a concept which has so far proved elusive in OA research. While this review does not recommend a change in current practice, it should prompt readers to rethink the OA treatment paradigm. The global pandemic has added another layer of consideration when managing patients with OA. At a time when there is more strain on hospital systems, there is a need to expand our pharmacological armamentarium in order to manage OA without elective surgery and hospital admission.

Identifying small molecules for protecting chondrocyte function and matrix integrity after controlled compressive injury

Objective

Articular cartilage injury is central for the development of post-traumatic osteoarthritis (PTOA). With few disease-modifying therapies successful at offsetting progressive osteoarthritis (OA), our goal is to use a high throughput screening platform of cartilage injury to identify novel chondroprotective compounds. Targeting articular cartilage damage immediately after injury remains a promising therapeutic strategy to overcome irreversible tissue damage.

Method

We constructed a single impact-cartilage screening method using a multi-platen system that simultaneously impacts 48 samples and makes use of engineered cartilage tissue analogs (known as CTAs). Drug libraries were screened and assessed for their ability to alter two crucial biological responses to impact injuries, namely matrix degradation and cell stress.

Results

Over 500 small molecules were screened for their ability to alter proteoglycan loss, matrix metalloproteinase activity, and cell stress or death. Fifty-five compounds passed through secondary screening and were from commercial libraries of natural and redox, stem cell related compounds, as well as protease, kinase and phosphatase inhibitors. Through secondary screening, 16 promising candidates exhibited activity on one or more critical function of chondrocytes. While many are mechanistically known compounds, their function in joint diseases is not known.

Conclusion

This platform was validated for screening drug activity against a tissue engineered model of PTOA. Multiple compounds identified in this manner have potential application as early protective therapy for treating PTOA, and require further study. We propose this screening platform can identify novel molecules that act on early chondrocyte responses to injury and provide an invaluable tool for therapeutic development.

Functions of exogenous FGF signals in regulation of fibroblast to myofibroblast differentiation and extracellular matrix protein expression

Fibroblasts are widely distributed cells found in most tissues and upon tissue injury, they are able to differentiate into myofibroblasts, which express abundant extracellular matrix (ECM) proteins. Overexpression and unordered organization of ECM proteins cause tissue fibrosis in damaged tissue. Fibroblast growth factor (FGF) family proteins are well known to promote angiogenesis and tissue repair, but their activities in fibroblast differentiation and fibrosis have not been systematically reviewed. Here we summarize the effects of FGFs in fibroblast to myofibroblast differentiation and ECM protein expression and discuss the underlying potential regulatory mechanisms, to provide a basis for the clinical application of recombinant FGF protein drugs in treatment of tissue damage.

The recombinant human fibroblast growth factor-18 (sprifermin) improves tendon-to-bone healing by promoting chondrogenesis in a rat rotator cuff repair model

BACKGROUND

Rotator cuff healing is improved by reconstructing the fibrocartilaginous structure of the tendon-to-bone enthesis. Fibroblast growth factor (FGF)-18 (sprifermin) is a well-known growth factor that improves articular cartilage repair via its anabolic effect. This study aimed to investigate the effect of recombinant human FGF-18 (rhFGF-18) on the chondrogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) in vitro and tendon-to-bone healing in a rat model of rotator cuff repair.

METHODS

Histological and reverse transcription-quantitative real-time polymerase chain reaction analyses of chondral pellets cultured with different concentrations of rhFGF-18 were performed. Bilateral detachment and repair of the supraspinatus tendon were performed on rats. The rats were administered 0.2 mL of sodium alginate (SA) hydrogel with (rhFGF-18/SA group, n = 12) or without (SA group, n = 12) 20 μg of rhFGF-18 into the repaired side. The simple repair group (n = 12) served as a control. At 4 and 8 weeks after surgery, histological analysis and biomechanical tests were performed.

RESULTS

After chondrogenesis induction, compared with the control group, 10 ng/mL of rhFGF-18 increased pellet volume significantly (P = .002), with improved histological staining. It was noted that 10 ng/mL of rhFGF-18 upregulated the mRNA expression (relative ratio to control) of aggrecan (2.59 ± 0.29, P < .001), SRY-box transcription factor 9 (1.88 ± 0.05, P < .001), and type II collagen (1.46 ± 0.18, P = .009). At 4 and 8 weeks after surgery, more fibrocartilage and cartilaginous extracellular matrix was observed in rhFGF-18/SA-treated rats. The semiquantitative data from picrosirius red staining test were 31.1 ± 4.5 vs. 61.2 ± 4.1 at 4 weeks (P < .001) and 61.5 ± 2.8 vs. 80.5 ± 10.5 at 8 weeks (P = .002) (control vs. rhFGF-18/SA). Ultimate failure load (25.42 ± 3.61 N vs. 18.87 ± 2.71 N at 4 weeks and 28.63 ± 5.22 N vs. 22.15 ± 3.11 N at 8 weeks; P = .006 and P = .03, respectively) and stiffness (18.49 ± 1.38 N/mm vs. 14.48 ± 2.01 N/mm at 8 weeks, P = .01) were higher in the rhFGF-18/SA group than in the control group.

CONCLUSION

rhFGF-18 promoted chondrogenesis in the hBMSCs in vitro. rhFGF-18/SA improved tendon-to-bone healing in the rats by promoting regeneration of the fibrocartilage enthesis. rhFGF-18 (sprifermin) may be beneficial in improving tendon-to-bone healing after rotator cuff repair.

Elucidation of the Underlying Mechanism of Gujian Oral Liquid Acting on Osteoarthritis through Network Pharmacology, Molecular Docking, and Experiment

Gujian oral liquid (GJ), a traditional herbal formula in China, has been widely used to treat patients with osteoarthritis (OA). Nevertheless, the active component and potential mechanism of GJ are not fully elucidated. Thus, we investigate the effect of GJ and explore its underlying mechanism on OA through network pharmacology and experimental validation. First, a total of 175 bioactive compounds were identified, and 134 overlapping targets were acquired after comparing the targets of the GJ with those of OA. 8 hub targets, including IL6 and AKT1, were obtained in PPI network analysis. Then, we built up GJ-target-OA network and protein-protein interaction (PPI) network, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. The results underlined inflammatory tumor necrosis factor (TNF) as a promising signaling pathway of GJ for OA treatment. Moreover, molecular docking also verified the top two active compounds had direct bindings with the top three target genes. Finally, we verified the effect of GJ on OA in vivo and in vitro. In vivo experiments validated that GJ not only significantly attenuated OA phenotypes including articular cartilage degeneration and subchondral bone sclerosis but also reduced the expressions of tumor necrosis factor-α (TNF-α) and p-p65 in articular chondrocytes. Besides, GJ serum also had a protective effect on chondrocytes against inflammation caused by TNF-α in vitro. Hence, our study predicted and verified that GJ could exert anti-inflammation and anticatabolism effects partially via regulating TNF-α/NF-kappa B (NF-κB) signaling.

Engineering of MSC-Derived Exosomes: A Promising Cell-Free Therapy for Osteoarthritis

Osteoarthritis (OA) is characterized by progressive cartilage degeneration with increasing prevalence and unsatisfactory treatment efficacy. Exosomes derived from mesenchymal stem cells play an important role in alleviating OA by promoting cartilage regeneration, inhibiting synovial inflammation and mediating subchondral bone remodeling without the risk of immune rejection and tumorigenesis. However, low yield, weak activity, inefficient targeting ability and unpredictable side effects of natural exosomes have limited their clinical application. At present, various approaches have been applied in exosome engineering to regulate their production and function, such as pretreatment of parental cells, drug loading, genetic engineering and surface modification. Biomaterials have also been proved to facilitate efficient delivery of exosomes and enhance treatment effectiveness. Here, we summarize the current understanding of the biogenesis, isolation and characterization of natural exosomes, and focus on the large-scale production and preparation of engineered exosomes, as well as their therapeutic potential in OA, thus providing novel insights into exploring advanced MSC-derived exosome-based cell-free therapy for the treatment of OA.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Imaging in Osteoarthritis

Osteoarthritis (OA) is the most frequent form of arthritis with major implications on both individual and public health care levels. The field of joint imaging, and particularly magnetic resonance imaging (MRI), has evolved rapidly due to the application of technical advances to the field of clinical research. This narrative review will provide an introduction to the different aspects of OA imaging aimed at an audience of scientists, clinicians, students, industry employees, and others who are interested in OA but who do not necessarily focus on OA. The current role of radiography and recent advances in measuring joint space width will be discussed. The status of cartilage morphology assessment and evaluation of cartilage biochemical composition will be presented. Advances in quantitative three-dimensional morphologic cartilage assessment and semi-quantitative whole-organ assessment of OA will be reviewed. Although MRI has evolved as the most important imaging method used in OA research, other modalities such as ultrasound, computed tomography, and metabolic imaging play a complementary role and will also be discussed.

Human Mesenchymal Stem Cell-Derived Miniature Joint System for Disease Modeling and Drug Testing

Diseases of the knee joint such as osteoarthritis (OA) affect all joint elements. An in vitro human cell-derived microphysiological system capable of simulating intraarticular tissue crosstalk is desirable for studying etiologies/pathogenesis of joint diseases and testing potential therapeutics. Herein, a human mesenchymal stem cell-derived miniature joint system (miniJoint) is generated, in which engineered osteochondral complex, synovial-like fibrous tissue, and adipose tissue are integrated into a microfluidics-enabled bioreactor. This novel design facilitates different tissues communicating while still maintaining their respective phenotypes. The miniJoint exhibits physiologically relevant changes when exposed to interleukin-1β mediated inflammation, which are similar to observations in joint diseases in humans. The potential of the miniJoint in predicting in vivo efficacy of drug treatment is confirmed by testing the "therapeutic effect" of the nonsteroidal anti-inflammatory drug, naproxen, as well as four other potential disease-modifying OA drugs. The data demonstrate that the miniJoint recapitulates complex tissue interactions, thus providing a robust organ chip model for the study of joint pathology and the development of novel therapeutic interventions.

Joint Cartilage in Long-Duration Spaceflight

This review summarizes the current literature available on joint cartilage alterations in long-duration spaceflight. Evidence from spaceflight participants is currently limited to serum biomarker data in only a few astronauts. Findings from analogue model research, such as bed rest studies, as well as data from animal and cell research in real microgravity indicate that unloading and radiation exposure are associated with joint degeneration in terms of cartilage thinning and changes in cartilage composition. It is currently unknown how much the individual cartilage regions in the different joints of the human body will be affected on long-term missions beyond the Low Earth Orbit. Given the fact that, apart from total joint replacement or joint resurfacing, currently no treatment exists for late-stage osteoarthritis, countermeasures might be needed to avoid cartilage damage during long-duration missions. To plan countermeasures, it is important to know if and how joint cartilage and the adjacent structures, such as the subchondral bone, are affected by long-term unloading, reloading, and radiation. The use of countermeasures that put either load and shear, or other stimuli on the joints, shields them from radiation or helps by supporting cartilage physiology, or by removing oxidative stress possibly help to avoid OA in later life following long-duration space missions. There is a high demand for research on the efficacy of such countermeasures to judge their suitability for their implementation in long-duration missions.

Update: Posttreatment Imaging of the Knee after Cartilage Repair

Focal cartilage lesions are common pathologies at the knee joint that are considered important risk factors for the premature development of osteoarthritis. A wide range of surgical options, including but not limited to marrow stimulation, osteochondral auto- and allografting, and autologous chondrocyte implantation, allows for targeted treatment of focal cartilage defects. Arthroscopy is the standard of reference for the assessment of cartilage integrity and quality before and after repair. However, deep cartilage layers, intrachondral composition, and the subchondral bone are only partially or not at all visualized with arthroscopy. In contrast, magnetic resonance imaging offers noninvasive evaluation of the cartilage repair site, the subchondral bone, and the soft tissues of the joint pre- and postsurgery. Radiologists need to be familiar with the different surgical procedures available and their characteristic postsurgical imaging appearances to assess treatment success and possible complications adequately. We provide an overview of the most commonly performed surgical procedures for cartilage repair at the knee and typical postsurgical imaging characteristics.

The Extracellular Matrix of Articular Cartilage Controls the Bioavailability of Pericellular Matrix-Bound Growth Factors to Drive Tissue Homeostasis and Repair

The extracellular matrix (ECM) has long been regarded as a packing material; supporting cells within the tissue and providing tensile strength and protection from mechanical stress. There is little surprise when one considers the dynamic nature of many of the individual proteins that contribute to the ECM, that we are beginning to appreciate a more nuanced role for the ECM in tissue homeostasis and disease. Articular cartilage is adapted to be able to perceive and respond to mechanical load. Indeed, physiological loads are essential to maintain cartilage thickness in a healthy joint and excessive mechanical stress is associated with the breakdown of the matrix that is seen in osteoarthritis (OA). Although the trigger by which increased mechanical stress drives catabolic pathways remains unknown, one mechanism by which cartilage responds to increased compressive load is by the release of growth factors that are sequestered in the pericellular matrix. These are heparan sulfate-bound growth factors that appear to be largely chondroprotective and displaced by an aggrecan-dependent sodium flux. Emerging evidence suggests that the released growth factors act in a coordinated fashion to drive cartilage repair. Thus, we are beginning to appreciate that the ECM is the key mechano-sensor and mechano-effector in cartilage, responsible for directing subsequent cellular events of relevance to joint health and disease.

Can metformin relieve tibiofemoral cartilage volume loss and knee symptoms in overweight knee osteoarthritis patients? Study protocol for a randomized, double-blind, and placebo-controlled trial

BACKGROUND

Osteoarthritis (OA) is the most common joint disease, and is most frequently seen in the knees. However, there is no effective therapy to relieve the progression of knee OA. Metformin is a safe, well-tolerated oral medication that is extensively used as first-line therapy for type 2 diabetes. Previous observational studies and basic researches suggested that metformin may have protective effects on knee OA, which needs to be verified by clinical trials. This study, therefore, aims to examine the effects of metformin versus placebo on knee cartilage volume loss and knee symptoms in overweight knee OA patients by a randomized controlled trial over 24 months.

METHODS

This protocol describes a multicenter, randomized, double-blind, and placebo-controlled clinical trial aiming to recruit 262 overweight knee OA patients. Participants will be randomly allocated to the two arms of the study, receiving metformin hydrochloride sustained-release tablets or identical inert placebo for 24 months (start from 0.5 g/day for the first 2 weeks, and increase to 1 g/day for the second 2 weeks, and further increase to 2 g/day for the remaining period if tolerated). Primary outcomes will be changes in tibiofemoral cartilage volume and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score over 24 months. Secondary outcomes will be changes in visual analogue scale (VAS) knee pain, tibiofemoral cartilage defects, effusion-synovitis volume, and tibiofemoral bone marrow lesions maximum size over 24 months. The primary analyses will be intention-to-treat analyses of primary and secondary outcomes. Per-protocol analyses will be performed as the secondary analyses.

DISCUSSION

If metformin is proved to slow knee cartilage volume loss and to relieve knee symptoms among overweight knee OA patients, it will have the potential to become a disease modifying drug for knee OA. Metformin is a convenient intervention with low cost, and its potential effects on slowing down the structural progression and relieving the symptoms of knee OA would effectively reduce the disease burden worldwide.

TRIAL REGISTRATION

ClinicalTrials. gov NCT05034029 . Registered on 30 Sept 2021.

Repurposed and investigational disease-modifying drugs in osteoarthritis (DMOADs)

In spite of a major public health burden with increasing prevalence, current osteoarthritis (OA) management is largely palliative with an unmet need for effective treatment. Both industry and academic researchers have invested a vast amount of time and financial expense to discover the first diseasing-modifying osteoarthritis drugs (DMOADs), with no regulatory success so far. In this narrative review, we discuss repurposed drugs as well as investigational agents which have progressed into phase II and III clinical trials based on three principal endotypes: bone-driven, synovitis-driven and cartilage-driven. Then, we will briefly describe the recent failures and lessons learned, promising findings from predefined post hoc analyses and insights gained, novel methodologies to enhance future success and steps underway to overcome regulatory hurdles.

99mTc-NTP 15-5 is a companion radiotracer for assessing joint functional response to sprifermin (rhFGF-18) in a murine osteoarthritis model

With the emergence of disease modifying osteoarthritis drugs (DMOAD), imaging methods to quantitatively demonstrate their efficacy and to monitor osteoarthritis progression at the functional level are urgently needed. Our group showed that articular cartilage can be quantitatively assessed in nuclear medicine imaging by our radiotracer ^99mTc-NTP 15-5 targeting cartilage proteoglycans. In this work, surgically induced DMM mice were treated with sprifermin or saline. We investigated cartilage remodelling in the mice knees by ^99mTc-NTP 15-5 SPECT-CT imaging over 24 weeks after surgery, as wells as proteoglycan biochemical assays. OA alterations were scored by histology according to OARSI guidelines. A specific accumulation of ^99mTc-NTP 15-5 in cartilage joints was evidenced in vivo by SPECT-CT imaging as early as 30 min post-iv injection. In DMM, ^99mTc-NTP 15-5 accumulation in cartilage within the operated joints, relative to contralateral ones, was observed to initially increase then decrease as pathology progressed. Under sprifermin, ^99mTc-NTP 15-5 uptake in pathological knees was significantly increased compared to controls, at 7-, 12- and 24-weeks, and consistent with proteoglycan increase measured 5 weeks post-surgery, as a sign of cartilage matrix remodelling. Our work highlights the potential of ^99mTc-NTP 15-5 as an imaging-based companion to monitor cartilage remodelling in OA and DMOAD response.

EGFR Signaling Is Required for Maintaining Adult Cartilage Homeostasis and Attenuating Osteoarthritis Progression

The uppermost superficial zone of articular cartilage is the first line of defense against the initiation of osteoarthritis (OA). We previously used Col2-Cre to demonstrate that epidermal growth factor receptor (EGFR), a tyrosine kinase receptor, plays an essential role in maintaining superficial chondrocytes during articular cartilage development. Here, we showed that EGFR activity in the articular cartilage decreased as mice age. In mouse and human OA samples, EGFR activity was initially reduced at the superficial layer and then resurged in cell clusters within the middle and deep zone in late OA. To investigate the role of EGFR signaling in postnatal and adult cartilage, we constructed an inducible mouse model with cartilage-specific EGFR inactivation (Aggrecan-CreER Egfr^Wa5/flox , Egfr iCKO). EdU incorporation revealed that postnatal Egfr iCKO mice contained fewer slow-cycling cells than controls. EGFR deficiency induced at 3 months of age reduced cartilage thickness and diminished superficial chondrocytes, in parallel to alterations in lubricin production, cell proliferation, and survival. Furthermore, male Egfr iCKO mice developed much more severe OA phenotypes, including cartilage erosion, subchondral bone plate thickening, cartilage degeneration at the lateral site, and mechanical allodynia, after receiving destabilization of the medial meniscus (DMM) surgery. Similar OA phenotypes were also observed in female iCKO mice. Moreover, tamoxifen injections of iCKO mice at 1 month post-surgery accelerated OA development 2 months later. In summary, our data demonstrated that chondrogenic EGFR signaling maintains postnatal slow-cycling cells and plays a critical role in adult cartilage homeostasis and OA progression. © 2022 American Society for Bone and Mineral Research (ASBMR).

Heterogeneity of cartilage damage in Kellgren and Lawrence grade 2 and 3 knees: the MOST study

OBJECTIVE

Eligibility for clinical trials in osteoarthritis (OA) is usually limited to Kellgren-Lawrence (KL) grades 2 and 3 knees. Our aim was to describe the prevalence and severity of cartilage damage in KL 2 and 3 knees by compartment and articular subregion.

DESIGN

The Multicenter Osteoarthritis (MOST) study is a cohort study of individuals with or at risk for knee OA. All baseline MRIs with radiographic disease severity KL2 and 3 were included. Knee MRIs were read for cartilage damage in 14 subregions. We determined the frequencies of no, any and widespread full-thickness cartilage damage by knee compartment, and the prevalence of any cartilage damage in 14 articular subregions.

RESULTS

665 knees from 665 participants were included (mean age 63.8 ± 7.9 years, 66.5% women). 372 knees were KL2 and 293 knees were KL3. There was no cartilage damage in 78 (21.0%) medial tibio-femoral joint (TFJ), 157 (42.2%) lateral TFJ and 62 (16.7%) patello-femoral joint (PFJ) compartments of KL2 knees, and 17 (5.8%), 115 (39.3%) and 35 (12.0%) compartments, respectively, of KL3 knees. There was widespread full-thickness damage in 94 (25.3%) medial TFJ, 36 (9.7%) lateral TFJ and 176 (47.3%) PFJ compartments of KL2 knees, and 217 (74.1%), 70 (23.9%) and 104 (35.5%) compartments, respectively, of KL3 knees. The subregions most likely to have any damage were central medial femur (80.5%), medial patella (69.8%) and central medial tibia (69.9).

CONCLUSIONS

KL2 and KL3 knees vary greatly in cartilage morphology. Heterogeneity in the prevalence, severity and location of cartilage damage in in KL2 and 3 knees should be considered when planning disease modifying trials for knee OA.

Osteoarthritis Pathophysiology: Therapeutic Target Discovery may Require a Multifaceted Approach

Molecular understanding of osteoarthritis (OA) has greatly increased through careful analysis of tissue samples, preclinical models, and large-scale agnostic "-omic" studies. There is broad acceptance that systemic and biomechanical signals affect multiple tissues of the joint, each of which could potentially be targeted to improve patient outcomes. In this review six experts in different aspects of OA pathogenesis provide their independent view on what they believe to be good tractable approaches to OA target discovery. We conclude that molecular discovery has been high but future transformative studies require a multidisciplinary holistic approach to develop therapeutic strategies with high clinical efficacy.

Roles of Chondroitin Sulfate Proteoglycans as Regulators of Skeletal Development

The extracellular matrix (ECM) is critically important for most cellular processes including differentiation, morphogenesis, growth, survival and regeneration. The interplay between cells and the ECM often involves bidirectional signaling between ECM components and small molecules, i.e., growth factors, morphogens, hormones, etc., that regulate critical life processes. The ECM provides biochemical and contextual information by binding, storing, and releasing the bioactive signaling molecules, and/or mechanical information that signals from the cell membrane integrins through the cytoskeleton to the nucleus, thereby influencing cell phenotypes. Using these dynamic, reciprocal processes, cells can also remodel and reshape the ECM by degrading and re-assembling it, thereby sculpting their environments. In this review, we summarize the role of chondroitin sulfate proteoglycans as regulators of cell and tissue development using the skeletal growth plate model, with an emphasis on use of naturally occurring, or created mutants to decipher the role of proteoglycan components in signaling paradigms.

Glucosamine as a Treatment for Osteoarthritis: What If It's True?

No disease-modifying treatments are currently available for osteoarthritis (OA). While many therapeutic approaches are now being investigated it is ethical to resort to alternative solutions as that we already possess. There are many reasons for thinking that, at sufficiently high doses, glucosamine (GlcN) sulphate possesses a clinically relevant effect on OA pain. Wide inter-individual variations in the symptomatic effects of GlcN are explained by the extreme variability of its bioavailability. In studies evaluating its structure-modifying effect, GlcN was more effective than placebo in reducing the rate of joint space narrowing in patients with knee OA. More recent data suggest that GlcN may be effective in the primary prevention of OA in sportsmen. There is no controversy concerning the safety of GlcN which does not differ to that of placebo. Several studies have recently revealed an unexpected effect of GlcN on cardiovascular mortality. After adjusting for confounding factors, the regular consumption of GlcN correlated with a 27% reduction in mortality and a 58% reduction in deaths from cardiovascular causes. These data confirm animal studies demonstrating a protective effect of GlcN against cancer and cardiovascular diseases due to modulation of the O-GlcNAcylation pathway. Disorders in O-GlcNAcylation are involved in diabetes, obesity and cancers, which all feature chronic low-grade inflammation (CLGI). By regulating CLGI, GlcN may be beneficial to the symptoms of OA, its outcome and to that of the concomitant chronic pathologies, making GlcN as a valuable candidate for the treatment of OA in patients with metabolic syndrome, diabetes or cardiovascular diseases.

Roles of the fibroblast growth factor signal transduction system in tissue injury repair

Following injury, tissue autonomously initiates a complex repair process, resulting in either partial recovery or regeneration of tissue architecture and function in most organisms. Both the repair and regeneration processes are highly coordinated by a hierarchy of interplay among signal transduction pathways initiated by different growth factors, cytokines and other signaling molecules under normal conditions. However, under chronic traumatic or pathological conditions, the reparative or regenerative process of most tissues in different organs can lose control to different extents, leading to random, incomplete or even flawed cell and tissue reconstitution and thus often partial restoration of the original structure and function, accompanied by the development of fibrosis, scarring or even pathogenesis that could cause organ failure and death of the organism. Ample evidence suggests that the various combinatorial fibroblast growth factor (FGF) and receptor signal transduction systems play prominent roles in injury repair and the remodeling of adult tissues in addition to embryonic development and regulation of metabolic homeostasis. In this review, we attempt to provide a brief update on our current understanding of the roles, the underlying mechanisms and clinical application of FGFs in tissue injury repair.

Recombinant fibroblast growth factor-18 (sprifermin) enhances microfracture-induced cartilage healing

Posttraumatic osteoarthritis is a disabling condition impacting the mostly young and active population. In the present study, we investigated the impact of intra-articular sprifermin, a recombinant truncated fibroblast growth factor 18, on the outcome of microfracture treatment, a widely used surgical technique to enhance cartilage healing at the site of injury. For this study, we created a cartilage defect and performed microfracture treatment in fetlock joints of 18 horses, treated joints with one of three doses of sprifermin (10, 30, or 100 μg) or with saline, hyaluronan, and evaluated animals functional and structural outcomes over 24 weeks. For primary outcome measures, we performed histological evaluations and gene expression analysis of aggrecan, collagen types I and II, and cartilage oligomeric matrix protein in three regions of interest. As secondary outcome measures, we examined animals' lameness, performed arthroscopic, radiographic, and computed tomography (CT) scan imaging and gross morphology assessment. We detected the highest treatment benefit following 100 μg sprifermin treatment. The overall histological assessment showed an improvement in the kissing region, and the expression of constitutive genes showed a concentration-dependent enhancement, especially in the peri-lesion area. We detected a significant improvement in lameness scores, arthroscopic evaluations, radiography, and CT scans following sprifermin treatment when results from three dose-treatment groups were combined. Our results demonstrated, for the first time, an enhancement on microfracture outcomes following sprifermin treatment suggesting a cartilage regenerative role and a potential benefit of sprifermin treatment in early cartilage injuries.

Adherence to the OARSI recommendations for designing, conducting, and reporting of clinical trials in knee osteoarthritis: a targeted literature review

Background

The Osteoarthritis Research Society International (OARSI) updated their guideline for clinical trials on knee osteoarthritis (KOA) in 2015, which contains recommendations for the conduct, design, and reporting of clinical trials. The purpose of this study was to assess the quality of clinical trials published between 2010 and 2020 investigating intra-articular interventions in patients with KOA using the OARSI recommendations.

Methods

A targeted literature review was conducted to identify randomized controlled trials in patients with KOA receiving intra-articular interventions, published between 2010 and 2020. Included studies were assessed using the OARSI recommendations. For a comparison between the time periods before and after the introduction of the new OARSI recommendations, the year 2016 was selected as the cut-off.

Results

One hundred forty-eight publications, representing 139 unique trials, were included in this review. Included studies adhered to between 9 and 24 recommendations (median: 19). The highest increase in adherence from studies published in 2016 or earlier compared to after 2016 was seen in the reporting and registration of trials and the use of structural outcome measures. Overall, adherence to the recommendations related to the collection of biochemical biomarkers and the use of structural outcome measures remained low.

Conclusion

An improvement can be made in the conduct, design, and reporting of clinical trials for intra-articular therapies in KOA. Despite proper guidelines, quality of clinical trials varies, and the methodological deficiencies found are preventable and can be corrected. The quality of research should be considered when making treatment decisions for patients with KOA in clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05116-z.

Hierarchical functional nanoparticles boost osteoarthritis therapy by utilizing joint-resident mesenchymal stem cells

Utilization of joint-resident mesenchymal stem cells (MSC) to repair articular cartilage is a promising strategy in osteoarthritis (OA) therapy but remains a considerable research challenge. Here, hierarchical targeting and microenvironment responsive peptide functionalized nanoparticles (NPs) are used to achieve cartilage repair in situ. Ultrasmall copper oxide (CuO) NPs are conjugated with type 2 collagen and MSC dual-targeting peptide (designated WPV) with a matrix metalloproteinase 2 (MMP-2)-sensitive sequence as a spacer to achieve hierarchical targeting. Guided by this peptide, WPV-CuO NPs initially penetrate cartilage and subsequently expose the inner MSC-targeted peptide to attract MSCs through MMP-2 clearance. CuO further promotes chondrogenesis of MSCs. In an anterior cruciate ligament transection rat model, intraarticular injection of WPV-CuO NPs induces significant reduction of cartilage destruction. The therapeutic mechanism involves inhibition of the PI3K/AKT/mTOR pathway, as determined via transcriptome analysis. In conclusion, a novel therapeutic strategy for OA has been successfully developed based on localized MSC recruitment and cartilage repair without transplantation of exogenous cells or growth factors.

Osteoarthritis year in review 2021: biology

This year in review on osteoarthritis biology summarizes a series of research articles published between the 2020 and 2021 Osteoarthritis Research Society International (OARSI) World Congress. Research hightlights were selected and discussed based on the new discoveries of OA's cellular molecular mechanism, anatomical signatures, potential therapeutic targets, and regenerative therapy. The recently developed potential therapeutic targets are summarized, and the research focuses on TGFβ and WNT signaling in joint tissue homeostasis, joint aging and the dynamic of synolytics in OA joint, and the roles of TRP2, LDHA, OSCAR in cartilage homeostasis and OA joints are highlighted. Subsquencially, new anatomical structures and OA features are introduced, such as synovitis-induced venous portal circulation, horiozontal fissures between cartilage and subchondral bone, the cellular derivation of osteophytes formation, OA subtypes, and subchondral remodeling and pain biology. Then, research on the possibility of tissue regeneration in OA joints are discussed; skeletal stem cells in OA cartilage regeneration, and preclinical results of regenerative therapy for meniscus tear and osteochondral tissue morphoghesis are included. At last, the clinical evidence of the importance of delivery site of bone marrow stem cells for OA treatment is discussed. These findings represent advances in our understanding of OA pathophysiology.

Medial Tibial Osteophyte Width Strongly Reflects Medial Meniscus Extrusion Distance and Medial Joint Space Width Moderately Reflects Cartilage Thickness in Knee Radiographs

BACKGROUND

The presence of medial tibial osteophytes on knee radiographs suggests cartilage wear, but may be associated with medial meniscus extrusion (MME). The joint space width of the medial compartment consists anatomically of cartilage and the medial meniscus, but which is most responsible for joint space narrowing remains unclear. Magnetic resonance imaging (MRI) reveals MME and cartilage thickness.

PURPOSES

To determine which radiographic medial tibial osteophyte width correlates better with cartilage thickness or MME distance and which radiographic medial joint space width correlates better with cartilage thickness or MME distance.

STUDY TYPE

Cross-sectional.

POPULATION

Total of 527 subjects, 253 females and 274 males, aged 30-79 years, included in the Kanagawa Knee Study.

FIELD STRENGTH/SEQUENCE

3 T/fat-suppressed spoiled gradient echo and proton density weighted.

ASSESSMENT

The medial tibial osteophyte width and "the minimum joint space width at the medial compartment" (mJSW) were measured from plain radiographs. The cartilage region was automatically extracted from MRI data using software. The medial femoral and tibial cartilage regions were each divided into nine subregions, and the average thickness of the cartilage was determined in each region and subregion. MME was manually measured by two orthopedic surgeons using MRI coronal section images.

STATISTICAL TESTS

Pearson's correlation coefficient and their comparison, with P < 0.05 considered statistically significant.

RESULTS

The absolute values of the correlation coefficients were 0.33 at maximum between osteophyte width and cartilage thickness and 0.76 between osteophyte width and MME; the value was significantly higher with MME than with cartilage thickness (P < 0.001). The absolute values of the correlation coefficients were 0.50 at maximum between mJSW and cartilage thickness and 0.16 between mJSW and MME; the value was significantly higher with cartilage thickness than with MME (P < 0.001).

DATA CONCLUSION

The medial tibial osteophyte width strongly reflected MME and the medial joint space width moderately reflected cartilage thickness.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 3.

Axial alignment is a critical regulator of knee osteoarthritis

Although osteoarthritis (OA), a leading cause of disability, has been associated with joint malalignment, scientific translational evidence for this link is lacking. In a clinical case study, we provide evidence of osteochondral recovery upon unloading symptomatic isolated medial tibiofemoral knee OA associated with varus malalignment. By mapping response correlations at high resolution, we identify spatially complex degenerative changes in cartilage after overloading in a clinically relevant ovine model. We further report that unloading diminishes OA cartilage degeneration and alterations of critical parameters of the subchondral bone plate in a similar topographic fashion. Last, therapeutic unloading shifted the articular cartilage and subchondral bone phenotype to normal and restored several physiological correlations disturbed in neutral and varus OA, suggesting a protective effect on the integrity of the entire osteochondral unit. Collectively, these findings identify modifiable trajectories with considerable translational potential to reduce the burden of human OA.

Sprifermin: Effects on Cartilage Homeostasis and Therapeutic Prospects in Cartilage-Related Diseases

When suffering from osteoarthritis (OA), articular cartilage homeostasis is out of balance and the living quality declines. The treatment of knee OA has always been an unsolved problem in the world. At present, symptomatic treatment is mainly adopted for OA. Drug therapy is mainly used to relieve pain symptoms, but often accompanied with adverse reactions; surgical treatment involves the problem of poor integration between the repaired or transplanted tissues and the natural cartilage, leading to the failure of repair. Biotherapy which aims to promote cartilage in situ regeneration and to restore endochondral homeostasis is expected to be an effective method for the prevention and treatment of OA. Disease-modifying osteoarthritis drugs (DMOADs) are intended for targeted treatment of OA. The DMOADs prevent excessive destruction of articular cartilage through anti-catabolism and stimulate tissue regeneration via excitoanabolic effects. Sprifermin (recombinant human FGF18, rhFGF18) is an effective DMOAD, which can not only promote the proliferation of articular chondrocyte and the synthesis of extracellular matrix, increase the thickness of cartilage in a dose-dependent manner, but also inhibit the activity of proteolytic enzymes and remarkedly slow down the degeneration of cartilage. This paper reviews the unique advantages of Sprifermin in repairing cartilage injury and improving cartilage homeostasis, aiming to provide an important strategy for the effective prevention and treatment of cartilage injury-related diseases.

Low levels of type II collagen formation (PRO-C2) are associated with response to sprifermin: a pre-defined, exploratory biomarker analysis from the FORWARD study

OBJECTIVE

Osteoarthritis (OA) is characterized by the gradual loss of cartilage. Sprifermin, a recombinant FGF18, is being developed as a cartilage anabolic drug. PRO-C2 is a serum marker of type II collagen formation and low levels have been shown to be prognostic of radiographic progression. The aim of the study was to investigate whether the patient groups with either high or low PRO-C2 levels responded differently to sprifermin.

DESIGN

PRO-C2 was measured in synovial fluid (SF) (n = 59) and serum samples (n = 225) from participants of the FORWARD study, a 2-year phase IIb clinical trial testing the efficacy of intra-articular (IA) sprifermin over placebo. The difference between sprifermin and placebo in respect to in change cartilage thickness (measured by quantitative (q) MRI) was analyzed in groups with either high or low (3^rd vs 1^st-2^nd tertiles) baseline serum PRO-C2 levels.

RESULTS

SF levels of PRO-C2 increased over time in response to sprifermin, but not to placebo. In the placebo arm, significantly (p = 0.005) more cartilage was lost in the low vs high PRO-C2 group over the 2-year period. The contrast between sprifermin and placebo was significant (p < 0.001), ranging from 0.104 mm at week 26 to 0.229 mm at week 104 in the low PRO-C2 group. This result was not significant in the high PRO-C2 group ranging from -0.034 to 0.142.

CONCLUSIONS

Patients with low serum PRO-C2 levels lost more cartilage thickness over time and grew more cartilage in response to sprifermin vs a placebo when compared to patients with high PRO-C2 levels.

New developments in osteoarthritis pharmacological therapies

OA is an increasingly common, painful condition with complex aetiology and limited therapies. Approaches to expanding our therapeutic armamentarium have included repurposing existing therapies used for other rheumatological conditions, modifying existing OA preparations to enhance their benefits, and identifying new therapeutics. HCQ and low-dose MTX have been unsuccessful in improving hand OA pain or reducing structural progression. Anti-IL-6 and anti-GM-CSF also did not improve symptoms in hand OA trials, but IL-1 remains an intriguing target for large-joint OA, based on reduced joint replacements in a post hoc analysis from a large cardiovascular disease trial. The peripheral nociceptive pathway appears an attractive target, with mAbs to nerve growth factor and IA capsaicin demonstrating efficacy; tropomyosin receptor kinase A inhibitors are at an earlier stage of development. Limited evidence suggests pharmacological therapies can modify cartilage and bone structural progression, though evidence of synchronous symptom benefits are lacking.

Mechanosignalling in cartilage: an emerging target for the treatment of osteoarthritis

Mechanical stimuli have fundamental roles in articular cartilage during health and disease. Chondrocytes respond to the physical properties of the cartilage extracellular matrix (ECM) and the mechanical forces exerted on them during joint loading. In osteoarthritis (OA), catabolic processes degrade the functional ECM and the composition and viscoelastic properties of the ECM produced by chondrocytes are altered. The abnormal loading environment created by these alterations propagates cell dysfunction and inflammation. Chondrocytes sense their physical environment via an array of mechanosensitive receptors and channels that activate a complex network of downstream signalling pathways to regulate several cell processes central to OA pathology. Advances in understanding the complex roles of specific mechanosignalling mechanisms in healthy and OA cartilage have highlighted molecular processes that can be therapeutically targeted to interrupt pathological feedback loops. The potential for combining these mechanosignalling targets with the rapidly expanding field of smart mechanoresponsive biomaterials and delivery systems is an emerging paradigm in OA treatment. The continued advances in this field have the potential to enable restoration of healthy mechanical microenvironments and signalling through the development of precision therapeutics, mechanoregulated biomaterials and drug systems in the near future.

Osteoarthritis: A Review of Novel Treatments and Drug Targets

Osteoarthritis affects over 10% of our population over the age of 60 years old, significantly reducing their quality of life and increasing morbidity. A number of aetiological factors contribute to the development of osteoarthritis including obesity, genetic factors, injury and increasing age. Many of the pathological processes which underlie the condition remain poorly understood and therefore limited progress has been made in developing effective disease modifying treatments. This review article aims to summarise our current understanding of osteoarthritis, the molecular mechanisms which drive the disease and current progress in developing therapeutic strategies to target these. 

An up to date on clinical prospects and management of osteoarthritis

The rising prevalence of osteoarthritis (OA) in the general population has necessitated the development of novel treatment options. It is critical to recognize the joint as a separate entity participating in degenerative processes, as well as the multifaceted nature of OA. OA is incurable because there is currently no medication that can stop or reverse cartilage or bone loss. As this point of view has attracted attention, more research is being directed toward determining how the various joint components are impacted and how they contribute to OA pathogenesis. Over the next few years, several prospective therapies focusing on inflammation, cartilage metabolism, subchondral bone remodelling, cellular senescence, and the peripheral nociceptive pathway are predicted to transform the OA therapy landscape. Stem cell therapies and the use of various biomaterials to target articular cartilage (AC) and osteochondral tissues are now being investigated in considerable detail. Currently, laboratory-made cartilage tissues are on the verge of being used in clinical settings. This review focuses on the update of clinical prospects and management of osteoarthritis, as well as future possibilities for the treatment of OA.

•

Osteoarthritis (OA) is a general term that incorporates several different joint diseases.

•

The exact pathophysiology of OA remains unclear.

•

OA is incurable because there is currently no medication that can stop or reverse cartilage or bone loss.

•

Nonsteroidal anti-inflammatory drugs are the most frequently prescribed medications to alleviate arthritic discomfort.

•

Stem cell therapies to target articular cartilage and osteochondral tissues are now under investigation.

The future of deep phenotyping in osteoarthritis: How can high throughput omics technologies advance our understanding of the cellular and molecular taxonomy of the disease?

Osteoarthritis (OA) is the most common form of musculoskeletal disease with significant healthcare costs and unmet needs in terms of early diagnosis and treatment. Many of the drugs that have been developed to treat OA failed in phase 2 and phase 3 clinical trials or produced inconclusive and ambiguous results. High throughput omics technologies are a powerful tool to better understand the mechanisms of the development of OA and other arthritic diseases. In this paper we outline the strategic reasons for increasingly applying deep phenotyping in OA for the benefit of gaining a better understanding of disease mechanisms and developing targeted treatments. This editorial is intended to launch a special themed issue of Osteoarthritis and Cartilage Open addressing the timely topic of "Advances in omics technologies for deep phenotyping in osteoarthritis". High throughput omics technologies are increasingly being applied in mechanistic studies of OA and other arthritic diseases. Applying multi-omics approaches in OA is a high priority and will allow us to gather new information on disease pathogenesis at the cellular level, and integrate data from diverse omics technology platforms to enable deep phenotyping. We anticipate that new knowledge in this area will allow us to harness the power of Big Data Analytics and resolve the extremely complex and overlapping clinical phenotypes into molecular endotypes, revealing new information about the cellular taxonomy of OA and "druggable pathways", thus facilitating future drug development.

Blockade of Fgfr1 with PD166866 Protects Cartilage from the Catabolic Effects Induced by Interleukin-1β: A Genome-Wide Expression Profiles Analysis

OBJECTIVE

Previously we showed that genetic deletion of Fgfr1 in chondrocytes protected mice from progression of osteoarthritis (OA). The aim of this study is to evaluate the effect of PD166866, a potent selective inhibitor of Fgfr1, on cartilage degeneration induced by interleukin-1β (IL-1β) and to clarify underlying global gene expression pattern.

DESIGN

Cartilage explants and primary rat chondrocytes were stimulated with IL-1β to establish an inflammatory OA in vitro model. The effects of PD166866 were determined by measuring the release of glycosaminoglycans (GAG) in cartilage explants and primary rat chondrocytes, and the underlying molecular mechanism was analyzed by microarray and RT-PCR analysis in primary chondrocytes.

RESULTS

In cartilage explants, PD166866 significantly counteracts IL-β stimulated GAG release. In addition, PD166866 impede IL-1β-stimulated nuclear translocation of p65 in rat chondrocytes. Based on microarray analysis, a total of 67 and 132 genes with more than 1.5-fold changes were identified in IL-1β-treated versus control and PD166866 cotreatment versus IL-1β treatment alone, respectively. Only 19 thereof were coregulated by IL-1β and PD166866 simultaneously. GO and KEGG pathway analysis showed that some pathways, including "cytokine-cytokine receptor interaction," "chemokine signaling pathway," and "complement and coagulation cascades," as well as some key genes like chemokines, complement, and matrix metalloproteinases may relevant for therapeutic application of Fgfr1 blockade in IL-1β-stimulated chondrocytes.

CONCLUSION

Our results clearly demonstrated that blockade of Fgfr1 with PD166866 could effectively suppress the catabolic effects induced by IL-1β, and elucidated whole genomic targets of Fgfr1 inhibition responsible for the therapeutic effects of Fgfr1 blockade against inflammatory OA.

Challenges and opportunities of pharmacological interventions for osteoarthritis: A review of current clinical trials and developments

Objective

Osteoarthritis (OA) is the most common cause of disability in older adults, and leads to a huge unmet medical need, as no registered disease modifying OA drugs (DMOADs), but only symptomatic treatments, are available. New targets and compounds for these targets, are currently under investigation. The objective of this paper is to provide an overview of compounds under investigation for OA in phase II and III.

Design

We performed a review of OA trials for pharmacological interventions registered on the National Library of Medicine ClinicalTrials.gov website with a completion date in 2017 or later.

Results

The database search yielded 255 results, of which 184 studies were included in this review. These were structured in compounds targeting pain, immunomodulators, stem cell therapy, platelet rich plasma and DMOADs with cartilage and/or bone resorption modifying properties.

Conclusions

The results provide an overview of the fields in development and may include future treatment options for OA, by which a registered DMOADs may become more than a utopic vista. Further knowledge on pathophysiology and new approaches of value-based drug development could be an opportunity for the optimization of drug development in OA.

Emerging and New Treatment Options for Knee Osteoarthritis

Osteoarthritis (OA) is the most prevalent type of arthritis worldwide, resulting in pain and often chronic disability and a significant burden on healthcare systems globally. Non-steroidal anti-inflammatory drugs (NSAIDs), analgesics, intra-articular corticosteroid injections are of little value in the long term, and opioids may have ominous consequences. Radiotherapy of knee OA has no added value. Physical therapy, exercises, weight loss, and lifestyle modifications may give pain relief, improve physical functioning and quality of life. However, no single treatment has regenerating potential for damaged articular cartilage. Due to a better understanding of osteoarthritis, innovative new treatment options have been developed. In this narrative review, we focus on emerging OA knee treatments, relieving symptoms, and regenerating damaged articular cartilage that includes intra-articular human serum albumin, conventional disease-modifying anti-rheumatic drugs (DMARDs), lipid-lowering agents (statin), nerve growth factors antagonists, bone morphogenetic protein, fibroblast growth factors, Platelet-Rich Plasma (PRP), Mesenchymal Stem Cells (MSC), exosomes, interleukin-1 blockers, gene-based therapy, and bisphosphonate.

Uncovering associations between data-driven learned qMRI biomarkers and chronic pain

Knee pain is the most common and debilitating symptom of knee osteoarthritis (OA). While there is a perceived association between OA imaging biomarkers and pain, there are weak or conflicting findings for this relationship. This study uses Deep Learning (DL) models to elucidate associations between bone shape, cartilage thickness and T₂ relaxation times extracted from Magnetic Resonance Images (MRI) and chronic knee pain. Class Activation Maps (Grad-CAM) applied on the trained chronic pain DL models are used to evaluate the locations of features associated with presence and absence of pain. For the cartilage thickness biomarker, the presence of features sensitive for pain presence were generally located in the medial side, while the features specific for pain absence were generally located in the anterior lateral side. This suggests that the association of cartilage thickness and pain varies, requiring a more personalized averaging strategy. We propose a novel DL-guided definition for cartilage thickness spatial averaging based on Grad-CAM weights. We showed a significant improvement modeling chronic knee pain with the inclusion of the novel biomarker definition: likelihood ratio test p-values of 7.01 × 10^–33 and 1.93 × 10^–14 for DL-guided cartilage thickness averaging for the femur and tibia, respectively, compared to the cartilage thickness compartment averaging.

Soluble biological markers in osteoarthritis

In recent years, markers research has focused on the structural components of cartilage matrix. Specifically, a second generation of degradation markers has been developed against type II collagen neoepitopes generated by specific enzymes. A particular effort has been made to measure the degradation of minor collagens III and X of the cartilage matrix. However, because clinical data, including longitudinal controlled studies, are very scarce, it remains unclear whether they will be useful as an alternative to or in combination with current more established collagen biological markers to assess patients with osteoarthritis (OA). In addition, new approaches using high-throughput technologies allowed to detect new types of markers and improve the knowledge about the metabolic changes linked to OA. The relative advances coming from phenotype research are a first attempt to classify the heterogeneity of OA, and several markers could improve the phenotype characterization. These phenotypes could improve the selection of patients in clinical trials limiting the size of the studies by selecting patients with OA characteristics corresponding to the metabolic pathway targeted by the molecules evaluated. In addition, the inclusion of rapid progressors only in clinical trials would facilitate the demonstration of efficacy of the investigative drug to reduce joint degradation. The combination of selective biochemical markers appears as a promising and cost-effective approach to fulfill this unmet clinical need. Among the various potential roles of biomarkers in OA, their ability to monitor drug efficacy is probably one of the most important, in association with clinical and imaging parameters. Biochemical markers have the unique property to detect changes in joint tissue metabolism within a few weeks.

Pro-regenerative Dialogue Between Macrophages and Mesenchymal Stem/Stromal Cells in Osteoarthritis

Osteoarthritis (OA), the most common degenerative and inflammatory joint disorder, is multifaceted. Indeed, OA characteristics include cartilage degradation, osteophytes formation, subchondral bone changes, and synovium inflammation. The difficulty in discovering new efficient treatments for OA patients up to now comes from the adoption of monotherapy approaches targeting either joint tissue repair/catabolism or inflammation to address the diverse components of OA. When satisfactory, these approaches only provide short-term beneficial effects, since they only result in the repair and not the full structural and functional reconstitution of the damaged tissues. In the present review, we will briefly discuss the current therapeutic approaches used to repair the damaged OA cartilage. We will highlight the results obtained with cell-based products in clinical trials and demonstrate how the current strategies result in articular cartilage repair showing restricted early-stage clinical improvements. In order to identify novel therapeutic targets and provide to OA patients long-term clinical benefits, herein, we will review the basis of the regenerative process. We will focus on macrophages and their ambivalent roles in OA development and tissue regeneration, and review the therapeutic strategies to target the macrophage response and favor regeneration in OA.