Hyaluronan concentration and size distribution in human knee synovial fluid: variations with age and cartilage degeneration

Predictors of lower knee function improvement two years after anterior cruciate ligament reconstruction

OBJECTIVES

The extent to which knee functions improve after anterior cruciate ligament reconstruction (ACLR) varies. This study aimed to determine the factors that affect lower knee function improvement after two years of ACLR.

METHODS

The study included 159 patients who underwent ACLR in the Indonesian ACL community between August 2018 and April 2020. The concomitant injury and graft types of ACLR were determined using patients' pre-surgical MRI and medical records. The five subscales of the knee injury and osteoarthritis outcome score (KOOS) were used to evaluate the patient at baseline, first year, and second year following ACLR. A linear mixed-effect model (LMEM) was used to predict the longitudinal improvement models for the five-subscales KOOS score after ACLR.

RESULTS

The LMEM predicted lower KOOS subscales scores improvements by 0.5 for QOL, 0.1 for symptom, ADL, and QOL, and 0.2 for sports/recreation, respectively, for a one score increase of age and time from injury to surgery. Male patients had higher KOOS subscale scores with the improvement of pain, symptom, and ADL by 5.7, 5.9, and 6.3 compared to female patients, respectively, while patients with patellar tendon grafts had lower improvement of KOOS score pain by 6.5 compared to hamstring tendon grafts.

CONCLUSION

As the age and time from injury to surgery increased, the KOOS subscales scores of QOL and symptoms, ADL, sports/recreation, and QOL decreased. Male patients reported higher KOOS subscales scores for pain, symptoms, and ADL, while patients with patella tendon grafts had a lower improvement in pain score.

Hyaluronic Acid and Large Extracellular Vesicles (EVs) in Synovial Fluid and Plasma of Patients With End-Stage Arthritis: Positive Association of EVs to Joint Pain

OBJECTIVE

Hyaluronic acid (HA) in synovial fluid (SF) contributes to boundary lubrication with altered levels in osteoarthritis (OA) and rheumatoid arthritis (RA). SF extracellular vesicles (EVs) may participate in arthritis by affecting inflammation and cartilage degradation. It remains unknown whether HA and EVs display joint-specific alterations in arthritic SFs.

DESIGN

We investigated the numbers and characteristics of HA-particles and large EVs in SF from knees and shoulders of 8 OA and 8 RA patients and 8 trauma controls, and in plasma from 10 healthy controls and 11 knee OA patients. The plasma and SF HA concentrations were determined with a sandwich-type enzyme-linked sorbent assay, and EVs and HA-particles were characterized from plasma and unprocessed and centrifuged SFs with confocal microscopy. The data were compared according to diagnosis, location, and preanalytical processing.

RESULTS

The main findings were: (1) OA and RA SFs can be distinguished from trauma joints based on the distinctive profiles of HA-particles and large EVs, (2) there are differences in the SF HA and EV characteristics between shoulder and knee joints that could reflect their dissimilar mobility, weight-bearing, and shock absorption properties, (3) EV counts in SF and plasma can positively associate with pain parameters independent of age and body adiposity, and (4) low-speed centrifugation causes alterations in the features of HA-particles and EVs, complicating their examination in the original state.

CONCLUSIONS

Arthritis and anatomical location can affect the characteristics of HA-particles and large EVs that may have potential as biomarkers and effectors in joint degradation and pain.

An update on the study of synovial fluid in the geriatric patient

BACKGROUND

The characteristics of synovial fluid (SF) in geriatric patients differ from those in younger patients. In Mexico, epidemiologic data on the incidence of different rheumatic diseases in geriatric patients are scarce.

OBJECTIVE

To describe the physical characteristics of geriatric SF and the prevalence of crystals in knee and other joint aspirates from patients with previously diagnosed joint disease.

MATERIALS AND METHODS

A retrospective study was performed with a baseline of 517 SF samples between 2011 and 2023. White blood cell count was performed by Neubauer chamber and crystals were identified by polarized light microscopy. Descriptive statistical analysis was performed and prevalence was reported as a percentage.

RESULTS

The mean age of the adults was 73.5±5.0 years, 54.4% were women and 45.6% were men. The mean SF volume was 6.3±9.5mL in older adults and 15.3±24.9mL in those younger than 65 years. The mean viscosity in older adults was 9.5±4.5mm and the mean leukocyte count was 7352±16,402leukocytes/mm3. Seventy percent of the older adults' SFs were referred to the laboratory for osteoarthritis (OA), with lower proportions for rheumatoid arthritis (RA) (14.6%) and gout (5.1%). Of the crystals observed in the geriatric population, 14.6% corresponded to monosodium urate crystals (CUM) and 18.9% to calcium pyrophosphate crystals (CPP).

CONCLUSIONS

The characteristics of LS in older adults were smaller volume, increased viscosity, and non-inflammatory. The main diagnoses were OA, RA, and gout. The crystal content of the SF of the geriatric population corresponded mainly to CPP.

Age related changes in hyaluronan expression leads to Meibomian gland dysfunction

The prevalence of dry eye disease (DED) ranges from ∼5 to 50 % and its associated symptoms decrease productivity and reduce the quality of life. Approximately 85 % of all DED cases are caused by Meibomian gland dysfunction (MGD). As humans and mice age, their Meibomian glands (MGs) undergo age-related changes resulting in age related-MGD (ARMGD). The precise cause of ARMGD remains elusive, which makes developing therapies extremely challenging. We previously demonstrated that a hyaluronan (HA)-rich matrix exists surrounding the MG, regulating MG morphogenesis and homeostasis. Herein, we investigated whether changes to the HA matrix in the MG throughout life contributes towards ARMGD, and whether altering this HA matrix can prevent ARMGD. For such, HA synthase (Has) knockout mice were aged and compared to age matched wild type (wt) mice. MG morphology, lipid production, PPARγ expression, basal cell proliferation, stem cells, presence of atrophic glands and MG dropout were analyzed at 8 weeks, 6 months, 1 year and 2 years of age and correlated with the composition of the HA matrix. We found that as mice age, there is a loss of HA expression in and surrounding the MGs of wt mice, while, in contrast, Has1-/-Has3-/- mice present a significant increase in HA expression through Has2 upregulation. At 1 year, Has1-/-Has3-/- mice present significantly enlarged MGs, compared to age-matched wt mice and compared to all adult mice. Thus, Has1-/-Has3-/- mice continue to develop new glandular tissue as they age, instead of suffering MG atrophy. At 2 years, Has1-/-Has3-/- mice continue to present significantly larger MGs compared to age-matched wt mice. Has1-/-Has3-/- mice present increased lipid production, increased PPARγ expression and an increase in the number of proliferating cells when compared to wt mice at all-time points analyzed. Taken together, our data shows that a loss of the HA matrix surrounding the MG as mice age contributes towards ARMGD, and increasing Has2 expression, and consequently HA levels, prevents ARMGD in mice.

Ex Vivo Functional Benchmarking of Hyaluronan-Based Osteoarthritis Viscosupplement Products: Comprehensive Assessment of Rheological, Lubricative, Adhesive, and Stability Attributes

While many injectable viscosupplementation products are available for osteoarthritis (OA) management, multiple hydrogel functional attributes may be further optimized for efficacy enhancement. The objective of this study was to functionally benchmark four commercially available hyaluronan-based viscosupplements (Ostenil, Ostenil Plus, Synvisc, and Innoryos), focusing on critical (rheological, lubricative, adhesive, and stability) attributes. Therefore, in vitro and ex vivo quantitative characterization panels (oscillatory rheology, rotational tribology, and texture analysis with bovine cartilage) were used for hydrogel product functional benchmarking, using equine synovial fluid as a biological control. Specifically, the retained experimental methodology enabled the authors to robustly assess and discuss various functional enhancement options for hyaluronan-based hydrogels (chemical cross-linking and addition of antioxidant stabilizing agents). The results showed that the Innoryos product, a niacinamide-augmented linear hyaluronan-based hydrogel, presented the best overall functional behavior in the retained experimental settings (high adhesivity and lubricity and substantial resistance to oxidative degradation). The Ostenil product was conversely shown to present less desirable functional properties for viscosupplementation compared to the other investigated products. Generally, this study confirmed the high importance of formulation development and control methodology optimization, aiming for the enhancement of novel OA-targeting product critical functional attributes and the probability of their clinical success. Overall, this work confirmed the tangible need for a comprehensive approach to hyaluronan-based viscosupplementation product functional benchmarking (product development and product selection by orthopedists) to maximize the chances of effective clinical OA management.

ROS-Mediated Fragmentation Alters the Effects of Hyaluronan on Corneal Epithelial Wound Healing

A buildup of reactive oxygen species (ROS) occurs in virtually all pathological conditions. Hyaluronan (HA) is a major extracellular matrix component and is susceptible to oxidation by reactive oxygen species (ROS), yet the precise chemical structures of oxidized HA products (oxHA) and their physiological properties remain largely unknown. This study characterized the molecular weight (MW), structures, and physiological properties of oxHA. For this, high-molecular-weight HA (HMWHA) was oxidized using increasing molar ratios of hydrogen peroxide (H2O2) or hypochlorous acid (HOCl). ROS lead to the fragmentation of HA, with the oxHA products produced by HOCl exhibiting an altered chemical structure while those produced by H2O2 do not. HMWHA promotes the viability of human corneal epithelial cells (hTCEpi), while low MWHA (LMWHA), ultra-LMWHA (ULMWHA), and most forms of oxHA do not. HMWHA and LMWHA promote hTCEpi proliferation, while ULMWHA and all forms of oxHA do not. LMWHA and some forms of oxHA promote hTCEpi migration, while HMWHA does not. Finally, all native forms of HA and oxHA produced by HOCl promote in vivo corneal wound healing, while oxHA produced by H2O2 does not. Taken together, our results show that HA fragmentation by ROS can alter the physiological activity of HA by altering its MW and structure.

Treatment with CR500® improves algofunctional scores in patients with knee osteoarthritis: a post-market confirmatory interventional, single arm clinical investigation

BACKGROUND

Knee osteoarthritis (OA) is a progressive and degenerative condition. Several pharmacological and non-pharmacological treatments are able to improve the OA symptoms and the structural characteristics of the affected joints. Among these, infiltrative therapy with hyaluronic acid (HA) is the most used and consolidated procedure for the pain management. The addition of skin conditioning peptides to HA promotes the cartilage remodeling processes and a better permeation of the HA-based gel containing a peptide mixture, CR500®. Furthermore, the topic route of administration is convenient over the routinely used intra-articular injective procedures. In this study, the effectiveness of CR500® was evaluated in terms of improvement of the algo-functional symptoms related to unilateral knee OA.

METHODS

38 mild and moderate OA patients were enrolled at a screening visit (V-1), treated at baseline visit (V1), and then continued the topical application of CR500® twice a week for 4 weeks, and followed-up for 3 visits (V2-V4) from week 2 to 4. Lequesne Knee Index (LKI) and Knee injury and Osteoarthritis Outcome Score (KOOS) were collected. Synovial fluid was collected and used for the quantification of neoepitope of type II collagen (C2C), C-terminal telopeptide of type II collagen (CTX-II), type II collagen propeptide (CPII), tumor necrosis factor alpha (TNFα) and HA. The expression of CD11c and CD206 was evaluated on cell pellets.

RESULTS

Three patients were excluded, thus 35 patients were included in the analysis. The treatment with CR500® was safe and well tolerated, with 7.9% patients had mild adverse events, not related to the device. The LKI total score showed a significant decrease from V1 to V4. KOOS score also showed a significant improvement of patient condition at V2, V3 and V4 in comparison with V1 for all subscales, except for KOOS sport subscale which improved only from V3. At V1 a negative correlation among KOOS pain subscale values and C2C, CPII and TNFα levels was observed, as well as a positive correlation between KOOS pain subscale and CD11c/CD206 ratio.

CONCLUSION

CR500® is safe and appear to be effective in improving pain and function in OA patients during the 4 weeks of treatment.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT05661162. This trial was registered on 22/12/2022.

Extracellular matrix in synovium development, homeostasis and arthritis disease

Extracellular matrix (ECM) is a three-dimensional network entity composed of extracellular macromolecules. ECM in synovium not only supports the structural integrity of synovium, but also plays a crucial role in regulating homeostasis and damage repair response in synovium. Obvious disorders in the composition, behavior and function of synovial ECM will lead to the occurrence and development of arthritis diseases such as rheumatoid arthritis (RA), osteoarthritis (OA) and psoriatic arthritis (PsA). Based on the importance of synovial ECM, targeted regulation of the composition and structure of ECM is considered to be an effective measure for the treatment of arthritis disease. This paper reviews the current research status of synovial ECM biology, discusses the role and mechanism of synovial ECM in physiological status and arthritis disease, and summarizes the current strategies for targeting synovial ECM to provide information for the pathogenesis, diagnosis and treatment of arthritis disease.

Histological features of knee osteoarthritis treated with triamcinolone acetonide and hyaluronic acid

Osteoarthritis (OA) is one of the most common degenerative joint diseases leading to disability in the end stage. Although intra-articular triamcinolone acetonide (TA) is one of the OA treatments that have been widely used, the side effects of such corticosteroids are still controversial. Intra-articular hyaluronic acid (HA) injection is another therapeutic option for patients with OA who do not want to use corticosteroids because of their side effects. However, the difference between the histological features associated with TA and HA in the treatment of OA remains unclear. Thus, the present study aimed to compare the histological effects of TA and HA on the cartilage of patients with knee OA. In the current study, 31 patients diagnosed with grade 3-4 knee OA on the Kellgren-Lawrence radiographic grading scale were separated into three groups: TA (n=12); HA (n=7) and untreated group (n=12). Histological examination of the whole articular cartilages of the patients was performed with hematoxylin and eosin and Alcian staining, as well as using a TUNEL assay. Clinical data such as cartilage thickness, structural and component deterioration, proteoglycan levels, apoptosis and empty lacunae were compared between the three groups. The results showed a high level of deterioration in both TA and HA groups but not in the untreated group, although the thickness of cartilage in the HA group was lower compared with that in the TA and untreated groups. The proteoglycan levels in the TA group were lower compared with those in the HA group. Moreover, the number of empty lacunae in the HA group was higher compared with that in the TA group, while no difference in apoptosis was found between TA and HA groups. A significant difference was not found in the histological staining between TA and HA groups. On the other hand, a significant difference was found in cartilage deterioration between the medial and lateral sides in these groups. TA and HA groups showed comparable histological results. TA injection is cheaper and easier but has more adverse effects for patients with knee OA than HA injection. Therefore, orthopaedists should select TA or HA based on the economic and specific needs of patients.

Carbohydrate polymer-based bioadhesive formulations and their potentials for the treatment of ocular diseases: A review

Eyes are directly exposed to the outer environment and susceptible to infections, leading to various ocular disorders. Local medication is preferred to treat eye diseases due to its convenience and compliance. However, the rapid clearance of the local formulations highly limits the therapeutic efficacy. In the past decades, several carbohydrate bioadhesive polymers (CBPs), such as chitosan and hyaluronic acid, have been used in ophthalmology for sustained ocular drug delivery. These CBP-based delivery systems have improved the treatment of ocular diseases to a large extent but also caused some undesired effects. Herein, we aim to summarize the applications of some typical CBPs (including chitosan, hyaluronic acid, cellulose, cyclodextrin, alginate and pectin) in treating ocular diseases from the general view of ocular physiology, pathophysiology and drug delivery, and to provide a comprehensive understanding of the design of the CBP-based formulations for ocular use. The patents and clinical trials of CBPs for ocular management are also discussed. In addition, a discussion on the concerns of CBPs in clinical use and the possible solutions is presented.

Hyaluronan in the pathogenesis of acute and post-acute COVID-19 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recently emerged as the cause of a global pandemic. Infection with SARS-CoV-2 can result in COVID-19 with both acute and chronic disease manifestations that continue to impact many patients long after the resolution of viral replication. There is therefore great interest in understanding the host factors that contribute to COVID-19 pathogenesis. In this review, we address the role of hyaluronan (HA), an extracellular matrix polymer with roles in inflammation and cellular metabolism, in COVID-19 and critically evaluate the hypothesis that HA promotes COVID-19 pathogenesis. We first provide a brief overview of COVID-19 infection. Then we briefly summarize the known roles of HA in airway inflammation and immunity. We then address what is known about HA and the pathogenesis of COVID-19 acute respiratory distress syndrome (COVID-19 ARDS). Next, we examine potential roles for HA in post-acute SARS-CoV-2 infection (PASC), also known as "long COVID" as well as in COVID-associated fibrosis. Finally, we discuss the potential therapeutics that target HA as a means to treat COVID-19, including the repurposed drug hymecromone (4-methylumbelliferone). We conclude that HA is a promising potential therapeutic target for the treatment of COVID-19.

Rejuvenation of Senescent Mesenchymal Stem Cells to Prevent Age-Related Changes in Synovial Joints

Mesenchymal/medicinal stem/signaling cells (MSCs), well known for regenerative potential, have been involved in hundreds of clinical trials. Even if equipped with reparative properties, aging significantly decreases their biological activity, representing a major challenge for MSC-based therapies. Age-related joint diseases, such as osteoarthritis, are associated with the accumulation of senescent cells, including synovial MSCs. An impaired ability of MSCs to self-renew and differentiate is one of the main contributors to the human aging process. Moreover, senescent MSCs (sMSCs) are characterized by the senescence-messaging secretome (SMS), which is typically manifested by the release of molecules with an adverse effect. Many factors, from genetic and metabolic pathways to environmental stressors, participate in the regulation of the senescent phenotype of MSCs. To better understand cellular senescence in MSCs, this review discusses the characteristics of sMSCs, their role in cartilage and synovial joint aging, and current rejuvenation approaches to delay/reverse age-related pathological changes, providing evidence from in vivo experiments as well.

Endogenous production of hyaluronan, PRG4, and cytokines is sensitive to cyclic loading in synoviocytes

Synovial fluid is composed of hyaluronan and proteoglycan-4 (PRG4 or lubricin), which work synergistically to maintain joint lubrication. In diseases like osteoarthritis, hyaluronan and PRG4 concentrations can be altered, resulting in lowered synovial fluid viscosity, and pro-inflammatory cytokine concentrations within the synovial fluid increase. Synovial fibroblasts within the synovium are responsible for contributing to synovial fluid and can be targeted to improve endogenous production of hyaluronan and PRG4 and to alter the cytokine profile. We cyclically loaded SW982 synoviocytes to 0%, 5%, 10%, or 20% strain for three hours at 1 Hz. To assess the impact of substrate stiffness, we compared the 0% strain group to cells grown on tissue culture plastic. We measured the expression of hyaluronan turnover genes, hyaluronan localization within the cell layer, hyaluronan concentration, PRG4 concentration, and the cytokine profile within the media. Our results show that the addition of cyclic loading increased HAS3 expression, but not in a magnitude-dependent response. Hyaluronidase expression was impacted by strain magnitude, which is exemplified by the decrease in hyaluronan concentration due to cyclic loading. We also show that PRG4 concentration is increased at 5% strain, while higher strain magnitude decreases overall PRG4 concentration. Finally, 10% and 20% strain show a distinct, more pro-inflammatory cytokine profile when compared to the unloaded group. Multivariate analysis showed distinct separation between certain strain groups in being able to predict strain group, hyaluronan concentration, and PRG4 concentration from gene expression or cytokine concentration data, highlighting the complexity of the system. Overall, this study shows that cyclic loading can be used tool to modulate the endogenous production of hyaluronan, PRG4, and cytokines from synovial fibroblasts.

Knee Diameter and Cross-Sectional Area as Biomarkers for Cartilage Knee Degeneration on Magnetic Resonance Images

Background and Objectives: Osteoarthritis (OA) of the knee is a degenerative disorder characterized by damage to the joint cartilage, pain, swelling, and walking disability. The purpose of this study was to assess whether demographic and radiologic parameters (knee diameters and knee cross-sectional area from magnetic resonance (MR) images) could be used as surrogate biomarkers for the prediction of OA. Materials and Methods: The knee diameters and cross-sectional areas of 481 patients were measured on knee MR images, and the corresponding demographic parameters were extracted from the patients' clinical records. The images were graded based on the modified Outerbridge arthroscopic classification that was used as ground truth. Receiver-operating characteristic (ROC) analysis was performed on the collected data. Results: ROC analysis established that age was the most accurate predictor of severe knee cartilage degeneration (corresponding to Outerbridge grades 3 and 4) with an area under the curve (AUC) of the specificity-sensitivity plot of 0.865 ± 0.02. An age over 41 years was associated with a sensitivity and specificity for severe degeneration of 82.8% (CI: 77.5-87.3%), and 76.4% (CI: 70.4-81.6%), respectively. The second-best degeneration predictor was the normalized knee cross-sectional area, with an AUC of 0.767 ± 0.04), followed by BMI (AUC = 0.739 ± 0.02), and normalized knee maximal diameter (AUC = 0.724 ± 0.05), meaning that knee degeneration increases with increasing knee diameter. Conclusions: Age is the best predictor of knee damage progression in OA and can be used as surrogate marker for knee degeneration. Knee diameters and cross-sectional area also correlate with the extent of cartilage lesions. Though less-accurate predictors of damage progression than age, they have predictive value and are therefore easily available surrogate markers of OA that can be used also by general practitioners and orthopedic surgeons.

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

N-Butyrylated Hyaluronic Acid Achieves Anti-Inflammatory Effects In Vitro and in Adjuvant-Induced Immune Activation in Rats

Previously synthesized N-butyrylated hyaluronic acid (BHA) provides anti-inflammatory effects in rat models of acute gouty arthritis and hyperuricemia. However, the mechanism of action remains to be elucidated. Herein, the anti-inflammatory and antioxidative activities of BHA and the targeted signaling pathways were explored with LPS-induced RAW264.7 and an adjuvant-induced inflammation in a rat model. Results indicated that BHA inhibited the generation of pro-inflammatory cytokines TNFα, IL-1β and IL-6, reduced ROS production and down-regulated JAK1-STAT1/3 signaling pathways in LPS-induced RAW264.7. In vivo, BHA alleviated paw and joint swelling, decreased inflammatory cell infiltration in paw tissues, suppressed gene expressions of p38 and p65, down-regulated the NF-κB and MAPK signaling pathways and reduced protein levels of TNFα, IL-1β and IL-6 in joint tissues of arthritis rats. This study demonstrated the pivotal role of BHA in anti-inflammation and anti-oxidation, suggesting the potential clinical value of BHA in the prevention of inflammatory arthritis and is worthy for development as a new pharmacological treatment.

Synovial inflammation in osteoarthritis progression

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. Synovial inflammation is present in the OA joint and has been associated with radiographic and pain progression. Several OA risk factors, including ageing, obesity, trauma and mechanical loading, play a role in OA pathogenesis, likely by modifying synovial biology. In addition, other factors, such as mitochondrial dysfunction, damage-associated molecular patterns, cytokines, metabolites and crystals in the synovium, activate synovial cells and mediate synovial inflammation. An understanding of the activated pathways that are involved in OA-related synovial inflammation could form the basis for the stratification of patients and the development of novel therapeutics. This Review focuses on the biology of the OA synovium, how the cells residing in or recruited to the synovium interact with each other, how they become activated, how they contribute to OA progression and their interplay with other joint structures.

Low density neutrophils are increased in patients with Behçet’s disease but do not explain differences in neutrophil function

Background

Behçet’s disease (BD) is a multisystem autoinflammatory disease characterised by mucosal ulceration, ocular, neural, joint and skin inflammation. The cause of BD is not known but there is a strong genetic association with HLA-B*51, IL10 and IL23R. Neutrophils are a first line of defence against invading pathogens and have been described as activated in patients with BD. Neutrophils can now be separated into different subsets, such as low density (LDN) and normal density (NDN) that have diverse functional roles. We wished to address neutrophil heterogeneity in patients with BD.

Methods

Peripheral blood neutrophils were obtained from 32 BD patients and 37 healthy aged-matched controls. Percoll isolation was used to isolate all neutrophils, while Ficol-Hypaque was used to obtain LDN and NDN. Phagocytic capacity and production of reactive oxygen species (ROS), and neutrophil extracellular traps (NET) stimulated with phorbol 12-myristate 13-acetate (PMA) and Escherichia coli (E.coli) were assessed in both groups.

Results

We have demonstrated reduced phagocytic capacity and ROS production but greater NET production by total neutrophils stimulated with PMA or E.coli from BD patients in comparison with healthy controls. Patients with BD had elevated numbers of LDN and lower number of NDN compared with healthy controls. However, both neutrophil subsets showed the same reduced ROS production and phagocytic function as total neutrophils in both groups.

Conclusion

Our novel findings indicate that the neutrophil population in BD is heterogeneous and the increased number of LDN in combination with greater NET production may contribute to the inflammatory response and pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12950-022-00302-1.

Optimizing the sensitivity and resolution of hyaluronan analysis with solid-state nanopores

Hyaluronan (HA) is an essential carbohydrate in vertebrates that is a potentially robust bioindicator due to its critical roles in diverse physiological functions in health and disease. The intricate size-dependent function that exists for HA and its low abundance in most biological fluids have highlighted the need for sensitive technologies to provide accurate and quantitative assessments of polysaccharide molecular weight and concentration. We have demonstrated that solid state (SS-) nanopore technology can be exploited for this purpose, given its molecular sensitivity and analytical capacity, but there remains a need to further understand the impacts of experimental variables on the SS-nanopore signal for optimal interpretation of results. Here, we use model quasi-monodisperse HA polymers to determine the dependence of HA signal characteristics on a range of SS-nanopore measurement conditions, including applied voltage, pore diameter, and ionic buffer asymmetry. Our results identify important factors for improving the signal-to-noise ratio, resolution, and sensitivity of HA analysis with SS-nanopores.

Rapid Temperature-Dependent Rheological Measurements of Non-Newtonian Solutions Using a Machine-Learning Aided Microfluidic Rheometer

Biofluids such as synovial fluid, blood plasma, and saliva contain several proteins which impart non-Newtonian properties to the biofluids. The concentration of such protein macromolecules in biofluids is regarded as an important biomarker for the diagnosis of several health conditions, including cardiovascular disorders, joint quality, and Alzheimer's. Existing technologies for the measurements of macromolecules in biofluids are limited; they require a long turnaround time, or require complex protocols, thus calling for alternative, more suitable, methodologies aimed at such measurements. According to the well-established relations for polymer solutions, the concentration of macromolecules in solutions can also be derived via measurement of rheological properties such as shear-viscosity and the longest relaxation time. We here introduce a microfluidic rheometer for rapid simultaneous measurement of shear viscosity and longest relaxation time of non-Newtonian solutions at different temperatures. At variance with previous technologies, our microfluidic rheometer provides a very short turnaround time of around 2 min or less thanks to the implementation of a machine-learning algorithm. We validated our platform on several aqueous solutions of poly(ethylene oxide). We also performed measurements on hyaluronic acid solutions in the clinical range for joint grade assessment. We observed monotonic behavior with the concentration for both rheological properties, thus speculating on their use as potential rheo-markers, i.e., rheological biomarkers, across several disease states.

Increasing Concentration of Sinovial: Effect on Cartilage Protection in a Rabbit ACLT Model

OBJECTIVE

This study aimed to test the hypothesis that administration of increasing doses of Sinovial (hyaluronic acid [HA]), would exhibit a dose-dependent effect on the prevention of cartilage degradation, without local and systemic toxicity.

METHODS

Twenty-seven adult rabbits were subjected to anterior cruciate ligament transection (ACLT). Two Sinovial products containing HA concentrations of 1.6% and 2.4% were used as active treatment, and 0.9% saline was used as control and injected intra-articularly 7 days post ACLT. Radiographs were taken prior to surgery, at injection and sacrifice times. After euthanasia, 8 weeks postsurgery, knee joints were observed macroscopically using India ink staining with OARSI (Osteoarthritis Research Society International) scoring and histologically using modified Mankin scoring. The synovial membranes were analyzed using Cake classification.

RESULTS

No intraoperative complications were observed. One week postinjection, 4 animals in the HA 2.4% group developed subcutaneous nodules that disappeared spontaneously. No inflammation of the synovial membrane was ever observed. The control group exhibited the maximum uptake of India ink 2.22 ± 0.14. HA groups exhibited a dose-dependent (P = 0.02) reduction in India ink uptake: 1.75 ± 0.17 for HA 1.6% and 1.58 ± 0.14 for HA 2.4%. The most marked dose-dependent effect of this study was a reduction of modified Mankin score for HA groups, with the 2.4% treatment achieving a statistically significant improvement as compared with the control group (7.19 ± 0.85 for saline, 4.65 ± 0.66 for HA 1.6%, and 3.53 ± 0.59 for HA 2.4%; P = 0.005).

CONCLUSIONS

A dose-dependent protective effect on cartilage was observed after injection of both HA solutions.

The Influence of a Single Intra-Articular Lidocaine Injection on the Viability of Articular Cartilage in the Knee

OBJECTIVE

To evaluate the in vivo effect of a single intra-articular injection of local anesthetic (LA) lidocaine on the viability of articular cartilage in the intact or osteoarthritic (OA) human knees, and to measure the synovial postinjection concentration of lidocaine in the knee.

DESIGN

This study includes 3 interconnected experiments: (A) Synovial LA concentration measurement after a 2% lidocaine injection before knee arthroscopy in 10 patients by liquid chromatography-tandem mass spectrometry (LC-MS/MS). (B) Human osteochondral explants (N = 27) from intact knees procured at autopsies were incubated for different time intervals (30 minutes, 2 hours, 24 hours) with 2% lidocaine, 0.04% lidocaine (measured), or culture medium (control), and later evaluated for cell viability by LIVE/DEAD staining. (C) Ten out of 19 matched patients scheduled for knee replacement received a single intra-articular injection of 2% lidocaine approximately 30 minutes prior to the procedure; 9 patients served as control. Osteochondral samples with OA changes were harvested during surgery and analyzed for chondrocyte viability by LIVE/DEAD staining.

RESULTS

(A) The synovial LA concentration was significantly lower than the primary concentration injected: average 0.23 mg/mL (0.02%), highest measured 0.37 mg/mL (0.04%). (B) In vitro exposure to a reduced LA concentration had no significant influence on chondrocyte viability in intact cartilage explants (24-hour averages: control, 93%; 0.04% lidocaine, 92%; 2% lidocaine, 79%). (C) Viability of chondrocytes in OA knees was similar between 2% lidocaine injection (85%) and control (80%).

CONCLUSIONS

A single intra-articular knee injection of 2% lidocaine did not influence the chondrocyte viability neither in healthy nor in OA cartilage. A fast postinjection reduction of synovial LA concentration (more than 40 times) is the most likely protective mechanism.

Proprioceptive Training for Knee Osteoarthritis: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: There is increased interest in proprioceptive training for knee osteoarthritis (KOA). However, little consensus supports the effectiveness of this intervention.

Objective: This meta-analysis aimed to assess the effects of proprioceptive training on symptoms, function, and proprioception in people with KOA.

Methods: The PubMed, Cochrane Library, Web of Science, and EMBASE databases were systematically searched from the inception dates to April 16, 2021 for relevant randomized controlled trials (RCTs). Data were pooled by calculating the standardized mean differences (SMDs) and 95% confidence intervals (CIs). A random-effects model was used for the analyses.

Results: A total of 24 RCTs involving 1,275 participants were included in our analysis. This study indicated that compared to no intervention, proprioceptive training significantly improved pain, stiffness, physical function, joint position sense (JPS), muscle strength, mobility, and knee ROM (P < 0.05) in people with KOA. When compared to other non-proprioceptive training, proprioceptive training provided better results in terms of JPS (SMD = −1.28, 95%CI: [−1.64, −0.92], I² = 0%, P < 0.00001) and mobility (timed walk over spongy surface) (SMD = −0.76, 95%CI: [−1.33, −0.18], I² = 64%, P = 0.01), and other results are similar. When proprioceptive training plus other non-proprioceptive training compared to other non-proprioceptive training, the two groups showed similar outcomes, but there was a greater improvement for JPS (SMD = −1.54, 95%CI: [−2.74, −0.34], I² = 79%, P = 0.01), physical function (SMD = −0.34, 95%CI: [−0.56, −0.12], I² = 0%, P = 0.003), and knee ROM (P < 0.05) in the proprioceptive training plus other non-proprioceptive training group. When proprioceptive training plus conventional physiotherapy compared against conventional physiotherapy, the two groups demonstrated similar outcomes, but there was a significant improvement for JPS (SMD = −0.95, 95%CI: [−1.73, −0.18], I² = 78%, P = 0.02) in the proprioceptive training plus conventional physiotherapy group.

Conclusions: Proprioceptive training is safe and effective in treating KOA. There is some evidence that proprioceptive training combined with general non-proprioceptive training or conventional physiotherapy appears to be more effective and should be considered as part of the rehabilitation program. However, given that the majority of current studies investigated the short-term effect of these proprioceptive training programs, more large-scale and well-designed studies with long-term follow up are needed to determine the long-term effects of these proprioceptive training regimes in KOA.

Systematic Review Registration:https://www.crd.york.ac.uk/prospero/#recordDetails, PROSPERO, identifier: CRD42021240587.

Update on Novel Non-Operative Treatment for Osteoarthritis: Current Status and Future Trends

Osteoarthritis (OA) is a leading cause of pain and disability which results in a reduced quality of life. Due to the avascular nature of cartilage, damaged cartilage has a finite capacity for healing or regeneration. To date, conservative management, including physical measures and pharmacological therapy are still the principal choices offered for OA patients. Joint arthroplasties or total replacement surgeries are served as the ultimate therapeutic option to rehabilitate the joint function of patients who withstand severe OA. However, these approaches are mainly to relieve the symptoms of OA, instead of decelerating or reversing the progress of cartilage damage. Disease-modifying osteoarthritis drugs (DMOADs) aiming to modify key structures within the OA joints are in development. Tissue engineering is a promising strategy for repairing cartilage, in which cells, genes, and biomaterials are encompassed. Here, we review the current status of preclinical investigations and clinical translations of tissue engineering in the non-operative treatment of OA. Furthermore, this review provides our perspective on the challenges and future directions of tissue engineering in cartilage regeneration.

Effects of Viscosupplementation on Quality of Knee Joint Arthrokinematic Motion Analyzed by Vibroarthrography

OBJECTIVE

To evaluate the influence of viscosupplementation on osteoarthritic knee arthrokinematics analyzed by VAG. It is considered that intra-articular hyaluronic acid injection may improve the function of synovial joints by recovery of friction-reducing properties of articular environment.

DESIGN

Thirty-five patients with knee osteoarthritis (grade II according to the Kellgren-Lawrence system) and 50 asymptomatic subjects were enrolled in the study. Patients were analyzed at 3 time points: 1 day before and 2 weeks and 4 weeks after single injection of 1.5% cross-linked hyaluronate. Control subjects were tested once. The vibroarthrographic signals were collected during knee flexion/extension motion using an accelerator and described by variation of mean square (VMS), mean range (R5), and power spectral density for frequency of 50 to 250 Hz (P1), and 250 to 450 Hz (P2).

RESULTS

Patients before viscosupplementation were characterized by about 2-fold higher values of vibroarthrographic parameters than controls. Two weeks after the procedure, the values of R5, P1, and P2 significantly decreased, in comparison to pre-injection. At 4 weeks post-injection, we noted a significant increase in R5, P1, and P2 values, when compared to 2 weeks post-injection. Finally, at 4 weeks post-injection, the level of VMS, R5, and P2 parameters did not differ from values obtained at pre-injection.

CONCLUSIONS

We showed that viscosupplementation may be effective in providing arthrokinematics improvement, but with a relatively short period of duration. This phenomenon is observed as decreased vibroacoustic emission, which reflects a more smooth movement in the joint.

Molecular Structure and Surface Accumulation Dynamics of Hyaluronan at the Water-Air Interface

Hyaluronan is a biopolymer that is essential for many biological processes in the human body, like the regulation of tissue lubrication and inflammatory responses. Here, we study the behavior of hyaluronan at aqueous surfaces using heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Low-molecular-weight hyaluronan (∼150 kDa) gradually covers the water–air interface within hours, leading to a negatively charged surface and a reorientation of interfacial water molecules. The rate of surface accumulation strongly increases when the bulk concentration of low-molecular-weight hyaluronan is increased. In contrast, high-molecular-weight hyaluronan (>1 MDa) cannot be detected at the surface, even hours after the addition of the polymer to the aqueous solution. The strong dependence on the polymer molecular weight can be explained by entanglements of the hyaluronan polymers. We also find that for low-molecular-weight hyaluronan the migration kinetics of hyaluronan in aqueous media shows an anomalous dependence on the pH of the solution, which can be explained from the interplay of hydrogen bonding and electrostatic interactions of hyaluronan polymers.

Treatment of Knee Osteoarthritis with Intraarticular Umbilical Cord-Derived Wharton's Jelly: A Case Report

We present the case of a 27-year-old male with grade II knee osteoarthritis (OA) that was intraarticularly injected with a 2 mL umbilical cord-derived Wharton’s jelly (UC-derived WJ) formulation. The patients’ baseline radiographs were taken and baseline numeric pain rating scale (NPRS), knee injury and osteoarthritis outcome score (KOOS), 7-point Likert scale, and a 36-item short form survey (SF-36) were recorded. The NPRS was re-recorded immediately after the injection, and at 24 h, 48 h, 1 week, 6 weeks, and at 3 months follow-up post-injection. The KOOS and 7-point Likert scale was re-recorded at the patients’ 1week, 6 week, and 3month follow-up, and SF-36 was re-recorded at 3 months. A final set of X-rays were also performed at 3 months follow-up post-injection. No adverse effects from the injection were reported over the duration of the study. No significant difference nor progression in OA on X-rays compared to baseline was observed. NPRS decreased by 50% and the 7-point Likert scale increased to Extremely Satisfied. KOOS increased overall by 10% and the SF-36 overall change was 25%. These results indicate the potential application of UC-derived WJ in the treatment of knee OA. Larger, long term, non-randomized and randomized control trials are warranted to adequately assess the safety and efficacy of UC-derived WJ and ultimate clinical use.

Hyaluronic acid synthesis, degradation, and crosslinking in equine osteoarthritis: TNF-α-TSG-6-mediated HC-HA formation

BACKGROUND

TNF-α-stimulated gene 6 (TSG-6) protein, a TNF-α-responsive hyaladherin, possesses enzymatic activity that can catalyze covalent crosslinks of the polysaccharide hyaluronic acid (HA) to another protein to form heavy chain-hyaluronic acid (HC-HA) complexes in pathological conditions such as osteoarthritis (OA). Here, we examined HA synthase and inflammatory gene expression; synovial fluid HA, TNF-α, and viscosity; and TSG-6-mediated HC-HA complex formation in an equine OA model. The objectives of this study were to (1) evaluate the TNF-α-TSG-6-HC-HA signaling pathway across multiple joint tissues, including synovial membrane, cartilage, and synovial fluid, and (2) determine the impact of OA on synovial fluid composition and biophysical properties.

METHODS

HA and inflammatory cytokine concentrations (TNF-α, IL-1β, CCL2, 3, 5, and 11) were analyzed in synovial fluid from 63 OA and 25 control joints, and HA synthase (HAS1-3), TSG-6, and hyaluronan-degrading enzyme (HYAL2, HEXA) gene expression was measured in synovial membrane and cartilage. HA molecular weight (MW) distributions were determined using agarose gel electrophoresis and solid-state nanopore measurements, and HC-HA complex formation was detected via immunoblotting and immunofluorescence. SEC-MALS was used to evaluate TSG-6-mediated HA crosslinking, and synovial fluid and HA solution viscosities were analyzed using multiple particle-tracking microrheology and microfluidic measurements, respectively.

RESULTS

TNF-α concentrations were greater in OA synovial fluid, and TSG6 expression was upregulated in OA synovial membrane and cartilage. TSG-6-mediated HC-HA complex formation was greater in OA synovial fluid and tissues than controls, and HC-HA was localized to both synovial membrane and superficial zone chondrocytes in OA joints. SEC-MALS demonstrated macromolecular aggregation of low MW HA in the presence of TSG-6 and inter-α-inhibitor with concurrent increases in viscosity.

CONCLUSIONS

Synovial fluid TNF-α concentrations, synovial membrane and cartilage TSG6 gene expression, and HC-HA complex formation were increased in equine OA. Despite the ability of TSG-6 to induce macromolecular aggregation of low MW HA with resultant increases in the viscosity of low MW HA solutions in vitro, HA concentration was the primary determinant of synovial fluid viscosity rather than HA MW or HC-HA crosslinking. The TNF-α-TSG-6-HC-HA pathway may represent a potential therapeutic target in OA.

Human Umbilical Cord Mesenchymal Stem Cells in Combination with Hyaluronic Acid Ameliorate the Progression of Knee Osteoarthritis

The aim of this study is to evaluate the feasibility and usefulness of the human umbilical cord mesenchymal stem cells (hUC-MSCs) and hyaluronan acid (HA) combination to attenuate osteoarthritis progression in the knee while simultaneously providing some insights on the mitigation mechanism. In vitro, the effect of hUC-MSCs with HA treatment on chondrocyte cell viability and the cytokine profile were analyzed. Additionally, the antioxidation capability of hUC-MSCs-CM (conditioned medium) with HA towards H2O2-induced chondrocyte cell damage was evaluated. The HA addition increased the hUC-MSC antioxidation capability and cytokine secretion, such as Dickkopf-related protein 1 (DKK-1) and hepatocyte growth factor (HGF), while no adverse effect on the cell viability was observed. In vivo, the intra-articular injection of hUC-MSCs with HA to a mono-iodoacetate (MIA)-induced knee osteoarthritis (KOA) rat model was performed and investigated. Attenuation of the KOA progression in the MIA-damaged rat model was seen best in hUC-MSCs with a HA combination compared to the vehicle control or each individual element. Combining hUC-MSCs and HA resulted in a synergistic effect, such as increasing the cell therapeutic capability while incurring no observable adverse effects. Therefore, this combinatorial therapy is feasible and has promising potential to ameliorate KOA progression.

Protein Adsorption Enhances Energy Dissipation in Networks of Lysozyme Amyloid Fibrils

Hydrogels of amyloid fibrils are a versatile biomaterial for tissue engineering and other biomedical applications. Their suitability for these applications has been partly ascribed to their excellent and potentially engineerable rheological properties. However, while in biomedical applications the gels have to function in compositionally complex physiological solutions, their rheological behavior is typically only characterized in simple buffers. Here we show that the viscoelastic response of networks of amyloid fibrils of the protein lysozyme in biologically relevant solutions substantially differs from the response in simple buffers. We observe enhanced energy dissipation in both cell culture medium and synovial fluid. We attribute this energy dissipation to interactions of the amyloid fibrils with other molecules in these solutions and especially to the adsorption of the abundantly present protein serum albumin. This finding provides the basis for a better understanding of the performance of amyloid hydrogels in biomedical applications.

Spatially and time-resolved SAXS for monitoring dynamic structural transitions during in situ generation of non-lamellar liquid crystalline phases in biologically relevant media

Formation of high viscous inverse lyotropic liquid crystalline phases in situ upon exposure of low viscous drug-loaded lipid preformulations to synovial fluid provides a promising approach for design of depot formulations for intra-articular drug delivery. Rational formulation design relies on a fundamental understanding of the synovial fluid-mediated dynamic structural transitions occurring at the administration site. At conditions mimicking the in vivo situation, we investigated in real-time such transitions at multiple positions by synchrotron small-angle X-ray scattering (SAXS) combined with an injection-cell. An injectable diclofenac-loaded quaternary preformulation consisting of 72/8/10/10% (w/w) glycerol monooleate/1,2-dioleoyl-glycero-3-phospho-rac-(1-glycerol)/ethanol/water was injected into hyaluronic acid solution or synovial fluid. A fast generation of a coherent drug depot of inverse bicontinuous Im3m and Pn3m cubic phases was observed. Through construction of 2D spatial maps from measurements performed 60 min after injection of the preformulation, it was possible to differentiate liquid crystalline rich- and excess hyaluronic acid solution- or synovial fluid-rich regimes. Synchrotron SAXS findings confirmed that the exposure of the preformulation to the media leads to alterations in structural features in position- and time-dependent manners. Effects of biologically relevant medium composition on the structural features, and implications for development of formulations with sustained drug release properties are highlighted.

Fast nanoparticle rotational and translational diffusion in synovial fluid and hyaluronic acid solutions

Nanoparticles are under investigation as diagnostic and therapeutic agents for joint diseases, such as osteoarthritis. However, there is incomplete understanding of nanoparticle diffusion in synovial fluid, the fluid inside the joint, which consists of a mixture of the polyelectrolyte hyaluronic acid, proteins, and other components. Here, we show that rotational and translational diffusion of polymer-coated nanoparticles in quiescent synovial fluid and in hyaluronic acid solutions is well described by the Stokes-Einstein relationship, albeit with an effective medium viscosity that is much smaller than the macroscopic low shear viscosity of the fluid. This effective medium viscosity is well described by an equation for the viscosity of dilute polymer chains, where the additional viscous dissipation arises because of the presence of the polymer segments. These results shed light on the diffusive behavior of polymer-coated inorganic nanoparticles in complex and crowded biological environments, such as in the joint.

Sweet systems: technologies for glycomic analysis and their integration into systems biology

Found in virtually every organism, glycans are essential molecules that play important roles in almost every aspect of biology. The composition of glycome, the repertoire of glycans in an organism or a biological sample, is often found altered in many diseases, including cancer, infectious diseases, metabolic and developmental disorders. Understanding how glycosylation and glycomic changes enriches our knowledge of the mechanisms of disease progression and sheds light on the development of novel therapeutics. However, the inherent diversity of glycan structures imposes challenges on the experimental characterization of glycomes. Advances in high-throughput glycomic technologies enable glycomic analysis in a rapid and comprehensive manner. In this review, we discuss the analytical methods currently used in high-throughput glycomics, including mass spectrometry, liquid chromatography and lectin microarray. Concomitant with the technical advances is the integration of glycomics into systems biology in the recent years. Herein we elaborate on some representative works from this recent trend to underline the important role of glycomics in such integrated approaches to disease.

Umbilical cord-derived Wharton's jelly for treatment of knee osteoarthritis: study protocol for a non-randomized, open-label, multi-center trial

Background

Osteoarthritis (OA) is the most common joint disorder in the USA, and knee OA has the highest prevalence. Inflammation and decrease in vascularization are key factors in the degeneration of articular cartilage and the associated pain and decrease in function. To combat this process, the use of biologics including umbilical cord-derived Wharton’s Jelly (UC-derived WJ) has grown. UC-derived WJ contains large quantities of regenerative factors, including growth factors (GFs), cytokines (CKs), hyaluronic acid (HA), and extracellular vesicles (EVs). The proposed study evaluates the safety and efficacy of intraarticular injection of UC-derived WJ for treatment of knee OA symptoms.

Methods and analysis

This is a non-randomized, open-label, multi-center, prospective study in which the safety and efficacy of intraarticular UC-derived WJ in patients suffering from grade II/III OA will be assessed. Twelve patients with grade II/III OA who meet the inclusion and exclusion criteria will be recruited for this study which will be conducted at up to two sites within the USA. The participants will be followed for 1 s. Participants will be assessed using the Numeric Pain Rating Scale (NPRS), Knee Injury and Osteoarthritis Outcome Score (KOOS), 36-item short form survey (SF-36), Single Assessment Numeric Evaluation (SANE), physical exams, plain radiography, and Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score for improvements in pain, satisfaction, function, and cartilage regeneration.

Discussion

This prospective study will contribute to the limited amount of data on UC-derived WJ, particularly with regard to its safety and efficacy. The outcomes from this study will also lay the groundwork for a large placebo-controlled trial of intraarticular UC-derived WJ for symptomatic knee OA.

Trial registration

ClinicalTrials.gov NCT04719793. Registered on 22 January 2021

Strong Reduction of the Chain Rigidity of Hyaluronan by Selective Binding of Ca2+ Ions

The biological functions of natural polyelectrolytes are strongly influenced by the presence of ions, which bind to the polymer chains and thereby modify their properties. Although the biological impact of such modifications is well recognized, a detailed molecular picture of the binding process and of the mechanisms that drive the subsequent structural changes in the polymer is lacking. Here, we study the molecular mechanism of the condensation of calcium, a divalent cation, on hyaluronan, a ubiquitous polymer in human tissues. By combining two-dimensional infrared spectroscopy experiments with molecular dynamics simulations, we find that calcium specifically binds to hyaluronan at millimolar concentrations. Because of its large size and charge, the calcium cation can bind simultaneously to the negatively charged carboxylate group and the amide group of adjacent saccharide units. Molecular dynamics simulations and single-chain force spectroscopy measurements provide evidence that the binding of the calcium ions weakens the intramolecular hydrogen-bond network of hyaluronan, increasing the flexibility of the polymer chain. We also observe that the binding of calcium to hyaluronan saturates at a maximum binding fraction of ∼10–15 mol %. This saturation indicates that the binding of Ca²⁺ strongly reduces the probability of subsequent binding of Ca²⁺ at neighboring binding sites, possibly as a result of enhanced conformational fluctuations and/or electrostatic repulsion effects. Our findings provide a detailed molecular picture of ion condensation and reveal the severe effect of a few, selective and localized electrostatic interactions on the rigidity of a polyelectrolyte chain.

Connecting the Stimuli-Responsive Rheology of Biopolymer Hydrogels to Underlying Hydrogen-Bonding Interactions

Many biopolymer hydrogels are environmentally responsive because they are held together by physical associations that depend on pH and temperature. Here, we investigate how the pH and temperature responses of the rheology of hyaluronan hydrogels are connected to the underlying molecular interactions. Hyaluronan is an essential structural biopolymer in the human body with many applications in biomedicine. Using two-dimensional infrared spectroscopy, we show that hyaluronan chains become connected by hydrogen bonds when the pH is changed from 7.0 to 2.5 and that the bond density at pH 2.5 is independent of temperature. Temperature-dependent rheology measurements show that because of this hydrogen bonding the stress relaxation at pH 2.5 is strongly slowed down in comparison to pH 7.0, consistent with the sticky reptation model of associative polymers. From the flow activation energy, we conclude that each polymer is cross-linked by multiple (5-15) hydrogen bonds to others, causing slow macroscopic stress relaxation, despite the short time scale of breaking and reformation of each individual hydrogen bond. Our findings can aid the design of stimuli-responsive hydrogels with tailored viscoelastic properties for biomedical applications.

Biomechanically, structurally and functionally meticulously tailored polycaprolactone/silk fibroin scaffold for meniscus regeneration

Meniscus deficiency, the most common and refractory disease in human knee joints, often progresses to osteoarthritis (OA) due to abnormal biomechanical distribution and articular cartilage abrasion. However, due to its anisotropic spatial architecture, complex biomechanical microenvironment, and limited vascularity, meniscus repair remains a challenge for clinicians and researchers worldwide. In this study, we developed a 3D printing-based biomimetic and composite tissue-engineered meniscus scaffold consisting of polycaprolactone (PCL)/silk fibroin (SF) with extraordinary biomechanical properties and biocompatibility. We hypothesized that the meticulously tailored composite scaffold could enhance meniscus regeneration and cartilage protection.

Methods: The physical property of the scaffold was characterized by scanning electron microscopy (SEM) observation, degradation test, frictional force of interface assessment, biomechanical testing, and fourier transform infrared (FTIR) spectroscopy analysis. To verify the biocompatibility of the scaffold, the viability, morphology, proliferation, differentiation, and extracellular matrix (ECM) production of synovium-derived mesenchymal stem cell (SMSC) on the scaffolds were assessed by LIVE/DEAD staining, alamarBlue assay, ELISA analysis, and qRT-PCR. The recruitment ability of SMSC was tested by dual labeling with CD29 and CD90 by confocal microscope at 1 week after implantation. The functionalized hybrid scaffold was then implanted into the meniscus defects on rabbit knee joint for meniscus regeneration, comparing with the Blank group (no scaffold) and PS group. The regenerated meniscus tissue was evaluated by histological and immunohistochemistry staining, and biomechanical test. Macroscopic and histological scoring was performed to assess the outcome of meniscus regeneration and cartilage protection in vivo.

Results: The combination of SF and PCL could greatly balance the biomechanical properties and degradation rate to match the native meniscus. SF sponge, characterized by fine elasticity and low interfacial shear force, enhanced energy absorption capacity of the meniscus and improved chondroprotection. The SMSC-specific affinity peptide (LTHPRWP; L7) was conjugated to the scaffold to further increase the recruitment and retention of endogenous SMSCs. This meticulously tailored scaffold displayed superior biomechanics, structure, and function, creating a favorable microenvironment for SMSC proliferation, differentiation, and extracellular matrix (ECM) production. After 24 weeks of implantation, the histological assessment, biochemical contents, and biomechanical properties demonstrated that the polycaprolactone/silk fibroin-L7 (PS-L7) group was close to the native meniscus group, showing significantly better cartilage protection than the PS group.

Conclusion: This tissue engineering scaffold could greatly strengthen meniscus regeneration and chondroprotection. Compared with traditional cell-based therapies, the meniscus tissue engineering approach with advantages of one-step operation and reduced cost has a promising potential for future clinical and translational studies.

Primary Human Chondrocytes Affected by Cigarette Smoke-Therapeutic Challenges

Although several researchers have attested deleterious effects of smoking to the musculoskeletal system, the association between smoking and the onset of osteoarthritis (OA) remains unclear. Here, we investigate the effect of cigarette smoke extract (CSE) on primary human chondrocytes. The present study demonstrates that physiological concentrations of CSE (0.1%–10%) inhibit the viability, proliferation, and matrix formation of chondrocytes in a dose- and time-dependent manner. Significant amounts of free radicals were generated by 10% of CSE and led to cell death. A clinical dosage (4 mg/mL) of dexamethasone (Dex) showed toxic effects on chondrocytes, and the long-time treatment by lower doses (4–400 μg/mL) induced hypertrophic changes in the chondrocytes. To substitute Dex, diclofenac (Dic, 1 μg/mL) and acetaminophen (Ace, 10 μg/mL) were tested and did not worsen the metabolic activity of CSE-exposed chondrocytes. Hyaluronic acid (HA, 5 mg/mL) combined with Dic or Ace significantly inhibited the oxidative stress and enhanced the viability and matrix formation of CSE-exposed chondrocytes. This study shows for the first time that CSE mediates the disruption of cartilage through inducing cell death by increasing oxidative stress, and that this effect is fortified by Dex. The deleterious effects of CSE on chondrocytes could be reversed by treatment with HA combined with first-line analgesic/anti-inflammatory agents.

A Century of Cartilage Tribology Research Is Informing Lubrication Therapies

Articular cartilage is one of the most unique materials found in nature. This tissue's ability to provide low friction and low wear over decades of constant use is not surpassed, as of yet, by any synthetic materials. Lubrication of the body's joints is essential to mammalian locomotion, but breakdown and degeneration of cartilage is the leading cause of severe disability in the industrialized world. In this paper, we review how theories of cartilage lubrication have evolved over the past decades and connect how theories of cartilage lubrication have been translated to lubrication-based therapies. Here, we call upon these historical perspectives and highlight the open questions in cartilage lubrication research. Additionally, these open questions within the field's understanding of natural lubrication mechanisms reveal strategic directions for lubrication therapy.

Biolubrication synergy: Hyaluronan - Phospholipid interactions at interfaces

The manner in which nature has solved lubrication issues has fascinated scientists for centuries, in particular when considering that lubrication is achieved in aqueous media. The most outstanding system in this respect is likely the synovial joint, where close to frictionless motion is realized under different loads and shear rates. This review article focuses on two components present in the synovial area, hyaluronan and phospholipids. We recapitulate what has been learned about their interactions at interfaces from recent experiments, with focus on results obtained using reflectivity techniques at large scale facilities. In parallel, modelling experiments have been carried out and from these efforts new detailed knowledge about how hyaluronan and phospholipids interact has been gained. In this review we combine findings from modelling and experiments to gain deeper insight. Finally, we summarize what has been learned of the lubrication performance of mixtures of phospholipids and hyaluronan.

Age-related alterations of articular cartilage in pituitary adenylate cyclase-activating polypeptide (PACAP) gene-deficient mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is an evolutionarly conserved neuropeptide which is produced by various neuronal and non-neuronal cells, including cartilage and bone cells. PACAP has trophic functions in tissue development, and it also plays a role in cellular and tissue aging. PACAP takes part in the regulation of chondrogenesis, which prevents insufficient cartilage formation caused by oxidative and mechanical stress. PACAP knockout (KO) mice have been shown to display early aging signs affecting several organs. In the present work, we investigated articular cartilage of knee joints in young and aged wild-type (WT) and PACAP KO mice. A significant increase in the thickness of articular cartilage was detected in aged PACAP gene-deficient mice. Amongst PACAP receptors, dominantly PAC1 receptor was expressed in WT knee joints and a remarkable decrease was found in aged PACAP KO mice. Expression of PKA-regulated transcription factors, Sox5, Sox9 and CREB, decreased both in young and aged gene deficient mice, while Sox6, collagen type II and aggrecan expressions were elevated in young but were reduced in aged PACAP KO animals. Increased expression of hyaluronan (HA) synthases and HA-binding proteins was detected parallel with an elevated presence of HA in aged PACAP KO mice. Expression of bone related collagens (I and X) was augmented in young and aged animals. These results suggest that loss of PACAP signaling results in dysregulation of cartilage matrix composition and may transform articular cartilage in a way that it becomes more prone to degenerate.

The time course and mechanisms of change in biomarkers of joint metabolism in response to acute exercise and chronic training in physiologic and pathological conditions

PURPOSE

The benefits of exercise across the lifespan and for a wide spectrum of health and diseases are well known. However, there remains less clarity as to the effects of both acute and chronic exercise on joint health. Serum biomarkers of joint metabolism are sensitive to change and have the potential to differentiate between normal and adverse adaptations to acute and chronic load. Therefore, the primary objective of this review is to evaluate how serum biomarkers can inform our understanding of how exercise affects joint metabolism.

METHODS

A comprehensive literature search was completed to identify joint biomarkers previously used to investigate acute and chronic exercise training.

RESULTS

Identified biomarkers included those related to joint cartilage, bone, synovium, synovial fluid, and inflammation. However, current research has largely focused on the response of serum cartilage oligomeric matrix protein (COMP) to acute loading in healthy young individuals. Studies demonstrate how acute loading transiently increases serum COMP (i.e., cartilage metabolism), which is mostly dependent on the duration of exercise. This response does not appear to be associated with any lasting deleterious changes, cartilage degradation, or osteoarthritis.

CONCLUSION

Several promising biomarkers for assessing joint metabolism exist and may in future enhance our understanding of the physiological response to acute and chronic exercise. Defining 'normal' and 'abnormal' biomarker responses to exercise and methodological standardisation would greatly improve the potential of research in this area to understand mechanisms and inform practice.

Hyaluronic Acid-Based Activatable Nanomaterials for Stimuli-Responsive Imaging and Therapeutics: Beyond CD44-Mediated Drug Delivery

There is a rapidly increasing interest in developing stimuli-responsive nanomaterials for treating a variety of diseases. By enabling the activation of function locally at the sites of interest, it is possible to increase therapeutic efficacy significantly while simultaneously reducing adverse side effects. While there are many sophisticated nanomaterials available, they are often highly complex and not easily transferrable to industrial scales and clinical settings. However, nanomaterials based on hyaluronic acid offer a compelling strategy for reducing their complexity while retaining several desirable benefits such as active targeting and stimuli-responsive degradation. Herein, the basic properties of hyaluronic acid, its binding partners, and natural routes for degradation by hyaluronidases-hyaluronic-acid-degrading enzymes-and oxidative stresses are discussed. Recent advances in designing hyaluronic acid-based, actively targeted, hyaluronidase- or reactive-oxygen-species-responsive nanomaterials for both diagnostic imaging and therapeutic delivery, which go beyond merely the classical targeting of CD44, are summarized.

Hydrogen and Water Bonding between Glycosaminoglycans and Phospholipids in the Synovial Fluid: Molecular Dynamics Study

Synovial fluid is a lubricant of the synovial joint that shows remarkable tribological properties. These properties originate in the synergy between its components, with two of its major components, glycosaminoglycans (GAGs) and phospholipids (PLs), playing a major role in boundary and mixed lubrication regimes. All-atom molecular dynamic simulations were performed to investigate the way these components bond. Hyaluronic acid (HA) and chondroitin sulphate (CS) bonding with three types of lipids was tested. The results show that both glycosaminoglycans bind lipids at a similar rate, except for 1,2-d-ipalmitoyl-sn-glycero-3-phosphoethanolamine lipids, which bind to chondroitin at a much higher rate than to hyaluronan. The results suggest that different synovial fluid lipids may play a different role when binding to both hyaluronan and chondroitin sulphate. The presented results may help in understanding a process of lubrication of articular cartilage at a nanoscale level.

Hyaluronan: molecular size-dependent signaling and biological functions in inflammation and cancer

Hyaluronan (HA) is a linear nonsulfated glycosaminoglycan of the extracellular matrix that plays a pivotal role in a variety of biological processes. High-molecular weight HA exhibits different biological properties than oligomers and low-molecular weight HA. Depending on their molecular size, HA fragments can influence cellular behavior in a different mode of action. This phenomenon is attributed to the different manner of interaction with the HA receptors, especially CD44 and RHAMM. Both receptors can trigger signaling cascades that regulate cell functional properties, such as proliferation migration, angiogenesis, and wound healing. HA fragments are able to enhance or attenuate the HA receptor-mediated signaling pathways, as they compete with the endogenous HA for binding to the receptors. The modulation of these pathways could be crucial for the development of pathological conditions, such as inflammation and cancer. The primary goal of this review is to critically present the importance of HA molecular size on cellular signaling, functional cell properties, and morphology in normal and pathological conditions, including inflammation and cancer. A deeper understanding of these mechanisms could contribute to the development of novel therapeutic strategies.