The biophysical mechanisms of altered hyaluronan concentration in synovial fluid after anterior cruciate ligament transection

Zwitterionic Poly-Carboxybetaine Polymers Restore Lubrication of Inflamed Articular Cartilage

Osteoarthritis is a degenerative joint disease that is associated with decreased synovial fluid viscosity and increased cartilage friction. Though viscosupplements are available for decades, their clinical efficacy is limited and there is ample need for more effective joint lubricants. This study first evaluates the tribological and biochemical properties of bovine articular cartilage explants after stimulation with the inflammatory cytokine interleukin-1β. This model is then used to investigate the tribological potential of carboxybetaine (CBAA)-based zwitterionic polymers of linear and bottlebrush architecture. Due to their affinity for cartilage tissue, these polymers form a highly hydrated surface layer that decreases friction under high load in the boundary lubrication regime. For linear pCBAA, these benefits are retained over several weeks and the relaxation time of cartilage explants under compression is furthermore decreased, thereby potentially boosting the weeping lubrication mechanism. Bottlebrush bb-pCBAA shows smaller benefits under boundary lubrication but is more viscous than linear pCBAA, therefore providing better lubrication under low load in the fluid-film regime and enabling a longer residence time to bind to the cartilage surface. Showing how CBAA-based polymers restore the lost lubrication mechanisms during inflammation can inspire the next steps toward more effective joint lubricants in the future.

Mechanobiology of Hyaluronan: Connecting Biomechanics and Bioactivity in Musculoskeletal Tissues

Hyaluronan (HA) plays well-recognized mechanical and biological roles in articular cartilage and synovial fluid, where it contributes to tissue structure and lubrication. An understanding of how HA contributes to the structure of other musculoskeletal tissues, including muscle, bone, tendon, and intervertebral discs, is growing. In addition, the use of HA-based therapies to restore damaged tissue is becoming more prevalent. Nevertheless, the relationship between biomechanical stimuli and HA synthesis, degradation, and signaling in musculoskeletal tissues remains understudied, limiting the utility of HA in regenerative medicine. In this review, we discuss the various roles and significance of endogenous HA in musculoskeletal tissues. We use what is known and unknown to motivate new lines of inquiry into HA biology within musculoskeletal tissues and in the mechanobiology governing HA metabolism by suggesting questions that remain regarding the relationship and interaction between biological and mechanical roles of HA in musculoskeletal health and disease.

Assessment of joint pharmacokinetics and consequences for the intraarticular delivery of biologics

Intraarticular (IA) injections provide the opportunity to deliver biologics directly to their site of action for a local and efficient treatment of osteoarthritis. However, the synovial joint is a challenging site of administration since the drug is rapidly eliminated across the synovial membrane and has limited distribution into cartilage, resulting in unsatisfactory therapeutic efficacy. In order to rationally develop appropriate drug delivery systems, it is essential to thoroughly understand the unique biopharmaceutical environments and kinetics in the joint to adequately simulate them in relevant experimental models. This review presents a detailed view on articular kinetics and drug-tissue interplay of IA administered drugs and summarizes how these can be translated into reasonable formulation strategies by identification of key factors through which the joint residence time can be prolonged and specific structures can be targeted. In this way, pros and cons of the delivery approaches for biologics will be evaluated and the extent to which biorelevant models are applicable to gain mechanistic insights and ameliorate formulation design is discussed.

Synovial Fluid Mesenchymal Stem Cells for Knee Arthritis and Cartilage Defects: A Review of the Literature

Mesenchymal stem cells (MSCs) are adult stem cells that have the ability to self-renew and differentiate into several cell lineages including adipocytes, chondrocytes, tenocytes, bones, and myoblasts. These properties make the cell a promising candidate for regenerative medicine applications, especially when dealing with sports injuries in the knee. MSCs can be isolated from almost every type of adult tissue. However, most of the current research focuses on MSCs derived from bone marrow, adipose, and placenta derived products. Synovial fluid-derived MSCs (SF-MSCs) are relatively overlooked but have demonstrated promising therapeutic properties including possessing higher chondrogenic proliferation capabilities than other types of MSCs. Interestingly, SF-MSC population has shown to increase exponentially in patients with joint injury or disease, pointing to a potential use as a biomarker or as a treatment of some orthopaedic disorders. In this review, we go over the current literature on synovial fluid-derived MSCs including the characterization, the animal studies, and discuss future perspectives.

Increase in molar mass distinguishes chondroitin sulfate from osteoarthritis and normal extracellular cartilage matrix

PURPOSE

To determine alterations of chondroitin sulfate (CS) that reflect cartilage damage in an experimental osteoarthritis (OA) model as well as in human OA samples.

MATERIALS AND METHODS

Rats were subjected to anterior cruciate ligament transection (ACLT; OA) or a sham procedure and sacrificed 14, 28, or 70 days after ACLT for histopathology and analysis of extracted CS. Cartilage samples from 14 patients undergoing hip or shoulder arthroplasty secondary to OA or fracture (control) were subjected to the same protocol. The CS content (µg/mg dry cartilage) after proteolysis was determined by densitometry, using agarose-gel electrophoresis. Molar mass (MM) and peak MM of CS were determined using high-performance size-exclusion chromatography (HPSEC).

RESULTS

OA and sham joints at 70 d had 24 [22-24] and 3 [1-6] median histopathology scores, respectively (p < 0.001). Relative CS content (77.7 ± 8.3 µg/mg) was significantly increased in OA samples 70 d after ACLT, as compared to sham (53.5 ± 10.0 µg/mg). Peak MM of CS was higher in OA than in sham samples (P < 0.05). Similarly, CS content and peak MM were higher in cartilage from human OA patients, as compared to fracture samples, reproducing experimental data.

CONCLUSION

Cartilage matrix from experimental and human OA samples has increased in the relative CS content. Increase in the peak MM distinguishes CS of the extracellular matrix of OA from normal cartilage.

Effects of an articular cartilage lubrication with a viscosupplement in vitro and in vivo following osteochondral fractures in horses

OBJECTIVE

To assess whether the combination of hyaluronan, sodium chondroitin sulfate, and N-acetyl-d-glucosamine (HCSG) lubricates articular cartilage in vitro and modulates joint lubrication in vivo.

ANIMALS

16 healthy adult horses.

PROCEDURES

The effects of HCSG injections on SF lubricant properties and joint health, immediately after injury and 2 weeks later, were analyzed by use an equine osteochondral fracture model of post-traumatic osteoarthritis (OA). Middle carpal joints of adult horses were randomly assigned to 1 of 4 surgical treatment groups as follows: normal nonsurgical group (n = 8), normal sham-surgical group (8), OA-induced surgical group with HCSG injection (8), or OA-induced surgical group with saline (0.9% NaCl) solution injection (8). Synovial fluid was aspirated periodically and analyzed for boundary lubrication function and lubricant molecules. At 17 days, joints were screened for gross pathological changes.

RESULTS

Induction of OA led to an impairment of SF lubrication function and diminished hyaluronan concentration in a time-dependent manner following surgery, with HCSG injection lessening these effects. Certain friction coefficients approached those of unaffected normal equine SF. Induction of OA also caused synovial hemorrhage at 17 days, which was lower in joints treated with HCSG.

CONCLUSIONS AND CLINICAL RELEVANCE

After induction of OA, equine SF lubricant function was impaired. Hyaluronan-sodium chondroitin sulfate-N-acetyl-d-glucosamine injection restored lubricant properties at certain time points and reduced pathological joint changes.

Detection of synovial sepsis in horses using enzymes as biomarker

Background

Synovial sepsis is a commonly occurring, potentially career‐ending or even life‐threatening orthopaedic emergency. Diagnosis of synovial sepsis is currently primarily based on synovial fluid analysis, which often leaves diagnostic ambiguity due to overlap of clinicopathological parameters between septic and aseptic inflammatory synovitis.

Objectives

To evaluate the reliability of lysozyme (LYS), myeloperoxidase (MPO) and elastase (ELT) as biomarkers for synovial sepsis in horses using a photometric assay to measure increased enzyme activity.

Study design

Prospective, single‐blinded, analytical, clinical study.

Methods

Equine synovial samples were assigned to one of three groups: (1) healthy controls (n = 10), (2) aseptic (n = 27) and (3) septic synovitis (n = 30). The enzyme activity assays (LYS, MPO and ELT) were compared with standard synovial fluid parameters and broad‐range bacterial 16S rDNA PCR.

Results

LYS and MPO activities were significantly different between septic synovial samples, and both aseptic and control samples (P < .001, LYS: confidence interval [CI]: 2.25‐3.41, resp., 2.21‐3.8, MPO: CI 0.752‐1.6, resp., 0.639‐1.81). LYS achieved a 100% sensitivity and 100% specificity in differentiating between septic and aseptic (cut‐off value 751.4) or control (cut‐off: 484.6) samples (P < .001). MPO reached 93.33% sensitivity, 100% specificity for distinguishing septic from control (cut‐off value: 0.1254) synovial samples and 93.33% sensitivity, 81.48% specificity for discriminating between septic and aseptic (cut‐off value: 0.1305) synovial samples (P < .001). ELT activity could not be measured in any synovial sample. Both the LYS and the MPO measurements showed a highly significant correlation with PCR (LYS r = .79, MPO r = .69), synovial leukocyte count (LYS r = .752, MPO r = .571), % neutrophils (LYS r = .751, MPO r = 0.663) and each other (r = .744, all P < .001).

Main limitations

Variation in horses’ signalment, affected synovial structures and synovial fluid freezing times may have affected the discriminative power of this study.

Conclusions

Increased MPO and LYS activities allow reliable, rapid diagnosis of synovial sepsis with high sensitivity and specificity.

Upregulation of Systemic Inflammatory Pathways Following Anterior Cruciate Ligament Injury Relates to Both Cartilage and Muscular Changes: A Pilot Study

In conjunction with cartilage breakdown, muscle maladaptation including atrophy and increased fibrosis have been observed in the quadriceps following anterior cruciate ligament (ACL) injury. Previously observed upregulated muscle-related proteins in the synovial fluid following ACL rupture allude to cellular communication between the joint and muscle. Therefore, the purpose of this study was to determine whether muscle-related analytes are differentially expressed in the serum. Sixteen patients with an acute ACL tear participated in this IRB-approved study. Serum was obtained at two different time points at a mean of 6 and 14 days post-injury, and serum was analyzed by a highly multiplexed assay of 1,300 proteins. Pathway analysis using DAVID was performed; genes included met three criteria: significant change between the two study time points using a paired t test, significant change between the two study time points using a Mann-Whitney non-parametric test, and significant Benjamini post hoc analysis. Twelve analytes significantly increased between time points. Proteins chitinase-3-like protein 1 (p = 0.01), insulin-like growth factor binding protein 1 (p = 0.01), insulin-like growth factor binding protein 5 (p = 0.02), renin (p = 0.004), and lymphotoxin alpha 1: beta 2 (p = 0.03) were significantly upregulated in serum following acute ACL injury. The current results confirm the inflammatory pattern previously seen in the synovial fluid thought to play a role in the progression of post-traumatic osteoarthritis after ACL injury, and this data also provides further insights into important communication between the joint and quadriceps group, whose function is important in long term health. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:387-392, 2020.

Temporal changes in synovial fluid composition and elastoviscous lubrication in the equine carpal fracture model

The objective of this study was to examine temporal variations in synovial fluid composition and lubrication following articular fracture. Post-traumatic osteoarthritis (PTOA) was induced by creating an osteochondral fracture in the middle carpal joint of four horses while the contralateral limb served as a sham-operated control. Horses were exercised on a high-speed treadmill, and synovial fluid was collected pre-operatively and at serial timepoints until 75 days post-operatively. Lubricin and hyaluronic acid (HA) concentrations were measured using sandwich ELISAs, and the molecular weight distribution of HA was analyzed via gel electrophoresis. Synovial fluid viscosity and cartilage friction coefficients across all modes of lubrication were measured on days 0, 19, 33, and 61 using a commercial rheometer and a custom tribometer, respectively. HA concentrations were significantly decreased post-operatively, and high molecular weight HA (>6.1MDa) did not recover to pre-operative values by the study termination at day 75. Lubricin concentrations increased after surgery to a greater extent in the OA as compared to sham-operated limbs. Viscosity was significantly reduced after surgery. While boundary and elastoviscous mode friction coefficients did not vary, the transition number, representing the shift between these modes, was lower. Although more pronounced in the OA limbs, similar derangements in HA, HA molecular weight distribution, viscosity, and transition number were observed in the sham-operated limbs, which may be explained by synovial fluid washout during arthroscopy. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

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

Background

One potential mechanism for early superficial cartilage wear in normal joints is alteration of the lubricant content and quality of synovial fluid. The purpose of this study was to determine if the concentration and quality of the lubricant, hyaluronan, in synovial fluid: (1) was similar in left and right knees; (2) exhibited similar age-associated trends, whether collected postmortem or antemortem; and (3) varied with age and grade of joint degeneration.

Methods

Human synovial fluid of donors (23–91 years) without osteoarthritis was analyzed for the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5–7 MDa, 1–2.5 MDa, 0.5–1 MDa, and 0.03–0.5 MDa. Similarity of data between left and right knees was assessed by reduced major axis regression, paired t-test, and Bland-Altman analysis. The effect of antemortem versus postmortem collection on biochemical properties was assessed for age-matched samples by unpaired t-test. The relationships between age, joint grade, and each biochemical component were assessed by regression analysis.

Results

Joint grade and the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5–7 MDa, 1–2.5 MDa, and 0.5–1 MDa in human synovial fluid showed good agreement between left and right knees and were similar between age-matched patient and cadaver knee joints. There was an age-associated decrease in overall joint grade (–15 %/decade) and concentrations of hyaluronan (–10.5 %/decade), and hyaluronan in the molecular weight ranges of 2.5–7 MDa (–9.4 %/decade), 1–2.5 MDa (–11.3 %/decade), 0.5–1 MDa (–12.5 %/decade), and 0.03–0.5 MDa (–13.0 %/decade). Hyaluronan concentration and quality was more strongly associated with age than with joint grade.

Conclusions

The age-related increase in cartilage wear in non-osteoarthritic joints may be related to the altered hyaluronan content and quality of synovial fluid.

Cartilage boundary lubrication of ovine synovial fluid following anterior cruciate ligament transection: a longitudinal study

OBJECTIVE

To assess ovine synovial fluid (oSF) from different post-injury time points for (1) proteoglycan-4 (PRG4) and hyaluronan (HA) concentration, (2) HA molecular weight (MW) distribution, (3) cartilage boundary lubrication function, and (4) lubricant composition-function relationships. The association between cartilage boundary lubrication and gross cartilage changes after injury was also examined.

METHODS

oSF was collected 2, 4, 10, and 20 weeks post anterior cruciate ligament (ACL) transection in five skeletally mature sheep. PRG4 and HA concentrations were measured using sandwich enzyme-linked immunosorbent assay, and HA MW distribution by agarose gel electrophoresis. Cartilage boundary lubrication of oSF was assessed using a cartilage-cartilage friction test. Gross damage to articular cartilage was also quantified at 20 weeks using modified Drez scoring protocol.

RESULTS

Early (2-4 weeks) after ACL injury, PRG4 concentrations were significantly higher (P = 0.045, P = 0.037), and HA concentrations were substantially lower (P = 0.005, P = 0.005) compared to 20 weeks. The HA MW distribution also shifted towards lower ranges in the early post-injury stage. The kinetic friction coefficients were significantly higher 2-4 weeks post injury (P = 0.008 and P = 0.049) compared to 20 weeks. Poor cartilage boundary lubricating ability early after injury was associated with cartilage damage at 20 weeks.

CONCLUSION

Altered composition and diminished boundary lubrication of oSF early after ACL transection may pre-dispose the articular cartilage to degenerative changes and initiate osteoarthritis (OA). These observations also provide potential motivation for biotherapeutic interventions at earlier time points post injury.

Synovial Fluid Lubricant Properties are Transiently Deficient after Arthroscopic Articular Cartilage Defect Repair with Platelet-Enriched Fibrin Alone and with Mesenchymal Stem Cells

BACKGROUND

Following various types of naturally-occurring traumatic injury to an articular joint, the lubricating ability of synovial fluid is impaired, with a correlated alteration in the concentration and/or structure of lubricant molecules, hyaluronan and proteoglycan-4. However, the effect of arthroscopic cartilage repair surgery on synovial fluid lubricant function and composition is unknown.

HYPOTHESIS

Arthroscopic treatment of full-thickness chondral defects in horses with (1) platelet-enriched fibrin or (2) platelet-enriched fibrin+mesenchymal stem cells leads to equine synovial fluid with impaired lubricant function and hyaluronan and proteoglycan-4 composition.

STUDY DESIGN

Controlled Laboratory Study.

METHODS

Equine synovial fluid was aspirated from normal joints at a pre-injury state (0 days) and at 10 days and 3 months following fibrin or fibrin+mesenchymal stem cell repair of full thickness chondral defects. Equine synovial fluid samples were analyzed for friction-lowering boundary lubrication of normal articular cartilage (static and kinetic friction coefficients) and concentrations of hyaluronan and proteoglycan-4, as well as molecular weight distribution of hyaluronan. Experimental groups deficient in lubrication function were also tested for the ability of exogenous high-molecular weight hyaluronan to restore lubrication function.

RESULTS

Lubrication and biochemical data varied with time after surgery but generally not between repair groups. Relative to pre-injury, kinetic friction was higher (+94%) at 10 days but returned to baseline levels at 3 months while static friction was not altered. Correspondingly, hyaluronan concentration was transiently lower (-64%) and shifted towards lower molecular weight forms, while proteoglycan-4 concentration was increased (+210%) in 10-day samples relative to pre-injury levels. Regression analysis revealed that kinetic friction decreased with increasing total and high molecular weight hyaluronan. Addition of high molecular weight hyaluronan to bring 10-day hyaluronan levels to 2.0mg/ml restored kinetic friction to pre-injury levels.

CONCLUSION

Following arthroscopic surgery for cartilage defect repair, synovial fluid lubrication function is transiently impaired, in association with decreased hyaluronan concentration. This functional deficiency in synovial fluid lubrication can be counteracted in vitro by addition of high molecular weight hyaluronan.

CLINICAL RELEVANCE

Synovial fluid lubrication is deficient shortly following arthroscopic cartilage repair surgery, and supplementation with high molecular weight hyaluronan may be beneficial.