Evaluation of the effect of experimentally induced cartilage defect and intra-articular hyaluronan on synovial fluid biomarkers in intercarpal joints of horses

Intravenous Injection of Sodium Hyaluronate Diminishes Basal Inflammatory Gene Expression in Equine Skeletal Muscle

Following strenuous exercise, skeletal muscle experiences an acute inflammatory state that initiates the repair process. Systemic hyaluronic acid (HA) is injected to horses routinely as a joint anti-inflammatory. To gain insight into the effects of HA on skeletal muscle, adult Thoroughbred geldings (n = 6) were injected with a commercial HA product weekly for 3 weeks prior to performing a submaximal exercise test. Gluteal muscle (GM) biopsies were obtained before and 1 h after exercise for gene expression analysis and HA localization. The results from RNA sequencing demonstrate differences in gene expression between non-injected controls (CON; n = 6) and HA horses. Prior to exercise, HA horses contained fewer (p < 0.05) transcripts associated with leukocyte activity and cytokine production than CON. The performance of exercise resulted in the upregulation (p < 0.05) of several cytokine genes and their signaling intermediates, indicating that HA does not suppress the normal inflammatory response to exercise. The transcript abundance for marker genes of neutrophils (NCF2) and macrophages (CD163) was greater (p < 0.05) post-exercise and was unaffected by HA injection. The anti-inflammatory effects of HA on muscle are indirect as no differences (p > 0.05) in the relative amount of the macromolecule was observed between the CON and HA fiber extracellular matrix (ECM). However, exercise tended (p = 0.10) to cause an increase in ECM size suggestive of muscle damage and remodeling. The finding was supported by the increased (p < 0.05) expression of CTGF, TGFβ1, MMP9, TIMP4 and Col4A1. Collectively, the results validate HA as an anti-inflammatory aid that does not disrupt the normal post-exercise muscle repair process.

Plasma and Synovial Fluid Cell-Free DNA Concentrations Following Induction of Osteoarthritis in Horses

Biomarkers for osteoarthritis (OA) in horses have been extensively investigated, but translation into clinical use has been limited due to cost, limited sensitivity, and practicality. Identifying novel biomarkers that overcome these limitations could facilitate early diagnosis and therapy. This study aimed to compare the concentrations of synovial fluid (SF) and plasma cell-free DNA (cfDNA) over time in control horses with those with induced carpal OA. Following an established model, unilateral carpal OA was induced in 9 of 17 healthy Thoroughbred fillies, while the remainder were sham-operated controls. Synovial fluid and plasma samples were obtained before induction of OA (Day 0) and weekly thereafter until Day 63, and cfDNA concentrations were determined using fluorometry. The SF cfDNA concentrations were significantly higher for OA joints than for sham-operated joints on Days 28 (median 1430 μg/L and 631 μg/L, respectively, p = 0.017) and 63 (median 1537 μg/L and 606 μg/L, respectively, p = 0.021). There were no significant differences in plasma cfDNA between the OA and the sham groups after induction of carpal OA. Plasma cfDNA measurement is not sufficiently sensitive for diagnostic purposes in this induced model of OA. Synovial fluid cfDNA measurement may be used as a biomarker to monitor early disease progression in horses with OA.

Who Is Healthy? A Review of How Equine Control Groups Are Defined in Clinical Orthopaedic Research 1999-2021

INTRODUCTION

 Proper identification of healthy subjects is essential in case-control studies. However, standardized definitions of healthy controls are lacking in equine orthopaedic research.

OBJECTIVES

 The aim of this study was to define the non-invasive methods used for selecting healthy control horses in osteoarthritis (OA), desmitis and tendinitis research.

METHODS

 Systematic review. Case-control studies with a healthy control group and longitudinal studies where horses had to be healthy at the start were included. Studies where joints were visualized by arthroscopy or post-mortem examination were excluded.

RESULTS

From 2,472 OA papers and 2,746 desmitis/tendinitis papers, 127 and 84 papers met the inclusion criteria respectively. For OA, 11 methods were identified for defining healthy subjects with a median of three methods used per paper. Dynamic examination, radiographic evaluation and clinical examination were the most frequent. Eight different methods were identified in the desmitis/tendinitis papers with a median of three methods per paper; ultrasonography, clinical- and dynamic examination were the most frequent.

CONCLUSIONS

 Overall, the OA and desmitis/tendinitis studies used similar methods for defining subjects as healthy, but the way the examinations were performed and interpreted was inconsistent. In several studies, healthy controls were not examined for lameness. The most common methods have limitations for detecting horses with early OA, which may have implications for interpretation of results. Standardized use of more sensitive and objective methods could be beneficial.

Structural, compositional, and functional effects of blunt and sharp cartilage damage on the joint: A 9-month equine groove model study

This study aimed to quantify the long-term progression of blunt and sharp cartilage defects and their effect on joint homeostasis and function of the equine carpus. In nine adult Shetland ponies, the cartilage in the radiocarpal and middle carpal joint of one front limb was grooved (blunt or sharp randomized). The ponies were subjected to an 8-week exercise protocol and euthanized at 39 weeks. Structural and compositional alterations in joint tissues were evaluated in vivo using serial radiographs, synovial biopsies, and synovial fluid samples. Joint function was monitored by quantitative gait analysis. Macroscopic, microscopic, and biomechanical evaluation of the cartilage and assessment of subchondral bone parameters were performed ex vivo. Grooved cartilage showed higher OARSI microscopy scores than the contra-lateral sham-operated controls (p < 0.0001). Blunt-grooved cartilage scored higher than sharp-grooved cartilage (p = 0.007) and fixed charge density around these grooves was lower (p = 0.006). Equilibrium and instantaneous moduli trended lower in grooved cartilage than their controls (significant for radiocarpal joints). Changes in other tissues included a threefold to sevenfold change in interleukin-6 expression in synovium from grooved joints at week 23 (p = 0.042) and an increased CPII/C2C ratio in synovial fluid extracted from blunt-grooved joints at week 35 (p = 0.010). Gait analysis outcome revealed mild, gradually increasing lameness. In conclusion, blunt and, to a lesser extent, sharp grooves in combination with a period of moderate exercise, lead to mild degeneration in equine carpal cartilage over a 9-month period, but the effect on overall joint health remains limited.

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.

Effect of a single intra-articular high molecular weight hyaluronan in a naturally occurring canine osteoarthritis model: a randomized controlled trial

BACKGROUND

Osteoarthritis (OA) is a complex joint disease and chronic pain source, affecting a patient's quality of life and posing a financial burden. As the dog is considered a nearly ideal species for translation research of human OA and the most used model for research, exploring spontaneous dog OA under the One Health/One Medicine concept can improve both humans and dogs' health and well-being.

METHODS

In a clinical treatment experiment, forty (N=40) joints were selected and randomly assigned to a control group (CG), which received 0.9% NaCl or a treatment (HG), which received Hylan G-F 20. Evaluations were performed on treatment day (T0), 8, 15, 30, 90, and 180 days post-treatment. They consisted of four different Clinical Metrology Instruments (CMI), evaluation of weight distribution, joint range of motion, thigh girth, radiographic and digital thermography imaging, synovial fluid interleukin-1 (IL-1), and C-reactive protein concentrations. Results were compared with repeated measures ANOVA, with a Huynh-Feldt correction, Paired samples T-test, or Wilcoxon signed-ranks test, with p<0.05.

RESULTS

Patients had a mean age of 6.5±2.4 years and a bodyweight of 26.6±5.2kg, and joints graded as mild (n=28, 70%), moderate (n=6, 15%), and severe OA (n=6, 15%). No differences were found between groups at T0. Symmetry index and deviation showed significant improvements in HG from 30 days (p<0.01) up to 180 days (p=0.01). Several CMI scores, particularly pain scores, improved from 90 to 180 days. Radiographic signs progressed in both groups. In both groups, increasing body weight and age corresponded to worse clinical presentation. IA hyaluronan administration produced increased lameness in six cases, which resolved spontaneously.

CONCLUSIONS

This study characterizes the response to treatment with Hylan G-F 20, which can produce significant functional and pain level improvements in patients with OA, even those with factors related to worse response to treatment.

Peripheral mechanisms of arthritic pain: A proposal to leverage large animals for in vitro studies

Pain arising from musculoskeletal disorders such as arthritis is one of the leading causes of disability. Whereas the past 20-years has seen an increase in targeted therapies for rheumatoid arthritis (RA), other arthritis conditions, especially osteoarthritis, remain poorly treated. Although modulation of central pain pathways occurs in chronic arthritis, multiple lines of evidence indicate that peripherally driven pain is important in arthritic pain. To understand the peripheral mechanisms of arthritic pain, various in vitro and in vivo models have been developed, largely in rodents. Although rodent models provide numerous advantages for studying arthritis pathogenesis and treatment, the anatomy and biomechanics of rodent joints differ considerably to those of humans. By contrast, the anatomy and biomechanics of joints in larger animals, such as dogs, show greater similarity to human joints and thus studying them can provide novel insight for arthritis research. The purpose of this article is firstly to review models of arthritis and behavioral outcomes commonly used in large animals. Secondly, we review the existing in vitro models and assays used to study arthritic pain, primarily in rodents, and discuss the potential for adopting these strategies, as well as likely limitations, in large animals. We believe that exploring peripheral mechanisms of arthritic pain in vitro in large animals has the potential to reduce the veterinary burden of arthritis in commonly afflicted species like dogs, as well as to improve translatability of pain research into the clinic.

Evaluation of the inflammatory response to two intra-articular hyaluronic acid formulations in normal equine joints

Intra-articular (IA) hyaluronic acid (HA) is commonly used to treat equine arthritis. Inflammatory response or "joint flare" is a recognized potential side effect. However, the incidence and severity of inflammation following IA HA injection in horses is not well documented. This study compared the effects of two IA HA formulations of different molecular weight (MW) and a saline control on clinical signs and synovial fluid markers of inflammation in normal equine joints. Eight adult horses each had three healthy fetlock joints randomly assigned to treatment with either 1.4 mega Dalton HA, 0.8 mega Dalton HA or saline control once weekly for three weeks. Clinical evaluation and synovial fluid analysis were performed by blinded assessors. Outcomes of interest were lameness score, joint effusion score and synovial fluid white cell count and differential, total protein, viscosity and serum amyloid A. Joints injected with HA developed significant mild-to-moderate inflammatory responses often associated with lameness and joint effusion compared with saline control joints. The higher MW HA formulation elicited a significantly greater inflammatory response than the lower MW HA after the first injection. In HA injected joints, viscosity remained poor for the entire study. Both IA HA formulations in this study induced an inflammatory response in healthy equine joints. This may have implications for the use of HA in equine joints. The findings in this study are limited to the two HA formulations used. Further investigation of different HA formulations and the use of HA in normal and arthritic equine joints is warranted.