Equine osteoarthritis modifies fatty acid signatures in synovial fluid and its extracellular vesicles

Pain and functional limitations in knee osteoarthritis are reflected in the fatty acid composition of plasma extracellular vesicles

This study investigated relationships between fatty acid (FA) profiles of extracellular vesicles (EVs) and cartilage degradation, functional limitations, pain, and psychological well-being in knee osteoarthritis (KOA). Fasting plasma was collected from controls (n = 10), end-stage KOA patients at baseline (n = 12) and at 3 and 12 months (n = 11 and 9) after joint replacement surgery, and from KOA synovial fluid (SF) at baseline (n = 10). EVs were isolated with the exoEasy Maxi Kit or size-exclusion chromatography, and EV FAs were analyzed with gas chromatography-mass spectrometry. Articular cartilage loss was determined by magnetic resonance imaging, and knee pain and function were assessed through questionnaires and physiatric and neuromuscular examinations. The associations of these data with EV FA proportions were tested with the univariate analysis of variance adjusted for age and body adiposity. Higher proportions of 16:1n-7, 18:1n-7, and total monounsaturated FAs in plasma EVs were associated with less severe KOA symptoms, while higher 24:1n-9, total saturated FAs, and ratios of arachidonic acid to long-chain n-3 polyunsaturated FAs (PUFAs) were linked to KOA pain, independent of age and body adiposity. In SF EVs, higher product/precursor ratios of n-6 PUFAs were associated with increased joint stiffness, and higher total dimethyl acetals were linked to physical disability. EV FAs emerged as significant indicators of knee pain and function. The results can be utilized to discover novel biomarkers for KOA and may have implications for targeted prevention and treatment of KOA symptoms by using EVs with a specific FA cargo.

The role of metabolites in the progression of osteoarthritis: Mechanisms and advances in therapy

Osteoarthritis (OA) is a progressive degenerative disease affected by many factors, and there is currently no effective treatment. In recent years, the latest progress in metabolomics in OA research has revealed several metabolic pathways and new specific metabolites involved in OA. Metabolites play significant roles in the identification and management of OA. This review looks back on the development history of metabolomics and the progress of this technology in OA as well as its potential clinical applications. It summarizes the applications of metabolites in the field of OA and future research directions. This understanding will advance the identification of metabolic treatment goals for OA.

The translational potential of this article

The development of metabolomics offers possibilities for the treatment of OA. This article reviews the relationship between metabolites associated with chondrocytes and OA. Selectively altering these three metabolic pathways and their associated metabolites may hold great potential as new focal points for OA treatment.

Extracellular Vesicles: A Novel Diagnostic Tool and Potential Therapeutic Approach for Equine Osteoarthritis

Osteoarthritis (OA) is a chronic progressive degenerative joint disease that affects a significant portion of the equine population and humans worldwide. Current treatment options for equine OA are limited and incompletely curative. Horses provide an excellent large-animal model for studying human OA. Recent advances in the field of regenerative medicine have led to the exploration of extracellular vesicles (EVs)-cargoes of microRNA, proteins, lipids, and nucleic acids-to evaluate their diagnostic value in terms of disease progression and severity, as well as a potential cell-free therapeutic approach for equine OA. EVs transmit molecular signals that influence various biological processes, including the inflammatory response, apoptosis, proliferation, and cell communication. In the present review, we summarize recent advances in the isolation and identification of EVs, the use of their biologically active components as biomarkers, and the distribution of the gap junction protein connexin 43. Moreover, we highlight the role of mesenchymal stem cell-derived EVs as a potential therapeutic tool for equine musculoskeletal disorders. This review aims to provide a comprehensive overview of the current understanding of the pathogenesis, diagnosis, and treatment strategies for OA. In particular, the roles of EVs as biomarkers in synovial fluid, chondrocytes, and plasma for the early detection of equine OA are discussed.

Genetically predicted circulating linoleic acid levels and risk of osteoarthritis: a two-sample mendelian randomization study

OBJECTIVES

This study aimed to provide insight into the effect of genetically predicted linoleic acid (LA) levels on osteoarthritis (OA).

METHODS

The LA dataset was obtained from the UK Biobank (UKBB) consortium and contained 114,999 samples. The OA discovery dataset was derived from MRC-IEU consortium and included 38,472 cases and 424,461 controls. The OA validation set was derived from a summary-level genome-wide association study (GWAS) and included 39,427 cases and 378,169 controls. Genetic variants strongly associated with LA (p < 5 × 10- 8) were extracted as instrumental variables (IVs). The inverse variance weighted (IVW) approach was adopted as the primary analysis method in this study. In addition, multiple sensitivity analysis methods were used to assess the reliability of our results.

RESULTS

The IVW approach showed that circulating LA levels were negatively associated with OA risk in the discovery set (odds ratio (OR) = 0.993, 95% confidence interval (95% CI): 0.988-0.998, p = 0.011). A consistent result was obtained in the validation set (OR = 0.904, 95%CI: 0.845-0.967, p = 0.003). These results were validated by sensitivity analysis.

CONCLUSION

This study provides new evidence for the causal relationship between LA and OA, which provides new insights for the treatment of OA.

Landscape of the Lumbar Cartilaginous End Plate Microbiota and Metabolites in Patients with Modic Changes

BACKGROUND

Modic changes (MCs), vertebral end plate and bone marrow damage observed by magnetic resonance imaging, are an independent risk factor for low back pain. The compositions of and interaction between microbiota and metabolites in the lumbar cartilaginous end plates (LCEPs) of patients with MCs have not been identified.

METHODS

Patients with lumbar disc degeneration who were undergoing lumbar spinal fusion surgery were recruited between April 2020 and April 2021. LCEPs were collected for 16S rRNA sequencing and liquid chromatography-mass spectrometry (LC/MS)-based targeted metabolomic profiling. Of the 54 patients recruited, 24 had no MCs and 30 had changes classified as Modic type 2 or 3. The primary goal was to identify specific genera of microbiota associated with MCs, and secondary goals included investigating differences in metabolites between patients with and without MCs and exploring the correlation between these metabolites and microorganisms.

RESULTS

Investigation of the microbiota community structure revealed that both alpha diversity and beta diversity were significantly different between patients with and without MCs, and the abundances of 26 genera were significantly different between these 2 groups. Metabolomic analysis revealed that 26 metabolites were significantly different between the 2 groups. The unsaturated fatty acid pathway was found to be the main pathway related to MCs. Multiomic correlation analysis suggested that Caulobacteraceae (unclassified) and Mycobacterium, Clostridium, Blautia, and Bifidobacterium at the genus level were linked to dysregulation of fatty acid metabolism, contributing to the pathogenesis of MCs.

CONCLUSIONS

Our study represents a foundational effort to examine the landscape of the microbiota and metabolites in patients with MCs, informing future studies on the pathogenesis of and targeted therapy for MCs.

LEVEL OF EVIDENCE

Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.

Synovial fluid extracellular vesicles as arthritis biomarkers: the added value of lipid-profiling and integrated omics

Arthritis, a diverse group of inflammatory joint disorders, poses great challenges in early diagnosis and targeted treatment. Timely intervention is imperative, yet conventional diagnostic methods are not able to detect subtle early symptoms. Hence, there is an urgent need for specific biomarkers that discriminate between different arthritis forms and for early diagnosis. The pursuit of such precise diagnostic tools has prompted a growing interest in extracellular vesicles (EVs). EVs, released by cells in a regulated fashion, are detectable in body fluids, including synovial fluid (SF), which fills the joint space. They provide insights into the intricate molecular landscapes of arthritis, and this has stimulated the search for minimally invasive EV-based diagnostics. As such, the analysis of EVs in SF has become a focus for identifying EV-based biomarkers for joint disease endotyping, prognosis, and progression. EVs are composed of a lipid bilayer and a wide variety of different cargo types, of which proteins and RNAs are widely investigated. In contrast, membrane lipids of EVs, especially the abundance, presence, or absence of specific lipids and their contribution to the biological activity of EVs, are largely overlooked in EV research. Furthermore, the identification of specific combinations of different EV components acting in concert in EVs can fuel the definition of composite biomarkers. We here provide a state-of-the-art overview of the knowledge on SF-derived EVs with emphasis on lipid analysis and we give an example of the added value of integrated proteomics and lipidomics analysis in the search for composite EV-associated biomarkers.

Plasma and synovial fluid extracellular vesicles display altered microRNA profiles in horses with naturally occurring post-traumatic osteoarthritis: an exploratory study

OBJECTIVE

The objective of this study was to characterize extracellular vesicles (EVs) in plasma and synovial fluid obtained from horses with and without naturally occurring post-traumatic osteoarthritis (PTOA).

ANIMALS

EVs were isolated from plasma and synovial fluid from horses with (n = 6) and without (n = 6) PTOA.

METHODS

Plasma and synovial fluid EVs were characterized with respect to quantity, size, and surface markers. Small RNA sequencing was performed, and differentially expressed microRNAs (miRNAs) underwent bioinformatic analysis to identify putative targets and to explore potential associations with specific biological processes.

RESULTS

Plasma and synovial fluid samples from horses with PTOA had a significantly higher proportion of exosomes and a lower proportion of microvesicles compared to horses without PTOA. Small RNA sequencing revealed several differentially expressed miRNAs, including miR-144, miR-219-3p, and miR-199a-3l in plasma and miR-199a-3p, miR-214, and miR-9094 in synovial fluid EVs. Bioinformatics analysis of the differentially expressed miRNAs highlighted their potential role in fibrosis, differentiation of chondrocytes, apoptosis, and inflammation pathways in PTOA.

CLINICAL RELEVANCE

We have identified dynamic molecular changes in the small noncoding signatures of plasma and synovial fluid EVs in horses with naturally occurring PTOA. These findings could serve to identify promising biomarkers in the pathogenesis of PTOA, to facilitate the development of targeted therapies, and to aid in establishing appropriate translational models of PTOA.

Beneficial Impact of Eicosapentaenoic Acid on the Adverse Effects Induced by Palmitate and Hyperglycemia on Healthy Rat Chondrocyte

Osteoarthritis (OA) is the most prevalent form of arthritis and a major cause of pain and disability. The pathology of OA involves the whole joint in an inflammatory and degenerative process, especially in articular cartilage. OA may be divided into distinguishable phenotypes including one associated with the metabolic syndrome (MetS) of which dyslipidemia and hyperglycemia have been individually linked to OA. Since their combined role in OA pathogenesis remains to be elucidated, we investigated the chondrocyte response to these metabolic stresses, and determined whether a n-3 polyunsaturated fatty acid (PUFA), i.e., eicosapentaenoic acid (EPA), may preserve chondrocyte functions. Rat chondrocytes were cultured with palmitic acid (PA) and/or EPA in normal or high glucose conditions. The expression of genes encoding proteins found in cartilage matrix (type 2 collagen and aggrecan) or involved in degenerative (metalloproteinases, MMPs) or in inflammatory (cyclooxygenase-2, COX-2 and microsomal prostaglandin E synthase, mPGES) processes was analyzed by qPCR. Prostaglandin E2 (PGE2) release was also evaluated by an enzyme-linked immunosorbent assay. Our data indicated that PA dose-dependently up-regulated the mRNA expression of MMP-3 and -13. PA also induced the expression of COX-2 and mPGES and promoted the synthesis of PGE2. Glucose at high concentrations further increased the chondrocyte response to PA. Interestingly, EPA suppressed the inflammatory effects of PA and glucose, and strongly reduced MMP-13 expression. Among the free fatty acid receptors (FFARs), FFAR4 partly mediated the EPA effects and the activation of FFAR1 markedly reduced the inflammatory effects of PA in high glucose conditions. Our findings demonstrate that dyslipidemia associated with hyperglycemia may contribute to OA pathogenesis and explains why an excess of saturated fatty acids and a low level in n-3 PUFAs may disrupt cartilage homeostasis.

Multi-Omic Temporal Landscape of Plasma and Synovial Fluid-Derived Extracellular Vesicles Using an Experimental Model of Equine Osteoarthritis

Extracellular vesicles (EVs) contribute to osteoarthritis pathogenesis through their release into joint tissues and synovial fluid. Synovial fluid-derived EVs have the potential to be direct biomarkers in the causal pathway of disease but also enable understanding of their role in disease progression. Utilizing a temporal model of osteoarthritis, we defined the changes in matched synovial fluid and plasma-derived EV small non-coding RNA and protein cargo using sequencing and mass spectrometry. Data exploration included time series clustering, factor analysis and gene enrichment interrogation. Chondrocyte signalling was analysed using luciferase-based transcription factor activity assays. EV protein cargo appears to be more important during osteoarthritis progression than small non-coding RNAs. Cluster analysis revealed plasma-EVs represented a time-dependent response to osteoarthritis induction associated with supramolecular complexes. Clusters for synovial fluid-derived EVs were associated with initial osteoarthritis response and represented immune/inflammatory pathways. Factor analysis for plasma-derived EVs correlated with day post-induction and were primarily composed of proteins modulating lipid metabolism. Synovial fluid-derived EVs factors represented intermediate filament and supramolecular complexes reflecting tissue repair. There was a significant interaction between time and osteoarthritis for CRE, NFkB, SRE, SRF with a trend for osteoarthritis synovial fluid-derived EVs at later time points to have a more pronounced effect.

Acute joint inflammation induces a sharp increase in the number of synovial fluid EVs and modifies their phospholipid profile

Inflammation is the hallmark of most joint disorders. However, the precise regulation of induction, perpetuation, and resolution of joint inflammation is not entirely understood. Since extracellular vesicles (EVs) are critical for intercellular communication, we aim to unveil their role in these processes. Here, we investigated the EVs' dynamics and phospholipidome profile from synovial fluid (SF) of healthy equine joints and from horses with lipopolysaccharide (LPS)-induced synovitis. LPS injection triggered a sharp increase of SF-EVs at 5-8 h post-injection, which started to decline at 24 h post-injection. Importantly, we identified significant changes in the lipid profile of SF-EVs after synovitis induction. Compared to healthy joint-derived SF-EVs (0 h), SF-EVs collected at 5, 24, and 48 h post-LPS injection were strongly increased in hexosylceramides. At the same time, phosphatidylserine, phosphatidylcholine, and sphingomyelin were decreased in SF-EVs at 5 h and 24 h post-LPS injection. Based on the lipid changes during acute inflammation, we composed specific lipid profiles associated with healthy and inflammatory state-derived SF-EVs. The sharp increase in SF-EVs during acute synovitis and the correlation of specific lipids with either healthy or inflamed states-derived SF-EVs are findings of potential interest for unveiling the role of SF-EVs in joint inflammation, as well as for the identification of EV-biomarkers of joint inflammation.