Correlations between metabolites in the synovial fluid and serum: A mouse injury study

Abstract

Osteoarthritis, the most common degenerative joint disease, occurs more frequently in joints that have sustained injury. Currently, osteoarthritis is diagnosed with imaging that finds radiographic changes after the disease has already progressed to multiple tissues. The primary objective of this study was to compare potential metabolomic biomarkers of joint injury between the synovial fluid and serum in a mouse model of post-traumatic osteoarthritis. The secondary objective was to gain insight into the pathophysiology of osteoarthritis by examining metabolomic profiles after joint injury. 12-week-old adult female C57BL/6 mice (n=12) were randomly assigned to control, day 1 post injury, or day 8 post injury groups. Randomly selected stifle (i.e., knee) joints were placed into a non-invasive injury apparatus and subjected to a single dynamic axial compression causing anterior translation of the tibia relative to the femur to tear the anterior cruciate ligament. At days 1 and 8 post injury, serum was extracted then mice were immediately euthanized prior to synovial fluid collection. Metabolites were extracted and analyzed by liquid chromatography coupled to mass spectrometry. We detected ~2500 metabolites across serum and synovial fluid. Of these metabolites 179 were positively correlated and 51 were negatively correlated between synovial fluid and serum, indicating potential for the development of metabolomic biomarkers. Synovial fluid appeared to capture differences in metabolomic profiles between injured mice at both day 1 and 8 after injury whereas serum did not. However, synovial fluid and serum were distinct at both days 1 and 8 after injury. In the synovial fluid, pathways of interest across different time points mapped to amino acid synthesis and degradation, bupropion degradation, and the tRNA charging pathway. In the serum, notable pathways across time points were amino acid synthesis and degradation, the phospholipase pathway, and nicotine degradation. These results provide a rich picture of the injury response at early time points following traumatic joint injury. Furthermore, the correlations between synovial fluid and serum metabolites suggest that there is potential to gain insight into intra-articular pathophysiology through analysis of serum metabolites.

Metabolomic Phenotypes Reflect Patient Sex and Injury Status: A Cross-Sectional Analysis of Human Synovial Fluid

“… 30 , 31 Proline, a downstream product of arginine, contributes to collagen synthesis 32 and has also been associated with OA 20 , 31 , 33 , 34 . A prior study found higher concentrations of asparagine, arginine, and proline at day 1 that then decreased by day 8 in a non-invasive mouse ACL tear model 29 , suggesting these amino acids could be protective after injury and might be measured over time to monitor OA development. Similarly, NMR analysis of sheep SF following ACL injury found increased levels of serine and asparagine post-injury compared to non-injured sheep 28 .…”

“…Previous studies have applied metabolomics to examine metabolic shifts post-injury in animal models [26][27][28][29] , but no study to date has examined metabolic shifts in human SF induced by different injuries. Here, metabolic phenotypes were generated and differences in pathway regulation between injuries were detected.…”

The impact of omics research on our understanding of osteoarthritis and future treatments

“…This study provides excellent baseline data on metabolic effects of these two lifestyle modifications on joint metabolism, as well as how these changes correlate to systemic parameters. A related study compared 2500 serum and synovial fluid metabolites after a single injury in mice and showed both similarities and differences between the two body fluids [21].…”

Subchondral bone and synovial fluid metabolomic profiles are altered in injured and contralateral limbs 7 days after non-invasive joint injury in skeletally-mature C57BL/6 mice

“…Synovial fluid was extracted from the stifle joint immediately following euthanization consistent with our previously published protocol 26 . Briefly, an incision was made anteriorly into the synovium and synovial fluid was collected by adsorption using Melgisorb alginate dressing (Tendra).…”

“…Since bone is highly cellular and vascularized compared with cartilage, assessing metabolic shifts in synovial fluid is expected to produce data that can help contextualize early bone changes after joint injury. Recent studies find distinct metabolic profiles between injured and sham-injured synovial fluid 7d after joint injury in mouse models 25,26 . However, the relevance of shifts in synovial fluid metabolism in injured versus sham-injured, and contralateral-to-injured soon after joint injury on bone outcomes remains uncertain.…”