The molecular profile of synovial fluid changes upon joint distraction and is associated with clinical response in knee osteoarthritis

Abstract

Objective: Surgical knee joint distraction (KJD) leads to clinical improvement in knee osteoarthritis (OA) and also apparent cartilage regeneration by magnetic resonance imaging. We investigated if alteration of the joint's mechanical environment during the 6 week period of KJD was associated with a molecular response in synovial fluid, and if any change was associated with clinical response. Method: 20 individuals undergoing KJD for symptomatic radiographic knee OA had SF sampled at baseline, midpoint and endpoint of distraction (6 weeks). SF supernatants were measured by immunoassay for 10 predefined mechanosensitive molecules identified in our previous pre-clinical studies. The composite Knee injury and OA Outcome Score-4 (KOOS 4) was collected at baseline, 3, 6 and 12 months. Results: 13/20 (65%) were male with mean age 54 ± 5yrs. All had KellgreneLawrence grade !2 knee OA. 6/10 analytes showed statistically significant change in SF over the 6 weeks distraction (activin A; TGFb-1; MCP-1; IL-6; FGF-2; LTBP2), P < 0.05. Of these, all but activin A increased. Those achieving the minimum clinically important difference of 10 points for KOOS 4 over 6 months showed greater increases in FGF-2 and TGFb-1 than non-responders. An increase in IL-8 during the 6 weeks of KJD was associated with significantly greater improvement in KOOS 4 over 12 months. Conclusion: Detectable, significant molecular changes are observed in SF following KJD, that are remarkably consistent between individuals. Preliminary findings appear to suggest that increases in some molecules are associated with clinically meaningful responses. Joint distraction may provide a potential opportunity in the future to define regenerative biomarker(s) and identify pathways that drive intrinsic cartilage repair.

Gene Expression Signatures of Synovial Fluid Multipotent Stromal Cells in Advanced Knee Osteoarthritis and Following Knee Joint Distraction

“…Our analysis of SF MSC transcriptome half-way through (week 3) and in the end of KJD (week 6) provided interesting insights into the dynamics of SF MSC responses in relation to previously reported SF cytokine changes (Watt et al, 2020). In a separate cohort of 20 KJD patients, mild but sustained increases in SF levels of FGF2 and TGFb1 have been recently documented, which were particularly prominent in patients who responded better to their treatment (Watt et al, 2020).…”

“…Another promising joint-preserving regenerative treatment for severe OA, a combination of intra-articular and intra-osseous infiltrations of autologous platelet-rich plasma (PRP), has been shown to reduce SF MSC numbers measured by flow cytometry (Muiños-López et al, 2016;Sánchez et al, 2016), presumably by attraction of MSCs to the exposed osseous surface. In our cohort of KJD patients, SF MSC numbers measured by CFU-F assay did not increase or fall following the treatment, although higher colony densities during treatment pointed toward their slightly increased proliferative capacity that may in part be driven by KJD-associated changes in SF FGF2 concentration (Coutu et al, 2011;Watt et al, 2020). We acknowledge that aspirated SF MSC numbers could not be volumetrically counted, as the volumes of fluid taken from the patients could not be precisely controlled and depended on patient's clinical status; therefore, the data were presented as total aspirated MSCs.…”

“…In contrast to an animal model studies where a significant effect of KJD on joint inflammation was found (Chen et al, 2015;Wiegant et al, 2015), early results on the effects of KJD on SF proinflammatory mediators in OA patients remain puzzling. For example, pro-inflammatory IL-6 and MCP1 SF levels were found increased following KJD in Watt et al (2020) study, although IL-6 was negatively correlated with pro-chondrogenic TGFb1, as would be expected (Wiegertjes et al, 2019). Larger studies investigating more SF analytes and SF MSC transcripts using the same cohort of patients (validation cohort), ideally at more time-points, during the course of distraction and comparing responders and non-responders, would be needed to shed more light on the effects of joint off-loading on SF cellular and molecular responses.…”

“…Indeed, in the canine groove model of OA, we showed that MSCs injected in the SF, following KJD, were capable of integrating into cartilage injury sites (Baboolal et al, 2016). Furthermore, a recent study provided evidence for anabolic molecular responses in SF following KJD, which may act on SF MSCs and represent potential pathways for cartilage regeneration (Watt et al, 2020).…”

Of mice and men: converging on a common molecular understanding of osteoarthritis

“… 14 , 16 When the synovial fluid levels of candidate molecules were examined over the course of joint distraction, out of ten analytes examined, only two, FGF2 and TGFβ (both pro-regenerative growth factors), predicted a good clinical response. 104 …”