TNF-α Carried by Plasma Extracellular Vesicles Predicts Knee Osteoarthritis Progression

Objectives To identify plasma extracellular vesicles (EVs) associated with radiographic knee osteoarthritis (OA) progression. Methods EVs of small (SEV), medium (MEV) and large (LEV) sizes from plasma of OA participants (n=30) and healthy controls (HCs, n=22) were profiled for surface markers and cytokine cargo by high-resolution flow cytometry. The concentrations of cytokines within (endo-) and outside (exo-) EVs were quantified by multiplex ELISA. EV associations with knee radiographic OA (rOA) progression were assessed by multivariable linear regression (adjusted for baseline clinical variables of age, gender, BMI and OA severity) and receiver operating characteristic (ROC) curve analysis. Results Based on integrated mean fluorescence intensity (iMFI), baseline plasma MEVs carrying CD56 (corresponding to natural killer cells) predicted rOA progression with highest area under the ROC curve (AUC) 0.714 among surface markers. Baseline iMFI of TNF-alpha in LEVs, MEVs and SEVs, and the total endo-EV TNF-alpha concentration, predicted rOA progression with AUCs 0.688, 0.821, 0.821, 0.665, respectively. In contrast, baseline plasma exo-EV TNF-alpha (the concentration in the same unit of plasma after EV depletion) did not predict rOA progression (AUC 0.478). Baseline endo-EV IFN-gamma and exo-EV IL-6 concentrations were also associated with rOA progression, but had low discriminant capacity (AUCs 0.558 and 0.518, respectively). Conclusions Plasma EVs carry pro-inflammatory cargo that predict risk of knee rOA progression. These findings suggest that EV-associated TNF-alpha may be pathogenic in OA. The sequestration of pathogenic TNF-alpha within EVs may provide an explanation for the lack of success of systemic TNF-alpha inhibitors in OA trials to date.

Automated summary

Plasma extracellular vesicles (EVs) carrying specific cytokines were found to predict the progression of knee osteoarthritis, with EVs carrying CD56 and TNF-alpha showing higher predictive capability, while the predictive capability of exo-EV TNF-alpha was poor.