Specialized pro-resolving mediators alleviate inflammation and cartilage breakdown in vitro and may play a pivotal role in platelet-rich plasma.

Platelet-rich plasma (PRP) is widely used for osteoarthritis, though its mechanism of action remains unclear. Platelet-derived lipoxygenases generate specialized pro-resolving mediators (SPMs), lipids that aid inflammation resolution, potentially contributing to PRP's therapeutic effects. This study investigated SPMs in human PRP and their correlation with anti-inflammatory and anti-degradative effects in vitro. Levels of Maresin 1 (MaR1) and Resolvin D1 (RvD1), two species of SPMs, were measured in PRP from patients receiving injections. A proof-of-concept model with IL-1β-stimulated bovine osteochondral (bOC) explants treated with MaR1, RvD1, or vehicle assessed the effects of purified SPMs. Additionally, five samples with lowest (PRP/SPM-low) and five with highest (PRP/SPM-high) SPM levels were tested on IL-1β-stimulated human chondrocytes. PRP from 40 patients (57.5% male, mean age 55.9 ± 18.0) was analyzed. PRP volume averaged 7.2 ± 2.6 ml, platelet count 8.5 ± 4.1 billion, MaR1 667.5 ± 241.2pg/ml, and RvD1 139.5 ± 84.2pg/ml. SPM levels showed no correlation with age, sex, or BMI, but MaR1 correlated with RvD1 (r = 0.33, p = 0.04) and platelet count (r = 0.38, p = 0.02). In bOC explants, purified MaR1 significantly reduced IL-6 (p = 0.035) and CTX-II (p = 0.043), while RvD1 reduced CTX-II (p = 0.003) but not IL-6 (p > 0.999). PRP/SPM-low showed less pronounced anti-inflammatory effects, whereas PRP/SPM-high demonstrated stronger anti-inflammatory activity in human chondrocytes, and reduced inflammatory, degradative gene expression of IL-6 (p = 0.056), MMP-13 (p = 0.034), and COL2A1 (p = 0.054), and CTX-II levels (p = 0.014). This study reveals that PRP contains variable MaR1 and RvD1 concentrations, with higher SPMs associated with reduced inflammation and cartilage breakdown. These findings highlight the role of SPMs in PRP's therapeutic effects and provide insight into its mechanisms of action.