Perfluoroalkyl and polyfluoroalkyl substances crossing the blood-joint barrier: Their occurrence and distribution in synovial fluid

Per- and polyfluoroalkyl substances (PFASs) have garnered considerable research attention due to their potential adverse effects on human health. Epidemiological studies have indicated a possible association between PFASs exposure and the prevalence of osteoarthritis (OA). However, the presence of PFASs in the synovial fluid of OA patients and the distribution of PFASs across the blood-joint barrier remains unreported. This study identified significant differences in PFASs profiles between patients and controls, with a markedly higher PFOS-to-PFOA ratio observed in patients. Additionally, the blood-joint transfer efficiency of PFOS was significantly greater in patients than in controls (0.75 vs. 0.53, p < 0.05). Furthermore, PFOS levels were elevated in patients with advanced OA compared to those in the early stages. Positive correlations were observed between synovial fluid PFOS and inflammatory markers C-reactive protein (CRP) and tumor necrosis factor-α (TNF-α), implying that inflammation may facilitate the distribution of PFOS across the joint barrier. This study represents the first documented evidence of the human joint exposure to PFASs and their blood-joint transfer abilities.