Impact of 45S5-Bioactive Glass on Chondrocytes in Knee Osteoarthritis—In Vitro Study Exploring Cellular Responses

Osteoarthritis (OA), the most common joint disease, is marked by cartilage degradation and chronic inflammation. While 45S5-bioactive glass (45S5-BG) is well-established in bone regeneration and has been suggested to exert immunomodulatory effects, its impact on OA chondrocytes remains largely unexplored. Therefore, this in vitro study investigated the effects of 45S5-BG microparticles (0.125 mg/mL) on chondrocytes derived from OA patients, evaluating its therapeutic potential in OA. Chondrocytes were cultured with or without 45S5-BG for 1 and 7 days. Gene expression of cartilage markers, cytokines, matrix metalloproteinases (MMPs), and toll-like receptors (TLRs) was analyzed by qPCR. Protein levels were assessed by ELISA. 45S5-BG stimulation significantly altered chondrocyte activity, inducing upregulation of IL-6, IL-1β, TNF-α, MMP-1/-3/-13, and TLR4. Expression of ACAN and COL2A1 was reduced, while COL10A1-a marker of chondrocyte hypertrophy-was significantly increased at day 1. These findings show a catabolic and pro-inflammatory shift in chondrocyte phenotype upon 45S5-BG exposure, showing no therapeutic benefit of 45S5-BG on OA chondrocytes. However, considering the pronounced effects on chondrocyte activity and the well-established bioactivity and biocompatibility of 45S5-BG, our findings suggest that modified BG formulations could be developed to enhance chondroprotective and anti-inflammatory properties, warranting further investigation in co-culture and in vivo models.