Developing a Functional Osteoarthritis Model Using Human Osteochondral–Synovial Explants

Osteochondral explants can serve as valuable <i>ex vivo</i> models for investigating joint development and testing therapeutic interventions in osteoarthritis (OA). The incorporation of synovial tissue in coculture settings more closely reproduces the inflammatory milieu characteristic of OA joints; however, no report exists regarding the culture media that can support such <i>ex vivo</i> systems. We investigated the reactivity of osteochondral explants using two media types: Dulbecco's modified essential medium (DMEM) and chondrogenic medium (CHONDRO). Additionally, we tested the potential therapeutic effect of serum-free conditioned media (CM) derived from allogeneic adipose-derived stem cells (ADSCs) in the context of OA. Osteochondral fragments with or without homologous synovium were cultured in DMEM and CHONDRO for up to 30 days. A subset of explants received treatment with CM. Explant reactivity was assessed by cytokine release, synovial cellularity, and osteochondral protein content using Western blot and immunohistochemistry. Explants kept in DMEM displayed diminished levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFα), together with increased Collagen II (Col II) expression. Notably, consistent suppression of TNFα was observed following CM treatment. Conversely, the CHONDRO-kept samples exhibited an increased prevalence of chondrocyte clusters; heightened Perlecan presence as well as IL-1β levels in response to CM treatment and synovial tissue-dependent fluctuations in Col II levels. Remarkably, significantly increased β-galactosidase levels could be detected in osteochondral tissues treated with CM, regardless of the culture media type. In the experimental conditions created, DMEM provided a neutral milieu and was less prone to confounding experimental outcomes, rendering it suitable for evaluating potential therapies. CHONDRO apparently increased chondrocyte clusters and facilitated extracellular matrix synthesis; however, its usage requires caution due to potential interference with experimental readouts. CM could exert an antisenescence effect, an effect that warrants further investigation.