Cigarette Smoke Extract Alters the Inflammatory Secretome of Osteoarthritis‐Affected Synovium Increasing Joint Tissue Oxidative Stress in an Indirect Co‐Culture Model

Dysregulation of synovial homeostasis has been implicated in the pathophysiology of osteoarthritis (OA), but the effects that cigarette smoking has on OA-affected synovium have yet to be studied. To further the knowledge on how cigarette smoke alters OA progression, we investigated the direct effects of cigarette smoke extract (CSE) on synovial explants and the indirect impact this has on cartilage explant degradation in an in vitro model of OA-like inflammation. Porcine synovium explants were cultured under control (n = 8), OA only (IL-1β and TNF-α, n = 8), and CSE + OA (10% CSE, IL-1β and TNF-α, n = 8) conditions. The resulting changes in viability/metabolic activity, reactive oxygen species (ROS) production, inflammatory cytokine and matrix metalloprotease profile, and macrophage polarization were evaluated. Using an indirect co-culture model, cartilage explants (n = 8/group) were cultured in synovium conditioned media (SCM) under the aforementioned conditions to evaluate changes in viability/metabolic activity, ROS, and extracellular matrix (ECM) integrity. CSE + OA treated synovium had increased production of ROS, IL-8, MMP-2, and MMP-8 compared to OA only treated synovium. In response, cartilage explants under CSE + OA SCM had more chondrocytes stained positively for ROS, with accelerated losses in GAGs and ECM integrity compared to those exposed to OA only SCM. CSE may accelerate OA progression by altering the inflammatory secretory profile of synovium and contributing to increased oxidative stress and the pathological crosstalk between synovium and cartilage.