NOVEL THERAPEUTIC COMPOUNDS MODULATE THE INFLAMMATORY RESPONSE OF STIMULATED EQUINE SYNOVIOCYTES

Osteoarthritis (OA) is prevalent in equine and can be career-ending for performance horses due to lameness limitations and decreased quality of life. OA is a progressive, multifactorial disease that compromises the synovial joints' normal function, resulting in subchondral bone and articular cartilage deterioration over time. OA is a complex disease that impacts the entire joint, wherein activation of the innate immune system has an essential role in the disease progression and the development of pain. The synovial membrane, or the synovium, is a crucial contributor to the inflammation of diseased joints, regardless of the intra-articular tissue type initially affected. Synoviocytes are a predominant cell type of the synovium and contribute to inflammation by releasing key mediators and degradative enzymes, such as interleukin (IL)-6, IL-1β, a disintegrin, and metalloproteinase (ADAM) domains, and matrix metalloproteinases (MMPs). The production of pro-inflammatory molecules sequentially influences the expression of degradative enzymes and cartilage destruction. Therefore, the pathophysiological processes within synovial joints afflicted by OA can be further understood by studying the characteristics of synoviocytes.

We aimed to investigate the inflammatory component of OA in an in vitro model using a primary cell line of equine fibroblast-like synoviocytes (eqFLS) stimulated with tumor necrosis factor-alpha (TNF-α) to represent an initial inflammatory stimulus. Our studies have shown that stimulating eqFLS with TNF-α for 24 hours significantly increased the gene expression of pro-inflammatory biomarkers. Among several pro-inflammatory candidate genes assayed, only pro-inflammatory cytokine IL-6 gene expression could be detected reproducibly following stimulation with the TNF-α gene in eqFLS. We characterized the pro-inflammatory response of eqFLS and utilized this system to examine the impact of novel therapeutic compounds designed in-silico with the goal of reducing the inflammatory response of eqFLS. A piperazine-based compound (C3) and its derivative (02-09) were primarily designed to mimic the interactions of the growth factor pigment epithelium-derived factor (PEDF) with its receptor, the non-integrin laminin receptor 1 (LAMR1). Based on previous in vitro studies in the laboratory, C3 and 02-09 had been proposed to have a strong potential for inhibiting inflammation while reducing angiogenesis and chondrocyte hypertrophy. The efficacy of these two novel compounds on eqFLS was examined in the present work by assessing the gene expression levels of inflammatory biomarkers, including IL-6, IL-1β, IL-8, ADAMs, and MMPs relative to a control housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in various study designs. An in-vitro screen with the IL-1β promoter driving a reporter green fluorescent protein (GFP) was also designed to detect and track the inflammatory response of eqFLS by imaging following stimulation with or without (+/-) TNF-α relative to controls. This screen will be utilized in future studies to potentially identify more effective compounds in the LAMR1-interacting series. The current findings suggest that the novel compounds, especially 02-09, might exhibit an anti-inflammatory effect on eqFLS; therefore, it is a potential therapeutic agent in modulating inflammation during OA development.