Repurposing glutamate receptor antagonists to prevent post-traumatic osteoarthritis

Abstract

Purpose: Synovial fluid glutamate concentrations increase in arthritis and after joint injury. Activation of kainate (KA) and AMPA glutamate receptors (GluRs) increase interleukin-6 release by synoviocytes and cause joint pain. We previously found that AMPA and KA GluRs localise to osteoarthritic bone, cartilage and synovium and that NBQX (AMPA/KA GluR antagonist) reduced knee swelling, gait abnormalities and joint destruction in a rat inflammatory arthritis model and two models of post-traumatic osteoarthritis: rat medial meniscal transection (MNX), mouse non-invasive anterior cruciate ligament (ACL) rupture. Since NBQX is not approved for use in humans, we have tested 4 AMPA/KA GluR antagonists (anonymised to A, B, C and D), which have passed Phase 1 clinical trials, and compared these to current approved treatments: hyaluronic acid (HA) and steroid intra-articular injections. HA and steroids have not previously been tested in rodent models intra-articularly at the time of injury. We hypothesise that drugs A-D will reduce pain, inflammation and degeneration in the mouse ACL rupture post-traumatic osteoarthritis model. Methods: The right stifle of 12-week-old C57Bl6 mice was held in flexion and a 12N load (ElectroForce® 3200, BOSE) applied under anaesthetic until ACL rupture (in accordance with Animals (Scientific Procedures) Act 1986. Project License number: P287E87DF). A single 10μl intra-articular injection of drug A (n=4), B (n=3), C (n=3), D (n=4), hyaluronic acid (HA) (n=8, Durolane, 8mg/kg, Bioventus) or steroid (n=7, Depo-medrone, 10mg/kg, Pfizer) was administered to mice immediately following ACL rupture, whilst additional mice received an intra-articular injection of vehicle (100mM NaOH vehicle for drug A, n=4; DMSO vehicle for drugs B, C and D, n=4; saline for HA and steroid, n=7) immediately following ACL rupture. Contralateral knees (intact ACL) were used as controls. All mice received analgesia (Temgesic) prior to ACL-rupture. Over 21 days, lameness was scored and stifle swelling measured (electronic calipers, mean of 3 measurements, days 0, 1, 2, 3, 7, 14, 21). On day 21, all animals were culled and knees scored for degradation (OARSI score). Measurements are mean of 2 observers blinded to treatment. Results: By day 2, drug A had reduced mean knee swelling by ∼50% and did not differ significantly from day 0 pre-ACL rupture measurements, whereas vehicle control knee swelling was significantly increased until day 7 (p<0.01, general linear model (GLM)) (Fig. 1a). Drug C also reduced knee swelling to day 0 levels by day 2, whereas drug D (p<0.05, GLM) and vehicle control (p<0.001, GLM) were significantly increased until day 7. Drug B did not reduce swelling until day 14 (Fig. 1b). On day 1, steroid injection significantly reduced knee swelling (∼50% reduction) compared to vehicle (p<0.001, GLM) and HA (p<0.05, GLM), but this was short-lived with no reductions from day 2 onwards (Fig. 1c). HA did not reduce knee swelling (Fig. 1c). Lameness scores were reduced by drugs A-D, with significant reductions compared to vehicle control (4.13±0.13) on day 3 by drug B (1.83±0.17, p<0.001, GLM), drug C (2.33±0.6, p<0.05, GLM) and drug D (2.5±0.2, p<0.05, GLM). HA and steroid injections did not significantly reduce lameness at any time point. Drug A showed ∼40% reduction in mean degradation score at day 21, whereas HA had no effect and depo-medrone significantly increased degeneration by ∼50% (p<0.05, one-way ANOVA). Conclusions: This study provides evidence that AMPA/KA GluR antagonists, already approved for use in humans, relieve inflammation, lameness and joint degradation in post-traumatic OA. GluR antagonists exceeded anti-nociceptive and anti-inflammatory effects of HA and steroids. Drugs A and C reduced knee swelling to control levels by day 2, whereas HA did not reduce swelling at all, and steroid effects were not apparent beyond day 1. All GluR antagonists reduced lameness scores whereas HA or steroid injections did not. Drug A reduced mean degeneration whereas HA had no effect and depo-medrone significantly increased degeneration. An estimated 52.5 million adults in the United States are reported to have some form of arthritis, with OA (approximately 27 million) being the most prevalent (Centers for Disease Control and Prevention). Joint injuries, such as ACL rupture or meniscal tear, are extremely common, with 50-90% of these patients going on to develop OA within 5-15 years. There is currently no cure for OA and where pain/disability is intolerable, joint replacement is performed. Surgery is costly, carries significant risks, with 20% of knee replacements unsuccessful. Although not yet fully powered, our data indicate that AMPA/KA GluR antagonists, already approved for human use, have exciting potential for rapid repurposing as new disease modifying drugs to prevent and treat OA.