An innovative view on osteoarthritis: Investigating the effect of chondrodystrophy and the continuous release of celecoxib on osteoarthritic cartilage

Abstract

Osteoarthritis (OA) is a disease of the joint as a whole and leads to progressive degeneration. Even though OA is a frequent cause of (chronic) pain and disability among humans and canines, the pathobiology is still unclear and treatment remains symptomatic. In humans, chondrodystrophy has been related to less susceptibility for OA. In canines chondrodystrophic breeds are frequently encountered, as it is regarded a characteristic for several breeds and a distinction can be made between chondrodystrophic (CD) and non-chondrodystrophic (NCD) dogs. CD breeds express intervertebral disc degeneration differently than NCD breeds. How chondrodystrophy affects the cartilage and could influence the disease course of OA has, however, not been clarified yet. In the first chapter, an innovative in vitro model for OA was tested. Canine cartilage micro-aggregates derived from NCD and CD were cultured in the presence of osteoarthritic synovial fluid. Culturing with synovial fluid proved to be challenging. Synovial fluid does seem to elevate prostaglandin E2 (PGE2) content in the medium, but this was the most pronounced in healthy synovial fluid. There were indications that NCD cartilage micro-aggregates were influenced in a greater extent by inflammatory conditions, as after 14 days of culturing in osteoarthritic synovial fluid the NCD micro-aggregates majorly disintegrated. In the second chapter, the cartilage explants derived from NCD and CD donors were cultured for 21 days with or without an inflammatory stimulus and/or non-steroidal inflammatory drug (NSAID, namely celecoxib). NCD derived cartilage seemed to be more susceptible for the inflammatory stimulus (tumour necrosis factor alpha (TNF-α)). Moreover, treatment with celecoxib was only in NCD cartilage able to reduce the upregulation of PGE2 caused by TNF-α. Moreover, indications of a difference in the activity of the Wnt pathway were revealed by gene expression levels. AXIN2 and DKK3 were both more expressed in CD cartilage, possibly indicating activation of the Wnt pathway in CD cartilage. Altogether, there seems to be a difference at the biomolecular and biochemical level between CD and NCD cartilage. In the third and final chapter, the in vitro effects of the controlled release of celecoxib by loaded polyester amide (PEA) microspheres in a 4-week follow-up were researched. NCD derived chondrocytes were cultured in monolayers and stimulated with TNF-α. Subsequently, the monolayers were treated with two different dosages of microspheres, 10-4 M and 10-7 M, or unloaded PEA microspheres and compared to free added celecoxib (10-6 M). We demonstrated no cytotoxicity, gradual celecoxib release of the PEA microspheres, and a PGE2 suppression by the 10-4 M loaded microspheres for 28 days. An innovative view on osteoarthritis is provided by looking into the differences between CD and NCD dogs on a cartilage level and studying the in vitro the applicability of celecoxib-loaded (PEA) microspheres as a treatment option for OA.