Joris van Dongen

116 Chapter 5 DISCUSSION This study demonstrates that enzymatically processed cells from tSVF – which was mechanically derived by means of the FAT procedure – have a pro-regenerative and anti-inflammatory effect on chondrocytes in vitro . Proliferation of chondrocytes was stimulated by tSVF-derived cells as shown in the significant higher ratio of chondrocytes in different co-cultureswith tSVF-derived cells as compared to cultures of chondrocytes alone. A pro-regenerative effect of tSVF is postulated as it enables regeneration of functional cartilage by stimulating GAGs formation in vitro . Downregulation of IL- 1 β and COX2 gene expression due to addition of tSVF to inflammatory chondrocytes in vitro suggests an anti-inflammatory effect. These aforementioned inflammatory processes are involved in osteoarthritis and can be influenced by the heterogenous cell population of tSVF, Hence, tSVF is a potential effective therapy for the treatment of OA. Elevated levels of COX2 and IL-1 β are found in chronic inflammatory state of joints. 34,35,36 Overexpression of COX2 in osteoarthritis results in an increased production of matrix metalloproteinases (MMPs), reduction of collagen synthesis and stimulation of chondrocyte apoptosis. 34 All of these processes contribute to cartilage degradation leading to more inflammation. This vicious circle of cartilage degradation and inflammation is enhanced by PGE2, a pro-inflammatory mediator produced after stimulation with COX2 and IL-1 β . 34 Eventually, cartilage degradation will result in pain. Thus far, several COX inhibitors e.g. NSAIDs and selective COX2 inhibitors have been used to treat clinical symptoms of osteoarthritis by blocking synthesis of COX1 and COX2. 37,38 Although, these oral medicaments seem beneficial, there is a serious risk of systemic complications e.g. gastro-intestinal ulceration or bleeding and cardiotoxicity. 37,38 Comparable to COX2, IL-1 β is a major contributor to inflammatory reactions and catabolic effects to articular cartilage as well. 36,39 In osteoarthritic joints, elevated levels of IL-1 β are present in synovial fluid in cartilage and the subchondral bone layer. 36,39 IL-1 β inhibits the ability of chondrocytes to repair cartilage by blocking synthesis of type II collagen and aggrecan in ECM. 39,40 IL-1 β seems to have a direct adverse effect on chondrocytes as it stimulates the synthesis of MMPs, mainly MMP-1, -3 and -13, which have a deteriorating effect on cartilage. 39,40 Indirectly, IL-1 β also degrades cartilage ECM by stimulating the production of the aggrecan molecule proteolytic enzyme ADAMTS metalloproteinases, especiallyADAMTS-4. 39,41 Considering the downregulation of IL-1 β and COX2 gene expression by tSVF as shown in this current study, local treatment of OA by autologous tSVF might be effective and substantially reduces the risk of systemic complications. 32 Moreover, ASCs have shown to secrete high levels of tissue inhibitors of metalloproteinases TIMP-1 and -2 which