Joris van Dongen

282 Chapter 12 Systemic, often chronic, diseases such as diabetes mellitus (DM) impact the clinical efficacy of autologous SVF injections. For DM, long term hyperglycaemic exposure of ASC and ECM influences their biological properties 14-16 . High levels of glucose impair the regenerative function of ASC by intracellular reactive oxygen species (ROS) accumulation 17 . ROS inhibits the proliferation and proangiogenic capacities of ASC, which are important processes in wound healing 17 . Furthermore, high levels of glucose and their glycolytic products such as methylglyoxal result in glycation of proteins.These so-called advanced glycation end products (AGEs), bind to a receptor of AGE (RAGE) that is expressed by virtually all tissue cells, and causes pro-inflammatory activation. Inflammation is relevant for wound repair, but increased chronic inflammation acts adverse and results in decreased vascularization and tissue necrosis as observed in diabetic ulcers. Glycation affects ECM molecules rather than circulating proteins due to their slow turnover i.e. long half-life 18 . Elevated AGEs damage ECM potentially in three different critical sites: compromised cellular binding site in the ECM which inhibits cell adhesion, survival and proliferation. Secondly, molecular sites in the ECM that are involved in turnover (both proteolytic degradation and cross-linking) may be affected which may result in adverse ECM remodelling, accumulation, changes in mechanical features and associated changes of biological responses of bound tissue cells 14,19,20 . Affected subunits of ECM molecules lead to more crosslinks between proteins and thus an unwanted higher stability and stiffness of ECM proteins 14 . In soft tissues, increased stiffness promotes fibrotic processes in a feed-forward looped fashion. For those reasons, non-diabetic SVF is likely to be more suitable than diabetic SVF as treatment for e.g. wound healing of diabetic ulcers in diabetic patients. This would, however, implicate an allogeneic tissue transplantation, which will result in an immunological rejection of the administrated SVF. We surmised that the SVF’s biological activity is primarily contained within the ECM and its bound paracrine factors in which parenchymal and stromal cells no more than serve to continuously replenish this biological entity. In particular, for short(er) term applications such as wound healing, ECM loaded with paracrine factors might show therapeutic efficacy. ECM can be obtained by decellularization of (adipose) tissue. Literature is littered with a host of decellullarization protocols that often dictate the use of detergents such sodiumdodecyl sulphate (SDS) aswell as acids and bases to remove cellular constituents. This procedure not only removes all cell types but also the paracrine factors 21 . A decellularized extracellular matrix that is devoid of cells and paracrine factors is of reduced clinical value compared to mechanically derived SVF in which both ECM and paracrine factors are retained. Therefore, re-charging of ECMwith factors e.g. released from cultured ASC might restore a comparable clinical effect as mechanically derived SVF while preserving the option for inter-patient administration.