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Background and aims: Platelet rich plasma (PRP) obtained from blood anticoagulated with acid-citrate-dextrose (ACD) or sodium-citrate (SC) is used for regenerative medicine as source of platelet-derived growth factors. Allergic reactions against citrate were reported in patients after local injection of PRP allowing us to hypothesize that anticoagulants exert a harmful and local effect that interferes with the regenerative proprieties of platelets. Herein we test this hypothesis by analyzing the effect of ACD and SC on angiogenic and regenerative responses mediated by platelets. Methods: PRP was obtained from SC-or ACD-anticoagulated blood; platelets were lysed to release growth factors; and PRP releasates (PRPr) were used to induce in vitro endothelial proliferation and 2D-migration, and regeneration of mouse skin wounds. Results: We first compared proliferation and migration of endothelial cells mediated by anticoagulated-PRPr supplemented or not with CaCl 2. Alteration of endothelial adhesion and impediment of proliferation and migration was observed without CaCl 2. Although endothelial morphology was normalized in SC-and ACD-PRPr after calcium restitution, angiogenic responses were only markedly induced by SC-PRPr. In vivo studies revealed a delay in mouse skin regeneration after treatment with anticoagulated-PRPr without CaCl 2. Healing was only induced after calcium restitution in SC-but ACD-PRPr. Moreover, the development of inflammatory intradermal papules was evidenced after injection of ACD-PRPr. Supplementation of SC-PRPr with the equivalent concentration of dextrose (D-Glucose, 18 mM) present in ACD-PRPr resulted in reduction of endothelial proliferation and migration, delay of mouse skin regeneration and development of intradermal papules. Finally, collecting blood with half amount of SC significantly improved all the angiogenic and regenerative responses mediated by PRPr. In contrast, the delay of skin regeneration and the development of inflammatory papules remained stable after dilution of ACD. Conclusion: Our findings indicate that (1) calcium restitution is required to impair the cellular and tissue alterations induced by citrated-anticoagulants contained in PRP; (2) ACD-derived dextrose confers anti-angiogenic, anti-regenerative and pro-inflammatory proprieties to PRP; and (3) half concentration of SC improves the angiogenesis and regeneration mediated by PRP.

Introduction and Aim: Haemarthroses cause major morbidity in haemophilia resulting in chronic haemophilic synovitis (CHS) and arthropathy. Oxidation of haemoglobin-coupled iron released in synovium after haemolysis induces chondrocytes death and cartilage damage, allowing postulate using iron-chelating drugs as potential therapeutic tool for haemophilic joint damage. Considering that albumin, the most abundant plasma protein, is a physiologic iron chelator, we aim to demonstrate that impediment of haemoglobin oxidation is exerted by plasma as a mechanism involved in the therapeutic effect of intra-articular injection of platelet-rich plasma in CHS. Methods: Oxidation of haemoglobin (Hb) to methaemoglobin (MeHb) through Fenton reaction was induced in vitro by addition of potassium ferricyanide in the presence or absence of peripheral blood-derived platelets-rich or platelets-poor plasma (PRP/ PPP) or albumin. The relevance of in vitro findings was analysed in synovial fluid (SF) samples from one patient with CHS obtained before and after 6 months of PRP intraarticular injection. Results: MeHb formation was completely impaired either by of PPP, PRP or albumin indicating that PRP exerts an anti-oxidative effect, probably due by plasma albumin. Analysis of SF samples revealed the presence of MeHb levels and haemosiderinladen macrophages in SF obtained before PRP treatment. Reduction of synovial MeHb, normalization of cellular composition and improvement of health joint haemophilic score, pain and bleeding episodes were registered after 6 months of PRP intra-articular injection. Conclusion: Inhibition of Fenton reaction and the consequent normalization of joint cellular composition is a noncanonical mechanism underlying the therapeutic effect of PRP intra-articular injection in CHS. K E Y W O R D S haemophilia, methaemoglobin, platelets-rich plasma, PRP intra-articular injection, synovitis e188 | CAVIGLIA et AL.

Introduction Hemarthrosis causes chronic haemophilic synovitis (CHS). Although neutrophils are major immune cells infiltrating joints after bleeding, their role on the pathogenesis of CHS is unknown. Neutrophils release extracellular DNA traps (ETs), structures of DNA with bound granular enzymes that were associated with tissue damage. Aims To evaluate the presence of ETs as pathogenic biomarker and the protective effect of intraarticular injection of platelet‐rich plasma (PRP) in patients with CHS. Methods Haemophilia Joint Health Score (HJHS) and bleeding episodes (BE) were measured and correlated with ETs indicators (DNA/DNA‐Elastase) in synovial fluids (SF), PRP and plasma of 21 patients. Results Soluble DNA and DNA‐Elastase were detected in SF and plasma of patients. The synovial and plasma levels of DNA‐Elastase positively correlated with worse HJHS/BE. Interestingly, remaining ETs‐inducer factors were present in SF that induced the in vitro release of ETs from blood‐isolated neutrophils. This phenomenon was impaired by adding plasma or PRP. Finally, preliminary data obtained from five patients indicate that levels of DNA‐Elastase and HJHS/BE decreased after receiving intraarticular injection of PRP. Conclusions The synovial and plasma levels of DNA‐Elastase correlated with worse HJHS/BE suggesting that ETs formation could be a biomarker and potential therapeutic target for CHS. The intraarticular injection of PRP underlined a new potential alternative therapy, decreasing ETs formation in synovia of patients with CHS. However, our hypotheses must be confirmed in the future with better designed and more statistical power studies. Meanwhile, the use of intraarticular injections of PRP for the treatment of CHS remains controversial.