Inhibition of Fenton reaction is a novel mechanism to explain the therapeutic effect of intra-articular injection of PRP in patients with chronic haemophilic synovitis.

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 intra-articular 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 haemosiderin-laden 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.