Stimulus-dependent release of tissue-regenerating factors by equine platelets

Reasons for performing the study: Platelet‐rich plasma (PRP) is increasingly used for treatment of orthopaedic injuries. However, the effects of different stimuli on the release pattern of regenerative and proinflammatory factors from equine platelets are largely unknown and an optimal treatment protocol remains to be established. Objectives: The aim of this study was to identify a stimulus that enhanced release of histopromotive factors (platelet‐derived growth factor BB [PDGF] and transforming growth factor 1β[TGF]) without causing concurrent release of a proinflammatory mediator (CCL5). Methods: Washed platelets were prepared from 6 healthy ponies and release of growth factors and CCL5 measured using commercially available ELISAs for human proteins following incubation with or without thrombin, chitosan or equine recombinant tumour necrosis factor (erTNF) over 24 h and subsequently over 96 h. Additionally, noncoagulated samples were analysed. Results: Regardless of whether a stimulus was present or what stimulus was used, PDGF and TGF release was maximal by 0.5–1 h when clot formation took place and very little release was observed after 24 h. Growth factor release was minimal in noncoagulated samples. In contrast, CCL5 release was not associated with coagulation and appeared to persist for much longer. High concentrations of erTNF caused significantly greater release of CCL5 at 6 h than any other stimulus tested. Conclusions: Growth factor release from equine platelets is dependent on coagulation but independent of the initiating stimulus, and is accompanied by more sustained release of proinflammatory mediators. Potential relevance: Supernatants collected from coagulated platelets could be an alternative treatment to PRP.