Increasing Platelet Concentration in Leukocyte-reduced Platelet Rich Plasma Decreases Collagen Gene Synthesis in Tendons

<b>Background: </b> Platelet-rich plasma (PRP) is used for the treatment of tendinopathy. There are numerous PRP preparations, and the optimal combination of platelets and leukocytes is not known. <br><b>Hypothesis: </b> Within leukocyte-reduced PRP (lrPRP), there is a plateau effect of platelet concentration, with increasing platelet concentrations being detrimental to extracellular matrix synthesis. <br> <b>Study design: </b> Controlled laboratory study. <br> <b>Methods: </b> Different formulations of lrPRP with respect to the platelet:leukocyte ratio were generated from venous blood of 8 horses. Explants of the superficial digital flexor tendon were cultured in lrPRP products for 96 hours. Platelet-derived growth factor-BB (PDGF-BB), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β