title: Increasing platelet concentrations in leukocyte-reduced platelet-rich plasma decrease collagen gene synthesis in tendons.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  Within leukocyte-reduced PRP (lrPRP), there is a plateau effect of platelet concentration, with increasing platelet concentrations being detrimental to extracellular matrix synthesis.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  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-β1), and interleukin-1β (IL-1β) concentrations were determined in the media by enzyme-linked immunosorbent assay. Gene expression in tendon tissue for collagen type I and III (COL1A1 and COL3A1, respectively), matrix metalloproteinase-3 and -13 (MMP-3 and MMP-13, respectively), cartilage oligomeric matrix protein (COMP), and IL-1β was determined. Data were divided into 3 groups of lrPRP based on the ratio of platelets:leukocytes and evaluated to determine the effect of platelet concentration.
  
  
  RESULTS
  Complete blood counts verified leukocyte reduction and platelet enrichment in all PRP preparations. In the lrPRP preparation, the anabolic growth factors PDGF-BB and TGF-β1 were increased with increasing platelet concentrations, and the catabolic cytokine IL-1β was decreased with increasing platelet concentrations. Increasing the platelet concentration resulted in a significant reduction in COL1A1 and COL3A1 synthesis in tendons.
  
  
  CONCLUSIONS
  Increasing the platelet concentration within lrPRP preparations results in the delivery of more anabolic growth factors and less proinflammatory cytokines, but the biological effect on tendons is diminished metabolism as indicated by a decrease in the synthesis of both COL1A1 and COL3A1. Together, this information suggests that minimizing leukocytes in PRP is more important than maximizing platelet numbers with respect to decreasing inflammation and enhancing matrix gene synthesis.
  
  
  CONCLUSIONS
  This study suggests that reducing leukocytes to minimize catabolic signaling appears to be more important than increasing platelets in an effort to maximize anabolic signaling. Further, a maximum biological threshold of benefit was demonstrated with regard to the number of platelets beyond which further increases in platelet concentration did not result in further anabolic upregulation. In vivo investigations documenting the use of platelets for the treatment of tendinopathy are justified as well as further in vitro characterization of the ideal PRP product for the treatment of tendinopathy and other musculoskeletal applications.
authors.affiliation: Lisa A. Fortier, Cornell University, VMC C3-181, Ithaca, NY 14853. laf4@cornell.edu.
authors.forename: Stacie G
authors.initials: SG
authors.lastname: Boswell
authors.forename: Lauren V
authors.initials: LV
authors.lastname: Schnabel
authors.forename: Hussni O
authors.initials: HO
authors.lastname: Mohammed
authors.forename: Emily A
authors.initials: EA
authors.lastname: Sundman
authors.forename: Tom
authors.initials: T
authors.lastname: Minas
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Fortier
mesh_terms: D000818:Animals; D000077214:Becaplermin; D001792:Blood Platelets / Q000502:physiology*; D003094:Collagen / Q000096:biosynthesis* / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression; D006736:Horses; D053583:Interleukin-1beta / Q000378:metabolism; D007962:Leukocytes / Q000502:physiology; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D019278:Matrix Metalloproteinase 3 / Q000378:metabolism; D053657:Platelet-Rich Plasma / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D052256:Tendinopathy / Q000378:metabolism; D013710:Tendons / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D053583:Interleukin-1beta; D020574:Proto-Oncogene Proteins c-sis; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha; D000077214:Becaplermin; D003094:Collagen; D053509:Matrix Metalloproteinase 13; D019278:Matrix Metalloproteinase 3
keywords: growth factor; platelet; platelet-rich plasma; tendon