title: Platelet-rich plasma preparation for regenerative medicine: optimization and quantification of cytokines and growth factors.
abstract: BACKGROUND
  Platelet-rich plasma (PRP) is nowadays widely applied in different clinical scenarios, such as orthopedics, ophthalmology and healing therapies, as a growth factor pool for improving tissue regeneration. Studies into its clinical efficiency are not conclusive and one of the main reasons for this is that different PRP preparations are used, eliciting different responses that cannot be compared. Platelet quantification and the growth factor content definition must be defined in order to understand molecular mechanisms behind PRP regenerative strength. Standardization of PRP preparations is thus urgently needed.
  
  
  METHODS
  PRP was prepared by centrifugation varying the relative centrifugal force, temperature, and time. Having quantified platelet recovery and yield, the two-step procedure that rendered the highest output was chosen and further analyzed. Cytokine content was determined in different fractions obtained throughout the whole centrifugation procedure.
  
  
  RESULTS
  Our method showed reproducibility when applied to different blood donors. We recovered 46.9 to 69.5% of total initial platelets and the procedure resulted in a 5.4-fold to 7.3-fold increase in platelet concentration (1.4 × 10(6) to 1.9 × 10(6) platelets/μl). Platelets were highly purified, because only <0.3% from the initial red blood cells and leukocytes was present in the final PRP preparation. We also quantified growth factors, cytokines and chemokines secreted by the concentrated platelets after activation with calcium and calcium/thrombin. High concentrations of platelet-derived growth factor, endothelial growth factor and transforming growth factor (TGF) were secreted, together with the anti-inflammatory and proinflammatory cytokines interleukin (IL)-4, IL-8, IL-13, IL-17, tumor necrosis factor (TNF)-α and interferon (IFN)-α. No cytokines were secreted before platelet activation. TGF-β3 and IFNγ were not detected in any studied fraction. Clots obtained after platelet coagulation retained a high concentration of several growth factors, including platelet-derived growth factor and TGF.
  
  
  CONCLUSIONS
  Our study resulted in a consistent PRP preparation method that yielded a cytokine and growth factor pool from different donors with high reproducibility. These findings support the use of PRP in therapies aiming for tissue regeneration, and its content characterization will allow us to understand and improve the clinical outcomes.
authors.forename: Paola Romina
authors.initials: PR
authors.lastname: Amable
authors.forename: Rosana Bizon Vieira
authors.initials: RB
authors.lastname: Carias
authors.forename: Marcus Vinicius Telles
authors.initials: MV
authors.lastname: Teixeira
authors.forename: Italo
authors.initials: I
authors.lastname: da Cruz Pacheco
authors.forename: Ronaldo José Farias
authors.initials: RJ
authors.lastname: Corrêa do Amaral
authors.forename: José Mauro
authors.initials: JM
authors.lastname: Granjeiro
authors.forename: Radovan
authors.initials: R
authors.lastname: Borojevic
mesh_terms: D000328:Adult; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism; D002498:Centrifugation; D018925:Chemokines / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D005260:Female; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D053657:Platelet-Rich Plasma; D044968:Regenerative Medicine; D013696:Temperature; D013997:Time Factors
chemical_list: D018925:Chemokines; D016207:Cytokines; D036341:Intercellular Signaling Peptides and Proteins