title: The phospholipid composition and cholesterol content of platelet-derived microparticles: a comparison with platelet membrane fractions.
abstract: BACKGROUND
  The processes that govern the distribution of molecules between platelets and the microparticles (MP) they release are unknown. Certain proteins are sorted selectively into MP, but lipid sorting has not been studied.
  
  
  OBJECTIVE
  To compare the phospholipid composition and cholesterol content of platelet-derived MP obtained with various stimuli with that of isolated platelet membrane fractions.
  
  
  METHODS
  Washed platelets from venous blood of healthy individuals (n = 6) were stimulated with collagen, thrombin, collagen plus thrombin, or A23187. Platelet activation, MP release and antigen exposure were assessed by flow cytometry. MPs were isolated by differential centrifugation. Platelet plasma-, granule- and intracellular membranes were isolated from platelet concentrates (n = 3; 10 donors each) by pressure homogenization and Percoll density gradient fractionation. The phospholipid composition and cholesterol content of MPs and membrane fractions were analyzed by high performance thin layer chromatography.
  
  
  RESULTS
  The phospholipid composition of MPs was intermediate compared with that of platelet plasma- and granule membranes, and differed significantly from that of intracellular membranes. There were small but significant differences in phospholipid composition between the MPs produced by the various agonists, which paralleled differences in P-selectin exposure in case of the physiological agonists collagen, thrombin, or collagen plus thrombin. The cholesterol content of MPs tended to be higher than that of the three-platelet membrane fractions.
  
  
  CONCLUSIONS
  Regarding its phospholipid content, the MP membrane is a composite of the platelet plasma- and granule membranes, showing subtle differences depending on the platelet agonist. The higher cholesterol content of MPs suggests their enrichment in lipid rafts.
authors.affiliation: Department of Clinical Chemistry, Academic Medical Center, University of Amsterdam, The Netherlands. e.biro@amc.nl
authors.forename: E
authors.initials: E
authors.lastname: Biró
authors.forename: J W N
authors.initials: JW
authors.lastname: Akkerman
authors.forename: F J
authors.initials: FJ
authors.lastname: Hoek
authors.forename: G
authors.initials: G
authors.lastname: Gorter
authors.forename: L M
authors.initials: LM
authors.lastname: Pronk
authors.forename: A
authors.initials: A
authors.lastname: Sturk
authors.forename: R
authors.initials: R
authors.lastname: Nieuwland
mesh_terms: D001792:Blood Platelets / Q000737:chemistry* / Q000648:ultrastructure; D000001:Calcimycin / Q000494:pharmacology; D002458:Cell Fractionation; D002784:Cholesterol / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D003094:Collagen / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry; D021962:Membrane Microdomains / Q000737:chemistry; D008566:Membranes / Q000737:chemistry*; D010316:Particle Size; D010743:Phospholipids / Q000032:analysis*; D015539:Platelet Activation; D013917:Thrombin / Q000494:pharmacology
chemical_list: D010743:Phospholipids; D000001:Calcimycin; D003094:Collagen; D002784:Cholesterol; D013917:Thrombin