title: Platelet alpha- and beta-secretase activities: A preliminary study in normal human subjects.
abstract: beta-amyloid (Abeta) arises from an amyloid precursor protein (APP) via beta- and gamma-secretase proteolysis. Platelets are the primary depot of APP in the circulation and may be a source of cerebral Abeta. We measured the platelet activities of alpha- and beta-secretases in normal individuals. Platelet alpha- and beta-secretase activities were linear with respect to incubation time and quantity of platelet extract included in the assays. beta-secretase activity, calculated relative to platelet count (PC) and platelet protein (PP), varied between individuals 3.5-fold and 4.6-fold, respectively. Meanwhile, alpha-secretase varied 3.75-fold and 5.8-fold. beta-secretase/alpha-secretase ratios varied 4.1-fold (PC) or 10.5-fold (PP). beta-secretase correlated with age (r = 0.779, p < 0.02, PP) and mean platelet volume (MPV) (r = 0.702, p < 0.05, PC). alpha-secretase correlated negatively with high-density lipoprotein (HDL) (-0.76, p < 0.01, PP). beta-secretase/alpha-secretase ratios correlated with MPV (r = 0.67, p < 0.05, PC) and HDL (r = 0.77, p < 0.02, PP). These data could indicate that platelet secretase activity is related to aging, platelet size and plasma lipoprotein levels. Clearly, however, this is a preliminary study involving a limited number of individuals and further, more detailed, investigations are required to establish that such relationships are valid.
authors.affiliation: The Hatter Cardiovascular Institute, University College London Hospital and Medical School, London WC1E 6HX, UK. christopher.smith@ucl.ac.uk
authors.forename: Christopher C T
authors.initials: CC
authors.lastname: Smith
authors.forename: Brian N C
authors.initials: BN
authors.lastname: Prichard
authors.forename: Michael B
authors.initials: MB
authors.lastname: Cooper
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D053829:Amyloid Precursor Protein Secretases / Q000097:blood / Q000378:metabolism*; D001792:Blood Platelets / Q000737:chemistry / Q000166:cytology / Q000201:enzymology*; D002384:Catalysis; D048429:Cell Size; D002784:Cholesterol / Q000097:blood; D005260:Female; D006801:Humans; D007700:Kinetics; D008074:Lipoproteins / Q000097:blood; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D008074:Lipoproteins; D002784:Cholesterol; D053829:Amyloid Precursor Protein Secretases