title: Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation.
abstract: Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Santa Cruz, Santa Cruz, CA, USA.
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Ikei
authors.forename: Jennifer
authors.initials: J
authors.lastname: Yeung
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Apopa
authors.forename: Jesús
authors.initials: J
authors.lastname: Ceja
authors.forename: Joanne
authors.initials: J
authors.lastname: Vesci
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Holman
authors.forename: Michael
authors.initials: M
authors.lastname: Holinstat
mesh_terms: D001092:Arachidonate 12-Lipoxygenase / Q000097:blood / Q000737:chemistry / Q000378:metabolism*; D005228:Fatty Acids, Essential / Q000096:biosynthesis / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D010084:Oxidation-Reduction; D015539:Platelet Activation / Q000187:drug effects*; D013379:Substrate Specificity
chemical_list: D005228:Fatty Acids, Essential; D001092:Arachidonate 12-Lipoxygenase