title: Inhibition of Glycoprotein VI Clustering by Collagen as a Mechanism of Inhibiting Collagen-Induced Platelet Responses: The Example of Losartan.
abstract: Exposure of platelets to collagen triggers the formation of a platelet clot. Pharmacological agents capable of inhibiting platelet activation by collagen are thus of potential therapeutic interest. Thrombus formation is initiated by the interaction of the GPIb-V-IX complex with collagen-bound vWF, while GPVI interaction with collagen triggers platelet activation that is reinforced by ADP and thromboxane A2. Losartan is an angiotensin II (Ang II) type I receptor (AT1R) antagonist proposed to have an antiplatelet activity via the inhibition of both the thromboxane A2 (TXA2) receptor (TP) and the glycoprotein VI (GPVI). Here, we characterized in vitro the effects of losartan at different doses on platelet responses: losartan inhibited platelet aggregation and secretion induced by 1 μg . mL(-1) and 10 μg . mL(-1) of collagen with an IC50 of ~ 6 μM. Losartan inhibited platelet responses induced by the GPVI specific collagen related peptide but not by the α2β1 specific peptide. However, losartan did not inhibit the binding of recombinant GPVI to collagen, which is not in favor of a simple competition. Indeed, the clustering of GPVI observed in flow cytometry and using the Duolink methodology, was inhibited by losartan. The impact of a therapeutic dose of losartan (100 mg/day) on platelet responses was analyzed ex vivo in a double blind study. No statistically significant differences were observed between losartan-treated (n=25) and non-treated (n=30) patients in terms of collagen and U46619-induced platelet activation. These data indicate that in treated patients, losartan does not achieve a measurable antiplatelet effect but provide the proof of concept that inhibiting collagen-induced GPVI clustering is of pharmacological interest to obtain an antithrombotic efficacy.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00763893.
authors.affiliation: Inserm, UMR_S1148, Paris, France; Univ Paris Diderot, Sorbonne Paris Cité, UMR_S1148, Paris, France.
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.affiliation: Inserm, UMR_S1148, Paris, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Loyau
authors.affiliation: APHP- CNMR Syndrome de Marfan et apparentés, Service de Cardiologie, Hôpital Bichat, Paris, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Tchitchinadze
authors.affiliation: Unité de Recherche Clinique, Hôpital Ambroise Paré-UFR Médecine Paris-Ile-de-France-Ouest, Université Versailles St-Quentin, Boulogne, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Ropers
authors.affiliation: Inserm, UMR_S1148, Paris, France; Univ Paris Diderot, Sorbonne Paris Cité, UMR_S1148, Paris, France; APHP- CNMR Syndrome de Marfan et apparentés, Service de Cardiologie, Hôpital Bichat, Paris, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Jondeau
authors.affiliation: Inserm, UMR_S1148, Paris, France; Univ Paris Diderot, Sorbonne Paris Cité, UMR_S1148, Paris, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Jandrot-Perrus
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism*; D003094:Collagen / Q000494:pharmacology*; D006736:Horses; D006801:Humans; D055767:Immobilized Proteins / Q000494:pharmacology; D038982:Integrin alpha2beta1 / Q000378:metabolism; D019808:Losartan / Q000008:administration & dosage / Q000494:pharmacology*; D008382:Marfan Syndrome / Q000188:drug therapy; D010455:Peptides / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D018179:Receptors, Thrombin / Q000378:metabolism; D012212:Rheology / Q000187:drug effects; D013927:Thrombosis / Q000473:pathology
chemical_list: D055767:Immobilized Proteins; D038982:Integrin alpha2beta1; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; D018179:Receptors, Thrombin; C098341:platelet membrane glycoprotein VI; D000244:Adenosine Diphosphate; D003094:Collagen; D019808:Losartan