P149	The Losartan metabolite EXP 3179 inhibits collagen-induced platelet activation via blockade of the GPVI receptor.
1Chr.Grothusen, 2S.Kerstan, 2I.Konrad, 2Chr.Schulz, 3S.Umbreen, 3B.Schmidt, 2S.Massberg, 1B.Schieffer, 4M.Gawaz
1Abteilung Kardiologie und Angiologie, Medizinische Hochschule Hannover, Hannover, DE; 2Deutsches Herzzentrum und 1. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, DE; 3Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Darmstadt, DE; 4Medizinische Klinik III, Universität Tübingen, Tübingen, DE.

Background: Collagen-induced platelet activation via the glycoprotein (GP) VI receptor is critically involved in thrombus formation following vessel injury, including atherosclerotic plaque rupture. EXP 3179, an active metabolite of the angiotensin II type 1 receptor (AT1)-antagonist Losartan (LOS) mediates anti-aggregatory effects, but the underlying mechanisms as well as a possible individual therapeutical potential of EXP 3179 remain unknown. We investigated the influence of EXP 3179 on collagen-dependent platelet activation,GPVI receptor activation and thrombus formation in vivo after acute vessel injury. Methods and Results: EXP 3179 (5x10-4mol/ 285µg) enhanced in-vitro-bleeding time (n=3; p<0.05) using the Platelet Function Analyser (PFA)-100. Human platelet activation was analyzed by optical aggregometry using adenosine diphosphate (ADP, 5μM), thrombin-receptor activating protein (TRAP, 25μM), collagen I (2μg/ml) or HGP-4C9-1 (0.1μg/ml), a GPVI receptor stimulating antibody. EXP 3179 inhibited collagen I and HGP-4C9-1 induced platelet activation (n=7; p<0.001). EXP 3179 also diminished general human platelet activation (n=7; p<0.001; p<0.01) determined as PAC-1 und LIBS-1 expression by FACS after collagen I or HGP-4C9-1 stimulation. EXP 3179 also inhibited human platelet adhesion on collagen I (n=5; p<0.001) under high shear conditions (1000sec-1) analyzed by flow chamber. EXP 3179 reduced collagen I stimulated murine platelet activation in vitro (n=8; p<0.01) measured by optical aggregometry. In-vivo effects of EXP 3179 were investigated using intravital fluorescence microscopy (IVM) in a murine model of endothelial denudation. Here, EXP 3179 inhibited murine platelet adhesion following vessel injury (p<0.05). Conclusion: EXP 3179 diminished collagen-induced platelet activation via GPVI receptor blockade in vitro and reduced murine platelet adhesion after vessel injury in vivo. These findings suggest a novel anti-thrombotic potential of EXP 3179 and may indicate a new therapeutic approach to prevent occlusive thrombosis following atherosclerotic plaque rupture by non-peptide antagonists such as EXP 3179.

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