Efficacy of antithrombin in the prevention of microvascular thrombosis during endotoxemia: An intravital microscopic study

Introduction: The KyberSept trial in septic patients showed that antithrombin (AT) reduced 90-day mortality significantly in a subgroup of patients not receiving concomitant heparin for thrombosis prophylaxis. Microvascular thrombosis is a key pathophysiologic mechanism during sepsis, ischemia/reperfusion and disseminated intravascular coagulation (DIC). Therefore, this study investigated the antithrombotic property of AT as potential monotherapy in an experimental endotoxemia model in order to omit concomitant heparin. Materials and methods: Using a light/dye injury model in the ear and the cremaster muscle preparation of mice, we quantitatively assessed microvascular thrombus formation in a total of 30 endotoxemic mice by means of intravital fluorescence microscopy. Before thrombus induction animals received a single i.v. bolus of AT (100 or 250 IU/kg), heparin (100 IU/kg) or saline (NaCl). Results: In NaCl-treated endotoxemic animals, light/dye exposure led to complete thrombotic occlusion in arterioles and venules within < 450 s in the ear model. Heparin delayed thrombotic vessel occlusion by more than 50%. AT significantly prolonged times until thrombotic vessel occlusion in a dose-dependent manner and more effectively than heparin (p < 0.05 vs. NaCl and heparin). This anti-coagulative effect of AT was especially pronounced in arterioles. Upon light/dye exposure to cremaster muscle preparations in endotoxemic mice AT also caused a 4-fold delay in microvascular thrombus growth with 827 +/- 77 s until complete thrombotic occlusion. Conclusions: We could characterize for the first time AT-mediated antithrombotic activity during endotoxemia in two models of phototoxicity-induced microvascular thrombosis. Our results clearly demonstrate an additional AT mechanism of action that may be responsible for beneficial effects observed during endotoxemia and DIC. This AT profile may allow future high-dose AT application without giving heparin for thrombosis prophylaxis, an intriguing strategy that is to be tested under clinical conditions. (c) 2007 Elsevier Ltd. All rights reserved.