The direct thrombin inhibitor melagatran counteracts endotoxin-induced endothelial leukocyte adherence and microvascular leakage in the rat mesentery. Rationale for the treatment of inflammatory disorders beyond sepsis?

The activation of the coagulation system in the course of an inflammatory reaction impairs the function of the microcirculation. By means of intravital videomicroscopy the effect of the direct thrombin inhibitor melagatran on endotoxin-induced microvascular permeability and leukocyte adhesion to microvascular endothelium of rat mesentery was evaluated. Secondly, plasma concentrations of melagatran or interleukin-6 in response to endotoxin or after treatment with melagatran respectively, were determined. Male Sprague-Dawley rats (300-400 g bw) were infused with 0.5 mg/kg lipopolysaccharide (LPS) (E. coli O55:B5) over 80 minutes. Vascular leakage was detected with FITC-marked rat serum albumin by fluorescence microscopy and evaluated by grey value analysis with a computer assisted image processing system. Light microscopy was used to evaluate the adherence of leukocytes to the vessel wall. Two treated groups received either 0.3 or 0.6 mg/kg bw melagatran iv in addition to LPS-infusion. The observation period was 3 hours after the beginning of LPS infusion. Groups of animals not infused with LPS or solely treated with melagatran (0.3 or 0.6 mg/kg) served as controls. Infusion of LPS led to a significant increase of microvascular permeability, leukocyte adherence and thrombin-antithrombin complex plasma concentration compared to unstimulated controls. These effects were significantly reduced by melagatran at both dosage levels. Elevated plasma concentrations of melagatran were observed in animals infused with endotoxin and higher plasma levels of interleukin-6 were found in endotoxemic animals treated with melagatran. The results indicate that thrombin is one of the most important clotting enzymes involved in inflammatory microvascular disturbance. Moreover, it should be clarified whether direct thrombin inhibitors themselves play a role within the immune response to endotoxin.