To activate perivascular mast cells in vivo extending previo

To activate GSK256066 perivascular mast cells in vivo extending previous observations as plasmin has been reported to directly activate cultured mast cells. In line with these results, we also show that blockade of mast cell activation almost completely abolished plasmin-dependent intravascular firm adherence and transmigration of neutrophils. Moreover, it is interesting that treatment with aprotinin or with the plasmin inhibitors as well as blockade of mast cell activation did not affect microvascular leakage in the early reperfusion phase. Accordingly, interaction of extravasated plasminogen with plasminogen receptors on perivascular mast cells is suggested to Olaparib accelerate the conversion of plasminogen to plasmin, to protect plasmin from inactivation by endogenous inhibitors, and to enhance the biological activity of this protease. Collectively, these data indicate a divergent role of plasmin in the regulation of postischemic leukocyte recruitment and microvascular permeability and, moreover, strongly suggest that extravasated plasmin mediates neutrophil recruitment in vivo indirectly via activation of perivascular mast cells. Following recent in vitro studies, surface-bound plasmin is supposed to specifically interact with different cell-surface receptors, to activate intracellular signaling pathways, and to induce the generation of inflammatory mediators. Here, we demonstrate that plasmin is able to induce the expression of 5- lipoxygenase and lyso-PAF-acetyltransferase, key enzymes controlling the synthesis of leukotrienes and PAF, respectively. Moreover, inhibition of leukotriene synthesis or blockade of the PAF receptor significantly diminished plasmin-dependent firm adherence and transmigration of neutrophils. Thus, our results indicate that plasmin facilitates neutrophil extravasation in vivo via endogenous generation of lipid mediators. Consequently, in the early reperfusion phase, extravasated plasmin is suggested to induce the generation of leukotrienes and PAF which, in turn, directly activate neutrophils and promote intravascular adherence as well as transmigration of these inflammatory cells in postischemic tissue. Since inhibition of leukotriene synthesis or blockade of the PAF receptor only partially reduced plasmin- as well as I/R-elicited activation of mast cells, the postischemic generation of lipid mediators is, at least in part, suggested to occur downstream of mast cell activation. In conclusion, our experimental data suggest that extravasated plasmin mediates firm adherence and transmigration of neutrophils to the reperfused tissue indirectly through activation of perivascular mast cells and a sequential generation of leukotrienes and PAF. The plasmin inhibitors tranexamic acid and e-aminocaproic acid as well as the broad-spectrum ser