NEUTROPHIL-DERIVED CATHEPSIN-G INDUCES POTENTIALLY THROMBOGENIC CHANGES IN HUMAN ENDOTHELIAL-CELLS - A SCANNING ELECTRON-MICROSCOPY STUDY IN STATIC AND DYNAMIC CONDITIONS

Activated neutrophils may promote thrombus formation by releasing prot eases which may activate platelets, impair the fibrinolytic balance an d injure the endothelial monolayer. We have investigated the morpholog ical correlates of damage induced by activated neutrophils on the vasc ular wall, in particular the vascular injury induced by released cathe psin G in both static and dynamic conditions. Human umbilical vein end othelial cells were studied both in a cell culture system and in a mod el of perfused umbilical veins. At scanning electron microscopy, progr essive alterations of the cell monolayer resulted in cell contraction, disruption of the intercellular contacts, formation of gaps and cell detachment. Contraction was associated with shape change of the endoth elial cells, that appeared star-like, while the underlying extracellul ar matrix, a potentially thrombogenic surface, was exposed. Comparable cellular response was observed in an ''in vivo'' model of perfused ra t arterial segment. Interestingly, cathepsin G was active at lower con centrations in perfused vessels than in culture systems. Restoration o f blood flow in the arterial segment previously damaged by cathepsin G caused adhesion and spreading of platelets on the surface of the expo sed extracellular matrix. The subsequent deposition of a fibrin networ k among adherent platelets, could be at least partially ascribed to th e inhibition by cathepsin G of the vascular fibrinolytic potential. Th is study supports the suggestion that the release of cathepsin G by ac tivated neutrophils, f.i. during inflammation, may contribute to throm bus formation by inducing extensive vascular damage.