METALLOPROTEINASES IN VASCULAR WALL REMOD ELING

Metalloproteinases (MTP) are enzymes that degrade the extracellular ma trix, mainly collagen tissue. Normally these enzymes are expressed in vascular walls as proenzyme together with inhibitors of the active enz ymes. By effect of different citokines, produced by an inflammatory pr ocess in the vascular wall, these proenzymes are activated to an exten t that surpasses the action of the inhibitors and degrade collagen. Th is action may partly explain the rupture of atherosclerotic plaques (' 'vulnerability'') and also the remodelling of the vessel wall with ''c ompensatory enlargement'' of the vessel (increase in the outer size of the vessel) that allows the plaques to develop inside the arterial wa ll without protruding into the vessel lumen for many years. The occlus ion of safenous vein in aortocoronary bypass grafts is due to fibromus cular proliferation and atheroma development and therefore the partici pation of MTP in the occlusion of these vessels is a reasonable hypoth esis. However, the structural features of safenous vein bypass grafts are different from those of atheroma in native coronary arteries. Main ly the compensatory enlargement of the vessels does not occur because of intense fibrous tissue development including the adventitia and the refore the new tissue in the wall is forced to protrude into the vesse l lumen. The reason for this difference in the vessel wall remodeling is not clear and the article by Grez et al in this tissue of this Jour nal is an starting and promising study in this regard.