[Metalloproteinases in vascular wall remodelling]

Metalloproteinases (MTP) are enzymes that degrade the extracellular matrix, mainly collagen tissue. Normally these enzymes are expressed in vascular walls as proenzyme together with inhibitors of the active enzymes. By effect of different cytokines, produced by an inflammatory process in the vascular wall, these proenzymes are activated to an extent that surpasses the action of the inhibitors and degrade collagen. This action may partly explain the rupture of atherosclerotic plaques ("vulnerability") and also the remodelling of the vessel wall with "compensatory enlargement" of the vessel (increase in the outer size of the vessel) that allows the plaques to develop inside the arterial wall without protruding into the vessel lumen for many years. The occlusion of saphenous vein in aortocoronary bypass grafts is due to fibromuscular proliferation and atheroma development and therefore the participation of MTP in the occlusion of these vessels is a reasonable hypothesis. However, the structural features of saphenous vein bypass grafts are different from those of atheroma in native coronary arteries. Mainly the compensatory enlargement of the vessels does not occur because of intense fibrous tissue development including the adventitia and therefore the new tissue in the wall is forced to protrude into the vessel lumen. The reason for this difference in the vessel wall remodeling is not clear and the article by Grez et al in this issue of this Journal is an starting and promising study in this regard.