ELN and aneurysm: Loss of elastin and collagen is caused by an increase in the activity of matrix proteinases (elastase and collagenase) or a decrease in the activity of anti-proteases [mellaproteinase tissue inhibitor (TIMP)] and alpha-1-antitrypsin.2 Increase in the levels of intercellular adhesion molecules induces migration of macrophages to this region, with the resultant increase in the production of MMP2 and MMP9, fragmentation of elastin and triggering of aneurysm formation.