MMP9 and atherosclerosis: Interestingly, the activity of the blood phagocytic NADPH oxidase correlates positively with carotid intima-media thickness (IMT) [14] (a surrogate marker of atherosclerosis), and with matrix metalloproteinase-9 plasma levels [15] (a marker of vascular remodelling and an independent risk factor for atherothrombotic events), in healthy subjects without clinical atherosclerosis.