Abstract

Introduction Fibrous plaques are less prone to rupture than lipid laden ones, but the reasons for this are not clear. Methodology Ultrasound imaging of 15 carotid plaques revealed 9 echolucent (lipid-laden) and 6 echogenic (fibrous) plaques. Levels of matrix metalloproteinase-3 (MMP- 3), nitric oxide synthases (NOS) enzymes and Chlamydia pneumoniae (CP) were determined using immunohistochemical and Western blotting techniques. Results MMP-3 levels were higher in echolucent than in echogenic plaques. High levels of MMP-3 and of its precursor (pro-MMP3) were observed near regions of ulceration, necrosis and where fibrous cap was thin or torn. NOS enzymes were present in all plaques irrespective of intraplaque features. However, levels of inducible NOS (NOS-II) were higher in echolucent than in echogenic plaques. Intense immunoreactivity for C pneumoniae was observed in two thirds of echolucent plaques, clustering near endothelial cells of intimal and neo-endothelial regions. No CP immunoreactivity was observed in echogenic plaques. Conclusion MMP3 or its pro-enzyme may play important role in digesting fibrous tissue of carotid plaques, leading to thinning/tearing of their fibrous cap.This might result in subsequent destabilisation of plaques, leading to embolisation and cerebrovascular events. MMP-3 and NOS identified in this study may have been influenced by CP which might be responsible for triggering cascades of inflammatory events leading to activation of these enzymes.