Fig. 2
Plaque composition affects systemic elevation of MMP9 after its disruption, which is independent of the myocardial injury and systemic inflammatory response. Coronary artery plaques were imaged using optical coherence tomography (OCT) prior to plaque disruption, in 36 patients undergoing percutaneous coronary intervention (PCI), comparing with subjects who underwent diagnostic coronary angiography without PCI (Dx). These plaques were classified as either lipid-rich (yellow, n = 23) or non-lipid-rich plaques (green, n = 13) based on OCT characteristics. Lipid-rich and non-lipid rich plaques were observed in patients with either acute coronary syndrome (ACS-red, n = 21) or stable angina (SA-blue, n = 37) (a). More prompt elevation in plasma MMP9 was observed in patients who presented with ACS (b, red bars) at 1 h after plaque disruption (compared to those who presented to SA, blue bars), but there was no difference in the peak MMP9 levels observed after 6 h. In contrast, disruption of lipid-rich plaques (b, yellow bars) led to more prompt elevations of MMP9 and higher peak level after 6 h. To test for possible confounding effects of myocardial injury and systemic inflammatory response after plaque disruption, we measured circulating troponin I (TnI) and c-reactive protein (CRP) in all participants (PCI n = 58; Dx n = 23). Myocardial injury was only observed in the group with plaque disruption. Modest elevation in CRP was observed in both groups, with or without plaque disruption (c). Calculation of area under curve (AUC) revealed no correlation between MMP9 and either TnI or CRP (d) during this time course. These observations indicate that MMP9 release is specific to the upstream event of plaque disruption, and independent of the downstream myocardial injury and systemic inflammation as a result of the procedure. “*” denotes significant statistical comparison against the baseline measurement (paired comparison); “#” denotes significant statistical comparison between the two groups (lipid-rich vs. non-lipid-rich)