Metalloproteinase levels are decreased in symptomatic carotid plaques

Matrix metalloproteinase enzymes (MMP) have been identified in carotid atherosclerotic plaques, but their role in the development of clinical symptoms remains ill defined. We correlated the activity and levels of metalloproteinase enzymes and their inhibitors in human carotid plaques to ischemic neurologic events.

Carotid plaques were collected at the time of endarterectomy from 23 patients with carotid stenosis. Sixteen patients were asymptomatic and 7 patients had symptoms of stroke or transient ischemic attack within 6 weeks of surgery. Protein was extracted from the plaques, proteolytic activity was determined by gelatin zymography, and pro-MMP and tissue inhibitor of metalloproteinase (TIMP) enzyme content were measured by ELISA assay. Macrophage accumulation in the plaque was determined using immunohistochemistry.

Plaques from symptomatic patients had decreased proteolytic activity on substrate gel zymography at the 62- and 92-kDa regions (corresponding to active MMP-2 and pro-MMP-9). A decrease in pro-MMP-9 (8.21 +/- 2.35 vs 17.42 +/- 3.14 ng, P < 0. 05) and an increase in TIMP-2 protein (12.62 +/- 0.58 vs 10.56 +/- 0. 77 ng, P < 0.05) were noted on ELISA in plaques from symptomatic patients. No difference was noted in macrophage accumulation in the plaques between the two groups.

Plaques from patients who present with ischemic neurologic symptoms have decreased proteolytic activity associated with decreased pro-MMP-9 and increased TIMP-2 protein levels. These data suggest that metalloproteinase enzymes are not responsible for plaque instability in the carotid circulation and may in fact promote plaque stability.