Human carotid plaque calcification and vulnerability. Relationship between degree of plaque calcification, fibrous cap inflammatory gene expression and symptomatology.

Background: Inflammation is a key mechanism in human atherosclerotic plaque vulnerability and disruption. The objective was to determine the differential gene expression of pro- and anti-inflammatory factors in the fibrous cap and shoulder region of noncalcified and calcified carotid endarterectomy plaques.

Methods: Thirty carotid endarterectomy plaques were classified as type Va (noncalcified, n = 15) and type Vb (calcified, n = 15) in accordance with the American Heart Association consensus. Using laser capture microdissection, fibrous cap and shoulder regions were excised from frozen sections. Gene expression of pro- [interleukin 1 (IL-1), IL-8 and monocyte chemoattractant protein 1 (MCP-1)] and anti-inflammatory (IL-10) factors, and bone formation (bone morphogenetic protein 6 and osteocalcin) mediators were quantitated by real-time PCR. Protein levels were determined using Western blotting.

Results: Mean percent carotid stenosis and calcification area were 79 and 5% in Va-plaques (40% symptomatic) and 77 and 42% in Vb-plaques (20% symptomatic). Macrophages infiltrating the region of the fibrous cap and the shoulder were more numerous in non-calcified plaques compared with calcified plaques (p < 0.01]. mRNA expression of MCP-1 and IL-8, and protein levels of IL-8 were also greater in Va plaques compared to Vb plaques (p < 0.05). Protein levels and mRNA expression of osteocalcin were greater in Vb compared to Va plaques (p < 0.05).

Conclusions: Fibrous cap inflammation is more likely to occur in noncalcified than in calcified plaques. These findings suggest that carotid atherosclerotic plaque calcification is a structural marker of plaque stability.