Pathogenesis of Atherosclerotic Plaques

The primary event in atherosclerosis is thought to be damage caused to the endothelium of arterial walls, resulting in endothelial dysfunction. This damage may be caused by a variety of factors; haemodynamic forces (shear stress caused by e.g. hypertension), a number of vasoactive substances, mediators (cytokines) from blood cells, cigarette smoke, atherogenic diet, elevated glucose levels and oxidised LDL-C.¹ Initially, damage causes the endothelial cells to express cellular adhesion molecules such as cytokines (interleukin-1, IL-1; tumour necrosis factor alpha, TNF-alpha), chemokines (monocyte chemoattractant factor 1, MCP-1; IL-8) and growth factors (platelet-derived growth factor, PDGF; basic fibroblast growth factor, bFGF).¹ This ‘sticky’ surface encourages inflammatory cells such as monocytes and T lymphocytes to attach to the endothelial surface. Once attached they migrate through the intact endothelium into the subendothelial space. Many of the monocytes differentiate into macrophages and take up oxidised LDL, which is more atherogenic than native LDL; these macrophages then become foam cells.¹

Oxidised LDL promotes death of endothelial cells and an inflammatory response resulting in impairment of normal function of the endothelium. In addition, it modifies the response to angiotensin II, resulting in vasodilatory impairment, and induces a prothrombic state by affecting platelets and coagulation factors. Thus, the endothelium responds to damage by inducing a protective response which will eventually lead to the formation of fibrofatty and fibrous lesions, the atherosclerotic plaque, preceded and accompanied by inflammation.²

This schematic linear diagram represents part of a network of complex processes that include various disease (and protecting) mechanisms that occur simultaneously.

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References
1. Koenig W. Eur Heart J Supplements 1999:1:T19–26.
2. Ross R. Nature 1993;362:801–809.

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