Intraplaque haemorrhages as the trigger of plaque vulnerability

Abstract

Atherothrombosis remains one of the main causes of morbidity and mortality in the western countries. Human atherothrombotic disease begins early in life in relation to circulating lipid retention in the inner vascular wall. Risk factors enhance the progression towards clinical expression: dyslipidaemia, diabetes, smoking, hypertension, ageing, etc. The evolution from the initial lipid retention in the arterial wall to clinical events is a continuum of increasingly complex biological processes. Current strategies to fight the consequences of atherothrombosis are orientated either towards the promotion of a healthy life style and preventive treatment of risk factors, or towards late interventional strategies. Despite this therapeutic arsenal, the incidence of clinical events remains dramatically high, dependent, at least in part, on the increasing frequency of type 2 diabetes and ageing. But some medical treatments, focusing only on prevention of the metabolic risk, have failed to reduce cardiovascular mortality, thus illustrating that our understanding of the pathophysiology of human atherothrombosis leading to clinical events remain incomplete. New paradigms are now emerging which may give rise to novel experimental strategies to improve therapeutic efficacy and prediction of disease progression. Recent studies strengthen the concept that the intraplaque neovascularization and bleeding (Figure 1, upper panel) are events that could play a major role in plaque progression and leucocyte infiltration, and may also serve as a measure of risk for the development of future events. The recent advances in our understanding of IntraPlaque Hemorrhage as a critical event in triggering acute clinical events have important implications for clinical research and possibly future clinical practice.

Figure 1

Macroscopic view and schematic representation of the detrimental consequences of intraplaque haemorrhages on plaque biology and stability.

Figure 2

Histology of intraplaque haemorrhage (A: Masson's trichrome, mosaic reconstituted section, ×2.5) showing the presence of intact RBCs and free haemoglobin (inset, ×20). (B) Iron visualized by Prussian blue (Perl's) stain with nuclear red counterstaining, showing the haemoglobin-dependent presence of iron, mainly localized in the vicinity of neocapillaries and within phagocytic cells (insets, ×20 and ×40, arrow).

Figure 3

Centripetal angiogenesis and erythrodiapedesis in early stages of human atheroma. (A) General view of an asymptomatic lesion in human common carotid artery showing both cholesterol crystal clefts (arrow) and centripetal angiogenesis (square) (haematoxylin/eosin, HE ×4); (B) enlarged view of the neovessel showing the presence of RBCs within the circulating lumen, and erythrodiapedesis outside the vessel (arrow, HE ×40); (C) erythrophagocytosis (entosis) evidenced by the presence of RBC skeletons within a phagocyte (arrow, HE ×40); (D) enlargement of cholesterol crystal clefts surrounded by immuno-staining of glycophorin A (brown, ×40).

Figure 4

(Left panel) Immunostaining of phagocytes (CD 68) in the border area of the necrotic core (mosaic reconstituted section, ×2.5) showing CD 68⁺ smooth muscle-like cells (left inset, ×20) and phagocytosed RBCs (right inset, ×40). (Right panel) Immunostaining of platelets (C41) showing an important enrichment of the core by the platelet membrane marker (mosaic reconstituted section, ×2.5), particularly in the shoulder area, near the neovessels (×20). Thrombin immunostaining and phosphotungstic acid haematoxylin (PTAH) staining of fibrin are diffuse showing the fibrin-rich nature of intraplaque haemorrhages (×20).

Figure 5

(Left panel) Immunostaining of endothelium (CD 31, ×20) showing the abundance of neovessels, and the presence of rolling polymorphonuclear cells within these neo-venules (inset, ×40, arrows). (Right panel) Diffuse immunostaining of neutrophil membranes (CD 66b, mosaic reconstituted section, ×2.5) and presence of a rolling CD 66⁺ polymorphonuclear cell and a mononucleate cell (arrow head) in a neovessel (inset, ×100).