Cardiovascular disease is the leading cause of death among adults worldwide (1996) Coronary disease 7.2 million Cancer 6.3 Cerebrovascular disease 4.6 Acute lower respiratory tract infections 3.9 Tuberculosis 3.0 COPD (chronic obstructive pulmonary disease) 2.9 Diarrhea (including dysentery) 2.5 Malaria 2.1 AIDS 1.5 Hepatitis B 1.2 Figure 1 Atherosclerosis (AS) is the leading cause of death in adults worldwide. There are 11.8 million deaths per year from cerebrovascular and coronary disease combined – almost double that from cancer.

Coronary mortality: alarming worldwide forecasts Figure 2 The coronary mortality rate is increasing alarmingly and is predicted to rise from 8 million deaths in 2000 to 11 million in 2020.

Atherosclerosis: a multifactorial disease Figure 3 Traditional risk factors include age, male sex, dyslipidemia, hypertension, smoking, and diabetes. More recently identified risk factors include obesity and a sedentary lifestyle.

Arterial wall: structure and function Figure 7 In order to understand AS, one must understand the structure and function of the artery. The artery has three structural components: adventitia (which carries blood and nerve supply to the artery itself); media (comprised of smooth muscle, which controls vascular tone); intima (a basement membrane covered by endothelium which regulates hemostasis, thrombosis, vascular tone and permeability). The intima is the site of AS.

Different stages of atherosclerotic plaque development Figure 8 There are six stages of development of AS: Grades I – IV: accumulation of lipids, first intracellularly, then extracellularly; Grade V: fibrosis around the lipid core forming an atherosclerotic plaque; Grade VI: complicated plaque (rupture, clot or bleed) leading to a clinical event.

Vascular endothelium modification in atherosclerosis Figure 9 During AS, the integrity of the endothelium is compromised which results in: increased permeability, which facilitates the penetration of the intima by atherogenic lipoproteins; increased adhesion, which facilitates migration of monocytes into the subendothelium; diminished vasodilation, which compromises hemodynamic control.

Plaque formation 1 — Fatty streak Figure 10 Monocytes penetrate the intima and are transformed into macrophages and eventually cholesterol-rich foam cells. These activated macrophages scavenge and ingest oxidized low-density lipoprotein (LDL) in the subendothelial space. The progressive accumulation of lipids (intra- and extracellular) forms the fatty streak.

Lipid core constitution LDL oxidation Figure 23 Atherogenic lipoproteins (LDL or other apo B-containing lipoproteins) penetrate the intima. This renders them susceptible to oxidation – the auto-oxidation lipid cycle. Oxidized LDL contains modified apo B which is not recognized by the normal receptors. Instead, it is recognized by the non-regulated scavenger receptor on the activated macrophage. 8

Lipid core constitution Activated macrophages accumulate lipids Figure 22 Excessive atherogenic lipoproteins penetrate the intima from the bloodstream and are oxidized by free radicals in the subendothelium. oxidized LDL induces formation of adhesion molecules on the cell surface of the endothelium; monocytes are ‘captured’ from the bloodstream by adhesion molecules and enter the subendothelial space; monocytes penetrate the intima and differentiate into macrophages which bind and absorb oxidized LDL via the non-regulated scavenger receptor. As macrophages accumulate cholesterol esters (CEs) they transform into foam cells. 9

Plaque formation 2 — Fibrous cap Figure 11 The growing fatty streak eventually forms the lipid core, which becomes isolated by the progressive formation of a fibrous cap. The fibrous cap contains collagen, proteoglycans and activated smooth muscle cells. The sturdier the cap, the less likelihood there is of plaque rupture.

Plaque formation 3 — Lipid core Figure 12 Further lipid accumulation in the lipid core results in cell death (apoptosis).

From plaque to thrombosis, key event: plaque rupture Figure 13 The key event in transformation of a stable plaque to an unstable plaque is rupture, which results in either partial or complete occlusive thrombosis.

Plaque vulnerability Key role of macrophages Figure 14 Factors which play a key role in increasing plaque vulnerability. These include: lipid core formation; parietal vascular inflammation; thinning of the fibrous cap; thrombus formation.

Vulnerable plaque Key role of the macrophage in vascular wall inflammation Figure 15 Macrophages play a key role in the formation of a vulnerable plaque. This is achieved because they: liberate cytokines, which cause vascular wall inflammation; produce Tissue Factor (TF), which results in further cell recruitment; decrease fibrous cap resistance.

Vulnerable plaque Key role of the macrophage in the degradation of the fibrous cap Figure 17 Macrophages weaken the fibrous cap by releasing metalloproteases. This release results in: degradation of the fibrous cap around the lipid core; degradation of connective tissue within the lipid core.

Parietal vascular inflammation The activated macrophage produces inflammatory cytokines Figure 24 Oxidized LDL contains large amounts of cholesterol ester (CE). When macrophages are full of CE they secrete cytokines (IL-6, CRP, TNFa) which, in turn, induce vascular inflammation, cell recruitment, and weakening of the fibrous cap.

Parietal vascular inflammation NFkB action in the inflammation process Figure 25 NFkB (a nuclear receptor) plays a major role in inflammation. After internalization and activation within the cell nucleus, NFkB activates genes responsible for synthesis of inflammation factors (IL-6, COX-2, TNFa, ICAM, VCAM). NFkB is, in turn, activated by cytokines, prostaglandins and leukotrienes.

Thrombus formation The macrophages release coagulation factors Figure 18 Activated macrophages increase TF production, which results in: further cell recruitment (monocytes and platelets); increased coagulability, which facilitates thrombosis; increased predisposition to plaque rupture.

Oxidized LDL and thrombogenesis Figure 20 Oxidized LDL activates macrophages and stimulates TF expression. It also stimulates increased production of plasminogen activator inhibitor type 1 (PAI-1), which inhibits fibrinolysis. The end result is a state of hypercoagulability around the plaque, which plays a major role in thrombus formation during plaque rupture.

Plaque disruption (plaque cracking, fissuring, rupture – thrombosis start point) Figure 21 Plaque rupture produces occlusive thrombosis. The occlusion may be partial (such as a wall thrombus, which is fibrin- and platelet-rich) and gives rise to unstable angina, or complete myocardial infarction (the thrombi of which are thrombin-rich). Partial occlusions are prone to embolization and, as such, can give rise to distal occlusions.

Dyslipidemia and atherosclerosis Figure 28 Atherogenic lipoproteins (e.g. LDL, apo B-rich particles like Lp-B:C-III) penetrate the arterial wall and induce: expression of adhesion molecules (which capture monocytes which then migrate into the intima); differentiation of macrophages (which release inflammatory cytokines); increased lipoprotein capture and penetration.

Diabetes and atherosclerosis Figure 26 Chronic hyperglycemia leads to accumulation of glycated proteins in the blood. This causes an increase in vascular permeability which, in turn, increases the level of oxidized LDL. There is also a release of cytokines, which increases the level of vascular inflammation.

Tobacco and atherosclerosis Figure 27 Smoking increases the formation of oxidative free radicals, which raises the level of oxidized LDL. Nicotine has several direct effects, which include: increased cytokine production (which raises the level of vascular inflammation); direct cytotoxicity; vasospasm.

HTN, hemodynamic factor and atheroclerosis Figure 29 Hypertension creates areas of low shear stress within arteries, which in turn results in: increased endothelial permeability; increased duration of lipoprotein contact with the endothelium; increased lipoprotein penetration; decreased endothelium-dependent vasodilation.

Atherosclerosis Figure 6 Atherosclerosis is a silent killer with plaques forming early in life, developing progressively over time. Clinical manifestations of AS commonly involve the brain, heart, and legs.

Inflammation links classic risk factors to altered cellular behavior within the arterial wall and secretion of inflammatory markers in the circulation.

Fibrinogen is an independent risk factor for atherosclerosis Figure 16 Activated macrophages release pro-inflammatory cytokines (IL-6, IL-1, TNFa). Cytokines increase hepatic fibrinogen expression and hence plasma concentration. The risk of cardiovascular disease increases with increasing fibrinogen concentrations. 27

Pathophysiology of atherosclerotic plaque Plaque rupture  inflammation markers (CRP (C-reactive protein), amyloid A) Intracoronary thrombus  increased coagulation factors and proteins (prothrombin fragments F1+2; II – ATIII (thrombin – antithrombin III complex)  increased soluble fibrin monomers  increased P-selectin (a platelet membrane protein) reduced blood coronary flow  imaging changes  fibrinolytic system activation (spontaneous / therapeutic)  increased P-AP2 (plamin – antiplasmin 2) complexes, fibrin degradation products (D- dimer) Myocardial ischemia  early ischemic indicators: glygogen phosphorylase BB  ECG - ST depression Myocardial necrosis  biochemical markers: CKMB, cTnT, cTnI  ECG - ST elevation

Cardiac markers Enzymes: CK, isoenzyme CK-MB, isoforms CK-MB2 and CK-MM3 CK-MB mass ASAT, ALAT LDH, isoenzyme LDH1 Non-enzymatic markers: Troponins cTnT, cTnI Myoglobin H-FABP NT-proANP, NT-proBNP Galectin Inflammatory markers: hsCRP IL6 VCAM1 Fibrinogen

Figure 1 Atherosclerosis (AS) is the leading cause of death in adults worldwide. There are 11.8 million deaths per year from cerebrovascular and coronary disease combined – almost double that from cancer. Fig. 1

Figure 1 Atherosclerosis (AS) is the leading cause of death in adults worldwide. There are 11.8 million deaths per year from cerebrovascular and coronary disease combined – almost double that from cancer. Fig. 2