1. B: Basic science update: Molecular mechanisms of atherosclerosis
Recruitment of monocytes into the vascular wall
Content points:
Atherosclerosis can be considered an inflammatory response of macrophages and lymphocytes.1
Monocytes are attracted to lesion-prone sites by cell-adhesion molecules expressed on activated endothelial cells.
Initial rolling adhesion is mediated by selectins. This is followed by firm adhesion, which is mediated by integrins such as vascular cell adhesion molecule 1 (VCAM-1) and intracellular cell adhesion molecule 1 (ICAM-1).
Monocytes migrate through the endothelial layer into the intima where, under the influence of factors such as monocyte colony-stimulating factor (M-CSF), they take up oxidized LDL (oxLDL) to become macrophages. Receptors for oxLDL such as scavenger receptor A (SRA) and CD36 are involved.
1 Li AC, Glass CK. The macrophage foam cell as a target for therapeutic intervention. Nat Med. 2002;8:

2. Formation of small, dense LDL particles Content points:
Small, dense LDL particles are seen in the insulin-resistant state. They are independent risk factors for CV disease.
Insulin resistance in fat cells causes increased release of free fatty acids (FFA).1
Increased FFA flux to the liver, in turn, stimulates the assembly and secretion of very low-density lipoproteins (VLDL), resulting in hypertriglyceridemia.
In the presence of cholesteryl ester transfer protein (CETP), VLDL transfers triglycerides (TG) to LDL in exchange for cholesteryl esters (CE). This results in formation of small, dense LDL particles.
1 Ginsberg HN. Insulin resistance and cardiovascular disease. J Clin Invest. 2000;106:

3. Lipid entry into the vascular wall Content points:
After penetrating the arterial wall, LDL adheres to proteoglycans, which entrap it and increase its susceptibility to oxidation by lipoxygenases (LO), myeloperoxidase (MPO), and inducible nitric oxide synthase (iNOS).1
Scavenger receptors such as CD36 and SRA take up oxLDL, resulting in foam cell formation by macrophages.
VLDL is modified by lipoprotein lipase (LPL) to form remnants that are trapped by proteoglycans, oxidized, and taken up by macrophages.
1 Li AC, Glass CK. The macrophage foam cell as a target for therapeutic intervention. Nat Med. 2002;8:

4. Importance of LDL modification in foam cell formation Content points:
The fatty streak lesions typical of early atherosclerosis are made up mainly of cholesterol-rich foam cells.1
Formation of foam cells from monocytes is dependent upon LDL modification, because the native LDL receptor (LDLR) is downregulated to protect against cholesterol overloading.
In vitro acetylation of LDL enabled cloning of the acetyl LDLR, renamed SRA. However, there is no evidence that acetyl LDL occurs in vivo.
Oxidation is the best studied LDL modification that could account for foam cell formation. OxLDL occurs in cultured endothelial cells, smooth muscle cells, and macrophages, or can be generated in vitro with a copper catalyst.
Cellular oxLDL uptake is mediated by receptors such as SRA and CD36.
1 Steinberg D. Atherogenesis in perspective: Hypercholesterolemia and inflammation as partners in crime. Nat Med ;8:

5. OxLDL correlates with subclinical atherosclerosis and inflammatory activity
Content points:
Hulthe and Fagerberg investigated whether circulating oxLDL is correlated with subclinical atherosclerosis, as assessed by ultrasound of the carotid and femoral arteries.1
This study of 391 clinically healthy, 58-year-old men showed that oxLDL is related to intima-media thickness (IMT) in the common carotid and femoral arteries (Ptrend = and 0.006), respectively.
Levels of circulating oxLDL also correlate with levels of the pro-inflammatory cytokine tumor necrosis factor-a (TNF-a) and CRP.
The results support the concept that oxidatively modified LDL plays an important role in atherosclerosis development.
1 Hulthe J, Fagerberg B. Circulating oxidized LDL is associated with subclinical atherosclerosis development and inflammatory cytokines (AIR Study). Arterioscler Thromb Vasc Biol. 2002;22:

6. Role of vascular smooth muscle cells in early lesion formation
Content points:
The proliferation of vascular smooth muscle cells (VSMCs) is another key process in the development of atherosclerosis.1
The transition from fatty streaks to more complex lesions is characterized by migration of VSMCs from the media to the intima.
Vascular and inflammatory cells release cytokines and growth factors that generate an environment promoting mitosis.
VSMCs migrate to the luminal side of the vessel wall, where they proliferate.
1 Dzau VJ, Braun-Dullaeus RC, Sedding DG. Vascular proliferation and atherosclerosis: New perspectives and therapeutic strategies. Nat Med. 2002;8:

7. Key cytokines marking inflammatory activity Content points:
Activated inflammatory cells (T lymphocytes, macrophages) seen in atherosclerosis release cytokines, including TNF-a, interleukin (IL)-1, interferon-g (INF-g), and IL-6, that circulate to the liver and also affect endothelial cells in the vasculature.1
IL-6 is responsible for inducing hepatic production of CRP and serum amyloid A (SAA).
Activated endothelial cells release plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (tPA) and stimulate the expression of ICAM and VCAM that mobilize inflammatory cells towards the vascular lumen, creating unstable plaque.
1 Kinlay S, Selwyn A. Effects of statins on inflammation in patients with acute and chronic coronary syndromes. Am J Cardiol. 2003;91(suppl 4A):9B-13B.

8. Formation of advanced lesions Content points:
In formation of advanced lesions, VSMCs proliferate and secrete extracellular matrix proteins, forming a fibrous plaque.1
This step is also marked by accumulation of extracellular calcium.
1 Dzau VJ, Braun-Dullaeus RC, Sedding DG. Vascular proliferation and atherosclerosis: New perspectives and therapeutic strategies. Nat Med. 2002;8:

9. Plaque rupture Content points:
VSMCs may be important in maintaining the stability of plaque through formation of a firm fibrous cap, composed of extracellular matrix components.1
Proteases expressed by inflammatory mediators induce cap thinning, rendering the plaque weak and susceptible to rupture and thrombus formation.
1 Dzau VJ, Braun-Dullaeus RC, Sedding DG. Vascular proliferation and atherosclerosis: New perspectives and therapeutic strategies. Nat Med. 2002;8:

10. Increased pro-inflammatory cytokines in unstable vs stable angina
Content points:
Yamashita et al analyzed the concentrations of high-sensitivity CRP (hsCRP) and pro-inflammatory ILs in 40 patients with unstable angina (UA), 39 patients with stable angina (SA), and 38 healthy subjects.1
Compared with the control group, hsCRP levels were significantly higher in the unstable angina group (P = ) and tended to be higher in the stable angina group (P = 0.06).
Concentrations of IL-6 were significantly higher in both unstable angina and stable angina patients compared with controls (P = and P < , respectively).
Levels of hsCRP and IL-6 were significantly higher for unstable angina compared with stable angina patients (hsCRP, P = 0.03; IL-6, P = 0.009).
IL-12 concentrations were increased significantly in both unstable angina (P < ) and stable angina (P = 0.02) groups compared with healthy subjects.
The unstable angina patients also had significantly higher IL-12 relative to stable angina patients (P = 0.04).
IL-18 levels tended to be higher in unstable angina patients compared with controls (P = 0.08).
The results are consistent with the view that pro-inflammatory cytokines such as IL-6 play an important part in atherosclerosis and the development of angina pectoris.
1 Yamashita H, Shimada K, Seki E, Mokuno H, Daida H. Concentrations of interleukins, interferon, and c-reactive protein in stable and unstable angina pectoris. Am J Cardiol. 2003;91:

11. Plaque instability beyond the culprit lesion Content points:
Rioufol et al used intravascular ultrasound (IVUS) to measure plaque ruptures in the three coronary arteries of 24 patients with first acute coronary syndrome (ACS).1
There were 50 distinct plaque ruptures detected, with a range of 0 to 6 per patient and a mean of 2.08.
In all, 79% of patients showed at least one plaque rupture somewhere other than the culprit lesion, and 12.5% of patients had at least one rupture in all three arteries.
These results support the idea that unstable atherosclerotic plaques occur throughout the coronary tree.
1 Rioufol G, Finet G, Ginon I, André-Fouët X, Rossi R, Vialle E, et al. Multiple atherosclerotic plaque rupture in acute coronary syndrome: A three-vessel intravascular ultrasound study. Circulation. 2002;106:

12. New therapeutic goal: Plaque stabilization Content points:
A “vulnerable” atherosclerotic plaque is especially prone to physical disruption, thereby exposing the thrombogenic components of the subendothelium and plaque core.1
This phenomenon suggests a therapeutic goal of plaque stabilization, which will increase an atheroma’s resistance to rupture.
Vulnerable plaque contains many inflammatory cells, few smooth muscle cells, and a large lipid pool covered by a thin fibrous cap that ruptures easily under the influence of mediators secreted by the inflammatory cells.
Stable plaque, in contrast, has few inflammatory cells, dense extracellular matrix, a smaller lipid pool, and a thick fibrous cap.
1 Libby P, Aikawa M. Stabilization of atherosclerotic plaques: New mechanisms and clinical targets. Nat Med. 2002;8:

13. Potential therapeutic strategies to stabilize plaque Content points:
Understanding the cell biology of ACS suggests five new potential therapeutic strategies to stabilize plaque1:
Endothelial passivation, to reduce inflammation
Reduction of LDL in vessel walls
by aggressive reduction of serum LDL
by increasing reverse transport of cholesterol
Inhibition of LDL oxidation, to reduce macrophage expression of inflammatory cytokines and proteolytic enzymes
Platelet inhibition, to prevent thrombus formation
1 Forrester JS. Prevention of plaque rupture: A new paradigm of therapy. Ann Intern Med. 2002;137:

14. Potential plaque stabilizing effects of cholesterol lowering
Content points:
Cholesterol lowering changes atherosclerotic plaque in ways that may stabilize lesions.1
Macrophages decline in number and mature smooth muscle cells increase.
Levels of matrix metalloproteinases MMP-1, MMP-3, and MMP-9 decrease, and interstitial collagen in lesions increases.
Tissue factor, part of the coagulation cascade that leads to thrombus formation following plaque rupture, decreases.
Lipid lowering substantially reduces superoxide radical formation, leading to less endothelial expression of VCAM-1 and monocyte chemoattractant protein-1 (MCP-1).
1 Libby P, Aikawa M. Mechanisms of plaque stabilization with statins. Am J Cardiol. 2003;91(suppl 4A):4B-8B.

15. Beneficial effects of statins on endothelial function Content points:
Statins improve endothelial function by their effects on several pathways.1
Endothelial nitric oxide synthase (eNOS) is upregulated by statin treatment via effects on eNOS transcription, stability, and protein level.
In addition, statins decrease cellular caveolin, normally an inhibitor of eNOS activity.
Statins reduce expression of tissue factor, endothelin, PAI-1, adhesion molecules, cytokines, and P-selectin, thus benefiting pathways involved in plaque formation and stability.
1 Sowers JR. Effects of statins on the vasculature: Implications for aggressive lipid management in the cardiovascular metabolic syndrome. Am J Cardiol. 2003;91(suppl 4A):14B-22B.

16. Nasal vaccination with HSP decreases lesion size and inflammation
Content points:
Maron et al looked at the effects of nasal vaccination with heat shock protein- 65 (HSP) on the atherosclerotic process, using a mouse model deficient in LDL receptors (LDLR).1
Mice treated orally or nasally with mycrobacterial HSP for 1 week were subsequently fed a high-cholesterol diet, and treated once a week for 8 weeks with oral or nasal HSP or ovalbumin (OVA; the control group).
Atherosclerotic lesions (measured by plaque area) were significantly reduced in nasally and orally treated mice compared with controls (P = 0.05).
Inflammatory macrophage and T-cell levels were likewise significantly lower in the nasal-HSP group compared with controls (P = 0.05).
These results show that nasal vaccination with HSP ameliorates inflammation associated with atherosclerosis, and suggests a new possible approach to treatment.
1 Maron R, Sukhova G, Faria A-M, Hoffman E, Mach F, Libby P, Weiner HL. Mucosal administration of heat shock protein-65 decreases atherosclerosis and inflammation in aortic arch of low-density lipoprotein receptor-deficient mice. Circulation. 002;106: