41. Cardiovascular Pathology (HT) Flashcards
What is atherosclerosis?
- A pathological process that damages the major arteries and leads to cardiovascular disease (CVD).
- Atherosclerosis is a disease in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque.
What are some possible consequences of atherosclerosis?
- Acute coronary syndromes:
- Stable & unstable angina
- Myocardial infarction
- Cerebrovascular disease:
- Strokes
- Transient ischaemic attacks (TIAs)
- Peripheral vascular disease:
- Intermittent claudication
- Renal failure
Give some statistics relating to the prevalence of atherosclerosis.
Where does atherosclerosis occur?
- In large arteries, not veins
- Particularly at bifurcations
- Lesions in these arteries are particularly important:
- Carotid arteries
- Femoral arteries
- Coronary arteries
What is this?
Carotid atherosclerosis, near the carotid bifurcation.
What is claudication?
- Pain and/or cramping in the lower leg due to inadequate blood flow to the muscles.
- It is caused by atherosclerosis in the peripheral vessels.
How common is claudication?
It affects around 5% of over 65s.
What is it important to remember about claudication?
Patients with claudication nearly always have disease in other parts of the circulation, especially the coronary arteries.
Describe and explain the different stages of an atherosclerotic lesion.
[IMPORTANT]
- Fatty streak -> The initial accumulation of lipids in the tunica intima, which is taken up by macrophages that become foam cells. Most of the lipid is intracellular.
- Fibro-fatty plaque (a.k.a. atheroma?) -> The progessed form of a fatty streak, with increased infiltration of macrophages, smooth muscle cells and T-cells. Contains a core of extracellular lipids and some connective tissue.
- Complicated lesion -> When the atheroma ruptures, leading to surface events such as thrombosis.
Describe the progression of an atheroma.
- In your 20s and 30s, fatty streaks develop in your arteries.
- These develop and become early atheromas (a.k.a fibro-fatty plaques?)
- As these atheromas grow, they can become vulnerable plaques
- In these cases, the plaque is separated from the lumen by a thin fibrous cap
- If the fibrous cap thickens, the plaque stabilises
- If the fibrous cap ruptures, platelets are activated and a thrombus forms -> This is known as a complicated lesion
- This can then heal, which leads to a very narrow lumen due to mass smooth muscle cell proliferation
- It can also lead to myocardial infarction if it blocks the artery
In which layer of arteries does atherosclerosis happen?
Tunica intima
Summarise the main clinical manifestations of atherosclerosis that are mentioned in the spec.
[IMPORTANT]
- Angina
- Myocardial infarction
- Claudication
- Embolism
- Aneurysm
- Ischaemic stroke
What are the cell types involved in atherosclerotic plaques?
- Endothelial cells
- Smooth Muscle Cells
- Platelets
- Macrophages
- CD4+ helper T cells
Draw the different layers of an artery, showing their relative thickness.
Do you need to know how atherosclerosis happens (in terms of cellular and molecular mechanisms)?
No, it is on the right hand side of the spec.
Describe the functions of endothelial cells that are relevant to atherosclerosis.
[EXTRA?]
Describe the factors released by endothelial cells that are relevant to atherosclerosis.
[EXTRA?]
- Vasodilators
- Nitric oxide (EDRF)
- Prostaglandin I2 (PGI2)
- Vasoconstrictors
- Endothelin
- Angiotensin II
- Anti-thrombotic factors
- Tissue Plasminogen Activator (tPA)
- Prostaglandin I2 (PGI2)
- Prothrombotic factors
- Thromboxane A2
- Plasminogen Activator Inhibitor-1(PAI-1)
How is NO implicated in atherosclerosis?
- In normal individuals, NOS is used to synthesis NO in endothelial cells
- In atherosclerosis, the NOS is uncoupled and instead synthesises superoxide radicals that further damage the endothelium
Thus, it is worth remembering that NOS has both positive and negative effects.
What are platelets and what is their function?
- Small cytoplasmic fragments of megakaryocytes (2-5µM)
- Play a key role in endothelial cell repair
- Essential role in haemostasis
What is the lifespan of platelets in circulation?
8-10 days
How do platelets adhere to the sub-endothelium?
Via collagen receptors.
What do platelets secrete that is relevant to atherosclerosis?
- Smooth muscle cell growth factors (esp. PDGF)
- Vasoactive mediators (TxA2, 5HT)
How are smooth muscle cells involved in atherosclerosis?
[EXTRA?]
- Secrete elastin and collagens in stable plaques
- Macrophage-induced smooth muscle cell apoptosis is seen in vulnerable plaques
How are monocytes/macrophages recruited to the site of atherosclerosis?
Monocytes are recruited because atherosclerosis involves inflammation. These then turn into macrophages.
How are macrophages involved in atherosclerosis?
[EXTRA?]
- Accumulate modified LDL via Scavenger Receptors (SRs) -> This forms foam cells, which are the main cell type in fatty streak lesions
- Secrete inflammatory mediators and chemokines -> e.g. IL-1, TNF-a, LTB4
- Secrete growth factors (M-CSF, PDGF, FGFs)
- Involved in plaque rupture (via MMPs & TIMPs secretion)
Draw the life cycle of macrophages in atherosclerosis.
[EXTRA?]
What builds up the fibrous cap that holds the atherosclerotic plaque apart from the lumen of the artery?
Synthetic smooth muscle cells
What effect do macrophages have on the fibrous cap in atherosclerosis?
[EXTRA?]
They weaken it by:
- Secreting proteases, such as matrix metalloproteinase (MMP), which break down the collagen, etc.
- Secreting platelet derived growth factor (PDGF), which promotes smooth muscle cell proliferation (the SMC then die and damage the fibrous cap too) [CHECK THIS]
What is seen here?
- On the left of each artery, there is the atherosclerotic plaque
- The red bridge across the centre is the fibrous cap
Describe the different effects that different cell types have on the stability of atherosclerotic plaques.
What are some important plasma components involved in atherosclerosis?
[EXTRA]
- Lipoproteins (LDL, mod.LDL, HDL)
- Coagulation cascade components
- C-Reactive Protein (CRP)
- Complement components
- Oxidants / anti-oxidants
Describe the structure of a lipoprotein particle.
- The central core is filled with lipids, cholesterol and cholesterol esters
- It is surrounded by a shell of phospholipids, cholesterol and apoproteins
How are lipoproteins classified and what are the different types?
They are classified based on density:
- Chylomicrons
- Very low density lipoprotein (VLDL)
- Intermediate density lipoprotein (IDL)
- Low density lipoprotein (LDL)
- High density lipoprotein (HDL)
Which lipoproteins are pro and anti-atherogenic?
- VLDL, IDL and LDL are pro-atherogenic
- HDL is anti-atherogenic
Why is HDL anti-atherogenic?
- Mediates reverse cholesterol transport
- Has anti-oxidant properties
How can the effects of HDL be increased?
- Medical intervention (e.g. niacin, fibrates)
- Lifestyle changes (e.g. diet, exercise)
Is all HDL the same?
Give two examples of studies relating to atherosclerosis and CVD.
[EXTRA]
- Framingham heart study
- MRFIT (Multiple Risk Factor Intervention Trial)
Describe the Framingham heart study and its findings.
[EXTRA]
- It was a prospective study of CHD in 5,209 men and women aged 30-62, started in 1948. Recruited 5,124 more adults and spouses in 1971.
- Conducted physical examinations and lifestyle interviews then monitored every two years (BP, LDL-C, TGs, smoking etc)
- Findings:
- 1960 -> Cigarette smoking increases risk of CHD
- 1961 -> Cholesterol level, hypertension and abnormal ECG increase risk of CHD
- 1967 -> Obesity increases risk of heart disease
- 1970 -> Hypertension increases risk of stroke
- 1976 -> Menopause increases risk of heart disease
- 1978 -> Psychosocial factors affect heart disease
- 1988 -> High HDL reduces risk of death
- 1996 -> Progression from hypertension to heart failure described
Describe the MRFIT study and its findings.
[EXTRA]
- Prospective study of 361,662 middle aged men, recruiting from 1973-1975 at 22 centres in 18 US cities
- 16 year follow up
- Findings:
- Showed a continuous graded relationship of mortality relative risk versus cholesterol levels -> JAMA (1999)
- Reinforced the importance of muliple stimulatenous risk factors, such as smoking, cholesterol, blood pressure, etc.
Compare the meaning of relative risk and absolute risk in the context of CHD.
- Relative Risk -> The ratio of the likelihood of CHD developing in persons with and without a given risk factor
- Absolute Risk -> The probability of developing CHD in a finite period, e.g. within the next 10 years
Describe the absolute and relative risk of CVD in a young adult with a high plasma cholesterol level.
- A young adult with a high plasma cholesterol level carries a low absolute risk for CHD
- But that young adult has a high relative risk compared with a young adult with a low serum cholesterol level
What are some non-modifiable risk factors for CHD?
- A personal history of CHD
- A family history of CHD
- Advanced age
- Gender
What are some modifiable risk factors for CHD?
- High plasma LDL Cholesterol (>5.2mmol/L)
- Hypertension (>140/90mm Hg)
- Physical inactivity / Obesity (BMI > 30)
- Smoking
- Diabetes
What are the main risk factors for atherosclerosis that are mentioned in the spec?
[IMPORTANT]
- Smoking
- Diabetes
- Genetic (LDL receptors)
- Endocrine (sex)
- Hypertension
- Hyperlipidaemia (raised LDL as opposed to HDL)
- Oxidised LDL
Describe the process of LDL receptor cycling and who discovered it.
- LDL binds to its receptor, which is then internalised
- The cholesterol joins the endogenously synthesised cholesterol
- The receptor is then recycled
This was discovered by Michael Brown and Joseph Goldstein, who won the Nobel Prize for it in 1985.
What are some examples of genetic disorders that can increase or decrease the risk of atherosclerosis?
What genetic disorder may be caused by changes to LDL receptors?
[IMPORTANT]
- Familial Hypercholesterolaemia
- This is where there are mutations in the LDL receptors, so that there is reduced uptake into cells and therefore hypercholesterolaemia occurs
- This increases the risk of atherosclerosis, etc.
What are some examples of genetic variation that contributes to CHD risk factors (i.e. not genetic disorders, just variations in enzymes, etc.)?
What are the main stages of atherogenesis?
- Initiation
- Progression
- Complication
- Clinical Sequelae (e.g. myocardial infarction)
Describe how initiation occurs in atherogenesis.
[EXTRA?]
- LDL is transported to the sub-endothelial space of arteries (this is a primary iniating event)
- The protein and lipids of LDL damaged (forming MM-LDL, oxLDL)
- Endothelial damage leads to expression of ICAM-1, VCAM and MCP-1
- This allows monocyte adhesion, diapedesis and chemotaxis
- Monocytes differentiate into macrophages
- Macrophage uptake modified LDL via scavenger receptors and become foam cells (found in fatty streak lesions)
Describe how progression occurs in atherogenesis.
[EXTRA?]
- There is continued mononuclear cell recruitment
- A lipid-rich necrotic core develops in atheromatous lesions
- There is continued smooth muscle cell migration and proliferation -> These form a fibrous cap
- Macrophage-smooth muscle cell interactions are important for plaque growth (see flashcards)
- Microvessels develop within the plaque of intra plaque
- Raised fibro-fatty plaques may cause arterial stenosis and are the sites of arterial thrombosis
- It is worth noting the presence of T cells, which could be activated by dendritic cells and then contribute to further immune cell recruitment
How might T cells be involved in atherosclerosis?
(Hansson, 2011):
- Dendritic cells patrol the atherosclerotic lesion
- They can recognise epitopes on LDL and oxidised LDL, such as ApoB
- In the lymph nodes, these dendritic cells activate naive T cells
- These effector T cells then contribute to the recruitment of further cells to the atherosclerosis, etc.
Describe the complications that can occur in atherogenesis.
[EXTRA?]
Potential fates of fibro-fatty plaques:
- Ulceration
- Thrombosis
- Vasospasm
- Embolism
- Plaque haemorrhage
- Aneurysm (local dilatation)
- Artery rupture (especially in cerebral arteries)
Is the mechanism of atherogenesis agree on?
- No, there have been lots of hypotheses and these is still some uncertainty
- For example, the “Response to Injury Hypothesis” (Russell Ross, 1976) argues that atherosclerosis can be viewed as an unusual form of inflammation which shows many features of wound repair
What are some experimental models of atherosclerosis?
- Cholesterol-fed primates
- Cholesterol-fed or Watanabe rabbits
- Diabetic pigs on a high fat diet
- Mouse models of atherosclerosis (LDLR knockout or ApoE knockout)
What two genes can be knocked out in mice to induce atherosclerosis?
[EXTRA]
- LDL receptor
- ApoE (this is an apoprotein that is part of VLDL, LDL, etc. that allows the molecule to bind to the LDL receptor)
How can the likelihood of LDL receptor / ApoE knockout mice developing atherosclerosis be increased?
[EXTRA]
- Mice are highly resistant to atherosclerosis.
- But it helps to feed them a very high cholesterol diet containing cholic acid (Paigen diet) or a Western diet
Describe the lipoprotein levels in normal mice and ApoE knockout mice.
[EXTRA]
- LDL is generated from VLDL after its secretion.
- But VLDL clearance is more efficient in mice than in humans, so LDL remains lower than in humans.
- Part of this VLDL clearance is due to the content of apoE, which is better at binding to the LDL receptor than apoB.
- Mice VLDL has comparatively more apoE, so it is cleared faster. A higher fraction is removed fast enough to avoid conversion to LDL.
- However, in ApoE knockout mice, this does not happen and therefore the VLDL and LDL levels are increased, predisposing to atherosclerosis.
How can atherosclerosis in mice models be measured?
[EXTRA]
How can ApoE knockout mice be used to study the influence of different factors on atherosclerosis?
[EXTRA]
- ApoE knockout mice can be bred with other knockout mice for a different factor, such as CCR2
- The offspring that are knockouts for both genes are identified
- The development of atherosclerosis (especially the number of macrophages) in these mice is compared with the mice with just ApE knockout
- This tells us how important the CCR2 is in atherosclerosis and also helps us understand the pathogenesis of atherosclerosis (since it shows that CCR2 is involved in macrophage migration across the endothelium)
(Boring, 1998)
What causes an atherosclerotic plaque to progress to thrombosis?
The plaque gets large enough and ruptures through the endothelium, leading to the activation of platelets.
What is a common histological feature of arterial thrombus formation? What does it indicate?
- Lines of Zhan
- These are alternating layers of RBCs trapped in fibrin and platelets
- This is characteristic of sites of rapid arterial blood flow