Lecture 40: Atherosclerosis and Restenosis Post-PCI, Moelcular and Cellular Mechanisms Flashcards
What is PCI?
Percutaneous Coronary Intervention
What is the significance of PCI?
Transformational for patients with acute coronary syndromes
What is an acute coronary syndrome? Significance?
Unstable angina
Myocardial infarction
Patients who benefit from PCI
What does PCI do for STEMI patients?
PCI leads to improved LV function and survival
Decreased mortality from 11 to 7%
Better than conversvative management (2007 Keeley and Hillis)
For UNSTABLE CAD
What is the significance of the COURAGE trial?
Showed that there is no advantage of PCI over medical treatment in patients with STABLE angina pectoris
Decreased PCI use by 30% since 2007…that is the significance
What forms the internal elastic lamina? Significance?
Made from secretiosn by both tunica intima and media
If internal elastic lamina breaks down, bad things happen
What is the significance of the tunica media?
They are the primary determinants of what regulates blood pressure
Smooth muscle cells are the most plastic of all the cells
What is the significance of the tunica adventitia?
Does all kinds of things lol
If you see normal lumen, can you assume that you don’t have atherosclerosis?
No, lumen could be fine even though there is surrounding atherosclerosis
What initiates restenosis?
- Endothelial cell denudation
- exposure of ECM
- platelet activation
- release of cytokines
Restenosis is initiated by the PCI (blowing up the balloon)
What is the pathogenesis of restenosis?
- SMC activation and proliferation
2. arterial remodeling
What is the histology of restenosis?
- synthetic SMCs and ECM
What is the clinical course of restenosis?
Predictable (within 6 months)
If it doesn’t happen in the first 6 months then it is not going to happen
What causes restenosis following PCI?
All about the migratory effects of smooth muscle cells
What accounts for bulk of restenotic lesion?
ECM accumulation
What is the significance of SMC with restenosis?
SMC proliferation main cause of restenosis
SMCs then reenter the cell cycle, modulate their phenotype from contractile to synthetic and secrete abundant ECM, migrate from media to the intima forming a neointima within seven days of injury
What is the significance of growth factors in restenosis following PCI?
Growth factors induce proliferation of SMC proliferation
What are the growth factors that lead to restenosis?
- PDGF
- Basic FGF
- Angiotensin II
- TGF-beta
The first three promote SMC proliferation
The last promotes secretion of ECM
What are the characteristics of PDGF?
A growth factor that can lead to restenosis
Induces SMC MIGRATION
-secreed by platelets, endothelial cells, and SMCs
What are the characteristics of FGF?
Induces SMC proliferation
Secreted by SMC
How does angiotensin II contribute to restenosis?
Promotes SMC proliferation
Binds to AT1 receptor on SMCs
How does TGF-beta contribute to restenosis?
Extracellular matrix secretion by SMC
Produced by SMCs, endothelial cells and platelets following PTCA
What is the most important growth factor leading to restenosis?
TGF-beta
Because it secretes ECM, which is 90% of restenotic area
What is the point of stents?
They prevent the geometric remodeling of smooth muscle cells that occurs after PCI’s are placed
However smooth muscle cells can migrate through the stent and still occlude the artery
Why use rapamycin to treat restenosis?
Rapamycin inhibits SMC proliferation
This is the drug that is “eluted” for drug-eluting stents
What is being eluted in drug-eluting stents?
Drugs that prevent smooth muscle cell proliferation like rapamycin
What is the MoA of rapamycin?
Aka sirolimus
A macrolide antibiotic that inhibits cytokine and growth factor-mediated cell proliferation
Binds to FKBP-12 receptor and inhibits TOR required for protein synthesis and cell proliferation
Arrests SMCs at the end of G1 phase of cell cycle
What is the mechanism of paclitaxel (taxol)?
Inhibits mitotic mechanism (so cell doesn’t go back to G1)
Polymerizes tubulin resulting in non-functional microtubules and inhibition of replication at G2/M phase
What does DES stand for?
Drug eluting stents
To what extent is atherosclerosis an inflammatory disease?
There is inflammation present but not sure if this is the main etiology (trials being done now to see whats good)
What are the stages of progression of atherosclerotic lesions?
Type I = isolated macrophage foam cells in artery
Type II = intracellular lipid accumulation
Type III = addition of small extracellular lipid pools
Type IV = addition of core of extracellular lipid (atheroma stage)
Type V = fibrotic layer forms with lipid core (can be calcific and AKA fibroatheroma stage)
Type VI = surface defect, hematoma-hemorrhage, thrombus
What are the key steps to the formation of the fatty streak (Type II step)?
Characterized by lipid-laden foam cells intracellularly
Responds to injury by endothelial dysfunction, monocyte adhesion emigration, etc.
Foam cell recruitment + formation
Monocyte receptor CCR2 binds MCP-1 in the intima
Foam cells secrete pro-inflammatory cytokines that amplify inflammatory response
What are the key characteristics of type IV and V lesions?
Atheroma and Fibroatheroma develop primarily in elastic arteries and large/medium sized arterioles (coronaries)
What are the components of the atherosclerotic plaques (fibroatheroma)?
Formed by
A. SMCs, macrophages, leukocytes
B. collagen, elastic fibers, PGs
C. lipids
What is the anatomy of a fibroatheroma?
- fibrous cap
2. core of macrophages, lipid and debris-apoptosis
How do atherosclerotic plaques expand?
Because the vasa vasorum can feed them cells and what not Leads to i. leukocyte infiltration ii. cell death and degeneration iii. synthesis of ECM Leads to formation of thrombus
If you see a normal lumen, can there still be plaques?
Yes the plaques may be underlying
What are vulnerable plaques characterized by?
Thin fibrous cap and large hypocellular lipid-rich core
Large percentage of lymphocytes and activated macrophages
Abundant cytokine production and MMPs (low pH, hot)
What initiates atherosclerosis?
- genetics
- risk factors
- LDLox
What types of plaques never rupture?
Fibrotic plaques
What types of plaques rupture?
Lipid-rich core with thin cap
What is the pathogenesis of atherosclerosis?
- endothelial cell injury
- chronic inflammation
- monocyte infiltration/foam cell
- slow progression/complex lesion
- plaque stabilization/rupture
What is the histology of atherosclerosis
Lipid rich
Fibrous cap
Prone to rupture
What is the clinical course of atherosclerosis?
- unpredictable
2. small plaques rupture
What is the difference between atherosclerosis and restenosis?
Restenosis made of SMCs and ECM
Atherosclerosis made of fibrous cap, lipid rich
Restenosis = arterial injury by PCI leading to SMC activation
Atherosclerosis = endothelial cell injury that leads to chronic inflammation and rupture
Clinical course of restenosis is predictable while atherosclerosis is unpredictable
