Atherosclerosis & Lipid-lowering Drugs Flashcards
what defines the type of lipoprotein?
the apoproteins present
what are the differences in apoprotein in HDL and LDL?
HDL- apoprotein A-1
LDL- apoprotein B
what is the exogenous pathway for lipid metabolism?
food is broke down into chylomicrons (large)
these a further broken down into FFAs and chylomicrons remnants (taken by the liver)
what is the relevance of chylomicron remnants?
these deposit in vessels and become atheroma
which pathway do most HDL/LDL originate from?
the endogenous pathway
what does the endogenous pathway of lipid metabolism involve?
acetyl CoA (liver)–> cholesterol–> VLD (TG+chol)
VLDL–>IDL–>LDL
- this conversion involves progressive release of TG by Lipoprotein lipase
- LDL is concentrated in cholesterol (low TG content)
- LDL can be removed from circulation by the liver, LDL receptors located on the liver
- LDL can be used by peripheral tissue for use of cholesterol
Hepatic lipase in metabolism
which lipoproteins are usually deposited in atheroma formation?
IDL and LDL
what is reverse cholesterol transport?
the removal of cholesterol from vessel walls back to the liver by HDL
what is the detailed process of atherosclerosis?
- LDL enters endothelium (into tunica intima)
- LDLs are oxidised by macrophages and VSMCs.
- Release of growth factors and cytokines.
- Additional monocytes/macrophages recruited.
- Foam cell accumulation.
- VSMC (in the media) migration.
- VSMC proliferation.
- Plaque growth.
what endothelial dysfunctions occur as a result of atherosclerosis?
- Increased endothelial permeability.
- Upregulation of adhesion molecules.
- Leucocyte adhesion.
- Migration of leucocytes into artery wall.
what causes the formation of the fatty streak in atherosclerosis?
- Migration of VSMCs.
- Activation of T-cells.
- Adherence & activation of platelets.
- Formation of foam cells.
what leads to the formation of the complicated plaque in atherosclerosis?
- Formation of fibrous cap.
- Accumulation of macrophages.
- Formation of necrotic core
what are the stages of the atherosclerotic lesion over time? [6]
- Lesion-prone location – Adaptive thickening.
- Type 2 lesion – foam cells.
- Type 3 lesion (preatheroma) – extracellular lipid.
- Type 4 lesion (atheroma) – bigger core of extracellular lipid.
- Type 5 lesion (fibroatheroma) – fibrous thickening.
- Type 6 lesion (complicated lesion) – fissure & haematoma.
what lipids are considered as remnants? what do remnants do?
VLDL, chylomicron remnants and IDL
these can infiltrate the endothelial wall easily, play a more important role than LDL alone
why do remnants have a very important role in atherosclerosis?
the inflammatory component of atherosclerosis is caused by the remnants rather than LDLs by its self
what is the difference between a stable and unstable plaque?
stable plaque: thick fibrous cap. Prognosis is better
unstable plaque: thin fibrous cap, rich core of lipids and macrophages, less VSMC proliferation
what are the effects of LDL on disease?
strongly associated with atherosclerosis & CHD events
10% increase LDL –> 20% increase in CHD events.
what modifies the risk associated with LDL?
smoking
low HDL
hypertension
diabetes
what are the effects of HDL on disease?
protective effect for atherosclerosis & CHD events
what levels are HDL when Triglycerides are high?
HDLs are low
high TG promotes LDL
what lowers HDL levels?
smoking
obesity
physical inactivity
which drug is no longer used? why?
bile acid sequestrants
poor compliance
what is the effect of nicotinic acid?
increases HDL well but has side effects
not used often
what is the first line of treatment for raised dyslipidaemia?
statins (HMG-CoA reductase inhibitor):
- blocks cholesterol production
- upregulates LDL receptors in liver
- highly effective at lowering LDL
- good compliance
what are statins?
HMG-CoA reductase inhibitors
e.g. atorvastatin, simvastatin, pravastatin
metabolism by CYP3A4 (pravastatin is not metabolised)
what is the role of HMG-CoA reductase?
conversion of HMG-CoA to mevalonic acid, therefore halts the cholesterol pathway
what is the significance of inhibiting the HMG-CoA reductase enzyme?
the rate-limiting step is being targeted
what is the effect of statins in halting the cholesterol synthesis pathway?
- Reduces the modification of proteins involved in modifying gene translation to create LDL
- has the effect of UP-REGULATING the LDL receptors expressed on hepatocytes in the liver
- so more LDL being removed from the blood as the liver is starved of cholesterol
blood HDL is also increased
Liver is depleted of cholesterol as synthesis has stopped, so LDL receptors increase to replenish cholesterol
how does selectivity ratio affect binding of statins?
the higher the selectivity ratio, the greater the chance of it being concentrated in the hepatocyte.
oSimvastatin gets into many cells as it’s very lipid soluble. Pravastatin is mainly hepatocytes.
how does potency number affect the usefulness of the statin?
the lower the number, the more powerful the drug is as an inhibitor of the enzyme.
what are the effects of rosuvastatin?
has the greatest effect in reducing LDL and raising HDL
however, just a modest effect in reducing TG.
what is the “Rule of 6” in statin therapy?
doubling the dose ONLY makes a 6% extra reduction.
when do CHD risk patients benefit from statin therapy? what was side effect of reducing LDL too much?
when there is a 30% risk reduction
but too little LDL resulted in problems in the CNS and memory
what kind of effect does statin have, which is both good and bad at the same time?
pleiotropic effect
N.B has other effects outside effects on cholesterol e.g. anti-inflammatory action
what are the drug therapies used in reducing cholesterol?
- HMG-CoA reductase inhibition i.e. statins
- fibrates e.g. gemofibrozil (PPAR-alpha receptor agonist–> reduce plasma TGs)
- nicotinic acid
- ezetimibe (cholesterol absorption inhibitor in small intestine)
- CETP inhibitor e.g. torcetrapib (can have off target activation of aldosterone synthase causing increased BP)
what are fibrates? e.g. gemfibrozil
PPAR-alpha receptor agonist.
PPAR= Peroxisome Proliferator Activated Receptors
- act on the liver to reduce plasma TG and fatty acid levels
what do fibrates do?
Decrease FFAs and TGs.
Increases HDL very effectively
but LDL doesn’t change a lot
what should fibrates not be confused with?
Thiazolidinediones – PPAR-GAMMA receptor agonists.
These act on adipose.
what is ezetimibe?
Inhibits cholesterol absorption in the small intestine to reduce LDL levels
how does ezetimibe become activated?
converted to glucuronide in the intestines
how can the “rule of 6” be avoided in ezetimibe administration?
co-administer with statins to have a greater reduction in LDL
what are CETP inhibitors?
give an example
why is it discontinued?
CETP= Cholesterol Ester Transfer Protein
e. g. Torcetrapib
- inhibits LDL increase due to reduced TG transfer towards LDL
- leads to unexpected deaths
- off target activation of aldosterone synthase increases BP
what does CETP do?
converts HDL into LDL
- responsible for moving cholesterol esters and triglycerides between VLDL, LDL, and HDL
- Lower CETP levels promote HDL formation, thereforte aim to inhibit e.g torcetrapib
what is PCSK9?
inhibitor of the LDL receptor.
how can PCSK9 be targeted to increase LDL absorption in the liver?
Monoclonal anti-PCSK9 antibodies have been made to inactivate PCSK9 and so more LDL can be absorbed by the liver
in which patients are PCSK9 antibodies particularly useful?
Familial Hypercholesterolemia
what transfers TGs from VLDL to LDL?
where does it take TGs from?
Cholesterol Ester Transport Protein
VLDLs
Chylomicrons
HDL
how is cholesterol created endogenously?
by the liver using acetyl CoA
can use TGs and cholesterol from diet
what does cholesterol in the liver release during fasting?
VLDL
made of TGs and cholesterol
what happens to VLDL when released?
becomes IDL then LDL via lipoprotein lipases
how does VLDL become LDL?
via lipoprotein lipase
this releases TGs from the VLDL to concentrate the cholesterol into a small dense LDL particle via the IDL form
before this TGs must be transferred to LDL via CETP
how are chylomicron remnants taken up by the liver in the exogenous pathway?
via remnant receptors on the liver
what is the role of HDL?
removes cholesterol from tissues
where can LDL produced from VLDL go next [2]?
- either into the liver again via LDL receptor
- into peripheral tissues to provide cholesterol
how does HDL dump cholesterol into the liver?
via scavenger receptors
why does HDL dump cholesterol from other cells into the liver?
for later use or excretion
which subendothelial layer of arteries do LDLs enter?
tunica intima
what are LDLs oxidised by?
free radicals
how does the macrophage endocytose the oxidised LDL?
via scavenger receptor
N.B that scavenger receptors are also on the liver for HDL to dump its cholesterol
what do macrophages become when they endocytose the oxidised LDL?
foam cells
what do foam cells stimulate?
chronic inflammation: vicious cycle of
- lipoprotein oxidation
- monocyte/macrophage recruitment
- phagocytosis/endocytosis
what do the present macrophages stimulate?
proliferation of smooth muscles and increased collagen synthesis
wound healing
what cells leads to the formation of the fibrous cap around the foam cells?
macrophages
how is the fibrous cap formed?
macrophages stimulateproliferation of smooth muscles and increased collagen synthesis
what is the fatty streak?
fibrous cap around foam cell mass
what how can a fatty streak lead to thrombosis?
rupture though the cap and endothelium
which lipoproteins are atherogenic?
what kind of fat contribute these lipoproteins?
LDLs, IDL
small dense LDLs
saturated fat
VLDLs are the least atherogenic (low cholesterol concentration)
what effect will the inhibition of HMG-CoA reductase have?
what effect does it have on the liver itself?
- blockage of cholesterol production in liver
- up regulation of LDL receptors on liver to increase LDL uptake
what metabolises statins?
CYP3A4
which statin is not metabolised?
pravastatin
what is the effect of doubling the statin dosage?
6% reduction in LDLs
what is PPAR-alpha?
- transcription factor active during starvation
- allows concentration of fatty acids which are ligands to PPAR
- expression of genes involved in fatty acid uptake and metabolism
- fibrates are ligands of PPAR, mimicking fatty acids
what is torcetrapib?mechanism of action
CETP inhibitor
reduced the formation of LDLs as the transfer for TGs is reduced
why is torcetrapib discontinued?
off target activation of things like aldosterone synthase
leads to increased BP
