Dyslipidemia Flashcards
What is the definition of atherosclerosis?
a condition that afflicts the large and medium-sized arteries of almost every human, at least in societies in which cholesterol-rich foodstuffs are abundant and cheap
begins in childhood and in the absence of accelerating factors, develops slowly until it is widespread in old age
How is atherosclerosis accelerated?
genetic and environmental factors
What is the pathogenesis of atherosclerosis?
infiltration of LDL into the subendothelial region
the endothelium is subject to shear stress
most marked at points where the arteries branch, and this is where lipids accumulate to the greatest degree
Describe each layer of an artery.
inner layer (intima):
-endothelium that lines the lumen of all vessels
middle layer (media):
-smooth muscle cells and elastic fibers
outer layer (adventitia):
-collagen fibers
Describe the initiation of atherosclerosis.
transport of plasma LDL-cholesterol through the endothelial cell layer into the extracellular matrix of the subendothelial space
at low levels, this may not be problematic (LDL is naturally occurring)
How does an atherosclerotic plaque cause a heart attack?
plaque ruptures
the exposed core of an atherosclerotic plaque is highly stimulating to circulating platelets
platelets are fooled
blood flow is blocked
What are the most common plasma lipids in humans?
cholesterol
triglycerides
Describe cholesterol.
a “sterol” or modified steroid molecule
a type of lipid molecule synthesized by all animal cells
essential structural component of all animal cell membranes
allows cells to function without a cell wall
What is cholesterol a precursor for?
bile acids
vitamin D
steroid hormones
-includes glucocorticoids, mineralocorticoids, androgens,
estrogens, and progestogens
Describe triglycerides.
3 fatty acids connected by a glycerol backbone
fatty acids can be oxidized for energy by many tissues
-except brain
glycerol backbone can be used for gluconeogenesis
How are cholesterol and triglycerides transported?
not water soluble so must have specialized vehicles to circulate in the blood
these vehicles are made from apolipoproteins
apolipoprotein’s are proteins that bind lipids (to form lipoproteins)
How is the density of lipoproteins determined?
relative amount of protein vs lipid
What is the role of the protein component of lipoproteins?
provide structural stability and also may function as ligands in receptor interactions or as cofactors in enzymatic processes that regulate lipoprotein metabolism
the type of protein defines the use of the particle
What is contained within the lipid component of lipoproteins?
free cholesterol
esterified cholesterol (>1 cholesterol molecule linked together to improve storage efficiency)
triglycerides
phospholipids
What are the major lipoproteins?
chylomicrons
VLDL
LDL
HDL
What are chylomicrons?
large lipoproteins contains lots of TGs (80-95%)
major vehicle to carry dietary fat (and cholesterol) immediately after absorption from gut
present in plasma for 3-6h after a fat-containing meal has been ingested
What is the role of chylomicrons?
source of TG for adipose tissue and muscle (skeletal and cardiac)
-capillaries in these tissues contain LPL that liberates free fatty
acids for a cellular energy source
source of TG and cholesterol for liver to produce VLDL
What happens when chylomicron remnants are taken up by the liver?
chylomicron remnants contain cholesterol
when taken up by liver cells, increases intra-cellular cholesterol levels
liver responds by downregulation of LDL-receptors (to prevent further uptake of LDL from blood)
LDL accumulates in blood
What is VLDL?
very similar to chylomicron molecule
synthesized in liver
main source of FFA in the fasting (chylos are low)
provides FFA to tissues similar to chylomicrons (LPL in capillary bed steal the TG from VLDL)
True or false: blood tests measure VLDL and chylomicrons separately
false
blood tests measures all TG levels in the blood
What is the fate of VLDL?
eventually VLDLs are stripped of most of TG in the tissues and transform into IDLs
What would a blood test show for an individual with high VLDL and chylomicrons?
high TGs
What is the fate of IDL and where does this occur?
additional loss of TG by LPL will change IDL to LDL
occurs in the liver or peripheral tissues that use TG
Describe LDL.
main carrier of cholesterol in blood (60-70%)
most LDL is derived from VLDL metabolism
however, many tissues can synthesize their own cholesterol
contains apo B (affinity for LDL receptor)
What can a cell do if intracellular cholesterol is needed?
upregulate an LDL receptor
the LDL is internalized and degraded
Which cells express the LDL receptor constantly? Why?
liver cells
to eliminate excess LDL from the circulation
liver disposes of 3/4 of circulating LDL
What is familial hypercholesterolemia?
genetic trait that is associated with no LDL receptors
LDL is not cleared from the circulation and intracellular production is increased
people with FH has high LDL from young age and experience ACVD at very young ages
What will high levels of intracellular cholesterol result in?
inhibits intracellular production
decreases synthesis of LDL receptors
increased cholesterol storage within cells
How is LDL eliminated?
bile
What makes up the measurement of “non-HDL lipoproteins”?
chylomicrons
VLDL
IDL
LDL
When is non-HDL a useful measure?
when TG levels are high
can also be used as a target of cholesterol therapy
Where is HDL derived?
periphery (mainly gut) and in the liver
can be formed by remodeling of chylomicrons or by VLDL catabolism
Describe the role of HDL.
reverse cholesterol transport
excess cholesterol is acquired from cells and transferred to the liver for excretion
“full” HDL can donate cholesterol to LDL and VLDL
allowing tissues (such as coronary arteries) to eliminate excessive cholesterol may be a reason why HDL is considered protective
What has been associated with lower risks for ACVD events?
Apo A-I (major HDL apolipoprotein) and HDL levels
True or false: there are good drugs on the market that increase HDL levels
false
pharmaceutical companies have failed to produce HDL increasing drugs that protect against events
True or false: atherosclerosis is though to arise from transport of LDL through the endothelial layer into the subendothelial space
true
What is a chemical modification to LDL that makes it problematic?
oxidation
True or false: studies of atherosclerotic lesions show that LDL within plaques are rarely ever modified by oxidation
false
LDL within plaques are almost always modified by oxidation
What will oxidized LDL elicit?
oxidized LDL in the subendothelial space triggers signals to recruit monocytes into the artery wall
monocytes are attracted and are activated into macrophages
Describe the entire process of what occurs when LDL is oxidized.
- oxidized LDL stimulates endothelial cells to recruit monocytes and oxidized LDL also appears to stimulate T cells to secrete cytokines
- monocytes cross the subendothelial space and become macrophages (triggered by cytokines)
- macrophages take up oxidized LDL and become foam cells, the cytokines cause smooth muscle to proliferate
- under the influence of growth factors the smooth muscle moves to the subendothelial space and produce collagen to take up LDL, adding to the foam cells
What event appears to be a key trigger of the atherosclerotic process?
oxidization of LDL
True or false: HDL may serve to reduce the oxidation of LDL
true
What is the conclusion regarding the use of antioxidants to prevent the oxidation of LDL?
clinical studies of antioxidant supplementation have been disappointing
the risk ratio was basically 1 in every trial=they arent good
evidence suggests antioxidant supplements do now lower risk for ACVD events
What does oxidized LDL trigger the LDL receptor to change to?
scavenger receptor in macrophages and migrated muscle cells