Lipoprotein Metabolism Flashcards
what are lipoproteins
- transport vehicles for triglycerides, phospholipids, cholesterol, and cholesterol esters
what do lipoproteins work with?
- apoproteins
lipoproteins consist of
- central core
- surface monolayer
central core composed of
- triglycerides
- cholesterol esters
surface monolayer composed of
- phospholipids
- proteins
- cholesterol
plasma lipoproteins classified by density from least dense to most dense
- chylomicrons
- VLDL (remnants of IDL)
- LDL
- HDL
exogenous pathway
- dietary lipids from intestine -> peripheral tissue and liver
endogenous pathway
- synthesized lipids from liver -> peripheral tissue
reverse cholesterol transport pathway
- cholesterol from peripheral tissue -> liver
role of apo C
- activator of lipoprotein lipase
role of apo A
- binding of HDL to peripheral tissues
- activator of LCAT
role of apoB-100
- binding of LDL to LDL receptor
role of apo E
- binding of chylomicron, VLDL, and HDL remnants to the liver after their TGs have been removed
role of apoB plus apoE
- binding of IDL to the liver
lipoprotein lipase located on
- endothelial surface of blood capillaries adjacent to tissues capable of using fats
lipoprotein lipase required for
- TG hydrolysis from chylomicrons and VLDL
lipoprotein lipase activated by
- apoC
- insulin
hepatic lipase located on
- endothelial surface of blood capillaries adjacent to the liver
role of hepatic lipase
- hydrolyzes TGs in final stage of conversion of VLDL, IDL, and LDL
- removal of cholesterol during final stages of HDL metabolism
regulation of hepatic lipase
- not regulated
removal of triglycerides primarily catalyzed by
- lipoprotein lipase
removal of triglycerides yields
- remnant particles
remnant particles targeted to
- liver for destruction
where can cholesterol diffuse
- among lipoproteins and between lipoproteins and tissue
until cholesterol esters are esterified, where do they remain
- with lipoproteins
what can lipoprotein particles exchange with each other
- apoproteins
- cholesterol
- cholesterol esters
- phospholipids
role of HDL
- important acceptor and donor
exogenous pathway - chylomicrons synthesized by
- intestinal mucosal cells with apoA and apoB48
exogenous pathway - chylomicrons pick up
- apoC, poE, and CE from HDL
exogenous pathway - because chylmicrons have apoC now, what can they do?
- bind to LPL at muscle and adipose and TG
- release free fatty acids
exogenous pathway - after triglyceride is removed
- apoA and apoC transferred to HDL
- leaves chylomicron remnant
exogenous pathway - chylomicron remnant taken up by
- liver via apoE receptors
half life of chylomicron remnant
- very short (minutes)
endogenous pathway (triglycerides) - VLDL synthesized
- in liver with TG, CE, C, and apoB 100
- in the fed state
endogenous pathway (triglycerides) - VLDL then obtains
- apoE and apoC from HDL
endogenous pathway (triglycerides) - apoC->LPL
- hydrolyzes TGs to FFA in muscle and adipose
- then picks up CE and transfers apoC to HDL
endogenous pathway (triglycerides) - after TG removed and apoC lost of HDL
- becomes remnant particle called IDL
two classes of IDL
- rich in apoE
- low in apoE
particles that are rich in apoE
what kind of process is this?
- binds to apoE and apoB receptors in liver and is destroyed
- this is a rapid process (hours)
endogenous pathway (cholesterol) - remnant IDL with little apoE what happens
- loses TG to hepatic lipase
- converted to LDL
- LDL also picks up CE from HDL
LDL then loses cholesterol to
- peripheral tissues by passive diffusion
- and binding to apoB receptor
LDL eventually binds to
how long does this process take?
- apoB receptor in liver
- internalized and destroyed
- this process takes days
role of chylomicrons and VLDL
- transport triglycerides and cholesterol to the peripheral tissue
what happens apoC binds to LPL at the muscle and adipose tissue
- removal of triglycerides
what does the removal triglycerides caused
- remnant particle
- guided to liver by apoB
clearance rate of the apoE-low LDL
- cleared very slowly
role of LCAT
- esterifies cholesterol associated with HDL
- traps cholesterol in the interior of the HDL particle
what activates LCAT
- apoA
role of CETP
- transfers cholesterol esters from HDL to VLDL, IDL, and LDL
- main mechanism for delivery of cholesterol to the liver
CEPTP with PLTP
- transfers triglycerides and phospholipids from particles to HDL
role of Apoprotein A
- facilitates binding of HDL particles to ApoA receptors on peripheral tissues
- activates transport protein called ABC1
- activates LCAT reaction
role of ABC1
- responsible for efflux of cholesterol from peripheral tissue
Reverse cholesterol transport - nascent HDL synthesized by
- liver and intestine with ApoA and apoE
Reverse cholesterol transport - HDL picks up
- apoA and apoC from VLDL remnants and chylomicron remnants
Reverse cholesterol transport HDL then donates
- apoC and apoE to chylomicrons
Reverse cholesterol transport - nascent HDL then binds to
- apoA receptor on peripheral tissue
- picks up cholesterol
Reverse cholesterol transport - HDL particles contain
- LCAT
- CETP
Reverse cholesterol transport - VLDL, IDL, and LDL bind to
- receptors on liver
- internalized and destroyed
Reverse cholesterol transport - HDL finally binds to
- apoE receptors on the liver
- internalized and destroyed