Lipoproteins and Apolipoproteins (TOPIC 1) Flashcards
are spherical shape which transports lipids such as cholesterol and triglycerides.
Lipoproteins
Composed of lipids and protein (apolipoproteins).
Lipoproteins
are found on the surface of the lipoproteins.
Apolipoproteins
Functions are maintenance of structural integrity, binds to cell receptor and activators or inhibitors of enzymes.
Apolipoproteins
Types of lipoproteins
ULDL- Chylomicrons
VLDL
IDL
LDL
HDL
Largest lipoprotein, produced in the intestinal mucosal cells.
CHYLOMICRONS
Composition: 80-90 % triglycerides (majority)
CHYLOMICRONS
Transports exogenous (dietary lipids) to liver and peripheral cells such as adipose tissue.
CHYLOMICRONS
Forms a milky or creamy layer at the top of the plasma. (lipemic).
CHYLOMICRONS
Contain lipase which hydrolysed cholesterol and triglycerides resulting to formation of chylomicron remnants which uptake by the liver.
CHYLOMICRONS
Lowest density and no electrophoretic mobility.
CHYLOMICRONS
Lipemic sample means high amount of chylomicrons and triglycerides.
CHYLOMICRONS
Pre beta lipoprotein.
VLDL(Very low density lipoprotein)
Composition: 45-65 % triglycerides.
VLDL(Very low density lipoprotein)
Triglyceride composition of Chylomicrons
Composition: 80-90 % triglycerides (majority)
Triglyceride composition of VLDL(Very low density lipoprotein)
Composition: 45-65 % triglycerides.
Apolipoproteins of VLDL
apo B-100, C-I, C-II, C-III and E.
Synthesized from chylomicron remnant
VLDL(Very low density lipoprotein)
Apolipoprotein of chylomicrons
apo B-48
Transports endogenous triglycerides from hepatic to peripheral tissues.
VLDL(Very low density lipoprotein)
deposits fats to the adipose tissue eventually degraded by lipoprotein lipase resulting decrease in size.
VLDL(Very low density lipoprotein)
Intermediate between VLDL and LDL.
IDL(intermediate density lipoprotein)
Partly depleted triglyceride.
IDL(intermediate density lipoprotein)
interacts with HDL giving off most of its TAG content in exchange of cholesterol resulting to formation of LDL.
IDL(intermediate density lipoprotein)
Composition: 45-50 % cholesterol.
LDL(low density lipoprotein)
LDL(low density lipoprotein)
cholesterol composition
Composition: 45-50 % cholesterol.
apolipoprotein of LDL
B-100
“Bad cholesterol” by transporting cholesterol from liver to tissues. Used as a marker for coronary artery disease.
LDL(low density lipoprotein)
Beta lipoprotein, follow the mobility of
beta globulin.
Composition: 15-20 % cholesterol and 45-55 % proteins.
HDL(high density lipoprotein)
HDL cholesterol and protein composition
15-20% cholesterol
45-55% proteins
Produce by liver and intestines.
HDL(high density lipoprotein)
“Good cholesterol” because it acts as “scavenger of lipids”,
HDL(high density lipoprotein)
Apolipoprotein of HDL
apo A-I
apo A-II
apoC
transport cholesterol from tissues to liver for catabolism to form bile acids. (reverse cholesterol transport).
HDL(high density lipoprotein)
Alpha lipoprotein, follow mobility of
alpha globulin
Fastest migrating lipoprotein.
Alpha lipoprotein
transporting cholesterol from liver to peripheral tissues such as adrenal gland, gonads, and blood vessels.
LDL
transport cholesterol from peripheral tissues to liver for recycling
HDL
Also known as the “sinking beta lipoprotein”.
Abnormal lipoprotein
Same with LDL except in density and mobility.
Abnormal lipoprotein
Associated with increase risk of coronary artery disease and cerebrovascular disease.
Abnormal lipoprotein
Apolipoprotein of Abnormal Lipoprotein
apo (a) bound to apo B-100 by disulfide bonds
Floating beta lipoprotein.
Beta VLDL
Contains higher cholesterol than triglycerides.
Found in VLDL density range, electropheritically found in LDL.
Beta VLDL
Seen in type III hyperlipoproteinemia.
Beta VLDL
Homologous with plasminogen which interfere with clot lysis.
Abnormal lipoprotein
Composed mainly by unesterified cholesterol and phospholipids.
LpX
Migrates towards the cathode in electrophoresis.
LpX
Found in patient obstructive biliary disease.
LpX
Separation of lipoproteins
Ultracentrifugation
Electrophoresis
Separation is based on net charges.
Serum Electrophoresis
Lipoproteins are run in gel , electric current in apply to facilitate migration along the surface of gel. Stain is applied to visualize the band formation.
Serum Electrophoresis
Stain/dye for Serum Electrophoresis
Fat Red 7B,
Sudan Black B,
Oil Red O
Lipoprotein migration pattern in Electropheresis
HDL
VLDL
LDL
Chylomicrons
Alpha region
Pre-beta region
Beta region
Does not migrate
Other techniques of Separation of plasma proteins
Chromatographic technique
Standing plasma test/plasma appearance test-
Immunochemical methods-
use of antibody to specific apolipoproteins.
Immunochemical methods-
stand EDTA blood for 10-18 hours in dark refrigerator
Standing plasma test/plasma appearance test-
found on the surface of the lipoproteins.
Apolipoproteins
Functions
structural integrity
binds to cell receptor
activators or inhibitors of lipoprotein associated enzymes.
Apolipoproteins
catalyses the transfer of excess cellular cholesterol from peripheral tissues to the liver to be catabolized to bile this process is known as Reverse cholesterol transport (RCT).
Lecithin cholesterol acyl transferase (LCAT)-
catalyses the metabolism of serum triglycerides by hydrolysis in chylomicrons and VLDL into FFA and glycerol for energy production or storage.
Lipoprotein lipase (LPL)-
Types of
Apolipoprotein A
(major protein of HDL)
A1 – activates LCAT(Lecithin-cholesterol acyl transferase)
A2 – inhibits L-CAT
Types of
Lipoprotein Little A Antigen
occurs in variant forms of LDL known as “sinking pre-beta lipoprotein”
Types of
Apolipoprotein E
found in chylomicrons, VLDL, HDL and LDL
Increase the hepatic uptake of lipoproteins due to LDL receptor.
Involves in the metabolism of chylomicron remnant and VLDL
E2 – associated with dysbetalipoproteinemia
(ApoE2/E2 homozygosity
genotype)
E4- associated with Alzheimer’s disease
Types of
Apolipoprotein C
(mostly found in chylomicrons, VLDL and HDL)
C1 – activates L-CAT
C2 – LPL (lipoprotein lipase enzyme) activators, inhibits binding of VLDL and chylomicron to hepatic receptor
C3 – inhibits LPL (lipoprotein lipase)
Types of
Apolipoprotein B
(major content of VLDL and chylomicrons)
B100 – found in VLDL, synthesized in the liver.
B48 – found in chylomicrons and in patient with defects in chylomicron clearance. Synthesized in the intestine (enterocytes).