Lecture slides on Lipoprotein metabolism

1. Department of Biochemistry, Nepalgunj Medical College, Nepal
Formation and secretion
Sunday, July 10,
2016
Rajesh Chaudhary
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2. Biomedical importance
Lipoprotein mobilization and utilization after oxidation
during the energy requirement process or stage.
Abnormalities in lipoprotein metabolism leads to either
hypo- or hyperlipoproteinemia.
Example: Hypertriacylglycerolemia during T2DM.
Hypercholesterolemia and premature atherosclerosis.
Sunday, July 10,
2016
Rajesh Chaudhary
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3. Plasma consists of: triacylglycerol
(16%), phospholipids (30%),
cholesterol (14%), cholesterol ester
(36%), and free fatty acids (4%).
Sunday, July 10,
2016
Rajesh Chaudhary
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4 major lipid classes

4. 1. Chylomicrons
2. VLDL
3. LDL
4. HDL
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2016
Rajesh Chaudhary
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4 major plasma lipoproteins

5. Lipoprotein particle
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2016
Rajesh Chaudhary
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6. Lipoprotein particle
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2016
Rajesh Chaudhary
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7. Density of lipoproteins
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2016
Rajesh Chaudhary
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𝐋𝐢𝐩𝐢𝐝
𝐏𝐫𝐨𝐭𝐞𝐢𝐧
If,
Is high, density is
lower and vice-
versa.

8. Plasma lipoproteins
Spherical macromolecular complexes of
lipids + specific proteins
(apolipoproteins / apoproteins)
Examples: Chylomicrons, VLDL, LDL,
HDL.
Lipid deposition contributes to plaque
formation, causing the narrowing of
blood vessels (atherosclerosis).
Sunday, July 10,
2016
Rajesh Chaudhary
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9. The distribution of apolipoproteins
characterizes the lipoproteins
Of HDL: Apolipoprotein A
Of VLDL and LDL: apolipoprotein B (B-100)
Of Chylomicrons: apolipoprotein B (B-48) – truncated form of
apolipoprotein B.
Apo C I, C II, C III and apoE are freely transferrable between
lipoproteins.
NOTE: B-100 is synthesized in liver while B-48 in intestine.
Sunday, July 10,
2016
Rajesh Chaudhary
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10. So, what are the functions of
apolipoproteins?
1. They can form part of the structure of
lipoproteins.
2. They are enzyme cofactors. (C-II for lipoprotein lipase)
3. They acts as ligands to interact with the receptors
in tissues.
Sunday, July 10,
2016
Rajesh Chaudhary
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11. Formation and secretion of
Chylomicrons and VLDL
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2016
Rajesh Chaudhary
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ApoB
ApoB +
lipoprot
ein
ApoB +
lipoprote
in
+carboh
ydrates

12. Formation and secretion mechanism
of both Chylomicrons and VLDL are
common. Why?
Sunday, July 10,
2016
Rajesh Chaudhary
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13. NOTE: The inability of particulate lipid of the size
of chylomicrons and VLDL to pass through
endothelial cells of capillaries without prior
hydrolysis is probably the reason dietary fat enters
the circulation through lymphatic and not through
the hepatic portal system.
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2016
Rajesh Chaudhary
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-- Harper’s Illustrated Biochemistry

14. Abetalipoproteinemia and apoB
ApoB is not able to function because of a defect in a
triacylglycerol transfer protein which prevents loading of the
apoB with lipid; therefore, lipoprotein containing this
apolipoprotein are not formed, and lipid droplets accumulate
in the intestine and liver.
Sunday, July 10,
2016
Rajesh Chaudhary
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15. Characteristics of abetalipoproteinemia
 Vitamin deficiency because of inability of the cells to
absorb vitamins – particularly fat-soluble vitamins – Vit. E
in particular.
Failure to gain weight, growth retardation, diarrhea,
abnormal star-shaped RBC, fatty, foul-smelling stools.
Impaired nervous system, poor muscle coordination, ataxia,
progressive degeneration of retina.
Sunday, July 10,
2016
Rajesh Chaudhary
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16. Catabolism of chylomicrons and VLDL
Chylomicrons and VLDL are very rapidly metabolized.
Triacylglycerol of chylomicrons and VLDL are hydrolyzed
by lipoprotein lipase.
The action of lipoprotein lipase forms remnant lipoproteins.
The liver is responsible for the uptake of remnant
lipoproteins.
Sunday, July 10,
2016
Rajesh Chaudhary
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17. Sunday, July 10,
2016
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Metabolism of

18. Lipoprotein lipase
1. Located on the wall of blood capillaries, anchored to the
endothelium by negatively charged proteoglycan chain of
heparin sulfate.
2. Found in: Heart, adipose tissue, renal medulla, lungs,
aorta, diaphragm, lactating mammary gland and
neonatal liver.
3. Not active in adult liver.
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2016
Rajesh Chaudhary
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20. Rajesh Chaudhary
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Metabolic fate of
chylomicrons

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Metabolism of

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Metabolic fate
of VLDL and
formation of
LDL
Receptors are defective in familial hypercholesterolemia.

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Metabolism of

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26. Sunday, July 10,
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Metabolism
of HDL

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