Bm2-Lipid Transport and Storage

7/28/2019 Bm2-Lipid Transport and Storage

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Abdul Salam M. Sofro

Faculty of Medicine

YARSI University



Learning objectives

• By the end of lectures, the students are

expected to:

– Understand lipid transport in the body (or the

blood plasma)

– Recognize various lipoprotein and the role of liver

in lipid transport and metabolism

– Understand lipid storage for energy reserve



Lipid are insoluble in water

• How to transport in the blood plasma?

– Solved by associating non-polar lipid (TAG &

cholesteryl ester) with amphipathic lipids

(phospholipids & cholesterol) and protein to

make water-miscible lipoprotein





Four major lipid classes are present in

lipoprotein

• Triacylglycerol (TAG)

• Phospholipids

• Cholesterol

• Cholesteryl ester

Another plasma lipid: Free Fatty Acids (FFA)

only 5% of the total FA present in the plasma

and the most metabolically active plasma lipid



Sites of action of the phospholipases A1, A2, C and D.



Phospholipid Structures

Phosphatidylcholine (PC)

Phosphatidylethanolamine (PE)

Phosphatidylserine (PS)







Cont.

•

Chylomicron – derived from intestinal absorption of TAG

• Very Low Density Lipoproteins (VLDL of pre-β-

lipoproteins) – derived from the liver for export of TAG

• Low Density Lipoproteins (LDL or β-lipoproteins) –

representing the final stage in the catabolism of VLDL

• High Density Lipoproteins (HDL) or α-lipoproteins) –

involved in VLDL & chylomicron metabolism and also incholesterol transport



Function of lipoproteins

•Chylomicrons

Transport triacylglycerols from intestines to othertissue – except kidneys

• VLDL

Bind triacylglycerols in liver and carry them to fattissue

• LDL

Carry cholesterol to peripheral tissues• HDL

Bound to plasma cholesterol. Transport cholesterolto liver





Composition of lipoproteins in human plasma

Fraction Source Protein(%)

Total lipid(%)

TAG(%)

Chylomicrons

Chylomicron

remnants

VLDL

IDL

LDL

HDL1

HDL2

HDL3

Pre-β-HDL

Intestine

Chylomicrons

Liver (intestine)

VLDL

VLDL

Liver & intestine

VLDL

Chylomicrons

1-2

6-8

7-10

11

21

32

33

57

70

98-99

92-94

90-93

89

79

68

67

43

30

88

80

56

29

13

2

16

13

-

Albumin-FFA Adipose tissue 99 1 0



Protein moiety of a lipoprotein is known as

apolipoprotein or apoprotein

• One or more apolipoproteins are present in

each lipoprotein:

– Apo A is major apoprotein of HDL

– Apo B is major apoprotein of LDL (Apo B-100), but is

found also in VLDL (Apo B-100) & chylomicrons

(Apo B-48)

–Apo C-I, C-II & C-III are smaller polypeptides freelytransferable between several different lipoproteins

– Apo E (arginine rich) are present in VLDL & HDL



Apolipoproteins of human plasma lipoproteins

Apolipoproteins Lipoproteins MolecularMass (Da)

Apo A-I HDL, Chylomicrons 28,000

Apo A-II HDL, Chylomicrons 17,000

Apo A-IV Secreted with chyomicrons but

Transfer to HDL

46,000

Apo B-100 LDL, VLDL, IDL 550,000

Apo B-48 Chyloicrons, chylomicron remnants 260,000

Apo C-I VLDL, HDL, chylomicrons 7,6000

Apo C-II VLDL, HDL, chylomicrons 8,916

Apo C-III VLDL, HDL, chylomicrons 8,750

Apo D Subfraction of HDL 19,300

Apo E VLDL, IDL, HDL, Chylomicrons,

Chylomicron remnants

34,000









Note:

• FFAs in the plasma arise from lipolysis of TAG

in adipose tissue or as a result of the action of

lipoprotein lipase during uptake of plasma

TAG into tissues. They found in combination

with albumin, rapidly metabolized to form

energy or esterified, the level may arise in

uncontrolled DM



• TAG is transported from the intestines in

chylomicrons and from theliver

in VLDL.• Chylomicrons are found in chyle formed by the

lymphatic system draining the intestine andresponsible for the transport of all dietary lipids

into the circulation.

• Smaller & denser particles having the physicalcharacteristics of VLDL are also to be found in

chyle. Their formation occurs even in the fastingstate, their lipids originating mainly from bile &intestinal secretion



• Chylomicrons & VLDL are rapidly metabolized.Larger particles are catabolized more quicklythan smaller ones.

• Liver does not metabolize native chylomicronsor VLDL significantly

• TAG of chylomicrons & VLDL are hydrolyzed by

lipoprotein lipase located on the walls of blood capillaries



• The action of lipoprotein lipase (results in the

loss of approx. 90% of TAG of chylomicron &the loss of Apo C) forms remnant lipoproteinsor chylomicron remnant.

• Liver is responsible for the uptake of remnantlipoproteins, mediated by a receptor specificfor Apo E.

• LDL is metabolized via the LDL receptor

• HDL takes part in both lipoprotein TAG &cholesterol metabolism



• Liver plays a central role in lipid transport &

metabolism:

– Facilitate digestion & absorption of lipids by

the production of bile

– It has active enzyme systems for synthesizing

& oxidizing FA aand synthetizing TAGs &

phospholipids

– It converts FA to ketone bodies (ketogenesis)

– It plays an integral part in the synthesis &

metabolism of plasma lipoprotein.



Clinical aspects & others

• Imbalance in the rate of TAG formation & export

causes fatty liver when accumulation of lipid in

the liver becomes chronic, fibrotic changes occur

in the cell that progress to cirrhosis & impaired

liver function.

• Ethanol also causes fatty liver.

• Adipose tissue is the main store of TAG in the

body.

• Lipolysis is controlled by hormone-sensitive lipase



• Increased glucose metabolism reduces the output of

FFA

• Insulin reduces the output of FFA fall in circulating

plasma FFA.• Several hormones promote lipolysis:

– Glucocorticoids

– Thyroid hormones

– Catecholamines

• Brown adipose tissue promotes thermogenesis.

















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Bm2-Lipid Transport and Storage