A video by:
Dr. Bharat KC ( MBBS 2014, BPKIHS)

LIPOPROTEIN METABOLISM AND DISORDERS
Dr. Apeksha Niraula
Assistant Professor
Department Of Biochemistry
BPKIHS

“Cholesterol” the most feared among Lipids, speaks:

“ Consumed through the diet and produced in the body,
participate in innumerable cellular functions.
Implicated in several Health complications,
And blamed I am, for no fault of Mine.”

OBJECTIVES
Lipids: General Concepts

Types of Lipids, Lipoproteins, Nomenclature of Lipoproteins, Apolipoproteins

Metabolism of individual lipoproteins

Types of Lipoprotein metabolism disorders

Lipids

Lipids are the compounds which are soluble in organic solvents and virtually insoluble in water

Lipoproteins are macromolecular protein complexes that allow hydrophobic lipids to be transported within the hydrophilic environment of the circulation

Lipids can be broadly divided into
Sterols Cholesterol

Fatty acids or substances containing fatty acids Triglycerides and Phospholipids;

Eicosanoids Thomboxanes, Prostaglandins, Leukotrienes
Fat-soluble vitamins (A, D, E and K), and sphingolipids

Sterols
Cholesterol:

Major sterol in humans, being present in all body cells and most body fluids

Major from: Free, Unesterified form

Free and unesterified form is the structural component of cell membranes

Cholesteryl esters in normal cells: represent a store for future use and appear microscopically as intracellular droplets

De novo synthesis of cholesterol in the body is made by from acetate

Liver is responsible for most cholesterol synthesis

Cholesterol is a precursor for the synthesis of gonadal and adrenal steroid hormones, vitamin D and bile acids

Although only a small amount of the body’s cholesterol pool comes from dietary cholesterol, this has an important role in regulating the rate of cholesterol synthesis

Liver: key organ in maintaining cholesterol balance; any excess cholesterol is excreted by the liver into the bile, either directly, for after conversion into bile acid

Lipoproteins
The various classes are:

Chylomicrons (CM)
Very low density lipoproteins (VLDL)
Low density lipoproteins (LDL)
High density lipoproteins (HDL)

Functions of Lipoproteins:
The lipoprotein particles have three important functions in human body

Transport the dietary fat from the intestinal mucosa, where it is absorbed, to liver by exogenous lipid transport (Chylomicrons)

Transfer triacylglycerols and cholesterol from liver to other tissues by endogenous lipid transport (VLDL and LDL)

Transport cholesterol from extrahepatic tissues to the liver by reverse cholesterol transport (HDL performs this role)

All lipoproteins contain various types of lipids:

Triacylglycerols, phospholipids, and cholesterol-free and esterified

Bulk of plasma cholesterol is transported associated with LDL

Bulk of plasma triacylglycerol is transported associated with chylomicrons or VLDL

Proteins
Five main classes of apolipoproteins (A–E) have been identified in lipoproteins

Synthesized in liver [Smaller quantities are produced in almost all organs]

Group-A are found in highest amounts in HDL

Group-B are associated with VLDL, LDL and chylomicrons: Tightly integrated into the PL layer

Members of C and E group are less tightly associated and exchange among lipoproteins with HDL acting as the distributor

Functions of Apolipoproteins

Transport

Enzyme activation

Ligand

Metabolism of Chylomicrons
Chylomicrons: Transporter of dietary triacylglycerols

Synthesized in the intestine and transport dietary triacylglycerols to skeletal muscles and adipose tissue, and dietary cholesterol to the liver

As the chylomicrons pass through the capillaries of various tissues, the triacylglycerols are hydrolyzed by the action of lipoprotein lipase (LPL), an enzyme located on the endothelial cells

The fatty acids and mono acylglycerols released by the hydrolysis diffuse directly into the tissue either for metabolism or for storage

Apo B-48 and Apo A- Nascent Chylomicron

Apo B-48, Apo A- Apo C and Apo E- Mature Chylomicron

Metabolism of VLDL and LDL
Nascent VLDL particles occurs in the hepatocytes

Involves assembly of triacylglycerols, phospholipids, cholesterol and ApoB- 100

RER is involved in the production of apoB-100 and
SER in its assembly with the lipid components
Glycosylation occurs in the Golgi to produce nascent VLDL

Music credit:
Aakash Gandhi – lifting dreams

@DIP -Medical Videos | 2020
#biochemistry #lipidmetabolism #dip_medical_videos