Significance of Lipoproteins

Case details

A 50 -year-old male presents with weakness in his left leg. History reveals that he is a known hypertensive and a diabetic from the past 5 years, but is non- compliant to medication.

Based on the clinical findings and imaging of the brain, he has been diagnosed with “Brain stroke”. His serum total cholesterol is abnormally elevated. Which of the following would also be expected to be abnormally high?

A. Chylomicrons

B. LDL

C. HDL

D. VLDL

E. IDL

The correct option is- B, LDL (Low density lipoprotein)

Lipids absorbed from the diet and synthesized by the liver and adipose tissue must be transported between various cells and organs for utilization and storage.

Lipids are insoluble in water; the problem of transportation in the aqueous plasma is solved by associating nonpolar lipids (triacylglycerols and cholesteryl esters) with amphipathic lipids (phospholipids and cholesterol) and proteins to make water-miscible lipoproteins.

LDL is a transporter of cholesterol from the liver to peripheral tissues (figure). Excess LDL triggers the process of atherosclerosis, hence called “Bad cholesterol”. A positive correlation exists between the incidence of coronary atherosclerosis and the plasma concentration of LDL cholesterol.

Chylomicrons are found in chyle formed only by the lymphatic system draining the intestine (figure).

They are responsible for the transport of all dietary lipids into the circulation.

HDL (high density lipoprotein) transports cholesterol from peripheral tissues back to liver for degradation by the process of “Reverse cholesterol transport”(figure). High HDL reduces the risk for Ischemic heart disease that is why labeled as “Good cholesterol”.

There are striking similarities in the mechanisms of formation of chylomicrons by intestinal cells and of VLDL(very low density lipoprotein) by hepatic parenchymal cells. VLDL act as transporters of endogenous lipids from liver to peripheral tissues for their utilization (figure)

IDL (intermediate density lipoprotein) is formed from VLDL upon its metabolism.

IDL is subsequently converted to LDL; Each LDL particle is derived from a single precursor VLDL particle.

Lipoproteins

Figure- Summary of functions of lipoproteins

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