HDL

Question 1

How is HDL synthesized?

Answer 1

Nascent HDL forms from liver/intestine via apoA-1 + phospholipids (discoidal shape).

Question 2

What is the role of ABCA1 in HDL metabolism?

Answer 2

Transports free cholesterol from cells to apoA-1 → forms nascent HDL.

Question 3

How does LCAT modify HDL?

Answer 3

Converts free cholesterol → cholesterol esters (via apoA-1 activation) → forms spherical HDL3.

Question 4

What transforms HDL3 to HDL2?

Answer 4

Continued cholesterol esterification by LCAT + uptake of more cholesterol (via ABCG1/SR-B1).

Question 5

How does HDL remove cholesterol from macrophages?

Answer 5

ABCA1/ABCG1 pathways → reduces foam cell formation in arteries.

Question 6

What is reverse cholesterol transport?

Answer 6

HDL transports excess cholesterol from tissues → liver for excretion (bile).

Question 7

How does HDL provide antioxidant effects?

Answer 7

Paraoxonase-1 (PON1) enzyme on HDL reduces oxidized LDL formation.

Question 8

How does HDL inhibit inflammation?

Answer 8

Reduces endothelial adhesion molecules (VCAM-1/ICAM-1) → less monocyte recruitment.

Question 9

How does HDL improve endothelial function?

Answer 9

Stimulates NO production → vasodilation.

Question 10

How does HDL prevent thrombosis?

Answer 10

Downregulates PAI-1 → enhances fibrinolysis.

Question 11

What is the cardioprotective HDL-C level?

Answer 11

> 40 mg/dL (men), >50 mg/dL (women); higher = better outcomes.

Question 12

Why might dysfunctional HDL lose protection?

Answer 12

Inflammation oxidizes HDL → impairs reverse transport (e.g., in diabetes).

Question 13

How does CETP affect HDL?

Answer 13

Transfers cholesterol esters from HDL → VLDL/LDL → lowers HDL-C (blocked by CETP inhibitors).

Question 14

What is the fate of HDL cholesterol?

Answer 14

1) Direct liver uptake via SR-B1. 2) Transfer to LDL via CETP → hepatic LDL receptors.