High-Density Lipoprotein (HDL)

What sample is needed for High-Density Lipoprotein (HDL)?

1. This test is done on serum.
2. A fasting sample is preferred. Advise the patient to fast for 12 to 14 hours.
3. This test can be done on plasma as well.
4. Serum or plasma can be stored at 4 °C for 4 days (5 to 7 days).

What are the precautions for High-Density Lipoprotein (HDL)?

1. Don’t use oxalate, fluoride, citrate, or heparin to collect blood.
2. HDL values are age- and sex-related.
3. HDL value is increased in Hypothyroidism and decreased in Hyperthyroidism.
4. Drugs that increase the value are oral contraceptives, aspirin, phenothiazine, steroids, and sulphonamides.
5. Smoking and alcohol decrease HDL value.

What are the Indications for High-Density Lipoprotein (HDL)?

1. Advised to evaluate coronary artery disease risk.
2. This can be advised as part of a lipid profile.

How will you discuss the pathophysiology of Lipoproteins?

1. Lipoproteins are insoluble and are transported in plasma as macromolecular complexes.
2. Lipoproteins are spherical particles with:
   1. Nonpolar lipids are triglycerides and free cholesterol.
   2. Polar lipids are phospholipids and free cholesterol.

How will you classify lipoproteins?

• It is classified on  electrophoresis based on its physical and chemical structure as follows:

1. Chylomicron:

   1. These are primarily triglycerides.
   2. These are the vehicles that carry lipids absorbed from the intestine and enter the bloodstream.

2. LDL (Low-density lipoprtien):

   1.  Beta-lipoprotein is the primary carrier of cholesterol.
   2. It arises primarily from the degradation of VLDL into LDL1, called intermediate-density lipoprotein (IDL).
   3. LDL-1  is short-lived, and it is converted into LDL-2.
   4. LDL-2 will remove some of the triglyceride load.
   5. LDL is a membrane protein.
   6. There are tissue receptors on the cells, which are engulfed by the cells and degraded by the lysosomal enzymes.

3. VLDL (Very-low density lipoprotein):

   1. It is pre-β-lipoproteins, which is mainly triglycerides.
   2. It originates in the liver and transports triglycerides from the liver to other tissues.

4. HDL (High density lipoprotein):

   1. α–Lipoproteins are mainly proteins with a small amount of cholesterol.
   2. It arises from the liver and intestine and primarily contains apolipoproteins A-I and A-II.
   3. It is a cholesterol scavenger and removes cholesterol from the tissues.
      1. HDL esterifies cholesterol and carries it to the liver for removal.
      2. HDL converts cholesterol into bile acids and excretes them into bile.

What are the apoproteins?

1. The outer covering of lipoproteins is called Apoproteins.
2. These are proteins that bind to lipids and are called lipoproteins.
3. They play an essential role in transporting lipids through the bloodstream, activating enzymes, and allowing lipoproteins to bind receptors on cells.
4. For cardiovascular risk, the important ones are Apo-B and Apo-A-1.

5.  These are classified into:
   1. Apo-1.
   2. Apo-II.ee
   3. Apo- B.
   4. Apo-D.
   5. Apo-E.

How will you classify apolipoproteins?

5. Apolipoproteins are a hydrophilic component of lipoproteins.
6. Lipids like cholesterol and triglycerides are hydrophobic and must be placed in water-soluble micellar structures (Apolipoproteins) to be transported in the plasma.

7. In the case of endogenous pathways, the lipoproteins are synthesized in the liver from carbohydrates and fats.

High-density lipoprotein (HDL)

What are the important facts about HDL?

1. HDL cholesterol is synthesized and secreted into the liver and intestine.
2. This can be separated by electrophoresis and ultracentrifugation.
3. HDL comprises phospholipids and apolipoprotein (Apo A-1 and Apo A-II), almost 90% of the total protein.
4. The ratio of Apo-A-1 to Apo-A-II is ∼ 3:1 by weight.
   1. HDL from the intestine does not contain Apo-C or Apo-E and only contains Apo-A.
5. The dominant Apoprotein is Apo-A I (67%), followed by Apo-A II, C, and E.
6. This may be responsible for transporting dietary cholesterol.
7. HDL plays a role in transporting cholesterol to the liver from the tissues, where it is excreted in the bile.
8. HDL transports cholesterol to the liver, where cholesterol is the precursor of the bile acids or part of the VLDL component.
9. While lipoproteins transport cholesterol, triglycerides, and other insoluble fats.
10. The ratio of esterified and free cholesterol is 3:1.
11. A decreased level of HDL is atherogenic.

What is the composition of HDL?

1. HDL (Composition) consists of the following:
   1. Cholesterol = 6%.
   2. Cholesterol ester = 13%.
   3. Triglycerides = 3%.
   4. Phospholipids = 28%.
   5. Protein  = 50%.
   6. HDL has very few triglycerides.
   7. There is a high percentage of proteins, phospholipids, and cholesterol.
2. Another source says:
   1. Triglycerides = 5%
   2. Cholesterol = 15%
   3. Phospholipids = 30%
   4. Proteins = 50%

1. HDL level protects against atherosclerosis by removing cholesterol from the arteries and taking it to the liver.
2. HDL and LDL may combine to maintain cellular Cholesterol balance by moving cholesterol into the arteries and HDL removing it from the arteries.
3. HDL-C is good cholesterol proportional to coronary artery disease (CAD) risk.

4. Treatment is not indicated when a high HDL exists with a high cholesterol level.

What are the Functions of High-density lipoprotein (HDL)?

1. HDL is the carrier of cholesterol from the peripheral tissue.
2. HDL carries cholesterol from peripheral tissue to the liver for excretion in the bile, a process known as reverse cholesterol transport.
3. HDL has a protective role by preventing cellular uptake of cholesterol and lipids.
4. HDL protects against cardiovascular diseases.

What is the relationship between HDL and coronary heart disease?

What is the total cholesterol/HDL-cholesterol ratio?

1. The ratio is very important to know the risk of coronary heart disease.
2. A high ratio is associated with increased risk.
3. How to calculate cholesterol/HDL ratio?
   1. Total cholesterol /HDL = Ratio.
   2. The normal ratio should be at least 5:1, and the best is 3:1.

 What is the relationship between the total cholesterol/HDL-cholesterol ratio and risk for Coronary disease?

• An HDL-cholesterol level of 70 mg/dL or greater is associated with longevity.

What is the normal High-density lipoprotein (HDL)?

Source 1

HDL-Cholesterol

• To convert into SI unit x 0.0259 = mmol/L

Source 2

HDL

• Male = >50 mg/dL
• Female = >55 mg/dL

Another source

HDL

• Men = 36 to 65 mg/dL or > 45 mg/dL (>0.75 mmol/L).
• Women = 35 to 80 mg/dL or > 55 mg/dL (>0.91 mmol/L).

What are the abnormal values of HDL?

What are the causes of increased High-Density Lipoprotein (HDL)-C?

1. When it is >60 mg/dL.
2. Chronic liver diseases like cirrhosis, hepatitis, and alcoholism.
3. Long-term vigorous exercise.
4. Familial hyper-alpha-lipoproteinemia.
5. The increased level may be due to some drugs.
   1. Estrogen therapy.
   2. Moderate intake of alcohol.
   3. Insulin therapy.
6. Hypobetalipoproteinemia.

What are the causes of decreased High-Density Lipoprotein (HDL)-C?

1. When it is <40 mg/dL.
2. Poorly controlled diabetes
3. Cholestasis.
4. Chronic renal failure, uremia, and nephrotic syndrome.
5. Hypertriglyceridemia.
6. Familial hypo-alpha-lipoproteinemia.
7. Alpha and beta–lipoproteinemia.
8. The decreased level may also be seen in some of the drugs.
   1. Steroids.
   2. Antihypertensive drugs.
   3. Diuretics.
   4. Beta-blockers.
   5. Thiazide.
9. The secondary causes are:
   1. Stress and recent illnesses like AMI, stroke, and surgery.
   2. Starvation and a nonfasting sample are 5% to 10% lower.
   3. Diabetes mellitus.
   4. Hypothyroidism.
   5. Liver diseases.
   6. Uremia and nephrosis.

How will you summarize the characteristics of the lipoproteins?

Questions and answers: