Cholesterol Measurement Methods
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Questions and Answers

What is the major protein found in HDL?

Apo A-1

What is the major protein found in LDL?

Apo B-100

What is the independent risk factor associated with impaired plasminogen activation?

Lp(a)

Match the following Apo proteins with their major lipoprotein:

<p>Apo A-1 = HDL Apo B-100 = LDL Lp(a) = Independent risk factor associated with impaired plasminogen activation</p> Signup and view all the answers

What is used in the LDL cholesterol test methodology to precipitate LDL and VLDL cholesterol?

<p>Dextran sulfate-magnesium chloride or heparin sulfate-manganese chloride</p> Signup and view all the answers

What is the Liebermann-Burchardt Reaction used for?

<p>Hydrolysis of fatty acids on triglycerides and measurement of glycerol</p> Signup and view all the answers

Which method uses the L-B reaction for measuring cholesterol?

<p>Bloors Method: 2 Step Principle</p> Signup and view all the answers

Ultracentrifugation is used for quantitative purposes and preparative isolations.

<p>True</p> Signup and view all the answers

A lipase-free reagent is incubated for triglyceride measurement to measure only endogenous free ____________.

<p>glycerol</p> Signup and view all the answers

What is the primary constituent of all living cells and is composed mostly of C-H bonds?

<p>Lipids</p> Signup and view all the answers

What is the classification of fatty acids based on their length?

<p>All of the above</p> Signup and view all the answers

Phospholipids contain phospholipid head groups at the 3rd position.

<p>True</p> Signup and view all the answers

Endogenous lipid metabolism involves releasing fatty acids to the cells for __________.

<p>energy</p> Signup and view all the answers

Match the following lipoproteins with their descriptions:

<p>Chylomicrons = Largest lipoproteins formed in the intestines, contain triglycerides VLDL = Carries endogenous triglycerides synthesized in the liver IDL = Transitional form formed from VLDL and further modified in the liver LDL = Transports a large amount of endogenous cholesterol, known as 'bad cholesterol' HDL = Synthesized in intestine and liver, known as 'good cholesterol'</p> Signup and view all the answers

Study Notes

Lipids

  • Lipids are constituents of all living cells, composed mostly of C-H bonds
  • They serve as energy storage for excess calories, and are precursors for steroid hormones, prostaglandins, leukotrienes, and lipoxins

Classification of Fatty Acids

  • Based on length:
    • Short: 4-6 carbon atoms
    • Medium: 8-12 carbon atoms
    • Long: more than 12 carbon atoms
  • Based on the number of C=C double bonds:
    • Saturated: no double bonds
    • Monounsaturated: one double bond
    • Polyunsaturated: contain 2 or more double bonds

Triglycerides

  • Contain 3 fatty acids attached to 1 molecule of glycerol by ester bonds
  • No charged groups, water insoluble, neutral lipid

Phospholipids

  • Contain 2 fatty acids attached to 1 molecule of glycerol
  • 3rd position contains phospholipid head groups, which are amphipathic (hydrophobic head and hydrophilic tail)

Cholesterol

  • Unsaturated steroid alcohol containing 4 rings and a single C-H side chain tail
  • Synthesized from acetyl-CoA
  • Also an amphipathic lipid

Classification of Lipoproteins

  • Chylomicrons:
    • Largest lipoproteins, lowest density
    • Contain 86% triglyceride, 5% cholesterol, 7% phospholipid, and 2% apolipoprotein
    • Apoproteins B-48, A-I, C-I, C-II, and C-III on their surface
  • VLDL (Very-Low-Density Lipoprotein):
    • Carries endogenous triglycerides synthesized in the liver
    • Composed of 55% triglycerides, 19% cholesterol, 18% phospholipid, and 8% apolipoprotein
    • Apoproteins B-100, C-I, C-II, C-III, and E on their surface
  • IDL (Intermediate-Density Lipoprotein):
    • Transitional form, formed from VLDL and modified in the liver to LDL
    • Carries endogenous triglycerides and cholesterol esters
    • Composed of 23% triglycerides, 38% cholesterol, 19% phospholipid, and 19% apolipoprotein
    • Apoproteins B-100, and some E on their surface
  • LDL (Low-Density Lipoprotein):
    • Also known as "bad cholesterol"
    • Transports a large amount of endogenous cholesterol
    • Composed of 50% cholesterol, 22% phospholipids, 6% triglycerides, and 22% protein
    • Apoprotein B-100 on their surface
  • HDL (High-Density Lipoprotein):
    • Also known as "good cholesterol"
    • Synthesized in the intestine and liver cells
    • Recycled chylomicron and VLDL molecules
    • Composed of 50% protein, 28% phospholipids, 19% cholesterol, and 3% triglycerides
    • Apoproteins A-I, mainly, and A-II on their surface
  • Lp(a) (Lipoprotein(a)):
    • Composed primarily of cholesterol esters, phospholipids, and apolipoprotein (a) and B-100
    • Elevated levels are associated with increased risk for coronary heart disease, myocardial infarction, and cerebrovascular disease

Lipid Disorders

  • Arteriosclerosis: deposition of esterified cholesterol in artery walls
  • CAD, PVD, CVD: associated with abnormal lipid metabolism
  • Dyslipidemia: abnormal levels of lipids in the blood
  • Hypercholesterolemia: high levels of cholesterol in the blood
  • Hypertriglyceridemia: high levels of triglycerides in the blood
  • Combined hyperlipidemia: high levels of both cholesterol and triglycerides in the blood

Lipid and Lipoprotein Analyses

  • Decision cutpoints used to characterize CHD risk developed by NCEP
  • Standardization programs facilitate reliable classification of patients
  • Pre-analytical considerations:
    • Age: cholesterol levels increase with age
    • Sex: women have lower levels than men except in childhood and early 50's
    • Season: cholesterol levels are slightly higher in cold periods
    • Food intake: daily intake of fat increases cholesterol levels
    • Acute illness: recommended to wait 8 weeks after any form of trauma or acute bacterial/viral infection and 3-4 months after child birth
    • Lifestyle: higher in sedentary and poor diet habits
    • Prolonged venous occlusion: leads to an increase in cholesterol by 10-15%

Cholesterol Measurement

  • Non-enzymatic (chemical) method: Abell-Kendall or Bloors method
  • Enzymatic method: Glycerol Kinase method
  • Reference method: GC-MS

Triglyceride Measurement

  • Non-enzymatic (chemical) method: chloroform and phospholipids removal by zeolite absorption
  • Enzymatic method: Glycerol Kinase method
  • Reference method: GC-MS

Lipoprotein Measurement

  • Polyanion precipitation: lipoproteins are precipitated with polyanions (heparin sulfate, dextran sulfate, and phosphotungstate)

  • Electrophoresis: used to identify rare familial disorders

  • Ultracentrifugation: preparative ultracentrifugation for quantitative purposes and preparative isolations

  • Immunochemical methods: use antibody-coated plates for specific epitopes on apolipoproteins### Lipoprotein Measurement

  • Immunoturbidimetry is the most common method used to measure apolipoproteins, which can be easily adapted to spectrophotometric analyzers.

  • Immunonephelometry measures light scattering, but may be affected by larger triglyceride-rich lipoproteins and VLDL.

  • Other immunochemical methods include ELISA, Radial Immunodiffusion, and RIA.

Hyperlipoproteinemias

  • Type I: Elevated chylomicrons, characterized by a creamy layer of chylomicrons over clear serum, extremely elevated triglycerides, and normal to moderately elevated total cholesterol.
  • Type IIa: Increased LDL, characterized by clear serum, generally elevated total cholesterol, and normal triglycerides.
  • Type IIb: Increased LDL and VLDL, characterized by clear or slightly turbid serum, elevated total cholesterol, and elevated triglycerides.
  • Type III: Increased IDL, characterized by a creamy layer sometimes present over a turbid layer, elevated total cholesterol, and Apo E-II increased.
  • Type IV: Increased VLDL, characterized by turbid serum, moderately to severely elevated triglycerides, and normal to slightly elevated total cholesterol.
  • Type V: Increased VLDL with increased chylomicrons, characterized by turbid serum with a creamy layer, severely elevated triglycerides, and slightly to moderately elevated total cholesterol.

Familial Hyperlipoproteinemias

  • Familial combined hyperlipidemia (FCHL): Characterized by increased plasma levels of total cholesterol, triglyceride, or both, and increased Apo B-100.
  • Hyperapobetalipoproteinemia: Characterized by normal or moderate elevation of LDL cholesterol, elevated apo B-100, and VLDL and apo B-100 overproduction in the liver.
  • Familial hypertriglyceridemia: Characterized by moderate elevation of triglyceride with excess production of VLDL.
  • Familial hypercholesterolemia: Characterized by increased LDL cholesterol, normal or slightly increased triglyceride, and slightly decreased HDL cholesterol.

Secondary Lipoproteinemia

  • Many conditions can cause abnormal lipoprotein metabolism, including diabetes mellitus, hyperthyroidism, obesity, pregnancy, nephrotic syndrome, pancreatitis, alcoholism, and myxedema.

Hypolipoproteinemias

  • Abetalipoproteinemia: Characterized by very low total cholesterol, undetectable triglyceride, and absent LDL and Apo B-100.
  • Hypobetalipoproteinemia: Characterized by inability to synthesize apo B-100 and apo B-48, low total cholesterol, and normal to low triglyceride.
  • Hypoalphalipoproteinemia: Characterized by severely elevated triglyceride and low HDL.
  • Tangier disease: Characterized by absent HDL, very low apo A-I and apo A-II, low LDL, low total cholesterol, and normal to slightly increased triglyceride.

Apo A-1, Apo B, and Lp(a) Clinical Significance

  • Apo A-1 is antiatherogenic, activates lecithin-cholesterol acyltransferase (LCAT), and removes free cholesterol from extrahepatic tissues.
  • Apo B-100 is associated with increased risk of coronary artery disease.
  • Lp(a) is an independent risk factor associated with impaired plasminogen activation and decreased fibrinolysis.

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Description

This quiz covers different methods for measuring cholesterol, including the Liebermann-Burchardt reaction and Bloors method.

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