Lipids and Lipoproteins Flashcards
Lipids are commonly referred to as
Fats
Lipids are composed mainly of
C-H bonds; sometimes C-H-O bonds
Important roles of lipids
Storing energy
Aiding in proper digestion and absorption of food
Acting as structural components on cell membranes
Acting as messengers and signaling molecules within the body
Lipid soluble substances
Vitamins A, D, E, K
Lipids can also be used to synthesize other compounds in the body like steroid hormones. True or False?
True
Precursors of Steroids
Cholesterol
Examples of Steroid Hormones
Estrogen
Progesterone
Testosterone
Androgen
Lipids are soluble in water, but insoluble in organic solvents. True or False?
False; Lipids are insoluble in water (nonpolar), but soluble in organic solvents (chloroform and ether)
Special transport mechanism for lipids to be circulated in blood
Lipoproteins
Lipids transported by lipoproteins
Triglycerides (Triacylglycerol/TAG)
Phospholipids
Cholesterol
Components of Phospholipids
Lipids with attached phosphate groups
Components of Cholesterol
Carbon ring structure with alcohol functional groups
Cholesteryl esters
4 major classes of lipids
Fatty acids
Triglycerides
Phospholipids
Cholesterol
Linear chains of C-H bonds that terminate with a carboxyl group (-COOH)
Fatty acids
Components of TAG
3 Fatty Acid + 1 glycerol molecule
Number of carbon atoms in short-chain fatty acids
4-6 carbon atoms
Number of carbon atoms in medium-chain fatty acids
8-12 carbon atoms
Number of carbon atoms in long-chain fatty acids
> 12 carbon atoms
Straight chain compounds with even number of carbons (4-24 carbon atoms)
Dietary fatty acids
Fatty acid without double bonds
Saturated fatty acid
Example of fatty acid
Palmitic acid
Fatty acid with one double bond
Monounsaturated fatty acid
Example of monounsaturated fatty acid
Oleic acid
Fatty acid with two or more double bonds
Polyunsaturated fatty acid
Examples of polyunsaturated acid
Linoleic acid
Linolenic acid
Omega-3
Omega-6
Omega-9
Benefits of omega fatty acids
Lowers the risk of CVD
Consumption of trans fatty acids is good for patients with Congenital Heart Disease. True or False?
False; Consumption of trans fatty acids increases the risk of Congenital Heart Disease
Major dietary trans fatty acid
Elaidic acid
Contain three fatty acid molecules attached to one molecule of glycerol by ester bonds
Triglycerides
Main storage form of lipids
Triglycerides
TAG is also known as
Neutral Fat
Consistency of triglycerides containing saturated fatty acids, which do not have bends in their structure
Solid at RT
Consistency of triglycerides, containing cis unsaturated fatty acids
Oils at RT
Similar with TAG but have two esterified fatty acids
Phospholipids
Phospholipids are amphipathic. True or False?
True
Forms of phospholipids
Lecithin/ Phosphatidylcholine - 70%
Sphingomyelin - 20%
Cephalin - 10%
Composition of myelin in the axons of the neurons
Sphingomyelin
Examples of cephalin
Phosphatidyl ethanolamine
Phosphatidyl serine
Lysolecithin + Inositol Phosphatide
The only phospholipid in membranes that is not derived from glycerol but from an amino alcohol
Sphingomyelin
Sphingomyelin is derived from
Sphingosine
Accumulation of sphingomyelin in the liver and spleen is seen in
Niemann-Pick disease
An unsaturated steroid alcohol containing four rings (A, B, C, and D)
Cholesterol
Amphipathic lipid found on the surface of lipid layers along with phospholipids
Cholesterol
Characteristics of cholesterol
Can be converted in the liver to primary bile acids (Cholic acid and chenodeoxycholic acid)
Can be converted to steroid hormones (glucocorticoids, mineralocorticoids, and estrogens)
Can also be transformed to vitamin D3
2 forms of cholesterol
Esterified / cholesteryl ester (70%)
Unesterified / free cholesterol (30%)
Form of cholesterol that forms an ester bond with another molecule
Esterified / cholesteryl ester
Cholesterol is used as precursor the synthesis of different steroid hormones and vitamin C. True or False?
False; Vitamin D
Increased cholesterol in blood
Hypercholesterolemia
Increase of fats in the blood
Hyperlipidemia
Cholesterol: Animal; _____: Plants
Phytosterol
Cholesterol is not readily catabolized by most cells and, therefore, an excellent source of fuel. True or False?
False; Does not serve as source of fuel
Characteristics of phytosterols
Lower plasma total cholesterol and LDL-C
Raise HDL-C
Catalyzes the esterification of cholesterol
LCAT (Lecithin-Cholesterol Acyltransferase)
Organ that synthesize LCAT
Liver
The activator of LCAT
Apo A-1
Enables HDL to accumulate cholesterol as cholesterol ester
LCAT (Lecithin-Cholesterol Acyltransferase)
Liberating cholesterol or breaking ester bonds
Saponification
Importance of APO A-1 and HDL
APO A-1 is a composition of HDL which helps in the activation of LCAT and esterification of cholesterol
Cholesterol can be converted in the liver to primary bile acids. True or False?
True
Cholesterol can be converted to steroid hormones. True or False?
True
Cholesterol can be transformed to vitamin K. True or False?
False; Vitamin D3
Examples of primary bile acids
Cholic acid
Chenodeoxycholic acid
Examples of steroid hormones
Glucocorticoids
Mineralocorticoids
Estrogens
Macromolecule of lipids and proteins
Lipoproteins
It constitutes the body’s “petroleum industry”
Lipoproteins
Shape and size of lipoproteins
Spherical; 10-1200 nm
Lipoprotein surface is composed of
Amphipathic phospholipids and
cholesterol
Lipoprotein core is composed of
Neutral triglycerides and cholesteryl ester
Protein associated to plasma lipoproteins
Apolipoproteins
Where does apolipoproteins are located?
Surface of lipoprotein particles
Functions of apolipoproteins
Help maintain the structural integrity of lipoproteins
Help to keep lipids in solution during circulation through the blood stream
Interact with specific cell-surface receptors and direct the lipids to the correct target organs and tissues in the body
Serve as ligands for cell receptors and as activators / inhibitors of the various enzymes that modify lipoprotein particles
Aid in the solubilization of lipids in the circulation
Responsible for the ability of apolipoproteins to bind to lipids
Amphipathic helix
Major protein of HDL
Apo A
Function of Apo A-I
Major activator of LCAT
Function of Apo A-II
Activates hepatic lipase
Function of Apo A-IV
Cofactor of LCAT
Principal protein of LDL, VLDL, and chylomicrons
Apo B
Function of Apo B-100
Binds to LDL/VLDL cell receptor
Function of Apo B-48
Structural role in chylomicrons
Major protein of VLDL
Apo C
Function of Apo C-I
Activates LCAT
Function of Apo C-II
Potent activator of LPL
Function of Apo C-III
Regulates rate of clearance of TAG – rich lipoprotein (inhibit LPL)
Apo A-III, thin line apolipoprotein, serves as lysolecithin carrier
Apo D
Function of Apo E
Serves as a ligand for the LDL receptor and the chylomicron remnant receptor
Genotypes of Apo E
Apo E2
Apo E3
Apo E4
Apo E2 is an indication of
Increased risk for developing Type III hyperlipoproteinemia
Most common Apo E genotype that doesn’t seem to influence risk
Apo E3
Apo E4 is an indication of
Increased risk for developing Alzheimer’s disease
Main purpose of lipoproteins
Delivery of fuel to peripheral cell
Largest lipoprotein particles
Chylomicrons
Diameter of chylomicrons
80-1200 nm
Least dense lipoprotein particles
Chylomicrons
Density of chylomicrons
<0.93 g/mL
Appearance of chylomicrons in plasma when stored for hours at 4 degCel
Turbid (milky appearance)
Apolipoprotein in chylomicrons
Apo B-48
Organ responsible for the production of chylomicrons
Intestine
Chylomicrons are rich in phospholipids. True or False?
False; rich in triglycerides
Principal role of chylomicrons
Transportation of triglycerides and cholesterol to the peripheral tissue and liver
VLDLs are produced primarily by the
Liver
Apolipoproteins in VLDL
Apo B-100
Apo E (MAIN)
Apo C
Appearance of VLDL in fasting hyperlipidemic plasma specimens
Turbid; without a creamy top layer
Principal function of VLDL
Carry and transfer endogenous triglycerides from liver to peripheral tissue for energy utilization and storage
Intermediate-Density Lipoproteins (IDLs) are also known as
VLDL remnants
(After conversion of VLDL to LDL)
IDLs are primarily seen in normal plasma. True or False?
False; cannot be seen in normal plasma
Elevated IDLs are seen in patients with
Type III hyperlipoproteinemia
LDLs are also known as
Beta lipoprotein
Primary apolipoprotein in LDLs
Apo B-100
Most cholesterol rich lipoproteins
LDLs
Organ that synthesize LDLs
Liver (consequence of the lipolysis of VLDL)
LDLs are readily taken up by cells via the LDL receptor in the liver and peripheral cells. True or False?
True
Macrophages filled with lipids
Foam cells
LDLs are larger than chylomicrons and VLDL. True or False?
False; smaller
Most atherogenic lipoproteins
LDLs
Foam cells are culprit to
Hypercholesterolemia leading to atherosclerosis
Smaller and denser LDLs are marker of
Cardiovascular disease risk
LDL-like particle that contain one molecule of apo (a) linked to apo B-100
Lipoprotein (a)
Characteristics of Lp(a)
Larger than LDL and has a higher lipid content and a slightly lower density
Lp(a) is related structurally to plasminogen. True or False?
True
Lp(a) levels vary among individuals in a population but remain relatively constant within an individual. True or False?
True
Indication of elevated Lp(a) level (>30 mg/dL)
Increased risk of premature CHD and stroke
Importance of measuring Lp(a)
Useful in patients with a strong family history of CHD, particularly in the absence of other known risk factors, such as increased LDL-C
Lipoprotein (a) is also known as
Sinking pre-B lipoprotein
HDLs are also known a
Good cholesterol
Alpha lipoprotein
Smallest lipoprotein particle
HDLs
Most dense lipoprotein particle
HDLs
Diameter of HDLs
5-12 nm
Density of HDLs
1.063-1.21 g/mL
Shape of HDL
Disk-shaped
Spherical
HDLs are synthesized by
Liver and intestines
Apolipoprotein in HDLs
Apo A-1
Two major types of HDL
HDL 2
HDL 3
Lipoprotein with Anti-atherogenic property
HDLs
Characteristics of HDL 2
Larger in size, richer in lipid (more efficient vehicles for the transfer of cholesterol from peripheral tissue to the liver)
1.063 – 1.125g/mL (less dense)
Characteristics of HDL 3
Smaller and less efficient
1.125 – 1.21 g/mL (denser)
Represents newly secreted HDL
Discoidal HDL
Composition of Discoidal HDL
2 molecules of Apo A-I
Function of Discoidal HDL
Removes excess cholesterol from peripheral cells through a mechanism called Reverse Cholesterol Transport
Abnormal lipoprotein found in patients with obstructive biliary disease
Lipoprotein X
Abnormal lipoprotein found in patients with LCAT deficiency
Lipoprotein X
Composition of Lipoprotein X
90% phospholipids, unesterified cholesterol, and very little cholesterol
Lipoprotein X is formed by what organ?
Liver (within bile canaliculi)
Lipoprotein X is removed by
RES
Spleen
Kidney
Beta-VLDL is also known as
Floating Beta Lipoprotein
Beta-VLDL levels in patients with type III hyperlipoproteinemia
Elevated/Accumulates
Preferred sample for lipoprotein assays
Ethylenediaminetetraacetic acid (EDTA) plasma
Most preferred serum sample
Collected in SST; defibrinated
Fibrinogen can interrupt in electrophoresis and spectrophotometry
Plasma or serum is used to test for
TC
TAG
HDL-C
LDL-C
Why do we need to fast for 12-14 hours before collecting specimen for lipid testing?
Because chylomicrons can cause turbidity and cause false increased result. Chylomicrons are almost completely cleared within 6-9 hours
TC and HDL-C can use non-fasting specimen. True or False?
True
According to NCEP guidelines, patients must be seated for _____ before sampling to prevent hemoconcentration
5 minutes
Long period storage of serum and plasma
-70 degree Celsius or lower
Short-term storage (up to a month or two)
-20 degree Celsius
Major Pathways involved in Lipoprotein Metabolism
Lipid absorption pathway
Exogenous pathway
Endogenous pathway
Reverse cholesterol transport pathway
Principal way that peripheral cells maintain their cholesterol equilibrium
Reverse cholesterol transport pathway
Women have higher HDL-C levels and lower total cholesterol and triglyceride compared to Men due to sex hormone levels. True or False?
True
HDL-C remain stable after the onset of puberty and drop in women with the onset of menopause. True or False?
False; do not drop in women with the onset of menopause
Circulating levels of total cholesterol, LDL- C, and triglycerides in young children are generally much higher than those seen in adults True or False?
False; lower than adults
Values vary according to location. True or False?
True
Reference value for total cholesterol
140–200 mg/dL (3.6–5.2 mmol/L)
Reference value for HDL-C
40–75 mg/dL (1.0–2.0 mmol/L)
Reference value for LDL-C
50–130 mg/dL (1.3–3.4 mmol/L)
Reference value for triglycerides
60–150 mg/dL (0.7–1.7 mmol/L)
Diseases associated with abnormal lipid concentrations
Dyslipidemias
Dyslipidemias are associated with CHD and arteriosclerosis. True or False?
True
Genetic and acquired dyslipidemias may lead to lipid deposits in the liver and kidney, resulting in impaired function of these vital organs. True or False?
True
Nodules due to lipid deposition in the skin
Xanthomas tendinous
Cardiovascular disorders due to atherosclerosis
Peripheral Vascular Disease (PVD)
Coronary Artery Disease (CAD)
Cerebrovascular Disease (CVD)
Increased amount of lipids in the blood
Hyperlipidemia
Decreased amount of lipids in the blood
Hypolipidemia
Narrowing and hardening of artery due to the deposition of lipids in the artery that later forms fatty streaks and plaques resulting to thrombosis
Atherosclerosis
Diseases associated with elevated lipoprotein levels
Hyperlipoproteinemia
Used to describe individuals for whom the cause of hypercholesterolemia is likely multifactorial
Polygenic (nonfamilial) hypercholesterolemia
What does multifactorial mean?
Not only limited in the family, may include environmental factors etc.
Increased cholesterol in the blood
Hypercholesterolemia
Cause of familial hypercholesterolemia
Defective or deficient LDL-receptor gene on chromosome 19
Function of Chromosome 19
Responsible for the protein synthesis of the said LDL receptor
How does defective or deficient LDL-receptor gene cause high LDL levels?
The resulting defective receptors cannot bind or clear LDL form the circulation
A.K.A. Type III Hyperlipoproteinemia
Familial dysbetalipoproteinemia
Cause of Familial dysbetalipoproteinemia
Accumulation of cholesterol-rich B-VLDL and chylomicron remnants
Tests for familial dysbetalipoproteinemia
Ultracentrifugation: VLDL (high)
Electrophoresis: LDL (high)
Is an extremely rare autosomal recessive disorder wherein phytosterols (plant sterols) are absorbed and accumulate in plasma and peripheral tissues
Sitosterolemia
Cause of sitosterolemia
Mutations in the ABCG8 or ABCG5 gene, both of which are located at chromosome 2p21
Treatment for sitosterolemia
Restrict dietary phytosterol intake or medications to limit sterol accumulation
Abetalipoproteinemia is also known as
Bassen-Kornzweig Syndrome
Defective RBC seen in Bassen-Kornzweig Syndrome
Acanthocytes (thorny-shaped RBCs)
Cause of Abetalipoproteinemia
Defective Apo B synthesis
In Abetalipoproteinemia, VLDL, LDL and CMs are all found in plasma. True or False?
Not found
Abetalipoproteinemia is associated with defects in absorption of Fat-soluble vitamins AEK. True or False?
True
Abetalipoproteinemia is characterized by
Cerebellar ataxia
Acanthocytosis
Fat malabsorption
Diseases associated with decreased lipoprotein levels
Hypolipoproteinemia
Cause of Hypobetalipoproteinemia
Apo-B deficiency resulting from point mutation in Apo-B
A rare autosomal recessive disorder characterized by very low level of HDL due to a mutation in the ABCA1 gene on chromosome 9
Tangier Disease
Differentiate Hypobetalipoproteinemia and Tangier Disease
Affected LDL: Hypobetalipoproteinemia Affected HDL: Tangier Disease
Cause of Lecithin:Cholesterol Acyltransferase (LCAT) Deficiency
Mutation in the LCAT gene
2 forms of LCAT deficiency
Classic (or complete) familial LCAT deficiency
Milder partial LCAT deficiency (fish-eye disease)
Cause of Fish-eye Disease
LCAT deficiency
Fish-eye Disease is characterized by
Corneal opacities
Normochromic anemia
Renal failure
How does LCAT deficiency cause Fish-eye Disease?
When problems in LCAT occur, it can’t esterify cholesterol, therefore free cholesterol accumulates in the sclera
Results to inability to clear chylomicron particles, creating the classic type 1 chylomicronemia syndrome
Lipoprotein Lipase (LPL) Deficiency
Deficiency of Apo C-II also results to chylomicronemia. True or False?
True
Lab findings of LPL deficiency
TAG = 10,000 mg/dL or 113 mmol/L (postprandial result)
How does LPL deficiency cause chylomicronemia?
Very High TAG value basically because it is not hydrolyzed by LPL
Lipoprotein Lipase is absent which destroys lipoproteins
Presence or abundance of chylomicrons in the blood
Chylomicronemia
Disease associated with too many chylomicrons in the circulation
Chylomicron Retention Disease (Anderson’s Disease)
Anderson’s Disease is characterized by
Hypocholesterolemia
Chronic diarrhea
Failure to thrive
Deficiency of fat-soluble vitamins (Vit E in particular)
Findings in Anderson’s Disease
Fat malabsorption
Low levels of plasma lipids
Conversion factor for cholesterol
0.026
Conversion factor for triacylglycerol
0.0113
Principle of chemical methods in cholesterol measurement
Dehydration and oxidation of cholesterol to form a colored compound
Chemical methods in cholesterol measurement
Liebermann Burchardt Reaction
Salkowski Reaction
End product of Liebermann Burchardt Reaction
Cholestadienyl Monosulfic Acid
End color of Liebermann Burchardt Reaction
Green
Positive result of Liebermann Burchardt Reaction indicates
Presence of cholesterol
Color developer mixture for Liebermann Burchardt Reaction
Glacial acetic acid
Acetic anhydride
Concentrated sulfuric acid
End product of Salkowski Reaction
Cholestadienyl Disulfic Acid
End color of Salkowski Reaction
Red
Positive result of Salkowski Reaction indicates
Presence of cholesterol
One-step method for cholesterol determination
(C) COLORIMETRY (Pearson, Stern, and Mac Gavack)
Two-step method for cholesterol determination
(EC) EXTRACTION + COLORIMETRY (Bloors)
Three-step method for cholesterol determination
(SEC) SAPONIFICATION + EXTRACTION + COLORIMETRY (Abell-Kendal)
Four-step method for cholesterol determination
(SEPC/SPEC) SAPONIFICATION + EXTRACTION + PRECIPITATION + COLORIMETRY (Schoenheimer, Sperry, Parekh, and Jung)
CDC Reference Method for Cholesterol Determination
Abell, Levy, and Brodie Method
Principle of Abell, Levy, and Brodie Method
Uses hexane extraction/petroleum ether after hydrolysis with alcoholic KOH followed by reaction with Liebermann-Burchardt color reagent
Enzymatic Method for Cholesterol Determination
Cholesterol Oxidase Reaction
CDC Reference Method for Triglyceride Measurement
Saponification: Alcoholic KOH
Extraction: Chloroform
Treatment with silicic acid (to remove phospholipids)
END PRODUCT: PINK CHROMOPHORE
Chemical Methods for Triglyceride Measurement
Colorimetric Method
Fluorometric Method
Colorimetric Method for Triglyceride Measurement
Van Handel Zilversmith
End-product of in Van Handel Zilversmith Method
Chromogen (blue color compound)
Fluorometric Method for Triglyceride Measurement
Hantzsch Condensation Method
End-product of Hantzsh-Condensation Method
Diacetyl lutidine compound
Enzymatic Method for Triglyceride Measurement
Glycerol Kinase Method
The reference method for quantification of lipoproteins
Ultracentrifugation Methods
Ultracentrifugation Method is based on
CHON and TAG contents of lipoproteins
The most commonly used support medium in Electrophoretic Methods
Agarose gel
Medium used for the separation of lipoprotein classes, subclasses, and the apolipoproteins
Polyacrylamide gels
During electrophoresis, HDL (α-lipoprotein) migrates with
α1-globulins
During electrophoresis, LDL (β-lipoprotein) migrates with
β-globulins
During electrophoresis, VLDL (pre-βlipoprotein) migrates with
β2-globulins
Lipoprotein electrophoretograms are usually visualized with a lipid-staining dye such as
Oil Red O
Fat Red 7B
Sudan Black B
Explain the Chemical Precipitation Method for Lipoproteins
Most common for HDL using polyanions (heparin and dextran sulfate) together with divalent cations (manganese or magnesium)
Explain the Chromatographic Method for Lipoproteins
Take advantage of size differences in molecular sieving methods or composition in affinity methods
Explain the Preparative Ultracentrifugation Method for Lipoproteins
Uses sequential density adjustments of serum to fractionate major and minor lipoprotein classes
Explain the Density Gradient Methods for Lipoproteins
Non-equilibrium
Separations are based on the rate of flotation
Equilibrium
Lipoproteins separate based on their density
Explain the Immunochemical Method for Lipoproteins
Using antibodies specific to epitopes on the apolipoproteins
HDL-C value that indicates high risk for Coronary Heart Disease (CHD)
<35-40 mg/dL
HDL-C value that indicates Borderline risk for CHD
40–59 mg/dL
HDL-C value that indicates Protective for CHD
> 60 mg/dL
The most popular method for HDL-C
Homogenous Assays
Fully automated two-reagent procedures in Homogenous Assays for HDL-C
First reagent: forms a stable complex with non-HDL lipoproteins
Second reagent: releases HDL-C
Reference method for HDL-C by CDC
Three-step Procedure
- Involves ultracentrifugation to remove VLDL
- Uses heparin manganese precipitation from the 1.006 g/mL infranate to remove LDL
- Analyze supernatant cholesterol by the Abell-Kendall assay
Indirect Methods for LDL-C
Friedewald Method
De Long Method
Only use De Long Method when the triglyceride (TGY) value is greater than equal to 400 mg/dL. True or False?
True
Reference Method for LDL-C
Beta Quantification
Method that is not suitable for fasting since LDL-C will be directly measured and not computed
Homogeneous Direct LDL-C Method
Explain the Standing Plasma Test for Chylomicrons
2 mL plasma is placed into a 10×75-mm test tube and allowed to stand in the refrigerator at 4°C undisturbed overnight
Result:
(+) floating “creamy” layer
(-) VLDL
These techniques rely on measurement of the turbidity caused by apolipoprotein antigen–antibody complexes
Turbidimetric assays
Nephelometric assays
Enzyme-linked immunosorbent assay (ELISA)
Radial immunodiffusion (RID)
Radioimmunoassay (RIA)
Cigarette smoking helps build up cholesterol plaques. True or False?
True
The build-up of cholesterol plaque in the surface of the endothelial wall of the artery/blood vessels causing decreased diameter and decreased pressure. True or False?
False; increased pressure
POCT test (device) of common lipids and lipoproteins
Compact Analyzers
Analysis done in Phospholipid measurement
Quantitative measurements
Enzymatic analysis
Explain the enzymatic analysis for Phospholipid measurement
Measures choline-containing phospholipids, lecithin, lysolecithin, and sphingomyelin using phospholipase D, choline oxidase, and horseradish peroxidase
Fatty acid measurement is commonly analyzed by
Gas-Liquid Chromatography