LIPIDS & LIPOPROTEINS

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LIPIDS

Are commonly referred to as FATS → organic molecules that are fatty acids or derivatives of fatty acids

Composed mainly of C-H bonds

Lipids are composed of?

insoluble ; soluble

Are — in water, but — in organic solvents (chloroform and ether)

non-polar ; non-polar ; insoluble

lipids are insoluble in water because water are polar molecules

Lipids are — and soluble only in — solvents, and — in water.

False.

They require special transport mechanisms for circulation of the blood

T or F

Lipids can circulate properly even without transport mechanism

Lipoproteins

What are the special transport mechanisms of lipids for circulation of the blood?

○ Triglycerides

○ Phospholipids

○ Cholesterol → specifically cholesteryl esters

tricycle, plane, car

Lipids transported by lipoproteins:

C-H bonds ; carboxyl group (-COOH or Carboxylic Acids)

FATTY ACIDS - Linear chains of — that terminate with a —

○ Short-chain (4-6 carbon atoms)

○ Medium-chain (8-12 carbon atoms)

○ Long-chain (more than 12 carbon atoms)

FATTY ACIDS:

Variable in length:

○ Short-chain:

○ Medium-chain:

○ Long-chain:

○ Saturated - no double bonds

○ Unsaturated - contains double bonds

■ Monounsaturated (one double bond)

■ Poly unsaturated (two or more double bonds)

FATTY ACID:

Based on C=C double bonds:

TRUE

T or F

typically the arrangement of a C=C double bond have both hydrogen atoms located on the same side

TRIGLYCERIDES / TRIACYLGLYCEROLS

Contain three fatty acid molecules attached to one molecule of glycerol.

ester bonds

TRIGLYCERIDES / TRIACYLGLYCEROLS:

What attaches the three fatty acid to one molecule of glycerol.

“Neutral Fat”

What are TRIGLYCERIDES / TRIACYLGLYCEROLS called?

the structure of the saturated fatty acids does not contain bends, so TG containing saturated fatty acids is packed more closely

application: TG from animal sources contain saturated fatty acids and are usually solid at room temp.TG are the main storage lipid in man (adipose tissue)

How?

TG containing saturated fatty acids tend to be solid at RT

the structure of the unsaturated fatty acids does contain bends

application: TG from plant sources (like corn, and sunflower seeds) are rich in poly unsaturated fatty acids and they form oils at room temp.

How?

TG containing cis unsaturated fatty acids form oils at RT

Triglycerides (TG)

• TG are the main storage lipid in man (stored in adipose tissue)

• application: when we eat the body converts the extra calories into TG and are stored in the adipose tissue. When the body needs energy, TG will be released

The major type of lipid that the human body stores as an energy reserve.

Triglycerides (TG)

The most common type of fat in the body

PHOSPHOLIPIDS

Are similar in structure to triglycerides except that they only have two fatty acids

• 1 Glycerol + 2 Fatty Acids

contains hydrophilic and hydrophobic components)

Phospholipids are amphipathic molecules. Explain ‘Amphipathic‘.

Head (hydrophilic) - point outward either toward the cytoplasm or the extracellular fluid

Two tails (hydrophobic) - interior of the membrane

Explain the body/structure of Phospholipids.

1. LECITHIN / PHOSPHATIDYLCHOLINE - 70 %

2. SPHINGOMYELIN - 20 %

3. CEPHALIN - 10 %

a. Phosphatidyl ethanolamine

b. Phosphatidyl serine

c. Lysolecithin + Inositol phosphatide

Letche Si Ceph

FORMS OF PHOSPHOLIPID BILAYER

• enumerate + percentage

SPHINGOMYELIN

derived from an amino alcohol called sphingosine

FORMS OF PHOSPHOLIPID BILAYER

The only phospholipid in membranes that is not derived from glycerol.

SPHINGOMYELIN

FORMS OF PHOSPHOLIPID BILAYER

Essential component of cell membranes (RBC and nerve sheath), others are the brain, peripheral nervous tissue and the ocular lenses.

Niemann-Pick disease

Disease caused by reduced breakdown of sphingomyelin, resulting this fat to accumulate in the cells which causes cells to malfunction and eventually die. Sphingomyelin to accumulates in the liver and spleen of patients suffering from this disease.

affects the brain, lungs, liver and spleen

Niemann-Pick disease

characterized by the deficiency of the enzyme acid sphingomyelinase, an enzyme that is found in the lysosomes

acid sphingomyelinase

— is responsible for the conversion of sphingomyelin into its end product/another type of lipid called ceramide

ceramide

end product of lipid

CHOLESTEROL

An unsaturated steroid alcohol containing four rings

Cholesterol sits among the phospholipids of the membrane, with its OH group near the surface.

The OH group on the A ring faces outward and is hydrophilic.

The four rings (A, B, C, D) and side chain tail are buried in the membrane and are hydrophobic.

Explain how Cholesterol is also amphipathic like phospholipids?

Esterified / cholesteryl ester

2 FORMS OF CHOLESTEROL:

Contains OH group

Unesterified / free cholesterol

2 FORMS OF CHOLESTEROL:

does not contain OH

Esterified / cholesteryl ester

2 FORMS OF CHOLESTEROL:

hydrophilic form

Unesterified / free cholesterol

2 FORMS OF CHOLESTEROL:

hydrophobic form

Esterified / cholesteryl ester

2 FORMS OF CHOLESTEROL:

approx 70% of cholesterol in the body

It is not readily catabolized by most cells and, therefore, does not serve as a source of fuel

Explain why Cholesterol does not serve as source of fuel

bile acids promote fat absorption in the intestines by acting as detergents

Why cholesterol can be converted in the liver bile acids (cholic acid and chenodeoxycholic acid)? Explain.

Emulsification

Process of detergent action on particles of dietary fats which causes fat globules to be broken down or be emulsified into minute or microscopic droplets.

by the Adrenal Gland:

• Glucocorticoids (particularly cortisol)

• Mineralocorticoids (particularly aldosterone)

by the Ovaries:

• Estrogen

Enumerate:

Steroid Hormones Cholesterol can be converted to?

cholesterol first being converted into 7-dehydrocholesterol can also be transformed into vitamin D3 in the skin by the radiation of sunlight.

Cholesterol → 7-dehydrocholesterol + radiation of sunlight (skin) → vitamin D3

Explain how cholesterol can also be transformed into vitamin D3.

LECITHIN-CHOLESTEROL ACYLTRANSFERASE (LCAT)

cholesterol ester-making enzyme synthesized in the liver.

Catalyzes the esterification of cholesterol by promoting the transfer of fatty acids from lecithin to cholesterol which results in the formation of lysolecithin and cholesterol ester

Fatty acid transfers from lecithin to cholesterol → lysolecithin + cholesterol ester

Explain Mechanism of LCAT

Apo A-1

Activator of LCAT

HDL

LCAT enables — to accumulate cholesterol as cholesterol ester / esterified cholesterol → this explains why cholesterol ester is abundant in the —

LIPOPROTEINS

Spherical in shape and range in size from 10 to 1200nm

the delivery of fuel to peripheral cells

Main purpose of lipoprotein

cholesterol and phospholipid (both amphipathic)

Surface of lipoprotein

triglyceride and cholesteryl ester (both hydrophobic)

Core of lipoprotein

Chylomicrons, VLDL, LDL and HDL

Major human lipoproteins

DENSITY

Chylomicrons: <0.93

VLDL: <0.93- 1.006

LDL: 1.019 - 1.063

HDL: 1.063 - 1.21

DENSITY (g/mL)

Chylomicrons:

VLDL:

LDL:

HDL:

MOLECULAR WEIGHT (kD)

Chylomicrons: [0.4-30] × 10⁹

VLDL: [10-80] × 10⁶

LDL: 2.75 × 10⁶

HDL: [1.75-3.6] × 10⁵

MOLECULAR WEIGHT (kD)

Chylomicrons:

VLDL:

LDL:

HDL:

DIAMETER (nm)

Chylomicrons: 80-1200

VLDL: 30-80

LDL: 18-30

HDL: 5-12

DIAMETER (nm)

Chylomicrons:

VLDL:

LDL:

HDL:

TOTAL LIPID (% by weigh)

Chylomicrons: 98

VLDL: 89-96

LDL: 77

HDL: 50

TOTAL LIPID (% by weigh)

Chylomicrons:

VLDL:

LDL:

HDL:

TRIGLYCERIDES (% by weigh)

Chylomicrons: 84

VLDL: 44-60

LDL: 11

HDL: 3

TRIGLYCERIDES (% by weigh)

Chylomicrons:

VLDL:

LDL:

HDL:

TOTAL CHOLESTEROL (% by weigh)

Chylomicrons: 7

VLDL: 16-22

LDL: 62

HDL: 19

TOTAL CHOLESTEROL (% by weigh)

Chylomicrons:

VLDL:

LDL:

HDL:

APOLIPOPROTEINS

Are primarily located on the surface of lipoprotein particles

Functions:

• Help maintain the structural integrity of lipoproteins

• 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

Functions of APOLIPOPROTEIN

1. Chemical Methods

2. General Methods

3. Enzymatic Methods

4. CDC Reference Methods

5. Other

Cholesterol Measurement:

ENEMERATE ALL METHODS

Liebermann-Burchardt’s Reaction

Cholesterol is dehydrated and oxidized to a green cholestadienyl monosulfonic acid

Salkowski Reaction

Cholesterol is dehydrated and oxidized to a red cholestadienyl disulfonic acid

Cholesterol Oxidase

Intensity of the resulting color is measured by a spectrophotometer at 500 nm

Gas Chromatography-Mass Spectrometry (GC-MS)

More accurate than the classical and enzymatic methods

Gas Chromatography-Mass Spectrometry (GC-MS)

First, the sample will be volatilized, then the mass-to-charge ratio of cholesterol will be determined by a mass spectrometer

1. Chemical

2. Enzymatic

3. CDC

TAG Measurement:

ENEMERATE ALL METHODS

Van Handel and Zilversmith ; Blue color compound

Colorimetric Method for TAG Measurement + Chromogen used

“Hantzsch Condensation” + Diacetyl lutidine

Fluorometric Method for TAG Measurement + Compound used

Abell-Levy-Brodie-Kendall Method

Saponification: alcoholic KOH

Extraction: hexane

Colorimetry: Liebermann-Burchardt color reagent

This method id the CDC reference method before

Isotope Dilution Mass Spectrometry

A known amount of stable isotope will be added to the sample, and then the ratio of the isotopes will be measured using a mass spectrometer

Glycerol Kinase/ Glycerokinase

Enzymatic Method for TAG Measurement

Modified Van Handel and Zilversmith

● Saponification - alcoholic KOH

● Extraction - Chloroform

• Treatment with silicic acid (to remove phospholipids)

● Colorimetry - Chromotropic acid

● End product: PINK chromophore

Gas Chromatography-Mass Spectrometry (GC-MS)

Hydrolysis of fatty acids on TGY and measurement of glycerol

1. Ultracentrifugation

2. Electrophoresis

3. Polyanion Precipitation Methods

Lipoprotein Measurement:

ENEMERATE ALL METHODS

ULTRACENTRIFUGATION METHODS

The reference method for quantification of lipoproteins

separation of lipoprotein particles based on their densities

Principle of Ultracentrifugation

Agarose Gel

ELECTROPHORETIC METHODS: Most used support medium

densitometer ; lipid-staining dye,

Lipoprotein electrophoretograms are usually visualized using a — after staining with a — such as Oil Red O, Fat Red 7B, or Sudan Black B.

HDL (α-lipoprotein) moves with the α1-globulins

LDL (β-lipoprotein) migrates with the β-globulins

VLDL (pre-β lipoprotein) migrates with the α2- globulins

Results of Electrophoretic Methods

POLYANION PRECIPITATION METHODS

Uses polyanions such as heparin sulfate, dextran sulfate, phosphotungstate which react with positive lipoproteins in the presence of divalent cations such as Ca++, Mg++ and Mn++.

POLYANION PRECIPITATION METHODS

traditionally used to determine HDL using a polyanion so that non-HDL particles will be precipitated, and the remaining lipoprotein particle is the HDL

➔ HDL-C < 35 mg/dL: high risk for coronary heart disease

➔ HDL-C > 60 mg/dL: protective (higher HDL=better)

HIGH-DENSITY LIPOPROTEIN CHOLESTEROL MEASUREMENT

HOMOGENEOUS ASSAYS

first reagent: forms a stable complex with non-HDL lipoproteins

second reagent: releases HDL-C

1. Indirect

2. Beta Quantification

3. Homogenous Mehods

4. Standing Plasma

5. Apolipoprotein Analysis

Enumerate all methods: LOW-DENSITY LIPOPROTEIN CHOLESTEROL

LDL Values

Optimal: <100

Near/Above Optimal: 100-129

Borderline High: 130-159

High: 160-189

Very High: >= 190

LDL Values

Optimal:

Near/Above Optimal:

Borderline High:

High:

Very High:

Desirable: <200

Borderline High: 200-239

High: >= 240

TC Values:

Desirable:

Borderline High:

High:

Low: <40

High: >=60

HDL Cholesterol

Low:

High:

Normal: <150

Borderline High: 150-199

High: 200-499

Very High: >= 500

TAG VALUES

Normal:

Borderline High:

High:

Very High:

• Cigarette Smoking

• Hypertention

• Low HDL

• CHD

• Age

• DM

ENUMERATE RISK FACTORS THAT MODIFY LDL GOALS

ATHEROSCLEROSIS

Condition in which the arteries becomes stiff - The main cause is deposition of cholesterol plaques in the arteries

Myocardial infarction

A portion of the heart stops beating because it does not receive sufficient oxygen supply because the artery is blocked caused by atherosclerosis

Cerebrovascular disease

if plaques develop in the brain

Peripheral vascular disease

if it is dislodged and went to other areas of the body

Hypercholesterolemia

The cholesterol in the blood is high

Familial Hypercholesterolemia

Caused by defective or deficient LDL-receptor gene on chromosome 19.

The resulting defective receptors cannot bind or clear LDL from the circulation. Expected that there is high LDL in the patient

Tendinous - nodule; in particular is a yellowish nodule; it is called tendinous if the nodule is localized in the achilles tendon, xanthoma if localized in elbows, knees or buttocks)

Tuberous xanthomas

Arcus senilis - a white gray/blue ring localized in the cornea

Xanthelasma- yellowish fatty deposits which can be found in the fore eyelids

Symptoms of Familial Hypercholesterolemia

Drugs - Simvastatin, Atorvastatin

LDL Apheresis - removal of blood, removing cholesterol, and then returned back to the patient

Treatment of Familial Hypercholesterolemia

HYPERTRIGLYCERIDEMIA

Can be consequence of familial hypercholesterolemia can be result of secondary causes such as hormonal abnormalities, associated with pancreas(patient with pancreatitis-they experience high triglyceride), adrenal glands, pituitary or of diabetes

HYPERTRIGLYCERIDEMIA

Result of imbalance synthesis and clearance of VLDL in the region

Severe Hypertriglyceridemia

Is caused by deficiency of LPL (need for further hydrolysis of triglyceride to free fatty acid and cholesterol), Apo C2 (cofactor of LPL, LPL can only hydrolyze triglycerides in the presence of Apo C2), or one of the other genes involved in TGY metabolism

>880 mg/dL

Measure of Severe Hypertriglyceridemia that can cause acute and recurrent pancreatitis

Dietary Modification

Fish Oil'

TGY-Lowering Drugs

Treatment for Severe Hypertriglyceridemia