LIPIDS AND LIPOPROTEINS

Four Major Lipids

Phospholipids

Fatty Acids

Triglycerides

Cholesterol

PHOSPHOLIPIDS

Contain TWO FA and a PHOSPHOLIPID HEAD group

Amphipatic (hydrophobic and

hydrophilic ends) Main component of lipid bilayer

FATTY ACIDS

LINEAR chains of C-H bonds that

terminate with a carboxyl group (-

COOH) Types of FA:

o Saturated o Monounsaturated o Polyunsaturated

TRIGLYCERIDES

Contain THREE FA attached to one

molecule of GLYCEROL SOLID: Saturated FA from animals

LIQUID: Unsaturated FA from plants

CHOLESTEROL

Unsaturated steroid alcohol containing FOUR RINGS and a SINGLE

C-H side chain HYDROPHOBIC in nature, except on

the HYDROXYL part of the A-RING AMPHIPATIC: found on the

SURFACE of lipid layers ESTERIFIED FORM: CHOLESTERYL

ESTER (hydrophobic)

Converted to:

o 10 BILE ACIDS Cholic acid

Chenodeoxycholic acid: detergents

o STEROID HORMONES Adrenal

Testis

Ovary o VITAMIN D3

Irradiation of skin

LIPOPROTEINS Composed of lipids and proteins

(APOLIPOPROTEINS)

SURFACE: amphipathic (P and C)

CORE: hydrophobic (T and CE)

*Lipid content = larger core region = lighter density

Chylomicrons

VLDL

LDL

HDL

APOLIPOPROTEINS

CHON components of lipoproteins

Maintains structural integrity of

lipoproteins

LIGANDS for cell receptors Activators and inhibitors of enzymes

With AMPHIPATHIC HELIX

o Protein segments in coils accounting to the ability to

bind to lipids

Apo A1

Apo B (Apo B-100 and Apo B-48)

Apo C (I, II, III) Apo E (Apo E2, E3 and E4): affects

lipoprotein metabolism

MAJOR ENZYMES OF CLINICAL

SIGNIFICANCE

ENZYME CLINICAL SIGNIFICANCE

Acid phosphatase (ACP)

Prostatic Carcinoma

Alanine aminotransferase (ALT)

Hepatic Disorder

Aldolase (ALD) Skeletal Muscle Disorder

Alkaline phosphatase (ALP)

Hepatic Disorder Bone Disorder

Amylase (AMS) Acute pancreatitis

Angiotensin-converting enzyme (ACE)

Blood Pressure regulation

Aspartate amino-transferase (AST)

Myocardial infarction Hepatic Disorder Skeletal Muscle Disorder

Chymotrypsin (CHY) Chronic pancreatitis insufficiency

Creatinine kinase (CK)

Myocardial Infarction Skeletal Muscle Disorder

Elastase-1 (E1) Chronic Pancreatitis Insufficiency

Glucose-6-phosphate dehydrogenase (G-6-PD)

Drug induced hemolytic anemia

Glutamate dehydrogenase (GLD)

Hepatic disorder

γ-glutamyltransferase (GGT)

Hepatic disorder

Glutathione-S-transferase (GST)

Hepatic Disorder

Glycogen phosphorylase (GP)

Acute myocardial infarction

Lactate Dehydrogenase (LDH)

Myocardial infarction Hepatic Disorder Hemolysis Carcinoma

Lipase (LPS) Acute Pancreatitis

5’-Nucleotidase Hepatic Disorder

Pseudocholinesterase (PChE)

Organophosphate poisoning Genetic variants Hepatic Disorder Suxamethonium sensitivity

Pyruvate Kinase (PK)

Hemolytic anemia

Trypsin (TRY) Acute Pancreatitis

CHYLOMICRONS Largest and the least dense

(1200nm) Account to the turbidity of post

prandial plasma Readily FLOAT on top of plasma

(creamy layer)

Deliver dietary lipids to hepatic and peripheral cells

VERY LOW DENSITY LIPOPROTEINS

(VLDL)

CARRIERS OF ENDOGENOUS

TRIGLYCERIDES Transfer TG from the liver to the

periphery

Causes turbidity in fasting hyperlipidemic plasma

Increases o Diet CHO, Sat. FA o Hepatic synthesis of TG o VLDL

LOW DENSITY LIPOPROTEINS (LDL)

More cholesterol rich Formed due to lipolysis of VLDL

PROARTHEROGENIC LIPOPROTEIN HIGH DENSITY LIPOPROTEIN (HDL)

SMALLEST and MOST DENSE

lipoprotein Synthesized by both liver and

intestines

Delivers lipids to the liver With ANTIATHEROGENIC property Discoidal (most active form) or

spherical (HDL2 and HDL3)

MINOR LIPOPROTEINS

Lipoprotein A

LDL-like particles Confer increased risk of CHD and stroke HOMOLOGOUS to plasminogen

o Compete for binding sites o Promotes clotting = Myocardial

Infarction

Intermediate Density Lipoprotein Formed from catabolism of VLDL

Precursor for LDL synthesis

LIPOPROTEIN METABOLISM

1. EXOGENOUS LIPOPROTEINS (Chylomicrons)

2. ENDOGENOUS LIPOPROTEINS (VLDL, HDL)

3. Chylomicrons – TG = chylomicron remnants

4. VLDL – TG = LDL

Important Enzymes:

LPL (lipoprotein lipase) LCAT (Lecithin-cholesterol

acetyltransferase) ACAT (acyl-CoA: Cholesterol Acyl

Transferase) HMG CoA reductase (3-hydroxy-3-

methyl-glutaryl-CoA reductase) CHOLESTEROL MEASUREMENT

1. Enzymatic Method: Cholesterol

Oxidase and Esterase 2. Non-enzymatic: Liebermann-

Burchard

Cholesterol +H2SO4 + acetic anhydride = green solution

ABELL KENDALL

HYDROLYSIS with KOH Extraction of

unesterified

cholesterol with

petroleum ether

Measurement using L-B reaction

TRIGLYCERIDE MEASUREMENT

1. Enzymatic Method: GLYCEROL KINASE (Lipase,

GK, PK, LD) Disappearance of NADH at

340 nm

2. Non-enzymatic: Extraction of lipids using

chloroform

A. VAN HANDELL AND

ZILVERSMITH

Hydrolysis with KOH

(Glycerol + FA) Formaldehyde +

chromotropic (blue

solution)

B. HANTZCH CONDENSATION

(Fluorometric Method) Hydrolysis with KOH

(glycerol + FA) Glycerol + PA

(formaldehyde) Formaldehyde +

acetylacetone + NH3 (YELLOW)

ESTIMATION OF LIPOPROTEINS

1. Ultracentrifugation:

o Based on MOLECULAR DENSITY

o LIGHTEST to HEAVIEST (Chylomicrons, VLDL, LDL, HDL)

2. Electrophoresis o MIGRATION in electrical field o Stains o 4 Bands

α, Pre-β, β, chylomicrons

3. Polyanion Precipitation o Based on PARTICLE SIZE,

CHARGE and APOLIPOPROTEIN CONTENT

o Heparin SO4, dextran SO4,

phosphotungsten with Ca2+, Mg2+, Mn2+

Determination of LDL-C

LDL-C = TC – (HDL + VLDL) o Friedwald Equation

VLDL = TG / 5 (mg/dL) VLDL = TG / 2.175

(mmol/L)

o De Long Equation: VLDL = TG / 6.5 (mg/dL) VLDL = TG / 2.825

(mmol/L)

Determination of Chylomicrons STANDING PLASMA TEST

o Sample refrigerated OVERNIGHT at 40C

o Chylomicrons appear as floating cream

CLINICAL CORRELATIONS Dyslipidemia: abnormal lipid concentration

Atherosclerosis

Myocardial infarction

Hypertension

Hyperlipoproteinemia (hyperchole, hyperTG)

Lp (a) elevations

Hypolipoproteinemia o Abetalipoproteinemia

(BASSEN-KORNZWEIG SYNDROME)

o Hypoalphalipoproteinemia (TANGIER’S DISEASE)

Hyperlipoproteinemia

TYPE LIPOPROTEIN APPEARANCE OF PLASMA

I Chylomicrons Creamy Layer

over clear plasma

IIA LDL clear

IB LDL, VLDL Slightly turbid

III β-VLDL Turbid

IV VLDL Turbid to milky

V VLDL chylomicrons

Creamy layer over turbid