C - Chapter IX: Lipids and Lipoproteins Flashcards
: organic substances which are soluble in nonpolar organic solvents (chloroform and ether) and insoluble in polar solvents (water)
Lipids
nonpolar organic solvents
(chloroform and ether)
polar solvents
(water)
: yield fatty acids on hydrolysis OR complex alcohols the can combine with fatty acids to form esters
Lipids - chemically
: cholesterol, triglycerides, phospholipids and non-esterified fatty acids
human plasma lipids
: macromolecule which consists of varying proportions of protein, cholesterol, triglyceride and phospholipid
Lipoproteins
water-soluble, thus, it facilitates the transport of the lipids in the circulation
Lipoproteins
are diverse in terms of their structure and function
Lipids
Secondary energy source
TRIGLYCERIDE / Neutral FAT
Serves as a thermal insulator
TRIGLYCERIDE / Neutral FAT
Protects tissues from physical trauma
TRIGLYCERIDE / Neutral FAT
Precursor of biological hormones
CHOLESTEROL
Source of bile acids
CHOLESTEROL
Component of the Cell membrane
CHOLESTEROL
Component of the Cell membrane
PHOSPHOLIPIDS
Associated with vital life processes (e.g. CNS)
PHOSPHOLIPIDS
also known as triacylglycerol
TRIGLYCERIDES
transported by chylomicrons (exogenous) and VLDL (endogenous)
TRIGLYCERIDES
Complete Hydrolysis:
3 FA + glycerol
Partial Hydrolysis:
2 FA + monoglyceride
Absorption: = via the portal route
Glycerol (H2O-soluble)
Absorption: = via the lymphatic route
Fatty acids (H2O-insoluble)
Monoglyceride (H2O-insoluble)
Synthesis of TG from
monoglyceride & glycerol
: degradation of the fatty acids by 2C atoms with subsequent production of Acetyl CoA
β-oxidation of fatty acids in the mitochondria
found exclusively in animals and humans
CHOLESTEROL
contains cyclopentanoperhydrophenanthrene ring
CHOLESTEROL
contains 27 C atoms
CHOLESTEROL
(?) in the intestines comes from the diet, bile, intestinal secretions and cells
cholesterol
to be absorbed, it has to solubilized by the formation of mixed micelles containing unesterified cholesterol, fatty acids, monoglycerides, phospholipids and conjugated bile acids
cholesterol
90% of body’s (?) is synthesized by the liver and gut from simpler molecules like Acetyl CoA
cholesterol
complexing of cholesterol with a fatty acid; this process enhances the lipid carrying capacity of lipoproteins
Esterification
is mainly esterified in the vascular compartment
Cholesterol
Cholesterol
Catalyzed by:
− LCAT
− ACAT
− LCAT –
Lecithin Cholesterol Acyltransferase (in plasma)
− ACAT –
Acyl Cholesterol Acyltransferase (intracellularly)
transported by LDL to the cells
Cholesterol
transported by HDL out of the cells
Cholesterol
(?) that reaches the liver is either secreted unchanged into bile (free cholesterol) or metabolized to form bile acids
cholesterol
LIPOPROTEINS: MAJOR CLASSES
- Chylomicron (CM)
- Very-Low-Density Lipoprotein (VLDL)
- Intermediate Density Lipoprotein (IDL)
- Low-Density Lipoprotein (LDL)
- High-Density Lipoprotein (HDL)
Synthesized & released from the SI (Exogenous pathway)
Chylomicron (CM)
very rich in triglycerides (80%)
Chylomicron (CM)
transports dietary fat
Chylomicron (CM)
relatively poor in cholesterol, phospholipids and proteins
Chylomicron (CM)
Proteins: Apo B-48, AI, AII, AIV, C (1-2%)
Chylomicron (CM)
when present in high levels : milky plasma (floating creamy layer)
Chylomicron (CM)
synthesized and released from the liver
Very-Low-Density Lipoprotein (VLDL)
transports cholesterol & triglyceride which are synthesized in the liver (endogenous pathway)
Very-Low-Density Lipoprotein (VLDL)
smaller than chylomicrons
Very-Low-Density Lipoprotein (VLDL)
elevated levels produce a turbid plasma
Very-Low-Density Lipoprotein (VLDL)
contain : 50% triglycerides, 40% cholesterol and phospholipid, 10% protein
Very-Low-Density Lipoprotein (VLDL)
Proteins: Apo B-100 & Apo C-II
Very-Low-Density Lipoprotein (VLDL)
endogenous pathway
Very-Low-Density Lipoprotein (VLDL)
Exogenous pathway
Chylomicron (CM)
derived from VLDL hydrolysis by lipoprotein lipase (LPL)
Intermediate Density Lipoprotein (IDL)
partly depleted of triglyceride
Intermediate Density Lipoprotein (IDL)
contains an almost equal amount of triglyceride & cholesterol
Intermediate Density Lipoprotein (IDL)
Proteins: Apo B and E
Intermediate Density Lipoprotein (IDL)
produced from the action of LPL on IDL
Low-Density Lipoprotein (LDL)
consists of 50% cholesterol, 25% protein, 20% phospholipid and 5% of triglycerides
Low-Density Lipoprotein (LDL)
produced & catabolized in the liver & intestines
High-Density Lipoprotein (HDL)
Contains Apo AI & Apo AII
High-Density Lipoprotein (HDL)
richest in protein (50% of its weight is protein)
High-Density Lipoprotein (HDL)
involved in reverse cholesterol transport (excess cholesterol is returned from the tissues to the liver)
High-Density Lipoprotein (HDL)
ABNORMAL LIPOPROTEINS
Lipoprotein(a) or Lp(a)
LpX Lipoprotein
β-VLDL (“floating β” lipoprotein)
similar to LDL in terms of density and overall composition
Lipoprotein(a) or Lp(a)
abnormal lipoprotein found in patients with obstructive biliary disease, and in patients with familial lecithin:cholesterol acyltransferase (LCAT) deficiency
LpX Lipoprotein
abnormal lipoprotein that accumulates in type 3 hyperlipoproteinemia
β-VLDL (“floating β” lipoprotein)
Richer in cholesterol than VLDL
β-VLDL (“floating β” lipoprotein)
– protein portion of lipoproteins
APOLIPOPROTEINS
: major protein of HDL and chylomicron
Apolipoprotein A
- originate in the intestine or liver
Apolipoprotein A
: major protein of all lipoproteins except HDL
Apolipoprotein B
(found in lipoprotein formed in the liver)
Large B or B100
(found in lipoprotein formed in the S.I.)
Small B or B48
: major protein of VLDL and chylomicrons and a minor protein of HDL and LDL
Apolipoprotein C
: function as a transfer protein •
Apolipoprotein D
: plays a significant role in the recognition & catabolism of chylomicron remnant and IDL via specific receptors in hepatic cells
Apolipoprotein E
Biologic variation
fasting – ideally fast for
12 hours3.
Posture- [?] decrease noted in TC, LDL-C, HDL-C after [?] of recumbent position4.
10%
20 mins
Venous vs capillary samples – capillary levels generally [?] than venous
lower
Plasma vs serum – either can be used when only [?] and [?] are measured and [?] is calculated from these three measurements
cholesterol, triglycerides
HDL-C
LDL-C
Storage – generally, [?] can be satisfactorily analyzed
frozen samples
A. COLORIMETRIC DETERMINATION of CHOLESTEROL Stepwise Methods
- Direct Colorimetric / One-Step
- Two-Step Method
- Three-Step Method
- Four-Step Method
serum is combined with the color reagent then incubated to allow color reaction to occur
Direct Colorimetric / One-Step
Direct Colorimetric / One-Step Methods:
Watson’s, Ferro-Ham, Pearson, Zlatkis
Liebermann-Burchard Reaction Reagents:
Acid anhydride, conc. H2SO4
Liebermann-Burchard Reaction End-product:
cholestapolyene sulfonic acid (emerald green)
Salkowski’s Reaction Reagents:
conc. HAc, Ferric ions
Salkowski’s Reaction End-product:
cholestapolyene carbonium ion (reddish-purple)
Involves 1extraction step prior to 2colorimetric reaction
Two-Step Method
Eliminates protein interference
Two-Step Method
Two-Step Method - Methods:
Carr-Drekter, Saifer-Kammer, Leoffler-McDougold
Requires 1extraction w/ petroleum ether followed by 2 saponification and then 3colorimetric determination
Three-Step Method
Standard method
Three-Step Method
Three-Step Method - Method:
Abell-Kendall
Requires 1extraction, 2saponification, 3purification with digitonin then 4colorimetric determination
Four-Step Method
Considered as the reference method
Four-Step Method
Four-Step Method - Methods:
Schoenheimer-Sperry, Sperry-Webb
cholesteryl ester + water —-[?] —-> cholesterol + FFA
cholesterol esterase
cholesterol + O2 —-[?]—-> cholest-4-en-3-one + H2O2
cholesterol oxidase
Colorimetric (most common)
Hantzsch-Lutidine Reaction
Hantzsch-Lutidine Reaction
Formaldehyde + acetylacetone + NH4 [?] (yellow @ 410 nm)
3,5-diacetyl-1,4- dihydrolutidine
Van Handel and Zilversmit
Formaldehyde + H2SO4 + chromotropic acid (CTA) [?]
pink chromophore
Weiland Method
glycerophosphate + NAD —[?] —> DHAP + NADH + H
glycerophosphate DH
Weiland Method
NADH + tetrazolium dye —[?]—> formazan + NAD (340nm)
Trinder Reaction
glycerophosphate + O2 —[?]—> DHAP + H2O2
glycerophosphate oxidase
Trinder Reaction
H202 + reduced chromogen –→ [?]
Quinoneimine dye
Eggstein and Kreutz method
ADP + PEP —[?] —> ATP + pyruvate
pyruvate kinase
Eggstein and Kreutz method
pyruvate + NADH + H —LDH—> [?] (340 nm)
lactate + NAD
automated homogenous assays
HDL-C Determination
enzymatic method
HDL-C Determination
for calculation of LDL-c and VLDL-c
Friedewald calculation
cannot be used when TG is >400 mg/dL
Friedewald calculation
LDL-c
VLDL-c
VLDL-C in mmol/L
DeLong, 1986:
VLDL in mmol/L =
VLDL in mg/dL
LDL Cholesterol (mg/dL) Optimal
<100
LDL Cholesterol (mg/dL) Near optimal/above optimal
100 – 129
LDL Cholesterol (mg/dL) Borderline high
130 – 159
LDL Cholesterol (mg/dL) High
160 – 189
LDL Cholesterol (mg/dL) Very high
≥ 190
Total cholesterol (mg/dL) Desirable
<200
Total cholesterol (mg/dL) Borderline high
200 – 239
Total cholesterol (mg/dL) High
≥ 240
HDL cholesterol Low
HDL cholesterol <40
HDL cholesterol High
≥ 60
Triglycerides Normal
<150
Triglycerides Borderline high
150 – 199
Triglycerides High
200 – 499
Triglycerides Very high
≥ 500
diseases associated with abnormal lipid concentrations
Dyslipidemias
Dyslipidemias - multifactorial :
− genetic abnormalities
− environmental/lifestyle imbalances
− secondary to other diseases
Hyperchylomicronemia
Type I
Creamy layer; Clear to Slightly Turbid
Type I
Mod. Increase to markedly increased TG
Type I
Increased LDL
Type IIa
- Premature atherosclerosis
Type IIa
- Familial Hypercholesterolemia
Type IIa
Clear w/ Yellow Orange tint
Type IIa
Increased cholesterol & normal TG
Type IIa
Increased β and pre-β due to deficiency of LDL receptors
Type IIb
Clear to Slightly Turbid
Type IIb
Increased cholesterol & mod. Increased TG
Type IIb
Broad merging of β and pre-β Increased IDL
Type III
Thin cream layer Turbid to opaque
Type III
Increased cholesterol & mod. to marked increase in TG
Type III
Inc. pre-β Increased VLDL
Type IV
Turbid to opaque
Type IV
Normal to slight increase in cholesterol & mod. to marked increase in TG
Type IV
Increased chylomicron & VLDL
Type V
Thick creamy layer Turbid to opaque
Type V
Mod. increase in cholesterol & marked increase in TG
Type V
