1. CLINICAL CHEMISTRY CHAPTER 12
LIPIDS AND LIPOPROTEINS

2. INTRODUCTION
When was the last time you ordered a Double Bacon Cheeseburger, Supersized French Fries, a large shake and an fired apple turnover?
Did you wonder how all that fat got dissolved into your blood? … Try dissolving a stick of butter in a glass of water.
Whenever it was, thank your LIPOPROTEINS!
It’s your Lipoproteins that allow all the disgusting fat you eat to enter your plasma without “cloging” things up.
Lipoproteins provide the transportation system for different types of water insoluble fatty crap
Actually, sometimes things do get clogged up - It’s called a Heart Attack!!! We need to study lipoproteins because of their relationship to heart disease - The #1 cause of death in the United States

3. KEY TERMS Arteriosclerosis CAD Cholesterol Chylomicrons
Endogenous lipoproteins
Exogenous lipoproteins
Fatty Acids
Friedwald Calculation
HDL
LDL
Lipoprotein
Triglycerides
VLDL
Saturated Fatty Acids
Unsaturated Fatty Acids
“Good Cholesterol”
“Bad Cholesterol”
Lipid
Lipemic
Fasting blood specimen

4. List the reference ranges for the lipoproteins
Objectives
Define the general function, origin and structure of the lipoproteins
Define the names, general composition and function of the following
HDL
LDL
VLDL
Chylomicrons
Discuss the relationships between various lipoproteins and CAD
List the reference ranges for the lipoproteins
Discuss the basic test methodologies for lipoprotein testing

5. What are lipoproteins and why do we need them?
Lipoproteins are a handful of different molecules that interact with water insoluble fat molecules, and transports those fats in the plasma
The textbook describes the lipoproteins as “oil tankers”
Different lipoproteins are responsible for the transportation of different fats
Lipoproteins allow fat to be dissolved into the plasma

6. There are 4 types of lipoproteins Chylomicrons
Transport of dietary triglycerides from the GI tract to the liver
Very Low Density Lipoproteins ( VLDL )
Transport of triglycerides from the liver to tissues for storage and energy
Low Density Lipoproteins ( LDL )
Transports cholesterol to peripheral tissues
High Density Lipoproteins ( HDL )
Transports cholesterol away from the peripheral tissues to the liver

7. Lipid Chemistry
Lipids include
Cholesterol
Triglycerides
Phospholipids
Glycolipids
Lipids are important components of cell membranes

8. Fatty acids are short to long carbon chained molecules
Saturated fatty acids
No double bonds between carbons ( C – C )
Solid at room temperature
Animal sources
Unsaturated fatty acids
Double bonds between carbon bonds ( C = C )
Usually liquid at room temp
Plant sources

9. Triglycerides
Glycerol with 3 attached fatty acids
Exogenesis source : Dietary
Endogeneous : Liver and tissue storage
95 % of body fat is triglycerides
Energy source when plasma glucose is decreased
Triglyceride catabolism is regulated by lipase, epinephrine and cortisol
Triglycerides transported by Chylomicrons ( exogeneous ) and VLDL ( endogenous )

10. Transported by HDL and LDL
Cholesterol
Found only in animals
Important component of membranes, steroid hormones, bile and Vitamin D
Exogeneous cholesterol comes from diet
Endogeneous cholesterol is synthesized by the liver
70 % of cholesterol associated with cellular components
30 % is in the plasma ( ⅓ free form , ⅔ esterfied )
Transported by HDL and LDL

11. Phospholipids
Important components of cell membranes
Lecithin and sphingomyelin are utilized to determine fetal lung maturity from amniotic fluid ( L / S Ratio )
Glycolipids
Lipids with a carbohydrate component
ABO antigen are glycolipids

12. Apoliproproteins
Outer protein “shell” of the lipoprotein molecule
The protein – lipid interaction allows the water insoluble lipid to become soluble in plasma
The apolipoprotein is responsible for the interactions with cell membranes and enzymes to transport lipids to specific locations

13. Lipoproteins
Classified according to density and electrophoresis migration
Lipoproteins differ in their sizes, weights, chemical composition and artherogenicity ( association with heart disease )
There are four main types of lipoproteins
CHYLOMICRONS
VLDL
LDL
HDL

14. Chylomicrons
Transports exogeneous ( dietary ) triglycerides
% by weight is triglycerides
Absent from fasting plasma
Removed from the plasma within 6 hours by the liver
Inadequate clearance produces a creamy layer on the plasma
VLDL ( Very Low Density Lipoproteins )
Transports endogeneous triglycerides from liver to tissues
% by weight is triglycerides
Excess dietary carbohydrates are converted to triglycerides by the liver

15. LDL ( Low Density Lipoproteins )
Transports cholesterol from liver to the tissues
Synthesized in the liver
Approximately 50 % by weight cholesterol
Most atherogenic lipoprotein … “ Bad Cholesterol “

16. HDL ( High Density Lipoprotein )
Transports excess cholesterol from the tissues back to the liver ( reverse transport )
Synthesized in the liver and intestines
Composition
30% PHOSPHOLIPIDS
20% CHOLESTEROL
50% APOPROTEIN
The “good “ cholesterol

18. Lipoprotein physiology and metabolism
Water insoluble lipids are digested unto more water soluble ( polar ) compounds in the GI tract
Triglycerides are digested into fatty acids
Cholesterol – esters are converted into free cholesterol
Fatty acids are converted into triglycerides by the liver anf adipose tissues ( fat )
Most cholesterol synthesis occurs in the liver - Most cholesterol lowering drugs target this synthesis
Cholesterol is a main component of bile ( needed for dietary absorption of fat )

19. Exogeneous Pathway
Transport of dietary lipids, mostly the chylomicrons transportation of triglycerides to the liver
Endogeneous Pathway
Transportation of lipids from the liver to the tissues ( VLDL & LDL )

20. Effects of hormones
Insulin
Remember, insulin always decreases plasma glucose
Inactivates lipase … decreases lipolysis and the catabolism of triglycerides to fatty acids / glucose
Stimulates lipogenesis ( fatty acid conversion to triglycerides )
Insulin helps make fat
In diabetes mellitus, insulin deficiency promotes the release of fatty acids and their conversion to triglycerides by the liver

21. Lipoprotein analysis
Laboratory measurement of the lipoproteins is important because of their association with Coronary Artery Disease ( CAD )
CAD is the # 1 cause of premature death in the United States
Because of its connection with public health, lipid testing and interpretation has been standardized to provide consistent results that can be utilized for the risk assessment of CAD

22. Total Cholesterol Methodologies
Cholesterol ester Free cholesterol
Free cholesterol H2O2
H2O Chromogen Colored Chromogen
Cholesterol-Ester-Hydrolase
Cholesterol Oxidase
Peroxidase

23. Triglyceride testing
Most methodologies utilize enzymes that break glycerol from its fatty acids
Free glycerol is proportional to the initial triglyceride concentration

24. HDL ( High Density Lipoprotein ) testing
Non – HDL is precipitated from plasma
Dextran sulfate ( precipitating agent ) is added to patient’s plasma
Non – HDL precipitates and is centrifuged to the bottom
The supernate contains only HDL
HDL in the supernate is measured using a conventional total cholesterol methodology
Elevated triglycerides ( > 400 mg / dl ) may interfer with the separation of non – HDL
Many labs will not perform HDL testing when triglyceride concentrations exceed 400 mg / dl

25. LDL ( Low Density Lipoprotein ) testing
“Bad cholesterol “ … Artherogenic
Direct measurement if LDL is uncommon because of technical difficulities
Friedewald estimation ( calculation )
Test: Total Cholesterol, Total Triglycerides and HDL with routine procedure
Estimate the LDL with the following :
VLDL = Trig / 5

26. Disease prevention and treatment Arteriosclerosis
#1 cause of death and disability
Cholesterol deposits ( plaque ) in coronary arteries occlude blood flow
Heart ( CAD )
Arms / Legs ( PVD )
Brain (CVD )
Plaque formation is associated with
Increased plasma cholesterol
Increased plasma LDL
Decreased plasma HDL
Diet, exercise and diabetes are major contributory factors of CAD

27. Target Ranges ( NECP ) Reference Ranges
Total Cholesterol < 200 mg / dl
High Density Cholesterol ( HDL ) > 35 mg / dl
Low Density Cholesterol ( LDL ) < 130 mg / dl
Triglycerides
Reference Ranges
Total Cholesterol mg / dl
HDL mg / dl
LDL mg / dl
Triglycerides mg / dl

28. Other Risk Factors for CAD
Gender – Males at higher risk
Increased age
Family history
Genetic Abnormalities
Stress – Type A personalities
Hyperlipidemia
Physical inactivity
Hypertension
Smoking
Diabetes
Elevated CRP
Elevated homocysteine
Elevated Lp(a)

29. Ultracentrifuge
High plasma lipid concentrations can cause excessive plasma turbidity and interfere with
spectrophotometric methods.
Lipoproteins can be spun
down in this special centrifuge.
Plasma is placed inside
the “donut.” Lipids spin to
the outside of the donut.

30. Lipoprotein Top 10
Lipoproteins transport various lipids ( fats ) thru plasma to different locations
High relationship between specific lipoproteins and CAD
Apolioproteins are the protein “shells” that interact with lipids and allow them to be water soluble
HDL ( Good Cholesterol ) transports cholesterol away from tissues to the liver
LDL ( Bad Cholesterol ) transports cholesterol to the tissues from the liver
VLDL transports endogenous triglycerides from liver to tissues
Chylomicrons transport exogenous triglycerides from GI tract to liver
Accurate Lipoprotein testing requires a fasting specimen
LDL is not directly measured , but calculated from the Friedwald Calculation

31. Lipid Links