CLINICAL CHEMISTRY CHAPTER 12

1
CLINICAL CHEMISTRYCHAPTER 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!
• Its 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 -
  Its 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
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

• 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 ( ? free form , ?
  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
• 90 - 95 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
• 50 - 65 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

17
(No Transcript)
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 H2O2
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 patients 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 ( gt 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 )
• Total Cholesterol lt 200 mg / dl
• High Density Cholesterol ( HDL ) gt 35 mg / dl
• Low Density Cholesterol ( LDL ) lt 130 mg / dl
• Triglycerides
• Reference Ranges
• Total Cholesterol 140 - 200 mg / dl
• HDL 30 - 75 mg / dl
• LDL 55 - 130 mg / dl
• Triglycerides 65 - 155 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

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
http//www.indstate.edu/thcme/mwking/lipids.html
http//www.nhlbi.nih.gov/chd/chdexp.htm http//ww
w.fda.gov/fdac/features/1999/199_chol.html http/
/www.lifeclinic.com/focus/cholesterol/about_it.asp