Lecture 7 - Lipids in Health and Disease Flashcards
Describe the structure of LDL
-
Core:
- Esterified cholesterol
- TAGs
-
Coat:
- ApoB-100
- Phospholipid monolayer
- Free cholesterol (unesterified)
What are the various lipoprotein classes?
- Chylomicrons
- VLDL
- LDL
- IDL
- HDL
Describe the correlations with the various classes of lipoprotein and CVD
- High LDL correlates with high risk of CVD
- High HDL correlates with low risk of CVD
- Ratio of total cholesterol / HDL:
- Increased ratio correlates with increased risk
When are total cholesterol levels ‘too high’?
After around 5 mM CVD risk rises significantly
Describe the structure of chylomicrons
- Core:
- TAGs
- Cholesteryl esters
- Coat:
- Phospholipid monolayer
- Apoproteins:
- B-48, C-II, C-III
- Cholesterol
What are cholesteryl esters?
- Esterified cholesterol
- Polar group (-OH) has been removed and replaced with an acyl group
- These are the cholesterol molecules present in the core of lipoprotein molecules
Where are chylomicrons formed?
In the intestinal mucosa from dietary lipids
Compare the apoproteins found in the following:
- Chylomicrons
- VLDL
- IDL
- LDL
-
Chylomicrons:
- ApoB-48
- ApoC-II
- ApoC-III
-
VLDL:
- ApoB-100
- ApoE
- ApoC-II
-
IDL:
- ApoB-100
- ApoE
-
LDL:
- ApoB-100
Compare the following features in the various classes of lipoprotein:
- Density
- Protein content
- TAG content
- Cholesterol content
-
Density (lowest to highest)
- CM → VLDL → LDL → HDL
-
Protein content:
- CM → VLDL → LDL → HDL
-
Cholesterol content:
- CM → HDL → LDL & VLDL
-
TAG content
- HDL → LDL → VLDL → CM
What are the three stages of lipid transport?
Give a brief overview of each
-
Exogenous pathway:
- Uptake of dietary TAGs in intestine, delivery to adipose cells and liver
-
Endogenous pathway
- Transport of cholesterol from liver to tissues
-
Reverse cholesterol transport
- Recycling of cholesterol from macrophages / foam cells in artery walls back to liver
Compare TAG and TGs
Describe their structures
- These are the same thing
- TAG: Triacylglycerol
- TG: Triglyceride
- Structure:
- Glycerol backbone
- Three fatty acids
Outline exogenous lipid transport
-
Digestion:
- Bile salts emulsify dietary lipids
-
Lipases degrade TAGs into:
- FFAs
- Glycerol
- Monoglycerides
- Di-glycerides
-
Absorption
- FFAs and glycerol taken up into enterocytes
- FFAs and glycerol are converted back into TAGs
- TAGs incorporated into CMs with apoproteins
- CMs taken up into lacteals and move into lymphatics
- CMs drain into circulation at thoracic duct
- Lipoprotein lipase digests TAGs back into FFAs and glycerol
-
Storage
- FFAs enter cells (myocytes or adipocytes)
- FFAs are oxidised for energy of stored as TAGs
- CM remnants (depleted of TAGs) circulate to the liver and are taken up by RME
Describe endogenous lipid transport
- Cholesterol and TAGs are packaged into VLDL with ApoB-100 (acting like a scaffold) in hepatocytes
- VLDL circulate in blood where ApoE and ApoC-II are incorporated
- Lipoprotein lipase digests TAGs to FFA
- FFAs taken up into tissues:
- Myocytes (for oxidation)
- Adipocytes (for storage as TAGs)
- Gonads
- Adrenal glands
- VLDL depleted of TAGs and C, and have lost ApoC-II are now IDL
- Released ApoC-II activates lipoprotein lipase (which plays a role at step 3.)
- 50% of IDL taken back up by hepatocytes
- Through LDLR which binds ApoE
- 50% of IDL loses ApoE and undergoes further lipolysis to become LDL
- 70% LDL taken up LDLR into hepatocytes
- Other LDL taken up by extra hepatic tissue
Describe reverse cholesterol transport (RCT)
- HDL produced in blood
- HDL picks up excess free cholesterol from artery walls
- Cholesterol converted to CE
- HDL recirculates back to liver
- HDL binds SR-B1 on hepatocytes, transferring its cargo to the cells
- CE excreted by liver in bile
Where is VLDL synthesised?
Describe its synthesis
- In the ER of hepatocytes:
- ApoB-100:
- Acts as a scaffold
- Has binding sites for MTP: microsomal transfer protein
- MTP is necessary for the assembly of VLDL
- VLDL then enters circulation, where it associates with:
- ApoE
- ApoC-II
- ApoB-100:
What is an atheroma?
Describe its structure
- The fibro-fatty plaque formed by atherosclerosis
- Core: fatty material
- Cap: fibrous
Where is HDL produced?
In the blood