lecture 14 lipoprotein and cholesterol metabolism
TRANSCRIPT
![Page 1: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/1.jpg)
Lecture 14
Lipoprotein and Cholesterol Metabolism
![Page 2: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/2.jpg)
Delivery of Fat to TissuesChylomicrons interact with tissues through lipoprotein lipase (LPL)
LPL is on the surface of cells
Fat in chylomicrons hydrolysed to fatty acids and glycerol
Insulin stimulates LPL
Also increases the supply of glycerol 3-phosphate for re-esterification
![Page 3: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/3.jpg)
Fate of FAs and Chylomicrons
• Fatty acids from chylomicron after lipolysis can be:– Burnt in the heart and muscle– Stored in WAT (hopefully not elsewhere)
• NB. Build up of fat in the muscle in Type 2 diabetes
• FAs in WAT mainly re-esterified FAT– Re-esterification needs glycerol phosphate (Glyc3P)– WAT cannot make Glyc3P from glycerol– Instead Glyc3P is made by glycolysis
• As fatty acids stripped out, chylomicron becomes smaller– And more cholesterol rich
• NB. Cholesterol in lipoproteins mainly in the form of cholesterol esters
– Form chylomicron remnants
![Page 4: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/4.jpg)
Cholesterol Ester
• Cholesterol ester is totally hydrophobic
![Page 5: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/5.jpg)
Liver: Import/Export ControlChylomicron remnants taken up by liver
Endocytotic process
Internal digestion of remnants
Release of cholesterol into the liver
Liver assembles VLDL from fat and cholesterol esters
The fat could have been made by lipogenesis
VLDL excreted into the blood stream
![Page 6: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/6.jpg)
VLDL & LDL - Transport of Cholesterol
LPL in peripheral tissues works on VLDL just as it did on chylomicrons
VLDL becomes depleted in fat
Remaining particle (LDL) relatively cholesterol rich
Tissues take up LDL through LDL receptor
Endocytotic process like chylomicron remnants.
This is how cholesterol is delivered to the tissues
![Page 7: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/7.jpg)
LDL & Cholesterol
• Tissues express LDL receptors ONLY if they want cholesterol
• Nearly all of our cells can produce cholesterol themselves when cells have enough cholesterol, they will stop
making cholesterol & stop expressing LDL receptor• Macrophages take up LDL without control, especially if LDL is
oxidized produce foam cells form plaques• HMG-CoA reductase is the rate limiting step in making cholesterol
– Can be inhibited by statins
![Page 8: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/8.jpg)
Reverse Cholesterol Transport
![Page 9: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/9.jpg)
Ways to Reduce Blood Cholesterol
• Reduce consumption of cholesterol– Less meat, dairy products– But intake of cholesterol is very small vs stores
reabsorption of bile salts by using resins that bind to bile salts – liver has to make more bile salts from cholesterol
• Inhibit absorption of cholesterol from gut– Phytosterols as competitive inhibitors?
• Inhibit cholesterol synthesis by using “statins” which inhibit HMG-CoA reductase
• Consume polyunsaturated fatty acids – high saturated fat results in HDL and LDL
![Page 10: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/10.jpg)
Cholesterol Flux
• Total cholesterol in body ~140g• ~1g of cholesterol enters the body each day from diet
– But only 0.5 g absorbed• ~18g bile salts secreted into gut per day
– and 17.5g is reabsorbed per day – the net loss of bile salt is very little (~0.5 g/day)
• So amount absorbed = amount lost as bile salts– A reduction in intake will most likely be met by an increase in
endogeous choleseterol synthesis• But compare the store size to the intake
– 140 g to 0.5 g– vs carbohydrate for which the store size and intake are similar
magnitude– vs fat – intake (100 g) < store (15,000 g)
![Page 11: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/11.jpg)
Importance of Cholesterol
• Cholesterol is important for:– Steroid hormone synthesis– Regulating membrane fluidity
• Membrane fluidity is important for:– Structural integrity– Receptor/enzyme activity
![Page 12: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/12.jpg)
Membrane with Saturated FA
• saturated FA – No double bond in FA
• Membrane crystalline
![Page 13: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/13.jpg)
Membrane with Unsaturated FA
• Unsaturated FA Kinks• Membrane is less crystalline, more fluid and
more permeable
![Page 14: Lecture 14 Lipoprotein and Cholesterol Metabolism](https://reader036.vdocuments.us/reader036/viewer/2022082414/56649e7e5503460f94b81006/html5/thumbnails/14.jpg)
Cholesterol & Membrane Fluidity
• Cholesterol “fine tunes” membrane fluidity