Lecture 8 Flashcards
What is lipoprotein classification determined by?
- ratio of lipid-to-protein (affects density)
- specific apolipoprotein (Apo) content (affects receptor interactions)
What are the 5 lipoproteins?
Chylomicron: high lipid, low protein
VLDL: very low-density
IDL: intermediate density
LDL: low-density (bad cholesterol)
HDL: high-density, low lipid, high protein
What are some characteristics of absorption and circulation in chylomicrons?
- increase in circulation after a meal, enter at a slow rate
- peaks between 30 min-3 hr after eating
- since they enter lymphatic system before blood, dietary lipids are available to adipose and muscle before arriving at the liver
Where is LPL located?
Lipoprotein lipase is located on the surface of endothelial cells lining small blood vessels and capillaries
Where is LPL expressed?
adipose and muscle
How is LPL activated?
by ApoC in chylomicrons
What does LPL do?
hydrolyzes the TAG in chylomicrons into 2 MAG + 2 FA, becomes a chylomicron remnant
What is a chylomicron remnant?
chylomicron without the TAG
How are chylomicron remnants removed?
the remnants are removed from circulation through ApoE-mediated interactions with receptors in the liver
What is the process of chylomicron hydrolyzation in chylomicron remnant?
Produced in the intestine (fed state):
chylomicron with ApoE, ApoC, ApoB48 is has a dietary TAG that is hydrolyzed by LPL which is activated by insulin
What is the process of hydrolyzing a VLDL to an LDL in the liver?
In the liver (fasted state):
VLDL with ApoE, ApoC, ApoB100 has a liver TAG that is hydrolyzed by LPL (acts on ApoC) to create LDL
What are the lipoproteins produced by the intestine and the liver?
Intestine: Chylomicron
Liver: VLDL and HDL
How are LDL’s taken up and where?
By LDL receptors in the liver
How much blood cholesterol in LDL in a fasting subject?
60%
What does LPL do with the TAG once it has hydrolyzed it from VLDL?
TAG is used for either storage or energy
What is reverse cholesterol transport?
When HDL picks up cholesterol around the body and brings it to the liver
Where is HDL made and where is it taken up?
liver
What is the function of HDL in terms of cholesterol?
Cholesterol is extracted from plasma membranes and then esterified directly onto HDL
What is blood cholesterol esterified with?
a fatty acid
What does LCAT do?
esterifies a fatty acid to cholesterol
What is the function of SR-BI?
a transport that brings cholesterol from HDL to the liver
What is the function of CETP?
cholesterol ester transfer protein that transfers cholesterol from HDL to VLDL and/or LDL
What is a hepatocyte?
liver cell
What are the three fates of cholesterol in the liver?
- converted into bile acids to replenish the bile acid pool
- Secreted “as is” directly with bile, to be eliminated in feces
- packaged into VLDL and sent around the body
What is the issue with LDL?
delivers cholesterol for essential functions but can also deposit cholesterol in unwanted places
What do higher HDL levels mean?
more cholesterol returning to the liver
What is the process of lipid metabolism in the liver following a meal?
- Left cylinder - portal vein, contains chylomicron remnants, high levels of glucose and amino acids as well
- Right cylinder - lymphatic veins
- Middle - hepatocytes (inside of liver cell)
- Glucose enters hepatocytes, becomes glucose-6-phosphate by action of glucokinase (can enter several pathways)
- G6P → 2 trioses, can be sent off to make glycerol (backbone for attaching fatty acids)
- G6P → acetyl CoA, can go into
- Krebs cycle or go towards fatty acid synthesis
- G6P → fatty acid synthesis is called de novo lipogenesis (DNL)
- Cholesterol can make acids, be secreted, etc
- Apolipoproteins are required to make VLDL and HDL
What is the process of lipid metabolism in the adipose cell following a meal?
- blood vessels are carrying chylomicrons and glucose
- adipocytes: store fat in cells
- VLDL, IDL, LDL -> fats -> triglycerides -> triglyceride pool
What occurs during lipolysis and gluconeogenesis for lipids?
- lipolysis - lipases hydrolyze ester linkages
- in adipose tissue, HSL (hormone sensitive lipase) cleaves a fatty acid from the glycerol backbone (HSL is inhibited by insulin)
- the complete breakdown of a
TAG molecule releases 1 glycerol
and 3 fatty acids - Glycerol -> G3P can enter into glycolysis or gluconeogenesis (depends on the needs of the cell)
- Fatty acids -> acetyl CoA can undergo β-oxidation and be used to generate energy
What are the four steps to beta oxidation and krebs cycle in lipids?
- dehydrogenation
- hydration
- oxidation
- thiolysis
How many NADH and FADH2 are produced from one round of B-oxidation?
each round of the B-oxidation removes 2 carbons (acetyl CoA) and produces 1 NADH and 1 FADH2
What is the recommended caloric intake for men and women?
Men: 2500 kcal/day
Women: 2000 kcal/day
How to figure out nutritional contribution to daily caloric intake?
[g of protein x 4 kcal/g] / 2500 kcal/day x 100%
[g of carb x 4 kcal/g] / 2500 kcal/day x 100%
[g of fat x 4 kcal/g] / 2500 kcal/day x 100%
What are the recommendations of nutrient percentage of daily caloric intake for 19+
protein is 10-35% of daily calories (218 g max)
carbohydrate is 45-65% of daily calories (406 g max)
fat is 20-35% of daily calories (97 g max)
How does limiting dietary cholesterol affect people?
for healthy people, limiting dietary cholesterol does not change blood cholesterol much
but for those with high blood cholesterol, lower dietary cholesterol will lower LDL’s
How are industrial trans fats produced?
during the hydrogenation of vegetable oils
- hydrogen atoms are added catalytically across double bonds
What is partial vs complete hydrogenation?
partial: results in double bonds being converted from cis to trans
complete: results in all double bonds becoming fully saturated
Why do companies create industrial trans fatty acids?
to increase stability during cooking, longer shelf-life and for palatability
What is the relationship between the amount of hydrogenation and the degree of saturation?
higher amount of hydrogenation, higher degree of saturation
Where else are trans fats found naturally?
ruminant fat
How much trans fat does milk fat contain?
4-8%
How are trans fats made in the rumen?
through bacterial fermentation
What are the effects of high intake of industrial trans fatty acids?
high LDL - cholesterol
high total - cholesterol
high inflammation
low HDL - cholesterol
linked to CVD
What are the health outcomes of eating trans fats?
(processed foods)
- higher risk for heart disease
- higher inflammation
- higher diabetes
What are the health outcomes of eating monounsaturated fats?
(Mediterranean diet)
- lower risk for heart disease
- lower risk for metabolic syndrome
- lower risk for certain cancers
What are the health outcomes of eating polyunsaturated fats?
(fish, fish oil)
- lower risk for heart disease
- lower risk of arthritis
- lower inflammation
