SM 125a - Lipoprotein Metabolism Flashcards
What are the symptoms of familial hypercholosterolemia?
(Achilles) Tendon xanthoma
Eyelid xanthelasma
Arcus corneae in people <45 years old
What is the function of lipoprotein lipase (LPL)?
LPL lyses triglycerides to release free fatty acids to peripheral cells
What is the mechanism of action of bile acid binding sequestrants?
Bile acid binding sequestrants bind bile acid in the gut to prevent recycling
- Decrease hepatic cholesterol (more is used to make new bile salts)
- Inrease LDL receptor production
What is the efficacy of Omega-3 Fatty Acids?
- Decrease triglycerides
- Slight increase in HDL-C
- Decrease coronary heart disease deaths in MI survivors
But: Slight increase in LDL-C
Why aren’t PCSK-9 monoclonal antibodies prescribed for everyone with high cholesterol?
- Expensive
- Must be injected
- Allergic reactions possible
Which lipoprotiens are the main carriers of triglycerides?
Chylomicrons (after a big meal)
VLDL (in the fasted state)
What are the 4 major pathways of lipoprotein transport?
Exogenous
Endogenous
Reverse cholesterol transport
Enterohepatic Circulation
What is the clinical efficacy of statin use?
- Decrease LDL-C 20-22% regardless of risk
- Prevent atherosclerotic CVD
- Not efficacious if pt. is on hemodialysis or has chronic heart failure
What is “good cholesterol?”
What is “bad cholesterol?”
Good cholesterol = HDL-C
Bad cholesterol = LDL-C
What is the recomended lipid-lowering treatment for somebody with acute coronary syndrome?
Moderate intensity statin + Ezetimibe
In which pathway of lipoprotein transport does the liver produce VLDL?
Endogenous pathway
Which drug is best for lowering triglyceride levels?
Fibrates
Omega-3 Fatty Acids
Describe the endogenous pathway of lipoprotein transport
Liver production of VLDL
- VLDL is produced by the liver
- Lipoprotein lipase converts VLDL to IDL by removing ApoE
- IDL is converted to LDL
- LDL is taken up by LDL receptors in the liver
- If LDL is oxidized, it is instead taken up by macrophages. They are converted to foam cells and contribute to the progression of atherosclerosis
ApoB48 is specific to which lipoproteins?
Chylomicrons
What is the inheritance pattern of familial hypercholesterolemia?
Autosomal dominant
People who are homozygous for the mutation have a more severe phenotype than heterozygotes
(up to 1000 mg/dL vs. up to 300 mg/dL; Normal < 130 mg/dL)
A lipoprotein contains ApoB100, ApoE, and ApoC
What class of lipoprotein is it?
VLDL
What do bile salts do?
Solubilize fats so they can be taken up by enterocytes
Which statins are metabolized by CYP2C9?
What substances are contraindicated?
- Statins
- Fluvastatin
- Rosuvastatin
- Contraindicated:
- Coumadin (warfarin)
- Fluconazole
Who should fibrates be prescribed to?
- Patients with high triglycerides
- Patients with mixed hyperlipidemia and/or low HDL
- Patients intolerant of statins
What is the fate of oxidized LDL?
Instead of binding to LDL receptors and being cleared from the circulation, oxidized LDL is recognized as non-self and taken up by macrophages. This causes them to turn into foam cells and contribute to the development of atherosclerosis
What makes some lipoproteins more dense than others?
High density = more proteins
Low density = fewer proteins (and more fat)
What would happen to cholesterol levels if fewer bile salts were recycled?
Cholesterol levels would decrease, becuase more would be used to make new bile salts
Who should NOT be treated with fibrates?
- Patients wtih severe renal or hepatic disease
What is the mechainsm of action of fibrates?
(Gemfibrozil, fenofibrate)
Fibrates have a major triglyceride-lowering effect
- Block ApoC3 expression to remove inhibition of LPL activity
- Block liver VLDL secretion
What would happen to HDL-C if CETP were inhibited?
HDL-C would increase
(CETP transfers cholesteryl ester from HDL to LDL)
ApoA1 is the major protein of which lipoprotein?
HDL
A lipoprotein contains ApoB100 and ApoE
What class of lipoprotein is it?
IDL
(VLDL contians ApoC in addition to these two)
Which apolipoproteins are found on HDL?
- ApoA1 (major protein of HDL)
- ApoA2
- ApoE
Describe the pathophysiology of Apolipoprotein B Deficiency
Abnormal ApoB structure causes increased LDL-C because LDL receptors cannot recognize LDL-C and remove it from the circulation
Describe the pathophysiology of dysbetalipoproteinemia
Defect in ApoE2 synthesis
- IDL is not recognized by its receptors
- This leads to increased IDL -> increased risk of atherosclerosis
Which apolipoproteins are found on IDL?
- ApoB100 (single copy)
- ApoE (multiple copies)
What are the possible adverse effects of statin use?
- Muscle myositis
- Increase creatin kinase (<0.5%)
- Myalgias are common
- Rhabdomyolysis is rare
- Increased incidence fo taking anythign that inhibits CYP3A4
- Hepatotoxicity
- Worry if ALT is 3x the upper limit of normal
What is the function of Cholesteryl Ester Transfer Protein (CETP)?
CETP transfers cholesterol esters from HDL to LDL
What is the mechanism of action of statin drugs?
- Inhibit HMG-CoA Reductase (primarily)
- This inhibits the conversion of HMG-CoA to Melevonate, which is the rate-limiting step of cholesterol synthesis
- Increase the number of LDL receptors
What happens to circulating cholesterol levels if LDL receptors are not working?
LDL-C levels in the body increase because they cannot be cleared from the circulation
If they are oxidized, they are taken up by macrophages. The macrophages turn into foam cells and contribute to the progression of atherosclerosis
What should be prescribed if a patient cannot tolerate a full dose of statin?
Prescribe a bile acid binding sequestrant in addition to the statin
Describe enterohepatic ciruculation, as it relates to lipoprotein transport
Recirculation fo bile salts in the gut
- Bile salts make fats more solube so they can be taken up by enterocytes
- Cholesterol is a precursor for bile acid
- Recycling less bile acid means that more cholesterol will be used to make bile acid
- This reduces cholesterol levels in the body
Which lipoproteins have one ApoB?
There is one ApoB on every atherogenic particle (LDL, IDL, VLDL)
Familial Hypercholesterolemia and Apolipoprotein B Deficiency are both genetic disorders that result in increased LDL-C
How are they different?
- Familial hypercholesterolemia
- Defect in LDL receptor that prevents uptake of LDL-C
- Apolipoprotein B deficiency
- Abnormal ApoB structure that prevents the normal receptor from recognizing and uptaking LDL-C
Why would you want to combine a statin with a bile acid sequestrant?
What is the effect?
Combine statin with bile acid sequestrant if they…
- Can’t tolerate a full dose of statin
- Have familial hypercholesterolemia
Effect
- Decrease LDL production
- In addition to decreasing cholosterol syntheisis and increasing LDL receptors (statins)
- Incresae fractional catabolic rate
- More powerful lowering of LDL-C