Cholesterol Lowering Drugs Flashcards
Describe the structure of lipoproteins
Central core of hydrophobic lipid
Hydrophilic coat of polar substances
Hydrophobic lipids
Triglycerides or Cholesterol esters
Hydrophilic coat of substances
Phospholipids
Free Cholesterol
Associated proteins
State the 5 main classes of lipoproteins
High density lipoproteins
Intermediate density lipoproteins
Low density lipoproteins
Very Low density lipoproteins
Chylomicrons
Describe chylomicrons
Massive, huge diameter lipoproteins, thus storing fatty acids and cholesterol from the diet.
How do the 5 main classes of lipoproteins vary ?
Vary in :
- Size
- Density
- Apoproteins
- Core lipids
State the 2 pathways for cholesterol synthesis
Endogenous pathway
Exogenous pathway
Exogenous pathway
External source of cholesterol
Endogenous pathway
Internal ability of the body to produce a source of cholesterol
Function of chylomicrons
Transport tri-acylglycerides and cholesterol esters from the GI to the tissues.
Function of lipoprotein lipase
Chylomicrons are split by lipoprotein lipase to release free fatty acids.
These free fatty acids are taken up by muscle and adipose tissue
What happens to chylomicrons after interacting with lipoprotein lipase ?
The cholesterol enriched, fatty acid depleted chylomicron (chylomicron remnant) is taken up in the liver.
The cholesterol is stored and oxidised into bile acids or released to VLDL.
Function of VLDL (very low density lipoprotein)
Transports cholesterol and newly synthesised tri-acylglycerols to the tissues.
TGs removed from VLDL leaving LDL with a high cholesterol.
Function of HDL
Absorbs cholesterol from cell breakdown and transfers it to VLDL.
Requirements for endogenous creation of cholesterol
A source of acetyl-CoA
A source of enzymes
What does regulation of the endogenous pathway depend on ?
Based on how much cholesterol you already have in your body.
XS cholesterol - you don’t need to synthesise as much endogenous cholesterol
What is synthesised from cholesterol ?
Bile acids
(important for GI function of the body)
What happens if we have elevated plasma cholesterol ?
Elevated plasma cholesterol is associated with high LDL which is a risk factor for ATHEROMATOUS DISEASE.
What does atheromatous disease lead to ?
Atherosclerosis
Ischaemic Heart disease
Myocardial infarction
Cerebral Vascular Accidents
Hyperlipidaemia
An increase in plasma concentration of lipids
What causes an increased risk of atherosclerosis and CHD ?
High plasma conc. of total and LDL cholesterol.
State the average total cholesterol level in the UK
5.7 mmol/L
State the ideal levels of cholesterol
<5 mmol/L
State the mildly high levels of cholesterol
5 - 6.4 mmol/L
State the moderately high levels of cholesterol
6.5 - 7.8 mmol/L
State the very high levels of cholesterol
> 7.8 mmol/L
When considering high cholesterol, what other factors have to be taken into account ?
The ratio between ‘good’ HDL and ‘bad’ LDL cholesterol.
Other risk factors for CVD
Where is cholesterol derived from ?
De novo synthesis in the liver
Uptake from circulating LDLs
Uptake of chylomicron remnants
What is the aim of lipid lowering drugs ?
Reduce plasma cholesterol
- lifestyle modification
- drug therapy should be secondary
Describe how lipid lowering drugs work
Work by either reducing production of lipoproteins
OR
Increasing their removal from the blood
State the drugs that are used to lower blood cholesterol levels
Bile Acid sequestrants
PCSK9 inhibitors
Ezetimibe
Fibrates
Statins , Bempedoic acid
State the mechanism of action of Bile Acid sequestrants
Sequester bile acids in the intestine / decrease hepatic stores of cholesterol.
State the mechanism of action of PCSK9 inhibitors
Enhances the removal of LDL
State the mechanism of action of ezetimibe
Inhibits transport protein for cholesterol in the brush border of enterocytes in the duodenum
State the mechanism of action of fibrates
Alter the levels of plasma lipoproteins
State the mechanism of action of statins, bempedoic acid
Inhibit the synthesis of cholesterol in the liver
What are statins ?
HMG-CoA reductase inhibitors
Function of HMG-CoA reductase
Major rate limiting step in cholesterol synthesis.
Converts HMG-CoA to mevalonic acid (MVA)
State some examples of statin
Atorvastatin
Simvastatin
Pravastatin
Rosuvastatin
These are all long-lasting HMG-CoA reductase inhibitors.
Describe the steps in the mevalonate pathway
One Half - Cholesterol synthesis
Other Half - Protein Prenylation
What is protein prenylation ?
Addition of lipid tails to small GTPase signalling molecules
Ensures they are localised correctly.
Lipoprotein lipases function
An enzyme that helps remove and strip fatty acids from lipoproteins
Clinical uses of statins
2ndary prevention of myocardial infarction and stroke in those who have atherosclerotic diseases.
1ary prevention of arterial diseases in patients with high serum cholesterol.
Function of atorvastatin
Lowers serum cholesterol in familial hypercholesterolaemia.
What to use if statins don’t work ?
Ezetimibe
PCSK9 inhibitors
Bempedoic Acid
Function of ezetimibe
Specifically reduces intestinal cholesterol absorption by inhibiting a sterol carrier protein in the brush border of the enterocytes.
Inhibits uptake of cholesterol
Function of PCSK9 inhibitors
PCSK9 mediates the degradation of LDL receptors on the surface of liver cells, inhibiting this enzyme increases the amount of LDL bound and removed by the liver.
State some PCSK9 Inhibitors
Antibodies :
Alirocumab
Evolcumab
Function of bempedoic acid
Reduces cholesterol synthesis in the liver by inhibiting ATP citrate lyase.
Lipid targeting treatments
Colestyramine
Fibrates
What is colestyramine ?
Basic anion exchange resin
Describe the action of colestyramine
Sequesters bile acids to prevent enterohepatic recirculation.
Increases the metabolism of endogenous cholesterol into bile acids
Increases the LDL receptor numbers in the liver resulting in the removal of LDLs from the blood.
Function of bile-sequestering drugs
Bile sequestering drugs and inhibitors of cholesterol biosynthesis can lower blood cholesterol by 50%.
What are fibrates ?
Activators of lipoprotein lipase
State some fibrates
Fenofibrate
Gemfibrozol
Main action of fibrates
Stimulation of lipoprotein lipase which decreases the triglyceride concentration of VLDL.
What are the clinical uses of fibrates ?
Patients with :
- Diabetes
- Mixed dyslipidaemia
- Elevated LDL cholesterol
- high cardiovascular risk
- marker hypertriglceridaemia
- low HDL cholesterol
Side effects of statins
Myositis
Angio-oedema
GI disturbances
Insomnia
Rash
(not used in pregnancy)
Side effects of bempedoic acid
Anaemia
Gout
Hyperuricaemia
Side effects of PCSK9 inhibitors
Flu-like symptoms
Muscle pain
Side effects of Fibrates
Myositis
GI disturbances
Side effects of colestyramine and ezetimibe
GI symptoms
Nausea
Abdominal Bloating
Constipation
Diarrhoea