L7 L8 L9 Dyslipidemia and Coronary Heart Disease Flashcards
What are the 4 essential functions of cholesterol?
- structural component of all cell membranes
- precursor of bile acids in liver
- Precursor of vitamin D
- Precursor of steroid hormones.
Where does the synthesis of aldosterone, cortisol and androgens from cholesterol occur?
In the adrenal cortex.
Name the 2 systems in which cholesterol is derived.
- Endogenous system: intracellular synthesis of cholesterol
2. Exogenous system: cholesterol is derived from dietary sources.
Briefly describe the process of cholesterol synthesis.
Acetyl CoA is converted to HMG CoA. HMG CoA reductase converts HMG CoA to mevalonic acid, which is converted to cholesterol.
HMG CoA reductase regulates cholesterol synthesis in the adrenal cortex.
Enzyme regulation is controlled by gene expression, degradation, hormones and drugs.
List the 4 plasma lipoproteins.
Chylomicrons
VLDL
LDL
HDL
Describe HDL
Synthesised in the liver and intestine.
Has lowest triglyceride concentration of all lipoproteins, and high cholesterol content.
Delivers cholesterol to the liver for elimination.
Describe LDL.
Synthesised from VLDL.
Has low TG content and highest cholesterol content.
Delivers cholesterol to the peripheral tissues and the liver.
Describe VLDL.
Synthesised in the liver.
Has high TG content and low cholesterol content.
Delivers de novo TG to peripheral tissues
Describe chylomicrons.
Generated in the intestine. Has highest TG content and lowest cholesterol content.
Delivers dietary TG to peripheral tissues.
How do plasma HDL levels relate to atherosclerosis?
Plasma HDL levels are inversely related to atherosclerotic risk.
HDL removes cholesterol from plaque, thus decreasing cardiovascular risk.
In what ways does HDL protect against atherosclerosis?
Reverse cholesterol transport Inhibition of LDL oxidation Modulation of pro-atherogenic properties of oxidised LDL Anti-inflammatory anti-apoptotic antithrombotic vasodilation
Why is it necessary to fast before a lipoprotein blood test?
If a patient does not fast before the sample is drawn, only total cholesterol and HDL cholesterol levels will be valid. This is because the concentration of LDL and triglycerides is affected by recent consumption of food.
Describe the process of development of atherosclerosis.
- leukocytes adhere to endothelial monolayer (innermost layer of the blood vessel).
- Bound leukocytes migrate into the intima (middle layer of vessel wall)
- Monocytes (major leukocyte recruited) mature into macrophages
- Macrophages uptake lipids, yielding foam cells.
- SMCs migrate from the media to the intima and proliferate. Synthesis of collagen, elastin and proteoglycans is heightened. Extracellular lipids derived from dead and dying cells accumulate in the central region of the plaque. advancing plaques also contain cholesterol crystals and micro vessels.
- plaque ruptures and forms a thrombus, reducing blood flow. occurs when plaques fibrous cap ruptures.
What are the 4 ways in which lowering cholesterol can reduce the risk of coronary artery disease?
- Prevents progression of existing lesions
- changes composition of atherosclerotic plaques
- restores endothelial function
- combats inflammation associated with atherogenesis
List 6 lifestyle interventions for lowering cholesterol.
- healthy eating recommendations
- smoking cessation
- physical activity
- weight reduction
- limit alcohol intake
- reduce salt intake
What is the mechanism of action of statins?
Competitively inhibit HMG-CoA reductase, thus preventing the conversion of HMG-CoA to mevalonic acid in an early, rate limiting step in cholesterol synthesis.
Mevalonic acid is a cholesterol precursor.
What are 3 indications for use of statins?
Hypercholesterolemia
Mixed hyperlipidemia
High risk of CHD, with or without raised cholesterol
What are 3 precautions for use of statins?
- Severe intercurrent illness such as infection, trauma or metabolic disorder increases risk of adverse effects.
- Avoid stopping statins during acute coronary syndromes (MI, unstable angina), as this is associated with increased cardiovascular events, especially during first week.
- Myopathy with lipid lowering agent
Describe dosing advice for statins?
Dose should be titrated according to lipid concentration and CV risk.
Dose should be increased at 4 week intervals for maximum effect.
Fluvastatin, Simvastatin and pravastatin are slightly more effective when taken as an evening dose, but this is irrelevant if compliance will be compromised.
Compare the LDL-lowering potency of rosuvastatin, fluvastatin, atorvastatin, pravastatin and simvastatin.
R > A > S > P = F
Describe the general dose response of statins (i.e. lipid lowering effectiveness).
Statins lower LDL by 20-40% with initial doses, and then by 35-60% with maximal doses.
Decrease triglycerides by 10-45%, and increase HDL by 5-15%.
list 5 mild and more common adverse effects of statins.
Statins are generally well tolerated, however may have the following side effects:
headache
dizziness
insomnia
myalgias
GI symptoms (flatus, constipation, pain) which usually disappear with continued treatment.
Describe potentially harmful adverse effects of stains.
Dose-related risk of myopathy (muscle ache, pain and weakness associated with increased serum creatine kinase) and rhabdomyolosis. Risk is increased by illness and drug interactions.
Describe drug interactions of statins.
Simvastatin and atorvastatin are metabolised by CYP450 3A4, and so plasma concentrations are effected by enzyme inducers or inhibitors.
Fluvastatin is significantly metabolised by CYP450 2C9, and is effected by inducers or inhibitors of this enzyme. rosuvastatin is metabolised 10% by this enzyme.
Grapefruit juice increases plasma concentrations of atorvastatin and simvastatin.
Gemfibrozol is a potent CYP2C8 inhibitor. this enzyme extensively metabolises simvastatin.
give 5 examples of CYP3A4 inhibitors.
Clarithromycin (strong) Erythromycin (moderate) calcium channel blockers used for hypertension grapefruit juice itraconazole
list practice points of statin therapy.
monitor baseline AST and ALT as these may become elevated on statins. Also monitor CK.
cease statin if CK is 10x upper normal limit
cease statin if aminotransferases are persistently 3x more than upper limit of normal
cease statin if patient has persistent, unexplained muscle pain even if CK is normal.
list 2 bile acid binding resins.
Cholestyramine (powder form) and colestipol (granules).
What is the mechanism of action of bile acid binding resins?
anion exchanging agents that bind bile acids in intestinal lumen, causing them to be eliminated in the stool. (i.e. they disrupt enterohepatic recirculation of bile acids).
This increases the demand for cholesterol for new bile acid synthesis, –> increased LDL uptake and removal from plasma.
What are the indications for use of bile acid-binding resins.
Hypercholesterolaemia
Mixed hyperlipidaemia
What are the precautions for use of bile acid-binding resins?
Bile acid binding resins may worsen hypertriglyceridaemia (when triglycerides > 3mmol/L)
Resins are ineffective in complete billiard obstruction
May worsen constipation, divertiular disease and severe haemorrhoids
What are the usual doses of cholestyramine and colestipol?
Cholestyramine: 12-16g daily in 2-3 divided doses
Colestipol: 10-30g daily in 2-4 doses (increase every 1-2 months).
Describe the administration of bile acid binding resins.
Take dose before main meals.
Mix with water, juice or highly fluid foods.
Cholestyramine: can mix and stand in fridge for at least 4 hours or overnight to reduce grittiness.
To reduce bloating - avoid mixing in carbonated fluids and use a straw
maintain adequate intake of fluids and fibre
Describe the dose response of bile acid binding resins.
decrease LDL by 15-30%
Increase TG by 3-10%
increase/decrease HDL by 3%
What are the adverse effects of bile acid binding resins?
Often cause GI symptoms such as constipation, diarrhoea, indigestion, dyspepsia, nausea, flatulence, abdominal pain
can raise TG levels
reduce the absorption of fat-soluble vitamins and folic acid
Describe drug interactions of bile acid binding resins.
result in GI binding and reduced absorption of anionic drugs (such as warfarin, beta-blockers, digitoxin, thyroxine).
Take other medicines at least 1 hour before or 4-6 hours after resin.
What is the mechanism of action of ezetimibe?
reduces absorption of dietary and billiard cholesterol by inhibiting its active transport across the intestinal wall.
Also inhibits the absorption of the plant sterol sitosterol from the gut, resulting in 40% decrease in blood sitosterol levels. Provides effective treatment for sitosterolemia.
What are the indications for use of ezetimibe.
hypercholesterolaemia and homozygous sitosterolaemia.