module 12-13 Flashcards
What is coronary heart disease?
- when coronary blood circulation fails to adequately supply the heart with blood
What is the primary cause of coronary heart disease?
athlerosclerosis
what is athlerosclerosis?
when plaques build up on the walls of the arteries, causing the artery to narrow, resulting in decreased blood flow to the heart
what is the relation between coronary heart disease and cholesterol levels?
people with high blood cholesterol are at risk of developing coronary heart disease
Cholesterol’s role in the body (3)
- cell membranes
- precursor of steriod hormones
- precursor of bile salts
where does cholesterol come from? (2)
- diet (exogenous)
- through synthesis (endogenous)
what percent of body’s cholesterol is endogenous vs exogenous
- endogenous = 80%
- exogenous = 20%
Lipoproteins - structure
- outer hydrophillic shell = phospholipids
- core = lipophilic cholesterol and triglycerides
- Apolipoproteins - embeded in phospholipid shell
Lipoproteins - function
transport cholesterol and triglycerides in the blood (since both are lipophilic, they cannot disolve in blood otherwise)
Apoplipoproteins function (3)
1) allow recognition by cells which may bind and ingest lipoproteins
2) activate enzymes that metabolize lipoproteins
3) increase the structural stability of lipoproteins
Lipoproteins with apoplipoprotein AI - function
transport cholesterol from non-hepatic tissue back to the liver
lipoproteins that contain apoplipoprotein B-100
transport cholesterol to non-hepatic tissue
how do we classify lipoproteins
based on density
very-low density lipoproteins, low density lipoproteins, high density lipoproteins
Very low density lipoproteins - function
- deliver triglycerides from the liver to adipose tissue and muscle
Very low density lipoproteins - core composition
very rich in triglycerides
Very low density lipoproteins - athlerosclerosis
- some studies show link to atherosclerosis
Very low density lipoproteins - apoplipoprotein
contain apoplipoprotein B-100, which allows them to bind to cells and transfer their lipid to cells
Low density lipoproteins - function
deliver cholesterol to non-hepatic tissue
Low density lipoproteins - core composition
- cholesterol rich core = 60-70% of cholesterol in blood
Low density lipoproteins - apoplipoprotein
- apoplipoprotein B-100 - which allows them to bin to cells and transfer their lipid to cells
Low density lipoproteins - athelosclerosis
- clear link between LDL cholesterol adn development of atherosclerosis
- higher the blood LDL level, the greater the risk of developing coronary heart disease
- reducing blood LDL levels halts or even reverses atherosclerosis and has ben proven to decrease death from coronary heart disease
- AKA “bad cholesterol”
High density lipoproteins - function
deliver cholesterol from non-hepatic tissue back to the liver. Promote cholesterol removal from the blood.
- aka the “good cholesterol”
High density lipoproteins - core composition
have cholesterol as their main core lipid and account for 20-30% of total blood cholesterol
High density lipoproteins - and coronary heart disease
elevated HDL decreases risk of coronary heart disease
High density lipoproteins - apoplioproteins
- Apoplipoprotein - A-I (mediates benefical effect of HDL cholesterol)
- also apoplipoprotein A-II, and A-IV
High density lipoproteins
Role of LDL cholesterol in atherosclerosis (6)
- LDLs promote initiation of atherosclerosis
- LDLs may move from blood into the sub-endothelial space of arterial epithelium where they may become oxidized
- oxidation –> monocyte recruitment–> macrophage conversion
- macrophages take up oxidized LDL becoming larger and vacuolated (aka foam cells)
- Foam cells accumulate beneath epithelium, a fatty streak appears (followed by plateled adhesion, smooth muscle migration, collagen synthesis)
- RESULT = atherosclerotic lesion with a lipid core and a tough fibrous plaque
what actually causes atherosclerosis?
not just LDL - atherosclerosis is primarily an inflammatory process (LDL causes a mild injury to arterial endothelium but it is the subsequent inflammatory response that mediates the development of atherosclerosis
Who should have cholesterol screening? (8)
- males over 40, females over 50
- females post-menopausal
- patients with diabetes
- patients who have heart disease or a family history of heart disease
- patients with hypertension
- patients who have central obesity (waist circumference M102cm, F88cm)
- patients who smoke or have recently stopped smoking
- patients with inflammatory (arthritis, lupus) or renal disease
Framingham Risk Score (FRS) (what, how calculate, risk levels, problems)
- a cardiovascular risk assessment tool
- encompases gender, age, total blood cholesterol, smoking status, HDL cholesterol and systolic blood pressure to calculate a risk
- risk score = patients 10 year risk of developing coronary heart disease
- High risk = score greater than 20%, between 10-19% is moderate risk, below 10% is low risk
- NOTE - underestimates risk in youth, women, patients with metabolic syndrome
Patients with high risk of coronary heart disease- characteristics
- Framingham Risk score of >20%
- patients with diabetes
- patients with heart disease
Patients with high risk of coronary heart disease - initiate cholesterol lowering treatment when….
trick question - all patients should be treated
Patients with high risk of coronary heart disease - LDL cholesterol target
- <2mmol/L or >50% decrease in LDL cholesterol
Patients with moderate risk of coronary heart disease - characteristics
- framingham risk score of 10%-19%
Patients with moderate risk of coronary heart disease - initiate cholesterol lowering treatment when…
- LDL cholesterol >3.5 mmol/L
- ratio of triglycerides/HDL cholesterol is >5.0
- if significant inflammation is present
Patients with moderate risk of coronary heart disease - LDL cholesterol target
- <2mmol/L or
- >50% decrease in LDL cholesterol
Patients with low risk of coronary heart disease
- Framingham risk score <10%
Patients with low risk of coronary heart disease - initiate cholesterol lowering treatments when
- LDL-cholesterol is >5.0 mmol/L
Patients with low risk of coronary heart disease - LDL cholesterol target
- > 50% decrease in LDL cholesterol
Metabolic syndrome
- combination of medical disorders that cause increased risk of coronary heart disease + type II diabetes
Characteristics of metabolic syndrome (5)
diagnosed when a patient has three or more of….
- central obesity (waist circumference >102cm in men or 88cm in women)
- elevated triglycerides (blood triglycerides >1.7 mmol/L
- low HDL cholesterol (<1.03 mmol/L in men or 1.29 mmol/L in women)
- Hyperglycemia (fasting blood glucose >5.6mmol/L
- hypertension - BP > 135/85
Treatment of metabolic syndrom
- decreasing risk for coronary heart disease and type II diabetes
metabolic syndrome prevelance
1/4 canadians
non-drug treatment of LDL cholesterol (4)
- diet
- weight control
- exercise
- cigarette smoking
non-drug treatment of LDL cholesterol - Diet (4)
- intake less than 200mg/day of total cholesterol
- intake of saturated fats as 7% or less of total calories
- intake of soluble fiber 10-25 grams/day
- plant stanols and sterols of 2 grams/day
non-drug treatment of LDL cholesterol - weight control
- weight loss by dietary modification and exercise lowers LDL and decreases risk of coronary heart disease
non-drug treatment of LDL cholesterol - exercise (benefits x4, recommendation x1)
- cardiovascular exercise benefits =
- decrease LDL cholesterol,
- elevate HDL cholesterol,
- decrease insulin resistance,
- decrease blood pressure
- exercise for 30-60 minutes per day
non-drug treatment of LDL cholesterol - cigarette smoking
- cigarette smoke decreases HDL and increasees LDL
- counsel patients to quit smoking
Drug treatment of elevated blood lipids (5)
1) statins
2) bile acid sequestrants
3) nicotinic acid
4) cholesterol absorption inhibitors
5) fibric acid derivatives
How is cholesterol synthesized?
- in the liver via the mevalonic acid pathway
mevalonic acid pathway
1) acetyl CoA –>
2) HMG CoA –>
3) Mevalonic Acid –>
4) multiple other products –>
5) cholesterol
Statins (HMG-CoA Reductase Inhibitors) - mechanism of action
- decrease hepatic synthesis of cholesterol by inhibiting the enzyme HMG CoA reductase, the rate limiting step of cholesterol synthesis
- next, inhibition of HMG CoA reductase causes an upregulation of the hepatic LDL recelptors, allowing the liver to remove more cholesterol from blood
- RESULT = decrease in LDL cholesterol blood levels
Benefits of Statins
- decreased LDL cholesterol
- increased HDL cholesterol
- decreased triglycerides
Statins and Primary Prevention
- Statins are effective at preventing coronary heart disease
- statins decrease incidence of coronary events (ex heart attack) even in low risk patients with no history of coronary heart disease
Statins and secondary prevention
- effective at preventing recurrent CV events in higher risk patients
primary prevention
prevent an incident form occuring
secondary prevention
prevent an event from occurring again
Statins prescription rate
- atorvastatin (Lipitor) = highest prescribed drug in Canada
- Rosuvastatin is 4th highest prescribed drug in Canada
Pharmacokinetics of Atorvastatin (ADME) and bioavailibility
-
- A - large fraction of absorbed dose extracted by the liver, low oral bioavailibility (<14%)
- D - distribution is primarily to the liver but also to the spleen, adrenal glands, skeletal muscle
- M - metabolized by CYP3A4
- E - eliminated in the feces (minimal renal excretion)
pharmacokinetics of Rosuvastatin (ADME)
- A - low oral bioavailibility (<20%), large fraction of absorbed dose is extracted by the liver (site of drug action)
- D - distribution is primarily to the liver but also to skeletal muscle
- M - not extensively metabolized
- E - excreted in the feces, minimal renal excretion
Rosuvastatin considerations (2)
- plasma rosuvastatin concentrations are approx 2x higher in asian patients (dose should start low at 5mg and caution should be used before increasing the dose.
- should not be used in females who are pregnant or trying to become pregnant (cholesterol required for synthesis of cell membranes and hormones)
Adverse effects of statins (3)
- generally well tolerated
- most common = myopathy (muscle ache and weakness ) in about 1-5% of patients
- Rhabdomyolysis (rare)
- hepatotoxicity (rare)
Rhabdomyolysis (diagnosis, pathophysiology, associated symptoms, treatment)
- muscle lysis with severe muscle pain
- during significant muscle injury, muscle cell releases large a mounts of creatine kinase into blood stream…Rhabdomyolysis is diagnosed when blood creatine kinase is 10x above normal
- also accompanied with hyperkalemia and may cause acute kidney failure
- treatment = preserve kidney funciton via IV fluids
Nicotinic Acid - function
- inhibits the hepatic secretion of VLDL. (since LDL is a by-product of VLDL degredation, nicotinic acid effectively reduces both VLDL and LDL)
- also increases blood levels of HDL cholesterol
Nicotinic acid (Niacin) - adverse effects (5)
- side effects limit its use
- intense facial flushing,
- hepatotoxicity,
- hyperglycaemia,
- skin rash,
- increased uric acid levels
Bile-Acids - production
- negatively charged molecules produced in liver from CYP7A1 mediated cholesterol metabolism
Bile-Acids - function
Are secreted into the intestine and function to aid in the absorption of dietary fats and fat soluble vitamins
Bile acids reabosption
- undergo enterohepatic recycling and are therefore reabsorbed form the intestine
- 95% of bile acids are normally reabsorbed form teh intestine