Atherosclerosis Pharmacology Flashcards
How do cells obtain/regulate cholesterol?
- receptor-mediated uptake of LDL cholesterol
- de novo synthesis
- excess cholesterol stored as cholesterol esters (ACAT enzyme)
- diet
What is the relationship between HDL-C and CHD, for any level of LDL-C?
For any level of LDL-C, HDL-C is inversely related to CHD risk
Therapeutic overview: Why do we administer cholesterol treatment?
- Reduce formation and rate of progression in coronary and peripheral atherosclerosis from childhood to old age
- Prevention of coronary events and strokes in apparently healthy persons at risk, particularly middle-aged and elderly
- Prevention of heart attacks, strokes, need for revascularization in persons with established atherosclerosis
- Prevention and treatment of pancreatitis in hypertriglyceridemia
What is the dominant mechanism for controlling hepatic LDL plasma concentrations?
REGULATION OF HEPATIC LDL RECEPTOR PATHWAY
What is ASCVD?
Atherosclerotic cardiovascular disease
- Heart attacks + strokes + peripheral arterial disease
What is the basis of treating lipid disorders that cause ASCVD?
- Lowering LDL with statins lowers risk
- Base treatment on risk
- Secondary prevention (already has ASCVD event) is treated aggressively with high intensity statin
- Primary prevention (no clinical disease) is assessed.
- If 10-year risk
- > 7.5% ⇒ treat with statins
- 5% to 7.5% ⇒ review other risk factors
- < 5%, ⇒ lifestyle
- If 10-year risk
- Everyone else (kids) ⇒ primordial risk ⇒ lifestyle
List the HMG CoA Reductase Inhibitors/Statins:
- Atorvastatin (Lipitor) (synthetic compound)
- Lovastatin (Mevacor) (fungal metabolite)
- Simvastatin (Zocor) (synthetic compound)
- Pravastatin (Pravachol) (fungal metabolite)
- Rosuvastatin (Crestor) (synthetic compound)
- Fluvastatin (Lescol) (synthetic compound)
**Statins: **
Mechanism of Action
-
Competitive inhibitor for active site on HMG CoA reductase
- Rate limiting step in cholesterol biosynthesis
- statins inhibit HMGR by binding to the active site of the enzyme, thus sterically preventing substrate from binding
-
Structural analog of the HMG CoA intermediate
- All statins share a structural component that is very similar to the HMG portion of HMG-CoA
- more bulky and more hydrophobic than HMG-CoA
How do statins affect the LDL receptor?
-
increase in LDL receptor gene
-
mechanism:
- In response to the reduced free cholesterol content within hepatocytes, membrane-bound Sterol Regulatory Element-Binding Proteins (SREBPs) are cleaved by a protease and translocated to the nucleus
- transcription factors then bind the sterol-responsive element of the LDL receptor gene
- enhance transcription
- increase the synthesis of LDL receptors
-
mechanism:
-
up-regulation of LDL receptor results in increased catabolism of LDL
- Plasma concentration of LDL falls
- less LDL is available to react with cellular elements in blood and blood vessel walls
Pharmacokinetics of Statins:
Extensive first-pass metabolism by the liver
- Limits systemic bioavailability
-
Targets liver/site of action
- mediated primarily by the organic anion transporter OATP1B1
- All the statins, except simvastatin and lovastatin, are administered in the what form?
- What form are simvastatin and lovastatin adminstered?
- **-hydroxy acid **
- which is the form that inhibits HMG-CoA reductase
-
lactones
- converted to the -hydroxy acid form via the liver
What is the major CYP reponsible for metabolizing atorvastatin, lovastatin and simvastatin?
CYP3A4
What are the half-lives of the different statins?
- lovastatin (1 - 4 hours)
- simvastatin (1 - 2 hours)
- atorvastatin ( 20 hours )
What do statins have a high affinity for?
highly bound to plasma proteins
**Statins: **
Major Adverse Effect
all statins have been associated with myopathy and rhabdomyolysis
Definitions:
- Myopathy
- Rhabdomyolysis
-
Myopathy
- muscle pain without creatinine kinase (CK) elevation or less frequently with mild CK elevation
- Muscle disease/weakness
-
Rhabdomyolysis
- muscle symptoms with marked CK elevation and with creatinine elevation
- breakdown of muscle fibers that leads to the release of myoglobin into the bloodstream
- Myoglobin is harmful to the kidney and often causes kidney damage
What are minor adverse effects caused by statins?
- GI side effects
- Increase in liver enzymes
Myopathy risk increases in ______ relationship to statin dose and plasma concentration
Myopathy risk increases in direct relationship to statin dose and plasma concentration
How do genetics play a role in statin intolerance?
- A single nucleotide polymorphism in SLCO1B1
- which encodes an organic anion transporter that regulates the hepatic uptake of statins
- Genetic variants of SLCO1B1 lead to reduced hepatic uptake and increased levels of statins in the blood,
- provide the mechanism for increased risk of myopathy
What other drugs can increase the risk of myopathy when taken in combination with statins?
-
Drugs are those metabolized primarily by CYP3A4
- certain macrolide antibiotics (e.g., erythromycin )
- azole antifungals (e.g., itraconazole )
- cyclosporine
- HIV protease inhibitors
- gemfibrozil
- inhibits OAT1B1
- interferes with transformation of most statins by glucuronidases
- Associated with increased plasma concentrations of statins and their active metabolites
What is contraindicated in statin therapy?
- Hypersensitivity
- Active liver disease
-
Women who are pregnant, lactating, or likely to become pregnant should not be given statins
- May down-regulate biosynthesis of cholesterol as well as many important metabolic intermediates
- May have secondary effects on sterol-dependent signaling molecules (Sonic Hedgehog)
Statin Lipoprotein Profile:
- TG
- LDL
- HDL
-
TG
- > 250 mg/dl: decrease by 20-55%
- < 250 mg/dl: decrease by 25%
- the higher the baseline TG level, the greater the TG-lowering effect
-
LDL
- decrease by 20-55%
-
HDL
- increase by 5-10%
Statins:
Clinical Use
First line therapy in hypercholesterolemia when at risk for myocardial infarction
Statins are effective in almost all patients with high LDL-C levels. What is the exception?
patients with homozygous familial hypercholesterolemia
- have very attenuated responses to the usual doses of statins because both alleles of the LDL receptor gene code for dysfunctional LDL receptors
- the partial response in these patients is due to a reduction in hepatic VLDL synthesis associated with the inhibition of HMG-CoA reductase–mediated cholesterol synthesis
Statins:
Potential Cardioprotective Effects Other Than LDL Lowering
- Increased endothelium-dependent relaxation
- Stabilize plaques/prevent plaque rupture
- Decrease LDL oxidation
- Decrease platelet aggregation
- Decrease C-reactive protein
Bile Synthesis and Function
-
Cholesterol converted to bile acid by enzyme 7alpha-hydroxylase
- Conjugated bile acids secreted from the liver and stored in the gall bladder
- passed through the bile duct into the intestine
- Function is to emulsify lipids in food to enable fat digestion and absorption through the intestinal wall.
- Most bile acids are reabsorbed, returned to the liver via the portal vein, and re-secreted
- Conversion to bile salts is the only mechanism by which cholesterol is excreted (~0.8 g/day)
Name a bile acid-binding agent:
cholestyramine
**Cholestyramine: **
Mechanism of Action
-
anion-exchange resins
- highly positively charged and binds negatively charged bile acids
-
Large size ⇒ resins are not absorbed, and the bound bile acids are excreted in the stool
- more than 95% of bile acids are normally reabsorbed.
- interruption of this process depletes the pool of bile acids ⇒ hepatic bile-acid synthesis increases
- As a result, hepatic cholesterol content declines, stimulating the production of LDL receptors
- an effect similar to that of statins
How is cholestyramine similar to statins?
Like statins, bile acid binding resins lower intracellular cholesterol ⇒ activates the SREBP transcription factor ⇒ increases LDL receptor gene transcription
Cholestyramine:
Pharmacokinetics
- Quaternary amine, hygroscopic powder administered as chloride salt/insoluble in water
-
Pharmacokinetics
- not absorbed
- reduction in plasma cholesterol concentrations usually seen within first month of therapy
- stop drug, levels return to normal in 1 month