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
Cholestyramine:
Adverse Effects
- most common-constipation/bloating sensation
- gritty consistency
- nausea and vomiting
- constipation
- interferes with absorption of other drugs
- Digitalis, thiazides, warfarin, statins, aspirin
- modest INCREASE in TG/with time returns to baseline values
Cholestyramine Lipoprotein Profile
- TG
- LDL
- HDL
-
TG
- Normal levels: only transient increase
- Levels > 250 mg/dl: further significant increase
-
LDL
- decrease by 12-25%
-
HDL
- increase by 4-5%
**Cholestyramine: **
Clincal Uses
-
hypercholesterolemia
- Not recommended for individuals with hypercholesterolemia and increased TG
- most often used as second agents if statin therapy does not lower LDL-C levels sufficiently
- recommended for patients 11-20 years of age
What is the main effect of nicotinic acid (niacin)?
MAIN EFFECT IS TO DECREASE TG
- But it does decrease cholesterol
- Water-soluble B-complex vitamin
- Lipid lowering effect is unrelated to its effect as a vitamin
- Much larger doses required
Describe how niacin acts in adipose tissue:
inhibits FFA mobilization
- role for niacin receptor 1 (GPR109A) in adipose tissue
- Activation of receptor causes a decrease in cAMP
- No activation of PKA
- No phosphorylation of perilipin and Hormone Sensitive Lipase (HSL)
- No conformational change in perilipin
- So no access of HSL to TG in the fat droplet
- TG IS NOT broken down into glycerol and FFA
- A DECREASE in FFA that is delivered to the liver
- Decrease in VLDL synthesis means overall decrease in TG
Describe how niacin acts in the liver:
decreases synthesis of VLDL-TG
-
Inhibits DGAT2 (diacylglycerol acyltransferase 2),
- enzyme that catalyzes the final reaction in TG synthesis
- Inhibits synthesis and reesterification of fatty acids
-
Increases ApoB degradation
- apoB is major protein of VLDL/LDL
Describe how niacin affects HDL:
-
increases HDL-apoAI particles
- inhibits hepatocyte surface expression of ß-chain ATP synthase
-
increases HDL biogenesis
- increasing hepatic expression of ABCA1
This is a GOOD THING
**Nicotinic Acid (Niacin): **
Pharmacokinetics
- Oral administration
- 3 different formulations
- immediate release
- Long acting release
- extended release preparation
- Remember that doses used for lowering cholesterol/TG much greater than those used as vitamin
- Prescription only
Nicotinic acid (niacin):
Major Adverse effect
MAJOR ADVERSE EFFECT
-
Intense cutaneous flush/pruritus
- Occurs soon after taking the drug
- poor compliance
- Mediated by vasodilatory PGs
- PGD2 from dermal macrophages
- use of NSAIDs to block the effect
- Occurs soon after taking the drug
**Nicotinic acid (niacin): **
Other Adverse Effects
- GI effects
- nausea/vomiting, abdominal pain, diarrhea
- Avoid in patients with peptic ulcer
-
elevated liver enzymes/usually no hepatic toxicity
- BUT MAJOR concern if combined with statins
- Hyperurecemia
- Contraindicated in patients with gout
- Increases fasting glucose levels/niacin-induced insulin resistance
- Questionable use in patients with diabetes
What are the contraindications for niacin?
- Peptic Ulcer
- Gout
- Hepatic Disease
- Diabetes
What can happen if niacin is combined with statins?
Combined use with statin increases risk of myopathy
Niacin Lipoprotein Profile
- TG
- LDL
- HDL
- Lp(a)
-
TG decreased by 35-50%
- Within 4-7 days
-
LDL decreased by 25%
- 3-6 weeks for maximal effect
-
HDL increased by 15-30%
- added benefit is increased HDL
-
Lp(a) reduced by 40%
- May be risk factor
**Nicotinic acid (niacin): **
Clincal Uses
-
Hypercholesterolemia & hypertriglyceridemia
- High LDL and low HDL
- Typically not first line therapy for hypercholesterolemia
- Severe cases that do not respond to resins
- Not first choice because of side effects
- Only lipid-lowering drug that reduces Lp(a)
What inhibits cholesterol absorption?
Ezetimibe
**Ezetimibe: **
Mechanism of Action
- What is the net result?
inhibits cholesterol transfer from intestinal lumen into intestinal cell
- binds to a protein transporter called Niemann Pick Cl-like 1 protein (NPCL1)
- on or within brush border membranes of intestinal cells.
-
net result:
- decreased rate of cholesteryl ester incorporation into chylomicrons
- reduced flux of cholesterol from intestine to liver
- reduced flux of cholesterol to VLDL
- lowers plasma LDL-C because increased expression of LDL receptors
Ezetimibe:
Pharmacokinetics
- Oral administration
- Metabolized (glucuronidation) to active metabolite
- Half-life: 22 hours
**Ezetimibe: **
Adverse Effects
- Well tolerated
- Side effects increase if combined with other drugs, like statins
Ezetimibe Lipoprotein Profile
- TG
- LDL
- HDL
-
TG
- decrease by 5%
-
LDL
- decrease by 15-20%
-
HDL
- increase by 1-2%
Ezetimibe:
Clinical Uses
- Primary hypercholesterolemia
- Combined with statins
- Simvastatin + ezetimibe
- Further decrease in LDL-cholesterol
- Two differing pharmacological approaches
What is a potential downside to combination therapy of ezetimibe + statins?
may increase risk of myopathy
What are the Fibric Acids/Fibrates/PPAR activators?
What is the general function of these drugs?
- Gemfibrozil
- Fenofibrate (2nd generation drug)
- Primarily lower the levels of TG-rich lipoproteins
Fibric Acids/Fibrates/PPAR activators:
Mechanism of Action
- effects mediated by interaction with peroxisome proliferator activated receptors (PPARs) that regulate gene transcription
- bind to PPAR-alpha (expressed 1˚ in liver and brown adipose tissue)
- PPAR bind as heterodimers with retinoid X receptor to specific response elements and alter the transcription rate of target genes
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What are the net effects of fibric Acids/fibrates/PPAR activators?
- increased lipolysis and plasma clearance of TG-rich lipoproteins
- activation of lipoprotein lipase
- reduce production of lipoprotein lipase inhibitor, apoCIII
- reduced availability of FFA for TG synthesis
- increase B-oxidation pathway
- c. inhibition of de novo fatty acid synthesis
- decrease acetyl-CoA carboxylase
- decrease fatty acid synthase
- increases in HDL – cholesterol
- increases synthesis of 2 proteins in HDL: apoA1 and apoAII
**Fibric Acids/Fibrates/PPAR activators: **
Pharmacokinetics
- What is the difference of metabolism between fenofibrate and gemfibrozil?
- Oral administration
- Plasma protein binding
- Half-life varies (1 hr for gemfibrozil/20 hrs for fenofibrate (increased with renal impairment)
-
Fenofibrate is metabolized to active metabolite
- excreted predominantly as glucuronide conjugates
- 60-90% of an oral dose is excreted in the urine
- Gemfibrozil metabolized into inactive metabolites
Fibric acids/Fibrates/PPAR actvators:
Adverse effects
Generally well-tolerated
- GI symptoms-most common
- Increased risk of gall stones
- Less common are hematological/hepatic function abnormalities
- increased creatine kinase if also being treated with a statin….lead to renal failure
- Use is contraindicated in patients with renal impairment
- Gemfibrozil can increase systemic statin concentrations by blocking transporter in liver
What drugs does gemfibrozil interact with?
Statins
- Gemfibrozil inhibits uptake of active hydroxy acid forms of statins by transporter
- first-pass hepatic uptake of these statins by transporter OATP1B1 after their oral administration
- If not taken up into liver, increased plasma concentration
Fibric acid Lipoprotein Profile
- TG
- LDL
- HDL
-
TG
- decrease 30-50%
-
LDL
- decrease 15-20%
- HIGHLY VARIABLE
- 2nd generation drugs (fenofibrate) more likely to decrease LDL 15-20% in patients with TG < 400 mg/dL
- decrease 15-20%
-
HDL
- increase 5-15%
Fibric acids/Fibrates/PPAR activators:
Clinical Uses
patients with high TGs and low HDL associated with metabolic syndrome or type 2 diabetes
- treatment of hypertriglyceridemia
- reduces the risk of CHD development in Fredrickson type IIb
Drugs of choice for hypercholesterolemia:
What are some things to consider when choosing such drugs?
-
HMG CoA reductase inhibitors-first choice agents
- Which one?
- Safety?
- Lifetime treatment
-
Bile acid resins
- Long-term safety
- Younger patient age range
- Add on to statins
-
Ezetimibe
- Safety as monotherapy vs MAYBE…add-on to statins
-
Niacin
- Patient compliance side effects
- Both elevated TG and cholesterol
- Low HDL
- Care when combined with statins
Drugs of choice for hypertriglyceridemia:
-
gemfibrozil/fenofibrate
- drug of choice in patients with type III hyperlipoproteinemia and severe hypertriglyceridemia (TG > 1000 mg/dl)
-
niacin
- second line choice
- omega-3 fatty acid
What are the omega-3-fatty acids that have therapeutic effects?
-
Eicosapentaenoic acid
- (EPA 20:5 n−3)
-
Docosahexaenoic acid
- (DHA 22:6 n−3)
What is the therapeutic mechanism of omega-3-fatty acids?
-
inhibit (−) lipogenesis
- inhibit diacylglycerol acyl transferase (DGAT), phosphatidic acid phosphohydrolase (PA), and hormone-sensitive lipase
-
stimulate (+):
- β-oxidation
- phospholipid synthesis
- apolipoprotein (apo) B degradation
- end result is a reduced rate of secretion of very-low-density lipoprotein (VLDL) TG
Omega-3-fatty acids:
Pharmacokinetics
-
Oral:
- 4 g/day as a single daily dose or in 2 divided doses
- Onset of action is slow
Omega-3-fatty acids:
Adverse Effects
- Fish allergy
- May increase LDL levels
- May increase liver enzymes
- Prolongation of bleeding time has been observed in some clinical studies
What are omega-3-fatty acids clinically used for?
Adjunct to diet therapy in the treatment of hypertriglyceridemia (≥500 mg/dL)
What are targets of future drug therapies?
- Proprotein convertase subtilisin/kexin 9 (PCSK9) Inhibitors
- Microsomal triglyceride transfer protein (MTP) Inhibitors
- Apolipoprotein B-100 (apoB-100) Inhibition
Describe the physiological role of PCSK9 (Proprotein convertase subtilisin/kexin type 9):
Why is it a potential target for therapy?
- Decreases the steady-state level of expression of the LDL receptor on the hepatocyte cell membrane
- Autocatalytic cleavage in the ER followed by secretion into plasma where it binds the EGF-A domain of the LDLr
- LDLr/PCSK9 complex gets internalized and targeted to the lysosomal compartment for degradation ⇒
- Inhibition of the recycling of the LDLr back to the cell surface ⇒ increased plasma LDL levels (antibodies, siRNA)
- No change in plasma cholesterol levels in PCSK9/LDLr KO’s ⇒ effect of PCSK9 is mediated solely via LDLr
What does a PCSK9 antibody prevent?
- What is the result?
PCSK9 antibody prevents binding of PCSK9 to the LDLR-LDL complex
-
Result:
- increases the availability of cell-surface LDLRs
What is microsomal triglyceride transfer protein (MTP)?
What is its role?
- major cellular protein that transfers neutral lipids between membrane vesicles
-
essential chaperone for the biosynthesis of apolipoprotein B (apoB)-containing triglyceride-rich lipoproteins
- abetalipoproteinemia patients carry mutations in the MTTP gene resulting in the loss of its lipid transfer activity.
- Role in the regulation of cholesterol ester biosynthesis
What is the FDA approved MTP inhibitor?
What is the mechanism of action?
- Lomitapide
- directly binds to and inhibits MTP
- MTP inhibition prevents the assembly of apo-B containing lipoproteins in enterocytes and hepatocytes resulting in reduced production of chylomicrons and VLDL and subsequently reduces plasma LDL-C concentrations
**MTP Inhibitors: **
Clinical Use
Adjunct to dietary therapy and other lipid-lowering treatments to reduce:
- LDL-C
- total cholesterol
- apolipoprotein B
- non-HDL-C in patients with homozygous familial hypercholesterolemia
What is apolipoprotein B-100?
What is its function?
- structural apolipoprotein that is an essential component of LDL-C and VLDL
- ApoB-100 is the ligand that binds LDL to its receptor and is important for the transport and removal of atherogenic lipids
- Elevated levels of apoB, LDL-C and VLDL are associated with increased risk of atherosclerosis and cardiovascular diseases
What is the FDA approved Apo B-100 inhibitor?
What is the mechanism of action?
Mipomersen
- 20-base sequence second-generation antisense oligonucleotide developed to inhibit synthesis of apoB-100 in the liver
- hybridizes within the coding region of apoB-100 mRNA and activates RNase H
- __RNase H degrades the mRNA strand but leaves the antisense oligonucleotide intact
What is apo B-100 inhibition first-line therapy for?
first-in-class drug for treatment of homozygous familial hypercholesterolemia
How is apo B-100 inhibtion administered?
What are adverse effects?
- Pharmacokinetics:
- subQ
- Side Effects:
- injection site reactions
- flu-like symptoms
- headache
- elevation of liver enzymes