1

5. Anti-hyperlipidemic Agents Arteriosclerosis is excessive formation and deposition of endogeneous products from blood.

In 1984 a 1% drop in serum cholesterol was found to reduce the risk to coronary heart disease (CHD) by nearly 2%.

2

• Particles found in plasma that transport lipids including cholesterol

• Lipoprotein classes– chylomicrons: take lipids from small intestine

through lymph cells– very low density lipoproteins (VLDL)– intermediate density lipoproteins (IDL)– low density lipoproteins (LDL)– high density lipoproteins (HDL)

Lipoproteins

3

Lipoprotein Particles

Classification of lipoprotein particles

Composition Density Size

Chylomicrons TG (90%) >>, CE Low Large

VLDL TG (60%) > CE

IDL CE > TG

LDL CE (50%) >> TG

HDL CE (25%) > TG High Small

4

Role of Lipids (Lipoproteins) in Metabolism

Triglycerides Major energy source for cells

Cholesterol Cell growth, cell division, membranerepair, steroid hormone production

Lipids Transport of fat soluble vitamins

5

• age– men >45 years of age; women > 55 years

of age• family history of CHD• smoking• hypertension >140/90 mm Hg• low HDL cholesterol• obesity >30% overweight• diabetes mellitus• inactivity/ lack of exercise

Factors promoting elevated blood lipids

6

Strategy for Controlling Hyperlipidemia

Serum Cholesterol Cellular CholesterolLDL-R

Conversion to hormones within

cells or storageas granules

HMG CoA reductase

STATINSDiet Biosynthesis

Bile Acids

Intestine

Feces

Re-absorption

BILE ACIDSEQUESTRANTS

Lipoproteincatabolism

FIBRATES

Ezetimibe

7

– The drugs currently in use can be classified according to their main mode of action into:

5.1. Drugs affecting lipoprotein production through inhibition of different stages of lipid synthesis and lipoprotein formation.5.2. Drugs that induce substances that interfere with intestinal absorption and reabsorption of lipids during enterohepatic circulation.5.3. Compounds that directly enhance the rate of metabolic degradation.

8

5.1. Drugs affecting lipoprotein production

5.1.1. Nicotinic acid and derivatives

Nicotinic Acid (Niacin)

N

CO2H

It reduces serum cholesterol and TG levels

The exact mechanism is unknown. It is known that niacin decreases lipolysis in adipose tissue, decreases TG esterification in the liver and increase LPL (lipoprotein lipase) activity.  Niacin is rapidly absorbed.

9

Acipimox

N

N CO2H

H3C

O

2-Carboxy-5-methylpyrazine-4-oxide

It has greater antilipolytic activity than nicotinic acid (Niacin).

5.1.2. Aryloxyisobutyric acid and 3ry butylphenol derivatives (Fibrates)

– The drugs of this class have similar chemical, pharmacological, and clinical properties which act primarily as antihypertriglyceridemic agents, the decrease in cholesterol levels is only moderate.  The fibrates are almost never used alone. They are mostly used in combination with bile acid sequestering agents. 

10

Clofibrate O

OR

H3C CH3

O

Cl

R = H: Clofibric acid, 2-(4-chlorophenoxy)-2-methylpropionic acid.

R = C2H5: Clofibrate, ethyl 2-(4-chlorophenoxy)-2-methylpropionate

Clofibrate is metabolized to chlorophenoxyisobutyric acid (CPIB) which is the active form of the drug.

Synthesis

OONa

H3C CH3

O

Cl

Cl OH

O

NaOH+ + CHCl3C2H5I

OOEt

H3C CH3

O

Cl

11

Gemfibrozil

O CO2HH3C

CH3

H3C CH3

5-(2,5-Dimethylphenoxy)-2,2-dimethylpentanoic acid

It was introduced in 1981 and remains the second most useful antihyperlipidemic agent. It primarily decreases serum triglycerides.

Simfibrate

OO O

O

Cl Cl

O O

H3C CH3 H3C CH3

It is an identical twin ester prodrug of Clofibrate.

12

EtofibrateO

O

O

H3C CH3

Cl

O

O

N

It is a non-identical twin ester prodrug, combines the structural elements of nicotinic acid and Clofibrate, therefore, it is used in all types of hyperlipidemias.

5.1.3. Probucol

S S

CH3H3C

OH

CH3H3C

H3CCH3

CH3 H3CCH3

CH3

H3C CH3 H3C CH3

HO

It was developed for the plastics and rubber industry in 1960. The molecule has 2 identical groups of 3ry butylphenol groups linked by a dithiopropylidene bridge, giving it a high lipophilic character with strong antioxidant properties. In humans it reduces LDL and causes reduction of both liver and serum cholesterol.

13

5.1.4. HMG-CoA Reductase Inhibitors (Statins)

Statins are most effective cholesterol lowering drugs. Statins lower total cholesterol and LDL particles, they are competitive inhibitors.

The HMG-CoA has a conformation similar to the lactone moiety of statins resulting in binding at the same site without any productive effect.

CH3-C-SCoA -OOC-CH2-C-CH2-C-SCoA

O O

OH

CH3

acetyl coenzyme A 3-hydroxy-3-methyl-glutaryl-CoA

CH3-C-SCoA -OOC-CH2-C-CH2-C-SCoA

O O

OH

CH3

acetyl coenzyme A 3-hydroxy-3-methyl-glutaryl-CoA

HMG CoAreductase

CH3

CH3

CH3

CH3

CH3

OH

cholesterol

CH3

CH3

CH3

CH3

CH3

OH

cholesterol

-OOC-CH2-C-CH2-CH2-OH

OH

CH3

mevalonate

-OOC-CH2-C-CH2-CH2-OH

OH

CH3

-OOC-CH2-C-CH2-CH2-OH

OH

CH3

mevalonate

Acetyl CoA

d

HMG CoA

d

Mevalonic Acid

d

Cholesterol

HMG CoAReductase

14

O

OOH OH

OH

COONa OH

SCoA

COOH

O

For example, Mevastatin Lovastatin Simvastatin

For example, Fluvastatin Atorvastatin Cerivastatin

HMG CoA substrate

competitive binding due to Similarity in conformation of the active moiety.

15

Statins

• Inhibit the rate limiting step in cholesterol biosynthesis (HMG CoA reductase)• Lower total cholesterol and LDL• Competitive inhibitors with affinity higher than the substrate (HMG CoA)

CH3

CH2CH2O

O

CH3

R'

R''

O

OOH

R' R''

Mevastatin H HLovastatin H CH3

Simvastatin CH3 CH3

R

R

CH3

CH2CH2O

O

OH

CH3

OH

OH

COONa

Pravastatin

R

R

CH3

CH2CH2O

O

CH3

R'

R''

O

OOH

R' R''

Mevastatin H HLovastatin H CH3

Simvastatin CH3 CH3

R

R

CH3

CH2CH2O

O

CH3

R'

R''

O

OOH

R' R''

Mevastatin H HLovastatin H CH3

Simvastatin CH3 CH3

R

R

R

R

CH3

CH2CH2O

O

OH

CH3

OH

OH

COONa

Pravastatin

R

R

CH3

CH2CH2O

O

OH

CH3

OH

OH

COONa

Pravastatin

R

R

R

R

16

Statins

N

OH

OH

COONa

CH3

CH3

CH3 CH3

OCH3

F

Cerivastatin

NH

N

CH2

F CH2

OH

OH

COO Ca

CH3

CH3

O

Atorvastatin

_ +

N

OH

OH

COONa

CH3

CH3

F

Fluvastatin

17

Bioavailabilty Dosage (mg)

Protein Binding

Metabolites

Atorvastatin ~14% 10 – 80 >98% Active

Cerivastatin ~60% 0.2 – 0.3 >99% Active

Fluvastatin ~24% 10 – 80 98% Active

Lovastatin ~5% 10 – 80 >95%

Pravastatin ~17% 10 – 40 ~50%

Simvastatin ~5% 10 – 80 ~95%

All statins are highly protein bound (95-98%) except for pravastatin (50%)

Most statins have a short half-life of about 1-3 hr except for atorvastatin which has a t1/2 of about 14 h.

18

Small Intestine

Liver

Gall Bladder

Enterohepatic Circulation of Bile

Bile acids are created in the liver using cholesterol and are secreted into the small intestine to aid in digestion. They are reabsorbed in the distal end and are taken back to the liver in the portal circulation.

Bile acid binding resins prevent the reabsorption of bile acids, causing them to be eliminated via the large bowel. This forces the liver to remove cholesterol from the circulation (via an upregulation of LDL-C receptors) in order to make more bile, causing a decreases systemic cholesterol levels.

Side effects:ConstipationDyspepsiaGas bloating

5.2. Drugs affecting intestinal absorption and reabsorption

5.2.1. Ion-Exchange Resins and Sitosterol

19

Colestipol and cholestyramine are anion exchange resins that are approved in 1970s for the reduction of elevated serum cholesterol in patients with hypercholesterolemia.

One of greatest advantage of these polymeric agents is that they can be safely used for pregnant women.

20

b-Sitosterol CH3

CH3

HO

H3C

CH3 CH3

CH3

It has a structure very similar to that of cholesterol, it inhibits cholesterol absorption competitively.

Ezetimibe

NF

OH

F

O

OH

It is a once-daily orally active cholesterol absorption inhibitor, launched in 2002 as a hypolipidemic agent. It acts in the intestinal wall to inhibit cholesterol absorption through a novel mechanism with an as yet undiscovered target

It has no significant effect on the activity of the major drug-metabolizing enzymes.

21

5.3. Thyroxine Analogs

Thyroid hormones increase the catabolic rate of cholesterol and the elimination of LDL from the plasma, but LDL synthesis remains unchanged.

Dextrothyroxine (D-Thyroxine).

I

I

HO

I

I

CO2H

NH2

22

6. Anticoagulants

Compounds that do not allow blood to clot are called anticoagulants.

Drugs that dissolve pre-formed clot including streptokinase are not referred to as anticoagulants.

Hemostasis is a combination of events that occur due to physical and chemical forces. The initial steps lead to a reduction in the blood flow due to the formation of a cellular plug. The later steps utilize chemical energy to form a blood clot, medically known as thrombus.

23

The Physical Process

24

Types of Anticoagulants

6.1. Endogenous Inhibitors of Clotting

6.2. Exogenous Inhibitors of Clotting

The control of clotting is a major medical concern. Several inhibitors have been developed with different mechanisms of anticoagulant action. These include:

6.2.1. Heparins

Heparin is a mucopolysaccharide with a molecular weight ranging from 6,000 to 40,000 Da. The average molecular wt. of most commercial heparin preparations is in the range of 12,000 - 15,000.

25

26

The polymeric chain is composed of repeating disaccharide unit of D-glucosamine and uronic acid linked by 1¯¯>4 interglycosidic bond.

O

CH2

O3SO

O

OH

HN

O

O

COO

OH

OH

O

O

CH2

O3SO

OSO3

HN

SO3SO3

O

O

OSO3

O

O

CH2

O3SO

OH

HNSO3

O

OHCOO

Few hydroxyl groups on each of these monosaccharide residues may be sulfated giving rise to a polymer with that is highly negatively charged.

27

1. The key structural unit of heparin is a unique pentasaccharide sequence. This sequence consists of three D-glucosamine and two uronic acid residues.

SAR

2. The central D-glucosamine residue contains a unique 3-O-sulfate moiety that is rare outside of this sequence.

3. Four sulfate groups on the D-glucosamines are found to be critical for retaining high anticoagulant activity. Elimination of any one of them results in a dramatic reduction in the anticoagulant activity.

4. Removal of the unique 3-O-sulate group results in complete loss of the anticoagulant activity. Removal of sulfate groups other than the critical ones seems to not affect the anticoagulant activity.

28

Only a third of the chains in commercial heparin preparations have this unique pentasaccharide sequence. Thus, more than 2/3rd of heparin chains are probably not active as anticoagulants. LMW heparin preparations may have considerably varying proportion of chains with the active site.

Metabolism

Partially metabolized in the liver by heparinase to uroheparin, which has only slight antithrombin activity, 20-50% is excreted unchanged.

29

They are preparations that have lower average molecular weight than heparin. The average molecular weight of these LMWH typically ranges from 2,000 to 8,000 Da.

Low-Molecular-Weight Heparins (LMWH)

They are made by enzymatic or chemical controlled hydrolysis of unfractionated heparin. These molecules have very similar chemical structure as unfractionated heparin except for some changes that may have been introduced due to the enzymatic or chemical treatment. The overall advantage in the use of these LMWH appears to be in the decreased need for monitoring patients in comparison to heparin.

30

Properties of Heparin

– Because of its highly acidic sulfate groups, heparin (or LMW heparins) exists as a polyanion at physiologic pH.

–The heparin polysaccharide chain is degraded in the gastric acid and must therefore be administered intravenously or subcutaneously.

– LMW heparin, because of its smaller size, is more bioavailable when given subcutaneously.

– Heparin is typically not given intramuscularly because of the danger of hematoma formation.

– Peak activity of heparin is reached within minutes of administration and is found to last 2-6 h (iv) or 8-12 h (sc).

– Heparin is relatively non-toxic and can be safely used in pregnancy because it does not cross the placental barrier.

31

– Heparin overdose or hypersensitivity may result in excessive bleeding.

– If hemorrhage occurs the anticoagulant effect of heparin can be reversed in minutes by administration of protamine sulfate, a low molecular weight protein that has multiple positively charged groups.

32

Fondaparinux sodium

– It is introduced in 2002 in the US for prophylaxis of deep vein thrombosis which may lead to pulmonary embolism following major orthopaedic surgery.– It is the first of a new class of antithrombic agents distinct from LMWH and heparin. This entirely synthetic molecule is a copy of pentasaccharide sequence.

33

6.2.2. Coumarins

Coumarin and its derivatives are principal oral anticoagulants.

Coumarin is water insoluble, however 4-hydroxy substitution confers weakly acidic properties to the molecule that makes it water soluble under slightly alkaline conditions.

The followings are the structures of coumarin and its derivatives (Coumarin, 4-Hydroxycoumarin, Warfarin and Dicoumarol) :

34

Warfarin is marketed as the sodium salt as racemate , however, The S(-) isomer is about 5 - 8 times more potent than the R(+) isomer.

35

Warfarin is a competitive antagonist of Vitamin K

36Vitamin K-dependent clotting factors(FII, FVII, FIX, FX, Protein C/S/Z)

EpoxideReductase

-Carboxylase

Warfarin inhibits the vitamin K cycleWarfarin

Inactivation

CYP2C9

Pharmacokinetic

37

Synthesis of Warfarin

OH

OH

O

(CH3CO)2O

O

OH

O

CH3

O

Strong base

Nonaq.O

OH

O

CH2

O

O

O

O

OO

ONa

O

CH3

O

38

The minimal requirements for anticoagulant activity are:1. 4-hydroxy group. 2. A 3-substituent.

SAR :

ASSAY of Warfarin (EURP 2000)

Spectrophotometric assay of the its alkaline solution (NaOH) at the maximum at 308 nm.

39

6.2.3. 1,3-Indanediones

The 1,3-indanediones have been known to be anticoagulant since 1940s. A commercially available indandione is anisindione.

The molecule has a weakly ionizable proton on C-2 that is extracted in alkaline solutions to confer mildly soluble properties.

H

OCH3

O

O

O

O

OCH3

OH+ H2O

40

The anion so formed in alkaline solutions is reddish - orange. Thus patients on anisindione treatment may be alarmed to see reddish colored urine. This phenomenon may be easily distinguished from hematuria by acidification of the urine which should remove the red color.

6.2.4. Platelet affecting Drugs

6.2.4.1. Inhibition of prostaglandin (PG) synthesis

Substances that inhibit PG synthesis can prevent only one of the pathways by which platelets are able to mediate thrombogenesis. They include COX inhibitors

41

Acetylsalicylic acid (Aspirin)

It inhibits the platelet aggregation in a dose ranging from 160-230 mg.

COOH

O CH3

O

2-Acetoxybenzoic acid

42

6.2.4.2. Substances influencing cAMP

Increase of cAMP prevents the initial shape changes of the platelets, their adhesion to surface, the aggregation and release reaction.

Prostacyclin

O

OH

CO2HHO

It is the most active platelet aggregation inhibitor. It has a very short duration of action so it is administered in continuous infusion. It is unstable in aq. soln, its sod. salt is more stable in solid form.

43

6.2.4.3. Inhibition of platelet-specific agonists-receptor interaction.

The platelets are activated by substances that interact with specific receptors in the plasma membrane. Thus inhibition of these substances will limit the activation.

TiclopidineCl

N

S

It is a long acting platelet aggregation inhibitor (24-48 hrs).

44 From: Cleveland Clinic Journal of Medicine; 66(10):615

45

Direct Thrombin Inhibitors

NH

O

N

C H 3

H

S

O

O

CH 3 N H

N HNH 2

C O O H

A r g a t r o b a n

N H 2

NNH

O

N

O

NH R '

O

R O

X i m e l a g a t r a n R = - C H 2 C H 3 ; R ’ = - O HM e l a g a t r a n R = - H ; R ’ = - H

N H 2

N R 'NH

N

N

C H 3

O

N

N

R O

O

D a b i g a t r a n e t e x i l a t e R = - C H 2 C H 3 ; R ’ = - C O O - n C 6 H 1 3D a b i g a t r a n R = - H ; R ’ = - H

H 2 N - D - P h e - P r o - A r g - P r o - G l y - G l y - G l y - G l y - A s n - G l y

H O O C - L e u - T y r - G l u - G l u - P r o - I l e - G l u - G l u - P h e - A s p

B i v a l i r u d i n

F i g u r e 2 . S t r u c t u r e s o f d i r e c t t h r o m b i n i n h i b i t o r s ( D T I s ) . S h a d e d o v a l r e p r e s e n t s t h e g u a n i d i n e o r a m i d i n e g r o u p t h a t m i m i c s t h e a r g i n i n e s i d e c h a i n o f t h e P - 1 r e s i d u e r e c o g n i z e d b y t h r o m b i n .

NH

O

N

C H 3

H

S

O

O

CH 3 N H

N HNH 2

C O O H

A r g a t r o b a n

NH

O

N

C H 3

H

S

O

O

CH 3 N H

N HNH 2

C O O H

A r g a t r o b a n

N H 2

NNH

O

N

O

NH R '

O

R O

X i m e l a g a t r a n R = - C H 2 C H 3 ; R ’ = - O HM e l a g a t r a n R = - H ; R ’ = - H

N H 2

NNH

O

N

O

NH R '

O

R O

X i m e l a g a t r a n R = - C H 2 C H 3 ; R ’ = - O HM e l a g a t r a n R = - H ; R ’ = - H

N H 2

N R 'NH

N

N

C H 3

O

N

N

R O

O

D a b i g a t r a n e t e x i l a t e R = - C H 2 C H 3 ; R ’ = - C O O - n C 6 H 1 3D a b i g a t r a n R = - H ; R ’ = - H

N H 2

N R 'NH

N

N

C H 3

O

N

N

R O

O

D a b i g a t r a n e t e x i l a t e R = - C H 2 C H 3 ; R ’ = - C O O - n C 6 H 1 3D a b i g a t r a n R = - H ; R ’ = - H

H 2 N - D - P h e - P r o - A r g - P r o - G l y - G l y - G l y - G l y - A s n - G l y

H O O C - L e u - T y r - G l u - G l u - P r o - I l e - G l u - G l u - P h e - A s p

B i v a l i r u d i n

F i g u r e 2 . S t r u c t u r e s o f d i r e c t t h r o m b i n i n h i b i t o r s ( D T I s ) . S h a d e d o v a l r e p r e s e n t s t h e g u a n i d i n e o r a m i d i n e g r o u p t h a t m i m i c s t h e a r g i n i n e s i d e c h a i n o f t h e P - 1 r e s i d u e r e c o g n i z e d b y t h r o m b i n .

HIRUDIN – Isolated from leech, hirudino medicinalis. A polypeptide consisting of 65 amino acid residues that binds thrombin in the active site as well as another site called exosite I

46

6.2.5. Miscellaneous AnticoagulantsCitric Acid

Sodium citrate is an anticoagulant in vitro.

Sodium citrate cannot be used in vivo because of the toxic manifestations of sequestering Ca+2 ions.

47

Chelation of Ca2+ Blood Clotting Clot prevention Clinical Application

Chelate: claw

EDTA is used• to detoxify workers exposed to

toxic heavy metals, e.g., Pb, Cd …

• to decalcify atherosclerotic plaques (chelation therapy) that slows, halts, or reverses progressive hardening of arteries that can trigger clots (via platelet plugs and/or fibrin) thereby lowering risk for stroke and heart attacks.

O

C

C

O–

O–

R

C

O

Ca2+

RCOO–

COO– Ca2+

Structurerepresentations oxalate

Ethylenediaminetetraacetic acid

(EDTA, Versene)

Use: ● collect donated blood

● inhibit blood clotting

citrate

HC

C

C

N

O–

O–H

C

O

OC

C

N

O–

O–

O

O

Ca2+

Ca2+

HO

COOH

COO–

COO– Ca2+

COO–

COO– Ca2+

Metabolic and Chemical Chelators