1. Lipid-Lowering Drugs

2. What are lipoproteins? Lipoproteins are protein-lipid complexes.
Inner droplet of neutral (water-insoluble core lipids); primarily triglycerides and cholesteryl esters
A solubilizing surface layer of phospholipids and unesterified cholesterol
Specific proteins (apolipoproteins) attached to the outer lipid layer through their specific lipophilic domains

3. The Players – Lipids Triacylglycerol Phospholipids Cholesterol
Cholesteryl esters

4. The Players - Apolipoproteins
Apo AI (liver, small intestine)
Structural; activator of lecithin:cholesterol acyltransferase (LCAT)
Apo AII (liver)
Structural; inhibitor of hepatic lipase; component of ligand for HDL binding
Apo A-IV (small intestine)
Activator of LCAT; modulator of lipoprotein lipase (LPL)
Apo A-V (liver)
Direct functional role is unknown; regulates TG levels.

5. Apolipoproteins Apo B-100 (liver) Apo B-48 (small intestine)
Structural; synthesis of VLDL; ligand for LDL-receptor
Apo B-48 (small intestine)
Structural; synthesis of chylomicrons; derived from apo B-100 mRNA following specific mRNA editing
Apo E (liver, macrophages, brain)
Ligand for apoE receptor; mobilization of cellular cholesterol

6. Apolipoproteins Apo C-I (liver) Apo C-II (liver) Apo C-III (liver)
Activator of LCAT, inhibitor of hepatic TGRL uptake
Apo C-II (liver)
Activator of LPL, inhibitor of hepatic TGRL uptake
Apo C-III (liver)
Inhibitor of LPL, inhibitor of hepatic TGRL uptake

7. Amphipathic Helices
Lipoprotein Surface

8. Lipoprotein Classes LDL HDL > 30 nm 20–22 nm 9–15 nm
Chylomicrons, VLDL, and their catabolic remnants
LDL
HDL
Lipoproteins are classified into four groups which differ primarily in the amounts of cholesterol, trigyleride, phospholipids, and types of apolipoproteins they contain
Original classification was a function of hydrated density.
> 30 nm
20–22 nm
9–15 nm
D<1.006 g/ml
D= g/ml
D= g/ml
Doi H et al. Circulation 2000;102: ; Colome C et al. Atherosclerosis 2000; 149: ; Cockerill GW et al. Arterioscler Thromb Vasc Biol 1995;15:
Lipids Online

9. Lipoprotein Metabolism
Exogenous/chylomicron pathway (dietary fat)
Endogenous pathway (lipids synthesized by the liver)
HDL metabolism (apolipoprotein transfer, cholesteryl ester transfer, reverse cholesterol transport

10. Lipoprotein Metabolism
Exogenous/chylomicron pathway (dietary fat)
Endogenous pathway (lipids synthesized by the liver)
HDL metabolism (apolipoprotein transfer, cholesteryl ester transfer, reverse cholesterol transport

11. TG Rich: VLDL Surface Monolayer Phospholipids (12%)
Free Cholesterol (14%)
Protein (4%)
VLDL contain 60-70% triglycerides
Produced by the liver
Transport endogenously synthesized triglycerides to peripheral tissues
Hydrophobic Core Triglyceride (65%) Cholesteryl Esters (8%)
Cholesterol and Atherosclerosis, Grundy)

12. VLDL Metabolism
Apo C’s and apoE and cholesteryl ester are acquired from HDL in circulation
Cholesterol and Atherosclerosis, Grundy)

13. Fatty Acid Transport
ApoC-II activates lipoprotein lipase which catalyses the hydrolysis of TG
Cholesterol and Atherosclerosis, Grundy)

14. VLDL Conversion to LDL
Further action on IDL by hepatic lipase loses additional apolipoproteins (apoE) becomes and is converted to LDL
Cholesterol and Atherosclerosis, Grundy)

15. CE Rich: LDL Surface Monolayer Phospholipids (25%)
Free Cholesterol (15%)
Protein (22%)
Hydrophobic Core Triglyceride (5%) Cholesteryl Esters (35%)
Major cholesterol carrying lipoprotein
2/3 - 3/4 of serum cholesterol is carried by LDL
50% of mass is cholesterol
Produced as a product of VLDL metabolism
Delivers cholesterol to peripheral tissues for biosynthesis and steroid hormone production
Cholesterol and Atherosclerosis, Grundy)

16. LDL Metabolism
LDL is removed by apoB100 receptors which are mainly expressed in the liver
Hepatic Lipase
Cholesteryl ester transfer protein
Cholesterol and Atherosclerosis, Grundy)

17. X X LDL Uptake by Tissues
Defects in the LDL receptor leads to familial hypercholesterolemia
Cholesterol and Atherosclerosis, Grundy)

18. CE Rich: HDL Surface Monolayer Phospholipids (25%)
Free Cholesterol (7%)
Protein (45%)
Hydrophobic Core Triglyceride (5%) Cholesteryl Esters (18%)
Smallest of the lipoproteins
Synthesized by intestine and liver as nascent cholesterol-poor lipoprotein
Accumulates cholesterol and cholesteryl esters through interactions with peripheral cells and other lipoproteins
Participates in reverse cholesterol transport, removal of excess cholesterol from peripheral cells and delivery to the liver for metabolism
Cholesterol and Atherosclerosis, Grundy)

19. HDL Metabolism
Nascent HDL (lipid-poor apoA-I) is produced by the liver and intestine
Pathways involved in the generation and conversion of HDL. Mature HDL3 and HDL2 are generated from lipid-free apoA-I or lipid-poor pre-ß1-HDL as the precursors. These precursors are produced as nascent HDL by the liver or intestine or are released from lipolysed VLDL and chylomicrons or by interconversion of HDL3 and HDL2. ABC1-mediated lipid efflux from cells is important for initial lipidation; LCAT-mediated esterification of cholesterol generates spherical particles that continue to grow on ongoing cholesterol esterification and PLTP-mediated particle fusion and surface remnant transfer. Larger HDL2 particles are converted into smaller HDL3 particles on CETP-mediated export of cholesteryl esters from HDL onto apoB-containing lipoproteins, on SR-BI–mediated selective uptake of cholesteryl esters into liver and steroidogenic organs, and on HL- and EL-mediated hydrolysis of phospholipids. HDL lipids are catabolized either separately from HDL proteins (ie, by selective uptake or via CETP transfer) or together with HDL proteins (ie, via uptake through as-yet-unknown HDL receptors or apoE receptors). The conversion of HDL2 into HDL3 and the PLTP-mediated conversion of HDL3 into HDL2 liberated lipid-free or poorly lipidated apoA-I. A part of lipid-free apoA-I undergoes glomerular filtration in the kidney and tubular readsorption through cubilin. For further details, see text and Table 1 . Blue arrows represent lipid transfer processes, and red arrows represent protein transfer processes. TGRL indicates triglyceride-rich lipoproteins

20. Hepatic Cholesterol Metabolism

21. Hepatic Cholesterol Synthesis
Only pathway for cholesterol degradation
Rate Limiting
Energetically expensive; prefer to conserve what is already made/acquired – LDL receptor pathway
Cholesterol and Atherosaclerosis, Grundy)

22. LDL Cellular Metabolism
LDL are taken up by the LDL Receptor into clathrin-coated pits
Cholesterol and Atherosaclerosis, Grundy)

23. Endothelial Dysfunction
Increased endothelial permeability to lipoproteins and plasma constituents mediated by NO, PDGF, AG-II, endothelin.
Up-regulation of leukocyte adhesion molecules (L-selectin, integrins, etc).
Up-regulation of endothelial adhesion molecules (E-selectin, P-selectin, ICAM-1, VCAM-1).
Migration of leukocytes into artery wall mediated by oxLDL, MCP-1, IL-8, PDGF, M-CSF.
Ross, NEJM; 1999

24. Formation of Fatty Streak
SMC migration stimulated by PDGF, FGF-2, TGF-B
T-Cell activation mediated by TNF-a, IL-2, GM-CSF.
Foam-cell formation mediated by oxLDL, TNF-a, IL-1,and M-CSF.
Platelet adherence and aggregation stimulated by integrins, P-selectin, fibrin, TXA2, and TF.
Ross, NEJM; 1999

25. Formation of Advanced, Complicated Lesion
Fibrous cap forms in response to injury to wall off lesion from lumen.
Fibrous cap covers a mixture of leukocytes, lipid and debris which may form a necrotic core.
Lesions expand at shoulders by means of continued leukocyte adhesion and entry.
Necrotic core results from apoptosis and necrosis, increased proteolytic activity and lipid accumulation.
Ross, NEJM; 1999

26. Development of Unstable Fibrous Plaque
Rupture or ulceration of fibrous cap rapidly leads to thrombosis.
Occurs primarily at sites of thinning of the fibrous cap.
Thinning is a result of continuing influx of and activation of macrophages which release metalloproteinases and other proteolytic enzymes.
These enzymes degrade the matrix which can lead to hemorrhage and thrombus formation
Ross, NEJM; 1999

27. Role of LDL in Atherosclerosis
Steinberg D et al. N Engl J Med 1989;320:
Endothelium
Vessel Lumen
LDL
LDL Readily Enter the Artery Wall Where They May be Modified
Intima
Modified LDL
Modified LDL are Proinflammatory
Hydrolysis of Phosphatidylcholine to Lysophosphatidylcholine
Other Chemical Modifications
Oxidation of Lipids and ApoB
Aggregation
Role of LDL in inflammation
LDL readily enters the artery wall by crossing the endothelial membrane. Once in the arterial wall, if LDL accumulates, it is subject to a variety of modifications. The best known of these is oxidation, both of the lipids and of the apo B. LDL is also subject to aggregation, and its phospholipids are subject to hydrolysis by phospholipases to form lysophosphatidylcholine. Several other chemical modifications have also been reported. The net effect of these changes is the production of a variety of modified LDL particles, and the evidence is now very strong that these modified LDL particles are proinflammatory.
Reference:
Steinberg D, Parthasarathy S, Carew TE, Khoo JC, Witztum JL. Beyond cholesterol: modifications of low-density lipoprotein that increase its atherogenicity. N Engl J Med 1989;320:
Lipids Online

28. Role of LDL in Atherosclerosis
Endothelium
Vessel Lumen
Monocyte
Macrophage
MCP-1
Adhesion Molecules
Foam Cell
Intima
Modified Remnants
Cytokines
Cell Proliferation Matrix Degradation
Doi H et al. Circulation 2000;102:
Growth Factors Metalloproteinases
Remnant Lipoproteins
Remnants
The remnants of VLDL and chylomicrons are also pro-inflammatory
VLDL remnants and chylomicron remnants behave in much the same way as LDL. They enter the subendothelial space, where they become modified, and the modified remnants stimulate MCP-1, promote the differentiation of monocytes into macrophages, and are taken up by the macrophages to form foam cells. Like LDL, the remnant lipoproteins are proinflammatory and proatherogenic.
References:
Doi H, Kugiyama K, Oka H, Sugiyama S, Ogata N, Koide SI, Nakamura SI, Yasue H. Remnant lipoproteins induce proatherothrombogenic molecules in endothelial cells through a redox-sensitive mechanism. Circulation 2000;102:
Lipids Online

29. HDL Prevent Foam Cell Formation
LDL
Miyazaki A et al. Biochim Biophys Acta 1992;1126:73-80.
Endothelium
Vessel Lumen
Monocyte
Modified LDL
Macrophage
MCP-1
Adhesion Molecules
Cytokines
Intima
HDL Promote Cholesterol Efflux
Foam Cell
HDL prevent formation of foam cells
Perhaps the best-known function of HDL is the promotion of cholesterol efflux from cells. Efflux of cholesterol from foam cells leads to a reduction in foam cell formation; although the macrophages may accumulate, they are not converted into foam cells. As a result, the inflammatory process is arrested to a certain extent. Therefore, HDL is anti-inflammatory and also protects against the development of atherosclerosis.
Lipids Online

30. Atherosclerosis and lipoprotein metabolism
Atheromatous disease is ubiquitous and underlies the commonest causes
of death (e.g. myocardial infarction) and disability (e.g. stroke) in industrial
countries
Hypertension and dyslipidemia are ones of the most important risk factors, amenable to drug therapy
ATHEROMA is a focal disease of the intima of large and medium-sized arteries
A t h e r o g e n e s i s involves several stages:
endothelial dysfunction with altered PGI2 and NO synthesis
monocyte attachment
endothelial cells bind LDL
oxidatively modified LDL is taken up by macrophages
having taken up oxidised LDL, these macrophages (now foam cells) migrate
subendothelially
atheromatous plaque formation
rupture of the plaque

31. Atherosclerosis and lipoprotein metabolism
LIPIDS, including CHOLESTEROL (CHO) and TRIGLYCERIDES (TG), are transported in the plasma as lipoproteins, of which there are four classes:
- chylomicrons transport TG and CHO from the GIT to the tissues, where
they are split by lipase, releasing free fatty acids.There are taken up in muscle and adipose tissue. Chylomicron remnants are taken up in the liver
- very low density lipoproteins (VLDL), which transport CHO and newly synthetised TG to the tissues, where TGs are removed as before, leaving:
- low density lipoproteins (LDL) with a large component of CHO, some of which is taken up by the tissues and some by the liver, by endocytosis via specific
LDL receptors
- high density lipoproteins (HDL).which absorb CHO derived from cell breakdown in tissues and transfer it to VLDL and LDL

32. Atherosclerosis and lipoprotein metabolism
There are two different pathways for exogenous and endogenous lipids:
THE EXOGENOUS PATHWAY: CHO + TG absorbed from the GIT are transported in the lymph and than in the plasma as CHYLOMICRONS to capillaries in muscle and adipose tissues. Here the core TRIGL are hydrolysed by lipoprotein lipase, and the tissues take up the resulting FREE FATTY ACIDS
CHO is liberated within the liver cells and may be stored, oxidised to bile aids or secreted in the bile unaltered
Alternatively it may enter the endogenous pathway of lipid transpor in VLDL

33. Atherosclerosis and lipoprotein metabolism
ENDOGENOUS
PATHWAY
EXOGENOUS
PATHWAY

34. Atherosclerosis and lipoprotein metabolism
THE ENDOGENOUS PATHWAY
CHO and newly synthetised TG are transported from the liver as VLDL to muscle and adipose tissue, there TG are hydrolysed and the resulting
FATTY ACIDS enter the tissues
The lipoprotein particles become smaller and ultimetaly become LDL ,
which provides the source of CHO for incorporation into cell membranes, for synthesis of steroids, and bile acids
Cells take up LDL by endocytosis via LDL receptors that recognise LDL apolipoproteins
CHO can return to plasma from the tissues in HDL particles and the resulting cholesteryl esters are subsequently transferred to VLDL or LDL
One species of LDL – lipoprotein - is associated with atherosclerosis (localised in atherosclerotic lesions). LDL can also activate platelets, constituting a further thrombogenic effect

35. Dyslipidemia Dyslipidemia can be primary or secondary.
The normal range of plasma total CHO concentration < 6.5 mmol/L.
There are smooth gradations of increased risk with
elevated LDL CHO conc, and with reduced HDL CHO conc.
Dyslipidemia can be primary or secondary.
The primary forms are genetically determined
Secondary forms are a consequence of other conditions
such as diabetes mellitus, alcoholism, nephrotic sy,
chronic renal failure, administration of drug…

36. Lipid-lowering drugs Several drugs are used to decrease plasma LDL-CHO
Drug therapy to lower plasma lipids is only one approach to treatment
and is used in addition to dietary management
and correction of other modifiable cardiovascular risk factors

37. increase in synthesis of CHO receptors + increased clearance of LDL
LIPID-LOWERING DRUGS: Statins
HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) reductase inhibitors. The reductase catalyses the conversion of HMG-CoA to mevalonic acid; blocks the synthesis of CHO in the liver:
Simvastatin + pravastatin + atorvastatin
decrease hepatic CHO synthesis: lowers total and LDL
increase in synthesis of CHO receptors
+ increased clearance of LDL
Stimulates the exprssion of more enzyme  restores CHO synthesis to normal.
Several studies demonstrated positive effects on morbidity and mortality.
Reltatively few side-effects...
However, adverse effects: myopathy (incr in pts given combined therapy with nicotinic acid or fibrates. Should not be given during pregnancy.

38. Promising pharmacodynamic actions:
LIPID-LOWERING DRUGS
Statins
Promising pharmacodynamic actions:
improved endothelial function
reduced vascular inflammation and platelet aggregability
antithrombotic action
stabilisation of atherosclerotic plaques
increased neovascularisation of ischaemic tissue
enhanced fibrinolysis
immune suppression
osteoclast apoptosis and increased synthetic activity in
osteoblasts

39. LIPID-LOWERING DRUG Statins
Pharmacokinetics
well absorbed when given orally
extracted by the liver (target tissue), undergo extensive presystemic biotransformation
Simvastatin is an inactive pro-drug

40. LIPID-LOWERING DRUG Statins
C l i n i c a l u s e s
Secondary prevention of myocardial infarction and stroke in patients who have symptomatic atherosclerotic disease (angina, transient ischemic attacks) following acute myocardial infarction or stroke
Primary prevention of arterial disease in patients who are at high risk because of elevated serum CHO concentration, especially it there are other risk factors for atherosclerosis
Atorvastatin lowers serum CHO in patients with homozygous familiar hypercholesterolemia

41. LIPID-LOWERING DRUG Statins
A d v e r s e e f f e c t s:
mild gastrointestinal disturbances
increased plasma activities in liver enzymes
severe myositis (rhabdomyolysis)
and angio-oedema (rare)

42. LIPID-LOWERING DRUGS: Fibrates
- stimulate the β-oxidative degradation of fatty acids
- liberate free fatty acids for storage in fat or for metabolism in
striated muscle
- Are ligands for nuclear txn receptor, peroxisome proliferator-activated recptor-α (PARP-α)
- increase the activity of lipoprotein lipase,
hence increasing hydrolysis of triglyceride in chylomicrons
and VLDL particles.
reduce hepatic VLDL production and increase hepatic LDL
uptake.
Produce a modest decrease in LDL (~ 10%) and increase in HDL (~ 10%).
But, a marked decrease in TGs (~ 30%).

43. fenofibrate clofibrate gemfibrozil ciprofibrate
LIPID-LOWERING DRUGS
Fibrates
O t h e r e f f e c t s :
improve glucose tolerance
inhibit vascular smooth muscle inflammation
fenofibrate clofibrate
gemfibrozil ciprofibrate

44. A d v e r s e e f f e c t s: LIPID-LOWERING DRUGS Fibrates
in patients with renal impairment myositis (rhabdomyolysis)
myoglobulinuria, acute renal failure
Fibrates should be avoided in such patients and also in alcoholics)
mild GIT symptoms

45. LIPID-LOWERING DRUGS 1st-line defense for:
Fibrates
1st-line defense for:
*mixed dyslipidemia (i.e. raised serum TG and CHO)
* patients with low HDL and high risk of atheromatous disease (often type 2 diabetic patients)
* patients with severe treatment- resistant dyslipidemia (combination with other lipid-lowering drugs).
* Indicated in patients with VERY HIGH [TG]s who are at risk for pancreatitis

46. Bile acid binding resins (Anion-exchange resins)
LIPID-LOWERING DRUGS
Bile acid binding resins (Anion-exchange resins)
sequester bile acids in the GIT prevent their reabsorption
and enterohepatic recirculation
The r e s u l t is:
decreased absorption of exogenous CHO and increased metabolism of endogenous CHO into bile acid acids
increased expression of LDL receptors on liver cells
increased removal of LDL from the blood
reduced concentration of LDL CHO in plasma
(while an unwanted increase in TG)

47. Anion-exchange Resins
Increase the excretion of bile acids, causing more CHO to be converted to BAs.
The decr in hepatocyte [CHO]  compenatory incr in HMG CoA reductase activity and the number of LDLRs.
Because these resins don’t work in patients with homozygous familial hypercholesterolemia, increased expression of hepatic LDLRs is the main mechanism by which resins lower plasma CHO.

48. LIPID-LOWERING DRUGS Colestyramin colestipol C l i n i c a l u s e s:
Bile acid binding resins
Colestyramin colestipol
anion exchange resins
C l i n i c a l u s e s:
heterozygous familiar hypercholesterolemia
an addition to a statin if response has been inadequate
hypercholesterolemia when a statin is
contraindicated
uses unrelated to atherosclerosis, including:
pruritus in patients with partial biliary obstruction
bile acid diarrhea (diabetic neuropathy)

49. LIPID-LOWERING DRUGS A d v e r s e e f f e c t s:
Bile acid binding resins
A d v e r s e e f f e c t s:
GIT symptoms - nauzea, abdominal bloating,
constipation or diarrhea, bec resins not absorbed.
resins are unappetizing. This can be minimized by
suspending them in fruit juice
interfere with the absorption of fat-soluble vitamins
and drugs (chlorothiazide, digoxin, warfarin)
These drugs should be given at last 1 hour before or 4-6 hours after a resin

50. Others LIPID-LOWERING DRUGS
Nicotinic acid inhibits hepatic TG production and VLDL
Secretion (by ~ 30-50%)
modest reduction in LDL and increase in HDL.
Nicotinic acid was the 1st lipid-lowering drug to decr overall mortality in patients with CAD.
But its use is limited by the desirable
A d v e r s e e f f e c t s:
flushing, palpitations , GIT disturbances.
Currently, nicotinic acid is rarely used.

51. Others LIPID-LOWERING DRUGS
Fish oil (rich in highly unsaturated fatty acids)
the omega-3 marine TG
- reduce plasma TG but increase CHO (CHO is more strongly associated wih coronary artery disease)
the effects on cardiac morbidity or mortality is unproven
( although there is epidemiological evidence that eating fish regularly does reduce ischemic heart disease)

52. Others LIPID-LOWERING DRUGS
Inhibitors of Intestinal CHO Absorption: Ezetimibe:
Reduces CHO and phytosterol absorption and decreases LDL CHP by ~18%, but with little change in HDL CHO.
May be synergistic with statins: so good for combination therapy.

53. Drug Combinations
Severe hyperlipidemia often requires multiple LLDs to get the job done.
As usual, combinations should involve drugs with different mechanisms of action (e.g., statins with fibrates).
Even though some combinations (foregoing) may increase risk of, say, myopathy, the benefits of lowering LDL CHO outweigh the small incr in adverse effects.
Recent trial with gemfibrozil (fibrate) decr myocardial infarction, stroke, and overall mortality in men with CAD assoc with low HDL (this drug inc HDL CHO w/o decr LDL CHO).

54. Lipid-lowering drugs