Metabolism and Atherogenic Properties ofLDL

Dr Manal Al-Kindi

MD,DCH, FRCPA,AACB,ABCL

Chemical Pathologist & Lipidiologist

Royal Hospital

Muscat

The Sixth IAS-OSLA Course on

Lipid Metabolism and Cardiovascular Risk

Muscat, Oman, February 14-17,2020

Disclosure

• Non

Epidemiology

CVD Risk Factors

Age, Race, Sex4,5

Increased Cardiovascular

Risk

History of CV Event6

Smoking1

Dyslipidemia7

(LDL-C, HDL-C, TG, Lp(a))

Type 2 Diabetes, Metabolic Syndrome1

Modifiable factors

Non-modifiable factors

Obesity1

Genetics3

(e.g., HeFH, HoFH)

Sedentary Lifestyle and Diet1

Hypertension1

Inflammation?2

. Ridker PM, et al. Eur Heart J. 2014; 35(27):1782-1791. 3. Sharifi M, et al. Heart. 2016;102:1003-1008. 4. JellingerPS, et al. Endocr Pract. 2012;18:1-78. 5. Roger VL, et al. Circulation. 2012;125:e2-e220. 6. Stone NJ, et al. J Am CollCardiol. 2014;63:2889-2934.

Increased CV risk is due to modifiable and non-modifiable risk factors

At

INTERHEART Study

High GlobalCV Risk

Acceleratedherosclerosis and

CV disease

S. Yusuf et al. Lancet 2004; 364:937-52

ApoB / ApoAI

LDL accounted for ~ 50% of the population attributable risk LDL-C is a Major Modifiable CV Risk Factor

Effects of Increasing TC Levels on the Risk for CHD in the Presence of Other Risk Factors

05

10152025303540

185 210 235 260 285 310 335

Low HDL

Smoking

Hyperglycemia

Hypertension

No Other Risk Factors

Schaefer EJ, adapted from the Framingham Heart Study

Serum Cholesterol (mg/dL)

0

5

10

15

20

25

30

(2.60) (3.25)(3.90)(4.50) (5.15) (5.80)(6.45) (7.10) (7.75) (8.40)(9.05)

Cholesterol and CHD: Seven Countries Study

Total Cholesterol

CHDmortality

rates(%)

Verschuren WMM et al. JAMA. 1995;274:131-136.

100 125 150 175 200 225 250 275 300 325 350

Northern EuropeUnited StatesSouthern Europe, InlandSouthern Europe,MediterraneanSiberia, Japan

TC mg/dLTC(mmol/L)

Patients with Genetically Lower LDL have Better CV Event Reduction

Ference BA, et al. J Am Coll Cardiol. 2015;65(15):1552-1561.

10%

20%

30%

.003 .005 .078 .104 .130 .155 .181 .207 .233 .259 .285 .311 .330 .363 .389 .389 .440 .466 .492 .518 .5440

Lower LDL-C (mmol/L)

Pro

po

rtio

nal

Ris

k R

ed

uct

ion

(SE

) lo

g sc

ale

PCSK9 46Lrs11591147

ALLHAT-LLT

SEARCH

Pharmacologically Lower LDL-C

A to Z

Genetically Lower LDL-C

GISSI-P

NPC1L1 LDL-C ScoreHMGCR LDL-C Score

IMPROVE-IT

Combined NPC1L1 & HMGCR LDL-C Score

LDLRrs6511720

LDLRrs2228671

PCSK9rs11206510

ABCG5/8rs4299376

HMGCRrs12916

PCSK9rs2479409

NPC1L1rs217386

HMGCR LDL-C Score

NPC1L1 LDL-C Score

Genetic has a Greater effect than Pharmacologically Lower LDL-C− Possibly due to Lifetime Lower LDL levels

The Evidence Reviewed:

To avoid selection bias we evaluated the totality of evidence from separate meta-analyses of prospective epidemiologic studies, Mendelian randomization and other genetic studies, together with randomized clinical trials for causality of LDL in ASCVD

The database included more than 200 studies involving over 2 millionparticipants with over 20 million person-years of follow-up and morethan 150,000 cardiovascular events

LDL and ASCVD: Key Findings

➢ Cumulative LDL burden determines the initiation andprogression of ASCVD.

➢ There is a dose-dependent, log-linear association between absolute LDL-C level and CV risk. This association is independent of other CV risk factors and consistent across the multiple lines of evidence.

➢ Evidence accrued from >30 randomized trials involving >200,000 individuals and 30,000 cardiovascular events evaluating treatments specifically designed to lower LDL consistently show that reducing LDL-C reduces the risk of CV events.

➢ This benefit is proportional to the absolute reduction in LDL-C.European Heart Journal. doi:10.1093/eurheartj/ehx144.

Implications

• Cumulative LDL arterial burden is a central determinant of theinitiation and progression of ASCVD• The lower the LDL-C level attained by agents which primarilytarget LDL receptors, the greater the clinical benefit accrued.• Both proportional (relative) risk reduction and absolute risk

reduction relate to the magnitude of LDL-C reduction.• Lowering LDL-C in individuals at high cardiovascular risk

earlier rather than later appears advisable, especially in those with FH.

European Heart Journal. doi:10.1093/eurheartj/ehx144.

Endogenous Lipid Transport Pathway

TG/CE

B48

cholesterol

(exogenous)

CE/TG

B100

Dietary Carbohydrate

glucose pyruvate Acetyl CoA

mitochondriaAcetyl CoA

TG

FFA FFA TG VLDL

LIVER

VLDL

CMr Cholesterol

(endogenous)

ELDL receptor

Plasma

VLDL Assembly

VLDL1

VLDL2 LDL

Rem IDL

LPL

LPL

LDL

Rem IDL

LDLr/LRP

LDLr/LRP

HL

HL

Heterogeneity of VLDL and its Remnants

VLDL and Metabolism of Derivate LDL

VLDL1 VLDL2

Sf 60-400 20-60

TG/Col ratio 3.2 1.3

Transference to LDL% 17 ± 5 35 ± 5

LDL FCR of derivedLDL 0.2 ± 0.04 0.32 ± 0.06

(pools/day-1)

Adapted from de Demant e Packard Eur Heart J 1998;19 supl H:7-10

Lipoprotein Metabolism

- TGs - TGs

More Triglyceride Less Triglyceride

Lower Cholesterol Concentration

Higher Cholesterol Concentration

-Apolipoproteins

LPL HL

Lipoprotein Sub-Classes

1.20

1.10

1.06

1.02

1.006

0.95

5 10 20 40 60 801000

ChylomicronRemnants

VLDL

LDL

HDL2

HDL3DL3

Particle Size (nm)

Dens

ity (g

/ml)

Chylomicron

VLDLRemnants

Lp(a)

IDL

Atherogenic(found in plaque)

pre-β2 HDLpre-β1 HDL

5

NON HDL

Anti atherogenic

LDL-Cholesterol Hemostasis

Hepatic LDLRs Play a Central Role in Cholesterol Homeostasis

LDL particles consist mostly of cholesteryl esters packaged with a protein moiety called apolipoprotein B (apoB),

1 apoB molecule in each LDL particle.

LDL particles are the primary carriers of plasma cholesterol in humans, and high LDL levels have a strong and direct relationship with the development ofatherosclerosis.

The liver is responsible for the clearance and catabolism of plasma LDL, and hepatocyte expression of LDL receptors (LDLRs) are central to this process by binding and removing LDL from the plasma.

LDL/LDLR complex is internalized into the hepatocyte via clathrin-coated vesicles, thereby removing LDL from the blood. The affinity of the hepatic LDL receptor for apoBon LDL enables LDLRs to clear plasma LDL effectively.

Brown MS, et al. Proc Natl Acad Sci 1979;76:3330-3337. Qian YW, et al. J Lipid Res. 2007;48:1488-1498. Steinberg D, et al. Proc Natl Acad

Sci U S A. 2009;106:9546-9547

Recycling of LDLRs Enables Efficient Clearance of LDL-C Particles

Clathrin-coated vesicles containing internalized LDL/LDLR complexes fuse with endosomes, resulting in dissociation of the LDLs from LDLRs due to the acidic environment.

The free LDLRs then recycle back to the surface of the hepatocyte to bind and clear additional LDL from the blood.

Free LDL particles in the endosomes are transported to the lysosomes and degraded into lipids and amino acids.

The ability of hepatic LDLRs to be recycled is a key determinant of hepatic efficacy in lowering plasma LDL.

Brown MS, et al. Proc Natl Acad Sci 1979;76:3330-3337. Qian YW, et al. J Lipid Res. 2007;48:1488-1498. Steinberg D, et al. Proc Natl Acad Sci U S A. 2009;106:9546-9547

PCSK9 Regulates the Surface Expression of LDLRs by Targeting for LiposomalDegradation

PCSK9 is a proprotein that is produced in hepatocytes, and secreted into the plasma as functional PCSK9.Extracellular PCSK9 binds to the LDLR on the surface of the hepatocyte and is internalized within theendosome.LDLR/PCSK9 complex is routed to lysosome for degradation, preventing recycling of LDLR back to hepatocyte surface.By preventing LDLRs from recycling back to the surface, PCSK9 reduces the concentration of LDLRs on the surface of hepatocytes, resulting in a lower LDL clearance rate and elevated levels of plasma LDL. Brown MS, et al. Proc Natl Acad Sci

1979;76:3330-3337. Qian YW, et al. J Lipid

Res. 2007;48:1488-1498. Steinberg D, et al. Proc Natl Acad Sci U S A.

2009;106:9546-9547

ER TGN

EndosomeLysosome

LDL-R

PCSK9

pre-PCSK9

A:LDL-R pathway in

absence of PCSK9

B:Intracellular

PCSK9 route

C:Extracellular

PCSK9 route

MaturePCSK9

LDL

apoB

PCSK9

Deg

rada

tion

Michael S. Brown and Joseph L. GoldsteinNobel Prize in Physiology or Medicine onOctober 15, 1985.

LDL receptor discovery introduced three general concepts to cell biology: receptor-mediated endocytosis

receptor recycling feedback regulation of receptors.

Low-Density Lipoprotein (LDL) Consists of Multiple Distinct Subclasses Differing in Size and Lipid Content*

Berneis KK, Krauss RM. J Lipid Res. 2002;43:1363-1379.

Association with Cardiovascular Disease Risk

Large

Small

Less Atherogenic

* Distribution of subclasses is independent of LDL-C.

More Atherogenic

12

3

4

⚫ ↓ clearance by LDL-R⚫ ↑ arterial entry⚫ ↑ arterial retention⚫ ↑ oxidation

LDL particles comprise ~ 90% of

circulating apoB-containing

lipoproteins

• Under most conditions, LDL-C concentration and LDL particle number are highly correlated

LDL cholesterol terrible at predicting the amount of LDL particles in certain disease states.

Large LDL (Pattern A) Small LDL (Pattern B)

• Carries more cholesterol per particle

• Elevated in FH• Elevated with high sat fat

• Low in countries with low fat

diet(Costa Rica)

• Oxidized more rapidly

• Elevated in metabolic syndrome/

insulin resistance ,DM , Obesity

• Associated with low HDL-C, high TG

• Altered endothelial function Altered

fibrinolysis

Sacks and Campos, J Clin Endocrinol Metab 2003;88:4525-4532.

Increased small dense LDL particles associated with reduced IHD survival

St-Pierre AC et al. Arterioscler Thromb Vasc Biol. 2005;25:553-9.

N = 2072 men without IHD at baseline;13-yearfollow-up 1.00

0.90

0.80

Survival probabilities

0 2 4 6 8Follow-up (years)

10 12

P < 0.0001

Levels of smal dense LDL low normal high

IHD = ischemic heart disease

Pathogenicity of LDL & LDL : oxidation and inflammation

Diaz et al. N Engl JMed 1997;337:408–416

LDL : oxidation and inflammation

The Initial Accumulation of Foam Cells Is Seen as a Fatty Streak

Fatty streak

Arterial lumen

The atherosclerotic process can occur in any artery—

coronary, cerebral, or peripheral

1. Samson S, et al. Cholesterol. 2012;2012:571846. 2. Hall JE, et al. In: Guyton and Hall Textbook of Medical Physiology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:819-830.

As atheromatous plaques develop, remodeling occurs where the subendothelialspace expands in an outward direction, preserving the lumen, which appears normal when viewed with techniques restricted to luminal imaging such as angiography.

Ischemic Heart Is One Manifestation of Clinical ASCVD

ASCVD = atherosclerotic cardiovascular disease.Grundy SM, et al. J Clin Lipidol. 2014;8:29-60.

Stable Atherosclerosis Thrombotic Events

Plaque rupture

Fatty streak develops

Lipids accumulate, atheroma grows

Stable plaque Platelet adhesion,

activation, and aggregation

Clinical ASCVD is a systemic, progressive disease that affects multiple vascular beds and can lead to CV events, including stroke

Thrombus formation

Journal of thrombosis and hemostasis 2018;16:418-428

Effects of LDL-C Lowering on Atherosclerotic

Effects of LDL-C Lowering onAtherosclerotic Plaques

Libby P. Eur Heart J. 2015 ; 36:472–474.

Conclusion

• LDL Levels regulated by complexmechanisms• LDLRs Play a Central Role in Cholesterol Homeostasis

• Heterogeneous group ofparticles• Strong evidence that LDL is a strong risk factor forCVD• Pro-atherogenic properties

–Endothelial dysfunction–Pro-inflammatory–Pro-thrombotic

• Lowering LDL-C has an effect in onAtherosclerotic Plaques