Manfredi Rizzo, MD, PhDAssociate Professor of Internal Medicine

Faculty of Medicine, University of Palermo, Italy&

Affiliate Associate Professor of Internal Medicine School of Medicine, University of South Carolina, USA

MetabolismandAtherogenicPropertiesofLDL

DISCLOSURE

I have given talks, attended conferences and participated in advisory boards and trials sponsored by - Amgen- Astra Zeneca- Boehringer-Ingelheim- Lilly - Meda Pharma- Merck - Novo Nordisk- Roche - Servier

EPIDEMIOLOGY

courtesy of Prof. R. Santos

METABOLISM

Lipoprotein Subclasses

courtesy of Prof. R. Santos

courtesy of Prof. R. Santos

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

Lipoprotein Metabolism

- TGs - TGs

More Triglyceride Less Triglyceride

Lower Cholesterol Concentration

Higher Cholesterol Concentration

- Apolipoproteins

LPL HL

LDL Phenotype

• 7 distinct LDL subclasses

• Two primary LDL phenotypes (pattern A & pattern B)

• Pattern A is predominantly larger, more buoyant LDL

• Pattern B is primarily smaller, more dense LDL

Larger & More Buoyant

Smaller & More DenseEur Heart J 1998;19(Suppl A):A24-A30. Circulation

1996;94:2351-4.

Distribution of LDL particles according to size and density

B.A. Griffin

27.5 27.0 25.5 24.2 21.8

LDL-I II III IV

LDL Particle Size (Diameter nm)

1.065

1.025 1.034 1.044 1.060

Density (g/ml)

Healthy femaleMaleCAD patient

Rizzo M et al. Eur J Clin Invest 2003;33:126-33

LDL size and HDL-c

230

240

250

260

270

280

290

300LD

L Si

ze (Å

)

20 30 40 50 60 70 80 90

r= +.319; p< 0.0001

230

240

250

260

270

280

290

300

0 50 100 150 200 250 300 350 400

r= -.459; p< 0.0001

LDL size and TG

LDL

Size

(Å)

Rizzo M, Berneis K. Low-density-lipoproteins size and cardiovascular risk assessment QJM 2006; 99: 1-14.

Gradient Gel Electrophoresis (GGE)

Prof. Rizzo Lab

LDL-C Doubly Underestimates CV Risk in case of Small, Dense LDL

Large LDL Small, Dense LDL

Apo BLDL-C

130 mg/dL

Fewer Particles &Less Risk/Particle

More Particles &More Risk/Particle

CholesterolEster

More Apo B

Otvos JD, et al. Am J Cardiol. 2002;90:22i-29i.

Lipid profile:TC 198 mg/dLLDL-C 130 mg/dLTG 90 mg/dLHDL-C 50 mg/dL

Lipid profile:TC 210 mg/dLLDL-C 130 mg/dLTG 250 mg/dLHDL-C 30 mg/dL

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 isindependent of LDL-C.

More Atherogenic

12

3

4

l ↓ clearance by LDL-Rl ↑ arterial entry l ↑ arterial retentionl ↑ oxidation

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-year follow-up

1.00

0.90

0.80

Survivalprobabilities

Follow-up (years)0 2 4 6 8 10 12

P < 0.0001

Levels of smal dense LDL low normal high

IHD = ischemic heart disease

courtesy of Prof. R. Santos

BLOOD CHOLESTEROL HOMEOSTASIS

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

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), with 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 of atherosclerosis.

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 apoB on LDL enables LDLRs to clear plasma LDL effectively.

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 Lysosomal Degradation

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 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 the endosome.

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.

EPIDEMIOLOGY

Nature Reviews Cardiology 11, 130–132 (2014)

CONCLUSIONS

• Causal Risk factor for CVD

• Heterogeneous group of particles

• Levels regulated by complex mechanisms

• Pro-atherogenic properties-Endothelial dysfunction-Pro-inflammatory-Pro-thrombotic

(• LDL-C reduction is anti-atherogenic)