Pathobiochemistry of atherothrombosis and atherosclerosis

Question 1

LDL cholesterol increase

Answer 1

• deficient LDL receptors (hetero-/homozygous mutation)

- PCSK9⇒ breaks down LDL receptors

Question 2

Function of Scavenger receptors (pattern recognition receptors)

Answer 2

• recognize modified LDLs by oxidation/acetylation ⇒ take up negatively charged molecules
• macrophage-host cell interaction ⇒ macrophage adhesion to substrate
• endocytosis od modified lipoproteins and ligands
• phagocytosis of apoptotic cells
• phagocytosis of microbes
• clearance and detoxification of microbial products

Question 3

Structure of Scavenger receptors

Answer 3

Class A, B, E, F, G
A⇒ trimers that bind modified LDLs, 3PP chains
B⇒ oxidized LSL receptors e.g. SREBP-1, HDL uptake
E⇒ Lox1 lechitin like OxLDL receptor

Question 4

LOX 1

Answer 4

• lectin like oxidized receptor
• binds, internalizes and degrades oxidized LDLs
• places with turbulent current

Question 5

Consequence of LOX1 activation: Endothelial surface

Answer 5

• expression of adhesion molecules
• leukocyte migration and adhesion
• monocyte mobilization and migration into sub endothelial space where they they differentiate into macrophages
• platelet adhesion
• smooth muscle contraction

Question 6

Consequence of LOX-1 activation: Overexpression of NADH/NADPH oxidase

Answer 6

• typically in leukocytes as defence against infections
• generates superoxide to kill infection
• endothelial cells will produce ROS faster than they are eliminated ⇒ triggers lipid preoccupation chain reaction ⇒ LDL modification
• generate ligand of LOX1 ⇒ oxidized LDL

Question 7

Consequence of LOX 1 activation: NO synthase uncoupling

Answer 7

• can be uncoupled by formation of ROS as it oxidizes TH bipoterin
• electrons from NADPH will generate more ROS

Question 8

Consequence of LOX 1 activation: Toll like receptors

Answer 8

• TLR initiate inflammation, beneficial for promoting homeostasis and healing
• TLR2 promotes atherosclerosis progression
• TLR activation: Ox LDL binds to CD36 ⇒ endocytosis of CD36 -oxLDL complex along with TLR4 and 6

Question 9

Oxidative stress in diabetes 1

Answer 9

Hyperglycemia ⇒ arterial endothelial cells oxidize more glucose ⇒ citrate cycle and glycolysis produce more reducing equivalents ⇒ increased proton gradient ⇒ inhibits complex 3 ⇒ increased electrons from NADH are retained in semiubiquinone form ⇒ increased probability of ROS ⇒ increased risk of atherosclerosis as ROS produce oxLDL

Question 10

Oxidative stress in diabetes 2

Answer 10

high glucose levels ⇒ increased activity of polyol metabolic pathway ⇒ NADPH depletion ⇒ impaired elimination of H2O2

Question 11

Dyslipidemia in diabetes

Answer 11

• insulin normally increases the activity of LPL ⇒ takes up cholesterol from LDL
• in dyslipidemia insulin resistance:
  ⇒ decreased glucose uptake ⇒ increased lipolysis ⇒ increased FFA ⇒ increased sdLDL and sdHDL

⇒ inactivity of LPL ⇒ increased LDL in blood

Question 12

Foam cell formation

Answer 12

• monocytes go through dysfunctional endothelium ⇒ differentiate to macrophage
• sdLDL also goes through endothelium
  ⇒ macrophage takes up LDL with high affinity ⇒ foam cell

Question 13

Foam cell response

Answer 13

• cholesterol increase
• Na/K ATPase, adenylate cyclase and ATP-ADP translocase impaired
• formation of crystals in membrane ⇒ destroys organelles ⇒ foam appearance
• ACAT generates CE ⇒ droplets ⇒ foam appearance
• inhibition of ABCA1

Question 14

Pyroptosis

Answer 14

• when foam cells completely overcome by cholesterol ⇒ activation of Caspase 1
• cell swelling
• apoptosis of foam cell
• IL-1B ⇒ inflammation
• MMP, collagenase, elastase ⇒ fibrous cap rupture
• procoagulant ⇒ platelet aggregation
• cytokine release

Question 15

Plaque rupture

Answer 15

• leukocytes attracted to proptosis ⇒ WBCs release MMPs ⇒ remodeling of tissue under endothelial layer
• MMPs target collagens + extracellular proteins ⇒ degradation + regeneration of EC matrix by fibroblasts
• mineralization of plaque
• balance of proteolysis and resynthesis determines if stable fibrous cap or rupture

Question 16

Pharmacology

Answer 16

1. Ezetimibe: inhibit NPC1L1 ⇒ decreases uptake of cholesterol in GI ⇒ liver takes more from blood
2. Statin: inhibit HMG-CoA reductase ⇒ decreased cholesterol formation and increased LDL uptake from blood
3. CETP inhibition ⇒ decreased dLDL generation, less HDL elimination, reverse cholesterol transport
4. Red wine: antioxidants ⇒ reduce ROS
5. Unsaturated FA: lower Km for ACAT, increasing LDLR, lower plasma cholesterol
6. PCSK9 inhibition by antibodies and non-sense oligonucleotides

Question 17

ROS

Answer 17

• activates N Factor Kappa B⇒ causes gene expression of:
• Endothelin-1 (vasoconstrictor)
• MCP-1 (monocyte chemoattractant peptide 1)
• ICAM-1 (cell surface adhesion molecule)
• VCAM
• Selectins
• MCSF (monocyte colonine stimulating factor)