ML Watson Lec 3 & 4 Flashcards
1) What are Eicosanoids the product of?
2) What is the main Eicosanoid precursor in mammals?
1) The oxidation product of 20-Carbon fatty acids
2) Arachidonic acid
What are the 4 CLASSICAL eicosanoids?
1) Prostaglandins (E2)
2) Prostacyclins (I2)
3) Leukotrienes
4) Thromboxanes
What are the 4 NON-CLASSICAL eicosanoids?
1) Lipoxins
2) Resolvins
3) Isoprostanes
4) Endocannabinoids
PAF is an inflammatory mediator - what does it stand for?
Platelet activating factor
Explain in 3 steps how Phospholipids become either prostaglandins or thromboxanes
1) Cell damage activates PLA2
2) PLA2 liberates Arachidonic acid from phospholipid
3) Arachidonic acid is metabolised by COX-1 and COX-2 to form prostaglandins (PGI2, PGE2) and thromboxanes (TxA2)
Explain in 3 steps how Phospholipids become leukotrienes, lipoxins or other compounds
1) Cell damage activates PLA2
2) PLA2 liberates arachidonic acid from phospholipids
3) Arachidonic acid is metabolised by lipoxygenases to form leukotrienes (LTB4, LTC4, LTD4) lipoxins or other compounds
How is PAF derived?
- Derived from phospholipid precursors by PLA2 to give lyso-PAF
- Acetylation of lyso-PAF gives PAF
What do prostaglandins act via?
- Specific GPCRs on target cells (cell membrane receptors)
What is the receptor for prostacyclin (PGI2)
IP
There are 4 PGE2 receptors EP1-4 and an IP receptor. Which of these are vasodilators?
- What do these do?
- How are they coupled?
- EP2 and IP receptors
(receptors on smooth muscle) - Enhance plasma extravasation
- Gs coupled to adenylyl cyclase, increases cAMP (SM relax and inc blood flow)
What does the Thromboxane (TP) and PGF2 (FP) receptor do?
- Cause SM contraction
- Gq coupled to PLC - IP3 and calcium
TXA2 activates ____ and increases airway obstruction by inducing ____ muscle ____ and ____ cell mucus secretion
1) leukocytes
2) smooth
3) contraction
4) goblet
- Which of the following statements applies to COX-1
1) Is present in most cells as a constitutive enzyme that produces prostanoids that act as homeostatic regulators (e.g modulating vascular responses)
2) Is not normally present (at least in most tissues) but it is strongly induced by inflammatory stimuli and therefore believed to be more relevant to inflammation therapy
Statement 1:
COX-1 is present in most cells as a constitutive enzyme that produces prostanoids that act as homeostatic regulators (e.g modulating vascular responses)
How does PGE2 work?
- Inflamm
1)
- Promotes vasodilation
- Activates cAMP coupled EP2 receptors on vasc SM
- Inc vasc permeability by enhance release of histamine and other mediators from tissue leukocytes e.g mast cells
Prostaglandins sensitise peripheral _-____. This ____ pain response to other agents and ____ algesic response to C____
1) C-Fibres
2) Increases
3) Increases
4) Capsaicin
Which receptors in the dorsal root ganglia play a role in the pain pathway?
- EP1 receptors
- EPI receptor knock out mice have decreased inflammatory pain responses
How is fever regulated in relation to prostaglandins?
Which receptor plays a role?
- Production and action of PGE2 in the anterior hypothalamus
- Role for the EP3 receptor
Is fever regulated by PGE2 sensitive to NSAIDs or paracetamol?
- NO
Which of the following are induced by TNF-alpha, IL-1 and repressed by glucocorticoids?
COX-1 or COX-2?
COX-2
What is the definition of COX-2 specificity?
- Inhibition of COX-2 but not COX-1, across the entire therapeutic dose range
Arachidonic acid interacts with COX-1 and 2 by binding to a crucial residue in the binding site. Is arachidonic acid specific or non specific and why?
- NON-SPECIFIC
- There are no side chains to sit deep into the pocket so no specificity to either active site
____ is selective for COX-2.
Naproxen or Celecoxib
WHY?
Celecoxib.
It has a long side chain that sits deep into the pocket where the critical residence resides, giving specificity to the active site of COX-2
Naproxen has no such side chain making it non-specific
How can NSAID selectivity for COX-1 and COX-2 be studied?
- As a ‘potency ratio’
- The IC50 values for blocking the two enzymes
Put the following in order of COX-2 selectivity…
Ibuprofen
Rofecoxib
Celecoxib
Aspirin
1) Rofecoxib (COX-2)
2) Celecoxib (COX-2)
3) Ibuprofen (MIXED)
4) Aspirin (LOW DOSE COX-1)
What PGs are responsible?
1) Initiation of labour
2) Inhibition of gastric acid secretion, increased gastric mucus production
3) Inhibition of platelet aggregation and vasodilation
4) Platelet aggregation and vasoconstriction
1) PGF2-alpha and PGE2
2) PGE2
3) PGI2 from endothelium
4) TXA2 from platelets
What are some side effects of aspirin like drugs?
- GI irritation and bleeding
- Renal toxicity
- Bleeding due to blocking housekeeping COX-1
What was the issue with Rofecoxib?
HINT: PGI2 vs TXA2
- Rofecoxib is a COX-2 selective NSAID
- PGI2 is responsible for inhibition of platelet aggregation and vasodilation BUT is derived mostly from COX-2
- Rofecoxib suppresses PGI2 but has no effect on TXA-2 that is from COX-1
THUS… PGI-2 decreased (less inhibition of aggregation)
TXA-2 remains (so net increase of blood clotting)
Means increased incidence of thromboembolic events!
How does aspirin exert an anti-thrombotic action?
- Aspirin acetylates COX thus platelet TXA2 production ceases for the life of the platelet
- BUT endothelial cells make new endothelial COX so PGI2 is still released as it recovers rapidly compared to platelet COX
SO PLATELET COX-1 INHIBITION IS BENEFICIAL IN THROMBOSIS
Why are selective COX-2 inhibitors BAD?
- They affect PGI2 more than TXA2
- THUS, less anti platelet aggregation but same platelet aggregation and vasoconstriction
Leukotrienes are formed by 5-lipoxygenase conversion of arachidonic acid.
Which Leukotrienes are responsible for bronchoconstriction?
- LTC4 and LTD4
- They also increase effects of other constrictor agents
Which Leukotrienes are responsible for Oedema?
- Are they neutrophil dependent or independent?
- LTC4 and LTD4
- Stimulate increased vascular permeability (independent)
- LTB4
- Simulate increased vascular permeability (dependent)
Which Leukotrienes are responsible for Chemotaxis of inflammatory cells?
- LTB4 on the BLT1 receptor
Are there HIGH or LOW levels of leukotrienes in RA patients?
- HIGH
How do glucocorticoids inhibit COX?
- The indirectly inhibit COX by inhibiting PLA2 transcription
- Also induce synth of PLA2 inhibitor LIPOCORTIN
- ALSO inhibit COX-2 synthesis
- Therefore, PLA2 cannot liberate arachidonic acid from membrane phospholipids to make prostaglandins and leukotrienes
How does Zileuton work?
- It inhibits 5-lipoxygenase
- Prevents conversion of arachidonic acid to leukotrienes
How does Zafirlukast and montelukast work?
- These leukotriene antagonists inhibit action of LTC4 and LTD4
- Used in asthma
How do NSAIDs work?
- Inhibit COX
- Prevent Arachidonic acid conversion to Prostaglandins
Why are eicosanoids important?
List the ones responsible for the following…
1) Vasodilation (___,___)
2) Vascular permeability (__’s)
3) Synergy with other mediators e.g
____
____
____
4) Pain (___,___)
5) Fever (____)
1) PGE2, PGI2
2) LT’s
3)
Histamine
Bradykinin
Chemotaxins
4) PGE2, PGI2
5) PGE2
What is EPA (omega 3 fatty acid) metabolised by and to?
- BY COX
- TO PGI3 (potent pro-aggregatory) and TxA3 (weak pro-aggregatory)
Leukocytes move from the ____ to sites of ____ and ____ activation.
1) Blood
2) Inflammation
3) Immune
Directional control of Leukocytes is co-ordinated by tissue expression of ____ molecules and ____ stimuli for Leukocyte migration.
- Adhesion
- Chemical
What are the 4 steps in Leukocyte diapedesis?
1) Circulation e.g of neutrophils
2) Tethering/rolling
3) Firm adhesion
4) Transmigration
Explain the 4 steps in Leukocyte diapedesis…
- Inflammatory signals induce endothelial cells to exocytose P selection and synthesis PAF which appears on cell surface
- P selection molecules bind oligosaccharide groups at leukocyte cell surface
- Weak adhesion causes rolling along endothelial cells
- Leukocytes also have PAF receptors and integrins.
- Receptor binding to PAF results in activation of integrins
- Causes integrins to bind iCAM molecules expressed on endothelial cells
- Leukocyte then tightly adheres to endothelium
- Migrates between endothelial cells to reach underlying tissue
E-selectin expression on endothelial cells is induced by ____ or _ _ _
Cytokines or LPS
Expression of E selection is inhibited by ______
glucocorticoids
What does LAD II stand for?
- Leukocyte adhesion deficiency-II
What is LAD II?
- Patients suffer recurrent infections and die
- No pus and neutrophilia
- Leukocytes do not express selection ligands
- Decreased rolling response on E or P selections
- Severely impaired neutrophil accumulation in skin inflammation
Integrins are expressed on the surface of _____
Leukocytes
Leukocyte B2 interns can form _ heterodimers
3
alphaL/B2
alphaM/B2
alphaX/B2
Leukocyte activation induces ______ change - affinity
Leukocyte activation induces clustering of ___ - avidity
1) conformational
2) integrins
LAD I is…
- Patients suffer recurrent bacterial infections without pus
- Leukocytes do not adhere to extracellular material or endothelium in vitro
- Leukocytes deficient in B2 integrin
Which of the following integrins is induced by cytokines IL-1 and TNF?
ICAM-2 or ICAM-1
ICAM-1
ICAM-2 is basally expressed on endothelium
VLA-4 expressed on eosinophils, monocytes and _ cells
What is it induced by?
T
Induced by cytokines
Natalizumab is an anti _ _ _ - _ antibody
What does it do?
VLA-4
Prevents new inflammatory lesions. Dampens down inflammation by preventing T cell infiltration
Transmigration involves chemoattractants (chemotaxins) and ___s
CAMs - cellular adhesion molecules
Give some examples of non-selective chemotaxins…
1) LTB4
2) C3a, C5a
3) formyl peptides
Chemokines are SELECTIVE GPCRs and are produced in response to __, __ and ___
IL-1, TNF, bacteria
CXC chemokines are mainly _____ attractants
Neutrophil
CC chemokines are NOT neutrophil attractants! They target Eosinophils, Basophils, ____ and activated T cells
MONOCYTES
Which of the following are involved in chronic inflammation?
Neutrophils, monocytes, lymphocytes
Monocytes and lymphocytes
Neutrophils are involved in acute inflammation
Match the following
1) Different selection and CAM expression
2) Different chemokine expression
1) Different integrin expression
2) Different chemokine receptor expression
Tissues, Leukocytes
First two statements = Tissues
Second two statements = Leukocytes
