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IRM > L8 - Eicosanoids > Flashcards

L8 - Eicosanoids Flashcards

1
Q

From which group of molecules are eicosanoids derived?

A

Lipids.

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2
Q

What is the primary function of eicosanoids?

A

They contribute to the inflammatory response.

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3
Q

What are the 3 main categories of eicosanoids?

A

1 - Prostaglandins.

2 - Thromboxanes.

3 - Leukotrienes.

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4
Q

From which molecule are eicosanoids produced?

A

Arachidonic acid.

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5
Q

Which 2 enzymes are responsible for the liberation of arachidonic acid from the membrane?

A

1 - Phospholipase A2 (PLA2).

2 - Phospholipase C (PLC).

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6
Q

What are the stimuli that cause activation of the enzymes that are responsible for the first step of eicosanoid biosynthesis?

A

1 - Chemical (cytokines): Activate GPCRs.

2 - Mechanical: Ca2+ influx.

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7
Q

Which enzyme converts arachidonic acid into cyclic endoperoxides?

A

Cyclo-oxygenase (COX).

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8
Q

What are the variants of the COX enzyme and where are they found?

A

1 - COX-1 (constitutive, most cells).

2 - COX-2 (inducible, inflammatory cells).

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9
Q

What is the difference between a constitutive and inducible enzyme?

A

A constitutive enzyme is produced all the time, whereas an inducible enzyme is only produced under certain conditions.

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10
Q

Which enzymes of the COX pathway act on cyclic endoperoxides?

What are the products?

A

1 - Prostacyclin synthase (produces prostacyclin I2 (PGI2)).

2 - Thromboxane synthase (produces thromboxane A2 (TXA2)).

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11
Q

Where are the end products of the COX pathway found?

A

1 - Prostacyclin I2 (PGI2), found in the endothelium.

2 - Thromboxane A2 (TXA2), found in platelets.

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12
Q

What are prostanoids?

A

The subclass of eicosanoids consisting of:

1 - Prostaglandins (further divisible into prostacyclins).

2 - Thromboxanes.

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13
Q

List 4 effects of prostaglandins.

A

1 - Contribute to inflammatory response.

2 - Stimulate muscle contraction in the myometrium, GIT and bronchi.

3 - Inhibit gastric secretions.

4 - Inhibition of platelet aggregation.

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14
Q

List 3 ways in which prostaglandins contribute to the inflammatory response.

A

1 - Causes vasodilation.

2 - Raises temperature set-point (hypothalamus).

3 - Enhances activity of peripheral sensory nerves:

E.g. pain - sensitise nociceptors to e.g. bradykinin.

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15
Q

List 3 effects of thromboxanes.

A

1 - Vasoconstriction.

2 - Bronchoconstriction.

3 - Platelet aggregation.

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16
Q

How do non-selective non-steroidal anti-inflammatory drugs (NSAIDs) work?

A

By inhibiting both COX-1 and COX-2.

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17
Q

How do selective NSAIDs work?

A

By inhibiting COX-2 only.

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18
Q

List 2 examples of non-selective NSAIDs.

A

1 - Aspirin.

2 - Ibuprofen.

19
Q

List 2 examples of selective NSAIDs.

A

1 - Celecoxib.

2 - Rofecoxib (but increases risk of ischaemic heart disease!).

20
Q

How do glucocorticoids affect the COX and lipoxygenase pathways?

A
  • Decrease expression of COX-2.

- Increase expression of annexin-1 (inhibits PLA2, decreasing free arachidonic acid.).

21
Q

Which component of fish oil is important in eicosanoid biosynthesis?

A

Eicosapentaenoic acid (arachidonic acid is eicosatetraenoic acid)

22
Q

List 3 types of drugs that are involved in the modulation of the COX pathway to achieve anti-inflammatory effect.

A

1 - Non-selective NSAIDs.

2 - Selective NSAIDs.

3 - Glucocorticoids.

23
Q

Which enzyme converts arachidonic acid into HPETE?

A

5 - Lipoxygenase.

24
Q

List 2 types of drugs that are involved in the modulation of the lipoxygenase pathway.

A

1 - 5-lipoxygenase inhibitor (USA only).

2 - Glucocorticoids.

25
Q

List 4 effects of leukotrienes.

A

1 - Contributes to the inflammatory response.

2 - Causes bronchoconstriction.

3 - Stimulates mucus secretion (in the respiratory system).

4 - Causes vasodilation / vasoconstriction.

26
Q

List 3 ways in which leukotrienes contribute to the inflammatory response.

A

1 - Chemotaxis (of neutrophils and macrophages).

2 - Stimulates proliferation of immune cells.

3 - Stimulates release of cytokines.

27
Q

What type of receptors are prostanoid and leukotriene receptors?

A

G-coupled protein receptors.

28
Q

List 2 prostanoid receptors and their ligands.

A

1 - IP (prostacyclin) receptor.

Ligand: PGI2 (prostacyclin I2).

2 - TP (thromboxane) receptor.

Ligand: TXA2 (thromboxane A2).

29
Q

What do IP receptors do once activated?

A

Gs pathway:

The IP GPCR activates cAMP, which activates protein kinase A.

30
Q

What to TP receptors do once activated?

A

Gq pathway:

The LT GPCR activates phospholipase C, which leads to both Ca2+ influx (IP3 from PIP2) and protein kinase C activation (DAG from PIP2).

31
Q

What do LT receptors do once activated?

A

Gq pathway:

The LT GPCR activates phospholipase C, which leads to both Ca2+ influx (IP3 from PIP2) and protein kinase C activation (DAG from PIP2).

32
Q

Give an example of a receptor antagonist for the cysteinyl leukotriene receptor.

A

Montelukast.

33
Q

Give an example of a receptor agonist for the cysteinyl leukotriene receptor.

A

Epoprostenol.

34
Q

Which variants of the COX enzyme are found in platelets?

A

COX-1 only.

35
Q

Which variants of the COX enzyme are found in the endothelium?

A

Usually COX-1, but also COX-2 in some people.

36
Q

What are the products of biosynthesis of eicosanoids when using fish oil rather than arachidonic acid?

What does this make fish oil a suitable treatment for?

A
  • TXA3 (a weaker platelet aggregator than TXA2).
  • PGI3 (a more potent inhibitor of platelet aggregation than PGI2).
  • Therefore fish oil is a suitable treatment for heart disease as it reduces thrombosis.
37
Q

List 2 drugs used to prevent thrombosis.

A

1 - Fish oil.

2 - Aspirin (low dose).

38
Q

How does aspirin prevent thrombosis?

A
  • Permanently blocks COX in platelets (cannot resynthesise as platelets have no nucleus) so thromboxane reduces.
  • Blocks COX in the endothelium but COX resynthesises between doses so prostacyclin doesnt reduce much.
  • Aspirin therefore decreases vasoconstriction and platelet aggregation.
39
Q

How does the action of TXA2 in platelets differ from the action of PGI2 in the endothelium?

A

TXA2 in platelets: Aggregatory agent + vasoconstrictor.

PGI2 in the endothelium: Anti-aggregatory + vasodilator.

40
Q

How do allergens cause allergic asthma?

A

1 - Allergen increases IgE antibody production.

2 - IgE binds to mast cells, causing immediate and late phases.

3 - Immediate phase: Increase in leukotrienes, histamine and interleukins.

4 - Late phase: Activation of eosinophils and Th2 lymphocytes.

41
Q

How do glucocorticoids, zileuton and montelukast work to relieve the symptoms of asthma?

A
  • Glucocorticoids: Increase expression of annexin-1 (inhibits PLA2, decreasing free arachidonic acid.).
  • Zileuton: Inhibits 5-lipoxygenase (so decreases leukotrienes).
  • Montelukast: Acts as an antagonist for the leukotriene receptor.
42
Q

Why might non-selective NSAIDs lead to gastritis and ulcers?

A
  • Non selective NSAIDs inhibit COX-1 and COX-2 (selective only inhibits COX-2).
  • Prostaglandins produced in the gastric mucosa are formed by COX-1.
  • Prostaglandins decrease acid secretion and increase mucous secretions.
  • Inhibiting COX-1 decreases prostaglandins so increases acid secretion and decrease mucous secretions.
43
Q

What is HPETE converted to in the lipoxygenase pathway (what are the end products)?

A

1 - Cysteinyl leukotrienes (LTD4).

2 - Leukotriene B4.

44
Q

Which drugs are contraindicated with NSAIDs and why?

A
  • Ibuprofen and diclofenac.

- 31% increased risk of cardiac arrest when these drugs are taken with with NSAIDs.

IRM (21 decks)

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