Midterm II: Eicosanoids (Ben) Flashcards

1
Q

What structural molecules are eicosanoids formed from?

What is the first step (enzyme) in this process and its product?

A

Formed from membrane phospholipids

  • cleaved by phospholipase A2
  • forms Arachidonic Acid
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2
Q

What are the two pathways that arachidonic acid can take to form eicosanoids?

And their general products?

A
  1. COX Pathway - forms prostanoids (prostaglandins + thromboxanes)
  2. Lipoxygenase Pathway - forms leukotrienes + lipoxins
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3
Q

What is the important omega-6 PUFA in the creation of eicosanoids?

And its final product (after several steps)

A

Linoleic Acid 18:2 (9,12)

makes Arachidonic Acid 20:4 (5,8,11,14)

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4
Q

What is the important omega-3 PUFA in the creation of eicosanoids?

What is its product (after several steps)?

A

α-Linolenic Acid 18:3 (9,12,15)

  • makes EPA and DHA
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5
Q

What are the two steps of the COX pathway that convert arachidonic acid to the common precursor for all other COX pathway products?

(One enzyme system with 2 activities.)

A

PGH Synthase

  1. Cyclooxygenase - makes PGG2 from AA
  2. Peroxidase - makes PGH2 from PGG2
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6
Q

Describe the structure + location of PGH synthase.

A

Structure:

  • heme-protein homodimer
  • 2 catalytic sites/activities: COX + peroxidase
  • tetrahelical membrane-binding domains

Location:

  • ER + nuclear membrane
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7
Q

What is an eicosanoid product of platelets?

What is its effect?

A

Thromboxane A2

  • activates platelet aggregation (via calcium signal)

(and vascular smooth muscle contraction)

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8
Q

What is an eicosanoid product of endothelial cells?

What is its effect?

A

Prostaglandin I2

  • decreases platelet aggregation (via cAMP increase)

(and relaxes vascular smooth muscle)

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9
Q

What is an important effect of PGE2?

A
  • protects gastric mucosa
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10
Q

What are the COX isoenzymes?

And what are important characteristics of them?

A
  • COX I
    • Constitutively expressed in many tissues
    • cytosolic
    • narrow substrate-binding site
    • secretes PG products
  • COX II
    • Induced in inflammation + physio imbalance (via IL-1, TNFα, NFkB, cAMP)
    • in nuclear membrane
    • wider binding site
    • PG products go to nucleus
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11
Q

What part of the eicosanoid production pathway do steroids inhibit?

A

Creation of arachidonic acid via Phospholipase A2

(inhibits this enzyme)

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12
Q

How do aspirin differ from other NSAIDs in its action?

A
  • Aspirin - irreversible acetylation of Serine residue
  • Others - reversible competitive COX inhibition
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13
Q

How does aspirin’s effect on COX I and COX II differ?

A
  • COX I - inactivated via serine acetylation
  • COX II - changed activity to creation of lipoxins (anti-inflammatory eicosanoids)
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14
Q

How are selective COX II inhibitors selective?

What is an example of one?

A
  • they are too big to fit in COX I’s narrow substrate binding channel
  • Coxibs such as Vioxx are selective to COX II
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15
Q

How do selective COX-II inhibitors negatively effect vascular health?

A
  • In platelets…
    • only COX-I makes thromboxane A2 so platelet aggregation is not inhibited
  • In endothelial cels…
    • both COX-I and II make PGI-2, so its anti-aggregation effect is partially inhibited
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16
Q

Where are leukotrienes made?

And why?

A

in neutrophils, macrophages, and mast cells

  • induced by inflammatory stimuli
17
Q

What is the common pathway for the synthesis of the main leukotriene precursor from arachidonic acid?

What is the precursor it makes?

A

5-Lipoxygenase

  • with dioxygenase + dehydrase activity
  • makes Leukotriene A4 (LTA4)
18
Q

What 4 leukotrienes can be made from leukotriene A4 and how?

A
  1. LTB4 - directly
  2. LTC4 - conjugation with glutathione
  3. LTD4 - LTC4 loses glutamine
  4. LTE4 - LTD4 loses glycine
19
Q

What are lipoxins?

A

lipoxygenase products which are anti-inflammatory