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SMP - MNE Exam 2 > Lecture 35: Eicosanoids > Flashcards

Lecture 35: Eicosanoids Flashcards

1
Q

Other than being used to form lipid bilayers, what else are 5 important functions of lipids?

A
  1. Module activities of soluble and membrane-bound proteins
  2. Tether GPI-anchored membrane proteins (phosphatidylinositol)
  3. Act as molecular signals
  4. Have derivatives that act as intracellular second messengers in transduction pathways
  5. Potent short-lived hormone-like molecules = eicosanoids!
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2
Q

What is an example of a lipid functioning as a molecular signal?

A

Ether-linked glycerophospholipid platelet activating

factor

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3
Q

What is an example of a lipid having derivatives that act as intracellular second messengers in transduction pathways?

A

Phosphatidylinositol (PIP2) breaking into inositol 1,4,5-triphosphate and diacylglycerol, which
then go on to regulate other enzymes

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4
Q

How is an eicosanoid formed?

A
  1. Physical damage, hormonal signal, or neuronal signal
  2. PLP A2 cleaves a polyunsaturated FA on a glycerophospholipid
  3. Polyunsaturated FA either enter cyclic (cyclooxygenase) or linear (lipoxygenase) pathway depending on what enzyme acts on it
  4. Eicosanoid is produced
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5
Q

List 6 types of eicosanoids.

A
  1. Prostaglandins
  2. Thromboxanes
  3. Leukotrienes
  4. Lipoxins
  5. Hepoxilins
  6. Epi-lipoxins
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6
Q

What is the nomenclature to name eicosanoids?

A
  1. n series leukotrienes (LT)
  2. n-2 series prostaglandins (PG)
  3. n-2 series thromboxanes (TX)

n = number of unsaturated bonds in the FA

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7
Q

What does the ω-system of naming FAs mean? Note?

A

Number after omega = number of Cs before encountering a double bond starting from the omega end of the FA (aka the terminal methyl group)

Note: count the first C included in the double bond

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8
Q

Can mammals desaturate FAs?

A

Not very good at this, especially close to the omega end

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9
Q

What organisms are good at desaturating FAs close to the ω-end? What enzymes do they use?

A

Plants using plant acyl desaturases in chloroplasts

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10
Q

Can mammals synthesize ω-3 FAs?

A

NO, we can only get them from the diet

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11
Q

In what food do we find ω-3 FAs?

A

Cold water fish and flax seed

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12
Q

What are the 3 ω-3 FAs?

A
  1. alpha-linoleic acid
  2. Eicosapentaenoic acid
  3. Docosahexaenoic acid
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13
Q

Describe the synthesis of unsaturated FAs starting with palmitic acid. Which 2 are essential for us?

A
  1. Palmitic acid - 16:0
  2. Stearate - 18:0
  3. Oleate - 18:1
  4. Linoleate - 18:2 (ESSENTIAL)
    5a. γ-linoleate - 18:3
    5b. alpha-linoleate (ESSENTIAL)
  5. Eicosatrienoate - 20:3
  6. Arachidonic acid - 20:4
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14
Q

What is a health benefit of eating ω-3 FAs?

A

Reduced risk of heart attack

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15
Q

Glycerophospholipid cleavage: phospholipase D: cleavage site? products?

A

Cleavage site = bond between polar head group and P

Products = phosphatidic acid + polar head group

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16
Q

Glycerophospholipid cleavage: phospholipase C: cleavage site? products?

A

Cleavage site = bond between P and O attached to C3

Products = head group-P-O2 + DAG

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17
Q

Glycerophospholipid cleavage: phospholipase A1: cleavage site? products?

A

Cleavage site = FA-O bond at C1

Products = FA + lysophospholipid

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18
Q

Which glycerophospholipids are resistant to phospholipase A1? Why?

A

Ether-linked glycerophospholipids: plasmalogens and platelet activating factor because PLPAs can only cleave ester bonds

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19
Q

What are 2 ether-linked glycerophospholipids? What is the difference with normal glycerophospholipids?

A
  1. Plasmalogens
  2. Platelet-activating factor
    They have an ether-linked alkane/alkene chain instead of an FA at position 1
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20
Q

What are the 2 possible head groups for plasmalogens?

A
  1. Choline

2. Ethanolamine

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21
Q

Where is the double in plasmalogens? What do we call these molecules?

A

Between C1 and C2 of the alkene chain

Vynil ethers

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22
Q

Describe the composition of the platelet-activating factor. What does the position 2 portion of it allows it do to?

A
  1. Ether linked alkane chain at position 1
  2. Acetyl ester at position 2: small group allowing the molecule to circulate and be soluble in blood
  3. Phosphocholine head group at position 3
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23
Q

Glycerophospholipid cleavage: phospholipase A2: cleavage site? products?

A

Cleavage site = FA-O bond at C2

Products = FA + lysophospholipid

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24
Q

What enzyme is the rate-limiting step of eicosanoid synthesis?

A

PLP A2 activation

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25
What hormones can inhibit PLP A2?
Glucocorticoids
26
Describe the mechanism used in the cyclic pathway of eicosanoid synthesis with an ω-6 FA? Include locations
Step 1: SER: |protaglandin synthase=cyclooxygenase + hydroxiperoxide|: arachidonic acid => Prostaglandin H2 Step 2: Prostaglandin H2 => - Prostaglandins - Prostacyclin synthase: Prostacyclins (PGI2) - Thromboxane synthase: Thromboxanes (TXA2)
27
Why does aspirin have an anti-clotting effect? What is the side product?
INHIBITS cyclooxygenase (COX1 and 2 equally) by IRREVERSIBLE binding Ser at active site and acetylating it (side product: salicylate)
28
How do NSAIDs other than aspirin work?
INHIBIT cyclooxygenase (COX1 and 2 equally) by REVERSIBLE binding Ser at active site
29
What are the 3 isoforms of cyclooxygenase?
1. COX1 2. COX2 3. COX3
30
COX1 function? Where is it expressed? Examples?
Normal housekeeping function in many tissues: - Limits HCl secretion in stomach to protect lining - Helps with blood clotting - Helps with vascular homeostasis
31
COX2 function?
Involved in inflammation and pain
32
What is acetaminophen best for? What does it inhibit?
Best for fever and pain because it inhibits COX3 and has more effects on CNS
33
What difference between COX1 and 2 could potentially be used by pharma to make more targeted drugs? Which COX would you ideally want to target? What were the names of the 2 drugs that tried to do this but had cray side effects?
COX1 has a little more steric hindrance for a substrate to reach the active site because it has an Ile instead of a Val in COX2 The target is COX2 Celecoxib and rofecoxib
34
Why is research on eicosanoids difficult?
Because they are short-lived and spontaneously decompose
35
What is prostacyclin's function?
Very potent platelet ANTI-aggregator
36
What is thromboxane's function?
Very potent platelet aggregator
37
What is the purpose of baby aspirin? How does it work?
It irreversibly inhibits COX but because vascular endothelial cells are nucleated they can generate new COX but platelets can't (anucleated) thereby shifting the balance toward more platelet anti-aggregating activity (prostacyclins) and can prevent inappropriate platelet aggregation that could lead to thrombotic events
38
Describe the mechanism used in the cyclic pathway of eicosanoid synthesis with ω-3 FAs. How does this explain why they are healthy?
Step 1: |protaglandin synthase=cyclooxygenase + hydroxiperoxide|: ω-3 FA => Prostaglandin H3 Step 2: Prostaglandin H3 => - Prostaglandins - Prostacyclin synthase: Prostacyclins (PGI3) - Thromboxane synthase: Thromboxanes (TXA3) Healthy because TXA3 is weaker than TXA2 thereby shifting the balance toward more platelet anti-aggregating activity (prostacyclins) and can prevent inappropriate platelet aggregation that could lead to thrombotic events
39
What are the 3 forms of omega 6 eicosanoids?
1. Linoleic acid 2. Arachidonic acid 3. gamma-linoleic
40
How does PGI3 compare to PGI2?
Pretty much the same
41
How does TXA3 compare to TXA2?
Pretty weak platelet activator compared to TXA2
42
Why are ω-3 FAs considered heart healthy?
Because they are substrates for TXA3 (instead of TXA2) which is a weak platelet aggregator
43
Describe the 2 mechanisms of the linear pathway of eicosanoid synthesis.
1. 5-lipoxygenase + activator protein: polyunsaturated FA => leukotrienes 2. 15-lipoxygenase + 5lipoxygenase : polyunsaturated FA => lipoxins
44
What are the 2 types of leukotrienes?
1. LTB4 | 2. Cyteinyl-leukotrienes (LTC4, LTD4, LTE4)
45
What is the function of LTB4?
Chronic inflammation associated with atherosclerosis
46
What is the function of cyteinyl-leukotrienes?
Inflammatory reactions of anaphylaxis
47
What do some anti-asthmatic treatments use?
Anti-leukotriene agents that inhibit 5-lipoxygenase OR the binding of the activator protein
48
What are the 2 functions of lipoxines?
1. Inhibit bronchial spasms | 2. Anti-inflammatory
49
What triggers epi-lipoxins synthesis? What is their function?
Aspirin: anti-inflammatory
50
What triggers resolvins and protectins synthesis? From what? What is their function?
Aspirin acetylation of COX2 followed by 5-lipoxygenase with 20:5 and 22:6 ω-3 FAs = resolvins/protectins: anti-inflammatory
51
Where do elongation steps of FAs happen in the cell? Where do the carbons come from?
SER and mito | From CoA
52
What is the delta nomenclature of FAs?
Number after delta = number of Cs before encountering a double bond starting from the delta end of the FA (aka the carboxyl group) Note: count the first C included in the double bond
53
What is the only saturation humans can do from palmitate?
Oleate
54
What does COX and lipoxygenase do?
Add 2 O2
55
What are thrombocytes?
Platelets
56
Where does thromboxane synthesis occur?
Platelets
57
What happens to TXA2 after a few seconds?
Spontaneously decomposes to TXB2 with water
58
Where does prostacyclin synthesis occur?
Vascular endothelial cells
59
What happens to PGI2 after a few seconds?
Spontaneously decomposes to PGF2 with water
60
Other than through their particular eicosanoid precursor function, why else are omega-3 FAs heart healthy?
They reduce the amount of TAGs in the blood
61
What does the number before lipoxygenases mean?
Where the OOH will be added
62
Describe the synthesis of cysteinyl-leukotrienes and why they are named that way.
Polyunsaturated FA => LTA4 + glutathione (added via S of cysteine) => LTC 4 - glutamic acid => LTD4 - glycine => LTE4
63
What are the 2 other NSAIDs which reversibly inhibit COX?
1. Ibuprofen | 2. Naproxen

SMP - MNE Exam 2 (17 decks)

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