Eicosanoids Lecture Oct 3

Question 1

What are the 6 classes of eicosanoids?

Answer 1

prostaglandins

thromboxanes

leukotrienes

HETE

lipoxins

Isoprostanes

Question 2

What two eicosanoids are produced by the cyclooxygenase (cyclic) pathway?

Answer 2

prostaglandins and thromboxanes

Question 3

What 3 eicosanoids are produced by the lipoxygenase (linear) pathway?

Answer 3

Luekotrienes

HETE

lipoxins

Question 4

Which eicosanoid is produced by nonenzymatic free radical attack?

What is it’s clinical use?

Answer 4

Isoprostanes

There doesn’t seem to be a biological purpose for these yet, but they are great for lab test purposes because having elevated isoprostanes int h urine is indicative of oxidative stress and damage in the body

Question 5

Which eicosanoids will be produced by the cytochorme p450 enzymes?

Answer 5

epoxides

HETE

diHETE

Question 6

What is the method of action for prostaglandins?

Answer 6

they function as autocrine and paracrine hormones because htey have a very short half life

Question 7

Which blood cell is the most affected by thromboxanes?

Answer 7

platelets - thromboxanes mediate vasoconstruction and platelet aggregaton

Question 8

What is the precursor for the eicosanoids?

Answer 8

arachidonic acid

Question 9

What do we need to take in from the diet to make arachidonic acid?

Answer 9

We have to eat linoleic and linolenic fatty acids because our fatty acyl desaturate enzyme can’t make double bonds if the desired location is too far away from the CoA end.

Question 10

How is most of the arachidonic acid in the cell stored?

Answer 10

It’s stored in phospholipids located in the cytosolic side of the plasma membrane. PIP2 is the most common, but phosphtidylcholin often has it as well.

The arachidonic acid is usually attached to the 2nd carbon of the glycerol backbone

Question 11

Different phospholipases cleave at different locations. WHere do the following cleave?

PLA1

PLA2

PLC

PLD

Answer 11

PLA2 cleaves at the 2 position on the glycerol

PLA1 cleaves on the 1 position

PLC cuts off the head group WITH the phosphate attached

PLD cuts off the head group WITHOUT the phosphate

Question 12

What are the two methods for freeing arachidonic acid from the membrane in our cells?

Answer 12

1. PLC will cleave the phosphoinositol bisohpate into DAG and IP3. DAG lipase will then cleave the arachidonic acid off of the DAG.
2. PLA2 will directly clave the arachidonic acid off the phospholipid

Question 13

What receptors activate the lipases required to free arachidonic acid from the membrane?

Answer 13

GPCRs on the membrane

Question 14

Prostaglandin nomeclature provides what information?

Answer 14

PGI2

PG = prostaglading

I = the shape of the ring

2 = # of double bonds in the linear portions

Question 15

What do ALL prostaglandins have structurally?

Answer 15

A hydrosyl at carobn 15

double bonds between carbons 13 and 14

a 5-carbon ring structure

Question 16

What are the steps in prostaglanding and thromboxane synthesis?

Answer 16

1. COX acts on arachidonic acid to make PGG2.
2. PGG2 is acted on by peroxidase (using reduced glutathione) to form PGH2, which is the precursor
3. PGH2 is converted to thromboxane by TXA synthease and prostaglandings by PG_ synthase (depends on what prostaglanding you want)

Question 17

What makes thromboxanes different from prostacyclins structurally?

Answer 17

they have an epoxide oxygen bridge in the 6-C ring structure

Question 18

How are leukotrienes synthesized? how are they different structurally from prostaglandings and thromboxanes?

Answer 18

They are synthesized through the linear pathway with lipoxygenase creating HPETE, which is then converted to HETE which has an epoxide, which is then reduced to make leukotrienes

Leukotrienes are structurally different because they do not have a run structure

Question 19

Wha do prostaglandings do?

Answer 19

Trick question: some of them are pro-inflammatory and others are antiinflammatory

PGI, PGE, and PGD are anti-inflammatory and increase basodilation

PGF is pro-inflammatory and icnreases vasoconstriction, bronchoconstriction and smooth muscle

Question 20

What is happenin gin terms of prostaglandin secretion/action in healthy blood vewwels?

Answer 20

The vascular endothelial cells are releasing PGI2, which prevents platelet clotting and keeps blood vessels open.

Question 21

What happens when blood endothelia is damaged?

Answer 21

Damage reults in a proteolytic cascade which causes calcium release which culminates in thrombin activation

thrombin is a protease which cleaves soluble fibrinogen to form fibrin, which polymerizes into a wound covering matrix

When the platelets contact thrombin (or each other in a clot), they will release thromboxanes, which act as paracrine and autocrine hormones to induce platelet aggregation and other wound responses

Question 22

What are endocannabinoids?

Answer 22

They are arachidonic acid with an attached ethanolamine

Question 23

What is the protoypical endocannabinoid?

Answer 23

Anandamide

Question 24

What receptors do endocannabinoids bind to?

Answer 24

CB1 and CB2

CB1 receptors are in nerve synapses, which is how endocannabinoids can have thei analgesic effects

CB2 receptors are in the spleen and immune cells

Question 25

What effect does anandamide have on mast cells and macrophages?

Answer 25

It inhibits their release of TNF-alpha, thus blunting the signalling in the immune system and reducing inflammation

Question 26

What do NSAIDs target?

Answer 26

They target cyclooxygenase so that you don’t get the formation of prostaglandins, which helps in treating pain, fever, and inflammation

Question 27

What are the negative effects of COX inhibitors?

Answer 27

NSAIDs cannot selectively inhibit COX2 inhibitors (which would be nice because COX2 is what forms inflamatory PGs), so they inhibit COX1 as well.

COX1 forms prostaglandins that are anticlotting and stimulate mucin secretion in the gastric mucosa.

This is good in a way because it means NSAIDs have an anti-clotting ability, but it increases the risk of stomach ulcers

Question 28

Describe the general structure of COX enzymes?

Answer 28

THe two isoforms have very similar active sites

they both act as homodimers

they have amphipathic domains that anchor them in the membrane of SR

they both contain heme catalytic domains

Question 29

What does it mean to say that spirin is a suicide inhibitor?

Answer 29

It means it’s a noncompetitive inhibitor

The acetyl group from aspirin is transferred to the side chain of a serine amino acid near the active site of the COX enzyme

This is a covalent bond that permamently disables the enzyme and takes it out of circulation

Question 30

Why does using aspirin for preventative purposes only require a minimum dose?

Answer 30

Because aspirin in that case is targeting platelets to block the formation of clots

since platelets do not have a nucleus, they are not capable of making for COX is need be. So that small amount of aspirin is effectively able to eliminate prostablanding synthesis for the lifetime of that platelet

Question 31

WHat are some other NSAIDs that (unlike aspirin) do not covalently modify the COX enzymes?

Answer 31

ibuprofen (advil)

acetominophen (TYlenol)

Naproxen (Aleve)

Question 32

What will aspiin do to the kinetics of COX?

Answer 32

It will reduce Vmax because it’s a suicide inhibitor

Question 33

What were the adverse effects of the selective COX 2 inhibitors like celebrex and vioxx?

Answer 33

they have an increased risk of stroke and heart attack

Question 34

How do prostaglandins prevent inflammation?

Answer 34

Hyrosycortisone, prednisones and dexamethasone interfere with the transcription of the genes for phospholipase 2 and cyclooxygenase

This prevents inflammation by blocking the production of both leukotrienes and prostalgandins

Question 35

What were the corticosteroids we learned?

Answer 35

hydroxycortisone

prednisone

dexamethasone

Question 36

What is the negative effect of systemic corticosteroid use?

Answer 36

They are gluconeogenic because they increase transcription of genes for PEP-CK synthesis and icnrease muscle protien breakdown

this leads to hyperglycemia

Question 37

What are two ways we can treat the inflammation of asthma?

Answer 37

We can use inhaled corticosteroids (for acute attacks)

or we can use drugs that block the cys-leukotriene receptor (for daily use)

Question 38

What were the cys-Leukotriene receptor blockers that we learned?

Answer 38

montelukast (singulair)

zafirlukast (accolate)