Lecture 62

Question 1

What are characteristics of prostaglandins and related compounds (thromboxanes & other eicosanoids)?

Answer 1

1) Eicosa means 20 (20 carbon molecules)
2) Potent cell signaling molecules - paracrine hormones
3) Multiple effects, including pain and inflammation associated with arthritis
4) Synthesized from essential dietary fatty acids, especially linoleic acid

Question 2

What are characteristics of prostaglandins in particular?

Answer 2

1) Discovered in the 1930s by Ulf von Euler
2) Synthesized in virtually every cell in the body
3) Unsaturated 20 carbon molecules, also contain a 5-member ring
4) Work right within the cells where they are synthesized - “act locally”
5) Have an extremely short half-life and are not stored

Question 3

Describe the structure of prostaglandins

Answer 3

1) The number of double bonds is indicated after the name (PGE2, PGF2, etc.)
2) Prostaglandins contain a 5 membered ring

Question 4

What is the first step in the synthesis of prostaglandins?

Answer 4

1) Oxidative cyclization of free arachidonic acid to yield PGH2 by prostaglandin endoperoxide synthase
2) PGH2 is converted to a variety of prostaglandins & thromboxanes by a variety of cell-specific synthases
3) Dietary linoleic acid —> (Elongation Desaturation) –> Arachidonic acid –> (cyclooxygenase (COX)) –> PGG2 –> (Peroxidase) –> PGH2
4) Peroxidase and cyclooxygenase activities both mediated by COX (two catalytic activities)

Question 5

Describe the the COX-1 isoform of cyclo-oxygenase

Answer 5

1) COX-1 is constitutive, expressed in most tissues
2) COX-1 plays a physiological & homeostatic role, cell signaling
3) COX-1 is not influenced by steroid administration
4) Not increased by cytokines nor bacteria
5) Produces house keeping substances such as platelets for blood clotting, prostaglandin E2 for kidney function & prostaglandin I2 for stomach protection

Question 6

Describe the the COX-2 isoform of cyclo-oxygenase

Answer 6

1) COX-2 is inducible following inflammation, trauma, etc.
2) COX-2 is found in immunocompetent cells (e.g. leukocytes)
3) Pathophysiological role, maintains inflammation
4) Contributes to pain, heat, & swelling
5) Induced by cytokines (interleukin-1)
6) Inhibited by steroids

Question 7

What is similar about COX-1 & COX-2?

Answer 7

Two isoforms of COX both produce prostaglandins (PGE2, PGF2alpha, PGI2)

Question 8

Describe the pathway of prostaglandin production, revisited, with insights into pro-inflammatory regulation

Answer 8

1) Membrane phospholipids –> Arachidonic acid (uses phospholipase A2)
2) Arachidonic Acid –> Prostaglandin H2 (Uses COX-1 or COX-2)
3) Prostaglandin H2 –> PGI2, PGD2, PGE2, PGF2 alpha (uses prostaglandin synthases)
4) PGD2 –> 15-d-PGJ2

Question 9

What are positive regulators of COX-2?

Answer 9

1) LPS
2) IL-1
3) TNF-alpha

Question 10

What are functions of prostaglandins?

Answer 10

1) PGE2 plays an important role in the development, regulation, & activity of different immune cells. Activation of the inflammatory response, production of pain, & fever. When tissues are damaged, white blood cells are mobilized to the site to minimize tissue destruction. Prostaglandins are produced as a result.
2) Prostaglandins play an integral role in a myriad of infections & diseases, including cancer & periodontal disease
3) Blood clots form when a blood vessel is damaged. Closely related molecules called thromboxanes stimulate constriction and clotting of platelets. Conversely, PGI2 is produced to have the opposite effect on the walls of blood vessels where clots should not be forming
4) Certain prostaglandings (i.e. PGE2) are involved with induction of labor by inducing uterine contractions
5) Prostaglandins are involved in several other organs:
- regulate salt and fluid balance in body
- increase blood flow in kidneys
- increase secretion of protective mucus in GI tract
- inhibit acid synthesis in GI tract
- leukotrienes, related molecules, promote constriction of bronchi associated with asthma

Question 11

How do NSAIDs work?

Answer 11

1) Inhibit COX enzymes
2) Reduce production of prostaglandins & thromboxanes
3) Reduce pain, fever, & inflammation

Question 12

What are some side effects of some NSAIDs in some people?

Answer 12

1) Include gastrointestinal irritation, ulcers, bleeding, etc.
2) If untreated, lead to death (~16,000/year in US)
3) Led to hunt for better anti-inflamatory drugs

Question 13

What are the effects of aspirin & other pain killers?

Answer 13

1) Aspirin works on both COX-1 & COX-2 to inhibit arachidonic acid’s entry int othe active site of the enzyme
2) Acetyl group of aspirin binds to serine in COX
3) By blocking the activity of the COX enzymes, this relieves some of the effects of pain & fever
4) Nonselective
5) Many side effects

Question 14

How does tylenol work?

Answer 14

Tylenol is thought to have effects through inhibiting the activity of COX-3, an alternatively spliced form of COX-1

Question 15

What is low dose aspirin therapy?

Answer 15

1) Aspirin irreversibly inhibits COX-1 (and COX-2)
2) Has a short half-life
3) New platelets are constantly being made
4) Will therefore reduce but not abolish the ability for blood to clot, thereby reducing heart attacks & stroke

Question 16

When COX drugs were first being developed, what was a hypothesis about them?

Answer 16

Hypothesis: selective inhibition of COX-2 might reduce inflammation without the GI side effects

Question 17

When designing a rational drug to use to inhibit JUST COX-2 and not COX-1, what did scientists discover?

Answer 17

Valine in position 523 of COX-2 causes a side pocket that does not exist in COX-1 (there is an isoleucine at position 523 instead). A drug could therefore bind to this side pocket in COX-2 without affecting COX-1

Question 18

What are examples of COX-2 inhibitors (Coxibs)?

Answer 18

Merck:
1) Vioxx (rofecoxib)
2) Arcoxia (etoricoxib)
Pfizer:
1) Celebrex (celecoxib)
2) Bextra (valdecoxib)

Question 19

What drug did MERCK remove from the market related to COX-2 inhibitors?

Answer 19

Vioxx

Question 20

What makes the COX-2 inhibitors very attractive?

Answer 20

Freedom from GI side effects