Eicosanoids are signaling molecules derived from 20-carbon fatty acids such as eicosapentaenoic acid, arachidonic acid, and di-homo gamma-linolenic acid, playing key roles in various bodily functions like inflammation and blood regulation. They include prostanoids (prostaglandins, thromboxanes), leukotrienes, and lipoxins, each with distinct structures and functions. Eicosanoids are short-lived, acting locally and quickly inactivated by enzymatic processes.

1. METABOLISM OF EICOSANOIDS
By S. PRISCILLA, M.Sc.CN, I yr

2. WHAT ARE EICOSANOIDS?
★ The term Eicosanoid is derived from the greek term ‘Eicosa’ means ‘twenty’.
★ They are oxygenated derivatives of 3 different 20-Carbon fatty acids:
○ Eicosapentaenoic acid(EPA), ω-3 fatty acid with 5 double bonds
○ Arachidonic acid(AA), ω-6 fatty acid with 4 double bonds
○ Di - homo gamma- linolenic acid(DHGLA), ω-6 fatty acid with 3 double bonds
★ Eicosanoids are derived from either omega 3 or omega 6 fatty acids.

3. ★ Signalling molecules made by oxidation - Paracrine hormones.
★ They act locally by diffusing from its source to target cells in the
neighborhood.
○ Reproductive functions
○ Inflammatory responses, fever and pain associated with injury or diseases
○ Formation of blood clots and regulation of blood pressure.
○ Gastric acid secretion.
.

4. CLASSIFICATION
★ Prostanoids
○ Prostaglandins (PG)
○ Prostacyclins (PGI)
○ Thromboxanes (TX)
★ Leukotrienes and lipoxins

5. PROSTAGLANDINS(PG)
★ The first eicosanoid to be discovered, in
the seminal fluid
★ They have impact over the reproductive,
cardiovascular systems, CNS,
gastrointestinal tract etc.,
★ They structurally resemble prostanoic
acid, a 20-Carbon fatty acid, has a 5-C
ring and 2 side chains attached to the
chain.

6. THROMBOXANES(TX)
★ Thromboxanes are similar in structure to
prostaglandins, differ in that they have 6 -
oxane ring.
★ There are several types named according
to the number of double bonds in the side
chains.

7. LEUKOTRIENES (LT)
★ They are 20 carbon polyenoic fatty acids having a number of substituents,
depending on which they are divided into LTA, LTB, LTC, LTD, LTE
★ Each type is subdivided upon the number of double bonds which vary from 3 -
5
★ The most important leukotrienes are LTC4(Glutathione),
LTD4(Cysteinylglycine), LTE4(Cysteine).

9. ANABOLISM OF EICOSANOIDS
cyclooxygenase pathway and lipoxygenase pathway

11. CATABOLISM OF EICOSANOIDS

12. ★ All eicosanoids are short lived compounds ; lasting from seconds to minutes.
★ They produce their effects locally and are quickly inactivated.
★ Prostaglandins are inactivated by self catalyzed destruction of
cyclooxygenase - 15-hydroxyprostaglandin dehydrogenase(suicide enzyme).
★ Thromboxanes of type A are inactivate by hydration to type B.
★ Leukotrienes are catabolized by ω- oxidation followed by β-oxidation from ω-
end

13. ACTIONS OF EICOSANOIDS

14. PROSTAGLANDINS
★ Inhibits lipolysis in adipose tissues.
★ Increase contractility of uterine muscle; induce labour.
★ They are bronchodilators and hence used in the treatment of bronchial
asthma.
★ Decrease gastric HCl secretion.
★ Cause vasodilation and hence decrease BP.
★ Increase permeability of capillaries.
★ Inhibit aggregation of platelets.
★ Stimulate intestinal peristalsis.
★ Tubular resorption of sodium and water
★ Formation, maturation and transport of sperms

15. THROMBOXANES
★ Stimulates aggregation of platelets.
★ Vasoconstriction and hence increases BP.

16. LEUKOTRIENES
★ Increases capillary permeability.
★ Chemotactic agents, attract leukocytes to the site of inflammation.
★ Powerful bronchoconstrictors ; hence have a role in asthma and allergy
reactions.

17. References:
Harpers “Textbook of Biochemistry”
U.Sathyanaryana “Textbook of Biochemistry”
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