EICOSANOID BIOSYNTHESIS
• The term Eicosanoids is a collective name for molecules derived from
20-carbon fatty acids.
• The term Eicosanoid is derived from a Greek word “eicosa” meaning
twenty.
• They are oxygenated derivatives of 3 different 20-carbon fatty acids:
1. Eicosapentanoic acid
2. Arachidonic acid
3. Di-homo-gamma-linolenic acid
Introduction Cont..
• Eicosapentanoic acid: An omega-3 fatty acid with 5 double bonds
• Arachidonic acid: An omega-6 fatty acid with 4 double bonds
• Dihomo-gamma-linoleic acid: An omega-6 with 3 double bonds.
There are three groups of eicosanoids that are synthesized from C20
eicosanoic acids derived from the essential fatty acids linoleic acid
(omega 6) and linolenic acid (omega-3)
Classification of Eicosanoids
Classified into two main groups
• Prostanoids
• Leukotrienes
• Lipoxins
• Prostanoids are sub classified into three groups:
1. Prostaglandins (PGs)
2. Prostacyclins (PGIs)
3. Thromboxanes (TXs)
• Prostaglandins(PG), thromboxane (TX), leukotrienes(LT), and lipoxins (LX)
physiologically, are considered to act as local hormones functioning
through G-protein-linked receptors to elicit their biochemical effects.
BIOSYNTHESIS
• Two families of enzymes catalyze fatty acid oxygenation to produce
the eicosanoids:
• Cyclooxygenase (suicide Enzyme), or COX, generates the prostainoids.
• Lipoxygenase, or LOX, in several forms
• 5-Lipoxygenase generates the leukotrienes and via transcellular
biosynthesis is also involved in lipoxin generation.
• Eicosanoids are not stored within cells, but are synthesized as
required.
• Derived from fatty acids that make up cell
• Arachidonate, is usually derived from the 2 position of phospholipids
in the plasma membrane by the action of phospholipase A2, but also
from the diet
SITES OF HYDROLYTIC ACTIVITY OF PHOSPHOLIPASE
FORMATION OF ARACHIDONIC ACID FROM
LINOLEIC ACID
THE CYCLOOXYGENASE PATHWAY
THE LIPOXYGENASE PATHWAY