Lipids - Eicosanoids

Question 1

Eicosanoids

Answer 1

Eicosanoids are made by the oxidation of omega-3 and 6 fats. They are locally-acting hormone-like signalling molecules.
* They have a short life span and are involved in:
o Inflammation.
o Blood vessel permeability and constriction.
o Blood coagulation.
o Immune cell behaviour.
o Lipid accumulation.
o Central nervous system signalling.
* Eicosanoids include prostaglandins, leukotrienes, thromboxanes, resolvins and protectins.
eicosa = 20 (carbon atoms)

Question 2

Eicosanoid conversion

Answer 2

Fatty acids are released from the membrane phospholipids by the enzyme phospholipase A2.
* These are converted to eicosanoids by cyclooxygenase(COX) and lipoxygenase (LOX) —this is dependent on the starting fatty acid and an outside stimulus.
* Eicosanoids can be made from arachidonic acid (AA), eicosapentaenoic acid (EPA) and dihomo-y-linolenic acid (DGLA).
* They can have both pro-and anti-inflammatory effects.

Question 3

Prostaglandins

Answer 3

Prostaglandins fall into three families or series, depending on which fatty acid they are made from:

Series 1 Prostaglandins (PG1) —made from DGLA:
* Keep blood platelets from sticking together.
* Remove excess sodium and water from the body.
* Relax blood vessels promoting circulation.
* ANTI-INFLAMMATORY

Series 2 Prostaglandins (PG2) —made from AA:
* Mostly promote platelet aggregation.
* Promote sodium and water retention (↑ BP)
* Oppose functions of series-1 prostaglandins.
* PRO-INFLAMMATORY

Series 3 Prostaglandins (PG3) —made from EPA:
* Some have weak platelet aggregating properties.
* Prevent the release of AA from cell membranes.
* EPA is the most important factor limiting PG2 production.
* ANTI- INFLAMMATORY

Question 4

Eicosanoids inflammation and shut off

Answer 4

Eicosanoids made from arachidonic acid produce initial inflammation. This is ‘shut off’ by the introduction of eicosanoids made from DGLA and EPA.

See Diagram