Lipoxin

Lipoxins are members of the family of bioactive products generated from Arachidonic Acid (AA). They have a number of immunomodulatory and anti-inflammatory actions. Lipoxins are short lived endogenously produced nonclassic eicosanoids whose appearance in inflammation signals the resolution of inflammation. They are abbreviated as LX, an acronym for lipoxygenase (LO) interaction products. At present two lipoxins have been identified; lipoxin A₄ (LXA₄) and lipoxin B₄ (LXB₄).

History

Lipoxins were first described by Serhan, Hamberg and Samuelsson in 1984. They reported that the lipoxins stimulated superoxide anion (O₂⁻) generation and degranulation at submicromolar concentrations—as potent as LTB₄.

Biosynthesis

Lipoxins are derived enzymatically from arachidonic acid, an ω-6 fatty acid. One important precursor to the lipoxins is 15-hydroxyicosatetraenoic acid (i.e. 15(S)-HETE) and its 15-hydroperoxy precusor. Transcellular biosynthetic mechanisms play a key role in their production. They are formed by platelets but they alone cannot synthesize them. Platelets depend upon neutrophils for LTA₄, which is converted to LXA₄ and LXB₄ by the action of platelet 12-lipoxygenase. LTC₄, LTD_4, and LTE₄ are also synthesized in platelets from LTA₄. An analogous class, the resolvins, are derived from EPA and DHA, ω-3 fatty acids. Another analogous class, the epi-lipoxins, are formed by non-enzymatic peroxidation.