Lipid mediators: lipoxin and aspirin-triggered 15-epi-lipoxins.

Lipoxins (LX) and their 15-epimers, aspirin triggered lipoxins (ATL) are emerging as major promoters of resolution of the inflammatory reaction. These eicosanoids, that carry a tetraene chromophore, derive from sequential lipoxygenase (LO) metabolism of arachidonic acid. Three principal routes of LX/ATL biosynthesis have been uncovered. One involves cooperation between 15- and 5-LO, one other requires interactions between 12- and 5-LO and a third is characterized by 5-LO transformation of intermediary products generated by aspirin-acetylated cyclooxygenase (COX)-2. Thus, in a large majority of cases the biosynthesis of these eicosanois requires transcellular metabolic exchange during cell-cell interactions. LX and ATL are rapidly metabolized and inactivated by monocyte 15-hydroxyprostaglandin dehydrogenase (PGDH). A number of stable analogs that resist inactivation and retain biological activity has been synthesized. Accumulating evidence suggests that these analogs may have a potential therapeutic impact in a variety of diseases characterized by neutrophil-mediated persistent inflammation, such as reperfusion injury, gastro-intestinal and renal inflammatory disorders, periodontitis. Clinical evaluation of LXA4 and 15-epi-LXA4 formation and their pharmacological regulation may be now achieved using recently developed ELISA assays, that allow large-scale measurements in human biological fluids.