Mediator lipidomics: search algorithms for eicosanoids, resolvins, and protectins.

Within the domain of lipidomics, lipid mediator lipidomics and informatics is an exciting area because of the important roles of lipid-derived mediators in health and disease. It is well-appreciated that arachidonic acid is a precursor to potent bioactive mediators, such as prostaglandins, leukotrienes, and lipoxins. Recent experiments employing a mediator-lipidomic approach have uncovered that other major essential polyunsaturated fatty acids, such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), serve as precursors for the production of potent bioactive mediator families, coined "resolvins" and "protectins." These omega-3 polyunsaturated fatty acids have long been noted to have beneficial effects in human systems; however, molecular evidence for their beneficial actions has been lacking and/or subject to debate. In this chapter, we review the databases and search algorithms used to identify these novel lipid mediators using liquid chromatography-ultraviolet-tandem mass spectrometry (LC-UV-MS/MS). Cognoscitive-contrast-angle algorithms and databases (COCAD) and systematic naming and empirical fragmentation rules useful in MS/MS ion identification were developed. Examples of identifying eicosanoids, resolvins, and protectins are given in human and murine tissues. The findings reviewed in this chapter demonstrate the advantages of COCAD in profiling and identification of bioactive lipid mediators and documenting activation of their biosynthetic pathways as well as in establishing relationships between lipid mediator pathways with agonists and antagonists present in the biological system.