Resolvin D1 (RvD1) and protectin D1 (Neuroprotectin D1, PD1/NPD1) are newly identified anti-inflammatory lipid mediators biosynthesized from docosahexaenoic acid (DHA). In this report, the spectra-structure correlations and fragmentation mechanisms were studied using electrospray low-energy collision-induced dissociation tandem mass spectrometry (MS/MS) for biogenic RvD1 and PD1, as well as mono-hydroxy-DHA and related hydroperoxy-DHA. The loss of H2O and CO2 in the spectra indicates the number of functional group(s). Chain-cut ions are the signature of the positions and numbers of functional groups and double bonds. The observed chain-cut ion is equivalent to a hypothetical homolytic-segment (cc, cm, mc, or mm) with addition or extraction of up to 2 protons (H). The alpha-cleavage ions are equivalent to: [cc + H], with H from the hydroxyl through a beta-ene or gamma-ene rearrangement; [cm - 2H], with 2H from hydroxyls of PD1 through a gamma-ene rearrangement, or 1H from the hydroxyl and the other H from the alpha-carbon of mono-HDHA through an alpha-H-beta-ene rearrangement; [mc - H], with H from hydroxyl through a beta-ene or gamma-ene rearrangement, or from the alpha-carbon through an alpha-H-beta-ene rearrangement; or [mm] through charge-direct fragmentations. The beta-ene or gamma-ene facilitates the H shift to gamma position and alpha-cleavage. Deuterium labeling confirmed the assignment of MS/MS ions and the fragmentation mechanisms. Based on the MS/MS spectra and fragmentation mechanisms, we identified RvD1, PD1, and mono-hydroxy-DHA products in human neutrophils and blood, trout head-kidney, and stroke-injury murine brain-tissue.
Hong S, Lu Y, Yang R, Gotlinger KH, Petasis NA, Serhan CN. Resolvin D1, protectin D1, and related docosahexaenoic acid-derived products: Analysis via electrospray/low energy tandem mass spectrometry based on spectra and fragmentation mechanisms. J Am Soc Mass Spectrom. 2007 January Analytical Core, Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.