2013/04/03 by Gerhard Liebisch, Juan Antonio Vizcaíno, Harald Köfeler +5 · 31 citations
Biochemistry, Genetics and Molecular Biology · Chemistry · #Metabolomics and Mass Spectrometry Studies #Mass Spectrometry Techniques and Applications #Analytical Chemistry and Chromatography
paper · doi:10.1194/jlr.m033506
There is a need for a standardized, practical annotation for structures of lipid species derived from mass spectrometric approaches; i.e., for high-throughput data obtained from instruments operating in either high- or low-resolution modes. This proposal is based on common, officially accepted terms and builds upon the LIPID MAPS terminology. It aims to add defined levels of information below the LIPID MAPS nomenclature, as detailed chemical structures, including stereochemistry, are usually not automatically provided by mass spectrometric analysis. To this end, rules for lipid species annotation were developed that reflect the structural information derived from the analysis. For example, commonly used head group-specific analysis of glycerophospholipids (GP) by low-resolution instruments is neither capable of differentiating the fatty acids linked to the glycerol backbone nor able to define their bond type (ester, alkyl-, or alk-1-enyl-ether). This and other missing structural information is covered by the proposed shorthand notation presented here. Beyond GPs, we provide shorthand notation for fatty acids/acyls (FA), glycerolipids (GL), sphingolipids (SP), and sterols (ST). In summary, this defined shorthand nomenclature provides a standard methodology for reporting lipid species from mass spectrometric analysis and for constructing databases. There is a need for a standardized, practical annotation for structures of lipid species derived from mass spectrometric approaches; i.e., for high-throughput data obtained from instruments operating in either high- or low-resolution modes. This proposal is based on common, officially accepted terms and builds upon the LIPID MAPS terminology. It aims to add defined levels of information below the LIPID MAPS nomenclature, as detailed chemical structures, including stereochemistry, are usually not automatically provided by mass spectrometric analysis. To this end, rules for lipid species annotation were developed that reflect the structural information derived from the analysis. For example, commonly used head group-specific analysis of glycerophospholipids (GP) by low-resolution instruments is neither capable of differentiating the fatty acids linked to the glycerol backbone nor able to define their bond type (ester, alkyl-, or alk-1-enyl-ether). This and other missing structural information is covered by the proposed shorthand notation presented here. Beyond GPs, we provide shorthand notation for fatty acids/acyls (FA), glycerolipids (GL), sphingolipids (SP), and sterols (ST). In summary, this defined shorthand nomenclature provides a standard methodology for reporting lipid species from mass spectrometric analysis and for constructing databases. A comprehensive classification system for lipids was presented by the International Lipid Classification and Nomenclature Committee (ILCNC) in 2005 (1Fahy E. Subramaniam S. Brown H.A. Glass C.K. Merrill Jr, A.H. Murphy R.C. Raetz C.R. Russell D.W. Seyama Y. Shaw W. et al.A comprehensive classification system for lipids.J. Lipid Res. 2005; 46: 839-861Abstract Full Text Full Text PDF PubMed Scopus (1127) Google Scholar) and updated in 2009 (2Fahy E. Subramaniam S. Murphy R.C. Nishijima M. Raetz C.R. Shimizu T. Spener F. van Meer G. Wakelam M.J. Dennis E.A. Update of the LIPID MAPS comprehensive classification system for lipids.J. Lipid Res. 2009; 50: S9-S14Abstract Full Text Full Text PDF PubMed Scopus (1054) Google Scholar). This system places lipids into eight categories and is available online on the LIPID MAPS website (http://www.lipidmaps.org). The LIPID MAPS nomenclature precisely describes lipid structures. The key technology for lipid species analysis is mass spectrometry (MS) (3Wenk M.R. Lipidomics: new tools and applications.Cell. 2010; 143: 888-895Abstract Full Text Full Text PDF PubMed Scopus (434) Google Scholar, 4Blanksby S.J. Mitchell T.W. Advances in mass spectrometry for lipidomics.Annu. Rev. Anal. Chem. (Palo Alto Calif.). 2010; 3: 433-465Crossref PubMed Scopus (253) Google Scholar). Typically, MS analysis without intermediate chemical steps does not provide the structural details covered by the LIPID MAPS nomenclature, which led mass spectrometrists to use a variety of different notations for lipid species. Moreover, lipid species are frequently annotated based on assumptions. For example, a precursor ion scan of m/z 184, a standard approach to detect phosphatidylcholine (PC) and sphingomyelin (SM) species, is neither able to differentiate PC species containing an ether bond from diacyl species (Fig. 1A), nor is it able to differentiate the sphingoid base in SM (5Liebisch G. Lieser B. Rathenberg J. Drobnik W. Schmitz G. High-throughput quantification of phosphatidylcholine and sphingomyelin by electrospray ionization tandem mass spectrometry coupled with isotope correction algorithm.Biochim. Biophys. Acta. 2004; 1686: 108-117Crossref PubMed Scopus (247) Google Scholar). Similarly, annotation of phosphatidylethanolamine (PE) species, particularly plasmalogens, should not be based on head group-specific positive neutral loss (NL 141) or negative precursor ion (PIS m/z 196) scans (6Brugger B. Erben G. Sandhoff R. Wieland F.T. Lehmann W.D. Quantitative analysis of biological membrane lipids at the low picomole level by nano-electrospray ionization tandem mass spectrometry.Proc. Natl. Acad. Sci. USA. 1997; 94: 2339-2344Crossref PubMed Scopus (730) Google Scholar), which identify only the lipid class but do not provide specific mass spectrometric analysis (7Zemski Berry K.A. Murphy R.C. Electrospray ionization tandem mass spectrometry of glycerophosphoethanolamine plasmalogen phospholipids.J. Am. Soc. Mass Spectrom. 2004; 15: 1499-1508Crossref PubMed Scopus (219) Google Scholar) (Fig. 1B). Although lipidologists possess a “biological intelligence,” which allows them to interpret MS data in a manner that recognizes what is likely or not likely to be the correct structure of a particular lipid species, we think there is need for a standardized, practical shorthand notation of lipid structures derived from MS approaches that enables correct and concise reporting of data and their deposition in databases. Our proposal is based on common, officially accepted terms and on the LIPID MAPS terminology. In addition, it takes the different levels of structural information provided by MS into account (Fig. 2). At the lowest level of resolution, the respective LIPID MAPS abbreviation (Table 1) is followed either by the detected nominal mass (lipid class level mass) or by the sum of components that are expressed as their total number of carbon atoms and of double bonds (lipid species level); variable components of the species are not identified. In the presence of fatty acids with odd-numbered carbon atoms, ambiguities regarding functional groups or bond types may occur. Therefore, such species are either assigned by their molecular mass or based on assumptions which should be presented with the result.TABLE 1Lipid class abbreviationsLIPID MAPS Category/Class - Common NameLipid Class - LIPID MAPSAbbreviationFatty acyls [FA]Fatty acidsFatty acids and conjugates [FA01]FAGlycerolipids [GL]MonoglyceridesMonoradylglycerols [GL01]MGDiglyceridesDiradylglycerols [GL02]DGTriglyceridesTriradylglycerols [GL03]TGGlycerophospholipids [GP]Bis[monoacylglycero]phosphatesMonoacylglycerophosphomonoradylglycerols [GP0410]BMPCardiolipinsGlycerophosphoglycerophosphoglycerols [GP12]CLPhosphatidic acidsGlycerophosphates [GP10]PAPhosphatidylcholinesGlycerophosphocholines [GP01]PCPhosphatidylethanolaminesGlycerophosphoethanolamines [GP02]PEPhosphatidylgylcerolsGlycerophosphoglycerols [GP04]PGPhosphatidylgylcerolphosphateGlycerophosphoglycerophosphates [GP05]PGPPhosphatidylinositolsGlycerophosphoinositols [GP06]PIPhosphatidylinositol-monophosphateGlycerophosphoinositol monophosphates [GP07]PIPPhosphatidylinositol-3-phosphateGlycerophosphoinositol monophosphates [GP07]PIP[3′]Phosphatidylinositol-4-phosphateGlycerophosphoinositol monophosphates [GP07]PIP[4′]Phosphatidylinositol-5-phosphateGlycerophosphoinositol monophosphates [GP07]PIP[5′]Phosphatidylinositol-bisphosphateGlycerophosphoinositol bisphosphates [GP08]PIP2Phosphatidylinositol-3,4-bisphosphateGlycerophosphoinositol bisphosphates [GP08]PIP2[3′,4′]Phosphatidylinositol-3,5-bisphosphateGlycerophosphoinositol bisphosphates [GP08]PIP2[3′,5′]Phosphatidylinositol-4,5-bisphosphateGlycerophosphoinositol bisphosphates [GP08]PIP2[4′,5′]Phosphatidylinositol-trisphosphateGlycerophosphoinositol trisphosphates [GP09]PIP3PhosphatidylserinesGlycerophosphoserines [GP03]PSLysophospholipidsPrefix LSphingolipids [SP]CeramidesCeramides [SP02]CerCeramide-1-phosphatesCeramide-1-phosphates [SP0205]C1PSphingoid basesSphingoid bases [SP01]SPHSphingoid base-1-phosphatesSphingoid bases [SP01]S1PSphingomyelinsPhosphosphingolipids [SP03]SMHexosylceramidesNeutral glycosphingolipids [SP05]HexCerGlucosylceramideNeutral glycosphingolipids [SP05]GlcCerGalactosylceramideNeutral glycosphingolipids [SP05]GalCerDihexosylceramidesNeutral glycosphingolipids [SP05]Hex2CerLactosylceramideNeutral glycosphingolipids [SP05]LacCerSterol lipids [ST]SterolsSterols [ST01]STSteryl estersSteryl esters [ST0102]SEFree cholesterolCholesterol [LMST01010001]FCCholesteryl esterCholesteryl esters [ST0102]CEBile acidsBile acids and derivatives [ST04]Cholic acidCAChenodeoxycholic acidCDCADeoxycholic acidDCAUrsodeoxycholic acidUDCAHyodeoxycholic acidHDCALithocholic acidLCAGlycocholic acidGCATaurocholic acidTCAAbbreviations are in agreement with Table 3 in Fahy et al. (1Fahy E. Subramaniam S. Brown H.A. Glass C.K. Merrill Jr, A.H. Murphy R.C. Raetz C.R. Russell D.W. Seyama Y. Shaw W. et al.A comprehensive classification system for lipids.J. Lipid Res. 2005; 46: 839-861Abstract Full Text Full Text PDF PubMed Scopus (1127) Google Scholar) and the updated LIPID MAPS nomenclature (2Fahy E. Subramaniam S. Murphy R.C. Nishijima M. Raetz C.R. Shimizu T. Spener F. van Meer G. Wakelam M.J. Dennis E.A. Update of the LIPID MAPS comprehensive classification system for lipids.J. Lipid Res. 2009; 50: S9-S14Abstract Full Text Full Text PDF PubMed Scopus (1054) Google Scholar). Open table in a new tab Abbreviations are in agreement with Table 3 in Fahy et al. (1Fahy E. Subramaniam S. Brown H.A. Glass C.K. Merrill Jr, A.H. Murphy R.C. Raetz C.R. Russell D.W. Seyama Y. Shaw W. et al.A comprehensive classification system for lipids.J. Lipid Res. 2005; 46: 839-861Abstract Full Text Full Text PDF PubMed Scopus (1127) Google Scholar) and the updated LIPID MAPS nomenclature (2Fahy E. Subramaniam S. Murphy R.C. Nishijima M. Raetz C.R. Shimizu T. Spener F. van Meer G. Wakelam M.J. Dennis E.A. Update of the LIPID MAPS comprehensive classification system for lipids.J. Lipid Res. 2009; 50: S9-S14Abstract Full Text Full Text PDF PubMed Scopus (1054) Google Scholar). Bond type level additionally describes the type of linkage of the variable components to the lipid species’ backbone without knowing the single components. When MS resolves the variable components of the lipid species (in most cases fatty acids) the fatty acyl/alkyl level notation is applicable. Finally, when a specific analysis for backbone position (sn- for stereospecific numbering) in glycerolipids and glycerophospholipids categories has been carried out, the fatty acyl/alkyl position level is applicable. Fatty acyl/alkyl/sphingoid base structure level describes structural details of these components. Full structural analysis of the lipid species is covered by the LIPID MAPS nomenclature. The proposal presented here covers the major lipid classes of five of the eight LIPID MAPS categories, namely, fatty acyls (FA), glycerolipids (GL), glycerophospholipids (GP), sphingolipids (SP), and sterols (ST), with a focus on mammalian lipids. Other minor lipid classes or lipids from other organisms could be the subject of further proposals. All presentations of lipid species data include an a priori statement on structural resolution attained by the method of MS analysis. It should be a requirement that lipids are defined by both their class and their nominal mass (Da). The following rules apply to all lipid categories described below:•Lipid class abbreviation heads each species description.•Variable components (constituents), such as fatty acids, are assigned based on their mass as number of C-atoms and number of double bonds (C-atoms:double bonds).•Only experimentally proven structural details of constituent fatty acids are assigned according to the rules defined for fatty acyls (see below).•When structural ambiguities are present (e.g., bond type, hydroxyl groups, branched chains, see examples in Fig. 1 and TABLE 2., TABLE 3., TABLE 4., TABLE 5., TABLE 6.–7), species are assigned by one of the following rules:•Lipid class and the (uncharged) molecular mass (Da) in parentheses (preferred for reporting in databases lipid class level mass). For fatty acyl substituents, the mass of the corresponding free fatty acid is used (see example in Table 6).•Annotation based on assumptions must be clearly visible (preferred for publications lipid species level).TABLE 5.Sphingolipids with a free amino group: shorthand notation examplesSphingoid BaseLipid Class Level MassaUncharged molecular mass.Hydroxyl Group LevelLIPID MAPS Sphingoid Base Structure LevelSphingosineSPH (299)SPH d18:1SPH d18:1(4E)(1OH,3OH)SphinganineSPH (301)SPH d18:0SPH d18:0(1OH,3OH)SphingadieneSPH (297)SPH d18:2SPH d18:2(4E,8E)(1OH,3OH)PhytosphingosineSPH (317)SPH t18:0SPH t18:0(1OH,3OH,4OH)Sphingosine–C20SPH (327)SPH d20:1SPH d20:1(4E)(1OH,3OH)SphingosineS1P (379)S1P d18:1S1P d18:1(4E)(1OH,3OH)SphinganineS1P (381)S1P d18:0S1P d18:0(1OH,3OH)1-Deoxymethyl-sphinganineSPH (271)SPH m17:0SPH m17:0(2OH)1-Deoxy-sphinganineSPH (285)SPH m18:0SPH m18:0(3OH)a Uncharged molecular mass. Open table in a new tab TABLE 6.Sphingolipids containing an amide bound fatty acid: shorthand notation examplesLipid Class Level MassaUncharged molecular mass.Lipid Species LevelbAnnotation based on assumption of a sphingoid base with two hydroxyl groups.Hydroxyl Group LevelFatty Acyl LevelLIPID MAPS Sphingoid Base/Fatty Acyl Structure LevelCer (537)Cer 34:1Cer d34:1Cer d18:1/16:0Cer d18:1(4E)(1OH,3OH)/16:0Cer (539)Cer 34:0Cer d34:0Cer d18:0/16:0Cer d18:0 (1OH,3OH)/16:0C1P (617)C1P 34:1C1P d34:1C1P d18:1/16:0C1P d18:1(4E)(1OH,3OH)/16:0SM (702)SM 34:1SM d34:1SM d18:1/16:0SM d18:1(4E)(1OH,3OH)/16:0SM (704)SM 34:0SM d34:0SM d18:0/16:0SM d18:0 (1OH,3OH)/16:0SM (840)SM 44:2SM d44:2SM d20:1/24:1SM d20:1(4E)(1OH,3OH)/24:1(15Z)HexCer (701)HexCer 34:1HexCer d34:1HexCer d18:1/16:0GlcCer d18:1(4E)(1OH,3OH)/16:0HexCer (701)HexCer 34:1HexCer d34:1HexCer d18:1/16:0GalCer d18:1(4E)(1OH,3OH)/16:0Hex2Cer (861)Hex2Cer 34:1Hex2Cer d34:1Hex2Cer d18:1/16:0LacCer d18:1(4E)(1OH,3OH)/16:0a Uncharged molecular mass.b Annotation based on assumption of a sphingoid base with two hydroxyl groups. Open table in a new tab TABLE 7.Sterols: shorthand notation examplesSterolLipid Class Level MassaUncharged molecular mass.Lipid Species LevelBond Type LevelLIPID MAPS Structure LevelCholesterolST (386)ST 27:1OHST 27:1OHST 27:1/OH [5Z,3βOH ]3β-Hydroxycholestenoic acidST (416)ST A27:1OHST A27:1OHST A27:1/OH [5Z,3βOH,25(R),26CO2H]Lithocholic acidST (376)ST A24OHST A24OHST A24/OH [5βH,3αOH,24CO2H]ProgesteroneST (314)ST 21:3OH2ST 21:1O2ST 21:1/O2 [4Z,3O,20O]TestosteroneST (288)ST 19:2OH2ST 19:1 OHOST 19:1/OH/O [4Z,17βOH,3O]DehydroepiandrosteroneST (288)ST 19:2OH2ST 19:1OHOST 19:1/OH/O [5Z,3βOH,17O]17β-EstradiolST (272)ST 18:3OH2ST 18:3OH2ST 18:3/OH2 [1Z,3E,5E,3OH,17βOH]Taurocholic acidST (515)ST A24OH3TST A24OH3TST A24/OH3/T [5βH, 3αOH,7αOH,12αOH,24T]Glycochenodeoxycholic acidST (449)ST A24OH2GST A24OH2GST A24/OH2/G [5βH, 3αOH,7αOH,24G]Dehydroepiandrosterone sulfateST (368)ST 19:2OH2SST 19:1OHOSST 19:1/OH/O/S [5Z,3βOH,17O,3S]24(S)-Hydroxycholesterol 3-sulfate, 24-glucuronideST (658)ST 27:1OH2SGlcAST 27:1OH2SGlcAST 27:1/OH2/S/GlcA [5Z,3βOH,24(S)OH,3S,24GlcA]Cholesteryl palmitateST (624)SE 27:1/16:0SE 27:1/16:0CE 16:0Cholesteryl linoleateST (648)SE 27:1/18:2SE 27:1/18:2CE 18:2(9Z,12Z)Zymosteryl oleateST (648)SE 27:2/18:1SE 27:2/18:1SE 27:2 [5α,8E,24,3βFA]/18:1(9Z)a Uncharged molecular mass. Open table in a new tab •Detailed structures including stereochemistry are covered by LIPID MAPS nomenclature. Fatty acids in free form and as variable fatty acyls in lipids are prevalent lipid structures. Therefore, we use fatty acids and acyls as a paradigm for application of the shorthand notation. For the sake of simplicity, we include some frequent functional groups of fatty acids but do not treat complex FA classes, such as eicosanoids and docosanoids (8Murphy R.C. Fahy E. Fatty 2010; Full Text Full Text PDF PubMed Scopus Google Scholar). When an annotation of the fatty acid is only based on the mass mass usually it is that a fatty acid with functional groups is present double mass resolution with mass may identify functional groups. The following rules examples are in Table FA number of of double groups, in the acyl are not are the number of double bonds by an and followed by the number of groups of functional groups are the number of double bonds type of functional a of according to are in of the functional groups that are by a bond position is by a number according to or a number followed by for for for functional for hydroxyl for is to that the number of to an ether see for of functional bonds - - - acids and shorthand notation Class Level MassaUncharged molecular mass.Lipid Species LevelbAnnotation based on the assumption of a fatty acid with functional groups double Acyl LevelLIPID MAPS Fatty Acyl Structure Uncharged molecular mass.b Annotation based on the assumption of a fatty acid with functional groups double Open table in a new tab approaches frequently apply tandem MS a low mass resolution such as a mass S.J. Mitchell T.W. Advances in mass spectrometry for lipidomics.Annu. Rev. Anal. Chem. (Palo Alto Calif.). 2010; 3: 433-465Crossref PubMed Scopus (253) Google Scholar, electrospray ionization mass spectrometric analysis and of from of biological Spectrom. Rev. 2005; PubMed Scopus Google Scholar, M. Murphy R.C. Electrospray mass spectrometry of Spectrom. Rev. PubMed Scopus Google Scholar). In this lipid classes and species are by precursor and scans (6Brugger B. Erben G. Sandhoff R. Wieland F.T. Lehmann W.D. Quantitative analysis of biological membrane lipids at the low picomole level by nano-electrospray ionization tandem mass spectrometry.Proc. Natl. Acad. Sci. USA. 1997; 94: 2339-2344Crossref PubMed Scopus (730) Google Scholar). A major of lipid scans is that bond type, i.e., or to glycerol backbone of constituent alkyl-, and be these species are (Fig. such data are annotated based on the assumption that bonds are To this of Fig. 1 of the lipid species level for this could apply to glycerolipids and fatty approach to and ether bonds is the application of MS T. T. by analysis of mass Chem. PubMed Scopus Google Scholar). in groups be from linked (Fig. 1B). specific MS to clearly identify linked or further double bonds in the (7Zemski Berry K.A. Murphy R.C. Electrospray ionization tandem mass spectrometry of glycerophosphoethanolamine plasmalogen phospholipids.J. Am. Soc. Mass Spectrom. 2004; 15: 1499-1508Crossref PubMed Scopus (219) Google Scholar). The following rules apply for shorthand notation of both the major classes of and examples are in TABLE 3., TABLE lipid class abbreviation followed by number of of double acids linked to the glycerol are of the fatty acids is not of fatty acids is proven for or for FA linked types other bonds are as in of the sum of C-atoms or fatty proven is to that the number of a see proven ether bond in one bond is in of the bond type as for for rules for glycerophospholipids classes are as in the LIPID MAPS nomenclature (Table be presented by their respective class the by ether bonds are in of the bond type as and classes, the be and for information the position of on the are (see Table The is as the only is are presented as and in TABLE TABLE 2., TABLE 3., TABLE 4., we the annotation and for of by databases. species be this further shorthand notation Class Level MassaUncharged molecular mass.Lipid Species LevelbAnnotation based on assumption of carbon Type LevelFatty LevelFatty LevelLIPID MAPS Fatty Structure Uncharged molecular mass.b Annotation based on assumption of carbon Open table in a new tab TABLE shorthand notation Class Level MassaUncharged molecular mass.Lipid Species LevelbAnnotation based on assumption of carbon Type LevelFatty LevelFatty LevelLIPID MAPS Fatty Structure and containing ether of specific MS analysis of specific MS analysis or PC or PC or PC by Uncharged molecular mass.b Annotation based on assumption of carbon of specific MS analysis (7Zemski Berry K.A. Murphy R.C. Electrospray ionization tandem mass spectrometry of glycerophosphoethanolamine plasmalogen phospholipids.J. Am. Soc. Mass Spectrom. 2004; 15: 1499-1508Crossref PubMed Scopus (219) Google Scholar). Open table in a new tab MS for species analysis use from the sphingoid base E. S. Merrill Jr, A.H. Quantitative analysis of sphingolipids for and ion mass Lipid Res. 2009; 50: Full Text Full Text PDF PubMed Scopus Google Scholar), but the commonly used precursor ion scan of m/z for SM analysis is not able to differentiate the fatty acid and sphingoid base Y. Y. Merrill Jr, A.H. of mammalian sphingolipids by tandem mass spectrometry and mass spectrometry Biophys. Acta. PubMed Scopus Google Scholar), there is a that provide this information E. S. Merrill Jr, A.H. Quantitative analysis of sphingolipids for and ion mass Lipid Res. 2009; 50: Full Text Full Text PDF PubMed Scopus Google Scholar). In this lipid species level annotation could be based on the assumption of the major sphingoid backbone in the respective in or in This assumption must be a MS allows of the number of hydroxyl groups in sphingolipids with the sum of and double bonds in the sphingoid base and fatty acid R. M. R. on a mass by Mass Spectrom. PubMed Scopus Google Scholar). The following rules examples are in TABLE 5., TABLE sphingoid backbone is annotated by the number of hydroxyl groups in the sphingoid base for for for and by a from the number of of double bonds of the fatty of hydroxyl groups and double bonds including are as described for fatty acyls the sphingoid base is not the sum of sphingoid base and fatty acid is as number of of double are based on the number of hydroxyl groups of the major sphingoid base for that in When the number of hydroxyl groups is it is in of the number of for further of fatty acids, rules as described in an A fatty acid that is to an fatty acid is in as notation for is in Table This does not complex which we could be subject to a use the to all based on the All mammalian sterols are derived from or sterols be a The stereochemistry of the is to a by mammalian which all at one or to carbon at the lipid species we the has at one MS with mass may identify other functional groups, as precursor ion and neutral loss be defined by the to in some by The following rules for shorthand nomenclature been in the examples in Table number of carbon of double Annotation at the lipid species level is based on sterols or and at one hydroxyl at position groups, including all hydroxyl groups, are the number of double by an and followed by the number of groups of functional groups are the number of double by a stereochemistry of functional groups is in and are for stereochemistry and are in in In the of proven structures of and and be used (Table is followed by number of of double bonds of the fatty acid to the hydroxyl at position 3 (Table In the of structures and other esters the shorthand notation is used as followed by number of of double bonds of the fatty acid to the hydroxyl (Table In the of acids, the shorthand notation is by A to an and at the structure the of the acid is scans the presence of groups, i.e., or to the acid of acids an amide acid to a hydroxyl an acid and to be linked to a hydroxyl an In the stereochemistry is the in Table 1 be The presented shorthand notation for lipid structures provides a system to MS data in a The system two to species in the presence of when bond type or functional groups may not be by the analysis. Annotation may be either based on assumptions or according to the molecular mass. When these should be based on biological and should be clearly based on assumptions are for publications with annotation of molecular which should be for the reporting in databases. it is must be the that assumptions are not