Isolation and mass spectrometry characterization of molecular species of lactosylceramides using liquid chromatography-electrospray ion trap mass spectrometry

Mass Spectrometry Detects Sphingolipid Metabolites for Discovery of New Strategy for Cancer Therapy from the Aspect of Programmed Cell Death

Sphingolipids, a type of bioactive lipid, play crucial roles within cells, serving as integral components of membranes and exhibiting strong signaling properties that have potential therapeutic implications in anti-cancer treatments. However, due to the diverse group of lipids and intricate mechanisms, sphingolipids still face challenges in enhancing the efficacy of different therapy approaches. In recent decades, mass spectrometry has made significant advancements in uncovering sphingolipid biomarkers and elucidating their impact on cancer development, progression, and resistance. Primary sphingolipids, such as ceramide and sphingosine-1-phosphate, exhibit contrasting roles in regulating cancer cell death and survival. The evasion of cell death is a characteristic hallmark of cancer cells, leading to treatment failure and a poor prognosis. The escape initiates with long-established apoptosis and extends to other programmed cell death (PCD) forms when patients experience chemotherapy, radiotherapy, and/or immunotherapy. Gradually, supportive evidence has uncovered the fundamental molecular mechanisms underlying various forms of PCD leading to the development of innovative molecular, genetic, and pharmacological tools that specifically target sphingolipid signaling nodes. In this study, we provide a comprehensive overview of the sphingolipid biomarkers revealed through mass spectrometry in recent decades, as well as an in-depth analysis of the six main forms of PCD (apoptosis, autophagy, pyroptosis, necroptosis, ferroptosis, and cuproptosis) in aspects of tumorigenesis, metastasis, and tumor response to treatments. We review the corresponding small-molecule compounds associated with these processes and their potential implications in cancer therapy.

Biochemical and Microscopic Analyses for Sphingolipids and Its Related Molecules in Phagosomes

Glycosphingolipids (GSLs) form GSL-enriched microdomains, together with sphingomyelin (SM), cholesterol, glycosylphosphatidylinositol (GPI)-anchored proteins, and membrane-associated signaling molecules. GSL-enriched microdomains mediate a variety of physiological functions, including innate immune responses. Innate immune responses are initialized by the binding of host pattern recognition receptors (PRRs) to pathogen-associated molecular patterns (PAMPs) expressed in microorganisms. This binding triggers phagocytosis and leads to the formation of a phagosome-containing microorganism and the subsequent lysosomal fusion with a phagosome. To detect the molecular interaction between GSL-enriched microdomains, sphingolipids, and signaling molecules from the uptake of the microorganism until the phagosome-containing microorganism fuses with lysosomes, biochemical and microscopic approaches are indispensable. Here, we describe the detailed methods for isolating phagosomes and observing the molecular interaction using a superresolution microscope. Our methodology provides a strategy for exploring the molecular interaction between the host and pathogen and for developing new treatment approaches.

Identification of glycerophospholipids using self-built recognition software based on positive and negative ion high-resolution mass spectrometric fragmentation experiments

Glycerophospholipids (GPs) have a wide variety and complex structure, which makes their identification challenging. Our software affords a novel tool for the automated identification of non-target GPs in biological mixtures. Here, we explored the multi-stage fragmentation processes of GPs in positive and negative ion modes, and then constructed multi-stage fragment ion databases. This database includes 8214 simulated GP molecules from a random combination of fatty acids corresponding to 42,439 self-built predicted multi-stage fragment ions in positive ion mode and 31,487 self-built predicted multi-stage fragment ions in negative ion mode (MS ≤ 3). The automatic GP identification (AGPI) software can screen out GP candidates utilizing the MS¹ accurate mass. The isomers of fatty acid chains and the phosphoryl head group can be distinguished using the MS² and MS³ fragment spectra in positive-ion and negative-ion modes. All of the selected 45 GP standards were putatively identified using AGPI software; however, there were false positives because the software cannot distinguish positional isomers of fatty acids. Therefore, the AGPI software could be applied to identify GPs in samples, such as cancer cells; we successfully identified 41 GPs in cancer cells.

Multiplicity of Glycosphingolipid-Enriched Microdomain-Driven Immune Signaling

Glycosphingolipids (GSLs), together with cholesterol, sphingomyelin (SM), and glycosylphosphatidylinositol (GPI)-anchored and membrane-associated signal transduction molecules, form GSL-enriched microdomains. These specialized microdomains interact in a cis manner with various immune receptors, affecting immune receptor-mediated signaling. This, in turn, results in the regulation of a broad range of immunological functions, including phagocytosis, cytokine production, antigen presentation and apoptosis. In addition, GSLs alone can regulate immunological functions by acting as ligands for immune receptors, and exogenous GSLs can alter the organization of microdomains and microdomain-associated signaling. Many pathogens, including viruses, bacteria and fungi, enter host cells by binding to GSL-enriched microdomains. Intracellular pathogens survive inside phagocytes by manipulating intracellular microdomain-driven signaling and/or sphingolipid metabolism pathways. This review describes the mechanisms by which GSL-enriched microdomains regulate immune signaling.

Sphingolipids as Regulators of the Phagocytic Response to Fungal Infections

Fungal infections pose a significant risk for the increasing population of individuals who are immunocompromised. Phagocytes play an important role in immune defense against fungal pathogens, but the interactions between host and fungi are still not well understood. Sphingolipids have been shown to play an important role in many cell functions, including the function of phagocytes. In this review, we discuss major findings that relate to the importance of sphingolipids in macrophage and neutrophil function and the role of macrophages and neutrophils in the most common types of fungal infections, as well as studies that have linked these three concepts to show the importance of sphingolipid signaling in immune response to fungal infections.

Role of Ceramide from Glycosphingolipids and Its Metabolites in Immunological and Inflammatory Responses in Humans

Glycosphingolipids (GSLs) are composed of hydrophobic ceramide and hydrophilic sugar chains. GSLs cluster to form membrane microdomains (lipid rafts) on plasma membranes, along with several kinds of transducer molecules, including Src family kinases and small G proteins. However, GSL-mediated biological functions remain unclear. Lactosylceramide (LacCer, CDw17) is highly expressed on the plasma membranes of human phagocytes and mediates several immunological and inflammatory reactions, including phagocytosis, chemotaxis, and superoxide generation. LacCer forms membrane microdomains with the Src family tyrosine kinase Lyn and the Gαi subunit of heterotrimeric G proteins. The very long fatty acids C24:0 and C24:1 are the main ceramide components of LacCer in neutrophil plasma membranes and are directly connected with the fatty acids of Lyn and Gαi. These observations suggest that the very long fatty acid chains of ceramide are critical for GSL-mediated outside-in signaling. Sphingosine is another component of ceramide, with the hydrolysis of ceramide by ceramidase producing sphingosine and fatty acids. Sphingosine is phosphorylated by sphingosine kinase to sphingosine-1-phosphate, which is involved in a wide range of cellular functions, including growth, differentiation, survival, chemotaxis, angiogenesis, and embryogenesis, in various types of cells. This review describes the role of ceramide moiety of GSLs and its metabolites in immunological and inflammatory reactions in human.

Properties and functions of lactosylceramide from mouse neutrophils

Lactosylceramide (LacCer), which is essential for many cellular processes, is highly expressed on the plasma membranes of human neutrophils and mediates innate immune functions. Less is known, however, about the properties and biological functions of LacCer in mouse neutrophils. This study therefore analyzed the properties of mouse neutrophil LacCer. LacCer was observed on the surface of these cells, with flow cytometry indicating that mouse neutrophil LacCer could be detected by the anti-LacCer mAb T5A7, but not by the anti-LacCer antibodies Huly-m13 and MEM-74. The molecular species of LacCer were nearly identical in mouse and human neutrophils, including C24:0 and C24:1 fatty acid chain-containing species, although the LacCer content in plasma membranes was ∼ 20-fold lower in mouse than in human neutrophils. Surface plasmon resonance analysis revealed that T5A7 bound to a lipid monolayer composed of LacCer, DOPC, cholesterol and sphingomyelin (molar ratio 0.1 : 10 : 10 : 1), whereas Huly-m13 did not. T5A7 induced neutrophil migration, which was abolished by inhibitors of Src-family kinases, PI-3 kinases, and trimeric G (o/i) proteins. T5A7 also inhibited phagocytosis of non-opsonized zymosans by neutrophils. Taken together, these findings suggest that in mouse neutrophils, (i) LacCer is expressed as LacCer-enriched microdomains in cell surface plasma membranes, (ii) these microdomains are recognized by T5A7 but not by other known anti-LacCer antibodies and (iii) LacCer is involved in cell migration and phagocytosis.

Direct interaction, instrumental for signaling processes, between LacCer and Lyn in the lipid rafts of neutrophil-like cells

Lactosylceramide [LacCer; β-Gal-(1-4)-β-Glc-(1-1)-Cer] has been shown to contain very long fatty acids that specifically modulate neutrophil properties. The interactions between LacCer and proteins and their role in cell signaling processes were assessed by synthesizing two molecular species of azide-photoactivable tritium-labeled LacCer having acyl chains of different lengths. The lengths of the two acyl chains corresponded to those of a short/medium and very long fatty acid, comparable to the lengths of stearic and lignoceric acids, respectively. These derivatives, designated C18-[(3)H]LacCer-(N3) and C24-[(3)H]LacCer-(N3), were incorporated into the lipid rafts of plasma membranes of neutrophilic differentiated HL-60 (D-HL-60) cells. C24-[(3)H]LacCer-(N3), but not C18-[(3)H]LacCer-(N3), induced the phosphorylation of Lyn and promoted phagocytosis. Incorporation of C24-[(3)H]LacCer-(N3) into plasma membranes, followed by illumination, resulted in the formation of several tritium-labeled LacCer-protein complexes, including the LacCer-Lyn complex, into plasma membrane lipid rafts. Administration of C18-[(3)H]LacCer-(N3) to cells, however, did not result in the formation of the LacCer-Lyn complex. These results suggest that LacCer derivatives mimic the biological properties of natural LacCer species and can be utilized as tools to study LacCer-protein interactions, and confirm a specific direct interaction between LacCer species containing very long fatty acids, and Lyn protein, associated with the cytoplasmic layer via myristic/palmitic chains.

Organization and functions of glycolipid-enriched microdomains in phagocytes

Populations of glycolipids change markedly during leukocyte differentiation, suggesting that these molecules are involved in biological functions. About 70% of the glycosphingolipids in human neutrophils are lactosylceramide, a molecule also expressed on monocytes and dendritic cells, but not on lymphocytes. In contrast, phosphatidylglucoside is mainly expressed on neutrophils. STED microscopic analysis showed that phosphatidylglucoside and lactosylceramide form different domains on plasma membranes of neutrophils, with phosphatidylglucoside preferentially expressed along the neutrophil differentiation pathway. Phosphatidylglucoside was found to mediate the differentiation of HL-60 cells into the neutrophilic lineage, and to be involved in FAS-dependent neutrophil apoptosis. In contrast, lactosylceramide was only expressed on mature neutrophils. Complexes of lactosylceramide and the Src family kinase Lyn form membrane microdomains. LacCer-enriched membrane microdomains mediate neutrophil innate immune responses; e.g. chemotaxis, phagocytosis, and superoxide generation. C24 fatty acid chains of LacCer are indispensable for the formation of LacCer-Lyn complexes and for LacCer-dependent functions. Moreover, Lyn-coupled LacCer-enriched microdomains serve as signal transduction platforms for αMβ2 integrin-mediated phagocytosis. This review describes the organization and potential functions of glycolipids in phagocytes, as well as the roles of both phosphatidylglucoside and lactosylceramide in neutrophils. This article is part of a Special Issue entitled Linking transcription to physiology in lipidomics.

Membrane microdomains in immunity: glycosphingolipid-enriched domain-mediated innate immune responses

Over the last 30 years, many studies have indicated that glycosphingolipids (GSLs) expressed on the cell surface may act as binding sites for microorganisms. Based on their physicochemical characteristics, GSLs form membrane microdomains with cholesterol, sphingomyelin, glycosylphosphatidylinositol (GPI)-anchored proteins, and various signaling molecules, and GSL-enriched domains have been shown to be involved in these defense responses. Among the GSLs, lactosylceramide (LacCer, CDw17) can bind to various microorganisms. LacCer is expressed at high levels on the plasma membrane of human neutrophils, and forms membrane microdomains associated with the Src family tyrosine kinase Lyn. LacCer-enriched membrane microdomains mediate superoxide generation, chemotaxis, and non-opsonic phagocytosis. Therefore, LacCer-enriched membrane microdomains are thought to function as pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs) expressed on microorganisms. In contrast, several pathogens have developed infection mechanisms using membrane microdomains. In addition, some pathogens have the ability to avoid degradation by escaping from the vacuolar compartment or preventing phagosome maturation, utilizing membrane microdomains, such as LacCer-enriched domains, of host cells. The detailed molecular mechanisms of these membrane microdomain-associated host-pathogen interactions remain to be elucidated.

Analysis of mammalian sphingolipids by liquid chromatography tandem mass spectrometry (LC-MS/MS) and tissue imaging mass spectrometry (TIMS)

Sphingolipids are a highly diverse category of molecules that serve not only as components of biological structures but also as regulators of numerous cell functions. Because so many of the structural features of sphingolipids give rise to their biological activity, there is a need for comprehensive or "sphingolipidomic" methods for identification and quantitation of as many individual subspecies as possible. This review defines sphingolipids as a class, briefly discusses classical methods for their analysis, and focuses primarily on liquid chromatography tandem mass spectrometry (LC-MS/MS) and tissue imaging mass spectrometry (TIMS). Recently, a set of evolving and expanding methods have been developed and rigorously validated for the extraction, identification, separation, and quantitation of sphingolipids by LC-MS/MS. Quantitation of these biomolecules is made possible via the use of an internal standard cocktail. The compounds that can be readily analyzed are free long-chain (sphingoid) bases, sphingoid base 1-phosphates, and more complex species such as ceramides, ceramide 1-phosphates, sphingomyelins, mono- and di-hexosylceramides, sulfatides, and novel compounds such as the 1-deoxy- and 1-(deoxymethyl)-sphingoid bases and their N-acyl-derivatives. These methods can be altered slightly to separate and quantitate isomeric species such as glucosyl/galactosylceramide. Because these techniques require the extraction of sphingolipids from their native environment, any information regarding their localization in histological slices is lost. Therefore, this review also describes methods for TIMS. This technique has been shown to be a powerful tool to determine the localization of individual molecular species of sphingolipids directly from tissue slices.

An introduction to sphingolipid metabolism and analysis by new technologies

Sphingolipids (SP) are a complex class of molecules found in essentially all eukaryotes and some prokaryotes and viruses where they influence membrane structure, intracellular signaling, and interactions with the extracellular environment. Because of the combinatorial nature of their biosynthesis, there are thousands of SP subspecies varying in the lipid backbones and complex phospho- and glycoheadgroups. Therefore, comprehensive or “sphingolipidomic” analyses (structure-specific, quantitative analyses of all SP, or at least all members of a critical subset) are needed to know which and how much of these subspecies are present in a system as a step toward understanding their functions. Mass spectrometry and related novel techniques are able to quantify a small fraction, but nonetheless a substantial number, of SP and are beginning to provide information about their localization. This review summarizes the basic metabolism of SP and state-of-art mass spectrometric techniques that are producing insights into SP structure, metabolism, functions, and some of the dysfunctions of relevance to neuromedicine.

Sphingolipidomics: methods for the comprehensive analysis of sphingolipids

Sphingolipids comprise a highly diverse and complex class of molecules that serve as both structural components of cellular membranes and signaling molecules capable of eliciting apoptosis, differentiation, chemotaxis, and other responses in mammalian cells. Comprehensive or "sphingolipidomic" analyses (structure specific, quantitative analyses of all sphingolipids, or at least all members of a critical subset) are required in order to elucidate the role(s) of sphingolipids in a given biological context because so many of the sphingolipids in a biological system are inter-converted structurally and metabolically. Despite the experimental challenges posed by the diversity of sphingolipid-regulated cellular responses, the detection and quantitation of multiple sphingolipids in a single sample has been made possible by combining classical analytical separation techniques such as high-performance liquid chromatography (HPLC) with state-of-the-art tandem mass spectrometry (MS/MS) techniques. As part of the Lipid MAPS consortium an internal standard cocktail was developed that comprises the signaling metabolites (i.e. sphingoid bases, sphingoid base-1-phosphates, ceramides, and ceramide-1-phosphates) as well as more complex species such as mono- and di-hexosylceramides and sphingomyelin. Additionally, the number of species that can be analyzed is growing rapidly with the addition of fatty acyl Co-As, sulfatides, and other complex sphingolipids as more internal standards are becoming available. The resulting LC-MS/MS analyses are one of the most analytically rigorous technologies that can provide the necessary sensitivity, structural specificity, and quantitative precision with high-throughput for "sphingolipidomic" analyses in small sample quantities. This review summarizes historical and state-of-the-art analytical techniques used for the identification, structure determination, and quantitation of sphingolipids from free sphingoid bases through more complex sphingolipids such as sphingomyelins, lactosylceramides, and sulfatides including those intermediates currently considered sphingolipid "second messengers". Also discussed are some emerging techniques and other issues remaining to be resolved for the analysis of the full sphingolipidome.

Involvement of very long fatty acid-containing lactosylceramide in lactosylceramide-mediated superoxide generation and migration in neutrophils

The neutral glycosphingolipid lactosylceramide (LacCer) forms lipid rafts (membrane microdomains) coupled with the Src family kinase Lyn on the plasma membranes of human neutrophils; ligand binding to LacCer activates Lyn, resulting in neutrophil functions, such as superoxide generation and migration (Iwabuchi and Nagaoka, Lactosylceramide-enriched glycosphingolipid signaling domain mediates superoxide generation from human neutrophils, Blood 100, 1454-1464, 2002 and Sato et al. Induction of human neutrophil chemotaxis by Candida albicans-derived beta-1,6-long glycoside side-chain-branched beta glycan, J. Leukoc. Biol. 84, 204-211, 2006). Neutrophilic differentiated HL-60 cells (D-HL-60 cells) express almost the same amount of LacCer as neutrophils. However, D-HL-60 cells do not have Lyn-associated LacCer-enriched lipid rafts and lack LacCer-mediated superoxide-generating and migrating abilities. Here, we examined the roles of LacCer molecular species of different fatty acid compositions in these processes. Liquid chromatography-mass spectrometry analyses revealed that the very long fatty acid C24:0 and C24:1 chains were the main components of LacCer (31.6% on the total fatty acid content) in the detergent-resistant membrane fraction (DRM) from neutrophil plasma membranes. In contrast, plasma membrane DRM of D-HL-60 cells included over 70% C16:0-LacCer, but only 13.6% C24-LacCer species. D-HL-60 cells loaded with C24:0 or C24:1-LacCer acquired LacCer-mediated migrating and superoxide-generating abilities, and allowed Lyn coimmunoprecipitation by anti-LacCer antibody. Lyn knockdown by siRNA completely abolished the effect of C24:1-LacCer loading on LacCer-mediated migration of D-HL-60 cells. Immunoelectron microscopy revealed that LacCer clusters were closely associated with Lyn molecules in neutrophils and C24:1-LacCer-loaded D-HL-60 cells, but not in D-HL-60 cells or C16:0-LacCer-loaded cells. Taken together, these observations suggest that LacCer species with very long fatty acids are specifically necessary for Lyn-coupled LacCer-enriched lipid raft-mediated neutrophil superoxide generation and migration.

Structure-specific, quantitative methods for analysis of sphingolipids by liquid chromatography-tandem mass spectrometry: "inside-out" sphingolipidomics

Due to the large number of highly bioactive subspecies, elucidation of the roles of sphingolipids in cell structure, signaling, and function is beginning to require that one perform structure-specific and quantitative (i.e., "sphingolipidomic") analysis of all individual subspecies, or at least of those are relevant to the biologic system of interest. As part of the LIPID MAPS Consortium, methods have been developed and validated for the extraction, liquid chromatographic (LC) separation, and identification and quantitation by electrospray ionization (ESI), tandem mass spectrometry (MS/MS) using an internal standard cocktail that encompasses the signaling metabolites (e.g., ceramides, ceramide 1-phosphates, sphingoid bases, and sphingoid base 1-phosphates) as well as more complex species (sphingomyelins, mono- and di-hexosylceramides). The number of species that can be analyzed is growing rapidly with the addition of sulfatides and other complex sphingolipids as more internal standards become available. This review describes these methods as well as summarizes others from the published literature. Sphingolipids are an amazingly complex family of compounds that are found in all eukaryotes as well as some prokaryotes and viruses. The size of the sphingolipidome (i.e., all of the individual molecular species of sphingolipids) is not known, but must be immense considering mammals have over 400 headgroup variants (for a listing, see http://www.sphingomap.org), each of which is comprised of at least a few-and, in some cases, dozens-of lipid backbones. No methods have yet been developed that can encompass so many different compounds in a structurally specific and quantitative manner. Nonetheless, it is possible to analyze useful subsets of the sphingolipidome, such as the backbone sphingolipids involved in signaling (sphingoid bases, sphingoid base 1-phosphates, ceramides, and ceramide 1-phosphates) and metabolites at important branchpoints, such as the partitioning of ceramide into sphingomyelins, glucosylceramides, galactosylceramides, and ceramide 1-phosphate versus turnover to the backbone sphingoid base. This review describes methodology that has been developed as part of the LIPID MAPS Consortium (www.lipidmaps.org) as well as other methods that can be used for sphingolipidomic analysis to the extent that such is currently feasible. The focus of this review is primarily mammalian sphingolipids; hence, if readers are interested in methods to study other organisms, they should consult the excellent review by Stephen Levery in another volume of Methods in Enzymology (Levery, 2005), which covers additional species found in plants, fungi, and other organisms. It should be noted from the start that although many analytical challenges remain in the development of methods to analyze the full "sphingolipidome," the major impediment to progress is the limited availability of reliable internal standards for most of the compounds of interest. Because it is an intrinsic feature of mass spectrometry that ion yields tend to vary considerably among different compounds, sources, methods, and instruments, an analysis that purports to be quantitative will not be conclusive unless enough internal standards have been added to correct for these variables. Ideally, there should be some way of standardizing every compound in the unknown mixture; however, that is difficult, if not impossible, to do because the compounds are not available, and the inclusion of so many internal standards generates a spectrum that may be too complex to interpret. Therefore, a few representative internal standards are usually added, and any known differences in the ion yields of the analytes of interest versus the spiked standard are factored into the calculations. Identification of appropriate internal standards has been a major focus of the LIPID MAPS Consortium, and the methods described in this review are based on the development of a certified (i.e., compositionally and quantitatively defined by the supplier) internal standard cocktail that is now commercially available (Avanti Polar Lipids, Alabaster, AL). For practical and philosophical reasons, an internal standard cocktail was chosen over the process of an investigator adding individual standards for only the analytes of interest. On the practical level, addition of a single cocktail minimizes pipetting errors as well as keeping track of whether each internal standard is still usable (e.g., has it degraded while in solution?). Philosophically, the internal standard cocktail was chosen because an underlying premise of systems analysis asserts that, due to the high relevancy of unexpected interrelationships involving more distant components, one can only understand a biological system when factors outside the primary focus of the experiment have also been examined. Indeed, the first payoffs of "omics" and systems approaches involve the discoveries of interesting compounds in unexpected places when a "sphingolipidomic" analytical method was being used as routine practice instead of a simpler method that would have only measured the compound initially thought to be important (Zheng et al., 2006). Thus, routine addition of a broad internal standard cocktail at the outset of any analysis maximizes the opportunity for such discoveries, both at the time the original measurements are made and when one decides to return to the samples later, which can fortunately be done for many sphingolipids because they remain relatively stable in storage.

Convenient structural analysis of glycosphingolipids using MALDI-QIT-TOF mass spectrometry with increased laser power and cooling gas flow

Matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry (MALDI-QIT-TOF MS) was applied to the structural characterization of neutral glycosphingolipids. Lithium adduct ions of glycosphingolipids were analyzed using MALDI-QIT-TOF MS under strong conditions of increased laser power and cooling gas flow. The relative intensities of fragment ions were increased under the strong conditions, and the resulting spectra revealed the presence of oligosaccharide ions fragmented from the glycosphingolipids. Consequently, the oligosaccharide sequences of the glycosphingolipids were readily obtained. To obtain more detailed structural information, MS/MS (MS2) and MS/MS/MS (MS3) analyses were performed with selection of the lactosylceramide and ceramide ions, respectively. The resulting data were sufficient to determine the structures of both the oligosaccharide and the ceramide moiety of each glycosphingolipid. The fragmentation patterns of MS2 and MS3 for Forssman glycolipid under the strong conditions were comparable to those of MS3 and MS4 obtained under standard conditions, respectively. Thus, MALDI-QIT-TOF MS with increased laser power and cooling gas flow is a convenient method for glycosphingolipid analysis.