Glycosphingolipids--nature, function, and pharmacological modulation

Bifunctional Glycosphingolipid (GSL) Probes to Investigate GSL-Interacting Proteins in Cell Membranes

Glycosphingolipids (GSLs) are abundant glycolipids on cells and essential for cell recognition, adhesion, signal transduction, etc. However, their lipid anchors are not long enough to cross the membrane bilayer. To transduce transmembrane signals, GSLs must interact with other membrane components, whereas such interactions are difficult to investigate. To overcome this difficulty, bifunctional derivatives of II3-β-N-acetyl-D-galactosamine-GA2 (GalNAc-GA2) and β-N-acetyl-D-glucosamine-ceramide (GlcNAc-Cer) were synthesized as probes to explore GSL-interacting membrane proteins in live cells. Both probes contain photoreactive diazirine in the lipid moiety, which can crosslink with proximal membrane proteins upon photoactivation, and clickable alkyne in the glycan to facilitate affinity tag addition for crosslinked protein pull-down and characterization. The synthesis is highlighted by the efficient assembly of simple glycolipid precursors followed by on-site lipid remodeling. These probes were employed to profile GSL-interacting membrane proteins in HEK293 cells. The GalNAc-GA2 probe revealed 312 distinct proteins, with GlcNAc-Cer probe-crosslinked proteins as controls, suggesting the potential influence of the glycan on GSL functions. Many of the proteins identified with the GalNAc-GA2 probe are associated with GSLs, and some have been validated as being specific for this probe. The versatile probe design and experimental protocols are anticipated to be widely applicable to GSL research.

Stereoconvergent and Chemoenzymatic Synthesis of Tumor-Associated Glycolipid Disialosyl Globopentaosylceramide for Probing the Binding Affinity of Siglec-7

Disialosyl globopentaosylceramide (DSGb5) is a tumor-associated complex glycosphingolipid. However, the accessibility of structurally well-defined DSGb5 for precise biological functional studies remains challenging. Herein, we describe the first total synthesis of DSGb5 glycolipid by an efficient chemoenzymatic approach. A Gb5 pentasaccharide-sphingosine was chemically synthesized by a convergent and stereocontrolled [2 + 3] method using an oxazoline disaccharide donor to exclusively form β-anomeric linkage. After investigating the substrate specificity of different sialyltransferases, regio- and stereoselective installment of two sialic acids was achieved by two sequential enzyme-catalyzed reactions using α2,3-sialyltransferase Cst-I and α2,6-sialyltransferase ST6GalNAc5. A unique aspect of the approach is that methyl-β-cyclodextrin-assisted enzymatic α2,6-sialylation of glycolipid substrate enables installment of the challenging internal α2,6-linked sialoside to synthesize DSGb5 glycosphingolipid. Surface plasmon resonance studies indicate that DSGb5 glycolipid exhibits better binding affinity for Siglec-7 than the oligosaccharide moiety of DSGb5. The binding results suggest that the ceramide moiety of DSGb5 facilitates its binding by presenting multivalent interactions of glycan epitope for the recognition of Siglec-7.

Relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder

BACKGROUND

Alcohol use disorder is a chronic recurrent encephalopathy, and its pathogenesis has not been fully understood. Among possible explanations, neuroinflammation caused by the disorders of brain central immune signaling has been identified as one possible mechanism of alcohol use disorder. As the basic components of cells and important bioactive molecules, sphingolipids are essential in regulating many cellular activities. Recent studies have shown that sphingolipids-mediated neuroinflammation may be involved in the development of alcohol use disorder.

METHODS

PubMed databases were searched for literature on sphingolipids and alcohol use disorder (alcohol abuse, alcohol addiction, alcohol dependence, and alcohol misuse) including evidence of the relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder (formation, withdrawal, treatment).

RESULTS

Disorders of sphingolipid metabolism, including the different types of sphingolipids and regulatory enzyme activity, have been found in patients with alcohol use disorder as well as animal models, which in turn cause neuro-inflammation in the central nervous system. Thus, these disorders may also be an important mechanism in the development of alcohol use disorder in patients. In addition, different sphingolipids may have different or even reverse effects on alcohol use disorder.

CONCLUSIONS

The sphingolipids-mediated neuroinflammation plays an important role in the development of alcohol use disorder. This review proposes a potential approach to prevent and treat alcohol use disorders by manipulating sphingolipid metabolism.

The expanding boundaries of sphingolipid lysosomal storage diseases; insights from Niemann-Pick disease type C

Lysosomal storage diseases are inborn errors of metabolism that arise due to loss of function mutations in genes encoding lysosomal enzymes, protein co-factors or lysosomal membrane proteins. As a consequence of the genetic defect, lysosomal function is impaired and substrates build up in the lysosome leading to 'storage'. A sub group of these disorders are the sphingolipidoses in which sphingolipids accumulate in the lysosome. In this review, I will discuss how the study of these rare lysosomal disorders reveals unanticipated links to other rare and common human diseases using Niemann-Pick disease type C as an example.

Glycosidase-targeting small molecules for biological and therapeutic applications

Glycosidases are ubiquitous enzymes that catalyze the hydrolysis of glycosidic linkages in oligosaccharides and glycoconjugates. These enzymes play a vital role in a wide variety of biological events, such as digestion of nutritional carbohydrates, lysosomal catabolism of glycoconjugates, and posttranslational modifications of glycoproteins. Abnormal glycosidase activities are associated with a variety of diseases, particularly cancer and lysosomal storage disorders. Owing to the physiological and pathological significance of glycosidases, the development of small molecules that target these enzymes is an active area in glycoscience and medicinal chemistry. Research efforts carried out thus far have led to the discovery of numerous glycosidase-targeting small molecules that have been utilized to elucidate biological processes as well as to develop effective chemotherapeutic agents. In this review, we describe the results of research studies reported since 2018, giving particular emphasis to the use of fluorescent probes for detection and imaging of glycosidases, activity-based probes for covalent labelling of these enzymes, glycosidase inhibitors, and glycosidase-activatable prodrugs.

Pathophysiological roles and applications of glycosphingolipids in the diagnosis and treatment of cancer diseases

Glycosphingolipids (GSLs) are major amphiphilic glycolipids present on the surface of living cell membranes. They have important biological functions, including maintaining plasma membrane stability, regulating signal transduction, and mediating cell recognition and adhesion. Specific GSLs and related enzymes are abnormally expressed in many cancer diseases and affect the malignant characteristics of tumors. The regulatory roles of GSLs in signaling pathways suggest that they are involved in tumor pathogenesis. GSLs have therefore been widely studied as diagnostic markers of cancer diseases and important targets of immunotherapy. This review describes the tumor-related biological functions of GSLs and systematically introduces recent progress in using diverse GSLs and related enzymes to diagnose and treat tumor diseases. Development of drugs and biomarkers for personalized cancer therapy based on GSL structure is also discussed. These advances, combined with recent progress in the preparation of GSLs derivatives through synthetic biology technologies, suggest a strong future for the use of customized GSL libraries in treating human diseases.

Metabolism of sphingadiene and characterization of the sphingadiene-producing enzyme FADS3

Of the long-chain bases (LCBs) that comprise the ceramides (CERs) present in mammals, only 4,14-sphingadiene (sphingadiene; SPD) has a cis double bond (at C14). Because of this unique structure, the metabolism of SPD may differ from that of other LCBs, but whether this is the case remains unclear. FADS3 is responsible for introducing the cis double bond in SPD. However, the substrate specificity of FADS3 and cofactors involved in the FADS3-catalyzed reaction are also unknown. In the present study, a cell-based assay using a ceramide synthase inhibitor and an in vitro experiment showed that FADS3 is active toward sphingosine (SPH)-containing CERs (SPH-CERs) but not toward free SPH. FADS3 exhibits specificity with respect to the chain length of the SPH moiety of SPH-CERs (active toward C16-20), but not that of the fatty acid moiety. Furthermore, FADS3 is active toward straight-chain and isobranched-chain SPH-containing CERs but not toward anteiso-branched forms. In addition to SPH-CERs, FADS3 also shows activity toward dihydrosphingosine-containing CERs, but this activity is approximately half of that toward SPH-CERs. It uses either NADH or NADPH as an electron donor, and the electron transfer is facilitated by cytochrome b₅. The metabolic flow of SPD to sphingomyelin is predominant over that to glycosphingolipids. In the metabolic pathway from SPD to fatty acids, the chain length of the SPD is reduced by two carbons and the trans double bond at C4 is saturated. This study thus elucidates the enzymatic properties of FADS3 and the metabolism of SPD.

CRISPR/Cas9-mediated A4GALT suppression rescues Fabry disease phenotypes in a kidney organoid model

The objective of this study was to investigate whether CRISPR/Cas9-mediated suppression of A4GALT could rescue phenotype of Fabry disease nephropathy (FDN) using human induced pluripotent stem cells (hiPSCs) derived kidney organoid system. We generated FDN patient-derived hiPSC (CMC-Fb-002) and FD-specific hiPSCs (GLA-KO) by knock-out (KO) of GLA in wild-type (WT) hiPSCs using CRISPR/Cas9. We then performed A4GALT KO in both CMC-Fb-002 and GLA-KO to make Fb-002-A4GALT-KO and GLA/A4GALT-KO, respectively. Using these hiPSCs, we generated kidney organoids and compared alpha-galactosidase-A enzyme (α-GalA) activity, globotriaosylceramide (Gb-3) deposition, and zebra body formation under electron microscopy (EM). We also compared mRNA expression levels using RNA-seq and qPCR. Generated hiPSCs showed typical pluripotency markers without chromosomal disruption. Expression levels of GLA in CMC-Fb-002 and GLA-KO and expression levels of A4GALT in Fb-002-A4GALT-KO and GLA/A4GALT-KO were successfully decreased compared to those in WT-hiPSCs, respectively. Generated kidney organoids using these hiPSCs expressed typical nephron markers. In CMC-Fb-002 and GLA-KO organoids, α-GalA activity was significantly decreased along with increased deposition of Gb-3 in comparison with WT organoids. Intralysosomal inclusion body was also detected under EM. However, these disease phenotypes were rescued by KO of A4GALT in both GLA/A4GALT-KO and Fb-002-A4GALT-KO kidney organoids. RNA-seq showed increased expression levels of genes related to FDN progression in both GLA-mutant organoids compared to those in WT. Such increases were rescued in GLA/A4GALT-KO or Fb-002-A4GALT-KO organoids. CRISPR/Cas9 mediated suppression of A4GALT could rescue FDN phenotype. Hence, it can be proposed as a therapeutic approach to treat FDN.

Carbon-based glyco-nanoplatforms: towards the next generation of glycan-based multivalent probes

Cell surface carbohydrates mediate a wide range of carbohydrate-protein interactions key to healthy and disease mechanisms. Many of such interactions are multivalent in nature and in order to study these processes at a molecular level, many glycan-presenting platforms have been developed over the years. Among those, carbon nanoforms such as graphene and their derivatives, carbon nanotubes, carbon dots and fullerenes, have become very attractive as biocompatible platforms that can mimic the multivalent presentation of biologically relevant glycosides. The most recent examples of carbon-based nanoplatforms and their applications developed over the last few years to study carbohydrate-mediate interactions in the context of cancer, bacterial and viral infections, among others, are highlighted in this review.

Synthesis and Glycosidation of Anomeric Halides: Evolution from Early Studies to Modern Methods of the 21st Century

Advances in synthetic carbohydrate chemistry have dramatically improved access to common glycans. However, many novel methods still fail to adequately address challenges associated with chemical glycosylation and glycan synthesis. Since a challenge of glycosylation has remained, scientists have been frequently returning to the traditional glycosyl donors. This review is dedicated to glycosyl halides that have played crucial roles in shaping the field of glycosciences and continue to pave the way toward our understanding of chemical glycosylation.

In situ glucosylceramide synthesis and its pharmacological inhibition analysed in cells by 13 C5 -sphingosine precursor feeding and mass spectrometry

Glycosphingolipids fulfil diverse functions in cells. Abnormalities in their metabolism are associated with specific pathologies and, consequently, the pharmacological modulation of glycosphingolipids is considered a therapeutic avenue. The accurate measurement of in situ metabolism of glycosphingolipids and the modulatory impact of drugs is warranted. Employing synthesized sphingosine and sphinganine containing ¹³ C atoms, we developed a method to monitor the de novo synthesis of glucosylceramide, the precursor of complex glycosphingolipids, by the enzyme glucosylceramide synthase (GCS). We show that feeding cells with isotope-labelled precursor combined with LC-MS/MS analysis allows accurate determination of the IC₅₀ values of therapeutically considered inhibitors (iminosugars and ceramide mimics) of GCS in cultured cells. Acquired data were comparable to those obtained with an earlier method using artificial fluorescently labelled ceramide to feed cells.

Structural characterization and analysis of different epimers of neutral glycosphingolipid LcGg4 by ion mobility spectrometry-mass spectrometry

LcGg4, a neutral glycosphingolipid (GSL) and cancer antigen, its epimers GalNAc-LcGg4 and GlcNAc-LcGg4, and three lipid forms of GalNAc-LcGg4 were studied by mass spectrometry (MS). It was found that different forms of GalNAc-LcGg4 carrying homologous (d16:1/18:0) and (d18:1/18:0) lipids were easily separated and identified using liquid chromatography (LC)-MS. In addition, like gangliosides, homologous lipid forms of GalNAc-LcGg4 showed the same fragmentation pattern, except for a uniform shift of their glycolipid product ions by a certain m/z number determined by the varied lipid structure. It was also disclosed that LcGg4 and its epimers GalNAc-LcGg4 and GlcNAc-LcGg4, which are different only in the C4-configuration of their non-reducing end sugar residues, gave the same MS/MS product ions in similar relative intensities, as well as the same LC retention time, suggesting the challenge to differentiate epimeric GSLs by LC-MS. However, ion mobility spectrometry (IMS)-MS was able to efficiently separate and distinguish these epimers. This study has demonstrated the promise of IMS-MS for isomeric GSL characterization and the IMS-MS and LC-MS/MS combination for natural GSL analysis.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Chemoenzymatic Synthesis of Globo-series Glycosphingolipids and Evaluation of Their Immunosuppressive Activities

Glycosphingolipids (GSLs) play essential roles in many important biological processes, making them attractive synthetic targets. In this paper, a viable chemoenzymatic method is described for the synthesis of globo-series GSLs, namely, Gb4, Gb5, SSEA-4, and Globo H. The strategy uses a chemically synthesized lactoside acceptor equipped with a partial ceramide structure that is uniquely extended by glycosyltransferases in a highly efficient one-pot multiple engyme (OPME) procedure. A direct and quantitative conversion of Gb4 sphingosine to Globo H sphingosine is achieved by performing two-sequential OPME glycosylations. A reduction and N -acylation protocol allows facile incorporation of various fatty acids into the lipid portions of the GSLs. The chemically well-defined lipid-modified Globo H-GSLs displayed some differences in their immunosuprressive activities, which may benefit the structural modifications of Globo h ceramides in finding new types of immunosuppressive agents. The strategy outlined in this work should be applicable to rapid access to other complex GSLs.

Application of MS-Based Metabolomic Approaches in Analysis of Starfish and Sea Cucumber Bioactive Compounds

Today, marine natural products are considered one of the main sources of compounds for drug development. Starfish and sea cucumbers are potential sources of natural products of pharmaceutical interest. Among their metabolites, polar steroids, triterpene glycosides, and polar lipids have attracted a great deal of attention; however, studying these compounds by conventional methods is challenging. The application of modern MS-based approaches can help to obtain valuable information about such compounds. This review provides an up-to-date overview of MS-based applications for starfish and sea cucumber bioactive compounds analysis. While describing most characteristic features of MS-based approaches in the context of starfish and sea cucumber metabolites, including sample preparation and MS analysis steps, the present paper mainly focuses on the application of MS-based metabolic profiling of polar steroid compounds, triterpene glycosides, and lipids. The application of MS in metabolomics studies is also outlined.

Dynamic Tuning in Synthetic Glycosidase for Selective Hydrolysis of Alkyl and Aryl Glycosides

Enzymes use sophisticated conformational control to optimize the dynamics of their protein framework for efficient catalysis. Although it is difficult to employ a similar strategy to improve catalysis in a synthetic enzyme, we here report that modulation of the dynamics of the substrate in the active site is readily achievable in a complex between a molecularly imprinted nanoparticle and its acid cofactor, through tuning of the size and shape of the imprinted site. As the alkyl glucoside substrate is bound with increasing strength and held in a more tightly fitted pocket, the acid-catalyzed glycan hydrolysis becomes more difficult. A larger, wider active site, although less able to bind the substrate, affords a higher catalytic activity, likely due to easier alignment of the substrate and the acid cofactor for a general acid catalysis. The substrate selectivity is controlled by both the tightness of the aglycon-binding site and the orientation of the glycan-binding boroxole group.

Analysis and Comparison of Mouse and Human Brain Gangliosides via Two-Stage Matching of MS/MS Spectra

Glycosphingolipids (GSLs), including gangliosides, are essential components of the cell membrane. Because of their vital biological functions, a facile method for the analysis and comparison of GSLs in biological issues is desired. To this end, a new method for GSL analysis was developed based on two-stage matching of the carbohydrate and glycolipid product ions of experimental and reference MS/MS spectra of GSLs. The applicability of this method to the analysis of gangliosides in biological tissues was verified using human plasma and mouse brains spiked with standards. The method was then used to characterize endogenous gangliosides in mouse and human brains. It was shown that each endogenous ganglioside species had varied lipid forms and that mouse and human brains had different compositions of ganglioside species and lipid forms. Moreover, a 36-carbon ceramide is found to represent the major lipid form for mouse brain gangliosides, while the major lipid form for most human brain gangliosides is a 38-carbon ceramide. This study has verified that the two-stage MS/MS spectral matching method could be used to study gangliosides or GSLs and their lipid forms in complex biological samples, thereby having a broad application.

Probing the effects of sweet cherry (Prunus avium L.) extract on 2D and 3D human skin models

BACKGROUND

Natural products are not only positioned in the heart of traditional medicine but also in modern medicine as many current drugs are coming from natural sources. Apart from the field of medicine and therapeutics, natural products are broadly used in other industrial fields such as nutrition, skincare products and nanotechnology.

METHODS AND RESULTS

The aim of this study was to assess the effects of sweet cherry (Prunus avium L.) fruit extract from the Greek native cultivar 'Vasiliadi', on the human 2D and 3D in vitro models in order to investigate its potential impact on skin. We focused on 2D culture of primary normal human epidermal keratinocytes (NHEK) that were treated with sweet cherry fruit extract. In the first place, we targeted fruit extract potential cytotoxicity by determining ATP intracellular levels. Furthermore, we assessed its potential skin irritability by using 3D skin model. To better understand the bioactivity of sweet cherry fruit. extract, we used qPCR to study the expression of various genes that are implicated in the skin functions. Our experiments showed that sweet cherry fruit extract is non-toxic in 2D keratinocytes culture as well as non-irritant in 3D skin model. Our results revealed that the extract mediated important pathways for the optimum epidermis function such as cell proliferation, immune and inflammatory response.

CONCLUSION

The sweet cherry fruit extracts possesses significant activity in epidermis function without any potential of cytotoxicity or skin irritability, which makes it a rather promising active agent for skincare.

The Structural Diversity of Natural Glycosphingolipids (GSLs)

Glycosphingolipids (GSLs) are a subclass of glycolipids made of a glycan and a ceramide that, in turn, is composed of a sphingoid base moiety and a fatty acyl group. GSLs represent the vast majority of glycolipids in eukaryotes, and as an essential component of the cell membrane, they play an important role in many biological and pathological processes. Therefore, they are useful targets for the development of novel diagnostic and therapeutic methods for human diseases. Since sphingosine was first described by J. L. Thudichum in 1884, several hundred GSL species, not including their diverse lipid forms that can further amplify the number of individual GSLs by many folds, have been isolated from natural sources and structurally characterized. This review tries to provide a comprehensive survey of the major GSL species, especially those with distinct glycan structures and modification patterns, and the ceramides with unique modifications of the lipid chains, that have been discovered to date. In particular, this review is focused on GSLs from eukaryotic species. This review has listed 251 GSL glycans with different linkages, 127 glycans with unique modifications, 46 sphingoids, and 43 fatty acyl groups. It should be helpful for scientists who are interested in GSLs, from isolation and structural analyses to chemical and enzymatic syntheses, as well as their biological studies and applications.

Total synthesis of ceramides and β-O-glucosylceramides via intramolecular fatty acyl group migration

Fatty acyl group utilized as both protection and migratory group for the synthesis of ceramides and glucosylceramides.

Sphingolipids in foodstuff: Compositions, distribution, digestion, metabolism and health effects - A comprehensive review

Sphingolipids (SLs) are common in all eukaryotes, prokaryotes, and viruses, and played a vital role in human health. They are involved in physiological processes, including intracellular transport, cell division, and signal transduction. However, there are limited reviews on dietary effects on endogenous SLs metabolism and further on human health. Various dietary conditions, including the SLs-enriched diet, high-fat diet, and vitamins, can change the level of endogenous SLs metabolites and even affect human health. This review systematically summarizes the main known SLs in foods concerning their variety and contents, as well as their isolation and identification approaches. Moreover, the present review discusses the role of dietary (particularly SLs-enriched diet, high-fat diet, and vitamins) in endogenous SLs metabolism, highlighting how exogenous SLs are digested and absorbed. The role of SLs family in the pathogenesis of diseases, including cancers, neurological disorders, infectious and inflammatory diseases, and cardiovascular diseases, and in recently coronavirus disease-19 outbreak was also discussed. In the post-epidemic era, we believe that the concern for health and the need for plant-based products will increase. Therefore, a need for research on the absorption and metabolism pathway of SLs (especially plant-derived SLs) and their bioavailability is necessary. Moreover, the effects of storage treatment and processing on the content and composition of SLs in food are worth exploring. Further studies should also be conducted on the dose-response of SLs on human health to support the development of SLs supplements. More importantly, new approaches, such as, making SLs based hydrogels can effectively achieve sustained release and targeted therapies.

Plasma membrane glycosphingolipid signaling: a turning point

Plasma membrane interaction is highly recognized as an essential step to start the intracellular events in response to extracellular stimuli. The ways in which these interactions take place are less clear and detailed. Over the last decade my research has focused on developing the understanding of the glycosphingolipids-protein interaction that occurs at cell surface. By using chemical synthesis and biochemical approaches we have characterized some fundamental interactions that are key events both in the immune response and in the maintenance of neuronal homeostasis. In particular, for the first time it has been demonstrated that a glycolipid, present on the outer side of the membrane, the long-chain lactosylceramide, is able to directly modulate a cytosolic protein. But the real conceptual change was the demonstration that the GM1 oligosaccharide chain is able, alone, to replicate numerous functions of GM1 ganglioside and to directly interact with plasma membrane receptors by activating specific cellular signaling. In this conceptual shift, the development and application of multidisciplinary techniques in the field of biochemistry, from chemical synthesis to bioinformatic analysis, as well as discussions with several national and international colleagues have played a key role.

Who moves the sphinx? An overview of intracellular sphingolipid transport

Lipid bilayers function as boundaries that enclose their content from the surrounding media, and the composition of different membrane types is accurately and dynamically tailored so that they can perform their function. To achieve this balance, lipid biosynthetic machinery and lipid trafficking events are intertwined into an elegant network. In this review, we focus on the intracellular movement of sphingolipids mediated by sphingolipid transfer proteins. Additionally, we will focus on the best characterized and understood mammalian sphingolipid transfer proteins and provide an overview of how they are hypothesized to function. Some are already well understood, while others remain enigmatic. A few are actual lipid transfer proteins, moving lipids from membrane to membrane, while others may have more of a sensor role, possibly reacting to changes in the concentrations of their ligands. Considering the substrates available for cytosolic sphingolipid transfer proteins, one open question that is discussed is whether galactosylceramide is a target. Another question is the exact mechanics by which sphingolipid transfer proteins are targeted to different organelles, such as how four phosphate adapter protein-2, FAPP2 is targeted to the endoplasmic reticulum. The aim of this review is to discuss what is known within the field today and to provide a basic understanding of how these proteins may work.

Recent Development in the Design of Neoglycoliposomes Bearing Arborescent Architectures

This brief review highlights systematic progress in the design of synthetic glycolipid (neoglycolipids) analogs evolving from the conventional architectures of natural glycosphingolipids and gangliosides. Given that naturally occurring glycolipids are composed of only one hydrophilic sugar head-group and two hydrophobic lipid tails embedded in the lipid bilayers of the cell membranes, they usually require extraneous lipids (phosphatidylcholine, cholesterol) to confer their stability. In order to obviate the necessity for these additional stabilizing ingredients, recent investigations have merged dendrimer chemistry with that of neoglycolipid syntheses. This singular approach has provided novel glycoarchitectures allowing reconsidering the necessity for the traditional one to two hydrophilic/hydrophobic ratio. An emphasis has been provided in the recent design of modular arborescent neoglycolipid syntheses coined glycodendrimersomes.

Recent advances in multivalent carbon nanoform-based glycoconjugates

Multivalent carbohydrate-mediated interactions are fundamental to many biological processes, including disease mechanisms. To study these significant glycan-mediated interactions at a molecular level, carbon nanoforms such as fullerenes, carbon nanotubes, or graphene and their derivatives have been identified as promising biocompatible scaffolds that can mimic the multivalent presentation of biologically relevant glycans. In this minireview, we will summarize the most relevant examples of the last few years in the context of their applications.

Enzymatic Synthesis of Glycosphingolipids: A Review

Glycosphingolipids (GSLs) are the major vertebrate glycolipids, which contain two distinctive moieties, a glycan and a ceramide, stitched together by a β-glycosidic linkage. The hydrophobic lipid chains of ceramide can insert into the cell membrane to form ‘lipid rafts’ and anchor the hydrophilic glycan onto the cell surface to generate microdomains and function as signaling molecules. GSLs mediate signal transduction, cell interactions, and many other biological activities, and are also related to many diseases. To meet the need of biological studies, chemists have developed various synthetic methodologies to access GSLs. Among them, the application of enzymes to GSL synthesis has witnessed significant advancements in the past decades. This short review briefly summarizes the history and progress of enzymatic GSL synthesis.

1 Introduction

1.1 The Glycosphingolipid Structure

1.2 GSL Biosynthesis

1.3 Functions and Biological Significance

1.4 Overview of GSL Synthesis

1.5 Scope of the Review

2 Glycotransferases for GSL Synthesis

3 Glycosynthases for GSL Synthesis

4 Enzymatic Synthesis of Ceramide

5 Conclusion

Characterization of Glycosphingolipids and Their Diverse Lipid Forms through Two-Stage Matching of LC-MS/MS Spectra

Glycosphingolipids (GSLs) play a key role in various biological and pathological events. Thus, determination of the complete GSL compositions in human tissues is essential for comparative and functional studies of GSLs. In this work, a new strategy was developed for GSL characterization and glycolipidomics analysis based on two-stage matching of experimental and reference MS/MS spectra. In the first stage, carbohydrate fragments, which contain only glycans and thus are conserved within a GSL species, are directly matched to yield a species identification. In the second stage, glycolipid fragments from the matched GSL species, which contain both the lipid and glycans and thus shift due to lipid structural changes, are treated according to lipid rule-based matching to characterize the lipid compositions. This new strategy uses the whole spectrum for GSL characterization. Furthermore, simple databases containing only a single lipid form per GSL species can be utilized to identify multiple GSL lipid forms. It is expected that this method will help accelerate glycolipidomics analysis and disclose new and diverse lipid forms of GSLs.

Fabry Disease: Molecular Basis, Pathophysiology, Diagnostics and Potential Therapeutic Directions

Fabry disease (FD) is a lysosomal storage disorder (LSD) characterized by the deficiency of α-galactosidase A (α-GalA) and the consequent accumulation of toxic metabolites such as globotriaosylceramide (Gb3) and globotriaosylsphingosine (lysoGb3). Early diagnosis and appropriate timely treatment of FD patients are crucial to prevent tissue damage and organ failure which no treatment can reverse. LSDs might profit from four main therapeutic strategies, but hitherto there is no cure. Among the therapeutic possibilities are intravenous administered enzyme replacement therapy (ERT), oral pharmacological chaperone therapy (PCT) or enzyme stabilizers, substrate reduction therapy (SRT) and the more recent gene/RNA therapy. Unfortunately, FD patients can only benefit from ERT and, since 2016, PCT, both always combined with supportive adjunctive and preventive therapies to clinically manage FD-related chronic renal, cardiac and neurological complications. Gene therapy for FD is currently studied and further strategies such as substrate reduction therapy (SRT) and novel PCTs are under investigation. In this review, we discuss the molecular basis of FD, the pathophysiology and diagnostic procedures, together with the current treatments and potential therapeutic avenues that FD patients could benefit from in the future.

ORMDL2 Deficiency Potentiates the ORMDL3-Dependent Changes in Mast Cell Signaling

The systemic anaphylactic reaction is a life-threatening allergic response initiated by activated mast cells. Sphingolipids are an essential player in the development and attenuation of this response. De novo synthesis of sphingolipids in mammalian cells is inhibited by the family of three ORMDL proteins (ORMDL1, 2, and 3). However, the cell and tissue-specific functions of ORMDL proteins in mast cell signaling are poorly understood. This study aimed to determine cross-talk of ORMDL2 and ORMDL3 proteins in IgE-mediated responses. To this end, we prepared mice with whole-body knockout (KO) of Ormdl2 and/or Ormdl3 genes and studied their role in mast cell-dependent activation events in vitro and in vivo. We found that the absence of ORMDL3 in bone marrow-derived mast cells (BMMCs) increased the levels of cellular sphingolipids. Such an increase was further raised by simultaneous ORMDL2 deficiency, which alone had no effect on sphingolipid levels. Cells with double ORMDL2 and ORMDL3 KO exhibited increased intracellular levels of sphingosine-1-phosphate (S1P). Furthermore, we found that concurrent ORMDL2 and ORMDL3 deficiency increased IκB-α phosphorylation, degranulation, and production of IL-4, IL-6, and TNF-α cytokines in antigen-activated mast cells. Interestingly, the chemotaxis towards antigen was increased in all mutant cell types analyzed. Experiments in vivo showed that passive cutaneous anaphylaxis (PCA), which is initiated by mast cell activation, was increased only in ORMDL2,3 double KO mice, supporting our in vitro observations with mast cells. On the other hand, ORMDL3 KO and ORMDL2,3 double KO mice showed faster recovery from passive systemic anaphylaxis, which could be mediated by increased levels of blood S1P presented in such mice. Our findings demonstrate that Ormdl2 deficiency potentiates the ORMDL3-dependent changes in mast cell signaling.

Lipid rafts as platforms for sphingosine 1-phosphate metabolism and signalling

Spontaneous segregation of cholesterol and sphingolipids as a liquid-ordered phase leads to their clustering in selected membrane areas, the lipid rafts. These specialized membrane domains enriched in gangliosides, sphingomyelin, cholesterol and selected proteins involved in signal transduction, organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating cell homeostasis. Sphingosine 1-phosphate, an important biologically active mediator, is involved in several signal transduction processes regulating a plethora of cell functions and, not only several of its downstream effectors tend to localize in lipid rafts, some of the enzymes involved in its pathway, of receptors involved in its signalling and its transporters have been often found in these membrane microdomains. Considering this, in this review we address what is currently known regarding the relationship between sphingosine 1-phosphate metabolism and signalling and plasma membrane lipid rafts.

Sphingolipidomics in Translational Sepsis Research-Biomedical Considerations and Perspectives

Scientific Background: Sphingolipids are a highly diverse group of lipids with respect to physicochemical properties controlling either structure, distribution, or function, all of them regulating cellular response in health and disease. Mass spectrometry, on the other hand, is an analytical technique characterizing ionized molecules or fragments thereof by mass-to-charge ratios, which has been prosperingly developed for rapid and reliable qualitative and quantitative identification of lipid species. Parallel to best performance of in-depth chromatographical separation of lipid classes, preconditions of precise quantitation of unique molecular species by preprocessing of biological samples have to be fulfilled. As a consequence, “lipid profiles” across model systems and human individuals, esp. complex (clinical) samples, have become eminent over the last couple of years due to sensitivity, specificity, and discriminatory capability. Therefore, it is significance to consider the entire experimental strategy from sample collection and preparation, data acquisition, analysis, and interpretation.

Areas Covered: In this review, we outline considerations with clinical (i.e., human) samples with special emphasis on sample handling, specific physicochemical properties, target measurements, and resulting profiling of sphingolipids in biomedicine and translational research to maximize sensitivity and specificity as well as to provide robust and reproducible results. A brief commentary is also provided regarding new insights of “clinical sphingolipidomics” in translational sepsis research.

Expert Opinion: The role of mass spectrometry of sphingolipids and related species (“sphingolipidomics”) to investigate cellular and compartment-specific response to stress, e.g., in generalized infection and sepsis, is on the rise and the ability to integrate multiple datasets from diverse classes of biomolecules by mass spectrometry measurements and metabolomics will be crucial to fostering our understanding of human health as well as response to disease and treatment.

A Diversity-Oriented Strategy for Chemical Synthesis of Glycosphingolipids: Synthesis of Glycosphingolipid LcGg4 and Its Analogues and Derivatives

A diversity-oriented strategy was developed for the synthesis of glycosphingolipids (GSLs). This strategy was highlighted by using a simple lactoside containing the core structures of GSL glycan and lipid as the universal starting material to obtain different synthetic targets upon stepwise elongation of the glycan via chemical glycosylations and on-site remodeling of the lipid via chemoselective cross-metathesis and N-acylation. The strategy was verified with the synthesis of a lacto-ganglio GSL, LcGg4, which is a biomarker of undifferentiated malignant myeloid cells, and a series of its analogues or derivatives carrying different sugar chains and unique functionalities or molecular labels. This synthetic strategy should be widely applicable and, therefore, be utilized to rapidly access various GSLs and related derivatives by using different donors for glycosylations and different substrates for lipid remodeling following each glycosylation.

Glycosphingolipids

Glycosphingolipids are amphiphilic plasma membrane components formed by a glycan linked to a specific lipid moiety. In this chapter we report on these compounds, on their role played in our cells to maintain the correct cell biology.In detail, we report on their structure, on their metabolic processes, on their interaction with proteins and from this, their property to modulate positively in health and negatively in disease, the cell signaling and cell biology.

In vitro protective effects of Paeonia mascula subsp. hellenica callus extract on human keratinocytes

Natural ingredients have been used to improve the state of health in humans. The genus Paeonia has been studied only limited yet it’s reported to have many activities such as antioxidant and anti-inflammatory. To this context, here we focused on an endemic Paeonia species in Attica. This study aims to present the development of the Paeonia mascula subsp. hellenica callus extract and its pleiotropic bioactivity on human primary keratinocytes exploring its potential application as an active agent in skin-related products. This extract showed a high scavenging activity with high phenolic content and an interesting metabolic profile. At a molecular level, the study on the transcript accumulation of genes revealed that this extract exhibits in vitro skin-related protection properties by mediating mitochondrial energy, cell proliferation, immune and inflammatory response and positively regulates genes involved in epidermal and in stratum corneum function. Besides, the extract is proven not skin irritant on reconstructed human skin model. These findings indicate that the specific P. mascula subsp. hellenica extract possesses significant in vitro protection activity on human epidermis and provides new insights into its beneficial role in skin confirming that the advent of biotechnology contribution the past few decades.

N-Alkylated Iminosugar Based Ligands: Synthesis and Inhibition of Human Lysosomal β-Glucocerebrosidase

The scope of a series of N-alkylated iminosugar based inhibitors in the d-gluco as well as d-xylo configuration towards their interaction with human lysosomal β-glucocerebrosidase has been evaluated. A versatile synthetic toolbox has been developed for the synthesis of N-alkylated iminosugar scaffolds conjugated to a variety of terminal groups via a benzoic acid ester linker. The terminal groups such as nitrile, azide, alkyne, nonafluoro-tert-butyl and amino substituents enable follow-up chemistry as well as visualisation experiments. All compounds showed promising inhibitory properties as well as selectivities for β-glucosidases, some exhibiting activities in the low nanomolar range for β-glucocerebrosidase.

Recent advances in the mass spectrometric analysis of glycosphingolipidome - A review

Aberrant expression of glycosphingolipids has been implicated in a myriad of diseases, but our understanding of the strucural diversity, spatial distribution, and biological function of this class of biomolecules remains limited. These challenges partly stem from a lack of sensitive tools that can detect, identify, and quantify glycosphingolipids at the molecular level. Mass spectrometry has emerged as a powerful tool poised to address most of these challenges. Here, we review the recent developments in analytical glycosphingolipidomics with an emphasis on sample preparation, mass spectrometry and tandem mass spectrometry-based structural characterization, label-free and labeling-based quantification. We also discuss the nomenclature of glycosphingolipids, and emerging technologies like ion mobility spectrometry in differentiation of glycosphingolipid isomers. The intrinsic advantages and shortcomings of each method are carefully critiqued in line with an individual's research goals. Finally, future perspectives on analytical sphingolipidomics are stated, including a need for novel and more sensive methods in isomer separation, low abundance species detection, and profiling the spatial distribution of glycosphingolipid molecular species in cells and tissues using imaging mass spectrometry.

Mechanistic Insights into the Chaperoning of Human Lysosomal-Galactosidase Activity: Highly Functionalized Aminocyclopentanes and C-5a-Substituted Derivatives of 4-epi-Isofagomine

Glycosidase inhibitors have shown great potential as pharmacological chaperones for lysosomal storage diseases. In light of this, a series of new cyclopentanoid β-galactosidase inhibitors were prepared and their inhibitory and pharmacological chaperoning activities determined and compared with those of lipophilic analogs of the potent β-d-galactosidase inhibitor 4-epi-isofagomine. Structure-activity relationships were investigated by X-ray crystallography as well as by alterations in the cyclopentane moiety such as deoxygenation and replacement by fluorine of a “strategic” hydroxyl group. New compounds have revealed highly promising activities with a range of β-galactosidase-compromised human cell lines and may serve as leads towards new pharmacological chaperones for G_M1-gangliosidosis and Morquio B disease.

Sphingolipids in food and their critical roles in human health

Sphingolipids (SLs) are ubiquitous structural components of cell membranes and are essential for cell functions under physiological conditions or during disease progression. Abundant evidence supports that SLs and their metabolites, including ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (So), sphingosine-1-phosphate (S1P), are signaling molecules that regulate a diverse range of cellular processes and human health. However, there are limited reviews on the emerging roles of exogenous dietary SLs in human health. In this review, we discuss the ubiquitous presence of dietary SLs, highlighting their structures and contents in foodstuffs, particularly in sea foods. The digestion and metabolism of dietary SLs is also discussed. Focus is given to the roles of SLs in both the etiology and prevention of diseases, including bacterial infection, cancers, neurogenesis and neurodegenerative diseases, skin integrity, and metabolic syndrome (MetS). We propose that dietary SLs represent a "functional" constituent as emerging strategies for improving human health. Gaps in research that could be of future interest are also discussed.

Glucocerebrosidase: Functions in and Beyond the Lysosome

Glucocerebrosidase (GCase) is a retaining β-glucosidase with acid pH optimum metabolizing the glycosphingolipid glucosylceramide (GlcCer) to ceramide and glucose. Inherited deficiency of GCase causes the lysosomal storage disorder named Gaucher disease (GD). In GCase-deficient GD patients the accumulation of GlcCer in lysosomes of tissue macrophages is prominent. Based on the above, the key function of GCase as lysosomal hydrolase is well recognized, however it has become apparent that GCase fulfills in the human body at least one other key function beyond lysosomes. Crucially, GCase generates ceramides from GlcCer molecules in the outer part of the skin, a process essential for optimal skin barrier property and survival. This review covers the functions of GCase in and beyond lysosomes and also pays attention to the increasing insight in hitherto unexpected catalytic versatility of the enzyme.

Glycosphingolipid metabolism and polycystic kidney disease

Sphingolipids and glycosphingolipids are classes of structurally and functionally important lipids that regulate multiple cellular processes, including membrane organization, proliferation, cell cycle regulation, apoptosis, transport, migration, and inflammatory signalling pathways. Imbalances in sphingolipid levels or subcellular localization result in dysregulated cellular processes and lead to the development and progression of multiple disorders, including polycystic kidney disease. This review will describe metabolic pathways of glycosphingolipids with a focus on the evidence linking glycosphingolipid mediated regulation of cell signalling, lipid microdomains, cilia, and polycystic kidney disease. We will discuss molecular mechanisms of glycosphingolipid dysregulation and their impact on cystogenesis. We will further highlight how modulation of sphingolipid metabolism can be translated into new approaches for the treatment of polycystic kidney disease and describe current clinical studies with glucosylceramide synthase inhibitors in Autosomal Dominant Polycystic Kidney Disease.

Biosynthesis of the anti-lipid-microdomain sphingoid base 4,14-sphingadiene by the ceramide desaturase FADS3

Sphingolipids are multifunctional lipids. Among the sphingolipid-component sphingoid bases, 4,14-sphingadiene (SPD) is unique such that it has a cis double bond with a bent structure. Although SPD was discovered half a century ago, its tissue distribution, biosynthesis, and degradation remain poorly understood. Here, we established a specific and quantitative method for SPD measurement and found that SPD exists in a wide range of mammalian tissues. SPD was especially abundant in kidney, where the amount of SPD was ~2/3 of sphingosine, the most abundant sphingoid base in mammals. Although SPD is metabolized to ceramides and SPD 1-phosphate with almost the same efficiency as sphingosine, it is less susceptible to degradation by a cleavage reaction, at least in vitro. We identified the fatty acid desaturase family protein FADS3 as a ceramide desaturase that produces SPD ceramides by desaturating ceramides containing sphingosine. SPD sphingolipids were preferentially localized outside lipid microdomains, suggesting that SPD has different functions compared to other sphingoid bases in the formation of lipid microdomains. In summary, we revealed the biosynthesis and degradation pathways of SPD and its characteristic membrane localization. Our findings contribute to the elucidation of the molecular mechanism underlying the generation of sphingolipid diversity.

Glycosphingolipids and Infection. Potential New Therapeutic Avenues

Glycosphingolipids (GSLs), the main topic of this review, are a subclass of sphingolipids. With their glycans exposed to the extracellular space, glycosphingolipids are ubiquitous components of the plasma membrane of cells. GSLs are implicated in a variety of biological processes including specific infections. Several pathogens use GSLs at the surface of host cells as binding receptors. In addition, lipid-rafts in the plasma membrane of host cells may act as platform for signaling the presence of pathogens. Relatively common in man are inherited deficiencies in lysosomal glycosidases involved in the turnover of GSLs. The associated storage disorders (glycosphingolipidoses) show lysosomal accumulation of substrate(s) of the deficient enzyme. In recent years compounds have been identified that allow modulation of GSLs levels in cells. Some of these agents are well tolerated and already used to treat lysosomal glycosphingolipidoses. This review summarizes present knowledge on the role of GSLs in infection and subsequent immune response. It concludes with the thought to apply glycosphingolipid-lowering agents to prevent and/or combat infections.

The Iminosugar AMP-DNM Improves Satiety and Activates Brown Adipose Tissue Through GLP1

Obesity is taking on worldwide epidemic proportions, yet effective pharmacological agents with long-term efficacy remain unavailable. Previously, we designed the iminosugar N-adamantine-methyloxypentyl-deoxynojirimycin (AMP-DNM), which potently improves glucose homeostasis by lowering excessive glycosphingolipids. Here we show that AMP-DNM promotes satiety and activates brown adipose tissue (BAT) in obese rodents. Moreover, we demonstrate that the mechanism mediating these favorable actions depends on oral, but not central, administration of AMP-DNM, which ultimately stimulates systemic glucagon-like peptide 1 (GLP1) secretion. We evidence an essential role of brain GLP1 receptors (GLP1r), as AMP-DNM fails to promote satiety and activate BAT in mice lacking the brain GLP1r as well as in mice treated intracerebroventricularly with GLP1r antagonist exendin-9. In conclusion, AMP-DNM markedly ameliorates metabolic abnormalities in obese rodents by restoring satiety and activating BAT through central GLP1r, while improving glucose homeostasis by mechanisms independent of central GLP1r.

Glycosphingolipids and lysosomal storage disorders as illustrated by gaucher disease

Glycosphingolipids are important building blocks of the outer leaflet of the cell membrane. They are continuously recycled, involving fragmentation inside lysosomes by glycosidases. Inherited defects in degradation cause lysosomal glycosphingolipid storage disorders. The relatively common glycosphingolipidosis Gaucher disease is highlighted here to discuss new insights in the molecular basis and pathophysiology of glycosphingolipidoses reached by fundamental research increasingly using chemical biology tools. We discuss improvements in the detection of glycosphingolipid metabolites by mass spectrometry and review new developments in laboratory diagnosis and disease monitoring as well as therapeutic interventions.

Synthesis and anticancer profile of novel sphingoid base-like compounds with a quaternary stereocentre

The synthesis of novel sphingoid base-like compounds with a quaternary stereocentre was achieved in a sequence featuring [3,3]-sigmatropic rearrangements and olefin cross-metathesis transformation as the key reaction steps, which were accompanied by the rational selection of suitable functional group transformations. The stereochemistry of the desired tetra-substituted carbon bearing nitrogen functionality was determined via NOESY experiments of the advanced oxazolidine-2-thiones. Cell viability experiments revealed significant antiproliferative/cytotoxic activity of the target compounds 7, ent-7 and 29 against the Jurkat cell line, with the IC₅₀ values of 6.6 μM, 5.6 μM and 6.1 μM, respectively.