S1PR3 agonism and S1P lyase inhibition rescue mice in the severe state of experimental sepsis

Sepsis is characterized as life-threatening organ dysfunction caused by a dysregulated host response to an infection. Despite numerous clinical trials that addressed this syndrome, there is still no causative treatment available to dampen its severity. Curtailing the infection at an early stage with anti-infectives is the only effective treatment regime besides intensive care. In search for additional treatment options, we recently discovered the inhibition of the sphingosine 1-phosphate (S1P) lyase and subsequent activation of the S1P receptor type 3 (S1PR3) in pre-conditioning experiments as promising targets for sepsis prevention. Here, we demonstrate that treatment of septic mice with the direct S1P lyase inhibitor C31 or the S1PR3 agonist CYM5541 in the advanced phase of sepsis resulted in a significantly increased survival rate. A single dose of each compound led to a rapid decline of sepsis severity in treated mice and coincided with decreased cytokine release and increased lung barrier function with unaltered bacterial load. The survival benefit of both compounds was completely lost in S1PR3 deficient mice. Treatment of the murine macrophage cell line J774.1 with either C31 or CYM5541 resulted in decreased protein kinase B (Akt) and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) phosphorylation without alteration of the mitogen-activated protein kinase (MAPK) p38 and p44/42 phosphorylation. Thus, activation of S1PR3 in the acute phase of sepsis by direct agonism or S1P lyase inhibition dampened Akt and JNK phosphorylation, resulting in decreased cytokine release, improved lung barrier stability, rapid decline of sepsis severity and better survival in mice.

GT-11 impairs insulin signaling through modulation of sphingolipid metabolism in C2C12 myotubes

AIMS

Sphingolipids are involved in the regulation of insulin signaling, which is linked to the development of insulin resistance, leading to diabetes mellitus. We aimed to study whether modulation of sphingolipid levels by GT-11 may regulate insulin signaling in C2C12 myotubes.

MAIN METHODS

We investigated the effects of sphingolipid metabolism on Akt phosphorylation and glucose uptake using C2C12 myotubes. Either GT-11, an inhibitor of dihydroceramide desaturase 1 and S1P lyase, or siRNA targeting Sgpl1, the gene encoding the enzyme, was employed to determine the effect of sphingolipid metabolism modulation on insulin signaling. Western blotting and glucose uptake assays were used to evaluate the effect of treatments on insulin signaling. Sphingolipid metabolites were analyzed by high performance liquid chromatography (HPLC).

KEY FINDINGS

Treatment with GT-11 resulted in decreased Akt phosphorylation and reduced glucose uptake. Silencing the Sgpl1 gene, which encodes S1P lyase, mimicked these findings, suggesting the potential for regulating insulin signaling through S1P lyase modulation. GT-11 modulated sphingolipid metabolism, inducing the accumulation of sphingolipids. Using PF-543 and ARN14974 to inhibit sphingosine kinases and acid ceramidase, respectively, we identified a significant interplay between sphingosine, S1P lyase, and insulin signaling. Treatment with either exogenous sphingosine or palmitic acid inhibited Akt phosphorylation, and reduced S1P lyase activity.

SIGNIFICANCE

Our findings highlight the importance of close relationship between sphingolipid metabolism and insulin signaling in C2C12 myotubes, pointing to its potential therapeutic relevance for diabetes mellitus.

Molecular, immunological, and physiological evidences of a sphingosine-activated plasma membrane Ca2+-channel in Trypanosoma equiperdum

The hemoparasite Trypanosoma equiperdum belongs to the Trypanozoon subgenus and includes several species that are pathogenic to animals and humans in tropical and subtropical areas across the world. As with all eukaryotic organisms, Ca2+ is essential for these parasites to perform cellular processes thus ensuring their survival across their life cycle. Despite the established paradigm to study proteins related to Ca2+ homeostasis as potential drug targets, so far little is known about Ca2+ entry into trypanosomes. Therefore, in the present study, the presence of a plasma membrane Ca2+-channel in T. equiperdum (TeCC), activated by sphingosine and inhibited by verapamil, is described. The TeCC was cloned and analyzed using bioinformatic resources, which confirmed the presence of several domains, motifs, and a topology similar to the Ca2+ channels found in higher eukaryotes. Biochemical and confocal microscopy assays using antibodies raised against an internal region of human L-type Ca2+ channels indicate the presence of a protein with similar predicted molar mass to the sequence analyzed, located at the plasma membrane of T. equiperdum. Physiological assays based on Fura-2 signals and Mn2+ quenching performed on whole parasites showed a unidirectional Ca2+ entry, which is activated by sphingosine and blocked by verapamil, with the distinctive feature of insensitivity to nifedipine and Bay K 8644. This suggests a second Ca2+ entry for T. equiperdum, different from the store-operated Ca2+ entry (SOCE) previously described. Moreover, the evidence presented here for the TeCC indicates molecular and pharmacological differences with their mammal counterparts, which deserve further studies to evaluate the potential of this channel as a drug target.

Density of Sphingosine-1-Phosphate Receptors Is Altered in Cortical Nerve-Terminals of Insulin-Resistant Goto-Kakizaki Rats and Diet-Induced Obese Mice

Sphingosine-1-phosphate (S1P) is a phosphosphingolipid with pleiotropic biological functions. S1P acts as an intracellular second messenger, as well as extracellular ligand to five G-protein coupled receptors (S1PR1-5). In the brain, S1P regulates neuronal proliferation, apoptosis, synaptic activity and neuroglia activation. Moreover, S1P metabolism alterations have been reported in neurodegenerative disorders. We have previously reported that S1PRs are present in nerve terminals, exhibiting distinct sub-synaptic localization and neuromodulation actions. Since type 2 diabetes (T2D) causes synaptic dysfunction, we hypothesized that S1P signaling is modified in nerve terminals. In this study, we determined the density of S1PRs in cortical synaptosomes from insulin-resistant Goto-Kakizaki (GK) rats and Wistar controls, and from mice fed a high-fat diet (HFD) and low-fat-fed controls. Relative to their controls, GK rats showed similar cortical S1P concentration despite higher S1P levels in plasma, yet lower density of S1PR1, S1PR2 and S1PR4 in nerve-terminal-enriched membranes. HFD-fed mice exhibited increased plasma and cortical concentrations of S1P, and decreased density of S1PR1 and S1PR4. These findings point towards altered S1P signaling in synapses of insulin resistance and diet-induced obesity models, suggesting a role of S1P signaling in T2D-associated synaptic dysfunction.

S1PR2 inhibition mitigates cognitive deficit in diabetic mice by modulating microglial activation via Akt-p53-TIGAR pathway

Cognitive deficit is one of the challenging complications of type 2 diabetes. Sphingosine 1- phosphate receptors (S1PRs) have been implicated in various neurodegenerative and metabolic disorders. The association of S1PRs and cognition in type 2 diabetes remains elusive. Microglia-mediated neuronal damage could be the thread propagating cognitive deficit. The effects of S1PR2 inhibition on cognition in high-fat diet and streptozotocin-induced diabetic mice were examined in this work. We further assessed microglial activation and putative microglial polarisation routes. Cognitive function loss was observed after four months of diabetes induction in Type 2 diabetes animal model. JTE013, an S1PR2 inhibitor, was used to assess neuroprotection against cognitive decline and neuroinflammation in vitro and in vivo diabetes model. JTE013 (10 mg/kg) improved synaptic plasticity by upregulating psd95 and synaptophysin while reducing cognitive decline and neuroinflammation. It further enhanced anti-inflammatory microglia in the hippocampus and prefrontal cortex (PFC), as evidenced by increased Arg-1, CD206, and YM-1 levels and decreased iNOS, CD16, and MHCII levels. TIGAR, TP53-induced glycolysis and apoptosis regulator, might facilitate the anti-inflammatory microglial phenotype by promoting oxidative phosphorylation and decreasing apoptosis. However, since p53 is a TIGAR suppressor, inhibiting p53 could be beneficial. S1PR2 inhibition increased p-Akt and TIGAR levels and reduced the levels of p53 in the PFC and hippocampus of type 2 diabetic mice, thereby decreasing apoptosis. In vitro, palmitate was used to imitate sphingolipid dysregulation in BV2 cells, followed by conditioned media exposure to Neuro2A cells. JTE013 rescued the palmitate-induced neuronal apoptosis by promoting the anti-inflammatory microglia. In the present study, we demonstrate that the inhibition of S1PR2 improves cognitive function and skews microglia toward anti-inflammatory phenotype in type 2 diabetic mice, thereby promising to be a potential therapy for neuroinflammation.

New Therapeutic Options in Pulmonal Diseases: Sphingolipids and Modulation of Sphingolipid Metabolism

Sphingolipids are crucial molecules in the respiratory airways. As in most other tissues and organs, in the lung sphingolipids play an essential role as structural constituents as they regulate barrier function and fluidity of cell membranes. A lung-specific feature is the occurrence of sphingolipids as minor structural components in the surfactant. However, sphingolipids are also key signaling molecules involved in airway cell signaling and their dynamical formation and metabolism are important for normal lung physiology. Dysregulation of sphingolipid metabolism and signaling is involved in altering lung tissue and initiates inflammatory processes promoting the pathogenesis of pulmonal diseases including cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and asthma.In the present review, the important role of specific sphingolipid species in pulmonal diseases will be discussed. Only such an understanding opens up the possibility of developing new therapeutic strategies with the aim of correcting the imbalance in sphingolipid metabolism and signaling. Such delivery strategies have already been studied in animal models of these lung diseases, demonstrating that targeting the sphingolipid profile represents new therapeutic opportunities for lung disorders.

First-in-human single-dose study of nizubaglustat, a dual inhibitor of ceramide glucosyltransferase and non-lysosomal glucosylceramidase: Safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending and multiple doses in healthy adults

Nizubaglustat is a novel, orally available, brain penetrant, potent, and selective dual inhibitor of ceramide glucosyltranferase and non-lysosomal neutral glucosylceramidase (NLGase), which is currently under development for the treatment of subjects with neurological manifestations in primary and secondary gangliosidoses. The objectives of this first-in-human study were to evaluate the safety and tolerability, pharmacokinetics, and pharmacodynamics (PD) of single oral doses of nizubaglustat after single (1, 3, and 9 mg) and multiple oral doses (9 mg once per day (QD) over 14 days) in healthy adults. Nizubaglustat was rapidly absorbed and systemic exposure was dose-proportional. Steady-state was achieved after three days of QD multiple dosing with minimal accumulation. Renal clearance accounted for around 15% of nizubaglustat elimination. Following multiple dosing, plasma concentrations of glucosylceramide (GlcCer), lactosylceramide (LacCer), and monosialodihexosylganglioside (GM3) decreased to a nadir at Day 10. PD target engagement of GCS inhibition was shown by a median decrease from baseline of plasma concentrations of GlcCer, LacCer, and GM3 ganglioside by 70%, 50%, and 48%, respectively. NLGase inhibition was also manifested by increased concentrations of GlcCer in cerebrospinal fluid from Day 1 to Day 14. Nizubaglustat was safe and well-tolerated at all doses tested. Consistent with the high selectivity, and the absence of intestinal disaccharidases inhibition, no cases of diarrhea were reported. No decreased appetite or weight loss was noted. Only treatment-emergent adverse events with preferred terms belonging to the system organ class skin and subcutaneous disorders of mild intensity were reported as drug-related in the nizubaglustat arm, in line with the pharmacological mechanism targeting glucosylceramide metabolism. Taken together, these data support QD dosing of nizubaglustat and its ongoing development in patients with primary and secondary forms of gangliosidoses.

Legacy perfluoro-alkyl substances impair LDL-cholesterol uptake independently from PCSK9-function

Perfluoro-alkyl substances (PFAS) are pollutants, whose exposure was associated with altered levels of low-density lipoproteins (LDL) in humans. Here we investigated this clinical outcome in two groups of young male adults residing in areas of respectively low and high environmental exposure to perfluoro-octanoic-acid (PFOA). From the Regional Authority data on pollution areas, 38 not-exposed and 59 exposed age-matched participants were evaluated for serum levels of total cholesterol (Total-Chol), LDL-Chol, high-density lipoprotein cholesterol (HDL-Chol), triglycerides (Tgl) and chromatography quantified PFOA. Human hepato-carcinoma cell line HepG2 was exposed to PFOA or perfluoro-octane-sulfonate (PFOS), as legacy PFAAs, and C6O4 as new generation compound. Fluorimetry was used to evaluate the cell-uptake of labelled-LDL. Proprotein Convertase Subtilisin/Kexin 9 (PCSK9)-mediated LDL-receptor (LDL-R) degradation and sub-cellular localization of LDL-R were evaluated by western blot analysis. Serum levels of PFOA, were positively and significantly correlated with Total-Chol (ρ = 0.312, P = 0.002), LDL-Chol (ρ = 0.333, P = 0.001) and Tgl (ρ = 0.375, P < 0.001). Participants with high serum LDL-Chol and Tgl levels, according to the cardiovascular risk, were more prevalent in exposed compared to not-exposed subjects (respectively: 23.7% vs 5.3%, P = 0.023 and 18,6% vs 0%, P = 0.006). Exposure of HepG2 cells to PFOA or C6O4 100 ng/mL was associated with a significantly lower LDL uptake than controls but no major impact of any PFAAs on PCSK9-mediated LDL-R degradation was observed. Compared to controls, exposure to PFAS showed an unbalanced LDL-R partition between membrane and cytoplasm. Endocytosis inducer sphingosine restored LDL-R partition only in samples exposed to C6O4. These data suggest a novel endocytosis-based mechanism of altered lipid trafficking associated with the exposure to legacy PFAS.

via reducing sphingosine level was confirmed by network pharmacology with metabolomics

Background

Tribulus terrestris L. (TT) is one of the most common Chinese herbs and distributes in various regions in China. TT was first documented to treat breast cancer in Shen-Nong-Ben-Cao-Jing. However, the pharmacological activities of TT extract on liver cancer have not been reported. In this study, we investigated its anti-liver cancer activity and underlying mechanism.

Methods

Traditional Chinese Medicine Systems Pharmacology (TCMSP) and PharmMapper databases were used to obtain the active ingredients and the targets of TT. Genecards database was employed to acquire TT targets in liver cancer. Furthermore, Venny 2.1, Cytoscape 3.8.2, DAVID 6.8 software were utilized to analyze the relationship between TT and liver cancer. In vivo experiment: The animal model of liver cancer was established by injection of H22 cells into Balb/c mice. After five days, drugs were intragastrically administered to the mice daily for 10 days. Body weight, tumor size and tumor weight were recorded. Tumor inhibitory rate was calculated. Protein levels were examined by Western blotting. Pathological changes of liver cancer tissues were evaluated by HE and Tunel staining. Metabolomics study: LC-MS was used to analyze different metabolites between model and TTM groups.

Results

12 active ingredients of TT, 127 targets of active ingredients, 17,378 targets of liver cancer, and 125 overlapping genes were obtained. And then, 118 items of GO biological processes (BP), 54 items of GO molecular function (MF), 35 items of GO cellular component (CC) and 128 pathways of KEGG were gotten (P < 0.05). Moreover, 47 differential metabolites were affirmed and 66 pathways of KEGG (P < 0.05) were obtained. In addition, after TT and sorafenib treatment, tumor size was markedly reduced, respectively, compared with model group. Tumor weight was significantly decreased and tumor inhibitory rate was more than 44% in TTM group. After TT treatment, many adipocytes, cracks between tumor cells and apoptosis were found. The levels of pro-Cathepsin B, Cathepsin B, Bax, Bax/Bcl2, Caspase3 and Caspase7 were markedly increased, but the level of Bcl2 was significantly reduced after TT treatment.

Conclusion

TT has a broad range of effects on various signaling pathways and biological processes, including the regulation of apoptosis. It exhibits antitumor activity in an animal model of liver cancer and activates the apoptotic pathway by decreasing Sph level. This study provides valuable information regarding the potential use of TT extract in the treatment of liver cancer and highlights the importance of investigating the underlying molecular mechanisms of traditional medicines for the development of new therapeutic drugs in liver cancer.

Sphingolipid metabolism and its relationship with cardiovascular, renal and metabolic diseases

Sphingolipids (sphingomyelin, glycolipids, gangliosides) are located in cell membranes, plasma, and lipoproteins. In patients with cardiovascular, renal, and metabolic diseases, the profile of sphingolipids and their metabolites (ceramide, sphingosine, and sphingosine-1-phosphate) is modified, and these changes may explain the alterations in some cellular responses such as apoptosis. Furthermore, sphingosine and sphingosine-1-phosphate have been suggested to prevent COVID-19. This review also briefly mentions the techniques that allow us to study sphingolipids and their metabolites.

Fingolimod Alleviates Cognitive Deficit in Type 2 Diabetes by Promoting Microglial M2 Polarization via the pSTAT3-jmjd3 Axis

Sphingosine receptors (S1PRs) are implicated in the progression of neurodegenerative diseases and metabolic disorders like obesity and type 2 diabetes (T2D). The link between S1PRs and cognition in type 2 diabetes, as well as the mechanisms that underpin it, are yet unknown. Neuroinflammation is the common pathology shared among T2D and cognitive impairment. However, the interplay between the M1 and M2 polarization state of microglia, a primary driver of neuroinflammation, could be the driving factor for impaired learning and memory in diabetes. In the present study, we investigated the effects of fingolimod (S1PR1 modulator) on cognition in high-fat diet and streptozotocin-induced diabetic mice. We further assessed the potential pathways linking microglial polarization and cognition in T2D. Fingolimod (0.5 mg/kg and 1 mg/kg) improved M2 polarization and synaptic plasticity while ameliorating cognitive decline and neuroinflammation. Sphingolipid dysregulation was mimicked in vitro using palmitate in BV2 cells, followed by conditioned media exposure to Neuro2A cells. Mechanistically, type 2 diabetes induced microglial activation, priming microglia towards the M1 phenotype. In the hippocampus and cortex of type 2 diabetic mice, there was a substantial drop in pSTAT3, which was reversed by fingolimod. This protective effect of fingolimod on microglial M2 polarization was primarily suppressed by selective jmjd3 blockade in vitro using GSK-J4, revealing that jmjd3 was involved downstream of STAT3 in the fingolimod-enabled shift of microglia from M1 to M2 polarization state. This study suggested that fingolimod might effectively improve cognition in type 2 diabetes by promoting M2 polarization.

Genetic Tools for Studying the Roles of Sphingolipids in Viral Infections

Sphingolipids are a critical family of membrane lipids with diverse functions in eukaryotic cells, and a growing body of literature supports that these lipids play essential roles during the lifecycles of viruses. While small molecule inhibitors of sphingolipid synthesis and metabolism are widely used, the advent of CRISPR-based genomic editing techniques allows for nuanced exploration into the manners in which sphingolipids influence various stages of viral infections. Here we describe some of these critical considerations needed in designing studies utilizing genomic editing techniques for manipulating the sphingolipid metabolic pathway, as well as the current body of literature regarding how viruses depend on the products of this pathway. Here, we highlight the ways in which sphingolipids affect viruses as these pathogens interact with and influence their host cell and describe some of the many open questions remaining in the field.

Differences in the Distribution of Ceramides and Sphingosine among Lipoprotein and Lipoprotein-Depleted Fractions in Patients with Type 2 Diabetes Mellitus

AIM

In addition to the quantity and quality, the carriers, such as lipoproteins and albumin, can affect the physiological properties and clinical significance of lipids. This study aimed to elucidate the modulation of the levels of ceramides and sphingosine, which are considered as proatherosclerotic lipids, in lipoproteins and lipoprotein-depleted fractions in subjects with type 2 diabetes.

METHODS

We separated the serum samples collected from healthy subjects (n=22) and subjects with type 2 diabetes (n=39) into Triglyceride (TG)-rich lipoproteins (TRL), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and lipoprotein-depleted fractions via ultracentrifugation. Then, we measured the levels of six species of ceramides, sphingosine, and dihydrosphingosine via LC-MS/MS and statistically analyzed them to identify the sphingolipids in each fraction, which are associated with diabetes as well as cardiovascular and renal complications.

RESULTS

In subjects with diabetes, the levels of sphingosine and dihydrosphingosine in the TRL, LDL, and lipoprotein-depleted fractions were higher, whereas those in the HDL were lower. In addition, the ceramide levels in HDL were lower, whereas those in lipoprotein-depleted fractions were higher. Furthermore, The levels of ceramides in lipoproteins, especially LDL, were negatively associated with the presence of cardiovascular diseases and stage 4 diabetic nephropathy.

CONCLUSIONS

The contents of ceramides and sphingosine in lipoproteins and lipoprotein-depleted fractions were differently modulated in diabetes and associated with cardiovascular diseases and diabetic nephropathy. The carrier might be an important factor for the biological properties and clinical significance of these sphingolipids.

Lipid-protein interactions regulating the canonical and the non-canonical NLRP3 inflammasome

The inflammatory response is a complex regulated effector mechanism of the innate immune system that is initiated after tissue injury or infection. The NLRP3 inflammasome is an important initiator of inflammation by regulating the activation of caspase-1, the maturation of pro-inflammatory cytokines and the induction of pyroptotic cell death. Numerous studies demonstrate that the NLRP3 inflammasome could be modulated by lipids, existing a relation between lipids and the activation of different inflammatory processes. In this review we will summarize how the mechanism of NLRP3 inflammasome activation is regulated by different lipids and how these lipids control specific cellular localization of NLRP3 during activation. Although being a cytosolic protein, NLRP3 interacts with lipids accessible in neighbor membranes. Also, the modulation of NLRP3 by endogenous lipids has been found causative of different metabolic diseases and bacterial-pathogenic lipids lead to NLRP3 activation during infection. The understanding of the modulation of the NLRP3 inflammasome by lipids has resulted not only in a better knowledge about the mechanism of NLRP3 activation and its implication in disease, but also opens a new avenue for the development of novel therapeutics and vaccines, as NLRP3 could be modulated by synthetic lipids used as adjuvants.

Elevated testicular apoptosis is associated with elevated sphingosine driven by gut microbiota in prediabetic sheep

BACKGROUND

Men with prediabetes often exhibit concomitant low-quality sperm production or even infertility, problems which urgently require improved therapeutic options. In this study, we have established a sheep model of diet-induced prediabetes that is associated with spermatogenic defects and have explored the possible underlying metabolic causes.

RESULTS

We compared male sheep fed a normal diet with those in which prediabetes was induced by a rich diet and with a third group in which the rich diet was supplemented by melatonin. Only the rich diet group had symptoms of prediabetes, and in these sheep, we found impaired spermatogenesis characterized by a block in the development of round spermatids and an increased quantity of testicular apoptotic cells. Comparing the gut microbiomes and intestinal digest metabolomes of the three groups revealed a distinctive difference in the taxonomic composition of the microbiota in prediabetic sheep, and an altered metabolome, whose most significant feature was altered sphingosine metabolism; elevated sphingosine was also found in blood and testes. Administration of melatonin alleviated the symptoms of prediabetes, including those of impaired spermatogenesis, while restoring a more normal microbiota and metabolic levels of sphingosine. Fecal microbiota transplantation from prediabetic sheep induced elevated sphingosine levels and impaired spermatogenesis in recipient mice, indicating a causal role of gut microbiota in these phenotypes.

CONCLUSIONS

Our results point to a key role of sphingosine in the disruption of spermatogenesis in prediabetic sheep and suggest it could be a useful disease marker; furthermore, melatonin represents a potential prebiotic agent for the treatment of male infertility caused by prediabetes.

Analysis of the Sphingolipidome in NAFLD

The relationship between sphingolipid levels and NAFLD pathology has been recognized for some time. Numerous studies using pharmacological and genetic approaches in vitro and in animal models of NAFLD have demonstrated that modifications to sphingolipid metabolism can attenuate various facets of NAFLD pathology. However, a more precise understanding of the role of sphingolipids and NAFLD pathology is essential to creating therapeutics that target this pathway. This chapter touches on the scale and variety of sphingolipid metabolites at play in NAFLD, which vary widely in their chemical structures and biological functions. With advances in liquid chromatography and tandem mass spectrometry approaches, each of thousands of individual sphingolipid species and sphingolipid metabolites can be identified and precisely quantified. These approaches are beginning to reveal specific sub-classes and species of sphingolipids that change in NAFLD, and as such, enzymes that generate them can be identified and potentially serve as therapeutic targets. Advances in lipidomics technology have been, and will continue to be, critical to these gains in our understanding of NAFLD.

Structural insights into the substrate selectivity of α-oxoamine synthases from marine Vibrio sp. QWI-06

Pyridoxal phosphate (PLP)-dependent α-oxoamine synthases are generally believed to be responsible for offloading and elongating polyketides or catalyzing the condensation of amino acids and acyl-CoA thioester substrates, such as serine into sphingolipids and cysteate into sulfonolipids. Previously, we discovered vitroprocines, which are tyrosine- and phenylalanine-polyketide derivatives, as potential new antibiotics from the genus Vibrio. Using bioinformatics analysis, we identified putative genes of PLP-dependent enzyme from marine Vibrio sp. QWI-06, implying a capability to produce amino-polyketide derivatives. One of these genes was cloned, and the recombinant protein, termed Vibrio sp. QWI-06 α-oxoamine synthases-1 (VsAOS1), was overexpressed for structural and biochemical characterization. The crystal structure of the dimeric VsAOS1 was determined at 1.8-Å resolution in the presence of L-glycine. The electron density map indicated a glycine molecule occupying the pyridoxal binding site in one monomer, suggesting a snapshot of the initiation process upon the loading of amino acid substrate. In mass spectrometry analysis, VsAOS1 strictly acted to condense L-glycine with C12 or C16 acyl-CoA, including unsaturated acyl analog. Furthermore, a single residue replacement of VsAOS1 (G243S) allowed the enzyme to generate sphingoid derivative when L-serine and lauroyl-CoA were used as substrates. Our data elucidate the mechanism of substrate binding and selectivity by the VsAOS1 and provide a thorough understanding of the molecular basis for the amino acid preference of AOS members.

Profiling of glycosphingolipids with SCDase digestion and HPLC-FLD-MS

Lipid components of cells and tissues feature a large diversity of structures that present a challenging problem for molecular analysis. Glycolipids from mammalian cells contain glycosphingolipids (GSLs) as their major glycolipid component, and these structures vary in the identity of the glycan headgroup as well as the structure of the fatty acid and sphingosine (Sph) tails. Analysis of intact GSLs is challenging due to the low abundance of these species. Here, we develop a new strategy for the analysis of lyso-GSL (l-GSL), GSL that retain linkage of the glycan headgroup with the Sph base. The analysis begins with digestion of a GSL sample with sphingolipid ceramide N-deacylase (SCDase), followed by labelling with an amine-reactive fluorophore. The sample was then analyzed by HPLC-FLD-MS and quantitated by addition of an external standard. This method was compared to analysis of GSL glycans after cleavage by an Endoglycoceramidase (EGCase) enzyme and labeling with a fluorophore (2-anthranilic acid, 2AA). The two methods are complementary, with EGCase providing improved signal (due to fewer species) and SCDase providing analysis of lyso-GSL. Importantly the SCDase method provides Sph composition of GSL species. We demonstrate the method on cultured human cells (Jurkat T cells) and tissue homogenate (porcine brain).

Updates on sphingolipids: Spotlight on retinopathy

The sphingolipids ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (Sph), and sphingosine-1-phosphate (S1P)) are key signaling molecules that regulate many patho-biological processes. During the last decade, they have gained increasing attention since they may participate in important and numerous retinal processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Cer for instance has emerged as a key mediator of inflammation and death of neuronal and retinal pigment epithelium cells in experimental models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. S1P may have opposite biological actions, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1- phosphate may also contribute to uveitis. Furthermore, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), have been shown to preserve neuronal viability and retinal function. Collectively, the expanding role for these sphingolipids in the modulation of vital processes in retina cell types and in their dysregulation in retinal degenerations makes them attractive therapeutic targets.

Fumonisin B1 triggers carcinogenesis via HDAC/PI3K/Akt signalling pathway in human esophageal epithelial cells

Fumonisin B1 (FB1) is a contaminant that commonly present in the global environment, especially in food and feed. Epidemiologic studies have shown that esophageal cancer is associated with fumonisin toxicity. However, the molecular mechanism of FB1-induced esophageal cancer is unclear. In this research, the molecular mechanism of FB1-induced cell carcinogenesis in human esophageal epithelial cells line (HEEC) was explored. We found that FB1 (0.3125-5 μM) could promote cell proliferation, and the same phenomenon was found in a 3D cell model. FB1 could also accelerate cell migration. The expression levels of DNA damage markers were significantly increased after FB1 exposure. Meanwhile, the expression levels of cell cycle-regulated proteins and cancer-related genes were abnormal. Furthermore, FB1 significantly upregulated the histone deacetylase (HDAC) expression and activated the phosphoinositide 3 kinase (PI3K)/protein kinase B (Akt) signalling pathway. The HDAC inhibitor trichostatin A (TSA) could repressed FB1-promoted cell proliferation and abnormal phenomenon induced by FB1. Moreover, myriocin (ISP-1) could relieve FB1-enhanced HDAC expression and cell proliferation, which implied that ISP-1 may be used to block the fumonisin toxicity in the future. Our findings suggested that the HDAC/PI3K/Akt signalling pathway is a novel mechanism for FB1-induced cell carcinogenesis in HEEC and provided new ideas for the prevention and control of fumonisin toxicity, subsequently avoiding adverse effects on the ecosystem and human health.

Solving the enigma: Mass spectrometry and small molecule probes to study sphingolipid function

Sphingolipids are highly bioactive lipids. Sphingolipid metabolism produces key membrane components (e.g. sphingomyelin) and a variety of signaling lipids with different biological functions (e.g. ceramide, sphingosine-1-phosphate). The coordinated activity of tens of different enzymes maintains proper levels and localization of these lipids with key roles in cellular processes. In this review, we highlight the signaling roles of sphingolipids in cell death and survival. We discuss recent findings on the role of specific sphingolipids during these processes, enabled by the use of lipidomics to study compositional and spatial regulation of these lipids and synthetic sphingolipid probes to study subcellular localization and interaction partners of sphingolipids to understand the function of these lipids.

Biophysical impact of sphingosine and other abnormal lipid accumulation in Niemann-Pick disease type C cell models

Niemann-Pick disease type C (NPC) is a complex and rare pathology, which is mainly associated to mutations in the NPC1 gene. This disease is phenotypically characterized by the abnormal accumulation of multiple lipid species in the acidic compartments of the cell. Due to the complexity of stored material, a clear molecular mechanism explaining NPC pathophysiology is still not established. Abnormal sphingosine accumulation was suggested as the primary factor involved in the development of NPC, followed by the accumulation of other lipid species. To provide additional mechanistic insight into the role of sphingosine in NPC development, fluorescence spectroscopy and microscopy were used to study the biophysical properties of biological membranes using different cellular models of NPC. Addition of sphingosine to healthy CHO-K1 cells, in conditions where other lipid species are not yet accumulated, caused a rapid decrease in plasma membrane and lysosome membrane fluidity, suggesting a direct effect of sphingosine rather than a downstream event. Changes in membrane fluidity caused by addition of sphingosine were partially sustained upon impaired trafficking and metabolization of cholesterol in these cells, and could recapitulate the decrease in membrane fluidity observed in NPC1 null Chinese Hamster Ovary (CHO) cells (CHO-M12) and in cells with pharmacologically induced NPC phenotype (treated with U18666A). In summary, these results show for the first time that the fluidity of the membranes is altered in models of NPC and that these changes are in part caused by sphingosine, supporting the role of this lipid in the pathophysiology of NPC.

Eubacterium_coprostanoligenes_group combined with sphingosine to modulate the serum dyslipidemia in high-fat diet mice

BACKGROUND & AIMS

Although high-fat diet (HFD) could impact the composition of fecal microbiome and their metabolites, it is still largely unknown which fecal bacteria and metabolites are relatively important in responding to the HFD. This study aimed to identify the crucial fecal bacteria and metabolites in the HFD mice using a microbial-metabolite network, and to investigate the synergistic mediation effect of the crucial fecal bacteria and metabolites on serum dyslipidemia induced by the HFD.

METHODS

The 16srDNA sequencing and the ultra-performance liquid chromatography (UPLC/TOF MSMS) platform were performed to characterize the composition and function of fecal microbiome, and metabolites in the HFD. The microbial-metabolite network, correlation and mediation analyses were performed to examine the relationships among fecal microbiome, metabolites, and serum dyslipidemia indicators. Mice models were conducted to evaluate the effect of fecal metabolite on dyslipidemia.

RESULTS

Compared to the control, 32 genera were altered in the HFD, including 26 up-regulated and 6 down-regulated. A total of 42 altered pathways were observed between the control and HFD, and the "Glycosphingolipid biosynthesis" was identified as the most significant pathway (fold change = 0.64; p < 0.001). Meanwhile, 49 fecal metabolites were altered in the HFD, and the fecal microbiome was associated with the fecal metabolism (M2 = 0.776, p = 0.008). Based on the microbial-metabolite network, two major hub genera were screened (HUB1: g. Streptococcus, HUB2: g. Eubacterium_coprostanoligenes_group), and one bacterial metabolite, sphingosine, was found in this study. Further, the HUB2 was positively associated with fecal sphingosine (r = 0.646, p = 0.001), and its downstream metabolic pathway, "Glycosphingolipid biosynthesis" pathway (r = 0.544, p = 0.009). The regulatory relationship between the HUB2 and sphingosine synergistically mediated the effect of HFD on TCHO (33.7%), HDL-C (37.3%), and bodyweight (36.7%). Besides, compared to the HFD, the HFD with sphingosine supplementation had lower bodyweight (35.12 ± 1.23 vs. 39.42 ± 1.25, p < 0.001), TG (0.44 ± 0.08 vs. 0.52 ± 0.05, p = 0.002), TCHO (3.81 ± 0.34 vs. 4.51 ± 0.38, p = 0.002), and LDL-c (0.82 ± 0.09 vs. 0.97 ± 0.15, p = 0.016).

CONCLUSIONS

The g. Streptococcus and g. Eubacterium_coprostanoligenes are two hub genera in the fecal micro-ecosystem of the HFD, and the g. Eubacterium_coprostanoligenes mediates the effect of HFD on dyslipidemia through sphingosine. Sphingosine supplementation can improve dyslipidemia induced by HFD.

Fumonisin B1-Induced Toxicity Was Not Exacerbated in Glutathione Peroxidase-1/Catalase Double Knock Out Mice

Fumonisin B1 (FB1) structurally resembles sphingolipids and interferes with their metabolism leading to sphingolipid dysregulation. We questioned if FB1 could exacerbate liver or kidney toxicities in glutathione peroxidase 1 (Gpx1) and catalase (Cat) knockout mice. While higher serum levels of thiobarbituric acid reactive substances (TBARS) and sphinganine (Sa) were measured in Gpx1/Cat knockout mice (Gpx1/Cat KO) than wild type mice after 5 days of FB1 treatment, serum levels of alanine aminotransferase (ALT), sphingosine-1 phosphate (So-1-P), and sphinganine-1 phosphate (Sa-1-P) were found to be relatively low. Although Sa was highly elevated in Gpx1/Cat KO mice and wild mice, lower levels of So and Sa were found in both the kidney and liver tissues of Gpx/Cat KO mice than wild type mice after FB1 treatment. Paradoxically, FB1-induced cellular apoptosis and necrosis were hastened under oxidative stress in Gpx1/Cat KO mice.

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.

Probing the substitution pattern of indole-based scaffold reveals potent and selective sphingosine kinase 2 inhibitors

Elevated levels of sphingosine 1-phosphate (S1P) and increased expression of sphingosine kinase isoforms (SphK1 and SphK2) have been implicated in a variety of disease states including cancer, inflammation, and autoimmunity. Consequently, the S1P signaling axis has become an attractive target for drug discovery. Selective inhibition of either SphK1 or SphK2 has been demonstrated to be effective in modulating S1P levels in animal models. While SphK1 inhibitors have received much attention, the development of potent and selective SphK2 inhibitors are emerging. Previously, our group reported a SphK2 naphthalene-based selective inhibitor, SLC5081308, which displays approximately 7-fold selectivity for hSphK2 over hSphK1 and has a SphK2 K_i value of 1.0 μM. To improve SphK2 potency and selectivity, we designed, synthesized, and evaluated a series of indole-based compounds derived from SLC5081308. After investigating substitution patterns around the indole ring, we discovered that 1,5-disubstitution promoted optimal binding in the SphK2 substrate binding site and subsequent inhibition of enzymatic activity. Our studies led to the identification of SLC5101465 (6r, SphK2 K_i = 90 nM, >110 fold selective for SphK2 over SphK1). Molecular modeling studies revealed key nonpolar interactions with Val308, Phe548, His556, and Cys533 and hydrogen bonds with both Asp211 and Asp308 as responsible for the high SphK2 inhibition and selectivity.

Lipophilic tail modifications of 2-(hydroxymethyl)pyrrolidine scaffold reveal dual sphingosine kinase 1 and 2 inhibitors

The sphingosine 1-phosphate (S1P) signaling pathway is an attractive target for pharmacological manipulation due to its involvement in cancer progression and immune cell chemotaxis. The synthesis of S1P is catalyzed by the action of sphingosine kinase 1 or 2 (SphK1 or SphK2) on sphingosine and ATP. While potent and selective inhibitors of SphK1 or SphK2 have been reported, development of potent dual SphK1/SphK2 inhibitors are still needed. Towards this end, we report the structure-activity relationship profiling of 2-(hydroxymethyl)pyrrolidine-based inhibitors with 22d being the most potent dual SphK1/SphK2 inhibitor (SphK1 K_i = 0.679 μM, SphK2 K_i = 0.951 μM) reported in this series. 22d inhibited the growth of engineered Saccharomyces cerevisiae and decreased S1P levels in histiocytic lymphoma myeloid cell line (U937 cells), demonstrating inhibition of SphK1 and 2 in vitro. Molecular modeling studies of 22d docked inside the Sph binding pocket of both SphK1 and SphK2 indicate essential hydrogen bond between the 2-(hydroxymethyl)pyrrolidine head to interact with aspartic acid and serine residues near the ATP binding pocket, which provide the basis for dual inhibition. In addition, the dodecyl tail adopts a "J-shape" conformation found in crystal structure of sphingosine bound to SphK1. Collectively, these studies provide insight into the intermolecular interactions in the SphK1 and 2 active sites to achieve maximal dual inhibitory activity.

Sphingosine is able to prevent and eliminate Staphylococcus epidermidis biofilm formation on different orthopedic implant materials in vitro

Abstract

Periprosthetic infection (PPI) is a devastating complication in joint replacement surgery. On the background of an aging population, the number of joint replacements and associated complications is expected to increase. The capability for biofilm formation and the increasing resistance of different microbes to antibiotics have complicated the treatment of PPI, requiring the need for the development of alternative treatment options. The bactericidal effect of the naturally occurring amino alcohol sphingosine has already been reported. In our study, we demonstrate the antimicrobial efficacy of sphingosine on three different strains of biofilm producing Staphylococcus epidermidis, representing one of the most frequent microbes involved in PPI. In an in vitro analysis, sphingosine’s capability for prevention and treatment of biofilm-contamination on different common orthopedic implant surfaces was tested. Coating titanium implant samples with sphingosine not only prevented implant contamination but also revealed a significant reduction of biofilm formation on the implant surfaces by 99.942%. When testing the antimicrobial efficacy of sphingosine on sessile biofilm-grown Staphylococcus epidermidis, sphingosine solution was capable to eliminate 99.999% of the bacteria on the different implant surfaces, i.e., titanium, steel, and polymethylmethacrylate. This study provides evidence on the antimicrobial efficacy of sphingosine for both planktonic and sessile biofilm-grown Staphylococcus epidermidis on contaminated orthopedic implants. Sphingosine may provide an effective and cheap treatment option for prevention and reduction of infections in joint replacement surgery.

Key messages

• Here we established a novel technology for prevention of implant colonization by sphingosine-coating of orthopedic implant materials.

• Sphingosine-coating of orthopedic implants prevented bacterial colonization and significantly reduced biofilm formation on implant surfaces by 99.942%.

• Moreover, sphingosine solution was capable to eliminate 99.999% of sessile biofilm-grown Staphylococcus epidermidis on different orthopedic implant surfaces.

Matrine alleviates astrogliosis through sphingosine 1-phosphate signaling in experimental autoimmune encephalomyelitis

Expression of sphingosine/sphingosine 1-phosphate (SPH/S1P) in resident cells of the central nervous system plays an important role in the pathogenesis of multiple sclerosis (MS). Accumulated evidence has shown the protective effects of S1P receptor modulators on MS and its animal model, experimental autoimmune encephalomyelitis (EAE). However, effective therapies to regulate SPH/S1P molecules themselves have not been well addressed. Our previous studies showed that matrine (MAT), a natural alkaloid component extracted from the Sophora root, has beneficial effects in EAE through immunomodulation. Here we demonstrate that MAT alleviated astrogliosis in the CNS of EAE rats, and downregulated levels of SPH, S1P and S1P1 expression in CNS tissues and astrocytes. Expression of SPH kinases (SPHK) 1 and 2, which splice SPH into S1P, was also inhibited by MAT treatment. In vitro studies showed a direct inhibitory effect of MAT on S1P1 expression of activated astrocytes, suggesting that MAT could function as an S1PRs antagonist. Moreover, MAT upregulated the expression of plasma gelsolin, which combines with S1P to reduce its concentration. These findings indicate that MAT could alleviate astrogliosis in EAE through diminishing the SPH/SPHK/S1P1 pathway.

Sphingosine-coating of plastic surfaces prevents ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a major cause of morbidity and mortality in critically ill patients. Here, we employed the broad antibacterial effects of sphingosine to prevent VAP by developing a novel method of coating surfaces of endotracheal tubes with sphingosine and sphingosine analogs. Sphingosine and phytosphingosine coatings of endotracheal tubes prevent adherence and mediate killing of Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus, even in biofilms. Most importantly, sphingosine-coating of endotracheal tubes also prevented P. aeruginosa and S. aureus pneumonia in vivo. Coating of the tubes with sphingosine was stable, without obvious side effects on tracheal epithelial cells and did not induce inflammation. In summary, we describe a novel method to coat plastic surfaces and provide evidence for the application of sphingosine and phytosphingosine as novel antimicrobial coatings to prevent bacterial adherence and induce killing of pathogens on the surface of endotracheal tubes with potential to prevent biofilm formation and VAP. KEY MESSAGES: Novel dip-coating method to coat plastic surfaces with lipids. Sphingosine and phytosphingosine as novel antimicrobial coatings on plastic surface. Sphingosine coatings of endotracheal tubes prevent bacterial adherence and biofilms. Sphingosine coatings of endotracheal tubes induce killing of pathogens. Sphingosine coatings of endotracheal tubes ventilator-associated pneumonia.

Telmisartan and/or chlorogenic acid attenuates fructose-induced non-alcoholic fatty liver disease in rats: Implications of cross-talk between angiotensin, the sphingosine kinase/sphingoine-1-phosphate pathway, and TLR4 receptors

Renin-angiotensin-aldosterone system (RAS) has been implicated in non-alcoholic fatty liver disease (NAFLD); the most common cause of chronic liver diseases. There is accumulating evidence that altered TLR4 and Sphingosine kinase 1(SphK1)/sphingosine1phosphate (S1P) signaling pathways are key players in the pathogenesis of NAFLD. Cross talk of the sphingosine signaling pathway, toll-4 (TLR4) receptors, and angiotensin II was reported in various tissues. Therefore, the aim of this study was to define the contribution of these two pathways to the hepatoprotective effects of telmisartan and/or chlorogenic acid (CGA) in NAFLD. CGA is a strong antioxidant that was previously reported to inhibit angiotensin converting enzyme. Male Wistar rats were treated with either high-fructose, with or without telmisartan, CGA, telmisartan + CGA for 8 weeks. Untreated NAFL rats showed characteristics of NAFLD, as evidenced by significant increase in the body weight, insulin resistance, and serum hepatotoxicity markers (Alanine and Aspartate transaminases) and lipids as compared to the negative control group, in addition to characteristic histopathological alterations. Treatment with either telmisartan and/or CGA improved aforementioned parameters, in addition to upregulation of antioxidant enzymes (Superoxide dismutase and Glutathione peroxidase). Effect of inhibiting RAS on both sphingosine pathway and TLR4 was evident by the suppressing effect of telmisartan and/or CGA on high fructose-induced upregulation of hepatic SPK1 and S1P, in addition to concomitant up-regulation of Sphingosine-1-Phosphate receptor (S1PR)3 protein level and increased expression of S1PR1 and TLR4. As TLR4 and SPK/S1P signaling pathways play important roles in the progression of liver inflammation, the effect on sphingosine pathway and TLR4 was associated with decreased concentrations of inflammatory markers, enzyme kB kinase (IKK), nuclear factor-kB and tumor necrosis factor-α as compared to untreated NAFL group. In conclusion, the present data strongly suggests the cross-talk between angiotensin, the Sphingosine SPK/S1P Axis and TLR4 Receptors, and their role in the pathogenesis of fructose-induced NAFLD, and the protection afforded by drugs inhibiting RAS.

Chemical and Physicochemical Properties of Gangliosides

In this chapter, we briefly describe the structural features of gangliosides, and focus on the peculiar chemicophysical features of gangliosides, an important class of membrane amphipathic lipids that represent an important driving force determining the organization and properties of cellular membranes.

Acid Sphingomyelinase-Ceramide System in Bacterial Infections

Acid sphingomyelinase hydrolyzes sphingomyelin to ceramide and phosphorylcholine. Ceramide molecules spontaneously interact with each other and generate ceramide-enriched membrane domains. These ceramide-enriched domains further fuse, forming large ceramideenriched platforms that participate in the organization of receptors and in the amplification of signaling molecules. Recent studies have suggested several bacteria and bacterial toxins that stimulate the activation and the translocation of acid sphingomyelinase, which leads to the release of ceramide. The acid sphingomyelinase/ceramide system also regulates the internalization of bacteria into the host cell, the subsequent cytokine release, inflammatory response, and initiation of host cell apoptosis. In addition, ceramide has been implicated in the fusion of phagosomes and lysosomes upon bacterial infection. Thus, this system modulates the reorganization of cell membrane receptors and intracellular signaling molecules during bacteria-host interactions. The acid sphingomyelinase and ceramide system may thus serve as a novel therapeutic target for treating infections.

HPLC-MS/MS Methods for Diacylglycerol and Sphingolipid Molecular Species in Skeletal Muscle

HPLC-MS/MS has enabled the quantitative analysis of complex mixtures of lipid molecular species. Several separate analyses, using methods that have been optimized for individual lipid classes, provide good lipidomic profiles, but may not be desirable for laboratories constrained by available instrumentation and wanting a higher throughput. Here we describe two methods using binary gradient HiLiC HPLC and triple quadrupole MS that together provide a lipidomic profile for lipids of interest in type 2 diabetes research. Methods for analysis of molecular species of diacylglycerol, ceramide, dihydroceramide, sphingosine, glucosyl- and lactosylceramide, sphingomyelin, and acylcarnitine from skeletal muscle and primary culture cells are described.

Bi- and Trifunctional Lipids for Visualization of Sphingolipid Dynamics within the Cell

Investigations into lipid localization and transport are often hampered by a lack of methods and tools to faithfully visualize lipids in the context of living cells, since fluorescent modifications drastically change lipid properties. Here, we describe the use of bifunctional as well as trifunctional sphingosine to reveal its subcellular localization via crosslinking, fixation, and specific staining by click reaction with a fluorophore. Additionally, these probes allow investigations into lipid metabolism as revealed by thin-layer chromatography.

The role of sphingolipids in acute kidney injury

Acute kidney injury (AKI) is most simply defined as the rapid loss of kidney function in a matter of hours to days. AKI can manifest in a number of ways including pre-renal, post-renal, or intrinsic AKI. During acute kidney injury, multiple pathogenic processes are activated including inflammation, cell death, and the generation of reactive oxygen species, just to name a few. Sphingolipids are known to play a role in a number of the pathogenic pathways involved in the pathogenesis of many types of AKI, which suggests a role for sphingolipids in AKI. This short review will discuss the evidence for a role for sphingolipids in AKI.

Neutral ceramidase: Advances in mechanisms, cell regulation, and roles in cancer

Extensive research conducted in the last three decades has identified the roles for the main bioactive sphingolipids, namely ceramide, sphingosine, and sphingosine 1-phosphate (S1P) as key regulators of cellular homeostasis, growth and death. One of the major groups of enzymes in the ceramide pathway, ceramidases, converts ceramide into sphingosine and fatty acids, with sphingosine being further metabolized to S1P. Thus, these enzymes play important roles in the network controlling the functions associated with these bioactive sphingolipids. Among the family of ceramidases, neutral ceramidase (nCDase), which is named according to its optimal pH for catalytic activity, has received increased attention in the last decade. The goal of this review is to provide a brief background on bioactive sphingolipids and the ceramidases. We then describe more recent advances on nCDase, specifically the resolution of its crystal structure and understanding its roles in cell biology and physiology.

Impact of sphingolipids on osteoblast and osteoclast activity in Gaucher disease

Gaucher disease (GD) is an inherited disorder in which mutations in the GBA1 gene lead to deficient β-glucocerebrosidase activity and accumulation of its substrate glucosylceramide. Bone disease is present in around 84% of GD patients, ranging from bone loss including osteopenia and osteonecrosis to abnormal bone remodelling in the form of Erlenmeyer flask formation. The range of severity and variety of types of bone disease found in GD patients indicate the involvement of several mechanisms. Here we investigate the effects of exogenous sphingolipids on osteoclasts, osteoblasts, plasma cells and mesenchymal stem cells (MSC) and the interactions between these cell types. Osteoclasts were differentiated from the peripheral blood of Gaucher patients and control subjects. Osteoblasts were differentiated from mesenchymal stem cells isolated from bone marrow aspirates of Gaucher patients and control subjects. The human osteoblast cell line SaOS-2 was also investigated. Osteoclasts, osteoblasts and a human myeloma plasma cell line NCI-H929 were cultured with relevant exogenous sphingolipids to assess effects on cellular viability and function. Calcium deposition by osteoblasts differentiated from Gaucher patient MSC's was on average only 11.4% of that deposited by control subject osteoblasts. Culture with glucosylsphingosine reduced control subject MSC viability by 10.4%, SaOS-2 viability by 17.4% and plasma cell number by 40%. Culture with glucosylceramide decreased calcium deposition by control MSC-derived osteoblasts while increasing control subject osteoclast generation by 55.6%, Gaucher patient osteoclast generation by 37.6% and plasma cell numbers by up to 29.7%. Excessive osteoclast number and activity and reduced osteoblast activity may have the overall effect of an uncoupling between osteoclasts and osteoblasts in the GD bone microenvironment.

A rapid synthesis of sphingosine from phytosphingosine

A simple and efficient protocol for the synthesis of a sphingosine starting from cost-effective phytosphingosine has been described. Two alternative synthetic pathway have been disclosed based on the use of two different kinds of protective groups for the protection of the amino group in the phytosphingosine. The protected phytosphingosine was subsequently transformed into sphingosine in 5 steps i.e. protection of the amine group, protection of 1,3-diol, leaving group insertion, elimination, and one-pot deprotection.

Novel Sphingolipid-Based Cancer Therapeutics in the Personalized Medicine Era

Sphingolipids are bioactive lipids that participate in a wide variety of biological mechanisms, including cell death and proliferation. The myriad of pro-death and pro-survival cellular pathways involving sphingolipids provide a plethora of opportunities for dysregulation in cancers. In recent years, modulation of these sphingolipid metabolic pathways has been in the forefront of drug discovery for cancer therapeutics. About two decades ago, researchers first showed that standard of care treatments, e.g., chemotherapeutics and radiation, modulate sphingolipid metabolism to increase endogenous ceramides, which kill cancer cells. Strikingly, resistance to these treatments has also been linked to altered sphingolipid metabolism, favoring lipid species that ultimately lead to cell survival. To this end, many inhibitors of sphingolipid metabolism have been developed to further define not only our understanding of these pathways but also to potentially serve as therapeutic interventions. Therefore, understanding how to better use these new drugs that target sphingolipid metabolism, either alone or in combination with current cancer treatments, holds great potential for cancer control. While sphingolipids in cancer have been reviewed previously (Hannun & Obeid, 2018; Lee & Kolesnick, 2017; Morad & Cabot, 2013; Newton, Lima, Maceyka, & Spiegel, 2015; Ogretmen, 2018; Ryland, Fox, Liu, Loughran, & Kester, 2011) in this chapter, we present a comprehensive review on how standard of care therapeutics affects sphingolipid metabolism, the current landscape of sphingolipid inhibitors, and the clinical utility of sphingolipid-based cancer therapeutics.

The cross roles of sphingosine kinase 1/2 and ceramide glucosyltransferase in cell growth and death

Sphingosine-1-phosphate is synthesized by two sphingosine kinases, cytosolic SK1 and nuclear SK2 but SK2 expression was much higher than SK1in mouse skin fibroblasts. However, in SK2^-/- cells, SK1 expression was markedly increased to SK2 levels whereas in SK1^-/- cells, SK2 expression was unaffected. Ceramide, glucosylceramide and sphingosine levels were all increased in SK1^-/- but less so in SK2^-/- cells and S1P levels were not significantly reduced in either SK1^-/- or SK2^-/- cells. Greatly increased Ceramide glucosyltransferase expression was observed in SK1^-/- cells but less so in SK2^-/- cells suggested a role in drug resistance. SK2^-/- cells grew faster than control and SK1^-/-. The cell division gene PCNA was significantly overexpressed in SK2^-/- cells, suggesting a cross regulation between SKs and Ceramide glucosyltransferase.

Shotgun Sphingolipid Analysis of Human Aqueous Humor

This protocol provides a step-by-step guide to shotgun sphingolipid analysis of aqueous humor. We describe the Bligh and Dyer crude lipid extraction method and electrospray ionization tandem mass spectrometry (ESI-MS/MS) coupled with MZmine 2.21 data processing for identification and ratiometric quantitation of sphingosine, sphingosine-1-phosphate, sphingomyelin, and ceramide.

Diet Supplementation with Soy Protein Isolate, but Not the Isoflavone Genistein, Protects Against Alcohol-Induced Tumor Progression in DEN-Treated Male Mice

Diethylnitrosamine-treated male mice were assigned to 4 groups: a casein-based 35% high fat ethanol liquid diet (EtOH), an EtOH diet made with soy protein isolate protein (EtOH/SOY), an EtOH liquid diet supplemented with genistein (EtOH/GEN) and a chow group. EtOH feeding, final concentration 5% (v/v), continued for 16 wks. EtOH increased incidence and multiplicity of basophilic lesions and adenomas compared to the chow group, (p < 0.05). The EtOH/SOY group had reduced adenoma progression when compared to the EtOH and EtOH/GEN group, (p < 0.05). Genistein supplementation had no protective effect. Soy feeding significantly reduced serum ALT concentrations (p < 0.05), decreased hepatic TNFα and CD-14 expression and decreased nuclear accumulation of NFκB protein in EtOH/SOY-treated mice compared to the EtOH group (p < 0.05). With respect to ceramides, high resolution MALDI-FTICR Imaging mass spectrometry revealed changes in the accumulation of long acyl chain ceramide species, in particular C18, in the EtOH group when compared to the EtOH/SOY group. Additionally, expression of acid ceramidase and sphingosine kinase 1 which degrade ceramide into sphingosine and convert sphingosine to sphingosine-1-phosphate (S1P) respectively and expression of S1P receptors S1PR2 and S1PR3 were all upregulated by EtOH and suppressed in the EtOH/SOY group, p < 0.05. EtOH feeding also increased hepatocyte proliferation and mRNA expression of β-catenin targets, including cyclin D1, MMP7 and glutamine synthase, which were reduced in the EtOH/SOY group, p < 0.05. These findings suggest that soy prevents tumorigenesis by reducing inflammation and by reducing hepatocyte proliferation through inhibition of EtOH-mediated β-catenin signaling. These mechanisms may involve blockade of sphingolipid signaling.

Diverse Biological Functions of Sphingolipids in the CNS: Ceramide and Sphingosine Regulate Myelination in Developing Brain but Stimulate Demyelination during Pathogenesis of Multiple Sclerosis

Sphingolipids are enriched in the Central Nervous System (CNS) and display multiple biological functions. They participate in tissue development, cell recognition and adhesion, and act as receptors for toxins. During myelination, a variety of interactive molecules such as myelin basic protein, myelin associated glycoprotein, phospholipids, cholesterol, sphingolipids, etc., participate in a complex fashion. Precise roles of some sphingolipids in myelination still remain unexplored. Our investigation delineated participation of several sphingolipids in myelination during rat brain development as well as in human brain demyelination during pathogenesis of Multiple Sclerosis (MS). These sphingolipids included Ceramide (Cer)/dihydroceramide (dhCer), Sphingosine (Sph)/dihydrosphingosine (dhSph), and glucosyl/galactosylceramide (glc/galCer) as we detected these by column chromatography, high performance thin-layer chromatography, gas chromatography-mass spectrometry, and high-performance liquid chromatography. Cer/dhCer level rises during rat brain development starting at Embryonic stage (E) until postnatal day (P21), then gradually falls until the maturity (P30 and onwards), and remains steady maintaining a constant ratio (4–4.5:1) throughout the brain development. GlcCer is the initial Monoglycosylceramide (MGC) that appears at early Postnatal stage (P8) and then GalCer appears at P10 with an increasing trend until P21 and its concentration remains unaltered. Sph and dhSph profiles show a similar trend with an initial peak at P10 and then a comparatively smaller peak at P21 maintaining a ratio of (2–2.5:1) of Sph:dhSph. The profiles of all these sphingolipids, specifically at P21, clearly indicate their importance during rat brain development but somewhat unspecified roles in myelination. While Cer has been reported to involve in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, Sph being a potent inhibitor of protein kinase C has recently been implicated in CNS demyelination due to MS. Inflammatory cytokines stimulate Sph elevation in MS brains and lead to demyelination due to oligodendrocyte death as we examined by using human oligodendroglioma culture. In conclusions, sphingolipids are essential for brain development but they have deleterious effects in demyelinating diseases such as MS.

Neutrophils Kill Reactive Oxygen Species-Resistant Pseudomonas aeruginosa by Sphingosine

BACKGROUND/AIMS

Cystic fibrosis (CF) is dominated by chronic inflammation and infection of the lung resulting in lung destruction and early death of patients. The lungs of CF patients are characterized by a massive accumulation of neutrophils. It requires definition why these massive numbers of neutrophils fail to eliminate typical CF pathogens like Staphylococcus aureus and Pseudomonas aeruginosa (P. aeruginosa) in CF lungs.

METHODS

We determined ceramide, sphingosine and reactive oxygen species (ROS) in neutrophils from wildtype and CF mice and determined the effect of sphingosine and ROS alone or in combination on killing of different P. aeruginosa strains.

RESULTS

We demonstrate that wildtype neutrophils are able to kill non-mucoid and mucoid clinical P. aeruginosa strains, while neutrophils from CF mice are insufficient to kill these P. aeruginosa strains, although both types of neutrophils infected with P. aeruginosa produce comparable levels of superoxide. All three analyzed P. aeruginosa strains are resistant to reactive oxygen species. The inability of CF neutrophils to kill P. aeruginosa is caused by a marked decrease of surface sphingosine levels in CF neutrophils. Wildtype neutrophils contain much higher concentrations of surface sphingosine than CF neutrophils. Further, wildtype neutrophils, but not CF neutrophils, release sphingosine, most likely as microparticles, upon infection. Sphingosine kills P. aeruginosa in vitro at low micromolar concentrations. Reconstitution of sphingosine in CF neutrophils restores their ability to kill these pathogens, demonstrating the significance of sphingosine for bacterial killing.

CONCLUSION

The data provide evidence for a new paradigm explaining how neutrophils kill ROS-resistant P. aeruginosa, i.e. by sphingosine that kills P. aeruginosa at low concentrations. This mechanism is defective in CF neutrophils.

Inflammatory responses in Multiple Sclerosis normal-appearing white matter and in non-immune mediated neurological conditions with wallerian axonal degeneration: A comparative study

Inflammatory-like changes in the white matter (WM) are commonly observed in conditions of axonal degeneration by different etiologies. This study is a systematic comparison of the principal features of the inflammatory-like changes in the WM in different pathological conditions characterized by axonal damage/degeneration, focusing in particular on Multiple Sclerosis (MS) normal-appearing white matter (NAWM) compared to non immune-mediated disorders. The study was performed on sections of NAWM from 15 MS cases, 11 cases of non immune-mediated disorders with wallerian axonal degeneration (stroke, trauma, amyotrophic lateral sclerosis), 3 cases of viral encephalitis, 6 control cases. Common features of the inflammatory-like changes observed in all of the conditions of WM pathology were diffuse endothelial expression of VCAM-1, microglial activation with expression of M2 markers, increased expression of sphingosine receptors. Inflammation in MS NAWM was characterized, compared to non immune-mediated conditions, by higher VCAM-1 expression, higher density of perivascular lymphocytes, focal perivascular inflammation with microglial expression of M1 markers, ongoing acute axonal damage correlating with VCAM-1 expression but not with microglia activation. Inflammatory changes in MS NAWM share all the main features observed in the WM in non immune-mediated conditions with wallerian axonal degeneration (with differences to a large extent more quantitative than qualitative), but with superimposition of disease-specific perivascular inflammation and ongoing acute axonal damage.

Sphingosine rescues aged mice from pulmonary pseudomonas infection

BACKGROUND

Bacterial lung infection is a leading cause of death for those 65 y or older, often requiring intensive care unit admission and mechanical ventilation, which consumes considerable health care resources. Although administration of antibiotics is the standard of care for bacterial pneumonia, its overuse has led to the emergence of multidrug resistant organisms. Therefore, alternative strategies to help minimize the effects of bacterial pneumonia in the elderly are necessary. As studies have shown that sphingosine (SPH) has inherent bacterial killing properties, our goal was to assess whether it could act as a prophylactic treatment to protect aged mice from pulmonary infection by Pseudomonas aeruginosa.

METHODS

Aged (51 wk) and young (8 wk) C57Bl/6 mice were used in this study. Pulmonary SPH levels were determined by histology. SPH content of microparticles was quantified using a SPH kinase assay. Pneumonia was induced by intranasally treating mice with 10⁶ Colony Forming Unit (CFU) P aeruginosa. Microparticles were isolated from young mice, whereas some were further incubated with SPH.

RESULTS

We observed that SPH levels are reduced in the bronchial epithelial cells as well as the bronchoalveolar lavage microparticles isolated from aged mice, which correlates with a susceptibility to infection. We demonstrate that SPH or microparticle treatment can protect aged mice from pulmonary P aeruginosa infection. Finally, we observed that enriching microparticles with SPH before treatment eliminated the bacterial load in P aeruginosa-infected aged mice.

CONCLUSIONS

These data suggest that prophylactic treatment with SPH could reduce lung bacterial infections for the at-risk elderly population.

Ceramide synthase 2 deficiency aggravates AOM-DSS-induced colitis in mice: role of colon barrier integrity

Loss of intestinal barrier functions is a hallmark of inflammatory bowel disease like ulcerative colitis. The molecular mechanisms are not well understood, but likely involve dysregulation of membrane composition, fluidity, and permeability, which are all essentially regulated by sphingolipids, including ceramides of different chain length and saturation. Here, we used a loss-of-function model (CerS2^+/+ and CerS2^-/- mice) to investigate the impact of ceramide synthase 2, a key enzyme in the generation of very long-chain ceramides, in the dextran sodium salt (DSS) evoked model of UC. CerS2^-/- mice developed more severe disease than CerS2^+/+ mice in acute DSS and chronic AOM/DSS colitis. Deletion of CerS2 strongly reduced very long-chain ceramides (Cer24:0, 24:1) but concomitantly increased long-chain ceramides and sphinganine in plasma and colon tissue. In naive CerS2^-/- mice, the expression of tight junction proteins including ZO-1 was almost completely lost in the colon epithelium, leading to increased membrane permeability. This could also be observed in vitro in CerS2 depleted Caco-2 cells. The increase in membrane permeability in CerS2^-/- mice did not manifest with apparent clinical symptoms in naive mice, but with slight inflammatory signs such as an increase in monocytes and IL-10. AOM/DSS and DSS treatment alone led to a further deterioration of membrane integrity and to severe clinical symptoms of the disease. This was associated with stronger upregulation of cytokines in CerS2^-/- mice and increased infiltration of the colon wall by immune cells, particularly monocytes, CD4⁺ and Th17⁺ T-cells, and an increase in tumor burden. In conclusion, CerS2 is crucial for the maintenance of colon barrier function and epithelial integrity. CerS2 knockdown, and associated changes in several sphingolipids such as a drop in very long-chain ceramides/(dh)-ceramides, an increase in long-chain ceramides/(dh)-ceramides, and sphinganine in the colon, may weaken endogenous defense against the endogenous microbiome.

Sphingosine's role in epithelial host defense: A natural antimicrobial and novel therapeutic

Sphingosine is a natural sphingolipid found in membranes of all eukaryotic cells. In addition to its functions in cell signaling, sphingosine has broad-spectrum antimicrobial properties. Sphingosine's role as an antimicrobial is important in tissues such as the skin and respiratory epithelium. Reduction in the normal sphingosine level is associated with problems related to infection susceptibility. Therefore, exogenous sphingosine may be an effective antimicrobial therapeutic. Inhaled nebulized sphingosine has been shown to be effective at both preventing and treating pneumonia in multiple mouse models. We now show that inhaled sphingosine has low toxicity to the respiratory system, strengthening its case as an excellent candidate for a novel inhaled antimicrobial drug.

Cangrelor-Mediated Cardioprotection Requires Platelets and Sphingosine Phosphorylation

In animal models platelet P2Y12 receptor antagonists put the heart into a protected state, not as a result of suppressed thrombosis but rather through protective signaling, similar to that for ischemic postconditioning. While both ischemic postconditioning and the P2Y12 blocker cangrelor protect blood-perfused hearts, only the former protects buffer-perfused hearts indicating that the blocker requires a blood-borne constituent or factor to protect. We used an anti-platelet antibody to make thrombocytopenic rats to test if that factor resides within the platelet. Infarct size was measured in open-chest rats subjected to 30-min ischemia/2-h reperfusion. Infarct size was not different in thrombocytopenic rats showing that preventing aggregation alone is not protective. While ischemic preconditioning could reduce infarct size in thrombocytopenic rats, the P2Y12 inhibitor cangrelor could not, indicating that it protects by interacting with some factor in the platelet. Ischemic preconditioning is known to require phosphorylation of sphingosine. In rats treated with dimethylsphingosine to block sphingosine kinase, cangrelor was no longer protective. Thus cangrelor's protective mechanism appears to also involve sphingosine kinase revealing yet another similarity to conditioning's mechanism.