Simultaneous quantitation of sphingoid bases and their phosphates in biological samples by liquid chromatography/electrospray ionization tandem mass spectrometry

Neuroprotective potential of Erigeron bonariensis ethanolic extract against ovariectomized/D-galactose-induced memory impairments in female rats in relation to its metabolite fingerprint as revealed using UPLC/MS

Erigeron bonariensis is widely distributed throughout the world's tropics and subtropics. In folk medicine, E. bonariensis has historically been used to treat head and brain diseases. Alzheimer's disease (AD) is the most widespread form of dementia initiated via disturbances in brain function. Herein, the neuroprotective effect of the chemically characterized E. bonariensis ethanolic extract is reported for the first time in an AD animal model. Chemical profiling was conducted using UPLC-ESI-MS analysis. Female rats underwent ovariectomy (OVX) followed by 42 days of D-galactose (D-Gal) administration (150 mg/kg/day, i.p) to induce AD. The OVX/D-Gal-subjected rats received either donepezil (5 mg/kg/day) or E. bonariensis at 50, 100, and 200 mg/kg/day, given 1 h prior to D-Gal. UPLC-ESI-MS analysis identified 42 chemicals, including flavonoids, phenolic acids, terpenes, and nitrogenous constituents. Several metabolites, such as isoschaftoside, casticin, velutin, pantothenic acid, xanthurenic acid, C18-sphingosine, linoleamide, and erucamide, were reported herein for the first time in Erigeron genus. Treatment with E. bonariensis extract mitigated the cognitive decline in the Morris Water Maze test and the histopathological alterations in cortical and hippocampal tissues of OVX/D-Gal-subjected rats. Moreover, E. bonariensis extract mitigated OVX/D-Gal-induced Aβ aggregation, Tau hyperphosphorylation, AChE activity, neuroinflammation (NF-κBp65, TNF-α, IL-1β), and apoptosis (Cytc, BAX). Additionally, E. bonariensis extract ameliorated AD by increasing α7-nAChRs expression, down-regulating GSK-3β and FOXO3a expression, and modulating Jak2/STAT3/NF-ĸB p65 and PI3K/AKT signaling cascades. These findings demonstrate the neuroprotective and memory-enhancing effects of E. bonariensis extract in the OVX/D-Gal rat model, highlighting its potential as a promising candidate for AD management.

Development of an advanced liquid chromatography-tandem mass spectrometry measurement system for simultaneous sphingolipid analysis

Mass spectrometry-based lipidomics approaches offer valuable tools for the detection and quantification of various lipid species, including sphingolipids. The present study aimed to develop a new method to simultaneously detect various sphingolipid species that applies to diverse biological samples. We developed and validated a measurement system by employing a single-column liquid chromatography-mass spectrometry system utilizing a normal-phase separation mode with positive ionization. The measurement system provided precision with a coefficient of variant below 20% for sphingolipids in all types of samples, and we observed good linearity in diluted serum samples. This system can measure the following sphingolipids: sphingosine 1-phosphate (S1P), sphingosine (Sph), dihydroS1P (dhS1P), dihydroSph (dhSph), ceramide 1-phosphate (Cer1P), hexosylceramide (HexCer), lactosylceramide (LacCer), dh-ceramide, deoxy-ceramide, deoxy-dh-ceramide, and sphingomyelin (SM). By measuring these sphingolipids in cell lysates where S1P lyase expression level was modulated, we could observe significant and dynamic modulations of sphingolipids in a comprehensive manner. Our newly established and validated measurement system can simultaneously measure many kinds of sphingolipids in biological samples. It holds great promise as a valuable tool for laboratory testing applications to detect overall modulations of sphingolipids, which have been proposed to be involved in pathogenesis processes in a series of elegant basic research studies.

Sphingadienine-1-phosphate levels are regulated by a novel glycoside hydrolase family 1 glucocerebrosidase widely distributed in seed plants

Long-chain base phosphates (LCBPs) such as sphingosine-1-phosphate and phytosphingosine-1-phosphate function as abscisic acid (ABA)-mediated signaling molecules that regulate stomatal closure in plants. Recently, a glycoside hydrolase family 1 (GH1) β-glucosidase, Os3BGlu6, was found to improve drought tolerance by stomatal closure in rice, but the biochemical functions of Os3BGlu6 have remained unclear. Here we identified Os3BGlu6 as a novel GH1 glucocerebrosidase (GCase) that catalyzes the hydrolysis of glucosylceramide to ceramide. Phylogenetic and enzymatic analyses showed that GH1 GCases are widely distributed in seed plants and that pollen or anthers of all seed plants tested had high GCase activity, but activity was very low in ferns and mosses. Os3BGlu6 had high activity for glucosylceramides containing (4E,8Z)-sphingadienine, and GCase activity in leaves, stems, roots, pistils, and anthers of Os3BGlu6-deficient rice mutants was completely absent relative to that of wild-type rice. The levels of ceramides containing sphingadienine were correlated with GCase activity in each rice organ and were significantly lower in Os3BGlu6-deficient rice mutants than in the wild type. The levels of LCBPs synthesized from ceramides, especially the levels of sphingadienine-1-phosphate, were also correlated with GCase activity in each rice organ and were significantly lower in Os3BGlu6-deficient rice mutants than in the wild type. These results indicate that Os3BGlu6 regulates the level of ceramides containing sphingadienine, influencing the regulation of sphingadienine-1-phosphate levels and subsequent improvement of drought tolerance via stomatal closure in rice.

Lithium Hydroxide Hydrolysis Combined with MALDI TOF Mass Spectrometry for Rapid Sphingolipid Detection

Sphingolipids have diverse structural and bioactive functions that play important roles in many key biological processes. Factors such as low relative abundance, varied structures, and a dynamic concentration range provide a difficult analytical challenge for sphingolipid detection. To further improve mass-spectrometry-based sphingolipid analysis, lithium adduct consolidation was implemented to decrease spectral complexity and combine signal intensities, leading to increased specificity and sensitivity. We report the use of lithium hydroxide as a base in a routine hydrolysis procedure in order to effectively remove common ionization suppressants (such as glycolipids and glycerophospholipids) and introduce a source of lithium into the sample. In conjunction, an optimized MALDI matrix system, featuring 2',4',6'-trihydroxyacetophenone (THAP) is used to facilitate lithium adduct consolidation during the MALDI process. The result is a robust and high-throughput sphingolipid detection scheme, particularly of low-abundance ceramides. Application of our developed workflow includes the detection of differentially expressed liver sphingolipid profiles from a high-fat-induced obesity mouse model. We also demonstrate the method's effectiveness in detecting various sphingolipids in brain and plasma matrices. These results were corroborated with data from UHPLC HR MS/MS and MALDI FT-ICR, verifying the efficacy of the method application. Overall, we demonstrate a high-throughput workflow for sphingolipid analysis in various biological matrices by the use of MALDI TOF and lithium adduct consolidation.

Mechanism of sphingosine 1-phosphate clearance from blood

The interplay of sphingosine 1-phosphate (S1P) synthetic and degradative enzymes as well as S1P exporters creates concentration gradients that are a fundamental to S1P biology. Extracellular S1P levels, such as in blood and lymph, are high relative to cellular S1P. The blood-tissue S1P gradient maintains endothelial integrity while local S1P gradients influence immune cell positioning. Indeed, the importance of S1P gradients was recognized initially when the mechanism of action of an S1P receptor agonist used as a medicine for multiple sclerosis was revealed to be inhibition of T-lymphocytes' recognition of the high S1P in efferent lymph. Furthermore, the increase in erythrocyte S1P in response to hypoxia influences oxygen delivery during high altitude acclimatization. However, understanding of how S1P gradients are maintained is incomplete. For example, S1P is synthesized but is only slowly metabolized by blood yet circulating S1P turns over quickly by an unknown mechanism. Prompted by the counterintuitive observation that blood S1P increases markedly in response to inhibition S1P synthesis (by sphingosine kinase 2 (SphK2)), we studied mice wherein several tissues were made deficient in either SphK2 or S1P degrading enzymes. Our data reveal a mechanism whereby S1P is de-phosphorylated at the hepatocyte surface and the resulting sphingosine is sequestered by SphK phosphorylation and in turn degraded by intracellular S1P lyase. Thus, we identify the liver as the primary site of blood S1P clearance and provide an explanation for the role of SphK2 in this process. Our discovery suggests a general mechanism whereby S1P gradients are shaped.

High-endothelial cell-derived S1P regulates dendritic cell localization and vascular integrity in the lymph node

While the sphingosine-1-phosphate (S1P)/sphingosine-1-phosphate receptor-1 (S1PR1) axis is critically important for lymphocyte egress from lymphoid organs, S1PR1-activation also occurs in vascular endothelial cells (ECs), including those of the high-endothelial venules (HEVs) that mediate lymphocyte immigration into lymph nodes (LNs). To understand the functional significance of the S1P/S1PR1-G_i axis in HEVs, we generated Lyve1;Spns2^Δ/Δ conditional knockout mice for the S1P-transporter Spinster-homologue-2 (SPNS2), as HEVs express LYVE1 during development. In these mice HEVs appeared apoptotic and were severely impaired in function, morphology and size; leading to markedly hypotrophic peripheral LNs. Dendritic cells (DCs) were unable to interact with HEVs, which was also observed in Cdh5^CRE-ERT2;S1pr1^Δ/Δ mice and wildtype mice treated with S1PR1-antagonists. Wildtype HEVs treated with S1PR1-antagonists in vitro and Lyve1-deficient HEVs show severely reduced release of the DC-chemoattractant CCL21 in vivo. Together, our results reveal that EC-derived S1P warrants HEV-integrity through autocrine control of S1PR1-G_i signaling, and facilitates concomitant HEV-DC interactions.

Measurement of the Spatial Distribution of S1P in Small Quantities of Tissues: Development and Application of a Highly Sensitive LC-MS/MS Method Combined with Laser Microdissection

Sphingosine-1-phosphate (S1P) acts as an extracellular signaling molecule with diverse biological functions. Tissues appear to have an S1P gradient, which is functionally relevant in the biological significance of S1P, although its existence has not been measured directly. Here, we report a highly sensitive method to determine the distribution of S1P, using a column-switching LC-MS/MS system combined with laser microdissection (LMD). Column switching using narrow core Capcell Pak C18 analytical and trap columns with 0.3 mm inner diameter improved the performance of the LC-MS/MS system. The calibration curve of S1P showed good linearity (r>0.999) over the range of 0.05–10 nM (1–200 fmol/injection). The accuracy of the method was confirmed by measuring S1P-spiked laser microdissected mice tissue sections. To evaluate our S1P analytical method, we quantified S1P extracted from micro-dissected mouse brain and spleen. These results show that this method can measure low S1P concentrations and determine S1P distribution in tissue microenvironments.

Facile determination of sphingolipids under alkali condition using metal-free column by LC-MS/MS

Extraction and analysis of sphingolipids from biological samples is a critical step in lipidomics, especially for minor species such as sphingoid bases and sphingosine-1-phosphate. Although several liquid chromatography-mass spectrometry methods enabling the determination of sphingolipid molecular species have been reported, they were limited in analytical sensitivity and reproducibility by causing significant peak tailing, especially by the presence of phosphate groups, and most of the extraction techniques are laborious and do not cover a broad range of sphingolipid metabolites. In this study, we developed a rapid single-phase extraction and highly sensitive analytical method for the detection and quantification of sphingolipids (including phosphates) comprehensively using liquid chromatography-triple quadruple mass spectrometry. After validating the reliability of the method, we analyzed the intestinal tissue sphingolipids of germ-free (GF) and specific pathogen-free (SPF) mice and found significantly higher levels of free sphingoid bases and sphingosine-1-phosphate in the GF condition as compared to the SPF condition. This method enables a rapid extraction and highly sensitive determination of sphingolipids comprehensively at low femtomolar ranges. Graphical abstract Diagrammatic comparision of sphingolipid (phosphates) analysis between conventional and this method.

Determination of Sphingosine-1-Phosphate in Human Plasma Using Liquid Chromatography Coupled with Q-Tof Mass Spectrometry

Evidence suggests that high-density lipoprotein (HDL) components distinct from cholesterol, such as sphingosine-1-phosphate (S1P), may account for the anti-atherothrombotic effects attributed to this lipoprotein. The current method for the determination of plasma levels of S1P as well as levels associated with HDL particles is still cumbersome an assay method to be worldwide practical. Recently, a simplified protocol based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the sensitive and specific quantification of plasma levels of S1P with good accuracy has been reported. This work utilized a triple quadrupole (QqQ)-based LC-MS/MS system. Here we adapt that method for the determination of plasma levels of S1P using a quadrupole time of flight (Q-Tof) based LC-MS system. Calibration curves were linear in the range of 0.05 to 2 µM. The lower limit of quantification (LOQ) was 0.05 µM. The concentration of S1P in human plasma was determined to be 1 ± 0.09 µM (n = 6). The average accuracy over the stated range of the method was found to be 100 ± 5.9% with precision at the LOQ better than 10% when predicting the calibration standards. The concentration of plasma S1P in the prepared samples was stable for 24 h at room temperature. We have demonstrated the quantification of plasma S1P using Q-Tof based LC-MS with very good sensitivity, accuracy, and precision that can used for future studies in this field.

Metabolites involved in cellular communication among human cumulus-oocyte-complex and sperm during in vitro fertilization

BACKGROUND

Fertilization is a key physiological process for the preservation of the species. Consequently, different mechanisms affecting the sperm and the oocyte have been developed to ensure a successful fertilization. Thus, sperm acrosome reaction is necessary for the egg coat penetration and sperm-oolema fusion. Several molecules are able to induce the sperm acrosome reaction; however, this process should be produced coordinately in time and in the space to allow the success of fertilization between gametes. The goal of this study was to analyze the metabolites secreted by cumulus-oocyte-complex (COC) to find out new components that could contribute to the induction of the human sperm acrosome reaction and other physiological processes at the time of gamete interaction and fertilization.

METHODS

For the metabolomic analysis, eighteen aliquots of medium were used in each group, containing: a) only COC before insemination and after 3 h of incubation; b) COC and capacitated spermatozoa after insemination and incubated for 16-20 hours; c) only capacitated sperm after 16-20 h in culture and d) only fertilization medium as control. Six patients undergoing assisted reproduction whose male partners provided normozoospermic samples were included in the study. Seventy-two COC were inseminated.

RESULTS

The metabolites identified were monoacylglycerol (MAG), lysophosphatidylcholine (LPC) and phytosphingosine (PHS). Analysis by PCR and in silico of the gene expression strongly suggests that the cumulus cells contribute to the formation of the PHS and LPC.

CONCLUSIONS

LPC and PHS are secreted by cumulus cells during in vitro fertilization and they could be involved in the induction of human acrosome reaction (AR). The identification of new molecules with a paracrine effect on oocytes, cumulus cells and spermatozoa will provide a better understanding of gamete interaction.

Quantification of sphingosine 1-phosphate by validated LC-MS/MS method revealing strong correlation with apolipoprotein M in plasma but not in serum due to platelet activation during blood coagulation

Sphingosine 1-phosphate (S1P) is a signalling sphingolipid affecting multiple cellular functions of vascular and immune systems. It circulates at submicromolar levels bound to HDL-associated apolipoprotein M (apoM) or to albumin. S1P in blood is mainly produced by platelets and erythrocytes, making blood sampling for S1P quantification delicate. Standardisation of sampling is thereby of great importance to obtain robust data. By optimising and characterising the extraction procedure and the LC-MS/MS analysis, we have developed and validated a highly specific and sensitive method for S1P quantification. Blood was collected from healthy individuals (n = 15) to evaluate the effects of differential blood sampling on S1P levels. To evaluate correlation between S1P and apoM in different types of plasma and serum, apoM was measured by ELISA. The method showed good accuracy and precision in the range of 0.011 to 0.9 μM with less than 0.07 % carryover. We found that the methanol precipitation used to extract S1P co-extracted apoM and several other HDL-proteins from plasma. The platelet-associated S1P was released during coagulation, thus increasing the S1P concentration to double in serum as compared to that in plasma. Gel filtration chromatography revealed that the platelet-released S1P was mainly bound to albumin. This explains why the strong correlation between S1P and apoM levels in plasma is lost upon the clotting process and hence not observed in serum. We have developed, characterised and validated an efficient, highly sensitive and specific method for the quantification of S1P in biological material.

Maternal and Zygotic Sphingosine Kinase 2 Are Indispensable for Cardiac Development in Zebrafish

Sphingosine 1-phosphate (S1P) is synthesized from sphingosine by sphingosine kinases (SPHK1 and SPHK2) in invertebrates and vertebrates, whereas specific receptors for S1P (S1PRs) selectively appear in vertebrates, suggesting that S1P acquires novel functions in vertebrates. Because the developmental functions of SPHK1 and SPHK2 remain obscure in vertebrates, we generated sphk1 or sphk2 gene-disrupted zebrafish by introducing premature stop codons in their coding regions using transcription activator-like effector nucleases. Both zygotic sphk1 and sphk2 zebrafish mutants exhibited no obvious developmental defects and grew to adults. The maternal-zygotic sphk2 mutant (MZsphk2), but not the maternal-zygotic sphk1 mutant and maternal sphk2 mutant, had a defect in the cardiac progenitor migration and a concomitant decrease in S1P level, leading to a two-heart phenotype (cardia bifida). Cardia bifida in MZsphk2, which was rescued by injecting sphk2 mRNA, was a phenotype identical to that of zygotic mutants of the S1P transporter spns2 and S1P receptor s1pr2, indicating that the Sphk2-Spns2-S1pr2 axis regulates the cardiac progenitor migration in zebrafish. The contribution of maternally supplied lipid mediators during vertebrate organogenesis presents as a requirement for maternal-zygotic Sphk2.

Simultaneous Quantification of Sphingolipids in Small Quantities of Liver by LC-MS/MS

Sph, S1P, and Cer, derived from the membrane sphingolipids, act as intracellular and intercellular mediators, involved in various (path) physiological functions. Accordingly, determining the distributions and concentrations of these sphingolipid mediators in body tissues is an important task. Consequently, a method for determination of sphingolipids in small quantities of tissue is required. Sphingolipids analysis has been dependent on improvements in mass spectrometry (MS) technology. Additionally, decomposition of sphingosine-1-phosphate (S1P) in the tissue samples before preparation for MS has hindered analysis. In the present study, a method for stabilization of liver samples before MS preparation was developed using a heat stabilizer (Stabilizor™ T1). Then, a LC-MS/MS method using a triple-quadrupole mass spectrometer with a C8 column was developed for simultaneous determination of sphingolipids in small quantities of liver specimens. This method showed good separation and validation results. Separation was performed with a gradient elution of solvent A (5 mmol L(-1) ammonium formate in water, pH 4.0) and solvent B (5 mmol L(-1) ammonium formate in 95% acetonitrile, pH 4.0) at 300 μL min(-1). The lower limit of quantification was less than 132 pmol L(-1), and this method was accurate (∼13.5%) and precise (∼7.13%) for S1P analysis. The method can be used to show the tissue distribution of sphingolipids.

Lipid Analysis of Airway Epithelial Cells for Studying Respiratory Diseases

Airway epithelial cells play an important role in the pathogenesis of inflammatory lung diseases such as asthma, cystic fibrosis and COPD. Studies concerning the function of the lipid metabolism of the airway epithelium are so far based only on the detection of lipids by immunohistochemistry but quantitative analyses have not been performed. Although recent advances in mass spectrometry have allowed to identify a variety of lipid classes simultaneously in isolated tissue samples, up until now, these methods were not suitable to analyze lipids in the airway epithelium. To determine all major lipid classes in airway epithelial cells, we used an LC-MS-based approach that can easily be combined with the specific isolation procedure to obtain epithelial cells. We tested the suitability of this method with a mouse model of experimental asthma. In response to allergen challenge, perturbations in the sphingolipids were detected, which led to increased levels of ceramides. We expanded the scope of this approach analysing human bronchus samples without pathological findings of adenocarcinoma patients. For the human lung epithelium an unusual lipid class distribution was found in which ceramide was the predominant sphingolipid. In summary, we show that disease progression and lipid metabolism perturbation can be monitored in animal models and that the method can be used for the analysis of clinical samples.

Separation and quantification of 2-acyl-1-lysophospholipids and 1-acyl-2-lysophospholipids in biological samples by LC-MS/MS

Lysophospholipids (LysoGPs) serve as lipid mediators and precursors for synthesis of diacyl phospholipids (GPs). LysoGPs detected in cells have various acyl chains attached at either the sn-1 or sn-2 position of the glycerol backbone. In general, acyl chains at the sn-2 position of 2-acyl-1-LysoGPs readily move to the sn-1 position, generating 1-acyl-2-lyso isomers by a nonenzymatic reaction called intra-molecular acyl migration, which has hampered the detection of 2-acyl-1-LysoGPs in biological samples. In this study, we developed a simple and versatile method to separate and quantify 2-acyl-1- and 1-acyl-2-LysoGPs. The main point of the method was to extract LysoGPs at pH 4 and 4°C, conditions that were found to completely eliminate the intra-molecular acyl migration. Under the present conditions, the relative amounts of 2-acyl-1-LysoGPs and 1-acyl-2-LysoGPs did not change at least for 1 week. Further, in LysoGPs extracted from cells and tissues under the present conditions, most of the saturated fatty acids (16:0 and 18:0) were found in the sn-1 position of LysoGPs, while most of the PUFAs (18:2, 20:4, 22:6) were found in the sn-2 position. Thus the method can be used to elucidate the in vivo role of 2-acyl-1-LysoGPs.

Transcription repressor Bach2 is required for pulmonary surfactant homeostasis and alveolar macrophage function

Pulmonary alveolar proteinosis (PAP) results from a dysfunction of alveolar macrophages (AMs), chiefly due to disruptions in the signaling of granulocyte macrophage colony-stimulating factor (GM-CSF). We found that mice deficient for the B lymphoid transcription repressor BTB and CNC homology 2 (Bach2) developed PAP-like accumulation of surfactant proteins in the lungs. Bach2 was expressed in AMs, and Bach2-deficient AMs showed alterations in lipid handling in comparison with wild-type (WT) cells. Although Bach2-deficient AMs showed a normal expression of the genes involved in the GM-CSF signaling, they showed an altered expression of the genes involved in chemotaxis, lipid metabolism, and alternative M2 macrophage activation with increased expression of Ym1 and arginase-1, and the M2 regulator Irf4. Peritoneal Bach2-deficient macrophages showed increased Ym1 expression when stimulated with interleukin-4. More eosinophils were present in the lung and peritoneal cavity of Bach2-deficient mice compared with WT mice. The PAP-like lesions in Bach2-deficient mice were relieved by WT bone marrow transplantation even after their development, confirming the hematopoietic origin of the lesions. These results indicate that Bach2 is required for the functional maturation of AMs and pulmonary homeostasis, independently of the GM-CSF signaling.