Metabolism and functional effects of sphingolipids in blood cells

Sphingosine-1-phosphate signalling in the heart: exploring emerging perspectives in cardiopathology

Cardiometabolic disorders contribute to the global burden of cardiovascular diseases. Emerging sphingolipid metabolites like sphingosine-1-phosphate (S1P) and its receptors, S1PRs, present a dynamic signalling axis significantly impacting cardiac homeostasis. S1P's intricate mechanisms extend to its transportation in the bloodstream by two specific carriers: high-density lipoprotein particles and albumin. This intricate transport system ensures the accessibility of S1P to distant target tissues, influencing several physiological processes critical for cardiovascular health. This review delves into the diverse functions of S1P and S1PRs in both physiological and pathophysiological conditions of the heart. Emphasis is placed on their diverse roles in modulating cardiac health, spanning from cardiac contractility, angiogenesis, inflammation, atherosclerosis and myocardial infarction. The intricate interplays involving S1P and its receptors are analysed concerning different cardiac cell types, shedding light on their respective roles in different heart diseases. We also review the therapeutic applications of targeting S1P/S1PRs in cardiac diseases, considering existing drugs like Fingolimod, as well as the prospects and challenges in developing novel therapies that selectively modulate S1PRs.

Acute Cannabis Administration Transiently Reduces Mitochondrial DNA in Young Adults: Findings from a Secondary Analysis of a Double-Blind, Placebo-Controlled, Randomized Clinical Trial

Background: Cannabis is one of the world's most commonly used substances; however, many questions remain unanswered as to how cannabis impacts the body. Recently, there has been a resurgence of research into the effects of plant-derived cannabinoids on mitochondrial health. In particular, a number of studies implicate mitochondrial-Δ9-tetrahydrocannabinol (Δ9-THC) interactions with altered memory, metabolism, and catalepsy in mice. Although the research in this field is expanding rapidly, there is little known about the effects of cannabis on mitochondria health in human subjects either in acute or chronic term use. Methods: Blood samples were obtained from a double-blind, placebo-controlled, parallel-group randomized clinical trial in which adults who regularly use cannabis (1-4 days/week) aged 19-25 years were randomized 2:1 to receive either an active (12.5% Δ9-THC) cigarette or placebo (<0.01% Δ9-THC) cigarette containing 750 mg of cannabis before driving simulator testing. DNA was extracted from whole blood using commercial spin columns, followed by measurement of mt-ND1, mt-ND4, and β2M using quantitative polymerase chain reaction. One-way repeated measures analysis of variance (ANOVA) followed by Dunnett's multiple comparisons test was used to observe changes in mitochondrial DNA (mtDNA) copy number over time. A two-tailed Pearsons R test was used to assess correlations between mtDNA copy number and cannabinoid levels (Δ9-THC and metabolites) in blood. Results: We found that exposure to active cannabis containing Δ9-THC, as opposed to placebo, was associated with an acute reduction in mitochondrial DNA copy number in whole blood at 15 min and 1 h after smoking. The observed decrease in mtDNA copy number negatively correlated with blood concentrations of 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) and 11-Nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH), the two primary metabolites of Δ9-THC, but not Δ9-THC itself. Further, the negative correlation between 11-OH THC and THC-COOH concentrations and mtDNA copy number was found in only a subgroup of participants who use cannabis infrequently, suggesting a tolerance effect. Conclusions: These results illuminate mitochondrial alterations attributed to Δ9-THC consumption, which may be mediated by metabolites. These results appear to suggest stronger effects in individuals who consume cannabis less frequently, suggesting some form of tolerance to the effects of Δ9-THC and its metabolites on mtDNA content in whole blood. Keywords: Mitochondria; mtDNA; cannabis; THC; THC metabolites; blood; THC-COOH; 11-OH-THC.

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.

The Role of Obesity, Inflammation and Sphingolipids in the Development of an Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the vessel equal to or exceeding 3 cm. It is a disease with a long preclinical period commonly without any symptoms in its initial stage. Undiagnosed for years, aneurysm often leads to death due to vessel rupture. The basis of AAA pathogenesis is inflammation, which is often associated with the excess of adipose tissue, especially perivascular adipose tissue, which synthesizes adipocytokines that exert a significant influence on the formation of aneurysms. Pro-inflammatory cytokines such as resistin, leptin, and TNFα have been shown to induce changes leading to the formation of aneurysms, while adiponectin is the only known compound that is secreted by adipose tissue and limits the development of aneurysms. However, in obesity, adiponectin levels decline. Moreover, inflammation is associated with an increase in the amount of macrophages infiltrating adipose tissue, which are the source of matrix metalloproteinases (MMP) involved in the degradation of the extracellular matrix, which are an important factor in the formation of aneurysms. In addition, an excess of body fat is associated with altered sphingolipid metabolism. It has been shown that among sphingolipids, there are compounds that play an opposite role in the cell: ceramide is a pro-apoptotic compound that mediates the development of inflammation, while sphingosine-1-phosphate exerts pro-proliferative and anti-inflammatory effects. It has been shown that the increase in the level of ceramide is associated with a decrease in the concentration of adiponectin, an increase in the concentration of TNFα, MMP-9 and reactive oxygen species (which contribute to the apoptosis of vascular smooth muscle cell). The available data indicate a potential relationship between obesity, inflammation and disturbed sphingolipid metabolism with the formation of aneurysms; therefore, the aim of this study was to systematize the current knowledge on the role of these factors in the pathogenesis of abdominal aortic aneurysm.

An overview of ozanimod as a therapeutic option for adults with moderate-to-severe active ulcerative colitis

INTRODUCTION

Ulcerative colitis (UC) is a chronic inflammatory condition of the gastrointestinal tract involving a dysregulated immune response. Sphingosine-1-phosphate (S1P) is involved in immune cell regulation. S1P-receptor modulators, such as ozanimod, inhibit lymphocyte migration and have therapeutic potential in UC.

AREAS COVERED

Ozanimod is the first S1P-receptor modulator approved for the treatment of UC. It acts as a functional antagonist, causing internalization of S1P receptors on T-cells. Lymphocyte egress from lymph nodes is inhibited, and migration to sites of active inflammation is curtailed. There are several S1P-receptor subtypes, present in various organs, which inform understanding of ozanimod's side-effect profile including bradycardia and macular edema. In this review, the authors discuss the mechanism of action, pharmacokinetics, clinical efficacy, and safety profile of ozanimod in the treatment of patients with moderate-to-severe UC.

EXPERT OPINION

The S1P-receptor modulator ozanimod is an oral small molecule with a rapid onset of action and a novel therapeutic mechanism in the treatment of UC. It is an effective treatment both in bio-naïve and bio-exposed patients. Although the safety profile of ozanimod looks favorable, more long-term data are needed. Further studies are required to compare ozanimod to currently available therapies to best define its positioning in UC treatment algorithms.

Sphingolipids in HDL - Potential markers for adaptation to pregnancy?

Plasma high density lipoprotein (HDL) exhibits many functions that render it an effective endothelial protective agent and may underlie its potential role in protecting the maternal vascular endothelium during pregnancy. In non-pregnant individuals, the HDL lipidome is altered in metabolic disease compared to healthy individuals and is linked to reduced cholesterol efflux, an effect that can be reversed by lifestyle management. Specific sphingolipids such as sphingosine-1-phosphate (S1P) have been shown to mediate the vaso-dilatory effects of plasma HDL via interaction with the endothelial nitric oxide synthase pathway. This review describes the relationship between plasma HDL and vascular function during healthy pregnancy and details how this is lost in pre-eclampsia, a disorder of pregnancy associated with widespread endothelial dysfunction. Evidence of a role for HDL sphingolipids, in particular S1P and ceramide, in cardiovascular disease and in healthy pregnancy and pre-eclampsia is discussed. Available data suggest that HDL-S1P and HDL-ceramide can mediate vascular protection in healthy pregnancy but not in preeclampsia. HDL sphingolipids thus are of potential importance in the healthy maternal adaptation to pregnancy.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

Permissive Modulation of Sphingosine-1-Phosphate-Enhanced Intracellular Calcium on BKCa Channel of Chromaffin Cells

Sphingosine-1-phosphate (S1P), is a signaling sphingolipid which acts as a bioactive lipid mediator. We assessed whether S1P had multiplex effects in regulating the large-conductance Ca²⁺-activated K⁺ channel (BK_Ca) in catecholamine-secreting chromaffin cells. Using multiple patch-clamp modes, Ca²⁺ imaging, and computational modeling, we evaluated the effects of S1P on the Ca²⁺-activated K⁺ currents (I_K(Ca)) in bovine adrenal chromaffin cells and in a pheochromocytoma cell line (PC12). In outside-out patches, the open probability of BK_Ca channel was reduced with a mean-closed time increment, but without a conductance change in response to a low-concentration S1P (1 µM). The intracellular Ca²⁺ concentration (Ca_i) was elevated in response to a high-dose (10 µM) but not low-dose of S1P. The single-channel activity of BK_Ca was also enhanced by S1P (10 µM) in the cell-attached recording of chromaffin cells. In the whole-cell voltage-clamp, a low-dose S1P (1 µM) suppressed I_K(Ca), whereas a high-dose S1P (10 µM) produced a biphasic response in the amplitude of I_K(Ca), i.e., an initial decrease followed by a sustained increase. The S1P-induced I_K(Ca) enhancement was abolished by BAPTA. Current-clamp studies showed that S1P (1 µM) increased the action potential (AP) firing. Simulation data revealed that the decreased BK_Ca conductance leads to increased AP firings in a modeling chromaffin cell. Over a similar dosage range, S1P (1 µM) inhibited I_K(Ca) and the permissive role of S1P on the BK_Ca activity was also effectively observed in the PC12 cell system. The S1P-mediated I_K(Ca) stimulation may result from the elevated Ca_i, whereas the inhibition of BK_Ca activity by S1P appears to be direct. By the differentiated tailoring BK_Ca channel function, S1P can modulate stimulus-secretion coupling in chromaffin cells.

Red Blood Cell Count: An Unrecognized Risk Factor for Nonalcoholic Fatty Liver Disease

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is becoming a global public health challenge. A convenient NAFLD indicator will greatly facilitate risk appraisal and prevention. As a readily available and inexpensive hematological index in routine clinical examinations, red blood cells (RBCs) are gaining increasing attention in many diseases, such as metabolic syndrome, but their association with NAFLD is unknown.

METHODS

This health management cohort study included 27,112 subjects (17,383 non-NAFLD and 9,729 NAFLD) with up to 5 years of follow-up (median 2.8 years). NAFLD was diagnosed by ultrasonography. NAFLD severity was categorized as mild, moderate, or severe. The generalized estimation equation (GEE), an extension of generalized linear models that allows for analysis of repeated measurements, was used to analyze the association between RBC count and NAFLD.

RESULTS

Overall, 4,332 of 17,383 (24.9%) subjects without NAFLD at baseline developed NAFLD. Incident NAFLD risk was positively associated with RBC count. After adjustment for hemoglobin and other confounders, the risk of incident NAFLD was 21%, 32%, and 51% higher in the second, third, and fourth RBC count quartiles, respectively, than in the lowest quartile. In 1,798 of 9,476 (19.0%) subjects with NAFLD at baseline, the severity of NAFLD increased. NAFLD progression risk increased progressively as RBC count increased (P for trend < 0.001). Every one-unit (10¹² cells/L) increase in RBC count was associated with a 53% [OR 1.53 (95% CI 1.32-1.77)] increased risk for NAFLD progression.

CONCLUSIONS

Elevated RBC count was independently associated with a high risk of NAFLD incidence and progression. This finding revealed a convenient NAFLD risk indicator.

Emerging roles of lysophospholipids in health and disease

Lipids are abundant and play essential roles in human health and disease. The main functions of lipids are building blocks for membrane biogenesis. However, lipids are also metabolized to produce signaling molecules. Here, we discuss the emerging roles of circulating lysophospholipids. These lysophospholipids consist of lysoglycerophospholipids and lysosphingolipids. They are both present in cells at low concentration, but their concentrations in extracellular fluids are significantly higher. The biological functions of some of these lysophospholipids have been recently revealed. Remarkably, some of the lysophospholipids play pivotal signaling roles as well as being precursors for membrane biogenesis. Revealing how circulating lysophospholipids are produced, released, transported, and utilized in multi-organ systems is critical to understand their functions. The discovery of enzymes, carriers, transporters, and membrane receptors for these lysophospholipids has shed light on their physiological significance. In this review, we summarize the biological roles of these lysophospholipids via discussing about the proteins regulating their functions. We also discuss about their potential impacts to human health and diseases.

The role of sphingosine 1-phosphate and its receptors in cardiovascular diseases

There are many different types of cardiovascular diseases, which impose a huge economic burden due to their extremely high mortality rates, so it is necessary to explore the underlying mechanisms to achieve better supportive and curative care outcomes. Sphingosine 1‐phosphate (S1P) is a bioactive lipid mediator with paracrine and autocrine activities that acts through its cell surface S1P receptors (S1PRs) and intracellular signals. In the circulatory system, S1P is indispensable for both normal and disease conditions; however, there are very different views on its diverse roles, and its specific relevance to cardiovascular pathogenesis remains elusive. Here, we review the synthesis, release and functions of S1P, specifically detail the roles of S1P and S1PRs in some common cardiovascular diseases, and then address several controversial points, finally, we focus on the development of S1P‐based therapeutic approaches in cardiovascular diseases, such as the selective S1PR1 modulator amiselimod (MT‐1303) and the non‐selective S1PR1 and S1PR3 agonist fingolimod, which may provide valuable insights into potential therapeutic strategies for cardiovascular diseases.

Secrets and lyase: Control of sphingosine 1-phosphate distribution

The signaling lipid sphingosine 1-phosphate (S1P) plays key roles in many physiological processes. In the immune system, S1P's best-described function is to draw cells out of tissues into circulation. Here, we will review models of S1P distribution in the thymus, lymph nodes, spleen, and nonlymphoid tissues. These models have been challenging to construct, because of the lack of tools to map lipid gradients. Nonetheless, evidence to date suggests that S1P distribution is exquisitely tightly controlled, and that concentrations of signaling-available S1P cannot be predicted by standard rules of thumb. The fine regulation of S1P gradients may explain how S1P can simultaneously direct multiple cell movements both between tissues and circulation and within tissues. It may also make it feasible to develop drugs that enable spatially specific modulation of S1P signaling.

Sphingolipids in Alzheimer's disease, how can we target them?

Altered levels of sphingolipids and their metabolites in the brain, and the related downstream effects on neuronal homeostasis and the immune system, provide a framework for understanding mechanisms in neurodegenerative disorders and for developing new intervention strategies. In this review we will discuss: the metabolites of sphingolipids that function as second messengers; and functional aberrations of the pathway resulting in Alzheimer's disease (AD) pathophysiology. Focusing on the central product of the sphingolipid pathway ceramide, we describ approaches to pharmacologically decrease ceramide levels in the brain and we argue on how the sphingolipid pathway may represent a new framework for developing novel intervention strategies in AD. We also highlight the possible use of clinical and non-clinical drugs to modulate the sphingolipid pathway and sphingolipid-related biological cascades.

Sphingolipid signaling modulates trans-endothelial cell permeability in dengue virus infected HMEC-1 cells

Dengue has emerged as a major mosquito-borne disease in the tropics and subtropics. In severe dengue, enhanced microvascular endothelial permeability leads to plasma leakage. Direct dengue virus (DENV) infection in human microvascular endothelial cells (HMEC-1) can enhance trans-endothelial leakage. Using a microarray-based analysis, we identified modulation of key endothelial cell signaling pathways in DENV-infected HMEC-1 cells. One among them was the sphingolipid pathway that regulates vascular barrier function. Sphingosine-1-phosphate receptor 2 (S1PR2) and S1PR5 showed significant up-regulation in the microarray data. In DENV-infected cells, the kinetics of S1PR2 transcript expression and enhanced in vitro trans-endothelial permeability showed a correlation. We also observed an internalization and cytoplasmic translocation of VE-Cadherin, a component of adherens junctions (AJ), upon infection indicating AJ disassembly. Further, inhibition of S1PR2 signaling by a specific pharmacological inhibitor prevented translocation of VE-Cadherin, thus helping AJ maintenance, and abrogated DENV-induced trans-endothelial leakage. Our results show that sphingolipid signaling, especially that involving S1PR2, plays a critical role in vascular leakage in dengue.

Sphingolipids and Redox Signaling in Renal Regulation and Chronic Kidney Diseases

Significance: Sphingolipids play critical roles in the membrane biology and intracellular signaling events that influence cellular behavior and function. Our review focuses on the cellular mechanisms and functional relevance of the cross talk between sphingolipids and redox signaling, which may be critically implicated in the pathogenesis of different renal diseases. Recent Advances: Reactive oxygen species (ROS) and sphingolipids can regulate cellular redox homeostasis through the regulation of NADPH oxidase, mitochondrial integrity, nitric oxide synthase (NOS), and antioxidant enzymes. Over the last two decades, there have been significant advancements in the field of sphingolipid research, and it was in 2010 for the first time that sphingolipid receptor modulator was exploited as a therapeutic in humans. The cross talk of sphingolipids with redox signaling pathways becomes an important mechanism in the development of many different diseases such as renal diseases. Critical Issues: The critical issues to be addressed in this review are how sphingolipids interact with the redox signaling pathway to regulate renal function and even result in chronic kidney diseases. Ceramide, sphingosine, and sphingosine-1-phosphate (S1P) as main signaling sphingolipids are discussed in more detail. Future Directions: Although sphingolipids and ROS may mediate or modulate cellular responses to physiological and pathological stimuli, more translational studies and mechanistic pursuit in a tissue- or cell-specific way are needed to enhance our understanding of this important topic and to develop effective therapeutic strategies to treat diseases associated with redox signaling and sphingolipid cross talk. Antioxid. Redox Signal. 28, 1008-1026.

MFSD2B is a sphingosine 1-phosphate transporter in erythroid cells

Sphingosine 1-phosphate (S1P) is an intercellular signaling molecule present in blood. Erythrocytes have a central role in maintaining the S1P concentration in the blood stream. We previously demonstrated that S1P is exported from erythrocytes by a glyburide-sensitive S1P transporter. However, the gene encoding the S1P transporter in erythrocytes is unknown. In this study, we found that the mouse erythroid cell line, MEDEP-E14, has S1P export activity and exhibits properties that are consistent with those of erythrocytes. Using microarray analysis of MEDEP-E14 cells and its parental cell line, E14TG2a, we identified several candidate genes for S1P export activity. Of those genes, only one gene, Mfsd2b, showed S1P transport activity. The properties of S1P release by MFSD2B were similar to those in erythrocytes. Moreover, knockout of MFSD2B in MEDEP-E14 cells decreased S1P export from the cells. These results strongly suggest that MFSD2B is a novel S1P transporter in erythroid cells.

Lysophospholipids in laboratory medicine

Lysophospholipids (LPLs), such as lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), and lysophosphatidylserine (LysoPS), are attracting attention as second-generation lipid mediators. In our laboratory, the functional roles of these lipid mediators and the mechanisms by which the levels of these mediators are regulated in vivo have been studied. Based on these studies, the clinical introduction of assays for LPLs and related proteins has been pursued and will be described in this review. Although assays of these lipids themselves are possible, autotaxin (ATX), apolipoprotein M (ApoM), and phosphatidylserine-specific phospholipase A₁ (PS-PLA₁) are more promising as alternate biomarkers for LPA, S1P, and LysoPS, respectively. Presently, ATX, which produces LPA through its lysophospholipase D activity, has been shown to be a useful laboratory test for the diagnosis and staging of liver fibrosis, whereas PS-PLA₁ and ApoM are considered to be promising clinical markers reflecting the in vivo actions induced by LysoPS and S1P.

The balance between Gαi-Cdc42/Rac and Gα12/13-RhoA pathways determines endothelial barrier regulation by sphingosine-1-phosphate

The bioactive sphingosine-1-phosphatephosphate (S1P) is present in plasma, bound to carrier proteins, and involved in many physiological processes, including angiogenesis, inflammatory responses, and vascular stabilization. S1P can bind to several G-protein-coupled receptors (GPCRs) activating a number of different signaling networks. At present, the dynamics and relative importance of signaling events activated immediately downstream of GPCR activation are unclear. To examine these, we used a set of fluorescence resonance energy transfer-based biosensors for different RhoGTPases (Rac1, RhoA/B/C, and Cdc42) as well as for heterotrimeric G-proteins in a series of live-cell imaging experiments in primary human endothelial cells. These experiments were accompanied by biochemical GTPase activity assays and transendothelial resistance measurements. We show that S1P promotes cell spreading and endothelial barrier function through S1PR1-Gαi-Rac1 and S1PR1-Gαi-Cdc42 pathways. In parallel, a S1PR2-Gα12/13-RhoA pathway is activated that can induce cell contraction and loss of barrier function, but only if Gαi-mediated signaling is suppressed. Our results suggest that Gαq activity is not involved in S1P-mediated regulation of barrier integrity. Moreover, we show that early activation of RhoA by S1P inactivates Rac1 but not Cdc42, and vice versa. Together, our data show that the rapid S1P-induced increase in endothelial integrity is mediated by a S1PR1-Gαi-Cdc42 pathway.

Eryptosis in health and disease: A paradigm shift towards understanding the (patho)physiological implications of programmed cell death of erythrocytes

During the course of their natural ageing and upon injury, anucleate erythrocytes can undergo an unconventional apoptosis-like cell death, termed eryptosis. Eryptotic erythrocytes display a plethora of morphological alterations including volume reduction, membrane blebbing and breakdown of the membrane phospholipid asymmetry resulting in phosphatidylserine externalization which, in turn, mediates their phagocytic recognition and clearance from the circulation. Overall, the eryptosis machinery is tightly orchestrated by a wide array of endogenous mediators, ion channels, membrane receptors, and a host of intracellular signaling proteins. Enhanced eryptosis shortens the lifespan of circulating erythrocytes and confers a procoagulant phenotype; this phenomenon has been tangibly implicated in the pathogenesis of anemia, deranged microcirculation, and increased prothrombotic risk associated with a multitude of clinical conditions. Herein, we reviewed the molecular mechanisms dictating eryptosis and erythrophagocytosis and critically analyzed the current evidence leading to the pathophysiological ramifications of eryptotic cell death in the context of human disease.

Fluorescence-based rapid measurement of sphingosine-1-phosphate transport activity in erythrocytes

Sphingosine-1-phosphate (S1P) is present in the blood plasma and acts as a pivotal intercellular signal transmitter in the immune system by recruiting lymphocytes from the thymus and secondary lymphoid tissues. The plasma S1P concentration is maintained by the supply of S1P from erythrocytes. Previously, we showed that S1P release from erythrocytes is mediated by an ATP-dependent transporter. In this study, we attempted to establish a rapid and reliable method for measuring the S1P transport activity in erythrocytes by using a fluorescent S1P analog, 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD)-labeled S1P. NBD-S1P was released from erythrocytes in a time-dependent manner. The NBD-S1P release was reduced after exposure to glyburide, which is an inhibitor of the S1P transporter in erythrocytes. Moreover, the release of NBD-S1P and S1P from erythrocytes was competitively inhibited by intracellular S1P and NBD-S1P, respectively. These results showed that the erythrocyte S1P transporter exports NBD-S1P. We optimized the sample-preparation conditions and lipid extraction to increase the sensitivity of the assay. Furthermore, we successfully measured NBD-S1P release without lipid extraction by decreasing the concentration of BSA in the assay buffer to 0.1%. This method will be useful for the high-throughput screening of S1P transporter inhibitors using conventional fluorometers.

Sphingosine-1-phosphate restores endothelial barrier integrity in ovarian hyperstimulation syndrome

STUDY QUESTION

Are follicular fluid (FF) sphingosine-1-phosphate (S1P) levels in patients at risk of developing ovarian hyperstimulation syndrome (OHSS) altered and in part responsible for the high vascular permeability observed in these patients.

STUDY ANSWER

FF S1P levels are lower in FF from patients at risk of OHSS and treatment with S1P may reduce vascular permeability in these patients.

WHAT IS KNOWN ALREADY

Although advances have been made in the diagnosis, and management of OHSS and in basic knowledge of its development, complete prevention has proven difficult.

STUDY DESIGN, SIZE, DURATION

A total of 40 FF aspirates were collected from patients undergoing ART. The women (aged 25-39 years old) were classified into a control group (n = 20) or a group at risk of OHSS (n = 20). The EA.hy926 endothelial cell line was used to assess the efffects of FF from patients at risk of OHSS with or without the addition of S1P. An animal model that develops OHSS in immature Sprague-Dawley rats were also used.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Migration assays, confocal microscopy analysis of actin filaments, immunoblotting and quail chorioallantoic membrane (CAM) assays of in-vivo angiogenesis were performed and statistical comparisons between groups were made.

MAIN RESULTS AND THE ROLE OF CHANCE

The S1P concentration was significantly lower in FF from patients at risk of OHSS (P = 0.03). The addition of S1P to this FF decreased cell migration (P < 0.05) and prevented VE-cadherin phosphorylation in endothelial cells (P < 0.05). S1P in the FF from patients at risk of OHSS increased the levels of VE-cadherin (P < 0.05), N-cadherin (P < 0.05) and β-catenin (P < 0.05), and partially reversed actin redistribution in endothelial cells. The addition of S1P in FF from patients at risk of OHSS also decreased the levels of vascular endothelial growth factor (VEGF₁₂₁; P < 0.01) and S1P lyase (SPL; P < 0.05) and increased the levels of S1PR1 (P < 0.05) in endothelial cells. In CAMs incubated with FF from patients at risk of OHSS with S1P, the number of vessel branch points decreased while the periendothelial cell coverage increased. Additionally, in a rat OHSS model, we demonstrated that vascular permeability and VEGF₁₂₁ and its receptor KDR expression were increased in the OHSS group compared to the control group and that S1P administration decreased these parameters.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The results of this study were generated from an in-vitro system. This model reflects the microvasculature in vivo. Even though the ideal model would be the use of human endothelial cells from the ovary, it is obviously not possible to carry out this kind of approach in ovaries of patients from ART. More studies will be necessary to delineate the effects of S1P in the pathogenesis of OHSS. Hence, clinical studies are needed in order to choose the most appropriate method of prevention and management.

WIDER IMPLICATIONS OF THE FINDINGS

The use of bioactive sphingolipid metabolites may contribute to finding better and safer therapeutic strategies for the treatment of OHSS and other human diseases that display aberrant vascular leakage.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants ANPCyT (PICT 2012-897), CONICET (PIP 5471), Roemmers and Baron Foundation, Argentina. The authors declare no conflict of interest.

Platelet-derived sphingosine-1-phosphate and inflammation: from basic mechanisms to clinical implications

Beyond key functions in hemostasis and thrombosis, platelets are recognized as key players of inflammation, an underlying feature of a variety of diseases. In this regard, platelets act as a circulating source of several pro- and anti-inflammatory molecules, which are secreted from their intracellular stores upon activation. Among them, mounting evidence highlights a crucial role of sphingosine-1-phosphate (S1P), a multifunctional sphingoid mediator. S1P-induced pleiotropic effects include those crucial in inflammatory processes, such as the maintenance of the endothelial barrier integrity, and leukocyte activation and recruitment at the injured site. This review outlines the peculiar features and molecular mechanisms that allow platelets for acting as a unique factory that produces and stores S1P in large quantities. A particular emphasis is placed on the autocrine and paracrine roles of S1P derived from the "inflamed" platelets, highlighting the role of its cross-talk with endothelial and blood cells involved in inflammation, and the mechanisms of its contribution to the development and progression of inflammatory diseases. Finally, potential clinical implications of platelet-derived S1P as diagnostic tool of inflammatory severity, and as therapeutic target in inflammation are discussed.

Reduction of ceramide de novo synthesis in solid tissues changes sphingolipid levels in rat plasma, erythrocytes and platelets

PURPOSE

De novo sphingolipid synthesis does not occur in plasma, erythrocytes and platelets. The purpose of the study was to examine the effect of inhibition of sphingolipid synthesis in solid tissues on the level of the following bioactive sphingolipids: sphinganine, ceramide, sphingosine and sphingosine 1-phosphate in plasma, erythrocytes and platelets.

MATERIAL/METHODS

The experiments were carried out on male Wistar rats. Myriocin was used to inhibit serine palmitoyltransferase activity (the enzyme catalyzes the first step of ceramide de novo synthesis) and nicotinic acid was used to reduce the concentration of plasma free fatty acids (a substrate for the de novo ceramide synthesis). The sphingolipids were quantified by means of liquid chromatography/mass spectrometry.

RESULTS

Myriocin reduced the level of each compound in plasma. It reduced the level of sphinganine, sphingosine-1-phosphate and total ceramide and elevated the level of sphingosine in erythrocytes. In platelets, myriocin reduced the total level of ceramide. Nicotinic acid reduced the plasma level of sphinganine, sphingosine and total ceramide. It increased the level of sphingosine-1-phosphate in erythrocytes. In platelets, nicotinioc acid increased the level of sphinganine and sphingosine and reduced the level of sphingosine-1-phosphate and total ceramide.

CONCLUSIONS

Inhibition of serine palmitoyltransferase activity in solid tissues and reduction in plasma free fatty acids concentration affects sphingolipid level in plasma, erythrocytes and platelets. The changes in erythrocytes and platelets depend both on the cell type and the sphingolipid studied and only partially follow the changes in the plasma.

Evidence for fumonisin inhibition of ceramide synthase in humans consuming maize-based foods and living in high exposure communities in Guatemala

SCOPE

Fumonisin (FB) occurs in maize and is an inhibitor of ceramide synthase (CerS). We determined the urinary FB1 (UFB1 ) and sphingoid base 1-phosphate levels in blood from women consuming maize in high and low FB exposure communities in Guatemala.

METHODS AND RESULTS

FB1 intake was estimated using the UFB1 . Sphinganine 1-phosphate (Sa 1-P), sphingosine 1-phosphate (So 1-P), and the Sa 1-P/So 1-P ratio were determined in blood spots collected on absorbent paper at the same time as urine collection. In the first study, blood spots and urine were collected every 3 months (March 2011 to February 2012) from women living in low (Chimaltenango and Escuintla) and high (Jutiapa) FB exposure communities (1240 total recruits). The UFB1 , Sa 1-P/So 1-P ratio, and Sa 1-P/mL in blood spots were significantly higher in the high FB1 intake community compared to the low FB1 intake communities. The results were confirmed in a follow-up study (February 2013) involving 299 women living in low (Sacatepéquez) and high (Santa Rosa and Chiquimula) FB exposure communities.

CONCLUSIONS

High levels of FB1 intake are correlated with changes in Sa 1-P and the Sa 1-P/So 1-P ratio in human blood in a manner consistent with FB1 inhibition of CerS.

Sources, metabolism, and regulation of circulating sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that acts either as an intracellular messenger or as a ligand for its membrane receptors. S1P is a normal constituent of blood, where it is found both in plasma and blood cells. Compared with other cell types, sphingolipid metabolism in erythrocytes and platelets has unique features that allow the erythrocytes and platelets to accumulate S1P. In plasma, S1P is bound mainly to HDLs and albumin. Of note, metabolism and biological activity of S1P is to a large extent affected by the type of its carrier. Plasma S1P is characterized by a short half-life, indicating rapid clearance by degradative enzymes and the presence of high-capacity sources involved in maintaining its high concentration. These sources include blood cells, vascular endothelium, and hepatocytes. However, the extent to which each of these contributes to the plasma pool of S1P is a matter of debate. Circulating S1P plays a significant physiological role. It was found to be the key regulator of lymphocyte trafficking, endothelial barrier function, and vascular tone. The purpose of this review is to summarize the present state of knowledge on the metabolism, transport, and origin of plasma S1P, and to discuss the mechanisms regulating its homeostasis in blood.

A blood spot method for detecting fumonisin-induced changes in putative sphingolipid biomarkers in LM/Bc mice and humans

Fumonisins (FB) are mycotoxins found in maize. They are hypothesised risk factors for neural tube defects (NTDs) in humans living where maize is a dietary staple. In LM/Bc mice, FB1-treatment of pregnant dams induces NTDs and results in increased levels of sphingoid base 1-phosphates in blood and tissues. The increased level of sphingoid base 1-phosphates in blood is a putative biomarker for FB1 inhibition of ceramide synthase in humans. Collection of blood spots on paper from finger sticks is a relatively non-invasive way to obtain blood for biomarker analysis. The objective of this study was to develop and validate in an animal model, and ultimately in humans, a method to estimate the volume of blood collected as blood spots on absorbent paper so as to allow quantification of the molar concentration of sphingoid base 1-phosphates in blood. To accomplish this objective, blood was collected from unexposed male LM/Bc and FB1-exposed pregnant LM/Bc mice and humans and applied to two types of absorbent paper. The sphingoid base 1-phosphates, absorbance at 270 nm (A270), and total protein content (Bradford) were determined in the acetonitrile:water 5% formic acid extracts from the dried blood spots. The results show that in both mouse and human the A270, total protein, and blood volume were closely correlated and the volume of blood spotted was accurately estimated using only the A270 of the extracts. In mouse blood spots, as in tissues and embryos, the FB1-induced changes in sphingolipids were correlated with urinary FB1. The half-life of FB1 in the urine was short (<24 h) and the elevation in sphingoid base 1-phosphates in blood was also short, although more persistent than the urinary FB1.

Elevated adenosine signaling via adenosine A2B receptor induces normal and sickle erythrocyte sphingosine kinase 1 activity

Erythrocyte possesses high sphingosine kinase 1 (SphK1) activity and is the major cell type supplying plasma sphingosine-1-phosphate, a signaling lipid regulating multiple physiological and pathological functions. Recent studies revealed that erythrocyte SphK1 activity is upregulated in sickle cell disease (SCD) and contributes to sickling and disease progression. However, how erythrocyte SphK1 activity is regulated remains unknown. Here we report that adenosine induces SphK1 activity in human and mouse sickle and normal erythrocytes in vitro. Next, using 4 adenosine receptor-deficient mice and pharmacological approaches, we determined that the A2B adenosine receptor (ADORA2B) is essential for adenosine-induced SphK1 activity in human and mouse normal and sickle erythrocytes in vitro. Subsequently, we provide in vivo genetic evidence that adenosine deaminase (ADA) deficiency leads to excess plasma adenosine and elevated erythrocyte SphK1 activity. Lowering adenosine by ADA enzyme therapy or genetic deletion of ADORA2B significantly reduced excess adenosine-induced erythrocyte SphK1 activity in ADA-deficient mice. Finally, we revealed that protein kinase A-mediated extracellular signal-regulated kinase 1/2 activation functioning downstream of ADORA2B underlies adenosine-induced erythrocyte SphK1 activity. Overall, our findings reveal a novel signaling network regulating erythrocyte SphK1 and highlight innovative mechanisms regulating SphK1 activity in normal and SCD.

Dose-dependent effect of aspirin on the level of sphingolipids in human blood

PURPOSE

Aspirin is an antiplatelet drug which is commonly used in secondary prevention in ischemic heart disease and cerebrovascular events, and in newly diagnosed myocardial infarction. The aim of the present study was to examine effect of aspirin on the level of selected sphingolipid intermediates in plasma, erythrocytes and platelets.

MATERIAL AND METHOD

Forty two healthy volunteers participated in the study. They were divided into two groups. In one group aspirin was given orally, daily, for one week in a dose of 75 mg (n=25). The subjects from the second group received one 300 mg dose of the drug (n=17). In both groups the blood was taken 4h after the last dose of aspirin. The following sphingolipid intermediates were quantified using high-pressure liquid chromatography: sphinganine, sphingosine, sphingosine-1-phosphate (S1P), sphinganine-1-phosphate (SA1P) and ceramide.

RESULTS

It was found that lower dose of aspirin increased the level of S1P and ceramide in erythrocytes (by 23 and 37%, respectively) having no effect on plasma and platelet sphingolipid levels. Higher dose of the drug reduced S1P and SA1P concentration in the plasma (by 16 and 10%, respectively).

CONCLUSION

We conclude that aspirin interferes with sphingolipid metabolism in blood and that this effect depends on a dose of the drug. Since S1P is a potent cardioprotectant, the reduction in its plasma concentration after the loading dose of aspirin could be undesired side effect of the drug.

Integrin α9 on lymphatic endothelial cells regulates lymphocyte egress

Sphingosine 1-phosphate (S1P) plays a role in lymphocyte egress from lymphoid organs. However, it remains unclear how S1P production and secretion are regulated. We show that under inflammatory conditions, α9 integrin, which is closely associated with activated β1 integrin, and its ligand, tenascin-C, colocalize on medullary and cortical sinuses of draining lymph nodes (dLNs), which is a gate for lymphocyte exit, and that inhibition of lymphocyte egress is evident by blockade of α9 integrin-mediated signaling at dLNs. Based on in vitro analysis using lymphatic endothelial cells obtained from mice embryos, we suggested the possibility that stimulation of lymphatic endothelial cells by tenascin-C enhances S1P secretion in an α9 integrin-dependent manner without affecting S1P synthesis and/or degradation. Blockade of α9 integrin-mediated signaling reduced lymphocyte egress from dLNs in several models, including experimental autoimmune encephalomyelitis, where it improved clinical scores and pathology. Therefore, manipulating α9 integrin function may offer a therapeutic strategy for treating various inflammatory disorders.

Export of sphingosine-1-phosphate and cancer progression

Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that promotes cell survival, proliferation, migration, angiogenesis, lymphangiogenesis, and immune response; all are critical processes of cancer progression. Although some important roles of intracellular S1P have recently been uncovered, the majority of its biological effects are known to be mediated via activation of five specific G protein-coupled receptors [S1P receptor (S1PR)1-S1PR5] located on the cell surface. Secretion of S1P produced inside cells by sphingosine kinases can then signal through these receptors in autocrine, paracrine, and/or endocrine manners, coined "inside-out" signaling of S1P. Numerous studies suggest that secreted S1P plays important roles in cancer progression; thus, understanding the mechanism by which S1P is exported out of cells, particularly cancer cells, is both interesting and important. Here we will review the current understanding of the transport of S1P out of cancer cells and its potential roles in the tumor microenvironment.

Sphingosine-1-phosphate: a master regulator of lymphocyte egress and immunity

Sphingosine-1-phosphate (S1P) is a central factor responsible for lymphocyte distribution in the body. S1P is able to control the integrity of various effector cell populations within many lymphoid tissues by directing lymphocyte egress. In this review, we give an overview of the generation and degradation of S1P in specific lymphoid microenvironments. Furthermore, we discuss, sometimes contradictory, the functions of the five S1P receptors on different cells in diverse tissues and give an idea of additional counteracting chemotactic signals for lymphocyte immigration and emigration. We focus special attention to recent discoveries of S1P-specific transporters, like spinster-homolog-2 and the active secretion of S1P by endothelial cells, erythrocytes and platelets. In addition, we describe the microanatomical structures as well as entry and egress routes into lymphoid organs which lymphocytes use for efficient trafficking. Finally, we give an overview of open questions regarding the regulation of lymphocyte homing from primary lymphoid organs to secondary lymphoid organs and back again.

Barrier enhancing signals in pulmonary edema

Increased endothelial permeability and reduction of alveolar liquid clearance capacity are two leading pathogenic mechanisms of pulmonary edema, which is a major complication of acute lung injury, severe pneumonia, and acute respiratory distress syndrome, the pathologies characterized by unacceptably high rates of morbidity and mortality. Besides the success in protective ventilation strategies, no efficient pharmacological approaches exist to treat this devastating condition. Understanding of fundamental mechanisms involved in regulation of endothelial permeability is essential for development of barrier protective therapeutic strategies. Ongoing studies characterized specific barrier protective mechanisms and identified intracellular targets directly involved in regulation of endothelial permeability. Growing evidence suggests that, although each protective agonist triggers a unique pattern of signaling pathways, selected common mechanisms contributing to endothelial barrier protection may be shared by different barrier protective agents. Therefore, understanding of basic barrier protective mechanisms in pulmonary endothelium is essential for selection of optimal treatment of pulmonary edema of different etiology. This article focuses on mechanisms of lung vascular permeability, reviews major intracellular signaling cascades involved in endothelial monolayer barrier preservation and summarizes a current knowledge regarding recently identified compounds which either reduce pulmonary endothelial barrier disruption and hyperpermeability, or reverse preexisting lung vascular barrier compromise induced by pathologic insults.

Molecular and physiological functions of sphingosine 1-phosphate transporters

Sphingosine 1-phosphate (S1P) is a lipid mediator that plays important roles in diverse cellular functions such as cell proliferation, differentiation and migration. S1P is synthesized inside the cells and subsequently released to the extracellular space, where it binds to specific receptors that are located on the plasma membranes of target cells. Accumulating recent evidence suggests that S1P transporters including SPNS2 mediate S1P release from the cells and are involved in the physiological functions of S1P. In this review, we discuss recent advances in our understanding of the mechanism and physiological functions of S1P transporters. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Sphingolipids in lung endothelial biology and regulation of vascular integrity

Of the multiple and diverse homeostatic events that involve the lung vascular endothelium, participation in preserving vascular integrity and therefore organ function is paramount. We were the first to show that the lipid growth factor and angiogenic factor, sphingosine-1-phosphate, is a critical agonist involved in regulation of human lung vascular barrier function (Garcia et al. J Clin Invest, 2011). Utilizing both in vitro models and preclinical murine, rat, and canine models of acute and chronic inflammatory lung injury, we have shown that S1Ps, as well as multiple S1P analogues such as FTY720 and ftysiponate, serve as protective agents limiting the disruption of the vascular EC monolayer in the pulmonary microcirculation and attenuate parenchymal accumulation of inflammatory cells and high protein containing extravasated fluid, thereby reducing interstitial and alveolar edema. The vasculo-protective mechanism of these therapeutic effects occurs via ligation of specific G-protein-coupled receptors and an intricate interplay of S1P with other factors (such as MAPKS, ROCKs, Rho, Rac1) with rearrangement of the endothelial cytoskeleton to form strong cortical actin rings in the cell periphery and enhanced cell-to-cell and cell-to-matrix tethering dynamics. This cascade leads to reinforcement of focal adhesions and paracellular junctional complexes via cadherin, paxillin, catenins, and zona occludens. S1P through its interaction with Rac and Rho influences the cytoskeletal rearrangement indicated in the later stages of angiogenesis as a stabilizing force, preventing excessive vascular permeability. These properties translate into a therapeutic potential for acute and chronic inflammatory lung injuries. S1P has potential for providing a paradigm shift in the approach to disruption of critical endothelial gatekeeper function, loss of lung vascular integrity, and increased vascular permeability, defining features of acute lung injury (ALI), and may prove to exhibit an intrinsically protective role in the pulmonary vasculature ameliorating agonist- or sepsis-induced pulmonary injury and vascular leakage.

Sphingolipids and atherosclerosis

The atherosclerotic lesion contains a high amount of sphingolipids, a large group of structurally diverse lipids that regulate distinct biological functions beyond their role as structural membrane components. Assessment of their role in atherogenesis has been enabled after genes that regulate their metabolism had been identified and facilitated by the more wide availability of mass spectrometry. Here we discuss recent mechanistic insights obtained in animal and epidemiological studies that have greatly enhanced our understanding of mechanisms how sphingolipids affect the atherosclerotic process.

Sphingosine-1-phosphate modulates expression of vascular endothelial growth factor in human articular chondrocytes: a possible new role in arthritis

AIM

Although sphingosine-1-phosphate (S1P) is suggested to have an important role in arthritis, its function in chondrocytes remains unknown. In contrast, vascular endothelial growth factor (VEGF) has been speculated to contribute to the pathogenesis of osteoarthritis (OA), most likely by regulating angiogenesis. We here investigated the in vitro effect of S1P on VEGF expression in human articular chondrocytes from OA patients.

METHODS

Human articular cartilage samples were obtained from patients with OA under informed consent. Chondrocytes were isolated by an enzymatic procedure, grown in monolayer culture, and then stimulated with S1P in the presence or absence of mitogen-activated protein kinase (MAPK) inhibitors or the Gi protein inhibitor pertussis toxin (PTX). VEGF expression and secretion in culture supernatants were analyzed using real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Although S1P did not enhance basal secretion of matrix metalloproteinase (MMP)-1 and MMP-13, it stimulated VEGF expression in human articular chondrocytes, both at the messenger RNA and protein levels. MAPK inhibitors SB203580 and PD98059 were not effective at suppressing VEGF induction; rather, blocking extracellular signal-regulated kinase (ERK) MAPK enhanced VEGF expression. The Gi protein inhibitor PTX partially attenuated S1P-induced VEGF secretion.

CONCLUSION

Our results suggest that S1P may contribute to the regulation of VEGF expression in human chondrocytes. S1P may therefore play a unique role in the pathophysiology of OA by regulating VEGF expression in chondrocytes.

Shaping the landscape: metabolic regulation of S1P gradients

Sphingosine-1-phosphate (S1P) is a lipid that functions as a metabolic intermediate and a cellular signaling molecule. These roles are integrated when compartments with differing extracellular S1P concentrations are formed that serve to regulate functions within the immune and vascular systems, as well as during pathologic conditions. Gradients of S1P concentration are achieved by the organization of cells with specialized expression of S1P metabolic pathways within tissues. S1P concentration gradients underpin the ability of S1P signaling to regulate in vivo physiology. This review will discuss the mechanisms that are necessary for the formation and maintenance of S1P gradients, with the aim of understanding how a simple lipid controls complex physiology. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Differential expression of sphingosine-1-phosphate receptors in abdominal aortic aneurysms

Objective. Inflammation plays a key role in the pathophysiology of abdominal aortic aneurysms (AAAs). Newly discovered Sphingosine-1-Phosphate Receptors (S1P receptors) are critical in modulating inflammatory response via prostaglandin production. The aim of the current study was to investigate the expression of different S1P receptors in AAAs and compared with normal aortas at the protein level. Materials and Methods. Aortic specimens were harvested during aortic reconstructive surgery for the AAA group or during organ transplant for the control group. The protein expression of S1P1, 2 and 3 in AAAs and normal aortas was assessed by Western blotting and immunohistochemical analysis. Results. There were 40 AAAs and 20 control aortas collected for the receptor analysis. For Western blot analysis, S1P1 expression was not detected in either group; S1P2 protein was constitutively detected in both types of aortas but its expression level was significantly decreased by 73% (P < 0.05) in AAAs compared with the control group. In contrast, strong S1P3 expression was detected in AAAs aortas but not in normal aortas. Immumohistochemical staining showed similar results, except a weak S1P3 signal was detectable in normal aortas. Conclusions. Western blot and staining results consistently showed the down-regulation of the S1P2 protein with simultaneous up-regulation of the S1P3 protein in AAAs. Since those newly discovered receptors play an important role in the inflammatory cascade, the modulating of S1P signaling, particularly via S1P2 and S1P3, could represent novel therapeutic targets in future AAA treatments.

The sphingosine-1-phosphate transporter Spns2 expressed on endothelial cells regulates lymphocyte trafficking in mice

The bioactive lysophospholipid mediator sphingosine-1-phosphate (S1P) promotes the egress of newly formed T cells from the thymus and the release of immature B cells from the bone marrow. It has remained unclear, however, where and how S1P is released. Here, we show that in mice, the S1P transporter spinster homolog 2 (Spns2) is responsible for the egress of mature T cells and immature B cells from the thymus and bone marrow, respectively. Global Spns2-KO mice exhibited marked accumulation of mature T cells in thymi and decreased numbers of peripheral T cells in blood and secondary lymphoid organs. Mature recirculating B cells were reduced in frequency in the bone marrow as well as in blood and secondary lymphoid organs. Bone marrow reconstitution studies revealed that Spns2 was not involved in S1P release from blood cells and suggested a role for Spns2 in other cells. Consistent with these data, endothelia-specific deletion of Spns2 resulted in defects of lymphocyte egress similar to those observed in the global Spns2-KO mice. These data suggest that Spns2 functions in ECs to establish the S1P gradient required for T and B cells to egress from their respective primary lymphoid organs. Furthermore, Spns2 could be a therapeutic target for a broad array of inflammatory and autoimmune diseases.

Blood sphingolipids in homeostasis and pathobiology

Sphingolipids have emerged as key signaling molecules involved in the regulation of a variety of cellular functions including cell growth and differentiation, proliferation and apoptotic cell death. Sphingolipids in blood constitute part of the circulating lipoprotein particles (HDL, LDL and VLDL), carried by serum albumin and also present in blood cells and platelets. Recent lipidomic and proteomic studies of plasma lipoproteins have provided intriguing data concerning the protein and lipid composition of lipoproteins in the context of disease. Sphingolipids have been implicated in several diseases such as cancer, obesity, atherosclerosis and sphingolipidoses; however, efforts addressing blood sphingolipidomics are still limited. The development of methods to determine levels of circulating bioactive sphingolipids in humans and validation of these methods to be a routine clinical laboratory test could be a pioneering approach to diagnose disease in the population. This approach would probably evolve to be analogous in implication to determining "good" and "bad" cholesterol and triglyceride levels in lipoprotein classes.

Effects of lysophospholipids on tumor microenvironment

The effects of lysophospholipids (LPLs) on cancer microenvironment is a vast and growing field. These lipids are secreted physiologically by various cell types. They play highly important roles in the development, activation and regulation of the immune system. They are also secreted by cancerous cells and there is a strong association between LPLs and cancer. It is clear that these lipids and in particular sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) play major roles in regulating the growth of tumor cells, and in manipulating the immune system. These activities can be divided into two parts; the first involves the ability of S1P and LPA to either directly or through some of the enzymes that generate them such as sphingosine kinases or phospholipases, induce the motility and invasiveness of tumor cells. The second mechanism involves the recently discovered effects of these lipids on the anti-tumor effector natural killer (NK) cells. Whereas S1P and LPA induce the recruitment of these effector cells, they also inhibit their cytolysis of tumor cells. This may support the environment of cancer and the ability of cancer cells to grow, spread and metastasize. Consequently, LPLs or their receptors may be attractive targets for developing drugs in the treatment of cancer where LPLs or their receptors are up-regulated.

Sphingosine but not sphingosine-1-phosphate stimulates suicidal erythrocyte death

Sphingosine kinase 1 phosphorylates sphingosine, which is converted to ceramide by ceramide synthetase. Ceramide triggers eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and phosphatidylserine (PS) exposure at the erythrocyte surface. Erythrocytes lack sphingosine phosphate-degrading enzymes and thus store large quantities of sphingosine phosphate. The present study explored the influence of sphingosine and sphingosine phosphate on eryptosis. [Ca(2+)](i), was estimated from Fluo3 fluorescence, cell volume from forward scatter and PS exposure from annexin V-binding in FACS analysis. Sphingosine (0.1 - 10 μM) but not sphingosine-1- phosphate (0.1 - 10 μM) increased [Ca(2+)](i), decreased cell volume and increased PS-exposure. The observations disclose sphingosine, but not sphingosine-1-phosphate, as a strong inducer of eryptosis.

An emerging role for the lipid mediator sphingosine-1-phosphate in mast cell effector function and allergic disease

Sphingosine-1-phosphate (S1P) plays important roles regulating functions of diverse biological systems, including the immune system. S1P affects immune cell function mostly by acting through its receptors at the cell membrane but it can also induce S1P receptor-independent responses in the cells where it is generated. S1P produced in allergically-stimulated mast cells mediates degranulation, cytokine and lipid mediator production and migration of mast cells towards antigen by mechanisms that are both S1P receptor-dependent and independent. Even in the absence of an antigen challenge, the differentiation and responsiveness of mast cells can be affected by chronic exposure to elevated S1P from a nonmast cell source, whichmay occur under pathophysiological conditions, potentially leading to the hyper-responsiveness of mast cells. The role of S1P extends beyond the regulation of the function of mast cells to the regulation of the surrounding or distal environment. S1P is exported out of antigen-stimulated mast cells and into the extracellular space and the resulting S1P gradient within the tissue may influence diverse surrounding tissue cells and several aspects of the allergic disease, such as inflammation or tissue remodeling. Furthermore, recent findings indicate that vasoactive mediators released systemically by mast cells induce the production of S1P in nonhematopoietic compartments, where it plays a role in regulating the vascular tone and reducing the hypotension characteristic of the anaphy lactic shock and thus helping the recovery. The dual actions of S1P, promoting the immediate response of mast cells, while controlling the systemic consequences of mast cell activity will be discussed in detail.