Sphingosine-1 phosphate prevents monocyte/endothelial interactions in type 1 diabetic NOD mice through activation of the S1P1 receptor

Roles of Sphingosine Kinase and Sphingosine-1-Phosphate Receptor 2 in Endotoxin-Induced Acute Retinal Inflammation

PURPOSE

To investigate the roles of sphingosine kinases (SphKs) and sphingosine-1-phosphate receptors (S1PRs) in endotoxin-induced uveitis (EIU) mice.

METHODS

EIU model was induced using an intraperitoneal injection of lipopolysaccharide (LPS). The expression of SphKs and S1PRs in the retina was assessed using quantitative polymerase chain reaction (qPCR) and immunofluorescence. The effects of S1PR antagonists on the expression of inflammatory cytokines in the retina were evaluated using qPCR and western blotting. Effects of leukocyte infiltration of the retinal vessels were evaluated to determine the effects of the S1PR2 antagonist and genetic deletion of S1PR2 on retinal inflammation.

RESULTS

Retinal SphK1 expression was significantly upregulated in EIU. SphK1 was expressed in the GCL, IPL, and OPL and S1PR2 was expressed in the GCL, INL, and OPL. Positive cells in IPL and OPL of EIU retina were identified as endothelial cells. S1PR2 antagonist and genetic deletion of S1PR2 significantly suppressed the expression of IL-1α, IL-6, TNF-α, and ICAM-1, whereas S1PR1/3 antagonist did not. Use of S1PR2 antagonist and S1PR2 knockout in mice significantly ameliorated leukocyte adhesion induced by LPS.

CONCLUSION

SphK1/S1P/S1PR2 signaling was upregulated in EIU and S1PR2 inhibition suppressed inflammatory response. Targeting this signaling pathway has potential for treating retinal inflammatory diseases.

Signal Transduction and Gene Regulation in the Endothelium

Extracellular signals act on G-protein-coupled receptors (GPCRs) to regulate homeostasis and adapt to stress. This involves rapid intracellular post-translational responses and long-lasting gene-expression changes that ultimately determine cellular phenotype and fate changes. The lipid mediator sphingosine 1-phosphate (S1P) and its receptors (S1PRs) are examples of well-studied GPCR signaling axis essential for vascular development, homeostasis, and diseases. The biochemical cascades involved in rapid S1P signaling are well understood. However, gene-expression regulation by S1PRs are less understood. In this review, we focus our attention to how S1PRs regulate nuclear chromatin changes and gene transcription to modulate vascular and lymphatic endothelial phenotypic changes during embryonic development and adult homeostasis. Because S1PR-targeted drugs approved for use in the treatment of autoimmune diseases cause substantial vascular-related adverse events, these findings are critical not only for general understanding of stimulus-evoked gene regulation in the vascular endothelium, but also for therapeutic development of drugs for autoimmune and perhaps vascular diseases.

Saliva metabolomic profile of COVID-19 patients associates with disease severity

INTRODUCTION

Coronavirus disease 2019 (COVID-19) is strongly linked to dysregulation of various molecular, cellular, and physiological processes that change abundance of different biomolecules including metabolites that may be ultimately used as biomarkers for disease progression and severity. It is important at early stage to readily distinguish those patients that are likely to progress to moderate and severe stages.

OBJECTIVES

This study aimed to investigate the utility of saliva and plasma metabolomic profiles as a potential parameter for risk stratifying COVID-19 patients.

METHOD

LC-MS/MS-based untargeted metabolomics were used to profile the changes in saliva and plasma metabolomic profiles of COVID-19 patients with different severities.

RESULTS

Saliva and plasma metabolites were screened in 62 COVID-19 patients and 18 non-infected controls. The COVID-19 group included 16 severe, 15 moderate, 16 mild, and 15 asymptomatic cases. Thirty-six differential metabolites were detected in COVID-19 versus control comparisons. SARS-CoV-2 induced metabolic derangement differed with infection severity. The metabolic changes were identified in saliva and plasma, however, saliva showed higher intensity of metabolic changes. Levels of saliva metabolites such as sphingosine and kynurenine were significantly different between COVID-19 infected and non-infected individuals; while linoleic acid and Alpha-ketoisovaleric acid were specifically increased in severe compared to non-severe patients. As expected, the two prognostic biomarkers of C-reactive protein and D-dimer were negatively correlated with sphingosine and 5-Aminolevulinic acid, and positively correlated with L-Tryptophan and L-Kynurenine.

CONCLUSION

Saliva disease-specific and severity-specific metabolite could be employed as potential COVID-19 diagnostic and prognostic biomarkers.

Platelet-Derived S1P and Its Relevance for the Communication with Immune Cells in Multiple Human Diseases

Sphingosine-1-phosphate (S1P) is a versatile signaling lipid involved in the regulation of numerous cellular processes. S1P regulates cellular proliferation, migration, and apoptosis as well as the function of immune cells. S1P is generated from sphingosine (Sph), which derives from the ceramide metabolism. In particular, high concentrations of S1P are present in the blood. This originates mainly from erythrocytes, endothelial cells (ECs), and platelets. While erythrocytes function as a storage pool for circulating S1P, platelets can rapidly generate S1P de novo, store it in large quantities, and release it when the platelet is activated. Platelets can thus provide S1P in a short time when needed or in the case of an injury with subsequent platelet activation and thereby regulate local cellular responses. In addition, platelet-dependently generated and released S1P may also influence long-term immune cell functions in various disease processes, such as inflammation-driven vascular diseases. In this review, the metabolism and release of platelet S1P are presented, and the autocrine versus paracrine functions of platelet-derived S1P and its relevance in various disease processes are discussed. New pharmacological approaches that target the auto- or paracrine effects of S1P may be therapeutically helpful in the future for pathological processes involving S1P.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P₁, S1P₂, S1P₃, S1P₄, S1P₅, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

An Update on Sphingosine-1-Phosphate and Lysophosphatidic Acid Receptor Transcripts in Rodent Olfactory Mucosa

Olfactory neurons connect the external environment and the brain, allowing the translocation of materials from the nasal cavity into the brain. The olfactory system is involved in SARS-CoV-2 infections; early in the pandemic declared in 2020, a loss of the sense of smell was found in many infected patients. Attention has also been focused on the role that the olfactory epithelium appears to play in the entry of the SARS-CoV-2 virus into the brain. Specifically, SARS-CoV-2 enters cells via the angiotensin-converting enzyme 2 protein (ACE2), which is found on supporting cells in the olfactory epithelium. The intranasal administration of sphingosine has been proposed to prevent the binding of SARS-CoV-2 to ACE2. Further, sphingosine-1-phosphate (S1P) receptors appear to facilitate the entry of SARS-CoV-2 into the brain. The goal of these studies was to characterize S1P receptor expression status in rodent olfactory mucosa. The expression of receptors for a related sphingolipid, lysophosphatidic acid (LPA), was also assessed. The results confirm previous reports of S1P1 and S1P3 receptor expression, as well as LPA receptor 1, in mouse olfactory mucosa; moreover, they extend the previous findings to identify additional S1P and LPA receptor transcripts in rat and mouse olfactory mucosa, as well as in cultured olfactory neurons. These findings may enhance the utility of rodent models in identifying agonists and/or antagonists of S1P and LPA receptors that may block the entry of SARS-CoV-2 and other viruses into nasal epithelial cells, and prevent transmission from the nasal cavity into the brain.

Dysfunctional High-Density Lipoproteins in Type 2 Diabetes Mellitus: Molecular Mechanisms and Therapeutic Implications

High density lipoproteins (HDLs) are commonly known for their anti-atherogenic properties that include functions such as the promotion of cholesterol efflux and reverse cholesterol transport, as well as antioxidant and anti-inflammatory activities. However, because of some chronic inflammatory diseases, such as type 2 diabetes mellitus (T2DM), significant changes occur in HDLs in terms of both structure and composition. These alterations lead to the loss of HDLs’ physiological functions, to transformation into dysfunctional lipoproteins, and to increased risk of cardiovascular disease (CVD). In this review, we describe the main HDL structural/functional alterations observed in T2DM and the molecular mechanisms involved in these T2DM-derived modifications. Finally, the main available therapeutic interventions targeting HDL in diabetes are discussed.

Role of sphingosine-1-phosphate receptors in vascular injury of inflammatory bowel disease

Sphingosine‐1‐phosphate receptors (S1PRs) have an impact on the intestinal inflammation of inflammatory bowel disease (IBD) by regulating lymphocyte migration and differentiation. S1PR modulators as an emerging therapeutic approach are being investigated for the treatment of IBD. However, the role of S1PRs in intestinal vessels has not drawn much attention. Intestinal vascular damage is one of the major pathophysiological features of IBD, characterized by increased vascular density and impaired barrier function. S1PRs have pleiotropic effects on vascular endothelial cells, including proliferation, migration, angiogenesis and barrier homeostasis. Mounting evidence shows that S1PRs are abnormally expressed on intestinal vascular endothelial cells in IBD. Unexpectedly, S1PR modulators may damage intestinal vasculature, for example increase intestinal bleeding; therefore, S1PRs are thought to be involved in the regulation of intestinal vascular function in IBD. However, little is understood about how S1PRs regulate intestinal vascular function and participate in the initiation and progression of IBD. In this review, we summarize the pathogenic role of S1PRs in and the underlying mechanisms behind the intestinal vascular injury in IBD in order for improving IBD practice including S1PR‐targeted therapies.

Endothelial S1P1 Signaling Counteracts Infarct Expansion in Ischemic Stroke

RATIONALE

Cerebrovascular function is critical for brain health, and endogenous vascular protective pathways may provide therapeutic targets for neurological disorders. S1P (Sphingosine 1-phosphate) signaling coordinates vascular functions in other organs, and S1P1 (S1P receptor-1) modulators including fingolimod show promise for the treatment of ischemic and hemorrhagic stroke. However, S1P1 also coordinates lymphocyte trafficking, and lymphocytes are currently viewed as the principal therapeutic target for S1P1 modulation in stroke.

OBJECTIVE

To address roles and mechanisms of engagement of endothelial cell S1P1 in the naive and ischemic brain and its potential as a target for cerebrovascular therapy.

METHODS AND RESULTS

Using spatial modulation of S1P provision and signaling, we demonstrate a critical vascular protective role for endothelial S1P1 in the mouse brain. With an S1P1 signaling reporter, we reveal that abluminal polarization shields S1P1 from circulating endogenous and synthetic ligands after maturation of the blood-neural barrier, restricting homeostatic signaling to a subset of arteriolar endothelial cells. S1P1 signaling sustains hallmark endothelial functions in the naive brain and expands during ischemia by engagement of cell-autonomous S1P provision. Disrupting this pathway by endothelial cell-selective deficiency in S1P production, export, or the S1P1 receptor substantially exacerbates brain injury in permanent and transient models of ischemic stroke. By contrast, profound lymphopenia induced by loss of lymphocyte S1P1 provides modest protection only in the context of reperfusion. In the ischemic brain, endothelial cell S1P1 supports blood-brain barrier function, microvascular patency, and the rerouting of blood to hypoperfused brain tissue through collateral anastomoses. Boosting these functions by supplemental pharmacological engagement of the endothelial receptor pool with a blood-brain barrier penetrating S1P1-selective agonist can further reduce cortical infarct expansion in a therapeutically relevant time frame and independent of reperfusion.

CONCLUSIONS

This study provides genetic evidence to support a pivotal role for the endothelium in maintaining perfusion and microvascular patency in the ischemic penumbra that is coordinated by S1P signaling and can be harnessed for neuroprotection with blood-brain barrier-penetrating S1P1 agonists.

Serum Sphingosine-1-Phosphate Is Decreased in Patients With Acute-on-Chronic Liver Failure and Predicts Early Mortality

Sphingosine‐1‐phosphate (S1P) regulates pathophysiological processes, including liver regeneration, vascular tone control, and immune response. In patients with liver cirrhosis, acute deterioration of liver function is associated with high mortality rates. The present study investigated whether serum S1P concentrations are associated with disease severity in patients with chronic liver disease from compensated cirrhosis (CC), acute decompensation (AD), or acute‐on‐chronic liver failure (ACLF). From August 2013 to October 2017, patients who were admitted to the University Hospital Frankfurt with CC, AD, or ACLF were enrolled in our cirrhosis cohort study. Tandem mass spectrometry was performed on serum samples of 127 patients to assess S1P concentration. Our study comprised 19 patients with CC, 55 with AD, and 51 with ACLF, aged 29 to 76 years. We observed a significant decrease of S1P according to advanced liver injury from CC and AD up to ACLF (P < 0.001). S1P levels further decreased with progression to ACLF grade 3 (P < 0.05), and S1P highly inversely correlated with the Model for End‐Stage Liver Disease score (r = −0.508; P < 0.001). In multivariate analysis, S1P remained an independent predictor of 7‐day mortality with high diagnostic accuracy (area under the curve, 0.874; P < 0.001). Conclusion: In patients with chronic liver disease, serum S1P levels dramatically decreased with advanced stages of liver disease and were predictive of early mortality. Because S1P is a potent regulator of endothelial integrity and immune response, low S1P levels may significantly influence progressive multiorgan failure. Our data justify further elucidation of the diagnostic and therapeutic role of S1P in ACLF.

Isoflurane versus sevoflurane for early brain injury and expression of sphingosine kinase 1 after experimental subarachnoid hemorrhage

The first step to treat aneurysmal subarachnoid hemorrhage (SAH) is aneurysmal obliteration under general anesthesia but not treat the SAH itself and the secondary effects. However, the identification of anesthetics with properties that help to attenuate post-SAH brain injury can be useful for improving outcomes of SAH patients. We examined whether 2% isoflurane and 3% sevoflurane posttreatment are protective against early brain injury (EBI) after SAH. This study used 87 8-week-old male CD-1 mice. We induced SAH by endovascular perforation in mice. Animals were randomly divided into 4 groups: sham-operated (n = 16), SAH + vehicle-medical air (n = 26), SAH + 2% isoflurane (n = 22), and SAH + 3% sevoflurane (n = 23). Neurobehavioral function, brain water content and Western blotting were evaluated at 24 h. The expression of sphingosine kinase (SphK), cleaved caspase-3 and cyclooxygenase-2 (COX2) was determined by Western blotting. Cell death was examined by terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling staining. Both 2% isoflurane and 3% sevoflurane significantly improved neurobehavioral function, and brain edema at 24 h after SAH and attenuated cell death, associated with an increase in SphK1, a decrease in cleaved caspase-3 and COX2. The neuroprotective effects were similar between 2% isoflurane and 3% sevoflurane. These findings suggest that both 2% isoflurane and 3% sevoflurane significantly inhibited EBI by suppressing post-SAH apoptosis and brain inflammation possibly via the SphK1-related pathway.

On the dynamics of the human endocrine pancreas and potential consequences for the development of type 1 diabetes

Little is known about the human islet life span, and beta-cell neogenesis is generally considered rare in adults. However, based on available data on beta-cell proliferation, calculations can be made suggesting that the dynamics of the endocrine pancreas is considerable even during adulthood, with islet neogenesis and a sustained increase in size of already formed islets. Islet-associated hemorrhages, frequently observed in most mammals including humans, could account for a considerable loss of islet parenchyma balancing the constant beta-cell proliferation. Notably, in subjects with type 1 diabetes, periductal accumulation of leukocytes and fibrosis is frequently observed, findings that are likely to negatively affect islet neogenesis from endocrine progenitor cells present in the periductal area. Impaired neogenesis would disrupt the balance, result in loss of islet mass, and eventually lead to beta-cell deficiency and compromised glucose metabolism, with increased islet workload and blood perfusion of remaining islets. These changes would impose initiation of a vicious circle further increasing the frequency of vascular events and hemorrhages within remaining islets until the patient eventually loses all beta-cells and becomes c-peptide negative.

Hydroxysafflor yellow A attenuates high glucose-induced human umbilical vein endothelial cell dysfunction

High glucose (HG) induces vascular injury in diabetes. Hydroxysafflor yellow A (HSYA) has been used to ameliorate ischemic cardiovascular diseases in China for many years. In the present study, we assessed whether HSYA has a potential protective role in HG-induced human umbilical vein endothelial cell (HUVEC) injury. Cell viability was determined with an 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Cell apoptosis was detected by fluorescein isothiocyanate/propidium iodide staining assay. The endothelial cell permeability was measured with a permeability assay. Cell adhesion molecule (CAM) expression, vascular endothelial growth factor, and basic fibroblast growth factor levels were detected with an enzyme-linked immunosorbent assay. Reactive oxygen species (ROS) formation was measured with a DCF-DA assay. Protein expression of NADPH oxidase 4 (NOX4) was measured by Western blotting. Our data indicated that HG increases HUVEC apoptosis, vascular permeability, monocyte adhesion, the level of CAMs, the formation of ROS, and NOX4 expression. Our data revealed that HG increases vascular injury, which is attenuated by HSYA. Because vascular inflammation has a key role in the development of diabetes mellitus, our results implied that HSYA is considered as a potential agent for diabetic vascular injury treatment.

Potent anti-inflammatory properties of HDL in vascular smooth muscle cells mediated by HDL-S1P and their impairment in coronary artery disease due to lower HDL-S1P: a new aspect of HDL dysfunction and its therapy

Dysfunctional HDL is associated with coronary artery disease (CAD), but its effect on inflammation in vascular smooth muscle cells (VSMCs) in atherosclerosis is unknown. We investigated the effect of healthy human HDL and CAD-HDL on TNF-α-driven inflammation in VSMCs and examined whether HDL-associated sphingosine-1-phosphate (HDL-S1P) could modulate inflammation with the aim of designing novel HDL-based anti-inflammatory strategies. Healthy human HDL, human CAD-HDL, and mouse HDL were isolated by ultracentrifugation, S1P was measured by liquid chromatography-tandem mass spectrometry, and TNF-α-induced inflammation was characterized by gene expression and analysis of NF-κB-dependent signaling. Mechanisms of S1P interference with TNF-α were assessed by S1P receptor antagonists, mouse knockouts, and short interfering RNA. We observed that healthy HDL potently inhibited the induction of TNF-α-stimulated inflammatory genes, such as iNOS (inducible NO synthase) and MMP9 (matrix metalloproteinase 9), a process that was entirely dependent on HDL-S1P, as evidenced by loss-of-function using S1P-less HDL and mimicked by genuine S1P. Inhibition was based on suppression of TNF-α-activated Akt signaling resulting in reduced IkBαSer32 and p65Ser534 NF-κB phosphorylation based on a persistent phosphatase and tensin homolog activation by S1P through the S1P receptor 2. Intriguingly, S1P suppressed inflammation even hours after initial TNF-α stimulation. The anti-inflammatory effect of healthy HDL correlated with HDL-S1P content and was superior to that of CAD-HDL featuring lower HDL-S1P. Nevertheless, therapeutic loading of HDL with S1P completely restored the anti-inflammatory capacity of CAD-HDL and greatly boosted that of both healthy and CAD-HDL. Suppression of inflammation by HDL-S1P defines a novel pathophysiologic characteristic that distinguishes functional from dysfunctional HDL. The anti-inflammatory HDL function can be boosted by S1P-loading and exploited by S1P receptor-targeting to prevent and even turn off ongoing inflammation.-Keul, P., Polzin, A., Kaiser, K., Gräler, M., Dannenberg, L., Daum, G., Heusch, G., Levkau, B. Potent anti-inflammatory properties of HDL in vascular smooth muscle cells mediated by HDL-S1P and their impairment in coronary artery disease due to lower HDL-S1P: a new aspect of HDL dysfunction and its therapy.

The Role of High-Density Lipoproteins in Diabetes and Its Vascular Complications

Almost 600 million people are predicted to have diabetes mellitus (DM) by 2035. Diabetic patients suffer from increased rates of microvascular and macrovascular complications, associated with dyslipidaemia, impaired angiogenic responses to ischaemia, accelerated atherosclerosis, and inflammation. Despite recent treatment advances, many diabetic patients remain refractory to current approaches, highlighting the need for alternative agents. There is emerging evidence that high-density lipoproteins (HDL) are able to rescue diabetes-related vascular complications through diverse mechanisms. Such protective functions of HDL, however, can be rendered dysfunctional within the pathological milieu of DM, triggering the development of vascular complications. HDL-modifying therapies remain controversial as many have had limited benefits on cardiovascular risk, although more recent trials are showing promise. This review will discuss the latest data from epidemiological, clinical, and pre-clinical studies demonstrating various roles for HDL in diabetes and its vascular complications that have the potential to facilitate its successful translation.

Sphingosine kinase inhibitors: A patent review

Sphingosine kinases (SphKs) catalyze the conversion of the sphingosine to the promitogenic/migratory product, sphingosine-1-phosphate (S1P). SphK/S1P pathway has been linked to the progression of cancer and various other diseases including allergic inflammatory disease, cardiovascular diseases, rejection after transplantation, the central nervous system, and virus infections. Therefore, SphKs represent potential new targets for developing novel therapeutics for these diseases. The history and development of SphK inhibitors are discussed, summarizing SphK inhibitors by their structures, and describing some applications of SphK inhibitors. We concluded: i) initial SphK inhibitors based on sphingosine have low specificity with several important off-targets. Identification the off-targets that would work synergistically with SphKs, and developing compounds that target the unique C4 domain of SphKs should be the focus of future studies. ii) The modifications of SphK inhibitors, which are devoted to increasing the selectivity to one of the two isoforms, now focus on the alkyl length, the spacer between the head and linker rings, and the insertion and the position of lipidic group in tail region. iii) SphK/S1P signaling pathway holds therapeutic values for many diseases. To find the exact function of each isoform of SphKs increasing the number of SphK inhibitor clinical trials is necessary.

Fingolimod anti-inflammatory and neuroprotective effects modulation of RAGE axis in multiple sclerosis patients

BACKGROUND

We investigated Fingolimod treatment effects on the RAGE (receptor for advanced glycation endproducts) axis in multiple sclerosis (MS) patients. The primary outcome of the study was whether Fingolimod treatment increases serum levels of the soluble RAGE isoforms, sRAGE and esRAGE - both being considered putative endogenous inhibitors of RAGE signaling. Additional variables were serum levels of RAGE ligands, the high mobility group box (HMGB)1 and pentosidine.

METHODS

Serum levels of the study variables were measured by ELISA, and compared between baseline (before Fingolimod treatment) and 6 and 12 months post-drug treatment in 17 relapsing MS patients. Fingolimod treatment effects on MS disease progression were assessed by comparing pre- and post-Fingolimod values of the EDSS and rate of clinical relapse, and changes in the T1-and T2-enahncing lesions on the MRI scan.methods RESULTS: Twelve months treatment with Fingolimod increased serum levels of sRAGE and esRAGE by 32.4% (P = 0.004) and 48.5% (P = 0.007) respectively. In addition, Fingolimod treatment reduced serum levels of HMGB1 by 71.6% (P = 0.02) and pentosidine serum levels by 41.3% (P = 0.12). EDSS remained stable (baseline: 3.57 ± 1.56; post-Fingolimod: 3.54 ± 1.2, P = 0.96) and the rate of clinical relapse decreased near significantly (P = 0.094). T1-and T2-enhancing lesions remained stable, showing no significant changes pre-vs. post-Fingolimod treatment.

CONCLUSION

Fingolimod mediates modulation of the RAGE axis which apparently contributes to the Fingolimod's anti-inflammatory and neuroprotective effects. These findings may provide a rationale for the clinical efficacy of Fingolimod in pathological states other than MS, where dysregulation of the RAGE axis plays a role.

A Shift in ApoM/S1P Between HDL-Particles in Women With Type 1 Diabetes Mellitus Is Associated With Impaired Anti-Inflammatory Effects of the ApoM/S1P Complex

Objective—

Type 1 diabetes mellitus (T1D) patients have an increased risk of cardiovascular disease despite high levels of high-density lipoproteins (HDL). Apolipoprotein M (apoM) and its ligand sphingosine 1-phospate (S1P) exert many of the anti-inflammatory effects of HDL. We investigated whether apoM and S1P are altered in T1D and whether apoM and S1P are important for HDL functionality in T1D.

Approach and Results—

ApoM and S1P were quantified in plasma from 42 healthy controls and 89 T1D patients. HDL was isolated from plasma and separated into dense, medium-dense, and light HDL by ultracentrifugation. Primary human aortic endothelial cells were challenged with tumor necrosis factor-α in the presence or absence of isolated HDL. Proinflammatory adhesion molecules E-selectin and vascular cellular adhesion molecule-1 were quantified by flow cytometry. Activation of the S1P 1 - receptor was evaluated by analyzing downstream signaling targets and receptor internalization. There were no differences in plasma levels of apoM and S1P between controls and T1D patients, but the apoM/S1P complexes were shifted from dense to light HDL particles in T1D. ApoM/S1P in light HDL particles from women were less efficient in inhibiting expression of vascular cellular adhesion molecule-1 than apoM/S1P in denser particles. The light HDL particles were unable to activate Akt, whereas all HDL subfractions were equally efficient in activating Erk and receptor internalization.

Conclusions—

ApoM/S1P in light HDL particles were inefficient in inhibiting tumor necrosis factor-α–induced vascular cellular adhesion molecule-1 expression in contrast to apoM/S1P in denser HDL particles. T1D patients have a higher proportion of light particles and hence more dysfunctional HDL, which could contribute to the increased cardiovascular disease risk associated with T1D.

The role of sphingolipid signalling in diabetes‑associated pathologies (Review)

Sphingosine kinase (SphK) is an important signalling enzyme that catalyses the phosphorylation of sphingosine (Sph) to form sphingosine‑1‑phosphate (S1P). The multifunctional lipid, S1P binds to a family of five G protein-coupled receptors (GPCRs). As an intracellular second messenger, S1P activates key signalling cascades responsible for the maintenance of sphingolipid metabolism, and has been implicated in the progression of cancer, and the development of other inflammatory and metabolic diseases. SphK and S1P are critical molecules involved in the regulation of various cellular metabolic processes, such as cell proliferation, survival, apoptosis, adhesion and migration. There is strong evidence supporting the critical roles of SphK and S1P in the progression of diabetes mellitus, including insulin sensitivity and insulin secretion, pancreatic β‑cell apoptosis, and the development of diabetic inflammatory state. In this review, we summarise the current state of knowledge for SphK/S1P signalling effects, associated with the development of insulin resistance, pancreatic β‑cell death and the vascular complications of diabetes mellitus.

Sphingosine 1-Phosphate Receptor Modulators and Drug Discovery

Initial discovery on sphingosine 1-phosphate (S1P) as an intracellular second messenger was faced unexpectedly with roles of S1P as a first messenger, which subsequently resulted in cloning of its G protein-coupled receptors, S1P_1–5. The molecular identification of S1P receptors opened up a new avenue for pathophysiological research on this lipid mediator. Cellular and molecular in vitro studies and in vivo studies on gene deficient mice have elucidated cellular signaling pathways and the pathophysiological meanings of S1P receptors. Another unexpected finding that fingolimod (FTY720) modulates S1P receptors accelerated drug discovery in this field. Fingolimod was approved as a first-in-class, orally active drug for relapsing multiple sclerosis in 2010, and its applications in other disease conditions are currently under clinical trials. In addition, more selective S1P receptor modulators with better pharmacokinetic profiles and fewer side effects are under development. Some of them are being clinically tested in the contexts of multiple sclerosis and other autoimmune and inflammatory disorders, such as, psoriasis, Crohn’s disease, ulcerative colitis, polymyositis, dermatomyositis, liver failure, renal failure, acute stroke, and transplant rejection. In this review, the authors discuss the state of the art regarding the status of drug discovery efforts targeting S1P receptors and place emphasis on potential clinical applications.

Sphingosine-1-Phosphate Signaling in Endothelial Disorders

Numerous preclinical studies indicate that sustained endothelial activation significantly contributes to tissue edema, perpetuates the inflammatory response, and exacerbates tissue injury ultimately resulting in organ failure. However, no specific therapies aimed at restoring endothelial function are available as yet. Sphingosine-1-phosphate (S1P) is emerging as a potent modulator of endothelial function and endothelial responses to injury. Recent studies indicate that S1PR are attractive targets to treat not only disorders of the arterial endothelium but also microvascular dysfunction caused by ischemic or inflammatory injury. In this article, we will review the current knowledge of the role of S1P and its receptors in endothelial function in health and disease, and we will discuss the therapeutic potential of targeting S1PR not only for disorders of the arterial endothelium but also the microvasculature. The therapeutic targeting of S1PR in the endothelium could help to bridge the gap between biomedical research in vascular biology and clinical practice.

Sphingosine-1-Phosphate and Its Receptors: A Mutual Link between Blood Coagulation and Inflammation

Sphingosine-1-phosphate (S1P) is a versatile lipid signaling molecule and key regulator in vascular inflammation. S1P is secreted by platelets, monocytes, and vascular endothelial and smooth muscle cells. It binds specifically to a family of G-protein-coupled receptors, S1P receptors 1 to 5, resulting in downstream signaling and numerous cellular effects. S1P modulates cell proliferation and migration, and mediates proinflammatory responses and apoptosis. In the vascular barrier, S1P regulates permeability and endothelial reactions and recruitment of monocytes and may modulate atherosclerosis. Only recently has S1P emerged as a critical mediator which directly links the coagulation factor system to vascular inflammation. The multifunctional proteases thrombin and FXa regulate local S1P availability and interact with S1P signaling at multiple levels in various vascular cell types. Differential expression patterns and intracellular signaling pathways of each receptor enable S1P to exert its widespread functions. Although a vast amount of information is available about the functions of S1P and its receptors in the regulation of physiological and pathophysiological conditions, S1P-mediated mechanisms in the vasculature remain to be elucidated. This review summarizes recent findings regarding the role of S1P and its receptors in vascular wall and blood cells, which link the coagulation system to inflammatory responses in the vasculature.

FTY720 and two novel butterfly derivatives exert a general anti-inflammatory potential by reducing immune cell adhesion to endothelial cells through activation of S1P(3) and phosphoinositide 3-kinase

Sphingosine-1-phosphate (S1P) is a key lipid regulator of a variety of cellular responses including cell proliferation and survival, cell migration, and inflammatory reactions. Here, we investigated the effect of S1P receptor activation on immune cell adhesion to endothelial cells under inflammatory conditions. We show that S1P reduces both tumor necrosis factor (TNF)-α- and lipopolysaccharide (LPS)-stimulated adhesion of Jurkat and U937 cells to an endothelial monolayer. The reducing effect of S1P was reversed by the S1P1+3 antagonist VPC23019 but not by the S1P1 antagonist W146. Additionally, knockdown of S1P3, but not S1P1, by short hairpin RNA (shRNA) abolished the reducing effect of S1P, suggesting the involvement of S1P3. A suppression of immune cell adhesion was also seen with the immunomodulatory drug FTY720 and two novel butterfly derivatives ST-968 and ST-1071. On the molecular level, S1P and all FTY720 derivatives reduced the mRNA expression of LPS- and TNF-α-induced adhesion molecules including ICAM-1, VCAM-1, E-selectin, and CD44 which was reversed by the PI3K inhibitor LY294002, but not by the MEK inhibitor U0126.In summary, our data demonstrate a novel molecular mechanism by which S1P, FTY720, and two novel butterfly derivatives acted anti-inflammatory that is by suppressing gene transcription of various endothelial adhesion molecules and thereby preventing adhesion of immune cells to endothelial cells and subsequent extravasation.

HDL-bound sphingosine 1-phosphate acts as a biased agonist for the endothelial cell receptor S1P1 to limit vascular inflammation

The sphingosine 1-phosphate receptor 1 (S1P1) is abundant in endothelial cells, where it regulates vascular development and microvascular barrier function. In investigating the role of endothelial cell S1P1 in adult mice, we found that the endothelial S1P1 signal was enhanced in regions of the arterial vasculature experiencing inflammation. The abundance of proinflammatory adhesion proteins, such as ICAM-1, was enhanced in mice with endothelial cell-specific deletion of S1pr1 and suppressed in mice with endothelial cell-specific overexpression of S1pr1, suggesting a protective function of S1P1 in vascular disease. The chaperones ApoM(+)HDL (HDL) or albumin bind to sphingosine 1-phosphate (S1P) in the circulation; therefore, we tested the effects of S1P bound to each chaperone on S1P1 signaling in cultured human umbilical vein endothelial cells (HUVECs). Exposure of HUVECs to ApoM(+)HDL-S1P, but not to albumin-S1P, promoted the formation of a cell surface S1P1-β-arrestin 2 complex and attenuated the ability of the proinflammatory cytokine TNFα to activate NF-κB and increase ICAM-1 abundance. Although S1P bound to either chaperone induced MAPK activation, albumin-S1P triggered greater Gi activation and receptor endocytosis. Endothelial cell-specific deletion of S1pr1 in the hypercholesterolemic Apoe(-/-) mouse model of atherosclerosis enhanced atherosclerotic lesion formation in the descending aorta. We propose that the ability of ApoM(+)HDL to act as a biased agonist on S1P1 inhibits vascular inflammation, which may partially explain the cardiovascular protective functions of HDL.

Sphingosine-1-phosphate receptor 3 promotes leukocyte rolling by mobilizing endothelial P-selectin

Sphingosine-1-phosphate (S1P) participates in inflammation; however, its role in leukocyte rolling is still unclear. Here we use intravital microscopy in inflamed mouse cremaster muscle venules and human endothelial cells to show that S1P contributes to P-selectin-dependent leukocyte rolling through endothelial S1P receptor 3 (S1P₃) and Gα_q, PLCβ and Ca²⁺. Intra-arterial S1P administration increases leukocyte rolling, while S1P₃ deficiency or inhibition dramatically reduces it. Mast cells involved in triggering rolling also release S1P that mobilizes P-selectin through S1P₃. Histamine and epinephrine require S1P₃ for full-scale effect accomplishing it by stimulating sphingosine kinase 1 (Sphk1). In a counter-regulatory manner, S1P₁ inhibits cAMP-stimulated Sphk1 and blocks rolling as observed in endothelial-specific S1P₁^−/− mice. In agreement with a dominant pro-rolling effect of S1P₃, FTY720 inhibits rolling in control and S1P₁^−/− but not in S1P₃^−/− mice. Our findings identify S1P as a direct and indirect contributor to leukocyte rolling and characterize the receptors mediating its action.

The lipid sphingosine-1-phosphate (S1P) is known to mediate leukocyte recruitment in inflammation. Here, Nussbaum et al. show that S1P, via its receptor S1P3, also regulates leukocyte rolling on endothelium by promoting the presentation of the adhesion molecule P-selectin on the endothelial surface.

Switching the sphingolipid rheostat in the treatment of diabetes and cancer comorbidity from a problem to an advantage

Cancer and diabetes are among the most common diseases in western societies. Epidemiological studies have shown that diabetic patients have a significantly higher risk of developing a number of different types of cancers and that individuals with comorbidity (cancer and diabetes/prediabetes) have a poorer prognosis relative to nondiabetic cancer patients. The increasing frequency of comorbidity of cancer and diabetes mellitus, mainly type 2 diabetes, has driven the development of therapeutic interventions that target both disease states. There is strong evidence to suggest that balancing the sphingolipid rheostat, ceramide--sphingosine--sphingosine-1-phosphate (S1P) is crucial in the prevention of diabetes and cancer and sphingosine kinase/S1P modulators are currently under development for the treatment of cancer and diabetes. This paper will highlight some of the complexities inherent in the use of the emerging sphingosine kinase/S1P modulators in the treatment of comorbidity of diabetes and cancer.

Role of sphingosine-1-phosphate receptor 1 and sphingosine-1-phosphate receptor 2 in hyperglycemia-induced endothelial cell dysfunction

The hyperglycemia-induced production of oxidative stress results in endothelial cell dysfunction. Previous studies have demonstrated that sphingosine-1-phosphate (S1P) regulates an array of biological activities in endothelial cells mediated by sphingosine-1-phosphate receptors (S1PRs). However, the role of S1PR-mediated signaling pathways in hyperglycemia-induced endothelial cell dysfunction is currently unknown. In the present study, we aimed to explore the role of S1PRs in endothelial cell dysfunction. For this purpose, hyperglycemia-induced oxidative stress was examined using human umbilical vein endothelial cells (HUVECs) cultured with either normal (5.6 mM) or high (25 mM) levels of glucose. The levels of reactive oxygen species (ROS) and nitric oxide (NO) were determined by flow cytometric (FCM) analysis and nitrate reductase, respectively. Endothelial morphogenesis assay was performed in three-dimensional Matrigel. The mRNA and protein expression levels of S1PRs in the HUVECs were determined by RT-qPCR and western blot analysis, respectively. In addition, ROS, NO and endothelial morphogenesis assays were conducted using the high glucose-treated endothelial cells transfected with adenoviral vector expressing exogenous S1PR1 gene (pAd-S1PR1) or with adenoviral vector expressing S1PR2-specific shRNA (pAd-shRNA-S1PR2). The expression levels of S1PR1 and S1PR2 in the endothelial cells treated with high levels of glucose decreased and increased, respectively. However, the effects of high levels of glucose on S1PR3 were minimal. In addition, high levels of glucose enhanced ROS generation and markedly reduced NO generation and morphogenetic responses. Nevertheless, all the aforementioned changes were completely reversed by transfection with pAd-S1PR1 or pAd-shRNA-S1PR2, which increased S1PR1 and decreased S1PR2 expression, respectively. It can thus be concluded that S1PR1 and S1PR2 play crucial roles in hyperglycemia-induced endothelial cell dysfunction.

Different correlation of sphingosine-1-phosphate receptor 1 with receptor activator of nuclear factor kappa B ligand and regulatory T cells in rat periapical lesions

INTRODUCTION

Sphingosine-1-phosphate receptor 1 (S1P1) is crucial for regulation of immunity and bone metabolism. This study aimed to investigate the expression of S1P1 in rat periapical lesions and its relationship with receptor activator of nuclear factor kappa B ligand (RANKL) and regulatory T (Treg) cells.

METHODS

Periapical lesions were induced by pulp exposure in the first lower molars of 55 Wistar rats. Thirty rats were killed on days 0, 7, 14, 21, 28, and 35, and their mandibles were harvested for x-ray imaging, micro-computed tomography scanning, histologic observation, immunohistochemistry, enzyme histochemistry, and double immunofluorescence analysis. The remaining 25 rats were killed on days 0, 14, 21, 28, and 35, and mandibles were harvested for flow cytometry.

RESULTS

The volume and area of the periapical lesions increased from day 0 to day 21 and then remained comparably stable after day 28. S1P1-positive cells were observed in the inflammatory periapical regions; the number of S1P1-positive cells peaked at day 14 and then decreased from day 21 to day 35. The distribution of S1P1-positive cells was positively correlated with the dynamics of RANKL-positive cells but was negatively correlated with that of Treg cells.

CONCLUSIONS

S1P1 expression was differentially correlated with RANKL and Treg cell infiltration in the periapical lesions and is therefore a contributing factor to the pathogenesis of such lesions.

HDL and endothelial protection

High-density lipoproteins (HDLs) represent a family of particles characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver. In addition to this function, HDLs display pleiotropic effects including antioxidant, anti-apoptotic, anti-inflammatory, anti-thrombotic or anti-proteolytic properties that account for their protective action on endothelial cells. Vasodilatation via production of nitric oxide is also a hallmark of HDL action on endothelial cells. Endothelial cells express receptors for apoA-I and HDLs that mediate intracellular signalling and potentially participate in the internalization of these particles. In this review, we will detail the different effects of HDLs on the endothelium in normal and pathological conditions with a particular focus on the potential use of HDL therapy to restore endothelial function and integrity.

The compensatory enrichment of sphingosine -1- phosphate harbored on glycated high-density lipoprotein restores endothelial protective function in type 2 diabetes mellitus

Background

Glycation of high-density lipoprotein (HDL) decreases its ability to induce cyclooxygenase-2 (COX-2) expression and prostacyclin I-2 (PGI-2) release in endothelial cells. Whether lipid content of HDL, especially sphingosine-1-phosphate (S1P), plays any specific role in restoring the protective function of HDL in type 2 diabetes mellitus (T2DM) is still unknown.

Methods and results

Immunochemical techniques demonstrated that glycated HDL loses its protective function of regulating COX-2 expression compared with diabetic HDL. We proved that the lipid content, especially phospholipid content differed between diabetic HDL and glycated HDL. Levels of HDL-c-bound S1P were increased in T2DM compared with control subjects as detected by UPLC-MS/MS (HDL-c-bound S1P in control subjects vs. T2DM: 309.1 ± 13.71 pmol/mg vs. 382.1 ± 24.45 pmol/mg, P < 0.05). Additionally, mRNA levels of S1P lyase enzymes and S1P phosphatase 1/2 were decreased in peripheral blood by real-time PCR. Antagonist of S1P receptor 1 and 3 (S1PR1/3) diminished the functional difference between apoHDL&PL (HDL containing the protein components and phospholipids) and diabetic apoHDL&PL (diabetic HDL containing the protein components and phospholipids). With different doses of S1P reconstituted on glycated HDL, its function in inducing the COX-2 expression was restored to the same level as diabetic HDL. The mechanism of S1P reconstituted HDL (rHDL) in the process of regulating COX-2 expression involved the phosphorylation of ERK/MAPK-CREB signal pathway.

Conclusion/Significance

S1P harbored on HDL is the main factor which restores its protective function in endothelial cells in T2DM. S1P and its receptors are potential therapeutic targets in ameliorating the vascular dysfunction in T2DM.

Structural biology of the S1P1 receptor

The sphingosine 1 phosphate receptor family has been studied widely since the initial discovery of its first member, endothelium differentiation gene 1. Since this initial discovery, the family has been renamed and the primary member of the family, the S1P1 receptor, has been targeted for a variety of disease indications and successfully drugged for the treatment of patients with relapsing multiple sclerosis. Recently, the three-dimensional structure of the S1P1 receptor has been determined by X-ray crystallography and the specifics of the sphingosine 1 phosphate ligand binding pocket mapped. Key structural features for the S1P1 receptor will be reviewed and the potential binding modes of additional pharmacologically active agents against the receptor will be analyzed in an effort to better understand the structural basis of important receptor-ligand interactions.

Second generation S1P pathway modulators: research strategies and clinical developments

Multiple Sclerosis (MS) is a chronic autoimmune disorder affecting the central nervous system (CNS) through demyelination and neurodegeneration. Until recently, major therapeutic treatments have relied on agents requiring injection delivery. In September 2010, fingolimod/FTY720 (Gilenya, Novartis) was approved as the first oral treatment for relapsing forms of MS. Fingolimod causes down-modulation of S1P1 receptors on lymphocytes which prevents the invasion of autoaggressive T cells into the CNS. In astrocytes, down-modulation of S1P1 by the drug reduces astrogliosis, a hallmark of MS, thereby allowing restoration of productive astrocyte communication with other neural cells and the blood brain barrier. Animal data further suggest that the drug directly supports the recovery of nerve conduction and remyelination. In human MS, such mechanisms may explain the significant decrease in the number of inflammatory markers on brain magnetic resonance imaging in recent clinical trials, and the reduction of brain atrophy by the drug. Fingolimod binds to 4 of the 5 known S1P receptor subtypes, and significant efforts were made over the past 5 years to develop next generation S1P receptor modulators and determine the minimal receptor selectivity needed for maximal therapeutic efficacy in MS patients. Other approaches considered were competitive antagonists of the S1P1 receptor, inhibitors of the S1P lyase to prevent S1P degradation, and anti-S1P antibodies. Below we discuss the current status of the field, and the functional properties of the most advanced compounds. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Isoflurane on brain inflammation

Brain inflammation may play an important role in the pathophysiology of early brain injury after subarachnoid hemorrhage (SAH). Our aim was to demonstrate brain inflammation development and to determine whether isoflurane, a clinically available volatile anesthetic agent, prevents brain inflammation after SAH. This study used 162 8-week-old male CD-1 mice. We induced SAH with endovascular perforation in mice and randomly assigned animals to sham-operated (n=21), SAH+vehicle-air (n=35) and SAH+2% isoflurane (n=31). In addition to the evaluation of brain injury (neurological scores, brain edema and Evans blue dye extravasation), brain inflammation was evaluated by means of expression changes in markers of inflammatory cells (ionized calcium binding adaptor molecule-1, myeloperoxidase), cytokines (tumor necrosis factor [TNF]-α, interleukin-1β), adhesion molecules (intercellular adhesion molecule [ICAM]-1, P-selectin), inducers of inflammation (cyclooxygenase-2, phosphorylated c-Jun N-terminal kinase [p-JNK]) and endothelial cell activation (von Willebrand factor) at 24h post-SAH. Sphingosine kinase inhibitor (N, N-dimethylsphingosine [DMS]) and sphingosine-1-phosphate receptor-1/3 antagonist (VPC23019) were used to block isoflurane's effects (n=22, each). SAH caused early brain injury, which was associated with inflammation so that all evaluated markers of inflammation were increased. Isoflurane significantly inhibited both brain injury (P<0.001, respectively) and inflammation (myeloperoxidase, P=0.022; interleukin-1β, P=0.002; TNF-α, P=0.015; P-selectin, P=0.010; ICAM-1, P=0.016; p-JNK, P<0.001; cyclooxygenase-2, P=0.003, respectively). This beneficial effect of isoflurane was abolished with DMS and VPC23019. Isoflurane may suppress post-SAH brain inflammation possibly via the sphingosine-related pathway.

The structure and function of the S1P1 receptor

Sphingosine 1-phosphate (S1P) receptors (S1PRs) belong to the class A family of G protein-coupled receptors (GPCRs). S1PRs are widely expressed on many cell types, including those of the immune, cardiovascular, and central nervous systems. The S1PR family is rapidly gaining attention as an important mediator of many cellular processes, including cell differentiation, migration, survival, angiogenesis, calcium homeostasis, inflammation and immunity. Importantly, S1PRs are known drug targets for multiple sclerosis (MS), for which the newly developed oral therapy fingolimod, an S1PR modulator, has recently been approved for clinical use. Much progress has also recently been made in the field of structural biology and in the modeling of heterotrimeric GPCRs allowing the crystal structure of the S1PR1 subtype to be elucidated and key interactions defined. Here, we outline the structure and function of S1PR1, highlighting the key residues involved in receptor activation, signaling, transmembrane interactions, ligand binding, post-translational modification, and protein-protein interactions.

Critical role of sphingosine-1-phosphate receptor 2 (S1PR2) in acute vascular inflammation

The endothelium, as the interface between blood and all tissues, plays a critical role in inflammation. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid, highly abundant in plasma, that potently regulates endothelial responses through interaction with its receptors (S1PRs). Here, we studied the role of S1PR2 in the regulation of the proadhesion and proinflammatory phenotype of the endothelium. By using genetic approaches and a S1PR2-specific antagonist (JTE013), we found that S1PR2 plays a key role in the permeability and inflammatory responses of the vascular endothelium during endotoxemia. Experiments with bone marrow chimeras (S1pr2(+/+) → S1pr2(+/+), S1pr2(+/+) → S1pr2(-/-), and S1pr2(-/-) → S1pr2(+/+)) indicate the critical role of S1PR2 in the stromal compartment, in the regulation of vascular permeability and vascular inflammation. In vitro, JTE013 potently inhibited tumor necrosis factor α-induced endothelial inflammation. Finally, we provide detailed mechanisms on the downstream signaling of S1PR2 in vascular inflammation that include the activation of the stress-activated protein kinase pathway that, together with the Rho-kinase nuclear factor kappa B pathway (NF-kB), are required for S1PR2-mediated endothelial inflammatory responses. Taken together, our data indicate that S1PR2 is a key regulator of the proinflammatory phenotype of the endothelium and identify S1PR2 as a novel therapeutic target for vascular disorders.

High-density lipoprotein of patients with type 2 diabetes mellitus upregulates cyclooxgenase-2 expression and prostacyclin I-2 release in endothelial cells: relationship with HDL-associated sphingosine-1-phosphate

Background

Dysfunctional high-density lipoprotein (HDL) may have pro-inflammatory effects on the endothelial cells,which causes atherosclerosis in type 2 diabetes mellitus (T2DM). HDL is a major carrier of sphingosine-1-phosphate (S1P) in plasma while S1P exhibits multiple biological activities. However, potential role of HDL and S1P in T2DM remains unexplored. We hypothesized that diabetic HDL with higher contents of S1P exerts beneficial effects on the vascular system.

Methods

Subjects with T2DM with or without proved large arteries atherosclerosis and normal controls (n=15 for each group) were recruited in the present study. HDL was isolated from the subjects by ultracentrifugation. The levels of HDL-associated S1P were determined by UPLC-MS/MS. The protective function of diabetic HDL and S1P was evaluated by measuring cyclooxygenase-2 (COX-2) expression and prostacyclin I-2 (PGI-2) release by human umbilical vein endothelial cells (HUVECs) using western blot and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

The S1P levels in isolated HDL were significantly increased in T2DM subjects compared with controls (235.6 ± 13.4 vs 195.0 ± 6.4 ng/mg, P< 0.05). The diabetic HDL exerted greater protective effects on inducing COX-2 expression and PGI-2 release by HUVECs than those of control HDL (p < 0.05, p < 0.01, respectively). Pertussis toxin, a common inhibitor of G-couple protein receptors, and VPC 23019, an antagonist of S1P receptor 1 and 3 significantly attenuated HDL-induced COX-2 expression and PGI-2 release.

Conclusions

Diabetic HDL carries higher level of S1P compared with normal HDL, which has the potential to contribute to protective effects on endothelial cells by inducing COX-2 expression and PGI-2 release. These findings provide a new insight of S1P function in T2DM patients, possibly leading to a new therapeutic target.

Cardiovascular effects of sphingosine-1-phosphate (S1P)

Sphingosine-1-phosphate (S1P) regulates important functions in cardiac and vascular homeostasis. It has been implied to play causal roles in the pathogenesis of many cardiovascular disorders such as coronary artery disease, atherosclerosis, myocardial infarction, and heart failure. The majority of S1P in plasma is associated with high-density lipoproteins (HDL), and their S1P content has been shown to be responsible, at least in part, for several of the beneficial effects of HDL on cardiovascular risk. The attractiveness of S1P-based drugs for potential cardiovascular applications is increasing in the wake of the clinical approval of FTY720, but answers to important questions on the effects of S1P in cardiovascular biology and medicine must still be found. This chapter focuses on the current understanding of the role of S1P and its receptors in cardiovascular physiology, pathology, and disease.

[Sphingosine 1-phosphate receptors: from biology to physiopathology]

Sphingosine 1-phosphate (S1P) mediates critical physiological responses by its binding to G protein-coupled receptor (GPCR) subtypes, known as S1P receptors. Five distinct mammalian S1P receptors, designated S1P1-5 have been identified, each with a different cellular pattern of expression which influences the responses to S1P. In this review, we briefly outline our understanding of the modes of action and the roles of S1P receptors in the regulation of physiological and pathological functions in the cardiovascular, immune and central nervous system.

Engineering vascularized tissues using natural and synthetic small molecules

Vascular growth and remodeling are complex processes that depend on the proper spatial and temporal regulation of many different signaling molecules to form functional vascular networks. The ability to understand and regulate these signals is an important clinical need with the potential to treat a wide variety of disease pathologies. Current approaches have focused largely on the delivery of proteins to promote neovascularization of ischemic tissues, most notably VEGF and FGF. Although great progress has been made in this area, results from clinical trials are disappointing and safer and more effective approaches are required. To this end, biological agents used for therapeutic neovascularization must be explored beyond the current well-investigated classes. This review focuses on potential pathways for novel drug discovery, utilizing small molecule approaches to induce and enhance neovascularization. Specifically, four classes of new and existing molecules are discussed, including transcriptional activators, receptor selective agonists and antagonists, natural product-derived small molecules, and novel synthetic small molecules.

Berberine reduces fibronectin expression by suppressing the S1P-S1P2 receptor pathway in experimental diabetic nephropathy models

The accumulation of glomerular extracellular matrix (ECM) is one of the critical pathological characteristics of diabetic renal fibrosis. Fibronectin (FN) is an important constituent of ECM. Our previous studies indicate that the activation of the sphingosine kinase 1 (SphK1)-sphingosine 1- phosphate (S1P) signaling pathway plays a key regulatory role in FN production in glomerular mesangial cells (GMCs) under diabetic condition. Among the five S1P receptors, the activation of S1P2 receptor is the most abundant. Berberine (BBR) treatment also effectively inhibits SphK1 activity and S1P production in the kidneys of diabetic models, thus improving renal injury. Based on these data, we further explored whether BBR could prevent FN production in GMCs under diabetic condition via the S1P2 receptor. Here, we showed that BBR significantly down-regulated the expression of S1P2 receptor in diabetic rat kidneys and GMCs exposed to high glucose (HG) and simultaneously inhibited S1P2 receptor-mediated FN overproduction. Further, BBR also obviously suppressed the activation of NF-κB induced by HG, which was accompanied by reduced S1P2 receptor and FN expression. Taken together, our findings suggest that BBR reduces FN expression by acting on the S1P2 receptor in the mesangium under diabetic condition. The role of BBR in S1P2 receptor expression regulation could closely associate with its inhibitory effect on NF-κB activation.

Fenofibrate increases high-density lipoprotein and sphingosine 1 phosphate concentrations limiting abdominal aortic aneurysm progression in a mouse model

There are currently no acceptable treatments to limit progression of abdominal aortic aneurysm (AAA). Increased serum concentrations of high-density lipoprotein (HDL) are associated with reduced risk of developing an AAA. The present study aimed to assess the effects of fenofibrate on aortic dilatation in a mouse model of AAA. Male low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice were maintained on a high-fat diet for 3 weeks followed by 6 weeks of oral administration of vehicle or fenofibrate. From 14 to 18 weeks of age, all mice were infused with angiotensin II (AngII). At 18 weeks of age, blood and aortas were collected for assessment of serum lipoproteins, aortic pathology, aortic Akt1 and endothelial nitric oxide synthase (eNOS) activities, immune cell infiltration, eNOS and inducible NOS (iNOS) expression, sphingosine 1 phosphate (S1P) receptor status, and apoptosis. Mice receiving fenofibrate had reduced suprarenal aortic diameter, reduced aortic arch Sudan IV staining, higher serum HDL levels, increased serum S1P concentrations, and increased aortic Akt1 and eNOS activities compared with control mice. Macrophages, T lymphocytes, and apoptotic cells were less evident and eNOS, iNOS, and S1P receptors 1 and 3 were up-regulated in aortas from mice receiving fenofibrate. The present findings suggest that fenofibrate antagonizes AngII-induced AAA and atherosclerosis by up-regulating serum HDL and S1P levels, with associated activation of NO-producing enzymes and reduction of aortic inflammation.

Role of S-1-P receptors and human vascular smooth muscle cell migration in diabetes and metabolic syndrome

BACKGROUND

Sphingosine-1-phosphate (S-1-P) is a bioactive sphingolipid released from activated platelets that stimulates migration of vascular smooth muscle cells (VSMC) in vitro. S-1-P is associated with oxidized low-density lipoprotein (oxLDL) and is important in vessel remodeling. S-1-P will activate multiple G protein-coupled receptors (S-1-PR 1 to 5), which can regulate multiple cellular functions, including cell migration. The aim of this study is to examine the role of S-1-PR signaling during smooth muscle cell migration in response to S-1-P.

METHODS

Human VSMCs were cultured in vitro. Expression of S-1-PR 1 to 5 was determined in conditions mirroring diabetes (40 mM glucose) and metabolic syndrome (25 mM glucose with 20 μM linoleic acid and 20 μM oleic acid). Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of S-1-P with and without siRNA against S-1-PR 1 to 5. Assays were performed for activation of ERK1/2, p38(MAPK) and JNK.

RESULTS

Human VSMCs express S-1-PR1, S-1-PR2, and S-1-PR3. There was no significant expression of S-1-PR4 and S-1-PR5. The expression of S-1-PR1 and S-1-PR3 is enhanced under high glucose conditions and metabolic syndrome conditions. Migration of VSMC in response to S-1-P is enhanced 2-fold by diabetes and 4-fold by metabolic syndrome. In diabetes, S-1-PR1 expression is enhanced, while S-1-PR2 and S-1-PR3 expression are both maintained. In metabolic syndrome, S-1-PR1 and 3 expressions are enhanced and that of S-1-PR2 is reduced. siRNA to S-1-PR1 results in a 2-fold reduction in S-1-P-mediated cell migration under all conditions. siRNA to S-1-PR2 enhanced cell migration only under normal conditions, while siRNA S-1-PR3 decreased migration in metabolic syndrome only. Down-regulation of S-1-PR1 reduced ERK1/2 activation in response to S-1-P, while that of S-1-PR2 had no effect under normal conditions. In diabetes, down-regulation of S-1-PR1 reduced activation of all three MAPKs. In metabolic syndrome, down-regulation of S-1-PR1 and S-1-PR3 reduced activation of all three MAPKs.

CONCLUSION

S-1-PR 1, 2, and 3 regulate human VSMC migration and their expression level and function are modulated by conditions simulating diabetes and metabolic syndrome.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.

IL-6 signaling in autoimmunity, chronic inflammation and inflammation-associated cancer

IL-6 activates various cell types carrying the membrane bound IL-6R (classical IL-6 signaling) as well as IL-6R(-) gp130(+) cells via the soluble IL-6R (IL-6 trans-signaling). IL-6 signaling plays a pivotal role in controlling the differentiation and activation of T lymphocytes by inducing the Jak/STAT-3 and the Ras/Erk/C/EBP pathways. In particular, IL-6 modulates the resistance of T cells against apoptosis, induces activation of T helper cells and controls the balance between regulatory T cells and Th17 cells. Importantly, recent findings suggest that blockade of IL-6 signaling is effective in treating experimental models of autoimmune and chronic inflammatory diseases such as inflammatory bowel diseases, diabetes, multiple sclerosis, asthma and rheumatoid arthritis as well as models of inflammation-associated cancer. Thus, anti-IL-6/anti-IL-6R strategies emerge as promising novel approaches for therapy of inflammatory diseases in humans. In this review article, we discuss the latest findings on the role of IL-6 in experimental models of autoimmunity and cancer, as well as clinical perspectives.

Sphingosine-1-Phosphate-Specific G Protein-Coupled Receptors as Novel Therapeutic Targets for Atherosclerosis

Atherosclerosis is a chronic inflammatory process involving complex interactions of modified lipoproteins, monocyte-derived macrophages or foam cells, lymphocytes, endothelial cells (ECs), and vascular smooth muscle cells. Sphingosine-1-phosphate (S1P), a biologically active blood-borne lipid mediator, exerts pleiotropic effects such as cell proliferation, migration and cell-cell adhesion in a variety of cell types via five members of S1P-specific high-affinity G protein-coupled receptors (S1P₁-S1P₅). Among them, S1P₁, S1P₂ and S1P₃ are major receptor subtypes which are widely expressed in various tissues. Available evidence suggest that S1P and HDL-bound S1P exert atheroprotective effects including inhibition of leukocyte adhesion and stimulation of endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs) through the activation of G_i signaling pathway via S1P₃ and probably S1P₁, although there is still controversy. FTY720, the phosphorylation product of which is a high-affinity agonist for all S1P receptors except S1P₂ and act as an immunosuppressant by downregulating S1P₁ on lymphocytes, inhibits atherosclerosis in LDL receptor-null mice and apoE-null mice through the inhibition of lymphocyte and macrophage functions and probably stimulation of EC functions, without influencing plasma lipid concentrations. In contrast to S1P₁ and S1P₃, S1P₂ facilitates atherosclerosis by activating G_12/13-Rho-Rho kinase (ROCK) in apoE-null mice. S1P₂ mediates transmigration of monocytes into the arterial intima, oxidized LDL accumulation and cytokine secretion in monocyte-derived macrophages, and eNOS inhibition and cytokine secretion in ECs through Rac inhibition, NF-κB activation and 3′-specific phosphoinositide phosphatase (PTEN) stimulation downstream of G_12/13-Rho-ROCK. Systemic long-term administration of a selective S1P₂-blocker remarkably inhibits atherosclerosis without overt toxicity. Thus, multiple S1P receptors positively and negatively regulate atherosclerosis through multitudes of mechanisms. Considering the essential and multi-faceted role of S1P₂ in atherogenesis and the impact of S1P₂ inactivation on atherosclerosis, S1P₂ is a particularly promising therapeutic target for atherosclerosis.