S1P3 receptor-induced reorganization of epithelial tight junctions compromises lung barrier integrity and is potentiated by TNF

USP11 Exacerbates Radiation-Induced Pneumonitis by Activating Endothelial Cell Inflammatory Response via OTUD5-STING Signaling

PURPOSE

Radiation-induced pneumonitis (RIP) seriously limits the application of radiation therapy in the treatment of thoracic tumors, and its etiology and pathogenesis remain elusive. This study aimed to elucidate the role of ubiquitin-specific peptidase 11 (USP11) in the progression of RIP and the associated underlying mechanisms.

METHODS AND MATERIALS

Changes in cytokines and infiltrated immune cells were detected by enzyme-linked immunosorbent assays and immunohistochemistry after exposure to 20 Gy x-ray with whole-thorax irradiation. The effects of USP11 expression on endothelial cell proliferation and apoptosis were analyzed by costaining of CD31/Ki67 and CD31/caspase-3 in vivo, and the production of cytokines and reactive oxygen species was confirmed by reverse-transcription polymerase chain reaction and flow cytometry in vitro. Comprehensive proteome and ubiquitinome analyses were used for USP11 substrate screening after radiation. Results were verified by Western blotting and coimmunoprecipitation experiments. Recombinant adeno-associated virus lung vectors expressing OTUD5 were used for localized overexpression of OTUD5 in mouse pulmonary tissue, and immunohistochemistry was conducted to analyze cytokine expression.

RESULTS

The progression of RIP was significantly alleviated by reduced expression of proinflammatory cytokines in both Usp11-knockout (Usp11-/-) mice and in mice treated with the USP11 inhibitor mitoxantrone. Likewise, the absence of USP11 resulted in decreased permeability of pulmonary vessels and neutrophils and macrophage infiltration. The proliferation rates of endothelial cells were prominently increased in the Usp11-/- lung, whereas apoptosis in Usp11-/- lungs decreased after irradiation compared with that observed in Usp11+/+ lungs. Conversely, USP11 overexpression increased proinflammatory cytokine expression and reactive oxygen species production in endothelial cells after radiation. Comprehensive proteome and ubiquitinome analyses indicated that USP11 overexpression upregulates the expression of several deubiquitinating enzymes, including USP22, USP33, and OTUD5. We demonstrate that USP11 deubiquitinates OTUD5 and implicates the OTUD5-STING signaling pathway in the progression of the inflammatory response in endothelial cells.

CONCLUSIONS

USP11 exacerbates RIP by triggering an inflammatory response in endothelial cells both in vitro and in vivo, and the OTUD5-STING pathway is involved in the USP11-dependent promotion of RIP. This study provides experimental support for the development of precision intervention strategies targeting USP11 to mitigate RIP.

The Sphingosine Kinase 2 Inhibitor Opaganib Protects Against Acute Kidney Injury in Mice

Introduction

Acute kidney injury (AKI) is a common multifactorial adverse effect of surgery, circulatory obstruction, sepsis or drug/toxin exposure that often results in morbidity and mortality. Sphingolipid metabolism is a critical regulator of cell survival and pathologic inflammation processes involved in AKI. Opaganib (also known as ABC294640) is a first-in-class experimental drug targeting sphingolipid metabolism that reduces the production and activity of inflammatory cytokines and, therefore, may be effective to prevent and treat AKI.

Methods

Murine models of AKI were used to assess the in vivo efficacy of opaganib including ischemia-reperfusion (IR) injury induced by either transient bilateral occlusion of renal blood flow (a moderate model) or nephrectomy followed immediately by occlusion of the contralateral kidney (a severe model) and lipopolysaccharide (LPS)-induced sepsis. Biochemical and histologic assays were used to quantify the effects of oral opaganib treatment on renal damage in these models.

Results

Opaganib suppressed the elevations of creatinine and blood urea nitrogen (BUN), as well as granulocyte infiltration into the kidneys, of mice that experienced moderate IR from transient bilateral ligation. Opaganib also markedly decreased these parameters and completely prevented mortality in the severe renal IR model. Additionally, opaganib blunted the elevations of BUN, creatinine and inflammatory cytokines following exposure to LPS.

Conclusion

The data support the hypotheses that sphingolipid metabolism is a key mediator of renal inflammatory damage following IR injury and sepsis, and that this can be suppressed by opaganib. Because opaganib has already undergone clinical testing in other diseases (cancer and Covid-19), the present studies support conducting clinical trials with this drug with surgical or septic patients at risk for AKI.

Modulation of IL-4/IL-13 cytokine signaling in the context of allergic disease

Aberrant activation of CD4 T_H2 cells and excessive production of T_H2 cytokines such as IL-4 and IL-13 have been implicated in the pathogenesis of allergic diseases. Generally, IL-4 and IL-13 utilize Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways for induction of inflammatory gene expression and the effector functions associated with disease pathology in many allergic diseases. However, it is increasingly clear that JAK/STAT pathways activated by IL-4/IL-13 can themselves be modulated in the presence of other intracellular signaling programs, thereby changing the overall tone and/or magnitude of IL-4/IL-13 signaling. Apart from direct activation of the canonic JAK/STAT pathways, IL-4 and IL-13 also induce proinflammatory gene expression and effector functions through activation of additional signaling cascades. These alternative signaling cascades contribute to several specific aspects of IL-4/IL-13-associated cellular and molecular responses. A more complete understanding of IL-4/IL-13 signaling pathways, including the precise conditions under which noncanonic signaling pathways are activated, and the impact of these pathways on cellular- and host-level responses, will better allow us to design agents that target specific pathologic outcomes or tailor therapies for the treatment of uncommon disease endotypes.

Overexpression of Sphingosine Kinase-1 and Sphingosine-1-Phosphate Receptor-3 in Severe Plasmodium falciparum Malaria with Pulmonary Edema

Pulmonary edema (PE) is a major cause of pulmonary manifestations of severe Plasmodium falciparum malaria and is usually associated with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). The sphingosine kinase-1 (SphK-1)/sphingosine-1-phosphate receptor-3 (S1PR-3) pathway has recently been reported to affect the pathogenesis of lung injury, but the expression of these proteins in the lungs of severe P. falciparum malaria patients has not been investigated. The cellular expression of SphK-1 and S1PR-3 in lung tissues from autopsied patients with P. falciparum malaria was investigated using immunohistochemistry (IHC). Lung tissues from patients who died of severe P. falciparum malaria were classified into two groups based on histopathological findings: those with PE (18 patients) and those without PE (non-PE, 19 patients). Ten samples of normal lung tissues were used as the control group. The protein expression levels of SphK-1 and S1PR-3 were significantly upregulated in endothelial cells (ECs), alveolar epithelial cells, and alveolar macrophages (AMs) in the lungs of severe P. falciparum malaria patients with PE compared to those in the non-PE and control groups (all p < 0.001). In addition, the SphK-1 and S1PR-3 expression levels were significantly positively correlated in pulmonary ECs (r_s = 0.922, p < 0.001), alveolar epithelial cells (r_s = 0.995, p < 0.001), and AMs (r_s = 0.969, p < 0.001). In conclusion, both the SphK-1 and S1PR-3 proteins were overexpressed in the lung tissues of severe P. falciparum malaria patients with PE, suggesting that SphK-1 and S1PR-3 mediate the pathogenesis of PE in severe malaria. Targeting the regulation of SphK-1 and/or S1PR-3 may be an approach to treat pulmonary complications in severe P. falciparum patients.

Can PBDEs affect the pathophysiologic complex of epithelium in lung diseases?

Brominated flame-retardant (BFRs) exposure promotes multiple adverse health outcomes involved in oxidative stress, inflammation, and tissues damage. We investigated BFR effects, known as polybrominated diphenyl ethers (PBDEs) (47, 99 and 209) in an air-liquid-interface (ALI) airway tissue derived from A549 cell line, and compared with ALI culture of primary human bronchial epithelial cells (pHBEC). The cells, exposed to PBDEs (47, 99 and 209) (0.01-1 μM) for 24 h, were studied for IL-8, Muc5AC and Muc5B (mRNAs and proteins) production, as well as NOX-4 (mRNA) expression. Furthermore, we evaluated tight junction (TJ) integrity by Trans-Epithelial Electrical Resistance (TEER) measurements, and zonula occludens-1 (ZO-1) expression in the cells, and pH variations and rheological properties (elastic G', and viscous G″, moduli) in apical washes of ALI cultures. N-acetylcysteine (NAC) (10 mM) effects were tested in our experimental model of A549 cells. PBDEs (47, 99 and 209) exposure decreased TEER, ZO-1 and pH values, and increased IL-8, Muc5AC, Muc5B (mRNAs and proteins), NOX-4 (mRNA), and rheological parameters (G', G″) in ALI cultures of A549 cell line and pHBEC. NAC inhibited PBDE effects in A549 cells. PBDE inhalation might impairs human health of the lungs inducing oxidative stress, inflammatory response, loss of barrier integrity, unchecked mucus production, as well as altered physicochemical and biological properties of the fluids in airway epithelium. The treatment with anti-oxidants restored the negative effects of PBDEs in epithelial cells.

Sphingosine-1-phosphate receptor-independent lung endothelial cell barrier disruption induced by FTY720 regioisomers

RATIONALE

Vascular permeability is a hallmark of acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury pathobiology; however, the mechanisms underlying this vascular dysregulation remain unclear, thereby impairing the development of desperately needed effective therapeutics. We have shown that sphingosine-1-phosphate (S1P) and 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720) analogues are useful tools for exploring vascular barrier regulation mechanisms.

OBJECTIVE

To experimentally define the effects of FTY720 regioisomers on lung endothelial cell barrier regulation.

METHODS

Specific barrier-regulatory receptor and kinase inhibitors were utilized to probe signaling mechanisms involved in FTY720 regioisomer-mediated human lung endothelial cell barrier responses (trans-endothelial electrical resistance, TER). Docking simulations with the S1P1 receptor were performed to further evaluate FTY720 regioisomer signaling.

RESULTS

FTY720 regioisomers produced potent endothelial cell barrier disruption reflected by declines in TER alterations. Pharmacologic inhibition of Gi-coupled S1P receptors (S1P1, S1P2, S1P3) failed to alter FTY720 regioisomer-mediated barrier disruption; findings that were corroborated by docking simulations demonstrating FTY720 regiosomers were repelled from S1P1 docking, in contrast to strong S1P1 binding elicited by S1P. Inhibition of either the barrier-disrupting PAR-1 receptor, the VEGF receptor, Rho-kinase, MAPK, NFkB, or PI3K failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption. While FTY720 regioisomers significantly increased protein phosphatase 2 (PP2A) activity, PP2A inhibitors failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption.

CONCLUSIONS

Together, these results imply a vexing model of pulmonary vascular barrier dysregulation in response to FTY720-related compounds and highlight the need for further insights into mechanisms of vascular integrity required to promote the development of novel therapeutic tools to prevent or reverse the pulmonary vascular leak central to ARDS outcomes.

Serum sphingosine-1-phosphate levels in bladder pain syndrome/interstitial cystitis patients: could it help in diagnosis?

PURPOSE

To find if there is any potential benefit of serum Sphingosine-1-Phosphate (S1P) level in the diagnosis of Bladder Pain Syndrome/Interstitial Cystitis (BPS/IC).

METHODS AND MATERIALS

Patients newly or previously diagnosed with BPS/IC between September 2017 and December 2018 were included. Healthy individuals who volunteered to enter the study were included as control group. The measurements of serum S1P in both groups were compared. Multiple regression analysis was conducted to find out the significant factors affecting S1P results.

RESULTS

A total of 47 BPS/IC patients and 47 healthy controls were included. BPS/IC patients were older than controls (48.5 ± 12.4 vs 38.9 ± 8.1 years, p < 0.001). The female-to-male ratio was 46/1 for patient group and 29/18 for controls. 68.1% (32/47) of BPS/IC patients had previous treatments. 55.3%(26/47) of patient group had accompanying medical or psychiatric disease. The mean serum S1P level was notably elevated in BPS/IC group (median 213.6, mean ± SD 258.9 ± 167.2 vs median 125.4, mean ± SD 142.9 ± 54.8; p < 0.001). Using ROC curve analysis, a value of 165 was a good cutoff point between patient and control groups (AUC = 0.761, p < 0.001). On multiple regression analysis, being BPS/IC patient was the only significant predictor of a serum S1P level above the cutoff point documented on ROC analysis (OR 5.9; 95% CI 1.8-19.9; p = 0.004).

CONCLUSION

Sphingosine-1-phosphate (S1P) pathway seems to have a potential role in the pathogenesis of BPS/IC. High serum S1P level might support the diagnosis of BPS/IC.

Expression of sphingosine kinase 1 and sphingosine 1-phosphate receptor 3 in malaria-associated acute lung injury/acute respiratory distress syndrome in a mouse model

This study aimed to investigate the expression of sphingosine kinase 1 (SphK-1) and sphingosine 1-phosphate receptor 3 (S1PR-3) in a mouse model of malaria-associated acute lung injury/acute respiratory distress syndrome (ALI/ARDS). DBA/2 mice were infected with Plasmodium berghei ANKA to generate an experimental model of malaria-associated ALI/ARDS. The infected mice were divided into 2 groups based on the histopathological study of lung tissues: those with and those without ALI/ARDS. The expression of the SphK-1 and S1PR-3 proteins in the lung tissues was investigated using immunohistochemical staining and Western blot analysis. In addition, the S1P level was quantified in plasma and lung tissues using an enzyme-linked immunosorbent assay (ELISA). The results demonstrated that the cellular expression of the SphK-1 and S1PR-3 proteins was significantly upregulated in endothelial cells, alveolar epithelial cells and alveolar macrophages in the lung tissues of malaria-infected mice with ALI/ARDS compared with those in the control groups. The increased expression of the SphK-1 and S1PR-3 proteins was confirmed using Western blot analysis. The concentration of S1P in plasma and lung tissues was significantly decreased in malaria-infected mice with ALI/ARDS compared with non-ALI/ARDS and control mice. Furthermore, increased expression of the SphK-1 and S1PR-3 proteins significantly correlated with lung injury scores and S1P concentrations in malaria-infected mice with ALI/ARDS. These findings highlight increased expression of SphK-1 and S1PR-3 in the lung tissues of malaria-infected mice with ALI/ARDS.

Sphingosine-1-phosphate signaling and the gut-liver axis in liver diseases

The liver is the central organ involved in lipid metabolism and the gastrointestinal (GI) tract is responsible for nutrient absorption and partitioning. Obesity, dyslipidemia and metabolic disorders are of increasing public health concern worldwide, and novel therapeutics that target both the liver and the GI tract (gut-liver axis) are much needed. In addition to aiding fat digestion, bile acids act as important signaling molecules that regulate lipid, glucose and energy metabolism via activating nuclear receptor, G protein-coupled receptors (GPCRs), Takeda G protein receptor 5 (TGR5) and sphingosine-1-phosphate receptor 2 (S1PR2). Sphingosine-1-phosphate (S1P) is synthesized by two sphingosine kinase isoforms and is a potent signaling molecule that plays a critical role in various diseases such as fatty liver, inflammatory bowel disease (IBD) and colorectal cancer. In this review, we will focus on recent findings related to the role of S1P-mediated signaling pathways in the gut-liver axis.

Cytokine-Ion Channel Interactions in Pulmonary Inflammation

The lungs conceptually represent a sponge that is interposed in series in the bodies’ systemic circulation to take up oxygen and eliminate carbon dioxide. As such, it matches the huge surface areas of the alveolar epithelium to the pulmonary blood capillaries. The lung’s constant exposure to the exterior necessitates a competent immune system, as evidenced by the association of clinical immunodeficiencies with pulmonary infections. From the in utero to the postnatal and adult situation, there is an inherent vital need to manage alveolar fluid reabsorption, be it postnatally, or in case of hydrostatic or permeability edema. Whereas a wealth of literature exists on the physiological basis of fluid and solute reabsorption by ion channels and water pores, only sparse knowledge is available so far on pathological situations, such as in microbial infection, acute lung injury or acute respiratory distress syndrome, and in the pulmonary reimplantation response in transplanted lungs. The aim of this review is to discuss alveolar liquid clearance in a selection of lung injury models, thereby especially focusing on cytokines and mediators that modulate ion channels. Inflammation is characterized by complex and probably time-dependent co-signaling, interactions between the involved cell types, as well as by cell demise and barrier dysfunction, which may not uniquely determine a clinical picture. This review, therefore, aims to give integrative thoughts and wants to foster the unraveling of unmet needs in future research.

Pharmacokinetics, Pharmacodynamics, Tolerability, and Food Effect of Cenerimod, a Selective S1P₁ Receptor Modulator in Healthy Subjects

The pharmacokinetics, pharmacodynamics, tolerability, and food effect of cenerimod, a potent sphingosine-1-phosphate subtype 1 receptor modulator, were investigated in three sub-studies. Two double-blind, placebo-controlled, randomised studies in healthy male subjects were performed. Cenerimod was administered either as single dose (1, 3, 10 or 25 mg; Study 1) or once daily for 35 days (0.5, 1, 2 or 4 mg; Study 2). A two-period cross-over, open-label study was performed to assess the food effect (1 mg, Study 3). The pharmacokinetic profile of cenerimod was characterised by a t_max of 5.0–6.2 h. Terminal half-life after single and multiple doses ranged from 170 to 199 h and 283 to 539 h, respectively. Food had no relevant effect on the pharmacokinetics of cenerimod. A dose-dependent decrease in lymphocyte count was observed after initiation of cenerimod and reached a plateau (maximum change from baseline: −64%) after 20–23 days of treatment. Lymphocyte counts returned to baseline values at end-of-study examination. One serious adverse event of circulatory collapse (25 mg dose group, maximum tolerated dose: 10 mg) and adverse events of mild-to-moderate intensity were reported. Treatment initiation was associated with transient decreases in heart rate and blood pressure at doses >1 and ≥10 mg, respectively.

Sphingosine Kinases/Sphingosine 1-Phosphate Signaling in Hepatic Lipid Metabolism

The ever-increasing prevalence of metabolic diseases such as dyslipidemia and diabetes in the western world continues to be of great public health concern. Biologically active sphingolipids, such as sphingosine 1-phosphate (S1P) and ceramide, are important regulators of lipid metabolism. S1P not only directly functions as an active intracellular mediator, but also activates multiple signaling pathways via five transmembrane G-protein coupled receptors (GPCRs), S1PR1-5. S1P is exclusively formed by sphingosine kinases (SphKs). Two isoforms of SphKs, SphK1 and SphK2, have been identified. Recent identification of the conjugated bile acid-induced activation of S1PR2 as a key regulator of SphK2 opened new directions for both the sphingolipid and bile acid research fields. The role of SphKs/S1P-mediated signaling pathways in health and various human diseases has been extensively reviewed elsewhere. This review focuses on recent findings related to SphKs/S1P-medaited signaling pathways in regulating hepatic lipid metabolism.

Activated tumor cell integrin αvβ3 cooperates with platelets to promote extravasation and metastasis from the blood stream

Metastasis is the main cause of death in cancer patients, and understanding mechanisms that control tumor cell dissemination may lead to improved therapy. Tumor cell adhesion receptors contribute to cancer spreading. We noted earlier that tumor cells can expressing the adhesion receptor integrin αvβ3 in distinct states of activation, and found that cells which metastasize from the blood stream express it in a constitutively high affinity form. Here, we analyzed steps of the metastatic cascade in vivo and asked, when and how the affinity state of integrin αvβ3 confers a critical advantage to cancer spreading. Following tumor cells by real time PCR, non-invasive bioluminescence imaging, intravital microscopy and histology allowed us to identify tumor cell extravasation from the blood stream as a rate-limiting step supported by high affinity αvβ3. Successful transendothelial migration depended on cooperation between tumor cells and platelets involving the high affinity tumor cell integrin and release of platelet granules. Thus, this study identifies the high affinity conformer of integrin αvβ3 and its interaction with platelets as critical for early steps during hematogenous metastasis and target for prevention of metastatic disease.

Role of Sphingolipids in the Pathobiology of Lung Inflammation

Sphingolipid bioactivities in the respiratory airways and the roles of the proteins that handle them have been extensively investigated. Gas or inhaled particles or microorganisms come into contact with mucus components, epithelial cells, blood barrier, and immune surveillance within the airways. Lung structure and functionality rely on a complex interplay of polar and hydrophobic structures forming the surfactant layer and governing external-internal exchanges, such as glycerol-phospholipids sphingolipids and proteins. Sphingolipids act as important signaling mediators involved in the control of cell survival and stress response, as well as secreted molecules endowed with inflammation-regulatory activities. Most successful respiratory infection and injuries evolve in the alveolar compartment, the critical lung functional unit involved in gas exchange. Sphingolipid altered metabolism in this compartment is closely related to inflammatory reaction and ceramide increase, in particular, favors the switch to pathological hyperinflammation. This short review explores a few mechanisms underlying sphingolipid involvement in the healthy lung (surfactant production and endothelial barrier maintenance) and in a selection of lung pathologies in which the impact of sphingolipid synthesis and metabolism is most apparent, such as acute lung injury, or chronic pathologies such as cystic fibrosis and chronic obstructive pulmonary disease.

"Pulmonary Endothelial Cell Barrier Enhancement by Novel FTY720 Analogs: Methoxy-FTY720, Fluoro-FTY720, and β-Glucuronide-FTY720"

Effective therapeutic agents are lacking for the prevention and reversal of vascular leak, a frequent pathophysiologic result of inflammatory processes such as acute respiratory distress syndrome (ARDS) and sepsis. We previously demonstrated the potent barrier-enhancing effects of related compounds sphingosine 1-phosphate (S1P), the pharmaceutical agent FTY720, and its analog (S)-FTY720 phosphonate (Tys) in models of inflammatory lung injury. In this study, we characterize additional novel FTY720 analogs for their potential to reduce vascular leak as well as utilize them as tools to better understand the mechanisms by which this class of agents modulates permeability. Transendothelial resistance (TER) and labeled dextran studies demonstrate that (R)-methoxy-FTY720 ((R)-OMe-FTY), (R)/(S)-fluoro-FTY720 (FTY-F), and β-glucuronide-FTY720 (FTY-G) compounds display in vitro barrier-enhancing properties comparable or superior to FTY720 and S1P. In contrast, the (S)-methoxy-FTY720 ((S)-OMe-FTY) analog disrupts lung endothelial cell (EC) barrier integrity in TER studies in association with actin stress fiber formation and robust intracellular calcium release, but independent of myosin light chain or ERK phosphorylation. Additional mechanistic studies with (R)-OMe-FTY, FTY-F, and FTY-G suggest that lung EC barrier enhancement is mediated through lipid raft signaling, Gi-linked receptor coupling to downstream tyrosine phosphorylation events, and S1PR1-dependent receptor ligation. These results provide important mechanistic insights into modulation of pulmonary vascular barrier function by FTY720-related compounds and highlight common signaling events that may assist the development of novel therapeutic tools in the prevention or reversal of the pulmonary vascular leak that characterizes ARDS.

Pulmonary endothelial cell barrier enhancement by novel FTY720 analogs: methoxy-FTY720, fluoro-FTY720, and β-glucuronide-FTY720

Effective therapeutic agents are lacking for the prevention and reversal of vascular leak, a frequent pathophysiologic result of inflammatory processes such as acute respiratory distress syndrome (ARDS) and sepsis. We previously demonstrated the potent barrier-enhancing effects of related compounds sphingosine 1-phosphate (S1P), the pharmaceutical agent FTY720, and its analog (S)-FTY720 phosphonate (Tys) in models of inflammatory lung injury. In this study, we characterize additional novel FTY720 analogs for their potential to reduce vascular leak as well as utilize them as tools to better understand the mechanisms by which this class of agents modulates permeability. Transendothelial resistance (TER) and labeled dextran studies demonstrate that (R)-methoxy-FTY720 ((R)-OMe-FTY), (R)/(S)-fluoro-FTY720 (FTY-F), and β-glucuronide-FTY720 (FTY-G) compounds display in vitro barrier-enhancing properties comparable or superior to FTY720 and S1P. In contrast, the (S)-methoxy-FTY720 ((S)-OMe-FTY) analog disrupts lung endothelial cell (EC) barrier integrity in TER studies in association with actin stress fiber formation and robust intracellular calcium release, but independent of myosin light chain or ERK phosphorylation. Additional mechanistic studies with (R)-OMe-FTY, FTY-F, and FTY-G suggest that lung EC barrier enhancement is mediated through lipid raft signaling, Gi-linked receptor coupling to downstream tyrosine phosphorylation events, and S1PR1-dependent receptor ligation. These results provide important mechanistic insights into modulation of pulmonary vascular barrier function by FTY720-related compounds and highlight common signaling events that may assist the development of novel therapeutic tools in the prevention or reversal of the pulmonary vascular leak that characterizes ARDS.

The cooperative role of S1P3 with LYVE-1 in LMW-HA-induced lymphangiogenesis

Lymphangiogenesis, the formation of new lymph vessels, plays a significant role in the development and metastasis of various cancers. We and others have demonstrated that low molecular weight hyaluronan (LMW-HA) promotes lymphangiogenesis. However, the underlying mechanisms are poorly defined. In this study, using immunofluorescence and co-immunoprecipitation, we found that LMW-HA increased the colocalization of lymphatic vessel endothelial HA receptor (LYVE-1) and sphingosine 1-phosphate receptor (S1P3) at the cell surface. Silencing of either LYVE-1 or S1P3 decreased LMW-HA-mediated tube formation in lymphatic endothelial cells (LECs). Furthermore, silencing of either LYVE-1 or S1P3 significantly inhibited LMW-HA-induced tyrosine phosphorylation of Src kinase and extracellular signal-regulated kinase (ERK1/2). In summary, these results suggest that S1P3 and LYVE-1 may cooperate to play a role in LMW-HA-mediated lymphangiogenesis. This interaction may provide a useful target for the intervention of lymphangiogenesis-associated tumor progression.

Sphingosine-1-phosphate receptor 1 agonism attenuates lung ischemia-reperfusion injury

Outcomes for lung transplantation are the worst of any solid organ, and ischemia-reperfusion injury (IRI) limits both short- and long-term outcomes. Presently no therapeutic agents are available to prevent IRI. Sphingosine 1-phosphate (S1P) modulates immune function through binding to a set of G protein-coupled receptors (S1PR1-5). Although S1P has been shown to attenuate lung IRI, the S1P receptors responsible for protection have not been defined. The present study tests the hypothesis that protection from lung IRI is primarily mediated through S1PR1 activation. Mice were treated with either vehicle, FTY720 (a nonselective S1P receptor agonist), or VPC01091 (a selective S1PR1 agonist and S1PR3 antagonist) before left lung IR. Function, vascular permeability, cytokine expression, neutrophil infiltration, and myeloperoxidase levels were measured in lungs. After IR, both FTY720 and VPC01091 significantly improved lung function (reduced pulmonary artery pressure and increased pulmonary compliance) vs. vehicle control. In addition, FTY720 and VPC01091 significantly reduced vascular permeability, expression of proinflammatory cytokines (IL-6, IL-17, IL-12/IL-23 p40, CC chemokine ligand-2, and TNF-α), myeloperoxidase levels, and neutrophil infiltration compared with control. No significant differences were observed between VPC01091 and FTY720 treatment groups. VPC01091 did not significantly affect elevated invariant natural killer T cell infiltration after IR, and administration of an S1PR1 antagonist reversed VPC01091-mediated protection after IR. In conclusion, VPC01091 and FTY720 provide comparable protection from lung injury and dysfunction after IR. These findings suggest that S1P-mediated protection from IRI is mediated by S1PR1 activation, independent of S1PR3, and that selective S1PR1 agonists may provide a novel therapeutic strategy to prevent lung IRI.

Bile acids and sphingosine-1-phosphate receptor 2 in hepatic lipid metabolism

The liver is the central organ involved in lipid metabolism. Dyslipidemia and its related disorders, including non-alcoholic fatty liver disease (NAFLD), obesity and other metabolic diseases, are of increasing public health concern due to their increasing prevalence in the population. Besides their well-characterized functions in cholesterol homoeostasis and nutrient absorption, bile acids are also important metabolic regulators and function as signaling hormones by activating specific nuclear receptors, G-protein coupled receptors, and multiple signaling pathways. Recent studies identified a new signaling pathway by which conjugated bile acids (CBA) activate the extracellular regulated protein kinases (ERK1/2) and protein kinase B (AKT) signaling pathway via sphingosine-1-phosphate receptor 2 (S1PR2). CBA-induced activation of S1PR2 is a key regulator of sphingosine kinase 2 (SphK2) and hepatic gene expression. This review focuses on recent findings related to the role of bile acids/S1PR2-mediated signaling pathways in regulating hepatic lipid metabolism.

Pharmacokinetics and pharmacodynamics of ponesimod, a selective S1P1 receptor modulator, in the first-in-human study

AIMS

This study investigated the tolerability, safety, pharmacokinetics and pharmacodynamics of ponesimod, a novel oral selective sphingosine-1-phosphate (S1P1) receptor modulator in development for the treatment of auto-immune diseases.

METHODS

This was a double-blind, placebo-controlled, ascending, single-dose study. Healthy male subjects received doses of 1-75 mg or placebo control.

RESULTS

Ponesimod was well tolerated. Starting with a dose of 8 mg, transient asymptomatic reductions in heart rate were observed. Ponesimod pharmacokinetics were dose proportional. The median time to maximal concentration ranged from 2.0 to 4.0 h, and ponesimod was eliminated with a mean half-life varying between 21.7 and 33.4 h. Food had a minimal effect on ponesimod pharmacokinetics. Doses of ≥8 mg reduced total lymphocyte count in a dose-dependent manner. Lymphocyte counts returned to normal ranges within 96 h. A pharmacokinetic/pharmacodynamic model was developed that adequately described the observed effects of ponesimod on total lymphocyte counts.

CONCLUSIONS

Single doses of ponesimod up to and including 75 mg were well tolerated. The results of this ascending single-dose study indicate an immunomodulator potential for ponesimod and a pharmacokinetic/pharmacodynamic profile consistent with once-a-day dosing.

Multiple-dose tolerability, pharmacokinetics, and pharmacodynamics of ponesimod, an S1P1 receptor modulator: favorable impact of dose up-titration

This multiple-ascending-dose study investigated the safety, tolerability, pharmacokinetics, and pharmacodynamics of ponesimod, an S1P1 receptor modulator and a potential new treatment for autoimmune diseases. In part A, 10 healthy male and female subjects received once daily oral doses of ponesimod (5, 10, or 20 mg) or placebo for 7 days. Sinus bradycardia and, in some subjects, atrioventricular (AV) block occurred primarily on the first day of dosing, as desensitization developed to ponesimod-induced heart rate (HR) reduction and PR-prolongation. This elicited the design of an up-titration schedule in 17 subjects to a dose of 40 mg in part B. The up-titration regimen reduced HR and PQ/PR effects. Reported adverse events were mainly related to the cardiac and respiratory systems. Respiratory effects increased with higher doses. Ponesimod multiple-dose pharmacokinetics were slightly more than dose-proportional and characterized by a time to maximum concentration and an elimination half-life varying from 2.5 to 4.0 hours and 30.9 to 33.5 hours, respectively, and an accumulation of about 2.3-fold. Ponesimod caused a dose-dependent sustained decrease in total lymphocyte count, reversible within 7 days of discontinuation. A pharmacokinetic-pharmacodynamic model enabled comparing day 1 and steady-state conditions. These results warrant further investigation of ponesimod in patients.

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.

Sphingolipids in acute lung injury

Acute lung injury is a life-threatening disease that is characterized by pulmonary inflammation, loss of barrier functions, and hypoxemia. Sphingolipids are critically involved in the disease process that they can both expedite and extenuate: They expedite inflammation by promoting chemotaxis (neutral sphingomyelinase), increased endothelial permeability (acid sphingomyelinase, S1P3-receptors), increased epithelial permeability (S1P2- and S1P3-receptors), and delaying neutrophil apoptosis (neutral sphingomyelinase, S1P1-receptors). They extenuate inflammation by attenuating chemotaxis (S1P) and by stabilizing the endothelial and the epithelial barrier (S1P1-receptor). This chapter discusses the multiple roles and therapeutic options that sphingolipids offer with respect to acute lung injury.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

Suppression of inflammation and acute lung injury by Miz1 via repression of C/EBP-δ

Inflammation is essential for host defense but can cause tissue damage and organ failure if unchecked. How the inflammation is resolved remains elusive. Here we report that the transcription factor Miz1 was required for terminating lipopolysaccharide (LPS)-induced inflammation. Genetic disruption of the Miz1 POZ domain, which is essential for its transactivation or repression activity, resulted in hyper-inflammation, lung injury and increased mortality in LPS-treated mice while reduced bacterial load and mortality in mice with Pseudomonas aeruginosa pneumonia. Loss of the Miz1 POZ domain prolonged pro-inflammatory cytokine expression. Upon stimulation, Miz1 was phosphorylated at Ser178, which is required for recruiting histone deacetylase 1 to repress transcription of C/EBP-δ, an amplifier of inflammation. Our data provide a long-sought mechanism underlying resolution of LPS-induced inflammation.

The role of sphingosine-1-phosphate in breast cancer tumor-induced lymphangiogenesis

Sphingosine-1-phosphate (S1P) is a potent sphingolipid metabolite that regulates a number of biological processes critical for cancer. S1P produced inside cancer cells is exported and exerts its extracellular functions by binding to its specific receptors in an autocrine, paracrine, and/or endocrine manner, which is known as inside-out signaling. S1P is also known to exert its intracellular functions especially in the inflammatory process, but its relevance to cancer biology remains to be elucidated. Recently, there have been growing interests in the role of S1P in breast cancer progression, including angiogenesis and lymphangiogenesis. Our group demonstrated that activation of sphingosine kinase 1, the enzyme that catalyzes the phosphorylation of sphingosine to S1P, is a key step of this process. In this review, we will cover our current knowledge on the role of S1P signaling pathway in breast cancer progression with an emphasis on its role in tumor-induced lymphangiogenesis.

Reassessment of the pharmacology of Sphingosine-1-phosphate S1P3 receptor ligands using the DiscoveRx PathHunter™ and Ca2+ release functional assays

BACKGROUND AND PURPOSE

DiscoverRx's PathHunter™ assay measures GPCR agonist potency, via the recruitment of β-arrestin, independent of the subtype of G(α) protein activated. This assay is frequently used in drug discovery although little is known about the agonist pharmacology generated. Here we have compared agonist potency, efficacy and affinity values obtained in PathHunter™ assays with those from more established radioligand binding and functional techniques.

EXPERIMENTAL APPROACH

Using cells expressing the human sphingosine-1-phosphate S1P(3) receptor at four different densities, we compared pharmacological affinity and efficacy values of four structurally distinct ligands - FTY720-P, VPC24191, CYM5442 and the endogenous agonist S1P - obtained from competition binding, functional Ca(2+) release and PathHunter™ assays.

KEY RESULTS

The pK(i) values for S1P were significantly different (9.34 ± 0.10 and 8.92 ± 0.15) in clones expressing different receptor levels using the binding assay. In the PathHunter™ and Ca(2+) assays, S1P and CYM5442 were full agonists, FTY720-P was a partial agonist, while the efficacy of VPC24191 could not be detected in PathHunter™ assays. VPC23019, previously described as a S1P(1/3) receptor antagonist, behaved as an S1P(3) receptor partial agonist in the Ca(2+) release assay.

CONCLUSIONS AND IMPLICATIONS

Comparison of data from the PathHunter™ assay with binding and functional Ca(2+) assays suggest that PathHunter™ assays measured a different agonist-bound receptor conformation. While this assay has great utility in drug discovery, care must be taken as high-efficacy, low-affinity agonist compounds would not be detected. Therefore highly amplified, more traditional assays are necessary to identify agonists with low efficacy.

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.

Lysophospholipids and their receptors in the central nervous system

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), two of the best-studied lysophospholipids, are known to influence diverse biological events, including organismal development as well as function and pathogenesis within multiple organ systems. These functional roles are due to a family of at least 11 G protein-coupled receptors (GPCRs), named LPA(1-6) and S1P(1-5), which are widely distributed throughout the body and that activate multiple effector pathways initiated by a range of heterotrimeric G proteins including G(i/o), G(12/13), G(q) and G(s), with actual activation dependent on receptor subtypes. In the central nervous system (CNS), a major locus for these signaling pathways, LPA and S1P have been shown to influence myriad responses in neurons and glial cell types through their cognate receptors. These receptor-mediated activities can contribute to disease pathogenesis and have therapeutic relevance to human CNS disorders as demonstrated for multiple sclerosis (MS) and possibly others that include congenital hydrocephalus, ischemic stroke, neurotrauma, neuropsychiatric disorders, developmental disorders, seizures, hearing loss, and Sandhoff disease, based upon the experimental literature. In particular, FTY720 (fingolimod, Gilenya, Novartis Pharma, AG) that becomes an analog of S1P upon phosphorylation, was approved by the FDA in 2010 as a first oral treatment for MS, validating this class of receptors as medicinal targets. This review will provide an overview and update on the biological functions of LPA and S1P signaling in the CNS, with a focus on results from studies using genetic null mutants for LPA and S1P receptors. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Inhibition of sphingosine kinase-2 suppresses inflammation and attenuates graft injury after liver transplantation in rats

Inflammation mediates/promotes graft injury after liver transplantation (LT). This study investigated the roles of sphingosine kinase-2 (SK2) in inflammation after LT. Liver grafts were stored in UW solution with and without ABC294640 (100 µM), a selective inhibitor of SK2, before implantation. Hepatic sphingosine-1-phosphate (S1P) levels increased ∼4-fold after LT, which was blunted by 40% by ABC294640. Hepatic toll-like receptor-4 (TLR4) expression and nuclear factor-κB (NF-κB) p65 subunit phosphorylation elevated substantially after transplantation. The pro-inflammatory cytokines/chemokines tumor necrosis factor-α, interleukin-1β and C-X-C motif chemokine 10 mRNAs increased 5.9-fold, 6.1-fold and 16-fold, respectively following transplantation, while intrahepatic adhesion molecule-1 increased 5.7-fold and monocytes/macrophage and neutrophil infiltration and expansion of residential macrophage population increased 7.8-13.4 fold, indicating enhanced inflammation. CD4+ T cell infiltration and interferon-γ production also increased. ABC294640 blunted TLR4 expression by 60%, NF-κB activation by 84%, proinflammatory cytokine/chemokine production by 45-72%, adhesion molecule expression by 54% and infiltration of monocytes/macrophages and neutrophils by 62-67%. ABC294640 also largely blocked CD4+ T cell infiltration and interferon-γ production. Focal necrosis and apoptosis occurred after transplantation with serum alanine aminotransferase (ALT) reaching ∼6000 U/L and serum total bilirubin elevating to ∼1.5 mg/dL. Inhibition of SK2 by ABC294640 blunted necrosis by 57%, apoptosis by 74%, ALT release by ∼68%, and hyperbilirubinemia by 74%. Most importantly, ABC294640 also increased survival from ∼25% to ∼85%. In conclusion, SK2 plays an important role in hepatic inflammation responses and graft injury after cold storage/transplantation and represents a new therapeutic target for liver graft failure.

Role of sphingosine-1-phosphate inβ-adrenoceptor desensitization via Ca(2+) sensitization in airway smooth muscle

BACKGROUND

The correlation between inflammatory cells and airway smooth muscle plays fundamental roles in the pathophysiology of asthma. This study was designed to determine whether pre-exposure of airway smooth muscle to sphingosine-1-phosphate (S1P), which is released from mast cells by allergic reactions, causes a deterioration of β-adrenoceptor function.

METHODS

Isometric tension and the ratio of fluorescence intensities at 340 and 380 nm (F(340)/F(380)), an indicator of intracellular Ca2+ levels, were simultaneously measured using fura-2 loaded guinea-pig tracheal tissues. Intracellular cAMP levels were also measured.

RESULTS

Pre-exposure to S1P caused a reduction in the inhibitory effects of 0.3μM isoprenaline, a β-adrenoceptor agonist, and 10μM forskolin, a direct activator of adenylyl cyclase, against 1μM methacholine-induced contraction in concentration- and time- dependent manners. In contrast, the values of F(340)/F(380) were not augmented under this experimental condition. After incubation with S1P in the presence of 0.001-1μM Y-27632, a Rho-kinase inhibitor, the reduced responsiveness to forskolin induced by S1P was reversed in a concentration-dependent manner. Moreover, pre-treatment with pertussis toxin (PTX), an inhibitor of G(i), suppressed the loss of forskolin-induced relaxation induced by S1P. Pre-exposure to S1P markedly inhibited the augmentation of cAMP accumulation induced by forskolin. However, addition of Y-27632 and pre-exposure to PTX returned forsokin-induced cAMP accumulation to the control level.

CONCLUSIONS

Pre-exposure to S1P causes heterologus desensitization of β-adrenoceptors by increasing the sensitivity of airway smooth muscle to intracellular Ca2+. Ca2+ sensitization regulated by G(i) and Rho-kinase is involved in this phenomenon.

Hyperoxia disrupts pulmonary epithelial barrier in newborn rats via the deterioration of occludin and ZO-1

Background

Prolonged exposure to hyperoxia in neonates can cause hyperoxic acute lung injury (HALI), which is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and maintenance of barrier properties requires intact epithelial tight junctions (TJs). However, in neonatal animals, relatively little is known about how the TJ proteins are expressed in the pulmonary epithelium, including whether expression of TJ proteins is regulated in response to hyperoxia exposure. This study determines whether changes in tight junctions play an important role in disruption of the pulmonary epithelial barrier during hyperoxic acute lung injury.

Methods

Newborn rats, randomly divided into two groups, were exposed to hyperoxia (95% oxygen) or normoxia for 1–7 days, and the severity of lung injury was assessed; location and expression of key tight junction protein occludin and ZO-1 were examined by immunofluorescence staining and immunobloting; messenger RNA in lung tissue was studied by RT-PCR; transmission electron microscopy study was performed for the detection of tight junction morphology.

Results

We found that different durations of hyperoxia exposure caused different degrees of lung injury in newborn rats. Treatment with hyperoxia for prolonged duration contributed to more serious lung injury, which was characterized by increased wet-to-dry ratio, extravascular lung water content, and bronchoalveolar lavage fluid (BALF):serum FD4 ratio. Transmission electron microscopy study demonstrated that hyperoxia destroyed the structure of tight junctions and prolonged hyperoxia exposure, enhancing the structure destruction. The results were compatible with pathohistologic findings. We found that hyperoxia markedly disrupted the membrane localization and downregulated the cytoplasm expression of the key tight junction proteins occludin and ZO-1 in the alveolar epithelium by immunofluorescence. The changes of messenger RNA and protein expression of occludin and ZO-1 in lung tissue detected by RT-PCR and immunoblotting were consistent with the degree of lung injury.

Conclusions

These data suggest that the disruption of the pulmonary epithelial barrier induced by hyperoxia is, at least in part, due to massive deterioration in the expression and localization of key TJ proteins.

Perspectives on immunomodulation early in life

The immune system early in life is characterized by immature activation and function of immune cells and a preponderance of Th2 cytokines. Together with other factors such as genetics and epigenetics, these immature immune responses might prone newborns susceptible to severe infections as well as allergic diseases. Immunomodulation therapy may have potential as therapeutic strategy against those disorders and might have implication in early-life interventions in the future. In this review, we will focus on two immunomodulatory substance classes, Toll-like receptor (TLR) ligands and sphingolipids, which are the focus of extensive research to date. Both TLRs and sphingolipid receptors have a very distinct distribution pattern and function on immune cells. Therefore, they can potentially modulate and balance immune responses, which might be in particular beneficial for the immaturity of the immune response early in life.

Involvement of ceramide in cell death responses in the pulmonary circulation

Ceramides are signaling sphingolipids involved in cellular homeostasis but also in pathological processes such as unwanted apoptosis, growth arrest, oxidative stress, or senescence. Several enzymatic pathways are responsible for the synthesis of ceramides, which can be activated in response to exogenous stimuli such as cytokines, radiation, or oxidative stress. Endothelial cells are particularly rich in acid sphingomyelinases, which can be rapidly activated to produce ceramides, both intracellular and at the plasma membrane. In addition, neutral sphingomyelinases, the de novo pathway and the ceramide recycling pathway, may generate excessive ceramides involved in endothelial cell responses. When up-regulated, ceramides trigger signaling pathways that culminate in endothelial cell death, which in murine lungs has been linked to the development of emphysema-like disease. Furthermore, ceramides may be released paracellularly where they are believed to exert paracrine activities. Such effects, along with ceramides released by inflammatory mediators, may contribute to lung inflammation and pulmonary edema, because ceramide-challenged pulmonary endothelial cells exhibit decreased barrier function, independent of apoptosis. Reestablishing the sphingolipid homeostasis, either by modulating ceramide synthesis or by opposing its biological effects through augmentation of the prosurvival sphingosine-1 phosphate, may alleviate acute or chronic pulmonary conditions characterized by vascular endothelial cell death or dysfunction.

Altered expression of tight junction molecules in alveolar septa in lung injury and fibrosis

The dysfunction of alveolar barriers is a critical factor in the development of lung injury and subsequent fibrosis, but the underlying molecular mechanisms remain poorly understood. To clarify the pathogenic roles of tight junctions in lung injury and fibrosis, we examined the altered expression of claudins, the major components of tight junctions, in the lungs of disease models with pulmonary fibrosis. Among the 24 known claudins, claudin-1, claudin-3, claudin-4, claudin-7, and claudin-10 were identified as components of airway tight junctions. Claudin-5 and claudin-18 were identified as components of alveolar tight junctions and were expressed in endothelial and alveolar epithelial cells, respectively. In experimental bleomycin-induced lung injury, the levels of mRNA encoding tight junction proteins were reduced, particularly those of claudin-18. The integrity of the epithelial tight junctions was disturbed in the fibrotic lesions 14 days after the intraperitoneal instillation of bleomycin. These results suggest that bleomycin mainly injured alveolar epithelial cells and impaired alveolar barrier function. In addition, we analyzed the influence of transforming growth factor-β (TGF-β), a critical mediator of pulmonary fibrosis that is upregulated after bleomycin-induced lung injury, on tight junctions in vitro. The addition of TGF-β decreased the expression of claudin-5 in human umbilical vein endothelial cells and disrupted the tight junctions of epithelial cells (A549). These results suggest that bleomycin-induced lung injury causes pathogenic alterations in tight junctions and that such alterations seem to be induced by TGF-β.

Sphingosine kinase-2 inhibition improves mitochondrial function and survival after hepatic ischemia-reperfusion

BACKGROUND & AIMS

The mitochondrial permeability transition (MPT) and inflammation play important roles in liver injury caused by ischemia-reperfusion (IR). This study investigated the roles of sphingosine kinase-2 (SK2) in mitochondrial dysfunction and inflammation after hepatic IR.

METHODS

Mice were gavaged with vehicle or ABC294640 (50 mg/kg), a selective inhibitor of SK2, 1 h before surgery and subjected to 1 h-warm ischemia to ~70% of the liver followed by reperfusion.

RESULTS

Following IR, hepatic SK2 mRNA and sphingosine-1-phosphate (S1P) levels increased ~25- and 3-fold, respectively. SK2 inhibition blunted S1P production and liver injury by 54-91%, and increased mouse survival from 28% to 100%. At 2 h after reperfusion, mitochondrial depolarization was observed in 74% of viable hepatocytes, and mitochondrial voids excluding calcein disappeared, indicating MPT onset in vivo. SK2 inhibition decreased mitochondrial depolarization and prevented MPT onset. Inducible nitric oxide synthase, phosphorylated NFκB-p65, TNFα mRNA, and neutrophil infiltration, all increased markedly after hepatic IR, and these increases were blunted by SK2 inhibition. In cultured hepatocytes, anoxia/re-oxygenation resulted in increases of SK2 mRNA, S1P levels, and cell death. SK2 siRNA and ABC294640 each substantially decreased S1P production and cell death in cultured hepatocytes.

CONCLUSIONS

SK2 plays an important role in mitochondrial dysfunction, inflammation responses, hepatocyte death, and survival after hepatic IR and represents a new target for the treatment of IR injury.

Deletion of aquaporin 5 aggravates acute lung injury induced by Pseudomonas aeruginosa

BACKGROUND

Aquaporin (AQP) is a membrane protein that facilitates osmotic water transport. Aquaporin 5 (AQP5) expresses at type I alveolar epithelia of apical membrane that confers high osmotic water permeability. Osmosis or stretch challenge in alveoli significantly up-regulates AQP5 expression, which suggests that AQP5 may play a role in the maintenance of epithelia barrier function. Pseudomonas aeruginosa (PA), a leading gram-negative bacterial frequently isolated from ventilation-associated pneumonia patients, disrupts alveolar and airway epithelial cells and subsequently leads to blood dissemination. In this study, we hypothesized that AQP5 might be protective in acute lung injury induced by PA, and deletion of AQP5 might lead to aggravated lung injury.

METHODS

Lung injury model was induced by intratracheal instillation of PA (1 × 10(6) colony-forming unit) in wild-type and AQP5 knockout mice, 2 hours and 6 hours later, blood and lung lysate were cultured to detect blood dissemination, bronchoalveolar lavage fluid and lung tissue were collected for histology analysis. Lung injury assessment, wet/dry weight ratio, protein leakage, and Evan's blue dye extravasation were evaluated for pulmonary barrier function.

RESULTS

AQP5 deficiency led to increased bacterial blood dissemination and aggravated lung injury during PA infection, and AQP5 deletion also reduced mucin production in lung. Moreover, AQP5 deficiency showed declined activation of mitogen-activated protein kinase and nuclear factor-kappa B pathways in lungs before and after PA infection.

CONCLUSION

Our data demonstrated that AQP5 plays a protective role in the maintenance of pulmonary barrier function against PA infection.

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.

Interleukin-23-mediated inflammation in Pseudomonas aeruginosa pulmonary infection

Pseudomonas aeruginosa is an opportunistic pathogen that is capable of causing acute and chronic pulmonary infection in the immunocompromised host. In the case of cystic fibrosis (CF), chronic P. aeruginosa infection causes increased mortality by promoting overly exuberant airway inflammation and cumulative lung damage. Identifying the key regulators of this inflammation may lead to the development of new therapies that improve P. aeruginosa-related mortality. We report here that interleukin-23 (IL-23), the cytokine most clearly tied to IL-17-mediated inflammation, also promotes IL-17-independent inflammation during P. aeruginosa pulmonary infection. During the early innate immune response, prior to IL-17 induction, IL-23 acts synergistically with IL-1β to promote early neutrophil (polymorphonuclear leukocyte [PMN]) recruitment. However, at later time points, IL-23 also promoted IL-17 production by lung γδ T cells, which was greatly augmented in the presence of IL-1β. These studies show that IL-23 controls two independent phases of neutrophil recruitment in response to P. aeruginosa infection: early PMN emigration that is IL-17 independent and later PMN emigration regulated by IL-17.

Expression profile of the sphingosine kinase signalling system in the lung of patients with chronic obstructive pulmonary disease

AIMS

Chronic obstructive pulmonary disease (COPD) is a leading cause of death worldwide. Despite its importance, treatment methods are limited and restricted to symptomatic care, highlighting the urgent need for new treatment options. Tissue damage in COPD is thought to result from an inability of the normal repair processes with accumulation of apoptotic material and impaired clearance of this material by macrophages in the airways. Lung inflammation involves the bioactive sphingolipid sphingosine 1-phosphate (S1P).

MAIN METHODS

We investigated lung tissue samples from 55 patients (25 with COPD) undergoing lobectomies for management of cancer. We analysed the sphingosine-kinase (SphK) mRNA expression profile, SphK enzyme activity as well as the localisation and expression of individual proteins related to the SphK-signalling system.

KEY FINDINGS

We show in this study for the first time a comprehensive expression profile of all synthesising enzymes, receptors and degrading enzymes of the SphK-signalling system in the human lung. Multivariate ANOVA showed that the relative mRNA expression of S1P receptor (S1PR) subtype 5 was reduced in COPD. There were strong positive correlations between the mRNA expression of S1PR5 and S1PR1 and S1PR3, and between S1PR3 and S1PR2. A significant negative correlation was found between S1PR1 and SphK protein activity.

SIGNIFICANCE

The correlations between expression levels of receptors and enzymes involved in the sphingosine kinase signalling system in the lung suggest common regulatory mechanisms. Our findings of reduced S1PR5 in COPD and the correlation with other S1P receptors in COPD identify S1PR5 as a possible novel target for pharmacotherapy.

The Dual Role of TNF in Pulmonary Edema

—Pulmonary edema, a major manifestation of left ventricular heart failure, renal insufficiency, shock, diffuse alveolar damage and lung hypersensitivity states, is a significant medical problem worldwide and can be life-threatening. The proinflammatory cytokine tumor necrosis factor (TNF) has been shown to contribute to the pathogenesis and development of pulmonary edema. However, some recent studies have demonstrated surprisingly that TNF can also promote alveolar fluid reabsorption in vivo and in vitro. This protective effect of the cytokine is mediated by the lectin-like domain of the cytokine, which is spatially distinct from the TNF receptor binding sites. The TIP peptide, a synthetic mimic of the lectin-like domain of TNF, can significantly increase alveolar fluid clearance and improve lung compliance in pulmonary edema models. In this review, we will discuss the dual role of TNF in pulmonary edema.

Sphingosine-1-phosphate reduces hepatic ischaemia/reperfusion-induced acute kidney injury through attenuation of endothelial injury in mice

AIM

Hepatic ischaemia/reperfusion injury (IRI) frequently complicates acute kidney injury (AKI) during the perioperative period. This study was to determine whether hepatic IRI causes AKI and the effect of the sphingosine-1-phosphate (S1P) on AKI.

METHODS

S1P and vehicle were given to mice before ischaemia and mice were subjected to hepatic IRI. Plasma creatinine (PCr), alanine transaminase (ALT), urinary neutrophil gelatinase-associated lipocalin (NGAL) and renal histological changes were determined. As a marker of endothelial injury, vascular permeability was measured. The effect of VPC 23019, a S1P(1) receptor antagonist, was also assessed.

RESULTS

Hepatic IRI resulted in liver injury (increased ALT) and systemic inflammation. Kidneys showed elevated inflammatory cytokines, leucocyte infiltration, increased vascular permeability, tubular cell apoptosis and increased urinary NGAL, although PCr did not increase. Pretreatment with S1P resulted in an attenuation of systemic inflammation and kidney injury without any effect on plasma ALT or peripheral lymphocytes. The protective effect of S1P was partially reversed by VPC 23019, suggesting the important contribution of the S1P/S1P(1) pathway to protect against hepatic IRI-induced AKI.

CONCLUSION

The study data demonstrate the important contribution of systemic inflammation and endothelial injury to AKI following hepatic IRI. Modulation of the S1P/S1P(1) receptor pathway might have some therapeutic potential in hepatic IRI-induced kidney injury.

The role of sphingosine 1-phosphate in migration of osteoclast precursors; an application of intravital two-photon microscopy

Sphingosine-1-phosphate (S1P), a biologically active lysophospholipid that is enriched in blood, controls the trafficking of osteoclast precursors between the circulation and bone marrow cavities via G protein-coupled receptors, S1PRs. While S1PR1 mediates chemoattraction toward S1P in bone marrow, where S1P concentration is low, S1PR2 mediates chemorepulsion in blood, where the S1P concentration is high. The regulation of precursor recruitment may represent a novel therapeutic strategy for controlling osteoclast-dependent bone remodeling. Through intravital multiphoton imaging of bone tissues, we reveal that the bidirectional function of S1P temporospatially regulates the migration of osteoclast precursors within intact bone tissues. Imaging technologies have enabled in situ visualization of the behaviors of several players in intact tissues. In addition, intravital microscopy has the potential to be more widely applied to functional analysis and intervention.

Chronic sphingosine 1-phosphate 1 receptor activation attenuates early-stage diabetic nephropathy independent of lymphocytes

Sphingosine 1-phosphate (S1P), a pleiotropic lipid mediator, binds to five related G-protein-coupled receptors to exert its effects. As S1P1 receptor (S1P1R) activation blocks kidney inflammation in acute renal injury, we tested whether activation of S1P1Rs ameliorates renal injury in early-stage diabetic nephropathy (DN) in rats. Urinary albumin excretion increased in vehicle-treated diabetic rats (single injection of streptozotocin), compared with controls, and was associated with tubule injury and increased urinary tumor necrosis factor-α (TNF-α) at 9 weeks. These effects were significantly reduced by FTY720, a non-selective, or SEW2871, a selective S1P1R agonist. Interestingly, only FTY720 was associated with reduced total lymphocyte levels. Albuminuria was reduced by SEW2871 in both Rag-1 (T- and B-cell deficient) and wild-type diabetic mice after 6 weeks, suggesting that the effect was independent of lymphocytes. Another receptor, S1P3R, did not contribute to the FTY720-mediated protection, as albuminuria was also reduced in diabetic S1P3R knockout mice. Further, both agonists restored WT-1 staining along with podocin and nephrin mRNA expression, suggesting podocyte protection. This was corroborated in vitro, as SEW2871 reduced TNF-α and vascular endothelial growth factor mRNA expression in immortalized podocytes grown in media containing high glucose. Whether targeting kidney S1P1Rs will be a useful therapeutic measure in DN will need direct testing.

Pharmacological pre- and post-conditioning with the sphingosine-1-phosphate receptor modulator FTY720 after myocardial ischaemia-reperfusion

BACKGROUND AND PURPOSE

Our recent experiments demonstrated that the Sphingosine-1-phosphate (S1P) receptor agonist FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol hydrochloride) improves recovery of function after myocardial ischaemia-reperfusion ex vivo. Therefore, we tested the hypothesis that pharmacological post-conditioning with FTY720 reduces infarct size after myocardial ischaemia-reperfusion in vivo.

EXPERIMENTAL APPROACH

Myocardial ischaemia was induced in Wistar rats by ligation of the left coronary artery for 45 min. FTY720 (0.5 mg kg(-1)) was applied i.p. either once, before reperfusion, or twice, 24 h before myocardial ischaemia and before reperfusion. After 24 h reperfusion, we determined infarct size by triphenyltetrazolium chloride staining and granulocyte infiltration by immunohistochemistry. Tumour necrosis factor-alpha (TNF)-alpha concentration was determined by elisa. S1P receptor expression was studied by Western blot. Calcium transients were evaluated in Indo-1-loaded cardiomyocytes.

KEY RESULTS

In both groups, FTY720 significantly reduced lymphocyte count in peripheral blood. FTY720 treatment attenuated granulocyte infiltration and TNF-alpha protein expression in reperfused myocardium. However, both treatment regimens were not able to reduce infarct size. FTY720 increased mortality due to induction of fatal ventricular tachyarrhythmias when administered once before reperfusion, but protected against reperfusion arrhythmias when given 24 h prior to ischaemia. Pretreatment selectively down-regulated S1P(1) receptor expression within the myocardium. S1P receptor agonists did not induce calcium deregulation in cardiomyocytes.

CONCLUSIONS AND IMPLICATIONS

FTY720 applied during reperfusion did not reduce infarct size but increased mortality during myocardial ischaemia-reperfusion due to induction of arrhythmias. Pretreatment with FTY720 before ischaemia abrogated the deleterious pro-arrhythmic effects without reducing infarct size.

Functional repair of human donor lungs by IL-10 gene therapy

More than 80% of potential donor lungs are injured during brain death of the donor and from complications experienced in the intensive care unit, and therefore cannot be used for transplantation. These lungs show inflammation and disruption of the alveolar-capillary barrier, leading to poor gas exchange. Although the number of patients in need of lung transplantation is increasing, the number of donors is static. We investigated the potential to use gene therapy with an adenoviral vector encoding human interleukin-10 (AdhIL-10) to repair injured donor lungs ex vivo before transplantation. IL-10 is an anti-inflammatory cytokine that mainly exerts its suppressive functions by the inactivation of antigen-presenting cells with consequent inhibition of proinflammatory cytokine secretion. In pigs, AdhIL-10-treated lungs exhibited attenuated inflammation and improved function after transplantation. Lungs from 10 human multiorgan donors that had suffered brain death were determined to be clinically unsuitable for transplantation. They were then maintained for 12 hours at body temperature in an ex vivo lung perfusion system with or without intra-airway delivery of AdhIL-10 gene therapy. AdhIL-10-treated lungs showed significant improvement in function (arterial oxygen pressure and pulmonary vascular resistance) when compared to controls, a favorable shift from proinflammatory to anti-inflammatory cytokine expression, and recovery of alveolar-blood barrier integrity. Thus, treatment of injured human donor lungs with the cytokine IL-10 can improve lung function, potentially rendering injured lungs suitable for transplantation into patients.