Effect of FTY720, a novel immunosuppressant, on adjuvant- and collagen-induced arthritis in rats

Sphingolipid-Induced Bone Regulation and Its Emerging Role in Dysfunction Due to Disease and Infection

The human skeleton is a metabolically active system that is constantly regenerating via the tightly regulated and highly coordinated processes of bone resorption and formation. Emerging evidence reveals fascinating new insights into the role of sphingolipids, including sphingomyelin, sphingosine, ceramide, and sphingosine-1-phosphate, in bone homeostasis. Sphingolipids are a major class of highly bioactive lipids able to activate distinct protein targets including, lipases, phosphatases, and kinases, thereby conferring distinct cellular functions beyond energy metabolism. Lipids are known to contribute to the progression of chronic inflammation, and notably, an increase in bone marrow adiposity parallel to elevated bone loss is observed in most pathological bone conditions, including aging, rheumatoid arthritis, osteoarthritis, and osteomyelitis. Of the numerous classes of lipids that form, sphingolipids are considered among the most deleterious. This review highlights the important primary role of sphingolipids in bone homeostasis and how dysregulation of these bioactive metabolites appears central to many chronic bone-related diseases. Further, their contribution to the invasion, virulence, and colonization of both viral and bacterial host cell infections is also discussed. Many unmet clinical needs remain, and data to date suggest the future use of sphingolipid-targeted therapy to regulate bone dysfunction due to a variety of diseases or infection are highly promising. However, deciphering the biochemical and molecular mechanisms of this diverse and extremely complex sphingolipidome, both in terms of bone health and disease, is considered the next frontier in the field.

Pharmacological elevation of sphingosine-1-phosphate by S1P lyase inhibition accelerates bone regeneration after post-traumatic osteomyelitis

Posttraumatic osteomyelitis and the ensuing bone defects are a debilitating complication after open fractures with little therapeutic options. We have recently identified potent osteoanabolic effects of sphingosine-1-phosphate (S1P) signalling and have now tested whether it may beneficially affect bone regeneration after infection. We employed pharmacological S1P lyase inhibition by 4-deoxypyrodoxin (DOP) to raise S1P levels in vivo in an unicortical long bone defect model of posttraumatic osteomyelitis in mice. In a translational approach, human bone specimens of clinical osteomyelitis patients were treated in organ culture in vitro with DOP. Bone regeneration was assessed by μCT, histomorphometry, immunohistology and gene expression analysis. The role of S1P receptors was addressed using S1PR3 deficient mice. Here, we present data that DOP treatment markedly enhanced osteogenesis in posttraumatic osteomyelitis. This was accompanied by greatly improved osteoblastogenesis and enhanced angiogenesis in the callus accompanied by osteoclast-mediated bone remodelling. We also identified the target of increased S1P to be the S1PR3 as S1PR3-/- mice showed no improvement of bone regeneration by DOP. In the human bone explants, bone mass significantly increased along with enhanced osteoblastogenesis and angiogenesis. Our data suggest that enhancement of S1P/S1PR3 signalling may be a promising therapeutic target for bone regeneration in posttraumatic osteomyelitis.

Molecular and neuroimmune pharmacology of S1P receptor modulators and other disease-modifying therapies for multiple sclerosis

Multiple sclerosis (MS) is a neurological, immune-mediated demyelinating disease that affects people in the prime of life. Environmental, infectious, and genetic factors have been implicated in its etiology, although a definitive cause has yet to be determined. Nevertheless, multiple disease-modifying therapies (DMTs: including interferons, glatiramer acetate, fumarates, cladribine, teriflunomide, fingolimod, siponimod, ozanimod, ponesimod, and monoclonal antibodies targeting ITGA4, CD20, and CD52) have been developed and approved for the treatment of MS. All the DMTs approved to date target immunomodulation as their mechanism of action (MOA); however, the direct effects of some DMTs on the central nervous system (CNS), particularly sphingosine 1-phosphate (S1P) receptor (S1PR) modulators, implicate a parallel MOA that may also reduce neurodegenerative sequelae. This review summarizes the currently approved DMTs for the treatment of MS and provides details and recent advances in the molecular pharmacology, immunopharmacology, and neuropharmacology of S1PR modulators, with a special focus on the CNS-oriented, astrocyte-centric MOA of fingolimod.

Sphingosylphosphorylcholine ameliorates experimental sjögren's syndrome by regulating salivary gland inflammation and hypofunction, and regulatory B cells

Sjögren syndrome (SS) is an autoimmune disease in which immune cells infiltrate the exocrine gland. Since SS is caused by a disorder of the immune system, treatments should regulate the immune response. Sphingosylphosphorylcholine (SPC) is a sphingolipid that mediates cellular signaling. In immune cells, SPC has several immunomodulatory functions. Accordingly, this study verifies the immunomodulatory ability and therapeutic effect of SPC in SS. To understand the function of SPC in SS, we treated SPC in female NOD/ShiJcl (NOD) mice. The mice were monitored for 10 weeks, and inflammation in the salivary glands was checked. After SPC treatment, we detected the expression of regulatory B (B_reg) cells in mouse splenocytes and the level of salivary secretion-related genes in human submandibular gland (HSG) cells. Salivary flow rate was maintained in the SPC-treated group compared to the vehicle-treated group, and inflammation in the salivary gland tissues was relieved by SPC. SPC treatment in mouse cells and HSG cells enhanced B_reg cells and salivary secretion markers, respectively. This study revealed that SPC can be considered as a new therapeutic agent against SS.

Sphingosine 1-phosphate receptor-targeted therapeutics in rheumatic diseases

Sphingosine 1-phosphate (S1P), which acts via G protein-coupled S1P receptors (S1PRs), is a bioactive lipid essential for vascular integrity and lymphocyte trafficking. The S1P-S1PR signalling axis is a key component of the inflammatory response in autoimmune rheumatic diseases. Several drugs that target S1PRs have been approved for the treatment of multiple sclerosis and inflammatory bowel disease and are under clinical testing for patients with systemic lupus erythematosus (SLE). Preclinical studies support the hypothesis that targeting the S1P-S1PR axis would be beneficial to patients with SLE, rheumatoid arthritis (RA) and systemic sclerosis (SSc) by reducing pathological inflammation. Whereas most preclinical research and development efforts are focused on reducing lymphocyte trafficking, protective effects of circulating S1P on endothelial S1PRs, which maintain the vascular barrier and enable blood circulation while dampening leukocyte extravasation, have been largely overlooked. In this Review, we take a holistic view of S1P-S1PR signalling in lymphocyte and vascular pathobiology. We focus on the potential of S1PR modulators for the treatment of SLE, RA and SSc and summarize the rationale, pathobiology and evidence from preclinical models and clinical studies. Improved understanding of S1P pathobiology in autoimmune rheumatic diseases and S1PR therapeutic modulation is anticipated to lead to efficacious and safer management of these diseases.

Amelioration of complete Freund’s adjuvant-induced arthritis by Calotropis procera latex in rats

Background

Rheumatoid arthritis is the most common cause of disability, affecting 0.3–1% of the adult population worldwide. The latex of Calotropis procera possesses potent anti-inflammatory as well as analgesic properties. In light above facts, the present study was designed to evaluate anti-arthritic activity of Calotropis procera latex in complete Freund's adjuvant (CFA)-induced arthritis in Wistar albino rats. Complete Freund's adjuvant was injected into the left hind paw on day 0, and treatment of prednisolone and Calotropis procera latex was given from day 0 to 28. Various biochemical, hematological and functional parameters as well as radiological and histopathological changes of joint along with body weight and paw volume were measured.

Results

Calotropis procera treatment significantly lowered paw volume in CFA-induced arthritic rats. Significant improvement was observed in functional, biochemical and hematological parameters in Calotropis procera-treated rats. However, the body weight remained unaffected. Histological and radiographical examination of synovial joints in Calotropis procera-treated animals exhibited less synovial hyperplasia, infiltration and accumulation of inflammatory cell in synovial fluid, cartilage and bone erosion and joint space narrowing.

Conclusion

Calotropis procera latex possesses anti-arthritic activity, which is facilitated by modulation in the level of inflammatory mediators and oxidative stress. The improvement in hematological as well as biochemical parameters might be reflected on functional, histopathological, radiological changes and thereby disease progression.

Targeting S1PRs as a Therapeutic Strategy for Inflammatory Bone Loss Diseases-Beyond Regulating S1P Signaling

As G protein coupled receptors, sphingosine-1-phosphate receptors (S1PRs) have recently gained attention for their role in modulating inflammatory bone loss diseases. Notably, in murine studies inhibiting S1PR2 by its specific inhibitor, JTE013, alleviated osteoporosis induced by RANKL and attenuated periodontal alveolar bone loss induced by oral bacterial inflammation. Treatment with a multiple S1PRs modulator, FTY720, also suppressed ovariectomy-induced osteoporosis, collagen or adjuvant-induced arthritis, and apical periodontitis in mice. However, most previous studies and reviews have focused mainly on how S1PRs manipulate S1P signaling pathways, subsequently affecting various diseases. In this review, we summarize the underlying mechanisms associated with JTE013 and FTY720 in modulating inflammatory cytokine release, cell chemotaxis, and osteoclastogenesis, subsequently influencing inflammatory bone loss diseases. Studies from our group and from other labs indicate that S1PRs not only control S1P signaling, they also regulate signaling pathways induced by other stimuli, including bacteria, lipopolysaccharide (LPS), bile acid, receptor activator of nuclear factor κB ligand (RANKL), IL-6, and vitamin D. JTE013 and FTY720 alleviate inflammatory bone loss by decreasing the production of inflammatory cytokines and chemokines, reducing chemotaxis of inflammatory cells from blood circulation to bone and soft tissues, and suppressing RANKL-induced osteoclast formation.

Aryl Ether-Derived Sphingosine-1-Phosphate Receptor (S1P1) Modulators: Optimization of the PK, PD, and Safety Profiles

Efforts aimed at increasing the in vivo potency and reducing the elimination half-life of 1 and 2 led to the identification of aryl ether and thioether-derived bicyclic S1P₁ differentiated modulators 3-6. The effects of analogs 3-6 on lymphocyte reduction in the rat (desired pharmacology) along with pulmonary- and cardiovascular-related effects (undesired pharmacology) are described. Optimization of the overall properties in the aryl ether series yielded 3d, and the predicted margin of safety against the cardiovascular effects of 3d would be large enough for human studies. Importantly, compared to 1 and 2, compound 3d had a better profile in both potency (ED₅₀ < 0.05 mg/kg) and predicted human half-life (t _1/2 ∼ 5 days).

Does Siponimod Exert Direct Effects in the Central Nervous System?

The modulation of the sphingosine 1-phosphate receptor is an approved treatment for relapsing multiple sclerosis because of its anti-inflammatory effect of retaining lymphocytes in lymph nodes. Different sphingosine 1-phosphate receptor subtypes are expressed in the brain and spinal cord, and their pharmacological effects may improve disease development and neuropathology. Siponimod (BAF312) is a novel sphingosine 1-phosphate receptor modulator that has recently been approved for the treatment of active secondary progressive multiple sclerosis (MS). In this review article, we summarize recent evidence suggesting that the active role of siponimod in patients with progressive MS may be due to direct interaction with central nervous system cells. Additionally, we tried to summarize our current understanding of the function of siponimod and discuss the effects observed in the case of MS.

S1P-S1PR1 Signaling: the "Sphinx" in Osteoimmunology

The fundamental interaction between the immune and skeletal systems, termed as osteoimmunology, has been demonstrated to play indispensable roles in the maintenance of balance between bone resorption and formation. The pleiotropic sphingolipid metabolite, sphingosine 1-phosphate (S1P), together with its cognate receptor, sphingosine-1-phosphate receptor-1 (S1PR1), are known as key players in osteoimmunology due to the regulation on both immune system and bone remodeling. The role of S1P-S1PR1 signaling in bone remodeling can be directly targeting both osteoclastogenesis and osteogenesis. Meanwhile, inflammatory cell function and polarization in both adaptive immune (T cell subsets) and innate immune cells (macrophages) are also regulated by this signaling axis, suggesting that S1P-S1PR1 signaling could aslo indirectly regulate bone remodeling via modulating the immune system. Therefore, it could be likely that S1P-S1PR1 signaling might take part in the maintenance of continuous bone turnover under physiological conditions, while lead to the pathogenesis of bone deformities during inflammation. In this review, we summarized the immunological regulation of S1P-S1PR1 signal axis during bone remodeling with an emphasis on how osteo-immune regulators are affected by inflammation, an issue with relevance to chronical bone disorders such as rheumatoid arthritis, spondyloarthritis and periodontitis.

Triggering the Resolution of Immune Mediated Inflammatory Diseases: Can Targeting Leukocyte Migration Be the Answer?

Leukocyte recruitment is a pivotal process in the regulation and resolution of an inflammatory episode. It is vital for the protective responses to microbial infection and tissue damage, but is the unwanted reaction contributing to pathology in many immune mediated inflammatory diseases (IMIDs). Indeed, it is now recognized that patients with IMIDs have defects in at least one, if not multiple, check-points regulating the entry and exit of leukocytes from the inflamed site. In this review, we will explore our understanding of the imbalance in recruitment that permits the accumulation and persistence of leukocytes in IMIDs. We will highlight old and novel pharmacological tools targeting these processes in an attempt to trigger resolution of the inflammatory response. In this context, we will focus on cytokines, chemokines, known pro-resolving lipid mediators and potential novel lipids (e.g., sphingosine-1-phosphate), along with the actions of glucocorticoids mediated by 11-beta hydroxysteroid dehydrogenase 1 and 2.

Leukocyte trafficking between stromal compartments: lessons from rheumatoid arthritis

The trafficking of leukocytes from their site of production in the bone marrow through the circulation and into peripheral tissues is a highly coordinated and tightly regulated process in healthy individuals. Lymphocytes are long-lived cells that visit many lymphoid and peripheral tissues over their lifetime and can even recirculate back to the bone marrow, whereas granulocytes and monocytes are not thought to recirculate so widely. Using rheumatoid arthritis (RA) as an example, this Review explores the migratory journey of leukocytes during the establishment and resolution of disease - from the blood, through the lymphoid tissues and into peripheral sites such as the lungs and the gut before their entry into the synovium. This Review explores our current understanding of differences in the molecular processes that regulate leukocyte trafficking at different phases of disease and in different stromal compartments, which could help to explain the disease heterogeneity seen in patients with RA. Expanding our knowledge of these processes will open new avenues in the clinical management of RA, paving the way for personalized medicine that is founded on the pathological molecular signature of each patient, which varies according to their phase of disease or disease subtype.

Sphingosine-1-Phosphate Promotes the Persistence of Activated CD4 T Cells in Inflamed Sites

Inflammation can be protective or pathogenic depending on context and timeframe. Acute inflammation, including the accumulation of CD4 T cells, accompanies protective immune responses to pathogens, but the presence of activated CD4 T cells at sites of inflammation is associated with chronic inflammatory disease. While significant progress has been made in understanding the migration of CD4 T cells into inflamed sites, the signals that lead to their persistence are poorly characterized. Using a murine ear model of acute inflammation and intravital two-photon imaging, we have dissected the signals that mediate CD4 T cell persistence. We report the unexpected finding that the bioactive lipid, sphingosine-1-phosphate (S1P), is both necessary and sufficient for the persistence of activated CD4 T cells at peripheral tissues in acute inflammation. S1P mediated the enhanced motility of CD4 T cells at inflamed tissues but did not affect their migration to the downstream draining lymph node. We found that sphingosine kinase-1, which regulates S1P production is increased at inflamed sites in mice and in patients with the chronic inflammatory disease, rheumatoid arthritis. Together, these data suggest that S1P, or its regulators, may be key targets to promote or disrupt accumulation of CD4 T cells at inflamed tissues.

Inflammatory Cell Migration in Rheumatoid Arthritis: A Comprehensive Review

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that primarily affects the joints. Self-reactive B and T lymphocytes cooperate to promote antibody responses against self proteins and are major drivers of disease. T lymphocytes also promote RA independently of B lymphocytes mainly through the production of key inflammatory cytokines, such as IL-17, that promote pathology. While the innate signals that initiate self-reactive adaptive immune responses are poorly understood, the disease is predominantly caused by inflammatory cellular infiltration and accumulation in articular tissues, and by bone erosions driven by bone-resorbing osteoclasts. Osteoclasts are giant multinucleated cells formed by the fusion of multiple myeloid cells that require short-range signals, such as the cytokines MCSF and RANKL, for undergoing differentiation. The recruitment and positioning of osteoclast precursors to sites of osteoclast differentiation by chemoattractants is an important point of control for osteoclastogenesis and bone resorption. Recently, the GPCR EBI2 and its oxysterol ligand 7a, 25 dihydroxycholesterol, were identified as important regulators of osteoclast precursor positioning in proximity to bone surfaces and of osteoclast differentiation under homeostasis. In chronic inflammatory diseases like RA, osteoclast differentiation is also driven by inflammatory cytokines such as TNFa and IL-1, and can occur independently of RANKL. Finally, there is growing evidence that the chemotactic signals guiding osteoclast precursors to inflamed articular sites contribute to disease and are of great interest. Furthering our understanding of the complex osteoimmune cell interactions should provide new avenues of therapeutic intervention for RA.

Chemical Hypoxia Brings to Light Altered Autocrine Sphingosine-1-Phosphate Signalling in Rheumatoid Arthritis Synovial Fibroblasts

Emerging evidence suggests a role for sphingosine-1-phosphate (S1P) in various aspects of rheumatoid arthritis (RA) pathogenesis. In this study we compared the effect of chemical hypoxia induced by cobalt chloride (CoCl₂) on the expression of S1P metabolic enzymes and cytokine/chemokine secretion in normal fibroblast-like synoviocytes (FLS) and RAFLS. RAFLS incubated with CoCl₂, but not S1P, produced less IL-8 and MCP-1 than normal FLS. Furthermore, incubation with the S1P₂ and S1P₃ receptor antagonists, JTE-013 and CAY10444, reduced CoCl₂-mediated chemokine production in normal FLS but not in RAFLS. RAFLS showed lower levels of intracellular S1P and enhanced mRNA expression of S1P phosphatase 1 (SGPP1) and S1P lyase (SPL), the enzymes that are involved in intracellular S1P degradation, when compared to normal FLS. Incubation with CoCl₂ decreased SGPP1 mRNA and protein and SPL mRNA as well. Inhibition of SPL enhanced CoCl₂-mediated cytokine/chemokine release and restored autocrine activation of S1P₂ and S1P₃ receptors in RAFLS. The results suggest that the sphingolipid pathway regulating the intracellular levels of S1P is dysregulated in RAFLS and has a significant impact on cell autocrine activation by S1P. Altered sphingolipid metabolism in FLS from patients with advanced RA raises the issue of synovial cell burnout due to chronic inflammation.

FTY720 Abrogates Collagen-Induced Arthritis by Hindering Dendritic Cell Migration to Local Lymph Nodes

Because dendritic cells (DCs) play critical roles in the pathogenesis of rheumatoid arthritis, modulation of their functions could serve as a novel therapy. In this study, we demonstrated that FTY720 treatment significantly suppressed the incidence and severity of collagen-induced arthritis (CIA) in DBA/1J mice via the modulation of DC functions. In FTY720-treated CIA mice, a decrease in the number of DCs in local draining lymph nodes (LNs) was observed. In vitro, FTY720 inhibited the trafficking of LPS-stimulated bone marrow-derived DCs (BMDCs). Decreased secretion of CCL19 and downregulation of CCR7 on DCs may explain the mechanisms underlying the impairment of DC migration induced by FTY720. In a DC-induced mouse arthritis model, FTY720 treatment also suppressed the incidence and severity of arthritis, which was correlated with a decrease in the migration of injected BMDCs to draining LNs. Although lower levels of costimulatory molecules (CD40, CD80, and CD86) and I-A(q) expressed on LN DCs were observed in FTY720-treated mice, in vitro analysis showed no effect of FTY720 on LPS-stimulated BMDC maturation. Furthermore, LN cells from FTY720-treated CIA mice displayed diminished production of proinflammatory cytokines in response to collagen II and Con A stimulation. In addition, the ratio of Th1/Th2 in the draining LNs of mice with DC-induced arthritis was decreased upon FTY720 treatment. This finding was consistent with the fact that FTY720 suppressed IL-12p70 production in cultured BMDCs. Taken together, these results indicate that inhibition of DC migration by FTY720 may provide a novel approach in treating autoimmune diseases such as rheumatoid arthritis.

Development and optimization of a high-throughput micro-computed tomography imaging method incorporating a novel analysis technique to evaluate bone mineral density of arthritic joints in a rodent model of collagen induced arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease resulting in joint inflammation, pain, and eventual bone loss. Bone loss and remodeling caused by symmetric polyarthritis, the hallmark of RA, is readily detectable by bone mineral density (BMD) measurement using micro-CT. Abnormalities in these measurements over time reflect the underlying pathophysiology of the bone. To evaluate the efficacy of anti-rheumatic agents in animal models of arthritis, we developed a high throughput knee and ankle joint imaging assay to measure BMD as a translational biomarker. A bone sample holder was custom designed for micro-CT scanning, which significantly increased assay throughput. Batch processing 3-dimensional image reconstruction, followed by automated image cropping, significantly reduced image processing time. In addition, we developed a novel, automated image analysis method to measure BMD and bone volume of knee and ankle joints. These improvements significantly increased the throughput of ex vivo bone sample analysis, reducing data turnaround from 5 days to 24 hours for a study with 200 rat hind limbs. Taken together, our data demonstrate that BMD, as quantified by micro-CT, is a robust efficacy biomarker with a high degree of sensitivity. Our innovative approach toward evaluation of BMD using optimized image acquisition and novel image processing techniques in preclinical models of RA enables high throughput assessment of anti-rheumatic agents offering a powerful tool for drug discovery.

Prominence of central sphingosine-1-phosphate receptor-1 in attenuating aβ-induced injury by fingolimod

FTY720 (fingolimod), the sphingosine-1-phosphate (S1P) analogue, has been experimentally indicated to exert substantial ameliorating effects in animal models of Alzheimer's disease (AD). The present work aims to answer whether central S1P receptor 1 (S1P1) plays significant role in the impact of fingolimod in AD. To verify the prominence of central FTY720 phosphorylation, DMS (sphingosine kinase inhibitor) was infused intracerebrally in parallel with systemic FTY720 administration to prevent central formation of FTY720-P as the recognized active ligand for S1PRs. The corresponding S1P1 modulation was also investigated using the pharmacological blockage of central S1P1 by W123. Both DMS and W123 were efficiently capable of suppressing FTY720-ameliorating effects in AD animals, either on memory deficit or on COX-II and TNF-α expression. Our data conclude that experimental benefits of FTY720 in the context of AD depend on central S1P1 modulation, as well as on S1P kinase activity in the brain.

The role of sphingosine 1-phosphate in inflammation and cancer

The enzymes that catalyze formation of the bioactive sphingolipid, sphingosine 1-phosphate, sphingosine kinase 1 and 2, are predictive markers in inflammatory diseases and cancer as evidenced by data from patients, knockout mice and the use of available molecular and chemical inhibitors. Thus, there is a compelling case for therapeutic targeting of sphingosine kinase. In addition, there are several examples of functional interaction between sphingosine 1-phosphate receptors and sphingosine kinase 1 that can drive malicious amplification loops that promote cancer cell growth. These novel aspects of sphingosine 1-phosphate pathobiology are reviewed herein.

Gastric parietal cell atrophy and depletion after administration of a sphingosine-1-phosphate 1 inhibitor

Sphingosine-1-phosphate (S1P) is a major bioactive phospholipid, which binds to and activates a family of five G-protein-coupled receptors designated as S1P 1 (S1P1) through S1P5. The S1P1 receptor subtype, expressed primarily on lymphocytes, is known to play a critical role in the regulation of lymphocyte trafficking. S1P1 inhibitors result in the inhibition of lymphoid cell trafficking and are of interest to treat various inflammatory conditions. In this study, we describe a gastric finding associated with oral gavage administration of a small molecule S1P1 inhibitor to Sprague-Dawley rats. Rats were administered an S1P1 inhibitor once daily for 4 weeks and necropsies were conducted at the end of the dosing phase, and clinical pathology and histopathologic examination were performed. Lymphopenia and changes in lymphoid tissues were noted and were consistent with the pharmacodynamic effects for S1P1 inhibitory action. Histopathologic examination of the stomach revealed atrophy and depletion of gastric parietal cells in the glandular portion of the stomach. There are no literature data to suggest that this gastric effect is related to S1P1 pharmacology. Therefore, the mechanism of the observed gastric lesion is likely chemotype mediated.

Therapeutic use of a selective S1P1 receptor modulator ponesimod in autoimmune diabetes

In the present study, we investigated the therapeutic potential of a selective S1P₁ receptor modulator, ponesimod, to protect and reverse autoimmune diabetes in non-obese diabetic (NOD) mice. Ponesimod was administered orally to NOD mice starting at 6, 10, 13 and 16 weeks of age up to 35 weeks of age or to NOD mice showing recent onset diabetes. Peripheral blood and spleen B and T cell counts were significantly reduced after ponesimod administration. In pancreatic lymph nodes, B lymphocytes were increased and expressed a transitional 1-like phenotype. Chronic oral ponesimod treatment efficiently prevented autoimmune diabetes in 6, 10 and 16 week-old pre-diabetic NOD mice. Treatment withdrawal led to synchronized disease relapse. Ponesimod did not inhibit the differentiation of autoreactive T cells as assessed by adoptive transfer of lymphocytes from treated disease-free NOD mice. In addition, it did not affect the migration, proliferation and activation of transgenic BDC2.5 cells into the target tissue. However, ponesimod inhibited spreading of the T cell responses to islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP). Treatment of diabetic NOD mice with ponesimod induced disease remission. However, here again, upon treatment cessation, the disease rapidly recurred. This recurrence was effectively prevented by combination treatment with a CD3 antibody leading to the restoration of self-tolerance. In conclusion, treatment with a selective S1P₁ modulator in combination with CD3 antibody represents a promising therapeutic approach for the treatment of autoimmune diabetes.

Sphingosine kinase and sphingosine-1-phosphate: regulators in autoimmune and inflammatory disease

Sphingolipids and their metabolizing enzymes are beginning to be recognized as critical mediators in biological processes, specifically in inflammation and autoimmunity. Sphingosine kinases (SKs) and their lipid product sphingosine-1-phosphate (S1P) play essential roles in inflammatory signaling processes, as well as disease development and progression. SKs can be activated by numerous growth factors and cytokines, including TNF-α and IL-1β, leading to the generation of S1P. S1P exerts its biological effects on intracellular and extracellular targets, such as S1P receptors. In addition to roles in inflammatory signaling pathways SKs, S1P and S1P receptors have been implicated in immune cell function and trafficking, specifically in lymphocytes. This review will discuss the contribution of the bioactive sphingolipid S1P, its generating enzyme SK, and its cell surface receptors in the inflammatory and autoimmune diseases systemic lupus erythematosus, arthritis and inflammatory bowel disease.

Predictability of Peripheral Lymphocyte Reduction of Novel S1P1 Agonists by In Vitro GPCR Signaling Profile

Surrogate readouts of G-protein–coupled receptor signaling pathways using highly engineered systems are often employed in the drug discovery process. However, accumulating data have demonstrated the importance of selecting relevant biological activity rather than technically facile assays to support high-throughout screening and subsequent structure-activity relationship studies. Here we report a case study using sphingosine-1-phosphate receptor 1 (S1P1) as the model system to compare compound activity in six different in vitro assays with their ability to predict in vivo efficacy. S1P1 has long been validated as a therapeutic target for autoimmune diseases. In this article, in vivo and in vitro studies on 19 S1P1 agonists are reported. In vitro activities of these S1P1 agonists, together with S1P and FTY720p, on Ca2+ mobilization, adenylyl cyclase inhibition, extracellular signal-related kinase (ERK) phosphorylation, β-arrestin recruitment, and receptor internalization, were determined. The in vitro potency of these compounds was correlated with their ability to induce peripheral lymphocyte reduction. The results revealed that inhibition of adenylyl cyclase and induction of β-arrestin recruitment and receptor internalization are good indicators to predict in vivo efficacy, whereas induction of Ca2+ mobilization through Gqi/5 coupling and ERK phosphorylation is irrelevant. This study demonstrated the importance of identifying an appropriate in vitro assay to predict in vivo activity based on the biological relevance in the drug discovery setting.

Sphingosine 1-phosphate mediates hyperalgesia via a neutrophil-dependent mechanism

Novel classes of pain-relieving molecules are needed to fill the void between non-steroidal anti-inflammatory agents and narcotics. We have recently shown that intraplantar administration of sphingosine 1-phosphate (S1P) in rats causes peripheral sensitization and hyperalgesia through the S1P(1) receptor subtype (S1PR(1)): the mechanism(s) involved are largely unknown and were thus explored in the present study. Intraplantar injection of carrageenan in rats led to a time-dependent development of thermal hyperalgesia that was associated with pronounced edema and infiltration of neutrophils in paw tissues. Inhibition of 1) S1P formation with SK-I, a sphingosine kinase inhibitor, 2) S1P bioavailability with the S1P blocking antibody Sphingomab, LT1002 (but not its negative control, LT1017) or 3) S1P actions through S1PR(1) with the selective S1PR(1) antagonist, W146 (but not its inactive enantiomer, W140) blocked thermal hyperalgesia and infiltration of neutrophils. Taken together, these findings identify S1P as an important contributor to inflammatory pain acting through S1PR(1) to elicit hyperalgesia in a neutrophil-dependant manner. In addition and in further support, we demonstrate that the development of thermal hyperalgesia following intraplantar injection of S1P or SEW2871 (an S1PR(1) agonist) was also associated with neutrophilic infiltration in paw tissues as these events were attenuated by fucoidan, an inhibitor of neutrophilic infiltration. Importantly, FTY720, an FDA-approved S1P receptor modulator known to block S1P-S1PR(1) signaling, attenuated carrageenan-induced thermal hyperalgesia and associated neutrophil infiltration. Targeting the S1P/S1PR(1) axis opens a therapeutic strategy for the development of novel non-narcotic anti-hyperalgesic agents.

FTY720 on the way from the base camp to the summit of the mountain: relevance for remyelination

FTY720 (fingolimod; Gilenya®), a sphingosine 1-phosphate (S1P) receptor modulator, is the first oral disease-modifying therapy to be approved for the treatment of relapsing-remitting multiple sclerosis. FTY720 is rapidly converted in vivo to the active S-fingolimod-phosphate, which binds to S1P receptors. This action inhibits egress of lymphocytes from the lymph nodes, preventing entry into the blood and thus infiltration into the central nervous system. More recent studies, however, convincingly show that FTY720 crosses the blood-brain barrier, where it is thought to act on S1P receptors on cells within the central nervous system, such as astrocytes, oligodendrocytes or microglia. Here we discuss the evidence showing that FTY720 also plays a role in remyelination and repair within the brain. While the mechanisms of action still require firm elucidation, it is clear that FTY720 could also be reparative, extending its therapeutic potential for multiple sclerosis.

Fused tricyclic indoles as S1P₁ agonists with robust efficacy in animal models of autoimmune disease

Two series of fused tricyclic indoles were identified as potent and selective S1P(1) agonists. In vivo these agonists produced a significant reduction in circulating lymphocytes which translated into robust efficacy in several rodent models of autoimmune disease. Importantly, these agonists were devoid of any activity at the S1P(3) receptor in vitro, and correspondingly did not produce S1P(3) mediated bradycardia in telemeterized rat.

Sphingosine analogue AAL-R increases TLR7-mediated dendritic cell responses via p38 and type I IFN signaling pathways

Sphingosine analogues display immunosuppressive activities and thus have therapeutic potential in the treatment of autoimmune diseases. In this study, we investigated the effects of the sphingosine analogue AAL-R (FTY720 derivative) on dendritic cell (DC) response upon TLR stimulation. Unlike its known immunosuppressive activity, AAL-R increased TLR7-mediated DC responses by elevating the levels of MHC class I and costimulatory molecules and type I IFN expression and by enhancing the capacity of DCs to induce CD8(+) T cell proliferation. Importantly, the stimulatory activity of AAL-R was dependent on type I IFN signaling, as type I IFN receptor-deficient DCs failed to respond to AAL-R. Also, AAL-R activated p38 MAPK to increase type I IFN synthesis and TLR7-mediated DC maturation. These findings enhance our understanding of sphingosine regulation of the host immune system, in particular upon pathogenic infections.

Pharmacological effects of CS-0777, a selective sphingosine 1-phosphate receptor-1 modulator: results from a 12-week, open-label pilot study in multiple sclerosis patients

CS-0777 is a selective sphingosine 1-phosphate receptor-1 modulator under investigation for treatment of multiple sclerosis (MS). We conducted an open-label, pilot study in 25 MS patients to assess the safety, pharmacokinetics, pharmacodynamics and exploratory efficacy of oral CS-0777 (0.1, 0.3 and 0.6 mg), administered once weekly or every other week for 12 weeks. CS-0777 resulted in a pronounced, dose-dependent decrease in lymphocytes and CD4 T cell subsets, which returned to baseline within 4 weeks after the last dose. Overall, CS-0777 was safe and well-tolerated. These results require confirmation in a double-blind, placebo-controlled and adequately powered phase 2 study in MS.

FTY720 improves functional recovery after spinal cord injury by primarily nonimmunomodulatory mechanisms

Spinal cord injury (SCI) is an incapacitating injury that can result in limited functional recovery. We have previously shown increases in the lysophospholipid mediator, sphingosine-1-phosphate (S1P), in the spinal cord after contusion injury. To apply S1P receptor modulation to the treatment of SCI, we examined the therapeutic effects of FTY720, an S1P receptor agonist, on locomotor recovery after SCI in mice. Oral administration of FTY720 shortly after contusion SCI significantly improved motor function recovery, as assessed by both Basso Mouse Scale scores and Rotarod Performance test results. FTY720 induced lymphopenia and reduced T-cell infiltration in the spinal cord after SCI but did not affect the early infiltration of neutrophils and the activation of microglia. In addition, plasma levels and mRNA expression of inflammatory cytokines in the spinal cord after SCI were not attenuated by FTY720. Vascular permeability and astrocyte accumulation were both decreased by FTY720 in the injured spinal cord. The therapeutic effects of FTY720 were not solely dependent on immune modulation, as confirmed by the demonstration that FTY720 also ameliorated motor function after SCI in mice with severe combined immunodeficiency. Finally, the S1P(1) receptor agonist, SEW2871, partly mimicked the therapeutic effect of FTY720. Our data highlight the importance of immune-independent functions of FTY720 in decreasing vascular permeability and astrogliosis in the injured spinal cord and promoting locomotor function recovery after SCI.

Sphingosine 1-phosphate (S1P)/S1P receptor 1 signaling regulates receptor activator of NF-κB ligand (RANKL) expression in rheumatoid arthritis

Sphingosine 1-phosphate (S1P)/S1P receptor 1 (S1P1) signaling plays an important role in synovial cell proliferation and inflammatory gene expression by rheumatoid arthritis (RA) synoviocytes. The purpose of this study is to clarify the role of S1P/S1P1 signaling in the expression of receptor activator of NF-κB ligand (RANKL) in RA synoviocytes and CD4(+) T cells. We demonstrated MH7A cells, a human RA synovial cell line, and CD4(+) T cells expressed S1P1 and RANKL. Surprisingly, S1P increased RANKL expression in MH7A cells and CD4(+) T cells in a dose-dependent manner. Moreover, S1P enhanced RANKL expression induced by stimulation with TNF-α in MH7A cells and CD4(+) T cells. These effects of S1P in MH7A cells were inhibited by pretreatment with PTX, a specific Gi/Go inhibitor. These findings suggest that S1P/S1P1 signaling may play an important role in RANKL expression by MH7A cells and CD4(+) T cells. S1P/S1P1 signaling of RA synoviocytes is closely connected with synovial hyperplasia, inflammation, and RANKL-induced osteoclastogenesis in RA. Thus, regulation of S1P/S1P1 signaling may become a novel therapeutic target for RA.

Effect of atorvastatin with or without prednisolone on Freund's adjuvant induced-arthritis in rats

Rheumatoid arthritis is a chronic systemic inflammatory disease where cardiovascular diseases have been recognized as major determinants of early morbidity and mortality. Recently, there has been renewed interest in medication with glucocorticoids to decrease joint damage, but in long-term they incur substantial increase in the risk of cardiovascular diseases and their overall risk/benefit ratio is deemed unfavorable. So, the proposed role of statins in treatment of rheumatoid arthritis when corticosteroids indicated as traditional therapy needs to be investigated. Fifty albino rats were divided into 5 equal groups; normal control group, Freund's adjuvant induced arthritis group, group of induced arthritis treated with atorvastatin, group of induced arthritis treated with prednisolone, and group of induced arthritis treated with atorvastatin and prednisolone. The change in paw volume, serum levels of malondialdehyde (MDA), paraoxonase1 (PON1) activity, nitrites, C-reactive protein (CRP) and lipid profile was determined. The results revealed that treatment by atorvastatin in combination with prednisolone produced better satisfactory results than in either remedy alone evidenced by significant decrease in volume of hind paw, levels of MDA, nitrites, CRP, significant increase in PON1 activity and HDL and amelioration of other lipid profile parameters that were impaired by prednisolone. The present work demonstrated that statins exert beneficial anti-inflammatory and antioxidant effects beyond their basic cholesterol-lowering activity. Thus, we suggest that if corticosteroid therapy is indicated in rheumatoid arthritis, atorvastatin could be added to get benefit from its pleiotropic effects. However, further studies are needed to verify to what extent statin therapy contribute to clinical benefits in human.

The immunosuppressant FTY720 (fingolimod) enhances glycosaminoglycan depletion in articular cartilage

Background

FTY720 (Fingolimod) is a novel immunosuppressive drug investigated in clinical trials for organ transplantation and multiple sclerosis. It acts as a functional sphingosine-1-phosphate (S1P) receptor antagonist, thereby inhibiting the egress of lymphocytes from secondary lymphoid organs. As S1P is able to prevent IL-1beta induced cartilage degradation, we examined the direct impact of FTY720 on cytokine induced cartilage destruction.

Methods

Bovine chondrocytes were treated with the bioactive phosphorylated form of FTY720 (FTY720-P) in combination with IL-1beta or TNF-alpha. Expression of MMP-1,-3.-13, iNOS and ADAMTS-4,-5 and COX-2 was evaluated using quantitative real-time PCR and western blot. Glycosaminoglycan depletion from cartilage explants was determined using a 1,9-dimethylene blue assay and safranin O staining.

Results

FTY720-P significantly reduced IL-1beta and TNF-alpha induced expression of iNOS. In contrast FTY720-P increased MMP-3 and ADAMTS-5 mRNA expression. Furthermore depletion of glycosaminoglycan from cartilage explants by IL-1beta and TNF-alpha was significantly enhanced by FTY720-P in an MMP-3 dependent manner.

Conclusions

Our results suggest that FTY720 may enhance cartilage degradation in pro-inflammatory environment.

The selective sphingosine 1-phosphate receptor 1 agonist ponesimod protects against lymphocyte-mediated tissue inflammation

Lymphocyte exit from lymph nodes and their recirculation into blood is controlled by the sphingolipid sphingosine 1-phosphate (S1P). The cellular receptor mediating lymphocyte exit is S1P(1), one of five S1P receptors. Nonselective agonists for S1P receptors lead to blood lymphocyte count reduction. The effects of selective S1P(1) agonists on blood lymphocyte count and their impact in models of lymphocyte-mediated tissue inflammation have been less investigated. We describe here the general pharmacology of ponesimod, (Z,Z)-5-[3-chloro-4-((2R)-2,3-dihydroxy-propoxy)-benzylidene]-2-propylimino-3-o-tolyl-thiazolidin-4-one, a new, potent, and orally active selective S1P(1) agonist. Ponesimod activated S1P(1)-mediated signal transduction with high potency (EC(50) of 5.7 nM) and selectivity. Oral administration of ponesimod to rats led to a dose-dependent decrease of blood lymphocyte count. After discontinuation of dosing, blood lymphocyte count returned to baseline within 48 h. Ponesimod prevented edema formation, inflammatory cell accumulation, and cytokine release in the skin of mice with delayed-type hypersensitivity. Ponesimod also prevented the increase in paw volume and joint inflammation in rats with adjuvant-induced arthritis. These data show that selective activation of S1P(1) using ponesimod leads to blood lymphocyte count reduction and efficacy in models of lymphocyte-mediated tissue inflammation. Immunomodulation with a rapidly reversible S1P(1)-selective agonist may represent a new therapeutic approach in lymphocyte-mediated autoimmune diseases.

The sphingosine 1-phosphate receptor modulator FTY720 prevents iodide-induced autoimmune thyroiditis in non-obese diabetic mice

FTY720 is an immunomodulator that alters migration and homing of lymphocytes via sphingosine 1-phosphate receptors. This compound has been shown to be effective in suppressing autoimmune diseases in experimental and clinical settings. In the present study, we tested whether FTY720 prevented autoimmune thyroiditis in iodide-treated non-obese diabetic (NOD) mice, a model of Hashimoto's thyroiditis (HT) in humans. Mice were given 0.05% iodide water for 8 weeks, and this treatment effectively induced thyroiditis. Iodide-treated mice were injected intraperitoneally with either saline or FTY720 during the iodide treatment. FTY720 clearly suppressed the development of thyroiditis and reduced serum anti-thyroglobulin antibody levels. The number of circulating lymphocytes and spleen cells including CD4(+) T cells, CD8(+) T cells, and CD4(+)Foxp3(+) T cells was decreased in FTY720-treated mice. Our results indicate that FTY720 has immunomodulatory effects on iodide-induced autoimmune thyroiditis in NOD mice and may be a potential candidate for use in the prevention of HT.

Comparative efficacy of a secretory phospholipase A2 inhibitor with conventional anti-inflammatory agents in a rat model of antigen-induced arthritis

Introduction

Previously, secretory phospholipase A₂ (sPLA₂) inhibition has been used as an adjunct to conventional rheumatoid arthritis therapy in human clinical trials without significant improvement of arthritic pathology. In this study, we compared the efficacy of a potent and orally active group IIa secretory phospholipase A₂ inhibitor (sPLA₂I) to conventional anti-arthritic agents; infliximab, leflunomide and prednisolone, in a rat model of antigen-induced arthritis.

Methods

Initially, to establish efficacy and dose-response, rats were orally dosed with the sPLA₂I (1 and 5 mg/kg) two days prior to arthritis induction, and then daily throughout the 14-day study period. In the second trial, rats were orally dosed with the sPLA₂I (5 and 10 mg/kg/day) beginning two days after the induction of arthritis, at the peak of joint swelling. Separate groups of rats were also dosed with the tumour necrosis factor-alpha (TNF-α) inhibitor infliximab (single 3 mg/kg i.v. injection), leflunomide (10 mg/kg/day, oral) or prednisolone (1 mg/kg/day, oral) at this same time point and used as comparative treatments.

Results

In the pathology prevention trial, both 1 and 5 mg/kg dose groups of sPLA₂I demonstrated a significant reduction in joint swelling and gait disturbances; however, only the higher 5 mg/kg dose resulted in significantly reduced histopathology scores. In the post-induction trial, rats dosed with sPLA₂I showed a significant improvement in joint swelling and gait scoring, whereas none of the conventional therapeutics achieved a significant decrease in both of these two disease markers. Histopathological scoring at the end-point of the study demonstrated significantly reduced median scores in rats treated with 10 mg/kg sPLA₂I and leflunomide.

Conclusions

The results from this study suggest a pathogenic role for sPLA₂ enzymes in this model of arthritis in rats, and the potential clinical utility of sPLA₂ inhibition as a safer, and more effective, alternative to conventional anti-arthritic therapeutics.

Sphingosine 1-phosphate, a key mediator of the cytokine network: juxtacrine signaling

Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite, which has emerged as an important signaling mediator participating in the regulation of multiple cellular processes. The discovery of a family of S1P receptors, together with the more recently identified intracellular targets, has provided fundamental understanding of the multi-faceted actions of S1P. Evidence from both in vitro and in vivo studies has implicated the S1P signaling system in the control of immunity, inflammation and many associated diseases. Enigmatically, S1P appears to have both pro- and anti-inflammatory effects depending on the cell context. Here, we review this emerging area and argue for a pivotal role for S1P, as a key mediator of the cytokine network, acting through juxtacrine signaling in the immune system.

Sphingosine kinase: Role in regulation of bioactive sphingolipid mediators in inflammation

Sphingolipids and their synthetic enzymes are emerging as important mediators in inflammatory responses and as regulators of immune cell functions. In particular, sphingosine kinase (SK) and its product sphingosine-1-phosphate (S1P) have been extensively implicated in these processes. SK catalyzes the phosphorylation of sphingosine to S1P and exists as two isoforms, SK1 and SK2. SK1 has been shown to be activated by cytokines including tumor necrosis factor-alpha (TNF-alpha) and interleukin1-beta (IL1-beta). The activation of SK1 in this pathway has been shown to be, at least in part, required for mediating TNF-alpha and IL1-beta inflammatory responses in cells, including induction of cyclo-oxygenase 2 (COX2). In addition to their role in inflammatory signaling, SK and S1P have also been implicated in various immune cell functions including, mast cell degranulation, migration of neutrophils, and migration and maturation of lymphocytes. The involvement of sphingolipids and sphingolipid metabolizing enzymes in inflammatory signaling and immune cell functions has implicated these mediators in numerous inflammatory disease states as well. The contribution of these mediators, specifically SK1 and S1P, to inflammation and disease are discussed in this review.

Effects of the novel immunosuppressant FTY720 in a murine rheumatoid arthritis model

We investigated the effects and mechanisms by which FTY720 (FTY) inhibits arthritis development in the SKG mouse rheumatoid arthritis (RA) model. FTY (1mg/kg/day) administration suppressed the progression of laminarin-induced arthritis in SKG mice. FTY treatment decreased IL-6 and TNF-alpha expression in synovial fibroblast cells and the number of inflammatory cells overall. Bone destruction was also suppressed by treatment with FTY. The numbers of CD4(+) and CD8(+) T cells were significantly increased in the thymus and decreased in the spleen in FTY-treated SKG mice. FTY enhanced IL-4 production by CD4(+) T cells stimulated by allogeneic spleen cells and inhibited prostaglandin E(2) (PGE(2)) production by a TNF-alpha-stimulated synovial fibroblast cell line. These results indicate that FTY can inhibit arthritis in SKG mice via sequestration of autoimmune CD4(+) T cells in the thymus, enhancement of Th2 immune responses, and inhibition of PGE(2) production by synovial cells.

FTY720, a sphingosine 1-phosphate receptor modulator, inhibits CD1d-restricted NKT cells by suppressing cytokine production but not migration

FTY720, a sphingosine 1-phosphate (S1P) receptor modulator, suppresses immune responses by inhibiting T-cell migration into target tissues; however, it does not alter T-cell functions. In this study, we investigated the biological effects of FTY720 on NKT cells. Unlike T cells, FTY720 suppressed the production of IL-4, IFN-gamma, IL-10, and IL-13 by NKT cells through the S1P1 receptor (S1P(1)). Moreover, FTY720 also inhibited the expression of T-bet and GATA-3 of NKT cells in the presence of TCR engagement. However, it did not inhibit NKT cell migration in vitro or in vivo. In a K/BxN serum transfer arthritis model, FTY720 suppressed arthritis in B6, but not in CD1d(-/-) mice. Moreover, the adoptive transfer of control NKT cells restored arthritis in CD1d(-/-) mice, whereas FTY720-pretreated NKT cells did not. The number of NKT cells in the joints of B6 mice given FTY720 was similar to that in the joints of untreated B6 mice, whereas the production of IL-4 and IFN-gamma was reduced in the FTY720-treated B6 mice. Taken together, these data show that FTY720 suppresses cytokine production in NKT cells through S1P(1), but not NKT cell migration. Thus, FTY720 may be useful in the treatment of NKT cell-promoted immune diseases.

Lipids as targets for novel anti-inflammatory therapies

Lipids serve important functions as membrane constituents and also as energy storing molecules. Besides these functions certain lipid species have now been recognized as signalling molecules that regulate a multitude of cellular responses including cell growth and death, and also inflammatory reactions. Bioactive lipids are generated by hydrolysis from membrane lipids mainly by phospholipases giving rise to fatty acids and lysophospholipids that either directly exert their function or are further converted to active mediators. This review will summarize the present knowledge about bioactive lipids that either promote or attenuate inflammatory reactions. These lipids include polyunsaturated fatty acids (PUFA), eicosanoids including the epoxyeicosatrienoic acids (EET), peroxisome proliferation activating receptor (PPAR) activators, cannabinoids and the sphingolipids ceramide, sphingosine 1-phosphate and sphingosylphosphorylcholine.

Ascomycete derivative to MS therapeutic: S1P receptor modulator FTY720

Fingolimod (FTY720) represents the first in a new class of immune-modulators whose target is sphingosine-1-phosphate (S1P) receptors. It was first identified by researchers at Kyoto University and Yoshitomi Pharmaceutical as a chemical derivative of the ascomycete metabolite ISP-1 (myriocin). Unlike its natural product parent, FTY720 does not interfere with sphingolipid biosynthesis. Instead, its best characterized mechanism of action upon in vivo phosphorylation, leading to the active principle FTY720-P, is the rapid and reversible inhibition of lymphocyte egress from peripheral lymph nodes. As a consequence of S1P1 receptor internalization, tissue-damaging T-cells can not recirculate and infiltrate sites of inflammation such as the central nervous system (CNS). Furthermore, FTY720-P modulation of S1P receptor signaling also enhances endothelial barrier function. Due to its mode of action, FTY720 effectively prevents transplant rejection and is active in various autoimmune disease models. The most striking efficacy is in the multiple sclerosis (MS) model of experimental autoimmune encephalomyelitis, which has now been confirmed in the clinic. FTY720 demonstrated promising results in Phase II trials and recently entered Phase III in patients with relapsing MS. Emerging evidence suggests that its efficacy in the CNS extends beyond immunomodulation to encompass other aspects of MS pathophysiology, including an influence on the blood-brain-barrier and glial repair mechanisms that could ultimately contribute to restoration of nerve function. FTY720 may represent a potent new therapeutic modality in MS, combined with the benefit of oral administration.