A ceramide-1-phosphate analogue, PCERA-1, simultaneously suppresses tumour necrosis factor-alpha and induces interleukin-10 production in activated macrophages

Bioactive sphingolipids as emerging targets for signal transduction in cancer development

Sphingolipids, crucial components of cellular membranes, play a vital role in maintaining cellular structure and signaling integrity. Disruptions in sphingolipid metabolism are increasingly implicated in cancer development. Key bioactive sphingolipids, such as ceramides, sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and glycosphingolipids, profoundly impact tumor biology. They influence the behavior of tumor cells, stromal cells, and immune cells, affecting tumor aggressiveness, angiogenesis, immune modulation, and extracellular matrix remodeling. Furthermore, abnormal expression of sphingolipids and their metabolizing enzymes modulates the secretion of tumor-derived extracellular vesicles (TDEs), which are key players in creating an immunosuppressive tumor microenvironment, remodeling the extracellular matrix, and facilitating oncogenic signaling within in situ tumors and distant pre-metastatic niches (PMNs). Understanding the role of sphingolipids in the biogenesis of tumor-derived extracellular vesicles (TDEs) and their bioactive contents can pave the way for new biomarkers in cancer diagnosis and prognosis, ultimately enhancing comprehensive tumor treatment strategies.

Neosaxitoxin Inhibits the Expression of Inflammation Markers of the M1 Phenotype in Macrophages

(1) Background: Neosaxitoxin (NeoSTX) has been used as a local anesthetic, but its anti-inflammatory effects have not been well defined. In the present study, we investigate the effects of NeoSTX on lipopolysaccharide (LPS)-activated macrophages. (2) Methods: Raw 264.7 and equine PBMC cells were incubated with or without 100 ng/mL LPS in the presence or absence of NeoSTX (1µM). The expression of inflammatory mediators was assessed: nitric oxide (NO) content using the Griess assay, TNF-α content using the ELISA assay, and mRNA of inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) using a real-time polymerase chain reaction. (3) Results: NeoSTX (1 μM) significantly inhibited the release of NO, TNF-α, and expression of iNOS, IL-1β, and TNF-α in LPS-activated macrophages of both species studied. Furthermore, our study shows that the LPS-induced release of inflammatory mediators was suppressed by NeoSTX. Additionally, NeoSTX deactivated polarized macrophages to M1 by LPS without compromising its polarization towards M2. (4) Conclusions: NeoSTX inhibits LPS-induced release of inflammatory mediators from macrophages, and these effects may be mediated by the blockade of voltage-gated sodium channels (VGSC).

The cAMP Pathway Amplifies Early MyD88-Dependent and Type I Interferon-Independent LPS-Induced Interleukin-10 Expression in Mouse Macrophages

Interleukin-10 (IL-10) is a key anti-inflammatory cytokine, secreted by macrophages and other immune cells to attenuate inflammation. Autocrine type I interferons (IFNs) largely mediate the delayed expression of IL-10 by LPS-stimulated macrophages. We have previously shown that IL-10 is synergistically expressed in macrophages following a costimulus of a TLR agonist and cAMP. We now show that the cAMP pathway directly upregulates IL-10 transcription and plays an important permissive and synergistic role in early, but not late, LPS-stimulated IL-10 mRNA and protein expression in mouse macrophages and in a mouse septic shock model. Our results suggest that the loss of synergism is not due to desensitization of the cAMP inducing signal, and it is not mediated by a positive crosstalk between the cAMP and type I IFN pathways. First, cAMP elevation in LPS-treated cells decreased the secretion of type I IFN. Second, autocrine/paracrine type I IFNs induce IL-10 promoter reporter activity only additively, but not synergistically, with the cAMP pathway. IL-10 promoter reporter activity was synergistically induced by cAMP elevation in macrophages stimulated by an agonist of either TLR4, TLR2/6, or TLR7, receptors which signal via MyD88, but not by an agonist of TLR3 which signals independently of MyD88. Moreover, MyD88 knockout largely reduced the synergistic IL-10 expression, indicating that MyD88 is required for the synergism displayed by LPS with cAMP. This report delineates the temporal regulation of early cAMP-accelerated vs. late type I IFN-dependent IL-10 transcription in LPS-stimulated murine macrophages that can limit inflammation at its onset.

TLR-Induced SMPD3 Defects Enhance Inflammatory Response of B Cell and Macrophage in the Pathogenesis of SLE

B lymphocyte and macrophages may contribute to SLE pathogenesis through cytokine production after TLR stimulation. Emerging evidences suggested that defects of sphingolipid metabolism were responsible for SLE pathogenesis. However, it is not clear whether these defects exist in B cells and macrophages under SLE condition and whether TLR signalling pathway was related to the dysfunction of sphingolipid metabolism in SLE. Here, we demonstrated that the enzymes involved in the sphingolipid metabolism expressed abnormally in B cells from SLE patients and lupus-prone mice. Moreover, we found that TLR signalling induced the abnormal expression of sphingomyelin phosphodiesterase 3 (SMPD3), sphingosine-1-phosphate phosphatase 2 (SGPP2), ceramide kinase (CERK) and UDP glycosyltransferase 8 (UGT8), which were involved in sphingolipid metabolism. TLR signalling also induced the transportation of SMPD3 from Golgi apparatus. Furthermore, the dysfunction of SMPD3 enhanced TLR-induced inflammatory response of B cells and macrophages in turn. Thus, these findings provide an innovative direction and a new target for research and treatment of SLE.

Synthesis and evaluation of a tag-free photoactive phospho-ceramide analogue-1 (PCERA-1) probe to study immunomodulation in macrophages

Phospho-ceramide analogue-1 (PCERA-1), a synthetic analogue of ceramide-1-phosphate (C1P), has been previously shown to act as a potent modulator of macrophage activity and inflammation.

Exogenous ceramide-1-phosphate (C1P) and phospho-ceramide analogue-1 (PCERA-1) regulate key macrophage activities via distinct receptors

Inflammation is an ensemble of tightly regulated steps, in which macrophages play an essential role. Previous reports showed that the natural sphingolipid ceramide 1-phosphate (C1P) stimulates macrophages migration, while the synthetic C1P mimic, phospho-ceramide analogue-1 (PCERA-1), suppresses production of the key pro-inflammatory cytokine TNFα and amplifies production of the key anti-inflammatory cytokine IL-10 in LPS-stimulated macrophages, via one or more unidentified G-protein coupled receptors. We show that C1P stimulated RAW264.7 macrophages migration via the NFκB pathway and MCP-1 induction, while PCERA-1 neither mimicked nor antagonized these activities. Conversely, PCERA-1 synergistically elevated LPS-dependent IL-10 expression in RAW264.7 macrophages via the cAMP-PKA-CREB signaling pathway, while C1P neither mimicked nor antagonized these activities. Interestingly, both compounds have the capacity to additively inhibit TNFα secretion; PCERA-1, but not C1P, suppressed LPS-induced TNFα expression in macrophages in a CREB-dependent manner, while C1P, but not PCERA-1, directly inhibited recombinant TNFα converting enzyme (TACE). Finally, PCERA-1 failed to interfere with binding of C1P to either the cell surface receptor or to TACE. These results thus indicate that the natural sphingolipid C1P and its synthetic analog PCERA-1 bind and activate distinct receptors expressed in RAW264.7 macrophages. Identification of these receptors will be instrumental for elucidation of novel activities of extra-cellular sphingolipids, and may pave the way for the design of new sphingolipid mimics for the treatment of inflammatory diseases, and pathologies which depend on cell migration, as in metastatic tumors.

Ceramide-1-phosphate inhibits cigarette smoke-induced airway inflammation

Sphingolipids are involved in the pathogenesis of inflammatory diseases. The central molecule is ceramide, which can be converted into ceramide-1-phosphate (C1P). Although C1P can exert anti- and pro-inflammatory effects, its influence on cigarette smoke (CS)-induced lung inflammation is unknown. We aimed to clarify the role of C1P in the pathogenesis of CS-triggered pulmonary inflammation and emphysema in humans and mice. The effects of C1P were addressed on CS-induced lung inflammation in C57BL/6 mice, CS extract-triggered activation of human airway epithelial cells (AECs) and neutrophils from patients with chronic obstructive pulmonary disease. Differential cell counts in bronchoalveolar lavage fluid were determined by flow cytometry and pro-inflammatory cytokines were measured by ELISA. Expression and DNA binding of nuclear factor (NF)-κB and neutral sphingomyelinase (nSMase) were quantified by PCR, electrophoretic mobility shift and fluorometric assays. C1P reduced CS-induced acute and chronic lung inflammation and development of emphysema in mice, which was associated with a reduction in nSMase and NF-κB activity in the lungs. nSMase activity in human serum correlated negatively with forced expiratory volume in 1 s % predicted. In human AECs and neutrophils, C1P inhibited CS-induced activation of NF-κB and nSMase, and reduced pro-inflammatory cytokine release. Our results suggest that C1P is a potential target for anti-inflammatory treatment in CS-induced lung inflammation.

Modulation of drug resistance in ovarian adenocarcinoma using chemotherapy entrapped in hyaluronan-grafted nanoparticle clusters

Resistance to anticancer drugs is considered a major cause of chemotherapy failure. One of the major mediators of resistance is the multidrug extrusion pump protein, P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter with broad substrate specificity. In order to bypass this drug resistance mechanism, we have devised phospholipid-based nanoparticle clusters coated with the glycosaminoglycan hyaluronan, the major ligand of CD44, which is upregulated and undergoes different splice variations in many types of cancer cells. These particles, termed glycosaminoglycan particle nanoclusters or gagomers (GAGs), were self-assembled into ∼500 nm diameter clusters, with zeta-potential values of ∼-70 mV. Flow cytometry analysis provided evidence that, unlike free doxorubicin (DOX), a model chemotherapy, DOX entrapped in the GAGs (DOX-GAGs) accumulated in P-gp-overexpressing human ovarian adenocarcinoma cell line and dramatically decreased cell viability, while drug-free GAGs and the commercially available drug DOXIL (PEGylated liposomal DOX) did not produce therapeutic benefit. Furthermore, by using RNA interference strategy, we showed that DOX-GAGs were able to overcome the P-gp-mediated resistant mechanism of these cells. Most importantly, DOX-GAGs showed a superior therapeutic effect over free DOX in a resistant human ovarian adenocarcinoma mouse xenograft model. Taken together, these results demonstrated that GAGs might serve as an efficient platform for delivery of therapeutic payloads by bypassing P-gp-mediated multidrug resistance.

Interleukin 10 antioxidant effect decreases leukocytes/endothelial interaction induced by tumor necrosis factor α

Little is known about the endothelial mechanisms involved in the anti-inflammatory effects of interleukin 10 (IL-10). The goal of this study was to evaluate the effects of IL-10 on endothelial oxidative stress and endothelial inflammation induced by tumor necrosis factor α (TNF-α). Production of reactive oxygen species (ROS) in perfused human umbilical vein endothelial cells (HUVECs) was studied by fluorescent microscopy using dichlorodihydrofluorescein diacetate. Tumor necrosis factor α (1 ng/mL) was added to the perfusion medium in the absence and presence of IL-10 (1 ng/mL). The role of phosphatidylinositol 3-kinase (PI3-kinase) was assessed using wortmannin and LY 2940002 (inhibitors of PI3-kinase). Specific inhibition of p110 α and p110 γ/δ PI3-kinase subunits was studied using A66 and TG100-115. As well, levels of ceramide and intercellular adhesion molecule 1 (ICAM-1) expression were measured. Finally, the effect of IL-10 on TNF-α-induced leukocyte/endothelium interaction was examined using an ex vivo perfused vessel model. Interleukin 10 significantly reduced dichlorodihydrofluorescein diacetate fluorescence induced by TNF-α in HUVECs (12.5% ± 3.2% vs. 111.7% ± 21.6% at 60 min). Pretreatment by LY2940002 or wortmannin restored ROS production induced by TNF-α in the presence of IL-10. In HUVECs treated by TNF-α + IL-10, inhibition of p110 α PI3-kinase subunit significantly increased ROS production, whereas p110 γ/δ inhibition did not have a significant effect. Pretreatment with IL-10 significantly decreased TNF-α-induced increased levels of ceramide (TNF-α vs. TNF-α + IL-10: 6,278 ± 1,013 vs. 1,440 ± 130 pmol/mg prot), as well as ICAM-1 expression and leukocyte adhesion (TNF-α vs. TNF-α + IL-10: 26.8 ± 2.6 vs. 6.7 ± 0.4 adherent leukocytes/field at 15 min). Interleukin 10 decreases the level of inflammation induced by TNF-α in endothelial cells by reducing the TNF-α-induced ROS production, ICAM-1 expression, and leukocyte adhesion to the endothelium. The antioxidant effect of IL-10 is mediated through PI3-kinase and is paralleled by a decrease in ceramide synthesis induced by TNF-α.

Ceramide 1-phosphate induces macrophage chemoattractant protein-1 release: involvement in ceramide 1-phosphate-stimulated cell migration

The bioactive sphingolipid ceramide 1-phosphate (C1P) is implicated in inflammatory responses and was recently shown to promote cell migration. However, the mechanisms involved in these actions are poorly described. Using J774A.1 macrophages, we have now discovered a new biological activity of C1P: stimulation of monocyte chemoattractant protein-1 (MCP-1) release. This novel effect of C1P was pertussis toxin (PTX) sensitive, suggesting the intervention of Gi protein-coupled receptors. Treatment of the macrophages with C1P caused activation of the phosphatidylinositol 3-kinase (PI3K)/Akt, mitogen-activated protein kinase kinase (MEK)/extracellularly regulated kinases (ERK), and p38 pathways. Inhibition of these kinases using selective inhibitors or specific siRNA blocked the stimulation of MCP-1 release by C1P. C1P stimulated nuclear factor-κB activity, and blockade of this transcription factor also resulted in complete inhibition of MCP-1 release. Also, C1P stimulated MCP-1 release and cell migration in human THP-1 monocytes and 3T3-L1 preadipocytes. A key observation was that sequestration of MCP-1 with a neutralizing antibody or treatment with MCP-1 siRNA abolished C1P-stimulated cell migration. Also, inhibition of the pathways involved in C1P-stimulated MCP-1 release completely blocked the stimulation of cell migration by C1P. It can be concluded that C1P promotes MCP-1 release in different cell types and that this chemokine is a major mediator of C1P-stimulated cell migration. The PI3K/Akt, MEK/ERK, and p38 pathways are important downstream effectors in this action.

The bacterial quorum-sensing signal molecule N-3-oxo-dodecanoyl-L-homoserine lactone reciprocally modulates pro- and anti-inflammatory cytokines in activated macrophages

The bacterial molecule N-3-oxo-dodecanoyl-l-homoserine lactone (C12) has critical roles in both interbacterial communication and interkingdom signaling. The ability of C12 to downregulate production of the key proinflammatory cytokine TNF-α in stimulated macrophages was suggested to contribute to the establishment of chronic infections by opportunistic Gram-negative bacteria, such as Pseudomonas aeruginosa. We show that, in contrast to TNF-α suppression, C12 amplifies production of the major anti-inflammatory cytokine IL-10 in LPS-stimulated murine RAW264.7 macrophages, as well as peritoneal macrophages. Furthermore, C12 increased IL-10 mRNA levels and IL-10 promoter reporter activity in LPS-stimulated RAW264.7 macrophages, indicating that C12 modulates IL-10 expression at the transcriptional level. Finally, C12 substantially potentiated LPS-stimulated NF-κB DNA-binding levels and prolonged p38 MAPK phosphorylation in RAW264.7 macrophages, suggesting that increased transcriptional activity of NF-κB and/or p38-activated transcription factors serves to upregulate IL-10 production in macrophages exposed to both LPS and C12. These findings reveal another part of the complex array of host transitions through which opportunistic bacteria downregulate immune responses to flourish and establish a chronic infection.

The role of ceramide-1-phosphate in biological functions

In mammalian cells, cermide-1-phosphate (C1P) is produced via the ATP-dependent mechanism of converting ceramide to C1P by the enzyme, ceramide kinase (CERK). CERK was first described as a calcium-stimulated lipid kinase that co-purified with brain synaptic vesicles, and to date, CERK is the only identified mammalian enzyme known to produce C1P in cells. C1P has steadily emerged as a bioactive sphingolipid involved in cell proliferation, macrophage migration, and inflammatory events. The recent generation of the CERK knockout mouse and the development of CERK inhibitors have furthered our current understanding of CERK-derived C1P in regulating biological processes. In this chapter, the history of C1P as well as the biological functions attributed to C1P are reviewed.

Intrathecal cannabilactone CB(2)R agonist, AM1710, controls pathological pain and restores basal cytokine levels

Spinal glial and proinflammatory cytokine actions are strongly implicated in pathological pain. Spinal administration of the anti-inflammatory cytokine interleukin (IL)-10 abolishes pathological pain and suppresses proinflammatory IL-1β and tumor necrosis factor alpha (TNF-α). Drugs that bind the cannabinoid type-2 receptor (CB(2)R) expressed on spinal glia reduce mechanical hypersensitivity. To better understand the CB(2)R-related anti-inflammatory profile of key anatomical nociceptive regions, we assessed mechanical hypersensitivity and protein profiles following intrathecal application of the cannabilactone CB(2)R agonist, AM1710, in 2 animal models; unilateral sciatic nerve chronic constriction injury (CCI), and spinal application of human immunodeficiency virus-1 glycoprotein 120 (gp120), a model of peri-spinal immune activation. In CCI animals, lumbar dorsal spinal cord and corresponding dorsal root ganglia (DRG) were evaluated by immunohistochemistry for expression of IL-10, IL-1β, phosphorylated p38-mitogen-activated-kinase (p-p38MAPK), a pathway associated with proinflammatory cytokine production, glial cell markers, and degradative endocannabinoid enzymes, including monoacylglycerol lipase (MAGL). AM1710 reversed bilateral mechanical hypersensitivity. CCI revealed decreased IL-10 expression in dorsal spinal cord and DRG, while AM1710 resulted in increased IL-10, comparable to controls. Adjacent DRG and spinal sections revealed increased IL-1β, p-p38MAPK, glial markers, and/or MAGL expression, while AM1710 suppressed all but spinal p-p38MAPK and microglial activation. In spinal gp120 animals, AM1710 prevented bilateral mechanical hypersensitivity. For comparison to immunohistochemistry, IL-1β and TNF-α protein quantification from lumbar spinal and DRG homogenates was determined, and revealed increased DRG IL-1β protein levels from gp120, that was robustly prevented by AM1710 pretreatment. Cannabilactone CB(2)R agonists are emerging as anti-inflammatory agents with pain therapeutic implications.

Ceramide kinase regulates the production of tumor necrosis factor α (TNFα) via inhibition of TNFα-converting enzyme

Tumor necrosis factor α (TNFα) is a well known cytokine involved in systemic and acute inflammation. In this study, we demonstrate that ceramide 1-phosphate (C1P) produced by ceramide kinase (CERK) is a negative regulator of LPS-induced TNFα secretion. Specifically, bone marrow-derived macrophages isolated from CERK knock-out mice (CERK^−/−) generated higher levels of TNFα than the wild-type mice (CERK^+/+) in response to LPS. An increase in basal TNFα secretion was also observed in CERK^−/− murine embryonic fibroblasts, which was rescued by re-expression of wild-type CERK. This effect was due to increased secretion and not transcription. The secretion of TNFα is regulated by TNFα-converting enzyme (TACE also known as ADAM17), and importantly, the activity of TACE was higher in cell extracts from CERK^−/− as compared with wild type. In vitro analysis also demonstrated that C1P is a potent inhibitor of this enzyme, in stark contrast to ceramide and sphingosine 1-phosphate. Furthermore, TACE specifically bound C1P with high affinity. Finally, several putative C1P-binding sites were identified via homology throughout the protein sequence of TACE. These results indicate that C1P produced by CERK has a negative effect on the processing/secretion of TNFα via modulation of TACE activity.

The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 modulates cytokine expression in macrophages via p50 nuclear factor κB inhibition, in a PI3K-independent mechanism

The Phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002 (LY2), has been previously reported to inhibit nuclear factor κB (NFκB) activity, in a PI3K-independent mechanism. The goals of the current research were to determine the specificity of LY2 regarding NFκB subunits, and to identify relevant modulation of cytokine expression in LPS-stimulated macrophages. We found that LY2 specifically diminished the level of p50, but not p65, NFκB in the nucleus of LPS-stimulated mouse RAW264.7 macrophages and human THP-1 monocytes. This activity of LY2 was mimicked by its PI3K-inert analog LY303511 (LY3), but not by another PI3K inhibitor - wortmannin. We further show that LY2 inhibited LPS-induced IL-10 expression by RAW264.7 macrophages, in a PI3K-independent mechanism. Moreover, using a deletion mutant of an IL-10 promoter reporter gene we demonstrate that the activity of the NFκB enhancer site at the IL-10 promoter is regulated by LY2 in a PI3K-independent manner. Finally, both LY2 and LY3 elevated TNFα production in the LPS tolerant state which is regulated by p50 NFκB homodimers, but not before tolerance development. The effects of LY2 and LY3 on p50 translocation and on cytokine production in LPS-stimulated macrophages are thus consistent with specific PI3K-independent inhibition of p50 NFκB homodimer activity by LY2.

A ceramide analog inhibits cPLA(2) activity and consequent PGE(2) formation in LPS-stimulated macrophages

Prostaglandin E(2) (PGE(2)) is an important mediator of the inflammatory response. Phospho-ceramide analogue-1 (PCERA-1), a synthetic phospholipid-like molecule, was previously reported to modulate pro- and anti-inflammatory cytokine production. We show here that PCERA-1 inhibited LPS-stimulated PGE(2) production in RAW264.7 macrophages, without affecting COX-2 expression. Furthermore, PCERA-1 efficiently suppressed arachidonic acid (AA) release in response to LPS. The dephosphorylated derivative of PCERA-1, ceramide analogue-1 (CERA-1), mimicked the inhibitory effect of PCERA-1 on AA release and PGE(2) production in macrophages. Inhibition of PGE(2) production by CERA-1 was completely rescued by addition of exogenous AA. Importantly, PCERA-1 and ceramide-1-phosphate (C1P) stimulated the enzymatic activity of cPLA(2)α in an in vitro assay, whereas CERA-1 and ceramide inhibited both basal and C1P-stimulated cPLA(2)α activity. Collectively, these results indicate that CERA-1 suppresses AA release and subsequent PGE(2) production in LPS-stimulated macrophages by direct interaction with cPLA(2), and suggest that ceramide may similarly counteract C1P effect on cPLA(2) activity in cells. The suppression of PGE(2) production is suggested to contribute to the anti-inflammatory action of PCERA-1.

Lipoic acid attenuates inflammation via cAMP and protein kinase A signaling

Background

Abnormal regulation of the inflammatory response is an important component of diseases such as diabetes, Alzheimer's disease and multiple sclerosis (MS). Lipoic acid (LA) has been shown to have antioxidant and anti-inflammatory properties and is being pursued as a therapy for these diseases. We first reported that LA stimulates cAMP production via activation of G-protein coupled receptors and adenylyl cyclases. LA also suppressed NK cell activation and cytotoxicity. In this study we present evidence supporting the hypothesis that the anti-inflammatory properties of LA are mediated by the cAMP/PKA signaling cascade. Additionally, we show that LA oral administration elevates cAMP levels in MS subjects.

Methodology/Principal Findings

We determined the effects of LA on IL-6, IL-17 and IL-10 secretion using ELISAs. Treatment with 50 µg/ml and 100 µg/ml LA significantly reduced IL-6 levels by 19 and 34%, respectively, in T cell enriched PBMCs. IL-17 levels were also reduced by 35 and 50%, respectively. Though not significant, LA appeared to have a biphasic effect on IL-10 production. Thymidine incorporation studies showed LA inhibited T cell proliferation by 90%. T-cell activation was reduced by 50% as measured by IL-2 secretion. Western blot analysis showed that LA treatment increased phosphorylation of Lck, a downstream effector of protein kinase A. Pretreatment with a peptide inhibitor of PKA, PKI, blocked LA inhibition of IL-2 and IFN gamma production, indicating that PKA mediates these responses. Oral administration of 1200 mg LA to MS subjects resulted in increased cAMP levels in PBMCs four hours after ingestion. Average cAMP levels in 20 subjects were 43% higher than baseline.

Conclusions/Significance

Oral administration of LA in vivo resulted in significant increases in cAMP concentration. The anti-inflammatory effects of LA are mediated in part by the cAMP/PKA signaling cascade. These novel findings enhance our understanding of the mechanisms of action of LA.

The ceramide-1-phosphate analogue PCERA-1 modulates tumour necrosis factor-alpha and interleukin-10 production in macrophages via the cAMP-PKA-CREB pathway in a GTP-dependent manner

The synthetic phospho-ceramide analogue-1 (PCERA-1) down-regulates production of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) and up-regulates production of the anti-inflammatory cytokine interleukin-10 (IL-10) in lipopolysaccharide (LPS) -stimulated macrophages. We have previously reported that PCERA-1 increases cyclic adenosine monophosphate (cAMP) levels. The objective of this study was to delineate the signalling pathway leading from PCERA-1 via cAMP to modulation of TNF-alpha and IL-10 production. We show here that PCERA-1 elevates intra-cellular cAMP level in a guanosine triphosphate-dependent manner in RAW264.7 macrophages. The cell-permeable dibutyryl cAMP was able to mimic the effects of PCERA-1 on cytokine production, whereas 8-chloro-phenylthio-methyladenosine-cAMP, which specifically activates the exchange protein directly activated by cAMP (EPAC) but not protein kinase A (PKA), failed to mimic PCERA-1 activities. Consistently, the PKA inhibitor H89 efficiently blocked PCERA-1-driven cytokine modulation as well as PCERA-1-stimulated phosphorylation of cAMP response element binding protein (CREB) on Ser-133. Finally, PCERA-1 activated cAMP-responsive transcription of a luciferase reporter, in synergism with the phosphodiesterase (PDE)-4 inhibitor rolipram. Our results suggest that PCERA-1 activates a G(s) protein-coupled receptor, leading to elevation of cAMP, which acts via the PKA-CREB pathway to promote TNF-alpha suppression and IL-10 induction in LPS-stimulated macrophages. Identification of the PCERA-1 receptor is expected to set up a new target for development of novel anti-inflammatory drugs.

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.

Ceramide and ceramide 1-phosphate in health and disease

Sphingolipids are essential components of cell membranes, and many of them regulate vital cell functions. In particular, ceramide plays crucial roles in cell signaling processes. Two major actions of ceramides are the promotion of cell cycle arrest and the induction of apoptosis. Phosphorylation of ceramide produces ceramide 1-phosphate (C1P), which has opposite effects to ceramide. C1P is mitogenic and has prosurvival properties. In addition, C1P is an important mediator of inflammatory responses, an action that takes place through stimulation of cytosolic phospholipase A2, and the subsequent release of arachidonic acid and prostaglandin formation. All of the former actions are thought to be mediated by intracellularly generated C1P. However, the recent observation that C1P stimulates macrophage chemotaxis implicates specific plasma membrane receptors that are coupled to Gi proteins. Hence, it can be concluded that C1P has dual actions in cells, as it can act as an intracellular second messenger to promote cell survival, or as an extracellular receptor agonist to stimulate cell migration.

Distinct receptor-mediated activities in macrophages for natural ceramide-1-phosphate (C1P) and for phospho-ceramide analogue-1 (PCERA-1)

Ceramide-1-phosphate (C1P) is known as a second messenger regulating a multitude of processes including cell growth, apoptosis and inflammation. Exciting recent findings now suggest that C1P can stimulate macrophages migration in an extra-cellular manner via a G protein-coupled receptor (GPCR). Interestingly, a synthetic C1P analog, named phospho-ceramide analogue-1 (PCERA-1), was recently described as a potent in-vivo anti-inflammatory agent, and was suggested to act on macrophages in an extra-cellular manner via a GPCR. Here we summarize and compare the receptor-mediated as well as receptor-independent activities of natural C1P and its synthetic analog. We also provide experimental data in support of distinct C1P and PCERA-1 receptors.

Synergistic IL-10 induction by LPS and the ceramide-1-phosphate analog PCERA-1 is mediated by the cAMP and p38 MAP kinase pathways

Expression of the anti-inflammatory cytokine IL-10 can be induced either by TLR agonists such as lipopolysaccharide (LPS), or by various endogenous stimuli, in particular those acting via a cAMP-dependent signaling pathway. We have previously reported that the synthetic phospho-ceramide analogue-1 (PCERA-1) increases cAMP level and subsequently down-regulates production of TNFalpha and up-regulates production of IL-10 in LPS-stimulated macrophages. The objective of this study was to determine the mechanism of activity of PCERA-1 and the role of cAMP in LPS-induced IL-10 production. We show here that PCERA-1 induces IL-10 production in synergism with various TLR agonists in mouse RAW264.7 macrophages. Cooperativity is evident both at the mRNA and protein levels. IL-10 production by LPS and PCERA-1 is mediated by the cAMP pathway and by the p38 MAP kinase. Phosphorylation of p38 is cooperatively accomplished by LPS and PCERA-1 or other cAMP inducers. Furthermore, the activity of PCERA-1 can be partially mimicked by a cell-permeable analog of cAMP, and blocked by the protein kinase A (PKA) inhibitor H89. Finally, in the absence of PCERA-1, the residual IL-10 induction by LPS depends on the basal cAMP level as it can be largely elevated by the phosphodiesterase (PDE)-4 inhibitor rolipram. Our results thus indicate that IL-10 induction by LPS critically depends on basal cAMP level, and that a co-stimulus by a TLR agonist and a cAMP-elevating agent results in synergistic PKA-dependent and p38-dependent IL-10 production.

Modulation of TNFalpha, IL-10 and IL-12p40 levels by a ceramide-1-phosphate analog, PCERA-1, in vivo and ex vivo in primary macrophages

Phospho-ceramide analog-1 (PCERA-1) has been described as a potent in vivo suppressor of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha), and thus as a putative drug for the treatment of inflammatory diseases. However, the in vivo cell target of PCERA-1 has not been identified, and its in vivo effect on secretion of other relevant cytokines has not been reported. We have previously shown that PCERA-1 suppresses lipopolysaccharide (LPS)-induced TNFalpha production in RAW264.7 macrophages in vitro. We therefore hypothesized that PCERA-1 targets TNFalpha production by primary macrophages. In this study we thus investigated the effect of PCERA-1 on LPS-induced release of TNFalpha, interleukin (IL)-10 and IL-12p40, in vivo, and ex vivo. We found that PCERA-1 suppressed production of the pro-inflammatory cytokines, TNFalpha and IL-12p40, and increased production of the anti-inflammatory cytokine, IL-10, in LPS-challenged mice, and in primary peritoneal macrophages as well as bone marrow-derived macrophages (BMDM) stimulated with LPS and interferon (IFN)-gamma. These activities of PCERA-1 were independent of each other. In contrast, PCREA-1 only slightly affected TNFalpha production in the whole blood assay, where LPS-induced cytokines are mainly produced by monocytes. Moreover, isolated blood monocytes were inert to PCERA-1, but acquired responsiveness to PCERA-1 upon macrophage colony stimulating factor (M-CSF)-induced differentiation into macrophages. Pharmacokinetic analysis in mice showed that while the volume of distribution of PCERA-1 is low, the drug was rapidly exchanged between the peritoneum and the systemic circulation. Together, these results suggest that sensitivity to PCERA-1 increases upon differentiation of blood monocytes into tissue macrophages, and imply a mechanistic role for peritoneal macrophages in the in vivo anti-inflammatory activity of PCERA-1. Finally, we show that the mechanism of activity of PCERA-1 and prostaglandin E2 (PGE2) is distinct, and that PCERA-1 signaling is not mediated by EP2, a PGE2 receptor which is also activated by oxidized phospholipids. The independent and reciprocal modulation of production of TNFalpha and IL-12p40, vs. IL-10, suggests that PCERA-1 may be a candidate drug for the treatment of inflammation-linked diseases.