Photolysis of caged sphingosine-1-phosphate induces barrier enhancement and intracellular activation of lung endothelial cell signaling pathways

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates cellular functions by ligation via G protein-coupled S1P receptors. In addition to its extracellular action, S1P also has intracellular effects; however, the signaling pathways modulated by intracellular S1P remain poorly defined. We have previously demonstrated a novel pathway of intracellular S1P generation in human lung endothelial cells (ECs). In the present study, we examined the role of intracellular S1P generated by photolysis of caged S1P on EC barrier regulation and signal transduction. Intracellular S1P released from caged S1P caused mobilization of intracellular calcium, induced activation of MAPKs, redistributed cortactin, vascular endothelial cadherin, and β-catenin to cell periphery, and tightened endothelial barrier in human pulmonary artery ECs. Treatment of cells with pertussis toxin (PTx) had no effect on caged S1P-mediated effects on Ca(2+) mobilization, reorganization of cytoskeleton, cell adherens junction proteins, and barrier enhancement; however, extracellular S1P effects were significantly attenuated by PTx. Additionally, intracellular S1P also activated small GTPase Rac1 and its effector Ras GTPase-activating-like protein IQGAP1, suggesting involvement of these proteins in the S1P-mediated changes in cell-to-cell adhesion contacts. Downregulation of sphingosine kinase 1 (SphK1), but not SphK2, with siRNA or inhibition of SphK activity with an inhibitor 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole (CII) attenuated exogenously administrated S1P-induced EC permeability. Furthermore, S1P1 receptor inhibitor SB649164 abolished exogenous S1P-induced transendothelial resistance changes but had no effect on intracellular S1P generated by photolysis of caged S1P. These results provide evidence that intracellular S1P modulates signal transduction in lung ECs via signaling pathway(s) independent of S1P receptors.

Sphingosine kinase localization in the control of sphingolipid metabolism

The sphingosine kinases (sphingosine kinase-1 and -2) have been implicated in a variety of physiological functions. Discerning their mechanism of action is complicated because in addition to producing the potent lipid second messenger sphingosine-1-phosphate, sphingosine kinases, both by producing sphingosine-1-phosphate and consuming sphingosine, have profound effects on sphingolipid metabolism. Sphingosine kinase-1 translocates to the plasma membrane upon agonist stimulation and this translocation is essential for the pro-oncogenic properties of this enzyme. Many of the enzymes of sphingolipid metabolism, including the enzymes that degrade sphingosine-1-phosphate, are membrane bound with restricted subcellular distributions. In the work described here we explore how subcellular localization of sphingosine kinase-1 affects the downstream metabolism of sphingosine-1-phosphate and the access of sphingosine kinase to its substrates. We find, surprisingly, that restricting sphingosine kinase to either the plasma membrane or the endoplasmic reticulum has a negligible effect on the rate of degradation of the sphingosine-1-phosphate that is produced. This suggests that sphingosine-1-phosphate is rapidly transported between membranes. However we also find that cytosolic or endoplasmic-reticulum targeted sphingosine kinase expressed at elevated levels produces extremely high levels of dihydrosphingosine-1-phosphate. Dihydrosphingosine is a proximal precursor in ceramide biosynthesis. Our data indicate that sphingosine kinase can divert substrate from the ceramide de novo synthesis pathway. However plasma membrane-restricted sphingosine kinase cannot access the pool of dihydrosphingosine. Therefore whereas sphingosine kinase localization does not affect downstream metabolism of sphingosine-1-phosphate, localization has an important effect on the pools of substrate to which this key signaling enzyme has access.

Intracellular localization of sphingosine kinase 1 alters access to substrate pools but does not affect the degradative fate of sphingosine-1-phosphate

Sphingosine kinase 1 (SK1) produces sphingosine-1-phosphate (S1P), a potent signaling lipid. The subcellular localization of SK1 can dictate its signaling function. Here, we use artificial targeting of SK1 to either the plasma membrane (PM) or the endoplasmic reticulum (ER) to test the effects of compartmentalization of SK1 on substrate utilization and downstream metabolism of S1P. Expression of untargeted or ER-targeted SK1, but surprisingly not PM-targeted SK1, results in a dramatic increase in the phosphorylation of dihydrosphingosine, a metabolic precursor in de novo ceramide synthesis. Conversely, knockdown of endogenous SK1 diminishes both dihydrosphingosine-1-phosphate and S1P levels. We tested the effects of SK1 localization on degradation of S1P by depletion of the ER-localized S1P phosphatases and lyase. Remarkably, S1P produced at the PM was degraded to the same extent as that produced in the ER. This indicates that there is an efficient mechanism for the transport of S1P from the PM to the ER. In acute labeling experiments, we find that S1P degradation is primarily driven by lyase cleavage of S1P. Counterintuitively, when S1P-specific phosphatases are depleted, acute labeling of S1P is significantly reduced, indicative of a phosphatase-dependent recycling process. We conclude that the localization of SK1 influences the substrate pools that it has access to and that S1P can rapidly translocate from the site where it is synthesized to other intracellular sites.

Ceramide synthases 2, 5, and 6 confer distinct roles in radiation-induced apoptosis in HeLa cells

The role of ceramide neo-genesis in cellular stress response signaling is gaining increasing attention with recent progress in elucidating the novel roles and biochemical properties of the ceramide synthase (CerS) enzymes. Selective tissue and subcellular distribution of the six mammalian CerS isoforms, combined with distinct fatty acyl chain length substrate preferences, implicate differential functions of specific ceramide species in cellular signaling. We report here that ionizing radiation (IR) induces de novo synthesis of ceramide to influence HeLa cell apoptosis by specifically activating CerS isoforms 2, 5, and 6 that generate opposing anti- and pro-apoptotic ceramides in mitochondrial membranes. Overexpression of CerS2 resulted in partial protection from IR-induced apoptosis whereas overexpression of CerS5 increased apoptosis in HeLa cells. Knockdown studies determined that CerS2 is responsible for all observable IR-induced C(24:0) CerS activity, and while CerS5 and CerS6 each confer approximately 50% of the C(16:0) CerS baseline synthetic activity, both are required for IR-induced activity. Additionally, co-immunoprecipitation studies suggest that CerS2, 5, and 6 might exist as heterocomplexes in HeLa cells, providing further insight into the regulation of CerS proteins. These data add to the growing body of evidence demonstrating interplay among the CerS proteins in a stress stimulus-, cell type- and subcellular compartment-specific manner.

Stimulation of sphingosine 1-phosphate signaling as an alveolar cell survival strategy in emphysema

RATIONALE

Vascular endothelial growth factor receptor (VEGFR) inhibition increases ceramides in lung structural cells of the alveolus, initiating apoptosis and alveolar destruction morphologically resembling emphysema. The effects of increased endogenous ceramides could be offset by sphingosine 1-phosphate (S1P), a prosurvival by-product of ceramide metabolism.

OBJECTIVES

The aims of our work were to investigate the sphingosine-S1P-S1P receptor axis in the VEGFR inhibition model of emphysema and to determine whether stimulation of S1P signaling is sufficient to functionally antagonize alveolar space enlargement.

METHODS

Concurrent to VEGFR blockade in mice, S1P signaling augmentation was achieved via treatment with the S1P precursor sphingosine, S1P agonist FTY720, or S1P receptor-1 (S1PR1) agonist SEW2871. Outcomes included sphingosine kinase-1 RNA expression and activity, sphingolipid measurements by combined liquid chromatography-tandem mass spectrometry, immunoblotting for prosurvival signaling pathways, caspase-3 activity and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assays, and airspace morphometry.

MEASUREMENTS AND MAIN RESULTS

Consistent with previously reported de novo activation of ceramide synthesis, VEGFR inhibition triggered increases in lung ceramides, dihydroceramides, and dihydrosphingosine, but did not alter sphingosine kinase activity or S1P levels. Administration of sphingosine decreased the ceramide-to-S1P ratio in the lung and inhibited alveolar space enlargement, along with activation of prosurvival signaling pathways and decreased lung parenchyma cell apoptosis. Sphingosine significantly opposed ceramide-induced apoptosis in cultured lung endothelial cells, but not epithelial cells. FTY720 or SEW2871 recapitulated the protective effects of sphingosine on airspace enlargement concomitant with attenuation of VEGFR inhibitor-induced lung apoptosis.

CONCLUSIONS

Strategies aimed at augmenting the S1P-S1PR1 signaling may be effective in ameliorating the apoptotic mechanisms of emphysema development.

FTY720 inhibits ceramide synthases and up-regulates dihydrosphingosine 1-phosphate formation in human lung endothelial cells

Novel immunomodulatory molecule FTY720 is a synthetic analog of myriocin, but unlike myriocin FTY720 does not inhibit serine palmitoyltransferase. Although many of the effects of FTY720 are ascribed to its phosphorylation and subsequent sphingosine 1-phosphate (S1P)-like action through S1P(1,3-5) receptors, studies on modulation of intracellular balance of signaling sphingolipids by FTY720 are limited. In this study, we used stable isotope pulse labeling of human pulmonary artery endothelial cells with l-[U-(13)C, (15)N]serine as well as in vitro enzymatic assays and liquid chromatography-tandem mass spectrometry methodology to characterize FTY720 interference with sphingolipid de novo biosynthesis. In human pulmonary artery endothelial cells, FTY720 inhibited ceramide synthases, resulting in decreased cellular levels of dihydroceramides, ceramides, sphingosine, and S1P but increased levels of dihydrosphingosine and dihydrosphingosine 1-phosphate (DHS1P). The FTY720-induced modulation of sphingolipid de novo biosynthesis was similar to that of fumonisin B1, a classical inhibitor of ceramide synthases, but differed in the efficiency to inhibit biosynthesis of short-chain versus long-chain ceramides. In vitro kinetic studies revealed that FTY720 is a competitive inhibitor of ceramide synthase 2 toward dihydrosphingosine with an apparent K(i) of 2.15 microm. FTY720-induced up-regulation of DHS1P level was mediated by sphingosine kinase (SphK) 1, but not SphK2, as confirmed by experiments using SphK1/2 silencing with small interfering RNA. Our data demonstrate for the first time the ability of FTY720 to inhibit ceramide synthases and modulate the intracellular balance of signaling sphingolipids. These findings open a novel direction for therapeutic applications of FTY720 that focuses on inhibition of ceramide biosynthesis, ceramide-dependent signaling, and the up-regulation of DHS1P generation in cells.

Role of acylglycerol kinase in LPA-induced IL-8 secretion and transactivation of epidermal growth factor-receptor in human bronchial epithelial cells

LPA (lysophosphatidic acid) is a potent bioactive phospholipid, which regulates a number of diverse cellular responses through G protein-coupled LPA receptors. Intracellular LPA is generated by the phosphorylation of monoacylglycerol by acylglycerol kinase (AGK); however, the role of intracellular LPA in signaling and cellular responses remains to be elucidated. Here, we investigated signaling pathways of IL-8 secretion mediated by AGK and intracellular LPA in human bronchial epithelial cells (HBEpCs). Expression of AGK in HBEpCs was detected by real-time PCR, and overexpressed AGK was mainly localized in mitochondria as determined by immunofluorescence and confocal microscopy. Overexpression of lentiviral AGK wild type increased intracellular LPA production ( approximately 1.8-fold), enhanced LPA-mediated IL-8 secretion, and stimulated tyrosine phosphorylation epidermal growth factor-receptor (EGF-R). Furthermore, downregulation of native AGK by AGK small interfering RNA decreased intracellular LPA levels ( approximately 2-fold) and attenuated LPA-induced p38 MAPK, JNK, and NF-kappaB activation, tyrosine phosphorylation of EGF-R, and IL-8 secretion. These results suggest that native AGK regulates LPA-mediated IL-8 secretion involving MAPKs, NF-kappaB, and transactivation of EGF-R. Thus AGK may play an important role in innate immunity and airway remodeling during inflammation.

Akt activates NOS3 and separately restores barrier integrity in H2O2-stressed human cardiac microvascular endothelium

The integrity of microvascular endothelium is an important regulator of myocardial contractility. Microvascular barrier integrity could be altered by increased reactive oxygen species (ROS) stress seen within minutes after cardiac arrest resuscitation. Akt and its downstream target nitric oxide (NO) synthase (NOS)3 can protect barrier integrity during ROS stress, but little work has studied these oxidant stress responses in human cardiac microvascular endothelial cells (HCMVEC). We, therefore, studied how ROS affects barrier function and NO generation via Akt and its downstream target NOS3 in HCMVEC. HCMVEC exposed to 500 microM H2O2 had increased Akt phosphorylation within 10 min at both Ser-473 and Thr-308 sites, an effect blocked by the phosphatidylinositol 3-kinase inhibitor LY-294002. H2O2 also induced NO generation that was associated with NOS3 Ser-1177 site phosphorylation and Thr-495 dephosphorylation, with Ser-1177 effects attenuated by LY-294002 and an Akt inhibitor, Akt/PKB signaling inhibitor-2 (API-2). H2O2 induced significant barrier disruption in HCMVEC within minutes, but recovery started within 30 min and normalized over hours. The NOS inhibitor Nomega-nitro-L-arginine methyl ester (200 microM) blocked NO generation but had no effect on H2O2-induced barrier permeability or the recovery of barrier integrity. By contrast, the Akt inhibitor API-2 abrogated HCMVEC barrier restoration. These results suggest that oxidant stress in HCMVEC activates NOS3 via Akt. NOS3/NO are not involved in the regulation of H2O2-affected barrier function in HCMVEC. Independent of NOS3 regulation, Akt proves to be critical for the restoration of barrier integrity in HCMVEC.

Superoxide dismutase protects against apoptosis and alveolar enlargement induced by ceramide

The molecular events leading to emphysema development include generation of oxidative stress and alveolar cell apoptosis. Oxidative stress upregulates ceramides, proapoptotic signaling sphingolipids that trigger further oxidative stress and alveolar space enlargement, as shown in an experimental model of emphysema due to VEGF blockade. As alveolar cell apoptosis and oxidative stress mutually interact to mediate alveolar destruction, we hypothesized that the oxidative stress generated by ceramide is required for its pathogenic effect on lung alveoli. To model the direct lung effects of ceramide, mice received ceramide intratracheally (Cer(12:0) or Cer(8:0); 1 mg/kg) or vehicle. Apoptosis was inhibited with a general caspase inhibitor. Ceramide augmentation shown to mimic levels found in human emphysema lungs increased oxidative stress, and decreased, independently of caspase activation, the lung superoxide dismutase activity at 48 h. In contrast to their wild-type littermates, transgenic mice overexpressing human Cu/Zn SOD were significantly protected from ceramide-induced superoxide production, apoptosis, and air space enlargement. Activation of lung acid sphingomyelinase in response to ceramide treatment was abolished in the Cu/Zn SOD transgenic mice. Since cigarette smoke-induced emphysema in mice is similarly ameliorated by the Cu/Zn SOD overexpression, we hypothesized that cigarette smoke may induce ceramides in the mouse lung. Utilizing tandem mass spectrometry, we documented increased lung ceramides in adult mice exposed to cigarette smoke for 4 wk. In conclusion, ceramide-induced superoxide accumulation in the lung may be a critical step in ceramide's proapoptotic effect in the lung. This work implicates excessive lung ceramides as amplifiers of lung injury through redox-dependent mechanisms.

Apoptotic sphingolipid signaling by ceramides in lung endothelial cells

The de novo pathway of ceramide synthesis has been implicated in the pathogenesis of excessive lung apoptosis and murine emphysema. Intracellular and paracellular-generated ceramides may trigger apoptosis and propagate the death signals to neighboring cells, respectively. In this study we compared the sphingolipid signaling pathways triggered by the paracellular- versus intracellular-generated ceramides as they induce lung endothelial cell apoptosis, a process important in emphysema development. Intermediate-chain length (C(8:0)) extracellular ceramides, used as a surrogate of paracellular ceramides, triggered caspase-3 activation in primary mouse lung endothelial cells, similar to TNF-alpha-generated endogenous ceramides. Inhibitory siRNA against serine palmitoyl transferase subunit 1 but not acid sphingomyelinase inhibited both C(8:0) ceramide- and TNF-alpha (plus cycloheximide)-induced apoptosis, consistent with the requirement for activation of the de novo pathway of sphingolipid synthesis. Tandem mass spectrometry analysis detected increases in both relative and absolute levels of C(16:0) ceramide in response to C(8:0) and TNF-alpha treatments. These results implicate the de novo pathway of ceramide synthesis in the apoptotic effects of both paracellular ceramides and TNF-alpha-stimulated intracellular ceramides in primary lung endothelial cells. The serine palmitoyl synthase-regulated ceramides synthesis may contribute to the amplification of pulmonary vascular injury induced by excessive ceramides.

De novo biosynthesis of dihydrosphingosine-1-phosphate by sphingosine kinase 1 in mammalian cells

Sphingosine kinase 1 (SK1) is one of the two known kinases, which generates sphingosine-1-phosphate (S1P), a potent endogenous lipid mediator involved in cell survival, proliferation, and cell-cell interactions. Activation of SK1 and intracellular generation of S1P were suggested to be part of the growth and survival factor-induced signaling, and overexpression of SK1 provoked cell tumorigenic transformation. Using a highly selective and sensitive LC-MS/MS approach, here we show that SK1 overexpression, but not SK2, in different primary cells and cultured cell lines results in predominant upregulation of the synthesis of dihydrosphingosine-1-phosphate (DHS1P) compared to S1P. Stable isotope pulse-labeling experiments in conjunction with LC-MS/MS quantitation of different sphingolipids demonstrated strong interference of overexpressed SK1 with the de novo sphingolipid biosynthesis by deviating metabolic flow of newly formed sphingoid bases from ceramide formation toward the synthesis of DHS1P. On the contrary, S1P biosynthesis was not directly linked to the de novo sphingoid bases transformations and was dependent on catabolic generation of sphingosine from complex sphingolipids. As a result of SK1 overexpression, migration and Ca2+-response of human pulmonary artery endothelial cells (HPAEC) to stimulation with external S1P, but not thrombin, was strongly impaired. In contrast, selective increase in intracellular content of DHS1P or S1P through the uptake and phosphorylation of corresponding sphingoid bases had no effect on S1P-induced signaling or facilitation of wound healing. Furthermore, infection of human bronchial epithelial cells (HBEpC) with RSV A-2 virus increased SK1-mediated synthesis of DHS1P and S1P, whereas TNF-alpha enhanced only S1P production in HPAEC. These findings uncover a new functional role for SK1, which can control survival/death (DHS1P-S1P/ceramides) balance by targeting sphingolipid de novo biosynthesis and selectively generating DHS1P at a metabolic step preceding ceramide formation.

Quantitative analysis of sphingoid base-1-phosphates as bisacetylated derivatives by liquid chromatography-tandem mass spectrometry

Sphingosine-1-phosphate (S1P) and dihydrosphingosine-1-phosphate (DHS1P) are important signaling sphingolipids. The presence of nanomolar levels of S1P and DHS1P in tissues, cells, and biological fluids requires a highly sensitive and selective assay method for their reliable detection and quantitation. Preliminary findings employing positive ion electrospray ionization (ESI) liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicated significant sample carryover from previous injections of authentic standards of S1P and DHS1P. This article details a negative ion ESI LC-MS/MS technique following modification of the zwitterionic nature of S1P and DHS1P via derivatization. A highly selective and sensitive LC-MS/MS technique capable of reliable detection of less than 50 fmol of the derivatives of S1P and DHS1P without significant sample carryover was developed. Standard curves for S1P and DHS1P are linear over wide ranges (0-300 pmol) of analyte concentrations with correlation coefficients (r2) greater than 0.995. The levels of S1P and DHS1P in human platelet poor plasma were 590.8+/-42.1 and 130.7+/-20.7 pmol/ml, respectively. The levels of S1P and DHS1P in fetal bovine serum were 141.7+/-4.6 and 0.6+/-0.2 pmol/ml, respectively. The addition of sphingosine (1 microM) to human pulmonary artery endothelial cells in culture resulted in a more than 20-fold increase in the cellular level of S1P, whereas the level of DHS1P was unchanged.

[Effect of the cannabinoid receptor ligand WIN-55,212-2 on the TNF-alpha production by human mononuclear cells]

Synthetic cannabinoid WIN-55,212-2 produces a dose-dependent decrease on the TNF-alpha production by LPS-stimulated human mononuclear cells in vitro. The most pronounced inhibition of the TNF-alpha synthesis was observed for a drug concentration of 10 microM.

Cannabinoid receptor-inactive N-acylethanolamines and other fatty acid amides: metabolism and function

Although it is now generally accepted that long-chain N-acylethanolamines and their precursors, N-acylethanolamine phospholipids, exist as trace constituents in virtually all vertebrate cells and tissues, their possible biological functions are just emerging. While anandamide (N-arachidonoylethanolamine) has received much attention due to its ability to bind to and activate cannabinoid receptors, the saturated and monounsaturated N-acylethanolamines, which usually represent the vast majority, are cannabinoid receptor-inactive but appear to interact with endocannabinoids and to have other signaling functions as well. Also, primary fatty acid amides, including the amide of oleic acid, which acts as a sleep-inducing agent, do not interact with cannabinoid receptors but are catabolically related to endocannabinoids. Here we review published information on the occurrence, metabolism, and possible signaling functions of the cannabinoid receptor-inactive N-acylethanolamines and primary fatty acid amides.

Cannabinoid-receptor-independent cell signalling by N-acylethanolamines

Anandamide and other polyunsaturated N-acylethanolamines (NAEs) exert biological activity by binding to cannabinoid receptors. These receptors are linked to G(i/o) proteins and their activation leads to extracellular-signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAP kinase) activation, inhibition of cAMP-dependent signalling and complex changes in the expression of various genes. Saturated and monounsaturated NAEs cannot bind to cannabinoid receptors and may thus mediate cell signalling through other targets. Here we report that both saturated/monounsaturated NAEs and anandamide (20:4(n-6) NAE) stimulate cannabinoid-receptor-independent ERK phosphorylation and activator protein-1 (AP-1)-dependent transcriptional activity in mouse epidermal JB6 cells. Using a clone of JB6 P(+) cells with an AP-1 collagen-luciferase reporter construct, we found that 16:0, 18:1(n-9), 18:1(n-7), 18:2(n-6) and 20:4(n-6) NAEs stimulated AP-1-dependent transcriptional activity up to 2-fold, with maximal stimulation at approx. 10-15 microM. Higher NAE concentrations had toxic effects mediated by alterations in mitochondrial energy metabolism. The AP-1 stimulation appeared to be mediated by ERK but not JNK or p38 signalling pathways, because all NAEs stimulated ERK1/ERK2 phosphorylation without having any effect on JNK or p38 kinases. Also, overexpression of dominant negative ERK1/ERK2 kinases completely abolished NAE-induced AP-1 activation. In contrast with 18:1(n-9) NAE and anandamide, the cannabinoid receptor agonist WIN 55,212-2 did not stimulate AP-1 activity and inhibited ERK phosphorylation. The NAE-mediated effects were not attenuated by pertussis toxin and appeared to be NAE-specific, as a close structural analogue, oleyl alcohol, failed to induce ERK phosphorylation. The data support our hypothesis that the major saturated and monounsaturated NAEs are signalling molecules acting through intracellular targets without participation of cannabinoid receptors.

Activation of PAF receptors results in enhanced synthesis of 2-arachidonoylglycerol (2-AG) in immune cells

The endocannabinoid signaling system is believed to play a down-regulatory role in the control of cell functions. However, little is known about the factors activating endocannabinoid synthesis and which of two known endocannabinoids, 2-arachidonoylglycerol (2-AG) or N-arachidonoylethanolamine (20:4n-6 NAE, anandamide), is of physiological importance. We approached these questions by studying a possible link between cell activation with 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor, PAF) and the generation of 2-AG and anandamide in human platelets and mouse P388D1 macrophages. Human platelets responded to stimulation with the production of various 1- and 2-monoacylglycerols, including 2-AG, whereas stimulation of P388D1 macrophages induced the rapid and selective generation of 2-AG, which was immediately released into the medium. The effect of PAF was receptor mediated, as PAF receptor antagonist BN52021 blocked the effect. The treatment did not change the content of anandamide in either macrophages or platelet-rich plasma. The inhibitors of PI- and PC-specific phospholipases C (U73122 and D609) as well as PI3-kinase inhibitor (wortmannin) attenuated PAF-induced 2-AG production in macrophages. These data suggest a direct role for the endocannabinoid system in controlling immune cell activation status and indicate that 2-AG rather than anandamide is the endocannabinoid rapidly produced in response to proinflammatory stimulation of immune cells.

Cannabinoid receptors and the regulation of immune response

Cannabinoid research underwent a tremendous increase during the last 10 years. This progress was made possible by the discovery of cannabinoid receptors and the endogenous ligands for these receptors. Cannabinoid research is developing in two major directions: neurobehavioral properties of cannabinoids and the impact of cannabinoids on the immune system. Recent studies characterized the cannabinoid-induced response as a very complex process because of the involvement of multiple signalling pathways linked to cannabinoid receptors or effects elicited by cannabinoids without receptor participation. The objective of this review is to present this complexity as it applies to immune response. The functional properties of cannabinoid receptors, signalling pathways linked to cannabinoid receptors and the modulation of immune response by cannabinoid receptor ligands are discussed. Special attention is given to 'endocannabinoids' as immunomodulatory molecules.

Stress-induced generation of N-acylethanolamines in mouse epidermal JB6 P+ cells

It has long been known that N-acylethanolamine phospholipids [N-acylphosphatidylethanolamine (N-acyl PE)] and N-acylethanolamines (NAEs) accumulate in mammalian tissues undergoing degenerative membrane changes associated with necrosis. Here we studied the effects of stress factors (UVB irradiation and serum deprivation) on the endogenous levels of N-acyl PE and NAE in mouse epidermal JB6 P(+) cells. We found that 16:0, 18:0, 18:1,n-9 and 18:1,n-7 are the predominant amide-linked fatty acids in both N-acyl PE and NAE in these cells. UVB irradiation and serum deprivation resulted in significantly increased levels of N-acyl PE and NAE, especially 18:1, n-9 N-acyl PE and NAE. UVB challenge increased the cellular content of anandamide (20:4,n-6 NAE), but this increase was the lowest of all NAEs measured. Serum deprivation resulted in a decreased cellular anandamide level, as well as a decrease in 20:4,n-6 N-acyl PE. Interestingly, the replacement of serum-free medium with medium containing 5% (v/v) fetal calf serum after 36 h of serum deprivation restored N-acyl PE and NAE levels almost completely within 4-8 h. These data suggest the involvement of N-acyl PE and NAE in cellular responses to stress.

A sensitive endocannabinoid assay. The simultaneous analysis of N-acylethanolamines and 2-monoacylglycerols

Mammalian cells produce both N-arachidonoylethanolamine (20:4n-6 NAE, anandamide) and 2-arachidonoylglycerol (2-AG), lipid signaling molecules that activate cannabinoid receptors. Because both agonists occur in the presence of receptor-inactive congeners, we have developed a sensitive method for the simultaneous assay of N-acylethanolamines (NAEs) and 2-monoacylglycerols (2-MAG). These lipid classes are isolated from total lipids by solid phase extraction and converted to tert-butyldimethylsilyl (tBDMS) derivatives in the presence of deuterated analogs. The tBDMS derivatives are analyzed by gas chromatography/mass spectrometry using selected ion monitoring programs specific for NAE and 2-MAG. Individual NAEs and 2-MAGs can be quantified in the nanogram and subnanogram range. The NAE and 2-MAG compositions of rat organs and cultured JB6 cells are reported.

Inhibition of sea urchin fertilization by fatty acid ethanolamides and cannabinoids

The influence of saturated and unsaturated fatty acid ethanolamides as well as delta9-tetrahydrocannabinol (delta9-THC), WIN 55,212-2 and cannabinoid CB1 receptor antagonist SR 141716 on sea urchin fertilization was studied. The ethanolamides of arachidonic, oleic and linoleic acids but not saturated fatty acid (C14-C20) derivatives inhibited fertilization when pre-incubated with sperm cells. Delta9-THC and WIN 55,212-2 also inhibited fertilization, delta9-THC being ten times as potent as WIN 55,212-2. Selective cannabinoid CB1 receptor antagonist SR 141716 also blocked fertilization and did not antagonize the action of delta9-THC. The obtained results indicate that different unsaturated fatty acid ethanolamides may control sea urchin fertilization, and that sea urchin sperm cell cannabinoid receptor may differ from the known cannabinoid receptor subtypes.

Influence of fatty acid ethanolamides and delta9-tetrahydrocannabinol on cytokine and arachidonate release by mononuclear cells

The effects of arachidonic acid ethanolamide (anandamide), palmitoylethanolamide and delta9-tetrahydrocannabinol on the production of tumor necrosis factor-alpha (TNF-alpha), interleukin-4, interleukin-6, interleukin-8, interleukin-10, interferon-gamma, p55 and p75 TNF-alpha soluble receptors by stimulated human peripheral blood mononuclear cells as well as [3H]arachidonic acid release by non-stimulated and N-formyl-Met-Leu-Phe (fMLP)-stimulated human monocytes were investigated. Anandamide was shown to diminish interleukin-6 and interleukin-8 production at low nanomolar concentrations (3-30 nM) but inhibited the production of TNF-alpha, interferon-gamma, interleukin-4 and p75 TNF-alpha soluble receptors at higher concentrations (0.3-3 microM). Palmitoylethanolamide inhibited interleukin-4, interleukin-6, interleukin-8 synthesis and the production of p75 TNF-alpha soluble receptors at concentrations similar to those of anandamide but failed to influence TNF-alpha and interferon-gamma production. The effect of both compounds on interleukin-6 and interleukin-8 production disappeared with an increase in the concentration used. Neither anandamide nor palmitoylethanolamide influenced interleukin-10 synthesis. delta9-Tetrahydrocannabinol exerted a biphasic action on pro-inflammatory cytokine production. TNF-alpha, interleukin-6 and interleukin-8 synthesis was maximally inhibited by 3 nM delta9-tetrahydrocannabinol but stimulated by 3 microM delta9-tetrahydrocannabinol, as was interleukin-8 and interferon-gamma synthesis. The level of interleukin-4, interleukin-10 and p75 TNF-alpha soluble receptors was diminished by 3 microM delta9-tetrahydrocannabinol. [3H]Arachidonate release was stimulated only by high delta9-tetrahydrocannabinol and anandamide concentrations (30 microM). These results suggest that the inhibitory properties of anandamide, palmitoylethanolamide and delta9-tetrahydrocannabinol are determined by the activation of the peripheral-type cannabinoid receptors, and that various endogenous fatty acid ethanolamides may participate in the regulation of the immune response.

Sea urchins--a new model for PAF research in embryology

This study reports on the effect of PAF on sperm motility, fertilization and early embryo development in the sea urchin Strongylocentrotus intermedius. PAF proved to be the amplifier of sperm motility and fertilizing capability at 10(-8)-10(-9) M and was toxic at higher concentrations. BN 52201 did not counteract the PAF action. The advantages of using sea urchins for PAF research in embryology are discussed.

[Interaction of 1-O-alkyl-2-methoxy-sn-glycero-3-phosphocholine and platelet activating factor with blood and tumor cells]

The effects of the platelet-activating factor (PAF) and the methoxy-PAF analog, 1-O-alkyl-2-methoxy-sn-glycero-3-phosphocholine, on platelet activation, oxidative burst in neutrophils and proliferation of K-562 and P815 cells have been studied. It has been found that the biological activity of methoxy-PAF for human platelets and neutrophils is commensurate with that of PAF. However, the cytotoxic properties of methoxy-PAF are much stronger than the cytotoxicity of PAF for tumour cells. It is concluded that the biological activity of methoxy-PAF is, to a great extent, due to its close structural resemblance to PAF as well as to the inability of cells to perform rapid metabolism of methoxy-PAF.