Oxylipin patterns in human colon adenomas.

OBJECTIVE: Cyclooxygenase (COX)-derived prostaglandin E2 (PGE2) is an important lipid mediator in colorectal carcinoma (CRC) pathogenesis. Other lipid mediators derived from lipoxygenases (LOX) have also been implicated in neoplastic processes in the colon. In this study we aimed to characterize lipid mediators, so called oxylipins, in human colon adenomatous polyps. DESIGN: We quantified oxylipins in healthy colon tissue and colorectal adenoma tissue procured during routine colonoscopy examinations. Lipid metabolite profiles were analyzed by liquid chromatography-tandem mass spectrometry. RESULTS: Adenoma tissue showed a distinct prostaglandin profile as compared to normal colon mucosa. Interestingly, PGE2 was not higher in adenoma tissue as compared to normal mucosa. In contrast, we found significantly lower levels of prostaglandin D2, prostaglandin J2, and prostaglandin D1 in adenoma tissue. Furthermore, levels of 5-LOX and 12-LOX pathway products were clearly increased in adenoma biopsy samples. We also investigated the effect of aspirin treatment on prostaglandin profiles in adenoma tissue in a subset of patients and found a trend towards decreased prostaglandin levels in response to aspirin. CONCLUSION: The human data presented here show specific changes of oxylipin profiles in colon adenoma tissue with decreased prostaglandin D2 levels as well as increased 5- and 12-LOX metabolites.

Divergent Effects of Acute and Prolonged Interleukin 33 Exposure on Mast Cell IgE-Mediated Functions.

Background: Epithelial cytokines, including IL-33 and Thymic stromal lymphopoietin (TSLP), have attracted interest because of their roles in chronic allergic inflammation-related conditions such as asthma. Mast cells are one of the major targets of IL-33, to which they respond by secreting cytokines. Most studies performed thus far have investigated the acute effects of IL-33 on mast cells. In the current study, we investigated how acute vs. prolonged exposure of mast cells to IL-33 and TSLP affects mediator synthesis and IgE-mediated activation. Methods: Human lung mast cells (HLMCs), cord blood-derived mast cells (CBMCs), and the ROSA mast cell line were used for this study. Receptor expression and the levels of mediators were measured after treatment with IL-33 and/or TSLP. Results: IL-33 induced the release of cytokines. Prolonged exposure to IL-33 increased while TSLP reduced intracellular levels of tryptase. Acute IL-33 treatment strongly potentiated IgE-mediated activation. In contrast, 4 days of exposure to IL-33 decreased IgE-mediated activation, an effect that was accompanied by a reduction in FcεRI expression. Conclusion: We show that IL-33 plays dual roles in mast cells, in which its acute effects include cytokine release and the potentiation of IgE-mediated degranulation, whereas prolonged exposure to IL-33 reduces IgE-mediated activation. We conclude that mast cells act quickly in response to the alarmin IL-33 to initiate an acute inflammatory response, whereas extended exposure to IL-33 during prolonged inflammation reduces IgE-mediated responses. This negative feedback effect suggests the presence of a novel regulatory pathway that modulates IgE-mediated human mast cell responses.

The acute cardiorespiratory effects of centrally injected arachidonic acid; the mediation of prostaglandin E, D and F2α.

Arachidonic acid (AA), which is released from synaptic membrane phospholipid by neuroreceptor-initiated activation of phospholipase A2, is abundant in the brain and works as a neurotransmitter and/or neuromodulator in the central nervous system. Recently we reported that centrally injected AA generated pressor and hyperventilation effects by activating thromboxane A2 (TXA2) signaling pathway. The present study was designed to investigate the mediation of other metabolites of AA such as prostaglandin (PG) D, PGE and PGF2α alongside TXA2 in the AA-evoked cardiorespiratory effects in anaesthetized rats. Intracerebroventricular (i.c.v.) administration of AA caused pressor, bradycardic and hyperventilation responses by increasing pO2 and decreasing pCO2 in adult male anaesthetized Sprague Dawley rats. Pretreatment (i.c.v) with different doses of DP/EP prostanoid receptor antagonist, AH6809 or FP prostanoid receptor antagonist, PGF2α dimethylamine partially blocked the cardiorespiratory and blood gas changes induced by AA. In conclusion, these data plainly report that central PGD, PGE or PGF2α might mediate, at least partly, centrally administered AA-evoked cardiorespiratory and blood gas responses.

Cross-Linking Mast Cell Specific Gangliosides Stimulates the Release of Newly Formed Lipid Mediators and Newly Synthesized Cytokines.

Mast cells are immunoregulatory cells that participate in inflammatory processes. Cross-linking mast cell specific GD1b derived gangliosides by mAbAA4 results in partial activation of mast cells without the release of preformed mediators. The present study examines the release of newly formed and newly synthesized mediators following ganglioside cross-linking. Cross-linking the gangliosides with mAbAA4 released the newly formed lipid mediators, prostaglandins D2 and E2, without release of leukotrienes B4 and C4. The effect of cross-linking these gangliosides on the activation of enzymes in the arachidonate cascade was then investigated. Ganglioside cross-linking resulted in phosphorylation of cytosolic phospholipase A2 and increased expression of cyclooxygenase-2. Translocation of 5-lipoxygenase from the cytosol to the nucleus was not induced by ganglioside cross-linking. Cross-linking of GD1b derived gangliosides also resulted in the release of the newly synthesized mediators, interleukin-4, interleukin-6, and TNF-α. The effect of cross-linking the gangliosides on the MAP kinase pathway was then investigated. Cross-linking the gangliosides induced the phosphorylation of ERK1/2, JNK1/2, and p38 as well as activating both NFκB and NFAT in a Syk-dependent manner. Therefore, cross-linking the mast cell specific GD1b derived gangliosides results in the activation of signaling pathways that culminate with the release of newly formed and newly synthesized mediators.

Prostaglandin D(2) in inflammatory arthritis and its relation with synovial fluid dendritic cells.

Prostaglandin (PG)D2 has been shown to be an active agent in the resolution of experimentally induced inflammation. This study was undertaken to determine the presence of PGD2 in chronic joint effusions and to explore the potential contributions of dendritic cells (DC) and monocytes to the intra-articular synthesis of PGD2. Synovial fluid (SF) was obtained from patients with inflammatory arthritis and knee effusions. PGD2 and PGE2 were detected in SF by ultrahigh-performance tandem mass spectrometry. Cellular fractions in SF were separated by density-gradient centrifugation and flow cytometry. The expression of hematopoietic prostaglandin D-synthase (hPGDS) and PGE-synthase (PGES) mRNA was determined by RT-PCR. Both PGD2 and PGE2 were detected in blood and SF, with PGD2 being more abundant than PGE2 in SF. mRNA for hPGDS was more abundant in SF mDCs than SF monocytes (P < 0.01) or PB monocytes (P < 0.001). SF mDC expressed significantly more hPGDS than PGES. Expressions of PGD2 and hPGDS were inversely associated with serum C-reactive protein (P < 0.01) and erythrocyte sedimentation rate (P < 0.01). The findings suggest that synovial DCs may be an important source of hPGDS and that systemic disease activity may be influenced by actions of PGD2 in RA and other arthropathies.

Comparative defense-associated responses in salmon skin elicited by the ectoparasite Lepeophtheirus salmonis.

Susceptibility among salmonids to the ectoparasite Lepeophtheirus salmonis is related to inflammatory reactions at the site of parasite attachment. Salmon from two susceptible (Salmo salar, Oncorhynchus keta) and one resistant (Oncorhynchus gorbuscha) species were exposed to adult L. salmonis. After 24 and 48h, skin samples directly below the attachment site and at non-attachment sites were assessed for transcriptomic profiles of select innate defense genes. Abrasion of the skin permitted comparisons between abrasion-associated injury and louse-associated injury. Infection responses were consistently higher than those caused by abrasion. Temporal patterns of expression were evident in all species for the transcription factor CCAAT/enhancer-binding protein ß (C/EBP-ß), the cytokine interleukin-6 (IL-6) and the enzyme prostaglandin D synthase (PGDS) at attachment sites. O. gorbuscha was the highest responder in a number of genes while there was an absence of C-reactive protein (CRP) gene expression in S. salar and O. keta, indicating an altered acute-phase response. Moreover, O. keta displayed distinct interleukin-8 (IL-8) and serum amyloid P (SAP) responses. Impaired genetic expression or over-expression in these pathways may be evidence for species-specific pathways of susceptibility to the parasite. At L. salmonis attachment sites, reduced expression compared to non-attachment sites was observed for C/EBP-ß (S. salar), CRP (S. salar), SAP (S. salar, O. gorbuscha, O. keta), PGDS (S. salar, O. gorbuscha, O. keta), and major histocompatibility class II (MH class II, S. salar), suggesting local immunodepression.

MicroRNA expression profiling in the prefrontal cortex of individuals affected with schizophrenia and bipolar disorders.

MicroRNAs (miRNAs) are a large family of small non-coding RNAs which negatively control gene expression at both the mRNA and protein levels. The number of miRNAs identified is growing rapidly and approximately one-third is expressed in the brain where they have been shown to affect neuronal differentiation, synaptosomal complex localization and synapse plasticity, all functions thought to be disrupted in schizophrenia. Here we investigated the expression of 667 miRNAs (miRBase v.13) in the prefrontal cortex of individuals with schizophrenia (SZ, N = 35) and bipolar disorder (BP, N = 35) using a real-time PCR-based Taqman Low Density Array (TLDA). After extensive QC steps, 441 miRNAs were included in the final analyses. At a FDR of 10%, 22 miRNAs were identified as being differentially expressed between cases and controls, 7 dysregulated in SZ and 15 in BP. Using in silico target gene prediction programs, the 22miRNAs were found to target brain specific genes contained within networks overrepresented for neurodevelopment, behavior, and SZ and BP disease development. In an initial attempt to corroborate some of these predictions, we investigated the extent of correlation between the expressions of hsa-mir-34a, -132 and -212 and their predicted gene targets. mRNA expression of tyrosine hydroxylase (TH), phosphogluconate dehydrogenase (PGD) and metabotropic glutamate receptor 3 (GRM3) was measured in the SMRI sample. Hsa-miR-132 and -212 were negatively correlated with TH (p = 0.0001 and 0.0017) and with PGD (p = 0.0054 and 0.017, respectively).

Prostaglandin D production in FM55 melanoma cells is regulated by alpha-melanocyte-stimulating hormone and is not related to melanin production.

This study shows that prostaglandins in human FM55 melanoma cells and epidermal melanocytes are produced by COX-1. Prostaglandin production in FM55 melanoma cells was unrelated to that of melanin suggesting that the two processes can occur independently. Alpha-melanocyte-stimulating hormone, which had no effect on melanin production in FM55 cells, stimulated PGD(2) production in these cells without affecting PGE(2). While cAMP pathways may be involved in regulating PGD(2) production, our results suggest that alpha-MSH acts independently of cAMP, possibly by regulating the activity of lipocalin-type PGD synthase. This alpha-MSH-mediated effect may be associated with its role as an immune modulator.

Uptake of dihomo-gamma-linolenic acid by murine macrophages increases series-1 prostaglandin release following lipopolysaccharide treatment.

Administration of dihomo-gamma-linolenic acid is useful for atopic dermatitis and atherosclerosis in mice; however, the metabolites of dihomo-gamma-linolenic acid have been little studied. We employed a method which enabled simultaneous analysis of nine prostaglandins using liquid chromatography-tandem mass spectrometry, and determined the concentrations of prostaglandins in the supernatants of cultures of mouse peritoneal macrophages stimulated with lipopolysaccharide after pre-incubation with dihomo-gamma-linolenic acid, arachidonic acid, or eicosapentaenoic acid. Accumulated prostaglandin concentrations from mouse macrophages with dihomo-gamma-linolenic acid uptake increased in a dihomo-gamma-linolenic acid concentration-dependent fashion. These increases were mainly due to prostaglandin D(1) and prostaglandin E(1). The order of accumulated prostaglandin concentrations was dihomo-gamma-linolenic acid>arachidonic acid>eicosapentaenoic acid in supernatants with the same concentration of polyunsaturated fatty acid. Since mouse macrophages can clearly produce series-1 prostaglandins, they must be formed in vivo. These findings suggest that the effects of dihomo-gamma-linolenic acid on diseases may be due to series-1 prostaglandins.

The role of the prostaglandin D2 receptor, DP, in eosinophil trafficking.

Prostaglandin (PG) D2 is a major mast cell product that acts via two receptors, the D-type prostanoid (DP) and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) receptors. Whereas CRTH2 mediates the chemotaxis of eosinophils, basophils, and Th2 lymphocytes, the role of DP has remained unclear. We report in this study that, in addition to CRTH2, the DP receptor plays an important role in eosinophil trafficking. First, we investigated the release of eosinophils from bone marrow using the in situ perfused guinea pig hind limb preparation. PGD2 induced the rapid release of eosinophils from bone marrow and this effect was inhibited by either the DP receptor antagonist BWA868c or the CRTH2 receptor antagonist ramatroban. In contrast, BWA868c did not inhibit the release of bone marrow eosinophils when this was induced by the CRTH2-selective agonist 13,14-dihydro-15-keto-PGD2. In additional experiments, we isolated bone marrow eosinophils from the femoral cavity and found that these cells migrated toward PGD2. We also observed that BWA868c inhibited this response to a similar extent as ramatroban. Finally, using immunohistochemistry we could demonstrate that eosinophils in human bone marrow specimens expressed DP and CRTH2 receptors at similar levels. Eosinophils isolated from human peripheral blood likewise expressed DP receptor protein but at lower levels than CRTH2. In agreement with this, the chemotaxis of human peripheral blood eosinophils was inhibited both by BWA868c and ramatroban. These findings suggest that DP receptors comediate with CRTH2 the mobilization of eosinophils from bone marrow and their chemotaxis, which might provide the rationale for DP antagonists in the treatment of allergic disease.

The choroid plexus response to peripheral inflammatory stimulus.

Increased interest is being raised on the interaction between systemic inflammation and the brain. The choroid plexus (CP) constitutes a monolayer of epithelial cells located within the brain ventricles and is responsible for the production of cerebrospinal fluid (CSF). Despite the knowledge that the CP capillaries are fenestrated, allowing free passage of molecules and cells, the involvement of the vast blood-brain boundary represented by the CP/CSF barrier in brain inflammatory processes has seldom been considered. In the present study we investigate, in mice, how the expression of genes encoding major constitutively expressed CP proteins is influenced by a systemic inflammatory stimulus. Confirming that the CP responds to peripheral inflammation, the messenger RNA (mRNA) levels of the pro-inflammatory cytokines interleukin 1 beta and tumor necrosis factor alpha are rapidly induced. As for the constitutively expressed proteins, while the mRNA for genes encoding transthyretin and transferrin remain unaltered by the inflammatory challenge, that for prostaglandin D2 synthase (LPTGDS) is up-regulated at 6 h, and stays up-regulated up to 24 h after lipopolysacharide administration. Accordingly, LPTGDS CSF levels are also augmented. LPTGDS catalyzes the synthesis of the major prostanoid of the CNS and, being increased in the CSF, might mediate immune signaling into the brain. These observations emphasize that the CP must be considered a relevant mediator of immune signals between the periphery and the brain.

Depot-specific prostaglandin synthesis in human adipose tissue: a novel possible mechanism of adipogenesis.

Despite the magnitude of the obesity epidemic, the mechanisms that contribute to increases in fat mass and to differences in fat depots are still poorly understood. Prostanoids have been proposed as potent adipogenic hormones, e.g. metabolites of prostaglandin J2 (PGJ2) bind and activate PPARgamma. We hypothesize that an altered expression of enzymes in PGJ2 synthesis may represent a novel pathogenic mechanism in human obesity. We characterized adipose depot-specific expression of enzymes in PGJ2 synthesis, prostaglandin transporter and PPARgamma isoforms. Paired omental and subcutaneous adipose tissue samples were obtained from 26 women undergoing elective abdominal surgery and gene expression examined in whole tissue and cultured preadipocytes using an Affymetrix cDNA microarray technique and validated with quantitative real-time PCR. All enzymes involved in prostaglandin synthesis were expressed in both adipose tissues. Expression of prostaglandin synthase-1 (PGHS1), prostaglandin D synthase (PTGDS), human prostaglandin transporter (hPGT) and PPARgamma2 was higher in OM adipose tissue compared to SC, whereas 17beta-hydroxysteroid dehydrogenase 5 (AKR1C3) showed predominance in SC adipose tissue. In SC adipose tissue, PGHS1 mRNA expression increased with BMI. The differential, depot-specific expression of key enzymes involved in transport, synthesis and metabolism of prostaglandins may have an important impact upon fat cell biology and may help to explain some of the observed depot-specific differences. In addition, the positive correlation between PGHS1 and BMI offers the novel hypothesis that the regulation of PG synthesis may have a role in determining fat distribution in human obesity.

Levuglandinyl adducts of proteins are formed via a prostaglandin H2 synthase-dependent pathway after platelet activation.

The product of oxygenation of arachidonic acid by the prostaglandin H synthases (PGHS), prostaglandin H(2) (PGH(2)), undergoes rearrangement to the highly reactive gamma-ketoaldehydes, levuglandin (LG) E(2), and LGD(2). We have demonstrated previously that LGE(2) reacts with the epsilon-amine of lysine to form both the levuglandinyl-lysine Schiff base and the pyrrole-derived levuglandinyl-lysine lactam adducts. We also have reported that these levuglandinyl-lysine adducts are formed on purified PGHSs following the oxygenation of arachidonic acid. We now present evidence that the levuglandinyl-lysine lactam adduct is formed in human platelets upon activation with exogenous arachidonic acid or thrombin. After proteolytic digestion of the platelet proteins, and isolation of the adducted amino acid residues, this adduct was identified by liquid chromatography-tandem mass spectrometry. We also demonstrate that formation of these adducts is inhibited by indomethacin, a PGHS inhibitor, and is enhanced by an inhibitor of thromboxane synthase. These data establish that levuglandinyl-lysine adducts are formed via a PGHS-dependent pathway in whole cells, even in the presence of an enzyme that metabolizes PGH(2). They also demonstrate that a physiological stimulus is sufficient to lead to the lipid modification of proteins through the levuglandin pathway in human platelets.

Prostaglandin F synthase.

Prostaglandin (PG) F2 is synthesized via three pathways from PGE2, PGD2, or PGH2 by PGE 9-ketoreductase, PGD 11-ketoreductase, or PGH 9-, 11-endoperoxide reductase, respectively. The enzymological and molecular biological properties of these enzymes have been reported in work over the last 30 years. Here, these three pathways of PGF synthesis by these enzymes are reviewed, and the physiological roles of the enzymes are discussed.

[Clinical variability in two cases of systemic mastocytosis]. / Róznopostaciowosc kliniczna w dwóch przypadkach mastocytozy ukladowej.

Two cases of systemic mastocytosis with different clinical course were described. The first of them manifested with returning attacks of tachycardia with raise of blood pressure, followed by its drop and loss of consciousness. Abdominal pain and persistent diarrhea characterized the second one. The common signs in both cases were skin changes of urticaria pigmentosa, presence of Darier's symptom, very high blood levels of tryptase and prostaglandin D2 and rise in urinary LTE4 concentration. Differential diagnostic is discussed and histopathology bone marrow biopsies are presented.

Affinities, selectivities, potencies, and intrinsic activities of natural and synthetic prostanoids using endogenous receptors: focus on DP class prostanoids.

The prostanoid receptor-subtype binding affinities, selectivities, potencies, and intrinsic activities of four natural prostanoids and six synthetic DP class prostanoids were determined using binding and functional assays with endogenous receptors. SQ27986 exhibited the highest affinity for the human platelet DP receptor and the best DP receptor selectivity profile. Prostaglandin (PG)D(2) was the least DP receptor-selective. The rank order of compound affinities at the DP receptor was SQ27986 (K(i) = 10 +/- 2 nM) > RS93520 = ZK110841 = BW245C (K(i) = 23-26 nM) > ZK118182 (K(i) = 50 +/- 9 nM) > PGD(2) (K(i) = 80 +/- 5 nM). DP receptor agonists produced cAMP in embryonic bovine tracheal fibroblasts with different potencies (EC(50) values in nM): ZK118182 (18 +/- 6), RS93520 (28 +/- 6), SQ27986 (29 +/- 7), ZK110841 (31 +/- 7), BW245C (53 +/- 16), and PGD(2) (98 +/- 10). BW245C was more efficacious and RS93520 was less efficacious than PGD(2). ZK110841 and ZK118182 exhibited a relatively high potency at the adenylyl cyclase-coupled EP(2) receptor in human nonpigmented ciliary epithelial cells but were partial agonists. None of the DP class agonists showed any EP(4) receptor functional activity in Chinese hamster ovary cells. The DP receptor antagonist BWA868C competitively antagonized the PGD(2)-induced cAMP accumulation in embryonic bovine tracheal fibroblast cells (pA(2) = 7.83 +/- 0.08). The dissociation constants for BWA868C antagonizing PGD(2)-, BW245C-, and ZK118182-induced cAMP production were quite similar (apparent -log K(b) = 7.9-8.2, n = 5-9). The pharmacological properties of some natural and numerous DP class synthetic prostanoids have been determined using endogenous receptors.

New developments in the isoprostane pathway: identification of novel highly reactive gamma-ketoaldehydes (isolevuglandins) and characterization of their protein adducts.

The bicyclic endoperoxide prostaglandin (PG) H2 undergoes nonenzymatic rearrangement not only to PGE2 and PGD2, but also to levuglandins (LG) E2 and D2, which are highly reactive gamma-ketoaldehydes. Isoprostanes (IsoPs) are PG-like compounds that are produced by nonenzymatic peroxidation of arachidonic acid. PGH2-like endoperoxides are intermediates in this pathway. Therefore, we explored whether the IsoP endoperoxides also undergo rearrangement to form IsoLGs. Oxidation of arachidonic acid in vitro resulted in the formation of abundant quantities of compounds that were established to be IsoLGs by using mass spectrometric analyses. However, the formation of IsoLGs could not be detected in biological systems subjected to an oxidant stress. We hypothesized that this was due to extremely rapid adduction of IsoLGs to proteins. This notion was supported by the finding that LGE2 adducted to albumin at a rate that exceeded that of 4-hydroxynonenal by several orders of magnitude: >50% of LGE2 had adducted within 20 s. We therefore undertook to characterize the nature of LG adducts. Using liquid chromatography electrospray tandem mass spectrometry, we established that LGs form oxidized pyrrole adducts (lactams and hydroxylactams) with the epsilon-amino group of lysine. Oxidation of low density lipoprotein resulted in readily detectable IsoLG adducts on apolipoprotein B after enzymatic digestion of the protein to individual amino acids. These studies identify a novel class of ketoaldehydes produced by the IsoP pathway that form covalent protein adducts at a rate that greatly exceeds that of other known aldehyde products of lipid peroxidation. Elucidation of the nature of the adducts formed by IsoLGs provides the basis to explore the formation of IsoLGs in vivo and investigate the potential biological ramifications of their formation in settings of oxidant injury.

Human synovial mast cells. II. Heterogeneity of the pharmacologic effects of antiinflammatory and immunosuppressive drugs.

OBJECTIVE: To evaluate the in vitro effects of 4 antiinflammatory and 5 immunosuppressive agents on the release of preformed and de novo-synthesized mediators from human synovial mast cells (HSyMC) activated by immunologic and nonimmunologic stimuli. METHODS: The effects of antiinflammatory and immunosuppressive agents were evaluated on the in vitro release of histamine and tryptase and the de novo synthesis of prostaglandin D2 (PGD2) and leukotriene C4 (LTC4) by HSyMC challenged with anti-IgE and substance P. RESULTS: Nimesulide, a sulfonanilide nonsteroidal antiinflammatory drug (NSAID) chemically unrelated to other acidic NSAIDs (such as acetylsalicylic acid [ASA], diclofenac, and piroxicam) inhibited in a concentration-dependent manner the release of preformed (histamine and tryptase) mediators from HSyMC challenged with anti-IgE. In contrast, diclofenac and piroxicam had little or no effect on HSyMC activated by anti-IgE. ASA, diclofenac, piroxicam, and nimesulide caused a concentration-dependent inhibition of IgE-mediated PGD2 release from HSyMC. Nimesulide, but not diclofenac or piroxicam, also inhibited the de novo synthesis of LTC4 by HSyMC challenged with anti-IgE. Nimesulide, diclofenac, and piroxicam had no effect on HSyMC activated by substance P. Cyclosporin A (CSA) inhibited histamine release from HSyMC challenged with anti-IgE, whereas cyclosporin H (CSH) had no effect. FK-506 also inhibited histamine release from HSyMC activated by anti-IgE, whereas rapamycin had no effect. Neither CSA, CSH, FK-506, nor rapamycin inhibited the release of histamine from HSyMC induced by substance P. Methotrexate had no effect on the release of mediators from these cells, whereas adenosine (R-phenylisopropyl adenosine and 5'-N-ethylcarboxamide adenosine) enhanced histamine release from immunologically activated HSyMC in a concentration-dependent manner. CONCLUSION: Mast cells isolated from human synovia display 4 levels of pharmacologic heterogeneity with regard to 1) the inhibitory effects of 4 antiinflammatory drugs; 2) the capacity of different immunosuppressive drugs to exert antiinflammatory activity; 3) the inhibition of the release of different mediators; and 4) the capacity of antiinflammatory and immunosuppressive drugs to modulate HSyMC activated by different stimuli. This complexity of pharmacologic modulation of HSyMC in vitro might help explain the different activity of the compounds used to treat various pathophysiologic aspects of the inflammatory arthritides.