Differential release of mast cell mediators and the pathogenesis of inflammation

Summary:  Mast cells are well known for their involvement in allergic and anaphylactic reactions, during which immunoglobulin E (IgE) receptor (FcɛRI) aggregation leads to exocytosis of the content of secretory granules (1000 nm), commonly known as degranulation, and secretion of multiple mediators. Recent findings implicate mast cells also in inflammatory diseases, such as multiple sclerosis, where mast cells appear to be intact by light microscopy. Mast cells can be activated by bacterial or viral antigens, cytokines, growth factors, and hormones, leading to differential release of distinct mediators without degranulation. This process appears to involve de novo synthesis of mediators, such as interleukin-6 and vascular endothelial growth factor, with release through secretory vesicles (50 nm), similar to those in synaptic transmission. Moreover, the signal transduction steps necessary for this process appear to be largely distinct from those known in FcɛRI-dependent degranulation. How these differential mast cell responses are controlled is still unresolved. No clinically available pharmacological agents can inhibit either degranulation or mast cell mediator release. Understanding this process could help develop mast cell inhibitors of selective mediator release with novel therapeutic applications.     

Anti-inflammatory actions of flavonoids and structural requirements for new design

Flavonoids are low molecular weight compounds rich in seeds, citrus fruits, olive oil, tea and red wine, with potent antioxidant, cytoprotective and antiinflammatory activities. Flavonoids are composed of a three-ring structure (A,B and C) with various substitutions; they can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3 or a hydroxyl group in position 3 of the C (middle) ring. Particular hydroxylation patterns of the B ring of the flavones permit them to inhibit histamine, tryptase, interleukin-6 and interleukin-8 release from human umbilical-cord derived cultured mast cells, as well as from macrophages. The catechol (o-dihydroxy) group in the B ring as in quercetin confers potent inhibitory ability, while a pyrogallol (trihydroxy) group, as in myricetin, produces even higher activity. However, addition of one hydroxyl group on position 2′ of the B ring, as in the flavonol morin, renders this compound inactive. The C2-C3 double bond of the C ring appears to increase scavenger activity because it confers stability to the phenoxy-radicals produced, while the 4-oxo (keto double bond at position 4 of the C ring) increases free radical scavenger activity by delocalizing electrons from the B ring. The 3-OH group on the C ring appears tobe critical for anti-inflammatory activity. Inhibition of mast cell secretion was shown to be mediated by a 78-kD phosphoprotein which has been cloned and serves as a bridge between the cell surface and the cytoskeleton. Phosphorylation at particular sites in the C-terminus unfolds the three dimensional structure of this protein making actin binding sites accessible; crosslinking with actin in the cytoskeleton prevents secretion of inflammatory mediators. These properties present unique opportunities for the synthesis of new compounds for the treatment of inflammatory and possibly proliferative disorders.     

A Novel Model of Severe Gallstone Pancreatitis: Murine Pancreatic Duct Ligation Results in Systemic Inflammation and Substantial Mortality

Background: Suitable experimental models of gallstone pancreatitis with systemic inflammation and mortality are limited. We developed a novel murine model of duct-ligation-induced acute pancreatitis associated with multiorgan dysfunction and severe mortality. Methods: Laparotomy was done on C57/BL6 mice followed by pancreatic duct (PD) ligation, bile duct (BD) ligation without PD ligation, or sham operation. Results: Only mice with PD ligation developed acute pancreatitis and had 100% mortality. Pulmonary compliance was significantly reduced after PD ligation but not BD ligation. Bronchoalveolar lavage fluid neutrophil count and interleukin-1 β concentration, and the plasma creatinine level, were significantly elevated with PD ligation but not BD ligation. Pancreatic nuclearfactor kB (p65) and activator protein 1 (c-Jun) were activated within 1 h of PD ligation. Conclusion: PD-ligation-induced acute pancreatitis in mice is associated with systemic inflammation, acute lung injury, multiorgan dysfunction and death. The development of this novel model is an exciting and notable advance in the field.     

Niacin-induced "flush" involves release of prostaglandin D2 from mast cells and serotonin from platelets: evidence from human cells in vitro and an animal model

Niacin lowers serum cholesterol, low-density lipoprotein, and triglycerides, and it raises high-density lipoprotein. However, most patients experience cutaneous warmth and vasodilation (flush). Acetylsalicylic acid (ASA) can reduce this flush, presumably by decreasing prostaglandin D(2) (PGD(2)) release from macrophages. Here, we show that methylnicotinate induces significant PGD(2) release from human mast cells and serotonin from human platelets. Intradermal injection of methylnicotinate induces rat skin vasodilation and vascular permeability. Niacin increases plasma PGD(2) and serotonin in a rat model of flush. The phenothiazine prochlorperazine, the H(1), serotonin receptor antagonist cyproheptadine, and the specific serotonin receptor-2A antagonist ketanserin inhibit niacin-induced temperature increase by 90% (n = 5, p < 0.05), 90 and 50% (n = 3, p < 0.05), and 85% (n = 6, p = 0.0008), respectively, in this animal model. These results indicate that niacin-induced flush involves both PGD(2) and serotonin, suggesting that drugs other than ASA are required to effectively inhibit niacin-induced flush.     

Intravesical suplatast tosilate (IPD-1151T) inhibits experimental bladder inflammation

PURPOSE: Interstitial cystitis is a painful bladder disease characterized by urgency, frequency and variable inflammation but there is no curative therapy. Suplatast tosilate (IPD-1151T) is an immunoregulatory compound that decreases interstitial cystitis symptoms but to our knowledge its mechanism of action is unknown. We investigated the effect of intravesical IPD-1151T on mediator release from bladder explants in experimental cystitis. MATERIALS AND METHODS: A catheter was inserted into the bladder of female mice. After urine was emptied normal saline, carbachol (100 nM) or lipopolysaccharide (10 mg/ml) was introduced with or without 10-minute pretreatment with IPD-1151T. Urine was removed after 45 minutes for histamine and tumor necrosis factor-alpha assays. The bladder was removed after 4 hours, minced into 1 mm2 pieces and cultured with or without triggers overnight for mediator release. The effect of IPD-1151T was also tested on rat skin vascular permeability as well as on purified rat peritoneal mast cells and human cord blood derived mast cells. RESULTS: Carbachol significantly increased histamine release in urine (61.3% in 8 preparations, p<0.05) but not in explant medium. IPD-1151T inhibited this effect by 77%. Lipopolysaccharide induced a 350% urine histamine increase in 9 preparations (p<0.05) and a 300% tumor necrosis factor-alpha increase in explant medium. IPD-1151T inhibited the lipopolysaccharide induced medium tumor necrosis factor-alpha increase by 95% in 5 preparations (p<0.05). IPD-1151T did not inhibit rat skin vascular permeability or purified rat peritoneal mast cell activation by compound 48/80 or human cord blood derived mast cells by anti-IgE. CONCLUSIONS: IPD-1151T inhibits bladder release of histamine and tumor necrosis factor-alpha through a mechanism that does not appear to involve direct mast cell inhibition. These findings may justify a beneficial effect of IPD-1151T in interstitial cystitis.     

The isoflavone genistein inhibits proliferation and increases histamine content in human leukemic mast cells.

Mast cells are involved in allergic inflammation and some rare disorders such as systemic mastocytosis and mast cell leukemia. Certain naturally occurring flavonoids have been shown to inhibit mast cell activation and promote maturation of secretory granules. Here, we report that the isoflavone genistein inhibited the growth of human leukemic mast cells (HMC-1) by 68.8, 51.6, and 30.2% at 10(-4), 10(-5), and 10(-6) M, respectively, at day 3 (p < 0.001). Genistein at 10(-4) M increased the histamine content per 2 x 10(5) cells at day 3 from 5.9 +/- 1.2 micrograms/mL to 11.1 +/- 1.3 micrograms/mL (n = 6; p < 0.0001). These results indicate that genistein can inhibit proliferation and induce maturation of HMC-1 cells.