[Leukotriene D4 activates BV2 microglia in vitro]

OBJECTIVE

To investigate the effects of CysLT receptor agonist leukotriene D4(LTD4) and antagonists on activation of microglia BV2 cells.

METHODS

The expression of CysLT1 and CysLT2 protein was determined by Western blotting and immunostaining in microglia BV2 cells. BV2 cells were pretreated with or without CysLT1 receptor selective antagonist montelukast, CysLT2 receptor selective antagonist HAMI 3379, or CysLT1/CysLT2 receptor dual antagonist BAY u9773 for 30 min, then the cells were treated with LTD4 for 24 h. Cell viability was detected by MTT reduction assay. Phagocytosis and mRNA expression of IL-6 were determined by fluorescent bead tracking and RT-PCR, respectively.

RESULTS

In BV2 cells, LTD4 did not affect proliferation but significantly enhanced phagocytosis and increased IL-6 mRNA expression in a concentration-dependent manner. LTD4 at 100 nmol/L induced a 1.4-fold increase of phagocytic index and a 2-fold up-regulation of IL-6 mRNA expression (P<0.01). HAMI 3379 and BAY u9773 (100 nmol/L) further increased LTD4-induced phagocytosis; BAY u9773 and montelukast decreased LTD4-induced IL-6 mRNA expression, while HAMI 3379 had no effect on that.

CONCLUSION

LTD4 activates BV2 cells in vitro and enhances IL-6 mRNA expression mediated by CysLT1 receptor, LTD4 induces phagocytosis which might be negatively regulated by CysLT2 receptor in BV2 cells.

Agonist- and T(H)2 cytokine-induced up-regulation of cysteinyl leukotriene receptor messenger RNA in human monocytes

BACKGROUND

The cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic diseases, and their actions are mediated via specific receptors named CysLT1 receptor (CysLT1R) and CysLT2 receptor (CysLT2R). Little information is known about the role of T(H)2 cytokines in the regulation of both CysLT1R and CysLT2R expression.

OBJECTIVE

To investigate the possible modulation of both CysLT1R and CysLT2R messenger RNA (mRNA) expression, we have developed a real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay based on the TaqMan fluorescence method to quantify CysLT1R and CysLT2R mRNA in human monocytes.

METHODS

Human monocytes were stimulated with leukotriene D4 or interleukin (IL) 4 or IL-13, and the levels of CysLT1R and CysLT2R mRNA were measured by the quantitative RT-PCR.

RESULTS

CysLT1R and CysLT2R mRNA was increased after stimulation with leukotriene D4. CysLT1R mRNA was augmented 150-fold after treatment with IL-4; however, no significant increase was observed in CysLT2R mRNA level. IL-13 could induce a biphasic augmentation of CysLT1R mRNA level. In contrast to IL-4, IL-13 enhanced CysLT2R mRNA level, with a maximal effect at 2 hours of incubation.

CONCLUSIONS

CysLT1R and CysLT2R expression can be regulated by CysLT itself and T(H)2 cytokines at the transcriptional level.

Cysteinyl leukotrienes synergize with growth factors to induce proliferation of human bronchial fibroblasts

BACKGROUND

Cysteinyl leukotrienes (cys-LTs) are potent asthma-related mediators that function through their G protein-coupled receptors, cys-LT receptor type 1 (CysLT1R) and cys-LT receptor type 2 (CysLT2R).

OBJECTIVE

Because many G protein-coupled receptors transactivate the epidermal growth factor receptor (EGFR) through metalloprotease-mediated ligand shedding, we investigated the effects of cys-LTs on signal transduction and proliferation of bronchial fibroblasts.

METHODS

Human bronchial fibroblasts were grown from biopsy specimens of healthy subjects. Mitogenesis was assessed on the basis of tritiated methylthymidine incorporation.

RESULTS

Leukotriene (LT) D(4) alone did not increase mitogenesis but dose-dependently increased thymidine incorporation and cell proliferation in the presence of epidermal growth factor (EGF). The enhancement was not prevented by CysLT1R antagonists (MK-571 and montelukast) or by a dual antagonist (BAY u9773), which is consistent with the lack of detectable mRNA for CysLT1R and CysLT2R in bronchial fibroblasts. LTD(4) did not cause EGFR transphosphorylation nor was the synergism blocked by the metalloprotease inhibitor GM6001. The EGFR-selective kinase inhibitor AG1478 suppressed the synergy between LTD(4) and EGF but had no effect on synergistic interactions of LTD(4) with other receptor tyrosine kinase growth factors. The effect of LTD(4) involved a pertussis toxin-sensitive and protein kinase C-mediated intracellular pathway, leading to sustained growth factor-dependent phosphorylation of extracellular signal-regulated kinase 1/2 and protein kinase B (PKB/Akt).

CONCLUSION

Cys-LTs do not transactivate EGFR but have a broader capability to synergize with receptor tyrosine kinase pathways.

CLINICAL IMPLICATIONS

This study implies a critical role of cys-LTs in airway fibrosis in asthma and other chronic airway diseases, which might not be blocked by therapy with current LT receptor antagonists.

Distinct roles of CysLT1 and CysLT2 receptors in oxygen glucose deprivation-induced PC12 cell death

Cysteinyl leukotrienes are involved in ischemic brain injury, and their receptors (CysLT(1) and CysLT(2)) have been cloned. To clarify which subtype mediates the ischemic neuronal injury, we performed permanent transfection to increase CysLT(1) and CysLT(2) receptor expressions in PC12 cells. Oxygen glucose deprivation (OGD)-induced cell death was detected by Hoechst 33258 and propidium iodide fluorescent staining as well as by flow cytometry. OGD induced late phase apoptosis mainly and necrosis minimally. Over-expression of CysLT(1) receptor decreased and over-expression of CysLT(2) receptor increased OGD-induced cell death. An agonist LTD(4) (10(-7)M) also induced apoptosis, especially in CysLT(2) receptor over-expressing cells. A selective CysLT(1) receptor antagonist montelukast did not affect OGD-induced apoptosis; while non-selective CysLT receptor antagonist Bay u9773 inhibited OGD-induced apoptosis, especially in CysLT(2) receptor over-expressing cells. Thus, CysLT(1) and CysLT(2) receptors play distinct roles in OGD-induced PC12 cell death; CysLT(1) attenuates while CysLT(2) facilitates the cell death.

Membrane IgE Binds and Activates FcεRI in an Antigen-Independent Manner

Interaction of secretory IgE with FcepsilonRI is the prerequisite for allergen-driven cellular responses, fundamental events in immediate and chronic allergic manifestations. Previous studies reported the binding of soluble FcepsilonRIalpha to membrane IgE exposed on B cells. In this study, the functional interaction between human membrane IgE and human FcepsilonRI is presented. Four different IgE versions were expressed in mouse B cell lines, namely: a truncation at the Cepsilon2-Cepsilon3 junction of membrane IgE isoform long, membrane IgE isoform long (without Igalpha/Igbeta BCR accessory proteins), and both epsilonBCRs (containing membrane IgE isoforms short and long). All membrane IgE versions activated a rat basophilic leukemia cell line transfected with human FcepsilonRI, as detected by measuring the release of both preformed and newly synthesized mediators. The interaction led also to Ca(2+) responses in the basophil cell line, while membrane IgE-FcepsilonRI complexes were detected by immunoprecipitation. FcepsilonRI activation by membrane IgE occurs in an Ag-independent manner. Noteworthily, human peripheral blood basophils and monocytes also were activated upon contact with cells bearing membrane IgE. In humans, the presence of FcepsilonRI in several cellular entities suggests a possible membrane IgE-FcepsilonRI-driven cell-cell dialogue, with likely implications for IgE homeostasis in physiology and pathology.

A cysteinyl leukotriene 2 receptor variant is associated with atopy in the population of Tristan da Cunha

The clinical heterogeneity of asthma suggests that the contribution of genetic variability in candidate gene loci to well-defined phenotypes, such as atopy, may be examined to identify appropriate genetic risk factors for asthma. The gene encoding the cysteinyl leukotriene 2 (CysLT2) receptor has been implicated in atopy since it is localized to a region of chromosome 13q14 that has been linked to atopy in several populations and the cysteinyl leukotrienes are known to activate eosinophils and mast cells in atopy. Accordingly, we analysed the contribution of CysLT2 receptor gene variation to atopy in the inhabitants of Tristan da Cunha, a population characterized by both a founder effect and a 47% prevalence of atopy. Single-stranded conformational polymorphism analysis revealed four variants. Among these, the M201V [corrected] variant was activated with four-fold less potency by leukotriene D4 (LTD4) in a calcium flux assay. The CysLT2 receptor partial agonist, BAY u9773, also showed four-fold lower potency on the M201V [corrected] variant. The M201V [corrected] mutation is located within the extracellular region of the fifth transmembrane spanning domain of CysLT2 receptor, a position that may alter ligand binding and effector signalling. The novel M201V [corrected] CysLT2 receptor variant was associated with atopy (21%) on Tristan da Cunha compared with those who were non-atopic (7%) (Fisher's exact test, P=0.0016) in a manner that was independent of asthma (two-way ANOVA, P=0.0015). This represents the first association of a coding mutation in the CysLT2 receptor gene, located on chromosome 13q14, with the atopic phenotype found in the Tristan da Cunha population.

Cysteinyl-leukotrienes receptor activation in brain inflammatory reactions and cerebral edema formation: a role for transcellular biosynthesis of cysteinyl-leukotrienes

We studied the effect of intravascular activation of human neutrophils on the synthesis of cysteinyl leukotrienes (cysLT) and the formation of cerebral edema in guinea-pig brains. Challenge with the chemotactic formylated tripeptide fMLP (0.1 microM) of neutrophil-perfused brain in vitro resulted in blood-brain barrier disruption associated with a significant increase of cysLT. Both events were completely prevented by neutrophil pretreatment with a specific 5-lipoxygenase (5-LO) inhibitor. Perfusion with the 5-LO metabolite leukotriene B4 (10 nM), together with neutrophils treated with the 5-LO inhibitor, did not restore the alteration in permeability observed upon perfusion with untreated and activated neutrophils. The dual cysLT1-cysLT2 receptor antagonist BAYu9773 was more potent and more effective than a selective cysLT1 antagonist in preventing the brain permeability alteration induced by neutrophil activation. RT-PCR showed significant expression of cysLT2 receptor mRNA in human umbilical vein endothelial cells. Intravital microscopy in mice showed that inhibition of leukotriene synthesis significantly reduced firm adhesion of neutrophils to cerebral vessels without affecting rolling. These data support the hypothesis that neutrophil and endothelial cells cooperate toward the local synthesis of cysLT within the brain vasculature and, acting via the cysLT2 receptor on endothelial cells, may represent a contributing pathogenic mechanism in the development of cerebral inflammation and edema.

Carboxypeptidase A-catalyzed direct conversion of leukotriene C4 to leukotriene F4

Leukotrienes (LTs) are 5-lipoxygenase (5-LO)-derived arachidonic metabolites that constitute a potent set of lipid mediators produced by inflammatory cells. Leukotriene A(4), a labile allylic epoxide formed from arachidonic acid by dual 5-LO activity, is the precursor for LTB(4) and LTC(4) synthesis. LTC(4) is further transformed enzymatically by the sequential action of gamma-glutamyltranspeptidase and dipeptidase to LTD(4) and LTE(4), respectively. In this report, we present evidence that bovine pancreatic carboxypeptidase A (CPA), which shares significant sequence homology with CPA in mast cell granules, catalyzes the conversion of LTC(4) to LTF(4) via the hydrolysis of an amide bond. The identity of CPA-catalyzed LTC(4) hydrolysis product as LTF(4) was confirmed by several analytical criteria, including enzymatic conversion to conjugated tetraene by soybean LO, conversion to LTE(4) by gamma-glutamyltranspeptidase, cochromatography with the standard LTF(4) and positive-ion fast-atom bombardment mass spectral analysis. Thus, it appears that the physiological significance of this single-step transformation may point toward a major cellular homeostatic mechanism of metabolizing LTC(4), a potent bronco- and vasoconstrictor, to a less potent form of cysteinyl LTs.

Actions of cysteinyl leukotrienes in the enteric nervous system of guinea-pig stomach and small intestine

Conventional intracellular microelectrodes, neuronal tracer injection techniques and immunohistochemistry were used to study the actions of cysteinyl leukotrienes (CysLTs) on electrical and synaptic behavior of enteric neurons in guinea-pig stomach and small intestine. Bath application of leukotriene C(4), leukotriene D(4) or leukotriene E(4) evoked a slowly activating depolarizing response in most of the myenteric and submucous plexus neurons in the small intestine while no effect was observed in gastric neurons. The depolarization evoked by cysteinyl leukotrienes in intestinal neurons was associated with increased input resistance and enhanced excitability. Suppression of hyperpolarizing after-potentials occurred in AH type neurons. The depolarizing action of cysteinyl leukotrienes was resistant to tetrodotoxin and cyclooxygenase inhibitors. Neither the CysLT(1) receptor antagonists (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), 1-[2-hydroxy-3-propyl-4-[4-(1H-tetrazol-5-yl)butoxy]phenyl]-ethanone (LY 171883) and alpha-pentyl-3-(2-quinolinylmethoxy)-benzenemethanol (REV 5901), nor the dual CysLT(1)/CysLT(2) receptor antagonist 6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid (BAY u9773) significantly altered the depolarizing action of the cysteinyl leukotrienes. Neurotransmission was unaffected by the cysteinyl leukotrienes. The results suggested involvement of cysteinyl leukotrienes in enteric immuno-neural communication through excitatory actions on enteric neurons. The receptor mediating these effects was distinct from currently recognized cysteinyl leukotriene receptor subtypes (CysLT(1) and CysLT(2) receptors) and may represent a new receptor subtype.

Increasing sample throughput in pharmacological studies by using dual-column liquid chromatography with tandem mass spectrometry

A robust novel technology of parallel chromatography combined with tandem mass spectrometry was successfully applied to a biological matrix extract for analyte detection. The presented study shows how only by using an additional isocratic pump, a second column and a 10-port valve the throughput is twice of that of a conventional single column system with the same sensitivity. Analytes and matrix were separated and eluting peaks of the first column were detected while the second column was equilibrated. The system was tested and used for the determination of several drugs, metabolites and endogenous compounds (i.e., propiverine, talinolol, scopolamine and leukotrienes).

5-lipoxygenase inhibition reduces intrahepatic vascular resistance of cirrhotic rat livers: a possible role of cysteinyl-leukotrienes

BACKGROUND & AIMS

Cysteinyl-leukotrienes (Cys-LTs) increase intrahepatic vascular resistance in normal rat livers. CCl4 cirrhotic rat livers have increased Cys-LT production and 5-lipoxygenase messenger RNA (mRNA) expression. The aim of this study was to investigate the role of 5-lipoxygenase-derived eicosanoids regulating intrahepatic vascular tone in control and CCl4-induced cirrhotic rat livers.

METHODS

In different groups of portally perfused control and cirrhotic rat livers, the following were analyzed: a portal perfusion pressure (PP) dose-response curve to LTD4; the effects on PP caused by either vehicle, the selective 5-lipoxygenase inhibitor AA-861, the selective Cys-LT1 receptor antagonist MK-571, or the dual Cys-LT1 and Cys-LT2 receptor antagonist BAY u9773; and immunohistochemistry for 5-lipoxygenase in liver sections of cirrhotic and control livers.

RESULTS

Cirrhotic livers have a hyperesponse to LTD4. In control livers, AA-861 and MK-571 produced a moderate and similar reduction in PP. In cirrhotic livers, 5-lipoxygenase inhibition produced a marked and significantly greater reduction in PP than in controls. However, no effect on PP was observed after MK-571 or BAY u9773. 5-Lipoxygenase-positive cells were markedly increased in cirrhotic livers.

CONCLUSIONS

Our results suggest that 5-lipoxygenase-derived eicosanoids may contribute to the increased intrahepatic vascular resistance of cirrhotic rat livers and therefore the pathogenesis of portal hypertension.

Cysteinyl leukotrienes modulate angiotensin II constrictor effects on aortas from streptozotocin-induced diabetic rats

Angiotensin II (Ang II) is a vasopressor peptide involved in the pathogenesis of cardiovascular diseases associated with diabetes mellitus. We have previously reported that the 5-lipoxygenase-derived products, particularly the cysteinyl leukotrienes (CysLTs), are involved in Ang II-induced contraction. In this study, we demonstrated that CysLTs contribute to the contraction elicited by Ang II in isolated aortas from streptozotocin-induced diabetic (SS) rats but not from insulin-treated diabetic rats, fructose-fed rats, or control rats. In an organ bath, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 micromol/L) reduced by 37.6+/-8.2% and 30.1+/-10.9% the Ang II-induced contractions in intact and endothelium-denuded aortic rings, respectively, from SS rats. In contrast, the CysLT(1) receptor antagonist (MK571, 1 micromol/L) or the dual CysLT(1)/CysLT(2) receptor antagonist (BAY-u9773, 0.1 micromol/L) did not affect Ang II-induced contraction. In addition, Ang II induced a 6.2+/-1.5-fold increase in CysLT release through the stimulation of the Ang II type 1 receptor. Furthermore, the urinary excretion of leukotriene E(4) was increased in SS rats (leukotriene E(4), 13.7+/-2.9 ng/24 h [SS rats, n=10] versus 1.5+/-0.5 ng/24 h [control rats, n=6]; P<0.0004). These data suggest the activation of the 5-lipoxygenase pathway in SS rats and the involvement of 5-lipoxygenase-derived products, particularly the CysLTs, in Ang II-induced contraction in aortas from SS rats through stimulation of CysLT receptors different from the well-characterized CysLT(1) or CysLT(2) receptor.

Transformation of leukotriene A4 methyl ester to leukotriene C4 monomethyl ester by cytosolic rat glutathione transferases

Six major basic cytosolic glutathione transferases from rat liver catalyzed the conversion of leukotriene A4 methyl ester to the corresponding leukotriene C4 monomethyl ester. Glutathione transferase 4-4, the most active among these enzymes, had a Vmax of 615 nmol X min-1 X mg protein-1 at 30 degrees C in the presence of 5 mM glutathione. It was followed in efficiency by transferase 3-4 which had a Vmax of 160 nmol X min-1 X mg-1 under the same conditions. Transferases 1-1, 1-2, 2-2 and 3-3 had at least 30 times lower Vmax values than transferase 4-4.

An alternative pathway for metabolism of leukotriene D(4): effects on contractions to cysteinyl-leukotrienes in the guinea-pig trachea

Contractions of guinea-pig tracheal preparations to cysteinyl-leukotrienes (LTC(4), LTD(4) and LTE(4)) were characterized in organ baths, and cysteinyl-leukotriene metabolism was studied using radiolabelled agonists and RP-HPLC separation. In the presence of S-hexyl GSH (100 microM) the metabolism of [(3)H]-LTC(4) into [(3)H]-LTD(4) was inhibited and the LTC(4)-induced contractions were resistant to CysLT(1) receptor antagonism but inhibited by the dual CysLT(1)/CysLT(2) receptor antagonist BAY u9773 (0.3 - 3 microM) with a pA(2)-value of 6.8+/-0.2. In the presence of L-cysteine (5 mM), the metabolism of [(3)H]-LTD(4) into [(3)H]-LTE(4) was inhibited and the LTD(4)-induced contractions were inhibited by the CysLT(1) receptor antagonist ICI 198,615 (1 - 10 nM) with a pA(2)-value of 9.3+/-0.2. However, at higher concentrations of ICI 198,615 (30 - 300 nM) a residual contraction to LTD(4) was unmasked, and this response was inhibited by BAY u9773 (1 - 3 microM). In the presence of the combination of S-hexyl GSH with L-cysteine, the LTD(4)-induced contractions displayed the characteristics of the LTC(4) contractile responses, i.e. resistant to CysLT(1) receptor antagonism, increased maximal contractions and slower time-course. This qualitative change of the LTD(4)-induced contraction was also observed in the presence of S-decyl GSH (100 microM), GSH (10 mM) and GSSG (10 mM). S-hexyl GSH, S-decyl GSH, GSH and GSSG all stimulated a formation of [(3)H]-LTC(4) from [(3)H]-LTD(4). In conclusion, GSH and GSH-related compounds changed the pharmacology of the LTD(4)-induced contractions by stimulating the conversion of LTD(4) into LTC(4). Moreover, the results indicate that, in addition to the metabolism of LTC(4) into LTD(4) and LTE(4), also the formation of LTC(4) from LTD(4) may regulate cysteinyl-leukotriene function.

Molecular cloning and characterization of a second human cysteinyl leukotriene receptor: discovery of a subtype selective agonist

The cysteinyl leukotrienes (CysLTs) are potent biological mediators in the pathophysiology of inflammatory diseases, in particular of airway obstruction in asthma. Pharmacological studies have suggested the existence of at least two types of CysLT receptors, designated CysLT(1) and CysLT(2). The CysLT(1) receptor has been cloned recently. Here we report the molecular cloning, expression, localization, and functional characterization of a human G protein-coupled receptor that has the expected characteristics of a CysLT(2) receptor. This new receptor is selectively activated by nanomolar concentrations of CysLTs with a rank order potency of LTC(4) = LTD(4) >> LTE(4). The leukotriene analog BAY u9773, reported to be a dual CysLT(1)/CysLT(2) antagonist, was found to be an antagonist at CysLT(1) sites but acted as a partial agonist at this new receptor. The structurally different CysLT(1) receptor-selective antagonists zafirlukast, montelukast, and MK-571 did not inhibit the agonist-mediated calcium mobilization of CysLT(2) receptors at physiological concentrations. Localization studies indicate highest expression of CysLT(2) receptors in adrenal glands, heart, and placenta; moderate levels in spleen, peripheral blood leukocytes, and lymph nodes; and low levels in the central nervous system and pituitary. The human CysLT(2) receptor gene is located on chromosome 13q14.12-21.1. The new receptor exhibits all characteristics of the thus far poorly defined CysLT(2) receptor. Moreover, we have identified BAY u9773 as a CysLT(2) selective agonist, which could prove to be of immediate use in understanding the functional roles of the CysLT(2) receptor.

Characterization of the human cysteinyl leukotriene 2 receptor

The contractile and inflammatory actions of the cysteinyl leukotrienes (CysLTs), LTC(4), LTD(4), and LTE(4), are thought to be mediated through at least two distinct but related CysLT G protein-coupled receptors. The human CysLT(1) receptor has been recently cloned and characterized. We describe here the cloning and characterization of the second cysteinyl leukotriene receptor, CysLT(2), a 346-amino acid protein with 38% amino acid identity to the CysLT(1) receptor. The recombinant human CysLT(2) receptor was expressed in Xenopus oocytes and HEK293T cells and shown to couple to elevation of intracellular calcium when activated by LTC(4), LTD(4), or LTE(4). Analyses of radiolabeled LTD(4) binding to the recombinant CysLT(2) receptor demonstrated high affinity binding and a rank order of potency for competition of LTC(4) = LTD(4) LTE(4). In contrast to the dual CysLT(1)/CysLT(2) antagonist, BAY u9773, the CysLT(1) receptor-selective antagonists MK-571, montelukast (Singulair(TM)), zafirlukast (Accolate(TM)), and pranlukast (Onon(TM)) exhibited low potency in competition for LTD(4) binding and as antagonists of CysLT(2) receptor signaling. CysLT(2) receptor mRNA was detected in lung macrophages and airway smooth muscle, cardiac Purkinje cells, adrenal medulla cells, peripheral blood leukocytes, and brain, and the receptor gene was mapped to chromosome 13q14, a region linked to atopic asthma.

Prostacyclin modulation of contractions of the human pulmonary artery by cysteinyl-leukotrienes

The contractile response to cysteinyl-leukotrienes was studied in isolated human pulmonary arterial rings. Concentration-response curves for leukotriene C(4) were significantly potentiated by the cyclooxygenase inhibitor indomethacin (1.7 microM) and after endothelial denudation. Measurements of 6-keto prostaglandin F(1alpha) showed that cysteinyl-leukotrienes stimulated the release of prostacyclin. A single concentration (1 microM) of either leukotriene C(4) or leukotriene D(4) resulted in both contraction and relaxation. Indomethacin abolished the relaxant phase and enhanced the amplitude of the contraction, supporting that cysteinyl-leukotriene-induced contractions of the human pulmonary artery may be functionally antagonised by the release of prostacyclin. The contractions induced by leukotriene C(4) were resistant to the two cysteinyl-leukotriene receptor antagonists MK 571 ((3-(-2(7-chloro-2-quinolinyl)ethenyl)phenyl)((3-(dimethylamino-3-oxo propyl)thio)methyl)thio propanoic acid, 1 microM) and BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E), 11(Z)14(Z)-eicosatetrenoic acid, 3 microM), both in the absence and presence of indomethacin. These findings suggest a functional cysteinyl-leukotriene receptor in the human pulmonary artery with antagonist properties not previously described in human tissue.

Antagonist resistant contractions of the porcine pulmonary artery by cysteinyl-leukotrienes

The contractile response to cysteinyl-leukotrienes was studied in isolated porcine pulmonary arterial rings. In endothelium-denuded preparations, the concentration-response curves for leukotriene C(4) and leukotriene D(4) were identical, whereas leukotriene E(4) did not contract these tissues. The response to leukotriene C(4) was not blocked by either CysLT(1)/CysLT(2) receptor antagonism or by pre-treatment with leukotriene E(4). In preparations with an intact endothelium, leukotriene C(4) was somewhat more potent than leukotriene D(4) and the concentration-response curves were only slightly depressed in the presence of either ICI 204,219 (4-(5-cyclopentyloxycarbonylamino-1-methylindol-3-ylmethy l)-3-methoxy -N-o-tolylsulfonylbenzamide, 1 microM) or BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E), 11(Z)14(Z)-eicosatetrenoic acid, 3 microM). Indomethacin (1.7 microM) significantly reduced the response to leukotriene C(4) whereas the response to leukotriene D(4) was unchanged. These findings suggest that a CysLT receptor subtype resistant to current antagonists mediated the major part of the contractions to leukotriene C(4) and leukotriene D(4) in intact preparations, and was the sole receptor associated with contractions of endothelium-denuded preparations.

Agonist and antagonist activities of the leukotriene analogue BAY u9773 in guinea pig lung parenchyma

BAY u9773(6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11( Z),14(Z)-eicosatetraenoic acid) is a leukotriene E4 analogue used to define 'atypical' receptors for cysteinyl-leukotrienes. The aims of this study were first to characterise the intrinsic properties of BAY u9773 in guinea-pig lung parenchyma in vitro and second to study the influence of BAY u9773 on the concentration-response relation for leukotriene D4 in the same preparation. BAY u9773 in itself caused a concentration-dependent contraction, which was not inhibited by the cyclooxygenase inhibitor indomethacin nor by the 5-lipoxygenase inhibitor zileuton (N-(1-benzo-(12)-thien-2-ylethyl)-N-hydroxyurea). The CysLT1 receptor antagonist ICI 198,615 [(1-((2-methoxy-4-(((phenylsulfonyl)amino) carbonyl)phenyl)methyl)-1H-indazol-6-yl)carbamic acid cyclopentyl ester] alone blocked the contractile response to BAY u9773 1 microM, whereas a combination of the TP receptor antagonist BAY u3405 ((3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz olepropanoic acid) and ICI 198,615 was required to block the contraction induced by BAY u9773 10 microM. Together the findings suggest that BAY u9773 acted as a CysLT1 receptor agonist and in the higher concentration also as a TP receptor agonist. The CysLT1 receptor antagonist ICI 198,615 partly inhibited the contractile response to leukotriene D4. Pretreatment with BAY u9773 or leukotriene D4, caused concentration-dependent rightward displacement of the concentration-response curve for leukotriene D4. The inhibition by BAY u9773 was partial, and not greater than that produced by ICI 198,615. Combination of BAY u9773 and ICI 198,615 did not produce additive inhibition, suggesting that the major part of the leukotriene D4 induced contraction in guinea pig lung parenchyma is mediated by a CysLT receptor with properties distinct from those of previously described CysLT1 and CysLT2 receptors.

Functional characterization of receptors for cysteinyl-leukotrienes in sheep trachealis muscle

Cysteinyl-leukotrienes (CysLTs: LTC4, LTD4 and LTE4) are inflammatory mediators which significantly contribute to the airway obstruction in asthma. At least two distinct receptor subtypes exist for cysteinyl-leukotrienes, the CysLT1- and CysLT2-receptor. The purpose of this study was to test whether sheep trachealis muscle is a useful preparation for further characterization of CysLT2-receptors, previously implicated in contraction of human pulmonary veins. Leukotriene C4 and leukotriene D4 evoked contractile responses, leukotriene C4 being significantly more potent than leukotriene D4, whereas leukotriene E4 failed to elicit contractions. The response to leukotriene C4 exhibited tachyphylaxis upon repeated administration. There were no significant effects of epithelial denudation, NO-synthesis inhibition (L-NAME) or cyclooxygenase inhibition (indomethacin) on the responses to cysteinyl-leukotrienes or cholinergic agonists. Neither was responsiveness to different agonists changed by overnight storage. The responses to leukotriene C4 and leukotriene D4 were markedly potentiated when their metabolism was inhibited by S-hexyl glutathione and L-cysteine. The selective CysLT1-antagonist ICI 198,615 had no significant effect on these responses. However, the combined CysLT1- and CysLT2-antagonist BAY u9773 competitively antagonized leukotriene C4 and leukotriene D4 (pA2 values of 7.0 and 6.8 against leukotriene C4 and leukotriene D4, respectively). The findings support that leukotriene C4 and leukotriene D4 act predominantly on CysLT2-receptors in sheep trachea.

The cysteinyl-leukotriene receptor antagonist BAY u9773 is a competitive antagonist of leukotriene C4 in the guinea-pig ileum

Two main classes of receptors exist for leukotrienes C4, D4 and E4, collectively named cysteinyl-leukotrienes (CysLTs). The CysLT1 receptor is blocked by currently available leukotriene antagonists, and the CysLT2 receptor is defined by the absence of selective antagonists. The contractile response to leukotriene C4 in guinea-pig ileum longitudinal muscle is resistant to CysLT1 receptor antagonists. However, the leukotriene E4 analogue BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z), 14(Z)-eicosatetraenoic acid) has recently been reported to inhibit CysLT2 responses. Therefore BAY u9773 was evaluated for antagonism of the effect of leukotriene C4 in the guinea-pig ileum longitudinal muscle. We found that BAY u9773 (0.3-10 microM) did not contract the preparation, but produced a concentration-dependent rightward shift in the concentration-response relation for leukotriene C4. Schild plot analysis yielded a slope which was not significantly different from unity and a pA2 value of 6.1. The inhibition of leukotriene C4 by BAY u9773 was not altered by antagonism of CysLT1 receptors by ICI 198,615 {[1-[[2-methoxy-4-[[(phenylsulfonyl)amino]carbonyl]-phenyl] methyl]-1H-indazol-6-yl]carbamic acid cyclopentyl ester}(100 nM). The CysLT1 receptor agonist, leukotriene E4 (1 microM), contracted the preparation but did not inhibit the contraction induced by leukotriene C4. Taken together, the antagonism exerted by BAY u9773 appeared unrelated to actions on CysLT1 receptors. In conclusion, BAY u9773 was a useful selective competitive antagonist of leukotriene C4, and the findings support the classification of the receptors for leukotriene C4 in the guinea-pig ileum as CysLT2.

Alteration of n-3 fatty acid composition in lung tissue after short-term infusion of fish oil emulsion attenuates inflammatory vascular reaction

OBJECTIVES

To investigate whether modulation of the fatty acid profile can be achieved by the short-term infusion of a fish oil emulsion which may attenuate the pulmonary response to inflammatory stimulation. Changes of fatty acid pattern in-lung tissue and perfusate were analyzed and correlated with physiologic data after a 3-hr infusion of fish oil in comparison with a soybean oil preparation.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Forty standard breed rabbits of either gender.

INTERVENTIONS

Isolated lungs from anesthetized rabbits were ventilated and recirculation-perfused (200 mL/min) with 200 mL of cell-free buffer solution to which either 2 mL of saline (control, n = 6), 2 mL of a 10% soybean oil preparation (n = 6), or 2 mL of a 10% fish oil emulsion (n = 6) were added. Samples of perfusate and lung tissue were collected for analysis of fatty acid composition. Tissue and perfusate fatty acid composition were analyzed by capillary gas chromatography. To study metabolic alterations in states of inflammatory stimulation, lungs of each group were stimulated with small doses of the calcium ionophore, A23187 (10(-8) M), during the 180-min lipid perfusion period and again after washing out the lipids by exchanging the perfusion fluid. Pulmonary arterial pressure and lung weight gain were monitored, and eicosanoids were analyzed in the perfusate.

MEASUREMENTS AND MAIN RESULTS

Free eicosapentaenoic acids increased several-fold in lung tissue and perfusate during a 3-hr infusion with fish oil. The intravenously administered n-3 fatty acids were rapidly hydrolyzed, as indicated by the appearance of substantial quantities of eicosapentaenoic acid in the perfusate free fatty acid fraction. This increase of perfusion levels of eicosapentaenoic acid was paralleled by an attenuated pressure increase and edema formation due to calcium ionophore challenge and an altered eicosanoid spectrum determined in the perfusate compared with soybean oil-treated lungs.

CONCLUSION

Short-term n-3 lipid application (fish oil emulsion) exerts anti-inflammatory effects on lung vasculature, which may be due to the metabolism of eicosapentaenoic acid resulting in the generation of less potent inflammatory eicosanoids.

Leukotriene C4-stimulated contractions in bullfrog lung are affected by cold acclimation and calcium antagonists

Leukotriene C4 (LTC4) contracts isolated bullfrog lung. This study examined effects of cold-acclimation and the involvement of extracellular and intracellular Ca++ on the contractile response to LTC4. The response to LTC4 was greater in lungs from warm-acclimated (22 degrees C) frogs compared with cold-acclimated (5 degrees C) frogs at incubation temperatures of both 22 degrees C and 5 degrees C. LTC4, LTC5, and N-methyl LTC4 were equally effective in stimulating lung contraction at concentrations from 1-100 nM. Nicardipine (3 microM) partially antagonized the response to LTC4, but verapamil, nifedipine, or nitrendipine at the same concentration was ineffective. Ethylene glycol tetraacetic acid (EGTA, 0.3 mM) prevented the response to 30 nM LTC4, but the response was restored when the lung was retested in EGTA-free medium containing Ca++, suggesting that extracellular Ca++ was involved in the response. Caffeine (10 mM) or thapsigargin (1 mM) inhibited the responses to LTC4, suggesting a role for intracellular Ca++ in the contraction.

BAY u9773, a novel antagonist of cysteinyl-leukotrienes with activity against two receptor subtypes

The effects of BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E), 11(Z),14(Z)-eicosatetraenoic acid), a cysteinyl-leukotriene analogue, were investigated on a variety of smooth muscle preparations in order to determine its profile as a cysteinyl-leukotriene receptor antagonist. The tissues were contracted with leukotriene C4 or leukotriene D4 and their receptor characteristics defined as either 'typical' or 'atypical' according to the activity or inactivity, respectively, of the selective antagonists ICI 198615, MK 571 and SKF 104353. BAY u9773 antagonised 'typical' cysteinyl-leukotriene receptors with pA2 (or pKB) values in the range 6.8-7.4 and also antagonised 'atypical' receptors with pA2 values in the range 6.8-7.7. However, BAY u9773 had no effect at 10(-6) M against a selection of non-leukotriene stimuli in the same preparations. BAY u9773 competitively displaced [3H]leukotriene D4 binding to guinea-pig lung homogenate, with a pKi of 7.0 +/- 0.1. In the guinea-pig lung strip, BAY u9773 was found to be inactive at 10(-6)M against leukotriene C4- and leukotriene D4-induced contractions, which may suggest the existence of a third type of cysteinyl-leukotriene receptor. These data demonstrate that BAY u9773 is a selective cysteinyl-leukotriene receptor antagonist with comparable activity at both 'typical' and 'atypical' receptors and as such represents a valuable tool for the study of cysteinyl-leukotriene receptors.