[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.

BQ-153, a novel endothelin (ET)A antagonist, attenuates the renal vascular effects of endothelin-1

Endothelin (ET)-l, leukotriene D4 and the thromboxane analogue, U-44069, were all shown to produce dose-dependent reductions in renal blood flow after direct injection into the renal artery of anaesthetized pigs. The effects of ET-1 differed from the other two mediators in that ET-1 caused a transient vasodilator followed by a prolonged vasoconstrictor response. The pressor response was not mediated by the secondary release of either leukotriene D4 or thromboxane A2 as evidenced by the lack of effect of appropriate receptor antagonist MK571 (3-{-2(7-chloro-2 quinolinyl) ethenyl}phenyl{3-(dimethylamino-3-oxopropyl)thio}methyl thio propionic acid) and L-670,596 respectively. This response, however, could be inhibited in a dose-dependent fashion by the selective ETA antagonist, BQ-153 (cyclo-d-sulphalanine-l-Pro-d-Val-l-Leu-d-Trp-). Following blockade by BQ-153 the vasodilator response was unaffected and a residual pressor response remained, suggesting that either or both of these effects were mediated either through an ETB or a novel, as yet undefined, endothelin receptor.

Doing What I Like

I have spent my entire professional life at Harvard Medical School, beginning as a medical student. I have enjoyed each day of a diverse career in four medical subspecialties while following the same triad of preclinical areas of investigation—cysteinyl leukotrienes, mast cells, and complement—with occasional translational opportunities. I did not envision a career with a predominant preclinical component. Such a path simply evolved because I chose instinctively at multiple junctures to follow what proved to be propitious opportunities. My commentary notes some of the highlights for each area of interest and the mentors, collaborators, and trainees whose counsel has been immensely important at particular intervals or over an extended period.

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.

[Alternation of ion transport of airway epithelium by eicosanoids]

BACKGROUND

Airway surface liquid is thought to be regulated by the ion transport processes across the airway epithelium in a vectorial manner. Short circuit current (Isc) measured by Ussing chamber is an indication of electric permeability because of mutually related transportation of amount of ion between apical and basolateral membrane.

METHODS

Guinea pig trachea was mounted on Ussing chamber and short-circuited current was determined continuously. After basolateral application of eicosanoids such as PGD2 and LTC4/LTD4/LTE4, Ramatroban, CRTH2 receptor antagonist and Pranlucast, LT receptor antagonist was added from basolateral side. A typical Cl-channel blocker, NPPB, was added from apical side.

RESULTS

Isc were increased after basolateral application of eicosanoids. These effects were partly inhibited by each antagonist. Cl- channel blocker suppressed effects of each eicosanoids.

CONCLUSION

Eicosanoids alter the ion transport mechanism via chloride channels on the airway epithelium that can be blocked by those antagonists.

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.

Discovery of New Orally Active Phosphodiesterase (PDE4) Inhibitors

A series of 4-anilinopyrazolopyridine derivatives were synthesized and biologically evaluated as inhibitors of phosphodiesterase (PDE4). Chemical modification of 3, a structurally new chemical lead that was found in our in-house library, was focused on 1- and 3-substituents. Full details of the discovery of a new orally active chemical lead 5 are presented. Structure-activity relationship data, pharmacological evaluation, and the subtype selectivity study are also presented.

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.

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.

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.

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.

Lipoxygenase products regulate proliferation of granulocyte-macrophage progenitors

We studied the role of lipoxygenase products on the proliferation and recovery of granulocyte-macrophage progenitors (CFU-GM) in liquid cultures of normal human blood mononuclear cells containing physiologic or slightly higher than physiologic concentrations of hydrocortisone (HC). Lipoxygenase blockade by addition of nordihydroguaiaretic acid (NDGA) resulted in enhanced recovery of CFU-GM (mean increase of 230%). The number of CFU-GM recovered from 14-day liquid cultures containing 1.0 microM HC plus 10 microM NDGA was a mean of six times higher than the number present in the inoculum. Effects of addition of selected 5-lipoxygenase products into the culture containing a lipoxygenase blocker on the CFU-GM recovery and proliferative activity were dose- and metabolite-specific. Leukotriene (LT) B4 and 5-hydroxy-eicosatetraenoic acid (5-HETE) decreased recovery of CFU-GM while LTC4 and LTD4 had biphasic effects--lower doses decreased while higher doses had no effect on CFU-GM recovery. Lipoxygenase blockade decreased the percent of CFU-GM in DNA synthesis phase. Readdition of LTB4 did not reverse this effect while LTD4 had a biphasic effect--low concentrations increased the percent of CFU-GM in DNA synthesis phase to levels equivalent to CFU-GM in cultures without NDGA while higher concentrations had no effect. In semisolid CFU-GM assays, lipoxygenase blockade with NDGA completely prevented CFU-GM colony formation, suggesting that NDGA inhibits proliferation and/or differentiation of CFU-GM in semisolid culture assays. The results of our studies suggest that 5-lipoxygenase metabolites are physiologically important in regulating the proliferation of CFU-GM and, thus, granulopoiesis.

Effect of leukotriene D4 and platelet-activating factor on human alveolar macrophage eicosanoid and PAF synthesis

Leukotrienes (LT) and platelet-activating factor (PAF) can increase nonspecific airway reactivity in normal subjects, and they have been proposed as putative mediators of asthma. Alveolar macrophages (AM), which have receptors for and synthesize leukotrienes and PAF, also may play a role in the pathogenesis of asthma. The present study was designed to determine the effects LTD4 and PAF have on bronchoalveolar lavage (BAL) fluid and cells, including AM eicosanoid and PAF synthesis, and to relate them to changes in nonspecific airway reactivity. Airway reactivity to methacholine was measured in healthy, male volunteers at least 2 days before and 6 h, 1, 3, and 7 days after inhaling either LTD4 or PAF. At least 3 wk later subjects inhaled in random order either methacholine or the mediator to which they were previously exposed, and BAL was performed the next day. This sequence was repeated with the other chemical 3 wk or more later. LTD4 inhalation increased airway reactivity and stimulated AM thromboxane synthesis while it reduced stimulated AM LTB4 synthesis. LTD4 did not affect the number of percentage of BAL cells or the BAL fluid protein and histamine concentrations. PAF inhalation increased airway reactivity and the proportion of neutrophils and eosinophils recovered by BAL, but it did not alter AM eicosanoid and PAF synthesis or the BAL fluid protein and histamine concentrations. A relationship was identified between the PAF-induced increase in airway reactivity and the percentage of BAL neutrophils, but no correlation was found between LTD4- or PAF-induced changes in airway reactivity and stimulated AM eicosanoid or PAF synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of distinct receptors for the peptidyl leukotrienes LTC4 and LTD4/LTE4 coupled to the same signaling pathway in isolated gastric muscle cells

Receptors for the peptidyl leukotrienes, (LT)C4, LTD4 and LTE4, and the signaling pathways to which they are coupled were characterized in isolated guinea pig gastric muscle cells. The three LTs were equipotent contractile agonists (EC50 values = 0.10-0.12 nM), but they elicited their responses by interacting with distinct receptors. The contractile responses to LTD4 and LTE4, but not LTC4, were inhibited by the LTD4 antagonist, SKF 104353 [2-(S)-hydroxy-3-(R)-[(2-carboxyethyl)thiol]-3-[2-(8- phenyloctyl)phenyl]-propanoic acid]. Similar Ki estimates for SKF 104353 suggested interaction of LTD4 and LTE4 with a common receptor. Decisive evidence for distinct LTC4 and LTD4/LTE4 receptors was obtained by applying a receptor protection technique. Cells in which LTC4 was used as a receptor protective agent while other receptors were inactivated by N-ethylmaleimide retained their responses to LTC4 only. Cells in which LTD4, LTE4 or SKF 104353 were used as a receptor protective agent retained their responses to LTD4 and LTE4 only. Both LTC4 and LTD4/LTE4 receptors were coupled to Pl hydrolysis: all three LTs stimulated similar increases in inositol 1,4,5-trisphosphate (IP3) levels (3.9-4.3 pmol/10(6) cells), protein kinase C activity (85-94 pmol/mg/min) and cytosolic-free Ca++ ([Ca++]i) (278-306 nM). Contractile responses were abolished: 1) when Pl hydrolysis was inhibited by neomycin and 2) when Ca++ stores were depleted by pretreatment of muscle cells with caffeine in Ca(++)-free medium, but not when muscle cells were incubated in Ca(++)-free medium or with Ca++ channel blockers, suggesting that contraction and [Ca++]i were mediated by IP3-dependent Ca++ release.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotrienes C4 and D4 are potent endothelium-dependent relaxing agents in canine splanchnic venous capacitance vessels

In the present study, the vasomotor effects of the peptide leukotrienes (LTs) LTC4 and LTD4 on isolated canine venous capacitance vessels were evaluated. Both LTs evoked marked concentration-dependent relaxation of norepinephrine-contracted rings of mesenteric and splenic veins and inferior vena cava but had minimal activity in the femoral vein. Relaxation induced by either LT was abolished after physical removal of the vascular endothelium, whereas marked relaxation responses were evoked by glyceryl trinitrate in the same endothelium-denuded rings. The nitric oxide synthase antagonist NG-nitro-L-arginine methyl ester (L-NAME) completely abolished LT-induced mesenteric vein relaxation and unmasked a contractile effect of LTC4. Only partial attenuation of LT-induced relaxation of the inferior vena cava in the presence of L-NAME was observed. In the splenic vein, responses solely to LTC4 were very slightly reduced in the presence of L-NAME. Reduced hemoglobin (10(-6) and 10(-5) M) inhibited LTC4-evoked splenic vein relaxation and, in a concentration of 10(-5) M, inhibited LTD4-evoked relaxation of the splenic vein. On the other hand, methylene blue (10(-6) and 10(-5) M) attenuated splenic vein relaxation produced by both LTs but solely reduced LTC4-evoked inferior vena cava relaxation. Thus, the peptide LTs, the major components of the slow-reacting substance of anaphylaxis, exert a profound endothelium-dependent relaxant effect on venous capacitance vessels, which is only partially dependent on L-arginine and nitric oxide. A role for LT-evoked capacitance venodilation as a mechanism contributing to the reduced venous return and cardiac output associated with systemic anaphylaxis is postulated.

Sensitivity of tumoricidal function in macrophages from different anatomical sites of cancer patients to modulation of arachidonic acid metabolism

The sensitivity of cancer patient macrophages from different anatomical sites to arachidonic acid metabolism was investigated in tumor cell cytotoxicity assays. Alveolar macrophages and peripheral blood monocytes from 13 non-small cell lung cancer patients, peritoneal macrophages and peripheral blood monocytes from 13 ovarian cancer patients, and comparable macrophages from control patients with nonmalignant lung or gynecological diseases were tested. Inhibitors of either the cyclooxygenase pathway or the lipoxygenase pathway together with specific metabolites of each pathway were used to evaluate how these different macrophage populations are regulated by eicosanoids. In addition, metabolic studies were performed to compare directly the arachidonic acid metabolism of macrophages obtained from these different anatomical locations. The results demonstrate that the peripheral blood monocytes from lung cancer and ovarian cancer patients and the peritoneal macrophages from ovarian cancer patients are sensitive to cyclooxygenase inhibition; this was not seen with comparable macrophages from the relevant control patients. Sensitivity to modulation by cyclooxygenase inhibition correlated with increased cyclooxygenase metabolism and with the capacity of prostaglandin to mediate suppression of tumoricidal function in these populations of cancer patient macrophages. In contrast, alveolar macrophages from cancer patients were not sensitive to either cyclooxygenase inhibition or to prostaglandin-mediated suppression. No such differential influences were revealed for the lipoxygenase pathway of arachidonic acid metabolism in any macrophage population tested. Thus, eicosanoids, particularly those of the cyclooxygenase pathway, can be a critical immunoregulatory feature of certain tumor microenvironments.

Characterisation of the peptido-leukotriene receptor PL2 on the ferret spleen strip

The peptido-leukotriene receptor(s) (PL) on the ferret isolated spleen strip have been characterised by functional studies using the naturally occurring leukotrienes (LTs), a range of structurally distinct PL antagonists, and by ligand binding studies. LTB4 (0.01-10 microM) was inactive on ferret spleen whereas LTC4, LTD4 and LTE4 produced concentration-related contractions with maximal responses, relative to noradrenaline, of 57% (EC50 0.28 microM), 60% (EC50 0.5 microM) and 7% respectively. The leukotriene responses were unaltered by L-serine borate, L-cysteine, indomethacin, phentolamine, propranolol, mepyramine, methysergide or atropine, suggesting that the peptido-leukotrienes were acting through distinct PL receptors. The PL1 antagonists, FPL 55712 (0.01-10 microM), ICI 198615 (10 microM), SK&F 104353 (10 microM) and MK541 (10 microM) were all inactive against LTC4- or LTD4-induced contractile responses. LTE4 was a partial agonist with respect to LTC4 and LTD4 with pKB values of 5.8 and 5.5 respectively. Nifedipine (0.1 microM) produced a rightward shift of the concentration-response curves to both LTC4 and LTD4 and depressed their maximal responses. An unacceptably high level of non-specific binding of [3H]LTD4 to membrane preparations of ferret spleen prevented characterisation of this receptor by ligand binding. These results suggest that the ferret spleen has a homogeneous population of a PL receptor type which is insensitive to existing PL1 receptor antagonists. The functional characteristics of this PL receptor type are similar to those of the PL2 receptor on other tissues. The absence of PL1 receptors on this tissue makes it particularly useful in identifying new and selective drug tools for the PL2 receptor.

Leukotriene C4 modulation of muscarinic K+ current activation in bullfrog atrial myocytes

The effects of leukotriene C4 (LTC4) on activation of muscarinic acetylcholine receptor (mAChR)-stimulated, inwardly rectifying K+ current (IK[ACh]) were examined in single bullfrog atrial myocytes using the whole-cell patch clamp technique. LTC4 produced a reversible, concentration-dependent increase in steady-state, guanosine-gamma-thiotriphosphate (GTP gamma S)-activated IK[ACh], with a K0.5 of 3.1 microM. LTC4 also increased the rate of GTP gamma S-mediated IK[ACh] activation, both in the absence and presence of 1 nM ACh, with comparable K0.5 values of 4.7 microM under basal conditions and 4.9 microM in the presence of 1 nM ACh. LTC4 did not alter the relative affinities of the G protein, Gk, for GTP gamma S and GTP. We hypothesize that all of the effects of LTC4 on the kinetics of Gk-mediated IK[ACh] activation are produced at a common site with a K0.5 of 3-5 microM. The effects of LTC4 on IK[ACh] activation are fully reversible in the presence of GTP gamma S. Under physiological conditions (i.e., intracellular GTP), 10 microM LTC4 increased the ACh-activated peak IK[ACh]. Inhibitors of cellular LTC4 production, including 5,8,11,14-eicosatetraynoic acid, baicalein, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate, and alpha-pentyl-4-(2-quinolinylmethoxy)-benzene methanol, greatly attenuated ACh-dependent IK[ACh] activation, preventing activation of peak, and producing a lower steady-state IK[ACh] (when compared with the control response in the same cell). Addition of exogenous LTC4 was able to overcome the effects of LTC4 synthesis inhibitors, restoring both the peak and steady-state IK[ACh] responses. Although the mechanism of LTC4-mediated modulation of IK[ACh] activation is not known, our results suggest that endogenously produced lipoxygenase metabolites of arachidonic acid, specifically LTC4, are involved in the physiological process of IK[ACh] activation.

Role of nitric oxide in leukotriene C4-induced increases in microvascular transport

The goal of this study was to determine the role of nitric oxide in alterations in macromolecular transport of the hamster cheek pouch in vivo in response to leukotriene C4. We used intravital fluorescent microscopy to examine the transport of macromolecules across the hamster cheek pouch in response to leukotriene C4 before and after application of an enzymatic inhibitor of nitric oxide, NG-monomethyl-L-arginine (L-NMMA; 1.0 microM). Increases in transport of macromolecules across the hamster cheek pouch were quantitated by the formation of venular leaky sites and clearance of fluorescein isothiocyanate-dextran (FITC-dextran; mol wt = 70 K). Leukotriene C4 (1.0 and 3.0 nM) produced an increase in the number of venular leaky sites and clearance of FITC-dextran-70K. Superfusion of L-NMMA (1.0 microM) significantly decreased leukotriene C4-induced increases in venular leaky sites and clearance of FITC-dextran-70K. In addition, superfusion of LY-83583 (10 microM) significantly decreased leukotriene C4-induced increases in venular leaky sites. In contrast, superfusion of NG-monomethyl-D-arginine (D-NMMA; 1.0 microM), indomethacin (10 mg/kg iv), or diphenhydramine hydrochloride; 15-20 mg/kg iv) did not significantly alter leukotriene C4-induced increases in venular leaky sites. Thus these findings suggest that production of nitric oxide and subsequent activation of guanylate cyclase play an important role in formation of venular leaky sites and clearance of FITC-dextran-70K in response to application of leukotriene C4.

Alteration of eicosanoid production in the sensitized guinea pig lung by CS-518

The effects of CS-518 (sodium 2-(1-imidazolylmethyl)-4,5-dihydrobenzo [b]thiophene-6-carboxylate), a thromboxane A2 synthase inhibitor, on changes in arachidonic acid metabolism were investigated in the lung of actively sensitized guinea pigs. Antigen challenge enhanced the production of thromboxane A2 as well as histamine and peptide leukotrienes in lung fragments. Exogenous leukotriene D4 also stimulated significant thromboxane A2 production in the non-sensitized lung in vitro. CS-518 was effective in preventing the thromboxane A2 production induced by either antigen or leukotriene D4, and the IC50 values were 90 and 7.5 ng/ml (320 and 27 nM), respectively. CS-518 markedly potentiated the production of prostaglandin E2 and I2 with slight inhibition of leukotriene formation, but indomethacin significantly stimulated leukotriene production. When CS-518 was administered orally, it induced long-lasting inhibition of thromboxane A2 production and potentiation of prostaglandin I2 production in guinea pig lung. Thus, CS-518 not only inhibited thromboxane production but also improved the change in arachidonic acid metabolism in the guinea pig bronchoalveolar tissue during allergic reaction in vivo as well as in vitro, which suggests amelioration of the asthmatic condition.

Lung responsiveness to antigen in sensitised mice of different strains

A new model of the isolated perfused lung from different strains of mice was developed. Lungs from Swiss, Balb/C and CBA mice actively sensitised to ovalbumin were challenged intratracheally (i.t.) by antigen on day 14. In Swiss mice instillation of ovalbumin led to the release of leukotriene (LT) C4 significantly above basal values. Conversely, lungs from Balb/C and CBA mice were unresponsive to ovalbumin in terms of production of LTC4. All strains failed to release histamine when challenged with antigen. Intratracheal instillation of platelet-activating factor (PAF), to lungs from non-sensitised animals, induced the release of comparable amounts of LTC4, irrespective of the strain. In contrast, i.t. administration of fMLP to lungs from Swiss mice elicited release of significantly higher amounts of LTC4 as compared to Balb/C and CBA mice. In separate experiments, ovalbumin was injected into the paws and anaphylactic oedema was evaluated. Balb/C and CBA required 1 microgram to show an oedema formation, whereas the dose of ovalbumin for Swiss mice to develop a similar response was at least 30-fold lower. In conclusion, antigen provocation induced release of LTC4 from lungs from Swiss mice but not from Balb/C or CBA. This difference may be accounted for by strain-dependent factors, such as antibody production and requires further investigation.

[Effect of thromboxane A2 synthetase inhibitor (OKY-046) on leukotriene C4-induced airway hyperresponsiveness in guinea pigs]

In this study, we investigated the effects of peroral (p.o.) administration of a thromboxane A2 (TXA2) synthetase inhibitor, OKY-046, on the airway hyperresponsiveness (AHR) in guinea pigs induced by intravenous administration of leukotriene C4 (LTC4). A 3 micrograms/kg/hr LTC4 infusion induced airway wall thickening (AWT) and AHR to 1.8 and 3.6 micrograms/kg histamine bolus shot. OKY-046 100 mg/kg p.o. partially inhibited the AHR induced by LTC4 without inhibition of AWT. Previously, we have reported that LTC4-induced AHR was partially inhibited, to the same exert as by OKY-046, by TXA2 receptor antagonists, ONO-NT-126 and ONO-8809. These data suggest that intravenous administration of LTC4 generates TXA2, and TXA2 augments LTC4-induced AHR partially in guinea pigs.

Depolarization of cultured astrocytes by leukotriene B4. Evidence for the induction of a K+ conductance inhibitor

Since astrocytes have been shown to participate in intracerebral immunological processes we investigated the effect of the immune mediators, leukotrienes (LT) B4, LTC4 and LTD4 on membrane properties of cultured astrocytes from neonatal rat brain. When LTB4 was added to the bath solution the membrane potential slowly decreased from -96 mV to -38 mV. While LTB4 at a concentration of 500 nM was ineffective, depolarization occurred when concentrations of 750 nM and above were used. The depolarizing effect was specific for LTB4, since LTC4 and LTD4, other arachidonic acid derivates, failed to depolarize astrocytes at even higher concentrations (1 microM). When the K+ conductance blocker, Ba2+ (2 mM), was added to the bath solution, astrocytes depolarized to the same degree but no further depolarization was achieved when LTB4 was added. Bath application of Co2+ (1 mM), in order to reduce putative Ca2+ inward currents or reduced internal chloride concentration, did not alter the LTB4-induced depolarization, thus arguing against additional Ca(2+)- or Cl(-)-dependent depolarizing effects. The LTB4-induced depolarization could be markedly reduced, however, by preincubation of the cells with cycloheximide (2 microM), which blocks translation and thereby protein synthesis. Cycloheximide alone had no effect on the membrane potential. These data indicate that, in astrocytes, LTB4 stimulates the synthesis of a protein, which, in turn, inhibits K+ conductances. This effect could impair glial, as well as neuronal, functions during CNS diseases accompanied by immunological processes.

Effects of CS-518, a thromboxane synthase inhibitor, on the asthmatic response

The anti-asthmatic effects of CS-518 (sodium 2-(1-imidazolylmethyl)-4,5-dihydrobenzo[b]thiophene-6-carboxylate) , a specific thromboxane A2 (TXA2) synthase inhibitor, were investigated in the ovalbumin-sensitized guinea pig asthmatic model. Although CS-518 slightly inhibited (about 25%) whole bronchoconstriction, it significantly inhibited the antigen-induced bronchoconstriction mediated by slow-reacting substance of anaphylaxis (SRS-A), which was not reduced by chlorpheniramine, a histamine H1 antagonist. On the other hand, indomethacin, a cyclooxygenase inhibitor, potentiated the SRS-A-mediated constriction. CS-518 strongly, and indomethacin slightly, suppressed the leukotriene D4-induced bronchoconstriction. CS-518 clearly inhibited the antigen-induced airway hyperresponsiveness, but this compound had no effect on the airway hyperresponsiveness induced by U-46619, a TXA2-mimetic agent, and propranolol. These results suggest that CS-518 suppresses the development of bronchoconstriction and airway hyperresponsiveness in asthmatic models by inhibition of TXA2 synthesis with the concomitant increase in bronchodilating prostaglandins such as prostaglandin E2 and prostaglandin I2.

Inhibition by cyclosporin A of adenosine triphosphate-dependent transport from the hepatocyte into bile

BACKGROUND

Immunosuppressive treatment with cyclosporin A may be associated with impaired hepatobiliary elimination of bile salts and with cholestasis. Inhibition by cyclosporin A of the primary-active adenosine triphosphate (ATP)-dependent transport systems responsible for excretion of bile salts and cysteinyl leukotrienes across the hepatocyte canalicular membrane into bile may explain the cholestatic side effect.

METHODS

ATP-dependent transport of bile salt and of cysteinyl leukotrienes was studied in human liver plasma membrane vesicles and additionally in rat liver plasma membrane vesicles enriched in canalicular membranes.

RESULTS

Inhibition of ATP-dependent taurocholate transport in human liver by 50% was measured at 3 mumol/L cyclosporin A and at 4 mumol/L fujimycin. Kinetic analyses in rat liver indicated non-competitive inhibition by cyclosporin A with respect to ATP and competitive inhibition with respect to taurocholate with inhibition constant (Ki) values of 1.0 and 0.3 mumol/L, respectively.

CONCLUSIONS

The ATP-dependent export carriers for bile salts and cysteinyl leukotrienes in the hepatocyte canalicular membrane are novel targets for inhibitory side effects of cyclosporin A. Inhibition of ATP-dependent bile salt transport may induce cholestasis.

A specific endothelin-1 antagonist blocks inhaled endothelin-1-induced bronchoconstriction in sheep

In this study we used conscious sheep to compare the relative potencies of inhaled endothelin- (ET) 1 and ET-3 and to determine whether a newly described selective ET-1 receptor antagonist, [diaminopropionic acid1-Asp15]ET-1 ([Dpr1-Asp15]ET-1), when given as an aerosol blocks ET-1-induced bronchoconstriction. Partial concentration-response curves to ET-1 and ET-3 were obtained by measuring the change in pulmonary airflow resistance (RL) after aerosol challenge. Both ET-1 (n = 6) and ET-3 (n = 4) caused concentration-dependent (10(-10)-10(-7) bronchoconstriction, but ET-3 was 400-fold less potent than ET-1. Pretreatment (30 min) with 25 breaths of 5 x 10(-8) M [Dpr1-Asp15]ET-1 caused a 100-fold rightward shift of the ET-1 concentration-response curve. The activity of the ET-1 antagonist (25 breaths of 5 x 10(-8) M) was compared with that of various control peptides (25 breaths of 10(-8) M). ET-1 (50 breaths of 10(-7) M) caused an increase in RL of 133 +/- 33% (SE) over baseline. [Dpr1-Asp15]ET-1 significantly inhibited this response by 54%. No protection was seen with a monocyclic control peptide or a thrombin receptor peptide. There was, however, a small protective effect (38%, P < 0.05) seen with [Dpr1-Asp15]ET-3, a structurally homologous ET-3 antagonist. [Dpr1-Asp15]ET-1 had no effect on carbachol (n = 3) or leukotriene D4-induced bronchoconstriction. Thus inhaled ET-1 and, to a lesser extent, ET-3 cause concentration-dependent bronchoconstriction in conscious sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotriene E4 and granulocytic infiltration into asthmatic airways

Sulphidopeptide leukotrienes are potent bronchoconstrictors and increase bronchial hyperreactivity, one of the hallmarks of asthma. We have demonstrated that leukotriene LTE4, the most stable of the sulphidopeptide leukotrienes, elicited an increase in the numbers of eosinophils and neutrophils in the lamina propria of the airway mucosa 4 h after inhalation in 4 asthmatic subjects. The numbers of eosinophils were, on average, 10-fold greater than those of neutrophils. There was no significant change in numbers of lymphocytes, plasma cells, mast cells, or macrophages. Since LTE4 recruits granulocytes, the potential of antisulphidopeptide leukotriene drugs as anti-inflammatory and "steroid-sparing" agents should be tested.

Differential effects of leukotriene C4 on endothelin-1 and prostacyclin release by cultured vascular cells

Nanomolar concentrations of leukotriene C4 and phorbol 12-myristate acetate, a protein kinase C activator, stimulated endothelin-1 release by vascular endothelial but not smooth muscle cells. For both agonists, attenuation of this stimulatory effect was observed at higher concentrations, concomitant with but independent of enhanced prostacyclin biosynthesis.

Ketotifen inhibits exacerbation of allergic airway hyperreactivity by racemic salbutamol in the guinea pig

In passively sensitized anesthetized guinea pigs, intravenous infusion of low doses of antigen ovalbumin induced a marked increased responsivity of the airways to intravenous injection of leukotriene C4. Sustained infusion of racemic salbutamol intensified responses to leukotriene C4 both before and after infusion of ovalbumin. Hyperreactivity as a result of infusion of ovalbumin was inhibited by intraduodenal injection of either hydrocortisone or ketotifen at doses that did not diminish responses to leukotriene C4 in animals not exposed to antigen. Ketotifen, but not hydrocortisone, inhibited the enhanced hyperreactivity associated with infusion of racemic salbutamol.

Endothelial cell cytosolic free calcium regulates neutrophil migration across monolayers of endothelial cells

Polymorphonuclear leukocytes (PMN) traverse an endothelial cell (EC) barrier by crawling between neighboring EC. Whether EC regulate the integrity of their intercellular adhesive and junctional contacts in response to chemotaxing PMN is unresolved. EC respond to the binding of soluble mediators such as histamine by increasing their cytosolic free calcium concentration ([Ca++]i) (Rotrosen, D., and J.I. Gallin. 1986. J. Cell Biol. 103:2379-2387) and undergoing shape changes (Majno, G., S. M. Shea, and M. Leventhal. 1969. J. Cell Biol. 42:617-672). Substances such as leukotriene C4 (LTC4) and thrombin, which increased the permeability of EC monolayers to ions, as measured by the electrical resistance of the monolayers, transiently increased EC [Ca++]i. To determine whether chemotaxing PMN cause similar changes in EC [Ca++]i, human umbilical vein endothelial cells (HUVEC) maintained as monolayers were loaded with fura-2. [Ca++]i was measured in single EC during PMN adhesion to and migration across these monolayers. PMN-EC adhesion and transendothelial PMN migration in response to formyl-methionyl-leucyl-phenylalanine (fMLP) as well as to interleukin 1 (IL-1) treated EC induced a transient increase in EC [Ca++]i which temporally corresponded with the time course of PMN-EC interactions. When EC [Ca++]i was clamped at resting levels with a cell permeant calcium buffer, PMN migration across EC monolayers and PMN induced changes in EC monolayer permeability were inhibited. However, clamping of EC [Ca++]i did not inhibit PMN-EC adhesion. These studies provide evidence that EC respond to stimulated PMN by increasing their [Ca++]i and that this increase in [Ca++]i causes an increase in EC monolayer permeability. Such [Ca++]i increases are required for PMN transit across an EC barrier. We suggest EC [Ca++]i regulates transendothelial migration of PMN by participating in a signal cascade which stimulates EC to open their intercellular junctions to allow transendothelial passage of leukocytes.

Effect of nedocromil sodium on sulfidopeptide leukotrienes-stimulated human alveolar macrophages in asthma

Alveolar macrophages (AM) may take part in the amplification of the inflammatory mechanism involved in asthma. During an asthma attack, mast cells and eosinophils release arachidonic acid derivative mediators of inflammation such as sulfidopeptide leukotrienes. Among them, LTC4 has been shown to be present in bronchoalveolar fluid. In asthmatic patients, we showed that the ability of AM to transform LTC4 into its derivatives LTD4 and LTE4 was related to the intensity of the local inflammation observed during endoscopy. AM from asthmatics incubated in the presence of LTC4 or LTE4, generated LTB4 and 5-HETE, which are potent chemoattractants. Nedocromil sodium (10(-4) M) decreased LTB4 releasability and intracellular 5-HETE concentrations in zymosan-stimulated AM from asthmatic patients, and was shown to decrease the LTC4 or LTE4-promoted formation of LTB4 and 5-HETE.

Chronic growth stimulation of human adult melanocytes by inflammatory mediators in vitro: implications for nevus formation and initial steps in melanocyte oncogenesis

In the human epidermis, melanocytes are distributed at a distance from each other. In contrast, melanocytes in nevi, which are considered benign neoplasms of melanocytes, are grouped in nests. Although still not well defined, environmental factors are thought to play an important role in the development of nevi. We found that chronic growth stimulation by leukotriene C4, a compound found in increased amounts in inflamed skin, induced pleiotropic modifications in the normal melanocyte phenotype. These changes include loss of contact inhibition and formation of structures resembling tumor spheroids. In parallel with these changes, there was a constitutive expression of Fos protein. Switching these cultures to medium supplemented with phorbol ester sustained growth with reversion of the altered phenotype. In contrast, a cAMP stimulator, cholera toxin, induced features of terminal differentiation. Our findings suggest a role for inflammatory mediators in human epidermal melanocytes. This observation provides insight into melanocyte growth alterations which may have relevance in early stages of melanocyte oncogenesis.

Leukotrienes and histamine mediate IgE-dependent contractions of human bronchi: pharmacological evidence obtained with tissues from asthmatic and non-asthmatic subjects

Isolated human bronchi were challenged with anti-human IgE or specific allergen. The mediators of allergic constriction were characterized by pharmacological interventions. Experiments were performed on more than 180 preparations obtained from 48 non-asthmatic subjects and on 44 bronchial preparations from six asthmatic subjects. Addition of antihistamines (mepyramine and metiamide) to the organ bath abolished the response to exogenous histamine, but failed to alter the dose-response relationship of the reaction to cumulative challenge with rising titres of anti-IgE. On the other hand, pretreatment with drugs which blocked the action (receptor antagonists FPL55712, L-648,051 and ICI 198,615) or formation (biosynthesis inhibitors: U-60,257 and MK886) of leukotrienes consistently resulted in clear-cut inhibition of the allergic constriction in bronchi from both asthmatic and non-asthmatic subjects. In the presence of the most effective inhibitors (ICI 198,615 and MK886), the response to anti-IgE was depressed by more than 60%. In contrast, the cyclooxygenase inhibitor indomethacin and the antagonist of platelet activating factor (PAF) WEB 2086, failed to alter the response, indicating that prostanoids and PAF do not mediate IgE-dependent constriction of human bronchi. After the leukotriene antagonist ICI 198,615 had rendered the bronchi insensitive to exogenous leukotrienes, the residual component of the contractile response to anti-IgE was completely abolished by addition of antihistamines. Similar abolition of the Schultz-Dale reaction in bronchi of two allergic asthmatic patients was noted when antihistamines were administered together with ICI 198,615 or MK886. In conclusion, the leukotrienes appear to be the major and singularly most important mediators of the contraction, whereas histamine accounts for its minor residual component.

Leukotriene D4 receptors are not negatively coupled to adenylyl cyclase in guinea-pig lung parenchyma

1. The possibility that receptors for the peptide-containing leukotrienes may be negatively coupled to adenylyl cyclase in guinea-pig lung parenchyma was investigated by comparing the effect of leukotriene D4 (LTD4) on the intracellular cyclic nucleotide (cyclic AMP and cyclic GMP) content and on the activity of cyclic AMP-dependent protein kinase (PKA). In addition, the potential association between changes in the cyclic nucleotide content and the ability of LTD4 to increase lung parenchymal tone was also evaluated. 2. Non-cumulative challenge of parenchymal lung strips with LTD4 elicited concentration-dependent contractions (pD2 = 8.23) that were paralleled by concentration-related increases in the intracellular level of cyclic AMP and cyclic GMP, and in the activation state of PKA (Kact = 33 nM). Temporally, these biochemical effects of LTD4 were transient, peaking after approximately 5 min drug contact thereafter decaying, despite the continued generation of tone. Both the biochemical and mechanical effects of LTD4 were antagonized by the LTD4-receptor blocking drug, ICI 198,615 (1 microM for 60 min), indicating that they were receptor-mediated events. 3. Challenge of guinea-pig lung with LTD4 (200 nM; EC100 for tension generation) stimulated a 150 and 70 fold increase in the elaboration of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) respectively, relative to that generated spontaneously. 4. Pretreatment of lung strips for 60 min with an irreversible inhibitor of cyclo-oxygenase, flurbiprofen,at a concentration (8 microM) that abolished both basal and LTD4 (200 nM)-induced TXB2 and 6-keto-PGF1alpha release, relaxed rapidly the spontaneous tone of the tissues, reduced the cyclic AMP content by ~50%and lowered the PKA activity ratio from 29% to 17%. In addition, flurbiprofen abolished the ability of LTD4 (200 nM) to increase the cyclic AMP content and to activate PKA. Functionally, the magnitude of LTD4 (200 nM)-induced tone and the increase in cyclic GMP content were attenuated by approximately 20% and 50% respectively in flurbiprofen-treated tissues.5. In flurbiprofen-treated tissues, isoprenaline (10 microM for 10 min) increased the cyclic AMP content(from 4 to 27 pmol mg-1 protein) and activated PKA (from 15% to 26%). Preincubation (30 s or 5 min)of lung with LTD4 (200 nM) did not inhibit (or enhance) these isoprenaline-induced effects.6. Pretreatment of lung strips for 60 min with the thromboxane synthetase inhibitor, dazmegrel (10 microM),relaxed the spontaneous tone of the tissues, abolished the LTD4 (200 nM)-stimulated release of TXB2 and significantly enhanced (~two fold) the elaboration of 6-keto-PGF1alpha. In addition, dazmegrel attenuated (by ~50%) LTD4 (200 nM)-induced cyclic GMP accumulation but approximately doubled both the cyclic AMP content and PKA activity ratio. LTD4-induced contractions, in contrast, were not affected by dazmegrel.7. EP 092 (1 microM for 60 min), a selective TP-receptor blocking drug, had no effect on spontaneous tone,eicosanoid formation or on the cyclic GMP content of guinea-pig lung parenchymal strips. Likewise,EP 092 exerted no significant mechancial effect in lung challenged with LTD4 (200 nM) although it did potentiate, to a small extent, the ability of LTD4 (200 nM) to increase the cyclic AMP content.8. It is concluded that LTD4 can increase the intracellular level of cyclic AMP in guinea-pig parenchyma and activate PKA by a leukotriene-receptor-mediated mechanism sensitive to ICI 198,615. However,these biochemical actions of LTD4 are induced indirectly by an arachidonic acid-derived cyclo-oxygenase product(s) other than TXA2. Thus, contrary to reports of other investigators, no evidence was found to corroborate the finding that stimulation of leukotriene receptors on guinea-pig lung parenchyma results in a rapid lowering of the cyclic AMP content even in cyclo-oxygenase-blocked tissues. These data,therefore, do not support the hypothesis that leukotriene-induced tension generation is dependent upon a prior reduction in the cyclic AMP content.

Influence of atherosclerosis on the vascular reactivity of isolated human epicardial coronary arteries to leukotriene C4

Leukotrienes, lipid mediators derived from arachidonic acid by the 5-lipoxygenase pathway, have been implicated in a variety of myocardial ischemic events including myocardial infarction and coronary spasm. We have examined the comparative effects of leukotriene C4 in isolated human non-atherosclerotic and atherosclerotic coronary arteries to gain an insight into the role of leukotrienes in coronary heart disease. Human coronary arteries, obtained from recipient hearts at the time of cardiac transplantation, were cut into rings and examined in an isolated organ bath. In atherosclerotic arteries leukotriene C4 (1nM-100nM) produced a maximal contractile response of 54.9 +/- 7.98% KCI (n = 7) and the mean EC50 value was 11.1nM (95% confidence interval: 9.4-13.0). The leukotriene receptor antagonist ICI-198,615 (3 x 10(-8)M) produced an approximate 50-fold rightward shift of the leukotriene C4 dose-response curve (n = 5). In contrast, non-atherosclerotic arteries were either non-responsive (n = 5) or only weakly responsive (n = 2) to leukotriene C4 (1nM-100nM), producing an average maximum response of 3.65 +/- 3.05% KCI (n = 7; p < 0.01 atherosclerotic vs non-atherosclerotic). In the presence of indomethacin and in vessels denuded of endothelium, non-atherosclerotic arteries remained unresponsive to leukotriene C4 (n = 3). In addition, leukotriene C4 did not relax preconstricted vessels (n = 7). In vitro autoradiography showed specific [3H]-leukotriene C4 binding to smooth muscle in both non-atherosclerotic and atherosclerotic arteries, with no evidence of endothelium-dependent binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of leukotrienes in airway hyperresponsiveness in guinea-pigs

1. Repeated aerosolization of leukotriene C4 (LTC4) to guinea-pigs produced leftward shift in their pulmonary resistance (RL) dose-response curves to inhaled acetylcholine (ACh) without increasing the maximum responses. 2. Repeated LTC4 aerosolization did not increase airway eosinophils. 3. The 5-lipoxygenase-activating protein (FLAP) inhibitor, MK-886, prevented the leftward shift in RL dose-response curves to ACh following repeated antigen challenge in guinea-pigs. 4. MK-886 did not inhibit the increased maximal RL produced by repeated antigen challenge, nor inhibit the airway eosinophilia induced by repeated antigen challenge. 5. Our findings suggest that leukotrienes may account for the leftward shift in pulmonary resistance responses caused by antigen but do not cause the airway eosinophilia nor enhanced maximum broncho-constrictor response to antigen.