[Effects of cysteinyl leukotriene receptors on phagocytosis of mouse microglial cells]

OBJECTIVE

: To determine the effects of cysteinyl leukotriene receptors (CysLT₁R and CysLT₂R) on phagocytosis of mouse BV2 microglial cells.

METHODS

: BV2 cells were stimulated with microglial activators lipopolysaccharide (LPS) or CysLT receptor agonists LTD₄. The phagocytosis of BV2 cells was observed by immunofluorescence analysis and flow cytometry. The intracellular distributions of CysLT₁R and CysLT₂R in BV2 cells were examined with immunofluorescence staining.

RESULTS

: Both LPS and LTD₄ could significantly enhance the phagocytosis of BV2 cells, and such effect could be inhibited by CysLT₁R selective antagonist Montelukast and CysLT₂R selective antagonist HAMI 3379. The activation of BV2 cells induced by LTD₄ or LPS resulted in changes in intracellular distributions of CysLT₁R and CysLT₂R. CysLT₁R and CysLT₂R was co-localization with a similar distribution.

CONCLUSIONS

: CysLT₁R and CysLT₂R regulate the phagocytosis of mouse BV2 microglial cells with a synergistic effect.

[Effects of agonist and antagonist of cysteinyl leukotriene receptors on differentiation of rat glioma C6 cells]

OBJECTIVE

To investigate the role of cysteinyl leukotriene (CysLT) receptors in the differentiation of rat glioma C6 cells.

METHODS

Rat glioma C6 cells were treated with the agonist LTD(4), the CysLT(1) receptor antagonist montelukast and the differentiation inducer forskolin. Cell morphology and GFAP protein expression were determined after treatments.

RESULT

Forskolin (10 μmol/L) induced morphological changes and GFAP protein expression (cell differentiation) in C6 cells, but LTD(4) (0.1-100 nmol/L) did not induce these changes. Montelukast (1 μmol/L) alone did not affect C6 cell differentiation, while it induced the differentiation when combined with the LTD(4) (100 nmol/L).

CONCLUSION

The CysLT(2) receptor may modulate the differentiation of rat glioma C6 cells.

Activation of CysLT receptors induces astrocyte proliferation and death after oxygen-glucose deprivation

We recently found that 5-lipoxygenase (5-LOX) is activated to produce cysteinyl leukotrienes (CysLTs), and CysLTs may cause neuronal injury and astrocytosis through activation of CysLT(1) and CysLT(2) receptors in the brain after focal cerebral ischemia. However, the property of astrocyte responses to in vitro ischemic injury is not clear; whether 5-LOX, CysLTs, and their receptors are also involved in the responses of ischemic astrocytes remains unknown. In the present study, we performed oxygen-glucose deprivation (OGD) followed by recovery to induce ischemic-like injury in the cultured rat astrocytes. We found that 1-h OGD did not injure astrocytes (sub-lethal OGD) but induced astrocyte proliferation 48 and 72 h after recovery; whereas 4-h OGD moderately injured the cells (moderate OGD) and led to death 24-72 h after recovery. Inhibition of phospholipase A(2) and 5-LOX attenuated both the proliferation and death. Sub-lethal and moderate OGD enhanced the production of CysLTs that was inhibited by 5-LOX inhibitors. Sub-lethal OGD increased the expressions of CysLT(1) receptor mRNA and protein, while moderate OGD induced the expression of CysLT(2) receptor mRNA. Exogenously applied leukotriene D(4) (LTD(4)) induced astrocyte proliferation at 1-10 nM and astrocyte death at 100-1,000 nM. The CysLT(1) receptor antagonist montelukast attenuated astrocyte proliferation, the CysLT(2) receptor antagonist BAY cysLT2 reversed astrocyte death, and the dual CysLT receptor antagonist BAY u9773 exhibited both effects. In addition, LTD(4) (100 nM) increased the expression of CysLT(2) receptor mRNA. Thus, in vitro ischemia activates astrocyte 5-LOX to produce CysLTs, and CysLTs result in CysLT(1) receptor-mediated proliferation and CysLT(2) receptor-mediated death.

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.

[Effects of cysteinyl receptor agonist and antagonists on rat primary cortical neurons]

OBJECTIVE

To determine the effect of cysteinyl receptor agonist leukotriene D(4) (LTD(4)) and its antagonists on rat primary neurons.

METHODS

In the primarily cultured rat cortical neurons, the neuron injury was evaluated by measuring intracellular calcium, 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide (MTT) reduction, and propidium iodide (PI) and Hoechst 33258 staining. The in vitro ischemic injury was induced by oxygen-glucose deprivation (OGD) for 1.5 h and reperfusion for 24 h.

RESULT

LTD(4) (0.01-1 micromol/L) did not induce the elevation of intracellular calcium, neuron viability changes and neuron death. OGD-induced injury was not significantly ameliorated by the CysLT(1) receptor antagonists, pranlukast (0.2-10 micromol/L) and montelukast (0.2-10 micromol/L), as well as by the CysLT(1)/CysLT(2) receptor non-selective antagonist, BAY u9773 (0.02-1 micromol/L).

CONCLUSION

Neither agonist nor antagonists of cysteinyl receptors have the effects on the viability and ischemic-like injury in rat primary neurons.

Cysteinyl leukotriene 2 receptor and protease-activated receptor 1 activate strongly correlated early genes in human endothelial cells

Cysteinyl leukotrienes (cysLT), i.e., LTC4, LTD4, and LTE4, are lipid mediators derived from the 5-lipoxygenase pathway, and the cysLT receptors cysLT1-R/cysLT2-R mediate inflammatory tissue reactions. Although endothelial cells (ECs) predominantly express cysLT2-Rs, their role in vascular biology remains to be fully understood. To delineate cysLT2-R actions, we stimulated human umbilical vein EC with LTD4 and determined early induced genes. We also compared LTD4 effects with those induced by thrombin that binds to protease-activated receptor (PAR)-1. Stringent filters yielded 37 cysLT2-R- and 34 PAR-1-up-regulated genes (>2.5-fold stimulation). Most LTD4-regulated genes were also induced by thrombin. Moreover, LTD4 plus thrombin augmented gene expression when compared with each agonist alone. Strongly induced genes were studied in detail: Early growth response (EGR) and nuclear receptor subfamily 4 group A transcription factors; E-selectin; CXC ligand 2; IL-8; a disintegrin-like and metalloprotease (reprolysin type) with thrombospondin type 1 motif 1 (ADAMTS1); Down syndrome critical region gene 1 (DSCR1); tissue factor (TF); and cyclooxygenase 2. Transcripts peaked at approximately 60 min, were unaffected by a cysLT1-R antagonist, and were superinduced by cycloheximide. The EC phenotype was markedly altered: LTD4 induced de novo synthesis of EGR1 protein and EGR1 localized in the nucleus; LTD4 up-regulated IL-8 formation and secretion; and LTD4 raised TF protein and TF-dependent EC procoagulant activity. These data show that cysLT2-R activation results in a proinflammatory EC phenotype. Because LTD4 and thrombin are likely to be formed concomitantly in vivo, cysLT2-R and PAR-1 may cooperate to augment vascular injury.

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.

Inverse agonist activity of selected ligands of the cysteinyl-leukotriene receptor 1

Cysteinyl leukotrienes (CysLTs) are associated with several inflammatory processes, including asthma. Due to this association, considerable effort has been invested in the development of antagonists to the CysLT receptors (CysLT(1)R). Many of these molecules have been shown to specifically interact with CysLT(1)R, but little is known about their impact on the conformation of the receptor and its activity. We were especially interested in possible inverse agonist activity of the antagonists. Using a constitutively active mutant (N106A) of the human CysLT(1)R and the wild-type (WT) receptor coexpressed with the G(alphaq) subunit of the trimeric G protein, we were able to address this issue with ligands commonly used in therapy. We demonstrated that some of these molecules are inverse agonists, whereas others act as partial agonists. In cells expressing the CysLT(1)R mutant N106A exposed to Montelukast, Zafirlukast, or 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK571), the basal inositol phosphate production was reduced by 53 +/- 6, 44 +/- 3, and 54 +/- 4%, respectively. On the other hand, 6(R)-(4-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid (BayU9773) and 1-[2-hydroxy-3-propyl-4-[4-(1H-tetrazole-5-YL)-butoxy]-phenyl ethanone] (LY171883) acted as partial agonists and alpha-pentyl-3-[2-quinolinylmethoxy] benzyl alcohol (REV 5901) as a neutral antagonist. However, in cells expressing CysLT(1)R and G(alphaq), all antagonists used had inverse agonist activity. The decrease in basal inositol phosphate production by ligands with inverse agonist activity could be inhibited by a more neutral antagonist, confirming the specificity of the reaction. We demonstrate here that Montelukast, MK571, and Zafirlukast can act as inverse agonists on the human CysLT(1) receptor.

Co-expression of mCysLT1 receptors and IK channels in Xenopus laevis oocytes elicits LTD4-stimulated IK current, independent of an increase in [Ca2+]i

Addition of LTD4 (10 nM) to Xenopus laevis oocytes expressing the mCysLT1 receptor together with hBK or hIK channels resulted in the activation of both channels secondary to an LTD4-induced increase in [Ca2+]i. In addition, the hIK channel is activated by low concentrations of LTD4 (<0.1 nM), which did not result in any increase in [Ca2+]i. Even though activation of hIK by low concentrations of LTD4 was independent of an increase in [Ca2+]i, a certain "permissive" level of [Ca2+]i was required for its activation, since buffering of intracellular Ca2+ by EGTA completely abolished the response to LTD4. Neither hTBAK1 nor hTASK2 was activated following stimulations with LTD4 (0.1 and 100 nM).

Differential peristaltic motor effects of prostanoid (DP, EP, IP, TP) and leukotriene receptor agonists in the guinea-pig isolated small intestine

1. Since the role of prostanoid receptors in intestinal peristalsis is largely unknown, the peristaltic motor effects of some prostaglandin (DP, EP, IP), thromboxane (TP) and leukotriene (LT) receptor agonists and antagonists were investigated. 2. Propulsive peristalsis in fluid-perfused segments from the guinea-pig small intestine was triggered by a rise of the intraluminal pressure and recorded via the intraluminal pressure changes associated with the peristaltic waves. Alterations of distension sensitivity were deduced from alterations of the peristaltic pressure threshold and modifications of peristaltic performance were reflected by modifications of the amplitude, maximal acceleration and residual baseline pressure of the peristaltic waves. 3. Four categories of peristaltic motor effects became apparent: a decrease in distension sensitivity and peristaltic performance as induced by the EP1/EP3 receptor agonist sulprostone and the TP receptor agonist U-46619 (1-1000 nM); a decrease in distension sensitivity without a major change in peristaltic performance as induced by PGD(2) (3-300 nM) and LTD(4) (10-100 nM); a decrease in peristaltic performance without a major change in distension sensitivity as induced by PGE(1), PGE(2) (1-1000 nM) and the EP1/IP receptor agonist iloprost (1-100 nM); and a decrease in peristaltic performance associated with an increase in distension sensitivity as induced by the EP2 receptor agonist butaprost (1-1000 nM). The DP receptor agonist BW-245 C (1-1000 nM) was without effect. 4. The peristaltic motor action of sulprostone remained unchanged by the EP1 receptor antagonist SC-51089 (1 micro M) and the DP/EP1/EP2 receptor antagonist AH-6809 (30 micro M), whereas that of U-46619 and LTD(4) was prevented by the TP receptor antagonist SQ-29548 (10 micro M) and the cysteinyl-leukotriene(1) (cysLT(1)) receptor antagonist tomelukast (10 micro M), respectively. 5. These observations and their pharmacological analysis indicate that activation of EP2, EP3, IP, TP and cysLT(1) receptors, but not DP receptors, modulate intestinal peristalsis in a receptor-selective manner, whereas activation of EP1 seems to be without influence on propulsive peristalsis. In a wider perspective it appears as if the effect of prostanoid receptor agonists to induce diarrhoea is due to their prosecretory but not peristaltic motor action.

Studies of receptors and modulatory mechanisms in functional responses to cysteinyl-leukotrienes in smooth muscle

Cysteinyl-leukotrienes, i.e. leukotriene (LT) C4, D4 and E4, are inflammatory mediators and potent airway- and vasoconstrictors. Two different cysteinyl-leukotriene receptors have been cloned, CysLT1 and CysLT2. This report reviews recent data on CysLT receptor characterisation as well as studies of modulatory mechanisms involved in cysteinyl-leukotriene-induced responses. On the basis of functional studies in isolated smooth muscle preparations, the existence of an additional receptor for cysteinyl-leukotrienes is suggested. In addition, cysteinyl-leukotriene responses in pulmonary vessels were regulated by the release of modulatory factors, of which cyclooxygenase products dominated in the arteries and nitric oxide was the main modulator in porcine pulmonary veins. Moreover, the interconversion between LTC4 and LTD4 and the metabolism into LTE4 may represent a major modulatory mechanism in the guinea-pig trachea by deciding which CysLT receptor is activated by the cysteinyl-leukotrienes.

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.

A kinetic binding study to evaluate the pharmacological profile of a specific leukotriene C(4) binding site not coupled to contraction in human lung parenchyma

We report the identification of a novel pharmacological profile for the leukotriene (LT)C(4) binding site we previously identified in human lung parenchyma (HLP). We used a series of classic cysteinyl-LT (CysLT)(1) receptor antagonists belonging to different chemical classes and the dual CysLT(1)-CysLT(2) antagonist BAY u9773 for both binding and functional studies. Because the presence of (S)-decyl-glutathione interfered with cysteinyl-LT binding, with a kinetic protocol we avoided the use of this compound. By means of heterologous dissociation time courses, we demonstrated that zafirlukast, iralukast, and BAY u9773 selectively competed only for (3)H-LTD(4) binding sites, whereas pobilukast, pranlukast, and CGP 57698 dissociated both (3)H-LTC(4) and (3)H-LTD(4) from their binding sites. Thus, with binding studies, we have been able to identify a pharmacological profile for LTC(4) distinct from that of LTD(4) receptor (CysLT(1)) in HLP. On the contrary, in functional studies, all of the classic antagonists tested were able to revert both LTC(4)- and LTD(4)-induced contractions of isolated HLP strips. Thus, LTD(4) and LTC(4) contract isolated HLP strips through the same CysLT(1) receptor. The results of kinetic binding studies, coupled to a sophisticated data analysis, confirm our hypothesis that HLP membranes contain two cysteinyl-LT high-affinity binding sites with different pharmacological profiles. In functional studies, however, LTD(4)- and LTC(4)-induced contractions are mediated by the same CysLT(1) receptor. In conclusion, the specific LTC(4) high-affinity binding site cannot be classified as one of the officially recognized CysLT receptors, and it is not implicated in LTC(4)-induced HLP strip contractions.

Therapeutic options directed against platelet activating factor, eicosanoids and bradykinin in sepsis

Various autacoids, including the eicosanoids, platelet activating factor (PAF) and bradykinin, have been implicated in the pathogenesis of sepsis and septic shock. The precise role of these compounds as mediators of the diffuse inflammatory state characteristic of sepsis remains to be determined, but, in animal models, beneficial effects have been observed as a result of treatment with various inhibitors of eicosanoid biosynthesis or antagonists of PAF or bradykinin receptors. To date, however, it has been impossible to translate these encouraging results from animal models into convincingly positive results in the clinical setting.

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.

Characterisation of leukotriene receptors on rat lung strip

The leukotriene receptor(s) present on rat lung strip have been characterised using the natural agonists, a selective mimetic, and potent (cysLT1) selective leukotriene receptor antagonists. Leukotriene C4 and leukotriene D4 displayed comparable contractile potencies whilst leukotriene E4 was less potent. However, both leukotriene D4 and leukotriene E4 were found to be partial agonists relative to leukotriene C4. Responses to all three leukotrienes were competitively antagonised by ICI 198615 (1-((2-methoxy-(4-phenylsulfonyl)-aminocarbonyl)-phenyl) methyl)-1H-indazol-6-yl) carbonic acid cyclopentyl ester), SK&F 104353 (2-(R)-hydroxy-3(S)-(2-carboxyethylthio)-3-(2-[8-phenyloctyl ]- phenyl)propanoic acid, and MK571 (+/-(E)-3-[3-[2-(7-chloro-2-quinolin-yl)ethenyl]-phenyl)- ([3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]thio]propanoic acid) with comparable affinities irrespective of the agonist used. This indicates that rat lung contains a homogeneous population of leukotriene receptors and that they are of the CysLT1 type.