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

Intracerebroventricular injection of HAMI 3379, a selective cysteinyl leukotriene receptor 2 antagonist, protects against acute brain injury after focal cerebral ischemia in rats

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses by activating their receptors, CysLT(1)R and CysLT(2)R. We recently reported that CysLT(2)R is involved in neuronal injury, astrocytosis and microgliosis after focal cerebral ischemia in rats. Here, we determined whether HAMI 3379, a selective CysLT(2)R antagonist, protects against acute brain injury after focal cerebral ischemia in rats. We induced transient focal cerebral ischemia by 30 min of middle cerebral artery occlusion (MCAO), followed by 24h of reperfusion. HAMI 3379 (1, 10 or 100 ng) was injected intracerebroventricularly (i.c.v.) 30 min before MCAO, and the CysLT(1)R antagonist pranlukast (0.1mg/kg, i.p.) was used as a positive control. HAMI 3379 at 10 and 100 ng (but not at 1 ng) attenuated the neurological deficits, and reduced infarct volume, brain edema, IgG exudation, neuronal degeneration and neuronal loss. This protective effect was similar to that of pranlukast. Thus, HAMI 3339 at 10-100 ng i.c.v. is neuroprotective against acute brain injury after focal cerebral ischemia in rats. These findings suggest therapeutic potential for CysLT(2)R antagonists in the treatment of ischemic stroke.

Leukotriene pathways and in vitro adenotonsillar cell proliferation in children with obstructive sleep apnea

INTRODUCTION

The abundant expression of leukotrienes (LTs) and their receptors in adenotonsillar tissues of children with obstructive sleep apnea (OSA) suggest that LT antagonists could be useful in treating OSA.

METHODS

The effects of LTD4 and of LT receptor antagonists zileuton, montelukast, and BAY u9773 were examined on mixed cell cultures prepared from dissociated tonsils or adenoids harvested intraoperatively from children with polysomnographically diagnosed OSA. Proliferation was assessed by (3)[H]-thymidine incorporation, and inflammatory cytokine production (tumor necrosis factor [TNF]-alpha, interleukin [IL]-6, IL-8, IL-10, and IL-12) was assessed in supernatants using enzyme-linked immunosorbent assay.

RESULTS

LTD4 elicited dose-dependent increases in adenotonsillar cell proliferation (p < 0.001; n = 12). All LT antagonists exhibited dose-dependent reductions in adenotonsillar cellular proliferation rates, with montelukast more than BAY u9773 more than zileuton (n = 14/group; p < 0.001). However, BAY u9773 showed partial agonist effects and increased cellular proliferation at higher concentrations (10(-4) mmol/L; p < 0.01; n = 12). LTD4 effects were partially blocked by montelukast and BAY u9773 but not by zileuton. All three antagonists reduced TNF-alpha, IL-6, and IL-12 concentrations, with selective changes in IL-8 and no effects on IL-10 levels.

CONCLUSIONS

LT pathways mediate intrinsic proliferative and inflammatory signaling pathways in adenotonsillar tissues from children with OSA, and targeted pharmacologic disruption of these pathways may provide nonsurgical alternatives for prevention and treatment of this disease.

The quest for new cysteinyl-leukotriene and lipoxin receptors: recent clues

The metabolism of arachidonic acid via the 5-lipoxygenase enzymatic pathway leads to the formation of the cysteinyl-leukotrienes and lipoxins, which have been implicated in several inflammatory reactions. While these lipid mediators are responsible for a variety of effects, their actions occur through the activation of 3 specific types of cloned receptors (i.e., CysLT(1), CysLT(2), and ALX). Although receptor activation can explain several biological actions associated with the mediators, there is some evidence to suggest that not all responses fit the well-known characteristics of these cloned receptors. Other receptor subtypes may also exist. Interestingly, the indirect evidence for support of this observation is principally derived from work performed on either blood elements and/or vascular smooth muscle. Because the initiating events associated with inflammation are essentially of vascular origin, further work at the molecular level may be necessary to confirm the data, which do not fit the well-known CysLT and ALX receptor profiles.

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.

Functional characteristics of cysteinyl-leukotriene receptor subtypes

Cysteinyl-leukotrienes, i.e. leukotriene (LT) C4, D4 and E4, are inflammatory mediators and potent airway- and vasoconstrictors. Two different cysteinyl-leukotriene receptors, CysLT1 and CysLT2, have been cloned and functionally characterised using potent CysLT1 receptor antagonists and the dual CysLT1/CysLT2 receptor antagonist BAY u9773. However, the rank order of potency of the cysteinyl-leukotrienes at the CysLT receptors differs between tissues and studies, and a CysLT receptor classification based on agonist selectivity has not been established. In addition, the existence of more than two receptor subtypes for cysteinyl-leukotrienes has been suggested.

Receptor preferences of cysteinyl-leukotrienes in the guinea pig lung parenchyma

Two cysteinyl-leukotriene receptors, CysLT(1) and CysLT(2) receptors, have been cloned, but the contractions to cysteinyl-leukotrienes in the guinea pig lung parenchyma have been reported to be resistant to CysLT(2) receptor antagonism and to be only partially inhibited by CysLT(1) receptor antagonism. The receptor preferences of the individual cysteinyl-leukotrienes (leukotriene C(4), D(4) and E(4)) in the guinea pig lung parenchyma were studied in organ baths. CysLT(1) receptor antagonists competitively inhibited the contraction to leukotriene E(4), but exhibited only weak antagonism of contractions to leukotriene C(4) and D(4). In the presence of the cyclooxygenese inhibitor indomethacin and the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG), the CysLT(1) receptor antagonists did not further inhibit the leukotriene D(4)-induced contraction. These results suggest that leukotriene E(4) solely activates a CysLT(1) receptor, and that the CysLT(1) receptor antagonist-resistant contraction to leukotriene D(4) and C(4) is mediated via another CysLT receptor.

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.

Mechanisms in anti-inflammation and resolution: the role of lipoxins and aspirin-triggered lipoxins

Multicellular host responses to infection, injury or inflammatory stimuli lead to the formation of a broad range of chemical mediators by the host. The integrated response of the host is essential to health and disease; thus it is important to achieve a more complete understanding of the molecular and cellular events governing the formation and actions of endogenous mediators of resolution that appear to control the duration of inflammation. Lipoxins are trihydroxytetraene-containing lipid mediators that can be formed during cell-cell interactions and are predominantly counterregulators of some well-known mediators of inflammation. Since this circuit of lipoxin formation and action appears to be of physiological relevance for the resolution of inflammation, therapeutic modalities targeted at this system are likely to have fewer unwanted side effects than other candidates and current anti-inflammatory therapies. Here, we present an overview of the recent knowledge about the biosynthesis and bioactions of these anti-inflammatory lipid mediators.

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.

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.