L-649,923, sodium (beta S*, gamma R*)-4-(3-(4-acetyl-3-hydroxy-2-propylphenoxy)-propylthio)- gamma-hydroxy-beta-methylbenzenebutanoate, a selective, orally active leukotriene receptor antagonist

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.

Asthma therapy with agents preventing leukotriene synthesis or action

Elucidation of the biochemistry of leukotriene production and the pharmacology of its actions has led to the development of a number of therapeutic agents shown to be of value in the treatment of asthma. These agents either prevent the synthesis of the leukotrienes, by preventing the action of the 5-lipoxygenase-activating protein or the catalytic action of the 5-lipoxygenase, or by inhibiting the action of leukotrienes at the CysLT1 receptor. Numerous clinical trials in exercise-induced asthma, allergen-induced asthma, aspirin-induced asthma, and spontaneously occurring asthmatic episodes have indicated that these agents are safe and effective asthma treatments.

Leukotrienes as mediators of airway obstruction

The cysteinyl leukotrienes are potent mediators of airway narrowing derived from the lipoxygenation of arachidonic acid and the adduction of glutathione to this eicosanoid backbone. In lower animals and humans, the cysteinyl leukotrienes are among the most potent airway contractile substances ever identified. Furthermore, these moieties can be recovered from the urine during induced or spontaneous asthma attacks. Most important, inhibition of the synthesis of the leukotrienes or prevention of their action at the CysLT1 receptor is associated with an improvement in the airway dysfunction that occurs in both induced and spontaneous asthma. These data indicate that the cysteinyl leukotrienes have a clinically significant role in the airway obstruction that characterizes asthma.

Mechanisms of acute vasodilator response to bacterial lipopolysaccharide in the rat coronary microcirculation

1. In this study the mechanisms of the acute vasodilator action of bacterial lipopolysaccharide (LPS) were investigated in the rat Langendorff perfused heart. 2. Infusion of LPS (5 microg ml(-1)) caused a rapid and sustained fall in coronary perfusion pressure (PP) of 59 +/- 4 mmHg (n = 12) and a biphasic increase in NO levels determined in the coronary effluent by chemiluminescent detection. Both the fall in PP and the increase in NO release were completely abolished (n = 3) by pretreatment of hearts with the NO synthase inhibitor L-NAME (50 microM). 3. LPS-induced vasodilatation was markedly attenuated to 5 +/- 4 mmHg (n 3) by pretreatment of hearts with the B2 kinin receptor antagonist Hoe-140 (100 nM). 4. Vasodilator responses to LPS were also blocked by brief pretreatment with mepacrine (0.5 microM, n = 3) or nordihydroguaiaretic acid (0.1 microM, n = 4) and markedly attenuated by WEB 2086 (3 microM, n = 4). 5. Thirty minutes pretreatment of hearts with dexamethasone (1 nM), but not progesterone (1 microM), significantly modified responses to LPS. The action of dexamethasone was time-dependent, having no effect when applied either simultaneously with or pre-perfused for 5 min before the administration of LPS but inhibiting the response to LPS by 91 +/- 1% (n = 4) when pre-perfused for 15 min. The inhibition caused by dexamethasone was blocked by 15 min pretreatment with the glucocorticoid receptor antagonist RU-486 (100 nM) or by 2 min pre-perfusion of a 1:200 dilution of LCPS1, a selective antilipocortin 1 (LC1) neutralizing antibody. 6. Treatment with the protein synthesis inhibitor, cycloheximide (10 microM, for 15 min) selectively blunted LPS-induced vasodilatation, reducing the latter to 3 +/- 5 mmHg (n = 3), while having no effect on vasodilator responses to either bradykinin or sodium nitroprusside. 7. These results indicate that LPS-induced vasodilatation in the rat heart is dependent on activation of kinin B2 receptors and synthesis of NO. In addition, phospholipase A2 (PLA2) is activated by LPS resulting in the release of platelet-activating factor (PAF) and lipoxygenase but not cyclo-oxygenase products. These effects are dependent on de novo synthesis of an intermediate protein which remains to be identified.

Pharmacology of leukotriene receptor antagonists. More than inhibitors of bronchoconstriction

The cysteinyl leukotrienes (LTs) are chemical mediators that are thought to contribute to the pathophysiologic condition of asthma and other inflammatory diseases. The biological effects of the cysteinyl LTs in the lung are pleiotropic, including both bronchoconstrictor and a growing list of nonbronchoconstrictor activities that extend to inflammatory cell recruitment, vascular leakage, mucus production, neuronal dysfunction, and airways remodeling. This spectrum of effects of cysteinyl LTs is consistent with an expanded view of asthma that extends beyond simply bronchoconstriction and inflammation. Consequently, the clinical efficacy of cysteinyl LT receptor antagonists (LTRAs) in asthma may be related to antagonism of more than cysteinyl LT-induced bronchoconstriction. The relationship of antagonism of the multiple effects of cysteinyl LTs by cysteinyl LTRAs to their utility in the therapy of asthma is addressed, and the preclinical and clinical pharmacology of cysteinyl LTRAs is reviewed.

Pharmacology of montelukast sodium (Singulair), a potent and selective leukotriene D4 receptor antagonist

Montelukast sodium (Singulair), also known as MK-0476 (1-(((1(R)-(3-(2-(7-chloro-2-quinolinyl)-(E)-ethenyl)phenyl)(3-2-(1- hydroxy-1-methylethyl)phenyl)propyl)thio)methyl)cyclopropane) acetic acid sodium salt, is a potent and selective inhibitor of [3H]leukotriene D4 specific binding in guinea pig lung (Ki 0.18 +/- 0.03 nM), sheep lung (Ki 4 nM), and dimethylsulfoxide-differentiated U937 cell plasma membrane preparations (Ki 0.52 +/- 0.23 nM), but it was essentially inactive versus [3H]leukotriene C4 specific binding in dimethylsulfoxide-differentiated U937 cell membranes (IC50 10 microM) and [3H]leukotriene B4 specific binding in THP-1 cell membranes (IC50 40 microM). Montelukast also inhibited specific binding of [3H]leukotriene D4 to guinea pig lung in the presence of human serum albumin, human plasma, and squirrel monkey plasma with Ki values of 0.21 +/- 0.08, 0.19 +/- 0.02, and 0.26 +/- 0.02 nM, respectively. Functionally, montelukast antagonized contractions of guinea pig trachea induced by leukotriene D4 (pA2 value 9.3; slope 0.8). In contrast, montelukast (16 microM) failed to antagonize contractions of guinea pig trachea induced by leukotriene C4 (45 mM serine-borate), serotonin, acetylcholine, histamine, prostaglandin D2, or U-44069. Intravenous montelukast antagonized bronchoconstriction induced in anesthetized guinea pigs by i.v. leukotriene D4 but did not block bronchoconstriction to arachidonic acid, histamine, serotonin, or acetylcholine. Oral administration of montelukast blocked leukotriene D4 induced bronchoconstriction in conscious squirrel monkeys, ovalbumin-induced bronchoconstriction in conscious sensitized rats (ED50 0.03 +/- 0.001 mg/kg; 4 h pretreatment), and also ascaris-induced early and late phase bronchoconstriction in conscious squirrel monkeys (0.03-0.1 mg/kg; 4 h pretreatment). A continuous i.v. infusion of montelukast (8 micrograms.kg-1.min-1) resulted in a 70% decrease in the peak early response and a 75% reduction of the late response to ascaris aerosol in allergic conscious sheep. Montelukast, a potent and selective leukotriene D4 receptor antagonist with excellent in vivo activity is currently in clinical development for the treatment of asthma and related diseases.

Regulation of leukotriene biosynthesis

Leukotrienes are products of arachidonic acid metabolism derived through the action of the 5-lipoxygenase enzyme pathway. Leukotriene B4 has been implicated as a mediator of inflammation through induction of leukocyte and lymphocyte activation. The cysteinyl leukotrienes are important mediators of immediate hypersensitivity reactions and initiate smooth muscle contraction. Regulation of the production of leukotrienes can be achieved either through the action of direct 5-lipoxygenase inhibitors or indirect leukotriene biosynthesis inhibitors which bind to 5-lipoxygenase activating protein. Leukotriene C4 synthase and leukotriene A4 hydrolase represent alternative enzymic targets within the biosynthetic cascade. Leukotriene receptor antagonists also have important therapeutic possibilities and in particular, leukotriene D4 receptor antagonists have shown utility in the treatment of human bronchial asthma.

Partial agonist effect of the platelet-activating factor receptor antagonists, WEB 2086 and WEB 2170, in the rat perfused heart

1. WEB 2086 and WEB 2170 are potent platelet-activating factor (PAF) receptor antagonists and have been used widely as pharmacological tools to investigate the actions of PAF in a variety of biological systems. 2. Low concentrations of WEB 2086 and WEB 2170 blocked the vasoconstrictor action of PAF in the rat perfused heart. In this study, we observed that moderate concentrations of WEB 2086 and WEB 2170 increased the perfusion pressure in rat isolated hearts under constant flow perfusion. The vasoconstrictor actions of WEB 2086 and WEB 2170 were not observed with a structurally different PAF receptor antagonist, FR-900452. 3. To determine whether this vasoconstrictor action of WEB 2086 involved non-specific effects or was via the activation of PAF receptors, hearts were pretreated with 1000 pmol PAF or 50 microM FR-900452. These pretreatments attenuated the vasoconstrictor action of 1 microM WEB 2086, suggesting that the action of WEB 2086 may be mediated via PAF receptors. Pretreatment with the leukotriene receptor antagonist (L-649,923, 5 microM) and the leukotriene synthesis inhibitor (MK-886, 10 microM) that are known to block the vasoconstrictor action of PAF receptor activation also attenuated the vasoconstrictor action of WEB 2086. Pretreatment with PAF or MK-886 attenuated the vasoconstrictor action of 0.5 microM WEB 2170. 4. When PAF receptors were activated by PAF in the perfused heart, significant amounts of leukotriene C4 and leukotriene C4/D4/E4 were detected in the coronary effluent. However, no significant amount of these leukotrienes was detected in the coronary effluent when hearts were perfused with 1 microM WEB 2086 or 0.5 microM WEB 2170. 5. In summary, our results indicate that WEB 2086 and WEB 2170 possess partial agonist effects in the rat perfused heart where they produced vasoconstriction via the activation of PAF receptor. This action could be attenuated by PAF pretreatment or a PAF receptor antagonist. The vasoconstrictor action of WEB 2086 and WEB 2170 involved the production of leukotrienes. But unlike the vasoconstrictor action of PAF, no significant amount of leukotrienes was detected in the effluent suggesting that the vasoconstrictor action of WEB 2086 and WEB 2170 may be explained on the basis of intracellularly or locally produced leukotrienes.

Phospholipase A2-induced hypotension in the rat and its pharmacological modulation

1. An increase in circulating levels of extracellular group II phospholipase A2 (PLA2) has been detected in patients with septic shock as well as in rats, rabbits and human volunteers following intravenous endotoxin administration. 2. Group II PLA2 from Naja mocambique mocambique (NajaPLA2) snake venom (1-10 micrograms i.v.) induced a dose-dependent hypotension and leucopenia in the rat similar to that induced by intravenous administration of endotoxin. 3. NajaPLA2 did not aggregate rat platelet, but did aggregate purified rat neutrophils in vitro. However intravenous PLA2 caused rat platelets to aggregate in vivo. 4. The hypotensive effect was reduced either by inactivating NajaPLA2 in vitro with para-bromophenacyl bromide or by infusing in vivo polyclonal rabbit antiPLA2 antisera. Neither the hypotension nor the leucopenia was affected by several agonists and inhibitors. 5. The leukotriene D4 antagonist L-649,923 produced a dose-related (5-20 mg/kg i.v.) inhibition of NajaPLA2-induced hypotension while the dual inhibitor of lipo- and cyclooxygenase BW755c (5-50 mg/kg i.v.) was ineffective. 6. In rats rendered leucopenic with methotrexate the L-649,923 was ineffective implying that the L-649,923 effect could be partially mediated through its action on neutrophils.

Interaction of vasoactive substances released by platelet-activating factor in the rat perfused heart

1. The coronary vascular effects of platelet-activating factor (PAF) have been intensively studied and it has been proposed that they are mediated by the release of vasoactive substances. In this study, a cascade perfusion model using two rat perfused hearts was developed to investigate the properties of PAF-released vasoactive substances and the interplay of these substances. The properties of the vasoactive substances after an injection of PAF (100 pmol) in the rat perfused heart were examined by collecting the effluent from the first heart for the perfusion of a second (recipient) heart. The presence of vasoconstrictor substances in the effluent was characterized by an increase in the perfusion pressure of the recipient heart. 2. Previous exposure of the recipient heart of PAF (100 pmol) abolished the response of the heart to subsequent administration of PAF, but did not affect the response of the recipient heart to the effluent. This suggested that the coronary vasoconstrictor response of the recipient heart was not due to the presence of PAF in the effluent but to other vasoactive substances. 3. Pretreatment of the recipient heart with the leukotriene receptor antagonist, L-649,923 (5 microM), partially reduced the vasoconstrictor effect of the effluent. Pretreatment of the first heart with indomethacin (2.8 microM) also partially reduced the vasoconstrictor effect of the effluent. The combination of indomethacin pretreatment of the first heart and L-649,923 pretreatment of the recipient heart completely abolished the vasoconstrictor effect of the effluent suggesting that both prostaglandins and leukotrienes are involved in the vasoconstrictor effect of the effluent. 4. Pretreatment of both hearts with L-649,923 or the first heart with the leukotriene synthesis inhibitor (MK-886, 10 microM) completely abolished the vasoconstrictor effect of the effluent. This suggested that the indomethacin sensitive vasoconstrictor component of the effluent might be regulated by leukotrienes in the first heart. However, infusion of leukotrienes (LTB4, LTC4 and LTD4) to the first heart did not reproduce this vasoconstrictor component of the effluent in the recipient heart.5. In conclusion, our study demonstrated through the use of a leukotriene receptor antagonist, a leukotriene synthesis inhibitor and a cyclo-oxygenase inhibitor that the vasoconstrictor effect of the effluent of the rat perfused heart after an injection of PAF is mediated by leukotrienes and prostaglandins. The ability of leukotriene receptor blockade and inhibition of leukotriene synthesis to mimic the effect of indomethacin indicates that the production and/or release of cyclo-oxygenase products in the effluent by PAF can be modulated by leukotrienes. The inability of exogenously applied leukotrienes to modulate the production and/or the release of cyclo-oxygenase products in the effluent suggests that the PAF-induced production of prostaglandins may be mediated by intracellular leukotrienes or at sites not accessible to exogenously applied leukotrienes.

Relative potencies of 5-lipoxygenase inhibitors on antigen-induced contractions of guinea pig tracheal strips

A quantitative method to assess relative potencies (IC50) of 5-lipoxygenase (5-LO) enzyme inhibitors was established in antigen-induced contractions of tracheas isolated from actively sensitized guinea pigs (Schultz-Dale model). The relative potencies of four purported 5-LO inhibitors determined in this tissue assay were compared with those from a crude enzyme preparation isolated from guinea pig neutrophils. All compounds suppressed ovalbumin (OA)-induced tracheal contractions in a concentration-related manner in the presence of indomethacin and pyrilamine. IC50 Values, determined from the percent inhibition values obtained from responses at 30 ng/mL OA of these compounds ranged from 0.56-15 microM. A similar rank order of potency for inhibition of 5-HETE formation from a crude enzyme preparation was observed. This suggested that these agents had a common mechanism of action in the two assay systems and further validated the IC50 values determined in trachea assay. LY171883, an LTD4/LTE4 receptor antagonist, also suppressed OA-induced contractions concentration dependently with an IC50 of 4.9 microM determined by this method. LTD4 concentration-response curves were not altered by any of the four 5-LO inhibitors, ruling out the possibility that these agents were acting as LT receptor antagonists. Results of this study demonstrated that relative potencies of 5-LO inhibitors can be quantitatively assessed using this airway tissue model, which helps in identifying potential therapeutic agents for asthma.

Mechanisms of the coronary vascular effects of platelet-activating factor in the rat perfused heart

1. In a previous study it was demonstrated that bolus injections of platelet-activating factor (PAF) in the rat perfused heart resulted in coronary vasodilatation, vasoconstriction or the combination of both, depending on the amount of PAF that was injected. In the present study, the mechanisms of these coronary vascular effects of PAF in the rat perfused heart were investigated. 2. Pretreatment of the rat perfused heart with the PAF antagonists FR-900452 or BN-52021 did not affect the vasodilator effect of PAF but eliminated the vasoconstrictor effect of PAF. FR-900452 had no effect on the vasoconstrictor response to leukotriene C4 (LTC4) or LTD4. 3. The cyclo-oxygenase inhibitor, indomethacin, did not modify the coronary vascular effects of PAF. However L-649,923 (a leukotriene antagonist) and MK-886 (a leukotriene synthesis inhibitor) eliminated both the vasodilator and vasoconstrictor effects of PAF. 4. When leukotrienes were administered by bolus injection in the rat perfused heart, LTB4 produced vasodilatation while LTC4 and LTD4 produced vasoconstriction. L-649,923 blocked both the vasodilator and vasoconstrictor effects of the leukotrienes tested. 5. The results suggest that lipoxygenase products are responsible for both the vasodilator and vasoconstrictor actions of PAF in the coronary vasculature of the rat perfused heart while the cyclo-oxygenase products do not play a significant role. The ineffectiveness of PAF antagonists in blocking the vasodilatation produced by PAF is compatible with the concept that there may be multiple PAF receptors.

Effects of leukotrienes on susceptibility of the rat stomach to damage and investigation of the mechanism of action

The ability of various leukotrienes to alter the susceptibility of the rat gastric mucosa to injury by 20% ethanol and the possible mechanism of action were examined using an ex vivo gastric chamber preparation. Intraarterial infusions of leukotriene B4 or N-acetyl leukotriene E4 (0.01-1.0 microgram/kg per min for 10 min) had no significant effect on the extent of damage induced by topically applied 20% ethanol. However, infusion of leukotriene C4, D4, or E4 (1.0 micrograms/kg per min) significantly increased ethanol-induced damage, as measured macroscopically, histologically, and functionally. Lower doses of leukotriene C4, D4, or E4 were without significant effect in this model. The increase in damage induced by these three leukotrienes could be blocked by pretreatment with either of two structurally unrelated leukotriene D4 antagonists (L-649,923 or L-660,711). The augmentation of damage by leukotriene C4 was not affected by pretreatment with indomethacin or with a specific thromboxane A2-receptor antagonist (L-670,596). At the dose that increased ethanol-induced damage, none of the leukotrienes tested significantly altered gastric vascular permeability, as measured by Evan's blue leakage. However, using laser-Doppler flowmetry, leukotrienes C4 and D4 were found, when administered intraarterially at doses in the 0.05-1.0 micrograms/kg per min range, to produce dose-dependent reductions of gastric blood flow while N-acetyl leukotriene E4 was without effect and leukotriene B4 induced slight increases. The effects of leukotrienes C4 and D4 on gastric blood flow could be inhibited by the two leukotriene D4 antagonists but not by the thromboxane antagonist. These results demonstrate that although they do not produce damage by themselves, leukotrienes C4, D4, and E4 are capable of augmenting ethanol-induced injury to the gastric mucosa. Changes in vascular permeability do not appear to play a role in the mechanism of action of the leukotrienes, while their effects on gastric blood flow are likely to be important. Under certain condition it is therefore possible that local release of leukotrienes could, at least in part through reducing vascular perfusion, predispose the surrounding tissue necrosis.

The effect of a leukotriene antagonist on the early response to antigen

The sulfidopeptide leukotrienes (LT) C4, D4, and E4 increase in nasal secretions during the nasal response to antigen challenge, and nasal challenge with LTD4 induces nasal congestion. To further assess the role of leukotrienes, we administered an oral LTD4 antagonist, L-649,923, to 12 patients who had nasal allergy to grass and ragweed pollen, in a double-blind, placebo-controlled, crossover study. Patients were challenged intranasally with increasing doses of pollen on each of 2 days, and the recovered nasal lavage fluids were assayed for histamine, TAME-esterase activity, and immunoreactive LTC4/D4/E4. The patients graded runny nose, congestion, and throat irritation, and sneezes were counted. Significant (p less than 0.01) increases in all parameters were found when comparing antigen challenge with diluent challenge, but no differences were seen among the treatment groups. Thus, oral L-649,923 was not effective in blocking the symptoms of the early nasal allergic response.

A study of phospholipase A2-induced oedema in rat paw

The inflammaogenic action of four extracellular phospholipases A2 was tested in the rat paw oedema model. Subplantar injection of microgram amounts of the venom phospholipases A2 from Vipera russeli, Naja mocambique mocambique and honey bee, or the porcine enzyme produced a rapid but transient oedematous response. The venom enzyme from Vipera was the most potent in this respect, the pancreatic enzyme the least. Pretreatment of the enzymes with para-bromophenacylbromide profoundly inhibited the ability of the enzymes to produce oedema. The inflammatory response produced by the phospholipases was insensitive to indomethacin, BW755C or the LTD4 antagonist L649,923 but was inhibited by the local administration of methysergide or, by pretreatment of the rats with dexamethasone. The PAF-antagonist BN 52021, but not WEB2086, was an effective inhibitor. Degranulation of mast cells seem the most likely explanation for the inflammatory action of these enzymes in the rat paw.

L-648,051, a novel cysteinyl-leukotriene antagonist is active by the inhaled route in man

1. We have studied some of the pharmacological properties of inhaled L-648,051 which has been shown to be a selective cysteinyl-leukotriene (LT) antagonist in vitro and in vivo in various animal models. 2. The effects of three different doses (1.6, 6.0 and 12.0 mg) on the bronchoconstriction induced by inhaled LTD4 have been investigated in normal male subjects in a series of double-blind, placebo controlled studies. Furthermore, the specificity of the drug has been investigated by challenging subjects with histamine after pre-inhalation of 12.0 mg L-648,051. 3. At all doses L-648,051 partially blocked the bronchoconstriction induced by LTD4 inhalation in a dose related manner. At a dose of 12.0 mg, L-648,051 decreased the maximum fall in specific airways conductance (sGaw) (placebo, 49% vs L-648,051, 21%, P less than 0.01) and shortened the time to recovery from LTD4-induced bronchoconstriction (placebo, 41 min vs L-648,051, 19 min, P less than 0.01). 4. There was no evidence of partial agonist activity, and no effect on histamine-induced bronchospasm. Inhaled L-648,051 at all doses was well tolerated. 5. We conclude that LT antagonism is possible by the inhaled route in man. Inhaled L-648,051 is an active and selective LT-antagonist in man which is well tolerated and may prove to be a useful drug for assessing the role of leukotrienes in asthma and other lung diseases.

Wy-48,252 (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl]methane sulfonamide) an orally active leukotriene D4 antagonist: pharmacological characterization in vitro and in vivo in the guinea pig

The following communicates the pharmacology of Wy-48,252 (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl]methanesulfonamide) a chemically novel and orally potent leukotriene (LT) D4 receptor antagonist. In the isolated guinea-pig trachea pretreated with indomethacin (5 microM) and L-cysteine (10 mM), Wy-48,252 antagonized TD4-induced contraction with a pKB = 7.6. Against LTC4 on tissues pretreated with IND and glutathione (10 mM), Wy-48,252 had a pKB greater than 5. Wy-48,252 (10 microM) did not antagonize pilocarpine-, histamine- or PGF2 alpha-induced tracheal contraction. Further, in the presence of indomethacin and chlorpheniramine (1 microM), Wy-48,252 dose-dependently inhibited the antigen-induced contraction of guinea-pig trachea in a manner consistent with antagonism at the LTD4 receptor and inhibition of LT synthesis. In the Konzett-Rossler model of i.v. LTD4-induced bronchoconstriction in indomethacin treated guinea pigs, intragastric Wy-48,252 (2 hr) had an ID50 of 100 micrograms/kg and a functional half-life of 5 hr. Against i.v. antigen-induced bronchoconstriction in guinea pigs treated with indomethacin and chlorpheniramine, intragastric Wy-48,252 (2 hr) had an ID50 of 0.6 mg/kg and a 5 hr half life. Intragastric Wy-48,252 also selectively blocked the cutaneous wheal reaction to intradermal LTD4 but not histamine. We conclude that Wy-48,252 is distinguished from other selective LTD4 receptor antagonists by its oral potency and should be useful in ascertaining the role of LTD4 mediated processes in asthma, allergy and animal models.

Leukotriene-D4 induced cell shrinkage in Ehrlich ascites tumor cells

The nature of the leukotriene-D4 (LTD4) induced cell shrinkage in Ehrlich ascites tumor cells has been investigated. LTD4 treatment of Ehrlich cells induces net loss of cellular KCl and cell shrinkage independent of the initial cell volume. LTD4 also produces water loss and reduction in cell volume when all extracellular and all intracellular Cl has been replaced by NO3. On the other hand, LTD4 fails to produce any significant changes in cell volume in the presence of the K-channel blocker quinine, suggesting that LTD4 in Ehrlich cells induces Cl-independent K loss through the Ca2+-dependent K channels. However, the effect of physiological doses of LTD4 on cell volume seems not to be as potent in Cl-free, NO3 cells when compared to Cl-containing cells, indicating that LTD4 in Ehrlich cells also provokes Cl-dependent K loss. LTD4 seems not to produce K loss through an electroneutral K+/H+ exchange system. LTD4 still produces Cl-independent K loss and cell shrinkage in the presence of the anti-calmodulin drug pimozide but not in the presence of the LTD4 receptor antagonist L-649,923 or the 5-lipoxygenase inhibitor NDGA. Pretreatment of the cells with pertussis toxin, which inactivates inhibitory guanine nucleotide binding proteins (G-proteins), leads to partial inhibition of the LTD4-induced shrinkage. It is suggested that the LTD4-induced activation of K and Cl transporting systems in Ehrlich ascites tumor cells is mediated via a G-protein coupled receptor and that LTD4 might exert its effect through another lipoxygenase product. The Ca2+-calmodulin complex is not involved in the LTD4-induced activation of K and Cl transporting systems.

Effects of leukotriene D4, the antagonist L-649-923, and arachidonic acid on duodenal bicarbonate secretion in the rat in vivo

Prostaglandins of the E type stimulate bicarbonate secretion by the duodenal mucosa and inhibit gastric acid secretion, effects that have been related to their anti-ulcer activity. Leukotrienes constitute a more recently discovered branch of the arachidonic acid cascade, and C4 and D4 have been suggested to be ulcerogenic in the stomach. We have studied the effects of luminal administration of leukotriene D4 and the leukotriene C4/D4 antagonist L-649-923 on duodenal mucosal alkaline secretion in the anaesthetized rat. Leukotriene D4 (10(-8)-10(-6) M) had no significant effects, but the antagonist dose-dependently increased the bicarbonate secretion and also transiently increased the transmucosal electric potential difference. The precursor arachidonic acid (10(-7)-10(-6) M) caused a small increase in secretion. The increase in bicarbonate secretion in response to 10(-3) M of the antagonist was of about the same magnitude as that observed with 10(-5) of prostaglandin E2, and it was abolished by pretreatment with the cyclooxygenase inhibitor indomethacin. The gastroduodenal protective effects of L-649-923 in vivo may reflect an increase in mucosal prostaglandin production rather than leukotriene antagonism.

Thyroid and liver trophic changes in rats secondary to liver microsomal enzyme induction caused by an experimental leukotriene antagonist (L-649,923)

Thyroid hyperplasia and/or hepatomegaly were observed in a 14-week oral toxicity study with L-649,923, a leukotriene antagonist, at doses of 50 and 150 mg/kg/day. In a 16-day study, L-649,923 caused an increase in plasma TSH and hepatic enzyme induction, but did not affect plasma T3 and T4 levels. Light microscopy and ultrastructural examination of the liver and thyroid showed changes indicative of hepatic enzyme induction and increased stimulation of the thyroid by TSH. Because other hepatic enzyme inducers cause thyroid hyperplasia by increasing the turnover of plasma T3 and T4 it was hypothesized that L-649,923-induced thyroid hyperplasia might be occurring by the same mechanism. To examine this theory, rats were treated po with 300 mg/kg/day of L-649,923 for 17 days. On Day 15, all rats were dosed iv with [125I]thyroxine (33 microCi/rat). At various times after dosing, blood was collected and plasma levels of 125I were determined. The clearance and elimination rate constant were significantly larger in treated animals than in the control group (p less than 0.01). This work demonstrates that L-649,923 increases the plasma turnover of thyroxine which is associated with a stimulation of TSH and thyroid hyperplasia.

Antigen-induced contraction of guinea-pig isolated trachea: studies with novel inhibitors and antagonists of arachidonic acid metabolites

1. Responses of antigen-challenged isolated trachea from sensitized guinea-pigs were pharmacologically characterized by use of some novel inhibitors and antagonists of arachidonic acid metabolites. 2. The cyclo-oxygenase inhibitor, indomethacin, prolonged without altering the maximum response to antigen in the absence of the anti-muscarinic agent, atropine, and/or the H1-receptor blocker, mepyramine. In the presence of mepyramine, indomethacin both prolonged and increased the magnitude of the response. The selective (SQ-29548) and non-selective (L-640,035) thromboxane A2 (TXA2) antagonist and the TXA2 synthetase inhibitor, OKY-046, were essentially inactive. 3. Two novel inhibitors of 5-lipoxygenase product formation, AA-861 and L-651,896 produced complete inhibition of the response to antigen on tissues treated with atropine and mepyramine, with or without indomethacin. 4. Equimolar concentrations of the leukotriene D4 (LTD4) receptor antagonists LY-171883 greater than L-649,923 greater than or equal to L-648,051 greater than or equal to FPL-55712 blocked part of the response to antigen on tissues treated with atropine, mepyramine and indomethacin. All compounds tended to block a larger component of the response in the absence of indomethacin. A similar tendency was observed with the potent phosphodiesterase inhibitor, isobutylmethylxanthine (IBMX) but not the less potent phosphodiesterase inhibitor theophylline. 5. These results are consistent with the hypothesis that 5-lipoxygenase products acting on LTD4 receptors play only a minor role in the mediation of the contraction of guinea-pig trachea to antigen challenge. The nature of the residual contractile mediator is unknown; however, it can be completely blocked by the 5-lipoxygenase inhibitors AA-861 and L-651,896 and non-selectively blocked by the phosphodiesterase inhibitor, IBMX and non-selective LTD4 receptor antagonists, such as LY-171883.

U19052 (ICIAm): a novel leukotriene analog which antagonizes LTC4, LTD4, and LTE4

Chemically stable analogs of peptide leukotrienes (LT) have been developed in our laboratories by replacement of the natural triene backbone with a C7H15 substituted aromatic moiety (1). These analogs are potent agonists of airway smooth muscle. Substitution in the peptide region resulted in U19052, an LT receptor antagonist. U19052 antagonized LT-induced contractions of guinea-pig tracheal spirals in a concentration-related manner. The pA2 values versus LTD4 and LTE4 were 6.0 and 5.7, respectively, with slopes which were not significantly different from unity. LTC4-induced contractions were antagonized by U19052 with a pKB of 5.6 obtained either in the absence or presence of L-serine borate. In contrast, carbachol and histamine concentration-response curves were not altered by U19052. LTD4 or LTE4 contractions of isolated guinea-pig ileum were antagonized by U19052 with pKB values of 7.2. The results indicate that potent selective LT antagonists can be developed from stable analogs of leukotrienes. U19052, an example of this series, appears to be as effective in antagonizing LTC4- as well as LD4- and LTE4-induced contractions in guinea-pig tracheal spirals.

Effects of non-steroidal anti-inflammatory drugs on rat gastric mucosal leukotriene C4 and prostanoid release: relation to ethanol-induced injury

1. The effects of oral and subcutaneous administration of the non-steroidal anti-inflammatory drugs sodium salicylate, aspirin and indomethacin on ex vivo gastric mucosal release of leukotriene C4 (LTC4) prostaglandin E2 (PGE2), 6-oxo-PGF1 alpha and thromboxane B2 (TXB2) were investigated in rats under basal conditions as well as after challenge with ethanol. 2. Basal release of PGE2, 6-oxo-PGF1 alpha and TXB2 was inhibited by oral administration of aspirin (0.6-400 mgkg-1) and indomethacin (4 or 20 mgkg-1), but not by sodium salicylate (up to 400 mgkg-1), in a dose-dependent manner. Oral administration of aspirin in the dose range 3.2-400 mgkg-1 and of indomethacin (20 mgkg-1) additionally inhibited release of LTC4, while sodium salicylate (up to 400 mgkg-1) had no effect. Indomethacin (20 mgkg-1) and aspirin (400 mgkg-1) administered subcutaneously inhibited generation of cyclo-oxygenase products of arachidonate metabolism, but did not significantly affect LTC4 synthesis. 3. Oral instillation of ethanol caused gastric mucosal damage and simultaneously induced a selective increase in the ex vivo release of LTC4 from rat gastric mucosa, while release of cyclo-oxygenase products of arachidonate metabolism was not significantly affected. Oral pretreatment of rats with sodium salicylate protected the gastric mucosa and simultaneously inhibited the ethanol-stimulated gastric mucosal LTC4 release in a dose-dependent manner. Sodium salicylate had no effects on the release of PGE2 and TXB2, while that of 6-oxo-PGF1 alpha was slightly increased. 4. Pretreatment with indomethacin (4 or 20mg kg- p.o.) or aspirin in doses up to 25mg kg-1 p.o. prior to oral instillation of ethanol did not inhibit gastric mucosal damage and had no effect on the stimulatory action of ethanol on LTC4 release. Higher doses of aspirin (100mgkg-1 or 400mgkg-1 p.o.) reduced the mucosal damaging effect of ethanol and simultaneously inhibited LTC4 release. 5. The results suggest that aspirin and indomethacin in concentrations higher than those necessary to inhibit the cyclo-oxygenase pathway of arachidonate metabolism additionally inhibit gastric mucosal LTC4 synthesis under basal conditions, while sodium salicylate has no such effect. On the other hand, sodium salicylate, but not indomethacin or low doses of aspirin (up to 25mg kg 1), by an unknown mechanism inhibits stimulation of LTC4 biosynthesis by ethanol and simultaneously protects the gastric mucosa against ethanol-induced damage. Similar effects of high oral doses (> 100mgkg- 1) of aspirin might be due to significant formation of salicylate. These results suggest that there is a causal relationship between enhanced LTC4 biosynthesis and the development of ethanol-induced gastric injury.

L-648,051, a potent and specific aerosol active leukotriene D4 antagonist

L-648,051 (I) is a potent, competitive and selective antagonist of the leukotriene D4 receptor in guinea pig and human lung tissue. Its activity on isolated smooth muscle preparations and its superiority relative to other agents (L-649,923 (II) or FPL 55712) in reversing ongoing contraction to LTD4 was somewhat unexpected in light of the results of receptor binding studies (Ki = 6.2 microM for L-648,051 versus 0.4 microM for L-649,923 and 2.0 microM for FPL 55712 on guinea pig lung membranes). The reasons for this observed superiority are unknown but may relate to the rate at which various antagonists equilibrate with the leukotriene receptors on various tissues. The physical properties (polarity) of L-648,051 may contribute to this enhanced rate of equilibration. The rapid metabolism and elimination of L-648,051 in vivo should be an advantage for a topical agent by minimizing systemic exposure. The potential role for L-648,051 as a novel aerosol therapy for asthma is now being investigated.

Inhibition of allergen-induced bronchoconstriction in hyperreactive rats as a model for testing 5-lipoxygenase inhibitors and leukotriene D4 receptor antagonists

Sensitized inbred hyperreactive rats showed reproducible episodes of dyspnea when exposed to aerosols of antigen. Following inhibition of the serotonin component of the response by pretreatment with methysergide, the model was shown to be useful for studying the oral activity of compounds that affect the production or action of leukotrienes. This was shown through inhibition of the duration of dyspnea by two selective 5-lipoxygenase inhibitors, L-651,392 and L-615,919, and two selective leukotriene D4 receptor antagonists, L-647,438 and L-649,923. Selectivity of the compounds could be demonstrated by reducing inhibition of the antigen response in the absence of methysergide and failure to inhibit serotonin-induced dyspnea. It is concluded that the model provides a reproducible method for screening large numbers of leukotriene inhibitors and antagonists and gives a measurement of their duration of biological activity.

Isolated tissue and binding studies of YM-17690, a novel and non-analogous leukotriene agonist

YM-17690, 3-[4-carboxymethoxy-3-[p-(4-phenylbutoxy) benzamido]phenyl]propionic acid, produced a dose-dependent contraction of guinea-pig ileum and its EC50 value was 1.6 X 10(-8) M. The response was not affected by pretreatment with atropine, mepyramine, indomethacin, dazoxiben and AA-861 (a 5-lipoxygenase inhibitor), but was inhibited by FPL-55712 (an LTD4 and LTE4 antagonist). YM-17690 induced dose-dependent contractions of guinea-pig lung parenchyma and trachea with EC50 values of 3.9 X 10(-9) and 2.2 X 10(-8) M, respectively. Pretreatment of these tissues with FPL-55712 resulted in a parallel shift of the YM-17690 dose-response curves to the right. The pA2 values for FPL-55712 in lung parenchyma and trachea were 7.41 and 8.21, respectively, and the slopes of the regression lines of Schild plots were 1.00 and 1.02, respectively. YM-17690 produced a dose-dependent inhibition of [3H]LTD4 binding to guinea-pig lung membranes and its pKi value was 9.28. However, the compound showed only 25% inhibition of [3H]TLC4 binding to guinea-pig hippocampus membranes, even at 10(-5) M. These results suggest that YM-17690 is a selective leukotriene (LTD4 and LTE4) agonist and that it will therefore be a valuable tool in the study of actions of leukotrienes and for the characterization of their receptors.

Effects of L-serine borate on antagonism of leukotriene C4-induced contractions of guinea-pig trachea

The antagonist activity of three leukotriene D4 (LTD4) receptor antagonists and a number of bronchodilators was determined against LTC4-induced contractions of guinea-pig isolated tracheal chains in the absence and presence of the gamma-glutamyltranspeptidase inhibitor, L-serine borate (SB). The LTD4 receptor antagonists FPL-55712, L-649,923 and L-648,051 effectively antagonized LTC4 responses in the absence of SB but were ineffective in the presence of 15 and/or 45 mM SB. Salbutamol greater than isobutylmethylxanthine (IBMX) greater than dibutyryl cyclic AMP greater than aminophylline greater than nifedipine antagonized contractions to LTC4 in the absence of SB. In contrast, in the presence of SB the antagonist activity of all of these agents except nifedipine was significantly reduced. The antagonist activity of the Ca2+ entry blocker, nifedipine, was similar in the absence and presence of SB. Salbutamol and IBMX were potent functional antagonists of LTE4-induced contractions both in the absence and presence of SB. These results are consistent with the hypothesis that there are contractile LTC4 receptor mechanisms in guinea-pig trachea which are unmasked by SB and are not blocked by LTD4 receptor antagonists and which are less effectively down modulated by cyclic AMP-dependent bronchodilators.

The role of leukotriene D4 as a mediator of allergic conjunctivitis in the guinea-pig

The role of leukotriene D4 (LTD4) as a mediator of conjunctival microvascular permeability changes associated with immediate hypersensitivity reactions in the guinea-pig conjunctiva has been investigated using two novel, selective LTD4 receptor antagonists, L-648,051 and L-649,923. Changes in microvascular permeability were measured through the accumulation of [99mTc]albumin. LTD4 administered intravenously produced dose-related increases in conjunctival microvascular permeability through a mechanism which does not involve the generation of prostaglandins as indicated by the failure of indomethacin to attenuate the response. The response to LTD4 was significantly blocked by the receptor antagonists, L-648,051 and L-649,923. Topical application of antigen (either single challenge or 2 challenges separated by 24 h) to the eyes of sensitized guinea-pigs caused significant increases in conjunctival microvascular permeability. Following a single challenge, the antigen response was largely blocked by mepyramine (H1 receptor antagonist), but was unaffected by L-648,051 and L-649,923. Following a second challenge (24 h later) a substantial portion of the response was inhibited by L-648,051 and L-649,923. Indomethacin failed to inhibit either challenge. These results suggest that LTD4 may have a role in chronic allergic conjunctivitis.