The 5-lipoxygenase inhibitor zileuton blocks antigen-induced late airway responses, inflammation and airway hyperresponsiveness in allergic sheep

High ability of zileuton ((±)-1-(1-benzo[b]thien-2-ylethyl)-1-hydroxyurea) to stimulate IK(Ca) but suppress IK(DR) and IK(M) independently of 5-lipoxygenase inhibition

Zileuton (Zyflo®) is regarded to be an inhibitor of 5-lipoxygenase. Although its effect on Ca²⁺-activated K⁺ currents has been reported, its overall ionic effects on neurons are uncertain. In whole-cell current recordings, zileuton increased the amplitude of Ca²⁺-activated K⁺ currents with an EC₅₀ of 3.2 μM in pituitary GH₃ lactotrophs. Furthermore, zileuton decreased the amplitudes of both delayed-rectifier K⁺ current (I_K(DR)) and M-type K⁺ current (I_K(M)). Conversely, no modification of hyperpolarization-activated cation current (I_h) was demonstrated in its presence of zileuton, although the subsequent addition of cilobradine effectively suppressed the current. In inside-out current recordings, the addition of zileuton to the bath increased the probability of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels; however, the subsequent addition of GAL-021 effectively reversed the stimulation of channel activity. The kinetic analyses showed an evident shortening in the slow component of mean closed time of BK_Ca channels in the presence of zileuton, with minimal change in mean open time or that in the fast component of mean closed time. The elevation of BK_Ca channels caused by zileuton was also observed in hippocampal mHippoE-14 neurons, without any modification of single-channel amplitude. In conclusion, except for its suppression of 5-lipoxygenase, our results indicate that zileuton does not exclusively act on BK_Ca channels, and its inhibitory effects on I_K(DR) and I_K(M) may combine to exert strong influence on the functional activities of electrically excitable cells in vivo.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

Inhibition of allergic airway responses by heparin derived oligosaccharides: identification of a tetrasaccharide sequence

Background

Previous studies showed that heparin's anti-allergic activity is molecular weight dependent and resides in oligosaccharide fractions of <2500 daltons.

Objective

To investigate the structural sequence of heparin's anti-allergic domain, we used nitrous acid depolymerization of porcine heparin to prepare an oligosaccharide, and then fractionated it into disaccharide, tetrasaccharide, hexasaccharide, and octasaccharide fractions. The anti-allergic activity of each oligosaccharide fraction was tested in allergic sheep.

Methods

Allergic sheep without (acute responder) and with late airway responses (LAR; dual responder) were challenged with Ascaris suum antigen with and without inhaled oligosaccharide pretreatment and the effects on specific lung resistance and airway hyperresponsiveness (AHR) to carbachol determined. Additional inflammatory cell recruitment studies were performed in immunized ovalbumin-challenged BALB/C mice with and without treatment.

Results

The inhaled tetrasaccharide fraction was the minimal effective chain length to show anti-allergic activity. This fraction showed activity in both groups of sheep; it was also effective in inhibiting LAR and AHR, when administered after the antigen challenge. Tetrasaccharide failed to modify the bronchoconstrictor responses to airway smooth muscle agonists (histamine, carbachol and LTD₄), and had no effect on antigen-induced histamine release in bronchoalveolar lavage fluid in sheep. In mice, inhaled tetrasaccharide also attenuated the ovalbumin-induced peribronchial inflammatory response and eosinophil influx in the bronchoalveolar lavage fluid. Chemical analysis identified the active structure to be a pentasulfated tetrasaccharide ([IdoU2S (1→4)GlcNS6S (1→4) IdoU2S (1→4) AMan-6S]) which lacked anti-coagulant activity.

Conclusions

These results demonstrate that heparin tetrasaccharide possesses potent anti-allergic and anti-inflammatory properties, and that the domains responsible for anti-allergic and anti-coagulant activity are distinctly different.

Pharmacology of PF-4191834, a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain

5-Lipoxygenase (LOX) is an important arachidonic acid-metabolizing enzyme producing leukotrienes and other proinflammatory lipid mediators with potent pathophysiological functions in asthma and other inflammatory diseases. 4-(3-(4-(1-Methyl-1H-pyrazol-5-yl)phenylthio)phenyl)-tetrahydro-2H-pyran-4-carboxamide (PF-4191834) is a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain. In vitro and in vivo assays were developed for the evaluation of a novel 5-LOX inhibitor using conditions of maximal enzyme activity. PF-4191834 exhibits good potency in enzyme- and cell-based assays, as well as in a rat model of acute inflammation. Enzyme assay results indicate that PF-4191834 is a potent 5-LOX inhibitor, with an IC(50) = 229 +/- 20 nM. Furthermore, it demonstrated approximately 300-fold selectivity for 5-LOX over 12-LOX and 15-LOX and shows no activity toward the cyclooxygenase enzymes. In addition, PF-4191834 inhibits 5-LOX in human blood cells, with an IC(80) = 370 +/- 20 nM. This inhibitory concentration correlates well with plasma exposures needed for in vivo efficacy in inflammation in models of inflammatory pain. The combination of potency in cells and in vivo, together with a sustained in vivo effect, provides PF-4191834 with an overall pharmacodynamic improvement consistent with once a day dosing.

Optimization and structure-activity relationship of a series of 1-phenyl-1,8-naphthyridin-4-one-3-carboxamides: identification of MK-0873, a potent and effective PDE4 inhibitor

A SAR study of a series of 1-phenyl-1,8-naphthyridin-4-one-3-carboxamides is described. Optimization of the series was based on in vitro potency against PDE4, inhibition of the LPS-induced production of TNF-alpha in human whole blood and minimizing affinity for the hERG potassium channel. From these studies, compounds 18 and 20 (MK-0873) were identified as optimized PDE4 inhibitors with good overall in vitro and in vivo profiles and selected as development candidates.

Indole cytosolic phospholipase A2 alpha inhibitors: discovery and in vitro and in vivo characterization of 4-{3-[5-chloro-2-(2-{[(3,4-dichlorobenzyl)sulfonyl]amino}ethyl)-1-(diphenylmethyl)-1H-indol-3-yl]propyl}benzoic acid, efipladib

The optimization of a class of indole cPLA 2 alpha inhibitors is described herein. The importance of the substituent at C3 and the substitution pattern of the phenylmethane sulfonamide region are highlighted. Optimization of these regions led to the discovery of 111 (efipladib) and 121 (WAY-196025), which are shown to be potent, selective inhibitors of cPLA 2 alpha in a variety of isolated enzyme assays, cell based assays, and rat and human whole blood assays. The binding of these compounds has been further examined using isothermal titration calorimetry. Finally, these compounds have shown efficacy when dosed orally in multiple acute and chronic prostaglandin and leukotriene dependent in vivo models.

Interspecies in vitro metabolism of the phosphodiesterase-4 (PDE4) inhibitor L-454,560

L-454,560 is a potent phosphodiesterase 4 (PDE4) inhibitor which was identified as a development candidate for the treatment of asthma and chronic obstructive pulmonary disease (COPD). As part of the discovery of this compound, interspecies in vitro metabolism data was generated using liver microsomes and hepatocytes in order to understand the metabolic fate of the compound. In microsomes, metabolism of the 3-methyl-1,2,4-oxadiazole ring was the predominant pathway observed, including ring cleavage. In rat hepatocytes, hydroxylation of the methyl group on the oxadiazole ring and double-bond isomerization were the most abundant metabolites observed. No major species differences were found in terms of microsomal metabolite profiles. The use of LC with UV and MS detection is highlighted, as well as information from tandem mass spectrometry and NMR.

Discovery of a substituted 8-arylquinoline series of PDE4 inhibitors: Structure–activity relationship, optimization, and identification of a highly potent, well tolerated, PDE4 inhibitor

The discovery and SAR of a new series of substituted 8-arylquinoline PDE4 inhibitors are herein described. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of emesis to efficacy in several animal models. Typical optimized compounds from this series are potent inhibitors of PDE4 (IC(50)<1nM) and also of LPS-induced TNF-alpha release in human whole blood (IC(50)<0.5microM). The same compounds are potent inhibitors of ovalbumin-induced bronchoconstriction in conscious guinea pigs (EC(50)<0.1mg/kg ip) but require a dose of about 10mg/kg po in the squirrel monkey to produce an emetic response. From this series of compounds, 23a (L-454,560) was identified as an optimized compound.

IPL576,092, a novel anti-inflammatory compound, inhibits leukocyte infiltration and changes in lung function in response to allergen challenge

IPL576,092, a lead compound from a novel class of polyhydroxylated sterols, was tested in models of allergen-induced bronchoconstriction and airway inflammation. In a rat ovalbumin lung inflammation model, orally administered IPL576,092 significantly inhibited the challenge-mediated increase in total bronchoalveolar lavage leukocyte numbers, and macrophage and lymphocyte infiltration (1-10 mg/kg/day). There was a similar trend towards inhibition of eosinophil and neutrophil accumulation. Sheep were treated with IPL576,092 by inhalation (400 microg/kg/day), and lung resistance and airway hyper-responsiveness (AHR) were determined after Ascaris suum challenge. IPL576,092 significantly reduced the early and late phase bronchoconstrictor responses by 63+/-4.6 and 84+/-4.6%, respectively. IPL576,092 also blocked AHR (2.2+/-5.7% change from pre-challenge PC400), whereas control animals showed a 62.2+/-2.6% decrease in the PC400 (p<0.05). Oral IPL576,092 (5 mg/kg/day) also significantly decreased hyper-reactivity in mice. In a guinea pig model, IPL576,092 (5 mg/kg/day) significantly protected against allergen-induced increases in lung resistance (11.4+/-2.3 control versus 4.8+/-01.5 IPL576,092, area under the curve) and inhibited the increase in lung elastance (280+/-58 control versus 167+/-52 IPL576,092, p<0.05). IPL576,092, unlike dexamethasone, did not significantly decrease rat serum corticosterone levels or thymus and spleen weights, supporting a mechanism of action different from classic glucocorticoids. IPL576,092 significantly attenuates characteristics of an asthmatic response, indicating therapeutic potential for this drug class.

Optimization of a tertiary alcohol series of phosphodiesterase-4 (PDE4) inhibitors: structure-activity relationship related to PDE4 inhibition and human ether-a-go-go related gene potassium channel binding affinity

A SAR study on the tertiary alcohol series of phosphodiesterase-4 (PDE4) inhibitors related to 1 is described. In addition to inhibitory potency against PDE4 and the lipopolysaccharide-induced production of TNFalpha in human whole blood, the binding affinity of these compounds for the human ether-a-go-go related gene (hERG) potassium channel (an in vitro measure for the potential to cause QTc prolongation) was assessed. Four key structural moieties in the molecule were studied, and the impact of the resulting modifications in modulating these activities was evaluated. From these studies, (+)-3d (L-869,298) was identified as an optimized structure with respect to PDE4 inhibitory potency, lack of binding affinity to the hERG potassium channel, and pharmacokinetic behavior. (+)-3d exhibited good in vivo efficacy in several models of pulmonary function with a wide therapeutic index with respect to emesis and prolongation of the QTc interval.

Substituted 2-pyridinemethanol derivatives as potent and selective phosphodiesterase-4 inhibitors

The synthesis and the phosphodiesterase-4 (PDE4) inhibitory activity of 2-pyridinemethanol derivatives is described. The evaluation of the structure-activity relationship (SAR) in this series of novel PDE4 inhibitors led to the identification of compound 9 which exhibits excellent in vitro activity, desirable pharmacokinetic parameters and good efficacy in animal models of bronchoconstriction.

Substituted aminopyridines as potent and selective phosphodiesterase-4 inhibitors

The synthesis and the biological evaluation of new potent phosphodiesterase type 4 (PDE4) inhibitors are presented. This new series was elaborated by replacement of the metabolically resistant phenyl hexafluorocarbinol of L-791,943 (1) by a substituted aminopyridine residue. The structure-activity relationship of N-substitution on 3 led to the identification of (-)-3n which exhibited a good PDE4 inhibitor activity (HWB-TNFalpha=0.12 microM) and an improved pharmacokinetic profile over L-791,943 (rat t(1/2)=2 h). (-)-3n was well tolerated in ferret with an emetic threshold of 30 mg/kg (po) and was found to be active in the ovalbumin-induced bronchoconstriction model in guinea pig (54%, 0.1 mg/kg, ip) as well as the ascaris-induced bronchoconstriction model in sheep (64%/97%, early/late, 0.5 mg/kg, iv).

Substituted 4-(2,2-diphenylethyl)pyridine-N-oxides as phosphodiesterase-4 inhibitors: SAR study directed toward the improvement of pharmacokinetic parameters

A detailed SAR study directed toward the optimization of pharmacokinetic parameters for analogues of L-791,943 is reported. The introduction of a soft metabolic site on this structure permitted the identification of L-826,141 as a potent phosphodiesterase type 4 (PDE4) inhibitor that is well absorbed and that presents a shorter half-life than L-791,943 in a variety of animal species. The efficacy of L-826,141 is also demonstrated in different in vivo models.

Mediators of adenosine- and ovalbumen-induced bronchoconstriction of sensitized guinea-pig isolated airways

The mediators of bronchoconstriction of isolated lungs and trachea from ovalbumen sensitized guinea-pigs to adenosine and ovalbumen were examined using relevant antagonists. Changes in perfusion pressure and tension of paired lung halves and tracheal spiral strips, respectively, were recorded in response to adenosine (1 mM lung, 300 microM trachea), histamine (10 microM), methacholine (10 microM) and ovalbumen (10 microg). One half was perfused with antagonist while the other received vehicle. Tracheal strips were superfused throughout with the P(1) receptor antagonist 8-phenyltheophylline, to examine 8-phenyltheophylline-resistant responses. The histamine H(1) receptor antagonist, mepyramine (1.5 mM), the cyclooxygenase inhibitors, indomethacin (5 mM) and diclofenac (5 mM), the leukotriene receptor antagonist, zafirlukast (1 mM), and the lipoxygenase inhibitor, zileuton (20 mM), alone failed to inhibit bronchoconstriction by adenosine and ovalbumen of the lung and trachea. When two antagonists were combined, only mepyramine and zafirlukast significantly reduced the lung responses to adenosine and ovalbumen. The tracheal adenosine response was substantially reduced, although not significantly, while ovalbumen was significantly reduced. When mepyramine, indomethacin and zafirlukast were combined, the lung constriction by adenosine and ovalbumen were virtually abolished. Similarly, the combination of mepyramine, diclofenac and zafirlukast significantly attenuated the lung responses to adenosine and ovalbumen. Thus, histamine, cyclooxygenase products and leukotrienes alone are not responsible for the bronchoconstriction of isolated sensitized lung tissues to adenosine or ovalbumen, which appears to be due to the release of all three mediators.

Discovery of L-791,943: a potent, selective, non emetic and orally active phosphodiesterase-4 inhibitor

Structure-activity relationship studies directed toward improving the potency and metabolic stability of CDP-840 (3) resulted in the discovery of L-791,943 (11n) as a potent (HWB TNF-alpha = 0.67 microM) and orally active phosphodiesterase type 4 (PDE4) inhibitor. This compound, which bears a stable bis-difluoromethoxy catechol and a pendant hexafluorocarbinol, exhibited a long half-life in rat and in squirrel monkey. It is well tolerated in ferret with an emetic threshold greater than 30 mg/kg (po) and was found to be active in the ovalbumin-induced bronchoconstriction model in guinea pig and in the ascaris-induced bronchoconstriction models in sheep and squirrel monkey.

Eotaxin and RANTES enhance 5-oxo-6,8,11,14-eicosatetraenoic acid-induced eosinophil chemotaxis

BACKGROUND

The 5-lipoxygenase product 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent activator of human eosinophils and, among lipid mediators, is the most active chemoattractant for these cells. Studies have demonstrated the importance of 5-lipoxygenase products in allergen-induced pulmonary eosinophilia. Because CC chemokines such as eotaxin and RANTES also play critical roles in this phenomenon, it would seem likely that members of both classes of mediators contribute to this response.

OBJECTIVE

The study was designed to directly compare the effects of 5-oxo-ETE on eosinophils with those of eotaxin and RANTES and to determine whether these chemokines could enhance the chemotactic response to 5-oxo-ETE.

METHODS

Eosinophil chemotaxis was measured with microchemotaxis chambers. CD11b, L-selectin, and actin polymerization were measured by flow cytometry. Calcium mobilization was measured by fluorescence.

RESULTS

5-Oxo-ETE stimulated eosinophil chemotaxis with a potency between those of eotaxin and RANTES and a maximal response about 50% higher than that of eotaxin. Threshold concentrations of eotaxin and RANTES increased the chemotactic potency of 5-oxo-ETE by more than 4-fold. 5-Oxo-ETE and eotaxin were approximately equipotent in mobilizing cytosolic calcium in eosinophils. Eotaxin was more potent in inducing CD11b expression and actin polymerization, but the maximal responses to 5-oxo-ETE were about 50% higher. 5-Oxo-ETE strongly induced L-selectin shedding, whereas eotaxin elicited only a weak and variable response.

CONCLUSION

5-Oxo-ETE is a strong activator of human eosinophils with a chemotactic potency comparable to those of eotaxin and RANTES, both of wwhich enhance 5-oxo-ETE-induced chemotaxis. 5-Oxo-ETE and CC chemokines may combine to induce pulmonary eosinophilia in asthma.

Anti-inflammatory effects of zileuton in a subpopulation of allergic asthmatics

The objective of this study was to determine the effects of allergen exposure on leukotriene generation and inflammation within the airways of allergic asthmatics and evaluate the effects of the 5-lipoxygenase inhibitor zileuton on these responses. We measured leukotriene-B(4) (LTB(4)) and LTC(4)/D(4)/E(4), inflammatory cytokine mediators, and cellular responses in bronchoalveolar lavage fluid (BALF) before and 24 h after segmental ragweed antigen challenge in 18 asthmatic subjects at baseline. Before initiating therapy with the 5-lipoxygenase inhibitor or placebo, only nine of 18 asthmatic subjects had a significant increase (234 +/- 102-fold, mean +/- SE) in BALF LTC(4)/D(4)/E(4) levels 24 h after segmental antigen challenge, whereas leukotriene levels were essentially unchanged (1.14 +/- 0.22-fold) in the other nine subjects. The high LT producers also had higher postantigen BALF levels of LTB(4), total protein, IL-5, IL-6, TNF-alpha, and recovery of more eosinophils than the low LT producers. Treatment with the 5-lipoxygenase inhibitor zileuton reduced postantigen BALF eosinophil count by 68% in the high LT producers, but had no detectable effect on BALF composition in the low LT producers. These data suggest that leukotriene inhibition may be more effective in a subset of asthmatics in whom leukotrienes are a major contributory factor in causing allergic inflammation.

Inhibition of allergen-induced pulmonary responses by the selective tryptase inhibitor 1,5-bis-[4-[(3-carbamimidoyl-benzenesulfonylamino)-methyl]-phenoxy]-pen tane (AMG-126737)

Emerging evidence suggests that mast cell tryptase is a therapeutic target for the treatment of asthma. The effects of this serine protease are associated with both pathophysiologic pulmonary responses and pathologic changes of the asthmatic airway. In this study, the tryptase inhibitor 1,5-bis-[4-[(3-carbamimidoyl-benzenesulfonylamino)-methyl]-p henoxy]-pentane (AMG-126737) was evaluated for its pharmacologic effects against allergen-induced airway responses. AMG-126737 is a potent inhibitor of human lung mast cell tryptase (Ki = 90 nM), with greater than 10- to 200-fold selectivity versus other serine proteases. Intratracheal administration of AMG-126737 inhibited the development of airway hyperresponsiveness in allergen-challenged guinea pigs with an ED50 of 0.015 mg/kg. In addition, the compound exhibited oral activity in the guinea pig model. The in vivo activity of AMG-126737 was confirmed in a sheep model of allergen-induced airway responses, where the compound inhibited early and late phase bronchoconstriction responses and the development of airway hyperresponsiveness. These results support the proposed role of tryptase in the pathology of asthma and suggest that AMG-126737 has potential therapeutic utility in this pulmonary disorder.

5-oxo-ETE induces pulmonary eosinophilia in an integrin-dependent manner in Brown Norway rats

We have shown previously that the 5-lipoxygenase product 5-oxo-6,8, 11,14-eicosatetraenoic acid (5-oxo-ETE) is a highly potent eosinophil chemoattractant in vitro. To determine whether this substance can induce pulmonary eosinophil infiltration in vivo, it was administered to Brown Norway rats by tracheal insufflation. Eosinophils were then counted in lung sections that had been immunostained with an antibody to eosinophil major basic protein. 5-Oxo-ETE induced a dramatic increase in the numbers of eosinophils (ED50, 2.5 microg) around the walls of the airways, which reached maximal levels (five times control levels) between 15 and 24 h after administration, and then declined. LTB4 also induced pulmonary eosinophil infiltration with a similar ED50 but appeared to be somewhat less effective. In contrast, LTD4 and LTE4 were inactive. 5-Oxo-ETE-induced eosinophilia was unaffected by the LTB4 and PAF antagonists LY255283 and WEB 2170, respectively. However, it was inhibited by approximately 75% by monoclonal antibodies to CD49d (VLA-4) or CD11a (LFA-1) but was not significantly affected by an antibody to CD11b (Mac-1). In conclusion, 5-oxo-ETE induces pulmonary eosinophilia in Brown Norway rats, raising the possibility that it may be a physiological mediator of inflammation in asthma.

Mechanism of pyocyanin- and 1-hydroxyphenazine-induced lung neutrophilia in sheep airways

Pyocyanin (Pyo) and 1-hydroxyphenazine (1-HP) are extracellular products of Pseudomonas aeruginosa. To test whether these products were capable of producing an inflammatory response in the airways, combinations of Pyo and 1-HP at concentrations of 10(-4) and 10(-5) M were instilled into sheep airways, and indexes of inflammation were assessed by bronchoalveolar lavage (BAL) 24 h later. Challenge with the phenazines caused a significant dose-dependent increase in the number of cells and neutrophils recovered by BAL. Control challenges produced no such changes. The lung neutrophilia was accompanied by an increased concentration of albumin in BAL. The increases in BAL neutrophils and albumin could be blocked by treating the sheep with the 5-lipoxygenase inhibitor zileuton. Neither 1-HP nor Pyo was chemotactic to neutrophils when tested in vitro, but when alveolar macrophages (AM) were cultured in vitro in the presence of both Pyo and 1-HP (1 microM), the supernatants caused neutrophil chemotaxis. Analysis of AM culture supernatants incubated with the combination of pigments showed significant increases in leukotriene B4 and interleukin-8, and blocking these mediators separately or together reduced AM supernatant-induced neutrophil chemotaxis. We conclude that local instillation of Pyo and 1-HP can initiate an inflammatory response in the airways of sheep in vivo. This effect can be explained, in part, by the release of chemotactic factors produced by AM.

Interaction of secretory leukocyte protease inhibitor with heparin inhibits proteases involved in asthma

Protease inhibition by secretory leukocyte protease inhibitor (SLPI) is accelerated by the sulfated polysaccharides. The nature of the SLPI-polysaccharide interaction, explored with affinity chromatography, indicated that this interaction was sensitive to the charge and type of polysaccharide. Dextran and chondroitin had the lowest affinity for SLPI, followed by dermatan, heparan, and dextran sulfates. While heparin bound SLPI tightly, the highest affinity heparin chains unexpectedly contained a lower level of sulfation than more weakly interacting chains. Heparin oligosaccharides, prepared using heparin lyase I were SLPI-affinity fractionated. Surprisingly, undersulfated heparin oligosaccharides bound SLPI with the highest affinity, suggesting the importance of free hydroxyl groups for high affinity interaction. Isothermal titration calorimetry was used to determine the thermodynamics of SLPI interaction with a low molecular weight heparin, an undersulfated decasaccharide and a tetrasaccharide. The studies showed 12-14 saccharide units, corresponding to molecular weight of approximately 4,800, were required for a 1:1 (SLPI:heparin) binding stoichiometry. Furthermore, an undersulfated decasaccharide was able to bind SLPI tightly (Kd approximately 13 nM), resulting in its activation and the inhibition of neutrophil elastase and pancreatic chymotrypsin. The in vitro assessment of heparin and the decasaccharide and tetrasaccharide using stopped-flow kinetics suggested that heparin was the optimal choice to study SLPI-based in vivo protease inhibition. SLPI and heparin were co-administered by inhalation in therapy against antigen-induced airway hyperresponsiveness in a sheep bronchoprovocation model. Heparin, in combination with SLPI demonstrated in vivo efficacy reducing early and late phase bronchoconstriction. Heparin also increased the therapeutic activity of SLPI against antigen-induced airway hyperresponsiveness.

Substituted (pyridylmethoxy)naphthalenes as potent and orally active 5-lipoxygenase inhibitors; synthesis, biological profile, and pharmacokinetics of L-739,010

Dioxabicyclooctanyl naphthalenenitriles have been reported as a class of potent and nonredox 5-lipoxygenase (5-LO) inhibitors. These bicyclo derivatives were shown to be metabolically more stable than their tetrahydropyranyl counterparts but were not well orally absorbed. Replacement of the phenyl ring in the naphthalenenitrile 1 by a pyridine ring leads to the potent and orally absorbed inhibitor 3g (L-739,010, 2-cyano-4-(3-furyl)-7-[[6-[3-(3-hydroxy-6,8-dioxabicyclo[3.2.1] octanyl)]-2-pyridyl]methoxy]naphthalene). Compound 3g inhibits 5-HPETE production by human 5-LO and LTB4 biosynthesis by human PMN leukocytes and human whole blood (IC50S of 20, 1.6, and 42 nM, respectively). Derivative 3g is orally active in the rat pleurisy model (inhibition of LTB4, ED50 = 0.3 mg/kg) and in the anesthetized dog model (inhibition of ex vivo whole blood LTB4 and urinary LTE4, ED50 = 0.45 and 0.23 microgram/kg/min, respectively, i.v. infusion). In addition, 3g shows excellent functional activity against ovalbumin-induced dyspnea in rats (60% inhibition at 0.5 mg/kg, 4 h pretreatment) and Ascaris-induced bronchoconstriction in conscious sheep (50% and > 85% inhibition in early and late phases, respectively at 2.5 micrograms/kg/min, i.v. infusion) and, more particularly in the conscious antigen sensitive squirrel monkey model (53% inhibition of the increase in RL and 76% in the decrease of Cdyn, at 0.1 mg/kg, po). In rats and dogs, 3g presents excellent pharmacokinetics (estimated half-lives of 5 and 16 h, respectively) and bioavailabilities (26% and 73% when dosed as its hydrochloride salt at doses of 20 and 10 mg/kg, respectively, in methocel suspension). Based on its overall biological profile, compound 3g has been selected for preclinical animal toxicity studies.

Leukotrienes in the pathogenesis of asthma

Asthma is a chronic inflammatory disease that is associated with widespread but variable airflow obstruction. The mechanisms that lead to airflow obstruction in asthma are bronchoconstriction, mucosal edema, increased secretion of mucus, and an inflammatory-cell infiltrate that is rich in eosinophils. Leukotrienes (LTs) B4, C4, D4, and E4 have been shown experimentally to play a role in each of these inflammatory mechanisms and to mimic the pathologic changes seen in asthma. Inhaled LTC4 and LTD4 are the most potent bronchoconstrictors yet studied in human subjects. LTC4 and LTD4 also may cause migration of inflammatory cells into the asthmatic airway. LTs are derived from the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism, and increased production of LTs has been demonstrated in patients who have asthma. Leukotriene receptor antagonists and specific inhibitors of the 5-LO pathway hold great promise as new therapies to treat asthma. Because LTC4, LTD4, and LTE4 appear to interact with a common LTD4 receptor, selective LTD4 receptor antagonists (eg, pranlukast [SB205312/ONO-1078], zafirlukast [ICI 204,219], MK-571, and MK-679), as well as zileuton (A-64077, a direct inhibitor of 5-LO) have been developed as antiasthma agents. Clinical and experimental studies have demonstrated the efficacy of these compounds in reducing not only the symptoms of asthma, but use of beta 2-agonists and bronchoconstriction induced by exposure to allergens, exercise, aspirin, and cold air.

Effects of inhibitors of phosphodiesterase, on antigen-induced bronchial hyperreactivity in conscious sensitized guinea-pigs and airway leukocyte infiltration

1. The aim of this study was to determine the effects of inhibitors of phosphodiesterase (PDE) on the early and late phase bronchoconstriction in sensitized, conscious guinea-pigs and the subsequent development of acute airway hyperreactivity to the inhaled thromboxane mimetic, U46619, and leukocyte infiltration following ovalbumin (OvA) challenge. 2. Following an inhalation challenge with OvA, there was an early bronchoconstriction which peaked at 15 min with recovery after 3-4 h. A late phase bronchoconstriction occurred between 17 and 24 h after challenge. The PDE 4 inhibitors, Ro 20-1724 (3 mg kg-1, i.p.) and rolipram (1 mg kg-1, i.p.) administered 30 min before and 6 h after antigen challenge (double dosing regimen), did not affect the development of the early or late phase responses. 3. Seventeen to twenty four hours following an acute OvA or saline challenge, a consistently greater bronchoconstrictor response to inhaled U46619 was observed in the OvA challenged group. This increase in responsiveness was significantly attenuated by the administration of Ro 20-1724 and rolipram 30 min before and 6 h after antigen challenge (P < 0.05); this was not attributable to a residual bronchodilator effect of these compounds. There was a trend towards inhibition of the hyperreactivity to U46619 by aminophylline but not by the PDE3 inhibitors, siguazodan or SKF 95654. 4. Aminophylline, rolipram and Ro 20-1724 when administered as the double dose regimen attenuated the rise in macrophages, eosinophils and neutrophils recovered in bronchial lavage fluid 17 to 24 h after antigen challenge. 5. The dose of Ro 20-1724 given at 6 h post challenge was essential for attenuation of airway hyperreactivity and to protect against leukocyte influx. 6. In summary, aminophylline, rolipram and Ro 20-1724 have anti-inflammatory effects against antigen-induced airway leukocyte infiltration. Rolipram and Ro 20-1724 additionally attenuated the development of acute airway hyperreactivity, effects which are probably mediated through inhibition of PDE type 4. A dose of PDE inhibitor 6 h after the antigen challenge appears to be essential to achieve this protection. Inhibitors of PDE type 3 were generally without effect. However, there was no effect of rolipram or Ro 20-1724 on the development of either the early or late phase type responses.

Effect of a 5-lipoxygenase inhibitor, AL-3264, on propranolol-induced bronchoconstriction in guinea-pigs

The administration of propranolol can provoke bronchoconstriction in asthmatic patients. We hypothesized that such bronchoconstriction may result from the inflammatory mediators released by an allergic reaction. We investigated the effect of AL-3264, a 5-lipoxygenase inhibitor, on propranolol-induced bronchoconstriction (PIB) after antigen inhalation in passively sensitized and artificially ventilated guinea-pigs. Our goal was to determine whether products of arachidonate 5-lipoxygenase are involved in such PIB. Bronchoconstriction occurred when 10 mg/ml of propranolol was inhaled 20 min after antigen challenge. Pretreatment with AL-3264 given in intravenous doses of 0.01 and 0.1 mg/kg 15 min after the antigen challenge significantly reduced PIB in a dose-dependent manner. Pretreatment with 0.1 mg/kg of AL-3264 10 min before antigen challenge significantly inhibited both the immediate allergic bronchoconstriction and PIB, although the effect was minimal. Results suggest that arachidonate 5-lipoxygenase products (such as leukotriene B4, C4, D4 or E4) are involved in the pathophysiology of PIB but their contribution may be small. Further studies using selective antagonists for each of these leukotrienes are needed to clarify their role.

The effect of food on the pharmacokinetics of zileuton

The present study was undertaken to assess the effect of food on the pharmacokinetic parameters of zileuton. In a nonblinded crossover study, 18 healthy male volunteers who had fasted overnight were randomised to receive a single oral dose of zileuton 600mg in the presence or absence of food consisting of a standardised breakfast on the following morning. The mean zileuton peak plasma concentration (Cmax) increased significantly by 27% after food intake, while the mean area under the plasma concentration versus time curve increased by only 1.4%, a difference that was not statistically significant. The mean time to Cmax was unaffected by the presence of food, as were the other pharmacokinetic parameters assessed. Overall, the results suggest that food has a relatively small effect on the rate of zileuton absorption compared with the fasting state, while the bioavailability of the drug appears to be unaffected. Thus, it is concluded that it is appropriate to administer zileuton with or without food.

Leukotriene and thromboxane antagonists

It has been suggested that arachidonate metabolites, leukotrienes, and thromboxane may play important roles in the pathogenesis of bronchial asthma. Biologic activities of these mediators are much more potent than those of histamine and acetylcholine on a molar basis in inducing bronchoconstriction, increase in microvascular permeability, formation of mucosal edema, and mucus secretion, which are characteristic features of bronchial asthma. Furthermore, recent studies have demonstrated the presence of these mediators in plasma, BALF, and urine in asthmatic patients after allergen challenge. Therefore, the regulation of the activities of these mediators may provide a novel therapeutic approach for the treatment of bronchial asthma. A large number of 5-lipoxygenase inhibitors, peptide leukotriene antagonists, thromboxane synthase inhibitors, and thromboxane antagonists have been actively developed by the pharmaceutical industry, and there are increasing findings to demonstrate a clinical efficacy by these compounds. Among them, a thromboxane synthase inhibitor, OKY-046, first became available as an antiasthmatic agent in Japan. This is a significant step in the management of bronchial asthma. Preclinical and clinical results have suggested that these inhibitors and antagonists may be capable of inhibiting airway obstruction with airway inflammation and bronchial hyperresponsiveness, which are important characteristics of bronchial asthma. Further results from clinical studies with newly developed leukotriene and thromboxane antagonists are eagerly awaited.

The effects of a cysteinyl leukotriene antagonist (ONO-1078) on antigen-induced responses in allergic sheep

The cysteinyl leukotrienes (LTC4/D4/E4) are putative mediators of asthma. In this study we used sheep allergic to Ascaris suum antigen to examine the effects of a novel orally active cysteinyl LT antagonist, ONO-1078, on antigen-induced early and late responses, airway inflammation, post challenge (24 h) airway hyperresponsiveness (AHR) and mucociliary clearance. Airway responses to antigen were determined by measuring specific lung resistance (SRL) before and for 8 h after challenge, bronchoalveolar lavage (BAL) was used to estimate airway inflammation, and airway responsiveness was measured by determining the carbachol dose that increased SRL by 400% (PC400). We also used a radiographic technique to measure the antigen-induced change in tracheal mucus velocity (TMV), a marker of mucociliary clearance. In two trials separated by at least 21 days, sheep were treated once with ONO-1078 (30 mg/kg, p.o.) and once with placebo (0.5% methylcellulose), 2 h before and 4 h after antigen challenge. Treatment with ONO-1078 (n = 7) provided 40% protection (p < 0.10) against the peak early increase in SRL, resulted in a more rapid reversal of the early response, and provided 96% protection against the peak late (6-8 h) increase in SRL. ONO-1078 also inhibited the AHR 24 h after challenge. In the drug trial, PC400 was unchanged as compared to pre-challenge, whereas in the placebo trial, PC400 was decreased 1.4-fold (p < 0.05). Treatment however, did not affect BAL cell numbers or differential.(ABSTRACT TRUNCATED AT 250 WORDS)