Effects of leukotriene D on the airways in asthma

Correlation between cysteinyl leukotriene release from leukocytes and clinical response to a leukotriene inhibitor

STUDY OBJECTIVES

Antileukotriene drugs are widely used in patients with bronchial asthma, but not all patients show significant clinical improvements, and no factors have been identified that are correlated with the clinical response to these drugs. This study was designed to examine the factors correlated with a response to a leukotriene receptor antagonist, pranlukast, in patients with asthma.

DESIGN

WBC counts, IgE, and ex vivo leukotriene release from leukocytes were measured, and 31 patients with asthma were treated with pranlukast, a leukotriene receptor antagonist, for 4 weeks.

MEASUREMENTS

Outcome measurements included twice-daily peak expiratory flow rate (PEFR), daytime and nocturnal symptoms, and frequency of beta(2)-agonist use. Subjects with a reduction of > 20% in symptom scores or beta(2)-agonist use, or an improvement of PEFR of > 10% were designated as responders; others were designated as nonresponders. Logistic regression analysis assessed the efficacy of models using various allergic markers correlated with the response to pranlukast.

RESULTS

There were 16 responders and 15 nonresponders. The release of cysteinyl leukotrienes from the leukocytes of the responders was higher than that of the nonresponders (p < 0.05). There was a significant correlation between the clinical response and the release of cysteinyl leukotrienes, but not demographic features, WBC counts, percentage of eosinophils, or serum IgE levels (p < 0.05). Subjects with a release of cysteinyl leukotrienes of > 3,500 pg/mL were 11.0 times more likely to respond to pranlukast than those with < 3,500 pg/mL (95% confidence interval, 2.0 to 60.5).

CONCLUSION

Cysteinyl leukotriene release from leukocytes is correlated with leukotriene receptor antagonist response.

Exercise-induced bronchospasm in the elite athlete

The term exercise-induced bronchospasm (EIB) describes the acute transient airway narrowing that occurs during and most often after exercise in 10 to 50% of elite athletes, depending upon the sport examined. Although multiple factors are unquestionably involved in the EIB response, airway drying caused by a high exercise-ventilation rate is primary in most cases. The severity of this reaction reflects the allergic predisposition of the athlete, the water content of the inspired air, the type and concentration of air pollutants inspired, and the intensity (or ventilation rate) of the exercise. The highest prevalence of EIB is seen in winter-sport populations, where athletes are chronically exposed to cold dry air and/or environmental pollutants found in indoor ice arenas. When airway surface liquid lost during the natural warming and humidification process of respiration is not replenished at a rate equal to the loss, the ensuing osmolarity change stimulates the release of inflammatory mediators and results in bronchospasm; this cascade of events is exacerbated by airway inflammation and airway remodelling. The acute EIB response is characterised by airway smooth muscle contraction, membrane swelling, and/or mucus plug formation. Evidence suggests that histamine, leukotrienes and prostanoids are likely mediators for this response. Although the presence of symptoms and a basic physical examination are marginally effective, objective measures of lung function should be used for accurate and reliable diagnosis of EIB. Diagnosis should include baseline spirometry, followed by an appropriate bronchial provocation test. To date, the best test to confirm EIB may simply be standard pulmonary function testing before and after high-intensity dry air exercise. A 10% post-challenge fall in forced expiratory volume in 1 second is used as diagnostic criteria. The goal of medical intervention is to limit EIB exacerbation and allow the athlete to train and compete symptom free. This is attempted through daily controller medications such as inhaled corticosteroids or by the prophylactic use of medications before exercise. In many cases, EIB is difficult to control. These and other data suggest that EIB in the elite athlete is in contrast with classic asthma.

Leukotriene and prostanoid pathway enzymes in bronchial biopsies of seasonal allergic asthmatics

Cysteinyl-leukotrienes and prostaglandin D2 generated by the 5-lipoxygenase (5-LO) and cyclooxygenase (COX) pathways, respectively, cause bronchoconstriction, leukocyte recruitment, and bronchial hyperresponsiveness in asthma. We characterized the cellular expression of 5-LO and COX enzymes using immunohistochemistry on bronchial biopsies from 12 allergic asthmatic patients before and during seasonal exposure to birch pollen. Bronchial responsiveness (p = 0.004) and symptoms (p < 0.005) increased and peak expiratory flow (PEF; p < or = 0.02) decreased in the pollen season. In-season biopsies had 2-fold more cells immunostaining for 5-LO (p = 0.02), 5-LO-activating protein (FLAP; p = 0.04), and leukotriene (LT)A4 hydrolase (p = 0.05), and 4-fold more for the terminal enzyme for cysteinyl-leukotriene synthesis, LTC4 synthase (p = 0.02). Immunostaining for COX-1, COX-2, and PGD2 synthase was unchanged. Increased staining for LTC4 synthase was due to increased eosinophils (p = 0.035) and an increased proportion of eosinophils expressing the enzyme (p = 0.047). Macrophages also increased (p = 0.019), but mast cells and T-lymphocyte subsets were unchanged. Inverse correlations between PEF and 5-LO(+) cell counts link increased expression of 5-LO pathway enzymes in eosinophils and macrophages within the bronchial mucosa to deterioration of lung function during seasonal allergen exposure.

Cysteinyl leukotriene receptor 1 is also a pyrimidinergic receptor and is expressed by human mast cells

The cysteinyl leukotrienes (cys-LTs) LTC(4), LTD(4), and LTE(4) are a class of peptide-conjugated lipids formed from arachidonic acid and released during activation of mast cells (MCs). We now report that human cord-blood-derived MCs (hMCs) express the CysLT1 receptor, which responds not only to inflammation-derived cys-LTs, but also to a pyrimidinergic ligand, UDP. hMCs express both CysLT1 protein and transcript, and respond to LTC(4), LTD(4), and UDP with concentration-dependent calcium fluxes, each of which is blocked by a competitive CysLT1 receptor antagonist, MK571. Stably transfected Chinese hamster ovary cells expressing the CysLT1 receptor also exhibit MK571-sensitive calcium flux to all three agonists. Both hMCs and CysLT1 transfectants stimulated with UDP are desensitized to LTC(4), but only partially to LTD(4). Priming of hMCs with IL-4 for 5 days enhances their sensitivity to each agonist, but preferentially lowers their threshold for activation by LTC(4) and UDP (approximately 3 log(10)-fold shifts in dose-response for each agonist) over LTD(4) (1.3 log(10)-fold shift), without altering CysLT1 receptor mRNA or surface protein expression, implying the likely induction of a second receptor with CysLT1-like dual ligand specificity. hMCs thus express the CysLT1 receptor, and possibly a closely related IL-4-inducible receptor, which mediate dual activation responses to cys-LTs and UDP, providing an apparent intersection linking the inflammatory and neurogenic elements of bronchial asthma.

Attenuated zymosan-induced peritoneal vascular permeability and IgE-dependent passive cutaneous anaphylaxis in mice lacking leukotriene C4 synthase

Leukotriene C(4) synthase (LTC(4)S), the terminal 5-lipoxygenase pathway enzyme that is responsible for the biosynthesis of cysteinyl leukotrienes, has been deleted by targeted gene disruption to define its tissue distribution and integrated pathway function in vitro and in vivo. The LTC(4)S (-/-) mice developed normally and were fertile. LTC(4)S activity, assessed by conjugation of leukotriene (LT) A(4) methyl ester with glutathione, was absent from tongue, spleen, and brain and > or = 90% reduced in lung, stomach, and colon of the LTC(4)S (-/-) mice. Bone marrow-derived mast cells (BMMC) from the LTC(4)S (-/-) mice provided no LTC(4) in response to IgE-dependent activation. Exocytosis and the generation of prostaglandin D(2), LTB(4), and 5-hydroxyeicosatetraenoic acid by BMMC from LTC(4)S (-/-) mice and LTC(4)S (+/+) mice were similar, whereas the degraded product of LTA(4), 6-trans-LTB(4), was doubled in BMMC from LTC(4)S (-/-) mice because of lack of utilization. The zymosan-elicited intraperitoneal extravasation of plasma protein and the IgE-mediated passive cutaneous anaphylaxis in the ear were significantly diminished in the LTC(4)S (-/-) mice. These observations indicate that LTC(4)S, but not microsomal or cytosolic glutathione S-transferases, is the major LTC(4)-producing enzyme in tissues and that its integrated function includes mediation of increased vascular permeability in either innate or adaptive immune host inflammatory responses.

Zafirlukast: an update of its pharmacology and therapeutic efficacy in asthma

Zafirlukast is a selective and competitive orally administered inhibitor of the cysteinyl leukotrienes LTC4, LTD4 and LTE4. The drug is indicated for the prophylaxis and treatment of chronic asthma, and has been developed in response to mounting evidence indicating the importance of the cysteinyl leukotrienes in the pathogenesis of this disorder. The efficacy of zafirlukast 20 mg twice daily has been shown in double-blind placebo-controlled studies of up to 13 weeks' duration in patients aged > or = 12 years. Zafirlukast was consistently superior to placebo in improving objective measures of lung function and subjective measures such as symptom scores and use of as-required bronchodilator therapy. This dosage is also as effective when added to low-dosage inhaled corticosteroid therapy as doubling of corticosteroid dosages. Recent studies indicate superior efficacy over zafirlukast of twice-daily inhaled fluticasone propionate 88 microg or salmeterol 42 microg, although zafirlukast was nevertheless associated with clinical improvement. Data also show zafirlukast 40 mg to be of similar efficacy to pranlukast 225 mg (both twice daily). Overall, preliminary pharmacoeconomic data suggest that healthcare costs are reduced by zafirlukast therapy, although superior cost effectiveness has been reported with inhaled fluticasone propionate. and further studies are needed. Data are available to show improvements in patient-rated quality of life, and preference for and high rates of compliance with zafirlukast. In clinical trials, zafirlukast has shown an adverse event profile similar to that of placebo. Isolated reports of hepatic dysfunction in a small number of individuals receiving the drug have been received, and recommendations for monitoring of patients are in place. Although no causal relationship has been established between zafirlukast and Churg-Strauss Syndrome, patients undergoing corticosteroid dosage reductions require careful surveillance.

CONCLUSIONS

zafirlukast is an effective and well tolerated agent for preventive monotherapy in mild to moderate persistent asthma. Emerging data indicate benefit of the drug when added to low-dosage inhaled corticosteroids and show that it may be a viable alternative to inhaled adjunctive treatments and increased corticosteroid dosages in some patients. Although inhaled fluticasone propionate and salmeterol have been associated with greater clinical improvement than zafirlukast in clinical studies, compliance considerations and the confirmed clinical efficacy relative to placebo of the drug denote zafirlukast as an effective alternative in treatment programmes based on individualised therapy. As experience with zafirlukast accumulates, it is expected that the drug will be positioned more definitively in national and international treatment guidelines.

Low-dose fluticasone propionate compared with montelukast for first-line treatment of persistent asthma: a randomized clinical trial

BACKGROUND

Both inhaled corticosteroids and leukotriene modifiers are used in the maintenance treatment of persistent asthma.

OBJECTIVE

The goal was to compare the efficacy and safety of low-dose fluticasone propionate (FP) and montelukast as first-line maintenance therapy in symptomatic patients by using short-acting beta2-agonists alone to treat persistent asthma.

METHODS

In this multicenter, randomized, double-blind, double-dummy, parallel-group study, 533 patients (>15 years old) with persistent asthma who remained symptomatic while taking short-acting beta2-agonists alone were treated with FP (88 microg [2 puffs of 44 microg] twice daily) or montelukast (10 mg once daily) for 24 weeks.

RESULTS

Compared with treatment with montelukast, treatment with FP resulted in significantly greater improvements at endpoint in morning predose FEV(1) (22.9% vs 14.5%, P <.001), forced midexpiratory flow (0.66 vs 0.41 L/sec, P <.001), forced vital capacity (0.42 vs 0.29 L, P =.002), morning peak expiratory flow (PEF) (68.5 vs 34.1 L/min, P <.001), and evening PEF (53.9 vs 28.7 L/min, P <.001). Similar improvements in PEF were observed in patients with milder asthma (>70%-80% predicted FEV(1)). At endpoint, FP was more effective than montelukast at decreasing rescue albuterol use (3.1 puffs/day vs 2.3 puffs/day, P <.001), asthma symptom scores (-0.85 [48.6% decrease] vs -0.60 [30.5%], P <.001), and nighttime awakenings due to asthma (-0.64 awakenings/night [62% decrease] vs -0.48 awakenings/night [47.5%], P =.023), and FP increased the percentage of symptom-free days (32.0% vs 18.4% of days, P <.001) compared with montelukast. The adverse event and asthma exacerbation profiles for FP and montelukast were similar.

CONCLUSIONS

Low-dose FP is more effective than montelukast as first-line maintenance therapy for patients with persistent asthma who are undertreated and remain symptomatic while taking short-acting beta2-agonists alone.

Arachidonic acid metabolism in inflammatory cells of patients with bronchial asthma

Over the last few years, the demonstration of beneficial effects of leukotriene receptor antagonists in various forms of asthma has renewed clinical and pharmacologic interest in this class of lipid mediators. Several studies demonstrated an increased biosynthesis of cysteinyl leukotrienes (CysLT) in asthmatic patients. However, the reasons for the dysregulated production of CysLTs in asthmatic patients are not completely defined. An improved method of lipid mediator detection and the availability of cells isolated from human airways (by bronchoalveolar lavage [BAL] and bronchial biopsies) have allowed initial studies to address this issue. Eosinophils retrieved from inflamed airways of asthmatics have a larger arachidonic acid (AA) content than their blood counterpart. The high level of AA in these cells is primarily due to a remodeling of endogenous arachidonate pools with the accumulation of this fatty acid in a triglyceride-associated pool. In addition, elevated levels of a secretory form of phospholipase A2, the key enzyme initiating the cascade of CysLTs, are found in the BAL of asthmatics. Finally, eosinophils isolated from the BAL of asthmatics have an increased expression of LTC4 synthase. The level of expression of this enzyme correlates with the increased amount of CysLTs produced in the airways of these patients. Taken together, these data identify at least two possible mechanisms to explain the excessive CysLT production in asthmatics: 1) an increased content of AA in the glycerolipid pools of inflammatory cells 2) an enhanced activity of key biosynthetic enzymes involved in CysLT synthesis.

T helper cell type 2 cytokines coordinately regulate immunoglobulin E-dependent cysteinyl leukotriene production by human cord blood-derived mast cells: profound induction of leukotriene C(4) synthase expression by interleukin 4

Human mast cells (hMCs) derived in vitro from cord blood mononuclear cells exhibit stem cell factor (SCF)-dependent comitogenic responses to T helper cell type 2 (Th2) cytokines. As cysteinyl leukotriene (cys-LT) biosynthesis is a characteristic of immunoglobulin (Ig)E-activated mucosal hMCs, we speculated that Th2 cytokines might regulate eicosanoid generation by hMCs. After passive sensitization for 5 d with IgE in the presence of SCF, anti-IgE-stimulated hMCs elaborated minimal cys-LT (0.1 +/- 0.1 ng/10(6) hMCs) and abundant prostaglandin (PG)D(2) (16.2 +/- 10.3 ng/10(6) hMCs). Priming of hMCs by interleukin (IL)-4 with SCF during passive sensitization enhanced their anti-IgE-dependent histamine exocytosis and increased their generation of both cys-LT (by 27-fold) and PGD(2) (by 2. 5-fold). Although priming with IL-3 or IL-5 alone for 5 d with SCF minimally enhanced anti-IgE-mediated cys-LT generation, these cytokines induced further six- and fourfold increases, respectively, in IgE-dependent cys-LT generation when provided with IL-4 and SCF; this occurred without changes in PGD(2) generation or histamine exocytosis relative to hMCs primed with IL-4 alone. None of these cytokines, either alone or in combination, substantially altered the levels of cytosolic phospholipase A(2) (cPLA(2)), 5-lipoxygenase (5-LO), or 5-LO activating protein (FLAP) protein expression by hMCs. In contrast, IL-4 priming dramatically induced the steady-state expression of leukotriene C(4) synthase (LTC(4)S) mRNA within 6 h, and increased the expression of LTC(4)S protein and functional activity in a dose- and time-dependent manner, with plateaus at 10 ng/ml and 5 d, respectively. Priming by either IL-3 or IL-5, with or without IL-4, supported the localization of 5-LO to the nucleus of hMCs. Thus, different Th2-derived cytokines target distinct steps in the 5-LO/LTC(4)S biosynthetic pathway (induction of LTC(4)S expression and nuclear import of 5-LO, respectively), each of which is necessary for a full integrated functional response to IgE-dependent activation, thus modulating the effector phenotype of mature hMCs.

IL-5 up-regulates cysteinyl leukotriene 1 receptor expression in HL-60 cells differentiated into eosinophils

The cysteinyl leukotrienes, leukotriene (LT) C(4), LTD(4), and LTE(4), are lipid mediators that have been implicated in the pathogenesis of several inflammatory processes, including asthma. The human LTD(4) receptor, CysLT(1)R, was recently cloned and characterized. We had previously shown that HL-60 cells differentiated toward the eosinophilic lineage (HL-60/eos) developed specific functional LTD(4) receptors. The present work was undertaken to study the potential modulation of CysLT(1)R expression in HL-60/eos by IL-5, an important regulator of eosinophil function. Here, we report that IL-5 rapidly up-regulates CysLT(1)R mRNA expression, with consequently enhanced CysLT(1)R protein expression and function in HL-60/eos. CysLT(1)R mRNA expression was augmented 2- to 15-fold following treatment with IL-5 (1-20 ng/ml). The effect was seen after 2 h, was maximal by 4 h, and maintained at 8 h. Although CysLT(1)R mRNA was constitutively expressed in undifferentiated HL-60 cells, its expression was not modulated by IL-5 in the absence of differentiation. Differentiated HL-60/eos cells pretreated with IL-5 (10 ng/ml) for 24 h showed enhanced CysLT(1)R expression on the cell surface, as assessed by flow cytometry using a polyclonal anti-CysLT(1)R Ab. They also showed enhanced responsiveness to LTD(4), but not to LTB(4) or platelet-activating factor, in terms of Ca(2+) mobilization, and augmented the chemotactic response to LTD(4). Our findings suggest a possible mechanism by which IL-5 can modulate eosinophil functions and particularly their responsiveness to LTD(4), and thus contribute to the pathogenesis of asthma and allergic diseases.

Leukotriene receptor antagonists: efficacy and safety in children with asthma

To date, only one study of chronic use of a leukotriene receptor antagonist in children has been published. The efficacy and safety of montelukast in children 6-14 years of age with asthma (n = 336) was studied during an 8-week, double-blind, placebo-controlled trial. There was significantly greater improvement in forced expired volume in 1 sec (FEV(1)) from baseline for the montelukast group (8. 23%) compared to the placebo group (3.58%). There was a significant decrease in use of beta agonists for symptom relief and a significant decrease in the percentage of days and percentage of patients with asthma exacerbations. An asthma-specific quality of life questionnaire revealed significant overall improvement in quality of life and significant improvement in the quality of life domains for symptoms, activity, and emotions. Adverse effects were not significantly different for montelukast than for placebo, with the exception of allergic rhinitis which was more prevalent in the placebo group. A 6-month open follow-up of patients from the above study was undertaken. Effects of montelukast on FEV(1) were consistent over the 6 months, with the increase in FEV(1) not significantly different from a small control group treated with beclomethasone. Quality of life remained significantly improved throughout the open treatment period. In conclusion, leukotriene receptor antagonists are of value for the treatment of children with asthma.

Current treatment of asthma--focus on leukotrienes

Since their identification in 1979, the cysteinyl leukotrienes (cysLTs) have been shown to be prominent in many inflammatory conditions, including asthma, allergic rhinitis, rheumatoid arthritis, psoriasis, cystic fibrosis and inflammatory bowel disease. They are potent pro-inflammatory agents, as well as causing bronchoconstriction, and undoubtedly have a role in asthma. The cysLTs are products of arachidonic acid metabolism and have been shown to have effects via a cysteinyl leukotriene receptor (CysLTR1) on vascular permeability, mucus production, chemotaxis and bronchial smooth muscle. Their detection in certain body fluids in allergic, aspirin-sensitive and exercise-induced asthma is well documented and potential roles in pathogenesis, proposed. The development of agents affecting production or action offers an exciting new approach to the treatment of asthma. Two approaches to antileukotriene therapy have been developed: blocking their production by inhibiting the action of 5-lipoxygenase enzyme or blocking the CysLTR1. Both approaches have been tried in studies in asthma and overall the results are encouraging, with a decrease in both daytime and nocturnal symptoms, a decrease in additional beta 2 agonist usage and improvement in lung function. The changes, however, are small in some studies. This may be a reflection of disease severity in the study subjects, but of note is a heterogeneity of response to these treatments that may be genetically determined. Antileukotriene therapy has been shown to have an effect in specific types of asthma where the role of cysLTs seems well established--aspirin-sensitive/intolerant asthma and exercise-induced asthma. Longer term studies are needed in other areas such as severe asthma and chronic persistent asthma in both children and adults to provide evidence for the appropriate placement of antileukotriene treatment in current asthma guidelines, in comparison with other established treatments.

Effect of eotaxin and platelet-activating factor on airway inflammation and hyperresponsiveness in guinea pigs in vivo

Although eotaxin causes selective infiltration of eosinophils into the lung, its role in airway hyperresponsiveness remains unclear. We studied the effects of local administration of eotaxin on airway inflammation and hyperresponsiveness in guinea pigs in vivo. Airway responsiveness to inhaled histamine and differential cell counts in bronchoalveolar lavage fluid (BALF) were evaluated 12 h, 24 h, 3 d, and 7 d after intratracheal instillation of eotaxin. Significant eosinophilia in BALF was observed between 6 h and 7 d after eotaxin administration. Histologically, eosinophil accumulation was observed in the airways but not in the alveoli. In contrast, eotaxin did not affect airway responsiveness between 12 h and 7 d after its administration. We then studied the effects on airway responsiveness of subthreshold doses of interleukin 5, leukotriene D(4) (LTD(4)), and platelet-activating factor (PAF) combined with eotaxin. Neither interleukin 5 nor LTD(4) affected airway responsiveness. After eotaxin treatment, PAF significantly enhanced airway responsiveness without further increases in eosinophil counts. Eotaxin plus PAF significantly increased in eosinophil peroxidase activity in BALF compared with control and with eotaxin alone. These data indicate that eotaxin alone causes eosinophil accumulation in the airways but not hyperresponsiveness, and that additional factors such as PAF are needed to activate eosinophils for the development of airway hyperresponsiveness.

Clinical evidence with montelukast in the management of chronic childhood asthma

OBJECTIVE

The aim of this article is to review data on the efficacy and safety of montelukast in the treatment of children with asthma.

METHODOLOGY

Available published literature, including published abstracts, is reviewed.

RESULTS

In patients aged 6 to 14 years with asthma (n = 27), montelukast 5mg demonstrated a significant decrease in exercise-induced bronchoconstriction 20 to 24 hours postdose after 2 days of treatment. For children with chronic asthma, only one study of the regular use of a leukotriene receptor antagonist has been published. The efficacy and safety of montelukast in children aged 6 to 14 years with asthma (n = 336) were studied during an 8-week, double-blind, placebocontrolled trial. There was a significantly greater improvement in forced expiratory volume in 1 second (FEV1) from baseline for the montelukast group (8.23%) compared with the placebo group (3.58%). There was a significant decrease in the use of a 3-agonist for symptom relief, as well as in the percentage of days and percentage of patients with asthma exacerbations. An asthma specific quality-of-life (QOL) questionnaire revealed a significant overall improvement in QOL and a significant improvement in the QOL domains for symptoms, activity and emotions in montelukast recipients. There was no significant difference between montelukast and placebo recipients in the frequency of adverse events, with the exception of allergic rhinitis, which was more prevalent in the placebo group. An open label follow-up of patients from the above study was undertaken. The effect of montelukast on FEV1 was consistent for up to 1.4 years, with the increase in FEV1 being not significantly different from that in a small control group treated with inhaled beclomethasone dipropionate. QOL remained significantly improved during the open treatment period.

CONCLUSIONS

Montelukast appears effective and safe for the treatment of children with asthma.

Early increase in urinary leukotriene E4 (LTE4) is dependent on allergen dose inhaled during bronchial challenge in asthmatic subjects

BACKGROUND

Urinary leukotriene E4 (LTE4) excretion is a good marker of the rate of total body production of sulfidopeptide leukotrienes released during allergen challenge.

METHODS

Twenty-three subjects with allergic asthma were challenged with inhaled allergen, and the urinary excretion of LTE4 was determined by immunoenzymatic assay (associated with HPLC separation) at various intervals after challenge.

RESULTS

Allergen challenge caused an early airway response (EAR) with a drop in FEV1 of 40.3+/-9.9%. This was associated with an increase in urine LTE4 excretion for 0-3 h after allergen inhalation (296+/-225.25 pg/mg creatinine) in comparison with baseline values obtained during the night before challenge (101.02+/-61.97 pg/mg creatinine). Urinary LTE4 excretion was significantly higher in subjects who inhaled a higher dose of allergen during challenge (LTE4 during EAR: 211+/-192 pg/mg creatinine in subjects with inhaled total dose of allergen <0.1 biologic units; 408+/-223 pg/mg creatinine in subjects with inhaled total dose >0.1 biologic units). All subjects showed a late airway response (LAR) to allergen of different severity, from mild (FEV1 fall: 15-20%) to severe (>30%); no correlation was found between the increase in urine LTE4 excreted during LAR (3-7 h after challenge) and the severity of LAR, but only subjects with severe LAR showed a significant increase in LTE4 during LAR in comparison with baseline value.

CONCLUSIONS

A release of sulfidopeptide leukotrienes, as evaluated by urinary LTE4 excretion, can be documented during EAR and LAR to allergen in relation to the dose of inhaled allergen, and it can represent a useful index of the events underlying the airway inflammatory responses during allergen challenge.

Biochemistry and physiology of the leukotrienes

Based on the studies that have used human subjects and materials, and a much larger body of data from animal and in vitro experiments, one can conclude that the LTs are potent bronchoconstrictors in normal and asthmatic subjects. A major part of their action is mediated directly via the cysLT-1 receptor on airway smooth muscle. There is also evidence for an effect on airway hyperresponsiveness probably via eosinophil recruitment and activation, airway edema, and possibly airway nerves. Taken together, these studies support a key role for the leukotrienes in asthma. However, additional studies are needed to further define their effects on the airway inflammatory response.

Effect of inhaled leukotriene D4 on airway eosinophilia and airway hyperresponsiveness in asthmatic subjects

Inhaled cysteinyl leukotrienes may cause recruitment of eosinophils into asthmatic airways. We compared the effects of inhaled leukotriene D4 (LTD4), methacholine, and allergen on airway eosinophils in 10 nonsmoking, atopic, mildly asthmatic subjects in a double-blind, diluent-controlled, randomized crossover study. Concentrations of LTD4, methacholine, and allergen resulting in a 30% decrease in FEV1, and diluent controls (ethanol and saline), were inhaled with at least 7 d between challenges. Spirometry was conducted for 4 h after inhalation challenge, and airway hyperresponsiveness (AHR) to methacholine was measured before and 24 h after challenge. Sputum was induced before and 4 h, 7 h, and 24 h after challenge. The maximum decrease in FEV1 was 31.4 +/- 1.8% with LTD4, 39.4 +/- 2.8% with methacholine, and 30.1 +/- 3.4% with allergen. AHR to methacholine, at the provocative concentration causing a 20% decrease in FEV1 (PC20), was enhanced 24 h after allergen challenge, but remained unchanged 24 h after LTD4 and methacholine (p > 0.05). The percentage of eosinophils in sputum was increased after inhalation of allergen at 7 h and 24 h (p = 0.003), but not after LTD4 or methacholine (p = 0.70). We demonstrated that neither inhalation of LTD4 nor of methacholine at concentrations causing submaximal bronchoconstriction increases the number of sputum eosinophils in the airways of mildly asthmatic subjects. However, LTD4 may still be an important cofactor for eosinophil recruitment in asthma.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

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.

Zafirlukast. A review of its pharmacology and therapeutic potential in the management of asthma

Zafirlukast is a competitive and selective leukotriene receptor antagonist indicated for the prophylaxis and treatment of chronic asthma. The rationale for the development of leukotriene antagonists was based on in vitro and in vivo data demonstrating the extensive role of the cysteinyl leukotrienes C4 (LTC4), D4 (LTD4) and E4 (LTE4) in the pathogenesis of asthma. Initial data have demonstrated an improvement in pulmonary function and symptom control and a reduction in the use of short-acting inhaled beta 2-adrenoceptor agonist therapy in patients with mild to moderate asthma treated with oral zafirlukast at the recommended dosage of 20 mg twice daily. Available data also suggest that zafirlukast may significantly reduce the incidence of asthma exacerbations. Data on the comparative efficacy of zafirlukast and existing antiasthma medications are limited. Results from 2 double-blind randomised studies comparing zafirlukast 20 mg twice daily with sodium cromoglycate aerosol or dry powder inhalation reported similar efficacy for both drugs. In a comparison with inhaled beclomethasone dipropionate (0.2 to 0.25 mg twice daily), improvements in morning peak expiratory flow rate, forced expiratory volume in 1 second and daytime symptom score were significantly less with zafirlukast 20 mg twice daily for 6 weeks. However, available data suggest that patient compliance and patient preference may be greater with oral zafirlukast 20 mg twice daily than with twice-daily inhaled corticosteroid therapy. Confounding results from 2 studies preclude any clear conclusions regarding the potential steroid-sparing effect of zafirlukast at the recommended dosage of 20 mg twice daily. Furthermore, Churg-Strauss syndrome has been reported in 6 patients who were being withdrawn from oral corticosteroid therapy while receiving treatment with oral zafirlukast. It is, therefore, recommended that zafirlukast-treated patients who require a reduction in their oral corticosteroid therapy are closely monitored. Zafirlukast is generally well tolerated. Reports of elevated liver enzymes in patients receiving high dosages of zafirlukast (80 mg twice daily) preclude the use of dosages exceeding 40 mg twice daily. Careful monitoring is necessary in zafirlukast-treated patients receiving concomitant therapy with drugs such as warfarin, terfenadine and erythromycin because of the potential for drug interactions. Thus, zafirlukast is a potentially useful addition to current antiasthma therapies in patients with mild to moderate asthma. Because zafirlukast is administered orally, it may be particularly beneficial in patients poorly compliant with asthma therapy as a result of poor inhaler technique. Further investigation of the efficacy of zafirlukast is expected to more clearly define its position in the management of asthma.

The effects of a novel sulphidopeptide leukotriene antagonist, BAY x7195, against elicited bronchoconstriction in the anaesthetized guinea-pig

1. The novel leukotriene antagonist Bay x7195, has been evaluated against bronchoconstriction induced by leukotriene D4 (LTD4), the thromboxane A2 (TXA2) mimetic U46619, histamine and antigen, in the guinea-pig in vivo by use of a modified Konzett-Rössler preparation. 2. LTD4, given intravenously (i.v.) at 1 or 3 microg kg(-1) in the presence of indomethacin and sotalol, caused a 50-70% maximal bronchoconstriction in most animals. 3. BAY x7195, given i.v., orally (p.o.), by aerosol or dry powder insufflation, in lactose, reduced LTD4-induced bronchoconstriction dose-dependently. The approximate ID50 values were 83 microg kg(-1), 3 mg kg(-1), 0.0003% w/v for 20 breaths and 20 microg respectively. 4. The action of BAY x7195 (10 mg kg(-1), p.o.) was long lasting, causing significant inhibition of the LTD4-induced response (88% reduction) 8 h after dosing. 5. When given intravenously, in the presence of selected antagonists, BAY x7195 caused a dose-related reduction in the antigen-induced response, with an approximate ID50 of 2 mg kg(-1). 6. At 3 mg kg(-1), i.v., a dose which abolished the response to LTD4, BAY x7195 had no effect on U46619- or histamine-induced bronchoconstriction. 7. BAY x7195 is a potent, selective and long acting antagonist of LTD4-induced bronchoconstriction, in an anaesthetized, ventilated guinea-pig model. It is therefore worthy of clinical evaluation in diseases believed to involve the sulphidopeptide leukotrienes, such as asthma.

Dipeptidase inhibitor and epithelial removal potentiate leukotriene D4-induced human tracheal smooth muscle contraction

We investigated the role of epithelium in smooth muscle contraction induced by leukotriene D4 (LTD4) in isolated human trachea. The contractile response to LTD4 was potentiated by an inhibitor of dipeptidases L-cysteine and by removal of the epithelium. Both L-cysteine (3 x 10(-3) M) and removal of the epithelium shifted the concentration-response curves to LTD4, to lower concentrations by 0.7 and 0.6 log units, respectively. Incubation of cultured or isolated human tracheal epithelial cells with LTD4 resulted in the formation of LTE4, which was completely blocked by pretreatment with L-cysteine (3 x 10(-3) M). The isolated and cultured human tracheal epithelial cells contained microsomal dipeptidase (MDP) activity. Immunohistochemical study indicated MDP protein was present in the epithelium and endothelial cells of submucosal microvessels in the human trachea. These results suggest that the epithelium modulates the contractile response to LTD4 in human trachea by dipeptidases degrading LTD4.

Montelukast causes prolonged, potent leukotriene D4-receptor antagonism in the airways of patients with asthma

Montelukast, a new specific oral cysteinyl LT3-receptor antagonist was evaluated for its activity in attenuating inhaled leukotriene D4 (LTD4) bronchoconstriction in patients with asthma. In two double-blind, placebo-controlled, randomized crossover studies, patients with mild asthma (forced expiratory volume in 1 second [FEV1] > or = 70%) were studied. In trial A, LTD4 challenge began 4 hours (peak plasma concentration) after a single dose of placebo or 5, 20, 100, and 250 mg montelukast. In trial B, and LTD4 challenge was started 20 hours after administration of placebo, 40 mg montelukast, or 200 mg montelukast. During each challenge, twofold increasing concentrations of LTD4 were inhaled until specific airways conductance (sGaw) decreased by at least 50% (PC50) or the highest concentration of LTD4 was inhaled. In trial A with all doses and in trial B with the 200 mg dose, bronchoconstriction was attenuated (50% fall in sGaw was not observed) up to the highest dose of LTD4 administered. In trial B, during the 40 mg period, only two of six patients exhibited a 50% fall in sGaw; PC50 ratios (montelukast 40 mg/placebo) were 18 and 45 in these two patients. These results indicate that montelukast is a highly potent and long-lasting antagonist of LTD4-induced bronchoconstriction in patients with asthma.

Eicosanoids and asthma: an update

There have been significant advances in our understanding of the role of eicosanoids as mediators in inflammation since their discovery over 50 years ago. Our more recent understanding of asthma as an inflammatory disease has led to the appreciation of eicosanoids potentially being pivotal mediators in promoting some of the changes in asthma. Of particular importance are the cysteinyl LTs in producing bronchospasm and bronchial hyperresponsivenss, and PGE2 in modulating the bronchospastic and inflammatory response. Evidence from clinical studies suggests that other eicosanoids may also contribute, but their importance is secondary and their relative contributions vary between individuals. The development of new drugs based on our partial understanding of the role that eicosanoid mediators may play in asthma promises new approaches to the treatment of this common chronic inflammatory condition.

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.

Molecular cloning and expression of human leukotriene-C4 synthase

Leukotriene-C4 synthase (LTC4S; EC 2.5.1.37) catalyzes the committed step in the biosynthesis of the peptidoleukotrienes, which are important in the pathogenesis of asthma. Antibodies were generated to a synthetic peptide based on the partial amino acid sequence previously reported for human LTC4S [Nicholson, D.W., Ali, A., Vaillancourt, J.P., Calaycay, J.R., Mumford, R.A., Zamboni, R.J. & Ford-Hutchinson, A. W. (1993) Proc. Natl. Acad. Sci. USA 90, 2015-2019] and specifically bound detergent-solubilized LTC4S obtained from THP-1 cells, confirming that the published sequence is associated with enzyme activity. Inosine-containing oligonucleotides based on the partial protein sequence were used to isolate a 679-bp cDNA for LTC4S from THP-1 cells. The cDNA contains an open reading frame that encodes a 150-amino acid protein (M(r) = 16,568) that has a calculated pI value of 11.1. The deduced protein sequence is composed predominantly of hydrophobic amino acids; hydropathy analysis predicts three transmembrane domains connected by two hydrophilic loops. Analysis of the deduced sequence identified two potential protein kinase C phosphorylation sites and a potential N-linked glycosylation site. The amino acid sequence for human LTC4S is unique and shows no homology to other glutathione S-transferases. LTC4S was found to be most similar to 5-lipoxygenase activating protein (31% identity, 53% similarity), another protein involved in leukotriene biosynthesis. Active enzyme was expressed in bacterial, insect, and mammalian cells as shown by the biosynthesis of LTC4 in incubation mixtures containing LTA4 and reduced glutathione. The cloning and expression of human LTC4S provide the basis for a better understanding of this key enzyme in peptidoleukotriene biosynthesis.

Expression cloning of a cDNA for human leukotriene C4 synthase, an integral membrane protein conjugating reduced glutathione to leukotriene A4

Leukotriene (LT) C4 synthase, an integral microsomal membrane protein, conjugates LTA4, an epoxide intermediate, to reduced glutathione (GSH) to form a proinflammatory mediator, LTC4. A sensitive fluorescence-linked immunoassay for LTC4 was used to screen a KG-1 cDNA expression library for LTC4 synthase activity after transfection of COS cells and addition of substrate LTA4. Stepwise resolution of 240,000 colonies in 96 pools led to the identification of individual clones with maximal LTC4 synthase activity that contained a 694-bp cDNA insert. This insert was composed of a 54-bp 5' nontranslated region, an ATTAAA polyadenylylation signal, and a poly(A)+ tail. The open reading frame encodes a 16.5-kDa protein with a pI of 11.05. Hybridization with a cDNA probe demonstrated a mRNA transcript of 0.7 kbp in RNAs from human eosinophils and KG-1 cells, which contain LTC4 synthase. The nucleotide and deduced amino acid sequences of the LTC4 synthase cDNA show no significant homology to GSH S-transferases but share 31% overall amino acid identity with 5-lipoxygenase activating protein (FLAP). The identity at the N-terminal two-thirds of these two proteins is 44%, with some regions of near identity. Peptide structural analysis of the deduced LTC4 synthase predicts the presence of three transmembrane domains nearly superimposable on those of FLAP. Moreover, LTC4 synthase is inhibitable by a FLAP inhibitor, MK-886. Therefore, LTC4 synthase is distinct from the known GSH S-transferases by nucleotide and consensus amino acid sequences, and its GSH-conjugating function represents a distinct integral membrane protein belonging to a distinct gene family.

Leukotrienes as a target in asthma therapy

Asthma is a chronic inflammatory condition characterised by bronchial hyper-responsiveness and reversible airways obstruction. Research has demonstrated that these effects are mediated by a wide range of compounds. In the last decade leukotrienes have been identified as products of arachidonic acid metabolism. Their effects mimic the pathological changes seen in asthma both in vitro and in vivo. Further research has demonstrated increased production of leukotrienes both during episodes of asthma and in patients with stable asthma. The demonstration that leukotrienes have proinflammatory biological properties relevant to the pathogenesis of asthma has stimulated the development of many potential therapeutic compounds to block these actions. Early studies in laboratory-induced asthma in human volunteers have shown the efficacy of some of these compounds. They have been shown to attenuate the bronchoconstriction caused by allergen challenge, exercise, aspirin and exposure to cold air. Most encouraging of all have been recent placebo-controlled studies in clinical asthma where significant improvements in terms of spirometry, symptoms and beta 2-agonist use have been demonstrated. Leukotriene receptor antagonists and synthesis inhibitors are the first mediator antagonists to have been shown to be effective in treating clinical asthma and as such represent one of the most interesting new classes of antiasthma drugs in development at present.

Exercise-induced refractoriness in asthmatic subjects involves leukotriene and prostaglandin interdependent mechanisms

Exercise-induced bronchoconstriction is caused, in part, by leukotriene (LT)D4 release in asthmatic airways. Asthmatics become refractory to exercise bronchoconstriction with repeated challenges, due to inhibitory prostaglandin release. The purpose of this study was to test the hypothesis that exercise refractoriness is caused by LTD4-induced inhibitory prostaglandin release. Fourteen stable asthmatic subjects with exercise-induced bronchoconstriction were studied. On the first 2 days, subjects underwent two challenges, 1 h apart, with either exercise or inhaled LTD4. Eight subjects then took part in three double-blind, randomized, placebo-controlled, crossover studies with flurbiprofen, a prostaglandin synthetase inhibitor, to determine whether cross refractoriness occurs between exercise and LTD4, whether flurbiprofen attenuates this effect, and whether flurbiprofen attenuates LTD4 tachyphylaxis. There was a reduction in the intensity of bronchoconstriction to the second challenge both with exercise (refractoriness) and with LTD4 (tachyphylaxis). The degrees of refractoriness and tachyphylaxis were correlated (r = 0.72, p = 0.005). Flurbiprofen attenuated LTD4 tachyphylaxis. Cross refractoriness occurred between exercise and LTD4, and flurbiprofen treatment also attenuated this effect. One hour after LTD4 challenge, the mean fall in FEV1 after exercise was 12.3% (%SEM 2.3) on placebo and 17.1% (%SEM 3.8) on flurbiprofen (p = 0.027). Similarly, 1 h after exercise, the LTD4 PC20 increased to 0.73 (%SEM 1.4) microgram/ml on placebo and 0.30 (%SEM 1.8) microgram/ml on flurbiprofen (p = 0.026). These results suggest that LTD4 released in asthmatic airways as a result of exercise stimulates inhibitory prostaglandin release, resulting in exercise refractoriness.

Role of leukotrienes in airway hyperresponsiveness in guinea-pigs

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

Carbonate inhibition of leukotriene D4-dipeptidase in human serum

Human serum contains an inhibitor of leukotriene D4 (LTD4) dipeptidase which was separated from the enzyme by ultrafiltration (Amicon, YM-10). Removal of the inhibitor resulted in a 3- to 5-fold increase in total LTD4-dipeptidase activity in the material retained by the filter. Inhibitor activity (which was assayed with a partially purified LTD4-dipeptidase) was recovered in the filtrate. Ultrafiltration of serum using YM-3, YM-1, and YC-05 membranes suggested an inhibitor molecular weight of less than 500. Elution of inhibitor activity from a Bio Gel P2 gel filtration column was identical to the elution pattern of pure carbonate. The inhibitor was heat stable (95 degrees C, 30 min), stable in 0.1 N NaOH, but rapidly inactivated by 0.1 N HCl at both 4 degrees C and 30 degrees C. Partially purified LTD4-dipeptidase was inhibited by carbonate and phosphate but not by nitrate, sulfate, or chloride. Based on these observations it was concluded that the inhibitor of LTD4-dipeptidase in human serum either was carbonate or required carbonate. The relative concentrations of LTC4, LTD4, and LTE4 appear to be important parameters in determining the duration and intensity of LT mediated reactions. The relative concentration of carbonate in serum or extracellular fluids might, therefore, be a factor in modulating localized LT mediated responses.

Effects of catecholamines on eicosanoid synthesis with special reference to prostanoid/leukotriene ratio

Catecholamines (adrenaline, dopamine, and noradrenaline) stimulate prostanoid synthesis by acting as "cosubstrates." On the other hand, many inhibitors of leukotriene synthesis, such as nordihydroguaiaretic acid and caffeic acid, have a catecholic structure. Catecholamines have opposite effects on prostanoid and leukotriene synthesis in human polymorphonuclear leukocytes and whole blood. Basic phenols (catechol, hydroquinone, and phenol) also increase the prostanoid/leukotriene ratio in polymorphonuclear leukocytes. These actions correlate to their antioxidant capacities and oxidation potentials, and they are not mediated via adrenergic receptors. There is only limited knowledge about the effects of natural catecholamines on the prostanoid/leukotriene ratio in vitro and in vivo. Indirect data suggest that catecholamines could increase prostanoid production in physiological or pathological situations, such as heavy physical exercise, myocardial infarction, and surgical stress. This interaction may also be of clinical importance in asthma, gastric ulcer, and psoriasis, where decreased prostanoid/leukotriene ratios have been reported.

Bronchodilator properties of an inhaled leukotriene D4 antagonist (verlukast--MK-0679) in asthmatic patients

The safety, tolerability and bronchodilator properties of inhaled verlukast (MK-0679), a new potent and selective LTD4-receptor antagonist, were studied in 12 asthmatic subjects with more than 15% increase in FEV1 after salbutamol inhalation. On three separate study days the patients inhaled placebo, verlukast 2 mg and verlukast 8 mg from a metered dose inhaler according to a randomized, double-blind, cross-over allocation schedule. Pulmonary function and tolerability were assessed regularly and after 8 h a second dose of test drug was inhaled. Thirty minutes later a beta 2-agonist dose-response curve was performed by inhaling salbutamol in cumulative doses of 200, 400 and 800 micrograms. Verlukast (8 mg) caused significant improvement in mean FEV1 from 1.5 through 8 h after inhalation as compared to placebo (P less than 0.05). The maximum change in FEV1 occurred at 2 h after inhalation with mean percent increases above baseline of 3.5, 7.7, and 9.2% after placebo, verlukast 2 mg and 8 mg, respectively. The bronchodilator response to inhaled salbutamol was significantly larger after verlukast 8 mg than after placebo pretreatment (P less than 0.05), whereas verlukast 2 mg afforded no additive bronchodilator effect. We conclude that inhalation of the LTD4-antagonist verlukast induces modest but significant bronchodilatation and may be beneficial in the treatment of asthma.

Enhanced production of platelet activating factor by peripheral granulocytes from children with asthma

Granulocytes from 23 asthmatic children aged 4-15 years and 32 age-matched healthy children were studied. Cells were purified by Dextran sedimentation and Percoll gradient centrifugation from heparinized blood. After in vitro stimulation by ionophore A23187 the amount of newly synthesized PAF and LTC4 was assessed by radio receptor assay or radioimmunoassay respectively. Eight patients had symptoms of asthma within the last 3 weeks before examination. Granulocytes from the symptomatic patients showed a significantly higher PAF generation (median 125 ng/10(6) cells, range 7-189 ng/10(6) cells) when compared to asymptomatic patients (p less than 0.001, median 14 ng/10(6) cells, range 6-33 ng/10(6) cells) or controls (p less than 0.001, median 11 ng/10(6) cells, range 3-26 ng/10(6) cells). In contrast, LTC4 generation was increased in both patient groups. The results suggest a regulatory role of PAF in the exacerbation of asthma.

The pathobiology of bronchial asthma

Early studies of patients dying from status asthmaticus revealed marked inflammation of the bronchial tree. Subsequent histological studies of the airways and examination of bronchoalveolar lavage fluid of subjects with mild asthma have confirmed the presence of airway inflammation in life. There is epithelial edema and desquamation, subepithelial deposition of collagen and fibronectin, and an inflammatory cell infiltrate in the mucosa. There are increased numbers of activated eosinophils, CD25-positive T lymphocytes, and immature macrophages with the phenotypic characteristics of blood monocytes. An increased expression of HLA class II is present on epithelium, macrophages, and other infiltrating cells. The severity of clinical asthma correlates with several measurements of the severity of the inflammatory response, suggesting a crucial role for airway inflammation in the pathophysiology of the disease. There is considerable interest and research into the mechanisms underlying the pathogenesis and maintenance of the inflammatory response in asthma. The development and maintenance of the inflammatory response in asthma is likely to be a consequence of a complicated interaction between various cells and the mediators they generate. The characterization of an ever-increasing number of cytokines is of particular interest. Interleukin-3, interleukin-5, and granulocyte-macrophage colony-stimulating factor are hematopoietic growth factors that increase the survival of eosinophils in culture and enhance certain eosinophil functions, such as mediator generation and toxicity. Alveolar macrophages derived from asthmatic subjects produce twofold to threefold more GM-CSF than do those from normal control subjects. Using in situ hybridization, the presence of IL-5 mRNA has been demonstrated in bronchial biopsies from asthmatic subjects. Thus IL-3, IL-5, and GM-CSF influence eosinophil function and survival, and may be generated by T lymphocytes and/or alveolar macrophages within the airways in asthma. In addition to these three cytokines, IL-4 and interferon-gamma may be crucial to the regulation of IgE biosynthesis. TNF-alpha and IL-1 are potentially important in the up-regulation of endothelial adhesion molecules. An important step in the recruitment of leukocytes to an inflammatory focus is margination to the vascular endothelium. Our understanding of the molecular events involved in migration of leukocytes to an inflammatory focus has been advanced by the discovery and characterization of a variety of cell adhesion molecules. The potential role of ELAM-1 and ICAM-1 in allergic inflammation is suggested by their up-regulation on vascular endothelium in association with late cutaneous responses to allergen and by their role in certain primate models of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)