Effects of long-acting beta 2-adrenoceptor agonists on mast cells of rat, guinea pig, and human

Effects of intranasal salmeterol and fluticasone given alone and in combination in persistent allergic rhinitis

BACKGROUND

β(2)-Agonists have previously been shown to be effective inhibitors of mediator release from airway mucosal mast cells.

OBJECTIVE

To evaluate the effects of intranasal salmeterol and fluticasone propionate alone and in combination on the response to nasal adenosine monophosphate (AMP) challenge to assess mast cell activation.

METHODS

Twenty-three patients with persistent allergic rhinitis completed a randomized, double-blind, placebo-controlled, 4-way crossover trial. They received once daily treatment with placebo, salmeterol, 50 μg, fluticasone propionate, 500 μg, or fluticasone propionate and salmeterol combination, 500/50 μg, delivered via an antistatic spacer with nasal adapter for 1 week each, with trough measurements being made 12 hours after the first and last dose. The primary outcome was the maximum percentage decrease in peak nasal inspiratory flow after nasal AMP challenge.

RESULTS

For the primary outcome there was significant protection after single and long-term dosing with fluticasone alone and fluticasone-salmeterol combination, whereas salmeterol alone only afforded protection after the first dose. Fluticasone-salmeterol combination and fluticasone but not salmeterol conferred significant chronic dosing effects on secondary outcomes of nasal symptoms and disease-specific quality of life. There was no potentiation of the response to fluticasone by salmeterol on any outcomes when given in combination.

CONCLUSION

Chronic dosing with fluticasone but not salmeterol confers anti-inflammatory activity against nasal AMP challenge, but there was no potentiation of fluticasone when given in combination with salmeterol. Thus, salmeterol may not be an effective treatment for use in allergic rhinitis.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01388595.

The long-acting beta-adrenoceptor agonist, indacaterol, inhibits IgE-dependent responses of human lung mast cells

BACKGROUND AND PURPOSE

The long-acting beta(2)-adrenoceptor agonist, indacaterol, has been developed as a bronchodilator for the therapeutic management of respiratory diseases. The aim of the present study was to determine whether indacaterol has any anti-inflammatory activity. To this end, the effects of indacaterol on human lung mast cell responses were investigated.

EXPERIMENTAL APPROACH

The effects of indacaterol, and the alternative long-acting beta-agonists formoterol and salmeterol, were investigated on the IgE-dependent release and generation of histamine, cysteinyl-leukotrienes and prostaglandin D(2) from human lung mast cells. Moreover, the extent to which long-term (24-72 h) incubation of mast cells with long-acting beta-agonists impaired the subsequent ability of beta-agonists to inhibit mast cell responses was assessed.

KEY RESULTS

Indacaterol was as potent and as efficacious as the full agonist, isoprenaline (EC(50), approximately 4 nmol x L(-1)), at inhibiting the IgE-dependent release of histamine from mast cells. Formoterol was a full agonist whereas salmeterol was a partial agonist as inhibitors of histamine release. All three long-acting beta-agonists were effective inhibitors of the IgE-dependent generation of cysteinyl-leukotrienes and prostaglandin D(2). Long-term incubation of mast cells with long-acting beta-agonists led to a reduction in the subsequent ability of beta-agonists to stabilize mast cell responses. This tendency to induce functional desensitization was least evident for indacaterol.

CONCLUSIONS AND IMPLICATIONS

Indacaterol is an effective inhibitor of the release of mediators from human lung mast cells. This suggests that, as well as bronchodilation, mast cell stabilization may constitute an additional therapeutic benefit of indacaterol.

Inhibition of basal and stimulated release of endothelin-1 from guinea pig tracheal epithelial cells in culture by beta 2-adrenoceptor agonists and cyclic AMP enhancers

The effects of cyclic AMP-related compounds and beta adrenoceptor agonists on the basal and lipopolysaccharide (LPS)-stimulated release of endothelin-1 (ET-1) from guinea-pig tracheal epithelial cells (GPTEpCs) in culture were studied. Forskolin (a potent activator of adenylyl cyclase), 8-bromo-cyclic AMP (a cyclic AMP analogue), salbutamol and salmeterol (two beta 2-adrenoceptor agonists), were used to increase cyclic AMP levels. Cultured GPTEpCs released ET-1 continuously over a 24 h incubation period. The values reached 1,938 +/- 122 pg/mg of total cell proteins after 24 h. LPS (10 microg/ml) significantly stimulated the release of ET-1 by 1.6- to 1.8-fold, up to 1,262 +/- 56 pg/mg total cell proteins after an 8 h incubation period. Compound 8-bromo-cyclic AMP (10(-5), 10(-4) and 10(-3) M) reduced the basal release of ET-1 from GPTEpCs by up to 31% (P < 0.01) and the LPS stimulated release by up to 42% (P < 0.05), after an 8 h incubation period. Forskolin (10(-6), 10(-5) and 10(-4) M) also inhibited the basal release of ET-1 by up to 28% (P < 0.05) and LPS-stimulated release of ET-1 by up to 50% (P < 0.05), after an 8 h incubation period. At the concentration of 10(-5) M, forskolin increased cyclic AMP levels in GPTEpCs by 17-fold (P < 0.001) in the medium, 15 min after the beginning of the incubation. Salbutamol (10(-8) to 10(-6) M) had no effect on the basal production and release of ET-1 after 8 h. Conversely, this short acting beta 2-adrenoceptor agonist significantly reduced LPS-mediated increase of ET-1 production by up to 55% (P < 0.05) after an 8 h incubation period. Salmeterol (10(-9) M to 10(-5) M) inhibited basal and LPS-stimulated production and release of ET-1 after an 8 h incubation period (between 44 and 51%, P < 0.01). Both salbutamol and salmeterol (10(-6) M) increase cyclic AMP levels by five- and twofold, respectively (P < 0.05). In summary, these observations indicate that beta 2-adrenoceptor agonists or cyclic AMP enhancers can modulate both basal and more markedly, the enhanced production of ET-1 from LPS-activated guinea pig airway EpCs. In addition, these compounds increase cyclic AMP levels in the cells. It is suggested that there is a correlation between cyclic AMP increase and inhibition of ET-1 release by guinea pig airway EpCs. Since ET-1 production was shown to be elevated in asthmatic subjects and in patients suffering from other inflammatory lung disorders, the inhibition of its production by beta adrenoceptor agonists, such as salbutamol and salmeterol, could be added to their therapeutical benefits.

Influence of beta2-adrenoceptor gene polymorphisms on beta2-adrenoceptor-mediated responses in human lung mast cells

BACKGROUND AND PURPOSE

Previous studies have shown that beta(2)-adrenoceptor-mediated responses in human lung mast cells are highly variable. The aims of the present study were to establish whether polymorphisms of the beta (2)-adrenoceptor gene (ADRB2) influence this variability in (a) beta(2)-adrenoceptor-mediated inhibition and (b) desensitization of beta(2)-adrenoceptor-mediated responses in human lung mast cells.

EXPERIMENTAL APPROACH

Mast cells were isolated from human lung tissue. The inhibitory effects of the beta-adrenoceptor agonist, isoprenaline (10(-10)-10(-5) M), on IgE-mediated histamine release from mast cells were determined (n=92). Moreover, the inhibitory effects of isoprenaline were evaluated following a desensitizing treatment involving long-term (24 h) incubation of mast cells with isoprenaline (10(-6) M) (n=65). A potential influence of polymorphisms on these functional responses was determined by genotyping 11 positions, in the promoter and coding regions, of ADRB2 previously reported as polymorphic.

KEY RESULTS

There was no influence of any of the polymorphic positions of ADRB2 on the potency of isoprenaline to inhibit histamine release from mast cells with the exception of position 491C>T (Thr164Ile). There was no influence of any of the polymorphic positions of ADRB2 on the extent of desensitization of the isoprenaline-mediated response following a desensitizing treatment except for position 46G>A (Gly16Arg). Analyses at the haplotype level indicated that there was no influence of haplotype on beta (2)-adrenoceptor-mediated responses in mast cells.

CONCLUSIONS AND IMPLICATIONS

These data indicate that certain polymorphisms in ADRB2 influence beta(2)-adrenoceptor-mediated responses in human lung mast cells.

Regulation of mast cells by beta-agonists

The human lung mast cell is known to be a critical effector cell in the mediation of asthma. Activation of the mast cell by allergens and other stimuli leads to the release and generation of a wide variety of autacoids that cause bronchoconstriction, promote inflammation, and may influence airway remodeling. Therefore, the stabilization of mast cells has obvious value in the prevention of asthma. Among the drugs used to treat asthma, only beta-agonists are effective stabilizers of mast cells. Both short- and long-acting beta-agonists are effective against mast cells, but there are differences between agonists regarding the extent of inhibitory activity attained. Consequently, the type of beta-agonist prescribed influences the degree of mast cell stabilization possible. Despite the potential value of attenuating mast cell activity with beta-agonists, this benefit may diminish with time because of the development of tolerance. Both short- and long-acting beta-agonists can induce tolerance to mast cell stabilization, and generally, higher efficacy agonists tend to induce greater levels of tolerance; however, weaker agonists induce greater levels of tolerance than might be expected. Tolerance to the mast-cell-stabilizing effects of beta- agonists may be an issue clinically, because this occurs more readily than tolerance to smooth muscle relaxation. This could lead to a situation in which beta-agonists fail to prevent the release of mediators from mast cells but can still effectively relax airway smooth muscle. The continued ability to bronchodilate could mask the unfavorable consequences of unchecked mediator release from mast cells.

Differentiation and maintenance of mast cells from CD34+ human cord blood cells

OBJECTIVE

Establishment of a stable umbilical cord blood CD34(+) (UCB CD34(+)) cell culture system and identification of the cells in the cobblestone area differentiated from UCB CD34(+) long-term culture cells.

MATERIALS AND METHODS

Human UCB CD34(+) cells were cultured on MS-5 mouse stroma cells in the presence of stem cell factor (SCF), flt-3 ligand (FL), and thrombopoietin (TPO) for 4 to 16 weeks. Cells in the culture medium and in the cobblestone area were collected and characterized by flow cytometry and microscopy.

RESULTS

CD34(+) cells were stably expanded by culturing on MS-5 stroma cells in the presence of SCF, FL, and TPO for more than 4 months. Cells highly expressing CD117 (c-kit) appeared in the cobblestone area after 2 weeks and stably expanded. Isolation of cells highly expressing CD117 by fluorescence-activated cell sorter (FACS) revealed the cells were tryptase-positive and Fc epsilon receptor 1-negative mast cells. They showed typical mast cell morphology and released histamine upon stimulation by substance P or compound 48/80 in vitro.

CONCLUSION

Human UCB CD34(+) cells were stably expanded on MS-5 stroma cells in the presence of SCF, FL, and TPO. Under this condition, multipotent CD34(+) cells and mast cells differentiated from UCB CD34(+) cells were expanded in the cobblestone area. The expanded mast cells showed histamine release after substance P or compound 48/80 stimulation. These human mast cells will be useful as a source of human cells for evaluating the allergic effects of drugs.

Effect of salbutamol on nasal symptoms and mast cell degranulation induced by adenosine 5' monophosphate nasal challenge

BACKGROUND

In addition to its well-known functional agonism at the level of beta(2) adrenergic receptors on airways smooth muscle cells, salbutamol appears to have additional protective effects, possibly through an inhibition of mast cell activation.

OBJECTIVE

The aim of this study is to provide the first evidence in vivo of inhibition of human mast cell activation by salbutamol.

METHODS

Nine atopic subjects received placebo and salbutamol (5 mg/mL) 15 min before an adenosine 5' monophosphate (AMP) nasal provocation in a double-blind crossover study design. The nasal lavage was collected from these subjects prior to or 3, 5, 15 or 30 min after the AMP nasal challenge, and concentrations of histamine and tryptase in the nasal lavage were measured.

RESULTS

AMP nasal provocation produced considerable sneezing and induced a transient increase in histamine and tryptase release with peak values achieved at 3 min after the challenge in all the subjects studied. Compared with placebo, salbutamol significantly attenuated the release of histamine and tryptase induced by AMP challenge (P=0.048 and 0.020, respectively). Moreover, the AMP-induced sneezing was also inhibited by pre-treatment with salbutamol (P=0.004).

CONCLUSIONS

Intranasal salbutamol attenuates nasal symptoms and inhibits histamine and tryptase release caused by AMP nasal provocation thus supporting the hypothesis that salbutamol may play an additional protective role in the airways by inhibiting mast cell activation.

Influence of agonist intrinsic activity on the desensitisation of beta2-adrenoceptor-mediated responses in mast cells

1. The aim of the present study was to determine whether the intrinsic activity of an agonist influences the extent of desensitisation of beta(2)-adrenoceptor-mediated responses in human lung mast cells. 2. The effects of a wide range of beta-adrenoceptor agonists (10(-10)-10(-5) m) on the IgE-mediated release of histamine from mast cells were determined. The intrinsic activity of agonists was established by comparing the maximal inhibitory response (E(max)) of an agonist relative to the maximal response obtained with the full agonist, isoprenaline. The intrinsic activity order for the inhibition of histamine release was isoprenaline (1.0)>formoterol (0.94)>fenoterol (0.89)>terbutaline (0.84)>salbutamol (0.69)>clenbuterol (0.65)>salmeterol (0.30)>dobutamine (0.20). 3. There was a significant (P<0.05) positive correlation (r=0.81) between the extent to which beta-adrenoceptor agonists inhibited histamine release and the degree to which the agonists caused elevations in cAMP in mast cells. 4. Further studies investigated the effects of long-term (24 h) incubation of mast cells with beta-adrenoceptor agonists on the subsequent ability of isoprenaline to inhibit histamine release. At concentrations of agonists selected to occupy a large percentage (88%) of beta(2)-adrenoceptors, there was a significant (P<0.05) correlation (r=0.73) between the relative intrinsic activity of agonists as inhibitors of histamine release and the extent of functional desensitisation induced by the agonists. At lower receptor occupancies, however, there was no correlation between the relative intrinsic activity of agonists and the extent of agonist-induced desensitisation. 5. These data indicate that, under experimental conditions where high receptor occupancies prevail, agonist intrinsic activity influences the extent of desensitisation of beta(2)-adrenoceptor-mediated responses in mast cells.

Desensitisation of mast cell beta2-adrenoceptor-mediated responses by salmeterol and formoterol

1. The long-acting beta(2)-adrenoceptor agonist formoterol (10(-10)-10(-6) m) inhibited the IgE-dependent release of histamine from human lung mast cells in a concentration-dependent manner. Formoterol was more potent and a full agonist relative to the nonselective beta-adrenoceptor agonist isoprenaline. By contrast, the long-acting beta(2)-adrenoceptor agonist salmeterol (10(-10)-10(-6) m) was about two-thirds less efficacious than either formoterol or isoprenaline as an inhibitor of histamine release. 2. Isoprenaline, formoterol and salmeterol (all at 10(-5) m) increased total cell cAMP levels in mast cells over basal by 361+/-90 (P<0.05), 321+/-89 (P<0.05) and 64+/-24% (P>0.05), respectively. 3. Long-term (24 h) incubation of mast cells with formoterol (10(-6) m) or salmeterol (10(-6) m) essentially abolished the subsequent ability of isoprenaline to inhibit histamine release. Both formoterol and salmeterol were more effective at inducing the functional desensitisation than isoprenaline (10(-6) m) or the short-acting beta(2)-adrenoceptor agonist salbutamol (10(-6) m). 4. The desensitisation induced by long-term treatments with salmeterol and formoterol was specific for beta(2)-adrenoceptor-mediated inhibition of histamine release as the inhibitory effects of alternative cAMP-elevating compounds, prostaglandin E(2), a receptor-mediated activator of adenylate cyclase, and forskolin, a direct activator of adenylate cyclase, were unaffected by desensitising treatments. 5. Radioligand binding studies were performed to determine beta(2)-adrenoceptor density in cell membranes after pretreatment (24 h) of cells with agonists. Isoprenaline, formoterol and salmeterol (all at 10(-6) m) reduced beta(2)-adrenoceptor density by 13+/-5 (P>0.05), 49+/-13 (P<0.05) and 35+/-17% (P>0.05), respectively. 6. These data indicate that long-term exposure of mast cells to both salmeterol and formoterol can cause substantial levels of desensitisation to beta(2)-adrenoceptor-mediated responses in mast cells.

The effect of salmeterol on markers of airway inflammation following segmental allergen challenge

Inflammation is a critical component of asthma. Drugs that control asthma generally reduce the degree of airway inflammation. There is theoretical controversy surrounding the effects of beta(2)-agonists on airway inflammation, with some studies suggesting an anti-inflammatory effect, and others predicting a proinflammatory influence. We conducted a double-blind, placebo-controlled, crossover study of the effect of the long-acting beta(2)-agonist salmeterol on airway inflammation induced by segmental allergen challenge (SAC). We studied 13 allergic asthmatics controlled with as needed inhaled short-acting beta(2)-agonists alone, and used bronchoalveolar lavage 5 min and 48 h after SAC to assess airway inflammation, and the effects of salmeterol on this process. Salmeterol therapy improved FEV(1), but had no significant effect on the immediate or late cellular response to SAC. One measure of superoxide production was reduced, and interleukin-4 (IL-4) was reduced in baseline samples, but other indices of airway inflammation were unchanged by salmeterol therapy. We conclude that salmeterol therapy alone does not meaningfully reduce airway inflammation induced by SAC, but equally importantly, does not result in amplified inflammation.

The pathobiologic implications for treatment. Old and new strategies in the treatment of chronic asthma

An increased understanding of the pathobiology of asthma has led to improved treatment for chronic asthma. This article discusses the old and new strategies of asthma therapy based on a pathobiologic approach. Therapeutic agents discussed include beta-adrenergic agonists, methylxanthines, corticosteroids, cromolyn, nedocromil, leukotriene modifiers, and new investigational agents.

Influence of salmeterol and benzalkonium chloride on G-protein-mediated exocytotic responses of rat peritoneal mast cells

The long-acting beta(2)-adrenoceptor agonist salmeterol and the invert soap benzalkonium chloride share physicochemically important structures, namely a polar head group and a long aliphatic chain. Low concentrations of benzalkonium chloride have been shown to inhibit exocytotic responses in rat peritoneal mast cells by selectively interacting with heterotrimeric G-proteins of the G(i)-type. The present study investigates whether salmeterol inhibits, independently of beta-adrenoceptors, exocytotic responses of rat peritoneal mast cells induced by the direct agonists at G-proteins mastoparan or guanosine 5'-O-(3-thiotriphosphate) (++GTP gamma S++). Exocytosis was studied by secretion assays ([3H]5-hydroxytryptamine ([3H]5-HT)-release) using intact, streptolysin O-permeabilised or metabolically inhibited (antimycin, deoxyglucose) rat peritoneal mast cells. Both amphiphilics, salmeterol, and benzalkonium chloride, dose-dependently exerted biphasic effects on mastoparan-induced [3H]5-HT release in intact mast cells. In contrast to benzalkonium chloride, the dose-response curves for secretostatic and celltoxic effects of salmeterol markedly overlapped. Similar to benzalkonium chloride, salmeterol in non-cytotoxic concentrations (1-25 microg/ml) dose-dependently inhibited exocytosis induced by mastoparan (intact cells) or ++GTP gamma S (permeabilised cells). These findings indicate a direct, adrenoceptor-independent affection of G proteins by salmeterol in mast cells.

Effects of salmeterol on host resistance to Trichinella spiralis in rats

Salmeterol is a long-acting beta2-adrenoreceptor agonist. The compound has previously been screened for immunotoxic potential in a repeated dose toxicity study in rats for 28 days. The total serum IgG levels were increased at dose levels of 2 and 10 mg/kg/day. Presently, salmeterol was studied in an immune function assay addressing the host resistance to Trichinella spiralis parasites. Rats were daily treated with salmeterol for 28 days at dose levels of 0, 2, 6 and 10 mg/kg/day. On day 29, the animals were infected with T. spiralis parasites. After six weeks, host resistance was examined. The numbers of T. spiralis muscle larvae in the tongue nor the inflammatory reactions around the encapsulated larvae were affected by salmeterol treatment. The yield of muscle larvae in the whole carcass was not changed either. The IgM, IgA and IgE antibody responses to T. spiralis were unaffected. Only at the highest dose level tested, the anti-T. spiralis IgG antibody response was decreased significantly. However, salmeterol's interference with the generation of anti-T. spiralis antibodies of the IgG subclass apparently did not adversely affect the resistance to infection.

Differential effect of formoterol on adenosine monophosphate and histamine reactivity in asthma

Short-acting beta2-agonists provide greater protection against bronchoconstriction induced by adenosine 5'-monophosphate (AMP) than by direct-acting bronchoconstrictors such as histamine and methacholine. AMP is thought to cause bronchoconstriction via release of mediators from mast cells, which suggests that these drugs stabilize mast cells in vivo. This in vivo property has not yet been demonstrated for long-acting beta2-agonists. We undertook a double-blind, randomized, placebo-controlled, cross-over study to investigate the effects of a single dose of formoterol inhaled via Turbuhaler (12 micrograms) and of albuterol inhaled via Turbuhaler (200 micrograms) on airway responsiveness to AMP and histamine in 16 subjects with mild atopic asthma. Albuterol reduced airway responsiveness to AMP and histamine by 4.1 +/- 0.5 and 3.5 +/- 0.4 doubling doses, respectively. In contrast, formoterol caused a greater protective effect against AMP than against histamine challenge, decreasing airway responsiveness by 6.0 +/- 0.8 and 4.2 +/- 0.4 doubling doses, respectively (p < 0.05). Thus, the long-acting beta2-agonist formoterol appears to have a mast cell-stabilizing effect in vivo in mild asthma.

Regulation of human mast cell and basophil function by cAMP

1. Mast cells and basophils are important in mediating allergic disorders such as asthma. Activation of these cells results in the release of a wide variety of mediators that can promote inflammatory responses. 2. Receptor-mediated activators of adenylate cyclase such as the beta-adrenoceptor agonist, isoprenaline, and prostaglandin E2 (PGE2) are effective at inhibiting mediator release from human lung mast cells (HLMC) but not basophils. In HLMC, both isoprenaline and PGE2 elevate and sustain increases in cyclic adenosine 3',5'-monophosphate (cAMP) whereas in basophils, both compounds cause transient increases in cAMP. 3. Non-selective inhibitors of phosphodiesterase (PDE) such as theophylline and 3-isobutyl-1-methylxanthine are effective inhibitors of mediator release from both HLMC and basophils and both compounds cause elevations of cAMP that are sustained in both cell types. 4. Studies with selective inhibitors of PDE indicate that the cAMP-specific PDE, PDE 4, regulates the activity of basophils but not HLMC. The nature of the PDE regulating HLMC responses is uncertain. 5. These data indicate that agents that induce and sustain elevations in intracellular cAMP attenuate the stimulated release of mediators from mast cells and basophils. However, the responsiveness of HLMC and basophils to selected cAMP-active agents differs.

Long-acting inhaled beta2-agonists in asthma therapy

OBJECTIVE

To review the pharmacology of the long-acting inhaled beta2-agonists, salmeterol and formoterol, summarize results of their clinical trials, evaluate their safety records, and discuss their roles in the treatment of asthma.

DATA SOURCES

Preclinical and clinical studies involving salmeterol or formoterol were identified by a MEDLINE search, weekly computerized literature updates, and manual searches. Studies of satisfactory quality were chosen for review.

DATA SYNTHESIS

Salmeterol and formoterol are potent and selective beta2-adrenoceptor agonists with durations of action >12 h. Their major differences are that formoterol has a rapid onset of action and is a partial agonist of high intrinsic efficacy, whereas salmeterol has a delayed onset and is a partial agonist of low intrinsic efficacy. Twice daily use of either drug results in improved lung function, reduced symptoms, and a better quality of life. These agents protect against exercise-induced asthma for 12 h and eliminate nighttime awakening in most patients. Limited tolerance develops, especially to their bronchoprotective effects, but their improvement of lung function is sustained.

CONCLUSIONS

Regular use of salmeterol or formoterol provides subjective and objective amelioration of asthma in patients experiencing excessive symptoms or physiologic impairment despite the regular administration of low doses of inhaled corticosteroids (equivalent to approximately 500 microg/d of beclomethasone). Intermittent use of either long-acting beta2-agonist can provide prolonged protection against exercise-induced asthma or nighttime symptoms. Patients should be instructed to continue taking inhaled steroids when long-acting beta2-agonists are administered on a regular schedule and to not take long-acting beta2-agonists between regularly scheduled doses. Used properly, they are effective and safe adjunctive agents in the treatment of asthma.

Inhibition of rat peritoneal mast cell exocytosis by frusemide: a comparison with disodium cromoglycate

Among the loop diuretics, frusemide possesses unique airway protective activities which may be due to the inhibition of airway inflammatory cells such as the mast cell. We previously reported that frusemide and disodium cromoglycate (DSCG) demonstrated a similar profile of inhibitory activities against histamine release from rat peritoneal mast cells activated by various stimuli which increased intracellular calcium via different routes. Furthermore, the inhibitory activities of both compounds demonstrated marked tachyphylaxis and we hence postulated that frusemide and DSCG might share the same mechanism of action which involves the prevention of extracellular calcium influx into the mast cell cytoplasm. The present study confirmed the postulation by (a) demonstrating that cross-tachyphylaxis exists between the two compounds and (b) extending the observations on histamine release to the influx of extracellular calcium (45Ca) into rat peritoneal mast cells.

Salmeterol inhibition of mediator release from human lung mast cells by beta-adrenoceptor-dependent and independent mechanisms

1. The long-acting beta2-adrenoceptor agonist, salmeterol (10(-9)-10(-5) M), inhibited the IgE-mediated release of histamine from human lung mast cells (HLMC) in a dose-dependent fashion. Additional beta-adrenoceptor agonists were studied and the rank order of potency for the inhibition of histamine release from HLMC was isoprenaline > salmeterol > salbutamol. Approximate EC50 values for the inhibition of histamine release were 10 nM for isoprenaline and 100 nM for salbutamol. An EC50 value for salmeterol could not be calculated because maximal responses to salmeterol were not observed over the concentration range employed. 2. Both salmeterol and isoprenaline inhibited the generation of sulphopeptidoleukotrienes (sLT) more potently and more efficaciously than the release of histamine from immunologically-activated HLMC. Salmeterol (EC50 < 0.1 nM) was more potent than isoprenaline (EC50 0.4 nM) at attenuating sLT generation. 3. The beta-adrenoceptor antagonist, propranolol (1 microM), and the selective beta2-adrenoceptor antagonist, ICI 118,551 (0.1 microM), both caused rightward shifts in the dose-response curve for the inhibition of histamine release by isoprenaline. The antagonism of salmeterol effects by propranolol and ICI 118,551 was more complex. At lower concentrations (< 1 microM) of salmeterol, both antagonists shifted the dose-reponse curve to salmeterol rightward. At a higher concentration (10 microM) of salmeterol, neither ICI 118,551 nor propranolol was an effective antagonist of the salmeterol-mediated inhibition of histamine release. 4. Prolonged exposure (4 h) of HLMC to isoprenaline (1 microM) caused an approximately 50% reduction in the effectiveness of a second exposure to isoprenaline (10 microM) at inhibiting the release of histamine. whereas this pretreatment did not affect the salmeterol (10 microM) inhibition of histamine release. 5. Isoprenaline (10(-9)-10(-5) M) caused a dose-dependent increase in total cell cyclicAMP levels in purified HLMC which paralleled the inhibition of histamine release. Salmeterol (10(-9)-10(-5) M) was considerably less potent than isoprenaline at increasing HLMC cyclicAMP levels. 6. In summary, these data indicate that salmeterol is an effective inhibitor of the stimulated release of mediators from HLMC. The present data also suggest that salmeterol may act to inhibit mediator release from HLMC by beta-adrenoceptor-dependent and independent mechanisms.

Salmeterol. A review of its pharmacological properties and clinical efficacy in the management of children with asthma

Salmeterol xinafoate is a selective beta 2-adrenoceptor agonist indicated for the maintenance treatment of adults and children with asthma. When administered as a dry powder or aerosol, salmeterol produces bronchodilation for at least 12 hours and protects against methacholine and exercise-induced bronchoconstriction. Salmeterol is not recommended for the treatment of acute exacerbations of asthma. Recent clinical studies have demonstrated the efficacy and tolerability of inhaled salmeterol in the management of asthma in children. Salmeterol improved symptom control and lung function more effectively than placebo or regularly administered salbutamol. In children who were symptomatic despite regular inhaled corticosteroid therapy, the addition of salmeterol to treatment produced a significant improvement in morning and evening peak expiratory flow and forced expiratory volume in 1 second, and a significant reduction in the incidence of asthma exacerbations compared with placebo. Notably, the long duration of action of salmeterol makes it particularly suitable for the prevention of nocturnal asthma symptoms and exercise-induced asthma (EIA) in children. Current data suggest that salmeterol should not be used as a substitute for corticosteroid therapy in children, but rather as an adjunct to therapy. Thus, salmeterol may be a suitable adjunct to therapy in children with asthma receiving inhaled corticosteroids. In addition, salmeterol also has a potentially important role in the prevention of EIA and nocturnal asthma symptoms.

An immunotoxicity screening study on salmeterol in rats

Salmeterol, a long-acting beta 2-adrenoreceptor agonist without known immunotoxicity, was studied in a 28-day repeated dose toxicity test in Wistar rats. Several immunotoxicity screening parameters were incorporated in the study protocol to investigate the immunotoxic potential of the compound. Male rats were orally treated with 0, 0.2, 2 and 20 mg salmeterol/kg body weight/day. At the 20 mg/kg/day dose level, intubation errors occurred because the animals tried to resist intubation. Some of these animals died intercurrently. Therefore, the magnitude of the dose was lowered to 10 mg/kg/day at day 9 of treatment. Body weight and bone marrow cellularity were not affected. Hematological parameters were not altered either, except for platelet counts, that were decreased at all dose levels. Also liver weights were decreased at all dose levels tested. Absolute thymic weights were decreased at the 2 and 20/10 mg/kg/day dose levels. No treatment-related (histo)pathological lesions were seen in the (non)lymphoid organs. Serum IgM levels were increased at the 0.2, and IgG at the 2 and 20/10 mg/kg/day dose levels, respectively. B cell numbers in the spleen were decreased at all dose levels tested. The data indicate that the test battery applied to salmeterol is able to detect low immunotoxic potential. Further research is needed to elucidate whether salmeterol interferes with immune responses in rats upon antigenic challenge.