The beta-adrenoceptor

Beta2-adrenoceptor agonists induce the mammalian clock gene, hPer1, mRNA in cultured human bronchial epithelium cells in vitro

The mammalian Per1 gene is one of the most important components of circadian clock function of the suprachiasmatic nucleus and peripheral tissues. We examined whether the beta2-adrenoceptor agonists, procaterol and fenoterol, induce human Per1 mRNA expression in human bronchial epithelium. The in vitro stimulation of beta2-adrenoceptor agonists in BEAS-2B cells led to a remarkable increase in the level of hPer1 mRNA. Moreover, fenoterol or procaterol induced the phosphorylation of CREB in BEAS-2B cells as verified by immunoblot analysis. beta2-adrenoceptor agonists induced human Per1 mRNA expression by the signaling pathways of cAMP-CREB in BEAS-2B cells.

Inhibition of in vitro neutrophil migration through a bilayer of endothelial and epithelial cells using beta2-agonists: concomitant effects on IL-8 and elastase secretion and impact of glucocorticosteroids

BACKGROUND

Beta2-agonists and glucocorticosteroids are two common treatments for COPD and they are often used in combination. Glucocorticosteroids mediate the anti-inflammatory response through the glucocorticosteroid receptors (GRs). Beta2-agonists are potent bronchodilators but they can have some anti-inflammatory properties by elevating the level of intracellular cAMP. In this study we aimed to investigate the anti-inflammatory effect of combination therapy in vitro.

METHODS

Neutrophils or the bilayer of endothelial and epithelial cells were preincubated with salbutamol, budesonide or budesonide followed by salbutamol. FMLP-induced IL-8, elastase release and neutrophil migration through the bilayer was measured.

RESULTS

Salbutamol at concentrations of 10(-4), 10(-5) and 10(-9) M inhibited IL-8, elastase release and migration of neutrophils in an inverse bell-shaped concentration-response manner. When given after budesonide (10(-9) and 10(-8)M), the inhibitory effect on migration was additive. This additive effect was not observed for elastase and IL-8 release.

CONCLUSIONS

Salbutamol inhibits neutrophil migration and IL-8 and elastase release in a concentration-dependent manner. Preincubation with low concentration of budesonide enhanced the inhibition of migration achieved by low concentrations of salbutamol.

Are so many adrenergic receptor subtypes really present in domestic animal tissues? A pharmacological perspective

Adrenergic receptors (ARs) are the cellular membrane binding sites through which natural catecholamines and sympathomimetic drugs exert their physiological and pharmacological effects. In recent decades, studies to clarify the distribution and function of ARs have been performed mostly on cultured cells, laboratory animals and human target tissues, but little is known about these aspects in domestic animals. This review focuses on AR structure, classification and signalling pathways and on AR subtype distribution in target tissues of some domestic animals, namely dogs, horses and bovines. In these species, different alpha- and beta-AR subtypes have been characterized and the functions controlled by the adrenergic systems have been studied. In the dog, the role played by the adrenergic system in the pathogenesis of cardiovascular disorders and in the modulation of canine aggression has roused particular interest. In dogs affected by dilated cardiomyopathy a significant down-regulation of beta-ARs has been observed both in the heart and circulating lymphocytes. This finding confirms the involvement of the adrenergic system in the pathogenesis and progression of the disorder and suggests new therapeutic strategies. In the horse, AR distribution has been studied in the cardiac, respiratory and gastrointestinal systems as well as in digital veins and arteries. The cardiac beta-ARs in healthy horses seem to be predominantly represented by the beta(1) subtype. In this species, heart failure may increase the expression of the beta(2) subtype, rather than causing AR down-regulation. Different beta- and alpha-AR subtypes have been characterized in the smooth muscle of equine ileum. The sympathetic relaxation of equine ileum smooth muscle seems to depend mainly on beta(3)-AR subtype activation, with minor involvement of the beta(2) subtype. In the respiratory tract, regional differences have been evidenced in the functionality of beta-AR subtype. The beta(2) subtype predominates in all segments but the beta(2) subtype-mediated adenyl cyclase response is tissue-dependent, with higher activity in tracheal membranes than bronchial or pulmonary ones. Both alpha- and beta-AR subtypes are present in the genital tract of cows. Bovine ovarian and myometrial cell membranes express higher concentrations of beta(2)-ARs than the beta(1) subtype, whereas as far as alpha-ARs are concerned, a single class of alpha(1)-ARs and two distinct classes of alpha(2)-AR binding sites have been discriminated. Interestingly, it has been observed that the activation of the sympathetic system could play an important role in the pathogenesis of bovine ovarian cysts as suggested by the modifications in beta-AR levels in the hypophysis and ovary of cows affected by ovarian cysts. In this species, the phenomenon of down-regulation has been well studied in different organs of veal calves treated with clenbuterol as a "partitioning agent". Since differences exist in AR distribution among species, data obtained in laboratory animals or in human beings cannot be extrapolated to domestic animals and further investigation on AR subtypes in domestic animal tissues is necessary.

Adrenaline produces the relaxation of guinea-pig airway smooth muscle primarily through the mediation of beta(2)-adrenoceptors

The beta-adrenoceptor subtype that mediates adrenaline-induced relaxation was pharmacologically identified in smooth muscle cells of the isolated guinea-pig trachea. Adrenaline produced a concentration-dependent relaxation with a pD(2) value of 7.1. The concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by the beta(1)-/beta(2)-nonselective antagonists propranolol and bupranolol, with pA(2) values of 8.85 and 8.97, respectively. Adrenaline-induced relaxation was not affected by the beta(1)-selective antagonists atenolol and CGP-20, 712A within the concentration ranges supposed to antagonize the beta(1)-subtype (atenolol, <or=10(-6) M; CGP-20, 712A, <or=10(-8) M). By contrast, the concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by atenolol at concentrations >or=3x10(-6) M with a pA(2) value of 5.77. The concentration-response curve for adrenaline was also competitively antagonized by the beta(2)-selective antagonists butoxamine and ICI-118,551 with pA(2) values of 6.86 and 8.73, respectively. The pA(2) values of beta-adrenoceptor antagonists (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551) tested against adrenaline were consistent with the values when tested against salbutamol, a beta(2)-selective adrenoceptor agonist. The present findings provide evidence that the relaxant response of the smooth muscle of the guinea-pig trachea to the adrenal medulla hormone, adrenaline, is mainly mediated through beta(2)-adrenoceptors.

Differential effects of beta2-adrenoceptor desensitization on the IgE-dependent release of chemical mediators from cultured human mast cells

In the present study, we examined the inhibitory effects of the beta2-adrenoceptor agonists isoproterenol, salbutamol, fenoterol, and clenbuterol, on the release of chemical mediators from cultured human mast cells after prolonged treatment with the agonists. Although preincubation of sensitized mast cells for 10 min with beta2-adrenoceptor agonists potently inhibited mediator release, prolongation of the preincubation period up to 240 min attenuated the inhibition. The attenuation of histamine release inhibition was potent when compared with that of prostaglandin D2 (PGD2) and cysteinyl leukotriene (LT) release inhibition. In contrast, forskolin inhibited mediator release and the inhibition increased gradually in proportion to the preincubation period. The reduced inhibition by the beta2-adrenoceptor agonists was compensated for by simultaneous treatment with cholera toxin. The beta2-adrenoceptor agonists elevated intracellular cAMP levels after 10-min incubation and the elevated levels were almost comparable to those after 240-min incubation. Forskolin elevated the intracellular cAMP levels more potently after incubation for 240 min than after 10 min. When mast cells were incubated for 3 d with the beta2-adrenoceptor agonists, similar attenuation of mediator release inhibition was observed. Elevation of intracellular cAMP levels was also attenuated, although beta2-adrenoceptor mRNA expression was potentiated. The present results collectively indicate that the attenuation of mediator release inhibition by beta2-adrenoceptor agonists under the present experimental conditions involves uncoupling between beta2-adrenoceptors and Gs proteins. Furthermore, the beta2-adrenoceptor desensitization causes differential attenuating effects on the inhibition of histamine, PGD2, and LT release, suggesting that downstream events involved in each inhibitory pathway have different sensitivity to receptor desensitization.

A Randomized Controlled Trial To Assess the Optimal Dose and Effect of Nebulized Albuterol in Acute Exacerbations of COPD

STUDY OBJECTIVES

Despite the widespread use of short-acting, inhaled beta(2)-agonists in acute exacerbations of COPD (AECOPDs), little is known about their optimal dose. The aims of this study are to compare the bronchodilator response to incremental doses of inhaled albuterol during and after recovery from an AECOPD, and to compare the effects of regular nebulized albuterol, 2.5 mg and 5 mg, on the speed of recovery.

METHODS

Eighty-six patients admitted with an AECOPD were recruited. Each patient was administered incremental doses of inhaled albuterol on hospital admission and following recovery. Dose-response curves were constructed based on FEV(1) and peak expiratory flow rate (PEFR) recorded after each incremental dose. Patients were then randomized in a double-blind fashion to receive 2.5 mg or 5 mg of nebulized albuterol q4h until recovery. Twice-daily PEFR, the number of extra doses of bronchodilators, and side effects reported were recorded.

RESULTS

Maximal bronchodilation (Emax) FEV(1) (maximal bronchodilatory response to albuterol) increased from 0.64 +/- 0.27 L/min during the exacerbation to 0.94 +/- 0.38 L/min during recovery (p < 0.001). The Emax PEFR increased from 147.53 +/- 62.46 L/min to 222.94 +/- 73.82 L/min after recovery (p = < 0.001). There was no significant difference in rate of recovery of PEFR (p = 0.684), duration of hospital stay (p = 0.084), or side effects (p = 0.506) between the groups receiving 2.5 mg or 5 mg of nebulized albuterol.

CONCLUSIONS

There was significant improvement in Emax to inhaled albuterol as the COPD exacerbation resolved. There was no significant difference in outcomes including length of hospital stay or recovery of lung function between patients treated with regular 2.5 mg vs 5 mg of nebulized albuterol during an AECOPD.

Past, present and future--beta2-adrenoceptor agonists in asthma management

The beta-adrenoceptor agonists (beta-agonists) have been used to relieve bronchoconstriction for at least 5000 years. beta-agonists are based on adrenaline and early forms, such as isoprenaline, Lacked bronchial selectivity and had unpleasant side effects. Modern beta-agonists are more selective for the beta2-adrenoceptors (beta2-receptors) located in bronchial smooth muscle and have less cardiotoxicity. Traditional beta2-adrenoceptor agonists (beta2-agonists), such as salbutamol, terbutaline and fenoterol, were characterised by a rapid onset but relatively short duration of action. While valuable as reliever medication, their short duration gave inadequate night-time relief and limited protection from exercise-induced bronchoconstriction. beta2-agonists with longer durations of action, formoterol and salmeterol, were subsequently discovered or developed. When combined with inhaled corticosteroids they improved lung function, and reduced symptoms and exacerbations more than an increased dose of corticosteroids. However, tolerance to the bronchprotective effects of long-acting beta2-agonists and cross-tolerance to the bronchodilator effects of short-acting beta2-agonists is apparent despite use of inhaled corticosteroids. The role of beta2-receptor polymorphisms in the development of tolerance has yet to be fully determined. Formoterol is unique in having both a long-lasting bronchodilator effect (> 12 h) and a fast onset of action (1-3min from inhalation), making it effective both as maintenance and reliever medication. The recent change in classification from short- and long-acting beta2-agonists to rapid-acting and/or long-acting agents reflects the ongoing evolution of beta2-agonist therapy.

Determination of a novel haplotype of beta2-adrenergic receptor in the Japanese population by the combination of the electronic microchip assay using the NanoChip system with allele-specific PCR

The beta(2)-adrenergic receptor (B2AR) is a G protein-coupled cell surface receptor that is the key target for the beta(2)-agonist drugs used for bronchodelation in asthma and chromic obstructive pulmonary disease. To detect four SNPs with amino acid variations in the B2AR gene, we used the electronic microchip assay (NanoChip system), DHPLC and sequencing. Genomic DNA samples were obtained from the blood of 84 Japanese healthy volunteers. In sum, the agreement rates of the first data set with the final agreement data (allele calls) were 99.7% (328/329), 99.2% (243/245) and 96.7% (325/336). The percentages of no allele designation (ND) were 2.06% (7/336), 2.75% (7/252), and 0.00% (0/336) for the NanoChip system, DHPLC, and sequencing, respectively. As a result of SNP genotyping, we found three samples that might have a novel haplotype. Furthermore we identified the novel haplotype by a simple technique combining the NanoChip system and allele-specific PCR. These results indicated that NanoChip system was the useful method for clinical SNP genotyping and/or haplotyping because of its accuracy, simplicity and versatility.

Possible role of dexamethasone in sensitizing the beta-2-adrenergic receptor system in vivo in calves during concomitant treatment with clenbuterol

Beta(2)-Agonists blunt the function of the beta-adrenoceptor G-protein adenylate cyclase-signalling system, whereas glucocorticoids reverse the agonist-mediated diminished beta-adrenergic responses; however, these effects have not been reported in vivo in calf lymphocytes. In this study, we first investigated the presence of the beta(2)-adrenergic receptors on calf lymphocytes, and second we tested the effects of either clenbuterol alone or in combination with dexamethasone on receptor expression and function (isoproterenol-induced intracellular adenosine 3',5'-cyclic monophosphate (cAMP) formation) in vivo. (-)-[(125)I]-Iodocyanopindolol (ICYP) binding to intact calf lymphocytes was rapid, saturable (maximal number of binding sites 987 +/- 89 ICYP-binding sites/cell, n = 4) and of high affinity (K(D) value 17.23 +/- 2.8 pmol/l, n = 4). These binding sites were of the beta(2)-subtypes of adrenoceptors as indicated by the fact that beta-agonists inhibited ICYP binding with an order of potency: (-)-isoproterenol > (-)-adrenaline > (-)-noradrenaline. Furthermore, the selective beta(2)-adrenoceptor antagonist ICI 118.551 was about >1,500 times more potent in inhibiting ICYP binding than was the beta(1)-selective adrenoceptor antagonist CGP 20712A. Consequently, calves were treated with clenbuterol (1.0 microg/kg b.i.d., i.v.) for 9 days alone or simultaneously with dexamethasone (0.1 mg/kg, i.v., once a day for 4 days). Clenbuterol decreased the number of lymphocyte beta(2)-adrenergic receptors by about 40-50% after only 48 h of drug administration. This was accompanied by a decrement in isoproterenol-induced lymphocyte cAMP formation. Upon application of both drugs, dexamethasone restored the clenbuterol-mediated decrease in beta(2)-adrenoceptors and cAMP production. Dexamethasone elevated the number of beta(2)-adrenoceptors and cAMP almost 1.5- to 2-fold at 24 h of drug administration, an effect that persisted for up to 24 h following drug withdrawal. Neither clenbuterol nor the combination with dexamethasone had an influence on the affinity of the receptor for the ligand. The present results demonstrate that dexamethasone in vivo upregulates the number and function of calf lymphocyte beta(2)-adrenoceptors, and thus enhances the sensitivity of the beta(2)-adrenoceptor signal-transduction pathway for clenbuterol during concomitant treatment with both drugs.

cAMP-independent mechanism is significantly involved in beta2-adrenoceptor-mediated tracheal relaxation

The role of cAMP in the beta2-adrenoceptor-mediated relaxation in response to salbutamol was examined in guinea pig tracheal smooth muscle. The concentration-dependent salbutamol-induced relaxation was antagonized in a competitive fashion by a beta2-selective adrenoceptor antagonist, butoxamine, with a pA2 value of 6.90. Salbutamol (10 microM) elevated the tracheal smooth muscle cAMP content by about fivefold, a response which was significantly inhibited by an adenylyl cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536, 100 microM). However, the salbutamol-elicited relaxation was not diminished by SQ 22,536 (100 microM). These results provide evidence for the first time that a cAMP-independent mechanism(s) is involved in beta2-adrenoceptor-mediated tracheal smooth muscle relaxation in the guinea pig.

Airway reactivity is a determinant of bronchodilator responsiveness after methacholine-induced bronchoconstriction

Airway hyperresponsiveness (AHR) is one of the characteristics of asthma and a risk factor for persistent airflow limitation. Poor response to bronchodilator may be a cause of persistent airflow limitation. Multiple factors may determine bronchodilator responsiveness, including airway reactivity to nonspecific bronchoconstrictive agents. If patients with AHR have poor bronchodilator responsiveness, then it could be a potential mechanism for asthma and persistent airflow limitation in these patients. The objective of this study is to assess the relationship between airway reactivity to methacholine and responsiveness to beta-agonist and beta-agonist/anticholinergic combination in a large subject population. A retrospective data analysis was undertaken of 764 consecutive subjects with > or = 20% reduction in forced expiratory volume during the first second of exhalation from total lung capacity (FEV1) after < or = 189 cumulative units of methacholine. The first 382 subjects received 3 inhalations of metaproterenol and the second 382 subjects received 3 inhalations of albuterol and ipratropium combination after > or = 20% reduction in FEV1. Bronchodilator responsiveness was measured as the percent increase in FEV1 after the treatment. Airway reactivity was assessed as the log10 of methacholine dose response slope. In a simple linear regression model, airway reactivity was significantly related to bronchodilator responsiveness. The coefficient of determination (r2) was 0.15 for the whole groups; 0.14 for metaproterenol group and 0.18 for albuterol/ipratropium combination group (all p<0.0001). The regression coefficient (beta) was 14.0 for the whole group; 14.8 and 13.2, respectively, for the two bronchodilator groups. Airway reactivity to methacholine is a determinant of airway responsiveness to both beta-agonist and beta-agonist/anticholinergic combination. Subjects with higher airway reactivity have higher bronchodilator responsiveness.

Inhaled Corticosteroids in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a serious illness that affects over 5% of the adult population. It is one of the few conditions for which the mortality and morbidity are still increasing. Experts expect COPD to become the third leading cause of death and the fifth leading cause of disability worldwide by the year 2020. Thus far, the only treatments that have been shown to make a difference to survival are smoking cessation and the use of oxygen supplements for those who are hypoxaemic at rest. The use of inhaled corticosteroids as monotherapy or in combination with a long-acting beta2-adrenoceptor agonist for COPD is controversial. Experimental data indicate that the inflammatory process in COPD may be resistant to the anti-inflammatory effects of corticosteroids. However, several large clinical studies have shown that inhaled corticosteroids in relatively high doses (e.g. budesonide 800 microg/day or fluticasone propionate 1 mg/day) reduce exacerbations by 20-30% and improve the health status of COPD patients by a similar amount compared with placebo. Withdrawal of inhaled corticosteroids may increase clinical exacerbation rates by 50% in COPD patients and by 2-fold in those with severe disease. Combined therapy with inhaled corticosteroids and long-acting beta2-adrenoceptor agonists may be superior to individual component therapy in reducing exacerbations. However, these medications must be used cautiously, as they have been associated with certain adverse effects. Inhaled corticosteroids, for instance, increase the risk for dysphonia and oral thrush by 2- to 3-fold. Skin bruising is also more common in users than in non-users of inhaled corticosteroids. On balance, for those with moderate-to-severe COPD and those who experience frequent exacerbations, judicious use of inhaled corticosteroids alone or in combination with long-acting beta2-adrenoceptor agonists appears reasonable.

Long-acting beta 2-adrenoceptor agonists and exercise-induced asthma: lessons to guide us in the future

The safety and efficacy of long-acting beta(2)-adrenoceptor agonists (LABAs) taken intermittently for the prevention of exercise-induced asthma (EIA) in children is well established. However, the safety and efficacy of LABAs taken twice daily, either alone or in combination with inhaled corticosteroids, for the prevention of EIA is not as clear because of issues of tolerance (defined as being less responsive to the influence of LABAs). There have been many observations on short-acting beta(2)-adrenoceptor agonists (SABAs) and EIA that should have alerted us to the potential for tolerance and desensitization to occur with LABAs. For example, we expected that the use of LABAs for EIA would overcome the problem of the short duration of protection of SABAs, and to some extent they have. The protective period of a LABA is two to three times longer in duration than that of a SABA. However, when a LABA is taken daily it is apparent that the duration of its protective effect is reduced and there is a risk of EIA occurring well within the 12-hour administration schedules. Furthermore, daily use of LABAs attenuates the bronchodilator effect of SABAs, an effect that is greater the more severe the bronchoconstriction. This 'tolerance' increases both the time and the amount of therapy that is needed to recover from bronchoconstriction, and thus, could potentially impact on the success of rescue therapy should severe EIA occur. The daily use of LABAs also increases the sensitivity of the bronchial smooth muscle to contractile agents. This increase in sensitivity is almost equivalent to the extent to which inhaled corticosteroids reduce sensitivity to the same contractile agents. The increased sensitivity to contractile agents may occur either by a reduction in the inhibitory effect of beta(2)-adrenoceptor agonists on release of mediators from mast cells or by a direct effect on the bronchial smooth muscle. These unwanted effects of LABAs are not necessarily reduced by concomitant treatment with inhaled corticosteroids. As the number of children being treated with LABAs increases, it is predicted that problems with breakthrough EIA will also increase. We need to know the percentage of children taking a LABA daily who are requiring either extra doses of a beta(2)-adrenoceptor agonist to prevent (or reverse) EIA or other provocative stimuli. If this percentage is significant then we may need to reconsider the position of LABAs in the treatment of children with asthma who regularly perform strenuous physical activity.

A comparison of the effects of oral montelukast and inhaled salmeterol on response to rescue bronchodilation after challenge

OBJECTIVES

To compare the effects of addition of montelukast or salmeterol to inhaled corticosteroids (ICS) on the response to rescue beta2-agonist use after exercise-induced bronchoconstriction.

METHODS

A double-blind, placebo-controlled study was performed at 16 centers in the United States. Patients with asthma (n = 122, ages 15-58) whose symptoms were uncontrolled on Low-dose inhaled fluticasone and who had a history of exercise-induced worsening of asthma were randomized to receive either montelukast (10 mg once daily), salmeterol (50microg twice daily), or placebo for 4 weeks. Standardized spirometry after exercise challenge and beta2-agonist rescue was performed at baseline, week 1 and 4.

RESULTS

Maximum achievable forced expiratory volume in 1 s (FEV1) percent predicted after rescue beta2-agonist improved in the montelukast (+1.5%) and placebo (+1.2%) groups at 4 weeks, but diminished in the salmeterol (-3.9%) group (P < 0.001). Although pre-exercise FEV1 was greatest with salmeterol (P = 0.10), patients taking montelukast had significantly greater protection from an exercise-induced decrease in FEV1 than those taking salmeterol (P < 0.001). Both the magnitude and rate of rescue bronchodilation were greater with montelukast compared with salmeterol (P < 0.001). Five minutes after rescue beta2-agonist, 92% of patients taking montelukast and 68% of those taking placebo had recovered to pre-exercise levels, whereas only 50% of those taking salmeterol had recovered to pre-exercise levels.

CONCLUSION

In patients whose asthma symptoms remain uncontrolled using ICS, addition of montelukast permits a greater and more rapid rescue bronchodilation with a short-acting beta2-agonist than addition of salmeterol and provides consistent and clinically meaningful protection against exercise-induced bronchoconstriction.

Differences in beta-adrenergic receptor sensitivity between women and men with panic disorder

This study was conducted on patients with panic disorder (PD) to examine the gender differences in the pathophysiology of PD by evaluating and comparing the value of CD(25)/wt, the chronotropic 25 dose of isoproterenol (CD(25)) divided by the body weight, which reflects the in vivo index of beta-adrenergic receptor sensitivity. This study included a total of 70 subjects, including 35 patients with PD (female: 13, male: 22) along with 35 healthy control subjects (female: 13, male: 22). There were significant differences in the mean value of CD(25)/wt (0.073+/-0.045 microg/kg vs. 0.032+/-0.019 microg/kg; p=0.006) and the serum epinephrine (EPI) level (77.3+/-64.1 pg/ml vs. 31.6+/-10.3 pg/ml; p=0.001) between the female panic patients and the female control subjects. However, there were no differences in either the CD(25)/wt value or the EPI level between the male panic patients and the male control subjects. These results suggest that the beta-adrenergic receptor sensitivity decreased in the female patients, but not in the male patients, which provides evidence for the possible existence of a gender difference in the pathophysiology of PD.

The airway cholinergic system: physiology and pharmacology

The present review summarizes the current knowledge of the cholinergic systems in the airways with special emphasis on the role of acetylcholine both as neurotransmitter in ganglia and postganglionic parasympathetic nerves and as non-neuronal paracrine mediator. The different cholinoceptors, various nicotinic and muscarinic receptors, as well as their signalling mechanisms are presented. The complex ganglionic and prejunctional mechanisms controlling the release of acetylcholine are explained, and it is discussed whether changes in transmitter release could be involved in airway dysfunctions. The effects of acetylcholine on different target cells, smooth muscles, nerves, surface epithelial and secretory cells as well as mast cells are described in detail, including the receptor subtypes involved in signal transmission.

Quantitative estimation of myocardial fibrosis based on receptor occupancy for beta2-adrenergic receptor agonists in rats

To develop beta2-adrenergic receptor (AR) agonists with higher selectivity, it is essential to evaluate the cardiac side effects which are the most serious side effects of this class of drugs. We studied receptor occupancy of beta1-ARs in rats as a possible cause for the side effect of beta2-AR agonists, namely myocardial fibrosis. Myocardial fibrosis in rats was observed on Day 7 after the administration of salbutamol and terbutaline, both of which are selective beta2-AR agonists, at higher dose levels. To evaluate receptor occupancy, plasma concentrations of (R)-salbutamol and (R)-terbutaline, plasma protein binding and the EC50 for chronotropic effects in rats were determined. Based on the plasma concentrations, the plasma protein binding and EC50, receptor occupancy-time profiles were constructed. The relationship between the receptor occupancy-time profile under the curve, the AUCphi, and the degree of myocardial fibrosis was evaluated with a multiple correlation analysis. Myocardial fibrosis was significantly correlated (r2 > 0.78) to the AUCphi with the threshold above approximately 50%, but not to plasma concentrations. These results indicate that the receptor occupancy theory is also useful for the evaluation of the chronotropic side effects of beta2-AR agonists.

Differential control of TH1 versus TH2 cell responses by the combination of low-dose steroids with beta2-adrenergic agonists

BACKGROUND

Combination treatment with steroids and long-acting beta2-agonists provides greater asthma control than simply increasing the dose of steroids.

OBJECTIVE

Although the effects of combination treatment with steroids and long-acting beta2-agonists have been attributed to their anti-inflammatory and bronchodilator effects, the ability of this combination to act synergistically on T cells has not been explored.

METHODS

PBMCs from control subjects and allergic asthmatic patients were stimulated with PHA in the presence of low doses of fluticasone propionate (FP) with or without salmeterol for 72 hours. The inhibition of T-cell proliferation, cytokine production, and glucocorticoid receptor translocation was measured.

RESULTS

Both groups showed a similar degree of inhibition of PHA-induced T-cell proliferation with FP (inhibitory concentration of 50% approximately 10(-9) mol/L) alone. Use of lower concentrations of FP (10(-12) to 10(-11) mol/L) in combination with salmeterol (10(-10) to 10(-7) mol/L) in control subjects provided similar inhibition of proliferation. This combination treatment was associated with significantly greater glucocorticoid receptor translocation into the cell nucleus compared with that seen with FP alone (10(-12) mol/L; P <.01). In contrast, FP-salmeterol failed to act synergistically in asthmatic patients. The 2-drug combination significantly inhibited production of TNF-alpha and IFN-gamma in both groups (P <.05) but failed to inhibit TH2 cytokine (IL-5 and IL-13) production by PBMCs from asthmatic patients. Because allergic inflammation is associated with increased levels of cellular phosphodiesterases that might degrade salmeterol-induced cyclic adenosine monophosphate, rolipram (10(-6) mol/L), a phosphodiesterase 4 inhibitor, was added to the FP-salmeterol combination. This triple combination of drugs enhanced inhibitory activity of low-dose steroids on T-cell proliferation in asthmatic patients and inhibited IL-13 production.

CONCLUSION

These data suggest that beta2-agonists in combination with low doses of steroids can suppress T-cell proliferation and TH1 cytokine production from healthy individuals, but suppression of T cells with a combination of FP and salmeterol in asthmatic patients requires inhibition of phosphodiesterases.

Synthetic responses in airway smooth muscle

Human airway smooth muscle (ASM) has several properties and functions that contribute to asthma pathogenesis, and increasing attention is being paid to its synthetic capabilities. ASM can promote the formation of the interstitial extracellular matrix, and in this respect, ASM from asthmatic subjects compared with normal subjects responds differently, both qualitatively and quantitatively. Thus, ASM cells are important regulating cells that potentially contribute to the known alterations within the extracellular matrix in asthma. In addition, through integrin-directed signaling, extracellular matrix components can alter the proliferative, survival, and cytoskeletal synthetic function of ASM cells. ASM also functions as a rich source of biologically active chemokines and cytokines that are capable of perpetuating airway inflammation in asthma and chronic obstructive pulmonary disease by promoting recruitment, activation, and trafficking of inflammatory cells in the airway milieu. Emerging evidence shows that airway remodeling may also be a result of the autocrine action of secreted inflammatory mediators, including T(H)2 cytokines, growth factors, and COX-2-dependent prostanoids. Finally, ASM cells contain both beta(2)-adrenergic receptors and glucocorticoid receptors and may represent a key target for beta(2)-adrenergic receptor agonist/corticosteroid interactions. Combinations of long-acting beta(2)-agonists and corticosteroids appear to have additive and/or synergistic effects in inhibiting inflammatory mediator release and the migration and proliferation of ASM cells.

Therapeutic response to asthma medications: genotype predictors

Asthma is a major social and economic burden. Studies have shown that genetic polymorphisms can influence drug efficacy and/or toxicity. The understanding of the pharmacogenetics of asthma will allow therapeutic regimens to be tailored on an individual basis. It is hoped that linkage and association studies will define new therapeutic targets for asthma but until then, studies have focused on improving response to beta(2)-adrenoceptor agonist and leukotriene modifier therapy. Genetic polymorphism may account for interindividual differences in toxicity and efficacy of asthma medications. To date, single nucleotide polymorphism and limited haplotype analysis have provided inconclusive evidence as to how genotype predictors can be used to optimize current asthma therapies based on each patient's genetic profile.

Acute and chronic effects of FR-149175, a beta 3-adrenergic receptor agonist, on energy expenditure in Zucker fatty rats

Clinical therapies for both obesity and obese non-insulin-dependent diabetes mellitus require maintenance of reduced body weight after the initial successful reduction resulting from calorie control, exercise, or medication. Although beta(3)-adrenergic receptor (beta(3)-AR) agonists have been shown to stimulate whole body energy expenditure and lipid mobilization, whether stimulatory effects on oxygen consumption and lipolysis are influenced by chronic exposure to agonists has not been fully characterized. We therefore examined the acute and chronic effects of FR-149175, a selective beta(3)-AR agonist, on whole body oxygen consumption in genetically obese Zucker fatty rats. Chronic treatment with FR-149175 caused a decrease in both body weight gain and white fat pad weight at doses that induced lipolysis in acute treatment (1 and 3.2 mg/kg p.o.). Single administration of FR-149175 (0.1, 1, and 3.2 mg/kg p.o.) dose dependently increased whole body oxygen consumption. Repetitive administration did not cause attenuation of the thermogenic response at lower doses (0.1 and 1 mg/kg 2 times daily), whereas the highest dose (3.2 mg/kg 2 times daily) induced a progressive increase in oxygen consumption. PCR analyses of retroperitoneal white adipose tissue indicated little or no change in beta(3)-AR mRNA levels. Uncoupling protein 1 gene expression increased at 1 mg/kg, and drastic upregulation was detected at 3.2 mg/kg. FR-149175 also increased HSL mRNA levels in a dose-related manner, whereas there was no effect on genes involved in beta-oxidation. These results support that the thermogenic effect of beta(3)-AR agonists is not attenuated by chronic exposure to agonists.

Cardiovascular safety of beta(2)-adrenoceptor agonist use in patients with obstructive airway disease: a systematic review

BACKGROUND

beta(2)-Adrenoceptor agonists have been used as bronchodilators in the management of asthma and chronic obstructive pulmonary disease (COPD); however, there is evidence suggesting that beta(2)-adrenoceptor agonist use may increase morbidity and mortality.

METHODS

A systematic review of case-control studies and randomised controlled trials was performed to evaluate the cardiovascular safety of beta(2)-adrenoceptor agonist use in patients with obstructive airway disease, defined as asthma or COPD.

RESULTS

Case-control studies have shown that beta(2)-adrenoceptor agonist use is associated with an increased risk of myocardial infarction, congestive heart failure, cardiac arrest and sudden cardiac death. The degree of risk appears to be dose-dependent, and may be highest for new users and those with concomitant cardiac conditions. Pooled data from randomised placebo-controlled trials indicate that beta(2)-adrenoceptor agonist use increases the risk of adverse cardiovascular events by more than 2-fold compared with placebo, thus providing evidence that the association seen in case-control studies is a causal one. Single doses of beta(2)-adrenoceptor agonists significantly increase heart rate and decrease potassium concentrations compared with placebo.

CONCLUSIONS

Initiation of beta(2)-adrenoceptor agonist treatment increases heart rate and decreases potassium concentrations, while continued use may increase the risk of adverse cardiovascular events. It could be through these effects of beta-adrenergic stimulation that beta(2)-adrenoceptor agonists may induce ischaemia, congestive heart failure, arrhythmias and sudden cardiac death. In addition to increasing adverse cardiovascular events, beta(2)-adrenoceptor agonist use may induce respiratory tolerance and increase the risk of asthma attacks. It is not clear whether beta(2)-adrenoceptor agonists should be used regularly in the treatment of obstructive airway disease, with or without concomitant cardiovascular disease.

Efficacy of the novel phosphodiesterase-4 inhibitor BAY 19-8004 on lung function and airway inflammation in asthma and chronic obstructive pulmonary disease (COPD)

Selective inhibitors of phosphodiesterase-4 (PDE4) inhibit the hydrolysis of intracellular cAMP, which may result in bronchodilation and suppression of inflammation. We examined the effect of 1 week treatment with BAY 19-8004 (5 mg once daily), a novel orally administered PDE4 inhibitor, on trough FEV1 and markers of inflammation in induced sputum in patients with asthma or chronic obstructive pulmonary disease (COPD). Seven patients with asthma (mean [SD] FEV1 69.5 [9.3]% predicted; reversibility in FEV1 26.2 [10.1]%; all non-smokers) and 11 patients with COPD (FEV1 58.6 [8.3]% predicted; reversibility in FEV1 6.5 [4.7]%; median [range] 44 [21-90] pack years of smoking) were included in this randomized, double-blind, placebo-controlled trial. FEV1 was measured before and after 1 week of treatment; sputum was induced by 4.5% saline inhalation on the last day of treatment. FEV1 did not improve during either treatment in both patient groups (p>0.2). Sputum cell counts were not different following placebo and BAY 19-8004 treatment in asthma and COPD patients (p>0.2). However, only in patients with COPD, small but significant reductions in sputum levels of albumin and eosinophil cationic protein were observed (p<0.05). In conclusion, 1 week of treatment with the selective PDE4 inhibitor BAY 19-8004 does not affect FEV1 and sputum cell numbers in patients with asthma or COPD. However, such treatment does seem to reduce levels of albumin and eosinophil cationic protein in sputum samples obtained from patients with COPD.

MaxiK channel mediates beta2-adrenoceptor-activated relaxation to isoprenaline through cAMP-dependent and -independent mechanisms in guinea-pig tracheal smooth muscle

We examined the contribution of large-conductance, Ca(2+)-sensitive K+ (MaxiK) channel to beta2-adrenoceptor-activated relaxation to isoprenaline in guinea-pig tracheal smooth muscle focusing on the role for cAMP in the coupling between beta2-adrenoceptor and MaxiK channel. Isoprenaline-elicited relaxation was confirmed to be mediated through beta2-type of adrenoceptor since the response was antagonized in a competitive fashion by a beta2-selective adrenoceptor antagonist butoxamine with a pA2 value of 6.56. Isoprenaline-induced relaxation was significantly potentiated by a selective inhibitor of cyclic AMP-specific phosphodiesterase, Ro-20-1724 (0.1-1 microM). cAMP-dependent mediation of MaxiK channel in the relaxant response to isoprenaline was evidenced since the potentiated response to isoprenaline by the presence of Ro-20-1724 (1 microM) was inhibited by the channel selective blocker, iberiotoxin (IbTx, 100 nM). This concept was supported by the finding that the relaxation to a membrane permeable cAMP analogue, 8-bromo-cAMP (1 mM), was susceptible to the inhibition by IbTx. On the other hand, isoprenaline-induced relaxation was not practically diminished by an adenylyl cyclase inhibitor SQ 22,536 (100 microM). However, isoprenaline-induced relaxation in the presence of SQ 22,536 was suppressed by IbTx. Characteristics of isoprenaline-induced relaxant response, i.e., impervious to SQ 22,536 but susceptible to IbTx, were practically mimicked by cholera toxin (CTX, 5 microg/ml), an activator of adenylyl cyclase coupled-heterotrimeric guanine nucleotide-binding regulatory protein Gs. These findings indicate that in guinea-pig tracheal smooth muscle: 1) MaxiK channel substantially mediates beta2-adrenoceptor-activated relaxation; 2) both cAMP-dependent and -independent mechanisms underlie the functional coupling between beta2-adrenoceptor and MaxiK channel to induce muscle relaxation; and 3) direct regulation of MaxiK channel by Gs operates in cAMP-independent coupling between beta2-adrenoceptor and this ion channel.

Cardiovascular Effects of β-Agonists in Patients With Asthma and COPD

BACKGROUND

beta-Adrenergic agonists exert physiologic effects that are the opposite of those of beta-blockers. beta-Blockers are known to reduce morbidity and mortality in patients with cardiac disease. beta(2)-Agonist use in patients with obstructive airway disease has been associated with an increased risk for myocardial infarction, congestive heart failure, cardiac arrest, and acute cardiac death.

OBJECTIVES

To assess the cardiovascular safety of beta(2)-agonist use in patients with obstructive airway disease, defined as asthma or COPD.

METHODS

A meta-analysis of randomized placebo-controlled trials of beta(2)-agonist treatment in patients with obstructive airway disease was performed, to evaluate the short-term effect on heart rate and potassium concentrations, and the long-term effect on adverse cardiovascular events. Longer duration trials were included in the analysis if they reported at least one adverse event. Adverse events included sinus and ventricular tachycardia, syncope, atrial fibrillation, congestive heart failure, myocardial infarction, cardiac arrest, or sudden death.

RESULTS

Thirteen single-dose trials and 20 longer duration trials were included in the study. A single dose of beta(2)-agonist increased the heart rate by 9.12 beats/min (95% confidence interval [CI], 5.32 to 12.92) and reduced the potassium concentration by 0.36 mmol/L (95% CI, 0.18 to 0.54), compared to placebo. For trials lasting from 3 days to 1 year, beta(2)-agonist treatment significantly increased the risk for a cardiovascular event (relative risk [RR], 2.54; 95% CI, 1.59 to 4.05) compared to placebo. The RR for sinus tachycardia alone was 3.06 (95% CI, 1.70 to 5.50), and for all other events it was 1.66 (95% CI, 0.76 to 3.6).

CONCLUSION

beta(2)-Agonist use in patients with obstructive airway disease increases the risk for adverse cardiovascular events. The initiation of treatment increases heart rate and reduces potassium concentrations compared to placebo. It could be through these mechanisms, and other effects of beta-adrenergic stimulation, that beta(2)-agonists may precipitate ischemia, congestive heart failure, arrhythmias, and sudden death.

(S)-Albuterol activates pro-constrictory and pro-inflammatory pathways in human bronchial smooth muscle cells

BACKGROUND

Pro-constrictory and proinflammatory properties of (S)-albuterol have been widely reported both under in vivo and in vitro conditions. However, underlying mechanisms are unclear.

OBJECTIVE

We examined and compared the cellular effects of albuterol enantiomers on key intracellular molecules involved in constrictory and inflammatory pathways in human bronchial smooth muscle cells (hBSMCs).

METHODS

Primary hBSMCs were grown in culture and treated with various concentrations of albuterol enantiomers for various periods. Methacholine was used to stimulate cells. The expression and activity of Gs and Gi proteins, the intracellular free calcium concentration ([Ca2+]i), the activity of phosphatidylinositol 3'-OH-kinase (PI3) kinase, and the transcriptional nuclear factor kappaB (NF-kappaB) level were examined.

RESULTS

There was a significant increase in the expression and activity of Gialpha-1 protein and a decrease in the expression of Gs protein in hBSMCs after 8 hours of treatment with (S)-albuterol. These effects of (S)-albuterol were observed in a dose-dependent manner. Nonreceptor-mediated activation of adenylate cyclase by forskolin was attenuated with (S)-albuterol. Treatment of the cells for 24 hours with (S)-albuterol significantly increased [Ca2+]i on stimulation with methacholine. Interestingly, the effect of (R)-albuterol was opposite to that of (S)-albuterol. The effect of the racemic albuterol in some cases was similar to that of (S)-albuterol. (S)-Albuterol significantly activated both PI3 kinase and NF-kappaB in hBSMCs.

CONCLUSION

These studies demonstrated an (S)-albuterol-induced increase in the expression and activity of pro-constrictory pathways involving Gialpha-1 protein and [Ca2+]i and a decrease in the activity of the bronchodilatory pathway involving Gs proteins in hBSNMCs. Additionally, (S)-albuterol activated proinflammatory pathways involving PI3 kinase and NF-kappaB. Because (S)-albuterol metabolizes at least 10-fold slower than (R)-albuterol and has a longer elimination half-life, these cellular effects of (S)-albuterol might explain the detrimental effect seen with chronic administration of racemic albuterol in the treatment of airway diseases, such as bronchial asthma.

A simple and rapid genotyping method for beta-2 receptor (beta2 AR) gene using allele specific multiplex PCR

BACKGROUND

Polymorphism of the beta2-adrenergic receptor (beta2 AR) gene is an important determinant of the function of this receptor. It affects receptor down-regulation and beta2-agonist responses. It has also been a focus of interest in attempts to elucidate the genetic basis of asthma, hypertension, obesity and cystic fibrosis. Several different techniques have been established to determine beta2 AR genotypes but none of these methods are simple enough to detect simultaneously all the five alleles of our research interest (Arg16/Gly16, -20T/C, Gln27/Glu27, -47T/C and Thr164/Ile164).

OBJECTIVES

To develop a simple and rapid PCR based method for the simultaneous detection of five beta2 AR alleles.

METHOD

DNA was extracted from whole blood using standard alkali lysis method. Primers specific at the 3' end for the polymorphic sites were designed. The nested allele specific PCR was optimized for reproducibility and specificity. Parameters investigated included concentrations of MgCl2, Taq polymerase, primers and annealing temperature, to produce specific bands of interest. DNA samples were selected at random and submitted for direct PCR sequencing.

RESULT

The first PCR produced a fragment of size 710 bp, which was used as template for the subsequent duplex and triplex PCR to detect the mutation sites of the five alleles. The method was found reproducible and specific when used to genotype patients with bronchial asthma. The sequencing results confirmed the specificity of the PCR method.

CONCLUSION

The simple and rapid method for the simultaneous detection of the five beta2 AR alleles is suitable for the study of beta2 polymorphism and its clinical consequences.

The actions of dopamine on the airways

BACKGROUND

Dopamine exerts inhibitory and excitatory effects on different systems. In the lungs, dopamine modulates respiratory functions through carotid bodies and modulates pulmonary blood vessel tone, alveolar liquids, and bronchial exchange, and possibly participates in the regulation of airways diameter. It has been reported that dopamine has no acute effect on human airways in normal subjects or those with asthma background. However, inhaled or infused dopamine decreased histamine-induced bronchoconstriction in both normal and asthmatic subjects. We have examined the possible modulating effect of dopamine on bronchial diameter by administering inhaled dopamine and the DA2 dopaminergic blocker metoclopramide to subjects with various degrees of bronchial tone.

METHODS

We examined 56 volunteers. Arterial blood pressure and heart rate were determined in every subject. By means of spirometry, we measured forced vital capacity, forced expiratory volume in the first second, maximal forced expiratory flow, and forced expiratory flow at 50% of vital capacity, before and after each treatment. By inhalation with a nebulizer, we administered dopamine (0.5 microg/kg/min) to 10 healthy subjects, 10 subjects with asthma without acute bronchospasm, and 16 subjects with acute asthma attack; intravenous metoclopramide (7 microg/kg/min) was administered to 10 healthy subjects and 10 subjects with asthma without acute bronchospasm. For ethical reasons, metoclopramide was not used in subjects with acute asthma attack.

STATISTICS

non-parametric Wilcoxon tests for paired samples, ANOVA tests, and Bonferroni multiple comparison tests were performed.

RESULTS

Inhaled dopamine increased forced expiratory volume in the first second, forced vital capacity, maximal forced expiratory flow, and forced expiratory flow at 50% of vital capacity in the acute asthma attack group, but there were no modifications in the healthy group or in the asthma without acute bronchospasm group. Metoclopramide did not induce changes in respiratory parameters in healthy individuals or in those with asthma without acute bronchospasm.

CONCLUSIONS

Inhaled dopamine was able to induce bronchodilatation when the bronchial tone was already increased by acute asthma attack, but it did not modify the resting bronchial tone in normals or in asthmatics without acute bronchospasm. DA2 blockade with metoclopramide did not modify resting bronchial tone either. We suggest that dopamine exerts a modulatory effect on bronchial tone of human airways depending on the degree of existing basal tone.

β2-Adrenoceptor agonist fenoterol enhances functional repair of regenerating rat skeletal muscle after injury

β2-Adrenoceptor agonists such as fenoterol are anabolic in skeletal muscle, and because they promote hypertrophy and improve force-producing capacity, they have potential application for enhancing muscle repair after injury. No previous studies have measured the β2-adrenoceptor population in regenerating skeletal muscle or determined whether fenoterol can improve functional recovery in regenerating muscle after myotoxic injury. In the present study, the extensor digitorum longus (EDL) muscle of the right hindlimb of deeply anesthetized rats was injected with bupivacaine hydrochloride, which caused complete degeneration of all muscle fibers. The EDL muscle of the left hindlimb served as the uninjured control. Rats received either fenoterol (1.4 mg·kg-1·day-1) or an equal volume of saline for 2, 7, 14, or 21 days. Radioligand binding assays identified a ∼3.5-fold increase in β2-adrenoceptor density in regenerating muscle at 2 days postinjury. Isometric contractile properties of rat EDL muscles were measured in vitro. At 14 and 21 days postinjury, maximum force production (Po) of injured muscles from fenoterol-treated rats was 19 and 18% greater than from saline-treated rats, respectively, indicating more rapid restoration of function after injury. The increase in Poin fenoterol-treated rats was due to increases in muscle mass, fiber cross-sectional area, and protein content. These findings suggest a physiological role for β2-adrenoceptor-mediated mechanisms in muscle regeneration and show clearly that fenoterol hastens recovery after injury, indicating its potential therapeutic application.

Evidence showing that beta-adrenoceptor subtype responsible for the relaxation induced by isoprenaline is principally beta2 but not beta1 in guinea-pig tracheal smooth muscle

1. The present study was carried out to pharmacologically identify the beta-adrenoceptor subtype that mediates isoprenaline-elicited relaxation in the isolated guinea-pig tracheal smooth muscle, to answer the question whether it is beta(1)- or beta(2)-subtype? 2. Isoprenaline as well as salbutamol, a well-known beta(2)-selective adrenoceptor agonist, produced a concentration-dependent relaxation with a pD(2) value of 8.12 vs. 7.54 for salbutamol. 3. Isoprenaline-elicited relaxation was not affected by beta(1)-selective antagonists, atenolol and CGP-20,712A, within the concentration ranges supposed to antagonize beta(1)-subtype: atenolol, < or =10(-6) M; CGP-20,712A, < or =10(-8) M. 4. By contrast, the concentration-response curves for isoprenaline as well as salbutamol were shifted rightwards in a competitive fashion by atenolol at the concentrations > or =3 x 10(-6) M. However, pA(2) values of atenolol against isoprenaline (5.86) and salbutamol (5.71) were consistent with the value corresponding to beta(2)- but not to beta(1)-subtype (around 7.00), and these values were not significantly different from each other. 5. Competitive antagonism of the relaxations to isoprenaline and salbutamol were also obtained with beta(2)-selective antagonists, butoxamine and ICI-118,551. Against isoprenaline and salbutamol, the pA(2) values of butoxamine (6.51 vs. 6.81) and ICI-118,551 (8.83 vs. 8.90) were substantially identical. Thus the primary mediation of beta(2)-receptor in the relaxations was strongly supported. 6. The present findings provide evidence that the beta-adrenoceptor which mediates isoprenaline-elicited relaxation of guinea-pig tracheal smooth muscle is essentially beta(2)- but not beta(1)-subtype. The present study also indicates the importance of using multiple receptor antagonists with different pA(2) values to pharmacologically identify the responsible receptor subtype in smooth muscle mechanical responses.

Long-acting beta2-adrenergic formoterol and salmeterol induce the apoptosis of B-chronic lymphocytic leukaemia cells

B-cell chronic lymphocytic leukaemia (B-CLL) is a neoplastic disorder characterized by defective apoptosis, cell accumulation in G0/G1, and high expression of BCL2 oncogene. Intracellular cyclic adenosine monophosphate (cAMP) accumulation increases the chemosensitivity of B-CLL cells in vitro and in vivo. In the present study, we investigated the effects of beta2-adrenergic compounds, well known cAMP-inducing drugs, on the in vitro survival of leukaemia cells. In contrast to the short-acting beta2-mimetic (beta2Mim) salbutamol, a consistent pro-apoptotic effect was observed with the long-acting beta2Mim salmeterol and formoterol. Normal B cells isolated from control donors were totally resistant to the above molecules. These compounds also increased chlorambucil- and fludarabine-induced death of B-CLL cells. Blockade of beta-adrenergic receptor signalling or cAMP did not alter B-CLL apoptosis with beta2 Mimagents. Leukaemia cell apoptosis by beta2Mim correlated with an increase in calcium influx, decreased bcl-2 protein and mRNA levels, increase in BAX gene expression and a marked rise in BCL2/BAX mRNA ratios. Interleukin-4, a cytokine that increases bcl-2 expression in B-CLL cells, rescued leukaemia cell from apoptosis with beta2Mim. These data show that long-acting beta2-adrenergic agents promote apoptotic leukaemia cell death through an adrenoreceptor- and cAMP-independent, Ca2+-dependent mechanism.

BETA.1-Adrenoceptor-mediated relaxation with isoprenaline and the role of MaxiK channels in guinea-pig esophageal smooth muscle

The possible functional coupling between beta1-adrenoceptor and MaxiK channels which results in smooth muscle relaxation was examined in the guinea-pig esophageal muscularis mucosae. Isoprenaline-elicited relaxation of esophageal smooth muscle was confirmed to be mediated through beta1-adrenoceptors as the response was competitively antagonized by a beta1-selective antagonist atenolol with a pA2 value of 7.01. Iberiotoxin (IbTx, 10(-7) M), a selective MaxiK channel inhibitor, substantially diminished the relaxant response to isoprenaline. The extent of the MaxiK channel contribution to the relaxant response was 15-40% of the control response when estimated as the E50%-Emax responses to isoprenaline. The relaxation to isoprenaline was also attenuated by high-KCl (80 mM) to the same degree as the relaxant response generated in the presence of IbTx, and thus the estimated extent of the K+ channel contribution was 10-40%. These findings indicate that beta1-adrenoceptors are substantially coupled with MaxiK channels to produce relaxation of esophageal smooth muscle in the guinea-pig. Although MaxiK channels account for the contribution of K+ channels to the beta1-adrenoceptor-mediated relaxation in this smooth muscle preparation, their contribution seems to be less when compared to the beta2-adrenoceptor-mediated relaxation of tracheal smooth muscle.

Genotype Gly/Gly of the Arg16Gly polymorphism of the beta2-adrenergic receptor is associated with elevated fasting serum insulin concentrations, but not with acute insulin response to glucose, in type 2 diabetic patients

The beta(2)-adrenergic receptor (B2AR) is expressed in pancreatic beta-cells and modulates insulin secretion. The purpose of the present study was to evaluate the influence of the Arg16Gly variant allele of B2AR on insulin secretion in patients with type 2 diabetes. We used minimal model analysis of the frequently sampled insulin-modified intravenous glucose tolerance test (FSIGT) and polymerase chain reaction (PCR)-restriction fragment length polymorphism to examine differences of insulin secretion and insulin resistance among three genotypes. There were no significant differences in baseline clinical characteristics, HbA1c, uric acid, CRP or lipid profiles among the three groups. The Gly/Gly group had significantly higher levels of fasting insulin (38.2+/-4.7 pmol/l versus 23.6+/-3.5 pmol/l) and homeostasis model assessment of insulin resistance (HOMA-R) (1.90+/-0.19 versus 1.32+/-0.24), compared with the Arg/Arg group, but there were no significant differences in acute insulin response to glucose (AIRg) bolus, insulin sensitivity (Si), or glucose effectiveness (Sg) among the three genotypes. Several reports have speculated that the Gly16 allele of B2AR exhibits agonist-promoted downregulation, but our findings, elevated fasting insulin concentrations, and previous clinical studies of blood pressure and lypolysis are controversial. The direct mechanism by which the Gly16 allele of B2AR may influence insulin secretion of pancreatic beta-cells is unknown. Further studies of the expression of the allelic receptor in islet cells may help to resolve the role of B2AR in insulin secretion. However, increased sensitivity to catecholamine-induced lipolysis of the Gly allele promotes higher free fatty acids concentrations in the portal system, which could enhance the higher levels of fasting insulin.

Evidence for a significant role of a Gs-triggered mechanism unrelated to the activation of adenylyl cyclase in the cyclic AMP-independent relaxant response of guinea-pig tracheal smooth muscle

Cyclic AMP is a key molecule in the regulation of airway smooth muscle tone. Increased cyclic AMP leads to relaxation of this smooth muscle and its inhibition results in the muscle contraction. A constitutive role for cyclic AMP in the contraction and relaxation of airway muscle is supported by the observations that direct activators of adenylyl cyclase, such as forskolin and membrane-permeable cyclic AMP analogues, relax this smooth muscle potently. This traditional view of the role for cyclic AMP is the basis for the idea that relaxation of airway smooth muscle mediated through adenylyl cyclase-linked, G(s)-coupled receptors, including the beta(2)-adrenoceptor, is achieved mainly by the elevation of cyclic AMP content [cyclic AMP-dependent mechanism(s)]. However, recent pharmacological and biochemical evidence raises a fundamental question concerning the role of cyclic AMP; can G(s)-coupled receptor-mediated relaxation of tracheal smooth muscle be attributed exclusively to cyclic AMP-dependent mechanism(s)? In the present study, we show that cholera toxin (CTX, 5 microg/ml), an activator of the heterotrimeric guanine-nucleotide-binding protein G(s), relaxes guinea-pig tracheal smooth muscle. CTX also elevates tissue cyclic AMP content by about 30-fold and this is practically abolished by an adenylyl cyclase inhibitor, SQ 22,536 (100 microM). However, unexpectedly, the relaxant response to CTX is not affected by SQ 22,536. These results firstly show that activation of G(s) is able to produce a relaxation in tracheal smooth muscle independently of the elevation of cyclic AMP. G(s)-triggered, cyclic AMP-unrelated cellular mechanism(s) seem(s) to play a substantial role in smooth muscle relaxation mediated through adenylyl cyclase-linked receptors. This mechanism may account in part for the cyclic AMP-independent relaxant response of tracheal smooth muscle.

[Pharmacological action and clinical aspects of salmeterol]

Previous systemic beta(2) agonists such as procatrol tablets and tulobuterol patch were developed in Japan to address nocturnal symptoms and maintenance of lung function in asthmatic patients. Salmeterol, a potent and highly selective in beta(2) adrenocepter agonist with a duration of action greater than 12 h, was developed to provide long duration of bronchodilation with binding to a non-active site in the beta(2)-adrenocepter. Salmeterol is administrated via dry power inhalation and clinical studies have showed it has a good efficacy and a good safety profile, similar to inhaled steroids. Indeed, many clinical studies showed that salmeterol demonstrated better efficacy than long-acting beta(2)-agonist oral bronchodilators, theophyllines, and leukotriene-receptor antagonists in asthmatic patients and anticholinergic agents and theophyllines in COPD patients. Salmeterol will provide clinical benefits for Japanese asthma and COPD patients.

Beta-adrenergic agonists inhibit corticosteroid-induced apoptosis of airway epithelial cells

Airway epithelial damage is a feature of persistent asthma. Treatment with inhaled and oral corticosteroids may suppress inflammation and gain clinical control despite continued epithelial damage. We have previously demonstrated that corticosteroids elicit apoptosis of airway epithelial cells in culture. beta-Adrenergic receptor agonists are commonly used in asthma therapy and can inhibit corticosteroid-induced apoptosis of eosinophils. We tested the hypothesis that beta-adrenergic agonists would inhibit corticosteroid-induced airway epithelial cell apoptosis in cultured primary airway epithelial cells and in the cell line 1HAEo-. Albuterol treatment inhibited dexamethasone-induced apoptosis completely but did not inhibit apoptosis induced by Fas receptor activation. The protective effect of albuterol was duplicated by two different analogs of protein kinase A. The protective effect was not associated with increased translocation of the glucocorticoid receptor to the nucleus nor with changes in glucocorticoid receptor-mediated transcriptional activation or repression. We demonstrate that beta-adrenergic agonists can inhibit corticosteroid-induced apoptosis but not apoptosis induced by Fas activation. These data suggest that one potential deleterious effect of corticosteroid therapy in asthma can be prevented by concomitant beta-adrenergic agonist treatment.

Does a single dose of the phosphodiesterase 4 inhibitor, cilomilast (15 mg), induce bronchodilation in patients with chronic obstructive pulmonary disease?

Maintenance treatment with PDE(4) inhibitor cilomilast improves FEV(1) in chronic obstructive pulmonary disease (COPD) patients. We investigated the acute bronchodilating effects of a single dose of cilomilast with or without concomitant administration of inhaled salbutamol and/or ipratropium bromide in 21 patients with COPD (mean (SD) age 64 (8.1) y, post-salbutamol FEV(1) 47.7 (13.2) %predicted). FEV(1) was measured before and up to 8 hourly intervals after intake of placebo, cilomilast, or cilomilast in combination with inhaled salbutamol 400 microg and/or ipratropium bromide 80 microg. Maximum increase in FEV(1) from pre-dose baseline was calculated after each treatment and differences between treatment arms were analyzed by ANOVA. The mean (SEM) maximum increase in FEV(1) was 139.6 (18.5) ml following cilomilast and 151.5 (18.5) ml following placebo (95% C.I. for mean difference between cilomilast and placebo: -67.3, 43.6 ml). Furthermore, combined treatment of cilomilast with salbutamol or ipratropium resulted in a maximum increase in FEV(1) of 280.7 (25.6) and 297.0 (25.9) ml, respectively, while this was 379.0 (24.6) ml following cilomilast with both salbutamol and ipratropium (p < 0.01). We conclude that a single dose of cilomilast does not produce acute bronchodilation in patients with COPD who otherwise respond to inhaled bronchodilators. Our results implicate that the change in lung function seen after long-term treatment with cilomilast is not the result of acute bronchodilation in patients with COPD.

Possible role of alpha-adrenoceptor subtypes in acute migraine therapy

Even though the underlying mechanisms for the pathophysiology of migraine attacks are not completely understood, little doubt exists that the headache phase is explained by dilatation of cranial, extracerebral blood vessels. In this context, experimental models predictive for anti-migraine activity have shown that both triptans and ergot alkaloids, which abort migraine headache, produce vasoconstriction within the carotid circulation of different species. In contrast to the well-established role of serotonin (5-hydroxytryptamine; 5-HT) 5-HT1B receptors in the common carotid vascular bed, the role of alpha-adrenoceptors and their subtypes has been examined only relatively recently. Using experimental animal models and alpha1- and alpha2-adrenoceptor agonists (phenylephrine and BHT933, respectively) and antagonists (prazosin and rauwolscine, respectively), it was shown that activation of either receptor produces a cranioselective vasoconstriction. Subsequently, investigations employing relatively selective antagonists at alpha1- (alpha1A, alpha1B, alpha1D) and alpha2- (alpha2A, alpha2B, alpha2C) adrenoceptor subtypes revealed that specific receptors mediate the carotid haemodynamic responses in these animals. From these observations, together with the potential limited role of alpha1B- and alpha2C-adrenoceptors in the regulation of systemic haemodynamic responses, it is suggested that selective agonists at these receptors may provide a promising novel avenue for the development of acute anti-migraine drugs.

Roles of genotypes of beta2-adrenergic receptor in the relationship between eosinophil counts and lung function in Taiwanese adolescents

To examine the roles of genetic polymorphism of the beta2-adrenergic receptor (beta2AR) in the relationship between eosinophil (EOS) counts and eosinophil cationic protein (ECP) counts and lung function, we recruited a random sample from the 1996 nationwide survey of asthma prevalence in middle school children. A total of 149 subjects--42 asthmatic children, 38 asthmatics in remission (no reported attack for more than 12 months), and 69 nonasthmatics--completed a physical evaluation, pulmonary function test, and determination of EOS, ECP, and beta2AR genotypes at amino acids 16 and 27. Asthmatic children had higher EOS and ECP than did nonasthmatics. No association was found between asthma and beta2AR genotypes. Lung function was significantly and inversely correlated with EOS but not with ECP in asthmatic children. By genotype, an inverse correlation between lung function and EOS was found in asthmatic children with Arg16Arg or Gln27Glu. A nonsignificant but similar inverse correlation was found in asthmatic children with Arg16Gly or Gln27Gln. However, a nonsignificant but positive correlation was found in asthmatic children with Gly16Gly. In conclusion, we suggest that EOS is a better clinical indicator of airway inflammation than ECP when children are not having an asthma attack. The association between an increase of EOS and lower lung function can be differentiated by beta2AR genotypes at amino acid 16.

Innervation of equine airways

Equine obstructive pulmonary disease (COPD), or heaves or recurrent airway obstruction, is a common equine pulmonary disease similar to human asthma and/or CODP. Since bronchospasm and inflammation are the key features in heaves, the purpose of this paper is to review the contribution of neural mechanism that may be relevant to this disease. Equine airway receive cholinergic and adrenergic innervation, as well as observed in many species. It was suggested that the autonomic neural control in asthma might be defective with an imbalance between excitatory and inhibitory pathways, resulting in excessively twitchy airways. Moreover, the recognition that, in addition to classical adrenergic and cholinergic pathway there are non-adrenergic-non-cholinergic inhibitory (iNANC) and excitatory (eNANC) innervation and many mediators, which have potent effects on airway function, has revived interest in neural control of airway.

Adrenergic mechanisms in canine nasal venous systems

1 We investigated the adrenergic mechanisms of the two venous systems that drain the nasal mucosa, thereby their exact role in eliciting nasal decongestion. The action of endogenously released noradrenaline and exogenous adrenergic agonists on different segments of the nasal venous systems, i.e. collecting (LCV, SCV) and outflow (SPV) veins of posterior venous system, collecting (ACV) and outflow (DNV) veins of anterior venous system and venous sinusoids of the septal mucosa (SM), were studied. In vitro isometric tension of the vascular segments was measured. 2 Transmural nerve stimulation (TNS) produced constriction in ACV, DNV and SM, primary constriction followed by secondary dilatation in LCV and SCV and dilatation in SPV. Tetrodotoxin (10(-6) M) abolished all responses. Phentolamine (10(-6) M), prazosin (10(-6) M) and rauwolscine (10(-7) M) inhibited the constriction in all venous vessels. Propranolol (10(-6) M), atenolol (10(-6) M) and ICI 118,551 (10(-6) M) inhibited the relaxation in SPV but not in LCV and SCV. Phenylephrine and clonidine constricted whereas dobutamine and terbutaline relaxed all venous vessels dose-dependently. 3 These results indicate alpha(1)-, alpha(2)-, beta(1)- and beta(2)-adrenoceptors are present in both venous systems. TNS causes constriction of anterior venous system, venous sinusoids and posterior collecting veins primarily via postjunctional alpha(2)-adrenoceptors but relaxation of posterior outflow vein equally via postjunctional beta(1)- and beta(2)-adrenoceptors. The combined action of the two adrenergic mechanisms can reduce nasal airway resistance in vivo by decreasing vascular capacitance and enhancing venous drainage via the posterior venous system.

Metabolism of salbutamol differs between asthmatic patients and healthy volunteers

Patients with asthma are a target group for medication with beta2-agonists, often in combination with corticosteroids. Salbutamol is commonly marketed as racemate. R-Salbutamol carries beta2-agonistic property whereas S-salbutamol does not. The racemate undergoes stereoselective sulphatisation by sulfotransferases mainly in the gut and liver, so that S-salbutamol rests for a longer time in the body and reaches higher plasma levels than R-salbutamol. Ten patients with mild stable asthma and at present without cortisone medication were given racemic salbutamol as ventoline 4 mg orally. Plasma and urine levels were estimated until 24 hr after ingestion. For comparison healthy volunteers were treated in the same way. The group of asthma patients was then treated with budesonide inhalations 800 microg daily for one week and the initial programme resumed. Non-cortisone-treated asthmatic patients displayed higher levels of both R- and S-salbutamol in plasma than did healthy volunteers after one single ingestion of racemic salbutamol (CMAX both comparisons P<0.05). Plasma levels of salbutamol isomers in cortisone-treated asthmatic patients resembled the levels in volunteers. The most plausible explanation for the discrepancy in values between asthmatic patients and volunteers is a defective metabolic function by asthmatic patients possibly enzymatic in origin.

Distribution in allele frequencies of predisposition-to-atopy genotypes in Chinese children

Asthma is one of the most common chronic diseases in childhood; it is caused by a complex interaction between genetic factors and exposure to environmental allergens and irritants. Previous studies using the candidate gene approach showed that asthma was linked to a number of susceptibility genetic loci in Caucasian subjects. There are, however, only a few studies on asthma predisposition genes in the Chinese population. We studied the distribution of allele frequencies of I50V for the interleukin-4 receptor, two polymorphisms in intron 2 and exon 7 for the high-affinity IgE receptor (Fc epsilon RI-beta), R16G and E27Q for the beta(2)-adrenoceptor,and R275Q (824G/A) for CC chemokine receptor 3 in Chinese children.Seventy-six patients, with a mean age of 10.6 years, and 70 age- and sex-matched controls, were studied. Significantly more subjects in the asthma group had specific IgE antibodies against environmental allergens (P < 0.0001; odds ratio, 9.82). Genotyping of the six genetic markers showed that none of the six polymorphisms was associated with asthma in this cohort. The allele frequencies of I50V, R16G, and E27Q in our population were similar to those published for Asian subjects but not Caucasians. The R275Q substitution was a rare finding in our study and in the published reports. Our results demonstrate ethnic differences in polymorphisms of atopy candidate genes. Additional studies involving larger samples are required to investigate the association between asthma or atopy and the genotypes studied to date in Chinese children.

Uncoupling protein-1: involvement in a novel pathway for beta-adrenergic, cAMP-mediated intestinal relaxation

The pathway for adrenergic relaxation of smooth muscle is not fully understood. As mitochondrial uncoupling protein-1 (UCP1) expression has been reported in cells within the longitudinal smooth muscle layer of organs exhibiting peristalsis, we examined whether the absence of UCP1 affects adrenergic responsiveness. Intestinal (ileal) segments were obtained from UCP1-ablated mice and from wild-type mice (C57Bl/6, 129/SvPas, and outbred NMRI). In UCP1-containing mice, isoprenaline totally inhibited contractions induced by electrical field stimulation, but in intestine from UCP1-ablated mice, a significant residual contraction remained even at a high isoprenaline concentration; the segments were threefold less sensitive to isoprenaline. Also, when contraction was induced by carbachol, there was a residual isoprenaline-insensitive contraction. Similar results were obtained with the beta(3)-selective agonist CL-316,243 and with the adenylyl cyclase stimulator forskolin. Thus the UCP1 reported to be expressed in the longitudinal muscle layer of the mouse intestine is apparently functional, and UCP1, presumably through uncoupling, may be involved in a novel pathway leading from increased cAMP levels to relaxation in organs exhibiting peristalsis.

The beta 2-adrenergic agonist salbutamol potentiates oral induction of tolerance, suppressing adjuvant arthritis and antigen-specific immunity

Therapeutic protocols for treating autoimmune diseases by feeding autoantigens during the disease process have not been very successful to date. In vitro it has been shown that beta-adrenergic agonists inhibit pro-inflammatory cytokine production and up-regulate anti-inflammatory cytokine production. We hypothesized that the protective effect of oral administration of Ag would be enhanced by oral coadministration of the beta(2)-adrenergic agonist salbutamol. Here we demonstrate that oral administration of salbutamol in combination with the Ag mycobacterial 65-kDa heat shock protein increased the efficacy of disease-suppressive tolerance induction in rat adjuvant arthritis. To study the mechanism of salbutamol in more detail, we also tested oral administration of salbutamol in an OVA tolerance model in BALB/c mice. Oral coadministration of OVA/salbutamol after immunization with OVA efficiently suppressed both cellular and humoral responses to OVA. Coadministration of salbutamol was associated with an immediate increase in IL-10, TGF-beta, and IL-1R antagonist in the intestine. The tolerizing effect of salbutamol/OVA was maintained for at least 12 wk. At this time point IFN-gamma production in Ag-stimulated splenocytes was increased in the OVA/salbutamol-treated animals. In conclusion, salbutamol can be of great clinical benefit for the treatment of autoimmune diseases by promoting oral tolerance induction.

Acute effects of higher than customary doses of salmeterol and salbutamol in patients with acute exacerbation of COPD

Worsening of underlying bronchospasm may be associated with acute exacerbations of chronic obstructive pulmonary disease (COPD). As airway obstruction becomes more severe, the therapeutic option is to add salbutamol, but not salmeterol, as needed to cause rapid relief of bronchospasm. Unfortunately the most effective dosage of beta2-agonists may increase above that recommended during acute exacerbations. In this study, we compared the acute effects of higher than customary doses of salmeterol and salbutamol in 20 patients with acute exacerbation of COPD. A dose-response curve to salmeterol pMDI, 25 microg/puff or salbutamol pMDI, 100 microg/puff, was constructed using 1, 1, and 2 puff' i.e., a total cumulative dose of 100 microg salmeterol or 400 microg salbutamol on 2 consecutive days. After baseline measurements, dose increments were given at 30-min intervals with measurements being made 25 min after each dose. Hear rate (HR) and pulse-oximetry (SpO2) measurements were then taken. Both salmeterol and salbutamol induced a larg and significant (P < 0.05) dose-dependent increase in FEV1 [mean differences from baseline (L) = after 100 microg salmeterol 0.174 (95% CI: 0.112 to 0.237); after 400 microg salbutamol: 0.165 (95% CI: 0.080 to 0.249)], in IC [mean differences from baseline (L) = after 100 microg salmeterol: 0.332 (95% CI: 0.165 to 0.499); after 400 microg salbutamol: 0.281 (95% CI: 0.107 to 0.456)] (Fig. 2), and in FVC mean differences from baseline (L) = after 100 microg salmeterol: 0.224 (95% CI: 0.117 to 0.331); after 400 microg salbutamol: 0.242 (95% CI: 0.090 to 0.395)]. There was no significant difference between the FEV1 values (P=0.418), the ICvalues (P=0.585), and the FVCvalue (P=0.610) after 100 microg salmeterol and 400 microg salbutamol. HR [mean differences from baseline (beats/min) = after 100 microg salmeterol: 3.15 (95% CI: -0.65 to 6.96); after 400 microg salbutamol: 2.30 (95% CI: -0.91 to 5.51)] and SpO2 [mean differences from baseline (%) = after 100 microg salmeterol: -0.20 (95% CI: -1.00 to 0.60); after 400 microg salbutamol: -0.11 (95% CI: -1.00 to 0.79)] did not change significantly from baseline (P > 0.05). These data indicate that salmeterol is effective and safe in the treatment of acute exacerbation of COPD and support its use in this clinical condition.

Molecular haplotyping at high throughput

Reconstruction of haplotypes, or the allelic phase, of single nucleotide polymorphisms (SNPs) is a key component of studies aimed at the identification and dissection of genetic factors involved in complex genetic traits. In humans, this often involves investigation of SNPs in case/control or other cohorts in which the haplotypes can only be partially inferred from genotypes by statistical approaches with resulting loss of power. Moreover, alternative statistical methodologies can lead to different evaluations of the most probable haplotypes present, and different haplotype frequency estimates when data are ambiguous. Given the cost and complexity of SNP studies, a robust and easy-to-use molecular technique that allows haplotypes to be determined directly from individual DNA samples would have wide applicability. Here, we present a reliable, automated and high-throughput method for molecular haplotyping in 2 kb, and potentially longer, sequence segments that is based on the physical determination of the phase of SNP alleles on either of the individual paternal haploids. We demonstrate that molecular haplotyping with this technique is not more complicated than SNP genotyping when implemented by matrix-assisted laser desorption/ionisation mass spectrometry, and we also show that the method can be applied using other DNA variation detection platforms. Molecular haplotyping is illustrated on the well-described beta(2)-adrenergic receptor gene.