Beta-agonists

Salbutamol Transport and Deposition in the Upper and Lower Airway with Different Devices in Cats: A Computational Fluid Dynamics Approach

Simple Summary

Administration of inhaled salbutamol via metered-dose inhalers can effectively treat bronchoconstriction. Different devices are used for the delivery of this drug in cats, either in the hospital or at home, for long-term treatment. Effective drug administration may depend on the drug delivery device as well as patient cooperation. By using non-invasive computational fluid dynamics techniques, the impact of these devices on the deposition and transport of salbutamol particles in the cat airways was simulated and assessed. The results confirm a variable drug distribution depending on the device used. The percentage of particles reaching the lung was reduced when using spacers and increased when applied directly into an endotracheal tube.

Abstract

Pressurized metered-dose inhalers (pMDI) with or without spacers are commonly used for the treatment of feline inflammatory airway disease. During traditional airways treatments, a substantial amount of drugs are wasted upstream of their target. To study the efficiency of commonly used devices in the transport of inhaled salbutamol, different computational models based on two healthy adult client-owned cats were developed. Computed tomographic images from one cat were used to generate a three-dimensional geometry, and two masks (spherical and conical shapes) and two spacers (10 and 20 cm) completed the models. A second cat was used to generate a second model having an endotracheal tube (ETT) with and without the same spacers. Airflow, droplet spray transport, and deposition were simulated and studied using computational fluid dynamics techniques. Four regions were evaluated: device, upper airways, primary bronchi, and downstream lower airways/parenchyma (“lung”). Regardless of the model, most salbutamol is deposited in devices and/or upper airways. In general, particles reaching the lung varied between 5.8 and 25.8%. Compared with the first model, pMDI application through the ETT with or without a spacer had significantly higher percentages of particles reaching the lung (p = 0.006).

Anti-inflammatory effects of β2 adrenergic receptor agonists in experimental acute lung injury

These studies were undertaken to extend emerging evidence that β(2) adrenergic receptor (β(2)AR) agonists, in addition to their bronchorelaxing effects, may have broad anti-inflammatory effects in the lung following onset of experimental acute lung injury (ALI). Young male C57BL/6 mice (25 g) developed ALI following airway deposition of bacterial LPS or IgG immune complexes in the absence or presence of appropriate stereoisomers (enantiomers) of β(2)AR agonists, albuterol or formoterol. Endpoints included albumin leak into lung and buildup of polymorphonuclear neutrophils and cytokines/chemokines in bronchoalveolar fluids. Both β(2)AR agonists suppressed lung inflammatory parameters (IC(50)=10(-7) M). Similar effects of β(2)AR agonists on mediator release were found when mouse macrophages were stimulated in vitro with LPS. The protective effects were associated with reduced activation (phosphorylation) of JNK but not of other signaling proteins. Collectively, these data suggest that β(2)AR agonists have broad anti-inflammatory effects in the setting of ALI. While β(2)AR agonists suppress JNK activation, the extent to which this can explain the blunted lung inflammatory responses in the ALI models remains to be determined.

Mechanisms by which S-albuterol induces human bronchial smooth muscle cell proliferation

BACKGROUND

Racemic albuterol is a 50:50 mixture of the R-isomer, levalbuterol, and the S-isomer, S-albuterol. S-Albuterol increases airway hyperresponsiveness to spasmogens, exacerbates asthmatic conditions and stimulates cell growth, whereas levalbuterol attenuates cell growth in culture. The mechanisms of S-albuterol-induced cell proliferation are not well understood. We studied the role of albuterol isomers and intracellular cell cycle regulators on proliferation of human bronchial smooth muscle cells.

METHODS

Serum-starved cells (72 h) were fed test agents for 24 h and cell proliferation was measured. The expression of nuclear factor-kappaB inhibitory protein IkappaBalpha, nuclear factor-kappaB, cyclin-dependent kinases 2 and 4, interleukin (IL)-6, and retinoblastoma and platelet-activating factor (PAF) receptor protein were measured by Western blotting.

RESULTS

S-Albuterol, PAF and platelet-derived growth factor stimulated cell proliferation, but levalbuterol and the racemic mixture inhibited cell proliferation compared with the effect of 5% fetal bovine serum alone. The proliferative effect of platelet-derived growth factor on S-albuterol was not additive, suggesting that the 2 mediators act by different mechanisms. S-Albuterol induced greater expression of all the measured proteins than either levalbuterol, the racemic mixture or 5% fetal bovine serum. S-Albuterol stimulated IL-6 secretion and abolished the ability of levalbuterol to inhibit IL-6 secretion.

CONCLUSION

Our data show that S-albuterol stimulates cell proliferation by activating expression and phosphorylation of several intracellular mitogenic proteins and may exacerbate asthma by stimulating the release of IL-6. Induction of PAF receptor protein expression by S-albuterol strongly suggests that S-albuterol may exert its adverse effects by binding to a G protein-coupled receptor such as the PAF receptor.

Long-acting beta2-agonists versus theophylline for maintenance treatment of asthma

BACKGROUND

Theophylline and long acting beta-2 agonists are bronchodilators used for the management of persistent asthma symptoms, especially nocturnal asthma. They represent different classes of drug with differing side-effect profiles.

OBJECTIVES

To assess the comparative efficacy, safety and side-effects of long-acting beta-2 agonists and theophylline in the maintenance treatment of adults and adolescents with asthma.

SEARCH STRATEGY

We searched the Cochrane Airways Group trials register and reference lists of articles. We also contacted authors of identified RCTs for other relevant published and unpublished studies and pharmaceutical manufacturers. Most recent search: November 2006.

SELECTION CRITERIA

All included studies were RCTs involving adults and children with clinical evidence of asthma. These studies must have compared oral sustained release and/or dose adjusted theophylline with an inhaled long-acting beta-2 agonist.

DATA COLLECTION AND ANALYSIS

In original review, two reviewers independently assessed trial quality and extracted data, similarly in this update two reviewers undertook this. Study authors were contacted for additional information.

MAIN RESULTS

Thirteen studies with a total of 1344 participants met the inclusion criteria of the review. They were of varying quality. There was no significant difference between salmeterol and theophylline in FEV(1) predicted (6.5%; 95% CI -0.84 to 13.83). However, salmeterol treatment led to significantly better morning PEF (mean difference 16.71 L/min, 95% CI 8.91 to 24.51) and evening PEF (mean difference 15.58 L/min, 95% CI 8.33 to 22.83). Salmeterol also reduced the use of rescue medication. Formoterol, used in two studies was reported to be as effective as theophylline. Bitolterol, used in only one study, was reported to be less effective than theophylline. Participants taking salmeterol experienced fewer adverse events than those using theophylline (Parallel studies: Relative Risk 0.44; 95% CI 0.30 to 0.63, Risk Difference -0.11; 95% CI -0.16 to -0.07, Numbers Needed to Treat (NNT) 9; 95% CI 6 to 14). Significant reductions were reported for central nervous system adverse events (Relative Risk 0.50; 95% CI 0.29 to 0.86, Risk Difference -0.07; 95% CI -0.12 to -0.02, NNT 14; 95% CI 8 to 50) and gastrointestinal adverse events (Relative Risk 0.30; 95% CI 0.17 to 0.55, Risk Difference -0.11; 95% CI -0.16 to -0.06, NNT 9; 95% CI 6 to 16).

AUTHORS' CONCLUSIONS

Long-acting beta-2 agonists, particularly salmeterol, are more effective than theophylline in improving morning and evening PEF, but are not significantly different in their effect on FEV1. There is evidence of decreased daytime and nighttime short-acting beta-2 agonist requirement with salmeterol. Fewer adverse events occurred in participants using long-acting beta-2 agonists (salmeterol and formoterol) as compared to theophylline.

Levalbuterol inhibits human airway smooth muscle cell proliferation: therapeutic implications in the management of asthma

BACKGROUND

Racemic albuterol is a mixture of (R)- and (S)-enantiomers of albuterol. Its pharmacological activity and clinical efficacy reside in the (R)-enantiomer (levalbuterol), but the (S)-enantiomer exacerbates airway reactivity in nonclinical models. The role of albuterols in airway smooth muscle cell (SMC) proliferation is not well understood.

METHODS

The effect of levalbuterol on human bronchial SMC growth was compared with the effects of racemic albuterol and (S)-albuterol. Cells were fed albuterols and 3H-thymidine in 5% FBS and incubated for 24 h. The effect of (S)-albuterol on levalbuterol actions was also studied and so were the effects of cAMP/PKA, PI-3 kinase, NK-kappaB, and retinoblastoma (Rb) proteins on albuterols and human bronchial SMC proliferation.

RESULTS

Levalbuterol inhibited cell proliferation at low concentrations. The growth-inhibitory effect of levalbuterol occurs via activation of the cAMP/PKA pathway. Addition of (S)-albuterol to levalbuterol decreased the growth-inhibitory effect of levalbuterol, and (S)-albuterol attenuated levalbuterol-induced cAMP release by 65%. Levalbuterol inhibited NF-kappaB and Rb protein expressions. ICI-118551 abrogated the inhibitory properties of levalbuterol. The PAF receptor antagonist CV-3988 inhibited (S)-albuterol-induced cell growth, with no effect on levalbuterol.

CONCLUSIONS

Levalbuterol inhibits cell growth by activating the cAMP/PKA pathway and inhibiting PI-3 kinase, NF-kappaB and Rb protein expression, and (S)-albuterol induces cell growth by activating PAF-receptor-mediated cell signaling.

(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.

Prenatal cigarette smoke decreases lung cAMP and increases airway hyperresponsiveness

Epidemiologic studies suggest that in utero exposure to tobacco smoke, primarily through maternal smoking, increases the risk for asthma in children; however, the mechanism of this phenomenon is not clear. Cyclic adenosine monophosphate relaxes airway smooth muscles in the lung and acts as an antiasthmatic. In this study, we examined the effects of in utero cigarette smoke exposure of Balb/c mice on airway responsiveness, as determined by Penh measurements. Animals exposed prenatally but not postnatally to cigarette smoke exhibited increased airway hyperresponsiveness after a single intratracheal injection of Aspergillus fumigatus extract. The increased airway hyperresponsiveness was not associated with increased leukocyte migration or mucous production in the lung but was causally related to decreased lung cyclic adenosine monophosphate levels, increased phosphodiesterase-4 enzymatic activity, and phosphodiesterase-4D (PDE4D) isoform-specific messenger ribonucleic acid expression in the lung. Exposure of adult mice to cigarette smoke did not significantly alter airway responsiveness, cyclic adenosine monophosphate levels, or the phosphodiesterase activity. These results suggest that prenatal exposure to cigarette smoke affects lung airway reactivity by modulating the lung cyclic adenosine monophosphate levels through changes in phosphodiesterase-4D activity, and these effects are independent of significant mucous production or leukocyte recruitment into the lung.

Regulators of G protein signalling: potential targets for treatment of allergic inflammatory diseases such as asthma

Asthma, a disease that affects nearly 15% of the world's population, is characterised by lung inflammation and reversible airway obstruction, which leads to wheezing and dyspnoea. Asthma is a prototype for allergic processes initiated by tissue inflammatory leukocytes, such as mast cells, whose secreted mediators recruit lymphocytes and eosinophils to the lung parenchyma. Signals transmitted through G-protein-coupled receptors (GPCRs) contribute to both the development and perpetuation of allergic processes, and pharmacological agents that block or stimulate GPCR action have been a mainstay of allergic disease therapy. Despite the widespread use of GPCR-targeted agents, little is understood about intracellular regulation of G protein pathways in immune cells. Regulators of G protein signalling (RGS proteins) enhance G protein deactivation and may contribute to the specificity and precision characteristic of GPCR signalling pathways. This review discusses the emerging functions of RGS proteins in immune processes and inflammatory states such as asthma, and their potential value as therapeutic targets for the treatment of allergic disease.

Long acting beta-agonists versus theophylline for maintenance treatment of asthma

BACKGROUND

Theophylline and long acting beta-2 agonists are bronchodilators used for the management of persistent asthma symptoms, especially nocturnal asthma. They represent different classes of drug with differing side-effect profiles.

OBJECTIVES

To assess the comparative efficacy, safety and side-effects of long-acting beta-2 agonists and theophylline in the maintenance treatment of asthma.

SEARCH STRATEGY

Randomised, controlled trials (RCTs) were identified using the Cochrane Airways Group register. The register was searched using the following terms: asthma and theophylline and long acting beta-agonist or formoterol or foradile or eformoterol or salmeterol or bambuterol or bitolterol. Date of last search was April 2003. Titles and abstracts were then screened to identify potentially relevant studies. The bibliography of each RCT was searched for additional RCTs. Authors of identified RCTs were contacted for other relevant published and unpublished studies.

SELECTION CRITERIA

All included studies were RCTs involving adults and children with clinical evidence of asthma. These studies must have compared oral sustained release and/or dose adjusted theophylline with an inhaled long-acting beta-2 agonist.

DATA COLLECTION AND ANALYSIS

Potentially relevant trials, identified by screening titles and/or abstracts, were obtained. Two reviewers independently assessed full text versions of these trials to decide whether the trial should be included in the review, and assessed its methodological quality. Where there was disagreement between reviewers, this was resolved by consensus, or reference to a third party. Data were extracted by two independent reviewers. Inter-rater reliability was assessed by simple agreement. Study authors were contacted to clarify randomisation methods, provide missing data, verify the data extracted and identify unpublished studies. Relevant pharmaceutical manufacturers were also contacted.

MAIN RESULTS

Six trials originally met the inclusion criteria. Five used salmeterol and one, bitolterol. In an updated version of the review, six more trials were included. Four trials used salmeterol and two used formoterol. They were of varying quality. Salmeterol improved FEV1 significantly more than theophylline in five studies and salmeterol use was associated with significantly more symptom free nights in all the studies comparing these agents. Formoterol, used in two studies was reported to be as effective as theophylline. Bitolterol, used in only one study, was reported to be less effective than theophylline. Subjects taking salmeterol experienced fewer adverse events than those using theophylline (Parallel studies: Relative Risk 0.44; 95% CI: 0.30 to 0.63), Risk Difference -0.11 (95%CI: -0.16 to -0.07), NNT 9 (6, 14). Significant reductions were reported for central nervous system adverse events (Relative Risk 0.50; 95%Confidence Intervals 0.29, 0.86), Risk Difference -0.07(95% CI -0.12, -0.02), NNT 14(8, 50) and gastrointestinal adverse events (Relative Risk 0.30; 95%Confidence Intervals 0.17, 0.55), Risk Difference -0.11(-0.16, -0.06), NNT 9(6, 16).

REVIEWER'S CONCLUSIONS

Long-acting beta-2 agonists are at least as effective than theophylline in reducing asthma symptoms including night waking and improving lung function. Fewer adverse events occurred in subjects using long-acting beta-2 agonists(salmeterol and formoterol) as compared to theophylline.