Adenosine monophosphate and histamine induced bronchoconstriction: repeatability and protection by terbutaline

Extracellular cAMP: The Past and Visiting the Future in cAMP-Enriched Extracellular Vesicles

It is recently discovered that the cyclic nucleotide, cyclic adenosine monophosphate (cAMP) can be enriched in the extracellular vesicles (EVs) isolated from endothelial cells. In the current perspective a historical context for the discovery of the extracellular cAMP is provided. The story of extracellular cAMP through investigations addressing the molecule's role in the adenosine pathway is followed, which is widespread in mammalian physiology. The adenosine pathway mediates normal physiological conditions such as renin release, phosphate transport, etc., and participates in pathological conditions such as bronchoconstriction of the airways. Furthermore, adenosine mediated biological pathways are regulated via the receptor mediated intracellular cAMP pathway in mammalian cells. It then speculates on the question of whether cAMP enriched EVs could bypass typical receptor mediated cell signaling and directly activate cAMP signaling cascade in target cells. Preliminary studies to suggest cAMP enriched EVs are provided, added to naïve endothelial cells, results in an increase in intracellular cAMP. An alternate mechanism is proposed, apart from the traditional adenosine pathway, that extracellular cAMP may exert its effects and put into perspective how it might consider circulating cAMP moving forward.

Safety of hookworm infection in individuals with measurable airway responsiveness: a randomized placebo-controlled feasibility study

Background

Epidemiological evidence suggests that hookworm infection protects against asthma. However, for ethical and safety reasons, before testing this hypothesis in a clinical trial in asthma it is necessary to establish whether experimental hookworm infection might exacerbate airway responsiveness during larval lung migration.

Objective

To determine whether hookworm larval migration through the lungs increases airway responsiveness in allergic individuals with measurable airway responsiveness but not clinical asthma, and investigate the general tolerability of infection and effect on allergic symptoms.

Methods

Thirty individuals with allergic rhinoconjunctivitis and measurable airway responsiveness to adenosine monophosphate (AMP) but not clinically diagnosed asthma were randomized, double-blind to cutaneous administration of either 10 hookworm larvae or histamine placebo, and followed for 12 weeks. The primary outcome was the maximum fall from baseline in provocative dose of inhaled AMP required to reduce 1-s forced expiratory volume by 10% (PD₁₀AMP) measured at any time over the 4 weeks after active or placebo infection. Secondary outcomes included peak flow variability in the 4 weeks after infection, rhinoconjunctivitis symptom severity and adverse effect diary scores over the 12-week study period, and change in allergen skin test responses between baseline and 12 weeks.

Results

Mean maximum change in PD₁₀AMP from baseline was slightly but not significantly greater in the hookworm than the placebo group (−1.67 and −1.16 doubling doses; mean difference −0.51, 95% confidence interval −1.80 to 0.78, P=0.42). Symptom scores of potential adverse effects were more commonly reported in the hookworm group, but infection was generally well tolerated. There were no significant differences in peak-flow variability, rhinoconjunctivitis symptoms or skin test responses between groups.

Conclusion

Hookworm infection did not cause clinically significant exacerbation of airway responsiveness and was well tolerated. Suitably powered trials are now indicated to determine the clinical effectiveness of hookworm infection in allergic rhinoconjunctivitis and asthma.

Formoterol turbuhaler is as effective as salbutamol diskus in relieving adenosine-induced bronchoconstriction in children

Salbutamol diskus (SD) and formoterol turbuhaler (FT) are both fast-acting beta(2) agonists delivery systems used to relieve bronchoconstriction, such as that which accompanies acute exacerbations of asthma. Although SD (which is used only on an as-needed basis) is flow independent, the FT (currently recommended for regular therapy) requires a forceful deep inspiration. Thus, the efficacy of FT in children with bronchoconstriction may be inferior to that of SD. We have studied the bronchodilatation response induced by FT after a standard adenosine-5-monophosphate (AMP) bronchial challenge, and compared it to that induced by SD, and placebo. Seventeen children (mean age +/- SD 10.3 +/- 1.7 y) with asthma underwent three AMP challenges, each time followed by inhalation of either placebo, SD (200 mug) or FT (9 mug), in random order. Patterns of bronchodilatation (forced expiratory volume in 1 second recovery) to 90% of baseline levels were compared. Both SD and FT were significantly better than placebo. FT was slightly better than SD, but this difference was not statistically significant. FT and SD are both effective bronchodilators and may be of comparable efficiency during acute bronchoconstriction in young children with asthma.

The pulmonary effects of intravenous adenosine in asthmatic subjects

BACKGROUND

We have shown that intravenous adenosine in normal subjects does not cause bronchospasm, but causes dyspnea, most likely by an effect on vagal C fibers in the lungs [Burki et al. J Appl Physiol 2005; 98:180-5]. Since airways inflammation and bronchial hyperreactivity are features of asthma, it is possible that intravenous adenosine may be associated with an increased intensity of dyspnea, and may cause bronchospasm, as noted anecdotally in previous reports.

METHODS

We compared the effects of placebo and 10 mg intravenous adenosine, in 6 normal and 6 asthmatic subjects.

RESULTS

Placebo injection had no significant (p > 0.05) effect on the forced expiratory spirogram, heart rate, minute ventilation (Ve), or respiratory sensation. Similarly, adenosine injection caused no significant changes (p > 0.05) in the forced expiratory spirogram; however, there was a rapid development of dyspnea as signified visually on a modified Borg scale, and a significant (p < 0.05) tachycardia in each subject (Asthmatics +18%, Normals + 34%), and a significant (p < 0.05) increase in Ve (Asthmatics +93%, Normals +130%). The intensity of dyspnea was significantly greater (p < 0.05) in the asthmatic subjects.

CONCLUSION

These data indicate that intravenous adenosine does not cause bronchospasm in asthmatic subjects, and supports the concept that adenosine-induced dyspnea is most likely secondary to stimulation of vagal C fibers in the lungs. The increased intensity of adenosine-induced dyspnea in the asthmatic subjects suggests that airways inflammation may have sensitized the vagal C fibers.

Intravenous adenosine and dyspnea in humans

Intravenous adenosine for the treatment of supraventricular tachycardia is reported to cause bronchospasm and dyspnea and to increase ventilation in humans, but these effects have not been systematically studied. We therefore compared the effects of 10 mg of intravenous adenosine with placebo in 21 normal subjects under normoxic conditions and evaluated the temporal sequence of the effects of adenosine on ventilation, dyspnea, and heart rate. The study was repeated in 11 of these subjects during hyperoxia. In all subjects, adenosine resulted in the development of dyspnea, assessed by handgrip dynamometry, without any significant change ( P > 0.1) in lung resistance as measured by the interrupter technique. There were significant increases ( P < 0.05) in ventilation and heart rate in response to adenosine. The dyspneic response occurred slightly before the ventilatory or heart rate responses in every subject, but the timing of the dyspneic, ventilatory, and heart rate responses was not significantly different when the group data were analyzed (18.9 ± 5.8, 20.3 ± 5.5, and 19.7 ± 4.5 s, respectively). During hyperoxia, adenosine resulted in similar effects, with no significant differences in the magnitude of the ventilatory response; however, compared with the normoxic state, the intensity of the dyspneic response was significantly ( P < 0.05) reduced, whereas the heart rate response increased significantly ( P < 0.05). These data indicate that intravenous adenosine-induced dyspnea is not associated with bronchospasm in normal subjects. The time latency of the response indicates that the dyspnea is probably not a consequence of peripheral chemoreceptor or brain stem respiratory center stimulation, suggesting that it is most likely secondary to stimulation of receptors in the lungs, most likely vagal C fibers.

Effect of two breathing exercises (Buteyko and pranayama) in asthma: a randomised controlled trial

BACKGROUND

Patients with asthma are interested in the use of breathing exercises but their role is uncertain. The effects of the Buteyko breathing technique, a device which mimics pranayama (a yoga breathing technique), and a dummy pranayama device on bronchial responsiveness and symptoms were compared over 6 months in a parallel group study.

METHODS

Ninety patients with asthma taking an inhaled corticosteroid were randomised after a 2 week run in period to Eucapnic Buteyko breathing, use of a Pink City Lung Exerciser (PCLE) to mimic pranayama, or a PCLE placebo device. Subjects practised the techniques at home twice daily for 6 months followed by an optional steroid reduction phase. Primary outcome measures were symptom scores and change in the dose of methacholine provoking a 20% fall in FEV(1) (PD(20)) during the first 6 months.

RESULTS

Sixty nine patients (78%) completed the study. There was no significant difference in PD(20) between the three groups at 3 or 6 months. Symptoms remained relatively stable in the PCLE and placebo groups but were reduced in the Buteyko group. Median change in symptom scores at 6 months was 0 (interquartile range -1 to 1) in the placebo group, -1 (-2 to 0.75) in the PCLE group, and -3 (-4 to 0) in the Buteyko group (p=0.003 for difference between groups). Bronchodilator use was reduced in the Buteyko group by two puffs/day at 6 months; there was no change in the other two groups (p=0.005). No difference was seen between the groups in FEV(1), exacerbations, or ability to reduce inhaled corticosteroids.

CONCLUSION

The Buteyko breathing technique can improve symptoms and reduce bronchodilator use but does not appear to change bronchial responsiveness or lung function in patients with asthma. No benefit was shown for the Pink City Lung Exerciser.

Analysis of the stability of stored adenosine 5'-monophosphate used for bronchoprovocation

Adenosine 5'-monophosphate (AMP) bronchial challenge has been shown to be very useful tool in the diagnosis of asthma. Freshly test solutions are prepared just prior to each test in most of the studies. The objective of this study was to assess the stability of AMP solutions at different temperatures using a reversed-phase high-performance liquid chromatography assay. Sodium salt AMP solutions in concentrations of 0.03 mg/ml and 400 mg/ml were analyzed. One aliquot was kept at room temperature (20-25 degrees C) and the others were refrigerated at 4 degrees C. Room temperature stored samples were analyzed daily. Refrigerated stored samples were analyzed daily for first 15 days and then weekly. The duration of the study was 25 weeks. Samples were injected into the chromatograph column in quadruplicate and quantification was based on the arithmetic mean and standard deviation (+/-SD) of four measurements. Room temperature stored samples at concentrations of 0.03 mg/ml showed a mean percent variation greater than 10% at day 9 and greater than 75% at day 14. Samples at concentrations of 400 mg/ml maintained almost the initial concentration during the first 10 days, but decomposition occurred thereafter. In contrast, there was no significant degradation of refrigerated stored samples throughout the study period. We conclude the exposure to room temperature of AMP solutions results in a substantial loss of the initial concentration, but the shelf life of adequately prepared stock AMP solutions stored at 4 degrees C is at least 25 weeks.

Repeatability of bronchial hyperresponsiveness to adenosine-5'-monophosphate (AMP) by a short dosimeter protocol

BACKGROUND

To study bronchial responsiveness to adenosine 5'-monophosphate (AMP) in population surveys, repeatability of a rapid dosimetric method with quadrupling doses was evaluated.

METHODS

Volunteers with symptoms of airway respiratory allergy or asthma were invited for AMP challenges on two occasions. After each dose the fall in forced expiratory volume in one second (FEV(1)) compared with the post-saline value was determined. The cumulative doses of AMP needed to cause a fall in FEV(1) of 20% (PD(20)), 15% (PD(15)), and 10% (PD(10)) were calculated. Agreement was evaluated by means of kappa values. After excluding systematic differences in PD values on two occasions (t test), repeatability of a single estimation of the chosen PD values was calculated and expressed in doubling doses (DD).

RESULTS

In 28 of 76 subjects a PD(20) was estimated on the two visits, in 29 subjects a PD(15) was estimated, and in 32 a PD(10) was obtained. Kappa values for a positive threshold were 0.89 for a cut off level for a 20% fall in FEV(1), 0.78 for a 15% fall in FEV(1), and 0.76 for a fall in FEV(1) of 10%. The PD values did not differ between the two visits and 95% repeatability of a single estimation was +/-1.7 DD for PD(20), +/-2.2 DD for PD(15), and +/-2.4 DD for PD(10). The quadrupling dose method reduced time by 40% in non-hyperresponsive subjects and no adverse effects were observed.

CONCLUSION

The short dosimeter protocol with quadrupling doses for AMP challenges is a rapid, reproducible tool for estimating bronchial responsiveness in population surveys.

Bronchoconstriction induced by inhaled adenosine 5'-monophosphate in subjects with allergic rhinitis

Adenosine and its related nucleotide, adenosine 5'-monophosphate (AMP) induce bronchoconstriction in asthmatics, probably caused by histamine release from airway mast cells. The objective of this study was to determine the effect of inhaled AMP on lung function in subjects with allergic rhinitis. A total of 52 adults (28 subjects with allergic rhinitis, 14 asthmatics and 10 healthy subjects) were challenged with increasing concentrations of AMP and methacholine. Airflow was assessed after each concentration and the response to each bronchoconstrictor agent was measured by the provocative concentration required to produce a 20% fall (PC20) in forced expired volume in one second (FEV1). All 14 asthmatics, 10 subjects with allergic rhinitis and none of the healthy controls were hyperresponsive to AMP. Subjects with allergic rhinitis had higher prevalence of hyperresponsiveness to AMP than healthy controls (p=0.038). Although the prevalence of hyperresponsiveness for methacholine and for AMP in subjects with allergic rhinitis was similar (39% and 36%, respectively), four subjects had hyperresponsiveness to methacholine but not to AMP, whereas three subjects had hyperresponsiveness to AMP but not to methacholine. To conclude, inhaled adenosine 5'-monophosphate causes airway narrowing in a significantly higher proportion of subjects with allergic rhinitis than healthy volunteers. Furthermore, methacholine and adenosine 5'-monophosphate hyperresponsiveness are not detected in the same individuals with allergic rhinitis, thus suggesting that responsiveness to the two bronchoconstrictor stimuli is not reflecting the same abnormalities of the airways.

Effects of once-daily formoterol and budesonide given alone or in combination on surrogate inflammatory markers in asthmatic adults

OBJECTIVES

We wished to evaluate the effects of once-daily combination therapy on surrogate inflammatory markers.

METHODS

Fifteen patients with atopic persistent asthma were evaluated (mean age, 32.4 years; FEV(1), 75.2% predicted) in a randomized, double-blind, double-dummy, placebo-controlled crossover study with a 1-week placebo washout period, comparing the following once-daily nighttime treatments: (1) formoterol (FM), 12 microg, for 2 weeks and FM, 24 microg, for 2 weeks; or (2) budesonide (BUD), 400 microg, for 2 weeks and BUD, 800 microg, for 2 weeks; or (3) FM, 12 microg, plus BUD, 400 microg, for 2 weeks and FM, 24 microg, plus BUD, 800 microg, for 2 weeks. Adenosine monophosphate (AMP) bronchial challenge, exhaled nitric oxide (NO), and serum eosinophilic cationic protein (ECP) were evaluated at 12 h postdosing after administration of each placebo and after 2 and 4 weeks of each treatment.

RESULTS

The results of AMP challenge (provocative concentration causing a 20% fall in FEV(1)) at 4 weeks showed significant (p<0.05) improvements after patients had received all active treatments compared to placebo (20 mg/mL), with FM plus BUD, 261 mg/mL, being superior (p<0.05) to FM alone, 82 mg/mL, but not to BUD, 201 mg/mL. NO and ECP showed significant (p<0.05) reductions compared to placebo with FM plus BUD or BUD alone but not with FM alone. Combination therapy was associated with optimal patient preference (rank order, FM plus BUD > FM > BUD; p<0.0005), highest domiciliary peak expiratory flow, and lowest rescue inhaler usage. All three treatments produced equivalent improvements in spirometry.

CONCLUSIONS

Patients preferred once-daily combination therapy, but this had no greater effect on inflammatory markers than therapy with BUD alone. FM alone had no anti-inflammatory activity but exhibited bronchoprotection. This emphasizes the importance of first optimizing anti-inflammatory control with inhaled corticosteroids before considering adding a regular long-acting beta(2)-agonist.

In vivo effect of albuterol on methacholine-contracted bronchi in conjunction with salmeterol and formoterol

BACKGROUND

It has been shown in vitro that prior treatment with salmeterol and formoterol antagonizes the relaxant effect of albuterol in carbachol-contracted human bronchi.

OBJECTIVES

The primary aim of this study was to evaluate whether there is a potential in vivo interaction between long- and short-acting beta2-agonists in the presence of increased airway tone induced by methacholine. In addition, a post hoc analysis was made to evaluate the effects of beta2-adrenoceptor polymorphisms.

METHODS

Sixteen asthmatic subjects (mean age [+/-SD], 39 [13] years; FEV1, 81% [17%] of predicted value), all taking inhaled corticosteroids and having methacholine PD20 values of less than 500 micrograms, were randomized in double-blind, double-dummy, cross-over fashion to receive single doses of inhaled placebo, inhaled formoterol 12 micrograms, or inhaled salmeterol 50 micrograms followed 12 hours later by a single dose of inhaled albuterol 400 micrograms (low dose) or 1600 micrograms (high dose). Methacholine challenges were performed on each of 6 separate occasions 1 hour after albuterol.

RESULTS

There was a greater numerical difference in geometric mean PD20 values between low- and high-dose albuterol after placebo dosing (671 micrograms vs 1080 micrograms, a 1.61-fold difference; P <.05) compared with low- and high-dose albuterol after formoterol dosing (660 micrograms vs 799 micrograms, a 1. 21-fold difference; P =.4), or after salmeterol dosing (568 micrograms vs 847 micrograms, a 1.49-fold difference; P =.055). PD20 values with high-dose albuterol in combination with formoterol or salmeterol were numerically lower than those found with high-dose albuterol in combination with placebo, but they were not significantly different. There was a significant difference between PD20 values with low-dose albuterol after dosing with formoterol (PD20 = 660 micrograms, a 1. 6-fold difference; P <.05) or with salmeterol (PD20 = 568 micrograms, a 1.9-fold difference; P <.05) compared with PD20 with high-dose albuterol after placebo dosing (PD20 = 1080 micrograms). Post hoc polymorphism analysis for pooled pretreatment with formoterol and salmeterol (excluding placebo pretreatment) showed significantly (P <.05) lower PD20 values with homozygous glycine-16 compared with heterozygous glycine/arginine-16 and significantly (P <.05) lower PD20 values with homozygous glutamate-27 compared with either heterozygous glutamate/glutamine-27 or homozygous glutamine-27.

CONCLUSION

Compared with placebo, both salmeterol and formoterol caused a significant degree of antagonism of albuterol-induced bronchorelaxation in methacholine-contracted bronchi in vivo. This interaction could be caused by prolonged occupancy of airway beta2-adrenoceptors by long-acting beta2-agonists or by early tachyphylaxis 12 hours after a single-dose exposure. The degree of albuterol protection was also related to beta2-adrenoceptor polymorphism.

A bolus of inhaled budesonide rapidly reverses airway subsensitivity and beta2-adrenoceptor down-regulation after regular inhaled formoterol

BACKGROUND

Subsensitivity of airway beta2-adrenoceptors develops readily in asthmatics receiving regular long-acting beta2-agonists. This subsensitivity may be rapidly reversed by using systemic corticosteroids. The purpose of the present study was to investigate whether the same acute facilitatory effects occur when using a bolus dose of inhaled corticosteroid.

METHODS

Ten subjects with stable mild-to-moderate asthma, with a mean age of 27 years, mean (+/- SD) FEV1 of 2.95 L (0.94 L), 81% (15%) of predicted, all receiving inhaled corticosteroids, reactive to adenosine monophosphate (AMP) with a provocative concentration producing a 20% fall in FEV1 (PC20) < 200 mg/mL, were recruited into a randomized double-blind crossover study. The subjects received two separate 1-week treatment periods with formoterol dry powder, 24 microg bid, with an initial 1-week run-in and a 1-week washout period between the treatments. A single dose of placebo or budesonide turbuhaler, 1,600 microg, was taken in conjunction with the last dose of both treatment periods. AMP challenge was performed 2 h after the first and last dose of formoterol. Blood for lymphocyte beta2-adrenoceptor density (Bmax) was also measured before and after treatment with formoterol.

RESULTS

There was no significant difference in the geometric mean PC20 after the first dose of formoterol comparing the two treatment periods: 362 mg/mL vs 391 mg/mL. The PC20 after the last dose of formoterol was significantly higher (p < 0.05) in conjunction with budesonide than with placebo: 427 mg/mL vs 99 mg/mL, amounting to a 4.3-fold difference (95% confidence interval [CI], 1.1 to 16.6). For comparison within each treatment period, there was significant subsensitivity (p < 0.05) between the first and last dose of formoterol when the latter was given with placebo: 391 mg/mL vs 99 mg/mL, a 3.9-fold fall (95% CI, 1.0 to 15.2), but not when the latter was given with budesonide: 362 mg/mL vs 427 mg/mL, a 1.2-fold rise (95% CI, 0.5 to 2.8). Lymphocyte 02-adrenoceptor density (geometric mean Bmax: fmol/10(6) cells) also showed significant down-regulation (p < 0.05) by formoterol given with placebo: preformoterol 2.53 vs postformoterol 1.91, but not by formoterol given with budesonide: preformoterol 2.43 vs postformoterol 2.67. The Bmax was significantly higher (p < 0.05) with formoterol + budesonide as compared to formoterol + placebo, amounting to a 1.40-fold difference (95% CI, 1.09 to 1.80).

CONCLUSION

We have shown that a bolus dose of inhaled budesonide rapidly reverses subsensitivity to AMP bronchoprotection and associated beta2-adrenoceptor down-regulation in asthmatics taking regular formoterol. Further studies are indicated to assess whether high-dose inhaled corticosteroids should be administered as soon as possible along with beta2-agonists during an acute episode of bronchoconstriction.

Comparison of salmeterol and albuterol-induced bronchoprotection against adenosine monophosphate and histamine in mild asthma

Short-acting beta(2)-agonists provide greater protection to bronchoconstriction induced by adenosine-5'-monophosphate (AMP) than does methacholine. Because AMP produces bronchoconstriction through release of mediators from mast cells, and methacholine directly constricts airway smooth muscle, this suggests that beta(2)-agonists stabilize mast cells in vivo. This in vivo property has not been demonstrated with long-acting beta(2)-agonists. We undertook two double-blind, randomized, crossover, placebo-controlled studies to investigate the effects of salmeterol and albuterol on airway responsiveness (AR) to AMP and histamine in patients with mild asthma. In the first study, 19 patients attended on four occasions to inhale salmeterol 50 micrograms or placebo 2 h before challenge with AMP or histamine. In the second study 16 patients (13 of whom had participated in the first study) were studied in a similar fashion but inhaled albuterol 400 micrograms or placebo 30 min prior to challenge. Salmeterol reduced AR to AMP and histamine by 3.4 +/- 0.3 and 3.9 +/- 0.3 doubling doses, respectively (NS). In contrast, albuterol demonstrated a greater protective effect on AMP than on histamine, reducing AR by 5.1 +/- 0.3 and 3.8 +/- 0.2 doubling doses, respectively (p < 0.005). Thus, in contrast to albuterol, salmeterol did not demonstrate mast-cell stabilizing properties in vivo at a time corresponding to maximal bronchodilatation. These findings might be explained by the unique pharmacologic profile of salmeterol in combination with the differential beta(2)-adrenoceptor pharmacology of bronchial mast cells and bronchial smooth muscle.