A standard, single dose of inhaled terbutaline attenuates hyperpnea-induced bronchoconstriction and mast cell activation in athletes

A proposal to account for the stimulus, the mechanism, and the mediators released in exercise-induced bronchoconstriction

Exercise induced bronchoconstriction (EIB) describes the transient narrowing of the airways that follows vigorous exercise. It commonly occurs in children and adults who have asthma and in elite athletes. The primary stimulus is proposed to be loss of water, by evaporation, from the airway surface due to conditioning inspired air. The mechanism, whereby this evaporative loss of water provokes contraction of the bronchial smooth muscle, is thought to be an increase in osmolarity of the airway surface liquid. The increase in osmolarity causes mast cells to release histamines, prostaglandins, and leukotrienes. It is these mediators that contract smooth muscle causing the airways to narrow.

Muscle hypertrophic effect of inhaled beta2 -agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men

Abstract

Rodent studies highlight enhancement of glucose tolerance and insulin sensitivity as potential clinically relevant effects of chronic beta₂‐agonist treatment. However, the doses administered to rodents are not comparable with the therapeutic doses used for humans. Thus, we investigated the physiological effects of prolonged beta₂‐agonist treatment at inhaled doses resembling those used in respiratory diseases on insulin‐stimulated whole‐body glucose disposal and putative mechanisms in skeletal muscle and adipose tissue of healthy men. Utilizing a randomized placebo‐controlled parallel‐group design, we assigned 21 healthy men to 4 weeks daily inhalation of terbutaline (TER; 4 mg × day⁻¹, n = 13) or placebo (PLA, n = 8). Before and after treatments, we assessed subjects’ whole‐body insulin‐stimulated glucose disposal and body composition, and collected vastus lateralis muscle and abdominal adipose tissue biopsies. Glucose infusion rate increased by 27% (95% CI: 80 to 238 mg × min⁻¹, P = 0.001) in TER, whereas no significant changes occurred in PLA (95% CI: −37 to 195 mg × min⁻¹, P = 0.154). GLUT4 content in muscle or adipose tissue did not change, nor did hexokinase II content or markers of mitochondrial volume in muscle. Change in lean mass was associated with change in glucose infusion rate in TER (r = 0.59, P = 0.03). Beta₂‐agonist treatment in close‐to‐therapeutic doses may augment whole‐body insulin‐stimulated glucose disposal in healthy young men and part of the change is likely to be explained by muscle hypertrophy. These findings highlight the therapeutic potential of beta₂‐agonists for improving insulin sensitivity.

Key points

While studies in rodents have highlighted beta₂‐agonists as a means to augment insulin sensitivity, these studies utilized beta₂‐agonists at doses inapplicable to humans.

Herein we show that a 4‐week treatment period with daily therapeutic inhalation of beta₂‐agonist increases insulin‐stimulated whole‐body glucose disposal in young healthy lean men.

This effect was associated with an increase of lean mass but not with changes in GLUT4 and hexokinase II or basal glycogen content in skeletal muscle nor GLUT4 content in abdominal adipose tissue.

These findings suggest that the enhanced insulin‐stimulated whole‐body glucose disposal induced by a period of beta₂‐agonist treatment in humans, at least in part, is attributed to muscle hypertrophy.

Our observations extend findings in rodents and highlight the therapeutic potential of beta₂‐agonists to enhance the capacity for glucose disposal and whole‐body insulin sensitivity, providing important knowledge with potential application in insulin resistance.

Bronchial Provocation Testing for the Identification of Exercise-Induced Bronchoconstriction

Exercise-induced bronchoconstriction (EIB) occurs in patients with asthma, children, and otherwise healthy athletes. Poor diagnostic accuracy of respiratory symptoms during exercise requires objective assessment of EIB. The standardized tests currently available are based on the assumption that the provoking stimulus to EIB is dehydration of the airway surface fluid due to conditioning large volumes of inhaled air. "Indirect" bronchial provocation tests that use stimuli to cause endogenous release of bronchoconstricting mediators from airway inflammatory cells include dry air hyperpnea (eg, exercise and eucapnic voluntary hyperpnea) and osmotic aerosols (eg, inhaled mannitol). The airway response to different indirect tests is generally similar in patients with asthma and healthy athletes with EIB. Furthermore, the airway sensitivity to these tests is modified by the same pharmacotherapy used to treat asthma. In contrast, pharmacological agents such as methacholine, given by inhalation, act directly on smooth muscle to cause contraction. These "direct" tests have been used traditionally to identify airway hyperresponsiveness in clinical asthma but are less useful to diagnose EIB. The mechanistic differences between indirect and direct tests have helped to elucidate the events leading to airway narrowing in patients with asthma and elite athletes, while improving the clinical utility of these tests to diagnose and manage EIB.

Sex Differences in Exercise-Induced Bronchoconstriction in Athletes: A Systematic Review and Meta-Analysis

Exercise-induced bronchoconstriction (EIB) is a common complication of athletes and individuals who exercise regularly. It is estimated that about 90% of patients with underlying asthma (a sexually dimorphic disease) experience EIB; however, sex differences in EIB have not been studied extensively. With the goal of better understanding the prevalence of EIB in males and females, and because atopy has been reported to occur at higher rates in athletes, in this study, we investigated sex differences in EIB and atopy in athletes. A systematic literature review identified 60 studies evaluating EIB and/or atopy in post-pubertal adult athletes (n = 7501). Collectively, these studies reported: (1) a 23% prevalence of EIB in athletes; (2) a higher prevalence of atopy in male vs. female athletes; (3) a higher prevalence of atopy in athletes with EIB; (4) a significantly higher rate of atopic EIB in male vs. female athletes. Our analysis indicates that the physiological changes that occur during exercise may differentially affect male and female athletes, and suggest an interaction between male sex, exercise, and atopic status in the course of EIB. Understanding these sex differences is important to provide personalized management plans to athletes with underlying asthma and/or atopy.

Mechanisms and Biomarkers of Exercise-Induced Bronchoconstriction

Exercise is a common trigger of bronchoconstriction. In recent years, there has been increased understanding of the pathophysiology of exercise-induced bronchoconstriction. Although evaporative water loss and thermal changes have been recognized stimuli for exercise-induced bronchoconstriction, accumulating evidence points toward a pivotal role for the airway epithelium in orchestrating the inflammatory response linked to exercise-induced bronchoconstriction. Overproduction of inflammatory mediators, underproduction of protective lipid mediators, and infiltration of the airways with eosinophils and mast cells are all established contributors to exercise-induced bronchoconstriction. Sensory nerve activation and release of neuropeptides maybe important in exercise-induced bronchoconstriction, but further research is warranted.

Mast cell-neural interactions contribute to pain and itch

Mast cells are best recognized for their role in allergy and anaphylaxis, but increasing evidence supports their role in neurogenic inflammation leading to pain and itch. Mast cells act as a "power house" by releasing algogenic and pruritogenic mediators, which initiate a reciprocal communication with specific nociceptors on sensory nerve fibers. Consequently, nerve fibers release inflammatory and vasoactive neuropeptides, which in turn activate mast cells in a feedback mechanism, thus promoting a vicious cycle of mast cell and nociceptor activation leading to neurogenic inflammation and pain/pruritus. Mechanisms underlying mast cell differentiation, activation, and intercellular interactions with inflammatory, vascular, and neural systems are deeply influenced by their microenvironment, imparting enormous heterogeneity and complexity in understanding their contribution to pain and pruritus. Neurogenic inflammation is central to both pain and pruritus, but specific mediators released by mast cells to promote this process may vary depending upon their location, stimuli, underlying pathology, gender, and species. Therefore, in this review, we present the contribution of mast cells in pathological conditions, including distressing pruritus exacerbated by psychologic stress and experienced by the majority of patients with psoriasis and atopic dermatitis and in different pain syndromes due to mastocytosis, sickle cell disease, and cancer.

Repurposing drugs as inhaled therapies in asthma

For the first 40 years of the 20th century treatment for asthma occurred in response to an asthma attack. The treatments were given by injection or orally and included the adrenergic agonists adrenalin/epinephrine and ephedrine and a phosphodiesterase inhibitor theophylline. Epinephrine became available as an aerosol in 1930. After 1945, isoprenaline, a non-selective beta agonist, became available for oral use but it was most widely used by inhalation. Isoprenaline was short-acting with unwanted cardiac effects. More selective beta agonists, with a longer duration of action and fewer side-effects became available, including orciprenaline in 1967, salbutamol in 1969 and terbutaline in 1970. The inhaled steroid beclomethasone was available by 1972 and budesonide by 1982. Spirometry alone and in response to exercise was used to assess efficacy and duration of action of these drugs for the acute benefits of beta₂ agonists and the chronic benefits of corticosteroids. Early studies comparing oral and aerosol beta₂ agonists found equivalence in bronchodilator effect but the aerosol treatment was superior in preventing exercise-induced bronchoconstriction. Inhaled drugs are now widely used including the long-acting beta₂ agonists, salmeterol and formoterol, and the corticosteroids, fluticasone, ciclesonide, mometasone and triamcinolone, that act locally and have low systemic bio-availability. Repurposing drugs as inhaled therapies permitted direct delivery of low doses of drug to the site of action reducing the incidence of unwanted side-effects and permitting the prophylactic treatment of asthma.

The Effect of 400 µg Inhaled Salbutamol on 3 km Time Trial Performance in a Low Humidity Environment

The Objectives of the study were to investigate whether 400 µg inhaled salbutamol influences 3 km running time-trial performance and lung function in eucapnic voluntary hyperpnoea positive (EVH+ve) and negative (EVH-ve) individuals. Fourteen male participants (22.4 ± 1.6yrs; 76.4 ± 8.7kg; 1.80 ± 0.07 m); (7 EVH+ve; 7 EVH-ve) were recruited following written informed consent. All participants undertook an EVH challenge to identify either EVH+ve (↓FEV₁>10%) or EVH-ve (↓FEV₁<10%). Participants performed three separate 3 km running time-trials in a low-humidity (20-25%) environment on a non-motorized treadmill, 15 minutes following inhalation of salbutamol (400 µg), placebo (non-active inhalant) or control (no inhalant), in a randomized, single-blind, repeated measures design. Forced vital capacity maneuvers were performed at baseline, 10 minutes post inhalation and post time-trial. Time to complete 3 km and lung function data were analyzed using mixed model repeated measures ANOVA. Significance was assumed at p < 0.05. All EVH+ve participants had FEV₁ falls from baseline between 10-25% post-challenge. There was no difference in performance time between trial conditions in EVH+ve (1012.7 ± 129.6s; 1002.4 ± 123.1s; 1015.9 ± 113.0s) (p = 0.774) and EVH-ve (962.1 ± 99.2s; 962.0 ± 76.2s; 950.8 ± 84.9s) (p = 0.401) groups for salbutamol, placebo and control trials, respectively. Exercising heart rate was significantly higher (p = 0.05) in the salbutamol trial (183 ± 8 beatsˑmin^-1) compared to control (180 ± 9 beatsˑmin^-1) with a trend towards significance (p=0.06) in the placebo trial (179 ± 9 beatsˑmin^-1) for the pooled groups, no differences were seen between trials in groups individually. There was an increase in FEV₁ in both EVH+ve (4.01 ± 0.8L; 4.26 ± 0.7L; 4.25 ± 0.5L) and EVH-ve (4.81 ± 0.4L; 5.1 ± 0.4L; 5.1 ± 0.5L) groups which was significant post-inhalation (p = 0.01; p = 0.02), but not post-time-trial (p = 0.27; p = 0.06), respectively, following salbutamol. EVH+ve participants did not demonstrate significant falls (>10% from baseline) in FEV₁ following any time-trial. Administration of 400µg inhaled salbutamol does not improve 3 km time-trial performance in either mild EVH+ve or EVH-ve individuals despite significantly increased HR and FEV₁.

Comparable reductions in hyperpnoea-induced bronchoconstriction and markers of airway inflammation after supplementation with 6·2 and 3·1 g/d of long-chain n-3 PUFA in adults with asthma

Although high dose n-3 PUFA supplementation reduces exercise- and hyperpnoea-induced bronchoconstriction (EIB/HIB), there are concurrent issues with cost, compliance and gastrointestinal discomfort. It is thus pertinent to establish the efficacy of lower n-3 PUFA doses. Eight male adults with asthma and HIB and eight controls without asthma were randomly supplemented with two n-3 PUFA doses (6·2 g/d (3·7 g EPA and 2·5 g DHA) and 3·1 g/d (1·8 g EPA and 1·3 g DHA)) and a placebo, each for 21 d followed by 14 d washout. A eucapnic voluntary hyperpnoea (EVH) challenge was performed before and after treatments. Outcome measures remained unchanged in the control group. In the HIB group, the peak fall in forced expiratory volume in 1 s (FEV1) after EVH at day 0 (-1005 (sd 520) ml, -30 (sd 18) %) was unchanged after placebo. The peak fall in FEV1 was similarly reduced from day 0 to day 21 of 6·2 g/d n-3 PUFA (-1000 (sd 460) ml, -29 (sd 17) % v. -690 (sd 460) ml, -20 (sd 15) %) and 3·1 g/d n-3 PUFA (-970 (sd 480) ml, -28 (sd 18) % v. -700 (sd 420) ml, -21 (sd 15) %) (P<0·001). Baseline fraction of exhaled nitric oxide was reduced by 24 % (P=0·020) and 31 % (P=0·018) after 6·2 and 3·1 g/d n-3 PUFA, respectively. Peak increases in 9α, 11β PGF2 after EVH were reduced by 65 % (P=0·009) and 56 % (P=0·041) after 6·2 and 3·1 g/d n-3 PUFA, respectively. In conclusion, 3·1 g/d n-3 PUFA supplementation attenuated HIB and markers of airway inflammation to a similar extent as a higher dose. Lower doses of n-3 PUFA thus represent a potentially beneficial adjunct treatment for adults with asthma and EIB.

Compact Eucapnic Voluntary Hyperpnoea Apparatus for Exercise-Induced Respiratory Disease Detection

Eucapnic voluntary hyperpnoea (EVH) challenge provides objective criteria for exercise-induced asthma (EIA) or exercise-induced bronchoconstriction (EIB), and it was recommended to justify the use of inhaled β₂-agonists by athletes for the Olympics. This paper presents the development of a compact and easy-to-use EVH apparatus for assessing EIB in human subjects. The compact apparatus has been validated on human subjects and the results have been compared to the conventional EVH system. Twenty-two swimmers, including eleven healthy subjects and eleven subjects who had been physician-diagnosed with asthma, were recruited from sport and recreation centers throughout Auckland, New Zealand. Each subject performed two EVH challenge tests using the proposed breathing apparatus and the conventional Phillips EVH apparatus on separate days, respectively. Forced expiratory volume in one second (FEV₁) was measured before and after the challenges. A reduction in FEV₁ of 10% or more was considered positive. Of the eleven subjects who were previously diagnosed with asthma, EIB was present in all subjects (100%) in the compact EVH group, while it was presented in ten subjects (90.91%) in the conventional EVH challenge group. Of the eleven healthy subjects, EIB was present in one subject (4.55%) in the compact EVH group, while it was not present in the conventional EVH group. Experimental results showed that the compact EVH system has potential to become an alternative tool for EIB detection.