The Inhibitory Effect of Nebulized Albuterol on the Early and Late Asthmatic Reactions and Increase in Airway Responsiveness Provoked by Inhaled Allergen in Asthma'?

ORION P. TWENTYMAN, JAMES P. FINNERTY, and STEPHEN T. HOLGATE

Introduction

The llradrenoceptor agonists when administered by inhalation to patients with asthma produce rapid bronchodilatation and relief from symptoms (1). In addition to relaxing airway smooth muscle, these drugs are potent inhibitors of mediator release from activated mast cells (2-4). Both effects probably contribute to the protective effect against the early asthmatic response (EAR) provoked by inhaled antigen in atopic asthma (5). In such patients the mast-cell-dependent EAR is frequently followed by a late asthmatic response (LAR) and is accompanied by a progressive increase in airway responsiveness to a wide variety of stimuli (6, 7). It is reported that inhaled 132-agonists administered before allergen challenge have no effect on the LAR and increases in airways responsiveness beyond their bronchodilator action (8, 9). In a clinical setting these data have been interpreted as showing that 132-agonists are a symptomatic treatment only with little or no effect on the inflammatory processes that underlie the LAR, bronchial hyperresponsiveness, and clinical asthma. However, l3-receptorsare present on a variety of inflammatory cells (10-12), including mast cells (4), and I3ragonists may have the potential to modulate inflammatory processes. Such an effect is not obvious in clinical practice where conventional doses of 132-agonists inhaled from a metered-dose inhaler (MDI) do not alter underlying bronchial responsiveness (13, 14).In observing the effects of inhaled I3ragonists on the LAR, Cockcroft and Murdock (9) used small doses of the drug administered by MDI, whereas the subsequent allergen challenge was performed using a Wright nebulizer. These techniques produce aerosols of different particle size distributions and are likely to result in differing particle deposition within the lung (15, 16). 782

SUMMARY It is widely held that Inhaled (3,-adrenoceptor agonists inhibit the early asthmatic response (EAR) but not the late response (LAR) or attendant increase in bronchial responsiveness. In this stUdy of 10 atopic asthmatic SUbJects, we have investigated the effects of a high dose of nebulized albuterol (2.5 mg) on the allergen-provoked EAR, LAR, and increase in histamine responsiveness. In a randomized blinded fashion, stUdy SUbjects Inhaled the following combinations: albuterol followed 10 min later by allergen, placebo followed by allergen, albuterol followed by saline (albuterol, placebo, and control study periods, respectively). Airway caliber was measured as FEY, and followed at regUlar intervals for 7.5 h postallergen. Bronchial responsiveness to histamine was measured and recorded as the PC,. velue before and at 1.5,3.5, 5.5, and 7.5h after allergen or control challenge. During the placebo stUdy period, allergen challenge caused mean 29.6 ± 6.4 and 24.4 ± 6.4% falls in FEY, at 20 min and 7.5 h, respectively (both p < 0.05), and a progressive decrease in PC" amounting to a geometric mean of 1.9doubling dilutions at 7.5h (p < 0.05).Albuterol followed by allergen resulted in a 13.1 ± 2.2% Increase In FEY, prior to allergen followed by abolition of the EAR and inhibition of the LAR with only a 9.2 ± 3.5% fall In FEY, at 7.5 h, significantly different from that of placebo at 7.5h (p 0.048). Similarly, PC" histamine fell by only 0.64doubling dilutions at 7.5h, not significantly different from baseline velues but different from placebo values (p = 0.03). Albuterol during the control study period (sham allergen challenge) produced an increase In both FEY, and PC" histamine that lasted less than 7.5h. Thus, albuterolln the Inhaled dose administered in this study protected against the allergen-provoked EAR, LAR, and Increase In airways responsiveness by mechanlsm(s) that cannot be accounted for by bronchodilatation and functional antagonism of bronchoconstrlctlon. AM REV RESPIR DIS 1991; 144:782-787

=

Despite these potential confounding factors, we have recently demonstrated that albuterol in low dose (200 ug) administered by MDI attenuates the latephase fall in FEV, after allergenchallenge administered by Inspiron jet nebulizer (17). Because the FEV,/time curve on albuterol was displaced parallel to that on placebo by an amount equal to the initial bronchodilating effect of albuterol, it was unclear whether albuterol inhibited the late-phase bronchoconstrictor response because of the initial effect of bronchodilatation or if an effect on inflammation and associated bronchial hyperresponsiveness was also present. In the current study wehave investigated the effect of a high dose of nebulized albuter01 (2.5 mg) on the allergen-induced EAR, LAR, and increase in bronchial responsiveness in a group of atopic asthmatic subjects. The administration of the 132agonist and the bronchial challenges were undertaken using identical nebulizer equipment. The study was also designed to determine how much of any protec-

tive effect of the drug against late-phase bronchoconstriction and increase in responsiveness could be accounted for by bronchodilatation and functional antagonism of bronchoconstriction. Methods Subjects Ten atopic asthmatic subjects (six men, four women) with a median age of 21 yr (range, 20 to 31) participated in this study. On entry their mean ± SEM fEY, was 3.45 ± 0.231, (86.5 ± 3.9070 predicted), and their geometric mean (range) provocative concentration

(Received in original form July 24, 1990 and in revised form March 8, 1991) , From Medicine I, Southampton General Hospital, University of Southampton, Southampton, United Kingdom. 2 Supported in part by a program grant from the British Medical Research Council. 3 Correspondence and requests for reprints should be addressed to Dr. O. P. Twentyman, Papworth Hospital, Papworth Everard,Cambridge CB3 8RE, UK.

ALBUTEROL AND THE LATE ASTHMATIC RESPONSE

783

TABLE 1 SUBJECT CHARACTERISTICS

Subject No.

Age (yr)

Sex

1 2 3 4 5 6 7 8 9 10 Mean ± SEM

21 23 20 21 31 21 29 21 24 21

F F F M M M M M M F

Baseline FEV, (% pred)

Baseline PC•• Histamine (mglml)

80 88 81 71 106 95 102 71 77 94 86.5 ± 3.9

0.18 0.14 0.10 0.82 2.6 1.2 0.99 0.19 0.17 0.076 0.33*

23.2 ± 1.2

Drug Treatment S S.P S S. B None S SCG S S. B S

Definition of abbreviations: S = albuterol; P = budesonide; B = beclomethasone; SCG = sodium cromoglycate. * Geometric mean.

of inhaled histamine causing a 20% fall in FEV, (PC,.) was 0.33 (0.076 to 2.6) mg/ml (table 1).The subjects had mild asthma; eight required treatment with regular or as required inhaled albuterol, three regularly used inhaled corticosteroids, and one required regular inhaled sodium cromoglycate (SCG) alone. Inhaled albuterol was discontinued 8 h, SCG 12 h, and inhaled steroids at least 36 h before each study period. All subjects had positive immediate skin wheal reactions to Group B2 grass pollens and/or Dermatophagoides pteronyssinus (Bencard; Brentford, Middlesex, UK). The study was approved by the Southampton Hospitals and University Joint Ethical Committee, and written informed consent was obtained from each subject.

Physiologic Measurements and Bronchial Provocation Recordings of FEV, were made using a dry wedge bellows spirometer (Vitalograph Ltd., Buckingham, UK). The subjects wereexperienced at performing forced expiratory maneuvers, and single measurements of FEV, were made unless the record was technically unsatisfactory, for example, because of cough. Nebulized histamine acid phosphate (molecular weight, 307)(Sigma, Poole, Dorset, UK), 0.9% sodium chloride (saline), and allergen wereadministered via a valvebox and mouthpiece by taking five full inspirations over 30 s from FRC to TLC. The solutions were aerosolized using an Inspiron mini-neb jet nebulizer (Bard Ltd., Sunderland, UK) driven by compressed air at a flow rate of 8 L/min to achieve an output of0.35 ml-min? and a mass median particle diameter of 5.3 IJ.m. Histamine bronchoprovocation was performed by administering incremental doubling concentrations of inhaled histamine in saline. After recording baseline FEV" nebulized saline was administered, and FEV, was recorded at 3 min. Then doubling incremental concentrations of histamine were administered at 5-min intervals, with FEV, being recorded at 3 min until> 20% fall in FEV, from the postsaline value was obtained. For each subject the allergen producing the

largest skin wheal was used for the inhalation challenge. Dilutions of the allergen solutions (Group B2grass pollen 6070 wt/vol and Dermatophagoides pteronyssinus 1.2% wt/ vol) wereprepared in saline. Prior to the study a dose-ranging allergen challenge was performed to identify subjects with a LAR and to determine the dose of allergen to be used in the main study. Incremental 2- to lO-fold concentrations of aerosolized allergen in saline were inhaled in five breaths taken over 30 s through the nebulizer from FRC to TLC using a technique modified from that of Chai and coworkers (18). Each allergen concentration was inhaled at lO-min intervals, with FEV, being measured at 5 and 10 min until values had fallen by > 20% of the postsaline FEV,. Further measurements of FEV, were made at regular intervals over 7.5 h to identify whether a LAR occurred. Only subjects who experienced> 14% fall in FEV, from baseline 3.5 to 7.5 h after challenge were entered into the study. The cumulative concentration of allergen producing a > 20% fall in FEV, (PC,. allergen) identified for each subject in the prior dose-ranging experiment was used subsequently for allergen challenge in the study.

at least 12 days. During two study periods, inhaled albuterol or saline placebo were followed by allergen challenge (albuterol and placebo study periods). In a third study period, albuterol was followed by saline (control study period). In each study period, subjects attended in the late afternoon (6:00 P.M.), and a histamine bronchoprovocation test was performed. The following morning (9:00 A.M.) the histamine provocation test was repeated. After this, the baseline FEV, for the allergen or control challenge was established by allowing FEV, to recover spontaneously. Once this had been achieved, nebulized saline was administered, and FEV, was recorded at 3 min. Then, in a double-blind manner, either albuterol 2.5 mg in a total volume of 4 ml saline or saline placebo (4 ml) was administered by nebulizer. The subjects breathed normally through the mouthpiece until nebulization of the solution was complete. FEV, was recorded at 10 min (time 0) (figure I), and then the previously calculated PC,. allergen was administered to each subject via the nebulizer by taking five full inspirations over 30 s from FRC to TLC. Measurements of FEV, were recorded at lO-min intervals for the first hour and subsequently at 30-min intervals until 7.5 h after allergen challenge. Histamine bronchoprovocation tests wereperformed 1.5, 3.5, 5.5, and 7.5 h after allergen, with FEV, being allowed to recover spontaneously between tests. At the end of each study period, bronchoconstriction was reversed with inhaled albuterol and 2 mg of beclomethasone dipropionate administered by MDI. The third study period was included as a control period to assess the time course of the effects of nebulized albuterol on FEV, and the histamine bronchoprovocation test in these subjects. Thus, in a single-blind manner albuterol 2.5 mg was administered by nebulization and followedat 10min by a sham allergen challenge with normal saline. The various measurements were then recorded over 7.5 h as previously detailed.

Data Analysis For all analyses a probability value p < 0.05 wasaccepted as significant. The baselineFEV 1 values, defined as the FEV, prior to allergen or sham allergen challenge after recoveryfrom

Study Protocol Subjects attended the laboratory for three separate randomized study periods separated by

130 120 110 Fig. 1. Mean ± SEM FE\!, (% baseline) versus time. Open squares = placebo; closed squares = albuterol; closed diamonds = control.

1 0 0 -+-..lAt_iIl---------"","""-~

....

>

W LL

90

80 70 6 0 --'---...-.---f---.-------.--...-----, 5.5 3.5 7.5 hr

TWENTYMAN, FINNERTY, AND HOLGATE

784 the 9:00 A.M. histamine bronchoprovocation, were compared by two-way analysis of the variance (ANaYA). Within each study period, the baseline FEY I value was compared with the FEY I values at 20 min (EAR) and 7.5 h (LAR) by analysis of variance and the Newman-Keuls test. Between-study-period differences in FEYI values at 20 min and 7.5 h were determined by two-way ANaYA, and the source of the variance tested for significance was determined by Student's paired t test (19, 20). FEY I values were then normalized byexpressing them as a percentage of the baseline FEY I value obtained prior to allergen challenge. Differences in FEY I percent baseline between treatment periods at20 min and 7.5 h were compared using analysis of variance with Student's paired t test to determine the source of the variance. The FEY I response after challenge or sham allergen (saline) expressed as a percentage change from the prechallenge baseline was plotted against time. The area under the curve for each subject was calculated for the EAR between zero and 90 min (AUCo-9o) and the LAR between 3.5 and 7.5 h (AUC a .s _7 .s ) by trapezoidal integration. Differences between study periods were determined by Friedman's two-way ANaYA, and the sources of variance were tested for significance using Wilcoxon's signed rank test. The PC 20 histamine was determined by linear interpolation from the histamine doseresponse curve plotted as change in FEY I from postsaline baseline against the concentration of histamine plotted on a logarithmic scale. The 6:00 P.M. PC 20 histamine value in each study period was taken as the baseline for that study period. Differences in PC lO histamine within each study period between baseline and the 9:00 A.M. and 7.5 h values were compared by analysis of variance and the Newman-Keuls test using the logarithmically transformed data. Differences between each of the three study periods in PC 20 histamine values at baseline, 9:00A.M.,and 1.5 (n == 7) and 7.5 h were compared by ANaYA using logarithmically transformed data, and the source of the variance was tested for significance by Student's paired t test (19, 20). The baseline PC 20 histamine value obtained at 6:00 P.M. in each study period was used as a reference point, and the results of the other histamine bronchoprovocation tests in each study period were expressed as a change in responsiveness (APC 20) from this baseline in doubling dilutions of histamine [APC 20 = log2 (PC 20 baseline) log, (PC20 time x)]. Using these normalized data differences in the change in PC 20 histamine (APC 20), between-treatment-periods at 7.5 h were compared using ANaYA with Student's paired t test to determine the source of the variance. Results

There were no significant differences between study periods in baseline FEV I or baseline PC 20 histamine. No significant diurnal variation in PC 20 between 6:00 P.M.

and 9:00 A.M. within each study period was observed. Within study period, comparisons showed that after placebo, inhalation of allergen resulted in an EAR achieving a mean ± SEM fall in FEV, at 20 min of 29.6 ± 6.4070 from prechallenge baseline (p < 0.05). FEV, then gradually recovered and was followed by a LAR, with FEV, falling progressively by 24.4 ± 6.4% from baseline at 7.5 h (p < 0.05) (figure 1). In the albuterol study period, administration of inhaled albuterol produced a mean 13.1 ± 2.2% increase in FEV, and provocation with inhaled allergen failed to produce an EAR, with FEV, remaining 13.9 ± 2.2% above prealbuterol baseline at 20 min. FEV I gradually returned toward prealbuterol baseline and continued to fall to reach 9.2 ± 3.5% below prealbuterol baseline at 7.5 h. Inhalation of albuterol in the control study period resulted in an immediate 17.4 ± 6.3% increase in FEV, and a 19.7 ± 7.2% increase 20 min after inhalation of sham allergen. FEV, remained elevated for 1.5h and then gradually returned toward baseline at 7.5 h when FEV, was only 0.033 ± 3.4% above baseline. Between-treatment comparisons showed no significant difference in FEV, values between the albuterol and control study periods at 20 min, but both were significantly greater than achieved at the same time point in the placebo study period (p < 0.001 and p < 0.001, respectively). Similar between-group differences were seen for the LAR measured as the FEV I response at 7.5 h, albuterol producing significant protection when compared with placebo in both the albuterol and control study periods (P == 0.048 and p == 0.017, respectively); there was no significant difference between the albuterol and the control study periods at 7.5 h. Considering the airway response as an

area under the curve, the EAR in the control study period was not significantly different from the albuterol study period. After placebo the AUCo-9o was significantly different from both albuterol and control study periods (p == 0.003). During the LAR, the AUC a.5- 7 •5 after placebo was significantly different from the albuterol and control periods (P == 0.014 and p == 0.003, respectively); the albuterol period was also different from the control period (p == 0.011). In the placebo study period, allergen provocation resulted in a progressive decrease of 1.9 ± 0.37 doubling dilutions in PC 2 0 histamine over 7.5 h (p < 0.05) (figure 2). Inhaled albuterol administered prior to allergen protected the airways against histamine so that at 90 min postallergen challenge PC20 histamine had increased by 3.01 ± 0.51 doubling dilutions when compared with baseline values (n == 7). Histamine responsiveness returned to baseline 3.5 to 5.5 h after allergen, but by 7.5 h the PC 20 histamine was still only 0.64 ± 0.43 doubling dilutions lower than, but not significantly different from, baseline values. When albuterol was followed by a sham allergen challenge in the control study period, the PC2 0 histamine increased by 2.1 ± 0.39 doubling dilutions at 90 min (n == 7) and returned to baseline levels with an almost identical time course to that achieved when albuterol was followed by allergen. At 7.5 h in the control study period, the decrease in PC20 histamine of 0.42 ± 0.25 doubling dilutions from baseline was not significant. Between-treatment comparisons of PC 2 0 histamine measured at 90 min showed significant differences between placebo study period and both the albuterol (p == 0.002) and control (P < 0.(03) study periods, but not between the two active treatments. This pattern persisted at 7.5 h when albuterol in both the

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