To the editor
Asthma is a chronic airway disease with different endotypes. Recently,
endotype-specific treatment modalities have been gradually increasing by
the light of the advances of the asthma pathogenesis. As a component of
the atopic march, children with food allergy (FA) are at increased risk
for asthma.1 Since leukotrienes are implicated in the
pathogenesis of asthma and probably in food allergies, we hypothesized
that asthmatic children with concomitant FA may respond favorably to
anti-leukotriene treatment. To test this hypothesis, we conducted a
randomized, double-blind, placebo-controlled, cross-over study in
asthmatic children aged 6-18 years with and without FA. The protocol was
approved by the research ethics committee. Parents and children provided
written informed consent. The study is registered to Clinical trials
NCT01618929. All participants have physician-diagnosed asthma based on
spirometry or provocholineĀ® tests. Food allergy was diagnosed by the
current guideline.2 Children with severe asthma,
systemic or chronic lung disease, emergency room/hospital admission or
systemic steroid usage within 3 months for asthma exacerbation were
excluded. Of 149 patients who were invited, 113 included but 87
completed the study protocol between 2013 and 2015 (FigureS1). The
baseline characteristics of the whole study population and per-protocol
group were similar. The baseline characteristics of asthmatic children
with and without FA were similar. Recruited children entered a run-in
period of 2 to 6 weeks when all the drugs were discontinued except
inhaled salbutamol as needed. Total IgE levels, eosinophil counts,
spirometry tests (ZAN100 spirometry system, nSpire Health, Longmont,
Colorado, USA), methacholine challenge test, childhood Asthma Control
Tests (cACTs), Asthma Control Tests (ACTs), Fractional Exhaled Nitric
Oxide (FeNO) measurements (portable analyzer (NIOX-MINO; Aerocrine,
Stockholm, Sweden) and exhaled breath condensates (EBC) analysis were
performed at the beginning of the run-in period and repeated 4 more
times according to the protocol (Figure1). Cysteinyl leukotrienes
(CysLT) and Prostaglandin D2 (PGD2) (Cayman Chemical Company, USA) and
lipoxin A4 (Cusabio Biotech Co, China) levels were measured in the EBC
by ELISA. The lipoxin levels did not include in the statistical analysis
since they showed extreme variations. The primary outcome of the study
was improvement in FEV1. A placebo-subtracted montelukast effect of 2%
in FEV1% and a standard deviation of 5% 3, 4 with
80% power analysis and an alpha value of 0.05; the calculated sample
size with a drop-out rate of 15% nearly 60 patients was initially
planned to be included in each arm of the study. Twenty-six patients
showed violations of the study protocol mainly of the timelines for drug
and washout. All analyses were done both in the intention to treat (all
patients) and per-protocol populations.
The baseline PGD2 and CysLT levels, eosinophil counts and total IgE
levels of the asthma alone (AA) and food allergy and asthma (FAA) groups
were significantly different from each other. (TableS1). The comparison
of FEV1% did not show a statistically significant difference for within
group analyses both in AA and FAA in cross-over montelukast and placebo
phases (Table1 and 2). Comparison of montelukast and placebo effects in
AA versus FAA groups showed a significant difference in favour of FAA
group. However, this difference stemmed from the difference between AA
and FAA groups at the beginning of the study and cannot be attributed to
montelukast. PGD2, CysLT and FeNO measurements showed significant
differences between AA and FAA groups. We compared for each phase the
effect of montelukast/placebo for the two asthma groups. Significant
differences were found; however, the presence of differences with
respect to PGD2 and CysLT measurements at the beginning of the study
prevents us to make a conclusion about the effect of montelukast between
different groups. Both ACT scores and methacholine measurements did not
show any difference with respect to either treatment and placebo groups
in FAA and AA groups. We could not show a significant effect of
montelukast compared to placebo both within groups and between the
groupsā comparisons. Initial measurements of PGD2 and CysLTs were
significantly higher in the FAA group compared to AA group suggesting
that the presence of FA in asthmatic children may represent a different
phenotype which has distinct underlying pathophysiological mechanisms.
There may be several reasons why the presence of FA had no effect on the
montelukast in asthmatic children. All patients had mild asthma and
normal FEV1%. Thus, the change in FEV1% conferred by the treatment may
have been too small to detect a difference between montelukast and
placebo. In two separate studies in mild asthmatics, Weiss et
al.5 failed to show the effect of montelukast compared
to placebo with respect to days with worsening asthma. Montuschi et
al.6 showed a marginal effect of montelukast on FeNO
levels when asthmatic children were not exposed to the responsible
allergen. Knorr et al., showed montelukast has only modest effect on
FEV1% but reduced acute exacerbations and improved the
life-quality.7 Spahn et al. showed improvements in
lung function in asthmatic children by forced oscillometry and
plethysmography without any change in FEV1% and FeNO
levels.8 More sensitive techniques may be required to
detect a montelukast effect in children with mild asthma.
An important finding of our study was higher PGD2 and CystLTE4 levels in
FAA compared to AA group. The role of leukotrienes in FA is not clear.
PGD2 has two important receptors on mast cells called D prostanoid (DP)
and CRTH2. Selective CRTH2 agonists was shown to induce asthma
exacerbations and atopic dermatitis in mouse models.9Nakamura et al. showed exacerbation of food antigen induced mast cell
hyperplasia at PGD2 deficiency.10 A recent study
showed a new egg-white protein called lipocalin-type PGD synthase which
reacts with IgE antibodies in children with egg
allergy.11 According to the study investigated the
effect of montelukast during oral immunotherapy, LTRAs may prevent food
induced abdominal symptoms by inhibition of eosinophilic inflammation
and degranulation of mast cells.12 Lexmond et
al.13 showed an elevation in LTC4 synthase mRNA
expression in eosinophilic esophagitis patients. All of these studies
support our findings and suggest a possibly important role for
leukotrienes in the disease process of FA. In a recent study synergistic
effect of PGD2 with CystLT to stimulate the diverse functions of Th2
cells have been shown14. In our study, children with
FAA had higher levels of both PGD2 and CystLT.
Our study has some limitations. First, we could not reach the aimed
sample size because of the high protocol violations. Secondly, the
difference in FEV1% between the groups at baseline made it difficult to
evaluate the results. Most important strength of the study was the study
design.
In conclusion, despite we could not find any difference in montelukast
effect between FAA and AA groups, there is a significant difference
between baseline PGD2 and CystLT levels between FAA and AA groups. This
may be a different endotype of childhood asthma. Additionally, with a
higher patient number and more severe disease phenotype this study could
be repeated to see whether montelukast has any additional effect on
asthmatic children with food allergy compared to only asthmatics.