R E S E A R C H Open Access
Sulforaphane improves the bronchoprotective
response in asthmatics through Nrf2-mediated
Robert H. Brown
, Curt Reynolds
, Allison Brooker
, Paul Talalay
and Jed W. Fahey
Background: It is widely recognized that deep inspiration (DI), either before methacholine (MCh) challenge
(Bronchoprotection, BP) or after MCh challenge (Bronchodilation, BD) protects against this challenge in healthy
individuals, but not in asthmatics. Sulforaphane, a dietary antioxidant and antiinflammatory phytochemical derived from
broccoli, may affect the pulmonary bronchoconstrictor responses to MCh and the responses to DI in asthmatic patients.
Methods: Forty-five moderate asthmatics were administered sulforaphane (100 μmol daily for 14 days), BP, BD, lung
volumes by body-plethsmography, and airway morphology by computed tomography (CT) were measured pre- and
post sulforaphane consumption.
Results: Sulforaphane ameliorated the bronchoconstrictor effects of MCh on FEV
significantly (on average by 21 %;
p = 0.01) in 60 % of these asthmatics. Interestingly, in 20 % of the asthmatics, sulforaphane aggravated the
bronchoconstrictor effects of MCh and in a similar number was without effect, documenting the great heterogeneity
of the responsiveness of these individuals to sulforaphane. Moreover, in individuals in whom the FEV
response to MCh
challenge decreased after sulforaphane administration, i.e., sulforaphane was protective, the activities of Nrf2-regulated
antioxidant and anti-inflammatory genes decreased. In contrast, individuals in whom sulforaphane treatment enhanced
response to MCh, had increased expression of the activities of these genes. High resolution CT scans disclosed
that in asthmatics sulforaphane treatment resulted in a significant reduction in specific airway resistance and also
increased small airway luminal area and airway trapping modestly but significantly.
Conclusion: These findings suggest the potential value of blocking the bronchoconstrictor hyperresponsiveness in
some types of asthmatics by phytochemicals such as sulforaphane.
Keywords: Asthma, Bronchodilation, Oxidative stress
Although corticosteroids are currently the mainstay of
asthma treatment, some asthmatics do not respond to
corticosteroids even at high doses  at which adverse ef-
fects impose therapeutic limitations. Moreover, corticoste-
roids are almost universally effective in controlling many
types of asthma, and this obscures the heterogeneity of
the disease . Although inflammation may be an
important inciting factor, other molecular mechanisms of
airway disease may play a crucial role in asthma.
Antioxidant deficiencies have been associated with
poor asthma control and accelerated decline of lung
function [3–5]. Studies in mice suggest that disruption
of the nuclear factor erythroid-related factor 2 (Nrf2)
signaling pathway is a possible cause of chronic inflam-
mation, such as that associated with asthma . Nrf2 is
responsible for maintaining and restoring cellular
homeostasis through antioxidant, anti-inflammatory, and
other mechanisms. Thus Nrf2 regulates critical enzymes
concerned with the biosynthesis of glutathione (GSH),
the dominant, small molecule, intracellular antioxidant.
A protective effect of GSH on inflammatory pathologies
* Correspondence: email@example.com
Supported by: Flight Attendant Medical Research Institute (FAMRI)
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins
University School of Medicine, Baltimore, MD, USA
Division of Pulmonary Medicine and Critical Care, Department of Medicine,
Johns Hopkins University School of Medicine, Baltimore, MD, USA
Full list of author information is available at the end of the article
© 2016 Brown et al.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this
article, unless otherwise stated.
Brown et al. Respiratory Research (2015) 16:106
of the lung including asthma, has been demonstrated in
mice . Another potentially critical role of the Nrf2 path-
way in asthma is highlighted by the dramatic increase in
eosinophilic airway inflammation, airway hyperreactivity,
and T helper cell 2 (Th2) cytokine production in Nrf2
knockout mice .
Sulforaphane, a phytochemical derived from cruciferous
vegetables, is a potent inducer of a variety of cytoprotective
(antioxidant and anti-inflammatory) enzymes (reviewed by
[8, 9]). It also inhibits the production of nitric oxide, coun-
teracts mitochondrial dysfunction and corrects low oxida-
tive phosphorylation, reduces lipid peroxidation, and
upregulates the heat shock response. In many tissues, sulfo-
raphane transcriptionally upregulates the genes encoding
cytoprotective enzymes primarily through the Keap1-Nrf2-
ARE system [9, 10]. Sulforaphane also potently inhibits in-
flammation by inhibiting the nuclear factor kappa-light-
chain-enhancer of activated B cells (NfκB) cascade , the
macrophage migration inhibitory factor (MIF), the p38
mitogen-activated protein kinase (MAPK) activation cas-
cade, and by modulating β-catenin signaling [12–14].
Unlike direct antioxidants such as vitamin C, sulforaph-
ane is an indirect antioxidant and upregulates multiple
antioxidant pathways without being consumed in the anti-
oxidation process . Sulforaphane boosts the antioxidant
capacity of cells by at least two major indirect mechanisms:
by induction of phase 2 cytoprotective enzymes and by
dramatically increasing cellular GSH levels. Antioxidant
deficiencies have been strongly associated with poor
asthma control and accelerated lung function decline, and
represent a reasonable therapeutic target [16–18].
Nrf2-mediated signaling pathways limit airway eosino-
philia, mucus hypersecretion, and airway hyperresponsive-
ness to allergen challenge in a murine model of asthma
. Genetic disruption of the Nrf2 gene (knock-out
models) leads to severe allergen-driven airway inflamma-
tion and hyper-responsiveness in mice . An et al. 
recently showed that airway smooth muscle cells isolated
mice exhibited significantly higher contract-
ile force compared to cells isolated from Nrf2
Thus, there is strong evidence for the role of oxidative
stress, mediated through dysfunction of the Nrf2 pathway,
as a mechanism of airway hyper-responsiveness character-
istic of asthma.
Sulforaphane can be safely and consistently administered
to humans by feeding a broccoli sprout extract in which its
precursor glucosinolate (glucoraphanin) has been enzymati-
cally hydrolyzed . Sulforaphane has very low toxicity. Its
administration is well tolerated and it is extensively con-
sumed as a component of cruciferous vegetables. It may be
considered a food, a dietary supplement, or a drug, depend-
ing on dosage and its intended use [9, 20, 21].
It has been known for more than 20 years that deep
inspiration (DI) protects against MCh induced bronchial
constriction. This protective response is characteristic-
ally absent in even mild asthmatic patients [22, 23], and
indeed, DI can even exacerbate the bronchoconstrictor
effects of MCh in asthmatics . The beneficial effects
of DIs occurring before or after MCh challenge have
been designated bronchoprotection (BP) and broncho-
dilation (BD), respectively [22, 25]. Elucidation of the
pathways leading to the loss of the BP and BD responses
in asthma may give further insight into the disease
process and reveal new treatments.
The current study was designed with the primary ob-
jective to test the hypothesis that sulforaphane could
augment the deep inspiration (DI)-induced bronchopro-
tection (BP) and bronchodilation (BD) responses in indi-
viduals with airways hyperresponsiveness. Secondary
objectives included testing the hypotheses that sulfo-
raphane would also affect pulmonary function and lung
morphology as shown by high resolution CT scans.
The protocol was approved by the Johns Hopkins
IRB and written informed consent was obtained
(NA_00011275) and registered at ClinicalTrials.gov
(NCT00994604). A total of 51 individuals with airway
hyperresponsiveness were screened who reported
upper or lower respiratory symptoms (or both) in the
absence of upper respiratory infections in the previous
12 months. Five subjects withdrew, and one subject
failed the screen. Subjects were also required to have
≥70 % of predicted values, and a positive con-
ventional multi-dose methacholine (MCh) inhalation
provocative concentration causing a
20 % drop in FEV
)of≤25 mg/ml, as well as a BP ef-
fect of DI of less than 40 %. Short-acting or long-
acting bronchodilators were withheld before MCh
challenge for 12 or 48 hours, respectively. The demo-
graphic and baseline pulmonary functions of smokers
(n = 15) and non-smokers (n = 30) were similar (Table 1).
Thirty-one subjects were taking albuterol, 13 were tak-
ing fluticasone/salmeterol, 8 were taking fluticasone
alone, 3 were taking montelukast, 1 was taking beclo-
methasone, 1 was taking budesonide/formoterol, 3
were taking fluticasone nasal spray, 4 were taking lora-
tadine, 1 was taking fexofenadine, 1 was taking cetiri-
zine, and 1 was taking benedryl. All participants were
at least 45 days past the end of their most recent URI
for all of their visits, and were asked to withhold inhaled
bronchodilators prior to each study visit: 12 hours for
short-acting and 48 hours for long-acting beta agonists.
Full analysis was possible in 44 individuals. Exclusion cri-
teria included persistent respiratory symptoms suggesting
Brown et al. Respiratory Research (2015) 16:106 Page 2 of 12
Pulmonary function measurements
All subjects underwent baseline spirometry, body-
plethysmography, diffusing capacity of the lung for carbon
monoxide, and exhaled nitric oxide (eNO) measurements.
For spirometry, we used Hankinson's (NHANES III) pre-
dicted values . We further made the widely accepted
assumption that the reproducibility of FEV
0.1 L [27, 28], so that x-axis changes in Fig. 2a and b be-
tween −0.1 and +0.1 L were considered as no effect. In
addition, blood was obtained before and immediately after
sulforaphane administration to monitor standard blood
chemistries for safety (n = 45) and to measures mRNA ex-
pression of Nrf2 target genes in peripheral blood mono-
nuclear cells (n = 35).
Evaluation of beneficial effects of deep inspiration (DI)
DI-induced bronchodilation was performed by using
multiple modified single dose MCh challenges on separ-
ate days [22, 25, 29]. Briefly, after baseline spirometry, at
every single dose challenge, study participants were
instructed to abstain from DI for 20 min. At the end of
this period, a single dose MCh challenge (starting at
0.025 mg/ml) was delivered with five tidal inspirations
from a deVilbiss 646 nebulizer attached to a model 2A
Rosenthal-French dosimeter (Laboratory for Applied Im-
munology, Fairfax, VA). Three minutes later, a single full
spirometric maneuver was performed and the degree of
airways obstruction was calculated by comparing base-
line to post MCh FEV
. If the MCh-induced reduction
was less than 20 %, the participant was asked to
return on a separate day for another single dose MCh
challenge, using the next highest single dose of MCh
(e.g. 0.075 mg/ml). This process was continued with
additional single dose challenges (0.25, 0.75, 2.5,
7.5 mg/ml) on separate days, until the single dose in-
ducing ≥20 % reduction in FEV
was achieved. For the
challenge at this level, where 20 % or greater reduction
was obtained, the participant was instructed
to continue the procedure by taking 4 DI immediately
after the single post-MCh spirometry. Another spiro-
metric maneuver was performed immediately after the
4 DI to calculate the degree to which the participant
was able to reverse the MCh-induced airway obstruc-
tion (Figure below).
Measuring the difference between the post-MCh FEV
and the FEV
obtained after the 4 DI, we calculated a
measure of bronchodilation induced by the DI, which
we termed the bronchodilation (BD) index. This meas-
ure is calculated as follows:
BD index ¼ð1ðð1ððFEV1af ter MCh and af ter DIÞ
ðFEV1baselineÞÞÞ ð1ððFEV1af ter MChÞ
Essentially, the BD index is derived from two compo-
nents, the reduction in FEV
from baseline after MCh
and after DI and the reduction in FEV
after MCh, but before DI.
On a separate day, the same single MCh dose used to
achieve a 20 % or greater reduction in FEV
Table 1 Baseline demographics and pulmonary functions (mean ± SD) of 45 asthmatic patients
Non-smoker Smoker All
Number of subjects (n) 30 15 45
Male/female 10/20 9/6 19/26
Age (mean ± SD) 38 ± 14 40 ± 13 38 ± 13
Smoking (pack-years) 0 11 ± 10 -
Race (black/white/asian) 20/9/1 10/5/0 30/14/1
(provocative concentration causing a 20 % drop in FEV
, in mg/ml) 2.4 ± 4.2 2.6 ± 2.1 2.4 ± 3.6
(forced expiratory volume in 1-second, in L) 2.7 ± 0.7 2.8 ± 0.8 2.7 ± 0.7
% predicted (forced expiratory volume in 1-second) 87 ± 10 % 91 ± 13 % 88 ± 11 %
FVC % predicted (forced vital capacity) 90 ± 12 % 97 ± 15 % 92 ± 13 %
/FVC 0.80 ± 0.08 0.78 ± 0.01 0.79 ± 0.08
TLC (total lung capacity, in L) 5.0 ± 1.4 5.1 ± 1.2 5.0 ± 1.4
SVC (slow vital capacity, in L) 3.3 ± 1 3.5 ± 0.9 3.4 ± 1.0
FRC (functional residual capacity, in L) 3.0 ± 0.9 3.3 ± 1.5 3.1 ± 1.1
RV (residual volume, in L) 1.7 ± 0.7 1.7 ± 0.8 1.7 ± 0.7
RV/TLC 0.34 ± 0.09 0.33 ± 0.08 0.34 ± 0.09
Diffusing capacity of carbon monoxide (mL/min/mm Hg) 22.5 ± 5.9 22.9 ± 5.4 22.7 ± 5.6
Specific airway resistance, (in kiloPascals · s) 6.1 ± 3.4 6.0 ± 3.4 6.04 ± 3.3
Exhaled nitric oxide (ppb) 10.4 ± 11 6.15 9.1 ± 10
Brown et al. Respiratory Research (2015) 16:106 Page 3 of 12
administered after 20 min of quiet breathing, followed by 5
DI to prevent MCh-induced obstruction (Figure below).
Assessing the difference between the MCh-induced re-
duction in FEV
on the day no DI were taken to the day
on which 5 DI were taken prior to the challenge, we ob-
tained a measure of bronchoprotection induced by the
series of DI, which we termed the bronchoprotection
(BP) index which has been previously described [22, 29].
This measure is calculated as follows:
BP index ¼ð1ðð1ððFEV1af ter DI s and af ter MChBÞ
ðFEV1baselineBÞÞÞ ð1ððFEV1af t er MChAÞ
The BP index is derived from two components, the
MCh-induced reduction in FEV
from baseline on the day
that 5 DI preceded the single-dose MCh challenge and the
MCh-induced reduction in FEV
from baseline on the day
no DI were taken before the single-dose MCh challenge.
Acquisition and analysis of CT scans
All scans were performed with a single spiral CT scanner
(Siemens, Definition 64) with settings of 120 Kilovolt peak.
mAs (milliampere · second) was based on body size (small
= 80 mAs, medium = 100 mAs, large = 145 mAs), with a ro-
tation time of 0.5 s, pitch of 1.0 mm, thickness of 0.75 mm,
and interval of 0.5 mm. Images were reconstructed using a
B35 and B31 algorithm. All subjects were coached and
practiced the breathing maneuvers before scanning. For the
total lung capacity scans, while in the scanner, all subjects
were instructed to take a deep breath and blow it out. This
maneuver was repeated three times. On the third deep in-
spiration, the subjects were instructed to hold their breath.
They were then coached to continue to keep holding their
breath for the <10 s duration of the scan. For the functional
residual capacity (FRC) scans, all subjects were similarly
instructed to take a breath in and blow it out. This maneu-
ver was repeated three times. On the third time, the subject
was instructed to expel their breath and then hold their
breath for the duration of the scan (<10 s). Lung volumes
and airway dimensions were calculated using PW software
(VIDA Diagnostics, Inc. Coralville, IA) based on the lung
CT scans. The PW software calculates the total lung volume,
the lung air volume, the lung tissue volume, the lung density
in Hounsfield Units (HU), air trapping (% voxels < −856
HU), the luminal diameter, the wall thickness and the wall
fraction (wall area/total airway area). In addition, the airways
were arbitrarily divided into three groups (small, medium,
and large) of a similar number of airways per group.
Preparation and administration of sulforaphane-rich
broccoli sprout extract
The sulforaphane-rich broccoli sprout extract was prepared
at the Lewis B. and Dorothy Cullman Chemoprotection
Brown et al. Respiratory Research (2015) 16:106 Page 4 of 12
Center at Johns Hopkins University, essentially as previ-
ously described [30, 31]. We obtained IND approval from
the FDA for its use in this study (IND #79274). In brief,
specially selected BroccoSprouts™seeds were surface-
disinfected and grown for 3 days in a commercial sprouting
facility under controlled light and moisture. A boiling water
extract was prepared, filtered, cooled, and treated with the
enzyme myrosinase (from daikon sprouts) in order to con-
vert precursor glucosinolates to isothiocyanates, and then
lyophilized at a food processing facility (Oregon Freeze Dry,
Albany, OR). The lyophilized powder (227 μmol sulforaph-
ane/g powder) was packaged in sterile plastic tubes that
were unitized for daily doses by ALFA Specialty Pharmacy
(Columbia, MD); each tube contained 100 μmol sulforaph-
ane (440 mg of BSE). The powders (bulk and individual
doses) were maintained at −20 °C, repeatedly checked for
microbial contaminants and sulforaphane titer before con-
veyance to the study site to be dispensed to patients.
Study subjects were given both verbal and written in-
structions to avoid eating any food products that contain
the following vegetables (either cooked or raw) until com-
pletion of the study: Cruciferous vegetables (such as broc-
coli, broccolini, broccoli raab, rapini, kale, cabbage, brussels
sprouts, cauliflower, arugula, turnips, radish, turnip, turnip
greens, kohlrabi, rutabaga, mustard greens, collard greens,
chinese cabbage, pak choi, bok choi, napa, watercress, broc-
coli sprouts, daikon, sauerkraut, coleslaw), vegetables in the
onion family (onions, leeks, garlic, or chives), and the fol-
lowing condiments: mustard, horseradish, wasabi, soy
sauce, or Worcestershire sauce.
mRNA gene expression
Nrf2–regulated antioxidative genes were measured in per-
ipheral blood mononuclear cells with quantitative real-time
PCR (qRT-PCR). Total RNA was extracted from the cells
by use of the Qiagen RNeasy kit (Qiagen, Valencia, CA).
Total RNA was used for cDNA synthesis with random hex-
amers and MultiScribe reverse transcriptase, according to
the manufacturer’s recommendations (Applied Biosystems).
cDNA (100 ng) was used for quantitative PCR analyses of
selected genes: glutamate cysteine ligase catalytic (GCLC)
and modifier subunits (GCLM), NAD()H-quinone oxidore-
ductase 1 (NQO1), and glutathione S-transferase-1 (GST1)
by using primers and probe sets commercially available
from Applied Biosystems. Assays were performed by using
the ABI 7000 Taqman system (Applied Biosystems). β-
Actin was used for normalization.
After the baseline assessment of BP and BD, spirom-
etry, body-plethysmography, diffusion capacity of carbon
monoxide, exhaled NO, and CT scan measurements
were completed (Fig. 1), volunteers received a 1-week
supply of 20-ml bottles containing 100 μmol of sulfo-
raphane each dissolved in mango juice, which masks the
pungency of the BSE , to be stored in a freezer. Each
morning, a single bottle was allowed to thaw at room
temperature until consumption of the contents in the
evening. The subject then received a second 7-day sup-
ply from the laboratory, and the procedure was repeated.
At the end of this period, BP, BD, CT scan, spirometry,
body plethysmography, diffusion capacity of carbon
monoxide, and exhaled NO were re-assessed within
3 days of consumption of the last bottle (Fig. 1). In total,
the subjects consumed 100 μmol of sulforaphane per
day on 14 consecutive evenings.
Safety and adverse event monitoring
Adverse event monitoring and documentation by severity,
duration, and relatedness were performed by the study
Fig. 1 Time line of trial protocol
Brown et al. Respiratory Research (2015) 16:106 Page 5 of 12
physician at each visit. Standard laboratory chemistries
were drawn at baseline and after the two weeks of con-
suming sulforaphane. Study stopping rules were based on
the standard practice of our local IRB and the FDA. Study
drug safety and adherence to the protocol were monitored
annually by the IRB.
Data analysis was performed with JMP 11.0.0 software
(SAS Institute, Cary, NC). To compare the demographic
and baseline pulmonary function data, one-way ANOVA
and Chi-squared tests were used. To compare the effects
of sulforaphane on changes in BP and BD, lung function,
CT measurements, oxidative stress genes, and effects of
smoking, matched-pairs comparisons (pre- and post-
sulforaphane) with non-parametric Wilcoxon Sign Rank
Analyses were performed. In addition, one-way ANOVA,
and simple linear regressions were used where indicated.
To examine the effects of specific genes and changes in
interaction on the BP, we constructed a multivariate
regression model. Significance was assumed at p ≤0.05.
The time-line of the protocol for this study is presented
in Fig. 1.
Screening and selection of asthmatic subjects
A total of 51 individuals with airway hyperresponsive-
ness were screened. The demographic and baseline pul-
monary functions as shown in Table 1. Full analysis was
possible in 44 individuals.
The primary goal of these studies was to determine
whether sulforaphane administration to 44 asthmatic pa-
tients: (i) affected the magnitude of the bronchoconstric-
tor effect of single doses of MCh challenge, and (ii)
affected the protective effects of deep inspiration on the
magnitude of the bronchoconstrictor effect of MCh
challenge. The final metric in all these studies was FEV
The mean reduction in FEV
resulting from a single
dose MCh challenge was 28.7 ± 7.2 % (mean ± SD)
(Table 2), but individual asthmatics varied markedly in
their responses to sulforaphane (Fig. 2a and b). Whereas
in 60 % of the asthmatics sulforaphane blocked the
bronchoconstrictor effects of MCh challenge, in 20 % of
these subjects sulforaphane aggravated the bronchocon-
strictor effect of MCh, and in a similar proportion (20 %)
it had no effect.
When the change in FEV
response to MCh was
analyzed post hoc as either a decrease or an increase
in response to sulforaphane administration, the result-
ing BP and BD responses were dramatically different.
Those subjects whose FEV
response to MCh de-
creased (−13 ± 8 %), had a concomitant reduction in
BP response (p = 0.002; Table 3), whereas those sub-
jects whose FEV
response to MCh increased (11 ±
11 %), experienced an improvement in BP (p = 0.004,
Table 3). Changes in BD paralleled these changes in
BP, (p = 0.02 for the subjects whose FEV
MCh decreased and p = 0.04 for the subjects whose
response to MCh increase; Table 3). The impli-
cation of these paradoxical responses is not yet clear
and the mechanism is not understood.
Secondary outcomes examined changes in pulmonary
function (Table 4) and lung morphology as determined
by high-resolution CT scans (Table 5). We found a sig-
nificant reduction in specific airway resistance (p = 0.03,
Table 4), and a small but significant increase in the small
and medium airway luminal area (p = 0.03, Table 5).
Peripheral blood mononuclear cells were obtained from
35 subjects for the measurement of Nrf2–regulated anti-
oxidant genes, and we were able to compare 28 sample
Table 2 Effects of sulforaphane (SF) administration and deep inspiration on A. Changes in forced expiratory volume in 1-second
) produced by the bronchoconstrictor MCh, and B. Magnitudes of bronchoprotection (BP) and bronchodilation (BD) effects
A. Treatment % Change in FEV
(mean ± SD)
Before SF After SF p for SF effect
MCh −28.7 ± 7.2 −22.7 ± 12.7 0.006
MCh preceded by 4 deep inspirations (for BP)−23.0 ± 13.4 −19.1 ± 11.9 0.04
MCh followed by 4 deep inspirations (for BD)−18.4 ± 7.7 −16.3 ± 10.7 0.34
B. Magnitudes of deep inspiration effects Change in BP and BD (mean ± SD)
Before SF After SF p for SF effect
BP 15.5 ± 52.7 10.3 ± 57.1 0.83
BD 32.5 ± 32.7 26.7 ± 30.6
One value was outside the acceptable range (>2 S.D.) and has been censored
Brown et al. Respiratory Research (2015) 16:106 Page 6 of 12
pairs before and after sulforaphane treatment. When
gene activities were classified according to the changes
(either a decrease or an increase response to
MCh after sulforaphane administration), the results were
very different. When the FEV
response to MCh
decreased after sulforaphane administration, the activ-
ities of all three Nrf2-regulated genes (NQO1, HO1,
GCLM) decreased. In contrast, when the FEV
to MCh increased after sulforaphane administration, the
gene activities of all three genes increased (Table 6).
Comparing the changes in each gene expression with
changes in FEV
response to sulforaphane treatment, the
differences in gene expression was significant for GCLM
(p = 0.03) and NQO1 (p = 0.047).
Bronchoprotection (BP), bronchodilation (BD), and gene
The BP and BD responses were also analyzed according
to changes in gene expression (either a decrease or an
increase resulting from sulforaphane administration).
There was a significant relationship between the change
in NQO1 gene expression and BP (p = 0.03). When
NQO1 decreased after sulforaphane administration, the
BP worsened (−54.4 ± 78.3 %) and when NQO1 in-
creased after sulforaphane administration, the BP im-
proved (20.6 ± 72.8 %). There were no statistically
significant relationships for the other genes or for BD.
We next examined the potential interactions among
these factors. A multivariate regression model was con-
structed using the change in BP as the outcome variable.
Independent variables were the changes in MCh-
induced decrease in FEV
(the difference between base-
line before and after sulforaphane treatment), and the
change in GCLM, GST1, and NQO1 gene expression.
The overall model was significant (r
= 0.67, p = 0.0003).
Controlling for the other variables, there was a signifi-
cant negative correlation between the change in BP and
the change in FEV
from baseline (p = 0.002), and a sig-
nificant positive correlation between the change in BP
and the change in NQO1 gene expression (p = 0.007).
Bronchoprotection, bronchodilation, and smoking history
When BD and BP responses in the non-smokers and
smokers were partitioned by the change in FEV
sponse to MCh, they mirrored the overall changes. In
those subjects whose FEV
response to MCh de-
creased whether they were non-smokers or smokers,
there was a concomitant reduction in BP and BD re-
sponses (Table 7). Conversely, subjects whose FEV
sponse to MCh increased whether they were non-
smokers or smokers, showed improvement in BP and
BD values (Table 7).
Safety and tolerance
Sulforaphane treatment was safe and well-tolerated. In-
spection of the laboratory results among all the subjects
showed that only one set of laboratory values in one
subject showed a significant liver function (transamin-
ase) elevation after sulforaphane administration. On
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Effects of SF on the change in FEV1 (L) caused by MCh
Effects of SF on BD (% change)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Effects of SF on the change in FEV1 (L) caused by MCh
Effects of SF on BP (% change)
Fig. 2 Negative correlation between the changes (%) resulting from
sulforaphane (SF) administration on: a. bronchodilation (BD) and on
b. bronchoprotection (BP) in asthmatic subjects, and the effects of
sulforaphane administration on the reduction of FEV
MCh challenge. a: There was a significant negative correlation
between the changes in BD and the changes in FEV
p = 0.01). As the decrease in FEV
with MCh challenge (airway
narrowing) became larger with administration of sulforaphane, the
BD response became smaller. b: There was a significant negative
correlation between the changes in BP and the changes in FEV
= 0.26, p = 0.0005). As the decrease in FEV
with MCh challenge
(airway narrowing) became larger with administration of
sulforaphane, the BP response became smaller. The Mean control
was 2.7 ± 0.7 L, and a single MCh challenge caused a reduction
by 0.78 ± 0.3 L. We further made the widely accepted
assumption that the reproducibility of FEV
values was 0.1 L, so that
x-axis changes in Fig. 2a and b between −0.1 and +0.1 L were
considered as no effect
Brown et al. Respiratory Research (2015) 16:106 Page 7 of 12
further questioning, the subject reported that he had run
a marathon the day before the blood draw after sulfo-
raphane treatment, and this may have been responsible
for changes in liver enzymes. On repeating the blood
chemistries, one week later, all blood chemistries were
within normal limits.
To our knowledge, this is the first study that has ex-
amined the effects of the phytochemical sulforaphane
on the response to DI in individuals with asthma.
This study addressed the hypothesis that oxidative
stress and inflammation play roles in the mechanisms
of the beneficial effects of DI. While our a priori pri-
mary outcome was negative, post hoc analysis exam-
ining the groups according to whether they had an
increase or a decrease in FEV
response to Mch told
a very different story.
When sulforaphane attenuated the decline in FEV
lowing a single MCh challenge, BP worsened. In con-
trast, if the FEV
response to a single MCh challenge
remained the same or increased slightly after sulforaph-
ane treatment, BP improved dramatically. There were
similar changes for the BD responses. In addition when
sulforaphane increased NQO1 gene expression, there
was an associated increase in FEV
response to MCh
and independently associated improvement in the BP re-
sponse of DI in this cohort of asthmatics.
It is predictable that there should be a range of sulfo-
raphane responses among individuals, and that they be
related to some other biological phenomenon that we
have yet to understand. For example, we have observed
striking demonstrations of this effect in our clinical
studies of sulforaphane effects on autism spectrum dis-
order behavioral metrics in young men , and in clin-
ical evaluation of the effect of sulforaphane on both
aflatoxin and air pollutant metabolites [30, 32].
It is not yet fully explainable (although expected), that
multiple mechanisms could be at play in creating this
range of responses. The literature suggesting a bi-phasic
response, commonly referred to as the U-shaped or J-
shaped curve, or hormesis [33, 34] and well described in
the context of phytochemicals , points to many such
examples in which a compound may have a protective
or therapeutic effect at one concentration and a toxic or
detrimental effect at another higher level of exposure.
This is well demonstrated in the case of Nrf2-active
compounds, in particular in their effects on redox sig-
naling, and differential pro- and anti-oxidant activities
that are concentration dependent .
A limited number of animal and human studies have
examined the effects of sulforaphane on airway respon-
siveness. Park and colleagues showed that sulforaphane
Table 3 The BP and BD responses to sulforaphane treatment, classified according to initial increased or decreased forced expiratory
volume in 1-second (FEV
) response to MCh (mean ± SD). Wilcoxon sign rank test
Before SF After SF p-for SF effect Before SF After SF p-for SF effect
(from Table 2) 15.5 ± 52.7 10.3 ± 57 0.82 32.5 ± 32.7 28.2 ± 28 0.33
response to MCh
(n = 29)
37.6 ± 38.0 −0.8 ± 64 0.002 38.3 ± 34.6 23.2 ± 35.1 0.02
response to MCh
(n = 15)
−27.2 ± 51.7 31.7 ± 33 0.004 19.6 ± 25.1 33.4 ± 18.6 0.04
Table 4 Change in pulmonary function with sulforaphane (SF) treatment (mean ± SD)
Before SF After SF p for SF effect
% predicted (forced expiratory volume in 1-second) 88 ± 11 % 88 ± 11 % 0.79
FVC % predicted (forced vital capacity) 92 ± 13 % 92 ± 11 % 0.95
/FVC 0.79 ± 0.08 0.77 ± 0.01 0.56
TLC (total lung capacity, in L) 5.0 ± 1.4 4.9 ± 13 0.10
SVC (slow vital capacity, in L) 3.4 ± 1.0 3.3 ± 0.9 0.38
FRC (functional residual capacity, in L) 3.1 ± 1.1 3.1 ± 1.0 0.56
RV (residual volume, in L) 1.7 ± 0.7 1.6 ± 0.7 0.56
RV/TLC 0.34 ± 0.09 0.34 ± 0.1 0.97
Diffusing capacity of carbon monoxide, (mL/min/mm Hg) 22.7 ± 5.6 22.4 ± 5.7 0.46
Specific airway resistance (kiloPascals · s) 6.04 ± 3.3 4.8 ± 2.5 0.008
Exhaled nitric oxide (ppb) 8.8 ± 10 9.3 ± 10.9 0.80
Brown et al. Respiratory Research (2015) 16:106 Page 8 of 12
inhibits ovalbumin-induced airway inflammation in a
murine model of asthma . They further surmised
that this occurred though suppression of GATA-3 and
SOCS-3 and increased T-bet and SOCS-5 expression.
Whether this also occurs in humans has not been deter-
mined. Nrf2–antioxidant response element binding was
reduced in cultured airway smooth muscle cells from pa-
tients with severe asthma compared to similar cells from
patients with moderate asthma or with those from nor-
mal subjects . How this affects the asthmatic re-
sponse in vivo is unknown.
Sulforaphane effects on upper airway inflammation,
and on airway response to challenge, have also been
measured. Oral sulforaphane induced airway Phase 2
antioxidant enzyme expression in a dose-dependent
fashion in exfoliated human upper airway cells . In a
follow-up study, when sulforaphane in the form of a
broccoli sprout extract was administered orally for 4 days
before a diesel exhaust particle challenge, total cell count
in the nasal lavage was reduced by more than 50 % .
These studies establish that the oral administration of
sulforaphane is an effective means of inducing cytopro-
tective enzymes in the upper airway and by inference,
probably also in the lower airway. In addition, the doses
in these published studies were similar to those used in
the current study and thus support our choice of dosing
regimen. We chose to administer the sulforaphane for a
longer period of time, 14 days rather than 4 days, in
order to be confident that enough time had elapsed for
substantial enzyme induction.
It is well recognized that pro-inflammatory cytokines,
chemokines, as well as other cell mediators, play import-
ant roles in the allergic inflammatory process in asthma.
Dysfunction of the Nrf2 pathway has also been linked to
severe allergen-driven airway inflammation and hyper-
responsiveness in mice . Disruption of the Nrf2 sig-
naling pathway in mouse models has also been directly
linked to chronic inflammation such as that associated
with asthma . As a potent inducer of cytoprotective
enzymes (antioxidant and anti-inflammatory) via Nrf2,
sulforaphane thus directly affects both the antioxidant
deficiencies that have been associated with poor asthma
control and accelerated lung function decline [16–18],
and the inflammatory component of these conditions
[12–14], both of which represent attractive therapeutic
Upregulation of Phase 2 enzymes and of other Nrf2
targets by sulforaphane has previously been shown in
vitro and in animal models [9, 39, 41–43]. The use of
broccoli sprout extract as a vehicle for well-quantified
oral delivery of sulforaphane permitted us to examine
the role of oxidative stress mediated through the Nrf2-
signaling pathways on lung function in asthma. Edible
plants contain a wide variety of phytochemicals, some of
which are phase 2 enzyme inducers. Large quantities of
inducers of enzymes that are potent antioxidants can be
delivered in the diet by small quantities of broccoli
sprouts (e.g., three-day-old sprouts) that contain as
much inducer activity as 10–100 times larger quantities
of mature broccoli. A well-characterized, stable, clean,
standardized, homogeneous, sulforaphane-rich food ex-
tract can be produced and utilized across a range of cell
culture, animal, and clinical studies, permitting direct
comparison of results. Thus, a large body of evidence
has accumulated around the world in a variety of experi-
mental systems suggesting that sulforaphane is the active
agent in broccoli sprout extracts responsible for almost
all of the phase 2 response that is induced following
treatment with broccoli sprout extracts. Quantifiable
and reproducible extraction of sulforaphane from BSE
has thus permitted us to target specifically the Nrf2
pathway in order to elucidate the mechanisms of oxida-
tive stress in patients with asthma.
Table 5 CT scan measurements of changes in volume, luminal
area and airway wall thickness with sulforaphane (SF) treatment
measured at either total lung capacity (TLC) or functional
residual capacity (FRC) (mean ± SD)
Before SF After SF p for SF effect
TLC lung volume (mL) 4175 4195 0.68
FRC lung volume (mL) 1470 1647 0.44
Mean lung density
at TLC (HU)
−820 ± 34 −823 ± 33 0.13
Air trapping (%) (FRC) 4.6 ± 8.3 7.9 ± 11.8 0.10
Airway luminal area
44.7 ± 10.3 45.1 ± 8.5 0.07
Large 103 ± 13 102.9 ± 16 0.73
Medium 30.9 ± 1.8 32 ± 4.5 0.04
Small 13.1 ± 1.6 14.3 ± 3.4 0.01
Airway wall thickness
(fraction luminal diameter)
0.57 ± 0.03 0.57 ± 0.02 0.82
Large 0.45 ± 0.02 0.46 ± 0.03 0.12
Medium 0.58 ± 0.02 0.58 ± 0.03 0.96
Small 0.67 ± 0.02 0.66 ± 0.04 0.03
Table 6 Change in oxidative stress gene expression related to
changes in Forced Expiratory Volume in 1 second (FEV
response to single dose MCh challenge (mean ± SD). P-value for
pre vs. post sulforaphane
Gene Expression (% change from baseline)
GST1 NQO1 GCLM
−6.11 ± 27.0 −73.1 ± 255.4 −19.2 ± 40.6
p = 0.67 p = 0.23 p = 0.03
11.8 ± 56.0 141.9 ± 283.7 32.4 ± 75.0
p = 0.38 p = 0.047 p = 0.58
Brown et al. Respiratory Research (2015) 16:106 Page 9 of 12
Few studies have examined the consumption of foods
rich in antioxidants in general and sulforaphane specific-
ally, on airway reactivity and asthma. Early studies sug-
gested that changes in the diets of children was a
determinant of the worldwide increases in asthma and
allergies , and that infrequent consumption of fresh
fruit was associated with impaired lung function .
More recently, intake of some vegetables was also asso-
ciated with reduced prevalence of adult asthma .
Commonly consumed fruits, vegetables, and nuts, and
high adherence to a traditional Mediterranean diet dur-
ing childhood were shown to have beneficial effects on
symptoms of asthma and rhinitis . Adherence to a
Mediterranean diet during pregnancy also had a protect-
ive effect against asthma-like symptoms and atopy in
childhood . An intervention that administered a food
plant, (Moringa oleifera) known to be rich in glucosino-
lates similar to the precursor of sulforaphane, to 20 asth-
matic subjects daily for 3 weeks, significantly improved
symptom severity, which was accompanied by improve-
ments in FEV
, FVC, and peak expiratory flow rate .
Most impressively, a new meta analysis of 12 cohort, 4
population-based case–control, and 26 cross-sectional
studies came to the conclusion that reduced risk of
asthma in adults and children was associated with higher
intake of fruit and vegetables (RR = 0.54; 95 % CI, 0.41-
The relationship between DI, airway mechanics, and air-
way hyperresponsiveness has been a focus of asthma re-
search for over 2 decades . Several earlier studies have
shown that DI has beneficial effects on human airways
[51, 52]. In healthy individuals, DI taken before exposure to
MCh protected the airways from bronchoconstriction .
This property is largely lost in asthma, even in mild disease
(5). Deep inspirations can also reverse airway obstruction
that has been experimentally induced with a direct spasmo-
gen . The bronchodilatory effect of DI is minimally af-
fected in mild asthmatics (5), but decreases with increasing
severity of asthma , raising the possibility that the
impairment of this physiologic function of the lung is one
of the determinants of severe obstructive disease.
Our findings are consistent with previous demonstra-
tions that BP and BD effects of DI become more prom-
inent when the MCh-induced bronchoconstriction in
the absence of DI is of substantial magnitude . Our
findings are also consistent with the dependence of the
effects of DI on the magnitude of bronchoconstriction
(Fig. 2). When the responses of our subjects were evalu-
ated by group: (subjects with either a decrease or an in-
crease in response to MCh), the BD and BP outcomes
were dramatically different (Table 3). To our knowledge,
this is the first demonstration of a decrease in response
to MCh leading to a worsening of the BD and BP re-
sponses and not simply a diminution of the response
amplitude . Why this occurred and whether the ef-
fect of sulforaphane on the oxidative stress balance was
involved will require further exploration.
Among nonsmokers, both BP and BD decreased in
those subjects with a decreased FEV
response to MCh,
(Table 7). In contrast, if they had no change, or any in-
crease in their FEV
responses to MCh, both BD and BP
improved significantly. There were similar trends for
smokers, but the changes in BD for subjects with a re-
response to MCh was significantly worse
than those who had non- or marginal FEV
MCh. Since changes were of similar magnitude in both
smokers and nonsmokers, the difference in the signifi-
cance of that effect may reflect the lower number of
smokers enrolled in the study. Based on animal studies,
a greater effect of sulforaphane on BD and BP would be
expected in smokers. Stimulation of Nrf2 pathways has
been shown to protect against the harmful effects of
cigarette smoke (which releases large quantities of free
radicals and increases lung levels of reactive oxygen and
nitrogen species (ROS and RNS) in murine models .
Among all the subjects, there was a significant de-
crease in specific airway resistance (Table 4) with the ad-
ministration of sulforaphane. This is likely explained by
Table 7 BP and BD responses to sulforaphane (SF) arranged according to changes in forced expiratory volume in 1-second (FEV
MCh (mean ± SD). A. Non-smokers (n = 30), B. Smokers (n = 15).
BP (% change) BD (% change)
Before SF After SF p for SF effect Before SF After SF p for SF effect
response to MCh 40.4 ± 40.4 −3.8 ± 46.8 0.002 33.7 ± 39.4 23.8 ± 36.8 0.20
response to MCh −49.3 ± 29.7 23.5 ± 35.8 0.004 17.7 ± 27.0 36.3 ± 17.7 0.04
BP (% change) BD (% change)
Before SF After SF p for SF effect Before SF After SF p for SF effect
response to MCh 32.3 ± 34.2 5.1 ± 91.1 0.28 47.1 ± 21.8 22.1 ± 33.4 0.06
response to MCh 17.1 ± 60.7 48.1 ± 20.6 0.44 22.3 ± 23.1 27.4 ± 20.1 0.63
Brown et al. Respiratory Research (2015) 16:106 Page 10 of 12
the concomitant increase in small and medium airway
luminal area (Table 5) after sulforaphane administration.
While these changes did not translate into an improve-
ment in the more commonly used lung function mea-
surements such as FEV
, FVC, and FEV
/FVC, it does
suggests an overall beneficial effect of sulforaphane on
the airways of asthmatic individuals.
In conclusion, administration of sulforaphane, a potent
upregulator of genes protecting against oxidative stress
and inflammation, may be useful both to determine the
mechanisms that lead to asthma, as well as suggesting a
potential therapy to treat asthma. Sulforaphane adminis-
tration improved the BP response in asthmatics who had
an increase in NQO1 gene expression and did not have a
decrease in their initial response to the MCh challenge.
Therefore, sulforaphane administration was able to im-
prove a major defect of even mild asthma. This should en-
courage further examination of this major cytoprotective
signaling pathway as a potential mechanistic approach to
the treatment or prevention of asthma. Furthermore, since
the administration of anti-inflammatory drugs do not
completely prevent the symptoms or progression of the
disease in a substantial subset of asthmatics, these findings
also raise the possibility of the use of sulforaphane, or
foods rich in sulforaphane, as potential adjuvant treat-
ments for asthma.
BD: Bronchodilation; BP: Bronchoprotection; BSE: Broccoli sprout extract;
DI: Deep inspiration; ERV: Expiratory reserve volume; FEV
: Forced expiratory
volume in 1 second; FRC: Functional residual capacity; GST: Glutathione
transferase; GCLM: Glutamine-cysteine ligase, regulatory subunit; IC: Inspiratory
capacity; MAPK: Mitogen-activated protein kinase; MCh: Methacholine;
NfκB: Nuclear factor kappa-light-chain-enhancer of activated B cells;
NQO1: NAD(P)H, Nicotinamide-quinone oxidoreductase 1; Nrf2: Nuclear factor
erythroid-related factor 2; PBMC: Peripheral blood mononuclear cells;
: Provocative concentration causing a 20 % drop in FEV
; RV: Residual
volume; sRAW: specific airway resistance; SVC: Slow vital capacity; TGV: Thoracic
gas volume; TLC: Total lung capacity; TVC: Total vital capacity.
The authors declare that they have no competing interests.
RHB designed the study and analyzed the data. RHB, PT, and JWF wrote the
paper. JWF and PT prepared the sulforaphane-rich broccoli sprout extract.
RHB, CR and AB carried out the clinical and laboratory studies. All authors
read and approved the final manuscript.
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins
University School of Medicine, Baltimore, MD, USA.
Division of Pulmonary
Medicine and Critical Care, Department of Medicine, Johns Hopkins
University School of Medicine, Baltimore, MD, USA.
Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Lewis B. and Dorothy Cullman Chemoprotection Center, Department of
Pharmacology and Molecular Sciences, Johns Hopkins University School of
Medicine, Baltimore, MD, USA.
Department of Environmental Health
Sciences, Johns Hopkins University School of Public Health, Room E7614,
615 N. Wolfe Street, Baltimore, MD 21205, USA.
Center for Human Nutrition,
Department of International Health, Johns Hopkins University School of
Public Health, Baltimore, MD, USA.
Received: 19 May 2015 Accepted: 21 July 2015
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