Discussion:
Asthma is a chronic inflammatory lung disease which is characterized by
airway inflammation, intermittent airflow obstruction, and bronchial
hyper-responsiveness.[10] Allergic asthma can be sparked by allergen
sensitization in which house dust mites (HDM) are one of the most
prevalent indoor allergens.[11] The prevalence of allergic
sensitization is rising in developing countries, a phenomenon related to
rapid urbanization and an adult’s migration from a rural to an urban
area increases their risk of sensitization to mite allergens. It also
could contribute to a rapid increase of chronic respiratory diseases
(CRD). Exposure to dust mite allergens is a risk factor for clinical
asthma in sensitized subjects.[12]
The relationship between allergic asthma and intestinal permeability is
a subject of research interest. An increase in the intestinal
permeability may result in facilitating the entry of allergenic proteins
from the intestinal lumen into the systemic circulation. Consequently,
activation of the adaptive immune system, allergen sensitization and/or
extra-intestinal inflammation occurs.[13]
The current study is a case control study that aimed at
assessing the relation between
serum zonulin level as a marker of increased intestinal permeability and
the severity of house dust mites allergic asthma. Our study included 96
patients; 48 asthmatic patients and 48 control subjects. The mean age of
the asthmatic patients (n=48) was 30.67±15.609, 30 ( 62.5%) were
females and 18 ( 37.5%) were males and most of them, 26 patients, lived
in rural areas (54.16%). 39 patients (81.3%) had a positive family
history of atopy. All patients displayed positive skin prick test
results to house dust mites, most of the patients (70.8%) were
sensitive to D. pteronyssinus and 60.4% were sensitive to D. farina .
14 patients were mono sensitized to a single type of house dust mites
and 34 patients were polysensitized to both types. As for the grade of
asthma severity, 4 patients (8.3%) had grade 1 severity, 24 patients
(50%) had grade 2 asthma severity , 12 (25%) patients had grade 3
severity, and 8 patients (16.7%) had grade 3 asthma severity.
Several studies supported these current results indicating that
bronchial asthma was associated with females with an obvious sex bias.Ricciardolo FL et al., 2020 conducted a cross-sectional study
on 499 asthmatic patients to assess the potential difference between
asthmatic males and females in a real-life setting. Their study also
displayed a female predominance in which 301 patients 60.32% were
females.[14] In addition, Sabry, 2011 reported that
20–40% of asthmatic females of reproductive age suffer from worsening
of their symptoms during their menstrual period, suggesting that sex
hormones may have a major role in the biologic sex difference.
[15].
These results could be attributed to hormonal factors, environmental
exposure, and the presence of comorbidities. Since estrogen receptors
(ERs) are highly expressed in the lungs and their smooth muscles with a
special role in bronchoconstriction/dilatation, this explains the gender
bias. Moreover, another possible hormonal factor is the lack of male sex
hormone which plays an integral role in downregulation of innate and
adaptive immune response.[16] Genetic factors may also be involved.
The Cyclooxygenase (COX) pathways play an important role in the course
of bronchial asthma and
Cyclooxygenase-2(COX-2) gene
homozygosity is related to females.[17]
In fact, rural residence has higher prevalence of parental smoking,
higher number of siblings, advanced overcrowding rates, higher humidity
levels and greater exposure to chemicals and farm animals.[18]
Moreover, hot climatic conditions and high population density are
crucial for the development and reproduction of mites[19] . Hence,
the geographical situation of Egypt and its favorable climatic
conditions together with its overpopulation contribute to the abundance
of HDM especially in rural areas.[21]
The current results displayed that asthma patients were more commonly
living in rural areas (54%vs 45.84% urban asthmatics) and all of them
had positive skin prick test response to house dust mites, DP;Df
(70%,60% respectively). Lawson et al., 2017 likewise reported
that children with asthma who lived in rural areas were more likely to
wheeze or have more severe symptoms of wheeze. [20] Furthermore,
this also agreed with Müsken et al., 2002 study which concluded
that sensitization to storage mites in Germany was more frequently
sensitive to D. pteronyssinus and the prevalence of positive skin test
results to storage mites was greater in rural than in city dwellers.
Also, In vitro sensitization to B. tjibodas mites was also significantly
greater in rural than in city dwellers.[42] Besides, Hassan
and Hagrass 2017 reported that house dust mites (HDM) allergy occurs
more commonly than any other allergens among Egyptian asthmatic
patients. [21]
Several studies disclosed that the high frequency of family history of
allergy is common among asthmatics. Familial assemblage of asthma and
allergic disease has frequently been observed, indicating that a
positive familial history of atopy may be considered as an identifiable
risk factor of asthma. This may be due to the evidence hinting that
genetics play an essential role in the pathogenesis of asthma. In
alliance, Antonios et al. 2012 reported 60% of cases had a
positive family history and displayed 95% positive reactions to both D.
pteronyssinus and D. farinae allergens using SPT among asthmatic
patients in Gharbia Governorate, Egypt. [22] Similar results were
reached by Haggag MG et al, 2017 .Their study revealed that
62.5% of patients had positive family history.[23]
A detailed clinical history and physical examination followed by the
detection of total serum IgE level and IgE immunoreactivity against
specific allergens still represents the cornerstone in approaching
allergic disorders.[4]
On comparing serum total immunoglobulin E (IgE) level between asthmatic
patients and control subjects in the present study, asthmatic patients
displayed a higher statistically significant level of serum total IgE.
It was statistically significantly higher among male asthmatic patients.
There was a positive correlation between total serum IgE level and
asthma severity grade and skin prick test results.
Several studies disclosed high serum IgE levels among asthmatic
patients. This is in alliance with Kim et al. 2013 who stated
that the total IgE levels were significantly higher in males.[24]Fereidouni M et al.,2009 study uncovered that the mean total
IgE serum was significantly high among asthmatics. Males had higher mean
total IgE values than females (305 vs 252 IU/mL, P = 0.6), but the
difference was not significant.[25]
On the contrary, Somani ,2008 demonstrated that total IgE level
is higher in female patients and they attributed their results to the
possibility that total levels of IgE might be inheritable, especially in
females, because of the existence of two alleles at the X-linked
locus.[26]
The disparity in the development of total IgE between males and females
is the consequence of the fact that the levels of total IgE depend on
many other factors; such as parasitic infestations, smoking, pollution,
local diet and different genetic background in which males are at
greater risk of exposure.[25]
IgE is an antibody linked to allergic reactions and airway inflammation
which is associated with asthma severity. IgE is also linked to airway
hyperresponsiveness, and lower pulmonary function. Additionally, the use
of monoclonal anti-IgE has resulted in decreasing asthma severity.
Concerning the correlation between level of total IgE and asthma
severity, Kovač K et al,2007 also discerned that the greater
the asthma severity the greater the total serum total IgE level
(>288.0 kIU/L) and specific IgE to D pteronyssinus
(>44.1 kIUA/L). They conducted a study to evaluate the
correlation between serum total IgE level and asthma severity in
asthmatic children sensitive to D pteronyssinus.[27]
Kenawy et al ., 2017 found a highly significant
increase in serum level of IgE in patient with severe asthma than those
with mild asthma with P values < 0.001.[28] Likewise, a
study done by Rotsides and his coworkers (2010) reported a
strong positive association between high IgE level and asthma severity
in children and they proposed that serum IgE level is a strong predictor
for allergy in asthmatic children. [29]
Regarding the relation between serum IgE level and the positivity of
skin prick test, Baldacci S et al., 1996 concluded that the
higher IgE levels the greater the positivity of SPT regardless the
gender .[30] Rose et al., 1996 likewise assumed that there
is some inverse relationship between the quantitative level of IgE
antibody and the level of allergen necessary to cause symptoms of
asthma.[31]
The impairment of the epithelial barrier is a corner stone in the
development of allergic diseases.
Increased intestinal permeability,
either due to the exposure to antigens in asthmatic patients or due to a
barrier defect, play a critical role in susceptibility to environmental
allergens.[32] The mechanisms responsible for increased intestinal
permeability in asthma remain unclear. It seems that intestinal
permeability may be a ”bronchus to gut” consequence of bronchial
inflammatory process because a correlation with the severity of the
disease, airflow obstruction, could be demonstrated [33] This
supports that a primary general mucosal defect could be present
simultaneously in several organs and clinically expressed in a single
organ after an exogenous stimulation, such as antigenic or environmental
factors [41]. Duodenal histological changes mimicking those observed
in bronchial mucosa have been shown. In addition, gastrointestinal
abnormalities have been also reported in patients with asthma.[5]
Therefore, correction of the gut barrier defect may be an additional
novel approach for asthma treatment [34] via reduction of epithelial
susceptibility to damage and consequent inflammatory and remodeling
responses. In addition to growth factors, several other peptides have
been identified that have the ability to restore barrier function. One
such peptide is AT-1001, a peptide inhibitor of zonulin [35].
Zonulin is a prehaptoglobulin protein and a biomarker for gut barrier
leakiness that downregulates tight junction function, and it has been
proposed to play a role in several autoimmune diseases [8] and
asthma in children [32]. It would therefore be of interest to
examine zonulin expression in airways and its regulation in patients
with asthma.[36]
The present study disclosed that asthmatic patients displayed a higher
statistically significant level of serum zonulin than control subjects.
Patients living in rural areas had a significantly higher levels on
serum zonulin. Furthermore, there was a significant correlation between
zonulin level and asthma grade . The higher the zonulin level the
greater the grade of asthma severity. Nevertheless, we found that there
was no difference in serum levels of zonulin subjects regarding gender
and age. The cut of value of serum zonulin level to deffrentiate between
grade 1-2 asthma severity and grade 3-4 asthma severity. In addition,
serum zonulin showed a sensitivity equal to 80%, a specificity equal to
71.4%, a positive predictive value equal to 66.7% and a negative
predictive value equal to 83.3%. There was no statistically significant
correlation to serum total IgE concentration. Grade of asthma had
independent significant effect on zonulin level while serum total IgE
had no significant effect on zonulin level via linear regression
analysis.
Benard and colleagues in France were the first study in the
literature on intestinal permeability in asthma. They showed increased
intestinal permeability in adult patients with bronchial asthma compared
with patients with chronic obstructive pulmonary disease and healthy
control subjects. In their study, they used radioactive material
(CrEDTA) which was administered orally, and estimated its urinary
recovery. They noticed that both patients with allergic asthma and those
with nonallergic asthma were significantly different from the control
groups and reported that intestinal permeability was not correlated with
the severity of asthma as judged by FEV~ measurement.
Unlike the current results, they disclosed that intestinal permeability
did not significantly vary according to asthma severity score or steroid
treatment [37] This may be due to difference in method used to
assess intestinal permeability.
Furthermore, a study performed by Cervantes-García D and
collaborators aiming at assessing the outcome of oral Lactococcus
lactis NZ9000 use on airway inflammation and lung remodeling in
asthmatic rats and its relation to the preservation of the intestinal
barrier, concluded that oral L. lactis could be used for asthma
prevention through its maintenance of an adequately functioning
intestinal barrier.[38]
Preliminary data suggest that a subset of asthmatic patients have
increased serum zonulin levels and increased intestinal permeability
[39]. These data suggest that both the lung and intestinal mucosa
may be routes through which specific antigens can gain access to the
submucosa with subsequent exposure to the immune system leading to lung
inflammation [40].
Moreover, a study performed by Yamaide F et al. 2020 to examine
the differences between serum zonulin level among allergic children and
non- allergic children concluded that serum zonulin was significantly
greater in children with allergy (Food allergy, Bronchial Asthma). In
addition, it was significantly higher in patients with food allergy than
in bronchial asthma patients. However, their results are not completely
reliable as food allergy can be the main reason for increased intestinal
permeability and this explains the higher increase in zonulin level
among food allergy patients than among asthmatic ones. [32]
Up to the present moment no studies have been conducted to assess the
relationship between serum zonulin level and asthma severity or to
assess its correlation to different residential distribution. A study
performed by Sheen et al to assess serum zonulin level in atopic
dermatitis (AD) and its correlation to disease severity. They found that
AD group had a greater median serum zonulin level than the control group
and serum zonulin level had significantly positive correlations with age
and the SCORAD index, but not with total IgE, total eosinophil count
(TEC), or the number of allergens to which a child is sensitized. And
concluded that each 1 ng/mL increase in serum zonulin was associated
with a 15% greater risk of moderate-severe AD [6]. Their results
agree with the current results as regards the correlation between serum
zonulin level and total serum IgE level. Both revealed no statistically
significant correlation.
Conclusion:
Intestinal barrier dysfunction contributes in the pathogenesis of
allergic asthma. Serum zonulin level reflects an increase in intestinal
permeability and acts as prognostic factor of severity in Asthma.
Correction of the gut barrier defect may be an additional novel approach
for Asthma.
Funding: none.
Conflicts of interest: none.