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.