Keywords
Antioxidant, Comet assay, DNA Damage, Eosinophils, White blood cells
This article is included in the Cell & Molecular Biology gateway.
Eosinophilia serves as an indicator of allergy and parasite infestation. Eosinophil granules are believed to have adverse effects on cells and contribute to oxidative stress. In our current study, we investigated the relationship between eosinophilia and healthy subjects in terms of nuclear DNA damage in peripheral leukocytes. The comet assay was employed to test whole blood samples from 52 subjects in each group. The results revealed that eosinophilia subjects exhibited significantly higher levels of nuclear DNA damage in leukocytes compared to healthy subjects. Additionally, a weak positive association was observed between eosinophil counts and DNA damage. Our findings suggest that eosinophilia is linked to systemic oxidative DNA damage.
Antioxidant, Comet assay, DNA Damage, Eosinophils, White blood cells
Inflammation is a fundamental immune response. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in response to pathogens, but they can also cause DNA damage (Kay et al., 2019). The major immune cells involved in ROS production include neutrophils, macrophages, and eosinophils. Eosinophils have been found to exhibit a greater superoxide generation rate and longer latency period than neutrophils (Petreccia et al., 1987), while eosinophilia may indicate a chronic health condition (Valent et al., 2021).
Eosinophilia refers to an abnormal increase in eosinophils in peripheral blood. These cells possess bactericidal, anti-parasitic, and cell-killing functions, primarily targeting microbial parasite infections and participating in inflammatory responses (Lombardi et al., 2022). Activation of eosinophils by immunoglobulins, cytokines, and other lipid mediators triggers a cascade of inflammatory reactions in the body, leading to tissue damage (Ramirez et al., 2018). The oxidizing intermediates resulting from eosinophil-mediated inflammation significantly contribute to increased oxidative stress and DNA damage (Henderson et al., 2001). Basic proteins and cationic proteins released from eosinophil granules exert toxicity on mammalian cells (Muniz et al., 2012). Eosinophil peroxidase can generate free radicals in the presence of hydrogen peroxide (van Dalen et al., 2006). Animal studies demonstrate that allergens induce the formation of reactive oxygen species in human cell culture models (Chan et al., 2017). In developed countries, helminthic infestations are not major health concerns, but an increase in eosinophil counts is likely due to allergic reactions. Allergy represents an undesirable inflammatory response, and oxidants are released during this process, contributing to oxidative stress in the body. Eosinophils have also been reported to contribute to oxidative stress in uncontrolled asthma (de Groot et al., 2019), while children with allergic rhinitis are found to have higher plasma total oxidant status (Emin et al., 2012).
In the presence of chronic oxidative stress due to eosinophilia, the oxidative stress may contribute damage to peripheral cellular DNA. The aim of the current study was to investigate the association between eosinophils count and detectable leucocytic DNA damage if any.
Healthy and diseased subjects were recruited from the clinics. Among both groups of subjects, no known diseases were observed except for a high eosinophil count and/or eosinophil percentage in the eosinophilia group (test group). Eosinophil counts exceeding 450/μL or greater than 6% in white blood cell differential counts were indicative of eosinophilia. Samples with eosinophil counts between 150 and 450/μL and differential count below 6% were categorized into the control group. A total of 104 EDTA peripheral blood samples were analyzed. Complete blood counts were conducted within 4 hours of blood collection using the XN-1000 Hematology Analyzer (Sysmex, Kobe, Japan). An aliquot of the whole blood was stored at room temperature and subsequently transferred to -20°C within 2 days of collection. Demographically, the control group age ranged from 6 to 77 years and test group from 1 to 83 years. The male and female numbers were 33 and 19 respectively for both groups.
The microscopic slide was pre-coated with a layer of 1% regular agarose for adhesion enhancement. Eighty-five μL of 1% low gelling temperature agarose at about 40°C was mixed with 4 μL EDTA whole blood. The mixture was quickly transferred onto the slide in a circular motion to achieve about 1.5 cm diameter. Each slide had the capacity for accommodating 2 gels. The mixture of gel and blood was cooled down and solidified on the slide before transferring to the Coplin jar containing 40 mL cold lysis solution (2.5M NaCl, 0.1M EDTA, 10mM Tris, 1% Triton X-100, 10% DMSO, pH = 10). The slide remained in the lysis solution at 4°C for 1 hour and then transferred to another jar containing cold electrophoresis solution (0.3M NaOH, 1mM EDTA, pH > 13) for the first 10 min of alkaline treatment at 4°C. Fresh electrophoresis solution replaced and further 10 min of alkaline treatment proceeded. The change of fresh electrophoresis solution was to remove excessive salt trapped in the gel left from the lysis step. The slide was then transferred to an electrophoresis tank containing cold electrophoresis solution. Electrophoresis took place at constant voltage 25 V and about 300 mA for 30 min. Slide was transferred to Coplin jar containing tap water for 15 min to remove alkaline solution. To fix the DNA, 75% alcohol was added onto the gel for 30 min. Excess alcohol was drained, and the slide was dried before staining. One part of stock Giemsa stain was diluted with 9 parts of pH 6.8 phosphate buffer (PB). About 200 μL of freshly prepared working Giemsa stain was added onto the gel for 30 min and followed by destaining with pH 6.8 PB. Finally, the slide was dried and kept at room temperature before scoring under light microscope at 100X (Primostar 3, Zeiss, Baden-Württemberg, German). Scoring of comet cells was described in the previous study (Chan et al., 2023).
Unpaired t-test was used to compare the differences between 2 groups in age, white blood cell (WBC) count, eosinophil percentage, eosinophil count, and comet score. Pearson correlation was used to investigate the associations between comet score and eosinophil percentage, comet score and eosinophil count.
Results showed that eosinophilia subjects demonstrated a higher leucocytic DNA damage than normal group. Comet scores were 92.8 (124.0) in normal subjects while 161.8 (151.1) in eosinophilia group [Mean (SD)] (Figure 1). These findings support our initial hypothesis that DNA damage is elevated during inflammatory states. Additionally, weak positive associations between comet score and eosinophil percentage (r=0.3190, p=0.0010), comet score and eosinophil count (r=0.2608, p=0.0075) were observed. There were no statistically significant differences in age and WBC count between normal and test groups (p>0.05) (Table 1) (Szeto, 2024).
Statistically significant difference was seen between eosinophilia and normal subjects. Unpaired t-test (p<0.0124).
Eosinophil can degranulate and release cytotoxic content at the site of injury which in turn worsens inflammation and tissue damage (Rosenberg et al., 2013). Eosinophil peroxidase in eosinophils can generate potent oxidants to defend the invasion of parasite and likely cause eosinophil-mediated tissue damage (Henderson et al., 2001). It has been reported that blood eosinophil count is associated with eosinophil infiltration in the nasal polyps (El-Anwar et al., 2022) and in colorectal mucosal (Haasnoot et al., 2023). Researchers have also demonstrated the positive correlation between peripheral blood eosinophil count and disease severity in bullous pemphigoid (BP) (Gore Karaali et al., 2021).
Allergens, such as house dust mites, are known to induce DNA damage in bronchial epithelium (Chan et al., 2016). Although the mechanism remains unknown, plasma total antioxidant status is lower in children with asthma bronchiale (Zeyrek et al., 2009). The current results imply that eosinophils might not only be associated with tissue damage but also contribute to DNA damage in peripheral white blood cells. However, there is no evidence to conclude a causal relationship between eosinophil count and leucocytic DNA damage. Pretreatment with antioxidants in mice with induced airway inflammation has been found to lower oxidative stress (Park et al., 2009). Eosinophils in mild asthma have been suggested to contribute to oxidative stress, and treatment of oxidative stress could potentially relieve asthma in humans (de Groot et al., 2019) or serve as beneficial adjunctive therapy (Bowler & Crapo, 2002). This highlights the potential application of peripheral blood cell DNA damage assessment to evaluate the effectiveness of oxidative stress treatment.
This study was conducted in accordance with the principles of the Declaration of Helsinki, and all patients provided written informed consent prior to enrollment. Blood samples were from specimens for other laboratory tests and no additional blood sample was taken. The approval was obtained from the Research Ethics Committee. [Protocol No: 2022A]. Permission was obtained from the chairperson of Research Ethics Committee, Macao Society for the Study of Women’s Health on 3rd Jan 2022. Reference number 202201.
The data and full results of this study are available in the Zenodo repository.
Repository name: Eosinophilia and leucocytic DNA damage. DOI: https://doi.org/10.5281/zenodo.13841378 (Szeto, 2024).
The project contains the following underlying data:
• Age (yr), WBC count (/μL), Eosinophil (%), Eosinophil count (/μL), and Comet score of normal and eosinophilia subjects.
License: Creative Commons Attribution 4.0 International.
Views | Downloads | |
---|---|---|
F1000Research | - | - |
PubMed Central
Data from PMC are received and updated monthly.
|
- | - |
Provide sufficient details of any financial or non-financial competing interests to enable users to assess whether your comments might lead a reasonable person to question your impartiality. Consider the following examples, but note that this is not an exhaustive list:
Sign up for content alerts and receive a weekly or monthly email with all newly published articles
Already registered? Sign in
The email address should be the one you originally registered with F1000.
You registered with F1000 via Google, so we cannot reset your password.
To sign in, please click here.
If you still need help with your Google account password, please click here.
You registered with F1000 via Facebook, so we cannot reset your password.
To sign in, please click here.
If you still need help with your Facebook account password, please click here.
If your email address is registered with us, we will email you instructions to reset your password.
If you think you should have received this email but it has not arrived, please check your spam filters and/or contact for further assistance.
Comments on this article Comments (0)