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Hypochlorous acid potentiates hydrogen peroxide-mediated DNA-strand breaks in human mononuclear leucocytes
C E Van Rensburg1, A M Van Staden, R Anderson
1Department of Immunology, Faculty of Medicine, University of Pretoria, Republic of South Africa.
Abstract:
In this study the formation of DNA single-strand breaks in MNL in close proximity to activated phagocytes, or in contact with added H2O2 and/or HOCl, were evaluated. Neutrophils activated by phorbol myristate acetate (PMA), induced DNA-strand breaks in neighboring lymphocytes which increased after 1-2 h incubation in a repair medium. These DNA-strand breaks could be prevented by the addition of catalase or substitution of the neutrophils with cells from a patient with chronic granulomatous disease. Inclusion of the myeloperoxidase (MPO) inhibitor, sodium azide (NaN3), to the system was associated with less damage after 1-2 h incubation and a faster repair rate. Exposure of MNL to added reagent H2O2 (12-100 microM) was also accompanied by DNA damage. Addition of reagent HOCl (3-25 microM) did not induce any DNA-strand breaks. However, when combined with H2O2 (12.5 microM), HOCl increased H2O2-mediated DNA damage and compromised the repair process. Interactions between the phagocyte-derived reactive oxidants H2O2 and HOCl are probably involved in the etiology of inflammation-related cancer.
Insights
Activated neutrophils and reactive oxidants like hydrogen peroxide (H2O2) cause DNA damage in lymphocytes. This damage, linked to inflammation-related cancer, can be prevented by certain inhibitors and enzymes.
Area of Science:
- Cellular Biology
- Oxidative Stress Research
- Cancer Etiology
Background:
- Phagocytes, such as neutrophils, generate reactive oxygen species during immune responses.
- Chronic inflammation is increasingly linked to the development of various cancers.
- Understanding the mechanisms of DNA damage by phagocyte-derived oxidants is crucial for cancer prevention.
Purpose of the Study:
- To investigate DNA single-strand break formation in lymphocytes (MNL) exposed to activated phagocytes and reactive oxidants.
- To determine the role of hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) in DNA damage.
- To explore potential protective mechanisms against phagocyte-induced DNA damage.
Main Methods:
- Incubation of lymphocytes with activated neutrophils (stimulated by phorbol myristate acetate) or with added H2O2 and/or HOCl.
- Assessment of DNA single-strand breaks using established assays.
- Evaluation of the effects of catalase, chronic granulomatous disease neutrophils, and myeloperoxidase (MPO) inhibitor (sodium azide) on DNA damage and repair.
Main Results:
- Activated neutrophils induced DNA-strand breaks in neighboring lymphocytes, which increased over 1-2 hours.
- Catalase and neutrophils from chronic granulomatous disease patients prevented this DNA damage.
- Myeloperoxidase inhibition reduced damage and accelerated DNA repair.
- H2O2 caused DNA damage, while HOCl alone did not, but it enhanced H2O2-induced damage and impaired repair.
Conclusions:
- Phagocyte-derived reactive oxidants, particularly H2O2, play a significant role in causing DNA damage in adjacent cells.
- The combination of H2O2 and HOCl exacerbates DNA damage and hinders repair processes.
- These interactions may contribute to the development of inflammation-related cancers.