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Repair of products of oxidative DNA base damage in human cells
1Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaitersburg, MD 20899, USA.
Abstract:
Oxidative DNA damage is the most frequent type of damage encountered by aerobic cells and may play an important role in biological processes such as mutagenesis, carcinogenesis and aging in humans. Oxidative damage generates a myriad of modifications in DNA. We investigated the cellular repair of DNA base damage products in DNA of cultured human lymphoblast cells, which were exposed to oxidative stress by H2O2. This DNA-damaging agent is known to cause base modifications in genomic DNA of mammalian cells [Dizdaroglu, M., Nackerdien, Z., Chao, B.-C., Gajewski, E. and Rao, G. (1991) Arch. Biochem. Biophys. 285, 388-390]. Following treatment with H2O2, the culture medium was freed from H2O2 and cells were incubated for time periods ranging from 10 min to 6 h. DNA was isolated from control cells, hydrogen peroxide-treated cells and cells incubated after H2O2 exposure. DNA samples were analyzed by gas chromatography/isotope-dilution mass spectrometry. Eleven modified bases were identified and quantified. The results showed a significant formation of these DNA base products upon H2O2-treatment of cells. Subsequent incubation of cells caused a time-dependent excision of these products from cellular DNA. The cell viability did not change significantly by various treatments. There were distinct differences between the kinetics of excision of individual products. The observed excisions were attributed to DNA repair in cells. The rate of repair of purine lesions was slower than that of pyrimidine lesions. Most of the identified products are known to possess various premutagenic properties. The results of this work may contribute to the understanding of the cellular repair of oxidative DNA damage in human and other mammalian cells.
Insights
Human cells repair oxidative DNA damage, identified as modified bases, through distinct excision pathways. Purine lesions are repaired slower than pyrimidine lesions, contributing to understanding DNA repair mechanisms.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Oxidative DNA damage is prevalent in aerobic cells and linked to aging and cancer.
- Hydrogen peroxide (H2O2) induces various DNA base modifications in mammalian cells.
- Understanding cellular repair mechanisms is crucial for human health.
Purpose of the Study:
- To investigate the cellular repair of oxidative DNA base damage products.
- To quantify modified DNA bases induced by H2O2 in human cells.
- To determine the kinetics and characteristics of DNA repair pathways.
Main Methods:
- Cultured human lymphoblast cells were exposed to H2O2.
- DNA was isolated from treated and control cells at various time points.
- Gas chromatography/isotope-dilution mass spectrometry was used to identify and quantify modified DNA bases.
Main Results:
- H2O2 treatment significantly increased eleven types of DNA base products.
- Subsequent incubation led to time-dependent excision of these products, indicating DNA repair.
- Repair rates differed, with purine lesions being repaired more slowly than pyrimidine lesions.
Conclusions:
- Human cells possess active repair mechanisms for oxidative DNA base damage.
- The differential repair kinetics suggest specific pathways for different types of lesions.
- This study enhances understanding of oxidative DNA damage repair in mammals.