Oxidative Nucleobase Modifications Leading to Strand Scission

Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants.

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Oxidative DNA damage and disease: induction, repair and significance

Free radical-induced damage to DNA: mechanisms and measurement.

The literature contains conflicting evidence regarding the existence of DNA damage in spermatozoa from infertile male patients. To examine this phenomenon, we have studied ejaculated spermatozoa from normozoospermic semen donors and from a group of the unselected male partners of couples attending an infertility clinic for initial investigation. Classical semen analysis according to World Health Organization (WHO) guidelines was undertaken with computer-assisted sperm analysis (CASA). Spermatozoa were prepared by sequential washing and centrifugation and were analyzed for DNA fragmentation using three assays: 1) a single-cell gel electrophoresis (comet) assay, 2) in situ nick translation with prior chemical decondensation (ISNT-decondensed), and 3) in situ nick translation without prior chemical decondensation (ISNT-condensed). In addition, reactive oxygen species (ROS) generation by spermatozoa was measured, and seminal plasma was analyzed for its total reactive antioxidant potential (TRAP). When the donor and patient groups were compared, the latter had lower levels of semen quality and higher levels of DNA damage, which was particularly apparent using the comet assay. Highly significant negative correlations were observed between DNA fragmentation, detected by all three assays, and semen quality, particularly sperm concentration. In addition, multiple regression analysis indicated that other attributes of semen quality, such as sperm movement and ROS generation, were also related to DNA damage. We conclude that a significant proportion of infertile men have elevated levels of DNA damage in their ejaculated spermatozoa.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.1939-4640.2000.tb03273.x

DNA Integrity in Human Spermatozoa: Relationships With Semen Quality

Hyperoxia induces DNA damage in mammalian cells

The authors report on the elucidation of DNA-protein cross-links formed in isolated mammalian chromatin upon treatment with H{sub 2}O{sub 2} in the presence of iron or copper ions. Analysis of chromatin samples by gas chromatography/mass spectrometry after hydrolysis and derivatization showed the presence of 3-((1,3-dihydro-2,4-dioxopyrimidin-5-yl)methyl)-L-tyrosine (thymine-tyrosine cross-link) on the basis of the gas chromatographic and mass spectrometric characteristics of the trimethylsilylated authentic compound. Other DNA-protein cross-links involving thymine and the aliphatic amino acids and cytosine and tyrosine, which were known to occur in nucleohistone {gamma}-irradiated under anoxic conditions, were not observed. This was due to inhibition by oxygen as clearly shown by experiments that were carried out using ionizing radiation under both oxic and anoxic conditions instead of using H{sub 2}O{sub 2} and metal ions. The yield of the thymine-tyrosine cross-link was higher upon treatment with H{sub 2}O{sub 2}/chelated Fe{sup 3+} ions than with H{sub 2}O{sub 2}/unchelated Fe{sup 3+}ions. By contrast, h{sub 2}O{sub 2}/unchelated Cu{sup 2+} ions produced a higher yield than H{sub 2}O{sub 2}/chelated Cu{sup 2+}ions. Superoxide dismutase afforded partial inhibition only when chelated ions were used. The mechanism underlying formation of this DNA-protein cross-link is thought to involve addition of the hydroxyl radical generated allyl radical of thyminemore » to carbon-3 of tyrosine followed by subsequent oxidation of the adduct radical.« less

Marco A. Cacciuttolo

Papers

Hyperoxia induces DNA damage in mammalian cells

Chemical nature of DNA-protein cross-links produced in mammalian chromatin by hydrogen peroxide in the presence of iron or copper ions.

Formation of DNA-protein cross-links in cultured mammalian cells upon treatment with iron ions.

Structure of DNA-protein crosslinks formed in mammalian chromatin upon treatment with hydrogen peroxide and metal ions

DNA damage by hyperoxia in hybridoma cells is mediated by metal ions and hydroxyl radicals