Oxidative damage to DNA: do we have a reliable biomarker?

Abstract

Oxidized bases in DNA can be measured directly by high-performance liquid chromatography (HPLC). 7,8-Dihydro-8-oxo-guanine (8-OHgua), as the most abundant oxidation product, is often regarded as an indicator of oxidative stress. Estimates of endogenous 8-OHgua levels in human lymphocyte DNA are between 2 and 8 for every 10(5) unaltered bases--a high frequency in view of the potential mutagenicity of this base alteration and of the presence of an effective base excision repair pathway in eukaryotic cells. An alternative approach to the measurement of oxidized bases makes use of repair endonucleases with appropriate lesion specificities--endonuclease III, for oxidized pyrimidines and formamidopyrimidine glycosylase for 8-OHgua. These enzymes introduce breaks at sites of damage in DNA. The comet assay (single cell gel electrophoresis) can then be used to detect the DNA breaks. This modified comet assay, like other enzyme-linked DNA breakage assays, gives a value for endogenous oxidative base damage that is more than 10-fold lower than most estimated from HPLC. It is possible that HPLC-based estimates are artificially high because oxidation of guanine occurs during isolation, storage, or hydrolysis of DNA. Using a revised DNA isolation procedure designed to decrease in vitro oxidation, we have obtained results for 8-OHgua concentrations in human lymphocytes that are closure to the figures obtained by the comet assay. It is still an open question whether 8-OHgua, measured by HPLC or by the comet assay, is a valid marker for oxidative damage.

Reduction of lipid peroxidation and H2O2‐mediated DNA damage by a red alga (Grateloupia filicina) methanolic extract

“…DNA loops containing breaks extend under electrophoreses to form 'comet tails', and the relative intensity of the tail indicates the DNA break frequency. 27 This result implies that the G filicina extract contains compounds with high antioxidant activity. As a popular edible alga, its potential antioxidant activity can be used to make different food formulations.…”

Chronic inflammation and oxidative stress in the genesis and perpetuation of cancer: role of lipid peroxidation, DNA damage, and repair

“…For a long time an obstacle was the lack of sensitive and specific detection methods for oxidative DNA base damage that could be applied in clinical and epidemiological studies in humans. Until recently, many detection methods were too insensitive for human biomonitoring; one of the most widely used marker, 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), produced results that varied over several orders of magnitude, likely due to its artifactual formation [21]. Furthermore, the use of 8-oxodG as oxidative stress marker in chronically inflamed tissues is hampered by its degradation to ring-opened products by peroxynitrite, which is formed during inflammatory conditions (Fig.…”

New aspects in the biomonitoring of occupational exposure to styrene

“…In cells with lower repair capacity some breaks remain unrepaired. The number of SBs is estimated by alkaline comet assay, calibrated for the number of SBs (Collins et al 1996).…”