An ECVAG trial on assessment of oxidative damage to DNA measured by the comet assay.

The increasing use of single cell gel electrophoresis (the comet assay) highlights its popularity as a method for detecting DNA damage, including the use of enzymes for assessment of oxidatively damaged DNA. However, comparison of DNA damage levels between laboratories can be difficult due to differences in assay protocols (e.g. lysis conditions, enzyme treatment, the duration of the alkaline treatment and electrophoresis) and in the end points used for reporting results (e.g. %DNA in tail, arbitrary units, tail moment and tail length). One way to facilitate comparisons is to convert primary comet assay end points to number of lesions/10(6) bp by calibration with ionizing radiation. The aim of this study was to investigate the inter-laboratory variation in assessment of oxidatively damaged DNA by the comet assay in terms of oxidized purines converted to strand breaks with formamidopyrimidine DNA glycosylase (FPG). Coded samples with DNA oxidation damage induced by treatment with different concentrations of photosensitizer (Ro 19-8022) plus light and calibration samples irradiated with ionizing radiation were distributed to the 10 participating laboratories to measure DNA damage using their own comet assay protocols. Nine of 10 laboratories reported the same ranking of the level of damage in the coded samples. The variation in assessment of oxidatively damaged DNA was largely due to differences in protocols. After conversion of the data to lesions/10(6) bp using laboratory-specific calibration curves, the variation between the laboratories was reduced. The contribution of the concentration of photosensitizer to the variation in net FPG-sensitive sites increased from 49 to 73%, whereas the inter-laboratory variation decreased. The participating laboratories were successful in finding a dose-response of oxidatively damaged DNA in coded samples, but there remains a need to standardize the protocols to enable direct comparisons between laboratories.

Variation in the measurement of DNA damage by comet assay measured by the ECVAG inter-laboratory validation trial.

The comet assay has become a popular method for the assessment of DNA damage in biomonitoring studies and genetic toxicology. However, few studies have addressed the issue of the noted inter-laboratory variability of DNA damage measured by the comet assay. In this study, 12 laboratories analysed the level of DNA damage in monocyte-derived THP-1 cells by either visual classification or computer-aided image analysis of pre-made slides, coded cryopreserved samples of cells and reference standard cells (calibration curve samples). The reference standard samples were irradiated with ionizing radiation (0-10 Gy) and used to construct a calibration curve to calculate the number of lesions per 10(6) base pair. All laboratories detected dose-response relationships in the coded samples irradiated with ionizing radiation (1.5-7 Gy), but there were overt differences in the level of DNA damage reported by the different laboratories as evidenced by an inter-laboratory coefficient of variation (CV) of 47%. Adjustment of the primary comet assay end points by a calibration curve prepared in each laboratory reduced the CV to 28%, a statistically significant reduction (P < 0.05, Levene's test). A large fraction of the inter-laboratory variation originated from differences in image analysis, whereas the intra-laboratory variation was considerably smaller than the variation between laboratories. In summary, adjustment of primary comet assay results by reference standards reduces inter-laboratory variation in the level of DNA damage measured by the alkaline version of the comet assay.

Glycaemic status in relation to oxidative stress and inflammation in well-controlled type 2 diabetes subjects.

The aim of the present observational study was to investigate the relationships between glycaemic status and levels of oxidative stress and inflammation in well-controlled type 2 diabetes subjects. Metabolic variables (weight, BMI, waist circumference (waist), blood glucose, glycated Hb (HbA(1c)), insulin, blood lipids), biomarkers of oxidative stress (8-iso-PGF(2alpha), malondialdehyde, 8-oxo-7,8-dihydro-2'-deoxyguanosine, formamido pyrimidine glycosylase-sites, frequency of micronucleated erythrocytes, nitrotyrosine) and inflammatory markers (high sensitivity C-reactive protein (hsCRP), IL-6, cyclo-oxygenase-catalyzed PGF(2alpha)-metabolite) were measured. Fifty-six patients (thirty women and twenty-six men, age 62.3 (SD 7.0) years, HbA(1c) 6.1 (SD 0.9) %, BMI 28.3 (SD 3.8) kg/m(2), waist 99.6 (SD 11.1) cm) were included in the study. HbA(1c) (r 0.29, P=0.03) and blood glucose (r 0.33, P=0.01) correlated positively with 8-iso-PGF(2alpha). Positive correlations were also observed between HbA(1c) and nitrotyrosine (r 0.42, P=0.01), waist and hsCRP (r 0.37, P=0.005), hsCRP and IL-6 (r 0.61, P<0.0001) and between PGF(2alpha)-metabolite and 8-iso-PGF(2alpha) (r 0.27, P=0.048). The present study indicates that glycaemic status is associated with oxidative stress even in subjects with well-controlled type 2 diabetes. Furthermore, inflammation was more related to abdominal obesity than to glycaemic control. A large number of biomarkers of oxidative stress and inflammation were investigated, but only a few associations were found between the markers. This could be due to the fact that none of these biomarkers biosynthesises via similar pathways or simultaneously owing to their diverse nature and origin.

Down-regulation of oxidative DNA lesions in human mononuclear cells after antioxidant supplementation correlates to increase of gamma-tocopherol.

The protective effect of vitamin E supplements has been questioned, possibly because they often contain only alpha-tocopherol, and recent studies indicate that gamma-tocopherol also has important properties. The aim of this study was to investigate whether the levels of DNA lesions in middle-aged, overweight males could be reduced by consumption of low doses of an antioxidant supplement for six weeks, designed to imitate a balanced diet. The participants (n=60) were randomly divided into: placebo, single-, and double-dose groups. Genotoxic and oxidative DNA lesions in mononuclear cells were measured with the Comet assay, before and after supplement administration. Furthermore, a cell study was performed to investigate if pre-incubation of a human lung cell line (A549) with alpha- and gamma-tocopherol (5 and 50 microM for 23 hours) could protect against induced oxidative DNA lesions as measured by the Comet assay. The level of oxidative DNA lesions in the double-dose group was significantly lower than in the control group. Oxidative DNA lesions correlated only to changes in serum gamma-tocopherol, and not alpha-tocopherol. In the cell study, only gamma-tocopherol protected cells against induced oxidative DNA lesions. We therefore hypothesize that gamma-tocopheol rather than alpha-tocopherol is involved in reducing oxidative DNA lesions.

Oxidative stress and DNA damage caused by the urban air pollutant 3-NBA and its isomer 2-NBA in human lung cells analyzed with three independent methods.

The air pollutant 3-nitrobenzanthrone (3-NBA), emitted in diesel exhaust, is a potent mutagen and genotoxin. 3-NBA can isomerise to 2-nitrobenzanthrone (2-NBA), which can become more than 70-fold higher in concentration in ambient air. In this study, three independent methods have been employed to evaluate the oxidative stress and genotoxicity of 2-NBA compared to 3-NBA in the human A549 lung cell line. HPLC-EC/UV was applied for measurements of oxidative damage in the form of 8-oxo-2'-deoxyguanosine (8-oxodG), (32)P-HPLC for measurements of lipophilic DNA-adducts, and the Comet assay to measure a variety of DNA lesions, including oxidative stress. No significant oxidative damage from either isomer was found regarding formation of 8-oxodG analysed using HPLC-EC/UV. However, the Comet assay (with FPG-treatment), which is more sensitive and detects more types of damages compared to HPLC-EC/UV, showed a significant effect from both 3-NBA and 2-NBA. (32)P-HPLC revealed a strong DNA-adduct formation from both 3-NBA and 2-NBA, and also a significant difference between both isomers compared to negative control. These results clearly show that 2-NBA has a genotoxic potential. Even if the DNA-adduct forming capacity and the amount of DNA lesions measured with the (32)P-HPLC and Comet assay is about one third of 3-NBA, the high abundance of 2-NBA in ambient air calls for further investigation and evaluation of its health hazard.

Biomarkers of oxidative stress in overweight men are not influenced by a combination of antioxidants.

The effect of antioxidant supplementation on biomarkers of oxidative stress was investigated in a 6-week intervention study in 60 overweight men. The supplement contained a combination of antioxidants aiming to correspond to the antioxidant content found in a diet rich in fruit and vegetables. Placebo, single or double dose of antioxidants was provided to the subjects. Metabolic variables, plasma antioxidants and biomarkers of oxidative stress (lipid peroxidation and DNA damage) were measured. No effect of supplementation on biomarkers of oxidative stress was observed. Both intervention groups showed substantial increases of plasma antioxidants. This study demonstrated that supplementation with a combination of antioxidants did not affect lipid peroxidation and DNA damage in overweight men, despite increased concentrations of plasma antioxidants. The absence of antioxidant supplement effect might possibly be explained by the chosen study group having a normal level of oxidative stress, duration of the intervention and/or doses of antioxidants.