Differences In Levels Of DNA Damage Research Articles

DNA strand breaks in peripheral blood leucocytes of Polish blood donors.

Knowledge about the basal level of DNA damage in leucocytes of healthy control populations is essential before estimation of the effects of exposure to external agents in biomonitoring studies. The aim of this study was to analyse the effects of some lifestyle factors on baseline DNA damage in leucocytes of humans. The material consisted of the peripheral blood from 276 healthy volunteer blood donors. In addition to the standard blood donation questionnaire, they were asked about age, gender, occupation, radiological history, smoking habit, alcohol consumption, medicine use and pet ownership. The results showed marked intra-individual variability. Significant differences in DNA damage levels were observed between individuals in different age and sex groups, between smokers and non-smokers and between samples taken in different seasons of the year, with the highest DNA damage in those obtained in the summer. Significantly higher levels of DNA damage were noted in leucocytes of donors older than 29 years, in men compared with women and in male smokers. Significantly higher DNA strand breaks were observed in heavy smokers. A non-significantly higher level of DNA damage was observed in individuals subjected to radiological investigation and in those drinking alcohol, whereas lower levels were observed in leucocytes of pet owners and in donors taking medicines. Pet ownership influences the level of DNA damage and there is an interaction between this effect and that of smoking. The smoker/pet owners showed almost half the level of DNA damage of smokers without pets. The current results confirmed high intra-individual variability between the levels of DNA damage of individuals. The significant factors that influence the DNA damage in leucocytes are age, sex and smoking habit, especially in men and in heavy smokers. The finding of reduced DNA damage in the leucocytes of pet owners suggests the tendency towards a beneficial effect of such company.

Controlled exposure to diesel exhaust and traffic noise – Effects on oxidative stress and activation in mononuclear blood cells

Particulate air pollution increases risk of cancer and cardiopulmonary disease, partly through oxidative stress. Traffic-related noise increases risk of cardiovascular disease and may cause oxidative stress. In this controlled random sequence study, 18 healthy subjects were exposed for 3h to diesel exhaust (DE) at 276μg/m3 from a passenger car or filtered air, with co-exposure to traffic noise at 48 or 75dB(A). Gene expression markers of inflammation, (interleukin-8 and tumor necrosis factor), oxidative stress (heme oxygenase (decycling-1)) and DNA repair (8-oxoguanine DNA glycosylase (OGG1)) were unaltered in peripheral blood mononuclear cells (PBMCs). No significant differences in DNA damage levels, measured by the comet assay, were observed after DE exposure, whereas exposure to high noise levels was associated with significantly increased levels of hOGG1-sensitive sites in PBMCs. Urinary levels of 8-oxo-7,8-dihydro-2′-deoxyguanosine were unaltered. In auxiliary ex vivo experiments whole blood was incubated with particles from the exposure chamber for 3h without effects on DNA damage in PBMCs or intracellular reactive oxygen species production and expression of CD11b and CD62L adhesion molecules in leukocyte subtypes. Conclusion3-h exposure to DE caused no genotoxicity, oxidative stress or inflammation in PBMCs, whereas exposure to noise might cause oxidatively damaged DNA.

Both genetic and dietary factors underlie individual differences in DNA damage levels and DNA repair capacity

The interplay between dietary habits and individual genetic make-up is assumed to influence risk of cancer, via modulation of DNA integrity. Our aim was to characterize internal and external factors that underlie inter-individual variability in DNA damage and repair and to identify dietary habits beneficial for maintaining DNA integrity. Habitual diet was estimated in 340 healthy individuals using a food frequency questionnaire and biomarkers of antioxidant status were quantified in fasting blood samples. Markers of DNA integrity were represented by DNA strand breaks, oxidized purines, oxidized pyrimidines and a sum of all three as total DNA damage. DNA repair was characterized by genetic variants and functional activities of base and nucleotide excision repair pathways. Sex, fruit-based food consumption and XPG genotype were factors significantly associated with the level of DNA damage. DNA damage was higher in women (p=0.035). Fruit consumption was negatively associated with the number of all measured DNA lesions, and this effect was mediated mostly by β-cryptoxanthin and β-tocopherol (p<0.05). XPG 1104His homozygotes appeared more vulnerable to DNA damage accumulation (p=0.001). Sex and individual antioxidants were also associated with DNA repair capacity; both the base and nucleotide excision repairs were lower in women and the latter increased with higher plasma levels of ascorbic acid and α-carotene (p<0.05). We have determined genetic and dietary factors that modulate DNA integrity. We propose that the positive health effect of fruit intake is partially mediated via DNA damage suppression and a simultaneous increase in DNA repair capacity.

The influence of the number of cells scored on the sensitivity in the comet assay

The impact on the sensitivity of the in vitro comet assay by increasing the number of cells scored has only been addressed in a few studies. The present study investigated whether the sensitivity of the assay could be improved by scoring more than 100 cells. Two cell lines and three different chemicals were used: Caco-2 cells were exposed to ethylmethane sulfonate and hydrogen peroxide in three concentrations, and HepG2 cells were exposed to ethylmethane sulfonate, hydrogen peroxide and benzo[a]pyrene in up to four concentrations, in four to five independent experiments. The scoring was carried out by means of a fully automated scoring system and the results were analyzed by evaluating the % tail DNA of 100–700 randomly selected cells for each slide consisting of two gels. By increasing the number of cells scored, the coefficients of variance decreased, leading to an improved sensitivity of the assay. A two-way ANOVA analysis of variance showed that the contribution from the two variables “the number of cells scored” and “concentration” on the total variation in the coefficients of variance dataset was statistically significant (p<0.05). The increase in sensitivity was demonstrated by the possibility to detect an increase in % tail DNA with statistical significance at lower concentrations. The results indicated that for low levels of DNA damage, below 9% tail DNA, scoring of 600 cells increased the sensitivity compared with scoring of 100 cells. For relatively low levels of DNA damage, about 9–16% tail DNA, scoring of 300 cells increased the sensitivity. Thus, the recommendation for the optimum number of cells scored would be 600 and 300 for low and relatively low levels of DNA damage, respectively. The findings from this study could be particularly important for bio-monitoring studies where small differences in DNA-damage levels could be relevant.

Toxic vents and DNA damage: first evidence from a naturally contaminated deep-sea environment

Levels of DNA strand breakage were measured, using the comet assay, in cells from vent mussels, Bathymodiolus azoricus, from three contrasting vent fields on the mid Atlantic Ridge. Different levels of DNA damage were recorded in untreated mussels, shortly after collection, and it was animals from the shallowest, and less active, Menez Gwen vent field (840-m depth), which showed the greatest amount of damage. In contrast to animals from two deeper and putatively more toxic sites, Menez Gwen animals went on to repair this damage and were able to survive under laboratory conditions at 1 bar pressure for several months. Animals from the two deeper sites showed both higher levels of initial mortality and a much reduced capacity for survival at 1 bar. The differences in DNA damage levels at the time of collection were interpreted as an expression of differences in cell viability/enzyme activity rather than a reflection of any differences in their natural environmental conditions. Small B. azoricus showed a capacity to repair DNA damage, whereas this ability appeared to be lacking in large individuals. By reproducing at a relatively early age, the deep-sea vent fauna may be able to resist the toxic effects of its environment by exploiting this natural, stage specific capacity to repair damaged DNA.

A cross-sectional study of polycyclic aromatic hydrocarbon-DNA adducts and polymorphism of glutathione S-transferases among heavy smokers by race/ethnicity

Differences in lung cancer risk by race/ethnicity have been observed among smokers. To determine whether these observations might reflect differences in the formation of carcinogen-DNA adducts, we analysed blood specimens (n =151) collected from smokers who were recruited for possible participation in an antioxidant vitamin intervention study. Mononuclear cells were analysed for polycyclic aromatic hydrocarbon (PAH)-DNA adducts by competitive enzyme-linked immunosorbent assay. Genotypes of glutathione S-transferase M1 and P1 (GSTM1 and GSTP1), enzymes involved in the detoxification of PAH metabolites, were determined by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism, respectively. GSTM1 was present in 65 out of 88 (73.4%), 16 out of 32 (50.0%) and 16 out of 29 (54.8%) of African-Americans, Caucasians and Latinos, respectively (p =0.022). Homozygosity for the GSTP1 codon 105 variant was found in 25.6%, 6.3% and 10.0% of African-Americans, Caucasians and Latinos, respectively (p =0.023). Regression analysis of the log-transformed adduct levels confirmed that Caucasian and Latino subjects had lower PAH-DNA adduct levels than African-American subjects, after adjustment for gender, education,α -tocopherol and β-carotene levels, and GSTM1 status. Further adjustment for age and current smoking habits had no impact on these findings. Although crude analysis suggested that the GSTM1-positive genotype may be associated with lower PAH-DNA levels in Caucasians (but not in African-Americans or Latinos), a formal test for interaction between GSTM1 and ethnicity was not significant. We found no association between adduct levels and GSTP1 genotype. Although the mechanism is unclear, ethnic differences in DNA damage levels may in part explain why African-Americans have higher lung cancer incidence rates than other ethnic groups.

Single cell gel electrophoresis on peripheral blood leukocytes of patients with oral squamous cell carcinoma.

The single cell gel electrophoresis (SCGE) assay, also known as the comet assay, is a cytogenetic technique for measuring and analyzing DNA single stranded breaks (SSB) and/or alkali labile sites within individual cells. Peripheral blood leukocytes of 22 oral squamous cell carcinoma (OSCC) patients were subjected to SCGE and the DNA damage levels (SSB) were quantified with respect to clinical staging and histopathologic grading. Highly statistically significant differences in DNA damage levels were found between normal subjects and patients with OSCC of the same age group. DNA damage levels were altered in all clinical stages and histopathological grades of oral squamous cell carcinoma. The differences were generally significant between all the clinical stages of OSCC, while in histopathologic grading the results were significant only between grades I and III. The results support the concept of a systemic host response in malignancy.