Ex vivo time-dependent cell DNA-degradation shown by single cell gel electrophoresis

Effect of chemopreventive compounds from Brassica vegetables on NAD(P)H:quinone reductase and induction of DNA strand breaks in murine hepa1c1c7 cells

We have compared the effects of aqueous extracts of cooked Brussels sprouts, isolated glucosinolates and their breakdown products on the activity of quinone reductase [NADPH:quinone-reductase] (QR) and on DNA strand breaks induced by hydrogen peroxide in murine hepa1c1c7 cells. QR activity was not significantly altered after incubation of the cells with Brussels sprouts extracts. However, some of the glucosinolates and in particular their myrosinase-catalysed hydrolysis products and the degradation product of indole-glucosinolates, indole-3-carbinole (I3C), di(indol-3-yl)-methane (DIM) and 2,3-bis(indol-3-ylmethyl)indole (TRI) effectively induced QR activity. Isolated isothiocyanates did not influence the QR activity. The extracts of cooked and autolysed Brussels sprouts and some glucosinolates inhibited the DNA strand breaks induced by 100 microM hydrogen peroxide. Maximum inhibition was by 20-38% after 24 h of preincubation. Hydrolysis of the glucosinolates by myrosinase decreased the inhibitory effects, whereas I3C, DIM or TRI had no effect on DNA damage. Accordingly, the protective effect of Brussels sprouts constituents against induction of oxidative DNA damage appears to be unrelated to enzyme inducing properties via the antioxidant responsive element. Both of these effects could be part of the suggested cancer preventive effect of cruciferous vegetables.

Oxidative DNA damage: biological significance and methods of analysis

All forms of aerobic life are subjected constantly to oxidant pressure from molecular oxygen and also reactive oxygen species (ROS), produced during the biochemical utilization of O2 and prooxidant stimulation of O2 metabolism. ROS are thought to influence the development of human cancer and more than 50 other human diseases. To prevent oxidative DNA damage (protection) or to reverse damage, thereby preventing mutagenesis and cancer (repair), the aerobic cell possesses antioxidant defense systems and DNA repair mechanisms. During the last 20 years, many analytical techniques have been developed to monitor oxidative DNA base damage. High-performance liquid chromatography-electrochemical detection and gas chromatography-mass spectrometry are the two pioneering contributions to the field. Currently, the arsenal of methods available include the promising high-performance liquid chromatography-tandem mass spectrometry technique, capillary electrophoresis, 32P-postlabeling, fluorescence postlabeling, 3H-postlabeling, antibody-base immunoassays, and assays involving the use of DNA repair glycosylases such as the comet assay, the alkaline elution assay, and the alkaline unwinding method. Recently, the use of liquid chromatography-mass spectrometry has been introduced for the measurement of a number of modified nucleosides in oxidatively damaged DNA. The bulk of available chromatographic methods aimed at measuring individual DNA base lesions require either chemical hydrolysis or enzymatic digestion of oxidized DNA, following extraction from cells or tissues. The effect of experimental conditions (DNA isolation, hydrolysis, and/or derivatization) on the levels of oxidatively modified bases in DNA is enormous and has been studied intensively in the last 10 years.

BIOMarkers for occupational diesel exhaust exposure monitoring (BIOMODEM)--a study in underground mining

Methods for the assessment of exposures to diesel exhaust were evaluated, including various biomarkers of internal exposure and early biological effects. The impact of possible biomarkers of susceptibility was also explored. Underground workers (drivers of diesel-powered excavators) at an oil shale mine in Estonia were compared with surface workers. Personal exposures to particle-associated 1-nitropyrene (NP) were some eight times higher underground than on the surface. Underground miners were also occupationally exposed to benzene and polycyclic aromatic hydrocarbons, as indicated by excretion of urinary metabolites of benzene and pyrene. In addition, increased O(6)-alkylguanine DNA adducts were detected in the white blood cells of underground workers, suggesting higher exposure to nitroso-compounds. However, no differences between underground and surface workers were observed in the levels of other bulky DNA adducts determined by 32P-postlabelling, or in DNA damage. The study indicated that smoking, diet and residential indoor air pollution are important non-occupational factors to consider when interpreting biomonitoring results.

Effects of Brussels sprouts extracts on hydrogen peroxide-induced DNA strand breaks in human lymphocytes

Aqueous Brussels sprouts extracts inhibit oxidation of isolated DNA in vitro, possibly through scavenging oxygen radicals. We have studied the effect of preincubating human lymphocytes with aqueous extracts of raw, cooked and autolysed Brussels sprouts and the glucosinolate, sinigrin, on hydrogen peroxide-induced DNA damage, strand breaks and base oxidation, in vitro by means of the Comet assay. DNA repair enzymes endonuclease III (EndoIII) and formamidopyrimidine-DNA glycosylase (FPG) were used to examine the levels of oxidised pyrimidines and purines in DNA, respectively. Aqueous extracts of cooked and autolysed Brussels sprouts and sinigrin decreased DNA strand breaks in human lymphocytes exposed to 100 microM H2O2 for 5 min on ice, although the level of EndoIII and FPG sensitive sites was not reduced. The maximum inhibition was by 38 and 39% at concentrations of cooked and autolysed extracts of 10 microg/ml and 5 microg/ml, respectively, whereas the inhibitory effect decreased with increasing concentrations up to 100 microg/ml. The maximum inhibition by sinigrin was by 54% at 2 microg/ml. Extracts of raw Brussels sprouts or green beans had no DNA-protective effect. The results indicate that compounds, including sinigrin, in cooked and autolysed Brussels sprouts can enhance lymphocyte resistance towards H2O2-induced DNA strand breaks in vitro.

Diversity of peripheral blood mononuclear cells as revealed by a novel multiple microgel "comet assay"

Multiple microgel comet assay (MMCA) is a metho-dological adaptation of the single-cell gel electrophoresis assay in which we have introduced the use of standard agarose plug molds in an attempt to improve and expand the applications of the assay. We focused on the study of the heterogeneity of peripheral blood mononuclear cells (PBMC) at the level of the basal single-strand breakage and the DNA damage induction caused by ionizing radiation. Differences among subpopulations were also investigated at the level of chromatin organization and methylation after NotI digestion of microgel-embedded cells. In parallel experiments, the NotI-digested nucleoids were also analyzed with the use of pulsed-field gel electrophoresis (PFGE) and the DNA migration patterns were compared with the corresponding patterns from the MMCA. Significant heterogeneity in the distribution of the oxidative DNA damage, as well as intracellular variations in the NotI digestion patterns were observed in the cell population of PBMC. The combined use of both the comet assay and PFGE provides a useful model for analysis of variation in DNA damage in individual cells as well as information on size of DNA fragments.

Methods to detect DNA damage by free radicals: relation to exercise

Epidemiological investigations repeatedly show decreased morbidity from regular exercise compared with sedentary life. A large number of investigations have demonstrated increased oxidation of important cellular macromolecules, whereas other investigators have found no effects or even signs of lowering of oxidation of macromolecules. In particular, extreme and long-duration strenuous exercise appears to lead to deleterious oxidation of cellular macromolecules. The oxidation of DNA is important because the oxidative modifications of DNA bases, particularly the 8-hydroxylation of guanine, are mutagenic and have been implicated in a variety of diseases such as ageing and cancer. The methodologies for further investigation of the relationship between DNA oxidation and exercise are available. The preferred methods rely on HPLC or GC-mass spectrometry; whereas the theoretically-attractive liquid chromatography-tandem mass spectrometry is being developed. Caution should be taken to avoid artifacts because of the six orders of magnitude of difference between oxidized and non-oxidized DNA bases in tissues. The methods can be used to estimate tissue levels, i.e. a local concentration of oxidized DNA, or to estimate the rate of body DNA oxidation by the urinary output of repair products, the latter being a method that is independent of repair. During exercise there appears to be a shifting of dietary-dependent antioxidant, e.g. vitamin C and vitamin E, from muscle to plasma, and an increased oxidation in plasma of these antioxidants. Supplementation trials with antioxidants have not been able to increase exercise performance; however, optimum nutrition with antioxidants and possibly supplementation, could be important in the prevention of diseases in the long term. The pattern from these observations appears to be quite consistent; immediately after exercise, regardless of how intense, there do not appear to be any signs of oxidative damage to DNA. Acute or prolonged moderate exercise does not produce signs of oxidative DNA damage and might even be associated with lowering of the levels of oxidation of tissue DNA; however, after long-duration and intense exercise an increase in oxidative DNA modifications is apparent. We suggest as a hypothesis that the relationship between exercise and health is U-shaped. This hypothesis needs to be tested in detail in order to establish the maximum beneficial exercise level with regard to oxidative DNA modification, and also the level that could be deleterious and might even increase the risk for cancer and other diseases.

Detection of influenza virus induced DNA damage by comet assay

Influenza virus A2/HK/68 is known to be a biological mutagen and teratogen. Reports are available implicating influenza virus as a causative agent of chromosomal aberrations in cells in culture and also in circulating leukocytes of humans. Also, an increased incidence of abortions, prenatal mortality and congenital abnormalities during the periods of epidemics has also been reported. In view of these reports, it would be worthwhile to screen persons especially pregnant women exposed to influenza virus for possible DNA damage. The present study reports the use of Comet assay to measure influenza virus induced DNA damage. We have carried out in vitro infection experiments using human leukocytes. Our results clearly indicate that influenza virus A2/HK/68 induces DNA damage in leukocytes right from 2-h post-infection. Maximum damage was observed at 24-h post-infection. However, at 48-h post-infection, a slight decrease was observed which can be attributed to the DNA repair occurring in the cells. Thereafter, irreparable damage was noticed. Cell viability results have shown lack of cytotoxicity till 72-h post-infection. However, significant cytotoxicity was observed only at 96-h post-infection. The occurrence of DNA damage without cell death may result in chromosomal aberrations or mutations. Therefore, it is most advisable to get screened for the possible DNA damage especially persons frequently infected with influenza and pregnant women.

Enhanced benzene-induced DNA damage in PMA-stimulated cells in vitro and in LPS-treated animals

The present study investigated the interaction between inflammatory reactions and benzene in vitro and in vivo with respect to oxidative DNA damage. In the in vitro models the oxidative burst of cells was induced by the pretreatment with phorbol myristate acetate (PMA) and in the in vivo models of inflammation mice were pretreated with lipopolysaccharide (LPS). The oxidative DNA damage was indicated by 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and strand breaks as assessed by alkaline single cell gel electrophoresis (SCGE, Comet assay). The results showed that combination of PMA and benzene enhanced the level of 8-oxodG in DNA from mouse bone marrow cells by 197%, from human lymphocytes by 188% and from human neutrophils by 205% (p < .05). Pretreatment of mice with LPS and benzene resulted in an enhanced Comet score formation in bone marrow cells by 98% and in lymphocytes by 39% in Comet score (p < .05) and in an enhanced 8-oxodG level in bone marrow cells by 290%. The effects of the combined treatment with PMA/LPS and benzene exceeded the sum of the effects induced by PMA/LPS or benzene alone. The production of nitrate/nitrite showed a two fold increase in the supernatant from incubation of benzene and PMA-pretreated neutrophils. The increase in the 8-oxodG level in the human neutrophil incubation system demonstrated a correlation with nitrate/nitrite production, indicating a possible relationship with the generation of reactive nitrogen species.

Dexamethasone ameliorates oxidative DNA damage induced by benzene and LPS in mouse bone marrow

Mice were grouped to receive vehicle, dexamethasone (DEX), lipopolysaccharide (LPS), benzene (BZ, 200 mg/kg) and combinations: LPS + DEX, BZ + DEX, LPS + BZ, LPS + DEX + BZ. The DNA damage in bone marrow cells from BZ group was enhanced 2.8-fold measured by nuclear 8-hydroxy-2 '-deoxyguanosine (8-oxodG) and 1.4-fold measured by Comet score (index of DNA breaks) (p < 0.05). In the BZ + DEX group, 8-oxodG level and the Comet score were lowered to 65% and 76% respectively of that in the BZ group (p < 0.05). The BZ + LPS caused a 3.9-fold increase in 8-oxodG and a 1.6-fold increase in the Comet score (p < 0.05). The LPS + DEX + BZ lowered 8-oxodG level and the Comet score to 50% and 78% of the values in the LPS + BZ group, respectively (p < 0.05). Nitrate/nitrite levels in serum were higher after BZ + LPS treatment than after all other treatments. Both 8-oxodG level and the Comet scores were correlated to the serum nitrate/nitrite level across all the treatments (r = 0.55, p < 0.01 and r = 0.69, p < 0.01, respectively). In bone marrow cells the 8-oxodG correlated with the Comet scores (r = 0.80, p < 0.01). We conclude that DEX administration can reduce the DNA damage from BZ treatment and from the combination of BZ and LPS. The correlation of DNA damage with nitrate/nitrite indicates the possible involvement of reactive nitrogen species (RNS) in the interaction between BZ and the inflammatory reaction stimulated by LPS. The 8-oxodG determination is more sensitive than strand break analysis by the Comet assay in bone marrow in vivo in mice for measuring the BZ-induced DNA damage.

2-Nitropropane-induced DNA damage in rat bone marrow

DNA damage detected by the comet assay (single cell gel electrophoresis) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation in DNA in the bone marrow has been studied in groups of 6 male Wistar rats treated with a single i.p. injection of the carcinogen 2-nitropropane (2-NP, 100 mg/kg body weight) or vehicle. Twenty-four hours after 2-NP the average tail length in the comet assay in bone marrow cells was increased from 1.46 +/- 0.27 to 9.61 +/- 1.56 microm (mean /- SD, p < 0.01), and 8-oxodG levels in the DNA were increased from 1.04 +/- 0.50 to 5.14 +/- 2.42 per 10(5) dG (p < 0.01). There was a close correlation between the comet tail length and the 8-oxodG level (r = 0.89, p < 0.05). The results indicate that 2-NP inflicts DNA damage in the bone marrow cells and thus could be leukemogenic.