Correlation between age and DNA damage detected by FADU in human peripheral blood lymphocytes

Age dynamics of DNA damage and CpG methylation in the peripheral blood leukocytes of mice

Certain types of DNA damage are known to accumulate with age. Here we present the quantitative data describing the extent of the spontaneous DNA damage in 144 SHK mice of various ages. In each animal, we assessed double strand breaks, single strand breaks and alkali-labile sites, as well as amounts of oxidized purines, oxidized pyrimidines and misincorporated uracils. In addition, overall levels of genome DNA methylation were evaluated. The amounts of oxidized pyrimidines were correlated with age in males only, while the amounts of double strand breaks (DSB) in DNA samples were correlated with age in females only (R=0.26; p<0.035). No age-related accumulation of single-strand breaks (SSB) was observed. The hypomethylation of DNA was significant in aging females, but not in aging males. Various types of DNA damage were correlated to each other. In attempt to develop more stable indicator of age-dependent alterations in DNA, the DNA Damage Level Differential (DDLD) indices was developed for comet assaying of peripheral blood leukocytes. As expected, DDLD index was shown to be better correlated with age than any single quantitative measure reflecting certain type of DNA damage. A variability of effectiveness of various kinds of DNA repair in individual animals was larger than expected. This conclusion may have a substantial impact on subsequent studies of the mutagens and other kinds of environmental stressors in animal populations. Nor DDLD neither individual quantitative measures of DNA damage were capable of prediction post-sampling survival time.

Lifestyle impacts on the aging-associated expression of biomarkers of DNA damage and telomere dysfunction in human blood

Cellular aging is characterized by telomere shortening, which can lead to uncapping of chromosome ends (telomere dysfunction) and activation of DNA damage responses. There is some evidence that DNA damage accumulates during human aging and that lifestyle factors contribute to the accumulation of DNA damage. Recent studies have identified a set of serum markers that are induced by telomere dysfunction and DNA damage, and these markers showed an increased expression in blood during human aging. Here, we investigated the influence of lifestyle factors (such as exercise, smoking, body mass) on the aging-associated expression of serum markers of DNA damage (CRAMP, EF-1alpha, stathmin, n-acetyl-glucosaminidase and chitinase) in comparison with other described markers of cellular aging (p16(INK4a) upregulation and telomere shortening) in human peripheral blood. The study shows that lifestyle factors have an age-independent impact on the expression level of biomarkers of DNA damage. Smoking and increased body mass indices were associated with elevated levels of biomarkers of DNA damage independent of the age of the individuals. In contrast, exercise was associated with an age-independent reduction in the expression of biomarkers of DNA damage in human blood. The expression of biomarkers of DNA damage correlated positively with p16(INK4a) expression and negatively with telomere length in peripheral blood T-lymphocytes. Together, these data provide experimental evidence that both aging and lifestyle impact on the accumulation of DNA damage during human aging.

Determining the influence of telomere dysfunction and DNA damage on stem and progenitor cell aging: what markers can we use?

The decline in organ maintenance and function is one of the major problems limiting quality of life during aging. The accumulation of telomere dysfunction and DNA damage appears to be one of the underlying causes. Uncapping of chromosome ends in response to critical telomere shortening limits the proliferative capacity of human cells by activation of DNA damage checkpoints inducing senescence or apoptosis. Telomere shortening occurs in the vast majority of human tissues during aging and in chronic diseases that increase the rate of cell turnover. There is emerging evidence that telomere shortening can limit the maintenance and function of adult stem cells -- a cell type of utmost importance for organ maintenance and regeneration. In mouse models, telomere dysfunction leads to a depletion of adult stem cell compartments suggesting that stem cells are very sensitive to DNA damage. Both the rarity of stem and progenitor cells in adult organs and their removal in response to damage make it difficult to assess the impact of telomere dysfunction and DNA damage on stem and progenitor cell aging. Such approaches require the development of sensitive biomarkers recognizing low levels of telomere dysfunction and DNA damage in stem and progenitor cells. Here, we review experimental data on the prevalence of telomere dysfunction and DNA damage during aging and its possible impact on stem and progenitor cell aging.

Does metformin prevent short-term oxidant-induced dna damage? In vitro study on lymphocytes from aged subjects

Metformin(1-(diaminomethylidene)-3,3-dimethyl-guanidine), an anti-hyperglycemic agent, also has antioxidant effects. Although the origin is not clearly understood, the antioxidant activity of metformin might result from a direct effect on reactive oxygen species (ROS) or could have an indirect action on the superoxide anions produced by hyperglycemia. The ability of metformin to modulate DNA damage produced by oxidative stress is not known. For this reason, we examined the short term effect of metformin (50 microM, 2 h) on the DNA damage of cumene hydroperoxide (CumOOH)-induced lymphocytes from aged and young control groups (n = 10 each). In this study, DNA damage elicited by CumOOH (1 mM) was detected with the Comet Assay and the ELISA technique. Our results showed a significant increase in apoptotic DNA fragmentation and DNA strand breaks (Comet assay tail factor %) that was detected before and after CumOOH induction in lymphocytes of healthy elderly subjects when compared with healthy young control. Metformin significantly decreased CumOOH-induced apoptotic DNA fragmentation and DNA strand breaks in lymphocytes from aged subjects, although it did not produce a long-term effect. The in vitro results indicate that the short-term effect of metformin can protect against prooxidant stimulus-induced DNA damage in lymphocytes from elderly subjects.

Metformin does not prevent DNA damage in lymphocytes despite its antioxidant properties against cumene hydroperoxide-induced oxidative stress

Metformin (1-(diaminomethylidene)-3,3-dimethyl-guanidine), which is the most commonly prescribed oral antihyperglycaemic drug in the world, was reported to have several antioxidant properties such as the inhibition of advanced glycation end-products. In addition to its use in the treatment of diabetes, it has been suggested that metformin may be a promising anti-aging agent. The present work was aimed at assessing the possible protective effects of metformin against DNA-damage induction by oxidative stress in vitro. The effects of metformin were compared with those of N-acetylcysteine (NAC). For this purpose, peripheral blood lymphocytes from aged (n=10) and young (n=10) individuals were pre-incubated with various concentrations of metformin (10-50microM), followed by incubation with 15microM cumene hydroperoxide (CumOOH) for 48h, under conditions of low oxidant level, which do not induce cell death. Protection against oxidative DNA damage was evaluated by use of the Comet assay and the cytokinesis-block micronucleus technique. Changes in the levels of malondialdehyde+4-hydroxy-alkenals, an index of oxidative stress, were also measured in lymphocytes. At concentrations ranging from 10microM to 50microM, metformin did not protect the lymphocytes from DNA damage, while 50microM NAC possessed an effective protective effect against CumOOH-induced DNA damage. Furthermore, NAC, but not metformin, inhibited DNA fragmentation induced by CumOOH. In contrast to the lack of protection against oxidative damage in lymphocyte cultures, metformin significantly protected the cells from lipid peroxidation in both age groups, although not as effective as NAC in preventing the peroxidative damage at the highest doses. Within the limitations of this study, the results indicate that pharmacological concentrations of metformin are unable to protect against DNA damage induced by a pro-oxidant stimulus in cultured human lymphocytes, despite its antioxidant properties.

Enhanced Sensitivity to Oxidant-Induced Micronucleus Frequency in Elderly Individuals Is Not Associated with Glutathione S- Transferase M1 (GSTM1) Null Genotype in Lymphocytes

BACKGROUND

A large number of studies have demonstrated that various kinds of DNA damage accumulate during aging and that oxidative stress possibly contributes to this process. Glutathione S-transferase M1 (GSTM1) can prevent their possible effects on DNA via detoxification of reactive substances that induced oxidative stress.

OBJECTIVE

To investigate the relationship between GSTM1 polymorphism and DNA sensitivity to oxidative stress with age, we used micronucleus (MN) frequency as a marker of DNA damage in lymphocytes from young and elderly subjects.

METHODS

This study was performed in 30 young (age range 20-36 years) and 30 elderly (age range 66-87 years) healthy individuals who were chosen on the basis of their GSTM1 genotype (15 GSTM1 null and 15 GSTM1 positive for each group). Lymphocytes were cultured after Ficoll isolation and treated for 48 h with a 30-muM dose of cumene hydroperoxide (CumOOH), a dose that does not decrease cell viability.

RESULTS

There was no significant difference in the MN frequency observed in control cultures from young and elderly individuals. However, the MN frequency in CumOOH-treated cultures was significantly higher in the elderly group than the young group (p < 0.001). No association was found between the GSTM1 phenotype and CumOOH-induced MN frequency.

CONCLUSIONS

The results suggest that lymphocytes of elderly individuals are more susceptible to in vitro MN induction by CumOOH. However, this difference in susceptibility is not explained by the lack of GSTM1.

DNA damage and glutathione content in radiology technicians

BACKGROUND

We wanted to investigate the effect of X-rays on mononuclear blood cells (MNCs) and red blood cells (RBCs) of radiology technicians exposed to X-rays in hospital.

METHODS

DNA damage was detected by fluorometric analysis of DNA unwinding. Glutathione levels were measured with enzymatic method in mononuclear blood cells. Glutathione content and catalase (CAT) activity of erythrocytes, and plasma malondialdehyde (MDA) levels were determined by spectrophometric methods.

RESULTS

An insignificant increase in plasma malondialdehyde levels and a significant decrease in mononuclear blood cells glutathione levels were observed in nonsmoking radiology technicians. In smoking radiology technicians, on the other hand, in addition to an increase in plasma malondialdehyde levels, DNA damage was also significantly apparent. Besides mononuclear blood cells' glutathione depletion, the glutathione content of red blood cells was also found to be decreased.

CONCLUSION

It can be suggested that smoking seems to augment the toxic effects of radiation.

Protective action of copper (II) complex of a Schiff base against DNA damage induced by m-chloroperbenzoic acid using a novel DNA unwinding technique

DNA strand breaks can be detected with great sensitivity by exposing calf thymus DNA to alkaline solutions and monitoring the rate of strand unwinding. Fluorometric analysis of DNA unwinding (FADU) is a reliable method for detecting single-strand DNA breaks as an index of DNA damage induced by photosensitizer.m-Chloroperbenzoic acid (CPBA) was used as a photosensitizer in the photodamage of calf thymus DNA. When DNA is exposed to ionizing radiation, the radicals produced in the irradiated sample modify the base-pair regions of the double strands. The protective action of copper salt, Schiff base [ethylene diamine with ethyl acetate](L) and its Cu(II) complex (Cu(7) L Cl(14)) against DNA damage photoinduced by CPBA was studied using ethidium bromide as a fluorescent probe. Treatment of DNA with 5, 10, 50, 100, or 200 microM CPBA produced 75%, 48%, 38%, 32% and 30% double-stranded DNA remaining, respectively after 30 min of alkaline treatment at 15 degrees C. Treatment of calf thymus DNA irradiated with CPBA with a dose of 1 mM [Cu(7) L Cl(14)] produced 96% double-stranded remaining protection under the same conditions compared with irradiated DNA without addition of Cu(II) complex of Schiff base.

Reactive oxygen species and UV-B: effect on cyanobacteria

Reactive oxygen species (ROS) are involved in the damage and response of cyanobacteria to UV-B irradiation. In cyanobacteria, there are several targets for the potentially toxic ROS such as lipids, DNA and protein. The damage to photosynthetic apparatus induces the inhibition of photosynthesis that is mediated partially by ROS. UV-B-induced oxidative stress and oxidative damage increases with irradiation time and can be reversed after long-term irradiation. This raises the interesting question of whether cyanobacteria can acclimatize to the present UV-B stress. On one hand, ROS may also act as signal molecules and mediate the genetic regulation of photosynthetic genes and the induction of antioxidant enzymes. On the other hand, the efficient defense and repair system allows cyanobacteria to recover from the oxidative damage under moderate UV-B irradiation. In addition, the following methods are discussed: the fluorogenic probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), used to detect oxidative stress induced by UV-B; thiobarbituric acid reactive substances (TBARS), used to determine lipid peroxidation in cyanobacteria; fluorimetric analysis of DNA unwinding (FADU), used to quantify DNA strand breaks induced by ROS formation under UV-B stress.

Lymphocyte DNA damage in elevator manufacturing workers in Guangzhou, China

AIMS

To study the effect of smoking, passive smoking, alcohol drinking, and occupational exposure to low level of benzene on DNA strand breaks in elevator manufacturing workers in Guangzhou, China.

METHODS

Three hundred and fifty-nine workers (252 men and 107 women) of a modern elevator manufacturing factory, 205 were from production departments and 154 from managerial department. Information on the workers' health conditions, smoking, passive smoking, alcohol consumption and occupational exposure history was collected by personal interview. Lymphocyte DNA damage was measured by the Comet assay.

RESULTS

None of the women smoked and 20.6% of the men were daily smokers. In non-smokers, the prevalence of passive smoking at work was 25% for men and 11.2% for women, and at home, 37.8 and 48.6%, respectively. Smoking significantly increased tail moment (P<0.001). Daily smokers had the largest tail moment (geometric mean, 95% CI) (0.93 microm (0.81-0.94)), followed by occasional smokers (0.76 microm (0.59-0.95)), ex-smokers (0.70 microm (0.58-0.85)), and never smokers (0.56 microm (0.53-0.60)). Tail moment increased significantly with daily tobacco consumption (cigarettes per day) (r=0.26, P<0.001) after adjusting for age, gender, occupational exposure, passive smoking, and drinking. Analysis of covariance (ANCOVA) showed that smoking (P<0.001), passive smoking at home (P=0.026), occupational exposure (P<0.001), male gender (P<0.001), and age (P=0.001) had independent effects on tail moment, whereas passive smoking at work and alcohol drinking had no significant effect.

CONCLUSIONS

Smoking, passive smoking at home, male gender, age and occupational exposure independently increased lymphocyte DNA strand breaks. The presence of excess DNA damage under low level of occupational exposure to benzene or other solvents suggest that the current allowance concentrations may not be safe to prevent genotoxicity.

Microgels for estimation of DNA strand breaks, DNA protein crosslinks and apoptosis

This report describes a part of the evolution of microgel electrophoresis in the author's laboratory for the last 15 years. It also describes the importance of estimation of DNA single and double strand breaks, DNA crosslinks and apoptosis. Some experiments based on each methodology are included here. A new protocol for rapid and efficient precipitation of DNA in microgel is included. A step by step description of laboratory protocol is also included.

Lack of correlation between apoptosis and DNA single-strand breaks in X-irradiated human peripheral blood mononuclear cells in the course of ageing

The dependence on age of both the basal and the X-radiation-induced levels of apoptosis was examined in human peripheral blood mononuclear cells (PBMC). In the same samples, the base value and the extent of induced DNA single-strand breaks were determined, using a sensitive and fast microplate assay. PBMC were isolated from blood of donors of various age groups (20-30, 40-60 and > 70 years of age) and X-irradiated ex vivo using a 6 MV linear accelerator to give a total exposure of 4 Gy. The mean basal levels of apoptosis in PBMC from donors in the 40-60 year age group and the > 70 year age group were found to be only slightly higher (by 20-10%) compared to that of the 20-30 year age group, whereas the extent of DNA damage strongly and significantly (P < 0.01) increased with age by up to 2-fold. In contrast to the extent of induced DNA damage, which steadily increased in the course of ageing by up to 1.8-fold, there was only a transient increase in the level of induced apoptosis to 1.5-fold in PBMC from X-irradiated blood (4 Gy photons) from donors aged 40-60 followed by a decrease to 0.9-fold in PBMC from old donors (>70), compared to age group 20-30. The results show that X-ray-induced apoptosis and DNA damage in PBMC are not correlated during ageing.

Immunochemical detection of oxidative DNA damage in cancer and aging using anti-reactive oxygen species modified DNA monoclonal antibody

The formation of reactive oxygen species (ROS), although a normal cellular activity, is considerably enhanced under chronic inflammatory conditions and ischemia. These species have been implicated in various disorders, mutagenesis, carcinogenesis and aging. Of many macromolecules, DNA is the most susceptible to hydroxyl radical, the most reactive of the ROS. The present study is designed to detect oxidative DNA damage in cancer patients and healthy aged humans using an anti-ROS-DNA monoclonal antibody (mAb). Purified calf thymus DNA fragments (approximate size 400 bp) were modified with OH, generated by UV-irradiation (254 nm) of hydrogen peroxide. ROS-modified DNA was characterized by UV-spectroscopy, melting temperature, alkaline sucrose density gradient ultracentrifugation and ion-exchange chromatography. ROS-DNA showed single strand breaks, decrease in Tm, modification of thymine (58.3%) and guanine (20%). The mAb generated against ROS-DNA was characterized for antigen binding specificity by competition ELISA. Monoclonal antibody showed strong binding to ROS-modified DNA, its modified fragments, polynucleotides and bases. With the exception of native DNA, binding of unmodified polynucleotides and bases was much lower. The mAb distinctly recognized DNA samples from lymphocytes of healthy aged humans and gave maximum inhibitions of 49, 53, 64 and 70%, while not reacting with DNA from young population. Similarly, oxidative lesions in DNA from cancer patients were also efficiently recognized by the mAb. DNA from healthy controls served as negative control. The studies demonstrate that the mAb, although cross-reactive, preferentially binds ROS-modified epitopes on DNA. High reactivity of mAb to DNA samples from cancer patients and healthy aged humans indicates increased oxidative stress leading to DNA damage.

Application of the comet assay for monitoring DNA damage in workers exposed to chronic low-dose irradiation. I. Strand breakage

We examined a group of people professionally at risk of exposure to low doses of ionizing radiation (altogether 49 individuals). Age, use of therapeutic drugs, work-related exposure to hazardous agents, previous exposures to diagnostic X-rays, such as patient and nuclear medical examination, were registered. For each individual, the occupational radiation burden received over the past period of 5 years was taken from the official personal records based on film dosimetry controlled every month. A matched group of controls was chosen among the administrative employees (40 individuals). The mean age of the studied population at the time of blood sampling was 49 years (range 24-69). The individuals were divided into groups according to risk of exposure and sex. The alkaline comet assay was used to measure DNA breaks and alkali-labile sites. We compared the mean tail moments, tail length and percentage of DNA in the tail. There was a significant difference between the control and hazard groups in DNA damage. Higher DNA damage was also found for men than for women in the control group. There was no relation of DNA damage to age either in control or hazard group. Additionally, analysis of distributions of tail moment values pointed to a considerable individual diversity even in the control group. Therefore, further investigations were necessary into the suitability of the comet assay as a biological dosimetry method; the results obtained so far warrant such investigations.

Binding of circulating antibodies to reactive oxygen species modified-DNA and detecting DNA damage by a monoclonal antibody probe

Circulating antibodies in the sera of normal, healthy humans of different age groups to native DNA (nDNA) and reactive oxygen species modified DNA (ROS-DNA) was studied by competition ELISA. Sera from the young population (< 50 years of age) showed negligible levels of anti-DNA antibodies. In contrast, anti-DNA antibodies were found in three sera from the moderately aged group (50-59 years) with a high binding to ROS-DNA (43-47%). In the aged group (> 60 years), four sera showed higher recognition of ROS-DNA (> 60% inhibition) over nDNA (55-60%). Oxidative lesions in human genomic DNA were immunochemically detected using the monoclonal anti-ROS-DNA antibody as a probe. The antibody has a high specificity for ROS-DNA and preferentially recognizes ROS-modified epitopes on nucleic acids. The study indicates low recognition of DNA isolated from the younger population, while in the age group 50-59 years, one DNA isolate showed a high inhibition (57%) in monoclonal antibody binding. Four DNA isolates from the aged group showed substantial inhibition in antibody activity to the extent of 49, 53, 64 and 69%. The results demonstrate an age-related increase in the levels of anti-DNA antibodies, with a higher recognition and binding to ROS-DNA. A high reactivity of DNA isolated from aged individuals by the monoclonal antibody indicates increased oxidative stress leading to DNA damage. It is suggested that free radical damage to DNA in vivo, particularly in the aged, alters its antigenicity and stimulates an immune response against modified DNA. These antibodies are cross-reactive to nDNA.