DNA damage in exfoliated buccal cells of smokers assessed by the single cell gel electrophoresis assay

The effect of smoking and eating habits on DNA damage in Indian population as measured in the Comet assay

This study was undertaken with the aim of assessing the status of DNA damage in a normal healthy Indian population. The 62 male volunteers in this study belonged to the smoking, non-smoking, vegetarian and non-vegetarian categories, were well educated and aged between 23 and 57 years. The data revealed significant differences in the extent of DNA damage in the smokers versus non-smokers as well as between the vegetarians and non-vegetarians. A significant difference was also observed amongst the different groups of smokers depending on the extent of smoking. An age-dependent effect in DNA damage was also observed. This preliminary study has, for the first time, revealed differences in the extent of DNA damage in the normal Indian population depending on their eating and smoking habits as well as age.

Single cell gel electrophoresis assay: a new technique for human biomonitoring studies

Human biomonitoring using the single cell gel electrophoresis (SCGE) or comet assay is a novel approach for the assessment of genetic damage in exposed populations. This assay enables the detection of various forms of DNA damage in individual cells with ease and speed and is, therefore, well suited to the analysis of a large group in a population. Here, application of SCGE assay in the identification of dietary protective factors, in clinical studies and in monitoring the risk of DNA damage resulting from occupational, environmental or lifestyle exposures is reviewed. Also, the comparative sensitivity of SCGE assay and conventional cytogenetic tests to detect genetic damage is discussed. Finally, strengths and shortcomings of the SCGE assay are addressed.

Evaluation of DNA damage in exfoliated tear duct epithelial cells from individuals exposed to air pollution assessed by single cell gel electrophoresis assay

The search for relevant target cells for human monitoring purposes has increased during the last few years. Cells such as sperm, buccal or nasal and gastric epithelium are being used. In this study, we report the use of exfoliated tear duct epithelial cells as a potential material for human biomonitoring studies, since these cells are a target for environmental pollutants. We employed the alkaline single cell gel electrophoresis (SCGE) assay to evaluate for differences in the basal level of DNA damage between young adults from the south (exposed mainly to high levels of ozone) and from the north (exposed principally to hydrocarbons) regions of Mexico City. We found an increase in DNA migration in tear duct epithelial cells from individuals who live in the southern part of the city compared to those living in the northern part. Moreover, young people who live in the southwest part of the city with the highest values of ozone presented the highest values of DNA damage. These results show the feasibility of using exfoliated tear duct epithelial cells in human biomonitoring studies.

Laryngeal mucosa of head and neck cancer patients shows increased DNA damage as detected by single cell microgel electrophoresis

Major risk factors for cancer of the oral cavity, pharynx and larynx are smoking and excess alcohol consumption. Since long-term survival rates of head and neck cancer patients have not substantially been improved, new preventive strategies including the use of cancer chemopreventive agents have to be developed. With the aim of developing biomarkers which can verify the efficacy of chemopreventive interventions, a standardised alkaline microgel electrophoresis (MGE) assay was applied as a sensitive and rapid tool to detect DNA damage on a single cell level. Macroscopically normal laryngeal mucosa biopsies obtained by surgery from head and neck cancer patients (n=29) and from hospital controls (n=22) were analysed by MGE in a pilot study. As compared to controls, cells from head and neck cancer patients showed a significantly elevated DNA damage without any further genotoxic treatment (P<0.01). We conclude that this increased background DNA damage in laryngeal epithelia could result from genetic alterations caused by smoking and alcohol leading, in accord with the field cancerisation hypothesis, to a gradual decrease of genomic stability and malignancy. MGE should now be explored as a rapid screening method in larger clinical studies: (i) to identify high-risk subjects carrying cells with decreased genomic stability and (ii) to verify the efficacy of chemopreventive regimens to prevent or slow down the development of head and neck cancer in high-risk persons.

Lack of adverse effect of smoking habit on DNA strand breakage and base damage, as revealed by the alkaline comet assay

In our preceding papers [M. Wojewódzka, M. Kruszewski, T. Iwanenko, A.R. Collins, I. Szumiel, Application of the comet assay for monitoring DNA damage in workers exposed to chronic low dose irradiation: I. Strand breakage, Mutat. Res., 416 (1998) 21-35; M. Kruszewski, M. Wojewódzka, T. Iwanenko, A.R. Collins, I. Szumiel, Application of the comet assay for monitoring DNA damage in workers exposed to chronic low dose irradiation: II. Base damage, Mutat. Res. , 416 (1998) 37-57.], we evaluated the DNA breakage and base damage with the use of comet assay in a group of 49 workers chronically exposed to low doses of ionizing radiation. There was a statistically significant difference in the damage levels between the hazard and control group. In this paper we describe a confounding lack of effect of the smoking habit on the DNA damage in the tested groups. The genotoxic effect of the smoking habit, as well as its modifying effect on genome damage inflicted by other agents, have been firmly established. However, no statistically significant effect of smoking was found in our study, neither in the control nor in the hazard group. This lack of effect was seen in all DNA damage determinations, both direct (DNA strand breakage and alkali-labile lesions) and enzyme-combined (base damage) and did not depend on the comet parameters, which were taken as damage indicators.

Single cell gel electrophoresis assay: methodology and applications

The single cell gel electrophoresis or Comet assay is a sensitive, reliable, and rapid method for DNA double- and single-strand breaks, alkali-labile sites and delayed repair site detection, in eukaryotic individual cells. Given its overall characteristics, this method has been widely used over the past few years in several different areas. In this paper we review the studies published to date about the principles, the basic methodology with currently used variations. We also explore the applications of this assay in: genotoxicology, clinical area, DNA repair studies, environmental biomonitoring and human monitoring.

Biomonitoring using accessible human cells for exposure and health risk assessment

A major goal for genetic toxicologist is to provide precise information on exposure and health risk assessment for effective prevention of health problems. A frequently used approach for population study has been to utilize readily available blood cells (lymphocytes and red blood cells) as sentinel cell types to detect biological effects from exposure and to provide early warning signals for health risk. However, such approach still cannot be used reliably for developing strategies in risk assessment and disease prevention. It is possible that other available cell types which are more representative of the target cells for disease may be used to overcome the deficiency. In this report, the use of non-blood cells for biomonitoring is briefly reviewed. Their usefulness in certain exposure condition is highlighted and their effectiveness in documenting exposure compared with other cell types such as the traditional blood cells is presented. It is obvious that the decision in using these non-blood cells in biomonitoring is based on the exposure condition and the experimental design. Nevertheless, monitoring studies using non-blood cells should be encouraged with emphasis on providing dose-response information, comparative response with other cell types and effectiveness for health risk assessment.

Molecular epidemiology in cancer research

The use of molecular biomarkers in epidemiological investigations brings clear advantages of economy, speed and precision. Epidemiology--the study of the factors that control the patterns of incidence of disease--normally requires large numbers of subjects and/or long periods of time, because what is measured (the occurrence of disease) is a rare event. Biomarkers are measurable biological parameters that reflect, in some way, an individual's risk of disease-because they indicate exposure to a causative (or protective) agent, or because they represent an early stage in development of the disease, or because they allow an assessment of individual susceptibility. Biomarkers must be usable on one of the few materials available for biomonitoring of humans, i.e. blood, urine, exfoliated epithelial cells and, with some difficulty, biopsies. The approach of molecular epidemiology has a great potential is several areas of cancer research: investigating the aetiology of the disease; monitoring cancer risk in people exposed to occupational or environmental carcinogens; studying factors that protect from cancer; and assessing intrinsic factors that might predispose to cancer. The biomarkers most commonly employed in cancer epidemiology include: measurements of DNA damage--DNA breaks, altered bases, bulky adducts--in lymphocytes; the surrogate marker of chemical modifications to blood proteins, caused by agents that also damage DNA; the presence of metabolites of DNA-damaging agents (or the products of DNA damage themselves) in urine; chromosome alterations, including translocations, micronuclei and sister chromatid exchange, resulting from DNA damage; mutations in marker genes; DNA repair; and the differential expression of a variety of enzymes, involved in both activation and detoxification of carcinogens, that help to determine individual susceptibility. The molecular approach has been enthusiastically employed in several studies of occupational/environmental exposure to carcinogens. While the estimation of biological markers of exposure has certainly shown the expected effects in terms of DNA damage and adducts, the detection of the biological effects of exposure (e.g. at the level of chromosome alterations) has not been so clear-cut. This is true also when smokers are examined as a group compared with non-smokers. Several markers (especially of chromosome damage and mutation) show a strong correlation with age-indicating either an increasing susceptibility to damage with age, or an accumulation of long-lived changes. DNA repair--a crucial player in the removal of damage before it can cause mutation--may vary between individuals, and may be modulated by intrinsic or extrinsic factors, but limited data are available because of the lack of a reliable assay. Information on other enzymes determining individual susceptibility does exist, and some significant effects of phenotypic or genotypic polymorphisms have emerged, although the interactions between various enzymes make the situation very complex. The important question of whether oxidative DNA damage in normal cells is decreased by dietary antioxidants (vitamin C, carotenoids etc., from fruit and vegetables) has been tackled in antioxidant supplementation experiments. The use of poorly validated assays for base oxidation has not helped us to reach a definitive answer; it seems that, in any case, the level of oxidative damage has been greatly exaggerated. DNA-damaging agents lead to characteristic kinds of base changes (transitions, transversions, deletions). The investigation of the spectrum of mutations in cancer-related genes studied in tumour tissue should lead to a better understanding of the agents ultimately responsible for inducing the tumour. Similarly, studying mutations in a neutral marker gene (not involved in tumorigenesis) can tell us about the origins of the 'background' level of mutations. So far, interpretation of the growing databases is largely speculative. (ABSTRACT

Evaluation of auramine genotoxicity in primary rat and human hepatocytes and in the intact rat

Auramine, a dye previously found to be a liver carcinogen in both mice and rats, was evaluated for its DNA-damaging and clastogenic activities in primary cultures of rats and human hepatocytes and for the induction of DNA single-strand breaks in the liver and urinary bladder mucosa of intact rats. A similar dose-dependent frequency of DNA fragmentation was revealed by the alkaline elution technique in metabolically competent primary cultures of both rat and human hepatocytes exposed for 20 h to subtoxic concentrations ranging from 10 to 32 microM. In contrast, neither rat nor human hepatocytes displayed an increased frequency of micronuclei after a 48-h exposure to the same auramine concentrations. In rats given a single oral dose of 125, 250 or 500 mg kg-1 auramine, the Comet assay revealed a significant increase in the frequency of DNA lesions in the liver and in the urinary bladder mucosa, the effect being slightly more marked in the liver. Taken as a whole and compared with previous findings, these results suggest that auramine is biotransformed into reactive species in target organs of both rats and humans, and that this dye might play by itself the main role in the increased incidence of bladder cancer which has been judged as causally related to its manufacture.

An examination of DNA strand breakage in the comet assay and antioxidant capacity in diabetic patients

There are two forms of diabetes, insulin-dependent Diabetes mellitus (IDDM) and non-insulin dependent Diabetes mellitus (NIDDM). There is evidence to suggest that reactive oxygen is involved in the pathogenicity and complications arising from IDDM, but there is little to suggest a role of oxidative stress in the pathogenesis of NIDDM. In order to investigate this hypothesis further, peripheral blood samples were taken from control individuals and IDDM and NIDDM patients and examined for antioxidant capacity and in the Comet assay for DNA strand breakage. The individuals answered a questionnaire to provide information relating to lifestyle factors in case such factors might have a confounding effect. There were 20 controls, 22 IDDM patients and 23 NIDDM patients. No differences could be detected in control and diabetic patient groups in terms of creatinine levels and antioxidant capacity. DNA damage in the Comet assay was at a lower level than in the control in the IDDM patients and a slightly lower level in the NIDDM patients, which might indicate that these cells are handling more oxidative damage on a regular basis. As expected, there were differences in glycosylated haemoglobin (HbA(1C)) levels. The confounding factors (smoking, drinking and vitamin intakes, etc.) appeared to have no effect.

Alkaline single-cell gel electrophoresis and human biomonitoring for genotoxicity: a pilot study on breast cancer patients undergoing chemotherapy including cyclophosphamide

Alkaline single-cell gel electrophoresis (the 'comet assay') was used to evaluate DNA damage in lymphocytes from 17 breast cancer patients before and 1-21 h after chemotherapy including cyclophosphamide (600-1800 mg/m2). In order to control for the experimental variability over time, freshly isolated lymphocytes from female mice given physiological saline or cyclophosphamide (150 mg/kg b.wt.) were included as 'internal standards' in each individual electrophoresis run. There was an upward tendency of DNA damage in the mouse lymphocytes over the study period, but cyclophosphamide was constantly found to induce significant damage at all time points investigated (1-48 h). Although patients given up to 11 prior cycles of chemotherapy showed the same basal level of DNA damage as the patients coming to the clinic for their first treatment, the chemotherapy given at the time of the present blood sampling was associated with significant DNA damage in most samples. Considerable interindividual variations were observed both before and after the treatment. DNA single-strand breaks and alkali-labile sites in peripheral lymphocytes as evaluated by the comet assay seem to be useful molecular biomarkers for exposure to DNA damaging agents when monitoring ongoing exposures, but less impressive when monitoring accumulated exposures, at least in patients given high doses of cyclophosphamide and other antineoplastic agents.

DNA damage in leukocytes and buccal and nasal epithelial cells of individuals exposed to air pollution in Mexico City

There is an increased interest in using biological markers to monitor individuals for possible exposure to environmental toxicants. Test systems which permit the sensitive detection of DNA damage and DNA repair are critically important in such studies. The single cell gel electrophoresis (SCG) assay is a rapid and a sensitive method for the evaluation of DNA damage at the single cell level, providing information on the occurrence of DNA single-strand breaks and alkali labile sites using alkaline conditions. In this study, the differences in the basal level of DNA damage between young adults from the south (exposed principally to high levels of ozone) and young adults from the north (exposed principally to hydrocarbons and particles) of Mexico City were investigated by the SCG assay using three different cell types (leukocytes and nasal and buccal epithelial cells). We found an increased DNA migration in blood leukocytes and nasal cells from individuals who live in the southern part of the city compared to those living in the northern part; however, no differences were observed for buccal epithelial cells. These results show the feasability of using the SCG assay to evaluate DNA damage in different tissues and its great potential for use in the monitoring of humans potentially exposed to genotoxic pollutants.