A novel technique for the detection of DNA single-strand breaks in human white blood cells and its combination with the unscheduled DNA synthesis assay

Genotoxic effects of chromium(VI) and cadmium(II) in human blood lymphocytes using the electron microscopy in situ end-labeling (EM-ISEL) assay

Evaluation of genotoxic effects of potassium chromate (K2CrO4) and cadmium chloride (CdCl2) was carried out in human blood lymphocytes in vitro as measured by the electron microscopy in situ end-labeling (EM-ISEL). EM-ISEL was used to assess DNA single-strand breaks (SSBs) expressed as number of immunogold particles per microm2 of chromatin at both chromosomal and nuclear DNA levels. Human lymphocytes were cultured in supplemented RPMI medium for 72 h including treatment for 2 h with K2CrO4 (0-150 microM), CdCl2 (0-150 microM) or methyl methanesulfonate (500 microM) as a positive control. Quantification of SSBs by EM-ISEL showed that both compounds are genotoxic agents at non-cytotoxic concentrations. This study brings new information on the utility of EM-ISEL for the evaluation of genotoxicity and confirms the genotoxic effects induced by chromium and cadmium.

Minimizing cancer risk using molecular techniques: a review

This review article summarizes molecular markers that can signal enhanced risk of cancer and provide clinicians with these clues in order to attempt the use of natural and synthetic compounds to intervene in the early precancerous stages of carcinogenesis before invasive disease begins. With an aim such as this in mind, we have begun to apply molecular techniques based on many research articles to look for biomarkers capable of signaling a greater risk of cancer. It is possible to attain relatively quick answers by monitoring selected signs and damage in the body which provide the environment for abnormal cell growth and differentiation. These molecular techniques aim to uncover critical precancerous events taking place inside the body and identify measurable biologic flags signaling their occurrence. For years now, scientists have understood that the onset of cancer is a gradual, step-wise process that may unfold over the course of decades, rather than a single, fixed event that can be dated in a pathologist's report. Carcinogenesis usually encompasses the prolonged accumulation of injuries at several different biological levels and includes both genetic and biochemical changes in cells. At each of these levels there is an opportunity for intervention-a chance to prevent, slow or even halt the gradual march of healthy cells toward malignancy. It is estimated that 75% of cancers are induced by chemicals; thus, if exposure to chemicals is avoided, cancer can be prevented. Also, depending on the individual's genetic background, the ability to metabolize chemicals is different among the population. This means that, "you and I can be exposed to exactly the same amount of a chemical," yet our response will differ because we metabolize carcinogens differently due to different rates of deoxyribonucleic acid (DNA) repair, apoptosis, and mitosis or different levels of Phase I and Phase II detoxification enzymes. This, along with a more or less efficient immune system, may promote tumor formation or destroy a cancer cell at its earliest stage of development. Therefore, measurement of the biologic markers such as DNA and protein adducts, DNA damage, programmed cell death, DNA repair system, mitosis, gene activation, levels of antioxidants and efficient immune function described in this chapter and summarized in Figures 2 and 10, are biological clues indicating that the body has been assaulted by toxic (or cancer-causing) agents. This early identification of biomarkers for special vulnerability to the effects of chemicals and detection of selected signs of precancerous damage in the body may culminate preventive measures and the saving of lives.

Reproducibility of basal and induced DNA single-strand breaks detected by the single-cell gel electrophoresis assay in human peripheral mononuclear leukocytes

The aim of the reported study was to investigate the reproducibility of the single-cell gel electrophoresis (SCGE) assay in the determination of DNA single-strand breaks (SSBs) and to estimate the statistical requirements when the SCGE assay is used for the detection of genotoxicity in humans. In human peripheral mononuclear leukocytes (PMLs), we repeatedly measured the rate of SSBs after in vitro incubation of cells for 1 h at 4 degrees C in phosphate buffered saline (PBS, basal) or 10 microM or 50 microM H2O2 (induced). Intra-assay variation was determined from cryopreserved PMLs of a single donor. To assess intrasubject and intersubject variation, PMLs of ten healthy, nonsmoking subjects (aged 19-37 years) were tested 5-9 times. Cryopreserved cells revealed a mean coefficient of variation of 18% (PBS) and 7%-9% (H2O2). There were statistically significant differences between individuals in the rate of SSBs after incubation in PBS (P < 0.01), 10 microM H2O2 (P < 0.001), and 50 microM H2O2 (P < 0.001). The range of interindividual variability was 26% for basal and 12%-13% for induced SSBs, and the coefficient of intraindividual variation was 18%-72% (PBS) and 7%-23% (H2O2). Neither basal nor induced rates of DNA damage were related to gender or age. Estimates of the minimum detectable effects were based on these observed sources of variability (power 90%, level of significance 5%, assumed sample size 50). With two different groups, a difference of 31% in basal SSBs or 12% in induced SSBs would be detectable. Repeated measurement within one group could detect a difference of 26% in basal and 9% in induced SSBs. In summary, the SCGE assay appears to be suitable for the detection of single-strand breaks, e.g., in biomonitoring or environmental medicine, and the statistical requirements could be derived from our analysis of the sources of variability.

Determination of low level exposure to volatile aromatic hydrocarbons and genotoxic effects in workers at a styrene plant

OBJECTIVES

Low exposures to volatile aromatic hydrocarbons and cytogenetic effects in peripheral white blood cells were determined in 25 healthy workers employed in different areas of a styrene production plant in the former German Democratic Republic. The results were compared with 25 healthy unexposed controls (matched for age and sex) employed in the same company.

METHODS

The concentrations of aromatic hydrocarbons determined from active air sampling in all areas of the factory (styrene: 73-3540 micrograms/m3 (< 0.01-0.83 ppm); ethylbenzene 365-2340 micrograms/m3 (0.08-0.53 ppm); benzene 73-3540 micrograms/m3 ( < 0.02-1.11 ppm); toluene 54-2960 micrograms/m3 (0.01-0.78 ppm); xylenes 12-94 micrograms/m3 ( < 0.01-0.02 ppm)) were considerably lower than in the pump house ( > 4000 micrograms/m3 styrene, ethylbenzene, benzene, and toluene; > 500 micrograms/m3 xylenes), which was only intermittently occupied for short periods. Passive personal monitoring, biomonitoring of exhaled air and metabolites (mandelic, phenylglyoxylic, trans, trans-muconic, hippuric, o-, m- and p-methylhippuric acids, and phenol) in urine samples collected before and after an eight hour working shift was used to assess individual exposure. Questionnaires and examination of company records showed that the historical exposure was far higher than that measured. Genotoxic monitoring was performed by nuclease P1-enhanced 32P-postlabelling of DNA adducts in peripheral blood monocytes, and DNA single strand breaks, sister chromatid exchange, and micronuclei in lymphocytes. The content of kinetochores in the micronuclei was determined by immunofluorescence with specific antibodies from the serum of CREST patients.

RESULTS

No genotoxic effects related to exposure were detected by DNA adducts or DNA single strand breaks and sister chromatid exchange. The only effect related to exposure was an increase in kinetochore positive micronuclei in peripheral lymphocytes; the frequency of total micronuclei in peripheral lymphocytes did not change. Smoking was confirmed by measurement of plasma cotinine, and no confounding effect was found on any of the cytogenetic variables.

CONCLUSIONS

Low occupational exposure to styrene, benzene, and ethylbenzene did not induce alterations of genotoxicological variables except kinetochore positive micronuclei. This is the first reported use of the CREST technique for an in vivo study in occupational toxicology, which thus could serve as a valuable and sensitive technique for toxicogenic monitoring.

Detection of DNA single-strand breaks in lymphocytes of smokers

In a controlled study, ten male volunteers (five smokers and five nonsmokers) were subjected to different smoking conditions and compared to five nonsmokers, not exposed to cigarette smoke. During the 4 days of the study, nonsmoking periods were strictly controlled. On the first day the ten subjects were sham exposed. On the second day the five smokers smoked 24 cigarettes in 8 h, while the five nonsmokers were exposed to the environmental tobacco smoke. After another day of sham exposure the smoke exposure was repeated under the same conditions. Blood was drawn before and after exposure and DNA single-strand breaks (SSBs) were analyzed in lymphocytes immediately (1 h) after isolation of cells and after 4 h incubation at 37 degrees C, using a modified assay based on the nick translation reaction. Base levels of unscheduled DNA synthesis (UDS) and UDS levels were determined after 1 h incubation with methyl methanesulfonate. Duplicate analysis using the same method was performed in a second laboratory after transportation of blood samples at 0 degree C on a train from Munich to Hamburg. Tobacco smoke exposure of the subjects increased COHb and plasma cotinine levels. SSBs could be detected in all probands with some interindividual day-to-day and morning-to-evening variations. In four of five active smokers, SSB increases were found after smoking. In nonsmokers exposed to tobacco smoke no exposure-related variation in SSB levels could be detected.(ABSTRACT TRUNCATED AT 250 WORDS)