The use of silver-stained "comets" to visualize DNA damage and repair in normal and Xeroderma pigmentosum fibroblasts after exposure to simulated solar radiation

Amifostine (WR2721) confers DNA protection to in vivo cisplatin-treated murine peripheral blood leukocytes

Amifostine [S-2-3-aminopropyl amino ethyl phosphorotioic acid], a modulator agent for antineoplastic drugs involved in free radicals generation has given controversial results in cisplatin treated leukocytes in vitro. We have evaluated the amifostine protection over leukocytes in vivo, using comet assay. Groups of five OF1 male mice were given one of three doses of amifostine (56, 105 and 200 mg/Kg) after a cisplatin single injection (10 mg/Kg). Serum malonyldialdehyde levels, catalase and superoxide dismutase activity were also evaluated. Amifostine showed significant DNA protection (p< 0.01) at the two lower doses evaluated. Malonyldialdehyde decreased in all amifostine treatments with respect to cisplatin while antioxidant enzyme activities remained unchanged. However, DNA migration increased with the highest amifostine dose; in fact highest dose of amifostine did no protect damage caused by cisplatin this result have implications on amifostine treatment schedules in clinical practice.

Application of the comet assay in erythrocytes of Oreochromis niloticus (Pisces): A methodological comparison

The present study applied the comet assay to erythrocytes of Oreochromis niloticus with the aim of improving protocols to detect DNA damage in these cells, by using two distinct pHs (pH = 12.1 and pH > 13) and evaluating whether there is a correspondence between silver and ethidium bromide staining. Comets were visually examined and, the frequency of cells with and without damage was obtained, as well as the distribution of classes and scores. By using the Kruskal-Wallis test, our results revealed that pH 12.1 is more effective, although both pHs can be used. Our findings also suggest that silver staining can substitute ethidium bromide, an expensive and highly toxic stain that requires specific equipment for examination.

Measurements of DNA damage on silver stained comets using free Internet software

Silver stain offers the possibility to stain comets permanently, but up to now it was impossible to measure the majority of the comet parameters, because the distinction between head and tail was not recognised by software. Here, we report a silver staining protocol that allows the measurement of comet parameters using the free Internet software CASP. We validated the silver stain protocol by comparing the behaviour of the parameter '% DNA in tail' in silver and fluorescent stained comets. The range of % DNA in tail for different visual categories of damage in silver stained comets was similar to that reported with fluorescence staining. The range was for category 0 (no damage), <1%; category 1 (low damage), 1-25%; category 2 (medium damage), >25-45%; category 3 (high damage), >45-70%; category 4 (very high damage), >70%. The mean of % DNA in tail in silver stained comets was also similar to that reported with fluorescence staining. The mean was for category 0, 0.4+/-0.34%; category 1, 12+/-7%; category 2, 37+/-4%; category 3, 57+/-5% and category 4, 83+/-6%. Others comet parameters such as tail length, tail moment and Olive tail moment can be also measured. The silver staining protocol reported here opens new opportunities for those working in the assay without fluorescent microscope as the measurement of comet parameters using free Internet software and conventional microscope becomes possible.

Can individual repair kinetics of UVC-induced DNA damage in human lymphocytes be assessed through the comet assay?

The suitability of the comet assay for quantifying DNA repair capacity at individual level was studied following the kinetics of nucleotide excision repair (NER) in human lymphocytes from four healthy donors, at various time steps after a single dose of UVC. A significant increase of DNA migration was seen as soon as 20 min after UV exposure, reaching the peak within 60-90 min. Afterwards, a rapid decline was observed, approaching the basal level at 180-240 min. The increase could be ascribed to excision activity, while the reduction to gap filling and rejoining, as demonstrated by the effects of phase-specific inhibitors, novobiocin and aphidicolin. Therefore, the comet assay should allow following the biphasic kinetics of NER. Wide inter-individual differences were observed, although repeated tests on the same donor cells revealed a large experimental variation. To quantitatively compare the individual patterns, a mathematical model was developed that adequately fitted the experimental results and estimated appropriate descriptors for each phase and for each donor. A second approach was also used to directly compare the distributions of damaged cells and to assess the differences between donors and between experiments visualizing them as reciprocal distances on a two-dimensional space computed with a principal component analysis (PCA). The results confirmed the inter-individual differences, but also the strong influence of experimental factors of the comet assay. The two approaches provided the means of accurately comparing DNA repair kinetics at individual level, taking also into account the experimental variability which poses serious doubts on the suitability of the comet assay. Nevertheless, since this methodology allows a detailed analysis of repair kinetics and it is potentially very useful for identifying individual with reduced repair capacity, further efforts have to be addressed to improve the reproducibility of the comet assay.

Sevoflurane-induced oxidative stress and cellular injury in human peripheral polymorphonuclear neutrophils

Sevoflurane is an inhalation anesthetic used for general anesthesia. Several studies have demonstrated that reactive oxygen species (ROS) exist in cardioprotection when preconditioned with sevoflurane. Moreover, sevoflurane can also directly trigger the formation of peroxynitrite. Up to now, information pertinent to the effect of sevoflurane on cellular injuries in human polymorphonuclear neutrophils (PMN) is scant. In this study, we demonstrated that sevoflurane significantly increases intracellular H2O2 and/or peroxide, superoxide, and nitric oxide (NO) in PMN within 1h treatment. Intensification of intracellular glutathione (GSH) depletion in PMN has been demonstrated with the presence of sevoflurane. Inhibition of sevoflurane-mediated intracellular H2O2 and/or peroxide in PMN by catalase, mannitol, dexamethasone, N-acetylcysteine (NAC) and trolox, but not superoxide dismutase (SOD) pretreatment, was observed. Among them, catalase has the best effect scavenging intracellular H2O2 and/or peroxide, suggesting that H2O2 is the major ROS during sevoflurane treatment. Two apoptotic critical factors-lowering of the mitochondrial transmembrane potential (DeltaPsim) and activation of caspase 3/7-were significantly increased after 1h of sevoflurane treatment. Apoptosis of PMN were determined by comet assay and flow cytometric analysis of annexin V-FITV protein binding to the cell surface. Exposure of PMN to sevoflurane markedly increased apoptosis in a dose-dependent manner. In summary, these results are important for demonstrating the oxidative stress and cellular injury on sevoflurane-treated human PMN.

Sensitivity and variability of visual scoring in the comet assay. Results of an inter-laboratory scoring exercise with the use of silver staining

Nineteen scorers from seven Cuban laboratories participated in this slide exercise designed to test the influence of the scorer on the accuracy, sensitivity and variability of the comet assay when a visual method of DNA damage evaluation is used. The assay was performed using human lymphocytes from a single donor exposed in vitro for 5 min at 0 degrees C to doses of 0, 5, 10, 25, 50, 100 and 200 microM of hydrogen peroxide. Each participant scored the same set of 14 coded slides with silver stained comets. The comets were classified visually into five categories according to the appearance resulting from the relative proportion of DNA in the tail. The extent of DNA damage was expressed in arbitrary units. At zero dose the median values of 12 scorers out of 19 were included between the values of the overall 25 and 75 per thousand. This proportion remains practically the same as the dose increases. The lowest dose detected by this method for the majority of scorers (11) was 10 microM. The coefficient of variation at the control dose was the highest (median value 26%), progressively declined to 20%, and starting from 25 microM, values are around 10%. The results of the exercise show the reliability of the silver staining and visual scoring for the comet method.

Fluorescent in situ sequencing on polymerase colonies

Integration of DNA isolation, amplification, and sequencing can be achieved by the use of polymerase colonies (polonies) and cycles of fluorescent dNTP incorporation. In this paper, we present four advances that bring us closer to sequencing genomes cost-effectively using the polony technology. First, a polymerase trapping technique enables efficient nucleotide extension by DNA polymerase in a polyacrylamide matrix and eliminates loss of enzyme during sequencing cycles. Next, we present two novel types of reversibly dye-labeled nucleotide analogues, show that DNA polymerase can incorporate these analogues, and demonstrate that the dyes can be removed by thiol reduction or light exposure. Using these nucleotides, we have sequenced multiple polonies in parallel. In addition, we have found that a high density of polonies can be achieved with minimal overlap between adjacent polonies by limiting the concentration of free primer in the polony amplification reactions. Finally, we have developed software for automated image alignment and sequence calling.

Protection from solar simulated radiation-induced DNA damage in cultured human fibroblasts by three commercially available sunscreens

Exposure to solar radiation can produce both acute and chronic changes in the skin, including sunburn, edema, immunosuppression, premature skin aging, and skin cancer. At the cellular level, solar radiation can produce adverse structural and functional changes in membrane proteins and lipids and in chromosomal and mitochondrial DNA. The increasing awareness of these adverse effects has led the public to demand better photoprotection. In this study, the alkaline comet assay was used to evaluate the photoprotective effects of three commercially available sunscreens at sun protection factors (SPF) 15 and 30. Human fibroblasts were used as target cells to conveniently study the effects of solar simulated radiation on DNA damage in the presence and absence of sunscreens. When human fibroblasts were exposed to various doses of solar simulated radiation, DNA damage, as measured in sunscreen-protected cells by the comet assay, was not significantly different from that detected in unexposed cells. At 1.0 and 1.5 minimal erythemal doses (MED), all sunscreens, at both SPF 15 and 30, provided nearly 100% photoprotection to the fibroblasts. Further studies are required to elucidate the role of UVA in the production and repair of DNA damage in cells exposed to sunlight.

Prompt and delayed nonsteroidal anti-inflammatory drug-photoinduced DNA damage in peripheral blood mononuclear cells measured with the comet assays

Nonsteroidal anti-inflammatory drug (NSAID)-photoinduced DNA damage in human peripheral blood mononuclear cells measured using the alkaline comet assay is presented. Whereas Tiaprofenic Acid-photoinduced DNA damage was promptly induced (i.e. observed at relatively low radiation doses), Ketoprofen-photoinduced DNA damage was delayed. This prompt and delayed effect is observed with UVA (320-400 nm), UVB (290-320 nm) and solar-simulated radiation and is attributed to the different photochemical properties of NSAID. The results from these experiments, carried out in living cells, confirm the speculations of NSAID-photoinduced DNA damage brought up by the many experiments conducted in solution.

DNA damage detection technique applying time-resolved fluorescence measurements

A novel DNA damage detection technique based on the characteristic fluorescence lifetimes exhibited by Pico-Green-single-stranded DNA and -double-stranded DNA complexes is employed to establish the damage produced on DNA isolated from sheep white blood cells following gamma radiation. This technique, which incorporates key concepts such as alkaline unwinding buffers and higher unwinding rates of damaged DNA compared to undamaged DNA, allows for the differentiation of DNA damage resulting from doses of gamma radiation in the 0-100-Gy range, with the potential of analyzing samples consisting of as little as 10(4) cells. Experiments were carried out using commercial DNA sources as well as DNA isolated from sheep white blood cells, suggesting its potential for use with isolated DNA from virtually any eukaryotic cell.

A silver staining method for single-cell gel assay

The single-cell gel assay (comet assay) is a very useful microelectrophoretic technique for evaluation of DNA damage and repair in individual cells. Usually, the comets are visualized and evaluated with fluorescent DNA stains. This staining requires specific equipment (e.g., a high-quality fluorescence microscope), the slides must be analyzed immediately, and they cannot be stored for long periods of time. Here we describe, using human lymphocytes, some modifications of the silver staining for comets that significantly increase the sensitivity/reproducibility of the assay. This silver staining was compared with fluorescence staining and commercial silver stains. (J Histochem Cytochem 49:1183-1186, 2001)