Extent of DNA damage in density-separated trout erythrocytes assessed by the 'comet' assay

DNA damage and repair following In vitro exposure to two different forms of titanium dioxide nanoparticles on trout erythrocyte

TiO2 has been widely used to promote organic compounds degradation on waste aqueous solution, however, data on TiO2 nanotoxicity to aquatic life are still limited. In this in vitro study, we compare the toxicity of two different families of TiO2 nanoparticles on erythrocytes from Oncorhynchus mykiss trout. The crystal structure of the two TiO2 nanoparticles was analyzed by XRD and the results indicated that one sample is composed of TiO2 in the anatase crystal phase, while the other sample contains a mixture of both the anatase and the rutile forms of TiO2 in a 2:8 ratio. Further characterization of the two families of TiO2 nanoparticles was determined by SEM high resolution images and BET technique. The toxicity results indicate that both TiO2 nanoparticles increase the hemolysis rate in a dose dependent way (1.6, 3.2, 4.8 μg mL(-1) ) but they do not influence superoxide anion production due to NADH addition measured by chemiluminescence. Moreover, TiO2 nanoparticles (4.8 μg mL(-1) ) induce DNA damage and the entity of the damage is independent from the type of TiO2 nanoparticles used. Modified comet assay (Endo III and Fpg) shows that TiO2 oxidizes not only purine but also pyrimidine bases. In our experimental conditions, the exposure to TiO2 nanoparticles does not affect the DNA repair system functionality. The data obtained contribute to better characterize the aqueous environmental risks linked to TiO2 nanoparticles exposure.

Comparative toxicity of CuO nanoparticles and CuSO4 in rainbow trout

This study compared the toxicity and accumulation of two different Cu compounds, CuO nanoparticles (NPs) and soluble CuSO4, in erythrocytes and different tissues in rainbow trout (Oncorhynchus mykiss). The crystal structure of CuO NP analysed by XRD indicates that the NP are Tenorite, a monoclinic CuO. The in vitro toxicity results indicate that both Cu compounds increase the haemolysis rate in a dose-dependent way, but the effect was reduced treating cells with CuO NP. Moreover, both Cu compounds induce DNA damage and the entity of the damage, similarly to haemolysis, was more marked in cells treated with CuSO4. In vivo results, obtained after intraperitoneal injection, showed that Cu concentrations were significantly higher in gills (p<0.0001), kidney (p=0.007) and liver (p<0.05) of exposed fish with a significant increase in plasma Cu concentration 15h after CuSO4 treatment. Cu concentrations were significantly higher in fish exposed to CuSO4 than CuO in kidney (p<0.05) and gills (p<0.0001). Significant DNA damage with respect to controls was detected only when Cu was injected as CuSO4. The present data could serve to evaluate environmental Cu toxicity in fish depending on Cu speciation.

The ethyl acetate fraction of Polytrichum commune L.ex Hedw induced cell apoptosis via reactive oxygen species in L1210 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Polytrichum commune L.ex Hedw is a traditional Chinese herb for treatment of fever, hemostatic, uterine prolapse and especially for leukemia. Previous studies indicated its anti-leukemia effect but the potential mechanisms have not been fully explained.

AIMS OF THE STUDY

The present study was further to investigate the underlying mechanism of ethyl acetate extract of Polytrichum commune L.ex Hedw (EEF)-induced toxicity and apoptosis in L1210 cells.

MATERIALS AND METHODS

Viability, DNA damage and apoptotic protein expressions of L1210 cells were analyzed by ViaCount, comet assay and western blot, respectively. At different times after EEF treatment, Bax redistribution in L1210 cells was examined using confocal microscopy; loss of mitochondrial membrane potential (MMP) was monitored by fluorescence microscope using rhodamine 123 staining; Intracellular reactive oxygen species (ROS) generation and DNA fragmentation were measured by flow cytometry using fluorescent dye, DCFH-DA and PI, respectively.

RESULTS

EEF significantly inhibited L1210 cell survival, promoted Bax translocation onto mitochondria, stimulated caspase-9 activation and subsequent DNA damage in L1210 cells. Abundant ROS was detected in L1210 cells after EEF treatment, and the ROS scavenger NAC significantly relieved EEF-induced cell viability decline, MMP loss, and DNA fragmentation.

CONCLUSION

EEF could induce mitochondria-dependent cell apoptosis in L1210 cells, and ROS may play an important role in this action.

Assessment of genotoxic effects of flumorph by the comet assay in mice organs

The present study investigated the genotoxic effects of flumorph in various organs (brain, liver, spleen, kidney and sperm) of mice. The DNA damage, measured as comet tail length (µm), was determined using the alkaline comet assay. The comet assay is a sensitive assay for the detection of genotoxicity caused by flumorph using mice as a model. Statistically significant increases in comet assay for both dose-dependent and duration-dependent DNA damage were observed in all the organs assessed. The organs exhibited the maximum DNA damage in 96 h at 54 mg/kg body weight. Brain showed maximum DNA damage followed by spleen > kidney > liver > sperm. Our data demonstrated that flumorph had induced systemic genotoxicity in mammals as it caused DNA damage in all tested vital organs, especially in brain and spleen.

Early life permethrin insecticide treatment leads to heart damage in adult rats

Early life environmental exposure to xenobiotics could represent a critical period for the onset of permanent alterations in the structure and function of different organs. Cardiovascular diseases can be related to various factors including environmental toxicants. The aim of the present study was to evaluate the effect of early life permethrin treatment (1/50 LD(50), from 6th to 21st day of life) on heart of adult rats. Increased DNA damage, decreased heart cell membrane fluidity, increased cholesterol content, protein and lipid oxidation were measured in heart cells from adult rats treated with permethrin during the neonatal period with respect to control rats. Moreover, the same group showed higher levels of cholesterol, IL-1β, IL-2, IFN-γ, rat-Rantes and IL-10 cytokines and decreased albumin content in plasma. Lower cholesterol levels and perturbation in the phospholipid lateral diffusion together with decreased GSH levels and increased GPx activity were measured in heart mitochondria of the treated group. Our findings support the evidence that the neonatal period has a critical role in the development of heart disease in adulthood. We hypothesize that the alterations observed in adult rats could depend on epigenetic changes that occurred during this period which influence gene expression throughout the rat's life, leading to alterations of certain parameters related to cardiac function.

Leucocytes DNA damage in mice exposed to JS-118 by the comet assay

JS-118 is an extensively used insecticide in China. The present study investigated the genotoxic effect of JS-118 on whole blood at 24, 48, 72 and 96 h by using alkaline comet assay. Male Kunming mice were given 6.25, 12.5, 25, 50 and 100 mg/kg BW of JS-118 intraperitoneally. A statistically significant increase in all comet parameters indicating DNA damage was observed at 24 h post-treatment (p < 0.05). A clear concentration-dependent increase of DNA damage was revealed as evident by the OTM (arbitrary units), tail length (µm) and tail DNA (%). From 48 h post-treatment, a gradual decrease in mean comet parameters was noted. By 96 h of post-treatment, the mean comet tail length reached control levels indicating repair of damaged DNA. This study on mice showed different DNA damage depending on the concentration of JS-118 and the period of treatment. The present study provided further information of the potential risk of the genetic damage caused by JS-118.

Assessment of environmental stress in Parablennius sanguinolentus (Pallas, 1814) of the Sicilian Ionian coast

The blenny Parablennius sanguinolentus was selected as a useful bioindicator of environmental pollution. Chemical parameters in water and sediments from three different sampling sites along the Sicilian Ionian coast were determined and metal concentrations in fish muscle were measured. DNA fragmentation and oxidation in erythrocytes and hepatocytes was determined by the Comet assay and HSP70 expression levels were evaluated in the liver. The results show an increased level of chromium in sediments and high polycyclic aromatic hydrocarbon (PAH) concentrations in water at one site. The bioaccumulation of metals in muscle tissue shows high concentrations of lead in some samples. A high percentage of DNA damage in blood and liver cells, as well as high hepatic levels of HSP70, were found in all the sites. The results demonstrate the usefulness of an integrated chemical and biological approach for the determination of environmental stress.

Detection of DNA damage by alkaline single cell gel electrophoresis in 2,4-dichlorophenoxyacetic-acid- and butachlor-exposed erythrocytes of Clarias batrachus

The alkaline single cell gel electrophoresis, also known as comet assay, is a rapid, simple and sensitive technique for measuring DNA strand breaks in individual cells. The present study was undertaken to evaluate the genotoxic potential of two widely used herbicides; 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-chloro-2,6-diethyl-N-(butoxymethyl) acetanilide (butachlor) in erythrocytes of freshwater catfish, Clarias batrachus. Fish were exposed by medium treatment with three sub-lethal concentrations of 2,4-D (25, 50, and 75ppm) and butachlor (1, 2, and 2.5ppm) and alkaline comet assay was performed on nucleated erythrocytes after 48, 72, and 96h. The amount of DNA damage in cells was estimated from comet tail length as the extent of migration of the genetic material. A significant increase in comet tail length indicating DNA damage was observed at all concentrations of both the herbicides compared with control (P<0.05). The mean comet tail length showed a concentration-related and time-dependent increase as the maximum tail length recorded at highest concentration and longer duration of 2,4-D (9.59microm) and butachlor (9.28microm). This study confirmed that the comet assay applied on the fish erythrocyte is a useful tool in determining potential genotoxicity of water pollutants and might be appropriate as a part of a monitoring program.

Partial oxidative-stress perturbs membrane permeability and fluidity of fish nucleated red blood cells

We investigated the influence of partial oxidative stress on permeability and fluidity of nucleated fish red blood cells for simulating nucleated somatic cells. Peroxide value indicating lipid hydroperoxide level in nucleated red blood cells of common carp (Cyprinus carpio) increased with increasing body size. We detected that oxidation of nucleated red blood cells led to the degraded PUFA compositions and accelerated the permeability of calcein and ATP in the nucleated red blood cells restrictedly oxidized with 1 mM AAPH treatment for 30 min at 21 degrees C in the dark. Using fluorescence probes, PC3P, we found that oxidative stress reduced the membrane fluidity of nucleated red blood cells. It was also observed that AAPH had no significant influence on the osmotic fragility and electrophoretic profiles of red blood cell proteins. These results suggest that partial oxidative-stress, even if failure to fragment the membrane, may affect membrane permeability of fish nucleated red blood cells for an important energy molecule, ATP.

Use of the single cell gel electrophoresis/comet assay for detecting DNA damage in aquatic (marine and freshwater) animals

The comet assay is a rapid, sensitive and inexpensive method for measuring DNA strand breaks. The comet assay has advantages over other DNA damage methods, such as sister chromatid exchange, alkali elution and micronucleus assay, because of its high sensitivity and that DNA strand breaks are determined in individual cells. This review describes a number of studies that used the comet assay to determine DNA strand breaks in aquatic animals exposed to genotoxicants both in vitro and in vivo, including assessment of DNA damage in aquatic animals collected from contaminated sites. One difficulty of using the comet assay in environmental work is that of comparing results from studies that used different methods, such as empirical scoring or comet tail lengths. There seems to be a consensus in more recent studies to use both the intensity of the tail and the length of the tail, i.e. DNA tail moment, percentage of DNA in the tail. The comet assay has been used to assess DNA repair and apoptosis in aquatic animals and modifications of the comet assay have allowed the detection of specific DNA lesions. There have been some recent studies to link DNA strand breaks in aquatic animals to effects on the immune system, reproduction, growth, and population dynamics. Further work is required before the comet assay can be used as a standard bio-indicator in aquatic environments, including standardization of methods (such as ASTM method E2186-02a) and measurements.

Statistics of the Comet assay: a key to discriminate between genotoxic effects

The alkaline Comet assay is a widely used single cell gel electrophoresis technique for the quantification of DNA strand breaks, crosslinks and alkali-labile sites induced by a series of physical and chemical agents. DNA migration in an electric field, supposed proportional to strand breakage, is a proposed estimation of genotoxicity. Breaks are quantified from geometric and fluorescence measurements by image analysis of comet-shaped DNA, often reported parameters being tail DNA and tail moment. Although a variety of statistical approaches have been used in the literature, most of these do not take into account the distribution patterns of comet data. In order to investigate a methodology for statistically demonstrating a comet effect, two different experiments, a reproducibility study and a trend analysis, were undertaken on a murine lymphoma cell line (P388D1) photodynamically stressed after induction of porphyrins with delta-aminolaevulinic acid. This treatment results in significant heterogeneity of DNA damage, producing values ranging from 0 to 100% tail DNA in the same sample. The comparison of distribution curves for stressed and non-stressed samples shows that none of the application conditions are verified, either for parametric tests (which require normal distributions), or non-parametric tests (which assume essentially similar distributions). Meaningful statistics (median and 75th percentile) were consequently extracted from repeated experiments and found suitable for comparing stress conditions in an ANOVA and in a trend analysis; the 75th percentile is theoretically more sensitive but tends to more rapidly saturate at extensive stress levels. We conclude that a trend analysis of median comet metrics from repeated experiments at different stress levels is certainly an efficient way to statistically demonstrate a genotoxic effect. Whether the considered comet parameter is tail DNA or tail moment had no influence on the conclusions of our experiments, which were carried up to stress levels leading to a median 70% tail DNA.

Anesthesia of fish with benzocaine does not interfere with comet assay results

Fish blood erythrocytes are frequently used as sentinels in biomonitoring studies. Usually, fish blood is collected by painful cardiac or caudal vein punctures. Previous anesthesia could decrease animal suffering but it is not known at present whether anesthesia can cause confounding effects. Therefore, using the alkaline single cell gel (SCG)/comet assay with blood erythrocytes of the cichlid fish Nile tilapia, we tested for a possible modulation of induced DNA damage (methyl methanesulfonate; MMS) by the anesthetic benzocaine administered by bath exposure (80mg/l for approximately 10min). Furthermore, benzocaine (80-600mg/l) was tested for its genotoxic potential on fish erythrocytes in vitro and for potential interactions with two known genotoxins (MMS and hydrogen peroxide). Our results did neither indicate a significant increase in the amount of DNA damage (even after a 48h follow-up), nor indicated interactions with MMS-induced DNA damage when fish were exposed to benzocaine in vivo. There was also no increase in DNA damage after in vitro exposure of fish erythrocytes to benzocaine. Clear concentration-related effects were observed for the two genotoxins in vitro, which were not significantly altered by the presence of benzocaine. These results suggest that anesthesia of fish does not confound comet assay results and the use of blood samples from anesthetized fish can be recommended with regard to animal welfare.

Mitochondrial membrane potential in density-separated trout erythrocytes exposed to oxidative stress in vitro

Previous literature reports have demonstrated that nucleated trout erythrocytes in condition of oxidative stress are subjected to DNA and membrane damage, and inactivation of glutathione peroxidase. The present study was undertaken to investigate if mitochondrial membrane potential in stressed conditions was also influenced. Density-separated trout erythrocyte fractions, obtained using a discontinuous Percoll gradient, were submitted to stress conditions and the mitochondrial membrane potential was determined by means of cytofluorimetric analysis after incubation of each subfraction with JC-1, a mitochondrial specific fluorescent probe. The results clearly show that the mitochondrial membrane potential decreased significantly in all erythrocyte fractions, also if the oxidative effect on mitochondria is more severe with increased density (age) of the cell. Ebselen was very effective in preventing mitochondrial depolarization in young as well as in old erythrocytes.

Tail moment versus tail length--application of an in vitro version of the comet assay in biomonitoring for genotoxicity in native surface waters using primary hepatocytes and gill cells from zebrafish (Danio rerio)

In order to investigate the suitability of an in vitro version of the comet assay with primary hepatocytes and gill cells from zebrafish (Danio rerio), cells were isolated by immersion in trypsin/EDTA solution after whole-body perfusion with phosphate-buffered saline. Within the scope of an 18-month biomonitoring study, primary cells were used to identify the genotoxic potential of native water samples from different sites along the major German rivers, Rhine and Elbe, and to evaluate the sensitivity and practicability of the chosen assay. Depending on the endpoint measured, considerable differences were detected with respect to the number of genotoxic surface water samples: Whereas no differences could be recorded for tail moment and relative DNA contents of head and tail, the number of positively tested native surface water samples significantly increased with tail length as endpoint.

Monitoring airborne genotoxicants in the rubber industry using genotoxicity tests and chemical analyses

This research was designed to examine the presence of mutagenic/carcinogenic compounds in airborne pollutants in the rubber industry using an integrated chemical/biological approach. Inhalable airborne particulate matter (PM-10: <10 microm) was collected in four rubber factories using a high-volume sampler equipped with a cascade impactor for particle fractionation. The organic extracts of two different fractions (0.5-10 microm and <0.5 microm) were examined for mutagenicity with the Ames test and for in vitro DNA-damaging activity in human leukocytes by single-cell microgel electrophoresis (Comet assay). The extracts were also studied by gas chromatography/mass spectrometry (GC/MS) for polycyclic aromatic hydrocarbon (PAH) content. Nitrosamines in ambient air were sampled on cartridges and analysed by GC with a thermal energy analyser (TEA) detector. Airborne volatile genotoxins were monitored in situ using a clastogenicity plant test (Tradescantia/micronuclei test). The results showed that airborne particulates were mainly very fine (<0.5 microm) and that trace amounts of genotoxic nitrosamines (N-nitrosodimethylamine: 0.10-0.98 microg/m(3); N-nitrosomorpholine: 0.77-2.40 microg/m(3)) and PAH (total PAH: 0.34-11.35 microg/m(3)) were present in air samples. Some extracts, particularly those obtained from the finest fractions, were mutagenic with the Ames test and genotoxic with the Comet assay. In situ monitoring of volatile mutagens using the Tradescantia/micronuclei test gave positive results in two working environments. The results showed the applicability of this integrated chemical-biological approach for detecting volatile and non-volatile genotoxins and for monitoring genotoxic hazards in the rubber industry.

Morphological and functional changes of mitochondria from density separated trout erythrocytes

Density separated trout erythrocytes, using a discontinuous Percoll gradient, yielded three distinct subfractions (top, middle and bottom) since older cells are characterized by increasing density. Cells from each subfraction were incubated with mitochondria-specific fluorescent probe Mitotracker and JC-1 in order to assess mitochondrial mass and membrane potential by means of cytofluorimetric analysis, confocal microscopy and subsequent computer-aided image analysis allowing a detailed investigation at single cell level. Both cytofluorimetric data and image analysis revealed changes in size and redistribution of mitochondria starting from the light fraction to the bottom. In particular in young erythrocytes small mitochondria were detected localized exclusively around the nucleus in a crown-like shape, the middle fraction revealed enlarged mitochondria partially scattered throughout the cytosol, whereas the last fraction represented again mitochondria with reduced size being distinctly dispersed throughout the cytosol in the cells. Concerning membrane potential considerations, our study revealed a dramatic decrease of DeltaPsi(m) in the bottom layer cell mitochondria compared to the top and unusual membrane potential increase of a subpopulation of enlarged mitochondria. DeltapH was also investigated in the three fractions by pretreating the cells with nigericin, allowing to confirm a mitochondrial energetic impairment in older cells.

A comparative evaluation of aflatoxin B1 genotoxicity in fish models using the Comet assay

Aflatoxin B1 (AFB1) is classified as a Group I hepatocarcinogen in humans by the International Agency for Research on Cancer (IARC). The alkaline Comet assay is a simple and rapid method by which DNA damage can be demonstrated as a function of tail moment. The present work is the first to evaluate the genotoxicity of AFB1 in fish using the Comet assay. Two different species of fish were selected as models due to previously established sensitivity to AFB1: rainbow trout (sensitive) and channel catfish (resistant). Fish were i.p. injected with 0.5 mg AFB1/1 ml DMSO/1 kg body weight. The Comet assay was performed after 4 and 24 h on whole blood, liver, and kidney cells of both species. Trout blood and kidney tissue tested displayed significant (p < 0.05) and extensive DNA damage (shown by increased tail moment) after 4 h which then decreased by 24 h. In liver cells, damage progressively increased over time. Conversely, similarly treated catfish showed no elevation in DNA damage over controls at the same doses. These results suggest that the Comet assay is a useful tool for monitoring the genotoxicity of mycotoxins such as AFB1 and for evaluating organ specific effects of these agents in different species.