The mutagenicity of Gramoxone (paraquat) on different eukaryotic systems

Ecofriendly Approach on the Removal of Reactive Orange 107 from Aqueous Solutions Using Cladophora Species as a Novel Biosorbent

The efficiency of Cladophora species for the removal of Reactive Orange 107 (RO107) from the aqueous solution was evaluated through batch adsorption studies by optimising various process parameters such as pH (3-8), dye concentration (100-500 mg/l), biosorbent concentration (100-500 mg/l), temperature (25-45 °C) and contact time (12-108 h). The results revealed that the optimum conditions for RO107 decolourisation (87%) was found on 72 h of incubation with 100 mg/l dye concentration amended with 200 mg/l biosorbent at pH 6 at 25 °C. The mechanism of dye adsorption was evaluated using isotherms, kinetics and thermodynamic models. The experimental data fitted well with Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was endothermic, spontaneous and feasible in nature. Recovery of RO107 from the Cladophora sp. was maximum when 0.1 M HNO3 was used as an eluent. UV-Visible, FT-IR and SEM analyses reveal the interaction between the biosorbent-adsorbate and confirm the process of decolourisation by Cladophora sp. In order to evaluate the nature of the untreated and treated dye solutions, toxicological studies were conducted and the results revealed that the treated dye solution was non- toxic as compared with untreated dye solution. The results of the docking study proved that there was a substantial binding energy between RO107 and the protein (Cytochrome C6) of Cladophora sp. Hence, Cladophora sp. proves to be a promising biosorbent to decolourise RO107 and its potential can be explored in the textile sectors.

Paraquat induced oxidative stress, DNA damage, and cytotoxicity in lymphocytes

Paraquat (PQ) is a herbicide belonging to the group of bipyridylium salts. The objective of this study was to evaluate oxidative stress, DNA damage, and cytotoxicity induced by paraquat in peripheral lymphocyte cells in vivo as well as pathological changes in various tissues. For this purpose, 28 male Wistar rats in 6 different groups were poisoned by paraquat gavage and blood samples were taken from the hearts of rats after during the poisoning period. Oxidative stress, DNA damage, cell membrane integrity, serum lactate dehydrogenase, and cytotoxicity, were investigated by Ferric Reducing Antioxidant Potential (FRAP) test, alkaline comet assay, measuring serum lactate dehydrogenase (LDH), Hoechst staining and flow cytometry with propidium iodide (PI) respectively. The lung, kidney, and liver tissues were also examined pathologically. Paraquat caused dose-dependent DNA damage in peripheral lymphocyte cells and significant oxidative cell membrane damage. The most damage was caused by a single dose of 200 mg/kg b.w of paraquat by gavage. The gradual exposure to a dose of 300 mg/kg b.w of paraquat showed less damage, which could be due to the activation of the antioxidant defense mechanism.

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Paraquat induced oxidative stress.

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Paraquat increases serum lactate dehydrogenase.

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Oxidative stress Inducted by exposure to paraquat Inducted DNA damage.

Use of Lens culinaris Med test as environmental bioindicator to identify the cytogenotoxic effect of paraquat pesticide

Paraquat is the most widely used herbicide and the third most sold pesticide in the world, applied in more than 120 countries despite being banned in the European Union. It is a risk to ecosystems. The genotoxic effect of paraquat was evaluated using the Lens culinaris test. L. culinaris seeds were subjected to 6 concentrations of paraquat (0.1, 0.5, 1, 1.5, 1.5, 2, and 3 ppm) plus a control (distilled water). During 72 h, root development was measured every 24 h. After 3 days, root apices were analyzed to obtain the inhibition of the mitotic index, as well as the type and rate of chromosomal abnormalities present. A decrease in root growth of more than 50% (72 h of exposure) and an inhibition of the mitotic index of 2.9 times in the treatment with 3 ppm compared to the control were observed. The 2 ppm concentration presented all the anomalies found with a frequency of 84 ± 2.5 of micronuclei, 106 ± 3.5 of nuclear lesions, 14 ± 4.7 of nucleus absence, 8 ± 2.7 of telophase bridges, 7 ± 2.7 of binucleated cells, among others. It is also recommended to establish comparisons of L. culinaris with multiple biomarkers since it is presented as a practical and economic alternative.

Chromosomal Abnormalities in Allium cepa Induced by Treated Textile Effluents: Spatial and Temporal Variations

Appropriate effluent treatment processes are expected to significantly reduce the toxicity of effluents before they are released to the natural environment. The present study was aimed to assess the spatial and temporal variations of the physical and chemical water quality parameters of a natural water body receiving treated textile effluents and to assess the chromosomal abnormalities induced by the treated textile effluents. Four sampling sites (A: effluent discharge point; B: 100 m downstream from site A along the tributary; C: 200 m downstream from site A along the tributary; D: 100 m upstream from site A along the tributary) were selected associated to a tributary that received treated textile effluent. The physical and chemical water quality parameters were measured in the composite water samples collected from the study sites, and Allium cepa bioassay was conducted using aged tap water as the control. Sampling was conducted in both rainy and dry seasons. The conductivity, TDS, COD, and colour intensity of the water samples collected from the study sites were significantly higher during the dry season compared to those in the rainy season. Allium cepa root meristematic cells exposed to water samples from sites A, B, and C showed a significantly high interphase and prophase indices compared to those exposed to aged tap water and upstream site during both rainy and dry seasons. The mitotic index of the root tip cells of Allium cepa bulbs exposed to the water samples collected from the effluent discharge point (site A) and from the 100 m downstream site from site A (site B) was significantly lower than that of the other sites in both rainy and dry seasons. However, the mitotic index of the root tip cells of Allium cepa bulbs exposed to the water samples from the upstream site was not significantly different from that of the control treatment during both sampling seasons. The bioassay indicated that the mitotic index and phase index of the root meristematic cells of Allium cepa can be affected by the treated textile effluents released to the water body and the occurrence of C metaphase, chromosomal adherence, bridges, disturbed anaphase, vagrant chromosomes, and chromosomal breaks indicated that the treated textile effluent receiving tributary can possibly contain genotoxic and mutagenic compounds which can induce chromosomal abnormalities.

Yeast-based genotoxicity tests for assessing DNA alterations and DNA stress responses: a 40-year overview

By damaging DNA molecules, genotoxicants cause genetic mutations and also increase human susceptibility to cancers and genetic diseases. Over the past four decades, several assays have been developed in the budding yeast Saccharomyces cerevisiae to screen potential genotoxic substances and provide alternatives to animal-based genotoxicity tests. These yeast-based genotoxicity tests are either DNA alteration-based or DNA stress-response reporter-based. The former, which came first, were developed from the genetic studies conducted on various types of DNA alterations in yeast cells. Despite their limited throughput capabilities, some of these tests have been used as short-term genotoxicity tests in addition to bacteria- or mammalian cell-based tests. In contrast, the latter tests are based on the emergent transcriptional induction of DNA repair-related genes via activation of the DNA damage checkpoint kinase cascade triggered by DNA damage. Some of these reporter assays have been linked to DNA damage-responsive promoters to assess chemical carcinogenicity and ecotoxicity in environmental samples. Yeast-mediated genotoxicity tests are being continuously improved by increasing the permeability of yeast cell walls, by the ectopic expression of mammalian cytochrome P450 systems, by the use of DNA repair-deficient host strains, and by integrating them into high-throughput formats or microfluidic devices. Notably, yeast-based reporter assays linked with the newer toxicogenomic approaches are becoming powerful short-term genotoxicity tests for large numbers of compounds. These tests can also be used to detect polluted environmental samples, and as effective screening tools during anticancer drug development.

Evaluation of herbicides action on plant bioindicators by genetic biomarkers: a review

The use of pesticides has increased worldwide, owing to the demand for products of good quality and to satisfy a growing population. Herbicides represent almost half of the total amount of pesticides used. Although important to the reduction of costs and an increase of productivity, their indiscriminate use, as well as that of the other pesticides, is a global environmental problem, since they affect the living organisms. To evaluate the damage caused by herbicides to the environment, different organisms have been used as bioindicators, especially higher plants, due to several advantages. This is a literature review on herbicidal actions in plant bioindicators, as assessed by genetic biomarkers. Also, the present manuscript aimed to characterize the main organisms (Allium cepa, Vicia faba and Tradescantia spp.) and the most used biomarkers (mitotic index, chromosome aberrations, micronuclei, sister chromatid exchange and mutations). We concluded that herbicides induce cytotoxicity and genotoxicity in the assessed bioindicators. The data corroborate the existing warnings of the risks that the indiscriminate and increasing use of pesticides poses to the environment and its biodiversity.

Evaluation of the Phytotoxic and Genotoxic Potential of Pulp and Paper Mill Effluent Using Vigna radiata and Allium cepa

Pulp and paper mill effluent induced phytotoxicity and genotoxicity in mung bean (Vigna radiata L.) and root tip cells of onion (Allium cepa L.) were investigated. Physicochemical characteristics such as electrical conductivity (EC), biological oxygen demand (BOD5), chemical oxygen demand (COD), and total phenols of the pulp and paper mill effluent were beyond the permissible limit specified for the discharge of effluent in inland water bodies. Compared to control plants, seedling exposed to 100% effluent concentration showed a reduction in root and shoot length and biomass by 65%, 67%, and 84%, respectively, after 5 days of treatment. A. cepa root tip cells exposed to effluent concentrations ranging from 25 to 100% v/v showed a significant decrease in mitotic index (MI) from 32 to 11% with respect to control root tip cells (69%) indicating effluent induced cytotoxicity. Further, the effluent induced DNA damage as evidenced by the presence of various chromosomal aberrations like stickiness, chromosome loss, anaphase bridge, c-mitosis, tripolar anaphase, vagrant chromosome, and telophase bridge and micronucleated and binucleated cell in A. cepa. Findings of the present study indicate that pulp and paper mill effluents may act as genotoxic and phytotoxic agents in plant model system.

Chitosan nanoparticles loaded the herbicide paraquat: the influence of the aquatic humic substances on the colloidal stability and toxicity

Polymeric nanoparticles have been developed for several applications, among them as carrier system of pesticides. However, few studies have investigated the fate of these materials in the environment in relation to colloidal stability and toxicity. In nature, humic substances are the main agents responsible for complexation with metals and organic compounds, as well as responsible for the dynamics of these nanoparticles in aquatic and terrestrial environments. In this context, the evaluation of the influence of aquatic humic substances (AHS) on the colloidal stability and toxicity of polymeric nanoparticles of chitosan/tripolyphosphate with or without paraquat was performed. In this study, the nanoparticles were prepared by the ionic gelation method and characterized by size distribution measurements (DLS and NTA), zeta potential, infrared and fluorescence spectroscopy. Allium cepa genotoxicity studies and ecotoxicity assays with the alga Pseudokirchneriella subcapitata were used to investigate the effect of aquatic humic substances (AHS) on the toxicity of this delivery system. No changes were observed in the physical-chemical stability of the nanoparticles due to the presence of AHS using DLS and NTA techniques. However some evidence of interaction between the nanoparticles and AHS was observed by infrared and fluorescence spectroscopies. The ecotoxicity and genotoxicity assays showed that humic substances can decrease the toxic effects of nanoparticles containing paraquat. These results are interesting because they are important for understanding the interaction of these nanostructured carrier systems with species present in aquatic ecosystems such as humic substances, and in this way, opening new perspectives for studies on the dynamics of these carrier systems in the ecosystem.

Metaphase arrest and delay in cell cycle kinetics of root apical meristems and mouse bone marrow cells treated with leaf aqueous extract of Clerodendrum viscosum Vent

OBJECTIVES

To study cell cycle delay and metaphase arresting activity of leaf aqueous extract of Clerodendrum viscosum Vent. (LAECV) in root apical meristems and mouse bone marrow cells.

MATERIALS AND METHODS

Cell cycle delay and metaphase arresting activities of LAECV were analysed, in root apical meristems of onion and wheat, and in mouse bone marrow cells, by scoring mitotic index, metaphase frequency and transition of cells from metaphase to anaphase. Colchicine was used as the standard metaphase arresting drug. Phytochemicals present in LAECV were detected and their phytotoxic activity was evaluated by analysing green-gram (Vigna radiata) seedling's root growth retardation and branch root swelling phenomenon.

RESULTS

LAECV treatment resulted in dose-dependent root growth retardation of green-gram seedling root length (P < 0.01) and half maximal growth inhibitory concentration (IC(50) ) of LAECV was 0.87 mg/ml at 144 h. In onion and wheat root meristem cells the mitotic index decreased, metaphase frequency increased and transition from metaphase to anaphase reduced. Experimentation with mouse bone marrow cells indicated that LAECV induced metaphase arrest (164.3% increase in arrested metaphases per 300 mg/kg body weight, over 2.5 h). Phytochemicals like carbohydrates, glycosides, saponins, terpenoids, triterpenoids, tannins and trace amounts of alkaloids were detected in LAECV.

CONCLUSION

It may be said that LAECV contains mitostatic and metaphase arresting components that are able to induce significant metaphase arrest in root apical meristems and also in mouse bone marrow cells.

Protective effects of eicosapentaenoic acid on genotoxicity and oxidative stress of cyclophosphamide in mice

The aim of this article is to elucidate the mechanism by which eicosapentaenoic acid (EPA) acts against cyclophosphamide (CP)-induced effects. The prevalence of micronuclei, the extent of lipid peroxidation, and the status of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) in both liver and serum of mice were used as intermediate biomarkers of chemoprotection. Lipid peroxidation and associated compromised antioxidant defenses (CAT and GPX) in CP treated mice were observed in the liver, serum, and were accompanied by increased prevalence of micronuclei in bone marrow. The number of MN was significantly different (p < 0.01) between the groups treated with CP (group III, IV, V, VI) and the solvent control (group II) (3.2 ± 0.7‰). There was a dose-dependent reduction in formation CP induced micronuclei by treatment with 100, 200, or 300 mg EPA/kg BW mice. Activities of SOD, CAT, and extent of lipid peroxidation were statistically different in liver cells of mice exposed to EPA only with CP compared with the CP group (group III). The present findings imply that EPA may be a potential antigenotoxic, antioxidant and chemopreventive agent and could be used as an adjuvant in chemotherapeutic applications.

Cytotoxic and genotoxic effects of paraquat in Hordeum vulgare and human lymphocytes in vitro

Two phylogenetically distant types of test-systems-root tip meristems of barley (Hordeum vulgare) and human lymphocytes in vitro were used to detect genotoxicity and cytotoxicity induced by the herbicide paraquat (PQ) in the concentration range (10(-6) to 5 x 10(-4) mol/l). As an endpoint for cytotoxicity the mitotic index (MI) was evaluated. The frequency of chromosome aberrations (CA) and the frequency of micronuclei (MN) were used as endpoints for genotoxicity. A dose-dependent increase of CA and MN was observed in both test systems, although the values for PQ-induced MN were somewhat lower. The increase of the genotoxic effect corresponds to a decrease of mitotic activity. The structurally reconstructed barley karyotype MK14/2034 allowed the allocation of the PQ-specific features of aberration distribution patterns and gave information about which chromosome segments in different chromosomal positions were involved in induced aberrations. Paraquat produced preferably isochromatid breaks and "aberration hot spots" in a restricted number of heterochromatin-containing segments. The comparative analysis of susceptibility in the used test-systems to PQ with respect to its cytotoxic and clastogenic effect showed that the human lymphocytes were more sensitive than Hordeum vulgare.

Biological detection and analysis of toxicity of organophosphate- and azadirachtin-based insecticides in Lathyrus sativus L

In this study, attention was paid to investigate the effect of organophosphate insecticides, profenofos 40% EC, methyl parathion (metacid) 50% EC, and neem-based product nimbecidine 0.03% EC (from Azadirachta indica) on somatic chromosomal behavior, level of leaf protein, and activity of antioxidant enzymes in Lathyrus sativus L., the leguminous herb. The experiments on somatic chromosomes of root tip cells of L. sativus L. revealed that most common type of abnormalities were anaphase bridge, chromosome fragment, breaks, giant interphase, etc. Also, the mitotic index reduced and abnormality index enhanced, which were directly proportional to the rise in concentration as well as time period of exposure of chemicals. The profenofos and metacid induced drastic changes in mitotic index when compared with nimbecidine. The electrophoretic studies of leaf protein of L. sativus L. showed alteration of some major and minor protein bands subjected to spraying of organophosphate insecticides and induced to synthesize additional high molecular mass protein compared to untreated control. Analysis of SOD, EST, and POD activity by non-denaturing polyacrylamide gel electrophoresis showed different patterns of the isoforms. Complete inhibition of EST was observed in profenofos-treated plants, while with metacid- and nimbecidine-treated plants EST was suppressed. Induction and/or increased activities of SOD and POD were generally enhanced. Our present study not only provides the important information for better understanding of the toxic and tolerance mechanisms, but as well can be used as a bio-indicator for contamination by pesticides, which could cause genetic instabilities of natural plant populations and in crop varieties.

In vivo genotoxicity evaluation of a plant based antiarthritic and anticancer therapeutic agent Boswelic acids in rodents

The genotoxic potential of anti-inflammatory/anti-arthritic and anticancer plant based drug molecule Boswelic acids (BA) was studied by in vivo system. Systematic literature survey revealed that studies on the genotoxicity of BA are not available. Although reports on genotoxicity of Boswellia serrata dry extract and modified 3-O-acetyl-11-keto-beta-boswelic acid are available and these studies were conducted in in vitro systems. The earlier general toxicity study of BA has been conducted by us, revealed it to be non toxic. The genotoxicity was carried out in Wistar rats using different cytogenetic assay system-abnormalities viz. chromosomal aberrations; sperm morphology, micronuclei and comet assays. Six groups of animals, each comprised of five rats, were taken for each study. Group1-4 received BA at 125, 250, 500 and 1000 mg/kg p.o., respectively prepared as 2% gum acacia suspension, fifth group received a positive control cyclophosphamide (CP) 40 mg/kg p.o. or metronedazole (MTZ) 130 mg/kg p.o. or mercuric chloride (HgCl(2)) 0.864 mg/kg p.o. (as per the experiment requirement) whereas the sixth group kept as vehicle control. The results on the bases of the data obtained revealed that BA is quite safe as it did not show any genotoxicity at any dose level up to 1000 mg/kg. The positive controls used in different experiments showed highly significant abnormal cytogenetic changes in comparison to the control group.

Cancer incidence among paraquat exposed applicators in the agricultural health study: prospective cohort study

Paraquat (1,1'-dimethyl-4, 4'-bipyridinium dichloride) is a nonselective herbicide that is extremely toxic after acute exposure. It was once widely used in North America and is still used in some countries, including the United States. Although there is little firm evidence that paraquat is a carcinogen, previous studies have suggested a potential relationship with some cancers. This prospective cohort study was performed to evaluate the association between lifetime paraquat exposure and cancer incidence among licensed pesticide applicators with 9.1 years of median follow-up. The lifetime ever-use of paraquat was evaluated in 56,224 subjects at baseline and exposure-response relationship was evaluated in 24,667 subjects (44%) who provided detailed information on total life-time paraquat exposure in a second questionnaire. Among the total subjects, the risk for non-Hodgkin's lymphoma (NHL) in the exposed group was marginally elevated (Relative risk [RR], 1.47; 95% confidence interval [CI], 0.97-2.23) compared to the non-exposed group. However, among the 24,667 applicators who supplied total life-time exposure days, the highest tertile of lifetime exposure-days (LE) and intensity-weighted lifetime exposure-days (IWLE) was not significantly associated with NHL risk (RR, 1.57; 95%CI, 0.57-4.23 for LE; RR, 1.42; 95%CI, 0.40-4.71 for IWLE, respectively) and there was no significant exposure-response trend (p-trend > 0.1). There was some suggestion of a possible link between paraquat exposure and NHL risk in humans, but the inconsistency in exposure level trend suggests that this could be a chance finding.

Evaluation of DNA damage in Chinese toad (Bufo bufo gargarizans) after in vivo exposure to sublethal concentrations of four herbicides using the comet assay

Chinese toad, Bufo bufo gargarizans, is frequently found in rice fields, muddy ponds, wetlands and other aquatic ecosystems in China. Because of its habitat, it has many chances of being exposed to pesticides, such as acetochlor, butachlor, chlorimuron-ethyl, and paraquat, which are extensively used in rice or cereal fields. Amphibians may serve as model organisms for determining the genotoxic effects of pollutants contaminating these areas. In the present study DNA damage was evaluated in the Chinese toad using the comet assay, as a potential tool for the assessment of ecogenotoxicity. The first step was to determine the acute toxicity of the above-mentioned herbicides. In acute tests, tadpoles were exposed to a series of relatively high concentrations of acetochlor, butachlor, chlorimuron-ethyl, and paraquat for 96 h. The LC(50 )(96 h) of acetochlor, butachlor, chlorimuron-ethyl and paraquat were measured as 0.76, 1.32, 20.1 and 164 mg l(-1), respectively. Also, negative effects on the behavior of tadpoles were observed with acetochlor, butachlor, and paraquat. Secondly, the comet assay was used for detecting DNA damage in Chinese toad tadpoles exposed to sublethal concentrations of four herbicides. Significant (P < 0.05) concentration-dependent increase in DNA damage (as indicated by tail length, tail moment, olive tail moment) were observed from erythrocytes of tadpoles exposed to sublethal concentrations of acetochlor, butachlor, paraquat, and methyl methanesulfonate, except chlorimuron-ethyl. To our knowledge, this is the first report describing the use of Bufo bufo gargarizans for genotoxicity assessment of herbicides.

Genotoxic and cytotoxic effects in the bone marrow of rats exposed to a low dose of paraquat via the dermal route

The genotoxic effect of the herbicide paraquat was studied in rat bone-marrow by means of the micronucleus assay. Paraquat at dose levels of 6, 15 and 30 mg/kg body weight was given to rats in a single application via the dermal route. Marrow was collected at 24, 48 and 72 h after the application. The micronucleus assay was done as recommended by standard procedures. Paraquat gave rise to an increase in the number of micronuclei in a dose-dependent manner. The number of micronucleated polychromatic erythrocytes showed a maximum at 48 h and the toxicity was further prolonged, as there was no complete recovery at 72 h. These findings suggest a genotoxic effect of paraquat even after exposure via dermal application.

Paraquat embryotoxicity in the Xenopus laevis cleavage phase

The high Paraquat (PQ, 1-1'-dimethyl-4,4'bipyridylium dichloride) embryotoxicity in Xenopus laevis has been shown to be due to its rapid reduction and instantaneous re-oxidation which produces a reactive oxygen species, ROS. Nevertheless, PQ did not show any effects before hatching, stage 32, which showed a resistance, in early X. laevis development, to oxidative damage. Moreover, in view of its genotoxic properties in several experimental models, we studied PQ in the X. laevis cleavage phase that, characterized by a series of rapid mitotic divisions, might be damaged by genotoxic compounds. Embryos were exposed to 20, 40, 60, and 80 mg/l PQ concentrations from stage 2 to stage 9, and then left to develop in control FETAX solution until stage 47. The 80 mg/l PQ concentration gave 19% embryo mortality at the end of the exposure time, and 16.7% larvae mortality at the end of the test; both values were statistically different from the control, 5 and 6.8% respectively. These results confirmed the high resistance in early X. laevis development to PQ oxidative damage. The malformed larva percentages in the PQ exposed groups were higher as regards the control value but did not show any concentration-response; the most frequent malformed larvae found were affected by abnormal tail flexure coupled with abnormal gut coiling. A further experiment was carried out using the same methodology, but exposing embryos only to the 80 mg/l PQ concentration. The surviving blastulae were embedded in Paraplast, then the slides were stained with 4',6-diamidino-2-phenylindole (DAPI) and the nuclei were examined with a confocal microscope. This new preliminary procedure did not reveal any significant presence of micronucleated micromeres in PQ exposed blastulae with respect to the control. Nevertheless, the mechanism by which PQ induced abnormal tail flexure after cleavage exposure remained unknown. PQ seemed to pass through the jelly coats and vitelline membrane, but it expressed teratogenicity between the 2nd and 3rd day. PQ might be accumulated in the embryos during the exposure, and might express teratogenicity later, but it did not seem to induce genotoxicity during the cleavage phase of X. laevis even at very high concentrations.

Melatonin reduces paraquat-induced genotoxicity in mice

The protection afforded by melatonin against paraquat-induced genotoxicity in both bone marrow and peripheral blood cells of mice was tested using micronuclei as an index of induced chromosomal damage. Melatonin (2 mg/kg) or an equal volume of saline was injected i.p. into mice 30 min prior to the i.p. administration of paraquat (two injections of 15 mg/kg; the paraquat injections were given with a 24 h interval) and thereafter at 6 h intervals to the conclusion of the study (72 h). Using fluorescence microscopy, the number of micronuclei in polychromatic erythrocytes (MN-PCE) per 2000 PCE (1000 PCE/slide) per mouse was counted both in blood and bone marrow, and the ratio of PCE to normochromatic erythrocytes (NCE) (PCE/NCE) was calculated. Paraquat treatment increased the number of MN-PCE at 24, 48, and 72 h, both in peripheral blood and bone marrow cells, while no differences were observed in the PCE/NCE ratio. Melatonin inhibited the paraquat-induced increase in MN-PCE by more than 50% at 48 and 72h. Paraquat toxicity is believed to be due to free radical generation. Since melatonin is known to be an efficient free radical scavenger, it is concluded that melatonin's protection against paraquat-induced genotoxicity is mediated, at least in part, by its free radical scavenging activity.

Evaluation of the genotoxic properties of paraquat in V79 Chinese hamster cells

The genotoxic potential of the herbicide paraquat (PQ), an intracellular generator of superoxide, was comparatively tested in various genotoxicity tests with V79 Chinese hamster cells. PQ clearly induced cytotoxicity and chromosome aberrations but did not induce gene mutations at the HPRT locus or increased DNA migration in the comet assay under the same treatment conditions. Using a modified comet assay protocol with formamidopyrimidine-DNA glycosylase (FPG) protein, a DNA repair enzyme which specifically nicks DNA at sites of 8-oxo-guanines and formamidopyrimidines, we could not detect oxidative DNA base damage after PQ treatment. When cells were treated directly on the slides after lysis (i.e, after the cell membrane barrier was eliminated), increased DNA migration was observed after treatment with high PQ-concentrations. Our results suggest that PQ does not significantly induce DNA lesions relevant for HPRT gene mutations in cultivated V79 cells. Since PQ-induced chromosome aberrations only occur after treatment with high concentrations which totally prevent cell survival and are not preceded by an induction of DNA strand breakage in intact cells, their biological significance has to be questioned.

Mutagenicity of cobalt and reactive oxygen producers

Oxidative stress has been implicated in carcinogenesis yet there are chemicals that produce oxidative stress that are not carcinogenic. Mutations are the inherited results of DNA damage and are critical events in carcinogenesis. The mutagenicity of oxidative stress induced by peroxide, paraquat and cobalt compounds was examined in transgenic gpt+ Chinese hamster cell lines (G12 and G10). These two cell lines are known to be more sensitive to mutagens such as X-rays and UV than their parental V-79 cells. In these studies, the mutagenic activity of cobalt chloride, a metal that induces oxidative stress but is not carcinogenic, was measured to be 7.7 times higher than the spontaneous mutant frequency in G12, but was only 1.5 to 2.5 times higher than spontaneous mutant frequency in G10 cells. The mutant frequency of cobalt sulfide was somewhat lower. Hydrogen peroxide was found to be only weakly mutagenic in G12 cells, and treatment of cells with a combination of hydrogen peroxide and cobalt did not alter the mutation frequency induced by cobalt sulfide alone. Paraquat did not elicit mutagenesis in either cell line. These results indicate that agents producing oxidative stress are not necessarily mutagenic and these results are discussed in the context of the oxidative stress produced by other carcinogens such as nickel compounds.

The w/w+ somatic mutation and recombination test (SMART) of Drosophila melanogaster for detecting reactive oxygen species: characterization of 6 strains

The w/w+ somatic mutation and recombination test (SMART) of Drosophila melanogaster is a fast and low cost in vivo assay that has shown excellent results in the assessment of genotoxicity of a large number of compounds. However, recent studies have revealed that, when procarcinogens are to be evaluated, the performance of the assay is largely dependent on the genetic background of the strains used. To determine which one of the strains available for this test would be advisable to evaluate agents producing reactive oxygen species we have used two approaches. Firstly, the w/w+ assay was carried out using 6 different strains and two compounds: menadione and paraquat. Secondly, 3 biochemical traits were determined for the 6 strains: superoxide dismutase and catalase activities, and their capacity to induce reactive oxygen species. The results suggest that the strains Oregon K and Haag 79 would be usable when potential inducers of reactive oxygen species are to be investigated.

The action of the herbicide paraquat on somatic and germ cells of mice

The genotoxic potential of paraquat was evaluated in mouse somatic (bone marrow) and germ (spermatozoa) cells. Two exposure schedules were conducted: single and multiple treatment. Only for multiple treatment was an increased frequency of chromosomal aberrations observed. In germ cells, paraquat induced an increase of sperm-shape abnormalities when the animals were treated at three stages of cell development: spermatozoa, spermatid and preleptotene spermatogonial cells. These toxicogenetic effects might be attributed to the ability of paraquat to generate oxygen free radicals.