Bleomycin sulfate-induced micronuclei in human, rat, and mouse peripheral blood lymphocytes

Development of a data-processing method based on Bayesian k-means clustering to discriminate aneugens and clastogens in a high-content micronucleus assay

Genotoxicants can be identified as aneugens and clastogens through a micronucleus (MN) assay. The current high-content screening-based MN assays usually discriminate an aneugen from a clastogen based on only one parameter, such as the MN size, intensity, or morphology, which yields low accuracies (70-84%) because each of these parameters may contribute to the results. Therefore, the development of an algorithm that can synthesize high-dimensionality data to attain comparative results is important. To improve the automation and accuracy of detection using the current parameter-based mode of action (MoA), the MN MoA signatures of 20 chemicals were systematically recruited in this study to develop an algorithm. The results of the algorithm showed very good agreement (93.58%) between the prediction and reality, indicating that the proposed algorithm is a validated analytical platform for the rapid and objective acquisition of genotoxic MoA messages.

Interpreting in vitro micronucleus positive results: simple biomarker matrix discriminates clastogens, aneugens, and misleading positive agents

The specificity of in vitro mammalian cell genotoxicity assays is low, as they yield a high incidence of positive results that are not observed in animal genotoxicity and carcinogenicity tests, that is, "misleading" or "irrelevant" positives. We set out to develop a rapid and effective follow-up testing strategy that would predict whether apparent in vitro micronucleus-inducing effects are due to a clastogenic, aneugenic, or secondary irrelevant mode(s) of action. Priority was given to biomarkers that could be multiplexed onto flow cytometric acquisition of micronucleus frequencies, or that could be accomplished in parallel using a homogeneous-type assay. A training set of 30 chemicals comprised of clastogens, aneugens, and misleading positive chemicals was studied. These experiments were conducted with human TK6 cells over a range of closely spaced concentrations in a continuous exposure design. In addition to micronucleus frequency, the following endpoints were investigated, most often at time of harvest: cleaved Parp-positive chromatin, cleaved caspase 3-positive chromatin, ethidium monoazide bromide-positive chromatin, polyploid nuclei, phospho-histone H3-positive (metaphase) cells, tetramethylrhodamine ethyl ester-negative cells, cellular ATP levels, cell cycle perturbation, and shift in γ-H2AX fluorescence relative to solvent control. Logistic regression was used to identify endpoints that effectively predict chemicals' a priori classification. Cross validation using a leave-one-out approach indicated that a promising base model includes γ-H2AX shift and change in phospho-histone H3-positive events (25/30 correct calls). Improvements were realized when one or two additional endpoints were included (26-30/30 correct calls). These models were further evaluated with a test set of 10 chemicals, and also by evaluating 3 chemicals at a collaborating laboratory. The resulting data support the hypothesis that a matrix of high throughput-compatible biomarkers can effectively delineate two important modes of genotoxic action as well as identify cytotoxicity that can lead to irrelevant positive results.

Antineoplastic Drugs as a Potential Risk Factor in Occupational Settings: Mechanisms of Action at the Cell Level, Genotoxic Effects, and Their Detection Using Different Biomarkers

U članku je prikazana osnovna podjela antineoplastičnih lijekova prema mehanizmima djelovanja na razini stanice. Objašnjeni su mehanizmi genotoksičnosti najvažnijih vrsta lijekova koji se primjenjuju u okviru uobičajenih protokola za liječenje zloćudnih novotvorina. Navedena je važeća klasifikacija antineoplastika prema kancerogenom potencijalu, podaci o mutagenom potencijalu te je prikazana njihova podjela u skladu s anatomsko-terapijsko-kemijskim sustavom klasifikacije. Sustavno su prikazani najvažniji rezultati svjetskih i hrvatskih istraživanja na populacijama radnika izloženih antineoplasticima, provedenih u razdoblju 1980.-2009. s pomoću četiri najčešće primjenjivane metode: analize izmjena sestrinskih kromatida, analize kromosomskih aberacija, mikronukleus-testa i komet-testa. Objašnjena su osnovna načela navedenih metoda te raspravljene njihove prednosti i nedostaci. Biološki pokazatelji daju važne podatke o individualnoj osjetljivosti profesionalno izloženih ispitanika koji mogu poslužiti unaprjeđenju postojećih uvjeta rada i upravljanju rizicima pri izloženosti genotoksičnim agensima. Na osnovi prednosti i nedostataka citogenetičkih metoda zaključeno je da je mikronukleus-test, koji podjednako uspješno dokazuje klastogene i aneugene učinke, jedna od najboljih metoda dostupnih za otkrivanje štetnih djelovanja antineoplastičnih lijekova koji su u aktivnoj primjeni.

SFTG international collaborative study on in vitro micronucleus test I. General conditions and overall conclusions of the study

This study, coordinated by the SFTG (French branch of European Environmental Mutagen Society), included 38 participants from Europe, Japan and America. Clastogens (bleomycin, urethane), including base and nucleoside analogs (5-fluorouracil and cytosine arabinoside), aneugens and/or polyploidy inducers (colchicine, diethylstilboestrol, griseofulvin and thiabendazole), as well as non-genotoxic compounds (mannitol and clofibrate), were tested. Four cell types were used, i.e. human lymphocytes in the presence of cytochalasin B and CHO, CHL and L5178Y cell lines, in the presence or absence of cytochalasin B, with various treatment-recovery schedules. Mitomycin C was used as a positive control for all cell types. Mannitol and clofibrate were consistently negative in all cell types and with all treatment-recovery conditions. Urethane, known to induce questionable clastogenicity, was not found as positive. Bleomycin and mitomycin C were found positive in all treatment-recovery conditions. The base and nucleoside analogs were less easy to detect, especially 5-fluorouracil due to the interference with cytotoxicity, while cytosine arabinoside was detected in all cell types depending on the treatment-recovery schedule. Aneugens (colchicine, diethylstilboestrol and griseofulvin) were all detected in all cell types. In this study, the optimal detection was ensured when a short treatment followed by a long recovery was associated with a long continuous treatment without recovery. There was no impact of the presence or absence of cytochalasin B on the detection of micronucleated cells on cell lines. Scoring micronucleated cells in both mononucleated and binucleated cells when using cytochalasin B was confirmed to be useful for the detection and the identification of aneugens. In conclusion, these results, together with previously published validation studies, provide a useful contribution to the optimisation of a study protocol for the detection of both clastogens and aneugens in the in vitro micronucleus test.

Differential susceptibility to chromatid breaks induced by bleomycin in sub-fertile and fertile bovines

The rate of chromatid breaks was studied in cows with a history of sub-fertility by means of a test based on measurement of the average of breaks induced in lymphocytes of peripheral blood cultures. Fourteen female specimens were divided into two groups: fertile and sub-fertile. Peripheral blood lymphocytes were cultured and prepared for cytogenetic analysis. Two types of culture were established for each animal to evaluate the response of peripheral blood lymphocyte cultures to the genotoxic effects of bleomycin. The first culture did not receive bleomycin treatment (spontaneous chromosome aberrations). Our results showed that median breaks per cell (b/c) (+/-semirange) for spontaneous culture of the fertile and sub-fertile animals and bleomycin sensitivity assay for fertile and sub-fertile animals were 0.00+/-0.06, 0.02+/-0.03, 0.08+/-0.05 and 0.22+/-0.09, respectively. There was no significant difference (P>0.05) in the chromosomal breakage in lymphocytes not exposed to bleomycin; however, in comparing the number of chromatid breaks per cell in cultures treated with bleomycin, the sub-fertile group showed a significantly higher (P<0.05) level than the fertile group. These findings have implications both for identifying cattle with less than optimum fertility as well as for providing potential avenues to study the origins of sub-fertility.

Laserthermia enhances the clastogenic effects of antineoplastic agents in aerobic and chronically hypoxic HeLa cells in vitro

The interactive clastogenic effects of Nd-YAG laser induced hyperthermia (laserthermia) in combination with antineoplastic agents on normally oxygenated and chronically hypoxic HeLa cells were investigated. Exponentially growing HeLa cells were treated with bleomycin sulfate (BLM) (2-4 microg/ml), adriamycin (ADM) (2-4 microg/ml) and actinomycin D (ACT) (0.2-0.4 microg/ml) alone or in combination with laser at various powers (7-13 W) or different laser induced elevated temperatures (39.5-43.5 degrees C). HeLa cells were incubated with 3 microg/ml cytochlasin B for 36 h after treatments and the frequency of micronuclei (MN) were determined in binucleated cells. Results showed a relatively high frequency of MN formation after drug treatments in normally oxic and chronically hypoxic cells, although there was a decrease in the frequency of MN in hypoxic cells compared to oxygenated cells. Laserthermia at various powers and different induced temperatures produced a slight increase in MN formation both in oxic and hypoxic cells. When drug treatment and laserthermia was combined, a profound synergistic effect in MN formation was observed for all three drugs used in these experiments. ACT at a concentration of ten times lower than ADM and BLM produced similar effect. Also, ADM showed a marked synergistic effect with laserthermia compared to BLM at similar concentrations. This study suggests that laserthermia in combination with ADM, BLM or ACT would have a greater genotoxic effect on hypoxic cell populations. Therefore, Nd-YAG laser induced hyperthermia may be a useful modality for elimination of the radioresistant hypoxic cells.

Comparative study of the effects of vitamin C and bleomycin on smokers' and non-smokers' lymphocytes in clastogenicity assays

Free radicals are products of metabolic reactions and of external factors that can injure different biological molecules. However, different antioxidant agents can prevent the action of these reactive species and the damage they cause. Vitamin C (VC) is an important micronutrient found in the diet, which presents defense mechanisms against the free radicals that challenge the cells of the organism. The objective of the present study was to investigate the effect of VC as a modulator of the damage induced in DNA by bleomycin (BLM) in lymphocytes from smokers and non-smokers. The difference in response to the mutagenic potential of BLM between smokers and non-smokers was also investigated. Peripheral blood lymphocyte cultures were treated simultaneously with BLM (20 microg/ml) and/or VC (100, 200, and 400 microg/ml) in the G2 phase of the cell cycle. The results obtained did not demonstrate a statistically significant difference in the response to the antitumor agent BLM between smokers and non-smokers. The data also showed that VC had no significant modulating effect on the frequency of chromosome aberrations induced by BLM in the cells of smokers and non-smokers under the experimental conditions used.

Increased genomic damage in lymphocytes of patients before and after long-term maintenance hemodialysis therapy

This study investigates spontaneous genomic damage in peripheral lymphocytes of 19 patients with severe end-stage renal disease not enrolled onto a maintenance hemodialysis (MHD) program (creatinine level, 5.4 to 10.5 mg/dL) and 16 long-term MHD patients (111 to 282 months on MHD) and the possible association of genomic damage with the degree of renal insufficiency and duration of MHD. Genomic damage was assessed by evaluating the numbers of micronuclei (MN), which are cytoplasmic DNA-containing structures. The average number of MN in the control group of 23 healthy subjects was 15.3 +/- 4.7 MN/1,000 binucleate (BN) cells. The MN frequencies in the long-term MHD group were significantly greater (44.3 +/- 13.7 MN/1,000 BN) than the control frequencies. A significant increase in MN frequencies (28.2 +/- 9.4 MN/1,000 BN) was also seen in patients with advanced renal failure. The major findings of the study, high MN frequencies in long-term hemodialysis and advanced chronic renal failure patients, may result from decreased DNA repair previously shown and may contribute to the increased cancer incidence in these patients.

The mutagenic and toxic effects of bleomycin and trifluoperazine in Drosophila melanogaster

The mutagenic and toxic effects of trifluoperazine and bleomycin on Drosophila were investigated in the progenies of males injected with 0.2 microliter of bleomycin and/or trifluoperazine. The Muller-5 method was used to study the induction of complete- and mosaic-sex-linked recessive lethals induced by 0.1 microgram/ml bleomycin and/or 0.1 mM trifluoperazine in the five successive broods, mainly representing the different stages of spermatogenesis. Trifluoperazine increased the induction rate of sex-linked recessive mutations above the spontaneous rates of the control, but these increases were not statistically significant at the 5% level27 in any of the five different broods. Contrary to trifluoperazine, bleomycin significantly (5% level)27 increased the induction rate of the complete sex-linked recessive lethals over those of the control in the meiotic and premeiotic broods C and D, and the meiotic brood E. As with the separate treatment with bleomycin, the frequencies of the complete sex-linked recessive lethals induced by the simultaneous combination treatment of 0.1 microgram/ml bleomycin and 0.1 mM trifluoperazine were significantly higher than those of the control at the 5%27 level, only in the meiotic and premeiotic broods, but they were not significantly higher than those induced by bleomycin treatment alone19. Treatments with 0.1 mM trifluoperazine enhanced the toxicity, sterility and the number of mutated clusters induced by 0.1 mM bleomycin but did not significantly increase the rates of induced lethals over the additive effects of both drugs in the meiotic and premeiotic stages, suggesting no potentiation effects for trifluoperazine over those of bleomycin in Drosophila. Higher concentrations of the two drugs could not be used due to their high toxicity and sterility effects.

In vivo anticlastogenic effects of L-ascorbic acid in mice

The effects of l-ascorbic acid on the frequency of micronuclei induced by model mutagens, cyclophosphamide (CP), mitomycin-C (MMC) and bleomycin (BLM) hydrochloride were tested using mouse bone marrow. Three doses of ascorbic acid (AsA) viz., 10, 30 and 60 mg/kg b.w. were tested for anticlastogenic effects. The doses of positive mutagens used were, CP-50 mg/kg, MMC-4 mg/kg and BLM-20 mg/kg b.w. Bone marrow sampling was done at 24 h after the treatment. AsA was found to be effective in reducing MN frequency induced by CP and BLM. With MMC only, the highest dose showed a slight inhibitory effect.

Radiobiological evaluation of immigrants from the vicinity of Chernobyl

Eighty individuals (55 adults and 25 children) who were residents of four cities (Kiev, Mozyr, Gomel and Bobrujsk) located 100-200 km from Chernobyl at the time of the accident in 1986 were tested after immigrating to the US from 1989-1991. A whole-body counter was employed to quantitate radiocesium content. In addition, two biological measures of radiation effects, namely, chromosomal integrity using the micronucleus assay and somatic mutation analysis of erythrocytes at the glycophorin A (GPA) locus, were applied to this group. Radiocesium activity in the body ranged from 0 to 56.8 Bq/kg with a mean and standard deviation of 5.0 +/- 8.2 and a median value of 2.0 Bq/kg. Mean radiocesium content by groups was highest in adult males (9.0 +/- 11.7; range 0.21-56.8 Bq/kg) followed by adult females (3.3 +/- 4.5; range 0-21.3 Bq/kg), male children (3.0 +/- 5.7; range 0-20.2 Bq/kg) and lowest in female children (1.6 +/- 3.5; range 0-12.7 Bq/kg). Individuals with the highest radiocesium content in each group belonged to one family that lived in Mozyr (100 km from Chernobyl) until emigrating in 1989. The frequency of lymphocyte micronuclei and erythrocyte GPA allele-loss (O/N) somatic mutations were both significantly correlated with radiocesium content (r=0.57, p=0.002; r=0.75, p=0.002, respectively). The micronucleus frequency also correlated with the estimated internal absorbed dose from radiocesium in a subset of 20 immigrants for whom this calculation was possible (r=0.71, p=0.0005). Altogether, the biomonitoring data indicate that some subjects had radiation doses sufficient to produce gene and chromosomal mutations in blood cells, although these effects cannot be attributed solely to radiocesium exposure.

In vitro mutagenicity and genotoxicity study of 1,2-dichloroethylene, 1,1,2-trichloroethane, 1,3-dichloropropane, 1,2,3-trichloropropane and 1,1,3-trichloropropene, using the micronucleus test and the alkaline single cell gel electrophoresis technique (comet assay) in human lymphocytes

The main objective of this study was to compare the cytotoxic genotoxic and mutagenic activity of a number of chlorinated aliphatic hydrocarbons, which are widely used as chemical intermediates, solvents, degreasing agents etc. in industry, and to establish the structure-toxicity relationship of the chemicals by using the most adequate determinants in estimating their toxicity. The mutagenicity and cytotoxicity of some of the candidate chemicals, namely 1,2-dichloroethylene, 1,1,2-trichloroethane, 1,3-dichloropropane, 1,2,3-trichloropropane and 1,1,3-trichloropropene were evaluated in an in vitro micronucleus assay. The cytokinesis-block methodology was applied on human lymphocytes in the presence or absence of an external metabolic activation system (S9-mix). In the micronucleus assay, all test substances, except 1,2,3-trichloropropane with and without S9-mix and 1,1,2-trichloroethane without S9-mix in the repeated experiment, exhibited a low but statistically significant mutagenic activity, compared to the concurrent control. However, none of the five chemicals was able to induce a clear and reproducible linear dose-dependent increase in micronucleus frequencies in this assay. Generally, mutagenic activity of the chemicals was found in the absence of severe cytotoxicity and/or cell cycle delay. The DNA breakage capacity and the cytotoxicity of these chemicals were also assessed in the alkaline single cell gel (SCG) electrophoresis test (comet assay) with and without S9-mix in isolated human lymphocytes. All chemical compounds induced DNA breakage, in the presence or absence of the metabolic activation system, at the doses tested. The data showed that the DNA reactivity of the chemicals increased with increasing degree of halogenation. The results of the present work suggested that the comet assay might be a more suitable and sensitive screening method than the micronucleus test for this particular class of compound. However, both assays do detect different endpoints.