In vitro induction of micronuclei in lymphocytes: the use of bromodeoxyuridine as a proliferation marker

Nuclear envelope rupture: little holes, big openings

The nuclear envelope (NE), which is a critical barrier between the DNA and the cytosol, is capable of extensive dynamic membrane remodeling events in interphase. One of these events, interphase NE rupture and repair, can occur in both normal and disease states and results in the loss of nucleus compartmentalization. NE rupture is not lethal, but new research indicates that it could have broad impacts on genome stability and activate innate immune responses. These observations suggest a new model for how changes in NE structure could be pathogenic in cancer, laminopathies, and autoinflammatory syndromes, and redefine the functions of nucleus compartmentalization.

In vitro primary human lymphocyte flow cytometry based micronucleus assay: simultaneous assessment of cell proliferation, apoptosis and MN frequency

In order to minimise the number of positive in vitro cytogenetic results which are not confirmed in rodent carcinogenicity tests, biological systems that are p53 and DNA repair proficient should be recommended. Moreover, an appropriate cytotoxicity parameter for top dose selection should be considered. Recent International Conference on Harmonisation draft S2 and Organisation for Economic Co-operation and Development (OECD) 487 guideline accepted the in vitro micronucleus test (MNT) as a valid alternative method for in vitro chromosome aberration test within the in vitro cytogenetic test battery. Since mitosis is a prerequisite for expression of the micronuclei, it is compulsory to demonstrate that cell division occurred, and if possible, to identify the cells that completed mitosis. The OECD guideline recommends the use of a cytokinesis block for the assessment of proliferation in primary T-lymphocytes. The work presented in this manuscript was initiated to develop a novel flow cytometry-based primary human lymphocyte MNT method. This new assay is based on a three-step staining procedure: carboxyfluorescein succinimidyl ester as a proliferation marker, ethidium monoazide for chromatin of necrotic and late apoptotic cells discrimination and 4,6-diaminodino-2-phenylindole as a DNA marker. The proof of principle of the method was performed using genotoxic and non-genotoxic compounds: methyl methanesulfonate, mitomycin C, vinblastine sulphate, cyclophosphamide, sodium chloride and dexamethasone. It has been shown that the new flow cytometry-based primary human lymphocyte MNT method is at least equally reliable method as the standard Cytochalasin B MNT. However, further validation of the assay using a wide selection of compounds with a variety of mechanisms of action is required, before it can be used for regulatory purposes. Moreover, a miniaturisation of the technology may provide an additional advantage for early drug development.

Evaluation of chitosan gel containing liposome-loaded epidermal growth factor on burn wound healing

The objective of this study is to develop a chitosan gel formulation containing liposomes loaded with epidermal growth factor (EGF) and to evaluate their effects on the healing of second-degree burn wounds in rats by immunohistochemical, histochemical and histological methods. EGF-containing multilamellar liposomes which were carried in chitosan gel, EGF gel and EGF-loaded liposome formulations were prepared. The in vivo experiments were performed on female Sprague Dawley rats. Second-degree standard burn wounds were formed on rats and liposomes containing 10 µg/ml EGF in 2% chitosan gel, EGF-chitosan gel and EGF-loaded liposome formulations were applied daily to the burn wounds and biopsies were taken at the 3rd, 7th and 14th day of the treatment. When the results were evaluated immunohistochemically, there were significant increases in cell proliferation observed in the EGF-containing liposome in chitosan gel (ELJ) formulation applied group (P < 0·001). The histochemical results showed that the epithelisation rate in the ELJ group was the highest compared with the other group results (P < 0·001). The histological results indicated and supported these findings and faster epithelisation was observed in the ELJ group compared with the other groups.

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.

Evaluation of the genotoxicity of cis-bis(3-aminoflavone)dichloroplatinum(II) in comparison with cis-DDP

Short-term tests that detect genetic damage have provided information needed for evaluating carcinogenic risks of chemicals to man. The mutagenicity of cis-bis(3-aminoflavone)dichloroplatinum(II) (cis-[Pt(AF)2Cl2]) in comparison with cis-diamminedichloroplatinum(II) (cis-DDP) was evaluated in the standard plate-incorporation assay in four strains of Salmonella typhimurium: TA97a, TA98, TA100 and TA102, in experiments with and without metabolic activation. It was shown that cis-[Pt(AF)2Cl2] acts directly and is mutagenic for three strains of S. typhimurium: TA97a, TA98 and TA100. In comparison with cis-DDP this compound showed a weaker genotoxicity. Contrary to cis-DDP it has not shown toxic properties in the tester bacteria. The genotoxicity of both tested compounds was evaluated using chromosomal aberration, sister chromatid exchange and micronucleus assays, without and with metabolic activation, in human lymphocytes in vitro. The inhibitory effects of both compounds on mitotic activity, cell proliferation kinetics and nuclear division index were also compared. In all test systems applied, cis-[Pt(AF)2Cl2] was a less effective clastogen and a weaker inducer of both sister chromatid exchanges and micronuclei in comparison with cis-DDP, with and without metabolic activation. cis-[Pt(AF)2Cl2] has a direct mechanism of action and is less cytostatic and cytotoxic than the other compound. These results provide important data on the genotoxicity of cis-[Pt(AF)2Cl2] and indicate its beneficial properties as a potential anticancer drug, especially in comparison with cis-DDP.

Metabolic polymorphisms and the micronucleus frequency in buccal epithelium of adolescents living in an urban environment

Micronuclei and other biomarkers were evaluated in oral cells from 11- to 16-year-old girls living in a foster home in the central area of México City. Variables analyzed for possible association with these biomarkers include smoking habits, body mass index, metabolic polymorphisms for NAT1 and GSTM1 and whether the cells were obtained from the cheek or pharynx. The results indicated that individuals having the NAT1*10 homozygous genotype showed a significant increase in chromatin buds and binucleated cells. When the damage in the cheek was compared with damage in the pharynx, a significant increase in micronuclei and binucleated cells was found for the latter tissue in all the individuals analyzed.

Micronuclei and chromatid buds are the result of related genotoxic events

Chromatin buds (CHB), broken eggs, or budding cell nuclei are structures similar to micronuclei (MN) in shape, structure, and size, which are linked to the main nuclei of cells by a thread or stalks of chromatin. They have been observed in numerous cell types and there are reports of their existence relating them with MN or with genotoxic events. However, there is no systematic study reporting their frequency and no experiment has been done to ascertain whether they are really induced by genotoxins. Furthermore, they have been discarded as genotoxic events with the argument that they are not formed in dividing cells. Studies are presented here that indicate that CHB can be considered as genotoxic events and that their origin is comparable to that of MN. Bromodeoxyuridine (BrdU) was used to label proliferating lymphocytes, which were later identified by means of an immunohistochemical method, using the H2O2-DAB stain. The results show that CHB are consistently formed where MN are seen. CHB were induced by the clastogen mitomycin C (MMC) as well as by the aneuploidogen colcemid, with frequencies similar to MN in both cases, and to multinucleated cells in the case of colcemid. CHB occur in lymphocytes of smokers with frequencies similar to those of MN, and we found that the infection with Taenia solium metacestodes induced a comparable increase of both MN and CHB frequency in lymphocytes from pigs.

Genotoxic activity of praziquantel

Praziquantel is a synthetic drug with a remarkable activity against parasites, particularly treamatodes and cestodes. Initial genotoxicity tests used a spectrum of endpoints including tests in bacteria, yeasts, mammalian cells and Drosophila and each one gave negative results. Effects on reproductive cells of mice were negative as well. However, host mediated studies in mice and humans were contradictory and a comutagenic effect with several mutagens and carcinogens was found. Later studies, including monitoring in humans and pigs have shown that Praziquantel induces a greater frequency of hyperploid lymphocytes as well as structural chromosomal aberrations, but not in all the individuals treated. In vitro studies have demonstrated that Praziquantel can induce micronuclei in syrian hamster embryonic (SHE) cells and in lymphocytes of some individuals. The same was found about structural chromosomal aberrations. Fetal death and fetal resorption were found when Praziquantel was administered in high doses to pregnant rats between the 6th and 10th day of gestation. Due to its efficiency as a parasiticide, Praziquantel is in use in Latin-American, Asiatic, African and East-European countries where infections by trematodes and cestodes are frequent. However, the extensive use of Praziquantel in multiple reinfections, in non-infected and non-diagnosed individuals for prevention, in higher doses or repeated doses for cysticercosis treatment and in individuals exposed to environmental mutagens, in conjunction with new findings about its metabolism and genotoxic properties, make it necessary to further evaluate the potential of this drug not only to be mutagenic per se, but to contribute in the development of neoplasm.