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1.
Anticancer Res ; 21(6A): 3903-8, 2001.
Artigo em Inglês | MEDLINE | ID: mdl-11911267

RESUMO

Oxidative stress due to oxygen and various radical species is associated with the induction of DNA single- and double-strand breaks and is considered to be a first step in several human degenerative diseases, cancer and ageing. Naturally occurring antioxidants are being extensively analysed for their ability to protect DNA against such injury. We studied three naturally occuring compounds, Ascorbic Acid, Melatonin and Ellagic acid, for their ability to modulate DNA damage produced by two strong radical oxygen inducers (H2O2 and Bleomycin) in cultured CHO cells. The alkaline Comet assay was used to measure DNA damage and a cytofluorimetric analysis was performed to reveal the intracellular oxidative species. The data showed a marked reduction of H2O2- and Bleomycin-induced DNA damage exerted by Ellagic Acid. On the contrary Ascorbic acid and Melatonin appeared to induce a slight increase in DNA damage per se. In combined treatments, they caused a slight reduction of H2O2-induced damage, but they did not efficiently modulate the Bleomycin-induced one. The Dichlorofluorescein diacetate (DCFH-DA) cytofluorimetric test confirmed the strong scavenging action exerted by Ellagic Acid.


Assuntos
Antioxidantes/farmacologia , Ácido Elágico/farmacologia , Animais , Ácido Ascórbico/farmacologia , Bleomicina/metabolismo , Bleomicina/toxicidade , Células CHO/efeitos dos fármacos , Células CHO/metabolismo , Ensaio Cometa , Cricetinae , Dano ao DNA , Relação Dose-Resposta a Droga , Interações Medicamentosas , Peróxido de Hidrogênio/metabolismo , Peróxido de Hidrogênio/toxicidade , Melatonina/farmacologia , Oxidantes/metabolismo , Oxidantes/toxicidade , Espécies Reativas de Oxigênio/metabolismo , Espécies Reativas de Oxigênio/toxicidade
2.
Environ Res ; 83(3): 311-21, 2000 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-10944075

RESUMO

In a program coordinated by the Italian Ministry of Works, we tested in vitro four pesticides widely employed in a developed agricultural region of central Italy. The four commercial agents were chosen on the basis of their diffusion in agricultural practice, knowledge of their active principle(s), and scant availability of data concerning their toxic and genotoxic activity. The agents were Cirtoxin, Decis, Tramat Combi (TC), and Lasso Micromix (LM). All substances were tested in three in vitro systems: Chinese hamster ovary (CHO) cells, a metabolically competent hamster cell line (Chinese hamster epithelial liver; CHEL), and root tips of Vicia faba (VF). The cytotoxic and genotoxic end points challenged were micronuclei and root tip length (RTL) in VF and mitotic index (MI), proliferation index (PI), cell survival (CS), cell growth (CG), cell cycle length (CCL), sister chromatid exchanges, chromosomal aberrations, and single-cell gel electrophoresis, or comet assay, in CHEL and CHO cells. Tested doses ranged from the field dose up to 200x the field dose to take into account accumulation effects. On the whole, tested agents appear to induce genotoxic damage only at subtoxic or toxic doses, indicating a low clastogenic risk. MI, PI, CS, CG, RTL, and CCL appear to be the less sensitive end points, showing no effects in the presence of a clear positive response in some or all of the other tests. Using cytogenetic tests, we obtained positive results for TC and LM treatments in CHO but not in CHEL cells. These data could be accounted for by postulating a detoxifying activity exerted by this cell line. However, cytogenetic end points appear to be more sensitive than those referring to cytotoxicity.


Assuntos
Ciclo Celular/efeitos dos fármacos , Praguicidas/toxicidade , Agricultura , Animais , Células CHO , Linhagem Celular , Sobrevivência Celular , Ensaio Cometa , Cricetinae , Dano ao DNA , Relação Dose-Resposta a Droga , Fígado/citologia , Fígado/efeitos dos fármacos , Micronúcleos com Defeito Cromossômico , Índice Mitótico , Testes de Mutagenicidade , Raízes de Plantas/efeitos dos fármacos , Troca de Cromátide Irmã
3.
Mutat Res ; 429(2): 239-48, 1999 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-10526208

RESUMO

Among other targets, DNA demethylating agents are known to affect the sister chromatid exchange (SCE) frequency in mammalian cells in vitro. The SCE increase appears to be maintained for many (10-16) cell cycles after the end of the pulse in a given cell population, unlike SCEs induced by DNA damaging agents. Yet, epigenetic changes (such as demethylation) would not be expected to affect SCE at all. In the present report we challenge the working hypothesis of a relation between SCEs and demethylation by comparing SCE induction during different rounds of replication when the parental strands were normally methylated or demethylated. Azacytidine (AZA), ethionine (ETH), mitomycin-C (MMC), UV-irradiation (UV) and hydrogen peroxide (H(2)O(2)) were tested for SCE induction in a Chinese hamster ovary cell line after a single pulse, one or two cell cycles before fixation. Whereas MMC, UV and H(2)O(2) induce SCE in both protocols, AZA and ETH show an effect on SCEs only if administered two cycles before fixation. Because two cell cycles are needed in order to achieve demethylation of the parental DNA strand, the data reported here support our working hypothesis that demethylation in the parental DNA strand, at the level of the replication fork (i.e., the region where SCEs are formed), is responsible for an increase in mistaken ligations of processed damage, eventually yielding an increase in SCEs.


Assuntos
Dano ao DNA/genética , Metilação de DNA , Mutagênicos/farmacologia , Troca de Cromátide Irmã/genética , Animais , Azacitidina/farmacologia , Bromodesoxiuridina , Células CHO , Ciclo Celular , Cricetinae , Etionina/farmacologia , Peróxido de Hidrogênio/farmacologia , Mitomicina/farmacologia , Raios Ultravioleta
4.
Zygote ; 6(4): 351-8, 1998 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-9921646

RESUMO

The effects of two demethylating drugs with a different mechanism of action (5-azacytidine (Aza) and L-ethionine (Eth)) on mouse preimplantation development were investigated. Preimplantation embryos were cultured for 24 h in the presence of the drug and for an additional 24 or 48 h (depending on the cleavage stage) in medium supplemented with bromodeoxyuridine to reveal sister chromatid exchanges (SCEs) and the number of cell cycles performed before harvesting. Striking differences between the two drugs were observed in their influence on proliferation of blastomeres, primary differentiation and sister chromatid differentiation (SCD), and in the pattern of DNA methylation and the frequency of SCEs per cell. At a final concentration of 1 microM Aza had no effects, whereas higher concentrations stopped development of all stages except the zygote. In contrast Eth treatments (5 mM) resulted in a severe reduction of the mean cell number per embryo in comparison with controls. Moreover both the absence of blastocyst formation and no effects on mitotic activity were detected. The most prominent effect of Eth was detected at the zygote and 4-cell stages. An unexpected decrease in SCE frequency in Eth-treated morulae and 4-cell embryos has been observed. Data are explained taking into account the different mechanisms of action of the agents.


Assuntos
Azacitidina/farmacologia , Metilação de DNA/efeitos dos fármacos , Desenvolvimento Embrionário e Fetal/efeitos dos fármacos , Etionina/farmacologia , Animais , Blastocisto/efeitos dos fármacos , Divisão Celular/efeitos dos fármacos , Feminino , Marcação In Situ das Extremidades Cortadas , Técnicas In Vitro , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Troca de Cromátide Irmã/efeitos dos fármacos , Zigoto/efeitos dos fármacos
5.
Mutagenesis ; 12(4): 259-64, 1997 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-9237771

RESUMO

Variations in the genomic DNA methylation level have been shown to be an epigenetic inheritable modification affecting, among other targets, the sister chromatid exchange (SCE) rate in mammalian cells in vitro. The inheritable increase in SCE rate in affected cell populations appears as a puzzling phenomenon in view of the well established relation between SCE and both mutagenesis and carcinogenesis. In the present work we demonstrate that, in a treated cell population, demethylation could be responsible for the inheritable induction of damage proneness affecting both damage induction and repair. Normal and ethionine or azacytidine treated Chinese hamster ovary cells, subclone K1 (CHO-K1), were challenged with UV light (UV) or mitomycin-C (MMC) at different times from the demethylating treatment. The SCE rate was measured with two main objects in view: (i) the induction of synergism or additivity in combined treatments, where mutagen (UV or MMC) pulse is supplied from 0 to 48 h after the end of the demethylating treatment; and (ii) the pattern of damage extinction, for the duration of up to six cell cycles after the end of the combined (demethylating agent + mutagen) treatment. Results indicate both a synergism in SCE induction by mutagens in demethylated cells even if supplied up to four cell cycles after the end of the demethylation treatment and a delay in recovery of induced damage, compared with normally methylated cells. These data are discussed in the light of the supposed mechanism of SCE increase and of the possible biological significance in terms of mutagenesis and carcinogenesis.


Assuntos
Dano ao DNA/efeitos dos fármacos , Dano ao DNA/genética , Metilação de DNA/efeitos dos fármacos , Troca de Cromátide Irmã , Animais , Antimetabólitos/farmacologia , Azacitidina/farmacologia , Células CHO/efeitos dos fármacos , Células CHO/metabolismo , Carcinógenos/farmacologia , Cricetinae , Dano ao DNA/efeitos da radiação , Metilação de DNA/efeitos da radiação , Sinergismo Farmacológico , Etionina/farmacologia , Mitomicina/farmacologia , Mutagênicos/farmacologia , Inibidores da Síntese de Ácido Nucleico/farmacologia , Raios Ultravioleta
6.
Mutat Res ; 374(1): 99-108, 1997 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-9067420

RESUMO

Ethionine is the ethyl analogue of the amino acid methionine. The agent is well known to have a weak demethylating activity. In addition, its capacity to reversibly block the cell cycle progression in G1 human lymphocytes (HL) without interfering with blastic transformation has been reported. In order to better understand the mechanism by which the agent is able to induce cell cycle block, experiments have been performed by using flow cytometry, in HL. In particular the hypothesis of the involvement of a specific target at the G0/G1 boundary was tested by treating HL at different times after blastic transformation. Starting from the 40th hour after PHA stimulation, ethionine loses its blocking capacity in such a way that cells challenged by the agent do not differ from controls in any one of the tested cell cycle-related parameters. We suggest the agent exerts its blocking activity at a specific stage of the transformation pathway.


Assuntos
Etionina/farmacologia , Linfócitos/efeitos dos fármacos , Diferenciação Celular , Divisão Celular , DNA/análise , Citometria de Fluxo , Fase G1 , Humanos , Linfócitos/citologia , Fito-Hemaglutininas/farmacologia , Troca de Cromátide Irmã
7.
Carcinogenesis ; 18(1): 223-8, 1997 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-9054610

RESUMO

Naturally occurring antioxidants are extensively studied for their capacity to protect organisms and cells from damage induced by oxygen reactive species. In fact, oxidative stress is considered a cause of aging, degenerative disease and cancer. We have focused our attention on two agents, ascorbic acid and beta-carotene, commonly considered to be antioxidants, but whose protective activity against cancer is insufficiently known. This paper reports on the ability of these agents to act against damage induced by H2O2 and bleomycin, in Chinese hamster ovary cells cultivated in vitro. Cytogenetic and cytofluorimetric analyses were performed. Both vitamins proved effective in reducing H2O2-induced sister chromatid exchanges, but increased H2O2- and bleomycin-induced chromosomal aberrations. Cytofluorimetric data, in contrast, showed that ascorbic acid and beta-carotene act as scavengers of endogeneous and H2O2-induced oxygen species.


Assuntos
Antioxidantes/farmacologia , Ácido Ascórbico/farmacologia , Bleomicina/antagonistas & inibidores , Aberrações Cromossômicas , Dano ao DNA/efeitos dos fármacos , Peróxido de Hidrogênio/antagonistas & inibidores , Estresse Oxidativo/efeitos dos fármacos , Troca de Cromátide Irmã/efeitos dos fármacos , beta Caroteno/farmacologia , Animais , Bleomicina/toxicidade , Células CHO/efeitos dos fármacos , Cricetinae , Citometria de Fluxo , Peróxido de Hidrogênio/toxicidade
8.
Mutat Res ; 348(4): 187-92, 1995 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-8544872

RESUMO

The rate of ribosomal gene activity was evaluated by silver staining of the Nucleolus Organisers (NOs) in cultured CHO-K1 cells after a 12 h pulse with two demethylating agents (L-ethionine and 5-azacytidine). Silver staining of the NOs was measured every 24 h, from 24 up to 110 h after seeding. The purpose was to test the hypothesis that drug-induced demethylation is associated to heritable modifications of rDNA activity. Ribosomal gene activity was shown to be significantly increased by both agents. The increase persisted throughout the experiments, thereby suggesting the heritability of this epigenetic modification. The analysis of heritable DNA damage or modification is an important task in studying the risk of cancer onset and the mechanisms of cancer induction. In these studies two main results were obtained: (i) heritable DNA variations can be induced by both mutational and epigenetic changes; (ii) the modified end-point was not negatively selected.


Assuntos
Antimetabólitos/toxicidade , DNA Ribossômico/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Mutação em Linhagem Germinativa , Mutagênicos/toxicidade , Animais , Azacitidina/metabolismo , Azacitidina/toxicidade , Células CHO , Deleção Cromossômica , Células Clonais , Cricetinae , DNA Ribossômico/metabolismo , Etionina/metabolismo , Etionina/toxicidade , Metilação/efeitos dos fármacos , Índice Mitótico/efeitos dos fármacos , Mutagênicos/metabolismo , Região Organizadora do Nucléolo/efeitos dos fármacos , Região Organizadora do Nucléolo/metabolismo , Coloração pela Prata
9.
Environ Mol Mutagen ; 26(3): 248-54, 1995.
Artigo em Inglês | MEDLINE | ID: mdl-7588651

RESUMO

Naturally occurring antimutagenic compounds are extensively analyzed for their capacity to protect cells from induced damage. We selected two agents, taurine and ellagic acid, treated in the literature as antioxidants, but whose activity is insufficiently known. This paper reports on the ability of these agents to act against damage induced by mitomycin-C and hydrogen peroxide in Chinese hamster ovary cells cultivated in vitro. Cytogenetic and cytofluorimetric analyses were performed. Ellagic acid proved to have more than one mechanism of action, probably as a scavenger of oxygen species produced by H2O2 treatment, and as a protector of the DNA double helix from alkylating agent injury. In our experimental conditions, taurine seems able to scavenge oxygen species.


Assuntos
Antimutagênicos/farmacologia , Antioxidantes/farmacologia , Aberrações Cromossômicas , Ácido Elágico/farmacologia , Troca de Cromátide Irmã , Taurina/farmacologia , Animais , Células CHO , Cricetinae , Citometria de Fluxo , Peróxido de Hidrogênio/farmacologia , Mitomicina/toxicidade , Testes de Mutagenicidade , Mutagênicos/toxicidade , Troca de Cromátide Irmã/efeitos dos fármacos
10.
Exp Cell Res ; 209(1): 149-55, 1993 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-8223999

RESUMO

A hypothesis is proposed that sister chromatid pairing is due, at least in part, to the pairing between DNA strands belonging to each of the two sister chromatids (conservative pairing). To test this hypothesis interstrand DNA cross-links were induced in late G2-mitosis in CHO cells in order to bind covalently paired DNA strands eventually coming from both sister chromatids and detect the consequent chromatin bridges between sister chromatids (SCCBs). Therefore cells were treated with trimethylpsoralen (TMP) + UVA (365 or 405 nm). Chromatin bridges in ana-telophase were induced by an UVA irradiation at 365 nm, which gives rise to both monoadducts and cross-links, but not by a 405-nm irradiation, which gives rise only to monoadducts. An analysis of colchicine-induced c-anaphases demonstrated that such chromatin bridges were really SCCBs and that terminal regions of chromosomes were particularly involved. The evolution of SCCBs was studied to rule out that they were masked isochromatid exchanges. So TMP + UVA-treated cells were induced to polyploidize with colchicine and labeled with 5-bromodeoxyuridine. Cells treated with TMP + UVA in G2-mitosis appeared as M1 tetraploid c-metaphases; in such cell populations there was not an increase in isodicentric chromosomes, which are derived from isochromatid exchanges. The present data, as a whole, support the hypothesis that a "conservative pairing" between DNA strands of sister chromatids can be present in mitosis.


Assuntos
Cromátides/química , Interfase , Trioxsaleno/farmacologia , Animais , Células CHO , Cromátides/efeitos dos fármacos , Cromátides/efeitos da radiação , Cricetinae , DNA/ultraestrutura , Mitose , Raios Ultravioleta
11.
Mutagenesis ; 8(5): 445-8, 1993 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-8231826

RESUMO

The cytogenetic activity of 9-beta-D-arabinofuranosyladenine (ara-A), a known antitumor agent with an unknown mechanism of action (possibly acting via demethylation and/or decrease in DNA synthesis), has been tested in Chinese hamster ovary (CHO) cells cultivated in vitro, with respect to its ability to induce sister chromatid exchange (SCE). The agent shows no effect on cell cycle parameters (proliferation and mitotic indices) at concentrations up to 100 microM, when administered in pulses ranging from 3 to 12 h. Furthermore, even if administered over the entire treatment period (24 h), a severe cell cycle delay appears only at a concentration of 100 microM. A clear increase in the SCE frequency is produced starting from a concentration of 10 microM, irrespective of the treatment protocol (i.e. pulse versus continuous). This effect on the SCE frequency is maintained for as long as 10 cell cycles after removal of the agent. A partial inactivation of S-adenosyl-L-homocysteine (AdoHcy) hydrolase seems to be produced for as long as 6 h after agent removal. We suggest that under our experimental conditions ara-A exerts its action through a heritable epigenetic modification.


Assuntos
Troca de Cromátide Irmã , Vidarabina/toxicidade , Adenosil-Homocisteinase , Animais , Células CHO , Ciclo Celular , Divisão Celular/efeitos dos fármacos , Cricetinae , Cricetulus , Relação Dose-Resposta a Droga , Mutação em Linhagem Germinativa , Hidrolases/antagonistas & inibidores , Índice Mitótico , Fatores de Tempo , Vidarabina/administração & dosagem
12.
Mutat Res ; 299(1): 37-44, 1993 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-7679191

RESUMO

Humic acids are natural components of organic matter widespread in the environment. In spite of the incomplete knowledge about their composition, increasing interest in humic acid activity is justified by their ubiquity. Four different humic acids have been tested in Chinese hamster ovary cells in vitro, both alone and in combination with two well-known mutagens (mitomycin C and maleic hydrazide). Data about sister-chromatid exchanges, mitotic and proliferation indices were collected. Our results, on the whole, indicate: (i) a slight mutagenicity and toxicity of tested humic acids, probably due to chlorination during sample preparation; (ii) a desmutagenic rather than antimutagenic activity of the tested humic acids.


Assuntos
Antimutagênicos/farmacologia , Substâncias Húmicas/farmacologia , Hidrazida Maleica/antagonistas & inibidores , Mitomicina/antagonistas & inibidores , Animais , Células CHO , Divisão Celular/efeitos dos fármacos , Cricetinae , Cricetulus , Substâncias Húmicas/toxicidade , Hidrazida Maleica/toxicidade , Mitomicina/toxicidade , Índice Mitótico , Testes de Mutagenicidade , Troca de Cromátide Irmã
13.
Environ Mol Mutagen ; 18(3): 207-11, 1991.
Artigo em Inglês | MEDLINE | ID: mdl-1915315

RESUMO

Spermine and spermidine, ubiquitous polyamines present in bacteria and animal cells, are also involved in cell growth. Since they interact with the double helix, they can stabilize the DNA molecule. Recent evidence of the antimutagenic and anticarcinogenic capacity of spermine has focused attention on the mechanism(s) by which such agents can protect cells from induced damages. In the present paper we show the ability of spermine and spermidine to decrease the level of sister chromatid exchanges induced in Chinese hamster ovary cells cultivated in vitro, by treating them with Psoralen + UVA irradiation (able to induce mainly monoadducts and DNA cross-links). Two different mechanisms of polyamine action can be invoked to explain the preservative activity of this class of agents.


Assuntos
Antimutagênicos/farmacologia , Ficusina/farmacologia , Poliaminas/farmacologia , Troca de Cromátide Irmã/efeitos dos fármacos , Raios Ultravioleta , Animais , Células CHO , Divisão Celular/efeitos dos fármacos , Divisão Celular/efeitos da radiação , Cricetinae , Índice Mitótico/efeitos dos fármacos , Índice Mitótico/efeitos da radiação , Terapia PUVA , Troca de Cromátide Irmã/efeitos da radiação , Espermidina/farmacologia , Espermina/farmacologia
14.
Mutat Res ; 245(3): 211-5, 1990 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-1700295

RESUMO

Many carcinogenic agents are able to affect the methylation level in mammalian cells cultivated in vitro. The capacity of azacytidine (AZA) to demethylate DNA can be used to examine the relationship between the genomic methylation level and cytogenetic end-points. Here we compared the sister-chromatid exchange (SCE) level with the genomic % methylcytosine in a Chinese hamster ovary cell line in vitro after giving a single 10-microM pulse of AZA. Both parameters were followed up to 16 cell cycles after the agent was removed. While the SCE level increased starting 2 cycles from the treatment and persisted for the entire 16 cycles, the methylcytosine level, after an initial 50% decrease, approached the control value, completely returning to it after 10 cell cycles. The possibility that the persistence in the SCE increase is an inherited phenomenon is discussed.


Assuntos
Azacitidina/efeitos adversos , Troca de Cromátide Irmã/efeitos dos fármacos , 5-Metilcitosina , Animais , Ciclo Celular/efeitos dos fármacos , Cromatografia Líquida de Alta Pressão , Cricetinae , Citosina/análogos & derivados , Citosina/química , Técnicas In Vitro , Metilação/efeitos dos fármacos
15.
Anticancer Res ; 9(4): 1129-32, 1989.
Artigo em Inglês | MEDLINE | ID: mdl-2510581

RESUMO

Sister chromatid exchanges (SCEs) are a very sensitive genetic end-point for in vitro identification of presumed carcinogenic and mutagenic agents, although the mechanism of their formation is still to be elucidated. The present work shows the influence of spermidine on SCE induction by two different DNA damaging agents: Mitomycin-C (MMC) and N-Methyl-N'-Nitro-N-Nitrosoguanidine (MNNG). The SCE level induced by MMC was significantly decreased by spermidine. On the contrary, MNNG-induced SCEs were not affected. It has recently been suggested that MMC, via its reduced metabolite mitosene, produces bulky mono-and bi-adducts in DNA, mainly located in the minor groove of the double helix. MNNG, instead, directly methylates several electrophilic sites of DNA bases, such as the N7 and the O6 of guanines and the N3 of adenines. Both MMC and MNNG, despite their different mechanism of action, are potent SCE inducers. Spermidine, similarly to its structural analogue Spermine, is known to interact with DNA phosphate groups and to bind reversibly to the minor groove, thus stabilizing the double helix structure. Spermidine, being therefore ineffective on the MNNG-mediated DNA methylation, might affect DNA, making it structurally unavailable for MMC binding.


Assuntos
Metilnitronitrosoguanidina/farmacologia , Mitomicinas/farmacologia , Troca de Cromátide Irmã/efeitos dos fármacos , Espermidina/farmacologia , Animais , Linhagem Celular , Mitomicina
16.
Carcinogenesis ; 8(8): 1059-63, 1987 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-2440615

RESUMO

Eukaryotic DNA methylation has been extensively studied in recent years. The ability of many carcinogens to interfere with DNA methylation has not yet been directly related to their tumorigenic activity. Recent data obtained using L-ethionine and 5-azacytidine--both demethylating agents--showed a small but significant increase in the sister chromatid exchange (SCE) rate induced in mammalian cells (human lymphocytes and CHO cells). In this paper we show that the SCE increase induced by both these agents in Chinese hamster ovary (CHO) cells persists for as long as 10 cell cycles. On the other hand mitomycin-C and u.v. light-induced SCEs show a rapid decrease to the control value, as reported for all known SCE inducers. We suggest that DNA demethylation and SCEs are connected through a perturbation of the cell machinery at the level of the replication fork, producing an increase of the error-prone ligation. Since the methylation level is maintained (inherited), the SCE increase produced by these recombinational events will not be corrected through several cell cycles.


Assuntos
Azacitidina/farmacologia , Ciclo Celular , DNA/metabolismo , Etionina/farmacologia , Troca de Cromátide Irmã , Animais , Células Cultivadas , Cricetinae , Cricetulus , Humanos , Metilação , Mitomicina , Mitomicinas/farmacologia , Raios Ultravioleta
17.
Mutat Res ; 175(3): 171-7, 1986 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-3773929

RESUMO

The highest SCE frequency induced by HN2 in PHA-stimulated human lymphocyte cultures is obtained when cells are treated immediately before the S phase, about 27-30 h after PHA stimulation. When HN2 treatment occurs during the G1 phase, the induced SCE frequency is inversely related to the duration between treatment and the onset of the S phase, suggesting that removal of the SCE-inducing lesion occurs during G1. High concentrations of L-ethionine (15-30 mM) inhibit cell-cycle progression in G1. The SCE frequency induced by treatment with HN2 (0.5 muM) during liquid holding is always lower than the SCE frequency induced by treatment with HN2 after release of the cells from liquid holding. This result indicates that SCE-inducing lesions caused by HN2 are removed during the cell-cycle delay. Cultures treated with HN2 after release from 2-12 h of liquid holding in late G1 show a higher SCE frequency than non-arrested, HN2-treated cultures. This effect is likely due to an enrichment of cells in S after release from liquid holding.


Assuntos
Etionina/farmacologia , Linfócitos/citologia , Mecloretamina/toxicidade , Troca de Cromátide Irmã/efeitos dos fármacos , Ciclo Celular/efeitos dos fármacos , Células Cultivadas , Humanos , Interfase/efeitos dos fármacos , Ativação Linfocitária , Linfócitos/efeitos dos fármacos
18.
Mutat Res ; 175(2): 83-9, 1986 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-3762577

RESUMO

UV-irradiation (254 nm) was found to induce a smaller increase of SCE in human lymphocytes than in human fibroblasts and CHO cells. The UV-induced SCE frequency in human lymphocytes was not influenced by the duration between irradiation and the subsequent S-phase. UV-irradiated lymphocytes showed a slightly more than additive response to the SCE-inducing effect of HN2 and acetaldehyde in comparison with non-irradiated cells. The UV-induced SCE frequency was similar in lymphocyte cultures containing 20 and 100 microM of BrdUrd. The results suggest that human lymphocytes are relatively insensitive to the SCE-inducing effect of UV-irradiation, and that SCE-inducing damage caused by UV is not removed during the G1 phase in these cells.


Assuntos
Troca de Cromátide Irmã/efeitos da radiação , Raios Ultravioleta , Acetaldeído/farmacologia , Animais , Bromodesoxiuridina/farmacologia , Células Cultivadas , Cricetinae , Cricetulus , Relação Dose-Resposta à Radiação , Humanos , Interfase , Linfócitos/efeitos da radiação , Linfócitos/ultraestrutura , Mecloretamina/farmacologia , Troca de Cromátide Irmã/efeitos dos fármacos
19.
Mutat Res ; 128(2): 153-9, 1984 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-6433187

RESUMO

L-Ethionine is an ethyl analogue of the amino acid, methionine, well known as a carcinogen but not as a mutagen. Its activity is clearly related to its capacity to hypomethylate DNA and RNA. At a final concentration of 5 mM, L-ethionine completely inhibits DNA synthesis in PHA-stimulated human lymphocytes, probably acting on a methylation reaction critical for the initiation of the S phase. This block can be reversed. Utilizing this capacity of L-ethionine to block cell proliferation, we have studied the influence of G0 and G1 repair of premutational damage (PMD) (equivalent to liquid-holding recovery in bacteria) on spontaneous and MMC-induced SCEs in human lymphocytes. Our results clearly show that L-ethionine in our experimental conditions significantly increases the frequencies of spontaneous and MMC-induced SCEs. In view of the hypomethylating activity of the analogue, we hypothesize that this action at the replication fork level may increase the error-prone ligation of unrepaired lesions, thus influencing the frequency of occurrence of SCEs.


Assuntos
Antibióticos Antineoplásicos/toxicidade , Troca Genética/efeitos dos fármacos , Etionina/farmacologia , Interfase/efeitos dos fármacos , Linfócitos/citologia , Mitomicinas/toxicidade , Troca de Cromátide Irmã/efeitos dos fármacos , Divisão Celular/efeitos dos fármacos , Células Cultivadas , Técnicas de Cultura/métodos , Humanos , Cinética , Linfócitos/efeitos dos fármacos , Masculino , Mitomicina
20.
Chromosoma ; 56(3): 243-8, 1976 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-964104

RESUMO

The composition in segregated haploid sets of paternal and maternal chromosomes has been studied in order to verify whether their composition is uniparental of mixed, fixed or variable. Primary cultures where prepared using kidneys from hybrids of strains of Mus musculus in which the parental chromosomes are distinguishable; the maternal set consists of 20 teleocentric chromosomes, the paternal set of 9 metacentric chromosomes, derived by Robertsonian fusion and 2 telocentrics. Applying Seabright's banding technique, an analysis of segregated haploid and diploid cells, which have originated spontaneously through polyploidisation-segregation processes was carried out. It was concluded that the haploid sets have a variable composition of paternal and maternal chromosomes.


Assuntos
Mitose , Ploidias , Animais , Cruzamentos Genéticos , Feminino , Masculino , Camundongos , Linhagem
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