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Biomedical subjects

F Cortés

Publications and source records attributed to F Cortés.

At least 73 records · Page 4Linked to original sources
PubMed1992

Chromosome damage induced by restriction endonucleases recognizing thymine-rich DNA sequences in electroporated CHO cells.

The influence of BrdU substitution of DNA in Chinese hamster cells on the frequencies of chromosomal aberrations induced by three restriction endonucleases which recognize thymine-rich sequences in DNA has been studied. The restriction enzymes chosen were Eco RI (recognition site G/AATTC), Sca I (AGT/ACT), and Dra I (TTT/AAA). A restriction enzyme that does not have thymine in the recognition sequence, Hae III (GG/CC), was also tried. These enzymes were introduced into cells by electroporation after two cell cycles of BrdU substitution and the aberration yields compared with that observed in non-substituted cells. Our results seem to indicate that the BrdU-substituted chromatin becomes resistant to the chromosome-breaking activity of the restriction enzymes recognizing thymine-rich DNA sequences. These observations are compared with the patterns of cutting of isolated DNA as shown by agarose gel electrophoresis.

Animals↗
PubMed1992

Different effectiveness of 4-nitroquinoline-1-oxide, mitomycin C and ethyl methanesulfonate to induce lesions in DNA leading to sister chromatid exchange throughout successive cell cycles in Chinese hamster ovary cells.

The present study was carried out in Chinese hamster ovary cells in order to determine whether lesions induced by three different mutagens, namely 4-nitroquinoline-1-oxide (4-NQO), Mitomycin C (MMC) and Ethyl methanesulfonate (EMS), can persist for more than one cell generation leading to sister chromatid exchanges (SCE) or, alternatively, they are efficiently repaired during the next replicative period after treatment. In order to accurately score the number of SCEs arising during the first (S1), second (S2) and third (S3) DNA synthetic periods, third-cycle (M3) metaphases showing three-way differential (TWD) staining were analyzed. Our results show that, even though the three compounds tested were efficient in increasing the yield of SCE, the frequency of SCE was more dramatically increased after MMC treatment. Differences were also observed among the three mutagens with regard to the persistence of the lesions leading to SCE throughout successive cell generations. EMS-induced lesions appeared as more persistent than those induced by MMC. However, most of the damage induced by the UV mimetic agent 4-NQO seems to be efficiently repaired after the first round of DNA replication following treatment with the drug.

4-Nitroquinoline-1-oxide↗
PubMed1991

Inhibition of protein kinase C arrests proliferation of human tumors.

We have shown that inhibition of protein kinase C by 1-5-isoquinolinylsulfonyl-2-methylpiperazine, H7, induces differentiation and inhibits proliferation of Neuro 2a cells. We have now tested if H7 is able to inhibit proliferation of: 1) human tumor cell lines from tissues other than brain; and 2) primary cultured cells from several human brain tumors. H7 inhibits, in a dose-dependent manner, proliferation of all human tumor cell lines tested and of primary cultured cells from human brain tumors. These results indicate that inhibition of protein kinase C inhibits proliferation of tumoral cells, therefore, H7, and likely other inhibitors of protein kinase C, could be useful in the clinical treatment of brain (and probably other) tumors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Both cross-links and monoadducts induced in DNA by psoralens can lead to sister chromatid exchange formation.

The relative importance of DNA-DNA cross-links and bulky monoadducts in sister chromatid exchange (SCE) formation was investigated in three human fibroblast cell lines with different repair capabilities. These cell lines included normal cells, which can repair both classes of lesions; xeroderma pigmentosum (XP) cells, which cannot repair either psoralen-induced cross-links or monoadducts; and an XP revertant that repairs only cross-links and not monoadducts. SCEs were induced by two psoralen derivatives, 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) and 5-methylisopsoralen (5-MIP). After activation with long-wave ultraviolet light, HMT produces cross-links and monoadducts in DNA, whereas 5-MIP produces only monoadducts. In normal human cells both psoralens induced SCEs, but if cells were allowed to repair for 18 h before bromodeoxyuridine (BrdUrd) was added for SCE analysis, the SCE frequency was significantly reduced. XP cells showed an SCE frequency that remained high regardless of whether SCEs were analyzed immediately after psoralen exposure or 18 h later. In the XP revertant that repairs only cross-links, both psoralens induced a high yield of SCEs when BrdUrd was added immediately after psoralen treatment. When XP revertant cells were allowed 18 h to repair before addition of BrdUrd, the SCEs induced by HMT were greatly reduced, whereas those induced by 5-MIP were only slightly reduced. These observations indicate that both cross-links and monoadducts are lesions in DNA that can lead to SCE formation.

Bromodeoxyuridine↗
PubMed1991

Premature onset of mitosis and potentiation of chromosome damage induced by poly-D-lysine in plant cells: evidence for G2 repair.

Poly-D-lysine has been reported to induce a triggering of mitosis in plant cells due to a selective stimulatory effect on cells arrested in G2. Root-tip cells of Allium cepa L. were first exposed to maleic hydrazide (MH) early in the cell cycle and posttreated with different concentrations of the polycationic agent while in G2. The result was a dose-dependent potentiation of chromosome damage observed at metaphase without any apparent effect induced by poly-D-lysine itself. The enhancement of the yield of chromosomal aberrations was concomitant with an increase in the frequency of mitosis. In order to test further the stimulatory effect of poly-D-lysine on mitosis, as well as the consequences of a shortening of the time available for repair, cells synchronized by protracted treatment with 5-aminouracil (5-AU), which also induces chromosome damage, were allowed to recover in the presence of the polycationic compound. Our data show that a premature arrival at mitosis resulted in an increase in the frequency of damaged cells observed.

Chromosome Aberrations↗
PubMed1991

Induction of chromosomal aberrations in the CHO mutant EM9 and its parental line AA8 by EcoRI restriction endonuclease: electroporation experiments.

EcoRI restriction endonuclease (RE), which produces cohesive-ended double-strand breaks (dsb) in DNA, was tested in the ethyl methanesulfonate- and X-ray-sensitive CHO mutant EM9 and its parental cell strain AA8 for its chromosomal aberration-inducing effect. The RE was efficiently introduced by electroporation into AA8 cells, while the mutant cells showed a very high sensitivity to electroporation, which consistently resulted in cell death. Nevertheless, the incubation of EM9 cells in the presence of EcoRI, without electroporation, was sufficient to induce about three times the chromosome damage observed in the electroporated parental cell line AA8 for any given dose of the RE.

Animals↗
PubMed1990

Evidence for an adaptive response to radiation damage in plant cells conditioned with X-rays or incorporated tritium.

Allium cepa root-tip cells were first exposed to low 'conditioning' doses of ionizing radiation: to X-rays (0.06 or 0.26 Gy) or to incorporated tritium (1.8 x 10(4) or 7.2 x 10(4) Bq/ml; specific activity: 740.0 GBq/mmol) and subsequently given a 'challenge' dose of 1.5 Gy of X-rays. A reduction in X-ray-induced chromosomal damage was brought about by prior exposure to 0.26 Gy of X-rays, while cells receiving the lower conditioning dose (0.06 Gy of X-rays) did not show any significant reduction. In cells grown in the presence of [3H]TdR on the other hand, the adaptive response was evident after both doses given. The results are essentially in agreement with those published by Wolff's group for human lymphocytes in showing that plant cells in vivo can become 'adapted' by exposure to low-level irradiation so that they become more resistant to the clastogenic effects of X-rays delivered subsequently.

Adaptation, Biological↗
PubMed1990

Adaptive response in human lymphocytes conditioned with hydrogen peroxide before irradiation with X-rays.

Cultured human lymphocytes were first exposed to a low 'conditioning' dose of hydrogen peroxide and, subsequently, irradiated with a 'challenge' dose of 1.5 Gy of X-rays in order to analyse the induction of an adaptive response to oxidative damage. A significant reduction in X-ray-induced chromosome damage was evident when H2O2 was given as a single 30 min pulse 24 h after setting up the cultures and the lymphocytes were exposed to X-rays at 48 h. In contrast, when the cells underwent a repeated exposure to H2O2 before irradiation the yield of aberrations was that expected from the combined treatment.

Cells, Cultured↗
PubMed1990

Differences in the effectiveness of EDTA to induce SCEs and chromosomal aberrations in CHO and Allium cepa chromosomes.

The chelating agent EDTA was able to produce chromosome aberrations (CA) in CHO cells when it was administered simultaneously with BrdUrd (2 x 10(-5) M), without any concomitant effect on the yield of sister chromatid exchanges (SCEs). Root meristematic cells of Allium cepa did not show any type of CA when they were treated with different doses of EDTA (with or without BrdUrd 10(-4) M) while the SCE frequency was increased in a dose-dependent fashion. These effects of EDTA have not been previously reported. It is suggested that deprivation of divalent cations (Ca(+)+/Mg(+)+) probably play an important role in DNA replication and repair processes.

Allium↗
PubMed1989

Scoring of SCE frequency per cell cycle in CHO chromosomes by means of a standardized 3-way-differential staining method.

We have developed 2 alternative protocols to obtain 3-way differentiation (TWD) in Chinese hamster ovary (CHO) cells, in order to analyze the sister-chromatid exchange (SCE) frequency on a per-generation basis. In protocol A, 5-bromodeoxyuridine (BrdU) substitution into DNA was low during the first S period (S1) and high during the next 2 (S2 and S3). In protocol B, on the other hand, BrdU substitution was high during S1 and low during S2 and S3. The main advantage of our procedures is the high efficiency and reproducibility reached by controlling the relative incorporation of BrdU and deoxythymidine (dT) into replicating DNA in the presence of 5-fluorodeoxyuridine (FdU) throughout 3 consecutive S periods. The comparison of the results obtained for both protocols allowed us to evaluate the role of BrdU in the induction of SCEs in each cell cycle. Our results from M3 chromosomes seem to indicate that, under our experimental conditions, neither the concentration of BrdU in the medium nor the rate of BrdU incorporation into nascent DNA is the basic feature responsible for SCE formation. Indeed, the experiments reported here seem to demonstrate that the nature of parental DNA is crucial for the formation of the BrdU-induced SCEs.

Animals↗
PubMed1989

A standardized method for the three-way differential staining of plant chromosomes and the scoring of SCEs per cell cycle.

We have made use of 2 alternative methodologies to obtain 3-way differential staining (TWD) in third-mitosis (M3) chromosomes of Allium cepa, which involve different uptakes of bromodeoxyuridine (BrdU) through 3 cell divisions, in order to evaluate the sister-chromatid exchanges (SCE) frequency on a per-cell-cycle basis. The main innovation introduced by us to the original protocols previously reported has been the use of 5-fluorodeoxyuridine (FdU) to inhibit endogenous thymidine (dT) synthesis. By using different [BrdU]:[dT] ratios in the presence of FdU the relative incorporation of BrdU into replicating DNA can be controlled. The use of 2 different approaches to obtain 3-way differentiation of sister chromatids allowed us to evaluate the role of BrdU in the induction of SCEs in our system. Both procedures rendered nearly 100% of M3 chromosomes showing TWD. An additional advantage of our methodologies is their high degree of reproducibility.

Allium↗
PubMed1989

G2 effects of DNA-repair inhibitors on chromatid-type aberrations in root-tip cells treated with maleic hydrazide and mitomycin C.

In recent years the existence of a DNA-repair process in G2 has been proposed to explain the potentiating effects of DNA-repair inhibitors given in G2 on chromatid aberrations (CA) induced by S-dependent as well as S-independent DNA-damaging agents. In the present report, root-tip cells of Allium cepa were exposed to maleic hydrazide (MH) or mitomycin C (MMC) and post-treated in G2 with caffeine (Caff) and various inhibitors of DNA synthesis. No enhancement of chromosome damage was observed when Caff was present in G2, but hydroxyurea (HU) or 5-fluorodeoxyuridine (FdUrd) potentiated the frequencies of CA. A slight additional increase of CA frequencies was observed following treatment with Ara C and excess thymidine in G2. When MH-damaged cells were pulse-treated with Caff earlier during recovery, the yield of CA was enhanced. The earlier Caff was present following MH treatment, the stronger was the potentiation.

Caffeine↗
PubMed1987

Effects of caffeine and inhibitors of DNA synthesis on chromatid-type aberrations induced by acetaldehyde in root-tip cells.

Root-tip cells of Allium cepa were exposed to acetaldehyde (AA) and post-treated with caffeine and 3 inhibitors of DNA synthesis, namely hydroxyurea (HU), 5-fluorodeoxyuridine (FdUrd), and arabinofuranosylcytosine (araC). Caffeine strongly potentiated the frequency of chromatid-type aberrations when given immediately after the AA treatment or as a 5-h treatment starting 10 h before the addition of colchicine. In contrast, no enhancement was observed when caffeine was present for the last 2.5 h, simultaneously with colchicine. The inhibitors of DNA synthesis were given following this last schedule. Both HU and FdUrd clearly enhanced the yield of AA-induced chromatid aberrations, while no enhancement of chromosome damage was observed after exposure to araC.

Acetaldehyde↗
PubMed1987

Effect of exogenous thymidine on sister-chromatid exchange frequency in Chinese hamster ovary cells with bromodeoxyuridine- and chlorodeoxyuridine-substituted chromosomes.

There are conflicting reports on the effect of exogenous thymidine (dThd) on the frequency of sister-chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) cells. Thymidine has been reported either to increase or to have no effect on SCE frequency under similar experimental conditions. To resolve this controversy, we have carried out a series of experiments to examine the effect of dThd on CHO cells cultured with 5-bromodeoxyuridine (BrdUrd). In addition, we have examined the effect of dThd on CHO cells cultured with 5-chlorodeoxyuridine (CldUrd), a much more potent inducer of SCEs than BrdUrd. The addition of 100 microM dThd to the culture medium caused a consistent decrease in the yield of SCEs in cells grown in BrdUrd for two cell cycles. The decrease was even greater when cells were grown in dThd and CldUrd. Analysis of twin and single SCEs indicated that dThd must be present during the first cell cycle to reduce the frequency of SCEs. Because excess dThd is thought to have an effect when DNA replicates on a template substituted with a halogenated nucleoside, dThd at concentrations from 100 microM to 9 mM was added to cultures for the second cell cycle after a first cell cycle in BrdUrd. In this experiment, the presence of dThd increased SCE frequency in a dose-dependent manner. The results suggest that if dThd competes with halogenated nucleosides and thus decreases their incorporation into DNA, SCEs are suppressed in the subsequent cell cycle, whereas if excess dThd creates a dNTP pool imbalance, SCEs can be increased.

Animals↗
PubMed1987

Factors affecting the production of SCEs by maleic hydrazide in root-tip chromosomes of Allium cepa.

We have investigated the influence of pH on the induction of chromatid-type aberrations and sister-chromatid exchanges (SCEs) by maleic hydrazide (MH) in root-tip cells of Allium cepa. For both cytogenetic endpoints, the lower the pH of the treatment solution, the higher were the frequencies of chromosome alterations detected at metaphase. We have further studied the persistence of lesions giving rise to SCEs during successive cell cycles, as well as the influence of BrdU concentration in the post-treatment medium on the yield of MH-induced SCEs. Our results suggest that the cytogenetic action of MH in many respects resembles that of bifunctional alkylating agents.

Allium↗
PubMed1987

Unique DNA repair properties of a xeroderma pigmentosum revertant.

A group A xeroderma pigmentosum revertant with normal sensitivity was created by chemical mutagenesis. It repaired (6-4) photoproducts normally but not pyrimidine dimers and had near normal levels of repair replication, sister chromatid exchange, and mutagenesis from UV light. The rate of UV-induced mutation in a shuttle vector, however, was as high as the rate in the parental xeroderma pigmentosum cell line.

4-Nitroquinoline-1-oxide↗
PubMed1985

Induction of sister-chromatid exchanges (SCEs) by 5-fluorodeoxyuridine. The role of 5-bromodeoxyuridine incorporated into parental DNA.

The effect of thymidine (dT) and 5-fluorodeoxyuridine (FdU) on the frequency of sister-chromatid exchanges (SCEs) was examined in root-tip cells of Allium cepa. dT was unable to induce SCEs at all the concentrations tested. In contrast, FdU was efficient in the induction of SCEs. A nearly 3-fold increase in the frequency of SCEs was obtained with 5 X 10(-7) M FdU when it was given simultaneously with 5-bromodeoxyuridine (BrdU) for 2 consecutive cell cycles. Also, when FdU was present only for the first round of replication, the rate of SCEs in M2 chromosomes was notably higher than when it was given only during the second replication round. By analyzing M3 chromosomes treated during the second replication round with FdU the results also supported the hypothesis that the majority of the FdU-induced SCEs arise as a consequence of a higher rate of BrdU incorporation, and that most of them are formed when BrdU-containing strands are used as template for DNA synthesis.

Bromodeoxyuridine↗