Biomedical subjects

T Ortiz

Publications and source records attributed to T Ortiz.

At least 37 records · Page 2Linked to original sources

PubMed2001

Plasma total homocysteine levels and the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene: a study in an Italian population with dementia.

Hyperhomocysteinemia is a known risk factor for vascular disease and commonly occurs in the elderly. Several studies have shown an association between elevated plasma homocysteine levels and cognitive impairment, indicating that it may play a role in the pathophysiology of dementia. We studied plasma homocysteine, folate, vitamin B12 levels and the MTHFR C677T genotype in an Italian population of patients with dementia. We confirmed that elevated plasma tHcy (>14 micromol/l) is common in elderly subjects with dementia. Although we found a high prevalence of the MTHFR TT genotype (21.2%) the allele frequency is not over-represented relative to the control population. We also observed a high incidence of folate deficiency (38%) in subjects with dementia. Elevated homocysteine was associated with low plasma folate (<5.7 nmol/l) and the MTHFR TT genotype. Moderate to severe hyperhomocysteinemia (>26.1 nmol/l) was associated with a significantly lower MMSE score. Hyperhomocysteinemia may be neurotoxic by several different mechanisms affecting cognitive function. Further studies are needed to fully explore the potential of B vitamin supplementation to lower plasma homocysteine and improve cognitive function.

Aged↗

PubMed2000

Glucosylated isoflavones as DNA topoisomerase II poisons.

Since topoisomerase poisons allow the enzyme to cut and covalently bind to DNA but abort the subsequent rejoining of the molecule after relieving the torsional stress. To study their action we have made use of a supercoiled form of the pRYG plasmid that bears a specific topoisomerase recognition and binding region. The conversion of the supercoiled circular double-stranded DNA to the linear and open circle forms in the presence of a topoisomerase II poison and a denaturation step by proteinase K-SDS is indicative of the efficiency of our test agents to stabilize the cleavable complex. Using this system, three glucosylated isoflavones (6'-methoxy-pseudobaptigenin-7-O-beta-glucoside, genistin, and daidzin) isolated from cytotoxic chloroform and ethyl acetate extracts of Retama sphaerocarpa Boissier, were found to have the ability to stabilize the cleavage complex human DNA topoisomerase II.

DNA↗

PubMed1999

Topoisomerase activities and levels in irradiated Chinese hamster AA8 cells and in its radiosensitive mutant EM9.

PURPOSE: To investigate possible variations in topoisomerase (topo) I and II activities and levels after X-ray treatment in the radiation repair proficient AA8 Chinese hamster cell line for comparison with the radiation sensitive mutant EM9. MATERIALS AND METHODS: AA8 and EM9 cells were irradiated with 5 Gy of X-rays and the activities of topoisomerases I and II in nuclear extracts were studied. Immunological detection of both topoisomerases was carried out in order to detect any changes in the expression of these enzymes as a consequence of irradiation. RESULTS: Topoisomerase activities and levels in irradiated EM9 cells were the same as in control non-irradiated cells. In fact, both topo I and topo II activities clearly increased shortly after irradiation in the parental AA8 cells, with a more rapid increase for topo I than for topo II. In the AA8 cells, an increased level of topo I detectable immunologically was only observed at a later time (1 h) after irradiation, while no similar change was detectable for topo II. CONCLUSIONS: While this hypothesis needs further testing, an attractive idea is that DNA topoisomerases might be involved in the cellular response to radiation damage, either through a direct participation in repair mechanisms or indirectly.

Animals↗

PubMed1999

Inhibitory deficits in probable Alzheimer's disease. A study of movement related potentials and EMG response.

We have recently reported contralateral associated EMG responses to voluntary hand movement in Alzheimer's disease. Several aspects of this process were not fully explained in our last paper. In the present one we present data on the register of movement-related potentials (Negative Shift, NS) and Lateralized Readiness Potential (LRP), which have shown a very fine capacity to reveal processes that occur in the motor cortex while movement execution is being prepared. The associated EMG responses (so called by us) have almost all the characteristics of the partial errors revealed by cognitive psychology. First, it is a covert response, so it can only be detected by EMG recording; second, the appearance of this partial error changes the reaction time in the same way as described by Coles: mainly, by increasing reaction time as compared with clear responses. Nevertheless, contrary to partial errors, the associated EMG response does not constantly appear before the correct response. Associated EMG responses always appear after correct responses, with a constant delay of 54 +/- 28 ms. Our results show also an incorrect response preparation related to associated EMG response. We interpreted this specific feature in relation to inhibitory deficits in motor cortex and associated callosal pathways that avoid a correct response performance in Alzheimer patients.

Aged↗

PubMed1999

Increased levels of DNA topoisomerases in cultured CHO cells treated with the antitumour drug 5-azacytidine.

Cultured Chinese hamster ovary (CHO) cells were treated with the cytidine analogue 5-azacytidine (5-azaC) which, in good agreement with results previously described from studies carried out in other primary or established mammalian cell lines, resulted in extensive chromosome decondensation and a shift in the time of replication of normally late-replicating heterochromatin to earlier replication. DNA topoisomerases (mainly topo I) have been involved in transcription, and the hypomethylating effect of 5-azaC reportedly results in the expression of silenced genes. Whether such an increase in transcription is paralleled by increased levels of both topo I and topo II, as well as by an enhancement in the topoisomerase activities, has been investigated in this work. The results seem to suggest that both the relative amount of topoisomerases and their activities are enhanced after a protracted treatment with the cytidine analogue over those observed in untreated controls. These observations could be significant for antitumour therapy.

Animals↗

PubMed1998

Associated EMG responses to voluntary hand movement in probable Alzheimer's disease.

The goal of this work is to dilucidate the mechanism that yields the associated EMG responses in patients with probable Alzheimer's disease. Seventeen subjects fulfilling this criteria and ten normal subjects as a control group were selected. They were asked to perform an oddball task in which they had to discriminate between two kinds of stimuli and produce a response to one of them. Results show that reaction times in controls and in patients when there is no associated EMG are equal in latency. When the associated EMG response occurs in the pathological group reaction time is significantly increased. Furthermore, the associated EMG response is delayed in 55 milliseconds when compared to the voluntary movement. Although these results may reflect some controversy, we interpret this finding as a contralateral inhibitory deficit associated to the corpus callosum abnormalities that occur in the evolving course of Alzheimer's disease.

Aged↗

PubMed1998

Protection provided by exogenous DNA ligase in G0 human lymphocytes treated with restriction enzyme MspI or bleomycin as shown by the comet assay.

DNA double-strand breaks (DSB) may arise either spontaneously during cellular processes or as a result of exposure to DNA-damaging agents such as ionizing radiation, or radiomimetic agents such as restriction endonucleases or bleomycin. It is widely accepted that nonrepaired or misrepaired DSB are the main lesions leading to the production of chromosomal aberrations, mutagenesis, oncogenic transformation, and cell killing. Studies focusing on this relationship, as well as the possible modulation of DNA repair mechanisms, are currently of major interest. A wide variety of test systems are available to study DNA damage. In the last few years, single-cell gel electrophoresis, commonly known as "comet assay," has been considered a rapid, sensitive, and visual method for quantifying DNA strand breaks and alkali-labile damage in individual cells. In this study, making use of the comet assay, we tried to find out if under conditions that maintain chromatin structure the DNA ligase from T4 phage is able to facilitate the rejoining of strand breaks with different end structures, induced by the restriction endonuclease MspI or bleomycin in living human lymphocytes in a nonproliferating state. T4 DNA ligase, as well as the restriction endonuclease or bleomycin, were introduced together by electroporation into human lymphocytes. Our results support the idea that it is possible to modulate the DSB-rejoining of different DNA strand-breaking agents by exogenous T4 DNA ligase.

Bleomycin↗

PubMed1997

Apoptotic and necrotic cell death are both induced by electroporation in HL60 human promyeloid leukaemia cells.

Cell death was induced by electroporation in HL60 cells, a human promyeloid leukaemia strain, in order to determine by both morphological and biochemical criteria whether necrotic or apoptotic processes occurred. Cells sampled at several times after electroporation were analyzed for the assessment of the following end-points: (i) chromosomal DNA fragmentation; (ii) cell viability; (iii) mono- and oligonucleosomes in the cytoplasmic fraction; (iv) apoptotic index; and (v) morphology of treated cells. The results indicate that about 50% of the cells killed by electroporation die through necrosis, while the remaining 50% of the cells undergo apoptosis. Chromosome damage was also studied by cytogenetic analysis at metaphase. The possibility of killing tumour cells by electroporation, as a variant of electrotherapy, constitutes, in our opinion, a promising procedure in cancer therapy, avoiding the undesirable side effects normally derived from treatment with cytotoxic drugs.

Journal Article↗

PubMed1997

T4 DNA ligase reduces chromosome damage and enhances cell survival in CHO cells treated with bleomycin.

The effect of DNA ligase from T4 phage on the modulation of the damage induced by bleomycin was studied. CHO6 cells were electroporated with either bleomycin alone or bleomycin plus T4 DNA ligase, and both cytogenetic and clonogenic assays were carried out in parallel. Our results show that T4 DNA ligase is able to decrease the frequency of chromosome aberrations in bleomycin-treated cells while increasing cell survival.

Animals↗

PubMed1996

Both bovine and rabbit lymphocytes conditioned with hydrogen peroxide show an adaptive response to radiation damage.

We have carried out experiments to study the possible induction of an adaptive response in cultured bovine and rabbit lymphocytes conditioned with subtoxic doses of hydrogen peroxide after stimulation and subsequently challenged with 1 Gy of X-rays. Peroxide treatment was given at different doses 48 h after the addition of PHA to stimulate the cells. A protective effect of pre-exposure to H2O2 against radiation damage detected as micronuclei in binucleated cells was evident for all the animals tested regardless the dose of H2O2 used, although this effect was in general of greater magnitude in bovine than in rabbit cells. These results lend further support to our previous finding in human lymphocytes that DNA single strand breaks induced by H2O2 (most likely due to the generation of hydroxyl radicals) is the most important lesion to trigger the adaptive response.

Adaptation, Physiological↗

PubMed1996

Sister chromatid exchange induced by DNA topoisomerases poisons in late replicating heterochromatin: influence of inhibition of replication and transcription.

Previous studies have shown the importance of DNA replication fork progression for the cytotoxicity of topoisomerase inhibitors as well as for their ability to induce chromosomal aberrations and sister chromatid exchange (SCE). In the present report, we have carried out experiments in CHO cells in order to study the induction of SCE by topo I and topo II inhibitors in both euchromatin and late-replicating heterochromatin, as well as the possible influence of inhibition of DNA replication or transcription on the occurrence of SCE. Treatment with the DNA synthesis inhibitor aphidicolin reduced the frequency of SCE induced by topoisomerase inhibitors in constitutive heterochromatin of the X chromosome, while the RNA synthesis inhibitor actinomycin D also had an effect on SCE induced by high doses of the topoisomerase poisons, in spite of the lack of active transcription which characterizes this heterochromatic region.

Amsacrine↗

PubMed1996

On the importance of DNA strand breaks as the first event to initiate sister chromatid exchange (SCE): experiments with restriction endonuclease BglI.

The exact molecular mechanism of sister chromatid exchange (SCE) is still unknown, despite the many reports dealing with this cytogenetic end point published in the last 40 years. One point to be investigated is the nature of the original lesion(s) in DNA leading to the production of SCE. Whereas, for chromosomal aberrations, the importance of DNA double-strand breaks has been well established, there is still controversy about the relative importance of strand breaks and base modifications for triggering the process of SCE formation. In the present paper, we have taken advantage of the ability of the restriction endonuclease BglI to induce SCE and have exploited the fact that preincubation with 2,3-butanedione results in the loss of BgiI ability to cut DNA, while it is still able to recognize its sequence in DNA and bind to it, to see whether this alone is enough to initiate SCE formation, or if a physical DNA double-strand break is required. Our results seem to support the necessity of DNA breaks for SCE production.

Animals↗

PubMed1996

Expectancy and response strategy in a three-choice visual task.

We investigated the relationship between sensorial discrimination and motor response by means of movement-related potentials, in a task where subjects had to discriminate between 3 stimuli presented visually in a random way. The results indicate that subjects anticipate the response to each type of stimulus by following a probabilistic criterion in the absence of a warning stimulus. This criterion entails an erroneous lateralization of cerebral activation and a significant increase in reaction time, despite the reduction of errors.

Adult↗

PubMed1995

Chromosome damage induced by combined treatments with restriction endonucleases introduced into CHO cells by single or double electroporation.

The possible recombination between non-homologous termini produced by restriction enzymes (REs) introduced in CHO cells by electroporation was studied. For this purpose, different combinations of REs that produced blunt or 5' overhanging DNA double-strand breaks were electroporated into cells either at the same time or separately by double electroporation experiments. Prior to double electroporation, it was confirmed that, once the cells have been electroporated, they resist a second electroporation, as assessed by cell viability analysis. Besides, the efficient and homogeneous introduction of labelled, non-permeable molecules was assessed by fluorescence microscopy. Our results showed interaction for most of the conditions, mainly when the REs were introduced separately. Differences found in the degree of interaction between the combinations studied are discussed.

Animals↗

PubMed1995

T4 DNA ligase modulates chromosome damage induced by restriction endonucleases through an error-free process.

The possible modulation by T4 DNA ligase of the DNA double-strand breaks produced by restriction endonucleases in living mammalian cells was studied. A clear decrease in the frequency of chromosomal aberrations was observed when T4 DNA ligase was included in the electroporation treatment along with restriction enzymes inducing either cohesive- or blunt-ends in DNA. The relative proportions of exchange-type aberrations were similar for both kinds of treatments (with and without ligase), which seems to suggest an error-free ligation by T4 DNA ligase.

Animals↗

PubMed1994

P300 latency and amplitude in the diagnosis of dementia.

P300 latency and amplitude were investigated in 10 normal elderly individuals, 10 institutionalized elderly persons with dementia not of the Alzheimer's types, and 10 elderly people with Alzheimer's disease. Significant differences between control and dementia groups (but not between dementia groups) were noted in the P300 latency, but not amplitude. Such differential latencies were observed in the anterior and in the left temporal and parietal areas of the brain.

Aged↗

PubMed1993

Importance of replication fork progression for the induction of chromosome damage and SCE by inhibitors of DNA topoisomerases.

Previous studies have shown the importance of DNA replication fork progression for the cytotoxicity of topoisomerase inhibitors. Nevertheless, while it was concluded that an interference of moving forks with drug-stabilized topo I-DNA complexes is critical for cell death, in the case of topo II only a partial contribution to cell killing was proposed. We have studied the influence of inhibition of DNA replication by aphidicolin on the production of chromosomal aberrations and SCE by topoisomerase inhibitors. Our results seem to indicate that fork progression is necessary for both cytogenetic endpoints. Pulsed field gel electrophoresis also confirmed this conclusion at the level of DNA breakage (double-strand breaks) efficiently induced by m-AMSA treatment alone, but not when aphidicolin was present. Differences found between topo I and topo II inhibitors (camptothecin and m-AMSA, respectively) could be explained as due to differences in their persistence in trapping the 'cleavable complex'.

Amsacrine↗

PubMed1993

Poly-D-lysine enhances the genotoxicity of bleomycin in cultured CHO cells.

Cultured CHO cells were treated with the radiomimetic antitumor agent bleomycin (BLM) and post-treated with the polycationic compound poly-D-lysine (PDL), recently reported by us as able to potentiate chromosome damage induced by X-rays and chemical mutagens in both plant and mammalian cells. Our results seem to indicate that PDL enhances the genotoxic action of BLM measured as induced chromosomal aberrations, colony-forming ability and DNA strand breakage. Taking into account the reported low efficiency of BLM treatment due to problems with cellular uptake, enzymatic degradation and efficient repair, the possibility of optimizing the dose-effectiveness for cancer therapy is discussed.

Animals↗