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Biomedical subjects

D Martínez

Publications and source records attributed to D Martínez.

At least 19 recordsLinked to original sources
PubMed2004

Construction of an immunotoxin with the pore forming protein StI and ior C5, a monoclonal antibody against a colon cancer cell line.

Sticholysin I (StI), a potent cytolysin isolated from the sea anemone Stichodactyla helianthus, was linked to the monoclonal antibody (mAb) ior C5. StI acts by forming hydrophilic pores in the membrane of the attacked cells leading to osmotic lysis. ior C5 is a murine IgG1, which recognizes the tumor associated antigen (TAA) ior C2. The cytolysin and the mAb were coupled by using the heterobifunctional cross-linking reagent sulfosuccinimidyl 4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SMCC). Two hybrid molecules composed by one ior C5 and one or two StI molecules were obtained (named conjugated I and II, respectively). The purified conjugates were evaluated by a binding affinity assay against an ior C2-positive colon cancer cell line (SW948). Both molecules were able to recognize the antigen (Ag) in the same way that unconjugated ior C5 does. The activity of both conjugates against human erythrocytes and SW948 cells was assessed. They lost most of their hemolytic activity but their residual activity was very similar. Nevertheless, when their cytotoxicity was studied on the SW948 cell line, only conjugate II killed efficiently the cells, indicating a specific mAb-Ag interaction. In this chimeric molecule the ratio between the cytotoxic and the hemolytic activity was larger than that of the free cytolysin. This fact indicates an increase of the specificity of the toxic effect toward the SW948 cell line and consequently an increase of the difference between its hemolytic and cytotoxic doses. The results herein support the feasibility of directing StI to the surface of cancer cells expressing ior C2 Ag via the mAb ior C5.

Adenocarcinoma↗
PubMed2004

Non-linear filtering of ultrasonic signals using neural networks.

Structure noise from inhomogeneous micro-structures makes the detection of flaws present in highly scattering materials difficult. Several techniques have been applied to improve the signal-to-noise ratio (SNR) in order to make flaw detection easier. Linear filtering does not provide good results because both structure noise and flaw signal concentrate energy in the same frequency band. Non-linear filtering can be used to reduce the structure noise of ultrasonic signals. Therefore, neural networks are applied in this work for this purpose. In order to use neural networks for non-linear filtering, dynamic structures must be applied. The easiest way to implement a neural network with the capability of processing temporal patterns is to consider them spatial ones, applying the signal into a tapped delay line of finite extension, that is the input of a static neural network (for example, a multi-layer perceptron). In this work, a dynamic neural network has been built to filter ultrasonic signals with structure noise, and has been trained with the real-time back-propagation algorithm, using as inputs 3000 synthetic ultrasonic signals of 896 samples each. Target signals for training are the same as the ones used as inputs but without noise. The neural network is trained in order to generate as output the target signal when the noisy input one is applied. For testing the performance of the non-linear filter, a new set of 500 noisy signals has been used. The SNR improvement is about 6 dB average. The results show that this non-linear filtering method is quite useful as pre-processing stage in flaw detection systems.

Algorithms↗
PubMed2004

Treatment and follow-up of HIV-negative multidrug-resistant tuberculosis patients in an infectious diseases reference hospital, Buenos Aires, Argentina.

SETTING: An Argentinean reference hospital specialising in infectious diseases. OBJECTIVE: To assess the outcomes of all human immunodeficiency virus (HIV) negative multidrug-resistant tuberculosis (MDR-TB) patients referred to or diagnosed at Hospital Muñiz. DESIGN: Clinical study for the period 1996-1999, with follow-up until June 2002. RESULTS: One hundred and forty-one adult patients (52.5% female) with resistance to two to seven drugs were studied. Fifty patients (35.5%) had not been treated previously. The most frequently used second-line drugs were 5-F-quinolones, cycloserine and ethionamide in susceptibility based individually tailored three- to five-drug regimens. Hospital admission was associated with treatment success. Forty-five episodes of severe toxicity occurred. Treatment was successful in 51.8% of cases, but follow-up of 73 patients yielded 11.9% relapse. The mortality rate was 19.1% and default was 19.9%. Logistic regression analysis was statistically significant for treatment success in relation to patient admission, residence and resistance pattern. CONCLUSION: The burden of MDR-TB in this setting--prolonged infection, treatment cost and difficulties, low rates of cure and treatment adherence and high rates of fatality and relapse--can be improved by strengthening TB control programme activities and fighting against poverty and HIV/AIDS.

AIDS-Related Opportunistic Infections↗
PubMed2003

Comparison of pore-forming ability in membranes of a native and a recombinant variant of Sticholysin II from Stichodactyla helianthus.

Sticholysin II (St II) a potent cytolysin from the sea anemone Stichodactyla helianthus was obtained by recombinant procedures exhibiting six histidine residues in its N-terminus (St IIn6H). The functional comparison between St II and St IIn6H showed a lesser pore-forming ability for the recombinant than for the native in human or rat red blood cells (RBC) and in large unilamellar vesicles (LUV) of different phospholipid composition. However, binding of St IIn6H to small unilamellar vesicles (SUV) was higher with regard to St II. The explanation to the different permeabilizing capacity of both protein variants is not clear, but a different anchoring of St IIn6H to the lipid bilayer could delay the organization of the competent pore into membrane.

Amino Acid Substitution↗
PubMed2002

Molecular epidemiology of hepatitis B virus in Afro-Venezuelan populations.

Hepatitis B virus (HBV) infection among Venezuelan populations of African origin was analyzed. These populations exhibited lower HBV prevalence than the one found in the African continent. Sequence analysis of 6 isolates showed that 3 belonged to genotype F, while the 3 others were HBV genotype A. HBV genotype A was more common in the Afro-Venezuelan groups than in the general Venezuelan population. This might reflect the introduction of genotype A during the slavery period. The absence of the African genotype E among these isolates supports the hypothesis of a recent origin for this HBV genotype. HBV genotype F has already been introduced to these relatively isolated communities.

Africa↗
PubMed2001

Primary structure of two cytolysin isoforms from Stichodactyla helianthus differing in their hemolytic activity.

Sticholysin I (St-I) and sticholysin II (St-II) are cytolysins purified from the sea anemone Stichodactyla helianthus with a high degree of sequence identity (93%) but clearly differenced in their hemolytic activity. In order to go further into the structural determinants for the different behavior of St-I and St-II, we report here the complete amino acid sequences and the consensus secondary structure prediction of both proteins. The complete determination of St-II primary structure confirms the partial revision of cytolysin III amino acid sequence. All nonconservative changes between St-I and St-II are located at the N-terminal. According to our prediction these changes could be located at the same face of an alpha-helix during pore formation events and could account for the observed differences in hemolytic activity between St-I and St-II.

Amino Acid Sequence↗
PubMed2000

Solid-phase extraction coupling to capillary electrophoresis with emphasis on environmental analysis.

This article reviews the status of solid-phase extraction (SPE) coupled with capillary electrophoresis (CE). It focuses on some of the organic pollutants which have captured the interest of analytical chemists--phenols, surfactants, dyes, polynuclear aromatic hydrocarbons (PAHs), aromatic and aliphatic amines, aromatic acids and aromatic sulfonic acids--and, in particular, on monitoring pesticides from different sources. It shows that the coupling of SPE to CE has considerable potential in the analysis of environmental pollutants.

Amines↗
PubMed1999

Evaluation of different electrolyte systems and on-line preconcentrations for the analysis of haloacetic acids by capillary zone electrophoresis.

This study compares the sodium chromate, potassium hydrogenphthalate, 2,6-naphthalenedicarboxylic acid dipotassium and sodium tetraborate electrolyte systems, for determining haloacetic acids using capillary zone electrophoresis with and without modified electroosmotic flow. In order to detect low concentrations of these compounds, an on-line preconcentration step was carried out. Results were good when standard solutions were analysed, but when the method was applied to real samples, the sample had to be pretreated to decrease the interference of the matrix. For this reason, a solid-phase extraction process with LiChrolut EN cartridges was applied to clean up the sample before the injection.

Acetates↗
PubMed1999

Pheromone-triggered orientation flight of male moths can be disrupted by trifluoromethyl ketones.

In a wind tunnel trifluoromethyl ketones (TFMKs) have been found to disrupt the orientation flight of male moths to pheromone sources (virgin females or synthetic pheromone). This is demonstrated by comparison of the flight parameters of the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides, which had been topically treated with TFMKs, with those calculated for untreated insects. Inhibition occurred in all types of behavior and that of the source contact has been quantified and found to be dose-dependent. The same effect has also been noticed in Mediterranean corn borer males flying to an attraction source consisting of mixtures of (Z)-11-hexadecenyl trifluoromethyl ketone (8), a closely related analogue of the major component of the pheromone, and the natural pheromone blend. The most active TFMKs are those closest in structure to the natural pheromone, along with those chemicals which easily hydrate in solution, such as the beta-thiosubstituted derivatives. Along with the previously reported reduction of catches in the field, our results suggest the possible application of these chemicals in future new pest control strategies.

Animals↗
PubMed1999

Vagus nerve prolonged stimulation in cats: effects on epileptogenesis (amygdala electrical kindling): behavioral and electrographic changes.

PURPOSE: To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (VNS) on daily amygdaloid kindling (AK) in freely moving cats. METHODS: Fifteen adult male cats were implanted in both temporal lobe amygdalae, both lateral geniculate bodies, and prefrontal cortices. A bipolar hook (5-mm separation) stainless steel electrode also was implanted in the unsectioned left vagus nerve. AK only was performed on five of the cats as a control. The remaining 10 cats were recorded under the following experimental conditions: VNS (1.2-2.0 mA, 0.5-ms pulses, 30 Hz) for 1 min along with AK (1-s train, 1-ms pulses, 60 Hz, 300-600 microA), followed by VNS alone for 1 min, four times between 11:00 a.m. and 2 p.m. At different times, VNS was arrested, and AK was continued until stage VI kindling was reached. RESULTS: The behavioral changes evoked by VNS were as follows: left miosis, blinking, licking, abdominal contractions, swallowing, and eventually yawning, meowing, upward gaze, and short head movements. Compulsive eating also was present with a variable latency. Outstanding polygraphic changes consisted of augmentation of eye movements and visual evoked potentials while the animal was awake and quiet, with immobility and upward gaze. An increase of the pontogeniculooccipital (PGO) wave density in rapid eye movement (REM) sleep also was noticeable. AK was completed (to stage VI) in the control animals without a vagus nerve implantation in 23.4+/-3.7 trials. In animals with VNS, the AK was significantly delayed, remaining for a long time in the behavioral stages I-III and showing a reduction of afterdischarge duration and frequency. Stage VI was never reached despite 50 AK trials, except when the vagus nerve electrodes were accidentally broken or vagal stimulation was intentionally arrested. Under these circumstances, 24.4+/-8.16 AK trials alone were necessary to reach stage VI of kindling. CONCLUSIONS: Our results indicate that left, electrical VNS interferes with AK epileptogenesis. This anticonvulsant effect could be related to the increase of REM sleep.

Amygdala↗
PubMed1998

Comparative study of a solid-phase extraction system coupled to capillary electrophoresis in the determination of haloacetic compounds in tap water.

This study compares four different commercial sorbents, LC-SAX (a quaternary ammonium anion exchanger), LiChrolut EN (a highly crosslinked styrene-divinylbenzene), Envi-Carb (a graphitized carbon black) and Oasis HLB [a macroporous poly(divinylbenzene-co-N-vinylpyrrolidone) copolymer], for the solid-phase extraction (SPE) of various haloacetic compounds from aqueous samples. The recoveries with the different sorbents were studied by coupling an off-line SPE system to capillary electrophoresis with indirect photometric detection. The recoveries were highest when LiChrolut EN was used. The limits of detection for the compounds are in the low microgram per litre range and the recovery values are over 80% for dichloroacetic acid and trichloroacetic acid, two of the most habitual haloacetic acids in chlorinated water, when 500 ml of standard solution was preconcentrated using this sorbent. Finally, the performance of the method with different water samples, the effect of chlorination in a treatment plant and the evolution of the haloacetic acids in the water distribution system were tested and the results were compared with those obtained using liquid-liquid extraction and gas chromatography-mass spectrometry.

Dichloroacetic Acid↗
PubMed1998

Capillary zone electrophoresis with indirect UV detection of haloacetic acids in water.

A capillary zone electrophoresis (CZE) system for determining haloacetic acids in water was optimized with indirect photometric detection. Two different carrier electrolytes, potassium hydrogenphthalate and sodium 2,6-naphthalenedicarboxylate, were evaluated in terms of sensitivity and two different electroosmotic flow modifiers, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide, were tested. Parameters such as electrolyte concentration and pH, and the concentration of the electroosmotic flow modifiers, which affect the CZE separations, were investigated. The method was used to determine haloacetic acids in chlorine tap water using the liquid-liquid extraction process.

Acetates↗
PubMed1998

The role of ionic strength on the enhancement of the hemolytic activity of sticholysin I, a cytolysin from Stichodactyla helianthus.

Sticholysin I (St I) is a potent cytolytic polypeptide purified from the Caribbean sea anemone Stichodactyla helianthus. The hemolytic activity of sticholysin is potentiated by its preincubation at high ionic strengths. In the present work the mechanism of the potentiating action of the medium ionic strength on the toxin hemolytic capacity is investigated. It is suggested that preincubation with high saline concentration induces a transition of St I to a more relaxed conformation that facilitates the lytic process.

Animals↗