Ruy Barbosa | União Metropolitana de Educação e Cultura (original) (raw)

Papers by Ruy Barbosa

Analytical Letters, 2005

Oxidative stress can be caused by in vivo chemical generation of reactive oxygen species (ROS) an... more Oxidative stress can be caused by in vivo chemical generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) besides ultraviolet and ionizing radiation. Recently, DNA damage due to RNS became an interesting subject since high nitric oxide (NO) concentration in cells was reported to produce genotoxic effects. The DNA biosensor has been shown to represent a powerful tool for the study of biomolecular interaction mechanisms. The double strand DNA (dsDNA) biosensor was used to study the interaction between dsDNA immobilized on a glassy carbon surface and RNS released by a NO-releasing compound, diethylenetriamine/nitric oxide (DETA/NO). The results showed that it is possible to electrochemically generate NO metabolites such as peroxynitrite that damage dsDNA structures, causing contact between purinic bases and the electrode surface so that their oxidation can be easily detected. The formation of modified DNA bases such as 8-nitroguanine was observed after interaction of DNA with peroxynitrite radicals electrochemically 2525 generated at the electrode surface. The importance of DNA biosensors in the determination of the interaction between DNA and nitric oxide and its metabolites is clearly demonstrated.

Analyst, 1996

The electrochemical determination of zinc arising from zinc-insulin complexes was investigated an... more The electrochemical determination of zinc arising from zinc-insulin complexes was investigated and it was demonstrated that zinc in zinc-insulin solution can be measured in the presence of dissolved oxygen by square-wave anodic stripping voltammetry (SWASV) at mercury thin-film electrodes on glassy carbon disc minielectrode and cylindrical carbon fibre microelectrode substrates. Reoxidation signals arise from complexed zinc at low insulin concentrations ( < 100 nmol 1-*) and from labile zinc at higher concentrations; the latter can be quantified through linear calibration curves. Batch injection analysis with SWASV was successfully tested for the determination of zinc in zinc-insulin solutions in small sample volumes. Since intracellularly stored insulin exists in the form of a zinc-insulin complex, these techniques are very promising for the indirect study of insulin release from pancreatic P-cells.

Abstract In this article we describe the step-by-step implementation of an agent that can trade t... more Abstract In this article we describe the step-by-step implementation of an agent that can trade the USD/JPY currency pair using a 6 hours timeframe. The agent is capable of trading autonomously due to its ability to handle money management and to decide when to buy ...

In this paper we describe an infrastructure for implementing hybrid intelligent agents with the a... more In this paper we describe an infrastructure for implementing hybrid intelligent agents with the ability to trade in the Forex Market without requiring human supervision. This infrastructure is composed of three modules. The “Intuition Module”, implemented using an Ensemble Model, is responsible for performing pattern recognition and predicting the direction of the exchange rate. The “A Posteriori Knowledge Module”, implemented using a Case-Based Reasoning System, enables the agents to learn from empirical experience and is responsible for suggesting how much to invest in each trade. The “A Priori Knowledge Module”, implemented using a Rule-Based Expert System, enables the agents to incorporate non-experiential knowledge in their trading decisions. This infrastructure was used to develop an agent capable of trading the USD/JPY currency pair with a 6 hours timeframe. The agent’s simulated and live trading results lead us to believe our infrastructure can be of practical interest to the traditional trading community.

Abstract-Trading in financial markets is undergoing a radical transformation, one in which algori... more Abstract-Trading in financial markets is undergoing a radical transformation, one in which algorithmic methods are becoming increasingly more important. The development of intelligent agents that can act as autonomous traders seems like a logical step forward in ...

Journal of Craniofacial Surgery, 2004

Plastic and Reconstructive Surgery, 2005

Pflugers Archiv-european Journal of Physiology, 1993

In glucose-stimulated pancreatic β-cells, the membrane potential alternates between a hyperpolari... more In glucose-stimulated pancreatic β-cells, the membrane potential alternates between a hyperpolarized silent phase and a depolarized phase with Ca2+ action potentials. The molecular and ionic mechanisms underlying these bursts of electrical activity remain unknown. We have observed that 10.2–12.8 mM Ca2+, 1 μM Bay K 8644 and 2 mM tetraethylammonium (TEA) trigger bursts of electrical activity and oscillations of intracellular free Ca2+ concentration ([Ca2+]i) in the presence of 100 μM tolbutamide. The [Ca2+]i was monitored from single islets of Langerhans using fura-2 microfluorescence techniques. Both the high-Ca2+ and Bay-K-8644 evoked [Ca2+]i oscillations overshot the [Ca2+]i recorded in tolbutamide. Nifedipine (10–20 μM) caused an immediate membrane hyperpolarization, which was followed by a slow depolarization to a level close to the burst active phase potential. The latter depolarization was accompanied by suppression of spiking activity. Exposure to high Ca2+ in the presence of nifedipine caused a steady depolarization of approximately 8 mV. Ionomycin (10 μM) caused membrane hyperpolarization in the presence of 7.7 mM Ca2+, which was not abolished by nifedipine. Charybdotoxin (CTX, 40–80 nM), TEA (2 mM) and quinine (200 μM) did not suppress the high-Ca2+-evoked bursts. It is concluded that: (1) the channel underlying the burst is sensitive to [Ca2+]i rises mediated by Ca2+ influx through L-type Ca2+ channels, (2) both the ATP-dependent K+ channel and the CTX and TEA-sensitive Ca2+-dependent K+ channel are highly unlikely to provide the pacemaker current underlying the burst. We propose that the burst is mediated by a distinct Ca2+-dependent K+ channel and/or by [Ca2+]idependent slow processes of inactivation of Ca2+ currents.

Molecular Aspects of Medicine, 2004

Nitric oxide (NO Å ) is a diffusible regulatory molecule involved in a wide range of physiologica... more Nitric oxide (NO Å ) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO Å concentration is translated into a cellular signal. From our current knowledge of biological synthesis and decay, the kinetics and mechanisms that determine NO Å concentration dynamics in tissues are poorly understood. Generally, NO Å mediates its effects by stimulating (e.g., guanylate cyclase) or inhibiting (e.g., cytochrome oxidase) transition metal-containing proteins and by post-translational modification of proteins (e.g., formation of nitrosothiol adducts). The borderline between the physiological and pathological activities of NO Å is a matter of controversy, but tissue redox environment, supramolecular organization and compartmentalisation of NO Å targets are important features in determining NO Å actions. In brain, NO Å synthesis in the dependency of glutamate NMDA receptor is a paradigmatic example; the NMDA-subtype glutamate receptor triggers intracellular signalling pathways that govern neuronal plasticity, development, senescence and disease, suggesting a role for NO Å in these processes. Measurements of NO Å in the different subregions of hippocampus, in a glutamate NMDA receptor-dependent fashion, by means of electrochemical selective microsensors illustrate the concentration dynamics of NO Å in the sub-regions of this brain area. The analysis of NO Å concentration-time profiles in the hippocampus requires consideration of at least two interrelated issues, also addressed in this review. NO Å diffusion in a biological medium and regulation of NO Å activity. Ó 2004 Elsevier Ltd. All rights reserved.

Biosensors & Bioelectronics, 2008

The measurement of Nitric oxide ( • NO) in real-time has been a major concern due to the involvem... more The measurement of Nitric oxide ( • NO) in real-time has been a major concern due to the involvement of this ubiquitous free radical modulator in several physiological and pathological pathways in tissues. Here we performed a study aiming at evaluating different types of carbon fibers, namely Textron, Amoco, Courtaulds and carbon nanotubes (University of Kentucky) covered with Nafion ® /o-phenylenediamine (o-PD) for • NO measurement in terms of sensitivity, LOD, response time and selectivity against major potential interferents in the brain (ascorbate, nitrite and dopamine). The results indicate that, as compared with the other carbon fibers and nanotubes, Textron carbon fiber microelectrodes coated with two layers of Nafion ® and o-PD exhibited better characteristics for • NO measurement as they are highly selective against ascorbate (>30,000:1), nitrite (>2000:1) and dopamine (>80:1). These coated Textron microelectrodes showed an average sensitivity of 341 ± 120 pA/M and a detection limit of 16 ± 11 nM. The better performance of the Textron fibers is likely related to a stronger adhesion or more uniform coating of the Nafion ® and o-PD polymers to the fiber surface. In addition, the background current of the Textron carbon fibers is low, contributing to the excellent signal-to-noise for detection of • NO.

Journal of Neurochemistry, 2008

glutathione (amount of GSH + twice the amount of GSSG); LDH, lactate dehydrogenase; MM, minimal m... more glutathione (amount of GSH + twice the amount of GSSG); LDH, lactate dehydrogenase; MM, minimal medium; NO, nitric oxide; RNOS, reactive nitrogen/oxygen species.

Analytica Chimica Acta, 2005

The role of nitric oxide ( • NO) as a regulatory diffusible molecule in the brain requires the ev... more The role of nitric oxide ( • NO) as a regulatory diffusible molecule in the brain requires the evaluation of its concentration dynamics. In this work, we have developed microelectrodes suitable for real time electrochemical measurements of • NO in vitro. Nafion and o-phenylenediamine were used to modify the surface of carbon fiber microelectrodes (8 m diameter; ≈100 m tip length). Coating with Nafion was done at 170 • C and the o-phenylenediamine solution was electropolimerized on the carbon surface. • NO peak potential (+0.78 ± 0.03 V versus Ag/AgCl) was determined by square wave voltammetry with • NO solutions prepared from the-generating compound diethylenetriamine/nitric oxide (DETA/NO). Microelectrodes were calibrated by amperometry at a potential of +0.90 V versus Ag/AgCl. They showed good sensitivity (954 ± 217 pA/M; n = 6) and linearity to • NO in the concentration range of 100-1000 nM. They were also characterized in terms of detection limit (6 ± 2 nM, n = 4), response time at 50% (1 s), and selectivity against interferents, such as nitrite (780 ± 84:1, n = 6), ascorbic acid (750 ± 187:1, n = 6) or dopamine (18 ± 2:1, n = 6). Injections of 1 mM l-glutamate, 1 mM l-arginine, and 0.1 mM N-methyl-d-aspartate did not produce changes in background current. Finally, the microelectrodes were used to measure • NO concentration dynamics in rat hippocampal brain slices stimulated with l-glutamate and N-methyl-d-aspartate. Taken together, the data indicate that the microelectrodes exhibit the proper sensitivity and selectivity for studies of • NO dynamics in brain slices (in vitro) and possibly in whole brain (in vivo) recordings.

Methods in Enzymology, 2008

During the last two decades nitric oxide (.NO) gas has emerged as a novel and ubiquitous intercel... more During the last two decades nitric oxide (.NO) gas has emerged as a novel and ubiquitous intercellular modulator of cell functions. In the brain, .NO is implicated in mechanisms of synaptic plasticity but it is also involved in cell death pathways underlying several neurological diseases. Because of its hydrophobicity, small size, and rapid diffusion properties, the rate and pattern of .NO concentration changes are critical determinants for the understanding of its diverse actions in the brain. .NO measurement in vivo has been a challenging task due to its low concentration, short half-life, and high reactivity with other biological molecules, such as superoxide radical, thiols, and heme proteins. Electrochemical methods are versatile approaches for detecting and monitoring various neurotransmitters. When associated with microelectrodes inserted into the brain they provide high temporal and spatial resolution, allowing measurements of neurochemicals in physiological environments in a real-time fashion. To date, electrochemical detection of .NO is the only available technique that provides a high sensitivity, low detection limit, selectivity, and fast response to measure the concentration dynamics of .NO in vivo. We have used carbon fiber microelectrodes coated with two layers of Nafion and o-phenylenediamine to monitor the rate and pattern of .NO change in the rat brain in vivo. The analytical performance of microelectrodes was assessed in terms of sensitivity, detection limit, and selectivity ratios against major interferents: ascorbate, dopamine, noradrenaline, serotonin, and nitrite. For the in vivo recording experiments, we used a microelectrode/micropipette array inserted into the brain using a stereotaxic frame. The characterization of in vivo signals was assessed by electrochemical and pharmacological verification. Results support our experimental conditions that the measured oxidation current reflects variations in the .NO concentration in brain extracellular space. We report results from recordings in hippocampus and striatum upon stimulation of N-methyl-d-aspartate-subtype glutamate receptors. Moreover, the kinetics of .NO disappearance in vivo following pressure ejection of a .NO solution is also addressed.

Free Radical Biology and Medicine, 2007

Nitrite may be a source for nitric oxide ( U NO), particularly in highly acidic environments, suc... more Nitrite may be a source for nitric oxide ( U NO), particularly in highly acidic environments, such as the stomach. Diet products contribute also with reductants that dramatically increase the production of U NO from nitrite. Red wine has been attributed health promoting properties largely on basis of the reductive antioxidant properties of its polyphenolic fraction. We show in vitro that wine, wine anthocyanin fraction and wine catechol (caffeic acid) dose-and pH-dependently promote the formation of U NO when mixed with nitrite, as measured electrochemically. The production of U NO promoted by wine from nitrite was substantiated in vivo in healthy volunteers by measuring U NO in the air expelled from the stomach, following consumption of wine, as measured by chemiluminescence. Mechanistically, the reaction involves the univalent reduction of nitrite, as suggested by the formation of U NO and by the appearance of EPR spectra assigned to wine phenolic radicals. Ascorbic and caffeic acids cooperate in the reduction of nitrite to U NO. Moreover, reduction of nitrite is critically dependent on the phenolic structure and nitro-derivatives of phenols are also formed, as suggested by caffeic acid UV spectral modifications. The reduction of nitrite may reveal previously unrecognized physiologic effects of red wine in connection with U NO bioactivity.

Biochemical and Biophysical Research Communications, 1996

Methods in Enzymology, 2002

Abstract Nitric Oxide (NO) is known to mediate the excitotoxic injury caused due to overactivatio... more Abstract Nitric Oxide (NO) is known to mediate the excitotoxic injury caused due to overactivation of N-Methyl-D-Aspartate (NMDA) receptors. NO production in response to NMDA receptor activation is studied in three hippocampal subregions: the CA1, CA3 and the Dentate Gyrus (DG). These three regions are differentially sensitive to NMDA toxicity, with the degree of response being the highest in CA1 and the lowest in DG. The results show that the NO production in these regions is different and consistent with their sensitivity to NMDA

Proceedings of The National Academy of Sciences, 2005

Nitric oxide ( • NO) production in response to stimulation of the NMDA glutamate receptor is impl... more Nitric oxide ( • NO) production in response to stimulation of the NMDA glutamate receptor is implicated not only in the synaptic plasticity in hippocampus but may also participate in excitotoxic cell death. Using • NO-selective microssensors inserted into the diffusional field of • NO in acute hippocampal slices, we describe the • NO concentration dynamics evoked by NMDA receptor activation and report profound differences along the trisynaptic loop of the hippocampus. We measured the oxygen gradient across the slice thickness and conclude that • NO measurements were performed at cell layers experiencing physiological oxygen tensions. Recordings performed at increasing distances from the point of NMDA receptor stimulation resulted in a progressive decrease of • NO signals, reaching undetectable levels for distances >400 m, supporting the notion of a wide diffusional spread of endogenously generated • NO in the hippocampus. Neither a picoinjection nor a continuous perfusion of NMDA resulted in high steady-state • NO levels; rather all signals were transient, suggesting that cells are able to efficiently respond to high • NO concentrations (typically 200 -400 nM) bringing it to very low nM levels; the claimed high micromolar • NO range achieved by excessive stimulation of NMDA receptor may have to be reevaluated. The distinct responses to NMDA receptor stimulation along the trysynaptic loop suggest a differential • NO activity and͞or regulation among the hippocampal subregions. These findings may be relevant for the understanding of the role of • NO in physiologic mechanisms in the hippocampus and the differential sensitivity of the hippocampal subregions to NMDA receptor-dependent neurodegeneration. carbon fiber microelectrode ͉ NO diffusional spread ͉ hippocampus A neural role of nitric oxide ( • NO) as an intercellular signaling Materials and Methods Chemicals and Solutions. NMDA, D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), and N G -nitro-L-arginine (L-NNA) were ob-Conflict of interest statement: No conflicts declared.